DE4324800C2 - Device for determining defects of high quality surfaces - Google Patents

Description

The invention relates to a device in the preamble of Proverb 1 mentioned.

With such devices, surfaces of high quality, for example, optical surfaces of lenses or mirrors or other finely processed, e.g. B. polished surfaces on their Examine manufacturing quality. Depending on the desired subs Results can z. B. different quality classes or Committee can be determined.

The surface defects have different properties, at for example different size, different depth profile and different shapes in the surface (e.g. round Hole or elongated scratch). Determine the surface defects the quality of the test object depending on its shape and soluten size in different dimensions and are therefore according to the to evaluate these factors differently. It is also important that Surface defects and dust particles lying on the surface  can be differentiated to make dust-related wrong decisions to avoid gene.

Known devices use the fact that surfaces produce stray light. The angular distribution of the scattered light can be examined with a Fourier analysis and the form factor surface defect can be determined. The total intensity of the scattered light gives a measure of the absolute size of the error. The more precisely these factors are determined, the better it can be Classify surface defects and misinformation through distinguish adhering dust particles.

In order to obtain such precise information, one with a light beam, the scattered light over the Solid angle of the scattering is analyzed and it has to be extensive a statement about intensity and form factor is sufficient be hit. A quality assessment can be derived from this will.

Because the optical surface is scanned point by point and to determine small surface defects with a small measurement point must be worked, there is a very large number determining measuring points, in view of those for everyone Total complicated calculations to be carried out considerable amount of calculation.

From DE 41 05 509 A1 a device is known, which with the complicated mathematical formalism given there a very precise determination of surface form factors mistakes allowed. The working speed of this known front direction is therefore extremely slow.

Another device is known from DE 38 05 785 A1 scans with the high working speed of 2 MHz, thereby the Evaluation of the measurement results for a measuring point only with makes a greatly reduced, extremely simple formula of what  only a very rough estimate of the shape and type of waiter surface error results.

It should be noted here that today and in the foreseeable future ver available computers with a maximum clock frequency of 100 MHz a scanning frequency of 2 MHz per measuring point only very few Re can perform steps to obtain online form factors count. Should a device of the type mentioned to lau Quality control in a production line with a processing processing frequency of a few pieces per minute, So are with sufficient accuracy of the surface scan but sampling frequencies above 1 MHz are required.

From EP 0 249 798 A2 is a device of the beginning known type, for the purposes of online calculation data reduction is operated with reduced computing effort. The sensor signals from sensors of different viewing angles kel are with an analog addition and Ab weakening circuit offset to a signal, which then is digitally converted. However, this is a massive in formation loss connected. The possibilities of finer quality evaluations are strictly limited.

A similar method is described in DE 41 32 425 A1, at of the signals from two sensors with an OR circuit an output signal can be summarized. Hereby is only a simple yes / no statement can be determined.

The object of the present invention is to provide a to create direction of the type mentioned, which at high Ar speed allows a very precise quality assessment.

This object is achieved with the features of Identification part of claim 1 solved.

According to the invention, meh other MHz are scanned. There can be a larger number of  Sensors are used that have height angles and Raumwin are arranged distributed. The signals from the sensors become digi Talised and digitally processed, which also has the disadvantages of the prior art mentioned by partially analog signal processing is eliminated. According to the invention, not everyone will be pro Set of measurement values occurring on-line according to cost calculated against mathematical algorithms, but with tables compared. This way you can work in very few The required massive data reduction down to one Achieve quality assessment. To this end, the invention sees several series-connected reduction devices, each forms signals from several signals with regard to form factor and intensity have reduced content, i.e. are smaller. In several In this way, the high level of information from several sensors that take into account fine intensity  different with high bit resolution must be digitized, can be quickly reduced to the quality assessment included in the Memory locations of the last reducing device is included and which forms the output value of the evaluation device. In one strong This quality assessment can only be made from the simplified example both values "yes" (okay) and "no" (committee) exist. Of course, it can also be more complicated for quality assessment Classifications are used. Any previous reducer device performs a data reduction in parallel on two routes conditions by averaging intensity values and by summarizing form factor values. In this way it is ensured that in subsequent stages always intensity Values are available to form from intensity comparisons to determine factor values or, finally, from very strong intensity values a size statement about the surfaces to be able to make mistakes that are included in the quality assessment. The evaluation device required is relatively simple from Weni can be produced with integrated components to which no major components claims regarding the processing speed have to. Commercially available inexpensive memory chips are usable. Nevertheless, with a very high clock speed worked from measuring point to measuring point, i.e. a surface to be checked surface can be scanned in a short time, and it can be very make precise statements about the surface defects. Furthermore can be done by recalculating the reduction in the stores facilities available space very easily to other Be valuation systems are converted, the invention direction to very different test requirements be fitted. The ones saved in the memories can be saved Values in a highly complicated way using complex procedures be expected. The working speed of the device is there not affected by.

