LIBRARY ı6ıul 0) - Cranfield University

obot on the line must be individually programmed. Furthermore, it becomes very
tedious and time consuming when hundreds of points are required to be recorded,
such as in the automobile body manufacturing industry.
2.3.2 Off-line programming
Robot off -fine programming is by definition the technique of generating a
robot program without using a real machine. It presents several advantages over the
on-line programming technique, some of which are mentioned bellow: [ref. 68]
" reduction in robot down time due to programming;
" improvement in the work conditions for the operator by removing him from the
potential hazardous environment;
" it allows the incorporation of CAD information from the workcell as well as
from the workpieces into the programs.
" it permits program generation and its simulation without the use of a real robot;
" it allows the programmer to detect and correct in advance any problems;
" it facilitates the optimisation of robot programmes.
Off-line programming is classified according to the control level with which
the programmer defines the tool movements. This classification has four levels [refs.
67 , 68 , 69], which are described as follows.
a) Joint level - which requires the individual programming of each joint of the
robot structure to achieve the required overall position.
b) Manipulator level - which involves specifying the robot movements in
terms of world positions of the manipulator end-effector. Mathematical
techniques are used to determine the individual joint values.
c) Object level - which requires the specification of the task in terms of
movements and positioning of objects within the robot installation. This
implies the existence of a world model of the installation, from which the
information can be extracted in order to determine the necessary
manipulator positions.
d) Task level - which specifies the task in the most general form, for example
'weld the first inferior joint at the inner side of the door panel'. This
requires a comprehensive data base containing not only a world model, but
also knowledge of the application techniques. In the case of the example,
data on optimum welding parameters and methods would be necessary.
Algorithms would be required to interpret the instructions and to apply
them to the knowledge base to produce optimised collision free robot
programs.
Most of the currently available off-line programming systems use manipulator
and object levels of movement definition. Some attempts have been made to
implement task level programming [refs. 70,71] but it is still in the early stages of
development.
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