PID-filter routine (2nd try).

[daan.joubert]

Hi Alain and others,
Thank you all for info given, it is much appreciated.

Alain, regarding the linear problem - I have tested the actual distance travel of the servo arm by connecting a ruler to the arm.
To test I then adjusted the speed voltage, taking voltage readings and distance readings as I go along.
The distance values on Excel graph showed a non linear line in comparison to the linear nature of the voltage.
/Daan Joubert

[Acetronics2]

Hi Alain

The distance values on Excel graph showed a non linear line in comparison to the linear nature of the voltage.
/Daan Joubert

Hi, Daan

I hope you've considered the rotation angle of the arm is linear to the signal ...

But, whatever your transmission system ... only rack and pinion or cable and pulley can give a linear travel !!!

You could use a LOOKUP Table to correct your output ... but, once more, if it is a real PID controller, it will compensate for non-linearities ...

Or try to use ... FUZZY LOGIC !!!

Or find an old LINEAR R/C servo ( Kraft, Robbe, Varioprop, Lextronic ... produced some in the 70-80's )


Alain

[anonymouse]

Hi Alain and others,
Thank you all for info given, it is much appreciated.

Alain, regarding the linear problem - I have tested the actual distance travel of the servo arm by connecting a ruler to the arm.
To test I then adjusted the speed voltage, taking voltage readings and distance readings as I go along.
The distance values on Excel graph showed a non linear line in comparison to the linear nature of the voltage.
/Daan Joubert

Your gains might need to be fractional all the way up to 20 times and more via your vresistors via adc. Example engine running no load 1500 rpm, adc 1.5/5 * 256 = 77. setpoint = 77,unknown but say pwm 25, all gains apart from p set to zero. 25% load applied engine droops to 500rpm,adc 0.5/5 * 256 = 26. 77-26= 51, pwm output 51. If output to much p gain * 0.8 etc,to little * 1.5 etc. You should get to the stage of engine hunting turn the gain slightly below this. This is then where the data from i and d comes into play and slightly tweaking each one results in a reactive genset regardless of load.

[hadiengg]

Thanks Mr Henrik,Mr RodSTAR and Mr Anonymouse for help.
I succesfully run the motor at constant speed.Motor speed also change through given speed refrence.
Now one problem that i face is motor overshoot in slow speed refrence whenever i turn on the power.Its overshoot cycle comes down when i increase speed refrence.At full speed refrence it get exact speed never overshoot.I am using same PID gains used in original file.I think i must change the GAIN value to overcome this problem.
And also i am using variable for 0-5V to 0-1023 value through ADC.How i use this value to put the gain as used under.
pid_Kp = $0700 'Set Kp to 7.0
Please give some code to convert the value.

[HenrikOlsson]

Hello,
I thought I explained that in post #16 above. I'll simply quote myself:

Regarding the pots, you can set the PID gains in any number system you like. The reason I show it in hex is that it is easier IMO. You can simply do pid_Kp = myADResult if you like.

1023 in decimal is the same as $03FF which, in the PID filter, is treated as 3.996 basically. See, 03 is the number on the left side of the decimalpoint and FF is on the right side. FF represents 1/256*255 or 0.996. If you'd feed it 102 from the ADConverter it would be the same as $0066 or a gain of 0.258.

If you need more gain than 1023 then simply multiply your ADResult, pid_KP=myADResult*2, now you get a gain of 0-2046 or $0000-$07FE or 0.0-7.992

I don't really know how to explain it in any other way but let me know if doesn't make sense and I'll try, or perhaps someone else can attack it from another angle.

/Henrik.

[Acetronics2]

Hi, Hadienggggggg

At full speed refrence it get exact speed never overshoot.I am using same PID gains used in original file.I think i must change the GAIN value to overcome this problem

EACH system has its own set of parameters ( Kp, Ki, Kd ) and you are the one and only one who can find them ...

NOW, just Google around for the " Ziegler and Nichols method " ... sure it will help you !

FURTHER ... you can disable The Ki and Kd action at startup and engage then for a maximum error of ???, you can use retrieve tables for Kp,Ki,Kd as a function of the running point, you can program a rampup for engine start ...

But that is VERY typical to YOUR project ... and far out from Henrik's project shown here ...

BTW ... MERCI Henrik ...

Alain

[phoenix_1]

The QEI reading work good with count for position from 0-1000.
The PPWM give good voltage and signal too from 0 - 1024 at 20KHz.
The Henrik PID rutine work good but only when position and setpoint is max +/-50 !
and realy how make to motor clip +/- when position = setposition in some range about +/- 25% as break in position.
My output driver have next logic :
with PWM 512 motor STOP
0<--------512----->1024
left <---- stop-----> right
fast slow stop slow fast

Here is my debug program:

'****************************************************************
'                 Definicije PIC-a  18F4431                     *
'****************************************************************
    DEFINE OSC 20
    include "incPID.pbp"
'****************************************************************
'                        LCD DEFINE LCD 4X20 chr             *
'****************************************************************
    DEFINE LCD_DREG PORTD
    DEFINE LCD_DBIT 4
    DEFINE LCD_RSREG PORTC
    DEFINE LCD_RSBIT 0
    DEFINE LCD_EREG PORTC
    DEFINE LCD_EBIT 1
    DEFINE LCD_BITS 4
    DEFINE LCD_LINES 4
    DEFINE LCD_COMMANDUS 2000
    DEFINE LCD_DATAUS 50
                 
