Bistable snap-disks are typically utilized as mechanical cycling components in fluid operated switching devices, pressure cycling devices, and other mechanisms utilizing a two-position, bistable, snap-action switch. See, for example, U. S. Patent No. 5,198,631. Such snap-disks include a convex configuration and a concave configuration to engage or disengage electrical contacts and open and close an electrical circuit, respectively. The snap-disks snap, or"trip"between a convex and concave configuration depending on the application of sufficient external forces on one of the sides of the disk, such as, for example, a pressure, and snap or"reset" into an original configuration when those external forces fall below a predetermined value. The required forces causing a snap-disk to trip or reset between the convex and concave configurations, and vice-versa, vary from application to application, but for a given disk, the trip and reset force values are usually unequal.

Bimetallic and monometallic snap-disks are typically formed with a set of full radius punches, largely through a trial and error process complicated by an interdependency between the snap and reset forces. Trial and error experimentation typically determines which of the punches to use to form the opposite sides of the disks, and different punches are periodically determined by similar trial and error experimentation as snap-disk material properties change. Precise formation tolerances, however, are required in forming snap-disks so that the disks adequately react to external forces, such as temperature or pressure differentials, in a given switch application. The precise formation tolerances are difficult to consistently achieve using current snap-disk formation methods. Consequently, a one hundred percent sort of formed snap-disks is often required, and yields of acceptable snap-disks upon initial formation are as low as thirty percent. The low yield of acceptable disks decreases manufacturing efficiency and raises the costs of production of the snap- disks.

Accordingly, it would be desirable to increase the yield of acceptable snap-disks upon initial formation and decrease production costs in snap-disc formation.

BRIEF SUMMARY OF THE INVENTION In an exemplary embodiment of the invention, a snap-disk form assembly and method includes a form station coupled to a feedback station so that the formation of the snap-disks may be monitored in real time as the snap-disks are formed. Thus, correction of any deficiency in the formation process is detected and redressed nearly instantaneously.

More particularly, the form station includes a plurality of cams, with each cam including a respective tool. The plurality of cams and tools in the form station stretch the sides of disk blanks to plastic deformation and thereby form the reset and trip sides of the disk. The forces generated by the cams are adjustable with first and second stepper motors.

The feedback station includes a cam-driven probe that sequentially monitors the required peak force to snap the form disks into a respective alternative configuration after they are formed, and monitors the required peak reset force to snap the form disks into their original configuration. A force transducer is connected to the probe, and the probe is brought into engagement with one of the sides of the snap- disks. Therefore, the probe applies a force to the snap-disk that is measured by the force transducer and used for feedback control of the form station. Force is applied by the probe until the disk trips, and the measured peak force that caused the disk to trip is recorded by a feedback station controller. The force applied by the probe is then decreased until the disk resets into its original configuration, and the peak force before the disk resets is also recorded by feedback station controller.

A controller is coupled to the form station stepper motors and is configured to accept snap disk formation parameters and adjust the operation of the stepper motors in real time as the snap-disks are fabricated to produce snap-disks within the accepted parameters. Implemented by logic-driven controls, costly and time consuming trial and error fabrication methods are eliminated, thereby increasing manufacturing efficiency.

More specifically, the input parameters include a nominal trip force for activating the bistable snap-disks, a nominal reset force for resetting the bistable snap- disks, an allowable nominal trip force error, and an allowable nominal reset force error. Using an adaptive learning setup algorithm, the controller establishes an upper bound for the desired position of each of the first stepper motor and the second stepper motor, establishes a lower bound for the desired position of each of the first stepper motor and the second stepper motor, establishes a first adjusted position of each of the first stepper motor and the second stepper motor located between the respective upper and lower bound, and establishes at least a second adjusted position of each of the first stepper motor and the second stepper motor located between the first adjusted position and one of the upper bound and lower bound. By estimating and re-estimating stepper motor positions and measuring trip and reset force values of snap-disks formed at those settings, the controller efficiently works toward the desired stepper motor positions by adjusting the respective upper and lower bounds that capture the desired positions to progressively narrow a range of potential stepper motor settings to satisfy the input parameters.

The controller is also configured to compensate for changes in snap- disk forming material as nests of snap disks are formed. The controller measures at least one of a trip force or a reset force of the nest, calculates an error between the measured force and the respective target force, and adjusts the position of at least one of the first stepper motor and the second stepper motor based upon the calculated error.

Using real time feedback and logic driven controls to compensate for interaction between trip and reset forces to set stepper motor positions and adjust those positions as needed, snap-disks are formed in compliance with the input parameters. Production is boosted due to elimination of trial and error fabrication, initial pass rate of the snap-disks is increased, and the costs of snap-disk production are lowered.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic view of a snap-disk form assembly including a form station, an exercise station, and a feedback station; Figure 2 is a front plan view of the form station shown in Figure ;1

Figure 3 is a partial cross-sectional view and side plan view of the form station shown in Figure 2; Figure 4 is a front plan view of the exercise station shown in Figure ;1 Figure 5 is a front plan view of the feedback station shown in Figure ;1 Figure 6 is a partial cross-sectional view and side plan view of the feedback station shown in Figure 5; Figures 7-10 are flowcharts of a form station setup algorithm for controlling the form station shown in Figures 2 and 3 to generate required forces for forming snap-disks; and Figure 11 is a flow chart of a form station adjustment algorithm for controlling the form station shown in Figures 2 and 3 to compensate for incoming material variations.

