JPH0222401B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an industrial robot that performs processing while reproducing previously taught motions, and particularly when changing the posture of a processing tool and changing the effective length of the processing tool. The present invention relates to a control device that easily performs operations.

In general, in industrial robots, there are coordinate axes for relatively moving the processing tool and the workpiece (hereinafter these coordinate axes are referred to as principal coordinate axes). Posture control axes, which are sub-coordinate axes for determining the posture of the wrist that holds the
It is equipped with a Ψ-axis (hereinafter the Θ-axis and Ψ-axis are collectively referred to as the wrist axis) that rotates in a plane parallel to the axis, and each of these axes can be moved as instructed in a three-dimensional space. It is controlled to faithfully reproduce the formed processing line.

FIG. 1 is a perspective view showing an example of an industrial robot configured in this way. In the figure, 1 is a base, 2 is a column mounted on the base 1 so as to be able to move freely in the X-axis direction, and 3 is a column. An arm support 4 is attached to the column 2 so that it can move up and down in the Z-axis direction, and an arm 4 is supported on the arm support 3 so that it can move back and forth in the Y-axis direction. A wrist 5 having a torch is attached, and this wrist 5 can control the posture of the processing tool 6 by rotating it around the Θ axis in the XY plane and around the Ψ axis in a plane parallel to the Z axis. It's getting old. These column 2, arm support 3, and arm 4 each constitute a main coordinate axis consisting of orthogonal axes, and are each driven and positioned to a commanded position by a driving means (not shown) such as an electric motor or a hydraulic cylinder. Further, these robot bodies are installed in correspondence with a separately prepared mounting jig 8 for the workpiece 7. The workpiece mounting jig is configured to be rotatable around the U-axis and V-axis in the figure and movable in the W-axis direction as necessary.

In this type of industrial robot, the effective length of the processing tool is determined depending on the shape of the workpiece, the thickness of the workpiece, the inclination of the processing line, etc. For example, when used for welding, the selection of a welding gun or the selection of It is necessary to adjust the electrode height and the protruding length of the consumable electrode from the tip of the welding torch to appropriate values. In an industrial robot as shown in Fig. 1, if the mounting direction of the processing tool is parallel to one of these principal coordinate axes, the change in effective length, for example, the welding voltage or protrusion in a welding robot, It is sufficient to correct only the change in length from the data taught at the time of execution on the relevant axis and move the torch movement trajectory in parallel in the direction of that axis. However, the mounting direction of the processing tool is rarely parallel to the principal coordinate axes, and in general, the tool is in a normal use state in a posture that has a finite angle with respect to any of the principal coordinates. When the machining lines are curved or polygonal, the machining tools are required to always maintain a constant posture with respect to the machining lines. Therefore, as machining progresses, the angle of the attitude control axis of the machining tool from the origin is controlled to change, so the angle with respect to the main coordinate axis changes. To simplify the explanation, an arc welding torch is used as the processing tool, and Fig. 2a
As shown in Figure 2b, there are welding lines A to E bent at point C in the X and Y planes, and the required arc voltage is between A and B and between D and E as shown in Figure 2b. Consider the case where e ₁ is e 1 and e ₂ between B and D, and the welding torch also moves within the X and Y planes. In the same figure, point A-
Since point C is a straight line, the welding torch can be held at a fixed angle tilted by θ ₁ from the Y axis.Since it is bent at point C, rotate the wrist axis according to the bending angle of the welding line to align it with the Y axis. On the other hand, θ ₂ is required to be at an angle α with respect to the weld line between C and E as well as between A and C. Also, since the arc voltage needs to be changed at points B, D, and E, the distance from the welding torch support point to the welding point of the workpiece, that is, the effective length of the processing tool: L
between A and B and between D and E, and between B and E.
It is necessary to set it to lb between D. In general, when the effective length L of a welding torch, which has an angle of θ with respect to the Y-axis, changes by ΔL, in the Y-axis direction, ΔLy = ΔLcosθ, and in the X-axis direction, ΔLx =
This appears as a change in ΔLsinθ, so even if the required arc voltage changes and the effective torch length changes, the torch support point must be set in order to keep the pointing position of the torch tip unchanged and perform continuous welding without cutting. It is necessary to correct this amount. Therefore, depending on the value of the torch attitude θ, the amount of correction for each axis will vary greatly in the range from zero to ΔL even for the same change in effective length ΔL of the torch.

Therefore, in the conventional method of adding a certain shift amount to the teaching data to move the trajectory of the processing tool in parallel, it is not possible to freely change the attitude of the processing tool during a series of operations. Only when a slight predetermined attitude change is programmed can the processing tool be moved by adding up the shift amounts instructed by this program. Therefore, during execution, these can be adjusted arbitrarily, or other phenomena such as the type of welding gun in the welding robot, the arc voltage,
It has been impossible to control the position of the processing tool in response to changes in the protruding length of the electrode. Therefore, in the conventional device, when teaching the locus of the machining line, it was necessary to calculate the shift amount of the machining tool from the machining conditions determined through separate experiments, and to teach these along with the standard trajectory. For this reason, all experiments when finding machining conditions must rely on manual commands, and during automatic machining,
For example, in TIG welding using non-consumable electrodes,
In welding methods that use so-called arc voltage copying or consumable electrodes, the welding torch is moved toward the workpiece in a direction that detects the arc voltage, compares it with a reference value, and eliminates the difference. It is impossible to adopt a method of detecting a change in welding current due to a change in the protrusion length of the consumable electrode and moving the welding torch so as to restore the current. It was necessary to provide a dedicated means. Further, at point C in FIG. 2, it is necessary to rotate the wrist axis so that the welding torch forms the same angle α as between A and C. At this time, without changing the position of the wrist support part, that is, the tip of the arm 4 in FIG.
When it is rotated, the center of rotation is separated from the tip of the processing tool, so that the tip of the processing tool is at a position far away from the original pointing position, as shown by the dotted line in FIG.

