JP2010023128A - Robot system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a robot system capable of working along a desired working track even if a large-sized workpiece is supported by a plurality of robots. <P>SOLUTION: The robot system comprises a plurality of robots having a working device for working a workpiece by a tool, a machining controller and a workpiece holding hand, and a robot controller for controlling the machining controller and the plurality of robots for working the workpiece along a target machining line while moving the workpiece by the plurality of robots. A moving track of a reference point corresponding to the target machining line on a tool coordinate system having a hand tip as the origin is calculated per calculation cycle. A hand tip position of a first robot is calculated, and the hand tip position of the first robot is moved to the position. Thus, the workpiece is moved with respect to the tool so that the track of the tool coincides with the target machining line while a hand tip position of a second robot keeps relative positional relation with the hand tip position of the first robot. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a robot system for cooperatively operating a plurality of robots, and more particularly to a robot system for moving a workpiece gripped by a plurality of robots.

When processing a workpiece using a robot, it is common to attach an end effector such as a welding torch to the tip of the robot and move the end effector relative to the fixed workpiece by operating the robot.
On the other hand, there is a method in which an effector such as a welding torch is fixed to the outside of the robot without being attached to the tip of the robot, and the work is gripped by the robot and moved by the operation of the robot. In this case, since the position of the work point on the work as seen from the tip of the robot changes every moment, it is necessary to operate the robot appropriately in order to perform work on a desired location on the work. Patent Document 1 discloses a robot control method in which a robot grips a workpiece and moves the workpiece relative to a fixed welding torch (effector).

The outline of Patent Document 1 will be described with reference to FIG. In the figure, 101 is a welding torch fixed at a predetermined position, 103 and 104 indicate robot arms, and a workpiece 102 is held by a hand (not shown) at the tip of the arm. Prior to starting the work, the welding start point a1 on the workpiece is positioned at the tip P0 of the welding torch 101 (state W in FIG. 7), and the coordinate transformation matrix R1 from the origin O of the reference coordinate system to the tip of the arm at that time Ask for.
When the coordinate transformation matrix for the reference coordinate system of the coordinate system provided at the welding torch attachment position is [U] and the coordinate transformation matrix for the coordinate system provided at the welding torch attachment position at the welding torch tip position is [P], The coordinate transformation matrix [T1] from the arm tip to the welding torch tip P0 is
[T1] = [R1] ^-1 [U] [P] (1)
Can be obtained as [U] and [P] are known and constant, and [R1] can be obtained from information on each arm length and each joint angle of the robot. As a result, the coordinate transformation matrix [T1] at the welding start point can be obtained by Expression (1).
Similarly, the workpiece 102 is moved to W ′ in FIG. 7 so that the welding end point a2 is positioned at the tip P0 of the welding torch, and the arm tip from the origin O of the reference coordinate system is determined from information on each arm length and each joint angle of the robot. If the coordinate transformation matrix [R2] up to is obtained, the coordinate transformation matrix [T2] from the arm tip to the welding torch tip P0 is
[T2] = [R2] ^-1 [U] [P] (2)
Can be obtained as

When moving from a1 to a2 at the control cycle n times during the regeneration operation, the coordinate transformation matrix [Ti] from the arm tip to the welding torch tip P0 at the i-th time is obtained as follows. .
[Ti] = [T1] + (i / n) ([T2]-[T1]) (3)
On the other hand, the arm tip position between them is
[Ri] = [U] [P] [Ti] ^-1 Formula (4)
Therefore, the coordinate transformation matrix [Ri] corresponding to [Ti] can be obtained by this calculation, and each joint angle of the robot can be obtained.
By operating the robot along the joint angle thus obtained, a work locus from the welding start point a1 to the welding end point a2 can be realized on the workpiece 102.
JP-A-1-37603

