JP3982603B2 - Surface straightness sensor of spot welding electrode and surface straightness measurement method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
According to the present invention, a plurality of pressure-sensitive elements are equiangular at a circumferential position with respect to a head central axis along the forward drive direction of an electrode on a head formed in a shape simulating an electrode and attached to an electrode holder instead of the electrode. A surface-weldness sensor of a spot welding electrode that detects a deviation angle from a face-to-face state of an electrode that is driven forward toward a workpiece to be spot-welded by being arranged at intervals, and a surface straightness using this sensor This relates to the degree measurement method .
[0002]
[Prior art]
In a welding robot in which a spot welder is attached to an arm, it is necessary to teach the robot operation corresponding to the workpiece to be welded in order to advance the electrode in a plane perpendicular to the workpiece and make a spot. For this reason, according to Japanese Patent Laid-Open No. 10-216955, three or more piezoelectric elements are arranged on the tip surface of a head formed in the shape of an electrode so that the deviation of the detection signal level becomes zero. In addition, a method for setting the surface straightness of the electrode teaching the robot is disclosed.
[0003]
[Problems to be solved by the invention]
By using such a teaching method to press the electrode straight in response to the workpiece, welding can be performed uniformly in a short energization time and spatter can be prevented, but a piezoelectric element is placed on the tip of the head. As a result, there is a problem in terms of durability, and the shape of the work surface is likely to affect the measurement accuracy due to the protruding shape of the element. In addition, since the piezoelectric element is a pressure-sensitive element, the pressure-sensitive signal is accelerated. Therefore, there is a possibility that high-accuracy signal processing becomes difficult.
[0004]
In view of these points, the present invention provides a surface straightness sensor for a spot welding electrode and a surface straightness measurement method using the surface straightness sensor of the kind described at the beginning that can improve durability and measurement accuracy. The purpose is to provide.
[0005]
[Means for Solving the Problems]
In order to achieve this object, according to the present invention, a head formed in a shape simulating an electrode and attached to an electrode holder in place of the electrode is attached to a head central axis along the forward drive direction of the electrode. A spot welding electrode that detects a deviation angle of the electrode that is driven forward toward the workpiece to be spot welded from a perpendicular state with respect to the workpiece by arranging a plurality of pressure sensitive elements at equal angular intervals in the circumferential position. In the surface straightness sensor, three or more pressure-sensitive elements that detect pressure as a change in resistance value are formed on the front-side head portion and the base-side head portion obtained by dividing the head in the front-rear direction. An elastic body is interposed between the distal end side head portion and the proximal end side head portion so that they can be tilted together by expansion and contraction of the elastic body between the opposing surfaces. That.
[0006]
When the surface straightness sensor is driven forward and pressurized toward the workpiece, the distal-side head portion has an elastic body with respect to the proximal-side head portion according to the surface straightness of the electrode due to the shape imitating the electrode. Tilt by expansion and contraction. Each pressure sensitive element detects a pressure corresponding to the applied pressure, the tilt direction, and the tilt degree as a change in resistance value, and a pressure distribution corresponding to the detection signal of each pressure sensitive element is detected.
[0007]
A measuring method for measuring a deviation angle and a deviation direction from a perpendicular state of an electrode to a workpiece to be spot welded by using a surface straightness sensor of a spot welding electrode according to claim 1 comprises: A vector corresponding to the arrangement position of each pressure-sensitive element and the detection signal level is created on a two-dimensional coordinate plane that is assumed to be orthogonal to the axis and the origin is on this head central axis, and each vector is synthesized. The shift direction is measured from the shift angle from the size of the total composite vector and the ratio of the decomposition vector of the total composite vector to the X axis and the Y axis.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of an apparatus for carrying out a measuring method using the spot-welding electrode surface straightness sensor of the present invention will be described with reference to FIGS. FIG. 2 shows a robot welding machine using this measuring apparatus. A resistance spot welding gun yoke 5 is attached to the tip of the arm of the welding robot 1, and a cylinder 6 is attached to the upper open end thereof. A shank, i.e., an electrode holder 7a is attached to the open end. Spot welding is performed by sandwiching the workpiece 9 by pressurization of the cylinder 6 between the electrode 8a attached to the electrode holder and the electrode 8 attached to the electrode holder 7 attached to the tip of the cylinder rod 6a. During such a welding operation, the welding robot 1 is taught in advance so that the electrodes 8 and 8a pressurize the workpiece 9 in a face-to-face state by the forward drive of the cylinder 6 at the striking position.
