US3832617A

US3832617A - Motor control apparatus with geneva-type switch actuating mechanism

Info

Publication number: US3832617A
Application number: US00256267A
Authority: US
Inventors: B Spencer
Original assignee: Woodward Governor Co
Current assignee: Woodward Inc
Priority date: 1972-05-24
Filing date: 1972-05-24
Publication date: 1974-08-27
Anticipated expiration: 1991-08-27

Abstract

A Geneva-type drive unit with overlapping driving and driven wheels in which the driven wheel is advanced intermittently and carries cams which actuate switches for controlling a stepping motor operable to expand and contract an adjustable link interposed in the throttle linkage of an engine.

Description

United States Patent [191 Spencer, Jr.

[ 1 MOTOR CONTROL APPARATUS WITH GENEVA-TYPE SWITCH ACTUATING MECHANISM [75] Inventor: Bruce G. Spencer, Jr., Rockford, Ill.

[73] Assignee: Woodward Governor Company, Rockford, Ill.

22 Filed: May 24, 1972 211 App]. No.: 256,267

[52] US. Cl. 318/673, 318/467 [51] Int. Cl. G05b 11/14 [58] Field of Search 318/467, 673

[56] References Cited UNITED STATES PATENTS 2,982,335 5/1961 Garvey 318/467 X 1 Aug. 27, 1974 3,243,676 3/1966 Willman 318/673 X 3,249,877 5/1966 Eggman 318/467 X 3,250,566 5/1966 Rainey 318/467 X 3,395,323 7/1968 -Peters 318/673 X 3,517,287 6/1970- Scholl et a1. 318/673 Primary Examiner-T. E. Lynch Attorney, Agent, or Firm-Wolfe, Hubbard, Leydig, Voit & Osann, Ltd.

[ ABSTRACT A Geneva-type drive unit with overlapping driving and driven wheels in which the driven wheel is advanced intermittently and carries cams which actuate switches for controlling a stepping motor operable to expand and contract an adjustable link interposed in the throttle linkage of an engine.

6 Clains, 9 Drawing Figures zrw 2 0.416 KAWIPAMK MOTOR CONTROL APPARATUS WITH GENEVA-TYPE SWITCH ACTUATI'NG MECHANISM BACKGROUND OF THE INVENTION The invention relates in general to apparatus for controlling an electric motor and, more particularly, to apparatus which is especially suitable for controlling a motor operable to drive a mechanical adjusting device interposed in the throttle linkage of an engine.

Apparatus of this general type is disclosed in Leeson U.S. Pat. No. 3,206,640. In the previously patented system, the speed of a slave engine is maintained in synchronism with the speed of master engine by producing a signal representative of the difference in speed of the two engines and by using the signal to drive a reversible electric motor which actuates a mechanical adjusting device to change the effective length of the throttle linkage of the slave engine until the speed of that engine matches the speed of the. master engine. Auxiliary mechanism is provided for controlling the motor to in-- sure that the adjusting device is initially at thecenter of its range of adjustment prior to placing the system in its synchronizing mode. The auxiliary control mecha nism comprises a pair of switches which cause the motor to drive the adjusting device in the proper direction to its centered position, the appropriate one of the switches being automatically actuated to de-energize the motor once the adjusting device has reached its centered position.

SUMMARY OF THE INVENTION I The general aim of the present invention is to provide comparatively simple and compact auxiliary control mechanism of the above character whose elements may be assembled in operative relation with one another and with the motor in a quicker and easier manner than has been possible heretofore.

A more detailed object is to provide an auxiliary control mechanism comprising a Geneva-type drive unit adapted to be driven by the motor and adapted to actuate the control switches, the drive unit and the switches being properly positioned relative to one another automatically as an incident to assembly of the unit so as to avoid the need for complicated and time-consumin assembly operations.

In another of its important aspects, the invention is characterized by the compact construction of the Geneva-type drive unit and particularly by a unique overlapping relationship between the driving and driven wheels of the unit to enable enclosure of the unit within a relatively small housing.

