JP5904445B2 - Robot controller - Google Patents

Description

  The present invention relates to a robot control device that moves the tip of a robot arm to a changed target position even if the target position is changed while the hand of the robot arm, that is, the tip is moving to the target position. .

  Robots are employed for automation or efficiency improvement of workers (for example, Patent Documents 1-4).

  In Patent Document 1, in order to control the reaction wheel that controls the attitude of the satellite body and to cancel the inertial force generated by the operation of the work robot attached to the satellite body, the work robot is operated within the range in which the reaction wheel can be operated. A technique for generating an optimal trajectory using a database is disclosed.

  In Patent Document 2, it is possible to automatically detect the direction of the inertial force of the gripping part of the robot hand and perform posture control based on the detection result, thereby preventing the object to be gripped from falling due to the inertial force. A robot control technique is disclosed.

  Patent Document 3 discloses a technique for generating a smooth trajectory from a current position and orientation to a target position and orientation, such as a robot and a multi-joint arm, at high speed.

  In Patent Document 4, it is not necessary to calculate the speed of each axis necessary for the interpolation operation, the maximum speed interpolation operation can be performed within the operable range, and the path motion trajectory is shown regardless of the speed. A motor control technique that can be kept constant is disclosed.

  The motor control device disclosed in Patent Document 4 includes data generation means for generating trajectory generation data from a command value including a target position and target speed from a host controller, and a trajectory from the trajectory generation data to the target position. And a trajectory generating means for generating. The data generation means generates data for deceleration in which the rate of deceleration in the first section from the current position to the first target position that becomes the next target position changes in two stages when a relay operation command is received from the host controller. At the same time, acceleration data is generated in which the acceleration rate changes in two stages in the second section to the second target position that is the next target position after the first target position.

JP-A-7-200030 Japanese Patent Laid-Open No. 9-300255 JP 2010-155328 A JP 2007-164260 A

  However, in the conventional robot control technology, when the target position is changed while the tip of the robot arm is moving to the target position, the tip of the robot arm can be simply and quickly stopped without stopping the operation of the robot arm. It is difficult to move.

  FIG. 5 is a diagram for explaining a possible method for controlling the robot arm when the target position is changed while the tip of the robot arm is moving to the target position. FIG. (B) is a method for temporarily stopping and moving the tip of the robot arm, and (c) is a method disclosed in Patent Document 4. The case where is applied is shown.

In the above description, it is assumed that the robot arm is configured by connecting the arm portions, and the connecting axis of the arm portions is along the vertical direction. In any of FIGS. 5A to 5C, only the tip of the robot arm is schematically indicated by a solid circle or a broken circle, and is shown in plan view. 5A and 5B, as the position of the tip of the robot arm, the position P _i-1 indicates a position one before the change instruction, and the position P _i receives the change instruction. P _a indicates the target position before the change, and P _b indicates the target position after the change.

Here, let us consider adopting a method of moving the tip of the robot arm to the changed target position without performing any processing. As shown in FIG. 5A, the moving direction of the tip of the robot arm is indicated by a vector from the current position P _i toward the changed target position P _b . If the motor that drives the connecting shaft cannot generate a large torque, the torque is over and the tip of the robot arm stops. As a result, it is impossible to reach the target position P _b after changing the tip of the robot arm.

Next, consider adopting a method in which the tip of the robot arm is temporarily stopped and then moved to the changed target position. As shown in FIG. 5 (b), the tip of a robot arm, from the current position P _i until stopped temporarily, even slightly in the direction of the vector from the position P _i-1 to the position P _a mobile Then, it is stopped once at the position P _stop . Thereafter, the position is moved from the position P _stop toward the changed target position P _b in the direction of the arrow. Although in this case is not able be to reach the target position P _b after changing the tip of the robot arm, once it takes time until stopping, unless reduced even slight time on working process, action Efficiency cannot be improved. As a result, it is not possible to reduce the cost of products assembled by work.

  Therefore, it is conceivable to use the above-described technique disclosed in Patent Document 4. As shown in FIG. 5C, when the motor control device disclosed in Patent Document 4 receives a command for changing the target position from the host controller while moving from position P1 to position P2, for example, the position is changed from position P1 to position P2. Is decelerated in two stages, and the movement to position P3 is accelerated in two stages. Therefore, even when the target position is changed during the linear interpolation operation, the trajectory during the target position change can be defined.

