2. THE CONTROL DEVELOPMENT METHODOLOGY
2.1 Objective and benefits
The CDM (Putz and Man, 1992; Pntz and Elfving, 1992) provides principles and guidelines for the design of open and extendable robot control systems within a simple overall structure, using unified and unambiguous terminology, and above all maintaining traceability between solution- independent requirements and final realizations.
2.2 The Steps of the CDM
The CDM defines a life-cycle model for the robot control system (which is seen as part of a larger "robot system"). Figure 1 illustrates the phases and steps within this life cycle. Guidelines and methods are offered in (Putz and Mau, 1992) for each of these phases, but special attention has been devoted to the initial steps 1 - 3.
The first step is called activity analysis. Already, the initial user requirements need to be refined in a systematic (hierarchical) structure. The proposed output from this step is a so-called "activity script", a semi-formal and fairly detailed prescription of the process which has to be automated by the robot system (key question: "'FOR WHAT do I need automation and control ?").
The next step and phase is the refined analysis of the control (sub)system requirements. This has to take all the different kinds of requirements into account, most notably functional and performance requirements (stating WHAT control functions have to be performed HOW WELL) and (especially for space applications) operational requirements. The last step particularly emphasized in the CDM is the control system architectural design which, for the software part, coincides with the well-known S/W architectural design phase. Also, control hardware and human control operations Cbrainware") must be "designed" to the same level in this step. As opposed to the preceding requirements analysis phase, design starts to say HOW the required functions are going to be realized. This involves the specific processors, bus systems, real-time operating system services, algorithms, software communication schemes, operational procedures, etc.
The remaining steps after architectural design are the "conventional" detailed design and production/procurement (of control hardware and software), integration and testing of these parts to make the control system, and finally integration and testing of the control system into the overall robot system. This is by no means underestimated, but from its principles is so well known that it is not discussed any further here. For each step, the CDM offers support in the form of generic architectural schemes (reference models), guidelines on their use, and even computer-based tool assistance. The two most important tools are an activity analysis method (ActAM) for Step 1 and a functional reference model (FRM) for Step 2. They will be introduced below.