JP2557076B2 - Force sensor with posture change compensation function - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) When performing machining such as deburring of a workpiece by moving a machining tool along a locus taught in advance by an industrial robot, the state of burrs and The machining reaction force applied to the machining part of the machining tool changes due to wear of the tool, mounting error of the workpiece, and the like. For example, a force sensor for detecting the processing reaction force is required to perform control for correcting the locus of the processing tool so that the processing reaction force does not exceed a certain value. The present invention relates to a force sensor that detects a processing reaction force applied to a processing portion of a processing tool.

(Prior Art) As an industrial robot apparatus equipped with this type of force sensor, for example, there is a technology disclosed in Japanese Patent Laid-Open No. 62-103707. In this conventional technique, a drive shaft supported elastically inclinable is provided at the tip of a robot arm, and a processing tool composed of a rotary drive and a processing tool is attached to this drive shaft, and the processing reaction force applied to the processing tool is adjusted. The processing reaction force is detected based on the inclination of the drive shaft generated as a result.

(Problems to be Solved by the Invention) In such a conventional technique, a moment due to gravity acting on the center of gravity of a machining tool or the like is added to the support portion of the drive shaft in addition to the moment due to the machining reaction force. Since the moment due to changes depending on the posture of the machining tool, there is a problem that an accurate machining reaction force cannot be detected regardless of the posture. The present invention is intended to solve such a problem.

(Means for Solving the Problems) For this reason, the force sensor having the posture change compensation function according to the present invention is an industrial robot as illustrated in the accompanying drawings.
In a force sensor which is attached to a wrist portion 16 of 15 and detects a processing reaction force applied to a processing portion Ta of a processing tool T for processing a workpiece, a base body 21 fixed to the wrist portion 16 and a base end portion thereof are The first columnar body 22 fixed to the base body 21 and the machining tool T fixed to the tip of the first columnar body are supported so that the machining reaction force is always in a direction substantially orthogonal to the first columnar body. The bracket 23 and the first columnar body 22 have their base ends fixed to the base body 21 in parallel with each other, and the weight 27 is attached to the tip.
A second columnar body 26 fixed to the first columnar body 22, strain gauges 24 and 25 for measuring a reaction force which is attached to the side surface of the base end portion of the first columnar body 22 and detects a bending moment applied to the base end portion, 2 columns 2
The strain gauges 28 and 29 for posture detection, which are attached to the side surface of the base end portion 6 to detect the bending moment applied to the base end portion, and the reaction force based on the detection results of the strain gauges 28 and 29 for posture detection. The present invention is characterized by including a calculation unit 30 that corrects the detection results of the strain gauges 24, 25 for measurement and calculates only the processing reaction force.

(Operation) The strain gauges 24 and 25 for measuring the reaction force attached to the base end of the first columnar body 22 detect the sum of the bending moment due to the processing reaction force and the bending moment due to the weight of the processing tool T and the bracket 23. To do. The former bending moment is proportional only to the processing reaction force, and the latter bending moment changes only according to the posture of the processing tool T. Strain gauges 28 and 29 for posture detection attached to the base end of the second columnar body 26 detect a bending moment due to the weight of the weight 27 and the like, which changes only depending on the posture of the processing tool T. Since the first and second columnar bodies 22 and 26 are parallel to each other, the latter one of the bending moments detected by the reaction force measurement strain gauges 24 and 25 and the posture control strain gauges 28 and 29 are detected. The bending moments change in a predetermined relationship with each other. Therefore, the strain gauges 24 and 25 for measuring the reaction force are detected based on the bending moments detected by the strain gauges 28 and 29 for posture control by using the appropriate arithmetic expressions using the dimensions and weight of each part. The influence of the bending moment, which changes only depending on the posture of the processing tool T, can be removed from the bending moment. The calculation unit 30 performs the above calculation to calculate the bending moment only by the processing reaction force, and calculates the accurate processing reaction force that is not affected by the change in the posture of the processing tool T.

(Effects of the Invention) As described above, according to the present invention, an accurate processing reaction force can be detected without being affected by the change in the attitude of the processing tool.

(Examples) Hereinafter, the present invention will be described with reference to Examples shown in the attached drawings.

