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IndustryArena Forum > CNC Electronics > SmoothStepper Motion Control > Smoothstepper encoder setup with index out of encoder?
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  1. #1
    Join Date
    Mar 2016
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    68

    Smoothstepper encoder setup with index out of encoder?

    Hi!

    I have a hall sensor as a 1 pulse/ rev index for spindle feedback and threading on my mini lathe, using mach3 and a parallel port. And a Gecko G540 as a BOB.

    I just bought an ESS (didn’t receive it yet) and I want to install an encoder on my spindle to be able to have much more pulses/rev, using then ESS rather than the parallel port, so I can get better sync when threading at low speeds.

    I have available a cheap rotary incremental encoder with 600 lines of resolution, but it lacks the “Z” (index) output. It has only “A” and “B” outputs.

    So would it be possible to use my spindle hall sensor as a “Z” ondex on the ESS encoder setup, and the “A” signal from the encoder?

    Or the Index and the “A” signal must come from the same device (encoder)?

    Regards, Rodrigo

  2. #2
    Join Date
    Nov 2013
    Posts
    4280

    Re: Smoothstepper encoder setup with index out of encoder?

    Hi,
    in order to do threading YOU MUST have an index signal, it doesn't matter particularly form where it comes so long as it fires once and once only per rev.

    Traditionally the ESS, and many other controllers, used the index signal not only to synchronize the start of the thread but as a signal by which to calculate
    the spindle rpm. In more recent times the ESS can accept multiple pulses per rev and use that to calculate the spindle rpm. The advantage being that the calculation
    happens many times per rev and therefore Mach is updated as to the actual rpm that much sooner.

    The source of the multi pulse per rev signal is not important. Thus I believe you could use one channel of your spindle mounted encoder and a hall sensor,
    if it has one, as an index signal. Alternately you could mount a separate hall sensor for an index signal.

    Having a timely and accurate spindle speed allows Mach to fine tune the Z axis advance per rev, or the pitch. Having said that Mach calculates the Z axis advance only
    once per rev so any increase in the accuracy of the spindle speed offers only a marginal increase in thread accuracy.

    Mach has traditionally relied on the spindle speed being constant, or very nearly so. That requires a spindle with large angular inertia and/or a high torque drive
    such that the cutting forces do not adversely affect the spindle speed.

    The ESS in the Mach4 plugin (note this is NOT implemented in the Mach3 plugin) allows for spindle PID. Thus if your spindle is speed controlled by
    a PWM signal, the multi pulse per rev (encoder) signal can adjust the PWM duty cycle to maintain programmed speed. This means a spindle
    of low or marginal rotational inertia or spindle power can maintain a constant spindle speed irrespective of cutting load. Thus there is a distinct
    advantage to using Mach4 and the ESS.

    Craig

  3. #3
    Join Date
    Mar 2016
    Posts
    68
    Quote Originally Posted by joeavaerage View Post
    Hi,
    in order to do threading YOU MUST have an index signal, it doesn't matter particularly form where it comes so long as it fires once and once only per rev.

    Traditionally the ESS, and many other controllers, used the index signal not only to synchronize the start of the thread but as a signal by which to calculate
    the spindle rpm. In more recent times the ESS can accept multiple pulses per rev and use that to calculate the spindle rpm. The advantage being that the calculation
    happens many times per rev and therefore Mach is updated as to the actual rpm that much sooner.

    The source of the multi pulse per rev signal is not important. Thus I believe you could use one channel of your spindle mounted encoder and a hall sensor,
    if it has one, as an index signal. Alternately you could mount a separate hall sensor for an index signal.

    Having a timely and accurate spindle speed allows Mach to fine tune the Z axis advance per rev, or the pitch. Having said that Mach calculates the Z axis advance only
    once per rev so any increase in the accuracy of the spindle speed offers only a marginal increase in thread accuracy.

    Mach has traditionally relied on the spindle speed being constant, or very nearly so. That requires a spindle with large angular inertia and/or a high torque drive
    such that the cutting forces do not adversely affect the spindle speed.

    The ESS in the Mach4 plugin (note this is NOT implemented in the Mach3 plugin) allows for spindle PID. Thus if your spindle is speed controlled by
    a PWM signal, the multi pulse per rev (encoder) signal can adjust the PWM duty cycle to maintain programmed speed. This means a spindle
    of low or marginal rotational inertia or spindle power can maintain a constant spindle speed irrespective of cutting load. Thus there is a distinct
    advantage to using Mach4 and the ESS.

    Craig
    Thanks Craig!

    I do have an individual spindle index sensor based on a Hall sensor.

    So you’re saying that, even if I use an encoder on the spindle to get more steps from each revolution of the spindle, the ESS plugin for Mach3, although allows to read with more accuracy the RPM, it won’t change the way Mach3 corrects the speed of the spindle by PWM? Mach3 (with ESS plugin) will still use only one step per rev to send a signal to adjust the PWM and the spindle speed, in case of threading?

    So for threading the advantage won’t be ...real?

    I’ll only benefit from this “more steps per rev advantage” if I use Mach4?

    Thanks for your answer!

  4. #4
    Join Date
    Nov 2013
    Posts
    4280

    Re: Smoothstepper encoder setup with index out of encoder?

    Hi,

    So for threading the advantage won’t be ...real?
    That is not what I said, I said the improvement would be marginal....real but small.

    I’ll only benefit from this “more steps per rev advantage” if I use Mach4?
    You might interpret that way but its not what I said either. To my knowledge Mach4 calculates the Z axis advance only one per revolution just as Mach3 does.
    What the ESS Mach4 plugin allows for is spindle PID. Thus its the ESS and its plugin that cause the spindle PID to maintain constant spindle rpm resulting in
    a more accurate thread.

    Craig

  5. #5
    Join Date
    Mar 2016
    Posts
    68
    Quote Originally Posted by joeavaerage View Post
    Hi,



    That is not what I said, I said the improvement would be marginal....real but small.



    You might interpret that way but its not what I said either. To my knowledge Mach4 calculates the Z axis advance only one per revolution just as Mach3 does.
    What the ESS Mach4 plugin allows for is spindle PID. Thus its the ESS and its plugin that cause the spindle PID to maintain constant spindle rpm resulting in
    a more accurate thread.

    Craig
    Ok, got it!!

    Thanks!

    So for threading a low speed/high torque pulley setup would be as important..

    Rodrigo

  6. #6
    Join Date
    Nov 2013
    Posts
    4280

    Re: Smoothstepper encoder setup with index out of encoder?

    Hi,

    So for threading a low speed/high torque pulley setup would be as important..
    Yes, very much so. Spindle PID is useful when you have a marginally powered spindle or you are taking aggressive
    cuts in order to reduce the number of passes required for production purposes.

    Craig

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