Observer-based Disturbance Compensation Research Articles

Enhancing disturbance rejection in offshore drilling platforms: a dynamic positioning control scheme using equivalent-input-disturbance method with separated observers

This paper presents a dynamic positioning control scheme for offshore drilling platforms using the equivalent-input-disturbance (EID) method with separated observers. The scheme incorporates observer-based disturbance compensation, wave-filtering state estimation, input transformation, and state feedback control to achieve robust control performance. The main contributions include the design of an EID scheme with separated observers, enabling enhanced disturbance-rejection performance, incorporating a notch filter in the EID estimator to reduce energy loss, and giving an observer tuning scheme to achieve a balanced performance between disturbance rejection and wave filtering. Simulation results demonstrate the effectiveness of the proposed scheme. This work provides valuable insights into designing stable and efficient dynamic positioning systems for offshore drilling platforms.

Gaussian Process Based Disturbance Compensation for an Inverted Pendulum

This paper considers an inverted pendulum with velocity input to demonstrate the validity of a new method for estimating unknown disturbances such as nonlinear friction and damping. With only one run of a given swing-up strategy, the input and output data of the system are collected. They are the basis for a Gaussian process modelling that is used to estimate the unknown disturbance term. The learned Gaussian process model can be used subsequently to predict this disturbance and serve for an online disturbance compensation. Simulation results and a comparison with a classical observer-based disturbance compensation indicate the benefits of the proposed approach.

Robust guaranteed cost ILC with dynamic feedforward and disturbance compensation for accurate PMSM position control

This contribution presents a robust ILC control design based on guaranteed costs. By combining this ILC design with dynamic feedforward control and an observer-based disturbance compensation, the initial tracking errors in an early learning stage can be reduced. The benefits of the proposed design approach are pointed out at the example of a robust position control of a Permanent Magnet Synchronous Motor (PMSM), which is subject to uncertain model parameters. The paper is concluded with convincing experimental results from a dedicated test rig. Moreover, a comparison with a classical observer-based tracking control is provided.

Nonlinear Observer-Based Ship Control and Disturbance Compensation

Abstract: In this paper, a gain-scheduled nonlinear control structure is proposed for a surface vessel, which takes advantage of extended linearisation techniques. Thereby, an accurate tracking of desired trajectories can be guaranteed that contributes to a safe and reliable water transport. The PI state feedback control is extended by a feedforward control based on an inverse system model. To achieve an accurate trajectory tracking, however, an observer-based disturbance compensation is necessary: external disturbances by cross currents or wind forces in lateral direction and wave-induced measurement disturbances are estimated by a nonlinear observer and used for a compensation. The efficiency and the achieved tracking performance are shown by simulation results using a validated model of the ship Korona at the HTWG Konstanz, Germany. Here, both tracking behaviour and rejection of disturbance forces in lateral direction are considered.

Model-Based Nonlinear Trajectory Control of a Drive Chain with Hydrostatic Transmission

This paper presents an innovative nonlinear trajectory control scheme for drive chains based on a hydrostatic transmission, which are commonly used in working machines. Control-oriented modelling results in a system of four nonlinear differential equations including the actuator dynamics. It is shown that the differential pressure of the hydrostatic transmission and the angular velocity of the hydraulic motor as controlled variables represent flat control outputs. Therefore, the differential flatness of the system is exploited in combination with Ljapunov techniques to stabilize the error dynamics. Additionally, model uncertainties in the equation of motion like nonlinear friction are counteracted by an observer-based disturbance compensation. Simulation results show an excellent control performance.

Sliding-Mode Control of a High-Speed Linear Axis Driven by Pneumatic Muscle Actuators

