JPH0159671B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a positioning device for a magnetic head of a floppy disk.

These conventionally used devices generally have the following three configurations. First,
The first one uses a stepping motor, pulley, and steel belt. The second one is the stepping motor, lead screw shaft,
This is a combination of bolts and screws, and the third one uses a voice coil motor, position sensor, etc.

However, in order to manufacture highly accurate microfloppy disks using these methods, there were various problems such as high manufacturing costs.

For example, the first method requires an expensive hybrid stepping motor, and in order to maintain overall accuracy, it is necessary to make the outside diameter tolerance and runout of the pulley highly accurate, which reduces the cost. There were drawbacks such as being expensive. In addition, the second method has drawbacks such as being expensive because it uses a hard lead screw shaft and requiring a large number of man-hours to assemble related parts. Furthermore, in the third method, the position control circuit for the magnetic head must be implemented as a closed loop circuit, and an expensive circuit must be employed.

Therefore, the present invention aims to provide a step and actuator (hereinafter simply referred to as a magnetic positioner) for high-precision magnetic head positioning at low cost, and is an improvement on the second method. Such a configuration is disclosed.

The present invention has a structure in which a nut is formed in the center of the rotor of a motor, and a lead screw shaft, which is a male thread, can be moved linearly through the nut, and the tip of the lead screw shaft A simple mechanism for fixing the magnetic head to the head enables precise feeding of the head.

Conventionally, there have been many feeding devices that use screws, such as (1) bed feeding of lathes and tailstocks of lathes.
(2), slide table feeding device of tool microscope, etc. In the case of (1) above, the screw whose position is fixed is rotated, and the nut that does not rotate is slid in the axial direction.In the case of (2), there is a nut whose position is fixed, and the method is to By rotating the screw inside, the screw itself slides in the axial direction, and this mechanism allows the slide table of the tool microscope to be controlled in micron units.

The feeding mechanism adopted in the linear actuator of the magnetic head positioner according to the present invention fixes the position of the nut (rotor) and also fixes the rotational position of the screw (lead screw shaft). When the nut or rotor rotates, the screw or screw shaft slides axially. In this case, the screw shaft must be pulled in one direction (axial direction) with respect to the rotor in order to eliminate the crushing of the threaded portion.

Conventionally, in the above-described feeding mechanism, stepping errors tend to occur during rotation of the rotor, and it has been difficult to improve the overall stepping accuracy of the entire mechanism.

The configuration according to the present invention aims to reduce the above-mentioned step error and improve the overall step accuracy. However, the above object is achieved by configuring the screw shaft to maintain the rigidity at an appropriate value.

The configuration of a specific example of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a longitudinal sectional view of an actuator of a positioner according to the present invention. The structure according to the present invention includes a bearing part a, a rotor part b,
It consists of four mechanical parts: a lead screw shaft c and a stator part d. The bearing part a consists of ball bearings 8 and 10 supported between the mounting plate 2 and a rotor b, which will be described later, and between a spacer 6 provided inside the cover 4 and the rotor b, respectively.
The rotor b is made of a synthetic resin material such as plastic and is integrally formed with the magnet portion 12, and has a female thread 14 at its center. The reason for using plastic material for rotor b is the screw shaft c.
The purpose is to reduce the wear of both related parts caused by sliding and to reduce the coefficient of friction. However, in the present invention, it is optimal to use polyacetal containing carbon fiber for the rotor b.

The male threaded portion 16 formed on the lead screw shaft c is configured to be screwed together with the female threaded portion 14 of the rotor b and to be able to freely reciprocate within the cavity 18 inside the rotor b, thereby maintaining high pitch accuracy and facilitating mass production. It is recommended to cut free-cutting brass (JISC3604BD) using an NC lathe, etc. in consideration of its properties. Furthermore, in consideration of abrasion resistance with the plastic material of the rotor b, surface treatment with Teflon or the like may be applied. Further, although not shown, a slide portion of a floppy disk can be screwed onto the portion of the lead screw shaft c where the external thread is not formed, that is, the end portion 28 of the connecting portion 17.

The stator part d is installed between the mounting plate 2 and the cover 4 on the outside of the rotor magnet 12, and is made up of two pairs of magnetic pole plates 20, 22 and 20, 22, each housing a coil 24, 26 inside. . However, by inputting one rectangular wave voltage pulse to this stator portion d, the rotor b is rotated at a predetermined angle, for example, 15°.
It is configured to be rotatable.