Conventionally, when machining such a bending machining line or in order to prevent the pointing position of the tip of the machining tool from changing even if the attitude of the machining tool with respect to the machining line changes, there is a step of memorizing the machining line, that is, teaching. At times, the change in the position of the tip of the processing tool that occurred due to the change in wrist posture is handled by manually moving the X-axis and Y-axis, and after confirming that the tip of the processing tool has returned to its normal position, a teaching command is issued. Target values for the wrist axis, X-axis, and Y-axis are memorized, and during execution, the amount of movement required for each of the X and Y axes when changing the wrist posture is calculated by a computer from the previously memorized target values. A method was used in which this was done while When such a method is used, not only does the teaching work become very complicated, but also the rotation of the wrist axis and the correction operation of the position of the principal coordinate axes are performed independently during execution. By the way, mechanisms with different weights are attached to the X, Y, and Z axes, which are the main coordinate axes, and the loop gain and response speed are naturally different from the Θ and Ψ axes for wrist rotation, which are the polar coordinate system. It is quite difficult to adjust these accurately to match the dynamic characteristics. Moreover, the dynamic characteristics of each of these axes are not constant because the load weight and moment of inertia change depending on the adjustment position of each axis, and it is almost impossible to match these varying dynamic characteristics at all positions. Close to possible.

On the other hand, in order to facilitate the teaching work, the rotation command of the wrist axis is divided, and in order to hold the tip of the processing tool in the original position according to this command signal, the amount by which the main coordinate axis should be moved is calculated. This calculation result can be added to the position command signals for each of the X, Y, and Z axes to perform control while correcting the position of the main coordinate axes, or the rotation angle of the wrist axis can be detected and the X, Y, and Y axes can be controlled by , and a method of calculating and controlling the correction amount for each axis of Z has been proposed. However, in the former case, the rotation of the wrist and the driving of the main coordinate axes for correction are performed independently based on the rotation command signal of the wrist axis. On the other hand, in the latter case, the amount of rotation of the wrist axis is detected, and then the correction amount of the principal coordinate axes is calculated based on this detected value, and the principal coordinate axes are adjusted based on the result of this calculation. Since it will have to be moved, a considerable amount of operational delay is unavoidable. Furthermore, in order to accurately correct the position of the principal coordinate axes, it is necessary to detect the rotation angle of the wrist axis at as fine an interval as possible, but the calculation of this correction amount involves trigonometric functions as described later. Therefore, it is necessary to calculate a large number of trigonometric functions at high speed, which is simply not possible with the capabilities of microcomputers generally used in industrial robots. Therefore, the detection interval is restricted within the range of computing power, an increase in delay is inevitable, and accurate correction operation cannot be expected.

The present invention calculates the amount of change in the tip pointing position of the processing tool that occurs when changing the effective length of the processing tool from the current position signal of the attitude control axis of the processing tool and the effective length command signal of the processing tool. According to the result, a position correction signal is obtained for the main coordinate axes that are the means of supporting the processing tool, and in addition to this, when the wrist axis is rotated in response to an attitude control command signal, a position correction signal is obtained by receiving an attitude control command signal and changing the attitude. The amount of change in the pointing position of the tip of the processing tool that occurs is calculated, and the calculation results are sequentially stored, and the change in the pointing position of the tip of the processing tool that has been previously calculated and stored is calculated in accordance with the movement of the attitude control axis. The structure reads out the amount and uses this signal to correct the position correction signal for the main coordinate axes to control the position of the main coordinate axes. Even when the wrist axis rotates, the directional position of the tip of the processing tool does not change at all and is accurate. This also enables position control without delay.

