US3783662A

US3783662A - Control circuit for magnetic actuator

Info

Publication number: US3783662A
Application number: US00253039A
Authority: US
Inventors: J Keller; B Longenecker
Original assignee: AMP Inc
Current assignee: TE Connectivity Corp
Priority date: 1972-05-15
Filing date: 1972-05-15
Publication date: 1974-01-08
Anticipated expiration: 1991-01-08
Also published as: DE2322513A1; JPS5814147B2; IL42083A; BR7303508D0; CH561967A5; ZA732792B; CA988187A; BE799449R; JPS4956261A; DE2322513C2; FR2184692A2; IL42083A0; SE377010B; AR198987A1; AU474070B2; NL170577B; AU5495973A; NL170577C; NL7306603A; GB1406920A

Abstract

A control circuit for a magnetically actuated die closing apparatus, featuring force responsive die closing cycle termination circuitry as well as safety features for protecting the operator and the apparatus. The safety features include an electro-optic guard and clock circuit. The initial let down force of the ram as the dies make initial closing contact with the workpiece is limited by a let-down circuit incorporated into the control circuit.

Description

United States Patent 1191 1111 Keller et al. 1 Jan. 1974 CONTROL CIRCUIT FOR MAGNETIC 3,206,960 9/1965 Moxley 72/1 ACTUATOR 2,787,313 4/1957 Chernack 72/1 3,099,175 7/1963 Lawson 72/1 Inventors: J p Rlchard Keller; Bruce 3,665,742 5/1972 Felt et al 72/4 Cameron Longenecker, both of Harrsbmg imwy wmi ekR sh r l- Herbst [73] Assigneez AMP Incorporated, Harrisburg, Attorney- Donald W. Ph1ll10n & A M P Incorporated [22] Filed: May 15, 1972 [57] ABSTRACT [21] Appl 253039 A control circuit for a magnetically actuated die closing apparatus, featuring force responsive die closing [52 U.S. c1. 72 1, 72/430 cycle termination Circuitry as Well as Safety features 51 1111. c1 B2111 55/00 for protecting the operator and the pp The [58] Field of Search 72/1, 2, 4, 8, 9, f y ea ures include an electro-optic guard and 72/26, 28, 29 430 clock circuit. The initial let down force of the ram as the dies make initial closing contact with the work- [,56]' Referen Cit d piece is limited by a let-down circuit incorporated into UNITED STATES PATENTS Comm 3,584,496 6/1971 Keller 72/430 10 Claims, 5 Drawing Figures CONTROL CIRCUIT FOR MAGNETIC ACTUATOR BACKGROUND OF THE INVENTION In US. Pat. No. 3,584,496 to Joseph R. Keller, there is disclosed a system for effecting the controlled closure of dies in a material working apparatus featuring a magnetically actuated ram. The system disclosed in this patent represents a marked improvement over prior systems for controlling die closure in material working apparatus.

The magnetically actuated die closing system and how it relates to conventional die closing systems is fully described in the Keller patent. However, to aid the reader in understanding the present invention, the following brief disclosure of die closing systems including the Keller system is given below.

Prior to the Keller system die closing force control in material working apparatus, was generally provided by controlling the initial displacement between the dies. Where the apparatus is to be used in forming articles or in effecting a connection between a preformed article and another article at a relatively slow rate, the required force could be manually developed. For example, the force could be directly applied to the handles of a hand tool which operates as levers to drive the dies in a controlled displacement. The closing of the dies would effect an article forming operation if the dies are worked against sheet metal stock to cut away metal in a predefined pattern leaving a desired configuration. The metal cutting step could be followed by a forming step to form the cut pattern into an article such as an electrical terminal. The closing of the dies could also effect a connecting operation such as the crimping of a preformed electrical terminal to a wire. In this latter case, the terminal and wire are situated between the dies. As the dies close, portions of the terminal deform around the wire to thereby realize the desired connection of the terminal to the wire.

To simplify the following discussion of the invention, no further reference will be made to the use of the material working apparatus in the forming of an article. Further discussion will revolve around the use of the apparatus to effect connection between a preformed article such as an electrical terminal to another article such as a wire. It is to be understood, however, that the apparatus described is of the type which can be used either to form an article or to effect a connection between two articles. Multiple use of the apparatus may be provided by interchanging dies and/or controlling the die closing force.

Where numerous connections are to be made within a short period of time, hand tools do not permit the required rapid cycling. Therefore, the die closing apparatus must use an energy source for effecting die closure which is other than manual. More specifically, where rapid cycling rates are required, one die may be fixed to an anvil while the other die'would be fixed to a ram. Prior to the Keller'invention, the energy source for driving the ram took the form of an inertial system wherein energy is stored in a moving part such as a flywheel or the ram itself, or a pressure system wherein energy is stored in a fluid maintained under pressure in a vessel. As more fully described in the" Keller patent, each of these die closing systems create problems which affect the efficien'cy of the apparatus and the quality of the finished product.

