An apparatus and method for encoding input video data representative of a number of group of pictures (GOPs) each having a plurality of fields or frames. The apparatus includes a first encoder for processing received input video data so as to determine difficulty data of a field or frame which is indicative of the difficulty of the video data, a computing device for determining a target code amount representative of an amount of data to be utilized in accordance with the difficulty data of a number (N) of the fields or frames, and a second encoder for encoding the received video data in accordance with the target code amount. The computing device determines the target code amount such that the target code amount for an ith field or frame is determined in accordance with the difficulty data of the N fields or frames from a jth field or frame, the target code amount for an ith+1 field or frame is determined in accordance with the difficulty data of the N fields or frames from a jth+1 field or frame, the target code amount for an ith+2 field or frame is determined in accordance with the difficulty data of the N fields or frames from a jth+2 image, and so forth. As a result, an acceptable allocation of bits may be provided for the encoding processing such that an image may be restored with a relatively high quality.

The present invention relates to a method and apparatus for determining a target amount of code which may be used in a digital video disc (DVD) or the like or in a system for transmitting digital video broadcasting (DVB) digital data, and to a method and apparatus for compressing and coding noncompressed video data.
Techniques for reducing the amount of data during recording by converting video and audio signals to digital data and applying conversion and coding processing to the digital data have been standardized by MPEG (Moving Pictures Expert Group). Such processing may involve inter- or intra-coding of the video data for every macro block. In MPEG, a group of pictures (GOP) may include one frame or picture subjected to intra-coding (an I-picture), and a plurality of frames or pictures subjected to inter-coding which includes predictive coding (P-pictures) and bidirectional predictive coding (B-pictures).
In inter-coding processing, coding processing is applied to the difference between the video data of a current frame and the video data of a past frame. As is to be appreciated, the video data of the current frame may be easily obtained or restored if the video data of the past frame has been already sent.
In determining the above-described difference between frames of video data, motion detection and motion compensation processing may be performed.
Motion detection processing involves detecting or determining the position or macroblock in a past reference frame in which the sum of absolute values of differences of pixel values between such macroblock and the respective macroblock of the current frame is the smallest. Such detection may be performed by determining the number of pixels the macroblock needs to be moved from the position of the respective current frame macroblock in an X- and Y-direction such that the sum of absolute values of differences of the pixel values between the respective current frame macroblock and the reference frame macroblock is the smallest. Data representative of such amount of movement in units of pixels in the X- and Y-directions may be referred to as motion vector data.
Motion compensation processing involves determining a position based upon the motion vector data and the position of the past reference frame macroblock and extracting macroblock data pertaining to such position. Thereafter, the difference between the extracted past reference macroblock and the current respective macroblock, or the motion predictive error, is determined. The past reference frame may be obtained from a local decoder.
The motion predictive error signal may be subjected to orthogonal transformation, such as discrete cosine transformation (DCT) in units of predetermined blocks so as to remove the correlation in the space direction. From such DCT processing, transformed DCT coefficient(s) may be obtained which are subjected to quantization processing (that is, division by a quantization step) to eliminate fine signals whereafter the whole number value of such quotient and a quantization index are outputted. The quantized DCT coefficient(s), the quantized index, and the motion vector data may be variable length coded (VLC) and outputted.
In intra-coding processing, on the other hand, the above-described motion detection and motion compensation processing are not performed. Instead, pixel values are orthogonal transformed in block units, quantized, variable length coded, and outputted.
The above-described processing removes the redundancy in the time and space directions of the video data, thereby compressing the information data. Such compression enables image and audio data to be recorded on a single optical disk (such as a digital video disc-DVD), or a moving picture and audio data to be transmitted within the transmission line capacity of a telecommunications line or a satellite line.