DETAILED DESCRIPTION OF THE INVENTION Figure 1 schematically illustrates a snap-disk formation assembly 10 including a form station 12, an exercise station 14, and a feedback station 16 aligned along a communication axis 18. Flat metallic or nonmetallic disk blanks (not shown) are positioned in pockets (not shown) in dial fixtures (not shown) and are translated from form station 12, to exercise station 14, and to feedback station 16 along communication axis 18. Form station 12 provides the disk blanks with a convex and concave configuration on each side of the disk, respectively, with probing action punches (not shown in Figure 1) that stretch the disk to plastic deformation, thereby forming the reset and trip sides of the bistable disks. Exercise station 14 repeatedly subjects the reset and trip sides of the disk to predetermined forces, respectively, to exercise the snap action of the newly formed bistable snap-disks.

Feedback station 16 includes a force transducer (not shown in Figure 1) and controls (not shown) that are used to determine the actual force required to trip or reset each snap-disk in a batch of formed and exercised snap-disks. The trip and/or reset forces are recorded for each snap-disk, and the results are analyzed by comparing them to target values. Based on the differential between actual trip and/or reset values for each snap-disk, statistical process feedback control is used to adjust the probing action of form station 12 with a reset stepper motor 20 (further described below) and a

trip stepper motor 22 (also described below) to vary the forces used to form the reset and trip sides of the snap-disks, respectively.

Form station 12 comprises a reset portion 24 and a trip portion 26 separated by communication axis 18. Exercise station 14 includes a reset portion 28 and a trip portion 30 separated by communication axis 18, and feedback station 16 includes a reset portion 30 and a trip portion 32 separated by communication axis 18.

Form station 12 and exercise station 14 are substantially inversely symmetrical about communication axis 18. In other words, the trip portions 26,30 of form and exercise stations 12,14 are generally mirror images of reset portions 24,28 of form and reset stations 12,14, respectively, about communication axis 18, but rotated 180° so that trip portions 26,30 are reversed from side-to-side relative to reset portions 24, 28.

In operation, flat disk blanks of snap-disk material are individually loaded into pockets in the dial fixtures before reaching form station 12. A concave configuration is formed into a reset side of the snap-disk using a reciprocating reset form punch (not shown in Figure 1) that is actuated by a reset form cam 34 and a reset form cam follower 36 and stretches the reset side of the disk into plastic deformation.

Once the reset side of a snap-disk is formed, a convex configuration is formed into a trip side of the disk using a reciprocating trip form punch (not shown in Figure 1) that is actuated by a trip form cam 38 and a trip cam follower 40 and stretches the trip side of the disk into plastic deformation. Reset form cam 34 and trip form cam 38 are rotationally out-of-phase with one another to avoid interference of the reset and trip punches during formation of the snap-disks.

Each snap-disk is then indexed, while in the pocket, along communication axis 18 to exercise station 14. The reset side and the trip side of the snap-disk are then repeatedly subjected to a predetermined reset exercise force, a predetermined trip exercise force, or beyond, through actuation of a reset exercise punch (not shown) by a reset exercise cam 42 and actuation of a trip exercise punch (not shown) by a trip exercise cam 44, respectively, to exercise the snap action of the snap-disk.

Once exercised appropriately, each snap-disk is indexed along communication axis 18 to feedback station 16 that includes a reset and/or a trip force transducer (not shown in Figure 1) that determines the actual required force to cause each snap-disk to snap between the convex and concave configurations. The reset force and/or trip forces are recorded, analyzed, and compared to target reset force

values and trip force values. Using feedback control to stepper motors 20, 22, adjustments can be made in the applied force of the reset form punch and the reset trip punch to bring successively formed snap-discs within a desired reset force and trip force tolerance.

Snap disks are then indexed out of feedback station 16 and placed into one of three storage bins including a discard bin (not shown), a reform bin (not shown), or an acceptable pass bin (not shown). Thus, snap-disks are sorted based upon the measured values of the reset force and trip force for the disks. By providing instantaneous feedback to form station reset stepper motor 20 and trip stepper motor 22 to adjust the formation process while it is occurring, the yield of acceptable snap- disks upon initial formation of the disks can be improved dramatically.

Figure 2 is a front plan view of form station 12, including reset portion 24 and trip portion 26. Reset form cam 34 is attached to a reset form cam shaft 60 that is rotationally driven by a reset drive shaft assembly 62. Reset form drive shaft assembly 62 communicates with a trip form shaft assembly 64 via a belt (not shown) and therefore drives a trip cam shaft 66 attached to trip form cam 38. Reset cam follower 36 contacts reset form cam 34 to reciprocally move a reset form punch (not shown in Figure 2) and trip form cam follower 40 contacts trip form cam 38 to reciprocally move a trip form punch (not shown in Figure 2) inside a respective reset form tool housing 68 and trip form tool housing 70.

Reset and trip form cam followers 36,40 each include a pivot pin 72, a form bearing 74, and a cam follower bearing 76. Each cam follower bearing 76 contacts a respective cam surface 78 of reset form cam 34 and trip form cam 38. Each cam surface 78 is configured with a raised portion 80 that engages cam follower bearing 76 and causes the respective cam follower 36,40 to pivot about pivot pin 72.

As each cam follower 36,40 pivots, a respective form bearing 74 moves toward and away from communication axis 18. Each form bearing 74 engages a respective reset form punch (not shown) or trip form punch (not shown) to engage or disengage the punch from a disk of snap-disk material.

Reset and trip stepper motors 20,22, respectively, each include a driver adjust pulley 84, a driven adjust pulley 86 and a timing belt 88 connecting driver adjust pulley 84 and driven adjust pulley 86. Each driven adjust pulley 86 engages a lead screw 90 which varies the lateral position of a form stroke adjust slide 92 connected to each of reset form cam follower 36 and trip form cam follower 40.

