JPH0839465A - Deflection correcting method for industrial robot - Google Patents

Abstract

PURPOSE:To correct deflection of an arm of an industrial robot used in deburring work or the like applying a large load particularly in a point end of the arm. CONSTITUTION:A device comprises a means (22, 23) calculating reaction force during machining applied to a tool point end from a tool feed speed commanded by a control device of controlling an industrial robot, means (24) differentiating this reaction force by a digital amount, means (25) smoothing this differentiated reaction force and a means (30) converting a sum of the differentiated value of this smoothed reaction force and a detection value of a force sensor into force during machining applied to each articulation of an arm. A means (32), calculating a deflection amount of each articulation of the arm from this converted force during machining applied to each articulation of the arm and from force of gravity applied to each articulation of the arm, is provided to correct a command position of the tool point end commanded by the control device from this calculated deflection amount of each articulation of the arm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for correcting deflection of a robot arm when a work such as deburring is performed using an industrial robot (hereinafter referred to as "robot").

[0002]

2. Description of the Related Art Generally, in a production line composed of a plurality of machine tools, a dedicated deburring machine is arranged behind a cutting machine, and a transfer machine is provided with a deburring unit after a cutting unit. . Since most of these production facilities are for small-scale mass production, the deburring machine and deburring unit used for this can also be handled by a device with a relatively simple mechanism. However, in recent years, in order to cope with the production of a wide variety of products by promoting the flexibility of the production line, a method of deburring with a robot having a deburring tool has begun to be introduced.

The advantage of allowing the robot to carry out deburring work is that it is easy to cope with the production of a wide variety of products by means of programming means, and the movable area relative to the size of the robot main body is large compared to machine tools, so that the installation area of the main body It is small and generally cheaper than a deburring machine. However, in general, the speed reducer (hereinafter referred to as "speed reducer") used for the drive unit of the joint of a robot has low rigidity. Therefore, when the deburring tool is pressed against the work piece with a strong force, the reaction force causes the robot to react. The arm joint of the robot bends (hereinafter, the deflection of the robot arm joint is referred to as "arm deflection"), and also depending on the weight of the deburring tool attached to the arm tip and the chuck holding this. Similarly, the arm bends. For this reason, the positioning accuracy of the deburring tool deteriorates, and the deburring tool cannot be used in machining requiring high accuracy, and the application is limited to use with relatively rough accuracy.

In order to increase the rigidity of the arm, it is conceivable that the mechanism of the arm is of the orthogonal coordinate type instead of the joint type, but this makes the movable range small, and there is not much difference from a machine for deburring machine tools. Further, the use of a high-rigidity reducer leads to an increase in size of the robot body and an increase in cost.

Therefore, as a method of correcting the deflection of the arm, Japanese Patent Laid-Open No. 4-233602 discloses a joint torque applied to each axis of the robot from the posture of the robot corresponding to the command value of the arm tip position (tool tip position). Then, a bending angle is obtained as a bending amount of each axis from the joint torque, and a correction amount of a command value for each axis is calculated from the bending angle of each axis.

[0006]

However, this method is
Since the joint torque is obtained from the posture of the robot, only the flexure of the arm due to the influence of gravity when the arm is stationary, that is, in the static state is taken into consideration. It does not take into consideration the bending of the arm in the state of pressing the arm, that is, in the dynamic state. Therefore, this method reduces the weight of the arm,
Also, the moving speed of the arm is slow, and the load applied to the tip of the arm is small, which is effective in applications such as spot welding, but the load is applied to the tip of the arm for a long time such as deburring work, and There is a problem that it cannot be applied to work requiring high accuracy.

An object of the present invention is to precisely position an industrial robot used for deburring work or the like in which a large load is applied to the tip of an arm.

[0008]

Therefore, the present invention is a method for correcting the deflection of an arm of an articulated industrial robot that performs a predetermined process on a workpiece by a tool attached to the end of the arm. First, the reaction force during machining that acts on the tool tip is calculated from the tool feed speed instructed by the control device that controls the industrial robot, and the calculated reaction force is differentiated by a digital amount. The reaction force differentiated by the quantity is smoothed by the filter. Next, the sum of the smoothed differential value of the reaction force and the detection value of the force sensor installed near the tool is converted into the force during processing that acts on each joint of the arm, and the converted arm's The amount of bending of each joint of the arm is calculated from the force during processing that acts on each joint and the force of gravity that acts on each joint of the arm. Further, by correcting the commanded position of the tool tip commanded by the control device based on the calculated bending amount of each joint of the arm, the above-mentioned problems of the conventional technique are solved.

