Brushless DC permanent magnet motors overcome these problems and provide more beneficial electronic commutation than mechanical commutation. This type of motor is a DC motor manufactured from the inside out, consisting of a typical brushless motor magnetic rotor and a wound stator coil. Commutation is carried out by non-contact Hall-effect devices (HEDs) mounted inside the stator windings. HEDs are wired power transistor switching circuits that are mounted on separate external modules and internally mounted with a number of motors. In addition, encoders or software for other motors in the circuit can be exchanged in the motion controller or motor drive.
Brushless DC motors have higher efficiency due to their low inertia rotor and lower winding thermal resistance compared to brushed motors, and the magnets allow the use of shorter, smaller rotor diameters. In addition, because they are not loaded with sliding brush-type mechanical contacts, they can operate at higher speeds (>50 000r min) compared to brushed motors, providing higher continuous torque and faster speeds. However, in terms of increasing the cost and complexity of the overall motion control system, the cost of brushless motors is still much higher than that of brushed motors of the same level (although this **gap continues to narrow), Table 1 summarizes the characteristics of some stepper motors, permanent magnet brushed and brushless DC motors.
Compared to rotary motors, linear motors must operate in a closed feedback loop, often requiring a more expensive feedback system. In addition, electric motors need a certain amount of free space to move so that they can run back and forth along a linear path. In addition, their applications are limited due to poor heat dissipation, and they can easily pose a safety hazard to rotating motors and metal frames, cooling fins, and in some models where exposed magnetic fields can adsorb loose ferrous debris.