[0009]
FIG. 1 shows a surface straightness sensor 19 that is attached to the tip of the electrode holder 7 or 7a in place of the electrode 8 or 8a in order to perform such teaching, and is formed in a shape simulating the electrodes 8 and 8a. The head 10 is divided and a sheet-like pressure sensor 12 is interposed therein. The detection signal is supplied to the circuit device shown in FIG.
[0010]
The head 10 has a cylindrical shape made of another metal or synthetic resin having the same material or rigidity as the electrode. The head central axis A coincides with the central axis of the cylinder rod 6a and corresponds to the forward drive direction of the cylinder 6. . This head is cut in a direction orthogonal to the head center axis A, and a proximal-side head portion 10a and a distal-side head that is a convex curved surface that is point-symmetric with respect to the central axis A and that is perpendicular to the distal end portion. Dividing into portions 10b, opposite circular planar opposing surfaces 10c, 10d are formed. A hemispherical convex portion 11 is formed at the center of the opposing surface 10c, and a corresponding shallow hemispherical concave portion 14 is formed on the opposing surface 10d, with a slit 14a.
[0011]
A sheet-like pressure sensor 12 is joined to one facing surface 10c, and an elastic sheet 13 joined to the pressure sensing sensor is joined to the other facing surface 10d and integrated as a head 10. . In these sheets, openings 12b and 13b having a diameter corresponding to the convex portion 11 are formed. The sheet-like pressure sensor 12 has six or more pressure-sensitive elements 15 whose resistance values change according to the pressure at equal intervals, for example, 12 at 30 ° intervals in the circumferential position, and the same circular shape as the facing surface 10c. Between both sides of the base sheet 12a. This base sheet is made of a synthetic resin exhibiting flexibility. As a result, the proximal-side head portion 10a and the distal-side head portion 10b mainly tilt the elastic sheet 13 within an angle range defined by the slit 14a and tilt each other so that the pressure-sensitive element can be restored. 15 can be pressurized according to the degree of expansion / contraction. The direct pressure is applied to the convex portion 11.
[0012]
As shown in FIG. 3, the pressure sensitive element 15 is provided with a circuit device that takes a detection signal of the pressure sensitive element 15 as a pressure signal corresponding to the level and performs calculation processing by a computer, and is orthogonal to the head central axis A. In addition, vectors corresponding to the arrangement positions and detection signal levels of the twelve pressure-sensitive elements 15 are created with respect to the two-dimensional coordinate plane assumed to have the origin on the head central axis, The deviation angle α from the surface of the electrodes 8 and 8 with respect to the workpiece 9 and the direction of the deviation from the direction of the synthetic vector are measured from the size of the synthesized synthetic vector.
[0013]
That is, the detection signal of each pressure sensitive element 151, 152... 1512 is input, the vector data creating means 20 for creating vectors v1, v2. And vector component calculation means 21 that decomposes the vector components vX1, vX2... VX12 and vY1, vY2... VY12 in the Y-axis direction, and the total in the X-axis direction by adding the vector components vX1, vX2,. A total synthesized vector V obtained by synthesizing a total vector component VY in the Y-axis direction obtained by adding the vector component VX and the vector components vY1, vY2,... VY12 is calculated by V = √ (V 2X + V 2Y) and deviates from the magnitude. Deviation angle calculation means 22 for calculating the angle α, and deviation direction calculation for calculating the deviation direction θ from the Y axis based on θ = tan−1VX / VY. Means 23, surface straightness determination means 24 for determining whether or not the deviation angle α is within 3 °, for example, odd number groups 151, 153. The group is divided into two groups 152, 154... 1512, and the difference in the magnitude of the total composite vector VO, VE of each group is within a predetermined error range corresponding to a rotational position shift of 30 °. By determining whether or not any of the pressure sensitive elements 15 has failed, a pressure sensitive element monitoring means 25 for monitoring whether or not a failure has occurred, and a teaching pendant 26 as a display means for displaying the measurement results are configured. ing.
