US3191559A

US3191559A - Zigzag mechanism for sewing machines

Info

Publication number: US3191559A
Application number: US276310A
Authority: US
Inventors: Walter H W Marsh; William B Strait; Manfred R Laidig
Original assignee: Singer Co
Current assignee: Singer Co
Priority date: 1963-04-29
Filing date: 1963-04-29
Publication date: 1965-06-29
Anticipated expiration: 1982-06-29
Also published as: CH428402A; GB995226A; ES299249A1

Description

J 1965 'w. H. W. MARSH ETAL ZIGZAG MECHANISM FOR SEWING MACHINES Filed April 29, 1963 8 Sheets-Sheet l INVENTORS. WALTER H. W. MARSH,

WILLIAM B. STRAIT, mo MANFRED R. LAID/6.

ORA/E Y June 29, 1965 w. H. w. MARSH ETAL 3,191,559

ZIGZAG MECHANISM FOR SEWING MACHINES 3 Sheets-Sheet 2 Filed April 29, 1963 INVENTORS. WALTER H. w. MARSH WILLIAM B. STRAIT, 4N0 MANFRED R. LAIDIG. My?

omvsy WITNESS m i al June 1965 w. H. w. MARSH ETAL 3,191,559

ZIGZAG MECHANISM FOR SEWING MACHINES Filed April 29, 1963 3 Sheets-Sheet 3 INVENTORS. WALTER H. W. MARSH, wnmsss WILLIAM B. RAIT,

: BY ANDMANFRED R. LAID/6.

' A'TTORNEY United States Patent 3,191,559 ZIGZAG MECHANISM FOR SEWING MACHINES Walter H. W. Marsh, Scotch Plains, William B. Strait, East Paterson, and Manfred R. Laidig, Union, N.J., assignors to The Singer Company, a corporation of New Jersey Filed Apr. 29, 1963, Ser. No. 276,310 15 Ciaims. (Cl. 112-158) The present invention relates to a zigzag mechanism for sewing machines and particularly to a cam selector mechanism of a multi-cam zigzag sewing machine.

In a multi-cam zigzag sewing machine, there is normally provided a stack of stitch pattern cams together with a cam follower that is adapted to be moved along the cams and to be placed in operative engagement with any selected one of the cams. To move the cam follower along the cam stack, it must be raised to clear the highest point of all of the cams and held in this raised position as it is moved. With a cam follower that is biased into tracking engagement with the cam, which is a normal arrangement, the cam follower must be held raised against the action of the spring, which can be a difiicult operation for many sewing machine operators.

Accordingly, the object of this invention is to provide means for facilitating selection of the stitch pattern cam of a multi-cam zigzag sewing machine, and further, to provide such a mechanism that is simple, economical, efiicient, and reliable.

In accordance with this invention, the above objects have been obtained through the provision of means for releasing the bias on the cam follower mechanism to permit cam selection, which means is automatically actuated by the initial actuation of the cam selector mechanism and which includes means for automatically reestablishing the spring bias when the machine is operated.

Having in mind the above and other object that will be evident from an understanding of this disclosure, the invention comprises the devices, combinations andarrangements of parts as illustrated in the presently preferred filed March 29, 1961.

embodiment of the invention which is hereinafter set forth in such detail as to enable those skilled in the art readily to understand the function, operation, construction and advantages of it when read in conjunction with the accompanying drawings in which:

FIG. 1 is a top plan view of a sewing machine embodying the present invention, the top cover plate of the machine being removed and parts in section to illustrate the mechanism.

FIG. 2 is a fragmentary front elevational view of the machine of FIG. 1 illustrating the cam selector mechanism.

FIG. 3 is a vertical sectional view transversely of the machine of FIG. 1 and substantially on the line 33 of FIG. 1.

FIG. 4 is a vertical sectional view taken substantially on the line 4-4 of FIG. 1. 7

FIG. 5 is a fragmentary sectional view taken substantially on the line 5-5 of FIG. 3.

FIG. 6 is a fragmentary sectional view taken substanherein illustrated and described only insofar as it is believed to be necessary for an'understanding of this invention. The zigzag mechanism basically is the same as that which forms the subject matter of the Johnson patent,

.No. 2,862,468, December 2, 1915, to which reference is made for a more complete understanding of the same.

