JPH02160486A - Correction of position of robot - Google Patents

Abstract

PURPOSE:To efficiently correct the working position of a robot by finding the position determined from a teached work starting point, a position immediately thereafter, a tool fitting direction and the position of a robot arm, prior to the work starting, detecting the position by a visual sensor at this position and finding the slippage of a work object. CONSTITUTION:A position determined from the specific position of a teached work starting point and the position immediately thereafter, the direction to which a tool (welding torch) 6 is fitted and the position of a robot arm 2, is found prior to the starting of work. The position is detected by the visual sensor 3 of the robot arm tip at this found position and the slippage of a work object is found. This found slippage is added by the control device 1 of a robot to the work position to be teached and the work position of the tool 6 is corrected with good accuracy by controlling the robot arm 2 by its driving.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a position correction method using a visual sensor when working with an industrial Kawaguchi bot, particularly when performing arc welding.

Conventional technology The teaching method for arc welding robots is generally to have a welding wire, which is a consumable electrode, stick out an appropriate length, align the tip of the wire with the desired welding line, and memorize that position. A method is used to teach the robot where to weld. In this case, there are two main ways to use the visual sensor: one is to use the visual sensor continuously during the work to correct the position in small increments, and the other is before the work starts. This is a method that uses visual sensors only for

When the center of the field of view of the visual sensor coincides with the work point, there is no need to separately teach the position for the visual sensor, making teaching the position easier.

However, there are several problems when trying to match one working point with the center of the field of view. The first method has strong optical deviations that occur during welding operations, and there is also a related field of view problem with the second method.

That is, as shown in FIG. 9, the center of the visual field of the visual sensor 3,
In other words, when the focal point A on the optical path matches the robot's working position, the welding torch has a certain size and becomes an obstacle for the visual sensor to see the working point, and the welding wire also enters the field of view and becomes an obstacle as well. Therefore, in the image shown in FIG. 10, the welding line 35 may be hidden by the welding torch 6 or the welding wire 36. In order to avoid this, the following method has conventionally been adopted.

One method is to allow the welding torch to retreat independently of the sensor attached to the robot's wrist, and if the visual sensor is activated, the torch escapes from the field of view. The disadvantage of this method is that it requires a mechanical movement mechanism, which is undesirable for the tip of a robot arm both in terms of size and weight.

Additionally, even if welding torches can be solved by adjusting the geometrical position, when welding wire is welded, the length of the wire is not constant, and the shape of the tip of the wire is similar to that when cut with a knife. It is difficult to remove the welding wire because the shape of the molten metal varies from small to spherical as it cools, and must be treated as image noise.

Another method is a soft countermeasure.

For example, as shown in FIG. 5, if a welding line 17 is taught as a welding start point 18 and a welding end point 19, and a new workpiece is installed and the welding line is shifted as shown by a broken line 20, then the welding start point 21 is The deviation is detected and the subsequent welding position is corrected, and the actual welding line is 27, and the error at the welding end point is 28.

The center of the visual field and the work point are shifted in position, the robot is taught only to the work point, and the position where the visual sensor operates is automatically determined.

In addition, conventionally, regarding the relationship between the position detected by the sensor and the work point, the point to be welded detected by the sensor and the work point were made to match by correcting the difference between the center of the sensor's visual coordinates and the work point. Although it was corrected, the desired welding position and the position found by the sensor may not match.

For example, when the workpiece is L-shaped as shown in FIG. 7, the point to be welded detected by the sensor 3 is a corner 33.

However, in consideration of the welding conditions and the shape of the workpiece, better welding results may be obtained by welding at a point slightly distant from the corner 33. The position 32 of the torch 6 has a vector difference d between the position determined by the sensor 3 and the working point. This vector difference d is to be slightly changed in order to obtain a good welding result, and it is desirable that it can be handled in the same way as changing the welding current or welding speed in small increments. In a teaching beef robot without a sensor, this amount is adjusted when teaching the position.

Problems to be Solved by the Invention Since welding is a three-dimensional work, even when determining the position to be corrected prior to the welding work, in principle three spatial positions must be determined.

The most common targets for welding are relatively small and thin workpieces, and in the case of such workpieces, the weld length is not very long, so the amount of three-dimensional twist can be ignored.
Can work with three-dimensional parallel movement. In other words, it is sufficient to simply move the work start position three-dimensionally in parallel before starting the work.

When welding the above-mentioned workpieces, the method of automatically determining the sensing position described in the conventional technology is to start the work from the work start point, that is, from the position taught by the welding start point immediately before the welding start point. This generates a position that is offset by a specified amount in the direction along the line. Since the center of the image of the visual sensor is located near the work starting point at that position, the conventional method performs correction at the position of the work starting point. However, since the welding length is short, the three-dimensional twist can be ignored, but since the amount of twist is not zero, there is a drawback that the error increases as the distance from the work starting point increases.

In addition, when trying to correct the difference vector between the position determined by the sensor and the work point as in the conventional example, it is necessary to specify how much the vector should be depending on the welding location, and the teaching work The disadvantage was that it was complicated.

