[BillTodd]

Came across this while browsing patents:

Rotary to linear transmission

The clever thing here, is the way it uses a differential drive that allows large cable drums (for traction and maximum bend radius) without the need for reduction gearing .

It uses three cables (7,4,10) that are fixed to the drive drum (2), so no slippage, making it suitable for cnc drive.

[PaulRowntree]

The original patent describes its use in an aircraft simulator, where there is considerable weight keeping the cables in tension.

What keeps the moving cart and the right side idler from freely sliding to the left in a CNC application?

[SignTorch]

The original patent describes its use in an aircraft simulator, where there is considerable weight keeping the cables in tension.

What keeps the moving cart and the right side idler from freely sliding to the left in a CNC application?

I was thinking part #14 is a spring tensioner, and that it would work, but that it would be impractical for cnc purposes

but, it appears that for each revolution the slide would move a distance equal to the difference in circumferance of the drive spool diameters, so maybe it would work (for short travel spans)

[BillTodd]

The cable are tensioned by a 'tensioner adjuster pin' item 14 - so obtaining a fixed pre-load.

It's now really suitable for long axes (You'd need a lot of cable), but for short low-friction backlash-free movements, where a compact & forceful drive is necessary, this would be useful.

Bill

[rbraeking]

That is the system for running a log thru the blade on an old belsaw sawmill from the 50's. Nothing new here.

[BillTodd]

That is the system for running a log thru the blade on an old belsaw sawmill from the 50's. Nothing new here.

I don't think you've understood the differential drive system above.

From what i can see of it, the Belsaw uses a standard winch arrangement with a variable speed (variable slip) belt drive.

Have you an example of a Belsaw with differential winches?

[rbraeking]

Regardless the differential effect of having 3 drums versus having a single drum and the cable affixed at the ends of the carriage it is nothing more than a cable winch. I seriously doubt the precision capabilities of the system would be sufficient to achieve the tolerances required for CNC applications. Cable stretch and sag would introduce too much error to be acceptable.

[neilw20]

Same principal as endless chain hoist, just with two end pulleys.
Nothing new there. How can something that's obviously been used for 100 years get a patent by adding 1 extra pulley which just allows for motion push and pull?

[BillTodd]

Cable stretch and sag would introduce too much error to be acceptable.

Acceptable for what?

Cable stretch and sag will be no worse that that found in belt and chain drives

The major drawback with cable is usually resonance (like a guitar string) . Belts and chains fair better, because the internal and external damping is higher than the cable

Same principal as endless chain hoist, just with two end pulleys

Similar, although this affixes the cables to the drums more like a winch than a pulley.

How can something that's obviously been used for 100 years get a patent by adding 1 extra pulley which just allows for motion push and pull?

It seems patent clerks in the UK, USA and Europe found this idea original! Such are the vagaries of international patent systems

[rbraeking]

Bill,

Cable not acceptable for accuracy. I would expect that one would want his CNC machine to precisely position the cutter tool. Cable is manufactured with a twist. Normally there are 7 wires twisted together to make a strand and 19 strands are twisted to make a cable. As the cable is tensioned the cable untwists to an unpredictable point depending upon the hardness of the twist in its original manufacture which will vary along the length of the cable. Cables are great for hanging bridges where strength, flexibility, and shock absorption are desirable characteristics. For precise positioning look rather to acme screw, rack and pinion, or ball screw. Roller chain will work but is not as precise as the other options as they can be stretched out of shape and the manufacturing process is not meant to conform to the type of uniformity and precision of gears or screws.

Bob