LMAC - AC linear induction motor
The LMAC AC linear induction motor (LIM) is designed for highforce, long-stroke applications, such as material handling and people movers.
The single sided motor consists of a primary coil assembly and a secondary called a reaction plate. The coil assembly is comprised of steel laminations and phase windings with a thermal sensor encapsulated in thermal epoxy. The customer supplied reaction plate is made of 3.2mm (1/8 inch) thick aluminum or copper plate bonded to a 6.4mm (1/4 inch) thick cold rolled steel. The aluminum faces the coil assembly. The width of a reaction plate must be equal to the width of the coil assembly. A customer supplied bearing system is used to maintain the 3.2mm (1/8 inch) airgap between the coil and reaction plate over the length of the stroke.
When AC voltage is applied to the coil windings, a traveling magnetic field is created. This induces current in the reaction plate which in turn creates its own magnetic field. The interaction of the two magnetic fields generates the force and direct linear motion.
Either assembly or the reaction plate can be the moving member of the motor. Typically the reaction plate becomes part of the customer load moving over stationary coil assemblies placed end-to-end for the travel distance. In this configuration the length of the reaction plate must be equal to the center to center distance of two adjacent coil assemblies plus the length of one coil assembly. This will ensure the reaction plate covers adjacent coil assemblies at the point of transition from one coil to the next. Should the coil assembly be the moving element of the motor then the reaction plate length must be equal to the length of stroke plus the length of one coil assembly.
Using two LIMs facing each other can provide increased force. This is known as a double sided linear induction motor. Here the reaction plate will consist only of a 6.4mm (1/4 inch) thick aluminum plate without steel backing. The aluminum will require additional support over the length of the stroke.
A variable frequency inverter will provide velocity control of a linear induction motor. A Linear Induction Motor (LIM) equipped with a linear encoder can do point to point programmable positioning when driven with a vector control and motion controller. These motors are supplied in kit form with customer providing reaction plate (secondary) and bearing system to be integrated into the application.