JP2770570B2 - Welding robot - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a teaching playback type welding robot that automatically recognizes a welding point and a posture of an object to be welded and self-teaches an operation program while autonomously following a welding line.

Background Art Most of the currently operating welding robots are teaching playback robots. To cope with high-mix low-volume production, it is necessary to teach many operation programs to one robot. Since there is a shortage of skilled robot teaching operators, effective measures for reducing the number of teaching steps are desired.

At present, the most commonly used teaching work method is that a teaching worker uses an operation switch of an operation box for instructing a movement of a robot, and observes the movement of the robot and makes a predetermined movement while observing the movement of the robot. For the work to be taught, which involves a curve or a change of direction, etc., this teaching operation requires not only skill but also repeated trials to obtain the desired movement of the robot. There is a problem that it takes time.

For this reason, various teaching means independent of the operation box have been proposed, and are gradually being put into practical use.

One is the so-called off-line teaching method that teaches the absolute position on the coordinate system set in the workplace including the robot without actually moving the robot,
A method of teaching an absolute position by simulation on a computer, Japanese Patent Application Laid-Open No. Sho 60-136806,
As disclosed in Japanese Patent No. 4875, a position teaching working device provided with a plurality of light emitting elements is moved along a welding line of an object to be welded instead of a torch, and light emitted from the work is fixed to a work place. There is a method of detecting and teaching with the image sensor that has been used. With these methods, not only is the robot required to have high absolute positioning accuracy, but also it is necessary to confirm the presence or absence of interference between the robot arm, welding torch, welding cable, or the like and the workpiece or peripheral jig.

As another method, there is a method of teaching while actually operating the robot. The first method is that, while an operator grasps a welding torch fixed to the end of a robot arm or a grip portion imitating the same and guides the robot along a welding line, the robot detects and stores the movement momentarily. A method of detecting the movement is to detect the direction in which the worker guides the gripping portion and the magnitude of the guiding force, as disclosed in, for example, Japanese Patent Application Laid-Open No. 56-85106. There is a method of providing a force detector for calculating the position and orientation of the tip of the torch using the output signal. This direct teaching is a teaching method that is easy for the teaching worker to handle because the worker can intuitively operate the robot without being conscious of the robot's coordinate system, etc. Not only may operations not be possible due to interference with the workpiece or jig, but depending on the shape of the workpiece, the operator may be forced to take an unnatural posture, and there is a risk that the worker may be harmed by contact with the robot. high.

In the second method, the robot automatically recognizes a welding start point and a welding line using a sensor, and performs a teaching operation while autonomously following the welding line. The teaching work can be performed while performing the work, so not only is there no need to check for interference and correct the teaching points, but also because the worker does not need to work close to the robot, teaching work can be performed safely, and positioning can be performed. Since the robot automatically adjusts the posture using the sensor information, there is an advantage that the teaching quality can be homogenized regardless of the skill of the operator.

The means for automatically recognizing a welding start point and a welding line can be roughly classified into two types. The first means is a method using a distance sensor or an image sensor using laser light or ultrasonic waves, The second means utilizes a welding operation itself such as a welding arc itself of a welding wire.

Generally, most of the means for automatically recognizing a welding start point or a welding line using a distance sensor or an image sensor using a laser beam, an ultrasonic wave, or the like require the attachment of these sensors separately near a welding torch. In the current situation where it is difficult to obtain an accurate sensor, the interference between the sensor and the work or jig often becomes an obstacle, and the surface condition of the work, the environmental illuminance, the ambient temperature, etc. often greatly affect the work. There is a problem that it greatly imposes restrictions on the tool and the jig or the working environment.

As shown in Japanese Patent Publication No. 54-15441, a touch sensor based on a wire ground using a welding wire applies a voltage to the welding wire to form one electrode, and the work surface is used as the other electrode. The position of the work is recognized from the position of the robot arm at the time when the electrical connection is obtained by contacting the work with both electrodes, that is, the welding wire, by moving the wire, and the welding line is detected by repeating this at a plurality of points. Things. Since this method requires sensing at multiple positions for each teaching point, the detection operation is slow, the work becomes complicated, and the more the number of teaching points, the longer the time required for teaching, which significantly impairs the practicality. Had.

An arc sensor that uses a welding arc is
As disclosed in JP-A-54-55635, a change in the welding current signal is used as an information source to recognize the position of the welding line, so that the welding torch intersects the welding line within the groove of the weld joint. The position of the welding line is recognized using the fact that the distance between the welding tip and the base material changes by performing weaving, and the welding current changes accordingly. In this method, it is necessary to perform teaching work while performing welding in order to make the arc itself act as a sensor, so it is not possible to start over, and it is difficult to trace welding lines at high speed, practically applied to lap joints of thin plates However, there were problems such as difficulty in tracking, the tracking performance being greatly affected by welding conditions, and difficulty in controlling the torch attitude.

The present invention solves the above problems, has a size and shape that does not impair the accessibility to the work, can be applied to a wide range of work shapes and work environments, without performing welding work,
It is an object of the present invention to provide a sensor capable of automatically recognizing a position of a welding line and a posture of a torch with respect to a workpiece at a high speed, and a welding robot capable of realizing a simple, safe, and effective teaching man-hour reduction method using the sensor.

