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Author Topic: Optical Encoder  (Read 4650 times)

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Offline ziga

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Optical Encoder
« on: May 09, 2008, 10:44:35 AM »
Hello
I know this will be a little of topic, but i dunno in were should i post this.
Had anyone got any problems with machine keeping up with the steps? I am using a gecko drive and a 1.8°stepper motor, but when i was cutting wood, it seems to louse a few steps.
I do not like that, and i think this could be solved with encoders.
I was loking on the internet and when i was searching for some cheap encoders the most cheap ones i found were 100€ - 250€ so that is too much for me.
Does anyone know were i could get some cheap encoders wich would have a resolution of 400-500 resolutions per turn, or is the most cheap way to build one my self?
i found a link on optical encoders and i think it would not be so complicated to build one?

Offline Hood

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Re: Optical Encoder
« Reply #1 on: May 09, 2008, 10:51:05 AM »
Fitting an encoder wont stop you losing steps as Mach is not closed loop.
 You can get a board from Ron Rogers that will accept encoder input and if things get out of step it will halt Mach.
 You would be better finding out why you are losing steps as a well set up and sized stepper system should never lose steps unless something goes wrong such as a seized or sticking axis.
Hood

Offline ziga

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Re: Optical Encoder
« Reply #2 on: May 09, 2008, 11:02:00 AM »
I am using gecko drive g201, which have 10 microsteps. i think that it probably loses a micro step here and there.

Mach 3 is not closed Loop? i do not understand that, does that mean i cannot fit encoders on it?
I was looking at ports and pins settings in the program and i found some input pins for encoder a and b pulse, what does that mean that i can hook encoders on but mach will not correct if a pulse is lost?

I am sorry if i do not See the obvious.
« Last Edit: May 09, 2008, 11:03:36 AM by ziga »

Offline Hood

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Re: Optical Encoder
« Reply #3 on: May 09, 2008, 11:26:03 AM »
You can fit encoders but as you said you can just view the position that they show, Mach will not use them to correct the position. You can use a board called the encoder interface from www.rogersmachine.net and it will fault Mach if you get out of position but Mach will not automatically correct the position and carry on.
 As I said previously you need find out why you are losing steps and cure that, it may just be a case of you needing to tune your motors a bit better or it may be that your motors are undersized or even the ballscrew or slides are sticky.
Hood
Re: Optical Encoder
« Reply #4 on: May 09, 2008, 12:36:44 PM »
Ziga

I will confer with Hood

I started off buying a system that had closed loop. I had to sell it as it was rubbish.

I bought it as i was convinced i was going to lose steps. But now apart from a few collisions ::) i do not lose steps not even the odd one here or there. Getting fewer collisions as my experience grows. ;D

You must have a powerful enough stepper motor the next important thing is "Top Speed" go too fast you will lose steps

Then Acceleration again too fast and you will lose steps

Time spent fine tuning these settings will be time well spent.

Phil_H

The Good Thing About Mach3, Is It's very Configurable

The Bad Thing About Mach3, Is It's Too Configurable
Re: Optical Encoder
« Reply #5 on: May 13, 2008, 09:13:57 PM »
ziga,

what size motors do you have what voltage are you running to the drives, what speed are you running the router what type of drive system do you have?

I have a 24x24 router with ~400 oz motors with 4 amp 55v drives at 10uS direct drive 2 turn ballscrews and it runs over 400 IPM with out losing a single step with 10,000 line code.