  However, even with the technique disclosed in Patent Document 4, first, it is necessary to decelerate each time the trajectory is changed and perform re-acceleration by performing a transit operation, resulting in a time lag. This makes it difficult to change the trajectory instantaneously.

  Secondly, the trajectory is difficult to be smooth due to the two-stage deceleration, the torque fluctuation at the tip of the robot arm becomes large, and a load is applied to each axis. This shortens the service life of the components and necessitates maintenance.

  Thirdly, the movement of the tip of the robot arm is not smooth, which is a so-called awkward operation. As a result, the person working near the robot arm feels uncomfortable or uneasy.

  On the other hand, if a computer with a high processing capacity is provided so that the trajectory calculation can be performed at high speed, the calculation may be performed immediately even if the target position is changed. However, since the target position can be changed arbitrarily, there is a limit and the cost is increased. This method is also not preferable in consideration of installing a large number of robots at the work site.

  Therefore, an object of the present invention is to provide a robot control device that can easily move the tip of the robot arm even when the target position is changed during the movement of the tip of the robot arm to the target position. To do.

In order to achieve the above object, the present invention provides a robot control device for controlling a robot, comprising: a robot arm comprising an arm unit; and a drive unit that rotationally drives the arm unit. When the target position of the robot arm is input, the kinetic energy and moving direction of the tip of the robot arm are obtained from the current position information and velocity information of the tip of the robot arm, and the robot arm is determined from the obtained kinetic energy and moving direction . A trajectory generator that sets a position where the tip should be routed and obtains a curve connecting the current position of the tip of the robot arm and the position to be routed and the target position as a trajectory, along the trajectory obtained by the trajectory generator And a drive control unit that controls the drive unit so that the tip of the robot arm moves.

The trajectory generator obtains the current velocity from the current position information of the tip of the robot arm and the previous position information, obtains the kinetic energy of the tip of the robot arm, and multiplies the kinetic energy by the energy amount conversion coefficient. As a result, the position through which the tip of the robot arm should pass is set.
Further, it is determined whether or not the target position of the robot arm should be changed based on the detection signal from the sensor arranged at the installation position of the robot arm, and the target position to be changed is calculated and output to the trajectory generation unit A position calculation unit may be provided.

  According to the present invention, even if the target position is changed, the trajectory generation unit does not perform complicated calculations, so the trajectory of the tip of the robot arm is obtained and the trajectory is changed. Therefore, it is not necessary to stop the movement of the robot arm and to prevent the robot arm from performing unnecessary movement or movement. The trajectory generation unit requires a small amount of information when calculating the trajectory and does not perform complicated calculation processing, so that the trajectory generation unit is not required to have high calculation processing capability. Moreover, since a motor with a low torque can be employed as the drive unit, the robot can coexist with a human being such as an operator.

It is a figure for demonstrating the principle of this invention. 1 is a block configuration diagram of a robot system according to an embodiment of the present invention. It is a figure which shows typically an example of the actual machine about the robot in the robot system shown in FIG. It is a flowchart which shows the main operations in the robot system shown in FIG. It is a figure for demonstrating each method considered as control of a robot arm when a target position is changed in the middle of the front-end | tip part of a robot arm moving to a target position.

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

〔principle〕
As a premise for explaining the embodiment of the present invention, the principle of the present invention will be described. FIG. 1 is a diagram for explaining the principle of the present invention. For explanation, it is assumed that the robot system 1 is configured by connecting the arm portions 2a and 2b to form the robot arm 2, and the robot arm 2 is rotatably attached to the housing 3. It is assumed that the connecting shaft between 2a and 2b is along the vertical direction. As the position of the tip of the robot arm 2, the position P _i-1 indicates a position one before the change instruction, the position P _i indicates the position when the change instruction is received, and P _a represents the target position before the change, P _b indicates the target position after the change. Since the robot arm 2 is moving on the horizontal plane, a two-dimensional coordinate axis is set for convenience, the coordinates of the position P _i-1 are (X1, Y1), the coordinates of the position P _i are (X2, Y2), and P _a the coordinates (X0, Y0), the coordinates of P _b and (Xn, Yn).

