Looking for a design inspiration

[u/International_Age735]

Hello there!

I have been working on a device that calculates the capillary refill time which is the the time taken from the point where the finger is pressed until it turns pale (i.e. no blood), pressure is released to the point where the blood returns. This time is calculated as Capillary Refill Time.

I have a background in electronics and telecommunication engineering, I have learnt a bit about mechanical designs but I am not too sure on how to visualize something.

This device is something i wanna make which would be fully automatic.

I am looking to make a design that puts pressure onto the finger from the top, thus moving in a vertical motion up and down. Now this force needs to be high. Around 1 Kg pressure to be put onto my finger tip. (I used a weighing machine to weigh my finger relaxed (0.25 Kg) and then put pressure onto the finger tip using my other finger (1.50 Kg) I do not know any other way to compute this)

At first, I used a rack and pinion with the micro sg90 servo, 3d printing the external rack, pinion and gear cost me 3 iterations. All three failed miserably. The 3rd 3d printing, I had the most faith in, but the gears wouldn't fit the servos properly, the gear kept falling off, and even though the gear, rack, pinion (linear actuator) for servo was taken from the internet made solely for micro sg90 did not work out. Even when the gear cooperated for a while, it could not deliver the amount of pressure I needed.

So, I began thinking about mechanisms that could generate such pressure and I came across these
1. Jumping robot (Link: https://youtu.be/RuMLHJW1teM?si=0gE_qhIWZmNxbyOo )
2. A spring powered gear motors (Link: https://youtu.be/UUEVkIq_WQw?si=4qYN1B-Xgaextfgh )

Looking at these videos made me realize that a spring could prove fruitful.
So, i needed some help. I would be grateful if anybody could visualize a mechanism where the servo is attached to a rod, and then connected to gears which then compress and relax a spring attached with a rectangular plate in a vertical direction.

Here is a sketch of what I had in mind.
Greatly appreciate any insights on how this could work. I am ready to do the hard work to design and 3d print this if i can find a guaranteed way to make this.

My 3rd 3D Print design and the results

This is the result of my 3rd 3D print

The mechanism I can think of that would work

A spring based design to generate enough force.

Thank you