The Keller system solves these problems by providing a magnetically actuated die closing system. In this system, one die is fixed to an anvil while the second die is fixed to a ram. The anvil is mounted in a housing containing a first electromagnet. A second electromagnet is mounted on the ram and made moveable therewith. The force required for die closing is controlled by controlling the current in the coils of the electromagnets. More specifically, the coils in the first and second electromagnets are wound in an aiding sense so that when current flows therethrough the magnets attract. The closing of the magnets is imparted to the dies. The magnetically actuated die closing system permits precise control over the force applied to the terminal to be crimped to a wire by providing control over the velocity and acceleration of the ram as well as control over the dwell time, that is, the time during which the force is exerted on the terminal.

The Keller patent describes two circuit arrangements for controlling the current applied to the electromagnets. In one circuit embodiment, a pulse, predefined in both duration and amplitude, is applied to the magnets. In this case, the duration and amplitude of the pulse are derived from experience with a particular workpiece.

In the second embodiment of the control circuit, the connection of articles, which in this case, is the crimping of a terminal to a wire, is effected with a constant force through the use of a feedback system. Upon closure of the dies, a signal is developed by a force transducer. The force transducer may be any conventional transducer which converts a mechanical force into a proportional electrical signal. Examples of such transducers are piezoelectric, and semiconductor strain gages. The transducer produced signal is compared to a reference signal which is proportional to a predefined force. If the die produced force is greater than or less than the predefined force, the current in the magnets is varied tobring the developed force into agreement with the predefined force. The force is applied to the articles being connected for a predetermined dwell time through the use of a time constant circuit.

Although the control circuit described in the Keller patent provides adequate control under some conditions, they lack the efiiciency desired and safety features needed for a large scale production line set up, The present invention provides an improved control circuit which overcomes the deficiencies of the control circuits described in the Keller patent.

SUMMARY OF THE INVENTION featuring magnetic actuation.

It is further an object of the invention to provide a control circuit wherein no manual adjustment of apparatus elements need be made each time a different wire size is to be crimped to a suitable terminal.

It is still another object of the invention to provide a control circuit which includes safety features to protect the operator from injury as well as to protect the material working apparatus against damage due to the activation of the apparatus when aforeign object is between the dies.

These objects are attained in accordance with the present invention through the use of a unique control circuit which provides for the deactivation of the electromagnets in response to a predetermined critical force between the dies.

The control circuit also includes a let-down circuit for bringing the ram into initial contact with the workpiece which in the preferred embodiment is a contact to be crimped to a wire, at a relatively low average velocity, whereby the ram meets the terminal with little kinetic energy. After initial contact, the let-down circuit is deactivated to cause a rapid increase in the coil current thus developing the large force required to connect the preformed article to another article or to form the article by cutting, forming, etc. We have determined that in a crimping operation if the ram is allowed to approach the workpiece at a high velocity, the impulse developed as the ram meets the terminal may cause damage thereto as well as a deterioration of the quality of the crimp. However, if the ram is gently brought into initial contact with the terminal, with the crimping force subsequently applied, terminal damage is avoided and high quality crimps are realized.

To protect the operator and the apparatus from injury and damage respectively, the control circuit is provided with a clock circuit which triggers to end the die closing cycle if the critical force is not reached within a predetermined time.

An additional safety feature is provided in the form of an electro-optic guard. In operation, a die closing cycle can not be initiated or if previously started will be immediately tenninated if a foreign object of at least a predetermined size and shape is placed between the dies. Thus, if an operator should inadvertently place his hand between the dies, a die closing cycle cannot be initiated, and an initiated cycle is terminated.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a prospective view of a magnetic actuator for crimping terminals with a portion of an actuator housing section to show the electromagnet in an open position;

FIG. 2 is a view similar to that of FIG. 1 but with the electromagnets in a closed position with the electromagnets sectioned to show the magnet coils and bearing the structure supporting the upper electromagnet and the ram shaft of the mechanism;

FIG. 3 is a block diagram of a prior art control circuit for use with a magnetically actuated die closing apparatus;

FIG. 4 is a block diagram of the control circuit of the present invention;

FIG. 5 is a schematic diagram showing in detail the control circuit of the present invention;

DISCUSSION OF THE PREFERRED EMBODIMENTS OF THE INVENTION FIGS. 1 and 2 correspond essentially to the like numbered figures in the Keller patent. These figures have been modified by the inclusion of a switch 33 and photoresponsive elements 53 in accordance with the teachings of the present invention. A bench mounted press P is shown relative to terminating an open barrel electrical terminal T to a stripped insulated electrical lead L. The apparatus of FIGS. 1 and 2 will generally include a number of features not shown in these drawings. Specifically, the drawings do not show a feed mechanism for feeding terminals and/or a feed mechanism for feeding stripped leads between the dies. These details have been left off for the sake of clarity since they are not essential for a full understanding of the present invention.

