PMDC SERVO MOTOR WITH quadrature encoder DRIVE ?

[HenrikOlsson]

Hi,
The encoder outputs channels which has a 90° phase shift between them.

The QEI-module can be set to 2X or 4X mode (X4 is the most common) but the easiest to understand is the 1X mode....

Simply, if the B channel is high on the rising edge of the A channel then you count up, if the B channel is low on the rising edge of the A channel then you count down. In 2X mode you "trig" on the rising edge of both channels (giving you a resolution of 2X the line count of the encoder) and it 4X mode you trig on the rising AND falling edge of BOTH channels (giving you a resolution of 4X the line count of the encoder).

If you look up incremental or quadrature encoder on Wikipedia you'll find more details.

/Henrik.

[mackrackit]

Thanks Henrik,

I understand now.

[phoenix_1]

Now I am probe on many ways to do next but I cant to image how.
1. I was setup count for QEI with friends from these forum to count from 0 - 12500 - becous my motor have gear 6.25:1 and 6.25*2000 = 12500(reding of one turn of motor shaft with 500 lines encoder) give me full 360' of output shaft range.That work extra.
Next : If I want to move for example 1mm on my mechanic I need one turn of output shaft that give me easi to control position of count from CW 0-12500 or CCW 12500 to 0.That is all in 16bit counter.
But what if I need to move more then 16bit counter ?
OK I can use PBPL and define 32bit variable - I was probe and it work 100%.
I can easy set to se if X VAR LONG number 25000000 that give me 25000000/12500 = 2000mm - inpresive!
But how I can my software variable defined as LONG from 0 - 25000000 to increment or decrement from hardware COUNT buffer wich count in circle from 0-12500 and vice verse ?
Is any idea becouse all what I was probe give me garbage of result.

Regards Robert

[phoenix_1]

OK now next step are steped.
I write calculation to increment in CW my variable defined as LONG to be incremented from position buffer
which go from 0-12500 and again and again..

' Pic 18F4431 @ 20MHz true XTAL
    define osc 20
    DEFINE HSER_RCSTA 90h            
    DEFINE HSER_TXSTA 24h            
    DEFINE HSER_SPBRG 64              
    DEFINE HSER_CLROERR 1             
    ADCON0=0                          
    ANSEL0=0                          

    PortA = 0
    PortB = 0
    PortC = 0

    TRISA = %011100                 
    TRISB = %00000000
    TRISC = %10000000                 

    QEICON=%10011000
    DFLTCON = %00111000              
    MAXCNTL = %11010100             
    MAXCNTH = %00110000                
    PosLow VAR BYTE                    
    PosHigh VAR BYTE                   
    PosTemp VAR BYTE                   
    Position VAR WORD                     
    y var LONG
    x var BYTE
    x = 0 
    y = 0
    POSCNTL = 0                     
    POSCNTH = 0                       
    PIR3.2 = 0  
    CLEAR
        
    Start:
    Gosub GetPosition
    y =  (x * 12500) + position 
    HSEROUT [dec y]
    Pause 10                      
    Goto Start                       


GetPosition:
    PosHigh = POSCNTH                     
    PosLow = POSCNTL                       
    PosTemp = POSCNTL                         
    If PosLow - PosTemp = 0 then Goto Done  
    PosHigh = POSCNTH                     
    PosLow = POSCNTL  
Done: 
    Position = POSHIGH * 256 + PosLow    
    if PIR3.2 = 1 then x = x+ 1
    PIR3.2 = 0
    RETURN 
    END

Now I can count a long trip of mechanic of machine which is present in LONG variable in CW direction.
But I have new problem in my head all these days and it is next.
I have BIT which indicate direction of motor and it is in QEICON.5.
If QEICON.5 is 0 then we go CCW and if it is 1 then we go CW direction.
Now if we go CW and stop motor it wil be 1 all the time to next move
and if we go CCW it will be 0 and after we stop from CCW it will be 0 all time to next move..
Confuse how to make matematic to implement new formula for decrement LONG variable in CCW :
y = y - (12500-position) or similar becous in CCW position go from 12500-0 and again 12500-0....
If any idea or someone want to help THANKS.
Regards Robert

[mackrackit]

Maybe I am missing something but if you stop the motor and then restart it you know the direction?? Set the direction bit when you start the motor.

