JPH0411365A - Head speed control method for information storage device - Google Patents

Abstract

PURPOSE:To stably control the speed by providing a positive feedback loop of the head speed to a current amplifier and calculating the fluid friction constant in accordance with the head acceleration time for test operation and setting a friction compensation constant as the gain in the positive feedback loop based on this calculated value. CONSTITUTION:A head speed V detected by a speed detector 5 is multiplied by a friction compensation constant Kc set to a friction compensation constant setting part 9, and the output is fed back as the input of a current amplifier 3. An arithmetic circuit 20 consisting of an acceleration time measuring part 7 and an arithmetic part 8 is added. The speed control loop is provided with such control loop that a compensating current corresponding to the sped of an optical head 12 flows to a head driving mechanism 4 at the time of speed control. The constant dependent upon the friction characteristic required for determination of the compensating current is calculated and set in accordance with the acceleration time for test driving of the head. Thus, the head speed is stably controlled.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an information storage device, such as an optical disk device, which records and reproduces data on a recording medium by moving the head to a target track on the recording medium. This invention relates to a head speed control method for accessing. Note that in the following figures, the same reference numerals indicate the same or corresponding parts.

[Conventional technology]

FIG. 3 shows an example of the structure of a mechanical section of an optical disk device as an example of this type of information storage device. In the figure, an optical disk 10 on which information has been recorded is rotated at high speed by a spindle motor 11, and recording and reproduction of information on the optical disk 10 is performed via an optical head 12. Here, the optical head 12 is moved in the radial direction of the optical disk 10 via the head drive mechanism 4, and after being positioned on the target track,
Information is recorded and reproduced using a light beam 13 emitted from an optical head 12. FIG. 2 shows the optical disc 10 with a target track on the
FIG. 2 is a block diagram of speed control for moving 2 at high speed. Generally, digital control is used for speed control. The difference between the target track and the current track at the start of the seek, that is, the target track movement amount 01, is set as the target value, and the output of the movement amount detector 6 which counts the number of track crossings and detects the actual movement amount of the head. The deviation X between a certain head movement amount 6a and the target track movement amount 01 (that is, the remaining movement amount of the head required to reach the target track at that point) is input, and the reference speed generator 1 outputs the reference speed Vs. be done. The deviation between the reference speed Vs and the head speed ■ is input by the sampler 22 to the gain generator 2 at specific sampling intervals, and via the current amplifier 3, the head drive mechanism 4 drives the optical head 12 so that the speed follows the reference speed Vs. controlled. Here, the movement amount detector 6 and the speed detector 5 generally directly count the track error signal detected when the light beam 13 crosses the track, the output signal of an external encoder provided in the optical head 12, etc., and move the head. Methods such as detecting the amount and calculating the speed from these signal periods are used. FIG. 4 is a diagram showing operation waveforms of each part during speed control. That is, FIG. 5A shows an example of the relationship between the change in the actual speed V of the optical head 12 (solid line curve) and the reference speed Vs (dashed line curve) during speed control, and FIG. A)
3 shows the transition of the drive current i flowing through the head feeding mechanism 4 in response to the graph. Generally, the reference speed Vs has a maximum speed 'JaaxO section and a constant decrease section. Therefore, the current i flowing through the head drive mechanism 4 becomes the maximum current until the speed ■ of the optical head 12 reaches the reference speed Vs, and thereafter the sampling time t changes depending on the deviation between the reference speed Vs and the speed ■ of the optical head 12.
It varies with s. As a result, the speed ■ of the optical head 12 reaches the reference speed Vs, that is, the maximum speed V wax
After that, the speed is controlled so as to follow the pattern of the reference speed Vs, and the speed is decelerated to the target track through the constant section.

[Problem to be solved by the invention]

