JP2023030396A - Direct teaching system, direct teaching program, and direct teaching method - Google Patents

Abstract

To provide a direct teaching system for directly teaching a plurality of cooperative motions, which can reduce time and labor of a teacher.SOLUTION: A direct teaching system 1 includes: a workpiece 4 supported by a plurality of robots 2; force sensors 3 attached respectively to the plurality of robots 2; and a controller 11 for cooperatively controlling the plurality of robots 2. The control unit 11 includes: a geometric constraint calculation unit 14 for calculating geometric constraint conditions 59 of the workpiece 4 and the robots 2; and a work motion/position/posture calculation unit 15 for calculating a motion 55 and a position and posture 56 of the workpiece 4 caused by an external force applied to the workpiece 4 by a teacher; and a target position/posture calculation unit 16 for calculating a target position and posture 58 of each robot 2 on the basis of the motion 55 and the position and posture 56 of the workpiece 4.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a direct teaching system, a direct teaching program, and a direct teaching method for directly teaching cooperative motions to a plurality of robots.

In recent years, direct teaching techniques have been developed in which a teacher directly moves an industrial robot by hand to teach the robot a motion.

The motions taught to the robot include normal motions in which a single robot moves freely to a target position, and coordinated motions in which multiple robots move to a target position under geometric constraints while maintaining the positional relationship between tools. be. In particular, when transporting a long and narrow workpiece or a large workpiece, a single robot cannot stably transport the workpiece, so a coordinated movement of multiple robots is used.

In general, when directly teaching cooperative motions, a method is used in which a specific robot is designated as a "leader" and other robots are designated as "followers", and the followers are moved so as to follow the leader's movement. For example, Patent Document 1 discloses a direct teaching method in which a robot arm 10 to which an external force is applied by direct teaching is used as a master, and the other robot arm 20 is used as a slave, and the trajectory of the slave side is calculated based on the trajectory of the movement of the master side. is disclosed.

JP 2017-193011 A JP-A-63-034609

However, according to the method of Cited Document 1, since the leader is directly instructed and the follower follows, only the measurement value of the leader's sensor is reflected, and it is difficult to instruct the follower in detail. There was a problem. In particular, when the leader and the follower are far from each other, the leader needs to be elaborately taught in order to align the work position of the follower, which imposes a heavy burden on the instructor. Moreover, according to the apparatus of the cited document 2, the instructor moves the work to directly teach both of the multiple arms, but the weight and the gravitational position of the work cannot be estimated. There was a problem that it took time and effort to set the information related to

Therefore, an object of the present disclosure is to provide a direct teaching system that can reduce the burden on the instructor by saving the trouble of finely instructing the follower and the trouble of setting information about the work when directly teaching the cooperative movement. be.

In order to solve the above problems, the direct teaching system of the present disclosure is a direct teaching system that directly teaches a plurality of robots. A work weight/weight system comprising sensors and control means for cooperatively controlling a plurality of robots, wherein the control means estimates the weight and center-of-gravity position of the work based on the initial measurement values of the force sensor and the initial position and orientation of the robot. center-of-gravity position estimation means; workpiece motion/position/orientation calculation means for calculating the movement and position/orientation of the workpiece caused by an external force applied to the workpiece by the instructor based on the measured values of the force sensor and the position and orientation of the robot; target position/posture calculation means for calculating a target position/posture of the robot based on the motion and position/posture of the work, wherein the work motion/position/posture calculation means uses the estimated weight and center of gravity position of the work to: It is characterized by performing gravity compensation of the work.

According to the direct teaching system of the present disclosure, since the target position/posture of each robot is calculated based on the motion and position/posture of the work, the instructor can teach the robot a cooperative motion by moving the work. In addition, since the weight and center-of-gravity position of the work are estimated, it is possible to save the trouble of setting actual measurement values for the weight and the center-of-gravity position of the work. In this way, it is possible to reduce the burden on the teacher.

