JPH0782717B2 - Head drive controller for recording / reproducing apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to a head drive control device such as a magnetic disk device, and is particularly applied to a speed detector for detecting the moving speed of a head. The present invention relates to a head drive controller for a recording / reproducing apparatus.

(Prior Art) Conventionally, in a magnetic disk device, drive control of a magnetic head is shown in FIG. 3 when expressed in a simplified block diagram. That is, the detected speed (actual speed) signal V is subtracted from the target speed signal R of the magnetic head to generate an error signal E, and the VCM (voice coil motor) driver 11 is driven based on this error signal E. . VCM driver 11
Drives the actuator 12 by supplying a drive current I based on the error signal E to the voice coil motor. As a result, the magnetic head moves to the target track while approaching the target speed. Speed detector 13
Detects the speed of the magnetic head at this time and outputs the detected speed signal V.

By the way, the purpose of such speed control is to make the speed of the magnetic head follow the target speed faithfully, and at that time, it is important to control quickly and stably. As is well known, there is a tracking error as one index for evaluating the goodness of a speed control system. In the case of FIG. 3, it can be expressed as the following equation.

E = R / (1 + K ^A / K _M / _S / K _V ) ... R: Target speed K _A : VCM driver 11 gain K _M / _S : Actuator 12 transfer function K _V : Speed detector 13 gain Then, the speed control works during deceleration as shown in FIG. Therefore, R can be approximated by a ramp input. Therefore, when R = r ₀ / S ² is substituted into the equation and the steady-state error of E is obtained, Becomes From this equation, the steady-state error is the loop gain K _A
It can be seen that the larger K _M · K _V is, the more reduction is possible. The detected speed V in FIG. 4 is obtained by obtaining the time response with the target speed R as a ramp input. Obviously, the steady-state error r ₀ /
(K _A · K _M · K _V ) has occurred.

(Problems to be Solved by the Invention) As described above, if the loop gain K _A · K _M · K _V is increased, the steady-state error r ₀ / (K _A · K _M · K _V ) can be reduced. However, this is limited to the case where each element of the speed control system is operating ideally. Actually, in the speed detector 13,
Since it is difficult to secure a sufficient frequency band, as shown in FIG. 5, the ideal characteristic deviates particularly at high speed.
That is, the speed detection gain K _V decreases at high speed. When the speed detection gain K _V decreases, the steady-state error r ₀ / (K _A・ K _M・
K _V ) becomes large.

As shown in FIG. 4, since the moving speed of the magnetic head becomes maximum at the start of deceleration, the loop gain here is the fourth.
As indicated by the "Lower gain" in the figure, it causes a larger tracking error and adversely affects the control. Specifically, the moving speed at the end of speed control, that is, at the time of rush at the time of track following increases, which causes, for example, overshoot and increase in settling time.

The present invention has been made in view of the above points, and provides a head drive control device for a recording / reproducing device that can realize stable speed control by keeping the gain of a speed detector that detects the moving speed of the head constant. With the goal.

[Configuration of the Invention] (Means and Actions for Solving the Problems) That is, the present invention detects the moving speed of the head, and based on an error signal between the detected speed signal and a preset target speed signal, In a head drive control device of a recording / reproducing device that drives a head, a speed signal of the head is generated by differentiating a position signal indicating the current position of the head, and the speed signal is obtained with a gain according to the level of the speed signal. The speed signal is amplified and the amplified speed signal is output as the detected speed signal.

According to such a configuration, even if the moving speed of the head changes, the detected speed characteristic (gain) can be made constant and stable speed control can be realized.

(Embodiment) Hereinafter, a head drive control device of a recording / reproducing apparatus according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a speed detector used in a head drive control device of a magnetic disk device, for example. The differentiating circuit 21 receives a position signal S1 indicating the current position of the magnetic head, differentiates the position signal S1 and outputs a speed signal S2. GCA (Gain Contorollable Amplifier) 22
Is a variable gain amplifier and the signal from the filter 24
The speed signal S2 is amplified with a gain according to S5. Absolute value circuit
23 generates a signal S4 having a waveform in which the polarity of the speed signal S2 is canceled. The filter 24 is a reduction pass filter, and has a transfer gain setting function here.

Next, the operation of the speed detector in the embodiment will be described with reference to the timing chart shown in FIG.

The position signal S1 indicating the current position of the magnetic head is generated by a position signal generation circuit (not shown). The differentiating circuit 21 generates a speed signal S2 indicating the moving speed of the magnetic head by differentiating the position signal S1. The speed signal S2 thus generated is output to the GCA 22 and the absolute value circuit 23. Here, for example, if there is no loop through the GCA22 and the filter 24 and the gain of the GCA22 is fixed, the GCA22
As shown by the dotted line in FIG. 2, the output signal S3 of FIG. 2 reaches a peak at higher speeds and deviates from the ideal characteristics.

In this embodiment, the gain of the GCA 22 is controlled according to the level of the speed signal S2. In this case, since the speed signal S2 has polarity, the signal passed through the absolute value circuit 23 and the filter 24 is used as the gain control signal input to the gain control terminal of the GCA 22. That is, the absolute value circuit 23 takes the absolute value of the speed signal S2 having a polarity as shown in FIG. 2 and outputs the signal S4 to the filter 24. The filter 24 uses the signal S5 that cuts off the high frequency components of this signal S4.
Is generated and is output to the gain control terminal of GCA22. The GCA 22 amplifies the speed signal S2 from the differentiating circuit 21 with the gain set by the signal S5. As a result, the GCA 22 outputs a signal S3 that does not decrease as indicated by the dotted line even at high speed as the final detected speed signal, as shown in FIG.

Thus, by using the speed detector of the present invention, stable speed control can be realized by keeping the detected speed characteristic (gain) constant even if the moving speed of the magnetic head changes. Therefore, the rush speed when switching from the speed control to the track follow-up control can be accurately controlled, and for example, overshoot and settling time can be shortened.

As described above, according to the present invention, the gain of the speed detector can be controlled according to the level of the speed signal. Therefore, even if the moving speed of the head changes, the detected speed characteristic (gain) can always be kept constant and stable speed control can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram showing the structure of a speed detector according to an embodiment of the present invention, FIG. 2 is a timing chart for explaining the operation of the same embodiment, and FIG. 3 is a conventional head drive controller. FIG. 4 is a block diagram showing the configuration, FIG. 4 is a diagram for explaining conventional speed control, and FIG. 5 is a diagram showing conventional speed detection characteristics. 21 …… differential circuit, 22 …… GCA, 23 …… absolute value circuit, 24…
…filter.

Claims (1)

[Claims] 1. A head drive controller for a recording / reproducing apparatus, which detects the moving speed of a head and drives the head based on an error signal between the detected speed signal and a preset target speed signal. Differentiating means for differentiating the position signal indicating the current position to generate the speed signal of the head, gain setting means for setting a gain according to the level of the speed signal generated by the differentiating means, and this gain setting means A head drive controller for a recording / reproducing apparatus, comprising: a variable gain amplifying means for amplifying the speed signal with a set gain and outputting the amplified speed signal as the detected speed signal.