Thus, reset stepper motor 20 and trip stepper motor 22 are used to turn lead screws 90 and adjust the position of reset form cam follower 36 and trip form cam follower 40, respectively, relative to reset form cam 34 and trip form cam 38. The magnitude of the pivoting movement of reset cam follower 36 and trip cam follower 40, and hence the movement of form bearings 74, increases as the respective cam follower bearings 76 are positioned closer to reset form cam 34 and trip form cam 38. As the force applied to the snap-disks is directly related to the distance traveled by form bearings 74, stepper motors 20,22 can be used to adjust the applied force in form station 12 to improve the acceptable pass yield of snap-disks upon initial formation. Each stepper motor 20,22 provides two hundred stop points per revolution to reset form portion 24 and trip form portion 26, thereby allowing very fine incremental adjustments in position of cam followers 36,40, and hence allowing very fine incremental adjustments in applied force to the snap-disks.

Figure 3 is a partial cross-sectional view and side plan view of form station 12 including a spring loaded reset form tooling plate 110 slidingly mounted on cylinders 112 for reciprocating movement toward and away from communication axis 18. Reset tool housing 68 is connected to reset form tooling plate 110, and includes a spacer 114 communicating with form bearing 74 of reset cam follower 36 to actuate reset form punch 116 against the bias of a return spring 118. A nose tool 120 surrounds reset form punch 116 to guide reset form punch 116 along an actuation axis 122.

Trip form portion 26 includes a trip form tooling plate 124 slidingly mounted on cylinders 126 for reciprocating movement toward and away from communication axis 18. Trip tool housing 70 is connected to trip form tooling plate 124, and includes a spacer 128 communicating with form bearing 74 of trip cam follower 40 to actuate trip form punch 130 against the bias of a return spring 132. A form support 134 surrounds trip form punch 130 and guides trip form punch 130 along actuation axis 122.

A dial fixture 136 is supported by form support 134 and is aligned with communication axis 18. A pocket (not shown) in dial fixture 136 supports a circumference of a disk blank of snap-disk material (not shown) that is inserted into dial fixture 136 and positioned so that the center of the disk blank is substantially aligned with actuation axis 122. Reset form punch 116 and trip form punch 130 are

positioned a first distance from the disk and a second distance from the disk, respectively, to form the reset and trip sides of the snap-disk with respective forces.

Reset drive shaft assembly 62 rotates reset cam shaft 60 on reset form portion 24, and a belt 138 transfers rotational motion of reset cam shaft 60 to trip cam shaft 66. Thus, as reset cam shaft 60 is rotated, a form main cam 140 synchronously rotates with reset form cam 34 to provide a probing action of reset form punch 116 into a blank disk of snap-disk material, and a trip main cam 142 synchronously rotates with trip form cam 38 to provide a probing action of trip form punch 130 into the disk blank. As shown in Figure 2, cam surface raised portions 80 of reset form cam 34 and trip form cam 38 are rotationally out-of-phase with one another so that the reset probing action and trip probing action are performed sequentially and do not interfere with one another.

Once a disk of snap-disk material is properly aligned with actuation axis 122 within dial fixture 136, reset form cam 34 is rotated into engagement with reset form follower bearing 76, causing reset cam follower 36 to pivot about pivot pin 72 (shown in Figure 2). As reset form cam follower 36 pivots, reset form bearing 74 pushes spacer 114 and form punch 116 toward communication axis 18. Also, form main cam 140 engages a form tooling plate bearing 144 and moves reset form tooling plate 110 toward communication axis 18. Reset form punch 116 is therefore engaged with the reset side of the disk blank, stretching the disk material into plastic deformation and forming the reset side of a snap-disk. The distance traveled by reset form punch 116 is adjustable by moving reset form portion 24 form adjust slide 92 with reset stepper motor 20 (shown in Figure 2). The position of reset form adjust slide 92 determines the position of cam follower bearing 76 of reset cam follower 36 relative to reset form cam 34. Hence, the degree of pivoting of reset cam follower 36 is adjustable by adjusting the position of reset form adjust slide 92, which, in turn, varies the distance that form bearing 74 moves form punch 116, and consequently varies the forces developed in the disk by reset form punch 116.

As reset cam shaft 60 continues to rotate, form bearing 74 of reset cam follower 36 and main cam form tooling plate bearing 144 are disengaged from the respective cam surface raised portions of reset form cam 38 and form main cam 140, and the spring loaded reset form tooling plate 110 and form punch 116 are returned to a position wherein reset form punch 116 does not contact the snap disk and sufficient clearance is provided to allow formation of the trip side of the disk.

Once form bearing 74 of reset cam follower 36 is disengaged from reset form cam 38, trip form cam 34 raised surface portion 80 (shown in Figure 2) engages cam follower bearing 76 of trip form cam follower 36 and causes trip form cam follower 36 to pivot about pivot pin 72 (shown in Figure 2). As trip form cam 34 raised surface portion 80 pivots trip cam follower 40, trip form bearing 74 pushes spacer 128 and trip form punch 130 toward communication axis 18. Also, trip form main cam 142 engages a trip form tooling plate bearing 146 and moves trip form tooling plate 124 toward communication axis 18. Trip punch 130 is therefore engaged with the trip side of the disk blank, stretching the disk material into plastic deformation and forming the trip side of a snap-disk. The distance traveled by trip form punch 130 is adjustable by moving trip form portion 26 form adjust slide 92 with trip stepper motor 22. The position of trip form adjust slide 92 determines the position of cam follower bearing 76 of trip form cam follower 40 relative to trip form cam 38. Hence, the degree of pivoting of trip form cam follower 40 is adjustable by moving trip form adjust slide 92, which, in turn, varies the distance that form bearing 74 of trip form cam follower 40 moves trip form punch 130, and consequently varies the forces developed in the disk by trip form punch 130.

