US3329033A

US3329033A - Stepping drive

Info

Publication number: US3329033A
Application number: US469384A
Authority: US
Inventors: Guy C Caraway
Original assignee: Individual
Current assignee: Individual
Priority date: 1965-07-06
Filing date: 1965-07-06
Publication date: 1967-07-04
Anticipated expiration: 1984-07-04

Description

United States Patent 3,329,033 STEPPING DRIVE Guy C. Caraway, 9703 Wiley Burke Ave., Downey, Calif. 90240 Filed July 6, 1965, Ser. No. 469,384 11 Claims. (Cl. 74-166) ABSTRACT OF THE DISCLOSURE A stepping drive comprising a driven member having a series of openings therethrough, a plunger insertable completely through the openings in sequence, and a cam engageable by the plunger upon insertion thereof completely through successive openings for moving the plunger laterally so as to cause the plunger to advance the driven member in a step-by-step manner.

Summary and objects of the invention The present invention relates in general to a stepping drive, i.e., a mechanism for advancing a driven member along a predetermined path in a step-by-step manner, and primary objects of the invention are to provide a stepping drive which is extremely accurate and positive in its action, which is operative throughout a wide range of stepping frequencies, which is capable of precise control of the acceleration and deceleration of the driven member at the beginning and end of each step, and which is a compact device of simple construction.

The stepping drive of the invention is capable of many uses, such as driving motion picture film, stepping switches, counters, and the like, and, in general, any article or device requiring a drive which incorporates means for producing step-by-step movement.

Considering the invention more specifically, a basic object is to provide a mechanism for advancing a driven member along a predetermined path in a step-by-step manner, which includes a lateraly movable plunger capable of axial extension completely through an'opening, such as a hole, notch, slot, or the like, in the driven member, can means engageable by the plunger upon projection thereof through the opening for moving the plunger laterally along the desired path so as to cause the plunger to advance the driven member one step along such path, means for returning the plunger laterally to its initial position upon axial movement thereof into a retracted position, and means for guiding the plunger during its lateral movement to and from its starting position.

Still more specifically, an important object of the invention is to provide a stepping drive of the foregoing nature which includes: a supporting structure; a driven member mounted on the supporting structure. for movement along a predetermined path and having an opening therein; a laterally movable plunger located on one side of 3,329,033 Patented July 4, 1967 moving the plunger laterally from its final position to its initial position upon axial movement thereof into its retracted position.

Another object is to provide a stepping drive of the foregoing character wherein the guide means for guiding the plunger laterally between its initial and final positions is independent of the driven member and is carried by the supporting structure on the same side of the driven member as the actuating means for reciprocating the plunger.

Still another object is to provide the driven member with a series of openings uniformly spaced apart along the desired path of movement, the guide means and the spring return means for the plunger acting to position the plunger opposite the next opening in the series after the driven member has been advanced one step by the plunger 7 and the cam means with the plunger inserted through the the driven member and reciprocable axially between a I ,structure on the other side of the driven member and engageable by the plunger upon projection thereof completely through the opening for moving the plunger laterally along the path from its initial position to its final position so as to cause the plunger to advance the driven member one step along the path; and spring means interconnecting the plunger and the supporting structure for preceding opening in the series.

Another important object of the invention is to provide cam means having different configurations to provide the plunger,'and consequently the driven member, with different accelerations, velocities and decelerations. A related object is to provide a cam means having a configuration such as to provide the plunger and the driven member with a low initial acceleration, a high intermediate velocity and a low final deceleration.

Still another important object is to provide a stepping drive capable of advancing the driven member bidirectionally, either by using two stepping mechanisms acting in opposite directions, or by using a stepping mechanism having a bidirectional cam means capable of selectively advancing the driven member in opposite directions.

Other objects are to provide a stepping drive wherein the driven member is a rotary member, a rectilinearly movable member, and the like. A related object is to provide a stepping drive capable of advancing a rotary member through angles ranging upwardly to a full 360.

