JPS6177709A - Surface roughness tester - Google Patents

Abstract

PURPOSE:To make it possible to perform highly sensitive measurement, by providing an operating means, which obtains the surface roughness of a body to be measured, based on contrast data of a contrast operating means and corresponding data of a corresponding data table. CONSTITUTION:A central processing unit (CPU)14 comprises a microprocessor and the like, operates in accordance with algorithm specified by programs in a ROM17, computes the surface roughness of a body to be measured 7 based on the data received by an A/D converter 13, displays the results on a display device 19 and records the results with a plotter 20. Based on the image data including a speckle pattern from the A/D converter 13, at first contrast is computed. In a RAM18, a data table, which shows the corresponding relation of the contrast data of the speckle pattern and the surface roughness data, is formed beforehand. Based on the data table, the surface roughness is obtained from the computed contrast data. Thus the highly sensitive measurement can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention provides a method for transmitting coherent light from a laser to a measured object (
The present invention relates to a device that measures surface roughness by irradiating the surface of an object (with a rough surface) and using a speckle pattern generated by the diffusely reflected light.

(Background of the Invention) The measurement principle of this type of surface roughness measuring device has been well known for a long time, and is described in detail in, for example, Japanese Patent Laid-Open No. 51-124454.

However, the conventional surface roughness measurement device of this type uses a gas laser as a coherent light source and a photomultiplier tube as a photodetector to measure the intensity distribution (contrast) of the speckle pattern. I am using it.

Since this device uses a gas laser, it is extremely large and cannot be used in various surface processing sites. Furthermore, in order to measure the intensity distribution of a speckle pattern using a photomultiplier tube, a mechanical scanning mechanism is absolutely necessary, which increases the size of the device and makes it impossible to perform high-speed measurements with mechanical scanning. There were other problems.

(Objective of the Invention) The present invention has been made in view of the above-mentioned problems, and its purpose is to provide a surface roughness measuring device that can overcome the following technical problems.

First, when measuring the roughness of the surface of the object to be measured, the surface of the object to be measured must not be scratched.

Roughness can be measured in-process, semi-in-process, or online, and measurement can be performed even when the object to be measured moves at high speed.In particular, it is possible to perform mechanical operations without interrupting machining operations for measurement. It has no mechanism, is small and lightweight, and has good operability.

Measurements must be performed with high sensitivity, high precision, and high speed, with extremely high performance.

mechanical,! High environmental resistance against atmospheric or other ambient conditions.

It has a long lifespan, is low cost, and has stable measurement operation.

Furthermore, highly accurate measurement is possible without being affected even if the low frequency component of the intensity distribution of the reflected light from the object to be measured changes.

(Structure and Effects of the Invention) In order to achieve the above object, the surface roughness measuring device according to the present invention includes a semiconductor laser that generates coherent light for measurement, and a laser single-time control that controls the temperature condition of the semiconductor laser to be constant. system, an emission intensity control circuit that stabilizes the emission intensity of the semiconductor laser, an optical system that irradiates the coherent light of the semiconductor laser onto the surface of the object to be measured, and specs caused by diffuse reflection on the surface of the object to be measured. A self-scanning solid-state image sensor that converts changes in the LA element into an electrical signal, a sample-and-hold circuit that holds the electrical signal value of the self-scanning solid-state LA element for a predetermined period of time, and an electrical signal held in the sample-and-hold circuit. an analog-to-digital converter that converts the value into a digital quantity; an I/O port that interfaces the analog-to-digital converter with the central processing unit; and an I/O port that provides timing signals to the sample-and-hold circuit. a direct memory access controller that stores electrical signal values supplied to the random access memory in a random access memory; a contrast calculation means that calculates contrast data of a speckle pattern based on the electrical signal values stored in the random access memory; It has a corresponding data table storing data corresponding to the roughness data, and a surface roughness simulation means for calculating the roughness of the surface of the object to be measured based on the contrast data of the contrast calculation means and the corresponding data of the corresponding data table. It is characterized by

According to the present invention, many of the following effects can be obtained in the surface roughness measuring device.

First, since laser speckle is used for roughness measurement, the following effects can be obtained.

In contrast to the general proximal method, which measures roughness along a line, it is now possible to measure roughness along a line.

