Motors & Drives Information

They may be the key to high-speed machining

Real-world economics forces companies to look for ways to produce more products, faster, and with higher quality than ever before. This, search in turn, drives changes in processes and equipment to improve productivity.

Fortunately, changes in the design of CNC machine tools and machining equipment are helping production managers and engineers keep their sanity. One of the most dramatic changes to machine tool design today is the increasing use of linear motors, in preference to rotary motors and drivescrews. Linear motors offer a host of advantages, all of which contribute to improved manufacturing engineering.

Traditional drives are handicapped in relation to both current and future industry demands. Rotary motors have a limited maximum rotation speed, gear reducers add inertia and lower efficiency, motor couplings produce windup distortion, backlash, and hysteresis. Also, encoder couplings deflect during acceleration and deacceleration.

Additionally, traditional drives rely on drive screws, which come with their own set of limitations. These include: length restrictions, mechanical backlash, friction, windup, pitch-cyclic errors, long vibration decay times, coupled inertia to the motor, and the axial compression of the screw. These all limit the effectiveness and precision of conventional drives.

As the equipment wears, continual adjustments must be made to ensure ongoing accuracy. Once the machine is designed with rotary motors, it is locked into that design-even during scheduled equipment replacements. Incremental change is slow and evolutionary change is prohibitively expensive,

What Else Is New? Directdrive linear motor technology promises substantially higher levels of performance and greater simplicity than traditional motor drives that convert rotary motion to linear motion. Because the motor connects directly to the moving load there is no backlash and little compliance between the motor and load.

Speeds of less than 1 micron per second, or as high as 5 m/sec, are easily reached. Liear drive system can offer constant velocity characteristics with better than +/- 0.01% speed variation. In applications requiring high acceleration, smaller linear motors can easily deliver more than10gwhile conventional motors typically generate acceleration in the range of Ig. The accuracy of linear drive motors is only limited by feedback resolution, control algorithms, and motor construction.

# posted by Medical Information : 5:18 AM