Consider a situation wherein a DVD, a ROM disk, or the like is used. In such situation, the compressed and coded video data should be contained within the capacity of the disc. To accomplish such requirement, so-called variable rate coding may be utilized wherein the amounts of codes are allocated within the range of the amount of code so as to obtain the highest image quality. Such coding method utilizes or accounts for the fact that difficulty in image compression may fluctuate with time due to constant changes of the correlation strength of the video data in the time and space directions.
An example of the above-described fluctuation or change of correlation strength in the time direction will now be presented. A pattern of movement of a moving body in a moving picture may include not only simple parallel movement, but also complex movement patterns such as a change of movement speed, movement direction of the moving body, and shape of the moving body. In such a situation, the motion predictive error data may be increased by motion compensation in a manner as previously described. Alternatively, in moving picture data having little or no correlation in a time direction (such as random noise), the effect of compression by motion compensation may be negligible and motion predictive error data not much different in amount and/or data from that of the current frame may be generated. Such fluctuation in the difficulty of the image compression may exist not only with frame units, but also with other types of units such as GOP units, macroblock units, and so forth.
Accordingly, when compressing and coding data which fluctuates in difficulty (such as video data having a low correlation in the time and space directions) by a uniform bit rate (hereinafter, a "target code rate") per unit time, the DCT coefficient(s) may be quantized by a relatively large quantization step so that the generated code rate approaches the target code rate. As such, a relatively large quantization error may result and noticeable or conspicuous coding distortion may occur when expanding and decoding the data. On the other hand, when compressing and coding data having a low fluctuation in difficulty (such as video data having a high correlation in the time and space directions), the DCT coefficient (s) may be concentrated at the low frequency component side so as to finely quantize the same by a relatively small quantization step so that the generated code rate approaches the target code rate or target code amount. As a result, distortion after expansion and decoding of the data may be reduced.
Therefore, in recording on DVDs or the like, to avoid coding distortion due to image fluctuation over time and the deterioration of the image quality, variable length coding using a so-called 2 path or 2-pass encoding technique may be utilized. In such 2-pass encoding technique, video data is compressed and coded by a fixed quantization step, and the amount of codes generated is defined as the difficulty data and stored in a first pass or path, and, during a second path or pass, compression and coding are performed based on the difficulty data such that a relatively large amount of code may be allocated to difficult video data and a relatively small amount of code may be allocated to non-difficult video data. (The term "difficult data" refers to the amount of data necessary to obtain a certain constant image quality.)
In the above-described 2-pass encoding technique, the actual encoding (second pass) commences after encoding all of the video data in the first pass. As a result, it is very difficult, if not impossible, to perform such technique on supplied video and audio data with no interruption(s). Due to such limitation, such 2-pass encoding technique may not be suitable for encoding at the time of communication and broadcasts in which relatively long data streams should be encoded without interruption and in real time.
Alternatively, a 2-path or 2-pass technique may be utilized which uses two encoders, that is, a first encoder for encoding data passing through a memory having an FIFO (first-in first-out) configuration and a second encoder for encoding the data not passing through such memory. Hereinafter, this 2-pass encoding technique will be referred to as a "simplified 2-pass encoding" technique to distinguish it from the above 2-pass encoding technique. In the simplified 2-pass encoding technique, difficulty information of the received data is obtained in the first path or pass and the data is encoded using the obtained difficulty information in the next path or pass. Two types of simplified 2-pass encoding techniques may be utilized. In one type, a target amount of bits of each GOP is determined based on difficulty information of several GOPs. This type may be considered rate control in units of GOPs. The other type controls the target amount of bits in each picture unit in the GOP and may be considered rate control in units of pictures.
In the simplified 2-pass encoding, difficulty information may be obtained from a number (K) of GOPs and utilized for such GOPs. As such, information pertaining to patterns before and after the K number of GOPs may not be utilized in obtaining the difficulty information for any of such K GOPs. However, utilizing such obtained difficulty information, without using the information of the patterns before and after the K GOPs, may present a problem upon encoding the data. Such problem will be explained hereinbelow with reference to FIGS. 5A to 5D.
