Fractional Control of a Lightweight Single Link Flexible Robot Robust to Strain Gauge Sensor Disturbances and Payload Changes

Abstract

In this paper, a method to control one degree of freedom lightweight flexible manipulators is investigated. These robots have a single low-frequency and high amplitude vibration mode. They hold actuators with high friction, and sensors which are often strain gauges with offset and high-frequency noise. These problems reduce the motion’s performance and the precision of the robot tip positioning. Moreover, since the carried payload changes in the different tasks, that vibration frequency also changes producing underdamped or even unstable time responses of the closed-loop control system. The actuator friction effect is removed by using a robust two degrees of freedom PID control system which feeds back the actuator position. This is called the inner loop. After, an outer loop is closed that removes the link vibrations and is designed based on the combination of the singular perturbation theory and the input-state linearization technique. A new controller is proposed for this outer loop that: (1) removes the strain gauge offset effects, (2) reduces the risk of saturating the actuator due to the high-frequency noise of strain gauges and (3) achieves high robustness to a change in the payload mass. This last feature prompted us to use a fractional-order PD controller. A procedure for tuning this controller is also proposed. Simulated and experimental results are presented that show that its performance overcomes those of PD controllers, which are the controllers usually employed in the input-state linearization of second-order systems.

Fractional Control of a Class of Underdamped Fractional Systems with Time Delay—Application to a Teleoperated Robot with a Flexible Link

“…Then a feedback loop with high-gain controllers is implemented. Details of this servo motor system can be found in [38]. The equivalent transfer function of the inner loop is…”

In-Depth Review of Advanced Control Strategies and Cutting-Edge Trends in Robot Manipulators: Analyzing the Latest Developments and Techniques

“…By using simulations and experiments to validate the modeling and analysis of the composite manipulator, the suggested method's level of reliability is raised. One may see a two-nested loop-like control algorithm proposed by [93], [94]. In this, the proposed control strategy had been derived using singular perturbation theory and embedded with input-state linearization.…”

Fractional Modeling and Control of Lightweight 1 DOF Flexible Robots Robust to Sensor Disturbances and Payload Changes

“…Finally, ref. [31] implements an FO controller combined with a standard PD controller [32] robust to strain gauge disturbances and payload variations. The design of this controller was based on the closed-loop pole allocation technique using an integer order model.…”

“…Specific contributions are as follows: (1) proposing a new model of the dynamics of FLR that introduces a fractional order derivative in the inertia term of the Euler-Bernoulli equation instead of in the damping term, as is usually done; (2) proving experimentally the superior performance of this model; (3) modifying the control system [31]-which is based on a combination of the singular perturbation theory and the input-state linearization technique for an integer order model-to cope with the new FO model; and (4) proving experimentally that the resulting new control system outperforms the system presented in ref. [31].…”

“…Sections 5 and 6 develop a control system robust to strain gauge disturbances and payload changes, respectively, based on the previous model. Section 7 describes the experimental platform and illustrates the results obtained experimentally with the new controller scheme compared to the one proposed in [31]. Finally, Section 8 presents some conclusions.…”