Background—Field of the Invention—Fig 1

This invention relates to magnetic recording, particularly to a magnetic head and disc tester.

Backgroun —Description of Prior Ar —Fig 1

Prior to description of the present invention and for a better understanding of terminology used in the specification, it will be helpful to explain the structure of a typical head and disc tester and a testing procedure.

The main purpose of a head and disc tester is to measure the parameters of a magnetic head or a disc; the tester should simulate the motions of the head with respect to the disc which occur in an actual hard-disc drive.

A typical prior-art head and disc tester is shown schematically at 20 in Fig 1. It has a housing 10 which supports a rotating spindle 12 which in turn supports a hard magnetic disc 14. An arm 16 carries a magnetic head 18 and a drive mechanism (not shown) for moving magnetic head 18 with respect to disc 14. As shown, head 18 is aligned with

arm 16 and thus the long axes of the head and arm are aligned.

Disc 14 has an outer track OD and an inner track ID; these tracks are not visible in an actual disc since they are invisible magnetic patterns on a magnetic medium. Arm 16 moves head 18 between track ID and track OD.

Depending on the type of a drive unit used, known head and disc testers can be divided into three categories: 1) Testers in which arm 16 has a pivot point which is fixed with respect to the center of disc 14 and a fixed length from the pivot to the magnetic head. Such devices are custom-made, are not adjustable, and are intended only for a specific design. 2) Testers in which the movement of the head with respect to the disc is controlled by a cam. For simulating different types of disc drives, one must replace the cam. 3) Testers in which the head is positioned with respect to the disc by an X-Y manipulator.

In order to understand the difference between these three types of head and disc testers, it is necessary to define "skew angle".

Let us consider, e.g., the case of the tester of category 1), i.e., an non-adjustable tester with a fixed pivot point.

Arm 16 is shown in Fig 1 as tangent to track ID. In the course of testing the tracks, arm 16 pivots about its pivot point, so that head

18 moves along a curved path from track ID to track OD. The position of head 18 at track OD is shown by broken lines. It can be seen that in this position, arm 16 and the long axes of head 18 are not tangent to track OD, but rather forms an angle A with respect to the

OD tangent. This angle is called a skew or a tracking error angle. In the example illustrated, skew angle A iiss zzeerroo,, bbuutt tthhiiss iiss sshhoowwnn can have actual values as well only for simplicity of explanation; AID as zero.

A disc drive manufacturer usually wants a tester to imitate the head's motions in the same manner as they occur in the disc drive. Actual

disc drives usually have definite skew angles A and A , and these skew angles are used as input data for the tester. From this viewpoint, the testers of category 1) are suitable only for fixed skew anqles A and A and cannot be used for even slightly changed values ID OD of these angles.

The testers of category 2) allow variations of skew angle, but for that purpose a cam must be changed for each variation. This requires that a set of cams be provided. However, the cams permit skew angles to be changed only in discrete steps. Also because the cams are complicated to manufacture and require precision machining, the tester becomes very expensive. Another disadvantage of the testers of category 2) is that their mechanisms have play in their links.

The tester of category 3) can provide a stepless variation, but at a sacrifice of simplicity of the mechanism, as the X-Y manipulator requires separate drives on X and Y axes and the use of complicated and expensive parts and units. Also the testing procedure is time- consuming, as it requires two step motors to move the head in two directions.

Objects and Advantages of the Invention

It is therefore an object of the invention to eliminate the above disadvantages and to provide a magnetic head and disc tester which is simple in construction, reliable in operation, and universal in application. Other advantages and features of the invention will become apparent from a consideration of the ensuing description and drawings.

Brief Description of Drawings

Fig 1 is a schematic representation of a prior-art magnetic head and disc tester.

Fig 2 is a plan view of a tester of the invention.

Fig 3 is a graph which shows a relationship between a skew angle and a radius of measurement point in the tester.

Reference Numerals

10 - housing

12 - rotating spindle

14 - disc

16 - arm

18 - magnetic head

20 - magnetic head and disc tester

22 - base plate

24 - slide mechanism

26 - stepper motor

28 - output shaft

30 - lead screw

32 - bearings

34 - nut

36 - linear slide

38 - clamp

40 - guide

42 - spindle mechanism

44 - pivot pin

46 - arm

48 - front arm portion

50 - rear arm portion

52 - magnetic head

54 - pointer

56 - angular scale

58 - dial indicator

60 - screw

62 - measurer

ID - inner track

OD - outer track

A - skew angle on inner track

A - skew angle on outer track OD

R - inner-track radius ID

R - outer-track radius OD

X - line parallel to movement of the slide

B - parallel line passing through the center of pivot

M - parallel line passing through the center of the magnetic head

R - reference plane

L - distance between lines A and B

P - pivot point center

D - magnetic disc

0 - center of disc rotation

Figs 2 And 3—Description—Magnetic Head and Disc Tester

Fig 2 is a plan view of a magnetic head and disc tester 20 of the invention.

Tester 20 has a stationary base plate 22 which supports a slide mechanism 24. Slide mechanism 24 can be fixed on plate 22 in any required position, e.g., by conventional T-slots and bolts (not shown) .

Slide mechanism 24 comprises a stepper motor 26, an output shaft 28 of which is connected to a coaxially-arranged lead screw 30 which rotates in bearings 32. Lead screw 30 engages a nut 34 which is rigidly fixed to a linear slide 36 by means of a clamp 38, so that nut 34, clamp 38 and slide 36 form a rigid unit. Slide 36 slides along a guide 40 formed on mechanism 24.

When output shaft 28 of stepper motor 26 rotates, this rotation is converted through nut-and-screw engagement into translatory motion of slide 36.

