US 3584496 A
Description (OCR text may contain errors)
sis-1s 11R, Ell-584M861 3,333,335 8/1967 Sims 3,375,694 4/1968 Pratt Primary Examiner-Charles W. Lanham Assistant ExaminerGene P. Crosby Attorneys-Curtis, Morris and Safford, Marshall M.
Holcombe, William Hintze, William J. Keating, Frederick W. Raring, John R. Hopkins, Adrian J. LaRue and Jay L. Seitchik ABSTRACT: A means and method and system for working material forming dies is disclosed featuring a magnetically actuated ram. Ram drive is provided by a tractive magnet having a force versus displacement characteristic similar to the forcedisplacement characteristic required in certain types of metal working operations such as crimping sheet metal terminals onto lead wires. Circuits are disclosed for providing a control of applied field to motor elements which in turn permits a control of ram displacement, force, velocity, acceleration, and/or dwell time ofa die or dies drawn by the ram.
SHEET 1 OF 5 .7. INVENTOR JO SE9 IN'NARD KILL.
PATENTED Jun. 5 l9?! SHEET 2 OF 5 FORCE vs, DISTANCE ABOVE GRIMP HEIGHT 2 2000 E g 2 FORCE vs. MAGNET SEPARATION z M O I LL 1000 0 I00 200 300' 400 500 600 100 800 900 L00 INCHE'5 '7- DISTANCE BETWEEN MAGNETS JPRESS IOO MAGNETIC ACTUATOR 0') LL! I O 5 60. v
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w INVENTOR o 00 I20 I 200 240 280 TIME (MILLISECONDS) uosawn alumna KELLER.
PATENTED JUN] 51am SHEET 3 [IF 5 l m mNm PATENT ED JUN1 5 I97! SHEET l 0F 5 INVENTOR Josnn menu KELLER.
SHEET 5 OF 5 g E I: l-
BEJVL'IOA INVENTOR JOSEPH RI HAQD KELLE-V.
MAGNETIC ACTUATOR BACKGROUND OF THE INVENTION The sheet metal working art represents one kind of material forming which is by and large presently based upon a controlled displacement of dies of a configuration to produce a desired article. Typically, one of two dies is fixed to serve as an anvil, the other die being moved by a ram with displacement controlled by precisely limiting the extent of ram movement. The foregoing 'holds for sheet metal working in the manufacture of an article as well as in the application of an article to provide a functional product. In the former case, dies are worked against sheet metal stock by cutting away metal in a pattern to leave a desired configuration, by forming, by impact extrusion or coining, or by rolling, or any combination of these and other steps. Working of sheet metal to apply articles is represented by the controlled deformation of a portion of a preformed metal member around a further member to effect a connection of an article to such other member. The connection made, for example, may be of a terminal to an electric conductor such as a wire lead or to a tube providing a hydraulic or pneumatic connection with an appropriate hydraulic or pneumatic fitting.
Displacement control is relied upon by the art in sheet metal working for all types of manufacturing and'application tooling. In the case of tooling used for making or applying parts at a relatively low rate, the art relies by and large upon a manually developed force. This force may be directly applied as through the handles of a hand tool which operate as levers to drive dies'in a controlled displacement of closure to crimp a terminal onto a wire; or, by a bench mounted tool wherein dies are driven in a controlled displacement of closure through a ram actuated by hydraulic pressure supplied by a handoperated pump. For manufacture or application in production where higher'rates of production are required, die displacement through a controlled closure is effected'through a ram driven by force developed from an energy source which is not manual. Typical energy sources for metal working for both manufacturing and applying articles of sheet metal stock include inertial systems wherein energy is stored in a moving part which may be a flywheel or the ram itself; or, pressure systems wherein energy is stored in a fluid maintained under pressure in a vessel supplied by a pump in turn driven by some means such as an electric motor. In the case of manually operated tooling the main requirement is to get enough force to achieve the displacement of dies required. Excessive force is precluded by limiting displacement. The same holds with regard to production tooling with the additional complication that high production rates require a storage of considerably more energy for developing ram forces than is necessary for a single cycle with an incident problem of limiting the sampling of available energy so as not to overdrive the working dies. Even with manuallyoperated tools this latter problem exists but is usually accommodated by building the tooling considerably heavier and stronger than is actually required by the work to be done. This is one reason why hand tools are typically heavy and bulky and require what might be considered as a relatively complicated and expensive linkage and support structure.
In the case of production tooling this same problem is made considerably more difficult by the effect which a higher cycle speed has upon force impedance matching of a machine system. The nature of the problem can perhaps be mbre clearly presented by reviewing the operation of a J-press which has become a standard in the sheet metal forming art. A .l-press includes a relatively heavy flywheel, on the order of 30 to 40 pounds, driven by an electric motor through a V-belt to rotate at approximately 240 rpm. to provide a source of enerwith ram stroke determined by the travel of the eccentric. Typically, this stroke is on the order of l'ris inches. A mechanical linkage is made to engage the clutch of the press so as to operate the ram at approximately 250 cycles per minute, the ram and working due being driven 2% inches per cycle. The force-displacement characteristic of the ram and working die is generally in the form of a sine wave. Adjustments of the lower die by shimming are relied upon to provide the proper spacing of the working die and fixed die. In the case of crimping a terminal onto a wire, for example, die spacing is controlled to yield a fixed displacement which can be determined by the height of the crimped terminal after crimping. The various factors of extent of force, ram velocity, displacement, acceleration, rate of rise or fall of force and dwell time are all relatively fixed from cycle to cycle and cannot practically be altered either during a cycle or from cycle to cycle during operation of the press, These factors can be altered only by changes made to the driving linkage which are quite complicated. Since the basic criterion for proper operation is one of displacement, all elastic deformation in the press, its base and its linkage must be considered. Wear in the press, its linkage and in the dies are factors which can also change displacement. Perhaps more importantly, poor results can be caused by variations in the part being processed. Such variation can be due to varying oxidation of the parts, differences in plating thickness which are'frequently present on reel stock, or differences in the undeformed thickness of preinsulated terminals. The force requirements for crimping a typical terminal onto a wire run between 1,200 and 3,000 pounds with certain designs having a requirement extending up to 5,000 pounds. While a .I-press can quite adequately achieve a specific die force within this range, changes to a different force, even if slight, cannot be practically made without changing the relative position of dies. Moreover, little can be done to match the force characteristic during die displacement to the force requirement of the workpiece; the J-press sinusoidal wave force characteristic yielding only the maximum required force and possible input damage to a workpiece.
