JPH04368676A - Access servo mechanism of magnetic disk 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]

0001

[Field of Industrial Application] The present invention relates to an access servo mechanism for a magnetic disk drive, and in particular realizes high-speed, high-precision access operation by coordinating a high-response, small-stroke drive means and a low-response, large-stroke drive means. The present invention relates to the configuration of a control system for a head positioning servo mechanism.

0002

2. Description of the Related Art In an access servo mechanism for positioning the head of a conventional magnetic disk device, in order to read and write information to each track arranged concentrically on a magnetic disk, the A voice coil motor is used as a means to drive the head in this direction. In other words, the movable coil part of the voice coil motor is fixed to one end of a member called a carriage supported by a direct drive type or rotary type bearing, and moves the head fixed to the other end via a support mechanism. . However, there is a limit to the weight reduction of the equivalent mass of this carriage part due to restrictions on strength and rigidity, and there are restrictions on the thrust of the voice coil motor due to mass dimensions, heat generation, etc. Even if efforts are made to shorten access time and improve track following accuracy by increasing the response of the servo mechanism, there are limits.

[0003] Therefore, it has been considered to overcome this limit by using a drive means having higher responsiveness than a voice coil motor. Since the drive means for this generally has a small stroke, a method is used in which a voice coil motor is used in combination to form a two-stage servo system. For example, in Japanese Patent Application Laid-Open No. 60-35383, a high-response fine actuator is incorporated into the head support mechanism, the fine actuator is controlled according to a position feedback signal, and the amount of displacement of the fine actuator is detected by a detector. A method for controlling the operation of a coarse movement actuator is shown. In the field of optical discs, a similar method of configuring a two-stage servo system has been used, for example, as described in Japanese Patent Application Laid-Open No.
No. 109577 discloses a method in which a signal obtained by feeding back the detected head position and performing phase compensation calculation is divided into frequency bands and inputted to a coarse movement system and a fine movement system. Furthermore, Japanese Patent Application Laid-open No. 61-280080 discloses that a circuit for simulating the frequency characteristics of a fine actuator or a detector for detecting the movement of a fine actuator is provided,
A method is shown in which these outputs are used as deviation inputs of the coarse actuator.

0004

[Problem to be solved by the invention] In the first prior art,
It is necessary to provide a detector for detecting the amount of displacement of the fine movement actuator in the carriage section, and it is necessary to solve problems such as complication of the device and increase in the equivalent mass of the carriage. Furthermore, the control systems for the two actuators have characteristics that interfere with each other in a complicated manner, making it difficult to design the control system. In the second conventional technology, the phase margin of the servo system is reduced due to the phase delay characteristic of the filter used for frequency band division, so it is possible to achieve both faster and more stable response of the coarse actuator that handles the low frequency side. It becomes difficult to design with this in mind. In the third conventional technique, in a method in which a circuit is provided to simulate the frequency characteristics of a fine actuator, if there is an error between this circuit and the actual device, the operation of the coarse actuator may not be controlled correctly. Furthermore, the method of providing a detector for detecting the movement of the precision actuator presents the same problem as the first prior art.

[0005] An object of the present invention is to coordinate a drive means with a high response but a small stroke and a drive means with a large stroke but with lower responsiveness than the first drive means to create an access system with high response performance. The purpose is to obtain a servo mechanism.

[0006]

[Means for Solving the Problems] The present invention detects the relative position of the head with respect to the center of a target track from servo information recorded in advance on a magnetic disk, and compares it with the center position of the track, which is the target position. Then, by giving feedback to both the first drive means and the second drive means and adding the displacement amount of the first drive means to the target value of the control system of the second drive means, the two This realizes effective cooperative operation of the driving means, and also facilitates the design and adjustment of such a two-stage servo system.