As shown in FIG. 3, since the head drive mechanism 4 generally uses a bearing 21 to support the movable part, friction is generated from the bearing during driving. Frictional force consists of solid friction inherent to the bearing and fluid friction due to the viscosity of the lubricating oil used in the bearing. Fluid friction is proportional to the viscosity value of the lubricating oil and the driving speed, but since the viscosity value has temperature characteristics as shown in FIG. 5, its value increases rapidly as the temperature decreases. Therefore, when the optical head 12 is driven by the head drive mechanism 4, the relationship between the frictional force generated and the head speed (2) is as shown in FIG. In other words, when the speed 15 of the optical head 12 is sufficiently small, the frictional force is almost solid friction! IFs, but as the speed of the optical head 12 increases, fluid friction occurs and the frictional force increases accordingly. Furthermore, depending on the ambient temperature, the friction characteristics at low temperatures1
The friction property at high temperatures greatly exceeds 19. Incidentally, these phenomena appear more conspicuously when a sliding bearing, which is effective in simplifying the structure of the head drive mechanism 4 and reducing costs, is used for the bearing 21. Incidentally, the frictional force generated when the optical head is driven is equivalent to reducing the driving force of the head drive mechanism 4 as a result. Therefore, the loop gain during speed control decreases or fluctuates due to a decrease in ambient temperature or an increase in the diameter of the optical head 12, resulting in a problem that the time required to reach the target track increases. On the other hand, one way to solve this problem is to increase the speed control gain 2, but with digital control, the speed error increases due to the effect of sampling time delay, and as a result, when the target track is reached, the head A new problem arises in that the speed of the object does not fall within a predetermined speed range, making it impossible to perform stable positioning. Therefore, it is an object of the present invention to provide a head speed control method that can solve this problem.

[Means to solve the problem]

In order to solve the above-mentioned problems, the method of the present invention is to "move a head (to a target track on a recording medium (such as optical disk 10)
An information storage device that moves an optical head (such as an optical head 12) to record and reproduce data on the target track via the head, the information storage device comprising: a head drive mechanism (such as 4) that moves the head;
and a movement amount detector (such as 6) that detects the movement amount of the head.
a speed detector (such as 5) that detects the speed of the head; and a drive current to the head drive mechanism so that the detected speed follows a predetermined speed pattern depending on the amount of movement of the head to the target track. In an information storage device equipped with a control means (reference speed generator 1, sampler 22° gain 2, etc.) for variably controlling 1 so that a current proportional to the speed (at the rate of the friction compensation constant Kc) is added to the drive current of the head drive mechanism. The friction compensation constant Kc can be determined, for example, from the acceleration time when a predetermined drive current i is passed through the head drive device 4 in advance and the device 4 (therefore, the head 12) is accelerated to a predetermined speed.

[For use]

In order to compensate for the drop in driving force due to the frictional force generated in the head drive mechanism 4 during speed control, a control loop is included in the speed control loop that causes a compensation current to flow through the head drive mechanism 4 in accordance with the speed of the optical head 12. establish. Furthermore, by calculating and setting a constant that depends on the frictional characteristics required to determine the compensation current from the acceleration time during test drive of the head, it is possible to cope with individual differences in ambient temperature and frictional characteristics. Embodiment Next, the present invention will be explained in detail using FIG. 1 while referring to FIGS. 3 to 6. FIG. 1 is a block diagram of speed control as an embodiment of the present invention, and corresponds to FIG. 2. The difference between FIG. 1 and FIG. 2 is that the speed detector 5
The head speed detected by the head speed ■ is multiplied by the friction compensation constant Kc set in the friction compensation constant setting section 9, and the output thereof is fed back positively as the input of the current amplifier 3, and the friction compensation constant Kc is tested. In order to calculate from the acceleration time of
This is the addition of . First, the relationship between friction force and acceleration time will be explained from the equation of motion during speed control. First, during the acceleration time ta during speed control shown in FIG. 4, a constant current ia flows through the head drive mechanism 4, so the drive force Fh at that time and the friction force generated in the bearing 21 of the head drive mechanism 4 are expressed as Ff, If the weight of the optical head 12 is set as m, and the head position is set as X, then F h = m M +F f - (1). Here, the frictional force Ff consists of the fixed friction Fs specific to the bearing 21 and the fluid friction Fd depending on the lubricating oil used, so Ff = Fs + Fd = Fs + Kd -i・-(
2). Here, Kd is the fluid friction constant determined by the viscosity of the lubricating oil, and the friction characteristic in Fig. 6 is 18°19
is the slope of Therefore, by substituting equation (2) into equation (1), we get Fh = m52 + Ki + Fs - (3). (3)
Solving the equation by setting head speed V=X and setting the head speed after acceleration time ta as Visaχ. Here, solid friction F
s is a value specific to the bearing and hardly changes depending on the ambient temperature and speed. Therefore, if the solid friction Fs is measured in advance, the acceleration time ta can be determined from equation (4) using the fluid friction constant Kd as a parameter. In other words, if the relationship between the two is calculated and determined in advance, the acceleration time ta
The fluid friction constant Kd can be immediately obtained from . Next, a procedure for performing a test operation and setting the friction compensation constant Kc will be explained. Friction compensation constant setting section 9 at the start of test operation
The contents of are reset and set to zero. In other words, the friction compensation loop does not operate, and the operation is exactly the same as conventional speed control. Next, speed control is started using an appropriate distance (distance # in which the maximum speed Vmax can exist) as the amount of movement. At the same time, the acceleration time measuring section 7 starts measuring time, and the maximum speed VI
The acceleration time ta (see FIG. 4) until reaching Iax is determined. The acceleration time ta is input to the calculation unit 8, and for example, the acceleration time ta obtained in this way and the fluid friction constant Kd
The fluid friction constant Kd corresponding to the acceleration time ta is determined from a table using a ROM or the like showing the correlation with the acceleration time ta. Furthermore, the calculation unit 8 calculates a friction compensation constant Kc as shown in the following equation (5) based on the fluid friction constant Kd determined in this way. Kc - Kp where Kv is the speed detector sensitivity (Vol t/m/
s), Kf is the force constant of the head drive mechanism 4 (N/A■p
ere), Kp is the current amplifier sensitivity (A mpere /
V o 12 t), Kd is the fluid friction constant (N/m/
s). With the above steps, the acceleration time ta during test operation is
A friction compensation constant Kc is set in the setting section 9 from . After that, normal speed control is performed. Next, actual speed control will be explained. A reference speed Vs is output from the reference speed generator 1 by inputting the deviation X between the target track movement amount 01 and the head movement amount 6a. Next, the sampler 22 inputs the deviation between the reference speed Vs and the head speed ■ to the gain generator 2 at specific sampling intervals, and outputs the current command value is, but the head speed ■
Multiplying by the friction compensation constant Kc, the combined value is the current command value is
The current flowing through the head drive mechanism 4 has a current value that compensates for the driving force lost due to the fluid friction Fd. Therefore, the head driving mechanism 4 can stably control the speed of the optical head 12 without reducing the driving force even if frictional force is generated. Note that the ambient temperature may change over time, and the magnitude of the fluid friction force may also change, so test operations and calculation and setting of the friction compensation constant Kc should be repeated at specific time intervals. It is preferable.

