Re: Chinese to Quadrature conversion

Yes, I see your point.

I think most of the chinese scales output every 50ms.

Most glass scales seem to be pretty much interchangeable. Resolutions of 5um, 1um, 0.5um seem reasonably common and DRO heads can often be set to accept a range of resolutions on each scale.

My Chinese made DRO states "input signal frequency <= 5Mhz so I think you could fire pulses pretty darn fast to catch up to the scale. If my maths is not out by some enormous factor (it could well be!) a 5um scale sending pulses at 5Mhz represents 1m per second!

Certainly I'd be lucky to be able to traverse more than mm's per minute and still stop at the closest 0.1mm!

Not sure I follow the need for unit conversion, as long as you have a way of scaling between input and output that's all you need isn't it? EG. input says you moved 500 whatevers, device fires out 1300 pulses, DRO head displays inches or mm as you like, they do the unit conversion.

I have found this -
http://www.youtube.com/watch?v=_2Cni0XOvI0&feature=related
which shows a caliper being moved and a quadrature output on an oscilloscope. I'm trying to get in touch with the bloke but no luck so far.

Peter

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Stephen Wille Padnos <spadnos@...> wrote:

> I think it might be kind of not-so-simple.
>
> As far as I know, the output from the chinese scales is in a serial data
> format, and it only gets updated a few times a second (maybe between 10
> and 100 times). Each update contains the new position, which could be
> many "steps" away from the previous position. So what the
> microcontroller sees is position A, then A+delta. It then has to output
> enough quadrature pulses to make the DRO display change by "delta". So
> a question arises - how fast do you output those pulses?
>
> You would need to have settings for input scaling (how big is a unit
> from the sensor scale?), output scaling (how big is one encoder tick?),
> and how fast the DRO can accept quadrature state changes.
>
> It's doable for a specific scale/DRO combination, but I imagine a
> product to do it would be more complex, since it would need to handle a
> range of settings. (and of course I haven't even mentioned the math to
> convert between units - it's not too hard, but it's not trivial in a
> microcontroller either). And then you would have people who think they
> could use this product for servo feedback (they can't). :)
>
> - Steve
>