JPH03211418A - Optical position detector - Google Patents

Abstract

PURPOSE:To obtain excellent position detection accuracy without narrowing down the intervals between a scale and a reticle so much by using a spot light source as a light source and specifying the gap between the scale and reticle. CONSTITUTION:The position sensor for a magnetic head is constituted by arranging the reticle RC which has light transmission parts (a) - (d) and the scale SC which has plural slits SL between the light source 9 and photodetectors 5 - 8. Then the spot light source is used as the light source 9 to collimate all irradiation light into parallel light and the gap R between the scale SC and reticle RC is set nearly to P<2>/4lambda, where lambda is the wavelength of the light source and P is the pitch of the light transmission parts of the scale SC. Consequently, each position detection output hardly become dull and the excellent detection accuracy is obtained without narrowing down the gap between the scale SC and reticle RC to current 20mum.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical position detection device suitable for general use as a head position detection device of a magnetic disk drive device.

[Summary of the invention]

The present invention relates to a reticle having a light source, a plurality of photodetectors, and light transmitting portions corresponding to the plurality of photodetectors, and a scale having a plurality of light transmitting portions arranged at a predetermined pitch between the light source and the reticle. By relatively moving the detection outputs of the plurality of photodetectors and supplying the detection outputs of the plurality of photodetectors to the plurality of detection circuits, the plurality of detection circuits can detect a plurality of triangular wave positions having different phases from each other based on the relative movement. In an optical position detection device designed to obtain a detection output, when a point light source is used as a light source, the wavelength of the light generated from the light source is λ, and the pitch of the plurality of light transmitting parts of the scale is P, the scale And by selecting the distance R between the reticles as R=P2/4 λ, the triangular wave position detection outputs from the plurality of detection circuits are less likely to become dull even if the distance between the scale and the reticles is not so narrow. It was designed so that it would become possible.

[Conventional technology]

As the prior art related to the present invention, JP-A No. 63-1
No. 54916 and Japanese Utility Model Application Publication No. 62-187468 can be mentioned.

Conventional magnetic disk (hard disk) drives include
A position sensor for detecting the position of the magnetic head on the magnetic disk is attached to a portion of the head arm opposite to the portion where the magnetic head is attached.

This position sensor includes a light source, a plurality of photodetectors, a reticle having a light transmission section corresponding to each of the plurality of photodetectors, and a plurality of light transmission sections arranged at a predetermined pitch between the light source and the reticle. Move the scale relatively,
By supplying the detection outputs of the plurality of photodetectors to the plurality of detection circuits, a plurality of triangular wave position detection outputs having mutually different phases based on their relative movements are obtained from the plurality of detection circuits. .

As a light source for such a conventional position sensor, a surface emitting type LED (light emitting diode) was used as shown in FIG. 1B. Such an LED sequentially includes n-GaA on the cathode electrode.
An s-layer, an n-GaAs layer, and a p-GaAs layer are laminated, and a circular anode electrode is provided at the center of the p-GaAs layer above the p-GaAs layer, and the anode electrode is provided on the p-GaAs layer. The blank part is used as a light emitting part.

Then, the diverging light from the LED is converted into parallel light by a convex lens, and then irradiated onto the scale.

Note that the distance between the scale and the reticle is approximately the pitch (20 μm) of the light transmitting portion of the scale.

[Problem to be solved by the invention]

However, as mentioned above, such conventional position sensors use surface-emitting LEDs, so even if the diverging light from the LED is made into parallel light by a convex lens and then irradiated onto the scale, the scale will not be visible. Since it is difficult to say that all of the light irradiated on the scale is parallel, some of the light that passes through the light-transmitting part of the scale is deflected to some extent and does not pass through the light-transmitting part of the reticle. Therefore, there is a drawback that the waveform of the triangular wave position detection output obtained from each detection circuit becomes dull and the position detection accuracy becomes low.

Therefore, in order to prevent the waveform of the triangular position detection output obtained from each detection circuit from becoming too dull, the interval between the scale and the reticle is set as narrow as possible, for example, to the pitch of the light transmitting portion of the scale.

