BACKGROUND OF THE INVENTION δ Field of the Invention:

The present invention relates, in general, to presses an specifically, to hydraulic presses used in stamping or sheari operations and, more specifically, to control systems for hydraul presses . 0 Workpieces are commonly punched or stamped from sheet met in fluid operated or hydraulic presses. Such presses include a frn having a bed with a lower die mounted thereon. A fluid operat cylinder, such as a hydraulic cylinder, includes a movable pist mounted on the upper portion of the frame which drives a ram or pu 5 having an upper die mounted thereon into a metal sheet dispo between the dies to punch or shear a workpiecε from the metal she

As the punch or upper die engages and moves through

-H. ta] sheet, forces on the order of several tons are introduced i the dies and the surrounding frame of the press which progressiv 0 increase to a maximum force load at the point of breakthrough of upper die through the metal sheet. The forces are restrained dur the shearing or stamping operation and are stored as distortion deflection in the frame of the press and the dies.

These forces are suddenly released when the upper 5 breaks through the metal sheet resulting in objectionable sho noise and vibrations. These loads increase correspondingly with force employed in the stamping or shearing operation.

The shock, noise and vibrations adversely effect the pre surrounding equipment and persons located in the vicinity of 0 press. Further, these objections occur with each cycle of the pr and increase with the force and size of the press.

Because of the noise and shock generated by presses stamping and shearing operations, presses have been located in area separate from other manufacturing operations, such as a separ 5 building or a portion of a large building isolated from ot manufacturing operations. This requires shipping, storage additional handling of the stamped parts which increases their c and results in the possibility of damage to the parts.

In order to alleviate or minimize the objectionable charac teristics of stamping presses, attempts have been made to decreas the noise and vibration generated by a press. Such attempt incorporate shock dampening systems into the press which cushion th release of the stored forces via a hydraulic cylinder, restrictiv fluid flow path, etc. , in the hydraulic system of the press. Othe systems control the speed of the press during its advance so as t decelerate the press when breakthrough of the workpiece occurs i order to minimize the impact of the upper die on the bed and fram of the press.

However, such attempts have met limited success in reducin the noise and vibration levels generated during a stamping o shearing press operation. Further, such attempts require additiona components and controls which increases the cost of a press. Thus, it would be desirable to provide a control syste and method for a stamping or shearing press which reduces the nois cind vibrations associated with the operation of stamping or shearin presses. It would also be desirable to provide a control apparatu and method for reducing noise and vibration levels in a stampin press which can be easily adapted to conventional press construction

SUMMARY OF THE INVENTION The present invention is a control apparatus and meth for progressive fracture of a workpiece from a material sheet in press having a pressurizable fluid-operated cylinder reciprocall moving a punch through the material sheet.

The control apparatus includes a distance measuring means such as a transducer, connected to the luid-operated cylinder a providing an output indicative of the position of the piston of t cylinder. Valve means are connected to a fluid source and supp pressurized fluid to the cylinder to extend and retract the cylind in response to control signals from a control means. The contr means executes a stored control program and, in response to t output of the distance measuring means, controls the valve means extend the ram in a series of discrete steps, each of increasi distance, through the thickness of the material sheet, with each st including a stoppage of the advance of the punch at a predetermin distance less than the total thickness of the sheet, and a relea of the pressure on the press due to the pressurized advance of t ram through the material sheet before advancing to the ne

incremental advance position within the thickness of the materi sheet.

In a preferred embodiment, the control means, whi comprises a controller in the form of a microprocessor based comput which executes a control program stored in memory, generates contr signals to the valve means to advance and retract the cylinder a thereby the ram in a series of increasing distances through the tot thickness of the material sheet, with the number of discrete ste or distances being dependent upon the thickness of the materi sheet, its strength, the desired press cycle time and acceptab noise levels.

The valve means preferably provide selective accelerati and deceleration of the cylinder of the press by controlling the ra of flow of fluid to the cylinder in progressive steps in response control signals from the control means. Preferably, the valve mea comprises a first bi-directional, proportional, high volume, flu control valve which is used during rapid extension and retraction the ram. A second proportional valve, such as a fine control serv valve, is connected in parallel with the first proportional valve a provides discrete movement of the ram in minute steps through t material sheet.

