Walking Beam Assembly

Does anyone have any pictures of applications using a walking beam indexer? I need to assemble two parts using a walking beam and am looking for ideas to feed on...

Thanks

wht exactly does walking beam means?

what do u mean by walking beam??
where is it used??
and how is it related to PLC??

Steel industry?

I couldn't find any animations of a walking beam, but Commercial Cam (CAMCO) has a picture of a walking beam unit HERE.

Basically, a walking beam just takes a rotary motion (i.e. a motor) as input, and outputs a square (or "box" motion) motion that moves UP, then FORWARD, then DOWN, then BACKWARD to the starting position (it moves in a square). You can have variations on that sequence (like DOWN and BACKWARD combined).

They have their applications, like when you need move products linearly from nest to nest. Instead of moving the nests with the product in them, a walking beam allows you to leave the nests stationary, and just move the product.

beerchug

-Eric

I Found an Application!...

Everyone had something similar to this as a kid, so you know what it does...
[attachment]
The penguins climb the 'stairs' thanks to a walking beam mechanism!...

I don't know how well it would hold up in an industial environment though...

beerchug

-Eric

Walking Beam

I worked on a program for a walking beam fce. We had two axis. Both axis were shadowed via a LVDT unit. As the up axis crossed the pass line for the nested steel ( started to do the heavy lifting ) a snap shot of the linear axis reading was taken. The lift reached maximum lift ( holding the product well above the nested pass line ) the linear movement would begin. At the end of the linear movement travel. The vertical axis would start to lower the product back to the nested position. As the vertical axis crossed the nested passline a second snapshot was taken....With a little math.. we had a very good measurement of the linear movement of the product. The product...30 to 40 20 ton steel slabs could be tracked within 1" over a 60' span.


hope this helps

Steve

"Walking beams" are widely used in automated assembly/inspection systems. By means of a WB, a product may be advanced through the track from station to station - all at once, in sync. Of course, the product itself should not be too fragile and should be of a shape that allows track feeding. Most of automotive and some electronic components fall into this category just right.
Eric's description is right, but this is just one type of a WB. There are versions that, instead of up/down motion, engage the fingers (i.e. metal beams that actually apply force to the product) laterally, "from aside". Another type might have the fingers spring-loaded, so the WB has only back-and-forth motion, pushing the product on the forward stroke and allowing the fingers to deflect safely on the back stroke.

Depending on these considerations as well as on the machine throughput requirements and on the flexibility criteria (how often would one need to change over to a different stroke length, if ever), the following controls options come to my mind:

1. As described by Eric, a combination of two air cylinders - back/forth and up/down. Simple but rather slow. A simple 4-step sequencer in ladder logic plus basic fault detection.

2. If flexibility (frequent changeovers) required, the servo version of the previous (rather for back-and-forth motion, don't see much justification for switching up-and-down move to a servo; it is usually a short stroke anyway). Pretty much the same, although can be a bit faster, the obvious extra work to make the servo work right.

3. For higher speeds, one should be interested in complete synchronization of WB motion with a station cycle, i.e. working "by a timing diagram" (a.k.a. "cyclogram" in some parts of the world). Here both WB motions will be implemented via a set of cams (hey, now it is the mechanical guy's concern, not yours!). An AC motor, possibly with some kind of speed control, will run the camshaft, which, in turn, will drive not only the WB, but all the stations also. A "must" in this case is a master encoder to monitor the WB position so obvious interlocks and fault conditions can be programmed. For example, you may want to have your vision inspection station to fire at 60 deg position and to trigger a fault if the inspection will have not complete by 285 degree. Since homing would only be a nuisance, an absolute Gray code encoder (8 to 10 bit resolution) is quite typical.

4. The most expensive solution - same as above, but everything is servo driven and cammed through software. Certainly may be justified for high flexibility along with high speed. Requires most complicated programming, including coordinated motion control using cam tables, master/follower things, virtual axes and such. This also means some higher-end PLC - a ControlLogix, a CS1 and so on. I personally like Yaskawa MP900 series for that. A CNC controller would probably be an overkill, though

One more thing - with a walking beam, product tracking is reliable and easy. A sensor at the beginning of the track - and a shift register in ladder logic - that's all it takes, really...

I built a walking beam system for a goat evisceration chain we exported to India. The chain was hydraulically driven and the controls were not complex enough to warrant the use of a PLC - however if you need to track products then the PLC becomes necessary.

Goat "evisceration"?.... Had to look that one up, then wished I didn't...

LadderLogic... I was actually describing your #3 version, as that's the only 'walking beam' I knew about. That's why I gave the link to CAMCO's site. I use air cylinders to do that motion all the time, but I'd call that a 'pick and place' (even if it works from below). Regarding your #4 version, have you looked at Trio's line of motion coordinators? (HERE'S a link) I've only used them for fairly simple servo applications, but these things can do some pretty cool stuff! (Not too pricey either... An MC202 is ~US$800).

beerchug

-Eric

LadderLogic said:

[BEric's description is right, but this is just one type of a WB. There are versions that, instead of up/down motion, engage the fingers (i.e. metal beams that actually apply force to the product) laterally, "from aside". Another type might have the fingers spring-loaded, so the WB has only back-and-forth motion, pushing the product on the forward stroke and allowing the fingers to deflect safely on the back stroke.

Depending on these considerations as well as on the machine throughput requirements and on the flexibility criteria (how often would one need to change over to a different stroke length, if ever), the following controls options come to my mind:

1. As described by Eric, a combination of two air cylinders - back/forth and up/down. Simple but rather slow. A simple 4-step sequencer in ladder logic plus basic fault detection.


One more thing - with a walking beam, product tracking is reliable and easy. A sensor at the beginning of the track - and a shift register in ladder logic - that's all it takes, really... [/B]

Click to expand...

Thanks for the great reply. I have not seen a walking beam that had fingers like you describe. That is quite intersting and might apply to this project. I found the walking beam drive web sites. I was hoping to find some pictures of different applications using walking beams. Your description puts some pictures in my mind.

Thanks
John

Hi

I have been in machine tool automation for some time now.I have seen very effective designs of walking beem mechanisms in assembly presses used for the cup / case drawing operation of small caliber cartridge cases & also for bullet assy. m/cs. some of these are 14 to 16 station m/cs with
component sensing arrangement in the holding fingers. Normally the speed of m/c is 100 pcs/min!!
All these machines are invariably CAM driven.
( CAM - mechanical element & not computer aided machining). In this design a transfer bar is driven by a cam which is synchronised with the punch slide with the gear box.A single motor drives all the elements & positive drive (like gears,coupling )are used to avoid any slipping 7 maintain the synchronisation.
If you get a chance pl see these kind of assembly presses & you would really appreciate how reliable the design is.

I was actually describing your #3 version, as that's the only 'walking beam' I knew about.

Click to expand...

Eric, all too often terminology differs at different places... The one I work for, all those things I have described are called "walking beams". It is quite possible that the one of yours is the true walking beam, and the rest are just... whatever we call them.

Thank you for the reference to Trio, never heard of them before (or, maybe, heard but forgot). Interesting stuff, at the first glance, however I am not at liberty to choose a controller outside of approved brands, corporate policies and all. Nevertheless, I was quite astonished to realize that it is Trio that makes the misterious SERCOS add-on for Yaskawa servos! This has been a matter of heated discussions in our place for quite a while so I will definetely take a closer look at their site.