GB2126407A - Holder for a disc record signal pickup stylus - Google Patents

Abstract

A stylus holder for e.g. a video disc capacitive stylus provides vertical a decoupling of the pickup stylus from the stylus support pickup arm (12'), a shim stock stylus holder 56 being provided for coupling the stylus 8' to arm 12'. Preferably the holder (56) is of plastic and crimped into arm 12' of aluminium tube. Damping means 28' prevents or reduces mechanical oscillation. Dimensions are given. Alternative damping means (64, 66), (64', 66') are disclosed (Figures 3, 4), and further embodiments with damping facilities as in (Figures 5a-6b). The stylus holder may be wedge-shaped. <IMAGE>

Description

SPECIFICATION Holder for a disc record signal pickup stylus The present invention relates to a holder for a disc record signal pickup stylus. Illustratively the holder is for holding a signal pickup stylus of a capacitive video disc, and reference is is made herein by way of example to such a holder and to a capacitive video disc system.

In U.S. Patent No. 3,842,194, issued to J.K. Clemens, video disc playback systems of a variable capacitance form are disclosed. In one configuration of the Clemens system, information representative of recorded picture and sound is encoded in the form of a relief pattern in a relatively fine spiral groove (information track) on a surface of a disc record.

During playback, a stylus engages the spiral groove.

Capacitive variations between a conductive electrode on the stylus and a conductive property of the disc record are sensed to recover the pre-recorded information.

In commercial capacitive disc systems, the stylus is secured to one end of a relatively long stylus arm while the other end is compliantly secured to a carriage mechanism. The carriage mechanism translates the stylus-stylus arm assembly across the disc in a radial direction at a speed in consonance with the radial movement associated with the stylus following the information track.

The stylus arm is arranged so that it is substantially tangent to the information track from which the signal is being recovered. To maintain proper stylusdisc relative velocity an arm stretcher transducer is coupled to one end of the stylus arm and secured to the carriage for the purpose of creating longitudinal movement in the stylus arm. Further, a transducer or motor is coupled to the stylus arm for selectively producing lateral or side-to-side translations of the stylus. This second transducer is provided to effect stylus tracking to maintain the stylus in the correct groove convolution.

In order to facilitate these features in a video disc player, the stylus arm should be relatively long and relatively rigid or stiff. Even though the stylus arm may be rigid, the stylus should be secured to the stylus arm to afford a degree of vertical decoupling.

When the stylus tracks over imperfections in the groove (e.g., craters or dust particles along the groove) there is a tendency for the stylus to be lofted out of contact with the disc surface. Thus, it has been found to be advantageous to mount the stylus in a less rigid (resilient) holder, e.g., plastic, which, in turn, is fixed to the stylus arm. In general, the resilient holder has an elongated section colinear with the longitudinal axis of the stylus arm and yields vertically to permit the stylus to ride over bumps on the disc independent of the vertical inertia of the stylus arm itself. For an example of a stylus arm-stylus holder-cartridge assembly for use in a video disc player reference may be made to U.S.

Patent No. 4,030,124, entitled "VIDEO DISC PLAY BACK SYSTEM AND PICKUP CARTRIDGE THERE OF", issued on June 14, 1977 to J.A. Allen.

In the prior art, the stylus holder has been formed of molded plastic. The molded part is generally expensive to manufacture and tool, hard to modify and subject to deleterious deformation. The plastic mold used for manufacturing a small part such as the video disc stylus holder is relatively expensive.

Additionally, the piece cost for molded parts is relatively high when compared to non-molded parts of similar size. For example, the molding process generally requires a deflashing operation which increases piece cost, further, such an operation may deform it.

Another problem associated with a molded stylus holder is its inflexibility of design. Sometimes it is necessary to change the stylus holder so that it may be used with a different stylus or cartridge. A molded part designed for a specific structure seldom lends itself to modifications for use with a different structure. Thus, adapting a molded stylus holder for other designs has been practically impossible and generally has required the manufacture of a new mold.

Furthermore, molded plastic parts must be inspected for deformation after the molding process.

Cooling, ejection, etc. during the molding operation can affect the shape and form of the part. For this reason, a careful inspection of molded plastic parts is required before assembly.

