GB2104219A

GB2104219A - Measuring sizes by means of ultrasonic waves

Info

Publication number: GB2104219A
Application number: GB08220437A
Authority: GB
Inventors: Sakae Sugiyama
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1981-07-27
Filing date: 1982-07-14
Publication date: 1983-03-02
Also published as: DE3227640C2; GB2104219B; JPS5818111A; DE3227640A1

Abstract

A method of measuring a size of an object (1), such as the thickness of the object or the depth of an internal defect (C, D), is disclosed in which a surface of the object (1) is scanned by an ultrasonic probe (2), an ultrasonic beam is emitted from the probe at a plurality of positions (P1, P2, P3) on the surface to receive an ultrasonic echo at each of these positions, received echoes are employed obtain an echo propagation distance at each position, thereby obtaining a plurality of circular arcs (M11, M21, M22, M31, M1, M2, M3) which have the center thereof at each of the above positions and have a radius equal to the associated propagation distance, and then the point (C) of intersection of the circular arcs is judged to be the position of an echo source when the point of intersection (C) lies in an area where ultrasonic beams emitted at the above positions would overlap each other. <IMAGE>

Description

SPECIFICATION Method and apparatus for measuring sizes by means of ultrasonic waves The present invention relates to a method of and an apparatus for measuring sizes of an object to be inspected by means of ultrasonic waves, and more particularly to a method of measuring the thickness of a plate having a rough surface or the depth of a defect in a to-be-inspected object with high accuracy and an apparatus for carrying out the above method.

There have been generally and widely used a method of measuring a size of a to-be-inspected object having a form of a plate by emitting an ultrasonic beam from an ultrasonic probe kept in contact with the object and receiving an echo of the ultrasonic beam at the probe, and an apparatus for carrying out this method. However, in the case where the object has a rough surface on the back side thereof or in the case where internal defects are close to each other in the object, there arises a technical problem that measuring errors tend to be made in the above-mentioned conventional apparatus due to the fact that the ultrasonic beam emitted from the ultrasonic probe is a directional beam having a lateral spread. The above technical problem will be explained below.

First, explanation will be made on the case where the thickness of a to-be-inspected object having a rough surface on the back side thereof is measured, by reference to Figures 1 and 2. In Figure 1, an ultrasonic probe 2 receives a transmitted signal T from an ultrasonic receiver 3 to emit an ultrasonic beam having a lateral spread 6 from a point P on a surface of a to-be-inspected object 1 in a direction PB perpendicular to the surface, and receives an echo generated by reflection of the emitted ultrasonic beam. A received signal R is sent from the ultrasonic probe 2 to the ultrasonic receiver 3 on the basis of the received echo.

Figure 2 shows a relation between transmitted and received waveforms and time. Waveform T' at a point O on the time-axis and a waveform RA at a point tB indicate a transmitted wave and a received wave, respectively. The distance between the points P and B shown in Figure 1 will be determined by multiplying the sound velocity by one-half of the time period tB. However, when a recess is present in the lower surface of the object 1 as shown in Figure 1, the bottom A of the recess being within the lateral spread 6 of the ultrasonic beam provides an echo source where ultrasonic energy will be reflected. Since distance PB is larger than distance PA, a reflected waveform RA appears at a point tA on the time-axis, as shown in Figure 2.

In the conventional apparatus, it has been impossible to discriminate between the reflected waveforms RA and R8, and a thickness of the object 1 calculated on the basis of the waveform RA at the point tA may be mistaken for the true thickness PB. Such a mistake occu rs not only with the ultrasonic probe 2 being fixed at the particular point P on the surface of the object 1 to measure the thickness thereof, but also with the probe 2 scanning the surface of the object 1 to carry out thickness measurements. If only one point source of echo is present within the object 1, the above mistake can be avoided by detecting the echo source at two positions on the surface of the object 1. This method will be explained below in connection with Figure 3.