However, in the invention of Patent Document 1, only the case of handling a workpiece by one robot is considered.
If the end effector is attached to the tip of the robot and the robot is operated to move the end effector relative to the fixed work, there is no need to consider the work size and mass.
On the other hand, when the effector is fixed to the outside of the robot and the workpiece is gripped by the robot and moved by the movement of the robot, the size and mass of the workable workpiece depends on the handling ability of the robot. In order to cope with machining work for larger workpieces, it is necessary to use a larger robot or to handle the robots properly by gripping the workpieces with multiple robots. . The latter method is advantageous in view of dealing with workpieces of various sizes and masses. In other words, when the size and mass of a workpiece is sufficient with one robot, each robot is used individually and handled in parallel, and when the size and mass of the workpiece are large, a plurality of robots can be used to grip the workpiece. It becomes possible to handle workpieces.
In view of such a situation, the present invention provides a robot system capable of performing work along a work locus intended for a work even when a work having a large size and mass is handled by a plurality of robots. Objective.

In order to solve the above problem, the present invention is configured as follows.
The invention of the robot system according to claim 1 includes a tool for processing a workpiece, the processing device that processes the workpiece by moving the tool relative to the workpiece, and controls the processing device. And a plurality of robots each having a hand for gripping the workpiece, and a robot controller for controlling the processing control device and the plurality of robots. A robot system that moves the workpiece in a state of being moved by the plurality of robots and performs machining along a target machining line on the workpiece by the tool, wherein the robot control device is misaligned during machining operations. Is set as a reference point, and the point corresponding to the target machining line in the tool coordinate system with the hand tip as the origin is set. The movement locus of the reference point is obtained every calculation cycle, the hand tip position of the first robot among the plurality of robots for realizing the movement locus is calculated, and the hand tip position of the first robot is calculated. The tool trajectory coincides with the target machining line while the relative position of the hand tip of the second robot is kept constant relative to the hand tip position of the first robot. The workpiece is processed by moving the workpiece relative to the tool.
According to a second aspect of the present invention, in the robot system according to the first aspect, the robot control device uses the position of the tip of the tool when the tool processes the work as the reference point as the reference point. It is characterized by controlling the position of the robot hand.
According to a third aspect of the present invention, in the robot system according to the first or second aspect, the robot control device outputs a command to the machining control device to control the operation of the tool.
According to a fourth aspect of the present invention, in the robot system according to the first aspect, the plurality of robots are vertical articulated robots.

According to the first aspect of the present invention, the workpiece is gripped by a plurality of robots and handled with the relative positional relationship between the hands kept constant, so that the workpiece can be stably processed even for workpieces having a large size and mass. Can contribute to the improvement of machining quality. In addition, since a reference point that does not cause misalignment due to the machining operation is provided and the positions of the hands of the plurality of robots are controlled based on the reference point, the machining can be performed according to the target machining line.
According to the second aspect of the present invention, since the position of the tool tip when the tool performs machining on the workpiece is set as a reference point that does not cause misalignment due to the machining operation, a plurality of robots are set based on the reference point. Thus, the position control of each hand can be simplified, and machining can be easily performed according to the target machining line.
According to the invention described in claim 3, since the timing of operating the tool can be controlled in accordance with the workpiece handling operation by the robot, the machining quality can be improved.
According to the invention described in claim 4, since the posture of the workpiece with respect to the tool can be maintained in an optimum state in accordance with the shape of the target machining line, machining quality can be improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing a configuration of a robot system according to the present invention.
In the present invention, in order to achieve the purpose of moving a workpiece along a target trajectory line even when the size and mass of the workpiece held by the robot is large, the position of the workpiece being worked by handling the workpiece by a plurality of robots. It was set as the structure which adjusts. In FIG. 1, a configuration using two robots is used.
In the figure, 1 is a first robot and 2 is a second robot, each of which is a multi-joint robot having a plurality of joint axes. The two robots are connected to the robot control device 5 and their operations are controlled by the robot control device 5. The first robot 1 and the second robot 2 have hands 3 and 4 at their tips, respectively, and these hands open and close to grip a workpiece.
In order to ensure the freedom of the position and posture of the workpiece, each robot is desirably a vertical articulated type.
6 is a processing apparatus, which processes the workpiece. The processing device 6 is installed in the reachable area of the hands of the first robot 1 and the second robot 2. Reference numeral 9 denotes a machining control device that controls the machining device 6.