Plate 22 also removable supports a conventional spindle mechanism (not shown) which can be fixed to the plate in any required position (e.g., by means of T-slots and bolts) and which contains a conventional rotary drive unit, a spindle, and a disc holder (also not shown). The

purpose of this mechanism is to support and rotate magnetic disc d accurately around center 0.

Slide 36 supports a pivot pin 44 which has a center P as a fulcrum point for an arm 46. Pivot pin 44 is located in an intermediate location on arm 46, so that it divides arm 46 into a front arm portion 48 and a rear arm portion 50. Front portion 48 carries a magnetic head 52 which is rigidly fixed to the arm. Rear portion 50 has a pointer 54 which, when arm 46 rotates on pivot pin 44, moves with respect to an angular scale 56 fixed to slide 36. The scale is graduated in degrees.

Distance L is the dimension between two lines X and B which are parallel to the movement of slide 36 and pass through centers 0 and P, respectively. Distance L can be accurately set by loosening the clamping bolts (not shown) of slide mechanism 24 and adjusting the position of a reference plane R on slide mechanism 24 with respect to a dial indicator 58. After completion of the adjustment, slide mechanism 24 is fixed to base plate 22 by the clamping bolts.

The angular position of arm 46 ( ^' and hence the aligned long axes of head 52) with respect to line B is adjusted by means of pointer 54 and scale 56 and is fixed by a screw 60 which is threaded into a tapped hole (not shown) formed in the center of pivot pin 44. The angle between line B and arm 46 is designated as angle Q.

Figs 2 and 3—Operation

Let us assume that a disc manufacturer has to adjust the tester for given new input data, i.e., A , A_ , and radii R and R of the inner and outer tracks of magnetic disc D, respectively.

At first _/ angle Q and distance L are determined from the above- mentioned input data by a simple geometrical calculation. This can be done manually, by using a simple program, or with graphs. After determining angle Q and distance L, which may be called output data, slide mechanism 24 is positioned on stationary plate 22 with the aid

of dial indicator 58 and reference plane R, so that the required distance L is obtained.

Those skilled in the art will understand that distance L is used only because it can be easily calculated from the results of measurement of a distance from reference plane R to line X. hat in fact is to be determined is a distance K between line X and line M which is parallel to line B and passes through the center of head 52. In fact, line M is the path of head 52 in the course of testing. Distance K can be measured and calculated ^y other suitable means.

Slide mechanism 24 is then locked to plate 22 by fixing the clamping bolts (not shown).

The next adjustment relates to angle Q and is set by loosening screw 60 and rotating arm 46 on its pivot pin 44 with respect to angular scale 56. Once angle Q is set, the position of arm 46 is fixed by tightening screw 60. Now the tester is automatically set for the required input data (A , A , R , and R ) , When slide 36 moves linearly in guide 40 and carries head 52 across disc D from inner track ID to outer track OD, this movement will simulate the motion of the magnetic head on a disk drive (not shown), albeit with some error.

This error will now be considered in some detail. It will be shown that in measuring the parameters of a magnetic disc or a head, this error is small enough to be neglected.

Fig 3—Skew Angle and Radius

Fig 3 shows the relationship between the skew angle and radius of the disc. The solid-line corresponds to the variation of the skew angle in a disc drive (the measurements were obtained on a disk drive unit, Mod XT 8380, manufactured by Maxtor Corporation of California). In this disc drive the movement of the magnetic head follows a circular path between the inner and outer tracks. The broken line corresponds to the variation of the skew angle on the head tester of the present invention in which the head follows a linear path; skew angles A _ID and

A correspond to those on disk drive . OD

The tester whose parameters are illustrated in Fig 3 had the following specific characteristics: R _τ „ = 28.45 mm ( 1.120" ) , R = 59.69 mm o ID ₀ OD

(2.350"); A = 3.050 ? and A = 15.400 . It can be seen from Fig 3 that an error introduced by the approximation method of the invention o is less than 3 ; this is negligible for practical purposes. But even this error can be halved by selecting the angle at which the curve will assume an intermediate position between the solid and broken lines in Fig 3. It is understood that the above calculations are given only by way of example and that the invention is not limited to the illustrated case.

As the head is moved from track Id to track Od (or vice-versa) by the tester of the invention, the parameters of disc D or head 52 are measured in conventional fashion by a suitable measurer 62.

Summary, Ramifications, Scope

Thus the reader will see that at the expense of a minute and negligible error, the tester of the invention provides great simplicity of construction and operation, versatility, increased speed of use, and substantially reduced cost of manufacture. It accommodates a wide range of skew angles, it can be changed in continuous steps, it has no play in its linkage, and does not require two stepper motors.

Although the invention has been shown and described in the form of a specific embodiment, it is understood that this embodiment, its parts, materials, and configurations have been given only as examples, and that many other modifications of the magnetic head and disc tester are possible. The pivot point of arm 46 is shown in an intermediate position, but it also can be located at one of the arm's ends. While the arm is clamped in an adjusted angular position by screw 60, any other clamping means can be used for this purpose. Linear motion of the slide can be achieved by means other than a rotary stepper motor and screw-and-nut engagement, e.g., by means of a piston-and-cylinder

unit, or another linear actuator. Distance L can be measured by an optical instrument and adjusted by moving spindle mechanism 42 instead of slide mechanism 24. While it is shown for use with a head and hard disc tester, it is applicable to any other similar type of mechanism which uses a spinning disk and a scanning or tracking head, such as testers for phonographs, CDs, floppy discs, etc.

Therefore the scope of the invention should be determined, not by the example given, but by the appended claims and their legal equivalents.