JPH065579B2 - Optical disk drive - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical disk drive device,
In particular, the present invention relates to an optical disk drive device for controlling access to an arbitrary track on an optical disk with a light spot.

[Conventional technology]

FIG. 8 is a block diagram of an access control system described in, for example, Japanese Patent Application No. 60-101439 filed by the same applicant and filed on May 15, 1960, entitled [Optical disk drive]. .

In FIG. 8, a large number of recording tracks including high-density pit rows are formed on the optical disc (101) in a concentric or spiral shape. The optical disc (101) is mounted on a spindle and rotated by a disc motor (102). The rotation of the disc motor (102) is drive-controlled by a disc motor drive control circuit (103).

On the other hand, the optical head (104) forms a required light spot on the optical disc (101), and this light spot is adapted to move in the radial direction of the optical disc (101). The optical head (104) includes a frame (105), a light source (106) such as a semiconductor laser, a collimator lens (10
7), polarization beam splitter (108), λ / 4 plate (109), optical path changing mirror (110), light beam from the light source (106) is focused on the medium surface of the optical disc (101) to form a light spot. Objective lens (111) forming (115), optical spot (101)
Objective lens for accurate positioning on the recording track of
Tracking actuator (112) that slightly moves (111) in the radial direction of optical disc (101), and optical disc (101)
It is composed of a split photodetector (113) of two splits for detecting the return light reflected by.

The adder / subtractor amplifier circuit (114) outputs the sum signal as the required information signal by taking the sum of the outputs from the split photodetector (113), or subtracts the output from the split detector (113). By doing so, the tracking error signal is output to the track crossing number counter (118) and the speed detection circuit (120).

This track crossing counter (118) is an addition / subtraction amplifier circuit.
By receiving the output from (114), the optical head (10
It is for detecting the number of tracks traversed by 4), and its output is sent to the target speed generating circuit (119).

This target speed generation circuit (119) receives the output from the track crossing number counter (118), generates a target speed signal of the light spot (115) at the time of access, and directs it to the head actuator drive control circuit (117). Then, the target speed signal is output.

The head actuator drive control circuit (117)
Is also adapted to receive the outputs from the polarity switching circuit (2), and based on the reception of these outputs, the head actuator drive control circuit (117) controls the drive of the head actuator (116). Has been done.

The head actuator (116) is driven by the head actuator drive control circuit (117) to drive the optical head.
(104) is moved in the radial direction of the optical disc (101).

In the speed detection circuit (120), the optical spot (115)
01) is for detecting the speed when crossing the track, and its output is added to the polarity switching circuit (2). The speed detection circuit (120) and the polarity switching circuit (2) constitute a speed detection circuit (124).

The polarity switching circuit (2) has an access direction command generation circuit (123)
The output from the access direction command generation circuit (123) is used to add the output from the polarity switching circuit.
(2) is adapted to switch the polarity of the output from the speed detection circuit (120). That is, the polarities are switched such that the detected speed (scalar amount) in the direction becomes the detected speed (vector amount).

FIG. 9 is a transfer function block diagram of the speed control system expressing FIG. 8 by a transfer function. In FIG. 9, the output V _{r of the} target speed generation circuit (119) and the speed detection circuit (12
The subtraction result from the detected speed V _s ^* from 4) is input to the gain compensation circuit (5). The gain compensation circuit (5) is for determining the band of the speed control system.

The gain compensation circuit (5), the notch filter (122) and the head actuator drive circuit (6) are included in the head actuator drive control circuit (117), and the notch filter (122) among them is included. ) Is for compensating the mechanical resonance characteristic G _L (S) of the head actuator, as shown by the block (8) in the head actuator (116).

Further, as the head actuator drive circuit (6), since a current drive type is usually adopted,
It also has a built-in drive current detection circuit.

The block (7) in the head actuator (116) shows the force constant of the head actuator. Further, the block (8) described above shows the transfer characteristics of the head actuator when the acceleration is input and the speed V _L of the head actuator is output. In this block (8), M is the mass of the movable part, G _L (S) is the mechanical resonance characteristic of the head actuator, and S is the Laplace operator. The other configuration is similar to that of FIG. 7, and therefore its explanation is omitted. However, K _V in the target speed generation circuit (119) and the speed detection circuit (124) means speed detection sensitivity, and τ is a light spot
It should be pointed out that this means the track crossing period of (115).

