JPS6114506A - Optical sensor - Google Patents

Abstract

PURPOSE:To perform optical sensing in the presence of noises due to external light by projecting laser light which has different modulation frequencies upon a work, calculating outputs corresponding to modulation frequencies from reflected light, and calculating their difference. CONSTITUTION:A modulation frequency setting means 14 which sets sections of mutually different modulation frequencies periodically, a means which modulates and projects laser light on the work 5 through said means 15, and the photodetecting means consisting of an interference filter 16, semiconductor position sensor 7, etc., which photodetect reflected light from the work 5 are provided. Further, current-voltage converting circuit 8 and 9 which convert the output of the photodetecting means into an electric signal, filters 17 and 18 which are connected to the circuits 8 and 9 to pass a signal of modulation frequency f1, output sample means 19 and 20 which receive outputs of the filters 18 and 19 and detect an output A corresponding to a section of frequency f1 and an output B corresponding to a section of frequency f2, and an arithmetic means 23 which calculates the difference between the outputs A and B are provided. Then, a filter 16 cuts off the majority of arc light to prevent the sensor 7 and electric signal converting circuits 8 and 9 connected thereto from being saturated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical sensor for arc welding.

Conventional Structure and Problems The biggest problem with conventional optical sensors for arc welding is that detection accuracy is reduced due to the influence of arc light noise.

FIG. 1 shows a conventional example of an optical distance sensor that detects the distance to an object to be welded (hereinafter referred to as a work) in a non-contact manner. 1 is a 10-track modulation circuit, 2 is a drive circuit that drives the laser diode 3, 4 is a collimator lens that focuses the output light of the laser diode 3 into a spot light, 5 is a workpiece, 6 is a condensing lens, 7 is a semiconductor position sensor ( PSD)
, s and 9 are current-voltage conversion circuits composed of operational amplifiers, 1
0 and 11 are 10% band-pass filters made up of operational amplifiers, etc., 12 and 13 are addition circuits and subtraction circuits made up of operational amplifiers, etc., and 14 is an analog division circuit. The principle of distance detection in this example is as follows. When a laser spot light modulated to 10kl (Z) is irradiated onto the workpiece 5 and the image is received by the PSD 7, the PS
A photocurrent corresponding to the imaging position of D ends flows out from the output terminal of the PSD 7. This is converted into voltage by current-voltage conversion circuits 8 and 9, and then passed through 10 band-pass filters 10 and 11 to cut disturbance light noise such as normal illumination light, and laser light modulated to 10%. Extract only the signal. By taking the sum and difference of each of these outputs and dividing the sum by the difference, the PSDT
The imaging position above can be determined. Therefore, the displacement of the workpiece 6 can be detected as a displacement of the imaging position of the spot light on the PSDY, so the distance to the workpiece 5 can be detected.

However, in the case of arc light, the intensity is much stronger than that of normal illumination light, and as shown in Figure 2, its frequency components exist up to the laser modulation frequency range, so the In conventional methods and circuits, the signal output after passing through a band-pass filter is a combination of laser light components and arc light components, as shown in Figure 2, resulting in a decrease in detection accuracy. . Note that the modulation frequency cannot be increased above about 30 klb due to limitations in the response characteristics of the PSD.

Therefore, it has been difficult to apply conventional optical sensors to arc welding.

OBJECTS OF THE INVENTION The present invention aims to eliminate the above-mentioned drawbacks of the conventional technology, and particularly aims to enable optical sensing in an environment with large disturbance light noise such as arc light.

Structure of the Invention In order to achieve this object, the present invention includes a modulation frequency setting means for periodically setting sections of different modulation frequencies f and 12 sections, and a laser beam modulated by the modulation frequency setting means to control the workpiece. a light projecting means for projecting light to;
a light receiving means for receiving reflected light of the laser beam from the workpiece; an electrical signal converting means for converting the output of the light receiving means into an electrical signal; and a filter connected to the electrical signal converting means and passing the modulation frequency 11; Output (A) corresponding to the section of the modulation frequency 11 among the outputs of the filter
and output sampling means for detecting the output (B) corresponding to the section of the modulation frequency 12;
This optical sensor is composed of a calculation means (1) for calculating the difference between the light receiving means B and a calculation means (II) for calculating the imaging position of the laser beam of the light receiving means B from the output of the calculation means (1).

