JPH0464562B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a device for controlling the posture of a probe of a three-dimensional shape measuring machine, an ultrasonic probe of an ultrasonic flaw detection scanner, and the like.

B. Prior art Fig. 12 and Fig. 13 showing a three-dimensional shape measuring machine
The prior art will be explained with reference to figures.

The probe 1 is held movably in the x-axis, y-axis, and z-axis directions, and the tip of the probe 1 is brought into contact with the surface to be measured 2 manually or automatically while maintaining the same posture.
Read the x, y, and z positions at that time. Generally, the probe 1 has a shaft portion 1a as shown in FIG.
and a spherical portion 1b at the tip thereof, and when brought into contact with the surface to be measured 2, the measuring instrument body reads the position of the tip P of the spherical portion 1b as a measurement value. The above operation is repeated at a plurality of positions to measure the shape of the surface to be measured 2. Note that the position of the center O of the spherical portion 1b may be read.

C Problems to be Solved by the Invention However, when the surface to be measured 2 is inclined by α degrees with respect to the horizontal plane HP as shown in FIG. Contact with surface 2. This results in an error in which the position of the contact point Q and the measurement position P are deviated by δx and δz.

Conventionally, several points are measured in the vicinity of the inclined surface, the points are interpolated to obtain the inclination angle α, and based on this angle α, the deviations δx and δz are calculated to correct the measured values. In this case, a correction calculation is required, and even if this is performed by a computer, real-time measurement will not be possible, which will hinder automation of shape measurement. Note that although the above description has been made in two dimensions, essentially the same correction is required in three dimensions as well, just because δy is included.

Although this type of probe 1 can move in the x-axis, y-axis, and z-axis, its posture remains constant. Therefore, if the inclination angle α of the surface to be measured 2 becomes 90 degrees or more, the probe 1
The tip ball portion 1b cannot be brought into contact with the surface to be measured 2. In this case, it is necessary to perform measurements by manually changing the posture of the object to be measured, which poses an obstacle to automation.

As a device to solve such problems,
Some of these are disclosed in Japanese Patent Publication No. 57-148209 and Japanese Patent Publication No. 58-32644.

JP-A-57-148209 discloses the following measuring device. A measuring element (hereinafter referred to as a probe) is swingably supported on a measurement head by a swing shaft, and is provided with a pair of displacement sensors that measure the swing amount of the probe as a displacement amount in a direction perpendicular to the axis of the probe. There is. When the probe is pressed against the inclined surface to be measured in its axial direction, the probe swings around the swing axis according to the inclination of the surface to be measured.
The amount of oscillation is detected by displacement sensors, and the measurement head is rotated with the center of the probe as the center of rotation and with the probe in contact with the surface to be measured until these sensors no longer detect the amount of oscillation. In this way, in this measuring device, the probe is brought into contact with the surface to be measured perpendicularly.

Further, Japanese Patent Publication No. 58-32644 discloses the following measuring device. This measuring device is also similar to the above device, in that a pair of displacement sensors measure the amount of displacement of a probe that is displaced according to the inclination angle of the surface to be measured, and the normal direction of the surface to be measured is calculated from the detection results of the displacement sensors. do.

However, the devices disclosed in Japanese Patent Application Laid-open No. 57-148209 and Japanese Patent Publication No. 58-32644 measure the displacement of the probe to orient the probe perpendicularly to the surface to be measured. Since the probe is supported by a support member with low rigidity, there is a problem in that when the probe is pressed against the target point on the surface to be measured, the position of the probe deviates from the target point.

In addition, the device disclosed in Japanese Patent Application Laid-Open No. 57-148209 is configured to rotate the probe while keeping it in contact with the surface to be measured, so the distance between the probe and the surface to be measured during rotation is There is a problem in that the displacement sensor detects an undesired displacement caused by the frictional force, making it impossible to accurately orient the probe perpendicularly to the surface to be measured.

The above-mentioned problems are not limited to three-dimensional shape measuring machines, but also apply to various types of equipment that perform measurements by bringing the probe into contact with the surface to be measured, such as an automatic ultrasonic flaw detection scanner equipped with an ultrasonic probe. That applies.

