On Wed, 1 Mar 2017, Kirk Wallace wrote:
> Date: Wed, 1 Mar 2017 09:55:49 -0800
> From: Kirk Wallace <kwall...@wallacecompany.com>
> Reply-To: "Enhanced Machine Controller (EMC)"
> <emc-users@lists.sourceforge.net>
> To: emc-users@lists.sourceforge.net
> Subject: Re: [Emc-users] MPG detents
>
> On 03/01/2017 04:42 AM, Roland Jollivet wrote:
>> I had always assumed that machine MPG's generated one state change per
>> click, but following Gene's discussion, I pulled out my 1988 Fanuc MPG, and
>> saw that it was also 4-states per click. Obviously, one 'pulse'/detent
>>
>> Does anyone know the rationale behind this?
>
> I don't know, but in my opinion ...
> there are four pulses per quadrature cycle and the pulses have to follow
> a proper sequence for forward and reverse rotation. This can produce a
> more reliable input for each detent location because a proper set of
> pulses are needed. If there is any electrical or mechanical noise
> (detent close to a pulse, machine vibration) and we use only valid
> cycles, rather than raw pulses, we will have a more robust input. It is
> sort of like using parity checking on data words and maybe hysteresis
> (more than one pulse to change a state either way).
>
>
> --
> Kirk Wallace
> http://www.wallacecompany.com/machine_shop/
> http://www.wallacecompany.com/E45/
>
I agree, I think the optimum is to use a 100 PPR MPG with 1X quadrature
mode (so 100 counts per rev) with the count occuring 1/2 way between detents
This means
1. You can move a known distance by feel
2. The MPG will not jitter back and forth with minor vibration/ hand motion
since it needs to move all the way to the "hump" between detents to count
Peter Wallace
Mesa Electronics
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