Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: dingbatca on August 05, 2008, 05:25:21 PM
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Does any one have the datasheet for a HP HEDS-7500 Optical Encoder??
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Have a look in the links section, electronics, Datasheet catalog I think it is. Hopefully you can find it there.
Brett
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No luck. I managed to stump google on this one. Any other ideas?
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Oh man, sorry. :( Have you tried contacting the manufacturer?
Brett
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I think that is the next step
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HAHAHAHA, that is who I bought them from. He does not have the data sheet.
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Posted by: LAWAUTO
Insert Quote
Maybe this can help! Try to contact the seller for more info.
Good luck, Lou
http://cgi.ebay.com/HP-HEDS-7500-OPTICAL-ENCODER-ROTARY-PULSE-GENERATOR-CNC_W0QQitemZ320282415373QQihZ011QQcategoryZ4660QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
Doing some testing. This was originally posted by LAWAUTO. All is well, just testing somehting.
Brett
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I know they are running 5V TTL compatible logic. From there I should be able to reverse engineer the rest. I bought one extra to blow up :-). What does Mach require form an encoder? Just a square wave?
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yes just 5v square wave A and B channels.
What are you going to use the encoder for? if its your motors then it doesnt matter to Mach anyway as they go to your servo drives.
Hood
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My cnc is stepper based, and home brew. It likes to jam. I am hoping if I add the encoders I can help solve that issue.
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in what way? Mach is open loop so wont do anything with your encoders except display what they are reading.
Hood
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Is there any way I can have Mach use the encoders as its point of reference? Kinda like a servo based system?
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No not really. You could use the encoder input to cause a fault if the position is out by a user set following error. Ron Rogers sells a board that makes this easy to do. www.rogersmachine.net
Hood
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Link was dead, found it with google.
Is a servo based system closed loop? How does that work, from a mach stand point? Sorry about the dumb questions, I have only built stepper based systems.
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Ah sorry about that, missed out the S in rogers :(
Its not what I would call closed loop. What it does is you set a limit you are willing to accept (following error) then if the position Mach thinks the machine should be is out by the amount you have set then the board will tell Mach and the programme will stop.
Hood
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ok, so the driver board does the work, not Mach. Good to know. Is there a way to get Mach to through the error, with out the aid of extra hardware?
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You could probably write a macropump or a Brain to compare the axis DRO and the Encoder DRO and if different by a defined amount then fault Mach.
Hood
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Can I pass "jog" corrections to Mach, when there is a offset? I would guess the logic would be something like: pause, jog, start.
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Not sure, Mach as far as I know can only get its reference position (machine coords zero) from a homing routine and you cant change it. It may be possible to pause and then offset your work offset by the error amount.
Hood
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Thinking about it you should be able to feedhold then write to the DRO the correct position from the encoder then start again. Not sure how Mach would respond to that but it should be similar to a feedhold, jog then restart. The difference would be you have not actually jogged away you have just changed the DRO. Cant test it out as my machine is busy at the moment and after that I am off home but will mess with it after I get home as it is an intersting thought.
Hood
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Just tested it out and Mach wont let the Axis DRO be changed while in feedhold so looks like it cant be done the way I was thinking :(
Hood
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Bummer. Well, at least the encoder will let me get back to zero. I wonder if this could be a feature request? Adding simple closed loop support to Mach.
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Would it be possible to tie the encoders into smooth stepper?
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The SmoothStepper can accept encoder input I think but it still wont allow compensation from them, it may change in the future but thats just a hope rather than a fact.
Hood
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dingbatca, Have a look at Rogers machine i think it is. He has an encoder interface board and a plug-in that will do what your looking for I think. If nothing else, it may help you see some posobilities.
http://www.rogersmachine.net/encoderinterface.html
Brett
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That was what I wanted to know. So let me see if I get the order right. Computer --> smooth stepper --> Rogers machine --> HobbyCNC?
Does the Rogers machine just stop when there is a missed steps, or does it correct for missed steps?
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Ok first off thats the board I mentioned on page 2. Unless the plugin has been updated and Ron hasn't mentioned it on his site then it only halts on a following error.
Setup is Mach to SmoothStepper (if you have one) then Rons board to port 2 and normal BOB on port 1. Can probably just have Rons board if dont have too many axis for the I/O and use it as a BOB as thats what it is but with added functions.
Hood
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Hood, you did mention it first, I was just not to sure what it did. I am looking for a board that can correct errors, not just stop on them. I think I can do that with a plug-in. At this point, and that cost $129, I think I will build my own close loop Mach plugin, if that is possible. Currently know NOTHING about Mach's plugins, yet :-)
My CNC is a simple 3 axis, home brew CNC. Nothing special. Here it is, with out the dust shield covering the X and Y. It was about 95% built at that point.
http://www.batbuilds.com/~adam/cnc_rev5/dsc05431.jpg
I do not have a smooth stepper, yet. I think my CNC could benefit from one. I am trying to keep the total cost for my CNC down. But, if something will allow my CNC to run for 10+ hours, with out jamming (think closed loop with correction) I do not mind putting in a good amount of cash. I think the current jamming problem is from the computer. When I run slow, I have know problems.
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I don't have the datasheet for these encoders but I do have the wiring details. Is this still a proble out there?
email me on bobcohen@optusnet.com.au - I'd love to assist
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If you bite the bullet and go with real servo, you will have what you want . . a system that corrects for errors. That is essentially exactly how servo drives work; they constantly correct the following error. Some folks measure perfomance by torque or IPM or $. I measure performcnae this way:
Steppers: 3 to 5 almost identical parts before rehoming.
Servos: 50 identical parts without a restart, reset or rehome.
I have owned and run both. I'm 100% servo now and will never go back.