As shown in FIG. 2, the processing tool T is attached to the wrist 16 of the articulated industrial robot 15 installed on the base 10 via the detection unit 20. The industrial robot 15 is controlled by the robot controller 17 to move the processing tool T as instructed in advance, and the base 10 is moved via the mount 11.
The burr generated on the workpiece Wa supported by the workpiece Wa is removed by the processing portion Ta of the processing tool T. The detection unit 20 detects all the forces (the processing reaction force applied to the processing unit Ta and the force due to the weight of the processing tool T, etc.) applied to the preceding portion, and the calculation unit 30 calculates the processing unit Ta from the detected force. The robot controller 17 inputs this machining reaction force, corrects the movement locus and movement speed of the machining section Ta from the taught values according to the value, and the machining reaction force is calculated. Try to keep it at a predetermined value. The detection unit 20 and the calculation unit 30 constitute a force sensor having a posture change compensation function of the present invention.

Next, the structure of the detection unit 20 will be described with reference to FIG. The base 21 of the detection unit 20 has a box-like shape, and the base end of the first columnar body 22 having a uniform circular cross section is fixed to the inner surface of the base 21, and the tip of the first columnar body 22 protruding slightly outward from the base 21. Processing tool T
A bracket 23 for supporting is fixed. bracket
The reference numeral 23 includes an L-shaped portion 23a fixed to the first columnar body 22 and a gripping portion 23b for detachably fixing the main body Tb of the processing tool (portable grinder) T. As shown in FIG. 2, the machining tool T is attached so that its rotation Tc is parallel to the first columnar body 22, and therefore, the machining reaction generated in the machining section (grinding wheel) Ta mounted at the tip of the rotary shaft Tc. The force F (in FIG. 1, the in-plane component of F is shown as F _x ) is orthogonal to the first columnar body 22. A base end portion of a second columnar body 22 having a uniform circular cross section is fixed to the inner surface of the base body 21 in parallel with the first columnar body 22, and a weight 27 is fixed to the tip thereof. In the present embodiment, the central axes of the first and second columnar bodies 22 and 26 and the rotation axis Tc are in the same plane.

As shown in FIG. 1, the position M of the base end portion of the first columnar body 22, in a position perpendicular to each other, the moment M _x bending occurs in the first columnar body 22, the reaction force measurement for detecting the M _y Strain gauge 24, 2
5 is attached. One strain gauge 24 attached along a generatrix in the plane of FIG. 1 detects a bending moment M _x in a plane parallel to the plane of the paper, and the other strain gauge 25 is a plane orthogonal to the plane of the paper. The bending moment M _y inside is detected. Similarly, at the position of the base end portion m of the second columnar body 26, a strain gauge 28 for posture detection for detecting a bending moment m _x generated in the second columnar body 26 in a plane parallel to the paper plane, and a paper plane A strain gauge 29 for posture detection is attached to detect a bending moment m _y in a plane orthogonal to. The bending moments M _x and M _y are generated by the processing reaction force F applied to the processing portion Ta and the weight W applied to the center of gravity G of all the parts ahead of the position M, and the former component is the magnitude of the processing reaction force F. And the component due to the latter changes only in accordance with the posture of the base 31, that is, the posture of the processing tool T. Bending moment
m _x and m _y are caused by the weight w added to the center of gravity g of all the parts located ahead of the position m, and their values change only depending on the posture of the base 31.

Calculation unit 30 is detected bending moment M _x by each strain gauges 24,25,28,29, M _y, and based on the m _x, m _y, machining tools T orientation and regardless processing reaction force F is The value is calculated.

Next, the operation of this embodiment will be described together with the calculation performed by the calculation unit 30.

The rotation axis of the processing tool T is tilted in any direction from the vertical state shown in FIG. 1, and the tilt angle from the vertical line projected on the paper surface of FIG. 1 becomes θ _x , which corresponds to the paper surface of FIG. Assuming that the inclination angle from the vertical line projected on the orthogonal vertical plane is θ _y , the directions of the forces W and w due to the gravity applied to the centers of gravity G and g are not shown in the drawing on the paper surface of FIG. As described above, the first columnar body 22 is inclined by θ _x from the central axis, and the projection on the vertical line orthogonal thereto is also inclined by θ _y from the central axis of the first columnar body 22. If as illustrating the size of each part in FIG. 1 M portions to the resulting bending moment M _x of the first columnar body 22, M _y and m part to produce bending moments m _x of the second columnar body 26, the m _y The values are as follows.

