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Suggested distractor mechanism, any help?
11

Suggested distractor mechanism, any help?

Suggested distractor mechanism, any help?

(OP)
Dear all mechanical engineers,

I have a problem and I would like to know if you can help me to get a solution:

Our system consists of a fixed plate, a mechanism, and a mobile plate. When the force applied to the mobile plate is equal to Fa =150 N, the mobile plate is stable (Case 1). As this force decreases, the mobile plate must move upward till the applied force is once again equal to Fa (Case 2). The mechanism should be locked after this movement. What type of mechanism could we use to achieve this giving that the initial distance between the plates is 5 mm and the maximum allowed distance is 10 mm?

Illustration: http://files.engineering.com/getfile.aspx?folder=ebb48677-a214-49b6-ba8e-53c60e5e539b&file=Idea.bmp
 


Thank you in advance;
Chaabain

RE: Suggested distractor mechanism, any help?

Pneumatic actuator would give constant force with position. However locking would then render that facility inoperative.

 A linear motor like SMAC or Linmot can be positioned and detect load on axis.  Again not sure if it can hold position and react change in load.  Only thing I think would work would be some sort of servo axis with a load sensor.
  
Getting it to fit into 5 mm and expand to 10 mm would be some engineering feat. Some sort in miniature scissors lift?

Sorry if this is no help

RE: Suggested distractor mechanism, any help?

Custom air bellows with constant pressure and a check valve to dump/equalize pressure during change?  5-10mm is a tiny space to do anything though.

James Spisich
Design Engineer, CSWP

RE: Suggested distractor mechanism, any help?

(OP)
Thanks Alansimpson and Jspisich for your replies.
I think that the miniature scissor lift is a good solution, but we need to actuate the lift and consequently is it possible to find a miniature actuator that can push the upper mobile plate with the suitable force?
On the other hand, air bellows may also be used, but I dont'k know about these bellows if they need a source of air because I need my system to be completely independent. In other words, I need the source of kinetic power (electrical, pneumatic, ...) to be also embedded within the system.

I would be so grateful for any more information may help.

Thank you in advance,
Chaabain

RE: Suggested distractor mechanism, any help?

If you had room for an accumulator tank you could go the pneumatic way and keep the unit self contained.  Hydraulic would also be a solution. There are are nitrogen accumulator tanks used with hydraulics. Pressure from tank should be even if movement isnt too big. A check valve on hydraulic circuit would lock movement since hydraulic fluid is incompressible.
The bellows might be low enough profile to fit into 5 mm space.  Something like a bladder or inner tube.  Look into metal bellows.  

RE: Suggested distractor mechanism, any help?

(OP)
Ok, I'll add some details to clarify the problem:
The dimensions of the lower and upper plate are:
Width: 32 mm
Length: 37 mm
Height: 2 mm
and as I said before, the initial distance between the two plates is 5 mm and the maximum allowed distance is 10 mm. I need the distractor to fit into this space. For the pneumatic and hydraulic way, I don't think that it works because I don't have enough space for the accumulator tank. A miniature electric actuator may work, but are there linear motors that can fit into this space or even the metal bellows, is it possible to fit overthere.

Thank you in advance for any further information.

Chaabain

RE: Suggested distractor mechanism, any help?

2
So, when the force is reduced, the mechanism expands, and then locks?

After it's locked what happens if the applied force increases?  It doesn't move?  Ever?

I.e., how many times does this mechanism have to actually work?  Example:  If the answer is 'one', then the mechanism could be a spring in a balloon filled with wet concrete.

How many can you sell?

How much money have you got?

 

Mike Halloran
Pembroke Pines, FL, USA

RE: Suggested distractor mechanism, any help?

(OP)
Non, when the force increases, the upper plateau must move downward until the force is once again equal to Fa (Case 1). Anyway, if the wet concrete becomes dry before the decrease of force, what can we do?

To present, I can't tell you how many I can sell before you tell me how to do with this problem !!!

Thank you Mark for your idea,
Chaabain

RE: Suggested distractor mechanism, any help?

