JP3101099B2 - Apparatus and method for measuring three-dimensional position and orientation of robot by ultrasonic wave - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for measuring a three-dimensional position and orientation of a robot using ultrasonic waves.

[0002]

2. Description of the Related Art Conventionally, the following can be cited as technical documents in such a field.

(1) Investigation and Research on Standardization of Industrial Robots, Result Report, Japan Industrial Robot Association, (1988) pp. 6-31 (2) Masaki Saito: Actual behavior of robots Check system to confirm, automation technology, Vol. 18, No.
11, (1986) pp. 117-122 (3) K.K. Lau, R .; J. Hocken and
W. C. Height: Automatic race
r tracking interferometer
system for robot metrolo
gy, Precision Engineerin
g, Vol. 8, No. 1, (1986) pp. 3-8 (4) GP-8-3D Sonic Digitize
r Operator's, Manual, Scie
nce Accessories Corp. , (19
85) Pages 1 to 85 (5) Mitsuo Goto, Yoshihisa Tanimura, Toshiro Kurosawa: Coordinate measurement system using tracking laser interferometer-Basic design and prototype of elements-, 1988 Shu, (1988) pp. 315-316 (6) Large-scale project of the Industrial Technology Research Institute, R & D technical report on extreme working robots, Technical Research Association of Extreme Working Robots,
(1990) pp. 168-173 (7) Akira Shimokawabe, Kimoto Ma: Measurement of three-dimensional coordinates by multiple phase differences of intermittent ultrasound, Journal of the Japan Society of Precision Engineering, Vol. 5
3, No. 9, (1987) pages 72 to 77 (the number of pages is 1408 to 1413) (8) Mami Matsukawa, Takahiko Ohtani: Influence of discharge circuit conditions on discharge impulse sound source, Ultrasonics Research Society, (198)
8) pp. 37-44 (9) Ken Sasaki, Katsuhisa Ono, Masaharu Takano: Research and development of high-accuracy ultrasonic sensors for robots, precision machinery, Vo
l. 51, No. 6, (1985) pp. 142-147
Pages (the number of pages in the scroll is 1238 to 1243) (10) D. E. FIG. Whitney, C.A. A. Lozin
ski and J.S. M. Rourke: Indust
real Robot Forward Calibr
ation Methods and Results,
Transactions of the ASME,
Journal of Dynamic System
s, Measurement and Contro
1, Vol. 108, no. 1, page (1986)
Page 8 (11) Nobuyuki Furuya, Hiroshi Makino: Calibration of SCARA Robots by Teaching, Precision Machinery, Vol.
49, no. 9, (1983) 69-74 pages (the number of pages is 1223-1228) The robot is used not only for simple tasks such as pick and place, but also for tasks requiring high precision such as assembly. At present, it is an important issue for both manufacturers and users to accurately evaluate the motion performance of a robot.

[0004] In particular, the evaluation of the absolute positioning accuracy of a robot is important because it is a premise of off-line programming which is expected as an alternative to manual teaching.

However, a measuring instrument for measuring the position and orientation of a robot moving while taking an arbitrary trajectory in a wide three-dimensional space in a non-contact, real-time, and highly accurate manner has not yet reached a practical stage. .

[0006] For this reason, at present, as an evaluation of the motion performance of a robot, it is common practice to evaluate the accuracy of repeated positioning at several points in space using a proximity sensor.

[0007]

However, this method has a relatively high measurement accuracy, but is a static measurement, and can obtain only local data, which is sufficient for evaluating the motion performance of a robot. Absent.

On the other hand, as a non-contact measuring device of three-dimensional coordinates, a system using LED light, a laser beam, and an ultrasonic wave has been studied, and a part thereof has been commercialized.

[0009] Of these, the former two perform triangulation using an angle, as described later, so that it is difficult to obtain positional accuracy in a wide measurement range. In addition, since an image processing apparatus and a laser interferometer are required, the system is large and expensive, and it is difficult for each manufacturer and user to own the system independently. There are reports that distances are measured using a laser, but the system is expensive and is not suitable for robot measurement.

By the way, the position repeatability of the current industrial robot is ± 0.3 m for a vertical articulated type having six degrees of freedom.
m, but the absolute positioning accuracy is not usually displayed in catalogs, and is said to be considerably poor for robots other than DD robots and scalar type robots with relatively high accuracy. The causes include dimensional errors of the mechanism such as link length and misalignment of each shaft, and backlash of the speed reducer. Therefore, the coordinates in a three-dimensional space of about 2 m square are expressed by ±
If there is a simple and inexpensive measurement system with a measurement accuracy of about 0.3 mm, it is effective for evaluating robot motion performance such as absolute positioning accuracy, posture accuracy, path repeatability, absolute path accuracy, and speed accuracy.

Since the ultrasonic range finder uses the speed of sound which is easily affected by temperature and local fluctuations of air, there is a problem that the accuracy of the distance measurement is slightly deteriorated when the measurement is performed in a normal room which is not closed. However, the accuracy is within an allowable range, and the measurement system using ultrasonic waves is considered to be sufficiently effective for performance evaluation of the robot.

Although this method uses triangulation using distance as a measurement principle, there is another measurement method using triangulation using angle. As an example of triangulation using an angle, consider a system in which a beam from a laser head is reflected by a mirror rotatable around two axes provided at a reference point and is irradiated on a target such as a corner cube.