The press includes a frame or housing comprised of a metal base plate 12 resting on the top of a work bench or the like 10. To the metal base plate 12 is attached an upstanding support portion 18 carrying a box like structure in which is mounted a magnetic actuator mechanism. The mechanism is connected to a ram 20 having a die 22 on its lower end. As can be seen more clearly in FIG. 2, ram 20 is connected to a ram shaft 24 which extends vertically up through the support structure 18. The top of the ram shaft 24 includes a flange member 26 which serves as a stop for a spring member 28 made to surround the upper portion of the shaft 24 and bear against the top of housing 18 around the aperture therein through which shaft 24 travels during operation of the press. A suitable auxilary 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 compression 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 a force drawing the magnets together. The lower magnet 30 of the die closing apparatus is fixed to a transverse plate 55 which is part of the housing structure 18 and is thereby fixed relative to ram shaft movement. This magnet 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 32 of the die closing apparatus is fixed to the shaft 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 should the unit be activated with no material between the dies. Sheet 34 also maintains a maximum gap between the two magnets to prevent the magnets from sticking together.

Each of the magnets includes a recess which extends around in an angular fashion with the body of the magnet. The recesses are shown as 40 and 43 in FIG. 2. These recesses contain coils WI and WII and are terminated in a suitable manner, to be described more fully below, to a power supply and control circuit.

The plate 12 contains a fixed die 50 secured thereto in alignment with die 22. A force transducer 52 is provided beneath die 50. This force transducer is coupled in a manner to be described to the control circuitry of the present invention illustrated generally in FIGS. 1 and 2 as box 63.

The apparatus also includes switch 33, one contact of which is mounted on magnet 32 while the other contact is mounted on magnet 30. This switch is associated with the let-down circuit and acts to deactivate the circuit after initial engagement of die 22 with the terminal or other workpiece.

Further, the metal base plate 12 includes photoresponsive element 53. These elements may take the form of conventional photoconductors. On the underside of plate 55 there is mounted light sources (not shown) for controlling the electrical output of the photoresponsive elements 53. Operation of these elements in relation to the control circuit of the present invention will be discussed more fully below.

In operation of press P, the apparatus is initially in the position shown in FIG. 1 with die 22 in an upward position displaced from lower die 50. When used for crimping, a terminal T is positioned on the lower die with the stripped portion of the lead L positioned in the crimp portion of the terminal. Energization of coils WI and WII results in the generation of a magnetic field in

magnets

30 and 32 which develops a force attracting the two magnets together. Due to the fact that magnet 30 is so fixed tothe support structure 18, magnet closure draws or forces ram downwardly carrying die 22 against the terminal T and against the lower die 50. As this occurs, the force involved is detected or sensed by the transducer 52 which develops a signal which is used to selectively terminate the die closing cycle.

FIG. 3 illustrates a prior control circuit for use with a magnetically actuated die closing apparatus. The details of this system are fully disclosed in the above referenced Keller patent. In operation, a power supply 66 provides an input signal to a control circuit 68. The output of the control circuit is used to actuate the electromagnets denoted generally as 70. The force created on the terminal T is converted into an electrical signal by the force transducer corresponding to transducer 52 of FIGS. 1 and 2 and shown generally as 74 of FIG. 3.

The output of the transducer is fed to a comparator 72 which compares the voltage proportional to the applied force to a voltage proportional to a reference force. When these two voltages are not in agreement, an error signal is supplied to the control circuit 68 to increase or decrease the signal to the electromagnets to respectively increase or decrease the magnetic force between

magnets

30 and 32 until the force developed on the terminal T and die 50 corresponds to the desired force. It should be noted, however, that the reaching of the predetermined force does not terminate the crimping cycles. The dwell time is controlled by a timing circuit. Further, the circuit of FIG. 3 does not possess safety features necessary for protecting both the apparatus and operator.

The unique control circuit of the present invention will now be described with reference to FIGS. 4 and 5. FIG. 4 is a block diagram of the control circuit. We have determined that excellent quality crimps are obtained with a wide variety of wire sizes if the crimping cycle is terminated when the force on the terminal reaches a predetermined critical force. Based on this discovery, the control circuit is provided with a force responsive control circuit 114 which causes termination of a crimping cycle when the force on the terminal reaches the critical value.

Generally, operation of the die closing apparatus utilizing the control circuit of the present invention follows the following sequence.

