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Automatic Control of Automotive components in Mass ProductionN.V. Lyachenkov, V. Kokotov - AO Avtovaz 'Russia
Means of automatic control for automotive components in mass production gave been developed. The base is eddy current primary converters and eddy current measuring modules, made with the help of circuit engineering.
Russian car factories and AvtoVAZ in particular, have declared a car quality as a priority trend in their activity and have started extensive practical work on improving the product quality. The work is based on meeting the international standards ISO 9000.
The ISO 9000 requirements establish the principles of production quality control system being one of the facets in the complex company management system. In essence, the quality control system is an organizational and technical system, which main components are organizational subsystem (quality control management), technical aids (instrumentation, office mechanization facilities, means of automation, etc.), diverse tools (methodical, software, etc.).
The development of the quality control system is carried out in various directions:
However, one of the main and general ideas adopted at AvtoVAZ deserves special attention. It is a process-type approach with respect to description, analysis and optimization of production activity. In the course of car building a great number of different processes are performed - financial, procurement, manufacturing, inspection, etc. All processes play their specific roles in ensuring the final product quality. The quality is affected by all technological processes: from simple assembly operations to the so-called «special» processes, as vacuum spraying, electrophoresis or spraying in electrostatic field.
Technological processes should feature extra stability in mass production environment. Any irregular process inevitably results in higher rejects, which increase manufacturing cost and makes the product less competitive.
Inspection and test processes, performed at various product building stages, are of significant importance. Product inspection and testing supply the manufacturer with:
One of the ways to maintain stability of manufacturing processes is their automation. It is possible to automate diverse technological processes on the basis of eddy-current measuring modules, which are distinguished by wide functional capabilities, high precision and noise immunity.
Efficient operation of measuring and control systems, along with maximum benefit from their potential, depend on the extent the systems are equipped with sensors. Manufacturing process and test automation with employment of special-purpose sensors can not only increase the process reproducibility and optimize the process as to material resources or time saving, but provide collection and analysis of complete process-related data.
One of the most important issue in creating modern automated systems for technological processes is the selection of hardware components which help obtain realistic original information on the processes under control.
The demands to the converter parameters are rather tough and controversial in many respects. They should:
These requirements are met by prospective converters operating on eddy current effects. To this end, the problem of creating new versions of eddy-current primary converters (ECC) is rather acute.
Eddy current-based methods of quality control can be widely used in automotive industry. For example, during the production and improvement of the internal combustion engine, it is important to measure clearances in the piston-rod mechanism, piston-cylinder assembly, crankshaft endfloat, angular oscillation of shaft and parameters of multi-dimensional oscillation of bearings.
Note, that the measurements should be made without a mechanical contact in adverse conditions of high temperatures, severe vibration and polluted environment. On the basis of the converters offered automated systems can be created for manufacturing processes and control of coating thickness in the paintshops and plating facilities. The converters in question can also be used in non-destructive quality control systems for weld joints of the car assembly shop since they can measure the weld width and detect hidden defects, such as cavities, pin holes or inclusions. The proposed objective control methods feature enhanced productivity and reliable results, and thus considerable technical, economical and scientific effect.
The quality of process performance depends greatly on the efficiency of control and monitoring systems in mass production environment.
An increase in efficiency of control and monitoring is related to the level of process automation which is determined by available original means of receiving the information pertinent to the fulfillment of a physical (mechanical) process. The measurement module offered possesses the features required. We would like to note, that the matter under our consideration can be widened by monitoring schemes, where the principles of automatic control and monitoring are not realized to the full extent and the operator (setter) is responsible for making decisions.
Among the advantages the module can suggest for serial production is possible commonization of their usage in tackling various tasks.
This allows to carry out development of:
From the viewpoint of possible technical realization of the control systems, it may be beneficial to implement the diagram «input - conversion-output», where the output is an electrical pulse, converted to discrete code. It makes possible to put together the converter and PC.
From the viewpoint of feasibility it is essential to use the measurement modules commonized by their application layout and used for quality analysis of dissimilar processes.
As a typical example, we would like to refer to body-in-white painting. In machine-building industry there is a number of different methods for applying protective and trim coatings. Among them are electrophoresis, electrostatic film adhesion, air spraying. One of the major parameters of coating quality is coating thickness which can be checked by the commonized measuring modules. Similarly, the modules can be used for checking the thickness of car body preserving layers.
The modules are highly universal, taking into account their capabilities to control processes in the area of plating, mechanics (clearances), analysis of metal surface blemishes (minor cracking, hairline fissures), analysis of inner metal defects (cracks, blowholes, draws).
