Servo drive alarms: overcurrent, overvoltage, encoder and following error
A drive alarm is a consequence, not a cause. The answers below give the most common alarms with the physical reason behind them and the order in which to check. For the alarm code itself, always use the drive's own manual.
7 questions answered
Troubleshooting
Troubleshooting
01
The drive trips on overcurrent as soon as it is enabled.
Overcurrent at the moment of enable usually points to a problem in the power stage wiring: a short between U/V/W phases or to earth, a damaged motor cable, or the wrong phase order. The same alarm appears when the motor parameters do not match the motor fitted, or when the gains are far too high.
With power off, disconnect the motor cable and measure insulation phase-to-phase and to earth
Compare the U-V-W order with the motor label
Confirm the motor code is set correctly in the drive
I get a DC-bus overvoltage alarm while decelerating.
While braking, the motor works as a generator and pushes the load's kinetic energy back into the drive's DC bus. If that energy has nowhere to go, the bus voltage rises and the drive stops to protect itself. The fix is a braking resistor of suitable power that turns the energy into heat, or a longer deceleration time; with a load moving down vertically the energy is continuous.
The resistance must not go below the minimum the drive allows
Size the resistor power for the average braking power of the worst cycle
Resistors with a thermostat warn before overheating
I get encoder communication errors, sometimes at random.
A constant encoder error is the wrong cable type (an incremental cable on a BiSS motor, for instance), an unplugged or damaged connector, or a broken core. A random error is almost always noise: the encoder cable in the same duct as the motor power cable, an unconnected shield, or a cable fatigued in a moving drag chain.
If errors rise while the axis moves, check the cable in the drag chain
In moving applications use cable rated for drag chains
Why does a following-error (position deviation) alarm occur?
A following error is the gap between commanded and actual position exceeding the allowed limit: the motor cannot keep up with the command. Causes: not enough torque for the demanded acceleration or speed, a torque limit set too low, weak gains, binding in the mechanics, or motion starting before the brake has released. Enlarging the limit does not solve it, only hides it.
Watch the current during the move: if it sits at peak, the motor or drive is too small
Try turning the mechanics freely by hand with the motor removed
The motor vibrates or whines at standstill or while moving.
A whine at one frequency is mechanical resonance: a belt, a long ball screw or a flexible coupling excited by the speed-loop gain. Find the resonance frequency with the drive's frequency analysis or automatic notch filter and suppress it. A low-frequency wobble, on the other hand, usually means the gains are too high or the inertia ratio is too large.
Check the coupling and shaft connection are tight and free of play
Lowering the gain quietens it but also slows the response
Heating is set by the average (RMS) torque over the cycle, not the peak torque. Short but frequent accelerations, holding against gravity while waiting, and friction all raise the RMS torque. The RMS torque must stay below the motor's continuous rated torque; if it does not, soften the motion profile, add a gearbox or use a larger motor.
Acceleration is when the most current is drawn from the supply. If the supply is weak, the cable cross-section small, a phase missing, or many axes accelerate from one line at once, the DC bus sags. Measure the mains voltage during acceleration, and check the rating of the main switch and fuses and the balance of the three phases.