As shown in FIG. 1, the target position of the distal end portion of the robot arm 2 is changed to the position P _b from the position P _a in the state shown in FIG. 1 (a). Then, the current position of the distal end portion of the robot arm 2 is assumed to be P _i. At the tip of the robot arm 2, the position information of the current position P _i and the previous position P _i-1 is known by a sensor provided in the drive unit of the robot arm 2. The speed of the tip of the robot arm 2 at this time P _i can be calculated as the position P _i-1 of the displacement from the position P _i. Therefore, the kinetic energy and the moving direction of the tip can be obtained. Therefore, a position (hereinafter abbreviated as “route point”) through which the tip of the robot arm 2 should pass is obtained from these kinetic energy and moving direction. Then, a curve L that smoothly connects the current position P _i of the tip of the robot arm 2, the via point P _via, and the new target position P _b is obtained. At that time, spline interpolation or the like may be used.

For the current position P _i and the previous position P _i−1 , a sensor is attached to the drive unit that drives the rotation axis and the connection axis of the robot arm 2, and the number of rotations is monitored from the sensor. Can be easily obtained. The speed can also be obtained if the previous position P _i-1 is known from the coordinates of the current position P _i .

Therefore, since the mass of the tip of the robot arm 2 is known, the kinetic energy can be obtained. By multiplying this kinetic energy by a constant, the amount of displacement from the current position P _i to the via point P _via can be obtained.

When the target position of the robot arm 2 is changed, the moving distance to stop the movement of the tip of the robot arm 2 due to the inertia is obtained from the kinetic energy of the tip. Then, a displacement amount from the current position P _i to the via point P _via can be obtained. This is based on the idea that the kinetic energy of the tip of the robot arm 2 when the target position is changed is equivalent to the energy required for the tip of the robot arm 2 to stop. . That is, the following equation holds.
(Kinematic energy at the tip of the robot arm when the target position is changed)
= (Force required to stop) x (travel distance to stop)
Here, if the force for stopping the tip of the robot arm 2 is constant, the displacement distance from the current position to the via point is proportional to the kinetic energy of the robot arm 2 when the target position is changed.

In the present invention, this proportionality constant k is called an energy amount conversion coefficient. The following relationship is obtained from the above relational expression.
Xp = mk (X2-X1) 2/2 + X2
Yp = mk (Y2-Y1) 2/2 + Y2
Here, (Xp, Yp) is the coordinates of the via point P _via , (X1, Y1) is the previous position coordinate, and (X2, Y2) is the current position coordinate. m is the mass of the robot arm tip. Since the waypoint is calculated based on the amount of change in the x direction and the y direction, the displacement direction is determined by the extension obtained by combining these vectors. The robot arm 2 is guided in the same manner even if the movement of the robot arm 2 is not two-dimensional but three-dimensional.

Here, the energy amount conversion coefficient k is a coefficient for converting the kinetic energy of the tip of the robot arm 2 into the distance that the tip moves, and this coefficient k is expressed by the following equation.
k = (attenuation rate) × 1 / (force to stop)
Here, the attenuation rate indicates how much the vehicle decelerates from the current speed, and is set to 0.6 to 0.9, for example.
The force for stopping the tip of the robot arm 2 can be calculated from the motor torque by the dynamics of robot engineering. In this case, it is necessary to verify the operation pattern. Accordingly, the coefficient k may be set by actually measuring the torque by actually moving the robot arm, and the relationship between the motor output and the magnitude of the kinetic energy of the robot arm tip.

〔System configuration〕
A system configuration according to an embodiment of the present invention will be described. FIG. 2 is a block diagram of the robot system according to the embodiment of the present invention, and FIG. 3 is a diagram schematically showing an example of an actual machine for the robot in the robot system 1 shown in FIG. The robot system 1 includes a robot 10 and a robot control device 20. The robot 10 includes a robot arm 11 and a drive unit 15 that drives the robot arm 11. In FIG. 2, the robot arm 11 is not shown, but representative ones necessary for the relationship with the robot control device 20 are shown.

