We have had significant discussions over the years about the different types of robots versus more modularized mechanics. So, we have written various articles…
That leaves open the discussion about using pre-engineered “
Cartesian Robots” versus more
modularly designed gantries. At first, the answer seems obvious because the Cartesian Robots are already designed, pre-engineered, easier and faster to quote, and are just a few part numbers to buy, typically one for the mechanics and one for the controller. Compare that to learning everything in the educational videos found at
www.TheMotionControlShow.com, starting at Episode 2, about actuators and, yes, the pre-engineered solution seems the way to go.
However, when you stop and consider what needs to be known to size actuators as found in
Episode 19’s LOSTPED: What to Know About Selecting Mechanics to properly meet the life-span requirements as discussed in these episodes…
…what you should quickly realize is that mechanical solutions aren’t so black and white as to what the load capacity is. When you dig further into the
speed/torque curves of the motors used, you’ll find you can get both high torque and high speed, but perhaps not both at the same time!
When designing a cartesian system (aka Cartesian Robot or Gantry System), there are usually several design trade-offs that need to be made. What is more important, speed or load capacity? Load capacity or life span? Life span or size? Size or cost? That short sequence shows just five factors that can be traded off with each other to tailor a modular gantry system specifically for an application whereas a pre-engineered solution is going to make all those design decisions for you up front and not give you the option to prioritize size over lifespan.
How do we approach this dilemma then? Typically, after getting the LOSTPED requirements, we’ll start with a budgetary solution of a pre-engineered Cartesian Robot and discuss whether taking the time to design a more customized solution would make sense or not. Once all the LOSTPED and machine requirements have been accounted for, something as simple as the vertical payload, the communications protocol, or even the travel could make the decision for you between it being a modular design or the pre-engineered solution since the pre-engineered solutions often do not lend themselves well to special features.
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