2010/4/24 Andy Pugh <[email protected]> > The usual sort of encoder is not desperately convenient for mounting > on a machine tool spindle, as such applications generally require a > sizeable through-hole. > > Car engines nowadays use a pickup on the crank to tell the engine > controller the current crank angle. These used to be a proximity > sensor on the starter ring-gear. To get an index pulse one or two gear > teeth were machined short, a scheme normally referred to as 32-minus-1 > or 64-minus-1 or whatever the engine actually had. Thus the index and > the pulses were detected by the same sensor. > > Nowadays this is rarely the case, the typical crank sensor ring is a > magnetically encoded disc mounted behind the crank pulley. Typically > with a pressed-steel hub with a 3" or bigger through-hole. In fact I > have pressed one onto the outside of a 4" 2-Jaw-chuck on a test rig. > > The advent of stop-start-stop systems on vehicles (which I hated the > idea of but actually quite like in practice) has meant that engines > are now required to start from hot in 0.3s or less. The single-sensor > systems can't tell when the crank has rotated backwards as the engine > stopped, so it has to wait to see an index before it can inject fuel > and start. This can take a significant proportion of the allowed time. > So, the latest development is a dual-pickup using quadrature to detect > back-rotation. This suddenly makes them look quite attractive for CNC > machine use. > > These devices are inexpensive commodity items intended for rough > service. I think the sensor is $5 and the ring $20. The only reason > that we can't use them on tool spindles is that the "missing tooth" > index scheme is not suported by EMC2. I wonder if it is worth adding > it? > > Missing tooth scheme can be very good idea to EMC. In that case the sensor are cheap, the gear can be made with drill press (thing can do the work with only 3 tooth and 1 missing) and at least the only one pin on printer port is needed. The best way I think is to make just one more RT component that have one input pin from outside world (missing pulse input) and two output pins (phaseA and Index) so in HAL that can be coupled on just any other component.
Slavko. ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
