US2164396A - Driving and control mechanism for turrets - Google Patents

Description

July 4, 1939.

B. N. FOSTER ET AL DRIVING AND CONTROL MECHANISM FOR TURRETS Filed March l1, 1938 2 Sheets-Sheet l July 4, 1939. B. N. FsTER Er Al.

DRIVING ANU coN'Tg'oL MECHANISM FOR .TURRETS Filed March 11, 1958 y2 sheds-sheet l 2 P. .mf NDL mm j i si tion:

'Patented July '4, v1939 UNITED STATES PATENT oEFlcE 2,161,391: narvmc AND common rmcmimsn ron runners Beniamln Norton Foster, Keene,

Frank L; Fisher, Wauwatosa, Wis., said .assigner to Allen-Bradley Company, Milwau- A' koe, Wis., a corporation'of-Wisconsin Anpueaien Miren.' 11, 193s, sei-n1 No. 195,492 14 claims. (ci.A zs-so) cally presented to a succession of power driven tools. Examples of this type of machine are illustrated in United States Letters Patent No.- V1,975,005 and No.'2,01.1,487, issued to E'. J. Kingsbury et al., lSeptember 25, 1934, and August' 13, 1935, respectively. l 'A 'Ihe p object of this invention is to provide an imp oved manner ofdriving and indexins the turret.

VMore .speciiically it is an object of this inven- 16 tion to provide. a completely electrical driving and control for indexing turrets and like apparatus wherein'I the advance of the turret and -also its securement at indexing positions is accomplished by a/singleelectric motor.

Another object of this invention is to provide means wherebythe turret is held in an indexing position by the torque of its driving motor.

Another obiect'of this invention is to provide a novel manner of reducing the potential across the. driving motor at the time it functions to .hold the turret in an indexing position so that the torque employed for this purpose is less than that which obtains during the advance of the turret.

Another object of this invention resides in the provision of-a simple, but eectlve manner'of interlocking thel forward and reverse switches which control the connection of the reversible motor with its lines so that closure of the reverse switch cannot takeplace until the forward switch is completely open and any arc across its contacts ceases.

With the above and The drawings illustrate -one complete .ample of the physical-'embodiment of ,-,0 me inveniionleonstrueted 1n accordance with me best mode so far devised for the practical application of the principles thereof, and in which: Figurel is'a diagrammaticillustrat'ion of a metal' working machine .embodying this inven- -speciilc manner in which this mechanism funcotner objects in view which will appear as the description proceeds, 40 thisinvention resides in the novel construction,

' Figure 2 is a cross sectional view through Figure 1 on the plane of the line 2-2'; and v Figure 3 is a wiring diagram of the complete t control System.

Referring now particularly to the accompany- 6 lng drawings in which iike numerals, indicate like parts, the numeral 5 designates the base of the machine upon which the turret 8 rotates.

Inside the base, which is hollow, is the turret advancing mechanism. This mechanism, in its mechanical aspects, consists of areversible electric motor 1 drivingly connected through gearing t with the turret.

vas lwill be readily apparent, may have any one of a wide variety of tools attached thereto. In the present instance, two of the spindles carry drills i5 while the third drives a tap i6.

The descent of the tools onto the pieces of work W .which are clamped to the .turret and also their retraction to elevated inoperative positions is eected by cams, motor driven, through clutches which' are operated by solenoids. The

"tions, however, forms no part of this invention, and therefore has not been shown, suiilce it to say that the solenoids are energized at the dictation of the control system to be hereinafter described.

As will be readily apparent, the functionl of the turret 6 is to carry the work W cyclically to the successive tools, and to ,properly position and hold the .same stationary` while the ytools perform their work; and it is to be understood that while in ythe diagrammatic illustration.v shown, only three individual tool heads are'illustrated, and the turret has only four positions of rest, `one` to provide for ytheapplication of the work W to and its renoval from the turret. in

-actual practice there 'may be more tool heads and the turret would then have an equivalently greater vnumber ofpositions of rest'.

