JP2019141976A - Control device, control method of robot, and robot system - Google Patents

Abstract

To provide a control device and a control method of the robot which can reduce separation of an object from a holding part during operation of a robot arm, and provide a robot system provided with the same control device.SOLUTION: A control method of a robot includes steps of : measuring minimum holding force as minimum holding force by which a holding part mounted on a robot arm can hold an object during a standstill of a robot arm; calculating necessary holding force as holding force by which the holding part can hold the object under an operation condition based on the minimum holding force and an estimated acceleration as an estimation value of acceleration received by the object based on the operation condition of the robot arm; and comparing the necessary holding force and a maximum holding force as a maximum holding force by which the holding part can hold the object.SELECTED DRAWING: Figure 2

Description

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

  Robots such as a vertical articulated robot and a horizontal articulated robot have a robot arm, and generally an end effector such as a hand holding an object is attached to the tip of the robot arm.

  For example, the robot hand described in Patent Literature 1 includes two gripping members, an actuator that moves each gripping member, a load detection unit that detects a load acting on the gripping member, and two actuators that drive the actuator. Gripping the object with, and changing the gripping force of the object by these gripping members, changing the state between the state where the gripping member slides with respect to the surface of the object and the state where the gripping member moves the object, both And a controller that determines a gripping force required when the object is moved based on the gripping force of the object in the state and a load acting in a direction along the surface of the object detected by the load detecting means.

JP 2009-148863 A

  However, since the robot hand described in Patent Document 1 does not consider the acceleration applied to the object during the operation of the robot hand to determine the gripping force, if the object is handled at high speed, the object will not move between the two gripping members. There is a problem that it may come off and fall.

A control device according to an application example of the present invention is a control device that controls a robot arm to which a holding unit that holds an object is attached,
When the robot arm is stationary, the holding unit measures a minimum holding force that is a minimum holding force that can hold the object,
Based on the minimum holding force and an estimated acceleration that is a value obtained by estimating an acceleration received by the object held by the holding unit when the robot arm operates according to an operation condition, Calculating a necessary holding force that is a holding force with which the holding unit can hold the object when the object is held and operated under the operation condition;
Comparing the required holding force with a maximum holding force which is a maximum holding force with which the holding unit can hold the object;
When the maximum holding force is greater than or equal to the required holding force, the holding unit holds the object with the required holding force, and operates the robot arm under the operating conditions.
When the maximum holding force is smaller than the necessary holding force, holding of the object by the holding unit is limited, or the robot arm is operated under a condition different from the operation condition.

1 is a perspective view showing a robot system according to a first embodiment of the present invention. It is a block diagram of the robot system shown in FIG. It is a flowchart for demonstrating the control method of the robot which concerns on 1st Embodiment of this invention. It is a perspective view which shows typically the state where the + Z-axis direction of a holding | maintenance part has faced the perpendicular direction lower side. It is a perspective view which shows typically the state where the -Y-axis direction of a holding part has faced the perpendicular direction lower side. It is a perspective view which shows typically the state where the -X-axis direction of a holding part has faced the perpendicular direction lower side. It is a figure which shows typically the state in which the target object is correctly hold | gripped (hold | maintained) by the holding | maintenance part in case the target object is the bent shape. It is a graph which shows the relationship between the finger | toe space | interval of a holding | maintenance part, and grip force (holding force). It is a figure which shows typically the state in which the target object is not correctly hold | gripped (hold | maintained) by the holding | maintenance part, but is caught when the target object is the bent shape. 10 is a graph showing the relationship between the finger spacing of the gripping part and the gripping force (holding force) when the state shown in FIG. 9 occurs. It is a flowchart for demonstrating the control method of the robot which concerns on 2nd Embodiment of this invention. It is a flowchart for demonstrating the control method of the robot which concerns on 3rd Embodiment of this invention.

  Hereinafter, a control device, a robot control method, and a robot system of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.

<First Embodiment>
FIG. 1 is a perspective view showing a robot system according to the first embodiment of the present invention. FIG. 2 is a block diagram of the robot system shown in FIG. Hereinafter, the base 110 side of the robot 100 is referred to as “base end side”, and the opposite side (end effector 17 side) is referred to as “tip side”.

