We talked to Ruland Manufacturing’s Bobby Watkins to learn more about the role inertia plays in servo coupling applications. Here is what he had to say.
“Failure most often occurs when maximum speed is exceeded. Every type of motion control coupling has a different max speed rating. It varies. It’s something to be mindful of when you’re designing a system. Making sure you pick a coupling that can handle the RPM is critical. Here’s a speed application example, printing. Here’s an example, our print equipment manufacturers had an issue with banding. We did an analysis and determined that one band was equivalent to one coupling rotation. Again, this is an example of higher RPM without a balanced design and the fact that it was not a balanced design coupling is showing up in the end product as banding on a printing application.
What role is inertia playing here? Servo coupling inertia is distributed, it is determined by the mass and distribution about the axis. Too much coupling inertia, especially in systems with intermittent starts and stops, can introduce resonance into the system causing premature failure or poor system performance. With a beam coupling, sometimes to get more torque, go to a stainless steel version, which is much heavier. We have a fairly common occurrence where a beam coupling was chosen and doesn’t have enough torque capacity. These are typically light-duty, fractional horsepower applications. A stainless steel beam coupling is put into place to replace the aluminum one and the inertia itself of the coupling is just too much for the system to handle and you have a tripping out of the motor. The motor is tripping out, electrical overload because of trying to handle too much inertia from the coupling itself.