Galil Motion Controllers Support 2-Phase Closed-Loop Brushless (Step) Motors
- Posted on November 21, 2013
You don't have to purchase a servo motor anymore for accurate positioning! Now you can save money and achieve the positional accuracy you need for your high torque, slow speed application with Galil's integrated, high power (8 Amps continuous), 2-phase drive for closing the loop on a step motor.
Two types of electrical motors have traditionally been used in automation applications; step motors with open loop operation and servo motors with incremental or absolute feedback.
Step motors are low cost, easy to use and are prime candidates for applications that require slow movement, high torque and low positional accuracy. Feedback for step motors isn't necessary because the current is kept constant through the phases which allow a position to be held with a fairly high level of static torque.
Step motors are not candidates for applications that require positional accuracy, smooth motion, fast speeds or power efficiency.
Applications that require accuracy and smoothness typically need servo motors with analog or digital feedback, where the motion controller provides a PID filter or something similar. 3-phase brushless motors are higher cost, and require more effort to stabilize than step motors, but they handle fast or slow speeds with perfect accuracy and smooth motion, at all times.
There are some occasions when applications desire the benefits of step motors but also need the accuracy of a servo motor. Additional accuracy can be achieved on step motors with half, quarter, and microstepping motion. While these modes provide some advantages, they do not reach the level of positional accuracy achievable with a servo motor.
A solution for these distinct applications can be a closed-loop step motor. Adding a feedback device to the step motor, and controlling it like a servo motor, achieves the positional accuracy of a servo motor. In this configuration the step motor acts like a 2-phase brushless servo motor. Because it's acting as a servo motor, current is only drawn when it is needed greatly improving the power efficiency and eliminating wasted heat. However, like an open loop step motor, this solution provides high torque at low speeds. The closed loop step motor will not achieve as high speed or run as smoothly as a 3-phase brushless DC servo motor.
This solution is available on the DMC-30017 and the DMC-40×0.