JPH048328Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a disk shape measuring device that measures horizontal runout due to surface runout and eccentricity of a disk. In particular, the present invention relates to improving the responsiveness of a disk shape measuring device that measures the amount of disk shake by monitoring an amount proportional to the control error of an automatic control system that controls the position of an optical head following disk shake.

〔overview〕

The present invention is a disk shape measuring device that measures horizontal runout due to surface runout and eccentricity of a disk, and detects the displacement of an actuator that is controlled by tracking the position of the optical head to the amount of disk runout. When measuring the amount of runout, the disk is rotated at a speed lower than the rated rotation speed, and the above displacement amount is temporarily accumulated in accordance with a pulse signal with a frequency proportional to the low rotation speed, and the displacement amount is proportional to the rated rotation speed. By reading out the data according to the frequency pulse signal, it is possible to practically measure the amount of disk runout at the rated rotational speed even if the automatic control system has insufficient responsiveness.

[Conventional technology]

In order to read, write, or rewrite information from an optical disk, it is necessary for the laser light emitted from the optical head to accurately focus on the optical disk and to trace it so that it does not deviate from the desired track. .

Since the optical disk causes vertical deflection within a range of approximately 500 μm during rotation, in order to accurately record and reproduce information, the objective lens of the optical head must be moved up and down to keep the laser beam focused on the optical disk. I have to do it. The error needs to be kept below the depth of focus of the lens system, that is, about 1 μm. Furthermore, the horizontal deflection of the pit row or guide groove due to eccentricity of the disk is approximately ±100 μm at most, and the light spot of the laser beam must follow the target track with an error of ±0.1 μm or less.

In order to accurately control the position of such an optical head, automatic control means is used that optically detects each of the focusing error and tracking error on the optical disk and feeds this back to the operation of the optical head.

On the other hand, the quality of the produced optical disk is determined by measuring the amount of the above-mentioned surface runout and runout due to eccentricity, and comparing it with a specified value.

The amount of deflection Δ due to surface runout and eccentricity of an optical disk has conventionally been directly measured using a complicated mechanical-optical system. Devices that calculate the amount of runout Δ from y have come into use.

[Problem that the invention attempts to solve]

However, measurements using such conventional optical disk shape measuring devices are performed at the high frequency gradually decreasing portion of the automatic control system gain characteristics, so as the disk rotation speed increases, the gain tends to be small and unstable. . In addition, as the rotational speed of the disk increases, the gain and phase deviation between the actuator drive signal and the amount of actuator displacement in response to minute vibrations of the disk increases, resulting in a difference of several tens of Hz.
In the above case, there was a problem that accurate measurement could not be performed.

The present invention solves these conventional problems by creating an optical disk shape measuring device that can measure the amount of runout with high precision, regardless of the responsiveness of the automatic control system that controls the position of the optical head. The purpose is to provide

[Means for solving problems]

The present invention includes a motor that rotationally drives the disk to be measured, and an optical head that optically illuminates a point on the disk to be measured and detects the reflected light. It includes an automatic control means for controlling the position of this optical head so as to follow the horizontal runout due to surface runout or eccentricity, and an amount proportional to the control error of this automatic control means is determined by the amount of the disk movement caused by the rotation of the disk to be measured. A disk shape measuring device equipped with a means for outputting a measured value of horizontal runout due to surface runout or eccentricity, a means for rotating the motor at a speed lower than the rated rotational speed, and a frequency proportional to the rotational speed of the motor. a circuit for generating a pulse signal, a means for temporarily accumulating an amount proportional to the control error as a digital signal according to the pulse signal when the motor rotates at a low speed; and means for reading out an amount proportional to the control error accumulated in the accumulating means in accordance with the pulse signal at the time of the accumulation.

Preferably, the temporary storage means is a shift register or equivalent memory, and the pulse signal when the motor rotates at the rated rotational speed is obtained from a fixed frequency oscillator.

[Effect]

The amount of deflection in the horizontal direction due to disk surface deflection and eccentricity is determined from an amount proportional to the control error of an automatic control system that controls the position of the optical head that follows the disk deflection. At this time, the present invention temporarily accumulates measurement data at a slow rotation speed that ensures the responsiveness of the automatic control system using a pulse signal with a frequency proportional to this rotation speed as a clock, and then By reading out the data using the pulse signal as a clock, an estimated value of the amount of runout at the rated rotational speed is obtained. This makes it possible to compare data measured on various disks at various rotational speeds as the amount of runout at a uniform rated rotational speed.

