Design optimization of long-reach flexible M/m robots using integrated design method

Traditionally, the mechanical and control design of a robot are performed separately based on various objectives. This research is aimed at enhancing (optimizing) the design of long-reach flexible macro/micro robots by integrating the mechanical and control design stages. The scope of the work is general in the sense that it covers a wide range of applications of such robots. A framework is provided for the integrated design of flexible macro/micro robots. Nonlinear programming methods are used for generating the optimal values of mechanical and control design variables for given objective functions (performance measures) and design constraints. Formulation of a performance measure for integrated design purposes requires a knowledge of the task requirements, and dynamics and control of the robot. In this context, a modular systematic procedure is proposed for the automatic generation of finite element model of a robot with arbitrary number of flexible/rigid links. A comparative analysis is performed to establish the advantage of using the Integrated Design Method (IDM) over Traditional Design Method (TDM). The analysis is based on the results of three design case studies. The first case study represents TDM, where the control design is initiated after the mechanical design is completed; and the second and third case studies use IDM to minimize the total mass and tracking error of an unconstrained flexible M/m robot, respectively. The comparative analysis clearly shows the superiority of IDM over TDM. To facilitate the usage of IDM, performance measures are proposed for different applications of long-reach M/m robots. The applications of such robots are identified and classified into three general groups: non-contact, contact, and bracing; and a performance measure is proposed for each group of applications. The performance measures are general in the sense that they can be applied to robots with various configurations and degrees of freedom. A type of contact tasks is proposed with a new micro robot configuration. It is shown that, the flexible macro can be designed separately from the rigid micro, and a performance measure is proposed for minimizing the cycle time of the flexible bracing macro by using IDM. To reduce the dynamic forces generated by the micro on the bracing point, a novel conceptual/configuration design of the micro is proposed. The new design of the micro reduces the weight, dynamic interactions between the micro and macro, and simplifies the control design. This research is a first step towards the integration of specific design processes in order to achieve better products. Some limitations of this work are: (i) the effect of axial load (due to external and centrifugal forces) on the stiffness matrix has been ignored; the validity of this assumption has been numerically verified for the case studies; (ii) the proposed performance measures are formulated based on the linearized closed-loop model of a flexible M/m robot with a simple joint variable PD controller; new formulations of performance measures are required for more complicated non-linear control methods in which the closed-loop system behavior cannot be expressed adequately by the linearized model. The work can be extended by considering a wider variety of tasks, other robot configurations, other control methods, and by integrating other design processes which are part of flexible automation systems.