US1233854A - Motor-control system. - Google Patents

Description

J. EATON.

MOTOR CONTROL SYSTEM.

APPLICATION r1150 APR.23. 1915.

1,233,854. Patentedjuly 17, 1917.

Inve htor' John Ean I f His aqttor'neg.

JOHN EATON,

OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COM- IPANY, A CORPORATION OF NEW' YORK.

MOTOR-CONTROL SYSTEM.

Specification of Letters Patent.

Patented July 17, 1917.

Application filed April 23, 1915. Serial No. 23,338.

To all whom it may concern.

Be it known that 1, JOHN EA'roN, a subject of the King of Great Britain, residing at Schenectady, county of Schenectady, State of New York, have invented certain new and useful Improvements in Motor- Controlsystems, of which the following is a specification.

This invention relates to the electrical operation of machine tools such as laners and the like, and has for its object t e provision of means'whereby the operation may be carried out and properly controlled in a reliable, simple and efficie'nt manner.

More specifically, my invention relates to the electrical operation of planers, in which in addition to the electric motor for driving the planer there is employed a feed motor for operating the feed mechanism. In the electrical operation of planers, especially the larger sizes, it has been found desirable to employ such a feed motor especially since this motor may also be utilized to rapidly traverse the tool back to its starting position after the out has been completed in addition to performing its function of feeding the too was of necessity of the reversible type, but I have found that it is possible to dispense with the reversing feature thereby greatly simplifying and improving the apparatus. One of the objects of my invention is to provide a control system in which the feed motor always operates in the same direction.

Another object of my invention is to provide means whereby the feeding operation will begin before the main motor stops or at least before it starts in to rotate in the opposite direction. By starting the feed motor before the main motor reverses, a considerable saving of time is effected since the amount of overtravel of the tool which would'otherwise be necessary in order to give time for the feeding will be reduced. Another object is to provide means where by the beginning of the operation of the feed motor depends upon the speed of the main motor, that is, when the speed of the main motor has dropped to a predetermined point the feed motor will be started. Other objects and purposes of my invention will appear in the course of the follow1ng -spec1- fication, in which I have shown my inven- As heretofore employed, the feed motor tion embodied in concrete form for purposes of illustration.

In the accompanying drawing illustratmg one embodiment of my invention, Figure 1 is a diagrammatic view of a system of motor control embodying my invention; and Fig. 2 is a detail of the feed mechanism of the planer.

The features of the control in so far as the main driving motor is concerned, forms no part of my present invention, the specific system herein disclosed being described and claimed in patent to Murphy and Eaton, 1,O%i,8 l5. However, in order that the sys tem as a whole may be clearly understood I shall describe the system in general and then point out the features of novelty.

Referring to Fig. 1, A represents the armature and F the shunt field of an electric motor for driving a planer or the like. The direction of rotation of this motor is con trolled by four electromagnetic switches or contactors, two for each direction ofrotation. Two of these switches are designated C and C respectivel since the connect the y, 3

motor for driving the planer in the forward or cutting direction, while the other two switches are designated R and R respectively, since when closed they drive the planer in the opposite or return direction. These four switches are operated by shunt windings controlled by the master switch S. In the drawing the electromagnetic switches are shown in the positions which they assume when the main line is deenergized and.

the master switch is shown in its intermediate or off position. l/Vhen the master switch S is moved to the posit-ion a, and the line is energized, the windings of the contactors C and C are energized in series across the line, while with the switch in the opposite position b, the windings of the two contactors R- and R are similarly connected across the line. I

A starting resistance D is provided for the motor A, this resistance being controlled by an electromagnetic switch 10, connected so as to close and short circuit the resistance when the counter electromotive force of the motor rises to a predetermined value. For

varying the speed of the motor, two field.

