LamaPLC: Stepper motor basic

A stepper motor, also known as step motor or stepping motor, is an electrical motor that rotates in a series of small angular steps, instead of continuously. Stepper motors are a type of digital actuator. Like other electromagnetic actuators, they convert electric energy into mechanical position can be commanded to move and hold at one of these steps without any position sensor for feedback (an open-loop controller), as long as the motor is correctly sized to the application in respect to torque and speed.

Switched reluctance motors are very large stepping motors with a reduced pole count, and generally are closed-loop commutated.

Brushed DC motors rotate continuously when DC voltage is applied to their terminals. The stepper motor is known for its property of converting a train of input pulses (typically square waves) into a precisely defined increment in the shaft’s rotational position. Each pulse rotates the shaft through a fixed angle.

Stepper motors effectively have multiple “toothed” electromagnets arranged as a stator around a central rotor, a gear-shaped piece of iron. The electromagnets are energized by an external driver circuit or a micro controller. To make the motor shaft turn, first, one electromagnet is given power, which magnetically attracts the gear's teeth. When the gear's teeth are aligned to the first electromagnet, they are slightly offset from the next electromagnet. This means that when the next electromagnet is turned on and the first is turned off, the gear rotates slightly to align with the next one. From there the process is repeated. Each of the partial rotations is called a “step”, with an integer number of steps making a full rotation. In that way, the motor can be turned by a precise angle.

There are three main types of stepper motors:

1. Permanent magnet stepper motors
2. Variable reluctance stepper motors
3. Hybrid stepper motors

Permanent magnet motors use a permanent magnet (PM) in the rotor and operate on the attraction or repulsion between the rotor magnet and the stator electromagnets. Pulses move the rotor clockwise or anticlockwise in discrete steps. If left powered at a final step, a strong detent remains at that shaft location. This detent has a predictable spring rate and specified torque limit; slippage occurs if the limit is exceeded. If the current is removed, a lesser detent still remains, holding the shaft position against spring or other torque influences. Stepping can then be resumed while reliably being synchronized with control electronics.

Variable reluctance (VR) stepper motors have a plain iron rotor and operate based on the principle that minimum reluctance occurs with minimum gap, hence the rotor points are attracted toward the stator magnet poles.

Whereas hybrid stepper motors are a combination of the permanent magnet and variable reluctance types, to maximize power in a small size. Variable reluctance motors have detents when powered on, but not when powered off.

The US National Electrical Manufacturers Association (NEMA) standardizes various dimensions, marking, and other aspects of stepper motors, in NEMA standard (NEMA ICS 16-2001). NEMA stepper motors are labeled by faceplate size, NEMA 17 being a stepper motor with a 1.7 by 1.7 inches (43 mm × 43 mm) faceplate and dimensions given in inches.

The standard also lists motors with faceplate dimensions given in metric units. These motors are typically referred to with NEMA xx, where xx is the diameter of the faceplate in inches multiplied by 10 (e.g., NEMA 17 has a diameter of 1.7 inches). There are further specifiers to describe stepper motors, and such details may be found in the ICS 16-2001 standard.

https://www.moonsindustries.com/c/stepper-motors-a02