Abstract
In this paper, a state observer design for a walking in-pipe robot is studied. The necessity of using a state observer is related to the fact that sensors have limited accuracy and are prone to producing noise. This is especially problematic for in-pipe walking robots, since they use model-based control and require accurate information of their current state. The paper shows that an iterative state observer based on solving Riccati equation provides significant improvements in the behaviour of the control system. It allows to smooth out the spikes in the control actions requested by controller and to minimize tremor of the robot links. In order to study the behaviour of the observer when different sensors are used, a performance function was introduced. It was shown that the observer allows to improve the performance of the control system for a wide range of sensor parameters. Additionally, it was shown that the introduction of the observer allows to choose higher feedback controller gains, enabling more precise control. Simulations on the full robot model, taking into account mechanical constraints and contact forces showed that the linear observer is capable of improving the behaviour of the control system of the walking robot, if measurements of the reaction forces are provided. The effects that the noise and quantization in the reaction forces measurements have on the behaviour of the state observer is studied.
Highlights
Pipeline inspection robots are complex electromechanical systems that are designed to move inside pipelines while carrying necessary equipment
Where x = [qΤ q Τ ]Τ is a vector of state coordinates, u = τ, A = ∂f ∂x, B = ∂f ∂u and c = f − Ax − Bu are constant linearization matrices and vectors calculated at a given point x0 and f = H−1(τ − c0 ) is the function describing the dynamics of the robot
The robot is controlled by a computed torque controller (CTC), which is given by the following control law: τ = H(q * + Kd e + K pe) + c0, (4)
Summary
Pipeline inspection robots are complex electromechanical systems that are designed to move inside pipelines while carrying necessary equipment. All types of in-pipe robots require solving a number of sensor-related challenges These include estimation of the robot’s position and configuration, navigation and mapping. The contact elements of walking in-pipe robots, whose trajectories need to controlled [12,13,14,15], are located at the ends of sequential kinematic chains and their positions are hard to infer exactly This motivates the use of special configuration estimation algorithms. In papers [16,17,18] state observers had been used to control DC motors, underwater robots and wheeled mobile robots This shows that these methods are developed for linear systems, they can be used for nonlinear mechanical systems as well.
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