These and other objects and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of an exemplary system equipped with new and improved control apparatus embodying the novel features of the present invention.

FIG. 2 is a diagram showing the circuit of the control apparatus.

FIG. 3 is an enlarged view taken along the line 3-3 of FIG. 1.

LII

FIGS. 4 and 5 are fragmentary cross-sections taken substantially along the lines 44 and 5-5, respectively, of FIG. 3.

FIG. 6 is a perspective view of part of the Genevatype drive unit.

FIGS. 7 and 8 are enlarged views of parts illustrated in FIG. 3 and showing successive steps in the operation of the-drive unit.

FIG. 9 is a view similar to FIG. 7 and showing still another step in the operation of the drive unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT For purposes of illustration, the invention is shown in the drawings as incorporated in an engine synchronizing system of the same general type as disclosed in the aforementioned patent to which reference may be had for a more detailed explanation of the overall system. The purpose of such a system is to keep two engines (not shown), such as marine or aircraft engines, operating at the same speed in order to avoid objectionable beats, throbbing or vibration. In carrying out this end, it has been the practice to designate one engine to be the master and to make the other a slave which is automatically controlled to operate at the same speed as the master even though their throttle lever settings or their loads are not identical.

Now referring specifically to FIG. 1, hand throttle levers l5 and 16 are coupled by flexible wire cables 17 and 18 to the

speed setting arms

19 and 20 of master and

slave governors

21 and 22 for the two respective engines. Manual adjustment of the levers l5 and 16 either individually or in unison severs to shift the

arms

19 and 20 in directions to increase or decrease the speeds of the engines, for example, by opening or closing the fuel throttles (not shown).

The position of the speed-controlling arm 20 for the slave'engine can be adjusted, and the fuel input to the slave engine changed, independently of the setting of the slave control lever 16. Herein, this is accomplished by a signal-responsive electric motor 25 enclosed in a housing 26 (FIG. 3) and serving to move the arm 20 in small steps in either a speed increasing or speed decreasing direction. As here shown, a flexible cable 27 (FIG. 1) is connected to one end of the drive shaft 29 of the motor and extends to a lengthwise expandable and contractible link 30 interposed between two portions 18a and 18b of the cable 18. The link includes a body 31 joined to the cable portion 18a and supporting a movable output element 33 to which the cable portion 18b is connected. In order to change the effective length of the link 30, the movable object element 33 is mounted in a threaded bushing 34 which is received in a threaded bore 35 in the body 31, the output element and the bushing being permitted to rotate relative to one another and being held together by a retaining ring 36. For the purpose of rotating the threaded bushing 34, a gear 37 is formed integrally thereon and cooperates with a drive pinion 39 connected to the flexible cable 27 extending to the motor 25.

One exemplary motor 25 which is suitable for use in the present instance is a bi-directional stepping motor which is commercially ayailable under the trade name Ledex. The details of such a stepping motor are familiar to those skilled in the art and it-will suffice here to observe that the motor includes forward and reverse windings FW and RW (FIG. 2) which, in response to each voltage or current pulse applied thereto, cause the drive shaft 29 to step in a forward or reverse direction. Simply for purposes of discussion, it will be assumed that pulses applied to the forward winding FW cause the motor to step the shaft 29 in a direction to contract the output element 33 into the body 31, thus causing the cable portion 18b to swing the arm 20 in a direction to increase the speed of the slave engine. Conversely, pulses applied to the motor winding RW cause the link 30 to expand lengthwise so that the bias spring associated with the arm 20 causes the latter to move in a speed decreasing direction. Accordingly, the motor windings FW and RW may conveniently be called the slave speed increasing and decreasing windings, respectively.

