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The technical characteristics, advantages and applications of an automated optoelectronic measuring system for inspection of mounting parameters of gas-turbine engine (GTE) blades in cascades, designed by "Optel" company Ltd of Ufa State Aviation Technical University is presented in this paper. The measuring apparatus can be applied for research and in industry. Its main advantages are non-contact non-destructive inspection and high productivity. The unique laser computer-aided system for automated measurements of geometrical parameters of GTE blades is designed and introduced.
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As industrial technologies of manufacturing parts are developed, the problem of an estimation of quality and accuracy of their manufacturing has appeared. At present the important problem in air-engine industry is the design of new GTE with improved characteristics. While new information technologies developing, design of technical vision computer-aided systems for non-contact and accurate measurement of geometrical parameters of complex-shaped objects becomes more and more vital. In this case the problem of inspection and control of GTE cascade blade parameters such as the blades weight, open flow area, etc., should be solved. In addition it is necessary to supervise a blades angle in compressors of new engines. For modern GTE it is possible to satisfy the given requirements only through the use of new tools for the manufacturing and inspection. Often such measurements have to be done very rapidly to respond to the specific phase of a fast process.
At present in industry the subjective contact manual clock indicators are used for inspection blades angle, process of measurement is inaccurate and takes a lot of time. Besides big GTE the small GTE for GCU (gas compressor unit), , which have very small blades (with a chord up to 15mm), are also made. The angle of mounting of these blades depends on stress, which is imposed on the indicator. So, under small stress the blade return to initial position. When stress on blade increases, the blade can be bent and spoiled, as blade thickness can be less than 1 mm. Those measuring means have become outdated and do not meet the modern requirements.
To improve the quality of measurement the optoelectronic methods, which use a laser principle, are of particular interest. They can be applied for universal purposes, are very accurate and efficient and require no contact with the object to be measured.
The labour intensity of GTE manufacturing is largely dependent on labour intensity of gas-air track manufacturing. It includes up to 10-20 rotors and stators (jet) steps, each of which contains up to 100-200 blades. Every GTE contains up to 1000-4000 blades of 20-40 types and sizes. Each gas-air track element requires inspection of many geometrical parameters. That is why inspection means and technologies are considerable part of GTE manufacturing; they influence engine prime cast and define introduction period for new GTE.
The new high-efficiency laser computer-aided "OPTEL" systems of new generation for measurements of complex shaped object geometry with flexible and fast switch to various types and sizes are designed in "OPTEL" company1-4. The system described in this paper can be used for measurement of blade cascade mounted on rotors and stators of GTE gas-air track.
The optimum blade placement in GTE blade cascade is also important.
The latest models of "OPTEL" systems allow carrying out the all-inclusive inspection of production stage of manufacturing of GTE gas-air track. It can be done from the beginning of primary part to final inspection of finished GTE blade cascade, with database on stages and the whole GTE being created.
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Application of triangulation and "shape from shadow" method in combination with electronic and software processing of information signals guarantees high accuracy and efficiency of non-contact measurements, performance reliability under plant conditions.
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Figure 1. Shape from shadow method illustration
The measuring principle is based on a non-contact "shape from shadow" method (figure 1), which uses a laser scanner. During operation, two lasers scan the object and the lasers illuminates on a two photo sensors. The generated signals (figure 2) are filtered to eliminate noise; they are digitized and then processed by a computer. A small diameter laser beam is used to obtain a high complexity.
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Figure 2. Timing waveform of two photodiode (depends on blade cascade rotation speed); dt1, dt2 - blade shadow time; t1, t2 - period of blades in the cascade
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The measurements are based on comparison method and consist of two steps. The first step is to measure caliber - a plate with known sizes and tilt angle. It's placed next to the blade cascade and installed on a mount. The second step is to measure blade cascade. So, geometrical caliber parameters and shadow time being known, we can measure geometrical parameters of cascade blades.
Measurands needed to calculate cascade blades mounting angles are shown on Figure 3:
В В Р°1 - angle of the first laser beam axis to vertical;
В В Р°2 - angle of the second laser beam axis to vertical;
В В dx1 - blade movement distance between response of sensors to the first and second laser beam;
В В dx2 - caliber movement distance between response of sensors to the first and second laser beam.
