JPH01245103A - Step difference detecting system - Google Patents

Abstract

PURPOSE:To exactly decide a step difference point by taking a difference of distance data, executing addition if the difference is the same code and deciding a scanning position at the time when an absolute value of its added value is maximum, as the step difference point. CONSTITUTION:The title system is provided with a projecting means 1 for projecting a light beam P to the surface of an object to be detected 2, a deflecting means 7 for allowing the beam P to scan on the surface of the object 2, an optical system 3 for a light receiving for condensing a reflected light of the beam P by the object 2, and a position detecting means 4Z which is provided on the condensing surface of the optical system 3, moves in the condensing surface in accordance with a distance to the object 2, and can obtain an output corresponding to a position of a condensing spot S. Also, said system is provided with an optical scanning type displacement sensor having a first arithmetic means for calculating a distance to the object 2, based on an output of the means 4Z, and a second arithmetic means for calculating a scanning position of the beam P. In this state, in accordance with the scan of the beam P by the means 7, a difference of distance data obtained from the first arithmetic means is taken, and if the difference is the same code, it is added, and when the added value is maximum, the scanning position obtained from the second arithmetic means is decided as a step difference point.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a level difference detection method using an optical scanning displacement sensor, and is useful, for example, when using an optical scanning displacement sensor in a welding tracing sensor, etc. In addition, it is used to accurately detect steps using a simple algorithm, and to detect tracing point coordinates, gaps, etc. necessary for controlling welding robots.

[Conventional technology] In recent years, factory FA (factory automation)
There is a demand for displacement sensors on production lines that can position objects and recognize the presence or absence of objects using information about the distance to the object. Displacement sensors that meet these demands and detect the distance to the detected object in a non-contact manner include those that optically measure the distance to the detected object, and those that use triangulation are relatively simple in configuration. It has been put into practical use because it is simple.

As shown in FIG. 2, this type of displacement sensor irradiates a detected object 2 with a light beam emitted from a light projecting means 1 equipped with a semiconductor laser, a light emitting diode, etc., and detects the diffusely reflected light. is focused by the light receiving optical system 3, and the focused spot S formed on the light collecting surface of the light receiving optical system 3 is
The position detecting means 4 is configured to receive the light.

The position detection means 4 is an element capable of obtaining an electric signal corresponding to the position of the focused spot S, and based on this electric signal, the distance to the detected object 2 is calculated by a triangulation method. That is, as shown in FIG. 2, when the position of the detected object 2 changes from A to B to C and the distance between the light projecting means 1 and the detected object 2 changes, the light receiving surface of the position detecting means 4 changes. Since the position of the condensed spot S to be formed moves from a to b to c on the paper surface, by using a one-dimensional position detection means 4 that can detect the position on the paper surface, it is possible to detect the distance to the detected object 2. It is capable of detecting distance.

FIG. 3 is a perspective view showing the overall configuration of an optical scanning displacement sensor using the above-mentioned distance measurement principle. As shown in FIG. 4, the light projection means 1 includes an oscillation circuit 10 that generates a clock pulse for setting the light projection timing, a modulation circuit 11 that generates a modulation signal in response to the clock pulse from the oscillation circuit 10, and a modulation circuit 11 that generates a modulation signal in response to the clock pulse from the oscillation circuit 10. a laser drive circuit 12 that drives a light emitting element for projecting light such as a semiconductor laser 13 according to a modulation signal from the circuit 11;
The projecting optical system 14 includes a projecting optical system 14 consisting of a convex lens, and the projecting optical system 14 narrows the light emitted from the semiconductor laser 13 and projects it as a light beam.

This light beam is scanned over the object to be detected 2 in the X-axis direction by a deflection means 7 consisting of a scanning mirror 70 and its driving circuit 71.

A portion of the light beam is guided by the beam splitter 6 to the position detection means 4X, and the scanning position in the X-axis direction is detected. The position detecting means 4X outputs contradictory position signals I, L corresponding to the position where the light beam is irradiated onto its light receiving surface. This position signal 11°■ is the arithmetic circuit 5 in the X-axis direction.
The signal is input to X and converted into a scanning position signal (X output).

