JP3865158B2 - Impedance control device for robot arm - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a robot arm impedance control apparatus suitable for handling work and the like.
[0002]
[Prior art]
A conventional general position control based torque impedance control system is as shown in FIG. 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 from 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 equilibrium angle setting unit 607 and becomes an angle command for the arm 601. This angle command is compared with a digital value obtained by converting the electrical signal detected by the rotation angle detector 608 by the rotation angle conversion circuit 609, and an output value obtained by multiplying this difference by the gain integrator 610 is obtained. This output value is converted into an analog signal by the D / A circuit 611 and 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 according to the target trajectory, it is possible to realize a smooth response to the reaction force from a human (or an object) while following the target trajectory.
[0003]
When such an arm is used to perform highly accurate work in an environment where there is a possibility of contact with a human (or an object), there are two problems.
One is the characteristics of the spring-damper system used as a virtual mechanical impedance model. As the arm's displacement angle increases due to a large force from a human (or object), the restoring force that the arm returns to the human (or object) also increases. Is to grow. This is dangerous in an environment where a human (or object) keeps in contact with the arm and may receive a large force from the arm. However, on the other hand, if the virtual mechanical impedance is set small and the restoring force is kept small, this time, even if only a slight contact force is received from a human (or object), it will deviate greatly from the target trajectory. . This makes it difficult to perform the target operation with high accuracy.
The other is that the measured value of the torque sensor placed on the joint axis includes the generated torque or friction torque based on the inertia of the arm and centrifugal force in addition to the external force torque, so the actual arm and human (or object) The force generated between and cannot be determined. As a method for discriminating this, a method using a disturbance observer has been proposed, but since a model is used, it is difficult to know an accurate value due to its identification error and the like.
[0006]
[Problems to be solved by the invention]
As described above, the conventional torque impedance control method 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 the range of minute external force.
(3) An accurate contact force cannot be known from the joint shaft torque sensor.
Therefore, the present invention directly detects the contact force with a human (or object) applied to the robot arm and uses this information to reduce the restoring force and increase the safety when a large force is applied to the arm. An object of the present invention is to provide a device capable of increasing the restoring force and ensuring the operation accuracy when a slight force is applied to the arm.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides an impedance control device for a robot arm that controls the force of each joint motor based on information from a torque sensor attached to each joint of the robot arm. A sheet-like pressure sensor capable of detecting contact pressure information is attached to the surface, and based on the pressure information, the magnitude of the contact force between the robot arm and the person or object is detected. When the value is less than the value, the elastic parameter of the virtual mechanical impedance is reduced as the contact force increases.
Since the contact force on the arm surface can be directly measured by the above means, a safer and more reliable operation can be realized. Further, since the arm escape amount can be adjusted in accordance with the contact force, it is possible to always take optimum measures for various contact forces.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In FIG. 1, when the arm 101 comes into contact with a human (or object) 102, the reaction torque is converted into a voltage by the 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. A sheet-like pressure sensor 106 is attached to the surface of the arm 101, and converts contact force from a human (or object) 102 into voltage. The pressure 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 that 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 information by the impedance parameter calculation unit 107. 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. This angle command is compared with a digital value obtained by converting the electrical signal detected by the rotation angle detector 109 by the rotation angle conversion circuit 110, and an output value obtained by multiplying this difference 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.
[0009]
An example of conversion in the impedance parameter calculation unit is shown in FIG. In the figure, the horizontal axis represents the pressure information Fp input from the A / D converter 104, and the vertical axis represents the elastic parameter k among the virtual mechanical impedance parameters output to the displacement angle calculation unit 105. For example, when the arm is not in contact with a person (or an object) (including when the arm is operating), the pressure information Fp is zero, so the elasticity parameter k takes the maximum value kmax. For this reason, the influence of the generated torque or the friction torque based on the inertia and the centrifugal force during the arm acceleration / deceleration operation can be suppressed to be small, and highly accurate positioning can be performed.
[0010]
Next, in a state where the arm is in contact with a human (or an object) and a small contact force is generated, the elastic parameter k keeps a large value to some extent. For this reason, it is possible to continue the work while keeping the accuracy as high as possible within a range of a small contact force that does not cause harm to humans (or objects).
If the contact force between the arm and a person (or object) increases further as the work continues, the elastic parameter k decreases with the pressure information Fp, so the arm becomes easier to move in the direction to release the contact force. . In addition, since the restoring force of the arm is small, there is no danger that a human (or an object) will receive a large force from the robot.
[0011]
By the above means, the contact force with the human (or object) applied to the robot arm is directly detected, and this information is used to reduce the restoring force and increase the safety when a large force is applied to the arm. When a slight force is applied to the motor, it is possible to increase the restoring force and ensure the operation accuracy.
Another example of conversion in the impedance parameter calculation unit is shown in FIG. Here, the elastic parameter k is increased again when the pressure sensation 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 the person (or object), there is a possibility that the person may come into contact with another person (or object) existing in the space where the arm escapes.
[0012]
Another example is shown in FIG. Here, the conversion formula is a smooth curve in order to avoid a sense of incongruity at the time of contact due to abrupt changes in the elastic parameters with respect to continuous changes in pressure information.
In this apparatus, contact between the robot arm and a human (or object) is detected by a tape-like switch. In this case, since the pressure information is binary, a conversion example in the impedance parameter calculation unit is as shown in FIG. In the figure, Fsw represents a pressure threshold value at which the switch is turned on.
[0013]
【The invention's effect】
As described above, according to the present invention, when a large force is applied to the arm, the arm easily escapes and the restoring force is small, which is safe. In addition, the accuracy can be maintained even in the range of a minute external force. Further, an accurate contact force can be known by a pressure sensor used in combination with a joint axis torque sensor.
[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 calculation unit according to the present invention. FIG. 4 is a diagram showing an example (3) of an impedance parameter calculation unit in the present invention. FIG. 5 is a diagram showing an example (4) of an impedance parameter calculation unit in the present invention. Conceptual block diagram [Explanation of symbols]
101 robot arm
102 Human (or object)
103 Torque sensor
104 A / D converter
105 Displacement angle calculator
106 Pressure sensor
107 Impedance parameter calculator
108 Balance angle setting section
109 Rotation angle detector
110 Rotation angle conversion circuit
111 Gain integrator
112 D / A converter
113 Driver 114 Motor

Claims (1)

In the impedance control device of the robot arm that controls the force of each joint motor based on the information of the torque sensor attached to each joint of the robot arm,
A sheet-like pressure sensor capable of detecting contact pressure information is provided on the surface of the robot arm that contacts the person or the object, and the contact force between the robot arm and the person or the object based on the output of the pressure sensor. The robot arm impedance control device is characterized in that, when the contact force is less than a predetermined value, an elastic parameter is reduced among virtual virtual impedances as the contact force increases. .

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