Magnets

30 and 32 are initially in their displaced position illustrated in FIG. 1. Switch 116, which may be a foot switch, for example, is closed to initiate energization of the electromagnets. As switch 116 is closed, the start circuit generates a start signal to energize the driving circuit 104. The start signal is present during the entire cycle. The energized driving circuit 104 permits current to flow from the D.C. power supply 100 through coils WI and WII of the

electromagnets

30 and 32. A regulated DC power supply 102 is used to energize the circuit elements of the control circuit. The output of D.C. power supply 100 is substantially greater than the output of the regulated supply 102. Typically, power supply 100 supplies approximately 130 volts DC while the regulated power supply 102 supplies 30 volts D.C. The relatively high potential provided by the power supply 100 is needed to produce the large crimping force, in a given time often in the area of 2,000 pounds, required to effect a quality crimp.

As current from the power supply 100 energizes the coils of the electromagnets, shown generally as 70 in FIG. 4 and corresponding to the individually shown

electromagnets

30 and 32 of FIGS. l and 2, the magnets are brought together. The initial velocity at which the magnets approach each other is controlled by the let-down circuit 112. In operation, this circuit limits the average drive current to the electromagnets to thereby bring die 22 into initial engagement with the terminal T with little kinetic energy. This protects the terminal T from the damage which often results if the die 22 is rapidly brought into initial engagement with the terminal. After initial contact is made, the let-down circuit is deactivated thereby increasing the drive current which causes the attractive force between the magnets to increase. The increased drive current permits the required crimping force to be rapidly developed between the dies. As will be described in detail below, the letdown circuit operates to intermittently deactivate the disable circuit 109 thereby intermittently interrupting the drive current passing through the driving circuit I04. Intermittent interruption of the drive current reduces its average value thus limiting the closing force.

The force between the dies and thus the force on the terminal T is detected by the force transducer 52 which is applied to the force control circuit N4 and transformed into a proportional potential. The force control circuit 114 also includes a reference potential proportional to a critical, force, the attainment of which signities that a crimp has been effected. Circuit 1'14 also includes a comparator which compares the reference potential with the force transducer supplied potential and when the two correspond, generates an output signal which operates on the start circuit 106 to cut off the signal thus terminating the crimping cycle.

If a foreign object of at least a predetermined size and shape is accidently positioned in the crimping area, the electro-optic guard 12] comes into action to produce an output signal which operates on start circuit 108 to cut off the start signal.

It is possible for a foreign object such as a wrench or screwdriver to appear between the dies and not activate the electro-optic guard. As will be described more fully below, the control circuit includes another safety feature which operates to terminate the closing cycle should such a foreign object appear between the dies.

' When the dies close on a screwdriver or wrench, for example,

magnets

30 and 32 are kept apart at a distance sufficient to keep the contacts of switch33 from closing. Thus, the critical force is not reached and only a very small force is exerted on the object between the dies. The added safety feature for terminating a cycle is the clock circuit 110. This circuit is a timing circuit activated upon the initiation of a die closing cycle. If the critical force is not reached within a predetermined time, the clock circuit generates an output signal which signals the start circuit 106 to cut off the start signal. It also signals the disable circuit 109 to function. The output fromthe disable circuit 109 causes the generation of a warning signal to notify the operator that there is trouble in the apparatus and also prevents further cycles from being initiated until the control circuit is manually reset by the operator.

Operation of the control circuit of the present invention may be more fully understood by referring to FIG. 5. Like numbered elements in FIGS. 1-5 correspond to common elements. To initiate a die closing cycle which in the specific embodiment disclosed results in a crimping cycle, switch 116 is closed. Prior to the closing of switch 116, capacitor C has charged through the 30 volt line 113 from the regulated DC power supply line 102. The closing of switch 116 causes the potential across capacitor C to appear at the anode of unijunction transistor 0,. This transistor may be a 2N 6027 unijunction transistor. The unijunction transistor becomes conductive when the anode potential is in predetermined relationship with the gate potential. To turn the transistor off a negative pulse may be supplied to the anode to bring the anode potential to approximately ground potential. The application of the capacitor C voltage to the anode of transistor Q causes it to conduct. As a result, the potential at node a in the driving circuit 104 rises thereby turning on transistor Q,,. When transistor Q,, conducts,, transistors Q, Q also conduct, to energize WI and W1] thereby creating an attractive force between the

magnets

30 and 32.