In this case, the displacement of the beam caused by the movement of the target is detected by an optical position detector, and the rotation angle of the mirror is constantly controlled so as to eliminate the displacement. A method of calculating a position by knowing a corner is used. In this system, for example, to measure a target 1 m away from the reference point with an accuracy of ± 0.2 mm, tan ⁻¹ (± 0.2 / 1000) = ± 0.01
High angle measurement accuracy of ° is required. Furthermore, even if the detector has this angular accuracy, in order to accurately track the target with this angular accuracy in real time, extremely advanced control technology is required, and the development cost of the system will be enormous. Become.

As a method of measuring a distance by using an ultrasonic wave, there is a method of transmitting an ultrasonic wave of several tens of wavelengths intermittently and obtaining a distance from a phase difference between a transmitted waveform and a received waveform. This method requires transmitting several types of amplitude-modulated sound waves,
Further, since it is necessary to remove unnecessary reflected waves, there is a problem that it takes time to measure the coordinates once.

[0015] In view of the above situation, the present invention measures the position and orientation of a robot using three transmitters and four receivers by applying distance measurement by measuring the propagation time of an ultrasonic pulse. Accordingly, it is an object of the present invention to provide a three-dimensional position / posture measuring apparatus of a robot using ultrasonic waves, which can be configured simply and inexpensively, and which can improve accuracy, and a measuring method thereof.

[0016]

In order to achieve the above object, the present invention provides: (A ) a three-dimensional position / posture measuring device for a robot using ultrasonic waves, wherein three electric sparks attached to a robot hand are provided; An ultrasonic transmitter for generating the used ultrasonic pulse, four receivers fixed at predetermined positions for receiving the ultrasonic pulse from the ultrasonic transmitter, and the ultrasonic pulse is measured by measuring the propagation time of the ultrasonic pulse. Measurement means is provided for calculating four variables of the X, Y, and Z coordinates of the sound wave transmitter and the speed of sound in the measurement space, and performing three-dimensional position / posture measurement of the robot by triangulation using distance.

Further, it has the following subordinate configuration.

(1) The receiver is a condenser microphone.

(2) An apparatus for adjusting the elevation angle and the turning angle of the receiver is provided.

(3) An electric spark timing control board for generating an electric spark from the ultrasonic transmitter, reading a transmission time from the transmitter, and obtaining a distance based on a reception signal from the receiver 4 It has a channel distance calculation board and an arithmetic processing unit connected thereto.

(4) A sound speed monitoring unit connected to the arithmetic processing unit is provided.

( B ) In the method of measuring the three-dimensional position and orientation of a robot using ultrasonic waves, an ultrasonic transmitter for generating ultrasonic pulses using three electric sparks is installed in the hand of the robot, and the ultrasonic transmitter The ultrasonic pulse from the receiver is received by four receivers fixed at a predetermined position, the propagation time of the ultrasonic pulse is measured, and the X, Y, and Z coordinates of the ultrasonic transmitter and the position in the measurement space are measured. Four variables of sound velocity are calculated, and three-dimensional position / posture measurement of the robot is performed by triangulation using distance.

Further, the following subordinate configuration is provided.

(1) While detecting the transmission time of the ultrasonic transmitter, the receiver detects a first zero-cross point after the amplitude of the pulse wave due to the electric spark exceeds a threshold value,
Based on this, the propagation time of the ultrasonic pulse is measured.

(2) The velocity of sound in the measurement space is estimated and calculated from the propagation time of the ultrasonic pulse from the ultrasonic transmitter to the four receivers.

(3) Using the receiver, measure the distance between the receivers and calibrate the initial coordinate system.

(4) In the calibration of the initial coordinate system, a sound speed monitoring unit is used.

[0028]

According to the present invention, as shown in FIG. 13, the ultrasonic transmitter T ₁ through T ₃ for generating ultrasonic pulses with three electrical spark to be attached to the hand 46 of the robot 45
And four receivers R _{1 to} R ₄ fixed at predetermined positions for receiving ultrasonic pulses from the ultrasonic transmitters T _{1 to} T _3, and measuring the propagation time of the ultrasonic pulses. And three-dimensional position / posture measurement of the robot by triangulation using distance.

Therefore, since an inexpensive ultrasonic transmitter and receiver are used, the configuration can be made simple and inexpensive. The sound velocity in the measurement space is always accurately calculated, and the triangulation using the distance is performed. The precision required for robot measurement can be obtained.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a principle view of a measuring system using an ultrasonic pulse showing a first embodiment of the present invention, FIG. 2 is a partially exploded perspective view of a transmitter of the measuring system, and FIG. FIG. 4 is a perspective view of a receiver of the measuring system, and FIG. 5 is a received pulse waveform diagram of an electric spark discharge transmitted from the transmitter.

Since the robot takes various positions and postures,
It is desirable that the ultrasonic transmitter is an omnidirectional point sound source from the viewpoint of measurement accuracy and directivity. Therefore, in the present invention, an electric spark that can approximate an omnidirectional point sound source is used as the ultrasonic transmitter.

As shown in FIG. 2, the ultrasonic transmitter 10
The bakelite stand 11 has a support portion 11a on both ends of which a V-groove 12 is formed.
2, the holder 14 is pressed by the screw 15, so that the discharge needle 13 is fixed so as to have a gap 25 (for example, 30 μm) at the center. Incidentally, in FIG. 2, L ₁ is 80 mm, L ₂ is 10 mm, φ ₁ is 1 m
m.

Therefore, as shown in FIG.
A shocking high voltage is applied to the That is, a DC voltage of 30 V from the power supply 21 is applied to the capacitor 22 (44 μF),
The accumulated charge is triggered by the FET 23 to perform switching, and the intermittent current is caused to flow to the primary side of the ignition coil 24 (coil ratio: 1: 100). A voltage is generated and an electric spark is generated in the gap 25. Then
Accordingly, an ultrasonic pulse is generated.

