Ball Bearing Cam Assembly

The invention generally relates to the field of precision cam assemblies and more particularly relates to the field of the use of such assemblies for controlling the selection of different track positions for a magnetic tape head in a magnetic tape player/recorder.

Prior art cam assemblies generally comprise a cam member having cam surfaces, a cam follower which is mechanically coupled to the cam member and an apparatus for providing relative movement of the cam member with respect to the cam follower. Relative movement of the cam member causes different portions of the cam surfaces to contact the cam follower and produce corresponding movement of the cam follower. Whenever precise movement of the cam follower is required, such as when the cam follower movement controls the track (height) position of a magnetic tape head in a tape player, various cam surfaces must be provided which bear a precise relationship to each other. Generally, prior art cam assemblies have used a unitary cam member which has a plurality of cam surfaces on it, all of which bear a precise dimensional relationship with respect to each other. These precision cam members have therefore been relatively expensive due to the exact tolerances which must be maintained for their manufacture. U.S. Pat. No. 3,624,309, which is by the same inventor and assigned to the same assignee as the present invention, illustrates the use of such a prior art cam assembly to control the track position of a magnetic tape head.

An object of the present invention is to provide an improved, inexpensive and accurate cam assembly which overcomes the aforementioned deficiencies of the prior art cam assemblies.

A more particular object of the invention is to provide an improved cam assembly for use in selecting the different track positions for a magnetic tape head in a magnetic tape player/recorder.

A further object of the invention is to provide an improved cam assembly in which precise ball bearings are used in conjunction with a reference surface to provide accurate displacement of a cam follower member.

Another object of the invention is to provide an improved multi-track tape player in which an improved cam assembly is used to position the magnetic tape head with respect to the several tracks on a magnetic tape.

In one embodiment of the present invention a cam assembly is provided which includes; at least one reference surface, at least one cam follower member adaptable for being positioned at several different predetermined distances away from the reference surface, and cam means including at least a first and second ball bearing for selectively altering the position of the cam follower member with respect to the reference surface by selectively providing the first and second ball bearings between the cam follower member and the reference surface.

A portion of a multi-track tape player/recorder which has a magnetic tape head, tape drive apparatus and tape track selection apparatus is illustrated. The multi-track tape player/recorder includes an improved cam assembly having at least one reference surface, at least one cam follower member for controlling the track position of the tape head and a cam means including a first ball bearing having a first diameter and a second ball bearing having a second diameter for selectively altering the position of the cam follower member with respect to the reference surface by selectively positioning the first and second ball bearings between the cam follower member and the reference surface. The selective use of the first and second ball bearings thereby provides the selection of different precise positions for the cam follower member and thus results in the selection of different precise positions of the magnetic tape head. By using inexpensive precise ball bearings in conjunction with a reference surface, the requirement for a precisely formed cam having a plurality of precise surfaces is eliminated. Therefore an inexpensive and relatively simple cam assembly has been provided in which the diameters of precision ball bearings are used to create the selection of different precise positions for the magnetic tape head of a tape player/recorder. The structural details of the present invention are more fully elaborated on subsequently in the detailed description of the preferred embodiment.

For a more complete understanding of the invention, reference should be made to the drawings, in which:

FIG. 1 is an assembled side view of an improved cam assembly in a magnetic tape player/recorder which is used for positioning the height of a magnetic tape head; and

FIG. 2 is an exploded perspective view of portions of the cam assembly illustrated in FIG. 1.

FIGS. 1 and 2 illustrate an improved cam assembly 10 which in part of a magnetic tape player/recorder (not fully shown). The tape player/recorder includes a magnetic tape head 11 adaptable for sensing several tracks of a magnetic tape, drive apparatus (not shown) for moving the magnetic tape past the tape head 11 and selection apparatus which includes the cam assembly 10 and which actuates a solenoid 12 for adjusting the track position of the magnetic tape head 11 with respect to the magnetic tape so that one of several tape tracks of the tape is selected for sensing by the head. Since the identical apparatus is illustrated in FIGS. 1 and 2, identical reference numbers will be used to designate corresponding components.

