Stepper Motor Detent Torque

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om_tech_support_AC
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Joined: Tue Jan 03, 2017 2:53 pm

Stepper Motor Detent Torque

Postby om_tech_support_AC » Wed May 16, 2018 12:14 pm

Q: My application is an indexing conveyor with an incline at 10 degrees. I would like to use a geared stepper motor for this application, but if power is lost, I want to ensure there is enough resistance to hold the position.

A: The resistance in a non-excited stepper motor is known as detent torque or residual torque, cogging torque and non-excitation retention torque.

The Detent torque is found in between the rotor and stator which depends on 3 factors.

① iron plate material, ② magnet strength, ③ gap. Naturally the larger the magnet, the stronger the product, and the greater the detent torque. Therefore, the detent torque tends to increase as the product size increases. If the stepper motor is a single shaft or double shaft it won’t affect the detent torque. The wiring difference, unipolar or bipolar, of a stepper motor also does not affect the detent torque.

Detent torque is measured by a torque meter while slowly rotating the output shaft (including the gearhead). Several samples are measured to get an average which is set as a reference value. As a guide, an individual motor’s detent torque could be +/- 20% the reference value. Please note detent torque is NOT a specification we provide. We do not design motors for detent, it is a result of a stepper motor’s structure.

For your holding application, it would be preferred to have a larger detent torque. Usually a larger detent torque is associated with less machining accuracy such as rotor outer diameter, stator inner diameter, etc., resulting in higher torque fluctuation. Generally it is better to have a smaller detent torque because the smaller torque fluctuation, the less vibration and uneven rotation.

Using only the detent torque is not the most reliable option to hold a position. It would be recommended to get an electromagnetic brake which engages when power is removed. For more information about stepper motor Emag brakes please refer to the forum below.

viewtopic.php?f=18&t=5475&p=9630&hilit=brake#p9630

If detent torque is still required please contact us for reference values as needed.

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