[0009]

According to the flexure correction method for the industrial robot of the present invention, the robot controller uses the force applied to the tool tip detected by the force sensor attached to the tip of the arm to flexure the arm in a dynamic state. Is calculated to correct the tool tip position. However, if the deflection amount of the arm is obtained only from the force applied to the tool tip detected by the force sensor and this deflection amount is used as the correction amount, the tool tip is equivalent to the scan time of the calculation required to calculate this correction amount. Position correction is delayed.

The graph shown in FIG. 6 (a) shows the relationship between the force F actually applied to the tool tip during cutting (machining) and the force Fs detected by the force sensor. The horizontal axis of the graphs shown in FIGS. 6A to 6D and FIGS. 7A to 7B is time t and the vertical axis is force f, and a and b are the cutting start point and the cutting end, respectively. Show points. As shown in FIG. 6A, the force Fs detected by the force sensor immediately after the cutting start point a rises later than the force F actually applied to the tool tip due to the scan time of the calculation required to calculate the correction amount. Also, immediately after the cutting end point b, the force Fs detected by the force sensor falls behind the force F actually applied to the tool tip. Therefore, an accurate arm deflection amount cannot be obtained immediately after the start of cutting and immediately after the end of cutting, and as a result, appropriate correction cannot be performed.

Therefore, according to the present invention, the cutting reaction force Fr acting in the direction opposite to the tool feeding direction and the cutting torque Tr acting around the rotation axis of the tool are calculated from the tool feeding speed instructed by the controller, These are converted to the wrist coordinate system of the tool tip to obtain the reaction force Ft acting on the tool tip, and the value ΔFt ′ obtained by smoothing the differential value thereof is the force F detected by the force sensor.
By adding to s, the detection value of the force sensor immediately after the start of cutting and immediately after the end of cutting is compensated, and the deflection amount of the arm is obtained from the compensated force F ', and an appropriate correction is performed.

Here, FIG. 6 (b) shows the reaction force Ft acting on the tool tip calculated from the tool feed speed instructed by the controller, and FIG. 6 (c) shows this reaction force Ft as a digital amount. 6 (d) shows a value ΔFt 'which is smoothed by filtering the differentiated reaction force ΔFt, and this ΔFt' serves as a compensation value for the detected value of the force sensor. Further, FIG. 7A shows a value ΔFt ′ obtained by smoothing the reaction force differentiated from the force Fs detected by the above-mentioned force sensor, and FIG. 7B shows the force obtained by adding these. That is, it shows the compensated force F '.

If the compensated force F'matches the above-mentioned force F actually applied to the tool tip, the deflection amount of the arm can be accurately obtained. However, an operation test assuming several kinds of operation conditions is required. As a result, by appropriately selecting the parameters of the filter for smoothing, the processing accuracy at the cutting start point a and the cutting end point b was improved. From this, it can be judged that it is appropriate to obtain the arm deflection amount from the differential value ΔFt ′ of the reaction force finally calculated from the tool feed speed instructed by the control device.

[0014]

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, a force sensor 2 is attached to the tip of an arm of a robot 1 controlled by a control device 4, and a deburring tool (hereinafter referred to as “tool”) 3 is attached to the tip of the force sensor 2, and a workpiece 5 is attached to the workpiece 5. An outline of a system for deburring by using the following is shown.

FIG. 2 is a block diagram showing the configuration of the control device. The coordinate converter 10 converts a voltage signal proportional to the load applied to the tool 3 detected by the force sensor 2 attached to the tip of the arm 1 into a reaction force Fs shown in the wrist coordinate system. The tool reaction force calculation unit 12 calculates the reaction force Ft applied to the tip of the tool 3 during deburring work from the feed speed Sr of the tool 3 commanded by the position control unit 9, and the differentiator 11 calculates the tool reaction force calculation unit 12 After calculating the value ΔFt obtained by differentiating the reaction force Ft calculated in step 1 by a digital amount, a value ΔFt ′ obtained by smoothing this by a filter is calculated. Here, the reaction force Ft applied to the tip of the tool 3 refers to the cutting reaction force Fr that acts in the direction opposite to the feed direction of the tool 3 and the cutting torque Tr that acts around the rotation axis of the tool 3.

