JPH0721508B2 - Acceleration calculation method for optical disc inspection device - Google Patents

Description

The present invention relates to an acceleration calculating method for calculating the acceleration from the output of a displacement sensor corresponding to eccentricity or shake in an optical disk inspection device for measuring the mechanical characteristics of an optical disk. It is a thing.

[Conventional technology]

Conventionally, in this type of optical disc inspection apparatus, a tracking servo and a focus servo are applied to a guide groove of the optical disc, an optical head (condensing lens) is made to follow the movement of the optical disc, and the reading state of the optical disc is maintained. The movement of the condenser lens at that time is detected by the displacement sensor to obtain an output signal corresponding to the amount of eccentricity and the amount of shake. Further, the output signal of the displacement sensor is passed through an analog acceleration filter to perform acceleration calculation to obtain the eccentric acceleration and the shake acceleration.

FIG. 3 is a block diagram showing an example of a conventional optical disc inspection apparatus. In the figure, 1 is an optical disk, 2 is a spindle motor for rotating the optical disk 1 at a constant speed, 3
Is an optical head which is fed by the feeding mechanism in the radial direction of the optical disc 1 and has a tracking servo mechanism and a focus servo mechanism, and which traces the recording surface of the optical disc 1 along the guide groove, 4 is a low-pass filter having standard characteristics, Reference numeral 5 is an analog acceleration filter, 6 is an analog / digital converter (hereinafter abbreviated as A / D converter), and 7 is a computer. The optical head 3 causes the focusing lens to follow the movement of the optical disc 1 by the tracking servo and the focus servo to maintain the reading state of the optical disc 1, and at the same time, the movement of the focusing lens is detected by the displacement sensor to determine the amount of eccentricity. Alternatively, the output signal Ss corresponding to the shake amount is obtained. This output signal Ss is applied to the acceleration filter 5 via the low pass filter 4, and the acceleration (2
Calculation is performed to find the (differential derivative). The output of the acceleration filter 5 is A / D converted by the A / D converter 6 and then input to the computer 7 for desired data processing.

FIG. 4 is a frequency characteristic diagram showing the characteristics of the low-pass filter 4 and the acceleration filter 5. As shown in the figure,
The transfer function G (s) of the acceleration filter 5 is expressed by G (s) = ks ² k: displacement-acceleration conversion constant, and is a straight line of 40 [dB / dec].

Therefore, when the output signal Ss obtained from the optical head 3 is applied to the low pass filter 4 and the acceleration filter 5,
A signal proportional to the acceleration component can be obtained.

[Problems to be solved by the invention]

However, in such an acceleration calculation method,
Since the acceleration output is obtained by analog calculation,
Signal processing such as correction and averaging of non-linearity in the displacement sensor output is not easy. For example, the correction curve of the displacement sensor is complicated, and an accurate correction amplifier cannot realize accurate correction. Furthermore, when attempting to average the measurement data in order to remove noise or improve reproducibility, the measurement data for n rounds must be saved, which requires a huge storage capacity. Will end up. Therefore, the averaging process is performed after the acceleration is calculated by the computer 7, and the process at the data stage cannot be performed. Further, since the acceleration filter 5 is an arithmetic filter, strict frequency characteristics are required, and its adjustment is troublesome.

The present invention eliminates the above-mentioned drawbacks of the conventional method, and realizes an acceleration calculation method for an optical disc inspection apparatus, which is easy to process at the data stage in the output of the displacement sensor and is capable of highly accurate acceleration calculation. It is intended for.

[Means for solving problems]

An acceleration calculation method for an optical disc inspection apparatus according to the present invention includes a servo mechanism for displacing a condenser lens in a tracking direction and a focus direction to maintain a reading state of an optical disc, and detecting a displacement amount of the condenser lens at this time by a displacement sensor. In the optical disc inspection apparatus for obtaining a signal corresponding to the eccentricity or the shake in the optical disc and calculating the acceleration of the eccentricity or the shake from the sensor output, an analog-digital converter for analog-digital converting the sensor output, and The data processing means for processing the sensor output digitally converted by the analog / digital converter, the low-pass filter and the acceleration filter whose transfer function G _(S) is represented by ks ² (k: displacement-acceleration conversion constant) are provided. The di-state obtained by bi-linear Z-transformation of the combined characteristics ; And a Tarufuiruta, in addition to the digital filter after processing the sensor output said is analog-digital converted by the data processing means, is obtained by to obtain the acceleration of the optical disc from the output of the digital filter.

[Work]

In this way, the characteristics of the low-pass filter and the acceleration filter are realized by the digital filter, and the output of the displacement sensor is A / D converted, processed through data, and then passed through the digital filter. Thus, it becomes possible to perform processing at the data stage such as correction of nonlinearity and averaging, and highly accurate acceleration calculation can be performed. Also, by using a digital filter, accurate filter characteristics can be obtained without adjustment.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of an acceleration calculation method for an optical disc inspection apparatus according to the present invention. In the figure, the third
The same parts as those in the figure are designated by the same reference numerals. Reference numeral 8 is a data processing means for performing data processing such as correction of non-linearity and averaging on the output signal Ss of the displacement sensor, and 9 is a digital filter. That is, the output signal Ss of the displacement sensor is
A / D conversion is performed by the A / D converter 6, data processing is performed, and the result is passed through the digital filter 9. Here, the data processing means 8 handles the digitized displacement sensor output and is realized as a part of the function of the computer 7. The characteristic of the digital filter 9 is a combination of the characteristics of the low-pass filter 4 and the acceleration filter 5 described above, and is represented as shown in FIG. Note that fn in the figure is A / D
It is a Nyquist frequency determined by the sampling frequency of the converter 6.

