US2262399A - Feed control - Google Patents

Description

Nov. 11,1941. G. E. KING 2,262,399

FEED CONTROL Filed July 19, 1940 Con fro/ Equip/nan INVENTOR Georqe E K171 0225 r. W

ATTORN EY WITNESSES:

Patented Nov. 11, 1941 FEED CONTROL George E. King, Wilkinlburg, Pa., aslignor to Westinghouse Electric Manufacturing Company, East Pittsburgh, PL, a corporation of Pennsylvania Application July 19, 1940, Serial No. 346,247

11 Claims.

My invention relates to an electrical control system which is particularly useful for controlling the feed motor drive in reciprocating machine tool elements such as in planers.

Various methods are used to feed the tools on planers and similar reciprocating types of machine tools. In order to obtain accurate and uniform feeds it is essential to effect the lateral feeding movement before the beginning of the table cut stroke. In many applications feed cannot occur during the return" stroke such as is the case wherein the planing occurs within a pocket or against a shoulder. In such instances the only time that feed should occur is at the moment of zero speed of the planer platen. On constant voltage planer equipments this can be accomplished very simply, since dynamic braking is used to stop the table drive motor at the end of the stroke. Interlocks on the reversing contactors are used to initiate the feed operation.

The use of variable voltage drives has introduced several problems. The table drive motor is brought to rest and reversed by reversing the generator shunt fields. This means that interlocks on the reversing contactors cannot be used since they operate before the table has reached the end of the stroke. Assume it is desired to feed at the beginning of the cut stroke. The table operates the reversing limit switch near the end of the return stroke. The "return contactor drops out immediately and the cut contactor closes. The potential on the generator shunt fields is reversed and the generator armature voltage is forced down to zero and builds up in the opposite direction. The table motor is accordingly brought to rest by plugging and then accelerated in the "cut" direction. It is obvious that an interlock on the cut contactor would initiate the feed while the table was still operating in the return direction, which is very unsatisfactory.

To overcome this difl'lculty, there has been provided in the past, a zero speed switch mechanically connected to the table drive motor. The type used generally consisted of a friction belt over a pulley. When the table motor would reverse, it would tend to drive the pulley in the reverse direction. The pulley could move only a limited number of degrees which were suflicient to operate contacts fixed to the pulley. These contacts were used to initiate the feed. The use of the zero speed switch meant special mounting on the end of the motor shaft. It was also a source of trouble and required considerable maintenance.

It also meant that the platen drive motor had to reverse and start the planer platen in the cut" direction before the zero speed switch contacts closed to establish the feed motor set up circuit. Since some time is required for the feed motor contactors to close after the zero speed switch contacts have closed, the planer platen had moved an appreciable distance before the feed motor had started. It is desirable to complete the feed in the shortest distance of table travel since that part of the stroke used for feeding cannot be used for cutting. This, of course, is not true for certain classes of work where it is considered satisfactory to feed during the return stroke, but a large part of the work on a planer requires feeding the tool at the beginning of the cut stroke.

To eliminate the zero speed switch I have worked out a scheme using a standard relay.

An object of my invention is to provide a simple relay which will eliminate the above-mentioned disadvantages by making it impossible for the feed motor control circuit to be completed until the driving motor has come to almost zero speed.

Another object of my invention is to provide a relay capable of adjustment so that the feed motor may be started at exactly zero speed of the planer platen drive motor.

Other objects and advantages will become more apparent from a study of the following specification when considered in conjunction with the accompanying drawing, in which the single figure is a schematic showing of a control system embodying the principles of my invention.

