No abstract

This paper validates a novel instrumented object, the iBox, dedicated to the analysis of grasping and manipulation. This instrumented box can be grasped and manipulated, is fitted with an Inertial Measurement Unit (IMU) and can sense the force applied on each side and transmits measured force, acceleration and orientation data wirelessly in real time. The iBox also provides simple access to data for analysing human motor control features such as the coordination between grasping and lifting forces and complex manipulation patterns. A set of grasping and manipulation experiments was conducted with 6 hemiparetic patients and 5 healthy control subjects. Measures made of the forces, kinematics and dynamics are developed, which can be used to analyse grasping and contribute to assessment in patients. Quantitative measurements provided by the iBox reveal numerous characteristics of the grasping strategies and function in patients: variations in the completion time, changes in the force distribution on the object and grasping force levels, difficulties to adjust the level of applied forces to the task and to maintain it, along with movement smoothness decrease and pathological tremor.

Traveling wave ultrasonic motors are actuators relying on piezoelectric ceramics that combine many advantageous features, such as high stalling torque, fast response, compactness, and magnetic resonance compatibility. However, they suffer from nonlinear dynamics, loaddependent dead zones, and the difficulty to control low speeds. In this paper, we present a novel second-order model for traveling wave ultrasonic motors. It is based on a dry friction driving principle and features dead zone effects. Based on the model, a two-input sliding mode controller is designed. It controls both phase difference and frequency of the traveling wave, without the necessity of implementing a signum function. With this controller, the state-of-the-art is extended to the position control case, while at the same time using fine-grained phase difference control for low velocities. Moreover, we show global uniform asymptotic stability for bounded disturbances and that velocity jumps do not appear when the control domains of phase difference and frequency are switched. Finally, both the model and the controller are evaluated via simulations and experiments that include the response to a position step input under various opposing torques. Index Terms-Control engineering, piezoelectric resonators, switched systems.0278-0046

Robots that are not only robust, dynamic, and gentle in the human robot interaction, but are also able to perform precise and repeatable movements, need accurate dynamics modeling and a high-performance closed-loop control. As a technological basis we propose robots with intrinsically compliant joints, a stiff link structure, and a soft shell. The flexible joints are driven by Variable Stiffness Actuators (VSA) with a mechanical spring coupling between the motor and the actuator output and the ability to change the mechanical stiffness of the spring coupling. Several model based and model free control approaches have been developed for this technology, e.g. Cartesian stiffness control, optimal control, reactions, reflexes, and cyclic motion control.