  The robot arm 11 is configured by connecting a plurality of arm portions 12 a and 12 b with a rotation shaft 13, but may be configured by attaching one arm portion to the housing 3 so as to be directly rotatable. The tip of the robot arm 11 is provided with a grasping unit (not shown) that is necessary when the robot 10 performs work. The robot 10 shown in FIG. 3 is a so-called scalar robot. A motor, for example, a servo motor 15a, as a component of the drive unit 15 is attached to the rotation shaft 13, and one arm portion 12a is rotated around the rotation shaft 13 at the tip of the other arm portion 12b. Further, the other arm portion 12b is rotatably attached to the frame 14 by the rotation shaft 13, and this attachment portion functions as a joint portion. For example, a servo motor 15a is attached to this joint portion, and the arm portion 12b. Is rotated about the rotation axis 13. A servo amplifier 15b as a motor driver is provided at the front stage of the servo motor 15a.

  A sensor 16 such as an encoder is attached to each drive unit 15, counts the number of rotations, and outputs it to the robot controller 20. As shown in FIG. 3, the embodiment of the present invention is not limited to a scalar type robot in which the arm portions 12a and 12b rotate around the vertical axis, and may rotate around the horizontal axis. You may rotate around other axes.

  The robot control device 20 includes a sensor information processing unit 21, a target position calculation unit 22, a trajectory generation unit 23, a drive control unit 24, a position coordinate conversion unit 25, and a program operation unit 26.

  In the robot system 1, in particular, in an area where the robot 10 is installed, various sensors for detecting the position of the worker, the work object, the presence or absence of an obstacle, and the distance thereof are installed. Signals from the various sensors are input to the sensor information processing unit 21 via the interface unit 31.

  Since the sensor information processing unit 21 receives signals from the various sensors described above via the interface unit 31, the sensor information processing unit 21 performs various conversions such as unit conversion so that the target position calculation unit 22 can use the signals. Transmission and reception from the interface unit 31 to the sensor information processing unit 21 may be wired or wireless.

  Since various conditions from the program operation unit 26 are input to the target position calculation unit 22 and sensor information is input from the sensor information processing unit 21, the final target position is calculated by performing a comparison operation or the like based on the sensor information. Is calculated.

  The program operation unit 26 outputs parameters set in advance to the target position calculation unit 22. The set parameter is a value related to whether the robot 10 is currently operating or is in a state of accepting a target position change.

  The target position calculation unit 22 calculates the target position of the distal end portion of the robot arm 2 in accordance with the work process from information related to the installation position of the robot 10 and information related to the shape of the robot arm 2. In addition, the target position calculation unit 22 receives the position information of the worker, the work object, and the obstacle from the sensor information processing unit 21 as sensor information, determines whether or not the target position has been changed, and changes the target position. Calculate the target value after the change. Even if sensor information is input from the sensor information processing unit 21, the target position calculation unit 22 may change the position of the tip of the robot arm 2 according to the work process depending on the positions of the worker, the work object, and the obstacle. If it is determined that there is no need to change the movement, the target position is output to the trajectory generation unit 22 without being affected by the sensor information input from the interface unit 31 via the sensor information processing unit 21.

  The trajectory generation unit 23 receives real-time position information and speed information of the tip of the robot arm from the sensor 16 via the position coordinate conversion unit 25, and receives the input information and the target position calculated from the target position calculation unit 22. From this, the trajectory of the robot arm tip is generated.

  The drive control unit 24 controls the drive unit 15 so that the tip of the robot arm moves along the trajectory curve generated by the trajectory generation unit 23. The drive control unit 24 inputs a command value such as the rotation speed of the servo motor 15a in the drive unit 15 to the drive unit 15, and rotationally drives the servo motor 15a via the servo amplifier 15b. Thereby, the servo motor 15a moves the robot arm tip along the trajectory curve.

  The position coordinate conversion unit 25 performs coordinate conversion of a signal from an encoder as the sensor 16 attached to the servo motor 15a of the drive unit 15, and the robot arm tip is determined from the number of rotations by the servo motor 15a of the drive unit 15. And the position information and speed information are input to the trajectory generator 23.

  FIG. 4 is a flowchart showing main operations in the robot system shown in FIG. In the embodiment of the present invention, first, the program operation unit 26 sets various conditions for rotationally driving the robot arm 11 (STEP 1). As a result, the basic operation is set for the robot 10. Then, the target position is calculated by the target position calculation unit 22 in accordance with the condition input from the program operation unit 26, and the trajectory generation unit 23 performs the trajectory calculation so that the tip of the robot arm moves along the trajectory. The drive control unit 24 outputs a command value related to the target position to the drive unit 15. Then, the robot arm 11 is driven by the drive unit 15.