An object of the present invention is to provide a probe attitude control device that controls the attitude of a probe and solves the above-mentioned problems.

D. Means for Solving the Problems The present invention will be explained based on the claim correspondence diagram shown in FIG. , a driving means 102 such as a DC motor for driving these supporting means 101;
A probe 103 provided on the support means 101;
Force detection means 1 for detecting the force acting on the probe 103 when the probe 103 comes into contact with the surface to be measured
04, attitude detection means 105 for detecting the attitude and initial contact position of the probe 103, and inclination calculation means 1 for calculating the inclination of the probe 103 with respect to the surface to be measured based on the force detected by the force detection means 104.
06, a target attitude calculation means 107 for calculating a target attitude in which the probe 103 is perpendicular to the surface to be measured based on the calculated inclination and the detected attitude; It has a drive control means 108 that drives and controls the drive means 102 so as to change the attitude to the target attitude and guide the probe 103 to the detected initial contact position.

As in the probe attitude control device according to claim 2, the force detection means 104 detects the force due to the probe's own weight when the probe 103 is separated from the surface to be measured, and the inclination calculation means 106 detects the force due to the probe's own weight when the probe 103 is separated from the surface to be measured. The force detected by the force detection means 104 when the probe 103 is pressed against the surface to be measured is corrected by the force due to the self-weight, and the probe 10 is corrected based on the correction value.
Alternatively, the inclination of No. 3 with respect to the surface to be measured may be calculated.

Further, as in the probe attitude control device according to claim 3, the force detection means 104 may detect the probe's own weight when the probe 103 is held in the air.

E Effect The force that the probe 103 receives when it comes into contact with the surface to be measured is detected by the force detection means 104.
The inclination calculation means 10 calculates the inclination angle of the probe 103 with respect to the surface to be measured from the detection result.
6 calculates. Further, the attitude detection means 105 detects the attitude and initial contact position of the probe 103. Based on such an inclination and attitude, the calculation means 107 calculates a target attitude in which the probe 103 is perpendicular to the surface to be measured. The drive control means 108 drives the drive means 102 so that the probe 103 is once separated from the surface to be measured so that the probe 103 assumes a target attitude in space, and then drives the drive means 102 so as to guide the probe 103 to the initial contact position. 102 is driven. As a result, the probe 10 is not affected by the frictional force.
3 is precisely oriented perpendicular to the surface to be measured.

Further, the probe's own weight is measured when the probe 103 is separated from the surface to be measured, the force detected when the probe 103 is pressed against the surface to be measured is corrected by this weight, and the inclination is calculated from the correction result.

Furthermore, the dead weight of the probe 103 is
03 is detected when it is held in the air to change its attitude.

F Example One example of the present invention will be described with reference to FIGS. 2 to 11.

FIG. 2 shows a schematic overall configuration of a probe attitude control device, in which a probe 1 similar to the conventional one is provided at the tip of a robot 50 having five degrees of freedom via an axial force sensor 3, and each joint of the robot 50 is is JIS
It is indicated by the symbol specified in . The robot 50 can rotate relative to the base 51 by a rotation mechanism 52 (including a motor M1). A rotation shaft 53 is connected to the rotation mechanism 52, and a first arm 55 can be rotated by a rotation mechanism 54 (including a motor M2) connected to the tip of the rotation shaft 53. The second arm 57 can be rotated by a second arm rotation mechanism 56 (including a motor M3), and by a third arm rotation mechanism 58 (including a motor M4) connected to the tip of the second arm 57. A third arm 59 is pivotable. A wrist 61 is rotatably provided at the tip of the third arm 59 via a wrist rotation mechanism 60 (including a motor M5). For example, a multi-axial force sensor 3 shown in FIG. 3 is provided at the tip of the wrist 61.
A probe 1 is attached to this multiaxial force sensor 3. The multi-axis force sensor 3 has an x-axis that acts on the probe 1 when the probe 1 is brought into contact with the surface to be measured;
It detects the axial force on the y-axis and the z-axis.

