JPH03245375A - Digital servo device - Google Patents

Abstract

PURPOSE:To exactly control a head and to enable high-speed seek by detecting the velocity of the head for each prescribed moving distance and calculating the command value of an actuator each time the velocity is detected. CONSTITUTION:A digital signal processor (DSP) 8 is provided as a means to calculate the target velocity of a head 2 corresponding to a residual distance until the commanded target position of a recording medium 1, and a tracking error detector 2 detects the velocity of the head 2 each time the head 2 is moved to the recording medium 1 for the prescribed moving distance. Each time this means detects the velocity, the DSP 8 calculates the command value of an actuator 12 for driving the head from the detected value and the target velocity at that time so that the head 2 can follow up the target velocity. Thus, while enabling the high-speed seek, the exact control is enabled as well.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a digital servo device that controls a head used for recording or reproducing information on a magnetic disk, magneto-optical disk, or the like.

[Prior Art] Conventionally, as a speed control for this type of head, for example, the ninth
As shown in the figure, closed-loop control is common in which a reference speed is generated that is proportional to the square root of the residual distance to the target position, and the head is caused to follow this reference speed. In such a control method, the actual head speed is detected by a speed detection circuit. Then, control to follow the above-mentioned reference speed is performed using this speed signal.

FIG. 10 shows an example of the speed detection circuit, and 100 is a shaping circuit that shapes the waveform of the tracking error signal into a binary signal. Further, 101 is a digital differential circuit composed of a delay circuit 102 and an exclusive OR circuit 103, and 104 is a monostable multivibrator.

To explain the operation of this speed detection circuit, as shown in FIG. 11, the AT error signal is first binarized by the shaping circuit 100 and converted into a pulse signal. The pulse width of the obtained binary signal is the pulse width of a half cycle of the AT error signal. Next, the digital differentiator circuit 101 generates trigger pulses at the rising and falling timings of the binarized signal and outputs them to the monostable multi-by-break 104. When the monostable multivibrator 104 receives a trigger pulse, it outputs a pulse signal with a pulse width τ as a speed signal. The obtained speed signal is a pulse signal whose period changes in accordance with the change in the period of the AT error signal. In other words,
Since the period and speed of the AT error signal are in a proportional relationship, the speed signal can be generated by signal processing using the AT error signal as described above. Further, as shown in the figure, this digital speed signal can be converted into an analog signal by averaging it.

However, in this speed detection circuit, when the speed approaches zero, the interval between the output pulses of the monostable multivib break becomes long, so that it cannot be used as a substantial speed signal. Therefore, with the speed control method described in FIG. 9, accurate closed-loop control is difficult. In addition, in the above control method, the closed loop band is limited by the resonance (usually 2 to 3 kHz) of the actuator mechanism for driving the head. Therefore, if a sudden deceleration is performed, followability deteriorates, and the speed at the time of completion of the seek operation cannot be brought to zero, resulting in a problem that the target position is exceeded. In order to avoid this problem, as shown in the figure, a method is adopted in which a large current is passed through the actuator during acceleration to accelerate the vehicle in a short period of time, and to control the vehicle to decelerate slowly. However, with this control method, the acceleration capacity is not fully used during deceleration and the vehicle is gradually decelerated, resulting in an increase in seek time.

Therefore, as a control method that solves these problems,
There is a method shown in FIG. This control method is a method in which most of the access distance is controlled by open-loop Bang-Bang drive, and the control is switched to closed-loop control immediately before the target position. With this control method, the seek time can be shortened because rapid deceleration can be achieved using a large current during deceleration.

[Problem to be solved by the invention] However, in this control method, Bang-Bang
Since the control is open-loop control, if it deviates from an appropriate acceleration or deceleration point due to the influence of friction, external force, etc., there is a problem that it may overrun or a residual distance may remain with respect to the target position. Additionally, with the closed-loop control method described above, seek time must be sacrificed to avoid overruns, making it difficult to achieve both high speed and accuracy at the same time. .

The present invention was made by paying attention to the above-mentioned circumstances.
The purpose is to provide a digital servo device that can perform high-speed yet accurate control and is not affected by friction or external forces.

[Means for Solving the Problems] In order to achieve the above object, there is provided a means for calculating a target speed of a head according to a residual distance to a commanded target position of a recording medium; means for detecting the movement distance every predetermined movement distance, and means for calculating a command value for the head driving actuator so that the head follows the target speed from the detected value and the target speed at that time every time the means detects the movement distance. A digital servo device is provided.