【Effect of the invention】

According to the present invention, in order to prevent a decrease in driving force due to fluid frictional force depending on the ambient temperature and lubricating oil viscosity generated in the bearing of the head drive mechanism during speed control for moving the head to a target track at high speed, fluid friction A positive feedback loop from the head speed to the current amplifier is provided in order to add a compensation current to the drive current of the head drive mechanism so as to obtain a drive force corresponding to the force, and the fluid friction constant is also tested by measuring the head acceleration time during operation. Based on this value, the friction compensation constant Kc, which is the gain in the positive feedback loop, is determined, so even if frictional force is generated during speed control, the driving force of the head drive mechanism will decrease. Therefore, speed control can be performed stably, and the number of openings upon reaching the target trunk will not increase. Furthermore, since the loop gain for friction compensation is set by performing a test operation, stable control can be performed even if the friction characteristics change due to individual differences, changes in the circumference, etc.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of speed control as an embodiment of the present invention, Fig. 2 is a conventional block diagram corresponding to Fig. 1, and Fig. 3 shows the configuration of an optical disk device as an example of an information storage device. Figure 4 is a diagram showing an example of the speed and drive current waveforms during head speed control, Figure 5 is a diagram showing an example of the relationship between the temperature and viscosity of lubricating oil for a bearing, and Figure 6 is a diagram showing an example of the relationship between the temperature and viscosity of the lubricating oil of the bearing. FIG. 3 is a diagram showing an example of frictional force generated in the mechanism. Reference speed generator, 2nd gain generator, 3: Current amplifier, 4: Head drive mechanism, 5: Speed detector, 6: Travel amount detector, 7: Acceleration time measuring section, 8: Arithmetic section, 9: Friction Compensation constant setting section, 2o: Arithmetic circuit, 22: Sampler, Kc
：Friction compensation constant, ■：Hega 4 Figure 3 Figure 3

Claims (1)

[Scope of Claims] 1) An information storage device that moves a head to a target track on a recording medium and records and reproduces data on the target track via this head, which head moves the head. a drive mechanism, a movement amount detector for detecting the amount of movement of the head, a speed detector for detecting the speed of the head, and a predetermined speed in which the detected speed corresponds to the amount of movement of the head to a target track and a control means for variably controlling a drive current to the head drive mechanism so as to follow a pattern, wherein the detected speed is adjusted to compensate for a frictional force generated in the head drive mechanism when the head moves. A head speed control method for an information storage device, characterized in that a proportional current is added to the drive current of the head drive mechanism.