Assume that the difficulty of input materials or data is as shown in FIG. 5A. (In FIG. 5A, the ordinate axis represents the difficulty, and the abscissa axis represent time in GOP units. Further, in FIG. 5, the amount or length of the difficulty data which may be obtained in advance, that is, the capacity of the FIFO memory, is 2 GOPs.) As shown in FIG. 5A, the difficulty of the input data gradually rises to a high value in the period of the first two GOPs, falls to a low value at the start of the period of the next two GOPs and remains at such low value for the remainder of this period, rises to a high value after entering the period of the next two GOPs and gradually falls to a low value thereafter. (In FIG. 5, the difference of difficulty according to picture type is ignored for simplification.) Ideally, input data having a difficulty distribution as shown in FIG. 5A should have an amount of bits allocated in proportion to such difficulty distribution as shown in FIG. 5B. Such ideal bit amount distribution provides equitable arrangement in that it enables a large amount of bits to be used for a difficult pattern and a small amount of bits to be used for a simple pattern. Further, such distribution may enable encoding to be performed without deteriorating (or without significant deterioration of) the image quality. (As a reference, the average amount or rate is shown in FIG. 5B by a broken line.)
FIG. 5C illustrates an allocation of the amount of bits in GOP units obtained by the simplified 2-pass encoding. As shown therein, such bit allocation is flat or constant within each GOP unit and is not proportional to the difficulty distribution shown in FIG. 5A. Such flat or constant allocation in each GOP is the result of allocating the amount of bits in units of GOPs.
FIG. 5D illustrates an allocation of the amount of bits in picture units obtained by the simplified 2-pass encoding. Since the allocation of the amount of bits is performed in units of pictures, such bit allocation is proportional to the difficulty distribution shown in FIG. 5A. However, such bit allocation of FIG. 5D is smaller in several portions thereof (that is, the first and last third) than that shown in FIG. 5B. Such difference in bit allocation is a result of allocating the amount of bits in units of two GOPs. That is, if the allocation of the amount of bits is determined in units of two GOPs, the amount of allocated bits may be insufficient within two GOPs having a difficult pattern or wherein a difficult pattern continues, and the amount of allocated bits may be excessive within two GOPs having a simple pattern or wherein a simple pattern continues.
Therefore, the above-described simplified 2-pass encoding technique may not provide a proper allocation of bits.
Further, when compressing and coding noncompressed digital video data by the method of the MPEG (Moving Picture Experts Group) or the like and recording the same on a recording medium such as a magneto-optical disc (MO disc), it is necessary to reduce the amount of data (bit amount) of the compressed video data after the compression and coding to less than the recording capacity of the recording medium while enhancing the quality of the video after expansion and decoding as much as possible.
In order to satisfy this need, there has been adopted a method of first preliminarily compressing and coding the noncompressed video data and estimating the amount of data after the compression and coding (first path), then adjusting the compression rate based on the estimated amount of data and carrying out the compression and coding so that the amount of data after the compression and coding becomes less than the recording capacity of the recording medium (second path) (hereinafter, such a compressing and coding method will be described as "two-path encoding" too).
When carrying out the compression and coding by the two-path encoding, however, it is necessary to apply similar compressing and coding processing two times with respect to the same noncompressed video data, so a long time is taken. Further, since the final compressed video data cannot be generated by one compressing and coding processing, it is not possible to compress and code and record the captured video data in real time as it is.
Furthermore, when compressing and coding noncompressed digital video data in units of GOPs (groups of pictures) comprised by I-pictures (intra-coded pictures), B-pictures (bi-directionally coded pictures), and P-pictures (predictive coded pictures) by the method of the MPEG (Moving Picture Experts Group) or the like and recording the same on a recording medium such as a magneto-optic disc (MO disc), it is necessary to reduce the amount of data (amount of bits) of the compressed video data after the compression and coding to less than the recording capacity of the recording medium or less than the transmission capacity of the communication line while maintaining a high quality of the video after expansion and decoding.
