JPH01146645A - Profile control system - Google Patents

Abstract

PURPOSE:To facilitate prevention of the damage of an object and a work, by a method wherein, when an monitoring force exerted in a position control direction exceeds an allowable range, an output from a blind zone computing means is added to a speed command in the direction of a normal extending vertically to a profile direction. CONSTITUTION:By means of a deviation between a detecting force Fr produced by coordinate-converting a force detected by a force detecting means and a force command Fo indicating a press force, a speed command Vf is outputted in a direction, extending vertically to the profile direction, to a force control means B. A monitoring force exerted in the direction of position control is computed by a blind zone computing means C, and it is decided by the blind zone computing means whether the monitoring force is in an allowable range. Meanwhile, a deviation between a present position coordinate Xp and a target position Xo is determined by means of a position control means A, and is outputted in a profile direction as a speed command Vp. When the monitoring force exceeds a given allowable range, an output from the blind zone computing means C is added to a speed command Vf by means of the blind computing means C. The damage of an object and a work when an abnormal force is exerted can be prevented from occurring.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to a tracing control method for machining along the surface of an object using an industrial robot, etc., which can easily respond to abnormalities on the surface of the object, and The present invention aims to provide contouring control that does not damage the surface or workpiece, and according to the present invention, a force command indicating the detected force and pressing force obtained by coordinate transformation of the force detected by the force detection means is provided. a force control means for outputting a speed command in the normal direction perpendicular to the tracing direction based on the deviation from the profiling direction; a means provided within the force control means for calculating a monitoring force acting in the position control direction; A dead zone calculation means comprising a dead zone calculation section for setting a predetermined permissible range for the monitoring force, and a position control means for outputting a speed command in the tracing direction based on the deviation between the current position coordinates and the target position, The dead zone calculating means is configured to add the output of the dead zone calculating means to the speed command when the monitoring force exceeds the allowable range.

[Industrial application field]

The present invention relates to a profiling control method, and more particularly to a profiling control method used in industrial robots for operations that require machining a workpiece by tracing the shape of the surface of the object.

[Prior art and problems to be solved by the invention] It is already known that robots are used for processing the surface of objects, such as deburring, wiping, etc., and the profiling control method used at this time is also known. Already proposed.

The basic method of profiling control is as shown in Fig. 4, in which a hand H attached to an arm A constituting a workpiece via a rotation mechanism R is placed in a restraining direction (X direction) at a contact point P with an object O. ) as the force control direction, and the other directions (Y and Z
direction) as the position control direction and are controlled completely separately from each other.

Already, in this tracing control, a force command is given in the normal direction (X direction) at the contact point P on the object surface, and a movement command is given in an arbitrary direction within the tangential plane of the object. By the way, in order to correctly apply the above-mentioned forces and movement commands to the hand H, it is necessary that the surface shape of the object is accurately described numerically, and furthermore, it is necessary to be able to subtly follow changes in the surface shape. High-precision visual equipment capable of real-time processing is required.

On the other hand, in the above-mentioned profile control method, the direction of position control is highly susceptible to disturbances during work, errors in positioning, or abnormal shapes on the surface of the target object. It may be given pointing out of the tangential plane.

FIG. 5 is a diagram explaining this, and when the surface of the object changes abnormally as shown, it is possible to accurately follow the surface when the hand A moves from point P to Pb. For control, it is possible to accurately follow the motion by giving a force command in the x0 direction and a movement command in the Y0 direction. However, as shown by the dotted line, if a force command is given in the X direction and a movement command is given in the Y direction, the force in the Y direction and even the Yb direction will gnaw at the surface of the object. This will damage the surface and workpiece.

In this case, it can be avoided to some extent by capturing the surface of the object as microscopically as possible and quantifying it, and controlling the force command in the X direction and the movement command in the Y direction as finely as possible, but it is difficult to capture a certain moment. This results in the same problem as described above. FIG. 8 shows an example of a conventional configuration, in which a force control section 21 outputs a speed command ■ through a predetermined calculation from a detected force F, which will be described later, and a force command F0 indicating a pressing force, and a position control section 22 In this case, a speed command V is output from the current position X and the target position X0 of the robot coordinate system, and these are added to output a speed command ■. As is clear from the figure,
It can be seen that no feedback control is performed in either the force control section or the position control section. For this reason, an abnormality occurs in the speed command V in response to an abnormality on the surface of the object, resulting in damage such as galling. This will be discussed later.

