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Automated laser system for measurement of geometric parameters of toroidal corrugations

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"OPTEL" РЎРѕ., Ltd, Ufa State Aviation Technical University (USATU), 12, K. Marx. Str., Ufa, 450000, Republic Bashkortostan, Russian Federation

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ABSTRACT

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The technical characteristics, advantages and applications of an automated optoelectronic measuring system for measurement of geometric parameters of toroidal corrugations, designed by "Optel" company, Ltd of Ufa State Aviation Technical University is presented in this paper. The described set of algorithms and software allow converting measured profile into discrete model for subsequent comparison with dimensioned drawing model. Also this method includes specification of tolerance range for membrane profile deviation from theoretical one: the object is fitted if the profile deviation doesn't exceed the specified tolerance range. The new method of measurement and result estimation with the help of non-contact laser measurement is offered and implemented. The unique laser computer-aided system for automated measurements of geometrical parameters of toroidal corrugation profile based on described methods is designed and introduced.

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1. INTRODUCTION

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Under the current development of CAD/CAM systems and new technologies of shaping there is a need to increase productivity and automate the measurement of geometric parameters of complex-shaped parts. The parts can be made from various materials. The problem of modern professional equipment is to design devices for measurement of pressure and flow of liquids, gas, oil, etc., which has extended o perational characteristics, such as precision, reliability, simplicity of producing, etc. The special attention must be applied to the fact that sensors of pressure and flow can be used for operating with hostile environment (acids, gases, fuels, etc.) under various temperatures. It is clear that it is impossible to provide such characteristics without proper quality control of devices being produced and their parts. Means of automated control, which allow improve control process due to removal of 'human factor', which was inherent to old control methods. That is why the development of new generation of automated system for measurement of geometry of complex-shaped objects is important.

Previously used methods of measurement of wave profile geometry of toroidal corrugation, which were used in manufacturing of devices for measurement of pressure (manometers) and flow (flow meters) are time-consuming, non-accurate and not free from human factor. To monitor geometry micrometers and calipers were used to measure cylinder surface, and clock indicators were used to measure heights and cavity depths of toroidal corrugation. But this method cannot measure the wave surface in full and has too low measurement accuracy.

On bases of above mentions facts the alternative method of measurement and result estimation with the help of non-contact laser measurement are offered. This measurement approach allows measuring of complex-shaped parts with wave profile geometry (toroidal corrugations) at the high speed. The problem is that the dimensioned drawing of object under control is specified in discrete form (i.e. the set of two-dimensional primitives: rounding, straight-line segments and it's conjugations), but laser-measuring system allow to obtain planar profile (i.e. a number of 2D point-samples) of profile under control.

Labor intensity of manufacturing of pressure and flow sensors depends on labor intensity of manufacturing of parts, which surface is in a form of toroidal corrugations. In manometer such surfaces has base and membrane, which work as a pair and, since any of them has its own geometrical parameters (such as the number of waves, peak height, depth of cavity, etc.), it is important to pay a great attention to its workmanship. Another feature is large number (up to 20) of types and sizes. Some types and sizes can contain several membranes of various sizes and, accordingly, several surfaces in a form of toroidal corrugations on the base. Thus, assortment of measured parts and their surfaces can reach hundred pieces. Means and technologies of measurement of geometrical parameters make significant part of labor intensity of manufacturing of mature product and specify the pre-production time of new one.

The new laser computer-aided "OPTEL" system1-2 for non-contact automated measurements of geometrical parameters of toroidal corrugation (wave) profile. High precision and productivity of non-contact measurements allow providing 100% testing of parts with results being saves in computer memory. Labor intensity and cost of production of new parts with wave profile and repair of used ones as well as other equipment, tools, etc.

"OPTEL" system of new generation is laser hardware and software complex for measurement of corrugation profile geometry of various types and sizes. The system is high technology product, which has wide functional capability.

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2. EARLIER USED TOROIDAL CORRUGATIONS MEASUREMENT TECHNIQUE

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Previously used measuring methods of geometrical parameters of toroidal corrugation surfaces don't meet modern requirements. Let's examine existing measuring method of toroidal corrugation (wave profile), which is used for manufacturing of devices for measurements of pressure and flow (manometers and flow meters).