1 is a conceptual diagram of a direct teaching system showing an embodiment of the present disclosure; FIG. 3 is a block diagram showing the configuration of a control unit; FIG. FIG. 4 is an explanatory diagram of a coordinate system used in the direct teaching system; FIG. 5 is a schematic diagram showing the motion of the robot when the teacher applies an external force to the work; FIG. 4 is a schematic diagram showing (a) geometric quantity and (b) external force applied to a work. 4 is a flow chart showing the operation flow of the direct teaching system;

An embodiment in which the present disclosure is embodied in a direct teaching system will be described below with reference to the drawings. In the following description, a number from 1 to n is assigned to a plurality of robots, and a suffix i (i: 1 to n) is used.

As shown in FIG. 1, the direct teaching system 1 of the present disclosure is mounted between a plurality of robots 2, a robot controller 5 that cooperatively controls the plurality of robots 2, a flange 21 of the robot 2, and a tool 22. A force sensor 3, one workpiece 4 supported by all of the plurality of robots 2, and a PC 6 for arithmetic processing are provided. Here, the tool 22 indicates a part of the robot 2 that performs a predetermined process on an object such as the work 4 or the like.

A control unit 11 that cooperatively controls the robot 2 is implemented as a program in the robot controller 5 and the PC 6 of the robot 2 . Although the functions of the control unit 11 are distributed to the robot controller 5 and the PC 6 in this embodiment, it is also possible to mount the functions of the control unit 11 on the robot controller 5 and eliminate the need for the PC 6 .

As shown in FIG. 2, the control unit 11 includes a measurement value conversion unit 12 that converts a measurement value 51i of each force sensor 3i into a calibrated value 52i representing an external force applied to the tool tip 22ai based on calibration; Work weight/center of gravity position estimator 13 for estimating weight and center of gravity position of work 4; A workpiece motion/position/orientation calculator 15 for calculating a motion 55 and a position/orientation 56 of the workpiece 4 caused by the applied external force, and a target position/orientation calculator 16 for calculating a target position/orientation 58 of the robot 2 are provided. Each function (12 to 16) of the control unit 11 will be described below.

We now describe the mathematical preparations in this disclosure. Let <a, b> be the inner product of three-dimensional vector a and vector b, and a×b be the cross product. A matrix exponential function for a square matrix X is defined as Equation 2.

As shown in FIG. 3, the coordinate system C used in the present disclosure includes a flange coordinate system Cf (origin Of) based on the flange 21, a tool coordinate system Ce with the tool tip position 22a as the origin Oe, and a robot 2 A world coordinate system Cw having a point common to all as an origin Ow. A flange coordinate system Cfi and a tool coordinate system Cei are provided for each robot 2i, and a world coordinate system Cw is provided for all the robots 2 in common. In addition, in the present disclosure, “the position and orientation 57 of the robot 2” is actually the position and orientation of the flange 21, that is, the position and orientation of the flange coordinate system Cf.

A "position" is a point in a three-dimensional space and is represented by a three-dimensional vector. The “attitude” is a three-dimensional tilt and is represented as a rotation matrix of 3 rows and 3 columns. The pair of pose R and position t (R; t) means the homogeneous transformation matrix of Eq.

Also, (R; t) is regarded as an affine transformation, and the action on the point p is expressed as Equation 4.

(measured value converter)
Based on the calibration, the measured value conversion unit 12 converts the measured value 51i of each force sensor 3i into a calibrated value 52i representing the external force applied to the tip end 22ai of the tool, and converts the calibrated value 52i into each tool coordinate system Cei to the world coordinate system Cw to calculate a transformed value 53i.

The translational force F(Fx, Fy, Fz) and the moment M(Mx, My, Mz), which are the measured values 51 of the force sensor 3, measure the external force (translational force and moment) at the reference point Of of the force sensor 3. However, the external force at the tool tip position 22a is not measured. Therefore, by converting the measured value 51 into a calibrated value 52 that indicates the external force applied to the tool tip 22a based on the calibration, errors caused by the force sensor and the mounting state of the tool are compensated for and a more accurate force can be obtained. It allows control. Specific processing of the measured value conversion unit 12 will be described below.

