CHAPTER 5.0 Functional Overview
5-39
CDS7324 (FORMERLY LSF-0819)
Rev. A
INSTALLATION & USER’S MANUAL
5.11.2.2
Acceleration/Deceleration limiting
The acceleration/deceleration limiting is performed on the velocity command. In position control mode this is the
output of the position compensator.
The acceleration limiting parameter is
acceleration_limit
(1335 ), and has units of rad/s
2
.
The deceleration limit can be set separately from the acceleration limit. The deceleration limiting parameter is
deceleration_limit
(1668 ), and has units of rad/s
2
.
The deceleration limits for fault mode and for quickstop can be set separately from the normal deceleration limit.
The fault mode deceleration limiting parameter is
deceleration_limit_-_fault
(1671 ), and has units of rad/s
2
.
The quickstop mode deceleration limiting parameter is
deceleration_limit_-_quickstop
(1670), and has units of
rad/s
2
.
Note that writing to the acceleration limit has the effect of setting all of the deceleration limits to the same value as
the acceleration limit, so if a deceleration limit is required to be different then it must be written after the
acceleration limit.
Note that writing to the deceleration limit has the effect of setting all of the deceleration limits to the same value as
the deceleration limit, so if either the fault or quickstop deceleration limit is required to be different then it must be
written after the deceleration limit.
The velocity command input to the acceleration-limiting block is
velocity_command
(1156). The output of the
acceleration-limiting block is
velocity_command_acceleration_limited
(1157). These may both be monitored using
the GUI scope to view the effect of acceleration limiting.
These velocity terms have embedded units of “increments/(velocity loop sample period)” and can be converted to
rad/s using the expression (where vcmdsav =
velocity_command_acceleration_limited
),
vcmdsav
veldiv
swifrq
s
rad
command
velocity
16
2
2
)
/
(
π
=
This expression can also be used to convert velocity (1151), and velocity_filtered (1165) to rad/s.
5.11.2.3
Velocity Limiting
There are several ways in which the velocity is limited. These are listed below: -
1. The
parameter
velocity_maximum
(1800) sets the maximum value for the velocity command. This value is
stored in NVM.
2. The
parameter
velocity_limit
(1802) can be used to limit the velocity temporarily to some value less than
the maximum velocity. This parameter can be used in real-time messages, but is not stored to NVM.
3. The velocity of the drive is reduced when in manual mode. This reduces the velocity of the drive to a
percentage (default is 10%) of the max velocity. This functionality is outlined earlier in the digital input
section of the manual.
4. The velocity of the drive is also reduced/controlled when in torque mode. There is no velocity loop when
in torque mode so the following method is applied. A linear de-rating of the torque applied to the motor is
implemented when the velocity of the drive exceeds the velocity limit of the drive (i.e. limit in either
manual or automatic mode). The de-rating is such that the demand torque is applied when at the velocity
limit, but that torque is reduced to zero, when at 5% above the velocity limit. The de-rating gives a
smoother profile, than simply zeroing torque if the velocity limit is exceeded. The following diagram
shows the implementation:
