JPH0518717A - External diameter measuring apparatus - Google Patents

Abstract

PURPOSE:To output laser light with low interfering ability to a measurement object and measure the external diameter with little error at constant and high slability by limiting the intensity amplitude alteration of a diffraction image of an edge of the measurement object at laser light source to a noise level. CONSTITUTION:A laser light source 3 oscillates with the intensity amplitude alteration DELTA of an edge diffraction image of a measurement object W formed by the laser light from the light source being below noise contained in the laser light. The light source 3 mixes not stabilized light with various wavelength and carrys out multi-mode oscillation and emits laser light to the measurement object W through a light deflector 5 to carry out scanning. Here, in the case of using a He-Ne laser for the light source 3, there are spontaneously emitting light noise, beat noise, discharging current noise, mechanical vibration noise, noise by dust, which become a noise source, as the noise and the noise level is several % or less as light intensity. By making the interfering ability of the light source low, the alteration of the measured value becomes little and constantly stable external diameter measurement becomes possible while being scarcely affected even if the environmental temperature changes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an outer diameter measuring machine for measuring the outer diameter of, for example, a metal wire, a glass tube, an optical fiber or the like in an in-line process.

[0002]

2. Description of the Related Art For continuously produced wires such as metal wires and optical fibers, the outer diameter is measured in an in-line process such as manufacturing and inspection for quick quality control. As a measuring instrument in this case, a laser beam scanning type outer diameter measuring instrument capable of non-contact, high-speed and highly accurate measurement is generally used.

FIG. 6 shows a principle structure of such a laser beam scanning type outer diameter measuring machine. The configuration and measuring principle of the outer diameter measuring machine will be described below. The outer diameter measuring machine includes an optical system 1 that scans the object to be measured W with a laser beam, and a signal processing system 2 that demodulates a signal from the optical system 1 and converts the signal into a signal proportional to the outer diameter of the object to be measured W. It has a general structure. The optical system 1 includes a laser light source 3 that outputs laser light of a predetermined wavelength, an optical deflector 5 that deflects the laser light by a reflection mirror 4, a lens 6 that makes the deflected laser light parallel light, and one of the deflected laser light. A monitor circuit 7 for taking out a portion, and a light receiving circuit 8 for scanning the object to be measured W and receiving the laser light that has passed therethrough are configured. Then, in this optical system 1, when the laser light is incident on the reflection mirror 4 of the optical deflector 5 and is deflected and is made into parallel light by the lens 6 and passes through, the space in which the object to be measured W is placed is moved in the Y-axis direction. Scan sinusoidally. DUT W
The laser light scanned by is condensed on the light receiver of the light receiving circuit 8 and becomes an electric signal Q1 by photoelectric conversion. Further, a part of the laser light deflected by the optical deflector 5 is part of the monitor circuit 7.
Is taken out by the scanner and converted into monitor signals Q2 and Q3 for detecting the phase and amplitude of the scanning beam.

Here, FIG. 7 shows the relationship between the position of the laser beam scanning over the object to be measured W and the received light signal Q1 with the horizontal axis as the time axis. In the figure, the position of the scanning beam is S = S ₀ s
Let inω ₀ t and Ra and Rb be the positions of both edges of the object to be measured W that is stationary in the scanning space, the received light signal Q1 falls at time ta1 when the scanning beam passes the edge Ra, and the edge Rb is It rises at time tb1 when passing. As a result, the following relationships are established. Ra = S ₀ sinω ₀ ta 1 Rb = S ₀ sinω ₀ tb 1 (1)

On the other hand, the signal processing system 2 outputs a constant pulse signal based on the received light signal Q1, and a reference signal V = V ₀ for simulating the position of the scanning beam based on the monitor signals Q2 and Q3. Reference signal generator 10 for generating sin ω ₀ t, and sample and hold circuit 1 for sampling and holding each voltage of the reference signal based on the pulse signal
1 and 12, a differential amplifier 13 that differentially amplifies each sampled and held signal, and an A / D converter 14 that converts the amplified signal into a digital signal.

