Development of a Drive Unit of a Powered Glove for Finger Rehabilitation by Using SMA Actuators

Authors have been developing a powered glove for rehabilitation use. The powered glove is operated by pulling or releasing drive strings configured inside of the glove from outside. A new drive unit is prototyped for the powered glove by using two kinds of SMA springs as actuators. One is an active spring and the other is a passive spring. The active spring is a wave-shaped flat spring that shrinks under heating operations. Polyester-coated copper-nickel wires are wrapped around the active spring and used as a heater.  Cooling fans and a cooling spray are used as means for cooling. The passive spring is a superelastic coil spring that is connected to the active spring in series and always strains the active spring. The drive point at which the drive string is fixed moves back and forth by switching the operation mode between heating and cooling. The drive strings are pulled in heating mode and released in cooling mode. Through the temperature control of the active spring, the drive unit maneuvers the drive strings and thus the flexion/extension exercises of paralyzed fingers can be performed by using the powered glove. Finger exercises have been successfully demonstrated by using the prototyped drive unit. The characteristics and performance of the prototyped drive unit are evaluated though several tests. The results of the tests are reported in this paper.