FIG. 3 shows the application of the first invention to an industrial robot having three orthogonal axes X, Y, and Z as principal coordinate axes and two rotational axes Θ and Ψ as wrist axes, as shown in FIG. FIG. In the figure, 9 is a controller that generates command signals for each axis, 11a is an X-axis drive control circuit, 11b is an X-axis drive motor, and 11c is an encoder for detecting the X-axis position.
c constitutes a servo control circuit for X-axis positioning. Similarly, 12a, 13a, 14a, and 15a are drive control circuits for the Y-axis, Z-axis, Θ-axis, and Ψ-axis, respectively, 12b, 13b, 14b, and 15b are electric motors for driving each axis, and 12c, 13c, 14c, and 15c are drive control circuits for each axis. Encoders for detecting the position of each axis, 12a to 12c are for the Y axis, 13a to 13c are for the Z axis,
14a to 14c are for Θ axis, 15a to 15
c constitutes a positioning servo control device for the Ψ axis. 16 and 17 are Θ-axis and Ψ-axis current position storage registers that integrate and store the Θ-axis position command signal and Ψ-axis position command signal from the controller 9, respectively, and when each axis returns to its home position, It will be reset. This register 1
6 and 17 may integrate the outputs of the encoders 14c and 15c, and in this case it is possible to obtain a signal that corresponds to the actual operation. 1
8 receives the position increment commands θc, φc for both axes with respect to the Θ and Ψ axes from the controller 9, and calculates the X, Y, and Z at this time.
An arithmetic circuit that calculates the amount of correction for each axis according to the current position of the Θ and Ψ axes; 19 is a teaching operation box for manually commanding the movement of each axis; 20 is a teaching operation box for starting, stopping, etc. during automatic operation. The automatic operation boxes 21 to 23 that issue commands output the output of the controller 9 to the arithmetic circuit 18.
This is a correction circuit that corrects the output of and obtains a total output.

In FIG. 3, the controller 9 outputs a position command signal xc to φc for each axis in each command unit at a pulse interval corresponding to a separately determined moving speed, and each axis receives this position command signal to perform servo control. It is driven by a circuit in response to an input signal. This positioning result is transmitted to the encoder 11 provided in each
c to 15c, and is fed back to the control circuits 11a to 15a of the respective axes, and stops at the position where there is no deviation from the input signal. Position command signal θc, φc for wrist axis
Also, Θ-axis and Ψ-axis current position recording register 1
6 and 17 are integrated. The registers 16 and 17 integrate the rotation angles θ and φ of the wrist axis from the origin and output the result to the arithmetic circuit 18.

On the other hand, the controller 9 also outputs a signal a that commands the effective length of the processing tool, and this signal a is supplied to the arithmetic circuit 18, and is sent along with the signals θ and φ of the registers 16 and 17 to the X, Y, and Z axes. The amount of correction is calculated, and this amount of correction is calculated using the command signal xc,
Yc, zc are added and combined by correction circuits 21 to 23, and then supplied to drive circuits 11a to 13a for each axis. As a result, the tip of the processing tool always faces the same pointing position regardless of changes in the effective length signal of the processing tool.

Here, the arithmetic circuit 18 will be explained in detail.

FIG. 4 is an explanatory diagram showing the relationship with the coordinate axes in which only the processing tool portion of the apparatus shown in FIG. 1 is extracted. Fourth
In the figure, a ₀ indicates the length of the wrist from the rotation center of the Θ axis of the wrist to the attachment position of the processing tool, and a ₁ indicates the effective length of the processing tool. The center of rotation of the wrist is now at point Q, and the wrist is rotating by Θ around the Θ axis in the direction shown in the figure and by φ around the Ψ axis, then the tip position of the welding head P ₁ (x ₁ , y ₁ , z ₁ ) is x ₁ = a ₀ cos θ a ₁ sin θ sin φ … (1) y ₁ = a ₀ sin θ + a ₁ sin φ cos θ … (2) z ₁ = a ₁ (1 − cos φ) … (3).

Here, the wrist length _a0 is determined by the structure of the robot body, so it can be considered that it is usually constant. Processing tool 6
As mentioned above, the effective length a ₁ is specified to have various values depending on the purpose. Now consider a case where the effective length of the processing tool 6 changes from _a1 to _a2 . At this time, the coordinates P ₂ (x ₂ , y ₂ , z ₂ ) of the tip position of the processing tool 6 are as described above.
It can be obtained by substituting a ₂ instead of a ₁ in equations (1) to (3), and the amount of movement of the tip of the processing tool 6 at this time is Δx ₁ = x ₂ − x ₁ = (a ₁ −a ₂ ) sinθ sinφ …(4) Δy ₁ =y ₂ −y ₁ = (a ₂ −a ₁ ) sinφ cosθ …(5) Δz ₂ =z ₂ −z ₁ = (a ₂ −a ₁ )(1 −cosφ)…(6). In order to return this to its original position where the effective length was a ₁ , it is sufficient to move the mounting portion Q of the processing tool by (-Δx ₁ , -Δy ₁ , -Δz ₂ ) along the principal coordinate axes. When the effective length command of the processing tool further changes from a ₂ to a ₃ from the state corrected in this way, Δx ₂ = x ₃ −x ₂ Δy ₂ = y ₃ −y _{2 Δz 2 =} z ₃ −z ₂ (however, P ₃ (x ₃ , y ₃ , z ₃ ) has an effective length from a ₁
a Shows the position of the tip when it changes to ₃ . ) has moved from point _P2 .

As is clear from equations (4) to (6), these correction amounts are generally calculated as follows: Δx=−Δa sinθ sinφ …( 7) Δy＝Δa sinφ cosθ …(8) Δz＝Δa(1−ocsφ) …(9) Therefore, the calculation circuit 18 may be a circuit that calculates equations (7) to (9) from the amount of change Δa in the effective length a of the processing tool and the wrist postures θ and φ.

