JP7070114B2 - Robot control device and robot control method - Google Patents

Description

The present invention relates to a robot control device and a robot control method.

In recent years, at product manufacturing sites and the like, automation of work using robots has been promoted against the background of a shortage of workers due to a decrease in the working population. For example, in machining processes such as cutting and grinding, automation using a machining robot is promoted, and in a welding process, automation using a welding robot is promoted. Further, in the painting process, automation using a painting robot is promoted, and in the finishing process, automation of deburring, chamfering, rounding, polishing, etc. using a finishing robot is promoted.

Such a robot operates along a trajectory in which straight lines and curves are connected under the control of a robot control device. When the orbit consists of a plurality of straight lines and curves, the velocity changes abruptly at the joint between the straight lines and the curves. For example, at a place where a straight line changes to a curved line, a robot operating at a constant speed along the straight line moves in a circular motion along the curved line, so that the angular velocity rises sharply from 0. For this reason, when the robot is made to follow exactly along the trajectory, an excessive load is applied to the robot drive device (for example, a motor) at the joint between a straight line and a curve where a discontinuity of velocity (angular velocity) occurs. It takes.

In order to avoid such an excessive load on the drive device, it is necessary to correct the trajectory and suppress a sudden change in speed before the robot is operated along the trajectory. The following Patent Documents 1 and 2 disclose an example of a conventional correction method for suppressing a sudden change in speed. Specifically, in the following Patent Documents 1 and 2, the trajectory is corrected based on the maximum acceleration and the acceleration section.

Japanese Unexamined Patent Publication No. 2008-132595 Japanese Unexamined Patent Publication No. 2014-161918

By the way, when controlling the various robots described above, the orbital followability is important. That is, when controlling the various robots described above, it is important that the tracking error with respect to the target trajectory is within the predetermined target tracking error. In Patent Documents 1 and 2, it is necessary to change the parameters used for correction of the acceleration section and the like by trial and error so that the tracking error with respect to the target trajectory is within the target tracking error, and in order to obtain the optimum trajectory. There was a problem that it took time.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a robot control device and a robot control method capable of obtaining an optimum trajectory that can avoid an excessive load in a short time.

In order to solve the above problems, the robot control device according to one aspect of the present invention has an acquisition unit (21) for acquiring a target trajectory and an allowable error with respect to the target trajectory, and an error with respect to the target trajectory. A track generation unit (22) that generates a machining trajectory within the margin of error, and a control unit (23) that controls a robot (10) to follow the machining trajectory generated by the trajectory generation unit. Be prepared.
Further, in the robot control device according to one aspect of the present invention, the trajectory generation unit generates the processing trajectory in which the acceleration of the robot is continuous.
Further, in the robot control device according to one aspect of the present invention, the track generation unit selects the one having the smallest maximum acceleration among the plurality of generated processing tracks.
Further, in the robot control device according to one aspect of the present invention, the permissible error includes the permissible error of position and posture.
Further, in the robot control method according to one aspect of the present invention, the acquisition step (S11) for acquiring the target trajectory and the permissible error with respect to the target trajectory, and the error with respect to the target trajectory are within the permissible error. It includes a trajectory generation step (S12) for generating a machining trajectory and a control step (S13) for controlling the robot (10) so as to follow the machining trajectory generated in the trajectory generation step.

According to the present invention, there is an effect that an optimum trajectory that can avoid an excessive load can be obtained in a short time.

It is a figure which shows the outline structure of a robot system. It is a figure which shows an example of the processing trajectory required by the robot control device by one Embodiment of this invention. It is a flowchart which shows the operation of the robot control apparatus by one Embodiment of this invention. It is a figure which shows an example of the workpiece and the target trajectory used in one Embodiment of this invention. It is a figure which shows an example of the processing track generated in the example of welding the workpiece shown in FIG. 4.

Hereinafter, the robot control device and the robot control method according to the embodiment of the present invention will be described in detail with reference to the drawings.

<Robot system>
FIG. 1 is a diagram showing an outline configuration of a robot system. As shown in FIG. 1, the robot system 1 includes a robot 10 and a robot control device 20, and performs predetermined processing on the work W. Here, examples of the processing performed by the robot system 1 on the work W include processing (cutting, grinding, etc.), welding, painting, finishing (deburring, chamfering, rounding, polishing, etc.), and other processing. .. In this embodiment, it is assumed that the robot system 1 performs welding (laser welding) of the work W.

