JPH10329071A - Impedance control device for robot arm - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a restoration force when a high force is exerted on an arm and to ensure operation precision even by a slight external force by a method wherein a sensor to obtain contact force sense information with a object is stuck on the surface of an arm and based on the contact force sense information, a virtual mechanical impedance is changed. SOLUTION: When an arm 101 makes contact with a human being 102, reaction force torque information is inputted to a displacement angle calculating part 105. Further, a contact force sense sensor 106 is stuck on the surface of the arm 101, and a contact force sense with a human being 102 is converted into a voltage. The contact force sense information Fp is inputted to an impedance parameter calculating part 107 by a digital value. In the displacement angle calculating part 105, a displacement angle to be moved is calculated through an input, such as an elastic parameter (k), based on a mechanical impedance model, the displacement angle to be moved is calculated to generate an angle command for the arm 101. This constitution reduces a restoration force when a high force is exerted on the arm, improves safety, and ensures operation precision by increasing the restoration force during a slight force.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a robot arm impedance control apparatus suitable for handling work and the like.

[0002]

2. Description of the Related Art FIG. 6 shows a conventional position control-based torque impedance control system. When the arm 601 comes into contact with a human (or object) 602,
The reaction torque is converted into a voltage by the torque sensor 603. This torque information is converted into a digital value by the A / D converter 604 and then input to the displacement angle calculation unit 605. The displacement angle calculation unit 605 calculates the displacement angle at which the arm angle should move from the equilibrium point based on the mechanical impedance model from the virtual inertia, viscosity, and elasticity parameters (fixed values) set by the impedance setting unit 606. . The displacement angle is added to the output of the balance angle setting unit 607, and the
Angle command. This angle command is output from the rotation angle detector 608
Is compared with the digital value converted by the rotation angle conversion circuit 609, and the gain is multiplied by a gain integrator 610 to obtain an output value. The output value is converted into an analog signal by the D / A circuit 611 and is output to the motor 613 by the driver 612 to drive the arm 601. In this state, by changing the output of the equilibrium angle setting unit 607 in accordance with the target trajectory, it is possible to realize a response that follows the target trajectory and smoothly responds to a reaction force from a human (or an object).

There are two problems when attempting to perform a high-precision work in an environment where there is a possibility of contact with a human (or an object) using such an arm. One is the characteristic of the spring-damper system used as a virtual mechanical impedance model,
The greater the force applied from the arm, the greater the displacement angle of the arm, the greater the restoring force that the arm returns to a human (or object). This is dangerous because humans (or objects) may receive a large force from the arm in an environment where they continue to contact the arm. On the other hand, if the virtual mechanical impedance is set small and the restoring force is reduced, the target trajectory will greatly deviate even if only a slight contact force is received from a human (or object). . This makes it difficult to perform the intended operation with high accuracy. The other is that the measured value of the torque sensor arranged on the joint axis includes the generated torque or friction torque based on the inertia and centrifugal force of the arm in addition to the external force torque. And the force generated between them cannot be determined. As a method for determining this, a method using a disturbance observer has been proposed. However, since a model is used, it is difficult to know an accurate value due to an identification error or the like.

[0006]

As described above, the conventional torque impedance control system has the following problems. (1) If a large force is applied to the arm, the restoring force increases, which is dangerous. (2) Accuracy cannot be maintained in a small external force range. (3) An accurate contact force cannot be obtained with a torque sensor for a joint shaft. Therefore, the present invention directly detects the contact force with a human (or an object) applied to the robot arm and uses this information to reduce the restoring force when a large force is applied to the arm, thereby improving safety. It is another object of the present invention to provide a device capable of increasing a restoring force when a small force is applied to an arm and ensuring operation accuracy.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to a torque impedance control device for force-controlling each joint motor based on information of a torque sensor attached to each joint of a robot arm. A sensor capable of acquiring contact pressure sense information with an object in an analog manner is attached to the surface, and a virtual mechanical impedance is changed based on the pressure sense information.
By the above means, the contact force on the arm surface can be directly measured, so that a safer and more reliable operation can be realized. Further, since the relief amount of the arm can be adjusted according to the contact force, it is possible to always optimally deal with various contact forces.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, when the arm 101 comes into contact with a human (or an object) 102, the reaction torque thereof is converted into a voltage by a torque sensor 103. This torque information is converted into a digital value by the A / D converter 104 and then input to the displacement angle calculation unit 105. Arm 10
A pressure sensor 106 in the form of a sheet is affixed to the surface of the device 1, and converts a contact force from a human (or an object) 102 into a voltage. This pressure sense information is converted into a digital value by the A / D converter 104 and input to the impedance parameter calculation unit 107. The displacement angle calculation unit 105 calculates the displacement angle at which the arm angle should move from the equilibrium point based on the mechanical impedance model from the virtual inertia, viscosity, and elasticity parameters calculated based on the pressure sense information in the impedance parameter calculation unit 107. Is calculated. The displacement angle is added to the output of the equilibrium angle setting unit 108, and becomes an angle command for the arm 101. The angle command is compared with a digital value obtained by converting an electric signal detected by the rotation angle detector 109 by the rotation angle conversion circuit 110, and an output value obtained by multiplying the difference by a gain by the gain integrator 111 is obtained. This output value is converted into an analog signal by the D / A circuit 112 and output to the motor 114 by the driver 113 to drive the arm 101.