The foregoing objects, advantages, features and results of the present invention, together with various other objects, advantages, features and results thereof which will be evident to those skilled in the art to which the invention relates in the light of this disclosure, may be achieved with the exemplary embodiments of the invention described in detail hereinafter and illustrated in the accompanying drawing, in which:

FIG. 1 is a perspective view of an apparatus which incorporates a stepping drive that embodies the invention;

FIG. 2 is an enlarged, fragmentary sectional view of one embodiment of the stepping drive of the invention and is taken approximately along the arrowed line 2-2 of FIG. 1;

FIGS. 3 and 4 are views similar to FIG. 2, but illustrating successive operating positions of various components;

FIGS. 5 and 6 are fragmentary sectional views illustrating alternative cam means usable with the stepping drive of the invention;

FIG. 7 is an elevational view illustrating an alternative plunger actuating means usable with the stepping drive of the invention;

FIG. 8 is a view, partially in section and partially in elevation, illustrating another embodiment of the stepping drive of the invention;

FIG. 9 is a fragmentary elevational view, partially in section, illustrating still another embodiment of the stepping drive -of the invention;

FIG. 10 is a sectional view taken along the arrowed line 10-10 of FIG. 9; and

FIG. 11 is an elevational view of yet another embodiment of the stepping drive of the invention.

' Referring initially to FIG. 1 of the drawing, illustrated therein is an apparatus 20 inoorporatinga stepping drive 22 of the invention which includes and is actuated by a solenoid 24 to advance a driven device 26 in a stepby-step manner, the apparatus 20 providing a supporting structure 28 for the stepping drive and its actuating solenoid. The apparatus 20 shown in FIG. 1 is merely intended to illustrate generally one possible environment for the stepping drive 22 of the invention. Consequently, the stepping drive 22 will be considered hereinafter without describing the over-all apparatus in detail since such a description is not necessary to a disclosure of the stepping drive per se.

Considering the stepping drive 22 in more detail. with reference to FIGS. 1 to 4 of the drawing, it includes a driven member 30 in the form of a disc rotatably mounted on the supporting structure 28, as by being provided with a hub 32 mounted on a shaft 34 rotatable relative to the supporting structure. The driven member 30 is provided therein with openings 36 uniformly spaced apart along a predetermined arcuate path, and movable along such path in response to rotation of the driven member. More particularly, the openings 36 are uniformly circumferentially spaced about the axis of the shaft 34.

The stepping drive 22 also includes a laterally movable, axially reciprocable plunger 38 located on one side of the driven member 30. More particularly, the plunger 38 is laterally oscillatable between an initial position, shown in FIG. 2, and a final position, shown in FIG. 4, and is axially reciprocable between a retracted position, shown in FIG. 2, and an extended position, shown in FIG. 4.

An actuating means 40 carried by the supporting structure 28 and connected to the plunger 38 serves to axially reciprocate the plunger between its retracted and extended positions. In the particular embodiment under consideration, the actuating means 40 comprises the solenoid 24 mentioned previously, the plunger 38 being flexibly connected to the armature 42 of the solenoid to permit lateral movement of the plunger between its initial and final positions. In the particular construction illustrated, the flexible connection comprises a ball-and-socket means 44, although other flexible connections may be utilized.

When the plunger 38 is in its retracted position, as shown in FIG. 2, it is disengaged from and disposed on one side of the driven member 30. However, when the plunger 38 is in its extended position, as shown in FIG. 4, for example, it projects completely through one of the openings 36 in the driven member and extends beyond the other side thereof.

A guide means 46 carried by the supporting structure 28 on the same side of the driven member 30 as the actuating means 40 serves to guide the plunger 38 laterally thereof between its initial and final positions, and to prevent return lateral movement of the plunger beyond its initial position. As shown in FIG. 2, when the plunger 38 is in its initial lateral position, it is also in its retracted axial position and is in alignment with one of the openings 36 in the driven member 30. Referring to FIG. 4, when the plunger 38 is in its final lateral position, it is also in its extended axial position and projects through such opening in the driven member to the other side of the driven member. In the construction illustrated, the guide means 46 comprises simply a guide slot 48 in a guide member 50 suitably connected to the supporting structure 28. The guide slot 48 extends in the direction of the path along which the openings 36 in the driven member 30 move as the latter is rotated step by step in a manner to be described.

A plunger return means acts on the plunger 38 to return it to its initial lateral position upon axial movement thereof into its retracted axial position. In the particular construction illustrated, the plunger return means comprises tension spring means 52 interconnecting the plunger 38 and the supporting structure 28.

