Their simplicity comes with trade-offs though, and some of those trade-offs require special attention. For example, step motors are traditionally run open loop, which means that if the torque demand from the machine is greater than the motor can produce, the motor either loses position or stalls. Unless there's a feedback device—like an encoder—attached to the rear shaft of the motor, the drive/controller isn't aware that the motor has lost position or stalled, which can cause numerous problems for machine performance. Additionally, open loop step motors typically run hotter than other types of motors because they always run at full current, regardless of load conditions—this also causes the system to have significantly higher energy consumption.
A newly released motor technology from Applied Motion Products®, and provided by PBC Linear®, referred to as StepSERVO™ wraps a step motor and encoder inside a servo control loop improving performance, speed, quality and reliability substantially.
Speed and Performance
StepSERVO Motors offer a closed-loop design that provides a peak torque range, helping to maintain accuracy. The closed-loop design also increases the available torque of the motor by 85% at speeds under 750 RPM, making it more economically efficient by consuming less power.
Quality & Positional Precision
Traditional stepper motors can lose position if the maximum torque output is exceeded. The StepSERVO motor features a 20,000-count encoder and closed loop system that helps the motor know its position at all times, providing better accuracy with higher repeatability.