The receiver uses a condenser microphone 31 having a resonance frequency of 85 kHz as shown in FIG. 3
Reference numeral 3 denotes a support shaft of the condenser microphone 31,
Further, the support shaft 33 is supported by an L-shaped support plate 34, and the support plate 34 has a support shaft 35. Therefore, the condenser microphone 31 is driven by a DC servo motor (not shown), and the elevation angle can be adjusted by the support shaft 33. Further, the condenser microphone 31 including the support shaft 33 is driven by a DC servo motor (not shown), and the rotation angle of the support shaft 35 is adjustable. That is,
The condenser microphone 31 can adjust the direction of the receiver. Here, for example, the receiving surface of the condenser microphone 31 is configured as a circular surface having a diameter of 26 mm.

FIG. 5 shows a reception waveform of an ultrasonic pulse generated by an electric spark. The waveform has a sharp rising edge sufficient to capture the moment when the ultrasonic pulse arrives, and its sound pressure is sufficient for distance measurement of about 2 m required for application to a robot. Microscopic observation of the electrode surface after 100,000 discharges showed slight crater-like wear, but the change in the received waveform due to electrode wear was small and did not affect measurement accuracy. Met.

Hereinafter, a method of measuring the distance will be described in detail.

As shown in FIG. 5, the distance meter according to the present invention uses the first zero-cross point after the amplitude of the pulse wave exceeds the threshold value as the time point when the ultrasonic pulse arrives.
It is less susceptible to the effects of amplitude due to changes in the measurement distance. This rangefinder multiplies the arrival time of an ultrasonic pulse by the speed of sound to obtain a distance, and therefore has a known constant distance (about 1350 m).
m), the time required for the ultrasonic pulse to propagate is monitored in real time to obtain an accurate sound speed.

The measurement accuracy of this distance meter was verified using an NC machine tool having a positioning accuracy of 1 μm as a calibration standard.

As shown in FIG. 6A, the transmitter T is connected to the NC
Fix to the machine tool bed, and move the bed 50
Positioning was performed with an accuracy of 1 μm at each point up to 800 mm per mm, and the distance between the transmitter T and the receiver R at each point was calculated 1000 times by this distance meter.

The receiver R is moved about 20 from the position of the first transmitter.
Approximately 1200m when installed 0mm apart (Case A)
The measurement was performed for the case of being placed m apart (case B).

FIGS. 6B and 6C show the results obtained by subtracting the measurement distance at the origin from the measurement distance at each point as the relative coordinates, with the first measurement point as the origin. here,
● is the average value Ex of the measurement errors in 1000 measurements,
○ indicates the standard deviation σx.

The average value of the measurement errors of this rangefinder is within ± 0.1 mm within a 1 m measurement range, and within ± 0.1 mm within a 2 m measurement range.
Within 3 mm, with a standard deviation of 0.1 over a 1 m measurement range.
mm or less and 0.2 mm or less in a measurement range of 2 m.

The cause of the measurement error is that the place where the measurement is performed and the place where the distance meter for sound velocity correction is installed are separated from each other by about 1 m for the sake of the experiment, and in a factory where constant temperature and air stabilization are not considered at all. It is considered that the measurement was performed, and that the temperature, humidity, air flow, and the like were different in both places, and accurate sound velocity correction was not performed.

The variation of the measurement error is caused by the fluctuation of air in the measurement space. This rangefinder including a rangefinder for sound velocity correction for comparison was installed in a closed wind tunnel device,
A distance of about 2 m was measured 1000 times over a period of about 4 hours in an approximately calm state.

As a result, the standard deviation of the measurement error is 0.07 m despite the drift of the sound speed due to the change in temperature.
m, the difference between the maximum value and the minimum value of the measurement error was 0.34 mm, and higher accuracy was obtained as compared with the case without sealing. Thus, it can be understood that the variation of the measurement error is not caused by the variation of the discharge position of the electric spark as the transmitter, but is caused by the fluctuation of the air in the measurement space.

Therefore, it is considered that the accuracy of the distance meter of the present invention will be further improved if the sound velocity correction is performed near the measurement position and the air in the measurement space is stabilized.

Next, the principle of measuring the three-dimensional position / posture of the robot of the present invention will be described.

Here, the principle of measuring the position and orientation using three transmitters and three receivers will be described.

As shown in FIG. 7, three receivers R _{1 to} R _1
3 and three transmitters T _{1 to} T ₃ are arranged, and three transmitters T
First transmitter of _{1 ~T 3 T 1 (X 1} , Y 1,
Let L _i be the measured distance between Z ₁ ) and the receiver R _i (x _i , y _i , z _i ). Here, i = 1 to 3.

At this time, (X ₁ −x _i ) ² + (Y ₁ −y
_i ) ² + (Z ₁ −z _i ) ² = L _i ²
Three-dimensional position of the transmitter T ₁ is determined.

The remaining transmitters T ₂ (X ₂ , Y ₂ , Z ₂ )
The three-dimensional position of the transmitter T ₃ (X ₃ , Y ₃ , Z ₃ ) can be obtained in the same manner.

Here, assuming that the center of gravity of the triangle formed by the three transmitters and the tip of the hand are positioned prior to the measurement, the coordinates of the center of gravity G are the transmitters T ₁ and T ₁ .
It can be obtained by calculating from the measured coordinates of T ₂ and T ₃ .

Next, the three-dimensional posture calculation is performed as follows.

As shown in FIG. 7, the reference vectors e ₁ and e
Let ₂ and e _{3 be used} to represent the posture of the robot.
First,

[0056]

(Equation 1)

Is calculated. q is the transmitter T ₁ , T ₂ , T ₃
And a vector orthogonal to p ₁ on a plane formed by the tip G of the hand.