According to the present invention, a resilient, nonconductive sheet of material is used as the holder for a signal pickup stylus.

In accordance with one embodiment of the present invention, the stylus arm for use in recovering information from a disc record comprises a sheet of nonconductive, resilient material having stylus and distal end sections and a support member having first and second end sections. The support member is attached to a cartridge. A crimp, attached to the support member, is provided to grip the distal end section of the sheet of resilient material, thus holding it in position.

In accordance with another embodiment of the present invention the stylus arm for use in recovering information from a disc record, comprises a tubular member having first and second end sections. The first end section of the tubular member is coupled to a supporting wall of a cartridge. Further, the stylus arm includes a flat, non-conductive, resilient slip having stylus and distal end sections. In one configuration the second end section of the tubular member is crimped on the distal end section of the slip such that the slip is fixedly mounted to the tubular member. During certain information recovery the slip member may experience mechanical oscillation, i.e., the slip may have resonant modes at which it may be mechanically excited into oscillation. The mechanical oscillation may affect the information recovered from the disc record.Therefore, when desirable, damping means are coupled to the slip for mechanically damping the mechanical oscillation. A signal pickup stylus is secured to the stylus end section of the slip.

In the drawings: Figure 1 is a cut-away side view of a prior art video disc player signal pickup cartridge; Figures 2a and 2b are perspective and cross sectional views, respectively, of an illustrative video disc signal pickup arm according to the present invention; Figures 3 and 4 are perspective views of a portion of another illustrative video disc signal pickup arm according to the present invention; Figures 5a and 5b are plan and side views, respectively, of an illustrative holder according to the present invention; and Figures 6a and 6b are plan and side views, respectively, of another illustrative stylus holder according to the present invention.

Referring to Figure 1, there is shown a cut-away view of a signal pickup cartridge 2. The cartridge has side walls 4 (only one shown) and a top wall 6 rigidly holding the side walls in a spaced apart relationship.

The bottom plane of cartridge 2 is open. The top wall 6 and side walls 4 of cartridge 2 form an enclosure in which a signal pickup stylus 8 is supported.

In the prior art, pickup stylus 8 is mounted to a molded stylus holder 10 (e.g., a molded plastic element) which is rigidly attached to one end of an elongated, lightweight, tubular stylus arm 12.

Illustratively, stylus arm 12 may be made from aluminum tubing 0.044 inches in diameter having a wall thickness of 0.002 inch. The other end of stylus arm 12 is suspended from the top surface 6 of cartridge 2 by compliant suspension 14. Leaf spring 16, deformed into a compressive arc, is connected between stylus 8 and a shelf 18 integral to cartridge 2, and arranged to tend to expel stylus 8 through the bottom plane of cartridge 2. Leaf spring 16 is secured to shelf 18 by a metallic rivet 20. Leaf spring 16 is typically electrically conductive and serves the dual functions of (a) providing the necessary stylus-disc interactive pressure when the cartridge is positioned for signal recovery (as shown in Figure 1), and (b) for providing electrical connection between the pickup stylus electrode and the signal processing circuitry (not shown).

In the Figure 1 configuration, stylus 8 is shown engaging the top surface of disc 22. The end of stylus arm 12 nearest suspension 14 is hollow for reception therein of a permanent magnet 24 having north and south poles aligned along the longitudinal axis of stylus arm 12. Magnet 24 is designed to cooperate with an electromagnetic coil mounted in the player to provide longitudinal translations of stylus arm 12 for the purpose of performing stylus-disc velocity corrections, i.e., arm stretching, during signal recovery.

A second, generally elongated, permanent magnet 26 is mounted perpendicular to the longitudinal axis of stylus arm 12 and arranged so that its longitudinal axis is substantially vertical, i.e., substantially per pendicu lar to the longitudinal axis of arm 12. The width of magnet 26 is less than the diameter of stylus arm 12 and is inserted in a hole punched therethrough. The north-south poles of magnet 26 lie along its longitudinal axis. Magnet 26 is arranged to cooperate with a second electromagnetic coil (not shown) mounted in the player for the purpose of twisting the stylus arm to effect lateral translations of the stylus. Reference may be made to U.S.Patent No. 4,183,059, entitled "TRACK SKIPPER FOR A VIDEO DISC PLAYER", issued on January 8, 1980 to R.C. Palmerforan illustration of a groove skipper for a grooved video disc system.