The control apparatus of the present invention al includes pump means for pressurizing the fluid from the fluid sour 1'referably, the pump means is connected to a pressure regulat means, controlled by the control means, to provide a plurality discrete pressure levels to the fluid supplied to the cylinder selectively control the pressure exerted by the cylinder during e cycle.

The method of the present invention comprises the st of:

(a) advancing the ram from a normally open position which the ram is retracted from the material sheet to a first s point within the material sheet which is less than the to thickness of the material sheet; (b) measuring the distance of travel of the ram;

(c) controlling the supply of pressurized fluid to cyliπder to stop the advance of the ram at the first stop point;

(d) relieving the pressure on thε press due to pressurized advance of the ram through the material sheet;

(e) advancing the ram to a second position complete through the material sheet, and

(f) retracting the ram from the material sheet to t open, retracted position. Preferably, the method comprises sequentially advancin relieving pressure on the press and then again advancing the cylind in a plurality of discrete steps of progressing distance through t total thickness of the material sheet.

In a preferred embodiment, the pressure on the press relieved by retracting the ram a predetermined distance from ea stop point before advancing the ram to the next stop poin

Preferably, the ram is smoothly accelerated and decelerated duri each extension and retraction movement.

The control apparatus and method of the present inventi uniquely reduces the noise and vibration levels associated with shearing or stamping press in which a workpiece is stamped from material sheet. By reducing noise and vibration levels, the stampi or shearing press can be located adjacent to other manufacturi operations instead of being located in a separate building remotely from other manufacturing operations as is current required. This eliminates the need for separate handling, shippi and storage of stamped parts between the stamping or sheari operations and further manufacturing operations.

The reduced noise and vibration levels provided by t control apparatus and method of the present invention is achiev by a simple control apparatus and method which does not sigπificant iπcrease the cycle time of a stamping press.

BRIEF DESCRIPTION OF THE DRAWING The various features, advantages and other uses of t present invention will become more apparent by referring to t following detailed description and drawing in which:

Figure 1 is a block diagram of the control apparatus the present invention employed to operate a fluid operated press;

Figures 2A and 2B are detailed block diagrams of the co trol apparatus of the present invention;

Figure 3 is a schematic diagram of the fluid circuit the control apparatus of the present invention;

Figure 4 is a graph depicting pressure or press force a function of time during one cycle of a press;

Figure 5 is a graph depicting ram position as a functi of time during one cycle of the press;

Figure 6 is a flow chart depicting the "self teach" mo of operation of the control program executed by the control apparat of the present invention in establishing the set points; and

Figure 7 is a flow chart depicting the automatic mode operation of the control program executed by the control means. DESCRIPTION OF THE PREFERRED EMBODIMENTS Throughout the following description and drawing, identical reference number is used to refer to the same compone shown in multiple figures of the drawing.

The presεnt invention is a control apparatus and meth for reducing the noise and vibrations generated by energy stored a fluid-operated press during a stamping or shearing operation. As shown in Figures 1, 2 and 3, the present inventi comprises a control apparatus denoted in general by reference numb

10 which controls the operation of a fluid operated press 12. described in greater detail hereafter, the press 12 includes a flu operated cylinder 14. Although the control apparatus 10 may be employed with a conventional fluid-operated press having one or more fluid-operat cylinders, as shown in Figure 3 in an exemplary embodiment, the pre preferably 12 includes a generally C-shaped frame 18 having spac upper and lower portions 20 and 22, respectively. A sing reciprocal cylinder 14 is mounted in the upper portion 20 of t frame 18.

The cylinder 14 includes a movable piston 24 from whi extends a movable piston rod 26. The rod 26 has a ram or punch mounted at an outer end which carries a first or upper die 30. correspondingly shaped lower die 32 is mounted in the lower porti or bed 22 of the frame 18 of the press 12.

