System characteristic / transfer function

Hello,

 

I am working with a PMAC2 control, using the PMAC Executive Suite 3.2 for communications. My objective is to get a transfer function of the controlled (closed loop) system, obtained by frequency sweeps.

The PMAC TuningPro software includes a possibility to sweep, but it is:

 

1. limited to 225 Hz (servo loop cycle is 9.0346 kHz)

2. limited to integer numbers for the time range

3. not permitting any control of the capturing rate

 

My questions are related to these problems:

 

Can I manually change the deposited programs for these kind of motions? Where can I find them? How can I gather data from terminal, plotting them into a file? The LIST GATHER command only plots them in the terminal, where I am unable to save them for further processing.

On the other hand there is the PMAC Plot tool, where I can gather data at any desired capturing rate and time range, but there I cannot initiate a commanded sweep simultaneously.

 

I found that program for getting a step response. But then I cannot read the data out at the end, even though they were captured. SIZE returns 34546 at the beginning. Then I capture 10000 values, so SIZE would return 24546. For capturing I set:

 

I19=1

I20=3

I21=$800028

I22=$80002B

I45=0

DELETE GATHER

DEFINE GATHER 10000

GATHER or CMD "GAT"

...

ENDGATHER or CMD "ENDGAT"

 

Now the data are captured. But how to get them into a file? I will be able to transform the hex data into counts surely, once I have them I a file, but how to? Copy and paste from the terminal is not working.

Now I tried it with a step response program. The program looks like:

 

_____________________________________________________________

; Setup and Definitions

; ################################################

CLOSE

P80=1000; ; step size in counts

M88->X3,18 ; Data gather prep bit

M89->X3,19 ; Data gather on bit

M0 ->X0,24 ; Servo cycle counter (=timer)

M85->X$07F0,24 ; Memory allocation for start time

M86->X$07F1,24 ; Memory allocation for elapsed time

M81->D$0028 ; #1 cmd position register

 

; Setup Gathering variables

; ###############################################

I19=1 ; gather each servo cycle

I20=3 ; gather two variables

I21=$800028 ; gather cmd position

I22=$80002B ; gather act position

I45=0

 

; ###############################################

OPEN PLC 2

CLEAR

 

CMD"DEL GAT"

CMD"DEF GAT 20000"

CMD"GAT" ; Start data gathering

P81=P80*I108*32 ; step time

P86=P85*8388608/I10 ; step time in servo cycles

M81=M81+P81 ; increment the commanded position

M85=M0 ; start of the timer

M86=M0-M85 ; time elapsed so far

While (M86 < P86)

M86=M0-M85

EndWhile

M81=M81-P81 ; now decrement commanded position again

M85=M0 ; Restart timer

M86=M0-M85 ; Time elapsed

While (M86 < P86)

M86=M0-M85

EndWhile

CMD"ENDGATHER"

DISABLE PLC 2 ;

CLOSE

; ###############################################

I5=3;

____________________________________________________________

 

Now typing LIST GATHER on the shell, there will be just 2 hex numbers.

 

Using the same settings be online command data gathering, following:

 

DELETE GATHER

DEFINE GATHER 20000

GATHER

ENDGATHER

 

LIST GATHER

 

I will get the values out. Now I can even export them by PMAC PLOT, what I found, by simply pressing on 'upload'. But then I don't have the step response.

Why won't that work for the PLC program? The step response is indeed carried out by the drive (a little click noise), but the data are not captured correctly.

The aim is actually to define several sweeps in different frequency ranges to obtain transfer functions, which can be concatenated. But then for the higher frequencies one needs to make the sweep time quite short in order to enable a storage of the full response.

Is that because the PLC program starts anew after execution, before it is cancelled by the DISABLE command and so the buffer would be initialized twice and the data cannot be captured? If so, what can I do against it?

Or is there another reason for my capturing endeavor to fail? What goes wrong?

When using the CMD"" in a PLC you will need to have a one pass while loop to force the execution otherwise these will not execute until one pass of the PLC:

CMD"GAT"

p99=1

while (p99=1)

p99=0

endwhile

It works now. I use a program like that, where I only have to change the four sweep parameters:

 

; Initiate sweep definition

; ####################################################

CLOSE

DELETE GATHER

P70=1 ; start frequency [Hz]

P71=10 ; stop frequency [Hz]

P80=400; ; sweep magnitude [cnt] -> 100 nm

P85=1000; ; sweep time [ms]

 

; Set addresses

; ####################################################

M88->X3,18 ; Data gather prep bit

M89->X3,19 ; Data gather on bit

M0 ->X0,24 ; Servo cycle counter (=timer)

M85->X$07F0,24 ; Memory allocation for start time

M86->X$07F1,24 ; Memory allocation for elapsed time

M81->D$0028 ; #1 cmd position register

 

; Setup gathering variables

; ####################################################

I19=1 ; gather each servo cycle

I20=3 ; gather two variables

I21=$800028 ; gather cmd position

I22=$80002B ; gather act position

I45=0

DEFINE GATHER 20000 ; prepare data buffer for gathering

 

; ####################################################

OPEN PLC 4

CLEAR

CMD"GAT" ; Start data gathering

 

P99=1 ; one pass while loop

While (P99=1) ; to address gathering delay

P99=0

EndWhile

 

P75=P85/LN(P71/P70) ; calcutate time constant

P76=360*P70/1000; ; calculate omega 0

 

P81=P80*I108*32 ; amplitude inkrement (position register)

P86=P85*8388608/I10 ; sweep time in servo cycles

P82=M81 ; current commanded position

 

M85=M0 ; start of the timer

M86=M0-M85 ; time elapsed so far in servo cycles

P87=M86*I10/8388608 ; time elapsed in ms

P72=P76*exp(P87/P75) ; current omega

M81=P82+P81*sin(P72*P87); update position

 

While (M86 < P86)

M86=M0-M85 ; time elapsed

P87=M86*I10/8388608 ; time elapsed [ms]

P72=P76*exp(P87/P75) ; current omega

M81=P82+P81*sin(P72*P87) ; update position

EndWhile

 

DISABLE PLC 4 ;

 

CLOSE

; ####################################################

I5=3;

Now I just type:

 

P70=..... ; start frequency [Hz]

P71=..... ; stop frequency [Hz]

P85=....; ; sweep time [ms]

del gat

def gat 34500

ena plc 4

 

After capturing I go to PMAC PLOT and press 'upload data' which will take a while and then 'plot data'. So I'll finally have my desired data set.

 

Thanks, problem solved

BUR