DISCLOSURE OF THE INVENTION The welding robot of the present invention measures a robot arm, a first coordinate system set at the tip of the robot arm, a second coordinate system set at the target work, and a distance to the target work. A non-contact distance sensor attached to the distal end of the robot arm that outputs information; a rotation scanning unit that is provided with a rotation center axis fixed to the first coordinate system and rotationally scans the non-contact distance sensor; A rotational phase detecting means for detecting a rotational phase of the sensor and outputting rotational phase information, and a signal waveform for extracting characteristic points of a signal waveform obtained from the distance information and the phase information and outputting distance information and phase information for each characteristic point Processing means; a positional relationship calculating means for calculating a position and orientation relationship (hereinafter simply referred to as a positional relationship) between the first coordinate system and the second coordinate system based on information from the signal waveform processing means; A positional relationship setting storage unit that presets and stores a positional relationship serving as a reference between the coordinate system and the second coordinate system; and a positional relationship between the first coordinate system and the second coordinate system calculated by the positional relationship calculating unit. The apparatus has a configuration including a robot control unit that operates a robot arm so that the positional relationship between the first coordinate system and the second coordinate system preset and stored by the positional relationship setting storage unit matches.

According to the present invention, the non-contact distance sensor is rotated by the rotation scanning unit, and the characteristic point of the signal waveform is extracted by the signal waveform processing unit using the distance information to the target work and the rotation phase information. Calculating the positional relationship between the first coordinate system and the second coordinate system, that is, the position and orientation of the welding line and the workpiece and the welding torch, from the distance information and the rotation phase information for each feature point, Since the robot control means operates the robot arm so that the calculated positional relationship matches the positional relationship set and stored in advance, the desired positional relationship set in advance and stored, that is, the target position or posture of the welding torch is automatically adjusted. The robot arm can be operated effectively.

In addition, by using a capacitance-type non-contact distance sensor as the non-contact distance sensor, a small sensor that can perform high-accuracy detection without being affected by the surface condition of the work, environmental illuminance, and ambient temperature is configured. It is possible to do.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an external view showing an overall configuration of the present invention, FIG. 2 is a block diagram showing a data flow of the present invention, and FIG. 3 is a configuration of a two-channel capacitive distance sensor. FIG. 4 is an explanatory diagram of a first coordinate system, FIG. 5 is an explanatory diagram of a second coordinate system,
FIG. 6 is a schematic diagram when the torch coordinate system and the work coordinate system match, FIG. 7 is a sensor signal waveform diagram when the torch coordinate system and the work coordinate system match, and FIG. 8 is a torch coordinate system and the work coordinate. FIG. 9 is a schematic diagram of a system where the system is shifted in the Xt direction, FIG. 9 is a sensor signal waveform diagram when the torch coordinate system and the work coordinate system are shifted in the Xt direction, and FIG.
FIG. 11 is a schematic diagram showing a case where the torch coordinate system and the work coordinate system are displaced around Zt, and FIG. 12 is a diagram showing a sensor signal waveform when the torch coordinate system and the work coordinate system are displaced around Zt. FIG. 13 is a sensor signal waveform diagram when the torch coordinate system and the work coordinate system are displaced in the Zt direction, and FIG. 14 is a schematic diagram when the torch coordinate system and the work coordinate system are displaced around Yt. Fig. 15 is a sensor signal waveform diagram when the torch coordinate system and the work coordinate system are displaced around Yt. Fig. 16 (A) uses a two-channel capacitance type distance sensor, and the torch coordinate system and the work are used. FIG. 16 (B) is an enlarged view of the vicinity of the tip of the capacitance type distance sensor of FIG. 16 (A), and FIG. 17 is a torch coordinate system and a workpiece when the coordinate system is displaced around Yt. Coordinate system
Sensor signal waveform diagram when it is shifted around Xt, FIG. 18 is a phase relationship diagram when the torch coordinate system and the work coordinate system are shifted around Xt, and FIG. 19 is within one scan between the torch coordinate system and the work coordinate system. FIG. 20 is a perspective view of a workpiece to be used in the teaching example of the present invention in the case where the displacement occurs in FIG.

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail with reference to the accompanying drawings.

In FIG. 1, reference numeral 1 denotes a vertical articulated robot arm, and a welding torch (hereinafter referred to as a torch) 13 is attached to the leading end of the arm. Reference numeral 2 denotes a work having a fillet joint. Reference numeral 5 denotes a capacitance type non-contact distance sensor (hereinafter referred to as a capacitance type distance sensor) eccentrically mounted on the tip of the torch 13 eccentrically from the center axis (Xt axis described later) of the torch 13. Servo motor (not shown) as drive source
The rotary scanning means 6 is used to perform rotational scanning with a predetermined radius around the center axis of the torch 13 as the rotation center axis. An encoder for controlling the servomotor is provided in a torch coordinate system 3 described later.
It functions as a rotational phase detecting means 7 for detecting the rotational phase of the non-contact distance sensor 5 with the Yt axis direction as a reference position. Numeral 8 denotes a signal wave type processing means for obtaining a signal waveform indicating the relationship between the distance and the rotation phase from the output signal of the capacitance type distance sensor 5 and the output signal of the rotation phase detection means 7 and extracting the characteristic points. The information for each feature point is output to the positional relationship calculating means 9. The positional relationship calculating means 9 calculates a positional relationship between a first coordinate system 3 and a second coordinate system 4, which will be described later.