FIG. 10 is an illustration of a gain characteristic of G _L (S) in the block (8) of FIG. 9, in which a certain predetermined frequency ω
It is shown as having a large resonance peak at _L (usually KH _Z ). On the other hand, FIG. 11 is an exemplary diagram of the gain characteristic | G _{N (S)} | of the notch filter (122) in FIG. 9, and here, ω _N = ω _L and | G _{N ( S)} ｜
It is designed to select G _N (S) so that | 1 / GL _(S) |.

12 and 13 are illustrations of open loop characteristics for those of FIG. Figure 12 in it shows G
_It means that _N (S) = 1 / _GL (S), and
Figure 3 means the case of G _N (S) 1 / G _L (S).

Next, the operation of the above conventional example will be described. In FIG. 8, first, the disc motor drive control circuit (103) causes the disc motor (102), that is, the optical disc (101) to start rotating. Then, after the number of rotations of the optical disc (101) reaches a certain steady value, the tracking error detected by the photodetector (113) and the addition / subtraction amplifier circuit (114) is performed by the well-known operation of the optical head (104). Drive control of the tracking actuator (112) is performed based on the signal.
Thus, the light spot (115) is made to follow the center of a certain track on the optical disc (101).

In addition, when tracks are being accessed, the number of tracks on the optical disc (101) that the optical spot (115) has crossed is counted by the track crossing counter (118), and the number of tracks remaining up to the target track is calculated. In response, the target speed output from the target speed generation circuit (119) and the light spot detected by the speed detection circuit (124)
By the head actuator drive control circuit (117) added with the track traverse speed of (115), the light spot (115)
The speed is controlled so that the speed approaches zero as the target approaches the target track.

Further, referring to FIG. 9, the operation of the speed control system when the track is accessed will be described in detail. The speed deviation signal V _e , which is the difference between the target speed signal V _r output from the target speed generation circuit (119) and the detected speed signal V _s ^* output from the speed detector (124), is calculated by the gain compensation circuit (5 ) And a notch filter (122) to the actuator drive circuit (6), which results in a certain drive current being applied to the head actuator (116). Therefore, the head actuator (116) starts moving at a speed of V _L , and the light spot (115) moves to the optical disk (10
1) Cross the upper track groove.

On the other hand, detected by the optical disc when the (101) track swing speed is assumed to be V _d generated by the rotation, the difference is the speed detection circuit of the velocity and the track runout velocity V _d of the head actuator (116) (124) Speed It is detected as signal V _s ^* . Then, by feeding back the detected speed signal V _s ^* , the speed control system as a whole operates so that the detected speed signal V _s ^* matches the target speed signal V _r .

In this speed control system, the open loop transfer function (open loop characteristic) from the speed deviation signal V _e to the detected speed signal V _s ^* is It is expressed as.

Here, when the design condition G _N (S) = 1 / G _{L (S)} is selected, as shown in FIG. 12, the mechanical resonance characteristics of the head actuator in the high range do not appear. , G _{N (S)} 1 / G _{L (S)} due to variations among devices, the mechanical resonance characteristics of the head actuator appear in the high range as shown in FIG. . And if the peak exceeds O _dB , the speed control system becomes unstable.

Further, due to the dead time of the zero-order hold characteristic of the speed detection circuit (124), the phase delay near the track crossing frequency becomes large.

[Problems to be solved by the invention]

Since the conventional optical disk drive device is configured as described above, it has the following problems.

(1) Since the speed at which the light spot (115) crosses the track is detected based on the track crossing cycle, if the track is crossed slowly at low speed, a time delay (dead time) will occur in the speed detection. Therefore, the speed control system is likely to be unstable, and the cutoff frequency of the speed control system must be designed to be low, so that the speed deviation is likely to be large.

(2) When the light spot (115) passes the dropout portion or the data address recording portion of the optical disc (101), it is assumed that the dropout or the data address recording period is erroneously detected as a track crossing period. Although the light spot is actually moving at low speed, the speed detection circuit (124) malfunctions as if it is moving at high speed, resulting in disturbance of the speed control system. become.

The (3) head actuator (116), usually is for large mechanical resonance in the vicinity of several KH _Z is present, inserts in order to remove this, a notch filter (122) to the head actuator drive control circuit However, when there are a plurality of resonance frequencies, the circuit scale becomes large and the resonance frequencies vary from device to device.
When this is different from the frequency of the notch filter,
The speed control system becomes unstable.

