Stephen,
I think I have located the answer for keeping the encoders on
the motors. Follow this link:
http://www.usdigital.com/products/etach2/
Please tell me what you think.
Dave
----- Original Message -----
From: "Paul Keeton" <pkeet...@woh.rr.com>
To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net>
Sent: Saturday, March 20, 2010 1:13 PM
Subject: Re: [Emc-users] G52 and Fanuc conversion to EMC
> So is there a converter that anyone is aware of or a method in emc that
> would allow you to take quadrature encoder signals and convert them into
> an
> analog tach signal? I have other Fanuc systems in the shop that use tach
> feed back on the motor and Linear Scales on the axis with no issues. Drive
> MUST see a tach signal or it will not work. The signal originally (On a
> Fanuc) is brought into the CNC master PCB and then routed to the drive
> from
> there. If an encoder is brought back to the CNC then the signal is
> converted
> on the Master PCB and then routed to the drive. Any way it goes the drive
> must see an analog tach signal. Fanuc uses a custom chip called an "LSI"
> to
> do this. Are you saying that a separate encoder or scale is impossible
> without an encoder on the motor or just more difficult? Difficult can be
> worked with. I suppose I could also modify the motor to use both.....Now
> that might be a simpler solution to get the best of both. Drive would get
> what it needs and emc should like it also.
>
>
> ----- Original Message -----
> From: "Stephen Wille Padnos" <spad...@sover.net>
> To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net>
> Sent: Saturday, March 20, 2010 12:10 PM
> Subject: Re: [Emc-users] G52 and Fanuc conversion to EMC
>
>
>> Paul Keeton wrote:
>>>> If there's a tach on the motor, then you should be able to route that
>>>> directly to the drive. My understanding is that some controls would
>>>> synthesize the tach feedback from encoder feedback. If you have one of
>>>> those, then it gets more complex (and I don't know the answer)
>>>>
>>> I would think that the simplest solution would be to change the motors
>>> to
>>> tach feedback and then install either linear scales on the iron or
>>> install
>>> encoders on the ballscrews. I would think this would be the simplest way
>>> to
>>> handle it?
>>>
>> It may be, it may not be.
>>
>> If there are already encoders on the motors, you should keep those
>> installed if at all possible. PID only works well when the feedback
>> device is rigidly coupled to the actuator - ie, when the encoder is
>> mounted on the motor. If you use only a linear scale for feedback, and
>> there is any backlash, then it will be difficult or impossible to tune
>> the PID. You can use a scale in addition to an encoder, as was done on
>> the G&L at MPM (I think there's a case study on the linuxcnc.org
>> website, but I'm not sure where).
>>
>> Encoders on the screws should be OK if there's no backlash between the
>> motor and the screw. It's a good rule of thumb to consider that every
>> step the encoder is moved away from the motor makes PID tuning harder.
>>
>> - Steve
>>
>>
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>
>
>
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