November/December 2017

24 SERVODRIVES November/December 2017 What is the smallest speed increase you can set on a servomotor? W hen designing a drive system, particularly for critical applications, there are several issues that might seem self- evident or obvious but are fundamental to achieving optimum performance, efficiency and accuracy. One such issue is speed control and determining the smallest speed increments that can be set on a servomotor. This is particularly relevant on applications where high-precision speed control is critical – a common requirement for many modern industrial applications. For instance, imagine you need a motor to drive a pump and provide a flow rate covering the range 0–500 ml/min. Due to the pump’s design, the torque required to drive it over this range is relatively constant, but it might be necessary to adjust the flow rate down to 0.1 ml/min. You first need to consider the type of motor-and-drive combination that is best suited to the demands of the application. Simple variable-frequency drives (VFDs) quote speed control ranges down to 1:40. Even more capable open-loop vector drives support speed control ranges as wide as 1:200. Andrew Fallows, managing director of Motor Technology, considers a frequently asked question on the issue of servomotor speed control and offers advice on how to determine the smallest possible increase in speed. Speed control is a critical factor in machine-tool spindle applications