Laser length measure

ArikBY · Jun 9, 2004

Hello everybody

I have a big problem in my current project and I need some help.
The problem is like that. I have trolly who running on rail in length of 30 meter
The trolly picks full carton boxes from assembling machines. When I have more then one carton I send the trolly to pick the carton from the station. I located the trolly with encoder. The problem I facing is I losing the location because of mechanical problem with the encoder mechanism.
What I looking for is laser length measure for that range with output of RS485
Do someone have any experience with that ?

Any help would be appreciate

Thanks in advance

Hester · Jun 9, 2004

Laser Interferometer System

Barak:

I think you are referring to a Laser Interferometer encoder system.
Something like this maybe:
http://www.renishaw.com/client/product/UKEnglish/PGP-83.shtml

Most of the Laser Interferometer Systems I have dealt with have been on precision stages for X Y positioning.

At least this may put you in the ball park. I'm sure some of the other guys here have better ideas and resources.

Greg Fowlds · Jun 9, 2004

A company "SICK" makes laser range sensors.

DME 3000
DME 5000
The 5000 has a range of 0.15 to 150mtrs with +/- 3mm resolution

Try this link.
http://www.sick.de/de/products/categories/industrial/distancesensors/dme5000/en.html

markep12 · Jun 9, 2004

infared measurement

You should check into a Sick diffusion reflective measurement sensor.

ArikBY · Jun 9, 2004

Thank you very much for your help.
Sick rep is 10 min drive from me I will go to see him today.

ChuckM · Jun 9, 2004

A more inexpensive option may be to use the encoder you have now, but not try to go the entire 30 meters based on the encoder's feedback. Update the distance you have traveled every 5 meters or so by some kind of sensor (prox switch or whatnot). If you space the sensors at a known distance, you can also compensate for wheel wear on your trolly by udating your scaling as it passes by the two sensors.

Eric Nelson · Jun 9, 2004

You may want to consider Chuck's idea once you see the price for a Sick measurement sensor...

Paul (Lucas) does something very similar with his container cranes and may offer suggestions... :nodi:

Paul, you have the floor...

beerchug

-Eric

ArikBY · Jun 10, 2004

That what I doing now.
I dont think it reliable.I dont like to solve problems in wrong way.

Alan Case · Jun 10, 2004

Banner make a reasonable priced laser measurement unit. You need to mount a reflector on the item.
I have some documentation at home on another laser unit that will go to 100 metres and does not need the reflector. Price was about 3000 AUS (2200 US) Post here if you wish me to dig it out. Regards Alan Case

elevmike · Jun 10, 2004

Arik,

I'm assuming that your using a friction drive to turn the encoder.

You may want to consider using an open ended timing belt to drive the encoder. https://sdp-si.com/eStore/default.asp

You can get a 9mm 5HTD belt up to 83 meters long. They also sell pullys of various diamaters to fit the belt. We use a stationary belt and the encoder rides on the car. This is a very accurate, and reliable way to get feedback on distance, speed and direction.

You could also use a stationary encoder and have the belt hitched to the trolly through a pully system.

Mike

hesham · Jun 10, 2004

Linear Encoder

Arik

I think you are referring to a Laser Interferometer encoder system.

This is a very expensive soultion.
you can go with a linear encoders solution it will be accurate because the cursor will be mechanically attached to the moving part so any errors/backlash in the mechanical system can be eliminated.
I know this german company Siko they produce linear encoders up to 80m.with a very good accuracy.
Good luck

elevmike · Jun 10, 2004

Just to give a better explaination, The pully mounts directly onto the encoder shaft. (8mm dia). There is a keeper roller mounted on the encoder mount, to keep the belt engaged with the pully. The belt is tensioned on one end with a compression spring, like a clothsline hitch. The other end is fixed. This will elimanate all slip, and you should only have to correct due to a power cycle.

Here are some links.

Timing Belt: https://sdp-si.com/eStore/PartDetail.asp?Opener=Group&PartID=30471&GroupID=343

Timing pully: https://sdp-si.com/eStore/PartDetail.asp?Opener=Group&PartID=59889&GroupID=346

Good luck with it..

Mike.

Sliver · Jun 10, 2004

Have you eliminated wheel slip as a source of the error?
I have a similar issue on a bulk material reclaimer.
(I used a timing belt to eliminate error as well)

I couldn't explain an approx 1 meter error/day after travelling back and forth approx 10,000 meter/day total travel.
With 100 tons of reclaimer it was hard to think of it slipping.
I decided to mark the wheel and rail and after 1 pass there was the error. Wheel slip on direction change or start/stop? I built in a calibration feature for the production guys and they have to recal it monthly. In this case relative position is more important than actual location on the track but it has been bothering me how to fix it.

good luck,

Brian

Guest · Jun 10, 2004

You may want to try www.stahltronic.com. They offer an opto-electric position encoder with RS485 interface, as well as other. Price for your application would be about $1000.00. They originaly developed the system for use on the cranes and monorails that Stahl manufactures.

Andrew Evenson · Jun 10, 2004

I like Eric's and Chuck's Idea...

ArikBY

We do something simular to what Chuck and Eric recommended. On our process lines, we track a coil(s) through the line through via a weld position. We know when we make a weld, and start to track then. Along the way we use weld detectors to compensate for slippage. These weld detectors are at known distances from a datem point. This is being done on a process running 500 mpm and works well.(If the weld detectors are working!) I believe this is a simular idea that Eric and Chuck expressed to you. You could use your encoder to track the trolly, and use some photo eye's and make the calculated distance to what if SHOULD be, if there is slip. This also gives you a way to alarm for slippage.

Hope this helps..

Andrew Evenson

Laser length measure

ArikBY

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Greg Fowlds

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markep12

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ArikBY

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ChuckM

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Eric Nelson

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ArikBY

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elevmike

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hesham

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