LSMs Ride the Wave of Modular Manufacturing

Jan. 25, 2007
Speedy linear synchronous-motor systems outrun conventional conveyors.

Speedy linear synchronous-motor systems outrun conventional conveyors.

Joe Meagher
Jim Olsen
MagneMotion Inc.
Acton, Mass.

SmartPods from AGR Automation in the U.K. incorporate QuickStick LSM modules (seen through lower windows). SmartPods are modular, expandable, automated assembly and packaging platforms. Platform operations include six-axis pick-and-place, laser welding and drilling, and liquid dispensing. Gull-wing doors let workers access equipment inside the pods.

An LSM module mounted to a turntable lets vehicles round 90° turns and go in multiple directions. A node controller coordinates communication between the LSM and turntable. The wheeled vehicles ride on tracks flanking the LSM module.

MagneMover DB 1.0 (double-bogie) vehicles negotiate curves with a 1.0-m radius. An electromagnetic switch routes the vehicle.

LSMs power this proof-of-concept Advanced Weapons Elevator, which is to be deployed on the U.S. Navy's CVN 78 Series aircraft carrier.

Manufacturers typically employ belt, roller, or chain-driven conveyors on the factory floor to move and position product. But the elaborate supervisory-control systems needed to run the equipment complicates changeovers for new products and processes.

QuickStick linear-synchronous motors (LSMs), in contrast, use a comparably simple extended, integrated supervisory-control system. Motor modules located between a set of guide rails generate electromagnetic force along the modules' top faces, creating a wavelike field for propulsion. A wheeled vehicle fitted with a permanent-magnet array on its underside "rides" the wave. Vehicles can travel in either direction to precise, programmed positions at speeds to 5 m/sec, 4 faster than conventional belt conveyors.

Higher-thrust LSMs can propel vehicles weighing tens of thousands of pounds with sufficient power to negotiate diagonal, vertical, or inverted runs. Standard models may serve as pallet accelerators that rapidly deliver product to a process station, eliminating workflow bottlenecks.

Vehicles are passive and need no batteries, wires, or power transfer to work. Each LSM module houses up to 10 motor blocks, position sensors, and control electronics. Embedded software coordinates vehicle movement, payload positioning, and module-to-module communication for traffic management. The arrangement greatly simplifies control-system and communication architecture. One user estimates LSMs eliminate 80% of the 3,000 I/O nodes needed for their original process and conveyor control system, as well as thousands of lines of controller code.

A PC or PLC host controller communicates position commands to a LSM node controller via Ethernet, Ethernet IP, or other protocol. LSMs communicate with each other through a series of vehicle-transfer requests over RS-422.

A motor occupied by a vehicle denies all further vehicle-transfer requests until the present vehicle moves to another motor.

This permission-request cycle repeats hundreds of times per second, allowing motors to slow and stop vehicles long before they would collide. A foreign object blocking a vehicle causes subsequent vehicles to line up behind it in an orderly fashion until the first vehicle resumes travel along the guide way. This traffic-management system lets hundreds of vehicles coexist without colliding.

Installations need no hard stops for positioning. Magnets in the vehicles provide braking in the event power is lost to the motors. E-stops and other shutdown circuits should maintain power for a few seconds to quickly bring vehicles to halt.

Control circuitry in individual LSM modules consumes roughly 5 to 10 W. Vehicle count, mass, and acceleration duty determine size of the power supply. Applications that transport heavy loads up and down slopes can return power to the line during vehicle deceleration (regenerative braking), which boosts efficiency.

LSMs are about 65 to 75% efficient compared with the 15 to 20% efficiency of conventional linear-induction motors (LIMs). The use of untethered vehicles with longstator LSMs lengthens travel distances compared to conventional moving-coil linear motors. The arrangement also gives design options not possible with conventional linear motors.

For example, a turntable fitted with an LSM lets vehicles navigate tight turns or switch to one of several pathways. A node controller coordinates communication between the LSM and turntable.

Vehicles equipped with a magnet array on each end (double-bogie) can also negotiate curves and switch points. As a double-bogie vehicle enters a curve, the rear bogie pushes the front of the vehicle around the curve and into position over the next module. The front bogie then pulls the rear bogie out of the curve and the vehicle continues on its path.

Clean rooms are another application for LSMs. The electromagnetic coupling between magnet and motor lets the motor reside outside of a plastic or nonmagnetic metal glove box while the permanent-magnet array (attached to a wheeled vehicle) runs inside. This lets workers operate sterile filling systems or handle hazardous materials without touching them. The system's direct drive and lack of mechanical actuation generates fewer debris particles.

Lack of power-transmission components also lowers maintenance compared with conventional conveyors, and boosts reliability. A recent durability study ran 10 QS100 LSMs 24/7 for 120 days with no failures. Theoretical mean time between failures for the QS100 LSM is 6.5 yr per MILHDBK-217.

AGR Automation,
Magnemotion Inc.,

Watch video of proof-of-concept systems in action at

QuickStick specs
Top speed: 5 m/sec
Maximum acceleration: 3g
Standard positioning accuracy: ±0.05 mm
Maximum load: ›10,000 lb
Magnet-array length: 150 mm to 1.0 m. Propulsive force scales linearly with magnet-array length.
Maximum vehicle count/meter: 5

Design example
A standard QuickStick LSM 100 produces 225 N of continuous thrust and 485 N at a 20% duty cycle.

A 100-lb payload and 1-m-long vehicle (and magnet array) rides 3 mm above the surface of the LSMs on wheels with a rolling friction coefficient of 0.025. The system can move this load 1 m in 1.25 sec, or 5 m in under 5.5 sec. The same setup propels a 2,200-lb vehicle 10 m in 14 sec.

Guide rails on which the vehicles roll typically are held flat to within ±1 mm, with a LSM-to-magnet array gap of 1 or 2 mm more than the tolerance of the track and vehicle. For example, a track held to ±1 mm should have a nominal magnet-to-motor gap of about 3 mm, with a total gap range of 2 to 4 mm. Vehicles that carry payloads sensitive to magnetic fields should separate the payload from the magnet array by 50 to 100 mm.

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