JP2743882B2 - Integral type feedforward compensation method for positioning servo mechanism and magnetic head positioning control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a head speed control method and a head positioning apparatus suitable for a magnetic disk drive, in which overshoot and undershoot of a head are reduced and a head is positioned at a target track at high speed. About.

[0002]

2. Description of the Related Art In a head speed control device of a magnetic disk drive, accurate speed control can be realized by widening a control band. That is, at the switching point where the speed control is switched from the speed control to the position control in the vicinity of the target track, the loop gain can be sufficiently increased, so that the residual speed of the magnetic head can be suppressed low, and the magnetic head moves beyond the target position. Can be prevented. As a result, the seek time can be reduced.

In recent years, digitization of a positioning control device has been advanced. However, in such a digitized control device, particularly in a system having a long sampling time, if the control band is widened, the stability of the control system is deteriorated.

[0004] For this reason, it has become difficult to widen the control band with a digitized control device.

Conventionally, several methods have been known to solve such a problem. For example, Japanese Patent Application Laid-Open
182169, JP-A-59-117760 and JP-A-61-39985 disclose a method in which a target speed trajectory is differentiated or differentiated in a speed control deceleration process.
It discloses that this is input to a control target as an acceleration feed forward so that the target speed trajectory can be accurately followed without widening the band.

[0006] Also, Japanese Patent Application Laid-Open No. 58-21366,
JP-A-59-198572, JP-A-60-168
Japanese Patent Laid-Open Publication No. 2000-209,1992 discloses that speed control is performed smoothly in the vicinity of a target track by using an acceleration feedforward amount that is sequentially reduced according to the number of moving tracks and a deviation between the target track and the current track to be controlled. Has been disclosed.

Further, Japanese Patent Application Laid-Open No. 3-58357 discloses that
A constant value is multiplied by a correction gain according to the speed deviation between the target speed and the speed of the controlled object, and the resulting value is used as an acceleration feedforward amount for a time corresponding to the positional deviation between the target position and the position of the controlled object. It discloses inputting and preventing overshoot and undershoot.

[0008]

In the above prior art,
If the target velocity trajectory is made steeper, it will not accurately follow the target velocity trajectory, and the overshoot increases due to an increase in the residual velocity of the head at a switching point near the target position where the control switches from speed control to position control. . As a result, there is a problem that the seek time cannot be reduced.

[0009]

According to the present invention, the control target is two or more.
The present invention is directed to a positioning servo mechanism capable of observing the next state (for example, the position and speed of a head in a head positioning device) and the state quantity thereof. In such a servo mechanism, the difference between the speed of the control target and the target speed is integrated from the deceleration start point, an appropriate gain is multiplied, and the result is input to the control target as a feedforward compensation amount. Also, when approaching the vicinity of the target position so that the feedforward compensation amount does not suddenly become zero, the feedforward compensation amount proportional to the speed of the control target is input to the control target.

For example, in Japanese Patent Application Laid-Open No. 59-198572, a feedforward compensation amount corresponding to a speed profile is input irrespective of a difference between a speed of a controlled object and a target speed (hereinafter referred to as a speed deviation). In the above solution, the feedforward is created by using the integral value of the speed deviation of the control target (accumulation of the past speed deviation) generated with respect to the target speed trajectory, so that the speed deviation can be made extremely small. In the method of inputting the feedforward compensation amount for a fixed time according to the position deviation as in Japanese Patent Application Laid-Open No. 3-58357, a transient response occurs when the feedforward compensation amount is cut off. 0 smoothly near the target position
Therefore, it is possible to prevent a transient response when the feedforward compensation amount runs out, and to cause the control target to follow the target trajectory with high accuracy. Further, in the present invention, since the speed deviation is always kept small only by looking at the accumulation of the speed deviation, it is possible to prevent the correction of the control object in the reverse direction when the speed crosses the target speed trajectory, thereby preventing the controlled object from making an oscillating movement. By these,
The control target can be rapidly decelerated, and the seek time of the positioning servomechanism system can be reduced.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS.
An embodiment of the present invention will be described.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. The signal recorded on the data surface 103 of the thin-film magnetic disk 102 fixed to the rotating spindle 101 is read by the composite head 106, and the data head position deviation signal 109 is reproduced. Composite head 10
Reference numeral 6 denotes a thin-film inductive head for reading / writing data from / on the data surface on the thin-film magnetic disk 102 and an MR head.
(Magnetoresistance effect) The head is integrated.

The servo surface 104 of the thin-film magnetic disk 102
Is read by the servo head 105, and the servo head position deviation signal 110 is reproduced. The head position detecting means 111 uses the data head position deviation signal 109 and the servo head position deviation signal 110 to count the number of times the servo head 105 has traversed the track including its direction. The position is continuously detected from the innermost circumference to the outermost circumference of the thin-film magnetic disk 102 regardless of the traveling direction of the composite head 106, and a head position signal 112 is generated.

