On 02/16/2016 12:42 PM, Lester Caine wrote: > On 16/02/16 10:21, Bertho Stultiens wrote: >> It seems that the micro-switches are well suited for the purpose, but I >> guess some hard (unbiased) data has yet to be gathered (outside of a mill). > > The alternatives seem to have the same problems of repeatability. Using > a hall sensor or optical one will give the same problems. Micro-switches > are at least inherently mechanically constrained.
Indeed, unless you can crush them. There must be a run-into-the-wall protection, as mentioned earlier, to prevent killing your switch. > I do look at the kit available and wonder if simply adding scale bars > locked to the table aren’t a sensible compromise here? You have an > absolute on on the machine which can be used not only to define a home > position, but also to add limits based on the actual job? Which could be > used where the natural home position IS in the middle of the work piece. > I'm not talking about a set of inputs that are used as part of any > closed loop control, but simply as has been done in the past, a check > that particular points are in the right place. It could be used to > measure the current backlash between the motion elements and the base > machine, with a 'calibrate' cycle as part of the home process? The point of the switches is not to be correct in perfection. The background here is that the router is located at the local hackerspace, where many will have access to the machine. Not all have the same experience and a run-into-the-wall can be expected from a novice. Well, an experienced person might just hit the wrong button too ;-) The router has currently end-stop switches, but none on the other end of the axes. I'd like to have the controller limit the movement such that it will stop the machine when running into the wall. This will not prevent hitting anything with the spindle. Using a "proper" home (0,0,0 position) will not only make it a lot easier to recover from an error, but, it allows the machine to be shut down. Especially the "shut down" is important because it is not expected that this machine runs 24/7, but mere hours at a time, losing its position in space every power-cycle. The natural home, as you say, is the work piece. But that is just an offset. > Cheap Chinese readout bars can be used as one can easily compensate for > the latency between readings, and I know in essence you are discussing > the provision of a 'hardware' zero point on the axis, but as a cross > check that the machine has not missed steps, or a flexible means of > moving the machine to a fixed position to recover after a collision or > stall it has merit? You are right. It is a hardware zero point. Losing steps is my least worry at this moment, but it surely has crossed my mind. It is, as you say, the collisions I am (slightly) worried about. And then, the power-cycling of the machine. It is mostly a balance of how much it'll cost and how much I can prevent problems when many different operators with different experience and volatile g-code handle the machine. The machine was cheap, so investing perfection is a bit off. -- Greetings Bertho (disclaimers are disclaimed) ------------------------------------------------------------------------------ Site24x7 APM Insight: Get Deep Visibility into Application Performance APM + Mobile APM + RUM: Monitor 3 App instances at just $35/Month Monitor end-to-end web transactions and take corrective actions now Troubleshoot faster and improve end-user experience. Signup Now! http://pubads.g.doubleclick.net/gampad/clk?id=272487151&iu=/4140 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
