Delta Tau GEO BRICK LV User Manual

 

Ixx06 for the inner loop’s motor also controls how the outer loop’s corrections interact with commanded 
positions for the inner loop.  When Ixx06 bit 1 (the following mode control bit) is set to 0, the inner 
loop’s commanded positions are relative to a fixed origin, and these commanded moves effectively cancel 
out whatever corrections have come in through the master position port.  When Ixx06 bit 1 is set to 1 
(offset mode), the corrections that come in through the master position port effectively offset the origin 
for programmed commanded moves, permitting commanded moves and master corrections to be 
superimposed.  This distinction in mode is true even if following is disabled. 

When the outer loop is engaged (Ixx06 bit 0 = 1), usually the following must be in offset mode (Ixx06 bit 
1 =1), making the required value of Ixx06 be 3 for this operation.  Even if there are no explicit commands 
in the motion program for the axis assigned to the inner loop’s motor at this time, any motion command 
for the coordinate system containing this motor implicitly commands that motor to its previous 
commanded position.  If the following is not in offset mode, this will take out the corrections that have 
come in since the last programmed move or move segment. 

When the following is disabled (Ixx06 bit 0 = 0), to command the inner loop’s motor to a definite 
physical position, put the following in normal mode (Ixx06 bit 1 = 0), making the required value of Ixx06 
be 0 for this operation. 

Inner-Loop Master Scale Factor: Ixx07 

The Ixx07 variable for the inner loop’s motor, the master scale factor, is a gain term for the outer loop in 
this use.  Set to 1 to keep the net outer-loop gain (inner-loop Ixx07 times outer-loop Ixx30) as low as 
possible.  It can be set to a negative value if necessary to invert the sense of the coupling between the two 
loops. 

In the cases of hybrid control, typically you will need only proportional gain (Ixx30) in the outer loop or 
possibly integral gain as well (Ixx33).  Most applications will require no derivative gain (Ixx31), and 
because in most applications the outer loop is just trying to maintain a constant command value, usually 
feedforward terms (Ixx32 and Ixx35) are not important. 

If you are integrating the outer loop’s command value before using it in the inner loop, your Ixx30 
proportional gain term probably will be extremely low (often around 10). 

It is possible to use the Executive’s tuning tools to tune the outer loop gains as you would a standard loop. 

With the outer loop engaged, commanding the position of the outer-loop motor will cause the outer loop’s 
feedback loop to calculate offsets into the inner loop command in an attempt to drive the outer-loop’s 
feedback device to the commanded value.  This outer-loop command can be a motor jog command, or it 
can be a programmed axis command.  If a programmed axis command, the axis to which the outer-loop 
motor is assigned can be in the same coordinate system as the inner-loop motor, or in a different 
coordinate system. 

Most commonly, the outer-loop motor will be assigned to an axis in the same coordinate system as the 
inner-loop motor, and commanded in the same coordinate system.  Axis-naming conventions and 
standards (e.g. RS/EIA-267) consider these as secondary axes and suggest the name of U when matched 
with an X axis, V when matched with Y, and W when matched with Z.