First, let the position and orientation 57i of each flange coordinate system Cfi (each robot 2i) in the flange coordinate system Cfi be (R _i ; t _i ), and let the position and orientation of the tool coordinate system Cei in the flange coordinate system Cfi be (R _{i; e} ; Let t _i;e ).

The unit vector ξ in the direction of gravity is obtained by averaging the unit vectors ξ _i in the direction of gravity obtained by haptic calibration. In other words, it suffices to estimate the unit vector ξ that maximizes Equation 5.

Based on force calibration, the measurement value conversion unit 12 converts the measurement value 51i (translational force F _i and moment M _i ) of the force sensor 3i into a calibrated value 52i (translational force F ^e _i and moments M ^e _i ). The measured value conversion unit 12 further coordinates-transforms the calibrated value 52i into the world coordinate system Cw to obtain a transformed value 53i (translational force F ^wi _and moment M ^wi ₎ (equation 6).

(workpiece weight/center of gravity position estimator)
The work weight/center-of-gravity position estimator 13 estimates the weight and center-of-gravity position of the work 4 based on the initial measured value 51i ₀ of each force sensor 3i and the initial position/orientation 57i ₀ of the robot 2i.

In the present disclosure, as shown in FIG. 4, the work 4 is regarded as a virtual rigid body, and it is assumed that the external force detected by the force sensor 3 causes the work 4 to move via the tool 22. It is assumed that each robot 2i follows the movement of the workpiece 4. FIG. As a result, unlike the leader/follower type, the measured values 51i of all the force sensors 3 are reflected in the coordinated motion, making it easier to move the work 4 and improving the operability of direct teaching.

However, under this assumption, the measured value 51i of the force sensor 3i always includes the translational force and moment based on the weight and the position of the center of gravity of the workpiece 4. Therefore, when direct teaching is started, the workpiece 4 descends along the gravity. There is a problem that Therefore, measures are taken to estimate the weight and center of gravity of the workpiece 4 before starting direct teaching, and compensate for the gravity during teaching.

As shown in FIG. 5, in the workpiece weight/center-of-gravity position estimation 13, for the i-th robot 2i, the initial position/orientation 57i ₀ of each flange coordinate system Cfi (each robot 2i) in the world coordinate system Cw is set to (R _i;0 ; t _i;0 ). An initial measurement value 51i ₀ (translational force F _i;0 and moment M _i;0 ) of each force sensor 3i is acquired, and the initial external force applied to the tool tip 22ai in the world coordinate system Cw is indicated by the measurement value conversion unit 12. Obtain an initial transformation value 53i ₀ (translational force F ^w _i;0 and moment M ^w _i;0 ).

An initial external force 54 ₀ (translational force F ^s ₀ and moment M ^s ₀ about the center of gravity) applied to the workpiece 4 is given by Equation (7). Here, m is the weight of the work 4 and _th0 is the initial center of gravity position of the work 4 in the world coordinate system Cw, both of which are unknown. Also, g is the gravitational acceleration, and u _i;0 is the initial position of the tool tip 22ai in the world coordinate system Cw. u _i;0 is expressed as in Equation 8.

Here, for the gravitational force m, an error function relating to the balance of the translational force F ^s ₀ is defined by Equation 9, and m that minimizes E(m) can be estimated. For the center of gravity position t _h0 , the error function for the balance of moment M ^s ₀ is defined by Equation 10, and t _h0 that minimizes G(t _h0 ) can be estimated. Hereinafter, let the position of the center of gravity t _h0 be the initial position of the work 4, and let the initial orientation R _h0 of the work 4 be the identity matrix.

(Geometric Constraint Calculator)
The geometric constraint condition calculator 14 calculates the geometric constraint conditions 59i of the work 4 and each robot 2i based on the position of the center of gravity of the work 4 and the initial position/orientation 58i ₀ of each robot 2i.

When the position and orientation of the workpiece 4 is (R _h ; _th ), the geometric constraint condition of the position and orientation 57i (R _i ; t _i ) of each flange coordinate system Cfi (each robot 2i) is expressed as shown in Equation 11. be able to. At this time, the initial values of the velocity vector v and the angular velocity vector ω of the workpiece 4 are set to zero.