As trip cam shaft 66 continues to rotate, form bearing 74 of trip form cam follower 40 and trip form tooling plate bearing 146 are disengaged from the respective cam surface raised portions of trip form cam 38 and trip main form cam 140, and the spring loaded trip tooling plate 124 and trip form punch 130 are returned to a position wherein trip form punch 130 does not contact the snap disk. The formation process in form station 12 may then be repeated or the dial fixture may be indexed to exercise station 14 (shown in Figure 1).

Figure 4 is front plan view of exercise station 14, including reset portion 28 and trip portion 30 similar in structure and operation to form station 12, but without the adjustability of stepper motors 20,22 (shown in Figures 1 and 2) and with different cam surface configurations. Reset exercise cam 42 is attached to a reset exercise cam shaft 160 that is rotationally driven by an exercise drive shaft assembly 162. Reset exercise drive shaft assembly 162 communicates with a trip exercise shaft assembly 164 via a belt (not shown) and therefore drives a trip exercise cam shaft 166 attached to trip exercise cam 44. An exercise reset cam follower 168 contacts reset exercise cam 42 to reciprocally move a reset exercise punch (not shown in Figure 4) and an exercise trip cam follower 170 contacts trip exercise cam 44 to reciprocally

move a trip exercise punch (not shown in Figure 4) inside a respective reset exercise tool housing 172 and trip exercise tool housing 174, respectively.

Exercise reset and trip form cam followers 168,170 each include a pivot pin 176, a form bearing 178, and a cam follower bearing 180. Each cam follower bearing 180 contacts a respective cam surface 182 of reset exercise cam 42 and trip exercise cam 44. Each cam surface 182 is configured with a raised portion 184 that engages cam follower bearing 180 and causes each respective cam follower 168,170 to pivot about pivot pin 176. More specifically, each cam surface raised portion 184 includes a rising profile 186 and a falling profile 188 that produces a pulsating reset force or pulsating trip force for exercising snap disks. As each cam follower 168,170 pivots, a respective form bearing 178 moves toward and away from communication axis 18. Form bearings 178 engage a respective reset or trip exercise punch (not shown) to engage or disengage the respective punch from a snap-disk, as substantially described above with respect to Figure 3. Once formed snap disks have been sufficiently exercised, the snap disks are indexed to feedback station 16 (shown in Figure 1).

Figure 5 is a front plan view of feedback station 16 including a reset portion 30 and a trip portion 32. Reset portion 30 includes a feedback drive assembly 210 for driving a reset cam shaft 212 and an attached feedback cam 214. A feedback cam follower 216 is attached to a spring-loaded feedback tooling plate 218 and includes a feedback follower bearing 220 that contacts a cam surface 222 of feedback cam 214, and a force transducer unit 224. A probe 226 extends from force transducer unit 214 along a probe axis 228.

Feedback trip portion 32 includes a trip feedback shaft 230 and an attached hub 232 that are rotationally driven by feedback drive assembly 210 and a belt (not shown in Figure 5). A spring loaded trip feedback tooling plate 234 supports a feedback support 236 that facilitates force measurement with probe 226.

Figure 6 is a side plan view of feedback station 16, illustrating a feedback reset main cam 250 that is attached to reset cam shaft 212 and rotates synchronously with feedback cam 214. Feedback main cam 214 engages a feedback form bearing 252 and reciprocally moves feedback reset tooling plate 218 toward and away from communication axis 18. Feedback cam 214 contacts a cam follower bearing 220 of feedback cam follower 216 and moves probe 226 toward and away from communication axis 18. A feedback trip main cam 256 is attached to a

feedback trip shaft 258 and driven by feedback drive assembly 210 and belt 260 to move feedback trip tooling plate 234 relative to communication axis 18. In one embodiment, feedback trip main cam 256 is circular so that feedback trip tooling plate 234 does not move relative to communication axis 18.

Dial fixture 136 is indexed to feedback station 16 with a formed and exercised snap-disk contained therein. Feedback reset main cam 250 and feedback cam 214 engage respective cam form bearings 220,252 and move reset feedback tooling plate 254 and probe 226 closer to communication axis 18. Probe 226 contacts reset side of the snap-disk and exerts force against it as probe 226 is moved toward communication axis 18 until the snap-disk snaps or trips into its alternative configuration. The peak force that caused the disk to trip is electronically recorded for each disk passing through feedback station 16, and a mean or average peak trip force is calculated over a specified number of disks, such as, for example, five disks. As feedback cam 214 continues to rotate, the applied force of probe 226 decreases, and the disk eventually resets. A peak reset force is also electronically recorded for each disk passing through feedback station 16, and a mean or average peak reset force is calculated over a specified number of disks.

Using a controller (not shown), the mean trip force and mean reset force are then compared with respective target values loaded into a controller memory (not shown), and analyzed using known statistical process control methods. If corrective action is required, the controller is coupled to stepper motors 20,22 (shown in Figures 1 and 2) for independent, real time adjustment of the applied reset and trip forces in form station 12 to correct deficiencies in the formation of the disks.