Referring to Figure 3, a to-be-inspected object 1 has one echo source C. An ultrasonic beam is emitted from each of points P1 and P2 by causing an ultrasonic probe (not shown) to perform a scanning operation. The ultrasonic beam emitted from the point P1 has a lateral spread 6, and therefore is propagated in a range indicated by a triangle P1Q1S1. Part of the emitted beam is reflected from the echo source C, and the echo is received at the point P1. The position of the echo source Cannot be determined only by the above operation, but it is known that the echo source C exists on a circular arc M1 having its center at the point P1 and having a radius equal to the distance between the points P1 and C.Similarly, a circular arc M2 is obtained on the basis of the fact that part of the ultrasonic beam emitted from the point P2 is reflected from the echo source C. It is apparent that the echo source C exists on the circular arc M2. Accordingly, the position of the echo source C is given by the point of intersection of the circular arcs M1 and M2.

Next, a problem produced when internal defects are close to each other in an object will be explained by reference to Figure 4. That is, explanation will be made on the case where respective positions of two adjacent internal defects are detected by making use of the detecting method shown in Figure 3. Referring to Figure 4, an ultrasonic beam is first emitted from point P1, and therefore a triangle P1Q1S1 forms a first detection area. Next, an ultrasonic beam is emitted from point P2, and a triangle P2Q2S2 forms a second detection area. When an echo source D exists outside the triangle P1Q1S1 but exists inside the triangle P2Q2S2, the position of the echo source D cannot be determined for the following reason. When ultrasonic energy is emitted from and received at the point P1, it is judged that an echo source C exists on a circular arc M11.Next, when ultrasonic energy is emitted from and received at the point P2, a circular arc M21 intersecting the point C and another circular arc M22 intersecting the point Dare obtained, and not only the point of intersection of the circular arcs M11 and M21 indicates the point C but also the point D' of intersection of the circular arcs M11 and M22 is detected as a false echo source.

It is accordingly an object of the present invention to provide an ultrasonic size measuring method in which, when a to-be-inspected object has a rough surface or internal defects and therefore ultrasonic echoes from a plurality of echo sources are received, respective positions of the echo sources can be precisely determined to measure sizes of the object or respective positions of the internal defects with high accuracy, and an apparatus for carrying out the above method.

In order to attain the above object, according to the present invention, a surface of a to-be-inspected object is scanned by an ultrasonic probe for emitting and receiving ultrasonic energy, a received ultrasonic echo at a position on a scanning line and one or more ultrasonic echoes received in one or more steps before the step at the above position are employed to obtain two or more circular arcs which have their centers at an ultrasonic energy emitting/receiving position in each step and have a radius equal to a propagation distance of the ultrasonic echo in each step, and then that point of intersection of the circular arcs which exists in an area where ultrasonic beams emitted from the ultrasonic probe overlap each other, is judged to be an echo source.

The present invention will becomes more apparent from the following description taken in conjunction with the accompanying drawings, in which: Figure 1 is a schematic view for explaining a principle of a method of measuring the thickness of a plate by means of ultasonic waves; Figure 2 is a waveform chart showing a reflected ultrasonic wave caused by a recess in a surface of a plate when the thickness of the plate is measured by the method shown in Figure 1; Figure 3 is a schematic view for explaining a principle of a method of measuring an internal defect in a plate by means of ultrasonic waves; Figure 4 is a schematic view for explaining a problem produced in the method shown in Figure 3; Figure 5 is a schematic view for explaining an embodiment of a method of measuring the position of an echo source according to the present invention;; Figure 6 is a block diagram showing a procedure for measuring the position of an echo source according to the present invention; and Figure 7 is a schematic view for explaining the procedure shown in Figure 6.

Now, explanation will be made on a method of and an apparatus for measuring the position of an echo source according to the present invention, by reference to Figures 5 to 7. First, an embodiment of a method of measuring the position of an echo source according to the present invention will be explained on the basis of Figure 5.

As mentioned previously, when two echo sources are present as shown in Figure 4, it is not possible to determined respective positions of the echo sources merely by emitting from and receiving at points P1 and P2 ultrasonic energy to obtain circular arcs M11, M21 and M22. Therefore, as shown in Figure 5, ultrasonic energy is further emitted and received at a point P3 to receive ultrasonic waves reflected from the echo sources C and D, and to obtain circular arcs each having a radius equal to a propagation distance of the reflected ultasonic wave. In the example shown in Figure 5, since a distance between the points P3 and the echo source C is equal to a distance between the point P3 and the echo source D, only one circular arc M31 is obtained which has its center at the point P3.