With a solenoid operated press the basic shortcoming of the .l-press tied to achieving a ram force by displacement through momentum given to many parts is still present. There is some simplification in the energy transferring mechanism by the elimination of a flywheel and clutch and there may be further simplification by the elimination of some part of the linkage, but the motor involved is a relatively heavy and expensive structure and the weight ofthe ram is fixed. Additionally, solenoid presses presently being used have a practical limitation on available force of less than 2,500 pounds. Die opening or crimp height adjustment which is a basic criterion for most metal working operations at present can be accommodated only by controlling the effective kinetic energy of the solenoid driven ram. The control must be accomplished through a circuit capable of handlingand modifying relatively high currents in a relatively short time.
Hydraulic or pneumatic presses have a basic limitation tied to a dependence upon relatively high fluid pressure and means for achieving such pressure which do not lend themselves to high speed press operation. While the various factors of force adjustment, dwell time, ram velocity, acceleration and the like can theoretically be controlled by modulating a fluid supply, very little has been done to make such control practical and as yet the need for so doing has not been fully appreciated.
In all of the foregoing apparatus, problems of energy storage, energy transfer, impedance matching, clutching, displacement variations due to elastic deformation and wear and lack of control over ram displacement, velocity, acceleration and the extent of force, represent limitations which are expressed in terms of apparatus complexity, number of parts, reliability and performance in terms of cycle speed and quality of product manufactured or applied.
SUMMARY OF THE INVENTION The present invention relates to a means, method and system for working material forming dies through the use of a magnetically actuated motor driving a ram in displacement and under a force precisely controllable by controlling only the field of the motor.
It is an object of the present invention to provide a means and method for working material forming dies which is more efficient and more reliable than that provided by present day techniques and apparatus including inertial and fluid operated devices. It is a-further object to provide a method and means for working material forming dies which provides a precise control of ram displacement, force, velocity, acceleration and/or dwell time within a given operating cycle or between operating cycles. It is a still further object to provide a system for controlling a material working die in a manner to improve the quality of crimped devices by minimizing the effect of tolerance as to crimped parts and crimping apparatus. It is another object of the invention to provide a system capable of controlling a tractive magnet motor so as to provide a relatively fast operation cycle.
The foregoing objectives are attained and the problems mentioned relative to the background of the invention are overcome by the invention through an electric motor ofa type based upon what is called a tractive magnet concept. This type of motor features in a preferred embodiment a pair of electromagnets with one of the pair being fixed and the other being movable. The movable magnet is attached to a ram which is driven by closure of the movable element magnet toward the fixed element magnet. The pair of electromagnets are arranged with the faces thereof positioned for flux closure therebetween developing a mutual attraction driving the two magnets relatively together to close an air gap between the magnet faces. The resulting force is applied through a ram fixed to the movable magnet having a die driven and carried by the ram against a fixed die.
In conjunction with the particular type of motor featured by the present invention a circuit is provided which in one embodiment operates to control the voltage and current applied to the electromagnets to in turn control field buildup in the magnets and thus control the force applied through the ram in terms of velocity, acceleration, extent of the force, displacement and dwell time. In accordance with one embodiment of the invention, a calibrated force sensing transducer placed beneath the fixed die is made to produce a force measuring signal which is then compared with a reference voltage to produce a feedback signal to control these factors. A solid state circuit embodiment for effecting control of this latter type is disclosed along with generalized circuits for the system of the invention. The foregoing is in part based upon my discovery that the force-displacement characteristic obtainable with a tractive magnet motor not only can provide control of ram displacement and force factors, but further that such characteristic can be made to very nearly match the force distance curve required for a large number of existing material working operations. Crimping of a sheet metal ferrule structure inwardly against an electrical lead wire represents one such operation.
In the drawings:
FIG. 1 is a perspective view of a magnetic actuator for crimping terminals with a portion of an actuator housing sectioned to show the electromagnets in an open position;
FIG. 2 is a view similar to that of FIG. I, but with the clectromagnets in a closed position with the electromagnets sectioned to show the magnet windings, and the bearing structure supporting the upper electromagnet and the ram shaft of the mechanism;
FIG. 3 is a plot of force-displacement characteristic curves available with an electromagnet of a given material and the force required for a typical crimping operation;
FIG. 4 is a schematic diagram of a control circuit in accordance with one embodiment ofthe invention;
FIG. 5 is a schematic diagram of a control circuit in accordance with another embodiment of the invention;
FIG. 6 is a plot showing ram and die displacement versus time for a J-press and for a magnetic actuator in accordance with the present invention;
FIG. 7 is a schematic diagram showing in detail a circuit capable of use to provide motor control; and
FIGS. 8-11 are waveforms depicting power requirements ofthe invention system in a dynamic state.
In the description hereinafter to be given the invention system, means and method are described relative to a particular type ofmetal working to crimp a sheet metal terminal onto an electrical lead wire. It is to be understood, however, that the invention is contemplated as being applicable to many types of material working operations of similar requirements for application, installation or manufacturing by blanking, stamping, forming, coining, rolling, molding and the like. The use of the term sheet metal is not intended to preclude applicability to forming parts which are, for example, comprised of tubing. While the description hereinafter given is particularized to a bench mounted press for application of terminals to electrical lead wires, the invention is also contemplated as being fully applicable in portable tools which may be hand carried.
