JPH03257510A - Digital servo device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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 fifth
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. 6 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. 7, 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 multi-bi break 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 multivibrator becomes longer, making it impossible to use it as a substantial speed signal. Therefore, with the speed control method described in FIG. 5, accurate closed-loop control is difficult. Additionally, in the aforementioned 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.

The present invention has been made to solve these problems, and its purpose is to provide a digital servo device that can perform accurate control at high speed and is not affected by friction or external force. It is in.

[Means for Solving the Problem] In order to achieve the above object, a means for calculating a target speed of the head according to a residual distance to a target position of the recording medium, a means for detecting the speed of the head, means for calculating a command value for a head driving actuator so that the head follows the target speed from the detected speed and the target speed at that time; There is provided a digital servo device characterized in that the head is switched to a plurality of positions until the head reaches the target, and the calculation interval of the parentheses is made smaller as the head approaches the target.

[Function] According to the present invention, the head can be controlled accurately at high speed by switching the actuator command value calculation interval to multiple values until the head reaches the target, and decreasing the calculation interval as the head approaches the target. This is how it was done.

[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, l 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 a D/A converter, 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. Also, the deceleration region is deceleration region I
and deceleration range H, each with different speed control accuracy. In this example, the deceleration area work is the same as the acceleration area <1
Speed control is performed for each /21-rack, and speed control is performed for each 1/41-rack in order to perform more precise control in the deceleration region (3). Specifically, in the acceleration region and deceleration region I, the target speed and actuator command value are determined every 1/2 track, and in the deceleration region 2, every 1/4 track, and the speed control is performed.

Further, target speeds for each 172 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 shown in Fig. 3, since tracks 10 to 12 are in deceleration region I, the speed of each 1/2 track is calculated, and the difference from the target speed at that time is added to the reference acceleration to drive the actuator. do. 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 Va is calculated from the time Ta using the following equation.

Va = 1/2λXI/Ta However, E is the track pitch.

The target speed is the V ref value at point A in FIG. 2, and as a result, the actuator control amount act
Calculate.

act = -a+k (Vref -Va) However,
−α is the deceleration reference acceleration, and k is the feedback gain for speed control.

Next, since the tracks 12 to 14 in Fig. 3 are in the deceleration region (2) described 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 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 Tb using the following equation.

Vb = 1/4 circle X l/T b The target speed at this time is V re at point B in Figure 2.
f value, and as a result, the command value act of the actuator is calculated using the following equation.

act = -a+k (Vref -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 V ref.

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

In general, when the residual distance S to the target position is, the target velocity V to make v = 0 after seconds at the acceleration ability α
ref is obtained by solving the following two simultaneous equations.

Vref-t-1/2 at" = S (distance formula) V
ref −at=o (Velocity equation) When t is eliminated from these two simultaneous equations, the following equation, which is the target speed equation, is obtained.

Vref=YTy From this equation, it can be seen that the target speed 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, such a speed detection method not only eliminates the need for a complicated speed detection circuit, but also solves the conventional problem that detection near zero speed is not accurate. I can do it. 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 range and deceleration ranges I and II.

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.
. is detected. Then, the tracking error signal Sl
, are digitally converted by the A/D converter 5 and input to the DSP 8 via the I10 control section 7.

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',1 is determined using the input tracking error signal S7 and the previous tracking error signal Sn-1 stored in the memory 9. This estimated signal is obtained by the following equation.

S', ,=2S,-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 in S3
When a zero crossing point is detected, the process proceeds to 84. In addition, DSP
8 is open until the next sampling except when a zero cross point is detected in S3, so other processing is executed.

S4 is a process for determining the current speed Vt and target speed Vref explained in FIGS. 2 and 3. The current speed Vt is
As explained in FIG. 3, the half-cycle time T of the tracking error signal at that time is calculated, and this time and 1/2 L
It can be obtained by performing the following calculation using .

Vt=1/2mm x l/T Further, the target speed is obtained by the following equation as described above.

, Vref=-rYTy In S5, the DSP 8 calculates the actuator command value act from the obtained current speed and target speed.

