Design Article
The Top 10 Robotics Application Mistakes
George E. Martin
5/2/2005 12:44 PM EDT
As simple as it may seem, cable management is often overlooked, possibly because it seems so simple. However, optimizing cable routing to end-of-arm tooling or peripheral devices is crucial for unrestricted movement of the robot mechanic. Failure to design out this potential problem can lead to unnecessary movements of the robot to avoid tangling or stressing wires. Also, failure to use dynamic cables or to minimize cable stresses can lead to broken wires and down time.
Mistake 4: Failure to Consider All Application Elements
Bosch Rexroth uses the acronym LOSTPED, explained below, to describe the application elements required to size a mechanical system. By working through these considerations for each application, you will be sure to consider the application from every possible angle, and to avoid mistakes during planning that could result in severe cost overruns when the system is installed. You may even discover that you need to consider a different type of robotics solution altogether; you may discover, for example, that you need a Cartesian system as opposed to a SCARA robot or six-axis robot.
The LOSTPED elements are: Load " consider the payload, orientation and moment;
Orientation " consider the plane of travel, potential obstacles in the plane of travel, and any impact on lubrication and maintenance;
Speed " consider speed, acceleration and deceleration and the inertia they create;
Travel " consider the length of travel, alignment, lubrication intervals, potential ball screw whip;
Precision " consider travel accuracy and final position; Environment " consider environmental temperature, cleanliness, the presence of corrosive agents;
Duty Cycle " consider the proportion of time operating and not operating and any thermal effects on components.
Mistake 5: Misunderstanding Accuracy Vs Repeatability
An accurate mechanic can be repeatable but a repeatable mechanic may or may not be accurate. Repeatability is demonstrated by returning accurately to a taught position point in the work envelope of the robot. Accuracy is demonstrated by moving precisely to a calculated point in the work envelope. Pallet commands use a robot's accuracy capability by calculating an array of robot positions based on a few taught points. Accuracy is directly related to the mechanical tolerances or precision of the robotic arm.
Mistake 6: Choosing a System Solely On Controls
Most robot manufacturers would agree that much more consideration is given to the robot controller than to the mechanic. This is ironic because once the robot is deployed, the uptime is mostly dependent upon the robustness of the mechanic. Loss of production throughput is less likely to be caused by a broken controller, an electronic device, than a broken mechanic. Most often a robotics system is chosen based on the familiarity of the user with the controller and the software. If the robot in question also has a top-notch mechanic, then this is a competitive advantage. If on the other hand the robot needs constant servicing after installation, then any time savings from controls familiarity will be quickly squandered.
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