Patent Publication Number: US-10758966-B2

Title: Processor-controlled tape feed apparatus and method for a self-piercing rivet machine

Description:
FIELD 
     The present disclosure relates to a tape feed apparatus and method for a self-piercing rivet machine. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     Existing tape feed systems for self-piercing rivet machines typically have a ratcheting wheel between the self-piercing rivet fastener supply reel and the receiver. The exhausted tape leaving the receiver is typically left as a free end and allowed to fall on the floor. Cleaning up this exhausted tape can cost a surprisingly large amount of money for a manufacturer to clean up; hundreds of thousands of dollars, if not millions of dollars annually. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     According to one aspect of the present disclosure, a tape carried, self-pierce rivet may be moved into alignment with a rivet driving spindle by conveying the tape between a supply reel and an exhaust reel, the supply reel having a supply motor and the exhaust reel having an exhaust motor. Specifically, the tape is moved in an advancing direction until the rivet has traveled past being in alignment with the spindle, by controlling the supply and exhaust motors using a first tension regimen. Thereafter the tape is moved in a retracting direction until the rivet is in alignment with the spindle by controlling the tape supply and exhaust motors using a second tension regimen. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a diagrammatic view of a self-piercing rivet machine employing the disclosed processor-controlled tape feed system. 
         FIG. 2  is a perspective view of a self-piercing rivet carrier tape, illustrating the relation between rivets and rivet positioning apertures. 
         FIG. 3 a    is an electronic circuit diagram of a first embodiment of the processor-controlled tape feed system. 
         FIG. 3 b    is an electronic circuit diagram of a second embodiment of the processor-controlled tape feed system. 
         FIG. 4  is a flowchart illustrating the overall riveting process using the processor-controlled tape feed system. 
         FIG. 5  is a flowchart detailing the ‘advance tape’ subprocess defined in  FIG. 4 . 
         FIG. 6  is a flowchart detailing a first embodiment for adaptive reel tensioning. 
         FIG. 7  is a flowchart detailing a second embodiment for adaptive reel tensioning. 
         FIG. 8  is a flowchart detailing the ‘maintain torque’ subprocess defined in  FIG. 4 . 
         FIG. 9  is a graph showing how the torque of the servomotor is ramped up to implement the subprocess illustrated in  FIG. 5 . 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
     Referring to  FIG. 1 , an exemplary embodiment of the self-piercing rivet machine in accordance with the present disclosure is illustrated generally at  22 . The machine includes a spindle  24  with associated driver mechanism, which operates to drive the rivet punch  26  in a reciprocating direction along the centerline axis  34  of the rivet punch. Rivets are delivered and positioned in the receiver with extreme accuracy beneath the rivet punch  26  by means of a tape assembly which will be next described. For additional details of mechanical systems that may be used to implement the self-piercing rivet machine, reference may be had to co-pending U.S. patent applications, entitled “Tape Feed Apparatus And Method For A Self-Piercing Rivet Machine”, Ser. No. 15/901,236 (filed Feb. 21, 2018), and “Tool-Free Opening Tape Feed Receiver For A Self-Piercing Rivet Machine”, Ser. No. 15/901,264 (filed Feb. 21, 2018), the entire specifications and drawings of each are incorporated herein by reference. 
     Rivets to be applied are first installed on an elongated tape, in a spaced apart configuration as illustrated in  FIG. 2 . The tape has a series of regularly spaced apertures  58  that are designed to register with a pawl mechanism  64  ( FIG. 1 ). The engagement of pawl mechanism with a selected aperture positions the associated rivet precisely in alignment with the centerline  34  of punch  26  during operation of the machine as will be described. 
     The elongated tape  44  is supplied, wound up on a supply reel  36 . The supply reel is installed on the spindle of a supply motor  48 , which is preferably implemented using a servomotor. The rivet machine also includes an exhaust reel  38  to receive the spent tape, thus solving the problem of having the spent tape exhaust onto the floor. The exhaust reel is carried on the spindle of an exhaust motor, also preferably implemented using a servomotor. To sense when the end of the portion of the tape containing rivets has been reached, an inductive sensor  77  is provided downstream of the supply reel but upstream of the punching zone. To sense when a rivet is positioned approximately within the punching zone, a rivet-present sensor  78  is employed. In the illustrated embodiment this sensor is an inductive sensor available from Turck, Inc. Note the sensor  78  is positioned so that it will not interfere with reciprocating movement of the rivet punch. 
