JPH0780786A - Impedance control device of robot - Google Patents

Abstract

PURPOSE:To maintain the speed at a constant value regardless of a discontineous object instruction, by correcting an imaginary damping coefficient not to exceed a speed limited value, when an impedance control is being carried out by setting an imaginary mechanical impedance to a manipulator. CONSTITUTION:An impedance controller 1 has a parameter setting member 2 to set an imaginary inertia characteristics coefficient M, an imaginary damping coefficient D, and an imaginary sprig coefficient K; and a speed limit value setting member 3. While the ratio of the present speed and the limited speed is calculated 4, the increase part of the imaginary damping coefficient D depending on the obtained speed ratio is calculated 5. An object instruction calculating member 6 is provided, the amount the force applied to an object is measured by a force sensor 9 at the tip of a manipulator 8, and the object instruction of the manipulator in the following control cycle is calculated depending on the above value. The speed obtained depending on the object instruction is compared with the limited speed so as to increase or decrease the imaginary damping coefficient D, and the speed is limited not to exceed the limited value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a robot impedance control device for performing impedance control (also referred to as compliance control), and more particularly to a device having a speed limiting function.

[0002]

2. Description of the Related Art Impedance control is a control method for causing a manipulator to perform a flexible operation by using the position of the manipulator tip and the force acting on the manipulator tip. This control method is expressed by the following characteristic equation.

[0003]

[Equation 1]

Here, M is a virtual inertial characteristic coefficient, D is a virtual damping coefficient, K is a virtual spring coefficient, F is a force acting on the tip of the manipulator, x is a current position of the tip of the manipulator, and x ₀ is a target position. There is. The force F acting on the tip of the manipulator is measured by a force sensor, and the manipulator is controlled according to the equation (1). Generally, the position control is performed by obtaining the position x (t) to be followed by the manipulator from the equation (1). That is,

[0005]

[Equation 2]

By substituting these into the equation (1), x
Solving for (t), we obtain (3). x (t) is the target command for the next control cycle. Here, x (t-1) indicates the position in the previous control cycle.

[0007]

[Equation 3]

In conventional impedance control, M, D,
Since the control is performed while keeping the value of K constant, the speed of the tip of the manipulator is determined by the position in the previous control cycle, the target command in the current control cycle, and the control cycle. On the other hand, in JP-A-5-189008,
It is disclosed that the value of the parameter is changed based on the force detected by the force detector.

[0009]

However, in the prior art, it is necessary to purposely create a target command such that the speed of the target position xo of the formula (3) becomes constant when the speed of the manipulator tip is kept at a certain constant value. was there. Further, there is a problem that an excessive speed is generated when the target command and the current position are largely different in the initial state of control. This problem is related to JP-A-5-1890.
The same is true of the technique of the '08 publication. Therefore, in order to solve the above problems, an object of the present invention is to provide a control device capable of controlling the target position and the posture to follow at a set speed even if a discontinuous target command is given. There is.

[0010]

In order to solve the above-mentioned problems, the present invention provides a speed limit value setting means for setting a limit value for the speed of a control position and the rotational speed of an attitude, and the speed of an impedance-controlled manipulator. And a means for correcting the virtual damping coefficient so as not to exceed the set limit value.

[0011]

By the above means, the speed of the control position of the manipulator tip and the rotation angle of the posture are controlled so as not to exceed the set limit values. That is, when it is desired to maintain a certain constant value, it is possible to maintain the velocity at a certain constant value without modifying the target instruction to generate a corrected target instruction that makes the velocity constant.

[0012]

FIG. 1 shows an embodiment of the present invention. FIG. 1 shows a main portion of a robot (manipulator) and a portion related to the present invention in a robot controller. The impedance control unit 1 calculates a virtual inertia characteristic coefficient M, a parameter setting unit 2 for setting the virtual damping coefficient D and the virtual spring coefficient K, a speed limit value setting unit 3, and a ratio between the current speed and the speed limit. The speed ratio calculation unit 4 and the increment calculation unit 5 that calculates the increment of the virtual damping coefficient based on the speed ratio.
And a target command calculator 6 that calculates an actual target command (position command). The position controller 7 drives the manipulator based on the position command. The magnitude of the force (external force) applied to the object is measured by the force sensor 9 attached to the tip of the manipulator 8, the target command of the manipulator in the next control cycle is calculated from the equation (3), and the previous control is performed. The speed is calculated from the cycle and its target command and compared with the speed limit, and the virtual damping coefficient D is increased or decreased based on the speed ratio so that the actual speed does not exceed the speed limit.
Now, assuming that the manipulator is controlled in the control cycle T, the speed V is given by the following equation.