rheostatsare provided, one of which has a resistance 1" which is controlled by the arm of the resistances 1' and r are short circuited through wire 13 and switch 14., which is spring closed. When the switch 10 closes, the switch 14 is opened so as to break the short circuit. When the master switch S is in the position a, that is in the cutting position, a portion of the resistance 1', the amount of which will depend upon the position of the lever 11, will be connected in the field circuit. When the master switch is moved to the position b, the connection to the arm 11 is broken atthe interlock 15 by the closin' of the line contactor R. The field circu1t will then be completed through wire 16 so that all of the resistance 1" and a portion of the resistance 0*, depending upon the osition of the lever 12, will then be in the eld circuit. V

In order tobring the motor armature to rest quickly a.brake resistanceds provided through which the motor armature isshort circuited. This brake resistance is composed of two sections BR and BR. The purpose of these two sections of resistance is to graduate the dynamic braking current as the motor field builds up and the speedof the socmotor slows down. For making the brakin connection, thecontactor B is provide which is normally closed by a spring 17.

The winding of this contactor is connected across the motor armature so that while the motoris operating, the winding tends to close thecontacts. This contactor is also provided with a series winding 18, which is not energized until the contactor is closed.

The five'contactors R, R, C, C and B being arranged as shown in the drawings, are providedwith four mechanical interlocks, 19, 20, 21 and 22, coiiperating with the contactors so as to compel operation in a predetermined' manner. Whilevthe contactor B is closed by a spring, this spring is not sufliciently stifiz to apply any considerable pressure to the contacts, since the two windings are provided for holding the contacts tightly closed. p

An electromagnetic switch or relay 23, is

provided with. a winding having one. terminal-connected with the shunt field winding F, while the'other terminal is connected to resistance '1'. The winding of the relay isv divided into two halves which are wcund differentially ,to each other so that when the two halves are energized, they neutralize.

each other and the relay will not close. It is obvious that. when theswitch 14 is open, the field current must pass through the two divided portions of'the relay winding and through any field resistance which may be in the circuit. The relay is therefore inoper-- ative under this condition. When, however, the switch l t, is closed, the lower half of the relay windingand the field resistance are short circuited so that one-half of the winding is energized and the relay is operative. The winding of this relay is so adjusted that when the field current ap' oaches a maximum, that is-when the fie d reaches nearly full strength, the relay will close but when the field is weak, the relay will not close even though only the upper winding is energized.

relay 23 closes, 'to short circuit the braking resistance BR, it connects in circuit a contactor 24 of the series or current limit type. This type of contactor is now well known and has the property of holding open when the current is high and closing when the current falls to a predetermined value. When,

however, the relay 23 is closed and the section of resistance BR is short circuited, the braking current will rise to the limit of safety As the motor slows down, the current will decrease to proper'value and series contactor 24 will close and short circuit the other section of resistance BR.

It is to be understood that the master switch S is operated by dogs-on the planer so that when the platen of the planer reaches the end of the stroke, the switch S willhe thrown from one extreme position over to the opposite position which will stop the mo- I tor and start it in the opposite direction.- The operation up to this point is the same as that described in the patent above re ferred to. I

For feeding the tool up to the work, I provide a feed motor having armature A" and field F. The operation of this feed motor is controlled in the first instance by the master switch S, the operation of which initiates the circuit for the feed motor. The feed mo-,

tor is also controlled by the speed-of the main motor so that although the master switch is thrown over, the feed motor will not operate untilthe main motor; speed.

stopped after making a predetermined numat my present invention. The feedimotor is v ber of revolutions by means of a controller driven by the'feed' motor. The feedniotor is not controlled directly through the con 'tacts ofthe master switch S and the 'controller' E, but is controlled by'a double throw contactor J having a shunt operating winding 25 which. when energized closes the contacts26 and completes the, feed motor circuit. Contacts 27 when closedmakes a dynamic braking circuit for stopping the feed motor. When the winding 25 is deenergized the contacts 26 open and contacts 27 close.