(4) The light spot (115) does not have a function to detect the direction traversing the track, and the required speed can be obtained simply by switching the speed polarity depending on the direction (inner circumferential direction or outer circumferential direction) that should be accessed. Therefore, if the transverse direction is reversed from the direction to be accessed due to track shake or disturbance speed at that low speed, positive feedback may be applied to the speed control system and the optical head may run away. There is.

The present invention has been made to solve such a problem, and compensates the dead time of the speed detection circuit, improves the stability of the speed control system, widens the band of the system, and can reduce the speed deviation, Disturbance of the speed control system is reduced by dropouts on the disk and malfunctions of the speed detection circuit in the address data section.The notch filter is removed to simplify the circuit and suppress the effects of mechanical resonance at any frequency. It is an object of the present invention to obtain an optical disk drive device in which the optical head does not run away even if the track crossing direction of the light spot is reversed due to the disturbance velocity.

[Means for solving problems]

An optical disk drive device according to the present invention is an optical head provided with a photodetector for forming a light spot on an optical disk having a large number of tracks and receiving reflected light from the optical disk. A head actuator for moving the movable part of the head in the radial direction of the optical disk, and a track crossing detection pulse by binarizing a photoelectric conversion signal photoelectrically converted by the photodetector when the light spot crosses a track on the optical disk. A track crossing distance detecting means for generating a signal, integrating the track crossing detection pulse signal, and outputting the integrated value as a track crossing distance signal, a drive current detection circuit for detecting the drive current of the head actuator, the track crossing detection pulse The signal is counted and the tiger crossed by the above light spot. Target speed generating means for generating a target speed according to the number of remaining tracks up to the target track, the first gain element converts the drive current signal into an acceleration signal, and a first-order lag element and a second gain element. An element converts the acceleration signal into a speed signal, a feedback gain element corrects the acceleration signal and the speed signal with the track crossing distance signal, and outputs the corrected speed signal as an estimated speed signal across the track of the light spot. State observer, and a head actuator drive control circuit that controls the speed of the head actuator by a drive current so that the target speed and the estimated speed match, and the cutoff frequency of the state observer is the optical head or the optical head. Mechanical resonance frequency of head actuator and above-mentioned track crossing detection pulse signal Lower than the frequency,
Further, it is higher than the track swing fundamental wave frequency of the optical disc.

[Work]

According to the present invention, when the track is accessed, the track crossing speed of the light spot is estimated by the state observing device based on the track crossing distance signal output from the track crossing distance detection means and the output signal from the drive current detection circuit of the head actuator. , The track crossing speed control of the light spot is performed depending on the estimation result.

〔Example〕

An embodiment of an optical disk drive device of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the embodiment. In FIG. 1, the same parts as those in FIG. 8 are designated by the same reference numerals to avoid repetitive description thereof, and mainly different parts from FIG. 8 will be described.

In FIG. 1, reference numerals (101) to (119) are the same as those in the conventional device.

Reference numeral 20 denotes a track crossing detection circuit, to which the difference signal and the sum signal output from the addition / subtraction amplification circuit (114) are added so that the light spot (115) crosses the track on the optical disc (101). It is for detecting the timing to do. Reference numeral 1 is a direction detection circuit for detecting the direction in which the light spot (115) crosses a track on the optical disc (101) when an output from the track crossing detection circuit 20 is added. The distance detection circuit is for integrating the output from the track crossing detection circuit 20 in the positive or negative direction based on the output from the direction detection circuit 1.

The state observer 3 includes a drive current signal detected by a drive current detection circuit (121) for detecting a drive current of the head actuator (116) and a track crossing distance detection circuit (2
It is for receiving the track crossing distance detection signal output from A) and estimating the speed closer to the true value. The output of the state observer (3) is applied to the head actuator drive control circuit (117).

The control mode detection circuit (4) is for outputting a reset command for the integrator included in the state observer (3) when the light spot (115) follows the track center. is there.

FIG. 2 is a transfer function block diagram of the speed control system expressing FIG. 1 by a transfer function. In FIG. 2, a state observer (3), a control mode detection circuit (4), and a track crossing distance detection circuit (2A) are the same as those in FIG. 1, and a gain compensation circuit (5), Head actuator drive circuit (6),
The force constant block (7) and the mechanical resonance characteristic block (8) of the head actuator are the same as in FIG.

The state observer (3) is composed of a gain element (9),
(10), (21), feedback gain elements (11), (12) and first-order lag element (13).

