The Okuma MIV Unit and DC Power Supply
The Okuma Motion Control System (MCS) drives spindle motors and axis drive motors from MIV inverter units. A DC power supply unit supplies 300 VDC and 24 VDC control power to those MIV units. The MPS power supply unit uses power regeneration and goes on systems with a spindle drive motor. On systems with axis drive motors only the MPR unit uses resistor regeneration.
A built-in control board in each MIV unit controls the motor. MIV unit types differ by unit capacity, control board, and software (ROM). The Okuma manual calls for a replacement unit of the same type.
Okuma Drive and Amplifier Repair Shops
Global Electronic Services
Buford, GA
Brands: Fanuc, Haas, Okuma
Northline Industrial
Redford, MI
Brands: Fanuc, Makino, Okuma
Paragon Technologies
Warren, MI
Brands: Okuma
Precision Zone
Wheeling, IL
Brands: Haas, Okuma
Compare Okuma Drive and Amplifier Repair Shops
This table lists turnaround, warranty, and evaluation terms from each shop's published information.
| Shop | Repair type | Turnaround (business days) | Warranty (months) | Free evaluation | Rush service |
|---|---|---|---|---|---|
| Global Electronic Services | Ship-in repair | 3-5 | 24 | Yes | Yes |
| Northline Industrial | Ship-in and on-site | Not listed | 12 | Yes | Not listed |
| Precision Zone | Ship-in repair | 7-10 | 12 | Yes | Yes |
Drive Alarms on the OSP Control
Alarm 1151 MCS INVERTER UNIT DETECTED AN ERROR usually points to an inverter problem such as a faulty control board, motor overcurrent, abnormal voltage, or a shorted motor. In most cases the code that follows the alarm points to the input or output location of the fault. Okuma warns that a faulty motor can damage the whole drive unit.
Alarm 1181 MCS DIFF OVER means an axis cannot move to its commanded position. Mechanical problems, broken tools, chip buildup, or a damaged servo amp, cable, or motor can trigger that alarm. Okuma advises calling a service technician instead of resetting it. Alarm 2160 MCS SUPPLY VOLTAGE FLUTTER reports abnormally high or low power voltage and shows up most often during heavy spindle acceleration or deceleration. Clearing it takes power supplied to the machine’s KVA rating and a check of the power line connections.
Narrowing Down the Fault
The 7-segment LED on the front of an MIV unit shows the operating status and displays an error number at an alarm. Okuma’s drive manual matches each error number with a corrective action. Encoder link errors call for a check or change of the encoder link cable. An overcurrent in the power cable at the DC power supply unit calls for a check of that cable. A motor overcurrent alarm on an MIV unit can call for a motor change.
Alarm 812 ERROR DURING INITIALIZATION OF MCS means the control found a serial link discrepancy at boot-up. In the servo link the FCP board acts as the master and the MIV units act as slaves. Each new MIV unit needs its controller ID number set from the manual or the circuit diagram.
Before a Drive Comes Out
An MIV unit holds a large-capacitance capacitor. The charge indicating lamp has to go out before work on the unit starts. Okuma calls for a wait of at least 2 minutes after the power shuts off. High voltage sits on the upper and lower terminal blocks in the unit. The plastic terminal block cover stays in place while power is on.
Okuma’s power loss recovery steps start with the breaker off for a minute or two so the drives and power supply discharge. All three incoming power legs then get checked because an outage can blow a buss fuse. A lost leg can single phase a motor and damage it.