[Operation] According to the present invention, the speed of the head is detected every predetermined distance of movement, and from a target speed corresponding to this speed and the residual distance to the target, the actuator is commanded so that the head follows the target speed. By calculating values, it is possible to perform high-speed seek while also being able to perform accurate control.

[Examples] Examples of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the digital servo device of the present invention. Note that FIG. 1 shows an example in which the digital servo device of the present invention is implemented in an optical disk recording/reproducing device.

In FIG. 1, 1 is an optical disk, 2 is an optical system, 3 is a tracking error detector that detects a tracking error signal based on the output from the optical system 2, and 4 is a focus error signal based on the output from the optical system 2. This is a focus error detector that detects. Further, 5 is an A/D converter that A/D converts the error signal output from each error detector into a digital signal, and 6 is a digital signal processing section. The digital signal processing section 6 includes an I10 control section 7, a digital signal processor (hereinafter abbreviated as DSP) 8, and memories 9 and 10. Furthermore, 11 is D/A
12 is a tracking actuator, 13 is a focus actuator, and 14 is an external data input device.

Next, the basic operation of this embodiment will be explained.

Figure 2 shows the target speed and position of the head during multi-jump (
FIG. Although an ideal target speed is also shown in FIG. 2, what is actually used is a discrete target speed.

In this example, the final target truck is truck 14,
The area up to track 7 in the middle is an acceleration area, and the area from there to track 14 is a deceleration area. In addition, the deceleration area is the deceleration area■
and deceleration range ■, each with different speed control accuracy. In this example, the deceleration region I is the same as the acceleration region <
1/21 - Speed control is performed for each rack, and in deceleration region (3), speed control is performed for each 1/4 track for more precise control.

Specifically, speed control is performed by determining the target speed and actuator command value every 1/2 track in the acceleration region and deceleration region I, and every 1/4 track in the deceleration region (3). Further, the target speed for each 1/2 track or 1/4 track may be stored in advance in the memory, and control may be performed based on this.

FIG. 3 shows the relationship between the tracking error signal from four tracks before the target track and the command value and speed of the actuator.

In the example of FIG. 3, since tracks 10 to 12 are in the deceleration region (2), the calculation is performed every 1/2 track, and the difference from the target speed at that time is added to the reference acceleration to drive the actuator.

In this case, the speed calculation for each 1/2 track is actually performed by detecting the zero-crossing point of the tracking error signal and calculating the speed at that point. For example, at point A in FIG. 3, the time from point 2 to point A is measured, and the current speed 1 is calculated from the time T using the following formula.

V, = 1/2 LX 1/T.

However, E is the track pitch.

The target speed is the V r e r value at point A in Fig. 2, and as a result, the control amount a of the actuator is
Calculate ct.

a c t = a + K (Vret Va
) However, -α is the deceleration reference acceleration, and K is the feedback gain of speed control.

Next, since tracks 12 to 14 in Fig. 3 are in the deceleration region (■) mentioned above, the speed is calculated for each 1/4 track, and the difference from the target speed at that time is added to the reference acceleration and the actuator is adjusted. to drive. In this case, the calculation for each 1/4 track is performed by alternately detecting zero-crossing points and peak points of the tracking error signal, and using the time between pixels. In FIG. 3, the zero-crossing points of the tracking error signal are marked with *, and the peak points are marked with *.

For example, at point B in FIG. 3, the time from point Y to point B is measured, and the current speed vb is determined from the time T by using the following equation.

■ゎ = 1/4 × 1/Tb The target speed at this time is V r at point B in Figure 2.
et value, and as a result, the actuator command value act
is calculated using the following formula.

act=a+K (Vtet-Vb) When the calculation was performed in this manner and control was performed based on the obtained value, a speed curve as shown in FIG. 3 was obtained. As is clear from this figure, it can be seen that the actual speed Vt closely follows the ideal speed Vr@f.

Here, the calculation formula for determining the target speed vref shown in FIGS. 2 and 3 will be explained.

Generally, when the residual distance S to the target position is, the target velocity V is set to make V=O after seconds at the acceleration ability α.
r@f can be obtained by solving the following two simultaneous equations.

Vr,, -t-1/2αt2=S (distance formula) V r
s -αt=0 (speed equation) If t is eliminated from these two simultaneous equations, the following equation, which is the target speed equation, is obtained.

v, ,, = 'Ding T Ding From this equation, it can be seen that the target velocity is proportional to the square root of the residual distance.