As described hereafter, the control means 10 controls operation of the press 12 by extending and retracting the piston and piston rod 26. Overall machine functions associated with press 12 are controlled by a machine controller 34 which controls supply of electrical power to the press 12, the starting and stopp of the hydraulic power unit, described hereafter, and conveyors other feeding apparatus used to feed a material sheet 16 through pi .-as 12. Preferably, by way of example only, the machine control

34 is a programmable controller, such as a Allen-Bradley PLC2/30 The machine controller 34 communicates with the control apparatus 1 via a standard RS-232-C link 36 at 9600 baud. The signals on th link 36 provide commands to close or open the die 30 in the press 1 as well as sending various status data to the machine controller 3 depicting the operative state of the press 12.

As shown in Figures 1, 2A, 2B and 3, the control apparatu 10 comprises a control means or a central processing unit 40 preferably a microprocessor based computer capable of executing control program stored in a memory 42. By way of example, the CP 40 is an Intel SBC-88/25 single board computer utilizing a 5 Mhz Intel 8088 microprocessor. The memory 42 is electrically connecte to the central processing unit 40 for the transfer of data an signals therebetween. Inputs to the central processing unit 4 include the RS-232-C data link 36 from the machine controller 34, th output 44 of a distance measuring means or transducer 48 and th output 46 of a pressure transducer 50.

In a preferred embodiment, the distance measuring mean or transducer 48 is a device capable of providing an outpu indicative of the distance of travel or position of the piston 2 or the piston rod 26 of the cylinder 14 on the press 12. Preferabl a Temposonics transducer, model number 011003050208, is employed i the present invention. The transducer 48 is mounted on the end the cylinder 14 and includes an elongated wire 49 which exten through a bore formed in the piston 24 and piston rod 26. permanent magnet 51 is mounted in or on the piston 24 and surroun the bore and wire 49. The wire 49 is formed of a magnetσstricti aterial and distorts or twists under the magnetic field of t magnet 51. Pulses are sent from the transducer 48 along the wire and the time interval of the return signal, which is influenced the position of the distortion or twist in the wire 43, provides indication of the position or distance of travel, in thousandths an inch increments, of the piston 24 and piston rod 26 and tl CJ - Lached ram 28 and upper die 30. The output signal 44 from the transducer 48, Figure 2 is conditioned by a Temposonics digital interface circuit 45, mod number 0110030540103, and a Temposonics counter circuit 47 mod.- number 0110030591005 before being input to the CPU 40 through Intel digital interface circuit 53, model number SBC-519.

Thε pressure transducer 50 may be any type of pressu transducer capable of providing an output signal indicative of th fluid pressure in the hydraulic circuit. Preferably, the pressu transducer 50 is an Ashcroft pressure transducer model number H-K 5—050-D-5—MRW-15-CL. As shown in Figure 3, the pressure transduc 50 is connected to the hydraulic circuit flow path input to t cylinder 14 as described herεafter. The output from the pressu transducer 50 is an analog signal varying from one to five volts D . A suitable signal conditioning circuit 52 is employed with t pressure transducer 50 to convert the output signal from the pressu transducer 50 to the voltage levels required by the centr processing unit 40.

A plurality of digital outputs are driven by the centr processing unit 40 through I/O modules 55. The I/O modules provide signal conditioning and compatible voltage levels and m be I/O modules sold by Opto-22 and others.

The central processing unit 40 generates outputs to I modules 55 which respectively generate output signals 68 and 70 whi are supplied to blocking valves 72 and 74 respectively associat with a proportional valve 57 and a servo-valve 62.

Pump pressure is provided by the central processing un 40 via outputs to a pump control valve circuit which generates plurality of discrete pressure signals denoted by reference numbe 76, 78 and 80 which are connected to pump control valves 82, 84 a 86, respectively, shown in Figure 3 and described in deta hereafter. The output signals 76, 78 and 80 are digital in natu and vary between zero and +24 volts D.C.

The central processing unit 40 also generates an outp signal 88 through an I/O module 55 to control a combined pump fl valve 92, the purpose of which will be described in greater detj. hereafter. The signal 88 varies between zero and -.24 volts D.C.

