APPARATUS FOR DETECTING POSITION OF OBJECT BEING MEASURED

Abstract: An apparatus for detecting the position of an object being measured comprises a means which transmits and receives ultrasonic waves by an ultrasonic wave transmitter-­ receiver element (53, 73, 93) with respect to an object (65, 82, 103) being measured, such as a small-diameter hole or a narrow groove in a surface, a means (50, 72, 91) which changes the relative positional relationship between the object (65, 82, 103) and the ultrasonic wave transmitter-­ receiver element (53, 73, 93) and a signal-processing means which detects the position of the object (65, 82, 103) using changes in reflected signal intensity (P₁, P₂, P₃) near the central position of the object (65, 82, 103) when the relative positional relationship is changed, thereby enabling a highly-­ accurate detection of the position of the object.

Description: TECHNICAL FIELD This invention relates to a position sensing apparatus for an object to be measured, which utilizes ultrasonic waves. An object of the invention is to provide a position sensing apparatus simple in construction and sensible with high accuracy of the position of a bore smaller in diameter or a groove smaller in width. BACKGROUND ART The conventional position sensing apparatus for an object to be measured includes apparatus allowing an ultrasonic wave transmit-receive element to rotary-scan with respect to the object so as to sense its position and posture through the intensity of signal obtained by scanning. Next, explanation will be given on the outline of the conventional apparatus. Fig.1 is a schematic block diagram of the conventional apparatus and Fig.2 is a perspective view of form sensing by use of the conventional apparatus. In Fig.1, when high voltage pulse 17 shown in Fig.3 is applied to the ultrasonic wave transmit-receive element 1 in Fig.1, ultrasonic pulse of the predetermined frequency is fixed into the atmosphere, the ultrasonic pulse being reflected by an object 13 in Fig.2. The reflected signals from the sides 14, 15 and 16 at the object 13 reach the ultrasonic wave transmit-receive element 1 and are amplified by a received signal amplifier 3 and thereafter analog-digital-converted to be stored is a memory 5. Fig.3 is a waveform chart of operation wave of ultrasonic wave transmit-receive elemtn 1 stored in the memory 5, in which reference numerals 37, 38 and 39 designate reflected signals from the sides 14, 15 and 16 at the object 13 respectively. The reflected signals stored in the memory 5 are transferred to a compact electronic computer 6, by which the propagation times 40, 41 and 42 of reflected signals 37, 38 and 39 shown in Fig.3 and the reflected signal intensities 43, 44 and 45, are sensed. In Fig.2, the ultrasonic wave transmit-receive element 1 is adapted to be given a control signal from the compact electronic computer 6 and rotary-scan in the direction of the arrows A and B through a pulse motor drives 11 and a pulse motor 10, thereby moving in steps at a predetermined angle to sense the propagation time and intensity of reflected signal between the element 1 and the object 13 to be measured. Fig.4 plots the reflected signal intensity from the object 13 to be measured when the ultrasonic wave transmit-receive element 1 rotary-scans, in which the axis of abscissa represents an angle of rotation of the ultrasonic wave transmit-receive element and the axis of ordinate represents the intensity of reflected signal. Reference numerals 46, 47 and 48 designate reflected signals in arrangement from the sides 14, 15 and 16 at the object 13 to be measured respectively, so that the directions of the sides 14, 15 and 16 are sensed from the rotary scanning angle of ultrasonic wave transmit-receive element when an angle of the reflected signal becomes the maximum. Since a distance between the ultrasonic wave transmit-receive element 1 and each side 14, 15 or 16 at the object 13 is obtainable from the propagation time of the aforesaid reflected signal, the coordinates of sides 13, 14 and 15 at the object 13 are obtainable to thereby enable sensing of the position and posture of object 13 to be measured. The conventional position sensing apparatus, however, when applied to the form sensing of a bore or a groove, is sensible of the form of a bore larger in width, but for a bore smaller in diameter or a groove smaller in width, the signals reflected from the sides of bore or groove are superposed on each-other, thereby having created a problem in that unless the attenuation for the ultrasonic wave transmit-receive element is largely improved, the position and posture of object 13 to be measured are impossible to be sensed. It is also known in the prior art, for instance from US-A-3893838, to utilize the intensity of the reflected signal to maximize the efficiency of the scanning. This document describes a system in