BACKGROUND AND SUMMARY OF THE INVENTION 
       [0001]    The invention concerns a clip machine for dividing up and closing tubular packagings filled with filling material, and a method of controlling such a clip machine. 
         [0002]    In particular the invention concerns a clip machine for dividing up and closing tubular packagings filled with filling material by means of closure clips, comprising at least a first and a second closure tool unit which for setting and closing at least one closure clip (clip) are reversibly movable relative to each other between an open position and a closure position. The invention further concerns a method of controlling such a clip machine. 
         [0003]    A clip machine of the kind set forth hereinbefore is typically used to close bags or tubular packagings (tubular casing or sausage case) filled with liquid to thick-pasty or also (in part) granular content. Firstly in that procedure the filling material is introduced into the packaging and thereafter, in the case of a tubular packaging, divided up into portions by means of displacement elements. For that purpose the displacement elements constrict the tubular casing in the radial direction and displace the filling material which is in the constriction region in the axial direction, with respect to the tube axis. A tubular plaited portion is thus formed in the constriction region. In the next working cycle a closure element or in the case of a double clip arrangement two closure elements such as closure clamps or clips are applied to the tubular plaited portion formed, by means of the two closure tools which are moved relative to each other. The closure tools respectively include in paired relationship a punch and a die, between which the clip is converted in shape during the closure operation until the closure position is reached (reversal point of the movement). After closure the closure tools are moved back into their starting or open position. 
         [0004]    High demands are made on the quality of such a closure. On the one hand it may not be so firm that the packaging casing is damaged in the closure procedure whereby filling material can escape or be contaminated. On the other hand however the closure must be sufficiently sealing so that for example in subsequent handling of the closed product it does not slip out of the packaging casing. 
         [0005]    To ensure secure closure of the closure clips, in known clip machines the closure spacing or closure height, that is to say the smallest distance between the punch and the die when the clip is closed around the tubular plaited portion, is checked and adjusted. As is known for that purpose the rest position of at least one of the closure tools is altered. 
         [0006]    EP patent application 0 900 733 (U.S. Pat. No. 6,202,785) discloses a clip machine having a distance sensor for detecting the closure spacing with a distance sensor arranged stationarily with respect to the closure tools, and a reference surface. That makes it possible to actually detect a value corresponding to the closure clip height. However the distance sensor is directly subjected to the acceleration forces acting on the closure tools as it is fixedly connected thereto and is moved therewith. Depending on the sensitivity of the respective sensor the function thereof can be adversely affected thereby or the sensor itself can be damaged, whereby reliable accurate detection of the closure spacing is no longer guaranteed. A further possible error source is formed here by the connecting lines of the distance sensor, which by virtue of the movement of the sensor in each closure operation are also moved and deformed and in that way can be damaged. 
         [0007]    German laid-open application No 10 2005 026 219 (US 20060272374) further discloses a clip machine having a measuring device which detects the resilient deflection or spring travel of a spring upon closure of a clip, deduces the closure force therefrom and compares it to predetermined values. If a predetermined value for the spring travel is exceeded the rest position of one of the closure tools can be re-adjusted manually or by motor means. If the spring travel exceeds a maximum value it is provided that the clip machine is stopped. The arrangement further has a position sensor for monitoring the rest position of the closure tool. That known clip machine permits an approximately constant pattern in respect of the spring travel and thus indirectly the closure force. The measuring device of that clip machine is however of a complicated structure with many components which can represent potential sources of error. 
         [0008]    Therefore the object of the present invention is to improve a clip machine and a method of controlling that clip machine such that the risk of misdirected manipulation is lessened, the loading on the closure tools is reduced and closure of a closure clamp or clip around the packaging casing is made into a more reliable procedure. 
         [0009]    In particular there is proposed a clip machine for dividing up and closing tubular packagings filled with filling material by means of closure clips, comprising at least a first and a second closure tool unit which for setting and closing at least one closure clip (clip) are reversibly movable relative to each other between an open position and a closure position. In accordance with the invention in that respect there is provided at least one piezoelectric sensor which is connected to one of the closure tool units and which is adapted to measure a closure force applied upon closure of a closure clip and to output a measurement value representing the closure force. 