  Assume that a sensor detection signal is input from the interface unit 31 to the sensor information processing unit 21 in such a state. Then, the sensor information processing unit 21 receives the sensor detection signal from the interface unit 31, converts the signal into a data that can be compared, and outputs it to the target position calculation unit 22 (STEP 2).

  The target position calculation unit 22 receives the input of various conditions from the program operation unit 26, calculates the target position of the tip of the robot arm 2 by calculation, and sequentially outputs the target position to the trajectory generation unit 23. Calculate and output to the drive control unit 24. In response to this, the drive control unit 24 outputs a command value to the servo motor 15b (STEP 8). In such a state, when receiving the sensor detection signal from the sensor information processing unit 21, the target position calculation unit 22 first determines whether or not to change the target position of the tip of the robot arm (STEP 3).

  Next, when the target position calculation unit 22 determines to change the target position, the target position after the change is calculated by the target position calculation unit 22 and output to the trajectory generation unit 23 (STEP 4). The energy and direction are calculated (STEP 5), the waypoints are set as described above (STEP 6), the trajectory to the target position is calculated and output to the drive control unit 24 (STEP 7).

  When the data related to the trajectory calculated from the trajectory generating unit 23 is input, the drive control unit 24 outputs a command value for the target position to the servo motor 15b.

  Then, it is determined whether or not the tip of the robot arm 2 has reached the target position (STEP 9). If not, the process returns to target position detection (STEP 2). On the other hand, when it has reached, the driving of the robot arm 2 is stopped.

  As described above, even if an arbitrary new target position is input, the trajectory generation unit 23 obtains the kinetic energy and moving direction of the robot arm tip, and the position to which the robot arm tip should pass from these information And a curve L that smoothly connects the current position, the waypoint, and the new target position is generated as a new trajectory.

  When a new trajectory is generated, it is only necessary to calculate the transit point by calculating the energy amount conversion coefficient k and the position information of the tip, and since the calculation amount is small, a computer such as a server with high calculation capacity is used. No need. In addition, since the trajectory is simply and instantaneously calculated, the trajectory of the robot arm can be changed instantaneously. Combined with the fact that the robot arm is never stopped, the working efficiency of the robot is improved.

  As a motor to be installed as a component of the drive unit, a low torque motor can be adopted and there is no problem of torque over.

  Thus, in the embodiment of the present invention, even when the target position is newly changed while the robot arm is moving toward the target position, the rotational energy at the tip of the robot arm is changed at the time when the target position is changed. It can be used to the maximum, and the torque for acceleration and deceleration in the drive unit can be minimized.

1: Robot system 2: Robot arm 2a, 2b: Arm unit 3: Housing 11: Robot arm 12a, 12b: Arm unit 13: Rotating shaft 14: Frame 15: Drive unit 15a: Motor (servo motor)
15b: Driver (servo amplifier)
16: Sensor (encoder)
20: Robot control device 21: Sensor information processing unit 22: Target position calculation unit 23: Trajectory generation unit 24: Drive control unit 25: Position coordinate conversion unit 26: Program operation unit 31: Interface unit

Claims (3)

In a robot control device for controlling a robot comprising a robot arm composed of an arm unit and a drive unit that rotationally drives the arm unit,
Upon receiving the input of the target position of the tip of the robot arm, the kinetic energy and moving direction of the tip of the robot arm are obtained from the current position information and speed information of the tip of the robot arm, and the obtained motion A trajectory generator that sets a position through which the tip of the robot arm should pass from energy and a moving direction, and obtains a curve connecting the current position of the tip of the robot arm and a position to be passed through and a target position as a trajectory;
A drive control unit that controls the drive unit so that the tip of the robot arm moves along the trajectory obtained by the trajectory generation unit;
A robot control device comprising: The trajectory generation unit obtains the current velocity from the current position information of the tip of the robot arm and the previous position information, obtains the kinetic energy of the tip of the robot arm, and adds the energy amount to the kinetic energy. The robot control device according to claim 1, wherein a position through which a tip portion of the robot arm should pass is set by multiplying by a conversion coefficient. Further, it is determined whether or not the target position of the robot arm is to be changed based on a detection signal from a sensor arranged at the installation location of the robot arm, and the target position to be changed is calculated to the trajectory generation unit. characterized in that it comprises a target position calculating unit which outputs the robot control apparatus according to claim 1 or 2.

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