# Linear displacement by flexure, spring or ?

• CharleyK
In summary: You could also use a liquid or gas filled bag to reduce the stiffness of the suspension.In summary, the project is having trouble with the third direction because the weight of the device is not supported by the gravitational force. The solution is to use a different method for the third direction or to use a different weight for the device.
CharleyK
Linear displacement by flexure, spring or ?

I'm doing a little project of mine and I have encountered a problem..

The project is basically a motion platform that moves in three directions at very low forces (few mN). I got the first two direction done (X,Y), but the third is giving me trouble due to the gravitational force.

Basically I use some very thin metal sheets (flexures) that allow deflection in one direction and none in all others. In X and Y I have no issues with gravity, but in the Z direction the beams own weight and as the force is not applied directly at the centre of the flexures, my whole thing starts to rotate which I don't want. In this image you can see how X and Y sort of look like; you can imagine Z has a problem with it's own weight. http://www.precisionballs.com/images/flexure_fig21.jpg

So I was thinking of maybe using a linear spring that is very stiff in the other directions, or maybe a different method. Do such springs exist at such a stiffness (20 N/m)? Maybe other options? It is at milimeter/few centimeter scale. I can elaborate on the design if necessary!

You should model the narrow metal straps as thin wires. Then you will see that your first stage is stable, like a pendulum, and hangs from it's 4 corners. But the next stage is an inverted pendulum that will want to fall sideways slightly. That unstable sideways movement may result in some rotation. This becomes a column stability problem.

To control rotation you need a wide strap at the centre of the hinge rather than one narrow strap at each end. Think of the stage as a circle rather than a rectangle and you will see why the middle is important.
I would consider using continuous metal shim sheet rather than two narrow strips since it will reduce rotation. Very thin cold rolled brass shim stock is widely available.
An alternative would be to use two diagonal fibres, (Kevlar or carbon?), in addition to the corner straps, (or fibres where in tension), to prevent rotation.

When a heavy object is suspended with the intention that it be able to rotate slightly with minimal force, it is not hung from a circular section wire but from a thin band having the same cross sectional area as the wire.

To counter gravity you will need to present an opposite force. You have not specified how you will set the 3D position of the stage. That missing information will be critical to solving the gravitational bias problem.

You could design something where the weight of the device is supported by a large airbag. The pressure in the bag will support the weight, and the larger the volume of the bag, the smaller the "spring stiffness" of the air when you deform it by moving your the device vertically.

You could adjust the vertical "zero position" with a separate device to deform the shape of the bag slightly.

## What is linear displacement by flexure, spring or ?

Linear displacement by flexure, spring or is a method used to measure the movement or displacement of an object in a straight line. It involves using a flexure mechanism or a spring to translate the movement into a linear displacement, which can then be measured using sensors or other instruments.

## How does linear displacement by flexure, spring or work?

The flexure mechanism or spring is attached to the object whose displacement needs to be measured. As the object moves, the flexure or spring will bend or stretch, which will then translate into a linear displacement. This displacement can then be measured using sensors or other measurement devices.

## What are the advantages of using linear displacement by flexure, spring or ?

One of the main advantages of this method is its high precision and accuracy. The flexure or spring mechanism is very sensitive to even small movements, making it ideal for measuring tiny displacements. It also has a wide range of applications and can be used in various industries such as engineering, medicine, and robotics.

## Are there any limitations to using linear displacement by flexure, spring or ?

One limitation is that the measurement can be affected by external factors such as temperature and vibrations. Additionally, the flexure or spring mechanism may wear out over time, leading to a decrease in accuracy. It is important to calibrate the system regularly to maintain its accuracy.

## How is linear displacement by flexure, spring or different from other displacement measurement methods?

Linear displacement by flexure, spring or is different from other methods such as linear encoders or potentiometers in that it does not require physical contact with the moving object. This makes it less prone to wear and tear and can be used in applications where contact with the object is not possible or desirable.

• Mechanics
Replies
4
Views
1K
• Introductory Physics Homework Help
Replies
11
Views
285
• Classical Physics
Replies
4
Views
531
• Introductory Physics Homework Help
Replies
8
Views
1K
• Mechanical Engineering
Replies
1
Views
1K
• Materials and Chemical Engineering
Replies
29
Views
7K
• Classical Physics
Replies
6
Views
817
• Mechanical Engineering
Replies
9
Views
1K
• Introductory Physics Homework Help
Replies
3
Views
984
• Classical Physics
Replies
2
Views
183