[phoenix_1]

Here is code which can measure and put to Y variable defined as LONG position of mechanic on machine to 32bit and count up and down.
I am not good programmer but code work good.

' Pic 18F4431 @ 20MHz true XTAL
    define osc 20
    DEFINE HSER_RCSTA 90h              ' Enable serial port & continuous receive
    DEFINE HSER_TXSTA 24h              ' Enable transmit, BRGH = 1
    DEFINE HSER_SPBRG 64               ' 19200 Baud @ 20MHz, 0.16%
    DEFINE HSER_CLROERR 1              ' Clear overflow automatically
    ADCON0=0                           'Turn of ADC
    ANSEL0=0                           'Make Port A inputs Digital

    PortA = 0
    PortB = 0
    PortC = 0

    TRISA = %011100                    'QEI pins as inputs.
    TRISB = %00000000
    TRISC = %10000000                  'USART RX pin as input.

    QEICON=%10011000
    DFLTCON = %00111000                ' enable error filter for all capture inputs
    MAXCNTL = %11010100                'low set for maxcnt of 12500 becouse have gear 6.25:1
    MAXCNTH = %00110000                'hig set for maxcnt of 12500 becouse have gear 6.25:1
    'MAXCNTL = %00000001               'lowbyte = 207
    'MAXCNTH = %00000000               'highbyte = 7 but after math: highbyte * 256 = 1792 + 207 = 1999
    'QEICON = %00010100                'Setup QEI, 4X mode, reset on index. 
    PosLow VAR BYTE                    'Storage for the low byte of encoder count
    PosHigh VAR BYTE                   'Storage for the high byte of encoder count
    PosTemp VAR BYTE                   'Temporary storage for low byte of encder count
    Position VAR WORD                  'Actual encoder position, 16bit word.
    y var long                         'Total pulse count storage variable 32bit
    x var byte                         'Number of full shaft rotation of 360'
    z var BIT                          'Actual bit if any move of shaft to any direction
    h var BIT                          'direction bit 0 for left , 1 for right turn of encoder
    z = 0                                 
    x = 0 
    y = 0
    h = 0
    POSCNTL = 0                        ' clear lowbyte of counter for start
    POSCNTH = 0                        ' clear highbyte of counter for start 
    PIR3.2 = 0 
    CLEAR
        
    Start:
    Gosub GetPosition
    y =  (12500 * x) + position                    ' increment  total counter
    if z = 1 and h = 0 then y = y-(12500-position) ' dectement  total counter
    HSEROUT [DEC y]                                 ' debug via rs232 @ 19200
    Pause 100                                       'Wait....  
    Goto Start                                     '...and do it again.


GetPosition:
    z = 0
    PosHigh = POSCNTH                           'Get high byte of counter
    PosLow = POSCNTL                            'Get low byte of counter
    PosTemp = POSCNTL                           'Get low byte again  
    If PosLow - PosTemp = 0 then Goto Done      'Compare, if equal we're done.
    PosHigh = POSCNTH                           'If not, get values again.
    PosLow = POSCNTL
    z = 1 
Done: 
    Position = POSHIGH * 256 + PosLow           'Put high and lowbyte together. 
    h = QEICON.5                                'QEICON.5 for right = 1 for left = 0 
    if PIR3.2 = 1 and h =1 then x = x+ 1
    if x <> 0 and PIR3.2 = 1 and h =0 then x = x- 1
    PIR3.2 = 0                                  'PIR3.2 maxcount transition down or up was detected
    h = 0
    RETURN  
    END

[mackrackit]

Here is code which can measure and put to Y variable defined as LONG position of mechanic on machine to 32bit and count up and down.
I am not good programmer but code work good.

What is a good programmer???
If it works as you want then it is good.