For the purpose pf. applying pulses to the motor 25, electrical pulse generators PG-M and PG-S (FIG. 2) produce first and second trains of recurring pulses having frequencies respectively proportional to the speeds of the master and slave engines. Such pulses are applied as input signals to a synchronizing unit 40 and, if the slave engine is below the speed of the master, pulses appear on the output terminal 41 of the synchronizing unit and are routed to the increase speed winding FW of the motor to step the latter in a direction to contract the link and increase the throttle setting of the slave engine until the speed of the latter matches the speed of the master engine. If the slave engine is overspeeding, pulses appear on the output terminal 42 of the synchronizing unit and are applied to the decrease speed winding RW of the motor to reduce the speed of the slave unit. Exemplary pulse generators and synchronizing units are disclosed in the above-mentioned patent and in Leeson US. Pat. No. 3,367,1 l0 and thus the details of the construction and operation of these components need not be discussed here.

The synchronizing unit may be selectively placed in or taken out of operation by actuating a manually operable switch 45 (FIG. 2) to close or open ganged

switch contacts

46 and 47 which connect the output terminals 41 and 42 of the synchronizing unit with the motor windings FW and RW, respectively. As an incident to actuating the switch to take the synchronizing unit out of operation, a third set of ganged contacts 49 is closed to place the motor 25 under the direction of auxiliary control apparatus 50 which serves to step the motor shaft 29 either forwardly or rearwardly until the output element 33 0f the link 30 is centered within its range of adjustment. In this way, the adjustable link 30 is placed in midposition each time the synchronizing unit 40 is taken out of operation thereby to insure that an adequate range of adjustment is available in either direction when the unit is next put back into operation.

When the motor 25 is under the control of the auxiliary centering apparatus 50, pulses are routed directly from the master pulse generator PG-M to either the winding FW or the winding RW by way of the switch contacts 49 and first and second circuits 53 and 54 (FIG. 2) connecting with the windings FW and RW, respectively. If the link 30 is extended beyond its centered position, the contacts 55 of a switch LS-l is the circuit 53 are closed and cause signal pulses to be applied to the winding FW until the link has been contracted to its centered position, at which time the switch opens to de-energize the motor. Conversely, the contacts 56 of a switch LS-Z in the circuit 54 are closed as long as the link is contrasted past its centered position, and thus cause signal pulses to be applied to the winding RW until the link expands to mid-position. The switch LS-2 then opens and de-energizes the motor 25 so that the link remains in its centered position until the synchronizing unit 40 is again activated.

The present invention contemplates the provision of new and improved auxiliary control apparatus 50 which is comparatively compact and may be installed within the relatively small motor housing 26 and which, at the same time, may be easily and rapidly assembled in operative relationship with the motor 25 and the switches LS-l and LS-2 so as to open and close the latter at the proper times. In general, the control apparatus 50 includes a Geneva-type drive unit 60 (FIG. 3) with a driving wheel 61 adapted to be rotated by the motor output shaft 29 and with a driven wheel 63 adapted to be advanced intermittently in response to rotation of the driving wheel. Rotatable with the driven wheel 63 are cams 64 and 65 (FIGS. 2 and 6) which actuate the switches LS-l and LS2, respectively, in such a manner as to cause both switches to be open if the link 30 is in its centered position but to cause the appropriate one of the switches to be closed if the link is out of its centered position and stepping of the motor is required to restore the link to such position.

More specifically, the driving wheel 61 of the Geneva-type drive unit 60 is mounted on the end of the motor drive shaft 29 opposite the end to which the flexible cable 27 is connected and, as shown in FIGS. 1 and 3, an eccentric drive pin 66 projects axially from the outer side of the driving wheel and is rigidly connected thereto in radially offset relation with the shaft. The driving wheel 61 is telescoped onto the shaft 29, which preferably is formed with two oppositely disposed flat sides to prevent relative rotation between the shaft and the wheel.

The driven wheel 63 herein is molded of plastic and is formed integrally with an axially extending tubular hug 67 (FIGS. 5 and 6). The latter is telescoped rotatably over a bearing stud 69 (FIG. 5) whose inner end is staked within a counterbored hole 70 formed through a supporting plate 71, the bearing stud extending parallel to and being located below the motor shaft 29. Two screws 73 (FIG. 3) secure the supporting plate in face-to-face relation with a mounting bracket 74 connected to'the end of the motor 25 and serving to support the motor within the housing 26.