Means for Solving the Problem If it is desired to minimize the overall positional deviation by correcting one point for one weld length, it is sufficient to find the center of gravity of the deviation and correct it at that point.

A short weld length means that in most cases the work start point and work end point are adjacent. In other words, this means that there are almost no teaching points within one weld length. In such a case, the center of gravity coincides with the geometric midpoint between the work start point and the work end point. Therefore, the position can be corrected by operating the visual sensor at the geometric midpoint between the work start point and the work end point.

Therefore, the present invention provides a robot arm having a tool attached to its tip, a control device for the robot arm,
The robot arm is equipped with a visual sensor attached to the tip of the robot arm separately from the tool, and a processing device for the visual sensor that is linked to the robot arm control device, and the robot arm is equipped with a visual sensor that is attached to the tip of the robot arm, and a processing device for the visual sensor that is linked to the robot arm control device. and the position immediately after that.

The position determined from the direction in which the tool is attached and the posture of the robot arm is determined before starting work, and the position is detected using a visual sensor at this determined position to determine the displacement of the workpiece. A robot position correction method is used in which the determined deviation is added to the taught working position and the robot arm is made to work.

Since the present invention employs the method described above, it is possible to check the weld line with a welding wire or torch and perform correction operations, and in the case of workpieces that require welding with a short weld length, the position of the actual center of gravity can be adjusted. This can be corrected, the deviation becomes average for one welding length, errors at the welding start point and end point can be reduced, and more preferable welding can be performed.

Embodiment FIG. 1 is an external perspective view showing a specific embodiment of a robot that carries out the method of the present invention. 1 is a robot control device,
2 is a robot arm, 3 is a visual sensor attached to the tip of arm 2, and 4 is a processing device for the visual sensor 3, which is connected to the control device 1 of the robot, and is connected to the control device 1 of the robot. Based on the amount, the robot control device 1 corrects the position of the robot arm 2 and operates it.

A cable 5 connects the sensor 3 and the processing device 4. 6 is a welding torch, 7 is a welding power source, 8 is a torch cable, and 9 is a welding gas cylinder! 0 is a gas hose sent from the cylinder 9 to the power source.

FIG. 2 is an enlarged perspective view of the tip of the robot arm 2. FIG. 1! is the wrist of the robot arm 2, 12 is the welding torch 6
Wrist! In this embodiment, the torch holder is fixed in parallel to the visual sensor 3. Various methods can be used to fix the sensor.

FIG. 3 is an explanatory diagram showing the optical path of the visual sensor. Reference numeral 13 indicates a light projecting section of the visual sensor 3, 14 indicates a light receiving section, 15 indicates light emitted from the light projecting section 13 to the workpiece, and 16 indicates received light reflected by the workpiece. The visual sensor 3 uses light that is projected onto the workpiece and reflected, and the irradiated light is a swept spot light or slit light, and may also be a spot-shaped light.

Although the focal length does not need to be fixed, if the focal length is variable, the sensor 3 will be large and calculations to calculate the deviation value from the obtained image will be complicated.
A fixed focal point is often used.

The position of the robot is corrected by the method of the present invention using the above-mentioned apparatus.

If the center of the field of view of the visual sensor 3, that is, the focal position on the optical path, matches the working position of the robot, the welding line may be hidden in the image by the welding wire or welding torch. Therefore, in the method of the present invention, as shown in FIG.
and work point B are spaced apart by a distance β in the direction along the welding torch 6.

FIG. 5 shows the relationship between the taught welding line, the new workpiece welding line, and the actual welding line.

In order to minimize the overall deviation by correcting one point for one weld length, it is sufficient to find the center of gravity of the deviation and correct it at that point, so the correction is made as shown in FIG. In Figure 5,
17 is a taught welding line, 18 is a welding start point, and 19 is a welding end point. When a new workpiece is installed and the welding line is shifted as shown by the broken line 20, the intermediate point 23 between the welding start point 21 and the welding end point 22 is detected and the position is corrected,
Obtain the actual weld line 24. The welding start point side error 25 and end point side error 26 at this time are the welding line 2 by the conventional method.
The error can be approximately 28 degrees.

Next, the method of determining the sensing position will be explained with reference to FIG.

29 is a welding start point, and 30 is a welding end point. It is assumed that the welding torch is taught as in the first position 31. The tip of the wire, which has been drawn out in an appropriate length, accurately points to the welding start point 29. Let the vector a give the position of the starting point 29 and the vector give the position of the ending point 30. Note that the coordinates are fixed to the robot arm. Let C be a normalized vector indicating the direction of the torch as shown by arrow C. Further, the distance between one working point and the center of the visual field is assumed to be β as shown in FIG. The position 32 to be sensed is -〇・c
It is given by +(a+b)/2. The orientation of the torch at this sensing position 32 is parallel to the first position 31 .

Correcting the position with a sensor means moving the robot arm by the amount of deviation detected prior to work, so if you move from position 32 in Figure 6 to the welding start point with the deviation added, the position will be corrected. Providing 32 is not a wasteful operation. Since it is a prerequisite that the welding length itself is short, the distance between the sensing position 32 and the welding start point is originally short. However, if the distance is a problem, let L be a positive number smaller than 1 and calculate -β・c+ [a・(1−j)+b−tl at position 32
All you have to do is give it. The smaller t is, the closer the position 32 is to the welding start point. However, since the error becomes worse when looking at the overall welding result, it must be determined depending on the specific workpiece.

