Daniela Constantinescu Ph.D.

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• Thesis title: "Efficient & Transparent Haptic Rendering of Rigid Body Motion with Constraints" (PDF copy)

• Abstract:

This work presents general purpose simulation and control techniques for efficient and transparent haptic rendering of rigid body motion with constraints. Transparent interaction is achieved by enabling users to feel collisions and to manipulate both virtual objects and virtual linkages. Efficient rendering is acomplished through fast approximations of rigid body interaction implemented in a local model with haptic performance.

Hapic rendering of impacts is based on a new representation of rigid body contact. In this representation, contacts are infinitely stiff when they arise and have limited stiffness thereafter. Multiple impacts are resolved simultaneously, in a manner consistent with conservation of energy principles and with the force capabilities of the haptic device. Haptic rendering of impacts is beneficial in training simulators for dental procedures and bone surgeries, as well as CAD and virtual prototyping systems with force feedback.

Realistic linkage manipulation is enabled by permitting users to operate linkages from any link and through singularities while restricting their motion according to the virtual environment geometry and the linkage topology. Linkage topology is imposed on users through penalizing users' departure from the configuration manifold of the virtual linkage. Operation of links with insufficient degrees of freedom is important in applications like training for laparoscopy, where the scope limits the tool motion at the entry point.
 

Efficient rendering of rigid body motion with constraints is enabled by interfacing the device to a simulation through a local model of interaction. The model comprises constraints imposed on the virtual tool by virtual objects within an e-active neighborhood of the virtual tool and a dynamic proxy of the virtual tool. This model is the first that can be used to constrain both the translation and the rotation of the device and to add realistic forces to virtual environments generated using any commercial simulation package with interactive performance. The model is beneficial in consumer-grade haptic applications, because it allows easy development of haptic applications by users without detailed haptic knowledge. It can also be used to enable cooperative haptic manipulations in applications that involve two-handed operations and/or multiple users.

• Thesis title: "Smooth and Time-Optimal Trajectory Planning for Industrial Manipulators along Specified Paths" (PDF copy)

• Abstract:

  The thesis proposes and demonstrates a strategy for planning smooth path-constrained time-optimal trajectories for industrial manipulators. Such trajectories are obtained by limiting the actuator jerks required by the planned motion.

  Existing planning strategies incorporate the smoothness requirement either as smoothness of the actuator torques or as smoothness of the joint trajectories. The smoothness requirement is desirable for reducing strain on robot actuators while still requiring low cycle times. In this work, the trajectory smoothness is defined in the phase plane and the planning observes the limits on the actuator jerks.

  The solution proposed for determining the optimal trajectories consists of approximating the time optimal control problem by a nonlinear parameter optimization problem which is solved using the flexible tolerance method. It is shown that the approximate solution converges to the time optimal motion when the actuator jerks become very high.

  A number of simulations are performed to demonstrate the proposed strategy. These simulations show that actuator jerk limits have a negative impact on robot motion time, but they do not give any indication about robot trajectory feasibility. This aspect is studied through further simulations and experiments on an industrial robot. The results of this work show that the tracking accuracy is directly related to the actuator jerk limits. Therefore, it is necessary to impose such limits when planning feasible optimal trajectories.

  Finally, the performance of the smooth time optimal motion is compared to the performance of both the non-jerk limited optimal trajectory, as well as a smooth quintic trajectory. For similar actuator jerks and controller effort, the smooth path-constrained time-optimal trajectory results in a significantly shorter motion time with nearly the same tracking accuracy as a quintic polynomial. Based on the results in this work, actuator jerk limits are shown to provide an improved method of achieving a compromise between high tracking accuracy, smooth joint behaviour, and optimal motion time.