User Manual Chapter 5
GFK-1742F Jan 2020
DSM314 to Host Controller Interface 154
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 host controller 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 host controller 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 and Analog Torque Mode only. The velocity
control loop gain for a digital servo axis and Analog Torque mode servo 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 host controller reset or power cycle returns
VLGN to the value set in the configuration software. A suggested starting point for
Velocity Loop Gain is:
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
configuration software.
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