Referring now to FIGS. 1 and 2, a bench mounted press P is shown relative to terminating an open barrel electrical terminal T to a stripped insulated electrical lead L. The version depicted in FIGS. 1 and 2 would, in normal practice, include a number of features not shown in the form ofa feed mechanism for feeding terminals and/or perhaps a feed mechanism for feeding stripped leads; these details being left off for the sake of clarity in describing the invention. Numeral 10 may be taken to represent the top of a workbench or the like upon which the press P is mounted. The press includes a frame or housing comprised of a metal base plate 12 having attached thereto an upstanding support portion 14 carrying a boxlike structure 18 in which is mounted a magnetic actuating mechanism. This mechanism is connected to a ram 20 having a die 22 on the lower end. As can be seen better in FIG. 2, ram 20 is connected to a ram shaft 24 which extends vertically up through the housing structure 18. The top of ram shaft 24 includes a flange member as which serves as a stop for a spring member 28 made to surround the upper portion of shaft 24 and bear against the top of housing 18 around an aperture therein through which shaft 24 travels during operation of the press. A suitable auxiliary bearing shown as 29 may be provided in the top of housing 18 to support shaft 24 for sliding movement relative thereto. Spring member 28 is a compres sion spring of sufficient strength to push the ram shaft and connected structure rapidly upward to the position shown in FIG. 1 in the absence of force drawing the magnets of the actuator together. The lower magnet of the actuator structure shown as 30 is affixed to a transverse plate which is part of the housing structure 18 and is thereby fixed relative to ram shaft movement. The lower magnet 30 has a central aperture through which the ram shaft 24 extends, the latter being supported therein for longitudinal sliding movement relative to the housing 18 by means of a conventional main bearing 36. The upper magnet of the actuator structure shown as 32 is affixed to the shaft as by a keyed and threaded sleeve shown as 38 in FIG. 2. The upper surface of the fixed magnet 30 carries a cushion in the form of a sheet 34 of plastic such as Mylar or the like which prevents surface engagement of the two magnets during closure in the position shown in FIG. 2. Sheet 34 also maintains a minimum gap between the two magnets to prevent the magnets from sticking together. The thickness of sheet 34 is somewhat exaggerated in FIGS. 1 and 2, being in practice quite thin; in an actual example on the order of0.003 of an inch.
As can be discerned from FIG. 2, each of the magnets includes a recess which extends around in an annular fashion with the body ofthe magnet. The recesses are shown as 40 and 42 in FIG. 2. These recesses contain magnet windings WI and WII, which are terminated in a suitable manner, not here shown, to a power supply circuit.
The plate 12 contains a fixed die 50 secured thereto in alignment with die 22. In the embodiment shown in FIGS. 1 and 2 a force transducer 52 is provided beneath die 50.
In general, operation of press P begins with the press in the position shown in FIG. 1 and with die 22 in an upward position displaced from lower die 50. A terminal T is positioned on the lower die with the stripped portion of lead L positioned in the crimp portion of T. Energization of the windings WI and WII results in the generation ofa magnetic field in magnets 30 and 32, which develops a force drawing the two magnets relatively together. Due to the fixed support structure 18, magnet closure draws or forces ram downwardly carrying die 22 against the terminal T and against the lower die 50. In accordance with one embodiment, as ,this occurs the force involved is detected or sensed by transducer 52 which develops a signal which is fed back to the power supply circuit for comparison and control of applied force. In accordance with a different embodiment of the invention, the pulse energizing the windings WI and WII is shaped by a suitable circuit to provide a force-displacement characteristic predetermined by experience with the press and a given terminal and die design. In the latter instance the force transducer 52 is not utilized.
From FIGS. 1 and 2 the general features and operation of the press P of the invention should now be apparent. It is pointed out that the press P, insofar as effecting die drive, has really only one moving part consideringelements 20, 22, 24 and 32, as mechanically tiedtogether. It is also pointed out that press P may have but a single main bearing surface, that being bearing 36; with any auxiliary second bearing surface such as 29 being used or not, depending onithe size, weight and attitude of use of the press. The single bearing 36 or the two bearings 36 and 29 and the surfaces against which these bearings work are then the only controlling factors for tolerance wear of the drive mechanism. In accordance with the invention, the forces which these bearings much carry are minimal, being only that required to support the moving structure against sidewise displacementpln use of the mechanism with shaft 24 mounted vertically as depicted in FIGS. 1 and 2 or vertically in an opposite sense, which may be preferred in certain applications, the loading of these bearing surfaces is not only quite small but is not concentrated on any point of the bearing. In certain uses and particularly in uses of the invention in hand-carried tools the bearing load may be somewhat more concentrated but is still overall far less of a problem than is the case in prior art devices. In each instance, care should be taken to prevent relative rotation of the magnets, which effect has been observed. This may be done by any suitable means such as a keying of shaft 24 or the magnet 32.
Turning now to FIG. 3, an important aspect ofthe invention is revealed in the form of a plot of force-displacement characteristics; the solid lines representing magnetforce versus air gap and the dotted lines representing a work curve required for a standard type of terminals. A generalized representation of the cross-sectional configuration of the terminal is associated with the work curve. These curves are based upon working models and are included to depict the principle forming a basis of one aspect of my discovery which led to the present invention. The magnet force curve represents ampere turns for one type of magnetic material presently available and practically useful in forming the magnets of an actuator in accordance with the present invention. As an important point, it is to be observed that the characteristics of tractive magnets may be made to be very similar to the characteristics required by crimping operations thus providing an inherent advantage of potential efficiency. Perhaps more importantly, the similarity of actual magnet force characteristics of tractive magnets to the actual force-displacement characteristics of various crimps permits a control of applied force which is very simple to achieve in comparison with the requirement for controlling force in a J-press or the like. Such similarity also enhances feedback control.