Referring more particularly to the drawing, numeral I denotes an electric motor such as an alternating current motor which is energized from a source of alternating current indicated by terminals 2. A generator armature 3 is mechanically coupled to the motor I. A planer driving motor 4 is connected across the generator armature. The driving motor 4 is provided with a field winding 5 which is excited by a suitable source of potential (not shown). A generator shunt field winding 6 is provided, having a variable resistor 'l in series therewith and having connected in parallel therewith, a cut limit switch 8 and a return limit switch 9, together with an actuating coil [0 of a contactor 20, presently to be described. Cut and return" reversing contactors H and I2, respectively, are provided and are alternately energizable by means of well-known control equipment indicated broadly by numeral l3 including the well-known limit switches (not shown) so that the ultimate effect will be to complete an energizing circuit through contactor II for the duration of the cut" stroke and then to complete an energizing circuit through the return contactor I2 for the duration of the return stroke. Such control equipment is wellknown to those skilled in the art and forms no part or my presentinvention. A description of the details of such control equipment may be found in my Patent No. 1,955,334, issued April 1'1, 1934, which is directed to a variable voltage control system for a planer. More specifically, when the cut stroke is initiated and contactor II is energized, a circuit will be completed extending from the positive terminal source of energizing potential i4 through contact members I5, conductor l6, coil l0, limit switches 9 and 9, respectively, conductor lla, the contact members of contactor l2, its conductor it, which is the negative terminal of the energizing potential source. It will also be apparent that a parallel energizing circuit extends from conductor H to contact members I5, conductor I 9, resistor 1, generator field winding 6, conductors i1 and Ha. contact members of contactor I2, to conductor l8. Such circuits remain completed during the entirety of the out stroke. However, at the end of the "cut stroke, the cut limit switch 9 opens, thereby deenergizing the circuit through coil I0. If this coil in were used alone on contactor 20, faulty operation would arise due to the fact that for effecting return, contactor i2 is energized at the moment that the cut limit switch 9 is opened, hence, effecting plugging or reversal of the direction of energization of the generator field winding 6. This would mean that the feed motor control circuit which will be described hereinafter, would be initiated by closing of the contactor 20 before the planer table (not shown) would come to very nearly a standstill. This would have the eiTect of feeding while the planer platen is in the course of its cutting stroke which, of course, would give an undesirable cutting action. In other words, near the end of the cutting movement, if lateral feed motion takes place, the cutting stroke,instead of being straight,. will be curved in the direction of the lateral Iced direction so as to give a curved cut on the workpiece.

In order to avoid the possibility of lateral feeding during the reciprocating movement of the planer platen, an additional coil 2! is provided on contactor 20 across the generator armature 9. It will now be seen that two conditions must be fulfilled before contactor 20 can become deenergized so as to'initiate a feed motor control circuit, namely, coil it must be deenergized as a consequence of opening one of the limit switches (8 or 9) and coil 2| must be sufiiciently deenergized as the result of a decrease of generator voltage so as to insure that the planer platen has slowed down to zero speed. For example, relay coil 2| may be designed so as to drop out when the generator voltage has decreased to, say, 20 volts. A variable dropout voltage may be secured by adjusting the tension of spring 59 by means of screw 69. Of course, other adjusting means (not shown) could be used in addition or insubstitution and as a variable air gap between the relay armature and contact member. Thus, it will be seen that coil 2i acts as a holding coil pending theattainment of almost zero speed of the planer platen.

A feed motor 22 is provided with a field winding 23 which is energized by a suitable source of potential (not shown). The feed motor drives suitable reduction gearing indicated as 2!, and a measuring relay indicated generally by numeral 25. An electromagnetic clutch having a magnetic coil 29 is interposed between the reduction gearing 24 and the measuring relay 2!. End of stroke" selector switches 21 and 29 are provided so as to selectively eflect lateral feeding of the i'eed motor either at the end of the cut" or return" stroke, respectively. 1! cutting is in both directions, the feed is effected at the end of each stroke. The "directional feed selector switches 29 and are provided so as to selectively control the directional feed of the motor. That is, they will determine whether the forward contactor II or the reverse contactor 92, respectively, will be energized so as to complete an energizing circuit in one direction or a reverse direction through the feed motor 22. Assuming that contactor II is energized for iorward operation, a circuit can then be traced from conductor 99a. to contact members 94, conductor 99, armature of motor 22, accelerating resistor 39, conductor 99, contact members 39, to conductor 99. In addition, the accelerating relay 49 will effect shunting of the accelerating resistor 99. As soon as contactor II is deenergized on account of opening 0! the limit switch, a dynamic braking circuit is established extending from the lower terminal of motor armature 22 through the dynamic braking resistor 40 through contact members ll and 42, conductor 49, to the upper terminal of motor 22. This will eflect energization of back contact coils 44 and 45 by the counter electromotive force produced by the motor armature during dynamic braking so as to prevent bouncing of the back contacts of the respective contactors II and 92.