Forming part of the let-down circuit 112 is a feedback coil L, physically placed in the vicinity of coils WI and W1] whereby current in these coils cause an induced current in the feedback coil. Switch 33 is initially open. One terminal of feedback coil L, is connected to the 30 volt line 113 through a suitable resistance while the second terminal is coupled to the inverting input of an operational amplifier OP, connected as a trigger circuit. Operational amplifier OP, can be a conventional Schmitt trigger. Prior to encrgization of coil L the output potential of the trigger circuit OP, is low thereby retaining transistor Q, in its non-conducting state. As current is induced in feedback coil L, the potential across the capacitor C previously charged from line 113, drops. When the trigger voltage is reached, the output of circuit OP, rises to a potential sufficient to turn on transistor O,,,. The emitter of 0, is tied to the base of transistor 0 in the disable circuit 109. Thus, when transistor Q, conducts a positive bias is applied to the base of 0,, thereby turning this transistor on. As transistor 0,, turns on, the potential at the node a rapidly drops thereby turning off transistor Q Which in turn turns off transistors O Q of the driving circuit. This blocks further current from flowing through the coils WI and Wll. As the current in the feedback coil now decreases, the potential across capacitor C increases returning the output of the trigger circuit OP, to its low state causing transistors Q10 and O to turn off. As a result, the potential at node a of the driving circuit 104 again increases to turn on the driving circuit to cause current flow in coils W1 and Wll. The driving circuit 104, thus, rapidly energizes and de-energizes limiting the average current flow in coils WI and Wll. This small average current causes a small attractive force to be developed between the magnets thus limiting the velocity at which the

magnets

30 and 32 initially approach each other. As a result, die 22 is brought gently down upon the terminal T. As die 22 meets the terminal, switch 33 is closed to keep the output of the trigger circuit OP, at a low level thereby retaining transistors Q, and 0, off.

Operation of switch 33 can best be understood by referring to FIGS. 1 and 2. One contact of the switch is mounted on magnet while the other contact on magnet 32. The contacts close when these magnets are separated by a predefined distance. This distance corresponds to the distance between die 22 and when die 22 makes initial contact with terminal T.

With Q off, the potential at node a rises and remains at this high level for a time sufficient to allow the current in coils WI and W1] to build up to a value sufficient to cause a large attractive force to be developed between the magnets. This force is of course transferred to the ram 20 which causes the ram to come down hard on terminal T. Thus, dies 22 and 50 come together with sufficient force to create a quality crimp.

The force on the terminal is monitored by the force transducer 52. The output of transducer 52 is coupled to the force control circuit 114. The force control circuit also includes an operational amplifier OP connected as a comparator circuit. The output of circuit OP is connected to the gate terminal of unijunction transistor Q The anode of transistor 0,, is connected to a reference voltage source in the form of a potentiometer 122. The potential at the wiper of the potentiometer 122 is proportional to the desired critical force. As the force on the strain gage 52 increases, the potential thereacross increases thereby increasing the input to the inverting side of 0P This causes a decrease in the potential at its output. When the force on terminal T corresponds to the critical force, transistor 0,, is triggered on. The cathode of transistor 0,, is coupled to the base of transistor 0, of the start circuit 108. Conduction of transistor Q,, biases transistor 0, into conduction causing the anode of transistor 0,, to ap proach ground potential turning it off. When transistor Q turns off, the potential at anode a of the driving circuit 104 drops to a value sufficient to turn off transistor 0,, thereby disabling the driving circuit 104. In this manner, as soon as the critical force is reached, driving current is blocked from the coils and the die closing cycle is terminated. The magnets return to their initial open position under the control of bias spring 28. The critical force for terminating the closing cycle can be easily varied by varying the potential with the potentiometer 122.

Let it now be assumed that a foreign object, such as a screwdriver rests on die 50. The control circuit is provided with a clock circuit operating in conjunction with the let-down circuit 112. When the start circuit 108 is activated to cause transistor O to conduct, transistor Q of the clock circuit turns on thereby allowing capacitor C, to charge. Capacitor C, forms a portion of a time constant circuit which includes

resistors

124 and 126 as well as transistor 0;. Capacitor C, continues to charge to a threshold voltage which turns on transistor 0,. It should be remembered that as capacitor C, charges, die 22 is being slowly brought down into engagement with the screwdriver through the operation of a let-down circuit 112. The applied force is so low that no damage is caused to the dies. Switch 33 is so arranged that its contacts will not close when a relatively large object such as the screwdriver is resting on the die 50. This assumes that the height of the foreign object is greater than that of the contact to be erimped. Since this is generally the case, when die 22 makes its initial contact with the foreign object, the

magnets

30 and 32 have not closed a sufficient distance to permit the contacts of switch 33 to engage. Thus, the let-down circuit remains operative thereby limiting the force applied by the magnet and the critical force will never be reached.

When the threshold voltage of transistor Q is reached, it conducts thereby causing transistor Q of the start circuit to turn on which results in the turning off of transistor Q The turning on of transistor 0., also causes transistor O to conduct which biases transistors Q and Q of the disable circuit 109 into conduction. When Q conducts, light 111 glows indicating to the operator that there is trouble in the apparatus. When Q, is on, node a is prevented from rising to the potential necessary to turn on the driving circuit 104 even if another die closing cycle is initiated. Transistor Q and Q remain conducting until the control circuit is manually reset by the operator by closing reset switch 115. It should be noted that even though the turning on of transistor Q, causes transistors Q Q, to turn off, transistorQ remains conducting. So long as Q, conducts, transistors Q and 0 remain on. If the operator attempts to initiate another cycle without resetting the circuit, no cycle will start since the cathode of Q is shorted to ground through conducting transistor 0-,. When switch 115 is closed, 0, turns off thus turning off

transistor

0, and 0 allowing node a to rise to the drive circuit turn on potential upon a subsequent closing of. switch 116.

