A working process end point real time determination method by which a working process end point can be determined accurately without an error even if a working process measurement signal has such a great variation that; the variation cannot be removed fully from and still remains in resulting smoothed data is disclosed. In the method, a working process end point is estimated by extrapolation from the variation of the average gradient of the averaged data in a predetermined period of the working process measurement signal to perform determination of the end point. Where the working process does not allow such extrapolation, it is first determined that the working process is near the working process end point based on the absolute value of the average gradient of the averaged data, and then the working process end point is determined using a short time gradient calculated from a value at the present measurement point of time and another value in the nearest past of the averaged data of the working process measurement signal.

1. Field of the Invention
The present invention relates to a working process end point real time determination method for determining an end point of a working process on a real time basis while the working process is proceeding using a working process measurement signal which exhibits, as the working process proceeds, a great increase or decrease once while including variations and then enters steady state as the working process comes to an end.
2. Description of the Related Art
Some working process apparatus such as a semiconductor process apparatus includes a working process measuring instrument for monitoring the progress of a working process.
One of working process measurement signals obtained from a working process measuring instrument exhibits such a variation with respect to time that it exhibits a great increase or decrease once as a working process proceeds after the lapse of a fixed period of time after the working process is started, and then enters a steady state as the predetermined working process is completed. The steady state in this instance signifies a state wherein the signal exhibits little variation, and more specifically signifies a state wherein the variation amount of the signal per unit time has a very low value close to zero.
The working process measurement signal includes periodical variations because a measurement position is scanned in a fixed cycle or, although the measurement position is fixed, the working process side includes a periodical operation from such a reason that the procedure of the working process involves some irregularity depending upon the spatial position and so forth, and the progress of the working process appears on a signal variation from which the periodical variations are removed. Accordingly, the determination that the working process comes to an end determines a point at which the working process measurement signal completes entrance into a steady state from the condition wherein it includes variations.
Though not particularly shown in the accompanying drawings, in order to determine a process end point from a working process measurement signal which exhibits such a variation as described above, a method is generally used wherein the point of time at which the working process measurement signal exhibits a variation to a value equal to or lower than a predetermined value or a value equal to or higher than a predetermined value is determined as a working process end point.
More particularly, since the working process measurement signal exhibits an increase or a decrease once and then enters a steady state, the working process measurement signal is compared with a predetermined threshold value set in advance, and the point of time at which the working process measurement signal exhibits a change to a value equal to or higher than the threshold value or equal to or lower than the threshold value is determined as a working process end point. The method can be applied to working processing end point determination in a CMP process for performing chemical and mechanical polishing (CMP) of a semiconductor wafer.
FIG. 7 is a cross sectional view showing an example of a semiconductor wafer (hereinafter referred to simply as wafer) which is a working object (polishing object). Referring to FIG. 7, the wafer generally denoted at 1 includes a substrate 4 having a high reflection factor with respect to inspection light, an insulator layer 2 applied to the surface of the substrate 4 and having a low reflection factor with respect to the inspection light or transparent to the inspection light, and a metal layer 3 having a high reflection factor with respect to the inspection light and applied to the entire face of the insulator layer 2 in such a manner that it covers over the insulator layer 2. In a CMP process, the metal layer 3 is polished by a CMP apparatus until the insulator layer 2 is exposed to form metal wiring lines. Accordingly, the point of time at which the metal wiring lines are formed completely is the polishing end point.
An example of an application to such a CMP process as just described is disclosed in Japanese Patent No. 2, 561, 812. The method is illustrated in a flow chart of FIG. 19. Referring to FIG. 19, the working process end point real time determination method illustrated includes a first step A1 and a second step A2. In the first step A1, an average value after each predetermined interval of time of a reflected light amount measured by a polished condition monitoring apparatus of the reflected light amount measurement type is calculated as measured light amount averaged data. Then, in the second step A2, the measured light amount averaged data calculated in the first step A1 is compared with a predetermined threshold value which depends upon the reflection factor of a material formed on the wafer with respect to inspection light and the structure of the wafer such as a pattern density, and the point of time at which the measured light amount averaged data becomes a value lower then the threshold value is determined as the polishing end point.
The measured light amount averaged data calculated in the first step A1 exhibits the following variation with respect to time. In particular, in an initial stage of polishing, since the metal layer 3 having a high reflection factor with respect to the inspection light is applied to the overall area of the uppermost layer of the wafer 1 as seen in FIG. 7, the measured light amount averaged data exhibits a high value. Then, as the polishing proceeds, the metal layer 3 is removed, and the insulator layer 2 having a low reflection factor with respect to the inspection light is exposed and begins to be polished. Or, where the insulator layer 2 is transparent to the inspection light, the inspection light begins to pass through the insulator layer 2 thus exposed and is reflected by the substrate 4 having a low reflection factor. Consequently, the reflected light amount gradually decreases. As the polishing further proceeds, metal wiring lines are finally formed completely. Consequently, even if the polishing thereafter proceeds, the area ratio between the insulator layer 2 and the metal layer 3 does not exhibit a variation any more, and accordingly, the measured light amount averaged data does not vary any more and exhibits a fixed value.
Accordingly, since the point of time at which the metal wiring lines are formed completely is the polishing end point, the point at which the measured light amount averaged data does not exhibit a variation any more but exhibits a fixed value indicates the polishing end point.
The measured light amount averaged data at the point of time of the end of the polishing exhibits the same value for each wafer if the reflection factor of the material formed on the wafer with respect to the inspection light and the structure of the wafer such as the pattern density are the same.
Therefore, in the second step A2, the measured light amount averaged data calculated in the first step A1 is compared with a predetermined threshold value which depends upon the reflection factor of a material formed on the wafer with respect to the inspection light and the structure of the wafer such as a pattern density, and the point of time at which the measured light amount averaged data becomes a value lower then the threshold value is determined as the polishing end point.
However, the conventional method wherein a measured light amount averaged data is compared with a predetermined threshold value to determine a working process end point has a problem in that, where the working process measurement signal exhibits a great variation, the determination of the working process end point cannot be performed with a high degree of accuracy.
Where the variation of the working process measurement signal is great, the working process measurement signal cannot be smoothed sufficiently unless the time interval upon averaging of the signal is sufficiently great. In the conventional method illustrated in FIG. 19, the working process measurement signal cannot be smoothed sufficiently unless the time interval when the reflected light amount is averaged in the first step A1 is great.
However, if the time interval for the averaging is increased, then the measurement signal smoothed data includes a greater amount of influence of data in the past and a delay is produced in the variation of the same. Consequently, a delay is produced in the determination of the working process end point. In this instance, according to the conventional method illustrated in FIG. 19, the determination of the polishing end point is delayed, and this gives rise to excessive polishing.
On the other hand, if the time interval for the averaging is decreased in order to prevent the delay, the variation cannot be smoothed sufficiently, and consequently, the determination accuracy of the working process end point is deteriorated. In this instance, according to the conventional method illustrated in FIG. 19, the determination of the polishing end point is dispersed, which gives rise to shortage of the polishing amount or excessive polishing.
It is an object of the present invention to provide a working process end point real time determination method by which the working process end point can be determined with a high degree of accuracy without an error even if a working process measurement signal has such a great variation that, even if it is smoothed, the variation cannot be removed fully from and still remains in resulting measurement signal smoothed data.
In order to attain the object described above, in a working process end point real time determination method according to a first aspect of the present invention, from a working process measurement signal which indicates the progress of a working process and exhibits a fluctuation, a point of time at which transition of the working process measurement signal into a steady state is completed after the working process measurement signal experiences a great variation once as the working process proceeds is determined on the real time basis while the working process is proceeding.
The working process measurement signal is obtained from a working process measuring instrument and includes a periodical variation because a measurement position is scanned in a fixed cycle or, although the measurement position is fixed, the working process side includes a periodical operation from such a reason that the procedure of the working process involves some irregularity depending upon the spatial position and so forth. Since the progress of the working process appears on a signal variation from which the periodical variation has been removed, in the first step, averaging is performed at intervals equal to an integral number of times the period of the variation to discretely calculate averaged data for each interval equal to the integral number of times the predetermined period.
Because the initial state prior to the working process is not fixed, the working process measurement signal in an initial stage of the working process exhibits a different variation from the procedure of the working process even if the periodical variation is removed from the working process measurement signal in the first step. The variation of the working process measurement signal in an initial stage of the working process is different among different working processes and may sometimes be a very great variation. Therefore, in the second step, end point determination based on the working process measurement signal is not performed for a time which exceeds the time within which such a variation of the working process measurement signal as described above may possibly occur.
Further, in order to cope with a dispersion of the initial variation period of the working process measurement signal which arises from a dispersion of the rate of the working process, in the third step, end point determination based on the working process measurement signal is not performed before the working process measurement signal exhibits a great variation as the working process proceeds, for example, before the working process measurement signal reaches a predetermined value or a predetermined multiple.
Then, determination of the working process end point is performed. However, even if the working process measurement signal is averaged to remove a periodical variation in the first step, the averaged data of the working process measurement signal obtained in the first step still includes remaining noise components originating from irregularity of the working process, the accuracy of a measuring apparatus or mixture of noise. Accordingly, transition of the working process to a steady state cannot be determined from the fact that the gradient (differential value) of the averaged data of the working process measurement signal at the present measurement point of time comes to the proximity of 0, but, for the determination of the working process end point, it is necessary to use data whose noise components have been smoothed sufficiently.
Therefore, in the fourth step, as such smoothing processing, it is possible to calculate an average value of a plurality of ones of the averaged data of the working process measurement signal obtained in the first step which belong to a predetermined period in the past including the value of the averaged data at the present measurement point of time and an average value of another plurality of ones of the averaged data which belong to another predetermined period in the further past and calculate a variation amount between the two average values as an average gradient.
However, if the point of time at which the average gradient obtained in the fourth step comes to the proximity of 0 is detected to determine the working process end point, then since a time delay caused by use of the data in the past is involved in the average gradient, the working process end determination is delayed.
