OKUMA Servo Drive

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AC Servo Drive Unit BL-II Series – OKUMA BLII-D50/50A

The BLII-D50/50A is an AC brushless servo drive module (“AC Servo Drive Unit”) belonging to OKUMA’s BL-II (Brushless II) series, designed for closed-loop axis control on the Japanese manufacturer’s CNC machine tools. The designation identifies a 50 A rated unit from the second generation of OKUMA brushless drives, typically installed in vertical and horizontal machining centres and CNC lathes equipped with OSP controllers (OSP5000, OSP5020, OSP700 and related variants), produced from the late 1980s through the early 1990s. The unit manages current and speed regulation of the axis motor, interfacing with the CNC controller via a proprietary OKUMA bus and with the motor via incremental encoder or resolver. Available in multiple size variants; compatibility with the specific machine model and hardware revision must always be verified before replacement.

The servo drive is the power electronics unit that converts position and velocity commands from the CNC into phase current for the brushless axis motor: it closes the current loop in real time and ensures each axis follows the programmed trajectory with precision. In the event of a fault the affected axis becomes uncontrollable and the machine stops immediately with an alarm — production cannot resume until the module has been replaced or repaired, making this component critical for plant operational continuity.

OKUMA Corporation is a Japanese manufacturer of CNC machine tools founded in 1898 in Nagoya; it is one of the few manufacturers in the world to design and produce both machine tools and CNC controllers (OSP – Open System Platform), motors, and servo drives entirely in-house, ensuring full vertical integration that delivers high performance but results in strictly proprietary components. Products in the BL-II series are legacy / discontinued: procurement is possible only through used, surplus, or specialist repair channels.

Main Technical Specifications