Page 26 - Electric Drives and Electromechanical Systems

18 Electric Drives and Electromechanical Systems

of the real-time solution of dynamic equations and adaptive control algorithms, as
discussed in Chapter 5, Brushed direct-current motors.

1.3.2 Robotic end effectors

Dextrous manipulation is an area of robotics where an end effector with co-operating
multiple fingers is capable of grasping and manipulating an object. The development
of such hands is a significant electromechanical design challenge, as the inclusion of
multiple fingers requires a significant number of actuators to be fitted into a confined
space. A dexterous end effector can manipulate an object so that it can be arbitrarily
relocated to complete a task. One of the main characteristics of the dextrous manipu-
lation is that it is object and not task centred. It should be noted that dexterity and
dextrous are being used to define attributes to an end effector: a dexterous end effector
may not have the ability to undertake a task that a human considers as dexterous. As
dexterous manipulation is quintessentially a human activity, a majority of the dexterous
robotic end effectors developed to date have significant anthropomorphic characteris-
tics. In view of the importance of this research area a considerable body of research
literature on the analysis of the grasp quality and its control is currently available; the
reviews by Okamura et al. (2000) and Biagiotti et al. (2008) provide an excellent intro-
duction to the field.
As a dextrous end effector needs to replicate some or all the functionality of the human
hand, an understanding of human hand functionality is required in the design process. It
is recognised that there are five functions attributed to the hand: manipulation, sensation
and touch, stabilisation as a means of support, protection, and expression and commu-
nication, in robotic systems only the first three need to be considered. The hand can
function either dynamically or statically, its function is the sum of many sub-movements;
these movements may be used to explore an object and be involved in actions such as
grasping and carrying as well as provide dexterity and maintaining stability.
The hand may be used in a multitude of postures and movements, which in most
cases involve both the thumb and other digits. There are two basic postures of the hu-
man hand: the power grasp and the precision grasp. The power grasp, Fig. 1.9A, is used

FIG. 1.9 The power grasp (A) and precision grasp (B) of the human hand.