If the mechanism expands with decreasing force, and shrinks with increasing force, in what sense is it 'locked', when at the outer position in your original specification?

I.e., so far you've described a spring.

 

Mike Halloran
Pembroke Pines, FL, USA

RE: Suggested distractor mechanism, any help?

(OP)
Hi Mike,

It's exactly like a spring but must be locked by user whenever needed. That means I don't need this operation to last forever. I should lock and unlock the mechanism whenever I want and in this case, I don't care about the decrease or increase of force. It's like a spring with controlled lock, does it exist?

If you have any idea about that, Mike, I'll be so grateful.

Chaabain

RE: Suggested distractor mechanism, any help?

So, you require a spring, and a manually operated lock... which the user accesses how?  

Insert a shim between the platens?  There's your lock.

User puts his fingers between the platens?  Need guards and/or interlocks to protect the fingers.

Manual operation of electric switch controlling a solenoid that places a shim between the platens?  Requires a power source.

Is a shim sufficient, or does the 'lock' need to prevent further outward motion in the event of an extra force applied in an outward direction?



You probably thought your first message carried a complete specification.  Not so.
 

Mike Halloran
Pembroke Pines, FL, USA

RE: Suggested distractor mechanism, any help?

I dont understand your diagram, specifically the Fb=Fa relation.

I think what you are saying is that you need the mechanism to equalize reflexively by expanding, is that correct?  Like a locking spring, like mike said?

This thing is small, is there any more space to be had?  what about what's under the fixed plate?

I'm thinking of using a custom stepping motor setup, with holding/breaking voltage acting as the lock

stepping  motors are big though...i mean, they arent 37 mm across.

RE: Suggested distractor mechanism, any help?

(OP)
Hi again Mike and DragonTSD,

The electric switch controlling a solenoid, it's a good idea. But can it fit into the space that I talked about. For the power source, the mechanism may be powered by an exterior induction coil without the need to put a source of power in. Th lock must prevent the movements in all DOF if it's possible.
DragonTSD, for the relation, Fb = Fa, that means: when the force exreted on the upper plate decreases, the upper plate must move until the force Fb becomes again equal to Fb.
Yes, it's like Mike said. The problem is that I've to find a stepping motor that can fit into this space, and I've alread made a research about that, but I couldn't find this motor. The motor I need has a height of 5 mm and can expand to 10 mm and like that it's impossible, especially with the torque required to push the upper plate. Under the fixed plate, there is no space to be used.

Finally, I would like to thank you for your help and I'll be so grateful for any further help.

Yes Mike, you are right, the first message didn't carry a complete specification because I couldn't expect that I'll have such a help. If you are interested, I can describe the whole idea again with the application I need.

Many thanks,
Chaabain

RE: Suggested distractor mechanism, any help?

So far, you've described a spring in a cage.  Because of the stroke, the cage has to be compound, but it's doable.
Except for the 'lock', the specification for which seems to keep changing.
You can get a solenoid in the specified envelope.  Less likely a motor.
Transmission of power by induction requires two coils.  Is there space outside of the problem gap for a coil?

Yes, please try to write a complete and coherent specification.  Try to design something to meet it yourself; that's one way to improve a spec, by forcing you to ask the questions we would ask of you.

 

Mike Halloran
Pembroke Pines, FL, USA

RE: Suggested distractor mechanism, any help?

What about an elliptical shape on a simple motor. As the motor rotates you can 'lock' and unlock the movement by stopping the motor. And you can move the plates from case 1 to case 2 and vise versa with one rotation of the motor.
Kind of like a cam.  

peace
Fe

RE: Suggested distractor mechanism, any help?

(OP)
Hi all,

Dear Mike, I'll try to write a complete specification as you said and back again.

Dear FeX32, for this motor with elliptical shape, can it fit into the small space that I have and is it able to push and expand with the required force?
And for the scissor mechanism,as I said before, it's very good idea but I didn't understand how to actuate it and lock it when needed with taking into account the small space that we have, do you have a full description of that?

Thanks again for all of you,
Chaabain

RE: Suggested distractor mechanism, any help?

