Boris Curk

Neural network sliding mode robot control

This paper develops a method for neural network control design with sliding modes in which robustness is inherent. Neural network control is formulated to become a class of variable structure (VSS) control. Sliding modes are used to determine best values for parameters in neural network learning rules, thereby robustness in learning control can be improved. A switching manifold is prescribed and the phase trajectory is demanded to satisfy both, the reaching condition and the sliding condition for sliding modes.

Observer-based sliding mode control of a robotic manipulator

This paper presents a new approach for the design of variable structure control (VSC) of nonlinear systems. The approach is based on estimation of joint acceleration signals with introduction of load estimation with the asymptotic observer. The control system is insensitive to parameter variations for a chosen switching hypersurface in conditions when it is reached by the dynamic motion with the required dynamics. The parameter insensitive response provided by this control method is demonstrated on the model of the SCARA robot. Simulation results confirm the validity of accurate tracking capability and the robust performance.

Robust motion control of XY table for laser cutting machine

The position control algorithm for a belt-driven servomechanism of a laser cutting machine is described. A high-accuracy position tracking control procedure for systems with inherent elasticity due to the low-cost belt-driven servomechanism is derived based on a continuous sliding mode technique. The proposed robust position tracking control algorithm was tested by simulations and used in the industrial application of a motion controller for the CNC machine. Simulation and experimental results are also reported.

Sliding mode control with perturbation estimation: application on DD robot mechanism

In this work another perturbation estimation sliding mode based control algorithm is introduced for a class of robotic systems in the presence of structured and unstructured uncertainties and external disturbances. The effects of these uncertainties are combined into a single quantity. A full order device with the actuator voltages as control inputs is assumed in control design. The decentralized control scheme with only a partial state feedback is applied. A modification of the switching functions with perturbation estimation is introduced. The salient features of this approach is that the perturbations are effectively treated by a computationally straightforward procedure. The proposed controller is applied to a minimal configuration direct drive robot mechanism.

Chattering Reduction in VSC Systems of Robotic Manipulators

Abstract The sliding mode motion design is considered for the nonlinear plants linear with respect to the control input. The dynamics of the robotic manipulators is treated with and without the dynamics of the actuators. When the dynamics of the actuators is included, design of the sliding modes for the systems with discontinuous control is performed. If actuators dynamics is neglected the control is assumed to be continuous quantity. By combining variable structure systems and Lyapunov design a new discrete-time algorithm has been developed. It possesses all the good properties of the sliding mode systems and avoids the unnecessary discontinuity of the control input, thus eliminating chattering. Neither the explicit calculation of the equivalent control nor the implicit high gain feedback inside the boundary layer are used. Control parameters depend on the plant gain matrix and on the gradients of the sliding mode manifold. Simulations justify the solutions developed in this paper.

Modelling of the robotic Powerball®: a nonholonomic, underactuated and variable structure-type system

The Powerball® is the commercial name for a gyroscopic device that is marketed as a wrist exerciser. The device has a rotor with two underactuated degrees of freedom, which can be actuated by the appropriate motion of human or robot wrist axes. After the initial spin, applying the appropriate motion and torques to the housing leads to a spin-up of the rotor. Finding these torques intuitively is an easy task for human operators, but a complex task for a technical consideration, for example, in robotics. This articles main contribution is a novel dynamic model that considers friction effects. The presented model includes all three working principles of the device: free rotor mode and both modes of rotor rolling in the housing. The work introduces models with one and two degrees of freedom actuation, both of which are suitable for laboratory control experiments. An estimation of the friction is discussed, and both the simulation and the experimental results are presented to evaluate the models.

Robust sliding mode based impedance control

Industrial robots are confronted with performing tasks where a contact with their environment occurs. Therefore, a need for control algorithms with position tracking performance and force control ability appears. Many algorithms have been proposed which deal with robot motion and force control. They could be mainly separated into two classes, namely: hybrid control, where constrained and unconstrained DOFs of the robot are observed separately based on the principle of the orthogonality; and impedance control where the robot should adopt some physical properties such as mass, damping and stiffness in order to assure stable dynamic interaction with the environment. In this paper the robust impedance control law based on the attractive theory of sliding mode is proposed. The control law guarantees a robot predefined impedance and therefore force regulation based on impedance properties is discussed. Experimental results on a simple 1 DOF mechanism is shown to verify theoretical statements.

Control of nonholonomic robotic load

Powerballreg is a commercial name for gyroscopic device that is marketed as a wrist exerciser. The device has rotor with two unactuated degrees of freedom and can be actuated with suitable rotational motion of human or robot wrist axis [1]. After substantial initial rotors spin, the properly applied torque and motion about two wrist axis lead to spin-up of the rotor. Finding this torque intuitively is easy job for most peoples, but not so easy for technical consideration for example in robotics. In the paper, a modeling of different modes of the device is presented first. A dynamic model with nonholonomic rolling connection which appear in normal operational mode is discussed. With the rotor and housing connection the additional friction effect is observed. When the nutation reaction torque is to low, only dissipation of energy is observed and rotor stops. But when the reaction torque causes normal forces on a connection in a degree that the friction is high enough, the rotor shaft begins to roll. The connection with the housing takes place in a gap so two connecting pairs are possible. One is up-down for left precession and another is down-up for opposite precession rotation. Developed models are used as a basis for control structure in the second part when the experiments are performed with the robot. The control strategy is oriented towards underactuated system, active and passive robots degrees of freedom.

Continuous Sliding Mode Control of DD Robot Mechanism

Abstract A non-model-based discrete-time chattering-free sliding mode control scheme is applied. In the discrete-time expression the discontinuous operation of controllers in the sliding mode has been replaced by the continuous one. The chattering of control input has been attenuated and the excitation of the dynamic system without high frequency oscillations has been achieved. The proposed control solution is near an ideal control function in the sliding mode. Unlike other algorithms intended to avoid chattering, this non model based approach uses only the information about the distance from the sliding mode manifold to derive the control. The proposed control scheme is applied on a mininal configuration direct drive robot mechanism.

Discontinuous and continuous sliding mode motion control

An advanced discrete-time chattering-free sliding mode control scheme is presented. The distinctive feature of the scheme is its robustness to different initial condition values and parameter mismatch. Nonlinear control principles will be used namely, the combined feedforward and the robust negative feedback part based on VSS controllers. In the discrete-time expression the discontinuous operation of controllers in the sliding mode has ben replaced by the continuous one. In this way the chattering of control input has been eliminated and the excitation of the dynamic system without high-frequency oscillations has been achieved. The proposed control solution is near an ideal control function in the sliding mode. Unlike other algorithms intended to avoid chattering, this nonmodel-based approach uses only the information about the distance from the sliding mode manifold to derive the control. The advantage of the proposed control scheme prevail over those conventional model-based control scheme since no precise knowledge of mathematical model is necessary. In order to implement the control it must be only known the structure of input matrix and the mean values of its parameters. The input-output linear behavior of the closed control loop is predominantly determined by the controllers gain matrix.