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area. An additional challenge included within this part of
the project is to use electric servo motors rather than
pneumatics. This has advantages for use of tool
exchange and minimises the size of the tool. This tool
also includes cameras for visual servoing. In the model
below it can be seen that there are four cameras on
each tool, two on each side. The more distal cameras
are mounted on the snake-arm wrist and are required
both for tool exchange and provide an extra ‘shorter’ but
lower resolution inspection tool. The more proximal
cameras on the tool itself are required because the tool
obscures the view of the wrist mounted cameras.
Figure 9 - Swage tool
A SEALANT TOOL
This tool will incorporate a standard sized sealant
cartridge and nozzle, with cameras to allow automatic
orientation of the toolpiece to the seam.
Figure 10 - Sealant tool
In production, many tasks in the wing box involve very
restricted geometry, requiring long tool noses with shark
bites for clearance or offset heads. The purpose of the
demonstrator is to show the feasibility of using
representative tools on a snake-arm robot rather than
recreating precise worksite geometries. Future work may
include adapting the tools for specific work sites with
restricted geometry, and developing the tools to achieve
the tasks to acceptable production quality.
MODES OF OPERATION
Various modes of operation of automation equipment
have been identified by Airbus UK, and have been
identified as requirements for the system. These are
outlined below.
FULLY AUTOMATIC OPERATION
The system has been designed to allow automatic
operation without an operator being present. The
operator is only required if the system encounters a
problem, or when a manual operation is necessary, such
as a non-routine task or quality control check.
SEMI-AUTOMATIC OPERATION
The system has been designed to allow semi-automatic
operation. The operator initiates a program. The robot
executes the program and waits for the next manually
selected start signal. The semi-automatic selection also
allows the operator to drive the robot to a position before
selecting a program, the program runs automatically,
and the operator then drives the robot out of the area
manually.
MANUAL OPERATION (TELE-OPERATION)
This is where the operator controls the motion of the tip
of the snake-arm using a robot control pendant and
visual feedback from the various cameras. Manual
control also allows functions such as jogging, zeroing,
homing and maintenance checks etc to be made.
Control of a snake-arm is never fully manual. It is not
practical for an operator to control all 27 degrees of
freedom, hence the operator’s tip motion requirements
are used as inputs to he robot control software that
ensure that the remainder of the arm, and in this case
the industrial robot move in a way to avoid collision with
the environment.
VISUAL SERVOING
Industrial robots work on the principle of being
adequately rigid so that the position of the tip is known to
better than the process tolerances required. This ability
can be affected by variable loading conditions, the
complex configuration dependent ability to react loads
and time. These disturbances, some of which are
dynamic, can be compensated for by calibration and the
use of external tracking and measurement devices such
as laser scanners [1]. The same issues apply to snakearm
robots, although whereas line of sight is possible in
a typical industrial robot environment this is not the case
when working within enclosed spaces.
The important relationship in the various production
processes under consideration is the relative position of
the tool with respect to the component and how the
forces are transmitted during the process. This line of
thinking leads to the concept of tools that take their
reference from local features of the aircraft structure.
The kinematic challenge is to deliver these tools to the
work place and provide the range and motion resolution
necessary to adapt to the local environment.
The approach taken within this work for responding to
geometrical variation is to use visual servoing – using
cameras to identify features within the enclosed spaces
in order to control motion. This is particularly challenging
for real situations such as sealant bead application
where it is necessary to find the end of a bead and
recommence the bead whilst ensuring there is no leak
path.
The static/dynamic force challenge is to react process
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