An object of the present invention is to provide a profiling control method that easily responds to abnormalities on the surface of an object and does not damage the surface of the object or the workpiece.

[Means for solving problems]

FIG. 1 is a diagram showing the principle configuration of the present invention. In the figure, A is a position control means that controls movement commands in the tangential plane direction of the object surface, B is a force control means that controls force commands in the normal direction of the object surface, and C is provided within the force control means. This is a dead zone calculation means that acts as a dead zone for a predetermined range of force.

[Operation] In the present invention, the deviation between the detected force obtained by coordinate transformation of the force detected by the force detection means and the force command indicating the pressing force is determined, and the deviation is determined by the force control means in a direction perpendicular to the tracing direction. A speed command is given to the force control means, a monitoring force acting in the position control direction is calculated by a dead zone calculating means provided in the force control means, and it is further determined whether this monitoring force is within an allowable range. On the other hand, the position control means determines the deviation between the current position coordinates and the target position, and outputs this as a speed command in the tracing direction. In the dead zone calculation means, when the monitoring force exceeds a predetermined allowable range, the output of the dead zone calculation means is added to the speed command.

〔Example〕

FIG. 2 is a block diagram of an embodiment of the profiling control method according to the present invention. In the figure, 21a is a force control unit;
2 is a position control section. In such a configuration, a moving speed command v0 in the tracing direction is used for tracing motion, a force command F0 indicating force for pressing, and a detected force F expressed in the robot coordinate system.
The speed command ■ is generated by the force control unit 21a based on the deviation between , and the position control unit 22 generates the speed command based on the deviation between the target position X0 and the current position Based on the speed commands V and , the sums v, +v, +y are output as the speed command V.

In this case, in order to generate a speed command V in a reference coordinate system such as a robot coordinate system, the operating speeds of each joint of the manipulator are calculated by a calculation unit 2o, which will be described later, and the inverse Jacobian matrix of the manipulator is expressed as J-1. Then, it is expressed as δ=J-1·V. Here, as shown in Fig. 7, the unit vector in the force control direction given by the force command F0 indicating the pushing force on the object is "n", and the position control given by the movement speed command V0 in the tracing direction. When expressed as a unit vector "0" in the direction, yet another orthogonal vector "a" whose position is controlled is a=nx.

is given by

If this is represented as a component using the reference coordinate system, n= (nx nv nz)"o= (
oX Gy Oz)r. Here, T indicates a transposed matrix. On the other hand, the coordinate transformation R of the calculation unit 1 is given by:

The calculation unit 2 converts the force deviation displayed in the reference coordinate system and displays it in the coordinate system. By setting the force control direction and the Y' and Z' directions as position control directions, the selection matrix Sf of the selection matrix I node calculation unit 3
is given by . In this case, in general, pressing, such as tightening the lid of a can, etc., gives a torque around the axis in the direction, so if torque is given, s = 1, and if not, s = o.

In the feedback gain calculating section 4, the feedback gain C1 is given by:

Further, in the position feedback gain calculating section 6, the position feedback gain C2 is similarly given.

Further, "I" in the selection matrix calculation unit 5 represents a unit matrix.

From each of the above equations, the speed command V output from the force control unit 21a is calculated by equations (1), (2), (3) and the detected force F,
According to the deviation between the force command F0 and the force command F0, ■ f Tomi Cr RS
t R-cho (Fr-F,”) ... (5)
In addition, the speed command ■9 output from the position control section 22 is
Equations (1), (2), (4) and current position X.

According to the deviation between the target position X0 and the target position
...(6) is given by.

In this case, in the present invention, the force control section 21a is provided with a selection matrix calculation means 5 and a dead zone calculation means 7 in order to also monitor the force acting in the position control direction. By these means, if the position control direction does not match the tangential plane at the point of contact with the object during the tracing operation, a large frictional force will be generated on the object surface, which will bite the surface and cause damage to the object surface or workpiece. This is something that can be prevented from giving. This is because when a force exceeding an allowable range is applied to the contact point of the object, force feedback is also applied in the position control direction.