Furthermore, the light beam that has passed through the beam splitter 6 is irradiated onto the object 2 to be detected. The reflected light diffusely reflected on the surface of the object to be detected 2 is collected by the light receiving optical system 3. The position detecting means 4Z disposed on the condensing surface generates contradictory position signals 1. ．． 1. Output. Device signal I composed of this position detection means 4Z:
1. A distance measurement signal (Z output) in the Z-axis direction can be obtained by arithmetic processing of I< by a calculation means 5Z as shown in FIG. These ranging signals (Z
output) and the scanning position signal (X output), the detected object 2
It is possible to detect a two-dimensional shape on the scanning line on the surface of the object.

The calculation means 5X shown in FIG. 4 is an I/V conversion circuit 41 that amplifies the device signals (contradictory current signals 1° I2) constituted by the position detection means 4X and converts them into voltage signals.
a, 41b, and an I/V conversion circuit 41a.

Bypass filters 42a and 42b which take out the modulated high frequency component from the output of 41b, and the bypass filter 42
Check the output levels of a and 42b based on the output of the oscillation circuit 10 (determine the level in synchronization with the clock pulse)
The detection circuits 43a, 43b and the detection circuits 43a, 43
A low-pass filter 4 that extracts low frequency components from the output of b.
4a, 44b, a subtraction circuit 45X that performs subtraction of the outputs of the low-pass filters 44a, 44b (corresponding to the level of the position signal 11.I2, 1=1, so hereinafter referred to as I,, I2), and a low-pass filter. 44a, 44b output 1. The addition circuit 46X that performs the addition of step 2, the first signal (z + - I 2) output from the subtraction circuit 45X, and the second signal (Il + I
2) and a division circuit 47X that calculates the ratio between
It is composed of an A/D conversion circuit 48X that converts the analog signal output obtained from 7X into a digital signal,
A scanning position signal (I I I
2)/Hl+I 2) is output. Further, the arithmetic circuit 5Z for the device signals I, I4, which is composed of the position detecting means 4Z in the Z-axis direction, has exactly the same configuration as the arithmetic circuit 5X in the X-axis direction, and is capable of performing A/D conversion. From the circuit 48Z, a ranging signal (I
3-I4)/(I3+I4) is obtained.

[Problems to be Solved by the Invention] The above-mentioned optical scanning displacement sensor has problems in the horizontal direction (X-axis direction).
There are two outputs: scanning position data of You should get the output shown in the figure. However, in reality, a measurement output accompanied by noise as shown in FIG. 6 is obtained due to irregularities on the surface of the iron plate, electrical noise, and the like. Here, we will consider a welding tracing sensor for automatically welding two steel plates using a welding robot. For welding robots, the coordinates of the welding tracing point +X (N2).

Z (N 2 )l and the coordinates (
It is necessary to give X (N1) and Z (NIN).The differential method and the difference method are conventionally known as methods for determining the coordinates of the above two points from the measurement output accompanied by noise as shown in Figure 6. First, in the differential method, the difference: Z(I+ΔN>-Z(1)) is calculated for each scanning position I=1.
2. ..., (N-ΔN), and find X(I+ΔN), Z(I+AN) and X(I
) and Z(I) respectively as coordinates (X(N2).

Z (N 2 )), (X (N 1 ), Z (N
1)) There is also a note, depending on how to choose ΔN, N 1 ,
N2 changes. As described above, when attempting to find the welding tracing point using the conventional differential method or differential method, it is difficult to select ΔN, and good operation cannot be expected for any workpiece.

