A step motor consists of basically two parts, a stator and a rotor. The rotor in turn is made up of three components; rotor cup 1, rotor cup 2 and a permanent magnet. In a 2 phase stepper motor, the stator is made up of 8 magnetic poles with small teeth. The poles in the stator are each provided a winding. A 2 phase stepper motor has two phases, an "A" phase and a "B" phase. Essentially, the number of phases refers to the different combinations of poles that are energized in sequence to attract the rotor.
The use of three phases inherently helps to reduce torque ripple and smooth motor performance. 3 phase stepper motor requires a 3 phase drive that is different than the drive for 2 phase motors. As compared to the 1.8 degree two phase motors, the low speed torque is somewhat less. But design improvements introduced by MOONS', minimizes this difference. High speed torque can also be comparable. In addition, MOONS' size 24 three phase motors are available with PowerPlus technology, for maximon torque. 3 phase stepper motors are used where maximum performance, and very quiet, smooth precise movement is need. An example of a good application for three phase motors is in performance lighting. These spotlights lights need quick movement, and quiet operation so as not disturb the performance.
Step angle of special stepper motor is proportional to pulse rate. Special stepper motor outputs its maximum torque at the moment it stops running (when winding excitation). The precision of every step is controlled within the range from 3% to 5%.
Stepper driver operates at a fixed – but adjustable (open loop) – current level and the motor can be stalled by exceeding the torque being generated. This is unlike a servo, which will increase current/torque to correct for errors in motor speed. The stepper driver will then “Ratchet” as the field continues to rotate, but this causes no inherent damage to the stepper system. This is advantageous in applications where jams may occur either as a result of process errors or the normal process flow (running to a hard stop). This feature has been utilized in finger safe small conveying, small transfer wheels and screw and nut driving applications. Unlike servo systems, stepper driver do not dither (oscillate around the set point ) when standing still. This is an advantage for applications where high magnification vision and or high precision sensing is being used.
The performance of the closed loop stepper system is better than the open-loop setting. Only the relationship between torque and acceleration is considered. The torque speed curve shows the peak and continuous torque range of the closed loop stepping system and the available torque range of the open loop stepping system. Usually, the actual torque will be converted into acceleration, therefore, the motor with more torque can accelerate the rated load faster.
The advantages of closed loop stepper motor are low cost, high-performance feedback system and advanced DSP to close the loop of the step motion control system. Such control can improve the performance of the closed-loop stepper motor driver, making it superior to open-loop systems.
Because brushless DC motor can develop high torque with good speed response, they may be used for applications that require variable speeds, such as pumps and fans. The motors achieve a variable speed response by operating in an electromechanical system with a rotor position feedback sensor and electronic motor controller. Thanks to their lower cost and versatility, brushless DC motors are often used as extruder drives. They function by turning a screw that compresses polymer materials. While the action might seem simple the motor offers precision to avoid variations in the part density, which ensures accuracy. Incidentally, the motor offers high torque over its speed range with little to no short-term positional errors.