Numeral 10 is a positional relationship setting storage unit for setting and storing a desired target position and a torch attitude with respect to the work 2 as a positional relationship between the first coordinate system 3 and the second coordinate system 4 in advance. The robot control unit 11 and each axis driving motor 20 attached to the robot arm 1 are driven so that the positional relationship calculated and the positional relationship calculated by the positional relationship calculation unit 9 match. As shown in FIG. 2, the robot control unit 11 includes a movement target position calculation unit 14, a current position management unit 15, a third coordinate conversion unit 16, a first coordinate conversion unit 17, a second coordinate conversion unit 18, The servo control unit 19 and the like are the same as the conventional robot, and are provided in the robot control device 12 together with the positional relationship calculating unit 9 and the positional relationship setting storage unit 10. In FIG. 2, reference numeral 21 denotes an encoder attached to the motor 20 for driving the robot arm. In FIG. 2, the motor 20 and the encoder 21 show only one axis, and other axes are omitted.

As shown in FIG. 3, the capacitance type distance sensor 5 of the present invention has two sensor electrodes 22 and 23 concentrically, and these two sensor electrodes 22 and 23 are predetermined in the Xt axis direction described later. The two-channel electrostatic capacitance type distance sensor 5 which is arranged at a distance and operates independently is constituted. Further, since the work 2 is a fillet joint, the shape of the sensor electrode is configured to be conical so that the effective electrode area with respect to the electrode diameter increases. Further, the torch 13 and the capacitance type distance sensor 5 can be joined via a member having a high electrical insulation property, so that the center axis of the welding torch 13 and the rotation center axis of the rotary scanning means 6 can be aligned and statically fixed. Capacitance type distance sensor 5
, And the electrostatic capacitance type distance sensor 5 and the work 2 as the other electrode are connected via a welding cable, a welding wire, a circuit in a welding power source, and the like. To prevent short circuit.

The operation of the welding robot configured as described above will be described below. First, a coordinate system serving as a reference of the positional relationship between the torch 13 and the work 2 is shown in FIGS.
It is defined using the figure.

FIG. 4 shows a torch 13 attached to the robot arm 1.
Is set as the first coordinate system 3 (hereinafter, referred to as the torch coordinate system 3). In the torch coordinate system 3, the point of action of the tip of the torch 13 is defined as a first coordinate origin Ot (hereinafter referred to as the torch origin Ot), and the center axis of the torch 13 is defined as the Xt axis. The positive direction of the Xt axis is indicated by an arrow in FIG. A straight line orthogonal to the Xt axis on a plane including the Xt axis and the rotation center axis TW of the foremost wrist axis of the robot arm 1 is defined as a Zt axis. Positive direction of Zt axis is torch 13
The direction of the broken line arrow in the drawing drawn as a perpendicular from the rotation axis TW with respect to the point P provided above. Further, a direction orthogonal to the Xt and Zt axes and forming a right-handed system is defined as a Yt axis.

Next, FIG. 5 shows a second coordinate system 4 set on the target work 2 (hereinafter, referred to as a work coordinate system 4). When the robot arm 1 is positioned near the welding line on the work 2, the Xt axis of the torch coordinate system 3 is extended and a point that intersects with the work 2 is defined as Q. The intersection of the welding line is set to the second coordinate origin Ow (hereinafter, the work origin Ow).
). From the work origin Ow, the direction of the welding line
The Yw axis is perpendicular to the Yw axis.
The direction of equal division is defined as the Xw axis. At this time, the positive direction of the Yw axis may be any direction, but the positive direction of Xw is a direction from the work origin to the back surface of the work 2, and the remaining Zw axes are Xw,
The direction is orthogonal to the Yw axis and forms a right-handed system.

First, the capacitance-type distance sensor 5 utilizes the fact that the capacitance between two electrodes is inversely proportional to the distance between the electrodes. The electrode provided on the sensor is one electrode, and the measurement object itself is used. A circuit is formed by giving a potential difference between the two electrodes as the other electrode, and the capacitance between the two electrodes is measured to indirectly determine the distance between the two electrodes, that is, the capacitance type distance sensor 5 and the workpiece. Set the distance between two.

The distance information measured by the capacitance type distance sensor 5 and the phase information obtained from the rotation phase detecting means 7 are input to a signal waveform processing means 8 and processed into distance information and phase information for each feature point, and It is input to the calculating means 9. The positional relationship calculating means 9 calculates the positional relationship between the torch coordinate system 3 and the work coordinate system 4.

The operations of the signal waveform processing means 8 and the positional relationship calculation means 9 will be described later in detail.

