JPH06206185A - Robot controller - Google Patents

Abstract

PURPOSE:To permit the smooth transition to the 'position control impedance control' by eliminating the sharp variation of the input signal in step form to a servoamplifier in closure, by installing an opening/closing means in the forestage where the force feedback signal is inputted into an impedance control means. CONSTITUTION:A robot control means is equipped with a position control means 1 which position-controls a robot 8 on the basis of the position instruction Xrel and the position feedback signal Xfb, and further equipped with an impedance control means 2 for the impedance control on the basis of the feedback signal F supplied from a force sensor 7 installed on the robot 8, and the force feedback signal Fex is inputted into as impedance control means 2 through an opening closing means 4. The output of the impedance control means 2 is added to the position instruction Xref by an adding means 3, and the result of the addition is inputted into a position control means 1. Accordingly, the smooth transition from the 'position control' to the 'position control impedance control' can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a robot control apparatus suitable for gripping an object by a robot, particularly when gripping a tightly stretched rope with a plurality of arms.

[0002]

2. Description of the Related Art As a robot control device, there is known one in which various controls are combined or switched. The example shown in Japanese Patent Laid-Open No. 61-273269 (conventional example 1) is applied to a spot welding robot and is usually driven by position control, and when the welding gun reaches the welding site, the pressure applied to the wrist is applied. The feedback signal of the sensor is also used to switch to position control + force control (adding a force loop outside the position loop). The example shown in Japanese Patent Laid-Open No. 2-83188 (conventional example 2) is applied to a deburring robot, and switches to impedance control when the load applied to the work is smaller than a predetermined value and force control when the load is large. Is. Further, in the example shown in JP-A-63-295191 (conventional example 3), a two-arm robot controls the position of one arm and the force control of the other arm.

[0003]

However, when a strongly stretched rope having a high rigidity is gripped by a plurality of arms, the conventional example has the following problems. In Conventional Example 1, continuous transition of the control system due to switching cannot be performed smoothly. In the conventional example 2, in addition to the same problem as in the conventional example 1, impedance control is performed even in a no-load state, so that it takes time to perform arithmetic processing and the robot operation becomes slow. In Conventional Example 3, in order to grip a strongly stretched rope with a high rigidity by a plurality of arms, it is necessary for each arm to have a function of conforming to an object, but one arm cannot cope with the position control. Therefore, it is an object of the present invention to provide a robot control device capable of gripping a rope with high rigidity which is stretched by a plurality of arms without slowing the robot operation.

[0004]

According to the present invention, as shown in FIG. 1, position control means 1 for controlling the position of a robot 8 on the basis of a position command X _ref and a position feedback signal X _fb is attached to the robot 8. Impedance control means 2 for controlling the impedance based on the force feedback signal F _ex from the force sensor 7, means 3 for adding the output of the impedance control means to the position command, and inputting the force feedback signal to the impedance control means. The opening / closing means 4 is provided in the preceding stage.

[0005]

Since the opening / closing means 4 is provided in the preceding stage of the impedance control means 2, the input signal 6 to the servo amplifier 5 does not suddenly change stepwise at the time of closing, and smoothly changes from "position control" to "position control (however, + Impedance control ”, which is the position control that uses the equilibrium point as the position command.

[0006]

EXAMPLE An example in which the present invention is applied to a multi-arm robot will be described below with reference to FIG. Reference numeral 11 is a robot arm, and a force sensor 12 is provided at the tip of the robot arm to detect the force acting on the object W. The detected force is the coordinate conversion unit 13
After being coordinate-converted by (1) and matching with the coordinate system of the set impedance, it is input to the impedance control unit 15 via the switching unit 14. Impedance control unit 15
Then, the position command in the working coordinate system is determined based on the impedance coefficient set in advance. The position command in the work coordinate system is converted into the joint coordinate system by the coordinate conversion unit 16, and the command is sent to the servo amplifier 17 for joint control, and each servo control unit performs joint position control or speed control. Here, the equilibrium point of the impedance state variable is input to the impedance control unit from the cooperative control controller 18 as a position command. The impedance control unit controls according to the following equation.