In the present embodiment, at a time after ultrasonic energy has been emitted and received at the point P3, data obtained at the point P2 in the preceding step and data obtained at the point P, in the step before the preceding step are employed to make the following judgements.

(a) As to the point C, it is judged that the point C is a true echo source, since the circular arc M11 obtained when ultrasonic energy is emitted and received at the point P1, the circular arc M21 obtained at the point P2, and the circular arc M31 obtained at the point P3 intersect in the point C.

(b) As to a point D', it is judged that the point D is a false echo source, since the circular arc M31 obtained when ultrasonic energy is emitted and received at the point P3 does not intersect the point D'. Thus, the point D' is not adopted.

(c) As to the point D, no ultrasonic wave is reflected from the point D when ultrasonic energy is emitted and received at the point P1, since the point D exists outside the lateral spread 6 of the ultrasonic beam emitted from the point P,. That is, at a time after ultrasonic energy has been emitted from and received at the point P3, the pint D is considered to be now in the course of evaluation, and therefore the judgment with respect to the point D is deferred until the next step.

Next, it will be explained how many steps are required to judge whether an echo source is true or not.

An ultrasonic probe is caused to perform a scanning operation on a surface of a to-be-inspected object to emit ultrasonic energy and receive echoes successively. In the case where one circular arc is obtained on the basis of a single received echo in the i-th step and a plurality of circular arcs are obtained on the basis of received echoes in the next step (namely, the (i+1 )-th step) to form L points of intersection with the circular arc in the i-th step within an areas where two ultrasonic beams emitted in these steps overlap each other, in order to ascertain whether a first echo source is true or not, the point of intersection of circular arcs obtained in two successive ones ofthe i-th, (i+1)-th, (i+2)-th and (i+L)-th steps is checked in succession.When L+1 circular arcs obtained in the i-th, (i+1 )-th, ..., and (i+L)-th steps intersect in a point, this point is judged to be a true echo source.

As mentioned above, in the present embodiment, a received echo at a position on a scanning line and one or more echoes received in one or more steps before the step at the above position are employed to obtain two or more circular arcs which have their center at an ultrasonic energy emitting!receiving position in each step and have a radius equal to a propagation distance of ultrasonic echo in each step, and then that point of intersection of the circular arcs which exists in an area where ultrasonic beams emitted from the above-mentioned ultrasonic probe overlap each other, is judged to be the position of an echo source.

In order to carry out the above-mentioned measuring method rapidly and easily, an ultrasonic size measuring apparatus according to the present invention includes an automatic arithmetic unit in addition to an ultrasonic probe and means for causing the ultrasonic probe to perform a scanning operation.The automatic arithmetic unit is supplied with the results of measurements at a plurality of successive positions, and has a function of calculating a plurality of circles which have their center at an ultrasonic energy emitting/receiving point and have a radius equal to a distance between the ultrasonic energy emitting receiving point and an echo source, on the basis of analytical geometry at the successive positions and calculating a point in which the circles intersect, and another function of judging whether the calculated point of intersection lies within a predetermined numerical formula or not. Thus, when the calculated point of intersection lies within the predetermined numerical formula, it is judged to be an echo source.

Next, an embodiment of an ultrasonic size measuring apparatus according to the present invention will be explained by reference to Figure 6.

Referring to Figure 6, an electric signal R indicating the waveform of an echo received by an ultrasonic probe 2 is applied to propagation time detecting circuits 5-1, 5-2, and and 5-n through a threshold gate 4.

Respective propagation times of a plurality of ultrasonic echoes are detected by these propagation time detecting circuits, and are inputted to a position locating circuit 6.