The positional relation calculated by the positional relation calculating means 9 is input to the movement target position detecting means 14 together with the reference positional relation previously set and stored in the positional relation setting storing means 10, and the calculated positional relation is set and stored in advance. The movement target position represented by the torch coordinate system 3 is calculated such that the reference positional relationships are equal. The movement target position represented by the torch coordinate system 3 is represented by a first coordinate system represented by an orthogonal coordinate system calculated by the third coordinate conversion unit 16 using the current position of each axis stored in the current position management means 15. With the current position of the coordinate system 3
After being input to the coordinate conversion unit 17 and converted to the movement target position represented by the orthogonal coordinate system, it is input to the second coordinate conversion unit 18 and further converted to the movement target position represented by the joint coordinate system. The movement target position expressed in the joint coordinate system is input to the servo control unit 19 and is simultaneously controlled for each axis.

That is, the movement target position is determined by the current position management unit 15 described above.
Is compared with the current position information of each axis from
And outputs a motor rotation command to the motor 20 incorporated in the controller.
The encoder 21 attached to the motor 20 outputs feedback information and is input to the servo control unit 19 to configure a servo system, and is also input to the current position management unit 15 to be used for updating the current position.

Next, a specific method of calculating the positional relationship between the torch coordinate system 3 and the work coordinate system 4 by the signal waveform processing means 8 and the positional relationship calculating means 9 will be described with reference to the drawings.

First, FIG. 6 is a schematic diagram when the torch coordinate system 3 and the work coordinate system 4 match. In FIG. 6, the capacitance type distance sensor 5 is rotated counterclockwise as indicated by a dashed arrow with the Xt axis as the rotation center axis by the rotation scanning means 6 (not shown) in the Xt axis direction to the work 2. , That is, the lengths of a plurality of arrows parallel to Xt in the figure are successively measured. In the meantime, the rotation phase of the capacitance type distance sensor 5 can be simultaneously detected by the rotation phase detection means 7, and a signal waveform as shown by a solid line in FIG. 7 is obtained. The vertical axis in FIG. 7 is the distance to the work 2 measured by the capacitance type distance sensor 5, and the horizontal axis is the rotation phase at the time of measurement.

As shown in FIG. 7, the signal waveform indicating the relationship between the rotational phase and the distance is theoretically a waveform obtained by folding a sine waveform every half cycle, but the capacitance-type distance sensor 5 has a measurement symmetry. The average distance based on the total amount of capacitance between the object (work 2) and the sensor electrode is measured. Since the work 2 is captured not as a point but as a surface, the actually obtained signal waveform is indicated by a broken line in FIG. As shown, the waveform is similar to a sine wave having two cycles per rotation without any discontinuity. However, here, the description will be made using a theoretical signal waveform as shown by the solid line in FIG. 7 unless otherwise specified.

Since this signal waveform changes according to the positional relationship between the torch coordinate system 3 and the work coordinate system 4, the positional relationship between the torch coordinate system 3 and the work coordinate system 4 can be known by detecting a change in this signal waveform. it can.

A method of extracting a characteristic point to know a change in the signal waveform and analyzing a change in the waveform, that is, a positional relationship between the torch coordinate system 3 and the work coordinate system 4 from information of each characteristic point, is simple. Since the processing can be performed at high speed by using the extreme points of the signal waveform, in the present invention, the extreme points of the waveform as shown in FIG. The positional relationship between the torch coordinate system 3 and the work coordinate system 4 is calculated by the positional relationship calculating means 9 from the information on the extreme points of the waveform.

Naturally, the signal waveform includes noise, and when the difference between the value and the phase difference between two consecutive extreme points is equal to or less than a predetermined amount so that the extreme points are not erroneously extracted by the noise, These extreme points are not extracted as feature points. Also, as described above, since the capacitance type distance sensor is used, discontinuity points do not originally appear in the signal waveform, so that even when the extreme point is a discontinuity point, it is a noise. Have been excluded as being.

As is clear from FIG. 6, the minimum point among these extreme points is located at the position where the left and right inner surfaces of the joint of the work 2 intersect with the Xt-Zt plane, and the left and right minimum points are hereinafter referred to as LB and RB, respectively.
(LB0 and RB0 in FIG. 7 where the two coordinate systems match). In addition, the local maximum points are located before and after in the traveling direction of the workpiece 2 on the welding line, and the local maximum points before and after this are defined as FP and BP (FP0 and BP0 in FIG. 7).

According to FIG. 7, when the torch coordinate system 3 and the workpiece coordinate system 4 coincide, the values of the minimum points RB0 and LB0 and the maximum point FP
The values of 0 and BP0 are respectively equal, and the phase of these four extreme points divides one revolution into four. In addition, since the reference position of the rotational phase is in the positive direction of the Yt axis, the phase of the point FP0 coincides with the reference position of the phase.

Next, FIG. 8 shows that the torch coordinate system 3 and the work coordinate system 4 are Xt
The state shifted in the direction by the distance X is shown. FIG. 8 is a schematic view of FIG. 6 viewed in the direction of Yw. At this time, the obtained signal waveform is shown by a solid line in FIG. The extreme points at this time are defined as FP1, BP1, RB1, and LB1. The waveform shown by the broken line in FIG. 9 is a waveform when the torch coordinate system 3 and the work coordinate system 4 shown in FIG. 7 match.