Now, in the digital filter 9, the characteristic corresponding to the analog acceleration filter 5 is as described above: G (s) = ks ² (1) The characteristic corresponding to the low-pass filter 4 is changed by the sixth-order Butterworth When this is approximated and bilinear Z-transformed, the following state transition equation is obtained.

Here, U (K) is input data in the digital filter 9, and Y (K) is output data. If the number of data corresponding to one rotation of the optical disc 1 is N, K is an integer from 1 to N. Further, c ₀ and ci, di are obtained as in the following equation.

b ₀ = a ₀ / ωc ⁶ a ₀ = ωc ⁶ b ₁ = a ₁ × h / ωc ⁶ a ₁ = ωc ⁵ (a + b + c) b ₂ = a ₂ × h ² / ωc ⁶ a ₂ = ωc ⁴ (3 + ab + bc + ac) b ₃ = a ₃ × h ³ / ωc ⁶ a ₃ = ωc ³ {2 (a + b + c) + abc} b ₄ = a ₄ × h ⁴ / ωc ⁶ a ₄ = ωc ² (3 + ab + bc + ac) b ₅ = a ₅ × h ⁵ / ωc ⁶ a ₅ = ωc (a + b + c) b ₆ = a ₆ × h ⁶ / ωc ⁶ a ₆ = 1 ωc = 2πfc, h = 2 / TT: sampling period d ₀ = 1 × kh ² d ₁ = 2 × kh ^{_{2 d 2 = -1 × kh 2}} d 3 = -4 × kh 2 d 4 = -1 × kh 2 d 5 = 2 × kh 2 d 6 = 1 × kh 2 Accordingly, the digital filter based on these values By configuring the above, the digital filter 9 having the characteristics as shown in FIG. 2 can be realized. Although the gain is reduced at the Nyquist frequency fn, this frequency is out of the usable range of the digital filter 9, so that there is no problem in operation.

In this way, when the characteristics of the low-pass filter 4 and the acceleration filter 5 are realized by the digital filter 9, the output signal Ss of the displacement sensor can be A / D converted in advance,
Processing such as correction of nonlinearity and averaging of the output signal Ss can be performed in the data stage. Therefore, the acceleration calculation can be performed using the preprocessed measurement data, and the highly accurate acceleration calculation can be performed. Further, since the characteristics of the digital filter 9 are specified by numerical values, accurate filter characteristics can be obtained without adjustment.

In the above description, the case where the characteristic of the low-pass filter 4 is approximated by the sixth-order Butterworth is exemplified.
The approximate expression is not limited to this. Further, the conversion from analog to digital for forming the digital filter 9 is not limited to bilinear conversion.

〔The invention's effect〕

As described above, in the acceleration calculation method for the optical disc inspection apparatus of the present invention, the servo lens displaces the condenser lens in the tracking direction and the focus direction to maintain the reading state of the optical disc, and the displacement amount of the condenser lens at this time. In the optical disc inspection device that detects the displacement sensor to obtain a signal corresponding to eccentricity or shake in the optical disc and calculates the acceleration of eccentricity or shake from this sensor output, A / D that converts the sensor output into A / D A D converter, a data processing means for processing the A / D converted sensor output, and a digital filter having a characteristic of integrating a low pass filter and an acceleration filter, and the A / D converted sensor output Since the data is processed by the data processing means and then passed through the digital filter, the displacement sensor Respect of output, such as correction and averaging of nonlinearity enables processing at data phase,
It is possible to realize an acceleration calculation method for an optical disc inspection apparatus that can perform highly accurate acceleration calculation. Also, by using a digital filter, accurate filter characteristics can be obtained without adjustment.

[Brief description of drawings]

1 and 2 are configuration diagrams and frequency characteristic diagrams showing an embodiment of an acceleration calculation method for an optical disc inspection apparatus according to the present invention, and FIGS. 3 and 4 are examples of acceleration calculation methods for a conventional optical disc inspection apparatus. 3 is a configuration diagram and a frequency characteristic diagram showing FIG. 1 ... Optical disc, 2 ... Spindle motor, 3 ... Optical head, 4 ... Low-pass filter, 5 ... Acceleration filter, 6 ... A / D converter, 7 ... Computer, 8 ... Data processing means, 9: Digital filter.

Claims (1)

[Claims] 1. A servo mechanism is used to displace the condenser lens in the tracking direction and the focus direction to maintain the reading state of the optical disc, and the displacement amount of the condenser lens at this time is detected by a displacement sensor to detect eccentricity or shake of the optical disc. In an optical disk inspection device which obtains a corresponding signal and calculates acceleration of eccentricity or shake from this sensor output, an analog / digital converter for analog / digital converting the sensor output, and a digital signal by this analog / digital converter. A bilinear Z characteristic is obtained by combining data processing means for processing the converted sensor output, a low-pass filter and an acceleration filter whose transfer function G _(S) is represented by ks ² (k: displacement-acceleration conversion constant). And a digital filter obtained by conversion. In addition to the digital filter after processing by Gu digital conversion data processing means of the sensor output, the acceleration calculation method of an optical disc inspection device is characterized in that so as to obtain the acceleration of the optical disc from the output of the digital filter.