For this purpose, there is adopted a method in which the noncompressed video data is first preliminarily compressed and coded and the amount of data after the compression and coding is estimated (first path), then a compression rate is adjusted based on the estimated amount of data and the compression and coding are carried out so that the amount of data after the compression and coding becomes less than the recording capacity of the recording medium (second path) (hereinafter, such a compressing and coding method will be also referred to as "two-path encoding").
When carrying out the compression and coding by the two-path encoding, however, it is necessary to apply similar compressing and coding processing two times with respect to the same noncompressed video data, so a long time is taken. Further, since the final compressed video data cannot be generated by one compressing and coding processing, it is not possible to compress and code and record the captured video data in real time as it is.
Further, when a plurality of series of noncompressed video data (hereinafter, also referred to as scenes) not correlated in the time direction are continuously connected to obtain one series of noncompressed video data by edit processing (edited video (Y data) and this edited video data is compressed and coded by for example a picture type sequence I, B, P, B, P, B, P, B, P, B, P, B, the first picture after the compression and coding sometimes becomes the P-picture. In order to expand and decode this first P-picture, it is necessary to refer to the picture immediately before the compressed video data generated from the other scene. When a picture generated from another scene not having correlation is used for the expansion and decoding of the first P-picture, however, the motion prediction error is considerably increased and therefore an enormous amount of data becomes necessary. Where only a limited amount of data can be used, the video after the expansion and decoding is deteriorated.
Japanese Unexamined Patent Publication No. 7-193818 discloses an image processing method and an image processing apparatus to solve such a problem. In the image processing method and the image processing apparatus disclosed in Japanese Unexamined Patent Publication No. 7-193818, when the noncompressed edited video data containing for example two scenes (a first scene and a second scene) is compressed and coded by for example the above picture type sequence I, B, P, B, P, B, P, B, P, B, P, B, the compression and coding are carried out by changing the leading P-picture of the second compressed video data (I.sub.2, B.sub.2, P.sub.2 in the following picture type sequence) obtained by compressing and coding the second scene to the I-picture not referring to the last picture of the first compressed video data (I.sub.1, B.sub.1, P.sub.1 in the following picture type sequence) obtained by compressing and coding the first scene and further changing the last I-picture of the first compressed video data to the P-picture so as to suppress an increase of the amount of the data generated.
That is, specifically, the image processing method and the image processing apparatus disclosed in Japanese Unexamined Patent Publication No. 7-193818 are constituted so that when the compression and coding are carried out without a change of the picture type sequence and the first compressed video data and the second compressed video data are obtained by a picture type sequence B.sub.1, I.sub.1, B.sub.1, P.sub.1, B.sub.1, P.sub.1, B.sub.1, P.sub.2, B.sub.2, P.sub.2, B.sub.2, P.sub.2, B.sub.2, the last I-picture of the first compressed video data is changed to the P-picture, and further the first P-picture of the second compressed video data is changed to the I-picture to perform the compression and coding and thereby obtain the first compressed video data and the second compressed video data of the picture type sequence B.sub.1, P.sub.1, B.sub.1, P.sub.1, B.sub.1, P.sub.1, B.sub.1, I.sub.2, B.sub.2, P.sub.2, B.sub.2, P.sub.2, B.sub.2.

Method and apparatus for controlling a target amount of code and for compressing video data


A high voltage DC power supplier includes: a transformer driven by a switching device, transforming an input voltage to a certain level of high voltage, and outputting the transformed high voltage; a diode and a capacitor for rectifying and smoothing the high voltage outputted from the transformer, and supplying the smoothed voltage to an ER fluid application unit; a discharge circuit for forcibly discharging the output voltage when an output voltage of the capacitor descends; and a controller for controlling a turn-on operation of the switching device on the basis of a difference value between the output voltage and a reference voltage so that the output voltage can follow a target voltage, and outputting a control signal for driving the discharge circuit to the discharge circuit when it reaches a discharge period.

