JPH03106570A - Method and device for profile control of weld line - Google Patents

Abstract

PURPOSE:To detect the weld line with high accuracy without scanning a flat part by deciding the misalignment direction of the weld line by comparing the time when a reflected wave is not received in both end parts of a reciprocating motion of an ultrasonic wave transmitting/receiving means. CONSTITUTION:A data storage part 14 inputs a scanning position signal Ss from a scanning position detector 9 and checks whether a sensor reaches the right end or not, drives the sensor to the right side again if it does not reach and inputs continuously distance data Sa and a receiving pulse signal Sj. When the sensor reaches the right end of scanning, a timer circuit 15 is started by outputting a timer start signal St, and by bringing a counter of the right side to increment, a period in which the sensor is not receiving an ultrasonic wave is counted. When it is detected that the sensor goes into the receiving period, the counter of the right side is saved in a memory, the counter is reset again and this time a left direction instruction flag is set, and until the scan is ended, the distance data Sa and the receiving pulse signal Sj are inputted, and stored in a storage part 14.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to automatic welding, and in particular to welding line tracing control that detects a welding line using an ultrasonic distance meter and causes a welding torch to follow the welding line. METHODS AND CONTROL APPARATUS.

[Conventional technology]

As described in Japanese Patent Application Laid-open No. 59-11398l, this type of conventional device scans an optical distance meter in a direction approximately perpendicular to the welding line, and uses the obtained distance information to determine whether the workpiece has a groove. A method for detecting the position of a weld line is known.

This conventional method has the advantage of being cheaper and simpler than the method of determining the weld line through image processing using a TV camera.

[Problem to be solved by the invention]

However, in the above conventional technology, in order to find the weld line, it is necessary to scan the optical distance meter to include at least one flat part of the workpiece and detect distance data.
As the groove angle increases, the scanning width of the optical rangefinder also increases, resulting in a problem that the detection device becomes bulky. In addition, the target workpieces are limited to those with flat parts and grooves, and there is a problem that it cannot be applied to fillet joints. The present invention has been made in view of the above points, and its purpose is to accurately detect a welding line without scanning a flat area using a small and simple device, and to move a welding torch to the welding line. The purpose is to imitate the following. [Means for Solving the Problem] The above problem is solved by a welding line tracing control method in which a welding torch automatically follows a welding line on a workpiece using a sensor attached to the welding torch. is placed in front of the welding torch in the traveling direction, and while the ultrasonic transmitting/receiving means is reciprocated at a predetermined frequency in a direction substantially perpendicular to the welding line, the workpiece is rotated to intersect with the welding line and the reciprocating direction. A procedure for transmitting ultrasonic waves at a substantially right angle to The output procedure includes detecting the power spectrum of the predetermined frequency component from the waveform of the received pulse signal, and when the power spectrum is greater than a predetermined value, the center position of the reciprocating motion of the ultrasonic transmitting/receiving means is located at the welding line. The ultrasonic transmitting/receiving means relative to the welding line is determined by comparing the procedure for determining that the ultrasonic transmitting/receiving means deviates from the This is achieved by providing a procedure for determining the direction of deviation of the weld line.

