HU185306B - Device for contactless detecting surfacial quality of the moving material - Google Patents

Abstract

The present invention relates to a device for determining the contact quality of a surface of a moving material without contact with an optical heterodyne unit (10), a light sensor (20) and a signal processing unit (40) connected to the light sensor. The essence is that the signal processing unit (40) is a preamplifier (41), a variable gain amplifier (43), a selective amplifier (42) coupled between the preamplifier (41) and the variable gain amplifier (43) as needed, and a variable gain amplifier (42). 43) to a monostable multivibrator (48) and a timing unit (49) for measuring the output width of the monostable multivibrator (48). -1-

Description

(57) EXTRAS

The present invention relates to an apparatus for contactless determination of the surface quality of a moving material having an optical heterodyn unit (10), a light sensor (20) and a processing unit (40) coupled to the light sensor. In essence, the signal processing unit (40) has a preamplifier (41), a variable gain amplifier (43), a selective amplifier (42) coupled between a preamplifier (41) and a variable gain amplifier (43) as needed, and a variable gain amplifier (42). 43) is connected via a comparator (47) connected to its output to a monostable multivibrator (48) and a timing unit (49) measuring the output signal width of the monostable multivibrator (48).

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The present invention relates to an apparatus for continuously determining the surface quality (roughness or smoothness) of a moving material having an optical heterodyn unit, a light sensor and a signal processing unit coupled to the light sensor.

Many methods and equipment are known for contactless testing of surface quality. The most common of these is pneumatic methods, where surface quality is characterized by the amount of air passing through a gap between the surface shapes of the material and a probe (such as a flat counter surface) at a specified pressure. Parker-Print Surf (PPSa), Bekk, Bendtsen and Sheffield operate on this or similar principle. Their common disadvantage is that they do not provide information on the shape and distribution of surface shapes, and the surface quality measure can be the same for different microgeometries. In addition, different devices provide different metrics when measuring the same surface, so the results obtained with each device do not correlate with each other. In addition, the surface to be certified must not move during measurement, so continuous in-process control (for example, in papermaking) cannot be performed.

Another known method is the so-called. Optical evaluation of the contact ratio by means of, for example, Fogra-KAM. The essence of this method is to illuminate the material to be classified through a prism printed on its surface, and to examine the percentage of the illuminated surface that does not have full reflection due to the perfect contact between the prism and the test surface. This gives them a percentage of smoothness. So this method also provides a single metric. However, it has the advantage over pneumatic methods that, for example, when examining paper surfaces, a very good correlation was found between the measurement data obtained with the fygra-KAM device and the print debris. However, it also has the disadvantage that the material to be tested must be sampled beforehand, ie it cannot be used for production measurement or continuous monitoring.

No. 1,507,702. The Canadian patent describes a method and apparatus for overcoming the latter defect, for example by continuously examining the surface quality of the paper during manufacture. The solution is to illuminate the surface of a moving object (such as paper) with a common light source, collect light scattered from the surface in a different direction on a detector surface, and then process the electrical signal of the detector proportional to the intensity of the scattered light. (DC) and AC (AC) components, and their quotient defines a measure of surface quality. The results obtained are correlated with those of the Sheffield apparatus (pneumatic method). Since the measure of any pneumatic method is essentially a barrier property of the surface against gas flow, no good correlation is expected - as can be seen in the graph presented in the patent. However, this does not mean the main disadvantage of the solution, but the fact that it measures surface quality with a single measure, which is difficult to correlate with the measures of other methods, while at the same time obtaining the same measure with different microgeometry of the paper surface. Another problem is that since the intensity of the scattered light is very low, it is necessary to ensure that no light is emitted into the detector in order to obtain the correct signal-to-noise ratio, i.e. the optics and detector should be placed close to the surface to be measured.

In summary, each of the conventional methods requires one of two conditions that cannot be required in production. These conditions are: removal of the test surface from the production process, which does not allow continuous testing; No. 1,507,702, permitting continuous examination and, in the case of a Canadian patent, the elimination of the effects of external interfering lights.

This latter problem can be overcome by using coherent light (e.g., laser) as the light source and detecting diffused light by a heterodyn method. This type of process and equipment is known from T / 24,697. Hungarian patent application published under. The solution allows low light intensities to be detected with high sensitivity and does not require interferometric adjustment accuracy. It is stated in the patent that, when the surface to be examined consists of well-defined elements, the size of these elements in the direction of motion can be determined by processing the heterodyn signal.

However, most of the surfaces (including the paper surface, for example) are not so, their irregularities vary over a wide size range, which is much larger than the wavelength of light, and the length of the wave packets in the signal is not clearly defined. Such a surface can be considered macroscopically coarse with respect to light scattering and should be subjected to statistical evaluation for diffused light. The surface quality of such surfaces cannot be directly determined using the method and apparatus described in this patent application, nor does it allow the production of compressible data.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an apparatus for eliminating the problems encountered in the conventional surface classifications described above and for making measurements in an industrial environment.