[0007]

FIG. 1 is a block diagram showing signal transmission characteristics in a servo system according to the present invention. The transfer function of the first driving means and dynamic characteristic compensation element is G1 (s), and the transfer function of the second driving means and dynamic characteristic compensation element is G2 (s).
Then, the characteristic equation of this servo system is

[0008]

[Math 1]

[0009] here,

0010

[Math 2]

##EQU1## is a characteristic equation when the feedback control system is configured only with the first driving means and the dynamic characteristic compensation element,

0012

[Math 3]

[0013] is a characteristic equation when a feedback control system is constructed with only the second drive means and dynamic characteristic compensation element, so if each individual servo system is stable, it can also be used when a two-stage servo system is constructed. It can be seen that it always operates stably and that the poles of the single servo system combined become the poles of the two-stage servo system. This is a very convenient characteristic when designing and adjusting the servo system.

On the other hand, FIG. 2 shows a block diagram showing signal transfer characteristics in an example of a conventional two-stage servo system. In this system, the characteristic equation is

[0015]

[Math 4]

[0016] Further, FIG. 3 shows a block diagram showing signal transfer characteristics in another example of a conventional two-stage servo system. In this system, the characteristic equation is

[0017]

[Math 5]

[0018] In these configurations, a favorable relationship between each individual servo system and a two-stage servo system, such as the servo system according to the present invention, cannot be established, and it is necessary to reconsider the design and adjustment as a two-stage servo system. .

Furthermore, the closed loop transfer function G(s) of the servo system of FIG. 1 based on the present invention is as follows:

[0020]

[Math 6]

[0021] If each individual servo system settles to the target value without offset, it is obvious that this two-stage servo system also settles to the target value without offset. Here, the response of this servo system will be explained by taking as an example a case where the response of the first drive means is fast and the response of the second drive means is slow. In the servo system based on the present invention, if the current head position deviates from the center of the target track,
A control deviation occurs in the control systems of the first and second drive means. Both control systems calculate and output manipulated variables according to their respective control operations, and these signals are input to their respective corresponding drive means. In response to this, both drive means start correcting the positional deviation, but since the first drive means has a faster response than the second drive means, the head settles at the center of the target track and the control error occurs. At the time when becomes 0, the amount of displacement of the first driving means is large, and the amount of displacement of the second driving means is small. In this state, the first drive means is located at a position that is largely deviated from the neutral point, but since the amount of displacement of the first drive means is added to the target value of the second drive means, the second drive means The means continues to operate in the direction of decreasing the displacement amount of the first driving means even when the control deviation becomes zero. Along with this, the first driving means also operates, so the amount of displacement of the first driving means decreases while keeping the head on the center of the target track, and eventually when the amount of displacement reaches 0, that is, the neutral position. The entire servo system is in a steady state.

[0022]

Embodiments Hereinafter, embodiments of the present invention will be explained in detail with reference to the drawings. FIG. 4 is a block diagram showing the configuration of a servo system of a magnetic disk device based on the present invention. In Figure 4,
The lower surface 111 of the magnetic disk rotated at a constant speed by the spindle motor 101 is a servo surface.
Servo signals are recorded in advance. This servo signal is detected by a servo head 112 provided opposite the servo surface, and is input to a position detection circuit 120 via an amplifier 113. In addition, the upper surface 11 of the magnetic disk
5 is a data surface for storing data,
Data is read and written by a data head 116 provided opposite to this surface. Now, the position detection circuit 120 processes the servo signal and converts it into a position signal used in the positioning control system. The positioning servo system of this embodiment, like a normal magnetic disk drive, has two operation modes: a seek operation mode in which the head moves between tracks toward the target track, and a following operation mode in which the head follows the center of the target track. It has a mode of operation. First, in the seek operation mode, when starting the operation, the input changeover switch 150, the input changeover switch 151
are both connected to the upper side. The position signal is processed by track crossing detection circuit 131 to generate a pulse when the head passes a track boundary. This pulse is applied to the remaining track number counter 13.
2 is input. This remaining track number counter 132 is set with a value 133 of the difference between the target track number and the current track number at the start of the seek operation, and the value is updated by counting track crossing pulses, so that the current head is constantly updated. The value of the difference between a certain track number and the target track number, that is, the number of remaining tracks is detected. This value of the number of remaining tracks is input to the target speed signal generation circuit 140. The target speed signal generation circuit 140 refers to the target speed table and the acceleration feedforward table corresponding to this target speed, and outputs a speed command value according to the number of remaining tracks. This speed command value is input to a subtraction circuit 141, and the difference from a speed signal, which will be described later, is calculated to calculate a speed deviation. This speed deviation is amplified by power amplifier 161 to drive voice coil motor 170. The value of the current flowing through the voice coil motor 170 and the position signal are input to the speed detection circuit 180, subjected to speed estimation calculation processing to calculate a speed signal, and input to the subtraction circuit 141. On the other hand, the piezoelectric element clamp command circuit 190 operates according to the state of the remaining track number counter 132, and outputs a displacement command signal for displacing the piezoelectric element in the seek direction to the stroke end. This displacement command signal passes through the input changeover switch 151, and then passes through the piezoelectric element drive amplifier 1.
The signal is amplified at 91 and drives a piezoelectric element 192.

