JPH048327Y2 - - 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 a disk shape measuring device that measures the amount of wobbling by monitoring the amount of displacement of an actuator of an automatic control system that follows the wobbling of the disk and controls the position of an optical head.

[Summary] The present invention is a disk shape measuring device that measures horizontal runout due to surface runout and eccentricity of a disk. In this case, by monitoring whether the controlled variable of the automatic control means is between a predetermined upper limit value and lower limit value, it can be determined whether the measurement of the amount of disk runout exceeds the measurement limit, and accurate measurement can be performed. This is what we do.

[Conventional technology]

FIG. 3 is a diagram showing the basic configuration of the optical disk file device. Reference number 31 is an optical disk,
Reference number 32 is a motor, reference number 33 is an optical head, and reference number 34 is a linear actuator.

FIG. 4 is a diagram schematically showing a focus error and tracking error detection system of the optical head 33. Reference number 41 is a semiconductor laser, reference number 42 is a lens system, reference number 43 is a half mirror,
Reference number 44 is a light detection sensor. In the case of detecting a focus error, the light detection sensor 44
Detection is performed using addition and subtraction of a 4-segment detector that imparts astigmatism to the reflected laser beam.In the case of tracking error detection, addition and subtraction are performed using the same 4-segment detector (an addition/subtraction method that is different from the method used to detect focus errors). Detection using .

Furthermore, the optical head 33 includes a light detection sensor 4.
an automatic control circuit that obtains a signal for controlling the position of the optical head 33 according to each error signal detected in step 4;
Further, an actuator is provided (not shown in the figure) that finely adjusts the light spot of the laser beam in the vertical and horizontal directions based on this control signal.

To read information from, write, or rewrite information from an optical disk, use the optical head 3.
It is necessary for the laser beam emitted from the optical disc 31 to be accurately focused on the optical disk 31 and to be traced so that it does not deviate from the target track.

Since the optical disk 31 causes vertical vibration within a range of about 500 μm during rotation, it is necessary to use the objective lens 42 of the optical head 33 to accurately record and reproduce information.
to keep the focus of the laser beam on the optical disk 3.
It must be tied on top of 1. The error needs to be kept below the depth of focus of the lens system 42, that is, about 1 μm. Furthermore, the horizontal deflection of the pit row or guide groove 45 due to eccentricity of the disk is approximately ±100 μm at maximum, 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, such a conventional optical disk shape measuring apparatus has a problem in that the loop gain of the automatic control system decreases in the high frequency region, resulting in large control errors, making it impossible to measure accurately.

The present invention solves these conventional problems, and aims to provide an optical disk shape measuring device that can determine whether or not measurements have been performed with high accuracy in a high frequency region.

[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 the optical head so as to follow the horizontal deflection due to surface runout or eccentricity, and an amount proportional to the displacement of the actuator of the automatic control means is determined by the displacement of the disk as the measured disk rotates. In a disk shape measuring device equipped with a means for outputting a measured value of horizontal runout due to surface runout or eccentricity of the disk, the control amount of the automatic control means is monitored to ensure that it is between a predetermined upper limit value and a predetermined lower limit value. It is characterized by being equipped with a circuit.

Here, the control amount of the automatic control means is the amount (δ-
y).

[Effect]

To measure horizontal runout due to disk surface runout and eccentricity, take the displacement amount y of the actuator that controls the position of the optical head that follows the disk runout, and use this displacement amount y to correspond to the runout amount. Measure it as if it were to be measured. At this time, the present invention provides an output δ of the photodetection sensor corresponding to the shake amount.
The difference signal between the displacement amount y of the actuator and the displacement amount y of the actuator (control amount of the automatic control system) is monitored via a control preamplifier. In other words, the controlled amount is δ−y, and the displacement amount y
When can follow the change in δ, δ−y=0, so y is adopted as the measured value corresponding to the shake amount Δ.

Here, the loop gain of the automatic control system decreases in a high frequency region, making it impossible for the displacement amount y of the actuator to follow the output δ of the photodetection sensor. The control amount δ-y at this time is monitored to see if it satisfies -e<δ-y<+e with respect to the predetermined upper limit value +e and lower limit value -e, and an error signal is sent when it is out of the range. By outputting the output, it is possible to determine whether or not the measurement of the amount of runout exceeds the measurement limit.

