JPS6214912B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a head positioning device, and more particularly to a head positioning device suitable for application to a magnetic disk drive.

In general, magnetic disk drives record and reproduce information by positioning heads in concentric areas (tracks) on a disk, which is a magnetic recording medium. Positioning in this case is performed using servo information recorded on the disk, and errors in thermal expansion are automatically absorbed.

FIG. 1 is a plan view showing an example of a head positioning mechanism of a magnetic disk device, FIG. 2 is a perspective view showing an example of the configuration of the drive unit, and FIGS. 3 to 5 are diagrams for explaining the tracking servo operation. , FIGS. 6 to 8 are diagrams for explaining the initial seek operation.

In FIG. 1, numeral 1 is a disk rotating in the direction of arrow C. 2 is a head, 3 is an arm, 4 is a moving coil, and 5 is a field magnet. The arm 3 is rotatably supported around a shaft 3a, and the moving coil 4 is fixed to one end of the arm 3. , and a head 2 is attached to the other end.
The head 2 moves in the radial direction of the disk 1 (arrows A and B) by the swinging of the arm 3.

On the other hand, the moving coil 4 is wound so that it interlinks with the magnetic field generated by the field magnet 5 as shown in FIG. 2, and so that the current flowing through the coil 4 is perpendicular to the swing direction of the arm. and is away from the field magnet 5.

Because of this structure, terminal 4 of moving 4
When electricity is applied through a and 4b, the arm 3 swings and the head 2 can be moved to a desired track.

At this time, moving coil 4 is used to position head 2 on a desired track and hold it there.
It is necessary to control the current flow. In order to position the head 2 on a desired track, the positional deviation between the head 2 and the desired track may be detected and the current may be controlled to reduce this positional deviation.

First, to explain the detection of positional deviation, a track is recorded on one surface of the disk that is shifted by half the track width from the tracks on the other surfaces. On this one surface (servo surface), as shown in FIG. The positional deviation can be obtained by detecting the amplitude of each signal. That is, as shown in FIG. 4b, the reproduced signal amplitude of the even-numbered tracks changes depending on the position (horizontal axis), and similarly, the reproduced signal of the odd-numbered tracks changes as shown in FIG. 4c. Therefore, these b,
If the difference in c is taken, the result will be as shown in the figure d, and when this difference becomes zero, the head 2b will be located at the boundary between the track STe and the track STo on the servo plane (Figure 3b). Therefore, in other words, in the data plane (Fig. 3a), head 2a
is located at the center of the track DT, and its reproduced signal becomes maximum (as an average) as shown in FIG. 4a.

Figure 5 shows such a position deviation signal (Figure 4 d)
The signal from the head 2b on the servo surface is amplified in the reading circuit 10, and then the odd signal extraction circuit 20o and the even signal extraction circuit 20e respectively amplify the signals of the odd track. The signal components and the signal components of even tracks are extracted. These odd-numbered signals and even-numbered signals pass through the differential circuit 21 to become a signal representing the difference between the two, that is, a position error signal, which is converted into a current in the amplifier circuit 30 and then sent to the driving device (i.e., the moving device shown in FIG. 2). coil). Although only the main components of this servo system are shown, like other general servo systems, differentiating circuits, integrating circuits, delay circuits, filters, etc. are appropriately combined in order to suppress the occurrence of vibrations and steady-state deviations. It is possible to perform phase compensation or the like.

Now, as described above, the head can be positioned on a desired track and held at that position.
In recent years, magnetic disk drives often use a floating type head that performs recording and reproduction with the head floating a small amount above the disk surface. Further, when the rotation of the disk is stopped, this floating head is brought into contact with the disk surface.

Therefore, a portion of the disk surface that the head comes into contact with is damaged by friction with the head, and the head itself is also damaged. As a result, information cannot be recorded and reproduced better than in other parts. For this reason, the disk surface is divided into a portion that contacts the head and a non-contact portion, and information is recorded and reproduced only in the non-contact portion.

