Optical signal processing apparatus for detecting the direction of movement of an optical reading device relative to an optical disk

According to this invention, an optical signal processing apparatus for an optical disk has an actuator for moving an optical head in an radial direction of the optical disk, a plurality of first photodiodes for receiving a light beam reflected by the optical disk, an addition circuit for generating a first sum signal representing a sum of signals from the first photodiodes, a polarizing beam splitter for splitting the light beam reflected by the optical disk in accordance with directions of polarization, a plurality of second photodiodes for receiving light passing through the polarizing beam splitter, a subtraction circuit for generating a difference signal representing a difference between signals from the second photodiodes, and a circuit for determining a moving direction of the optical head, using the sum signal and the difference signal during a seek operation. Since the sum signal includes no data signal component, the moving direction of a light spot during a seek operation can be accurately determined, thereby performing a reliable seek operation.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an optical signal processing apparatus 
such as a magneto-optic disk apparatus for reading data recorded in, e.g., 
a magneto-optic disk. 
2. Description of the Related Art 
An optical disk apparatus or a magneto-optic apparatus is known well as a 
recording medium signal processing apparatus using a recording medium 
(disk). In such an apparatus, physically recessed areas called pits, areas 
in which magnetic characteristics are changed, or areas in which the state 
of a metal is changed are formed on data tracks called concentric or 
spiral grooves on a disk, and data is written (recorded) or read out 
(reproduced) by using these areas. 
In a conventional apparatus in which data is recorded/reproduced along 
recording tracks, an optical head is controlled to form a light spot on a 
track. When data in a target track distant from a current position of the 
optical head is to be written or read, the optical head is moved to access 
the target track. This operation for accessing a track is called a seek 
operation. 
In the seek operation, as disclosed in Published Unexamined Japanese Patent 
Application No. 2-14430, when a head carriage assembly having an optical 
head is moved in the radial direction of the disk while the speed of the 
head is controlled, a light spot from the optical head traverses recording 
tracks to quickly move to a target track. 
Although the speed of the optical head must be detected to control the 
speed, in this case, the speed is detected as follows. A beam reflected by 
the optical disk is received by a four-divided photodiode for generating a 
tracking control signal. Electrical signals generated from the photodiode 
are added in adders and a difference between two signals from the adders 
is detected. A difference signal representing the difference is binarized 
by using a predetermined threshold level. A period of the binary signal is 
counted using a predetermined clock, and the reciprocal of the number of 
the count result is calculated, thereby detecting the speed of the optical 
head. 
In order to cause the light spot to traverse recording tracks to quickly 
and reliably reach a target track, the moving direction (the direction 
from the inside to the outside of the disk or vice versa) of the optical 
head must also be detected during the control operation of the speed. A 
reason for this will be described below. 
For example, when the light spot is moved from the inside to the outside of 
a rotating disk, and when the grooves on the disk is shifted in the same 
direction of the light spot at a speed higher than that of the light spot 
due to the eccentricity of the disk or the like, the traversing speed of 
the light spot relative to the grooves is temporarily reversed. That is, 
the moving direction of the light spot is reversed due to the eccentricity 
of the disk. 
Therefore, in an apparatus using a disk having inevitable eccentricity to 
some extent, the moving direction of the optical spot must be quickly and 
reliably determined. This determination is a necessary condition for the 
head speed control operation. 
The direction of the light spot is detected from the two signals generated 
from the adders. The direction is detected by binarizing the difference 
signal (to be referred to as a tracking difference signal) representing a 
difference between the two signals and a sum signal (to be referred to as 
a tracking sum signal) representing a sum of the two signals, and using a 
phase difference between the binarized difference signal and sum signal. 
The signal level of the binary difference signal is held at a timing of the 
leading edge of the binary sum signal obtained while the optical head is 
moved, and the moving direction of the optical spot is determined by the 
level of the held signal. That is, when the held signal is at a high 
level, the light spot is moved from the outside to the inside of the disk; 
and when the signal is at a low level, the light spot is moved from the 
inside to the outside. 
As described above, the speed is detected by using the tracking difference 
signal, and the direction is detected in accordance with the phase 
difference between the sum signal and the difference signal. Therefore, 
the speed can be accurately controlled, and a high-speed seek operation on 
the basis of a remaining track count to a target track can be realized. 
When the optical head is moved over tracks in which data are written, a 
data signal is superposed on a tracking signal. For this reason, an 
accurate binary signal may not be obtained. Conventionally, the data 
signal in the tracking sum signal used in a seek operation is neglected. 
