US2464032A

US2464032A - Stylus construction and method

Info

Publication number: US2464032A
Application number: US583559A
Authority: US
Inventors: Franz Frederick
Original assignee: Dictaphone Corp
Current assignee: Dictaphone Corp
Priority date: 1945-03-19
Filing date: 1945-03-19
Publication date: 1949-03-08
Anticipated expiration: 1966-03-08

Description

March 8, 1949. FRANZ 2,464,032

STYLUS CONSTRUCTION AND METHOD 2 Sheets-Sheet 1 Filed March 19, 1945 I I &

INVENTOR Z,/ Frederick 1 171222! March 8, 1949. F. FRANZ 2,464,032

STYLUS CONSTRUCTION AND METHOD Filed March 19, 1945. 2 Sheets-Sheet 2 Grinding Angle of Recession Fuce\ Grinding Angle of Recession Angle Recession Approach 12 Cylinder Angle Approach x" Cylinder Tracing 50 intersection 48 5 11. n 1a.

Included Angle Included Angle of Recession of Approach 0 ession of A In of Approach --of An le'of rfnding ()sqjllu ion Grinding scil olion lNVENTOR E'ecbrwfi F'ranz Rccession A preach BY Radius I Radius \z AL AL. mu amf MWQ RGCBSSIOD cylinder Grinding Surface Approach cylinder -li Patented Mar. 8, 1949 UNITED STATES PATENT OFFICE STYLUS CONSTRUCTION AND METHOD Frederick Franz, West Haven, Conn., assignor to Dictaphone Corporation, New York, N. Y., a corporation of New York Application March 19, 1945, Serial No. 583,559

3 Claims. 1

This invention relates to styli for recording and/or reproducing sound vibrations, and for translating vibrations in general between a translating head and a record medium. More speciflcally it pertains to a type of stylus for recording and/or reproducing with an embossed sound track as distinguished from that type of sound track which is produced by the removal of a chip. It also relates to methods of forming such styli. And it is an object of the invention to provide styli of the character described which have'greater mechanical strength and better frequency response than known styli, and to provide methods of making such styli. Other objects will be in part pointed out as the description proceeds and will in part become apparent therefrom.

By way of explaining the present invention it will be described as embodied in an embossing stylus for use in recording upon a plastic sheet. The invention accordingly consists in the features of construction, combinations of elements, methods of operations and arrangements of parts as will be exemplified in the structure to .be hereinafter described and the scope of the application of which will be set forth in the accompanying claims. The following description will refer to the accompanying drawings illustrating this embodiment in which:

Figure 1 is a diagram illustrating on an enlarged scale a portion of a sound wave;

Figure 2 is a cross-sectional elevational view on an enlarged scale taken through a recording medium which has been embossed with a sound wave;

Figure 3 is a fragmentary side elevational view on an enlarged scale, partly in section, showing the point of a previously known embossing stylus in operative relat onship with a record medium;

Figure 4 is an angular view of the stylus point taken along the line 4-4 of Figure 3;

Figure 5 is an angular view of the stylus point taken along the line 55 of Figure 3;

Figure 6 is a diagrammatic plan View on an enlarged scale showing some of the relationships between the tip of a recording stylus and a sound wave being recorded upon a record medium;

Figure 7 is a plan view on an enlarged scale of a stylus embodying the present invention and lying on one side:

Figure 8 is an elevational view of the stylus of Figure '7 looking in the direction of the arrows 8-8;

Figure 9 is an elevational view of the other side of the stylus of Figure 7 looking in the direction of the arrows 9--9;

Figure 10 is an enlarged elevational view showing some of the geometrical relationships between the point of a stylus embodying the invention and a record surface;

Figure 11 is a view of a .portion of the stylus of Figure 10, taken along the line ll-ll; and

Figure 12 is a view of a portion of the stylus of Figure 10, taken along the line |2-|2.

Sound recordings may be made upon comparatively soft plastics such as wax, or upon harder materials such as aluminum, or upon a number of the thermo-plastic compoundsparticularly ethyl cellulose, cellulose acetate, cellulose nitrate and several of the vinyl compounds.

