Introduction:
A Hydrostatic slide is non-contact in that the slide is supported by a film of high pressure oil, in the order of 10 Um. It functions by producing a continuous flow of high pressure oil through and out of the bearing. The flow rate being controlled by restrictors. The restrictors allow the slideway to cope with varying loads and maintain a near constant film thickness. Throughout the bearing surface, small pockets or pads are machined to create areas of high pressure fed by these restrictors and from which the oil flows ,to the rest of the bearing surfaces before exiting the bearing. The oil is then collected, filtered, repressurized, and recirculated. [Handbook, pg. 294]
ANANT JAIN
Integration of Linear Motor
Introduction:
A linear motor is an electric motor that has had its stator and rotor "unrolled" so that instead of producing a torque (rotation) it produces a linear force along its length.Linear Motor was invented by Prof. Eric Laithwaite, a British researcher at Imperial College London. He described his invention as
“no more than an ordinary electric motor spread out.”
A Linear motor is made up of two major components:
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A coil slider which is made up of a 3-phase winding, which is mounted on the moving slide
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A permanent magnet which is attached to the stationary slide
A Schematic of a Linear Motor Drive
Advantages of a Linear Motor
Linear Motors offer many advantages over the traditional rotary motor with ball screw drive:
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The number of moving parts is much lower in case of a Linear Motor, thereby significantly reducing the inertia of moving parts
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Linear motors are free from typical errors associated with ball screw drives such as pitch error and backlash, hence linear motors are capable of achieving higher precision as compared to ball screw drive
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Linear motors offer much higher stiffness. In case of a ball screw drive, the stiffness of the slide is restricted by the stiffness of the ball screw but in case of Linear Motors, the stiffness depends on the max. force capacity of the motor.
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Due to reduced inertia, less moving parts, no mechanical contact the slide can now achieve higher speeds and accelerations
Need for Linear Motor
Linear motors are capable of achieving high speeds and acceleration and hence offer a great advantage for high-speed applications such as Non-Round Grinding. Non-Round Grinding involves rapid oscillation of wheel in-feed axis. The Linear motor was required for this particular application.
Personal Contribution:
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Knowledge Integration: Linear Motors have never been used in our organization and are extremely rare among Indian Machine tool Builders. My initial work was in understanding the concept, science as well as mechanical design, electrical and assembly requirements for using these motors.
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Motor Selection: Next major work was regarding selecting the correct configuration for our application. I made the speed-time curves for the entire grinding process which further helped in plotting the duty cycle required from the motor.
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Mechanical Assembly: Assembly of Linear motors is complex process especially when being done for the first time. Due to the presence of strong permanent magnets the magnet plate attracts the coil slider as well as any magnetic object with a force of 22,000 N. This makes the whole process complex and safety critical. I created detailed assembly procedures and personally supervised the entire assembly, and ensured complete and proper integration of the motor.
Accomplishments
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This was first successful Linear Motor assembled MGT as well as Fanuc India.
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The Machne response has also improved:
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The Machine can achieve speeds of 15000 mm/min as compared to 8000 mm/min achieved in conventional CNC machine
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The Machine can achieve accelerations of 7 m/s^2 as compared to 1 m/s^2 achieved in conventional CNC machine
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A Graph indicating the acceleration the wheel-head in-feed slide will experience during non-round grinding
Team from Micromatic Grinding and Fanuc India after successful assembly of Linear Motors