That is, in FIG. 3, the multiaxial force sensor 3
are the first ring 4, the second ring 5 opposite thereto, the three flexible beams 6 connecting both rings 4 and 5, and the tension/compression force provided on the inner surface of the flexible beams 6. It consists of a detection gauge 7 and a shear force detection gauge 8 provided on the outer surface of the flexible beam 6. Then, the first ring 4 is connected to the wrist 61, the second ring 5 is connected to the probe 1,
When the flexible beam 6 deflects in response to the force acting on the probe 1, a signal corresponding to the amount of strain is obtained from each gauge,
Each axial force F _X , F _Y , F _Z is known.

Referring again to FIG. 2, the rotation mechanism of each joint is provided with rotation angle sensors such as rotary encoders R1 to R5 that detect the rotation angle thereof, and the detected rotation angles θ ₁ to _{θ 5} are input to the control device 9. . Also,
The axial forces F _X , F _Y , F _Z detected by the axial force sensor 3 are also input to the drive control device 9 . The control device 9 supplies drive signals i ₁ to i ₅ to the motors M1 to M5 of the angular rotation mechanism so that the probe 1 is perpendicular to the surface to be measured based on calculations to be described later. In addition, in Figure 2,
A signal line D ₁ related to the third arm rotation mechanism 58,
D ₂ and the signal line D ₃ of the axial force sensor 3 are connected to the control device 9.
, and other connections are omitted.

As shown in FIG. 4, the control device 9 includes an interface 9a that inputs an analog signal from the axial force sensor 3 and adjusts its voltage level and zero point as a signal input section from the axial force sensor 3, and an interface 9a that inputs the analog signal from the axial force sensor 3 and adjusts its voltage level and zero point. a multiplexer 9b that selectively outputs
It has an A/D converter 9c that converts the analog signal from the multiplexer 9b into a digital signal and inputs the digital signal to the CPU 9d. Further, as a signal input section from the rotary encoders R1 to R5, there is a counter circuit 9e that counts serial pulse signals from the rotary encoders R1 to R5 and converts them into parallel angle signals, and a CPU 9d to which signals from the counter circuit 9e are input. It has an input interface 9f for outputting to. Furthermore, as a signal control unit, ROM 9g that stores processing procedures and RAM 9h that temporarily stores various numerical values, data, etc.
and control each device according to the processing procedure,
It has a CPU 9d that performs various calculations based on the input signal, compares it with the joint angle at that time, and outputs a joint speed command signal. Furthermore, as an output unit, a D/A converter 9i that converts the digital joint speed command signal output from the CPU 9d into an analog signal, and a joint speed command signal calculated from the joint speed command signal and the rotation angle signal from the rotary encoders R1 to R5. and a servo driver 9j that controls the motors M1 to M5 so that the speeds match the motors M1 to M5.

In addition, in the configuration of the above embodiment, the base 5
1. Arms 53, 55, 57, 59 and wrist 6
1 is a support means, motors M1 to M5 are drive means, axial force sensor 3 is a force detection means, rotary encoders R1 to R5, counter 9e, CPU 9d.
constitutes an attitude detection means, the CPU 9d constitutes an inclination calculation means and a target attitude calculation means, and the CPU 9d and the servo driver 9j constitute a drive control means.

Next, the procedure for controlling the attitude of the probe will be explained with reference to FIG.

Now, assume that the probe 1 is in contact with the surface to be measured 2 as shown in FIG. 6a. In step S1, the angles θ ₁ to θ ₅ of each joint are detected by the output of the counter circuit 9e that counts pulse signals from the rotary encoders R1 to R5. In step S2, the position and orientation of the center point O of the spherical portion 1b of the probe 1 are determined based on these angles θ ₁ to _{θ 5} and the lengths l ₁ to _{l 5} of each part of the robot 50 shown in FIG. calculate. In FIG. 2, l ₁ is the distance from the attachment point of the base 51, that is, the robot coordinate origin O ₁ to the first arm rotation mechanism 54, and l ₂ is the distance between the first and second arm rotation mechanisms 54 and 56. l ₃ is the distance between the second and third arm rotation mechanisms 56 and 58, l ₄ is the distance from the third arm rotation mechanism 58 to the probe z along the third arm 59. The distance l ₅ to reach the axis is the distance from the center O of the probe sphere 1b to the axis of the third arm 59 along the wrist 61.