We have discovered that the solution contained in Hungarian Patent Application Publication No. T / 24 697 can be further developed using a heterodyn measuring device, which enables continuous measurement: the surface can be examined continuously during manufacture and the external interfering lights do not affect the measurement. Similarly, our aim is to make the process applicable to industrial conditions; this can also be achieved with the apparatus according to the invention, which is as follows:

It is known that when a surface is electromagnetic

185 306 waves, such as light, the roughness of the surface affects the propagation of the wave. In the case of a rough surface, the wave is reflected not only in the direction of reflection, but scattered in all directions. Even when this rough surface is moving, the frequency of its scattered waves changes due to the Doppler shift. Therefore, by studying diffused light, it is also possible to obtain information about the roughness of the surface, but this requires a statistical evaluation of the wave diffused by the surface, its reflected (ie smooth surface) and diffuse diffused portions. It can be shown ,. that if the amplitude of the resulting wave can be regarded as the fall of contributions from randomly distributed parts of the surface, then the probability distribution of the amplitude can be well determined. In general, however, we can say that the diffuse diffuse component, a probability variable, has some p (A) distribution function, the shape of which is not necessarily known.

It is obvious that the distributions measured from different elements of the surface depend on the quality of the surface. If the surface is illuminated continuously during movement, the probability that the intensity of the reflected light 1 over a given length is greater than a given intensity Ιθ can be described by a well-defined probability function which decays slowly on smooth surfaces and rapidly on rough surfaces. . The change of the function is called the so-called. correlation length, with a high value for smooth and a low value for rough surfaces. '__

With the help of correlation lengths it is possible to compare surfaces with the same microscopic roughness.

The method underlying the apparatus of the invention is thus the use of optical heterodyn detection to contactlessly determine the surface characteristics of a moving material by illuminating the surface with a coherent light source (e.g., a laser) and detecting reflected light by optical heterodynamic detection - R. Provides an electrical signal proportional to intensity, where A is the amplitude of light bounced from the surface and R is the amplitude of the reference or local oscillator light. The frequency of the resulting electrical signal corresponds to the Doppler diffusion frequency of the light reflected from the moving surface. By bringing the U electrical signal to a workable level, we compare it with a predetermined electrical level U _k - k · I _n and examine the time intervals t over the U _k level. The time interval t on the moving surface corresponds to a segment of length X = v · l, where v is a component of the velocity of the moving surface perpendicular to the light beam. The frequency distribution of the various t intervals and their corresponding section lengths, which can be measured by known methods, gives exactly the probability function from which the correlation lengths and other quantities characteristic of the moving material surface can be determined.

Choosing the correct correlation length is crucial. This can be done by optically selecting the optics or electronically by not yet issuing the end-of-interval signal at the time corresponding to the end of the measurement interval, when the U electrical signal falls below the U _k level, if, within this waiting time T, the signal does not return above the level U _k , then the interval is considered complete. If, within the waiting time T, the electrical signal is above _the level U _k , the interval continues and, once again, the waiting time T is resumed. Thus, shorter signal fluctuations than né do not affect the measurement.

To achieve this object, a device is provided for contactless determination of the surface quality of a moving material having an optical heterodyn unit, a light sensor and a signal processing unit coupled to a light sensor, and according to the invention, the light sensor via a comparator and a monostable multivibrator, a timing unit for measuring the output signal width of the monostable multivibrator is connected to the variable amplifier output.

In a preferred embodiment of the apparatus according to the invention, a variable gain amplifier output is connected to a rectifier, an rectifier output integrator, an error signal amplifier is connected to an integrator output, and a variable gain output is connected to the variable gain actuator input. Preferably, the comparator is configured such that its level of comparability is variable, and the monostable multivibrator can be restarted and adjusted with a tilt time unit in time.

With the device of the invention, the effect of shorter signal fluctuation can be eliminated and a value characteristic of surface quality can be obtained.

The invention will be described in more detail with reference to the drawings, in which an exemplary embodiment of the invention is shown. In the drawing it is

Figure 1 illustrates an apparatus according to the invention as an example. while the

Figures 2 and 3 illustrate changes in the signals displayed in the apparatus over time. ·

The apparatus shown in Figure 1 is used to examine the surface of papers and to determine the statistical size distribution function.

The paper to be measured is mounted on the periphery of a rotating roll 30. The paper 31 has a beam of light emitted from a coherent light source 11 at a measuring point 32 at 32 measurement points. The optical heterodynamic unit 10 is a beam divider 12, preferably a planar parallelepiped element 13, preferably comprising a lens. In the path of the beam diverted by the beam splitter 12, there is a light sensor 20, preferably a photodiode, the electrical output of which is connected to a signal processing unit 40.

The diameter of the light beam at the 32 measuring points is preferably a few pm. At the 32 measurement points, the light is scattered, and the portion of this scattered light that is correctly oriented and phase-oriented,

185 to 306 optical heterodyn units, with 20 light sensor outputs, generates 2V VAT-f-— sina c electrical signal, where VAT is heterodyn frequency, wood laser frequency, V is the peripheral speed of the rotating cylinder 30, and c is the incident light angle, relative to the light beam. The amplitude of this electrical signal is representative of the reflectivity of the surface 31 and its position relative to the incident light beam at the measurement point 32. If the reflection coefficient of the surface 31 is constant, in most cases constant, the amplitude modulation of the signal at the output of the light sensor 20 is caused solely by the unevenness, circumferential and radial distribution of the surface 31.

