Need For Velocity Measurements Research Articles

Novel adaptive backstepping control of uncertain electrically driven haptic robot for surgical training systems

The following paper presents the design, implementation, and validation of a new adaptive control system based on the Modified Function Approximation Technique (MFAT) augmented with backstepping control for a haptic robot with unknown dynamic and actuator parameters, employed in a spinal surgical simulator. The combination of backstepping control and the MFAT policy ensures the continuous performance tracking of the haptic manipulator's trajectories using state and output feedback. Contrary to the conventional FAT, the use of basis functions in dynamic and actuator parameter approximations is completely eliminated. Besides, the proposed control scheme was improved by integrating a high order sliding mode observer to eliminate the need for velocity measurements. Consequently, offline simulation and comparative studies were carried out to validate the effectiveness of the proposed control scheme, and controlled experimental cases were conducted using the haptic manipulator (Entact W3C) for validating the system in real time.

Tracking Control of Electrically Driven Robots Using a Model-free Observer

SummaryThis paper presents a robust tracking controller for electrically driven robots, without the need for velocity measurements of joint variables. Many observers require the system dynamics or nominal models, while a model-free observer is presented in this paper. The novelty of this paper is presenting a new observer–controller structure based on function approximation techniques and Stone–Weierstrass theorem using differential equations. In fact, it is assumed that the lumped uncertainty can be modeled by linear differential equations. Then, using Stone–Weierstrass theorem, it is verified that these differential equations are universal approximators. The advantage of proposed approach in comparison with previous related works is simplicity and reducing the dimensions of regressor matrices without the need for any information of the systems’ dynamic. Simulation results on a 6-degrees of freedom robot manipulator driven by geared permanent magnet DC motors indicate the satisfactory performance of the proposed method in overcoming uncertainties and reducing the tracking error. To evaluate the performance of proposed controller in practical implementations, experimental results on an SCARA manipulator are presented.

Output-feedback formation control of wheeled mobile robots with actuators saturation compensation

This paper addresses output-feedback formation control of a group of wheeled mobile robots with saturating actuators. A virtual leader–follower strategy and a passivity-based design procedure are utilized to propose an adaptive neural network formation controller together with a nonlinear observer for the performance improvement of robots formation. The main tactic for the enhancement of the formation controller performance is the effective compensation of the actuators saturation nonlinearity by using neural networks and saturation functions. The need for velocity measurements is eliminated by a saturated observer that reduces unwanted peaks in the velocity estimates. A stability analysis is presented by using Lyapunov’s direct method. Finally, simulation results illustrate the efficiency of the proposed controller compared with existing results.

FAT-based robust adaptive control of electrically driven robots without velocity measurements

Recently, regressor-free control approach has been presented in which uncertainties are estimated using function approximation techniques (FAT) such as the Fourier series expansion or Legendre polynomials. However, FAT-based observer design remains as an open problem. With this in mind, this paper presents a robust adaptive controller for electrically driven robots, without any need for velocity measurements. The mixed observer/control design procedure is based on universal approximation theory and using Stone–Weierstrass theorem. To highlight the contribution of the paper, it should be emphasized that in comparison with previous related FAT-based controllers, the proposed controller is simpler and less computational. In addition, the number of required Fourier series expansions, control laws, and also adaptation rules has been reduced. Moreover, the observer design is free of model. Simulation results of the controller on a 6-DOF industrial robot manipulator have been presented which proves robustness of the proposed controller against various uncertainties. The results are also compared to those obtained from Chebyshev neural network.

An Output-Feedback PID-type Global Regulator for Robot Manipulators with Bounded Inputs

An output-feedback PID-type controller for the global stabilization of manipulators with bounded inputs is proposed. It guarantees the global regulation goal preventing input saturation while avoiding the exact knowledge of the system model and parameter values as well as the need for velocity measurements. Furthermore, it adopts an SPD-SI structure by keeping both the P and D actions together within a generalized saturation function while including an additional similar saturating integral action separately. So far, a formal analytical formulation for such a saturating PID-type control structure was not available under the absence of velocity measurements. Experimental results on a 2-degree-of-freedom direct-drive manipulator corroborate the efficiency of the proposed controller. Copyright© 2015 IFAC

A generalized trajectory tracking controller for robot manipulators with bounded inputs

A generalized controller based on stability theory of singularly perturbed systems is proposed, to deal with the problem of bounded actuator inputs in robot trajectory tracking control. The saturation function with error-gain matrix is applied in the torque control law, which ensures the upper bound of torque inputs in any given limited range. Through appropriately setting the entries of the error-gain matrix, the tracking performance can be improved. Moreover, a pseudo signal is generated from a linear filter to substitute for the actual velocity error, eliminating the need for velocity measurements. Finally, to verify the effectiveness of the generalized controller, a new saturated controller with error-gain-contained arc tangent function is designed. Comparison experiments show that the proposed controller can strictly guarantee the bound of the torque inputs in situations with non-zero initial tracking errors, and gives a better tracking result than other controllers.

A planar Mie scattering visualization technique for turbo machinery application

A planar Mie scattering technique is described which allows for the systematical analysis of three-dimensional shock configurations without the need for velocity measurements. For that, small particles are added to the flow upstream of the shock and illuminated by a laser light sheet. The scattered light is captured by a CCD camera so that the position of the shock wave can be determined from the increase of the light intensity across the shock. To analyze the three-dimensional structure of a shock wave, the light sheet is moved perpendicular to the flow direction. The measurement technique is applied to both a supersonic wedge flow at Ma = 2.43 and a more complex shock wave configuration in a transonic cascade flow at Ma = 1.09. The gathered results are conclusive with Schlieren photographs, numerical simulations and surface pressure measurements. As the chosen setup allows the application to test sections with restricted optical access and a synchronization of the image capturing process with an external triggering signal, the three-dimensional shock configurations inside a transonic compressor rotor can also be visualized.

A redesigned DCAL controller without velocity measurements: theory and demonstration

A link position tracking controller is formulated for an n-link, rigid, revolute, serially-connected robot. The controller generates torque commands to the individual robot links based on adaptive estimates of the system parameters and measurements of only link positions. A filtering technique, based on the link position signal, is used to alleviate the need for velocity measurements. A complete development of the controller is presented along with a proof of semiglobal asymptotic link position-velocity tracking performance. Experimental validation of the proposed controller on the Integrated Motion Inc. (IMI) two-link direct drive robot is also presented. Several extensions to the basic controller are described that consider the use of fixed parameter estimates.