_{M x = W x (B +} A tanθ x) cosθ x + F x · C = W x (Bcosθ x + A sinθ x) + F x · C ··· (1) M y = W y · A sinθ y + F y · C ·・ ・ (2) m _x = w _x・ a sin θ _x・ ・ ・ (3) m _y ＝ w _y・ a sin θ _y・ ・ ・ (4) where W _x = W / (1 + cos ₂ θ _x・ tan ² θ _y ) _1/2 W _y = W / (1 + cos ₂ θ _y · tan ² θ _x ) _1/2 w _x = w / (1 + cos ₂ θ _x · tan ² θ _y ) _1/2 w _y = w / (1 + cos ₂ θ _y · tan ² θ _x ) _1/2 These values M _x , M _y , m _x , and m _y are detected by the strain gauges 24, 25, 28, 29. Calculation unit 30 the values M _x, M _y, based on the m _x, m _y, calculates the component F _x and component F _y perpendicular thereto in the plane of the first view of the processing reaction force F by the following respective operations Then, the processing reaction force F is calculated from these values.

○ Calculation of the component F _x of the processing reaction force F From the equations (3) and (4), sin θ _x , cos θ _x , tan θ _x , sin θ _y , co
sθ _y and tan θ _y are calculated, and R _x is calculated by the following equation.

R _x = W _x (B cos θ _x + A sin θ _x ) The component F _x is calculated from the above R _x and the equation (1) by the following equation.

F _x = (M _x −R _x ) / C ○ Calculation of component F _y of processing reaction force F Similarly, R _y is calculated by the following equation.

R _y = W _y · A sin θ _{y The} component F _y is calculated from the above R _y and the equation (2) by the following equation.

F _y = (M _y −R _y ) / C ○ Calculation of processing reaction force F The processing reaction force F is calculated from F _x and F _y by the following formula.

F = (Fx ² + Fy ² ) _1/2 As described above, according to the present embodiment, the processing reaction force F generated in the processing portion Ta of the processing tool T is determined by the force sensor including the detecting portion 20 and the calculating portion 30. It can be detected without the influence of the inclination angle of the processing tool.

In the above embodiment, each bending moment M _x , M _y , m _x , m
One strain gauge 24, 25, 28, 29 was used to detect _y , but each bending moment was detected by a pair of strain gauges attached to the columns 22 and 26 at positions opposite to each other. However, according to this, an error due to an axial force applied to the columnar bodies 22 and 26 can be eliminated. Further, when the machining tools T are inclined only in the vertical planes parallel to each other during machining, one strain gauge to be attached to each columnar body 22, 26 is sufficient.

The present invention can be applied not only to the deburring work of the above embodiment but also to the polishing work and other works by changing the processing portion Wa.

[Brief description of drawings]

The attached drawings show an embodiment of a force sensor having a posture change compensating function according to the present invention. FIG. 1 is an overall side view in which essential parts are broken, and FIG. 2 is a side view in use. 15 …… Industrial robot, 16 …… Wrist, 20 …… Detector,
21 ... Base, 22 ... First columnar body, 23 ... Bracket, 2
4,25 …… Strain gauge (for reaction force measurement), 26 …… Second column,
27 …… Weight, 28,29 …… Strain gauge (for attitude detection), T…
… Machining tool, Ta …… Machining department.

Claims (1)

(57) [Claims] 1. A force sensor attached to a wrist of an industrial robot to detect a processing reaction force applied to a processing portion of a processing tool for processing a workpiece, wherein a base fixed to the wrist and a base end portion. A first columnar body fixed to the substrate,
A bracket that is fixed to the tip of the first columnar body and that supports the machining tool so that the machining reaction force is always in a direction substantially orthogonal to the first columnar body, and a bracket that is parallel to the first columnar body. A second columnar body whose base end is fixed to the base body and a weight is fixed to the tip, and a second columnar body which is attached to the side surface of the base end of the first columnar body and detects a bending moment applied to the base end. A strain gauge for force measurement, a strain gauge for posture detection which is attached to the side surface of the base end portion of the second columnar body and detects a bending moment applied to the base end portion, and a strain gauge for this posture detection A force sensor having a posture change compensating function, comprising: a calculation unit that corrects the detection result of the strain gauge for measuring the reaction force based on the result and calculates only the processing reaction force.