-. 're insure the turret remaining at a standstilngdw during the work` period, each tool head controls a. limit switch which is opened as its quill starts A limit switches must be closed thereat to effectadvance of the turret, it follows that as long as any one tool is still functioning, or has not as yet been fully retracted, advance of the turretv cannot take place.

As will be hereinafter more fully described,

upon retraction of all of the tools and the consequent closure of all of the A linut switches,- the reversible motor 1 is connected with its supply lines for forward rotation to cause a forward indexing motion of the turret.

Approximately at the time the turret reaches its nextindexing position, a snap switch I1 is actuated to effect certain changes in the control circuits whereby the motor 1 is plugged by being connected with the lines through a reverse switch. The snap switch may be of the Burgess type, but as its specific construction'is immaterial, it has been only diagrammatically illustrated.

As shown, the snap switch has a spring pro- .iected depressible actuating plunger I 8, and the switch is so mounted that its actuator is depressible by an arm I9 carried by a spring pressed plunger 20. 'Ihe plunger 20 rides on the periphery of a ange 2I moving with the turret and snaps into recesses 22 in the flange as they come opposite the plunger. There is one recess 22 for each indexing position so that the snap switch I1 is actuated to effect the desired plugging as each indexing position is reached; and as; the plunger 20 rides out of each recess, the snap switch is actuated in the opposite direction for a purpose4 to be brought out hereinafter.

Upon plugging of the motor, forward advance of the turret ceases, and inasmuch as the plugging is so timed as to permit the turret to advance slightly beyond its proper indexing positions, it

follows that 4a slight retrograde movement of the turret 'is necessary in each instance lto bring it back to its proper indexing position.

To define these positions, the shoulders 23 formed by the abrupt ends of the recesses 22 are engageable with the spring pressed plunger 20. At the time of this engagement, the turret is accurately positioned; and to insure unimpaired accuracy, the shoulders 23 may beprovided by hardened inserts 24.

`While merel plugging of the motor, if ,the plugging switch were notopened, would eifect the desired retrograde movement of the turret. the fact that the plugging is done on ,full line voltage makes it undesirable to bring the turret back` in this manner. The necessary retrograde movement ofthe turret should be gentle, and means must be provided for holding the turret' against the,.striiaionarystop 'I'his invention accomplishes'these objects in a simple but eifective Amanner by reducing the potential across the motor-the instantv that the turret commences its retrograde movement, and for -this purpose a plugging relay 25, is provided with its actuator 26 operablev through friction means 21 byethe motor shaft.

The motor 1 operating in a reverse directie and on lowvoltage thus lbrings the turret gently against its stationary-stop, and as the low voltage connection to the motor is not broken ftir the stop has been engaged, it is evident that the torque of the motor holds the turret in its indexed position. Y

After the turret has been brought toits indexed position and while it is being held there by the reduced torque of the motor, the tool heads feed their tools to the work and retract them to theirv inoperative positions, itbeing remembered that during the time the tools move towardthe work and until they return to their inoperative'positions, the A limit switches remain open so that the next successive cycle cannot begin until the slowest tool has performed its function and has.

been returned to inoperative position.

The control system for effecting `thesequence' an electromagnetic main switch 30. 'I'his switch is of the conventional typecontrolled by start and stop push buttons 3I and 32.

Deriving energy from the lines T1, T2, and T3 is a transformer 33, the purpose of which is to supply low voltage for operating the motor 1 with reduced torque to impart retrograde movement to the turret and hold the turret against its stop.

Forward operation of the motor,1 is effected upon closure of an electromagnetic forward switch 34, which upon being closed connects the lines T1, and T3, respectively, with the terminals I, and 3 of the motor. The manner in winch this power circuit is establishedis clearly traceable on the diagram. It is desired to note, however, that line 'I2 is connected directly with the terminal 2 of the lmotor and that only the lines Tl and T'a-re broken at the switch. 3l.