The above problem also requires a procedure for calculating the distance between the ultrasonic transmitting/receiving means and the workpiece based on the received reflected waves, and a procedure for calculating the distance between the ultrasonic transmitting/receiving means and the workpiece. and a step of comparing the obtained average distance data with a predetermined reference value to determine a deviation in the height direction of the welding torch. This can also be achieved by the weld line tracing control method according to claim 1. ．． The above problem is further solved by: transmitting ultrasonic waves substantially perpendicular to a plane that is disposed in front of the welding torch in the traveling direction and that includes the welding line and makes a substantially uniform angle with respect to the surface of the workpiece that constitutes the welding line; an ultrasonic transmitting/receiving means for converting and outputting the received reflected wave into an electric signal; a scanning means for reciprocating the ultrasonic transmitting/receiving means at a predetermined frequency substantially perpendicular to the welding line and substantially parallel to the plane; an ultrasonic control means connected to the ultrasonic transmitting/receiving means and converting the electrical signal outputted by the ultrasonic transmitting/receiving means into a received pulse signal and a distance data signal; A storage means for storing a data signal, and a power spectrum connected to the storage means and the ultrasonic control means to extract a power spectrum at a certain scanning frequency from the received pulse signal waveform stored in the storage means and compare it with a predetermined value. a welding line detection means for determining the presence or absence of deviation of the center position of the reciprocating movement from the welding line; and a time period during which reflected waves are not received at both ends of the reciprocating movement of the ultrasonic transmitting and receiving means connected to the welding line detecting means. and a timer means for recording the weld line detection means,
A welding line that compares the time during which reflected waves are not received at both ends of the reciprocating motion, calculates the direction and magnitude of deviation of the center position of the reciprocating motion from the welding line, and causes the welding torch to follow the welding line. This can also be achieved by a tracing control device. The above problem also occurs when the welding line detection means detects the workpiece of the ultrasonic transmitting and receiving means based on the average value during the reflected wave reception period in one scan of the distance data signal stored in the storage means and a predetermined reference value. This can also be achieved by the welding line tracing control device according to claim 3, wherein the distance in the height direction between the welding torch and the workpiece is controlled based on the value of the deviation. Ru. [Function] As shown in FIG. 3, a case will be described in which the workpiece 1 is assembled and a welding line 2 is formed, and the welding torch is made to follow this welding line 2.

The ultrasonic transmitting/receiving means 4 reciprocates (scans) in a direction substantially perpendicular to the welding line 2 (direction indicated by arrow C in the figure), and moves in a direction substantially perpendicular to the welding line 2 and substantially in the direction of the arrow C. Ultrasonic waves are transmitted to the workpiece 1 in a perpendicular direction.

The ultrasonic wave A emitted when the ultrasonic transmitting/receiving means 4 is at the solid line position is reflected by the workpiece 1 and the reflected wave is received by the ultrasonic transmitting/receiving means 4, as shown by the solid line. The ultrasonic wave B transmitted while the ultrasonic transmitting/receiving means 4 is moved to the position indicated by the broken line is reflected as shown by the broken line, and the reflected wave is not received by the ultrasonic transmitting/receiving means 4. The reflected waves of the ultrasonic waves transmitted from the ultrasonic transmitting/receiving means 4 are transmitted to the ultrasonic transmitting/receiving means 4.
If the size of the ultrasonic transmitting and receiving part of the ultrasonic transmitting and receiving means 4 is constant, the position of the ultrasonic transmitting and receiving means 4 where the ultrasonic wave is not received is between the center of the ultrasonic transmitting and receiving means 4 and the lateral direction of the welding line 2 (ultrasonic It is determined by the amount of deviation in the reciprocating direction of the sound wave transmitting/receiving means 4). Since the scanning width of the ultrasonic transmitting/receiving means 4 is made sufficiently large, even if the scanning center position deviates from the position of the welding line 2,
At both ends of the scan, there is always a period in which no reflected waves are received. Receiving pulse signals of different magnitudes are output from the ultrasonic control means when the reflected waves of the transmitted ultrasonic waves are received and when they are not received, and the pulse signals are frequency-analyzed and transmitted to the ultrasonic transmitting/receiving means 4. The positional relationship between the scanning center position of and welding line 2 in the direction perpendicular to the welding line is determined. In other words, when the scanning center position is on the welding line, the unreceivable periods near both ends of the scan are the same on the left and right sides, and the power spectrum of the scanning frequency (reciprocating frequency) component of the received pulse signal waveform becomes very small. The power spectrum of twice the frequency component increases. On the other hand, when the scanning center position shifts from welding line 2, the length of the unreceivable period near both scanning ends differs between the left and right sides, and as a result, the power spectrum of the scanning frequency distribution in the received pulse signal waveform changes. It will start to increase. The welding line detection means extracts the power spectrum of the scanning frequency component from the waveform of this received pulse signal, and determines whether there is a deviation of the scanning center, that is, the welding torch, from the welding line. The direction of deviation is determined by comparing the unreceivable periods near both ends of the scan, with the larger side being the deviation side, and the unreceivable periods are measured and compared using the welding line detection means and easily determined.
Further, the deviation in the height direction of the ultrasonic transmitting/receiving means (i.e., the welding torch) is determined based on the distance data outputted by the ultrasonic control means in the storage means, and the welding line detection means based on the stored distance data. Then, the average distance data during the period in which the reflected waves are received during one scan is calculated, and this is compared with a preset standard. The welding line detection means detects the welding line and the horizontal direction (
The position of the welding torch and the ultrasonic transmitting/receiving means attached to the welding torch is controlled based on the deviation in the scanning direction) and the deviation in the height direction. [Examples] Examples of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of a welding device equipped with a welding line tracing control device according to an embodiment of the present invention. A pair of workpieces 1 are assembled together to form a weld line 2 that is a fillet weld joint, and a welding torch 3 is placed at a position to weld the weld line 2. A holding member 5 is attached to the rear part of the welding torch 3 (the side close to the welding line is referred to as the tip), and the holding member 5 is held by a connecting jig 7 via a rotating part 6. The connection jig 7 is fixed to a robot body 10, and the robot body 10 is connected to a robot control device 12.

