Frank Tkalcevic wrote: >My lathe CNC conversion uses a servo motor to drive the spindle. It is >4000ppr, with an index pulse, controlled by a 5i20 and 7i33. It uses a 1:3 >pulley ratio. Can I set this up for threading? > > Not without adding some hardware.
>I had a quick try, machining a simple test thread, but as I expected, using >a standard setup, I got a 3 start thread because there are 3 index pulses >per spindle revolution. I suspect adding a simple pulse divider (divide the >index pulses by 3) wont work either, because there is the index-enable pin >which not only signals an index, but resets the encoder count to zero at the >5i20 level. > > Yep. There must be exactly one index per revolution for threading to work. >If there is no component already out there, I was thinking of a component >that sits between "motion" and the 5i20 encoder. It knows how many counts >per revolution, so when it gets to 2 1/2 revolutions, it can set up the >index-enable link to notify "motion" and reset the 5i20 - "set up" meaning >set index-enable to true. Any thoughts? > > I'm pretty sure that trying anything in HAL, after the 5i20 hardware/driver, will be futile. The index-enable and index pins are on the driver, anything that goes between the driver and motion would have to deal with having the position change suddenly, but only when it's the "right" index, etc. I think there are two options here, both require you to put a sensor on the spindle itself (something that turns at the same speed as the chuck). First, there's an index mask option in the hostmot2 firmware. You set the -index-mask (and optionally -index-mask-invert) bits to true, and the index will only be active when another input is on. Connect that other input to the correct Index Mask physical pin, and you have an encoder that only works when the spindle is close to the right spot. Second, you can just connect the spindle sensor to the index input for the encoder. There's no requirement for the index input to come from the same device as the quadrature signals. The advantage to using index mask is that the index is tightly coupled to the encoder - it's still using the encoders index mark. Additionally, the spindle sensor doesn't have to be very accurate, as long as it's on over some range that covers the index mark, you're golden. The advantage to using an independent index sensor is that you can change pulley ratios, and even use non-integral ratios, and it will still work. Additionally, any belt slip will be accounted for (in the index position anyway, but not for velocity control). The disadvantage, of course, is that you need to be more careful when installing the index detector, since it should have a very repeatable trip point. Hope this helps - Steve ------------------------------------------------------------------------------ The NEW KODAK i700 Series Scanners deliver under ANY circumstances! Your production scanning environment may not be a perfect world - but thanks to Kodak, there's a perfect scanner to get the job done! With the NEW KODAK i700 Series Scanner you'll get full speed at 300 dpi even with all image processing features enabled. http://p.sf.net/sfu/kodak-com _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
