US3653275A

US3653275A - Geneva gear mechanism

Info

Publication number: US3653275A
Application number: US100715A
Authority: US
Inventors: Ronald Leacock
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-12-22
Filing date: 1970-12-22
Publication date: 1972-04-04
Anticipated expiration: 1989-04-04

Abstract

A geneva gear mechanism includes an intermittently rotated indexing member having four tapered pins which are spaced at respective corners of a square and which are axially urged into and captivated by a pair of similarly tapered concentric circular channels in a locking ring which projects from a continuously rotated driving member. The channels are interrupted by a generally diamond-configured cam which effects a smooth 90* rotation of the indexing member during each revolution of the driving member, the cam and locking ring defining transition paths for the pins during rotation of the indexing member. The cam and transition paths are configured to effect uniform rotation of the driven member and to captivate at least two pins during indexing member rotation. Transition path configuration is determined with the aid of large and small gear wheels, the latter having four holes spaced identically to the tapered pin spacing. Rotation of the small gear by 90* about the periphery of the large gear causes the four holes to describe the requisite transition paths.

Description

United States Patent Leacock [54] GENEVA GEAR MECHANISM Ronald Leacock, 4719 Frelder St., Tampa, Fla. 33611 [22] Filed: Dec. 22, 1970 [21] Appl.No.: 100,715

[72] Inventor:

Primary Examiner-Leonard l-l. Gerin At1orney-l-loward L. Rose [57] ABSTRACT A geneva gear mechanism includes an intermittently rotated indexing member having four tapered pins which are spaced at respective corners of a square and which are axially urged into and captivated by a pair of similarly tapered concentric circular channels in a locking ring which projects from a continuously rotated driving member. The channels are interrupted by a generally diamond-configured cam which efiects a smooth 90 rotation of the indexing member during each revolution of the driving member, the cam and locking ring defining transition paths for the pins during rotation of the indexing member. The cam and transition paths are configured to effect uniform rotation of the driven member and to captivate at least two pins during indexing member rotation. Transition path configuration is determined with the aid of large and small gear wheels, the latter having four holes spaced identically to the tapered pin spacing. Rotation of the small gear by 90 about the periphery of the large gear causes the four holes to describe the requisite transition paths.

10 Claims, 6 Drawing Figures GENEVA GEAR MECHANISM BACKGROUND OF THE INVENTION The present invention relates to mechanisms for converting continuous rotational motion into intermittent rotational motion, and more particularly to a geneva gear mechanism in which the indexing member is rotated uniformly and without backlash during a relatively small portion of the cycle of the driving member.

Geneva mechanisms have particular utility in motion picture projectors wherein each frame of the film must be successively disposed in alignment with the projecting lens. Preferably the time during which the film is moved is short relative to the time during which it is stationary in order to provide higher quality projection. In addition, to avoid damag' ing the film, it must be driven at uniform speed during its intermittent periods of motion and must be held stationary at all other times.

Attempts to provide geneva mechanisms capable of operating as described above have not been 100 percent successful in the prior art. For example, in US. Pat. No. 1,033,477 to Schustek, an intermittently driven member is engaged at two of its four pins and at an interconnecting surface by a continuously rotating driving member during the intervals between rotation of the driven member. This is insufficient to prevent either small radial movement (jitter) and backlash (small reverse rotation) of the driven member. Further, during rotation of the driven member only a single pin of the latter is engaged, thereby rendering the driven member susceptible to erratic rotation. Moreover, Schustek requires at least 90 of the driving member rotation path to effect a quarter rotation of the driven member. This provides for only a three-to-one ratio of rest interval to movement interval for the driven member.

In US Pat. No. 1,088,364 to Power (FIGS. 4, 5), a quarter revolution of the driven member is efi'ected by a diamond shaped cam over 60 of the rotation path of the driving member, thereby providing a five-to-one rest interval to movement interval ratio. However, this mechanism also is susceptible to jitter and backlash during the rest interval since only two of the four pins on the driven member are engaged by the locking ring at that time. Moreover, during rotation of the driven member only a single pin is engaged, thereby permitting erratic rotation to occur in the driven member.