This paper presents a cascaded sliding-mode (SM) control scheme for a new pneumatic linear axis which could be seen as alternative to an electric direct linear drive. Its guided carriage is driven by a nonlinear mechanism consisting of a rocker with an antagonistic pair of pneumatic muscle actuators arranged at both sides. This innovative drive concept allows for both an increased workspace of approximately 1 m as well as higher carriage velocities of approximately 1.3 m/s as compared to a direct actuation. Modeling of the muscle-driven positioning system leads to a system of four nonlinear differential equations including polynomial approximations of the volume characteristic as well as the force characteristic of the pneumatic muscles. The differential flatness of the system is exploited in combination with SM techniques to stabilize the error dynamics in view of unmodeled dynamics. The internal pressure of each pneumatic muscle is controlled by a fast underlying control loop. Hence, the control design for the outer control loop can be simplified by considering these controlled muscle pressures as ideal control inputs. The control design of the outer control loop involves a decoupling of rocker angle as well as mean internal pressure of both pneumatic muscles as flat outputs. Additionally, model uncertainties in the equation of motion like nonlinear friction are directly counteracted by an observer-based disturbance compensation which reduces the chattering problem. Experimental results show an excellent control performance that outperforms alternative control approaches in a comparison.

Backstepping Control of a High-Speed Linear Axis Driven by Pneumatic Muscles

Abstract This paper presents a backstepping control scheme for a new linear axis. Its guided carriage is driven by a nonlinear mechanism consisting of a rocker with a pair of pneumatic muscle actuators arranged at both sides. This innovative drive concept allows for an increased workspace as well as higher carriage velocities as compared to a direct actuation. Modelling leads to a system of nonlinear differential equations including polynomial approximations of the volume characteristic as well as the force characteristic of the pneumatic muscles. The proposed control has a cascade structure: The internal pressure of each pneumatic muscle is controlled by a fast underlying control loop, whereas in an outer control loop the carriage position and the mean internal pressure of the muscles are controlled. Remaining model uncertainties as well as nonlinear friction can be counteracted either by an observer-based disturbance compensation or an adaptive control strategy. Experimental results from an implementation on a test rig show a high control performance.

The Artificial Muscle as an Innovative Actuator in Rehabilitation Robotics

This paper presents the application of artificial pneumatic muscle actuators in a novel motorized orthosis for an intensive home-based gait training in patients with neurological disorders. Owing to the inherent elasticity of these actuators, they are an ideal choice in realizing a soft and tractable assistance to aid the physiological movements of the lower extremities. Special focus is paid to the modeling of the dynamic nonlinear force characteristics of the muscles as a steerable mass-damper system, and to the approximation of the variation of muscle volume under different operating conditions. The model description uses polynomial functions for which coefficients are identified by minimizing a quadratic performance index. Based on the mechanical model of the knee joint of the apparatus, a nonlinear stability-oriented backstepping control supported by observer-based disturbance compensation is derived and applied to the prototype of the rehabilitation robot.

Flatness-based trajectory control of a pneumatically driven carriage with model uncertainties

This paper presents a flatness-based control under uncertainties for a carriage driven by two pneumatic muscle actuators. First, the modelling of the mechatronic system is addressed. The pneumatic system part is characterised by dominant non-linearities, which have been identified and approximated by polynomial functions. Exploiting differential flatness with carriage position and mean muscle pressure as flat outputs, a trajectory control is designed and implemented. Disturbance behaviour and tracking accuracy concerning remaining model uncertainties are significantly improved by observer-based disturbance compensation. Measurements demonstrate an excellent control performance and emphasize both applicability and potential of this innovative actuator.

Model Based Trajectory Control of an Overhead Travelling Crane

AbstractUntil now, most papers concerning control of overhead travelling cranes have only focussed on position control of the translational degrees of freedom, see for example [1], [3], [4], and [5]. With more advanced robotic applications envisaged, however, there is a demand for both trajectory control in six degrees of freedom and active damping of the weakly damped load oscillations due to the rope suspension [2]. Hence, a model based trajectory control is presented for an overhead travelling crane that has been upgraded with an orientation unit providing three additional axes. Starting from a central multibody model, decentralised design models are derived for each crane axis. By this, couplings between the axes are identified and appear as disturbance inputs in these decentralised design models. Each decentralised axis controller consists of linear state feedback, feedforward control, and observer based disturbance compensation and is derived in symbolic form. This allows for an adaptation of the complete control structure employing the gain scheduling technique with respect to varying system parameters like rope length and load mass. Couplings between the crane axes are compensated by feedforward control, whereas the e.ects of nonlinear friction forces are counteracted by combination of feedforward control and disturbance estimation. Experimental results, taken at a 5 t ‐ bridge crane, show the bene.ts of the proposed control scheme as regards control performance and steady‐state accuracy.