Before turning to examples of control circuits and further explanation of the system of the invention, some consideration of the concept of tractive magnet operation may be worthwhile. In this regard reference is made to the book, Electromagnetic Devices by Herbert C. Roters, for a review of theoretical and practical tractive magnet designs, energy requirements and limitations. As evidenced in FIG. 3, the tractive force developed in an electromagnet increases from some minimum amount to some maximum amount as magnetic intensity increases. The increase of tractive force has a nonlinear relationship to magnetic intensity which is determined for a given applied current and number of turns by the characteristics of the magnetic material employed. For the moment, considering a fixed system wherein magnet elements like 30 and 32 shown in FIGS. 1 and 2 are held fixed, tractive force can be increased from a minimum approaching zero pounds per square inch to a maximum by increasing ampere turns per inch. For example, with one material, tractive force in a fixed system can be raised from approximately zero pounds per square inch to a maximum of about pounds per square inch. For another matei'ial the maximum will exceed 300 pounds per square irich. There exists a substantial choice of magnetic material providing different tractive force versus magnetic intensitycharacteristics. There is also a choice of force quantity and operating characteristics which is dependent upon the size of the tractive magnet and the extent of the area of the magnet surface. In general, one should choose a material having a sufficient force for a given application with a minimum magnetic intensity required to provide efficiency and to minimize current requirements.
As a further consideration, the choice of magnetic material to achieve a given requirement for magnetic intensity may be made with respect to whether or not saturation is to be achieved or substantially approached within the duty cycle of the tractive magnet system. The invention contemplates both alternatives depending upon the force characteristics required by a given application. For example, one may select a magnetic material which approaches saturation before the gap between the magnets is closed and before the workpiece is fully deformed. This will mean that applied force will rise at a substantial rate and then level off toward a more constant value as saturation is achieved. It is to be noted that as the magnets close and the gap between the magnet surfaces is reduced there is an increased coupling between the magnets which tends to increase the force developed by the magnets for a given magnetic intensity.
An alternative is to select a magnetic material so that saturation is not reached during the duty cycle and the workpiece is completely deformed before the magnets reach saturation. If the force requirement of a given application permits, this latter choice is preferred. In applications where the force requirement tends to flatten out towards the end of the duty cycle as shown by example in FIG. 3, a material experiencing at least an approach towards saturation will yield a more similar magnet force versus gap and displacement characteristic.
As a further consideration, once a given magnetic material is chosen and a geometry for the magnets is selected to yield a sufficient area for a given application, the number of turns to give a sufficient magnetic intensity at a maximum peak current must be selected. The geometry chosen operates to some extent to limit the number of turns which can be physically disposed in or on a given tractive magnet. Heat dissipation also has a significant bearing on the number and disposition of winding turns. Generally, a low impedance winding is preferred to minimize heat generation and ease power requirements. For practical reasons, consideration should be given to available power supplies; available line power for bench actuators as used in production or available battery power for portable actuators which must be carried about.
As yet a further practical consideration the design ofthe actuator must provide a sufficient working space to permit feeding of workpieces. For actuators employed solely for hand feed operations a working space on the order of an inch or less is usually satisfactory. With automatic feed apparatus the gap between tractive magnets may be somewhat reduced. In the example shown in FIGS. 1 and 2, the ram is shown connected directly to a working die. It is contemplated that the ram may be utilized to drive existing applicator mechanisms which contain means to feed stock into the die working area and to eject workpieces after deformation.
In a direct application as shown in FIGS. 1 and 2, consideration must be given to the gap between the tractive magnets in the open position as regards achieving a sufficient force to initiate closure of the magnets together. Since a tractive magnet actuator is a dynamic system with effective magnetic intensity increasing as a working gap is closed the initial gap should be minimized to reduce generation of heat.
For a given magnetic material, a given number of turns and a given working gap, magnetic intensity becomes basically a function of current at a given gap. It should now be apparent that force can be controlled as a function of current at a given gap and that ram force, velocity, acceleration, dwell and displacement can be regulated directly by control of applied current.
With the preceeding in mind, reference is now made to FIG. 4 showing a schematic control system including a power supply 60 connected to a pulse control component 62, in turn connected to an actuator 64. The actuator may be considered as that shown in FIGS. 1 and 2, with the pulse control device driving the windings WI and WII carried in magnets 30 and 32. In general, supply 60 may be any suitable power supply capable of supplying energy in the form of a given current at a given voltage to meet the requirements of the pulse control device 62. The device 62 may be any suitable device capable of providing pulses of a current and voltage level for a given duration in accordance with the requirements of the actuator. As an example, an actuator like that shown in FIGS. 1 and 2 contained magnets each approximately 6 inches in diameter and about lVdnches thick with each magnet wound with about 90 turns of No. 16 AWG wire. The 90 turns had a resistance on the order of H29 and the windings were connected in a series aiding relationship. With the spring 28 removed from the assembly and the upper die 22 resting on an uncrimped terminal to create an air gap of about 0.050 of an inch, a pulse I milliseconds in duration, 47 amperes in amplitude at 50 volts developed a force of 3,000 pounds against the terminal. In actual use, the working gap of the actuator was approximately 0.090 of an inch. FIGS. 8--I1 show waveforms of an embodiment of the invention circuit in a dynamic state and some appreciation of voltage, current and therefore power requirements can be gained therefrom. During the first part of the duty cycle the magnetic intensity developed by current from 60 power supply to pulse control circuit 62 must be sufflcient to overcome the friction of the system and the force developed by spring 28. As the die 22 begins to work against the workpiece the force requirements increase in the manner illustrated in FIG. 3. Thereafter the force requirements increase even further, but as this happens the gap between the magnets 30 and 32 is closing to increase magnetic intensity and the magnet force developed by the system. The current pulse from circuit 62 is accordingly adjusted to achieve a proper magnetic intensity.
In accordance with the concept illustrated in FIG. 4, the characteristics of the pulse developed by the circuit 62 are based upon experience with a given workpiece so as to cause a closure of dies to affect a displacement crimp, the gap between magnets 30 and 32 being held fixed. By controlling the duration of applied pulse the period of timing of bottoming can be readily controlled. By controlling the amplitude of applied current the instantaneous force during ram displacement can also be controlled very precisely. Both of these controls can be accomplished by pulse control through potentiometers or the like rather than by shimming or making adjustment in driving linkage as is the case with a l press. Press wear and noise can thus be readily minimized.