For example, if a given disk snaps too soon. i. e., at lesser force than desired, this indicates that the snap-disks are being stretched too much in form station 12 (shown in Figures 1-3), which can be cured by sending a signal to one or both of stepper motors 20,22 (shown in Figures 1 and 2) to move the respective form adjust slide 92 (shown in Figures 2 and 3) of reset form punch 116 and/or trip form punch 130 (shown in Figure 3) to reduce the distance traveled by reset form punch 116 and/or trip form punch 130 during formation of the snap-disks. Therefore, successive disks will be stretched to a lesser extent and exhibit a greater resilience. Similarly, stepper motors 20,22 can be used to increase the distance traveled by reset form punch 116 and or and/or trip form punch 130 when a mean snap force is higher than

desired. In this fashion, snap-disks can be formed within desired trip force and reset force tolerances.

Stepper motors 20,22 could be controlled independently or identically.

Identical control of both motors 20,22 is sufficient in cases where the difference in reset formation force and trip formation force is relatively small, as the same adjustment of both formation forces will yield approximately the same increase or decrease in resultant actual snap forces. With larger differentials in applied reset and trip formation forces, however, independent feedback and control of both reset and trip sides of the snap-disks is necessary.

After passing through feedback station 16, the snap-disks are placed into one of three storage bins (not shown). An acceptable first pass bin collects snap- disks within specified tolerances. A discard bin collects unusable snap-disks that have been stretched too much and therefore snap too easily. A reform bin collects snap- disks that have not been stretched enough and that may be reformed in form station.

By using instantaneous feedback control, acceptable yield pass rates upon initial formation of snap-disks are dramatically improved. Pass rates of 90% or more may be realized, thereby significantly increasing manufacturing efficiency and reducing material costs by minimizing scrap. Using the fully automated process described, the labor burden may also be reduced. Thus, the costs of production of snap-disks are reduced.

Figures 7-10 are flowcharts of a form station setup algorithm 300 for controlling form station 12 (shown in Figures 1-3). and more specifically for controlling stepper motors 20,22 (shown in Figures 1 and 2) to generate required forces for forming snap-disks within a specified force tolerance. In the embodiment described below, the snap-disks are heat treated after formation according to known techniques. It is appreciated however, that one of ordinary skill in the art could easily modify setup algorithm 300 to obtain the benefits of the invention for non-heat treated snap-disks.

As will be seen below in detail, algorithm 300 generally includes a first sub-algorithm to establish a lower bound of possible positions of stepper motors 20, 22, a second sub-algorithm to establish an upper bound of possible positions of stepper motors 20,22, a third sub-algorithm to generate an adjusted position of each stepper motor between the respective upper and lower bounds, and a fourth sub-

algorithm to further narrow the potential range of step motor settings between the adjusted position and one of the upper and lower bounds. Thus, a series of stepper motor position estimates are made and used to form snap-disks that are tested, and based upon the test results the estimates are revised and the desired positions of the stepper motors are found by an iterative process. Implemented by control logic, algorithm 300 employs adaptive learning to efficiently drive the stepper motors toward the desired positions to form snap-disks within specified parameters, thereby eliminating costly and time consuming trial and error setup methods.

Referring first to Figure 7, a plurality of operator selected inputs 302 are communicated to a controller (not shown) including a processor and a memory.

Inputs 302 include a nominal trip force value (Tforce) 304 for snap-disks, a nominal reset force value (Rtiv) 306 for the snap-disks, expected changes (ATht, ARht) 308, 310 in the input trip and reset force values 304, 306, respectively, after heat treating of the snap-disks, and allowable trip force error (Ts) and allowable reset force error (Rg) inputs312.

Using force inputs 304,308, the processor calculates 314 a target trip force (Ttarg) according to the following relationship: arg=-ce"0).

Likewise, the processor calculates 316 a target reset trip force (Rtarg) according to the relationship: rarg=./b/-ce"(2).

To begin formation of snap-disks, the controller signals form station 12 to set 318 to a "home"position wherein stepper motors 20,22 are in a designated state or position.

Modification of the positions of stepper motors 20,22 are monitored by the controller in relation to the home position according to known techniques.

A first sub-algorithm 320 is executed to set stepper motors 20,22 to position cam followers 40,36, (shown in Figure 2) respectively, for a stroke to form snap-disks having a trip force less than Ttarg (Eq. 1) and a reset force less than Rtarg (Eq. 2). Sub-algorithm 320 begins by indexing 322 dial fixture 136 and determining 324 whether a formed setup snap-disk is located at test station 16 (shown in Figures 1,

5 and 6). If a formed snap-disk is not located at test station 16, dial fixture 136 is indexed 322 again.

When a formed snap-disk is located at test station 16, actual trip and reset forces Tforce and Rforceare measured 326 as described above in relation to Figures 5 and 6. A position of stepper motor 22 is then assigned 328 based upon a change trip force value ATforce defined by the following relationship: /o/-cece''farg) A new position Typos for stepper motor 22 can then be determined to generate the ATforce by advancing or retarding the motor by a number of steps from the home position.

Likewise, a position of stepper motor 20 is then assigned 330 based upon a changed reset force value OR force defined by the following relationship: AR force = R forceRt arg (4) A new position R pos for stepper motor 20 can then be determined to generate the ARforce by advancing or retarding the motor by a number of steps from the home position.

Once positions of stepper motors 22,20 have been assigned 328, 330, respectively, the controller processor determines 332 whether the sum of ATforce and the allowable trip force error Te is greater than zero and also whether the sum of ARforce and the allowable reset force error RE is greater than zero. In other words, it is determined whether both ATforce and jorce are sufficiently positive so that both stepper motors 22, 20 are assigned 328,330 respectively a number of steps so as to increase the force generated by stepper motors 22,20 at the assigned step positions to form snap-disks having actual trip and reset forces nearer to the nominal trip and reset forces inputs 304, 306.