As the seek operation progresses and the head approaches the target track and reaches a predetermined position, the input changeover switch 151 is switched to the lower side, and the displacement command signal becomes the output of the following control circuit 200. Further, when a predetermined positional deviation amount or speed value is reached, the input changeover switch 150 is switched to the lower side. Next, the contents of the following control circuit 200 will be explained.

FIG. 5 is a block diagram showing an example of the configuration of a following control circuit 200 based on the present invention. A position signal is input to the input section 201 . This position signal is processed by the first phase compensation circuit 202, passes through the notch filter 203 and the adder circuit 204, and is output to the first output section 206. The adder circuit 204 uses an offset voltage source 205 to expand and contract the piezoelectric element around the neutral point.
The offset signals supplied from the Further, the position signal is also input to the adding circuit 207. The other input of this adder circuit is connected to the output of the first phase compensation circuit 202, and the addition result is output to the second output section 210 via the second phase compensation circuit 208 and notch filter 209. The first output section 206 is connected to the input changeover switch 151 of FIG. 4, and the second output section 210 is connected to the input changeover switch 150 of FIG. In this embodiment, the first drive means is a piezoelectric element, producing a displacement approximately proportional to the input signal. In order to configure a feedback control system for such elements, the phase compensation circuit is provided with integral characteristics. Furthermore, in order to extract the displacement amount signal of the piezoelectric element, instead of providing a detector, a piezoelectric element drive signal that is approximately proportional to the displacement amount is used, and this is input to the phase compensation circuit of the voice coil motor.

FIG. 6 is a circuit diagram showing the configuration of the first phase compensation circuit 202. This circuit has an integral characteristic, and supplies the integrated value of the signal from the input section 201 in FIG. 5 to the notch filter 203 and the adder circuit 207. A limit value is set by 232 and 233, and a voltage exceeding the limit value will not appear as an integral value. This limit value is set corresponding to the limit voltage of the piezoelectric element, and determines the stroke of the driving means by the piezoelectric element.

FIG. 7 is a circuit diagram showing another configuration of the first phase compensation circuit 202. This circuit has first-order lag characteristics, and compared to the circuit in Figure 6, the feedback resistance is 2.
34 is added, and the gain on the low frequency side is set low, but otherwise have the same characteristics.

[0027]

According to the present invention, a drive means with a high response but a small stroke and a drive means with a large stroke but a lower response than the drive means are effectively coordinated, thereby achieving high response performance. In addition to providing an access servo mechanism with a high level of control, the design and adjustment of such a two-stage servo system become easy.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing signal transfer characteristics in a servo system according to the present invention.

FIG. 2 is a block diagram showing signal transfer characteristics in an example of a two-stage servo system with a conventional configuration.