The gain element 9 has a gain K _F equal to that of the force constant of the head actuator (block 7), receives the drive current signal detected in the head actuator drive circuit (6), and estimates the drive force thereof. Is to be output. The gain element (10) has a gain 1 / M that is equal to the reciprocal of the moving part mass when the head actuator and the optical head are accessed. Further, the feedback gain elements (11) and (12) receive the track crossing distance detection signal X _s ^* detected by the track crossing distance detection circuit (2A).

The first-order lag element (13) inputs a more accurate estimate of the acceleration signal, such as that obtained by subtracting the output from the feedback gain element (12) from the acceleration signal that is the output from the gain element (10). It is what is done. And
The first-order delay element (13) can be reset by the output of the control mode detection circuit (4).

The gain element (21) is for simulating the track crossing distance detection circuit (2A). Then, the sum of the output from the feedback gain element (11) and the output from the gain element (21) is the estimated speed signal. Will be output from the state observer (3).

FIG. 3 is an exemplary diagram when the state observer (3) in FIG. 2 is equivalently converted. In FIG. 3, the components denoted by the same reference numerals are the same as those in FIG. Then, the sum of the output from the calculation element (22) including the differential element and the output from the gain element (21) is the estimated speed signal. Is output from the state observer (3). Further, the predetermined calculation unit included in the calculation element (22) also has a control mode detection circuit (4) as in the case of the first-order delay element (13).
It can be reset by the output of.

FIG. 4 is a transfer function block diagram of a speed control system in which FIG. 1 is expressed by a transfer function of a mode different from that of FIG.
Especially regarding the state observing device (3), as shown in FIG. 2 and FIG.
It is shown in a different form from the drawing. It is to be noted that, in this FIG. 4, those denoted by the same reference numerals are the same as those in FIG. Here, (23) is a feedback gain element, and (24) and (25) are integrators. The integrators (24) and (25) can be reset by the control mode detection circuit (4).

FIG. 5 is a view showing an example of the waveform of each part when speed control is performed. (14) is an output from the addition / subtraction amplifier circuit (114) in FIG. 1 and represents a track crossing sensor signal. (15) is an output signal from the track crossing distance detection circuit (2A) (track crossing distance detection signal)
It represents X _s ^* . Then, (16) represents the true track crossing distance, which is not actually detected.

FIG. 6 is a relationship diagram between the track groove and the detection signal. FIG. 6 (a) is a sectional view of the optical disc,
In the figure, (18) represents a track groove portion, and (19) represents a groove portion.

FIG. 6 (b) is a subtraction output signal (tracking error signal) from the addition / subtraction amplifier circuit (114) in FIG. 1, and FIG. 6 (c) is an addition output signal (sum signal). Also, FIG.
(d) and FIG. 6 (e) are respectively FIG. 6 (b) and FIG. 6 (c).
Is a comparison signal of.

FIG. 7 shows the open-loop transfer characteristic of the speed control system shown in FIG. 2 and shows frequency characteristics of gain and phase.

Next, the operation of the above embodiment will be described. Light source (106)
The light from is collimated by the collimator lens (107), linearly polarized through the polarization beam splitter (108), further passed through the λ / 4 plate (109) and reflected by the mirror (110). Therefore, the objective lens (111) forms a light spot on the optical disc (101) which is constantly rotating.

Then, the light reflected from the optical disc (101) is returned from the objective lens (111) to the polarization beam splitter (108), and after being reflected by the polarization beam splitter (108),
It is incident on the split photodetector (113).

Next, the light incident on the split photodetector (113) is photoelectrically converted by the split photodetector (113), and the photoelectrically converted signal is converted into a sum signal and a tracking error signal by the adder / subtractor amplifier circuit (114). .

When track access is being performed, the sum signal and tracking error signal are detected by the track crossing detection circuit (20).
Is input to the direction detection circuit (1), the track crossing distance detection circuit (2A) and the track crossing number counter (118).

The pulse-shaped track crossing detection signal output from the track crossing detection circuit (20) is based on the detection result of the direction detection circuit (1), and the moving direction of the light spot (115) is the outer peripheral direction of the optical disc (101). The track crossing distance detection circuit (2A) switches the polarity depending on whether the track is in the inner circumference direction or not, and the result is integrated and the status is observed as the total track crossing distance after the access operation starts. vessel
It is input in (3).

For example, if the optical spot (115) is moving in the outer peripheral direction when the optical disc (101) is to be accessed in the outer peripheral direction, the track crossing detection pulse signal output from the track crossing detection circuit (20). Is counted up by an appropriate counter, and if it is moving in the inner circumferential direction, it is counted down to detect the desired total track crossing distance.

