Eric Laithwaite of Manchester University, later Professor of Heavy Electrical Engineering at Imperial College in London developed the first full-size working model. The German engineer Hermann Kemper built a working model in 1935. Patent 782,312 (1905 - inventor Alfred Zehden of Frankfurt-am-Main), for driving trains or lifts. A feasible linear induction motor is described in the U.S. The history of linear electric motors can be traced back at least as far as the 1840s, to the work of Charles Wheatstone at King's College London, but Wheatstone's model was too inefficient to be practical. This Line 6 Guangzhou Metro train manufactured by CRRC Sifang and Kawasaki Heavy Industries propels itself using an aluminium induction strip placed between the rails. The electrical current is typically provided from a stationary servo drive to the moving coil by a moving cable inside a cable carrier. A Hall effect sensor is attached to the rotor to track the magnetic flux of the stator. In high precision industrial automation linear motors are typically configured with a magnet stator and a moving coil. Examples include coilguns and the motors used on some maglev systems, as well as many other linear motors. For cost reasons synchronous linear motors rarely use commutators, so the rotor often contains permanent magnets, or soft iron. In this design the rate of movement of the magnetic field is controlled, usually electronically, to track the motion of the rotor. However, they require higher maintenance since their brushes wear out. Brush linear motors have lower cost since they do not need moving cables and three phase servo drives. Compared with three phase Brushless motors, which are typically being used today, brush motors operates with a single phase. Brush īrush (electric) linear motors were used in industrial automation applications prior to the invention of Brushless linear motors. Invented in late 1980s by Anwar Chitayat at Anorad Corporation, now Rockwell Automation, and helped improving throughput and quality of industrial manufacturing processes. They are typically used in standard linear stages or integrated into custom, high performance positioning systems. The motor for the Shanghai maglev train, for instance, is an LSM.īrushless linear motors are members of the Synchronous motor family. These magnets can be permanent magnets or electromagnets. The low-acceleration, high speed and high power motors are usually of the linear synchronous motor (LSM) design, with an active winding on one side of the air-gap and an array of alternate-pole magnets on the other side.
However, the direct current homopolar linear motor railgun is another high acceleration linear motor design. They are usually of the AC linear induction motor (LIM) design with an active three-phase winding on one side of the air-gap and a passive conductor plate on the other side.
High-acceleration linear motors are typically used in studies of hypervelocity collisions, as weapons, or as mass drivers for spacecraft propulsion. High-acceleration linear motors are normally rather short, and are designed to accelerate an object to a very high speed, for example see the coilgun. Low-acceleration linear motors are suitable for maglev trains and other ground-based transportation applications. Many designs have been put forward for linear motors, falling into two major categories, low-acceleration and high-acceleration linear motors. It is a thriving field of applied research with dedicated scientific conferences and engineering text books. Linear motors are by far most commonly found in high accuracy engineering applications. Characteristically, a linear motor's active section has ends, whereas more conventional motors are arranged as a continuous loop.Ī typical mode of operation is as a Lorentz-type actuator, in which the applied force is linearly proportional to the current and the magnetic field ( F → = I L → × B → ). However, linear motors are not necessarily straight. Synchronous linear motors are straightened versions of permanent magnet rotor motorsĪ linear motor is an electric motor that has had its stator and rotor "unrolled", thus, instead of producing a torque ( rotation), it produces a linear force along its length.