Geared Stepper Motor- A Motor for Precise Positioning Equipment

Posted by Jack Wang on October 1st, 2015

A stepper motor is an electromechanical device that induces mechanical movements by converting electrical pulses. In this case, digital pulses—not the application of continuous voltage cause stepper motors to move. Stepper motors step or rotate in increments that are fixed and angular. Hence, they are commonly used in applications that require position control. The stepper motor + driver + controller system design ensures that the geared stepper motor can follow digital instructions. Stepper motors lack position feedback, making them open-loop systems. A geared stepper motor needs an external control unit to provide energy to each electromagnet and enable the motor shaft to turn. 

In a geared stepper motor, the stepper motor is integrated with the gearbox. Some units come with a planetary gearbox in NEMA 23, 17, and 11, as well as in models with spur gearboxes in NEMA 34 and 23. Some suppliers can provide the motors and gearboxes separately, in case you require a unique gear or size ratio. The difference between various geared stepper motors is their performance quality. A stepper gearmotor's main function is to convert the stepper motor's input into output with low RPM and high torque. 

Stepper motors that come with spur gearboxes are efficient, compact, and widely available. They come in gear ratios that range from 3:1 to 150:1, and they are useful in applications that require high output torque and either a reduction or an increase in speed. Stepper motors with a planetary gearbox are as compact and as efficient as the ones with spur gearboxes, but they come in different stack lengths and follow a system made up of three important parts: the ring gear, two or more planet gears, and the sun gear. A planetary stepper gearmotor is typically used in applications that require shock resistance, low backlash, enhanced lubrication, and high efficiency. 

Some geared stepper motors have high accuracy per step and require more torque. They are designed to ensure constant holding torque—even without powering the motor—as long as the appropriate motor is utilized within limits. Geared stepper motors have pre-defined stations to minimize or eliminate positioning errors. Gearing ensures high positioning resolution. This way, a 32:1 gear train applied to an output of the eight-steps per revolution motor results in a 512 step motor. A gear train can increase a motor's torque. 

Stepper motors come in two kinds: bipolar and unipolar. Bipolar motors are the most powerful with eight or four leads. Unipolar motors can step without reversing the path of current in the coils to make electronics simpler. However, they usually have less torque than bipolar motors due to the center tap, which can energize only half of every coil at a time. 

There are companies that design and manufacture AC and DC motors. They can customize the winding and housing of geared stepper motors to meet your specific application and dimensional requirements. You have options in lead wire such as heat shrink, cable harnesses, connectors, pins, and special lengths, as well as a lubricant and bearing options for humid or high temperature operations. Just be sure that the geared stepper motors you are buying meet the standard NEMA 11, 14, 17, 23, 34, and 42 frame sizes. 

About the Author: 

This article is written by Jack Wang who is associated with GEMS Motor. Jack got his Bachelor's degree in Mechanical Engineering and Master's degree in Electrical Engineering, specialized in electric motor design and motor driver development. Jack was born in greater Shanghai area, China, and had several years of study and work experience in the United States. With the deep knowledge of electric motors and great bilingual skills in Mandarin and English, Jack helps market our electric motor products worldwide. Jack currently holds the position of Director of Marketing at GEMS Motor.