If either of the sum of ATforce and the allowable trip force error TE or the sum of ARforce and the allowable trip force error R£ is less than zero, the processor checks 334 whether a maximum number of iterations of sub-algorithm 320 have been executed. If the maximum number of iterations has not been executed, i. e., if fewer than the maximum number of iterations has been executed, form station stepper motors 22,20 are adjusted 336 so that form station punches 116,132 (shown

in Figure 3) are located a new distance from a snap-disk located in dial fixture 136 (shown in Figure 3) according to the new stepper motor positions TpoS and Rpos determined in steps 328 and 330 (described above). Dial fixture 136 is then indexed 322 and sub-algorithm 320 repeated.

If the maximum number of iterations has been executed, the process terminates 338, and, in one embodiment, the controller prompts an error message, indicator or flag to prompt an operator of a fault condition in which stepper motors 22, 20 were not properly calibrated to form snap-disks according to the desired inputs 304,306,308, 310, and 312.

If the sum of ATforce and the allowable trip force error Te is greater than zero and the sum of ARforce and the allowable reset force error RE is greater than zero, then Tpos Tforce RposS and Rforce is saved 340 in the controller memory as TXI C Tl, RXI and Ri, respectively, for future use described below.

First sub-algorithm 320 therefore establishes, through repeated attempts, if necessary, a lower bound of stepper motor positions to form snap-disks with desired properties.

Referring now to Figure 8, after sub-algorithm 320 parameters are saved 340 (see Figure 7), a second sub-algorithm 342 is executed to set stepper motors 20,22 to position cam followers 40,36, (shown in Figure 2) respectively, for a stroke to form to form snap-disks having a trip force greater than Ttarg (Eq. 1) and a reset force greater than Rtarg (Eq. 2). Sub-algorithm 342 begins by setting stepper motors 22,20 to their home positions plus a known machine constant (dependent upon form punch dimensions) so as to position stepper motors to generate increased force via cam followers 40,36 (shown in Figures 1 and 2), indexing 344 dial fixture 136 and determining 346 whether a formed setup snap-disk is located at test station 16 (shown in Figures 1, 5 and 6). If a formed snap-disk is not located at test station 16, dial fixture 136 is indexed 344 again.

When a formed snap-disk is located at test station 16, actual trip and reset forces Tforce and Rforce e measured 348 as described above in relation to Figures 5 and 6. A position of stepper motor 22 is then assigned 350 based upon a change trip force value ATforce defined by Equation 3 above. A new position Tpos for stepper motor 22 can then be determined to generate the ATforce by advancing or retarding the motor by a number of steps from the home position.

Likewise, a position of stepper motor 20 is assigned 352 based upon a changed reset force value OR force defined by Equation 4 above. A new position Rpos for stepper motor 20 can then be determined to generate the ARforce by advancing or retarding the motor by a number of steps from the home position.

Once positions of stepper motors 22,20 have been assigned 350, 352, respectively, the controller determines 354 whether the sum of ATforcend the allowable trip force error Te is less than zero and also whether the sum of OR force and the allowable trip force error R£ is less than zero. In other words, it is determined whether both ATforce and ARjorce are sufficiently negative so that both stepper motors 22,20 are assigned 350,352 respectively a number of steps so as to decrease the force generated by stepper motors 22,20 at the assigned step positions to form snap-disks having actual trip and reset forces nearer to the nominal trip and reset forces inputs 304, 306.

If either of the sum of ATforce and the allowable trip force error Te or the sum of ARforce and the allowable trip force error R£ is greater than zero, the processor checks 356 whether a maximum number of iterations of sub-algorithm 342 have been executed. If the maximum number of iterations has not been executed, i. e., if fewer than the maximum number of iterations has been executed, form station stepper motors 22,20 are adjusted 358 to position cam followers 40,36, (shown in Figure 2) respectively, for a stroke to from a snap-disk located in dial fixture 136 (shown in Figure 3) according to the new stepper motor positions Tpos and Rpos determined in steps 350 and 352 (described above). Dial fixture 136 is then indexed 322 again and sub-algorithm 342 repeated. If the maximum number of iterations has been executed, the process terminates 360, and, in one embodiment, the controller prompts an error message, indicator or flag to inform an operator of or otherwise indicate a fault condition in which stepper motors 22,20 were not properly calibrated to form snap-disks according to the desired inputs 304,306,308, 310, and 312 (shown in Figure 7).

If the sum of ATforce and the allowable trip force error Te is less than zero and the sum of ARfOrceand the allowable trip force error Re is less than zero, then T pos is saved 362 in the controller memory as Tx2, Tforce is saved 362 in the controller memory as T2, Rposis saved 362 into controller memory as RX2 and R force is saved 362 in the controller memory as R-) for future use described below.

Second sub-algorithm 342 therefore establishes, through repeated attempts, if necessary, an upper bound of stepper motor positions to form snap-disks with desired properties.

While in the illustrated embodiment, the lower bound of stepper motor positions is first determined with sub-algorithm 320 (shown in Figure 7) and then the upper bound is determined with sub-algorithm 342, in an alternative embodiment the order of sub-algorithms 320,342 could be reversed so that the upper bound is first established and the lower bound is then established without departing from the scope of the present invention.

After sub-algorithm 342 parameters are saved 362 (see Figure 8), it is determined 364 whether ATforce nd ARjorceare less than the respective allowable error TE and RE inputs 312 (shown in Figure 7). If both ATforce and AR force are less than the respective allowable errors Te and Ru inputs 312, setup algorithm 300 completes 366 and stepper motors 22,20 are calibrated for forming snap-disks with the desired trip and reset forces within the specified tolerances.

