US3868861A

US3868861A - Stepping motor

Info

Publication number: US3868861A
Application number: US433102A
Authority: US
Inventors: Harold W Scholin
Original assignee: SCHOLIN IND Inc
Current assignee: SCHOLIN IND Inc
Priority date: 1974-01-14
Filing date: 1974-01-14
Publication date: 1975-03-04
Anticipated expiration: 1992-03-04
Also published as: JPS50101815A

Abstract

A stepping motor is disclosed for use in imparting to a rotatable member an intermittent step-by-step rotating motion by means of a linearly reciprocating driving member. The driven, rotatable member has a shaft which carries a ratchet wheel and is advanced intermittently by two oppositely positioned pawls, mounted on a reciprocating driving member so that both movements of the driver will rotate the driven member another step. Means are also provided for preventing undesirable rotation of the ratchet, not only in the drive direction thereof, but also in the reverse direction, and may include a stop block cooperating with each pawl or a second ratchet wheel cooperating with other stop members. Furthermore, novel means for reciprocating the driver which may include electrical, pneumatic or mechanical means or a combination thereof is also disclosed.

Description

United States Patent [191 Scholin 1 Mar. 4, 1975 STEPPING MOTOR [75] Inventor: Harold W. Scholin, Park Ridge, 111.

[73] Assignee: Scholin Industries, llnc., Chicago, Ill.

[22] Filed: Jan. 14, 1974 [21 App]. No: 433,102

Primary E.raminer-Samuel Scott Assistant Examiner-F. D. Shoemaker Attorney, Agent, or Firm-Root & OKeeffe 57 ABSTRACT A stepping motor is disclosed for use in imparting to a rotatable member an intermittent step-by-step rotating motion by means of a linearly reciprocating driving member. The driven, rotatable member has a shaft which carries a ratchet wheel and is advanced intermittently by two oppositely positioned pawls. mounted on a reciprocating driving member so that both move ments of the driver will rotate the driven member another step. Means are also provided for preventing undesirable rotation of the ratchet, not only in the drive direction thereof, but also in the reverse direction, and may include a stop block cooperating with each pawl,

or a second ratchet wheel cooperating with other stop members. Furthermore, novel means for reciprocating the driver which may include electrical, pneumatic or mechanical means or a combination thereof is also disclosed.

24 Claims, 12 Drawing Figures PATENTED MAR 4 5 SHEET 3 0F 6 PATENTEUHAR 4W5 I sum 5 er a q368,861

STEPPING MOTOR BACKGROUND OF THE INVENTION Stepping motors have been known heretofore, wherein a reciprocating pawl engages a ratchet wheel to advance a rotary member intermittently which is coupled thereto. Also, means have been provided in the past to restrain the rotation of the ratchet wheel in both the drive and reverse directions, such as, for example, as disclosed in the Fredell US. Pat. No. 3,501,968, issued Mar. 24, 1970. Such devices, however, have limitations, such as the speed or frequency of the stepping action. The present device involves a novel design which enables the frequency of the stepping action to be increased by at least double that which was previously known.

When the frequency of stepping is thus increased, however, other problems arise in connection with the means for restraining movement of the wheel in both directions and novel means have been provided herein to effectively restrain unwanted movement of the ratchet wheel, even at very high speeds.

BRIEF SUMMARY OF THE INVENTION The invention is directed to a novel stepping motor for rapidly rotating, intermittently, a shaft for the performance of some additional function. It involves more particularly, the use of a driving member reciprocating a linear path on which is mounted two pawls in opposing relation. A ratchet wheel mounted on the driven shaft is disposed in operative relation to both pawls so that the wheel and shaft are advanced one step for each direction of reciprocation of the driving member.

In one form of the invention, a stop block is mounted adjacent each pawl on the supporting frame of the driving member which wedges its associated pawl at the end of the driving stroke thereof in such a way as to lock the ratchet wheel against movement in both directions.

This function may also be accomplished in another form of the invention by providing two ratchet wheels on the driven shaft having teeth disposed in opposite directions, one of which is driven by the pawls and the other of which cooperates with stop members mounted on the driving member to restrain movement of the driven member in either direction.

A further feature of the invention is the novel means for reciprocating the driving member. Although any known means may be used for this purpose, such as a crank or eccentric, I prefer .to use a combination of electrical and pneumatic forces wherein an electrically operated spool valveis used to direct air to one or the other of two cylinders which moves a piston member, which, in turn, controls the operation of the driving member.