With the motor operating in a forward direction, plugging thereof results from closure of an Upon closure of this switch, the connections to the y motor are reversed,l that is, the line '1'1 is now connected with terminal. 3 of the motor, and the line T3 is connected with terminal I of the L motor.

After plugging of the motor by closure of -the switch 35, it'is desirable to reduce the potential across the motoras pointed out hei-einbefore, and tothis end the switch 35 drops open' and alow voltage reverse switch 36 goes in. 'I'he closure of this switch 36, which is ,also an electromag netic switch, does not alter the polarity on the 31 and 38 on the transformer3`3 through the contacts Bland of the switch 35 and conductors 4I and I2.

The closure of the main switch 30 also starts all of the individual motors I2 of the tool heads inasmuch as the power for these ootors is derived from the lines T1, T2, and T3 through The solenolds (notshown) which controlthe mechanism effecting the descent and retraction of the tools are also energized by power derived from the lines T1, Tl, and 'I'3 through lines HS,

but only when a head trip solenoid switch 43 is closed. `The control circuits fori the various switches just referred to, vaid the manner in which they function, will now be described. A

Assuming that the tools are up or retracted so that all of the A limit switches are closed. closure v 3,104,390 of the main switch 30 renders vthelilies T1, Tl,

and 'I3 live and immediately effects energization of a relay 44. The current for energizing the coil of the relay 44 beginning with line TI at the point where this line leads to the head trip switch 43, follows conductor 45 to one side of the coil and from the other side thereof continues through a conductor 46 to a. normally closed bridging contact 41on the head trip switch, and from there continues` along conductor 43 to' the A limit switches and through these switches onto .conductor 49 to line -'IG at'the point this line connects with the transformer.

Concomitantly with the energization. of the relay 44, and as result of the closure of its nor- 1 mally open bridging contact 50, the coil of .the

. forward switch 34 is energized to close the switch 34 and connect the motor across the lines forforward operation. 1

The circuit for energization of the coil of the forward switch 34 is as follows:

Starting at line T3 at the point this line co nects with the transformer, the circuit follows conductor 49 through the A limit switches onto conductor 48, one branch of which connects with the now closed contact 50 of the relay 44. From this closed contact.5ll the circuit continues along conductor 5 I to a normally closed contact 52 of a relay 53, and passing through this normally closed contact continues along conductor 54 to a normally closed contact 55 on the low-voltage reverse switch 36 to continue along conductor 56 to one'side of the coil. The other side of the coil is connected through' a conductor 51 with the conductor 4I which leads'to'terminal I on the, motor.

j Inasmuch as no potential is now impressed on the motor, the circuit can be continued through the windings of the motor to' its terminal 2 which is directly connected with the live line T.

Thecoil of forward switch 34 having been en. .ergized, the forward switch closes and as a result the motor begins to run in a forward direction to advance the turret to its next indexing position.

With the application of potential on the motor, it is necessary to maintain the energizing circuit of the coil of switch 34 through ahlding circuit independent of the motor windings. This circuit is completed from live line Tl through the now closed contact 55 of forward switch' 34, part of line.4.I-. conductor 51 to' one side 8f the coil, and from the other side of the coil back to line ".i'3 along conductor 55, etc., in the manner hereinbefore described.

Directly after the forward motion of the turret begins,"the snap switch I1 is actuated to reverse theposition of its movable .contactor 53,' this being effected by the depression of its actuator I8 bythe plunger carriedarm I9 moving in .response to the plungers rise out'of therecess 22 in which it was engaged. Thecontactor 53 yof snap switch 11 thusnowbridges its common terminal 6I! and its terminal 6I. Concomitantly with a bridging of the terminals 5l and 3| of the snap switch I1, the coil of relay 53 is energized. The circuit for' energizing this coil, beginningl with line '12 at the point this line leads to the head trip .switch 43,` extendsalong conductor 45 to one side of 'the coil, and from the other side thereof vcontinues through conductor 53 -to .th center terminal 6|! of snapswitch I1, through the snap switch to its terminal-5I, conductor 64, normally closed contact55 of relay 5 3, conductor 5I, to then closed contact 5l of relay 44,

switch l1.