By the way, as magnetic disk drive devices become smaller (thinner), if the distance between the scale and reticle becomes too narrow, the tolerances will become quite strict, so dimensions such as the height of the parts that make up the position sensor will become smaller. Strict precision control is required, and if this is not done, there is a risk that the scale and reticle will come into contact. Furthermore, if the distance between the scale and reticle is so narrow, even if the precision of dimensions such as the height of the parts that make up the position sensor is strictly controlled, there is a risk that the scale and reticle will come into contact due to thermal expansion of the parts. There is also.

In view of this, the present invention provides a reticle having a light source, a plurality of photodetectors, and a light transmitting portion corresponding to each of the plurality of photodetectors, and a plurality of light beams arranged at a predetermined pitch between the light source and the reticle. By relatively moving a scale having a transmission part and supplying the detection outputs of the plurality of photodetectors to the plurality of detection circuits, from the plurality of detection circuits,
In an optical position detecting device that obtains a plurality of triangular wave position detection outputs having different phases based on their relative movement, each signal from a plurality of detection circuits can The purpose is to propose a triangular wave position detection output that is less likely to become dull.

[Means to solve the problem]

The present invention includes a light source (9) and a plurality of photodetectors (5) to (8).
), a reticle RC having light transmitting parts a to d corresponding to the plurality of photodetectors (5) to (8), respectively, and a light source (9).
) and reticle RC, a scale SC having a plurality of light transmitting parts SL at a predetermined pitch, and a plurality of detection circuits (to which detection outputs of the plurality of photodetectors (5) to (8) are respectively supplied). 1) to (4), a light source (9), a plurality of photodetectors (5) to (8), and the plurality of photodetectors (5) to (
8) Optical positioning in which a plurality of triangular wave position detection outputs having mutually different phases are obtained from a plurality of detection circuits based on relative movement between a reticle RC and a scale having light transmitting portions a to d respectively corresponding to 8). In the detection device, when a point light source is used as the light source (9), the wavelength of the light generated from the light source (9) is λ, and the pitch of the plurality of light transmitting parts of the scale SC is P, the scale SC and the reticle The spacing R between RCs is chosen to be R=P''/4λ.

[Effect]

According to the present invention, the light source (9
), a reticle RC having a plurality of photodetectors (5) to (8) and light transmitting parts a to d corresponding to the plurality of photodetectors (5) to (8), respectively, and relative movement between the scales. Multiple triangular wave position detection outputs with different phases can be obtained based on the
Even if this is not done, the triangular wave position detection outputs from the plurality of detection circuits are less likely to become dull.

〔Example〕

First, with reference to FIG. 2, an example of a magnetic disk (hard disk) drive device to which the present invention is applicable will be described. A magnetic head HD is provided that moves approximately in the radial direction of the rotating magnetic disk DS, and this magnetic head HD is attached to a head arm HM that rotates around a rotation axis AX by a voice coil motor VM. At the same time, a position sensor PS consisting of a scale SC and a sensor SE is provided on the other part of the head arm HM, and the position of the magnetic head HD on the magnetic disk DS is detected by this position sensor PS. .

Next, with reference to FIG. 3, an embodiment of the present invention applicable to such a position sensor SC will be described in detail. This position sensor includes a light emitting diode (9), four photodiodes (5) to (8) for light detection, and a light transmitting section corresponding to each of the four photodiodes (5) to (8). a-
d, a scale SC having a plurality of light transmitting parts SL with a predetermined pitch, and a light emitting diode (9) disposed between the light emitting diode (9) and the reticle RC, and a light emitting diode (9).
It is composed of a convex lens LS that converts the diverging light from the parallel light into parallel light and makes it incident on the scale SC.

As the light emitting diode (LED) (9), for example, a point-emitting type LED (infrared light LED) as shown in FIG. 1A is used.
D) is used. This point-emitting LED has an n-GaAs layer, an n-GaAs layer, and a p-GaA layer sequentially formed on the cathode electrode.
At the same time as laminating the s layer, an anode electrode having a circular hole in the center is provided on the p-GaAs layer on the - layer, and the p-GaAs
The portion of 1i exposed through the circular hole is used as a light emitting portion.

In this way, as the light emitting diode (9), the point-emitting type L
By using ED, the wave nature of light becomes noticeable,
If the diverging light from the light emitting diode (9) is made into parallel light by the convex lens LS and then irradiated onto the scale SC, the degree of parallelism of the light irradiated onto the scale SC increases, and the light transmitting portion SL of the scale SC After passing through the reticle, the light does not spread much, and almost all of it passes through the light transmitting parts a to d of the reticle RC.

