Friday, June 15, 2018

Parameters to be considered for a stepper motor system

Parameters to be considered for a stepper motor system

a) Distance – The distance to be traversed to complete the motion.
b)Time – The maximum time allowed for a traverse.
c)Accuracy – The desired detent (static) accuracy.
d)Overshoot – The desired dynamic accuracy (overshoot).
e) Settling Time - The time allowed for dynamic accuracy to return to static accuracy specification (settling time).
f) Step Resolution – The required step resolution (combination of step size, gearing, and mechanical design).
g) Friction – The system friction: All mechanical systems exhibit some frictional force. When sizing the stepper motor, remember that the motor must provide torque to overcome any system friction. A small amount of friction is desirable since it can reduce settling time and improve performance.

Parameters to be considered for a stepper motor system

h)Inertia - System inertia: An object's inertia is a measure of its resistance to changes in velocity. The larger the inertial load, the longer it takes a stepper motor online to accelerate or decelerate that load. The speed at which the stepper motor rotates is independent of inertia. For rotary motion, inertia is proportional to the mass of the object being moved times the square of its distance from the axis of rotation.
i) Speed/Torque – There a specific speed/torque characteristics to each stepper motor, which will determine your overall system performance. Torque is defined as rotational force (in ounce-inches) defined as a linear force (in ounces) multiplied by a radius (in inches).
IMPORTANT NOTE: When selecting a stepper motor/driver, the capacity of the stepper motor must exceed the overall requirements of the load. The torque any stepper motor can provide varies with its speed. Individual speed/torque curves should be consulted by the designer for each application.
j) Torque-to-Inertia Ratio - This number (ratio) is defined as a stepper motor's rated torque divided by its rotor inertia. This ratio (measurement) determines how quickly a stepper motor can accelerate and decelerate its own mass.
Note: Stepper motors with similar torque ratings can have different torque-to-inertia ratios as a result of varying construction. Performance will vary among different manufacturers.
k) Torque Margin: Whenever possible, a digital stepper motor driver that can provide more torque than is absolutely necessary should be specified. Torque margin allows for mechanical wear, lubricant hardening, and other unexpected friction. Resonance effects can cause the motor's torque to be slightly lower at some speeds. Selecting a stepper motor drive that provides at least 50% margin above the minimum required torque is ideal. More than 100% may prove too costly.

Some Question about NEMA 17 motor

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