Patent Publication Number: US-6339990-B1

Title: Gripping device, particularly for automatic printing and/or inserting machines

Description:
The invention concerns on the one hand a gripping device, particularly for automatic printing and/or inserting machines, with a first and second gripping element of which at least one gripping element can be moved relative to the other gripping element to grab sheet-like materials such as printed pages as well as with a measuring device for the recording of at least one position of the gripping elements towards each other, and on the other hand a method for recording a relative position of gripping elements within a gripping device. 
     Gripping devices of the kind described above are used, for example, by banks or insurance companies on machines for the automatic insertion of bank statements or invoices. Such machines take printed pages such as bank statements or invoices individually off a stack, fold them and slide them into an envelope, which is then sealed. 
     In familiar gripping devices at least one gripping element, for example, is opened with a cam controller or a compressed air cylinder and then closed again with spring elasticity. It could happen that due to a malfunction in the paper feed two or more sheets are grabbed by the gripping device and forwarded for further processing. It could therefore happen that, for example, two bank statements or two invoices that were meant for different customers are wrongly placed in one envelope. Such an error must be absolutely avoided, also in light of data protection issues. 
     In order to be able to avoid this error, the suggestion was made to attach an additional lever arm on at least one gripping element, which operates one or two limit switches, depending on the opening of the gripping device. The switch positions are evaluated in order to determine whether the gripping device grabbed no sheet, one sheet or more than one sheet. 
     However, this familiar solution has the disadvantage that the limit switches have complex mechanic adjustment features and have to be readjusted with every order due to changes in paper thickness. Also, the stability of the mechanical system is not sufficient so that the system is unsafe and prone to malfunctions despite complex adjustment procedures. 
     The invention is based on the task of further developing a gripping device of the kind described above in such a way that it is not prone to malfunctions and that adjustments to different paper thicknesses can be done in a simple maimer. 
     The problem is resolved with the device by equipping the measuring device with a transmitter and a sensor that is allocated to it for the continuous recording of the relative position between the first and the second gripping element, with the transmitter being arranged in a moveable gripping element and the sensor in a fixed gripping element, or vice versa. The signal emitted by the sensor can then be evaluated in a subsequent evaluating circuit. Due to the continuous recording process of the position between the two gripping elements, the evaluation of the signal can show whether—as desired—one sheet or—wrongly—more than one sheet is located between the gripping elements. Mechanical adjustments to changes in paper quality or paper thickness are no longer required. 
     The measuring device preferably releases an analog signal, the height of which is proportional to a distance formed between the gripping elements. 
     In a particularly preferred version, the transmitter has the design of a magnet and the sensor that of a Hall effect sensor. Here, the sensor can be arranged in the fixed gripping element and the magnet in or on the moveable gripping element. It is ensured that the magnet exercises an immediate effect on the sensor, i.e. moves closely in front of the sensor so that the position of the moveable gripping element can be recorded continuously. 
     Depending on whether the gripping device is empty, has grabbed one sheet or several sheets, the magnet reaches a different position with regard to the Hall effect sensor. The Hail effect sensor releases a slightly modified analog electric potential, which is evaluated. Apart from the number of sheets that were grabbed, this analog electric potential is also dependent on the thickness of one sheet. 
     The sensor is connected to a signal processing device for the purpose of evaluating the signals; the device consists of a compensating circuit, an amplifying circuit and an evaluating circuit. The sensor is connected to a first inlet of the compensating circuit, whose outlet on the one hand is connected to an inlet of the amplifying circuit and on the other hand to a first inlet of the evaluating circuit. The outlet of the amplifying circuit is connected to a second inlet of the evaluating circuit. 
     In order to compensate for the no-voltage of the sensor, a second inlet of the compensating circuit can be connected to a potentiometer. In this case, adjustment of no-voltage is done manually. In a preferred version, the second inlet of the compensating circuit is connected to a second outlet of the evaluating circuit in order to feed supply voltage from auxiliary circuits. The evaluating circuit releases analog supply voltage from circuits to the compensating circuit. In order to adjust the amount of supply voltage from auxiliary circuits, it is useful to feed the evaluating circuit also the non-amplified differential potential. 
     It has proven particularly beneficial to use an intelligent sensor with integrated compensating and amplifying circuits. In this sensor, the compensating and amplifying circuits are connected to a logic circuit such as a microprocessor, which in turn is connected to data storage such as EEPROM. The intelligent sensor has the particular advantage that no-voltage is compensated for internally and that amplification can be adjusted internally. 