When recording on these materials, two different systems have been used. One, used particularly with the softer plastics, consists in the actual cutting of a groove out of the material. This requires a cutting stylus made from very hard steel or preferably sapphire or diamond. The tip of such a stylus is usually made in a V-shape with a flat front face practically perpendicular to the material which is being engraved. The point of the V is not sharp but is rounded off at a small radius of from 0.001 in. to 0.003 in. The standard for disc recording is 0.0022 inv The cutting of these harder materials requires a sharp stylus. In order to maintain the requisite sharpness, it is necessary to regrind or replace the stylus at frequent intervals.

The other system of recording is the embossing method. It does not require frequent stylus replacement and does not involve throwing oil. a chip which would have to be eliminated in some manner. When embossing, the recording stylus causes the material to flow to each side of the stylus. The record material has to be soft enough for this flowing to occur smoothly and uniformly and the stylus has to be so shaped that the flowing occurs in such a manner that the smoothest possible groove is produced; and

it must give a recording of satisfactory frequency response.

Among the earlier embossing styli constructions was one made by axially rotating an engraving type stylus through with respect to the translating head and then tipping it at a slight angle from the perpendicular and toward the approaching recording medium, thus producing a V-groove in the record surface. This stylus gave excellent frequency response characteristics but the comparatively sharp point was very easily broken, particularly if the recording medium for any reason was reversed in its direction of travel. In the event of such reversal, the point tended to dig into the record material, piercing it and striking a metal backing which in turn caused the point to be chipped.

Some of this difficulty was overcome by using a conical stylus with a spherical end having a radius of 0.001 to 0.002 in. This had somewhat greater strength but its use required displacement of a greater amount'of recording medium. The frequency response in this case was largely determinded-by the tip radius and this could not be made small enough to give the best high frequency response without again reducing its mechanical strength. Various combinations of flattened and/or rounded stylus surfaces were tried at one time or another, but unsuccessfully, because no stylus having good recording qualities over a wide frequency range was of sufilcient mechanical strength to render satisfactory commercial service.

Because of these physical difilculties many theoretical studies have been made of this problem to determine just how a better stylus could be produced. I have discovered a certain relationship of shapes which result in an enormous improvement, as far as mechanical strength is concerned, and which, at the same time, give excellent recording properties over a broad frequency band and which prevent digging into the record material upon reversal of direction. Before going into the details of these relationships some general observations regarding sound recordings will first be made. Some of these observations have previously. been made by others but they serve as an introduction for my own discoveries.

The track traced on a moving record by a stylus which is vibrated by sound may be described as having two components-first, a longitudinal, and second, a lateral, component. The longitudinal component is generally described as the wave length, and the lateral component as the amplitude, of the vibration. Both of these elements ar e indicated by line 20in Figure 1. Here, a 200 cycle per second sound wave having a 0.002 in. double amplitude has been drawn to a scale of 200 to 1 as it would appear on a record surface moving with respect to the stylus at a rate of 22 feet per minute. This wave length, however, is represented by only the center line 20 of the groove which would be produced in the record stylus. (Note: I use throughout a, record surface velocity of 22 feet per minute because it is one of the standard speeds of such machines as are illustrated in Yerkovich Patent No. 2,318,828, issued May 11, 1943.)

In Figure 6 may be seen both the shape of the wave form and also the width of the track for a 2500 cycle wave having an amplitude of 0.00075 in. similarly recorded and drawn on a scale of 1000 to 1. Assuming that the width of the tracing part of the stylus were a straight line 0.0021 in. in length, as indicated in Figure 6 at 2i, the two enveloping curves of the track would be produced, and would be disposed symmetrically in regard to the center line of the path- The curves (outside envelopes and centralpath) would be identical since longitudinal and lateral motions are identical.