At the same time, the drive current signal of the head actuator (116) detected by the drive current detection circuit (121) is also input to the state observing device (3).

Further, at this time, the output of the control mode detection circuit (4) releases the reset of the integrator included in the state observer (3), and the state observer (3) is operated. So that

On the other hand, the output from the track crossing counter (118) is transmitted to the target speed generation circuit (119),
The target speed corresponding to the number of remaining tracks is output from (119).

The head actuator drive control circuit (117) is based on the output from the target speed generation circuit (119), the output from the state observer (3), and the output from the drive current detection circuit (121). (116) is drive-controlled, and as a result, the track crossing speed of the light spot (115) is controlled.

Next, the operation of the state observer (3) will be mainly described with reference to FIGS. 2, 3, and 4. The output from the gain compensation circuit (5) that determines the band of the speed control system corresponds to the drive command signal of the head actuator (116), and is converted into a drive current in the head actuator drive circuit (6), In the actuator (116), the driving force is made based on the force constant K _F [N / A] and multiplied by 1 / M which is the reciprocal of mass to obtain the acceleration. Then, this acceleration is integrated to obtain the velocity, and this velocity is further integrated to obtain the desired distance. Incidentally, when the band is in the high frequency range, further, the influence of the high-band resonance characteristic G _L (S) of the head actuator (116) also receiving, the head actuator (116) is moved by the desired distance X _L become.

Also, the track deflection amount due to eccentricity of the optical disc (101) is assumed to be X _d, so that the difference between X _L and X _d is corresponding to the track crossing distance of the light spot (115). Then, this is detected by the track crossing distance detection circuit (2A) and converted into an electric signal with a gain of position detection sensitivity K _X [V / m].

At this time, as shown in FIG. 5, the track crossing distance signal (15) detected based on the track crossing cycle of the sensor signal (14) which is the output from the addition / subtraction amplifier circuit (114).
Is obtained as the average traverse speed for the last half track only after a track crossing is detected. Therefore, at the time of deceleration, the staircase waveform shown in the figure is obtained, and the track crossing distance detection circuit of FIG.
It will have a zero-order hold characteristic as shown in (2A). Moreover, since the track crossing cycle becomes longer as the track crossing speed becomes lower, the value of τ is made smaller at the high speed and made larger at the low speed.

The state observer (3) is basically a head actuator.
(116) and the track crossing distance detection circuit (2A) transfer characteristics are simulated by an appropriate electronic circuit, and the high-range resonance characteristic G _L (S) of the head actuator (116) and the track crossing distance detection circuit ( 2A) zero-order hold characteristic (1-e ^-Sτ ) / Sτ
Is not included.

In this state observer (3), first, the drive current signal i _L of the head actuator (116) detected by the drive current detection circuit (121) is converted into acceleration information by the gain elements (9) and (10). It

Further, this acceleration information is converted into a velocity signal via the first-order lag element (13) and the gain element (21). And
The speed signal thus obtained is subjected to the required correction by the track crossing distance detection signal X _s ^* via the feedback gain elements (11) and (12), and then the true track crossing speed is estimated. value Will be obtained.

By the way, the estimated speed which is the output from the state observer (3) from the drive current signal i _L of the head actuator (116) and the track crossing distance signal X _s ^* which are two inputs to the state observer (3). The transfer characteristics up to It is represented by.

That is, from the drive current signal i _L to the estimated speed signal Estimated speed signal to and from the track crossing distance signal X _s ^* Since the time constant of the transfer characteristic to is 1 / L, the state observer (3) is stable as long as L> 0. That is, L
Is the estimated speed signal Is a parameter that determines the speed of convergence of
When trying to converge with a time constant of ms, L = 10
00 will be selected.

Here, the meaning of Eq. (2) is examined by separating the bands. First, K _F i _L / M is the head actuator (11
Since an item corresponding to the acceleration of 6), the track deflection amount X _d disk is made sufficiently smaller than the moving distance X _L of the head actuator (116), the following equation (3) is approximately To establish.