Therefore, in the fifth step, after an absolute value of the average gradient of the averaged data of the working process measurement signal assumes a value equal to or higher than a predetermined value, the average gradient value at the present measurement point of time and another one of the average gradient values in the near past are joined to perform extrapolation to the future to calculate an estimated value of a time at which the average gradient is estimated to become equal to 0 and the working process comes to an end.
In this instance, since the estimated value of the time includes some delay in time caused by use of the data in the past, in the sixth step, the delay time is subtracted from the estimated value up to the end of the working process, and it is temporarily determined that the working process has come to an end if the working process time obtained by the subtraction indicates a time prior to the present measurement point of time.
The estimated value of the time up to the end of the working process includes some error caused by mixture of noise and so forth and the error makes a factor of wrong determination. Therefore, in the seventh step, overlooking some error, a short time gradient of the averaged data of the working process measurement signal is calculated only from the value at the present measurement point of time and the value in the nearest past from within the averaged data of the working process measurement signal calculated in the first step, and it is determined that the working process has come to an end from a logical AND between when the short time gradient reaches a value within a predetermined range successively more than a predetermined number of times, that the short time gradient exhibits a value within the predetermined range totally by more than the predetermined number of times after the absolute value of the average gradient assumes a value equal to or higher than the predetermined value or that the ratio at which the short time gradient assumes a value within the predetermined range is equal to or higher than a predetermined ratio and a result of the determination in the sixth step that a time obtained by subtracting the delay time caused by use of the data in the past from the estimated value up to the end of the working process indicates a time prior to the present measurement point of time.
Where the working process end point real time determination method is applied to a working process with which there is no sufficient time margin in which estimation by extrapolation of a working process end point is to be performed because average data of a working process measurement signal exhibits a sudden variation at the working process end point from a characteristic of a working process object article or a working process apparatus or extrapolation cannot be performed because the manner of the variation with respect to time of the averaged data of the working process measurement signal is different among different working processes, after it is determined that the working process at present is in the proximity of the working process end point from the fact that the absolute value of the average gradient of the averaged data of the working process measurement signal assumes a value equal to or higher than the predetermined value, a short time gradient of the averaged data of the working process measurement signal is calculated only from a value at the present measurement point of time and another value in the nearest past from within the averaged data of the working process measurement signal, and then it is determined that the working process has come to an end if the short time gradient reaches a value within a predetermined range successively more than a predetermined number of times, if the short time gradient exhibits a value within the predetermined range totally by more than the predetermined number of times after the absolute value of the average gradient assumes a value equal to or higher than the predetermined value or if the ratio at which the short time gradient assumes a value within the predetermined range is equal to or higher than a predetermined ratio.
According to a second aspect of the present invention, there is provided a working process end point real time determination method which comprises the first to fourth steps described above and further comprises, next to the fourth step, an eighth step of waiting for an absolute value of the average gradient of the averaged data of the working process measurement signal calculated in the fourth step to become equal to or higher than a first threshold value set in advance, and a ninth step of calculating a short time gradient of the averaged data of the working process measurement signal only from the value at the present measurement point of time and the value in the nearest past of the averaged data of the working process measurement signal calculated in the first step after the absolute value of the average gradient of the averaged data of the working process measurement signal calculated in the fourth step to become equal to or higher than the first threshold value and determining that the working process has come to an end if the short time gradient reaches a value within a second threshold value set in advance successively more than a predetermined number of times, if the short time gradient assumes a value within the second threshold value totally by more than the predetermined number of times after the absolute value of the average gradient becomes equal to or higher than the first threshold value or if the ratio at which the short time gradient assumes a value within the second threshold value is equal to or higher than a predetermined ratio.
According to a third aspect of the present invention, there is provided a working process end point real time determination method which comprises the first to fourth steps described above and further comprises, next to the fourth step, a 23rd step of multiplying a maximum value, a minimum value or an average value of the averaged data obtained for a time between a point of time when a fixed time for excepting a signal variation in an initial stage of the working process elapses and another point of time when the working process measurement signal begins a great variation by different predetermined values to calculate relative values as first and second threshold values, a 24th step of joining the average gradient value at the present measurement point of time and another one of the average gradient values in the near past after a point of time when an absolute value of the average gradient of the averaged data becomes equal to or higher than the first threshold value to perform extrapolation to the future to calculate a time at which the average gradient becomes equal to zero in the future as an estimated value of a working process end time, a 25th step of subtracting a delay time caused by use of the data in the past from the estimated value of the working process end time and temporarily determining that the working process has come to an end if the time obtained by the subtraction indicates a time prior to the present measurement point of time, and a 26th step of calculating a short time gradient of the averaged data only from a value of the averaged data at the present measurement point of time and another value of the averaged data in the nearest past and determining that the working process has come to an end from a logical AND between that the short time gradient assumes a value within the second threshold value successively more than a predetermined number of times, that the short time gradient assumes a value within the second threshold value totally by more than the predetermined number of times after the absolute value of the average gradient assumes a value equal to or higher than the first threshold value or that the ratio at which the short time gradient assumes a value within the second threshold value exceeds a predetermined ratio and the determination result in the 25th step.
The estimated value of the time before the working process end point includes an error originating from noise and so forth mixed thereto, and the error makes a factor of wrong determination. Therefore, in the 26th step, taking it into consideration that some error is involved, a short time gradient of the averaged data of the working process measurement signal is calculated only from a value of the averaged data of the working process measurement signal at the present measurement point of time calculated in the first step and another value of the averaged data in the nearest past, and it is determined that the working process has come to an end from a logical AND between that the short time gradient assumes a value within the second threshold value successively more than a predetermined number of times, that the short time gradient assumes a value within the second threshold value totally by more than the predetermined number of times after the absolute value of the average gradient assumes a value equal to or higher than the first threshold value or that the ratio at which the short time gradient assumes a value within the second threshold value exceeds a predetermined ratio and that the time obtained by subtracting a delay time caused by use of the data in the past from the estimated value of the working process end time is prior to the present measurement point of time.
The first and second threshold values to be used in the 24th and 26th steps are calculated as relative values in the 23rd step by multiplying a maximum value, a minimum value or an average value of the averaged data of the working process measurement signal obtained for a time between a point of time when a fixed time for excepting a signal variation in an initial stage of the working process elapses in the second step and another point of time when the working process measurement signal begins a great variation by different predetermined values.
Since the end point determination based on the working process measurement signal is not performed until the working process measurement signal reaches a predetermined multiple in the third step and besides the threshold values are formed from relative values, even if the magnitude of the working process measurement signal varies generally depending upon a difference in the working object article, the process condition or the measurement condition or the like, the working process end point can be determined correctly.
It is to be noted that, in such a process that the working process measurement signal exhibits little variation in overall magnitude, the threshold values may be formed as fixed values.
When it is determined in the 26th step that the short time gradient exhibits a value within the predetermined threshold value totally by more than the predetermined number of times after the absolute value of the average gradient exhibits a maximum value, if the absolute value of the average gradient assumes a maximum value by a plurality of times before the working process comes to an end, then each time a maximum value is detected, the total number of times is reset to re-start counting.
Where the working process end point real time determination method is applied to a working process with which there is no sufficient time margin in which estimation by extrapolation of a working process end point is to be performed because average data of a working process measurement signal exhibits a sudden variation at the working process end point from a characteristic of a working process object article or a working process apparatus or extrapolation cannot be performed because the manner of the variation with respect to time of the averaged data of the working process measurement signal is different among different working processes, it is first determined that the working process at present is in the proximity of the working process end point from the fact that the absolute value of the average gradient of the averaged data of the working process measurement signal assumes a value equal to or higher than the predetermined threshold value. Then, a short time gradient of the averaged data of the working process measurement signal is calculated only from a value at the present measurement point of time and another value in the nearest past from within the averaged data of the working process measurement signal, and then it is determined that the working process has come to an end if the short time gradient reaches a value within a predetermined threshold value successively more than a predetermined number of times, if the short time gradient exhibits a value within the predetermined range totally by more than the predetermined number of times after the absolute value of the average gradient assumes a value equal to or higher than the predetermined threshold value or if the ratio at which the short time gradient assumes a value within the predetermined threshold value is equal to or higher than a predetermined ratio.
According to a fourth aspect of the present invention, there is provided a working process end point real time determination method which comprises the first to fourth steps and the eighth and ninth steps described above and further comprises, prior to the eighth step, a 23rd step of multiplying a maximum value, a minimum value or an average value of the averaged data obtained for a time between a point of time when a fixed time for excepting a signal variation in an initial stage of the working process elapses and another point of time when the working process measurement signal begins a great variation by different predetermined values to calculate relative values as first and second threshold values.
Each of the working process end point real time determination methods according to the first to fourth aspects of the present invention may be constructed in the following manner.
In the first step of averaging a working process measurement signal at intervals equal to an integral number of times a predetermined period to discretely calculate an average value for each interval equal to the integral number of times the predetermined period as averaged data, the working process measurement signal may be averaged after each time interval within which a working object makes one rotation.
In the first step of averaging a working process measurement signal at intervals equal to an integral number of times a predetermined period to discretely calculate an average value for each interval equal to the integral number of times the predetermined period as averaged data, the working process measurement signal may be averaged after each time interval within which a working object makes an integral number of rotations.