As shown in FIGS. 3 and 6, several radially extending and angularly spaced slots 75 are formed around the driven wheel 63 and open out of the periphery thereof. As the driving wheel 61 is stepped by the motor 25 and the drive pin 66 moved along the lower arc of its path of movement, the drive pin enters one of the slots 75 and, upon continued stepping of the driving wheel, bears against one edge of the slot to rotate the driven wheel 63 in a direction opposite to that of the driving wheel (see FIG. 7). After the driven wheel 63 has been indexed through a distance equal to the angular spacing between adjacent slots (i.e., one step), the pin leaves the slot and the driven wheel dwells idly and is held in a stationary position while the pin moves through the upper arc of its path and is stepped around into registry with the next slot (see FIG. 8).

In carrying out an important aspect of the invention, a lobed disc (FIGS. 6 and 7) coacts with the driving wheel 61 to hold the driven wheel 63 in a stationary position during the time the pin 66 is being stepped from slot-to-slot, the disc preferably being molded integrally with the inner side of the driven wheel and being rotatable with the latter on the bearing 69. As shown in FIG. 7, the disc 80 is significantly smaller in diameter than the driven wheel 63 so that the periphery of the disc is located radially inwardly of the periphery of the driven wheel and is positioned just inwardly of the closed ends of the slots 75. The disc is disposed in the plane of rotation of the driving wheel 61 and its outer periphery is formed with a series of angularly spaced pockets 83 (FIG. 7) separated by outwardly protruding lobes 84 which are alined angularly with the slots 75.

When the pin 66 is being stepped from slot-to-slot, the periphery of the driving wheel 61 is received in one of the pockets 83 in the disc 80 and is engaged by the two lobes 84 which define the ends of the pocket (see FIGS. 8 and 9). As a result, the disc 80 and the driving wheel 61 coact to hold the driven wheel 63 stationary so that the next slot 75 will remain in the proper angular position to receive the pin 66. When the pin subsequently enters the slot, rotation of the disc 80 and the driven wheel 63 is permitted by virtue of a relief or cutout 86 (FIGS. 3 and 7) formed in and extending chordwise across the outer side of the driving wheel 61 and opening out of the periphery thereof. The pin 66 is centered within the cut-out 86, and the latter is of sufficient axial depth that the bottom thereof is spaced inwardly from the inner face of the disc 80 (see FIG. 4). Accordingly, the cut-out 86 clears the disc 80 as shown in FIG. 7 from the time the pin 66 enters the slot 75 until the time the pin leaves the slot and thus the'driving wheel 61 disengages the disc and permits free rotation of the driven wheel 63 while the latter is being advanced by the pin.

Because the driven wheel 63 is held in its indexed position by the lobed disc 80 located on the inner side of the wheel, it is possible to space the driven wheel axially outwardly of the driving wheel 61 (see FIGS. 4 and 5) and to advantageously position the driven wheel such that it radially overlaps the driving wheel. In other words, the lobed disc makes it possible to position the rotational axes of the

wheels

61 and 63 much closer together than is otherwise the case with wheels of a comparable diameter in which the'periphery of the driving wheel directly engages the periphery of the driven wheel to hold the latter stationary. Accordingly, the wheels can be fitted compactly into a comparatively small space within the motor housing 26. In addition, the disc 80 avoids the need for forming pockets in the circular periphery of the driven wheel and, as shown in FIG. 7, the corners 87 between the edges of the slots 75 and the periphery of the driven wheel may be gradually rounded as opposed to being sharp as in the case of the corresponding corners of a conventional Geneva wheel. The use of rounded corners is made possible with the present Geneva-type unit 60 because there is less criticality involved in the timed relationship between the pin 66 entering and leaving the slots 75 on the one hand and the driving wheel 61 releasing and engaging the lobed disc 80 on the other hand.