The mechanical resonance removing means 113 uses the head position signal 112 to generate a head position signal 114 from which a mechanical resonance component has been removed from the head position detection 112.

The head speed detecting means 115 includes a head position signal 114 from which a mechanical vibration component has been removed and a driving amplifier 108.
, The speed of the composite head 106 with respect to the data surface 103 is detected, and a head speed signal 116 is generated.

The target speed generating means 117 comprises a mathematical approximation model of the VCM actuator 107.

An algorithm for generating the target speed signal 118 generated by the target speed generating means 117 will be described below.
As an example, a mathematical approximation model of the VCM actuator 107 is 1 / s ² . In order to move the VCM actuator 107 at high speed, it is necessary to reach the maximum speed as quickly as possible in the acceleration section, and to decelerate at the maximum deceleration within the range of the capability of the VCM actuator 107 in the deceleration section. Therefore, the target speed signal 11
8 is as follows.

[0018]

(Equation 1) Here, v _max is the maximum speed, α is the deceleration, x is the current position, x _t is the target position, and x _ch1 and x _ch2 are the switching points of the speed trajectory. However, in this state, the speed largely changes in the vicinity of the target position, so that overshoot is likely to occur. Therefore, when x = x _ch2 before the target position, the deceleration is smoothly shifted to a speed trajectory less than or equal to the speed.

V = β (x _t −x) (x _ch2 < x < x _t ) (3) At this time, β is a constant determined by the switching point x = x _ch2 and the speed v = v _{ch2 at} that time.

The target speed generating means 117 may store the speed for each position in a table in a memory so as to satisfy the above equation.

The servo compensating means 121 is of a velocity trajectory following type within a predetermined range, for example, up to 0.5 track before the target track.
6 is an input 12 for following the target speed signal 118.
2 is generated and output to the drive amplifier 108. The position control mode is set within 0.5 track of the target track, and the head position signal 114 from which the mechanical vibration component has been removed is made to follow the target track to position the composite head 106. Further, the servo compensating means 121 has means for estimating the loop gain of the actuator 107, and adjusts the internal gain according to the individual difference of the disk device.

The feedforward compensator 119 generates a signal input to the drive amplifier, that is, a feedforward input value 120, in order to improve the followability of the head speed signal to the target speed signal. Next, the feedforward compensator 119 will be described.

The feedforward input value 120 improves the followability of the head speed signal to the target speed signal. At the time of acceleration, the target speed signal 118 is fixed at the maximum speed v = _vmax.
Accelerate using the maximum capacity of the drive amplifier 108 until 16 reaches v = _vmax . Therefore, the feedforward input value 120 has no meaning even if present. Also,
Feed forward input value 120 is set to 0 even in constant speed section
And feed forward input value 120 only in the deceleration section
Set. In the first half of deceleration, the difference between the target speed signal 118 and the head speed signal 116 is integrated, an appropriate gain is applied, and the result is used as the feedforward input value 120.

Ff = (v−v _ref ) + ff ′ (4) FF = Ki * ff (5) At this time, Ki is an appropriate gain, v _ref is a target speed signal 118, FF is a feedforward input value, and ff is The feedforward integral value, ff ', indicates the feedforward integral value of the previous sample.

If the feedforward input value is suddenly cut off near the target position, the response of the head position signal 112 is disturbed in a step response. Therefore, after the switching point x = x _ch2 at which the target speed becomes gentle, a value proportional to the head speed signal is set as the feedforward input value 120, and smoothly becomes 0 near the target position.

FF = Kc * v (6) At this time, Kc is a constant determined so that the feedforward input value does not become discontinuous at the switching point x = x _ch2 .

Next, the feedforward compensation operation will be described with reference to the flowchart of FIG. During the head positioning operation, the feedforward compensator 119 first takes in the head position signal 114, the head speed signal 116, and the target speed signal 117 after removing the mechanical vibration (step 2).
01). Next, the head position signal 11 after removing the mechanical vibration
It is calculated whether or not 4 has become larger than the deceleration start point x = x _ch1 (202). If the condition of step 202 is satisfied, the feedforward input value 120 is calculated according to equations (4) and (5).
Calculation is performed according to (203). Next, it is calculated whether or not the point x at which the deceleration is relaxed becomes larger than x = x _ch2 (20
4). When the condition of step 204 is satisfied, the feedforward input value 120 is calculated according to equation (6) (205). When the condition of step 204 is not satisfied, the feedforward input value 120 is set to 0.
(206). Further, the obtained feedforward input value is output to the drive amplifier 106 (207).