which the sensing element is moved linearly with respect to the object and the angle of the sensing element is periodically adjusted during scanning to maximize the intensity of the reflected signal. By this means the axis of the sensing element is maintained to be normal to the surface being scanned despite any change in the inclination of that surface. According to the present invention the intensity of the reflected signal is used to determine the position of a bore of groove in a scanned surface. The present invention provides a position sensing apparatus for an object to be measured which comprises: a first means including an ultrasonic wave transmit-receive element for transmitting an ultrasonic wave to the object to be measured and for receiving a reflected wave therefrom; a second means arranged to maintain said ultrasonic wave transmit-receive element at a predetermined distance from said object, to effect a linear movement of said element with respect to said object, and to maintain a wave transmit-receive surface of said wave treatment-receive element at a predetermined angle of inclination with respect to a measured surface of said object wherein if the wavelength of said ultrasonic wave transmitted and received by said ultrasonic wave transmit-receive element is represented by λ and a diameter of said ultrasonic wave transmit-receive element is represented by D, then ϑ=sin⁻¹ (1.22 λ/D) (rad) and said predetermined angle of inclination is substantially equal to Θ; and a third means adapted to detect a minimum value of intensity of a signal corresponding to said reflected wave from said measured surface of said object and to determine a centre position of a bore or groove formed in a surface of said measured object, said determination being based on the relative position of said ultrasonic wave transmit-receive element with respect to said object at the point of detection of said minimum value. Fig. 1 is a schematic block diagram of the conventional ultrasonic position sensing apparatus, Fig.2 is a perspective view of position sensing by use of the conventional apparatus, Fig.3 is a wave form chart for operation of the conventional apparatus, Fig.4 is a wave form chart arranged for operation of the conventional apparatus, Fig.5 is a schematic block diagram of a first embodiment of a position sensing apparatus of the invention, Fig.6 is a perspective view of the first embodiment of the invention, showing position sensing for a bore, Fig.7 is a plan view of the same, Fig.8 is a flow chart exemplary of a program for bore position sensing in the first embodiment of the invention, Fig.9 is a wave form chart for operation of the first embodiment of the position sensing apparatus of the invention, Fig.10, 11 and 12 are wave form charts showing operation waveforms arranged in the first embodiment of the invention, Fig.13 is a perspective view of a second embodiment of a position sensing apparatus of the invention, showing position sensing for a groove, Fig.14 is a schematic block diagram of the second embodiment of the invention, Fig.15 is a flow chart exemplary of a program for position-sensing the groove in the second embodiment of the invention, Fig.16 is a wave form chart for operation of the second embodiment of the invention, Fig.17 is a chart showing the sensitivity for bore-position sensing in the second embodiment of the invention, Fig.18 is a schematic block diagram of a third embodiment of a position sensing apparatus of the invention, showing position sensing for a groove, Fig.19 is a perspective view of the third embodiment of the invention, showing position sensing for the groove, Fig.20 is a flow chart exemplary of a program for sensing the groove position in the third embodiment of the invention, Fig.21 is a wave form chart of operation in the third embodiment of the invention, and Fig.22 is a chart showing the sensitivity for sensing the groove position is the third embodiment of the invention. BEST MODE FOR CARRYING OUT THE INVENTION Next, explanation will be given on the first embodiment of the invention with reference to the drawings. Fig.5 is a schematic block diagram of the first embodiment of the position sensing apparatus of the invention, which is used for sensing a smaller diameter bore, Fig.6 is a perspective view of position sensing using the first embodiment, and Fig.7 is a plan view of the came. In Fig.5, reference mumeral 50 designates a means (to be hereinafter called the manipulator) for changing the relative position between an object to be measured (to be hereinafter called the bore at the object) and an ultrasonic wave transmit-receive element 531 to be hereinafter called the transducer), so that a control signal from a data processing control unit 51 controls the manipulator 50 in operation through a manipulator control unit 52, the manipulator 50 carrying thereon an ultrasonic transducer 