Method To Exert a Downwards Force (Force created by screw threads?)

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Discussion Overview

The discussion centers around methods to exert a downward force of approximately 250N onto a plate, exploring various mechanical and automated solutions. Participants consider different systems including hydraulic, pneumatic, and screw mechanisms, as well as alternative methods like springs and presses.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that existing force testing machines may use a screw mechanism powered by an electric motor, inquiring about the mechanics of how screw threads generate force.
  • Another participant proposes using a large spring that can be compressed to generate the required force, referencing Hooke's Law (F=-kx) to describe the relationship between force, spring constant, and compression distance.
  • A question is raised about the required displacement and the potential use of a 3-bar roller type mechanism as a solution.
  • One participant mentions the feasibility of using a pneumatic cylinder and relay to achieve the desired force, noting that this might be simpler than designing a power screw due to the unpredictability of friction coefficients.
  • Another participant suggests considering an arbor press as a possible method to exert the required force.

Areas of Agreement / Disagreement

Participants express multiple competing views on the best method to exert the force, with no consensus reached on a single solution. Various approaches are discussed, each with its own advantages and challenges.

Contextual Notes

Participants have not fully defined the requirements for the force application, such as displacement or specific constraints, which may influence the effectiveness of the proposed methods.

Who May Find This Useful

This discussion may be of interest to engineers, designers, and students exploring mechanical systems for force application in experimental or practical settings.

Kalus
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I am trying to come up with an automated method to exert a force of around 250N downwards onto a plate.

The possibilites that i have looked at so far are Weight (although this has been discounted due to the size of the weight that would be needed), Hydraulic and Pneumatic systems. However, it has just occurred to me that the sort of Force testing machines that are avaliable in in Mech/Mat labratories (such as http://www.forcegauge.net/catalog/products/specification/mx500n-e.pdf) are electrically powered and use none of the above methods.

My thoughts are that they use some screw mechanism... although, i would like more information as to how the screw works? Is it a case of an electric motor with enough torque to turn a long thread that has the force implement on?
Also, how is Force created by screw threads (like in workshop vices?) In the case of these where they hold the force is it a case of friction between the metals that hold them tight?

If anyone has a diagram of how the above force testing machine works, that would be brilliant.

Many thanks,

Kalus
 
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how about using a big spring that you can compress with screws to generated the force required depending on the amount of compression you produce?

F=-kx
F-Force
k-spring constant
x-compression distance (negative as you force direction is opposite to your direction of motion, compression)
 
How much displacement do you require? Would a 3-bar roller type mechanism work?
 
What are the rest of the requirements? It is easy to hook up a pneumatic cylinder and relay with a known pressure and area to put that small of a load on a plate.
 
FredGarvin said:
What are the rest of the requirements? It is easy to hook up a pneumatic cylinder and relay with a known pressure and area to put that small of a load on a plate.

I agree this would probably be easier than designing a power screw because the force depends on coefficient of friction which may not be easy to predict.
 

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