Flex Sensor System

Main Point

In this project we refined and implemented a flex sensor that was recently invented here in Utah. This sensor uses light to measure how much something is bending. This method of sensing has many advantages over current carbon-based sensors including linear output, ability to make two sensors with identical output (nearly impossible with carbon-based sensors), reduced hysteresis, improved accuracy, and reduced power consumption. Perhaps most importantly, these sensors can be made from a wide variety of materials.

Implementation

In our implementation we built several flex sensors and placed them on the finger, wrist, elbow, and shoulder of the arm using a custom sleeve that we built. We then used the output from these sensors to control the movements of a robotic arm.

Justification

This sensor has great potential to benefit a wide variety of industries. Physical therapists can use it to measure patient’s range of motion progress. Athletes can gether real-time data of their movements. It also has great potential to be implemented as an intuitive controller for virtual reality gaming.

Creating the Sensor

Given the customizable nature of this new sensing technology we had to build custom sensors to meet our specifications for the project. After choosing the materials, testing had to be done to determine the ideal ratio of tube length to tube diameter. This testing was done using a protractor and tube lengths from two to six inches. In the end we decided on a five-inch tube.

Building the Sleeve

Next was the problem of mounting the sensors to the user. The challenges included keeping the sensors in place over the joints while still allowing the sensor to move enough so as to not cause discomfort for the user. The sensors also had to closely follow the form of each joint while it moves. We decided it would be best to build a fabric sleeve that could be easily taken on and off. Sensors were attached to the sleeve using rings of velcro. Sensors were then made to fit snuggly using a secondary elastic sleeve as an outermost layer.

Controlling the Motors

For controlling the servo motors we chose the I2C device, PCA9685. This device interfaces easily with an arduino and can control up to 16 servos at a time.

Results

What we learned

• The ratio of tube length vs diameter is determined empirically
• Sensors can be comfortably mounted on a user using a soft inner sleeve and an elastic outer sleeve with the sensors placed in between.
• Modulating the frequency of the light source and light sensor can be used to reduce the influence of exterior light and reduce error from the light sensor overheating.

How is it useful

• This sensor allows for development for robotics, gaming, and more.
• This sensor allows for an easy to use but reliable technology

Further Development

• Develop the sensor as a multi-directional sensor.
• Miniaturize the sensor to be less obtrusive
• Use alternate light sources and light sensors to improve accuracy.
• Develop the sensor to be reliably powered by battery.