There's a saying that nothing happens until something moves.
Motors convert electric (and in some cases, pneumatic or hydraulic) energy into physical force. The following is a rundown of the main motor types.
The most common and simple industrial motor is the three-phase AC induction motor, sometimes known as the "squirrel cage" motor. The simple design of the AC motor -- simply a series of three windings in the exterior (stator) section with a simple rotating section (rotor). The changing field caused by the 50 or 60 Hertz AC line voltage causes the rotor to rotate around the axis of the motor.
Brushed DC motors
There are two basic DC motor types, brushed and brushless. One of the first motor designs ever developed, the brushed DC motor is the motor of choice in the majority of variable speed and torque control applications. The magnetic force can be provided by permanent or electromagnets, but most small motors generating less than three to five horsepower use permanent magnets. The brushes referred to in the description are metal or graphite-copper contacts that contact the section of the rotor (the commutator) where the electricity enters the rotor windings. Controlling the speed of a brushed DC motor is simple. The higher the armature voltage, the faster the motor’s rotation. This relationship is linear to the motor's maximum speed.
Brushless DC and Stepper Motors
The Brushless DC motor has a rotor with permanent magnets, a stator with windings and commutation that is performed electronically. Stepping motors are available in permanent magnet, variable reluctance, and hybrid variations. Variable reluctance motors usually have three (sometimes four) windings, with a common return, while permanent magnet motors usually have two independent windings, with or without center taps. Center-tapped windings are used in unipolar permanent magnet motors. Stepping motors come in a wide range of angular resolution, from a coarse 90° per step to high-resolution motors able to handle less than 2° or even under 1° degree per step. With an appropriate controller, most permanent magnet and hybrid motors can be run in half-steps or microsteps. For both permanent magnet and variable reluctance stepping motors, if just one winding of the motor is energised, the rotor (under no load) will snap to a fixed angle and then hold that angle until the torque exceeds the holding torque of the motor, at which point, the rotor will turn, trying to hold at each successive equilibrium point.
Direct drive motors are different from the average motor, providing a surface enabling you to mount your load directly to the motor. Some direct drives can produce repeatability and resolutions of 0.1 arc seconds, carry loads up to 6,000 lb., and produce a torque of 200 ft lb.
Rather than having a stator and rotor like a typical rotary motor, a linear motor has a primary and a secondary (also called the platen and forcer.) The platen or the static element is the equivalent of the stator. Electrically similar to rotary motors, types include DC (brushed and brushless), stepper motors, and single-phase AC motors. Capacity is measured in terms of force, from a few pounds to 2,500 lb. Speeds range from 40 to 100 inches per second.
A linear motor generates force only in the direction of travel. Linear motors are capable of extremely high speeds, quick acceleration, and accurate positioning.
For the linear induction motor, by applying a voltage across the primary winding in the platen, a linear traveling magnetic field is formed, inducing currents into the secondary conductive windings in the forcer, which results in a thrust force.
The linear step motor is basically an unrolled variable reluctance step motor. The windings of the platen (symbolized by the circles in the diagram) produce a magnetic field. Both components have teeth projecting towards the other, which concentrate the magnetic flux. When a current flows through the windings, the forcer teeth attract and repel sequential teeth on the platen, causing step motion.
In the linear servomotor, the primary produces magnetic fields just as the stator of the rotary motor. But in this case, these magnetic fields produce a force on themselves as they react with the stationary permanent magnets of the secondary.
There are also pneumatic and hydraulic linear actuators, using pressure from air or a working fluid, typically oil, to move a piston connected to the motion arm. These can often provide force levels beyond that of an electric device of similar weight. They can also reduce the amount of demand on a system's batteries.