The stepping drive 22 also includes cam means 54 carried by the supporting structure 28 on the other side of the driven member 30 from the actuating means 40 and engageable by the plunger 38 upon projection thereof completely through one of the openings 36, for moving the plunger 38 laterally along the predetermined path from its initial position to its final position so as to cause the plunger to advance the driven member one step along such path. This action of the cam means 54 will be clear from FIGS. 2, 3 and 4 of the drawing.

Considering the operation of the stepping drive 22 of the invention, it will be assumed that the various parts are in the positions shown in FIG. 2, wherein the spring means 52 holds the plunger 38 against one end of the guide slot 48 in its initial lateral position, wherein the plunger is aligned with one of the openings 36, and wherein the plunger is in its retracted axial position. Upon movement of the plunger 38 axially into its extended position by the solenoid 24, the plunger is inserted through the opening 36 with which it is aligned and engages the cam means 54. More accurately, the plunger 38 engages a cam surface 56 which is inclined in the direction of the path of the opening through which the plunger extends. The cam surface 56 deflects the plunger 38 laterally into its final position, shown in FIG. 4, to advance the driven member 30 one step. Preferably, the cam surface 56 terminates in a shoulder 58 providing a positive stop to limit the advance of the driven member 30 to a distance precisely equal to the spacing of the openings 36. Alternatively, the corresponding end of the guide slot 48 may perform this function.

With the parts in the positions shown in FIG. 4, the solenoid 24 retracts the plunger 38, whereupon the spring means 52 returns the plunger to its initial position under the guiding influence of the guide slot 48. Thus, the parts are restored to the positions of FIG. 2, except that the driven member 30 has been advanced one step. If the solenoid 24 is again energized, the foregoing sequence of events is repeated.

The stepping frequency may be varied throughout a wide range by varying the frequency of energization of the solenoid 24 in any suitable manner. For example, the driven member 30 may remain stationary for long intervals between steps by energizing the solenoid 24 at a corresponding frequency. At the other end of the range, the driven member 30 may be advanced many, many times per second. Also, the stepping frequency may be varied within this range by correspondingly varying the energization frequency of the solenoid 24.

To insure that the driven member 30 will not inadvertently be displaced into a position such that none of the openings 36 is in register with the plunger 38 when it is in its initial lateral position, the supporting structure 28 may carry a brake 60, FIG. 1, in frictional engagement with the driven member 30.

As will be apparent from the foregoing, the invention provides a stepping drive 22 which is positive and accurate in its action, which is capable of achieving stepping frequencies varying throughout a wide range, and which is compact and of simple construction.

It will be noted that the cam means 54 has a straight cam surface 56. With this construction, the plunger 38 and the driven member 30 are accelerated substantially instantaneously to a constant velocity, and are then decelerated substantially instantaneously. However this acceleration-velocity-deceleration pattern can be varied widely. Referring of FIG. 5, illustrated therein is a cam means 62 having a curved cam surface 64 which results in gradually increasing acceleration and velocity and substantially instantaneous deceleration. In FIG. 6 is shown a cam means 66 having a reversely curved, generally S- shaped, cam surface 68 which produces progressively increasing acceleration to a maximum velocity and then progressively decreasing acceleration to zero velocity. With this construction, mechanical shock effects are minimized since the plunger 38 and the driven member 30 are accelerated and decelerated gradually. As will be apparent, various other cam-surface configurations capable of achieving other acce1eration-velocity-deceleration patterns may be used. Another advantage of both the cam surfaces 64 and 68 is that they provide ahigh starting torque for the driven member 30, due to the low initial acceleration provided thereby.

In FIG. 7 of the drawing is shown an alternative plunger actuating means 70 comprising a crank 72 provided with an eccentric crank pin 74 having a connecting rod 76 journalled thereon. The connecting rod 76 is connected to a plunger 78, corresponding to the plunger 38, by a suitable flexible connecting means 80, such .as a ball-and socket means. It will be understood that actuating means 40 and 70, such as hydraulic, magnetic, or the like, may be used also.

Turning now to FIG. 8 of the drawing, illustrated therein is a stepping drive 90 which includes a rotary driven member in the form of a drum 92 provided with ,a cylindrical wall 94 having uniformly-circumferentially spaced opening 96 therein. The stepping drive 90 includes circumferentially spaced stepping means 98 each of which comprises a plunger 100, a guide means 102 and a cam means 104 (only one of which is visible). The plungers 100 may be actuated and laterally biased in the Ways hereinbefore discussed, and cooperate with the openings 96, the cam means 104 and the guide means 102 as previously described. One of the cam means 104 is so oriented so as to step the drum 92 in one direction, and the other is so oriented as to step the drum in the opposite di rection.

