Delta RMC151 - Manual (Page 110)

RMC70/150 and RMCTools User Manual
Unidirectional Mode will prevent the Control Output from going negative even if the Actual
overshoots the Target. When this occurs, the Control Output will be truncated at the Output
Bias, and the Integral Term will not wind up.
Unidirectional Mode applies only to closed-loop position, velocity, pressure, and force control.
It does not affect open loop commands, but it does affect the Quick Move commands. The
open loop portion of the Quick Move is adjusted in the same way as a closed loop move.
For more details, see the Unidirectional Mode axis parameter.
3.5.11. Velocity and Torque Mode
Most actuators, together with their power source and/or drive electronics, can be classified in
two types: velocity mode or torque mode. Which type it is affects the tuning procedure and
how the actuator handles certain RMC commands.
Definition
The actuator type is defined by its response to the Control Output voltage applied by the
RMC:
• A velocity mode actuator produces a speed proportional to the Control Output.
• A torque mode actuator produces a torque or force proportional to the Control
Output.
In practice, this means that if you issue an Open Loop Rate command with a certain
amount of Control Output to a velocity mode actuator, the actuator will move at a speed
roughly proportional to the Control Output voltage. If you issue the Open Loop Rate
command to a torque mode actuator, the actuator will provide a torque proportional to
the voltage. The actuator speed will keep increasing until the torque is equal to the
friction in the system. The final drive speed for a torque mode actuator is not necessarily
proportional to the voltage.
Note:
It is not recommended that you issue Open Loop commands to a torque mode system during
normal operation, because you cannot predict the final speed. Use closed loop commands
instead.
Examples
Velocity mode actuators:
• Hydraulic cylinder
• Motors with a velocity drive
Torque mode actuators:
• Motors with an amplifier (without an inner velocity loop)
Effect on Tuning
Whether an actuator is velocity or torque mode affects the tuning of a system in the
following ways:
• Damping
Velocity mode systems typically have high damping because they use a velocity-mode
drive, or for hydraulic cylinders, they have high damping during motion, and when
stopped, don't move because of the low compressibility of oil. In these cases, the
system has, or appears to have, significant damping. Torque mode systems, however,
typically have little damping. That means that if given some Control Output, they will
coast after the Control Output goes back to zero. When tuning a torque drive, some
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