With reference to the drawings, there is illustrated a sewing machine having a frame 1 including a bracket arm 2, a head 3, and a panel 4 in the front face of the bracket arm 2, such as disclosed and claimed in the US. patent application of H. Dreyfuss, Serial No. 99,252

Mounted in the head 3 for endwise reciprocation and for vibration laterally of the line of stitch formation, or in other Words, for zigzag movements, is a needle bar 5. Lateral vibration is imparted to the needle bar 5 by a bracket 6 pivotally mounted intermediate its ends on the presser bar bushing 7, the opposite arms of the bracket 6 being connected to the needle bar 5 and to one end of an endwise movable pitman 8 whereby upon actuation of the pitman, lateral vibration is imparted to the needle bar. The opposite end of the pitman 8 carries a plate 9 pivotally mounted thereon by a pivot pin 10.

The plate 9 and thus the pitman 8 and the needle bar mechanism are biased toward the right, as seen in FIG. 1, by a bias element or spring 11 connected at one end to the pitman 8 at a point adjacent to its connection with the bracket 6 and anchored at the other end to the end of a lever 12. There is also provided a spring 13 that acts upon an arm 14 pivotally mounted in the frame on a post 15, the free end of which arm 14 abuts against the plate 9 to resist over-throw thereof. The plate 9 is thus biased against the cam followers 16 and 17 which are in turn biased into tracking engagement with any selected ones of the cams in a cam stack 187 The cam stack 18 is mounted for rotation on a vertical post 19 and-rotation is imparted thereto by a worm wheel 20 on the stack that cooperates with a worm 21 on the main shaft 22 which is journaled longitudinally of the bracket arm 2.

The pitman 8 is adapted to be shifted to place the pivot pin 10 alternatively substantially over the points of con the end of the pitman 8 by a connection including a ball 26 and a socket 27.

To provide for placing the followers 16 and 17 in tracking engagement with a selected one of the cams in the cam stack 18, each of the followers are pivotally mounted and are slidable endwise on

posts

28 and 29, respectively, which are parallel to the axis of the cam stack 18. The post 28 is provided with a plurality of notches 30, each corresponding to one of the individual cams in the cam stack 18, which notches are adapted to be entered selectively by a knife-like element 31 that extends through a slot in the hub 32 of the follower 16 and into the notch,

.thus positioning the follower 16 and locking the same endwise of the post 28 with respect to the selected one of the cams. Similarly, the post 29 has a plurality of notches 33 adapted to be entered by a knife-like element 34 extending through a slot in the hub 35 of the follower 17.

In the normal manner, to effect cam selection with either of the followers 16 or 17, the respective knife-

like element

31 or 34 is retracted from the notches in the post to free the follower for endwise movement, but without retracting the same from the hub of the follower. Thus, as the

element

31 or 34 is moved, the respective follower will be moved with it. At the same time, the cam-engaging portion of the follower is lifted clear of the cams so that it can be moved freely along the cam stack.

With respect to the follower 16, the cam selector mechanism comprises a shaft 36 rotatably and slidably mounted in the frame by means of a lug 37 and a bushing 38 in the rear wall of the frame that receives a reduced end 39 of the shaft. Secured to the shaft 36 in a crank arm 4%) that carries the knife-like element 31 and which is adapted to abut against an arm 41 integral with the follower 16. Thus, as the shaft 36 is movedendwise inwardly, the element 31 is moved out of the notches and the follower 16 is pivoted so that the cam engaging end thereof is clear of all of the cams. The shaft 36 can then be turned to move the follower 16 along the stack to a position opposite any selected cam. The means for moving and for turning the shaft 36 comprises an actuating arm 42 secured to the shaft 36 and having a handle portion 43 extending through the panel 4 to the exterior of the machine. Movement of the shaft 36 inwardly is is limited by engagement of the shoulder at the base of the reduced portion 39 with the bushing 38. A coil spring 44 is disposed between the arm 40 and the frame to force the shaft 36 outwardly when it is released, this motion being limited by seating of the element 31 in the notch 36.

With respect to the follower 17, the cam select-or mechanism comprises a bracket 45 slidably and rotatably mounted on the shaft 36 and having an actuating arm 46 that extends through the panel 4 and terminates in a handle portion 47. The bracket 45 has a crank arm 48 carrying a knife-like element 34 which is adapted to abut against an arm 49 integral with the follower 17. Thus, when the bracket 45 is forced inwardly, the element 34 is withdrawn from the slot 33-and the cam engaging end of the follower 17 is lifted clear of the cams in the stack 18. When the bracket is then turned by manipulation of the handle 47, the follower 17 is shifted endwise of the post 29. When the handle 47 is released, a spring 50 biases the bracket 45 to its normal position. Endwise movement of the bracket 45 on the shaft 36 is limited by a stop 51, FIGS. 1 and 4.

