Chapter 2. Prehension

Appendix D - Prosthetic and Robotic Hands 419
as an antagonist to the three tendons at the three joints. For
positioning the fingers and using them to apply forces, Salisbury used
stiffness control. By running the tendons past small strain gauges on
cantilevers, tendon tension can be sensed. The relationship between a
small change in tendon displacement ax and tendon tension F follows
the mass-spring law, that is, F=KaX. Using an algorithm that
displaces the tendon by a small amount, the tension on the tendons can
be read from the strain gauges, since the stiffness K of the tendon is
fixed. Sensing a small change in tension will provide the controller
with knowledge about the change in tendon length.
This hand has been used in various systems, including Stansfield
(1991).
D.3.2 Utah/MIT hand
The Utah/MIT hand (see Figure D.2), built by Steve Jacobsen
and colleagues, has four fingers, with each having four DOFs
(Jacobsen, Iversen, Knuti, Johnson, and Biggers 1986). Control of
its 16 degrees of freedom is performed at a ‘high’ level in the
computer.
Figure D.2 The Utah/MIT hand. It consists of three fingers and
one thumb, each of which has four degrees of freedom (from
Jacobsen et al., 1986; reprinted by permission).