A further safety device in the form of an electro-optic guard 121 is also included with the control circuit of the invention. This safety device is directed primarily to protecting the operator should he inadvertently place his hand between the dies and close switch 116. Referring to FIGS. 1 and 2, a plurality of photoresponsive elements, such as photoconductors, are mounted on the base 12 of the support 18. A light source for energizing these photoresponsive elements may be mounted on the underside of member 55 of support frame 18. The resistance of a photoconductor varies inversel'y with the intensity of received light. Thus, when the light paths between a light source and the photoconductors are not interrupted, the resistance of each of the photoconductors is at its lowest value.

When the light to a photoconductor is interrupted, its

resistance increases. The photoconductors are coupled to an operational amplifier 0P forming a portion of the electro-optic guard circuit 121. Whenever the photoconductors 53, noted individually by-PC, PC do not have their'impinging light interrupted, their resistances are at their lowest value and thus the output of OP 3 is at its lowest level. As the light to the photoconductors become interrupted as would be the case if the operator places his hand in the area of the dies, the resistances of some of the photoconductors lPC PC, increase thereby increasing the output of 0P When a sufficient number of photoconductors possess a high resistance the potential at the anode and gate of transistor 0,, assumes a predetermined relationship necessary for triggering 0,, into conduction. When Q turns on, transistor 0 turns on thereby either preventing the driving circuit 104 from becoming activated or if previously activated, causing it to become deactivated. in this manner, should the operator place his hand in the vicinity of the die, he will interrupt the light to a suffi- 6 While the invention has been particularly shown and desscribed with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

We claim:

1. In a cyclically operated, magnetically actuated material working apparatus comprising a stationary housing, a first electromagnet affixed to said housing, a ram movable with respect to said housing, a second electromagnet afi'rxed to said ram and movable with said ram, said ram and said second electromagnet having a first position when said electromagnets are deenergized, said first and second electromagnets and said ram being positioned so that said first and second electromagnets are magnetically attracted towards each other when energized to impart a force to said ram to cause said ram to move along a predetermined path during each cycle of operation of said apparatus, a first die positioned at a first end of said ram, and a second die secured to said housing at a distance from said first die when said electromagnets are deenergized and in a position to close with said first die when said electromagnets are energized; a control means for controlling the characteristics of motion and force of said ram along said predetermined path when said electromagnets are energized;

said control means constructed to respond to the position of said ram along a first portion of said predetermined path to maintain the force and velocity of movement of said ram at a predetermined low rate;

said control means further constructed to respond to the position of said ram along a second portion of said predetermined path to create a progressively increasing attractive force between said first and second electromagnets as said ram moves said first die into close proximity to said second die;

said control means further constructed to respond immediately to the attainment of a predetermined force upon the material, which is being worked and which is positioned between said first and second electromagnets, after contact of said first and second dies with said material to deenergize said electromagnets; and

means for returning said ram to said first position when said electromagnets are deenergized.

2. In the apparatus of claim 1 in which said housing comprises a work surface upon which is secured said second die' and in which said control means further comprises:

a plurality of light sensitive devices mounted upon said housingand a light source also mounted upon said housing;

said light sensitive devices and said light source being positioned to enable the interception of light between said light source and said light responsive devices by an object, such as a person's hand, placed upon said work surface to abort said cycle of operation and deenergize said electromagnetic means.

3. A control circuit in accordance with claim 1, comprising:

means for initiating a cycle of operation of said apparatus; and

timing means responsive to the initiation of a cycle of operation of said apparatus to abort said cycle of operation if said cycle of operation is not completed in a predetermined interval of time.

4. In the apparatus of claim 1 in which said housing comprises a work surface upon which is secured said second die and in which said control means is constructed to cause said first portion of said predetermined path to be of a length to cause said first die to come into sufficiently close proximity to said work surface to make contact with small tools, such as screw drivers, which are present upon said work area surface, and to have the progress of said ram halted thereby.

