Specifications

42 ζ ZETA6104 Installation Guide
Active Damping Active damping monitors the ZETA6104’s motor terminals and, like anti-resonance, uses the
same current command modulator to modify motor current.
Active damping uses a different method to extract information about rotor position error,
however. The circuit’s gains are adjustable—you can configure it for your particular system.
The DMTIND and DMTSTT commands scale the circuit for motor inductance and static torque,
respectively. The DACTDP command scales the circuit for system inertia.
The active damping circuit uses this information for two purposes:
1. It determines error in rotor position very accurately.
2. It adjusts the gains of its feedback loop, based upon how much inertia the system has,
and how much torque the motor can produce.
If the rotor rings or vibrates, the active damping circuit will detect the corresponding error in
rotor position. It will then modify the motor current command to damp the ringing.
DIP switches on top of the ZETA6104 set the amount of motor current during normal
operations; this current is constant. To damp ringing, the active damping circuit can cause the
ZETA6104 to produce up to twice as much current as is set by the DIP switches. The extra
current is only applied during damping oscillations, and lasts a very brief time.
Electronic Viscosity
(EV)
The ZETA6104 uses closed-loop current control to develop and maintain precise currents in
the motor phases. When EV is off, the current loops have a bandwidth of approximately 1000
Hz. Because this bandwidth is well beyond the knee of step motor speed-torque curves, the
current loop dynamics do not limit the response of the motor.
EV monitors motor velocity, and turns on below 3 rps. It “detunes” the current loop
compensation values and brings the bandwidth down to 150 Hz. With this lower bandwidth,
the drive electronics become “sluggish.” Ordinarily, when the rotor oscillates, it generates
current in the motor’s coils; but with EV’s lower bandwidth, the drive’s electronics impede the
flow of current caused by oscillations.
The effect on the motor is as if there were a viscous drag on the rotor. At the end of a move,
oscillations are damped, and the rotor quickly comes to rest. After accelerating or decelerating
to velocities below 3 rps, the rotor quickly settles at the commanded velocity. During moves
below 3 rps, EV significantly reduces low speed velocity ripple.
EV is a “passive” circuit. It imposes viscosity on the system, but has no feedback loop to
monitor the effect of the viscosity. EV keeps the amount of viscosity the same, regardless of
the response of the system.
You can adjust the amount of viscosity by using the DELVIS command. This allows you to
tailor the circuit for different motor sizes and system inertias, and adapt it to your application.
Recommendations We recommend that you configure active damping and electronic viscosity. Even if you
believe resonance and ringing will not cause problems in your system, you may find that the
ZETA6104’s damping circuits provide increased smoothness, reduced audible noise, and better
performance. Refer to the configuration procedures beginning on page 26.
If you choose not to use active damping and electronic viscosity, at least use anti-resonance.
The ZETA6104 is shipped from the factory with anti-resonance enabled (DAREN1).