JPS60151881A - Detector of speed in magnetic disk servo track writer - Google Patents

Abstract

PURPOSE:To detect a speed in fine displacement with high accuracy by detecting fine displacement in high resolution. CONSTITUTION:A laser measuring device 2 to detect the position of a carriage 1 iradiates a laser beam L1 from the back of the carriage 1, detects a reflecting light beam L2 from the carriage 1, and outputs an up-count pulse S1 (at the time of advancing) and a down-count pulse S2 (at the time of regressing) to an up/ down counter 3. The output of a counter to count these output signals is divided into two systems and D/A-converted. Then a speed signal is obtained by differ- entiating them, and speed signals of these two system are alternately outputted by avoding the time when the module of a counter is switched.

Description

[Detailed Description of the Invention] Technical Field This invention creates a servo disk for a magnetic disk device (writes predetermined reference data on the servo disk).
Regarding servo track writers used for
The present invention relates to a speed detection device that detects the moving speed of a carriage on which a read/write head is mounted in the servo track writer and can be used for accurate positioning of the scarlet carriage (that is, the read/write head).

In conventional servo track writers, positioning control is performed using a speed servo method to position the read/write head with high precision and high speed. speed detection is required.

However, since this type of speed detection device has conventionally used a magnetic signal generator such as a mechanical tachogenerator, it has the following drawbacks.

(1) In the servo track writer, a current flows through the voice coil motor to drive the carriage in which the head is mounted.On the other hand, since the magnetic signal generator uses electromagnetic induction, the current ζ of the voice coil motor is There is a risk of errors occurring due to the influence of the generated magnetic flux.

(2) The magnetic signal generator mechanically vibrates due to the rotational vibration of the spindle motor for rotating the magnetic disk, which may cause errors.

(3) Highly accurate speed signals cannot be obtained due to limitations in mechanical accuracy.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a speed detection device for a magnetic disk servo track writer that can detect speed with high accuracy by eliminating the drawbacks of the conventional speed detection device as described above.

Summary of the Invention The speed detecting device of the present invention includes a displacement detecting means for detecting the position of a read/write head with high resolution for minute displacements using a laser or the like, and outputting a pulse signal in accordance with the displacement of the head; a counting means for counting, a signal forming means for obtaining two systems of periodic signals that change while maintaining a predetermined phase difference from each other in accordance with changes in the counted value based on the counted value; and a switching means for selecting one of the two speed signals according to the counted value and outputting it as speed information of the head. It is something that can be achieved. It is preferable to use highly accurate displacement detection means that is not influenced by magnetism. In order to enable highly accurate velocity detection even for minute displacements, it is necessary to generate pulse signals from this displacement detection means with high resolution (for example, at a rate of 1 pulse for a displacement of about 0.02 microns). be. Generation of such highly resolved position pulses is possible using, for example, a laser length measuring device. On the other hand, since the modulo number of the counting means (the number corresponding to one cycle of change in the count value) has a limit, the modulo number is reached with a slight displacement, and the count value does not change while the head moves all the tracks. It switches over many cycles. Basically, this count value corresponds to the position of the head, and the speed is reduced by differentiating it, but at the cycle switching point of the count value, the count value changes discontinuously, causing disturbances in the differential output. This occurs, making accurate speed detection impossible. In view of this point, in the present invention, a predetermined phase difference of 2
A periodic signal of the system is formed based on the count value, and when the period of one periodic signal changes (at this time, the speed signal, which is the differential output thereof, is disturbed), a speed signal (this is the differential output of the other periodic signal) is generated. is not disturbed). Due to the phase difference between the periodic signals, even if the speed signal corresponding to the hole is disturbed when one of the periods is switched, the speed signal corresponding to the other hole is not disturbed. Therefore, if the switching means switches and selects the undisturbed speed signal at any time according to the count value and outputs it as speed information, accurate speed detection becomes possible.

Embodiment Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

In the figure, the position of a carriage 1 on which a read/write head (not shown) is mounted is detected by a laser length measuring device 2. The laser length measuring device 2 irradiates a laser beam L1 from the back side of the carriage 1, detects the reflected light L2 from the carriage 1, and counts up each time the carriage 1 moves forward or backward by a certain distance. Pulse S1 (when moving forward) and down count pulse 82 (when moving backward) are output to up/down counter B. Such a laser length measuring device 2 is well known, and detects displacement using, for example, the Doppler effect, and generates a pulse corresponding to the displacement.