  The robot system 1 shown in FIG. 1 uses the robot 100 to which the end effector 17 is attached, for example, to perform operations such as feeding, removing, transporting, and assembling precision equipment and parts (objects) constituting the precision equipment. It is a system to do. The robot system 1 includes a robot 100, an end effector 17 attached to the robot 100, and a control device 50 that controls these operations. Hereinafter, first, an outline of the robot system 1 will be described.

  The robot 100 is a so-called 6-axis vertical articulated robot. As shown in FIG. 1, the robot 100 includes a base 110 and a robot arm 10 that is rotatably connected to the base 110.

  The base 110 is fixed on, for example, a floor, a wall, a ceiling, or a movable carriage. The robot arm 10 includes an arm 11 (first arm) that is rotatably connected to the base 110, an arm 12 (second arm) that is rotatably connected to the arm 11, An arm 13 (third arm) connected to the arm 12 so as to be rotatable, an arm 14 (fourth arm) connected to the arm 13 so as to be rotatable, and a rotation relative to the arm 14. It has the arm 15 (5th arm) connected so that movement is possible, and the arm 16 (6th arm) connected so that rotation with respect to the arm 15 is possible. A portion of the base 110 and the arms 11 to 16 that bends or rotates two members connected to each other forms a “joint portion”.

  As shown in FIG. 2, the robot 100 includes a drive unit 130 that drives each joint part of the robot arm 10, and an angle sensor 131 that detects a drive state (for example, a rotation angle) of each joint part of the robot arm 10. Have. The drive unit 130 includes, for example, a motor and a speed reducer. The angle sensor 131 includes, for example, a magnetic or optical rotary encoder.

  An end effector 17 is attached to the distal end surface of the arm 16 of the robot 100. A force sensor may be disposed between the arm 16 and the end effector 17.

  The end effector 17 is a gripping hand that grips an object. As shown in FIG. 1, the end effector 17 includes a main body 171, a driving unit 170 installed in the main body 171, a pair of gripping units 172 that are opened and closed by a driving force from the driving unit 170, and a gripping unit 172. And a gripping force sensor 173 provided in the device.

  Here, the driving unit 170 includes, for example, a motor and a transmission mechanism such as a gear that transmits a driving force from the motor to the pair of gripping units 172. The pair of gripping portions 172 are opened and closed by a driving force from the driving portion 170. As a result, the object can be grasped and held between the pair of gripping parts 172, or the object held between the pair of gripping parts 172 can be detached. The gripping force sensor 173 is, for example, a resistance-type or electrostatic-type pressure-sensitive sensor, and is disposed between the gripping unit 172 or the gripping unit 172 and the driving unit 170 and applied between the pair of gripping units 172. Is detected. The end effector 17 is not limited to the gripping hand described above, and may be an end effector that holds an object by suction, for example. In this specification, “holding” is a concept including both adsorption and gripping. “Adsorption” is a concept including adsorption by magnetic force, adsorption by negative pressure, and the like. Further, the number of fingers of the gripping hand used for the end effector 17 is not limited to two, and may be three or more.

  The control device 50 shown in FIGS. 1 and 2 has a function of controlling the driving of the robot arm 10 based on the detection result of the angle sensor 131. The control device 50 has a function of determining the gripping force of the end effector 17 and changing the operating condition of the robot 100 based on the detection result of the gripping force sensor 173 and the operating condition of the robot 100. The control device 50 includes a processor 51 such as a CPU (Central Processing Unit), a memory 52 such as a ROM (Read Only Memory) and a RAM (Random Access Memory), and an I / F (interface circuit) 53. The control device 50 implements processes such as control of operations of the robot 100 and the end effector 17, various calculations, and determinations by the processor 51 appropriately reading and executing the program stored in the memory 52. The I / F 53 is configured to be able to communicate with the robot 100 and the end effector 17.

  In addition, although the control apparatus 50 is arrange | positioned in the base 110 of the robot 100 in illustration, it is not limited to this, For example, you may arrange | position outside the base 110. The control device 50 may be connected to a display device having a monitor such as a display, for example, an input device having a mouse, a keyboard, or the like.