In particular, when the thickness of the workpiece is small and the surface condition is rough, it becomes difficult to distinguish between a step and noise, as shown in Figure 7, and if ΔN is too small, there is a risk that noise may be mistaken for a step. be. Therefore, in order to obtain good judgment results, it was necessary to optimally select ΔN by taking into consideration the level difference that occurs depending on the thickness of the steel plate, and the amplitude and frequency of noise that occurs depending on the surface condition of the steel plate. . Further, even if ΔN is optimally selected, as shown in FIG. 7, there is a possibility that the difference DZa caused by noise becomes larger than the difference DZb caused by the step.

Furthermore, in conventional differential and difference methods, the optimal Δ
It is necessary to obtain the differential coefficient and the difference while maintaining the pitch of N, and when ΔN is small and the step search range covers a relatively wide range, there is a problem that the calculation time becomes long. Furthermore, since the pitch of ΔN cannot be made as fine as desired, there is a limit to the accuracy of level difference detection.

The present invention has been made in view of these points, and its purpose is to accurately and quickly locate step points by processing the output of an optical scanning displacement sensor using a relatively simple algorithm. An object of the present invention is to provide a method for detecting a level difference.

[Means for Solving the Problems] In order to solve the above problems, in the step detection method of the present invention, as shown in FIGS. 1 to 4, a light beam is applied to the surface of the detected object 2. A light projecting means 1 for projecting light P, and a deflecting means 7 for scanning the light beam P on the surface of the object to be detected 2.
, a light-receiving optical system 3 that collects the reflected light of the light beam from the detected object 2; a position detection means 4Z that obtains an output corresponding to the position of the condensed spot S that moves at a position; a first calculation means 5Z that calculates the distance to the object to be detected 2 based on the output of the position detection means 4Z; It is equipped with an optical scanning displacement sensor having a second calculation means 5X for calculating the scanning position of the beam P, and distance data Z ( 1) difference DZ(I)-Z(I+1)-
Take Z(I>, add it if the difference DZ(I) has the same sign, and when the absolute value of the added value DSUM is maximum, the second
This is characterized in that the scanning positions Nl and N2 obtained from the calculation means 5x are determined to be step points.

[Function] Figure 8 is a diagram explaining the principle of the level difference detection method of the present invention. In Figure 8, the horizontal axis indicates scanning position 1 (=1.2...,N), and the vertical axis indicates each scanning position In the conventional differential sensing method, which indicates distance data Z(I) at I, adjacent scanning positions I, I
Difference of distance data Z(I) at +1 DZ(I)=Z
(I+1)-Z(I) was calculated, and the scanning position when this difference DZ(1) became maximum was determined to be the step point.

In this method, if the difference DZ(7) is maximum, I=7
It can be determined that D is a step point, but due to the influence of noise etc.
If Z (4) and DZ (2) become maximum, then! =4 or I=
2 is mistakenly recognized as a step point.

On the other hand, the determination method of the present invention is a difference accumulation method, and the difference DZ(I)=Z(I
+1)-Z(I) as I=1.2. ..., N-
1, and if the difference DZ(I) has the same sign continuously, it is added up, and when the added value becomes the maximum, the scanning position I is determined to be a step point. . Therefore, in the case of FIG. 8, the locally large difference D
Even if Z (2) or D Z (4) exists, it will no longer be mistaken as a true step, and the maximum step Z
(10)-Z(7) can be reliably discovered and the scanning position of the step point can be correctly determined to be I=7.10.

[Embodiment] FIG. 1 is a flowchart showing an algorithm for level difference detection in an embodiment of the present invention. Here, it is assumed that distance data Z (I>) has already been obtained for each scanning position I (=1.2, . . . , N-1, N).

In step (2), variables used in the following determination process are initialized. Specifically, the variable DZSUM indicating the added value of the difference
is set to O, a variable DZMAX indicating the maximum value of the added value is set to 0, the current scanning position (■) is set to 1, and the scanning position J at which the addition of the difference is started is set to 1.

In step ■, distance data Z(I
) and 'distance data Z(I+1) at the adjacent scanning position (I+1) DZ(I)=Z(I+1)-Z
Find (1).

