JPH0495805A - Optical displacement detector - Google Patents

Abstract

PURPOSE:To improve the detecting accuracy of an optical displacement detector by providing a detecting means for detecting the sum of amplifying signals output from each amplifier, and a setting means for setting the amplifying ratio to hold the sum approximately constant for each amplifier. CONSTITUTION:An amplifying signal detecting part 9 is provided with an adder 23, an amplifier 25 and an A/D converter 27. A feedback ratio setting part 11A is comprised of a multiplexer 31 and eight resistors R1, R2,..., R8. When a signal of each element 1A-1D of a four-dividing photodetector 1 is amplified by each negative feedback amplifier circuit 3, a signal diverged from the output of the circuit 3 is added at 23 and amplified at 29. In this manner, a signal related to the sum of the outputs of each circuit 3 is obtained. The quantity of light of a luminous flux of an inspecting light reaching the device 1 differs depending on the reflectivity of an object to be measured. Since the feedback ratio is set for each circuit 3 so that the quantity of light appears constant even if the detecting quantity of light of the device 1 is changed, the errors due to the change of the quantity of light can be compensated without using a subtracter. Accordingly, the inspecting accuracy is improved more.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical deviation detector, and more specifically, each element of a divided light-receiving element receives and outputs a beam of inspection light. The present invention relates to an optical deviation detector that detects deviation based on an output signal.

[Prior Art] As a conventional optical deviation detector, there is a focus error detector used in a focusing servo mechanism to which an astigmatism method is applied, for example. The focus error detector is mainly composed of a four-part light receiving element and an arithmetic circuit. The action is as follows.

First, a beam of inspection light reflected from the object to be measured is converged through an objective lens, and the converged light is passed through a cylindrical lens. Then, the light that has passed through the cylindrical lens is received by a four-part light receiving element.

Next, the output signals received and output by each element of the four-division light-receiving element are amplified, and each amplified signal is calculated by an arithmetic circuit. The arithmetic circuit adds or subtracts each amplified signal. The signal passed through this arithmetic circuit is output as a focus error signal. Since the magnitude of the focus error signal obtained in this way corresponds to the shift in focus of the objective lens with respect to the object to be measured, it is possible to adjust the focus based on the focus error signal.

This focus error signal includes an error caused by, for example, a difference in the reflectance of the surface of the object to be measured. The difference in reflectance changes the amount of light received by the four-split light receiving element, which in turn changes the magnitude of the focus error signal.

Conventionally, a divider is added after the arithmetic circuit to compensate for this error. A signal obtained by further dividing the signal from the arithmetic circuit by the sum of the amplified signals of each element is output as a focus error signal. By the above-mentioned division, it is possible to apparently eliminate a change in the amount of light received by the four-part light-receiving element due to a difference in reflectance on the surface of the object to be measured, and a focus error signal in which the above-mentioned error is compensated can be obtained.

[Problems to be Solved by the Invention] As described above, the conventional focus error detector described above can compensate for errors using a divider, but there is a problem in that it is difficult to further improve detection accuracy.

This is because the accuracy of the divider is generally not high, which prevents improvement in detection accuracy that depends on the accuracy of the divider. However, even if the change in the amount of light received by the four-part light receiving element is suppressed by simply controlling the amount of light emitted from the light source, the adjustment range of the amount of light emitted is narrow depending on the light source, so it may not be possible to sufficiently compensate for errors. Furthermore, in order to adjust the amount of light emitted, a large current is passed through the light source, which shortens the life of the light source.

The optical deviation detector of the present invention aims to solve the above problems and improve the detection accuracy of this type of optical deviation detector.

Configuration for Chu [Means for Solving the Problems] The optical deviation detector of the present invention is characterized in that each element of a divided light receiving element whose light receiving surface is divided into a plurality of regions receives and outputs a beam of inspection light. An optical deviation detector that amplifies the output signal with an amplifier provided corresponding to each element, calculates the amplified signal output from each amplifier with an arithmetic circuit, and outputs a signal according to the deviation. amplified signal sum detection means for detecting the sum of amplified signals outputted by each of the amplifiers; and an amplification factor that keeps the sum substantially constant based on the sum of the amplified signals detected by the amplified signal sum detection means; The apparatus is characterized in that it includes an amplification factor setting means for setting each of the amplifiers.

