VMC 186/40 Motion Control Module Control Parameters
22
Requested Position
The
Requested Position
is the position the axis is to move to. This value is bounds checked by the VMC
186/40 using the
Extend Limit
and
Retract Limit
and then used as the
Command Position
.
Command
Note: The
Command
parameter is set to zero by the VMC 186/40 after the command is accepted.
The following commands are accepted by the VMC 186/40:
'P' - Set parameters (50H)(80)
This command should be given as the first command after startup and only
when all of the axes are stopped. All initialization parameters are updated when a 'P' command is given.
The minimum requirement of this command is to set the
Extend
and
Retract Limits
to their proper values
(see Getting Started on page 27). When a 'P' command is given, the VMC 186/40 will wait for a few
milliseconds to get the actual position of the axis. This position is then copied into the
Target
and
Command Position
. This keeps the axis from moving until a 'G' command is issued.
'
G' - Go to Requested Position (47H)(71)
The VME controller is responsible for making sure all
parameters are valid when the 'G' or GO command is given. Normally, once the
Mode, Acceleration,
Deceleration
and
Requested Speed
are set, only the
Requested Position
needs to be changed. Once set, a
'G' put in the
Command
parameter is used to get the axis to move.
Note: The 'G' command can be given while the axis is in motion. If given while the axis is in motion, the
motion controller module will ramp to the new speed at the rate specified by the
Acceleration
and
Deceleration
parameters and go to the
Requested Position
.
'H' - Halt (48H)(72)
The Halt command is used for emergency stops, jogging the axis, or when the drive
power is off. If the axis is moving and an 'H' is used, the axis will ramp down until it stops and the null
update will be disabled. The
Status Word
can be used to determine the difference between a halted axis
(caused by a control error) or
At Command Position
(caused by the 'H' command). Jogging an axis is
accomplished by alternating Go and Halt commands.
'F' - Set Feed Forward (46H)(70)
The 'F' command is used to automatically set the feed forward values.
After a move is made where the axis is allowed to reach constant velocity and both the
Overdrive
and
Valve Out of Null
Status Word
bits were not set, an 'F' command will set the feed forward for the direction
last moved. This command is quick and easy, and it will allow the system to adjust for changes in system
dynamics. This will also make setup easier.
CAUTION: If the axis oscillates or doesn't reach steady state during the move, the 'F' command will produce
erroneous results.
'
'O' - Override (4FH)(79)
This command allows the user to control the drive independently of closed loop
control. The command is used in connection with
Requested Speed
, and
Requested Position
parameters to
change the drive output. The parameter definitions for the override command are as follows:
Requested Speed
Maximum drive offset limit (both
±
)
Requested Position
Drive offset (Range 0 - ±2047)
The value placed in the
Requested Speed
parameter is the maximum offset from null that is permitted. The
value placed in the
Requested Position
parameter will be added to the present null drive value. The default
null drive value is 2048 which produces 0.0 mA/0.0 V output. When an Override command is given, the
null update will be disabled.
