[dinko]

Hi !!

I make my own CNC. but i have problems with sincronisation of 2 Stepper motors on X axis:

after some time is an X axis a few mm behind od A(other stepper motor on x axis) axis... but i heard that i need encoder to controle this thinhg... but my machine is an lo cost bild... adn i want to make as cheap as posible to arrange this.... can you hell me with something


thanx

[handlewanker]

A CNC build could be anything.......assuming it is a router with two steppers to twin screws on the Y which is the table drive.......(you wouldn't be putting two steppers on the X axis which is the cross beam drive).

If you are fitting two steppers to the table to prevent the slewing effect on the gantry when the cutter is to one side of the table either left or right, then you may have some drag which means you get lost steps and out of synchro movement.

For a DIY simple solution you could try driving each of the two screws with a seperate toothed belt and have the stepper motor in the centre.

If your steppers are too weak you will get lost steps when the cutter overcomes the drive of the steppers when the cutter is to one side of the table or the other.

If your gantry has the bearings on the guide rails too close together (longitudenally) in relationship to the span you will get a lack of guidence and a tendency to "crab" which puts a load on one stepper or the other and so lost steps.

The steppers may not be fully synchronised at start and so lead to misallignment.

If you are using a cheap controller you might not get enough power to drive twin steppers.

Your power supply might not be sufficient to drive twin steppers simultaneously.
Ian.

[cnc2]

Hi dinko !

Your problem requires linear encoders (glass scales...etc.) which are VERY expensive ! in your situation you'd need two linear encoders on X axis =>VERY VERY expensive

A cheap solution I can think of is to use two cheap rotary encoders $20each, converted to linear encoders you should also have two separate steppers drivers on the X axis for the steppers you're using so they are independent, How...should be simple.

First I hope you have an idea about how the cable driven photocopiers work. So you'd need two accurate/concentric flat pulleys (no teeth no V groove), then you'd mount the rotary encoders on these pulleys and secure it to the X axis with a plate so the encoder is mounted to the plate with the pulley spinning freely on a bearing...now you have an encoder that senses the position of a freewheeling pulley.

Now you stretch a cable along the X axis on each side, you turn the cable two or three times around the pulley and tighten the cable...now, should have one pulley on each side and when you move the X axis you should see these pulleys turning along the cable, turning the encoders.

You now have two quadrature incremental linear encoders on the X axis, and your next concern would be: how to use linear encoders with the software you're using.

I hope it helps...let us know if this is genius or brain fart.
cnc2.

[handlewanker]

Hi, you could use twin screws and a single stepper motor.......the stepper drives the right hand screw and the left hand screw is driven by a toothed belt connected to the right hand one....the screws will always be synchronised even if the belt has a small bit of slack in it.....at least you will have the two screws always driving which is better than missing a step on one stepper motor of a twin stepper drive system and having the cross beam crabbing or even worse jamming up if one stepper fails completely.

Having the left hand screw as a slave drive to the right hand screw makes it follow the drive at all times.

You could also have the stepper in the middle and drive both screws with toothed belts from one motor which will keep both belts short and reduce the stretch better than if you have one long one.

Another belt and braces method would be to have both screws driven by seperate stepper motors, BUT couple the two screws together by a long toothed belt so that if you miss a step with one motor the other will compensate and pick up the drive thereby always keeping the two screws sysnchronised without going to extreme lengths of encoders etc.
Ian.

[Al_The_Man]

CNC2 I can't answer your email, it shows recipient not allowing P.M.'s !
Al.

[Bob Adams]

Hi,
I have an Encoder that senses the rotational direction for CW or CCW, has one PCB for IR Detectors and Emitters. I it made for my MPG (Manual Pulse generator) for my lathe. You could make this work for what you want to do, if 50 ppr is OK. There is a PDF on how to make it.
Take a look at my webpage for more info.
Attachment 196796

Optical MPG and Switch Idea's

MPG (Manual Pluse Generator) Test using Mach3 - YouTube
Cheers
Bob Adams
CNC Projects