With the circuit of FIG. 4 the pulse control device 62 can be triggered manually as by a foot switch to develop a pulse with proper amplitude and duration and permit a working rate compatible with a given operator. If an automatic feed mechanism is utilized the device 62 can be ofa type which will produce pulses of a given rate compatible with such mechanism. It is contemplated than an automatic feed mechanism may be made to contain some sensing device developing appropriate trigger signals to initiate 62.
The embodiment of FIG. 4 is contemplated as being a displacement controlled actuator. This does not mean that it is displacement controlled in the same sense as a J-press or the like, because ram force, velocity, acceleration and dwell time can be electrically controlled by controlling the characteristics of the applied pulse. The ram may be made to travel downwardly very rapidly by a pulse having an initially high amplitude and then quite slowly as first engagement of the die with the terminal workpiece is made with a surge of force then being developed and quickly released or maintained as deformation takes place. The system of FIG. 4 may be free running or it may be regulated by using a microswitch or the like which is operated by ram displacement. The use of a microswitch which is actuated by a ram or some portion thereof may also be coupled to a circuit for providing a delay before the current applied to the magnets is terminated. This delay may be made adjustable to control dwell time. Such a circuit could be made to reduce the rate at which the current applied to the magnets is dropped to control fall time and minimize induced current pulses caused by rapidly collapsing field in the magnets.
The immediately foregoing modifications to the circuit of FIG. 4 represent in a sense a type of feedback. FIG. 5 shows an alternative version for control of an actuator in accordance with a further aspect of the invention wherein feedback is an essential part of the system. A supply shown as 66 is connected to a gate which is in turn connected to the actuator shown as 7'0. The gate is controlled by a comparator 72, which may include means to provide voltage adjustment such as a potentiometer. The comparator is supplied by a signal developed from a transducer 74. The transducer 74 may be disposed in the system in the manner indicated in FIGS. 1 and 2 with respect to the transducer 52. The transducer 74 may be disposed elsewhere in the system and may be comprised ofany ofa number of different types of force measuring transducers. Piezoelectric, barium titanite units or semiconductor strain gauge units are commercially available. Transducers are also available which sense changes in reluctance or capacitance and a number of optical transducers are available which are capable of providing an accurate and dynamic indication which can be translated into a signal representing force.
In accordance with the system control of FIG. 5, supply 66 is gated on by gate 68 to provide a pulse to the actuator 70 causing the ram thereof to be driven downwardly. Assuming that a strain gauge type transducer is utilized for transducer 74, upon initial closure of the dies against the workpiece a signal is immediately developed and supplied to the comparator 72. In a simple system, comparator 72 can be made to merely sense the quantity of the signal from 74 and to operate to shut the gate when such quantity matches the quantity preset to the comparator. At this time the actuator is deenergized to enter into a restoring phase of the cycle. As with the previous embodiment, the next cycle can be initiated either by a switch under manual control by an operator, by a clock producing trigger pulses or by resetting the gate to the open condition at some rate related to a feed mechanism associated by the system.
Some appreciation of the concept of the invention system can be gained from FIG. 6 depicting time versus stroke operating cycles for a J-press and for a magnetic actuator in ac cordance with the invention. The cycle time is chosen to be identical for comparison purposes, but it should be understood that a magnetic actuator in accordance with the invention can be readily changed to have a cycle time which is less than or greater than that ofa typical .I-press. As shown, a
J-press has a sinusoidal characteristic which starts with dies in an open position and extends in time to zero displacement or closure which is representative of die bottoming and is controlled by shimming of a lower die relative to the stroke of an eccentric. As can perhaps be visualized from FIG. 6, if a .1- press displacement stroke is too great a substantial compressive load will be experienced by the entire linkage mechanism including both dies and the press base. The resulting characteristic would show a flattening of the curve at the point of zero displacement in FIG. 6. Insufficient stroke would result in the curve appearing as it does in FIG. 6 but moved slightly upward so that it does not touch the zero displacement line. This would result in a deformation of workpiece which is less than desired. As previously mentioned, tolerances in setup may cause a J-press to be overdriven so as to bottom and overload the working parts to the extent of overdrive. Insufficient die closure is usually caused by wear in a J-press driving train or wear of the die surfaces which gradually tends to reduce the effective stroke of the press. Variations in tolerance of the workpieces will, if oversized, result in an overstroke tending not only to overdeform the workpiece, but also to overwork the mechanical system and dies. Tolerance variations in the workpiece which result in less than what it should be will result in the workpiece not being sufficiently deformed. For example, in crimping preinsultated terminals a tolerance variation in the metal and/or plastic sleeve of a given amount such as .005 of an inch over nominal will result in an overload of the press mechanism causing an elastic deformation of the dies, press base and/or driving train sufficient to accommodate such overload. As a further example, if the wire which is inserted within the terminal is undersize 'as by having a strand or two accidentally removed, the workpiece will be insufficiently deformed to result in a high' resistance connection.
Comparing now the operation of the circuit of FIG. 4 to the characteristics of FIG. 6, displacement control is provided by first adjusting the lower die of the apparatus to an approximately correct position with all further adjustment achieved through the pulse control device 62. The pulse control device 62 can be made to provide a pulse shape resulting in an operating characteristic similar to that shown in FIG. 6 with a somewhat lower velocity of ram and diein the initial portion of the cycle and with a more rapid velocity in the last portion of the cycle before closure. The pulse may be controlled so as to provide a substantially constant die position for a period of time which effectively provides a die dwell time as indicated in FIG. 6. As indicated by the dotted lines in FIG. 6, the dwell time may be reduced to a desired value with an incident reduction in cycle time and higher operating speed. Contrasting the operation of a J-press or any inertia type press, the invention permits a dwell time which may be an appreciable portion of the cycle time. With certain materials having a relatively high resistance to flow or certain geometries of standard materials wherein the length of the deformed member is appreciable, it has been found advantageous to provide a considerable dwell time to permit completion of inelastic deformation. This cannot be practically achieved by the type ofimpact deformation resulting from standard presses or inertia apparatus.