If, however, the tracing end of the stylus, instead of having only one dimension, that is length by the up and down on the sheet, also has lateral dimensions, the envelope shown would no longer be traced with fidelity. In Figure 6 this lack of tracing fidelity is shown for a stylus having a tracing point of approximately the triangular cross-sectional shape outlined by the dotted curved lines 34. It will be noted that as this point proceeds along its path (Figure 6) a crosshatched area is wiped out before the widest portions of the stylus reach this area, so that when 4 the upper corner of the stylus traces its true curve in the cross-hatched area the record of the truly traced curve is not impressed on the record material. The amount of obliteration of the yet ungenerated sound track depends upon the dimensions and shape of the stylus and upon the direction of motion of the stylus upon the record material. If the tracing point of the stylus approximates a straight line, as shown at 2|, the track left on the record will be more nearly in conformity with the original motion of the recorder than if the stylus dimensions are as shown by the curved lines 34 of Figure 6.

In Figures 2-5 the exact shape of the end of one of the commonest embossing styli, in contact with and pressing upon the record material, is shown.

This type of stylus is sometimes called a spade stylus. and in Figure 3 it is drawn to scale and shown enlarged, 1,000 times. Here a recording medium 22 appears bearing a sound groove 24 made by a stylus point 26. In Figure 4 a crosshatched area 28 appears. This is the area of the record surface which is in contact with point 26 at any given time and itis bounded on its approach side by a line' 30.

In order to obtain an undistorted simple harmonic curve when this shape is used as a generating point, it is necessary to limit the maximum slope of the recorded sound track (and hence the maximum recorded frequency) to 24. This is because the angle of the slope of line 30 (see Figure 5) is 24. When the maximum curve slope is 53, for example, as in thecase when a. 2500 cycle wave of 0.00075 in. amplitude is recorded (illustrated in Figure 6), this wave will be partly obliterated by the generating point (see crosshatched area of Figure 6) before thegenerating portions of the stylus will have recorded the curve.

It will be noted (Figure 3) that the leading face of this stylus makes an angle of 13 with the plane of the recording medium. It will also be noted that the-trailing face makes an angle of 117 with the plane of the recording medium. This leaves an included angle of 50 between the faces'of the stylus. This small and sharp point is weak and is a source of many breakages. A primary object of this invention was to increase the strength of this point and simultaneously to improve its 'recording properties. This object was achieved by structurally strengthening the point and reshaping the various surfaces so that the point would trace sound grooves in fidelity with the movement of the stylus.

In the discussion of this new stylus, it will be well first to define three angles:

1. The angle of approach.This is the angle between the leading edge of the stylus which produces the groove-and the recording surface.

2. The angle of recession-This is the angle between the trailing edge of the recording stylus and the recording material.

3. The included angle of approach or of recession-This is a dihedral angle formed in the approach (or recession) face of the stylus. The

record material is flowed to both sides of the stylus under the influence of this dihedral approach face in somewhat the same manner that water flows past both sides of the prow of a ship.

The approach angle is determined by-the depth of groove required, the hardness of the material and the frequency response desired. The greater the angle, the greater the depth of the groove and the better the high frequency response-within certain limits. The" harder the material, the

greater this angle may be. The pressure on the .chosen because the greater the pressure, the

smaller the approach angle must be to retain a suitable depth of groove.

Approach angles varying from to 38 have been found workable but an angle of about has been found to give the best balance of various characteristics for most recordings. This can produce recordings with not more than 6 decibels difference between 300 and 2500 cycles when used on a'machine of the type described and claimed in the aforementioned Yerkovich patent. The top useful frequency response runs up to about 4500 cycles.

The recession angle has great effect on the mechanical strength of the embossing point. It has a somewhat lesser effect on the depth of the groove. The smaller this angle, the shallower is the embossing. Recession angles of from 10 to 75 have been used but one of about 60 has been found advantageous for most purposes. Unless the recession angle is equal to, orgreater than, the approach angle some obliteration of the sound track may result at higher frequencies from interference by the recession face.