The correction amount calculation unit 8 calculates the force Fs applied to the tool 3 detected by the force sensor 2 previously obtained and the tool 3
By adding the differential value ΔFt ′ of the reaction force applied to the tip of the arm, the force F ′ applied to each joint of the arm is calculated, and the correction amount of the tip position of the tool 3 is obtained from the bending amount of each joint obtained from this. . The CPU 6 corrects the tool tip position coordinates in the program data from the program data read from the memory 7 and the previously obtained correction amount of the tip position of the deburring tool 3, and transmits this to the position control unit 9. Position control unit 9
Instructs the robot 1 to move the tip position of the tool 3 to the position instructed by the corrected tool tip position coordinates.

Next, the method of calculating the correction amount of the tool tip position in the embodiment of the present invention will be described with reference to the flowchart shown in FIG. As shown in FIG. 3, when the feed speed of the tool 3 is Sr, the cutting reaction force Fr acts in the direction opposite to the feed direction of the tool 3, and the cutting torque Tr is It acts around the rotation axis of the tool 3 (step 22). Expressions (1) and (2) show the relationship between the cutting reaction force Fr and the feed speed Sr, and the cutting torque Tr and the feed speed Sr, respectively, and fa and fb respectively show the cutting reaction force Fr from the feed speed Sr. This is a function for obtaining the cutting torque Tr from the feed rate Sr.

[0018]

[Equation 1]

[0019]

[Equation 2]

The rotation axis of the tool 3 is an arbitrary one axis of a three-dimensional (X, Y, Z) orthogonal coordinate system, and the coordinates at the tip of the tool 3 are the planes of the remaining two axes orthogonal to the rotation axis of the tool 3. If the wrist coordinate system that can be expressed by coordinates is set, equations (1) and (2)
Is decomposed into force Ft in the wrist coordinate system as shown in equation (3) (step 23). Here, the first column to the sixth column of the matrix on the right side of Expression (3) are the X component (Frx) of force, the Y component (Fry) of force, and the Z component (F) of force in the wrist coordinate system, respectively.
rz), torque X component (Trx), torque Y component (Try), and torque Z component (Trz).

[0021]

(Equation 3)

In the wrist coordinate system defined here, the torque component of the axis designated as the rotation axis of the tool 3 becomes equal to the cutting torque Tr, and further, the force component of this axis and the torque component of other than this axis. Is 0. For example, when the rotation axis of the tool 3 is set to the Y axis, the tip coordinates of the tool 3 are represented by XY coordinates, at which time the Y component (Try) of the torque becomes equal to the cutting torque Tr, and the force Y component (Fr
y), the X component of torque (Trx), and the Z component of torque (Trz) are both zero.

Next, the reaction force Ft in the wrist coordinate system expressed by the equation (3) is differentiated by a digital amount and smoothed by using a filter. The reaction force at a certain sampling time tn is F
Assuming that t (tn) and the reaction force in the sampling one time before the sampling time tn are Ft (tn−1), the differential value ΔFt of this reaction force is as shown in equation (4) (step 24). .

[0024]

[Equation 4]

Differential value ΔF of reaction force obtained from equation (4)
For t, the calculation shown in Expression (5) is performed for each sampling period from the initial value 0 of the register R of the filter. Here, Ts is the time constant of the filter.

[0026]

(Equation 5)

When the register R obtained by the equation (5) is used, the differential value ΔFt 'after smoothing with a filter is performed.
Becomes as shown in equation (6) (step 25).

[0028]

(Equation 6)

FIG. 4 shows the deflection of the arm during the deburring work. The solid line 15 shows the arm at the commanded position instructed by the control device 4, and the broken line 16 applies force to the tip of the tool 3. It is the state of the arm when it is hit. Where δH
n is a bending angle as a bending amount in the joint n17.

The force sensor 2 detects the force applied to the tip of the tool 3 during the deburring work, and the coordinate converter 10 converts it into the force Fs in the wrist coordinate system, as shown in equation (7). Step 26). Here, the first to sixth columns of the matrix on the right side of the equation (7) are respectively X of forces in the wrist coordinate system.
Component (fx), Y component of force (fy), Z component of force (f
z), X component of torque (mx), Y component of torque (m
y) and the Z component (mz) of the torque.

[0031]

(Equation 7)

As shown in equation (8), the force Fs detected by the force sensor 2 shown in equation (7) and the reaction applied to the tip of the tool 3 as the compensation value shown in equation (6). When the differential values ΔFt 'of the forces are summed, the force F'applied to the tip of the tool 3 that compensates the calculation delay due to the scan time required to calculate the correction amount is obtained (step 27).