The magnetic tape head 11 is mounted in a generally rectangularly shaped metal bracket 13 which is coupled to a support plate 14 by four parallel arm members 15 which are pivotal at their connection points to the support plate 14. The support plate 14 is rotatably mounted to a support bracket 16 by a relatively large circular rivet 17. The rotational position of the support plate 14 with respect to the bracket 16 is controlled by a spring 18 and a screw 19 which passes through an extending portion 20 of the support plate 14, through the center of the coil spring 18 and is received by a threaded opening in a chassis 21 of the tape player. The support bracket 16 is rigidly attached to the chassis 21. Adjustment of the screw 19 provides for rotating the plate 14 with respect to the bracket 16 and thereby provides rotation of the magnetic tape head 11.

A pair of springs 22 are coupled between the support plate 14 and the head mounting bracket 13. The springs are mounted such that they are in tension and normally extend in a downward direction from the support plate 14 to the bracket 13. This positioning results in biasing the tape head 11 in an upward direction as generally indicated by the reference arrow A. A cam follower member 23 is riveted to an extending portion 24 of the head mounting bracket 13 and has a portion 23a which extends away from the tape head 11 and support bracket 13. The cam follower portion 23a has angled side projections 23b which aid in providing smooth transistions between the different vertical positions of the cam follower portion 23a that will be selected by the cam assembly 10.

Basically, all of the components described so far provide a rotatably adjustable tape head 11 having a cam follower member 23 rigidly coupled to the tape head and mechanically biased in the direction A. While the specific components which provide this result have been described, the use of any tape head positioning assembly which provides this result is contemplated by the present invention.

A cylindrical mounting stud 24 has one end rigidly mounted directly to the chassis 21 and extends in an upward direction corresponding to the direction A. The stud is threaded at its upper one-third extending end portion. A wave washer 25 is mounted on the stud 24 and is positioned adjacent to the chassis 21. The wave washer provides a slight mechanical spring bias in the A direction for the subsequent components which are to be mounted on the stud 24. A flat washer 26 having a larger outer diameter than the wave washer 25 is mounted on the stud 24 on the top of the wave washer. A ratchet wheel member 27 is mounted on the stud 24 on top of the washer 26 and is rotatable about the central longitudinal axis of the stud which is designated by the reference number 28. The ratchet member 27 comprises a lower ratchet wheel portion 29 and an upper ball bearing cage structure 30 which has a generally cylindrical shape. Pawl members 31 are positioned about the ratchet wheel portion 29 and are connected to a bracket 32 which is rigidly connected to an armature 33 of the solenoid 12. A spring 34 is used for mechanically biasing and positioning the pawl members 31 when the solenoid 12 is deenergized. The operation of the solenoid 12, pawl members 31 and ratchet wheel 29 is well known to those of ordinary skill in the art and therefore will not be discussed in any detail. The basic function of these members is to provide for a quarter turn revolution of the ratchet member 27 about the axis 28 in response to the actuation and deactuation of the solenoid 12. Thus four nominal rotary positions of the member 27 with respect to the axis 28 are provided.

The ball bearing cage 30 is generally disc shaped and has a larger diameter than the ratchet portion 29. This creates an outer peripheral area of the ball bearing cage 30. Four cylindral through holes 35 each having different diameter dimensions are provided in the outer peripheral portion of the ball bearing cage 30. Each of the holes 35 comprise a first diameter portion 35a which opens onto a top surface 36 of the cage member 30 and a smaller diameter portion 35b which does not open onto the top surface 36 but opens onto the bottom surface of the ball bearing cage 30. Four precision metallic ball bearings 37 are positioned in each of the openings 35, each ball bearing having a different diameter dimension. The first diameter portion 35a is larger than the diameter of its corresponding ball bearing and the second diameter portion 35b is smaller than the diameter of its corresponding ball bearing. Thus the smaller diameter portion 35b forms a seating structure for the ball bearing.

Four short cylindrically shaped spacing projections 38 are present on the surface 36 and are used for determining the minimum possible distance between the top surface 36 of the ball bearing cage 30 and a reference surface 40 which forms the bottom surface of a generally disc shaped member 41 which is screwed on to the threaded portion of the stud 24 on top of the ratchet member 27. The reference surface 40 is planar and lies in substantially a single plane. This reference surface together with the smaller diameter portions 35b form a captivating structure for the ball bearings 37 and retain these ball bearings such that they will remain substantially positioned between the smaller diameter portions 35b and the reference surface 40. The minimum spacing between the surface 40 and the smaller diameter portions 35 b is determined by the spacing projections 38, not by the ball bearings 37. The wave washer 25 provides spring bias for biasing the ball bearing cage member 30 toward the reference surface 40 and therefore insuring that the ball bearings will remain captivated during the rotation of the ratchet wheel 27.