A method of correcting the position of a robot using a value on the coordinates of the visual sensor detected by the visual sensor is known.

Next, the relationship between the position detected by the sensor and the working point, ie, the tip of the wire that has been properly drawn out, will be explained with reference to FIG.

The seventh tooth shows the positional relationship taught.

If the workpiece is L-shaped, the position to be welded is corner 3.
It is 3. However, depending on the shape of the workpiece, welding conditions, etc.
In some cases, a better welding result can be obtained if the actual welding position is slightly away from the corner 33. In this case, the torch position has a vector difference d between the position determined by the sensor and the actual working point. However, correcting the vector difference d in order to obtain good welding results complicates the teaching work.

Therefore, in the method of the present invention, the difference between the center of the image of the sensor and the angle, that is, the position to be welded detected by the sensor, is already taught, regardless of the difference between the amount of deviation detected by the sensor and the lj''73Q vector. It is corrected by adding it to the subsequent positions.In other words, if the taught work point position is far from the corner, it is corrected while it remains separated.

First, the positional relationships shown in FIG. 7 are taught. The torch position 32 is stored. The difference vector from the corner 33 is set to (1).Next, in a confirmation operation after teaching, the point to be welded detected by the sensor on the image coordinates with the image center as the origin, that is, the 7th
Memorize the corners in the diagram. This memorization is performed for each point at which a command to check the position using a sensor is written. Let this coordinate be ξ.

In FIG. 7, there is an angle at the origin of the image coordinates, so ξ is zero.

Next, suppose that the condition shown in FIG. 8 occurs during operation.

The center of the image and the corner of the workpiece differ by a difference vector e. Do this this year. At this time, the position of the robot is corrected by T·(ξ+ζ), where T is the transformation matrix from 5 image coordinates to robot arm coordinates. It is important that there is no difference vector d in this value. That is, it means that it is not necessary to specify the difference vector d. The angle can be determined correctly by shifting the position of the robot arm by the above value when this value is determined. The difference between the corner and the working point is d, so if the torch is properly aligned with the corner, the working point will be located at a position d different from the corner, so the torch will be located at position 34 in FIG. This position 34 differs in robot arm coordinates from the torch position 32 of FIG. 7, but provides the same position relative to the corner of the workpiece.

As described above, in the method of the present invention, the data on the sensor image in the state taught in the confirmation operation is stored, so that the proper welding position can be freely taught in exactly the same way as in the case without the sensor.

Effects of the Invention Since the present invention adopts the method described above, it is possible to improve the correction of the robot's welding position with excellent accuracy when looking at the entire welding line, and it is applicable in cases where accuracy is not required. The weld length becomes longer. Furthermore, the process is extremely simple and highly practical, and by using the sensor during the confirmation run, it has the effect of giving free offsets to workpiece joints and welding points in exactly the same procedure as without a sensor. .

[Brief explanation of the drawing]

Fig. 1 is an external perspective view showing a specific example of a robot that implements the method of the present invention, Fig. 2 is an enlarged perspective view of the tip of the robot arm, and Fig. 3 is an explanation showing the optical path of the visual sensor in the same device. 4 is a perspective view showing the positional relationship between the working point and the center point of the visual field in the method of the present invention, and FIG. 5 is an explanatory diagram comparing and contrasting the welding results of the method of the present invention and the conventional method. . Figure 6 is an explanatory diagram of the sensing position, Figure 7 is an explanatory diagram showing the positional relationship during teaching or confirmation operation, Figure 8 is an explanatory diagram showing the positional relationship during operation, and Figure 9 is an explanatory diagram of the visual sensor. FIG. 1O is an explanatory diagram showing a conventional example in which the center of the visual field and the working position are made to coincide with each other, and FIG. 1O is an explanatory diagram showing an example of the image in FIG. 9. Figure 1

Claims (2)

[Claims] (1) A robot arm having a tool attached to its tip, a control device for the robot arm, a visual sensor attached to the tip of the robot arm separately from the tool, and linked to the robot arm control device. a processing device for the visual sensor, and the robot arm is configured to detect a position determined from a specific position that is a taught work starting point, a position immediately after that, a direction in which the tool is attached, and a posture of the robot arm. This is determined before starting work, and the position is detected using a visual sensor at this determined position to determine the displacement of the work object.The determined displacement is added to the taught work position and the robot arm is instructed to perform the work. Position correction method. (2) Use an arc welding torch as the tool, set the specific position that is the taught work start point as the welding start point,
The visual sensor has predetermined coordinates whose origin is approximately at the center of the image, and on these coordinates, the welding line position detected by the visual sensor during a confirmation operation after the teaching operation is memorized, and the visual sensor 2. The robot position correction according to claim 1, wherein the difference between the welding line position determined by and the stored position is calculated, and this difference is converted into coordinates of the robot arm and added to the position taught for welding. Method.