What is a geared stepper motor? This phrase may be unfamiliar to you. Geared stepper motor generally refers to a stepper motor with gearbox or gearheads. In the previous post, you may get to know what a stepper motor is and “how does a stepper motor work“. As we know, the gearbox is usually used for altering speed and torque. That’s to say, a geared stepper motor is a brushless DC motor that divides a full rotation into individual steps with gear changing its speed and torque (generally reducing speed, increasing torque).
Basic Working Principle
While the brush DC motor will keep rotating if connected to a DC power supply, the geared stepper motor is not the thing. It will convert the input pulse into a precisely defined increment in the shaft position. The shaft is moved by each pulse with a fixed angle. That means every pulse inputs, the rotator will move a step or rotate at a fixed angle. The rotating speed is proportional to the pulse frequency. Therefore, you can control the rotating speed by changing the frequency of the input pulse, realizing precise positioning.
There are various standards when it comes to categorizing the geared stepper motors. They can be divided into three types according to magnet force source: permanent magnet stepper, variable reluctance stepper, and hybrid synchronous stepper. If classified by the gearbox of stepper gear motors, planetary gearbox stepper motor (you can check some examples of 1.5-12V geared stepper motor) is the most common one.
Why Choose It?
Stepper motors, or step motors/stepping motors, are known for their precise positioning capabilities and high torque output at low speeds, but their sizes need to be carefully verified to match the load and application parameters and minimize the possibility of out-of-step or motor stall. Here comes the geared stepper motor. Adding a gearbox to a stepper motor system can improve motor performance by reducing the inertia ratio of the load to the motor, increasing the load torque, and reducing motor oscillation.
- Reduce inertia ratio
One reason for the lack of step in stepper motor applications is inertia. The ratio of load inertia to motor inertia determines how the motor can drive or control the load, especially in the acceleration and deceleration parts of the motion curve. If the load inertia is significantly higher than the motor inertia, it will be difficult for the motor to control the load, and overshoot (the number of overspeed steps is beyond the command range) or undershoot (the number of understeps) may occur. A high load inertia ratio may also cause the motor to consume too much current and stall. One way to reduce the inertia ratio is to use a larger inertia motor. But this means higher costs, more weight, and trickling effects on other parts of the system (such as couplings, cables, and drive components). Instead, a gearbox is added to the system to reduce the inertia ratio of the load to the motor by the square of the gear ratio.
- Increase Torque
Another reason for using gearboxes with stepper motors is to increase the torque to drive the load. When the load is driven by the high torque DC brushless gear motor, the gearbox multiplies the torque of the motor by an amount proportional to the gear ratio and gearbox efficiency.
- Reduce Vibration
The stepper motor with gearbox shows significantly less vibration than the stepper motor without gearbox, especially at low speeds in the resonance frequency range.
All in all, a geared stepper motor has the following advantages:
- Precise positioning. Backlash can be limited to 3%.
- No brush. It saves cost and improves service life since you don’t need to change the brush and the service life is only determined by the life of the shaft.
- High torque available. Equipped with the gearbox, the geared stepper motor is enabled with high torque. And the torque is customizable since you can alter the gear ratio.
It has disadvantages as well. The stepper gear motor has low starting torque, which is not suitable for heavy load. For geared stepper motor customization and application, you can check details at parameters and customized development of geared stepper motor.