With the foregoing construction, the stepping drive 90 may be used to actuate an add and subtract counter, not shown, one of the stepping means 98 operating to advance the counter in an adding direction and the other to advance it in a subtracting direction.

Considering FIGS. 9 and of the drawing, illustrated therein is ,a stepping drive 110 which comprises a driven member 112 mounted on a supporting structure 114 for movement along a predetermined rectilinear path and having openings 116 therein uniformly spaced apart along such path. The driven member 112 may be a bidirectionally movable slide member, an elongated strip such as a film strip, an endless belt, or any other member movable along a rectilinear path during at least a portion of its movement.

The stepping drive 110 includes a plunger 118, a guide means 120 and a cam means 122 having a cam surface 124. These elements are relate-d in the same Way as the corresponding elements hereinbefore described, and the plunger 118 is axially reciprocated and laterally biased toward its initial position in the ways hereinbefore described. In the construction illustrated, the cam means 122 includes another cam surface 126 oriented oppositely to the cam surface 124. As will be apparent, when the plunger 118 operates on the cam surface 124, the driven member 112 is advanced in a step-by-step manner from left to right, as viewed in FIGS. 9 and 10. By so mounting the plunger 118, the guide means 120, and the actuating means (not shown) for the plunger,'that these elements may be shifted to the right to cause the plunger to operate on the cam surface 126, the driven member 112 will be stepped to the left, instead of to the right. (It will be understood that the spring means, not shown, for biasing the plunger 118 to its initial position must have its orientation reversed when so shifting the guide means 120 and the actuating means for the plunger.) With this construction, the driven member 112 may be stepped in either direction along its path, depending upon whether the plunger 118 operates on the cam surface 124, or on the cam surface 126'.

Turning now to FIG. 11 of the drawing, .fragmentarily illustrated therein is a stepping drive 130 for producing a full 360 of rotation of a rotary driven member 132.

in .a single step. The driven member 132, which is mounted on a rotary shaft 134, is provided with .a single opening having the form of a radial slot 136. Movable radially in the radial slot 136 is a plunger 138 which is biased toward an initial position at the outer end of the radial slot 136 by a tension spring means 140. The plunger 138 is axially reciprocated between extended and retracted positions in the manner hereinbefore described, but remains in the radial slot 136 when in its retracted position so that the radial slot 136 performs .a guiding function for the plunger 138 as hereinbefore described in connection with the guide slot 48.

When the plunger 138 is in its extended position, it extends entirely through the radial slot 136 into engagement with a spiral cam surface 142 which is inclined away from the driven member 132 from the outer end of such cam surface to the inner end thereof, the inner and outer ends of the cam surface being radially aligned. The spiral cam surface 142 is formed by the bottom wall of a spiral groove 144 which also performs a guiding function for the plunger 138.

Considering the operation of the stepping drive 130, as the plunger 138 is displaced axially into its extended position (away from the eye of the observer), the plunger 138 follows the spiral cam surface 142 from its outer end to its inner end, thereby advancing the driven member 132 through a full 360. At the same time, the plunger 138 moves radially inwardly along the radial slot 136 to the inner end thereof. Upon axial movement of the plunger 138 to its retracted position after rotating the driven member 132 through a full 360, the spring means returns the plunger laterally outwardly to the outer end of the radial slot 136 in preparation for a repetition of the foregoing sequence of events.

It will be understood that the various stepping-drive embodiments of the invention hereinbefore described are susceptible of various applications. For example, they may be used in indexing film strips, tapes, counters, stepping switches, and, in general, any element or device requiring step-by-step movement. Furthermore, such stepby-step movement can be caused to occur at varying frequencies and either unidirectionally or bidirectionally.

Although exemplary embodiments of the invention have been disclosed herein for purposes of illustration, it will be understood that various changes, modifications and substitutions may be incorporated in such embodiments without departing from the spirit of the invention as defined by the claims which follow.