As may become more apparent, as the description proceeds, in one form ofthis latter feature, such piston 472,489 filed May 22, 1974, there may be conditions wherein the natural frictional forces of the drum may be overcome by other forces associated with the drum and drive the assembly ahead of the indexing pawl. To overcome this, I have provided an additional feature which includes a deceleration plunger assembly operable to control the ratchet assembly and index drum to prevent the drum from accelerating away from the driving pawl.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational view of one form of present invention with the reciprocating driving member in its lower position, but showing the driving means to reciprocate the driving member in vertical section.

FIG. 2 is a side elevational view of the assembly, shown in FIG. 1.

FIG. 3 is a view similar to FIG. 1 but illustrating the reciprocating driving member in an intermediate positron.

FIG. 4 is a view similar to FIGS. 1 and 3 but showing the driving member in its uppermost position.

FIG. 5 is a somewhat diagrammatic view of the device of FIG. 1 on a smaller scale, showing a modified form of the means for reciprocating the driving member.

FIG. 6 is a view similar to FIG. 1 but showing a still further modified form of the means for reciprocating the driving member.

FIG. 7 is an elevational view of the reciprocating driving member in its lowest position, illustrating a modified arrangement of restraining means for preventing unwanted rotation of the driven member in both directions.

FIG. 8 is a view similar to FIG. 7 but showing the re ciprocating driving member in the uppermost position thereof.

FIG. 9 is a vertical sectional view taken substantially along the plane of line 9--9 of FIG. 7.

FIG. 10 is an elevational view similar to FIG. 7 with parts broken away and shown in section and illustrating additional means for restraining unwanted rotation of the driven member in a situation where external forces tend to overcome the frictional forces of the driven member and move it an additional amount.

FIG. 11 is a fragmentary vertical sectional view, taken substantially along the plane of line 11-11 of FIG. 10, and

FIG. 12 is a fragmentary, vertical sectional view, taken substantially along the plane of line l212 of FIG. 11.

DETAILED DESCRIPTION OF THE INVENTION Referring now, more particularly, to FIGS. 1 through 4, there will be seen a frame, generally indicated by the numeral 1, which consists of the two

side members

2 and 3, a top crossbar 4, and a bottom crossbar 5. This frame is mounted on a supporting plate 6.

A driving member 7 is mounted within the frame I for reciprocating sliding movement, as will appear presently. This driving member is provided with an opening 8 in substantially the center thereof and has a lower extension 9, extending downwardly from one side thereof on which is pivotally mounted the pawl 10 by means of the pivot pin 11. A tension spring 12 is secured at one end thereof to the driving member 7 by means of the pin 13 and at the other end thereof to a pin 14 on the pawl. This spring, then, normally urges the pawl toward the left, as viewed in the various figures.

At the upper part of the driving member, there is provided an upper extension at one side thereof indicated at 15. A second pawl is pivotally mounted on this upper extension by means of the pivot pin 17, and this pawl is normally urged toward the right, as viewed in the various figures, by means of a tension spring 18 anchored at one end thereof to the pin 19 on the driving member, and at the other end thereof to a pin 20, mounted on the pawl.

A ratchet wheel 21 has a hub portion 22 thereon which receives the shaft 23 and is coupled thereto by means of the key 24. The ratchet wheel 21 and the teeth 25 thereon are arranged to be in the same plane with the two pawls l and 16, so that, on reciprocation of the driving member 7, the two pawls will drive the ratchet wheel and the shaft 23 to which it is coupled. It is apparent in viewing these various figures that when the driving member moves upwardly, the pawl will advance the ratchet wheel one step because the upper end thereof contacts the teeth of the wheel and moves it from the position shown in FIG. 1 through the position shown in FIG. 3 and to the position thereof shown in FIG. 4.

During this movement, the upper pawl 16 will be carried upwardly with the driving member from the posi tion shown in FIG. 1 through the position thereof shown in FIG. 3, and to its position shown in FIG. 4. During downward movement of the driving member, the reverse action takes place, wherein the upper pawl 16 will move downwardly and will move the ratchet wheel and the shaft 23 another step in a counterclockwise direction, as viewed in the various figures. The opposed sides of the driving member 7 are received in guideways provided on the inner surfaces of the two

side members

2 and 3 of the frame 1. Thus, the driving member will be guided in its reciprocating movement.

It will be evident that any suitable device can be con nected to the shaft 23 to be driven thereby in a step-bystep fashion. As mentioned hereinabove, the particular device which has been designed for use in connection with the present invention is more fully disclosed and claimed in my co-pending application above referred IO.

In any event, it is important in any indexing device of this nature that means be provided to prevent any unwanted motion of the ratchet wheel and shaft, such as by overrunning in the driving direction or rotating in the reverse direction after completing an indexing step.

