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Shear Sensor

Shear is a force that is applied parallel or tangentially to a face of a material, as opposed to a normal force that is applied perpendicularly. A Shear Sensor is an electronic device that can measure shear forces directly at the interface point of two mating surfaces. Figure 1 is an illustration of shear force. The shear causes the surfaces to slide in the direction of the force.

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Fig 1: Shear Force Illustration

The ability to measure actual contact shear at the interface surface is a recent development. Previously, engineers had to rely on predictions from computer models requiring finite element analysis (FEA) software or other analytical tools for solving the complex modeling equations. Now, for the first time, engineers using the Tactilus Shear Sensor System can place a sensor at the interface surface and collect shear data in real time.

Tactilus is a matrix-based tactile surface sensor that works by the principle of piezoresistance. Each Tactilus sensor is carefully assembled to exacting tolerances and individually calibrated and serialized. The sensor has a 2 in. 2 in. (5.1 5.1 cm) total sensing area, and its thickness is 0.024 in. (0.6 mm). There are 16 sensing points arrayed in a 4 4 matrix. The force range is 0 to 1.5 Newtons, and the pressure range is 0 to 3.87 psi (0 to 200 mm Hg).

The scan speed is 30 Hertz. Accuracy is 10%, repeatability is 2%, hysteresis is 5%, and non-linearity is 1.5%.

Figure 2 shows the Tactilus Shear Sensor System. Item A is the electronic controller; item B is the connection cable; and item C is the shear sensor element.

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Fig 2: Tactilus Shear Sensor System

Shear data from the sensor are collected and processed using a Windows-based tool kit. The technology also uses advanced electronic shielding techniques to maximize the sensors immunity to noise, temperature, and humidity. The architectural philosophy of Tactilus is modular allowing for portability, and easy expansion.

Figure 3 is a screen shot showing the Tactilus software. The software reveals the vector of the shearing action in real time. This information is updated every two seconds. The software also provides a statistical analysis of the forces being measured.

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Fig 3: Screenshot of the Tactilus Software

The Tactilus Shear Sensor System is a valuable aid in human factors engineering and ergonomics. It can be used for research or as a clinical assessment tool. It has been successfully used for studying the interfaces of the human body in shear against clothing, shoes, gloves, backpacks or other objects which contact body surfaces.