Introduction to Stepper Motors: Construction, Types and Operation
In this video, we show the operating principle and design of a stepper motor.
The stepper motor works like an electrical machine and converts electrical energy into mechanical energy, which it releases via a shaft. With the help of a highly realistic 3D animation, we describe, among other things, the design features of a stepper motor, such as the toothed rotor whose electromagnets are slightly offset from each other. It allows the motor to achieve a very high torque, maintain a constant speed or approach a certain position very accurately and with no additional feedback.
This animation explains the components that make up a stepper motor. First, we see the permanent magnet core of the rotor. Attached to it are the soft-magnetic, toothed dynamo sheets for mounting the shaft and the ball bearings.
Shown next is the stator, which is also made up soft-magnetic plates that are insulated from one another. Seated in this is the coil body, which is made of plastic and wound with copper wire. These windings are connected to the connection cables of the motor.
In the final step, the rotor and stator are assembled and secured to the front and rear bearing shells. The corrugated washers provide axial spring suspension for the rotor and also serve to compensate for tolerances.
The individual components will be discussed again later in detail.
The die-cast aluminum end caps used on a standard motor perform an important function on a stepper motor: on the one hand, they serve to precisely align the motor shaft with the motor housing in order to achieve precise and smooth running characteristics. On the other hand, they are used to align the rotor with the stator, so that the air gap between the two parts is just 0.05 mm.
A permanent magnet is seated in the core of the rotor and forms the magnetic antipole to the electromagnet in the stator. The additional toothing in combination with the small air gap between rotor and stator allows the motor to achieve high position accuracy as well as a high torque. Toothing is provided by means of soft metal plates, which are punched to form a rotor body.
Plastic cover (Bobbin)
Located in the stator is a plastic body with 8 pole shoes, which are wound onto the coils of the electromagnet. Here a temperature-resistant, high-performance plastic is used, allowing the motor to reach insulation class F (= 130 degrees Celsius).
The enameled copper wires of the stator are available in various thicknesses and vary in resistance and inductance. Depending on whether a slowly or quickly rotating motor is desired, different wires are used.
The motor strands are either soldered directly to the enameled copper wire of the windings or connected to a board that is integrated in the rear bearing shell. The motor windings can be wired in series or in parallel. The resistance and inductance and, thus, the motor behavior, change accordingly. Motors wired in parallel are very well suited for dynamic operation.
Hybrid stepper motors are produced exclusively with ball bearings. They are the only moving element in the motor and determine its service life. Systems with proper mechanical design reach a service life > 20,000 hours provided that the maximum permissible axial and radial forces are not constantly exceeded. In harsh environmental conditions, specially protected ball bearings must be used.
The permanent magnet installed in the rotor is made of especially strong rare earth metals. In combination with the soft-metal rotor plates, it forms a magnetic unit and, simultaneously, the magnetic antipole to the electromagnet in the stator.
Like the rotor, the stator of the stepper motor consists of punched, soft-metal plates that are electrically separated from one another. It is equipped with eight pole shoes situated opposite one another with teeth at the end. The geometric arrangement of rotor and stator teeth results in a rotating movement when power is supplied to the electromagnet in the stator.
The shaft is the part of the stepper motor that transfers the kinetic energy. It is manufactured with very high precision from electrically non-conductive stainless steel. For motors on which an encoder or brake will be mounted, the shaft is extended and led out of the rear bearing seat. Hollow shafts can also be mounted.
With the help of the corrugated washers, the springs of the motor shaft are preloaded. This increases the life expectancy of the ball bearings and compensates for production-related tolerances. Using special bearing shells, it is possible to preload the motor shaft in a defined manner, e.g., to achieve a low axial play.