One of the means which has been found useful for this purpose includes a stop block or wedge member associated with each of the pawls. As shown herein, there is a stop block 26 mounted on the frame for cooperation with the pawl 10, and another stop block 27 on the opposite side of the frame which cooperates with the pawl 16. The action of each of these blocks is such that the pawl which is driving the ratchet wheel and the edge of the block, after completion of the indexing stroke. as may be seen in FIG. 4, thereby preventing rotation of the ratchet wheel in either direction.

As may be seen in FIG. 1, the driving member 7 is in its lowermost position where the upper pawl 16 has just completed an indexing advance of the ratchet wheel. In this position of the parts, the upper end of the lower pawl 10 is spaced downwardly from the tooth on the wheel which it will engage to advance the wheel. FIG.

3 shows the driving member after it has moved up wardly a short distance to the point where the upper end of the pawl 10 just contacts the next tooth on the wheel. It will be noted here that the outermost end of each of the pawls l0 and 16 is provided with an inclined 10a and 16a, respectively, which forms an acute angle with the inner side of the pawl and an obtuse angle with the outer side of the pawl, thereby forming the corners 10b and 161; respectively.

The angle of this inclined surface is such that, when a pawl reaches the tooth on the ratchet wheel to begin the next indexing movement, the corner which forms the obtuse angle on the opposite pawl is at a position where it just clears the rounded corner of its associated stop block. For example, in FIG. 3, it will be noted that the pawl 10 has moved upwardly to the point where it has just contacted a tooth on the ratchet wheel. In this position, the outer corner 16b of the pawl 16 is in a position where it just clears the corner of the stop block 27. This is necessary because when the ratchet wheel begins to rotate, the pawl opposite the driving pawl will be urged outwardly and it must be free to do this. For example, if the outer side ofthe pawl is of such length that it does not clear the stop block at the moment the driving pawl begins to rotate the ratchet wheel, then such rotation cannot take place because the opposite pawl would still be locked or wedged between the ratchel wheel and the stop block. On the other hand,

if such outer side of the pawl is too short, it will not reach the stop block, as soon as it should when it is driving the ratchet wheel and, therefore, will not become locked to prevent overrunning of the ratchet wheel in the driving direction thereof.

If desired, as an additional precautionary measure, a supplemental stop member 28 may be pivotally mounted on the frame, at a suitable location, by means of the pivot pin 29. A tension spring 30 urges the outer end 31 of such member against the toothed surface of the ratchet, so that, when the ratchet is being advanced, the stop member will be cammed out of the way, but as soon as a tooth has passed the end of the member, it will return to be positioned in the path of such tooth and prevent rotation of the ratchet in the opposite direction.

The corners of the stop blocks 26 and 27 are rounded, as mentioned above, and this is an important feature where two pawls are used, as disclosed herein, and this is where the proper angle of the inclined ends and 16a thereon comes into play, as will presently be seen.

It is possible that, in the use of compressed air, the air pressure may drop, or may be turned off, or the spool in the control valve might shift arbitrarily. Any of these things could happen at any point in the cycle. If, for example, the driving member stops or reverses itself before the driving pawl has reached the tooth on the ratchet wheel, then there is no problem. On the other hand, if the driving pawl has moved far enough in the driving direction to begin rotation of the ratchet wheel, but is reversed before the other pawl has reached the next tooth, then the device is out of phase and the face of the ratchet must be repositioned. In this event, the other pawl, which was supposed to be leaving the ratchet wheel, moves in the reverse direction and the inclined surface on the end thereof will cam the pawl on the rounded corner of the stop block against the ratchet wheel, which will thereby reposition the wheel by rotating it a slight amount in the reverse direction thereof, and the device will not jam.

In the preferred form of the invention, a novel electro-pneumatic drive system for reciprocating the driving member 7 is provided. Although other drive systems may be used for this purpose, depending upon the type of member being indexed, and its function, the present system has been found in actual practice to perform rapidly and effectively.

Referring again to FIGS. 1 through 4 of the drawings, the preferred embodiment of this electro-pneumatic drive system includes an air cylinder and piston at each end of the frame having a member movable with the piston and against the driving member, whereby upward movement of the lower piston will drive the driving member upwardly, and downward movement of the upper piston will drive the driving member downwardly.

Electrical control means operable in response to movement of the driving member 7 operates an air valve to direct air to one or the other of the air cylinders.

In the drawings, the lower air cylinder is indicated by the numeral 32, and is mounted on the lower cross member 5. It is provided with an air inlet 33 in the bottom thereof, to which may be connected an air conduit (not shown). The other end of such conduit is connected to a source of air under pressure.

