MCE Ph.D. Thesis Seminar
Mobile Manipulation is the use or study of mobile robots that interact with physical objects using tools mounted on robotic arms. In order for mobile manipulators to be successful, a thorough understanding of their kinematics – descriptions of mechanism geometries and tool paths in space without regard for causes of motion – is required, as well as efficient tools to plan and control complex motions as part of various tasks. This thesis derives, analyzes and applies the local kinematics of mobile-manipulators that support their own weight in arbitrary settings.
First, the kinematics of multi-limbed legged robots are provided. The fundamental stance con- straint that arises from simple assumptions about contact friction and feasible motions is derived. Thereafter, a local relationship between joint motions and motions of the robot abdomen is provided. This relationship is extended to include one or more reaching limbs. With these relationships, one can define and analyze local kinematic qualities including limberness, wrench resistance and local dexterity. Stance and reach kinematics allow the intuitive analogy between dexterous manipulation and legged stance adjustment to be made explicit.
The local kinematics are applied to practical problems by introducing a local planning problem, that accounts for Stance Stability. This problem is naturally translated mathematically as a convex quadratic program entitled the balanced priority solution, that is easy to analyze for existence and uniqueness. This problem is related in spirit to the classical redundancy resolution and task-priority approaches. With some simple modifications, this local planning and optimization problem can be extended to handle a large variety of goals and constraints that arise in mobile-manipulation. This local planning problem applies readily to other mobile bases including wheeled and articulated bases. This thesis describes the use of the local planning techniques to generate global plans, as well as for use within a feedback loop. The work in this thesis is motivated in part by many practical tasks involving the Surrogate and RoboSimian robots at NASA/JPL, and a large number of examples involving the two robots, both real and simulated, are provided.
This thesis provides an analysis of force kinematics and simultaneous force and motion control for multi-limbed legged robots. Starting with a classical linear stiffness relationship, novel extensions to account for multiple point contacts are described. The local velocity planning problem is extended to include generation of forces, as well as to maintain stability using force-feedback. This thesis also provides a concise, novel definition of static stability, and using the theory of alternatives from convex analysis, a novel unique perspective on stability: the strong alternative to static equilibrium.