The pulse width modulation (PWM) is a key technique in many power converter systems. Since the control-loop bandwidth is primarily determined by the implemented modulator and sampling strategy, accurate models are crucial for system design and analysis. In this paper it is shown that the commonly used zero-order-hold (ZOH) element represents a too optimistic small-signal PWM approximation, while a pure time delay model is far too conservative. Introducing an additional degree of freedom, a new modulator model is proposed, which can be adapted to model the small-signal PWM behavior accurately for different switching and sampling schemes. The proposed model is validated by a simulative modulator identification and it is exemplarily demonstrated how the new PWM model can be applied for the design and analysis of digital DC-AC converter systems.

This paper presents motion control concepts on parallel robots with explicit focus on anti-windup-design and trajectory-tracking. Starting from modeling and exact feedback linearization, a cascade control is designed. Improvements to control laws with respect to input-saturations are derived by using concepts of anti-windup compensation. A multiple-axis anti-windup-control is presented, guaranteeing tracking in case of input-saturation. Control schemes are implemented on a planar parallel manipulator for performance evaluation of high dynamic operation. Efficiency of control is highlighted with respect to trajectory tracking i. e. Cartesian distortion. All concepts are derived in a formal way guaranteeing manipulator-independent results and transferability.

Force guided assembly is attractive but the implementation is challenging when uncertainties are present. In these cases, contact models that guide the assembly process are attractive. This article elaborates the usage of static contact models, which map displacements to force-torque vectors of particular contact situations (force-torque map). This model, a map of discrete points, contains force and torque values that correspond to position errors. The inversion of this map, using forces and torques measured from an assembly attempt, yields correction movements in order to accomplish the assembly iteratively. A hypothesis stating the dependency of the model's quality on its injectivity is investigated. This aspect is studied thoroughly in so-called redundancy maps, which reveal regions of considerable ambiguity of the model. Experimental results are presented, which validate the hypothesis about the dependency of the convergence of the assembly process on the ambiguity of the initial position. In addition to the peg-in-hole problem, which has become a standard scenario to validate force guided assembly, the scope of this article also covers force guided assembly of more complex parts. Here, the analysis gives evidence to believe that it is unlikely that the implementation convergences acceptably, which is validated by experimental results.

A 2 DOF parallel redundant manipulator (PA-R-MA) is introduced. The manipulator is redundantly actuated by three servomotors with high-reduction gears. It is equipped with structurally integrated torque sensors. An elastic model of the null-space dynamics is derived needed for feedback control of redundant torques. A cartesian rigid-body dynamic model of the motion DOF is shown to be decoupled from the elastic model. Experimental results show the validity of the models.

The control of a prototype 2 DOF parallel redundant manipulator (PA-R-MA) is outlined. The manipulator has a redundant chain and is actuated by 3 servomotors and high-reduction gears, giving it the potential of high accelerations and a uniform force transmission. Link torques are picked up by strain gauges, null-space torques are controlled to avoid backdriving of the gearboxes and to allow the use of torque optimization. A decoupled cartesian motion controller then allows operation with accelerations exceeding 100 m/s/sup 2/ and velocities up to 4 m/s. Experimental results show the feasibility of this high-speed robot concept.

A 2-DOF parallel manipulator with actuation redundancy is examined for high-speed and stiffness-controlled operation. Advantages of actuation redundancy are outlined. The kinematics and singularity-free workspace of the manipulator are presented together with a force transmission analysis. Finally, a novel control scheme that guarantees a lower bound of the end-effector stiffness (LBSC) is presented. Simulation results are compared with a traditional control scheme for high-speed applications using the minimal 2-norm of actuator torques.