1. Field of the Invention
The present invention relates to a high voltage DC power supplier and, more particularly, to a high voltage DC power supplied used for an electro-rheological (ER) fluid application units.
2. Description of the Background Art
In general, a strong electric field is to be formed in fluid in an ER fluid application unit to control a damping factor. The damping factor is adjusted by changing a strength of the electric field. Thus, in order to control the damping factor in the ER fluid application unit, a high voltage DC power supplier is needed to apply a strong electric field and vary a voltage.
The ER fluid application unit has capacitance load characteristics with an equivalent resistance and a capacitor component mixed therein. In order to obtain a fast transient response characteristics, a current should be supplied or cut off at a high speed so that electric charges can be charged quickly in the equivalent capacitor or already charged electric charges can be quickly discharged.
The equivalent resistance value of the ER fluid application unit varies depending on an applied voltage of both ends. That is, the equivalent resistance value is in inverse proportion to the applied voltage and exponentially changes. Accordingly, if the applied voltage is high, a resistance value is small and thus a high current flows. Meanwhile, if an applied voltage is xe2x80x980xe2x80x99, the resistance value is infinite and thus no current flows. This will now be described with reference to FIG. 1.
FIG. 1 is a circuit diagram of a high voltage DC power supplier in accordance with a conventional art.
As shown in FIG. 1, the high voltage DC power supplier includes: a transformer T1 for transforming an input voltage (Vs) to a high voltage of a certain level according to an electromagnetic induction operation, and outputting the transformed high voltage; a MOS transistor M1, a main switching device, for driving the transformer T1; and a diode D1 and a capacitor C1 for rectifying and smoothing the high voltage excited through secondary coil of the transformer T1 and supplying the smoothed voltage toward an ER fluid application unit.
The operation of the high voltage DC power supplier will now be described with reference to FIG. 2.
FIG. 2 is a graph showing discharge characteristics of an output voltage of FIG. 1.
First, the MOS transistor M1 is repeatedly turned on/off at a certain period by a controller (not shown). When the MOS transistor M1 is turned on, the input voltage (Vs) flows through the primary coil of the transformer T1 and the MOS transistor M1, according to which a high voltage with a certain level is excited in the secondary coil of the transformer T1.
The high voltage excited in the secondary coil of the transformer T1 is rectified by the diode D1 and smoothed by the capacitor C1, and an output voltage (Vo) of the capacitor C1 is supplied to the ER fluid application unit. The ER fluid application unit signifies an equivalent circuit 1 of the ER fluid application unit.
For reference, a ratio (Vo/Vs) of the input/output voltage is determined by a duty ratio of the MOS transistor M1 and a turn ratio of the primary and secondary coils of the transformer T1.
However, the high voltage DC power supplier with the structure as shown in FIG. 1 has a difficulty obtaining quick response characteristics when an output voltage (Vo) descends. The reason is because, in order to obtain quick response characteristics, the electric charges stored in the capacitors (C1, CL) should be quickly discharged when the output voltage (Vo) descends, but the electric charges are not transmitted to the secondary coil of the transformer T1 by the diode D1 and when the output voltage (Vo) is low, the resistance (RL) value is very high and thus the discharge time constant is increased. Therefore in the high voltage DC power supplier in accordance with the conventional art, since the output voltage (Vo) is gradually discharged as shown in FIG. 2, it fails to obtain a quick response characteristics.
As aforementioned, the conventional high voltage DC power supplier fails to obtain quick response characteristics since the voltage stored in the capacitor is gradually discharge when the output voltage descends in terms of the circuit characteristics.