Here, the position of the probe 1 is expressed as a position vector from the origin O ₁ of the robot coordinates to the center O of the probe sphere 1b as follows: = (Ox, Oy, Oz) = f ₁ (θ ₁ ~ θ ₅ , l ₁ ~ l ₅ ). This position vector indicates the initial contact position of the probe 1. Also, the attitude of the probe 1 is determined by the direction cosine vector as the inclination of the coordinate system of the axial force sensor 3 with respect to the robot coordinate system.
It is obtained by calculating h).

If the direction cosine vector is = fx fy fz, and the angle between the probe The vector can be expressed as = cosθxx cosθxy cosθxz. Similarly, the angles that the probe y-axis and z-axis make with the x-axis, y-axis, and z-axis of the robot coordinate system are respectively θyz, θyy, θyz and θzx, θzy,
If θzz, the direction cosine vectors can be expressed as: =gx gy gz=cosθyx cosθyy cosθyz =hx hy hz=cosθzx cosθzy cosθzz. For example, the direction cosine vector h is expressed as x in the robot coordinate system, as shown in FIG.
When the respective axes of the coordinate system of the axial force sensor 3 are located at x', y', and z' with respect to the axis, y-axis, and z-axis, y
The projections to the axis and z axis are hx, hy, and hz, respectively.

When the position and orientation of the probe 1 are calculated in this way, the process proceeds to step S3, where the axial force sensor 3
In _{step S4 ,} the three _axial forces _F
Correct the axial forces F _X , F _Y , F _Z by W _Z to obtain the true axial force
Find R _X , R _Y , and R _Z. That is, calculate R _X =F _X −W _X R _Y =F _Y −W _Y R _Z =F _Z −W _Z (1).

Now, as shown in FIG. 8a, if the axial center (z-axis) of the probe 1 is oriented in the vertical direction, each axial force W _X due to the probe's own weight W detected by the axial force sensor 3,
W _Y and W _Z are as follows: W _X =0, W _Y =0, W _Z =W. On the other hand, as shown in FIG. 8b, if the axial center of the probe 1 is tilted with respect to the vertical direction, each axial force W _X , W _Y , W _Z due to the probe's own weight W detected by the axial force sensor 3 becomes W _X = W _X ′ W _Y = W _Y ′ W _Z = W _Z ′. Since the probe's own weight always acts on the axial force sensor 3 regardless of the orientation of the probe 1, the true axial force due to the drag force R that acts on the probe 1 when bringing the probe 1 into contact with the surface to be measured 2
It is necessary to find R _X , R _Y , and R _Z using the above equation (1).

Then, in step S5, the inclination of _the probe 1 with respect to _the surface to be measured (attitude angle _ξ ,
ψ).

FIGS. 9a and 9b are diagrams for explaining the respective axial forces R _X , R _Y , and R _Z when the probe sphere 1b is brought into contact with the surface to be measured 2. FIGS.

As shown by the solid line J, when the z-axis of the probe 1 is inclined with respect to the surface to be measured 2, the direction of the drag force R acting on the probe 1 does not match the probe z-axis, and the component force of the drag force R is Each axial force R _X , R _Y , R _Z is detected. Further, when the probe z-axis is perpendicular to the surface to be measured 2 as shown by the dashed line I, the direction of the drag force R acting on the probe 1 coincides with the probe z-axis. From this, the attitude angles ξ and ψ of the probe 1 shown by the dashed-dotted line I with respect to the attitude of the probe 1 shown by the solid line J are as follows: ξ=tan ^-1 (√R _X ² +R _Y ² /R _Z ) ψ=tan ^-1 It is obtained by (R _Y /R _X ).

Next, the process proceeds to step S6, in which it is determined whether the inclination angle ξ between the normal to the surface to be measured 2 and the probe z-axis is zero (whether or not the probe z-axis is perpendicular to the surface to be measured). If ξ=0, end; if ξ≠0, step
Proceed to S7.

In step S7, using the attitude angles ξ and ψ obtained in step S5, the target attitude such that the probe z-axis is perpendicular to the surface to be measured 2 is set as the target direction cosine (s, s, s). s, s, s)=f ₃ (ξ, ψ(,,)).