[Function] In the optical deviation detector of the present invention having the above configuration, each element of the divided light receiving element receives a beam of inspection light and outputs an output signal, which is amplified by an amplifier. During this amplification, the amplified signal sum detection means detects the sum of the amplified signals output from each amplifier. Then, based on the total sum of the detected amplified signals, the amplification factor setting means sets an amplification factor for each amplifier to keep the above-mentioned sum substantially constant. Each amplifier amplifies the output signal of each element based on the amplification factor thus set. The arithmetic circuit operates on the amplified signals output from each amplifier, and outputs a signal corresponding to the deviation. In other words, even if the intensity of the beam of inspection light that reaches the divided light-receiving element changes due to differences in the reflectance of the object to be measured, the amplification factor is such that the sum of the amplified signals amplified by each amplifier remains constant. Depending on the settings,
An output equivalent to a constant amount of received light can be obtained without using a divider.

[Example] As an example of the optical deviation detector of the present invention, a focus error detector used in a focusing servo mechanism to which an astigmatism method is applied will be described below.

FIG. 1 shows a circuit diagram of a focus error detector according to an embodiment. As shown in the figure, the focus error detector includes a four-part light receiving element 1, four negative feedback amplifier circuits 3, and an arithmetic circuit 5.
, an output section 7, an amplified signal summation inspection section 9, and a feedback rate setting section]1.

4-division light-receiving element] is four light-receiving elements IA and IB.

It is made by combining IC and ID on a matrix.

Each of the four negative feedback amplifier circuits 3 is an operational amplifier] 3,
Feedback rate setting section 1]. Each operational amplifier 13A, 1
The negative input terminals of 3B, 13C, and 13D are connected to the output lines of each element A, 1B, IC, and ID of the four-division light receiving element, respectively.

The feedback rate setting unit] is a feedback circuit of the operational amplifier 13.

The details will be described later.

The arithmetic circuit 5 includes two differential amplifiers 15 and 17 and an adder 1.
It consists of 9. The calculation performed here is shown by the following equation (1).

Se = (Sa + 5c) - (Sb + Sd) - (1)
Here, Se is the output of the arithmetic circuit 5. Sa.

Sb, Sc, and Sd are elements IA, IB, respectively.
Negative feedback amplifier circuits 3A and 3B to which IC and ID are connected.

These are 3C and 3D outputs.

In the arithmetic circuit 5, in order to perform an arithmetic operation equivalent to the above equation (1), a differential amplifier]5 is connected to an adjacent element IA.

Output Sa of negative feedback amplifier circuits 3A and 3B related to 1B.

Outputs the sbO difference. The differential amplifier 17 uses the output Sc of a negative feedback amplifier circuit 3C93D related to another adjacent element IC, ID.
, Sd is output. The adder 19 is formed by connecting the output lines of the differential amplifier] 5 and the differential amplifier 17 in parallel via a resistor, and generates a signal S obtained by adding the outputs of the differential amplifier] 5.17.
Output e.

The output section 7 is a negative feedback amplifier circuit equipped with an operational amplifier 2, and amplifies and outputs the signal Se calculated by the calculation circuit 5.

The amplified signal sum detection section 9 includes an adder 23, an amplifier 25,
An AD converter 27 is provided.

Adder 231, negative feedback amplifier circuits 3A, 3B,
It is formed by connecting branch lines branched from the 3C and 3D output lines in parallel via resistors. Therefore, the adder 23 outputs a signal related to the sum of the outputs of the negative feedback amplifier circuits 3A, 3B, 3C, and 3D.

The amplifier 25 is a negative feedback amplifier circuit including an operational amplifier 29. An adder 23 is connected to the negative input terminal of the operational amplifier 29.
output line is connected. The output line of amplifier 25 is connected to the input terminal of AD converter 27.

