Email: Password: Remember Me | Create Account (Free)

Back to Subject List

Old thread has been locked -- no new posts accepted in this thread
???
03/01/05 14:19
Read: times


 
#88779 - Yes it can but only...
Responding to: ???'s previous message
Yes it can but only if you take into account the sequence of two phase transitions like Russell has said.

If you use the digital approach such as the software sampled approach as Peter has implemented or an equivalent hardware approach without filtering then the uncertainty will accumulate always up to 1 count each time you stop on a fuzzy/buzzy edge where the fuzz is at a frequency that is higher than your sampling time but at such rate that the software or hardware sees it sometimes high and sometimes low at a different number of times than it has actually transitioned back and forth.

If you need full resolution of the quadrature wavefrom it then becomes necessary to design your system in a manner that it can live with this 1 count uncertainty accumulation. If the long term implication of this accumulation is unaccaptable to your design (where long term can be defined as say one or more revolutions of your encoder) then it is necessary to use an encoder with an INDEX pulse that you can re-sync to.

In the case of a linear encoder such as you may find along the slide on an X-Y table or in a linear actuator resyncing to null out the 1 count uncertainty accumulation can be more problematic since often the index pulse occurs only once along the whole encoder and is sometimes used as the HOME signal. In these cases it is necessary to get an encoder that has a TICK (my term ... but commonly known as a repeating INDEX) output that occurs at a repeatitive output say every 1024 quadrature periods. Such output does of course require extra wires and conditioning and capture circuitry at the microcontroller. If the linear encoder only offers a single extra output (TICK or single INDEX) then it would be necessary to select the TICK type encoder and implement the home position as a logical AND of a TICK pulse and an optical or proximity detector on the mechanism.

Michael Karas


List of 51 messages in thread
TopicAuthorDate
Digital position encoder            01/01/70 00:00      
   Dont do this.            01/01/70 00:00      
      Signals are not connected directly            01/01/70 00:00      
   Is assembly ok?            01/01/70 00:00      
      For Mehdi            01/01/70 00:00      
   its easy in software            01/01/70 00:00      
      but            01/01/70 00:00      
         same resolution            01/01/70 00:00      
      But...what if ?            01/01/70 00:00      
         So what is the solution?            01/01/70 00:00      
         absolutely no problem            01/01/70 00:00      
      Thank you            01/01/70 00:00      
         PLEASE not again            01/01/70 00:00      
            Sorry            01/01/70 00:00      
               list.hw.cz            01/01/70 00:00      
                  thank you            01/01/70 00:00      
            Re: PLEASE not again            01/01/70 00:00      
               Re frequency            01/01/70 00:00      
                  So what frequency do we sample at?            01/01/70 00:00      
                  I try to explain Peter's idea again            01/01/70 00:00      
                     We know it !            01/01/70 00:00      
                        Nothing ???            01/01/70 00:00      
                           it takes time            01/01/70 00:00      
      Code doesn't function            01/01/70 00:00      
         reverse direction !            01/01/70 00:00      
            This is not a problem            01/01/70 00:00      
               incorrect operation?            01/01/70 00:00      
               right connection ?            01/01/70 00:00      
   I dunno            01/01/70 00:00      
   Now...            01/01/70 00:00      
   check the sample condition !            01/01/70 00:00      
   clarify            01/01/70 00:00      
      @Erik            01/01/70 00:00      
         @Peter            01/01/70 00:00      
            Grey code            01/01/70 00:00      
               Grey code more            01/01/70 00:00      
                  Grey INCREMENTAL ?            01/01/70 00:00      
                     I guess 98            01/01/70 00:00      
                  Gray code            01/01/70 00:00      
      Not a gray code            01/01/70 00:00      
         Grey            01/01/70 00:00      
   Yes of course its Grey code            01/01/70 00:00      
      Absolute Vs Incremental            01/01/70 00:00      
         So now...            01/01/70 00:00      
            Yes it can but only...            01/01/70 00:00      
               Peter is right!            01/01/70 00:00      
   Lover not a fighter :-)            01/01/70 00:00      
      Lover of software            01/01/70 00:00      
         steps lost or not            01/01/70 00:00      
   Determining direction            01/01/70 00:00      
   Its not Grey, its Gray !            01/01/70 00:00      

Back to Subject List