FIG. 6a is a diagram showing an example of such a division form, where CSS is a contact area that contacts and slides with the head 2b when the disk 1 starts and stops rotating, PS is an area where information is recorded and reproduced, and LS is an area where information is recorded and reproduced. is a low-speed moving region that is the boundary between these two regions. Corresponding to these areas, on the servo surface of the disk, only odd track signals are provided for the low speed moving area LS, and both odd and even track signals are provided for the recording/reproducing area (position servo area) PS. Therefore, as shown in FIG. 6b, servo signals (outputs of the differential circuit in FIG. 5) corresponding to the positions of the heads on these regions are obtained.

By the way, in order to start recording and reproducing to a disk, the head at the position indicated by the solid line a in FIG. It won't happen.
Then, position servo is performed there.

At this time, the speed at which the head enters track "0" is limited to the extent that the position servo system can stop the head. This speed decreases as the width of the track decreases, and in recent magnetic disk devices, this speed is extremely low, at several cm/second.

Conventionally, in order to make the head reach the target position (track "0") at such a low speed, a low-speed movement region LS was provided just before the target position, as shown in Fig. 8, and the speed was lowered below the above-mentioned limit speed. I'm trying to keep it down. That is, the head is moved at high speed _VH until reaching the low speed movement region LS, and then moved at low speed _VL . Low speed moving area LS
The entry of the head into the target position is detected by comparing the rise of the servo signal with an appropriate threshold value E, as shown in Figure 8b, and similarly, reaching the target position is detected when the servo signal falls. detected by.

FIG. 7 is a diagram illustrating a speed servo system configured to operate based on these matters. To explain the operation, first, a high speed target speed signal V _H is generated from a constant voltage source 60, and this is divided by resistors R ₁ and R ₂ to generate a low speed target speed signal V _L. The switching circuit 70 initially selects the high speed target speed signal V _H and applies it to the differential circuit 50 . The other input of the differential circuit 50 is applied with the actual head movement speed signal. This moving speed signal is created in the adding circuit 90 by adding the output of the differential circuit 50 to the voltage applied to the drive device 40 via the correction value extraction circuit 80. That is, the correction value extraction circuit 80 has an impedance equivalent to the impedance when the moving coil of the driving device 40 is fixed, for example, and thereby generates a voltage that is lower by the speed electromotive force generated in the moving coil. If the difference between this voltage and the voltage of the drive device 40 is generated in the adding circuit 90, a speed electromotive force, that is, a speed signal can be obtained.

In this way, since the speed signal is applied to the differential circuit 50, the head is driven according to the target speed, and when it enters the low speed region LS, a servo signal is generated from the head 2 via the position servo signal generation circuit 20. , the comparison circuit 55 detects this occurrence and switches the switching circuit 70. As a result, in the low speed region LS, the head moves according to the low target speed V _L and reaches track "0" (target position).

However, as the track density increases, the track width decreases and the low target speed V _L is limited to an increasingly lower value, and as shown in Figure 7, the error caused by indirectly measuring the moving speed of the head increases. Increases as a relative amount. For example, errors are caused by increases in the resistance value of the moving coil due to temperature changes, changes in the magnetic field, and the like. Due to this error, the low speed region
The difference between the upper and lower limits of the target speed in LS becomes extremely small, making it difficult to adjust and extremely difficult to obtain stable operation.

An object of the present invention is to provide a positioning control system that can reduce the influence of the above error by half.

This purpose is achieved by a head detection means for detecting passage of the head at a predetermined starting point, and for detecting a minute positional deviation between the head and a target stopping point spaced a certain distance from the starting point, and driving the head. a position servo means for returning the head to a source, and the head positioning device is configured to actuate the position servo means after the head has moved through at least the starting point and reached the target stopping point at a predetermined speed. A target speed generating means for generating a target speed formed by a monotonically increasing function based on the output of the detecting means, and a speed servo means for detecting the moving speed of the head and feeding back the deviation from the target speed from the target speed generating means to the driving source. This is achieved by providing the following, and one embodiment thereof will be described in detail below with reference to the drawings.

FIG. 9 is a block diagram of the speed servo system which constitutes the essential part of the present invention, and FIG. 10 is a diagram for explaining its operation.