Using these, the reference vectors e ₁ , e ₂ ,
e ₃ can be determined as follows.

E ₁ = p ₁ / | p ₁ | e ₂ = q / | q | e ₃ = e ₁ × e _{2 As described} above, the position and orientation of the robot are determined by three transmitters and three receivers. It can be uniquely obtained by using a wave filter.

When converting the measured position / posture into values in the robot coordinate system (X _R , Y _R , Z _{R in} FIG. 7), it is necessary to calibrate the relative positional relationship between the robot coordinate system and the measurement coordinate system. As a method for this, various methods have been proposed as a method in which the robot performs positioning at several points, and uses the measured coordinate values at each point and the reading of the encoder of each joint.

Next, the robot 3 of the ultrasonic wave according to the present invention is used.
The outline of the three-dimensional position and orientation measurement system and its features are described.

As shown in FIG. 8, three transmitters T _{1 to} T ₃ for generating ultrasonic pulses by the electric spark are provided, and each of the transmitters T _{1 to} T ₃ is connected to a transmission time detecting circuit 41. Is done. The transmission time detection circuit generates a trigger based on the transmission time of each of the transmitters T _{1 to} T ₃ and transmits the trigger to the A / D converter 42.

On the other hand, the ultrasonic pulses transmitted from the _three transmitters T _{1 to} T ₃ are received by the _three receivers R _{1 to} R ₃ , and the received ultrasonic pulses are A / The signal is sent to the D converter 42 and converted into a digital signal.

The digital signal is supplied to the arithmetic processing unit 44
In, arithmetic processing is performed.

An output signal from the sound speed monitoring unit 43 provided near the measurement position is input to the arithmetic processing unit 44, and the sound speed correction is performed near the measurement position.

Further, in the present invention, the receiver R is configured to be rotatable.

That is, since the directivity of the receiver is as sharp as a half-reduction angle of 6 °, as shown in FIG. Accordingly, the transmitter T can be rotated in the vertical direction so as to face the transmitter T in front.

As a result, the directivity of the receiver common to the systems using the conventional fixed ultrasonic receiver eliminates the problem that the measurable space is limited. The space that can be measured with high accuracy has been expanded.

Further, by making the receiver having a considerably sharp directivity face the front of the transmitter, it is possible to prevent the noise in the ultrasonic region frequency coming from other than the transmitter.

Next, the radius r for arranging the transmitter shown in FIG.
Will be described.

Here, considering the real-time property of measurement,
The positions of the three transmitters are measured while the receivers are not pointed in front of the three transmitters, but face the front end G of the hand.

Therefore, if the allowable deflection angle at which the receiver can accurately measure the distance to the transmitter is α, and the distance from the receiver to the tip G of the hand is L, the radius r must satisfy r <Ltanα. There is. Here, L is | R ₂ G |.

On the other hand, the larger the radius r, the smaller the attitude measurement error. As an example, in FIG. 7, when the position measurement error of the transmitter T ₁ is a .delta.d, e ₁ with the angular error of ^{δθ = tan -1 (δd / r} ) is measured.

The ultrasonic range finder of the system according to the present invention is capable of measuring the size of the receiver within an error of the receiver half angle of 6 ° when the receiver is facing the transmitter. The effect was about 0.2 mm in a measurement range of 500 mm.

Therefore, in the system of the present invention, based on the received waveform and the sound pressure, the influence is eliminated so that the receiver faces the front end G of the hand with an error of about ± 3 °.

Therefore, in this system, α = 3
°, condition r <26.0 assuming L = 500 mm
mm, r = 25.0 mm. At this time, δd =
Assuming 0.1 mm, the posture measurement error is δθ = 0.2
Estimated at 3 °.

Next, the calibration of the initial coordinate system is performed as follows.

Prior to measurement, it is necessary to know the relative positional relationship between the three receivers. In the system of this embodiment, since the receiver itself can actively transmit an ultrasonic pulse as a vibrating membrane, the relative positions can be determined by exchanging pulses between the receivers and measuring the distance between them.

Therefore, as shown in FIG. 9, three receivers R _{1 to} R ₃ are arranged at appropriate positions, and R ₁ (0,
0,0), R ₂ (a, 0,0), R ₃ (b, c, 0), and the mutual measurement distance between the receivers is p, q, r, and a = p b = (r ²⁻ q ² + p ² ) / 2p, c = {r ² − [(r ² −q ² + p ² ) / 2p] ² }, a, b, and c are obtained and the reference coordinate system is calibrated.

In measuring the distance between the receivers, the receiving surfaces were kept parallel, so that the size and directivity of the receiver did not affect the measurement accuracy.

As described above, since the system of this embodiment performs calibration internally, there is no need to externally calibrate the initial coordinate system, and the receiver can be arranged at any position.
It has the feature that it has great flexibility for changes in the measurement object.

Next, an experiment for verifying the accuracy of position / posture measurement according to this embodiment was performed.

FIG. 10A shows the experimental conditions.
FIG. 10B shows the result of the experiment. That is, FIG.
0 (a), the arm tip positions at several points on the circular orbit of the spatial rotation arm (accuracy ± 0.06 mm),
The three-dimensional position / posture measurement accuracy of the system of the present invention was verified by measuring the arm posture (accuracy ± 30 arcsec) as a calibration reference and measuring it. Note that a DD motor with a resolver (positioning accuracy ± 3
0 arcsec).

