Zero Backlash Detent Mechanism

Technical Field

This invention relates to a detent mechanism and, more particularly, to a mechanism that floats in one direction and has substantially zero backlash in a direction at right angles thereto.

Background Art

The use of a movable detent pin assembly to align and lock two relatively movable elements, one with respect to the other, has been known for some time, as is evidenced, for example, by the Hopkins U. S- Pat. No. 3,986,701, issued October 19, 1976, and by the Samide U.S. Pat. No. 4,067,415, issued January 10, 1978. In particular, a detent pin assem¬ bly is often used in a multi-station manufacturing apparatus to position and hold a specific work station in a predetermined relationship with a tool element. Proper operation of the detent pin assembly generally requires axial alignment of the detent pin with its complementary receiving fixture so that the pin may be thrust home without conflict. The more massive the pin assembly and its related machine parts, the more necessary it becomes to achieve proper align- ment of the pin with its receiving fixture' ^* . Often it is required that the cavity in which the pin is positioned and the receiving fixture of the pin be align-bored. This is an expensive and time-consuming operation when performed on large machines. The elements of the machine or apparatus must be assembled

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into working relationship.- The align-boring procedure is then performed on the necessary parts at the machine situs with the parts properly positioned.

An alternative to this procedure which allows the pin assembly and its related machine parts to be produced singularly, as in a machine shop, and then assembled afterwards at the machine situs, would de¬ mand a gauging fixture be designed and produced. This is needed to assure accurate manufacture of the separate parts, and their proper positioning in assembly. A methodology, such as this, increases expenditures and time requirements further by requir¬ ing the design and production of these gauging fix¬ tures which often are of a size and complexity equiva- lent to the parts for which they are used to manufacture.

Detent pin designs which provide for a tap¬ ered end to make contact with the receiving fixture are also known.. The tapered pin is intended to seat in a similarly shaped recess in the mating member. The narrow point-shaped end of the pin, the relatively large recess in the receiving member, and the co¬ operating tapered side walls of both elements permits an extended stopping range of the machine by allowing a larger area for initial pin engagement. The tapered surfaces of the parts then tend to move the mating elements into alignment so the pin may seat home. However, this still requires very accurate machining for the pin to align the parts and seat home properly. If the machining is not precise, the side of the taper- ed f ce of the pin contacts only one side of the receiving recess and is precluded from finding its proper fully seated position. With the pin improperly

seated, a significant amount of backlash could be experienced when the machine or apparatus being positioned begins its operation. This is not desir¬ able. The present invention is directed to over¬ coming one or more of the problems as set forth above.

Disclosure of Invention

One aspect of the present invention pertains to an improved detent pin assembly which retains all the advantageous features inherent in a known detent pin with a tapered end, but which allows the pin to float in a plane perpendicular to the relative direction of motion of the member in which it will be received, thereby allowing the pin to seat home in its receiving fixture through a wider range of alignment positions than has previously been permissible while providing zero backlash in a direction parallel to the plane of relative movement. The improved detent pin assembly is especially beneficial when used to index and hold large machine elements, such as a large multi-station manufacturing apparatus. By such use, expensive align-boring procedures or gauging fixtures may be eliminated. The improved detent pin assembly allows for a larger tolerance in the manufacture of mating parts than has heretofore been permissible. These parts may be singularly made by simple methods maintaining the flexibility of subsequent assembly at the machine situs with adequate alignment positioning.

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In another aspect of the invention, a de¬ tent pin having a tapered end for engaging a receiving fixture in an adjacent moving element, and an opposite end connected to a driving motor, is slidably position- ed in a housing. The housing is secured to a primary element, such as a machine frame. A longitudinal cavity extends through the housing for receiving the pin and for guiding the pin through its intended reciprocal movement into engagement and disengagement with complementary receiving fixtures in the adjacent moving element. A central portion of the detent pin and the longitudinal cavity in the housing have similarly shaped cross-sections with the fitment of the pin within the cavity being loose, though bounded t,y contact of the pin with a wall of the cavity, in one direction, and being more restrictively guided in a perpendicular direction. The loose fit of the pin within the housing in only one direction provides a unilateral floating pin assembly while the restrictive fit of the pin in a direction perpendicular thereto provides zero backlash in said perpendicular direction.

By utilizing the pin assembly, such that the direction of the limited loose fit of the pin within the housing is positioned normal to the direction of motion of the adjacent moving element, the pin is allowed more freedom to guide into its receiving fixture and thereby assures complete engagement of the pin within the adjacent element without disturbing the relative alignment of the moving element.

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Brief Description of Drawings

Fig. 1 is a top schematic view of a detent pin assembly mounted on a multi-station manufacturing apparatus; Fig. 2 is a side plan view of the detent pin asse bly; and

Fig. 3 is a fragmentary end plan view of the detent pin assembly.

Best Mode for Carrying Out the Invention With reference to the drawings, Fig. 1 shows the improved detent pin assembly 10 mounted on a frame 12 of a multi-station manufacturing apparatus 14. The pin assembly 10 is used to index a selected one of several work stations 16 in aligned position with a tool 18. A detent pin 20 is reciprocably guided within a housing 22 and is moved by an operating means 24 into engagement and disengagement with a recess or tapered socket 26 of a receiving fixture 28. A plurality of receiving fixtures 28 are located in predetermined positions around the circumference of a rotatable worktable 30.

