1 Continuous MCPWM at a time

[HenrikOlsson]

Hi,
What is this encoder you're using? Is it some kind of resolver with digital output? And why does the seqeunce change (not just reversing) when you reverese the direction of rotation? Or am I missunderstanding?

If knowing the intended direction of rotation isn't enough then I currently don't see how it's going to be done since the sequence is the same in both directions.

Are you sure you don't have a second output on that encoder? This looks like a low resolution sine-wave to me which leads me to belive what you have is some kind of SIN/COS resolver with a digital interface. (?) Do you have a datasheet you can link to?

The MCPWM module on the '4431 has dedicated faultinputs which can be setup to shut down the PWM. Either until the fault-input is cleared (good for cycle-by-cycle current limit) or untill a fault reset of the module is performed. Perhaps you could use that to stop the commutation. Otherwise you'll simply need to check the state of the switch as often as you need to - or use an external interrupt.

/Henrik.

[barneyfrance]

Hello,

Sorry for the late reply, it is nothing complicated like that. it is just 6 optical switches mounted on the rotor therefore 6 inputs on my pic that gives me a truth table. (in function of the inputs ON or OFF, I know what phases of the motor I need to turn ON/OFF).
For the clockwise rotation, it goes like this :
000000
000001
000011
000111
001111
011111
111111
111110
111100
etc

and for anti clockwise it goes like this :
000000
100000
110000
111000
111100
111110
111111
111110
111100
etc, as you can see for anti clockwise I am getting the same values but it is not the same phases ON, I need to turn ON (for 360 mechanical degrees, I have 3 times these 12 "cases").

Otherwise you'll simply need to check the state of the switch as often as you need to

Can you give me a simple example ?

Many thanks again for your answers

[HenrikOlsson]

Hi,
OK, if I get this right it should be enough to remember the previous state of the input.

FWD: 0,1,3,7,15,31,63,62,60,56,48,32
REV: 0,32,48,56,60,62,63,31,15,7,3,1

If the current state is 15 and the previous state is 7 we're going forward, if the current state is 15 and the previous state is 31 we're going backwards.

EncoderState = PortA
If EncoderState <> OldState THEN  ' Don't run commutation code if shaft hasn't moved. 
 
Select Case EncoderState
 
Case 0
  If OldState = 32 THEN  'We're moving FWD
  'Code for FWD
  ELSE
  'Code foe REV
  ENDIF

Case 1
  If OldState = 0 THEN   'We're moving forward
  'Code for FWD
  ELSE
  'Code for REV
  ENDIF
 
Case 3
  If OldState = 1 THEN   'We're moving forward
  'Code for FWD
  ELSE
  'Code for REV
  ENDIF
 
' And so on for all twelve states.
 
OldState = EncoderState  'Remember current state.
ENDIF

As for the switch, I just mean that if you don't think it's enough to check at the beginning of the loop you'll have to check it as often as you think is neccessary, for example in each case statement. Personally I think that it's enought to check it one time in the main loop since only one of the Case blocks will get executed anyway. But I may have missed something.

[barneyfrance]

mhhh that sounds great !!! this will work I think ! I have a switch that tells me to go forward or backward I can add it to this !
yes effectively the switch at the top of the loop in "case code" is enough.
However when I start my pic it won't move, will it ? because no previous state ? or am I missing something ?

[HenrikOlsson]

That's correct, since the shaft can be in any location on powerup you need to establish the proper encoderstate at bootup and then initialise OldState to the apropriate value depending on the desired direction of rotation - before entering the Main routine. You could do it with something like this but please doublecheck the sequence here, I'm not sure I've got it right.

'Get index of current encoderstate, Temp will be 0-11
Lookdown EncoderState, [0,1,3,7,15,31,63,62,60,56,48,32],Temp
 
'Now initialise OldState to correct value depending on desired direction of rotation.
If DesiredDirection = Forward THEN
  Lookup Temp, [32,0,1,3,7,15,31,63,62,60,56,48], OldState
ELSE
  LookUp Temp, [1,0,7,15,31,63,62,60,56,48,32], OldState
EndIf

[barneyfrance]

thx i'll keep try that in the morning =)

[barneyfrance]

actually this can't work because my reverse values are :
0, 32, 48, 60, 62, 63, 62, 60, 56, 48, 32....
I'm getting desesperate with these switches...

[barneyfrance]

fwd values : 0, 1, 3, 7, 15, 31, 63, 62, 60, 56, 48, 32
reverse values : 0, 32, 48, 60, 62, 63, 62, 60, 56, 48, 32

I have 2 truth tables with switches to turn on/off for these values.
Now i have a pot and a switch start/stop and a switch fwd/reverse..
Now we should not be able to change the sequence commutation if the pot is not 0 so I did a little code like this :

Direction VAR bit
direction = 0

Main:

        encoderstate1 = PORTA
        
        GoSub GetADC
        
        If ADRESH = 0 Then 'value of the pot stored in ADRESH
            If ADRESL = 0 Then ''value of the pot stored in ADRESH
                direction = PORTE.1 'switch for direction
            EndIf
        EndIf

if encoderstate = 0  then
'switches turn ON/OFF
elseif encoderstate = 1 then 
'switches turn on OFF
elseif encoderstate = 3 then 
..... etc
endif

goto main

I'm getting desesperate to put all this together with my switches
and my reverse sequence with if then. ifelse isn't working properly (need to have oldstate stored like you told me, Olson no ?)

[barneyfrance]

also, if my motor is moving forward and then suddendly i turn on switch to go backward, that won't be beautiful... I need to add some sort of security that allow to start the commutation code only if my pwm is 0 or something like that, no ?