Kollmorgen AKD series

AKD User Guide | 8 Configuring Motor Settings
automatically engaged (motor brake, not holding brake) after the WS process is complete. The brake may cause
unexpected movement if the DRV.OPMODE used prior to WS does not retain position. If a force component is
present parallel to the track on a linear motor (gravity, load, etc.), or tangential on a rotary motor, the motor may
move from the startup position after WS completes and the brake is engaged.
If theapplicationrequires that thestartuppositionberetained, havethecontrollersystemready totakecontrol
immediately afterWS is complete. Oneway toset this control is tohave thedriveinDRV.OPMODE 1(digitalveloc-
ity)orDRV.OPMODE 2(positionmode)on power-up. This precautionkeeps themotorstationary afterenable.
End of Travel Limits
If anything restricts the motion of the motor, a commutation fault can occur. Examples of situations that may
result in faults include the following:
1. If the motor is resting against a rigid endstop, the movement of the motor may be impeded below the mini-
mum threshold set by WS.DISTMIN. This lack of movement causes a fault.
2. If the motor is actuating a limit sensor/switch, the system (PLC, SWLS.LIMIT0 and SWLS.LIMIT1) may
be preventing the AKD from producing motion. If descriptive motion is not achieved, the system faults.
Large Load Inertia or High Friction System
Systems with a large load mismatch may need more current than the default setting for correct commutation.
Begin with the default value for WS.IMAX and gradually increase or decrease as needed. If adjusting WS.IMAX
does not result in a successful commutation, the width of the search pulse can be increased by increasing WS.T.
8.3.9.3 Using WS: Advanced
WS is performed upon enable in order to establish a valid value for MOTOR.PHASE at startup. For the AKD,
MOTOR.PHASE is used to calculate electrical phase. With absolute feedback devices, MOTOR.PHASE is a
fixed offset between absolute mechanical position and the electrical position. With incremental devices, position
is accumulated relative to an initial MOTOR.PHASE. However, at startup, MOTOR.PHASE is invalid since the
initial position is random, thus the requirement for the WS process.
WS is a two-step process:
1. The drive sequentially pulses a user-specified current, WS.IMAX, at each electrical quadrant (0°, 90°,
180°, 270°). Based on the resulting observed movement, an approximate location is calculated.
2. The drive pulses current and adjusts the commutation angle at small increments to find a precise position.
The amplitude of the current pulses in this process does not exceed WS.IMAX. The AKD repeats these two
steps for a user-specified number of times (WS.NUMLOOPS) to produce a more accurate estimate of the elec-
trical phase.
The drive normally indicates warning 478 before WS is initiated and successful. If WS fails, the commutation is
not valid and the drive indicates one of faults 473 to 479.
Maximizing WS Reliability
The following suggestions will help you achieve successful commutation:
l Incorrect determination of MOTOR.PHASE may cause a system runaway. Since the typical movement
during correct operation of WS is very small, you can use the velocity overspeed parameters
(WS.VTHRESH and DRV.VTHRESH) to prevent a runaway. Prior to enabling the drive, set
DRV.VTHRESH 100 mm/s for linear motors or 200 rpm for rotary motors. After a successful enable,
DRV.VTHRESH can be returned to the normal operating value.
l Set WS.IMAX to its default value, WS.IMAX=0.5*min(MOTOR.IPEAK, DRV.IPEAK).
l Set WS.NUMLOOPS 20 for best results in many applications.
l WS.T specifies the duration for which the search current is applied. With a stable velocity loop, most appli-
cations work well with the default value of WS.T 0. The default value causes the software to calculate the
width of the search pulse based on the velocity loop proportional gain, VL.KP. Increasing WS.T effec-
tively increases the movement of the motor during WS, which may be necessary for systems with a low-
resolution feedback or high load inertia.
66 Kollmorgen | December 2010