53 used for both transmitting and receiving of ultrasonic waves, and the manipulator control unit 52 being made operable in the two axes X and Y perpendicular to each other. The ultrasonic transducer 53 transmits therethrough the ultrasonic wave of the predetermined frequency from an oscillator 55 toward a bore 65 at an object 54 and receives a reflected signal therefrom. The reflected signal received by and output from the ultrasonic transducer 53 is amplified by a receiving signal amplifier 56 and then digitally converted by an analog-digital converter 57 (to be hereinafter called the A/D converter) and stored in a memory 58. Furthermore, the data processing control unit 51 comprises an interface control unit 59 (to be hereinafter called ICU), a floppy disc drive unit 60 (to be hereinafter called FDD), and a compact electronic computer 61 (to be hereinafter called CPU), the ICU 59 being connected to FDD60 and CPU61 and to the oscillator 55 and memory 58, and FDD60 giving to ICU59 a program or various conditions for position sensing by use of this position sensing apparatus of the invention. Also, the data processing control unit 51 outputs the control signal for actuating the oscillator 55, outputs the control signal to the manipulator control unit 52 for controlling the operation of manipulator 50, preprocesses the input data transferred from the memory 58, thereby sensing by CPU61 the intensity of reflected signal, processing the position of bore at the object, and computing an amount of movement of the manipulator 50 in accordance with the program previously given from FDD60 and stored in the memory 58. Next, explanation will be given on operation of the first embodiment of the position sensing apparatus constructed as foregoing. In addition, in the first embodiment as shown in Figs.6 and 7, a diameter of ultrasonic transducer 53 is 36 mm, the drive frequency is 66 KHz (wavelength λ = 5.14 mm), a distance between the object 54 and the ultrasonic transducer 53 is 100 mm, a diameters of bore 65 at the object 54 is 5 mm, and the transmit-receive surface at the ultrasonic transducer 53 is planted at a predetermined angle ϑ₁ (in the first embodiment, ϑ₁ is 10° independently in the respective axes X and Y) with respect to the object 54, so that the transducer 53 scans the object 54 in the step of 0.1 mm and keeping the constant distance from the object 54. The position sensing is carried out in accordance with the procedure of the position sensing program shown in the Fig.8 flow chart and previously given from FDD60. In the flow chart in Fig.8, firstly in the step 1, the control signal from the data processing control unit 51 drives the manipulator 50 through the manipulator control unit 52 to thereby move the ultrasonic transducer 53 in the direction of the axis X toward the sensing start position 63. In Fig. 6, reference numeral 62 designates the axis of ultrasonic beam transmitted from the ultrasonic transducer 53, and 64 designates the intersection of the axis 62 of ultrasonic beam and the object 54, when the sensing is finished, so that the sensing in the direction of the axis X is carried out in a section between the position 63 and the intersection 64. In addition, in the first embodiment, the sensing section is 40 mm long and defined to include the bore 65. Next, in the step 2, the control signal from the data processing control unit 51 actuates the oscillator 55 so that the ultrasonic transducer 53 transmits the ultrasonic wave of the predetermined frequency toward the object 54 and simultaneously actuates the A/D converter 57 and memory 58 to thereby store in the memory 58 the reflected signal from the object 54. Fig.9 showns the reflected signal stored in the memory 58, in which reference numeral 69 designates the reflected signal from the object 54. Next, in the step 3, the reflected signal stored in the memory 58 is transferred to CPU61 through ICU59, the CPU61 sensing the intensity P₁ of reflected signal 69 from the object 54 in accordance with the program previously given from FDD60 and stored in memory 58. Next, in the step 4, the manipulator 50 is moved by 0.1 mm in the direction of the axis X and the steps 2 and 3 are repeated. Upon completion of the predetermined times of sensing (400 times in this embodiment), the execution proceeds to the step 5. In the step 5, the center of the objective bore 65 is position-sensed in the direction of the axis X on the basis of the intensity of reflected signal obtained by the steps 2 and 3 and coming from the object 54 including the bore 65. Fig.10 plots the intensity of reflected signal from the object 54, when the ultrasonic transducer is of 36 mm in diameter and of 66 KHz (wavelength λ = 5.14 mm) in the drive frequency, scans at the wave transmitting surface 66 slanted at an angle of ϑ₁ = 10° in the direction of the axis X with respect to the object 54 and in parallel to