Re: [CAD_CAM_EDM_DRO] Auto tool changer

Jason Cox wrote:

> Hello,
>
> I was wondering if someone could please explain how an automatic tool changer on an industrial cnc mill works? Is there still a drawbar and are there sensors which tell me machine the tool is correctly engaged?

Generally, on the CAT-30 through -50 machining centers, they use a 'retention knob' which is
a bolt with a roughly ball-like head. They don't use a drawbar, but a spring-loaded clamp
that grips the retention knob with 1000 Lbs of inward pull, or thereabouts. Something
in the spindle assembly allows the clamp to release the knob for tool change. This way,
there are no drawbar threads to get stripped, and a consistant retention force can be
applied.

Generally, they have some sort of mechanism that will bind if the tool is not properly
engaged, or a sensor on the clamp that can tell there's no knob in the clamp, or the clamp
couldn't close because the tool wasn't all the way in the taper. Some of the controls have
elaborate dances they use to joggle a sticky tool into the spindle, others will just fault
on any improper condition and require manual attention.

Most of these CAT-xx systems have drive dogs on the spindle that engage drive teeth
on the tool holder, so the spindle has to be properly aligned before the tool can be
inserted.

As for how the tools are actually placed in the spindle and removed, there is no standard.
There are a large number of designs, and I'm not sure there is any clear benefit of one
over the other. Some just use air cylinders and jam the tools in, others have DC servo
motors that can feel and respond to insertion forces, etc.

Jon