The features of claim 2 are advantageously provided. On in this way the principle of Table reading from memories can be used, just like to form the form factor values. That in every reduction  direction required two memories for form factor determination and the averaging can be done in a memory that is only logical is divided, structurally summarized.

Alternatively, the averaging can be done by simple sum Miereinrichtung according to claim 3.

The features of claim 4 are advantageously provided. This Embodiment takes advantage of the fact that shape anisotropies in the Plane of the surface that is attached at several circumferential angles ordered sensors can be determined, with sensors in small Elevation angles, that is, arranged close to the reflected beam, are easier to grasp while at higher elevation angles no more essential information is coming. Therefore simplify the evaluation device considerably by evaluation the sensors for larger elevation angles only by sum mening. Sensors for larger elevation angles can be advantageous also provided as a ring sensor for the entire elevation angle be. Only three sensors are advantageous in accordance with claim 5 a small elevation angle and one or more sen sensors at another higher elevation. After formation of the The evaluation device becomes the sum for the higher elevation angle only four signals fed. Then there are only two reducers simple training facilities required.

The features of claim 6 are advantageously provided. Here a strictly symmetrical arrangement of the sensors is possible Lich with simplified calculation of the sensor signals.

In the drawings, the invention is exemplary and schematic represented table. Show it:

Fig. 1 is a side view of the scanner of a erfindungsge MAESSEN device via a to be examined Lin senoberfläche in section according to line 1-1 in Fig. 2,

Fig. 2 is a view of the scanner taken along line 2-2 in Fig. 1,

Fig. 3 is a block diagram of an evaluation of a device with a total of six sensors, which are arranged in two elevation angles of three,

Fig. 4 is a block diagram of an evaluation device of a device with a total of four sensors, which are arranged at two height angles and

Fig. 5 is an evaluation device for a device with a total of eighteen sensors, each of which is arranged at six heights at three heights.

Fig. 1 shows a side view of a biconvex lens 1 , the upward, a scanning device 2 facing surface is scanned by the water. In the exemplary embodiment shown, the scanning device 2 has a circuit board 3 in the form of a circular disk, on the rear side of which a light source 4 , preferably a laser diode, generates a light beam 5 , which has a measuring point 7 on the surface of the circuit board through a central hole 6 in the circuit board 3 Illuminated lens 1 .

In the preferred embodiment, the scanning device 2 is guided by a drive (not shown) in such a way that the light beam 5 always strikes the surface at an angle of 90 ° and is thus reflected in itself. The light beam 5 thus consists of both the incoming and the reflected beam. The drive (not shown) for the scanning device 2 ensures that it scans the entire surface line by point point by point in the angular range shown in dashed lines.

On the side of the board 3 facing the surface to be scanned, light sensors are arranged, in the exemplary embodiment six sensors. These are, based on the light beam 5 and the point of origin in the measuring point 7 , arranged in different spatial angles, which are referred to below as the circumferential angle and height angle. The angular distance between the sensor and the light beam 5 is referred to as the height angle (origin at the measuring point 7 ) and the angle in the plane of the circuit board 3 as the circumferential angle.

The embodiment of FIGS. 1 and 2 consequently has three order angles and two elevation angles. Sensors A₁, A₂ and A₃ are symmetrically arranged in a first low elevation angle in order to 120 ° distance. Sensors B₁-B₃ are arranged at a larger angle at the same circumferential angles. The sensors A₁-A₃ can be attached and contacted directly on the circuit board 3 . The sensors B₁-B₃ are held on the supports shown in Fig. 1, which can simultaneously accommodate the leads.

All six sensors A₁-A₃ and B₁-B₃ are connected to an evaluation device, not shown, which is shown in a first exemplary embodiment in FIG. 3 as a block diagram.

In Fig. 3 above are marked with A₁-A₃ and B₁-B₃ signal lines, which come from the sensors shown in FIGS . 1 and 2 and lead analog brightness signals. In these lines lines are interposed with circles A / D converter 8 , with which the analog signals are converted into digital signals, in the example shown with the bit width 8 . The converted signals from the sensors are therefore 8-bit signals.

The bit width of all lines is shown in FIGS . 3-5 in each case in rectangular boxes marked on the lines.

According to Fig. 3, the digitized signals of the sensors A₁-A₃, which are at a low elevation angle in different circumferential order from the intermediate A / D converters 8 via the three lines shown, a first reducing device supplied from a memory 9 and an adder 10 , in parallel, as the line branch shows.