Finally, accumulator charge and discharge valves 94 a 96 are controlled by control signals 98 and 100, respectivel generated by I/O modules 55 controlled by output signals from t central processing unit 40. The output signals 98 and 100 a digital signals ranging between zero and +24 volts D.C. and are us to charge and discharge an accumulator, described hereafter. Anal outputs are provided by the CPU 40 to drive the proportional val 57 and the servo-valve 62 to provide varying rates of fluid flow

the cylinder 14. As shown in Figure 2B, the CPU 40 generates sele signals to a 3:8 multiplexor 200. The multiplexor 200 provid output signals selecting one of two digital/analog converters. Thu one output from the multiplexor 200 is directed to a first oct flip-flop 202; while a second output from the multiplexor 200 connected to a second octal flip-flop 204. Digital data in the fo of an eight bit word is output from the CPU 40 on the ISBX port the SBC88/25 computer and is latched into the flip-flops 202 or 2 as selected by select data from the multiplexor 200. The data in t flip-flop 202 is clocked into a digital/analog converter 206. T output of the digital/analog converter 206 is a plus or minus 10 vo D.C. signal which is amplified by an amplifier 208 and input to driver circuit 210, such as a driver circuit formed of valve dri circuits sold by Bosch, model numbers 0811405026 and 081140502 Such driver circuits are primarily current drivers matched to t proportional valve 57.

A similar circuit is provided for the servo-valve 62 which the output of the flip-flop 204 is connected to digital/analog convertεr 212. The output of the digital/anal converter 212 is amplified by an amplifier 214 and input to a drive circuit 216, such as a current driver, matched to the servo—valve 6 The driver circuit 216 may be any suitable current driver circu such as one sold by Dyval, model number 23-5030.

Referring now to Figure 3, there is depicted a hydrau circuit containing elements controlled by the control means 10 controlling the extension and retraction of the piston 24 and pist rod 26 on the press 12. A source 102 of fluid, such as hydraul fluid, provides a supply of fluid to the hydraulic circuit. T source 102 is mounted above the motor 106 and the pumps 108 and 1 for gravity prime and flow considerations. Pump means 104 a provided for supplying fluid from the source 12 to the cylinder on the press 12. Preferably, the pump means 104 comprises a moto pump unit having a motor 106 driving a first pump 108 and a seco pump 110. Both of the pumps 108 and 110 are connected throu filters 112 to thε source 102. In a preferred embodiment, the mot 106 is a 40 h.p., 3 phase, 1200 rpm motor. The first pump 108 is 40 g.p.m. high volume pump used for rapid advance and retraction the piston 24. The second pump 110 is a 10 g.p.m. high pressu piimp .

The valves 82, 84 and 86 comprise a means for pressurizi the pumps 108 and 110. Preferably, three valves 82, 84 and 86 in t form of 24 volts D.C , solenoid-operated cartridge valves a employed to generate three distinct pressure levels. For exampl cartridge valves manufactured by Hydra-Force, model number SV-16-2 0-N-24DG may be employed.

Pilot operatεd pressure valvεs 114, 116 and 118 a connected between the source 102 through valves 82 and 84 and t regulator port of the second pump 110. Each of the pressu regulator valves 114, 116 and 118 is set to a different predetermin pressure, such as 600 psi for the first pressure regulator valve 11 2000 psi for the second regulator valve 116 and 2800 psi for t third regulator valve 118.

A similar pressure regulating circuit formed of pressu regulating valves 120 and 122 is connected through the pump contr valve 86 connected to the regulator port of the first pump 108. T valves 120 and 122 provide two distinct preset pressures of 600 p and 2000 psi for the first pump 108. The outputs from the pumps 1 and 110 are connected through check valves 124 and 126, respectivel to the pressure input or inlet of the proportional valve 57 and t servo-valve 62, respectively. A second check valve 128 is connect in series with the check valve 124.

A combine pump valve 92 in the form of a two-way, 24 vo D.C. , solenoid-operated, cartridge valve, under the control of t control means 10, is connεctεd bεtwεεn the check valves 124 and 1 as shown in Figure 3. The purpose of the combine pump valve 92 to combine the output of the pumps 108 and 110 to supply pressuriz fluid at a predetermined pressure to either of the proportional val 57 or thε servo-valve 62. The pressure is selected depεnding up which one of the pressure control valves 82, 84 and 86 is energize

Thε output of the combine pump valve 92 is also cαnπect to an accumulator 130 through an accumulator charge valve 94. T accumulator 130 provides additional fluid volume during rapid advan and return of the piston 24 in the cylinder 14. The accumulator 1 is precharged on the gas side with 1200 p.s.i.g. of nitrogen.