  The outline of the robot system 1 has been described above. This robot system 1 has a mode for determining the gripping force (holding force) of the end effector 17 and the operating conditions of the robot arm 10 that are optimal for holding and transporting the object by the end effector 17. This mode is executed at the time of teaching or the like prior to work on the object, for example. Hereinafter, this point will be described in detail.

  FIG. 3 is a flowchart for explaining the robot control method according to the first embodiment of the present invention. FIG. 4 is a perspective view schematically showing a state in which the + Z-axis direction of the holding portion is directed downward in the vertical direction. FIG. 5 is a perspective view schematically showing a state in which the −Y-axis direction of the holding portion is directed downward in the vertical direction. FIG. 6 is a perspective view schematically showing a state in which the −X axis direction of the holding portion is directed downward in the vertical direction. FIG. 7 is a diagram schematically illustrating a state in which the object is correctly gripped (held) by the holding unit when the object has a bent shape. FIG. 8 is a graph showing the relationship between the finger interval of the holding unit and the gripping force (holding force). FIG. 9 is a diagram schematically illustrating a state in which the object is not properly gripped (held) by the holding unit and is caught when the object has a bent shape. FIG. 10 is a graph showing the relationship between the finger spacing of the gripping portion and the gripping force (holding force) when the state shown in FIG. 9 occurs.

  First, the robot 100 holds the object O with the end effector 17 while the robot arm 10 is stationary (Step S11). At this time, the posture of the end effector 17 is set in accordance with the moving direction of the end effector 17 in a scheduled operation condition of the robot arm 10 (hereinafter also referred to as “scheduled operation condition”).

  Specifically, as shown in FIGS. 4 to 6, the end effector 17 is set with an orthogonal coordinate system including an X axis, a Y axis, and a Z axis that are orthogonal to each other. This orthogonal coordinate system is associated with a robot coordinate system (a three-axis orthogonal coordinate system used by the control device 50 for driving control of the robot 100), which is a coordinate system set for the robot 100, in the control device 50. Yes. Here, the “X axis” is parallel to the direction of opening and closing the pair of gripping portions 172. The “Z axis” is parallel to the direction from the proximal end side to the distal end side of the end effector 17. A direction parallel to the X axis is referred to as “X axis direction”, a direction parallel to the Y axis is referred to as “Y axis direction”, and a direction parallel to the Z axis is referred to as “Z axis direction”. Further, the direction from the proximal end side (main body 171 side) to the distal end side (gripping part 172 side) of the end effector 17 is referred to as “+ Z axis direction”, and the opposite direction is referred to as “−Z axis direction”. The origin of the orthogonal coordinate system set for the end effector 17 is, for example, the tool center point of the end effector 17.

  When the object O is held by the end effector 17, for example, when the movement direction of the end effector 17 in the planned operation condition is the Z-axis direction, the tip of the end effector 17 is moved downward in the vertical direction as shown in FIG. Turn to the side (direction of gravitational acceleration G). When the movement direction of the end effector 17 in the scheduled operation condition is the Y-axis direction, as shown in FIG. 5, the tip of the end effector 17 is moved horizontally (the direction of the gravitational acceleration G) so that the Y-axis direction is the vertical direction. In a direction orthogonal to When the movement direction of the end effector 17 in the scheduled operation condition is the X-axis direction, as shown in FIG. 6, the tip of the end effector 17 is directed in the horizontal direction so that the X-axis direction becomes the vertical direction.

  Then, it is determined whether or not the end effector 17 can hold the object O (step S12). Specifically, the position or posture of the object O sandwiched between the pair of gripping portions 172 in the posture as described above does not change with respect to the pair of gripping portions 172 over a predetermined time (for example, 10 seconds). On the other hand, it is determined that the data can be held. On the other hand, if not, it is determined that the data cannot be held.

  If it is determined that the object cannot be held (NO in step S12), it is determined that the object O cannot be held and transported by the end effector 17, and such holding and transport are not performed (step S13).