The included angle of approach influences the width of the groove for a given depth and also influences the depth of thegroove for a given pres sure. An included angle of 60 has been found satisfactory, although if very high frequency response is desired it may be well to increase the included angle of approach to something over 100 and at the same time to increase the angle of approach.

The intersection of the two planes forming the dihedral on the approach side (also on the recession side) is not sharp, but terminates in a radius. This radius ordinarily varies from about 0.0005 to 0.003 in. although the amount of the radius will depend upon the hardness of the particular material upon which the sound groove is embossed and the spacing between adjacent grooves. The recession faces come together with a somewhat greater radius, depending, however, upon the radlus on the approach side, as will be described hereinafter. These radii give the stylus a rounded point, when viewed in profile along the groove being embossed, somewhat like the profile of the spade stylus pont of Figures 2-5. Such a point is both mechanically stronger and produces a higher quality of recording than would result from the sharp point which would be present if the approach and recession faces were true dihedrals lacking the intermediate central radii.

The obtuse angle which occurs at the recording point between the approach and recession faces permits a reversal of the direction of the recording medium under the stylus without causing the point to dig into it. Rather, it has a tendency to raise the point out of the groove.

Tests made with points constructed according to the invention have given recordings of improved frequency response in both high and low frequencies, showing less distortion and surface noises, and having higher efficiency of reproduction. And these points have demonstrated enor-. mously increased resistance to impact over spade or conical styli.

In Figure 7 a stylus embodying the invention is generally indicated at 40 having a flat 42 for conventional use in correctly orienting the stylus shank in the recording head. Stylus 40 preferably is made of aluminum or similar material and has a shank diameter on the order of 0.062 in. At the point of the stylus a sapphire 44 on 6 the order of 0.018-0.040 in. diameter is embedded in the stylus shank. The stylus is ground to a point indicated at 46 consisting of an approach surface 48 and a recession surface 50. These two surfaces intersect to form a tracing intersection indicated (Figure '7) at 52.

Figures 10, 11 and 12 illustrate on an enlarged scale the ground sapphire with various legends on the drawings pointing out particular portions. Figure 10 shows the jewel point superimposed upon a pair of X and Y (to-ordinates intersecting at O and with the tip of the jewel coinciding with point 0. The jewel axis is indicated as also passing through point 0 and the angle between the Y axis and the jewel axis is identified as the angle of presentation. With the relationship illustrated in Figure 10, relative movement of the surface of the recording medium with respect to thejewel would be to the left, along the X axis or else along a curved surface wherein tangents to the surface at the point of contact would correspond to the X axis. 7

As pointed out previously, the angle between the front face of the stylus point and the X axis is indicated as the approach angle. Similarly the angle between the rear face of the stylus point and the X axis is indicated as the recession angle. The approach face of the point is ground or lapped on the stylusby establishing an approach grinding axis (see Figure 12) parallel to the grinding surface and spaced therefrom by an amount greater than the approach radius. The stylus is then oscillated about this axis to grind the approach face and is fed toward the grinding surface until separated from it by an amount equal to the approach radius. Thereafter a recession grinding axis is established parallel to the grinding surface and spaced therefrom by an amount greater than the recession radius. The stylus is then oscillated through an angle to grind the recession face and simultaneously is fed toward the grinding surface until the recession radius is reached. It is notessential that the grinding axes be parallel to the grinding surface at the beginning of the grinding opera.- tions but each axis should be substantially parallel to the grinding surface as the grinding of each face is completed in order to maintain accuracy among the various ground surfaces. The angles through which the stylus must be oscillated to form these surfaces are indicated in Figures 11 and 12 as the angles of oscillation. The grinding angle of the approach face and the grinding angle of the recession face are pointedout in Figure 10. They are, respectively, the angle between the jewel. axis and the approach grinding axis and between the jewel axis and the recession grindmg axis.

With the process described it will be observed that the approach face is formed by a pair of pane surfaces bounded at the center by a por tion of a cylinder tangentially blended therebetween and indicated as the approach cylinder.

