JPH03255305A - Method and apparatus for measuring surface profile - Google Patents

Abstract

PURPOSE:To make it possible to measure the profile of a surface highly accurately by computing the minute suspending amount of a piece of wire as the reference of straightness based on the natural frequency of the wire, and compensating for the measurement error. CONSTITUTION:A piece of wire 2 such as a piece of piano wire is provided in parallel with an object to be measured 1. The wire 2 is made to be the reference of temporary straightness. A distance detecting device detects the distribution of the distances to the object to be measured with the wire 2 as a reference. At this time, one distance detector is moved along a guide rail 4, and the distribution of the distances between the object to be measured 1 and the wire 2 are measured. The natural frequency (f) of the wire 2 is measured with a detecting device 5. The suspending amount as the change in straightness of the wire 2 is computed with an operating device 6 based on the natural frequency (f). The measured value of the distribution of the distances is corrected with the suspending amount. Thus, the measured value of the profile of the surface is obtained highly accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method and apparatus for measuring the surface profile or straightness of a measurement object with high precision.

(Prior Art) Generally, as shown in FIG. 8, as a method for measuring the surface profile of a measurement target, a guide track 4 is provided parallel to the measurement target 1, and the target is movable along this guide track. A method is known in which the distance detector 3 measures the distance distribution to the object to be measured 1 to determine the surface profile. However, especially when the object to be measured is a long object, there is a problem in that the guide/trajectory is warped or deflected.

This is because such a change in the straightness of the guide track directly affects the measured value of the surface profile and causes a large measurement error.

As a countermeasure to this problem, the so-called sequential three-point method proposed in Japanese Patent Application Laid-Open No. 59-57112, etc., and a method using a wire such as a straight edge or piano wire as a straightness standard have been developed. In the former method, three distance detectors are connected at equal intervals β, and the distance to the object to be measured is measured each time the distance detectors are moved by a distance I2 along the guide trajectory. By comparing the measured values, an attempt is made to calculate a surface profile that is independent of changes in the straightness of the guide track. In the latter method, a straight edge or wire whose straightness can be considered to be constant is installed parallel to the object to be measured, and the surface profile of the object is measured using this as a straightness standard.

(Problem to be Solved by the Invention) However, in the r-sequential three-point method, only discrete surface profile information can be obtained at discrete points for each distance ρ, and the accidental measurement error of each distance detector The drawback is that it accumulates and makes it impossible to obtain accurate measurement results. In addition, in methods that use a straight edge as a straightness standard, especially when the object to be measured is a long object, the straight edge, which is supposed to be the standard, may also change in straightness due to warping or deflection.
There was a problem that it was not possible to measure the surface profile with high precision. Furthermore, the method of using the wire as a straightness standard has the advantage of avoiding such warpage and deflection of the straightness standard, but if a slight change in the tension of the wire occurs, the wire may hang slightly, There was a possibility that this would cause a measurement error.

An object of the present invention is to solve the problems of the prior art and provide a method and apparatus for measuring a surface profile with high precision.

[Structure of the Invention (Means for Solving the Problem) The method for measuring a surface profile according to claim 1 includes, when measuring the surface profile of an object, stretching a straightness reference wire parallel to the object to be measured; The distance distribution between the wire and the object to be measured is measured, the natural frequency of the wire is measured, the amount of suspension of the wire is calculated from the natural frequency, and the distance distribution measurement value and the amount of suspension are calculated. The surface profile of the object to be measured is determined from the following.

The surface profile measuring device according to claim 2 includes a wire stretched parallel to the object to be measured, a distance detecting device for measuring a distance distribution between the wire and the object to be measured, and a natural frequency of the wire. a natural frequency detection device that calculates the amount of suspension of the wire from the natural frequency,
The apparatus includes a calculation device that calculates the surface profile of the object to be measured from the wire suspension amount and the distance distribution measurement value.

(Function) According to the present invention, a wire is installed parallel to the object to be measured as a straightness standard for measuring the distance distribution to the object to be measured, and the minute amount of suspension (change in straightness) of this wire is Since it is calculated from the vibration frequency and compensates for measurement errors due to the suspension of the wire, an accurate straightness standard can be obtained and the surface profile of the object to be measured can be measured with high precision.

(Example) FIG. 1 shows one embodiment of the present invention. Hereinafter, the specific configuration of the present invention will be explained with reference to this figure.

A wire 2 such as a piano wire is installed parallel to the object 1 to be measured, and this is used as a temporary straightness standard. It is necessary to construct this wire 2 under a sufficiently large tension to prevent it from sagging.

The distance detection device 3 detects the distance distribution to the object to be measured using the wire 2 as a reference, and in this embodiment, the distance detection device 3
This figure shows a case where the distance distribution between the object to be measured 1 and the wire 2 is measured while moving the distance detectors along the guide track 4.

If the straightness of the wire 2 does not change at all and is kept constant, an accurate surface profile of the object to be measured 1 can be determined from the distance distribution measurement result by the distance detection device 3. However, especially in measurement environments with temperature changes and vibrations, the tension of the wire may change due to minute displacements of the parts that fix both ends of the wire 2 or changes in the weight of the wire 2 due to minute deposits on the wire 2. The straightness of the wire 2 may change as shown in FIG.

