First let’s explore how high performance closed-loop stepper motor system compare to traditional open-loop stepper systems in terms of torque and efficiency.
There’s superior performance from closed-loop stepper systems over open-loop setups as demonstrated in laboratory test results comparing the two systems’ acceleration (torque), efficiency (power consumption), position error (accuracy), heat generation, and noise levels. Just consider the relationship between torque and acceleration. Torque-speed curves show the peak and continuous torque ranges of a closed-loop stepper system alongside the usable torque range of an open-loop stepper system. Very often, torque in the real world translates into acceleration — so motors with greater torque can accelerate a given load faster.
To test this difference in torque performance in the lab, equally sized open-loop and closed-loop step motor systems get identical inertial loads. Programming commands the two systems to perform identical move profiles, except that acceleration rate and top speed are slowly increased in each system until they make positioning errors.
Here we have a move profile comparison between a open-loop vs. closed-loop system. This is a comparison between that from a StepSERVO closed-loop system and that from an open-loop system. The closed-loop system (due to its higher torque producing capability) gets a maximum acceleration rate of 2,000 rev/sec2 and a top speed of 20 rev/sec (1,200 rpm)
as seen here.
Say that the open-loop system gets a maximum acceleration rate of 1,000 rev/sec2 and a top speed of 10 rev/sec (600 rpm). This top speed of 10 rev/sec correlates to where the flat portion of the torque-speed curve ends. The closed-loop system (due to its higher torque producing capability) gets a maximum acceleration rate of 2,000 rev/sec2 and a top speed of 20 rev/sec (1,200 rpm). This is double the performance of the open-loop system and cuts the move time nearly in half — from 110 msec down to 60 msec.
For applications requiring high throughput (such as indexing, edge guide positioning and pick-and-place systems) the closed-loop stepper motor driver system provides a clear performance advantage.