Another prior art geneva mechanism is disclosed in US. Pat. No. 1,129,121, also to Power. Again a diamond-shaped cam effects a quarter rotation of the driven member during 60 of rotation of the driving member. In this device Power provides better protection against jitter and backlash than in his prior patent by providing an annular locking ring on the driving member which is straddled by four pins on the driven member during the rest interval. Nevertheless, this mechanism has been found to be susceptible to a certain degree of jitter and backlash, primarily because only small peripheral portions of the pins are engaged by the annular ring and any slight imperfection in the ring surfaces can result in pin disengagement therefrom. Moreover, during most of the rotation interval of the driven member only one of the pins on the driving member is engaged, leaving this member susceptible to erratic rotation. Also, Power specifically provides a peak on the cam to trip one of the pins on the driven member and assure rotation. This tripping action is inconsistent with the smooth rotation required for the driven member.

It is therefore an object of the present invention to provide a geneva mechanism which is devoid of the aforementioned problems.

It is another object of the present invention to provide a geneva mechanism wherein the driven member is uniformly rotated during its movement interval and wherein the rest interval to movement interval ratio is higher than any achieved in the prior art.

It is another object of the present invention to provide a geneva mechanism wherein backlash and jitter are virtually eliminated.

It is still another object of the present invention to provide a simple method for configuring a geneva mechanism to assure that the paths followed by the pins of the driven member are those which automatically effect uniform rotation of the driven member.

SUMMARY OF THE INVENTION In accordance with the present invention the driven member pins are tapered rollers and the locking ring of the driving member includes a pair of concentric circular channels which are likewise tapered to assure engagement of the pins in the channels without backlash upon axial loading of the driven member. A generally diamond-shaped cam is positioned opposite a recess in the locking ring to define transition paths for the tapered pins during rotation of the driven member. Cam and recess configuration for optimally uniform driven member motion is obtained with the aid of large and small gear wheels, the latter having four holes spaced identically to the tapered pins. Rotating the small gear by about large gear periphery causes the holes to describe respective optimum paths to be followed by the pins for uniform rotation of the driven member.

BRIEF DESCRIPTION OF DRAWING The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of specific embodiments thereof, especially when taken in conjunction with the accompanying drawing, wherein:

FIG. 1 is a view in plan of the driving member and driven member (in section) of the geneva mechanism of the present invention;

FIG. 2 is a view in section taken along lines 22 of FIG. 1;

FIGS. 3, 4 and 5 are respectively progressive diagrammatic illustrations of the relative motion between the driving and driven members of FIG. 1 during the movement interval for the driven member; and

FIG. 6 is a diagrammatic illustration of a pair of gears employed in the mechanism of FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring specifically to FIGS. 1 and 2, there is illustrated the essential elements of a geneva mechanism according to the present invention comprising a driving member 10 and a driven member 11. Driving member 10 is a wheel arranged to be continuously rotated at constant angular velocity by means of a shaft or the like about a central axis AA. The direction of rotation of driving member 10 is counterclockwise as viewed in FIG. 1. An annular locking ring 13 projects from one surface of driving member 10 and is centered about axis AA. A pair of concentric circular channels l4, 15 are defined in locking ring 13 and are also centered about axis AA.

Channels

14, 15 are of the same cross-sectional configuration and are tapered such that they are wider at the surface of the locking ring than at the bottom of the channels. The tapered walls of the channels are preferably of smooth metal, such as steel or the like. The channels are interrupted in a transition region of driving member 10, as more fully described below.

Driven member 11 is adapted to be rotated about an axis B-B, radially displaced from and parallel to axis AA. The spacing between the axes is the same as the spacing between axis A--A and an imaginary circle lying equidistant between

channels

14 and 15. Four generally

cylindrical indexing pins

1, 2, 3 and 4 project from driven member 11 toward driving member 10 and into

slots

14, 15. More particularly, two of the pins extend into channel 14 and the other two pins extend into channel 15. The pins are spaced to define respective corners of a square. Each pin is secured to and surrounded by a tapered or frusto-conically configured bushing of nylon or the like, the taper being configured to match that of

channels

14, 15. Driven member 11 is axially loaded along B-B; that is,

the driven member is urged toward driving member such that the tapered bushings on

pins

1, 2, 3 and 4 mate with the tapered channels l4, 15. The channels thus captivate and prevent movement of the pins radially of axis AA. Even minor surface irregularities in the walls of the channel cannot effect radial movement or backlash in the driven member since the axial loading of the driven member acts to maintain engagement between the bushings and channels. On the other hand the nylon

bushings surrounding pins

1, 2, 3 and 4 roll as necessary and permit driving member 10 to rotate smoothly without channels 14, binding on the pins; this is true in spite of the axial loading of the driven member.