The spacing projections 38 prevent the reference surface 40 from exerting a large force against the ball bearings 37 when the member 41 is screwed on to the stud 24 during the assembly of all the components which are mounted on the stud 24. The member 41 is contemplated as being constructed such that it forms a self-locking locknut when it is screwed onto the stud 24. Thus the member 41 will not rotate about the axis 28 during the rotation of the ratchet wheel 27 and ball bearings 37. The locknut construction of the member 41 provides for easily adjusting the position of the reference surface 40 with respect to the chassis 21 and retaining the member 41 in its adjusted position.

The cam follower projection 23a is positioned with respect to the threaded stud 24 and ball bearing cage 30 such that at the four different nominal rotational positions of the ratchet wheel member 27, each one of the four different diameter ball bearings 37 will be positioned between the reference surface 40 and the cam follower projection 23a. The cam follower 23 is located in a substantial fixed rotary position with respect to the axis 28 in a plane perpendicular to the axis 28. In other words, the cam follower 23 is not rotatable about the axis 28 and only moves in directions parallel to the axis 28 in response to the rotation of the wheel 27.

The operation of the present invention will now be discussed in detail. The cam follower member 23 determines the vertical position of the tape head 11 in the A direction. The cam follower portion 23a is adaptable for being positioned at several different predetermined distances with respect to the reference surface 40 and the position of the reference surface with respect to the chassis 21 is adjustable. The solenoid 12, the pawl members 31, the ratchel wheel 27 and the ball bearings 37 generally form a cam means which includes at least a first and second ball bearing which selectively alters the position of the cam follower 23 with respect to the reference surface 40 by selectively positioning the first and second ball bearings between the portion 23a of the cam follower member and the reference surface 40. The cam follower 23 is biased toward the reference surface 40 in the A direction by the springs 22 and the distance between the cam follower portion 23a and the reference surface, in each of the four rotary positions of the wheel 27, is determined by the diameter of one of the precision ball bearings 37, as is clearly illustrated in FIG. 1.

When a change in the vertical position of the tape head 11 is desired, the solenoid 12 is actuated and subsequently deactuated. This results in linear movement of the solenoid armature 33 which imparts a linear movement to the pawl members 31 in response thereto. The linear movement of the pawl members 31 results in a quarter turn revolution of the ratchet wheel 27 by principles which are well known to those of ordinary skill in the art. This quarter turn of the ratchet wheel results in positioning a different one of the ball bearings 37 between the cam follower portion 23a and the reference surface 40. Thus a different vertical position of the magnetic tape head 11 has been provided.

Both the cam follower 23 and the reference member 40 remain in fixed rotary positions with respect to the axis 28 during the rotation of the ratchet wheel 27. Thus the rotation of the rachet wheel results in the vertical movement of the tape head 11 and the amount of this vertical movement is totally determined by the difference in the diameters of the ball bearings 37 which are provided between the cam follower portion 23a and the reference surface 40. Precision ball bearings are extremely inexpensive compared to the cost of a manufactured cam which has cam surfaces that are precisely positioned with respect to each other. Thus the present invention has provided an improved cam assembly in which precision changes in the position of a cam follower has been implemented by the use of precision ball bearings rather than by the use of an expensive cam having surfaces which are precisely formed on it.

Initial adjustment of the vertical position of the tape head 11 is accomplished by altering the position of the reference member 41 on the stud 24. Thus the initial vertical position of the tape head is accomplished by a simple screw adjustment of the reference member 41. Rotation of the tape head 11 is accomplished by rotating the plate 14 in response to the adjustment of the screw 19. Four different vertical positions of the tape head 11 are provided by the cam assembly 10 illustrated in FIGS. 1 and 2 and the movement of the tape head between these positions is precisely controlled by the diameters of precision ball bearings. Thus an inexpensive, accurate, and readily adjustable cam assembly has been provided for adjusting the position of a magnetic head in a tape player/recorder.

While the preferred embodiment of the present invention illustrates the rotation of the wheel 27 by the combination of a ratchet portion 29 and pawl members 31, any rotation drive apparatus can be used with the present invention. In fact, the use of a ball bearing cam assembly can be implemented without the use of any rotational movement. While I have shown and described a specific embodiment of this invention, further modifications and improvements will occur to those skilled in the art. All such modifications which retain the basic underlying principles which are disclosed and claimed herein are within the scope of this invention.