Principle of Operation

Electric motors run by electromagnetism. However, there are also other types of motors that utilize electrostatic forces or piezoelectric effect. In the case of a PMDC {Permanent Magnet DC) motor, motion is produced by an electromagnet (armature) interacting with a fixed field magnet (housing assembly).

In a brushed motor, electrical current flows through the motor terminals in the endcap assembly that comes in contact with the commutator in the armature assembly through the carbon brushes or brush leaves. The electrical current powers the coils generating a magnetic field causing the armature to rotate as it interacts with the magnets encased in the housing assembly. Flemming’s Left Hand Rule helps to determine the direction of the force, the current and the magnetic flux.

In a brushless motor, when electricity is applied across the motor termination, a current flows through a fixed stator field and is interacting with a moving permanent magnet or a moving induced magnetic field inside a rotor / armature. After the motion and force load have been met by the available source current it returns back to the source exiting the motor.

Key Elements Interacting to Produce Motion

Magnetic Flux - A motor can have a fixed wound coil or a permanent magnet stator and a moving wound coil armature or PM rotor that will have interacting magnetic flux fields to produce a force and motion.

Force - The amount of current that flows through the electromagnetic field is proportional to the amount of interacting electromagnetic field force required to achieve the opposing work load. In addition to the force and motion needed by the device one must consider any efficiency loss in the conversion of electrical power into mechanical work (watts).

Stepper Motor Overview

What is a Stepper Motor

Stepper motors operate differently from other DC motors, which simply spin when voltage is applied. A rotational stepper motor is an electromechanical device that can divide one full rotation (360°) into a large number of rotational steps. Stepper motors are controlled electronically and do not require costly feedback devices. The linear stepper motor is similar to the rotational motor other than the shaft moves in a linear or lengthways fashion. Both types have two winding arrangements for their electromagnetic coils: unipolar and bipolar. Unipolar means that every coil end has one polarity. A recommended Zener diode is used to ensure a fast current decay in the switched-off coil. This will give an increased motor torque especially at higher frequencies.

Bipolar indicates that every coil end has both polarities. The coil will be positive and negative during each drive cycle. Since every coil is fully used, the motor has a higher torque compared to a unipolar coil. A bipolar driver can incorporate a constant current drive capability, called chopper drive. This will provide an increased torque output during higher frequencies and reduces the effects of temperature and supply voltage variations.

Stepper Motor Basics

The PM or "tin can" stepper motor is a low cost solution for your positioning applications with typical step angles of 7.5° - 15°. Smaller step angles can be obtained trough Microstepping. The shaft of the motor moves in distinct step increments when electrical control pulses are applied. The current polarity and frequency of the applied pulses determines the direction and speed of the shaft’s movement.

One of the most significant advantages of a stepper motor is its ability to be accurately controlled in an open loop system. Open loop control means no feedback information about shaft position is needed. This type of control eliminates the need for expensive feedback devices by simply keeping track of input step pulses. A stepper motor is a good choice whenever controlled movement is required. They are recommended in applications where you need to control rotation angle, speed, position and synchronism. Detent, Holding, Pull-In and Pull-Out torque capabilities, speed (RPM) and steps per revolution (step angle) characterize a stepper motor.

Detent torque defines the maximum torque that can be applied to a de-energized motor without causing the motor to rotate.

Holding torque defines the maximum torque with which an energized motor can be loaded without causing rotary movement.

Pull-In performance defines the motor’s capability to start or stop. This is the maximum frequency at which the motor can start or stop instantaneously, with a load applied, without loss of synchronization.

Pull-Out defines the maximum torque when applying an acceleration/deceleration ramp without loosing steps. It defines the maximum frequency at which the motor can operate without losing synchronism.

Our rotational stepper motor can be combined with our full line of Gearboxes to increase torque and reduce speed.

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