[0033]

(Equation 8)

Based on the force F'applied to the tip of the tool 3 obtained by the equation (8), the force applied to each joint at this time is obtained.
When the transposed matrix Jn ^T of the Jacobian matrix Jn is used, the force Fn applied to an arbitrary joint n becomes as shown in Expression (9) (step 30). Here, the first to sixth columns of the matrix on the right side of the equation (9) are respectively the X component (fn) of the force in the wrist coordinate system.
x), the Y component of force (fny), the Z component of force (fnz),
X component of torque (mnx), Y component of torque (mn
y), and the Z component (mnz) of the torque. Also,
The Jacobian matrix Jn is a matrix represented by 6 rows and 6 columns, and the component thereof changes depending on the posture of the robot, and therefore needs to be calculated for each scan time of calculation.

[0035]

[Equation 9]

Equation (9) is for any joint n in the dynamic state.
In addition to this, the force Fng applied to an arbitrary joint n due to a static state, that is, gravity, must be taken into consideration, and this is as shown in equation (10) (step 31). . Here, the first to sixth columns of the matrix on the right side of the equation (10) are respectively the X component (fn) of the force in the wrist coordinate system.
gx), force Y component (fngy), force Z component (fng)
z), the X component of torque (mngx), the Y component of torque (mngy), and the Z component of torque (mngz).

[0037]

[Equation 10]

After all, the force applied to any joint n is given by the equation (9).
It is represented by the sum of the force Fn in the dynamic state shown by and the force Fng in the static state shown by the equation (10). The bending angle δ as the bending amount of the arbitrary joint n obtained from this
If this joint is a rotation axis around the X-axis, Hn is expressed by the equation (11), and is similarly obtained when the joint is a rotation axis around the Y-axis or a rotation axis around the Z-axis (step Three
2). Here, mnx and mngx are the X component of the torque in the dynamic state and the X component of the torque in the static state, respectively, and Kn is the reduction gear spring constant of the joint n.

[0039]

[Equation 11]

A correction amount δX of the tip of the tool 3 is calculated from the bending amounts of all joints obtained by the equation (11) (step 34). By commanding the tool tip position by shifting the correction amount δX, the tip of the tool 3 can be positioned at the position where the bending amount of the arm is corrected.

[0041]

According to the present invention, the arm is calculated from the force acting on the tool tip detected by the force sensor attached to the tip of the arm and the reaction force acting on the tool tip calculated from the feed speed of the tool. It is now possible to determine the amount of flexure of the robot and command the tool tip position with the amount of arm flexure corrected to the robot.Therefore, even when the robot is used for work that requires a large load such as deburring, the rigidity of the reducer It has become possible to perform highly accurate positioning without particularly increasing.

Further, by determining the deflection amount of the arm during operation, the programming accuracy of the offline teaching that is generally performed is also improved, so that the positioning accuracy when actually executing the offline taught program. Will also improve.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of a system for deburring, which is an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a control device of the present invention.

FIG. 3 is a conceptual diagram showing a force acting on a tool tip.

FIG. 4 is a conceptual diagram showing bending of an arm when a force is applied to the tip of the tool.

FIG. 5 is a flowchart showing a method for calculating a correction amount of a tool tip position according to the present invention.

FIG. 6 is a graph showing a differential value ΔFt ′ obtained from a force Fs detected by a force sensor and a reaction force Ft acting on the tool tip calculated from the tool feed speed.

FIG. 7: Force Fs detected by force sensor and differential value Δ
6 is a graph showing a force F ′ that compensates for a calculation delay due to a scan time obtained by adding Ft ′.

[Explanation of symbols]

 1 Industrial Robot 2 Force Sensor 3 Tool 4 Controller 5 Workpiece

Claims (1)

[Claims] 1. A method for correcting deflection of an arm of an articulated industrial robot that performs a predetermined process on a workpiece with a tool attached to the tip of the arm, the control controlling the industrial robot. A means for calculating a reaction force during machining that acts on the tool tip from the tool feed speed instructed by the device, a means for differentiating the calculated reaction force by a digital amount, and a means for differentiating by the digital amount Means for smoothing the reaction force by a filter, and the sum of the differential value of the smoothed reaction force and the detection value of the force sensor installed in the vicinity of the tool to the force during processing that acts on each joint of the arm. A means for converting, and means for calculating the amount of bending of each joint of the arm from the force during processing that acts on each joint of the converted arm and the force of gravity acting on each joint of the arm,
A deflection correction method for an industrial robot, comprising: correcting a commanded position of the tool tip commanded by the control device based on the calculated bending amount of each joint of the arm.