The count value of the counter 6 indicates the position of the carriage 1, and this is inputted as is to the D/A converter 5, and the signal MOB, which is the most significant bit MSB inverted by the inverter 4, is combined with the lower bit S3. The thing is D
/A converter 6. This numerical data consisting of the MSB and 83 has a phase difference of one cycle with respect to the original count value (consisting of the MSB and 83),
In this way, two systems of periodic signals with a predetermined phase difference (however,
The horizontal axis or parameter of this period is not time but the position of the read/write head or carriage 1) is obtained digitally. The D/A converters 5 and 6 convert the above two systems of periodic signals into analog signals S, , S,.

These analog signals S, , S, are input to differentiating circuits 7 and 8, respectively, and the speed signals S6 and S7 are obtained by differentiating them. This speed signal 86.87 is input to the switching circuit 9,
One is selected according to the most significant bit MSB of the count value,
It is output as speed information S8.

The analog signal S4, which is one periodic signal, is the MS of the count value.
When B switches from II I Jl to °゛0'', its period changes.The other periodic signal, analog signal S,
The cycle changes when the MSB switches from 0' to 1'. At the time of such a cycle change, the corresponding speed signals S, S7 are disturbed (whisker-like pulse noise).
occurs. Therefore, selection switching control is performed in the switching circuit 9 so that when the hole occurs in one system, the speed signal of the other system is selected, and when the other system is reversed, the opposite selection is performed.

This switching point can be determined as appropriate based on the change in the MOB value of the count value. For example, when moving forward, the MSB is
t A predetermined time t from when OIT is switched to "1"
1 (This means that the pulses S1 and S2 are
(preferably corresponding to a specific number of pulses, that is, a specific amount of displacement), the state is switched to select one of the speed signals S7, and the predetermined time t starts from when the MSB does not switch from IJ# to '0''.

A method of later switching to a state in which the other speed signal S is selected may be considered. When moving forward, noise appears in the signal S7 when the MSB switches from "0" to η", but at this time the S
Since 6 is selected, there will be no inconvenience, and from "1" to I
When switching to IO71, noise appears in the signal S6, but since S is selected at this time, no inconvenience occurs. In addition, when moving backward, switching control is performed in the opposite manner to that described above.

Next, the operation of this embodiment will be explained with reference to the waveform diagram of each signal during forward movement shown in FIG.

The laser length measuring device 2 outputs an up count pulse 81% down count pulse S2 in accordance with the movement of the position of the carriage 1. That is, for example, when the carriage 1 is 0°0
One pulse of the up-count pulse signal S1 is generated every time it moves forward by 2 μm, and one pulse of the down-count pulse signal S2 is generated every time it moves back by 0.02 μm. This up/down pulse signal S1. The up/down counter 6 changes its count value from S2+, but the carriage 1
In order to count the distance required for one stroke to move across the entire track portion of the servo disk, the laser length measuring device 2 sends an up-count pulse signal S1. Since the moving distance, which is a unit for generating one pulse of the down-count pulse signal S2, is shortened, the consistency of the up-down counter 6 also overflows, and the counted value changes over many cycles. That is, the count value signal S of the up/down counter 6 is sent to the D/A converter 5.
The analog signal S4 converted into an analog signal becomes a discontinuous sawtooth wave as shown in FIG. And this analog signal S
As shown in FIG.
In this case, whisker-like pulse noise W is generated. Regarding the speed signal S7 corresponding to the output S of the other D/A converter 6, noise W is also generated with a cycle shift. still,
The horizontal axis in FIG. 2 indicates the position of the carriage 1, but in the case of uniform motion, it also corresponds to time.

The MSB of the count value is switched as shown in the figure, and if the selection is switched after a predetermined time t1 from the switching point as described above, the speed signals S, S7 output as the speed information S8 become as shown in the figure. As is clear from the illustration, the speed information S8 from which the noise W is removed is selected as the speed information S8.

When going backwards, MSB (7) “0” -+ 1” or “l”
Signal S6 corresponding to switching from # to “0”. The selection pattern of S7 is opposite to that when moving forward. Such switching control according to the distinction between forward and backward movement is performed using an up count pulse S1. input to the switching circuit 9. This can be done without any problem depending on the presence or absence of the down count pulse S2.