〔Example〕

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

FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 1, the output δ of the photodetection sensor 44 corresponding to the amount of deflection of the disk and the displacement amount y of the actuator 1 are input to the comparator 2 to generate a control amount. The control amount is the control preamplifier 3.
The signal becomes the main feedback amount and is input to the comparator 4. The control target value is input to the comparator 4,
A control error signal ε is generated. The control error signal ε is input to the control amplifier 5, and is input to the actuator 1 as a control operation signal. Further, the displacement amount y of the actuator 1 is branched and input to the sensor amplifier 6.

On the other hand, the output of the control preamplifier 3 is branched and connected to the positive and negative inputs of two comparators 7 and 8, respectively. A reference voltage is connected to the negative input of the comparator 7 and the positive input of the comparator 8, respectively. The outputs of the comparators 7 and 8 are input to an AND gate 9, and the output thereof is taken out as an error signal E.

FIG. 2 is a diagram showing the standard value of the amount of runout and the gain characteristics of the automatic control loop.

The loop gain of this automatic control loop is ₂ and OdB
However, the gain characteristics of the automatic control loop gain are generally set so as to correspond to the disk standard runout amount. That is, as shown in FIG. 2, the automatic control loop is designed to have a gain characteristic that can cover the disk standard runout amount. Therefore, until the frequency is ₂ , the displacement y of the actuator 1 can follow the output δ of the photodetection sensor, so the deflection amount Δ can be measured from the displacement y of the actuator. As long as the measured disk has a standard runout amount within the range of the automatic control loop gain, the displacement amount y of the actuator can follow the output δ of the photodetection sensor.
The amount of deflection Δ can be measured based on the amount of displacement y of the actuator. Expressing this in a formula, if the disk is a standard product and the automatic control loop gain characteristic is within the range in which it is operating normally, δ - y = 0, and y = δ holds, so the displacement y Runout amount Δ
It is possible to measure

However, for example, when measuring the shape of a disk that is a non-standard product and has characteristics shown at a frequency ₃ at a position outside the automatic control loop gain characteristic ₃ in Figure 2, the amount of displacement y will be added to the amount of runout. is no longer able to follow, and with this loop gain of automatic control, the control error ε exceeds the specified runout amount ε ₀ . In other words, if the difference in displacement is δ-y=x, if x exceeds the predetermined upper and lower limits, the displacement y no longer corresponds to δ, and the error increases, making the measurement difficult. It shows that you have exceeded your limits. Therefore, by only measuring the displacement amount y of the actuator 1, it is not possible to determine the corresponding amount of deflection of the disk. In this case, a certain value +
By setting e and -e and observing the error signal E output when the controlled variable exceeds the range, it is determined whether the measurement limit has been exceeded. The output value y at this time cannot be used as a measurement value.

[Effect of idea]

As explained above, the present invention monitors the difference signal (control amount of the automatic control system) between the output δ of the photodetection sensor corresponding to the amount of disk shake and the displacement amount y of the actuator 1 (control amount of the automatic control system) via the control preamplifier. By doing so, it is possible to determine whether the measurement limit has been exceeded, and the reliability of the measured value can be ensured.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 2 is a diagram showing the standard value of the runout amount δ and the gain characteristics of the automatic control loop. FIG. 3 is a diagram showing the basic configuration of an optical disk file device. FIG. 4 is a diagram schematically showing an optical head. 1... Actuator, 2, 4... Comparator, 3
...Control preamplifier, 5...Control amplifier, 6...
...Sensor amplifier, 7, 8...Comparator, 9...And gate, 31...Optical disk, 32...Motor, 33...Optical head, 34...Linear actuator, 41...Semiconductor laser, 42... ... Lens system, 43 ... Half mirror, 44 ... Light detection sensor, 45 ... Guide groove.

Claims (1)

[Claims for Utility Model Registration] A motor for rotationally driving a disk to be measured, and an optical head for optically irradiating a point on the disk to be measured and detecting the reflected light; The optical head includes an automatic control means for controlling the position of the optical head so as to follow horizontal deflection due to surface runout or eccentricity as the disk rotates, and an amount proportional to the displacement of the actuator of the automatic control means is determined by an amount proportional to the displacement of the actuator of the optical head. In a disk shape measuring device equipped with a means for outputting a measured value of surface runout of the disk due to rotation or horizontal runout due to eccentricity, the control amount of the automatic control means is between a predetermined upper limit value and a lower limit value. A disk shape measuring device characterized in that it is equipped with a circuit for monitoring.