In step (2), it is determined whether the value of the difference DZ(I) is zero. If DZ(I)=O, there is no point in determining whether the signs match or adding the difference, so the process moves to step (2) to determine the end of data.

If DZ(I>≠0), the process moves to step (2) to determine whether the codes match.

In step ■, the difference DZ(
It is determined whether the sign of I) matches the sign of the difference DZ(1-1) at the previous scanning position f(I-1), and if the signs match, the process moves to step ■ and the sign is determined. If they do not match, proceed to step (■).

Specifically, when DZ(I)xDZ(I-1)>O, move to step ■, and when DZ(I)xDZ(I-1)>O, move to step ■. .

It should be noted that when I=1, the process moves to step (2) unconditionally. Furthermore, when the previous difference DZ(1-1) is zero, it is compared with the difference DZ(I-2) two times before.

In step ■, the difference DZ(
The absolute value IDZ(I)I of 1) is added to the variable DZSUM, and the process moves to step (2). Difference DZ(I) in step ■
If the signs match consecutively, the absolute value IDZ(I)l of the difference DZ(1) is added to the variable DZSUM in step 2, so that the variable DZSUM has consecutive signs. An added value of the difference DZ(I) that corresponds to the sum of the values is obtained.

In step (2), it is determined whether the variable DZSUM is larger than the variable DZMAX. If DZSUM>DZMAX, move to step ■ and set DZSUM>DZMAX
Otherwise, move to step ■.

Step ■ Teha, because DZSUM>DZMAX,
Added value DZSU of the difference obtained up to the current scanning position I
In order to make M the maximum value of the addition value, the value of the variable DZSUM is assigned to the variable DZMAX.

In addition, the scanning position J where the addition to obtain the maximum value DZMAX of the added values is started is set as the candidate position N1 of the starting end of the step section, and the current scanning position In order to store it as candidate position N2,
The values of variables J and I are assigned to variables Nl and N2, respectively.

In step (2), in order to start a new addition of differences, the absolute value of the difference DZ(I) at the current scanning position I is added to the difference addition value DZSUM! IDZ(I)1 is substituted, and the current scanning position I is substituted as the scanning position J at which addition is started.

In step (2), it is determined whether processing for all data has been completed. Specifically, it is determined whether the scanning position has reached I=N-1. If it is 1N5-1, the process moves to step (2), the scanning position I is advanced by one, and the processing from step (2) is repeated.

In step (2), if I=N-1, the step detection process is finished and the last obtained candidate position N1. Let N2 be the start and end of the stepped section, and position IX (Nl).

Output Z(Nl) and coordinates X(N2) and Z(N2).

Note that the algorithm in Figure 1 can determine a level difference whether the level difference DZ(I) is positive or negative, but for example, if the level difference is downward to the right as shown in Figure 6. If you know this, you can perform the steps below in step ■ only when DZ(I) is negative in step ■, or conversely, if you know that there will be an upward step to the right, In this case, only when DZ(I) is positive in step (2), the steps following step (2) need to be executed. It goes without saying that if this is done, the recognition accuracy rate of the difference in level will be improved.

Of the coordinates of the two points obtained in this way, the distance data Z
(Nl) and Z(N2> are compared, the one with the smaller distance is set as the tracing point coordinates, and the absolute value of the difference in distance data is calculated to determine the step difference Δt.

Δt=l Z(N2)−Z(Nl)1 and step difference Δ
By subtracting the plate thickness T from t, the gap t=Δt−T between the plates to be welded is calculated, and these data are output to the automatic welding robot.

Since the above processing is a simple repetition of addition/subtraction and comparison processing, real-time processing is possible even with microcomputer software processing, but in order to further increase the speed, the following steps are required. In this case, the scanning range including the step point may be limited in advance.

FIG. 9 is a flowchart showing an algorithm for level difference detection in another embodiment of the present invention, and FIG. 10 is an explanatory diagram of its operation. Then, in steps #1 to #10, among the distance data Z(I), the difference DZ(I)=Z(I+ΔN)−Z(
I), and if the differences have the same sign, they are added, and the scanning section M1 to M2 in which the absolute value of the added value is the maximum is determined.