In detecting the current speed described above, the current speed can be easily detected using the tracking error signal. Therefore, this speed detection method not only eliminates the need for a complicated speed detection circuit, but also solves the conventional problem of inaccurate speed detection near zero speed. be able to. Therefore, by using this speed detection, the configuration of the apparatus can be simplified and the speed of the head can be accurately controlled.

Next, the specific operation of this embodiment will be explained. FIG. 4 is a flowchart showing, as an example, a control operation during a multi-jump in one direction (inner circumferential direction). In addition, the fourth
The figure shows a control operation when performing a multi-jump from track O to track 14 shown in FIG. Therefore, as described above, control is performed with predetermined accuracy in each of the acceleration region, deceleration region I, and IT.

First, in S (step) 1, the tracking error signal is
Enter into SP8. To explain this operation in detail, in FIG. 1, reflected light from the optical disc 1 enters the optical system 2,
Tracking error signal S is detected by tracking error detector 3.
n is detected. 1 Then, the tracking error signal S is sent to the A/D converter 5.
is converted into digital data and sent to the DSP via the I10 control unit 7.
8 is input.

The DSP 8 detects the zero-crossing point of the tracking error signal in S2. - As an example, the next estimated tracking error signal S'ni+ is determined using the input tracking error signal Sn and the previous tracking error signal Sn-I stored in the memory 9. This estimated signal is obtained by the following equation.

S'n,,=2Sn-3,.

Next, multiply the obtained estimated value by the current value, and the sign is O
Or, when it is negative, it is determined to be the zero-crossing point of the tracking error signal. In other words, when this multiplication value is O or negative, it means that the estimated value is on or beyond the zero-crossing point of the tracking error signal and is negative, so that point is considered to be the zero-crossing point. be. In S2, the above-mentioned zero-crossing point is detected every time the tracking error signal is sampled, and when the zero-crossing point is detected in S3, the process proceeds to 84. Note that the DSP 8 is open until the next sampling except when a zero cross point is detected in S3, and therefore executes other processing.

S4 is a process for determining the current speed ■ and the target speeds r and f explained in FIGS. 2 and 3. As explained in FIG. 3, the current speed vt can be obtained by finding the half-cycle time T of the tracking error signal at that time and performing the following calculation using this time and 1/2 person.

V, = 1/2λ×1/T Further, the target speed is obtained by the following equation as described above.

■,. , = "In the S5, the DSP 8 determines the command value act of the actuator from the obtained current speed and target speed. Since the current speed is in the acceleration range, this command value is determined by the following equation.

act t=a+K (Vrer Vt) The command value obtained here is sent to the D/A converter 1 via the I10 control unit 7.
Output to 1. Then, the command value is this D/A converter 1
1 is converted into an analog signal, and the tracking actuator 12 is driven by this converted value. S6 is for determining whether or not the target track has been reached halfway, and is for determining whether or not the acceleration range explained in FIG. 2 has ended. In this case, the number of tracks is counted using a tracking counter (not shown), and when the count value reaches half of the target track, the process proceeds to the next step S7. Therefore, in the acceleration range that is half of the target track, the actuator is driven with the command value obtained for every 1/2 track by repeating the operations 81 to S6.

When half of the target track is reached, the process advances to S7 and the control operation for deceleration region I explained in FIG. 2 is performed. First, in S7, a tracking error signal is input, in S8, a zero-crossing point is detected in the same manner as described above, and in S9, it is determined whether or not the zero-crossing point has been reached. When the zero crossing point is detected, the current speed and target speed are determined in S10 using the same method as in S4.

Next, the DSP 8 determines the actuator command value act using the current speed and target speed in S12.

The command value at this time can be obtained from the following equation.

act=-α+K (Vr, f-Vt) Based on this command value, the actuator is similarly driven. Si2 is a process for determining whether the vehicle has reached two tracks ahead of the target track, that is, whether the deceleration area work has been completed. In this case, this determination is similarly made using a tracking counter. If it is determined in Si2 that the deceleration area work has been completed, the process advances to 313 and the deceleration area H is controlled. Therefore,
In the deceleration region I, by repeating S7 to S12, a command value for the actuator is obtained every 1/2 track as in the acceleration region, and the actuator is driven with the command value obtained each time.

