JPH01163808A - Noninteracting control system for robot - Google Patents

Abstract

PURPOSE:To improve the stability of a control system by eliminating not only a linear interference between arms but also a nonlinear interference. CONSTITUTION:Arithmetic operation eliminating interference terms of the other shafts is performed based on an equation of motion of the robot arm of each shaft including nonlinear terms and the equation of motion of the robot arm of each shaft for noninteracting among respective shafts of the robot. Each shaft is controlled based on an interference eliminating torque command of each shaft solved as the function of the torque command of each shaft. Thus, a signal subjected to simple arithmetic processing using signals of the other shafts is only added to the conventional control system to improve the stability of the control system.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a robot having mechanical interference between control axes, and more specifically, the dynamic equation of the mutual interference between the axes is a nonlinear differential equation. This invention relates to a non-interference control method for robots, which is known in advance as a robot control method.

[Conventional technology]

Typically, a robot is driven by a single electric motor in terms of degrees of freedom. In that case, in order to compensate for the lack of torque or force output from the shaft end of the electric motor, and to minimize the influence of torque disturbance force or force disturbance force from the load side, a gear such as a harmonic drive with a large reduction ratio is used. The load-side arm is driven through. Therefore, since it is not so affected by the load side, it is possible to assemble a control system for the - axis alone, and it is possible to perform stable control.

However, problems with such robots include backlash in gears and lost motion in harmonic drives, making it impossible to perform highly accurate positioning.
Due to low mechanical rigidity, the gain of the servo system cannot be large, making it impossible to perform high-speed positioning, and there is backlash and torque loss in the reducer, making it difficult to perform force control. There was a problem.

In order to solve these problems, a direct drive system in which the robot arm is directly connected to the output shaft of an electric motor, and a system in which the robot arm is driven through a reduction gear with a low reduction ratio and low backlash (high efficiency) have emerged. The drive system for this new type of robot was similar to the drive system for conventional robots, and was performed by assembling a control loop for each electric motor.

[Problem that the invention seeks to solve]

When driving a direct-drive robot, the conventional method of controlling each axis independently may reduce the stability of the control system or cause interference due to fluctuations in the inertia of other axes and the influence of nonlinear forces such as centrifugal force. Problems such as a decrease in positional accuracy due to force arise.

Below, the problems will be explained by taking as an example the control of a horizontal two-degree-of-freedom direct drive robot using a conventional control method.

FIG. 3 is a control block diagram of a horizontal two-degree-of-freedom robot using conventional control, and FIG. 4 shows a horizontal two-degree-of-freedom robot model. This control system is PI control (proportional-integral control)
The speed control system is based on the speed control system of 1 axis and 2 axis.
The speed control systems of the shafts are completely independent, and each interference force acts as a disturbance force for the other shaft control system. Here, the equation of motion for a horizontal two-degree-of-freedom robot is as follows.

Here, +L + =m+S+”10m2(1+”+s2
"2 j! l52Sillθ2)+Il++2
...(3) J12 = mz (S22
+ l 1S2CO3θ2)++2 ・−・・(4)J
22 = m2S2”+12 “””(5
)al = 3m, l +52Sinθa'
"'"" (6) a2 = m21 +52S
inθa °N−・−(7)a3 =ll1,
j! +5zS1nθ2 111(8)τ. , :
1-axis driving torque CN-m1 τ, 2: 2-axis driving torque CN-m] Further, each variable included in equations (3) to (8) is the following various quantities.

m,: l-axis system arm mass Ckg) m2: 2-axis system arm mass Ckg) j! +: 1-axis arm length [m] 12 = 2-axis arm length [m] SL: 1-axis arm system center of gravity distance (m) S, = 22-axis arm system center distance Cm) 11: Center of gravity of 1-axis arm system Moment of inertia of the 1-axis arm (kg-m') 2 = Moment of inertia of the 2-axis arm centered on the center of gravity of the 2-axis arm [kg-m']
[Go] θl: The angle that the 1-axis arm makes with the stationary coordinate system θ2: The angle that the 1-axis arm and the 2-axis arm make (See Figure 4 for θ1 and θ2.) To express this quantitatively, the 1-axis control system For J124
A torque of magnitude +a1^^+a2^2 acts as a load disturbance, and a torque of magnitude J12 +a, δ2 acts as a load disturbance for the two-axis control system. The load disturbance caused by this interference affects the stability of the control system. Figure 5 shows the step response when the robot shown in Figure 4 is controlled by the conventional control system shown in the block diagram of Figure 3, taking into account a certain delay time (calculation time in a digital control system). ing. In Figure 5, (a)
(5) shows the case of a one-axis control system, and (5) shows the case of a two-axis control system. On the other hand, FIG. 6 shows the following equations (9) and (1
0) is driven by the same controller as in FIG. 5. In FIG. 6, (a) shows the case of a one-axis control system, and (5) shows the case of a two-axis control system.

τm+=J++191...
...(9)τa2=J22Δ...
(10) From FIG. 5 and FIG. 6, it can be seen that stability is clearly degraded in a system with interference.

Next, we will discuss the problems that arise in position control due to disturbance forces caused by interference. The position control system is assumed to be the control system shown in the block diagram in Figure 7, and a comparison is made between the interference system of equations (1) to (8) and the non-interference system of equations (9) and (10). . It is assumed that both loop gains of the control system are controlled within a sufficiently stable range. In addition, as for the robot's motion, as shown in Figure 8, ^=π/2 (:
rad), the position commands of the two axes are set to 0, and one axis is driven with a constant acceleration/deceleration.