As can be easily understood from FIG. 9, the torch coordinate system 3
When the coordinate system 4 deviates in the Xt direction, the entire waveform moves up and down, so the average value of FP1 and BP1, which are the maximum points of the wave, the torch coordinate system 3 and the work coordinate system 4 match By comparing the average value of FP0 with the average value of BP0, the positional relationship between the torch coordinate system 3 and the work coordinate system 4 in the Xt direction can be calculated.

FIG. 10 shows a state in which the torch coordinate system 3 and the work coordinate system 4 are shifted (inclined) around the Zt axis by an angle γ.
FIG. 10 is a schematic diagram of FIG. 6 viewed in the direction of Zw. The signal waveform obtained at this time is shown by a solid line in FIG. The extreme points at this time are defined as FP2, BP2, RB2, and LB2, respectively. The waveform shown by the broken line in FIG. 11 is a waveform when the torch coordinate system 3 and the work coordinate system 4 shown in FIG. 7 match.

As can be easily understood from FIG. 11, the torch coordinate system 3
When the work coordinate system 4 is displaced around the Zt axis, there is a difference between FP2 and BP2, which are the maximum points of the waveform. Since the radius of the rotational scan is known, the positional relationship of the torch coordinate system 3 and the work coordinate system 4 around the Zt axis can be calculated from the difference between FP2 and BP2 and the rotational radius.

FIG. 12 shows a state in which the torch coordinate system 3 and the work coordinate system 4 are shifted by a distance Z in the Zt direction. FIG. 12 is a schematic diagram of FIG. 6 viewed in the direction of Yw, similarly to FIG. 8, and the signal waveform obtained at this time is shown by a solid line in FIG. The extreme points at this time are FP3, BP3, RB3, and LB3, respectively. However, FIG. 13 shows the signal waveform actually measured using the capacitance type distance sensor 5, and the waveform shown by the broken line is the signal when the torch coordinate system 3 and the work coordinate system 4 match. The waveform is also actually measured using the capacitance type distance sensor 5.

As can be easily understood from FIG. 13, the torch coordinate system 3
When the work coordinate system 4 deviates in the Zt direction, a difference occurs between the values of the minimum points LB3 and RB3 on the left and right surfaces of the work 2, and the phase scanning on the right inner surface, that is, the phase value of the maximum point FP3 and the maximum value A difference also occurs between the phase value difference RH3 at the point BP3 and the phase scanning on the left inner surface, that is, the phase value difference LH3 between the phase value of the local maximum point FP3 'and the phase value at the local maximum point BP3. Here, the maximum point FP3 'is obtained by measuring the same position as the maximum point FP3 one rotation before.

From the above, the torch coordinate system 3 and the work coordinate system 4
The shift in the Zt direction can be calculated by using either the difference between the two minimum points or the phase difference between the maximum points. However, as described above, the actual signal waveform of the capacitance type distance sensor 5 is shown in FIG. As shown in (1), no discontinuous point occurs at the maximum point, and the calculation method using the phase is inferior in detection accuracy. In the present invention, the minimum points RB3 and LB3
Of the torch coordinate system 3 and the work coordinate system 4 using the difference
The positional relationship in the direction is calculated.

FIG. 14 shows a state in which the torch coordinate system 3 and the work coordinate system 4 are shifted (inclined) about the Yt axis by an angle β.

FIG. 14 is a schematic diagram of FIG. 6 similar to FIGS. 8 and 10.
Seen in the direction of Yw.

The signal waveform obtained at this time is shown by a solid line in FIG. The extreme points at this time are FP4, BP4, RB4, and LB4, respectively.

However, also in this case, the signal waveform in FIG. 15 is a waveform actually measured using the capacitance type distance sensor 5 as in the case of FIG.

Regarding the positional relationship calculation result described so far, the same result can be obtained by using any of the two channels of the capacitance type distance sensor 5. However, as is clear from the comparison between FIG. 15 and FIG. 13, the case where the torch coordinate system 3 and the work coordinate system 4 are shifted by an angle β around the Yt axis and the case where the torch coordinate system 3 and the work coordinate system 4 are different from each other. A similar waveform is obtained when the distance is shifted by the distance Z in the Zt direction. Therefore, if the torch coordinate system 3 and the work coordinate system 4 are displaced around the Yt axis,
This means that it is not possible to determine when there is a deviation in the Zt direction. The two channels of the capacitance type distance sensor 5 are used to determine this.

FIGS. 16A and 16B show a calculation method when the torch coordinate system 3 and the work coordinate system 4 are inclined by an angle β around the Yt axis using the two-channel capacitance type distance sensor 5. As described above, since the capacitance-type distance sensor 5 obtains the distance from the total amount of capacitance between the measurement target and the sensor electrode as described above, the distance actually measured is the distance in the Xw-axis direction. The two channels of the capacitance type distance sensor 5 each measure the distance between the solid arrow and the broken arrow in the figure.

The distance SZ in the Zw direction between the solid arrow and the dashed arrow changes according to the angle β as is clear from FIGS. 16A and 16B, and the capacitance type distance sensor 5 is rotated and scanned. The shift amount in the Zt-axis direction is calculated for each of the two channels, and the difference between the calculation results is calculated.

