“Muscles” pulling “tendons”

The movement of a robotic hand is very similar to that of a human hand. The muscle contracts when an electric current passes through it1. It pulls tendons attached to an adjacent body part. That rotates around a joint connecting these two body parts. 

In a case of robot, it looks similar – a motor pulls a string. In order to deploy a reverse movement, two alternatives can be used: 

  • a spring, forcing a body part to an initial position; 
  • two-string system, pulling the body part both directions. 

In any of the cases, the motion is realized by special kind of motors, called servo-motors (or servo-actuators). These digital devices move to and stop only in certain positions, - differently to all-time rotating motors.

Figure 7. Mechanics, that moves a finger of a bionic hand

1 The muscle contractions are controlled by very small electrical pulses, that might be measured by special sensors. These pulses are comming from brain and might be used to contol a bionic hand, attached as a replacement of one, lost during an accident.