JPH054015B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for zero-point calibration of a three-directional force detector used, for example, by being attached to the working end of an industrial robot.

[Conventional technology]

A side view of the main parts showing the configuration when working with a 3-direction detector attached to the wrist of an industrial robot,
Three-directional force analysis diagrams are shown in Figures 1a and b.

Robot wrist 2 of industrial robot (arm) 1
A three-directional force detector 3 is attached to the holder, and a working tool 4 is fixed to the tip thereof.

The problem when using the three-direction force detector 3 to detect the external force that the work tool 4 receives during work is as follows.
This is due to the weight W of the work tool 4 itself.

For example, when the robot wrist 2 shown in FIG.
Zero point calibration is performed in which the output value of the directional force detector is assumed to be zero.

At this time, the weight W of the work implement 4 is apparently eliminated, and the output detected from the three-directional force detector 3 during work is recognized as an external force.

The work with the robot wrist 3 in a horizontal position is completed, and the robot wrist 3 is in the downward position as shown in FIG. Then, the weight W of the working tool 4 is detected as the Z-axis output of the three-direction force detector 3.

[Problem that the invention seeks to solve]

If the work is continued as is, the three-directional force detector 3 will detect the total of the weight W of the work tool 4 and the external force, and it will be difficult to separate them.

Therefore, zero point calibration must be performed again with the robot wrist 2 in a downward position.

As described above, in the past, it was necessary to carry out zero point calibration every time the working posture was changed, so there was a drawback that the posture of the robot wrist 2 could not be changed continuously during the working.

Here, the present invention eliminates the influence of the weight of the work tool regardless of the wrist posture during work performed by attaching a three-directional force detector between the wrist of the robot and the work tool to detect the force applied to the work tool. However, it is an object of the present invention to provide a zero point calibration method that can detect only external forces.

[Means for solving problems]

The present invention is intended to cancel detection errors caused by changes in the working tool in a system in which a three-directional force detector is installed between the tip of an automatic machine that moves freely in three dimensions and the working tool. In this calibration method, before work, the X-axis of the 3-direction detector is set vertically, the weight W of the work tool is not applied to the Y-axis and the Z-axis, and the output Y of the Y-axis at that time is Take Y ₀ and Z-axis output Z = Z ₀ , rotate the tip of the automatic machine 90 degrees around the Z-axis, make sure that the work tool weight W is not on the X-axis of the three-directional force detector, and then Take axis output X = X ₀ .

[Effect]

Then, using the outputs X ₀ , Y ₀ , and Z ₀ of each of these axes as reference values, calculate the X, Y, and Z axes of the three-direction force detector when an external force is applied in any working posture. Output value
= X ₁ , Y = Y ₁ , Z = Z ₁ From the information on the weight W of the work tool, the resultant force F of the external force is F = | { (X ₁ − X ₀ ) ² + (Y ₁ − Y ₀ ) It is calculated by ² + (Z ₁ - Z ₀ ) ² } ^1/2 - W|.

〔Example〕

A side view of essential parts and a force analysis diagram of a three-direction detector in an embodiment of the present invention are shown in FIGS. 1a and 1b.

A three-directional force detector 3 is attached to a robot wrist 2, and a working tool 4 is fixed to the tip thereof.

The procedure of the zero point calibration method for the three-directional force detector 3 will be explained below.

First, the weight W of the working tool 4 itself is measured in advance.

As shown in FIG. 1, when the X-axis of the three-directional force detector 3 is aligned with the vertical direction, the weight W of the work tool 4 is entirely applied to the X-axis and not to the Y- and Z-axes. The shaft output becomes essentially zero.

The outputs of the Y and Z axes at this time are Y=Y ₀ and Z=Z ₀
shall be.

Next, rotate the robot wrist 2 90 degrees around the Z axis,
Figure 2 [a is a side view of the main part, b is a 3-direction force analysis diagram]
Take the posture shown below.

The weight W of the work tool 4 is entirely applied to the Y axis, and
Since it is not applied to the axes, the outputs on the X and Z axes are substantially zero.

The output on the X axis at this time is assumed to be X=X ₀ .

Through the above zero point calibration, it is possible to recognize the output of each detection axis of the three-directional force detector 3 when there is no load.

Consider a case where the robot wrist posture shown in FIG. 4 (a is a front view of the main part in an arbitrary state, b is a three-direction force analysis diagram) is used as a working mode.

