I recently
listened to a talk radio program about manufacturing. As the conversation
went on, one caller’s statement stuck in my mind: ‘‘While automation has played
a large part in increasing productivity, we have not gotten the help from
robotics that we had hoped for.’‘ That took me by surprise, since I’ve
worked as a designer of all-electric, articulated robot systems for over ten
years, and know that robots have played a major role in improving manufacturing
efficiency. I just assumed they were talking about some other type
of hard automation besides robots. Then I got to thinking that there are
still designers so comfortable with hard automation that they have not yet
considered articulated robots.
Robots have
matured from their birth in specific industries with specific tasks to becoming
versatile mechanisms that are ideal for straightforward pick-and-place
applications, as well as challenging applications that can utilize the unique
capabilities inherently built into robotics. After working with automation
equipment for 20 years, I feel it’s important to provide insights into my
transition from hard tooling to robotics so that others can understand the
significant differences between the two. The purpose of this article is
to touch on several features that have made today’s robot a vital tool for any
application.
True
Flexibility:
The term
flexibility means a variety of things when discussing robots. Let me
first discuss flexibility in movement. With six-axis robots available,
movement is virtually unrestricted. The designer spends less time on how
the parts are moved and more time on the tooling at the end of the robot that
picks the parts. This flexibility allows the tooling to be designed with
an eye toward multiple tasks. For example, picking boxes and pallets or assembling
two different parts and then setting them on an exit conveyor. The idea
is having the robot do most of the work. In situations when the
end-of-arm-tool cannot accommodate all of the different shapes or sizes of the
parts, tool changers are added to allow the robot to pneumatically change
end-of-arm tools. This type of flexibility in movement is very useful
during the building of a robotic cell. Hard tooling does not lend itself
to minor positional changes as well as robots do. These changes made ‘‘on
the floor’‘ often help with the overall productivity of the cell.
Flexibility in
mounting. Floor, ceiling or rail-mount robots offer the designer an
option with most applications that does not require additional mounting
structures. This speeds up the engineering needed to develop mounts, as
well as the outside fabrication requirements.
Flexibility in
your long-term investment. Traditionally, the thought of reusing hard
tooling would be unheard of, but robots can be re-deployed to accommodate
changes in products or procedures. When reusing robots, only the tooling
and programming need modifications. They eliminate the question of
compatibility when attempting to blend a variety of hard tooling products from
different component manufactures together in one assembly. Because robots
offer multiple axes and are self-contained, there is no need for a structural
framework to mount the various components of hard tooling. They also
greatly reduce the time needed for hard wiring of the system. For most
applications, power is only required for the robot and air if needed for the end-of-arm-tool.
Another advantage of re-deploying robots to new applications is that it breeds
continuity throughout the plant. When reusing robots there is no learning
curve or additional spare part requirements, and only one point of contact for
its electrical and mechanical components.
When I first
started designing with robots, I had a tendency to limit their flexibility by
thinking of only a single task, similar to hard tooling. I now look at
the overall system and incorporate the robot to do as many tasks as
possible. The key point is that robot flexibility allows the designer
more options without having to deal with the compromises of hard tooling.
Programming:
Along with
advances in the drives and the mechanical unit, a robot’s programming language
is straightforward if you are accustomed to reading ladder logic. Each
line represents a separate robot command. The command lines that move the
robot have four components. These components tell the robot were to go,
how fast, how to get there, and whether to use all of the axes in unison or
individually. The development of these programs start with the hand held
‘‘teach pendant’‘ which is used to physically drive the robot to a desired
point where the four variables can be selected and the point recorded. It
is a point-by-point process after that. These programs can become as
complicated as the process demands, but even then the basic structure of the
language stays the same. This type of straightforward programming goes a
long way in removing the stigma of complicated controls and allows for a short
learning curve for any individual.
In addition,
FANUC Robotics offers a simulation program to set up a virtual cell on a
computer. Once the robot, tooling and other peripheral equipment are
selected, the user can construct the program off-line. The software
provides the ability to create and watch the process and adjust locations and
speeds in order to refine the system’s cycle time. This program can then
be loaded into a robot on the floor, and after verifying the positional points,
it’s ready to run.
Limitations:
Robots have
definitely made a positive impact on manufacturing, but there are a few key
points to remember when designing with robots. The first point is the
size of the control cabinet. With a footprint of 24 by 30 inches, it
consumes more floor space than many smaller robots. Because of its size,
designers must consider the controller during initial discussions of the system
or cell space requirements.
The second point
has to do with safety considerations. Because the available travel of a
six-axis robot resembles a sphere, when working with a specific application it
is advisable to limit the travel to only where the robot needs to go.
These limits must be accomplished with physical stops in order to adhere to the
Robotic Industries Association’s safety requirements. Software limits
cannot replace the physical stops. Once the maximum travel has been
established, guarding needs to be erected to prevent access by personnel. Including
physical stops in the design helps to minimize the amount of floor space the
robotic system consumes.
The last item is
more of a caution when designing robot-mounting bases. With the high
speeds of each axis, it is easy to underestimate the rigidity required of the
base, even with smaller robots. An adequately sized base insures that the
robot will be on solid ground and not quiver when stopping, and can help with
the accuracy of the process.
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