the axis X, in which the axis of abscissa represents an amount of parallel scanning of ultrasonic transducer 53 and the axis of ordinate represents the reflected signal intensity and every ten dots are plotted. Also, CPU61 senses the minimum value of reflected signal intensity in accordance with the program previously given from FDD60 and stored in memory 58, at which time the amount of parallel scanning of ultrasonic transducer 53 is sensed. In Fig.10, sensitivity S₁ for sensing the bore 65 was -16dB, the sensitivity S' being defined as follows: When the minimum value of the reflected signal from the object 54 is represented by P₁ and the maximum value of the same is represented by P₂, the sensitivity S(dB) for the object bore 65 is given in the following equation: S = 20 log (P₁/P₂) (dB) (1) At this time, the amount of parallel scanning of ultrasonic transducer 53 was 23.2 mm and the center of bore 65 was possible to be position-sensed by adding the aforesaid parallel scanning amount (23.2 mm) to the coordinate X of the sensing start position 63 of the ultrasonic transducer 53. Next, in the step 6, it is decided whether or not the sensing in the direction of the axis Y necessary to sense the center position of bore 65 at the object 54 is completed, and then this embodiment execution returns to the step 1 so that the sensing in the direction of the axis X is executed as the same as the aforesaid sensing in the direction of the axis X to thereby sense the center position. In addition, in the sensing in the direction of axis Y, the transmitting and receiving surface 66 at the ultrasonic transducer 53 is slanted at an angle ϑ₁ = 10° in the direction of axis Y with respect to the object 54 and scans in parallel thereto in the direction of axis Y. In Fig.6, the intersection 67 of the axis 62 of ultrasonic wave beam and the object 54, is assumed the sensing start point, and that 68, the sensing complete point, the sensing in the direction of axis Y being carried out in the section (of 40 mm in length in this embodiment) including the objective bore 65. Fig.11 shows the reflected signal intensity from the object 54 when the wave transmitting and receiving surface 66 of ultrasonic transducer 53 is slanted at the angle of ϑ₁ = 10° in the direction of axis Y with respect to the object 54 and scans in parallel thereto, in which the axis of abscissa represents the amount of parallel scanning of ultrasonic transducer 53 and the axis of ordinate represents the reflected signal intensity and every 10 dots are plotted. Also, CPU61 senses the minimum value of reflected signal intensity in accordance the program given from FDD60 and stored in memory 58, at which time the parallel scanning amount of ultrasonic transducer 53. In Fig.11, the sensitivity S₂ for sensing the bore 65 was -16 dB. At this time, the parallel scanning amount of ultrasonic transducer 53 was 13.5 mm and the center of bore 65 in the direction of axis Y could be position-sensed by adding the aforesaid parallel scanning amount (13.5 mm) to the coordinate Y of sensing start position 67 by the ultrasonic transducer 53. This embodiment, which has the surface 66 at the ultrasonic transducer 53 slanted at an angle of 10° in the scanning direction with respect to the object 54, may change the angle of inclination in order to change the sensitivity for the bore 65. In Fig.12, reference a designates the intensity of reflected signal from the object 54 when the wave transmitting and receiving surface 66 at the ultrasonic transducer 53 is slanted in the direction of axis X with respect to the object 54 and scans in parallel to the direction of axis Y as the same as the first embodiment, the axis of abscissa representing an angle of inclination at the ultrasonic transducer 53, the axis of ordinate representing the sensitivity for the bore 65, so that the sensitivity for the bore 65 has shown the maximum value when the angle ϑ₁ of inclination was 10°. A first zero radiation angle ϑ of ultrasonic transducer 53 used in this embodiment, when a diameter of ultrasonic transducer is represented by D(mm), the drive frequency by f(KHz), and the acoustic velocity by C(mm/S), is given in the following equation: In this embodiment, ϑ ≒ 10° is obtained so that it is seen that when the sensitivity for the bore 65 is of the maximum value, the radiation angle ϑ is about equivalent to the angle of inclination of ultrasonic transducer 53. Also, in Fig.12, reference b designates the arranged intensity of reflected signal from the object 54 when the drive frequency of ultrasonic transducer 53 is 51 (KHz) and the wave transmitting and receiving surface 66 thereof is slanted in the direction of axis X with respect to the object 54 and scans in parallel thereto in the direction of axis X as the same in construction as this embodiment, so that when the angle ϑ₁ of inclination is 13°, the sensitivity S for the