The adder 10 adds the signals on the three lines supplied and outputs an 8-bit sum signal to a line 14 which leads to the memory 11 of a second reducing device. The memory 9 receives the signals of the three lines coming from the sensors A₁-A₃ at address inputs. The signals are thus used as addresses for reading out the memory content of the memory 9 . In this case, values are stored in the memory locations of the memory which reflect form factors corresponding to the respective ratio of the signals supplied. These form factor values are also fed to the memory 11 with the bit width 4 on a line 15 .

The analog signals from the sensors B₁-B₃ of the larger height hen angle are supplied after digitization with 8 bit width to an ad dier 12 which supplies the sum signal to the memory 11 of the second reducing device on an output line 13 with 8 bit width.

So there is a first reducing device provided with the adder 10 generates an average (sum) of all signals of the sensors A₁-A₃, which is forwarded via line 14 , and with a memory 9 , which from the same signals from the sensors A₁ -A₃ by address reading of its memory locations generated values on its output line 15 , which form form factor values resulting from the circumferential angle distribution.

The memory 11 of the second reducing device consequently receives an average intensity signal from the first reducing device via line 14 and a form factor value via line 15 . He also receives from the three sensors B₁-B₃ via line 13 an average intensity of another (larger) Höhenwin angle.

The values on the lines 13 , 14 and 15 are in turn used in the memory 11 as addresses for reading out memory locations on which values are stored which form the output result of the evaluation device shown on an output line 16 . The values stored in the memory 11 are values for the quality assessment of the surface to be tested. They take into account both the form factor values for the surface anisotropy in the surface, which have already been determined in the memory 9 , and also for the shape profile values characteristic of the depth profile of surface defects, which are determined in the memory 11 by comparing the intensities of the two elevation angles, and they take into account the in the memory 11 taking into account the signals on the lines 13 and 14 , which are intensity signals, ascertainable total intensity.

The values stored in the memory 11 and read out on the line 16 can e.g. B. are only "yes" and "no". Then line 16 could only be a 1-bit line.

Fig. 4 shows another embodiment of the scanner, which is designed according to FIGS. 1 and 2 and also sen sensors in two elevation angles, namely in a low elevation angle three sensors A₁, A₂ and A₃, but in a higher elevation angle only a sensor B, which extends for example as a ring sensor over 360 ° at this height angle.

A / D converters 8 are again provided for all input lines. The bit widths are specified on the lines. The signals from the sensors A₁-A₃ are fed as addresses to a memory 17 which forms a first reducing device and form factor values on a 4-bit line 18 . The memory 17 is internally formed in this case with two parallel memories, both of which are controlled in parallel via the same address lines. With egg ner second output line 19 , the memory 17 from the Si signals of the sensors A₁-A₃ formed intensity averages. Two tables are thus stored in the memory 17 for form factor values and for average intensity values, both of which are read out simultaneously and are output via separate lines 18 and 19 .

The signal from the individual sensor B is digitized and output via an 8-bit line 20 .

The three lines 18 , 19 and 20 provide the addresses for a memory 21 of a second and last reducing device with an output line 22nd The second reducing device with the memory 21 works, as the comparison with FIG. 3 shows, identically to the second reducing device with the memory 11 of FIG. 3. Here again a 4 bit wide form factor value and an 8 bit wide intensity value for each of the fed both elevation angles. This is read in the memory 21 stored at the places Beur distributions for the surface quality on the line 22nd

If one considers the memories 9 and 11 of FIG. 3 or the memories 17 and 21 of FIG. 3 and takes into account the bit widths of the address lines and the output lines, the necessary memory sizes result from this. It can be seen that the memory sizes are of the order of magnitude available today.

The memory size is determined from these values according to the following Formula:

Memory size [bit] = (2 ^{address width} ) _* output ^width .

In the case of the memory 9 of FIG. 3 with the three lines to be fed, each 8 bits wide, this results in an address width of 24 with an output width of 4. The memory 9 thus requires 16 M (1 M = 1,048,576) bit memory locations, which each have 4 bits of content, i.e. a total size of the memory of 64 M bits corresponding to 8 M bytes. The memory 11 of FIG. 3 can be smaller depending on the complexity of the quality assessment information stored in it in the places, that is to say the output width of the line 16 . The memory 17 of FIG. 4 consists internally of two memories, one of which is 64 M bits in size and the other 128 M bits. The memory 17 thus has a total size of 192 M bits, corresponding to 24 M bytes.

Fig. 5 shows a more complex embodiment of a scanning device, the angles in three designated with A, B and C Höhenwin, where A is again the smallest height angle, each having six sensors.