Then, when the wavelength of the light generated from the light source (point-emitting LED) (9) is λ, and the pitch of the plurality of light transmitting parts of the scale SC is P, the interval R between the scale SC and the reticle RC is R. Select ≒P2/4λ.

As an example, if λ=890nm and P=20+'m,
The distance R between scale SC and reticle RC is 0.11m
m, which is much larger than the 20 μm of the conventional example described above.

Here, as the head arm HMO rotates, the scale SC is configured to move in the direction in which its light transmitting portions, that is, the slits SL are arranged.

The slits SL are formed at a constant pitch, and
The width of the slit and the width of the light-opaque portion between the slits are formed to be equal to each other.

The light transmitting parts a to d of the reticle RC have the same width as the width of the slit SL of the scale SC, and when the pitch of the slit SL of the scale SC is P, the light transmitting parts a to d of the reticle RC have the same width as the width of the slit SL of the scale SC.
) P + n P (however, n is 0.1.2.3,・
... (0 and 1 are used here).

The detection outputs of the photodiodes (5) to (8) provided corresponding to the light transmitting parts a to d of the reticle RC are separately supplied to detection circuits as shown in FIG. 4, respectively. This detection circuit includes a current/voltage conversion circuit (61) which also serves as a gain adjustment circuit (62) to which detection outputs from photodiodes (63) corresponding to photodiodes (5) to (8) are supplied.
) and a voltage offset amount adjustment circuit (67) at the subsequent stage.

The current/voltage conversion circuit (61) is an operational amplifier (64) to which the cathode of a photodiode (63) is connected to an inverting input terminal, and the anode of the photodiode (63) and a constant voltage source 10B are connected to a non-inverting input terminal. and a variable resistor (feedback resistor) (65) for gain adjustment connected between the output terminal and the inverting input terminal.

Further, in the voltage offset amount adjustment circuit (67), an input resistor (66) is connected between the inverting input terminal and the output terminal of the operational amplifier (64), and the non-inverting input terminal is connected to the constant voltage source 10B. a feedback resistor (69) connected between the output terminal and the inverting input terminal of the operational amplifier (68), and a feedback resistor (69) connected between the non-inverting input terminal of the operational amplifier (68) and ground, whose movable terminal is connected to the operational amplifier (68); (68) is composed of a variable resistor for adjusting the amount of offset connected to the inverting input terminal of (68). A triangular wave-shaped position detection output is obtained from the output terminal of the operational amplifier (68) to the output terminal (71).

When the detection outputs of the photodiodes (5) to (8) are supplied to the respective detection circuits as explained in FIG. 4, phase differences of 90 degrees are sequentially generated as shown in FIGS. A four-phase triangular wave detection output S a % S d is obtained. These four-phase triangular wave position detection output S
The positive slope of a - S d is the reference voltage, e.g.
．． Points Xa to Xd that cross the 5v line are connected to the magnetic disk DS.
The successively adjacent tracks, here, the reference tracks RTo, RTI to RT3, which have the same pitch, the data transistors DTo, DT1 to DT3, and the reference trunk R
It is made to correspond to T,, RT, to RT3, .

By using these four-phase position detection outputs Sa to Sd, the magnetic head HD can be moved to a desired track on the magnetic disk DS, as shown in FIG.

Next, when the wavelength of light generated from the light source (point-emitting LED) (9) is λ = 890 nm, the scale S
The distance R between C and reticle RC is 60 μm, 50
μm, 40 μm, 30 μm, 20 μm, 110 μm, 1
00μm, 90μm, 80μm, 80μm and 70μm
The waveform of a pair of triangular position detection outputs with a phase difference of 90 degrees and the pair of triangular position detection outputs are supplied to the X and Y axis input terminals of the off-scilloscope. The results are shown in FIGS. 6A-J, respectively.

By the way, the ideal triangular wave signal is
It is known that the surge waveform obtained by supplying the input terminals to the Y- and Y-axis input terminals is a rectangle whose pair of diagonals coincide with the X and Y-axis directions, so the surge waveform in Figure 6F meets this condition. do.

Therefore, the distance R between the scale SC and reticle RC is:
Above mentioned position 0. 11+m (= 110+'m), it is clear that the triangular wave-like position detection output with a phase difference of 90 degrees is the closest to the ideal triangular wave, and this can be calculated using the above formula % formula % It can be seen that this satisfies the following.