         [0010]    A piezoelectric sensor includes one (or more) so-called piezoelectric crystal, on the crystal surface of which, when a mechanical strain is involved, there occur electrical charges, the magnitude of which is proportional to the strain. In the above-described arrangement the charge produced is therefore proportional to the closure force. Hereinafter in this context to simplify the situation reference will be made to measuring the closure force by means of the piezoelectric sensor. It is possible to use piezoelectric crystals such as quartz, piezoelectric ceramics but also all other suitable piezoelectric materials. 
         [0011]    A piezoelectric sensor arranged in the proposed fashion is capable at any time of determining the force just acting on the closure clip. In that way the closure operation can be terminated immediately when a prescribed value for the closure force is reached. That therefore in practice excludes the closure force exceeding the predetermined value. 
         [0012]    In an advantageous embodiment of the clip machine according to the invention the piezoelectric sensor is arranged in at least immediate proximity with the main flow of the closure force. In such an arrangement the piezoelectric sensor is disposed directly in the flow of force acting on the closure clip. Therefore the same force or a force of the same magnitude acts on the piezoelectric sensor as on the closure clip. Additional recalculation or modification of the value delivered by the piezoelectric sensor in order for example to be able to take into consideration geometrical factors of a closure lever such as flexing by virtue of a lever action are not required. That means that determining the closure force is simpler and more accurate. 
         [0013]    In that respect it is further advantageous if in the rest position of the closure tool unit the piezoelectric sensor is subjected to a prestressing with in a further configuration can be adjustable. That prestressing simulates an initial force which is already present, in which case the fact of that force falling below the specified value can indicate a technical problem such as jamming of a closure tool, from which a tensile stress can result. The display of such a value which differs from the selected prestressing can lead to a corresponding reaction on the part of the control system. The measurement range of the piezoelectric sensor can be displaced by virtue of the adjustability of the piezoelectric sensor prestressing, thereby permitting adaptation of the piezoelectric sensor to the control arrangement or to different clip sizes. In addition, prestressing of the piezoelectric sensor can prevent an unwanted change in the sign of the measurement values, as can occur in the case of a wrongly adjusted variation in the neutral position or a defective variation in the neutral position which is caused by fluctuations in the ambient conditions. That can eliminate a further possible source of error in terms of measurement. 
         [0014]    In a preferred embodiment the piezoelectric sensor is in the form of an encapsulated sensor. In that way it is protected from almost all environmental influences whereby the accuracy of the measurement values can be increased. In particular the piezoelectric sensor can be efficiently protected from moisture in that way as clip machines have to be regularly cleaned for hygiene reasons. 
         [0015]    In a further preferred embodiment the piezoelectric sensor is arranged on the support mounting of the closure tool units or is arranged stationarily relative to the machine housing, whereby the feed lines of the piezoelectric sensor can also be arranged stationarily relative to the machine housing. Both the piezoelectric sensor and also the feed lines are therefore not moved with the closure tools and are not subjected to the acceleration forces occurring in that case. That arrangement protects the piezoelectric sensor and the feed lines from damage due to the acceleration forces which occur and thus permits reliable measurement. 
         [0016]    It is moreover advantageous for the piezoelectric sensor to be mounted in a protected position in order to additionally protect it from damage due to moving parts. That can be implemented by a covering for the piezoelectric sensor. The piezoelectric sensor however can also be disposed in an opening or recess in the support mounting or in the machine frame. 
         [0017]    In addition in the clip machine according to the invention there can be provided a control unit with an event data memory which is adapted to at least temporarily store the current measurement value and compare it to a first selected value range. With sufficient memory space it is also possible to store series of measurement values over a prolonged time. 
         [0018]    By virtue thereof it is possible to read deviations in the closure force out of the memory in ongoing operation or also subsequently in order to be able to draw conclusions about incorrect operation or a malfunction. That enables inter alia the manufacturer of the clip machine to more quickly discover the causes for an operating disturbance or a defect on the machine or to permit or support quality control. 
         [0019]    It is advantageous if the control unit is adapted to compare the current measurement value with a second selected value range and to output a control signal if the measurement value leaves the second selected value range. A third selected value range characterizes an increased closure force which could lead to damage to the clip machine, the closure clip or the packaging material. Therefore in an embodiment according to the invention the control unit is adapted to compare the current measurement value with a third selected value range and to stop the clip machine if the measurement value leaves the third selected value range. 