The control system of FIG. 5 facilitates not only a control of the velocity and/or acceleration of the ram and die during closure and opening, but provides a precise control of the actual force supply to the workpiece. While FIG. 6 depicts ram and die movement in terms of displacement, the lower and flat portion of the characteristic can with a control system like FIG. 5 also be thought ofin terms of force applied. The system can cause the ram and die to travel downwardly until it engages a workpiece, to continue until a predetermined force upon the workpiece is reached and then to maintain such force for a period of dwell. By a proper arrangement of ram and die to assure that mechanical closure of working parts never occurs except through the workpiece, the force transducer of the system can be made to accommodate all variations in tooling setup, wear and in workpieces.
Turning now to. a detailed circuit embodiment, FIG. 7 depicts a solid state version of the control system of FIG. 5, with several additional features. The circuit includes supply input terminals T1 and T2 which, in the illustrative embodiment, are negative and positive, respectively. Toward the lower right in FIG. 7 will be seen the actuator windings WI and WII which are, as previously mentioned, connected to be magnetically coupled in an additive sense. Current to windings WI and WII is controlled by a plurality of power transistors connected in parallel across the power supply leads 102 and 104, in series with the windings. To the left of the circuit in FIG. 7 are dwell time control components including a dwelltime control switch SW1 and a cycle initiating switch SW2. Toward the center are force range switch SW3 and force signal input terminals T3 and T4.
The dwell time control components include a pair of PNP transistors Q1 and 02 connected in parallel across the leads 102 and 104 through a common emitter supply through a relatively low value commutating resistor R7 connected to the positive supply lead 104. The collectors ofQI and 02 are connected to negative lead 102 via identical resistors R2 and R4, with the bases of the transistors connected to positive lead 104 through identical resistors R6 and R8. The base of O1 is tied to the negative supply lead 102 through a relatively large resistor R1 which serves to maintain the base of Q1 relatively positive so that Q1 is normally barely conducting. Resistors R3 and R8 provide a resistance maintaining the base of Q2 relatively less positive so as to be on, and driving more current than Q1. A base supply shunting path is provided around R8 through the cycle initiating switch SW2. A path connecting the positive supply through R6 to the negative supply through R4, between the base ofQl and the collector of 02, includes a variable resistor R9 and one or the other of capacitors C1 or C2 through switch SW1. Capacitors C1 or C2 are connected across the positive and negative leads 102 and 104 through the paths including R6, R9 and the path including R4.
The collector of Q1 is connected to the base of a PNP transistor Q3 which has its collector tied directly to negative supply lead 102. The emitterof O3 is connected to the collectors of a further PNP transistor Q4 having its base connected to the emitter of an N-P-N transistor 05 and its emitter connected to the collector of Q5. The base-emitter circuit ofQS is connected to the force signal input terminals through a current limiting resistor R10. The emitter circuit of O5 is also connected to a voltage comparison circuit through a variable resistor R11 tied to the collector of Q5. The resistor R11 is connected across a Zener diode Z1 and a bias voltage supply including a battery B1 in series with a resistor R14, through a resistor R13 and a shunting path through switch SW3 or the resistor R12, depending on whether the switch is open or not. The comparison circuit serves to provide a bias voltage to Q5 which can be adjusted for range by SW3 and in extent by R11. The transistor Q5 serves to modulate the extent of control obtained by a given force signal input.
The collector of OS is connected to a PNP transistor Q6 having its emitter tied to the positive supply lead 104 through a limiting resistor R15. This path is also connected to the negative side of a back bias voltage source B2 having its positive terminal connected tothe base of each of the PNP power transistors Q7-Q10 through appropriate limiting resistors RR19, respectively, to counteract the leakage path through 06. The collector of O6 is connected directly to the negative supply lead 102 and 06 operates as an emitter follower for Transistors Q7-O10 have the emitters thereof connected to the positive supply lead 104 through a pair of spike filtering diodes D1 and D2.
A shorting diode D3 is connected to WI and WII to provide a shunting path for heavy currents caused by the collapsing field in WI and WII.
In operation 01 is on sufficiently to provide a drop across R2 to hold the base of 03 positive and hold Q3 off, thus holding Q4, Q5, Q6 and 07-010 off.
Transistor O2 is on and the capacitor C1 or C2, then in circuit is substantially discharged. When SW2 is closed to short out R8 and drop the base of O2. cutting 02 off. the capacitor then in circuit is charged by being effectively connected through R4 to the negative supply voltage lead 102. As the switch SW2 is reopened to cause the base of O2 to go negative, Q2 comes back on sufficiently to cut 01 off, which causes the base of O3 to go more negative; Q3 being forward biased to come on and turn on Q4. Q5. Q6 and Q7Ol0. At this time the capacitor, C1 or C2, then in circuit and charged up will begin to discharge around the path R9, R6, R7 and the emitter-collector circuit of Q2. The rate of discharge will be determined by the setting of R9.
Assuming that ram movement resulting from the current supplied by Q7-Ql0 causes engagement with a workpiece to develop a signal input at T3-T4, this signal will tend to drive the base of O5 to an extent determined by the setting of R11 and SW3. As Q5 draws more or less current to offset the forward bias of Q4 and its amplifier Q6 follows to bias Q7Ql0 to draw more or less current developing an applied force balancing the sensed force as determined by the signal to OS from T3T4 and the setting of R11 and SW3. At some point the working gap of the magnets will be at a minimum with 07-010 drawing just enough current to maintain a force sufficient' to produce a balancing force signal input. At some point in time the charge on the capacitor C1 or C2 will be sufficiently dissipated to cause the base of O1 to be sufficiently negative for O1 to come on, cutting Q2 off and cutting off Q4, Q5, Q6 and Q7-Ql0 to complete a system cycle.