FIG. 3 is a block diagram showing signal transfer characteristics in another example of a two-stage servo system with a conventional configuration.

FIG. 4 is a block diagram showing the configuration of a servo system of a magnetic disk device based on the present invention.

FIG. 5 is a block diagram showing an example of the configuration of a following control circuit based on the present invention.

FIG. 6 is a circuit diagram showing the configuration of a first phase compensation circuit based on the present invention.

FIG. 7 is a circuit diagram showing another configuration of the first phase compensation circuit based on the present invention.

[Explanation of symbols]

r...Position target value, y...Displacement amount, 111...Servo surface, 11
2... Servo head, 161... Power amplifier, 170... Voice coil motor, 191... Piezoelectric element drive amplifier, 19
2...Piezoelectric element, 200...Following control circuit, 202
...integrator circuit.

Claims (4)

[Claims] What is claimed is: 1. A drive means with a high response but with a small stroke and a drive means that operates over the entire required range when positioning a magnetic head on a predetermined track in order to write or read information on a magnetic disk. The position of the magnetic head is detected in an access servo mechanism of a magnetic disk device that performs an access operation including moving between tracks and following a track by cooperating with a drive means having a possible stroke but slow response. Then, this position signal is fed back to the servo systems of both the first drive means and the second drive means and compared with the target position, and the displacement amount of the first drive means is calculated from the displacement of the second drive means. An access servo mechanism for a magnetic disk device, characterized in that a servo system is provided with means for adding as a target value to perform a track following operation. 2. When positioning a magnetic head on a predetermined track in order to write or read information on a magnetic disk, a driving means having a high response but with a small stroke, and a driving means that operates over the entire required range are provided. The position of the magnetic head is detected in an access servo mechanism of a magnetic disk device that performs an access operation including moving between tracks and following a track by cooperating with a drive means having a possible stroke but slow response. and means for feeding back this position signal to the servo systems of both the first driving means and the second driving means and comparing it with the target position, and for performing a displacement approximately proportional to the input signal as the first driving means. track following operation is performed by providing means for adding an estimated displacement signal proportional to the input signal to the first driving means to the servo system of the second driving means as a target value signal. access servo mechanism for magnetic disk drives. 3. When positioning a magnetic head on a predetermined track in order to write or read information on a magnetic disk, a drive means having a high response but with a small stroke, and a driving means that operates over the entire required range are provided. In the access servo mechanism of a magnetic disk device, the access servo mechanism of a magnetic disk device performs an access operation including movement between tracks and tracking operation by cooperating with a drive means that has a possible stroke but a slow response, and the first drive means receives an input signal. A control system for positioning the first driving means by performing a displacement approximately proportional to , outputs a value obtained by integrating the deviation between the target position and the current position as a manipulated variable;
comprising an integrating means for inputting this to the first driving means,
An access servo for a magnetic disk drive, wherein the integrating means includes a saturation means for limiting the integral value so that the manipulated variable signal is maintained within a range corresponding to the stroke of the first driving means. mechanism. 4. When positioning a magnetic head on a predetermined track in order to write or read information on a magnetic disk, a drive means having a high response but with a small stroke, and a driving means that operates over the entire required range are provided. In the access servo mechanism of a magnetic disk device, the access servo mechanism of a magnetic disk device performs an access operation including movement between tracks and tracking operation by cooperating with a drive means that has a possible stroke but a slow response, and the first drive means receives an input signal. A control system for positioning the first driving means by performing a displacement approximately proportional to , outputs a value obtained by integrating the deviation between the target position and the current position as a manipulated variable;
comprising an integrating means for inputting this to the first driving means,
The integrating means includes a saturation means for limiting the integral value so that the manipulated variable signal is kept within a range corresponding to the stroke of the first driving means, and is proportional to the input signal of the first driving means. 1. An access servo mechanism for a magnetic disk device, characterized in that the access servo mechanism for a magnetic disk device is provided with means for adding the signal to a target value signal of a second drive means.