In this case, an accurate relative moving direction between the tracks on 
the disk and the light spot traversing the tracks cannot be detected, and 
the speed of the light spot cannot be easily controlled. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an optical disk 
apparatus capable of accurately and reliably detecting the speed of a 
light spot, i.e., a relative speed between an optical head carriage and an 
optical disk and the moving direction of the light spot without being 
influenced by data written in the disk. 
In order to achieve the above object, according to the present invention, 
there is provided an optical disk apparatus including means for radiating 
a light beam on the optical disk, means for moving the radiating means in 
a radial direction of the optical disk, a plurality of first 
light-receiving means for receiving a light beam reflected by the optical 
disk to generate an electrical signal corresponding to the received light 
beam, first sum signal generating means for generating a first sum signal 
representing a sum of signals from the plurality of first light-receiving 
means, means for splitting a light beam reflected by the optical disk in 
accordance with directions of polarization of the light beam, a plurality 
of second light-receiving means for receiving light passing through the 
splitting means to generate an electrical signal corresponding to the 
received light, means for generating a difference signal representing a 
difference between signals from the plurality of second light-receiving 
means, and means for determining a moving direction of the radiating means 
by using the sum signal and the difference signal when the radiating means 
is moved by the moving means in the radial direction of the optical disk. 
Since the sum signal includes no data signal component, the moving 
direction of the light spot during a seek operation can be accurately 
determined, and, therefore, a reliable seek operation can be performed. 
Additional objects and advantages of the invention will be set forth in the 
description which follows, and in part will be obvious from the 
description, or may be learned by practice of the invention. The objects 
and advantages of the invention may be realized and obtained by means of 
the instrumentalities and combinations particularly pointed out in the 
appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
An embodiment of the present invention will be described below with 
reference to the accompanying drawings. 
FIG. 1 schematically shows the main part of the arrangement of an optical 
disk apparatus according to the present invention. A disk 11 is, e.g., a 
magneto-optic (MO) disk, and the disk 11 is rotated at a constant angular 
velocity or a constant linear velocity by a speed-controlled spindle motor 
(not shown). Data tracks called grooves are spirally or concentrically 
formed on the disk 11. A plurality of sector marks (header data) are 
recorded at predetermined intervals in the data tracks. Each of the sector 
marks is constituted by a combination of a plurality of physical pits 
(emboss bits) and indicates, e.g., the address (a track number or a sector 
number) of a data recording area following the sector mark. 
An optical head 13 radiates a laser beam on the disk 11, and the laser beam 
is focused on the disk 11 as a light spot. The laser beam is a polarized 
light beam having a first direction of polarization aligned along a 
predetermined angular orientation with respect to the optical axis. With 
the light spot, data can be written in a predetermined track on the disk 
11 or read out from the predetermined track. 
A movable portion 13b of the optical head 13 is driven by an actuator 27 of 
a head carriage assembly, and the movable portion 13b is moved in the 
directions (the radial directions of the disk 11, i.e., directions to 
cross the tracks on the disk) of an arrow in FIG. 1 during a seek 
operation of a track. That is, the light spot from the optical head 13 is 
accessed to a target track by driving the actuator 27. 
The optical head 13 has a plurality of photodiodes, and a laser beam 
reflected by the disk 11 is detected by the photodiodes. As shown in FIG. 
2, the optical head 13 comprises a fixed portion 13a, the movable portion 
13b, and the like. The fixed portion 13a includes a light source, i.e., a 
semiconductor laser 31, a collimator lens 32, a beam splitter 33, a beam 
shift correction plate 34, a galvano mirror (rotary mirror) 35, a 
detection optical system 36, a photodiode 37, a two-divided photodiode 38, 
a four-divided photodiode 39, an APC detector 40, and the like. The 
movable portion 13b incorporates a rising mirror 41. 
With the above arrangement, a light beam from the semiconductor laser 31 is 
converted into a parallel beam by the collimator lens 32, and is incident 
on the beam splitter 33. The light beam having an elliptic section is 
converted into a light beam having a circular section by a prism arranged 
on the incident side of the beam splitter 33. 
The light beam passing through the beam splitter 33 passes through the beam 
shift correction plate 34 and is reflected by the galvano mirror 35 
rotated on an axis in the direction of an arrow I. 
The light beam reflected by the galvano mirror 35 is incident on the 
movable portion 13b and reflected by the rising mirror 41 arranged inside 
the optical head 13. The parallel light beam is focused as a light spot on 
the disk surface of the disk 11 by an objective lens (not shown). 