When entering the deceleration region H, first a tracking error signal is input in S13, and a zero cross point is detected in S14. S1
If it is determined that the zero crossing point is reached in step 5, the current speed and target speed are determined in step 18 in the same manner as described above. On the other hand, 31
5, and if it is not 5 at the zero cross point, the peak value of the tracking error signal is detected in S16. If it is determined in S17 that the current speed is the peak value, the current speed and target speed are similarly determined in S18. That is, the zero-crossing points and peak points of the tracking error signal are detected alternately, and the current speed and target speed are determined at each detection point. In other words, by alternately detecting zero-crossing points and peak points, precise control is possible for each quarter track. In addition, in S18, the current speed Vt is calculated using the following equation.

V=1/4λ×1/T where T is the time from the zero cross point to the peak point.

In S19, the DSP 8 calculates the actuator command value act from the obtained current speed and target speed using the following equation in the same manner as described above.

a Ct ”-α+ K (Vr@t Vt ) S2
0 is used to determine whether or not the target track has been reached, and this determination is made based on the value of the tracking counter. Therefore, in the deceleration region (2), by repeating S13 to S20, a command value for the actuator is obtained every 1/4 track, and the actuator is driven with the command value obtained each time. Then, when the target track is reached in S20, the multi-jump operation ends.

Here, detection of the peak point of the tracking error signal in S16 will be explained. In this example, first, the difference ΔSr between the input tracking error signal S, and the tracking error signal S n-1 at the previous sampling time,
is calculated using the following formula.

ΔS,=Sn−S11 Next, the value of a similar difference ΔS n− one sampling before
1 and ΔS, l is multiplied. Note that ΔS n-1 is calculated using the following formula at the time of previous sampling and is stored in the memory.

△S n-+ = S n-I S n-a this △S
When the multiplication result of n and ΔS n-1 is negative, it is determined that the tracking error signal is at its peak point.

As described above, in this embodiment, the actuator command value is calculated for each 1/2 track or 1/4 track, and the head speed is controlled to follow the target speed curve. In addition, the head can ideally be moved to the target track without unnecessary movement. This enables high-speed seek without waste.

In addition, the actuator command value is calculated for each 1/2 track or 1/4 track, and the actuator is driven with the command value obtained each time, so accurate control is achieved without causing overruns with respect to the target track. It can be performed. Therefore, although it is high speed, accurate control is possible, and high speed and accuracy, which have been difficult to achieve in the past, can be achieved at the same time.

FIG. 5 shows a block diagram of another embodiment. This embodiment is characterized in that a speed position detection circuit 15 is provided.

Therefore, the other configurations are exactly the same as the embodiment shown in FIG.

The speed position detection circuit 15 is a circuit that detects the actual speed of the head and outputs a speed signal as a digital value. 1st
In the illustrated embodiment, the speed is calculated from the tracking error signal, but in this example, speed detection is performed using a speed detection circuit as shown in FIG. 10, for example. Furthermore, the present invention is not limited to this, and the speed may be detected by counting the reference clock within a predetermined track interval.

Next, the operation of this embodiment will be explained.

FIG. 6 is a flowchart showing the operation during multi-jump.

In FIG. 6, first, the speed position detection circuit 15 at Sl is
The speed is detected at a predetermined position and the speed signal is sent to the I10 control unit 7.
The signal is output to the DSP 8 via the . In this example, the velocity is detected at each zero-crossing point and peak point of the tracking error signal. Detection of zero crossing points and peak points for speed detection will be described in detail later. Next, DSP8
is the target speed Le at the timing of zero cross point and peak point.
Calculate f. That is, the residual distance S from the current position to the target track is determined, and the target speed V□ is calculated using the following equation.

9 v, , = r 10,000] In S3, the obtained target speed and speed position detection circuit 1
From the current speed Vt detected in step 5, the command value act of the actuator is calculated using the following equation.

a Ct = K (V r@t V t ) The obtained command value is sent to the D/A via the I10 control unit 7 in S4.
The signal is output to the converter 11, converted into an analog signal, and drives the tracking actuator 12. Then, in S5, it is determined whether or not the target track has been reached. If the target track has not been reached, the process returns to Sl again and repeats the process up to S5. In this way, the actuator is driven with the obtained command value at every zero-crossing point and peak point of the tracking error signal, that is, every 1/4 of the track interval, and the multi-jump operation is ended when the target track is reached.

