JPS644270B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to position control of recording and reproducing heads of disk devices, particularly magnetic disk devices, and relates to improvements in electronic control circuits for controlling track access.

Conventionally, the actuator as a head positioner is controlled by a closed-loop servo method to position a group of heads on a track. One side of the disk is provided with a magnetic disk on which a unique magnetic pattern (hereinafter referred to as a servo pattern) is permanently recorded, so that the head position can be recognized at all times. A closed loop servo system for positioning is constructed based on this recognition.

As this known system, there is one as shown in the block diagram of FIG. In FIG. 1, 1 is a servo head, and 2 is a position signal demodulation circuit that demodulates the aforementioned unique servo pattern signal read out by the servo head 1 to generate a voltage signal related to position (hereinafter referred to as a position signal). Reference numeral 3 denotes a track following control circuit for following the track according to the position signal to prevent off-tracking, and this usually includes a lead-lag filter for adding damping, an error amplification circuit, etc. Reference numeral 4 denotes a speed signal demodulation circuit for speed control during track access, which normally differentiates the position signal to obtain the voltage of the speed signal. 5 is a truck counter. Reference numeral 6 denotes a speed reference generation circuit which provides a desired speed every moment according to the contents of the track counter 5. A speed error amplification circuit 7 compares the speed signal with a speed reference and amplifies it appropriately. Reference numeral 8 denotes a switch device for switching between speed control during track access and positioning control during tracking control on the track. 9 is a drive circuit that drives an actuator as a head positioner. 10 is the actuator mentioned above.

FIG. 2 shows an example of voltage waveforms at various parts when accessing from one track to another in the known method, and _FIG . Figure 2 b shows the velocity E _v
(output of speed signal demodulation circuit 4). position signal
E _p is a two-track, one-week pseudo-triangular wave,
The point where it crosses zero potential corresponds to the center of each track. The speed signal E _v is obtained by differentiating the linear part of the position signal E _p and converting it into an absolute value ratio (non-polarized).
This is what I did. It is assumed that the curved portion does not capture the potential and holds the previous potential.

FIG. 2 shows typical position and velocity signals when a head accesses from one track to another track N tracks away. First, there is an acceleration section, then a maximum speed section, and finally a deceleration section, where the vehicle is sufficiently decelerated, and is slightly before the target track center (point P in Figure 2).
The figure shows how the vehicle enters track following control from time t=t _p ) and on-tracks to maintain its position. The period from the acceleration section to the deceleration section (from time t = 0 to t = _tp ) is called the access speed control section,
The period from there onwards is called the track following control section. This control is performed by the changeover switch device 8.

Now, in the series of controls described above, the point P at which access speed control switches to track following control is slightly before the center of the target track (usually about one-fifth to one-third of the track pitch). The speed of the head at this time (hereinafter referred to as the final speed) needs to be adequately controlled. From the standpoint of track following control, position control starts from time t=t _p , and the initial conditions at that time are the amount of displacement from the target track center at t=t _p and the final velocity. The track following control loop is usually designed to have a state close to critical braking by adding appropriate damping, but if the initial conditions are significantly different, it is difficult to expect a satisfactory on-track. For example, if the final speed is too high, the vehicle will pass through the center of the track and overshoot significantly, and in the worst case, the vehicle will fail to pull in the track. In this sense, it is important to manage the final speed when moving to track following control, and for this purpose, as shown in Figure 2b, there is a low constant speed section (hereinafter referred to as pedestal) 1 to 2 tracks before the target track. is provided so that the speed of the final part of speed control (final speed) is completely converged to the set target value.

Considering only that the track center can be stabilized reliably without overshooting, it is better to make the final speed as slow as possible and move the position (point P) at which the follow-up control is started closer to the center of the target track. However, if the final speed is slow, it will take longer to travel the pedestal section and the track access time will be longer, which is disadvantageous. Furthermore, if the final speed is low, there is a high risk of stalling (zero speed) when approaching the pedestal, which is inconvenient. Once the speed reaches zero, it is often difficult to recognize the direction after that, and seek errors are likely to occur. Therefore, a better method would be to move the position (point P) at which the follow-up control starts as far as possible from the center of the target track, approach the track at a relatively high speed, and instead suppress variations in the final speed as much as possible. However, since the position of point P is read from the voltage waveform of the position signal shown in FIG. 2a, there is a certain limit to the distance to the target track center, and the maximum distance is about one-third of the track pitch. Therefore, it is actually not possible to increase the final speed too much. FIG. 3 shows the vicinity of the target track, with distance plotted on the horizontal axis and position signal E _p plotted on the vertical axis. As mentioned above, point P is
At a position slightly in front of the target track center (maximum limit is about 1/3 of the track pitch),
It shows the position at which access speed control is switched to track following control.

