I like the idea of having a physical switch at the end of travel, say 1/4" past the hall, that drives the signal line as well, but in my case I use these sensors on a variety of machines (a Sherline, a Taig, several home-builts) so I could never design one that would always work.
That said I've never had a failure in operation (I did shear off a hall because of an incorrect setup once) The other thing I like about the hall based solution is there is no physical contact, so mounting is a breeze. In some cases I have used double-sided foam sticky tape to mount the sensor and industrial grade double-sided tape to mount the magnet. DougM On Wed, Jun 15, 2011 at 1:13 AM, Roland Jollivet <[email protected]>wrote: > On 14 June 2011 23:20, Peter Loron <[email protected]> wrote: > > > On 06/14/2011 08:53 AM, Kirk Wallace wrote: > > > On Mon, 2011-06-13 at 13:47 -0700, Peter Loron wrote: > > >> Hello, folks. Can anybody comment on using hall effect switches on a 3 > > >> axis mill for limit / home switches? Seems like they would have some > > >> possible advantages over physical contact switches. > > >> > > >> Thanks. > > >> > > >> -Pete > > > My Hardinge lathe uses Hall limit and home sensors. The Z axis target > > > magnet is small and mounted such that there is minor protection from > > > chips. There is a small gap between the magnet and sensors when > aligned. > > > If chips are in the magnet area, they get wiped off, but not too small > > > such that small chips don't bind in the gap. the magnets are weak > enough > > > to have largesh chips fall off. The trip location accuracy only needs > to > > > be within about 2 or 3mm because, in my case, the home sensor is used > in > > > conjunction with the screw encoder index, which should be accurate > > > to .002mm or better. What I like about Hall sensors is that they are > > > machining fluid proof and will practically never wear out or change the > > > trip point or behavior over time. I tend to think using mechanical > > > micro-switches is silly, but a lot people use them to good effect. The > > > Hardinge Z axis uses a Hall sensor with magnet in a micro-switch > > > housing: > > > > > > http://sensing.honeywell.com/index.cfm?ci_id=154286&la_id=1&Ne=7&sid=1308EB555700&ci_id=154286&N=3591+4294966517&la_id=1 > > > Short URL: http://alturl.com/v2jzu > > > > > > These are mounted in a location well protected from chips, but the area > > > is not sealed from coolant, which is fine because the sensors don't > mind > > > fluids. > > > > > > The Z sensors are in an aluminum threaded barrel similar to this one: > > > > > > http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=480-3256-ND > > > Short URL: http://alturl.com/netsd > > > > > > They tend to be expensive, but it should not be too difficult to > machine > > > a barrel and pot an IC sensor with leads into it > > > > Yeah, I'm going to roll my own...I have a pile of Allegro sensors here. > > Also, retail on the Honeywell sensors is probably more that I've got > > invested into the whole mill... :-) > > > > > > > The traditional way for use of these sensors is to trigger on direct > approach. > The problem is overshoot. If you approach in this manner, in an error > condition, you can crush the sensor. > However, if you mount the sensor at 90deg to a strip plate, then you > approach the plate/leaf with a 'wiping' action. Now overshoot is not a > problem. Also, you can have a foam or other strip, to wipe the sensor first > on approach. One would have to experiment to see if the trigger hysteresis > is OK using this method. > For better homing, there really should be two sensors interlinked, a simple > switch at end of travel, coarse, and one using an opto slot on the > feedscrew, fine, to give a repeat homing within one or two encoder > counts/steps. > > Regards > Roland > > ------------------------------------------------------------------------------ > EditLive Enterprise is the world's most technically advanced content > authoring tool. Experience the power of Track Changes, Inline Image > Editing and ensure content is compliant with Accessibility Checking. > http://p.sf.net/sfu/ephox-dev2dev > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > ------------------------------------------------------------------------------ EditLive Enterprise is the world's most technically advanced content authoring tool. Experience the power of Track Changes, Inline Image Editing and ensure content is compliant with Accessibility Checking. http://p.sf.net/sfu/ephox-dev2dev _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