Next, the process proceeds to step S8, and the target position vector s, which is the target attitude of step S6 at a position where the probe 1 is separated from the surface to be measured 2, is determined from the following equation.

s=f ₄ (, (s, s, s), k) = -k (s, s, s) Note that k is a constant indicating the amount of movement from the original position.

Then, in step S9, the target angle θ's ₁ ~
θ′s ₅ , (θ′s ₁ ~ θ′s ₅ ) = f ₅ (s, (s, s, s), l ₁ , l ₂ , l ₃ ,
l ₄ ). In step S10, the motor drive commands _i'1 to _i'5 are changed to D/D so that the target angles _θ's1 to _θ's5 are achieved.
Supplied from the A converter 9i to the servo drive 9j,
As a result, each of the motors M1 to M59 is driven, and as shown in FIG. 6B, the posture shown by the broken line I1 changes to the posture shown by the broken line I2, and then the posture shown by the solid line J1. The z-axis of the probe in this attitude is perpendicular to the surface to be measured.

Holding the posture shown by the solid line J1 in FIG. 6b, in step S11, the axial forces F _X , F _Y , F _Z detected by the axial force sensor 3 at this time are converted into self-weight correction values W _X , W _Y ,
Store as W _Z. These correction values W _X , W _Y , W _Z
is used in step S4 described above when moving the probe 1 to the next measurement point and controlling its vertical posture. That is, in this embodiment, when moving the probe 1 from one measurement point to the next measurement point,
Since it is assumed that the probe 1 is brought into contact with the next measurement point while remaining perpendicular to the previous measurement point, the probe dead weight correction value is obtained as described above. Therefore, when operating the probe 1 so that its attitude changes from the previous state when moving to the next measurement point, the probe self-weight correction value W _X , W _Y , W _Z
need to be detected.

Next, the process proceeds to step S12, where the initial position vector of the center O of the probe sphere 1 obtained in step S2 and the target direction cosine (s,
gs, s), the target angles θs ₁ to θs ₅ of each joint where the probe 1 contacts the surface to be measured 2 at the initial contact position and is perpendicular are calculated as follows: (θs ₁ to _{θs 5} ) = f ₆ (s, (,,), l ₁ , l ₂ , l ₃ , l ₄
, l ₅ ). Then, in step S13, motor drive commands _i1 to _i5 are supplied from the D/A converter 9i to the servo drive 9j so that each joint becomes _θs1 to _θs5 , thereby driving each motor M1 to M5. The position of the probe is controlled so that the z-axis of the probe comes into contact with the surface to be measured 2 perpendicularly. As a result, as shown in FIG. 6c, the posture shown by the broken line I3 changes to the posture shown by the solid line J2,
The probe z-axis abuts the surface 2 to be measured perpendicularly.

Such a probe attitude control device is used in a three-dimensional shape measuring machine to control the attitude of the probe sphere 1b so that the z-axis is perpendicular to the surface to be measured 2 so that point P of the sphere 1b is in contact with the surface to be measured 2. In the state, x, y, z of the sphere 1b
By measuring each axis position, shape and dimensions can be measured in real time without error without performing interpolation calculations as in the past, and continuous dimension measurements can be performed, contributing to measurement automation. In addition, the surface to be measured 2
Even if the inclination angle α is 90 degrees or more, the probe 1 can be brought into contact with the surface to be measured 2 perpendicularly, and there is no need to manually shift the position of the object to be measured, contributing to automation of measurement.

Furthermore, if this invention is applied to an ultrasonic flaw detection scanner device, the ultrasonic probe can be held perpendicularly to the surface to be inspected at all times, improving inspection accuracy. Autonomous driving will become possible.

Although the robot 50 described above has five degrees of freedom, five degrees of freedom are not particularly necessary if the shape of the surface to be measured is limited and known in advance. For example, as shown in FIG. 10, if the x-z cross section is a three-dimensional object that is the same along the y-axis, the present invention can be constructed using a robot with three degrees of freedom. Further, the driving means is not limited to the motor, the axial force sensor may be of another type, and the shape of the probe is not limited to the embodiment.

G. Effects of the Invention According to the present invention, since the attitude of the probe can be controlled so that it is perpendicular to the surface to be measured, automation of three-dimensional shape measuring machines and ultrasonic flaw detection scanners equipped with this type of probe is possible. It becomes possible. and,
This invention particularly has the following effects.