     The sensor  78  is designed to sense the presence of metal rivets with precision. As manufacturing with lighter materials is in demand today, the present inductive sensor is designed to sense rivets that are not necessarily made of ferrous metals, such as rivets made of aluminum. The inductive sensor has an internal inductive coil that is energized by an oscillator which produces an electromagnetic detection field emanating from the tip of the sensor. The presence of a metal object (such as the head of rivet  32 ) in the detection field alters the permeability of the space occupied by the detection field. This change in permeability results in a change in resonance of the oscillating energy, which is then sensed by the internal electronic circuitry associated with the oscillator. Although ferrous metals produce the strongest coupling with the detection field, other metals such as aluminum also produce changes in the detection field, which can be measured by the sensor. 
     Sensor  78  thus operates as a non-contact electromagnetic sensor. While the inductive sensor is well adapted to sensing non-ferrous rivets, such as aluminum rivets, other types of sensing technology can also be employed. Optical sensors, another form of electromagnetic sensing, for example, can be used where the rivet material is not suitable for inductive sensing. 
     In the disclosed embodiment, the sensor  78  is positioned at an angle, as illustrated, so that it can sense when the head of rivet  32  has traveled past the position where it is aligned with the centerline  34 . The disclosed processor-controlled tape feed apparatus and method specifically relies on having the rivet advance slightly past the point of perfect centerline alignment during the tape advancement tension regimen, so that the rivet can be retracted into perfect centerline alignment during the subsequent retracting tension regimen. It is the subsequent retracting tension regimen that allows the pawl mechanism  64  to engage with the corresponding aperture  58  in the tape  44 . In this way, high accuracy is achieved in placement of the rivet directly in registration with the punch centerline without requiring the machine itself to be manufactured to high tolerances. This is because accuracy is achieved by virtue of the high tolerance of the tape. 
       FIG. 3 a    illustrates a first embodiment of an electronic circuit which may be used to implement the processor-controlled tape feed apparatus and method. In this embodiment a digital command controller (DCC)  101  is employed. The digital command controller includes an internal CPU processor  102  and associated memory  104 , together with other digital signal processing components used to control other processes associated with setting the self-piercing rivets. The digital command controller may be implemented, for example, using a Texas Instruments TMS320F microcontroller. The digital command controller  101  communicates over a controller area network bus (CAN bus), depicted in  FIG. 3 a    at  105 . In  FIG. 3 a   , selected interface control pins have been illustrated at X 5 , X 13  and X 14 . Those of skill in the art will understand that the specific pins used for connection to sensors, solenoids and status indicators are a matter of design choice. Thus the pins illustrated here are merely exemplary. 
     In this embodiment one primary function of the digital command controller  101  is to send commands to the spindle driver  24  ( FIG. 1 ) causing it to drive the rivet punch  26  to impact and set the rivet. In addition, the internal CPU processor  102  of the digital command controller  101  also controls the tape feed apparatus to implement the methods described herein. 
     In this embodiment each of the supply servomotor  48  and the exhaust servomotor  54  may be implemented using a self-contained controller-motor package that includes a communication port  107  designed to interface with the CAN bus  105 . A suitable motor package is the model PD4-C6018L4204-E-08 available from Nanotec Electronic US Inc. The digital command controller  101  also has a communication port  109  to interface with the CAN bus  105 . Essentially each self-contained controller-motor package receives control data signals, addressed for it, on the CAN bus  105 . The motor responds by rotating to the position specified by control data placed on the CAN bus  105 . By virtue of the CAN bus interconnection, each of the respective servomotors can be controlled independently of one another through instructions from the digital command controller that are addressed for the particular servomotor. 
     As illustrated in  FIG. 3 a   , each motor  48  and  54  is supplied with 24 volt DC operating power from a cabinet-mounted power supply  111 . Each motor also includes a safety circuit  113  that interfaces with the digital command controller  101  to disengage or enter an off state when conditions warrant as determined by the digital command controller  101 . 
