Some aspects of control and diagnosis systems design for mechanisms of technological machines

01.03.1999

Bocharov Yu.A., Gladkov Yu.A.

Program, control, diagnosis, distant, system, technology, machine, complex

1.Introduction

Paper deals with some aspects of control and diagnosis design for technological machines, in particular for the hot die-forging complex based on the 16 MN mechanical press. The complex composition, control and diagnosis system functions and structure are discussed. Present requirements to the technological machines and to the metal-forming machines are based on the latest results of informational technology development. Modern presses and complexes are to be equipped with informational systems serving to programmable control, diagnosis, and system parameters and time schedule monitoring . Network informational technologies open new horizons for a distance diagnosis of technological equipment installed in the user industry located far away from designers and producers

2.Control and diagnosis system structure

The system structure (Fig. 1) based on the "process-machine control" strategy [Bocharov 1998] has been selected to answer the user needs most effectively. Three control and diagnosis levels are introduced: "rigid" relay logic for data accumulation and fixed logic control command processing; programmable logic control (PLC) and operator interface.

Three groups of functions are introduced: power drive and mechanical components control, operational time and output statistics and components diagnosis.

Human resource factor should be always considered in the course of automation. Operators should be trained to understand, properly implement and create new technologies [Bocharov at al.1997]. A special attention should be paid to the safety of a service personal in the course of the first group of problems implementation and selection of technical means. If it is done with a help of PLC, especially in the test mode, some program mistakes could cause a harmful situation for mechanisms or people. That is why means of the "rigid logic" should by used for the diagnosis tasks implementation. The information on the cases of harmful situations should be sent to the controller input and reflected at the operator monitor for the decision.

The first group of functions should be solved with the "rigid" relay logic providing means of emergency information delivery to the PLC input due to operational personal safety requirements. PLC level could not be recommended since there is a possibility of a program malfunction in the pilot and reprogramming tests.

The second group requires the use of rather complicated calculation algorithms and probability of mechanisms harmful malfunction could be very low. The PLC system is recommended as the most effective.

Both first and second groups have a common purpose to determine the possibility of power drive or mechanisms malfunction and to terminate their operation or to block "on" switch .

The third diagnosis group serves for information supplied to the operator's terminal. Preliminary information, coming from the different kind of cells has to be processed by PLC sub-program with the special algorithms. Then it comes to the information preparatory subsystem and operator's interface and finally to the operator's terminal.

The control system with diagnosis subsystem should forecast possible mechanisms refuses on the base of collecting parameters information and enables a necessary repair planing. However, there is always a possibility of some mechanisms malfunction or a component refusal. The diagnosis subsystem should identify them, find the reason and advice the most effective measures.

3. "Rigid" logic program

Some problems of blocking the mechanisms in a number of situations could be solved with the help of control signal generation in "rigid" program. The following blocking signals are introduced:

friction clutch switching-off and brake -on at the press over-loading, lack of lubricant, low air pressure, main eccentric shaft slide bearings over-heating;
press switching-on block at the out of limit increase or decrease lubricant pressure at the lubrication system;
clutch or brake switching-on block at the not synchronic valves operation;
electric motors switching-off in the case of the die setting mechanism over-loaded, and deficit of the oil in a hydraulic power station tank appeared;
switching-off the control net of the press main drive system if the brake is switched-on;
the clutch switching-off and the brake switching-on in the case the pressure in the compensator pneumatic system is out of limits;
switching-off the press main drive electric motor and braking the flywheel at the case of a stairway door is opened or any foreign item in the die block has appeared;

Sub-programs of PLC level diagnosis subsystem control the following parameters:

deformational force versus slide travel P=P(x) in relation to the estimated nominal force with permissible derivation limits and statistic registration of force values classified in the established ranges;
deformation energy in relation to the permissible value depending on the press operational mode;
die ejection force related to the controlled value range;
temperature in bearings, dies, hydraulic system and the limit signals generation;
pressure in the receiver, market cushion, slide balance mechanism and the limit signals generation;
seals and packs state in pneumatic systems of lower die extractor, clutch, brake at the time intervals;
overloading the drive motor of the slide position regulation mechanism and speed value registration ;
the flywheel rotation speed and registration of extreme values;
angular position of the eccentric shaft at any time and at the time of braking;

All those and other tasks realised by the real time diagnosis subsystem could be presented in the following gropes according to the mode of realisation:

1) Checking parameters going out of limits critical to the complex operation and halting the corresponding mechanisms;

2) Checking the main mechanism components operational dynamics to determine the

extreme values manifesting a possible failure situation.

3) Verification of assembly operational quality to plan the needed repair schedule.

4. Diagnosis system

The perspectives of the diagnosis systems development are widely discussed at present. Automation diagnosis systems implemented at present solve the problem of a preliminary emergency identification and its preventing with a help of the operator decision, interlocking the complex operation. Failure diagnosis algorithms and programs are not fully developed and are in a limited application. It is necessary to develop that kind of algorithms for the earliest possible discovery of a coming failure reason and for the means to prevent it. The economy efficiency is evident since preventive measures are always less costly.

The expert system for a statistical analysis of the operational conditions and working out particular recommendations on the die-forging complex servicing is very much perspective in this respect. Such a system should supply expert advises on the probability of any assembly or component failure and necessary preventive measures.

5.Distant diagnosis

It became possible to get a distance information on a technological machines and die-forging complexes with the help of a modem connection to the global communication network. A design and development of a distant diagnosis system is a current problem and its implementation could be economically justified in the global market conditions. The die-forging and other machines design and fabrication company could exercise an engineering follow-up of its product immediately at the user cite. A detailed information and statistic analysis on the machine or complex operation parameters at the user company permit the production company to diagnose any assembly or a component and to work out the recommendations for preventive or planned measures of improvement with a minimum cost and in the shortest time. That permits to lower usually very high requirements for a service personal qualification at the user company. Besides, a production company could use a positive information to promote a market.

6. Conclusion.

1) Modern technological machines and automated complexes have to be equipped with the systems of a programmable control and diagnosis based on the modern informational technologies.

2) The system approach to the design of technological machines, complexes and control and diagnosis systems secures their successful and economically justified implementation in the modern industry.

3) The use of distant diagnosis systems permits the production companies to receive the in-plant operational information on the produced and sold equipment and the user companies could lower usually very high requirements for a service personal qualification.

Reference:

Bocharov, Yu., Strategies of Program Control in Metal Forming Technologies "Machine Construction Technologies", BSTU, Moscow, 1998, p 82.

Bocharov, Yu., Antimonov V., Gladkov, Yu., Process and Machine Control in Metal Forming., "Industrial Control Systems", Moscow, 1997, p 87.