The difference between the present invention and the conventional circuit is in the circuit that generates the target speed in the low speed region LS, and the other difference is that the position servo circuit shown in FIG. 5 and the speed servo circuit shown in FIG. 7 are operated independently in terms of time. It is equivalent to the combination of the switching control circuit 100 and the switching circuit 100 so as to obtain the switching control circuit 100. Therefore, the basic operating principle of these equivalent parts remains unchanged. Therefore, only how the influence of speed detection error changes depending on the difference in target speed, that is, only the effects of the present invention will be described in detail.

In this example, for simplicity, the low speed region LS
The target speed is a ramp signal that is a simple monotonically increasing function. Solid line V in Figure 10
_L represents this target signal, and time t is the predetermined arrival time at the target position.

If the speed detection circuit produces an error-free head speed signal, the head can move along the target speed V _L and reach the target position at a predetermined time t. However, since there is an error involved in reality, let's assume that this error works relatively and that the detection speed is made to be 1/2 and 1/4 of the actual moving speed of the head, respectively. In other words, in order to move the head, it is not enough to generate a driving force that corresponds to the acceleration of the head; for example, it is also necessary to generate a driving force that overcomes the mechanical resistance (frictional force) that is proportional to the speed. current flows through the moving coil. Then, a detection error with respect to the speed electromotive force occurs in proportion to the voltage drop due to this current. In other words, the error due to the voltage drop becomes a signal having substantially the same waveform as the speed electromotive force, and is difficult to cancel using a filter circuit. Further, even in the case of a dummy circuit, a difference in resistance value occurs due to temperature change, making it difficult to cancel out the error. Furthermore, since the speed electromotive force is small relative to this error, the influence of the error is large. Because of this, it can be considered that the error occurs in proportion to the speed.

In Figure 10, Vt and Vy represent the actual moving speed of the head taking such errors into account. When the actual speed is twice the detected speed, Vt is
also corresponds to the case of 4 times.

In this example, the speed detection error is 2 times, 4 times
Even though they are twice as large, the error in the arrival speed at the target position can be made √2 times and √4 times, respectively. This is because the distance required to cross the low speed region LS is constant, and therefore the integral values of the velocities V _L , V _X , and Vy shown in FIG. This is because the arrival time becomes shorter (or longer), so the arrival speed does not increase much.

In this embodiment, the target speed is set in a ramp-like manner, but the same effect can be obtained by using other monotonically increasing functions.

In this way, the influence of speed errors is reduced, so
It is possible to perform stable movement of the head, especially the movement of starting disk rotation.

As described above, the present invention can be applied not only to the above-mentioned embodiments but also to various devices to stabilize the operation, as long as the present invention is a positioning device that switches from speed servo operation to position servo operation that detects minute position deviations. It can be done, and the effect is enormous.

[Brief explanation of the drawing]

1 to 2 are diagrams illustrating a head drive mechanism in a conventionally known magnetic disk device, and FIGS. 3 to 5 are diagrams illustrating an example of the configuration of a tracking servo system. 6 to 8 are diagrams for explaining an example of the configuration of a speed servo system, FIG. 9 is a configuration diagram of an embodiment of the present invention, and FIG. 10 is a diagram for explaining an example of the operation of the present invention. This is a diagram. 1...Disk, 2, 2a, 2b...Head,
3...Arm, 4...Moving coil, 5...
Field magnet, 10...Reading circuit, 20...Position servo signal generation circuit, 30...Voltage-current conversion amplifier circuit, 40...Drive source (drive device), 50...
Differential circuit, 60'...constant voltage source, 61...target speed generation circuit, 55...comparison circuit, 70...switching circuit, 80...correction signal extraction circuit, 90...addition circuit, 100...switching Control circuit, 110...Switching circuit.

Claims (1)

[Claims] 1 Head detection means for detecting passage of the head at a predetermined starting point; Position servo means for detecting minute positional deviation between the head and a target stopping point spaced a certain distance from the starting point, and returning this to the drive source. In a head positioning device, the position servo means is activated after the head is moved through at least the starting point and reaches the target stopping point at a predetermined speed, the output of the head detecting means is a monotonically increasing function. A head characterized in that it is provided with target speed generating means for generating a target speed of Positioning device.