The AD converter 27 converts the analog pressure of the amplifier 25 into a 3-bit digital signal. The output lines of the AD converter 27 are negative feedback amplifier circuits 3A, 3B, and 3C.

3D feedback rate setting units 11A, 11B, IIC
, 1] is connected to the input terminal of D.

The feedback rate setting section 11A includes a multiplexer 31 and eight resistors R1, R2, . . . , R8. In the figure, the feedback rate setting unit 11B, IIC, and IID are shown as blocks, but
Each feedback rate setting unit 11A has the configuration shown in the figure. The output line of the AD converter 27 described above is connected to the input terminal of the multiplexer 31. Resistors R1, R2,...
・The resistance values of R8 are different from each other. Then, the resistors R1゜R2,..., R8 and the multiplexer 31 (
The larger the value of the digital signal input to the multiplexer 31, that is, the larger the sum of the outputs of each negative feedback amplifier circuit 3, the smaller the resistance value of the resistor R that the multiplexer 3 connects to the feedback path of the operational amplifier 13. Conversely, the multiplexer 31 is connected in such a manner that the resistance value of the resistor R connected to the feedback path of the operational amplifier 3 increases as the sum of the outputs of the negative feedback amplifier circuits 3 becomes smaller.

The focus error detector having the above configuration operates as follows.

As is conventionally known, the ray bundle of inspection light reaches the 4-split light receiving element through the following path. First, the beam of inspection light reflected from the object to be measured is converged through an objective lens.
The converged light is passed through a cylindrical lens. Since the cylindrical lens functions as a lens only in one direction and does not function as a lens in other directions, it converges the convergent light in one direction and passes the convergent light in the other direction without converging. The light beam that has passed through the cylindrical lens in this way is received by the four-divided light receiving element. If the objective lens is focused on the object to be measured, a circular beam S will appear on the four-split light receiving element as shown in Figure 1, but if it is too close, the beam S will appear as a vertically elongated ellipse, for example. If it's too far away, the image will look like a horizontal oval.

When the four-divided light receiving element receives the beam S of the inspection light that has arrived through such a path, the circuit of the focus error detector having the above configuration behaves as follows. First, we will explain the basic behavior. Each element IA, IB,
The output signals outputted by the IC and ID upon receiving the beam S are amplified by the respective negative feedback amplifier circuits 3A, 3B, 3C, and 3D.

The output signal of each negative feedback amplifier circuit 3 is subjected to arithmetic operations in an arithmetic circuit 5, and further amplified in an output section 7, and outputted as a focus error signal. Specifically, for example, if the focus is correct, a circular beam S will be reflected on the 4-split light receiving element, so the magnitude of the focus error signal after the calculation process equivalent to equation (1) in the calculation circuit 5 is It becomes almost zero. However, if it is too close and, for example, the light beam S is reflected in a vertically elongated ellipse on the four-split light receiving element 1, the magnitude of the focus error signal becomes a magnitude with a positive sign. If the beam S is reflected in a horizontally elongated ellipse on the 4-split light receiving element], the magnitude of the focus error signal becomes a magnitude with a negative sign.

Therefore, by adjusting the distance between the objective lens and the object to be measured so that the magnitude of the focus error signal becomes approximately zero, the objective lens can be focused on the object to be measured.

In this way, a focus error signal is basically obtained, but in the above configuration, each negative feedback amplifier circuit 3 divides each element IA, 1B, and IC of the four-divided light receiving element.

When a 1D signal is amplified, a signal branched from the output of each negative feedback amplifier circuit 3 is sent to the adder 23 of the amplified signal sum detection section 9.
The output of the adder 23 is amplified by the amplifier 29. In this way, a signal related to the sum of the outputs of each negative feedback amplifier circuit 3 is obtained.

