Passive bilateral tele-operation and human power amplification with pneumatic actuators

In this paper a passive bilateral tele-operation between two pneumatic actuators is presented. The co-ordinated system is controlled to behave as a rigid mechanical tool that interacts with the human and other environment inputs. The input human forces when applied via a force sensor, can be amplified through the tele-operator to provide assistance for the human operator to perform the task either remotely or on-site. By ensuring that the system is energetically passive, robust stability is gauranteed during interaction with humans and various environments. Heat transfer during actuation affects the force output of a pneumatic actuator. The significance of this effect is studied by modeling the actuator dynamics for isothermal and adiabatic process. Control schemes for these two extreme cases of heat transfer are developed separately. Experimental evaluation of the controllers is done on two single d.o.f pneumatic actuators. Results show good co-ordination between master and slave actuators, both in free motion and during hard contact. The root mean square position co-ordination error for isothermal model is 1mm in free motion and 3.5mm during hard contact. The corresponding errors for adiabatic model are 0.8mm and 2.5mm respectively. Human force amplification, and force reflection during hard contact are also experimentally demonstrated for both isothermal and adiabatic model. From these results it is apparent that the difference between isothermal and adiabatic assumptions is not very significant.