     The components are selected by the implemented logic device (CPU), which during calibration of the sensor mounted on the gripping device obtains matching data from an external computer system via a communication line and stores it in a storage medium such as EEPROM. It has also proven beneficial to connect the sensor with a higher machine control system via an evaluating circuit and via a bus such as a CAN bus. 
     Furthermore, the invention refers to a method for recording a relative position of the gripping elements of a gripping device, which is characterized by the fact that the position of the gripping elements towards each other is continuously recorded, that in accordance with the number of sheet-like materials grabbed between the gripping elements a signal is generated with different signal values, that the signal values are compared to target values and that in the case of a deviation an error message is created. The signal released by the sensor is compensated, amplified and evaluated. During the evaluation process of the signal, the evaluating circuit can be fed auxiliary signals in order to be able to provide the time of the measurement (for example, gripping element closed). 
     For the adjustment of the evaluating circuit (Teach-In), a zero value U CLOSED  is determined in the case of closed gripping elements without sheet-like material and a target value U TARGET  in the case of closed gripping elements with sheet-like material. As described above, it is beneficial in certain versions to feed the evaluating circuit an auxiliary signal such as a trigger signal, which is generated when the gripping elements are closed. 
     On the other hand, a method where the gripping elements are brought into a defined position, preferably a closed position, after the sheet-like material has been filed would be feasible as well. Here, the gripping device can be closed for example on the way back, thus reached a defined position. A new measurement process is triggered with the subsequent opening. The signal emitted by the sensor is preferably determined in an analog-to-digital converter through continuous scanning and preferably further processed in a computer such as a micro-controller. The no-voltage U CLOSED  and/or target-value potential U TARGET  for a grabbed sheet is preferably determined in a learning phase. 
    
    
     Further details, benefits and features of the invention result not only from the claims and the features—either alone and/or in combination—derived from them, but also from the preferred examples as noted in the following description of the drawings. 
     They show: 
     FIG. 1 side view of a gripping device with a first and second gripping element, 
     FIG. 2 side view of the first gripping element in accordance with FIG. 1, 
     FIG. 3 a first version of a signal processing device, 
     FIG. 4 a second version of a signal processing device, 
     FIG. 5 a third version of a signal processing device, and 
     FIGS. 6 a / 6   b  time path of signals to be evaluated. 
    
    
     FIG. 1 depicts the side view of a gripping device  10 , which is equipped with a gripping arm  12  that is fastened with a first end  14  via a clamping device to the axis  18  of for example a machine for the automatic insertion of bank statements or invoices (not shown). At a second end  20  of the gripping arm  12  the gripping device  10  is equipped with a first gripping element  22  and a second gripping element  24 . The second gripping element  24  runs vertically to the gripping arm  12  and is firmly connected to it. The first gripping element  22  is part of a basically T-shaped lever  26  that is connected to the gripping arm  12  in a moveable fashion around an axis  28 . In order to be able to actuate the first gripping element  22 , the lever  26  is equipped with a leg  30 , which is connected to a protrusion  36  that extends from the gripping arm  12  via a spring element  32  and an actuating lever  34  such as a compressed air cylinder. 
     The design provides for the spring element  32  to be a tension spring so that the first gripping element  22  rests on the second gripping element  24  with spring tension for the gripping of sheet-like material such as printed pages. For the purpose of opening the gripping elements  22 ,  24 , the actuating element  34 , such as a compressed air cylinder, is opened by admitting compressed air. The gripping elements  22 ,  24  have opposing gripping areas  38 ,  40 , with the gripping area  40  being structured in order to enable safe gripping of the sheet-like material. 
     For the continuous recording of the relative position between the first gripping element  22  and the second gripping element  24 , the gripping device  10  is equipped with a measuring device  42 , which is connected to a signal processing device  46  via connecting lines  44 . In the example shown here, the connecting lines  44  are connected to a connecting area  48  in close proximity to the axis  18  so that a feed line  50  to the signal processing device experiences as little stress as possible when the gripping arm  12  is moved. 
     In the example described here, the measuring device  42  comprises a transmitter  52  and a sensor  54  that is allocated to the transmitter  52  for the continuous recording of the first gripping element&#39;s  22  position. 