If either of AT force or ARjorce are greater than the respective allowable error Te and R£ inputs 312 (shown in Figure 7), adjustment is made according to a third sub-algorithm 367 as illustrated in Figure 9 to establish an intermediate stepper motor position bound for each stepper motor 22,20 for location the desired stepper motor positions Tpos. and R pos as described below.

Referring now to Figure 9, sub-algorithm 367 begins by determining 368 whether ATforce is greater than the allowable trip force error Ts. If ATforce is less than the allowable trip force error T£, then Tpos is set 370 equal to TX2. If ATforce is greater than the allowable trip force error Te, then a new Tpos is calculated 372 according to the parameters determined by sub-algorithm 320 (shown in Figure 7) and sub-algorithm 342 (shown in Figure 8). Specifically, the new position Tpos for stepper motor 22 is calculated 372 according to the following relationship: <BR> <BR> <BR> Tpos=TxlxT2-Tx2xTi<BR> <BR> <BR> <BR> (72-Tl) Likewise it is determined 374 whether ARforceis greater than the allowable reset force error Rs. If OR force is less than the allowable reset force error

R£, then Rpos is set 376 equal to Rx2. If OR force is greater than the allowable trip force error Rs, then a new Repos ils calculated 378 according to the positions determined by sub-algorithm 320 (shown in Figure 7) and sub-algorithm 342 (shown in Figure 8). Specifically, the new position R pos for stepper motor 22 is calculated 372 according to the following relationship: <BR> <BR> <BR> <BR> <BR> (-)2'2-1).<BR> <BR> <BR> <BR> <BR> <BR> <P> (R2-R,) Once TPos and Rpos are set 370,376 and/or calculated 372, 378, respectively, stepper motors 22,20 are set 380 to the corresponding steps, and dial fixture 136 is indexed 382. It is evident from Equations 5 and 6 that the new stepper motor positions are located in between the positions determined by first sub-algorithm 320 and second sub-algorithm 342. The processor then determines 384 whether a formed setup snap-disk is located at test station 16 (shown in Figures 1,5 and 6). If a formed snap-disk is not located at test station 16, dial fixture 136 is indexed 384 again.

When a formed snap-disk is located at test station 16, actual trip and reset forces Tforce and Rforce are measured 388 as described above in relation to Figures 5 and 6. ATforce and jorce are then re-calculated using Equation 3 and Equation 4, and it is again determined 390 whether Tforce and Rforce are less than the respective allowable error Ts and R£ inputs 312 (shown in Figure 7). If both Tforce and Rforce are less than the respective allowable errors T£ and R£, sub- algorithm 367 terminates 392, algorithm 300 is complete, and stepper motors 20, 22 are setup to form snap-disks within the allowable error inputs.

If Tforce and Rforce are greater than the respective allowable errors T£ and R£, a fourth sub-algorithm 394 is executed, as illustrated in Figure 10, to further narrow the range of possible stepper motor positions toward the desired position while at the same time compensating for interaction between the trip forces and the reset forces of the snap-disks.

Referring now to Figure 10, the controller processor determines 396 whether ATforce is less than Te. If ATforce is greater than Te, the processor determines 398 whether ATl XATforce is less than zero wherein AT, is defined by the difference between the measured trip force Tforce when stepper motor 22 is operated

at position Tl (determined by first sub-algorithm 320 and saved at step 340 (shown in Figure 7)) and the target trip force Tt arg calculated at step 314. By determining 398 whether the product of #Tlx#Tforce is a positive number or a negative number, it may be determined whether the next estimate for the desired position of stepper motor 22 to produce acceptable snap-disks lies between the current position and Txl or between the current position and TX2.

If ATIxATforceis less than zero, then Tu2 ils set 400 equal to the current Tpos determined in step 380 of third sub-algorithm 367 (shown in Figures 8 and 9), and other parameters remain unchanged. If AT, xATforce is greater than zero, then Txl is set 402 equal to the current Tpos determined in step 380 of third sub- algorithm 367 (shown in Figures 8 and 9), and other parameters remain unchanged. A range of possible solutions is then reduced from all values between Txl and Tx2 to a smaller range between the current position Tpos of stepper motor 22 and either Tx1 or Tx2.

Using the set values from either step 400 or 402, whichever is applicable, an adjusted position Tpos for stepper motor 22 is then calculated 404 according to Equation 5 above.

Once the adjusted position Tpos is calculated 404, or if the processor determines 396 that ATforce is less than Te, then the processor determines 406 whether ARforce is less than #. If ARforce is greater than R#, the processor determines 408 whether ARIxRforce is less than zero wherein ARI is defined by the difference between the measured trip force Rforce when stepper motor 22 is operated at position Rxl (determined by first sub-algorithm 320 and saved at step 340 (shown in Figure 7)) and the target trip force Rtarge calculated at step 314. By determining 398 whether the product of ARlxRforce is a positive number or a negative number, it may be determined whether the desired position of stepper motor 22 to produce acceptable snap-disks lies between the current position and Rxl or between the current position and RX2.

If ARIxOR force is less than zero, then Rx2 is set 410 equal to the current Rpos determined in step 380 of third sub-algorithm 364 (shown in Figures 8 and 9), and other parameters remain unchanged. If ARI XRforce is determined 408 to be greater than zero, then RXI is set 412 equal to the current R pos determined in step

380 of third sub-algorithm 364 (shown in Figures 8 and 9), and other parameters remain unchanged.

Using the set values from either step 410 or 412, whichever is applicable, an adjusted position Rpos for stepper motor 22 is then calculated 414 according to Equation 6 above.