5. A magnetically actuated material working apparatus comprising:

a housing,

a ram means mounted in a given position on said housing and movable through a predetermined P a first die mounted on said housing;

a second die mounted on said ram means and positioned to close upon said first die when said ram means is moved through said predetermined path;

electromagnetic means constructed when energized to move said ram means along said predetermined path during each cycle of operation;

a control circuit means for controlling the characteristics of speed and force of said ram means as it moves along said predetermined path;

said control circuit means comprising a first control section constructed to restrain the average velocity and force of said ram means over a first portion of said predetermined path below predetermined levels;

said control circuit means further comprising a second control section constructed to respond to the passing of said ram means past a certain point along said predetermined path to progressively increase the force imparted to said ram means by said electromagnetic means above said predetermined level to a degree sufficient to work said material; and

said control means further comprising a third control section constructed to respond to the attainment by said ram means of a predetermined maximum force in the direction of said predetermined path to deenergize said electromagnetic means; and

means for returning said ram means to said given position to complete a cycle of operation.

6. The apparatus of claim 5 in which said housing comprises a work surface upon which is secured said first die and in which said control circuit means further comprises:

a plurality of light sensitive devices mounted upon said housing and a light source also mounted upon said housing;

said light sensitive devices and said light source being positioned to enable the interception of light between said light source and said light responsive de- 8. The apparatus of claim 5 in which said housing comprises a work surface upon which is secured said first die and in which said control circuit means is constructed to cause said first portion of said predetermined path to be of a length to cause said second die to come into sufficiently close proximity to said work surface to make contact with small tools, such as screw drivers, which are present upon said work area surface, and to have the progress of said ram means halted thereby.

9. In a cyclically operated, magnetically actuated material working apparatus comprising a stationary housing, a first electromagnet affixed to said housing, a ram movable with respect to said housing, a second electromagnet afiixed to said ram and movable with said ram, said ram and said second electromagnet having a first position when said electromagnets are deenergized, said first and second electromagnets and said ram being positioned so that said first and second electromagnets are magnetically attracted towards each other when energized to impart a force to said ram to cause said ram to move along a predetermined path during each cycle of operation of said apparatus, a first die positioned at a first end of said ram, and a second die secured to said housing at a distance from said first die when said electromagnets are deenergized and in a position to close upon said first die when said electromagnets are energized; a method for controlling the characteristics of motion of said ram along said predetermined path to obtain optimum working of said material and comprising the steps of:

moving said ram along a first portion of said predetermined path at a low rate of speed and with a low force imparted thereto; moving said ram along a second portion of said predetermined path when said first and second dies are in close proximity to each other to create a progressively increasing attractive force between said first and second electromagnets as said ram moves said first die closer towards said second die;

deenergizing said electromagnets immediately upon the attainment of a predetermined force between said first and second electromagnets after contact of said first and second dies with the material being worked on; and

returning said ram to said first position when said electromagnets are deenergized.

10. In a magnetically actuated material working ap paratus comprising a housing, a ram means mounted in a given position on said housing and movable through a predetermined path, first and second dies mounted respectively on said housing and said ram means and positioned to close upon each other when said ram is moved through said predetermined path, and electromagnetic means constructed, when energized, to move said ram means along said predetermined path; a method for controlling the characteristics of speed and force of said ram means as it moves along said predetermined path by controlling energization of said electromagnetic means to obtain optimum working of said material and optimum safety for the human operator, and comprising the steps of:

restraining the average velocity and force of said ram means to values below predetermined levels as said ram means moves over a first portion of said predetermined path;

between said dies and said material therebetween as said dies move towards each other while forming the said material positioned therebetween;

deenergizing said electromagnetic means immediately in response to the detection of said predetermined force; and

returning said ram to said given position.

Claims

1. In a cyclically operated, magnetically actuated material working apparatus comprising a stationary housing, a first electromagnet affixed to said housing, a ram movable with respect to said housing, a second electromagnet affixed to said ram and movable with said ram, said ram and said second electromagnet having a first position when said electromagnets are deenergized, said first and second electromagnets and said ram being positioned so that said first and second electromagnets are magnetically attracted towards each other when energized to impart a force to said ram to cause said ram to move along a predetermined path during each cycle of operation of said apparatus, a first die positioned at a first end of said ram, and a second die secured to said housing at a distance from said first die when said electromagnets are deenergized and in a position to close with said first die when said electromagnets are energized; a control means for controlling the characteristics of motion and force of said ram along said predetermined path when said electromagnets are energized; said control means constructed to respond to the position of said ram along a first portion of said predetermined path to maintain the force and velocity of movement of said ram at a predetermined low rate; said control means further constructed to respond to the position of said ram along a second portion of said predetermined path to create a progressively increasing attractive force between said first and second electromagnets as said ram moves said first die into close proximity to said second die; said control means further constructed to respond immediately to the attainment of a predetermined force upon the material, which is being worked and which is positioned between said first and second electromagnets, after contact of said first and second dies with said material to deenergize said electromagnets; and means for returning said ram to said first position when said electromagnets are deenergized.