Since the measuring member does not come into contact with the surface of the object to be measured for roughness measurement, the surface of the object to be measured will not be damaged.

Since it utilizes the interference phenomenon of light, it can be measured on the order of wavelengths, making it possible to perform highly sensitive measurements.

Highly accurate measurement becomes possible by performing statistical calculation processing on a large amount of data.

In-process measurement, semi-in-process measurement, or online measurement can be performed at metal processing sites and various surface treatment sites such as painting, and the measurement can be performed even when the object to be measured moves at high speed.

It can also be used as a flaw detection sensor, so its application fields are extremely wide.

Furthermore, since the surface of the object to be measured that is being moved is the object of measurement, the following effects can be obtained.

For example, at a honing site, it becomes possible to perform measurements without interrupting the machining operation.

Since a self-scanning solid-state image device such as a COD can be used, a mechanical scanning mechanism is not required at all and a completely stationary type can be used. Therefore, there is no failure of mechanical movable parts, and furthermore, by making the device smaller, operability on site can be improved, high-speed data acquisition becomes possible, and the cost of the device can be reduced.

Furthermore, since a semiconductor laser is used, the following effects can be obtained.

By making the device smaller and lighter, it becomes possible to improve the operability and also to reduce the cost of the device.

Since its temperature and output are controlled, it has high environmental resistance against mechanical, electrical, and other ambient conditions (this makes it possible to stabilize the output and wavelength, and therefore enables stable measurements).

Moreover, since they are used, it is also possible to extend the life of the device.

And since it becomes possible to detect diffused light at one point,
It becomes possible to obtain the following effects.

The signal processing circuit in the input section can be simplified, resulting in high-speed A
/D conversion processing becomes possible.

Even if the low frequency component of the reflected light intensity distribution of the measured object changes,
Highly accurate measurement is possible without being affected by this.

Furthermore, since the DMA method is adopted, it is possible to obtain data at high speed.

In addition, microprocessor systems can be used,
It becomes possible to obtain the following effects.

High-speed data processing is possible, and new functions can be easily added by changing or adding software.

The operation during measurement is simplified, and it is therefore possible to improve the operability of the device.

Output format can be digital, analog, serial, parallel,
It can be freely selected from GB-IS, etc., and synchronization with external triggers is also easy.

In addition, by feeding back the measurement results to the processing machine in the form of an analog signal, it is possible to control the processing with high precision.

By connecting to a host computer, it is possible to create a factory automation system.

This device can also be used as an intelligent sensor.

(Description of Embodiments) FIG. 1 shows the overall configuration of a surface roughness measuring device according to this invention. In this device, a laser diode 1 is used as a coherent light source. The laser diode 1 is mounted in a control block 2 for stably performing laser oscillation by keeping temperature conditions constant.

The temperature control block 2 is provided with a Peltier element whose heat absorption and exhaustion is controlled by a temperature control circuit 3, and control is applied to keep the ambient temperature of the laser diode 1, which is detected by a temperature sensor 4, constant. In addition, in order to stabilize the emission intensity of the laser diode 1, an automatic power control t
An Il (APC) circuit 5 is provided. As a result, the laser diode 1 generates a stable laser beam with a single wavelength and intensity.

Coherent light from the laser diode 1 is irradiated onto the surface of the object to be measured 7 via the collimating lens 6 . The diffusely reflected light generated from the surface of the object to be measured 7 forms a speckle pattern, a part of which is received by the charge conversion element 11.

The photoelectric conversion element 11 is composed of a self-scanning solid-state image element such as a COD or a BBD, which is called a one-dimensional line sensor or a two-dimensional area sensor. The photoelectric conversion element 11 is driven and controlled by a drive circuit (not shown), and outputs an electric signal corresponding to the intensity distribution of the speckle pattern imaged on its imaging surface.

Furthermore, the electrical signal of the photoelectric conversion element 11 is supplied to a sample-and-hold circuit 12, and when the measured/fixed holiday 7 is moved, the photoelectric conversion element 11 generates a series of voltage signals corresponding to the intensity changes of the speckle pattern. is obtained.