The detent pin assembly 10 generally com¬ prises the detent pin 20 and the housing 22 depicted in detail in Figs. 2 and 3. The detent pin 20 has a forward contact portion 32, a central guide portion

34 and a rearward connecting portion 36, and is slid- ably positioned in a longitudinal cavity 38 formed through the housing 22 which guides the pin 20 in a reciprocal motion. The detent pin housing 22 is generally U-shaped as shown in Fig. 3, having two opposite parallel sides 40,42 separated and inter¬ connected by a bridging side 44, and having an open

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side 46. The parallel sides 40 and 42 and the bridg¬ ing side 44 define the longitudinal cavity 38 which receives pin 20. The cavity 38 through the housing 22 is shown square shaped in cross-section with the U-shape opening in the direction parallel to the rotation of the worktable 30. It is to be understood that the cavity 38 in the housing 22 can be of any cross-sectional shape providing a pair of opposing parallel walls with similarly parallel surfaces. The open side 46 may be positioned in any manner to provide the desired fit for the detent pin 20.

The central guide portion 34 of the detent pin 20 is of a similar shape in cross-section to be received within the longitudinal cavity 38, and is slightly smaller in size. The detent pin 20 is held loosely in one direction within the longitudinal cavity 38 having a small space 48 between the pin 20 and the walls of the parallel sides 40,42 of the housing 22, thereby allowing a slight movement of the pin 20 in a plane perpendicular to the planes of the housing sides 40,42.

A block member 43 fixed to the frame 12 closes the open side 46 of the longitudinal cavity 38. The pin 20 is thereby secured within the enclosed cavity 38 having limited freedom of movement in a plane parallel to the direction of movement of said worktable 30, and being guided in reciprocal motion. The opposing parallel sides 40 and 42 standing parallel to the frame surface 50 are slightly shorter in length than the cross-sectional height of the pin central portion 34 positioned between said sides, allowing the pin 20 to extend slightly beyond the ends 52,54 of

the parallel sides 40,42.. A pair of shim elements 56 and 58 are positioned between the ends 52 and 54 of the sides 40,42 and the abutting face 53 of the block 43 for adjusting the fit of the pin 20 within the cavity 38 in a plane parallel to the parallel sides 40,42. The shim elements 56,58 are of a thickness to provide the pin 20 with a restrictive guiding fit between the bridging side 44 and the block face 53. Adjustments may be made to the restrictive fit of the pin 20 within the cavity 38 in the plane parallel to the sides 40,42 by changing the thickness of the shim elements 56,58. A plurality of fasteners 60 are provided to secure the housing 22 to the block 43, and simultaneously maintain the shim elements 56,58 in position between the housing 22 and the face 53 of the block 43.

Industrial Applicability

The limited loose fit of the detent pin 20 within the housing cavity 38 in one direction and the restrictive fit of the pin 20 within the housing cavity 38 in a direction perpendicular thereto pro¬ vides a unidirectional floating pin assembly. ' In a preferred embodiment of said pin assembly, the detent pin 20 has a tapered surface 33 on the forward con- tact portion 32. The tapered surface 33 on the con¬ tact portion 32 is received in a complementary shaped tapered recess 26 in the receiving fixture 28, one of several receiving fixtures positioned* on an index¬ able element, such as the rotary worktable 30. A narrow end 61 of the tapered surface 33 of the contact portion 32 is accepted in a relatively large mouth

portion 62 of a tapered surface 63 of the receiving recess 26 without maintaining perfect alignment of the pin 20 with the receiving fixture 2 ^* 8. After initial engagement, the surface 33 of the contact portion 32 makes contact with the tapered surface 63 of the receiving recess 26 and tends to move the receiving fixture 28 into alignment with the pin 20 as the pin is thrust forward into engagement. The ability of the pin 20 to float in the cavity 38 of the housing 22 through, limited movement of the pin in the plane perpendicular to the direction of motion of the rotary worktable 30 allows the pin to completely engage the receiving recess 26 without interference or binding. With the pin 20 completely seated in the receiving fixture 28, relative backlash between the worktable 30 and the frame 12 is reduced to a minimum approaching zero in the horizontal plane, that is, the plane parallel to the ^* plane in which the rotary worktable 30 turns. The effect of the clearance between pin 20 and sides 40 and 42 is cancelled because the rigid mounting of the worktable 30 through supporting bearings housed in frame 12 in the vertical plane. As a result, the work station 16 and the tool 18 have substantially no backlash.

By reversing the orientation of the restric¬ tive fit and the floating fit of the pin 20 in the housing 22, the backlash would be zero in the vertical plane. That is, with the fit between the walls 48 of the pin and the walls of the cavity 38 defined by the sides 40,42 made restrictive and a small tolerance between the central portion 34 of the pin and the bridging side 44 of the housing 22 to provide a floating movement in the horizontal direction, there would be a zero vertical backlash between the work station 16 and the tool 18 and a minimal backlash in the plane transverse thereto. Other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.