JPH0216965B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method of measuring the shape of an object in a non-contact manner using an optical displacement meter using laser light or the like. Concerning automatic measurement method of cross-sectional shape.

[Prior art]

Recently, with the development of optoelectronics,
BACKGROUND ART A method of measuring the shape of an object in a non-contact manner using optical means such as laser light has been developed. Among these methods, an example of the scanning measurement method will be explained with reference to FIG.

A drive table 2 placed outside the object to be measured 1 is three-dimensionally driven by a drive mechanism 3 or the like.
The optical system arranged on the drive table 2 includes a light source 4 such as a laser, a semi-transparent mirror 5, lenses 6 and 7, a vibrating pinhole 8, and a light receiver 9. The arithmetic and control device also includes an oscillator 10 of the vibration pinhole 8, an amplifier 11 for the output of the light receiver 9, and an arithmetic and control circuit 12 that calculates the outputs of the oscillator 10 and the amplifier 11 to control the drive mechanism 3. Become. Now, if the distance A between the object 1 and the lens 6 is equal to the focal length of the lens 6, the reflected light will be focused at the center of the amplitude of the vibrating pinhole as shown in FIG.
The output of is maximum, but regardless of whether the distance A is biased toward the focal length _f6 of the lens 6, the output from the light receiver 9
output decreases. Furthermore, as shown in Figure 2, due to the action of a vibrating pinhole that vibrates at a frequency,
When the distance A is equal to f ₆ , the frequency of the output of the receiver 9 is 2, but when the distance A is equal to f ₆ , the output is equal to the frequency 〓
The phase is the same or opposite to the phase of the vibrating pinhole, respectively. Therefore, if the arithmetic control circuit 12 drives the drive mechanism 3 based on the detection results of the frequency and phase of the output and makes the distance A match the focal length _f6 of the lens 6, the amount of drive The shape of the object 1 can be traced and measured.

This method has the following problems.

(a) Measurement time is long. This means that when measuring the shape of the x-y cross section of object 1 as shown in Fig. 1, in addition to driving in the x-axis direction, the y-direction
That is, this is because it is necessary to drive in the optical axis direction.

(b) Sensitive to vibration. This is because since a vibrating pinhole is used to detect the distance to an object, problems such as resonance are likely to occur due to external vibrations.

(c) Unable to measure large inclination angles of object surfaces. This is because as the angle α between the normal to the object surface and the irradiation optical axis in FIG. 1 increases, the amount of reflected light directed toward the light receiver decreases.

[Purpose of the invention]

An object of the present invention is to provide a measurement method that requires short measurement time and can automatically follow sudden changes in the shape of an object.

[Summary of the invention]

The main points of the measurement method of the present invention are as follows.

(a) A displacement meter that has a wide measurable range and does not use vibration in principle is used to measure the distance to an object.

(b) The displacement meter is attached to the three-dimensional drive device, and an angle change mechanism is attached to this attachment part.

(c) Set a limit range within the distance and angle measurement limits of the displacement meter, and if either the distance or angle at a measurement point is outside this limit range, before obtaining the measurement value at the next point. Control should be carried out to bring it back within the above limit range.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 shows its overall configuration. Above the object to be measured 1 placed on a base 20, a displacement meter 40 is attached to a crosshead 22 via an angle changing mechanism 21. This crosshead 22
slides on the arm 23 of the three-dimensional drive device, and its guide portion 24 is driven left and right by the rotation of the motor 26 coupled to the transverse feed screw 25, so the displacement meter 40 moves in the x-axis direction shown in the figure. It's becoming possible. Further, movement in the y-axis direction is performed by a longitudinal feed screw 28 coupled to a motor 27 and a gearbox 30 slidably fitted to the arm 29. Furthermore,
The motor 31 moves the entire device mounted on the base 32 to
Drive in the axial direction. Therefore, the displacement meter 40 is movable in the directions of the three axes x, y, and z, and can be rotated within a cross section perpendicular to the z-axis by the drive motor 33 (shown in FIG. 9) of the angle change mechanism 21. be.

Figure 4 shows how the displacement gauge is installed. In the following explanation, for simplicity, it is assumed that the rotation center D of the angle changing mechanism is on the irradiation optical axis, the intersection of the projection optical axis and the surface of the object 1 is called P, and the length L of PD is the displacement meter 4.
It is defined as the distance between 0 and the object. Also, the irradiation angle α
is defined by the angle between the irradiation angle θ _d and the angle θ _o of the normal n to the cross section of the object at point P. Here, α
is expressed by the following formula.

