JPH0617784B2 - Automatic output control device for optical sensor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic output control circuit for stabilizing the amount of light in an optical sensor having a light projector and a light receiver. In the present invention, the APC circuit means an automatic output control circuit. The optical sensor is, for example, an optical scratch sensor.

2. Description of the Related Art An optical sensor that inspects the surface condition of an object to be measured emits light of a certain intensity from a projector, receives the light reflected or transmitted from the object to be measured, and analyzes changes in the amount of light received. To determine the surface condition. If the amount of light cannot be stabilized, not only accurate measurement is not possible, but when measuring the surface condition of an object with a large amount of optical noise, for example, the surface condition of the polishing surface, there is a large disturbance in the amount of received light and it is necessary to determine an abnormal part. Complex processing is required, processing time becomes long, and processing equipment becomes complicated. Therefore, basically, the projected light amount and the received light amount must be stable.

A negative feedback technique is used to stabilize the amount of light in a reflective or transmissive optical sensor. In that case, the light of the projector is detected by a monitor light receiver arranged near the projector, and the drive output of the projector is controlled according to the amount of the detected light. Further, even if the monitor light receiver is not provided, the same control can be performed according to the amount of light detected by the original light receiver. These techniques are disclosed, for example, in JP-A-59-5.
2889 or JP-A-61-192044.

Problems to be Solved by the Invention When the light intensity is controlled by the monitor light receiver provided on the light emitter side, the light intensity can be controlled to be constant, but the light intensity greatly changes according to the surface reflectance or transmittance of the DUT. Therefore, accurate measurement becomes difficult. For example, in the case of a distance sensor that triangulates the distance to the object to be measured depending on the light receiving position of the reflected light from the surface of the object to be measured, such a variation in the amount of received light significantly lowers the measurement accuracy.

On the other hand, when the amount of light is detected by the original light receiver, the actual amount of light projected by the light projector cannot be monitored. Therefore, the amount of light projected may increase abnormally depending on the condition of the object to be measured, which shortens the life of the light projector.

Even if the amount of light is stabilized by the negative feedback technique, information that represents the change in the surface state of the object to be measured must not be suppressed at the same time.

The object of the present invention is, without harming the life of the floodlight,
An object of the present invention is to provide an automatic output control device for an optical sensor, which stabilizes the projected light amount and the received light amount, and does not suppress the change in the received light amount that represents the change in the surface state of the object to be measured.

Means for Solving the Problems The present invention relates to an optical sensor having a light transmitter and a light receiver, a monitor circuit including a monitor light receiver for detecting the light projection amount of the light projector, and the light projector according to the light projection amount detected by the monitor circuit. A first APC circuit that controls the drive output of the drive circuit, a light receiving circuit that detects the amount of light received by the light receiver, and a second APC circuit that controls the drive output of the projector drive circuit according to the amount of light received detected by the light receiving circuit. It is premised on an automatic output control device of an optical sensor provided with.

In such a device, this object is achieved according to the invention as follows. That is, a circuit that limits the amplitude of the signal is provided on the output side of the second APC circuit.

The same purpose can be achieved by providing a circuit for limiting the gradient of the signal on the output side of the second APC circuit.

Further, the same purpose can be achieved by providing both the circuit for limiting the amplitude of the signal and the circuit for limiting the gradient on the output side of the second APC circuit. The purpose is then to connect a circuit for limiting the amplitude of the signal and a circuit for limiting the gradient in series. However, both circuits may be connected in parallel.

Here, the circuit that limits the amplitude of a signal is, for example, a limiter, which limits a signal that exceeds a predetermined level, a signal that falls below a predetermined level, or both. On the other hand, the circuit that limits the gradient of the signal is, for example, a low-pass filter or an integrator.

Further, in the above-mentioned device of the present invention, the output of the first APC circuit and the output of the amplitude limiting circuit and / or the gradient limiting circuit are added as an appropriate ratio, and the signal is output to the projector drive circuit. Is provided.