The holding member 5 has a front side in the direction of movement of the welding torch 3, and a front side in the direction of movement of the welding torch 3.
The ultrasonic distance meter 4, which is an ultrasonic transmitting/receiving means, can be reciprocated in a direction substantially perpendicular to the welding line 2 (in the direction of arrow C), and the ultrasonic transmission direction is welded at a position where It is mounted in a direction that bisects the angle formed by workpiece 1 in a plane perpendicular to line 2. The holding member 5 is provided with a scanning drive motor 8, which serves as scanning means for reciprocating the ultrasonic distance meter 4 in the direction of arrow C, and a scanning position detector 9, which detects the scanning position. A scanning control section l1 is provided connected to the ultrasonic distance meter 4 and the scanning position detector 9, and the output side of the scanning control section 11 is connected to the robot control device 1.
It is connected to 2. The welding line tracing control device according to the embodiment of the present invention includes the above-mentioned ultrasonic distance meter 4, scanning position detector 9,
, a scanning drive motor 8, and a copying control section 11.

The robot main body 10 is controlled by a robot control device W112, which includes an ultrasonic distance meter 4
The positioning of the robot is performed in response to commands from the tracing control section l1, which performs tracing control of the welding line based on signals from the scanning position detector 9. Next, the operation of the weld line tracing control device of the present invention will be explained using FIGS. 2 to 10. The scanning control unit 11 is connected to the ultrasonic distance meter 4 and receives a received pulse signal Sj.
and a storage means connected to the ultrasound control circuit 13 and storing the received pulse signal Sj and the distance data signal Sa for each scan. a data storage section 14; a welding line detection circuit 16 which is a welding line detection means connected to the ultrasonic control circuit 13, scanning position detector 9 and data storage section 14; a timer generation circuit 15 which is a timer means for recording the time during which no reflected waves are received by the ultrasonic distance meter 4; and the welding line detection circuit 1.
6 and an output side connected to the scan drive motor 8; and a control start input section 18 welded to the welding line detection circuit 16. There is.

The ultrasonic control circuit 13 is adjusted to generate a reception pulse signal Sj that is "low" when the reflected wave of the ultrasound transmitted by the ultrasonic distance meter 4 is received, and "r high" when it is not received. It is equipped with a pulse signal generation circuit and a distance data generation circuit that generates an electrical signal (distance data signal) proportional to the detected distance. The welding line detection circuit 16 operates the timer generation circuit 15 based on the received pulse signal Sj, the distance data signal Sa' stored in the data storage section 14, and the scanning position signal Ss output from the scanning position detector 9. and calculates the relationship between weld line 2 and the scanning center position. Figure 3 is a diagram illustrating the ultrasonic transmission/reception {a state when the ultrasonic distance meter 4 is scanned almost perpendicularly to the welding line 2 as shown by arrow C. This shows that there are cases where the reflected wave is not received and cases where it is received. FIG. 4 shows the relationship between the detection distance Ls (1/2 of the ultrasonic wave passing distance) detected by the ultrasonic distance meter 4 and the corresponding distance data signal Sa output by the ultrasonic control circuit 13. . Lk is a distance corresponding to the transmission/reception switching time in the dead area, and is generally said to be an unusable detection distance. If the directivity of ultrasonic waves is sharp and can be expressed by a single line, it can be expressed as a propagation trajectory as shown in Figure 3 A and B, but in general, ultrasonic waves have the following equation: θ=0.704Xλ/D ( It spreads with a half-reduction angle θ, which is expressed as θ: half-reduction angle of sound pressure, λ: wavelength, D: diameter of ultrasonic rangefinder transducer.
Therefore, the scanning position is in the lateral direction from the weld 12 (in the direction of arrow C).
It has become clear from experimental results that the value obtained as the detection distance Ls increases as the distance increases. However, this increase is small, and using this, welding Ii
Experiments have also shown that the reliability of detection accuracy for detecting lateral deviations from A2 is low. FIG. 5 shows the received pulse signal Sj output by the ultrasonic control circuit 13 and the scanning position X (L: left edge of scanning, C: center of scanning,
R: right edge of scanning);
indicates the output voltage when not receiving data, and Low indicates the output voltage when receiving data.