In the first step of averaging a working process measurement signal at intervals equal to an integral number of times a predetermined period to discretely calculate an average value for each interval equal to the integral number of times the predetermined period as averaged data, the averaging of the working process measurement signal only over a predetermined interval of time within a time within which a working object makes one rotation may be performed after each period of rotation of the working object.
In the first step of averaging a working process measurement signal at intervals equal to an integral number of times a predetermined period to discretely calculate an average value for each interval equal to the integral number of times the predetermined period as averaged data, the working process measurement signal may be averaged at time intervals within which inspection light scans a working object.
In the fourth step of calculating an average gradient over a plurality of ones of the averaged data of the working process measurement signal which belong to a predetermined period in the past including the value of the averaged data at the present measurement point of time, an average value of a plurality of ones of the averaged data which-belong to a predetermined period in the past including the value of the averaged data at the present measurement point of time and an average value of another plurality of ones of the averaged data which belong to another predetermined period in the further past may be calculated, and a variation amount per unit time between the two average values may be calculated as the average gradient.
In the fourth step of calculating an average gradient over a plurality of ones of the averaged data of the working process measurement signal which belong to a predetermined period in the past including the value of the averaged data at the present measurement point of time, an expression of a straight line may be determined by a least square approximation method using a plurality of averaged data of a measured light amount which belong to a predetermined period in the past including a value of the measured light amount averaged data at the present measurement point of time, and a gradient of the straight line may be calculated as the average gradient.
In the fifth step of joining the average gradient at the present measurement point of time and another one of the average gradients in the near past to perform extrapolation to the future to calculate an estimated value of time until the working process comes to an end, an expression of a straight line which passes two points of the average gradient of the average gradient data at the present measurement point of time and another average gradient immediately preceding to the same may be determined, and a time at which the average gradient becomes equal to 0 may be calculated from the expression of the straight line only when the gradient of the straight line determined is in the positive if the averaged data exhibits a variation with respect to time wherein the averaged data drops by a great amount once and then enters a steady state or only when the gradient of the straight line determined is in the negative if the averaged data exhibits another variation with respect to time wherein the averaged data rises by a great amount once and then enters a steady state.
In the fifth step of joining the average gradient at the present measurement point of time and another one of the average gradients in the near past to perform extrapolation to the future to calculate an estimated value of time until the working process comes to an end, an expression of a straight line may be determined by a least square approximation method using three or more average gradients of the averaged data which belong to the past including the average gradient of the average gradient data at the present measurement point of time, and a time at which the average gradient becomes equal to 0 may be calculated from the expression of the straight line only when the gradient of the straight line determined is in the positive if the averaged data exhibits a variation with respect to time wherein the averaged data drops by a great amount once and then enters a steady state or only when the gradient of the straight line determined is in the negative if the averaged data exhibits another variation with respect to time wherein the averaged data rises by a great amount once and then enters a steady state.
An average gradient in a short time including a comparatively small number of averaged data in the past may be calculated and the number of times by which the average gradient in the short time assumes a value equal to or greater than 0 may be counted, and it may be determined that the working end point comes if the end point determination time calculated by such a method as described above is smaller than the present working time and the count number by which the relationship that the average gradient in the short time is equal to or greater than 0 is satisfied is equal to or greater than a predetermined number.
A predetermined time which exceeds a time within which a great variation of the averaged data in an initial stage of the working occurs may be set in advance, and the predetermined time and the working elapsed time till the present may be compared with each other and then the working end point determination operation is not performed until the present working elapsed time becomes equal to or greater than the predetermined time set in advance.
A maximum value of the averaged data till the present measurement point of time may be determined, and the working end point determination operation is not performed until it is determined, when the averaged data drops by a predetermined ratio from the maximum value, that a drop of the averaged data which is a characteristic of the averaged data in the proximity of the working end point has started.
When the end point determination time is to be calculated, a time obtained by adding or subtracting a predetermined time to or from a working time till the present since the oldest point of time in the past used for the calculation of the average gradient may be subtracted from a time at which the average gradient assumes a value equal to 0 to calculate the end point determination time thereby to delay or advance the determination of the working end point by a predetermined time.
Preferably, the threshold values are calculated as relative values by multiplying a maximum value, a minimum value or an average value of the averaged data of the working process measurement signal obtained for a time between a point of time when a fixed time for excepting a signal variation in an initial stage of the working process elapses and another point of time when the working process measurement signal begins a great variation by different predetermined values.
Since the threshold values are formed from relative values, even if the magnitude of the working process measurement signal is varied generally by a difference in a working object, a process condition, a measurement condition or the like, the effect that determination of the working process end point can be performed appropriately can be achieved.
Preferably, when it is determined that the short time gradient exhibits a value within the predetermined threshold value totally by more than the predetermined number of times after the absolute value of the average gradient exhibits a maximum value, in such a process that the absolute value of the average gradient assumes a maximum value by a plurality of times before the working process comes to an end, each time a maximum value is detected, the total number of times is reset to re-start counting.
Where the present invention is applied to a CMP apparatus which performs chemical and mechanical polishing of a semiconductor wafer, since the working object is a wafer, the working process end point real time determination method is preferably constructed in the following manner.
In particular, the working process end point real time determination method comprises a tenth step of calculating, as measured light amount averaged data, an average value after each predetermined interval of time of a reflected light amount measured by a polished condition monitoring apparatus of the reflected light amount measurement type mounted on the CMP apparatus for irradiating inspection light upon a polished face of the semiconductor wafer and monitoring a polished condition from a variation of the reflected light amount obtained then, an eleventh step of calculating, as average gradient data, an average rate of change over a plurality of measured light amount averaged data which belong to a predetermined period in the past including the value at the present measurement point of time of the measured light amount averaged data calculated in the tenth step, a twelfth step of joining, after an absolute value of the average gradient of the measured light amount averaged data calculated in the eleventh step assumes a value equal to or higher than a predetermined value, the average gradient at the present measurement point of time and another one of the average gradients in the near past to perform extrapolation to the future to estimate and calculate a time at which the relationship that the average gradient is equal to 0 is reached, a thirteenth step of subtracting a polishing time till the present since the oldest point of time in the past used for calculation of the average gradient in the eleventh step from the time at which the relationship that the average gradient is equal to 0 is reached to calculate an end point determination time, and a fourteenth step of comparing the end point determination time calculated in the thirteenth step and the present polishing time with each other and determining a point of time at which the end point determination time becomes equal to or smaller than the present polishing time as a polishing end point.
Alternatively, the working process end point real time determination method may comprise a tenth step of calculating, as measured light amount averaged data, an average value after each predetermined interval of time of a reflected light amount measured by a polished condition monitoring apparatus mounted on a CMP apparatus for performing chemical and mechanical polishing of a semiconductor wafer, an eleventh step of calculating, as average gradient data, an average rate of change over a plurality of measured light amount averaged data which belong to a predetermined period in the past including the value at the present measurement point of time of the measured light amount averaged data calculated in the tenth step, a twelfth step of joining, after an absolute value of the average gradient of the measured light amount averaged data calculated in the eleventh step assumes a value equal to or higher than a predetermined value, the average gradient at the present measurement point of time and another one of the average gradients in the near past to perform extrapolation to the future to estimate and calculate a time at which the relationship that the average gradient is equal to 0 is reached, a thirteenth step of subtracting a polishing time till the present since the oldest point of time in the past used for calculation of the average gradient in the eleventh step from the time at which the relationship that the average gradient is equal to 0 is reached to calculate an end point determination time, a 31st step of multiplying a maximum value or an average value of the measured light amount averaged data obtained for a time after a fixed time for excepting a signal variation in an initial stage of the polishing elapses until the measured light amount averaged data begins to drop a great amount by a predetermined value to calculate a relative value as a threshold value, a 32nd step of calculating a first average value of a plurality of ones of the measured light amount averaged data which belong to a predetermined period in the past including the value of the measured light amount averaged data at the present measurement point of time and a second average value of another plurality of ones of the measured light amount averaged data which belong to another predetermined period in the further past and calculating a variation amount per unit time between the first and second average values as an average gradient in a short time, a 33rd step of detecting that the average gradient data calculated in the eleventh step assumes a minimum value, a 34th step of counting an accumulated value of the number of times by which the average gradient data in the short time calculated in the 32nd step assumes a value equal to or higher than the counter threshold value after it is determined that the average gradient data calculated in the eleventh step assumes a minimum value, a 35th step of resetting, if the average gradient data calculated in the eleventh step assumes a maximum value after it is determined in the 33rd step that the average gradient data assumes a minimum value, the accumulated value counted in the 34th step and repeating the minimum value detection in the 33rd step, and a 36th step of comparing the end point determination time and the present polishing time with each other and determining that the polishing end time comes if the end point determination time is equal to or smaller than the present polishing time and the number of times by which the average gradient in the short time counted becomes within the predetermined threshold value is equal to or greater than a predetermined number.
With any of the working process end point real time determination methods according to the present invention, a working process end point is estimated by extrapolation from a manner of the variation of the average gradient of the averaged data in a predetermined period of the working process measurement signal to perform determination of the end point, or where the working process does not allow such extrapolation, it is first determined that the working process at present is in the proximity of the working process end point based on the absolute value of the average gradient of the averaged data of the working process measurement signal, and then the working process end point is determined using a gradient in a short time calculated only from a value at the present measurement point of time and another value in the nearest past from within the averaged data of the working process measurement signal. Consequently, even when the working process measurement signal exhibits such a great variation that, even if it is averaged, a variation remains in the averaged working process measurement signal data, the effect that determination of the working process end point can be performed appropriately with a high degree of accuracy without suffering from wrong determination can be achieved.
The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements are denoted by like reference symbols.