A piston 34, having a sealing ring 35 is snugly received within the cylinder 32 and is reciprocable therein. The piston 34 extends upwardly through a suitable opening in the lower cross member 5, and is provided with an axially extending bore 36. The bottom of the bore 36 is preferably tapered, as shown at 37 to receive the tapered lower end ofa pin 38. The sides of the taper on the lower end of the pin 38 preferably form a smaller angle than the sides of the taper 37 at the bottom of the bore 36, and the diameter of the pin 38 is less than the diameter of the bore 36, thereby to allow a certain amount of play or freedom of movement between the pin and the bore, which results in a floating pm.

The upper end of the pin 38 protrudes beyond the upper end of the piston 34, and is received within a recess in the bottom of the driving member 7, the inner end of which is tapered. The upper end of the pin 38 is likewise tapered and the sides of the taper form a smaller angle than do the tapered sides ofthe inner end of the recess 39, thereby to allow freedom of movement between the pin 38 and said recess.

An upper air cylinder 40 is secured to the upper cross member 4 of the frame, and is provided with a similar piston 41, reciprocable therein. The upper end of the cylinder 40 has an air inlet 42 to which is connected an air conduit (not shown). The other end of such conduit is likewise connected to the source of compressed air, so that when air under pressure is directed to the cylinder 40, it will drive the piston 41 downwardly.

The piston 41 is likewise provided with an axially extending bore 43, which receives the pin 44, having a smaller diameter than that of the bore. The upper or inner end of the bore 43 is likewise tapered, as at 45, to receive the tapered end 46 of the pin 44.

The outer or lower end of the pin 44 is similarly tapered, and is received within a recess in the top of the driving member 7, the sides at the bottom thereof being tapered, as at 47. The tapered ends of the pin 44 have a similar relationship to the tapered bottom of the bore and bottom of the recess to that described above, thereby to allow the pin to float. It will be evident from the foregoing, therefore, that when air under pressure is admitted to the opening 33 in the bottom of cylinder 32, the piston 34 thereof will move upwardly carrying with it the floating pin 38. The upper end of this pin, being received in a recess in the bottom of the driving member 7, will thereupon move the driving member in an upward direction. Prior to this movement of the driving member, it had been driven downwardly by the compressed air admitted through the inlet 42 of the cylinder 40. The valving is such that when air is admitted into the cylinder 32, the air pressure in the cylinder 40 above the piston 41 will be relieved through the opening 42, to allow the driving member to move upwardly.

When the driving member has reached its uppermost position and the ratchet wheel, together with the shaft on which it is mounted, has been indexed through one complete step, the cycle will be reversed, by admitting compressed air to cylinder 40 through the inlet 42 to drive the driving member downwardly, whereupon the air pressure in the cylinder 32 will be relieved through the opening 33 therein. This cycling of the motor and stepping of the ratchet wheel will continue under normal operation, very rapidly, and the construction is such that the reciprocation may take place at a very high speed.

As a matter of fact, it has been found very desirable, although not absolutely necessary, that some means be provided to buffer the movement of the driving member when it is being driven at relatively high speeds. While any type ofa yieldable member may be provided for this purpose, I have shown herein such a high speed buffer arrangement, consisting of a pin 48 at one end of the device, around which is located a coiled compression spring 49, one end of which bears against the upper surface of the driving member 7 and the other end of which bears against the underside of the upper cross member 4.

There is a similar arrangement at the bottom of the driving member, wherein there is: provided a pin 50, around which is located the coiled compression spring 51, the upper end of which bears against the lower end of the driving member, and the lower end of which bears against the lower cross member 5. When the motor is being operated at very high speeds, these

springs

49 and 51 will act as buffers and absorb any shocks due to the rapid reciprocating movement of the driving member.

As mentioned hereinabove, the compressed air is directed, alternately, to the upper and lower cylinders by means of a conventional 4 way spool valve (not shown). This valve may be controlled either pneumatically or electrically, but it has been determined that perhaps the more economical arrangement, and just as practical, is to control this valve electrically. As also mentioned above, the operation of the valve is controlled electrically by the operation of the driving member, itself.

The spool valve to direct air under pressure to the upper and lower cylinders may be of any common and well-known construction and need not be shown here. Furthermore, the actuation of such a spool valve, electrically, is also known by those skilled in the art. The novelty in this arrangement, however, resides in the operation of the electrical circuit to shift the valve in response to movement of the driving member. To this end, therefore, there is provided in association with the upper and lower ends of the driving member, a switch which may be contacted by actuating means on the upper and lower end of the driving member.

Referring more particularly to the drawings, it will be noted that below the frame member 1, there is mounted a switch 52, provided with an operating button 53 thereon. When this button is depressed, the spool valve of the control will be shifted to direct air under pressure to the cylinder 32 and move the driving member upwardly. This accomplished by means of the actuating stud 54, mounted on the lower extension 9 of the driving member, which extends downwardly through an opening in the lower cross member 5, and may be adjusted to such length that when the driving member is moved to its lowermost position, the lower end of the stud 54 will contact and depress the actuating button 53 of switch 52, to shift the valve.