By setting SW3 to shunt out R12 the voltage drop across the emitter-collector circuit of Q5 will be effectively increased to require a greater force input signal to achieve a given range of modulation by Q5. Conversely, having R12 in the comparator circuit will require a lesser force signal to effect modulation by Q5. By setting Rll, a more precise control of force signal quantity can be preset in either the high or low range.
Range of dwell time can be chosen by selecting C1 or C2 to provide a different RC time constant with a precise control effected by R9.
In an actual circuit the following components were used.
R1 SZKQ R2, R4 5. 6K0
3 27K0 R6, R8 IOKSZ R7, R13 1000 R9 2OKQ R10 K0 R11 1K9 R1 3800 R14 1509 R15 500 3 watts R16, R17, R18, R19 29 3 watts Ql- 4 2N2953 Q5 H 2N1306 Q6 2N2869 Q7-Q10 2N2730 1 1N3016A D1, D2 1N3194 D3 40212 Tl,at 24 B1,at +12 B2, at v 1. 5 C1, atmfd 4 G2, at mfd 10 Referring now in detail to FIGS. 8-11. photographs on a one by one centimeter grid depict dynamic parameters of an invention system to illustrate the system in operation. This system is not identical to that of FIG. 7. one difference being that a full wave bridge, capacitor input filter, power supply was used in lieu ofa battery power supply.
In FIG. 8 the trace beginning to the left represents magnet current; the first peak depicting the current required to initiate a substantial closing velocity of the magnets together and the second peak of the same trace depicting the current required for workpiece deformation. Photograph calibration is 10 amperes/centimeter on the ordinate axis. The trace in FIG. 8 peaking toward the center represents force measured on an anvil beneath the workpiece. Calibration of the latter trace is 500 pounds/centimeter plus 300 pounds on the ordinate axis; the latter force being a correction to the calibration of the load cell. Abscissa calibration is 0.050 seconds per centimeter. FIG. 9 is for an operation similar to that of FIG, 8 but with the press set for a different maximum force. FIG. 10 depicts dynamic conditions present in the operation shown for FIG. 8 in terms of a driving voltage supplied to the power transistors of the circuit. The photograph calibration is 5 volts per centimeter. As will be apparent, the turn-on time in integrated which, it is believed, helps in controlling the inrush current so that high currents are not applied to the magnet windings before the magnetic field has built up in the magnets.
Also, observe that the current pulse is turned off by a slowly rising voltage which helps to preclude secondary breakdown of the power transistors. FIG. 11 shows a trace of the voltage across the emitter-collector circuits of the power transistors for the turn-on pulse portion of FIG. 10 for 1 cycle of opera tion. The ordinate calibration for FIG. 11 is 10 volts per centimeter and the abscissa calibration is 0.050 seconds per centimeter.
Having now described the invention in terms intended to enable a preferred practice thereof in its preferred modes, claims are appended which define what is asserted as inventive.
What I claim is:
1. In an apparatus for working material through the compression of a workpiece by a die driven thereagainst having a given required force-displacement characteristic, an electromagnetic motor of a type having movable motor elements of magnetic material having winding mea'ns thereon and operable to develop a force proportional to magnetic intensity, control means including a power supply connected to said motor to energize said windings and develop a force-displacement characteristic of said elements similar to the said given characteristic, and die means connected to be driven by said motor to deform a workpiece.
2. The apparatus of claim 1 wherein the said elements are of a magnetic material selected to approach saturation as the said elements approach each other and the said die means approaches completion of deformation ofthe workpiece.
3. The apparatus of claim 1 wherein the said elements are of a magnetic material which remains substantially unsaturated throughout the movement cycle of said motor elements and the movement cycle of said die means to complete deformation ofa workpiece.
4. In an apparatus for working material through a controlled deformation of a workpiece by compression thereof between dies, a tractive magnet motor including at least a pair of motor elements with at least one of said elements containing a winding operable upon being energized to actuate said motor, first means connecting one die to one of said elements to be driven thereby, second means connecting the other of said elements to another die, and third means positioning at least one of said connecting means with said dies and elements spaced apart when said winding is deenergized and means guiding said dies relatively together deforming a workpiece inserted therebetween responsive to said winding being energized.
5. The apparatus of claim 4 wherein said third means includes means developing a force tending to drive said motor elements apart.
6. The apparatus of claim 4 wherein said first means includes a ram linked to said one die and to said one motor element and said third means includes a spring connected to said ram.
7. In a control system for a press or the like, including a tractive magnet motor, a solid state switch means connected to a power supply and operable in a closed condition to supply power to the press motor, first means for controlling said switch means to control the amount of power supplied to the motor and second means for limiting the extent of time power is applied to the motor to control the duty cycle of the press.
8. The system of claim 7 wherein said first means includes a force sensing transducer operable to sense force developed by said press.
9. In a system for working material by the controlled deformation of a workpiece by a die driven thereagainst, a tractive magnet motor, control means for said motor to supply power energizing said motor, a die and means connecting said motor to said die to drive said die against the workpiece in a single stroke to effect a controlled deformation thereof, said control means including means to control the extent of force developed by said tractive magnet motor and thereby control the extent of force driving said die against said workpiece during said single stroke 10. In a system for working material by the controlled deformation of a workpiece by a die driven thereagainst, a tractive magnet motor, control means for said motor to supply power energizing said motor, a die and means connecting said motor to said die to drive said die against the workpiece in a single stroke to effect a controlled deformation thereof, said control means including means to control the rate of force developed by said tractive magnet motor and thereby control the rate of force developed by said die against said workpiece during said single stroke.