The projector, the monitor circuit, the first APC circuit, and the projector drive circuit form, so to speak, a first negative return loop.
On the other hand, the light emitter, the light receiver, the light receiving circuit, the second APC circuit, and the light emitter drive circuit form a second negative feedback loop. Therefore, the automatic output control device according to the present invention functions as a light quantity stabilizing circuit having a double negative feedback loop. Therefore, the amount of light projected and the amount of light received are stabilized by these negative feedback loops.

When the amount of received light is stabilized, the change in the amount of received light that includes information on the surface state is suppressed at the same time. Therefore, the second of these double negative feedback loops has a signal in that loop. Includes circuitry to limit the amplitude or slope of.
As a result, changes in the signal having a predetermined value or more or a signal having a predetermined speed or more are not suppressed. According to the present invention, the occurrence of these large amplitudes or the occurrence of high-speed changes is determined to be the surface abnormality, and therefore the apparatus according to the present invention can clearly determine the surface abnormality.

Description of Embodiments The illustrated embodiment shows an example in which the present invention is applied to a distance sensor that measures the distance between the sensor and the DUT 1 by a so-called triangulation method. At the same time, it is possible to inspect the surface of the DUT 1 for scratches.

The sensor is provided with a light projector composed of a laser element 2 and a light receiver composed of a position detection element 3 facing the object to be measured. A monitor light receiver for receiving a part of the laser light is arranged near the laser element 2, and the monitor light receiver is composed of a photodiode 4.

In the embodiment shown in the figure, the output of the photodiode 4 is
It is supplied to the first APC circuit via an amplifier (not shown). Here, the first APC circuit is simply configured as a differential amplifier 6, and the light-emission-amount reference voltage VR1 is supplied to the other input terminal of this differential amplifier. The output of the differential amplifier 6 is supplied to the first input terminal of the weight addition circuit 5.

Most of the laser light strikes the DUT 1, is reflected there, and reaches the position detection element 3. The position detection element 3 has two output terminals, and when light hits the center of the position detection element 3, two output terminals produce outputs of the same magnitude, and one output terminal is output depending on the position where the light hits. Produces a larger output from the other output terminal. This allows so-called triangulation. That is, assuming that the output of one output terminal is V1 and the output of the other output terminal is V2, (V1-
V2) / (V1 + V2) can be used as distance data. Further, V1 + V2 is light quantity data, which is used for inspecting a flaw on the surface of the DUT 1.

In order to perform the above calculation, the output of the position detection element 3 is supplied to the calculation circuit 10 via the amplifiers 8 and 9, respectively.
At this time, since the output of the position detecting element is supplied as a current value here, the amplifiers 8 and 9 perform current-voltage conversion. A predetermined calculation is performed in the arithmetic circuit 10, the distance and the surface flaw are determined, and the result is displayed on a display (not shown).

The outputs of the amplifiers 8 and 9 are added by the adder circuit 11 and are supplied to the second APC circuit composed of the amplifier 12 again. In that case, it is obvious that the addition may be performed in the arithmetic circuit 10. The differential amplifier 12 forms the difference between the added voltage and the received light amount reference voltage VR2. According to the embodiment shown in FIG. 1, this difference is supplied to the second and third input terminals of the weighting circuit 5 via the amplitude limiting circuit 13 on the one hand and the gradient limiting circuit 14 on the other hand. It

In the present embodiment, the amplitude limiting circuit 13 is composed of two limiters having an upper limit value and a lower limit value, but may be composed of, for example, one limiter having a lower limit value.

On the other hand, although the gradient limiting circuit 14 is composed of a low-pass filter, it is obvious that it may be configured as an integrator, for example.

The weight addition circuit 5 is supplied to the output of the first differential amplifier 6 supplied to the first input terminal, the output of the amplitude limiting circuit 13 supplied to the second input terminal, and the third input terminal. The output of the gradient limiting circuit 14 is added as an appropriate ratio. At this time, by properly selecting this ratio, the feedback ratios of the two feedback loops can be appropriately selected, and, for example, the second feedback loop
Alternatively, if the weight of the signal supplied to the third input terminal is set to 0, a device having only one of the amplitude limiting circuit 13 and the gradient limiting circuit 14 is realized.