If S = jω, then (i), when ω << L (| S | << L), If L1000, from equation (3) Therefore, Becomes

(ii), when ω >> L (| S | >> L), According to equation (3) Therefore, Becomes

Estimated velocity crossing signal of the light spot output from the state observing device (3) Is in agreement with the differential value SX _s ^* of the track crossing distance detection signal X _s ^{* in} the low frequency region, and is in agreement with the integral of the head actuator drive current i _L in the high frequency region. Recognized from the ceremony. The frequency for branching both is L [rad / sec], which matches the band of the state observer (3). Now, assuming that ∽,
From equation (2) Therefore, the drive current i _L is not used, and a signal obtained by differentiating the track crossing distance detection signal X _s ^* is the estimated speed signal. Therefore, the dead time generated in the track crossing distance detection circuit (2A) cannot be compensated. On the other hand, L
Assuming that = 0, from equation (2) And the estimated speed signal Since the track crossing distance detection signal X _s ^* is not used for the drive, it is not affected by the dead time of the track crossing distance detection circuit (2A) or the high frequency resonance characteristics of the head actuator (116), Even if a slight offset is superimposed on the current i _L , the estimated speed signal The estimation error of is increased. Also, the estimated speed signal at this time Since the track shake amount X _d is not included in the Is not an estimated value of the track crossing speed of the light spot (115), but an estimated value of the moving speed of the head actuator (116). Therefore, at that low speed, the estimated speed signal (estimated value) of the track crossing speed is reached when the moving speed becomes so small that the track runout speed cannot be ignored. The error of becomes large.

Therefore, the parameter L corresponding to the band of the state observing device (3) is sufficiently lower than the high-frequency resonance frequency of the head actuator (116) and the track crossing frequency of the light spot (115), and the parameter of the optical disc (101). The estimated speed signal can be set by setting it sufficiently higher than the track swing fundamental wave frequency. Is an intermediate value between the value expressed by the equation (6) and the value expressed by the equation (9), and the dead time generated in the track crossing distance detection circuit (2A) is compensated to some extent. You can

Also, according to equation (2), the differential value of the track crossing distance signal X _s ^*
Estimated speed signal from SX _s ^* Since it can be expressed by the first-order low-pass filter characteristic that the transfer characteristic to 1 / (1 + S / L), SX _s ^* corresponding to the detected speed signal is disturbed by the dropout or recording pit on the optical disc (101). Estimated speed signal, even if Is rarely disturbed.

FIG. 3 is an equivalent conversion of FIG. 2, and the transfer characteristics of the state observing device (3) are exactly the same for both, so the explanation of the operation is omitted.

FIG. 4 is a block diagram of a speed control system in which the state observer (3) is realized in a different mode. Here, the gain factor (9),
(10), (21) and the integral elements (24), (25) imitate the transfer characteristics of the head actuator (116) and the track crossing distance detection circuit (2A) to be controlled. In FIG. 4, the drive current signal i _L of the head actuator (116) is converted into an acceleration signal through the gain elements (9) and (10), and then converted into a velocity signal by the integration element (24). Further, it is converted into a moving distance signal by the integral element (25) and the gain element (21). Then, the difference between this movement distance signal and the output X _s ^* from the track crossing distance detection circuit (2A) is fed back to the feedback gain elements (12) and (23), respectively, and integrated elements (24) and (25 ) Is applied to the input side to achieve the desired speed control. Ie gay element (21)
The required corrections are made to the acceleration and velocity signals so that the estimated value of the track crossing distance, which is the output of, is converged to the track crossing distance detection signal X _s ^* , and the acceleration signal thus modified is added to the integral element (24 ) Estimated value of track crossing speed As a result, the desired speed control is performed. In FIG. 4, the estimated speed is calculated from the drive current i _L of the head actuator (116) and the track crossing distance detection signal X _s ^*. The transfer characteristics up to are expressed by the following equation.

Now, as in the case of FIG. 2 and FIG.
Band of (3) As a boundary, Can be approximated by

Therefore, it is recognized that in the case of FIG. 4 as well, the same effect as in the cases of FIGS. 2 and 3 can be exhibited.

Incidentally, in general, the state observer (3) in FIG.
It is called the same-dimensional state observer because it has the same order (the same number of integration elements) as the head actuator (116). On the other hand, the state observer (3) in FIGS. 2 and 3 has an order of 1 with respect to the head actuator (116).
It is called a minimum dimensional state observer because it is lowered. It is also known that the same-dimensional state observer in FIG. 4 can be converted into the minimum-dimensional state observer in FIGS. 2 and 3 by the so-called Gopinath method.

Further, while the light spot (115) is tracking on the track, the integration elements (13), (22), (24), (25) (second one) are commanded by the control mode detection circuit (4). Figure through Fourth
(Fig.) Is reset to switch to the speed control mode, and at the same time, the reset is released. In this way, since the track crossing speed during tracking is obviously zero, there is no error in the initial value of the estimated speed output from the state observer (3) immediately after shifting to the speed control mode. . Even if an error occurs, the error converges with a correct estimated value with a time constant of 1 / L or 1 / √L ₂ .

