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Digital Read Out w Encoder

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  • Digital Read Out w Encoder

    Do most - some - all digital readouts accept rotary encoder input?
    I know there are several different encoders out puts.
    Which ones? Or what do I ask?
    Want to put encoders on my mills x and y axis. Not for
    control, just for position.
    Thanks for any help!!
    olf20 / Bob

  • #2
    The method/format is usually identical, a dual square wave quadrature signal, some use single ended, some differential, which is fairly easy to convert, either way.
    I have an old link somewhere for a rotary encoder digital read out using a small PC or laptop etc, using 1 to 3 encoders.


    • #3
      Thanks for the reply. How do I know
      which encoder to purchase?
      Here is one display I was looking at on
      Ebay. They have two axis displays with all
      the functions on one display.
      olf20 / Bob


      • #4
        Send an email to the seller and ask what resolutions it will accept in the way of scale.
        It may accept a number which can be selected either with entry or DIP switch setting.


        • #5
          I don't have a reply from the supplier yet, but
          here is a link with a diagram of different inputs.

          olf20 / Bob


          • #6
            So it looks like it takes single ended or differential input, the latter is better, but the input appears to be fixed at .02mm/div which means whatever resolution encoders you get, you have to gear them to suit the ratio between encoder and the required .02mm/div input.
            Could get tricky!
            How were you thinking of driving the encoders?
            Last edited by MaxHeadRoom; 08-30-2017, 05:55 PM.


            • #7
              My steppers are dual shaft. I was going to
              mount them to the shaft.
              olf20 / Bob


              • #8
                But what does one revolution of the stepper result in linear distance moved?


                • #9
                  While I am sure that there is probably one specification for this that is used more than the others, there are so many ways that this can be done that it is very difficult to guarantee compatibility. You talk about rotary encoders. There are many ways that a rotary encoder can be constructed and many types of output that they can have. Rotary is not as simple as linear but even linear encoders can have many different outputs.

                  Absolute rotary encoders will probably have an eight or ten or even more digit output. An eight digit output will only give 1.4... degree resolution. Each additional digit will cut that in half. This type of encoder would require one wire for each digit or a parallel to serial converter and only one wire. There are different ways in which the serial data can be encoded and some would require a clock signal on a second wire.

                  You may be talking about a quadrature rotary encoder which would output two digital signals "in quadrature" with each other. This type of output would require two wires and a decoder circuit at the receiving end.

                  Any of the above can operate with different logic Voltage levels ranging from around one Volt to 15 Volts or even more. Higher Voltage levels are more immune to random noise while lower ones are sometimes used for higher speeds. A transistor can swing an output through a difference of one Volt a lot faster than for 5 or 15 Volts.

                  To completely ensure compatibility, you would need to:

                  1. Specify the Voltage levels/logic family being used.
                  2. Specify the signals to be transmitted and received.
                  3. Specify the clock speed, if any.
                  4. Specify the mode of transmission: impedance, balanced or unbalanced, rise and fall times, and many more technical parameters.
                  5. Specify any encoding scheme being used.

                  And there are many more parameters that could come into play.

                  If you have a rotary encoder in mind or in hand, perhaps we can examine it and determine what it's output would be. Or if you have a specific readout that you want to use, we can look at it also. And keep in mind that it is possible to convert from just about any one of the above sets of specifications to any other. Modern PIC devices can almost make that easy.
                  Paul A.

                  Make it fit.
                  You can't win and there is a penalty for trying!


                  • #10
                    The OP's link shows the readout accepts either Quadrature input, for TTL single ended or RS422 differential.


                    • #11
                      Originally posted by olf20 View Post
                      Want to put encoders on my mills x and y axis. Not for control, just for position.
                      If your screws have any backlash, that will result in a discrepancy between your readout and the tables position.


                      • #12
                        The stepper motor shaft results in .200 per revaluation.
                        This is one of the several encoders that this supplier
                        And a 5V one

                        Don't have ball screws, but mill is within .0005 to .001 backlash.
                        Voltage for current control system is 5vdc, but this will be completely seperate
                        from the control system.
                        Thanks again for any help!
                        olf20 / Bob
                        Last edited by olf20; 08-30-2017, 09:53 PM.


                        • #13
                          Originally posted by RichR View Post
                          If your screws have any backlash, that will result in a discrepancy between your readout and the tables position.
                          Ditto with uneven wear, or even wear if there is no compensation available.

                          Open-loop measurements like that are always prone to errors from mechanical problems

                          Keep eye on ball.
                          Hashim Khan


                          • #14
                            So that's why glass scales are the preferred method.
                            I just did not want to mount them on the mill.
                            Maybe I'll have to relook at that.
                            olf20 / Bob


                            • #15
                              Got a reply back from supplier and they said the display
                              that I posted will not accept a rotary encoder.
                              O well on the something else.
                              Thanks for all the replies!
                              olf20 / Bob