A similar arrangement is provided at the upper part of the assembly, wherein it will be noted there is a switch 55, having the operating button 56 associated therewith. An upper actuating stud 57 is secured to the upper extension 15 of the driving member, and passes upwardly through the upper cross member 4. The length of this stud may be adjusted so that in the uppermost position of the driving member, it will depress the button 56, and electrically shift the control spool valve to direct air to the upper cylinder 40, thereby to move the driving member downwardly.

Since the spool constitutes a 4-way valve, its operation is such that when air is directed to the upper cylinder 40, the air pressure in the lower cylinder 32 will be relieved. Likewise, when the driving member has reached its lowermost position, the operation of the switching device is such that the spool will be shifted to direct air into the cylinder 32, and will simultaneously relieve the air pressure in the upper cylinder 40.

It will thus become evident upon consideration of the foregoing, that in this preferred form of the invention, I have provided a novel arrangement of electrical and pneumatic means for reciprocating the driving member of the stepping motor, and have further provided a novel connecting means between the pistons of the actuating mechanism and the driving member, comprising a floating pin, whereby there will be no binding or jamming of the operating parts, even at extremely high speeds. Furthermore, the provision of the two oppositely disposed pawls enables the motor to be operated rapidly, and to index at an extremely high rate of speed. The provision of the stop blocks with the rounded corners thereon cooperating with each of the pawls which have their ends inclined at a predetermined angle, makes it possible to prevent jamming or out-of-phase positioning of the ratchet wheel, when the air pressure is inadvertently reduced or is turned off.

The other forms of the invention now to be discussed also have these advantages. FIG. 5 shows a modified form of the invention wherein an eccentric or crank arrangement is utilized for reciprocating the driving member. For example, a motor 58 may be provided with a shaft 59, on which is mounted an eccentric 60 to which is connected one end of a link 61. The other end ofthis link may extend upwardly through the lower cross member 5 of the frame, and be connected to the driving member such as by means of the lower extension 9. It will be evident that rotation of the crank 60 will reciprocate the link 61 together with the driving member 7 to which it is connected.

-In this form of the invention, the two pawls are still provided, together with the two stop blocks 26 and 27 with their corners rounded, and thus the same advantages heretofore described with respect to FIGS. 1 through 4 are present in the construction of FIG. 5. This arrangement may be suitable for some uses wherein it is not necessary or desirable to reciprocate the driving member at an extremely high rate of speed.

Referring now to FIG. 6, there is illustrated therein a still further modified form of a driving means to reciprocate the driving member 7. This alternative form of the invention may also utilize the electrical circuitry for shifting the spool control valve, and compressed air, as the driving means. In this instance, however, there is but a single piston and cylinder arrangement, wherein air is directed to one end or the other of a double acting piston.

The cylinder in this form is indicated in FIG. 6 by the numeral 62, and the usual double acting piston may be disposed therein. An opening for compressed air below the piston is indicated at 63, and the other opening, above the piston, for admitting compressed air thereto is indicated by the numeral 64. The piston therein is provided with an upwardly extending piston rod 65, which may be suitably connected to a coupling member 66, secured to the bottom of the driving member 7.

It will thus be evident that when the piston within the cylinder 62 is moving upwardly, it will drive the member 7 in an upward direction in the same manner as heretofore described with respect to FIGS. 1 to 4. In this instance, however, as soon as the driving member reaches its uppermost position, the stud 57 will depress the switch button 56 to shift the control spool and relieve the air from below the piston, and admit air under pressure through the opening 64 into the cylinder above the piston, thereupon driving the member 7 in a downward direction. Other than this, the arrangement and operation are the same as or similar to that described with respect to FIGS. 1 to 4. In the same manner, when the driving member reaches its lowermost position, the actuating stud 54 will depress the button 53 to actuate the switch 52 and shift the control valve so that it will direct air into the cylinder 62 below the piston through the inlet 63, thereby to drive the member 7 upwardly.

Referring now to the modified form of the invention shown in FIGS. 7, 8 and 9, there is illustrated the same driving member 7 together with the same pawls l0 and 16 mounted thereon, as well as the electro-pneumatic driving system incorporating the upper and

lower cylinders

41 and 32, respectively, as described hereinabove. It will be noted, however, that this particular form of the invention has eliminated stop blocks 26 and 27, and has provided instead, an improved type of locking arrangement to prevent inadvertent or unwanted rotation of the ratchet wheel in either direction. Otherwise, the remainder of the structure may be the same as that disclosed in FIGS. 1 through 4, or in FIG. 5, or in FIG. 6.

