Development of a pneumatic-electromagnetic hybrid linear actuator with an integrated structure

Conventional hybrid actuators can achieve a better force/torque bandwidth than a single principle actuator without losing back-drivability. However, hybrid actuators occupy space at least equal to the sum of the volumes of two or more actuators and multiple transmissions consisting of timing belts, gears, links, tendons, or Bowden-cables. Designs in which space and structural elements of a hybrid actuator are integrated have not been sufficiently studied. This paper presents an original development work on the design of an integrated pneumatic-electromagnetic hybrid linear actuator (iPEHLA). In the integrated design, hybrid components of an air cylinder and a linear motor were arranged around a single shaft, and the pneumatic and electromagnetic actuators shared the same moving parts (i.e., piston and moving part) and internal cylindrical spaces (i.e., cylinder and stator). Consequently, space required was less than the sum of the volumes of the two actuators. To verify the feasibility of this novel integrated design, the iPEHLA was designed and prototyped by modifying parts of a commercially available pneumatic cylinder integrated with electromagnetic components. The performances of the iPEHLA under pneumatic actuation and hybrid actuation were compared with respect to a feedforward friction compensation. The experimental results demonstrated that the novel design maintained its hybrid properties.