The robot 10 includes a robot arm 11, a hand portion 12, a laser welding device 13, and a robot controller 14. The robot arm 11 has an articulated mechanism in which a plurality of arms are connected in series by a plurality of joints. Each joint of the robot arm 11 is provided with a motor (not shown) for driving each joint. The robot arm 11 can move, for example, in a three-dimensional space in a six-axis direction by driving a motor by a robot controller 14 under the control of a robot control device 20. Further, each joint is provided with an encoder that detects the rotation angle of the motor.

The hand portion 12 detachably connects the laser welding device 13 as a tool to the robot arm 11. The laser welding device 13 is attached to the tip of the robot arm 11 by the hand portion 12. By driving the robot arm 11, the position and orientation of the laser welding device 13 in the three-dimensional space can be changed. The laser welding device 13 irradiates the work W with a laser beam and locally melts and solidifies the work W to join the work W.

The robot controller 14 controls the operation of the robot arm 11 under the control of the robot control device 20. Specifically, the robot controller 14 controls the operation of the robot arm 11 by driving a motor provided at each joint of the robot arm 11. The robot controller 14 performs real-time communication with the robot control device 20. As a result, in the robot system 1, real-time control of the robot arm 11 is realized in a predetermined control cycle.

<Robot control device>
The robot control device 20 includes an acquisition unit 21, a trajectory generation unit 22, a control unit 23, and a storage unit 24, and controls the robot 10. The acquisition unit 21 acquires the target trajectory of the robot 10 and the permissible error with respect to the target trajectory. The acquisition unit 21 is a target trajectory and margin of error input from the input device, or a storage unit 24, in response to an instruction input from an input device (for example, a keyboard) (not shown) provided in the robot control device 20. Obtain the stored target trajectory and tolerance.

The above target trajectory is a trajectory for moving the laser welding device 13. For example, the trajectory for moving the injection port of the laser beam provided in the laser welding device 13 may be set as the target trajectory. The data indicating the target trajectory includes data indicating spatial coordinates (X, Y, Z) at fixed distance intervals and data indicating the posture (θX, θY, θZ) of the laser welding apparatus 13. Note that θX, θY, and θX are rotation amounts around the X-axis, Y-axis, and Z-axis, respectively. The above tolerance includes the tolerance (position margin) allowed for the spatial coordinates (X, Y, Z) and the posture (θX, θY, θZ). Tolerance (margin of error) is included.

The track generation unit 22 generates a smooth processing track in which the error with respect to the target trajectory acquired by the acquisition unit 21 falls within the tolerance acquired by the acquisition unit 21. Here, the smooth machining trajectory is a machining trajectory in which the acceleration of the robot 10 (laser welding device 13) is continuous. Continuous acceleration does not mean that the acceleration rises sharply (discontinuous) from 0, as in the case of transition from a linear orbit to a curved orbit, but indicates a continuous change in acceleration. That (for example, the acceleration is differentiable).

The track generation unit 22 obtains the above-mentioned processing track by an optimization calculation with the constraint that the error from the target trajectory falls within the margin of error. The evaluation function in the optimization calculation is determined by the machining content of the work W, and for example, the maximum value of jerk can be mentioned. Here, when the machining trajectory is obtained by the optimization calculation, a plurality of machining trajectories may be obtained. When a plurality of machining tracks are obtained, the track generation unit 22 selects the machining track having the smallest maximum acceleration.

Hereinafter, the processing performed by the orbit generation unit 22 will be described. Here, in order to facilitate understanding, an example of generating a machining trajectory when the robot 10 (laser welding apparatus 13) is moved along the X axis will be described. Let x be the target trajectory of the robot 10, and consider the trajectory near the teaching point. In the orbit connecting the teaching points with a straight line, the velocity changes at the teaching points. Assuming that the position of the teaching point is x = 0, the time t = 0 passing through the teaching point, and the velocities before and after the teaching point are v ₁ and v ₂ , respectively, the target trajectory x is expressed by the following equation (1).

The track generation unit 22 obtains a machining track x1 by, for example, dividing a section for obtaining a machining track into a plurality of sections and performing a process of smoothly connecting the machining tracks in each section. Here, assuming that the section for obtaining the processing track is divided into four, each section is divided into three points of t = −Δ, 0, Δ. Note that Δ is a value determined by using the margin of error e, and is represented by the following equation (2).