The accumulator charge valve 94 is a 24 volt D. solenoid-actuated, two-way, cartridge valve, connected to t accumulator 130 to charge the accumulator 130 to the preset pressu

provided by the first pump 108. A similar type of valve is employ a_; the accumulator discharge valve 96 also connected to t accumulator 130. The outlet of the discharge valve 96 is connect in parallel with the outlet of the combine pump valve 92 to t pressure inlet of the proportional valve 57.

A safety relief valve 103 is a 24 volt D.C, solenoi actuated, two-way, cartridge valve connected between the charge val 94 and the outlet of the accumulator 130 and enables the accumulat 130 to be drained for safety reasons when power is removed from t press 12. During normal operation, the safety dump valve 103 actuated by a control signal from the machine controller 34 to blo fi ow from the accumulator 130 to the tank 102.

The control apparatus 10 also includes valve means f controlling the direction of fluid flow into the cylinder 14 extend and retract the ram 28. Although a single, constant volu valve may be used, it is preferred that a proportional valve employed in the present invention to provide varying fluid flow rat to the cylinder 14. This provides controlled accelεration a deceleration of the ram 28 in response to control signals from t control means 40.

In a preferred embodiment, thε valve means includes t bi-directional proportional valve 57 for high volume flow duri rapid extension and retraction of the ram 28 to and from the materi sheet 16 and the bi-directional servo-valve 62 for fine contr during advance of the ram 28 through the material sheεt 16.

The proportional valve 57 is a four-way, blocked cente solenoid operated, valve which provides varying amounts pressurized fluid to the cylinder 14 of the press 12. By way example, the proportional valve 57 is a Bosch valve, model numb 0811404401. The pressure inlet of the proportional valve 57 connected to the parallel combination of the output of t accumulator 130 and the output of the combine pump valve 92 throu check valves as shown in Figure 3. The A outlet of the proportion valve 57 is connected to a port 135 on the cylinder 14 whi communicates with the extension chamber 136 of the cylindεr 14. T B outlet of the valve 57 is connected through a blocking valve 72 another port 137 on the cylinder 14 which communicates with t retraction chamber 138 of the cylinder 14.

A similar hydraulic circuit is provided for the servo-val 62 which also comprises a four-way, blocked center, soleno operated, valve. By way of example, the servo-valve 62 is one so by Dyval as model number 15. The pressure inlet of the servo-val 62 is connected to the combine pump valve 92 and the tank inlet connected through a check valve 132 and a filter 134 to the tank fluid source 102. A blocking valve 74 is connected betweεn the outlet of the servo-valve 62 to the port 137 of the cylinder 14. T A outlet of the servo-valve 62 is connected in parallel with the outlet of the proportional valve 57 to the port 135 of the cylind 14.

As shown in Figure 3, the pressure transducer 50 connected to the common connection of the A outlets of the valv 57 and 62 and the port 135 of the cylinder 14. The blocking valves 72 and 74 are two-way, 24 volt D. solenoid-actuated, cartridge valves and are used to prevent the d 30 from drifting downward when the pump means 104 is de-energize The blocking valves 72 and 74 are also employεd to prevent or st downward motion of the ram 28 and die 30 during an emergency stop when the control is not in manual or automatic mode of operation.

A safety relief valve 139 is connected to the outlet the blocking valve 72 and set to open at a predetermined pressur such as 3000 psi, to eliminate surges in the hydraulic circuit.

It will be understood that the present control apparat and method are described for example purposes as controlling o cylinder in a press. In this example, the proportional valve 5 the servo-valve 62, the blocking valves 72 and 74, the pressu transducer 50, the distance measuring transducer 48 and t accumulator discharge valve 96 are specifically dedicated to t cylinder 14. These elemεnts must bε duplicated for εach cylind in a press controlled by the control apparatus 10 of the prese invention, such as a multi-stage, progressive press containing plurality of cylinders, rams and dies. The accumulator 130, pu means 104 and the pressure regulating valves 82, 84 and 86 will common for all such cylinders in a multi-stage press.

