Steel Tape transmission - increasing friction

[greybeard]

I'm planning to try a tape driven x-axis on my small, but long, router cnc.

I've come across aerosol sprays to increase the friction of rubber belt drives,
but is there one for spraying onto steel tape, or the drive wheels, so that I increase the friction between the two ?

The set up will be to have a shaft coupled each end of the stepper motor driving two tapes directly each side of the gantry, and a pair of presser wheels on each side to maximise the area of tape in contact with the drive shaft. Probably another shaft across the other end with coupled wheels on that.

Another approach might be to change the material of the drive shaft/wheels to something with a high friction surface.
What would be suitable, any ideas ?

Many thanks
John

[JerryFlyGuy]

John, how are you going to garrentee that you don't lose position due to slippage? This style of motion would seem to be good for several applications, however I'm not convinced that it applies to well to CNC. Most people who are doing something similar are using drive belts which are "cogged" so as to not lose position.
If going to a long belt isn't apealing.. the next option is a rack & pinion setup.

My two cents..

Jerry

[greybeard]

Originally Posted by JerryFlyGuy John, how are you going to garrentee that you don't lose position due to slippage?

This is the reason why I'm asking (note the use of the word "try" in my first line).
John

[zoltan]

Hi,

Couple months ago I mentioned about the same idea here on forum, but at that time I was thinking about ruler tape for measuring and electromagnets. Later on I did some trials with metal reels in which I have inserted magnets from speakers and I preloaded the tape at the end and put it between two reels tangent to the drive reel. The last trial was with 40 mm diameter reel and stepper of 3 Nm. I could not believe the results. No slippage until I have obliged to stop as the MDF setup started to crack.

Try with magnets from speakers. I made a channel inside of reel where I inserted the magnet.
I definitely build a such a transmission in the future.

Zoltan

[Geof]

John;
You are probably, like me, old enough to remember reel to reel tape recorders. How about this for you steel tape drive: Have a reel at each end that the tape is firmly attached to with one reel full of a travel's worth of tape and the other with just a turn or two; i.e., you have just over two times the length of tape needed for the travel with the X carriage secured to the midpoint of the tape. When the axis drives the excess tape transfers from one reel to the other moving the carriage along but because everything is firmly attache you are not relying on friction. The distance moved by the tape per revolution will depend on the amount of tape on the reels but this is something that could be corrected by software with a lookup table. You would need a stepper at each end of the tape to keep it tight and the control of the steppers might require a bit of sophistication to make sure it stays tight. However, because there is no chance of tape slippage everything should be nicely predictable when it is all set up.

[greybeard]

Hi Zoltan.
I remember your posting, and thanks for posting your results.
There's a posting of mine somewhere in the archives, where I, too, suggested using a measuring tape, but from a slightly different perspective.
We were discussing a cheap approach to encoders, and I tought that the tape could not only be used for the drive, but have a magnetic signal impressed on it as an encoder. I'm not sure if I, or someone else suggested one could read the printing on the tape as a simpler method if you only needed an accuracy of 1mm !
Now that I've got z- and y- axis finished, I'm looking at the problems of x-, and I agree with you that this should be one method worth trying.

Cheers, and I'll give it a go.
John

[greybeard]

Geoff, that's interesting. I must get my head round the possibilities there.
Basically fixing the tape both ends, instead of a closed loop, with a tightener(stepper) each end....... mmmm ?

John

[greybeard]

Zoltan - I can produce an improvement in "friction" between the tape and the drive wheel, but I only have small neodinium magnets. I'm not sure I understand where the "slots" are that you cut.
Can you post a sketch of your arrangement, or pm me if you prefer, to john at fanmaker dot co dot uk.

Many thanks
John

[ahren]

Check these guys out -- they have perforated belts and sprockets that fit in the holes. No slippage there. Their applications department is also very helpful, so they might be able to recommend a strategy for you if you give them a call:

www.belttechnologies.com

Ahren

[greybeard]

Ahren - thanks, you've supplied the last piece of the jigsaw(see my signature !).
I've spotted an off the shelf source of perforated steel belt, but couldnt see how to produce the sprocket to drive it. These guys have shown me the method - ball bearings in holes around the face of the drive pulley.
Tape source ? The new digital retractable tapes have holes down the centre at 1cm intervals. Don't know the accuracy, but it will probably be fine for my use.

John

[NC Cams]

I recall the reel to reel tape recorders and also the grief on reel to reel memory tapes in the early computers. As you go to higher and higher speeds, you'll find that slipslide creep becomes harder and harder to avoid - especially at high speed direction changes in the data search on the computers.

Essentially, you're trying to improve the coefficient of friction. Until you go to mechanical interlocking (cogged belt, chain, rack and pinion) you'll only get better but you may never achieve the "nirvahnah" needed.

The challenge in ANY friction drive system is to get max traction without deteriouration in component life. CVT transmissions can be real oxymoronic in this nature as you MUST lubricate the device for it to live yet every lube used has to be used in a way so that it doesn't screw up/eliminate the friction so critical for it to transfer power from the drive to driven plate via the rolling wheel.

Mag clutches work well - 100% of the car A/C's I know of all have them.

The old Lionel trains had Magnetraction to help keep them on the track better and improve traction - dunno if it worked cause I could fly mine off at will.

The speaker magnet would help. So would pins and slots in the tape ala what they did in the old 8mm movie film. But that's essentially a chain and sprocket but it sure does keep the timing perfect.

Who'd have thunk that the nearly obsolete film product made so popular by Kodak would technology transfer to CNC so appropriately. Now, if we could only get the Stanley tape measure and the Kodak people interested in a joint venture....

Wanna bet neither would be interested???? Maybe Fuji Film and Kobe Steel. They've both done wonders with technologies that US competitors have abandoned over the years to the point that they rule the market in them, especially Kobe and the spring steel markets.

EDIT: in a final thought, check out what the bandsaw people do. They constantly have to deal with this exact same problem. Anybody who's walked a mile in their shoes would/should know the answer if anybody will. END EDIT

[greybeard]

NC Cams - coincidence you should mention Kodak. There is a current forum of film technicians, I think, looking for steel film, that used to be made by Kodak. Use it for sprocket registration in film projectors , as far as I could make out.

But your mention of bandsaws prompts other ideas. Mine is driven by the 1/2" blade running on the outside of a v-belt . With a 6" wheel and only about 5" length of blade in contact with it, there's no way I can make it slip.
Interesting thought - thanks.
John