bore 65 was -13 dB, at which time a first zero radiation angle ϑ is given in ϑ ≒ 13° from the aforesaid equation (2), which was about equivalent to the angle of inclination at the ultrasonic transducer 53 when the sensitivity for the bore 65 was of the maximum value. This invention as above-mentioned transmits and receives the ultrasonic wave of drive frequency of 66 KHz through the wave transmit-receive surface 66 of ultrasonic transducer of 36 mm in diameter, the surface 66 being slanted at angle of 10° with respect to the object 54 having the bore 65, and simultaneously actuates the manipulator 50 to allow the ultrasonic transducer 53 to scan with respect to the object 54 keeping the constant distance therefrom, thereby obtaining the reflected signal. Since the intensity thereof when the center of the ultrasonic beam is positioned in the vicinity of bore 65 largely decreases more than that when the center of the ultrasonic beam from the ultrasonic transducer 53, the amount of parallel scan of ultrasonic transducer 53, when the reflected signal intensity is of the minimum value, is sensed to thereby enable the center of bore 65 to be sensed in both the directions of axes X and Y. Thus, this embodiment obtained the bore position sensing by 0.1 mm with accuracy. Furthermore, the inventors have earnestly researched the angle of inclination at the wave transmit-receive surface 66 at the ultrasonic transducer 53 with respect to the object 54, so that an optimum value of the angle of inclination defined by the drive frequency (KHz) and diameter (mm) of ultrasonic transducer 53 can be formed to improve the sensitivity for position-sensing the bore 65, resulting in that the position sensing apparatus of high accuracy and reliability has been realizable. In addition, this embodiment, which has the bore 65 at the object 54 as the object to be measured, may alternatively have a groove provided at the object. In brief, the ultrasonic transducer 53 need only change the relative position thereof with the object to be measured to thereby reduce by the existence of object the reflected signal intensity obtained by transmitting and receiving the ultrasonic waves by the ultrasonic transducer 53. Next, explanation will be given on a second embodiment of the invention with reference to the drawings. Fig.13 is a perspective view of the second embodiment, showing the groove position-sensing. Fig.14 is a schematic block diagram of the second embodiment, which is the same as the first embodiment and omitted of its detailed description. Next, explanation will be given on operation of the second embodiment of the groove position sensing apparatus of the invention, in which the manipulator 72 and ultrasonic transducer 73 are the same in construction and usage as the first embodiment. An object to be measured in this embodiment is a groove 82 at an object 81 as shown in Fig.13, a distance between the object 81 and the ultrasonic transducer 73 is 100 mm, the groove 82 at the object 81 is 5 mm wide and 10 mm deep, and the ultrasonic transducer 73 is opposite and parallel at the wave transmit-receive surface 88 to the object 81 and scans with respect thereto in the step of 0.2 mm in parallel to the axis X. The position sensing is carried out in accordance with the procedure of position sensing program previously given from FFD78 and stored in memory 76 as shown in the Fig.15 flow chart, in which in the step 1, a control signal from a data processing control unit 70 drives a manipulator 72 through a manipulator control unit 71 to move the ultrasonic transducer 73 toward the sensing start position. In Fig.13, reference numeral 83 designates the axis of ultrasonic wave beam transmitted from the ultrasonic transducer 73, 84 designates the intersection of the axis 83 of ultrasonic wave beam and object 81 when the sensing starts, and 85 designates the same when the sensing is complete, the sensing being carried out with the section between both the intersections 84 and 85. In addition, the second embodiment has the sensing section of 40 mm in length and is set to keep the groove in the section. Next, in the step 2, a control signal from the data processing control unit 70 actuates an oscillator 80, the ultrasonic transducer 73 transmits the ultrasonic wave of the predetermined frequency toward the object 81 and simultaneously actuates an A/D converter 75 and a memory 76, and the reflected signal from the object 81 is stored in the memory 76. Fig.16 shows the reflected signal stored in the memory 76, in which reference numeral 89 designates a reflected signal from the flat portion at the object 81, and 90 designates the same from the bottom 87. Then, in the step 3, the reflected stored in the memory 76 is transferred to CPU79 through ICU77, the CPU79 senses the reflected signal intensity P₂ of reflected signal 89 from the flat surface 86 at the object 81 in