In FIGS. 7 through 9, there is provided not only the driving ratchet wheel 21, but also a second ratchet wheel 67, both of which may be formed with a hub 22a keyed to the shaft 23a. The teeth on the second ratchet wheel are disposed in a direction opposite to that in which the teeth 25 on the driving ratchet is directed.

These teeth may be seen in FIGS. 7 and 8, and are indicated by the numeral 68.

When the driving member is reciprocated so that either one of the

pawls

10 or 16 contacts a tooth on the ratchet wheel 21 to drive it in a counterclockwise direction, the second ratchet wheel 67 will likewise be driven in a counterclockwise direction, but the teeth thereon will be oppositely disposed.

The stop members in this form of the invention include a lower block 69 and a similar upper block 70, both ofwhich are mounted on the driving member 7 for movement therewith. Each of the stop blocks, preferably, has a substantially rectangular configuration with the block 69 having the inner edge 71 and the outer edge 72, and with the block 70 having an inner edge 73 and an outer edge 74. The uppermost edge 75 of the lower block 69 is preferably inclined, as shown, and the lower edge of the block 70 is likewise preferably inclined as indicated at 76.

In the lowermost position of the driving member, as shown in FIG. 7, the pawl 16 hasjust driven the ratchet wheel 21 one step in a counterclockwise direction, and it will be noted that in this position of the various parts, the upper stop block 70 will have been moved into a position where it is in the path of movement of a tooth 68 on the second ratchet wheel 67. Thus, in this position, the ratchet wheel will be positively stopped against any further movement in the indexing or driving direction thereof. The ratchet wheel likewise will be prevented from any inadvertent rotation in the reverse direction thereof because it is locked by the pawl itself.

When the direction of movement ofthe driving memher 7 is reversed, and while the pawl 10 is moving up- \vardly to the point where it contacts the next tooth on the ratchet wheel 21, the stop block 70 will likewise move upwardly and out of the path of the tooth 68 on the second ratchet wheel 67. Thus, when the ratchet wheels begin to rotate, the stop block 70 will be out of the way and the stop block 69 will be moving upwardly. Prior to the time that the indexing step is completed, the stop block 69 will have reached a position in the path of movement of the next tooth 68 on the second ratchet wheel 67, so that at the end of the indexing step, such tooth will come against the stop block 69 which will prevent any overrunning of the ratchet wheel in the driving direction.

Reference will now be made to FIGS. 10,11, and 12, where the same general arrangement of the driving means and the double ratchet wheels are shown, as in FIGS. 7, 8 and 9, but, in addition, there is illustrated as deceleration plunger assembly which may be desirable under some circumstances and the operation of which will appear presently. This particular improvement has been devised as an additional safety measure against overrunning of the ratchet wheel, where the device being indexed is such as to have some external forces which may tend to drive the ratchet wheel in the driving direction at such speed and at such force as to overcome the natural frictional forces in the assembly and drive the ratchet ahead of the indexing pawl.

This has been found to occur, on occasion, in the driving of the programming drum, which is the subject matter of my above-referred to co-pending application. It has been found, for example, that situations may arise where the index drum rotates at a speed greater than the driving pawl that is driving the drum. The construction is such that the net effect may be to overcome occur, the teeth on the second ratchet wheel will miss stopping engagement with thestop block on the driving member. This deceleration plunger assembly has been designed to overcome this problem.

In general, the assembly consists of an impact pin, a guide block and a stop block. Referring now to FIGS. 10, 11 and 12, the stop block is mounted on the frame 1 and is indicated by the numeral 77. The impact pin 78 is adapted to reciprocate in an axial direction within the guide block 79. The guide block 79 is provided with an axial bore 80 and is mounted on the supporting plate 6. A coiled compression spring 81. is positioned within the bore 80 above the impact pin 78, and normally urges the pin downwardly against the top of the stop block 77.

The spring force applied to the impact pin may be adjusted by means of a screw 82, which threadedly engages the upper cross member 4 and has a stud portion 83 extending downwardly into the bore 80, and around which the upper part of the spring 81 is located. Adjusting the screw member 82 upwardly or downwardly will control the compressive force of the spring.

Preferably, the stop block 77 is so positioned that its upper face is spaced slightly upwardly a distance .r from the normal position of a tooth 68 on the second ratchet wheel 67. By thus spacing the stop above the center line of the ratchet wheel, the impact forces of the pin 78 are absorbed by the stop block rather than a ratchet tooth, Also, by spacing the stop above the center line, there are no external forces tending to rotate the drum and the ratchet wheels in the opposite direction.