As driving member 10 rotates clockwise from the position illustrated in FIG. 1, driven member 11 remains stationary as tapered channel 14 slides along tapered pins 1 and 4 and tapered channel 15 slides along tapered pins 2 and 3. This condition is maintained until the transition region of driving member 10 approaches

pins

1, 2, 3 and 4. The transitionregion is illustrated in FIG. 1 as a 45 sector of driving member 10. The portion of locking ring 13 subsisting between

channels

14, 15 narrows in the transition region and terminates in opposing

cusps

17, 18, the latter being rounded for purposes to be described below. The wall of channel 14 closest to axis A- A is radially recessed in the transition region, the resulting recess 19 being in the shape of a smooth arc which peaks at the center of the region. Disposed centrally of the transition region between cusps l7, l8, and recess 19 is a generally diamond-shaped cam 20. Cam 20 has four surfaces a, b, c and d reading clockwise from the upper left surface a in FIG. 1.

The area between cam surfaces c and d and recess 19 defines a transition passage 21 for one of the pins of driven member 11.

Transition paths

22, 23 for two of the other pins are provided between cam surface a and cusp 17 and between cam surface b and cusp 18. The various transition paths have sidewalls which are tapered in the same manner as

slots

14, 15, as best illustrated in FIG. 2.

To illustrate the manner in which cam 20 acts to rotate driven member 11 reference is made to FIGS. 3, 4 and 5. In FIG. 3 driving member 10 is illustrated in a position wherein driven member 10 has just entered the transition region. Pin 4 makes initial contact with cam surface d and is therefore constrained to enter transition passage 21 as driving member 10 continues to rotate counterclockwise. This motion of pin 4 initiates a clockwise rotation of driven member 11, causing pin 1 to move toward transition passage 22 and pin 3 to move toward transition passage 23 as driving member 10 continues to rotate. Pin 2 follows a path which keeps it urged against the outer wall of channel 15.

In FIG. 4 driving member 10 has moved so that driven member I 1 is at the center of the transition region and cam 20 has passed half-way through

pins

1, 2, 3 and 4. Pin 4 has reached the peak of recess 19 and pins 1 and 3 have entered

transition passages

22 and 23 respectively. Pin 2 is still urged against the outer wall of slot 15 and is in radial alignment with pin 4. Entry of pin 3 into transition passage 23 is facilitated by rounding cusp l8 slightly, thereby preventing binding by assuring that pin 3 is not picked off above the cusp.

Completion of the rotation of driven member 11 is illustrated in FIG. 5 wherein the driven member is on the verge of leaving the transition region. Pin 1 has left transition passage 22, passed over cusp l8, and is following pin 2 into channel 15. Pin 3 has left passage 23 and is entering channel 14. Pin 4 is just leaving passage 21 and is entering channel 14 behind pin 3. Driven member 11 has thus rotated 90 within the transition region. It remains stationary for the next 315 of driving member rotation.

For the embodiment illustrated in FIG. 1 the transition region encompasses only 45 of the driving member configuration. The rest interval to movement interval ratio for the driven member is therefore seven to one, far superior to ratios achieved with prior art mechanisms of this type. In addition, at least two of the driven member pins 1, 2, 3 and 4 are engaged by tapered slots during the entire period of driven member rotation. This fact, combined with layout of the transition passages in the manner described below, assures smooth and uniform rotation of the driven member.

Cam 20 and locking ring 13 are configured to define

transition passages

21, 22 and 23 in a manner which assures uniform rotation of the driven member. These configurations are achieved with the aid of a pair of

gear wheels

31, 32 illustrated in FIG. 6. Gear wheel 32 is twice the diameter of gear wheel 31 and has twice the number of teeth about its periphery. The center of gear wheel 31 is spaced from the center of gear wheel 32 by the distance separating axes AA and 8-3 in FIG. 2, with gear wheel 31 being capable of rolling along the periphery of gear wheel 32 in toothed engagement therewith. Four

holes

5, 6, 7 and 8 are provided in gear wheel 31 and are spaced about the center identically to the spacing of

pins

1, 2, 3 and 4 about axis 8-8.

If gear wheel 31 is now rotated from its initial position (shown in phantom), the four

holes

5, 6, 7, 8 describe

paths

35, 36, 37 and 38. The rotation of gear wheel 32 is effected v with constant angular velocity,

paths

35, 36, 37 and 38 represent paths of smooth and uniform motion of

holes

5, 6, 7 and 8.

Cusps 17 and 18, cam 20, and recess 19 in FIG. 1 are contoured so that

transition passages

21, 22, 23 and 24 have the same configuration as

paths

35, 37, 38 and 36, respectively. In particular, the configuration of cam 20 is determined by the region between intersecting paths 35 and 37 and path 38; recess 19 is configured according to path 38; and the upper surfaces at cusps l7, 18 are cut away to conform to paths 37 and 35. By thusly configuring the components in the transition region, and by rotating driving member 10 at uniform angular velocity, smooth rotation of driven member 11 is assured.

