User's Manual

PMAC User Manual
Making Your Application Safe 119
PMAC only performs the integrated following error check if the Ix63 integration limit parameter is less
than zero. When this is the case, the magnitude of Ix11 is used for the normal unintegrated following
error check, but in addition, the value of the PID integrator is compared against the Ix63 integration limit
magnitude. If the integrator value has saturated at +/-Ix63 (the limiting function in the PID loop will not
let it exceed this value), then PMAC will trip (kill) this motor on an integrated following error fault, just
as it would for a normal following error fault.
For the integrated following error limit to be effective, the Ix33 integral gain must be greater than zero,
and preferably set as high as can be tolerated. Also, the Ix34 integration mode parameter must be set to 0,
so that the integrator is on during programmed moves.
Remember that the integrator stops increasing in magnitude if the command output has saturated at Ix69.
The magnitude of Ix63 must be small enough that it will trip before the output saturates. The magnitude
of Ix63 that would cause output saturation at Ix69 from the integrator alone is:






∗
∗
=
30Ix08Ix
23
269Ix
63Ix
The magnitude of Ix63 must be less than this value for the shutdown function to be effective. Remember
that there will be other components to the output, for instance from the proportional gain. With a bare
motor, test it to see that this limit can trip the motor reliably.
When a motor is killed due to integrated following error fault, the standard following error fault motor
status bit is set. In addition, a separate integrated following error fault motor status bit is set. Both bits
are cleared when the motor is re-enabled.
Note:
The integrated following error protection feature is not available on PMACs with
the Option 6 Extended Servo Algorithm firmware. That algorithm has no
integrator register in the servo to compare against a limit.
Velocity Limits
PMAC has a programmable velocity limit for each motor (Ix16) that is in effect for linear blended
program moves. Circular, PVT, rapid, and splined moves do not observe this limit. If the commanded
velocity requested of a motor exceeds the limit for the motor, the move is slowed so that the velocity limit
is not exceeded. In a multi-axis programmed move, all axes in the coordinate system are slowed
proportionally so that no change in path occurs. Velocities are compared to these limits assuming no
feedrate override (% value of 100); if feedrate override (a.k.a. time-base control) is used, the velocity
limits scale with the override. When PMAC is automatically segmenting moves (I13 > 0), the Ix16
velocity limits are not observed.
Acceleration Limits
PMAC has two programmable acceleration limits for each motor, one for jogging and homing moves
(Ix19), and one for linear blended program moves (Ix17). Circular, rapid, PVT, and splined moves do not
observe this limit. If the commanded acceleration requested of a motor exceeds the limit for the motor,
the acceleration is stretched out so that the acceleration limit is not exceeded. In a multi-axis blended
programmed move, all axes in the coordinate system are slowed proportionally so that no change in path
occurs. Accelerations are compared to these limits assuming no feedrate override (% value of 100); if
feedrate override (a.k.a. time-base control) is used, the acceleration limits scale with the override. When
PMAC is segmenting moves (I13 > 0) automatically, which is required for Circular Interpolation, the
Ix17 accelerations are not observed.