FIG. 9 shows the response of the interference system, and FIG. 10 shows the response of the non-interference system, where (a) shows the velocity on one axis, and (w) shows the position deviation on two axes. In the non-interference system shown in FIG. 10, there is naturally no influence on other axes, but in the interference system shown in FIG. 9, a position error occurs in the 02 axis due to interference due to linear interference force and centrifugal force.

The present invention has been made in view of such problems, and aims to eliminate not only linear interference between arms but also nonlinear interference.

Means for Solving Problem C] In order to achieve this object, the non-interference control method for a robot of the present invention is designed to reduce non-linear impulse Based on the equation of motion of the robot arm for each axis including The present invention is characterized in that each axis is controlled based on a non-interfering torque command for each axis, which is solved as a function of the torque command.

[Effect]

FIG. 1 is a block diagram showing the configuration of a control system using the non-interference control method of the present invention. In the same figure, τ,. is each axis torque command, 101.201. ..., 301 is a non-interfering torque command synthesis unit, τl*0 is each axis interference torque command, 102.202. ..., 302 represents the gain between the torque command and the actual torque, and 103 represents the equation of motion of the robot arm with interference.

Here, the non-interference torque command synthesis unit 101.201.・・・
. . , the non-interfering torque command synthesis method in 301 is shown.

Now, if the nonlinear impulse is expressed by fl+..., fl, then n
The equation of motion of the robot arm in the interference system with degrees of freedom can be expressed by the following equation.

Here, the non-interference torque command synthesis unit 101.201.・・・
. . , 301, the output M+ . . . +fjh for the torque commands τ, .

However, JI+"+...1Jn-1n-, etc. are constant values.

J. ′ is the moment of inertia of the tip and is a constant value.

The values actually output from the controller as torque commands for each motor are τl'',..., τ,..., and if we consider that the system shown in equation (11) is made non-interfering by that output, The following formula holds true.

・・・・・・・・・(13) By solving this equation (13) for τI0,
14) A composite non-interference torque command expressed by equation 14) is determined.

“””(Jan/Jan”) r,”+fh/Krh
(14) Each calculation of equation (14) is performed by the non-interfering torque command synthesis unit 101.201. of the block diagram shown in FIG.・・・・・・
.

By executing at 301, τ1゜, ..., τ1
, ', decoupling of the outputs i1, . . . , σ1 is achieved.

〔Example〕

FIG. 2 shows an embodiment in which the present invention is applied to speed control of a horizontal two-axis robot. In the figure, feedback control is performed using a speed loop on each axis, and the results of signal processing of the deviation using proportional and integral elements are processed by the deinterference control block that includes nonlinear compensation of the present invention, thereby canceling out the effects of interference. ing.

In conventional control systems, the system consists of the system shown in the block diagram with the parts shown by chain lines removed, but in this system, signals within each control system are exchanged to eliminate interference. The combined torques are combined and passed to the next stage as each new torque command. Since it involves many multiplications, building a control system based on conventional analog systems tends to result in a complicated system, but if software processing is performed using a microprocessor, it can be implemented with a relatively simple program. Also,
It is possible to compensate for not only the nonlinear term derived from the dynamic equation, but also characteristics such as friction.

〔Effect of the invention〕

As explained above, the present invention is based on the equation of motion of the robot arm for each axis including nonlinear impulse and the equation of motion of the robot arm for each axis when each axis of the robot is made non-interfering. A computation is performed to eliminate interference terms of other axes, and each axis is controlled based on a non-interfering torque command for each axis, which is solved as a function of the torque command for each axis. As a result, the stability of the control system can be improved by simply adding a signal after simple arithmetic processing using signals from other axes to the conventional control system. moreover,
By eliminating the effects of disturbance terms from other axes, force control can be facilitated, and increases in position deviation and speed deviation in the position control system and speed control system can be prevented.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a control system according to the control method of the present invention, Fig. 2 is a block diagram showing an embodiment in which the present invention is applied to speed control of a horizontal two-axis robot, and Fig. 3 is a block diagram showing a control system using the control method of the present invention. Control block diagram of a degree-of-freedom robot. Figure 4 is an explanatory diagram showing a horizontal two-degree-of-freedom robot model. Figures 5 and 6 are step response diagrams showing control responses in conventional control systems. Figure 7 is an interference diagram. Figure 8 is a block diagram of the position control system to explain problems caused by disturbance forces caused by the robot movement. Figures 9 and 10 show the responses of the interference system and non-interference system, respectively. , (a) is 1
The speed of the axes, and (b) the position deviation of the two axes. 101, 201. ..., 301: Non-interference torque command synthesis unit τI0: Non-interference torque command for each axis 102, 202. ..., 302:) Gain between torque command and actual torque 103: Equation of motion of robot arm with interference % formula %

Claims (1)

[Claims] 1. In a robot having a plurality of axes that interfere with each other's axis motion, the equation of motion of the robot arm of each axis including a nonlinear force term and the robot of each axis when each axis of the robot is made non-interfering It is characterized by performing calculations to eliminate interference terms of other axes based on the equation of motion of the arm, and controlling each axis based on a non-interfering torque command for each axis, which is solved as a function of the torque command for each axis. Non-interference control method for robots.