Improving the position control of a two degrees of freedom robotic sensing antenna using fractional-order controllers

ABSTRACT

Flexible links combined with force and torque sensors can be used to detect obstacles in mobile robotics, as well as for surface and object recognition. These devices, called sensing antennae, perform an active sensing strategy in which a servomotor system moves the link back and forth until it hits an object. At this instant, information of the motor angles combined with force and torque measurements allow calculating the positions of the hitting points, which are valuable information about the object surface. In order to move the antenna fast and accurately, this article proposes a new closed-loop control for driving this flexible link-based sensor. The control strategy is based on combining a feedforward term and a feedback phase-lag compensator of fractional order. We demonstrate that some drawbacks of the control of these sensing devices like the apparition of spillover effects when a very fast positioning of the antenna tip is desired, and actuator saturation caused by high-frequency sensor noise, can be significantly reduced by using our newly proposed fractional-order controllers. We have applied these controllers to the position control of a prototype of sensing antenna and experiments have shown the improvements attained with this technique in the accurate and vibration free motion of its tip (the fractional-order controller reduced ten times the residual vibration obtained with the integer-order controller).

KEYWORDS:

• Control of vibrations
• fractional-order phase-lag compensation
• robustness to sensor disturbances and spillover effects
• frequency domain control techniques
• sensing antennae
• robotic sensors.

Acknowledgments

This work has been supported by the Spanish Ministry of Economy and Competitiveness under the project DPI2012-37062-C02-01 and by the European Social Fund and by University of Castilla-La Mancha (E-13-2014-0169567).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

University of Castilla-La Mancha [grant number E-13-2014-0169567]; The Spanish Ministry of Economy and Competitiveness and the European Social Fund [grant number DPI2012-37062-C02-01].