  On the other hand, if it is determined that the robot can be held (YES in step S12), the minimum holding force that is the minimum holding force with which the end effector 17 (holding unit) can hold the object O is measured when the robot arm 10 is stationary. (Step S14). Specifically, as described above, after the object O is sandwiched between the pair of gripping portions 172, the gap between the pair of gripping portions 172 is widened to gradually reduce the gripping force (holding force). The gripping force immediately before the object O drops from between the pair of gripping parts 172 or the position or posture of the pair of gripping parts 172 changes is measured as the minimum holding force. At this time, the change of the position and posture of the object O is observed by a camera or visual observation. In addition, the minimum gripping force that can confirm that the object O sandwiched between the pair of gripping portions 172 does not change its position or posture with respect to the pair of gripping portions 172 for a predetermined time (for example, 10 seconds) or more is minimized. Determined as holding power.

  The gripping force is measured based on the detection result of the gripping force sensor 173. Further, it is detected based on the detection result of the gripping force sensor 173 that the object O falls from between the pair of gripping portions 172 or changes in position or posture with respect to the pair of gripping portions 172. Can do. For example, as shown in FIG. 7, from the state in which the object O is gripped by the pair of gripping portions 172, the gripping force (holding force) is gradually decreased by increasing the interval between the pair of gripping portions 172. When the object O falls from between the pair of gripping portions 172, the gripping force suddenly becomes zero as shown in FIG. Therefore, based on the detection result of the gripping force sensor 173, the gripping force immediately before the gripping force suddenly becomes zero is determined as the minimum holding force. Further, from the state shown in FIG. 7, the gripping force (holding force) is gradually decreased by widening the interval between the pair of gripping portions 172, and as shown in FIG. When the posture is changed by being caught between 172, the gripping force does not change as shown in FIG. Therefore, based on the detection result of the gripping force sensor 173, the gripping force immediately before the gripping force no longer changes is determined as the minimum holding force.

  After measuring the minimum holding force in this way, based on the minimum holding force and the estimated acceleration, which is a value obtained by estimating the acceleration received by the object O based on the scheduled operation condition of the robot arm 10, in the planned operation condition. A necessary holding force that is a holding force with which the end effector 17 can hold the object O is calculated (step S15). Specifically, when the minimum holding force is Pmin and the estimated acceleration is Gc, the required holding force is a value obtained by Pmin × Gc or a value slightly larger than that (for example, a value within 1.1 times). is there. Note that the estimated acceleration is the maximum value of the acceleration that the object O receives under the scheduled operation condition.

  Then, the required holding force is compared with the maximum holding force (maximum gripping force) that is the maximum holding force with which the end effector 17 can hold the object O (step S16). If the maximum holding force is greater than or equal to the required holding force (YES in step S16), the necessary holding force described above is set as the holding force of the end effector 17 (step S17), and the end effector 17 moves the object O with the required holding force. Then, the robot arm 10 is operated under a predetermined operation condition (step S18). On the other hand, when the maximum holding force is smaller than the required holding force (NO in step S16), the end effector 17 cannot hold or transfer the object O under the scheduled operation condition, and is limited to not perform the holding or transferring. (Step S13).

  As described above, as described above, the control method of the robot 100 includes the step S14 for measuring the minimum holding force (minimum gripping force), the step S15 for calculating the necessary holding force, the minimum holding force and the maximum holding force ( Step S16 for comparing the maximum holding force), step S18 performed when the maximum holding force is equal to or greater than the required holding force (required gripping force), and step S13 performed when the maximum holding force is smaller than the required holding force. Have.

  Here, in step S14, when the robot arm 10 is stationary, a minimum holding force that is a minimum holding force with which the end effector 17 (holding unit) attached to the robot arm 10 can hold the object O is measured. . In step S15, the robot arm 10 is based on the minimum holding force and the estimated acceleration that is a value obtained by estimating the acceleration received by the object O held by the end effector 17 when the robot arm 10 operates according to the operating conditions. Calculates a necessary holding force that is a holding force with which the end effector 17 can hold the object O when the object O is operated under the operating condition while holding the object O. In step S16, the required holding force is compared with the maximum holding force that is the maximum holding force with which the end effector 17 can hold the object O. In step S18, when the maximum holding force is greater than or equal to the required holding force, the end effector 17 holds the object O with the required gripping force and operates the robot arm 10 under the operating conditions. In step S13, when the maximum holding force is smaller than the required holding force, the holding of the object O by the end effector 17 is limited.

