توسعه ابزاری نرم افزاری برای شبیه سازی و طراحی سیستم محرک پنوماتیک

The ready availability of low cost microprocessors and mechantronic components allow industrial users to consider adopting servo-controlled pneumatic actuators with an acceptable cost. This leads to a demand for a software tool in pneumatic actuator system CAS/CAD. Therefore, the paper introduces a software tool developed by the research group in Liverpool for pneumatic actuator system computer aided simulation and design. Pneumatic system components are initially organised into five major classes. Those components are considered as subsystems to a complete pneumatic system and the mathematical models for the individual components are derived which can be combined in different ways to form a complete pneumatic system model. A library is built up to accommodate the five classes of components. Users can pick up different components from the library to formulate a complete pneumatic system based on the design requirements. The complete system dynamic behaviours can then be simulated in different operating modes. The graphic user interface (GUI) and animation techniques are adopted in software design to create a user-friendly environment. The software is still in its early stage and only used for research purpose but it has potential for further development.

Pneumatic actuators have been widely used in the applications for simple speed control in industrial process and automation. In recent years, the ready availability of low cost microprocessors and advanced mechantronic components allow industrial users to consider adopting pneumatic actuators to accomplish more sophisticated motion control tasks [1], [2], [3], [4] and [5]. However, there exist some difficulties in pneumatic system control and analysis which are associated with air compressibility, significant friction and non-linearities [5], [6] and [7]. This leads to a demand for an assistant software tool to be used for dynamic analysis of pneumatic systems to address those difficulties in system design. Most current available pneumatic system CAS, CAD software packages are mainly developed for the purpose of pneumatic circuit designs [8], [9] and [10], not for pneumatic system dynamic analysis. Therefore, development of a software tool for pneumatic actuator system simulation and design is proposed in this paper. The software should be easy to use, easy to understand, re-configurable, and easy to simulate the dynamic behaviours of pneumatic systems. From analysis of current software design technologies, a components-based software design method is adopted in the paper, together with the features of graphic user interfaces (GUI). Components-based software design method is a new phase in object oriented methodology evolution. The recent development in component technology enables the construction of complex software systems by assembling together off-the-shelf components [11] and [12]. The major characteristic of a component is to be considered as a unit of independent deployment and has no persistent state [13] and [14]. This design method is now widely used in CAD software design. A software component should show same dynamic behaviours as its real world counterpart and should adopt the standard interface for the convenience of system integration. The software implementation of a component contains program code and data, which can be considered as an independent unit for users to pick up to connect with other components to form a complete pneumatic system. Their interfaces allow them to accept input and feedback information from and also send output and feedback information to those components which are adjacent to them. A typical example of component structure is shown in Fig. 1. The pneumatic system components are initially organised into five major categories, which are compressed air supplies, valves, cylinders, control strategies and miscellaneous parts (for example, connection pipes). The above organisation is determined based on the mechanical structure of pneumatic systems, which is generally the classification shown in the manufacturers’ catalogues. The way of organising the components’ classes may lead the users to feel same when they pick up the components from the library as they are picking the components from the manufacturers’ catalogues. A component library accommodating these five classes of components is then built up on the basis of dynamic analysis of pneumatic systems and component models. Users can pick up different components from the library to construct a complete pneumatic system. The dynamic behaviours of the complete system can be simulated in different operating modes. The graphic user interface and animation techniques are adopted in software design to create a user-friendly environment. MATLAB-SIMULINK is used to implement the software design. Three different kinds of software structures have been investigated and compared in the paper which reflects the route of the authors’ thinking in designing the software.

A components-based design method is adopted in the development of the software for pneumatic system CAD and CAS. Although the paper does not discuss implementation of advanced control strategies such as fuzzy and non-linear control for pneumatic systems, it provides a flexible way for users to design and add different new components of control strategies into the library. So the structure of the software is open for further development. The software is still in its early stage and has only been used in the research group. Further development could provide a useful tool for engineers in pneumatic system design. Dynamical simulation offers an opportunity for the designers to test the system’s performance before it is implemented. MATLAB-SIMULINK is chosen to accommodate the whole package. So the software can also be used for embedded system design using a rapid prototyping system such as dSPACE.