The seven-to-one rest-to-movement ratio provided by the mechanism described above can be varied without loss of rotational smoothness by simply varying the sizes and tooth ratio of the gear wheels in FIG. 6. For example, if gear wheel 32 were three times the size of gear wheel 31 and had three times as many teeth, it would be possible to describe paths for the driving member pins which would permit one-quarter rotation of the driven member in a 30 transition region of the driving member. Configuration of the cam, cusps and recess would be adjusted accordingly.

While I have described and illustrated specific embodiments of my invention, it will be clear that variations of the details of construction which are specifically illustrated and described may be resorted to without departing from the true spirit and scope of the invention as defined in the appended claims.

I claim:

1. In combination a driving member adapted for continuous rotation about a first axis and having a plurality of concentric channels defined in one surface thereof about said first axis, said channels having tapered sidewalls which diverge toward said one surface;

a driven member adapted to be rotated about a second axis parallel to and spaced from said first axis and including a plurality of tapered projections extending into and urged into engagement with said concentric channels, the taper of said projections matching the taper of the sidewalls of said channels to prevent motion of said driven member as said channels pass along said projections;

a driving cam projecting from said one surface of said driving member in a transition region thereof in which channels are interrupted, said frusto-conical cam which is adapted to periodically engage said projections and partially rotate said driven member.

2. The combination according to claim 1 wherein said tapered projections each comprises a generally cylindrical pin secured to and surrounded by a frusto-conica] bushings which is tapered to match the taper of the sidewalls of said channels.

3. The combination according to claim 1 wherein said channels are two in number and said projections are four in number and spaced to define respective corners of a square having said second axis as its center, there being two projections extending into each channel, and wherein said driving cam is generally diamond-shaped and positioned to pass between said projections and partially rotate said driven member as said transition region passes said driven member.

4. The combination according to claim 3 wherein a first and radially smaller of said two channels includes an inner and outer sidewall, said inner sidewall being continuous but recessed radially inward in said transition region to define with said driving cam a first transition path for one of said projections, said outer sidewall being discontinuous in said transition region and flaring radially outward from both ends of said regions; wherein the second and radially larger of said two channels includes an inner sidewall which is discontinuous in said transition region and converges at both ends of said region to form respective cusps with said outer sidewall of said first channel, said cam and the two flaring portions of said first channel outer sidewall defining second and third transition paths for two further projections respectively, the sidewalls of said first, second and third transition paths being tapered in the same manner as the sidewalls of said channels to engage said projections in said transition region.

5. The combination according to claim 4 wherein said driving cam and the sidewalls of said first channel in said transition region are configured to define said first, second and third transition paths with configurations identical to paths described by three holes in a first gear wheel when the latter is partially rotated along the periphery of a second gear wheel having a center spaced from the center of said first gear wheel by a distance equal to the spacing between said first and second axes, said first, second and third holes being spaced relative to the center of said first gear wheel in the same manner as three of said projections are spaced relative to said second axis.

6. A mechanism for converting continuous rotational motion to intermittent rotational motion comprising:

a driving member adapted for continuous rotation about a first axis, said driving member including a first generally circular channel defined in a surface thereof and centered about said axis, said first channel including first and second sidewalls displaced from said axis in the order named, said first sidewall being continuous and radially recessed in an angular transition region of said driving member, said second sidewall being discontinuous and diverging from said first sidewall at both ends of said transition region and toward the center thereof, said driving member further including a second channel defined concentrically about said first channel and having a third sidewall which is discontinuous in said transition region, said second and third sidewalls converging at two locations in said transition region to form two opposed cusps;

a driven member adapted to be rotated about a second axis parallel to and spaced from said first axis and including four projections spaced at opposite comers of a square having said second axis as its center, two different projections extending into and captivated by each of said first and second channels to prevent motion of said driven member as said channels pass along said projections;

a driving cam formed in said surface of said driving member within said transition region for passing between said projections and partially rotating said driven member as said transition region passes said driven member, said cam having a first surface disposed opposite said recessed first sidewall to define a first transition passage for one of said projections, said cam having a second surface disposed opposite said second sidewall to define second and third transition passages for projections between said second surface and respective diverging sections of said second sidewall.

