Robot control

Abstract

Robot control (1) which causes a first workpiece (W1) mounted at a distal end of a robot (100) to move relative to a second workpiece (W2), wherein the robot (100) has a sensor (140) to detect either the magnitude of the force acting on the first workpiece (W1) or the magnitude of the torque acting on the robot (100), wherein the robot control (1) comprises: a calculation unit (5) configured to calculate a force acting on a contact point between the first workpiece (W1) and the second workpiece (W2) and a moment acting on the first workpiece (W1) based on the magnitude of the force or the magnitude of the torque detected by the sensor (140); a control (6) configured to perform force control such that the force and moment calculated by the computation unit (5) correspond to a predetermined force and moment; and a display device (2) configured to display a speed of the first workpiece (W1) and / or an angular velocity about a reference point defined for the first workpiece (W1), wherein the speed and the angular velocity occur as a result of control by the controller (6), wherein the speed or the angular velocity is superimposed on an image of the robot (100).

Description

[0001] The present disclosure relates to a robot control system.

[0002] When using a robot for polishing, deburring, or precisely fitting a variety of workpieces, a force or torque acting on the robot is detected using a force detector such as a force sensor or load cell. The robot's movements are then controlled so that the force or torque detected by the force detector becomes a setpoint, as described in publication JP H06-262563A.

[0003] If an assembly or fitting task fails, or if the quality of polishing or deburring is unsatisfactory, there are instances where confirmation of the magnitude or direction of the force is desired to either diagnose or correct the situation. In tasks involving robots, a force detected by a force detector is often graphically displayed to confirm the force acting on the robot.

[0004] The publication DE 10 2018 004 673 A1 describes a robot system with a model storage unit, a model display unit, an input unit for entering a permissible speed of the robot, a calculation unit for calculating a predicted maximum speed of the robot based on a trajectory planning of an operating command to be applied to the robot, and a speed modification unit for modifying a command speed of the robot.

[0005] The publication DE 10 2016 006 704 A1 describes a robot control system by which an operator can visually or intuitively recognize the direction and / or magnitude of an actual force applied to any section.

[0006] The publication DE 10 2015 015 503 A1 describes a robot system that uses an augmented reality compatible display capable of providing information about the status and / or operating guidance of a robot, added to a real image or real environment, to a user of the robot in order to improve the efficiency of the operating operations performed by the user.

[0007] The publication EP 2 011 610 A2 describes a fastening device for attaching a first fastening element, held in a hand attached to the front end of a robot arm, to a corresponding second fastening element, comprising a sensing unit for detecting the force generated when the first and second fastening elements come into contact with each other, and an evaluation unit for judging, based on the force detected by the sensing unit, whether the first and second fastening elements are in contact with each other.

[0008] Document US 2016 / 0354925A1 describes a robot controller with a display control unit that displays a manipulator's movement position, derived from a target force and an output from a force detector, as well as the target position on a screen.

[0009] The publication CN 1 03 507 070 A describes a robot control system with a force detection unit, a force estimation point determination device and a force estimation device.

[0010] When performing a precise fitting, it is not possible to intuitively determine, i.e., solely by graphically representing a quantity or direction of force, whether the robot is being controlled correctly. Therefore, a robot control system is desirable that can easily determine whether the robot is being controlled correctly. This problem is solved by a robot control system with the features of claim 1.

[0011] One aspect of the present disclosure provides a robot control system that causes a first workpiece, mounted at a distal end of a robot, to move relative to a second workpiece, the robot having a sensor for detecting the magnitude of a force acting on the first workpiece or the magnitude of a torque acting on the robot, the robot control system comprising: a computation unit configured to calculate a force acting on a contact point between the first workpiece and the second workpiece, and a torque acting on the first workpiece, based on the magnitude of the force or the magnitude of the torque detected by the sensor; a controller configured to perform force control such that the force and torque calculated by the computation unit correspond to a predetermined force and torque;and a display device configured to display a speed of the first workpiece and / or an angular velocity about a reference point set for the first workpiece, wherein the speed and the angular velocity occur as a result of control by the controller, wherein the speed and / or the angular velocity are superimposed on an image of the robot. Fig. Figure 1 is a view of an overall configuration illustrating a robot system including a robot controller according to an embodiment of the present disclosure. Fig. 2 is a block diagram that shows the Fig. The robot control system shown is illustrated. Fig. 3 is a view that shows the position correction during force control through the in Fig. The robot control system shown is illustrated. Fig. 4 is a view that shows the position correction during force control through the in Fig. The robot control system shown is illustrated. Fig. 5 is an example representation of an angular velocity, which is given by the in Fig. The robot control system shown is depicted in Figure 1. Fig. 6 is an example representation of a velocity determined by the in Fig. The robot control system shown is depicted in Figure 1. Fig. 7 is an example of a case where the in Fig. The angular velocity shown in section 5 is large. Fig. 8 is an example of a case where the in Fig. The angular velocity shown in section 5 is small. Fig. Figure 9 is another example of a case where the in Fig. The angular velocity shown in section 5 is large.