  Such a control method of the robot 100 is performed by the control device 50. Specifically, the control device 50 that controls the robot arm 10 to which the end effector 17 (holding unit) that holds the object O is attached performs steps S15, S16, S18, and S13 described above.

  According to the control method and the control device 50 of the robot 100 as described above, the end effector in the operation condition is based on the minimum holding force and the value estimated by the acceleration of the object O based on the operation condition of the robot arm 10. When the required holding force 17 is a holding force capable of holding the object O, and the maximum holding force is equal to or greater than the required holding force, the end effector 17 holds the object O with the required gripping force, and the robot arm Since 10 is operated under the operating conditions, the object O can be transported without being detached from the end effector 17. Further, when the maximum holding force is smaller than the required holding force, the robot arm 10 is operated under such a condition that the object O is detached from the end effector 17 in order to limit the holding of the object O by the end effector 17. Driving can be prevented.

  As described above, the robot system 1 includes the control device 50 and the robot 100. According to such a robot system 1, the object O can be transported as far as possible from the end effector 17.

Second Embodiment
FIG. 11 is a flowchart for explaining a robot control method according to the second embodiment of the present invention.

  Hereinafter, the second embodiment will be described with a focus on differences from the above-described embodiment, and description of similar matters will be omitted.

  In the present embodiment, as shown in FIG. 11, when the maximum gripping force is smaller than the required holding force (NO in step S16), an allowable acceleration capable of gripping and transporting the object O by the end effector 17 is set. Calculate (step S21). This allowable acceleration is obtained, for example, by (maximum holding force) / (minimum holding force). Then, the operating condition of the robot arm 10 is changed so that the acceleration received by the object O becomes the allowable acceleration (step S22), and the operating speed of the robot arm 10 is made slower than the scheduled operating condition to operate the robot arm 10. (Step S18).

  As described above, in the present embodiment, when the maximum holding force is smaller than the required holding force, the robot arm 10 is operated by making the operation speed of the robot arm 10 slower than the operation condition (initially planned operation condition). . Thereby, even if it is a case where holding | maintenance of the target object O by the end effector 17 is impossible on the initial operating conditions, it can convey, without removing | separating from the end effector 17. FIG.

  According to the second embodiment as described above, the same effect as that of the first embodiment described above can be exhibited.

<Third Embodiment>
FIG. 12 is a flowchart for explaining a robot control method according to the third embodiment of the present invention.

  Hereinafter, the third embodiment will be described with a focus on differences from the above-described embodiment, and description of similar matters will be omitted.

  In this embodiment, as shown in FIG. 12, when it is determined that holding is not possible (NO in step S12), or when the maximum holding force is smaller than the required holding force (NO in step S16), in step S11 It is determined whether there is another posture different from the posture of the end effector 17 (step S31). More specifically, it is determined whether or not there is a posture in the transport direction that requires less gripping force than the posture of the end effector 17 in the transport direction in step S11.

  Here, for example, in the case of the posture shown in FIG. 4 of the first embodiment described above, the necessary gripping force is the largest when the transport direction is the Z-axis direction, and the transport direction is the X-axis direction. The gripping force is the smallest. Moreover, when the conveyance direction is the vertical direction, the necessary gripping force in the posture shown in FIG. 6 is the smallest among the postures shown in FIGS. When the transport direction is the horizontal direction, the gripping force required when transporting in the X-axis direction in the posture shown in FIG. 4 or FIG. 5 among the postures shown in FIGS. In order to change the posture with respect to the transport direction, at least one of the posture and movement direction (transport direction) of the end effector 17 in the robot coordinates is changed. Here, when changing the movement direction (conveyance direction) of the end effector 17 in the robot coordinates, the movement path (conveyance path) of the end effector 17 in the robot coordinates is changed.

  And when there exists another attitude | position (Y of step S31), the attitude | position of the end effector 17 is changed (step S32) and it returns to step S11. Thereby, the robot arm 10 can be operated under conditions different from the operation conditions as much as possible. On the other hand, when there is no other posture (N of step S31), holding | maintenance and conveyance of the target object O by the end effector 17 are restrict | limited as impossible (step S13).