As above stated, the feed motor always operates in the same direction instead of operating first in one direction and then the opposite direction as has been the practice heretofore. It is understood of course, that ordinarily the motor will operate the feedupon one operation and on the succeeding operation will operate the ratchet. This is illustrated in Fig. 2 which shows the operation upon the standard feed mechanism of a planer. The feed motor drives the plate 28 first through one half of a revolution and then through the remaining half. During the feed operation, the crank pin 29 will be moved from position 30 to position 31, thereby rotating the feed screw shaft 32 in a clockwise direction by means of a segmental gear 33 and pinion 34 carrying a pawl 35- drivinga ratchet. wheel on the screw shaft. When the feed motor again operates, the crank pin moves from position 31 to position 30. The feed screw will not 'now operate since pinion 34 ratchets on the feed screw shaft in a manner well understood. By shifting the pawl the operation will be reversed.

the neXt operation being made at contact 37. These contacts 36 and 37 correspond with opposite positions of the master switch, that is when the master switch is in position a the feed motor will be started through contact 37 and when it is in the position b the motor will be started through contact 36. The feed circuit to the contacts 36 and 37 is through contact 38 which is in permanent engagement with its contact segment and the circuit to contact 38 is either through the contacts on relay 39 or through contacts 40 which are closed When'the electromagnetic switch J closes.

These contacts 40v short circuit the contacts on relay 39, so that after the feed motor circuit is closed, it can not be opened by the relay 39. A double throw switch Gr serves to place both the main motor and the feed motor in service in one position, whilein the other position it connects only the feed motor in circuit for traversing the tool'to any desired position.

As thus constructed and arranged, the operation is as follows: Assuming the master switch S to be thrown to the position a and switch G thrown to the left, contactors C and C will close and start the When the motor reaches a predetermined speed, starting resistance D is short circuited by the operation of counter E. M. F. relay 10. The closing of the relay 10 opens the switch contacts 14: which weakens the field by opening the short circuit on the field resistance. The field current now passes from the positive side of the line through the contacts 15 of contactor It through lever 11 and whatever portion of resistance 9 may be in circuit, through the two windings of relay 23 and the field F to the negative side of the line. iVhen the end of the stroke is reached, the reversing switch S will be thrown to position b. This will cause the contactors C and C to open and the brake contactor B, which has heretofore been held open by the mechanical interlock 19, to close, thereby completing the dynamic brake circuit through the brake resistance BR and BR' and the motor is quickly brought to restin the manner described in the patent above referred to.

The movement of the master switch to the position Z also initiates the movement of the feed motor. When the switch is thrown over to the position Z), connection is made from the positive side of the line through contact 41 to contact 36 on the controller E, thence by wire 42 to the contacts of the relay 39. These contacts are open when the master controller is thrown over to position b but closed when the speed of the main armature A drops to a predetermined value. /Vhen this speed, which is the speed at which it is desired that the feed motor shall start is reached, the circuit is completed from the contacts of relay 39 through the winding 25 of gontactor J to the negative side of the line. J now closes the contacts 26 and the armature circuit of the feed motor will be completed from the positive side of the line through wire at and the contacts of switch G to theswitch contacts 26 through the frame of the switch J to starting resistance H and the winding of series contactor 45, armature A and back to the negative side of the line through 46. As the armature A speeds up, the starting resistance H will be short circuited by the closing of series contactor 45 and after a predetermined number of revolutions, the feed motor stops because the circuit is opened at contact 36 and initiated for the next operation at contact 37. The feed motor will now operate to either feed or ratchet as the case may be. Preferably the feed operation will take place at the end of the return stroke, although in some cases, it will take place at the end of the cutting stroke. It will be noted that the feed motor begins to- The contactor t1on as desired.

site direction. By properly adjusting the relay 39, it can beeither made to start practically as soon as the reversing switch is thrown, by having the relay 39.drop when the speed of the main motor is high, or the operation may be delayed until the main motor is nearly stopped.