For the sensors A₁-A₆, the A / D converter 8 are shown. The digitized signals are fed over 8 bit wide lines to three a memory 25 and a memory 26 , namely the memory 25, the signals from the sensors A₁-A₃ and the memory 26, the signals from the sensors A₄-A₆. The memories 25 and 26 are each because the memory 17 of the embodiment of FIG. 4 forms out, that is, as a double memory with parallel address control. They each provide 27 or 30 intensity averages on an 8-bit line and 28 or 29 form factor values on a 4-bit line. The lines 27 to 30 are connected to the address of a subsequent memory 31 .

In the same way (omitted for the sake of simplification of the drawing), the signals from the sensors B₁-B₆ a mean height angle are summarized via two memories each and by means of four lines a memory 32 , which speaks the memory 31 , supplied. A to the memories 31 and 32 parallel Spei cher 33 receives signals formed in the same way from the signals from the sensors C₁-C₆ of the greatest height angle. Each of the parallel memories 31 , 32 and 33 thus receives intensity and form factor signals which are formed from the signals from the sensors of a height angle.

Each of these memories 31 , 32 and 33 is in turn designed as a double memory for determining average intensity values which are output on lines 34 , 35 and 36 with an 8-bit width. In addition, each of the memories 31-33 outputs 8 bit wide form factor values on lines 37 , 38 and 39 , respectively.

The intensity signals on lines 34 , 35 and 36 are used to read out a memory 40 , while the form factor signals on lines 37 , 38 and 39 read out a memory 41 .

The memory 41 receives only form factor signals of the individual height angles, that is to say from the memories 31 , 32 and 33 . It delivers on its single output line 42 a summarized form factor signal for the form factor of surface defects, based on the circumferential angle in the surface plane. The memory 40 , to which intensity signals from all three elevation angles are supplied, supplies a total intensity signal of all sensors on an output line 43 and a form factor value on a line 44 , which is determined by comparing the intensities of different elevation angles and is therefore a height angle-dependent form factor that is Depth profile represented by surface defects.

A last memory 45 with output line 46 thus receives a form factor value for the area shape (via line 42 ), a form factor value for the depth form (via line 44 ) and a total intensity signal (via line 43 ) and can read out a table with these input values serving as addresses which issues corresponding quality assessments on line 46 .

Claims (6)

1. Device for determining surface defects of surfaces of high quality, with a scanner that can be positioned over the upper surface, the measuring points of the upper surface are illuminated with a light beam of suitable wavelength at a constant angle of incidence and has light sensors arranged at different heights and circumferential angles around the reflected beam , which are connected to an electronic evaluation device, which processes all sensor signals of the sensors with at least one reduction device and at least one A / D converter to form a single output value containing a quality assessment, which is associated with the measurement point under consideration, characterized in that
that the evaluation device has A / D converter ( 8 ) for digitizing all sensor signals and these downstream reduction devices ( 9 , 10 , 11 ; 17 , 21 , 25 , 26 ; 31 , 32 , 33 ; 40 , 41 , 45 ), in each of which several signals are sent as addresses to an addressable memory ( 9 , 11 , 17 , 21 , 25 , 26 ; 31 , 32 , 33 ; 40 , 41 , 45 ) for reading out the contents of its memory locations,
wherein at least two reducing devices are connected in series such that the output values of the preceding reducing device are fed to the subsequent reducing device,
wherein each preceding reduction device in the addressable memories contains previously calculated and stored form factor values as space contents, and each has a mean value device in which mean values of the intensities are determined in parallel from the same supplied signals, the intensity mean values and the form factor values being passed on as separate signals from the reduction device will,
and wherein at least a first reducing device ( 9 , 10 ; 17 ; 25 , 26 ) is provided, to which the signals of a plurality of sensors (A₁-A₃, A₄-A₆) are fed, and a last reducing device ( 11 ; 21 ; 45 ) which contains quality assessments of the surface as initial values. 2. Device according to claim 1, characterized in that the mean value device determines the intensity mean values as the space contents of a memory ( 17 ) addressed with the supplied signals. 3. Apparatus according to claim 1, characterized in that the mean value device is designed as the summing device ( 10 ) adding the signals. 4. Device according to one of the preceding claims, there characterized in that several sensors (A₁-A₃) at different circumferential angles in the same small one Elevation angle are arranged and that signals from Sensors (B₁-B₃) different elevation angle only as Sum of an elevation angle can be processed. 5. The device according to claim 4, characterized in that three circumferential angles and two elevation angles are provided are.   6. Device according to one of the preceding claims, characterized in that the angle of incidence of the light beam ( 5 ) is 90 °.