Before describing the detailed operation of the contr apparatus and method of the present invention, a brief descripti of the pressures or forces and the sequence of operation involv in shearing or stamping a workpiece from a material sheet will

first described in conjunction with Figures 4 and 5. Figure 4 is graph of pressure versus time in a shearing operation. Thε pressur is the fσrcε imparted to the press and dies during the shearin operation and linearly increases from the start of the operatio cycle to a point 150 at which the material sheet 16 starts to give The pressure buildup continues from point 150, but at a lesser rate until material breakthrough occurs, as indicated by point 152. Afte breakthrough, the stored energy is rapidly released and the pressur drops as indicated by reference number 154. It is this rapid releas of energy during a short time interval that results in the high nois and vibration levels associated with a stamping or shearin operation.

The control apparatus 10 and method of the presen invention reduces such noise and vibration levεls by progressivel relεasing thε storεd energy in a plurality of steps in a single pres cycle thereby resulting in lower noise levels at each step and total noise level less than that associated with a single ste stamping or shearing of a metal sheet.

Figure 5 is a graph depicting the position of the ram 2 with respect to time during a single press cycle. In Figure 5, th circles indicated by various reference numbers depict the positio of the ram 28 and upper die 30 at each step during a single pre: ^; . cycle. These circles are referred to as "set points". The se points indicated by reference numbers 156 and 176 are zero set point indicating an open position of the dies 30 and 32, with the pisto 24 in the cylinder 14 fully retracted.

In operation, the control means 40 executes a contro program stored in the memory 42. The control means 40 iπitiall executes a "self teach" or setup sequence to locate the set point to be used to sequentially advance the ram 28 through the materi.- sheet 16. The "self teach" flow chart is depicted in Figure 6 whic after a start and initialization step 230 enters a manual mode. I this mode, step 232, thε ram 28 is manually advanced toward the to surface of the material sheet 16. When the ram 28 contacts the to surface of the material sheet 16, step 234, the first set point denoted by reference number 158 in Figure 5, is calculated in st 236 by the control means 40. A point up to 0.050 inches above t top surface of the material sheet 16 is selected for the first s oiπt 158.

The ram 28 is advanced through the material sheet 16 locate an end of travel position, step 238. The end of trav position is located by monitoring thε prεssure output of the pressu transducer 50 and distance, such as when the pressure exceeds second pre-sεt value and remains therε for tεn seconds with less th 0.002 inch increment in distance. A point 0.01 inch before th location is calculated and stored in the memory 42 as the last s point, denoted by referεncε numbεr 172 in Figure 5. This occurs step 240 as shown in Figure 6. Step 242 causes retraction of the r 28 to the normal, fully opened, retracted position.

Once the first and last set points 158 and 172 have be calculated, the control means 40 enters an automatic "self teac or setup mode of operation to determine and calculate the remaini set points. In step 244, the ram 28 is rapidly advanced toward t material sheet 16. The control mεans 40 monitors thε output of t distance measuring transducer 48 to determine when the ram 28 h reached the first set point as shown in step 246 and evidenced by s point 158 in Figure 5. At this point, the control means 40 recor the output of the pressure transducer 50 and stores the pressu output in the memory 42 for each 0.002 inch increment of distan travel of the ram 28 in step 248.

This forms a pressure/distance chart in the memory 42 whi is a series of pressure values stored sequentially in the memory for each incremental distance of advance and is used to monit machine performance during a normal cycle.

Upon further advance -of the ram 28 through the materi sheet 16, the control means 40 constantly monitors the pressu output from the transducer 50 to locate the "knee" of the pressu curve or point 150 in Figure 4 as shown in step 250 in the flow cbn of Figure 6. When point 150 is located, the control means 40 stor the distance measurement as the second set point, indicated reference number 160 in Figure 5. This corresponds to the transiti from the shear to fracture zone within the material sheet 16.

The control means 40 continues to monitor the output the pressure transducer 50 to locate the drop-off point 152, sho in Figure 4. This point 152 corresponds to the final fracture the material sheet as shown in step 254. When point 152 is locat as evidenced by a sharp decrease in the pressure values from t

transducer 50, the control means 40 stores the corresponding distan as a set point, indicated by reference number 168 in Figure 5.

