Two-stage slider 2

[zzz2000]

Hi,

I am designing a mechanical movement to drive two syringes that are parallel to each other. The issue is that one syringe is shorter than the other. I need to have one movement to push both syringes at the same time and when the shorter syringe is empty, the longer one needs to keep going until it is empty as well. Subsequently when I pull back the plungers, I need one movement to pull back the longer plunger when it reaches the same position as the shorter plunger then both plungers are pulled.

Thank you for your help.

 

[zzz2000]

Thank you to all who have replied. Great discussion and I learned a lot from you. I tried the hydraulic solution yesterday and it was not satisfactory, because I could not control precisely the timing of the movement of those two syringes.

An electronic solution is the best but right now I am looking for a mechanical solution for cost consideration and the overall size consideration. I forgot to mention that the syringes are quite small, both are 1 ml and the shorter one was cut short.

I am going to try the cam approach KENAT suggested and the spring approach Berkshire suggested. If you have additional suggestions, I would love to hear them.

Thanks again for all the helps.

 

[kjoiner]

How about something along the lines of what Kenat mentioned but using drum cams? You could have two disks with the cam profiles milled into their faces with followers that provide positive pushing and pulling of the syringe plungers. Maybe you could somehow arrange the short stroke cam so it depresses the plunger in sync with another cam that is operating the longer stroke syringe. Then when the short syringe is fully depresses, the follower rides along a constant radius groove and dwells for a period until the the longer syring completes its stroke. The cams continue to rotate until the retraction cycle begins - both syringes retract then the short syringe hits another dwell point while the long syringe completes its retraction. The two cams could be driven by a common shaft so they stay in sync.

Kyle

 

[PNachtwey]

See this

http://deltamotion.com/peter/Videos/EM 0405-06 PrePaint.mp4

I think it was for a painting platform.

I think the OP should tell us what his application is.

I can understand synchronizing two cylinders and one moving father than the other but what happens when the shorter cylinder gets to the end of its stroke. Does it hit the end and instantly stop or does it slow down to a stop at the end. During this time, what does the longer cylinder do? If the longer cylinder slows down like the shorter one then what? I see no other solution than to let the longer one keep moving.

Another option is to synchronize the motion so that both cylinders get to the end of stroke at the same time even though the actuators are moving different distances.



Peter Nachtwey
Delta Computer Systems

http://www.deltamotion.com

 

[dhengr]

Compositepro gave you the simplest and cleanest solution in his post on 9JUL13, 18:54. And I elaborate a bit...; a lever, with a pivot on the left, at 0"; the short syringe at 1" and the long syringe at 2", assuming the long syringe has twice the volume and travel as compared to the short syringe; and a force applied anyplace on that lever, but maybe at 2", over the long syringe. The exact lever arm lengths and the proportional travel distances can be adjusted for the actual conditions of the syringes and volumes, and the forcing device has a stop at the full length of travel of the long syringe.

The OP’er. insists on resisting the simplest solution and that would be to buy one syringe off the shelf and make a second syringe of the proper dia. I.D., as a function of the two volumes being dispensed, so that both syringes would have the same travel, and could be pushed/pulled with one forcing device with a fixed head, with stops on it. On this thread we have already spent more in engineering time, someone else’s dollars though, than making the second syringe would have cost. But, that would be too simple, that ain’t real engineering is it. It can’t be gooder engineering if it ain’t more complicateder. One other improvement, with such small volumes as 1ml, you might consider smaller I.D. syringes so you have finer control over the injection rate.

 

[MikeHalloran]

Many of the solutions proposed above do not comply with the specification as given, which is that the syringes must move together until the short one reaches end of stroke, but then the longer syringe must keep moving.

This would be a mandatory specification in a situation where, for instance, the smaller syringe is driving a sample, and the longer syringe is driving a carrier fluid or sheath or diluent, and both fluids flow through a lumen of substantial length after mixing or coming in contact and before reaching the core of the apparatus, so that when the sample has been fully introduced, additional carrier fluid is required to carry its tail through the apparatus core.

It happens that I faced a very similar situation 20 years ago, and used two cams driven by a stepper through a huge reduction. The instrument worked perfectly, except that it abruptly stopped the flow just as the last part of the fluid of interest reached the sensor, and left us wondering what might have been in the 'tail' that we couldn't see. The instrument program was scrapped for political reasons before we could re-engineer the cams or transition to a programmable screw drive or a servo, none of which was available off the shelf at the time.


Mike Halloran
Pembroke Pines, FL, USA