Further, when the multi-jump operation is to be terminated, it may be terminated when the current speed reaches O, as shown in FIG. That is, it is possible to determine whether the current speed has reached 0 at 85 in FIG. 7, and to end the multi-jump operation when the current speed has reached 0. Furthermore, it is of course possible to end the multi-jump operation when either one of the conditions shown in FIGS. 6 and 7 is satisfied.

Next, the detection of zero cross points and peak points of the tracking error signal by the speed position detection circuit 15 will be explained with reference to FIG.

FIG. 8(a) shows the tracking error signal (TE multiplied signal,
FIG. 8(b) shows the binarized signal. Also, Figure 8 (
c) is an RF multiplied signal whose phase is 90 degrees ahead of that of the TE multiplied signal. FIG. 8(d) shows the RF multiplied signal binarized signal. Generally, it is a difference signal of a sensor obtained by dividing a TE multiplied signal, but it is a sum signal of an RF multiplied signal. Therefore, the phases of the TE multiplied signal and the RF multiplied signal are shifted by 90 degrees as described above.

In this example, the TE multiplied signal and the RF multiplied signal are each binarized,
By calculating the exclusive OR of each of the binarized signals, the zero cross point and peak point of the TE multiplied signal are detected. Figure 8(e)
shows the exclusive OR output, and it can be seen that the rising edge coincides with the zero-crossing point of the TE multiplied signal, and the falling edge coincides with the peak point. Since the phases of the TE multiplied signal and the RF multiplied signal are shifted by 90 degrees, the zero cross point and peak point can be detected as described above. Speed position detection circuit 15
detects the speed at the detected zero cross point and peak point, respectively, and outputs a speed signal.

This embodiment also has the effect of accurately controlling the head even at high speed, just like the embodiment shown in FIG. 1 described above.

In the above embodiments, an information recording device using an optical disk was explained as an example, but the present invention is not limited to this, and a recording device using a magnetic disk or the like can of course be suitably used.

[Effects of the Invention] As explained above, according to the present invention, the speed of the head is detected every predetermined movement distance, and the command value of the actuator is calculated every time this detection is performed, so that the head can be controlled accurately. can. Moreover, since the head is controlled to follow the target speed, high-speed seek can be performed without unnecessary movement of the head. Furthermore, since it is a closed-loop control, it has the advantage of not being affected by friction or external forces.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the digital servo device of the present invention, FIG. 2 is an explanatory diagram showing the relationship between the target position and target speed during multi-jump in the embodiment, and FIG. 3 is a tracking error diagram. Fig. 4 is a time chart showing the relationship between signals, actuator command values, and speeds; Fig. 4 is a flowchart showing the flow of processing during multi-jump;
The figure is a block diagram of another embodiment, FIG. 6 is a flowchart showing the flow of the process in FIG. 5, FIG. 7 is a flowchart showing the flow of another process, and FIGS. Figure 5 is a time chart showing the zero-cross point and peak point detection operations of the tracking error signal in the speed position detection circuit of the embodiment, and Figure 9 shows the relationship between the reference speed and actuator current in the speed control system of the conventional optical head. Explanatory diagram, Fig. 10P is a block diagram showing the speed detection circuit used in the control method of Fig. 9, Fig. 11 is a time chart showing the operation of the speed detection circuit, and Fig. 12 is another conventional example. A certain Ba
FIG. 3 is an explanatory diagram showing the relationship between speed and current in the ng-Bang control method. 1... Optical disk 2... Optical system 3... Tracking error detector 6... Digital signal processing section 8... DSP 12... Tracking actuator 15... Speed position detection circuit 4

Claims (3)

[Claims] (1) means for calculating the target speed of the head according to the residual distance to the target position of the recording medium, and means for detecting the speed of the head at every predetermined distance of movement with respect to the recording medium;
A digital servo device characterized by comprising means for calculating a command value for a head driving actuator so that the head follows the target speed from the detected value and the target speed at that time every time the means detects the detected value. (2) The speed detecting means detects zero-crossing points of the servo error signal from the recording medium, and determines the speed of the head every 1/2 track based on the time between the zero-crossing points and the distance of 1/2 track pitch. 2. The digital servo device according to claim 1, wherein the digital servo device calculates . (3) The speed detecting means detects the zero-crossing point and peak point of the servo error signal from the recording medium, and determines the speed of the head from the time between the zero-crossing point and the peak point and the distance of 1/4 pitch of the track. 2. The digital servo device according to claim 1, wherein the digital servo device calculates 1/4 track by 1/4 track.