Let us now consider the signal corresponding to the above Δa. Generally, when teaching the movement trajectory of a processing tool, it is easier to perform the work by setting the shape and effective length of the processing tool to be constant, and it is also easy for the operator to conceptually understand. Therefore, in the present invention, during teaching, teaching is performed using a simulated processing tool having a specific effective length l ₀ that serves as a reference, and during execution, the effective length l ₁ of the processing tool to be used is instructed. By doing so, we can obtain Δa=l ₀ −l ₁ and perform the calculations of equations (7) to (9) above, thereby making the tip of the processing tool draw a trajectory as taught for any processing tool. can.
For example, in a welding robot, when the welding gun is automatically replaced depending on the welding location, or in arc welding, when teaching, the effective length is defined as the tip of the welding electrode, and when executing, the length is the addition of the necessary arc length. This also corresponds to cases where the command is given in place of a command. In addition, in TIG arc welding using a non-consumable electrode, a power source with drooping characteristics or constant current characteristics is generally used as the welding power source, and the welding voltage, that is, the arc voltage is proportional to the arc length. In other words, there are times when so-called arc voltage tracing is performed to keep the arc voltage constant by moving the welding torch forward and backward relative to the workpiece.
By making the difference between this arc voltage ea and the reference voltage er correspond to Δa in each of the above equations and correcting the main coordinate axis position of the welding torch, the arc voltage Copying can be carried out. In this case, the reference voltage er
By making it adjustable from the outside, it is possible to set any arc voltage regardless of the command signal for each axis, making it easy to set and change welding conditions.

In addition, in arc welding using a consumable electrode, the effective length of the processing tool is the length of the welding torch from the support point.
It is the sum of l ₄ , the protrusion length of the consumable electrode wire from the tip of the welding torch, l ₅ , and the arc length, l ₆ . When a power source with constant voltage characteristics is used as the welding power source, the welding current changes in response to changes in the wire protrusion length _l5 , and when a power source with constant current characteristics is used, the welding current changes as described above.
As with TIG welding, the arc voltage ea changes in response to changes in arc length, and both of these change the welding result. Therefore, the signals corresponding to the wire protrusion length and arc voltage, or the detected values of welding current and arc voltage, and the length of the welding torch
By using _l4 as the effective length signal _a2 of the welding head, the wire protrusion length and arc voltage can always be set to arbitrary values.

By the way, in microcomputers used in industrial robots, it is convenient for the above-mentioned calculations to be performed using a method in which digital signals are normally input and digital signals are output. and above
In the calculations of equations (7) to (9), when outputting the calculation results in digital quantities, values less than one single position are rounded down for each calculation, so (7) or (9) are simply converted into digital signals. If (Δx, Δy, Δz), which is the calculation result of equation (9), is used as the correction amount, fractions will be rounded down each time the calculation is performed, and this may be accumulated in sequence, resulting in a large error. To prevent this, when the arithmetic circuit 18 receives the second command signal an for the effective length of the processing tool,
Corresponding to the angle of the wrist axis from each origin, Δxn = (a ₁ − an) sinθ sinφ … (10) Δyn = (an − a ₁ ) sinφ cosθ … which corresponds to equations (4) to (6) above. (11) Main arithmetic circuit that calculates Δzn=(an−a ₁ )(1−cosθ) …(12) and correction of the principal coordinate axes calculated for each command change from the origin to the (n−1)th The sum of the quantities Δxi, Δyi, Δzi, _o-1 〓 ⁱ⁼¹ Δx′i, _o-1 〓 ⁱ⁼¹ Δy′i, _o-1 〓 ⁱ⁼¹ Δz′i, and Subtract the addition result of this adder from the calculation result of the arithmetic unit Δx′n=Δxz− _o-1 〓 ⁱ⁼¹ Δx′i …(13) Δy′n=Δyn− _o-1 〓 ⁱ⁼¹ Δx ′i...(14) Δz′n=Δzn− _o-1 〓 ⁱ⁼¹ Δx′i...(15) It may be configured from an auxiliary computing unit. By configuring the arithmetic circuit 18 in this manner, the above-mentioned error when performing arithmetic operations using digitized values can be compensated as needed for each command change of the effective length of the processing tool. As a result, the occurrence of errors is extremely reduced, and accuracy can be dramatically improved.

In the embodiment shown in FIG. 3, when the angles θ and φ of the wrist axes remain unchanged, when the effective length a of the processing tool changes, a command signal is sent to change the position of the wrist attachment part with respect to the main coordinate axes. We have described a device that keeps the oriented position of the processing tool immobile by moving it through correction, but as can be seen from equations (1) to (9) above, the oriented position of the processing tool is determined by the effective length a of the processing tool.
In addition, it also changes depending on the angles θ and φ of the wrist axis.
Therefore, when the angle of these wrist axes changes, it is necessary to keep the pointing position of the processing tool unchanged.

