Showing papers by "Septimiu E. Salcudean published in 2001"

Analysis of Control Architectures for Teleoperation Systems with Impedance/Admittance Master and Slave Manipulators

Abstract: A large number of bilateral teleoperation control architectures in the literature have been designed based on assumed impedance models of the master and slave manipulators. However, hydraulic or heavily geared and many other manipulators cannot be properly described by impedance models. In this paper, a common four-channel bilateral control architecture designed for the above impedance models is extended to teleoperation systems with master and slave manipulators of either the admittance or impedance type. Furthermore, control parameters that provide perfect transparency under ideal conditions are found for each type of teleoperation system. Because in practice such parameters may not lead to systems that are robust to time delays and model uncertainties, an analysis of the stability and performance robustness of this very general architecture and two-channel architectures is also presented. The analysis uses the passivity-based Llewellyn two-port network absolute stability criterion, as well as bounds on...

Nonlinear control of hydraulic robots

Abstract: This paper addresses the control problem of hydraulic robot manipulators. The backstepping design methodology is adopted to develop a novel nonlinear position tracking controller. The tracking errors are shown to be exponentially stable under the proposed control law. The controller is further augmented with adaptation laws to compensate for parametric uncertainties in the system dynamics. Acceleration feedback is avoided by using two new adaptive and robust sliding-type observers. The adaptive controllers are proven to be asymptotically stable via Lyapunov analysis. Simulation and experimental results performed with a hydraulic Stewart platform demonstrate the effectiveness of the approach.

Optimal kinematic design of a haptic pen

Abstract: This paper investigates the performance demands of a haptic interface and shows how this information can be used to design a suitable mechanism. A design procedure, previously developed by the authors (1996), consisting of a global isotropy index and a discrete optimization algorithm, allows one to compare a range of geometric variables, actuator scale factors, and even different robot devices for optimum performance. The approach is used to compare the performance of three 6-DOF robots including two well-known parallel platform robots and a novel hybrid robot called the Twin-Pantograph in terms of their semi-dextrous workspaces and static force capabilities. Since the Twin-Pantograph yields the best results, its design is refined to address practical constraints and it is implemented as a haptic pen. The performance of the resulting design is analysed and presented.

A user interface for robot-assisted diagnostic ultrasound

Abstract: A robot-assisted system for medical diagnostic ultrasound has been developed by the authors. This paper presents key features of the user interface used in this system. While the ultrasound transducer is positioned by a robot, the operator, the robot controller, and an ultrasound image processor have shared control over its motion. Ultrasound image features that can be selected by the operator are recognized and tracked by a variety of techniques. Based on feature tracking, ultrasound image servoing in three axes has been incorporated in the interface and can be enabled to automatically compensate, through robot motions, unwanted motions in the plane of the ultrasound beam. The stability and accuracy of the system is illustrated through a 3D reconstruction of an ultrasound phantom.

Active joystick with optical position sensor

Abstract: A joystick composed of a stator formed by an outer cage forming an inner cubic compartment containing an inner cube oriented with its wall spaced from and substantially parallel corresponding wall of the compartment. Opposed magnets are position in cooperating relationship on opposed walls of the compartment and cube and define a gap therebetween. A floater formed by a plurality of flat actuating coils, one positioned in each gap and each thinner than the width of the gap in which it is received. Preferably the ratio of coil thickness to gap width is at least 1:3. Preferably an optical position sensor is used to monitor the relative position of the flotor and stator and is composed of at least one linear light position sensor mounted on one of the stator and flotor and a plurality of planar light beams arranged at an angle to each other on the other of the stator and flotor and directed to the linear light position sensor(s) so that the light beams traverse the linear light position sensor(s).

Nonlinear control of a hydraulic parallel manipulator

Abstract: An adaptive nonlinear controller is proposed for position tracking in hydraulic robots by adopting the backstepping methodology. Full system models including rigid body and hydraulic dynamics are incorporated in the design. The tracking errors are shown to be asymptotically stable in the presence of parametric uncertainties using Lyapunov analysis. The controller is applied to a Stewart type hydraulic manipulator. Simulation and experimental results are provided to demonstrate the effectiveness of the approach.

A Virtual Environment for the Simulation and Programming of Excavation Trajectories

Abstract: An excavator simulator has been developed to facilitate the training of human operators and to evaluate control strategies for heavy-duty hydraulic machines. The operator controls a virtual excavator by means of a joystick while experiencing visual and force feedback generated by environment and machine models. The simulator comprises an impedance model of the excavator arm, a model for the bucket-ground interaction forces, a graphically rendered visual environment, and a haptic interface. This paper describes the simulator components and their integration.

Adaptive image servo controller for robot-assisted diagnostic ultrasound

Abstract: A robot-assisted system for medical diagnostic ultrasound has been developed by the authors. An ultrasound image servo controller has already been proposed and implemented by Abolmaesumi et al. (2000) to automatically compensate, through robot motions, unwanted motions in the plane of the ultrasound beam. This paper presents an adaptive image servo controller to enhance the performance of the ultrasound image servo controller. To increase safety, the control is shared between the operator and the image controller. The stability and accuracy of the system is illustrated through different experiments.