FIG. 6 is a diagram illustrating the temporal change of the received pulse signal Sj, where Tn indicates a receiving period of reflected waves, and Tf indicates a period during which no reflected waves are received.

FIG. 7 shows the waveform of the received valve input signal Sj when the ultrasonic distance meter is scanned above the welding line 2 of the workpiece 1 as indicated by the arrow in the figure, and the deviation (lb
, lc, ld. FIG. 2 is an explanatory diagram illustrating a comparison according to the amount of deviation (le is the amount of deviation). In FIG. 7, T f R indicates the unreceivable period on the right side, and T f L indicates the unreceivable period on the left side.

In FIG. 7, (a) shows the case where the scanning center position C coincides with the welding line 2, and the received pulse signal Sj with respect to the scanning position signal Ss is as shown in (a)'. That is, the unreceivable period T f R = T f L. Next, as shown in (b) to (e), the scanning center position C is located at the welding line 2.
On the other hand, if the signal shifts to the right or left, a difference occurs between the unreceivable periods on the left and right sides of the scan, and T f R≠T f L.
In this way, it is possible to determine the relationship between the scanning center position C and the welding line 2 by only comparing the unreceivable periods Tfu and TfL at the left and right ends of the scan, but instability of the scanning movement may cause disturbances and cause false detection. There is a possibility that reliability will decrease.

The present invention focuses on the frequency distribution of the received pulse signal Sj to reduce the influence of disturbance. Figures 8A to 8C are diagrams explaining the frequency analysis results of the received pulse signal Sj. Figure 8A shows when the scanning center position C coincides with welding line 2, and Figure 8B shows that it deviates from welding line 2. Indicates each case.

fO is the scanning frequency of the ultrasonic distance meter 4 (the vibration frequency of the curve indicated by SS in FIG. 7), and Psj is the frequency power spectrum. When the scanning center position 11C coincides with the welding line 2, as is clear from the curve Ss of FIG. 7 and (a)', the frequency of the received pulse signal Sj is exactly twice the frequency fo of Ss. The power spectrum of 2fo is large as shown in Figure 8A. As shown in Fig. 8B, when the scanning center position C is shifted from the welding line 2, the power spectrum of the scanning frequency division (fo) becomes large, and this magnitude, Psj (fo), is shown in Fig. 8C. Experiments have shown that the deviation increases proportionally with the amount of deviation l from the weld line 2. The welding line detection circuit l6 in FIG. 2 extracts the power spectrum Psj(fo) of the scanning frequency component from the waveform of the received pulse signal Sj, and determines the presence or absence of deviation from the welding line and the amount of deviation based on its magnitude. It is. Next, regarding the operation procedure of the welding line tracing control of the present invention, the second
This will be explained using FIGS. 9 and 10.

FIGS. 9 and 10 are operation flowcharts showing a copying control operation procedure according to an embodiment of the present invention.