A damping mass 28 is provided to damp resonant modes of stylus holder 10. Stylus holders without damping mass 18 provide very satisfactory performance in video disc players which reproduce monaural signals for reproduction on monaural television receivers where the audio bandwidth is typically below 7 KHz. It was discovered, however, that when wideband stereo signals are reproduced from a disc record an erratic noise is present in the recovered signal located in the audio band at about 10 KHz and which is manifested as a hissing sound. This tone is produced by the mechanical resonance of the stylus holder 10 which tends to cause an amplitude and phase modulation of the recovered carrier. When the recovered audio carrier is demodulated both amplitude and phase modulated components contributed by the stylus holder resonance appear in the baseband audio at the resonant frequency.

Cartridge 2 employs both a mechanically lossy mass 28 and a lossy material for securing the mass to holder 10. Stylus holder 10 is molded with a post 30 located approximately at the mid-point of the stylus holder. Lossy mass 28 is formed in an annular shape, e.g., a doughnut, and circumferentially installed over post 30 and secured to post 30 with silicon rubber (e.g., Dow-Corning No. Q3-6527AB or Dow Corning No. 734RTV). Damping mass 28 may be easily produced by cutting sections (0.050 inch) from a length of rubber tubing (0.045 O.D. x 0.019 l.D.

silicon rubber, durometer 30-40). In one particular example, a 1.5 mg. section of silicon rubber tubing installed on a commercially available video disc stylus holder having a 0.15 x 0.02 x 0.02 inch center section (approximately) will satisfactorily reduce the undesirable resonance characteristics in the audio spectrum.

As discussed above, molded stylus holders, for example, stylus holder 10 shown in Figure 1, have several drawbacks. They are generally expensive to manufacture. The tooling is expensive. Modification of the structure for new designs for experimental purposes or for production usually requires a redesign of the mold or major changes in tooling. If the molded parts are not handled properly they may be deformed, thus affecting assembly or playback operations. In accordance with an embodiment of the present invention a stylus holder is provided which may be manufactured from flat shim stock material.

This holder is easy and cheap to manufacture, easy to modify and generally not subject to deformations from the manufacturing process. Further, tooling cost are minimal, e.g., a small punch and die set is all that is required. For new designs a low-cost punch and die set may be purchased at a fraction of the cost of a mold, which was necessary for modifications in the prior art.

Referring to Figure 2a, a perspective view of one particular embodiment of a stylus suspension 50 is shown. In the figures elements designated with like numerals are the same or similar items in the various figures. Stylus suspension 50 includes a tubular stylus arm 12' (illustratively, stylus arm 12' may be manufactured from aluminum tubing as discussed above). Arm stretcher magnet 24' having north and south poles aligned along the longitudinal axis of stylus arm 12' is inserted into one end 52 of stylus arm 12'. A second, generally elongated permanent magnet 26', is fixed to the stylus arm 12' near end 52. Magnet 26' is mounted perpendicular to the longitudinal axis of stylus arm 12'. Magnet 26' effects lateral translations of stylus 8'. The other end 54 of stylus arm 12' is crimped over stylus holder 56.

In this embodiment the stylus holder 56 is formed as a rectangular piece of shim stock material which may be stamped from a large sheet. Stylus holder 56 must be relatively rigid in a direction parallel to a radial direction of the disc record to facilitate tracking of the spiral groove and, at the same time, must be resilient in a direction normal to the surface of the disc record so that stylus 8' is not lofted from the disc surface by disc imperfections. Illustratively, it has been found that a plastic shim stock material works well, e.g., Vinylite (Registered Trademark), clear, rigid 0.010 thick, available from All Plastics, Indianapolis, Indiana, USA, provides the resilience necessary for video disc applications.Stylus holder 56 should be non-conductive for capacitive video disc applications as described herein so that the recovered signal is coupled through the leaf spring to the signal processing circuitry. Further, the stylus holder 56 is formed from shim stock material in a flat shape. In one embodiment, the stylus holder may be formed in the shape of a rectangular parallelopiped having dimensions of .010 x .029 x .430 inch providing a width to thickness ratio of approximately three. In operation, the flat plane of stylus holder 56 is arranged in stylus arm 12' such that it is substantially parallel to the disc surface when stylus 8' engages a groove on the disc.

