I am currently working on a project where I am using flexiforce pressure sensors (resistive sensors) to design an insole that can measure pressures of the foot. However, i am having difficulties calibrating the sensors as I am unable to detect the amount of force that is being exerted onto the sensors when a person steps on the insole (with both foot on the floor). I really need help in determining the center of weight of a person and how their weight is distributed to each sensor if the sensors are placed on the heel, first metatarsal and fifth metatarsal point of the insole (approximately). Please if anyone has any suggestions, it would be of much help to me! Thanks in advance
I think it would be really hard to calibrate the sensor using a person standing on it. I know some peoples weight is not balanced on both feet. 1 foot would have more weight than the other.
To calibrate, use a weight that is known to you. like a 5lb bag of sugar…
Another idea is to get their total weight and divide it by 2 in software.
codlink:
I think it would be really hard to calibrate the sensor using a person standing on it. I know some peoples weight is not balanced on both feet. 1 foot would have more weight than the other.
To calibrate, use a weight that is known to you. like a 5lb bag of sugar…
Another idea is to get their total weight and divide it by 2 in software.
Thank you for your response. So I did try using known weights on the sensor as well ( I wanted to calibrate using up to 11 Kg) of masses that I got from the physics labs. However, I got very inconsistent voltage readings from the sensors as even the slightest changes in the placement of the masses altered the readings. I even used a concentrator that was approx. equal in size to the sensing area of the sensor (so I can transfer most of the load to the sensor) however, the masses were unstable when placed over the concentrator.
So now i’m thinking of making a flat wooden surface which would have three thumb screws secured into three locations (where approximately the heel, first and fifth metatarsal point of the foot are located) forming a triangular configuration. This wooden surface will be placed over the sensors that are attached to the insole and when weights are placed at the centroid of wooden surface, pressure will be applied to the sensors causing a change in voltage. Do you think this approach is better? And if so, do you know how I can approximate the distribution of the weight at the three locations (being the heel, first and fifth metatarsal point on the insole) if the weights are placed at the centroid?
The weight on one foot depends on the distance of the center of gravity to it. Likewise, the weight on the other foot is the complement. The sum of both should always be the same. That is, if all of the weight is concentrated on the sensors, and not bypassed to the supporting surfaces. With mechanics, always make a free-body-diagram, showing all forces and torques (moment) on the body. The sum of all forces should be 0, as well as the sum of all torques should be 0. Lest it will do a fliproll.
To make things repeatable i would replace the person with a stiff truss with 2 fixed feet (no floppy ankles) with appropriate known dummy weight. A triangle should do. People tend to be floppy and shift their weight alot.
