Electromagnetic Position Estimation Using Active Current Control and Nonlinear Observer

Heng Wang, Rajesh Rajamani

Research output: Chapter in Book/Report/Conference proceedingConference contribution


This paper proposes an electromagnetic position estimation system suitable for linear actuators. The inexpensive non-contacting position measurement system is composed of an electromagnet on the stationary cylinder and a magnetic sensor on the moving piston rod of the actuator. The current supply to the electromagnet is actively controlled to track a desired current profile based on the instantaneous position estimate. The desired current profile increases monotonically with position to achieve accurate position estimation even for regions with low magnetic sensitivity. A nonlinear observer is designed based on Lyapunov theory to ensure asymptotically stable position estimation and current tracking. The active position system is experimentally validated using a piston-cylinder setup with 20 cm stroke length. Experimental results show that the active position estimation system can achieve 1% measurement accuracy over the entire stroke length while a system with constant current consuming the same average power shows nearly twice the estimation error.

Original languageEnglish (US)
Title of host publication2020 American Control Conference, ACC 2020
PublisherInstitute of Electrical and Electronics Engineers Inc.
Number of pages6
ISBN (Electronic)9781538682661
StatePublished - Jul 2020
Event2020 American Control Conference, ACC 2020 - Denver, United States
Duration: Jul 1 2020Jul 3 2020

Publication series

NameProceedings of the American Control Conference
ISSN (Print)0743-1619


Conference2020 American Control Conference, ACC 2020
Country/TerritoryUnited States

Bibliographical note

Funding Information:
This research was supported in part by a research grant from the National Science Foundation (NSF Grant CMMI 1562006).

Publisher Copyright:
© 2020 AACC.


  • Industrial actuators
  • active sensing
  • electromagnetic position sensing
  • position estimation


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