conductor 4l, the A limit switches, and conductor the coil of forward switch 34 is completed through the normally closed contact 52 of relay 53, and as this contact opens with energization'of the relay 53; means must be provided to prevent the break which would .occur in the coil circuit of switch 34 as a. result of the openingof contact 52. For this purpose, the normally open contacts and 61 of the relay -53 overlap in their functions with the contact 52 so that these con-- tacts 66 and, 61 close.- prior to the opening of contact 52.to1maintain the circuits passing through contact 52.

Forinstance, the holding circuit for the coil of forward switch 34 instead of passing through contact 5 2 nowcontinues through that part of conductor 5,4 which leads to contact 66.- This contact being closed,- the circuit continues through a branch of conductor 64 whichv leads to terminal 6I of snap switch I1. -From this point the circuit continues through the snap lswitch to con. ductor 63 and a branch thereof to the then closed contact 81 of relay 53 which connects with conductor 5I to continue the circuit in the manner aforesaid.

At this point in the operation, relay 44 is energized, relay 53 is energized/and forward switch 34 is closed so that the motor is running in a .forward z direction vadvancing the turret to its next indexing Position.

I Itis to be observed that with the change of This actuation of the snap switch I1 is effected the turret and reaches the plunger -20 at an instant so timed with the inertia of the parts, that the opening of the forward switch and the closure ofthe reverse switch 35 to effect plugging of the motor which also follows as a result of this actuation of the snap switch I1, takes place vwhen the turret has advanced a short distance beyond its proper indexed position.

Energization ofthe coil of switch 35 is' effected by closure of the following circuit by the snap Beginning with line T3 this circuit continues... along conductor 49,- throu'gh the A limit switches, conductor 48, the closed contact 5I! of relay 44, conductor 5I,`. to the then closed contact 61 o-f relay 53, conductor 63 toterminal 5l of snap switch I1 and .passing through contactor 59 of snapswitch I1 to Aterminal 62. 'I'he circuit continues along conductor 68, to the then closed contact 69 of relay 53, a eonductor`1il lwhich leads to the center terminal 1I ofv snap switch 25. ThiS'snap switch at this. time has its contactor 12 engaging its'terminal 13 and disengagfd from its terminal 14, and as the terminal 13. is connected with one side of thecoil of reverse switch 35," the clrcu'it is completed to said side of the coil.-` Fromthe otherside of the coil, thef .circuit continues through aconductor 15' which leads to conductor 42 and thence to termi; nal 3 on vthe motor. f

by spring propelled outward projection of its actuator lpermitted by the entrance of the l plunger 20 into' the recess 22 which moves with motor, either through actual closure of the forward switch 34 or the hanging on of an arc across its contacts. In other words, with this manner of completing the energizing circuit for the coil of reverse switch 35, closure of the reverse switch is positively precluded until the motor is completely disconnected from the lines.

Hence, as soon as any arc hanging on across the contacts of the forward switch 34 is extinguished, conductor 42 assumes the polarity of .line T1 through the windings of the vmotor to complete the energizing circuit for the coil of reverse switch 35. When this occurs, the reverse switch 35 closesand connects the motor across the lines, but with a reverse polarity, as noted hereinbefore, so that the motor is plugged en full voltage.

With the closure of the reverse switch, the energizing circuit for its coil is completed independently of the motor windings inasmuch as conductor 42 with which one side ofthe coil is connected through conductor 15- becomes connected with line T1 through then closed contact 16 of switch 35. The coil of switch'35 is thus connected across lines Tl and T3.