     The circuit of  FIG. 3 a    also includes an RFID module  115 , implemented as an electronic circuit powered by power supply  111  that senses a corresponding RFID tag (not shown) placed on the supply reel  36 . The RFID tag system is used to ensure that the proper size and style of rivet has been loaded into the rivet machine. As illustrated, the RFID module  115  communicates this information to the digital command controller  101  over the CAN bus  105 . 
     In one embodiment, the supply and exhaust reels are secured by solenoid(s)  117  controlled by the digital command controller  101 . Status LED indicators  119  are provided to visually indicate the tape loading state. Solenoids  117  and status LEDs  119  are controlled by connection to the digital command controller  101 . 
       FIG. 3 b    illustrates a second embodiment of an electronic circuit which may be used to implement the processor-controlled tape feed apparatus and method. A microcontroller  100  comprising processor  102  and associated memory  104  issues drive instructions to the respective supply motor  48  and exhaust motor  54 . Suitable servomotor control circuitry  106  is provided as illustrated. Note that each of the respective servomotors is controlled independently. Thus the servomotor control circuit  106  has a first channel A for communication with servomotor  48  and a second channel B for communication with servomotor  54 . 
     Each servomotor includes a motor to produce torque in varying amounts based on received control signals from the processor  102 . In addition, each servomotor includes a position sensor to provide a feedback signal through the servomotor control circuit to the processor  102 . Knowing the position of the servomotor allows the processor to precisely control the servomotor&#39;s operation. This includes controlling the torque supplied by the motor, which some of the disclosed control regimens are able to exploit. 
     The processor  102  is also coupled to the sensor driver  108  which interfaces with the inductive sensor  78 . The processor reads the signals produced by sensor  78  to determine if a rivet is positioned at the point slightly beyond centerline registration, indicating that the processor can command a change from the advancing tape tension regimen to the retracting tape tension regimen. A discussion of the advancing and retracting tape tension regimens will not be provided. 
     Overall System Process 
     The advancement of the tape is a processor-controlled process, the processor being specifically programmed as described herein.  FIG. 4  shows the overall system process. The overall system process begins when the system is powered on at  200 . Using the rivet-present sensor  78  ( FIG. 1 ) to supply a binary (ON-OFF) rivet-present signal, the processor  102  ( FIG. 1 ) determines at step  202  whether to maintain torque, as at  204  (the details of which are described in connection with  FIG. 8 ), or to advance the tape, as at  206  (the details of how the tape is advanced will be described below in connection with  FIG. 5 ). In other words, after every rivet cycle the system will determine if it needs to advance the tape to the next position, as at step  206 , or to hold the current position by maintaining position as at step  204 . The processor  102  makes this determination by looking at both the state of the rivet-present sensor  78  (indicating whether there is a rivet in the receiver) and based on stored knowledge of whether the rivet has left the receiver during the previous rivet cycle. 
     Regarding this stored knowledge, the processor maintains a record in memory  104  as to whether the last rivet cycle resulted in a rivet being set in the workpiece. This record is maintained because certain faults can happen before the rivet is inserted into the work piece thereby leaving the rivet inside the nose piece. In this scenario the processor is programmed not to advance the tape because if the process is retried two rivets will be deployed in the receiver. If the processor determines that it doesn&#39;t need to advance it will simply maintain the positive location of the tape in its current position. 
     In performing the overall system process the processor  102  is also programmed to assess at step  208  whether a tape change is necessary. This happens when the last rivet in the tape has been used and the end of the tape is sensed by suitable mechanism. In the illustrated embodiment of  FIG. 1 , the sensor  77  detects when the end of tape is reached, that being the point at which no further rivets are sensed exiting the supply reel as the tape advances towards the spindle. 
     Instead of using a rivet sensor  77 , the end-of-tape condition may be sensed by detecting that there is no load on the supply servomotor  48 , or by using a suitable microswitch sensor, magnetic sensor or optical sensor to detect an end-of-tape marker or detent formed in the tape itself. Regardless of what sensing mechanism is used, when the end-of-tape condition is sensed, the processor  102  sends control commands, at step  210  to the servomotors  48  and  54  to disengage or enter an off state, to allow the tool operator to place a fresh reel of tape on the spindle of the supply motor  48  and to thread the fresh tape onto a newly installed exhaust reel. To alert the operator when it is time to replace the tape, the processor  102  may also issue an alert (e.g., audible or visual) locally at the machine, using the status LED&#39;s  119  ( FIG. 3 a   ) for example, or remotely at a control console within the plant. 