〔Example〕

Hereinafter, embodiments of the present invention will be explained based on the drawings.

The figure is a block diagram showing an embodiment of the present invention. In the figure, reference number 1 is a disk, and reference number 2 is a motor whose rotational speed is changed by switching a changeover switch 3. A pulse encoder 4 that generates a pulse signal with a frequency corresponding to the rotational speed of the motor 2 is attached to the motor 2 . The output of the optical head 5 for detecting the deflection of the disk 1 is connected to a shift register 7 via an analog-to-digital conversion circuit 6. shift register 7
The clock input of is connected to the output of the pulse encoder 4 or to the fixed oscillator 9 via the changeover switch 8. The readout output of the shift register 7 is connected to a correction calculation block 10, and this output is connected to a spectrum analyzer 12 via a digital-to-analog conversion circuit 11.

The motor 2 is rotated at a rotation speed N n (frequency _n ) slower than the rated rotation speed _{N 0} (frequency ₀ ) to be measured. The rotational speed N _n is selected at a value that allows the automatic control system of the optical head 5 to respond sufficiently to the vibrations of the disk 1 .

The signal from the optical head 5 is converted from analog to digital and is taken into a shift register 7 whose clock is the output pulse signal of the pulse encoder 4 corresponding to the rotational speed of the motor 2. The number of stages of the shift register 7 is made to correspond to at least one revolution of the motor 2.

The data stored in the shift register 7 is read out using the output pulse signal of the pulse encoder 4 as a clock when the motor 2 is rotated at the rated rotational speed _N0 , and the position error in the direction of deflection of the optical head 5 and the position error of the disk mounting head are calculated. A correction calculation block 10 corrects tilt errors, deformations caused by rotation of the disk 1, and the like. This correction output is digital-analog converted and input to the spectrum analyzer 12 to perform frequency analysis of disk shake.

The readout clock of the shift register 7 is obtained by switching the changeover switch 8 from a fixed oscillator 9 that generates the same frequency as the frequency of the output pulse signal of the pulse encoder ₄ when the motor 2 is rotated at the rated rotational speed N0. But that's fine.

Shift register 7 and correction calculation block 10
can be composed of a microprocessor having a memory, a counter, and an arithmetic processing circuit.

[Effect of idea]

As explained above, the present invention collects data corresponding to the amount of disk shake at a low rotational speed where the automatic control system of the optical head has good response, and clocks the frequency when rotating at the rated rotational speed. Since the data is read out as follows, data obtained by measuring disks of various sizes at various rotational speeds can be estimated as a uniform amount of runout of the rated rotational speed, and can be compared with the specified value of the rated rotational speed.

[Brief explanation of the drawing]

The figure is a block diagram showing an embodiment of the present invention. 1... Disk, 2... Motor, 3, 8... Selector switch, 4... Pulse encoder, 5... Optical head, 6... Analog-digital conversion circuit, 7... Shift register, 9... Fixed oscillator ,
10...Correction calculation block, 11...Digital/analog conversion circuit, 12...Spectrum analyzer.

Claims (1)

[Scope of claim for utility model registration] (1) A motor that rotationally drives the disk to be measured;
The optical head is equipped with an optical head that optically illuminates one point on the disk to be measured and detects the reflected light. It includes an automatic control means for controlling the position of this optical head, and an amount proportional to the control error of this automatic control means is output as a measured value of horizontal runout due to surface runout or eccentricity of the disk due to rotation of the disk to be measured. means for rotating the motor at a lower speed than the rated rotational speed; a circuit for generating a pulse signal with a frequency proportional to the rotational speed of the motor; means for temporarily accumulating an amount proportional to the control error as a digital signal in accordance with the pulse signal when the motor rotates at the rated rotational speed; 1. A disk shape measuring device comprising: means for reading out an amount proportional to an accumulated control error. (2) The temporary storage means is a shift register,
The disk shape measuring device according to claim 1, wherein the pulse signal when the motor rotates at the rated rotational speed is obtained from a fixed frequency oscillator.