Force Engineering's
'Introduction To Linear Motors'

Below is an introduction to Linear Induction Motors. You can either read straight through, or use the links below to jump to a specific section.

What Is A Linear Motor?

A Linear Induction Motor (LIM) is basically a rotating squirrel cage induction motor opened out flat. Instead of producing rotary torque from a cylindrical machine it produces linear force from a flat one. It is not a new technology but merely design in a different form. Only the shape and the way it produces motion is changed. But there are advantages: no moving parts, silent operation, reduced maintenance, compact size, ease of control and installation. LIM thrusts vary from just a few to thousands of Newtons, depending mainly on the size and rating. Speeds vary from zero to many meters per second and are determined by design and supply frequency. Speed can be controlled by either simple or complex systems. Stopping, starting, reversing, are all easy. Applications are many and varied, ranging from simple sliding doors to full control of a ten tonne vehicle.

What Can LIMs Do?

Horizontal travel is only limited by the length of the reaction plate or motor. Long conveyors use multi-motor systems. If the reaction plate is a disc then rotary motion is produced. Motion is not dependant on friction between wheels and rails so LIMs can be used in adverse conditions. Either LIM or reaction plate can move whilst the other is fixed. A non-magnetic stainless steel barrier can be used between LIM and reaction plate.

What Are The Advantages?

LIMs are simple to control and easy to use. Fast response, high acceleration and braking forces are developed. Speed is not dependant on contact friction. There are no gears or chains to cause backlash, no lubrication, no maintenance. Fewer moving parts mean simpler systems. Long term operating costs are reduced.

How Does It Work?

1. Take a squirrel cage induction motor...

2. open it out flat...

3. smooth the rotor bars into a conductor sheet...

4. apply AC power and you have a LIM

5. With two stators you can remove the reaction plate iron

Where Are LIMs Used?

Wherever straight line motion or reciprocating forces are needed, or where unusual rotary drives are an advantage. Mechanical transmissions are often eliminated, increasing reliability. The LIM is ideal for applications where space is at a premium. Rugged, they can be used in hazardous environments.

Power Supply

A 3 phase AC supply is required for most LIMs but 1 phase can be used to 600N. All standard voltages are available; 220 / 380 / 400 / 415 / 460 , 50 / 60 Hz.

Speed Control

The LIM makes an ideal variable speed drive. It behaves like a magnetic clutch and gives soft-start action. Maximum speed is fixed by design and frequency but load speed can be controlled in several ways. From on / off switching to phase control with tacho-feedback. LIMs can also be operated at stall to produce static thrust.

Forcepack Controllers

Forcepack control systems are built to power LIMs from 15 amps single phase to 250 amps 3 phase. They have variable acceleration and braking controls with several preset speeds. Built in safety circuits detects tacho and phase failure, overload etc. Controllers may be linked to PLCs for system supervision. A contact free data link is also available.

Which LIM To Use?

When selecting a LIM it is important to understand the interaction between LIM, reaction plate and airgap. The variety of designs suited to different speeds, airgaps and reaction plates are extensive. The correct choice is not always obvious. Let Force Engineering design the best motor and reaction plate combination for your particular application. Our extensive design and test facilities are available to you.

Typical Applications

Sliding Doors
Aluminium Can Propulsion
Mixer / Stirrer Drives
Wire Winding
Baggage Handling
Pallet Drives
Flexible Manufacturing Systems
Robotic Systems
Bogie Drives
Conveying Systems
Steel Tube Movement
Revolving Doors
Sheet Metal Movement
Linear Accelerators
Automated Postal Systems
Ship Test Tank Drive
Extrusion Pullers
Multi-Motor, In-Track Systems
Low Profile Drives Target Movement
Sewage Distributors
Slewing Drives
Crane Drives
Stage / Curtain Movement
Scrap Sorting / Movement
Research Machines
Turntable Drives
Automated Warehousing
Flat Circular Motors
Theme Park Rides
Personal, Rapid Transport Systems

Reaction Plates

Aluminium / Steel
Copper / Steel
Steel - Sheet, Tube, or Structural
Conductor Material Alone
These can be shaped to your individual requirements.

Manufacture

Forcepack LIMs are designed for ease of installation and connection. A stringent quality assurance system ensures that all LIMs are built to the highest standards using top grade materials. Motors are vacuum impregnated for complete protection. Each motor is thoroughly tested, including thermal overheat, before dispatch.
There is a choice of cable or terminal box, and various fixings may be selected. Several cooling methods are available depending on motor rating or environment.

Construction Options

-Epoxy Resin either Class F or H
-Stainless Steel with Replaceable cover Hermetically sealed
-Water Cooled with Baseplate Direct water cooling
-Forced Air Cooled with Heatsink Blown windings
-Narrow Motors / Low Height Motors
-Star / Delta Terminations
- Single / Double Sided Operation
- Thermal Switch / Thermistor Protection

Special Designs

Force have designed special LIMs for propelling steel tubes in both linear and rotary planes and a novel non-contact stirrer motor with accurate speed control. These and many other problems could not be solved with standard rotary machines.

Force Engineering Ltd

Forcepack linear motors have been supplied worldwide since 1979. The design team at Force has over 80 man years combined experience of LIM applications. New ideas and applications are constantly being applied and we welcome your enquires.

History Of Force Engineering Ltd

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