The distance between the "knee" point 150 and the "dro off" point 152 on the pressure/time curve of Figure 4 is divided a predetermined number of steps to calculate the remaining s points, such as set point 164, shown in Figure 5 and set forth step 258 in Figure 6. Finally, the ram 28, after reaching the e of travel set point 172 is retracted to the fully opened position. The remaining set back set points 162, 166 and 170 Figure 5 are calculated by using a predεtermined set back distan which is subtracted from the next advanced set point, such as s point 164 for the set back set point 162, set point 168 for the s point 166 and the set point 172 for the set back set point 170. Th determines the amount of reverse or retraction movement of the r 28 between each successive advance, as described in greater deta hereafter. The predetermined set back distance is calculated examining machine and die distortion to determine a distance requir- to relieve all of the stored energy in the press 12 caused by t pressurized advance of the ram 28 through the material sheet 16.

In an automatic operation mode, the control means executes an automatic sequence shown generally in Figure 7. Aft initializing the hydraulic circuit in step 280, the press 12 situated in the fully opened, retracted position.

Starting with the first set point 156, the piston 24 fully retracted and the pump means 104 is energized at low pressu (600 p.s.i.g.), step 282, to limit starting torque and in ru current of the motor 106.

The control means 40 then starts a press cycle, step 2 and generates control signals to the various valves to energize t pumps 108 and 110 at medium pressure (2000 p.s.i.g.), step 286, activating regulating valves 82 and 86. The combine pump valve is closed (off) and the accumulator charge valve 94 is opened charge the accumulator 130. The accumulator discharge valve 96 closed or off as are the proportional and servo-valves 57 and 62. To rapidly advance the ram 28 toward the material she

16, step 288, the control means 40 holds the servo— alve 62 and t accumulator charge valve 94 off. The accumulator discharge valve

and the combine pump valve 92 are opened to supply 2000 p.s.i.g. the proportional valve 57 from the pumps 108 and 110.

The control means 10 generates a signal 56 to the prop rtioπal valve 57 which opens the proportional valve 57 to a fu open position in ten incremental steps, each of ten milliseconds length. This creates an acceleration curve, step 290, to minimi shock and noise while maximizing speed and performance. As the r 28 approaches the first set point 158, the control means constantly monitors the output of the distance measuring transduc 48 and calculates the distance difference, in step 292, betweεn t current position of the ram 28 and the next set point, such as s point 158 in Figure 5. As mentioned above, the distance differen is utilized as a pointer to the pressure/distance chart stored in t memory 42 of the control means and calculated during thε "self teac procedure. The distance difference is the difference between dimension in the pressure/distance chart range and the next s point, such as set point 158. The actual dimension is in 0.0005 in increments. The lookup table for the first set point 158 contai 32 separate pressure/distance measurements or values for t proportional valve 57. The result of the subtraction of the actu distance versus the distance of the first set point 158 is calculat and divided by four. This value is used in the lookup table, st 294, to locate the proper corresponding pressure value from t pressure/distance chart storεd in the memory 42. This value employed by the control means 40 to generate an output signal to t proportional valve 57 to control and progressively decrease t amount of fluid flow through the flow valve 57 to the cylinder 14 smoothly decelerate the extension of the ram 28. This process repeated until the first set point 158 is reached in step 298. T deceleration of the cylinder 14 caused by the proportional valve does not stop forward motion of the ram 28; but rather slows t forward motion of the ram 28 to that of a full servo output which l/8th to 1/lOth of the full proportional valve output.

After reaching set point 158, switchover to the servo-val 62 takes place, step 300, and the servo-valve 62 is energized to full open position in three incremental steps of ten millisecond each by successive control signals 60 from the control means 1 Simultaneously, thε proportional valve 57 is closed the rεmaiπi amount in three incremental steps thereby providing a smo

transition from rapid advance to forward under high pressure control The control means 40 also switches the pump means 104 to a hi pressure (2800 p.s.i.) in step 302.