A divergent light beam reflected by the disk 11 has a second direction of 
polarization different from the first direction of polarization, and is 
converted by the objective lens into a parallel light beam, reflected by 
the rising mirror 41, and returned again to the beam splitter 33 through 
the galvano mirror 35 and the beam shift correction plate 34. 
The light beam reflected by the disk 11 and introduced to the beam splitter 
33 is split by the detection optical system 36 including a focus detection 
optical system, and the split beams are detected by the photodiode 37, 38, 
and 39. The detection optical system 36 is constituted by a polarizing 
beam splitter 36a, a non-polarizing beam splitter 36b, and an optical 
element 36c constituting the focus detection optical system. 
A light beam reflected by the non-polarizing beam splitter 36b passes 
through the optical element 36c and is detected by the four-divided 
photodiode 39. When detection signals F.sub.o1 and F.sub.o2 from the 
four-divided photodiode 39 are processed in a focus/track detection 
circuit 51 in FIG. 1, a focusing control signal (to be referred to as a 
focusing difference signal) F.sub.od is generated. That is, since the 
detection signals F.sub.o1 and F.sub.o2 from the four-divided photodiode 
39 are obtained from a beam which does not pass through the polarizing 
beam splitter 36a, the detection signals F.sub.o1 and F.sub.o2 do not 
include data components on the disk 11. 
The beam passing through the non-polarizing beam splitter 36b passes 
through the polarizing beam splitter 36a and is detected by the 
two-divided photodiode 38. Detection signals T.sub.r1 and T.sub.r2 from 
the two-divided photodiode 38 are processed by the focus/track detection 
circuit 51 in FIG. 1 to generate a tracking difference signal T.sub.rd 
which is referred to as deviation signal representing a deviation between 
the light beam radiated onto the optical disk and the track. That is, 
since the detection signals T.sub.r1 and T.sub.r2 from the two-divided 
photodiode 38 are obtained from a beam passing through the polarizing beam 
splitter 36a, the detection signals T.sub.r1 and T.sub.r2 include data 
components on the disk 11. 
In addition, when the signal from the two-divided photodiode 38 and the 
signal obtained from a beam passing through the non-polarizing beam 
splitter 36b, reflected by the polarizing beam splitter 36a, and detected 
by the photodiode 37 are processed, data recorded in the disk 11 is 
reproduced. 
In data recording and reproduction, a focusing servo mechanism 61 is driven 
in response to the focusing control signal F.sub.od from the focus/track 
detection circuit 51. In this manner, the objective lens is moved along 
the optical axis and kept in a focused state. As a result, the light beam 
from the objective lens forms a minimum beam spot on the disk 11. 
Similarly, a tracking servo mechanism 71 is driven in response to the track 
signal T.sub.rd from the focus/track detection circuit 51. In this manner, 
the objective lens is kept in an in-tracking state. As a result, a 
convergent light beam from the objective lens traces a desired track on 
the disk 11. 
FIG. 3 shows the arrangement of the focus/track detection circuit 51 in 
FIG. 1. 
The focus/track detection circuit 51 generates the tracking difference 
signal T.sub.rd used in the focusing servo mechanism 61 and a seek control 
circuit 25, the focusing difference signal F.sub.od used in the focusing 
servo mechanism 61, and a focusing sum signal F.sub.oa used in the seek 
control circuit 25 from the detection signals T.sub.r1, T.sub.r2, 
F.sub.o1, and F.sub.o2. 
A difference between the detection signals T.sub.r1 and T.sub.r2 is output 
by a subtracter 51a to obtain a tracking difference signal t.sub.rd. The 
tracking difference signal t.sub.rd is normalized by an AGC circuit 51b to 
generate the tracking difference signal T.sub.rd. A difference between the 
detection signals F.sub.o1 and F.sub.o2 is output by a subtracter 51c to 
obtain a focusing difference signal f.sub.od. The focusing difference 
signal f.sub.od is normalized by an AGC circuit 51d to generate the 
focusing control signal F.sub.od. The detection signals T.sub.r1 and 
T.sub.r2 are added to each other by an adder 51e to obtain a tracking sum 
signal t.sub.ra. The tracking sum signal t.sub.ra is filtered by a filter 
51f, peak-held by a peak hold circuit 51g in a seek operation, and input 
to the AGC circuits 51b, 51d, and 51i. The detection signals F.sub.o1 and 
F.sub.o2 are added to each other by an adder 51h to obtain a focusing sum 
signal f.sub.oa. The focusing sum signal is normalized by the AGC circuit 
51i to form the focusing sum signal F.sub.oa. 