When the control start signal Sk is output from the control start input section 18 in FIG. 2 to the weld line detection circuit 16, the weld line detection circuit 16
In step 1 of FIG. 9, various counters, memories, etc. are initialized, and the ultrasonic control circuit 13 and scanning movement circuit 17 are driven to move the ultrasonic distance meter 4 (hereinafter abbreviated as sensor) to the scanning position. Next, in step 2, the right direction flag R is set to the SIDE flag, and while driving the sensor to the right, the distance data signal Sa and the received pulse signal Sj are taken into the data storage section l4 at predetermined sampling intervals. Next, at step 3, the scanning position signal Ss from the scanning position detector 9 is taken in, and it is checked whether the sensor has reached the right end. If it has not reached the right end, the sensor is moved to the right again and the distance data Sa and the received pulse signal Sj are Continue importing. The width of the scan is set in advance so that reflected waves are not received at both the left and right ends of the scan. When the sensor reaches the right end position of scanning, in step 4, a timer start signal St is output to start the timer circuit 15 to start the timer, and the counter on the right side is incremented to determine the period during which the sensor is not receiving ultrasonic waves. Count.

When the sensor detects that it has entered the reception period in step 5, the counter on the right side (period of no reception) is set in step 6.
is saved in memory, the counter is reset again, this time the left direction flag is set to the SIDE flag, and the st
In ep7, until one scan (hereinafter abbreviated as one weaving) is completed, distance data Sa and received pulse signal Sj are captured in the same way as on the right side and stored in the data storage unit 14, and are not received when moving from the left end to the right. Load the period into the counter on the left and save it to memory. step
When one weaving is completed at step 7, the correction process indicated by symbol R is performed and the process proceeds to step 4. If the control is not completed, the process returns to symbol Q and repeats the same operation procedure. 10 shows the symbol R in FIG. 9, that is, the distance data signal Sa and received pulse signal Sj stored in the data storage section 14 in FIG. FIG. 3 is a detailed operational flowchart of the procedure for correcting the welding torch position based on the welding torch position (L, counter R). First, in step 8, the power spectrum Psj(fo) of the weaving frequency component is determined from the received pulse signal Sj stored in the data storage section 14. Next, in step 9, check that Psj(fo)>0. If Psj (fo) > O, it is determined that the weaving center position is deviated from the welding line, and the process proceeds to step. The robot control device 1 in FIG.
Output to 2. On the other hand, if there is no deviation, step 9 to step 2
In step 8, the average value Sav of the reflected wave reception period of the distance data received per weaving is calculated from the distance data Sa stored in the data storage unit 14, and in step 3, this value is compared with the reference value Ssv. Based on this value, a correction signal in the height direction is output to the robot control device 12. In this embodiment, the above-mentioned control operation is explained using an example of an operation procedure executed by software of a microcomputer, but it may also be executed by hardware.

Other methods for determining the presence or absence of a deviation include, for example, a method of comparing distance data at both ends of a scan in a receivable area, or a method of comparing detected distance data with reference distance data at each end of a scan. Conceivable. However, these methods are easily affected by the stability of the scanning operation and the characteristics of ultrasonic waves, and are vulnerable to these disturbances, resulting in a decrease in detection accuracy. In view of such disturbances, the present invention uses the received pulse signal instead of distance data. Since the presence or absence of deviation from the weld line is checked using the power spectrum of the frequency component, the part caused by disturbance is cut out, making it possible to achieve highly reliable weld line tracing. [Effects of the Invention] As described above, according to the present invention, the ultrasonic transmitting/receiving means is scanned in a direction substantially perpendicular to the welding line, and the reflected waves of the ultrasonic waves reflected by the inclined surface of the workpiece are transmitted to the ultrasonic transmitting/receiving means. The positional deviation of the welding torch relative to the welding line is detected by frequency analysis of the received pulse signal, which changes the output when it is received and when it is not received, by taking advantage of the fact that it may not be received depending on the scanning position of the means. Since the torch position is controlled to correct this positional deviation, accurate weld line tracing control is possible with a small device without being affected by external disturbances, even for fillet welded joints without flat parts. will be held.

