Frequency, amplitude, and phase information of the grid voltage are the main constraints for constructing a robust controller algorithm for grid connected applications under unbalanced and distorte...

This paper presents a novel algorithm for simultaneous position and interaction force control. In the classical algorithms, position and force control are executed concurrently by switching between two separate controllers: the position and force controller. Thus, one can consider the control system working in two modes, namely the position control and force control modes. Switching between these two modes often leads to oscillations in the controlled position and force. Therefore, the safe interaction between a controlled mechanical system and its environment is jeopardized. The above issues are tackled in this study by introducing a new control strategy. The proposed algorithm combines position and force control into a single controller, in which the transition between position and force control is smooth, removing the oscillations of classical methods. Therefore, the safe interaction between a mechanical system and its environment is enabled. In addition, using this method one can equip actuators with a control system capable of performing both position and force control. Thus, a step towards “smart actuators” is possible.

Summary This paper presents a unified formulation for the kinematics, singularity and workspace analyses of parallel delta robots with prismatic actuation. Unlike the existing studies, the derivations presented in this paper are made by assuming variable angles and variable link lengths. Thus, the presented scheme can be used for all of the possible linear delta robot configurations including the ones with asymmetric kinematic chains. Referring to a geometry-based derivation, the paper first formulates the position and the velocity kinematics of linear delta robots with non-iterative exact solutions. Then, all of the singular configurations are identified assuming a parametric content for the Jacobian matrix derived in the velocity kinematics section. Furthermore, a benchmark study is carried out to determine the linear delta robot configuration with the maximum cubic workspace among symmetric and semi-symmetric kinematic chains. In order to show the validity of the proposed approach, two sets of experiments are made, respectively, on the horizontal and the Keops type of linear delta robots. The experiment results for the confirmation of the presented kinematic analysis and the simulation results for the determination of the maximum cubic workspace illustrate the efficacy and the flexible applicability of the proposed framework.

This paper proposes a method for the scaled bilateral teleoperation with continuously variable position and force scaling. In the proposed method, the controller is reformulated to synchronize the forces and velocities which provides the operator with the ability to change the scaling gains during operation. For the derivation of the controller, exponentially decaying error dynamics are preferred over the assumption of disturbance compensation with Disturbance Observers (DOB). Following the mathematical derivation, the algorithm is tested on a setup containing single DOF master and slave robots with the ability of giving force feedback to the operator. In order to provide a complete analysis, several different sets of experiments are made with sinusoidal velocity and force scales having different amplitudes and frequencies. Experiment results illustrate the successful tracking responses and stable operation of the proposed control scheme for the continuously varying velocity and force scales.

In shared human-robot environments, control systems operate based on the information about both human and robot activities to facilitate the successful collaboration between the two. This paper contributes to the emerging field of human-robot collaboration (HRC) by unifying human action recognition (HAR) and high-level robot control technique into single control system. Approach in this paper includes artificial neural network based classifier for recognition of human activity and task-based control as an example of high-level control technique. Classifier is developed based on the data from wearable sensors attached on the human arms. Recognized human activity is used as the input for the selection of functions that describe robot's activity (task). This papers combines both the theoretical approach to the task-based control and it's synergy with HAR while the developed artificial neural network classifier is experimentally validated.

This paper presents a controller structure for the continuous and robust modification of motion for multi body systems encountering contact with an environment during free motion. The presented algorithm relies on the reformulation of the position tracking error with a term proportional to the reaction force. With the proposed method, fusion of the position and the force controllers can be achieved which provide the robot with certain level of compliance. The derivation of the proposed method is followed by experiments made on a pantograph mechanism actuated by direct drive linear motors. The results obtained from the experiments illustrate the success of the proposed control architecture in providing a natural behavior for the robotic systems working in constrained environments.

Abstract This article investigates a new current control strategy for grid connected doubly fed induction generators (DFIG) under unbalanced grid voltage conditions. DFIG dynamic model is represented in synchronously rotating symmetrical component dq frames of references. A proportional controller which feed forwards estimated disturbance terms is proposed for power control in unbalanced voltage conditions to accomplish positive sequence power demand and also to dissipate negative sequence components which cause double frequency oscillations in power. DFIG parameters are not required to be known since it estimates the machine parameters relevant nonlinear terms with a disturbance observer (DOB). The novel controller structure is implemented by using dSPACE ds1103 digital controller which controls a 1.1 kW DFIG experimental setup.

SUMMARY This paper proposes a bilateral control structure with a realization of the force derivative in the control loop. Due to the inherent noisy nature of the force signal, most teleoperation schemes can make use of only a proportional (P) control structure in the force channel of the bilateral controllers. In the proposed scheme, an α–β–γ filter is designed to smoothly differentiate the force signal obtained from a reaction force observer integrated to both of the master and slave plants. The differentiated force signal is then used in a proportional-derivative (PD) force controller working together with a disturbance observer. In order to design the overall bilateral controller, an environment model based on pure spring structure is assumed. The controller is designed to enforce an exponentially decaying tracking error for both position and force signals. With the presented controller design approach, one can independently tune the controller gains of the force and the position control channels. The proposed approach is experimentally tested in a platform consisted of direct drive linear motors. As illustrated by the experiment results, the contribution of the PD control in the force channel improves the teleoperation performance especially under hard-contact motion scenarios by attenuating the oscillations, hence, improving the transparency when compared to the structures using only a P force control.