Therefore, an object of the present invention is to provide a high voltage DC power supplier that is capable of quickly discharging a voltage stored in a capacitor by additionally installing a discharge circuit with a simple construction in an output stage of a high voltage DC power supplier and driving the discharge circuit at every discharge time point.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a high voltage DC power supplier including: a transformer driven by a switching device, transforming an input voltage to a certain level of high voltage, and outputting the transformed high voltage; a diode and a capacitor for rectifying and smoothing the high voltage outputted from the transformer, and supplying the smoothed voltage to an ER fluid application unit; a discharge circuit for forcibly discharging the output voltage when an output voltage of the capacitor descends; and a controller for controlling a turn-on operation of the switching device on the basis of a difference value between the output voltage and a reference voltage so that the output voltage can follow up a target voltage, and outputting a control signal for driving the discharge circuit to the discharge circuit when it reaches a discharge period.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.


In a network system having a network diagnostic facility, a plurality of control units are provided, each one of the control units being connected to a common communication line via its corresponding branch line to enable a mutual communication with the other control unit; and a normal state checking facility responsive to a diagnostic command signal from a network diagnostic device to transmit an interrogation signal from any one of the control units to all of the other control units which are connected to the common communication line and to output respective results of receiving acknowledgement signals from the all of the other control units within respective constant periods of time in response to the interrogation signal transmitted from the one of the control units to the diagnostic device, the health state checking facility being installed on each of the control units. The network diagnostic device generates a correlation map for an engineer to intuitively recognize a location of the failure in the network system.

a) Field of the Invention
The present invention relates to a network diagnostic device, a network diagnostic method, and a network system having diagnostic facility for the network.
b) Description of the Related Art
In a previously proposed diagnostic method for a network having a plurality of control units, each control unit being connected to a common communication line via a corresponding branch line, a communication malfunction indicative lamp installed for each control unit is illuminated to inform a user of an occurrence of the communication malfunction and, then, the user replaces the corresponding control unit on which the communication malfunction indicative lamp is illuminated with a new one so that the network is recovered to its original, normal communication state in a case where each control unit detects the occurrence of the malfunction of communications in itself, viz., within an internal of its control unit by means of its self-diagnostic function.
In the previously proposed diagnostic method for the network, in a case where the control unit itself has failed, the network system is recovered to its normal communication state with the failed control unit replaced with the new one.
However, in a case where a failure (or, so-called, a trouble) due to a broken line or due to a ground fault occurs in a certain point of place in the common communication line, the self-diagnostic function (facility) that each control unit has cannot identify the failed point of place (cannot locate the trouble) and the user must remove sequentially the related control units on each of which the communication failure indicative lamp is illuminated to identify the failed point of place, thereby lots of cost and time being required.
It is therefore an object of the present invention to provide a network diagnostic device, a network diagnostic method, and a network system having a diagnostic facility which can easily locate the trouble in communication even in the common communication line of the network in addition to the trouble in each branch line connected to its corresponding one of the plurality of control units when a communication malfunction in the network occurs.
The above-described object can be achieved by providing a network diagnostic device, comprising: a diagnostic communication line connected to all of a plurality of control units, each of the control units being connected to a common communication line via its corresponding branch line to enable a mutual communication with the other control unit; a normal state determining section that operatively performs such a network diagnostic processing as to cause each one of the control units to transmit an interrogation signal to all of the other control units and as to determine whether an acknowledgement signal is transmitted from each of the all of the other control units to the each one of the control units in response to the interrogation signal within a predetermined period of time to determine a normal state of a communication between each one of the control units and the other thereof; and a map display section that displays a correlation map in a matrix form having a plurality of matrix intersections, each matrix intersection being a one-to-one combination of any one of the control units and the other of the control units and being displayed in a pattern such as to be discriminated between the normal state of the communication and an abnormal state thereof.
