One of the most complex parts of our motor-driven highly underactuated robotic hands is the gear differential mechanism that provides the underactuation between the three fingers. A much simpler substitute of this differential could be used in the case of pneumatic or hydraulic actuation — just a distributer with one input and three outputs. While, in many applications, pneumatic or hydraulic actuation is not suitable, in many other, this type of actuation is standard. A plastic model was built using our rapid prototyping machine. The robotic hand is the smallest of all our underactuated hands.

    Fig. 1 : Pneumatically-driven highly underactuated 10-DOF robotic hand

    As described above, the differential was replaced by a multiple distributer. Three pneumatic cylinders are used for closing the fingers in combination with three flow control valves. The valves are currently manually adjusted to set the speed of closing the fingers. The force of the fingers can be controlled by the air pressure of the first air supply. A push button is used to let the air flow that closes the fingers.

    Two other pneumatic cylinders are used for orienting the fingers. The hand can have three discrete configurations — for cylindrical grasping, for spherical grasping, and for parallel two-finger grasping. A three-position switch is used to direct the flow to one of the cylinders or to disrupt it, thus selecting one of the three configurations.

    The result is a relatively low-cost multi-functional self-adaptive robotic hand that fits directly onto any industrial robot that can use pneumatic grippers. One pressure-regulated source is sufficient in addition to several binary outputs. Its design is covered by the same US patent (No. 6,505,870 and the same pending WIPO patent as our motor-driven highly underactuated hands SARAH.

    Video Clip

    The following video segment shows the pneumatically-driven highly underactuated 10-DOF robotic hand.