i The cams 64 and 65 (FIG. 6) for actuating the switches LS-l and LS-2 are molded integrally with the hub 67 and thus are rotated step-by-step in unison with the driven wheel 63. Each cam includes a fall surface extending approximately half-way around the hub and joining with a rise surface which extends the remaining distance around the hub. One adjacent pair of edges and 91 of the two rise surfaces are alined angularly with each other while the opposite edge 93 of one rise surface is spaced angularly from the corresponding edge 94 of the other rise surface by about 20 degrees as shown in FIGS. 6 and 9.

In this instance, the two switches LS-l and LS-2 are riveted in side-by-side relation on the mounting plate 71 (see FIGS. 3 and 4) and include pivoted

actuators

101 and 102 positioned to rise along the cams 64 and 65, respectively, and spring-biased outwardly against the cams. The switch LS-1 herein is wired such that its contacts 55 are open when its actuator 101 is depressed by the rise surface of the cam 64 and are closed when the actuator is extended and is riding on the fall surface of the cam. Conversely, the contacts 56 of the switch LS-2 are closed when the actuator 102 is depressed by the rise surface of the cam 65 and are opened when the fall surface allows the actuator to extend.

When the link 30 is centered, the driven wheel 63 is angularly disposed in a home position in which the

edges

93 and 94 of the earns 64 and 65 are positioned adjacent the

actuators

101 and 102 of the limit switches LS-l and LS-2. In this position, the rise surface of the cam 64 engages the actuator 101 of the switch LS-l while the fall surface of the cam 65 engages the actuator 102 of the switch LS-2. As a result, the contacts 55 and 56 of both switches are open and thus no pulses can be applied through the circuits 53 and 54 to the windings FW and RW of the motor 25. When the synchronizing unit 40 is in operation, pulses are applied to the motor via the output terminals 41 and 42 and the motor is stepped to expand or contract the link 30 and to advance the driven wheel 63 out of its home position. If the link is expanded, the driven wheel is rotated counterclockwise and, as a result, the fall surface of the cam 64 causes the switch contacts 55 to close while the fall surface of the cam 65 continues to keep the switch contacts 56 open. If the synchronizing unit 40 then is taken out of operation by actuating the switch 45, pulses are applied from the output terminals of the pulse generator PG-M to the winding FW via the switch contacts 49 and 55. The motor 25 thus is stepped to rotate the driven wheel 63 clockwise and to contract the link 30. Such stepping continues until the link reaches its centered position and the driven wheel reaches its home position, at which time the rise surface of the cam 64 rides past the switch operator 101 to open the contacts 55 and stop the motor.

When the link 30 is contracted beyond its centered position during operation of the synchronizing unit 40, the driven wheel 63 is rotated clockwise from its home position so that the rise surface of the cam 65 causes the switch contacts 56 to close while the rise surface of the cam 64 maintains the switch contacts 55 open. If the synchronizing unit then is taken out of operation, pulses are applied to the motor winding RW through the closed contacts 49 and 56 to cause the motor 25 to expand the link and step the driven wheel 63 counterclockwise. When the link is centered and the driving wheel reaches its home position, the fall surface of the cam 65 opens the contacts 56 to de-energize the motor.

Accordingly, it will be apparent from the foregoing that the adjusting link 30 is centered automatically by the auxiliary control apparatus 50 each time the synchronizing unit 40 is taken out of operation. While being comparatively simplein construction, the control apparatus 50 is very easy to assemble. Assembly is effected by slipping the driven wheel 63 over the bearing 69, by staking the latter in the hole 70 in the mounting plate 71 and by riveting the switches LS-l and LS-2 to the plate. Because the positional relationship between the switches and the earns 64 and 65 on the driven wheel is established by the mounting plate 71 itself, it is not necessary to adjust the switches relative to the cams prior to anchoring the switches in place. That is to say, the proper positional relationship between the cams and the switches is established automatically as an incident to attaching the switches to the plate in a predetermined location established by the rivetholes in the plate.