The movement of the arm is performed in a plane, but does not coincide with the XY plane of the measurement coordinate system, and the measurement is three-dimensional. At the time of measurement, it was noted that both planes were parallel using a surface plate, a jig or the like. The comparatively good parallel accuracy can also be confirmed from the Z coordinate measurement results shown in FIG.

The coordinates of the center of gravity (the tip of the hand) G were obtained by sequentially measuring the positions of the three transmitters. By matching the measured XY coordinates of the first two centers of gravity G with the arm coordinates, a two-dimensional coordinate conversion formula from the coordinate system of the measuring system to the arm coordinate system was obtained. From the third point onward, the measurement coordinates were converted into arm coordinates according to this equation. The attitude angle was obtained by obtaining P ₁ in FIG. 10A and converting the XY component into an arm coordinate system in the same manner.

FIG. 10B and FIGS. 11 and 12 show the results. In Figure 12, in the column of Z _M and E _Z showed deviations from the mean -22.1mm measurement Z coordinate. FIG.
In (b), the solid line represents the accurate position and orientation of the arm obtained from the reading of the resolver, and the broken line represents the measurement result of the system of the present invention with the measurement error enlarged by the magnification shown in the figure. Things. The position measurement error was 0.4 mm or less. Considering that the standard deviation is small, the first
If the accuracy of coordinate conversion is improved by matching not only the point and the second point but also more points, it is considered that the position measurement accuracy is improved.

The attitude angle measurement error was 0.4 ° or less, and the standard deviation was 0.2 ° or less.

In FIG. 11, θ _A is the arm attitude angle (calibration reference), θ _M is the measured attitude angle, Eθ, σθ
Is the measured attitude angle error and standard deviation. Further, in FIG. 12, (X, Y, Z ) A arm coordinate (calibration reference), (X, Y, Z) coordinate _M is measured, E _X,
E _Y and E _Z are the errors of the measured coordinates, σ _X , σ _Y and σ _Z
Is the standard deviation of the measured coordinates, and the position G and arm posture angle were measured 100 times for each data.

From the above results, it was confirmed that the measurement system according to the first embodiment of the present invention has a possibility that it can be used for actual robot measurement.

Next, a second embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 13 is a diagram showing the principle of a measuring system using ultrasonic pulses according to a second embodiment of the present invention, and FIG. 14 is a diagram illustrating the principle of measuring the three-dimensional position / posture of a robot according to the second embodiment of the present invention. FIG. 15 is a block diagram of the three-dimensional position / posture measuring system of the robot.

In this embodiment, as a method of calculating three-dimensional coordinates, a method for accurately estimating and calculating the sound speed in the measurement space as a parameter using four receivers (hereinafter referred to as sound speed estimation method) has been developed. I am trying to adopt.

As shown in FIG. 13 and FIG. 14, four receivers R _{1 to} R ₄ are arranged, and the first transmitter T ₁ (X ₁ , Y ₁ , Z ₁ )
And the measured value of the ultrasonic pulse propagation time between the receivers R _i is t _i ( _i = 1 to 4). At this time, the following four equations are established with the sound speed being C.

[0094] _{^{X 1 2 + Y 1 2 +}} Z 1 2 = (C · t 1) 2 ... (1) (X 1 -a) 2 + Y 1 2 + Z 1 2 = (C · t 2) 2 ... (2) ( ^{_{X 1 -b) 2 + (Y}} 1 -c) 2 + Z 1 2 = (C · t 3) 2 ... (3) (X 1 -d) 2 + (Y 1 -e) 2 + (Z 1 -f ) ² = (C · t ₄ ) ² (4) Equations (1)-(2), (1)-(3) and (1)-
From equation (4), T ₁ (X ₁ , Y ₁ , Z ₁ ) is represented by the following equation.

[0095]

(Equation 2)

The inverse matrix is obtained before the measurement when the four receivers are not on the same plane.

By substituting the above equation (5) into the above equation (1), a quadratic equation for C ² is obtained, and C is easily obtained analytically (calculation formula is omitted). By substituting this C into the above equation (5), T ₁ (X ₁ , Y ₁ , Z ₁ ) is obtained.

In this method, since the calculation is performed in real time using the sound velocity in the measurement space as a variable, accurate sound velocity correction can always be performed. Further, since the fourth receiver is installed above the measurement space, there is a feature that the measurement accuracy of the z coordinate is higher than the method using only three receivers. Further, since a separate sound speed correction sensor is not required, the system can be simplified.

In the same manner as described above, the coordinates T ₂ (X ₂ , Y ₂ , Z ₂ ) and T ₃ (X ₃ ,
Y ₃ , Z ₃ ) can also be determined. Here, if it is assumed that the center of gravity of the triangle constituted by the three transmitters and the tip G of the hand are positioned prior to the measurement, the coordinates of G are the measured coordinates of T ₁ , T ₂ , and T _3. It can be calculated and found more.

As shown in FIG. 14, the reference vectors e ₁ ,
Let e ₂ and e _{3 be used} to represent the posture of the robot. First,

[0101]

(Equation 3)

Is calculated. q is T ₁ , T ₂ , T ₃ and G
Is a vector orthogonal to e ₁ on the plane formed by
Using these, the reference vector can be obtained as follows: e ₁ = p ₁ / | p ₁ | e ₂ = q / | q | e ₃ = e ₁ × e ₂ (7)

As described above, the position / posture of the robot is 3
It can be uniquely obtained by using four transmitters and four receivers.

Next, the configuration of the measurement system will be described.

As the receiver, the same receiver as shown in FIG. 4 of the first embodiment is used. That is, since the directivity of the receiver is as sharp as a half angle of 6 °, the receiver can be rotated horizontally and vertically by a DC servomotor so that the receiver always faces the transmitter. This eliminates the problem of limited measurable space due to the directivity of the receiver that is common to systems that use conventional fixed ultrasonic receivers. The space to be expanded.