Working process end point real time determination method


An improved horizontal solder leveller for applying molten solder to boards while removing residual flux therefrom include a single pair of upper and lower solder sparge bars with outlet nozzles arranged so as to direct solder jets from one sparge bar toward the jets from the other sparge bar in the gap formed between the sparge bars. The gap between the sparge bars and the speed of the solder jets is sufficient to remove residual flux from a board passing therethrough as molten solder is applied to the board. An oil guide is included that directs oil to form curtains immediately upstream and downstream of the sparge bar gap to form a barrier to air flow in the gap. An oil trough upstream and downstream of the lower sparge bar limits the vertical extent of the oil curtains. Preferably a pair of castellated infeed rollers and outfeed rollers are used to move boards through the leveller.

The tern "horizontal solder leveller" means a machine through which printed circuit boards and the like (hereinafter called "boards") are passed substantially horizontally for application of molten solder and levelling of the applied solder. Accordingly such a machine comprises at least means for applying molten solder and means for levelling the applied solder. My early horizontal solder leveller is described in specification No: WO 87/07196, published on 3rd Dec., 1987, of my international patent application No: PCT/GB 87/00367.
My early horizontal solder leveller relies on passage of the board to be tinned beneath the surface of the molten solder in its solder bath. The board is passed between upper and lower tinning rollers, which at once--I believe --heat the board, assist transfer of solder onto the board and transport the board through the solder.
My early horizontal leveller has been developed as described in specification No: WO 91/06390, published on 16th May, 1991, of my international patent application No: PCT/GB 90/01685. The development included the provision of castellations in outfeed rollers for feeding the board from the solder bath to the air knives for levelling the solder applied to the board. The castellations allowed the air flow from the air knives to entrain oil, which can be sprayed onto these rollers, with the solder particles displaced from the board. This has assisted in keeping the machine clean and in returning the solder particles to the solder bath.
U.S. Pat. No. 4,563,974, issued on 14th Jan., 1986 to Monitrol, Inc., describes a horizontal solder leveller in which solder is poured onto the top surface of the board and is applied to the bottom surface of the board by a lower tinning roller. The solder application occurs entirely within flux oil and oil levelling is used.
Where boards include small pads for soldered contact with components, especially where the pads are for surface mount components, i.e. the pads do not have an associated bore through the board for a wire of the component to be soldered; a problem in tinning particularly with a horizontal leveller can arise of the solder not wetting some of the contact pads. I believe that this non-wetting results from the flux oil with which the board is preliminarily coated not being displaced by the solder.
It is conventional to include volatile chemicals in the flux oil. These are intended to vaporize as the board approaches the eutectic temperature of the solder and thus displace the oil from the contact pads. I have carried out extensive trials on these chemicals and concluded that they cannot be a complete solution to the problem of board pads not being completed wetted by solder in a horizontal leveller.

Limeworks Cottage, Kiln Lane, Buriton, Petersfield


A control equipment for a resistance welding machine for welding a material by the Joule's heat generated in the material by applying an electric power to the material, including an inverter for converting a DC voltage to an AC voltage by pulse width modulation control, a transformer having a primary winding to which the AC voltage is applied and having a secondary winding which supplies an AC current to the material, and a control unit for generating an AC current reference with a rectangular waveform of a specified frequency, comparing the AC current reference with an output current of the inverter to obtain an error, and for PWM controlling the inverter so that the error becomes zero.