' I claim:

1. In a stepping drive, the combination of:

(a) a supporting structure;

(b) a driven member mounted on said supporting structure for movement along a predetermined path and having an opening therein;

(c) a laterally movable plunger located on one side of said driven member and reciprocable axially between a retracted position and an extended position wherein it projects completely through said opening and extends beyond the other side of said driven member;

((1) actuating means carried by said supporting structure for axially reciprocating said plunger between its retracted and extended positions;

(e) guide means for guiding said plunger laterally thereof between initial and final positions;

(f) cam means carried by said supporting structure on said other side of said driven member and engageable by said plunger upon projection thereof completely through said opening for moving said plunger laterally along said path from its initial position to its final position so as to cause said plunger to advance said driven member one step along said path; and

(g) means for moving said plunger laterally from its 2. In a stepping drive, the combination of:

(a) a supporting structure;

(c) a later-ally movable plunger located on one side of said driven member and reciprocable axially between a retracted position and an extended position wherein it projects completely through said opening and extends beyond the other side of said driven member;

((1) actuating means carried by said supporting structure and connected to said plunger for axially reciprocating said plunger between its retracted and extended positions;

(g) spring means interconnecting said plunger and said supporting structure for moving said plunger laterally from its final position to its initial position upon axial movement thereof into its retracted position.

3. In a stepping drive, the combination of:

(a) a supporting structure;

(c) a laterally movable plunger located on one side of said driven member and reciprocable axially between a retracted position wherein it is spaced from said driven member and an extended position wherein it projects completely through said opening and extends beyond the other side of said driven member;

(d) actuating means carried by said supporting structure and connected to said plunger for axially reciprocating said plunger between its retracted and extended positions;

(e) guide means carried by said supporting structure on said one side of said driven member for guiding said plunger laterally thereof between initial and final positions;

4. In a stepping drive, the combination of:

(a) a supporting structure;

(b) a driven member mounted on said supporting structure for movement along a predetermined path and having openings therein uniformly spaced apart along said path;

(c) a laterally movable plunger located on one side of said driven member and reciprocable axially between a retracted position wherein it is spaced from said driven member and an extended position wherein it projects completely through one of said openings and extends beyond the other side of said driven member;

(f) cam means carried by said supporting structure on said other side of said driven member and engageable by said plunger upon projection thereof completely through one of said openings for moving said plunger laterally along said path from its initial position to its final position so as to cause said plunger to advance said driven member one step along said path; and

5. In a stepping drive, the combination of (a) a supporting structure;

(b) a driven member rotatably mounted on said supporting structure for movement along a predetermined arcuate path and having openings therein uni formly spaced apart along said path;

(0) a laterally movable plunger located on one side of said driven member and reciprocable axially be tween a retracted position wherein it is spaced from said driven member and an extended position wherein it projects completely through one of said openings and extends beyond the other side of said driven member;

(f) cam means carried by said supporting structure on said other side of said driven member and engageable by said plunger upon projection thereof completely through one of said openings for moving said plunger laterally along said pathfrom its initial position to its final position so as to cause said plunger to ad vance said driven member one step along said path; and

6. In a stepping drive, the combination of:

(a) a supporting structure;

(b) a driven member rotatably mounted on said supporting structure for movement along a predetermined arcuate path;

(c) said driven member comprising a disc having openings therein uniformly spaced apart along said path;

(d) a laterally movable plunger located on one side i of said driven member and reciprocable axially between a retracted position wherein it is spaced from said driven member and an extended position wherein it projects completely through one of said openings and extends beyond the other side of said driven member;

(e) actuating means carried by said supporting structure and connected to said plunger for axially reciprocating said plunger between its retracted and extended positions;

(f) guide means carried by said supporting structure on said one side of said driven member for guiding said plunger laterally thereof between initial and final positions;

(g) cam means carried by said supporting structure on said other side of said driven member and engageable by said plunger upon projection thereof completely through one of said openings for moving said plunger laterally along said path from its initial position to its final position so as to cause said plunger to advance said driven member one step along said path; and

(h) spring means interconnecting said plunger and said supporting structure for moving said plunger laterally from its final position to its initial position upon axial movement thereof into its retracted posi' tion.

