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A typical robotic arm controller performs the
following functions:
- To solve kinematics: Unlike many automated
machines, robots are mechanical coupling devices.
What this means is that by moving a single axis,
all the other axes will move too. As such, robotic
arm controller needs to provide a solution to
calculate kinematics and reverse kinematics
equations to enable the robotics arms to move
in coordinated fashion. Kinematics is the mathematical
representation of the robot, including its size,
configuration and the relationship of each axis
to the mechanism as a whole. This coordination
is the basis for sensor integration, path following,
straight line movements, and other features
common to industrial robots.
- To deliver speedy, accurate and repeatable
operation. Robots are expected to perform uniformly
throughout their whole work envelope, with a
range of payloads. In addition, mechanical coupling,
complex mechanisms, added to the complexity
of needing to balance speed and precision by
managing system resonance and vibration issues.
- To offer sensor integration: Robotics controller
is required to handle the integration of complex
sensors such as machine vision, force sensing,
and conveyor tracking. At minimum a robot motion
control system is expected to adjust points
and paths in real time based on sensor information.
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- Teach Method: A teach pendant
is used to control and program the robot. Operator
can teach the robot by driving individual robotic
joints independently (named joint co-ordinate),
drives robot's tool centre using the X, Y, Z
axes of the global axis system (called global
co-ordinate), or by utilising tool co-ordinate
system for teaching. The tool co-ordinate system
is similar to the global co-ordinate system
but the axes in this case are attached to the
tool centre point of the robot. This system
is especially useful when the tool is near to
the work piece.
With many robots it is possible to set up
a co-ordinate system at any point within the
working area (work piece co-ordinate) when teaching.
This method of programming is very simple
to use where simple movements are required.
However, when teaching, the robot cannot be
run in production, this reduces the machine
utilization rate.
- Lead Through: This programming
method is mainly used by spray painting robots.
The robot is programmed by being physically
moved through the task by an operator. This
is exceedingly difficult where large robots
are being used and sometimes a smaller version
of the robot is used for this purpose. Any hesitations
or inaccuracies that are introduced into the
program cannot be edited out easily without
reprogramming the whole task. The robot controller
simply records the joint positions at a fixed
time interval and then plays this back.
- Off-line Programming: Similar
to the way in which CAD systems are being used
to generate NC programs for milling machines
it is also possible to program robots from the
CAD models of the robots, fixtures and accessories.
The program structure is built up in much the
same way as for teach programming but intelligent
tools are available which allow the CAD data
to be used to generate sequences of location
and process information. The benefits of this
form of programming are:-
- Reduced down time for programming.
- Programming tools make programming easi06-Apr-2009uces
product lead time.
- Assists cell design and allows process
optimization.
However, because off-line programming is
not accurate, it requires adjustment interactively
on the factory floor until all positions and
orientations are correct because the robot can
run in the production.
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