1. Field of the Invention
This invention relates to a control equipment for a resistance welding machine, and more particularly to a control equipment for a resistance welding machine for welding a material by the Joule's heat generated in the material by applying an electric power to the material.
2. Description of the Related Art
As a control equipment for a resistance welding machine, there is an equipment which uses a commercial power source as it stands as the welding current power source. There is also an equipment which uses a commercial power source by first converting it to a DC voltage and then converting the DC voltage to an AC voltage of the desired frequency by using an inverter.
FIG. 41 shows a case of using a commercial power source as it stands. In FIG. 41(a), the voltage of a commercial frequency AC power source 101 is controlled of the trigger phase by thyristors 102 connected in antiparallel. Thus a controlled variable voltage is applied to the primary winding of a transformer 103. A secondary winding of transformer 103 is connected to welding electrodes 105. Resistance welding is performed by passing current to a metal object to be welded which is sandwiched by electrodes 105.
The magnitude of the welding current is set as an effective value by a current setting unit 107. The primary current of transformer 103, detected via a current detector 104 is converted to an effective value by an effective value computing unit 108. Both these currents are compared by a current control unit 109, and a control signal is outputted to reduce their error. The trigger phase is then determined by a phase control unit 110 based on the control signal. When a conduction starting instruction is applied from a starting circuit 112, a conduction instruction is outputted for a specific time period which has been set in timer 113. A driving circuit 111 outputs a trigger pulse at the trigger phase outputted from phase control unit 110 to switch thyristors 102 ON. In this case, as shown in FIG. 41(b), trigger phases .alpha.1, .alpha.2 of the positive half-wave and the negative half-wave of 1 cycle of the power source voltage are controlled as a pair. Also, due to the leakage inductance of transformer 103 and the floating inductance 106 which is present in the cable between the secondary winding of transformer 103 and welding electrodes 105, the load viewed from the primary side of transformer 103 becomes a delayed power factor. Thus, welding current I flows, as shown by FIG. 41(b).
In this method, the magnitude of the welding current always changes. Thus, there is great fluctuation in the heat at the welding portion and therefore there are limits to the welding quality. Also, since control is performed every one cycle of the commercial frequency, there are limits to the control response. Thus, if welding is performed by the optimum welding current without an enough margin, inferior products will sometimes occur. Also, as the power factor of the load becomes low and the load becomes a single phase load, there is the problem of unbalance occurring in a 3-phase power source load.
The inverter is used in a control equipment as shown in FIG. 42 is used to solve these problems. In FIG. 42(a) a DC voltage is obtained from 3-phase commercial frequency AC power source 101 via a rectifier 114. The DC voltage, which has been smoothed by a capacitor 115, is pulse-width modulated (PWM) by inverter 116 and is converted to AC voltage V1 with a high frequency of 600-1000 Hz, which is applied to the primary winding of transformer 103. The AC voltage which is induced in the secondary winding of transformer 103 is full-wave rectified by diodes 117 and is converted to DC voltage V2. Thus, DC welding current I flows in the object to be welded which is sandwiched by welding electrodes 105.
The design is such that the welding current is determined by current setting unit 107. A primary current of transformer 103 detected via current transformer 104 is converted to a welding current by a simulation circuit 118. These currents are compared by current control unit 109, and a control signal is outputted to make their error zero. This control signal is compared with a high-frequency triangular wave outputted from a carrier generating unit 119 in a PWM control unit 120 and is outputted to driving unit 111 as a PWM control signal. The PWM control signal is outputted from driving unit 111 while the conduction instruction is inputted via starting circuit 112 and timer circuit 13. Thus, inverter 116 outputs the PWM controlled AC voltage V1 shown in FIG. 42(b). A low AC voltage of a waveform similar to this voltage V1 is induced in the secondary winding of transformer 103, and is converted to a full-wave rectified DC voltage V2 by diodes 117 having a large conduction capacity. Thus, a DC welding current I flows as shown in FIG. 42(b).
This method makes high-quality welding possible by solving the problems described above. Moreover, there is advantage of making the transformer small and of light weight by adopting high frequency.
However, in the prior art control equipment for a resistance welding machine as described above in which an inverter is used, the power loss of the diodes provided on the secondary side of the transformer is great. The power loss of the diodes reaches as much as 10-15% of the inverter output, which causes an efficiency reduction of the control equipment, and requires a water cooling system for cooling the diodes. Moreover, since a DC welding current flows, the welding electrodes are electrolyzed and their wear are severe. Therefore, as welding processes become robotized, the down time for replacing the electrodes becomes an increasing problem.
FIG. 43 is a block diagram showing another example of this type of prior art control equipment for a resistance welding machine. An AC power from an AC power source 1 is converted to a DC power by a diode bridge 2 and initially charges a capacitor 6 via a resistor 3. By timing the completion of charging capacitor 6, an electromagnetic contactor 4 is closed via an ON-delay timer 5, and resistor 3 is shorted.
The DC voltage which has been smoothed by capacitor 6, is converted to a high frequency voltage by an inverter bridge 7 and is then voltage-transformed by a transformer 8. The voltage thus transformed is converted to a DC voltage by a diode 9 and a diode 10 and is then supplied to welding electrodes 11.
In this case, a welding current is detected by a current detector 12. The setting of a welding current I is set by a current setter 13. When a starting signal ST is inputted, a conduction signal contact 14 is set ON by a conduction timer 17 and a current reference is inputted to a comparator amplifier 15.
The welding current detected by current detector 12 is inputted to comparator amplifier 15. This current is compared and amplified with the current reference to control the welding current via a PWM circuit 16 by PWM (pulse-width modulation) controlling IGBTs (insulated gate bipolar transistors) which compose inverter bridge 7.
FIG. 44 shows an example of this conduction sequence. When starting signal ST is inputted once, it is held for a 1-cycle period hold and DC current I flows during a set conduction time t1.
A time to the next conduction is longer than time t1, and generally t1/t0 is 0.1-0.05 or less. t1/t0 is generally called the "duty (%)". In the case of a resistance welding machine, time (t0-t1) is the time in which welding point determination (generally by a robot) is executed. In general, time t1 is about 1 second in most cases. Welding is performed during this time t1. For welding, pressure is applied by the electrode tip to the material to be welded, and then the welding current flows through the conducting surface thus formed. The material is heated by a generated Joule's heat Q, that is to say EQU Q=I.sup.2 .multidot.R.multidot.t1
and melts, thus forming the weld, where R is a resistance of welding portion.
Welding is performed by the Joule's heat due to a DC welding current flowing between electrodes in this way. However, as the electrodes are fixed due to the DC current, the wear of the negative (-) electrode is severe and requires frequent maintenance. Thus, this requires consumable costs and lost time.
FIG. 45 is a block diagram showing another example of a prior art control equipment for a resistance welding machine.
The AC voltage of an AC power source 201 is converted to a DC voltage by a rectifier 202. After smoothing by a capacitor 203, this DC voltage is converted to an AC voltage with a high frequency of about 1 kHz by an inverter 204 which is composed of IGBT (switching devices) 241-244. After this AC voltage is converted to a low AC voltage by a transformer 205, a DC welding current is supplied to welding electrodes 209 by converting the low AC voltage to a DC voltage by a rectifier 207. Floating inductance 208 is present in the wiring to the welding electrodes 209, and it operates effectively to smooth the DC welding current.
The magnitude of the welding current is controlled by a current reference I*. That is to say, after the primary current of transformer 205 has been detected via a current transformer 206, DC welding current is detected by simulating the DC welding current (the reflux current of rectifier 207 out of the welding current does not flow in the primary side of transformer 205) by a welding current simulator circuit 212. DC welding current I thus detected is compared with current reference I* by a current controller 213 and a current control signal a is outputted by current controller 213 so that its error is reduced. This signal a is compared by a comparator 215 with a triangular wave b outputted from a carrier generator 214, and a PWM signal c is generated based on the comparison result. Carrier generator 214 also outputs a signal d which is synchronized with the cycle of triangular wave b. A distributing circuit 216 activates either of its output signals e of f in response to signal d. By this means, PWM signal c is supplied alternately to driving circuits 212 and 222 via AND circuits 217 and 218.
A timer 220 operates when a drive signal g is inputted from a starting circuit 219, and outputs a conduction signal h only for a set time to driving circuits 221 and 222. Thus, by rendering driving circuits 221 and 222 in the operating state, switching signals j and k are outputted alternately. Thus, the group of IGBT 241, IGBT 244 and the group of IGBT 243, IGBT 242 are switched ON alternately. Therefore a high frequency AC voltage is applied from inverter 204 to the primary side of transformer 205 to control the welding current and the welding time.
With the above prior art control equipment, there is the advantage that the transformer can be miniaturized because the current control response is swift, there is little current ripple and the inverter frequency is high.
However, since a DC welding current is passed, the wear of the welding electrodes due to electrolytic action is severe. Thus, when the welding process is robotized, frequent exchange of electrodes is required. For this reason, the assembly line must be stopped temporarily, and this causes reduction of availability.
Moreover, there are also some problems, such as the occurrence of a 10% to 20% power loss in rectifier 207 which rectifies a current of several tens of thousands of amperes, and the increase of cooling water due the generation of that power loss.

Control equipment for resistance welding machine


The invention relates to a steam generator in which the continuous heating panel of an evaporator is arranged in a heating gas channel which can be cross-flown in a more or less horizontal direction of a heating gas. Said continuous heating panel of the evaporator comprises a plurality of pipes of a steam generator which are connected in parallel to each other. Said pipes are constructed in such a way that they cross a flow medium and are provided with the part of a more or less vertical down pipe which can be cross-flown by the flow medium in a downward direction and with the part of a rising pipe connected downstream with respect to the down pipe on the side of the flow medium and which is more or less vertical and can be cross-flown by the flow medium in an upward direction. The continuous heating panel of the evaporator is arranged in such a way that one pipe of the steam generator which is hotter than the other pipe of the steam generator of the same continuous heating panel of the evaporator has a flow medium rate which is higher than that of the other pipe of the steam generator. The aim of said invention is to operate said steam generator in a relatively simple manner in association with a highly stable flow in the continuous heating panel of the evaporator. For this purpose, the flow medium of the continuous heating panel of the evaporator is supplied in such a way that the flow velocity thereof is higher than a minimum flow velocity predefined in the down pipe. The inventive steam generator is extremely well adapted for carrying out said method and comprises another continuous heating panel of the evaporator which is connected downstream with respect to the continuous heating panel of the evaporator on the side of the flow medium.