     Assuming no tape change is required (either because the current tape still has unspent rivets, or because a fresh reel has just been loaded) the processor  102  makes the fundamental decision at  212  whether a tape feed operation should be performed. As the flowchart of  FIG. 4  shows, when processor reaches step  212  there should be a rivet present in the receiver (as determined at step  202 ), unless a fault has occurred as discussed above. Thus at step  212 , if there is no rivet detected by the rivet presence sensor  78 , the processor reverts back to repeat step  202  and the ensuing steps. However, if there is a rivet present (as would normally be the case), the processor enters a waiting cycle at step  214  until the rivet cycle  216  is complete. Depending on the tool implementation, in one embodiment (using the circuit of  FIG. 3 a   , for example), the processor  102  within the digital command controller  101  may be programmed to issue the trigger instruction to the spindle driver mechanism, in which case the processor  102  has self-generated information indicating when the rivet cycle is complete. 
     In alternate embodiments (using the circuit of  FIG. 3 b   , for example) the spindle driver  24  ( FIG. 1 ) is controlled by a separate trigger mechanism, independent of processor  102 . In this embodiment the processor  102  includes an input that receives a signal from the spindle driver mechanism (or from the processor within the digital command controller  101 , indicating that the rivet cycle is complete. 
     Advance Tape Process 
     The advance tape process  206  is shown in detail in  FIG. 5 . In one embodiment, as depicted in  FIG. 5 , the processor  102  commands to supply servomotor  48  to create slack in the supply side reel to ease advancement of the tape, either by rotating the supply servomotor (clockwise as seen in  FIG. 1 ) or by turning off the motor torque. More specifically, this can be achieved by clocking the supply motor a set distance to create the slack after the rivet cycle  216  ( FIG. 4 ). 
     Alternatively this can be achieved by turning off the holding torque of the supply motor while the spindle  26  ( FIG. 1 ) is still fully advanced. The natural motion of the spindle returning to home position will then introduce slack in the system. 
     As yet another alternative, a higher torque may be used on the exhaust motor  54  to advance the tape without the need for slack to be created. 
     In order for the system to advance the tape, the processor  102  then switches the motors into an adaptive torque mode, one embodiment of which is illustrated in  FIG. 6  discussed below. The adaptive torque mode is designed to adjust the tension of the tape as it enters the receiver, to consistently align the rivet under the punch as the tape transitions from full to empty on the supply side and vice versa on the exhaust side. The adaptive torque mode can be accomplished in a variety of ways; three methods will be described below. 
     Continuing with a discussion of the advance tape process, after the processor switches to adaptive torque mode, it waits at step  222  until a rivet is detected by the rivet-present sensor  78 . Specifically, the processor waits until the rivet-present signal is in the ON state. Upon detection of the ON state, the processor, at step  224 , sends an instruction to the exhaust servomotor, causing it to switch to a low torque state to prevent slack. Thereafter, in step  226 , the processor sends a signal to the supply servomotor, causing it to switch to a high torque state, which will pull back on the tape allowing the pawl mechanism  64  to engage with the corresponding aperture  58  in the tape  44  ( FIG. 1 ). Such engagement positively locates the rivet in proper position along the axis  34  of the spindle. The advance tape process then ends at  228 . 
     Next follows a summary of three potential methods that can be employed to drive the system into adaptive torque mode. All of these methods adjust the tension of the tape as it enters the receiver, to consistently align the rivet under the punch as the tape transitions from full to empty on the supply side and vice versa on the exhaust side. These techniques for implementing an adaptive torque mode are referred to herein as: 
     1. Simplified Method for Adaptive Reel Tensioning (SMART) 
     2. Rivet Count Method 
     3. Running Average Method 
     Simplified Method for Adaptive Reel Tensioning (SMART): 
     Shown in  FIG. 6 , the simplified method  230  for adaptive reel tensioning takes advantage of closed loop servo mechanism of the servomotors  48  and  54  to command the supply and exhaust reel motors to maintain a specific torque set-point and uses the status of rivet presence sensor  78  to ramp up the torque set-point on the exhaust side motor until a rivet is sensed by the rivet presence sensor. Simultaneously, the status of the rivet presence sensor is also used to adjust the torque set-point on the supply servomotor  48  to aid the exhaust servomotor  54  to pull the tape far enough into the receiver until the rivet is positively sensed by the rivet presence sensor. Sensor-based adjustment of torque ramp up eliminates the need to calculate or derive the amount of tape present (rolled-up on the supply and exhaust side spools respectively) to maintain optimal tension on the tape as it enters the receiver that helps to consistently place the rivet under the punch. An example of how the processor controls torque ramp-up is illustrated in  FIG. 9 . 