Assume that the start push button 41 has been depressed which would eifect operation by control relays 49, then the complete control circuit may be traced from the positive terminal L1 through the stop push button 49, the start push button 41, contact members 59 of contactor 20, cut limit switch 5| (assuming that the selector switch 21 instead of 29 is closed), selector switch 29 (assuming that the selector switch 29 instead of 90 is closed), coil Ila, contactor Ii, conductor 52, measuring relay contact members 53, conductor 64, to the negative terminal L2. The operation of the feed motor 22 will impart a rotary motion to the heart-shaped cam 99, so as to rock a pivot arm 59, irrespective of the direction of rotation of cam 55 so as to finally open the spring biased contact members 53 after a predetermined angular movement of the cam 55. set-screw 51 which provides a vertically adjustable pivot and index aligned with a calibrated scale 99. The measuring relay 25 per se forms no part of my present invention.

It will thus be seen that after the planer table comes to nearly zero speed the i'eed motor will effect lateral feed motion of the tool to an extent determined by the adjustment of the measuring relay 2! so as to eventually open contact members 59 and interrupt the circuit for the contactor relay coil 9Ia, hence to effect interruption of the feed motor circuit.

From the above, it will be seen that the essence of my invention is directed to the operation of contactor 29, particularly to the addition-of coil 2i. The use of such contactor as 20 to initiate the ieed has the following advantages.

1. Requires no mechanical connections to the motor permitting the use of a standard motor.

2. Has longer life.

3. Requires less maintenance.

This angular movement is adjustable by 4. Is more accessible and less likely to be neglected when inspecting the equipment.

5. Permits starting or feed at exactly zero speed making a larger part of the cutting stroke useful, thus increasing production.

I am, oi course, aware that others, particularly after having had the benefit of the teachings of my invention, may devise other devices embodying my invention, and I, therefore, do not wish to be .limited to the specific showings made in the drawings and the descriptive disclosure hereinbefore made, but wish to be limited only by-the scope oi the appended claims and such prior art that may be pertinent.

I claim as my invention:

1. In a variable voltage control system including an energizing source of potential, a motor and generator for efiecting relative reciprocating movement between a machine tool element and a work piece, a feed motor for effecting lateral incremental feed between said tool element and work piece at the end of a reciprocating movement, feed control circuit means for said feed motor including limit switch means and a contactor having two separate cumulatively wound coils, said feed circuit means selectively energizing said feed motor in a predetermined direction at the ends of predetermined reciprocating strokes, one of said coils having in series therewith said energizing source and said limit switch means, the other of said coils being connected across said generator so that it will prevent dropping out of said contactor until the occurrence of a predetermined low value of generator voltage.

2. In a variable voltage control system including an energizing source of potential, a motor and generator for eifecting relative reciprocating movement between a machine tool element and a work piece, a feed motor for eiifecting lateral incremental feed between said tool element and work piece at the end of a reciprocating movement, feed control circuit means for said feed motor including directional contactors for controlling the direction of current fiow through said feed motor, limit switch means and a contactor, said limit switch means and double coiled contactor being connected in series with each of said directional contactors, having two separate cumulatively wound coils, said feed circuit means selectively energizing said feed motor in a predetermined direction at the ends of predetermined reciprocating strokes, one of said coils having in series therewith said energizing source and said limit switch means, the other of said coils being connected across said generator so that it will prevent dropping out of said contactor until the occurrence of a predetermined low value of generator voltage.

3. In combination with a variable voltage control system for a planer including a motor, a source of energizing potential therefor and a generator for effecting reciprocating movement of a planer platen with respect to a fixed planer tool, a feed motor for eflecting lateral incremental ieed of said platen with respect to said tool at the end of reciprocating movements of said platen, feed control circuit means for said feed motor including a limit switch and a double coiled set-up contactor connected in series therewith and adapted to set up a iced circuit, one of said coils of said set-up contactor being energizable by said source of energizing potential and the other said coil being connected across the terminals of said generator, last mentioned coil preventing closing of saidieed control circuit pending a predetermined decrease in generator voltage.