The analog signal (voltage signal) held in the sample-and-hold circuit 12 is input to the A/D converter 13 and converted into a digital signal. That is, the received light intensity sampled by the sample-and-hold circuit 12 at a certain time is converted into a digital signal of a predetermined number of bits (for example, 8 bits to 14 bits) by the A/D converter 13, A series of digital signal strings having the number of data (for example, 2 bytes) corresponding to the number of samples are obtained at the output side of the A/D converter 13.

The DMA 16 provides a timing signal to the sample-and-hold circuit 12, and also stores data (image data including a speckle pattern from the A/D converter 13) inputted through the I10 port 15 into the RAM 18 at high speed.

The central processing unit (CPU) 14 is composed of a microprocessor, etc., operates according to the control algorithm and arithmetic processing algorithm prescribed in the program in the ROM 15, and operates on the object to be measured 7 based on the data taken in from the A/D converter 13. The surface roughness is calculated and displayed on the display 17 and recorded on the plotter 18.

That is, based on the image data including the speckle pattern from the A/D converter 13, the contrast (
intensity distribution) is calculated. Further, a data table showing the correspondence between speckle pattern contrast data and surface roughness data is created in advance in the RAM 16. Based on this data table, surface roughness data is determined from the calculated contrast data. This is displayed on the display 17 and recorded on the plotter 18.

FIG. 2 shows in detail the contents of the surface roughness calculation processing performed by the CPU 14. Hereinafter, the surface roughness calculation process will be explained in order according to this figure.

The CPU 14 first takes in image data for one scan of the solid-state image sensor 11 from the A/D converter 13 using the DMA 16 (step 100). Next, the image data for one scan is temporarily stored in the RAM 16 in the form of a histogram (
Step 101). Roughly, based on the image data stored in the RAM 16, an unsampled average value (statistical collective average) <I> of the received light intensity ■ of each pixel is calculated (step 102). Then, the root mean square of the intensity ■ Value <I2>
is calculated (step 103). Furthermore, the standard deviation σ of the intensity I is calculated based on the above <I> and <I2> (step 104). Roughly speaking, the above <l> and standard deviation σ
Calculate the contrast C-σ/〈■〉 based on (
Step 105).

As described above, the contrast C is calculated for one scan of image data of the optical imaging element 11.

Thereafter, as shown in step 106, the same processing and calculations as above are performed for a preset plurality of scans of the solid-state image sensor 11, and the average value of the contrast C obtained in the zero scans is determined. Then, if the average contrast C for n times is calculated, then based on that Ct, RA
The above data table set in M16 is retrieved and the surface roughness data R corresponding to C is determined (Step 1
07) FIGS. 3A, 8, and 3C show other examples of optical systems that irradiate the surface of the object 7 with coherent light.

In FIG. 3 (A>), an elliptical beam generated from the laser diode 1 and passed through the collimating lens 6 is converted into a perfect circular beam by a perfect circular optical system 61 using a prism or cylindrical lens, and is applied to the surface of the object to be measured 7. By making the irradiation beam a perfect circle in this way,
The power efficiency is good, the beam intensity distribution becomes Gaussian distribution or something similar to Gaussian distribution, and the measurement accuracy of surface roughness is improved.

In FIG. 3(B), the light from the laser diode 1 is passed through a beam splitter 62 to irradiate the surface of the object to be measured 7 with a polarized beam in a fixed direction. By irradiating the surface of the object to be measured 7 with the polarized beam in this manner, the contrast of the speckle pattern is increased and measurement accuracy is improved.

In FIG. 3(C), since both the above-mentioned perfect circular optical system 61 and the polarizing beam splitter 62 are used, both of the above-mentioned effects can be obtained.

4(A), (8), and (C) show an irradiation optical system in an embodiment in which two colors of coherent light of different wavelengths are superimposed on the surface of the object to be measured 7. figure(
A> shows its basic configuration. In this example, two types of laser diodes 1a and 1b with different emission wavelengths are used,
Coherent light from both is collimated by a collimating lens 6a.

6b, the two beams are overlapped by a mirror 63 and a Hartz mirror 64, and are irradiated onto the surface of the object to be measured 7.

In this case, the structure of the imaging system and the solid-state image element side may be the same as that shown in FIG.