The signal related to this sum is converted into a 3-bit digital signal by an AD converter 27. The digital signal is input to the multiplexer 31 of the feedback rate setting section of each negative feedback amplifier circuit 3. , the multiplexer 31 connects the negative resistor R of the eight resistors R1, R2, . . . , R8 to the feedback path of the operational amplifier 13 according to the value of the digital signal. As mentioned above, when the value of the digital signal is large, the resistor R with a small resistance value is connected, and when the value of the digital signal is small, the resistor R with a large resistance value is connected.

Therefore, when the sum of the outputs of each negative feedback amplifier circuit 3 becomes large, the resistor R having a small resistance value is connected, and the feedback ratio becomes large, thereby reducing the sum of the outputs. On the other hand, if the sum of the outputs becomes small, a resistor R having a large resistance value is connected, and the feedback rate becomes small, thereby increasing the sum of the outputs. By switching the resistor R and changing the feedback rate color in this way, the sum of the outputs can be kept substantially constant.

As a result, each element IA is operated by each negative feedback amplifier circuit 3A, 3B, 3C, and 3D with a feedback rate that is kept substantially constant depending on the sum of the outputs.
, IB, IC, and ID are amplified, and a focus error signal is obtained based on the amplified signals.

In other words, even if the intensity of the beam of inspection light that reaches the four-split light receiving element 1 changes due to differences in reflectance of the object to be measured, etc., the feedback rate is set so that the sum of the amplified signals amplified by each amplifier remains constant. Therefore, behavior equivalent to a constant amount of received light can be obtained. Therefore, a focus error signal is obtained in which the error due to the change in the amount of light is compensated for.

According to the focus error detector of the embodiment described above, the light receiving element is divided into four parts due to the difference in reflectance of the object to be measured.]
Even if the amount of the light beam of the inspection light that reaches the test light changes and the amount of light received by the four-division light receiving element changes, a feedback rate is set in each negative feedback amplifier circuit 3 to keep the amount of light apparently constant.
This has the excellent effect of being able to compensate for the error caused by the change in the amount of light without using a divider, and further improving the inspection accuracy. In addition, the light source of the inspection light! Since there is no control, the control circuit for the light source is simple and the life of the light source is long.

Furthermore, in the embodiment, changing the feedback factor is realized by switching the resistor R. Since the resistor R generally has an extremely small inter-solid error, a high quality focus error detector can be realized.

Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments in any way, and it goes without saying that it can be implemented in various forms without departing from the gist of the present invention. For example, an optical disc player has a tracking servo mechanism that allows the pickup to accurately track the recording pits of the optical disc and send and receive laser light. May be applied to vessels. Further, the focusing servo mechanism may utilize the Foucault method and may be applied to a mechanism using divided light-receiving elements in which elements are arranged in a line on the light-receiving surface. Furthermore, the present invention may be applied to an optical force sensor (for example, a 6-axis force sensor) that connects a light source and a 4-split light receiving element with an elastic arm and detects force from minute deviations of the light source.

Effects of the Invention As detailed above, according to the optical deviation detector of the present invention, the amount of light beam of the inspection light reaching the split light receiving element changes due to, for example, a difference in the reflectance of the object to be measured. Even if the amount of light received by the split light-receiving element changes, the amplification factor of the amplifier is set as if the amount of light received was constant, so the effects of the above changes can be eliminated with high precision without using a divider, making inspection easier. This has the excellent effect of further improving accuracy.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a focus error detector as an embodiment of the present invention. 3]... Multiplexer R... Feedback rate switching resistor

Claims (1)

[Claims] 1. Each element of a divided light-receiving element whose light-receiving surface is divided into a plurality of regions receives a beam of inspection light and outputs an output signal, which is amplified by an amplifier provided corresponding to each element. In an optical deviation detector that calculates the amplified signals output from each of the amplifiers in an arithmetic circuit and outputs a signal according to the deviation, an amplified signal that detects the sum of the amplified signals output from each of the amplifiers. It is characterized by comprising: a sum detection means; and an amplification factor setting means for setting an amplification factor for each of the amplifiers to keep the sum substantially constant based on the sum of the amplified signals detected by the amplified signal sum detection means. Optical deviation detector.