FIG. 4 shows an example in which the state of the position signal from the pedestal section until the head settles at the center of the target track was actually measured using the final speed as a parameter in the above-mentioned known prior art. In this example, the position of point P is set approximately one-third of the track pitch before the center of the target track (set by the track following control switching voltage). Final speed 3cm/sec, 2.5cm/
sec, 2cm/sec, in this example 2.5
cm/sec has the best stability. Furthermore, in the example shown in FIG. 4, if the final speed is 2.5 cm/sec or more, overshoot will occur and a longer settling time will be required. If the overshoot becomes excessive, the probability of jumping out of the target track, failing to on-track, and causing a seek error increases rapidly.

The present invention proposes a system for eliminating such drawbacks, and the main feature of the present invention is to improve the above-mentioned track following control circuit 3. This is because the problem of settling to the track center becomes a problem after the speed control during track access ends and the switch is made to track following control.

The conventional track following control circuit 3 is basically a position control circuit for preventing off-track from the track center according to a position signal, and therefore includes an error amplification circuit for extracting position deviation and a damping circuit. and a lead-lag filter to increase the stability of the system (satisfying the so-called Nyquist condition).

FIG. 4 shows the most basic circuit for realizing such a conventional track following control circuit 3, in which an operational amplifier 11, a resistor, and a capacitor are used to form a lead-lag filter and an error amplification circuit.

FIG. 6a shows the frequency characteristics of the circuit of FIG.
This frequency characteristic represents so-called phase lead compensation in position control, and the transfer function is expressed as follows.

A/α・(αT)S+1/(T/a)S+
1 Here, α is taken to be around √10 to √20.

Figures 6b and 6c show the decomposition of the frequency characteristics in Figure 6a, where Figure 6b concerns only the feedback gain A/α with respect to position, and Figure 6c relates to the differential of position (velocity or damping). It shows the feedback gain. If you combine these Figure 6 b and c, you will get Figure 6 a
(has lead-lag filter characteristics). The reason why the high frequency region in FIG. 6c is made flat is that components in this region often become unnecessary and harmful to control.

In this way, conventional track following control circuits can be thought of as basically consisting of a feedback component related to position and a feedback component related to the differential (velocity) of the position, which are added together and the result is error amplified. You can also do it.

By adding nonlinearity to the feedback component, the present invention satisfies the Nyquist condition when the head is near the center of the track, and controls the vehicle in a state close to critical damping. When the head approaches from outside the track, a large braking force is suddenly generated to prevent overshoot and to settle the head towards the center of the track in a short period of time. By doing this, even if the head enters the target track at a final speed considerably higher than conventionally, it can be stabilized extremely stably and in a short time. Furthermore, even if the final speed varies, it can be stably settled without overshooting, although the settling time may be longer or shorter.

That is, the present invention is a control device for a disk device that positions a head on a recording or reproducing track using a closed-loop servo system, which includes a head that recognizes the position, and a position signal obtained by demodulating the position information obtained from the head. a position signal demodulation circuit that obtains the
The track following control circuit is provided with a track following control circuit for performing position control during track following based on this position signal, and this track following control circuit extracts a following position deviation based on the position signal and amplifies it. a circuit for obtaining feedback voltage related to position; a nonlinear circuit providing nonlinearity to the voltage of the position signal; a circuit for differentiating the position signal given this nonlinearity to obtain a speed damping voltage; and a feedback voltage related to the position. This configuration includes a circuit that adds a speed damping voltage given nonlinearity, and this allows stable settling even if the final speed is set to a fairly large value, resulting in a shortened access time. Furthermore, even with respect to variations in the final speed, it is possible to expect more stable settling than in the past.