Crimp 58 formed on end 54 of stylus arm 12' is flattened over one end of stylus holder 56. Crimp 58 may be made by deforming end 54 of stylus arm 12' by using a flat punch against a flat plate (the stylus holder-stylus arm interposed therebetween) mechanically holds stylus holder 56 to stylus arm 12'. In general, no other mechanical or chemical bonding is required to hold stylus holder 56. In accordance with one preferred embodiment the flattened portion of crimp 58 is formed such that the flattened portion of the crimp is offset with respect to longitudinal axis of stylus arm 12'. The crimp is offset from the centerline of stylus arm 12' so that the bottom edge of the crimp is substantially tangent to the bottom edge of the tube in order to provide improved clearance between the bottom of stylus arm 12' and the disc surface during playback operations.Referring to Figure 2b a cross-section of crimp 58 is shown.

Leaf spring 16', deformed in a compressive arc, is connected between stylus 8' and a metallic rivet (not shown) to provide the dual functions discussed herein.

In the embodiment shown in Figure 2, damping mass 28' may be provided to suppress resonant modes of stylus holder 56 which may deleteriously affect playback operations. Illustratively, damping mass 28' is of the type described with reference to the damping mass of Figure 1, and having a post 30.

Other forms of mass 28' may be used however.

In one particularly advantageous embodiment of a shim stock stylus holder, stylus 8' is staked directly into the flat holder 56. The staking operation provides the mechanical contact necessary to hold stylus 8' in position with respect to stylus holder 56.

Further, the staking operation eliminates any re quirementfor drilling a hole or the like into the shim stock material prior to placing stylus 8' in the shim stock.

Referring to Figures 3 and 4, two embodiments of stylus holder structure are shown. Reference can be made to U.S. Patent Application Serial No. 413,423, entitled "STYLUS HOLDER HAVING LAMINATED DAMPING MATERIAL", filed August 1982 in the name of G.H.N. Riddle for a further discussion of the damping technique of the embodiments of Figures 3 and 4. Attention is invited to British Patent Application 8309288 which, inter alia, includes a discussion of that damping technique.

Figures 3 and 4 show perspective views of a portion of a stylus suspension. Referring to Figure 3, stylus arm 12" is crimped over stylus holder 60.

Stylus 8" is staked into stylus holder 60 and leaf spring 16" provides the connection between stylus 8" and a metallic rivet (not shown) formed in the cartridge wall (not shown). Stylus holder 60 includes a thin, rectangular slip of flat shim stock material 62 (illustratively, the shim stock may be made from a thin plastic sheet of material). Overlying the shim stock are layers 64, 66 of damping material which are applied to the upper and lower surfaces of slip 62 respectively. Damping material 64 and 66 aids in suppressing the resonant modes of stylus holder 60.

Illustratively, damping material 64,66 may be formed of electrical tape (e.g., Scotch Brand No. 35 electrical tape).

Referring to Figure 4, another embodiment of a stylus holder is shown. According to Figure 4, the layers 64' and 66' of damping material are applied on one side of slip 62'. It is felt that application of the damping layers to the surface of slip 62' opposite the disc surface may prevent the tape from interfering with the playback process. Should the damping material peel off from age or the like it is less likely that it would interfere with playback if it is remote from the playback surface. It should be noted that in one preferred embodiment a single layer of damping material is applied on the top surface of slip 62' to effect damping. The number of layers of damping material is a function of the weight and resilience of the structure as a whole.

One feature of the present invention is described with reference to Figures 5a, 5b, 6a, and 6b. Figures 5a and 5b are plan and side views, respectively, of a stylus holder 100 comprising a slip 102 and a damping layer 104. Holder 100 has a width, W, to accommodate a stylus log 106 having a width, T.