FIG. 2 shows an example of the conversion in the impedance parameter calculator. In the figure, the horizontal axis represents the pressure sense information Fp input from the A / D converter 104, and the vertical axis represents the elasticity parameter k of the virtual mechanical impedance parameters output to the displacement angle calculation unit 105. For example, when the arm is not in contact with a human (or an object) (including when the arm is operating), the pressure parameter Fp becomes zero, and the elasticity parameter k takes the maximum value kmax. For this reason, the influence of generated torque or friction torque based on inertia or centrifugal force during arm acceleration / deceleration operation can be reduced, and highly accurate positioning can be performed.

Next, in a state where the arm comes into contact with a human (or an object) and a small contact force is generated, the elasticity parameter k keeps a relatively large value. Therefore, within a range of a small contact force that does not cause harm to a human (or an object), it is possible to continue the operation while keeping the accuracy as high as possible. When the work is further continued and the contact force between the arm and a person (or an object) increases, the elastic parameter k decreases in accordance with the pressure sense information Fp, so that the arm easily moves in a direction in which the contact force is released. . Also, since the restoring force of the arm is reduced, there is no danger that the human (or the object) receives a large force from the robot.

By the above means, the contact force with the human (or the object) applied to the robot arm is directly detected, and by using this information, when a large force is applied to the arm, the restoring force is reduced and the safety is reduced. When a small force is applied to the arm, the restoring force can be increased to ensure the operation accuracy. FIG. 3 shows another example of the conversion in the impedance parameter calculation unit. Here, the elasticity parameter k is increased again when the pressure sense information Fp exceeds a certain threshold value Fmax. This is because if the arm is released too rapidly in accordance with the contact force from a human (or an object), there is a possibility that the arm may come into contact with another human (or an object) existing in the space where the arm can escape.

Another example is shown in FIG. Here, the conversion equation is a smooth curve in order to avoid a sense of discomfort at the time of contact due to a sudden change in the elasticity parameter with respect to a continuous change in pressure sense information. In this device, a contact between a robot arm and a human (or an object) is detected by a tape-shaped switch. In this case, since the pressure sense information is binary, a conversion example in the impedance parameter calculation unit is as shown in FIG. In the figure, Fsw is ON
The pressure sense threshold value becomes

[0013]

As described above, according to the present invention, when a large force is applied to the arm, the arm can easily escape and the restoring force is small, so that the present invention is safe. In addition, it is possible to maintain accuracy even in a small external force range. In addition, an accurate contact force can be obtained by a pressure sensor used in combination with the torque sensor of the joint shaft.

[Brief description of the drawings]

FIG. 1 is a conceptual block diagram of control showing an embodiment of the present invention.

FIG. 2 is a diagram showing an example (1) of an impedance parameter calculating unit according to the present invention.

FIG. 3 is a diagram showing an example (2) of an impedance parameter calculator according to the present invention.

FIG. 4 is a diagram illustrating an example (3) of an impedance parameter calculation unit according to the present invention.

FIG. 5 is a diagram illustrating an example (4) of an impedance parameter calculation unit according to the present invention.

FIG. 6 is a conceptual block diagram of control in the related art.

[Explanation of symbols]

 101 Robot arm 102 Human (or object) 103 Torque sensor 104 A / D converter 105 Displacement angle calculation unit 106 Pressure sensor 107 Impedance parameter calculation unit 108 Balance angle setting unit 109 Rotation angle detector 110 Rotation angle conversion circuit 111 Gain accumulator 112 D / A converter 113 Driver 114 Motor

Claims (3)

[Claims] 1. A robot arm impedance control device for force-controlling each joint motor based on information of a torque sensor attached to each joint of the robot arm, wherein information on contact pressure sense with an object is detected on the surface of the robot arm. An impedance control apparatus for a robot arm, comprising: a sensor capable of changing a virtual mechanical impedance based on an output of the sensor. 2. The impedance control device for a robot arm according to claim 1, wherein an output of a sensor capable of detecting the contact pressure sense information is a continuous value. 3. The impedance control device for a robot arm according to claim 1, wherein an output of the sensor capable of detecting the contact pressure sense information is a discrete value.