     As shown in FIG. 2, the transmitter  52 , which has the design of a magnet, is incorporated in another leg  55  of the lever  26 , which runs basically parallel or roughly parallel to the gripping arm  12 . The sensor  54  allocated to it is arranged in the fixed gripping element  24  or the gripping arm  12  in the area of the transmitter  52  so that the movements of the lever  26  or the first gripping element  22  can be recorded. The design provides for the transmitter  52  to be incorporated into a recess  56  and fastened as well as glued. 
     Due to the sensor  54  in the gripping device  12 , a signal, e.g. analog electric potential, is released, which is evaluated in the signal processing device  46 . By actuating the first gripping element  22 , a relative movement occurs between the sensor  54  and the transmitter  52 , which can be recorded by the sensor. In particular, it can record whether any and how many sheets were grabbed by the gripping elements  22 ,  24  during the gripping process. In accordance with the number of sheets, e.g. whether no sheet, one sheet or several sheets were grabbed, the transmitter  52  takes on a different position in relation to the sensor  54  so that the sensor releases a slightly modified analog electric potential, which is evaluated in the signal processing device  46 . Apart from the number of sheets that were grabbed, the signal emitted by the sensor also depends on the thickness of the sheet. 
     FIG. 3 depicts a first version of the signal processing device  46 , which is connected to the measuring device  42  via a signal line  58 . The signal processing device  46  consists basically of a compensating circuit  60 , an amplifying circuit  62  and an evaluating circuit  64 . The signal line  58  is connected to a first inlet  66  of the compensating circuit  60 . A second inlet  68  of the compensating circuit is connected to a potentiometer  70  for no-voltage compensation. 
     One outlet  72  of the compensating circuit  60  is connected on the one hand with an inlet  74  of the amplifying circuit  62  and on the other hand with a first inlet  76  of the evaluating circuit  64 . One outlet  78  of the amplifying circuit  62  is connected to a second inlet  80  of the evaluating circuit  64 . 
     The evaluating circuit  64  is fed auxiliary signals, such as “Teach-In/1Sheet,” “Teach-In/0 Sheets,” as well as a trigger signal. Depending on the evaluation of the signal evaluated by the sensor  54 , the evaluating circuit  64  emits a signal “Error/more than 1 sheet” or a signal “O.K./1 sheet.” 
     The potential (no-voltage) released by the sensor  54  is compensated with a potential adjusted by the potentiometer  70  so that a change in potential or differential potential on the outlet  72  of the compensating circuit  60  is amplified by the subsequent amplifying circuit  62  and evaluated in the evaluating circuit  64 . The evaluating circuit  64  releases the signal “O.K./1 sheet” if there is one sheet between the gripping elements  22 ,  24  or the signal “error/more than 1 sheet” if there is more than one sheet or no sheet in the gripper. 
     For initial or regular adjustments of the evaluating circuit (Teach-In), the evaluating circuit is fed the signals “Teach-In/1 Sheet” or “Teach-In/0 Sheets,” with a zero value being determined in the case of closed gripping elements without sheet and a target value in the case of one sheet between the gripping elements  22 ,  24 , with the value being dependent particularly on the sheet thickness of pages that are utilized. The inlets and outlets for the signals are only symbolic for information. The respective information can occur in a different form (FIG. 5) also as data transfer via an interface such as a CAN bus. 
     FIG. 4 depicts a second version of a signal processing device  46 ′, which has basically the same design as the signal processing device  46 . Contrary to the signal processing device  46 , the evaluating circuit  64  has an outlet  82  for compensating auxiliary potential, which is connected to the second inlet  68  of the compensating circuit  60  via a line. In this version, the potentiometer  70  can be forgone, which for example has to be newly adjusted when changing the gripping device  12  or the transmitter  52 . In order to adjust the amount of the auxiliary potential, the version provides for the outlet  72  of the compensating circuit  62  to be connected directly with the inlet  76  of the evaluating circuit  64  so that the evaluating circuit  64  also receives the non-amplified differential potential available at the outlet  72 . 
     FIG. 5 shows another version of a signal processing device  84 , with the measuring device  42  being equipped with the transmitter  52  and an intelligent Hall effect sensor  86 . The intelligent Hall effect sensor  86  is connected to an inlet  90  of an evaluating circuit  92  via an outlet  88 . The evaluating circuit  92  is connected to a higher machine control system  96  via a data bus such as a CAN bus. 