The above-described object can also be achieved by providing a network diagnostic method, comprising: connecting a diagnostic communication line to all of a plurality of control units, each of the control units being connected to a common communication line via its corresponding branch line to enable a mutual communication with the other control unit; performing such a network diagnostic processing as to cause each one of the control units to transmit an interrogation signal to all of the other control units and as to determine whether an acknowledgement signal is transmitted from each of the all of the other control units to the each one of the control units in response to the interrogation signal within a predetermined period of time to determine a normal state of a communication between each one of the control units and the other thereof; and displaying a correlation map in a matrix form having a plurality of matrix intersections, each matrix intersection being a one-to-one combination of any one of the control units and the other of the control units and being displayed in a pattern such as to be discriminated between the normal state of the communication and an abnormal state thereof.
The above-described object can also be achieved by providing a network system having a network diagnostic facility, comprising: a plurality of control units, each one of the control units being connected to a common communication line via its corresponding branch line to enable a mutual communication with the other control unit; a normal state checking facility responsive to a diagnostic command signal from an external to the network system to transmit an interrogation signal from any one of the control units to all of the other control units which are connected to the common communication line and to output respective results of receiving acknowledgement signals from the all of the other control units within respective constant periods of time in response to the interrogation signal transmitted from the one of the control units to the external to the network system, the health state checking facility being installed on each of the control units.

Diagnostic device, diagnostic method, and network system having diagnostic facility


A single shaft type table feed device comprises a movable body and an auxiliary movable body 34. The movable body is supported by a guide rail 31 and can be freely moved by a feed screw shaft 35 in the axial direction thereof. The auxiliary movable body 34 includes an inside diameter portion through which the feed screw shaft 35 can be inserted. The auxiliary movable body 34 is supported by the guide rail 31 and freely movable in the axial direction thereof. The inside diameter portion 38a of the auxiliary movable body 34 is slidingly contacted with the feed screw shaft 35.

The present invention relates to a single shaft type table feed device including a movable body and an auxiliary movable body and, in particular, to a single shaft type table feed device in which the auxiliary movable body can fill a role of the part of an intermediate support, to thereby be able to enhance the critical speed of a feed screw shaft.
Conventionally, as a table feed device using a feed screw shaft, there are known various types of table feed devices. One of them is a single shaft type table Seed device which is a feed screw integrally combined linear guide device obtained by combining a Seed screw device with a linear guide device into an integrally united body.
In particular, a single shaft type table feed device to be improved by the invention is a single shaft type table feed device in which there are mounted not only a movable body including a screw nut portion engageable with the feed screw shaft but also an auxiliary movable body not including a screw nut portion so as to enhance the resistance of the feed screw shaft to a load applied thereto.
Recently, there has been increasing a demand for enhancing the feed speed of the single shaft type table feed device of this kind.
By the way, in the table feed device using a feed screw shaft, if the number of working rotations of the feed screw shaft approaches the natural frequency of the feed screw shaft, then it becomes a so called critical speed, thereby producing resonance. Since the critical speed is in inverse proportion to the square of the support distance of the feed screw shaft, if the support distance is set as short as possible to thereby enhance the natural frequency of the feed screw shaft, then the critical speed of the feed screw shaft can be increased effectively. Therefore, in a feed screw shaft having a long length, generally, as shown in FIG. 7, an intermediate support 2 in sliding engagement with the feed screw shaft 1 is set at an intermediate position in the support distance of the feed screw shaft on a base member. In this case, in order to prevent interference between the intermediate support 2 and a nut 4 which is in threadedly engagement with the feed screw shaft 1 and is mounted on a table 3, there is provided a limit switch 5; that is, when the table 3 passes, the intermediate support 2 can be retreated in accordance with the limit switch 5.
