Michel Gouget wrote: > Dear All, > > I am considering adding encoders and home switches to my Sherline CNC mill. > > I see 2 benefits: > 1) Being *sure* of not loosing steps (estop, ...) > 2) Using (low precision) home switches and the index of the encoder, I get > *excellent* repeatability when homing. > > The mill is equipped with regular sherline steppers (135 oz-in, 1.8 degrees) > and a P/N 8760 driver (800 step/rev.) connected to a parallel port. The > steppers have a double ended 1/4" shaft. They are driving a 1mm master > screw. Everything is connected to EMC2 running on a dedicated PC. All is > actually working fine, with rapids of 450 mm/mn. I have a 4th axis on a > turntable with the same stepper. > > I expect to use US digital E2 quadrature encoders with 400 CPR and index, > giving a maximal theorical resolution of 1/400 mm, more than needed :) for a > cost of about ~200$. > > I expect to use the E2 T model, which will be sticked on the rear of the > stepper, in place of the handwheel, using the US digital centering tool. > > I expect to connect the outputs of the encoders to a second parallel port on > a PCI card. > > My questions: > > 1) Is it stupid :) ? Basically - No - working via software - maybe
> 2) Has anyone already done that? The Taig closed loop controller does it via a modified step and direction board, which adds extra steps itself when it detects a missed step. If the required count is more than 200 steps adrift, it flags a fault. > 3) Is a parallel post fast enough for reading the 4 axis encoder pulses at > full speed? It probably can, but in combination with the pulse generation there may be a timing problem. You will only get the encoder edges sampled at the read rate, so while raw counts should be correct, there is a problem with fine control. As long as you do sample fast enough you should see all edges. > 4) Are there other encoders suitable? Is 400 CPR the correct value? If my calculations are correct that will give you 1600 edges in quadrature which will be fine with your 800 step motor. You should see two steps per one that you request. > 5) I suspect that HAL+classicladder is powerful enough to handle the > *complex* homing (eg. Zero till the home switch trips (low precision > microswitch), then forward to the encoder index pulse, for all joints). Am I > right? If not, is it possible to program the homing sequence in C ? > > 6) Any tips in setting up HAL? PID tuning? Best mode for the parallel port? > Any existing example? Not had the closed loop controller running with EMC, only the older open loop controller, but the hardware based solution does not require the encoder fed back to the computer anyway. -- Lester Caine - G8HFL ----------------------------- Contact - http://home.lsces.co.uk/lsces/wiki/?page=contact L.S.Caine Electronic Services - http://home.lsces.co.uk MEDW - http://home.lsces.co.uk/ModelEngineersDigitalWorkshop/ Firebird - http://www.firebirdsql.org/index.php ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