7. The mechanism according to claim 6 wherein said first,

second and third transition passages conform to the paths described by three respective holes in a first gear wheel when the latter is partially rotated about the periphery of a second gear wheel having a center spaced from the center of said first gear wheel by the spacing between said first and second axes, said holes being disposed relative to the center of said first gear wheel in a manner identical to the disposition of three of said projections relative to said second axis.

8. The mechanism according to claim 7 wherein said projections are tapered and wherein the sidewalls of said channels and said transition passages are likewise tapered to receive and engage said projections.

9. The mechanism according to claim 8 wherein said projections comprise generally cylindrical pins surrounded by frustoconical bushings of relatively low friction material.

10. The method of describing transition paths for pin-like projections from an intermittently driven member in a geneva mechanism of the type wherein a driving member rotates continuously about a first axis and during a portion of its rotation urges said pins through said transition paths to rotate said driven member about a second axis spaced from said first axis and through a prescribed angle, said method comprising the steps of:

placing first and second gear wheels in engagement with their centers spaced identically to the spacing between said first and second axes, said first gear wheel having holes therein which are positioned relative to the center of said first gear wheel in the same manner as said projections are positioned relative to said second axis;

rotating said first gear wheel in toothed engagement with said second gear wheel through an angle corresponding to said prescribed angle; and

configuring said transition paths to correspond to the paths described by said holes during said rotation of said first gear wheel.

Claims

1. In combination a driving member adapted for continuous rotation about a first axis and having a plurality of concentric channels defined in one surface thereof about said first axis, said channels having tapered sidewalls which diverge toward said one surface; a driven member adapted to be rotated about a second axis parallel to and spaced from said first axis and including a plurality of tapered projections extending into and urged into engagement with said concentric channels, the taper of said projections matching the taper of the sidewalls of said channels to prevent motion of said driven member as said channels pass along said projections; a driving cam projecting from said one surface of said driving member in a transition region thereof in which channels are interrupted, said frusto-conical cam which is adapted to periodically engage said projections and partially rotate said driven member.

2. The combination according to claim 1 wherein said tapered projections each comprises a generally cylindrical pin secured to and surrounded by a frusto-conical bushings which is tapered to match the taper of the sidewalls of said channels.

6. A mechanism for converting continuous rotational motion to intermittent rotational motion comprising: a driving member adapted for continuous rotation about a first axis, said driving member including a first generally circular channel defined in a surface thereof and centered about said axis, said first channel including first and second sidewalls displaced from said axis in the order named, said first sidewall being continuous and radially recessed in an angular transition region of said driving member, said second sidewall being discontinuous and diverging from said first sidewall at both ends of said transition region and toward the center thereof, said driving member further including a second channel defined concentrically about said first channel and having a third sidewall which is discontinuous in said transition region, said second and third sidewalls converging at two locations in said transition region to form two opposed cusps; a driven member adapted to be rotated about a second axis parallel to and spaced from said first axis and including four projections spaced at opposite corners of a square having said second axis as its center, two different projections extending into and captivated by each of said first and second channels to prevent motion of said driven member as said channels pass along said projections; a driving cam formed in said surface of said driving member within said transition region for passing between said projections and partially rotating said driven member as said transition region passes said driven member, said cam having a first surface disposed opposite said recessed first sidewall to define a first transition passage for one of said projections, said cam having a second surface disposed opposite said second sidewall to define second and third transition passages for projections between said second surface and respective diverging sections of said second sidewall.

7. The mechanism according to claim 6 wherein said first, second and third transition passages conform to the paths described by three respective holes in a first gear wheel when the latter is partially rotated about the periphery of a second gear wheel having a center spaced from the center of said first gear wheel by the spacing between said first and second axes, said holes being disposed relative to the center of said first gear wheel in a manner identical to the disposition of three of said projections relative to said second axis.

9. The mechanism according to claim 8 wherein said projections comprise generally cylindrical pins surrounded by frusto-conical bushings of relatively low friction material.

10. The method of describing transition paths for pin-like projections from an intermittently driven member in a geneva mechanism of the type wherein a driving member rotates continuously about a first axis and during a portion of its rotation urges said pins through said transition paths to rotate said driven member about a second axis spaced from said first axis and through a prescribed angle, said method comprising the steps of: placing first and second gear wheels in engagement with their centers spaced identically to the spacing between said first and second axes, said first gear wheel having holes therein which are positioned relative to the center of said first gear wheel in the same manner as said projections are positioned relative to said second axis; rotating said first gear wheel in toothed engagement with said second gear wheel through an angle corresponding to said prescribed angle; and configuring said transition paths to correspond to the paths described by said holes during said rotation of said first gear wheel.