The rotating cylinder 30 also performs slow alternating movement in the direction of the axis of rotation. Thus, the measuring point 32 can scan the entire surface 31 and, by analyzing the electrical signal at the output of the light sensor 20, determine the desired characteristics of the entire surface 31.

The operation of the apparatus according to the invention is as follows. In the optical heterodynic unit 10, one part of the light beam produced by the coherent light source 11 advances in the original direction to the measuring point 32 of the surface 31, while the other part R reaches the surface of the light sensor 20, preferably the photodiode. The measurement point 32 is the focal point of the optical imaging element 13. At the focal point, the diameter of the light spot essentially determines the resolution of the device. The optical imaging element 13 is mechanically adjustable relative to the surface 31 to provide the best possible measurement conditions.

If a 50 mm focal length lens and a 2 mm beam He-Ne laser are used, the diameter of the light spot may be about 15 µm. This value is sufficient for most paper surface tests.

A portion of the light scattered at the measuring point 32 is transmitted through the optical imaging element 13 and the beam splitter 12 to the coherent light source coupling element, such as a laser mirror, which is reflected to the beam splitter 12 from where E is transmitted to the light sensor 20. In this way, a portion of the scattered light transmitted to the surface of the light sensor 20, which is coherent in phase, interferes with direct laser light. Thus, the output of the light sensor 20 has an electric frequency of VAT and a corresponding U amplitude! appears, the probability characteristics of which are determined by the signal processing unit 40.

The electrical AC voltage provided by the light sensor 20 is amplified by a low-noise preamplifier 41. Because the useful signal voltage provided by the light detector member 20 is in most cases comparable to noise, a selective amplifier 42 is required to improve the signal-to-noise ratio, which only permits and amplifies the signal in a region of a few MHz, preferably within a few MHz. The output of the selective amplifier 42 is connected to the signal input of a controlled gain amplifier 43. The output of the controlled gain amplifier 43 has an average value of the appropriate U, constant over a long period of time and is independent of the magnitude of the signal at its input. This is done by rectifying the U 1 signal with rectifier 44 and then averaging it with an integrator 45 whose integration time constant is sufficiently large. The output of the integrator 45 is connected to one of the inputs of the error amplifier 46, while the other input is connected to a constant direct voltage U _r . If the output voltage of the integrator 45 is different from the voltage U _r , the output voltage of the error amplifier 46 as an actuator signal controls the gain of the variable gain amplifier 43 accordingly. The voltage U _s is connected to one of the inputs of the comparator 47, while the other input is connected to a variable voltage U _k . It is advisable to set the value of _the level U _k so that its absolute value is equal to the average value of the voltage U _s . When the voltage U ₁ exceeds the level U _k , a trigger pulse is output at the output of the comparator 47 for a monostable multivibrator with variable tilt time 48. The monostable multivibrator 48 can be restarted in time, and the tilt time T is also the resolution time.

Optical resolution is determined by the size of the focal spot and is difficult to change when calibrated, it is much easier to change the resolution electronically. Size resolution will eventually be characterized by the amount of VTcosx + d.

The output of the monostable multivibrator 48 is pulsed with the same amplitude but different widths for the 49 timer, preferably multi-channel analyzer used in the time analysis mode. The width of the U _p pulses is measured and stored in 50 units. The measurement result is directly the desired distribution function, from which the surface properties can be easily derived by mathematical methods.

Figure 3 shows an example of the voltage amplitude distribution U 1 and the U pulses generated from the voltage U 1. By replacing the position of the rotating roller 30 shown in Fig. 1 with a roll of a papermaking or printing machine, and adding the on-line evaluating unit 50 to the timing unit 49, which continuously produces the paper surface values or the resulting Fogra-K AM during measurement. , it is possible to continuously measure and control the surface quality providing non-contact compressible information during manufacture or use, and to adjust any industrial equipment accordingly.

Claims (3)

An apparatus for contactless determination of the surface quality of a moving material having an optical heterodyn unit, a light sensor and a signal processing unit coupled to the light sensor, characterized in that the light sensor (20) is connected to a preamplifier (41) in the signal processing unit (40). and, if necessary, through a variable gain amplifier (43) to a selective amplifier (42) and to the output of the variable gain amplifier (43) via a comparator (47) and a mono-41 Through 185,306 Stable Bubble Vibrators (48) in the Monoslab! a timing unit (49) for measuring the output signal width of the multivibrator (48) is connected. An embodiment of the apparatus according to claim 1, characterized in that a rectifier (44) is connected to the output of the variable gain amplifier (43), an integrator (45) is connected to the output of the rectifier, and a variable gain amplifier is connected to the output of the integrator. The actuator signal input (43) is connected to the output of the error amplifier (46). 3. Apparatus according to claim 1 or 2 5 embodiment, wherein the variable comparation level and resettable and variable tilt time (T) is monostable multivibrátora on time (48) (U _k) a comparator (47). 3 pieces of figure -5185 306