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Cha p te r
Ei g h t

are potentially useful in the present context, it is valuable to note
some important differences between the requirements of character
recognition and those associated with visual feedback for mechanical
assembly.
8.6.1 Shape and Size
All objects presented to the assembly machine are assumed to match
an exact template of the reference object. The object may have an arbi-
trary geometric shape, and the number of possible different objects is
essentially unlimited. Any deviation in shape or size, allowing for
errors introduced by the visual input system, is a ground for rejection
of the object (though this does not imply the intention to perform 100
percent inspection of components). The derived description must
therefore contain all the shape and size information originally presented
as a stored image. A character recognition system must tolerate con-
siderable distortion, or style, in the characters to be recognized, the
most extreme example being handwritten characters. The basic set of
characters, however, is limited. The closest approach to a template-
matching situation is achieved with the use of a type font specially
designed for machine reading, such as optical character recognition
(Fig. 8.8).

8.6.2 Position and Orientation
A component may be presented to the assembly machine in any ori-
entation and any position in the field of view. Though a position- and
orientation-invariant description is required in order to recognize the
component, the measurement of these parameters is also an impor-
tant function of the visual system to enable subsequent manipulation.
While a line character may sometimes be skewed or bowed, individual

FIGURE 8.8 Optical character recognition.