The following devices were used to measure geometry: For cylindrical surface, cavities and center-to-center distance - micrometers and calipers; For measurements of depth, height and cavities of toroidal corrugation - clock indicators.

But these methods don't allow measuring wave surface fully. The dimensioned drawing wave (toroidal corrugation) profile is specified as a combination of geometrical primitives - straight-line segments, arcs, etc. (figure 1). Center coordinates and radii specify arcs.

When profile is measured, center position of circles, which specifies the wave, was defined with the help of clock indicators as the position of maximums and minimums of peaks and cavities (i.e. the position of indicator probe, when its indicated values began to change in an opposite direction, was fixed). Then on the bases of deflections of measured coordinates of centers from dimensioned drawing ones the conclusion, if measured part of case is accepted, was made.

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Figure 1. Sample dimensioned drawing of wave profile

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The dimensioned drawing roughness is Rz=20 mm. Taking into account this roughness it is practically impossible to obtain an accepted part during one measurement. Let's examine the area of a typical maximum. The arc radius is 5 mm. Let tolerance range be 0.1 mm. As we can see in figure 2, the whole profile is inside tolerance range. Arrow points to maximum position on this profile area.

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Figure 2.

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If this local maximum (peak) height is 20 mm (which lays in specifies roughness range Rz=20 mm), the displacement of maximum point from theoretical one can be

The tolerance for its position, according to existing methods, is 0.05-0.1 mm. Thus, to obtain an accepted part one must provide profile nonuniformity in maximum area no more than 0.0005 mm. And even in this case the displacement the maximum point from theoretical one can be:

So, to provide the required quality of measurement according to these methods one must achieve the highest quality of processing, which is unattainable. If to measure and discard parts according to peaks and cavities diameters (to measure this diameters with the help of existing methods), practically all parts will be discarded, in particular those, which have profile deflection from theoretical one don't exceed tolerance.

Besides, it is apparent that when clock indicators are used, the wave profile areas between peaks and cavities (conjugation) aren't measured, although these areas are important for testing. Thus, existing measuring methods don't provide necessary quality of measurement.

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2. LASER MEASUREMENT PRINCIPLES OF GEOMETRICAL PARAMETERS OF TOROIDAL CORRUGATION PROFILES

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Alternative measuring method on the base of non-contact laser method with the help of "OPTEL-M" system is offered. This method is free from above-mentioned disadvantages due to utilization of laser triangulation method of measurement in combination with electronic and software information signal processing which provide high precision and productivity of non-contact measurements, reliability of operation under plant conditions.

Narrow laser beam is directed to object under control. The image of reflected, diffusing laser marker (beam) or beam overlaid by object is projected to integrated image device. Electronic unit provide deflection of integral multiple image device and appropriate video signal processing to extract information about marker image projection in required dynamic range. Digital codes, adequate to measured geometry, extracted and processed with the help of special software.

Measurements are carried out non-contact and with high productivity (hundreds - thousands times per second). This provides a possibility to carry out practically incessant measurements. Optoelectronic head and measured object are moved relatively each other.

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Figure 3. Manometer case. Wave profile from two sides. Diametric sections to be scanned are shown as red.

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After the diametric section is scanned (figure 3) the actual wave profile is build as array of two-dimensional points with X and Y coordinates.

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Figure 4. Toroidal corrugation profile. Result of diametric section scanning.

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Figure 4 shows the actual wave profile that is unfoundedly oriented within 2D coordinate system defined in the dimensioned drawing. The actual profile should be oriented so that it arranged symmetrically regarding 0Y axis and its profile base regions placed on the specified height. The procedure which orients the actual profile in such manner is called "basing procedure". In order the actual profile to be compared with the dimensioned drawing profile correctly the basing procedure has to be done. The basing procedure consist of two steps:

Step 1. The profile is turned so that its base regions placed on the specified height. To do this the middle points of the base regions are used: the profile is moved vertically so that the first middle point take it's height, and then the profile is rotated (pivot is the first middle point) so that the second middle point take it's height (figure 5).

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Figure 5. The Actual wave profile after first step of the basing procedure.

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Step 2. Since the profile was oriented horizontally at step 1 the axis of symmetry is parallel to the 0Y axis so the goal function F(t) will be:

Where yf and ym - curve fitting functions of fixed and moving profiles accordingly

TThe difference between 0Y axis and axis of symmetry equal T/2.