By the way, as shown in FIG. 3 [a is a side view of the main part tilted by θ to the Z-axis horizontally, b is a three-direction force analysis diagram], when the Z-axis is tilted by θ to the horizontal, the work tool 4 The weight W is applied as a component force to the X-axis and Z-axis,
The respective sizes are: X=Wcosθ Z=Wsinθ.

Furthermore, in a posture where the X-axis is tilted by α with respect to the vertical direction while maintaining the tilt of the Z-axis, the magnitude of the component force of the work tool 4 Wcosθ is applied to the X-axis and the Y-axis, and the magnitude of each is =Wcosθ・cosα Y=Wcosθ・sinα.

Combining these component forces, √ ² + ² + ² =√(・) ²
+(・) ² +() ² =√ ^{2 2} ( ² + ²
) + ^{2 2} = W Therefore, no matter what wrist posture, the weight of the work tool 4 is detected as a component force on each detection axis, but when these are combined, the weight of the work tool 4 itself is always detected. It can be seen that a certain W is obtained.

Therefore, when working with the wrist posture shown in FIG.
Both the component force of the external force being received by the work tool 4 and the component force of the weight of the work tool 4 will be applied, but since the influence of the weight W of the work tool 4 can be eliminated by calculating the resultant force, the remaining part will be the external force. .

If the above is expressed as an equation, it becomes as shown in (Equation 1).

However, the resultant force of the external force is F, the output of each detection axis of the three-direction force detector is X=X ₁ ,
Let Y=Y ₁ and Z=Z ₁ .

^The _resultant force _F of the external force is _F ⁼ _| { ⁽ _{X 1} ⁻ In addition, no matter what wrist posture you work in, the resultant force F of the external forces can be detected without being affected by the weight of the work tool 4, so if you perform zero point calibration before starting work, it will be possible to detect the resultant force F, which was previously impossible. You will be able to change your wrist posture while doing hot work.

〔Effect of the invention〕

Thus, according to the present invention, a three-directional force detector is installed between the robot wrist and a working tool, and when deburring work involves polishing work, force control can be performed while detecting the external force applied to the working tool. , maintaining the cutting reaction force at an appropriate value, which was difficult in the past,
It becomes possible to keep the pressing force constant.

For example, when the target workpiece in polishing work consists of a three-dimensional curved surface, the posture of the tool must change continuously when polishing the three-dimensional curved surface, but this is an important element for polishing work. A necessary condition for performing force control to keep the pressing force constant is to constantly detect an accurate external force, that is, the pressing force, regardless of the posture of the work implement. Such conditions can only be achieved by employing external force calculation means from the zero point calibration method for a three-directional force detector of the present invention.

In this way, the present invention provides X
Since each axis, Y-axis, and Z-axis output value is calculated and derived by correcting it with a reference value, the external force during work can be synthesized by simple calculations as described above, regardless of the posture of the work tool. can be detected.

Therefore, it is now possible to polish a three-dimensional curved surface with a constant pressing force, which was difficult with the conventional zero point calibration method, and this makes a great contribution to the field.

[Brief explanation of the drawing]

Figures 1 and 2 are side views and three-direction force analysis diagrams of essential parts in one embodiment of the present invention, Figures 3 and 4 are analysis diagrams of applied aspects of the present invention, and Figure 5 is a conventional example. FIG. 1...Industrial robot, 2...Robot wrist,
3...Three-directional force detector, 4...Work tool.

Claims (1)

[Claims] 1. In a system that performs work by installing a 3-directional force detector between the tip of an automatic machine that moves freely in three dimensions and a working tool, the detection error caused by changing the working tool is reduced. This is a calibration method performed to cancel the calibration.Before work, set the X-axis of the 3-direction detector in the vertical direction, make sure that the weight W of the work tool is not on the Y-axis, and the Z-axis, and then adjust the Take the output Y = Y ₀ and the Z-axis output Z = Z ₀ , rotate the tip of the automatic machine 90 degrees around the Z-axis, make sure that the weight W of the work tool is not on the X-axis of the 3-direction force detector, and _{3 - direction force} detection when an external force is applied in any working posture. Output value X of the X-axis, Y-axis, and Z-axis of the device
= X ₁ , Y = Y ₁ , Z = Z ₁ From the information on the weight W of the work tool, the resultant force F of the external force is F = | { (X ₁ − X ₀ ) ² + (Y ₁ − Y ₀ ) ² + (Z ₁ - Z ₀ ) ² } ^1/2 - W| Calibration method for a three-directional force detector, characterized in that the calculation is derived by