[Brief explanation of drawings]

Fig. 1 is a perspective view showing an example in which a welding device equipped with a welding line tracing control device according to an embodiment of the present invention is applied to a workpiece, and Fig. 2 shows an example of a circuit configuration of the welding line tracing controlling device of the present invention. Block diagram, Figure 3 is a sectional view showing the ultrasonic transmission/reception situation, Figure 4
The figure is a conceptual diagram showing the relationship between the detection distance and the distance data signal, Figure 5 is a conceptual diagram explaining the relationship between the received pulse signal and the scanning position, and Figure 6 is a conceptual diagram explaining the time change of the received pulse signal. 7 are conceptual diagrams explaining the relationship between the shift in the scanning center position and the received pulse signal waveform, FIGS. 8A to 8C are conceptual diagrams explaining the frequency analysis results of the received pulse signal, and FIGS. FIG. 10 is an operation flow diagram showing the scanning control operation procedure according to an embodiment of the present invention. 4... Ultrasonic distance meter, 8... Scanning deer motor, 9
...Scanning position detector, 13...Ultrasonic control circuit, 1
4...Data storage section, 15...Timer circuit, 16.
...Welding line detection circuit.

Claims (1)

[Scope of Claims] 1. In a welding line tracing control method in which a welding torch automatically follows a welding line of a workpiece by a sensor attached to the welding torch, an ultrasonic transmitting/receiving means, which is a sensor, is used to control the progress of the welding torch. the ultrasonic transmitting/receiving means is reciprocated at a predetermined frequency in a direction substantially perpendicular to the welding line, and transmits ultrasonic waves to the workpiece substantially perpendicular to the welding line and the reciprocating direction; a procedure for outputting a received pulse signal set corresponding to when the ultrasonic wave reflected by the workpiece is received by the ultrasonic transmitting/receiving means and when not received by the ultrasonic transmitting/receiving means, and the received pulse A procedure for detecting the power spectrum of the predetermined frequency component from the signal waveform, and determining that the center position of the reciprocating motion of the ultrasonic transmitting/receiving means is deviated from the welding line when the power spectrum is equal to or greater than a predetermined value. and a time period during which no reflected waves are received at both ends of the reciprocating movement of the ultrasonic transmitting/receiving means, which appears in the received pulse signal, is compared to determine the direction of deviation of the welding line of the ultrasonic transmitting/receiving means with respect to the welding line. A welding line tracing control method comprising: 2. A procedure for calculating the distance between the ultrasonic transmitting/receiving means and the workpiece based on the received reflected waves, and averaging the calculated distance during the time during which the reflected waves are received during one round trip of the ultrasonic transmitting/receiving means. a step of determining average distance data by comparing the obtained average distance data with a predetermined reference value to determine a deviation in the height direction of the welding torch;
The welding line tracing control method according to claim 1, comprising: 3. Placed in front of the welding torch in the direction of travel, it emits ultrasonic waves approximately perpendicular to a plane that includes the welding line and forms an approximately uniform angle with respect to the surface of the work that constitutes the welding line, and emits the received reflected waves. an ultrasonic transmitting/receiving means for converting and outputting an electric signal; a scanning means for reciprocating the ultrasonic transmitting/receiving means at a predetermined frequency substantially perpendicular to the welding line and substantially parallel to the plane; and the ultrasonic transmitting/receiving means. an ultrasonic control means connected to the ultrasonic wave transmitting/receiving means for converting the electric signal outputted by the ultrasonic transmitting/receiving means into a received pulse signal and a distance data signal; and an ultrasonic control means connected to the ultrasonic control means to store and store the received pulse signal and the distance data signal. a storage means for extracting a power spectrum of a scanning frequency component from a received pulse signal waveform connected to the storage means and the ultrasonic control means and stored in the storage means;
a welding line detection means for determining whether or not the center position of the reciprocating motion deviates from the welding line by comparing it with a predetermined value; and reflection at both ends of the reciprocating motion of the ultrasonic wave transmitting/receiving means connected to the welding line detecting means. timer means for recording the time during which the wave is not received, and the welding line detecting means compares the time during which the reflected wave is not received at both end portions of the reciprocating motion to determine the deviation of the center position of the reciprocating motion from the welding line. A welding line tracing control device that calculates the direction and size of the welding line and causes the welding torch to follow the welding line. 4. The weld line detecting means detects the height direction of the ultrasonic transmitting/receiving means relative to the workpiece based on the average value during the reflected wave reception period in one scan of the distance data signal stored in the storage means and a predetermined reference value. 4. The welding line tracing control device according to claim 3, wherein the distance deviation is determined and the distance in the height direction between the welding torch and the workpiece is controlled based on the value of this deviation.