Robust Stability and Performance Analysis of the Control Systems with Higher Order Disturbance Observer: Frequency Approach

2012 IEEE International Conference on Mechatronics and Automation

Ohnishi

2012

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The Disturbance Observer (DOB) guarantees the robustness of the system if the disturbances stay within the bandwidth of the DOB. Thus, high bandwidth is demanded to compensate the disturbances in a wide frequency range. The bandwidth of the DOB is limited by the noise and robustness of the system. The noise limitation depends on the measurement plant and sampling rate. The robustness limitation depends on the robustness analysis method. Conventionally, the robustness of the system with DOB is analyzed using the unstructured uncertainty and Small Gain theorem. Due to the nature of the Small Gain theorem, the conventional analysis includes conservatism. The conservatism unnecessarily limits the bandwidth of the DOB to obtain robust stability. However, the bandwidth of the DOB is demanded to be as high as possible to increase the performance of the system. In this paper the robust stability of the system with DOB is analyzed in the presence of the real parametric uncertainties. This analysis is not conservative and it gives a lower bound on the bandwidth of the DOB to obtain robust stability. The lower bound on the bandwidth of the DOB is derived for the interval and affinely linear polynomials and it shows us that the system with DOB is robustly stable if its bandwidth is higher than the lower bound in the presence of the real parametric uncertainties. The proposed method is applied to a general second order system model with the real parametric uncertainties and the simulation results are given to show the validity of the proposed method.

Section: Lemma: Robust Stability Of the Dob Based Controlmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Robust stability anaylsis of the system with disturbance observer: The real parametric uncertainity approach I

2012 IEEE International Conference on Mechatronics and Automation

Ohnishi

2012

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“…represents tractive force vector of the i th castor's wheels; and i i i Similarly, the dynamic model of the omni-directional platform can be directly derived from Fig. 2b as follows: Equations (16)(17)(18) can be rewritten in matrix form by using Joint Space: Operational Space:…”

Section: Com Smentioning

confidence: 99%

Modelling and control of a novel walker robot for post-stroke gait rehabilitation

IECON 2017 - 43rd Annual Conference of the IEEE Industrial Electronics Society

Cheng

Yagli

et al. 2017

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In this paper, a novel walker robot is proposed for post-stroke gait rehabilitation. It consists of an omnidirectional mobile platform which provides high mobility in horizontal motion, a linear motor that moves in vertical direction to support the body weight of a patient and a 6-axis force/torque sensor to measure interaction force/torque between the robot and patient. The proposed novel walker robot improves the mobility of pelvis so it can provide more natural gait patterns in rehabilitation. This paper analytically derives the kinematic and dynamic models of the novel walker robot. Simulation results are given to validate the proposed kinematic and dynamic models.Abstract-In this paper, a novel walker robot is proposed for post-stroke gait rehabilitation. It consists of an omni-directional mobile platform which provides high mobility in horizontal motion, a linear motor that moves in vertical direction to support the body weight of a patient and a 6-axis force/torque sensor to measure interaction force/torque between the robot and patient. The proposed novel walker robot improves the mobility of pelvis so it can provide more natural gait patterns in rehabilitation. This paper analytically derives the kinematic and dynamic models of the novel walker robot. Simulation results are given to validate the proposed kinematic and dynamic models.

“…Since there are several parameters and higher order dynamics in the inner-loop, the design of DOb and tuning of nominal parameters are not straightforward. For example, one drawback of this design is that the motion control system may suffer from conservatism due to high order dynamics as explained in [26,27]. Moreover, unexpected…”

Section: Introductionmentioning

confidence: 99%

A robust force controller design for series elastic actuators

2017 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS)

Huang

2017

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A Series Elastic Actuator (SEA) is designed by placing a passive compliant element between a conventional stiff actuator and link. The intrinsically compliant mechanical structure provides several superiorities, e.g., safety, energy efficiency, high force fidelity, low cost force measurement, high transparency, etc., in advanced robot applications, such as humanoids, quadrupeds and exoskeletons. However, the motion control problem of an SEA is more complicated than that of a conventional stiff actuator due to its higher order dynamics. This paper proposes a novel Active Disturbance Rejection (ADR) based robust force controller for SEAs by combining Differential Flatness (DF) and Disturbance Observer (DOb) in state space. The robust state and control input references are systematically generated in terms of a fictitious variable, namely differentially flat output, estimated disturbances and their successive derivatives. A second order DOb is designed in state space so that disturbances and their first and second order derivatives are estimated. It is experimentally shown that high performance force control applications can be performed without requiring the precise dynamic models of the actuator and environment when the proposed robust force controller is implemented. This conference paper is available at Research Online: http://ro.uow.edu.au/eispapers1/1197  Abstract-A Series Elastic Actuator (SEA) is designed by placing a passive compliant element between a conventional stiff actuator and link. The intrinsically compliant mechanical structure provides several superiorities, e.g., safety, energy efficiency, high force fidelity, low cost force measurement, high transparency, etc., in advanced robot applications, such as humanoids, quadrupeds and exoskeletons. However, the motion control problem of an SEA is more complicated than that of a conventional stiff actuator due to its higher order dynamics. This paper proposes a novel Active Disturbance Rejection (ADR) based robust force controller for SEAs by combining Differential Flatness (DF) and Disturbance Observer (DOb) in state space. The robust state and control input references are systematically generated in terms of a fictitious variable, namely differentially flat output, estimated disturbances and their successive derivatives. A second order DOb is designed in state space so that disturbances and their first and second order derivatives are estimated. It is experimentally shown that high performance force control applications can be performed without requiring the precise dynamic models of the actuator and environment when the proposed robust force controller is implemented.