When the triangular position detection output having a phase difference of 90 degrees becomes so dull that it approaches a sine wave, its Lissajous becomes close to a circle as shown in FIG. 6C.

According to such a position sensor, the position detection accuracy can be increased even if the interval between the scale SC and the reticle RC is wider than before, so the accuracy of dimensions such as the height of the parts constituting the position sensor can be strictly controlled. In addition, there is no need to worry about contact between the scale SC and reticle RC due to thermal expansion of the components, and there is no risk of deterioration of position detection accuracy due to thermal expansion of the components.

Incidentally, in this way, the interval between the scale SC and the reticle RC can be made much wider than before, but if this is done, there is a risk that the sensitivity of the position detection output will decrease.
In that case, by reducing the pitch of the light transmitting portions SL of the scale SC, the interval between the scale SC and the reticle can be reduced accordingly. by this,
It is possible to suppress a decrease in the sensitivity of the position detection output. or,
In this way, the radius of rotation of the scale SC can be shortened, making it resistant to surface runout and positional deviation due to temperature.

〔Effect of the invention〕

According to the present invention described above, there is provided a reticle having a light source, a plurality of photodetectors, and a light transmitting portion corresponding to each of the plurality of photodetectors, and a plurality of light transmitting portions arranged at a predetermined pitch between the light source and the reticle. By relatively moving a scale having a section and supplying the detection outputs of the plurality of photodetectors to the plurality of detection circuits, the plurality of detection circuits can detect a plurality of signals having different phases from each other based on the relative movement. To obtain an optical position detection device configured to obtain a triangular wave position detection output, in which each triangular wave position detection output from a plurality of detection circuits is not easily dulled even without narrowing the interval between a scale and a reticle. be able to.

Therefore, there is no need to strictly control the accuracy of dimensions such as the height of the parts that make up the position sensor, and there is no need to worry about contact between the scale and reticle due to thermal expansion of the parts.
Furthermore, there is no possibility that the position detection accuracy will deteriorate due to thermal expansion of the parts.

In this way, the distance between the scale and the reticle can be made much wider than before, but if this is done, there is a risk that the sensitivity of the position detection output will decrease, but in that case, the light transmission of the scale If the pitch of the reticle is made smaller, the interval between the scale and the reticle is made smaller accordingly, thereby suppressing a decrease in the sensitivity of the position detection output. In addition, by doing so, the radius of rotation of the scale can be shortened, making it resistant to surface runout and positional displacement due to temperature.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an LED, FIG. 2 is a layout diagram showing a suitable disk drive device using the present invention, FIG. 3 is an explanatory diagram showing an embodiment of the present invention, and FIG. 4 is a detection circuit thereof. 5 is a timing chart showing the detection output of the position sensor, and FIG. 6 is a diagram showing the waveform and Lissajous of the triangular position detection output having a phase difference of 90 degrees from each other. (5) to (8) are photodiodes, (9) is a light emitting diode (point light source), SC is a scale, and SL is a slit (
(light transmitting part), RC is a reticle, and a% d is a light transmitting part. Agent Hidemori Matsukuma Surface-emitting LED Fig. 147, F, “1v motion table! Fig. 2 q\fC7', iT? SCノ、曾62 t・14马1QuestionV roundabout#Exit path Fig. 4 I fIJt?Noah#Output nowaYu waveform NoserUth;Yu you Fig. 6 Noage waveform

Claims (1)

[Claims] A light source, a plurality of photodetectors, a reticle having a light transmitting portion corresponding to each of the plurality of photodetectors, and a plurality of reticles arranged at a predetermined pitch between the light source and the reticle. A scale having a light transmitting part and a plurality of detection circuits to which detection outputs of the plurality of photodetectors are respectively supplied, each corresponding to the light source, the plurality of photodetectors, and the plurality of photodetectors. In an optical position detection device, a plurality of triangular wave position detection outputs having mutually different phases based on relative movement between the reticle having a light transmitting part and the scale are obtained from the plurality of detection circuits, wherein the light source is , when a point light source is used, and the wavelength of the light generated from the light source is λ, and the pitch of the plurality of light transmitting parts of the scale is P, the distance R between the scale and the reticle is R≒P^ An optical position detection device characterized in that 2/4λ is selected.