How to setup Position Error Delay

How to SetUp Position Error Delay

	WARNING
	If working with CDHD Servotronix family of drives over EtherCAT pay attention that in order to get position proper error values it is extremely important to switch off the CDHD's smoothing feature by setting MOVESMOOTHMODE to 0. The CDHD's position smoothing is obsolete in applications with SoftMC as the SoftMC already smoothenizes its output (PCMD values).

First Step

• set PEDEL to 1 (minimum value)
• set high value in PeMax
• Run the axis back and forth and record PE and VCMD as :

Command Velocity recordings



Position Error recordings

Compute PEDEL as PE/VCMD, in this case it will be:

PE/VCMD = 0.94/57.74*1000 = 16.2 ms

Taking into account the used value of PEDEL (1) and the sampling time of 4ms we get the new PEDEL value of 5, e.i. PEDEL = 1 + 4 = 5

	NOTE
	in case of a simulated axis the same procedure will work, typically results will show round cycle of 1. eg, PE/VCMD = 0.4 / 100.0 * 1000.0 = 4 ms = 1 bus cycle

Second Step

Change the PEDEL(5) to the integer value estimated before and run the test again:

again estimate the error:

PE/VCMD = 0.18/57.74*1000 = 0.317 ms

	IMPORTANT
	This means the non-integer communication delay of the drive is 317 micro-seconds.

which is in units of one sample equal:

317/4000 = 0.078

Final

So setting PEDEL to 5.078 we get:

Example File

PDLtune.prg

'
common shared Ax as generic Axis

program
	
	dim i as long

	Ax = A1
	with Ax
		Attach	
			Pedel = 1 ' first run
			Pedel = 1 + round(1.68 / 100.0 * 1000.0 / (bus[0].cycleTime/1000)) ' 2nd run. extracted from recordings
			Pedel = Pedel + 0.075 / 100.0 * 1000.0 / (bus[0].cycleTime/1000) ' 3rd run. extracted from recordings
			PeMax = 10
			En=1
			Sleep 100
			Move 0 Vcruise=100 Abs=TRUE
			call waitMotion
			Record ax_PE.rec 100000 Gap=1 RecData = Ax.Pe, Ax.Vcmd
			RecordOn
				Sleep 100
				for i = 1 to 3
					Move 100 Vcruise=100 Abs=TRUE
					call waitMotion
					Sleep 100
					Move 0 Vcruise=100 Abs=TRUE
					call waitMotion
					Sleep 100
				next
			RecordClose		
			En=FALSE
			Sleep 100
			PeMax = 0.1
		Detach
	end with
	
terminate program


sub waitMotion
	while Ax.IsMoving
		Sleep 1
	end while
end sub

Expected Values For Different Devices

	NOTE
	These values are approximations to the values expected to be obtained with the script provided, and the values may vary depending on the system settings used.

Drivel Model	PEDEL [Motion-Bus cycle times]
CDHD CAN	5.23
CDHD ETH	5.078
CDHD2 ETH	4.404
DDHD CAN	4.06
stepIM CAN	4.37