(OP)
Hi again,

I've an idea about "Actuation in induction" but I don't know if it will works or not. Do you have any idea about that?

Thanx

RE: Suggested distractor mechanism, any help?

One possibility is to use a filled sealed metal bellows either with gas or low expansion media that could be controlled by heat or pressure. I have built similar devices using Naphthalene to control movement.

I would also contact Servometer with your problem. They can do many things with their bellows and are capable of making very small bellows.

http://www.servometer.com/

RE: Suggested distractor mechanism, any help?

(OP)
Hi Unclesyd,

But as I said before, the actuator of this mechanism must be inside the aforementioned available space. In case of metal bellows, I need either heat or pressure to actuate the bellow and that's impossible in my application. Can there bellows be actuated to expand and retract by providing them in an electrical power (from battery for example)?

Thank you in advance for any further information.

Chaabain

RE: Suggested distractor mechanism, any help?

I don't think that the space will matter as you can get small bellows from Servometer, down to 0.020". I mentioned using a low melting temperature material as the motive force as this was my approach to switch problem.
We also used a thermal heating fluid filled bellows that operated around 600F in a condensate trap.

Checkout this page on the Servometer website.

http://www.servometer.com/additionalinfo.php?Id=3036

RE: Suggested distractor mechanism, any help?

You could also look at construction of an automobile thermostat that uses a small can that is full of a wax that causes a rod to to extend to open the thermostat with an increase in temperature.  

RE: Suggested distractor mechanism, any help?

(OP)
Ok, about the size of bellows, it doesn't matter. But I didn't understand exactly how to actuate it by electric power. Anyway, is it possible to actuate these bellows, for examples by filling them with special gaz where there are two electrical poles in contact with this gaz. When varying the voltage, the bellow will expand or collapse as a response?

Do you have any reference that can explain exactly how do these bellows work?

Thank you in advance,
Chaabain

RE: Suggested distractor mechanism, any help?

I would contact Servometer, at one time they had a very good application manual for their bellows.

The thermostat uses a wax mixture with high thermal expansion to move the piston.

Here are some wax driven thermostatic elements from China. There is also a lot of good information on the design of temperature sensative switches and things.

http://www.wax-thermostatic-element.com/index4.htm







 

RE: Suggested distractor mechanism, any help?

Somehow, I am thinking of electrostrictive or magnetostrictive materials.

Does the mechanism have to be housed between the 2 plates? Why can it not be placed above the upper plate? Fully self-contained?

RE: Suggested distractor mechanism, any help?

(OP)
Thank you for your replies.

Unclesyd, I will contact servometer to get this application manual and I'll see what I can do with.
Htlyst, im my application, the mechanism must be between the two plates. Furthermore, the change of electrostrictive and magneostrictive materials as a response of the applied force or magnetic field is too small - of the order 10e-6. As I told before, the change must be between 5 and 10 mm.

Thank you a lot for any further suggestions.

Chaabain

RE: Suggested distractor mechanism, any help?

Could you use two connected bellows to balance out the forces. I'm try to visualize what would be the best working fluid.

RE: Suggested distractor mechanism, any help?

2
How about magnetic fluid? The lock will be the fluid and the fluid viscosity can be changed by coupling it with a force torque sensor.

No?

RE: Suggested distractor mechanism, any help?

(OP)
Hi Toastedhead,

Sorry but I didn't understand exactly how we can do that under the conditions that I've talked about.

Thank you in advance for any further information.

 

RE: Suggested distractor mechanism, any help?

(OP)
Hi again,

Using the metal bellows that you have suggested. I made an illustration of my application to get an answer to the following question:

Taking into account the initial force applied to the upper plate (given that F1 = 150 N), how could we actuate the bellow when F2<F1 untill F2 = 150 N once again? How could I lock the actuator when needed without taking into consideration the change of force exerted on the upper plate?


Thank you in advance,
Chaabain

RE: Suggested distractor mechanism, any help?

Did you notice that the mechanism you've illustrated, and improperly dimensioned, could not possibly have 5mm of stroke and a 5mm collapsed height?