[0012] A robot controller 1 according to an embodiment of the present disclosure is described below with reference to the drawings.

[0013] As in Fig. As shown in Figure 1, the robot control 1 according to this embodiment is a device that controls a robot 100 with a hand 110 for holding, for example, a column-shaped first workpiece W1.

[0014] The robot 100 performs a fitting task in which the first workpiece W1, held by hand 110, is fitted into a hole O defined in a second workpiece W2, which is fixed on a worktable 200.

[0015] However, the present disclosure also applies to robots that perform other tasks in which a force is generated, such as a deburring task, a threading task and similar tasks on a second workpiece as the work target.

[0016] The robot 100, for example, is a six-axis articulated robot and comprises an arm 120, a wrist unit 130 located at a distal end of the arm 120, and the hand 110 mounted at a distal end of the wrist unit 130. Furthermore, a six-axis force sensor 140, which detects a force acting on the hand 110, is provided between the wrist unit 130 and the hand 110 of the robot 100 in a section characterized by hatching. The force sensor 140 detects forces in three mutually orthogonal axial directions as well as torques about these three axes.

[0017] Information about the forces detected by force sensor 140 is transmitted to robot controller 1. Robot controller 1 performs force control such that the force acting between the first workpiece W1 and the second workpiece W2 assumes a preset value. A known impedance control, damping control, hybrid control, or similar method can be used for force control.

[0018] As in Fig. As shown in Figure 1, the robot controller 1 according to this embodiment is connected to a programming handheld device (display unit) 2 for confirming and setting the learning process for an operating program for the robot 100 or various conditions. A monitor 3 of the programming handheld device 2 is capable of displaying simulated images or videos of the robot 100, the worktable 200, the first workpiece W1, and the second workpiece W2. In the case of videos, an image of the robot 100 moves together with an actual movement of the robot 100.

[0019] While the programming handheld device 2 is shown as an example of a display device, the display device can be provided in a main body of the robot controller 1, or a PC, a tablet terminal, a mobile terminal or similar can be used as a display device.

[0020] As in Fig. As shown in Figure 2, the robot controller 1 according to this embodiment comprises a storage device 4, a computing unit 5, a controller 6 and an image processor 7.

[0021] The storage device 4 stores image information that is used to structure an image of the robot 100 based on geometric parameters of the robot 100 and state variables of the robot 100.

[0022] The calculation unit 5 calculates a force acting on a contact point between the first workpiece W1 and the second workpiece W2 and a moment acting on the first workpiece W1, based on a force detected by the force sensor 140, the geometric parameters stored in memory 4 and the state variables calculated by the control unit 6.

[0023] The geometric parameters include the length dimensions of the individual segments of the robot 100.

[0024] The state variables include a position, a velocity, or an acceleration rate of each joint of the robot 100, which are calculated in the control by the controller 6.

[0025] The controller 6 performs force control of the robot 100, so that the force and torque calculated by the computation unit 5 become predetermined values.

[0026] In particular, as in Fig. Figure 3 shows that when the first workpiece W1 is moved to a position defined by a learning program relative to the second workpiece W2, which is fixed to the worktable 200, the first workpiece W1 is brought into contact with the second workpiece W2 during the movement, receiving a reaction force from the second workpiece W2. A chamfered section A is provided in an opening of the hole O of the second workpiece W2, and when the first workpiece W1 is brought into contact with the chamfered section A, the robot controller 1 actuates the robot 100 so that the reaction force assumes a predetermined magnitude, causing the first workpiece W1 to move into a position indicated by a dashed line following the chamfered section A.

[0027] Furthermore, assuming a left-right direction in Fig. 3 an X-direction, in the damping control a velocity command in the X-direction is calculated to satisfy an expression (1) below: Vx=D1⋅(Fx−Fdx)

[0028] These are: Vx is a speed command in the X direction, Fx a reaction force (a value detected by force sensor 140), Fdx a target force in the X direction, and D1 is a coefficient.

[0029] In particular, assuming that the target force is 0, expression (1) is like expression (2) below, and while a rightward force Fx occurs, a velocity command is generated that is proportional to the magnitude of the force, causing the robot 100 and the first workpiece W1 to move to a right side in the figure: Vx=D1⋅Fx

[0030] Furthermore, as in Fig. Figure 4 shows that when the position and posture of the first workpiece W1, defined by a teaching program, are shifted relative to the second workpiece W2, which is attached to the worktable 200, the first workpiece W1 is brought into contact with the second workpiece W2 during the movement, receiving a reaction force and a moment from the second workpiece W2. When the first workpiece W1, whose posture has been shifted, is brought into contact with the chamfered section A, which is provided in the opening of the hole O of the second workpiece W2, the robot controller 1 actuates the robot 100 so that the reaction force and the moment become predetermined values, and the first workpiece W1 moves into a position indicated by a dashed line.

