Allen-Bradley PowerFlex 70 Reference Manual page 173

Speed/Torque Select
As shown, [Speed/Torque Mod] (parameter 88) is used to select the mode of
operation. Zero torque current is allowed when set to "0."
When set to a "1, " the drive/motor is operated in speed mode. The torque
command changes as needed to maintain the desired speed.
A value of "2" selects torque mode. In torque regulation mode, the drive controls
the desired motor torque. The motor speed will be a result of the torque
command and load present at the motor shaft.
Min and Max mode are selected by values 3 and 4, respectively. These two modes
offer a combination of speed and torque operation. The algebraic minimum or
maximum of speed/torque will be the operating point for the Min and Max
modes. The drive will automatically switch from speed to torque mode (or from
torque to speed) based on the dynamics of the motor/load.
The Min mode is typically used with positive torque and forward speed
operation, the minimum of the two being closest to zero. The Max mode is
opposite, typically used with reverse speed and negative torque, the maximum
being the least negative (closest to zero).
Sum mode is selected when set to "5." This mode allows an external torque
command to be added to the speed regulator output when desired.
Speed Regulation Mode
Operating as a speed regulator is the most common and therefore simplest mode
to setup. Examples of speed regulated applications are blowers, conveyors,
feeders, pumps, saws, and tools.
In a speed regulated application, the torque reference is generated by the speed
regulator output. Note that under steady state conditions the speed feedback is
steady while the torque reference is a constantly adjusting signal. This is required
to maintain the desired speed. At transient state, the torque reference will change
dramatically to compensate for a speed change. A short duration change in speed
is the result of increasing or decreasing the load very rapidly.
Torque Regulation Mode
A torque regulated application can be described as any process that requires some
tension control. An example of this is a winder or unwind where material is being
"drawn" or pulled with a specific tension required. The process requires another
element setting the speed. Configuring the drive for torque regulation requires
[Speed/Torque Mod] to be set to "2." In addition, a reference signal must be
selected (Torque Ref A or Torque Ref B). If an analog signal is used for the
reference, select that from the Torque Ref A or Torque Ref B selections.
When operating in a torque mode, the motor current will be adjusted to achieve
the desired torque. If the material being wound/unwound breaks, the load will
decrease dramatically and the motor can potentially go into a "runaway"
condition.
Rockwell Automation Publication PFLEX-RM001H-EN-P - June 2013 173