In view of the fact that the cam followers are biased by the springs 13 and 11 into tracking engagement with the cams, lifting the cam engaging end of the cam follower would normally require that the follower be lifted against the spring action. The present invention is di rected to facilitating cam select-ion and this is accomplished by rendering the spring '11 inoperative or relaxing the same during cam selection thereby eliminating the necessity of holding the follower raised against the action of the spring 11 while effecting cam selection. To this end, the spring 1 1 is anchored to one end of the lever 12 which is universally pivoted intermediate its ends by a pivot pin 52 mounted in an element 53 having a stud 54 on an axis normal to the axis of the pin 52 and journaled for turning in a mounting plate 55 in the frame, whereby the lever 12 is pivotally movable about the axis of the stud 54 to provide for stressing and relaxing the springland is pivotally movable about the axis of the pin 52 to provide for latching and unlatching the same.

The lever 12 is latched in the position in which the spring 11 is stressed and for this reason there is provided latch means comprising a groove 56 in the mounting plate 55, which groove receives the end of the lever 12 opposite from the end to which the spring 1 1 is anchored. The mechanism is arranged such that the line of action of the spring =11 tends to pivot the lever 12 about the pin 52 to force the end thereof upwardly against the plate 55 and into the groove 56. When the end of the lever is thus held by the groove 56, the lever 12 constitutes a stationary anchor for the spring 11.

The means for releasing the lever 12 from the notch 56, thereby permitting it to pivot about the stud 54 and to relax the spring 11, comprises a finger 57 on the end of the lever 12, which finger overlies the shaft 36 in front of a sleeve 58. The sleeve 58 has an inclined end 59 adjacent to the finger 57 and is adapted to cam the same upwardly as the sleeve is moved relatively to the finger, thereby pivoting the opposite end of the lever 12 down- 4 wardly out of the groove 56 to release the lever 12 and to permit the spring to relax. To limit endwise sliding of the sleeve 53 on the shaft 36, there is a slabbed portion 66 on the shaft 36 defining

shoulders

61 and 62 at the opposite ends thereof. The sleeve 53 is also slabbed endwise as at 63 to expose the periphery of the shaft 36 and to form a shoulder 64 in the sleeve at the base of the slabbed portion 63. A spring 65 is coiled about the sleeve 53 with the last coil 66 thereof against the groove 64 and disposed within the slabbed portion 66 of the shaft between the

ends

61 and 62. There is a spring 67 coiled about the shaft 36 and acting between the arm 40 and the sleeve 58 to bias the sleeve into the positionlas illustrated in FEGS. l, 3 and 4.

' With the above mechanism, when the shaft 36 is forced inwardly by the handle 43, the sleeve 53 moves forwardly with it, and engages the finger 57, thereby pivoting the lever 12 to release it from the groove 56 and permitting it to pivot about the stud to relax the spring 11. Thus, the spring 11 is relaxed automatically by the initial movement of the cam selector mechanism permitting further movement of the same to lift the follower 16 out of engagement with the cams without the resistance of the spring 11. When the handle 47 is actuated to effect a cam selection for the follower 17, the bracket 45 slides on the shaft 36 and engages the sleeve 58, forcing it along the shaft 36 to actuate the lever 12 in the same manner as with respect to the actuation of the handle 43.

For operatively stressing the spring 11, that is to reestablish the bias, there is provided a cam 68 on the main shaft 22, which cam is adapted to engage a lug 69 on the under side of the lever 12. With the end of lever '12 in engagement with the underside of the mounting plate 55, the lug 69 is in engagement with the cam 68, and when the end of the lever 12 is seated in the groove 56, the lug 69 is clear of the cam 68. Thus, after cam selection has been effected, the initial rotation of the main shaft 22, through the cam 68 and lug 63, pivots the 1everl2 to its operative position where, through the bias of the spring 11, the end of the lever 12 snaps into the groove 56.

With reference to FIGS. 2 and 3, there is illustrated mechanism for facilitating selection of the desired cam in the stack 18. With respect to the handle 43 it will be seen that, since the arm 42 moves in an are about the axis of the shaft 36, the slot 76 in the panel 4 through which it projects is made sufficiently wide to accommodate the vertical component of the motion of the handle. On the panel 4 there is provided indicia 71 corresponding to the cams and cooperating with a pointer 72 that follows the arm 42 and thus indicates the selected cam.