In the present embodiment, arc welding will be described as an example of the machining operation.
In the case of arc welding, the welding torch corresponds to a processing device, and the nozzle or wire at the tip of the welding torch corresponds to a tool. Further, a welding power source for supplying a welding current to the welding torch and a wire feeding device for supplying a wire to the welding torch correspond to the processing control device, but these are simplified as the processing control device 9 in FIG. Yes.
The machining control device 9 is connected to the machining device 6, and the machining control device 9 is further connected to the robot control device 5. The machining control device 9 sends a wire to the welding torch in accordance with a signal received from the robot control device 5. Or supply welding current.
In FIG. 1, the processing device 6 and the processing control device 9 are separate, but they may be configured integrally.

Hereinafter, the flow of processing when a workpiece is actually handled by the robot system of the present invention and welding is performed by the processing apparatus will be described.
(1) First, according to a command from the robot control device 5, the first robot 1 and the second robot 2 grip both ends of a workpiece placed on a workpiece placement table (not shown) with their respective hands. FIG. 2 shows a state in which the workpiece is gripped by the hands of the first robot 1 and the second robot 2 in this way. Similar to the processing device 6, the mounting table is installed in the reachable area of the hands of the first robot 1 and the second robot 2.
(2) Thereafter, the first robot 1 and the second robot 2 work together while maintaining the state of gripping the workpiece W, that is, while processing the workpiece W while keeping the relative positional relationship between the hands 3 and 4 constant. It conveys to the tool 7 of the apparatus 6, that is, directly below the tip of the welding torch. A series of cooperative operations for gripping the workpiece W and transporting it to the processing device 6 are taught in advance and stored in the robot control device 5. Further, since the cooperative operation is performed, the positional relationship between the first robot 1 and the second robot 2 is known.
(3) When the transfer of the workpiece W by the robot is completed, the robot control device 5 (FIG. 1) transmits a first trigger to the machining control device 9 (FIG. 1).
(4) When receiving the first trigger, the machining control device 9 starts a predetermined operation such as feeding a wire to the welding torch and supplying a welding current. It is assumed that the workpiece W and the ground wire of the welding power source are connected in advance.

(5) When the machining control device 9 confirms the start of work on the workpiece W, the machining control device 9 outputs a signal to the robot control device 5. Specifically, the operation is started by detecting arc generation by a welding power source.
(6) Upon receiving this signal, the robot controller 5 moves the hands 3 and 4 at the tips of the first robot 1 and the second robot 2 so that the movement locus of the tool 7 coincides with the target machining line on the workpiece W. To start.
(7) Since the workpiece W gripped as the hand moves also moves relative to the tool, the workpiece W is welded along the target machining line. This is shown in FIG. By moving the workpiece W in the direction of the white arrow by the hands 3 and 4, the workpiece is welded along the target processing line.
The first robot 1 and the second robot 2 operate in cooperation during the welding process. The operation during this time is also taught in advance and stored in the robot controller 5.
Although the target machining line is a straight line in FIG. 3, it goes without saying that the target machining line can be an arbitrary curve by giving appropriate teachings to the first robot 1 and the second robot 2.

Here, during the machining operation, the robot control device 5 controls the first robot 1 and the second robot 2 so that the trajectory of the tool 7 coincides with the target machining line instead of simply reproducing the taught operation.
Details of the control of the first robot 1 and the second robot 2 by the robot controller 5 during the machining operation will be described later.

(8) When the movement operation for workpiece machining by the first robot 1 and the second robot 2 is completed, the robot control device 5 outputs a second trigger to the machining control device 9.
(9) The machining control device 9 stops supplying the welding current and feeding the welding wire to the welding torch by the second trigger reception.
(10) When detecting the stop of the arc, the machining control device 9 outputs a machining end signal to the robot control device 5.
(11) The robot control device 5 receiving the processing end signal operates the first robot 1 and the second robot 2 in a coordinated manner to separate the workpiece W from the processing device 6 and conveys it to the mounting table. Open 4 and release work W.
The above is a series of processing procedures by the robot system of the present invention.