In this signal processing system 2, the two sample hold circuits 11 and 12 sample and hold the voltage V of the reference signal at times ta1 and tb1 as shown in FIGS. 7 (a) and 7 (b). As shown in FIG. 7C, a voltage Va corresponding to the positions Ra and Rb of the edge of the object W to be measured.
1 and Vb1 are generated. The voltages Va1 and Vb1 are converted from the equation (1) into the following equation: Va1 = V ₀ sinω ₀ ta1 = (V ₀ / S ₀ ) Ra (2) Vb1 = V ₀ sinω ₀ tb1 = (V ₀ / S ₀ ) Rb (3) These difference voltages V D1 are V D1 = Va1-Vb1 =
(V ₀ / S ₀ ) d, which is proportional to the outer diameter of the object W to be measured. As shown in FIG. 7D, this outer diameter voltage V Dn is held only for a value detected by one scan until the end of the next scan in the opposite direction (π / ω ₀ ), and A / D After the conversion, it is taken in by the CPU (not shown). CP
The data taken in U is processed according to various parameters such as the average number of times, target value, and upper and lower limit values set from a keyboard which is an external device, and the measurement data obtained by this processing is processed by a display controller, for example, LED. Is displayed.

[0007]

As is clear from the above principle, this type of outer diameter measuring machine is a light-shielding type measuring machine that utilizes the fact that a minute spot of laser light is blocked by the object to be measured. The change in the light energy incident on the light receiving circuit caused by the light shielding is photoelectrically converted and detected. In order to increase the S / N ratio of the photoelectric signal, the light source used at this time is preferably a so-called high-luminance light source having high energy density and good light converging property. Further, if the beam shape of the minute spot is a Gaussian shape with good symmetry along the scanning direction of the laser light, harmonics are not superimposed on the falling and rising waveforms of the square wave signal Q1 obtained from the light receiving circuit. It is possible to detect edges with high accuracy. Laser light is widely used as a light source for satisfying the above conditions.

However, due to the high coherence of the laser light depending on the object to be measured, if the measurement system is configured with a finite light receiving aperture, the received light energy is affected by the interference fringes and only the outer diameter variation occurs. Can be difficult to extract. For example, in an optical fiber with high light transmittance, since the beam diameter is finite, the light diffracted by the edge, the reflected light near the edge, and the light refracted into the fiber repeats internal reflection, and a part of the light leaked to the outside is As a result of interfering with the diffracted light or the reflected light, it is influenced by the wavelength change of the light source due to the temperature change, the circularity of the fiber, the uniformity of the refractive index, etc., and the fluctuation thereof appears in the outer diameter measurement output. Can be seen. In FIG. 3, a single-wavelength semiconductor laser light is used as a light source.
When a 5 μm optical fiber is held and the outside air temperature is changed between 0 and 40 degrees, the oscillation frequency of the laser light shifts abruptly (longitudinal mode hop) and its effect on the outer diameter measurement output. It is what is shown. In order to remove this phenomenon, a method using a frequency-stabilized laser or the like has been conventionally proposed, but this cannot remove the effect of the change in the structural parameter of the fiber.

Similarly, even when a metal wire coated with a transparent body with a thickness of a fraction or less of the size of the spot diameter around a metal having a high reflectance is used as an object to be measured, There is a problem that the diffracted light, the reflected light near the edge, and the light refracted in the coating are reflected by the metal wire, and the interference of these rays makes it impossible to measure the actual outer diameter variation.

Therefore, the present invention has been made in view of the above-mentioned problems, and an object thereof is to provide an outer diameter measuring machine which can always perform outer diameter measurement with high stability and little error in an in-line process. To provide.

[0011]

In order to achieve the above-mentioned object, an outer diameter measuring machine according to the present invention scans an object to be measured with a laser beam, and based on the detection of the timing at which the laser beam is blocked by the scanning. An outer diameter measuring machine for measuring an outer diameter of the object to be measured is characterized by comprising a low coherence laser light source in which a change in intensity amplitude of a diffraction image of an edge of the object to be measured is below a noise level. ..

[0012]

[Function] By setting the intensity amplitude change of the diffraction image of the edge of the object to be measured in the laser light source to be equal to or less than the noise level, laser light with low coherence is output to the object to be measured via the optical deflector and always stable. Outer diameter measurement with high accuracy and little error is performed.

[0013]

EXAMPLE An outer diameter measuring machine according to this example is used for measuring an object W to be measured.
For example, when measuring the outer diameter of a metal wire, a glass tube, an optical fiber, or the like in an in-line process, a laser light source with low coherence is provided in order to always realize a highly stable measurement.

To explain further, this laser light source is shown in FIG.
The intensity amplitude change Δ of the edge diffraction image of the DUT formed by the laser light from the light source shown in (1) oscillates at the noise level included in the laser light or less. Then, this laser light source mixes lights of various wavelengths which are not stabilized and oscillates in a multimode, and emits laser light to an object to be measured through an optical deflector to perform scanning.