The reversing switch being now in the position b as soon as the main motor stops,

'contactor R closes by reason of the opening of the-brake contactor B. The motor will now start in the opposite direction and come to speed as before. In this case, however, the speed will be higher since the contactor'R being closed, there will be no circuit through the contacts and the field circuit must pass through wire 16 so that all of the resistance r and a portion of 1" depending upon the position of the lever 12 will be in the field circuit. When the end of the stroke is reached, the master switch will be operated to the position a and the motor will be 'dynamicall braked and finally stopped as before. he controller E having been moved by the operation of the feed motor so thatcontact 37 is now in engagement with the segment instead of contact 36, the feed motor will be started as before. It will also operate in the same direction in which it operated before and this time, will operate the feed screw on the assumption that the feeding is to be done at the end of the return stroke.

This'operation will continue, the feed motoroperating the plate 28 one half a revolution to either feed orv ratchet and, upon the en of thenext stroke, operate in the same di rection, to either ratchet or feed. -The feed motor is brought torest quickly by a dy-.

namic braking circuit which is closed at B. On throwing the switch G to the oppoof the line through wire" 44,- contact on tion .or'

siteposition, the foodmotor can be caused to operate the feed screw in the opposite direction continuously without the control of the controller E. This is accomplished by energizing the winding 25 of contactorJ directly across the line. The circuit of this winding will now be fromthe positive side switch G, wire 48, winding 25 to thenegative side of the line throughwire 46. By

.throwingithe master switch S to one posit e other so as to actuate either the contactors C, C'- or Band R7 the feed motor will be caused to operate in either dlrec- What-I claim as new and desire to secure 'Fby Letters'l atent of the United States, is v 'I'I'The combinationof a main electr1c motor for driving a planer or the like, a reversing switch therefor operated by the movement of the planer, a feed motor, means whereby the feed motor is energized for the same direction of rotation each time the refeed motor after it has made a pre eterminednumber of revolutions.

3. The combination of a main electric motor for driving a planer or the like, a switch for stoppingand reversing the same periodically, a feed motor, means whereby the feed motor is energized for. the same directionof rotation each time the reversing switch is operated but before the motor. stops so that the feed motor operates before the main motor starts in the reverse direction, and means for stopping the feed motor, after it has made a predetermined numbenof revollitlOIlS. l

4. The combination of a main electric m0- tor for driving a planer or the like, a reversing switch therefor operated by the movement of the planer, means whereby the motor is dynamically braked and reversedwhen the switch is operated, a feed motor, means whereby the feed motor is energized for the same direction of rotation upon each operation of the reversing swi ch so that the, feed motor operates wh le the main motor is being dynamically braked, and means for stopping the feed motor after it-has made a predetermined number of revolutions.

5. The combination of amain electric motor for driving a planer or the like, a switch therefor operated by the movement of the planer, means whereby the motor is dynamically braked and reversed when the reversing switch is operated, a feed motor, means whereby the feed motor is energized for the same direction of rotation upon each operation of the reversing switch when the speed of the motor drops to a predetermined value so'that the. feed motor starts whenthe main after it has made a predetermined numbe of revolutions. I

6. The combination of a main electricmotor for driving a planer or the like, a switch therefor operated by themov'ement of the planer, a feed motor, means whereby the v feed motor is energized for the same direction of rotatlon each time the reversing switch is operated, means whereby succesalternate feeding and ratcheting operations, and means for stopping the feed motor after "sive operations of the feed motor cause it has made a predetermined number of revolutions.

7. The combination of a main electric motor for driving a planer or the like, a switch for stopping and reversing the same periodically, a feed motor, means whereby the feed motor is energized for the same direction of rotation when the reversing switch is operated and the speed of the main motor reaches a predetermined value, and means for stopping the feed motor after it has made a predetermined number of revolutions.

8. The combination of a main electric motor for driving a planer or the like, a switch therefor operated by the movement of the planer, a feed motor, means whereby the feed motor is energized for the same direction of rotation when the reversing switch is operated and the speed of the main motor reaches a predetermined value, means whereby successive operations of the feed motor cause alternate feeding and ratcheting oper ations, and means for stopping the feed mo- I tor after it has made a predetermined number of revolutions,

In testimony whereof, I have hereunto set my hand this 22nd day of April, 1915.

JOHN EATON.

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