demonicpicaxeguy
Senior Member
hi all yep me again for another adventure into the land of the bonkers.
I have my milling machine and currently have a pair of cordless drill motors attached,and currently i'm able to move it rapildy across from one limit to the other, my current trouble is linear position sensing,x 500mm, y 200mm ,z 200mm
so far as usaul money is a problem (isn't it always)
so actaully buying any type of linear positioning sensing device is not an option,,.. not at $600 odd for somthing badily made in china and all only do one axis.
i've looked at building myself a "string pot"
pro's : simple easy to construct
cons : datasheets specify up to 2% maximum backlash in 10 turn pot which would mean over 1 mm error.. no good
rotary encoders on the motors,
pros: backlash can be conpensated for in software, cheap
cons: backlash in the gearbox allows encoder wheel to reverse enough to give a false reading and losing position,
LVDT buying or building too expensive to buy to build however
pros: simple design and accurate with no backlash that developes,
cons: not easy to interface to requires a fair amount of processing to elminate noise,aparently,
resistive slider,
pros: dirt cheap, however cannot get one long enough to cover the x axis 500mm long
coms: requires a high res adc (not that it's a con)
so ladies and gentlemen, i'm down to a linear capacitive solution,
a simple parrallel plate design with one plate being a long triangle and the other being a rectangle, hooked into to some kind of capacitor based oscillator based circuit, which in turn can be measured by the cpp module,
i'm aiming for a resolution of 0.1mm over the full 500mm
sounds easy so far,
considering the wealth of knowledge on this forum, anyone got any ideas,comments,flames?
I have my milling machine and currently have a pair of cordless drill motors attached,and currently i'm able to move it rapildy across from one limit to the other, my current trouble is linear position sensing,x 500mm, y 200mm ,z 200mm
so far as usaul money is a problem (isn't it always)
so actaully buying any type of linear positioning sensing device is not an option,,.. not at $600 odd for somthing badily made in china and all only do one axis.
i've looked at building myself a "string pot"
pro's : simple easy to construct
cons : datasheets specify up to 2% maximum backlash in 10 turn pot which would mean over 1 mm error.. no good
rotary encoders on the motors,
pros: backlash can be conpensated for in software, cheap
cons: backlash in the gearbox allows encoder wheel to reverse enough to give a false reading and losing position,
LVDT buying or building too expensive to buy to build however
pros: simple design and accurate with no backlash that developes,
cons: not easy to interface to requires a fair amount of processing to elminate noise,aparently,
resistive slider,
pros: dirt cheap, however cannot get one long enough to cover the x axis 500mm long
coms: requires a high res adc (not that it's a con)
so ladies and gentlemen, i'm down to a linear capacitive solution,
a simple parrallel plate design with one plate being a long triangle and the other being a rectangle, hooked into to some kind of capacitor based oscillator based circuit, which in turn can be measured by the cpp module,
i'm aiming for a resolution of 0.1mm over the full 500mm
sounds easy so far,
considering the wealth of knowledge on this forum, anyone got any ideas,comments,flames?