We present the design of a backstepping controller for a triangular over-actuated marine platform, controlled by three rotating jets. Our goal is the stabilization of the position and the orientation of the platform, under realistic environmental disturbances, such as wind forces, wave forces and hydrodynamic forces. Actuator thrust and angle dynamics, as well as settling delays, in the rotation of the jets and in the response of the desired thrust, are included in the algorithm, despite the presence of an allocation scheme. Thrust and angle velocity, limitations are also taken into account. A Thrust Upper Limit (TUL) manipulation heuristic is introduced in order to reduce the thrust requirements and the energy consumed. The performance of the developed backstepping controller is compared to the case with and without the TUL. Simulation results show that the use of the heuristic reduces energy consumption.

This paper presents the analysis, design, and closed-loop motion control of a mobile microrobotic platform capable of micrometer positioning on a plane. The mobile microrobot, including chassis, actuators, drives, microprocessor, and electronics, is of low cost (less than $20), can be fabricated rapidly and is made of commercially available components. Its motion is induced by centrifugal forces generated by two vibration motors installed inside the platform body. The asynchronous operation of the vibration motors is shown by simulation to result in planar motions of two degrees-of-freedom locally, with micrometer resolution. A motion controller has been designed to generate controlled motions using sets of motor angular velocities. A prototype has been developed and used to validate the motion principle and the controller efficacy. Open loop experiments show that the platform motion resolution is approximately 20 μm, while its speed is greater than 2 mm/s. Closed-loop experiments demonstrate a 5 μm resolution, i.e., a fourfold improvement compared to the open loop experiments. The low cost, the rapid fabrication, and the micrometer motion resolution suggest that this microrobotic platform is a promising solution for low-cost microfactories, where a group of such robots performs high throughput, advanced microassembly of microsystems.

This paper presents the design and practical implementation of an autonomous dynamic positioning scheme, i.e., the stabilization of linear and angular velocities as well as the position and orientation, of a novel triangular floating sea platform. The required closed-loop forces and moments must be provided by three rotating pump jets, located at the bottom of three partly submerged cylinders located at the three corners of the platform. With this control configuration the platform is over-actuated, i.e., it has more control inputs than degrees of freedom (DOF). Design rules that maximize the manipulability of the platform, and a control allocation scheme that allows goal realization without violating thruster capabilities are developed. Simulations results, including environmental disturbances, are presented that demonstrate the performance of the controller, and the allocation scheme employed.

In this paper a study is conducted on the force capabilities of centripetal force actuated microrobotic platforms. The aim is to exploit the centripetal forces generated by platform mounted vibrating micro-motors for micromanipulation purposes. First, an overview of the platform dynamics and motion capabilities is presented. The type of forces generated by the actuation mechanism as well as due to the impulsive interaction with the working environment are studied. Then design steps are proposed for (i) the reduction or elimination of undesired impulsive forces, (ii) the attenuation of the force ripple transmitted to the manipulated object. The outcome is a smooth, controllable force transmitted to the manipulated object. A cantilever is mounted on the platform and preliminary experiments are conducted.

An OpenGL/C++ real-time graphic environment, part of a training simulator for urological operations, is presented. The graphic environment simulates endoscope insertion in a small diameter deformable tube and is used with a low-force 5-dof force-feedback haptic mechanism. Piecewise Bezier interpolations are used for smooth urethra deformations. A novel particle-based model computes the forces and torques fed to the haptics. Realistic textures from medical databases are employed and a 25 fps refresh rate is achieved using the Rendering Thread method. The overall simulator software is made of three processes running on two distinct platforms, communicating via Ethernet and TCP/IP.

This work presents a design methodology, which aims at the minimization of the mass, inertia and joint friction for a low - force five - dof haptic device. The haptic device is optimized along a typical path with proper tolerances, rather than at some workspace operating point. The device, part of a training medical simulator for urological operations, consists of a two dof, 5-bar linkage and a three dof spherical joint. The requirement for reliable reproduction of low torques and forces lead to the need for minimization of device induced parasitic forces and torques. The multiobjective optimization employed is based on two objective functions that include mass/ inertia properties and joint friction. The kinematical and operational constraints are taken into account. The resulting optimized mechanism is substantially improved with respect to an existing device.

Virtual reality is becoming very important for training medical surgeons in various operations. Interfacing users with a virtual training environment requires the existence of a properly designed haptic device. This paper presents the design and implementation of a new force feedback haptic mechanism with five active degrees of freedom (DOFs), which is used as part of a training simulator for urological operations. The mechanism consists of a 2-DOF, 5-bar linkage, and a 3-DOF spherical joint, designed to present low friction, inertia and mass, and to be statically balanced. The device is suitable for the accurate application of small forces and moments. All five actuators of the haptic device are base-mounted dc motors and use a force transmission system based on capstan drives, pulleys, and tendons. The paper describes the overall design and sizing considerations, the resulting kinematics and dynamics, the force feedback control algorithm, and the hardware employed. Experimental results are provided.

A haptic feedback mechanism with five active degrees of freedom (dof), part of a training simulator for urological operations, is presented. The mechanism consists of a 2-dof 5-bar linkage, and a 3-dof spherical joint. To reproduce very small forces and moments, the mechanism has low friction, inertia and mass, is statically balanced, and has a simple mass matrix. Roll-pitch-yaw motions of the tool result in motions of the corresponding actuator. Force feedback transmission is achieved via capstan drives and idler pulleys. The computation of the currents and the structure of the control loop are described.