A force sensing resistor changes its resistance as pressure is applied, allowing for touch and weight sensing. It has applications in monitoring, automation, and robotics. It works similarly to the first resistive speed control units but is designed to handle less electrical energy. The resistor uses a polymer with conductive materials to decrease resistance as pressure is applied. Different designs and types of force sensors exist, with applications in safety, scales, pressure sensing, and automation.
A force sensing resistor is an electrical component that changes its resistance as the pressure on the resistive material changes. It is used to sense touch, weight, and any entity characterized by a change in mechanical force. This resistor has many applications in sensing, monitoring and automation, such as robotics.
The first variable resistors for speed control used carbon discs which can be compressed or loosened from each other by the action of a spring. When the operator presses a pedal to accelerate an engine, the carbon discs are pressed together, resulting in almost zero resistance. This resistance is in series with the motor, resulting in higher speed. When the operator releases the foot pedal, the pressure between the discs is significantly reduced, resulting in a high resistance that cuts off any significant electrical current entering the engine, stopping the engine.
The modern force sensing resistor works on a similar principle to the first resistive speed control units. The difference is that the force sensing resistor material is very thin and is not designed to dissipate more than a few milliwatts of electrical energy. Any human-operated speed control that uses a force sensing resistor will control the analog or digital circuits that control higher power devices.
The force sensitive resistor uses a polymer between two plates with conductive materials suspended in some sort of regular formation. As pressure is applied, the conductive material moves closer together, resulting in less resistance. If the pressure is removed, the ability of the polymer material to recover from temporary deformation will return the force sensing resistor to its initial state. This results in a high strength rest position.
In general, all resistive components can be manufactured as force sensing resistors. Some designs use polymers with small conductive particles, while some force sensing resistor designs use printed sensing films. Other force sensing resistors come in arrays that can be used to sense two-dimensional tracking information such as in tracking pads for computing devices.
Force sensors come in a variety of types and designs. Piezoresistive sensors are able to decrease their electrical resistance as the compressive force exerted on the sensor increases. The resistance increases as the force exerted on the sensor decreases.
Applications for the force sensing resistor include contact sensing for safety applications, digital scales, water and air pressure sensing for pumps, and proximity sensing by weight or contact. In automation, robotic equipment is capable of partially emulating human touch or tactile sensing. This feature applies tactile sensing and variable force control to automatically handle items deemed too fragile for only machines and robots to handle.
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