11. In a system for working material by the controlled deformation of a workpiece by a die driven thereagainst, a tractive magnet motor, control means for said motor to supply power energizing said motor, a die and meansconnecting said motor to said die to drive said die against the workpiece to effect a controlled deformation thereof, said control means including means to control the length of time a given force is developed by said tractive magnet motor and thereby control the dwell time of said die against said workpiece.
12. In a system for working material by the controlled deformation of a workpiece by a die driven thereagainst, a tractive magnet motor, control means for said motor to supply power energizing said motor, a die and means connecting said motor to said die to drive said die against the workpiece to effect a controlled deformation thereof, said control means including means to control the extent, rate, and length of time of force developed by said tractive magnet motor and thereby control the working ofthe die against a workpiece.
13. In a system for working material by the controlled deformation of a workpiece by a die driven thereagainst, a tractive magnet motor and control means therefor to supply power energizing said motor, a die and means connecting said motor to said die to drive said die against the workpiece to effect a controlled deformation thereof, said control means including means to independently control the extent of force, the rate of force, and the length of time force is applied by said tractive magnet motor to said die and to said workpiece.
14. In a system for working material by the controlled deformation of a workpiece by a die driven thereagainst, a tractive magnet motor and control means therefor to supply power energizing said motor, a die and means connecting said motor to said to said die to drive said die against the workpiece to effect a controlled deformation thereof, said control means including sensing means for sensing the force developed by said die against said workpiece and means to provide a feedback signal representative of said sensed force to regulate said control means.
15. An apparatus for working material through a controlled deformation of a workpiece by compression thereof between dies, said apparatus comprising, in combination: a tractive magnet motor including at least a pair of motor elements with at least one of said motor elements containing a winding operable upon being energized to actuate said motor; first means connecting one die to one of said motor elements to be driven thereby; second means connecting the other of said motor elements to another die; and third means positioning at least one of said connecting means with said dies and said motor elements spaced apart when said winding is deener gized and means guiding said dies relatively together deforming a workpiece inserted therebetween responsive to said winding being energized; with said first means including a ram linked to said one motor element and to said one die, and with said second means including a frame affixed to said other motor element and to said other die, the said other motor element having a relief through which said ram is extended to position the dies in working relationship.
16. An apparatus for working material through a controlled deformation of a workpiece by compression thereof between dies, said apparatus comprising, in combination: a tractive magnet motor including at least a pair of motor elements with at least one of said motor elements containing a winding operable upon being energized to actuate said motor; first means connecting one die to one of said motor elements to be driven thereby; second means connecting the other of said motor elements to another die; and third means positioning at least one of said connecting means with said dies and said motor elements spaced apart when said winding is deenergized and means guiding said dies relatively together deforming a workpiece inserted therebetween responsive to said winding being energized; with said first means including a ram linked to said one motor element and to said one die, and with said second means including a frame affixed to said other motor element and to said other die, the said other motor element having a relief with a bearing disposed therein, said ram being extended through and supported by said bearing to position the dies in working relationship.
17. In an apparatus for working material through a controlled deformation of a workpiece by compression thereof between dies, a housing including a zone for workpiece insertion, a first die affixed to said housing in said zone, a tractive magnet motor disposed within said housing including a ram having a second die linked thereto positioned to be driven into said zone toward said first die, said tractive magnet motor further including at least two motor elements with one motor element affixed to said housing and the other motor element connected to said ram, first means for energizing said tractive magnet motor to drive said ram and said second die against a workpiece disposed on said first die, and second means for driving said ram and the second die to an open position out of said zone.
18. in an apparatus for working material through a controlled deformation of a workpiece by compression thereof between dies, a housing including a zone for workpiece insertion, a first die affixed to said housing in said zone, a tractive V least a pair of motor elements with at least one of said motor elements containing a winding operable upon being energized to actuate said motor, one motor element being affixed to said housing and the other motor element being connected to said ram, control means for energizing the winding of said tractive magnet motor to drive said ram and said second die against a workpiece disposed on said first die, sensing means for sensing the force developed by said dies against said workpiece, and means to provide a feedback signal representative of said sensed force to regulate said control means.
19. ln a method of working material the steps including providing a force through a motor of the tractive magnet type of a ram carrying a die driven against a workpiece by energization of the motor, controlling the power signal applied to said motor to control the extent of force applied to said ram, die and workpiece, sensing the force developed in said workpiece, and developing a feedback signal to limit the power signal and the force applied to said ram, die and workpiece.
20. in a method of working material the steps including providing a force through a motor of the tractive magnet type to a ram carrying a die driven against a workpiece by energization of the motor, controlling the power signal applied to said motor to control the extent of force applied to said ram, die and workpiece, and the steps of independently controlling the rate of application of said power signal, the amplitude of said power signal and the duration thereof to control the related force characteristics driving said ram and die against said workpiece.
21. In an apparatus for working material through a controlled deformation of a workpiece by compression thereof, a housing including a base carrying a fixed die, a frame carrying an element of magnetic material including a surface of appreciable area, a further element of magnetic material including a surface of appreciable area, means for positioning said elements with the surfaces thereof in facing relationship to define an air gap therebetween and supporting at least one of said elements for movement closing said air gap, at least one of said elements having a winding operable when energized to develop an electromagnetic force driving said elements together, at least one of said elements being linked to a mova' ble die positioned to move toward said fixed die as said force is developed in a movement proportional to the closing of said gap between said elements, and means limiting said air gap to prevent surface engagement of said elements.
22. In a method of working material the steps including providing a force through a motor of the tractive magnet type to a ram carrying a die driven against a workpiece by energization of the motor, controlling the power signal applied to said motor to control the extent of force applied to said ram, die, and workpiece, and controlling the velocity and acceleration characteristics of said ram and die by shaping said power signal in terms of amplitude and duration.
23. In a method of working material the steps including providing a force through a motor of the tractive magnet type to a ram carrying a die driven against a workpiece by energization of the motor, controlling the power signal applied to said motor to control the extent of force applied to said ram, die, and workpiece, and controlling the dwell time of said die on said workpiece by controlling the length of time said power signal is applied to said motor.