(work motion/position/orientation calculator)
The work motion/position/orientation calculation 15 calculates the motion 55 of the work 4 caused by the external force applied to the work 4 by the teacher and the position and orientation of the work 4 based on the measured values 51i of each force sensor 3 and the position and orientation 57i of each robot 2i. is calculated.

For the robot 2i, let (R _i ; t _i ) be the current position and orientation 57i of each flange coordinate system Cfi (each robot 2i) in the world coordinate system Cw. Measured values 51i (translational force F _i and moment M _i ) of each force sensor 3i are acquired, and the measured value conversion unit 12 converts values 53i (translational force F Find ^w _i and moment M ^w _i ). Let _ui be the current position of the tool tip 22ai in the world coordinate system Cw (equation 12).

An external force 54 (translational force F _s and moment M _s ) applied to the workpiece 4 is given by Equation (13). In Equation 13, gravity compensation is performed using the workpiece weight m and the workpiece center-of-gravity position _th . Acceleration α and angular acceleration ψ of workpiece 4 are calculated by equation (14).

where λ _F and λ _M are the motion acuity coefficients representing the virtual inertial mass and moment of inertia, respectively. The greater these values, the greater the motion of the workpiece 4 against the external force. Also, ρ _F and ρ _M are viscosity coefficients, and by making it difficult to move the workpiece 4 in proportion to the velocity v and the angular velocity ω, the workpiece 4 is gradually decelerated unless an external force is applied. These coefficients are determined experimentally.

The work motion/position/orientation calculator 15 calculates the motion 55 (velocity v, angular velocity ω) and position/orientation 56 (R _h ; th ₎ of the work 4 based on Equation (15).

In Equation 15, Δτ is the time interval of the cycle process. Also, W := [ω] _× .

(Target position/orientation calculator)
The target position/orientation calculation unit 16 calculates the target of each robot 2i based on the motion 55 of the workpiece 4, the position/orientation 56 of the workpiece, the position/orientation 57i of each robot 2i, and the geometric constraint conditions 59i regarding the workpiece 4 and each robot. The position and orientation 58i are obtained (equation 16).

Next, the operation of the direct teaching system 1 configured as described above, the operation of the direct teaching program, and the direct teaching method using the direct teaching system 1 will be described with reference to FIG. This operation and method consist of initial processing S1 in which initial processing is performed as a preparation before starting direct teaching, and cycle processing S2 in which the control unit 11 issues an operation command at a predetermined cycle while the teacher moves the workpiece 4. consists of

In the initial processing S1, the control unit 11 first acquires an initial position/orientation 57i ₀ of each flange coordinate system Cfi (each robot 2i) and an initial measurement value 51i ₀ of each force sensor 3i (S11). At this time, it is assumed that all the robots 2 are stopped and one workpiece 4 gripped by all the robots 2 is stable. Next, the measured value conversion unit 12 converts the initial measured value 51i ₀ of each force sensor 3i into an initial calibrated value 52i ₀ indicating the initial external force at the tip 22ai of the tool based on the calibration _. is coordinate-transformed from the tool coordinate system Ce to the world coordinate system Cw to obtain an initial transformation value 53i ₀ .

The work weight/center-of-gravity position estimation unit 13 estimates the weight and the position of the center-of-gravity position of the work 4 using the initial conversion value 53i ₀ (S12). After that, the geometric constraint calculation unit 14 calculates the geometric constraint 59i between the workpiece 4 and each flange 21 using the estimated position of the center of gravity of the workpiece 4 (S13). After the initial processing S1 is finished, the teacher holds the work 4 in hand and starts direct teaching.

In the cycle process S2, first, the control unit 11 acquires the current position and orientation 57i of each robot 2i and the current measurement values 51i of each force sensor 3 (S21). Next, the measured value converter 12 converts the measured value 51i of each force sensor 3i into a calibrated value 52i at the tool tip 22ai based on the calibration, and converts the calibrated value 52i from the tool coordinate system Ce to the world coordinate system Cw. to obtain a transformed value 53i. After that, the control unit 11 uses the converted value 53i to calculate the external force 54 (translational force F _s and moment M _s ) applied to the workpiece 4 (S22).

