ROBOT ASSEMBLY HANDLING CHARTS
The required attitude of a part, on insertion, influences the choice of
handling device and it also affects the number of robot degrees of
freedom required. A particular feeding device, if it can handle
the part under consideration, may be able to present a part in only one
unique orientation or it may be able to present the part in a number of
unique orientations. The orientation(s) of the part at the feeder exit
are determined by considering the design of orientation tooling that is
required. For vision system controlled feeders, knowledge is
required of whether or not the part's orientation can be deduced by the
vision system. If the attitude of the part at the feeder exit is the
same as that required for insertion then a minimum number of degrees of
freedom are required from the robot arm. If the attitude of the
part at the feeder exit is different from that required for insertion
then extra degrees of freedom are required. Parts which need to be
re-orientated from the horizontal to vertical position require an extra
roll or pitch axis and parts which are required to be turned end-to-end
need an extra yaw axis. Additionally, certain parts may require that
final orientation from the feeder is accomplished using a robot with
limited sensory capability to define the orientation. This is
applicable to feeders which present the part in a limited number of
known orientations. This knowledge can be collated to form a database
from which it is possible to predict handling and dexterity
requirements for the robot assembly system. Various organisations
have created database software applications for this design process.
ROBOT ASSEMBLY HANDLING EXPERT SYSTEM
It must be possible to describe a part being analysed so that the most
appropriate feeding device can be selected. A standard parts
coding system is used to describe a part, as mentioned
previously. The sequence of questions which are asked to describe
the part is very important. The response to certain questions may
create a need for further questions to fully describe the part.
Alternatively, no further questions may be required. Additionally, a
particular response to a question may dictate that only one handling
device is appropriate, even before the part has been fully classified.
Anybody using the 'selection of parts presentation device technique
doesn’t want to be asked a lot of irrelevant questions and so a
decision tree has to be developed to ask the minimum number of
questions. Statements are presented in a structured format and these
statements can be either true or untrue for a particular part.
Branching forward only takes place when a particular statement is true,
otherwise alternative questions are presented until a correct statement
is chosen. Questions are structured so that if a particular set
of statements are untrue then the previous true response to a statement
must have been incorrect and that statement is once again presented to
the user. By this method, the minimum number of questions are needed to
classify a part in terms of its handling suitability.
PRODUCT AND SYSTEM DESIGN FOR ROBOT ASSEMBLY SOFTWARE
The presentation of parts for robot assembly is one section of a
product and system design for robot assembly computer software
application. It operates on eight screen pages. The first screen page
allows the user to enter part numbers and descriptions to the
application. The last three screen pages contain economic information
and they provide the user with calculated information. The middle four
screen pages are all concerned with defining the handling, and to some
extent the insertion, requirements of the part under consideration.
These four screen pages are displayed consecutively for each part and,
when all the parts have been defined, the remaining three screen pages
are displayed. In the handling section, the first screen page deals
with adverse physical properties of the part. The second screen page
deals with the geometrical symmetry features of the part. The third
screen page deals with the geometrical asymmetry features of the part.
The fourth screen page is used to define the insertion direction of the
part and to determine if the part is potentially redundant.