Delta Tau GEO BRICK LV Reference Manual
Turbo PMAC/PMAC2 Software Reference
Turbo PMAC Global I-Variables
127
Ixx68 Motor xx Friction Feedforward
Range:
0 .. 32,767
Units:
16-bit DAC bits
Default:
0
Ixx68 adds a bias term to the servo loop output of Motor xx that is proportional to the sign of the
commanded velocity. That is, if the commanded velocity is positive, Ixx68 is added to the output. If the
commanded velocity is negative, Ixx68 is subtracted from the output. If the commanded velocity is zero,
no value is added to or subtracted from the output.
commanded velocity. That is, if the commanded velocity is positive, Ixx68 is added to the output. If the
commanded velocity is negative, Ixx68 is subtracted from the output. If the commanded velocity is zero,
no value is added to or subtracted from the output.
This parameter is intended primarily to help overcome errors due to mechanical friction. It can be
thought of as a friction feedforward term. Because it is a feedforward term that does not utilize any
feedback information, it has no direct effect on system stability. It can be used to correct the error
resulting from friction, especially on turnaround, without the time constant and potential stability
problems of integral gain.
thought of as a friction feedforward term. Because it is a feedforward term that does not utilize any
feedback information, it has no direct effect on system stability. It can be used to correct the error
resulting from friction, especially on turnaround, without the time constant and potential stability
problems of integral gain.
Ixx68 is used with both the PID servo algorithm executed if Iyy00=0, and the Extended Servo Algorithm
executed if Iyy00=1. If Turbo PMAC is commutating this motor, the Ixx68 bias is applied before the
commutation algorithm and so will affect the magnitude of both analog outputs.
executed if Iyy00=1. If Turbo PMAC is commutating this motor, the Ixx68 bias is applied before the
commutation algorithm and so will affect the magnitude of both analog outputs.
Note:
This direction-sensitive bias term is independent of the constant bias introduced by
Ixx29 and/or Ixx79.
Ixx29 and/or Ixx79.
Example:
For a control loop with +10V analog output, starting with a motor at rest, if Ixx68 = 1600, then as soon as
a commanded move in the positive direction is started, a value of +1600 (~0.5V) is added to the servo
loop output. As soon as the commanded velocity goes negative, a value of -1600 is added to the output.
When the commanded velocity becomes zero again, no bias is added to the servo output because of this
term.
For a control loop with +10V analog output, starting with a motor at rest, if Ixx68 = 1600, then as soon as
a commanded move in the positive direction is started, a value of +1600 (~0.5V) is added to the servo
loop output. As soon as the commanded velocity goes negative, a value of -1600 is added to the output.
When the commanded velocity becomes zero again, no bias is added to the servo output because of this
term.
Ixx69 Motor xx Output Command Limit
Range:
0 .. 32,767 (0 to 10V or equivalent)
Units:
16-bit DAC bits
Default:
20,480 (6.25V or equivalent)
Ixx69 defines the magnitude of the largest output that can be sent from Turbo PMAC’s PID
position/velocity servo loop. If the servo loop computes a larger value, Turbo PMAC clips it to this
value. When the PID output has saturated at the Ixx69 limit, the integrated error value will not increase,
providing anti-windup protection.
position/velocity servo loop. If the servo loop computes a larger value, Turbo PMAC clips it to this
value. When the PID output has saturated at the Ixx69 limit, the integrated error value will not increase,
providing anti-windup protection.
For the Extended Servo Algorithm (ESA) that is enabled if Iyy00/50 for the motor is set to 1, Ixx69 is
used to multiply a normalized command (-1.0 <= Normalized Command < +1.0) before outputting it or
using it for commutation. As such, it acts as both a scale factor and an output command limit for the
ESA.
used to multiply a normalized command (-1.0 <= Normalized Command < +1.0) before outputting it or
using it for commutation. As such, it acts as both a scale factor and an output command limit for the
ESA.
Ixx69 is always in units of a 16-bit DAC, even if the actual output device is of a different resolution, or
the command value is used for Turbo PMAC’s own internal current loop commands.
If using differential analog outputs (DAC+ and DAC-), the voltage between the two outputs is twice the
voltage between an output and AGND, so the Ixx69 value should be set to half of what it would be for a
single-ended analog output.
the command value is used for Turbo PMAC’s own internal current loop commands.
If using differential analog outputs (DAC+ and DAC-), the voltage between the two outputs is twice the
voltage between an output and AGND, so the Ixx69 value should be set to half of what it would be for a
single-ended analog output.
This parameter provides a torque (current) limit in systems with current-loop amplifiers, or when using
Turbo PMAC’s internal commutation; it provides a velocity limit with velocity-mode amplifiers. Note
that if this limit kicks in for any amount of time, the following error will start increasing.
Turbo PMAC’s internal commutation; it provides a velocity limit with velocity-mode amplifiers. Note
that if this limit kicks in for any amount of time, the following error will start increasing.