[EE]: USB stepper drive system

There has been a lot of talk lately on the list promoting the development
of
some "smart hardware" to supplement the PC's poor performance. The second
item that is rearing its ugly head is that pc's are rapidly losing their
ISA
slots and their serial/parallel ports. I also subscribe to the usb-devel
list and am getting a pretty good feel for what usb is capable of. I use
EMC
as the PC end smarts. It basically works well as an open source gcode
interpreter that expects to output a drive signal and receive back an
encoder signal for each axis every 1ms or so (programmable). The usb bus
can
be thought of as a fast 12mb/sec serial port (about 1/2 of this is actually
usable). I am starting to think along the lines of a usb board that
contains
some number of rate generators (like Marriss's DDS system or even pic based
software DDS) to generate the stepper drive signals smoothly and the same
number of encoder interfaces (either in hardware counters or possibly pic
based software interfaces). The interface would use an isosyncronous read
port and a write port to read/write the command/status signals every ms. A
four channel card would cover most applications although once design is a
little further along, it may be possible to put 6 axis on a card and
produce
them in various states of population. USB support is getting pretty good
under linux, with quite a few example drivers. Between the lists, there is
a
lot of talent available... where to we need to be in a year from now? Would
USB make sense in a shop environment for getting machine control
information
in/out of the computer?
Would DAC outputs for servos make sense? Would +-50ma outputs make sense
for
driving hydraulic servo valves? How much would the board cost to produce?
It
is going to be hard to beat the cost of an add-in parallel port. The card
would definitely make laptops or low end Macs like an iMac attractive as a
dedicated controller. Just some ideas to think about for the next
generation
cnc controllers.
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Lawrence Glaister VE7IT email: lg@...
1462 Madrona Drive http://jfm.bc.ca
Nanoose Bay BC Canada
V9P 9C9
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