User`s manual

DSM to PLC Interface
GFK-1742A Chapter 5 Motion Mate DSM314 to PLC Interface 5-23
5
time. For Analog mode, the “Vel at Max Cmd” configuration value must be set correctly for
proper operation of the
Position Loop Time Constant
. A PLC reset or power cycle returns this
value to the configured data.
4.13 Velocity Feedforward.
This command sets the
Velocity Feedforward
gain (0.01 percent).
It is the percentage of
Commanded Velocity
that is added to the DSM314 velocity command
output. Increasing
Velocity Feedforward
causes the servo to operate with faster response and
reduced position error. Optimum
Velocity Feedforward
values are 90-100 %. For analog servos,
the “Vel at Max Cmd” configuration value must be set correctly for proper operation of the
Velocity Feedforward
gain factor. A PLC reset or power cycle returns this value to the
configured data.
4.14 Integrator Time Constant.
(Milliseconds) This command sets the
Integrator Time
Constant
for the position error integrator. The value specifies the amount of time in which 63%
of the
Position Error
will be removed. The
Integrator Time Constant
should be 5 to 10 times
greater than the
Position Loop Time Constant
to prevent instability and oscillation.
It is
recommended that the position error integrator only be used in continuous follower
applications. Use of the integrator in point to point positioning applications may result in
position overshoot when stopping.
4.15 Follower A/B Ratio.
This command allows the PLC to update the slave
:
master A/B ratio
used in each follower loop. “A” is a 16-bit signed integer with a minimum value of -32,768 and a
maximum value of +32,767. “B” is a 16-bit integer with a minimum value of 1 and a maximum
value of 32,767. The magnitude of the A/B ratio must be in the range 32:1 to 1:10,000 or a status
error will be generated. Refer to Chapter 8 for additional information about the A/B ratio.
4.16 Velocity Loop Gain
. (VLGN
)
Digital Mode only. The velocity control loop gain for a GE
Fanuc digital servo axis may be set with the
Velocity Loop Gain
command. The VLGN value is
used to match the load inertia (J
L
) to the motor inertia (J
M
). VLGN is defined with a default
value of 16 representing an inertia ratio of 1 to 1. The VLGN value is calculated assuming that
the load is rigidly applied to the motor. Therefore, in actual machine adjustment the required
value may significantly differ from the calculated value due to rigidity, friction, backlash, and
other factors. A PLC reset or power cycle returns VLGN to the value set in the configuration
software. A suggested starting point for
Velocity Loop Gain
is:
Load Inertia (J
L
)
Velocity Loop Gain =
Motor Inertia (J
M
)
x 16
The allowed range of
Velocity Loop Gain
is 0 to 255.
For example
: The motor inertia (J
M
) of a particular servo is 0.10 lb-in-s
2
. The load inertia (J
L
) in
this application is 0.05 lb-in-s
2
. VLGN = (0.05 / 0.10)
*
16 = 8
The default
Velocity Loop Gain
is set using the
Velocity Loop Gain
setting in the VersaPro
Configuration Software.
Caution
An incorrect VLGN value may cause an axis to be unstable. Care should be
used when making any change to the VLGN value.