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AC Spindle Drive – OKUMA VAC D-22
The VAC D-22 is an AC spindle drive unit manufactured by OKUMA Corporation, designed for vector control of the spindle motor in OKUMA CNC machine tools. The unit belongs to the VAC (Variable AC Drive) series, typically employed on machining centers and CNC lathes equipped with the OSP (Open System Platform) CNC control. It manages torque, speed and current of the spindle motor, receiving references directly from the CNC via the proprietary OKUMA bus. The component is installed either as a standalone rack unit or as an integrated module within the machine’s electrical cabinet.
The spindle drive is the core of the spindle control system: it converts three-phase mains voltage into a variable-frequency, variable-voltage output applied to the spindle motor, maintaining stable rotational speed regardless of load variations during machining. A failure in this module causes immediate and uncontrolled spindle stop, rendering the machine completely inoperable: without the drive, no cutting operation can be performed, resulting in immediate production downtime.
OKUMA Corporation is a Japanese manufacturer founded in 1898 in Nagoya, Japan, and one of the world’s leading producers of CNC machine tools (lathes, machining centers, grinding machines) and related OSP series CNC controls. OKUMA designs both the machines and the drives and motors in-house, ensuring full hardware and software system integration. Products in the VAC series are legacy / discontinued: available only as used, NOS (surplus), or through specialist repair services.
Main Technical Specifications
| Type | AC Spindle Drive Unit |
| Part number | VAC D-22 (VACD22) |
| Brand | OKUMA Corporation |
| Known application | OKUMA CNC machining centers and lathes with OSP control |
| Function | Vector control of AC spindle motor speed, torque and current |
| Power supply | 3-phase ~200–400 V AC, 50/60 Hz (typical) |
| Rated current | ~22 A |
| Spindle power handled | ~5.5–15 kW |
| CNC interface | Proprietary OKUMA OSP bus; 40–60 pin connectors (typical) |
| Feedback | Spindle motor encoder / resolver |
| Weight | ~3–8 kg |
| Dimensions | ~250–400 mm × 150–300 mm |
| Production status | Legacy / discontinued — used/surplus/repair only |