FIG. 16 (B) is an enlarged view of the electrode section of the capacitance type distance sensor 5 shown in FIG. 16 (A). Fig. 16 (B)
, The first electrode 22 and the second electrode 23 measure the distance from the points S1 and S2 in the figure to the workpiece 2.
These points S1 and S2 are separated by a distance in the Xt 'axis direction parallel to the Xt axis.
SX is located away. Here, a straight line is drawn from the point S1 in the Zw direction, and assuming that the intersection with the broken arrow indicating the distance measured by the second electrode 23 is S ′, the angles S1, S2, S ′ in the straight triangle S1, S2, S ′. Is β, and if the arc sine is calculated by dividing SX by SZ, β, ie, the positional relationship of the torch coordinate system 3 and the work coordinate system 4 around the Yt axis (the capacitance type distance sensor 5
Is determined.

Finally, FIG. 17 shows the torch coordinate system 3 and the work coordinate system 4
The signal waveform obtained when the angle is shifted about the Xt axis by α
This is shown by a solid line in FIG. Each extreme point at this time is FP
5, BP5, RB5, and LB5. Further, a signal waveform when the torch coordinate system 3 and the work coordinate system 4 coincide with each other is indicated by a broken line.

From FIG. 17, when the torch coordinate system 3 and the workpiece coordinate system 4 are displaced around the Xt axis, the phases of the waveform maximum points FP5 and BP5 and the minimum points RB5 and LB5 from the reference position as a whole are It is easily understood that it deviates.

FIG. 18 shows that the torch coordinate system 3 and the work coordinate system 4 are in the Xt direction.
The phase of each extreme point of FP, BP, LB, and RB when the displacement occurs in the Zt direction and the displacement also occurs around the Xt axis, the Yt axis, and the Zt axis is determined by the capacitance type distance sensor 5. In the diagram shown on the rotational scanning trajectory, the positional relationship desired here is the amount of deviation around the Xt axis, that is, the angle α between the welding line of Yw and the Yt axis in the figure.

From the above, if the shift amount α around the Xt axis in this state can be obtained, the positional relationship around the Xt axis can be calculated independently irrespective of the positional relationship between the torch coordinate system 3 and the work coordinate system 4. You can do it.

Referring to FIG. 18, regardless of the positional relationship between the torch coordinate system 3 and the work coordinate system 4, the straight line connecting the straight lines FP and BP shown by broken lines in the figure connecting the minimum points RB and LB, that is, the Yw axis is the rotational scanning orbit plane. In the above, there is always an orthogonal relationship, and this can be understood from the definition of the workpiece shape and the coordinate system, and also from the geometrical consideration for the rotational scanning trajectory.

Accordingly, the angle α is defined as the direction indicated by the average value B of the phase from the reference position of RB and the phase from the reference position of LB, or the average value P of the phase from the reference position of FP and the phase of BP from the reference position. The direction can be calculated as a direction orthogonal to the indicated direction. According to this calculation method, the positional relationship around the Xt axis can be easily calculated.

With the above operation, it is possible to easily calculate five components of the six components representing the positional relationship between the torch coordinate system 3 and the work coordinate system 4 by rotating and scanning the capacitance type distance sensor 5. Become.

As described above, if the robot arm 1 is operated so that the positional relationship calculated as described above matches a desired positional relationship set and stored in advance, a workpiece whose direction and position are unknown is automatically detected. Then, the robot arm 1, that is, the torch 13 can be positioned at a desired target position and torch posture.

The positional relationship in the Yt direction, that is, the positional relationship in the welding line direction, which is the remaining one component representing the positional relationship, may be always set to 0 for the detection of the start point, and if a value other than 0 is given, the robot arm will move to the current position. The robot arm 1 moves to a position shifted from the welding line in the direction of the welding line, and if this operation is repeatedly performed, the welding line is automatically tracked while maintaining the predetermined target position and torch posture. Can be operated.

This means that the component in the Yt direction among the six components representing the positional relationship between the torch coordinate system 3 and the workpiece coordinate system 4 is a variable that determines the direction and speed at which the welding line is traced, By changing this value in accordance with the instruction of the user, the direction of the welding line and the welding speed can be arbitrarily selected or adjusted.

Further, for example, the curvature of the welding line, the operating speed of each axis of the robot arm, and the like are calculated from the positional relationship between the torch coordinate system 3 and the work coordinate system 4 obtained according to the above calculation method, and the value of the Yt direction component is accordingly calculated. Is increased or decreased, the welding speed can be automatically adjusted to an optimum value according to the situation at that time.

However, when the robot arm continuously operates by tracking the welding line, an error occurs in the calculation result of the positional relationship in the above-described calculation method. This calculation assumes that the robot arm is stationary, that is, the positional relationship between the torch coordinate system 3 and the work coordinate system 4 does not change within one rotation scanning time of the capacitance type distance sensor 5. The difference between this assumption and the actual situation increases as the speed of tracking the welding line increases, and the error increases. This is a factor that limits the welding line traceable speed.