Similarly, the recession face is made of two planes and an intermediate recession cylinder. Insofar as I know at present, either the approach face or recession face may be ground first although it is possible that the grinding or lapping process may leave a minute burr along the tracing intersection where these surfaces come together. If this is in fact so then the recession surface should be ground first and the approach surface second.

I have found it advisable to keep the intersection of the cylindrical faces at the approach and the recession edges (tracing intersection) such that it is always approximately normal to the plane of the recording medium. If approach and recession faces are otherwise symmetrical, the radii of the approach and recession cylinders should also be equal. This must be so in order to have theirintersection normal to the plane of the recording medium. As the recession angle approaches the normal, the recession radius should increase and when the recession face is normal to the plane of the recording'medium the recession radius becomes infinite, resulting in a. flat face. If the tracing intersection is not perpendicularto the plane of the recording surface, then the upper part of the embossed groove will either be ahead of or trailing behind the corresponding portion of the bottom of the groove so that the upper and lower portions of the groove will not be in phase. A reproducing stylus having a tracing intersection arranged at the same departure from the normal would reproduce such a groove but in general it is more satisfactory to maintain the tracing intersection perpendicular.

The manner in which the various surfaces are ground will determine the location of the tracing intersection and these in turn must be established with regard to the amount of the angle of presentation. After the approach angle and recession angle have been established and the angle of presentation is known, the tracing intersection can be made to determine a plane parallel to the Y axis by geometrical selection of the radius of the recession cylinder with respect to the correct radius of the approach cylinder and by the correct selection of the included angle of approach and included angle of recession. These two last-mentioned angles, as will be apparent from Figures 11 and 12, depend upon the amount of the angles of oscillation.

I have found that excellent results ensue if the following relationships are observed:

From the foregoing it will be observed that styli and methods of operations upon styli embodying my invention are well adapted to attain the Lids and objects hereinbefore set forth and in bein commercially exploited since all fea- +ures are readily suited to conventional manufaching expedients and lend themselves to such variations as will be necessitated in applying the invention to different applications.

As variousembodiments may be made of the above invention and as changes might be made in the embodiments above set forth, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. The method of shaping a vibration translatin point on a stylus by means of a. grinding surface which includes the steps of establishing a. first grinding axis about which a first partial cylindrical surface is to be ground, grinding said partial cylindrical surface by feeding said stylus toward said grinding surface and oscillating it back and forth through a predetermined angle about the grinding axis until said grinding axis is substantially parallel to said grinding surface and which a second partial cylindrical surface is to be ground, and grinding said second partial cylindrical surface by feeding said stylus toward said grinding surface and oscillating it back and forth through a second predetermined angle about the grinding axis until said second grinding axis is substantially parallel to said grinding surface and spaced therefrom by an amount equal to the desired radius of curvature of said second partial cylindrical surface.

2. The method of shaping a smoothly curved vibration translating point on a stylus by means of a fiat grinding surface which includes the steps of establishing a grindin axis about which a partial cylindrical surface is to be ground, and grinding said partial cylindrical surface by feeding said stylus toward said grinding surface and oscillating said stylus through a predetermined angle and about said grinding axis until said grinding axis is substantially parallel to said grinding surface and spaced therefrom by an amount equal to the desired radius of curvature of said partial cylindrical surface, whereby a dihedral-like surface is formed having the planes thereof set with respect to each other at the supplement of said predetermined angle and a cylindrically curved surface of said desired radius of curvature blending between the planes.

3. The method of putting a vibration translating point on a stylus which includes the steps of: presenting a portion of the stylus to a grinding surface for shaping; oscillating the stylus through a predetermined angle about a first axis spaced from the surface and thus shaping a first dihedral-like angle on the stylus; reorienting the stylus with respect to the grinding surface and presenting a symmetrically abutting portion of the stylus to the surface for shaping; and oscillating the stylus through a second predetermined angle about a second axis spaced from the surface, said second axis lying in the plane which bisects said first dihedral-like angle, and said axes intersecting at an angle.

. FREDERICK FRANZ.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS