Elmo HARSFEN0602, HARmonica software manual 197, Parameters of the Position Controller

HARSFEN0602ElmoHARmonicaSoftwareManual PRELIMINARYDRAFT

197

DV[3]

Position

com m and

			FF[2]	d/dt
			Fixed if
			GS[2]=0	Automatic
				Controller
				Selector
				0
					Speed command
			Position		(DV[2], Amp)
	Σ		Controller
-		ePos	KP[3],GS[9]	CommandPi	Σ
					Main Position
		Position feedback			sensor
				UM=5 UM=4
					Auxiliary Position
					Sensor

Figure 41 – Block Diagram of The Dual Loop Controller

15.3.2The Parameters of the Position Controller

The position controller is implemented as a cascaded loop, the inner loop is a speed controller and the outer loop is a simple gain: The simple gain operates on the position error, ePOS (t) :

ePOS (t) = PosCommand (t) − PosFeedback(t) [counts]

to give [Internal speed units, see “Units” section]

CommandPI (t) = KPOut ⋅ ePOS (t) .

However when the position error, ePOS (t) , is too large the gain is modified to avoid instability, KPOut is replaced by

min(KPOut ⋅ abs(ePOS (t)), 2 ⋅ α ⋅ abs(ePOS (t)) ) ⋅ sign(ePOS (t)) .

where

2 ⋅α = GS[9]

The above formula assures that the speed controller will not be demanded to decelerate beyond α count/sec2. GS[9] must be calculated with α as the 80% of the highest deceleration the motor can produce with the current of PL[1].

The inner loop is a speed controller, described previously in this chapter.

The parameters of the non-scheduled position controller are:

Parameter	Description
KP[3]	Proportional gain , K POut
GS[2]	Controller gain selector
GS[9]	Acceleration limit
VL[2],VH[2]	Maximum speed command
FF[2]	Speed Feed-forward
UM	For UM=4 the position feedback is taken from the auxiliary encoder