Electric motors operate using electromagnetic or electrostatic principles to produce motion. Permanent magnet DC motors have a fixed magnet and an electromagnet armature that interacts to cause rotation. Brushed motors use carbon brushes to conduct current to coils in the armature, generating a magnetic field. Brushless motors have a fixed stator and moving permanent magnet rotor.
Stepper motors divide a full rotation into discrete steps controlled by electronic pulses to the coils, allowing open-loop position control without feedback. They are useful when precise movement control is needed. Encoder motors integrate position sensors like optical encoders to provide closed-loop feedback for speed or position control in applications like printers.
Electric motors operate using electromagnetic or electrostatic principles to produce motion. Permanent magnet DC motors have a fixed magnet and an electromagnet armature that interacts to cause rotation. Brushed motors use carbon brushes to conduct current to coils in the armature, generating a magnetic field. Brushless motors have a fixed stator and moving permanent magnet rotor.
Stepper motors divide a full rotation into discrete steps controlled by electronic pulses to the coils, allowing open-loop position control without feedback. They are useful when precise movement control is needed. Encoder motors integrate position sensors like optical encoders to provide closed-loop feedback for speed or position control in applications like printers.
Electric motors operate using electromagnetic or electrostatic principles to produce motion. Permanent magnet DC motors have a fixed magnet and an electromagnet armature that interacts to cause rotation. Brushed motors use carbon brushes to conduct current to coils in the armature, generating a magnetic field. Brushless motors have a fixed stator and moving permanent magnet rotor.
Stepper motors divide a full rotation into discrete steps controlled by electronic pulses to the coils, allowing open-loop position control without feedback. They are useful when precise movement control is needed. Encoder motors integrate position sensors like optical encoders to provide closed-loop feedback for speed or position control in applications like printers.
Electric motors operate using electromagnetic or electrostatic principles to produce motion. Permanent magnet DC motors have a fixed magnet and an electromagnet armature that interacts to cause rotation. Brushed motors use carbon brushes to conduct current to coils in the armature, generating a magnetic field. Brushless motors have a fixed stator and moving permanent magnet rotor.
Stepper motors divide a full rotation into discrete steps controlled by electronic pulses to the coils, allowing open-loop position control without feedback. They are useful when precise movement control is needed. Encoder motors integrate position sensors like optical encoders to provide closed-loop feedback for speed or position control in applications like printers.
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. Flemmings 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 shafts 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 motors 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.
Design Considerations Power supply
DC
Battery supply possible
Driver electronics need
No
Speed accuracy
Low
Effected by load torque
Manufacture tol +-10% of no load speed
Speed control
Voltage
Open loop or closed loop speed control Closed loop - high
accuracy, but sensor need
Position control
High effort
Closed loop position control and sensor need
Overloadablity / load inertia
High
High start torque or peak load torque
Able to accelerate high load inertia
Lifetime
Low
300...2000h (limited by wear of brushes) Depend on speed, current
and brush config
Speed range [rpm]
1000...25000
No load speed
Efficiency
60...80%
At operating point of max. efficiency
Power vs. size
High
Winding thermal protection
Need
If overload (mechan.blocking) not excluded - Current limitation or
thermal contacts
Load sensing
Easy
Current rises with load
Stalling permissible
No
No or only short time (winding overheat)
Electromag.interference EMI
Critical
Suppression means (capacitors / varistors)
Braking/Holding torque
Low
Detent torque Braking improvable by winding short circuit
Max.output power from JE [W]
Linear motors from JE
No
Encoder Motors Encoders (Sensors) can be implemented inside the motor or mounted to motor rearside. They are needed for a precise speed control or angular position control. Typical application: Printers and scanners. There are different options:
Optical encoders
Hall-effect magnetic sensors
Resolvers
Johnson Electric offers a range of several optical encoders.
Basic principle: A slotted wheel or a black/transparent strip photo print is rotating with the motor shaft. A photo sensor provides a sine wave or pulse pattern that follows the speed of the motor. Output signal can be analog (0...3.3Vac) or digital (0...3.3 Vdc or 0...5Vdc). One signal or two signals phase shifted 90 (enabling detection of direction of rotation ; allows 4x resolution) Several options for resolution. Terminology: CPR (Counts Per Revolution) and LPI (Lines Per Inch).