In Fig. 2, the monitoring force Fer as a force acting in the position control direction is FC, = (1-3r)R' (Fr-F,)
- In the dead zone calculation means 7, which is set to the force tolerance range Ut (>O) given by (7) and expressed in the tracing coordinate system as in the dead zone, IFc, l≦U.

In this case, if the monitoring force is already smaller than the allowable force range, the speed command V is obtained by adding equations (5) and (6), and if l F cr l > U t , the monitoring force is already When the force is larger than the allowable force range, the speed command Vf of the force control section 21a is Vt = Ct R
(Sr R” (Fo Fr) +FC,,,)
... is given by (8). In this case, Fcra is determined by Fcrm = Fcr Ut (Fcr > 0) = F
It is given by cr+Ur (Fcr<O). Naturally, the speed command Vp in the position control section 22 may be expressed by equation (6).

FIG. 3 is a block diagram of an embodiment of a control device to which the present invention is applied. In the figure, 10 is a robot manipulator, 11 is a servo motor, 2 is a tachometer, 13 is a counter and encoder, 14 is an amplifier, and 15 is a D/
A converter, 16 is a compensator, 17 is a force sensor, 18
19 is a coordinate transformation section, 19 is a position/orientation calculation section, and 20 is an inverse Jacobian matrix calculation section. System 2 composed of 11-16
3 is a speed servo system that is provided as many times as there are degrees of freedom of the manipulator 10.

The force acting on one point of the hand at the tip of the manipulator IO is expressed as the value obtained by multiplying the offset between the hand position and the position at the manipulator's natural length by the stiffness of the manipulator object system, and this acting force is This is detected by a force sensor 17 attached to the wrist of the person. The hand coordinate system (Xh, Yh
, Zh ) is converted into a detected force F of the robot reference coordinate system (Xr, , Y, , Z, , ) by the coordinate conversion unit 18, and is input to the force control unit 21a.

The position and orientation of the hand Xr is determined by the encoder and counter 13.
The position/posture calculation section 9 calculates the joint angle θ3 from each joint angle θ3 detected by the above. Here, Pf is the force control parameter, P
p is a position control parameter.

The speed command V obtained from the force control section 21a and the position control section 22 is used in the inverse Jacobian matrix calculation section 20 to calculate the joint speed θ based on the above formula θ=J-1·V. is input to the compensator 16, and after being D/A converted, it is amplified and drives the servo motor.

〔Effect of the invention〕

As explained above, according to the present invention, when an abnormal force that may damage the object or workpiece is applied in the tracing direction due to an abnormality on the surface of the object, this can be easily avoided. .

[Brief explanation of the drawing]

Figure 1 is a diagram of the principle of the present invention; Figure 2 is a diagram of an embodiment of the present invention; Figure 3 is a block diagram of a control device to which the present invention is applied; Figure 4 illustrates the direction of force on the surface of an object. Figure 5 is a diagram explaining the force direction in the abnormal shape of the object surface. Figure 6 is a diagram explaining the robot coordinate system and hand coordinate system. Figure 7 is a diagram explaining the unit vector in the robot coordinate system. 8 and 8 are conventional configuration diagrams. (Explanation of symbols) 1.2... Calculation section, 3... Selection matrix calculation section, 4... Kafeedback gain calculation section, 5... Selection matrix calculation means, 6... Position feedback gain calculation Part, 7... Dead zone calculation means, 21, 21 a... Force control unit,
22...Position control unit. , 223 Block diagram of a control device to which the present invention is applied No. 3 yJ
5J Enter r Diagram explaining the robot coordinate system and hand coordinate system @Figure 6 r Diagram explaining all unit vectors in the robot coordinate system $7
figure

Claims (1)

[Claims] 1. In a profiling control method for machining along the surface of an object, a detected force (F_r) obtained by coordinate transformation of the force detected by a force detection means and a force command (F_o )
a force control means (B) that outputs a speed command (V_f) in the normal direction perpendicular to the tracing direction based on the deviation from a dead zone calculating means (C) comprising means (5) for calculating F_c_r) and a dead zone calculating section (7) for setting a predetermined tolerance range for the monitoring force (F_c_r); and a position control means (A) that outputs a speed command (V_p) in the tracing direction based on the deviation from the position (X_o), and when the monitoring force exceeds the permissible range in the dead zone calculation means, A tracing control system characterized in that the output of the dead zone calculation means is added to the speed command (V_f).