FIG. 5 is a block diagram showing an embodiment of a device that can meet such requirements. In the figure, numerals 9 to 23 indicate those having the same functions as those in FIG.
24 is a first calculation circuit that calculates a correction signal for the main coordinate axes from the outputs of registers 16 and 17 that integrate command signals for the Θ and Ψ axes from the controller 9 and the effective length signal a of the processing tool; Third
It has the same function as the arithmetic circuit 18 shown in the figure. 25 receives the position increment commands θc and φc for both axes with respect to the Θ and Ψ axes from the controller 9, and changes the amount of correction of the main coordinate axes, that is, the X, Y, and Z axes, to the current positions of the Θ and Ψ axes. a second arithmetic circuit, 26, which calculates accordingly;
is a storage circuit generally called a waiting queue or FIFO memory, which stores the calculation results in the order in which they arrive using the calculation completion signal m of the calculation circuit 25 as a write command, and stores the calculation results in the order in which they arrive, as well as the interpolation completion signal r of the interpolation circuit 27, which will be described later.
This is a circuit that reads out data from the beginning in the order in which they are stored as read commands.

Encoders 14c and 15c 27 receive the output of the memory circuit 26 and detect movements of the Θ and Ψ axes.
It is a linear interpolator that distributes pulses for each output of 21
to 23 input the output of the controller 9 to the first arithmetic circuit 2.
4 and the output of the linear interpolator 27 to obtain a total output.

In the apparatus shown in FIG. 5, the servo control circuit for each axis and the correction operation of the main coordinate axes by the first arithmetic circuit 24 in response to changes in the effective length a of the processing tool are the same as in the embodiment shown in FIG. The explanation will be omitted, and the operation will be explained regarding the correction operation when the wrist axis is rotated. The signals θc and φc for the wrist axis from the controller 9 are integrated in the Θ-axis and Ψ-axis current position recording registers 16 and 17, and are
It is also supplied to the arithmetic circuit 25 of. The registers 16 and 17 integrate the rotation angles θ and φ of the wrist axis from the origin and output them to the first arithmetic circuit 24 and the second arithmetic circuit 25. Second arithmetic circuit 25
As will be explained in detail later, from these θ, φ,
The amount of correction for each Z axis is calculated and output to the storage circuit 26. When the second arithmetic circuit 25 completes the computation, the memory circuit 26 receives the computation results and sequentially stores them. On the other hand, in response to command signals θc and φc from the wrist axis, the Θ and Ψ axes begin to rotate, and the encoder 1 accordingly begins to rotate.
4c and 15c generate output pulses. The interpolator 27 uses the output pulses from this encoder.
reads the contents of the memory circuit 26 in the order in which they were stored;
The stored contents are distributed in pulses according to the output pulses from the encoders 14c and 15c, and correction amounts for each of the X, Y, and Z principal coordinate axes are sequentially output by linear interpolation. This correction amount is determined by the correction circuits 21 to 23.
At the output of the first arithmetic circuit 24, the controller 9
The command signals xc, yc, and zc are added and combined and supplied to the drive control circuits 11a to 13a for the main coordinate axes. As a result, the tip of the processing tool always faces the same pointing position regardless of changes in the positions of the wrist axes Θ and Ψ axes.

Here, the arithmetic circuit 25, memory circuit 26, and interpolation circuit 27 will be explained in detail with reference to FIG.

FIG. 6 is an explanatory diagram showing only the processing tool portion of the apparatus shown in FIG. 1 and its relationship with the coordinate axes. 6th
In the figure, a ₀ indicates the length of the wrist from the rotation center of the Θ axis of the wrist to the attachment position of the processing tool, and a ₁ indicates the effective length of the processing tool. Now, consider the case where the wrist attachment position is at point Q and the tip of the processing tool is at point _P0 .
Let the coordinates of point P ₀ be P ₀ (x ₀ , y ₀ , z ₀ ), and from this, Θ
If the position of the tip of the processing tool when rotated by Θ around the axis and φ around the Ψ axis is P ₄ (x ₄ , y ₄ , z ₄ ), then
At this time, point P ₄ is from point P ₀ to Δx ₄ = a ₀ (cosθ−1)−a ₁ sinφ sinθ …(16) Δy ₄ =a ₀ sinθ＋a ₁ sinφ cosθ …(17) Δz ₄ =a ₁ (1− cosφ) …(18). Therefore, when the position of the wrist axis is (θ, φ), the position of the tip of the processing tool is
P ₄ (x ₀ +Δx ₄ , y ₀ +Δy ₄ , z ₀ +Δz ₄ ). In order to maintain this at the original position P ₀ , the wrist attachment portion Q only needs to be moved by (−Δx ₄ , −Δy ₄ , −Δz ₄ ) along the orthogonal coordinate axes. From the state corrected in this way, the wrist axis is further adjusted by θc, which is one command unit.
When rotated by φc, the position of the tip of the processing tool at this time (Δx ₅ , Δy ₅ , Δz ₅ ) can be determined by setting θ in equations (16) to (18) above as (θ + θc) and φ as (φ + φc). However, in reality, the wrist attachment part has already been corrected by (−Δx ₄ , −Δy ₄ , −Δz ₄ ), so the amount to be corrected this time is (Δx ₅ −Δx ₄ , Δy ₅ −
Δy ₄ , Δz ₅ −Δz ₄ ). Therefore, the second arithmetic circuit 25 calculates the above equations (16) to (18) for each command unit of the Θ-axis and Ψ-axis, and also stores the calculations. Any method may be used as long as it is subtracted from the values of Δx, Δy, and Δz one command unit before, and outputs the difference as correction signals for the principal coordinate axes X, Y, and Z to the storage circuit 26 together with the computation end signal m.
In the calculations of formulas (16) to (18), when outputting the calculation results in digital quantities, values less than one unit quantity are rounded down for each calculation, as explained in the example shown in Figure 3. Therefore, as mentioned above, (Δx, Δy, Δz) of the digitized operation result is simply
If the difference between the calculation result and the calculation result one command unit before is used as the correction amount, fractions will be rounded down each time calculation is performed, and this may be accumulated sequentially, resulting in a large error. Therefore, when the arithmetic circuit 25 receives the n-th command signal for the Θ and Ψ axes in the same way as the arithmetic circuit 18 in FIG. The main arithmetic unit that calculates Δyn, Δzn, and the correction amount Δx′ of the main coordinate axes calculated for each command unit from the origin to the (n-1)th
Accuracy can be improved by comprising an adder that calculates the sum of Δy' and Δz', and an auxiliary arithmetic unit that subtracts the addition result of this adder from the arithmetic result of the main arithmetic unit. .

