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Two-stage slider
2

Two-stage slider

Two-stage slider

(OP)
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.

RE: Two-stage slider

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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RE: Two-stage slider

(OP)
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,

RE: Two-stage slider

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.

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

RE: Two-stage slider

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.

RE: Two-stage slider

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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RE: Two-stage slider



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

RE: Two-stage slider

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.

RE: Two-stage slider

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

RE: Two-stage slider

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
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

RE: Two-stage slider

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

RE: Two-stage slider

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

Kenat had it in the first reply. A cam.

RE: Two-stage slider

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-p...

B.E.

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

RE: Two-stage slider

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

RE: Two-stage slider

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.

[quote=MileHalloran]
Two cams with different rise on a common shaft may be the least awful solution.
[/quote]
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.

Quote:


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

RE: Two-stage slider

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/mdri...

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
www.bluetechnik.com

RE: Two-stage slider

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.

NX 7.5.5.4 with Teamcenter 8 on win7 64
Intel Xeon @3.2GHz
8GB RAM
Nvidia Quadro 2000

RE: Two-stage slider

(OP)
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.

RE: Two-stage slider

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

RE: Two-stage slider

See this
http://deltamotion.com/peter/Videos/EM%200405-06%2...
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

RE: Two-stage slider

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.

RE: Two-stage slider

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

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