α=θ _d −θ _o () FIG. 5 shows the structure of the displacement meter used in this embodiment. A light beam emitted from a light source 41 such as a laser beam passes through the irradiation lens 42 and irradiates the measurement point P on the object surface, but this diffusely reflected light is placed on the receiving optical axis that forms a certain angle with the irradiating optical axis. condensing lens 43
The light is collected by the light receiver 44 and detected by the light receiver 44. The principle of distance measurement is based on the phenomenon that when the distance to the object displacement meter changes, the incident position of the reflected light on the light receiving surface on the light receiver 44 changes continuously.
Due to restrictions such as the size of the light-receiving surface, there is naturally a limit to the distance that can be measured with a displacement meter, and hereinafter the upper and lower limits of distance measurement limits will be referred to as L _nax and L _nio , respectively.

In addition, Figures 6 to 8 show the irradiation angle α of the displacement meter.
It is an explanatory view of the measurement limit of. First, FIG. 6 shows a case where the amount of reflected light reaches its maximum value. Since the irradiation angle α is half of the angle β between the irradiation optical axis and the light reception optical axis, the direction of the reception optical axis coincides with the direction of the maximum value of the light quantity distribution of the diffusely reflected light. On the other hand, FIGS. 7 and 8 show the upper and lower limits of the measurable irradiation angle α. From these figures, it can be seen that when α becomes too large or too small, the direction of the light receiving optical axis becomes a region where the amount of diffusely reflected light is small, so that an insufficient amount of light occurs in the light receiver 44. The upper and lower limits of this irradiation angle α are called α _nax and α _nio , respectively.

FIG. 9 shows the arithmetic control mechanism of the present invention. Information regarding the distance L obtained from the displacement meter 40 is input to the calculation control circuit 46 via the detection circuit 45. Further, the position information from the magnetic scale 47 that measures the amount of movement in the x, y, and z axes and the angle information from the rotary encoder 48 of the angle change mechanism 21 are sent to the arithmetic control circuit 46 via the respective detection circuits 49 and 50. is input. The calculation control circuit 46 calculates the coordinates (x, y, z) of point P of the object 1 based on this information, and displays the result on the display device 51. Further, regarding the distance L and the irradiation angle α, a comparison calculation, which will be described later, is performed, and the drive motors 26, 27, 31, and 33 are controlled based on the results.

Next, a specific drive control method of the displacement meter in this embodiment will be explained. FIG. 10 shows the relationship between the drive of the displacement meter and the measurement limit of the distance L. A in the diagram is
A case is shown in which the displacement meter is located approximately at the center of the detection limit with respect to the distance L, so that measurement can be performed without any problem. However, if you continue measuring while driving the displacement meter parallel to the x-axis direction and move it to B in the figure, the distance L will exceed the detection limit L _nax shown by the curve B in the figure.
, it becomes impossible to measure the distance. Therefore, on the way from A to B,
It is necessary to control the occurrence of this phenomenon and bring it back within the detection limit, as illustrated by C in the figure. A similar phenomenon can occur with respect to the illumination angle α, as shown in FIG. That is, in the process from A to B in the figure, only the drive in the x-axis and y-axis directions is performed, and the object 1
If the value of α is not changed in accordance with the change in the cross-sectional shape, a situation like B in the figure will occur and measurement will become impossible. Therefore, on the way from A to B, it is necessary to control α to prevent the occurrence of case B and return it to within the angle detection limit as illustrated in C in the figure.

On the other hand, from the viewpoint of shortening measurement time, there is a desire to reduce the number of times the length position and angle can be driven, and if possible, to only drive the x-axis necessary for measuring the cross-sectional shape.

In the present invention, these contradictory demands are resolved as follows. That is, first, the limit ranges L l to Lo and α l to α _o are set within the measurement limits L _nio to L _nax and _{α nio} to _{α nax} for the distance _L and the angle α. Now, if the measured value of L or α at a certain measuring point P _i is out of these limited ranges, then before measuring the next measuring point P _{i +1} , based on the data of P _i and previous ones, Control is performed to return L to α to values L _p and α _p within the limited range. Here, the following relational expression holds true.

L _nio ＜L _l ≦L _p ≦L _o ＜L _nax ………() α _nio ＜α _l ≦α _p ≦α _o ＜α _nax ………() In this case, the data before the P _i point is also used because the angle θ _o of the normal to that point is required to calculate the illumination angle α. As shown in FIG. 12, the coordinates of points P _i-2 to _{P i} in the figure are used to calculate θ _o , and the slope of the contact point of point P _i may be determined by polynomial approximation, for example.