By performing the feedforward compensation, the subsequent head speed signal can follow an arbitrary target speed signal. As a result, high-speed head positioning without overshoot or undershoot can be realized.

FIG. 3 shows the transient response of the speed signal at the time of head positioning when the feedforward compensation according to the present invention is not performed (FIG. 3A) and when the feedforward compensation is performed (FIG. 3B). Are compared. The solid line in the figure indicates the head speed signal, and the dotted line indicates the target speed signal. If feedforward compensation was not performed, a steady-state error remains between the head speed signal and the target speed signal.By performing the proposed feedforward compensation, the steady-state error between the head speed signal and the target speed signal, It is considered that the vibration is reduced, and as a result, the head can be positioned at a target position at high speed and with high accuracy without causing overshoot. FIG. 3C shows the feedforward input value at this time.

[0030]

As described above, according to the present invention, the steady-state deviation and vibration of the head speed signal, which have conventionally occurred with respect to the target speed signal, can be made extremely small. Overshoot caused by the steady-state deviation and vibration remaining near the position can be reduced, and the head can be positioned at the target position with higher accuracy and higher speed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a flowchart illustrating a process of a feedforward compensator in FIG. 1;

FIG. 3 shows a head speed transient response and a feedforward input value showing the effect of the present invention.

[Explanation of symbols]

 Reference Signs List 101 rotating spindle 102 thin film magnetic disk 103 data surface 104 servo surface 105 servo head 106 composite head 107 VCM actuator 108 drive amplifier 109 data head position deviation signal 110 servo head position deviation signal 111 head position detection means 112 head position signal 113 mechanical resonance Removal unit 114 Head position signal after mechanical vibration removal 115 Head speed detection unit 116 Head speed signal 117 Target speed generation unit 118 Target speed signal 119 Feedforward compensation unit 120 Feedforward input value 121 Servo compensation unit 122 Input to drive amplifier

Claims (3)

(57) [Claims] 1. A speed control method for a magnetic head positioning servo mechanism for performing speed control and position control on a magnetic head via an actuator to position the magnetic head on a magnetic disk, wherein data read by the magnetic head is provided. A head position signal indicating the position of the magnetic head is obtained from a head position deviation signal and a servo head position deviation signal generated based on the signal and the servo signal, and a target speed signal is generated based on the head position signal and a target position. A head speed signal is generated based on the head position signal and a signal supplied to a drive amplifier that drives the actuator; and the head speed signal and the target speed are used to bring the head speed signal closer to the target speed signal. A drive amplifier that drives the actuator using a signal corresponding to the signal difference as a drive signal. The speed control method of the magnetic head positioning servo mechanism to be supplied to the head speed signal, wherein the head speed signal is decreasing and the difference between the head position and the target position is greater than or equal to a predetermined value, the head speed signal and the target speed signal A feedforward compensation amount proportional to a value obtained by integrating the difference is added to the drive signal. When the head speed signal is decreasing and the difference between the head position and the target position is less than the predetermined value, the head speed signal is reduced. A control method for a magnetic head positioning servo mechanism, characterized in that a feedforward compensation amount proportional to the above is added to the drive signal and supplied to a drive amplifier that drives the actuator. 2. A magnetic head positioning control device for performing speed control and position control on a magnetic head via an actuator means to position the magnetic head on a magnetic disk, wherein a data signal and a servo read by the magnetic head are provided. A head position detecting means for outputting a head position signal indicating the position of the magnetic head from a head position deviation signal and a servo head position deviation signal generated based on the signals; and a target speed based on the head position signal and the target position. Target speed generating means for generating a signal, head speed detecting means for generating a head speed signal based on the head position signal and a signal supplied to a drive amplifier for driving the actuator, the target speed signal, the head A position signal and the head speed signal are supplied; Servo compensation means for supplying a signal corresponding to the difference between the head speed signal and the target speed signal as a drive signal to a drive amplifier for driving the actuator in order to approach a speed signal; and the target speed signal, the head position signal, and A head speed signal is supplied, and when the head speed signal is decreasing and the difference between the head position and the target position is equal to or greater than a predetermined value, a value obtained by integrating the difference between the head speed signal and the target speed signal is obtained. A proportional feedforward compensation amount is added to the drive signal, and when the head speed signal is decreasing and the difference between the head position and the target position is less than the predetermined value, the feedforward ratio is proportional to the head speed signal. Feedforward compensation means for adding a compensation amount to the drive signal and supplying the compensation signal to a drive amplifier that drives the actuator. For example was the head positioning control device. 3. The head position detecting means removes a mechanical resonance component from a signal obtained based on the servo head position deviation signal, the head position deviation signal, and a signal supplied to a drive amplifier for driving the actuator. 3. The head positioning control device according to claim 2, further comprising: means for outputting the head position signal.