'****************************************************************
'                          Definicije Portova                   *
'****************************************************************    
    ADCON0=0                                
    ANSEL0=0
    TRISB = %00000000
    PortA = 0                               
    PortB = 0                                  
    PortC = 0
    PortD = 0                                
    PortC.3 = 1                                 
                         
'****************************************************************
'                          Definicije  PPWM                     *
'****************************************************************   
    DTCON = 0 
    PTCON0 = %00000000 
    PTCON1 = %10000000 
    PTPERL=$FF      
    PTPERH=$00
    PWMCON0 = %00100000 
    PWMCON1 = 1 
    OVDCOND = %11111111                     
'****************************************************************
'                          Definicije QEI encodera              *
'**************************************************************** 
    'QEICON = %10011000
    'DFLTCON = %00111000                
    'MAXCNTL = %11001111              
    'MAXCNTH = %00000111
    QEICON=%10001000
    DFLTCON = %00111000                
    MAXCNTL = %11101000               
    MAXCNTH = %00000011               
    PosLow VAR BYTE                           
    PosHigh VAR BYTE                           
    PosTemp VAR BYTE                          
    Position VAR WORD                          
    POSCNTL = 0                                
    POSCNTH = 0
'****************************************************************
'                          Definicije  TMR0                     *
'****************************************************************     
    T0CON = %11001000
    INTCON.5 = 1
    INTCON.1 = 0
    INTCON.7 = 1
    INTCON.4 = 0
    INTCON.3 = 0
    INTCON.2 = 0
    INTCON2.2 = 1
    RCON.7 = 1
    TMR0L =254 
'****************************************************************
'                          Definicije PID filtera               *
'****************************************************************
    x var word
    y var word
    ADValue VAR word                           '<---This is your variable.
    Setpoint VAR WORD                          '<---This is your variable.
    Direction var bit                          '<---Direction bit to motor driver 
    pid_Kp = $0700                             'Set Kp to 7.0
    pid_Ki = $0080                             'Set Ki to 0.5
    pid_Kd = $0225                             'Set Kd to 2.14
    pid_Ti = 8                                 'Update I-term every 8th call to PID
    pid_I_Clamp = 100                          'Clamp I-term to max ±100
    pid_Out_Clamp = 511                        'Clamp the final output to ±511
    x = 0
    y = 0
    setpoint = 100                               
    pause 250                                  
    lcdout $fe,1                               
'****************************************************************
'                          Osnovna petlja                       *
'****************************************************************
on interrupt goto PIDcalc
     
     loop:
     if portc.3 = 1 then setpoint = setpoint + 1
     if setpoint > 1000 then setpoint = 0
     LCDOUT $fe,128,"POSITION = ",dec position  
     LCDOUT $fe,192,"SETPOINT = ",dec setpoint  
     LCDOUT $fe,148,"PID = ",dec pid_out        
     LCDOUT $fe,212,"PWM = ",dec y              
     pause 10                                   
     lcdout $fe,1                               
     goto loop                                  
         
     disable
PIDcalc:
     INTCON.1 = 0                                
     if INTCON.2 = 1 then                        
     PosHigh = POSCNTH                           
     PosLow = POSCNTL                            
     PosTemp = POSCNTL                           
     If PosLow - PosTemp = 0 then Goto Done      
     PosHigh = POSCNTH                           
     PosLow = POSCNTL
Done: 
     Position = POSHIGH * 256 + PosLow           
     advalue = position 
     pid_Error = Setpoint - ADValue               
     Gosub PID                                    
     Direction = pid_Out.15                       
     pid_out = ABS pid_Out
     x = (512 - pid_Out) + 512
     select case direction
     case 1
     y = pid_Out
     case 0
     y = x
     end select
     PDC0L = y.LowByte
     PDC0H = y.HighByte
     endif
     INTCON.2 = 0                                 
     resume                                       
     enable
     end

If any help pls.
Regards Robert

[HenrikOlsson]

The Henrik PID rutine work good but only when position and setpoint is max +/-50 !

OK, so what does it do if the setpoint is 51 then?

I see you're using On Interrupt and it seems you're using TMR0 as the source for the interrupt. It would be good if you could comment that section a bit so we don't have to read thru the datasheet in order to figure out what you're trying to do.

If I haven't missed anything you're running TMR0 in 8bit mode, clocked from the internal clock @20/4=5Mhz, prescaler selection is set to 1:2 which means the timer is clocked at 2.5Mhz, overflowing and generating interrupts at 9765.625Hz. There's no need to run the PID-loop at that speed, generally 1000Hz is good enough for motor control.

The Pause 10 statement needs to go away, and the LCDOut statements will likely mess with the timing as well. Read up on how On Interrupt works in the PBP manual. I highly recomend you look up Darrels Instant Interrupt routines as they don't suffer from the things On Interrupt does.

What do you mean by

and realy how make to motor clip +/- when position = setposition in some range about +/- 25% as break in position

It's really hard to understnad what you mean..... A deadband where anything within 25% of the setpoint is good enough or a following error trip and when the error is bigger than a set amount?

I've just received my copy of v2.60 so I can start using 32bit variables. I'm having a bt of a problem getting it going though. On top of that I fried my servo development board by connecting 24V to the 5V input so I need to get that sorted....