As the pawl assembly picks up a tooth on the first ratchet wheel, and starts to rotate it in a counterclock wise direction, the second ratchet wheel 67 will pick up the edge of the impact pin 78, causing the pin to slide upwardly in the guide block 79. As the ratchet wheel completes its index, the impact pin will slip off of the tooth of the second ratchet wheel and will drop down on the stop block ready for the next cycle. The impact pin has been positioned in such a manner that the stop block on the driving member will rise into engagement with the next ratchet tooth before the impact pin is free to drop down to the stop block. Thus, by this deceleration plunger assembly, I have provided additional or supplemental means for preventing an unwanted rotation of the ratchet wheel assembly, which might not be taken care of otherwise when the member being indexed provides speed or other forces which will tend to rotate the ratchet wheels at a greater speed than is pro vided by the normal operation of the pawls.

From the foregoing, it will be apparent that there has been provided herein a novel stepping motor, preferably, although not necessarily, operated by an electropneumatic arrangement, wherein an arrangement of double pawls operate to drive the motor at a high rate of speed. Furthermore, novel means have been provided in various forms of the invention to positively lock the ratchet wheel at the end of each indexing step so that it will be held against rotation in either direction. It will be apparent, also, that certain features of the invention may be utilized with only one pawl instead of two, if desired.

Changes may be made in the form, construction and arrangement of parts from those disclosed herein without in any way departing from the: spirit of the invention or sacrificing any of the attendant advantages thereof, provided, however, that changes fall within the scope of the claims appended hereto.

I claim:

1. A stepping motor for driving a rotary member intermittently, comprising,

a. a supporting frame,

b. a driving member mounted on said frame for reciprocating movement in a linear path,

means for reciprocating said driving member,

d. a ratchet wheel mounted on said rotary member,

e. two pawls mounted on and reciprocable with said driving member in opposed relation to each other and in the plane of said ratchet wheel, whereby reciprocation of said driving member will advance said ratchet wheel one step for each direction of movement of said driving member, and locking means associated with each of said pawls and cooperating therewith to restrain movement of said ratchet wheel in both directions when a pawl has completed its indexing movement.

2. A stepping motor, as defined in claim 1, wherein each of said locking means is mounted on said frame.

3. A stepping motor, as defined in claim 1, combined with a second ratchet wheel rotatable with the first ratchet wheel on the same axis and having the teeth thereon disposed in a direction opposed to those on the first ratchet wheel, and wherein each of said locking means is mounted on said driving member adjacent its associated pawl and is movable into the path of a tooth on said second ratchet wheel when its associated pawl is advancing said first ratchet wheel.

4. A stepping motor, as defined in claim 3, combined with supplemental means cooperating with said second ratchet wheel and operable to prevent movement of said first ratchet wheel away from the driving pawl in the indexing direction thereof.

5. A stepping motor, as defined in claim 4, wherein said supplemental means comprises a yieldable member mounted in the path of movement of the teeth on said second ratchet wheel and adapted to be moved away therefrom by rotation of said second ratchet wheel when being indexed, and to return to its position in the path of the next succeeding tooth thereon before the indexing step has been completed.

6. A stepping motor, as defined in claim 5, including a stop member mounted on said frame against which said yieldable member normally rests.

7. A stepping motor, as defined in claim 6, wherein the surface of said stop member against which said yieldable member normally rests is in a plane substantually parallel with and spaced from the plane of the face of said next'succeeding tooth, whereby, when said yieldable member returns to its position in the path of said next succeeding tooth it will come against said stop member instead of said tooth.

8. A stepping motor, as defined in claim 1, wherein said means for reciprocating said driving member includes pneumatically actuated piston means operatively associated therewith, and control valve means operable to actuate said piston means.

9. A stepping motor, as defined in claim 8, including electrical means for operating said control valve means.

10. A stepping motor, as defined in claim 8, wherein said pneumatically actuated piston means includes a cylinder adjacent each end of said frame, a piston reciprocable in each cylinder, and mean between each said piston and the adjacent end of said driving member operable to move said driving member in a direction away from one of said cylinders when air under pressure is admitted to said one cylinder.

11. A stepping motor, as defined in claim 10, wherein said last named means includes a floating pin within a bore of each said piston having one end thereof received within a recess in the adjacent end of said driving member.

12. A stepping motor, as defined in claim 10, wherein said control valve means is operable to direct air under pressure alternately to said piston means.

13. A stepping motor, as defined in claim 8, wherein said pneumatically actuated piston means includes a cylinder at one end of said driving member, a double acting piston therein, and a piston rod connected be tween said piston and one end of said driving member.

14. A stepping motor, as defined in claim 1, wherein said means for reciprocating said driving member includes crank means secured to one end of said driving member.

15. A stepping motor, as defined in claim 1, including control means operable in response to movement of said driving member in one direction, to cause movement of said driving member in the opposite direction.