As soon as the turret begins a retrograde movement, snapswitch 25 is actuated to cause its contactor '12 to leave terminal 13 and engage terminal 14. -This actuation of the snap switch 25 obviously deenergizes the coil of the reverse'v switchj35. It also effects energization of the coil of the low voltage reverse switch 36 to connect the motor with the low voltage derived from the transformer ,33, but with the same polarity conditions as obtain during the time the reverse switch 35 is closed.

The manner in which this actuation of snap switch 25 eiectsclosure of the low voltage reverse switch 36 is as follows:

Immediately upon engagement of the contactor 12 with the terminal 14, the coil of a relay 11 is energized. Inasmuch as the lcentral terminal 1| of snap switch 25 is connected with line 'I3 in the manner hereinbefore described,

the energizing circuit for the coil of the relay 11 may be traced from the terminal 1| through the contactor 12, to terminal 14 which connects directly with one side of the coil, the other side of the coil being connected through one branch of conductor 51 with conductor 4| which leads to terminal l on'the motor; and there being no voltagey impressed on the motor at this time, 4the circuit can be completed through itswindings to line T2.

With the energization of relay 11, the coil of the low voltage reverse switch 36 becomes energized. The circuit for this purpose, beginning with line T3, may be traced along conducto 49 and those branches thereof which lead to the relay 11. The contact 18 of this relay now being closed, the circuit continues through conductor 19 which leads to then closed contact 80 of relayl 53. Passingthrough this contact, vthe-circuit 'is continued through conductor 8|, to oneside of the coil. The. other 'side of the coil is connectedl through a conductor 82 with conductor 42 which leads to terminal 3 on the motor, which means that the circuit is completed through lthe motor windings to line T1.

Closure of the switch 36 in responsejto energization of its coil closes a holding circuit lfor its coil independent of the motor windingslwhich is established by.l its contact 40 bridgingl the gap in conductor 42 which now4 takes the Polarity of line T1. The holding circuit for the coil of the switch 36 is also now completed independent of theV relay 11. This'results from the fact that conductor 19 leads to the then closed contact 19 of switch 36, the open side of which is connected with conductor 49. With the. closure of the low voltage reverse switch 36, the coil of the head trip switch 43 is connected across lines 'I'2 and T3 for energization. Its circuit is as follows:

One side of the coil is directly connected with line T2, while the other side thereof is connected with the then closed contact 83 of switch 36 through a conductor 84. From this closed contact 83, the circuit continues along conductor 68 to snap switch I1, Yconductor 63 to thenclosed contact 61 of relay 53, conductor5| to closed contact 5|) of relay 44, through the A limit switches, and conductor 49 back to line T3.-

With the closure of the head tripr switch 63,

the lines HS leading to the solenoids which-initiatethe descent of the tools are energized. It is essential though that the turret be brought firmly against its stop by the motor operating in reverse on low voltage`prior to Athetools becoming operative. Hence, a suiiicient time lag must be provided in the functioning of the mechanism which effects the descent of the tools.

With the closure of the headtrip switch 43, its normally closed contact 41 through which the energizing circuit for the coil of relay 44 was completed, opens thus allowing the relay. to drop out with the result that its contact 50 opens and its normally closed contact 85 Acloses. The opening of contact 41 of head trip switch 43, however, lags behind the closure of a contact 86 of switch 43 and the closureof this contact 86 compensates for the dropping out of contact 50 on relay 44 to maintain the relay 53 and the coil of the low voltage reverse switch 36 energized vuntil the A linut switches open. l

To illustrate, the energizing circuit for the coil of the relay 53 where it continues along conductor 5| from then closed contacts 61 of relay 53 instead of going down on that branch of conductor 5| which leads to contact 50, now continues upwardly along the opposite branch thereof to the then closed contact 86 which is connected with conductor 48 which in turn leads through the A limit switches to conductor 49 and line T3.