[0031] Furthermore, assuming a right-left direction in Fig. 4 an X-direction and a vertical direction in the drawing is a Y-direction, in the damping control a velocity command and an angular velocity command are calculated such that expression (1) and expression (3) below are satisfied: Ay=D2⋅(My−Mdy)

[0032] These are: Ay, an angular velocity command around the Y-axis, My moment around the Y-axis (a value detected by force sensor 140) with TCP as the center, Mdy a target moment around the Y-axis, and D2 is a coefficient.

[0033] In particular, assuming that the target moment about the Y-axis is 0, expression (3) is expressed as shown in expression (4) below, and while a moment My occurs in a direction of an arrow, an angular velocity command proportional to a magnitude of the moment is generated, with the robot 100 and the first workpiece W1 moving in the direction of the arrow: Ay=D2⋅My

[0034] Since the velocity command in the X direction is generated due to effects of expression (1) and expression (2), the robot operates at speed and angular velocity by combining them.

[0035] Using the image information stored in the memory device 4, the image processor 7 structures an image of the robot 100 at that time, based on state variables such as positions, velocities, acceleration rates, etc. of the joints of the robot 100, which are received from the controller 6.

[0036] Furthermore, the image processor 7 generates a composite image G, where the directions and magnitudes of the force, velocity, torque, and angular velocity, calculated by the computation unit 5, are superimposed on the image of the robot 100. As in Fig. 5 or Fig. As shown in Figure 6, the directions and magnitudes of the velocity or angular velocity on the image of robot 100 are superimposed by arrows and letters. The resulting composite image G is displayed on monitor 3 of the programming handheld device 2.

[0037] An example of a method for displaying speed or angular velocity is a display method using arrows, as shown in Fig. 5 or Fig. 6 shown. As in Fig. 7 or Fig. As shown in Figure 8, the direction of the angular velocity represents a direction of the change in posture of robot 100 and is indicated by the direction of the arrow. As in Fig. Figure 6 shows that the direction of velocity represents the direction of change in the position of robot 100, which is represented by the direction of the arrow. Furthermore, the magnitude of the velocity or angular velocity represents the speed of movement of robot 100, which can be represented by the length of an arrow.

[0038] The magnitude or value of the velocity or angular velocity can be determined by the thickness of the arrow, as shown in Fig. 9, or expressed by the color of the arrow instead of the length of the arrow. Fig. Figure 9 shows an arrow of the same length, which is thicker than the arrow in Fig. 7, which indicates that the angular velocity is greater than the example in Fig. 7.

[0039] In a case where the representation is done by colors, by showing the arrow in red or similar, an operator can intuitively determine that the speed or angular velocity exceeds a predetermined threshold if the speed or angular velocity is excessive.

[0040] As described above, according to the robot controller 1 of this embodiment, not only the reaction force and the torque acting on the distal end of the first workpiece W1, but also the velocity or angular velocity of the robot 100 are represented by an arrow or letter. This has the advantage that it is possible to intuitively and visually recognize the direction and velocity of movement of the robot 100 resulting from the force control of the robot 100 and to easily determine that the robot 100 is being controlled correctly.

[0041] Furthermore, in this embodiment, a reference point TCP on the first workpiece W1 is represented by superimposing the reference point TCP onto image G. This has the advantage that the operator can easily and visually identify the center point of the angular velocity and easily follow the direction of movement of the robot 100.

[0042] It should be noted that this embodiment describes the geometric parameters as including the dimensions of the lengths of the individual limbs of the robot 100. However, the geometric parameters can also include the dimensions of the length and mass of each limb. By including the mass, it is possible to obtain the force and torque at a contact point, where a correction is made to eliminate the influence of inertial forces on the force and torque detected by the force sensor 140.

[0043] Furthermore, in a case where a tool that performs a rotary movement, such as a screwdriver, is mounted as a tool, the tightening torque can be detected by the force sensor 140 and superimposed on the image of the robot 100.

[0044] While in this embodiment the six axes of the force sensor 140, which is provided between the distal end of the wrist device 130 and the hand 110, are described as an example of the sensor, the force sensor 140 can instead be arranged in any position. For example, a torque sensor can be arranged on each of the axes, or torque sensors for the three axes and force sensors on the three axes can be arranged separately. Reference symbol list 1 Robot control 2 Control panel (display unit) 4 Storage setup 5 Calculation unit 6 Control 100 robots 140 Force sensor (sensor) TCP Reference Point W1 First workpiece W2 Second workpiece

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