Fuzzy logic and piezo technology optimise proportional valve operation

Citation

(2005), "Fuzzy logic and piezo technology optimise proportional valve operation", Assembly Automation, Vol. 25 No. 2. https://doi.org/10.1108/aa.2005.03325bad.001

Fuzzy logic and piezo technology optimise proportional valve operation

Fuzzy logic and piezo technology optimise proportional valve operation

Keywords: Fuzzy logic, Control systems

The latest developments in fuzzy logic and piezo technology are consolidating and expanding the role of electro- pneumatic proportional valves in all areas of industry and medical technology say David Share of ASCO Joucomatic.

Electro-pneumatic proportional valves play a major role in optimising production processes to improve quality and productivity in all areas of engineering, processing and medical technology. They are a key element in programmable control systems, the combination of intelligent electronics and powerful pneumatics constantly providing new and innovative solutions for the widest range of applications.

The latest generation of proportional valves has evolved as the pace of control system development has accelerated. These units offer far greater communication facilities for integration into modern digital control systems and also operating features such as minimum hysteresis and high levels of linearity and sensitivity to ensure extremely short response times and precise operation.

Modern digital proportional valves such as the newly introduced SENTRONIC^D from ASCO Joucomatic integrate their own control loop, facilitating highly precise adjustment and control of a host of variables including pressure, flow, force, speed and linear or angular motion (Plate 1). The standard Sentronic with its integrated PID controller valve is easily adaptable to these control tasks with or without a PC. Increasingly, however, applications are appearing in which standard logic control parameters – yes/no or 0/1 – are difficult to determine or set.

Plate 1

This is the realm of fuzzy logic, a control methodology used where boundaries are not clearly defined (i.e. fuzzy). Fuzzy logic is used in complex chemical processes, controllers for robotic welders, feature-definition controllers for robotic vision and even in consumer products such as washing machines, video cameras, and automobiles. It is a capability recently introduced to electro-pneumatic proportional valves, in the shape of ASCO Joucomatic's Sentronic valve with integrated self-optimising controller. Unlike logic 1s and Os, the self-optimising Sentronic uses continuous transitions and automatically defines optimal control parameters.

The basis of this operation is ten set point steps: the proportional valve electronics evaluate the feedback and control parameters are improved with fuzzy logic after each step. The optimised parameters are saved to memory after the ten steps and are subsequently operated upon by the proportional valve.

Complementing both the standard PID and fuzzy logic operation of the Sentronic is a package of Data Acquisition software. This provides the ability to automatically collect data, which is particularly useful in developing test and measurement applications either in the laboratory or in the factory. The DAS package also enables optimal system parameters, once they are determined, to be stored in a project file for use in fault detection, routine maintenance, or future serial production.

The market demands that have led to the development of fuzzy logic for proportional control have also impacted in other areas, resulting in new designs of proportional valves to address industry's requirements for reduced power consumption, and also operation in hazardous environments: recent research indicating that 50 per cent of all industrial applications now contain a hazardous area of one type or another.

The technology that effectively addresses both of these requirements – and more – is piezo based. Ceramic multilayer actuator (CMA) Piezo technology as employed in ASCO Joucomatic's Piezotronic proportional valve gives extremely low power consumption – as little as 0.007W, and is available as an intrinsically safe unit (rated II 1GD IP65 EEx ia IIC T6) for use in potentially explosive atmospheres.

The CMA technology employed by Piezotronic comprises of a monolithic piezo-ceramic strip with integrated electrodes that are specially configured so that the element “bends” when a voltage between 20 and 40V is applied. This bending action, which involves no moving parts, is a key in providing the precise levels of proportional control demanded in such typical medical applications as gas analysis and the micro-injection of aqueous solutions into living cells.

The fact that there are no moving parts in the operation of piezotronic offers several benefits: first, response times are exceptionally fast, 100ms typically. Secondly, service life is practically unlimited at around one billion cycles. Thirdly, the unique operation of the piezotronic valves also means that there are no inductive peaks when switching, so unlike conventional solenoid valves, no circuit protection is necessary. Lastly, no holding current is required for the valves to maintain position, so heat generation is not a problem either. This feature is particularly important in medical and analytical applications where it is imperative that no heat transfer takes place from the valve to the fluid, a condition that could otherwise spoil the accuracy of a process.

The functionality, size and weight advantages of the piezotronic mean that one of the units may be employed where two conventional solenoids were required previously. This advantage, and the fact that piezotronic can be operated by battery power or solar cells, makes piezotronic the ideal unit for use in portable equipment.

For further information visit the web site: www.ascojoucomatic.co.uk