     The intelligent Hall effect sensor  86  is equipped with a Hall effect sensor element  98 , which is connected to a compensating circuit  100  via a signal line. The compensating circuit  100  is connected on the outlet side with an amplifying circuit  102 , which on the outlet side is connected to the outlet  88  and the evaluating circuit  92 . 
     For the purpose of controlling the compensating circuit  100  or the amplifying circuit  102 , a logic device  104  such as a micro-controller is provided for, which is connected to the compensating circuit  100  or the amplifying circuit  102  via internal bus lines  106 ,  108 . Furthermore, the logic device  104  is connected to a data storage device  107  such as EEPROM. During the calibration process, the logic device  104  is furthermore connected to an external data processing system  112  via a bus  110 . In the case of the intelligent Hall effect sensor  86 , the internal logic device  104  can adjust both compensation of no-voltage and amplification. The data required for this is made available by the external data processing system  112 . Deviating data can ten be stored in the data storage system  107 . 
     A particularly beneficial version has proven to be a system where the evaluating circuit  92  is connected to a higher machine control system  96  via a bus such as a CAN bus. This offers the opportunity of being able to transmit for example data that conveys the quality of the paper (g/m 2 ) for adjusting the evaluating circuit and send messages “O.K./1 sheet” or “error/no or more than 1 sheet” in the opposite direction. 
     In the versions shown in FIG. 3 and 4, it is necessary to make a trigger signal available to the evaluating circuit in order to be able to provide information about the time of the measurement, i.e. gripper closed. A trigger signal can be forgone if the gripping elements  22 ,  24  taken on a defined position, e.g. a closed position, after filing a sheet. This way, the evaluating circuit  76 ,  92  can recognize the time of measurement autonomously. 
     In FIG. 6 the course of the signals  114 ,  116  that are to be evaluated is shown. The course of signal  114  shown in FIG. 6 a  describes an operating phase, where the gripping device  10  grabs a sheet as desired. On the other hand, FIG. 6 b  shows the course of signal  116 , which occurs during an operating phase if more than one sheet is grabbed. 
     The signal processing device  46 ,  46 ′ or the evaluating circuit  92  is adjusted as follows: 
     In a first operating phase I, the gripping elements  22 ,  24  take on a defined position—preferably a closed position—which causes the signal  114 ,  116  to take on a zero value U CLOSED . In a second operating phase II, the gripping elements  22 ,  24  are opened, which causes the signal  114 ,  116  again to take on a defined value U OPEN . In a following operating phase III, a sheet is grabbed in accordance with the invention, with the gripping elements  22 ,  24  taking on a defined position towards each other in accordance with the sheet thickness, with a signal U TARGET  being assigned to this position. The signal U TARGET  is then stored. 
     In the following operating phase IV, the gripping elements  22 ,  24  are then separated from each so as to release the grabbed sheet so that the signal  114  takes on the value U OPEN . The operating phase IV is followed by the operating phase I, where the gripping elements  22 ,  24  are closed and the signal  114  takes on the value U CLOSED . 
     The signal values U CLOSED , U OPEN  and U TARGET  are determined in a so-called learning phase and stored. FIG. 6 b  depicts the signal  116 , which is assigned an error. Starting from the operating phase I, the gripping elements  22 ,  24  take on an open position in the subsequent operating phase II, with the signal  116  taking on the value U OPEN . In the following operating phase III, the gripping elements grab more than one sheet so that the signal  116  takes on a value U ERROR , which differs from the value U TARGET . The difference in the determined signal values is recognized by the evaluating circuit and then an error message is generated. In the subsequent operating phase IV, the gripping elements  22 ,  24  are separated from each other so that the signal  116  takes on the value U OPEN . 
     In the version shown here, the signal is evaluated as potential released by the measuring device. The potential  114 ,  116  changes its value, depending on whether the gripping elements are open or whether they grabbed a sheet in closed condition or are empty. In particular, the course of the potential is determined in a learning phase through continuous scanning with an analog-to-digital converter and processed and stored in a micro-computer. Due to the stored values U CLOSED , U TARGET  and U OPEN  any further sequence of the signals can be checked for deviations. If in the operating phase III, in which the target value U TARGET  is expected, a larger or smaller potential U ERROR  occurs, the evaluating circuit reacts with an error message, which is used to stop the machine or sort the grabbed sheets.