This change in the straightness of the wire generally increases with the length of the wire, so if the object to be measured is a long object, this effect cannot be ignored. In such a case, the accuracy of measuring the surface profile of the object to be measured will deteriorate. Therefore, the natural frequency f of the wire 2 is measured by the natural frequency detection device 5, and from this natural frequency f, the change in the straightness of the wire 2, that is, the suspension amount is calculated by the calculation device 6, and this is used as the distance distribution measurement value. By correcting for , highly accurate surface profile measurements can be obtained. The natural frequency of the wire can be easily determined, for example, by applying vibration to the wire, detecting the change over time in the vibration amplitude of the wire using a displacement meter, and frequency-analyzing this data.

Next, a method for calculating the amount of suspension of the wire from the natural frequency f of the wire will be explained based on FIG. 2. Generally, the natural frequency of a wire is expressed as the length of the wire, the tension of the wire T, and the linear density of the wire σ. On the other hand, the amount of suspension of the wire (suspension curve) is expressed by taking the X-Y coordinates as shown in FIG.

(1) From equation (2), becomes.

Therefore, by measuring the natural frequency f of the wire, the catenary curve of the wire as shown in FIG. 2 can be calculated. By correcting the distance distribution measurements described above by this suspension amount, an accurate surface profile can be obtained even if the straightness of the wire changes.

FIG. 5 is an example of the results of measuring the relationship between wire tension T and natural frequency f. This example has a length of 2.4m and a thickness of 1φ.
A steel wire is used as the wire, and the changes in the output of the natural frequency detection device 5 when the tension of the wire is changed are plotted with circles. The theoretical value curve shown in the figure is based on the above equation (1). Also, Figure 6 shows an example of the relationship between the tension T of the wire and the amount of suspension at the center of the wire.One example is when a steel wire with a length of 2 m and a thickness of lφ is used as the wire. 0 For example, if this wire is stretched with a tension of 30 kg, this tension is ±1
When it changes by 0%, the amount of suspension changes by about 20 μm, which causes a measurement error. Actually, when using this wire, 5
It is desirable that the wire be stretched with a tension of 0 kg or more, but even in such a case, there is a risk of a measurement error of several microns in a measurement environment where the tension of the wire is likely to change. In such a case, it is necessary to indirectly detect the amount of change in tension using the natural frequency of the wire and correct it for highly accurate measurement.

FIGS. 3 and 4 are diagrams showing another embodiment of the present invention.

In the embodiment shown in FIG. 3, the distance detection device 3 is composed of a pair of distance detectors 11A and IIB. That is, the sum of the distance between the distance detector 11A on the upper side of the diagram and the measurement object 1 and the distance between the lower distance detector 11B and the wire 2 is taken, and the wire 2 of the measurement object 1 is used as a reference. This is surface profile data.

Further, in the embodiment shown in FIG. 4, the distance detecting device 3 is composed of a plurality of distance detecting devices 11A, IIB, 12A, 12B, . . . One distance detector is designed to also serve as a displacement meter 5 constituting the natural frequency detection device. This has the advantage that there is no need to separately provide a detection head of the natural frequency detection device.

Figure 7 shows an example of measuring the straightness of a rod-shaped body with a length of 2 m using the device configuration shown in Figure 4. In Figure 7, the solid line indicates the results measured by a contact displacement meter, and the broken line indicates the results according to the present invention. In the measurement results, the - dotted line shows the measurement results by the conventional method using the straight edge as the standard of straightness.In the conventional method, a measurement error of about 10μ occurred due to the deflection of the straight edge itself, but the measurement results according to the present invention The results agreed well with the measured values from the contact displacement meter.

[Effects of the Invention] The present invention uses a wire installed parallel to the object to be measured as a straightness standard for measuring the surface profile, and further calculates the minute amount of suspension of this wire from the natural frequency of the wire. By compensating for measurement errors due to suspension, highly accurate surface profile measurements using accurate straightness standards are now possible. In particular, when the object to be measured is a long object, the conventional method of simply erecting a straightness standard results in large measurement errors due to changes in the straightness of the straightness standard itself, which greatly reduces the effectiveness of the method of the present invention. Demonstrated.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing one embodiment of the present invention, Fig. 2 is a schematic diagram showing the measurement principle of the present invention, Fig. 3 is a schematic diagram showing another embodiment of the invention, and Fig. 4 is a schematic diagram showing the measurement principle of the present invention. A schematic diagram showing still another embodiment of the invention, FIG. 5 is a diagram showing the relationship between wire tension and natural frequency, FIG. 6 is a diagram showing the relationship between wire tension and suspension amount, and FIG. 7 8 is a diagram showing an example of a measurement result according to the present invention, and FIG. 8 is a schematic diagram showing the principle of a conventional surface profile measurement method. DESCRIPTION OF SYMBOLS 1... Measurement object, 2... Wire 3... Distance detection device, 4... Guide track, 5... Natural frequency detection device, 6... Arithmetic device.

Claims (2)

[Claims] (1) When measuring the surface profile of an object, a straightness reference wire is stretched parallel to the object to be measured, and the distance distribution between the wire and the object to be measured is measured,
Measuring the natural frequency of the wire, calculating the amount of suspension of the wire from the natural frequency, and determining the surface profile of the object to be measured from the measured distance distribution value and the amount of suspension, Surface profile measurement method. (2) a wire stretched parallel to the object to be measured; a distance detection device that measures the distance distribution between the wire and the object; a natural frequency detection device that detects the natural frequency of the wire; A surface profile measurement comprising: an arithmetic device that calculates the amount of suspension of the wire from the natural frequency and calculates the surface profile of the object to be measured from the amount of wire suspension and the distance distribution measurement value. Device.