         [0020]    In a further advantageous configuration of the clip machine according to the invention the control unit is adapted to record the variation in the closure force over travel and/or time and to analyze it in order upon deviations from a predetermined variation to output a signal which displays said deviation and/or acts in a predetermined manner on the clip machine. Analysis of the force-travel pattern and/or the force-time pattern permits conclusions to be drawn about the wear for example of the closure tools or also the quality of the closure clips. Ultimately it is possible to provide information about the quality of the closure, by means of that analysis. If in that respect an inadmissibly high level of wear is detected a corresponding signal can display that and automatically arrange maintenance of the clip machine or require the operator to perform maintenance. 
         [0021]    To ensure that the first and second closure tool units are in a predetermined position such as for example the rest position at the beginning of each closure operation there is further provided in accordance with the invention a position sensor, by means of which the rest position of at least one closure tool unit can be detected. The position sensor is connected to the control unit and can output a corresponding readiness signal upon detection of the at least one closure tool unit. The position sensor used can be for example a rotary sensor, the signal of which can be used to adjust the rest position of the at least one closure tool unit. 
         [0022]    In regard to the method according to the invention of controlling a clip machine, that affords the same advantages as are described hereinbefore in relation to the clip machine according to the invention. 
         [0023]    Further features and advantages of the clip machine according to the invention and the method according to the invention are described hereinafter in the following description of the embodiments by way of example with reference to the accompanying Figures. The terms “top”, “bottom”, “left” and “right” used in the description of the embodiments relate to the Figures of the drawings in an orientation with the references and Figure identifications being normally readable. In the Figures: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  shows a portion from a first embodiment of the clip machine according to the invention, 
           [0025]      FIG. 2  shows a portion from a further embodiment of the clip machine according to the invention, 
           [0026]      FIG. 3  shows a diagrammatic representation of an embodiment of the control system of the clip machine according to the invention, and 
           [0027]      FIG. 4  shows a flow chart of the closure operation and the clip machine control method according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]    The portion shown in  FIG. 1  illustrates a first closure tool unit of a first embodiment of the clip machine  100  according to the invention with a punch  110 . The punch  110  is driven by way of an elbow lever arrangement  112 . The elbow lever arrangement  112  has a first lever  114  and a second lever  116  which form a common elbow joint  118 . With its end remote from the elbow joint  118  the lever  114  is pivotally connected to a journal  122  stationarily connected to the punch  110 . The second lever  116  is pivotally connected to a support mounting  126 , with its end opposite to the elbow joint  118 . When the elbow lever joint  118  is bent or straightened by a force applied by way of a coupling bar  120  the punch  110  moves up and down between an upper open position and a lower closure position. In that case the punch  110  which is fixed on a punch carrier  124  is guided telescopically by a cylindrical guide  125  which is fixedly connected to the machine housing (not shown in greater detail). 
         [0029]    In the closure position the punch  110  has approached the die of a second closure tool unit (not shown), as far as a minimum closure spacing. When the elbow lever arrangement  112  is straightened and the punch  110  is thus moved into the closure position the force applied to deform and close a clip is therefore carried by way of the support mounting  126 . 
         [0030]    As shown in  FIG. 1  a piezoelectric sensor  138  is arranged at the support mounting  126 . It is fitted into a recess in the support mounting  126 , which in the illustrated embodiment is formed by two projections (not identified). A fixing device  140  (also not shown in greater detail) holds the piezoelectric sensor  138  in its position in the recess. It is possible by means of the fixing device  140  to brace the piezoelectric sensor  138  between the projections and thereby to act on it with a prestressing. For that purpose the fixing device  140  can be for example in the form of a manually actuable adjusting screw, by means of which the prestressing can be freely selectably adjusted. It will be appreciated that it is possible to provide an automated drive which can be connected to a control device and controlled thereby to adjust the prestressing. In this arrangement the piezoelectric sensor  138  is an autonomous measurement system, that is to say the closure force can be ascertained therewith, independently of further system components. 