As shown in FIG. 15, the measuring system of this embodiment detects the arrival time of the ultrasonic pulse from the transmitter 60 to the receiver 64 in real time by hardware using a four-channel arrival time measurement board. To be configured.
The arithmetic processing unit 50 has an extension unit 51 including a high-precision timer 52, an electric spark timing control board 53, a sound velocity calculation board 54, a four-channel arrival time measurement board 55, a parallel interface, and an interrupt 56.

According to a signal from the electric spark timing control board 53, a high voltage is applied from the electric spark power supply 58 to the transmitter 60 via the ignition circuit 59, and an ultrasonic pulse is transmitted. The transmission time from the transmitter 60 is detected by a transmission time detector 57, and the transmission time is input to the high-precision timer 52 and the 4-channel arrival time measurement board 55.

On the other hand, when the ultrasonic pulses are received by the four receivers 64, the received signals are read into the four-channel arrival time measurement board 55 via the preamplifier 63.
A sound speed monitoring unit 62 is connected to the sound speed calculation board 54 via a preamplifier 61 so as to monitor the sound speed.

Further, the arithmetic processing unit 70 includes a counter 7
2. Connected to an extension unit 71 having a D / A converter 73, a parallel interface and an interrupt 74, the counter 72 and the D / A converter 73 are connected to a motor signal distribution circuit 75, and the motor signal distribution circuit 75 The motor drive circuit 76 is connected to a DC servomotor 77. The parallel interface and interrupt 56
And the parallel interface and interrupt 74
The interval is configured so that parallel communication is performed. Each receiver can be rotated in the horizontal and vertical directions by two DC servo motors.

Therefore, the arithmetic processing unit 50 reads the arrival time of the transmission signal from the four-channel arrival time measurement board 55, and calculates the position of the transmitter according to the principle described above.

Next, the horizontal and vertical rotation angles of each of the receivers R _{1 to} R ₄ are calculated from the positions of the transmitters T _{1 to} T ₃ ,
Send it to the parallel boat. Arithmetic processing unit 70
Is, DC servo motor 7 for rotating the receiving transducer R ₁ to R ₄
When the order of the motor commands is sent from the extension unit 51, an interrupt is generated and the target value of the rotation angle is updated.

Prior to measurement, it is necessary to know the relative positional relationship between the _four receivers R _{1 to} R ₄ . Here, since the receiver itself can actively transmit an ultrasonic pulse as a vibrating membrane, the relative position can be obtained by exchanging pulses between the receivers and measuring the distance to each other. Therefore, as shown in FIG. 16, four receivers R _{1 to} R ₄ are arranged at appropriate positions, and R ₁ (0, 0, 0), R ₂ (a,
0, 0), R ₃ (b, c, 0), R ₄ (d, e, f), and the mutual measurement distance between the receivers is p, q, r, s, t,
As u, a = p b = ( r 2 -q 2 + p 2) / 2p c = √ {r 2 - ^{[(r 2 -q 2 + p 2} ) / 2p ] ^{2} d = (s 2 -t} 2 + a ² ) / 2a e = (s ² −u ² + b ² + c ² −2bd) / 2cf = ² (s ² −d ² −e ² ), so that a, b, c, d,
Find e and f and calibrate the reference coordinate system.

As described above, since the measurement system performs calibration internally, it is not necessary to calibrate the initial coordinate system from the outside, and since the receiver can be arranged at an arbitrary position, the measurement system is not affected by changes in the measurement object. It has the characteristic of having great flexibility.

Next, a verification experiment of the three-dimensional position measurement accuracy according to this embodiment was performed.

Here, the measurement accuracy of this measurement system was verified using an NC machine tool having an accuracy of 1 μm.

The transmitter is fixed to the chuck of the NC machine tool, and as shown in FIG. 17, three receivers R ₁ to R ₁ are mounted on the bed.
R ₃ is fixed, and the fourth receiver R ₄ is fixed above the bed. The transmitter was stopped on 36 grid points, and the coordinates of each point were measured. Here, X, Y, and Z are NC coordinate systems,
X ', Y', Z 'indicate a measurement coordinate system.

The experimental results of the measurement error and the standard deviation of the measurement coordinates are shown in FIGS. 18 (a) and 18 (b), respectively. In the analysis of the results, a coordinate conversion formula that gives the best match between the measured coordinates and the NC coordinates at the point marked with a circle in the figure is obtained by using the least squares method, and all the measured coordinates are calculated in the NC coordinate system accordingly. Was converted to a value.

Here, FIG. 18A shows the average of the errors of the three-dimensional coordinate measurement, and FIG. 18B shows the standard deviation of the three-dimensional coordinate measurement.

From these results, it is clear that this measurement system is xy
It was confirmed that the xyz coordinates can be measured with an error of ± 0.3 mm or less and a standard deviation of 0.2 mm or less in a relatively large space of 900 × 400 × 400 mm.

Next, measurement of the absolute positioning accuracy of the 6-DOF articulated robot will be described.

Here, the result of measuring the absolute positioning accuracy of the tip of the hand of a six-degree-of-freedom articulated robot is described.

A transmitter was fixed to the hand of a six-degree-of-freedom articulated robot shown in FIG. 19, the robot was positioned at 36 grid point coordinates as shown in FIG. 20, and the position was measured by this measuring system. . The results are shown in FIG.

From these results, at the 34th to 36th positioning points, the positioning accuracy of the x coordinate is considerably poor at 1 mm or more. However, this is because of the experimental conditions, the installation condition of the _fourth receiver R4 is poor. transmitter is probably because receivers R ₄ hidden in the shadow of the robot wrist picked up diffracted sound.

