Re: [CAD_CAM_EDM_DRO] Rotary Axis home and/or limit switches

Stephen Wille Padnos wrote:

> ya_nvr_no wrote:
>
>> I have added a couple of rotary axis's But am having an issue with coming up with a good way to home them. One switch gives me a home position but if I rotate one revolution the switch is made again. I am using CNCpro, it uses a limit switch as the home switch.(would another program handle this better?)
>>
>>
> EMC2 would ignore the home/limit input when it's not actively homing.
> Having a limit switch on a rotary axis that can revolve > 360 degrees
> doesn't make much sense, since there is no real limit to travel.
>

Actually, there can be if one uses something which is indexed to the
rotary shaft. For example, imagine the effect of a milling head which
must be "trammed" manually every time it is used vs. having a zero index
pulse to the index to the trammed position. The encoder/motor could
easily be driving a worm to locate the Bridgeport-type head and it
easily could make 180 turns per revolution of the head. The limit
switch should not be the home switch since home wants to be vertical and
driving the head 45º or 90º each cycle would be a poor choice, whereas
driving it to the "home" position might be easy, generally you would
already be there. However the home switch might not have enough
resolution, and the real "home" position would have to be the
motor/encoder home zero index pulse plus the home switch transition.

Home would be defined as "the first zero index pulse after the home
switch closes." just as the zero index pulse on some encoders is not
just the outer track, but the outer track plus one channel state or both
channel states (e.g. ZIP is true AND "A" is high AND "B" is high, which
is far narrower than the zero index pulse is on the encoder.) Index
pulses are often not one slit, but a large number of them set up so only
when they are properly aligned does the pulse go true. Similar to a
vernier in concept.


--
David G. LeVine
Nashua, NH 03060