A passive artificial hand that has no power source or control over its movement can be made from a range of materials whose physical properties are important to provide a lifelike visual impact, feel and durability. In contrast, a hand that needs to be designed to hold and manipulate objects requires as at least some form of mechanical structure, c.f., a skeleton but also other components so that it is functional. It has a palm or central structure for the attachment of finger joints and links that is similar to the anatomy of a natural hand. Also there is provision for actuators, i.e., electric motors or if the device is body powered, cables to react against the mechanism. For a powered anthropomorphic hand, choices are made about which of the fingers and thumb should be powered. A single actuator could move the first finger or groups of fingers and the thumb to form pinch grips where the fingertips oppose the thumb tip. With two actuators a finger or group of fingers can move independently of the powered thumb. Alternatively, one actuator could move both the first finger and thumb together and the second actuator moves the other fingers. Three actuators allow for the thumb to have two degrees of freedom with the third actuator powering all the fingers. Alternatively, the first finger could be powered with one actuator and the three other fingers with a second actuator. The powered thumb then has only one movement of extension/flexion and no rotation. The thumb can also have no power and be moved into position using a natural hand, in which case all three actuators are available for moving the fingers. With four actuators, there are more possible combinations for grip patterns but each additional actuator adds mass not only to the hand but also is in need of more coordination and algorithmic control of the fingers and thumb.

Chapter Contents:

• 2.1 Materials
• 2.2 Simple clamps
• 2.3 Natural curling fingers
• 2.4 Curling fingers and pulleys
• 2.5 Curling fingers and one four-bar linkage
• 2.6 Curling fingers and two four-bar linkages
• 2.7 Thumb
• 2.8 Actuators
• 2.9 Summary
• References

Inspec keywords: dexterous manipulators; actuators

Other keywords: actuator provision; powered thumb; finger joints; finger links; passive artificial hand; natural hand anatomy; mechanical structure; grip pattern

Subjects: Manipulators; Actuating and final control devices