Next, the open loop transfer function of the speed control system shown in FIG. 2 is obtained by calculating the following equation.

This is the high range resonance characteristic G of the head actuator (116).
_{If the} frequency at which _L (S) peaks is ω _L ,
By setting L so that L << ω _L , the following equation is established.

By doing so, the effect of the size of the high-frequency resonance peak of the head actuator (116) on the open-loop characteristics in equation (13) is suppressed to L / ω _L times.
Therefore, as shown in FIG. 7, it is recognized that the high frequency peak in the gain characteristic becomes smaller than that in FIG.

Further, unlike the frequency characteristic of the notch filter (122) in FIG. 11, the high frequency resonance frequency ω _L does not have to be a specific frequency. Then, generally, as long as the frequency satisfies the condition of ω _L >> L, the desired suppression effect can be obtained at any frequency. Further, even if there are a plurality of peaks, a uniform suppression effect can be obtained. Further, like the mechanical resonance characteristic G _L (S), the phase delay and the gain drop due to the zero-order hold characteristic of the track crossing distance detection circuit (2A) in the equation (13) are alleviated. For this reason, the phase of the open loop characteristic is extended to a high range, and as a result, the stability of the system is improved.

Referring now to FIG. 6, the light spot (115) (first
(Fig. 6) is a subtraction output signal of the addition / subtraction amplifier circuit (114) obtained when the track crosses the optical disk (101) (Fig.
It is recognized that (b)) and the addition output signal (Fig. 6 (c)) have a phase difference of 90 ° with each other. From this, the waveform level of FIG. 6 (e) is “H” at the rising edge of the waveform of FIG. 6 (d), or the waveform level of FIG. 6 (d) is at the falling edge of the waveform of FIG. 6 (e). When the waveform level of) is “L”, the light spot (115) moves from left to right. On the other hand, when the waveform level of FIG. 6 (e) is opposite to the above, It can be seen that the light spot (115) is moving from right to left.

As described above, the cross direction of the optical spot (115) is detected by the direction detection circuit (1), and the polarity of the cross track detection signal is detected by the direction detection circuit (2A) for crossing the track of the optical spot (115). By switching and integrating depending on the direction, the speed control system does not become a positive feedback, and its stable operation is ensured.

In the above embodiment, the track crossing distance detection circuit performs the operation of switching the polarity of the track crossing detection signal based on the detection result of the moving direction of the light spot and integrating the signal. No direction reversal occurs during control, and even if direction reversal occurs, if it is for a short time, the estimated speed that is the output of the state observer (3) is (9) Since the speed control system is determined based on the equation almost only depending on the drive current information i _L , the speed control system does not become the positive feedback. For this reason, the direction detection circuit can be omitted.

Further, although the case where a linear motor that is linearly driven is used as the head actuator is illustrated in FIGS. 2, 3, and 4, the present invention is not limited to this, and for example, a rotary actuator. Can also be used. In this case, the moment of inertia J of the movable portion is used instead of the mass M of the movable portion. Further, it is not necessary to drive the entire head, and it is possible to drive only a part of the head by using, for example, a separation type actuator. In any case, it is sufficient if the actuator can move the light spot largely in the radial direction of the disc when searching for a track.
Tracking actuator (112) in FIG. 2
It may be configured to be used also as. Further, in the above embodiment, the drive current detection means is used to detect the acceleration of the head actuator,
Instead of this, for example, an acceleration sensor may be attached to the head movable part to detect acceleration and input this to the state observing device.

Further, in the above embodiment, the track crossing speed or the direction of the light spot is detected based on the signal obtained by subjecting the output of the divided photodetector to moderate adjustment. However, the present invention is not limited to this, and for example, there is no track. When the sample servo method using an optical disk is adopted, the track crossing speed is determined based on the output of the tracking signal (track deviation signal) detecting means or the track crossing number detecting means and the means for detecting the signal corresponding to the total reflected light amount signal. Alternatively, the direction or the direction may be detected. Alternatively, the track crossing direction may be detected based on the disc address information.

