A multiple SMA hybrid actuator to generate expressions on the face

This paper presents part of an on-going project to design a wearable supportive device to enhance facial expressiveness, in particular for the facial paralyzed patients. Earlier we introduced the SMA actuator based Robot Mask that can be used to enhance the expressiveness of the face. The basic concept of that design was pulling of the skin through wires attached to the face and we explained the human anatomy based criteria of selecting these pulling points and directions. The major reason to use SMA instead of traditional actuators such as motors was their silent acting nature. However, their dynamic properties been governed by thermal energy and their mechanical properties been affected by the hysteresis due to their metallurgy, SMA based actuators tend not to perform too well under cooling. This paper introduces a novel controlling scenario that use the actuation of only a limited number of SMA wires out of the total connected in series on either sides of a slider to control the direction and amount of movement of the slider. The advantage of this method is by keeping some SMA wires at low temperatures it was possible to achieve a high speed of actuation even when the direction of motion was changed. This paper also investigates on the amount of actuation rates that are required to generate natural looking smiles and later attempts to recreate them using the proposed actuation unit.