Below, control of the 1st robot 1 and the 2nd robot 2 by the robot control apparatus 5 in welding work is demonstrated using FIG. 4, FIG.
(1) First, a coordinate system RB1 based on the first robot 1 and a coordinate system RB2 based on the second robot 2 are set in advance.
(2) Next, let the tip position of the tool which processes a workpiece be the reference point A. In this embodiment, the tip of the welding torch becomes the reference point A. The position of the reference point A does not change during the machining operation.
(3) Further, a vector from the origin of the coordinate system RB1 to the reference point A is obtained and set as ^RB1 T1.
(4) Further, the positional relationship between the coordinate system RB1 and the coordinate system RB2, that is, the positional relationship between the first robot 1 and the second robot 2 is obtained, and the conversion matrix from the coordinate system RB1 to the coordinate system RB2 is expressed as ^RB1 M And
The vector ^RB1 T1 and the transformation matrix ^RB1 M are uniquely determined once the first robot 1, the second robot 2, and the machining device 6 are installed, and do not change during machining operations.
(5) Here, when the first robot 1 is at a teaching point at which machining work is taught in advance, the coordinate value of the tool tip position of the first robot 1 in the coordinate system RB1 is ^RB1 B1, the coordinate value ^RB1 B1, and the reference point Let ^RB1 P1 be the vector connecting A.
The tool tip position is set at the grip at the tip of the hand. An example of the tool tip position in the present invention is shown as a black point K1 in FIGS.

(6) First, control of the first robot 1 will be described.
The coordinate value ^RB1 B1 uses the joint angle of each axis of the first robot 1 recorded at the time of teaching, the link parameter of each axis of the robot, and the positional relationship of the tool tip position based on the robot tip. It can be obtained by the robot controller 5 by kinematics. The positional relationship between the robot link parameters and the tool tip position with reference to the robot tip is also stored in the robot controller 5 in advance.
(7) When the first robot 1 moves from the coordinate value ^RB1 B1 to the next teaching point, the coordinate value of the tool tip of the first robot 1 in the coordinate system RB1 is ^RB1 B2, the coordinate value ^RB1 B2, and the reference point Let ^RB1 P2 be a vector connecting A.
(8) Subsequently, a tool coordinate system TF1 (FIG. 5) having the tool tip position of the first robot 1 as an origin is provided.
(9) While the tool tip of the first robot 1 moves from the coordinate value ^RB1 B1 to the coordinate value ^RB1 B2, the change in the position of the reference point A viewed from the tool coordinate system TF1 is as shown in FIG. That is, the tool coordinate system TF1 actually moves with respect to the reference point A along with the operation of the first robot 1, but the reference point A seems to move when viewed from the tool coordinate system TF1. appear.

Based on FIG. 4 and FIG. 5, the control method of the 1st robot 1 is demonstrated below.
As described above, when the movement from the coordinate value ^RB1 B1 to the coordinate value ^RB1 B2 of the tool tip position of the first robot 1 in FIG. 4 is viewed from the tool coordinate system TF1 of the first robot 1, as shown in FIG. This corresponds to a change in the coordinate value of the point A from ^TF1 P1 to ^TF1 P2.
^{Assuming that} the movement from the coordinate value ^RB1 B1 to the coordinate value ^RB1 B2 is taught as linear interpolation, let us consider the interpolation of the operation of the first robot 1 during this period.
Normally, the displacement amount for each calculation cycle for moving the tool tip position along the straight line connecting the coordinate value ^RB1 B1 and the coordinate value ^RB1 B2, which are teaching points, is calculated, and each axis of the first robot 1 is calculated by inverse kinematics. Ask for the command and operate.
Here, in the present invention, a reference point A that does not cause misalignment during work is set so that the actual movement locus from the coordinate value ^RB1 B1 to the coordinate value ^RB1 B2 becomes a straight line as intended, and tool coordinates The movement trajectory ( ^TF1 P1 → ^TF1 P2) of the reference point A corresponding to the target machining line in the system TF1 is obtained for each calculation cycle. Then, the tool tip position (hand tip position) of the first robot 1 for realizing the movement locus is calculated, and the tool tip position of the first robot 1 is moved to that position.