[0014]
The deviation angle calculation means 22 stores, as a table, change curve data that is roughly proportional to the magnitude of the deviation angle α with respect to the magnitude of the total composite vector V under a predetermined applied pressure, and thereby the deviation angle with respect to that magnitude. α is calculated in the range of about 0 to 10 °.
[0015]
On the display screen of the teaching pendant 26, a concentric deviation angle scale for every 1 °, for example, is displayed on the two-dimensional coordinate plane as a background image, and the total composite vector V as a measurement result is displayed on the coordinates. Then, the numerical values of the shift angle α and the shift direction θ, the pass / fail accuracy, the presence / absence of abnormality of the pressure-sensitive element 15 and the like are displayed at the corners of the display screen.
[0016]
The operation of the spot-welding electrode surface straightness measuring apparatus configured as described above is as follows. For example, a surface straightness sensor 19 is attached to the electrode holder 7 on the cylinder 6 side instead of the electrode 8. By operating the welding robot 1 in accordance with the teaching in advance, the surface straightness sensor 19 moves toward the striking position of the work 9, and then the cylinder 6 is operated, so that the head 10 is driven forward according to the posture of the robot. Then, the work 9 is sandwiched between the electrodes 8a with a predetermined pressure. At that time, each of the pressure sensitive elements 151, 152... 1512 exhibits an electrical resistance corresponding to a pressure corresponding to a tilt direction and a tilt degree of the distal-side head portion 10b with respect to the proximal-side head portion 10a.
[0017]
That is, when the head 10 is perpendicular to the workpiece 9 at the hitting position, each hemispherical concave portion 14 is engaged with the hemispherical convex portion 11 without the intervention of the elastic sheet 13, so that each pressure sensitive element 15 is Virtually no pressure is detected. That is, the pressure that is uniformly and slightly compressed according to the thickness of the elastic sheet 13 is detected at a low level, and the tilt is superimposed. When deviating from the surface, the facing surface 10d is tilted with respect to the facing surface 10c in the displacement direction θ according to the degree of displacement from the surface, and the pressure-sensitive element 15 at the close circumferential position is relative to the displacement angle α. The detection signal of the pressure sensitive element 15 in the separation region is relatively small, and becomes zero when the deviation angle α is increased to some extent. Therefore, a pressure distribution in which the pressure changes along the circumferential position is detected.
[0018]
As a result, the vector data creation means 20 creates vectors v1, v2,... V12 that become larger as they approach the shift direction θ, and the vector component calculation means 21 converts these vector data into vector components vX1, vX2,. And vY1, vY2,... VY12. Further, as shown in FIG. 4, the deviation angle calculation means 22 synthesizes the total vector components VX and VY, calculates the total synthesis vector V, and calculates the magnitude as the deviation angle α. Further, the deviation direction calculation means 23 calculates the deviation direction θ from the total vector components VX and VY in the orthogonal direction. Since this deviation direction is calculated based on the total composite vector V, the midway direction between 30 °, which is the arrangement interval of the pressure sensitive elements 15, is also measured without interruption.
[0019]
As a result of such calculation processing, the screen of the teaching pendant 26 is displayed on the teaching pendant 26 as shown in FIG. 3, for example, a synthetic vector that indicates that the deviation direction θ is about −150 ° and the deviation angle α is 4.5 °. V is displayed. Further, it is also warned that teaching angle correction is necessary when the deviation angle α is equal to or greater than a predetermined angle. An alarm is also given when an abnormality occurs in the pressure sensitive element 15. As a result, the attitude of the welding robot 1 can be quickly taught while monitoring the teaching pendant 26, and the confirmation or re-teaching can be performed quickly, and further teaching in a pressurized state can be performed while monitoring.
[0020]
During the measurement, even if a lateral impact is applied to the distal end side head portion 10b, the concave portion 14 is restrained by the hemispherical convex portion 11, and the surface straightness sensor 19 is prevented from being damaged.