One of the advantageous features of the present invention is its adjustability to new designs. Figures 6a and 6b show plan and side views, respectively, of stylus holder 100' comprising slip 102' and damping layer 104'. A stylus log 106' has a width, D, which is on the order of width, W, of the width of the stylus holder of Figures 5a and 5b. The wider log width, D, will not stake into a holder that is approximately equal to width, W. Log 106' may break out the sides around the log of stylus holder 100' if the width of the stylus holder is too narrow. Further, the wider log means, in general, a heavier mass on the end of holder 100', thus, requIring more rigidity to maintain tracking force. In accordance with Figures 6a and 6b, a wider and heavier stylus log is accomodated by providing a stylus holder 100' having a widened portion 108, i.e., width, U. These changes in shape of the stylus holder to accommodate various widths, thicknesses, lengths, etc. may be accomplished in the present invention without incurring heavy tooling costs. A relatively cheap die and punch set may be purchased for the various shapes and sizes of interest. Furthermore, experimental designs may be effected where the shape of the stylus holder may be changed for minimal cost.

Other embodiments of the invention will be apparent to those skilled in the art. For example, the shim stock stylus holder according to an embodiment of the present invention may be replaced with a wedge-shaped design instead of a uniformly thick rectangular design as shown herein. Further, the damping may be accomplished by using other masses, heavier or lighter, positioned at different points on the stylus holder.

Claims (21)

1. Apparatus in a cartridge for holding a signal pickup stylus used to recover information from a disc record, said apparatus comprising: an elongated sheet of nonconductive resilient material having stylus and distal end sections; and a support member having first and second end sections, said first end section of said support member being mechanically coupled to said cartridge, said second end section being crimped over said distal end section of said elongated sheet for holding said sheet of resilient material.

2. The apparatus according to Claim 1 wherein said sheet of resilient material is flat.

3. The apparatus according to Claim 2 wherein said sheet of resilient material is of uniform thickness.

4. The apparatus according to Claim 3 wherein said sheet of resilient material is rectangular in shape having length and width dimensions and being elongated along said length dimension to form a longitudinal axis.

5. The apparatus according to Claim 4wherein said sheet of resilient material includes an extension formed along said longitudinal axis and having width perpendicular to said longitudinal axis, the width of said extension being less than the width of said sheet.

6. The apparatus according to Claim 1, 2, 3 4 or 5 wherein said support member is a tubular body.

7. The apparatus according to claim 6 wherein said crimp comprises a flattened portion of said tubular support member.

8. Apparatus in a cartridge for holding a signal pickup stylus, said signal pickup stylus being used to recover information from a disc record, said apparatus including: a tubular member having first and second end sections, said first end section of said tubular member being coupled to a supporting wall of said cartridge; a flat, nonconductive, resilient slip having stylus and distal end sections, said second end section of said tubular member being crimped on said distal end section of said slip such that said slip is fixedly mounted to said tubular member; and signal pickup stylus means secured to said stylus end section of said slip.

9. The apparatus according to claim 8 wherein said flat, nonconductive, resilient slip is formed in the shape of a rectangular parallelopiped having length, width and thickness dimensions and having a longitudinal axis along said length dimension.

10. The apparatus according to claim 9 wherein said flat, nonconductive, resilient slip includes an extension having a width formed along said longitudinal axis, the width of said extension being less than said width of said slip.

11. The apparatus according to claim 8, 9 or 10 wherein the crimp formed on said tubular member is a flattened portion on said second end section of said tubular member.

12. The apparatus according to claim 11 wherein said flattened portion is formed tangentially to the outer surface of said tubular member.

13. The apparatus according to any one of claims 8 to 12 wherein said flat, nonconductive, resilient slip has a uniform thickness.

14. The apparatus according to claim 13 wherein said uniform thickness of said slip is 0.01 inch.

15. The apparatus according to any one of claims 8 to 14 wherein said flat, nonconductive, resilient slip isformed of plastic.

16. The apparatus according to claim 15 wherein said plastic is Vinylite (Registered Trademark).

17. The apparatus according to claim 16 wherein the ratio of the width of said slip to the thickness of said slip is approximately three.

18. A holder for a signal pickup stylus substantially as hereinbefore described with reference to Figures 2a and 2b; or to figures 6a and 6b.

19. A pickup arm comprising a holder according to claim 18.

20. Acartridge including a pickup arm according to claim 19.

21. Acartridge including a signal pickup stylus substantially as hereinbefore described with referenceto Figure 1.