An example of the switching circuit 9 is shown in Fig. S3. 1
1 to 16 are AND circuits, 17 to 19 are OR circuits, 20.
21 is an R, S flip-flop, 21 is a selector, 22
is a four-stage delay flip-flop array, and 26 is a three-stage delay flip-flop array. Amplifier count pulse S,
A signal obtained by summarizing the down count pulse S2 and the down count pulse S2 by the OR circuit 19 is used as a shift clock for the delay flip-flop arrays 22 and 25. The MSB of the count value is applied to delay flip-flop arrays 22 and 23, respectively, and outputted with a time difference of one stage (this time difference may be set to any number of stages). AND circuits 11, 12, inverter 24.2
The combination of 5 constitutes a QIT change detection circuit, and the MSB changes from "1" to
After a time delay of 3 stages from when it changed to 0", the output of the AND circuit 11 becomes 1" for a time of 1 stage, and the MS
After a time delay of three stages from when B changes from It O71 to "'l", the output of the AND circuit 12 becomes "1"' for a time of one stage. The predetermined time t1 mentioned above is 3 here.
This corresponds to a time delay of one stage.

The set output Q of the flip-flop 21, which is set by the pulse S1 and set by the pulse S2, indicates the forward mode F, and the reset output Q indicates the reverse mode R. This forward/reverse mode signal selectively enables AND circuits 16 to 16, and the AND circuits 11 to 16 are reversely enabled during forward movement and reverse movement.
12 is input to the input of the flip-flop 20 i9. ．． Communicate to R.

The set output Q of this flip-flop 20 is 1@111
When , the selector 21 selects the speed signal S of one system.

is selected, and when its reset output Q is °'1'', the other speed signal is selected.Of course, the delay flip-flop array 2
The number of stages of 2.23 may be arbitrarily determined as long as 26 is less than 22.

In the above, two periodic signals converted from D/A were differentiated, but
Differential calculations may be performed as they are digital. In addition, the displacement detection means is not limited to a laser length measuring device, but also means capable of generating up/down pulses with high resolution for minute displacements (e.g., other optical position detection means or ultrasonic Doppler radar principle). displacement detection means, etc.) may be used.

Effects of the Invention As described above, according to the present invention, a highly accurate displacement detection means is used, and the output of a counter that counts the output signal of the displacement detection means is divided into two systems, D/A converted, and then differentiated. A speed signal is obtained, and the speed signals of the two systems are switched and output alternately, avoiding the modulo switching of the counter, so minute displacements can be detected with high resolution, and the speed at that minute displacement can be detected with high precision. can do. In addition, a highly accurate speed signal that does not have limits on mechanical accuracy can be obtained, and a continuous and stable speed signal that is not affected by external magnetism etc. can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.
FIG. 2 is a diagram showing an example of signal waveforms of various parts of the circuit of FIG. 1 when the carriage moves forward, and FIG. 3 is a block diagram showing an example of the switching circuit of FIG. 1. 1... Carriage, 2... Laser length measuring device, 6...
・Up/down counter, 5, 6...D/A converter, 7.8...differentiation circuit, 9...switching circuit. Applicant Hitachi Electronics Engineering Co., Ltd. Agent Yoshihito Iizuka (15) 0fu υノ

Claims (1)

[Claims] 1. A speed detection device for a read/write head in a magnetic disk servo track writer for writing reference data on a servo disk of a magnetic disk device, which responds with high resolution to minute displacements of the read/write head. displacement detecting means for outputting a pulse signal from the displacement detecting means; counting means for counting the pulse signals output from the displacement detecting means; a signal forming means for obtaining two systems of periodic signals that change while maintaining a phase difference; a differentiating means for independently differentiating the periodic signals of the two systems to obtain a speed signal for each system; A speed detection device comprising a switching means for selecting one of the two systems of speed signals and outputting the selected one as speed information of the head. 2. The switching means selects the speed signal of the other system at the time of period switching of the periodic signal of the one system that can be predicted based on at least the count value. Speed detection device. 3. The speed detecting device according to claim 1, wherein the displacement detecting means comprises a laser length measuring device. 4. The signal forming means forms numerical data that changes while maintaining a predetermined phase difference with respect to the counted value;
The speed according to claim 1, which includes only digital analog converting means for independently converting the counted value and the numerical data into analog signals, and obtains the two systems of periodic signals as analog signals. Detection device.