The report addresses the following issues:
To control mechanical, electrical, mechanical and technological parameters, there have been developed the synthesis algorithms of eddy current converters. The algorithms take into account the required output characteristics of the converters, realize the pre-programmed sensitivity of eddy current converters for alternative product parameters, both adjusted and troublesome, taking into consideration the design limitations of the converter under development.
To do the synthesis equations, the methods are proposed which allow to obtain principal electrical parameters of the converter and to build constructive diagrams. There presented the results of synthesis of eddy current converters for checking both magnetic and non-magnetic products.
Based on the methods suggested, there were synthesized a number of converters with linear output responses for checking mechanical properties and quality of protective dielectric coatings. The developed eddy current converters outperform the known ones as to their basic parameters. The output ramp for the synthesized converters is 2-2.5 higher as compared with the ordinary ones of the same overall dimensions. It renders possible to significantly enhance the efficiency of product control in the environment of destabilizing factors, such as, scattered electrical and mechanical properties of the product material.
The application of methods illustrates the synthesis of transformer-type eddy current converters with complanar windings: distributed coil winding and concentrated windings - arranged in the same plane, being parallel to the surface of the product under control. The purpose of synthesis is to determine the density of turns, field winding connection pattern, ratio between the number of turns in such windings according to the preset conversion function. The superposition principle is used for doing the synthesis equations.
The resulted equations for the synthesized eddy current converters make possible to assess the converter properties, which are mandatory for application tasks. Sensitivity limits and errors of the eddy current converters have been calculated.
The analysis of the threshold sensitivity of the eddy current converters is carried out on the basis of information-energy approach, assuming an ideal measuring tool. The research has been conducted and results have been obtained from checking the conductivity, clearances and displacements, percent concentration of impurities and cold strain parameter - metal and alloy wear hardening. There have been studied only non-magnetic conducting materials, since ferromagnetic fabricated products feature high magnetic noise.
The analysis of ECC errors in measured thickness, clearances and item displacements has been performed on the basis of informational theory of measuring devices. The recommendations on selection of ECC generalized parameters at the preset output ramp have been employed to develop setups of measurement modules.
Basic commonized versions of eddy current measuring modules (ECMM) have been developed using pulse-harmonic circuit engineering.
The ECMM setups are highly noise protective due to several stages of interference suppression. The protection is ensured through:
It is known, that most properties of vector-dimensional measuring devices with quasi-sine pulse-harmonic converters are based on weight function of different origin, i.e. magnetic field, conductance, tension, etc.
The optimum selection of weight signal pulses allows to enhance noise immunity of phase-sensitive measuring devices. The consistent parameters of basic harmonic of weight oscillation determine the measuring accuracy of vector, which describes the sine signal measured. The high harmonic constituents in the spectre of weight function result in further measurement error in basic harmonic parameters.
The analysis of weight function parameters has been performed which ensure selectivity of the device to the main harmonic of the pulse measured. It is shown, that the most efficient way of realization of weight functions is to use commutative converters, which are distinguished by high reliability, consistent parameters and minor conversion error.
As a result, a basic diagram of a stabilized pulse shaper has been proposed and the analysis has been made as to stability of its operation, along with recommendations on the selection of pulse shaper parameters.
The ECMM setups feature acceptable metrological characteristics. The results have been obtained from the analysis of additional errors, caused by scattered design and process parameters and by destabilizing factors. It is shown, that without correction methods the measurement error is as high as 8% within the conductivity range of 10 to 40 MS/m.
Computers have been used in order to improve the metrological characteristics of the measuring module. In this case the output pulse is picked up not from the amplifier output, but rather from the differential output of synchronous detector. The function to determine the voltage differences is now transferred from the detector to computer. In these setups there is now a possibility to use test methods techniques of accuracy enhancement.
In order to minimize the measurement errors, a self-adjusting mode of measurements is realized in the basic version of ECMM. The mode covers the following operations:
The functional diagram of the self-adjusting ECMM is illustrated in Fig.1.
Fig. 1. Functional diagram of the self-adjusting measuring module
As it can be seen from the diagram, the multivibrator, key measuring circuit, commutator and measuring converter form the main conversion channel. Test increment of added resistance in main coils of eddy current sensitive element is enabled with the help of test coil.
The actions permit to practically stabilize the measurement error up to ±0.5% within the operating temperatures of -20 to +50°C. The self-adjusting measuring module suppresses not only the thermal error, but the error resulted from alterations in supply voltage.
The reviewed principles of building the eddy-current measuring modules made possible to realize the devices which are suitable for modern automatic production of automotive components.
The submitted developments of eddy current measuring modules feature extensive functional capabilities, high precision, noise immunity and consistent conversion function. All this helps successfully perform automatic control and monitoring of technological processes in mass production of automotive components.
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