Robot system activities relevant to such applications have been analysed and decomposed into the actions of the CDM catalog (Putz and Mau, 1992). Works by Weule and Timmermann (1990) and Mizugaki, et al. (1990) for robotized polishing, by Her and Kazerooni (1991) and Bone, et al. (1991) for deburring, and by Whitney (1982) have been taken as references. It has been found that, besides basic actions like MOVE and APPROACH/RETRACT (to control gross and proximity motion) and ATTACH/DETACH (to grip/release the tool), new actions should be implemented, involving exteroceptive sensor-control capabilities. Among the most representative are RUB, required for polishing and deburring, FOLLOW, for arc welding and tracking, and INSERT for part mating. Templates have been drawn up for each action and for each application, thus obtaining a complete description of a robot system's activities. As an example, the template for the RUB action for a polishing application is shown in Table 1.
4. ANALYSIS OF CONTROL FUNCTIONS FOR
HYBRID POSITION / FORCE CONTROL
The second step of the CDM consists in the specification of the controller's functionality in the form of an AA, to be obtained by summing up the functions required for each action listed in the activity script. For each action it is necessary to select a planning and a control algorithm, and then to split them according to the general ARM for robotics.
As an illustrative example, this section shows the derivation of the AA for the RUB action. First, general controller requirements and constraints influencing the selection of planning and control algorithms are discussed, and then the selected algorithms are described. Finally, the structure of the AA is shown.
4.1 General requirements and constraints
Industrial robot controllers are currently designed as positioning devices: independent positioning servomechanisms are implemented at each joint.
This solution is well established, and is based on motion control technology and on the relevant commercial products and experience. For this reason it is assumed here that the independent joint control scheme will also be adopted in the next generation of controllers