You keep saying "How could I lock.."  while defining an envelope that apparently allows no penetrations or extensions for remote control or energy storage or observation.  You have also not made it clear what "lock" means to you in this context.


You are talking in circles.  While it's possible to make a good living doing that, it's an unusual behavior among engineers.  When are you hoping to graduate?




 

Mike Halloran
Pembroke Pines, FL, USA

RE: Suggested distractor mechanism, any help?

(OP)
Hi Mike,

Sure you are right, it's improperly dimensioned, but it was just to illustrate the idea. Let's say that expanded height is 7 mm (I didn't use a CAD software to illustrate that). For the lock, you can penetrate the envelope by a good idea that I couldn't imagine."Lock" means that the upper plate will never move to balance the force else if the user allows. I'm still a young undergraduated engineer and I have no experience concerning the question that I've asked.

Anyway, thank you MikeHalloran for your reply. I look forward to get your suggestions.
 

RE: Suggested distractor mechanism, any help?

I'd separate out the two functions.
Function one is the phsyical control of the gap and the ability to lock it anywhere.
Function two is to measure the force and use that to control the mechanism.
Roller cams along the edges or paired wedges with strain gauge sensors.
Actuators for the cams (rotational) or wedges (linear).
Actuators controlled by micro processor based on feedback from the force sensor and with a programmable algorithm that controls cam/wedge movement anyway you like. Speed of response, smoothing, define and ignore transients, hysteresis, direct acting and reverse acting, fail safe overpressure response, and so on..... anything you like.  

 

JMW
www.ViscoAnalyser.com
 

RE: Suggested distractor mechanism, any help?

(OP)
Thank you JMW for your reply. It's still the main problem. Is there an actuator that can fit into the available gap and can provide the necessaire movement with considering the force applied?

Thank you in advance for any further suggestion.
 

RE: Suggested distractor mechanism, any help?

The only other thing I can think of is to join the fixed and moveable plates with a stainless steel triple ply bellows and make the cavity into a sort of bellows.
Then use hydraulic oil to fill the cavity. If you close the inlet/outlet valve, that will provide an effective lock.
Alan Simpson suggested looking into stainless steel bellows.
Try here:
http://www.sigmanetics.com/pages/bellows_overview.htm?gclid=CPa7nomr9pwCFU0A4wodlXZsaw
or
http://www.htproducts.co.uk/vac/vacbellows.html
for example.
A minature pump or a nitrogen pressurised bladder have already been suggested.
  

JMW
www.ViscoAnalyser.com
 

RE: Suggested distractor mechanism, any help?

I'm not aware of a bellows that has a stroke anywhere near as big as its collapsed length, unless you can tolerate a very limited life, e.g., one cycle.

 

Mike Halloran
Pembroke Pines, FL, USA

RE: Suggested distractor mechanism, any help?

Uhh, Chaabain, perhaps it would be helpful for you to explain what a 'distractor' is, or does.

 

Mike Halloran
Pembroke Pines, FL, USA

RE: Suggested distractor mechanism, any help?

(OP)
According to the information that Mike provided. I have to exclude the use of Metal bellows because really I need a mechansim whose collapsed height is 5 mm and expanded height at least 7 mm (It's better if I can get 10 mm).

RE: Suggested distractor mechanism, any help?

Well, how about a telescopic jack? (though I'm pretty sure that a bellows can be designed, with some complex geometry maybe, like the bellows from an aneroid barometer, that will expand sufficiently and not simply a straight bellows as shown on these sites.)  

JMW
www.ViscoAnalyser.com
 

RE: Suggested distractor mechanism, any help?

PS the miniature actuators search thread seems to address a similar problem.

JMW
www.ViscoAnalyser.com
 

RE: Suggested distractor mechanism, any help?

Window frame sealant guns use a very simple rod and lock plate to deliver linear movement and positional control.
In your case a helical spring fitted around the rod and between the plates would provide the saparating force.

The "unlock-reposition-lock"system would be controlled by a pressure sensor on the top plate actuating,by appropriate logic,a lock plate solenoid.

If you focus on the design of the lock plate you could reduce the actuating force to a level where quite a small battery could operate the system.  

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