Le 22.12.2011 17:45, Anders Wallin a écrit : >> I have been given a quote for electrochemical machining of an encoder >> for my project. >> http://www.photofab.co.uk/index.php/services/chemical-etch-photo-etch/ >> There is a £95 setup charge, then another £100 for a sheet of parts. I >> get 25 of my design (75mm dia) on a sheet, but only need 6 or so. >> The material I want to use is 0.3mm 304 stainless. I can add different >> designs to the sheet for no extra charge. >> Does anyone have anything intricate that they need making from >> stainless shim like this? > What resolution can they produce? > How do you read the encoder, transmission/reflection of IR-LED or ? > Would the pattern produce a square wave-signal, or a sine-wave (which > can be 'interpolated' to yield higher resolution) > > a dream project of mine would be a telescope mount. To minimize > tracking error one should measure the rotation directly on the geared > axis (not the motor) and one wants maybe 4 million pulses (22 bits) > per rev for that. > > From what I've understood it's done by A/D converting a sine-wave > encoder, so if you get e.g. 8 to 10-bits of reliable interpolated data > then you > want an encoder with 12 to 14 bits of sine-shaped counts, i.e. up to > 16k-counts/rev. How big a circle would that require?
interpolation on a 1Vpp coder can quite easily go to 12 bit for 1/4 of period (interpolation is done on the arctan of (sin/cos), there is 2 signals in quadrature). This give 16384x interpolation factor. In this case you only need about 250 pulse pet turn. for your application, an "industry standard" 1vpp encoder with 2500 period per turn, interpolated with 9 bit is enough. The interpolation can be done with an appropriate micro controller (must have simultaneous sampling of both channel) ------------------------------------------------------------------------------ Write once. Port to many. Get the SDK and tools to simplify cross-platform app development. Create new or port existing apps to sell to consumers worldwide. Explore the Intel AppUpSM program developer opportunity. appdeveloper.intel.com/join http://p.sf.net/sfu/intel-appdev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