In the case of a gas and steam turbine plant, the heat obtained from the operating means or the heating gas from the gas turbine is used to generate steam for the steam turbine. Heat is transferred to a waste-heat steam generator connected downstream of one of the gas turbines in which a plurality of heating panels are usually arranged to preheat the water in order to generate and superheat the steam. The heating panels are connected to the water-steam cycle of the steam turbine. The water-steam cycle usually includes a number of pressure stages, for example three, in which case, each pressure stage can feature an evaporator heating panel.
For the steam generator connected downstream on the heating gas side of the gas turbine as a waste-heat steam generator, several alternative embodiment concepts can be taken into consideration, namely, the embodiment as a continuous steam generator or the embodiment as a circulation steam generator. In the case of a continuous steam generator, when the steam generator pipes provided as evaporator pipes are heated, the flow medium in the steam generator pipes evaporates in a single through-flow. However, by contrast with this, in the case of a natural or forced circulation steam generator, the circulating water is only partially evaporated when flowing through the evaporator pipes. The water not evaporated in this case is again supplied to the same evaporator pipes for further evaporation after the generated steam has been separated.
Unlike a natural or forced circulation steam generator, the continuous steam generator is not subjected to a pressure limit so that in the case of initial steam pressures it can be embodied to exceed the critical pressure of water by far (PKri≈221 bar), in which case, it is not possible to differentiate between the water phase and the steam phase and, as a result, a phase separation is also not possible. A high initial steam pressure favors a high thermal degree of effectiveness and, therefore, low CO2 emissions of a fossil-heated power plant. In addition, a continuous steam generator compared to a circulation steam generator has a simple embodiment and can, as a result, be manufactured particularly cost-effectively. Therefore, the application of a steam generator embodied according to the through-flow principle as a waste-heat steam generator of a gas and steam turbine plant is, in this case, particularly favorable for obtaining a high overall degree of effectiveness of the gas and steam turbine plant with a simple embodiment.
Particular advantages with respect to manufacturing costs, but also with respect to maintenance work are offered by the horizontal waste-heat steam generator, for which the heating medium or the heating gas, that is the waste gas from the gas turbine is cross-flown in a more or less horizontal direction of flow through the steam generator. However, in the case of a horizontal steam generator, the steam generator pipes of a heating panel of the evaporator can, depending on their positioning, be exposed to greatly varying heating temperatures. Particularly in the case of the steam generator pipes of a continuous steam generator connected on the outlet side to a common accumulator, a different heating of the individual steam generator pipes, in each case, can lead to a joining together of the steam flows with the steam parameters deviating strongly from one another and, as a result, to undesirable losses in the efficiency, particularly to a relatively drop in efficiency of the heating panel involved and resulting reduced steam generation. A difference in heating of neighboring steam generator pipes can, in addition, damage the steam generator pipes or the accumulator particularly in the joining area of the accumulators in each case. Thus the desirable application of a horizontal continuous steam generator, in itself, embodied as a waste-heat steam generator for a gas turbine may cause considerable problems with respect to a sufficiently stabilized flow control.
From EP 0 944 801 B1, a steam generator designed for horizontal use is known and it also has the above-mentioned advantages of a continuous steam generator. In addition to this, the heating panel of the evaporator of the known steam generator is arranged as a continuous heating panel and is embodied in such a way that one pipe of the steam generator which is hotter than the other pipe of the steam generator of the same continuous heating panel of the evaporator has a flow medium rate which is higher than that of the other pipe of the steam generator. Thus, the continuous heating panel generally means a heating panel which is embodied for a cross-flow according to the through-flow principle. The flow medium supplied to the heating panel of the evaporator arranged as the continuous heating panel, therefore, completely evaporates in a single through-flow in each case through this continuous heating panel or through a heating panel system comprising a plurality of continuous heating panels which are connected in series to each other.
The evaporator panel of the evaporator of the known steam generator arranged as a continuous heating panel therefore shows, in the nature of the flow characteristics of a heating panel of a natural circulation evaporator (natural circulation characteristics) in the case of a different heating of the individual pipes of a steam generator, a self-stabilizing behavior, which without the requirement of external influences adjusts the temperatures on the outlet side even in the case of differently heated pipes of the steam generator which are connected in parallel on the flow medium side.
For this design of steam generator, in order to obtain a particularly low load through thermally-related stresses particularly in relation to the manufacturing and assembly costs kept particularly low in relation to the distribution of the flow medium on the water side and/or the steam side, the continuous heating panel of the evaporator of the steam generator can be designed as U-shape comprising a plurality of pipes of a steam generator which are connected in parallel to each other for through-flow of the flow medium, which each feature an almost vertically arranged down pipe section through which the flow medium can flow in a downwards direction and connected downstream from this on the flow medium side an almost vertically arranged riser pipe through which the flow medium can flow in an upwards direction. As has been shown, with this type of design, a pressure contribution through the geodetical pressure of the water column in the down pipe of the specific pipe of the steam generator can be utilized in a way that favors and promotes flow when the continuous heating panel is cross-flown.
However, such a design could basically promote the occurrence of flow instabilities on operating the continuous heating panel of the evaporator which could bring about operational disadvantages. Although supplying the pipes of the steam generator forming the continuous heating panel with a relatively low mass flow rate density and the relatively low frictional pressure loss associated with these allows the natural circulation characteristics of the flow in the pipe of the steam generator to be obtained, which has a stabilizing effect on the flow. Nevertheless, it is also desirable especially in the case of such a design with a pipe section which can be cross-flown downwards to contribute, to a particular extent to stabilizing the flow ratios when the continuous heating panel of an evaporator is operated.

Operating method for a horizontal steam generator and a steam generator for carrying out said method


An imaging apparatus includes a planar image acquisition unit configured to acquire a planar image of a subject, a tomographic image acquisition unit configured to acquire a tomographic image of the subject, and a polarization adjustment member disposed in a common optical path of a portion of an optical system in the planar image acquisition unit and a portion of an optical system in the tomographic image acquisition unit and configured to adjust polarization states of a measuring beam for the planar image and a measuring beam for the tomographic image.

1. Field of the Invention
The present invention relates to an imaging apparatus configured to capture of an image of a subject.
2. Description of the Related Art
An optical coherence tomography (OCT) technique using interference of multi-wavelength light enables acquisition of a high-resolution tomographic image of a sample (in particular, a fundus of the eye).
In recent years, an ophthalmologic OCT apparatus can acquire, in addition to a normal OCT image of a shape of a fundus tissue, a polarization-sensitive OCT image using a polarization parameter (i.e., retardation and orientation), which is an optical characteristic of the fundus tissue.
The polarization-sensitive OCT (PS-OCT) can form the polarization-sensitive OCT image using the polarization parameter to be formed, and perform distinguishing and segmentation of the fundus tissue. PS-OCT uses the fact that some layers in the retina (or fundus) of an eye reflect polarized light differently from other layers. International Publication No. WO 2010/122118 A1 discusses a polarization-sensitive OCT which employs a light beam that has been modulated to a circularly-polarized beam as a measuring beam for examining the sample. Detection is then performed by splitting the interference beam into two linearly-polarized beams perpendicular to each other, so that the polarization-sensitive OCT image is generated with different layers in the fundus being imaged differently depending on their interaction with the polarized light.
It is desirable that the imaging apparatus is capable of capturing a polarization-sensitive scanning laser ophthalmoscope (SLO) image in addition to the polarization-sensitive OCT image. In such an imaging apparatus, if a polarization-sensitive OCT optical system and a polarization-sensitive SLO optical system are separately provided, polarization states generated in an image acquired by the polarization-sensitive OCT optical system and an image acquired by the polarization-sensitive SLO optical system may be uneven.


