Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: Overloaded on March 04, 2008, 07:01:48 PM
-
Hi Folks,
I have a stepper motor that has a magnetic encoder on it. It has what looks like a small fine pitch gear on the shaft and a pick-up mounted adjacent to it with a small air gap. The head resembles the pick-up head on a cassette tape player....sort of.
Any way, there are 4 wires. 1 brown and 3 gray. I assume that there is 5v+, A, B, and 0V.
What is the procedure to determine which wire is which? I've got a good Fluke meter.
Thanks for anything,
RC
-
measure the resistance betwen all wire combinations and tell me. if one wire has not resistance whit the others verify this wire continuity whit chassis
i suspect this head has not suply voltage input and need amplification to get logic signals.
Josep
-
Hi, RC
Sounds like a small Tack-o (Tachometer) to me, But they usually only have 2 wires.
No part # Hu!!, Seen some similar, on small servos
Give us the values, Chip
-
Josep, it is connected to a PCB so you are probably right about the amp.
Chip, this is a Hybrid stepper/servo.
This is probably futile....here are the readings.
Brn to #1 .329k
Brn to #2 .431k
Brn to #3 .321k
#1 to #2 .315k
#1 to #3 .431k
#2 to #3 .324k
When the head is brought near the wheel these values roughly double.
Thanks,
RC
just an experiment....I can trash it.
Oh...I cut it loose from the pcb to check it.
-
Hi, RC
What's the Part number on the IC' the wires go to ?
Any difference if you reverse the meter leads ?
Thanks, Chip
-
Might be able to find some info. off of the ICs here that will help.
http://www.datasheetcatalog.com/datasheets_pdf/L/M/3/3/LM339N.shtml
Brett
-
Reversed leads, no difference.
I'll try to send pic. Multi layered traces, I cant track them.
Hope you can make out the #'s.
Hey Brett, Excellent resource. Thanks. I'll save that.
I fried the inputs on this board. Cost more to repair than to replace..at least that what the dealer says.
I have an application for this encoder if it doesn't get too complex.
Optical ones are cheap enough on FleaBay.
If we're getting in too deep, just cut me off. ;)
-
Hi, Rc
I think this would be a go to E-bay solution for sure, Your not going to get a true A-B pulse out-ua this one.
Chip
-
judging from the logo on the smaller SMD chip fitted to the board this looks like custom chip jobie
Looking at the tracks I would think it translates the magnetic changes in a similar way as the newal linear encoders
Wetter it is totally passive or actually active is unclear, coolmuscle is not very forthcoming in info on it.
You could look for patents in their name, often explains a lot.
The larger IC is a standard NEC micro which likely deals with the motion and communications
I scoured the net and could find no data in the IC (expected)
interresting product though
JB
-
Thanks for taking the time guys.
This one is history.
RC
-
this pik-up seems to be equipep whit HALL sensors, the colored wire is positive power suply the wire has no change resistance when aply magnetic field near is negative and the other two wires are chan A and chan B ouputs.
Josep
-
Thanks Josep,
I may tinker with it later. I'll go with 5V and see what happens.
RC
-
by all mean try it, however
if is was a simple AB encoder why would the manufacturer not directly interface with the micro, since it has a timer/counter input
further if it is a simple AB, how does it create 5000 steps out of that toothed wheel which only has 60 or so teeth...
as said before my bet is that these are two magnetic sensors, quite likely coils and that they are exited by the custom chip
both are set at a specific distance from eachother and they can both see the same teeth of the wheel, by measuring the loading on the coils induced by the proximity of the teeth, current and timing and smart analog stuff this thing can interpolate the position.
alternatively it is a Hal effect sensor, and they measure the analog level altough that would require extensive calibration and be subject to noise (especially magnetic)
We have been playing with a magnetic sensor to measure current on busbars ( think 400A and above), great idea only the local earth magnetic fields affected the measurements...
A better explanation can be found at the newal site, the sphersyn system
-
Thanks JB,
I realize now that it's not a simple encoder. This thing has a brain.
When the motor was working, it could be set to 50,000 PPR.
Thanks for the Spherosyn tip.
RC
-
If a hall efect sensor would require extensive calibration and be subject to noise (especially magnetic) whi are used in spark ingnition in cars ??
or near coils and magnets in a brushless motor conmutation ??
in this two examples have a lot of electromagnetic disturbances and requiere very precision in trigering.
if this encoder have litle coils in the pik-up whi varies the resistance when aprox. to the magnetic disk??
i`m not enable a discuss on this theme (simply my poor opinion).
Josep
-
first of all my last post seems harsh, it was not intended to be :-[
in most applications hall effects are used as switches, and thus either a schmitt trigger circuit is added or build-in
with the use of hall effect basically if it moves (as in cyclic) the electronics look at the flank of the signal, if it is not cyclic (like proximity) you look at a "arbitrary" level
and decide stop/move
generally in the electronics world , if you can reduce a real world analog signal into electronic timing signal it is always easier to measure/reproduce then a analog signal level
in order for the this encoder to work (and I was a factor of 10 out) it will have to interpolate to quite a small degree
so take the 50.000 CPR , that's 0.0072 degrees per click, so the positional change of any teeth is minute the change in distance change be teen the sensor and a teeth is even less, The hall effect sensor must thus be able to measure sub 0.001mm distance changes and translate in a proportional voltage level change.
this then has to be captured by the electronics, which if substantially below mV becomes hard to reproduce
this (analog 2 digital) is a large part of my dayjob and it gives me and my co-workers grey hears ..... :'(
Still these motors are cool .....intended
JB