In this video we will see why the stepper motor is considered, among other electric motor types, the ideal choice for all those applications that require maximum precision in angular movements and rotational speed. Stepper motors in fact offer excellent speed control, repeatability of movement and precise positioning.
The same precise positioning required during the operation of this robotic arm, used by JAES inside its automated video acquisition system.
In this case the robotic arm is powered by a stepper motor, that allows the arm to position the objects with extreme precision on the conveyor belt.
A stepper motor is an electromechanical device achieving mechanical movements through conversion of electrical pulses. These type of motor is in fact driven by digital pulses rather than by a continuous applied voltage. Unlike conventional electric motors which rotate continuously, stepper motors rotate or step in fixed angular increments.
Stepper motors are known by their property of converting a train of input pulses, typically square wave pulses, into a precisely defined increment in the shaft position. Each pulse moves the shaft through a fixed angle.
There are 3 types of stepper motors: Permanent magnet stepper motors, Variable reluctance stepper motors and Hybrid stepper motors.
In any stepper motor, eddy currents waste energy through heat and create electromagnetic forces that oppose the main motor force. For this reason its stator is made of magnetic core materials with lower electrical conductivity, in order to reduce the losses.
Here you can see a simple permanent magnet stepper motor, with 4 stator teeth, 2 windings which are separated into 2 coils and fed by 2 separate DC power sources. The rotor instead is made up of a permanent magnet.
Energizing a coil winding creates a rotating magnetic field with a north and south pole. The stator carries the magnetic field which causes the rotor to align itself with the magnetic field. The magnetic field can be altered by sequentially energizing or “stepping” the stator coils which generates rotary motion.
If you want to learn more about rotating magnetic field and synchronous speed, you can watch our video about the working principle of induction motors by clicking the link at the top right corner of this video.
The rotor poles are attracted by the moving polarities of the coils, so the rotor rotates 90 degrees, in the exact position that the stator will order.
Coils and magnets can be added to increase accuracy.
In this example we can observe the mechanical behaviour of a stator with eight teeth, 2 different windings which are separated into 2 coils, and a rotor with 2 pole pairs.
In the Variable reluctance stepper motor the rotor is made of soft iron. Here the coils are energized in a certain sequence, so only one pair of rotor teeth are alined to the stator at a time.
The rotor always has less teeth than the stator and the coils are excited in sequence.
In this way, the excited coil will always attract the nearest tooth to itself.
More than 10 years in industrial supplies have led JAES to become a qualified partner for some of the most important industrial automation companies, providing its technical support over a wide range of stepper motor types, installed in many robotic arms.
In the second part of this video we will see how the Hybrid stepper motor works. This is the most used stepper motor type today, which combines the features of a stepper motor with those of a variable reluctance stepper motor.
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