机电一体化模型英文文献和中文翻译(3)

菜单

The groups of basic physical elements are classified into three categories: Generalized resistor: examples of this category are; electric resistor, mechanical damper, and hydraulic resistor. Generalized capacitor: examples of this category are; electric capacitor, mechanical spring, and hydraulic reservoir. Generalized inductor examples of this category are; electric inductor, mechanical mass, and hydraulic inductor. Breaking down the physical system into subsystems and further into basic elements will provide us with a sharp insight about the evolution of the physical quantities within each subsystem, yielding to better understanding of the modes and the states that each subsystem would attain. The advantages of having such insight will become visible during the design phase of a local control system.

Modelling can be considered as the opposite procedure of decomposition. The difference is that, in decomposition, we pide the system into independent physical entities, while in modelling we reconnect the models of these physical entities. Therefore, modelling can be seen as the procedure of connection.

In modelling, we start at the bottom level of this hierarchy and move upwards. At each level, we propagate from a primitive system model to a connected system model. In the succeeding level, the primitive system model would then be established by aggregating the connected system models from the former level as shown in Figure 4.

At the bottom level of each subsystem, the primitive system model will be established by utilizing the governing equation or the fundamental law of each inpidual element. That fundamental law, such as Newton's law or Ohm's law, describes the local behavior of that element. Direct and indirect connections that resemble the internal constraints within the boundaries of each subsystem define the transformation from the primitive system model to the connected system model. For systems with linear connections such as direct current servomotor, the internal constraints are given by one connection object, the velocity object (V). The velocity object is a 2- dimensional array, the rows in that array correspond to the variables in the primitive system (local variables) and the columns correspond to the variables in the connected system (global variables). Thus, the velocity object is a transformation from the global variables in the connected system model to local variables in the primitive system model.

The model of the physical system is set up by aggregating diagonally the connected system models of the hydraulic subsystem and the boring spindle. Modelling the physical system resulted in a set of different all algebraic equations [7]. In a state space form, the behavior of the physical system is given by: y = ~ ( A , x , u , ~ ) Where ( x ) is the set of initial state variables, ( u ) is the set of input sources, ( A ) is the state transition matrix for the physical specific control function of truth or falsehood (1 0).

3.2 Control System Modelling

Before a control algorithm can be designed and implemented we need a description of its required properties or behavior. A precise and comprehensive mathematical model of the properties of the control system could be expressed by employing logic notation. This mathematical model provides us with means to reveal the inconsistency and conflicts in the control system and to verify that the control system meets design specifications. In order to carry out all control functions outlined in problem description, the control system should be decomposed into three subsystems. A process controller subsystem, which will be responsible to issue start and stop commands for the different physical entities and two continuos controllers. One controller for the servo valve in the hydraulic subsystem in order to regulate the feed forward motion of the hydraulic actuator. The second controller is for the servomotor in order to regulate the angular speed of the spindle motor. The decomposition is shown in Figure 5.