Linear Motors

Linear motors generate force only in the direction of travel. A linear motor applies thrust directly to a load, and does not require any intermediate mechanism to convert rotary motion into linear motion. Linear motors are capable of extremely high speeds, quick acceleration, and accurate positioning. 

Choices for linear motors include moving coil, moving magnet, AC switched reluctance design, AC synchronous design, AC induction or traction design, linear stepping design, DC brushed design, and DC brushless design.  In a moving coil design the coil moves and the magnet is fixed, such as an audio speaker.  In a moving magnet design the magnet moves and the coil is fixed.  AC synchronous motors are a class of motors that operate at constant speed up to full load. The rotor speed is equal to the speed of the rotating magnetic field of the stator; there is no slip.  Reluctance and permanent magnet are the two major types of synchronous motors.  Synchronous linear motors are often used where the exact speed of a motor must be maintained.  AC induction or traction design motors are a class of motors that derives its name from the fact that current is induced into the rotor windings without any physical connection with the stator windings (which are directly connected to an AC power supply); adaptable to many different environments and capable of providing considerable power as well as variable speed control.  Typically there is "slip," or loss of exact speed tracking with induction motors. Typically rolled flat version of rotary AC induction motors.  Stepper motors use a magnetic field to move a rotor in small angular steps or fractions of steps. Stepper motors provide precise positioning and ease of use, especially in low acceleration or static load applications.   Brush motors have the armature windings on the rotor.  The magnetic fields are commutated via direct contact of brushes with the rotor commutator.  Brushless linear motors have their armature windings on the stator and the field on the rotor.  They rely on internal noncontact sensing devices to activate external commutating electronics.

Important specifications to consider include rated continuous thrust force, peak force, maximum speed, maximum acceleration, nominal stator length, slider or carriage travel, slide or carriage width, and slider or carriage length.  The rated continuous thrust force is the maximum rated current that can be supplied to the motor windings without overheating.  The peak force is the maximum force of the linear motor.  The nominal stator length is the length of the fixed magnet or coil.  The slider or carriage travel is the range of travel of the moving coil or magnet.  The slider or carriage width and length are the dimensions of the moving coil or magnet.

Important electrical properties to consider when specifying linear motors include continuous current, rated current per phase, motor force constant, and number of leads.  The rated current per phase is the maximum rated current per phase or winding for a stepper motor.  The number of leads specifies unipolar = 6 leads, bi-polar = 4.  Mechanical properties to consider for linear motors include design units, linear stepper resolution, and maximum coil temperature.  For the linear stepper resolution the Units are typically in 'distance per step' or 'steps per unit distance'.  Common features include forced air-cooling, water-cooling, balanced design, integral position feedback, and modular stator.  Important environmental parameters to consider for linear motors include operating temperature, maximum shock, and maximum vibration.

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Part Numbers for Linear Motors