4. In combination with a variable voltage control system for a planer including a motor, a source of energizing potential therefor and a generator for efiecting reciprocating movement of a planer platen with respect to a fixed planer tool, a feed motor for efiecting lateral incremental Ieed of said platen with respect to said tool at the end of reciprocating movements of said platen, feed control circuit means for said feed motor including a limit switch and a double coiled set-up contactor connected in series therewith and adapted to set up a feed circuit, one of said coils of said set-up contactor being energizable by said source or energizing potential and the other said coil being connected across the terminals of said generator, last mentioned coil preventing closing of said teed control circuit pending a predetermined decrease in generator voltage, a geared limit switch also in said series i'eed control circuit which is operable upon predetermined and adjustable angular movement of said feed motor to interrupt said feed control circuit, and an electromagnetic clutch between said geared limit switch and feed motor which clutch is disengaged as the result of 7 operation of said geared limit switch at the end of a predetermined angular rotation of said feed motor.

5. In a variable voltage control system for a reciprocable platen element including an electric current source, a motor driven thereby, a generator mechanically coupled thereto, a second motor energized by said generator for driving said platen, limit switch means operable by; said platen near the end 01' the reciprocating stroke and a pair of reversing contactors alternately energizable by said limit switch means for alternately passing current, first in one direction, then in an opposite direction through a field winding of said generator for eflecting reciprocating motion of said platen, in combination with a feed motor for efiecting lateral feed motion of said platen at the end of the reciprocating stroke, teed control circuit means including said feed motor and a contactor having a pair of cumulatively wound operating coils, one connected to said electric current source and the other connected across the armature of said generator, said feed motor circuit also including limit switch means for interrupting current fiow through said generator field winding and for interrupting the flow of current from said electric current source through said aforementioned respective coil at the end of a particular reciprocating stroke, said feed control circuit, however, being withheld from completion by said other coil due to the maintenance of generator voltage for a predetermined period of time following interruption of said voltage for a predetermined period of time following interruption of said generator field winding circuit thereby allowing said generator armature to fall to a low value of speed before said ieedmotor circuit is completed.

6. In a variable voltage control system for a reciprocable platen element including an electric current source, a motor driven thereby, a generator mechanically coupled thereto, a second motor energized by said generator for driving said platen, limit switch means operable by said platen near the end of the reciprocating stroke and a pair of reversing contactors alternately energizable by said limit switch means for alternately passing current, first in one direction then in an opposite direction through a field winding of said generator for eflecting reciprocating motion of said platen, in combination with a feed motor for eilecting lateral teed motion or said platen at the end or the reciprocating stroke, teed control circuit means including said feed motor and a contactor having a pair of cumulatively wound operating coils, one connected to said electric current source and the other connected across the armature of said generator, said feed motor circuit also including cut and "retum limit switches connected in series with said generator field winding and with said coil and its aforementioned electric current source, cut and "return" contactors energizable at the beginning of the "cut" and "return" stroke, respectively, so as to have their respective contact members arranged to close said series circuit through the limit switches, coil and generator field winding during said respective strokes, said circuit being interrupted after a predetermined period of time following opening of one of said limit switches due to the maintenance of said double coiled contactor in an energizable condition due to the continuance of the voltage generated by said generator despite the interruption of the generator field winding circuit.

7. In a variable voltage control system for a reciprocable platen element including an electric current source, a motor driven thereby, a generator mechanically coupled thereto, a second motor energized by said generator for driving said platen, limit switch means operable by said platen near the end of the reciprocating stroke and a pair of reversing contactors alternately energizable by said limit switch means for alternately passing current, first in one direction then in an opposite direction through a field winding of said generator for effecting reciprocating motion of said platen, in combination with a feed motor for efiecting lateral feed motion oi. said platen at the end of the reciprocating stroke, ieed control circuit means including said teed motor and a contactor having a pair of cumulatively wound -operating coils, one connected to said electric current source and the other connected across the armature of said generator, said ieed motor circuit also including cut" and retum limit switches connected in series with said generator field winding and with said coil and its aforementioned electric current source, "cut andreturn" contactors energizable at the beginning of the cut and "return stroke, respectively, so as to have their respective contact members arranged to close said series circuit through the limit switches, coil and generator field winding during said respective strokes, said circuit being interrupted after a predetermined period of time at the end ot a predetermined angular rotation of said teed motor.

