Force Control of an Artificial Finger Driven by a Hose-Guided Wire

Abstract

In this paper, a force control of an artificial finger is described. Force transmitting with a wire which runs through a helical hose is very effective to make a compact and complicated finger driving system since the wire is guided in the hose and the route of force transmission can be selected freely. Because of the friction caused between the wire and hose, the force is not transmitted fully to the output. This friction effect is dealt with in the paper.
In the first part, given is the discussion for the force control servo system with a negative feedback loop using voltage drop of a small-valued resistance inserted in a armature circuit of D. C. motor.
In the second part, some factors affecting the magnitude of friction are considered. And the quantitative analysis of friction is given by solving iterative equations among these factors. An equation of dynamical motion of the wire obtained from the analysis clearly explains the nonlinear characteristics in the force transmitting system. The output torque of the motor is grouped into two types; namely the active type and passive type corresponding to the types of the finger's action on an object. In each case, the force controlling method little affected by the friction is established.
In the last part, descrived is the removal of the dead zone of the force control system by means of a dither signal of which the amplitude is proportional to the tension of the wire, for the correct control of the output force.