However, as soon as the A limit switches or any one of, them opens as a result of the descent or feeding stroke of the tools, the energizing circuits for the relays 43, 53 and 11 are broken, which deenergizes the solenoids of the tool heads, permits normally closed contacts 52 and 65 of relay 53 to reclose, and opens the contact 18 of relay 11. The deenergization of these relays, however, doesnot entail opening of the low voltage reverse'switch 3 6, as the energizing circuit for its coil is maintained "during the turrets period of standstill so as to hold the turret against its stop by the reduced torque of the motor.

'I'he circuit for this purpose, beginning with line 42 which is now live and has the polarity of linerTl, may be traced along conductor 82 to elf negoce one side-of the coil, and from the other side vof the coil along conductor Il and that branch thereof which leads to the then closed contact l5 of relay M. From the other side o! this contact, the circuit is continued along conductor 4I independent of the A limit their work and untii, an of the iimit switches are reclosed by the lifting or retraction of all oi the tools back to their inoperative positions.

When this occurs, relay M is again energized.

Energization of the relay M' now not only initiates the repetition of the entire cycle asin the manner aforesaid by the closure of its contact 5l, but in opening its contact 85, it also deenergizes the coil of the low voltage reverse switch Allof the instrumentalities are thus in the same positions they were at the initiation of the described cycle; and as will be readily apparent, this same sequence of operations continues the main Vswitch 30 remains closed.

From the foregoingdescription taken in connection with the accompanying drawings. it will be readily apparent to 'those skilled in the art. that this invention provides a driving and control mechanism for the turrets of machines of the character described wherein objectionable mechanical expediente for cyclically advancing the turret and holding it at a standstill are obviated; and wherein. the initiation of each cycle is directly controlled by the completion of the work being done by the slowest tool'so that no as long as time is wasted and greater exibility of adjustment tofdlierent types of work is effected.

What we claim as our invention is:

1. In a device of the character described: a

member which'is to be advanced to a definite pre-A determined position and there held for a period i of vtime;.a reversible electric motor; a positive continuously operative driving connection .between the motor and said member through which the motor operating in one direction advances said member forwardly beyond said deilniteposition and operating in the reverse direction imparts retrograde movement to said member; stop means for arresting retrograde movement of said member, said stop means being positioned to accurately define said predetermined position; and means for effecting a reduction in the torque of the electric motor upon retrograde movement of said member so that the electric motor holds said member against the stop means with a reduced torque.

2. In a device of the character described: a membery which is to be advanced to a predetermined deflnite position and .there .held for .a period of time; means for eilecting advance of said member forwardly beyond and back to said predetermined definite position; stop means for arresting retrograde movement of said member to accurately deiine said predetermined position of the member; an electric motor; and a positive and continuously operative driving connection between the motor and said member s o that the said member against` mined. definite position andv there held: for a` period of time; means foreffecting advance of' said member forwardly beyond and back to said predetermined deiinite position; stop means for arresting retrograde movement o! said member to accurately denne said predetermined position ing a tool positioned a't a definite location: a

work carrying member movable to position-work yin operative relationship to the tool; a stop against which the work carrying member is mov` `able to accurately locate the same; an electric motor; and a continuously operative driving connection between themotor and the work carrying member through which the work-carrying member is moved into engagement with the stop and there held by the torque of the motor.

5. `In a machine of the character described including a movable table: means for indexing the table comprising, a stationary stop for arresting movement .of the table; and an electric motor permanently and continuously drivingly connected with the table tobring the table against 'the stopand hold the same there by the torque oi the motor. 6. In a machine oi vthe character described including a movable table: means for -indexing the table comprising, a stationary stop for arresting movement of the table; a single electric energy translating vmachine for imparting a fast initial and a slow final indexing motion to the table; and a positive continuously operative'drlving connection between the translating machine and the table through which the translating machine drives the table and whereby the table is held against the stop by the dissipation of electrical energy.-

7. In a machine of the character described including: a movable table; means for indexingthe table comprising a stationary stop-for arresting movement of the table; a single electric energy translating machine; a positive continuously operative driving connection. between` the transtranslating machine drives the table and wherelating machine and the table through which the by the table is held against the stop by the dissi'- 50 pation of electrical energy; and means-for effecting 'a reduction in the potential impressed on the translating machine prior to engagement oi the table with the stop so that the table has"a slow iinal indexing motion and is held against the stop erative driving connection between the electric vmotor and the turret -through which the motor holds the .turret against said stop means by its torque.