As shown in Fig. 11a, when the probe z-axis is in contact with the surface to be measured 2 at an inclination angle ξ, ξ
= 0, when the probe 1 is rotated around the center O of the probe sphere 1b and the probe 1 is kept in contact with the surface to be measured 2 and the attitude is changed to the attitude shown in FIG. 11b.
A friction force Rμ is applied to the probe 1 due to the drag force R and the friction coefficient μ. Since the probe 1 and its supporting means such as the arm are not completely rigid bodies, they deflect due to the frictional force Rμ, and even after the probe z-axis changes its posture perpendicularly to the surface to be measured 2, this deflection is balanced. Therefore, a force corresponding to the frictional force Rμ is detected by the force detection means. Therefore, a drag force Rμ will act on probe 1,
The attitude is further changed so that the probe z-axis coincides with the direction of action of the drag force Rμ, so that the probe z-axis and the surface to be measured 2 are not perpendicular to each other.

Therefore, in the present invention, the probe is separated from the surface to be measured, changes its posture, makes the probe z-axis perpendicular to the surface to be measured, and then brings the probe into contact with the initial position. The probe can be held perpendicularly to the surface to be measured with high accuracy without the frictional force associated with attitude change. Furthermore, in the present invention, the inclination is calculated from the force after correction, which is obtained by subtracting the probe's own weight, thereby further improving accuracy.

Furthermore, if the above self-weight is detected by reading the output signal of the force detection means when the probe is held in the air and changes its attitude, there is no need to remove the probe from the surface to be measured just to measure the probe's self-weight. Therefore, the measurement efficiency can be improved.

Note that if the present invention is applied to a three-dimensional shape measuring machine, error-free shape measurement becomes possible.

[Brief explanation of the drawing]

FIG. 1 is a complaint correspondence diagram. Figures 2 to 9
The figures show one embodiment of the present invention, in which Fig. 2 is a general schematic diagram, Fig. 3 is a perspective view showing an axial force sensor, Fig. 4 is a block diagram showing a control device, and Fig. 5 is a probe. A flowchart showing the procedure of attitude control, Figures 6 a to c are diagrams explaining the attitude change of the probe, Figure 7 is a diagram explaining the direction cosine, and Figures 8 a and b are diagrams explaining the axial force due to the probe's own weight. figure to do,
FIGS. 9a and 9b are explanatory diagrams of the axial force detected by the axial force sensor, and FIG. 10 is a perspective view showing an example of a shape that can be measured with three degrees of freedom. FIGS. 11a and 11b are diagrams explaining the effects of the invention. 12 and 13 show a conventional example. FIG. 12 is a perspective view showing an example of a conventional three-dimensional shape measuring machine, and FIG. 13 is a detailed enlarged view of the probe. 1: Probe, 2: Surface to be measured, 3: Axial force sensor, 9: Control device, R1 to R5: Rotary encoder, M1 to M5: Motor.

Claims (1)

[Scope of Claims] 1. A supporting means having multiple degrees of freedom, a driving means for driving the supporting means, a probe provided on the supporting means, and a device that acts on the probe when the probe is brought into contact with a surface to be measured. force detection means for detecting the force to be measured; posture detection means for detecting the attitude and initial contact position of the probe; and tilt calculation for calculating the inclination of the probe with respect to the surface to be measured based on the force detected by the detection means. means for calculating a target orientation in which the probe is perpendicular to the surface to be measured based on the calculated inclination and the detected orientation; A probe attitude control device comprising: drive control means for driving and controlling the drive means so as to change the attitude to a target attitude and guide the probe to the detected initial contact position. 2. In the probe attitude control device according to claim 1, the force detection means detects the force due to the probe's own weight when the probe is separated from the surface to be measured, and the inclination calculation means The probe posture is characterized in that the force detected by the force detection means when pressed against the surface to be measured is corrected by the force due to the self-weight, and the inclination of the probe with respect to the surface to be measured is calculated based on the correction value. Control device. 3. The probe attitude control device according to claim 2, wherein the force detection means detects the probe's own weight when the probe is held in the air.