Since this command value is currently in the acceleration region, it can be obtained using the following equation.

act = a0k (Vref - 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 87. Therefore, in the acceleration range that is half of the target track, the actuator is driven with the command value obtained every 1/2 track by repeating the operations from Sl 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 SIO calculates the current speed and target speed using the same method as in S4.

Next, in %S12, the DSP 8 determines the actuator command value act using the current speed and target speed. The command value at this time can be obtained from the following equation.

act = -a1k (Vref - Vt) Based on this command value, the actuator is similarly driven. S
12 has reached two spots ahead of the target track.
That is, this is a process for determining whether deceleration region I has ended. In this case, this determination is similarly made using a tracking counter. When it is determined in S12 that deceleration area l has ended, S
The process proceeds to step 13, where control of the deceleration region H is performed. Therefore, deceleration region I
Now, by repeating steps 87 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 II, first, a tracking error signal is input manually in S13, and a zero cross point is detected in S14. S
If it is determined in step 15 that it is a zero cross point, step 18
Find the current speed and target speed in the same way as above. On the other hand, S
If it is not a zero cross point in S15, 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 1/4 track. In addition, in Si8, the current speed Vt is determined by the following formula.

Vt = 1/41xl/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.

act = -a+k (Vref -Vt) S20 is for determining 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 ■, by repeating steps 313 to S20,
A command value for the actuator is determined every 1/4 track, and the actuator is driven using 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 ΔS0 between the input tracking error signal S4 and the tracking error signal SI+-1 at the previous sampling time is calculated using the following equation.

Δ5n=S, -S,.

Next, the similar difference value △S 11 before that l sampling
'-1 and ΔS, , are multiplied. Note that Δ511-1 is calculated using the following formula during the previous sampling and is stored in the memory.

△S n-+ = S n-I S n-a this △
When the multiplication result of Sn and △S n −+ is negative,
It is determined that this is the peak point of the tracking error signal.

As described above, in this embodiment, the command value of the actuator is first calculated every 1/2 track in the deceleration region, and then the control is switched to every 1/4 track two tracks before the target track. Thereby, the closer the head is to the target track, the more accurate the control is, and the position of the head relative to the target track can be controlled even more accurately. Generally, when the head approaches the target track, its speed gradually approaches zero, and the time between zero-crossing points of the tracking error signal also becomes longer. Therefore, since the current speed mentioned above is the average time between zero crossing points, the error becomes larger as the speed approaches the target track. In this case, as described above, since control is switched to every 174 tracks before the target track, errors can be reduced and accurate control can be performed.

In addition, since 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, there is no waste in the head before the head reaches the target track. It does not move and can ideally be moved to the target track. Therefore, accurate yet high-speed seek can be achieved. Furthermore,
D
It is also possible to reduce the burden on SP8.

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 actuator command value calculation interval is switched to multiple values until the head reaches the target, and the calculation interval is made smaller as the head approaches the target, so that the head seek operation can be performed at high speed. It has the effect of being able to control accurately at high speed. Therefore, it is possible to provide a digital servo device that effectively combines high-speed seeking and accuracy. Furthermore, since it is a closed loop control, it has the advantage of not being affected by friction or external force.

[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. A time chart showing the relationship between signals, actuator command values, and speeds. Figure 4 is a flowchart showing the processing flow during multi-jump. Figure 5 is a reference speed and actuator current in a conventional optical head speed control system. An explanatory diagram showing the relationship between
A block diagram showing a speed detection circuit used in the control system shown in the figure, FIG. 7 is a time chart showing the operation of the speed detection circuit, and FIG. 8 is a block diagram showing the operation of the speed detection circuit, and FIG.
FIG. 3 is an explanatory diagram showing the relationship between speed and current in the g control method. 1: Optical disk, 2: Optical system, 3: Tracking error detector, 9: Digital signal processing section, 8: DSP, 12: Tracking actuator.

Claims (1)

[Claims] means for calculating a target speed of the head according to the residual distance to the target position of the recording medium; means for detecting the speed of the head; and the head follows the target speed based on the detected speed and the target speed at that time. means for calculating a command value of the actuator for driving the head so as to change the command value calculation interval of the actuator for each predetermined movement distance of the head relative to the medium to a plurality of intervals until the head reaches the target; A digital servo device characterized by decreasing a calculation interval as it approaches a target.