8. In a variable voltage control system iora reciprocable platen element including an electric current source, a motor driven thereby, a generator mechanically coupled thereto, a second motor energized by said generator for driving said platen, limit switch means operable by said platen near the end of the reciprocating stroke and a pair of reversing contactors alternately energizable by said limit switch means for alternately passing current, first in one direction then in an opposite direction through a field winding of said generator for effecting reciprocating motion of said platen, in combination with a feed motor for efiecting lateral feed motion of said platen at the end of the reciprocating stroke, feed control circuit means including said ieed motor and a contactor having a pair of cumulatively wound operating coils, one connected to said electric current source and the other connected across the armature oi. said generator, said ieed motor circuit also including "cut" and return" limit switches connected in series with said generator field winding and with said coil and its aforementioned electric current source, cut" and retum contactors energizable at the beginning of the "cut and return stroke, respectively, so as to have their respective contact members arranged to close said series circuit through the limit switches, coil and generator field winding during said respective strokes, said circuit being interrupted after a predetermined period of time following opening of one of said limit switches due to the maintenance of said double coiled contactor in an energizable condition due to the continuance of the voltage generated by said generator despite the interruption of the generator field winding circuit, said motor teed control circuit also including in series therewith, a parallel circuit, one having a "cut limit switch, a manually'operated switch and a contactor for completing a circuit so as to feed cur-- rent through said teed motor in a particular direction, and the other parallel circuit having a retum" limit switch, a manually operated switch and a second contactor for completing a circuit so as to Ieed current through said feed motor in an opposite direction.

9. In a variable voltage control system for a reciprocating platen element including an electric current source, a motor driven thereby, a generator mechanically'coupled thereto, a second motor energized by said generator ior driving said platen, limit switch means operable by said platen near the end of the reciprocating stroke and a pair of reversing contactors alterfollowing opening of one of said limit switches a nately energizable by said limit switch means for alternately passing current, first in one direction then in an opposite direction through a field winding of said generator for effecting reciprocating motion of said platen, in combination with a feed motor for effecting lateral ieed motion of said platen at the end of the reciprocating stroke, feed control circuit means including said feed motor and a contactor having a pair of cumulatively wound operating coils, one connected to said electric current source and the other connected across the armature of said generator, said feed motor circuit also including cut and*return" limit switches connected in series with said generator field winding and with said coil and its aforementioned electric current source, cut and "return contactors energizable at the begirming oi the cut" and return stroke, respectively, so as to have their respective contact members arranged to close said series circuit through the limit switches, coil and generator field winding during said respective strokes, said circuit being interrupted after a predetermined period of time following opening of one of said limit switches due to the maintenance of said double coiled contactor in an energizable condition due to the continuance of the voltage generated by said generator despite the interruption of the generator field winding circuit, said motor feed control circuit also including in series therewith, a parallel circuit, one having a cut limit switch, a manually operated switch and a contactor for completing a circuit so as to feed current through said teed motor in a particular direction, and the other parallel circuit having a return" limit switch, a manually operated switch and a second contactor for completing a circuit so as to feed current through said feed motor in an opposite direction, a geared limit switch also in said series feed control circult which is operable upon predetermined and adjustable angular movement of said feed motor to interrupt said feed control circuit, and an electromagnetic clutch between said geared limit switch and feed motor, which clutch is disengaged as the result of operation of said geared limit switch at the end of a predetermined angular rotation of said feed motor.

10. A variable voltage control system including a motor-generator set, a source of energizing potential for the motor and a second motor which is electrically connected to and energized by the generator, said generator having an armature and a field winding, a source of excitation potential for said field winding and means for alternately reversing the current flow through said field winding so as to alternately reverse the direction of drive 01. said second motor, a second electrical control system energized by said source energizing potential and having in series therewith a contactor which has two cumulatively wound energizing coils, one of which is connected across the armature of said generator, and the other, to said source through said current reversing means so as to be controllable thereby, said double coiled contactor thereby maintaining said second electrical control system deenergized until the voltage generator by said generator has diminished to a predetermined extent.

11. A variable voltage control system including a motor-generator set, a source of energizing potential for the motor and a second motor which is electrically connected to and energized by the generator, said generator having'a-n armature and a field winding, 9. source of excitation potential for said field winding and means for alternately reversing the current fiow through said field winding so as to alternately reverse the direction of drive of said second motor, a second electrical control system energized by said source of energizing potential and having in series therewith a contactor which has two cumulatively wound energizing coils, one of' which is connected across the armature of said generator, and the other, to said source through said current reversing means so as to be controllable thereby; said double coiled contactor thereby maintaining said second electrical control system deener-

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