2. In the apparatus of claim 1 in which said housing comprises a work surface upon which is secured said second die and in which said control means further comprises: a pluraliTy of light sensitive devices mounted upon said housing and a light source also mounted upon said housing; said light sensitive devices and said light source being positioned to enable the interception of light between said light source and said light responsive devices by an object, such as a person''s hand, placed upon said work surface to abort said cycle of operation and deenergize said electromagnetic means.

3. A control circuit in accordance with claim 1, comprising: means for initiating a cycle of operation of said apparatus; and timing means responsive to the initiation of a cycle of operation of said apparatus to abort said cycle of operation if said cycle of operation is not completed in a predetermined interval of time.

5. A magnetically actuated material working apparatus comprising: a housing, a ram means mounted in a given position on said housing and movable through a predetermined path; a first die mounted on said housing; a second die mounted on said ram means and positioned to close upon said first die when said ram means is moved through said predetermined path; electromagnetic means constructed when energized to move said ram means along said predetermined path during each cycle of operation; a control circuit means for controlling the characteristics of speed and force of said ram means as it moves along said predetermined path; said control circuit means comprising a first control section constructed to restrain the average velocity and force of said ram means over a first portion of said predetermined path below predetermined levels; said control circuit means further comprising a second control section constructed to respond to the passing of said ram means past a certain point along said predetermined path to progressively increase the force imparted to said ram means by said electromagnetic means above said predetermined level to a degree sufficient to work said material; and said control means further comprising a third control section constructed to respond to the attainment by said ram means of a predetermined maximum force in the direction of said predetermined path to deenergize said electromagnetic means; and means for returning said ram means to said given position to complete a cycle of operation.

6. The apparatus of claim 5 in which said housing comprises a work surface upon which is secured said first die and in which said control circuit means further comprises: a plurality of light sensitive devices mounted upon said housing and a light source also mounted upon said housing; said light sensitive devices and said light source being positioned to enable the interception of light between said light source and said light responsive devices by an object such as a person''s hand placed upon said work surface to abort said cycle of operation and deenergize said electromagnetic means.

7. The apparatus of claim 5 in which said control circuit means further comprises: means for initiating a cycle of operation of said apparatus; and timing means responsive to the initiation of a cycle of operation of said apparatus to abort said cycle of operation if said cycle of operation is not completed in a predetermined interval of time.

8. The apparatus of claim 5 in which said housing comprises a work surface upon which is secured said first die and in which said control circuit means is constructed to cause said first portion of said predetermined path to be of a length to cause saiD second die to come into sufficiently close proximity to said work surface to make contact with small tools, such as screw drivers, which are present upon said work area surface, and to have the progress of said ram means halted thereby.

9. In a cyclically operated, magnetically actuated material working apparatus comprising a stationary housing, a first electromagnet affixed to said housing, a ram movable with respect to said housing, a second electromagnet affixed to said ram and movable with said ram, said ram and said second electromagnet having a first position when said electromagnets are deenergized, said first and second electromagnets and said ram being positioned so that said first and second electromagnets are magnetically attracted towards each other when energized to impart a force to said ram to cause said ram to move along a predetermined path during each cycle of operation of said apparatus, a first die positioned at a first end of said ram, and a second die secured to said housing at a distance from said first die when said electromagnets are deenergized and in a position to close upon said first die when said electromagnets are energized; a method for controlling the characteristics of motion of said ram along said predetermined path to obtain optimum working of said material and comprising the steps of: moving said ram along a first portion of said predetermined path at a low rate of speed and with a low force imparted thereto; moving said ram along a second portion of said predetermined path when said first and second dies are in close proximity to each other to create a progressively increasing attractive force between said first and second electromagnets as said ram moves said first die closer towards said second die; deenergizing said electromagnets immediately upon the attainment of a predetermined force between said first and second electromagnets after contact of said first and second dies with the material being worked on; and returning said ram to said first position when said electromagnets are deenergized.

10. In a magnetically actuated material working apparatus comprising a housing, a ram means mounted in a given position on said housing and movable through a predetermined path, first and second dies mounted respectively on said housing and said ram means and positioned to close upon each other when said ram is moved through said predetermined path, and electromagnetic means constructed, when energized, to move said ram means along said predetermined path; a method for controlling the characteristics of speed and force of said ram means as it moves along said predetermined path by controlling energization of said electromagnetic means to obtain optimum working of said material and optimum safety for the human operator, and comprising the steps of: restraining the average velocity and force of said ram means to values below predetermined levels as said ram means moves over a first portion of said predetermined path; detecting when said second die comes into the immediate proximity of said material to be worked; progressively increasing the force imparted to said ram means by said electromagnetic means to a degree sufficient to work said material in response to the detection of said immediate proximity of said second die to said material; detecting the attainment of a predetermined force between said dies and said material therebetween as said dies move towards each other while forming the said material positioned therebetween; deenergizing said electromagnetic means immediately in response to the detection of said predetermined force; and returning said ram to said given position.