16. A stepping motor, as defined in claim 1, wherein said means for reciprocating said driving member includes pneumatically actuated piston means operatively associated therewith, control valve means operable to actuate said piston means, and means operable in response to movement of said driving member to actuate said control valve means and reverse the direction of movement of said driving member.

17. A stepping motor, as defined in claim 1, wherein said means for reciprocating said driving member in cludes pneumatically actuated piston means operatively associated therewith, control valve means operable to actuate said piston means, electrical switch means operable in response to movement of said driving member to actuate said control valve means and reverse the direction of movement of said driving member.

18. A stepping motor for driving a rotary member intermittently, comprising a. a supporting frame,

c. means for reciprocating said driving member,

d. a first ratchet wheel mounted on said rotary member,

e. a pawl mounted on and reciprocable with said driving member in the plane of said first ratchet wheel, whereby reciprocation of said driving member in the operating direction of said pawl will advance said ratchet wheel one step,

f. a second ratchet wheel mounted on said rotary -member having the teeth thereon oppositely disposed withh respect to the teeth on said first ratchet wheel, and

g. locking means movable into the path of a tooth on said second ratchet wheel during indexing thereof to prevent unwanted movement of said rotary member in the driving direction of movement of said pawl.

19. A stepping motor, as defined in claim 18, wherein said locking means is mounted on said driving member adjacent to said pawl.

20. A stepping motor, as defined in claim 18, wherein said means for reciprocating said driving member includes penumatically actuated piston means operatively associated therewith, and control valve means operable to actuate said piston means.

21. A stepping motor, as defined in claim 20, including electrical means for operating said control valve means.

22. A stepping motor, as defined in claim 21, includ ing means operable in response to reciprocation of said driving member to actuate said electrical means.

23. A stepping motor, as defined in claim 18, combined with supplemental means cooperating with said second ratchet wheel operable to prevent unwanted in the path of the next succeeding tooth thereon before completed.

the indexing step has been I l =l

Claims

1. A stepping motor for driving a rotary member intermittently, comprising, a. a supporting frame, b. a driving member mounted on said frame for reciprocating movement in a linear path, means for reciprocating said driving member, d. a ratchet wheel mounted on said rotary member, e. two pawls mounted on and reciprocable with said driving member in opposed relation to each other and in the plane of said ratchet wheel, whereby reciprocation of said driving member will advance said ratchet wheel one step for each direction of movement of said driving member, and f. locking means associated with each of said pawls and cooperating therewith to restrain movement of said ratchet wheel in both directions when a pawl has completed its indexing movement.

7. A stepping motor, as defined in claim 6, wherein the surface of said stop member against which said yieldable member normally rests is in a plane substantually parallel with and spaced from the plane of the face of said next succeeding tooth, whereby, when said yieldable member returns to its position in the path of said next succeeding tooth it will come against said stop member instead of said tooth.

13. A stepping motor, as defined in claim 8, wherein said pneumatically actuated piston means includes a cylinder at one end of said driving member, a double acting piston therein, and a piston rod connected between said piston and one end of said driving member.

17. A stepping motor, as defined in claim 1, wherein said means for reciprocating said driving member includes pneumatically actuated piston means operatively associated therewith, control valve means operable to actuate said piston means, electrical switch means operable in response to movement of said driving member to actuate said control valve means and reverse the direction of movement of said driving member.

18. A stepping motor for driving a rotary member intermittently, comprising a. a supporting frame, b. a driving member mounted on said frame for reciprocating movement in a linear path, c. means for reciprocating said driving member, d. a first ratchet wheel mounted on said rotary member, e. a pawl mounted on and reciprocable with said driving member in the plane of said first ratchet wheel, whereby reciprocation of said driving member in the operating direction of said pawl will advance said ratchet wheel one step, f. a second ratchet wheel mounted on said rotary member having the teeth thereon oppositely disposed withh respect to the teeth on said first ratchet wheel, and g. locking means movable into the path of a tooth on said second ratchet wheel during indexing thereof to prevent unwanted movement of said rotary member in the driving direction of movement of said pawl.

22. A stepping motor, as defined in claim 21, including means operable in response to reciprocation of said driving member to actuate said electrical means.

23. A stepping motor, as defined in claim 18, combined with supplemental means cooperating with said second ratchet wheel operable to prevent unwanted movement of said first ratchet wheel away from the driving pawl in the indexing direction thereof.

24. A stepping motor, as defined in claim 23, wherein said supplemental means comprises a yieldable member mounted in the path of movement of the teeth on said second ratchet wheel and adapted to be cammed by said second ratchet wheel in a direction away therefrom when being indexed, and to return to its position in the path of the next succeeding tooth thereon before the indexing step has been completed.