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to FIGS. 3 to 5 of the drawings. Components that are the same as those in FIG. 1 are given the same numbers and their explanations will be omitted. In FIG. 3, 15 is a modulation frequency setting means (modulation circuit), 16 is an interference filter, 17.18
is a band pass filter, 19.20 is a sample hold circuit, 21.22 is an A/D conversion circuit, and 23 is a calculation means (
Microco/Vita). The modulation frequency setting means 15 sets the modulation frequency f, an example of which is shown in FIG.
In order to set a modulation frequency that is a combination of '=30kJh and a modulation frequency of 12-1kHz+, it is composed of an oscillation circuit, a counter circuit, and a gate circuit. The light emitting means has a wavelength of 830n.
It consists of a laser diode 3 which generates a laser beam of m, a drive circuit 2 which drives them, and a collimator lens 4 which focuses the laser beam to 0.8 φ. The light receiving means is a convex lens 6 with a fish collecting distance of 30 mm and a light receiving device of 810 nm to 840 nm.
Interference filters and PSD that pass light with a wavelength of nm
It is composed of the end and the end. This interference filter 16 can cut most of the arc light as shown in FIG.
It is possible to prevent saturation of the PSD 7 and the electric signal conversion circuit connected thereto, and to dramatically improve the S/N of laser light with respect to arc light. The electrical signal conversion means is
It consists of current-voltage conversion circuits FNr8 and FNr9 made up of operational amplifiers and the like. The filter consists of sample-and-hold circuits 19 and 20 that sample and hold the output of a band filter composed of an operational amplifier, etc. signal is output from the microcomputer 23) and high-speed 8-bit A/
D conversion circuits 21 and 22 (The A/D start timing is set by the microcomputer 23, but it can also be configured by an analog circuit. The microcomputer 23 detects the current modulation frequency from the modulation frequency setting means 15, Outputs the timing of the output sampling means.Also, modulation frequency f1=30k)h interval (fifth
A/D conversion value v1f1 in the (tl-t3) interval in the figure)
v2f2 and modulation frequency f2=A/D conversion value v1f2 in the section of one song (section t3 in FIG. 5). v2f2, (vlfl-v1f2)=Δv1, (v2f1-
■ Perform subtraction geography of 2f2)=Δv2. Through this process, 30kHi of arc light passed through the Norichi interference filter.
The component (RP in Figure 2) can be cut. That is, in the section where the modulation frequency f1 = 3ok, what passes through the bandpass filter is the laser light modulated to 30klk,
The same (arc light with a frequency component of 30 klb).

In the interval f2=1k)h, only the arc' light having 30 frequency components passes through the bandpass filter. Therefore, by subtracting the bandpass output value in this image frequency range as described above, arc light noise can be removed. From ΔV and Δv2 obtained in this way, (Δv1-Δv2)/(Δv1+ΔV2) = X
By performing this calculation process, the image formation position (X) on the PSDT of the laser beam projected onto the workpiece 5 can be detected regardless of fluctuations in the amount of received light, and the distance between the workpiece and this sensor can be detected. Can be done. Regarding the sampling process of the output value of the bandpass filter, it is also effective to capture data multiple times and use the average value.
These can be easily done by using the microcomputer 23.

When the sensor of the present invention was used to measure the distance to the workpiece near the TIG arc light, it was found that at an arc current of 3ooA,
It was possible to detect up to 15 gourds in front of the arc. In the conventional sensor shown in FIG. 1, the distance is more than 600.

Effects of the Invention It becomes possible to detect the joint shape. If this sensor is installed in an arc welding robot or automatic welding equipment, it will be possible to accurately and quickly detect welding thermal distortion and joint fluctuations. The effect is like a dog.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional optical sensor, Fig. 2 is a frequency analysis characteristic diagram of arc light and laser light, Fig. 3 is a block diagram of an embodiment of the optical sensor according to the present invention, and Fig. 4 is an interference filter. FIG. 5 is a frequency analysis characteristic diagram showing an example of the arc light cutting effect according to the present invention, and FIG. 5 is an output characteristic diagram showing an example of laser light modulation in the optical sensor of the present invention.

Claims (5)

[Claims] (1) a modulation frequency setting means for periodically setting a section of different modulation frequencies f_1 and a section of f_2; a light projection means for modulating a laser beam by the modulation frequency setting means and projecting the light onto the workpiece; a light receiving means for receiving reflected light of the laser beam from the object to be welded; an electrical signal converting means for converting the output of the light receiving means into an electrical signal; and a filter connected to the electrical signal converting means and passing the modulation frequency f_1. , output sampling means for detecting an output (A) corresponding to the section of the modulation frequency f_1 and an output (B) corresponding to the section of the modulation frequency f_2 among the outputs of the filter; and the output (A) and the output. Calculating means (I) for calculating the difference between (B)
and a calculation means (II) for determining the imaging position of the laser beam on the light receiving means from the output of the calculation means (I). (2) The optical sensor according to claim (1), wherein the light projecting means includes a collimator lens and a laser diode. (3) The optical sensor according to claim (1), wherein the light receiving means is constituted by a condensing lens, an interference filter that passes the wavelength of laser light, and a semiconductor position sensor (PSD). (4) The output sample means is a sample hold circuit and an A/
An optical sensor according to claim (1), which comprises a D-conversion circuit. (5) The optical sensor according to claim (1), wherein the calculation means (I) and (II) are configured by a microcomputer.