[0021]
FIG. 5 shows a surface straightness sensor with a head 30 according to another embodiment. The proximal-side head portion 30a has a cylindrical distal end portion 35 having a small outer diameter, and the distal-side head portion 30b has a flange 36 that surrounds the opposing surface 35a that forms the outer peripheral surface of the distal end portion 35 with a gap. The inner peripheral surface is formed as a facing surface 36a. Further, a hemispherical convex portion 33 is formed on the opposing surface in the direction orthogonal to the head center axis A of the proximal end head portion 30a, and a slit 34a is formed on the corresponding opposing surface of the distal end head portion 30b. Thus, a shallow hemispherical concave portion 34 is formed and engaged with the convex portion 33.
[0022]
Between the opposing surface 35a and the opposing surface 36a, the sheet-like pressure sensor 31 and the elastic sheet 32 are wound in the form of strips so that the pressure-sensitive elements are arranged at the circumferential position, and the leading-end head portion 30b. The detection signal that detects the tilt of the base end side head portion 30a is subjected to signal processing by the same method as described above, and the shift direction θ and the shift angle α are measured.
[0023]
FIG. 6 shows a surface straightness sensor according to still another embodiment. A hemispherical convex portion 11 is formed at the center of the facing surface 10c of the head 10 described above, and a corresponding hemispherical concave portion 14 corresponding to a slightly shallower surface is formed on the facing surface 10d, and the thickness thereof so as to place the slit 14b. A thicker elastic sheet 13a is joined. As a result, the thickness of the slit 14b becomes zero due to the compression of the elastic sheet 13a in a pressurized state, and a minus (tensile direction) pressure is also detected due to the tilt of the tip side head portion 10b.
[0024]
In the above-described embodiment, if the number of pressure sensitive elements is acceptable for a decrease in measurement accuracy, it is possible to measure a deviation angle in a deviation direction in a 360 ° range with a minimum of three, and conversely measure it. When the accuracy is further improved, the pressure sensitive elements can be arranged at a finer interval than the aforementioned 30 °. In any case, it is preferable that the number is 6 or more, including the case where an element abnormality is determined by dividing into odd / even groups for normal spot welding electrode surface teaching.
[0025]
【The invention's effect】
According to the first aspect of the present invention, a surface straightness sensor capable of constantly detecting the distribution of the applied pressure of the electrode is realized, it becomes easy to improve measurement accuracy, and teaching in a pressurized state is also possible. Become. Furthermore, since the pressure-sensitive element is incorporated in the head, the durability is improved and the measurement accuracy due to the workpiece shape is not easily lowered.
[0026]
In this case, the invention according to claim 2 can narrow the dynamic range of the pressure-sensitive element without applying pressure to the pressure-sensitive element by tilting uneven engagement between the distal-side head portion and the proximal-side head portion. It is easy to ensure the linearity of detection. The pressure-sensitive element is formed between the opposing surfaces cut and separated in the direction orthogonal to the head central axis according to the invention of claim 3, or one of the distal-side head portion and the proximal-side head portion cut and separated according to the invention of claim 4. It is easily incorporated inside by being interposed between the outer peripheral surface and the other inner peripheral surface surrounding the outer peripheral surface. Further, according to the invention of claim 5, when a sheet-like pressure sensor in which a pressure-sensitive element is interposed between the base material sheets on both sides is used, the arrangement position is easily set and the incorporation into the head is facilitated.
[0027]
According to the sixth aspect of the present invention, the vector data of the pressure distribution on the two-dimensional coordinate plane is created based on each detection signal of the pressure sensitive element, and the deviation angle and its size are calculated from the size of the total synthesized vector obtained by synthesizing each vector. The direction of deviation from the direction is measured with high accuracy despite the intermittent arrangement of the pressure sensitive elements. In this case, according to the invention of claim 7, it is possible to detect that each pressure-sensitive element cannot generate a detection signal due to a failure in measurement by vector synthesis. According to the invention of claim 8, measurement by vector synthesis is performed. At this time, since the measurement result is displayed as a vector still image on the two-dimensional coordinate plane, teaching is easily performed, and teaching can be performed while measuring.
[Brief description of the drawings]
FIGS. 1A and 1B show a surface straightness sensor of a spot welding electrode according to an embodiment of the present invention. FIG. 1A is a sectional view thereof, and FIG.