[0124] Except that it seems that there was a problem on the measurement system side, the absolute positioning accuracy of the six-degree-of-freedom articulated robot is within approximately ± 0.7 mm within a space of 600 × 400 × 200 mm square. Met.

As described above, in particular, a three-dimensional position / posture measurement principle of a robot using three transmitters and four receivers was proposed, and a measurement system was constructed based on the principle. According to this measurement system, the speed of sound in the measurement space can be accurately corrected in real time.

The accuracy of the three-dimensional coordinate measurement of this measurement system was verified using an NC machine tool having an accuracy of 1 μm as a calibration standard. As a result, xyz is 900 × 400 × 400 mm
It was confirmed that three-dimensional coordinates in a relatively large space were measured with an error of ± 0.3 mm or less and a standard deviation of 0.2 mm or less for each of the xyz coordinates.

Further, the absolute positioning accuracy of the 6-DOF articulated robot was measured. As a result, it was found that the absolute positioning accuracy of the six-degree-of-freedom articulated robot was within approximately ± 0.7 mm in a space of about 1 m square.

As described above, according to the present invention, as a system for evaluating the motion performance of a robot, a simple three-dimensional position / posture measuring apparatus to which the measurement of the propagation time of an ultrasonic pulse is applied and a measuring method thereof are provided. Was completed.

The present invention is not limited to the above embodiments, but various modifications can be made based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0130]

As described above, according to the present invention, the following effects can be obtained.

(1) Since the ultrasonic element is inexpensive and triangulation using distance is performed, accuracy is easy to obtain. In other words, the measurement accuracy of three-dimensional coordinates is determined by the distance measurement accuracy.
It is easy to obtain high accuracy regardless of the size of the measurement space, and is most suitable for evaluating the motion performance of a robot.

(2) Since the propagation time of the ultrasonic pulse for detecting the zero-cross point and correcting the real-time sound velocity is measured by using the electric spark as the transmitter, the signal processing is easy, the measurement time is short, and the reflection time is short. It is also less affected by waves, and measurement accuracy can be improved. Incidentally, the average value of the measurement error is within ± 0.1 mm within a measurement range of 1 m and 2 m.
Was within ± 0.3 mm in the measurement range, and the standard deviation of the measurement error was 0.1 mm or less in the measurement range of 1 m and 0.2 mm or less in the measurement range of 2 m.

(3) The elevation angle and the turning angle are controlled by using a receiver having sharp directivity so that the reception surface always faces the transmitter, so that a space where coordinates can be measured with high accuracy is provided. Can be widely taken.

( 4 ) A three-dimensional position / posture measurement principle of a robot using three transmitters and four receivers was proposed, and a measurement system was constructed based on the principle. According to this measurement system, the speed of sound in the measurement space can be accurately corrected in real time.

( 5 ) The accuracy of the three-dimensional coordinate measurement of this measurement system was verified using an NC machine tool having an accuracy of 1 μm as a calibration standard. As a result, xyz is 9
3 in a relatively large space of about 00 × 400 × 400 mm
It was confirmed that the dimensional coordinates could be measured with an error of ± 0.3 mm or less and a standard deviation of 0.2 mm or less for each xyz coordinate.

( 6 ) Further, the absolute positioning accuracy of the articulated robot having six degrees of freedom was measured. As a result, it was found that the absolute positioning accuracy of the six-degree-of-freedom articulated robot was within approximately ± 0.7 mm in a space of about 1 m square.

[Brief description of the drawings]

FIG. 1 is a principle diagram of a measurement system using an ultrasonic pulse showing a first embodiment of the present invention.

FIG. 2 is a partially exploded perspective view of a transmitter of the measurement system using ultrasonic pulses, showing the first embodiment of the present invention.

FIG. 3 is an electric circuit diagram of a transmitter of a measurement system using ultrasonic pulses according to the first embodiment of the present invention.

FIG. 4 is a perspective view of a receiver of the measurement system using ultrasonic pulses, showing the first embodiment of the present invention.

FIG. 5 is a diagram showing a received pulse waveform of an electric spark discharge transmitted from a transmitter of the measurement system using ultrasonic pulses according to the first embodiment of the present invention.

FIG. 6 is a diagram illustrating the effect of the distance meter according to the first embodiment of the present invention.

FIG. 7 is an explanatory diagram of a three-dimensional position / posture measurement principle of the robot showing the first embodiment of the present invention.

FIG. 8 is a schematic overall configuration diagram of a robot three-dimensional position / posture measurement system using ultrasonic waves, showing a first embodiment of the present invention.

FIG. 9 is an explanatory diagram of a method for measuring a distance between receivers according to the first embodiment of the present invention.

FIG. 10 is an explanatory diagram for confirming the effect of the first embodiment of the present invention.

FIG. 11 is a diagram showing a result of angle measurement by confirming the effect of the first embodiment of the present invention.

FIG. 12 is a diagram showing a result of position measurement by confirming the effect of the first embodiment of the present invention.

FIG. 13 is a principle diagram of a measurement system using ultrasonic pulses according to a second embodiment of the present invention.

FIG. 14 is an explanatory diagram of a three-dimensional position / posture measurement principle of a robot according to a second embodiment of the present invention.

FIG. 15 is a block diagram of a robot three-dimensional position / posture measurement system showing a second embodiment of the present invention.

FIG. 16 is an explanatory diagram of a method of measuring a distance between receivers according to a second embodiment of the present invention.

FIG. 17 is a diagram showing an arrangement of a transmitter and a receiver for confirming the effect of the second embodiment of the present invention.