Next, the role and operation of the memory circuit 26 will be explained. As mentioned above, in a servo control system having a feedback loop, a delay with respect to a command signal always occurs at the time of startup and during steady state. In other words, the operation of the servo system is possible due to the presence of this delay. Therefore, when each axis receives a command signal, it moves in a direction toward the target with a delay unique to each axis. As explained in FIGS. 2 and 6, when the wrist axes Θ and Ψ axes receive a command signal, a predetermined calculation is performed on this command signal, and the result of this calculation is used to calculate the In cases where correction commands are issued for the X, Y, and Z axes, if these correction operations are performed by handling only the command signal, the axes that originally caused the correction (i.e., the Θ and Ψ axes) and the axes (i.e., X, Y,
The order of the operations may be reversed with respect to the Z-axis operations. In other words, if the response of the axis receiving the correction command is fast, the X, Y, and Z axes may perform unnecessary correction operations while the wrist Θ and Ψ axes have not yet rotated enough to require correction of the principal coordinate axes. Stowing away occurs. The memory circuit 26 is provided to prevent this.
It only calculates the correction amount of the principal coordinate axes for the command value of the wrist axes (Θ, Ψ axis), temporarily stores this calculation result, and then calculates the correction amount when the Θ and Ψ axes actually rotate. When the value is reached, the calculation results are sequentially read out and the principal coordinate axes are corrected. In this way, the amount of correction calculated in advance for the rotation command of the Θ and Ψ axes is output to the main coordinate axes when the Θ and Ψ axes actually rotate. Regardless of the situation, only the necessary amount of correction is always executed, making the operation extremely stable and reliable. The interpolation circuit 27 is connected to the memory circuit 26
The memory contents at the beginning are read out and temporarily stored, and pulses are distributed by linear interpolation using the outputs of encoders 14c and 15c which detect the rotations of the attitude control axes Θ and Ψ. Here, the outputs of encoders 14c and 15c are Θ and Ψ
When emitting a pulse of one unit for each command unit of each axis, the interpolation circuit 27 is naturally unnecessary, and the correction circuit 21 reads out the stored contents of the memory circuit 26 directly using the outputs of the encoders 14c and 15c as a readout command. It is advisable to supply it between 23 and 23. However, in this case, the amount of correction described above for one command unit of the Θ and Ψ axes is
The command unit is fine, but if the hand length a ₀ and processing tool length a ₁ in Figure 6 are large values, 1 of the Θ and Ψ axes.
The amount of correction for each axis of X, Y, and Z for the command unit is a number.
It can reach 10 to several 100 command units. If such a large amount of correction is made at once, the operation of the tip of the processing tool becomes irregular, and the initial purpose may not be achieved. To solve this problem, the outputs of encoders 14c and 15c must be set to Θ,
It is assumed that n times as many output pulses as the number of commands for the Ψ axis are generated, and the amount of correction read out from the storage circuit 26 using the n times as many pulses is linearly interpolated and distributed n times. In this way, the position of each of the X, Y, and Z axes can be corrected with n times the resolution for one command unit of the Θ and Ψ axes. In this case, X,
Command signals xc, yc, zc and Θ for Y and Z axes,
There is n:1 between the command signals θc and φc for the Ψ axis.
Although it is necessary to set the above pulse ratio, generally the amount of movement in each of the X, Y, and Z axes is several meters or more per minute, and the corresponding pulses reach tens of thousands of pulses. On the other hand, the amount of movement of both the Θ and Ψ axes is approximately several revolutions per minute, and the pulses required for this are several hundred to several thousand pulses. Therefore, n in the above ratio is
Setting it to around 10 is sufficient.

Of course, the interpolation circuit 27 may be omitted if the storage circuit 26 obtains an output obtained by linearly interpolating the output in accordance with an external pulse distribution command.

