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Clutch in push rod to disconnect drive?

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Peter Bell05/12/2010 19:40:26
399 forum posts
167 photos
Hello,
 
Not really sure how to describe this really but what I want to do is arrange for a rod which is driven continously off a crank to some how disengage to that it stops pushing and then be able to re engage on command so that it locks up and recommences pushes.
 
I cannot stop the crank as it drives another part of the machine as well, it would be ideal if the rod just compresses in its self The rod is around 12mm dia, stroke is about 35mm and 150 rpm, needs to push about 5kg when locked.
 
I am starting some experiments using ball bearings to lock sliding shafts together but I just wondered if I am re-inventing the wheel!
 
Thanks Peter
Speedy Builder505/12/2010 20:03:20
2878 forum posts
248 photos
Could the rod be made into a piston/cylinder arrangement, with a relief valve opened to stop motion, and closed to 'lock' the cylinder, using oil or something to hydraulically lock it.
 
I have seen electro magnetic clutches working off 24v Dc, but perhaps you wanted a mechanical soloution.
Peter Bell05/12/2010 20:11:31
399 forum posts
167 photos
I though of a hydraulic piston/cylinder arrangement but it looks awkward to make and I have this vision of oil flying everywhere!
 
Never seen an electromagnetic push clutch which would be ideal I suppose, only ever seen rotary ones
Stub Mandrel05/12/2010 20:31:52
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4318 forum posts
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What about having a cone clutch on the crank, with a release spring inside. Have a thrust bearing with a suitable lever to allow you to push the crank onto the cone and start pushing:
 
If you need to transfer more force, replace the cone with a dogged clutch. I do realise (now) that the bearing and leave would need to be arranged to push the crank outwards, so they don't foul the push rod...
 
Neil

Edited By Stub Mandrel on 05/12/2010 20:40:58

Peter Bell05/12/2010 20:57:18
399 forum posts
167 photos

Thanks for the sketch, I think that would be ideal if the shaft revolved but it pushes. I have a picture of the rod but I am dont know how to put it in the reply like you did?
Engine Builder05/12/2010 21:39:03
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267 forum posts
In a hit and miss engine the push rod to the exhaust valve is disconnected when the govenor kicks in. Something like this could be adapted. You should be able to see it working at the end of this video.


Edited By Engine Builder on 05/12/2010 21:40:42

Stovepipe05/12/2010 22:06:13
196 forum posts
What about a sleeve (which slides along) on the pushed member, secured to the pushing member by a form of fork arrangement, but secured by a locked collar on the pushed member to secure it. Lugs on the first sliding sleeve could fit into recesses in that securing collar to lock it, when you want to revolve the pushed rod.
 
(I'm no Picasso, but I could draw it given time)
 
Dennis
Stub Mandrel06/12/2010 18:14:32
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4318 forum posts
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Hi Peter,
 
Add a picture to your gallery (click my photos, top left and follow the cues, keep the picture smaller than about 350kB).
 
Once uploaded you cann use the inset image icon in the message editor (sun over 'Twin Peaks') to select a picture from your gallery to insert.
 
Neil
Peter Bell06/12/2010 18:51:09
399 forum posts
167 photos

Hi Neil,
 
Thanks for the advice, here is the rod in question.
 
 

It is driven from the crank at the bottom and pushes a numbering head up and down  mounted on linear bearings on the other side.
 
It is difficult to disengage the crank as there is also a pully mounted with it which drives other parts.
 
Odd I know but I thought there is bound to be someone out there who has done this before?
 
Peter
Stub Mandrel07/12/2010 20:56:19
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Perhaps a strong spring in the pushrod, and just clamp the head.
 
 You aren't printing dollar bills there? they look very green...
 
Neil
Peter Bell07/12/2010 23:03:26
399 forum posts
167 photos
 
Good idea Neil.
 
Not sure if the drive motor(stepper) is powerful enough to do this with the head clamped as it takes around 4kg to pull the head down--food for though--I'll see what springs I have.
 
The machine is for numbering Edmondson railway tickets, built by someone else who made a great job of it, I have just been modernising it a bit
 
Peter
Stub Mandrel09/12/2010 20:51:46
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I had a suspicion they were railway tickets. I assume you want to stop the printing while you feed the stock in?
 
Neil

Edited By Stub Mandrel on 09/12/2010 20:52:45

Peter Bell10/12/2010 07:48:59
399 forum posts
167 photos
Neil
 
The problem is that both the numbering head and ticket feed are driven  from the same motor and if a ticket fails to feed the ticket under the head gets  stamped again so the numbering sequence is wrong. I have electronics monitoring the ticket feed output which stops everything if it does not see a ticket out which has vastly improved things.
 
Ideally it should have two motors but the operations need to be "in time" and It is  difficult to synchronize them. I have tried operating the numbering head with solenoids as a lot of commercial machines do. This was fairly succesful but the numbering head became unreliable at the speed it worked at and generated errors.
 
Sorry to bore, I just thought someone may have a neat solution ie a clutch in the rod, dont want to spend the rest of my life rebuilding the machine!
 
Peter
Peter Bell17/12/2010 13:42:25
399 forum posts
167 photos
Hi,
 
Just an update on my rod link/clutch. Made a rod and sleeve with a pawl. The two are locked together until tripped by another  solenoid operdated rod which disengages the drive. I have some electronics to sense when and it it needs to do this.
 
 
 
 
 
 


To my surprise it seems to work fine!
 
 
Stub Mandrel17/12/2010 19:17:05
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4318 forum posts
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Another triumph of practical appication over theoretical wibbling!
 
Great stuff,
 
Neil
 
 
Andrew Johnston20/12/2010 11:10:28
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7061 forum posts
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Not surprising really:
 
In theory, theory and practice are the same, but in practice, practice and theory are completely different.
 
Regards,
 
Andrew

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