Advancing from the set point 158 to the next set poi 160, the first die 30 passes through the shear range 159 of t thickness of the material sheεt 16 as shown in Figurε 5 into t fracture range denoted by reference number 161. In this portion o the cycle, the control means 40 de-energizes the combine pump valv 92, energizes and opens the accumulator charge valve 94 and close the accumulator discharge valve 96. The first pump 108 is maintain at medium pressure (2000 p.s.i.g.) to charge the accumulator 130.

The control means 40 also generates signals to close valve 82 and 84 and to set pump 110 at a high pressure of 2800 p.s.i. Further, the proportional valve 57 is closed in a timed sequence an the servo-valve 62 is used to control the extension and retractio of the piston 24 and ram 28. In step 304, the servo-valve 62 i energized by the controller 40 to a full open position in thre incremental steps of ten milliseconds each for acceleration of t ram 28 between set points 158 and 160. A decelεration operati based on the distance from the set point 160 as measured by t transducer 48 is used to control the advance or retraction to ea set point. The deceleration operation is similar to that describ above and includes a calculation of the difference between the actu position of the ram 28 and the next set point 160, step 306, usi the difference as a pointer in a lookup table, step 308, similar l. the lookup table described above but containing only eight valves f the servo-valve 62, to generate output signals to the servo-valve to smoothly decelεratε the ram 28 to a stop at the next set poin step 312. Upon reaching the set point 160, a control signal 60 fr thε CPU 40 reverses the servo-valve 62, step 316, to retract the r a predetermined distance from the set point 160 to set point 16 During such travel, the servo-valve 62 is ramped open and closed smoothly accelerate and decelerate the ram 28 through steps 304, 30 308, 310 and 312. These steps are repeated for the sεt points 16 166, 168, 170 until the die 30 breaks through the material sheet and reaches the final set point 172 in step 314.

In each retraction step, the energy transferred from t pressurized cylinder 14 and punch 28 to the frame 18 of the pre 12 is relieved thereby minimizing overall noise and vibrati

generated by the press 12 during its operation. The control mea 40 includes means for reliεving the pressure or force built up the press 12 due to the pressurized advance of the ram 28 throu the material sheet 16. In a prefεrrεd embodiment, thε reliεvi means is implemented through a retraction of the ram 28 from ea advancε sεt point. Howεvεr, it will bε undεrstood that the relievi means could also be implemented without such retraction by relievi the pressure on the cylinder 13 extending the ram 28 upon reachi each advance set point. It should also be noted that the example illustrated

Figure 5 discloses four progressive steps of increasing distan through the thickness of the material sheεt 16, with retractions an intermediate set point between each progressive advance. This by way of example only and the number of steps to actually shear stamp a workpiece from the material sheet 16 are selected based the thickness of the shεet 16, its strength as determined by i alloy or material makeup, as well as the desired cycle time a acceptable noise levels of the press 12. More or less steps cou be employed in the progressive fracture method of the prese invention as needed.

Upon reaching the breakthrough set point 172, the pre 12 enters a dwell cycle in which the first die 30 is maintained i . s bottomed out position in the second die 32. The dwell may of any time length, such as 0.5 seconds at high pressure of 28 psi. During this dwell cycle, the servo-valve 62 is maintained a half open position by suitable control signals 60 from the CPU 4 The valve 62 is fully closed at the end of the dwell cycle indicated by set point 174. To retract to the full open set poi 176, the CPU 40 generates a control signal 56 to the proportio valve 57 opening the proportional valve 57 to a full open positi whilε closing the servo-valve 62 to rapidly retract thε ram 28 tow the sεt point 176, step 318. A predetermined distance befo reaching the set point 176, the controller generates a signal 56 the proportional valve 57 gradually decreasing the flow through proportional valve 57 to decεlεratε the ram 28 to the zero set poi indicated by reference number 176. The pressure during rapid ret or retract is the same as during rapid advance.

In summary, there has been disclosed a unique cont apparatus and method for progressively fracturing workpieces f

material sheets in which the noise and vibration typically generate during such an operation is significantly reduced. The contro apparatus and the method progressively advances the ram of the pres in a successive series of steps, each of increasing distance throug the thickness of the material sheet, and relieves the pressurε o forcε built up in thε prεss caused by the pressurized advance of th ram through the material sheεt at each step. Thus, the pressur built up in the press during each cycle is progressively releasεd a low lεvels through each cycle.