Note that in the above explanation, in order to simplify the explanation, an industrial robot that positions a processing tool along three orthogonal axes of X, Y, and Z was explained.
The number of these principal coordinate axes may be two or less, and the control device of the present invention can also be applied to a robot having only one of the Θ axis and the Ψ axis for the wrist axis. Furthermore, since machining is performed by relative movement between the processing tool and the workpiece, it goes without saying that any axis among these principal coordinate axes may be used as the axis for controlling the position of the workpiece. . For example, in the apparatus shown in FIG. 1, the apparatus of the present invention is applied to control the position of the W-axis of the workpiece mounting jig instead of the X-axis. When doing this, there is no need to make delicate corrections on the X-axis, where both the load and the moment of inertia are at their maximum, and where accurate positioning control is difficult. It is the sum of the adjustment ranges that can be used to measure the improvement in functionality.

Furthermore, the present invention is not only applicable to cases where the principal coordinate axes are constituted by a rectangular coordinate system as shown in the above embodiments, but also to cases where the principal coordinate axes are constituted by a polar coordinate system and a cylindrical coordinate system. It is easy to understand that the present invention can be applied to industrial robots configured with all kinds of coordinate systems, such as cases where these coordinate systems are used in combination, or cases where these coordinate systems are partially mixed. In these cases, it goes without saying that the calculation contents of the calculation circuit and the type of command signals for the coordinate axes are determined according to each coordinate system.

As described above, when using the apparatus of the present invention, the length of the processing tool can be changed arbitrarily, so that the processing tool can be easily selected and replaced. In particular, when this control device is used in a welding robot, the effective length of the welding torch, which is a processing tool, can be There is no need to redo the teaching operation even if there is a change in the length, the taught data remains as it was, and the position command for the principal coordinate axes is corrected by simply issuing a command to change the effective length. The length can be easily selected. This makes it extremely easy to select and change welding conditions. Also, when adding the detected welding voltage or welding current signal to this effective length command signal, use a non-consumable electrode.
Feedback control, such as arc voltage tracing control in TIG welding and control of the protrusion length of the electrode wire in arc welding using consumable electrodes, can be performed online while a teaching command is being executed. There is no need to provide a mechanism in the welding head, which not only simplifies the device and allows it to be manufactured at low cost, but also reduces the weight of the welding head, making it possible to operate faster and more accurately. Furthermore, in addition to the correction operation for the change in the effective length, the amount of position correction of the main coordinate axes caused by the change in posture is calculated in response to command signals for the wrist posture control axes Θ and Ψ.
This is sequentially memorized, and the memorized correction amount is sequentially read out using a detection pulse that detects the movement according to the movement of the wrist axis to correct the position command value of the main coordinate axes and drive each axis. Therefore, even when changing the wrist posture, it is possible to smoothly change the orientation position of the tip of the processing tool while keeping it at a predetermined position. In addition, since the calculation of the correction amount itself is performed for each command unit of the Θ and Ψ axes when the attitude command signal is transmitted, the calculation time can be relatively long.The calculation results are also temporarily stored in a memory circuit and sequentially stored. Since the principal coordinate axes are corrected by reading them out, there are no errors due to response delays or unnecessary correction operations, and corrections can be made stably and accurately. Furthermore, when correcting the memorized correction amount by linear interpolation using the output of an encoder that generates n times the number of output pulses of the movement command unit of the wrist axis, the position of the principal coordinate axes can be corrected with high resolution. It can be carried out.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the external shape of an industrial robot to which the present invention is applied; FIG. 2, FIG. 4, and FIG. 6 are explanatory views showing how the processing tool changes its effective length and posture; FIGS. 3 and 5 are configuration diagrams showing an embodiment of the apparatus of the present invention. 2...Column, 3...Arm support, 4...Arm,
5...Wrist part, 6...Processing tool, 9...Controller, 11a~
15a... Drive control circuit for each axis, 11b to 15b...
Drive motor, 11c to 15c...encoder, 1
8, 24, 25... Arithmetic circuit, 26... Memory circuit, 2
7...Interpolation circuit, 21-23...Correction circuit, X, Y,
Z...Orthogonal coordinate axes, Θ, Ψ...Attitude control axes.

Claims (1)