After the switches LS-1 and LS-2 and the driven wheel 63 have been attached to the mounting plate 71, the latter is slipped just over the extreme outer end of the shaft 29 and the driving wheel 61 is placed between the plate and the driven wheel 63. The driving wheel is turned to fit over the flat-sided shaft 29 and to place the drive pin 66 in one of the slots 75 and then the entire assembly is moved toward the motor 25 and secured to the bracket 74 by the screws 73. In the finally assembled position, the driving wheel 61 is captivated axially between the driven wheel 63 and the mounting plate 71 and thus need not be secured to the shaft 29.

Provision is made for stopping further stepping of the motor 25 when the link 30 approaches the limits of its expanded and contracted positions. Herein, this is achieved by omitting one slot from the equally spaced sequence of slots 75 in the driven wheel 63 so as to form the latter with one large lobe 105 (FIG. 7) whose arcuate periphery extends through a distance which is greater than the diameter of the circular path followed by the drive pin 66. Thus, upon leaving either of the slots 75 adjacent the lobe 105 and stepping back around to the lobe, the drive pin 66 engages the arcuate edge of the lobe as shown in FIG. 9 and prevents further stepping of the motor. When this occurs, an indicator light (not shown) may be energized to warn the pilot or the operator that the link 30 has approached one of its limits and that it is necessary to manually adjust the speed of the slave engine with the throttle lever 16in order to bring the synchronizing unit 40 back into effective operation. When the pin engages the lobe 105, the

switch actuators

101 and 102 both are located adjacent the angularly

alined edges

90 and 91 of the cams 64 and 65, and both are riding on either the rise surfaces of the cams or on the fall surfaces. It should be noted that the driven wheel stops before the

edges

90 and 91 pass across the switch actuators and thus these edges never affect the condition of the switches LS-l and 1.8-2.

Advantageously, the driven wheel 63 may be adjusted angularly about the axis of the driving wheel 61 to enable the driven wheel to be placed in such a position that the driving pin 66 will be just at the end of its stepping stroke when the pin stops against the edge of the lobe 105. For this purpose, the screws 73 for attaching the mounting plate 71 to the bracket 74 extend through elongated slots 106 (FIG. 3) formed in the mounting plate and curved arcuately about the axis of the shaft 29.

Prior to tightening the screws, the mounting plate may be adjusted angularly on the bracket so as to adjust the driven wheel 63 bodily and angularly about the shaft into a position to place the edge of the lobe against the pin 66 when the latter is stopped. Thus, when the pin subsequently engages the lobe during operation of the synchronizing unit 40, the motor 25 will be at the end of its stepping stroke and the pin will stop dead against the lobe. This reduces the tendency of the pin to bounce upwardly and downwardly on the lobe when the motor attempts to step further and also reduces bending stresses tending to deflect the pin since the motor is stalled at the end of its stroke and is not capable of developing as much torque to press the pin downwardly against the lobe. Accordingly, the service life of the pin is increased.

1 claim as my invention:

1. Apparatus including an electric motor having first and second control circuits and having an output shaft adapted to be rotated in a first direction in response to a signal applied through said first circuit and in a second direction in response to a signal applied through said second circuit, and switch means connected in said circuits and adapted to be conditioned to complete either said first circuit or said second circuit or to break both of said circuits, the improvement in said apparatus comprising, a driving wheel rotatable with said shaft, a driven wheel rotatable about an axis paralleling said shaft and having a series of generally radially extending slots spaced angularly around its outer periphery, said driven wheel being offset axially from said driving wheel and overlapping the driving wheel, an accentric drive pin projecting from said driving wheel and positioned to enter successive ones of said slots during rotation of said driving wheel thereby to index said driven wheel through successive steps, a disc rotatable in unison with said driven wheel about said axis and having an outer periphery spaced radially inwardly from the outer periphery of said driven wheel and disposed in the plane of rotation of said driving wheel, a series of pockets spaced angularly around the outer periphery of said disc and adapted to receive the outer periphery of said driving wheel to hold said driven wheel stationary when said pin is disposed out of said slots, and means rotatable with said driven wheel for conditioning said switch means to complete one of said circuits when said driven wheel is located in one angular direction past a home position, to complete the other of said circuits when said driven wheel is located in the opposite angular direction past said home position and to break both of said circuits when said driven wheel is in said home position.