An embodiment of the present invention will be described below based on the drawings. FIG. 7 is a block diagram showing the basic structure of the present invention (in particular, a block diagram of the improved track following control circuit portion which is the main part of the present invention). 7th
In the figure, numeral 21 is a circuit that provides feedback voltage regarding position, and provides the same characteristics as in FIG. 6b. 22 is a nonlinear circuit that gives nonlinearity to the position voltage, and 23 is a circuit that obtains a nonlinear speed damping voltage by differentiating the position voltage that has been given nonlinearity by 22, and gives the same characteristics as Fig. 6c. It is something. 24 is an adder circuit.

The nonlinear circuit 22 providing nonlinearity has a gain of 1 in the region where the position voltage is small, but the gain becomes 1 or more when a certain voltage (a certain distance from the track center) is exceeded. Therefore, when the head is in tracking control near the track center, the position error and speed are quite small, so there is no effect of the nonlinearity mentioned above, and critical damping is performed as in the conventional track tracking control circuit. controlled in a state close to . However, when the head is accessed toward a certain target track and enters the target track, the point at which access speed control is switched to track following control (time t=t _p in FIG. 2) Since the position voltage at point P is large, an even larger position voltage is obtained by the nonlinear circuit 22 that provides nonlinearity, and the speed damping obtained by the circuit 23 that differentiates this. The gain and amount of voltage increases even further. That is, when the vehicle approaches the target track at a high final speed, it is possible to generate a very large braking force. Therefore, the head positioner approaches the center of the track while rapidly decreasing its speed. When the vehicle approaches the center of the track, the position voltage has a sufficiently small value, so it is controlled in a state close to critical braking, and the vehicle stably on-tracks without overshooting. This means that even if the final speed varies from the set value, the settling is always stable. That is, the higher the final speed, the greater the braking force will be.

Further, in the circuit for producing speed damping (22 and 23 in FIG. 7) in the present invention, the nonlinear circuit 22 providing nonlinearity is provided before the circuit 23 for obtaining the speed damping voltage. Therefore, for example, compared with the configuration opposite to the configuration of the present invention (a configuration in which a circuit is first provided to obtain a speed damping voltage by differentiating the position voltage, and then a nonlinear circuit is provided to provide nonlinearity to this speed damping voltage). This circuit configuration, which is the opposite of the present invention, also imparts nonlinearity to the noise that is amplified and generated along with the differential function, which increases the gain of the noise and extremely deteriorates the S/N ratio. As a result, when the head approaches the target track, it tends to enter the target track in an oscillatory and unstable manner, and even when performing follow-up control, the differentiated noise may extend into the nonlinear region, so the nonlinear circuit As a result, this noise is further amplified, and as a result, the head tends to vibrate and become unstable. On this point, in the configuration of the present invention, since nonlinearity is first given to the position signal and then differentiated, there is no function that increases noise, and a simple low-pass function for noise removal and mechanical resonance prevention, which is normally thought of, is not present. By simply installing a filter at the rear of the track following control circuit, it is possible to cause the head to approach the target track and perform follow-up control in a state close to critical braking without causing the head to vibrate or become unstable. This is the result.

In addition, the configuration of the present invention does not have the above-mentioned noise increasing effect, so it is possible to make the gain in the nonlinear region of the nonlinear circuit that provides nonlinearity sufficiently large, and it is possible to cope with a considerably high final speed. It is what it is.

FIG. 8 is an actual measurement diagram of the head setting when the present invention is applied, and should be compared with the conventional example shown in FIG. In this example, the position voltage is
A nonlinear circuit is used in which the gain exceeds 1 and increases several times when the voltage exceeds 0.3 Volt (3.75 μm from the track center). As is clear from this example, a significant improvement can be seen.