9. In a turret structure: a turret to be cyclically advanced and brought to a standstill; stop means for 'd eiining the positions of rest for the turret; an electric motor connected with the tur- -ret for advancing the same; means to eiect plugging of the motor to stop the turret after it has traveled slightly beyond its positions of rest; and

means for effecting operation of the motor with reduced torque and in a reverse direction to bring and retracting it; stop means for arresting retrograde movement of said member and for accurately defining said predetermined position of the member; and control means for plugging the motor to effect retrograde movement of said member and for reducing the voltage across the motor substantially the instant retrograde movement of said member begins, whereby said motor operating with a reduced torque holds said member against the stop means.

. .11. In a device ofA the character described: a member adapted to be successively moved to definite positions of rst; a reversible electric motor drivingly connected with said member for successively advancing the same slightly beyond the proper positions of rest and imparting retrograde movement thereto; stop means for arresting retrograde movement of the member at the proper point to accurately define said positions of rest; means for connecting the electric motor With a source of electrical energy to have it run in a direction necessary to advance said member; means controlled by movement of said member' to effect plugging of the motor in time to arrest advance of said member at the proper instant to.

- allow for ashort retrograde movement thereof into engagement with said stop means; and

means controlled by retrograde movement of said` member for effecting a reduction of the potential on the motor the instant retrograde movement begins and foi' maintaining such reduced potential on the motor throughout the entire period of rest of said member so that the motor' gently moves said member against the stop means and holds it there.

12. A motor control system of the character described comprising: a reversible electric motor;

a forward magnetic switch for connecting the motor with supply lines to effect forward operation of the motor; a reverse magnetic switch for connecting'the motor With'the lines to plug the motor; a magnetic low voltage reverse switch for connecting themotor with a source of potential 'a reverse direction at low voltage.

Vtion of the motor with reduced torque; control v less than full line voltage to effect reverse operation of the motor with reduced. torque; control circuits for energizing said magnetic switches; and control means in said circuits for successively energizing the magnetic forward switch, the reverse switch, and the low voltage reverse switch, whereby the motoris operated iirst in a forwardly direction, then plugged, and then is operated in 13. A motor control system of the character described comprising: a reversible electric motor; a forward magnetic switch for connecting the motor with supply lines to effect forward operation of the motor; a reverse magnetic switch for connecting the motor with the lines to plug the motor; a magnetic low voltage reverse switch for connecting the motor with a source of potential less than full line voltage to effect reverse operacircuits for energizing said magnetic switches; control means in said circuits for successively energizing the magnetic forward switch, the reverse switch, and the low voltage reverse switch whereby the motoris operated first in a forwardly direction, then plugged, and then is operated ,25

in a reverse direction at low voltage; and an electrical connection between the forward and the reverse switches whereby energization of the magnet coil of the reverse switch cannot take place until the forward switch is completely open 30 and arcing across its contacts ceases.

14. In combination: a turret to be cyclically advanced to a sequence of deinite positions; a'

' stationary stop; a stop movable with the turret and engageablel .with the stationary stop for de- 35 ning said positions, engagement of said stops requiring retrograde movement of the turret; a reversible electric motor connected with the turret for advancing and retracting the same; means for controlling operaton of the motor to effect an advance of the turret slightly beyond said definite positions and for effecting retrograde movement thereof to engage said stops, said -means including a magnetic forward switch and a magnetic -reverse switch; and control circuits for controlling energization of the magnetic forward and reverse switches, said control circuits being completed through' the windings of the motor so that the energizing circuit for one switch cannot be established until the other switch is completely open.

BENJAMIN NORTON FOSTER. FRANK L. FISHER.

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