The position locating circuit 6 is supplied from a scanning position detecting circuit 9, with a position x of the ultrasonic probe 2 on a scanning line, and performs the following operations:

wherex indicates a coordinate axis in a scanning direction of the ultrasonic probe (refer to Figure 5), Z a coordinate axis in the directionof thickness of the object 1 (refer to Figure 5), x a position of the ultrasonic probe 2 in the i-th step, fj a propagation distance of echo in the i-th step, X an x-coordinate of the position of an echo source, and Z a z-cordinate of the position of the echo source.

As mentioned above, an arithmetic unit included in the present embodiment is supplied with the results of ultrasonic measurements in a plurality of successive steps (i-th, (i+1)-th, (i+2)-th ..., and (i+n)-th steps), calculates a plurality of circles which have their center at an ultrasonic energy emitting/receiving position and have a radius equal to a distance between the ultrasonic energy emitting/receiving position and an echo source, on the basis of analytical geometry in the above steps, and finds the point of intersection of the circles by solving simultaneous equations which indicate the circles.

An output signal which indicates the point of intersection of the circles calculated by the position locating circuit 6, is applied to an areas defining circuit 7, and a value indicating the lateral spread 6 and a maximum value T of thickness of the object 1 which have been previously stored in a memory 10, are also applied to the area defining circuit 7. In the circuit 7, it is judged whether the above-mentioned position (X, Z) of the echo source lies in an area where ultrasonic beams emitted from the probe 2 in the steps (the i-th to (i+n)-th steps) overlap each other, or not. The above judgement is made in the following manners.

Figure 7 shows a method of locating the position of an echo source by emitting and receiving ultrasonic energy in each of three successive steps, that is, at each of points P1, P2 and P3. In the case shown in Figure 7, since only one echo source C is present, the echo source is judged to be true or false according as the point of intersection of circles lies in a triangle u12Q2S1 where a triangle P1Q1S1 indicating the lateral spread of the ultrasonic beam emitted from the point P1 and a triangle P202S2 indicating the ultrasonic beam emitted from the point P2 overlap each other, or not.

When an area where an ultrasonic beam emitted in an i-th step and an ultrasonic beam emitted in the next step overlap each other is expressed generally by a triangle UQS, respective coordinates of the pointer U, Q and S are given by

When the point of intersection of circles which is supplied from the position locating circuit 6 lies in the triangle UQS, the area defining circuit 7 judges the above point of intersection to be a true echo source.

As mentioned previously, when L points of intersection of one circular arc obtained in the i-th step and circular arcs obtained in the (i+1 )-th step lie in an ultrasonic beam overlapping area, points of intersection of circular arcs are successively calcuated in (i+2)-th, (i+3)-th, and (i+L)-th steps. In addition to the above calculation, the arithmetic operation for obtaining respective coordinates of the above-mentioned points U, Q and S is performed in each of the above steps, that is, the above arithmetic operation is repeated each of the (i+ 1 )-th, (i+2)-th, ..., and (i+L)-th steps while shifting numerical values successively, to judge whether each point of intersection lies in a triangle UQS (indicating an ultrasonic beam overlapping area) or not.

That is, the automatic arithmetic unit included in the present embodiment judges, in the above-mentioned manner, whether the point of intersection of circular arcs obtained by calculation lies in a triangle UQS (namely, an ultrasonic beam overlapping area) given by a numerical expression or not.

An ultrasonic size measuring apparatus according to the present invention includes such an automatic arithmetic unit. Accordingly, in the apparatus, each of the propagation time detecting circuits 5-1, 5-2, and 5-n calculates a propagation time necessary for an echo to travel between an echo source and the ultrasonic probe 2 on the basis of echoes received by the probe 2, and supplies the calculated propagation time to the position locating circuit 6. On the basis of the fact that an echo source lies on a plurality of circular arcs having their center at each scanning position of the ultrasonic probe 2 and having a radius equal to a propagation distance of echo, the position locating circuit 6 calculates the point of intersection of the circular arcs to locate the position of the echo source.The area defining circuit 7 performs an arithmetic operation on the basis of numerical values supplied from the memory 10 to judge whether the above-mentioned point of intersection is a true echo source or not. A true echo source is displayed on display means 8.

