This simple sensor detects how much it is being bent. Its simplicity makes it versatile; it can be used to detect vibration, humidity, motion, impact, and air flow. For example, sew it into the arm of a stuffed animal to respond when a child moves the arm, or place it inside the tube of a medical device to monitor the velocity of air through the tube (the faster the air, the more the sensor will bend).
The bend sensor consists of a coated substrate, such as plastic, that changes in electrical conductivity as it is bent. This provides non-mechanical reliability in electronic sensing and actuator technology.
The sensor consists of a plastic film printed with a special carbon ink. The film is nothing unusual; the real innovation is the ink. The resistance of this ink increases the more it is bent. The ink can be printed on virtually any custom shape and size film.
It is designed primarily for detecting relative change. Because the plastic is hydrophilic (it absorbs moisture), the flexibility of the film changes with humidity. If you wanted to use the sensor as a scale to measure absolute weight, you would need to calibrate before each use.
The bend sensor is self-contained and requires no mechanical components. It is not prone to degradation through mechanical contact, so it has a longer life than many competing sensors. The longer life of components means fewer system breakdowns due to mechanical failure; it is more reliable and less expensive.
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The bend sensor has been printed on several different substrates, but one must keep in mind that the chosen material must be able to bend repeatedly without failure for the sensor to work. The curing temperatures also must be considered.
At this time, the carbon ink is not available separately for purchase.
It depends on the setup, but in some configurations as small as 0.005 in.
In essence, this sensor is just a variable resistor. The more it is bent, the less resistance there is. There are no moving parts and no contacts to wear out. It works in dirty environments (oil, dust, flour). It is used is in the manufacture of food products. There are no complicated electronics or software required to make this sensor work.
If you need incredibly precise and absolute measurement of bending, this is probably not what you are looking for. There are sensors that detect bending by monitoring how the light changes through fiber optic cables. They can be made very precise but are quite costly.
Most often this sensor is used as an alternative to potentiometers and switches. Potentiometers are the most common type of variable resistor. The volume knob on your home stereo is a common use of potentiometers. Also, they are sometimes connected to a long lever. For example, one company recently replaced the potentiometer in its variable speed control arm of an electric motor on a boat with a bend sensor.
Horn sensors are another place these bend sensors have found use. Typically horn sensors use a membrane switch, but these require something behind them that is fairly stiff for the membrane to collapse and the switch to work. But this bend sensor was molded directly into the rubber surface of the horn. When you pressed the rubber it deforms and the horn sounds. One interesting side benefit, the horn could sound louder the harder you pressed.
In one application, a whole array of sensors was used in the seat of an automobile. Using software that would compare how each of the sensors was bent, a rough shape of the user could be calculated. The car could determine if a child, adult, or car seat was sitting in the seat and properly deploy the airbag.