         [0031]    In the illustrated embodiment shown in  FIG. 1  the support mounting  126  is connected directly and rigidly to the machine housing by way of an adjusting drive  142 ,  144 . The adjusting drive  142 ,  144  includes a drive motor  142 , for example a stepping motor, and an adjusting device  144 . The stepping motor  142  drives the adjusting device  144  which for example can be a per se known adjusting screw or by way of a toothed belt which operates in slip-free fashion. The adjusting device  144  which is set in rotation by the drive motor  142  about its longitudinal center line which coincides with the longitudinal center line of the cylindrical guide  125  displaces the support mounting  126  along its longitudinal center line with respect to the machine housing. That permits adjustment of the rest position of the punch  110 . 
         [0032]    In the illustrated embodiment the closure force applied upon closure of a clip is transmitted to the housing by way of the elbow lever arrangement  112  and the support mounting  126 . In that case the support mounting  126  is compressed. That compression effect is slight but is sufficient to exert a force on the piezoelectric sensor  138  arranged in the recess of the support mounting  126 . That causes the piezoelectric sensor  138  to be deformed and it outputs an electric signal corresponding to the force causing the compression effect, that is to say the closure force. 
         [0033]    In addition a position sensor  132  is so arranged on the machine housing that it is capable of establishing the rest position of the punch carrier  124  and thus the punch  110  secured thereto. In the illustrated embodiment this is a contactlessly measuring sensor such as for example an optical or capacitive sensor. It is however also possible to use a mechanically operating sensor. In addition it is possible to use a rotary sensor as the sensor for detecting the rest position of the punch carrier  124  and the thus the punch  110  secured thereto, by means of the signal of which the stepping motor of the adjusting drive  142 ,  144  can also be directly actuated. 
         [0034]    The closure force applied in a closure operation is determined in the above-described manner solely by the piezoelectric sensor  138  arranged in the recess in the support mounting  126 . That very simple measurement arrangement avoids possible sources of error and improves the accuracy of the measurement result as the number of deformed components has been reduced and it is possible to dispense with additional or unnecessarily complicated measurement devices. Adjustment or correction of the rest position of the punch  110  is effected for example in the manner described in greater detail with reference to  FIG. 2 . 
         [0035]    The portion of a further embodiment of the clip machine according to the invention, shown in  FIG. 2 , substantially corresponds to the embodiment of  FIG. 1 . Components which are identical or involve the same function are denoted by the same references. The clip machine of  FIG. 2  has the first closure tool unit which is identical to the  FIG. 1  embodiment, with the punch  110 , the elbow lever arrangement  112 , the adjusting drive  142 ,  144  and the piezoelectric sensor  138  arranged on the support mounting. 
         [0036]    Unlike the  FIG. 1  embodiment the support mounting  126  is connected to the machine housing by way of a support and mounting device  128 . More specifically the support and mounting device  128  has inter alia a spring  130  and the adjusting drive  142 ,  144 . The spring  130  is a compression spring which at its end opposite the support mounting  126  is supported against a housing  134  fixed stationarily to the machine housing of the clip machine  100 . 
         [0037]    As can further be seen from  FIG. 2  a position sensor  232  is arranged in the region of the first closure tool unit. The position sensor  232  is fixedly connected to the machine housing. By way of a pickup sensor which is not identified in greater detail the position sensor  232  can detect variations in the position of the support mounting  126  with respect to the machine housing. The position sensor  232  shown here is in the form of a mechanically operating travel sensor. It will be appreciated however that it is also possible to use other sensors which are capable of detecting a change in the position of the support mounting  126 , such as inductive or optical sensors. 
         [0038]    In a closure operation the spring  130  is also compressed in accordance with its spring characteristic by an amount dependent on the closure force. By reference to the spring travel, in addition to the signal of the piezoelectric sensor  138 , it is possible to infer the level of the closure force. To limit the spring travel or to be able to approach a given region of the spring characteristic of the spring  130  it is possible to prestress the spring  130 . If adjustability of the prestressing is provided, that can provide for example for adaptation of the control system. 
         [0039]    Additionally or also alternatively thereto it is possible to provide for a safeguard against overload by means of such a spring arrangement. In that case it is possible to select a spring which deforms only when a given force is reached, such as for example the desired closure force or a slightly higher force, so as to avoid exceeding the closure force and thus prevent damage to the clip machine, the packaging material and/or the closure clip, by the spring yielding. If, as described hereinbefore, the arrangement provides for adjustability of the prestressing, in that way it is possible to adjust the force at which the overload-preventing means is activated. 