'With respect to the handle 47 which also moves in an are about the axis of the shaft 36, there is provided a slot 73 in the panel 4, which is also made sufliciently wide to accommodate the vertical component of the motion of the arm 46. There is also provided indicia 74 and a pointer 75 to indicate the selected cam.

Since the radius of the arm 46 relative to the shaft 36 is less than the radius of the arm 42 relative to the shaft 36, the are through which the arm 46 is swung to produce a given angular displacement of the lever 48 would be smaller than that required for the arm 42. To facilitate cam selection, the indicia 74 has the same spacing as the indicia 71, and there is provided a motion-multiplying mechanism for the pointer 75 whereby the distance that the pointer 75 will move is more than the distance that the lever 46 moves and the same as the distance that the pointer 72 for the arm 42 moves. This mechanism is illustrated in FIGS. 1, 5, 6 and 7 wherein there is shown a plate 76 secured at its ends in the bracket arm 2 immediately behind the panel 4 as by screws 77. The plate 76 has a slot 78 that receives a slide 79 having a firstor outer portion 80 disposed on one face of the plate and a second or inner portion 81 disposed substantially in the slot 78, the

portions

80 and 81 having

flanges

32 and 83 respectively that extend above and below the longitudinal edges of the slot 78 on the opposite sides of the plate to guide the slide along the slot. For assembly purposes and to accommodate the slide 79 in the extreme positions, the plate 76 has an offset at 84 and the slot '78 is enlarged at the end thereof to permit the flanges 83 to pass therethrough. The inner portion 81 has an aperture 85 through which the arm 46 passes and whereby the slide 79 follows the arm 46 as it is moved, the aperture 85 being enlarged vertically to accommodate the vertical component of the motion of the arm 46.

Extending upwardly and laterally from the inner portion 81 of the slide 79 at the back of the plate 76 is an arm 86 which at its free end is provided with a tongue 87 that overlies the upper edge of the plate 76 and serves to guide the slide 79. The upper edge of the arm 86 is formed with teeth to define a rack 38 that cooperates with a pinion 89 journaled on a shaft 90 carried by the plate 76.

.A second pinion 91, larger than the pinion 89, is also mounted on the shaft 90 and is pinned as by pin 92 to the pinion 89 for unitary rotation therewith. The shaft 90 and

pinions

89 and 91 are held in assembled relation by a spring clip 93, the ends of which embrace the opposite ends of the shaft 90. Meshing with the pinion 91 is a rack 94 formed on the upper edge of a slide 95 that is sandwiched between the arm 86 and the plate 76, the slide 95 being guided to move along a straight line parallel to the slot 78 by means of studs 96 carried by the arm 86 and having the ends thereof seated in a slot 97 in the slide 95. The slide 95 is also formed with a depending tongue 98 upon which the pointer 75 is placed.

The pointer 72 is formed on a flange 99 of a slide 180 that is disposed in a slot 101 in the plate 76, the slide 100 having a central portion 102 and end portions 193 and 104. The central portion 102 has flanges 105 disposed in 1 front of the plate 76 and the

end portions

103 and 104 have flanges 196 and 107 disposed to the rear of the plate 76. The central portion 102 is provided with an aperture 108 similar to the aperture 85 of the slide 79 and which receives the arm 42. 7

With reference to FIG. 5, while both

arms

42 and 46 move the same angularly of the shaft 36 as the

arms

42 and 46 are moved about the axis of the shaft 36 from the full line to the dotted line positions, the actual displacement of the arm 42 will be greater than that of the arm 46 because of the difference in radius of the arms from the shaft 36. The slide 100 moves with the arm 42, the setting thereof being indicated by the pointer 72. The slide 79 also moves with the arm 46, but the pointer 75 which is carried by the separate slide 95 is moved a greater distance T than the slide 79 by an amount determined by the ratio of the

pinions

89 and 91, the pinion 89 being rotated by the rack 88 on the slide 79 as the slide is moved, and the pinion 89 rotating the pinion 91 which in turn moves the slide 95 through the rack 94.

The elements comprising the plate 76 and the

slides

79, 95 and 100 are all adapted to be formed inexpensively of sheet metal and, by virtue of the offset 84 in the plate 76 together with the enlarged end of the slots 78 and 101 and the spring clip 93, can be conveniently assembled.