Under the condition that the connection point of each section is continuous up to the second derivative, the processing track x1 of each section is expressed by using the following equation (3).

However, a3 in the above equation ( ₃ ) is represented by the following equation (4).

With reference to the above equations (2) to (4), it can be seen that the machining track x1 is obtained by the velocities _v1 and _v2 and the margin of error e. That is, it can be seen that the machining track x1 is obtained from the target track x and the margin of error e.

FIG. 2 is a diagram showing an example of a machining trajectory required by a robot control device according to an embodiment of the present invention. In FIG. 2, the target trajectory TR0 and the machining trajectory when the velocity v ₁ = -1 [m / sec], the velocity v ₂ = 1 [m / sec], and the margin of error e = 0.5 [m]. TR1 and the margin of error range ER are shown. With reference to FIG. 2, it can be seen that the machining track TR1 is a smooth track that falls within the permissible error range ER in the entire section (-2 ≦ t ≦ 2).

The control unit 23 controls the robot 10 so as to follow the processing track x1 generated by the track generation unit 22. The storage unit 24 stores various data, various parameters, and various programs used in the robot control device 20. For example, data indicating a target trajectory, data indicating a processing trajectory generated by the trajectory generation unit 22, data indicating an allowable error with respect to the target trajectory, and other data are stored.

Such a robot control device 20 is realized by a computer such as a personal computer. Then, each function of the robot control device 20 (acquisition unit 21, trajectory generation unit 22, control unit 23, and storage unit 24) is software-like, for example, by executing a program stored in the storage unit 24 in a computer. It will be realized. That is, each function of the robot control device 20 is realized by the cooperation of software and hardware resources.

<Robot control method>
FIG. 3 is a flowchart showing the operation of the robot control device according to the embodiment of the present invention. FIG. 4 is a diagram showing an example of a workpiece and a target trajectory used in one embodiment of the present invention. As shown in FIG. 4, in the present embodiment, welding of a work W having a track shape in the XY plane (a work having two parallel straight lines along the Y axis and two curves connecting them) is welded. The case of doing this will be described as an example. As shown in the figure, the target trajectory TR10 of the laser welding apparatus 13 in this example has a straight line portion P1, a curved line portion P2, and a straight line portion P3 continuous.

When the processing of the flowchart shown in FIG. 3 is started, the processing of acquiring the target trajectory and the tolerance is first performed by the acquisition unit 21 of the robot control device 20 (step S11: acquisition step). For example, a process of acquiring a target trajectory (target trajectory TR10 shown in FIG. 4) and a tolerance stored in the storage unit 24 based on an instruction input from an input device (not shown) provided in the robot control device 20. It is performed by the acquisition unit 21.

Next, the orbit generation unit 22 performs a process of generating a smooth processing orbit in which the error with respect to the target trajectory acquired by the acquisition unit 21 falls within the tolerance acquired by the acquisition unit 21 (step S12: orbit generation step). ). For example, a smooth machining trajectory is generated by performing an optimization calculation in the trajectory generation unit 22 with the constraint that the error from the target trajectory is within the margin of error. When a plurality of machining tracks are obtained by the optimization calculation, the machining track having the smallest maximum acceleration is selected by the track generation unit 22.

FIG. 5 is a diagram showing an example of a processing track generated in the example of welding the workpiece shown in FIG. As described above, the data indicating the target trajectory includes data indicating spatial coordinates (X, Y, Z) and data indicating the posture (θX, θY, θZ) of the laser welding apparatus 13. Similarly, the processing trajectory generated by using the data indicating the target trajectory includes the data indicating the spatial coordinates and the data indicating the posture. In FIG. 5, in order to facilitate understanding, the target trajectory TR11 and the machining trajectory TR12 regarding the posture of the laser welding apparatus 13 (the angle (θZ) of the laser beam L emitted from the laser welding apparatus 13 with respect to the X axis) are shown. It is shown in the figure. The processing track TR12 shown in FIG. 5 is generated when the tolerance of the posture (angle) is 10 degrees.