If the movement from the coordinate values ^RB1 B1 to coordinate values ^RB1 B2 is linear interpolation, the movement locus of the coordinate value ^TF1 P1 in the tool coordinate system TF1 to coordinate values ^TF1 P2 becomes a straight line. If the taught moving speed is Vp [cm / sec], the length of the line segment connecting the coordinate value ^TF1 P1 and the coordinate value ^TF1 P2 is L [cm], and the operation period of the robot controller is m [sec]. The number N of operation cycles during the movement from the coordinate value ^TF1 P1 to the coordinate value ^TF1 P2 is expressed by Equation (5).
N = L / (Vp · m) (5)
Here, N is a natural number, and the fractional part of the right side of Expression (1) is rounded down.
Therefore, the position ^TF1 P (i) of the reference point A based on TF1 in the i-th calculation cycle (i is a natural number, N ≧ i) is expressed by Expression (6).
^TF1 P (i) = ^TF1 P1 + (( ^TF1 P2- ^TF1 P1) / N) * i Formula (6)
The coordinate value ^RB1 B (i) of the tool tip corresponding to this position ^TF1 P (i) with reference to the coordinate system RB1 can be obtained as equation (7) using ^RB1 T1.
^RB1 B (i) = ^RB1 T1. ( ^TF1 P (i)) ⁻¹ (7)
Thus, if the coordinate value ^RB1 B (i) of the tool tip is obtained for each calculation cycle, the position where the tool tip of the first robot 1 should be can be obtained. The first robot 1 is operated by obtaining a command to each axis of the first robot 1 from the coordinate value ^RB1 B (i) of the tool tip by inverse kinematics.

Next, a method for controlling the second robot 2 will be described.
When the tool tip position of the first robot 1 is the coordinate value ^RB1 B1, the coordinate value in the coordinate system RB2 of the tool tip position of the second robot 2 corresponding to this is ^RB2 C1. As shown as black point K1 in FIGS. 1 and 2, the tool tip position of the second robot 2 is also set at the grip at the tip of the hand.
When the tool tip position of the first robot 1 is the coordinate value ^RB1 B2, the coordinate value in the coordinate system RB2 of the tool tip position of the second robot 2 corresponding to this is ^RB2 C2.
Further, a tool coordinate system TF2 having the tool tip position of the second robot 2 as an origin is provided, and a conversion matrix from the tool coordinate system TF1 to the tool coordinate system TF2 is ^TF1 T2.
Since the hand of the first robot 1 and the hand of the second robot 2 perform a cooperative operation, the relative positional relationship between the hands is designated in advance and is constant during the machining operation. That is, the transformation matrix ^TF1 T2 is known and does not change during the machining operation.

Then, when the tool tip position of the first robot 1 is the coordinate value ^RB1 B1, when the coordinate value ^RB2 C1 is viewed from the coordinate system RB1 of the first robot 1, equation (8) is obtained.
^RB1 C1 = ^RB1 B1 · ^TF1 T2 (8)
When the first tool tip position of the robot 1 is tool tip position of the second robot 2 with to move to the coordinate value ^RB1 B2 is moved to the coordinate value ^RB2 C2, the first robot coordinate value ^RB2 C2 1 When viewed from the coordinate system RB1, the equation (9) is obtained.
^RB1 C2 = ^RB1 B2 · ^TF1 T2 (9)
Here, when a transformation matrix ^RB1 M from the coordinate system RB1 of the first robot 1 to the coordinate system RB2 of the second robot is used, the coordinate value ^RB2 C1 and the coordinate value ^RB2 C2 are expressed by the equations (10) and (11), respectively. Can be expressed as:
^RB2 C1 = ( ^RB1 M) ⁻¹ · ^RB1 B1 · ^TF1 T2 (10)
^RB2 C2 = ( ^RB1 M) ^-1 · ^RB1 B2 · ^TF1 T2 (11)
The movement from the coordinate values ^RB1 B1 to coordinate ^RB1 B2 is also performed by the calculation cycle N times time moving from the as well as the coordinate value ^RB2 C1 is performed by the operation cycle N times the time until the coordinate value ^RB2 C2, The coordinate value ^RB2 C (i) of the tool tip with reference to the coordinate system RB2 in the i-th calculation cycle can be expressed as in Expression (12) using the coordinate value ^RB1 B (i).
^RB2 C (i) = ( ^RB1 M) ⁻¹ · ^RB1 B (i) · ^TF1 T2 (12)
As described above, since the transformation matrix ^RB1 M and the transformation matrix ^TF1 T2 are known and constant, if the coordinate value ^RB1 B (i) is determined by the equation (7), the corresponding coordinate value ^RB2 C (i ) Is uniquely determined.
Thus, after ^obtaining the coordinate value ^RB1 B (i) of the tool tip of the first robot 1, the coordinate value ^RB2 C (i) of the tool tip with reference to the coordinate system RB2 in the i-th calculation cycle is obtained. By obtaining, the position where the tool tip should be can be obtained also for the second robot 2.
Then, the second robot is operated by ^obtaining a command from ^RB2 C (i) to each axis of the second robot 2 by inverse kinematics.