〔The invention's effect〕

As described above, the present invention provides an optical head provided with a photodetector that forms a light spot on an optical disc having a large number of tracks and receives reflected light from the optical disc.
A head actuator for moving the movable part of the optical head in the radial direction of the optical disc when the track of the optical disc is accessed, and a photoelectric conversion signal photoelectrically converted by the photodetector when the light spot traverses a track on the optical disc. To generate a track crossing detection pulse signal, integrate the track crossing detection pulse signals, and output the integrated value as a track crossing distance signal, a drive for detecting the drive current of the head actuator. A current detecting circuit, a target speed generating means for counting the number of tracks crossed by the light spot by counting the track crossing detection pulse signal, and generating a target speed according to the number of remaining tracks up to the target track, a first gain element The above drive current signal is converted into an acceleration signal by Element and a second gain element to convert the acceleration signal to a velocity signal, a feedback gain element to modify the acceleration signal and the speed signal with the track crossing distance signal, and the modified speed signal to the track of the light spot. A state observer that outputs a crossing estimated velocity signal, and a head actuator drive control circuit that controls the speed of the head actuator with a drive current so that the target velocity and the estimated velocity match, and a cutoff frequency of the state observer. Is lower than the mechanical resonance frequency of the optical head or the head actuator and the frequency of the track crossing detection pulse signal, and higher than the track swing fundamental wave frequency of the optical disc, so that the stability of the speed control system is improved. In addition to long distance, very short distance It is possible to even speed control during access, the access time for the optical disc apparatus can be greatly reduced.

In addition, since the performance of the speed control system does not depend on the variation of the mechanical resonance frequency of the head actuator or the optical head or the number of resonance points, the head actuator and the optical head can be easily assembled. It is a thing.

[Brief description of drawings]

FIG. 1 is a block diagram showing the overall configuration of the optical disk drive device of the present invention, FIG. 2 is a block diagram of a speed control system in the same optical disk drive device, and FIG. 3 is a different speed in the same optical disk drive device. Block diagram of control system,
FIG. 4 is a block diagram of yet another speed control system in the optical disc drive apparatus of the above, FIG. 5 is an operation explanatory diagram of a track crossing detection circuit in the optical disc drive apparatus of the above
FIG. 6 is a diagram for explaining the operation of the direction detection circuit in the same optical disk drive device, FIG. 7 is an illustration of the open-loop transfer characteristic of the speed control system in FIG. 2, and FIG. 8 is a conventional optical disk drive device. 9 is a block diagram showing the configuration of FIG.
FIG. 10 is a block diagram of a speed control system in a conventional optical disk drive, and FIG.
FIG. 1 is an exemplary diagram of frequency characteristics of a notch filter in the speed control system of FIG. 9, and FIGS. 12 and 13 are
FIG. 10 is an illustrative view of open loop transfer characteristics of the speed control system in FIG. 9 respectively. (1) …… Direction detection circuit, (2) …… Polarity switching circuit, (3) ……
State observer, (4) ... Control mode detection circuit, (101) ... Optical disk, (104) ... Optical head, (114) ... Addition / subtraction amplification circuit, (115) ... Optical spot, (116) ... … Head actuator, (117) …… Head actuator drive control circuit, (2A) …… Track crossing distance detection circuit, (20) …… Track crossing detection circuit. The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (2)

[Claims] 1. An optical head provided with a photodetector for forming a light spot on an optical disc having a large number of tracks to receive reflected light from the optical disc, and a movable part of the optical head when a track of the optical disc is accessed. A head actuator that moves the optical disc in the radial direction of the optical disc, and when the light spot traverses a track on the optical disc, the photoelectric conversion signal photoelectrically converted by the photodetector is binarized to generate a track crossing detection pulse signal. A track crossing distance detection means for integrating the track crossing detection pulse signals and outputting the integrated value as a track crossing distance signal; a drive current detection circuit for detecting the drive current of the head actuator; counting the track crossing detection pulse signals; The number of tracks crossed by the optical spot Target speed generating means for generating a target speed according to the number of remaining tracks until the first track, a first gain element converts the drive current signal into an acceleration signal, and a first-order lag element and a second gain element cause the acceleration signal. To a speed signal, and the acceleration signal and the speed signal are corrected by the feedback gain element with the track crossing distance signal, and the corrected speed signal is output as an estimated speed signal of the track crossing of the light spot. And a head actuator drive control circuit that speed-controls the head actuator by a drive current so that the target speed and the estimated speed match, and the cutoff frequency of the state observer is the mechanical resonance of the optical head or the head actuator. Lower than the frequency and the frequency of the track crossing detection pulse signal, One optical disk drive apparatus characterized by higher than the track runout fundamental frequency of the optical disc. 2. The first-order lag element provided in the state observing device is reset while the light spot is tracking along the track. The optical disk drive described.