Design of robot assistance for arm movement therapy following stroke

This paper describes the mechanical and control design of a robotic device for providing therapeutic assistance to arm movement following stroke. The device uses a single motor and a passively oriented linear constraint to allow patients to reach across their workspace. Experimental evaluation of two controllers for assisting in reaching is presented.     

Experimental study on fine motion control of underwater robots

This paper considers thruster dead zones and saturation limits, which are nonlinear elements that complicate fine motion control of underwater robots. If the vehicle is configured with redundant thrusters, the respective dead zones and their surrounding nonlinear regions could be avoided by implementing a null motion solution for the command input of the vehicle. This solution is derived from the vehicle's geometry and is realized before the application of the motion control algorithm. The result is an improvement in system performance exclusive of the implemented controller type. The approach is illustrated through simulation and experiment with an underwater robot, ODIN.     

Pouring control with prediction of filling weight in tilting ladle type automatic pouring system

Abstract

This paper presents an advanced control system in a tilting ladle type automatic pouring system. To improve the productivity and save energy, in the pouring process, it is important that the mould be filled precisely and quickly with molten metal. A sequence control employing prediction of filling weight is proposed in this paper. In the proposed control system, the sequence parameter varies depending on the predicted filling weight during the back tilting. The proposed control system has an advantage in that it can be performed by common control equipment such as a programmable logical controller. The effectiveness of the proposed filling weight control system is demonstrated through the experiments using water.     

Improved Control Strategy of 2-Sliding Controls Applied to a Flexible Robot Arm

Controlling a flexible robot arm driven by McKibben artificial muscles with direct transmission is delicate. The usual PID controller rapidly reveals itself to be inadequate and robust control tools are unavoidable. Classical sliding control, although robust, generates chatter. Several solutions are available to attenuate this phenomenon, among them the twisting and super twisting algorithms, which belong to the 2-sliding control set. It will be shown when to use the equivalent control and the effect of a noised sensor signal on control performance. Also, the use of an additional discontinuous term that increases robustness, performance and stability is put forward. Experimental results are presented and discussed.     

Vision-Based Task-Level Control of a Flexible-Link Manipulator

This paper discusses a vision-based approach to implement task-level control in flexible-link manipulators. The proposed approach emphasizes the advantage of using vision in the control of flexible manipulators. It is pointed out that taking advantage of the inherent robustness, implementation of an image-based visual servo can be regarded as a synthetic solution to precise task-level control of flexible manipulators. This approach is implemented in a three-dimensional flexible-link manipulator. The implementation makes good use of filters in decoupling task-level control and vibration suppression control. Moreover, we point out that although the robustness of the approach can help to overcome the difficulty in control resulting from the complex measurement of the link's elastic deformation, it lacks in capability of tip trajectory specification. This problem is analyzed in this research and it leads to the proposal for the integration of the image interpolation technique. This technique makes the proposed approach adequate for tasks involved with complex tip trajectories. For flexible-link manipulators, the proposed approach with the remedy is the first vision-based synthetic solution that attempts to make a flexible manipulator usable for a practical task.     

Pilot control of an auto-balancing two-wheeled cart

The control system of an auto-balancing two-wheeled cart (ABTWC) is inherently unstable, displays a non-minimum phase and can be piloted by a joystick that has 2 d.o.f. This paper employs a state feedback technique to design the stabilizing controller for an ABTWC and develops a pilot algorithm, i.e., differential steering, which converts two joysticks' commands into two torque directives for transportation. This allows the user to operate this cart linearly for both motion and orientation control via a joystick. Control examples are given to illustrate the feasibility and the effectiveness of the proposed controller and pilot algorithm.     

Sonar-based guidance of unmanned underwater vehicles

This paper addresses the problem of the design and coordination of guidance and sonarbased motion estimation algorithms for unmanned underwater vehicles. In the framework of a two-layered hierarchical architecture uncoupling the system's dynamics and kinematics, a couple of guidance laws for approaching a target with the desired orientation and following an environmental feature have been designed with Lyapunov-based techniques. Suitable acoustic-based estimators of the corresponding operational variables have been designed and integrated with the guidance and control system. A finite state machine combined with a suitable interface for event generation allows the coordinated execution of basic guidance and motion estimation tasks to carry out more complex functions. Experimental results of pool trials of a prototype unmanned underwater vehicle executing free-space maneuvering, wall-following tasks and the more complex mission of following the perimeter of the trial pool are reported and discussed.     

Final-state control of a two-link cat robot

In this study, we deal with the twisting motion of a falling cat robot by means of two torque inputs around her waist. The cat robot consists of two rigid columns and has two internal actuators at the joint to generate torque inputs around normal coordinates. This system is a nonholonomic system whose angular momentum is conserved. We formulate the state equation that has torque inputs to the joint by using the nonholonomic constraint and the Lagrange-d'Alembert principle. Then, we transform the system into a linear parameter varying system. In order to improve error learning of a final-state control method, we provide the initial inputs in order to determine the appropriate rotation direction in the early stage of the twisting motion. Next, we introduce the method of the artificial potential function to the final-state control in order to make the maximum bending angle small. The feedforward torque inputs can be obtained by the final-state control in order to bring the system from the initial state to the final state in the desired time. In simulations, we also demonstrate that the twolink cat robot can land on her feet by using the 2-d.o.f. control system even when her waist damping coefficient varies.     

Stability analysis and robust control for fixed-scale teleoperation

In this article we present a new theorem that reduces the stability problem of teleoperators from a structured singular value problem to a maximum singular value problem. A control scheme realizing an ideal response for fixed-scale teleoperation is proposed and its stability is proven analytically. Next, the ideal control scheme is extended to control schemes with a higher stability robustness. Also, for these more complicated schemes, stability analyses are performed making use of the new theorem and stability conditions are derived. Experiments on a 1-d.o.f. setup are conducted to confirm the validity of the proposed control schemes.