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.

 

[KENAT]

So you've ruled out using syringes of the same stroke length but different diameters?

Is the order of the syringe pushing important - i.e. rather than both starting at the same time could they both end at the same time?

You might be able to come up with something using cams &/or levers if you want a mechanical solution. You'd probably be able to achieve similar with pneumatics/hydraulics.

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[zzz2000]

Thanks for the quick reply and good suggestions. I will try with the pneumatic/hydraulic approach. Unfortunately both syringes have the same diameter and they have to start at the same time.

Best,

 

[KENAT]

You might be able to achieve it with a gear train/rack & pinion too. though getting a precise 'stop' could be tricky.

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[berkshire]

Can you put a compression spring on the plunger of the shorter cylinder?
This way when the plunger bottoms out, the spring compresses allowing the longer cylinder to finish emptying.
Then coming back, the spring will hold the shorter cylinder, until the longer cylinder is where you want it.
B.E.

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[Compositepro]

Use a lever arm with a pivot to actuate your syringes. The farther the syringe is from the pivot, the longer the stroke. The concept is used in this metering equipment:

http://www.sealantequipment.com/pdf/See-Flo7.pdf

Just substitute syringes for the piston pumps.

 

[GregLocock]

Berkshire's idea is sufficient to meet the stated problem with the minimum of complexity. This means that the OP will now say that it won't work because of some new requirement ... judging by the way these things go.

Cheers

Greg Locock


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[MintJulep]

Compositepro beat me to it while I was figuring out how to get the URL.

 

[Compositepro]

Mint, there has to be a fixed pivot point somewhere on the lever, typically at one end, while the actuator can be an air cylinder or handle at the opposite end of the lever.

 

[MintJulep]

Short cylinder bottoms out and provides the fixed point to allow the lever to pivot.

 

[JohnRBaker]

Yes, but that will only work if the forces applied to the two moving plungers are exactly the same. If one's friction. or resistance to movement. is greater than the other, this will not work reliably. The 'spring' mechanism, with a fixed crosshead, would appear to be the more practical approach.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
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[MintJulep]

Works reliably on millions of rail cars to accommodate different stroke at different axles.

 

[MintJulep]

Actually neither of the lever solutions or the spring satisfies the requirement as written.

Kenat had it in the first reply. A cam.

 

[KENAT]

Actually I had both cams & levers as options (with questions to clarify order of motion) but no one ever listens to the fat bearded Brit.

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[cloa]

How about piston driven electrically- preset a profile for each.

http://www.eng-tips.com/threadminder.cfm?pid=1529

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[berkshire]

All,
this problem was solved more or less in the 70's with resin metering equipment as Composite pro says.
Most of them used cylinders of the same size travelling different strokes. This was done by a sliding bar for each cylinder, altering the radius of a common lever.

Here is a link to a style of machine I used in 1972 that is still available today.

http://www.extec.com/mounting/equipment/labpro-1-proportioning-meter-system/

B.E.

You are judged not by what you know, but by what you can do.

 

[MikeHalloran]

Two cams with different rise on a common shaft may be the least awful solution.
Two cam or screw drives run by a single microprocessor may be the most flexible solution.

In the applications where syringe drives are commonly used, the cams have to be pretty good, because the syringe amplifies irregularities in motion of the syringe plunger. Amplifies, as in being able to observe the passage of bearing balls within a ball bearing based 'roller' cam follower with a pressure transducer in the plumbing downstream of the syringe.




Mike Halloran
Pembroke Pines, FL, USA

 

[PNachtwey]

This is easy if you use a servo hydraulic motion control.
Mechanical cams are not flexible. It is possible to inject at any ratio you want with a hydraulic motion controller. Hydraulic motion controllers have electronic cams.

This application sounds like a reaction injection molding or RIM application.

Two cams with different rise on a common shaft may be the least awful solution.

What zzz2000 has described doesn't really require a cam based solution but that doesn't mean zzz2000 wouldn't use one if a cam capability was available.

Two cam or screw drives run by a single microprocessor may be the most flexible solution.

Yes but if a microprocessor is used then why be limited by the mechanics? The hydraulic motion controller can do electronic camming or synchronizing easily.



Peter Nachtwey
Delta Computer Systems

http://www.deltamotion.com

 

[tygerdawg]

Agree with PNachtway. If you think beyond a mechanical solution, and your system can accommodate it, a mechatronic solution gives you so much more in the way of ease of deployment and flexibility of programming.

My first thought was a stepper motor with integrated ballscrew-as-shaft. There are a number of those offered on the market today, but here is the first one I recognized on a G search.

http://motion.schneider-electric.com/products/mdrive/mdrive_linear_step_direction_input.php?nema=14

I love the Intelligent Motion System products from Schneider...integrated controller built into the motor. (maybe I should ask for endorsement payment?)

TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering

http://www.bluetechnik.com

 

[Walterke]

From my limited experience on this forum, I've learned that, when the OP stops replying, it's better to stop discussing the subject. Since all you end up doing is speculating on the variables.

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