The following intermediate formulas are needed to calculate cascade blade angle:
В В В В В (1)
В В В В В (2)
where:
В В Ak - angle of the caliber to vertical;
В В lk - chord caliber length;
В В hk- caliber height (lk projection on vertical axis).
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Figure 3 - Laser beams and blade placement
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В В В В В (3)
В В В В В (4)
where Ab - angle of cascade blade.
The measurements are non-contact, fast (hundreds thousands times per a second) and high accurate. It allows to carry out practically continuous measurements, when optoelectronic head and item under control move relatively each other.
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The measuring apparatus consists of four basic units. They are the optoelectronic unit, including the laser and photo sensor, electronic control unit, computer and special software.
Figure 4. The architecture of the OPTEL system
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"OPTEL" system consists of two basic modules:
В В 1. Software for creation of database of bladings in rotors (stators). Blades can be selected according to blades mounting angle, weight, static moment, etc.
В В 2. Hardware-software complex for non-contact measurements of real parameters of blades mounting in rotors and stators of various types and sizes:
TThe following values are measured:
В В - Blade mounting (tilt) angle,
В В - Critical (open flow area) section of a blade cascade, etc.
The measuring range in the radial plane is determined by the design of the system; it can be 200 mm and more.
The measuring module have configuration, containing 2 measuring heads. The system configuration is selected to accommodate the measuring task to be performed. A continuous sequential measurement of the object shape is possible at discrete steps, maintaining a high scanning speed.
For measurement an object is placed on the platform or in a suitable position in the field of view of the measuring head. The laser scans the object sections according to a preselected program. The scanning speed can also be set. The measurements of the scanning unit are transmitted to the electronic signal processing / control module where noise is removed and an AD conversion is done to produce suitable signals for the computer; it performs the evaluation of the measurements and displays the information in a suitable form on a monitor.
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Automated "OPTEL-LR" system is intended for non-contact measurement of blade mounting parameters in specified sections of GTE blade cascade (rotor and stator).
Measuring principle is based on previously described methods. The laser beam scans blades. To measure blade-mounting parameters, corresponding blade scanning modes of item and calculation of its specified parameters are provided.
Set of profiles is measured as a result of blade mounting parameter scanning in specified section with various angles. Its gives full adequate information about real blade mounting parameters of GTE blades cascade, including design parameters, which are stored in a computer memory, transmit to Automated Control System of Technological Process and can be outputted to display or printer.
Automated measurements of blade mounting geometrical parameters are carried out under special system software, which calculates blade mounting parameters, displays and registers real parameter values of blade mounting for every item type and size.
Measurements of blade mounting parameters are carried out non-contactly and with high efficiency. Measuring results are displayed in visual form. They also can be outputted in the form of printed protocols in paper. Samples of measuring protocols are shown in figures 5 and 6.
System also allows grouping the measured blades in the bladings. Operator can also enter grouping initial data (angles, masses, vibration frequencies etc) from keyboard. System software places the blades in optimal location in blade cascade assembly. The user selects the algorithm of optimal blade location.
On the basis of the above-stated method of measurement for the first time the unique laser computer "OPTEL-LR " system for automatic measurement of the blade mounting parameters was created 1-4. It meets the modern requirements of air-enginer manufacturing and was introduced at one of plant.
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1. Galiulin Rav.M., Ilyasov B.G. etc., "Optoelectronic computer-aided systems for three-dimensional inspection of complex objects in Machine Vision and Three-Dimensional Imaging Systems for Inspection and Metrology", Kevin G. Harding, John W. V. Miller, Bruce G. Batchelor, Eds, Proceedings of SPIE (Vol. 4189), , pp. 268-275, Bellingham, USA, 2001.
2. Galiulin R.M. etc., "Laser Computer-Aided Systems for GTE Gas-Air Track Elements Inspection" in Proceedings of the 2nd International Workshop on Computer Science and Information Technologies, pp. 70-75, USATU Publishers, Ufa, Russia, 2000.
3. Galiulin R.M. etc., The laser computer control of air-gas track GTD. in the Control. Diagnostics (Vol. 2), pp. 26-33, RONKTD, Mechanical engineering, Moscow, 2000.
4. Galiulin R.Рњ. etc., "Computer-aided laser optoelectonic measurements of complex shaped objects geometry "OPTEL" " in Aviation engineering. News of university (Vol.1), pp. 100-106, 1997.
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Russian