7. In a stepping drive, the combination of:

(a) a supporting structure;

(b) a driven member rotatably mounted on said sup porting structure for movement along a predetermined arcuate path;

() said driven member comprising a drum including a cylindrical wall having openings therein uniformly spaced apart along said path;

(d) a laterally movable plunger located on one side of said wall and reciprocable axially between a retracted position wherein it is spaced from said wall and an extended position wherein it projects completely through one of said openings and extends beyond the other side of said wall;

(f) guide means carried by said supporting structure on said one side of said wall for guiding said plunger laterally thereof between initial and final positions;

(g) cam means carried by said supporting structure on said other side of said wall and engageable by said plunger upon projection thereof completely through one of said openings for moving said plunger laterally along said path from its initial position to its final position so as to cause said plunger to advance said driven member one step along said path; and

(h) spring means interconnecting said plunger and said supporting structure for moving said plunger laterally from its final position to its initial position upon axial movement thereof into its retracted position.

8. In a stepping drive, the combination of:

(a) a supporting structure;

(b) a driven member mounted on said supporting structure for movement along a predetermined rectilinear path and having openings therein uniformly spaced apart along said path;

9. In a stepping drive, the combination of:

(a) a supporting structure;

(c) a laterally movable plunger located on one side of said driven member and reciprocable axially between a retracted position within said opening and an extended position wherein it projects completely through said opening and extends beyond the other side of said driven member;

(e) cam means carried by said supporting structure on said other side of said driven member and engageable by said plunger upon projection thereof completely through said opening for moving said plunger laterally along said path from an initial position to a final position so as to cause said plunger to advance said driven member one step along said path;

(f) guide means comprising said cam means and said opening for guiding said plunger laterally thereof between its initial and final positions; and

10. A mechanism for advancing in a step-by-step manner a driven member having an opening therethrough, said mechanism including a plunger insertable completely through said opening and including cam means engageable by said plunger upon insertion thereof completely through said opening for moving said plunger laterally so as to cause said plunger to advance said driven member one step.

11. A mechanism as set forth in claim 10 wherein said cam means includes a curved cam which moves said plunger laterally at a varying speed so as to cause said plunger to advance said driven member at a correspondingly varying speed.

References Cited UNITED STATES PATENTS 1,252,070 1/1918 Ziegler 74-166 1,786,034 12/1930 Smith 74128 2,732,221 1/1956 Welch 74166 2,793,562 5/1957 Grenzig 74-166 FRED C. MATTERN, JR., Primary Examiner. W. S. RATLIFF, Assistant Examiner.

Claims

1. IN A STEPPING DRIVE, THE COMBINATION OF: (A) A SUPPORTING STRUCTURE; (B) A DRIVEN MEMBER MOUNTED ON SAID SUPPORTING STRUCTURE FOR MOVEMENT ALONG A PREDETERMINED PATH AND HAVING AN OPENING THEREIN; (C) A LATERALLY MOVABLE PLUNGER LOCATED ON ONE SIDE OF SAID DRIVEN MEMBER AND RECIPROCABLE AXIALLY BETWEEN A RETRACTED POSITION AND AN EXTENDED POSITION WHEREIN IT PROJECTS COMPLETELY THROUGH SAID OPENING AND EXTENDS BEYOND THE OTHER SIDE OF SAID DRIVEN MEMBER; (D) ACTUATING MEANS CARRIED BY SAID SUPPORTING STRUCTURE FOR AXIALLY RECIPROCATING SAID PLUNGER BETWEEN ITS RETRACTED AND EXTENDED POSITIONS; (E) GUIDE MEANS FOR GUIDING SAID PLUNGER LATERALLY THEREOF BETWEEN INITIAL AND FINAL POSITIONS; (F) CAM MEANS CARRIED BY SAID SUPPORTING STRUCTURE ON SAID OTHER SIDE OF SAID DRIVEN MEMBER AND ENGAGEABLE BY SAID PLUNGER UPON PROJECTION THEREOF COMPLETELY THROUGH SAID OPEINING FOR MOVING SAID PLUNGER LATERALLY ALONG SAID PATH FROM ITS INITAL POSITION TO ITS FINAL POSITION SO AS TO CAUSE SAID PLUNGER TO ADVANCE SAID DRIVEN MEMBER ONE STEP ALONG SAID PATH; AND (G) MEANS FOR MOVING SAID PLUNGER LATERALLY FROM ITS FINAL POSITION TO ITS INITIAL POSITION UPON AXIAL MOVEMENT THEREOF INTO ITS RETRACTED POSITION.