accordance with the program previously given from FDD78 and stored in memory 76. Next, in the step 4, the manipulator 72 is moved by 0.2 mm in the direction of the arrow A and the steps 1 and 2 are repeated so that upon completion of the predetermined times (200 times in this embodiment) of sensing, the execution proceeds to the step 5. In the step 5, the center of objective groove 82 is position-sensed on the basis of the reflected signal intensity from the object 81 including the objective groove 82 obtained by the steps 2 and 3. Fig.17 shows the reflected signal intensity from the object 81 when the ultrasonic transducer 73 is opposite at the wave transmitting and receiving surface 88 to the object 81 and scans in parallel thereto in the direction of the arrow A, in which the axis of abscissa represents an amount of parallel scanning of ultrasonic transducer 73, the axis of ordinate represents the reflected signal intensity, and every five dots are plotted. In CPU79, the minimum value of reflected signal intensity and the parallel scanning amount of ultrasonic transducer 73 at this time are sensed in accordance with the program previously given from FDD78 so as to be stored. In Fig. 17, the sensitivity S₃ for sensing the groove 82 was -12 dB, at which time the parallel scanning amount of ultrasonic transducer 73 was 23 mm, and the center of objective groove 82 in the direction of axis X was sensible by adding the parallel scanning amount (23 mm) into the coordinate X of sensing start position 84 at the ultrasonic transducer 73. The second embodiment as above-mentioned transmits and receives the ultrasonic wave with respect to the object 81 having the groove 82, through the wave transmit-receive surface 88 at the ultrasonic transducer 23 opposite and parallel to the object 81, and simultaneously actuates the manipulator 72 to allow the ultrasonic transducer 73 to scan with respect to the object 81 keeping a given distance therefrom thereby obtaining the reflected signal intensity from the object 81. The reflected signal intensity, when the center of ultrasonic wave beam from the ultrasonic transducer 73 is positioned in the vicinity of groove 81, is reduced more than that when the same is positioned away from the groove 81, the decrement ratio is reduced by about 3/4 in comparison with the first embodiment, but a sufficient sensitivity to sense the center of groove 81 was obtained so that the parallel scanning amount of ultrasonic transducer 73 when the reflected signal intensity is of the minimum value, is sensed, thereby enabling the sensing of the centre of groove 81 in the direction of axis X, the positions sensing accuracy obtained for this embodiment was 0.2mm long. As seen form the above, this invention transmits and receives the ultrasonic wave to and from the object to be measured and simultaneously changes the relative position between the ultrasonic wave transmit-receive element and the object to be measured, thereby obtaining the reflected signal intensity, so that the object is sensed of its position by utilizing change in the reflected signal intensity in the vicinity of the center position of the object. Hence, the position sensing apparatus simple in constructions and with high accuracy is obtainable, thereby having a largely practical effect.

Claims: A position sensing apparatus for an object to be measured which comprises: a first means including an ultrasonic wave transmit-receive element for transmitting an ultrasonic wave to the object to be measured and for receiving a reflected wave therefrom; a second means arranged to maintain said ultrasonic wave transmit-receive element at a predetermined distance from said object, to effect a linear movement of said element with respect to said object, and to maintain a wave transmit-receive surface of said wave treatment-receive element at a predetermined angle of inclination with respect to a measured surface of said object wherein if the wavelength of said ultrasonic wave transmitted and received by said ultrasonic wave transmit-receive element is represented by λ and a diameter of said ultrasonic wave transmit-receive element is represented by D, then ϑ=sin⁻¹(1.22 λ /D) (rad) and said predetermined angle of inclination is substantially equal to Θ; and a third means adapted to detect a minimum value of intensity of a signal corresponding to said reflected wave from said measured surface of said object and to determine a centre position of a bore or groove formed in a surface of said measured object, said determination being based on the relative position of said ultrasonic wave transmit-receive element with respect to said object at the point of detection of said minimum value.

Inventors: MARUYAMA, TERUO, OTSUKI, TOSHINORI 1C5-404, HACHIBOU
Applicants: MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1984
Main classification: G01B17
IPC codes: G01S15, G01B17