In the example of FIG. 3, the workpiece W is handled while being kept horizontal, but if the robot that holds the workpiece W is a vertical articulated type, the workpiece W can be processed in various postures. In addition, the posture of the workpiece W can be changed during the machining operation, and the case where the target machining line has a complicated shape can be handled.
The present invention has been described by taking arc welding as an example of processing on the workpiece W. However, the present invention can also be applied to cases where seam welding, sealing, cutting, cutting, or the like is performed as processing on the workpiece. For example, in the case of seam welding, the workpiece W is formed by stacking a plurality of metal plates W1 and W2 as shown in FIG. 6, and is gripped by the hands 3 and 4 in the stacked state, so that the first robot 1 and the second robot 2 are stacked. The seam welder (not shown) installed in the reachable area of the hand is handled.
In the above description, two robots are used. However, if the positional relationship between the processing apparatus 6 and each robot is known, the present invention can be applied to perform cooperative operation even when three or more robots are used. It goes without saying that you can do it. If three or more robots are used, heavier workpieces can be handled or the workpieces can be gripped firmly.

The figure which shows the structure of the robot system of this invention Front view showing a state where a workpiece is gripped by the first robot and the second robot The perspective view which shows the mode of joining by the robot system of this invention The figure explaining tool tip position calculation at the time of processing work of the present invention The figure which shows the mode of the movement of the reference point A seen from the tool coordinate system TF1 of the 1st robot of this invention. Front view showing a state where workpieces are stacked and gripped by the first robot and the second robot The figure which shows the conventional robot control method

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st robot 2 2nd robot 3, 4 Hand 5 Robot control device 6 Processing device 7 Tool 9 Processing control device 101 Welding torch 102 Work 103, 104 Arm

Claims (4)

A tool for machining the workpiece, and a machining device for machining the workpiece by moving the tool relative to the workpiece;
A processing control device for controlling the processing device;
A plurality of robots each provided with a hand for gripping the workpiece;
A robot control device for controlling the processing control device and the plurality of robots,
A robot system that moves the workpiece in a state of being gripped by the hand by the plurality of robots, and performs processing along a target processing line on the workpiece by the tool,
The robot controller sets, as a reference point, a point that does not cause misalignment during a machining operation, and calculates a movement locus of the reference point corresponding to the target machining line in a tool coordinate system with the hand tip as an origin. Obtained every calculation cycle, calculate the hand tip position of the first robot among the plurality of robots for realizing this movement locus, and move the hand tip position of the first robot to that position. The tool is placed on the tool so that the trajectory of the tool coincides with the target machining line while the relative position of the hand tip of the second robot is kept constant relative to the hand tip position of the first robot. The robot system is characterized in that the workpiece is machined by moving the workpiece.   The robot control device controls positions of the hands of the plurality of robots during a machining operation using the position of the tool tip when the tool performs machining on the workpiece as the reference point. The robot system described.   The robot system according to claim 1, wherein the robot control device outputs a command to the machining control device to control the operation of the tool.   The robot system according to claim 1, wherein the plurality of robots are vertical articulated robots.

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