An exhaust emission control device for an internal combustion engine, which is capable of terminating reduction control in proper timing when a NOx cleaning catalyst includes an auxiliary catalyst having an oxygen storage capacity, thereby making it possible to reduce exhaust emissions and improve fuel economy. The exhaust emission control device includes the NOx cleaning catalyst and an ECU. The NOx cleaning catalyst includes the auxiliary catalyst having an oxygen storage capacity. The ECU executes reduction control when predetermined conditions for executing the reduction control are satisfied. During execution of the reduction control, when exhaust gas temperature is higher than a predetermined value, if a second excess air ratio is lower than a predetermined value, the ECU determines that the reduction control should be terminated. When the exhaust gas temperature is not higher than the predetermined value, if the remaining NOx amount is not larger than a predetermined value, the ECU determines that the reduction control should be terminated.

1. Field of the Invention
The present invention relates to an exhaust emission control device for an internal combustion engine that includes a NOx cleaning catalyst for reducing trapped NOx under a reducing atmosphere in an exhaust passage thereof, the exhaust emission control device supplying a reducing agent to an upstream side of the NOx cleaning catalyst, so as to cause the NOx cleaning catalyst to perform a NOx reducing operation, a method of controlling the exhaust emission control device, and an engine control unit.
2. Description of the Related Art
Conventionally, as an exhaust emission control device of this kind, one disclosed in the publication of Japanese Patent Publication No. 2692380 is known. The exhaust emission control device shown in FIG. 1 in this publication is applied to a gasoline engine. The gasoline engine has an exhaust passage provided with a NOx cleaning catalyst. The NOx cleaning catalyst traps NOx (nitrogen oxides) in exhaust gases under an oxidizing atmosphere, and reduces the trapped NOx when exhaust gases under a reducing atmosphere are supplied thereto, to thereby clean the exhaust gases, i.e. reduce exhaust emissions. Further, the exhaust emission control device is disposed in the exhaust passage at a location downstream of the NOx cleaning catalyst, and is provided with an air-fuel ratio sensor for detecting an air-fuel ratio of exhaust gases.
As shown in FIGS. 12 and 13 of the publication, in the exhaust emission control device, during a lean burn operation of the engine, an operation time period T of the lean burn operation is counted, and when the operation time period T exceeds a predetermined value To, reduction control is carried out so as to reduce NOx trapped in the NOx cleaning catalyst. More specifically, by switching the engine from the lean burn operation to a rich burn operation, exhaust gases under the reducing atmosphere, containing unburned fuel as a reducing agent, are supplied to the NOx cleaning catalyst. During the reduction control, when the air-fuel ratio detected by the air-fuel ratio sensor changes over from a lean air-fuel ratio to a rich air-fuel ratio, presumably, all the NOx trapped in the NOx cleaning catalyst has been reduced, and hence it is judged that the reduction control should be terminated, so that the reduction control is terminated to switch the engine from the rich burn operation to the lean burn operation.
Further, there has been recently proposed a technique of applying an auxiliary catalyst provided with an oxygen storage capacity to the NOx cleaning catalyst so as to increase the NOx purifying capability of the NOx cleaning catalyst. As an auxiliary catalyst of this kind is used a ceria-zirconia composite oxide disclosed e.g. in Japanese Laid-Open Patent Publication (Kokai) No. H11-165067. If such an auxiliary catalyst is used, when exhaust gases under the reducing atmosphere are supplied to the NOx cleaning catalyst, the auxiliary catalyst absorbs oxygen, whereby an operation for reducing NOx trapped in the NOx cleaning catalyst is accelerated, whereas when exhaust gases under the oxidizing atmosphere are supplied to the NOx cleaning catalyst, the auxiliary catalyst releases oxygen, whereby a NOx trapping operation of the NOx cleaning catalyst is accelerated.
To increase the NOx purifying capability of the NOx cleaning catalyst, if the auxiliary catalyst disclosed in Japanese Laid-Open Patent Publication (Kokai) No. H11-165067 is applied to the exhaust emission control device disclosed in the publication of Japanese Patent Publication No. 2692380, there can arise the following problems: In the case of the auxiliary catalyst disclosed in Japanese Laid-Open Patent Publication (Kokai) No. H11-165067, as shown in FIG. 3 in Japanese Laid-Open Patent Publication (Kokai) No. H11-165067, when the temperature of the auxiliary catalyst is within a predetermined temperature range (temperature range between 400 and 750° C.), the auxiliary catalyst has a very high oxygen storage capacity, whereas when the temperature of the auxiliary catalyst is not within the predetermined temperature range, the auxiliary catalyst has only a fairly low oxygen storage capacity. Therefore, during execution of the above-described reduction control, when the temperature of the NOx cleaning catalyst is not within the predetermined temperature range mentioned above, due to the fairly low oxygen storage capacity of the auxiliary catalyst, the reliability of the air-fuel ratio detected by the air-fuel ratio sensor is lowered, which make it impossible to terminate the reduction control in proper timing. As a result, when a time period over which the reduction control is executed is too short, the degree of reduction of NOx trapped in the NOx cleaning catalyst is lowered to degrade the NOx purifying capability of the NOx cleaning catalyst, resulting in an increase in exhaust emissions. On the other hand, when the time period over which the reduction control is executed is longer than required, fuel economy is degraded.

Exhaust emission control device for internal combustion engine, method of controlling the exhaust emission control device, and engine control unit


An aero acoustic fan assembly is provided and generally includes a fan wheel, a frame, and first and second air outlet diffusing structures. The fan wheel generally, and typically includes an axial air inlet delimited by an air inlet cone, an annular air outlet, a back plate, and front plate opposite the back plate. The frame within supports the fan wheel for rotation about a central axis thereof. The first air outlet diffusing structure is supported by a portion of the frame, adjacent the back plate of the fan wheel and includes a peripheral region. The second air outlet diffusing structure is similarly supported by a portion of the frame, adjacent the front plate of the fan wheel, and also includes a peripheral region, air exiting the annular air outlet of the fan wheel passing between the peripheral regions of the diffusing structures.

Relatively inexpensive plenum or plug-type fans are well known in the industrial and commercial fan industry. They are commonly sold as an unhoused fan unit by the manufacturers although they are mounted in a suitable support structure that can include a front wall with an air inlet opening formed therein. These fans are used instead of, or to replace, centrifugal type fans which are commonly used in the air handling industry. The wheel of the plenum fan is used to pressurize a surrounding air plenum or housing in which the fan is installed. A number of air ducts can be connected to the housing and these can extend from any direction. In addition to being a reasonably inexpensive fan structure, a plenum or plug fan unit can save space by eliminating a special fan housing, transitions and diffusers commonly characterizing centrifugal air handling system. When required, two or more of these fans can be mounted side-by-side on common or separate support frames.
A common and well known difficulty of plug or plenum fans is that they can be inefficient in their operation and noisy compared to other types of fans. Furthermore, such assemblies are known to require considerably more electrical power for operation of the one or more fans than more efficient units that produce the same amount of or more air flow. With respect to the noise problem, it is noted that with many known plug type fans, low frequency noises are generally produced, and there is no currently available and practical solution to the noise problem. Traditionally, noise reduction in air moving assemblies has been achieved at the cost of dynamic performance, via the inclusion of dissipative silencers. Such silencers typically comprise acoustically lined fan housings, ducting, etc. In an air handling system, such structures create a static pressure drop which results in a lowered static efficiency. Furthermore, dissipative silencers are ill suited to reduce or eliminate the tone component of sound, namely, blade pass frequency tone.
U.S. Pat. No. 5,749,702 (Datta et al.) describes, among other things, a fixed center body for axially directing air flow to and within a bladed fan wheel having an annular air outlet. The center body extends through the axial air intake, and radially expands rearwardly, terminating at an end at the back of the fan wheel, close to the rear plate thereof. Both inlet and outlet structures, including the center body, incorporate sound attenuating material for broadband noise reduction. Increased fan wheel efficiency is alleged as attributable to a solid curved rear end section of the center body, which redirects air flow in a radial direction towards the annular outlet of the fan wheel. Furthermore, a wall, spaced from a fixed sidewall or front wall of a fan support structure so as to be positioned behind the fan wheel, is further provided. The additional wall is preferably filled with sound attenuating material, and more preferably still, has a perforated front surface facing the back plate of the fan wheel.
U.S. Pat. No. 5,426,268 (Yazici et al.) describes combined utilization of air duct inlet and outlet silencer apparatuses for an air handling system. Both apparatuses include interior walls, arranged between interior and exterior walls thereof, comprised of sound attenuating material, with at least portions of the interior walls constructed of perforated metal sheets. In the outlet duct apparatus, the main passageway is substantially straight and increases in transverse cross-section from the inlet to the outlet. The transverse cross-section changes from circular at the end of the passageway adjacent the fan to rectangular at the opposite end.
U.S. Pat. No. 5,066,194 (Amr et al.) describes a fan orifice structure intended for use in conjunction with an outside enclosure, usually containing a heat exchanger and compressor of an air conditioner. The orifice is defined by an annular curved surface that extends downwardly from a top wall of the cover. The curved surface is generated by rotating a planar and curvilinear line about a coplanar axis of generation. It is said that the contour of the orifice enhances fan efficiency and reduces radiated noise. The orifice cover is made from plastic materials by a molding process.
U.S. Pat. No. 4,576,549 (Lanier) is generally directed to a centrifugal fan having a plurality of vortex generators fixed onto the outer wall of an annular member leading into an air inlet of the fan wheel. An inlet cone is shown as a concave annular form tapered inwardly from the larger diameter air inlet in the fan wheel plate. Vortex generators are shown as formed plates having lateral edges contoured to fit the curved annular wall of the inlet cone. It is believed that such structures, so arranged, permit merger of skin friction induced air current with the lower velocity air being discharged from the rotating fan wheel blades
As is readily appreciated, it remains advantageous to provide a fan unit which is simple to build and construct which employs a bladed fan wheel having an axial air intake and an annular air outlet, and at least one outlet diffuser for directing airflow from the fan wheel such that static efficiency is improved, and noise is greatly reduced. It is further advantageous to enhance the noise reduction capabilities of fan assemblies for air handling systems, more particularly, both the broadband and tone aspects thereof.