FIG. 9 shows a specific embodiment of the basic configuration of the present invention shown in FIG. In FIG. 9, 31 is a circuit for obtaining a feedback voltage related to the position, and 21 in FIG.
This is a known non-inverting amplifier consisting of an operational amplifier 35 and a resistor. 32 is a nonlinear circuit that gives nonlinearity to the voltage of the position signal, and 22 in FIG.
This is a known nonlinear amplifier that corresponds to the above and is composed of an operational amplifier 36, a resistor, and diodes 37 and 38 as nonlinear elements. 33 is a nonlinear circuit 32
This circuit obtains the speed damping voltage by differentiating the position voltage given nonlinearity by 23 in Figure 7.
This is a well-known differentiating circuit that corresponds to the above and is composed of an operational amplifier 39, a resistor, and a differentiating capacitor. 3
4 is a circuit 3 that provides a feedback voltage regarding the position.
1 and the output of the circuit 33 for obtaining a speed damping voltage given non-linearity, this circuit corresponds to 24 in FIG.
This is a well-known summing amplifier consisting of a resistor and a resistor.

As described in detail above, according to the present invention, (1) track access time can be shortened by increasing the final speed when switching from track access speed control to track following control;

(2) By increasing the final speed, accidents due to stalling in the pedestal section are less likely to occur,
Seek error rate can be reduced and reliability can be increased.

(3) Velocity management becomes easier because variations in final velocity are allowed to some extent.

(4) When settling at the center of the target track, it is possible to prevent the overshoot phenomenon and shorten the settling time, and at the same time enable stable settling and prevent accidents such as on-track failure and seek error.

(5) When follow-up control is performed near the track center, optimal position control close to critical damping can be achieved, and in particular by applying the present invention, it is possible to eliminate negative effects on this position control. It will not affect you.

(6) Since the gain in the nonlinear region of the nonlinear circuit that provides nonlinearity can be made sufficiently large, it is possible to support a considerably high final speed.

(7) Since it can be realized with a relatively simple circuit, there is no disadvantage in terms of cost.

This makes it possible to realize a magnetic disk device with many excellent features such as.

Note that the present invention is not necessarily limited to those using magnetic disks, but generally has a recording track, and performs random access of the head using speed control, and then performs follow-up control on the target track. Needless to say, the present invention can be applied to all disk devices using the closed-loop servo system.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a closed-loop servo system for positioning the head of a conventional disk device.
The figures show the voltage waveforms of various parts during track access in the case of Fig. 1, Fig. 2 a is a waveform diagram of the position signal E _p , Fig. 2 b is a waveform diagram of the speed signal E _v , and Fig. 3 is a waveform diagram of the position signal E _p
The fourth figure is an enlarged diagram centered on the Nth track.
The figure is a waveform diagram showing an actual measurement example of the state of the position signal until the head settles at the center of the target track in relation to Figures 1 and 2. Figure 5 is the basics for realizing a conventional track following control circuit. Example circuit diagram, Figure 6a
are the frequency characteristics diagram of the circuit in Fig. 5, and Fig. 6 b and c.
7 is a block diagram showing an example of the basic configuration of the present invention, and FIG. 8 is a waveform showing an actual measurement diagram of the head setting when the present invention shown in FIG. 7 is applied. 9 are circuit diagrams showing a specific embodiment of the basic configuration of the present invention shown in FIG. 7. 1... Servo head, 2... Position signal demodulation circuit, 3... Track following control circuit, 4... Speed signal demodulation circuit, 5... Track counter, 6... Speed reference generation circuit, 8... Access speed control section and a track following control section changeover switch, 21,
31...Circuit for obtaining feedback voltage related to position, 2
2, 32...Nonlinear circuit providing nonlinearity, 2
3, 33...A circuit that differentiates the position to obtain a speed damping voltage, 24, 34...Synthesizes the output of a circuit that obtains a position-related feedback voltage and the output of a circuit that obtains a speed damping voltage given nonlinearity. A circuit that adds.

Claims (1)

[Claims] 1 configured to position the head on a recording or playback track using a closed-loop servo method;
and a position recognition head, a position signal demodulation circuit for demodulating position information obtained from this head to obtain a position signal, and a track following control circuit for performing position control during track following based on this position signal. The track following control circuit includes a circuit that extracts a tracking position deviation based on the position signal and amplifies it to obtain a position-related feedback voltage, and a non-linear circuit that provides non-linearity to the voltage of the position signal. a circuit that obtains a speed damping voltage by differentiating the position signal given the nonlinearity, and a circuit that adds the feedback voltage related to the position and the speed damping voltage given the nonlinearity. Control device for disk devices.