Input-state feedback linearization control of a single-link flexible robot arm moving under gravity and joint friction

Online Algebraic Identification of the Payload Changes in a Single-Link Flexible Manipulator Moving under Gravity

The aim of this paper is to investigate the performance of the hybrid controller for end-point vibration suppression of a flexible manipulator, while it is tracking a desired input profile. Due to large structural vibrations, precise control of flexible manipulators is a challenging task. A hybrid controller is used to track large movements of flexible robotic manipulators, which is a combination of inverse dynamics feedforward control, command shaping and linear state feedback control. The case study of a single-link flexible manipulator is considered, where the manipulator is controlled under open-loop as well as closed-loop control scheme. In the open-loop control scheme, the aim is to test the effectiveness of the command shaper in reducing the vibration levels. Moreover, the effect of payload variations on the performance of command shapers and the importance of more robust shapers is demonstrated in this work. Under the closed-loop control scheme, the control objective is to track the large-hub angle trajectory, while maintaining low vibration levels. In comparison to collocated PD control, being reported in the literature, large reductions in tip acceleration levels as well as input torque magnitudes are observed with the proposed hybrid controller.

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Vibration suppression during input tracking of a flexible manipulator using a hybrid controller

This paper discusses the open loop control problem of a flexible joint robot that is oriented in the vertical plane. This orientation of the robot arm introduces gravity constraints and imposes undesirable nonlinear behavior. Friction is also added at the joints to increase the accuracy of the model. Including these dynamics to the robot arm amplifies the open loop control problem. Differential flatness is used to propose a feed-forward control that compensates for these nonlinearities and is able to smoothly steer the robot from rest to rest positions. The proposed control is achieved without solving any differential equations which makes the approach computationally attractive. Simulations show the effectiveness of the open loop control design on a single link flexible joint robot arm.

Flatness based feed-forward control of a flexible robot arm under gravity and joint friction

Accurate trajectory tracking and control of the Double Flexible Joint Manipulator lead to design a controller with complex features. In this paper, we study two significant strategies based on improving the structure of the hybrid controller and training the controller parameters for an online estimation of time-varying parametric uncertainities. For this purpose, combination of feedback linearization with an adaptive sliding mode control by considering update mechanism is utilized to stabilize the DFJM system. The update mechanism is obtained based on gradient descend method and chain rule of the derivation. Following, in order to eliminate the tedious trial-and-error process of determining the control coefficients, an evolutionary algorithm (NSGA-II) is used to extract the optimal parameters by minimizing the tracking error and control input. In the second step, an online estimation of the designed parameters were proposed based on three intelligent methods; weighting function, Adaptive Neural Network Function Fitting (ANNF), and adaptive Neuro-fuzzy inference system (ANFIS-PSO). The proposed controller reliability finally was examined in condition of the mass and the length of the robot arm was changed and sudden disturbances were imposed at the moment of equilibrium position, simultanously. The results of the tracking error and control input of the trained proposed controller demonstrated minimal energy consumption and shorter stability time in condition that the control parameters are constant and training are not considered.

http://admt.iaumajlesi.ac.ir/article_683541_d25556448c54bfe3dfe8137d96f6dda1.pdf

An Online Trajectory Tracking Control of a Double Flexible Joint Manipulator Robot by Considering the Parametric and Non-Parametric Uncertainty

This paper presents a control scheme for a flexible single-link arm moving under gravity. The purpose of this controller is the precise positioning of the arm tip in presence of link vibrations and joint friction. In order to achieve this, a two nested loop control is used: The inner loop is responsible for the motor positioning, and the outer loop suppresses the vibrations in the arm structure. On the inner loop design, a linear algebraic controller is considered. On the outer loop, an input/state linearization control is chosen. Simulation results are presented to demonstrate the performance of the controller.

Feedback Linearizing Controller for a Flexible Single-Link Arm under Gravity and Joint Friction

In this paper, we present an experimental study concerning the gravity compensation of flexible link arms based on linear springs. In the field of flexible link robotics, the gravity compensation based on counterweights has been successfully applied in the past, but little effort has been made to examine the potential benefits and difficulties of using spring-based compensation mechanisms. This paper focuses on the modeling and identification of a single link flexible arm compensated with a spring based mechanism. As modeling approach, we followed the lumped-mass methodology to develop a model capable of reproducing the first vibrational frequency of the flexible link arm. Keeping in mind the forces that interact with the flexible link, a combination of sensors is suggested in order to measure and estimate the most important variables of the system. Subsequently, a very simple and reliable identification method based on the time and frequency response of the system is proposed. Finally, the results of the modeling and identification are validated on our experimental platform.

Jose Abel Chocoteco

Papers

Feedback Linearizing Controller for a Flexible Single-Link Arm under Gravity and Joint Friction

Modeling and Identification of a Single Link Flexible Arm with a Passive Gravity Compensation Mechanism