As has been explained in the foregoing description, in an ultrasonic size measuring method according to the present invention, a received echo at a position on a scanning line and one or more echoes received in one or more steps before the step at the above position are employed to obtain two or more circular arcs which have their center at an ultrasonic energy emittingireceiving position in each step and have a radius equal to a propagation distance of ultrasonic echo in each step, and then that point of intersection of the circular arcs which exists in an area where ultrasonic beams emitted from an ultrasonic probe overlap each other, is judged to be the position of an echo source.Accordingly, even when a to-be-inspected object has a rough surface and therefore contains a plurality of echo sources, respective positions of the echo sources are precisely determined, and the correct thickness of the object having the form of a plate can be measured with high accuracy.

Further, an ultrasonic size measuring apparatus according to the present invention includes an automatic arithmetic unit in addition to an ultrasonic probe and means for causing the ultrasonic probe to perform a scanning operation. The automatic arithmetic unit is supplied with the results of measurements at a plurality of successive positions, and has a function of calculating a plurality of circles which have their center at an ultrasonic energy emitting receiving point and have a radius equal to a distance between the ultrasonic energy emitting/receiving point and an echo source, on the basis of analytical geometry at the successive positions and calculating a point in which the circles intersect, and another function of judging whether the calculated point of intersection lies in an area expressed by a predetermined numerical formula or not.

Accordingly, the above apparatus can carry out the ultrasonic size measuring method according to the present invention rapidly and easily, and therefore can show an excellent effect of the measuring method.

Claims

1. A method of measuring a size by means of ultrasonic waves, comprising the steps of: scanning a surface of a to-be-inspected object by an ultrasonic probe; emitting an ultrasonic beam from said ultrasonic probe at a plurality of positions on said surface of said object to receive an echo of said ultrasonic beam; determining a propagation distance of ultrasonic echo at each of said positions on the basis of a received echo at one of said positions and received echoes at the remaining positions; determining a plurality of circular arcs, said circular arcs having the center thereof at each of said positions and having a radius equal to said propagation distance of ultrasonic echo at said position forming said center; and judging the point of intersection of said circular arcs to be the position of an echo source when said point of intersection lies in an area where said ultrasonic beams emitted at said positions overlap each other.

2. A method of measuring a size of a to-be-inspected object by scanning a surface of said object by an ultrasonic probe, comprising the steps of: receiving an ultrasonic echo at each of a plurality of positions on a scanning line; determining at least two circular arcs on the basis of an received echo at one of said positions and at least one echo received in at least one step before the step at said position, said circular arcs having the center thereof at an ultrasonic energy emitting receiving point in each step and having a radius equal to a propagation distance of ultrasonic echo in each step; determining the point of intersection of said circular arcs;; judging said point of intersection of said circular arcs to be the position of an echo source when said point of intersection lies in an area where ultrasonic beams emitted from said ultrasonic probe at said positions overlap each other.

2. An apparatus for measuring a size by means of ultrasonic waves, comprising: an ultrasonic probe; means for scanning a surface of a to-be-inspected object by said ultrasonic probe; means for calculating the point of intersection of a plurality of circular arcs, said circular arcs having the center thereof at a plurality of successive positions on said object and having a radius equal to a distance between each of said positions and a source of ultrasonic echo; and means for judging whether said calculated point of intersection lies in an area expressed by a predetermined numerical formula or not.

4. An apparatus for measuring a size by means of ultrasonic waves, including an automatic arithmetic unit in addition to an ultrasonic probe and means for causing said ultrasonic probe to perform a scanning operation, said automatic arithmetic unit comprising: means supplied with the results of measurements at a plurality of successive positions for calculating a plurality of circles on the basis of analytical geometry at said positions, said circles having the center thereof at an ultrasonic energy emitting/receiving point and having a radius equal to a distance between said ultrasonic energy emitting/receiving point and an echo source; means for calculating a point where said circles intersect; and means for judging whether said calculated point of intersection lies in an area expressed by a predetermined numerical formula or not.

5. A method of measuring size substantially as hereinbefore described with reference to, and as illustrated in, Figures 5 to 7 of the accompanying drawings.

6. An apparatus for measuring size substantially as herein before described with reference to, and as illustrated in, Figures 5 to 7 of the accompanying drawings.