In order to reduce this error, the rotation scanning cycle of the capacitance type distance sensor 5 should be made faster, and the time per one rotation scan should be shortened so that continuous operation of the robot arm can be ignored. Is effective, but there are practically limitations on the response frequency and various processing times of the capacitance type distance sensor 5 and on the achievable rotational scanning cycle.

Therefore, in the present invention, the positional relationship between the torch coordinate system 3 and the work coordinate system 4 is fixed based on actual data that changes within one rotation scanning time of the capacitance type distance sensor 5. Is virtually reduced to reduce this kind of error. A specific method will be described below with reference to the drawings.

FIG. 19 shows a state in which the robot arm moves at a constant speed in the Xt direction from the state in which the torch coordinate system 3 and the work coordinate system 4 are shifted in the Xt direction to the state in which the torch coordinate system 3 coincides while the capacitance distance sensor 5 performs one rotation scan. The signal waveform at the time of operation is shown by a solid line, and the extreme points in this case are FP6, RB6, BP6, and LB6.

In addition, a signal waveform when the torch coordinate system 3 and the work coordinate system 4 continue to be matched is indicated by a broken line, and the extreme points in this case are FP0, RB0, BP0, and LB0.

Here, one maximum point, the difference between the value of FP6 and the value of the same maximum point FP6 ′ about one rotation before, is divided by the phase difference FH6 between both extreme points to obtain the movement amount DDXt per unit phase, This DDXt is multiplied by the phase difference between FP6 of the other extreme points RB6, BP6, and LB6 located between the local maximum points to calculate a correction amount for each extreme point, and to correct each value.

Further, using the movement amount DXt in the Xt direction per one rotation scan obtained from the movement amount DDXt per unit phase, the minimum point P
A correction amount for the phases of B6 and LB6 is calculated, and correction is applied to each phase.

In this way, it is possible to correct an error caused by the movement of the robot arm in the Xt direction while the capacitance type distance sensor 5 performs one rotation scan.

Similarly, in the case where the robot arm operates at a constant speed in the Zt direction while the capacitance type distance sensor 5 performs one rotation scan, the straight line connecting the minimum points RB and LB and the maximum Using the fact that the straight line connecting the points FP and BP is in an orthogonal relationship, the amount of movement in the Zt direction during one rotation scan is obtained, and this can be used to correct the phase of each extreme point.

That is, when the robot arm moves in the Zt direction during one rotation scan, the straight line connecting the minimum points RB and LB and the maximum point FP,
When the straight line connecting BP is no longer orthogonal, the amount of movement in the Zt direction per rotation scan is obtained from the angle of the difference between the straight line and the right angle and the rotation scan radius, and it is used to move in the Xt direction In the same manner as described above, a correction amount for the phase of each extreme point is calculated, and correction is applied to each phase.

In this way, it is possible to correct an error caused by the movement of the robot arm in the Zt direction while the capacitance type distance sensor 5 performs one rotation scan.

When the robot arm is operating while actually tracking the welding line, the movement of the robot arm while the capacitance-type distance sensor 5 performs one rotation scan is not necessarily at a constant speed. The rotation scanning cycle of the mold distance sensor 5 is fast,
Since the time between one rotation is sufficiently short, there is no practical problem if correction is made on the assumption that the robot arm operates at a constant speed during one rotation scan.

As described above, the positional relationship between the torch coordinate system 3 and the work coordinate system 4 is accurately calculated by the positional relationship calculating means 9.

Table 1 shows a comparison between the teaching time of the welding robot according to the present invention and the teaching time by the conventional method using the operation box.

The teaching work was performed with the circle shown as the teaching point for the work shown in FIG. 20, the torch angle with respect to the horizontal plane was set at 45 degrees, and the advance or retreat angle with respect to the welding line was set at 0 degree. . The number of teaching points at this time was 22 points, and the welding length was 81
0 mm.

As is evident from Table 1, the teaching time in the welding robot of the present invention can be reduced on average to about 30% of that of the conventional method, and even beginners can enjoy the same level of skill as skilled workers regardless of the skill level of the workers. An excellent effect is obtained in that the teaching operation can be performed in a long time.

As described above, according to the present invention, the capacitance type distance sensor 5 is rotationally scanned by the rotational scanning means 6, and the characteristic points of the signal waveform are subjected to the signal waveform processing using the distance information to the target work 2 and the rotational phase information. The positional relationship between the torch coordinate system 3 and the work coordinate system 4 is calculated by the positional relationship calculator 9 from the extracted distance information and rotation phase information for each of the extracted feature points. Since the robot control means operates the robot arm 1 so that the relationship matches the positional relationship set and stored in advance, the desired positional relationship set in advance and stored, that is, the target position and posture of the welding torch is autonomously obtained. The robot arm 1, that is, the torch 13 can be operated.

Note that the electrostatic capacitance type distance sensor 5 is attached to the rotary scanning means 6 in advance, and the rotary scanning means 6 can be attached to and detached from the welding torch 13. However, the electrode rod can be rotated around the center axis of the torch. In a rotating torch for rotating arc welding, the rotary scanning means 6 has a structure in which the capacitance type distance sensor 5 can be replaced with a part of a member constituting the torch 13 such as a tip which rotates together with the electrode rod. A rotating mechanism may be used.