The output terminal of the weight adding circuit 5 is connected to the control input terminal of the projector driving circuit 7, and the projector driving circuit 7 depends on the outputs of the differential amplifier 6, the amplitude limiting circuit 13, and the gradient limiting circuit 4 to cause the laser The element 2 is driven.

In the embodiment shown in FIG. 2, the amplitude limiting circuit 13 and the gradient limiting circuit 14 are connected in series. Therefore, the output terminal of the differential amplifier 12 is connected to the second input terminal of the weight adding circuit 5'via the amplitude limiting circuit 13 and the gradient limiting circuit 14. The other points are the same as those of the embodiment shown in FIG. Second
In the illustrated embodiment, it is more sensitive to abnormal signals than that of FIG. Which one is applied may be selected according to each condition.

Effect According to the automatic output control device of the present invention, the light projecting amount and the light receiving amount of the optical sensor can be remarkably stabilized, and at the same time, the life of the projector is not damaged.

In the case of the reflection type sensor, even if the measured object has a poor surface roughness (polished surface, cast surface, etc.), the object whose surface color changes, or the object having a curved surface, minute scratches or surface abnormalities Since it can be clarified, the scratch discrimination process can be simplified and speeded up.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of an automatic output control device according to the present invention, and FIG. 2 is a block diagram showing a part of the same second embodiment. 1 ... Object to be measured, 2 ... Laser element, 3 ... Position detection element, 4 ... Photodiode, 5 ... Load addition circuit,
6, 12 ... APC circuit, 7 ... Emitter drive circuit, 8,
9 ... Amplifier, 10 ... Arithmetic circuit, 11 ... Addition circuit,
13 ... Amplitude limiting circuit, 14 ... Gradient limiting circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H05B 37/02 D 8715-3K

Claims (3)

[Claims] 1. An optical sensor having a light transmitter and a light receiver, wherein a drive circuit of a light emitter drive circuit is controlled according to a monitor circuit including a monitor light receiver for detecting the light emission amount of the light emitter, and the light emission amount detected by the monitor circuit. A first APC circuit, a light receiving circuit that detects the amount of light received by the light receiver, and a second APC circuit that controls the drive output of the light projector drive circuit according to the amount of light received detected by the light receiving circuit; A
A circuit that limits the signal amplitude is provided on the output side of the PC circuit.
A weight addition circuit is provided to add the output of the first APC circuit and the output of the amplitude limiting circuit provided on the output side of the second APC circuit as an appropriate ratio and output the signal to the projector drive circuit. An automatic output control device for an optical sensor. 2. An optical sensor having a light emitter and a light receiver, wherein a monitor circuit including a monitor light receiver for detecting the light projection amount of the light emitter, and a drive output of a light emitter drive circuit in accordance with the light projection amount detected by the monitor circuit. A first APC circuit, a light receiving circuit that detects the amount of light received by the light receiver, and a second APC circuit that controls the drive output of the light projector drive circuit according to the amount of light received detected by the light receiving circuit; A
A circuit that limits the gradient of the signal is provided on the output side of the PC circuit.
A weight addition circuit is provided to add the output of the first APC circuit and the output of the gradient limiting circuit provided on the output side of the second APC circuit as an appropriate ratio and output the signal to the projector drive circuit. An automatic output control device for an optical sensor. 3. An optical sensor having a light transmitter and a light receiver, wherein a drive circuit of a light emitter drive circuit is controlled in accordance with a monitor circuit including a monitor light receiver for detecting the light emission amount of the light emitter and the light emission amount detected by the monitor circuit. A first APC circuit, a light receiving circuit that detects the amount of light received by the light receiver, and a second APC circuit that controls the drive output of the light projector drive circuit according to the amount of light received detected by the light receiving circuit; A
A circuit for limiting the amplitude of the signal and a circuit for limiting the gradient of the signal are provided on the output side of the PC circuit, and the amplitude limiting circuit provided on the output side of the first APC circuit and the output side of the second APC circuit, An automatic output control device for an optical sensor, comprising a weight addition circuit for adding outputs of a gradient limiting circuit as an appropriate ratio and outputting the signal to a projector driving circuit.