Aux Axis Motor Sizing - Three Key Elements

In this video, Liang Chen, one of FANUC America’s senior engineers, simplifies the motor sizing criteria and gives a few quick pointers that are helpful to those new in the field. Servo motors must meet the three key element criteria to be considered a motor safe for operation: moment of inertia, rated speed, and torque. A real-life example is shown of a customer deciding to switch from a non-FANUC motor to a FANUC Servo Motor to help visualize the process. Torque-speed curves are the most useful tool in motor selection. The charts are available for all Servo motor specs, displaying the torque that a motor can produce across its working speed range, where you can see the Continuous Operating zone. When a motor runs within the Continuous Operating zone, the motor will not be overheated. The chart visualization helps understand the speed-torque characteristics and promotes a safe operation process. More time is dedicated to discussing the key element, load inertia. This element is essential for the operation to run smoothly. FANUC Servo motors require the load inertia ratio to be less than five for the most optimal servo stiffness control. A clip is played where there is a high load inertia ratio which leads to poor control, emphasizing why it should be prevented. In the circumstances that the machine is already on a manufacturing floor and its load inertia ratio is too large, there are a couple of solutions to fix the issue. The first is to use a bigger motor, but this is in most cases not enough on its own to solve the issue. The second choice is to use a gearbox with a larger gear ratio, which is typically more efficient to achieve better control. Both solutions have implications and more steps to follow but are important to know to be prepared.