Further, in the present invention, an example in which an encoder is provided as the rotational phase detecting means 7 has been described, but for example, the rotational scanning means 6 is accurately rotated at a constant speed, and time is measured to measure the rotational phase. Needless to say, it can be realized.

In the present invention, the correction method in the case where the robot arm continuously operates in the Xt axis direction and the Zt axis direction has been described, but the other positional relationship, that is, the robot arm continuously operates around each axis. According to the same concept, the extreme value can be corrected for each extreme value using the difference between the arbitrary extreme value and the extreme value approximately one rotation before. Further, as described above, the above-described correction is performed using the movement amount per one rotation scan in each direction, but the positional relationship calculated on the assumption that the positional relationship is fixed is described. By subtracting from the positional relationship calculated before one rotation scan, 1
Approximately calculating the amount of movement per rotation and using this approximated amount of movement to correct each extreme value and phase to calculate the positional relationship again to reduce this error Is possible.

In the present invention, a capacitance type sensor is used as the non-contact distance sensor, but another type of non-contact distance sensor such as a laser type distance sensor may be used.

INDUSTRIAL APPLICABILITY As described above, the welding robot of the present invention can be used by a worker who does not have a skilled teaching technique to perform a work requiring a lot of teaching points due to a complicated shape, or a multi-product small-lot production. Teaching for workpieces that require many operation programs to respond to
Moreover, it is suitable for high-precision execution.

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Claims (14)

(57) [Claims] 1. A robot arm, a first coordinate system set at a tip end of the robot arm, a second coordinate system set to a target work, and a distance to the target work are measured and distance information is output. A non-contact distance sensor attached to the distal end of the robot arm; a rotation scanning unit provided with a rotation center axis fixed to the first coordinate system to rotate and scan the non-contact sensor; and the non-contact distance sensor. A rotation phase detecting means for detecting a rotation phase of the signal and outputting rotation phase information; and a signal for extracting characteristic points of a signal waveform obtained from the distance information and the phase information and outputting distance information and phase information for each characteristic point. A waveform processing unit, a positional relationship calculating unit that calculates a positional relationship between the first coordinate system and the second coordinate system based on information from the signal waveform processing unit, the first coordinate system and the second coordinate system. And the positional relationship setting storage means for previously set and stored positional relationship serving as a reference for target system, the positional relationship the between the first coordinate system calculated by the calculating means second
Robot control means for operating the robot arm such that the positional relationship between the first coordinate system and the second coordinate system preset and stored by the positional relationship setting storage means coincide with each other. Welding robot consisting of 2. The welding robot according to claim 1, wherein the non-contact distance sensor is a capacitance type distance sensor that measures a distance based on a capacitance between an electrode portion of the sensor and a target work. 3. The welding robot according to claim 1, wherein the capacitance type distance sensor has a conical electrode portion. 4. A capacitance type distance sensor according to claim 1, wherein said capacitance type distance sensor is a plurality of capacitance type distance sensors which are arranged coaxially and operate individually. The welding robot according to the item. 5. The method according to claim 1, wherein said electrostatic capacitance type distance sensor is attached to said rotary scanning means via an electrically insulating member. Robot for welding. 6. The welding robot according to claim 1, wherein the characteristic point of the signal waveform extracted by the signal waveform processing means is an extreme point. 7. The method according to claim 1, wherein said signal waveform processing means does not extract these extreme points as feature points when the phase between two consecutive extreme values is equal to or smaller than a predetermined angle. 7. The welding robot according to claim 6. 8. The method according to claim 1, wherein the signal waveform processing means does not extract these extreme points as characteristic points when the difference between the two consecutive extreme points is less than a predetermined amount. Item 8. The welding robot according to Item 6 or 7. 9. The method according to claim 1, wherein said signal waveform processing means does not extract an extreme point as a feature point when the distance output by said non-contact distance sensor is out of a predetermined range.
Item 9. The welding robot according to item 7, item 7, or item 8. 10. The positional relationship detecting means uses a difference between a value of one feature point and a feature point about one rotation before the non-contact distance sensor to obtain distance information and phase information of a plurality of feature points between the two feature points. 2. The welding robot according to claim 1, wherein a positional relationship between the first coordinate system and the second coordinate system is calculated after correcting the information. 11. A first coordinate system and a second coordinate system after a positional relationship calculating means corrects distance information and phase information of a plurality of feature points with reference to a previous positional relationship calculation result. 11. The welding robot according to claim 1, wherein the positional relationship is calculated. 12. The method according to claim 1, wherein the positional relationship calculating means adjusts the positional relationship in the direction of the welding line by using a calculation result of the positional relationship between the first coordinate system and the second coordinate system. Tenth
Item 12. The welding robot according to item 11 or 11. 13. The welding robot according to claim 1, wherein said non-contact distance sensor and said rotary scanning means are structured so as to be detachable from a welding torch attached to a distal end portion of said robot arm. 14. The rotary scanning means is an electrode rod rotating means of a rotary arc welding torch attached to a robot arm, and a non-contact distance sensor is configured to be replaceable with a contact tip of the rotary arc welding torch. The welding robot according to claim 1.