Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
2000-05-23
2004-06-08
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
Reexamination Certificate
active
06747834
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a disk drive having a tracking position detection device enabling position detection of fine pitches by using one or two pairs of position detection signals of mutually inverted phases, a position detection device for position detection of a head of a hard disk drive and other applications requiring high precision, and a method of correction of the position detection signals.
2. Description of the Related Art
As a preferred circuit for position detection of, for example, a head of a disk drive, Japanese Unexamined Patent Publication (Kokai) No. 2-226012 discloses an optical position detection circuit configured as shown in FIG.
7
.
The position detection circuit
100
is connected to four light receiving elements (photo diodes)
201
to
204
as shown in FIG.
7
. The photo diodes
201
to
204
are struck by light from a light emitting diode
205
controlled by a drive circuit
206
. Between the light emitting diode
205
and the photo diodes
201
to
204
, while not particularly shown, are interposed two light blocking plates each provided with a plurality of rectangular slits. One is called a “scale” and has slits repeatedly arranged at a certain pitch in its longitudinal direction. The other is called a “reticle”, is a light blocking plate which moves in one direction together with a head, and has four slits arranged in a positional relationship a little different from the slits of the scale. The pitches and positional relationship of the slits on the scale and reticle are set so that the superimposed widths of the slits as seen from the light receiving side repeatedly increase and decrease substantially linearly when the head is moved at a constant speed and so that the phase of the repetition is shifted 90 degrees each. Thus, the four photo diodes
201
to
204
output triangular wave-shaped position detection signals having phases shifted by 90 degrees as the head moves.
The position detection circuit
100
shown in
FIG. 7
comprises first to fourth detection circuits
101
to
104
, a selector
110
, a maximum value detection circuit
120
, a minimum value detection circuit
130
, analog-to-digital (A/D) converters
121
and
131
, a microcomputer
140
, an erasable programmable read only memory (EPROM)
150
, a digital-to-analog (D/A) converter
160
, an input-output (I/O) port
170
, etc.
The first to fourth detection circuits
101
to
104
are amplifying circuits of a current/voltage conversion type having a function of adjusting a gain and a voltage offset.
The detection circuits
101
to
104
each comprise, as representatively illustrated by the first detection circuit
101
, two operational amplifiers
105
and
106
,
13
resistors R
1
to R
13
, and eight switches S
1
to S
8
.
Non-inverted inputs of the operational amplifiers
105
and
106
are connected to an anode of a photo diode
201
, while the connecting point is connected to a supply line of a constant voltage +B. An inverted input of the first operational amplifier
105
is connected to a cathode of the photo diode
201
. Between the inverted input and an output of the operational amplifier
105
are connected in series five resistors R
1
to R
5
. The switches S
1
to S
4
are respectively connected in parallel to the two ends of the four resistors R
2
to R
4
among them.
An output of the operational amplifier
105
is connected to an inverted input of the operational amplifier
106
via the resistor R
6
. A feedback resistor R
7
is connected between the inverted input and an output of the operational amplifier
106
. Further, five resistors R
8
to R
12
are connected in series between the inverted input of the operational amplifier
106
and a ground potential. The switches S
5
to S
8
are respectively connected in parallel to the two ends of the four resistors R
9
to R
12
among them. A mid-point of connection between the resistor R
8
closest to the inverted input of the operational amplifier
106
and the second closest resistor R
9
is connected to a supply line of a constant voltage +B via the resistor R
13
.
The output of the operational amplifier
106
is connected to an output terminal To of a position detection signal. Also, a switch circuit including the switches S
1
to S
4
is connected to a first control terminal Tc
1
, while a switch circuit including the switches S
5
to S
8
is connected to a second control terminal Tc
2
.
In the first to fourth detection circuits
101
to
104
configured in this way, the switches S
1
to S
4
are appropriately switched in accordance with a control signal transmitted from the microcomputer
140
via the I/O port
170
and input from the first control terminal Tc
1
, whereby a feedback resistance value of the operational amplifier
105
changes and the gain is adjusted. Therefore, it is possible to adjust the amplitude of the position detection signal output from the output terminal To. Hereinafter, the adjustment of the amplitude of the position detection signal will be referred to as “gain adjustment”.
On the other hand, the switches S
5
to S
8
are appropriately switched in accordance with a control signal transmitted from the microcomputer
140
via the I/O port
170
and input from a second control terminal Tc
2
, whereby the potential of the inverted input of the operational amplifier
106
changes. Therefore, the direct current voltage level of a position detection signal output from the output terminal To can be adjusted. Hereinafter, the adjustment of the direct current voltage level of the position detection signal will be referred to as “offset adjustment”.
At the time of the gain adjustment and the offset adjustment, one of the four position detection signals is selected by a selector
110
controlled by the microcomputer
140
. The selected position detection signal is input to the maximum value detection circuit
120
and the minimum value detection circuit
130
, which detect the maximum value and minimum value of the amplitude. The detected values are converted to digital signals by the A/D converters
121
and
131
and then input to the microcomputer
140
.
Such detection of a maximum value and a minimum value of the amplitude is performed for all position detection signals by successively switching the selector
110
.
The microcomputer
140
calculates a difference and sum of the maximum value and the minimum value of the amplitude for each of the position detection signals. Based on the calculation results, the microcomputer
140
controls the switches S
1
to S
4
in the detection circuits and performs gain adjustment so that the differences between the maximum value and the minimum value align at a constant value. Also, the microcomputer
140
controls the switches S
5
to S
8
in the detection circuits and performs offset adjustment so that the sums of the maximum value and the minimum value align at a constant value. The EPROM
150
stores control data of the switches at the time of the gain adjustment and the offset adjustment.
The microcomputer
140
then converts the control signal of a voice coil motor
210
from a digital to analog format, then transmits the same to the motor drive circuit
211
.
The position detection device
100
configured in this way can use the four position detection signals having phases successively shifted by 90 degrees to perform position detection by a pitch four times finer than the pitch of the slits provided on the scale.
Also, under control by the microcomputer, gain adjustment and offset adjustment of the position detection signals can be automatically performed based on control data stored in advance.
Summarizing the problem to be solved by the present invention, the position detection device
100
of the related art had the resistors R
1
to R
5
and switches S
1
to S
4
for the gain adjustment and the resistors R
8
to R
12
and switches S
5
to S
8
for the offset adjustment in the first to fourth detection circuits
101
to
104
provided corresponding to the four position det
Depke Robert J.
Holland & Knight LLP
Hudspeth David
Sony Corporation
Tzeng Fred F.
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