Subsequently, the work motion/position/orientation calculator 15 calculates the motion 55 of the work 4 and the current position/orientation 56 of the work 4 based on the external force 54 applied to the work 4 (S23). The target position/orientation calculator 16 calculates the target position/orientation 58i of each robot 2i based on the motion 55 of the work, the current position/orientation 56 of the work 4, the current position/orientation 57i of each robot 2i, and the geometric constraint conditions 59i. is calculated (S24). Finally, the control unit 11 issues an operation command to each robot 2i based on the target position/orientation 58i (S25). It is preferable that the cycle processing S2 is performed at a cycle of about 30 Hz while the teacher moves the workpiece 4 .

According to the direct teaching system configured as described above and the direct teaching method using the system, unlike the case where the leader/follower type is set and direct teaching is performed, all the force sensors are reflected in the coordinated motion. becomes easier to move, and the workability of direct teaching is improved.

In addition, under this assumption, the measured value of the force sensor always includes the translational force and moment based on the weight of the workpiece and the position of the center of gravity. , The weight and center of gravity position of the workpiece are estimated before starting direct teaching, and gravity compensation is taken during teaching, so there is no need to set the weight and center of gravity position of the workpiece each time.

In addition, the present disclosure is not limited to the above embodiments, and the configuration of each part can be arbitrarily changed without departing from the scope of the invention.

1 direct teaching system 2 robot 3 force sensor 4 workpiece 5 robot controller 6 PC
11 Control Unit 12 Measured Value Transformation Unit 13 Work Weight/Center of Gravity Position Estimation Unit 14 Geometric Constraint Condition Calculation Unit 15 Work Motion/Position/Posture Calculation Unit 16 Target Position/Posture Calculation Unit 21 Flange 22 Tool 51 Measurement Value 52 Calibration Value 53 Conversion Value 54 Work external force 55 Work motion 56 Work position/posture 57 Robot position/posture 58 Target position/posture 59 Geometric constraints

Claims (4)

A direct teaching system that directly teaches a plurality of robots,
A workpiece supported by a plurality of said robots, a force sensor attached to each of said robots, and a control means for cooperatively controlling said plurality of said robots,
The control means is
work weight and center-of-gravity position estimation means for estimating the weight and center-of-gravity position of the work based on the initial measurement values of the force sensor and the initial position and orientation of the robot;
Work motion/position/posture calculation means for calculating the motion and position/posture of the work caused by an external force applied to the work by a teacher based on the measured values of the force sensor and the position/posture of the robot;
a target position/orientation calculation means for calculating a target position/orientation of the robot based on the motion and position/orientation of the workpiece;
The direct teaching system, wherein the work motion/position/orientation calculation means performs gravity compensation of the work using the estimated weight and center of gravity position of the work. 2. The direct teaching system according to claim 1, wherein said control means includes measured value conversion means for converting measured values of the force sensor into calibrated values applied to the tip of the tool based on force sense calibration. A direct teaching program that, when executed in a computer, causes the computer to function as the control means according to claim 1 or 2. A method of directly teaching a plurality of robots using the direct teaching system according to claim 1 or 2,
An initial processing stage in which the control means performs initial processing for direct teaching; and a cycle processing stage in which the control means issues the operation command at a predetermined cycle while the instructor performs the direct teaching,
The initial processing step comprises:
obtaining an initial pose of the robot;
obtaining an initial measurement of the force sensor;
estimating the weight and center-of-gravity position of the workpiece;
The cycle processing step comprises:
obtaining a current position and orientation of the robot;
obtaining a current measurement of the force sensor;
calculating the motion and position/orientation of the workpiece based on the current position/orientation of the robot and the current measurement values of each of the force sensors;
calculating a target position and orientation of the robot based on the motion and position and orientation of the workpiece;
The direct teaching method, wherein the step of calculating the motion and position/orientation of the work includes the step of performing gravity compensation of the work using the estimated weight and center-of-gravity position of the work.

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