In this way, by irradiating the surface of the object to be measured with two-color non-coherent light of different wavelengths, the measurement range of surface roughness can be expanded compared to the case of irradiating with single-color coherent light.

FIG. 4(B) shows a device in which, in addition to the device shown in FIG. In addition to the above configuration, a polarizing beam splitter 62 for polarizing the irradiation beam is provided.The effects of these components are as described above.

FIG. 5 shows another example of an optical system that receives diffusely reflected light from the surface of the object 7 to be measured.

The reflected light is received by an imaging optical system consisting of lenses 8 and 9 and an aperture 10, and a surface image of the object to be measured 7 including a speckle pattern is formed.

A photoelectric conversion element 11 is provided on this imaging plane, and the reflected light is detected by this element.

According to this example, by adjusting the size of the aperture of the diaphragm 10, the average size of speckles can be freely changed, so that speckle changes may be too fast or too slow compared to the processing capacity of the device. By adjusting the diaphragm 10, it is possible to always achieve a processing speed commensurate with the capacity of the vi and the machine.

Note that the object to be measured 7 is not limited to a case where it is moving in a plane, and may be the surface of a rotating body, for example, as shown in FIG. 6.

The materials to be measured include iron, non-ferrous metals including soft metal scraps, plastics, ceramics, rubber,
Possible examples include paper.

Specifically, VTR3 [13
Single parts, video cameras, polycon mirrors used in laser printing, etc. can be measured, and extremely good measurement results can be obtained especially when measuring these items.

Furthermore, this device can also be used as a flaw detection sensor, and if there is a flaw on the surface of the object to be measured 7 and this flaw enters the irradiation area of the coherent light, the speckle pattern will show a higher contrast than normal, and other parts will Since there is a noticeable difference in the contrast due to the average roughness of the scratches, it is possible to reliably detect these scratches.

And this device is made of film sheets, threads, and electric wires.

It is also possible to measure the roughness and flaw detection of linear objects such as fibers.
In addition, inspection of painted surfaces, interior design, and tombstones.

It can be used to measure a wide range of objects such as works of art.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the overall configuration of the apparatus according to the present invention, FIG. 2 is a flowchart showing the procedure of arithmetic processing for determining surface roughness performed by the CPU 14 in FIG. 1, and FIGS. 3 and 4 are A configuration explanatory diagram showing another example of an optical system that irradiates the surface of the object to be measured 7 with coherent light, and FIG. 5 is a configuration diagram showing another example of an optical system that receives diffuse reflected light from the surface of the object to be measured 7. The explanatory diagram, FIG. 6, is a configuration explanatory diagram showing another example of the object 7 to be measured. 1... Laser diode 2... Temperature control block 3... Temperature adjustment circuit 4... Temperature sensor 5... Automatic power control circuit 6... Collimating lens 7... Measured object 11. ...Charging conversion element 12...Sample and hold circuit 13...A/
D converter 14...Central processing unit 15...I/O port 17...DMA 18...RAM

Claims (1)

[Claims] (1) A semiconductor laser that generates coherent light for measurement, a laser temperature control system that keeps the temperature conditions of the semiconductor laser constant, a light emission intensity control circuit that stabilizes the light emission intensity of the semiconductor laser, and a moving object to be measured. An optical system that irradiates coherent light from a semiconductor laser onto the surface of the body, a self-scanning solid-state imaging device that converts changes in speckle patterns caused by diffuse reflection on the surface of the object into electrical signals, and a self-scanning solid-state imaging device. A sample and hold circuit that holds the electric signal value of the element for a predetermined period of time, an analog-digital converter that converts the electric signal value held in the sample-and-hold circuit into a digital quantity, an analog-digital converter and a central processing unit. an I/O port that interfaces with the sample-and-hold circuit; a direct memory access controller that provides timing signals to the sample-and-hold circuit and stores electrical signal values supplied through the I/O port to the random access memory; A contrast calculation means for calculating contrast data of a speckle pattern based on stored electrical signal values, a correspondence data table storing correspondence data between contrast data and surface roughness data, and contrast data and correspondence of the contrast calculation means. A surface roughness measuring device comprising: surface roughness calculating means for calculating the roughness of a surface of a measured object based on corresponding data in a data table.