Numerous alterations of the structure herein disclosed will suggest themselves to those skilled in the art. However, it is to be understood that the present disclosure re lates to a preferred embodiment of my invention which is for purposes of illustration only and not to be construed as a limitation of the invention. All such modifications which do not depart from the spirit of the invention are intended to be included within the scope of the appended claims.

Having thus described the nature of the invention, what we claim herein is:

1. In a zigzag sewing machine, a plurality of rotatable stitch pattern cams, a cam follower mounted for pivotal movement about and sliding on an axis parallel to the axis of said cams, bias means for biasing said cam follower pivotally into tracking engagement with said cams, cam

operatively stressed and a second position wherein said bias means is relaxed.

2. In a zigzag sewing machine, a plurality of rotatable stitch pattern cams, a cam follower mounted for pivotal movement about the sliding on an axis parallel to the axis of said cams, bias means for biasing said cam follower pivotally into tracking engagement with said cams, cam selector means for pivotally retracting said cam follower from tracking engagement with said cams and for moving said cam follower into operative relation with a selected one of said cams, and means for rendering said bias means inoperative to facilitate actuation of said cam selector means comprising anchor means for said bias means movable between a first position wherein said bias means is operatively stressed and a second position wherein said bias means is relaxed, latch means for releasably securing said anchor means in said first position, means for releasing said latch means, and means for moving said anchor means to said second position.

3. In a zigzag sewing machine in accordance with claim 2 in which said means for releasing said latch means is responsive tothe actuation of said cam selector means.

4. In a zigzag sewing machine in accordance with claim 2 in which said means for moving said anchor means to 'said second position is responsive to the actuation of the main shaft of the machine.

5. In a zigzag sewing machine, having a frame, a main shaft journaled in said frame, a plurality of stitch pattern cams, mounted on a common axis, means operatively connecting said cams and said main shaft for imparting rotation to said cams u'pon rotation of said main shaft, a cam follower mounted for pivotal movement about and sliding on an axis parallel to the axis of said cams, bias means for biasing said cam follower pivotally into tracking engagement with said cams, cam selector means for pivotally retracting said cam follower from tracking engagement with said cams and for moving said cam follower into operative relation with a selected one of said cams, and means for rendering said bias means inoperative to facilitate actuation of said cam selector means comprising anchor means for said bias means movable between a first position wherein said bias means is operatively stressed and a second position wherein said bias means is relaxed, latch means for releasably securing said anchor means in said first position, means for releasing said latch means, and means responsive to the actuation of said main shaft for moving said anchor means to said second position comprising a cam on said main shaft and a lug on said anchor means and cooperating with said last named cam to move said anchor means to said second position.

6. In a zig-zag sewing machine in accordance with 5 in which the means for releasing said latch means is responsive to the actuation of said cam selector means.

7. In a zigzag sewing machine in accordance with claim 6 wherein said cam selector means is movable in one direction to retract said cam follower from tracking engagement with said cams and movable in a second direction to move said cam follower into operative relation with a selected one of said cams, and said means for releasing said latch means is actuated by said cam selector means as it is moved to retract said cam follower.

8. In a zigzag sewing machine, a plurality of rotatable stitch pattern cams, mounted on a common axis, a cam follower mounted for pivotal movement about and sliding on an axis parallel to the axis of said cams, cam selector means for pivotally retracting said cam follower from tracking engagement with said cams and for moving said cam follower into operative relation with a selected one of said cams, bias means operatively connected to said cam follower for biasing said cam'follower pivotally into tracking engagement wtih said cams, and anchor means for said bias means movable between a first position wherein said bias means is operatively stressed and a second position wherein said bias means is relaxed for rendering said bias means inoperative to facilitate actuation of said cam selecttor means, said anchor means comprising a lever pivotally mounted in said frame and connected at one end to said bias means, latch means for releasably securing said lever in said first position, means for releasing said latch means, and means for moving said lever to said second position.

9. In a zigzag sewing machine in accordance with claim 8 wherein said means for moving said lever to said second position comprises a cam on the main shaft of the machine and a lug on said lever and cooperating with said cam to move said lever to said second position.