Here, the noise is He-N in the light source.
When an e-laser is used, it is light that does not depend on stimulated emission and is a spontaneous emission light noise that becomes a large noise source near the laser oscillation threshold, beat noise generated by beats between modes,
There are discharge current noise due to plasma vibration in the discharge path of the laser tube due to discharge current, noise due to mechanical vibration of the resonator, noise due to dust inside the resonator, etc. is there.

Next, FIG. 2 shows the temperature characteristics when the outer diameter is measured with the object to be measured fixedly held and the outside air temperature arbitrarily changing, for example, between 0 and 40 degrees. Shows. From this figure, by reducing the coherence of the light source, there is little change in the measured value even when the outside air temperature changes, the influence on the measured value is extremely small, and stable outer diameter measurement is always possible. It turns out that

Next, FIG. 4 shows the relationship between the data of the length measuring device and the measured data for each position of the optical fiber when the laser light source with low coherence according to the present invention is used and the optical fiber is fixed. ing. Compared to FIG. 5 using the single-polarization laser light source, in the case of using the single-polarization laser light source, the distance between the data measured by the outer diameter measuring device and the data measured by the length measuring device is measured over the entire length of the optical fiber. While the absolute value error is not constant, in the case of using the laser light source with low coherence according to the present invention, the absolute value error between the data measured by the outer diameter measuring device and the data of the length measuring device is an optical error. It is constant over the entire length of the fiber.

Then, the absolute value error between the data measured by the outer diameter measuring device and the data measured by the length measuring device should be calibrated by shifting by the same value over the entire length of the optical fiber. Therefore, the measured data by the outer diameter measuring device of FIG. 4 shows almost the same value as the data by the length measuring device, and by using the laser light source of the present invention, the outer diameter measurement is always stable with an extremely small error. Obviously, it can be done.

In the above-mentioned embodiment, the case where the tuning fork vibrator is used as the optical deflector has been illustrated and described, but the one using the rotating mirror which has been conventionally used is also the same as the above-mentioned embodiment. The effect can be obtained.

[0020]

As described above, according to the outer diameter measuring machine of the present invention, a laser light source having a low coherence in which the intensity amplitude change of the diffraction image of the edge of the object to be measured is below the noise level is provided. Therefore, there is an effect that the outer diameter can always be measured in an in-line process with high stability and little error.

[Brief description of drawings]

FIG. 1 is a diagram showing a change in intensity amplitude of a diffraction image of an object to be measured which is formed by laser light output from a laser light source of an outer diameter measuring instrument according to the present invention.

FIG. 2 shows an outer diameter measuring device according to the present invention, which uses a laser light source having low coherence and holds an object to be measured fixedly, while changing the outer air temperature from 0 to 40 degrees. Diagram showing wavelength characteristics when measurement is performed

FIG. 3 shows a case where an unstabilized single-polarized laser is used as a light source, and an outer diameter is measured while the temperature of an object to be measured is fixed and changed while changing the outside air temperature between 0 degrees and 40 degrees. Diagram showing wavelength characteristics

FIG. 4 shows the relationship between the data of the length measuring machine and the measured data for each position of the optical fiber in a state where the laser light source with low coherence is used in the outer diameter measuring device according to the present invention and the optical fiber is fixed. Figure

FIG. 5 is a diagram showing a relationship between length measuring instrument data and measurement data for each position of an optical fiber in a state where the single polarization laser which is not stabilized is used as a light source and the optical fiber is fixed.

FIG. 6 is a configuration diagram for explaining the measurement principle of the outer diameter measuring machine.

FIG. 7 is a diagram showing the relationship between the position of the laser beam scanning the object to be measured and the received light signal Q1 with the horizontal axis as the time axis.

FIG. 8 is a diagram showing a configuration example of a conventional outer diameter measuring machine.

[Explanation of symbols]

 1 Optical System 2 Signal Processing System 3 Laser Light Source W DUT

Claims (1)

1. An outer diameter measuring machine for scanning an object to be measured with a laser beam and measuring an outer diameter of the object to be measured based on detection of a timing at which the laser beam is shielded by the scanning. 2. An outer diameter measuring machine, comprising: a laser light source having a low coherence in which a change in intensity amplitude of a diffraction image of an edge of the object to be measured is equal to or lower than a noise level.