There is disclosed an energy recovering circuit with boosting voltage-up and an energy efficient method using the same that are capable of boosting the voltage factor of an energy recovered from the panel to rapidly re-appl it to the panel, to thereby reduce the charging time of a panel capacitor and improve its energy recovery efficiency. An energy recovering circuit according to the present invention includes a voltage boosting circuit for boosting a voltage factor of an energy recovered from a panel and supplying the boosted energy to the panel. An energy efficient method according to the present invention includes steps of recovering an energy from a panel to a closed loop; and a controlling the closed loop in order to supplying the energy with its voltage factor boosted to the panel.

Generally, a plasma display panel (PDP) has a disadvantage of large power consumption. A reduction of such power consumption requires enhancing a light-emitting efficiency and minimizing an unnecessary energy waste occurring in a driving process without a direct relation to a discharge.
An alternating current (AC)-type PDP coats an electrode with a dielectric material to use a surface discharge occurring at the surface of the dielectric material. In this AC-type PDP, a driving pulse has a high voltage of dozens to hundreds of volts (V) to make a sustaining discharge of tens of thousand to millions of cells, and has a frequency of more than hundreds of KHz. If such a driving pulse is applied to the cells, a charge/discharge having a high capacitance occurs.
When such a charge/discharge is generated at the PDP, a capacitive load of the panel does not cause an energy waste, but a lot of energy loss occurs at the PDP because a direct current (DC) power source is used to generate a driving pulse. Particularly, if an excessive current flows in the cell upon discharge, then an energy loss is increased. This energy loss causes a temperature rise of switching devices, which may break the switching devices in the worst case. In order to recover an energy generated unnecessarily within the panel, a driving circuit of the PDP includes an energy recovering circuit.
Referring to FIG. 1, an energy recovering circuit having been suggested by U.S. Pat. No. 5,081,400 of Weber includes first and second switches Sw1 and Sw2 connected, in parallel, between an inductor L and a capacitor Css, a third switch Sw3 for applying a sustaining voltage Vs to a panel capacitor Cp, and a fourth switch Sw4 for applying a ground voltage GND to the panel capacitor Cp.
First and second diodes D1 and D2 for limiting a reverse current are connected between the first and second switches Sw1 and Sw2. The panel capacitor Cp is an equivalent expression of a capacitance value of the panel, and reference numerals Re and R-Cp are equivalent expressions of parasitic resistances of an electrode and a cell provided at the panel, respectively. Each of the switches Sw1, Sw2, Sw3 and Sw4 is implemented by a semiconductor switching device, for example, a MOS FET device.
An operation of the energy recovering circuit shown in FIG. 1 will be described in conjunction with FIG. 2 assuming that a voltage equal to Vs/2 should be charged in the capacitor Css.
In FIG. 2, Vcp and Icp represent charge/discharge voltage and current of the panel capacitor Cp, respectively.
At a time t1, the first switch Sw1 is turned on. Then, a voltage stored in the capacitor Css is applied, via the first switch Sw1 and the first diode D1, to the inductor L. Since the inductor L constructs a serial LC resonance circuit along with the panel capacitor Cp, the panel capacitor Cp begins to be charged in a resonant waveform.
At a time t2, the first switch Sw1 is turned off while the third switch Sw3 is turned on. Then, a sustaining voltage Vs is applied, via the third switch Sw3, to the panel capacitor Cp. From the time t2 until a time t3, a voltage of the panel capacitor Cp remains at a sustaining level.
At a time t3, the third switch Sw3 is turned off while the second switch Sw2 is turned on. Then, a voltage of the panel capacitor Cp is recovered into the capacitor Css by way of the inductor L, the second diode D2 and the second switch Sw2.
At a time t4, the second switch Sw2 is turned off while the fourth switch Sw4 is turned on. Then, a voltage of the panel capacitor Cp drops into a ground voltage GND.
In the energy recovering circuit, there are requirements for improving the discharge characteristics of the panel, obtaining stable sustaining time, and increasing the efficiency of the energy recovered from the panel. For this, the conventional energy recovering circuit of FIG. 1 makes the inductance of the inductor L small to have it fast a rising time supplied to the panel. Thereby, the discharge characteristics can be increased and the inductance of the inductor L is made big such that the energy recovering efficiency can be improved.
However, because the conventional energy recovering circuit as in FIG. 1 uses the same inductor L on the charge/discharge path, if the rising time is made to be fast by setting the inductance of the inductor L to be small, the energy recovering efficiency decreases as it peak current becomes big. On the contrary, in the conventional energy recovering circuit, if the energy recovering efficiency is improved by setting the inductance of the inductor L to be big, because the rising time of the voltage supplied to the panel is lengthened, the discharge characteristics is deteriorated and it becomes difficult to obtain the sustaining time.
Also, because the conventional energy recovering circuit requires many semiconductor switching devices Sw1 to Sw4, an inductor L and a recovering capacitor for the operation of recovery, charge and sustaining steps, its manufacturing cost is high.

Energy recovering circuit with boosting voltage-up and energy efficient method using the same


An object of the present invention is to provide a lighting device capable of properly performing a bounce motion and photography in the event of an unexpected motion. The lighting device of the present invention is a lighting device including a control unit that provides an instruction of an auto-bounce motion. When detecting an auto-bounce motion in S303, the control unit releases the brake of a motor for driving a light-emitting part and performs auto-bounce control in S304. When detecting that the bounce angle of the light-emitting part in the auto-bounce motion reaches a target position and the motor enters a stop period in S303, the control unit automatically switches to the application of an intermittently repeated regenerative brake to the motor. This can suppress a movement of the light-emitting part even in an accidental motion and perform a proper bounce motion with an easy manual operation.

In conventional bounce flash photography, light from a lighting device is directed to a ceiling or the like and then is reflected and diffused therefrom onto a subject. Bounce flash photography allows indirect illumination of a subject instead of direct illumination from a lighting device, achieving photography with soft light.
Moreover, in order to automatically change the radiation direction of a lighting device so as to properly perform bounce flash photography, the lighting device detects the position of a light-emitting part (the position of a subject or a ceiling) by means of a bounce starter of a camera or the lighting device, calculates a proper bounce angle by means of a position detector, and automatically changes the radiation direction of the lighting device. This technique is known as auto-bounce flash photography. It is also known that a bounce angle is manually changed for fine adjustments after auto-bounce flash photography.
In a driving mechanism for driving the light-emitting part, a clutch mechanism, e.g., a slipping clutch for protecting the driving mechanism including a motor is typically provided in consideration of a manual rotation of the light-emitting part and abnormalities such as collision of the light-emitting part rotated by the driving mechanism with an obstacle.
Patent Literature 1 describes a lighting device including a light-emitting part that can be manually rotated and can be stopped at a predetermined angle by a click mechanism or a locking mechanism. The click mechanism or the locking mechanism may interfere with an operation of a driving mechanism and thus is preferably omitted or provided with minimum holding power.
Patent Literature 2 discloses a technique of braking simply by short-circuiting both poles of the motor of a driving mechanism when the motor is stopped, so that the direction of radiation of a light-emitting part is not changed by an accidental external force to a direction unpredictable by a user.