         [0040]    The diagrammatic view in  FIG. 3  shows a control  200  by way of example for the clip machine according to the invention corresponding to the embodiments of  FIGS. 1 and 2 , which has a selection device  210  for the value ranges and a database  212  for the value ranges. The selection of one or more value ranges from the database is effected in dependence on the rest position value outputted by the position sensor  214  and/or on the basis of a read-in item of product information. The product information can be directly inputted manually by way of an input unit  216  for example before the commencement of production. Alternatively the product information can also be automatically read in out of a product information database (not shown). 
         [0041]    After the selection device  210  has made the selection of the value range or ranges a comparison device  218  of the control  200  makes a comparison of the value range or ranges with the measurement value which is outputted by the measuring device  220  and which represents the closure force applied upon closure of a clip. The comparison unit  218  then passes a command to a display device  222  to display the event and/or to an event data memory  224  for protocolling the event and/or to an adjusting drive  226  for adjusting or re-adjusting the rest position and/or to a main machine control  228  for stopping the clip machine. The comparison device  218  makes the choice to which of the components  222 ,  224 ,  226  and  228  is outputted, on the basis of the comparison of the measurement value obtained with the measuring device  220  with a plurality of value ranges, as described by way of example with reference to  FIG. 4 . The value ranges are typically different but can also be partly or completely coincident. 
         [0042]    The display device  222  displays the event. That can preferably be effected optically but also or additionally acoustically. Advantageously a display or screen in combination with an acoustic warning signal is appropriate for that purpose. 
         [0043]    An embodiment of the method according to the invention of controlling a clip machine will now be described with reference to  FIG. 4 . 
         [0044]    Each production start S 300  involves beginning initialization of the clip machine, which includes inter alia the control method according to the invention. At the same time a production selection is made with initialization at S 304 . The set-up method begins with determining the rest position S 302  by means of the position sensor which is coupled to an adjustable closure tool unit and which produces and outputs a rest position value representing the rest position of the set closure tool unit. On the basis of the product selection, a next method step S 306  involves checking whether the determined rest position value suits the selected product. If that is not the case the rest position is set in the method step S 308 . Setting is effected by means of a setting drive which can be controlled manually or automatically by a signal outputted by the control system in accordance with the product selection. In a further alternative any motor drive can be regulated by way of a rest position value which is virtually permanently detected so that it moves the closure tool into the desired reference position which suits the selected product. 
         [0045]    When the desired rest position value is reached the closure force is measured at S 310  with the first closure operation (and at each further closure operation). The measured closure force is compared in the interrogation step S 314  to the value range which was previously selected in the step S 312  and which is ascertained on the basis of the product selection made in step S 304 . If the comparison shows that the measured closure force lies outside the selected value range 3 the clip machine is stopped in the step S 316  and the event is protocolled and/or displayed in the step S 318 . 
         [0046]    If the measured closure force is in the selected value range 3 then in a next step S 320  the closure force is compared to a second selected value range. If the comparison shows that the closure force is outside the value range 2 the rest position is re-adjusted in the step S 322  and the event protocolled and/or displayed in the step S 324 . 
         [0047]    If the checking procedure in step S 320  shows that the measured closure force is also within the selected value range 2 then in a next step S 326  a check is made to ascertain whether it is in a first selected value range. If that is not the case the event is protocolled and/or displayed in step S 328 . 
         [0048]    In each of the steps S 318 , S 324  and S 328  the event protocol can contain items of information about the product selection, the set or determined rest position, the selected value range for the closure force and also the measured closure force and the action effected. 
         [0049]    If in contrast the checking operation in step S 326  shows that the measured closure force is also in the selected value range 1 then the next step S 330  involves querying whether production is concluded and/or whether in the meantime a manual command has been given to stop the machine. The same interrogation, whether production is concluded or whether a stop command has issued, in step S 330  is also effected in relation to step S 322  of adjusting the rest position if the measured closure force is outside the selected value range 2. If that is the case the machine is stopped in step S 332 . Otherwise the next closure cycle is set in operation with step S 310 . 