FIG. 18 is an explanatory diagram illustrating an effect check of the NC coordinate measurement according to the second embodiment of the present invention.

FIG. 19 is a perspective view of a six-degree-of-freedom articulated robot to which the measurement of absolute positioning accuracy is performed according to a second embodiment of the present invention.

FIG. 20 is a diagram showing an arrangement of a transmitter and a receiver for confirming the effect of the second embodiment of the present invention.

FIG. 21 is an explanatory diagram for confirming the effect of measuring the absolute positioning accuracy of a six-degree-of-freedom articulated robot according to a second embodiment of the present invention.

[Explanation of symbols]

1,45 robot 2,46 hand _{10, T 1, T 2,} T 3, 60 ultrasonic transmitter _{R 1, R 2, R 3} , R 4, 64 receivers 11 stand 11a supporting section 12 V grooves 13 discharge Needle 14 Holder 15 Screw 21 Power supply 22 Capacitor 23 FET 24 Ignition coil 25 Gap 31 Capacitor microphone 33, 35 Support shaft 34 Support plate 41 Transmission time detection circuit 42 A / D converter 43 Sound speed monitoring unit 44, 50, 70 Processing unit 52 High-precision timer 53 Electric spark timing control board 54 Sound velocity calculation board 55 4-channel arrival time measurement board 56, 74 Parallel interface and interrupt 51, 71 Expansion unit 58 Electric spark power supply 59 Ignition circuit 57 Transmission time detector 61, 63 Amplifier 62 sound speed monitoring unit 72 Counter 73 D / A converter 75 motor signal distribution circuit 76 a motor drive circuit 77 DC servomotors

Continuing from the front page Application for Patent Law Article 30 (1) application "Development of a robot position / posture accuracy measurement system using ultrasonic waves", Seiji Aoyagi, Sakiichi Okabe, Ken Sasaki, Masaharu Takano, Kamiya Favorable, Robotics and Mechatronics Conference '92 ROBOMEC '92 Proceedings (Vol.B), pp. 461-466, June 15, 1992 (56) References JP-A-60-242381 (JP, A) JP-A-62-282882 (JP, A) JP-A-2-183103 (JP, A) JP-A-64-6719 (JP, A) JP-A-2-145906 (JP, A) JP-A 62-282906 261913 (JP, A) JP-A-60-102580 (JP, A) JP-A-60-12581 (JP, A) JP-A-59-142486 (JP, A) JP-A-54-115266 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01B 17/00-17/08 G05D 3/00-3/20

Claims (10)

(57) [Claims] 1. An apparatus for measuring a three-dimensional position and orientation of a robot using ultrasonic waves, comprising: (a) an ultrasonic transmitter for generating ultrasonic pulses using three electric sparks attached to a hand of the robot; ) Four receivers fixed at predetermined positions for receiving ultrasonic pulses from the ultrasonic transmitter; and (c) X, Y, Z of the ultrasonic transmitter by measuring the propagation time of the ultrasonic pulse. The robot is equipped with measuring means for calculating four variables of coordinates and sound velocity in a measurement space, and measuring the three-dimensional position and posture of the robot by triangulation using a distance.
Attitude measurement device. Wherein said receivers are three-dimensional position and orientation measurement apparatus of a robot by ultrasound according to claim 1, wherein the condenser microphone. 3. A three-dimensional position and orientation measurement apparatus of a robot by ultrasound according to claim 1 or 2 wherein comprises an adjusting device for elevation angle and the turning angle of the receivers. 4. An electric spark timing control board for generating an electric spark from the ultrasonic transmitter, reading a transmission time from the transmitter, and arriving at an ultrasonic pulse based on a signal received from the receiver. and 4-channel arrival time measurement board seeking time, three-dimensional position and orientation measurement apparatus of a robot by ultrasound according to claim 1, further comprising a processing unit connected to these. 5. The three-dimensional position / posture measuring apparatus for a robot using ultrasonic waves according to claim 4 , further comprising a sound velocity monitoring unit connected to the arithmetic processing unit. 6. A method for measuring a three-dimensional position / posture of a robot using ultrasonic waves, comprising: (a) installing an ultrasonic transmitter for generating ultrasonic pulses using three electric sparks in a robot hand; (b) The ultrasonic pulse from the ultrasonic transmitter is received by four receivers fixed at a predetermined position. (C) The propagation time of the ultrasonic pulse is measured, and the X and Y of the ultrasonic transmitter are measured. , Z coordinate, and three variables of sound velocity in the measurement space, and three-dimensional position / posture measurement of the robot by triangulation using distance. . 7. While detecting the transmission time of the ultrasonic transmitter, the receiver detects a first zero-cross point after the amplitude of the pulse wave due to the electric spark exceeds a threshold, and based on this, 7. The method for measuring a three-dimensional position / posture of a robot using an ultrasonic wave according to claim 6, wherein a propagation time of the ultrasonic pulse is measured. 8. The sound velocity in the measurement space is estimated and calculated from the propagation times of ultrasonic pulses from the ultrasonic transmitter to the four receivers, thereby correcting the sound velocity without using a sound velocity monitoring unit. 7. The method of measuring a three-dimensional position / posture of a robot using ultrasonic waves according to claim 6, wherein: 9. The three-dimensional position / posture of an ultrasonic robot according to claim 6, wherein a distance between the receivers is measured using the receiver, and an initial coordinate system is calibrated. Measurement method. 10. The sound velocity monitoring unit is used in the calibration of the initial coordinate system.
9. The method for measuring a three-dimensional position / posture of a robot using ultrasonic waves according to 9 .