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DIY Bend or Flexion Sensor - Fabrication Guide

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Build Efficient and Econologic DIY Flexion Sensors: Learn how to build sensitive strips reacting to bend or flexions variations to be placed for instance along fingers, elbows or knees articulations and used for instance to monitor movements, and exploit the signal through Human Computer Interactions.

DIY Resistive Bend or Flexion Sensor Principle

Paper-based designs exposed for producing Force Sensing Resistors also enables to produce sensors that will be sensitive to flexion, as the multi-layers design will be submitted to a compression force over the curvature ray, which will be correlated to the bending curvature applied.

Such sensors are usually used along bodies or machines articulations and can be made relatively precise or sensitive and with various sizes. Consider the various related top-page tabs to optimise myour production and implementation skills.

It simply takes to firmly sandwich a resistive material layer between 2 Electrodes layers to obtain a resistive flexion sensors.

Shape and Size Design

Any shape or size of a multi-layers FSR design will be sensitive to flexion. However, these sensors are usually designed as long and narrow bands adapted in size to the articulation to be monitored.

Thus, a finger sized sensor should be below 1cm width and the length of the finger, while a sensor for knees could be larger and longer.

Connectors should preferably located on one fix end or the articulation, while the other end should preferably attached through and extensible and elastic material so as to extend along with gesture.

Sensitive Area

The sensitive area is equivalent to the one of an FSR, so you can follow the FSRs Fabrication guide to master this part production.

For an optimized response and sensitivity, metal adhesives should be covering the whole sensor length over the paper Electrodes. The use of a spacer is not appropriate here.

Connectors should preferably located on one fix end or the articulation, while the other end should preferably attached through and extensible and elastic material so as to extend along with gesture.

The sensitive area should be firmly wrapped inside a plastic adhesive to set the sensor with an initial stable resistance value and optimised its sensitivity for low bend angles.

The sensitive area and connectors should be wrapped inside a longer solid textile or plastic material that will also provide attachement strips.

Extensible Mounting support

When bending a material attached to both ends, the material will be submitted to traction and should be able to extend along with the gesture or move independently.

The best materials to be used in this case is technial textiles such as elastic bands and "velcro" or "scratch" systems for quick fixations implemented as shown below.

It is also possible not to use a spring mechanism but rather a slide link mechanism by having only one end fixed while the other end can move freely forward and backward while the whole is bending with the articulation.

Connectors should preferably located on one fix end or the articulation, while the other end should preferably attached through and extensible and elastic material so as to extend along with gesture.

The sensitive area and connectors should be wrapped inside a longer solid textile or plastic material that will also provide attachement strips.

Expectable results

In terms of sensitivity, the force exerted onto the sensor will be lower than when pressing on it, but you should be able to get quite stable signals for agiven angle, over 10 to 150 radius degrees of flexion with a precision of 1o degrees or below.

For more sensitivity, you can demultiply the paper sensitive layers or mount multi-layers is series.

For more sensitivity and better precision, you can design an articulated cardboard skeletton to wrap the sensitive area, as shown below...

Application Exemples

The most common use for this sensor is the production of data gloves detecting fingers flexion. In the pprototype below, 4 bend sensors are placed along the finger, except for the thumb being used to trigger force sensor placed at fingers bottom.

One can also build rigid and flexible blades that can be slapped or twisted while hodling them so as to trigger music events or control sound timbre or pitch.

Check out these fondamental applications to understand the potential and the power of electronics using everyday objects and complimentary tools and resources from the EduKit project.

Bend Sensors Implementation

Despite lower resistance range, voltage dividers can enable to obtain a valuable signal for radius from 10 degrees.

For lower bending radius, smaller design and other electronic circuits such as a Wheatstone Bridge are more appropriate. Such more complex design enable to measure small variation ranges of electronic signals. In the cae or resistance variations, MEMS such as micro on nanosized Strain Gauges have been used for long as highly reliable measurement sensors implemented throu Wheatstone Bridge

DSP & Mapping

Such sensors are great form the real-time control of continuous events such as sound timber, but they can also be used to trigger events from signal tresholds.

You can use resources provided in the DSP and mapping page to find useful programs for Arduinos and various mapping examples of Human Comupter Interfaces.

You can also check User'S blogs, such as the Singer Glove project, enabling the real-time control of voice through hand gestures.