Page 86 - Designing Autonomous Mobile Robots : Inside the Mindo f an Intellegent Machine

Closed Loop Controls, Rabbits and Hounds

‘Limit the output accumulator and flag the integrator
‘if the output goes out of range. (In a properly tuned
‘control, this should never happen).
If OutputAccum > 9999 Then
OutputAccum = 9999
IntegralHold = -1 ‘Allow only down integration
ElseIf OutputAccum < 0 Then
OutputAccum = 0
IntegralHold = 1 ‘Allow only upward integration
Else
IntegralHold = 0 ‘Allow both directions.
End If

DoPIDs = CInt(OutputAccum)

End Function
‘------------------------------------------------------------------------------------------
‘Prevent Terms from exceeding integer range for logging.
Private Function LimitTerm(Term As Single)
If Term > 9999 Then
LimitTerm = 9999
ElseIf Term < -9999 Then
LimitTerm = -9999
Else
LimitTerm = Term
End If
End Function

Figure 5.5. A band-limited hybrid control with integral hold-off

Robot drive controls

The drive system of a mobile robot is subject to widely varying conditions, and thus
it presents several challenges not found in the simpler control systems already dis-
cussed. These include:

1. Drive/brake asymmetry
2. Quadrant crossing nonlinearity due to gear backlash

3. Variable acceleration profiles due to unexpected obstacle detection

4. Variable drag due to surface variations
5. Variable inertia and drag due to payload variations.

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