The processing contents of steps #1 to #10 are the same as those shown in Fig. 1, except that the interval at which differences are taken is expanded from 1 pitch to ΔN pitch. Since it is wide, it is possible to detect steps at a higher speed.

In this way, the scanning section M1 to M2 including the step point is defined in advance, and for the scanning range M1-ΔN to M2+ΔN, which is slightly wider than the scanning section M1 to M2, the steps 1 to 1 shown in FIG. 1 are repeated again. Perform the same process as [phase]. In other words, for only the scanning range M1-ΔN to M2+ΔN, the difference DZ(I)-Z(1+1)-Z of each distance data Z(I)
(I), and if the differences have the same sign, add them, and scan positions Nl and N2 when the absolute value of the added value DSUM is maximum.
is determined to be a step point. In the processing in steps ① to [phase], the intervals at which the differences are taken are narrow, so that highly accurate level difference detection is possible.

In other words, in the method of this embodiment, the same algorithm is executed at a coarse pitch for the first level difference detection and at a finer pitch for the second level difference detection, thereby enabling high-speed and highly accurate level difference detection. It is. In addition, 1
In the second step detection, it is only necessary to narrow down the range where the true step points Nl and N2 exist, so the absolute value of the difference DZ (I) = DZ (I + ΔN) - DZ (I) is the maximum It is also possible to find a point where , and determine a certain range before and after that point as the range where the step exists.

FIG. 11 is an explanatory diagram showing an algorithm for level difference detection in still another embodiment of the present invention. In this embodiment, in order to more accurately determine the level difference section, when the absolute value of the added value is the maximum, the section N1 to N where the difference is added is
2 is the estimated step section, distance data Z AVI + Z AV2 of the upper and lower sections are obtained by averaging processing from a predetermined number of data outside both ends of the estimated step section, and the distance data Z AVI + Z AV2 of the middle section of the estimated step section is calculated. The slope α of the estimated step section is obtained by averaging a predetermined number of data, and both ends of the true step section are calculated based on these.

The algorithm will be specifically explained below.

First, the starting point N1 and ending point N2 of the estimated step section are determined using the algorithm shown in FIG. Next, the distance data ZAV+ of the upper part is obtained by averaging processing from a predetermined number of data from the starting end N1 of the estimated step section to the outside of the estimated step section.

nl + I I = N 1 Similarly to nl, distance data Z of the lower part is obtained by averaging processing from a predetermined number of data from the end N2 of the estimated step section to the outside of the estimated step section.
Find AV2.

nl + I I = N 2 n1 Next, the average value of the distance data ZAVI + Z AV2 of both the upper and lower steps is calculated.

Z c = = (Z AVI + Z AV2) / 2 Distance data Z (
The scanning position 1=Nc with I) is set as the center point of the step. The center point Nc of this step and all the coordinates of ±12 points before and after it IX (Nc-n2), Z (Nc-nz)) ~ (X
(Nc + n2), using Z (Nc + nz)l,
Determine the constants α and β of the linear approximation formula X=αZ+β. Then, by substituting Z −Z AVI I Z AV2 into this formula, both ends of the true step section (αZAVI+β, Z
AVI > and (αZAV2+β, Z AY□) are calculated. Further, the step difference Δt can be determined by the following equation.

Δt=l ZAVI−ZAV21 In this example, the constants α and β of the linear approximation formula were determined based on (2n2+1) pieces of coordinate data.
If there is no time for calculation, it may be approximated by a straight line connecting two points.For example, in Fig. 11, the coordinate (X (
Nc n*), Z (Nc n3)) and (X(Nc
+r++) and Z(Nc+n3)l may be used instead of the above-mentioned linear approximation formula.