[0013]

[Equation 4]

From equation (3)

[0015]

[Equation 5]

Therefore, if the virtual damping coefficient D is increased, the speed V is decreased. Here, the increase amount of the virtual damping coefficient is ΔD, and the actual speed which is smaller than the speed V due to the increase of the virtual damping coefficient is V ′, and the ratio Vr between the speed V and the actual speed V ′ is considered. When,

[0017]

[Equation 6]

And the increment ΔD of the virtual damping coefficient
Is

[0019]

[Equation 7]

[0020] The relationship between the speed ratio Vr and the increment ΔD of the virtual damping coefficient is shown in FIG. From this figure, when it is desired to suppress the actual speed V'to 1/2 of the speed V (Vr = 2), the value of ΔD can be set to M + D + K, and V'can be the same as V (Vr = 1). It can be seen that the value of ΔD should be set to 0 at that time. That is, the actual speed V'is set to 1 of the speed V.
When it is desired to set / α, the increase in the virtual damping coefficient can be obtained by setting the speed ratio Vr = α in the equation (7). From the above, the actual velocity V 'in order not to exceed the speed limit V _lmt there is the absolute value of the velocity V | V | the ratio Vr of the speed limit V _lmt' seek, Vr 'of The increment ΔD of the virtual damping coefficient may be determined based on the value. The relationship between the speed ratio Vr ′ and the virtual damping coefficient ΔD at this time is as shown in FIG. When the speed V is smaller than the speed limit V _lmt (Vr ′ <1), the increment of the virtual damping coefficient is almost 0, so the speed V and the actual speed V ′ are almost the same. However, when the speed V becomes larger than the speed limit V _lmt (1 <Vr '), the actual speed _V'is increased by increasing the virtual damping coefficient by ΔD.
Do not exceed After all, the actual target command x ′ (t) for _preventing the actual speed V ′ from _{exceeding a} certain speed limit V _lmt is x ′ (t) −x (t−1) = Δx ′

[0021]

[Equation 8]

It becomes Here, the position difference Δx = x (t)
−x (t−1), and the value of the increase ΔD of the virtual damping coefficient can be obtained from FIG. 3 by calculating the speed ratio Vr ′. Although the description given so far relates to the one-dimensional embodiment, in the general three-dimensional case, the equation (9) is also used.

[0023]

[Equation 9]

The same control can be performed by substituting for. Here, Vx is the x-axis direction component of the three-dimensional velocity vector, Vy is the y-axis direction component, and Vz is the z-axis direction component. In addition, it is obvious that the rotation speed can be limited by the same method for the rotation of the posture.

[0025]

As described above, according to the present invention, when the robot is controlled by impedance control,
When the manipulator approaches the target position, the speed automatically decreases and the impedance can be controlled according to the set impedance. Further, it is possible to operate at a constant speed without the purpose of creating a target command so as to keep the speed of the tip of the manipulator constant. Further, even if the target command and the current position are largely different in the initial state of control, an excessive speed does not occur, and the speed is always less than or equal to the speed limit V _lmt .

[Brief description of drawings]

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

FIG. 2 is a diagram showing a relationship between a speed ratio Vr and ΔD.

FIG. 3 is a diagram showing a relationship between a speed ratio Vr ′ and ΔD.

[Explanation of symbols]

 1 Impedance control unit 2 Parameter setting unit 3 Speed limit value setting unit 4 Speed ratio calculation unit 5 Increase amount calculation unit 6 Target command calculation unit 7 Position control unit 8 Robot 9 Force sensor

Claims (1)

[Claims] 1. A speed limit value setting means for setting a limit value to a speed of a control position and a rotation speed of a posture in a robot impedance control device for performing impedance control by setting a virtual mechanical impedance in a manipulator. An impedance control device for a robot, comprising: means for correcting a virtual damping coefficient so as not to exceed the speed limit value.