Because changes in one of the trip and reset forces typically affects the other, if the processor determines 406 that ARforce is less than R£, it again checks 416 whether ATforce is less than T£ input of step 312 (shown in Figure 7). If ATforce is less than T£, algorithm 300 is completed 418. If ATforce is greater than TE the processor checks 420 whether a maximum number of iterations of sub- algorithm 394 have been executed.

If the maximum number of iterations have been executed, the process terminates 422, algorithm 300 is complete, and, in one embodiment, the controller prompts an error message, indicator or flag to inform an operator of or otherwise indicate a fault condition in which stepper motors 22,20 were not properly calibrated to form snap-disks according to the desired inputs 304,306,308, 310, and 312 (shown in Figure 7) If the maximum number of iterations has not been executed, i. e., if fewer than the maximum number of iterations has been executed, form station stepper motors 22,20 are adjusted 424 to position cam followers 40,36, (shown in Figure 2) respectively, for a stroke corresponding to the current stepper motor positions Tpos and Rpos determined in sub-algorithm 394 (described above) A setup snap-disk is then formed using the new stepper motor positions, and the processor once again determines 426 whether the setup snap-disk is loaded onto dial fixture 136 at test station 16, and, if not, dial fixture 136 is indexed 428 until the formed snap-disk is loaded at test station 16. Once the formed snap- disk is loaded at test station 16, actual trip and reset forces Tforce and Rforce are measured 430 as described above in relation to Figures 5 and 6 and ATforce and ARfo,, are calculated 432 according to Equations 3 and 4 above. The calculated values are used to repeat sub-algorithm 394 until algorithm 300 is successfully completed 418 or terminated 422.

Thus, algorithm 300 estimates and re-estimates stepper motor positions to form progressively smaller ranges of potential positions that capture the desired stepper motor positions. Algorithm 300 executes in real time with feedback from newly formed setup snap-disks while compensating for interaction between the reset and trip forces until stepper motor positions are determined that will form snap-disks to specified parameters. Costly and time consuming trial and error methods and replacement of punches is therefore replaced with efficient, logic driven controls.

Figure 11 illustrates a form station adjustment algorithm 500 for controlling form station 12 (shown in Figures 2 and 3) to compensate for incoming material variations in snap-disk blanks after setup algorithm 300 is completed.

Algorithm 500 begins with the controller reading 502 a position of trip stepper motor 22 and reset stepper motor 20, and the controller assigning 504 appropriate positions of trip and reset motors 22,20, respectively, for each snap-disk forming nest i. Each nest i includes a selected number of snap-disks to provide a representative sample of formed snap-disk characteristics as the snap-disks are formed, and in various embodiments the nests include as few as one to a large number of snap-disks Assigned stepper motor positions are initially determined by algorithm 300 described above. Allowed error limits TE and Re are also assigned 506 in accordance with error inputs 312 (shown in Figure 7) of setup algorithm 300. Stepper motors are then set 508 to the assigned positions.

For each forming nest i, actual trip and reset forces Tforce and R jorce are measured 510 as described above in relation to Figures 5 and 6 at test station 16 after the snap-disks are formed, and Equations 3 and 4 above are used to calculate 512 ATForce d ARjorce values, or deviations between the actual measured forces and the target values. Once ATForce and ARforce are calculated 512, a number of steps, or counts, to adjust respective stepper motors 22,20 can be determined to generate ATForce and ARforcee In one embodiment, measured forces Tforce and Rforce are averaged over each forming nest and used to calculate 512 ATForce nd ARjorce values. In an alternative embodiment, ATForce and ARforce values are averaged over each forming nest and used to determine an averaged number of steps or counts to adjust respective stepper motors 22, 20.

Once ATporce and ARforce are known, a series of comparisons are made to determine whether the snap-disks in nest i are within the allowed error tolerances Tc and R#.

First, it is determined 514 whether #TForce is less than-T£. If so, Tpos (i) is reset 516 according to the following relationship: Tpos(i)=Tpos-Adj Counts (7) wherein Adj Counts is the number of steps or counts derived from calculation 512 of Forcez If #TForce is determined 514 to be greater than-T£, the controller then determines 518 whether #TForce is greater than T#. If so, Tpos (i) is reset 516 according to the following relationship: Tpos(i) = Tpos + Adj Counts (8) wherein Adj Counts is the number of steps or counts derived from calculation 512 of Forcez Once Tpos (i) is reset according to steps 516 or 520, or if #TForce is determined 518 to be less than Te, the controller determines 522 whether ARForce is less than -R#. If so, Rpos(i) is reset 524 according to the following relationship: R pos (i) = Rpos-Adj Counts (9) wherein Adj Counts is the number of steps or counts derived from calculation 512 of AR Force- If ARForce is determined 522 to be greater than -R#, the controller then determines 526 whether ARForce is greater than Rs. If so, R pos (i) is reset 526 according to the following relationship: R pos (i) = Rpos + Adj Counts (10) wherein Adj Counts is the number of steps or counts derived from calculation 512 of tR Force

Once Rpos (i) is reset according to steps 524 or 528, or if ARForce is determined 518 to be less than Rs, dial fixture 136 is indexed 530, stepper motors are set 508 in the applicable positions and algorithm 500 is repeated 530.

Material variations are therefore detected as the snap-disks are tested and found to be outside the allowed error Te and R£, and the stepper motors are adjusted accordingly in real time as the next nest is formed to compensate for incoming material changes in real time. The smaller the nest size, the more sensitive the system is to variation of material and fluctuation in performance of snap-disks as they are tested. With appropriate selection of nest size, scrapped snap-disks due to changing properties of incoming snap-disk material can be reduced dramatically, and costly and time consuming trial and error methods to consistently produce acceptable snap-disks are eliminated.

While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.