[Scope of Claims] 1. A control system that has a coordinate axis for relatively moving a processing tool and a workpiece, and an attitude control axis that determines the attitude of the processing tool, and that commands the operation of each of the axes. and a servo control circuit that positions each axis according to a command signal from the controller. an arithmetic circuit that receives a command signal instructing the effective length of the processing tool, calculates the amount of change in the pointing position of the processing tool tip that occurs when changing the effective length of the processing tool, and calculates a position correction signal for the coordinate axis; A control device for an industrial robot, comprising a correction circuit that corrects a position command signal for the coordinate axes among command signals using an output signal of the arithmetic circuit and transmits the corrected signal to the servo control circuit. 2. In the control device for the industrial robot, when teaching the movement trajectory of the processing tool, the reference processing tool length l ₀ is taught, and during execution it can be adjusted instead of the reference length l ₀ . 2. The control device for an industrial robot according to claim ₁ , further comprising a switching circuit for supplying the execution length l1 to the arithmetic circuit. 3. The processing tool is an arc welding torch using a non-consumable electrode, and the effective length signal of the processing tool is preset as the distance _l2 from the support point of the arc welding torch to the tip of the non-consumable electrode. The difference voltage between the set welding voltage er and the detected welding voltage ea (er−
The control device for an industrial robot according to claim 1 or 2, wherein the control device is the sum of the signal _l3 corresponding to ea). 4 The processing tool is an arc welding torch that uses a consumable electrode, and the effective length signal of the processing tool is the distance _l4 from the support point of the arc welding torch to the torch tip, and the consumable electrode protruding from the torch tip. is the sum of the length _l5 of the electrode and a signal _l6 corresponding to a predetermined welding voltage ea, and at least one of the protrusion length _l5 of the electrode and the signal _l6 corresponding to the welding voltage is adjustable. A control device for an industrial robot according to claim 1 or 2. 5. When the arithmetic circuit receives a command signal to change the effective length of the processing tool, the arithmetic circuit calculates the position of the coordinate axis according to the rotation angle from the origin of the posture control axis and the deviation amount of the effective length from the reference signal. A main computing unit that calculates a correction signal, and an auxiliary computing unit that subtracts the sum of correction amounts of the coordinate axes calculated before receiving the effective length change command signal from the output of the main computing unit. A control device for an industrial robot according to any one of items 1 to 4. 6. The control device for an industrial robot according to any one of claims 1 to 5, wherein the current position signal of the attitude control axis is an attitude control command signal output from the controller. 7. The control device for an industrial robot according to any one of claims 1 to 5, wherein the current position signal of the attitude control axis is an output of a detector that detects the operating position of the attitude control axis. . 8. A controller that has a coordinate axis for moving a processing tool and a workpiece in a relative direction and an attitude control axis that determines the attitude of the processing tool, and instructs the operation of each of the axes, and the controller In an industrial robot control device comprising a servo control circuit that positions each axis according to a command signal from the controller, the effective length of the processing tool is determined between the current position signal of the attitude control axis and the command signal from the controller. a first arithmetic circuit that receives a command signal for instructing and calculates the amount of change in the pointing position of the tip of the processing tool that occurs when changing the effective length of the processing tool, and calculates a position correction signal for the coordinate axes; and the attitude control axis. A detector is provided to detect the amount of movement of the position control axis, and a position correction signal for the coordinate axes is calculated by receiving a command signal for the posture control axis among the position command signals and calculating the amount of change in the pointing position of the tip of the processing tool that occurs when changing the posture. a second calculation circuit that stores the output of the second calculation circuit and reads it out in correspondence with the output of the detector; and a storage circuit that stores the output of the second calculation circuit and reads it out in correspondence with the output of the detector; A control device for an industrial robot, comprising a correction circuit that corrects the output signal of the circuit and the output signal of the storage circuit and transmits the corrected signal to the servo control circuit. 9 In the control device for the industrial robot, when teaching the movement trajectory of the processing tool, the reference processing tool length l ₀ is taught, and during execution, it can be adjusted in place of the reference length l ₀ . 9. The control device for an industrial robot according to claim 8, further comprising a switching circuit for supplying the execution length _l1 to the arithmetic circuit. 10 The processing tool is an arc welding torch using a non-consumable electrode, and the effective length signal of the processing tool is preset as the distance l ₂ from the support point of the arc welding torch to the tip of the non-consumable electrode. The difference voltage between the set welding voltage er and the detected welding voltage ea (er
-ea) and a signal _l3 corresponding to the signal l3. 11 The processing tool is an arc welding torch that uses a consumable electrode, and the effective length signal of the processing tool is the distance _l4 from the support point of the arc welding torch to the torch tip, and the consumable electrode protruding from the torch tip. is the sum of the length _l5 of the electrode and a signal _l6 corresponding to a predetermined welding voltage ea, and at least one of the protrusion length _l5 of the electrode and the signal _l6 corresponding to the welding voltage is adjustable. A control device for an industrial robot according to claim 8 or 9. 12 When the first arithmetic circuit receives a command signal to change the effective length of the processing tool, the first arithmetic circuit changes the effective length according to the rotation angle from the origin of the posture control axis and the deviation amount of the effective length from the reference signal. Consisting of a main computing unit that calculates a position correction signal for the coordinate axes, and an auxiliary computing unit that subtracts the sum of correction amounts for the coordinate axes calculated before receiving the effective length change command signal from the output of the main computing unit. A control device for an industrial robot according to any one of claims 8 to 11. 13 The second arithmetic circuit includes a main arithmetic unit that calculates a position correction signal of the coordinate axes according to a rotation angle from the origin of each axis when receiving a rotation command signal of the attitude control axis, and the main arithmetic unit. and an auxiliary computing unit that subtracts the sum of the correction amounts of the coordinate axes calculated before receiving the rotation command signal of the attitude control axis from the output of the attitude control axis. control equipment for industrial robots. 14. The control device for an industrial robot according to any one of claims 8 to 13, wherein the current position signal of the attitude control axis is an attitude control command signal output from the controller. 15. The industrial robot control device according to any one of claims 8 to 13, wherein the current position signal of the attitude control axis is an output of a detector that detects the operating position of the attitude control axis. . 16 The memory circuit divides the basic motion amount corresponding to one command unit of the attitude control command signal into n (n≧1)
Claim 8 is a circuit that includes a circuit that distributes and outputs a stored value by a linear interpolation method in which one command unit of an attitude control command signal is divided into n by the output of an encoder that outputs a signal. control equipment for industrial robots.