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Basic concepts and operational principle of linear motor(gears) design and manufacture.

Direct drive is an electric machine directly converting electromagnetic energy into linear or rotary movement.

From the engineering viewpoint the direct-drive motor is an electromagnetic system deployed within Cartesian dimensioning and inducing stationary or traveling magnetic field.

Controlling the forces of magnetic interaction between the spatial field of the systems mobile element and the field of the stationary element enables travel to be effected of the mobile element along any possible path within the first or the second system of coordinates.

The direct drive systems can be subdivided into the linear and rotary motors (platforms). In a classically linear motor the armature fed from an AC source is displaced above a stator consisting of a steel plate and permanent magnets (the so-called magnetic track) through the alternating field of the armature interacting with the static field of the stator.

A linear drive is understood as a device consisting of a transducer of linear bearing motion and a linear AC motor. The direct drive implements a gearless transmission of force and motion to the effector, thus eliminating the need for bushings, shafts or other parts of mechanical gearing.

Elimination of the parts common for ordinary mechanical drive is clearly useful in applications having high dynamics and precision of movement. It can therefore be concluded that direct dcrive is not only the optimal converter of electrical energy into mechanical motion, but also technically the most reliable electrical motor.


Applications of linear drive in various technologies, particularly in machine tools:
- operation within widely adjustable high-response .
electric actuators and in linear feed gears of NC metal-cutting machines;
- Laser cutting installations;
- Electroerrosion operations.

Manufacturing the semiconductor and electronic components:
- Installations for micro wire welding;
- Machine tools for drilling circuit boards;
- Installations for assembling electromechanical units; ;
-Installations for cutting wafers of silicon, glass, and ceramics

Systems for moving objects:
- Sorting machines;
- Conveyor systems.

Medical equipment:
- High-precision micromanipulators;
- Automatic laboratory equipment;
- Microscopes with coordinate tables.

The history of linear motors
The linear induction motor was patented in England by Zeden (Patent #12581, 02.06.1906)

Here is an excerpt from that patent:

The invention is related to devices for setting in motion the railroad cars, elevators, reciprocating machine parts and other devices by making use of traveling magnetic field. With regard to the rail transport systems the magnet (inductor) excited by three-phase or another type of current is mounted upon a vehicle close to the rail (strip) playing the role of a short-circuited armature of a polyphase motor. The strip can be made of steel, brass or another metal and perforated with openings of differing dimensions for starting the vehicle, or the like. The magnets (inductors) can be mounted above or beneath the strip to increase cohesion or to provide a partial compensation for the vehicle mass. Those can be placed at opposite sides of the strip, or else the electromagnet (inductor) can be placed at one side of the strip, with the laminated steel on the other. The device can have forces counterbalanced or non-counterbalanced. In case of the elevator, e.g., the inductors are directed outside to interact with the two guidepath strips: The initial operations on building the linear motors started simultaneously in Germany, France and Russia as far back as the early 1900s. In 1910 the first magnetic levitation car model was built. In 1911 B.P. Weinberg, Professor at the Technological Institute of Tomsk, designed a magnetic levitation train set in motion by a synchronous linear electric motor. Prof. Weinberg built an experimental test-bench model with a mock-up car weighing 10 kg. The tests of 1911 1913 in Russia and in France were successful proving the viability of linear motors in transportation systems, while the high-power semiconductor electronics had yet to be born at that time. The drawbacks of the prototype direct drive systems were low output and high energy consumption because of low-quality element base, making their cost prohibitive for mass production. One of the first linear induction electrical drives with a significant forward motion and a large, though briefly actualized output is the system of speeding-up aircraft developed by Westinghous for US Navy in 1945. The primary part of the motor was fixed on a bogie carrying the plane being launched. The bogie was connected to the three-phase power supply with one phase grounded. The stationary secondary part was a magnetic core several hundred meters long made of stacked steel plates with a short-circuited cage of copper alloy (high resistance on edges and less in the middle of the path). The motor developed the pull of 75 kH at 0 to 100 m/s, i.e. an output of the order of 7500 kVt. A jet plane with a mass of 4,5.103 kG was accelerated on a runway 165 m for 4,2 s up to 50 m/s (=12 /2, F=ma=55 , the remaining 20 kH were expended to counter the air resistance and to climb).
The linear induction motors have a number of advantages and disadvantages stipulating their applilcations. The advantages include low cost of components, no need for a motion transducer, feasibility of high velocities and accelerations. Among the disadvantages are: the need for a minute air bag, low efficiency (operational failure because of losses in the secondary part at low speed or in the force retention mode). Hence the applications: rail transport objectives demanding high speeds, acceleration and ride control with no precision qualities. The first modern direct drive was patented by an American engineer Bruce Sawyer in 1969. The patent application for a Magnetic Positioning Device) described a version of a 2D planar drive with magnetic elevation later recognized as a classical scheme. The device by Bruce Sawyer was designed to be used in printing industry as a copying machine when producing an engraving plate. The technical characteristics of the system exceeded the common devices with stepping motors, but their cost was too high. Promotion of innovative solutions was deterred for nearly a decade through an inopportune option of the assumed application (printing) and a complicated control system.