Pahl and Beitz provided five standard functions (channel, connect, vary, store, change) along with three general flows (energy, material and information). The eight function words are highly abstract for the engineering system. The validity and practicability of the Pahl and Beitz method is relatively poor. Altshuller presented 30 function words to describe overall mechanical design function and gradually developed the methodology of inventive problem solving.

In essence, a mechatronic system is a modern mechanical system with an ultimate goal of realizing the desired controlled motion behavior. In the highly abstract layer, the mechatronic function can be pided into three sub functions: generalized executive movement function, sensing and testing function and information processing and control function. Generalized executive function is the main function. The other two functions are auxiliary functions. The three sub functions can be respectively realized by the corresponding three subsystems. The following

sections first standardize function words and symbolic representations for the three sub functions and then integrate them to produce scheme representation of mechatronic system.

3 Symbolic representation of generalized executive mechanism subsystem

The function of a generalized executive mechanism is mainly realizing controlled, intelligent and flexible motion rules. The generalized executive mechanism is the integration between drive elements and executive mechanisms. The inputs of the drive elements are a variety of energies. The outputs are various motions that match executive mechanisms. The inputs and outputs of executive mechanisms are various motions.

3.1 Standardizing port class of energy flow

The drive elements in common use in mechatronic system need various input energy as shown in Fig. 1. The eight class words are literal symbolic representation.

3.2 Symbolic representation of motion function and motion relationship of input and output of executive mechanism 

The output motion of drive elements matches input motion of executive mechanism. The executive mechanism can realize variable input rotation and variable input translation. The generalized executive mechanism can better realize motion functions and improve dynamic characteristics. Traditional mechanisms with uniform input motion can be regarded as a special case of the generalized executive mechanism. In order to narrate it conveniently, the input motion type of generalized executive mechanism can be called rotation and translation. The symbolic representation of basic input-output motion function and basic motion relationship realized by the executive mechanism are shown in Tables 1 and 2.

3.3 Symbolic representation of generalized executive motion function

The input port of generalized executive motion function is port class of energy flow. The output port of those is various basic motion functions. The symbolic representation is shown in Fig. 2.The description can describe the realized motion function.

3.4 Function feature attributes of generalized executive mechanism

As space is limited, partial basic input-output motion functions, symbolic representations and function feature attributes of a generalized executive motion function are shown.

The author developed a basic motion function carrier base. Designers can retrieve corresponding function carriers according to symbolic representation and function feature attributes of generalized executive motion function listed here.

4 Symbolic representation of sensing and testing subsystem

The sensing and testing function tests a variety of information needed by generalized executive mechanism, such as displacement, velocity and force of executive links, and tests working state parameters of job object and job environment and the transmits these state parameters to information processing and control subsystem. Sensing and testing the subsystem executes sensing and testing functions. The sensing and testing subsystem includes sensors and microcomputers.