The amplitude of the tracking difference signal and the amplitude of the 
focusing difference and sum signals are decreased due to the reflection 
characteristics of the disk 11 and variations in the four-divided 
photodiode 39 and the two-divided photodiode 38, and a binary signal 
cannot be accurately generated. To prevent to this, in reading out and 
writing (or erasing) data, a switch SW is closed, the focusing difference 
signal f.sub.od and the tracking difference signal t.sub.rd are divided by 
the tracking sum signal t.sub.ra to obtain the normalized signals F.sub.od 
and T.sub.rd, and the signals F.sub.od and T.sub.rd are used in tracking 
control and focusing control. In a seek operation, the switch SW is 
closed, and each signal is normalized at a peak value of the tracking sum 
signal to assure a predetermined amplitude. 
As shown in FIG. 1, a track seeking operation, i.e., access to a target 
track, is performed using the tracking difference signal T.sub.rd and the 
focusing sum signal F.sub.oa from the focus/track detection circuit 51 by 
a feedback loop control system constituted by a circuit element 26, the 
circuit element 27, and the seek control circuit 25 including circuit 
elements 15 to 24. 
That is, the tracking difference signal T.sub.rd and the focusing sum 
signal F.sub.oa from the focus/track detection circuit 51 are filtered by 
filters 15 and 16, respectively, to remove high-frequency noise from these 
signals. 
The filtered difference and sum signals are binarized by binarizing 
circuits 17 and 18, respectively. The binarization is performed using, 
e.g., an intermediate level between the maximum and minimum values of an 
input signal level as a threshold value. 
FIG. 4A shows grooves 100 on the disk, FIG. 4B shows the focusing sum 
signal F.sub.oa corresponding to the grooves, and FIG. 4C shows a binary 
focusing sum signal 102 obtained by binarizing the sum signal. As 
described above, the focusing sum signal F.sub.oa is generated on the 
basis of the detection signals F.sub.o1 and F.sub.o2 obtained by causing a 
reflected beam, which does not pass through the polarizing beam splitter, 
36a to be incident on the four-divided photodiode 39. For this reason, as 
shown in FIG. 4B, a data signal component written in the disk 11 is rarely 
superposed on the focusing sum signal. Therefore, as shown in FIG. 4C, the 
binary sum signal includes no data signal component, and therefore, a 
binary sum signal having an ideal waveform can be obtained. 
FIGS. 5A, 5B, and 5C are views corresponding to FIGS. 4A, 4B, and 4C. FIG. 
5A shows grooves 100 on the disk 11, FIG. 5B shows a tracking sum signal 
T.sub.ra conventionally used in a seek operation, and FIG. 5C shows a 
binary tracking sum signal 104 obtained by binarizing the sum signal 
T.sub.ra. As described above, the tracking sum signal T.sub.ra is 
generated by using the signals T.sub.r1 and T.sub.r2 obtained by causing 
a beam reflected by the disk 11 to be incident on the two-divided 
photodiode 38 through the polarizing beam splitter 36a. These signals 
T.sub.r1 and T.sub.r2 include data signal components. Therefore, as shown 
in FIG. 5B, the tracking sum signal includes data signal components 106. 
As a result, as shown in FIG. 5C, when the tracking sum signal is 
binarized, the data components are superposed on the binary tracking sum 
signal 104, as illustrated in FIG. 5C by the changes in state 108. For 
this reason, the grooves cannot be accurately detected by the binary 
tracking sum signal. 
Referring back to FIG. 1, the binary difference signal binarized by the 
binarizing circuit 17 is input to a direction detection circuit 20, a 
track counter 21, and a speed detection circuit 23. The binary sum signal 
binarized by the binarizing circuit 18 is input to a sum signal 
compensating circuit 19. 
The sum signal compensating circuit 19 wave-shapes the binary focusing sum 
signal to remove noise remaining in the binary sum signal. The binary sum 
signal compensated by the sum signal compensating circuit 19 is input to 
the direction detection circuit 20 and the speed detection circuit 23. 
Data representing the number of tracks to be traversed (crossed) between a 
track at which a light spot is currently positioned and a target track is 
preset in the track counter 21 by a CPU 10 before a seek operation is 
started. For example, when the target track is a track positioned outside 
the current track, a positive value is preset; and when the target track 
is a track positioned inside the current track, a negative value is 
preset. The track counter 21 receives a one-shot binary difference pulse 
signal from the binarizing circuit 17 each time the optical head 13 is 
moved to cause the light spot to traverse one track on the disk 11. 