2. Apparatus including an electric motor having first and second control circuits and having an output shaft adapted to be rotated in a first direction in response to a signal applied through said first circuit and in a second direction in response to a signal applied through said second circuit, and first and second switches connected in said first and second circuits, respectively, and operable when opened to interrupt the signal through the respective circuits, the improvement in said apparatus comprising, a driving wheel rotatable with said shaft, a driven wheel rotatable about an axis paralleling said shaft and having a series of generally radially extending slots spaced angularly around its outer periphery, said driven wheel being offset axially from said driving wheel and overlapping the driving wheel, an eccentric drive pin projecting axially from one side of said driving wheel and positioned to enter successive ones of said slots during rotation of the driving wheel thereby to index said driven wheel intermittently through successive steps, a disc rotatable in unison with said driven wheel about said axis and having I an outer periphery spaced radially inwardly from the outer periphery of said driven wheel and disposed in the plane of rotation of said driving wheel, a series of pockets spaced angularly around the outer periphery of said disc and adapted to receive the outer periphery of said driving wheel to hold said driven wheel stationary when said pin is disposed out of said slots, and means rotatable with said driven wheel for opening one of said switches when said driven wheel is rotated into a home position from one direction and for opening the other of said switches when said driven wheel is rotated into said home position from the opposite direction.

3. Apparatus as defined in claim 2 further including a plate, means on said plate supporting said driven wheel for rotation about said axis, and means connecting said plate adjustably to said motor to permit said driven wheel to be adjusted to different angular positions around said shaft.

4. Apparatus as defined in claim 3 in which said switches are carried on and adjustable with said plate and include spring-loaded actuators disposed adjacent said driven wheel, said means for opening said switches comprising first and second cams rotatable with said driven wheel and engageable with the actuators of said first and second switches, respectively.

5. Apparatus as defined in claim 4 in which each of said cams includes a rise surface and a fall surface, the beginning of the rise surface of one of the cams being spaced angularly from the beginning of the rise surface of the other cam.

6. Apparatus as defined in claim 4 in which said driven wheel, said disc and said cams are formed integrally with each other.

Claims

2. Apparatus including an electric motor having first and second control circuits and having an output shaft adapted to be rotated in a first direction in response to a signal applied through said first circuit and in a second direction in response to a signal applied thRough said second circuit, and first and second switches connected in said first and second circuits, respectively, and operable when opened to interrupt the signal through the respective circuits, the improvement in said apparatus comprising, a driving wheel rotatable with said shaft, a driven wheel rotatable about an axis paralleling said shaft and having a series of generally radially extending slots spaced angularly around its outer periphery, said driven wheel being offset axially from said driving wheel and overlapping the driving wheel, an eccentric drive pin projecting axially from one side of said driving wheel and positioned to enter successive ones of said slots during rotation of the driving wheel thereby to index said driven wheel intermittently through successive steps, a disc rotatable in unison with said driven wheel about said axis and having an outer periphery spaced radially inwardly from the outer periphery of said driven wheel and disposed in the plane of rotation of said driving wheel, a series of pockets spaced angularly around the outer periphery of said disc and adapted to receive the outer periphery of said driving wheel to hold said driven wheel stationary when said pin is disposed out of said slots, and means rotatable with said driven wheel for opening one of said switches when said driven wheel is rotated into a home position from one direction and for opening the other of said switches when said driven wheel is rotated into said home position from the opposite direction.