Delta Tau GEO BRICK LV Manuel D’Utilisation

Ixx67: Following Error Limit 

Ixx67 is a saturation limit on the magnitude of the following error input to the P and I terms of the filter.  
It does not limit the true following error, or the error value compared to the Ixx11 and Ixx12 following 
error limit parameters.  Setting Ixx67 to 0 disables the PI control terms, while leaving the D derivative 
term (i.e. the velocity loop) and the feedforward terms active.  This setting is useful if only velocity 
control is truly desired.  If Ixx67 is set to 0, Ixx11 should also be set to 0 to make sure the motor does not 
trip on a fatal following error fault. 

Ixx68: Friction Feedforward 

Ixx68 is a non-linear friction feedforward term.  The magnitude of Ixx68, multiplied by the sign of the 
instantaneous commanded velocity, is added directly to the output of the servo filter.  It is meant to 
compensate for dry (Coulomb) friction. 

Ixx69: Output Limit 

Ixx69 is a saturation limit on the output of the servo filter.  If the output value is limited by Ixx69, the 
input to the position-loop integrator is turned off automatically, and the output of the integrator remains 
constant in this condition. 

Ixx29, Ixx79: Offset Terms 

If Turbo PMAC is not performing commutation for Motor xx, Ixx29 is a fixed offset term on the output 
of the servo filter, in units of a 16-bit DAC (even if some other device is used).  If Turbo PMAC is 
performing commutation for the motor, Ixx29 and Ixx79 serve as phase offsets in the commutation 
algorithm. 

For systems with more difficult dynamics, such as multiple resonances and low-frequency resonances, the 
Extended Servo Algorithm (ESA) may be used instead of the PID filter.  The choice of servo filter may be 
made on a motor-by-motor basis. 
The ESA, while more powerful and flexible than the PID, is not as easy to understand or tune 
interactively.  The PEWIN32PRO Executive program has auto-tuning software for the ESA.  However, 
tuning the ESA manually requires significant control-theory knowledge and experience.  This discussion 
assumes such knowledge. 
The ESA has 30 terms in seven blocks of polynomial coefficients.  As with the PID, it does support single 
and dual feedback using the Ixx03 and Ixx04 feedback address variables.  However, the ESA is more 
flexible with regard to what is done with dual feedback; it is not limited to separate position and velocity 
loops.  The feedback selected with Ixx03 and the commanded trajectory values are pre-multiplied by the 
Ixx08 scale factor; the feedback selected with Ixx04 is pre-multiplied by the Ixx09 scale factor. 
As with the PID, or a user-written servo, the ESA can be used with or without Turbo-PMAC based 
commutation.  If the motor is not commutated by Turbo PMAC, the computed control output is written to 
the register specified by Ixx02; if it is commutated by Turbo PMAC, the control output is the torque 
(quadrature) command into the commutation algorithm.