The direction detecting circuit 20 detects the moving direction of the 
moving optical head 13. For example, when the optical head 1B is moved 
outward, the direction detecting circuit 20 outputs a low-level signal; 
and when the optical head 13 is moved inward, the direction detecting 
circuit 20 outputs a high-level signal. When the direction detection 
circuit 20 outputs the low-level signal, the track counter 21 performs a 
count-down operation of a preset value using an output from the binarizing 
circuit 17. When the direction detection circuit 20 outputs the high-level 
signal, the track counter 21 performs a count-up operation of the preset 
value. In this case, as the light spot approaches the target track, the 
absolute value of the count value of the counter 21 is decreased. When the 
light spot reaches the target track, the count value becomes "0". 
The direction detecting circuit 20 performs the following operation to 
detect a track seek direction of the optical head 13. That is, when the 
light spot is moved from the outside to the inside of the disk 11, as 
shown in FIGS. 6A and 6B, the direction detecting circuit 20 samples/holds 
the signal level of the binary tracking difference signal 100 at the 
leading edge of the binary focusing sum signal 102 to generate a 
high-level signal. When the light spot is moved from the inside to the 
outside of the disk 11, as shown in FIGS. 7A and 7B, the direction 
detection circuit 20 samples/holds the signal level of the binary tracking 
difference signal 110 at the leading edge of the binary focusing sum 
signal 102 to generate a low-level signal. In this manner, the direction 
detection circuit 20 outputs a signal having a logic level which is 
changed depending on the directions (seek directions) of the movement of 
the light spot, and an output from the directing detecting circuit 20 is 
supplied to the up-count/down-count designation input terminal of the 
track counter 21. 
For example, it is assumed that the optical head 13 will be moved to an 
outer track of the disk 11. The CPU 10 presents a positive value in the 
track counter 21. The preset value of the counter 21 is input to the 
reference speed signal generator 22, and an analog value corresponding to 
the preset value is output to the differential amplifier 24. As a result, 
the actuator 27 moves the optical head 13 outward on the disk 11 at high 
speed. The direction detecting circuit 20 detects the direction of the 
movement of the optical head 13 to output a low-level signal, and the 
track counter 21 performs a count-down operation of the preset value using 
a pulse output from the binarizing circuit 17. While the optical head 13 
is moved outward on the disk 11, if a relative speed is reversed as 
described in the prior art due to the eccentricity of the disk 11, the 
direction detecting circuit 20 outputs a high-level signal in this period. 
As a result, the track counter 21 performs a count-up operation of the 
remaining track count in the period so as to correct the count value. When 
the count correction operation is performed, a correct cross track count 
can be detected regardless of the presence/absence of the eccentricity of 
the disk 11. 
The track counter output is input to the reference speed signal generator 
22 as described above. The reference speed signal generator 22 generates 
reference speed data corresponding to a remaining track count to a target 
track. Therefore, when the current light spot is considerably distant from 
the target track, i.e., when the remaining track count to a target track 
is large, the reference speed signal generator 22 generates a high 
reference speed and a reference speed which is gradually decreased as the 
light spot approaches the target track. 
The speed detecting circuit 23 supplies a signal to the differential 
amplifier 24 on the basis of a binary difference signal from the 
binarizing circuit 17 and a sum signal from the sum signal compensating 
circuit 19. The supplied signal represents the speed of the light spot 
which is moved at present. 
The differential amplifier 24 generates a signal proportional to a 
difference between a reference value from the reference speed signal 
generator 22 and a detection value from the speed detecting circuit 23, 
and this signal is supplied to the drive circuit 26. 
The drive circuit 26 drives the actuator 27 in response to the signal from 
the differential amplifier 24, thereby moving the optical head 13. As a 
result, the speed of the optical head 13 is controlled such that the light 
spot is moved at a speed to minimize the difference between the reference 
value and the detection value. 
That is, under the control of the speed, a seek operation is performed at a 
high reference speed when a remaining track count to a target track is 
large, and the reference speed is decreased as the remaining track count 
is decreased, thereby decreasing a seek speed. 
As described above, according to the present invention, a binary focusing 
sum signal is generated on the basis of a focusing sum signal on which a 
data signal written in a disk is not easily superposed, and a seek 
operation is controlled using the binary focusing sum signal. Therefore, a 
track can be more accurately detected when the focusing sum signal is used 
as compared with use of a tracking sum signal. That is, the moving speed 
and direction of the light spot can be more accurately detected regardless 
of the influence of written data. 
Additional advantages and modifications will readily occur to those skilled 
in the art. Therefore, the invention in its broader aspects is not limited 
to the specific details, representative devices, and illustrated examples 
shown and described herein. Accordingly, various modifications may be made 
without departing from the spirit or scope of the general inventive 
concept as defined by the appended claims and their equivalents.