Accelnet & Stepnet Plus Panels User Guide
16-01339 Rev 07
3.10 P
OSITION AND
V
ELOCITY
E
RRORS
E
RROR
-H
ANDLING
M
ETHODS
In position mode, the difference between the limited position output of the trajectory generator and the actual
motor position is the position or following
error. The drive’s position loop uses complementary methods for
handling position errors: following error fault, following error warning, and a position-tracking window.
Likewise, in velocity or position mode, any difference between the limited velocity command and actual velocity
is a velocity error. The drive’s velocity loop uses a velocity tracking window method to handle velocity errors.
(There is no velocity error fault.)
F
OLLOWING
E
RROR
F
AULTS
When the position error reaches the programmed fault threshold, the drive immediately faults. (The following
error fault can be disabled.) For detailed information, see
F
OLLOWING
E
RROR
W
ARNINGS
When the position error reaches the programmed warning threshold, the drive immediately sets the following
error warning bit in the status word. This bit can be read over a CAN, EtherCAT, or MACRO network. It can
also be used to activate a digital output.
P
OSITION AND
V
ELOCITY
T
RACKING
W
INDOWS
When the position error exceeds the programmed tracking window value, a status word bit is set. The bit is not
reset until the position error remains within the tracking window for the programmed tracking time.
A similar method is used to handle velocity errors.
F
OLLOWING
E
RROR
F
AULT
D
ETAILS
P
OSITION
E
RROR
R
EACHES
F
AULT
L
EVEL
As described earlier, position error is the difference between the limited position output of the trajectory
generator and the actual position. When position error reaches the programmed Following Error Fault level,
the drive faults (unless the following error fault is disabled.) As with a warning, a status bit is set. In addition,
the fault is recorded in the error log. Additional responses and considerations depend on whether the fault is
non-latched or latched, as described below.
D
RIVE
R
ESPONSE TO
N
ON
-L
ATCHED
F
OLLOWING
E
RROR
F
AULT
When a non-latched following error fault occurs, the drive drops into velocity mode and applies the Fast Stop
Ramp deceleration rate to bring the motor to a halt. The drive PWM output stage remains enabled, and the
drive holds the velocity at zero, using the velocity loop.
R
ESUMING
O
PERATIONS
A
FTER A
N
ON
-L
ATCHED
F
OLLOWING
E
RROR
F
AULT
The clearing of a non-
latched following error depends on the drive’s mode of operation. Issuing a new trajectory
command over the CAN bus or the ASCII interface, will clear the fault and return the drive to normal operating
condition.
If the drive is receiving position commands from the digital or differential inputs, then the drive must be disabled
and then re-enabled using the
drive’s enable input or though software commands. After re-enabling, the drive
will operate normally.
