How to measure changes in curvature?

Question

I am building a device to remind myself of keeping my spine straight.

I have a way to implement the "reminder" feature and the control package, but I have not found a way to measure changes in curvature in a small form factor.

I thought about using a simple light encoder with a marked rod that slides through it, but that would make it much too large to stay hidden under clothes. Rotary encoders suffer from the same problem. Plus, to get a reliable value, I would need multiple individual sensors.

One way I can think of is using something similar to this and monitoring changes in pressure in the different tubes, but this seems unviable to me.

A perfect solution would be something directly implemented in the flexible surface... Some sort of flexible PCB based solution perhaps.

How can I detect changes in curvature?

Answer 1

Some ideas:

• You try to could measure length on the surface or possibly between 2 points instead as a proxy. The arched back is longer than the unarched one.

  In fact when measuring bending of metal you use strain gauges to do just this. So in fact this would probably do it you just need a suitable gauge, container and attachment.

• You may want to measure relative of two points position instead of arc

• a good posture has different center of balance so you might measure that instead, this would mean you could instrument a chair for example.

Answer 2

My solution wouldn't be some thing that clings to the spine - it sounds far too much of an inconvenience to put the thing on! I think monitoring general upright posture is more useful anyway.

I would suggest a mini harness or shoulder holster that goes on over the arms and holds a slim package against the upper back, between the shoulder blades. This would hold a typical hobby accelerometer/gyro as well as the inevitable electronics.

The purpose would be to monitor the angle of the shoulders, effectively logging the wearer's stance or deportment, whether standing or sitting. It's to make sure the user is not slumping forward (and perhaps not twisting too).

A period of logging and analysis would be needed first to decide upon the preferred angles. Then once this is set it can send a reminder (using a vibrating motor) when the wearer is slouching.

Additional benefit - with recording, this might be useful for joggers and activity fans to monitor their daily footstep or activity count, in a device that is less affected by arm movements. The vibrating motor might be useful for a silent alert of various goals too.

(I accept this is not a specific measure of spine curvature. I suggest it as a more general measure of good posture, in a fairly compact package.)