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Robotics and Automation Lab Pneumatic cylinder with embedded MR-brake




This research explored a new linear hybrid actuator, which consists of a pneumatic cylinder with a magnetorheological (MR) brake embedded in its piston.  MR-brakes are promising actuators since they can apply large forces in a small actuator size, but they can only oppose motion, as they are passive actuators.  Pneumatic cylinders are desirable actuators due to their high force-to-weight ratio and ability to apply active forces.  However, they require expensive servo valves for precise position control.

The new hybrid actuator benefits from the advantages of MR-brakes and pneumatic cylinders.  It can apply forces using compressed air and can resist external forces using the MR-brake.  The embedded brake also eliminates the undesirable side effects of using compressed air and allows precise positioning of the piston anywhere in its stroke with simple solenoid valves.  Fields such as haptics and robotics might benefit greatly from the use of the hybrid actuator where a high force-to-weight ratio could be employed.

This research contributes (1) a triple helix flux guide, which solves the problem of applying current to the MR-brake on the piston inside the cylinder while the piston moves.  As a result, the coil can now be moved to the outside.  To the best of our knowledge, this is the first linear MR-brake with an external coil; (2) serpentine flux path was integrated into the piston, which enables larger braking force to be developed without making the device larger




  • “Pneumatic cylinder with magnetorheological brake using serpentine and helix flux guide as a linear hybrid actuator for haptics,” Journal of Intelligent Materials, Systems and Structures, vol. 28, issue 10, pp. 1303-1321, 2017.
  • “Pneumatic actuator with embedded MR-brake for haptics,” Proceedings of 2017 IEEE World Haptics Conference (WHC 2017), Furstenfeldbruck (Munich), Germany, June 2017.