FIG. 2 is a diagram showing a schematic configuration of a welding robot in which teaching is performed using the same-surface straightness sensor.
FIG. 3 is a diagram showing a configuration of a circuit device that processes a detection signal of the same-surface straightness sensor.
4A and 4B are diagrams for explaining the operation of the circuit device. FIG. 4A is a diagram for explaining an operation for measuring a deviation direction, and FIG.
FIG. 5 is a cross-sectional view of a surface straightness sensor according to another embodiment.
FIG. 6 is a cross-sectional view of a surface straightness sensor according to still another embodiment.
[Explanation of symbols]
7, 7a Electrode holder 8, 8a Electrode 10, 30 Head 10a, 30a Base side head portion 10b, 30b Tip side head portion 10c, 10d, 35a, 36a Opposing surface 11, 33 Hemispherical convex portion 12, 31 Sheet-like sensation Pressure sensor 13, 13a, 32 Elastic sheet 14, 34 Hemispherical recess 14a, 14b Narrow gap 15 Pressure sensitive element

Claims (8)

A plurality of pressure-sensitive elements are arranged at equiangular intervals at a circumferential position with respect to the head central axis along the forward drive direction of the electrode on a head formed in a shape simulating an electrode and attached to the electrode holder instead of the electrode. In the surface-weldness sensor of the spot welding electrode that detects the deviation angle from the face-to-face state of the workpiece that is driven forward toward the workpiece to be spot-welded,
Three or more pressure-sensitive elements that detect pressure as a change in resistance value are formed by overlapping an elastic body between the opposing surfaces formed on the distal-side head portion and the proximal-side head portion obtained by dividing the head in the front-rear direction. The surface of the spot welding electrode, wherein the front-side head portion and the proximal-side head portion are integrated so as to be tiltable with each other by expansion and contraction of the elastic body between the opposing surfaces. Straightness sensor.   A hemispherical convex portion is formed on one of the opposing surfaces in a direction orthogonal to the head center axis of the distal-side head portion and the proximal-side head portion, and the one of the opposing surfaces 2. The spot-welding electrode surface straightness sensor according to claim 1, wherein a hemispherical concave portion that engages with the hemispherical convex portion is formed so as to form a slit with respect to the opposing surface.   3. The pressure-sensitive element on which an elastic body is stacked is interposed between opposing surfaces in a direction orthogonal to the head center axis of the distal end head portion and the proximal end head portion. Spot welding electrode surface straightness sensor.   A pressure-sensitive element overlaid with an elastic body surrounds the opposing surface forming an outer peripheral surface with respect to the head central axis of the distal-end-side head portion or the proximal-end-side head portion, and the proximal-end head portion or the 3. The spot-welding electrode surface straightness sensor according to claim 2, wherein the sensor is interposed between opposing surfaces forming an inner peripheral surface of the tip-side head.   The sheet-like pressure sensor in which a plurality of pressure-sensitive elements are arranged and interposed between the base material sheets on both sides is interposed between the opposing surfaces. A surface straightness sensor of the described spot welding electrode. A measuring method for measuring a deviation angle and a deviation direction from an electrode face-to-face state with respect to a workpiece to be spot-welded using the spot-welding electrode face-degree sensor according to claim 1,
A vector corresponding to the arrangement position of each pressure-sensitive element and the detection signal level is created on a two-dimensional coordinate plane that is assumed to be orthogonal to the head center axis and the origin is on the head center axis. A surface straightness measurement method for a spot welding electrode, wherein a deviation direction is measured from a magnitude of a total synthetic vector obtained by combining and a deviation direction from a ratio of a decomposition vector of the total synthetic vector to an X axis and a Y axis.   Dividing six or more even pressure-sensitive elements into two groups selected every other group, and determining whether or not the difference in the magnitude of the total composite vector of each group is within a predetermined range The method of measuring the degree of surface straightness of the spot welding electrode according to claim 6. 8. The display screen of the display means displays a concentric deviation angle scale on a two-dimensional coordinate plane as a background image, and displays a synthetic vector on the two-dimensional coordinate plane. Measuring method of surface straightness of spot welding electrode

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