A modular approach for task based design and realization of redundant manipulators for cluttered environments

Abstract

Tremendously increasing variations in the robotic applications has led to the importance of customized changes preferred in the design of the robotic arms. Selection and installation of a conventional robotic arm, for a specific application, may involve var- ious changes in the working environment. In certain applications, the robotic assistance is required with least or no change in the workcell. Besides, for cluttered environments and challenging task-space locations, the available manipulator configurations may not suffice. To provide solutions for such workcells, i.e. to synthesis robotic manipulators which can work for the required applications, the interest of many researchers is inclined towards the task-based designs of robotic manipulators. Normally, a set of task space locations (TSLs) are specified in a given workcell, and the design procedure involves the possibilities of an end-effector to work at these TSLs. Along with these basic requirements, some other desirable conditions are also formulated as inherent part of the design process, to provide a most suitable robot design for a given environment. With the increasing demand in the task-based designs of robotic manipulators, the research directions which need attention include a generalized strategy applicable to a larger domain of applications, handling of realistic workcells and development of the task-based designs in cost-effective ways. A three-phase strategy is proposed in this work for the design and realization of serially-linked modular manipulators which can work in constrained environments. The utilization of kinematic redundancy and unconventional robotic parameters is involved for required maneuverability and to avoid obstacles. The concept of modularity is induced to acquire a unified approach for the realization of these customized designs. A literature digest is presented for quick visualization of the research directions related to the proposed work, arranged with respect to their era and area. The modular architectures which have been discussed in past are based on the conventional designs of robotic arms. The strategies have been presented for fixed number of links and normally with no information about the working environment. These points do need to be answered for utilizing the modular concept for general task-based designs. This work focuses at the conceptual design of modules which are adaptive to a larger range of robotic parameters. The major questions which have been raised and worked upon in this work are related to the trade-off required between the flexibility in the robotic parameters (kinematic and geometric) for providing solutions in different situations, and the less variation recommended for the modular architecture. To provide an adaptive modular library for easy correspondence between the design and the fabrication methodologies, a parameters-based modular approach is proposed. The modules can be adjusted and assembled to acquire the serial manipulators with designed robotic parameters. The D-H parameters have been studied for the kind of variations in twist angles. These aspects are accommodated in the proposed architectural design of the modules. The related details constitute the second phase of the proposed strategy. The optimized designs of various possible modular combinations and the selection of an optimal modular assembly for given tasks is the objective of the third phase. For each of this modular combination, a constrained design optimization problem is formulated to obtain an optimal solution within the computed limits of the variables. The reachability at each TSL is formulated as equality constraints. Inequality constraints are formulated for obstacle avoidance and for the design limits. To validate the concept, some standard 3R-configurations have been modelled using the proposed links. Various examples and case-studies have been included in the dissertation for illustration of the proposed concepts and for efficacy of the presented algorithms. A broad perspective is presented for the utilization of modular robotic arms in various industrial applications. A multi-layer approach is proposed for modules- inventory which can be preferred as base for the further additions in the types of modules required in the library. A case study on a realistic problem of challenging welding sites is presented as an example of the upper layer. The results present the designed configurations and corresponding modular assemblies. To the best knowledge of the author, this is the first attempt to design the parameters-based modules adaptable to the task-based designs, so as to adjust and assemble the modules according to the designed configuration.