         [0050]    In the  FIG. 4  embodiment the value ranges are so staggered that, when the values rise above or fall below first limit values, that is only protocolled and/or displayed in order for example to obtain an indication of a possible error source, the effects of which however are acceptable in regard to wear of the clip machine and the durability of the closure produced. If the closure force rises above or falls below second limit values which generally cover a greater value range, the rest position is re-adjusted in order to bring the closure force back into an acceptable value range again. Whether the adjustment of the rest position was sufficient is checked in the next closure cycle by again measuring the closure force. That produces a closed regulating circuit. It will be noted however that if the closure force should be outside a still wider third value range, which generally occurs as a consequence of a malfunction or serious incorrect operation, the machine is stopped immediately to be able to remove the error before the production or indeed the machine can suffer damage. 
         [0051]    The use of a piezoelectric sensor for measuring the closure force makes it possible to measure the force not only at the time at which the closure spacing is reached but at any time during a closing operation. With the values recorded in that way it is possible for any closing operation to record and evaluate a force-time relationship and/or a force-travel relationship. 
         [0052]    Evaluation of those relationships, for example by a comparison with predetermined force relationships, makes it possible to obtain information about the quality of the closure. It is also possible to infer possible quality fluctuations in regard to the closure clips or wear of the closure tools, from deviations from ideal force relationships. In a development of the above-described control it is possible for the results of such evaluation to be incorporated into the control of the clip machine, insofar for example with excessively severe wear of the closure tools, a corresponding signal is outputted or the clip machine is stopped. 
         [0053]    The flow chart in  FIG. 4  only represents an embodiment by way of example. The number of value ranges can be reduced or also increased. It is thus possible to effect finer gradation. The value ranges can be partially or completely identical. Instead of or in addition to the product selection in step S 304 , the value range or ranges can be selected on the basis of the rest position which is determined in step S 302 . The control method according to the invention S 310  through S 328  is also not necessarily incorporated into the production procedure in the manner shown in  FIG. 4 . In particular it is possible to integrate various intermediate steps or subprograms into the illustrated operating procedure, in particular before step S 310  and/or after steps S 326  and S 328 . It is to be considered optional for product selection to be effected in accordance with step S 304  and checking to be effected in accordance with step S 306 . Adjustment in step S 308  and re-adjustment in step S 322  of the rest position can be correspondingly effected manually or automatically. For example it can also be provided that the steps S 302  through S 308  for adjustment for the rest position are effected not after the start of production but after product selection which is effected independently of a start signal. 
         [0054]    In a further configuration (not shown) of the clip machine according to the invention it is possible for the  FIG. 2  embodiment to be modified in such a way that the adjusting drive  142 ,  144  is omitted and the support mounting  126  is connected directly to the machine housing. Adjustment of the rest position of the punch  110  would then no longer be possible. As already mentioned the force acting on the punch  110  can be measured by means of the piezoelectric sensor  138  at any moment of a closing operation. In that case therefore the control could be modified in such a way that the drive for the punch  110  is switched off when a given value of the closure force is reached and a movement is initiated in the opposite direction. The machine construction and the control could thus be markedly simplified. 
         [0055]    It is further possible for the piezoelectric sensor  138  to be fitted into an opening in the support mounting  126  such as a bore or the like. The piezoelectric sensor  138  would then be disposed directly in the center of the main flow of force, whereby it would be possible to achieve still more accurate measurement of the closure force. 
         [0056]    Irrespective of its function described in connection with the control  200  the piezoelectric sensor  138  can also be used as a pure monitoring device which triggers stoppage of the clip machine if the value rises above or falls below a given measurement value range. If it can be ensured that the closure force does not depart from a preset range under normal operating conditions the control of the clip machine according to the invention can be further simplified in that way. As the clip machine is then stopped by the piezoelectric sensor  138  only in emergency situations such as machine damage or wear phenomena and in which repair is to be effected, post-regulation of the closure force by the control  200  can then be entirely omitted.
A clip machine for dividing up and closing tubular packagings filled with filling material by closure clips, including at least a first and a second closure tool unit which for setting and closing at least one closure clip (clip) are reversibly movable relative to each other between an open position and a closure position. There is provided at least one piezoelectric sensor which is connected to one of the closure tool units and which is adapted to measure a closure force applied upon closure of a closure clip and to output a measurement value representing the closure force.