Delta MMC120 - Manual (Page 83)

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CAUTION: Use this command with care! Open Loop operation disables all safety
features on the motion controller!
NOTE: The open loop command will not affect drive output while the Simulate bit in
the Config word. Drive output is always 0 volts in simulate mode.
The Open Loop command allows the Controller to directly specify values for the analog
output. The output range is -10000 to 10000 where -10000 is -10 volts and 10000 is +10
volts.
The O command uses the following parameters from the last open loop profile specified:
The
COMMAND VALUE field specifies the desired drive in millivolts to output. The
current null drive is added to this value.
The
SPEED field is not used.
The ACCELERATION and DECELERATION fields control the rate at which the drive
output ramps to the requested value. Acceleration is used when the drive output is
moving away from 0 and deceleration is used when drive output is moving toward 0.
The actual meaning of the values depends on the Acceleration/Deceleration mode bits in
the MODE word. Notice that only modes 1 and 3 are used:
Mode 1 -Acceleration and deceleration are given in millivolts per millisecond. For
example, if the current drive output is 0 millivolts, and the Command
value is 1000 millivolts, and the Acceleration is 50, then it will take 20
milliseconds for the drive output to reach 1000 millivolts.
Mode 3 -Acceleration and deceleration are given in milliseconds. For example, if the
current drive output is 0 millivolts, the Command value is 1000 millivolts,
and the Acceleration is 50, then it will take 50 milliseconds for the drive
output to reach 1000 millivolts, as the drive will increase 20 millivolts
each millisecond.
NOTE: If a move cross 0 drive, then Deceleration will be used until the drive reaches
0, and then Acceleration would be used until the final drive is reached.
Tip: If you are going to be changing from closed loop to open loop, then you need to
be aware of the following trickiness. While in closed loop and holding a position, the
drive may be switching back and forth between small positive and negative drives. If
an open loop command is given to go to a non-zero drive, then it may happen that the
starting drive has an opposite sign than the requested drive, and therefore the drive
will decelerate down to zero millivolts and then accelerate up to the new drive. For
example, if the current drive is –10 millivolts and an open loop command requests a
drive of 2000 millivolts (2V), the drive will ramp from –10 to 0 and then accelerate
from 0 to 2000mV. Therefore, you should ensure that the deceleration is set so that
this deceleration happens quickly (by setting it to 0 in Mode 3, and to a high number
(1000 or greater) in Mode 1.