After the basing procedure is done the actual wave profile is ready for comparison with the dimensioned drawing profile. Since the dimensioned drawing data consist of discrete objects such as arcs, straight lines etc. we should construct the drawing profile on the bases of drawing data about wave profile (arcs, straight lines, conjugations etc.). Then the drawing profile is implemented with specified tolerance range. The conclusion about validity of the part is made depending if measured real profile lays within the tolerance range or not. According to this method the whole profile is measured and inspected including straight-line areas, not only profile peaks and valleys.

To make a decision whether profile being inspected is valid the control points are generated. Then the deviations are calculated for every control point. If the control point deviation exceeds its tolerance it marked as oversize or undersize according to the deviation sighting (figure 6). The toroidal corrugation profile is considered to be valid if there's no oversize or undersize control points.

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Figure 5. The Actual wave profile after first step of the basing procedure.

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4. IMPLEMENTATION OF METHOD

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"OPTEL-M" system consist of the following hardware and software components:

В В 1. Motorized computer-aided table based on the industrial toolmaker's microscope with the optoelectronic head mounted.

В В 2. Signal processing and control module.

В В 3. Industrial IBM Pentium-III personal computer.

В В 4. Special - purpose software.

The special - purpose software for new measuring system has been developed. The software carry out scanning of the parts by controlling motorized table and storing data received from the optoelectronic head. The measuring results are calculated, displayed and printed in forms, which are needed for user (charts, tables, measuring protocols, statistical data, etc.). Measuring results are saved in computer memory automatically, which allow creating parts database. Besides, the repeated measurements of parts after additional impacts, in particular, processing, mechanical loads and test running are possible.

Figures 7-9 contain the results of fast laser computer-aided measurements.

Unlike others inspection software the "OPTEL-M" software is very flexible. It has ability to customize both graphical and text inspection reports in accordance with plant requirements. Built-in command language allows creating custom inspection algorithms, scanning and basing procedures. All inspection algorithms are stored in the database and contain the picture of the part it should measure.

Software developed doesn't require special trained personnel and contains all the necessary reference information.

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Figure 7. Corrugation profile in tolerance range (expanded along axis Y).

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Figure 8. Corrugation profile out of tolerance range (expanded along axis Y).

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Figure 9. Reference point of corrugation and conjunction radius (expanded along axis Y).

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New "OPTEL" system has the following characteristics:

В В - Unique possibility to carry out fast non-contact automated computer-aided measurements of three-dimensional objects.

В В - Automation of labor-intensive measurements, inspection subjectivity elimination and provision of 100% testing with data logging in database.

В В - High productivity;

В В - Practically unlimited number of types and sizes of measured parts;

  - Measuring time of one section - up to 2 …5 c;

В В - High resolution - less than 0.001mm;

  - High accuracy - 0.005…0.01mm;

В В - High flexibility: measurement of hundreds of types and sizes are carried out in accordance with electronic dimensioned drawing (mathematical model) of part. The time of shift from one types and size to another is less than 1 min;

В В - Compatibility with CAD/CAM systems ("Unigraphics", "Cimatron", "AutoCAD", etc.).

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4. CONCLUSIONS

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The unique laser computer-aided system for automated measurements of geometrical parameters of toroidal corrugation profile is designed and introduced. The system meets modern requirements.

Introduction of high-productivity optoelectronic computer-aided measuring systems of news generation allow to automate measurements fully, makes them precise, objective and fast, as well as increases qualitative adjectives of pressure and flow sensors at expense of objective testing of surface with corrugation profile (membranes).

"OPTEL" systems are convenient and effective for assimilation of new parts and for their full-scale production. At present there is no alternative for this systems, which allow measuring 100% of parts of devices for measurement of pressure and flow.

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REFERENCES

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1. V.I. Syryamkin, V.S. Titov, Rav.M. Galiulin and others, Systems of technical vision: Reference book, Radio I svyaz, Tomsk, 1993.

2. Galiulin R.M. and others, "Computer-aided laser optoelectronic "OPTEL" systems for measurement of geometry of complex-shaped objects," in Aviatsionnaya technika. Izvestia VUZov (Vol 1), pp. 100-106, Moscow, 1997

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