Observed Zero-Frequency Behavior
An MX2 drive controls a thread unwinder with PID. When the commanded frequency reaches zero, the motor remains free to rotate, allowing thread to unwind from the reel. Treat zero frequency as the operating condition that exposes the problem; the evidence does not establish that it provides mechanical holding torque.
Select the Holding Method
| Option | Supported use | Engineering decision |
|---|---|---|
| Torque control | A similar unwinding application was reported as operating in torque control. | Evaluate whether the drive and motor can regulate the required winding tension at standstill. The evidence does not confirm MX2 support, settings, or available standstill torque. |
| Motor brake | A motor equipped with a brake was proposed to prevent reel movement. | Use a mechanical brake when the reel must remain physically stopped. Size and sequence it from measured reel torque and the actual machine stopping sequence. |
Implementation Decision Path
- Command zero frequency under the same PID condition that produces unwanted unwinding, then confirm whether external reel torque rotates the motor.
- If controlled tension must continue at zero speed, verify documented torque-control capability for the installed drive and motor before changing the control method.
- If the requirement is positive stationary holding, select a motor brake and coordinate its engagement with the drive stop command. Do not treat the zero-frequency command itself as proof that the reel is secured.
Commissioning Verification
Test with the actual reel, thread tension, and process load. Verify that the reel remains stationary after the speed command reaches zero, that the brake does not engage while the motor is still moving, and that restart releases the brake before commanded rotation. The evidence supplies no brake rating, delay, drive parameter, motor model, or wiring method; obtain those values from the selected hardware documentation and measured machine requirements.
FAQ
Why does the MX2 motor let the reel unwind at zero frequency?
In the reported PID application, the motor becomes free to rotate when frequency reaches zero. The available evidence does not establish that a zero-frequency command produces holding torque.
Can torque control stop thread unwinding at zero speed?
Torque control was identified from a similar unwinding application, but MX2 capability and configuration were not confirmed. Verify the installed drive and motor documentation before selecting this approach.
Should an unwinder motor use a mechanical brake?
Use a motor brake when the requirement is to keep the reel physically stationary. Size it for the measured reel torque and verify engagement, holding, release, and restart sequencing on the machine.