[Effects of the Invention] As described above, in the present invention, differences in distance data are taken, and if the differences have the same sign, they are added, and the scanning position when the absolute value of the added value is the maximum is determined as a step point. Since it is determined as follows, although it is a relatively simple algorithm, it has the effect of accurately determining the step point.

In addition, the difference in distance data for each predetermined scanning section is taken, and if the differences have the same sign, they are added together, the scanning section where the absolute value of the added value is the maximum is found, and the scanning range is slightly wider than the scanning section. If step points are determined using the same algorithm as above, the range in which the step points are included is limited in advance, so there is an effect that highly accurate determination can be performed at high speed.

Furthermore, when the absolute value of the added value is the maximum, the section where the difference is added is set as the estimated step section, and the upper and lower sections are calculated by averaging from a predetermined number of data outside both ends of the estimated step section. By obtaining distance data for each, calculating the slope of the estimated step section by averaging processing from a predetermined number of data in the middle of the estimated step section, and calculating both ends of the true step section based on these, it is possible to calculate the slope of the estimated step section. Even if both ends are affected by noise and are somewhat inaccurate, the averaging process alleviates the effect of noise and allows accurate calculation of the true ends of the step section, resulting in even higher accuracy. This has the effect of making it possible to detect differences in level.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing an algorithm for level difference detection in an embodiment of the present invention, FIG. 2 is a schematic configuration diagram of a ranging optical system used in the present invention, and FIG. 3 is a diagram of an optical scanning displacement sensor used in the present invention. FIG. 4 is a block circuit diagram of an arithmetic circuit used in the present invention; FIGS. 5 to 7 are diagrams explaining the operation of the conventional example; and FIG. 8 is an explanation of the operation of an embodiment of the present invention. 9 is a flowchart showing an algorithm for level difference detection in another embodiment of the present invention, FIG. 10 is an explanatory diagram of the same operation as above, and FIG. 11 is a flowchart showing an algorithm for level difference detection in yet another embodiment of the present invention. It is a figure for explaining. 1 is a light projecting means, 2 is an object to be detected, 3 is a light receiving optical system, 4
X and 4Z are position detection means, 5X and 5Z are calculation means, 6 is a beam splitter, and 7 is a deflection means.

Claims (3)

[Claims] (1) Light projecting means for projecting a light beam onto the surface of the detected object, deflection means for scanning the light beam on the surface of the detected object, and light receiving means for condensing the light reflected from the light beam by the detected object. an optical system for light receiving, and a position detection means for obtaining an output corresponding to the position of a condensing spot that is disposed on the condensing surface of the optical system for receiving light and moves within the condensing plane according to the distance to the detected object;
an optical scanning displacement sensor having a first calculation means for calculating the distance to the detected object based on the output of the position detection means and a second calculation means for calculating the scanning position of the light beam; The difference between the distance data obtained from the first calculation means in accordance with the scanning of the light beam by the is calculated, and if the differences have the same sign, they are added. When the absolute value of the added value is the maximum, the second calculation means A step detection method characterized by determining a scanning position obtained from a step as a step point. (2) Among the distance data obtained from the first calculation means in response to the scanning of the light beam by the deflection means, take the difference between the distance data for each predetermined scanning section, and if the differences have the same sign, add them together. Find the scanning section where the absolute value of the added value is the maximum, take the difference between each distance data for a scanning range slightly wider than the scanning section, and if the differences have the same sign, add them,
2. The step detection method according to claim 1, wherein the scanning position obtained from the second calculating means is determined to be a step point when the absolute value of the added value is maximum. (3) When the absolute value of the added value is maximum, the section where the difference is added is set as the estimated step section, and the average value of a predetermined number of distance data from both ends of the estimated step section to the outside of the estimated step section. The slope of the estimated step section is calculated from a predetermined number of distance data and scanning position data that exist before and after the average distance of the distance data of both the upper and lower parts, and the slope of the estimated step section is calculated. 2. The step detection method according to claim 1, wherein both ends of the true step section are calculated from the distance data and the slope of the estimated step section.