10. In a zigzag sewing machine, a plurality of rotatable stitch pattern earns, a cam follower mounted for pivotal movement about and sliding on an axis parallel to the axis of said cams, cam selector means for pivotally retracting said cam follower from tracking engagement with said cams and for moving said cam follower into operative relation with a selected one of said cams, and means for biasing said cam follower into tracking engagement with said cams comprising a lever, a bias element operatively connected between said cam follower and one end of said lever, means for mounting said lever for pivotal movement about a first axis for stressing and relaxing said bias element and a second axis normal thereto,

said bias element being arranged to urge said lever pivotally about said second axis, latch means for receiving said lever and holding the same in the position wherein said bias element is stressed, means for releasing said lever from said latch means to permit said bias element to relax, and means for returning said lever to said position wherein :said bias element is stressed.

11. In a zigzag sewing machine in accordance with claim. 10 wherein said means for returning said lever to said positionwherein said bias element is stressed comprises a cam on the'main shaft of the machine and a lug on said lever and cooperating with said cam.

12. In a zigzag sewing machine in accordance with claim 11 wherein said latch means comprises an aperture into which the end of said lever is received when in the position wherein said bias element is stressed and said means for releasing said lever from said latch means comprises a releasing element for depressing said lever from said aperture.

13. In a zigzag sewing machine in accordance with engagement with said cams and movable in a second direction to move said cam follower into operative relation with a seelcted one of said cams, and said releasing element is actuated by said cam selector as it is moved to retract said cam follower.

14. In a zigzag sewing machine, a plurality of stitch pattern cams mounted in a common axis,.a pair of cam followers mounted for sliding on an axis parallel to the axis of said cams, and cam selector means for individually moving each of said cam followers into operative relation with selected ones of said cams comprising a shaft disposed upon an axis normal to the axis of said cams, a pair of crank arms mounted on and pivotally movable about the axis of said shaft, means operatively connecting said crank arms individually to said cam followers for sliding said cam followers upon turning of said crank arms, a pair of actuating arms extending radially of said shaft and movable angularly about the axis of said shaft for turning said crank arms individually about the axis of said shaft, a slide for each of said actuating arms and movable therewith for indicating the selected ones of said cams, and means for modifying the motion of one of said slides relative tothe respective actuating arm for moving said slide a distance equal to the distance that the other one of said slides is moved upon the same angular displacement of said actuating arms.

15. In a zigzag sewing machine, a plurality of rotatable stitch pattern cams, mounted on a common axis, a cam follower mounted for sliding on an axis parallel to the axis of said cams, and cam selector means for moving said cam follower into operative relation with a selected one of said cams comprising a shaft disposed upon an axis normal to the axis of said earns, a crank arm carried by said shaft and operatively connected to said cam follower for sliding said cam follower upon turning of said shaft, an actuating arm connected to said shaft and providing for manually turning the same, a slide movable with said actuating arms, a rack on said slide, a first pinion in mesh with said rack, a second pinion coupled to said first pinion for unitary rotation therewith, a second slide, and a rack on said second slide and in mesh with said second pinion, and a pointer carried by said second slide for cooperating with indicia to indicate the selected one of said cams.

References ited by the Examiner UNITED STATES PATENTS 2,862,468 12/58 Johnson 112-158 2,900,938 8/59 Johnson 112 15s 3,066,623 12/62 Reeber etal. 112158 FOREIGN PATENTS 7 795,329 5/58 Great Britain.

JORDAN FRANKLIN, Primary Examiner. ROBERT V. SLOAN, Examiner.

Claims

1. IN A ZIGZAG SEWING MACHINE, A PLURALITY OF ROTATABLE STITCH PATTERN CAMS, A CAM FOLLOWER MOUNTED FOR PIVOTAL MOVEMENT ABOUT AND SLIDING ON AN AXIS PARALLEL TO THE AXIS OF SAID CAMS, BIAS MEANS FOR BIASING SAID CAM FOLLOWER PIVOTALLY INTO TRACKING ENGAGMENT WITH SAID CAMS, CAM SELECTOR MEANS FOR PIVOTALLY RETRACTING SAID CAM FOLLOWER FROM TRACKING ENGAGEMENT WITH SAID CAMS AND FOR MOVING SAID CAM FOLLOWER INTO OPERATIE RELATION WITH A SELECTED ONE OF SAID CAMS, AND MEANS FOR RENDERING SAID BIAS MEANS INOPERATIVE TO FACILITATE ACTUATION OF SAID CAM SELECTOR MEANS COMPRISING ANCHOR MEANS FOR SAID BIAS MEANS MOVABLE BETWEEN A FIRST POSITION WHEREIN SAID BIAS MEANS IS OPERATIVELY STRESSED AND A SECOND POSITION WHEREIN SAID BIAS MOUNTED IS RELAXED.