  As described above, in the present embodiment, when the maximum holding force (gripping force upper limit value) is smaller than the required holding force (required gripping force), the posture or movement direction of the end effector 17 (holding unit) is determined as the operating condition (planned). The robot arm 10 is moved in a posture or direction different from the operation condition. Thereby, even if it is a case where holding | maintenance of the target object O by the end effector 17 is impossible on the initial operating conditions, it can convey, without removing | separating from the end effector 17. FIG.

  According to the third embodiment as described above, the same effects as those of the first embodiment described above can be exhibited.

  The control device, the robot control method, and the robot system of the present invention have been described based on the illustrated embodiment. However, the present invention is not limited to this, and the configuration of each unit has the same function. Any configuration can be substituted. In addition, any other component may be added to the present invention.

  Further, the present invention may be a combination of any two or more configurations (features) of the above-described embodiments.

  The robot of the present invention is not limited to a single arm robot as long as it has a robot arm, and may be another robot such as a double arm robot or a scalar robot. Further, the number of arms (number of joints) included in the robot arm is not limited to the number of the above-described embodiments (six), and may be one or more, five or less, or seven or more.

DESCRIPTION OF SYMBOLS 1 ... Robot system, 10 ... Robot arm, 11 ... Arm, 12 ... Arm, 13 ... Arm, 14 ... Arm, 15 ... Arm, 16 ... Arm, 17 ... End effector, 50 ... Control device, 51 ... Processor, 52 ... Memory, 53 ... I / F, 100 ... Robot, 110 ... Base, 130 ... Driver, 131 ... Angle sensor, 170 ... Driver, 171 ... Main body, 172 ... Gripping part, 173 ... Gripping force sensor, G ... Gravity Acceleration, O ... object, S11 ... step, S12 ... step, S13 ... step, S14 ... step, S15 ... step, S16 ... step, S17 ... step, S18 ... step, S21 ... step, S22 ... step, S31 ... step , S32 ... step

Claims (6)

A control device for controlling a robot arm to which a holding unit for holding an object is attached,
When the robot arm is stationary, the holding unit measures a minimum holding force that is a minimum holding force that can hold the object,
Based on the minimum holding force and an estimated acceleration that is a value obtained by estimating an acceleration received by the object held by the holding unit when the robot arm operates according to an operation condition, Calculating a necessary holding force that is a holding force with which the holding unit can hold the object when the object is held and operated under the operation condition;
Comparing the required holding force with a maximum holding force which is a maximum holding force with which the holding unit can hold the object;
When the maximum holding force is greater than or equal to the required holding force, the holding unit holds the object with the required holding force, and operates the robot arm under the operating conditions.
When the maximum holding force is smaller than the required holding force, the holding of the object by the holding unit is limited, or the robot arm is operated under a condition different from the operation condition. Control device.   2. The control device according to claim 1, wherein when the maximum holding force is smaller than the necessary holding force, the robot arm is operated with a movement speed of the robot arm slower than the operation condition.   The control device according to claim 1, wherein when the maximum holding force is smaller than the necessary holding force, the posture of the holding unit is changed to a posture different from the operation condition to operate the robot arm.   2. The control device according to claim 1, wherein when the maximum holding force is smaller than the necessary holding force, the robot arm is operated by changing a moving direction of the holding unit to a direction different from the operation condition. Measuring a minimum holding force that is a minimum holding force with which a holding unit attached to the robot arm can hold an object when the robot arm is stationary; and
Based on the minimum holding force and an estimated acceleration that is a value obtained by estimating an acceleration received by the object held by the holding unit when the robot arm operates according to an operation condition, Calculating a necessary holding force that is a holding force with which the holding unit can hold the object when the object is held and operated under the operating condition;
Comparing the required holding force with a maximum holding force that is a maximum holding force with which the holding unit can hold the object;
When the maximum holding force is greater than or equal to the required holding force, the holding unit holds the object with the required holding force and operates the robot arm under the operating conditions;
When the maximum holding force is smaller than the required holding force, limiting the holding of the object by the holding unit, or operating the robot arm under a condition different from the operating condition. A robot control method characterized by the above. A control device according to claim 1;
A robot system comprising the robot arm.

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