[0006]

[Equation 1]

Where F _ex is an external force detected by the force sensor M _{d is an} impedance control coefficient (inertia) B _{d is an} impedance control coefficient (viscosity) K _{d is an} impedance control coefficient (rigidity) X is an impedance control state quantity X _ref: position equilibrium point command X _S: position command output to a servo system (1) (2) is a control relation of the impedance control unit. The function of this control system will be described in terms of on / off of control system switching and presence / absence of object contact. When the robot arm contacts an object with the switching on (closed), the force acting between the object and the robot arm is detected and fed back, and the equilibrium determined by the respective characteristics according to the set impedance of equation (1) and the object dynamics. Converge to a point. When the robot arm moves away from the object, it converges on the position equilibrium point X _ref according to the dynamics of the set impedance. That is, in this state, the control system functions as a force control system that operates at the set impedance. When the switching is off (open), when the output of the integrator in the impedance control block is 0, the output of the servo system is X _ref , and when the output of the integrator is not 0, X _ref follows the set impedance. Converge to. When X _ref changes, the response speed of the servo system follows it. Therefore, in this state, the control system functions as a position control system. When there is a change in the on / off state of switching when an object is in contact or when the integrator is not 0, the force command or position control system gradually changes the position command due to the effect of the set impedance and the integrator. (Fig. 3).

An example in which the impedance control section is configured by a discrete system control using a computer will be described. The discretization formula (1) is required to make the algorithm executable by a computer. Here, an expression using difference approximation is represented instead of strict discretization. First,
The position, velocity, and acceleration in equation (1) are replaced by the following difference equation.

[0009]

[Equation 2]

However,

[0011]

[Equation 3]

Kth position / posture state quantity of arm tip t ₀ : Sampling time At that time, the equation (1) becomes the following equation.

[0013]

[Equation 4]

However,

[0015]

[Equation 5]

Generally, M _d , B _d and K _d are set as follows.

[0017]

[Equation 6]

Since X _K can be considered as a small displacement amount around X _ref , it is assumed that the position / posture equilibrium point command can be expressed by the following (4, 4) matrix.

[0019]

[Equation 7]

In this case, the posture commanded to the servo system by impedance control is calculated by the following equation.

[0021]

[Equation 8]

However,

[0023]

[Equation 9]

Further, the position command to the servo system is determined by the following equation when the position equilibrium point is Pref = (x _ref , y _ref , z _ref ) ^T.

[0025]

[Equation 10]

The posture command A _SK and the position command P _SK are coordinate-converted into respective joint position commands by mechanical inverse conversion.

[0027]

[Equation 11]

However, i = 1 to n, n: degree of freedom of arm joint H (A, P): mechanical inverse transformation (hand posture A, hand position P) The joint angle calculated here is the servo system. Is output to the servo controller as a position command. The servo controller can execute similar control by using not only the position control type but also the speed control type and the torque control type. When a speed control type servo amplifier is used, a method of performing position control inside the computer or a method of outputting the time difference of equation (6) to the speed control type amplifier as a speed command can be used. When a torque control type amplifier is used, position control or speed control can be executed in a computer. The selection of force control and position control by impedance control described above can be performed for each arm, but in one arm, selection can also be made for each spatial degree of freedom of the arm tip. That is, it is also possible to divide the robot hand into a control space of 6 degrees of freedom and perform control by mixing position control and force control with one arm.

[0029]

As described above, by using the present control system, it is possible to smoothly shift the position control and the force control of a plurality of arms, and the working speed can be improved by the flexible working characteristics.

[Brief description of drawings]

FIG. 1 is a block diagram showing the principle of the present invention.

FIG. 2 is a diagram showing an embodiment in which the present invention is applied to a dual-arm robot.

FIG. 3 is a diagram showing a control response characteristic showing an effect of the present invention.

[Explanation of symbols]

 1 Position Control Section 2 Impedance Control Section 3 Addition Means 4 Opening / Closing Means 5 Servo Amplifier 7 Force Sensor 8 Robot

Claims (1)

[Claims] 1. A position control means for controlling a position of a robot on the basis of a position command and a position feedback signal, an impedance control means for controlling impedance on the basis of a force feedback signal from a force sensor mounted on the robot, and an impedance control means of the impedance control means. A robot controller comprising: a means for adding an output to the position command; and an opening / closing means in a stage before the force feedback signal is input to the impedance control means.