As shown in FIG. 5, the target trajectory TR11 for the posture of the laser welding apparatus 13 is the section SE1 (0 to 20 [sec]) in which the straight portion P1 shown in FIG. 4 is welded, and the curved portion P2 shown in FIG. It is roughly classified into a section SE2 (20 to 38 [sec]) where welding is performed and a section SE3 (38 to 56 [sec]) where welding of the straight portion P3 shown in FIG. 4 is performed. The target orbit TR11 of each section is as follows, and is discontinuous at the connection point of the section.
Section where the straight part P1 is welded SE1: 0 degrees Section where the curved part P2 is welded SE2: Gradually changes from 0 to 180 degrees Section where the straight part P3 is welded SE3: 180 degrees

On the other hand, the processing track TR12 generated by the track generation unit 22 becomes a smooth track within the margin of error range ER1. Specifically, the processing track TR12 is almost the same as the target track TR11 in the first half of the section SE1 where the straight portion P1 is welded, but in the latter half of the section SE1, near the lower limit of the margin of error range ER1 (- After smoothly changing to 10 degrees), the trajectory smoothly changes to near the upper limit (+10 degrees) of the margin of error range ER1.

Further, the machining track TR12 is a track that gradually changes from the vicinity of the upper limit of the margin of error range ER1 (+10 degrees) to the vicinity of the lower limit of the tolerance range ER1 (+170 degrees) in the section SE2 where the curved portion P2 is welded. .. Further, in the first half of the section SE3 where the straight portion P3 is welded, the machining track TR12 smoothly changes to the vicinity of the upper limit of the tolerance range ER1 (+190 degrees) and then near the lower limit of the tolerance range ER1 (+170 degrees). It changes smoothly up to, and in the latter half, it becomes almost the same trajectory as the target trajectory TR11.

When the above processing is completed, the control unit 23 performs a process of controlling the robot 10 so as to follow the processing track TR12 generated by the track generation unit 22 (step S13: control step). As described above, since the processing track TR12 generated by the track generation unit 22 is a smooth track within the margin of error, it is possible to prevent an excessive load from being applied to the drive device (motor) of the robot 10.

As described above, in the present embodiment, the target trajectory for the robot 10 (laser welding device 13) and the permissible tolerance for the target trajectory are acquired, and a machining trajectory in which the error for the target trajectory falls within the permissible error is generated. The robot 10 is controlled so as to follow the generated machining trajectory. Therefore, unlike the conventional case, it is not necessary to change the parameters used for correction by trial and error so that the tracking error with respect to the target trajectory is within the target tracking error. As a result, the optimum trajectory that can avoid an excessive load can be obtained in a short time.

Although the robot control device and the robot control method according to the embodiment of the present invention have been described above, the present invention is not limited to the above embodiment and can be freely changed within the scope of the present invention. For example, in the above embodiment, the case where the drive device of the robot 10 is a motor has been described as an example, but the drive device of the robot 10 is other than the motor (for example, a piezoelectric element, an air cylinder, a hydraulic cylinder, a hydraulic motor, etc.). It is also applicable when.

Further, in the above embodiment, an example in which the robot 10 includes the robot arm 11 as a moving device for moving the laser welding device 13 has been described. However, the robot 10 does not necessarily have to be provided with the robot arm 11, and may be provided with a moving device that is not an arm type (for example, a moving device having a linear motion axis or the like).

1 ... Robot system, 10 ... Robot, 20 ... Robot control device, 21 ... Acquisition unit, 22 ... Orbit generation unit, 23 ... Control unit

Claims (4)

An acquisition unit that acquires a target trajectory and an allowable error for the target trajectory,
It is provided with a trajectory generating unit that generates a machining trajectory in which an error with respect to the target trajectory falls within the margin of error, and a control unit that controls the robot so as to follow the machining trajectory generated by the trajectory generating unit.
The trajectory generation unit is a robot control device that selects the one having the smallest maximum acceleration among the plurality of generated processing tracks . The robot control device according to claim 1, wherein the trajectory generation unit generates the processing trajectory in which the acceleration of the robot is continuous. The robot control device according to claim 1 or 2 , wherein the tolerance includes a position and posture tolerance . An acquisition step for acquiring a target trajectory and an allowable error for the target trajectory, and an orbit generation step for generating a processing trajectory in which the error for the target trajectory falls within the tolerance.
Includes a control step that controls the robot to follow the machining trajectory generated in the trajectory generation step.
In the trajectory generation step, a robot control method for selecting the one having the smallest maximum acceleration among the plurality of generated machining tracks.

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