Also, in the Japanese Patent No. 2526816, there is disclosed another example of the intermediate support. In this intermediate support, as shown in FIG. 8, two guide rails 7 are fixed to two side portions of a base member in parallel to each other, a pair of table linear motion bearings (that is, table sliders) 8 are fitted on each of the two guide rails 7 in such a manner that they can be freely moved in the axial direction of the guide rails, and a table 3 is fixed to each of the table sliders 8 on the top surfaces thereof. A feed screw shaft 1 is interposed between and extended in parallel to the two guide rails; in particular, one end side of the feed screw shaft 1, which is to be connected with a drive motor 13, is supported by a support unit 11, whereas the opposite end side thereof is supported by a support bearing 12. An intermediate support 14 is interposed between the support bearing 12 and a table nut 4 which is threadedly engaged with the feed screw shaft 1 through balls. Also, the intermediate support 14 includes an intermediate support frame 16 which is supported by intermediate support linear motion bearings (that is, intermediate support sliders) 15, 15 respectively fitted with the guide rails 7, 7, and an intermediate support nut 17 which is threadedly engaged with the feed screw shaft 1 through balls and is supported in such a manner that it is prevented from moving in the axial direction with respect to the intermediate support frame 16 but can be rotated freely. On the other hand, between the feed screw shaft 1 and one guide rail 7, there is disposed an auxiliary feed screw device 20 which comprises an auxiliary feed screw 18 having an axis parallel to the feed screw shaft 1 and supported on the base member, and an intermediate support feed nut 19 which is threadedly engaged with the present auxiliary feed screw 18. And, the intermediate support feed nut 19 is fixed to and mounted on the intermediate support frame 16 of the intermediate support 14. Also, the end portion of the auxiliary feed screw 18 having a uniform pitch and the end portion of the feed screw shafts 1 are connected together by auxiliary feed screw drive means 21 which comprise a timing belt and a timing pulley in such a manner that the auxiliary feed screw 18 can be rotated at one half of the number of rotations of the feed screw shaft 1. With use of the intermediate support 14, if the feed screw shaft 1 is driven or rotated by the drive motor 13, then the table nut 4 is moved and, in linking with the movement of the table nut 4, the intermediate support 14 is moved in the same direction by an amount of one half of the moving amount of the table nut 4. Due to this, the intermediate support 14 is always allowed to support the feed screw shaft 1 almost centrally between the table nut 4 and support bearing 12, thereby being able to enhance the critical speed of the feed screw shaft 1.
Conventionally, a single shaft type table feed device including an auxiliary movable body increases a span between the nut portion of the movable body and the supporting shaft, because the auxiliary movable body having an unloaded hole which is not engaged with the feed screw shaft is interposed between a movable body including a nut portion to be threadedly engaged with a feed screw shaft and a bearing for supporting the end portion of the feed screw shaft.
As a result, the natural frequency of the feed screw shaft is lowered, that is, the critical speed is lowered, thereby often raising a problem that the use of the single shaft type table feed device at the high speed feed is limited. As a measure to deal with this problem, there can be provided an intermediate support in the single shaft type table feed device.
However, in the conventional intermediate support 2 shown in FIG. 7, there is found a drawback as follows: that is, it is necessary to provide a retreat mechanism which is capable of retreating the intermediate support 2 when the table 3 or table nut 4 passes through the intermediate support 2. In fact, the retreat mechanism is complicated in structure and, therefore, it is not proper from viewpoints of not only cost but also space to use the conventional intermediate support 2 including such complicated retreat mechanism as an intermediate support of a single shaft type table feed device inherently having a compact structure.
On the other hand, in the conventional intermediate support 14 shown in FIG. 8 as well, there is also found a drawback as follows: that is, it is necessary to provide the auxiliary feed screw device 20 which is capable of moving the intermediate support 14 in linking with the table nut 4, but the auxiliary feed screw device 20 is complicated in structure. Therefore, similarly to the intermediate support 2, it is not proper to use the conventional intermediate support 14 as an intermediate support of a compact single shaft type table feed device from viewpoints of cost and space.