The muscle of machinery: How to better control robotic movements

December 20, 2017

Researchers have improved the control of a key robotic component to better ensure the safety of humans. They published their results in IEEE/CAA Journal of Automatica Sinica (JAS), a joint publication of the IEEE and Chinese Association of Automation.

The team, based at Nankai University, China, focused on series elastic actuators. The actuator is the mover of a robotic limb--it's the piece that brings a screw to the assembly line or bends a digging scoop into the dirt of an excavation site. The actuator is the muscle of machinery.

Just as humans adjust their muscle control for various tasks, robots must also be equipped to handle external factors.

"For example, leg dynamics dramatically changes between the swing and the stance phase," wrote Prof. Lei Sun from Nankai University. "Also, damping and stiffness can be increased by muscle contraction, [such as] when we want to make a precise positioning or when we hold heavy loads."

A series elastic actuator not only allows for robotic movement, but it also allows for flexibility. It's not a perfect system, though.

"The high-performance control design for [series elastic actuators] is still a challenging problem, particularly in the presence of unknown payload parameters and external disturbances, which are common in [human-robot interactions]," wrote Sun.

To help the series elastic actuators better account for the unknown variables, Sun's team developed an algorithm to help understand the relationship between the motion of the payload and the full control system. The idea is that the robot can adjust its response and handling of the payload based only on the initial motion of the payload, which is controlled by humans in this system. The payload may be the same size and weight, but the way a person initiates the human-robot interaction may vary. The actuator should be able to move the payload safely, regardless if it was slammed or gently nudged into place.

"The framework is suitable for both linear and nonlinear [series elastic actuators], which implies that it is more generic," Sun wrote, pointing to the wide applicability of the method. "Experimental results illustrate that the proposed controller can achieve better control performance than the existing methods in a variety of interaction situations."

The researchers are now building a robot with three series elastic actuators to continue testing their proposed control method.
Fulltext of the paper is available:

IEEE/CAA Journal of Automatica Sinica (JAS) is a joint publication of the Institute of Electrical and Electronics Engineers, Inc (IEEE) and the Chinese Association of Automation. The objective of JAS is high quality and rapid publication of articles, with a strong focus on new trends, original theoretical and experimental research and developments, emerging technologies, and industrial standards in automation. The coverage of JAS includes but is not limited to: Automatic control,Artificial intelligence and intelligent control, Systems theory and engineering, Pattern recognition and intelligent systems, Automation engineering and applications, Information processing and information systems, Network based automation, Robotics, Computer-aided technologies for automation systems, Sensing and measurement, Navigation, guidance, and control. JAS is indexed by IEEE, ESCI, EI, Inspec, Scopus, SCImago, CSCD, CNKI. We are pleased to announce the new 2016 CiteScore (released by Elsevier) is 2.16, ranking 26% among 211 publications in Control and System Engineering category.

To learn more about JAS, please visit:

Chinese Association of Automation

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