Next, step accuracy, step error, and shaft rigidity will be explained in relation to the invention of the present application. The most important basic performance in the configuration of the present invention is step accuracy. If we now drive the rotor as one unit of rotation, the theoretical position of the screw shaft after n steps, X(n), is X(n) = /360 x P x n P: Lead screw pitch The actual If the position is x(n), then E(n)=x(n)-X(n), and this is called a step error. Further, the difference R between the maximum value and the minimum value of E(n) is called step accuracy. If you graph the relationship between step error and step accuracy R, please refer to attached 2nd page.
The state shown in the figure is reached. If the meshing state of the female thread and the male thread is ideal (see FIG. 3), screw feeding is performed with step accuracy R=0. However, it is technically impossible to mount the rotor female thread and the shaft male thread completely coaxially. Therefore, the fourth
As shown in the figure, the coaxiality of the female thread and male thread is △
If installed at y/2, a step error of △x=△y×tanθ/2 will occur during one rotation.

In this way, if the installation coaxiality of the rotor and screw shaft is △y/2, during one rotation of the rotor, △x
A step error occurs. In order to reduce this error, it is important to maintain the stiffness of the screwshaft at an appropriate value. As for this method, various problems will be considered below.

In the embodiment already described, and as shown in FIGS. 5 and 6, if the end 28 of the connecting portion 17 of the screw shaft c is supported by the floppy disc slide portion F, the screw threads can be It can be thought of as a cantilever beam that receives force from the screw 16. When a bending moment is applied to a part of a cantilever beam, the beam deflects due to elastic force. The amount of deflection is proportional to the magnitude of the bending moment and the distance from the fixed point to the load point, and inversely proportional to the moment of inertia of the beam, that is, the shaft diameter and the elastic modulus of the material. Therefore, in order to increase the amount of deflection, if other specifications are determined,
It turns out that the diameter of the shaft can be made smaller.
As a result, if the stiffness of the beam itself is large, as shown in Figure 7, even if the coaxiality of the male and female threads does not match, the force F acting on the screw shaft from the contact surface will cause the shaft to sag. As a result, as shown in FIG. 8, the threaded portions can maintain a nearly normal engaged state. In other words, it turns out that the flexibility of the screw shaft is an important factor in solving the problem.

9 to 13 of the accompanying drawings, by reducing the rigidity of the end floppy disk mounting portion 28 of the lead screw shaft c of the present invention and the connecting portion 17 of the lead screw portion, the rotor b is This figure shows that the step error during one rotation can be reduced and the overall step accuracy R can be improved. As shown in FIG. 11 to FIG. 13, as the diameter of the connecting portion 17 becomes smaller, the step error decreases, and it is possible to improve the integration step accuracy.

Furthermore, annealing a portion of the screw shaft c, such as the connecting portion 17, to a different heat quality helps to solve the problem of stiffness or flexibility of the screw shaft c.

As described above, the invention of the present application reduces the rigidity by forming the connecting portion between the screw shaft of the step actuator of the magnetic head positioner and the floppy disk into a suitably thin shape, and further reduces the rigidity of the connecting portion. By changing the heat quality of the shaft to a different temperature and applying annealing to maintain flexibility, the flexibility and appropriate rigidity of the shaft are maintained, step errors are reduced, and overall accuracy is improved. It has the effect of

[Brief explanation of drawings]

FIG. 1 is a sectional view of a step actuator of a magnetic head positioner according to the present invention. Second
The figure is a graph showing the relationship between step error and step accuracy. FIG. 3 is a schematic diagram showing an ideal meshing state of a male screw and a female screw. FIG. 4 is a schematic diagram showing step error. FIG. 5 is a schematic sectional view of the floppy disk attached, and FIG. 6 is a schematic diagram of the cantilever beam. FIG. 7 is a schematic diagram showing a state where the coaxiality of the male thread and the female thread do not match. FIG. 8 is a schematic diagram showing that the threaded portions are in a normal engaged state. FIG. 9 is a schematic side view of the connecting portion formed into a thin shape. 1st
0, FIG. 11, FIG. 12, and FIG. 13 are graphs showing the relationship between the diameter of the connecting portion and the step accuracy. a... Bearing part, b... Rotor part, c... Lead screw shaft, d... Stator part, 8...
Ball bearing, 10...Ball bearing,
14...Female thread part, 16...Male thread part, 17...
Connecting part.

Claims (1)

[Scope of Claims] 1. A rotor part, a bearing part that rotatably supports the rotor part, a screw shaft that is threadably engaged with a threaded part of the rotor part and can move linearly, and a stator part provided on the outer periphery of the rotor part. A magnetic head positioner comprising a linear step actuator and having one or several parts of a screw shaft made thin to reduce the rigidity of the shaft. 2. The magnetic head positioner according to claim 1, wherein a connecting portion between the threaded portion of the screw shaft and the floppy disk mounting portion is annealed.