     In the simplified method  230  the processor  102  turns on torque to a low threshold  232  and then waits a predetermined time  234  (typically on the order of a few milliseconds). After the brief wait, the processor then reads the state of the rivet-present signal (from rivet-present sensor  78 ) at step  236 . If the rivet-present signal is not in the ON state (i.e., it is in the OFF state) the processor  102  signals the motors to increase torque by a predetermined fixed percentage, but without exceeding a predetermined maximum threshold, as at step  238 . Conversely, if the rivet-present signal is in the ON state, the simplified method for adaptive reel tensioning ends at  240 . 
     Running Average Method: 
     Shown, in  FIG. 7 , the running average method takes advantage of the closed loop servo mechanism of the servomotors  48  and  54  to derive the position of the supply and exhaust servomotors driving the rivet spools after each rivet cycle. The position data from both supply and exhaust servomotors is then compared against a pre-calculated dataset that maintains running average of the position data from both the motors to accurately estimate the amount of tape left (i.e., rolled-up in the supply and exhaust side motors respectively). 
     As illustrated, the running average method  242  first captures the current position of both motors at  244 . In this regard, one feature of the servomotors is that they provide a data signal indicative of angular position of the motor shaft. Next, at step  246 , the processor turns on torque to the motors, based on a comparison of a position data running average maintained by the processor  102  in memory  104  to a table of predetermined torque settings also stored in memory  104 . These predetermined torque settings may be determined experimentally and stored in a table prior to use of the system. 
     The processor then waits at step  248  until the rivet-present signal is in the ON state, whereupon the processor captures new positions for both motors and calculates the angle rotated. Using this angle rotated and the known linear distance traveled for such rotation, the processor, at step  250 , calculates the approximate diameter of the tape extant on each of the supply and exhaust reels. The processor, at step  252 , then adds this calculated value to the running average of the last X advances (where X is an integer number reflecting how many times the motor position data have been captured for use in the described calculations. The running average method then terminates at step  254 . 
     Rivet Count Method: 
     This method uses data from a processor (possibly separate from processor  102 ) that is currently running a self-piercing riveting system, such as the Stanley Portariv® Pierce Riveting System, to count the number of rivet cycles since a reel load/change operation has occurred. The processor  102  uses this data to adapt the tension of the supply and exhaust servomotors  48  and  54  to consistently place the rivet under the punch in a tape feed riveting application. 
     Using one of the three adaptive tension mode methods described above, or equivalent, the tape will continue to be pulled through the receiver until the rivet presence sensor  78  detects that the rivet has completed the required advancement. 
     The following section provides a summary of “Maintain Torque” subprocess shown in Flowchart  1  which helps to positively lock the rivet in position under the punch until the riveting sequence begins. 
     Maintain Torque Process 
     As was discussed in connection with  FIG. 4 , processor  102  performs the maintain torque step  204  if a rivet is present in the receiver as determined at step  202 . This maintain torque process helps positively lock the rivet in precise position under the punch until the riveting sequence begins. The particulars of this maintain torque step  204  will now be described with reference to  FIG. 8 . 
     After the rivet presence sensor detects the presence of rivet in the receiver, the processor commands the exhaust servomotor  54  to switch to a constant low torque, as at  256 . This low torque is set to a level that will not overpower the supply servomotor, but to a level sufficient to ensure that all slack is taken up on that side of the receiver and to ensure that the reel won&#39;t free spin. The processor further commands the supply servomotor  48 , at step  258 , to switch to a constant high torque in order to positively align the tape into the locking pawls. The process then ends at  260 . Note that although steps  256  and  258  have been illustrated as being sequential, it is possible to execute steps  256  and  258  substantially simultaneously. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.