What does a stepper motor system consist of?
A stepper motor system typically consists of:
- Controller: capable of generating step pulses and direction signals for the driver
- Driver: converts the controller command signals into power to energize the motor windings
- Stepper Motor: electromagnetic device that converts digital pulses into mechanical shaft rotation
- Variable Reluctance: Has teeth on the rotor and stator but no rotor permanent magnet.
- Permanent Magnet: Has a permanent magnet for a rotor but no soft iron rotor teeth. Permanent magnet step motors can be subdivided into ‘tin-can or can-stack’ and ‘hybrid’, tin-can (can-stack) being an inexpensive version, and hybrid versions constructed with higher quality bearings, smaller step angle and higher power density.
- Hybrid Synchronous: Combines the magnet from the permanent magnet motor and the rotor and stator teeth from the variable reluctance motor.
A step motor has two primary pieces, the rotor and stator. The stator is made out of coils of wire called the windings and the housing. The rotor is a magnet with teeth which rotates on bearings inside the stator. When current is passed through the stator windings, it produces a magnetic force that holds the rotor in a locked position, the amount of torque needed to exceed this force is called the holding torque. As current is switched in the windings, the motor takes “steps” or small movements in one direction. This movement is similar to the second hand on a clock. The amount of rotational movement per step depends on the construction of the motor. If you increase the frequency of the steps you will eventually go from a stepping movement to continuous rotation.
Are stepper motors AC or DC?
Stepper motors are generally considered to be asynchronous (AC) motors. While stepper motors are largely the same as brushless DC motors (BLDC motors), they differ in their intended use. Stepper motors operate in steps whereas a BLDC motor provides smooth motion.
Steps / Revolution Explained
Steps per revolution equals 360° divided by step angle (0.9°, 1.8°, 3.75°, 7.5° and 15°) when the motors are driven in full-step excitation mode.
- 0.9° = 400 steps/rev
- 1.8° = 200 steps/rev
- 7.5° = 48 steps/rev
- 15° = 24 steps/rev
Rotary or Linear Step Motors?
Step motors can be linear or rotary. ATO offers a full line of low-cost short-delivery hybrid rotary stepper motors from sizes NEMA 17 to NEMA 42, including IP65 rated step motors and stepper gearmotors. ATO stepper motors are available in 4, 6 & 8 lead configurations for bipolar or unipolar operation, and can be wired in series or parallel. All our step motors have optional rear shaft extensions, encoders and gearboxes.
Linear step motors are also known as step motor linear actuators, and have a threaded rod/acme screw in place of a smooth shaft. Linear step motors provide a simple motion system at a fraction of the cost of conventional rotary stepper motors and traditional linear motion systems. Linear step motors offers a wide range of customizable options, including various screw pitches, screw lengths, bipolar or unipolar windings, and several operating voltages.
What size stepper motor do I need for my project?
Most motors have torque specifications – usually in inch/ounces or newton / centimeters. One inch/ounce means that the motor can exert a force of one ounce at one inch from the center of the shaft. For example, it could hold up one ounce using a 2″ diameter pulley.
When calculating the torque required for your project, be sure to allow extra torque required for acceleration and to overcome friction. It takes more torque to lift a mass from a dead stop than it does to simply hold it up.
How hot can we run a stepper motor without damaging it?
The temperature range of our motors is -20℃ to +150℃.
What is the difference between series and parallel connection on an eight lead stepper motor?
On eight lead motors, you have four independent windings with two leads coming out of the motor. Each winding is paired with another. When you connect the pairs to the motor, you are literally connecting them in series or parallel. Depending on how you connect your motor the electrical characteristics change. It is important to know how these characteristics change or else you could damage the motor.
What is stepper motor resonance?
Resonance is an unstable condition when running a step motor. Resonance usually occurs between 2-4 rev/sec and can be alleviated in most situations by putting a load on the motor, changing from full stepping to half or microstepping, or increasing your acceleration through the resonance zone.
When you know the torque required and your top motor speed (rev/sec), look at these curves to determine which motor will work for you. We recommend doubling (100% safety factor) your required torque at a given speed and then selecting a motor/drive/power supply combination that can deliver that torque (i.e. If you need 100 oz-in to the system, get a motor that produces 200 oz-in at that speed).
What is a reasonable inertia ratio between a stepper motor and load?
This depends on the acceleration that you expect out of a system. With stepper motors, it is best to target a 1:1 inertial load to motor ratio to expect good acceleration. For servo motors, target for a 5:1 mismatch.
Note: gearheads are a good option to reduce the ratio mismatch because the gearhead reduces the reflected inertia by the square of the gear ratio.