Coupling Two Shafts

[rosshollands]

Dear All,

Hope you may be able to offer some suggetions.

I have a servo motor with a 19mm OD shaft. I need to couple it with a 25mm OD shaft. No problem here I can used a stepped coupling. Further up the 25mm shaft I have a timing pulley which is linked to an encoder via a 10mm timing belt and a second timing pulley on the encoder shaft.

The problem I have is when the unit is fully assembled I am unable to replace the timing belt without disassembling a few too many parts. Unfortunately I cannot avoid this being the case.

The solution I came up with was to add a further 25mm shaft and coupling. The two 25mm shafts are assembled 11mm apart via a removable setting piece. The coupling covers the 11mm gap.

If I ever need to replace the belt I can move the coupling up revealing the 11mm gap and fit the belt.

Having said all this I am concerned about this set-up, for example the concentricity....am I in danger of running out of square? I have bearing housings local to the servo and also to the starwheel which mounts on the end of the 25mm shaft. Is there an easier way?

I would appreciate any help you can offer, or even any websites which you have found to be useful.

Thanks in advance.

Ross

 

[MintJulep]

The motor manufacturer probably offers an option for an encoder mounted on the back end of the motor.

 

[drawoh]

rosshollands,

How about a hollow shaft encoder? Just slide it onto your shaft and forget the timing belts completely.

How about spur gears?

Only do this if you cannot find a suitable motor/encoder assembly as suggested by MintJulep.

JHG

 

[rosshollands]

Hello to you both,

Thanks for your suggections. Unfortunately we are stuck with what we have (servo and encoder). This is an R&D project and we have to use existing parts laying around the factory!

I like the sound of spur gears though....are these accurate enough for precise positioning?

Cheers

Ross

 

[fwc]

rosshollands

Can you couple the encoder on the other end of the shaft?

 

[rosshollands]

No unfortunately not...

 

[Timelord]

Ross,

When you look for spur gears, look for anti-backlash gears. They eliminate the backlash error.
check out:

http://www.wmberg.com/catalog/catresults.cfm?CatType=GEARS&CatGroup=ANTI-BACKLASH GEARS

Timelord

 

[rosshollands]

Thanks for your help - I'll check those out...

Cheers

Ross

 

[Barry1961]

An O-ring pulley would be easy to cut and splice.

Barry1961

 

[diskullman]

Take a look at

http://www.lovejoy-inc.com/jawtypecouplings.htm

You may find a spacer type coupling with a drop-out spacer, that can be easily removed

Russell Giuliano

 

[fwc]

rosshollands

Have you considered connecting the motor and shaft with timing belt?

Please check this link:

http://www.rpmechatronics.co.uk/products/downloads/bp1b-006.pdf

'Triangular drive' might work.

 

[btrueblood]

Another trick used by old farm mechanics is to tie a spare belt in place (i.e. the second belt is installed alongside the first, slipped over the shafts, but off of the pulleys, and secured so it won't wear/rub). When the first belt is worn out, it is cut away, and the spare belt is then unlimbered and run onto the pulleys. This cuts down on the frequency of full tear-downs for belt repairs. Caveat: any heat, ozone, or other degradation causes that are present in/on/around your machine will degrade the spare belt too.

 

[bobc]

diskullman has the best answer. these couplings fit the bill and you are not reinventing anything. alignment is also perfect.

 

[rosshollands]

Thanks to you all for your suggestions. I've gone for the lovejoy coupling.

Thanks again.

Ross