In this way, in the automatic object shape measuring method of the present invention, if the measurement point of the object is outside the range where the light receiver 44 cannot measure the measurement point, when the displacement meter 40 is moved within the measurement distance and measurement angle limit range, the measurement point is detected. can be measured. As a result, measurement work can be performed continuously without stopping the operation of the object shape measuring device, and since it is only necessary to move the displacement meter 40 within the limit range, accurate adjustment is not required. This allows the measurement work time to be significantly reduced.

FIG. 13 shows the locus of the center point D _i of the angle changing mechanism when this control is adopted. Comparison with FIG. 10 shows that the adoption of this control prevents the phenomenon in which the distance L exceeds the measurement limit. A similar effect can be expected by controlling the illumination angle α in a similar manner.

Note that when performing these controls, the coordinates (X', Y') of D _i and the mounting angle θ _d ' after the control are
As shown in Figure 2, the coordinates (X, Y) of point D _i before control,
Using the mounting angle d〓 and the coordinates (x, y) of point P _i , it can be given by the following formula, so set the x, y axes of the three-dimensional drive device and the θ _d axis of the angle change mechanism to these values. All you have to do is drive it.

_{θ d ′ =} α _{p + θ o ………} ( ₎ , α _p are appropriate values within the respective limit ranges shown in equations () and ().

FIG. 14 shows a flowchart of this control method. In the above control method, after driving the x, y and θ axes, measurement is performed again at that point.
This is not always necessary, and the measurement may proceed to the next point as shown by the broken line in the figure.

Although the above explanation deals with the case of obtaining the shape of a cross section perpendicular to the z-axis, similar control can be used when measuring any cross section, although the calculation formula and control method are complicated. can be done.

The application of the present invention is not limited to the above-described embodiments, and various modifications and applications can be made to the configuration and arrangement of the three-dimensional drive mechanism and the angle change mechanism. Any use of the method is considered equivalent to the present invention.

〔Effect of the invention〕

According to the present invention, during the measurement, the distance L of the displacement meter is
It is possible to prevent the irradiation angle α from exceeding the detection limit, and because this control is only performed each time it is necessary, the measurement time can be shortened.

[Brief explanation of drawings]

FIG. 1 is a side view of a conventional shape measuring device, FIG. 2 is an explanatory diagram showing the relationship between displacement and output of the conventional device, FIG. 3 is a side view showing the overall configuration of an embodiment of the present invention, and FIG.
The figure is an explanatory diagram of the installation situation of the displacement meter, Figure 5 is a structural diagram of the displacement meter, Figures 6 to 8 are explanatory diagrams showing the measurement limit of the irradiation angle of the displacement meter, and Figure 9 is an illustration of the calculation control mechanism. An explanatory diagram, FIG. 10 is an explanatory diagram showing the relationship between the detector driving method and the measurement limit of the distance, FIG. 11 is an explanatory diagram showing the relationship between the detector driving method and the measurement limit of the irradiation angle, and FIG. 13 is an explanatory diagram showing the method of calculating the irradiation angle, FIG. 13 is an explanatory diagram showing the effects of the present invention, and FIG. 14 is a flowchart of the control method according to the present invention. 1...Object to be measured, 2...Drive table, 3...
... Drive mechanism, 8 ... Vibration pinhole, 9 ... Light receiver, 10 ... Oscillator, 11 ... Amplifier, 12 ...
Arithmetic control circuit, 21... Angle change mechanism, 40...
Displacement meter, 42... Irradiation lens, 43... Condenser lens, 44... Light receiver, 45... Detection circuit, 46...
...Arithmetic control circuit, 49, 50...Detection circuit.

Claims (1)

[Claims] 1. A displacement meter that measures the distance to the object by receiving the reflected light of the light beam projected onto the surface of the object, and a drive table to which the displacement meter is attached and drives the displacement meter three-dimensionally. and an angle changing mechanism that changes the mounting angle of the displacement meter; and an angle changing mechanism that inputs and calculates the distance measured by the displacement meter, the drive amount of the drive table, and the mounting angle of the displacement meter; and a calculation control mechanism that controls the movement of the angle changing mechanism, in which the cross-sectional shape of the object to be measured is continuously measured as a set of measurement points, the displacement meter obtained at each measurement point and the measurement Whether the distance to the point and the angle formed by the normal to the cross section of the object at the measurement point and the irradiation optical axis are within a limited distance range and a limited angle range within the measurement distance limit and measurement angle limit range of the displacement meter. If at least one of these is outside the limited range at a certain measurement point, before measuring the next measurement point,
An automatic method for measuring the shape of an object, characterized by performing control to return the object shape to within the limited range.