JPS6019570B2 - optical information reader - Google Patents

Description

[Detailed description of the invention] The present invention relates to a device for collecting optical information.

Conventionally, in a device that reads recorded information by converging a light beam into a minute spot 3 using a converging lens 2 and irradiating it onto a recording disk 4, a focal point is used to keep the diameter of the spot 3 constant as shown in FIG. In order to perform control, the light beam 1 is directed off the optical axis P of the converging lens 2, enters the converging lens 2, is reflected by the recording disk 4, and then passes through the converging lens 2 again.
After the light is incident on the photoelectric element 5 having at least two light receiving surfaces 5a, 5b, the two light receiving surfaces 5a, 5
A device is known that detects the positional deviation between the reading spot 3 and the recording disk 4 based on the output difference between the reading spot 3 and the recording disk 4.

However, in this type of device, when the position of the recording disk 4 changes in the optical axis direction, the optical path length changes, so the size of the beam spot 6 on the photoelectric element 5 changes. Due to conditions such as the shape of the light beam 6 being a circle or ellipse, or the light intensity distribution of the light beam 1 being uneven, the light reception may vary depending on the displacement of the recording disk 4 in the direction of the optical axis P. Even if the optical axis of the light beam 1 moves linearly on the surfaces 5a and 5b, the light receiving surface 5a
, 5b is not linear.

That is, as shown in FIG. 2, the change in the differential output v of the photoelectric element 5 with respect to the position x (focal shift) of the recording disk 4 is not linear, and in many cases appears asymmetrically with respect to the reference potential. Note that the position x=o in FIG. 2 is the position of the recording disk 4 where the focus was. Such a relationship means that the gain of the focus control system is not constant, making it difficult to perform good focus control. Therefore, in the present invention, the difference output v is passed through a nonlinear amplifier to obtain a linear output, thereby enabling accurate focus control.

Examples of the present invention will be described below.

Now, as shown in FIG. 1b, the two light receiving surfaces 5 of the photoelectric element 5
It is assumed that when the beam spot 6 is present at the center of a and 5b, it is in a focused state (the diameter of the discussion spot 3 on the recording disk 4 is the smallest).

When the focus shifts, the difference output v of the photoelectric element 5 with respect to the focus shift exhibits a nonlinear curve passing through the origin o as shown in FIG. If v loses its linearity near the origin o as shown in Figure 3, first determine whether the differential output is larger or smaller than o, and in each case, consider It is sufficient to obtain a linear lid output using the linear amplifier 7. That is, as shown in FIG. 4, the difference output v is sent to the comparator c,
and compares it with the o volt potential, and if it is a positive potential, the analog switch S. ○N, the amplifier A outputs the difference output v amplified by n times, and in the case of a negative potential, the analog switch S2 is turned to ○N via the inparator 1, and thereby the amplifier A outputs the difference output v which is amplified by n times. An amplified difference output v is outputted, and the difference output v is made approximately linear as a whole depending on the difference in the degree of amplification n. Then, the output from the nonlinear amplifier 7 is inputted to a converging lens driving device 8 to move the converging lens 2 in the direction of the optical axis P and control the diameter of the reading spot 3 to be kept constant. If the difference output v loses its linearity at point B' as shown in Figure 5a, first bias the difference output v at the adder D, and then at point B' as shown in Figure 5b. Shift to point B' so that output b becomes o.

Next, this output is compared with the o potential by the comparator C2, and as mentioned above, the analog switches S3 and S4 of the differential output multiplied by the amplifiers A3 and A4 are connected to the output from the comparator C2 and the output via the inverter 12. The output of the non-linear amplifier 9 is outputted after being linearly corrected as shown in FIG. 5c. Note that the output obtained here is then biased by the adder D2 in the converging lens driving device 10 to be used as an actual focus control signal.
It is preferable that the signal be converted into a signal passing through the origin o as shown in FIG. d.

In addition, the methods shown in FIGS. 7 and 8 can be considered as correction means when linearity is lost at point B as shown in FIG. 5a.

That is, as shown in FIG. 7b, one of the differential outputs v is amplified twice by the amplifier A5, and the other is amplified by the amplifier A6.
It will be amplified twice as much.

Then, each signal may be biased by adders D3 and D4 to obtain a substantially linear output as shown in FIG. 7c. However, the switching of the amplification factor at point B is performed by comparing the differential output v with the voltage b at point B by the comparator C3, thereby switching the analog switches S5 and S6. The signal obtained here is biased by the adder D5 of the converging lens driving device 12 as described above, and converted into a signal passing through the origin o in FIG. 7d, which is used for later focus control.

Further, as shown in FIG. 9a, the two light receiving surfaces 5a of the photoelectric element 5,
If it is specified that the beam spot 6 is at a position slightly deviated from the dividing line 5b so that the focus coincides with the beam spot 6, the difference output v appears as shown in FIG. 9b.

In this case as well, the difference output v can be corrected in the same way as in the above embodiment. For example, if the position where linearity is lost is point B or point C, the correction can be performed using the circuits shown in FIGS. 6 and 8. I can do it. The present invention is as described above, and in particular, the difference output from two light receiving sections is amplified by two different amplification factors.
and a switching means for inputting the output of one of the amplifiers to the converging lens driving device based on the output of the comparator. , it is possible to drive a converging lens by substantially linearly correcting a complex non-linear differential output, and therefore it is possible to perform easy and accurate focus control.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing the optical system for focus detection, where a is a light beam path diagram and b is an explanatory diagram showing the movement of the beam spot on the photoelectric element, when it is in focus when located at the center. , FIG. 2 is a diagram showing an example of the difference output with respect to the position of the recording disk 4 in FIG. 1b, FIG. 3 is an enlarged view of FIG. 2, and FIG. The circuit diagram of the embodiment, FIG. 5, shows another example of the differential output in FIG. 1b,
a, b, c, and d are diagrams for explaining the correction process; FIG. 6 is a circuit diagram of a second embodiment that performs the correction in the case of FIG. 5;
7a, b, c, and d are diagrams for explaining the correction process in the diamond output of FIG. 5a, and FIG. 8 is a circuit diagram of a third embodiment that performs the correction in the case of FIG. Figure 9 shows two photoelectric elements.
The figure shows the case where the beam spot is focused at a shifted position on one of the light-receiving surfaces, where a shows the movement of the beam spot, and b shows the differential output. 1... Light beam, 2... Converging lens,
3...reading spot, 4...recording disc,
5...Photoelectric element, 5a, 5b... Light receiving surface,
7,9,1 1....・Nonlinear amplifier, 8, 10,
12... Converging lens driving device, A,...
...Amplifier, C. ...Computer, P.
...Convergent lens. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9

Claims (1)

[Claims] 1 A light beam is focused on a minute reading spot by a converging lens and irradiated onto the recording disk to read the recorded information, and at the same time the light beam is shifted from the optical axis of the converging lens and is incident on this converging lens to be read by the recording disk. an optical system that detects a positional deviation between the reading spot and the recording disk based on the differential output from the two light receiving sections, by reflecting the light and making it incident on the converging lens again and then on a photoelectric element having at least two light receiving sections; a comparator that compares the differential output with a reference potential; and a comparator that amplifies the differential output with a different amplification factor.
and a switching means for inputting the output of one of the amplifiers in the comparator to the driving device of the convergent lens. Information reading device.