Singularity analysis and handling towards mobile manipulation

Ph.DDOCTOR OF PHILOSOPH

Laser-based sensing, measurement, and misalignment control of coupled Linear and angular motion for ultrahigh precision movement

This paper presents a novel methodology for position and orientation (pose) measurement of stages used for micro/nano positioning which produce coupled motions with three planar degrees of freedom (DOF). In the proposed methodology, counter-rotation of the entire mechanism prevents the misalignment of the measurement beams within a laser-interferometry-based sensing and measurement technique. To detect such a misalignment, a sensing strategy constructed around a position sensitive diode has been developed. A feedforward-feedback compound controller has been established to provide the necessary counter-rotation input to reduce the misalignment error. Experimental validation has been conducted through the measurement of the workspace of a three-DOF planar micro/nano positioning stage. Experimental results demonstrate the capability of the technique to provide combined linear/angular measurement

OSTEOCHONDRAL INJURY DURING SIMULATED DROP LANDING COMPRESSION: PRE AND POST IMPACT MICRO-COMPUTED TOMOGRAPHY

The purpose of this study was to investigate osteochondral injuries due to impact load. Average nominal strain of 34%±5% was applied to equine osteochondral plugs. The deformation of cartilage and bone on one plane was measured using real-time imaging during the impact. High resolution micro-computed tomography prior to and following the loading was used to investigate the extent of the damage to the specimens. The average peak strain in bone and cartilage was 0.11±0.01 and 0.20±0.08, respectively. Microfractures were found in the µCT images in the subchondral bone, ranging from 200µm to 30µm wide. The 3D images of micro-fractures, obtained here, can be used for future studies of bone remodeling as a result of such impact-induced damages. The strain in the bone was significantly large indicating the ability of bone to absorb the impact energy

Direct kinematics and analytical solution to 3RRR parallel planar mechanisms

This paper presents the direct kinematic solutions to 3DOF planar parallel mechanisms. Efforts to solve the direct kinematics of planar parallel mechanisms have concentrated on RPR mechanisms due to its inherent simplicity. It is established that the direct kinematic equations of a general 3DOF planar parallel mechanism can be reduced to a univariate polynomial of degree 8. This paper presents the derivation of this univariate polynomials for both 3RRR and 3RPR mechanisms, showing the similarities and differences between the two common configurations of 3DOF planar parallel mechanisms. This paper also presents the on the direct kinematic solution to a simplified case of the 3RRR planar parallel mechanisms, where it is possible to decouple the polynomial further into two quadratic equations, describing the position and orientation of the end-effector, respectively. This result will provide an efficient computation method for a very useful configuration of planar parallel manipulators

Robust control framework for piezoelectric actuation systems in micro/nano manipulation

Micro/nano manipulation has been identified as one of the key enabling technologies for many emerging challenges. Within this scope, piezoelectric actuators have played major roles in achieving the required nano-resolution motion. This paper proposes a robust control framework for piezoelectric actuation systems to follow specified motion trajectories. The basic concept associated with this methodology lies in the specification of a target performance and the robust control scheme formulation for piezoelectric actuation systems to ensure the convergence of the position tracking error to zero. This control methodology is attractive as its implementation requires only the knowledge of the estimated system parameters and their corresponding bounds, including bound of hysteresis and external disturbances. Feasibility study of the framework for piezoelectric actuation systems in micro/nano manipulation is described. Simulation results validated the suitability of the proposed control approach

Robust motion tracking control of piezoelectric actuation systems

This paper proposes a robust control methodology for piezoelectric actuation systems to track specified motion trajectories. This is motivated by the search for an effective control strategy to deal with the problem of nonlinear behaviour in the piezoelectric actuation systems. The basic concept associated with this approach lies in the specification of a target performance and the formulation of a robust control scheme for the system to ensure the convergence of the position tracking error to zero in the presence of parametric uncertainties and hysteresis effect inclusive of other un-modelled disturbances. Stability of the control system is proven theoretically and the robust control methodology is demonstrated to possess a promising tracking ability through the control experiments. Implementation of the control law requires only a knowledge of the estimated parameters and their corresponding bounds as well as the bound of the hysteresis effect including disturbances. Being capable of handling uncertainties and disturbances, the robust control methodology is very attractive in the field of micro/nanomanipulation in which high-precision control applications could be realised