Basically the PREX has a different winding style that uses magnetic fields rather than windings for excitement.
Some details below on PREX:
OKUMA’S PREX MOTOR: “SUPERIOR ENERGY-SAVING MACHINE” AWARD WINNER
Many of Okuma’s CNC machines are equipped with the company’s PREX motor, which in 2009 won the Superior Energy-Saving Machine Award sponsored by the Japan Machinery Federation.PREX motors are built-in reluctance motors incorporated in the many spindles used in Okuma machine tools. Numerous slits in the rotor make generation of reluctance power more efficient (See Figure 6). This unique rotor structure has a small amount of interpolated permanent magnets to increase performance. The PREX motor is more efficient than induction motors, which were the main power source of spindles in the past, and high torque in typical turning ranges raises the system efficiency by 4-9%.
PREX motors are also compact, with low mass in the rotating section that reduces inertial mass by 47%. This makes acceleration and deceleration highly responsive. The combination of all these features reduces energy consumption by 5-13%.
Okuma machines equipped with the PREX motor are: CNC lathes, the LB EX series of horizontal lathes, and the MULTUS series of multitasking machines.
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