To home, position, or press/push/pull to a given torque/force using an ACR controller a few simple steps must be taken to allow for a larger position error than would be typical in a strictly position controlled system. The idea is that the maximum torque will be limited to the desired magnitude, and then a move is commanded beyond the point of expected force limit. E.G. to home to a hard stop that is 1” away, a move of 1.25” is commanded to insure that the torque limit is met.
To accomplish this:
Set the Excess Position Error “EXC” to a sufficiently large value. If the EXC window is too small, the drive will fault due to position error.
Set the axis Torque Limit “TLM” to the desired SCALED value. The TLM is scaled linearly from 0 to +/-10 V; 10V being the peak torque.
Command a move that is farther than point of resistance.
Wait for motion to stop using an Inhibit command “INH”
Command a move that is the difference between commanded position and actual position (where motion stopped due to physical obstruction and torque limit)
X/((P12290 -P12289)/PPU Value)
Follow with a RES X to zero this location.
EXC X 3 : REM Set the Excess position Error to 3 inches
TLM X 1.5 : REM Limit torque output to 15% of maximum
INH -516 : REM Wait for Motion to stop
X/((P12290 -P12289)/4000) : REM Command a move to the point motion stopped
RES X : REM Zero position
For Aries-EPL or AriesCE.
It is possible to put the drive into a "torque" mode by setting all tuning gains to zero and then sending TRQOFF commands to the drive to control the torque offset. This effectively runs the drive open loop, although it is necessary to tell the controller to disregard position errors by clearing the "Enable EXC Response" control flag (bit 8469 for Axis0). Note that disabling this fault could cause servo run-away. ie, If doing a clamping operation, it'd be recommended to set EXC to a value just past the clamping position.
In a sample for Axis0, set up as EPLD0, it can be as simple as:
AXIS0 PGAIN 0
AXIS0 DGAIN 0
AXIS0 IGAIN 0
AXIS0 ILIMIT 0
AXIS0 FBVEL 0
AXIS0 FFVEL 0
AXIS0 FFACC 0
OPEN "EPLD0:" AS #3 : REM open a channel to EPLD drive 0 as device #3
PRINT #3, "TRQOFF 1" : REM set torque offset in % of DMTLIM for EPLD0 via device #3
CLOSE #3 : REM close channel to EPLD drive 0
C164 is the torque offset and is a % of the DMTLIM. Range is -100% to +100% and is Floating Point data type.
C14 is the drive's motor torque limit (DMTLIM), can range from 0 to 4000 and is Nm for rotary or N for linear and is Floating Point data type.