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Tactile Pressure Sensor
Tactile Pressure Sensors are devices that are used to detect the pressure distribution between a sensor and a target. They are used in robot grippers as well as flat tactile arrays. In addition, flexible sensors can be molded to curved surfaces such as the human body. Tactilus®, manufactured by Sensor Products, is a state-of-the-art, tactile pressure sensor system. Figure 1 shows five small pressure sensors superimposed onto a human finger. Figure 2 shows a Tactilus® data collection hub with eight connected sensor elements.
Various Sensor Shapes and Sizes
Fig 2: Data Collection Hub with Eight Sensor Elements Connected
Tactilus® is a matrix-based system that records and interprets pressure distribution and magnitude between any two contacting or mating surfaces. It assimilates the collected data into a powerful Windows®-based tool kit. The sensing points can be spaced as close as 2 mm (0.08 in) apart, and it can collect data as rapidly as 1,000 readings per second. Tactilus® can be used to sense pressures between 0.1 psi (0.007 Kg/cm²) and 200 psi (14.1kg/cm²).
The architectural philosophy of Tactilus® is modular, allowing for portability, easy scalability, and simultaneous data collection from up to four discrete sensor pads. Tactilus® employs sophisticated mathematical algorithms that intelligently separate signal from noise.
Advanced electronic shielding techniques maximize each sensor’s immunity to noise, temperature, and humidity. Each Tactilus® sensor is carefully assembled to exacting tolerances and is individually calibrated and serialized. The Tactilus® sensing element is very thin, allowing adaptation over curved surfaces and placement in invasive intolerant environments. The internal composition of the Tactilus® element is very durable, and it can be utilized thousands of times before replacement is necessary.
Tactilus® has been a useful tool to researchers studying tactile pressure. In a Tel Aviv University study entitled, “Real-time Continuous Monitoring of Sub-dermal Tissue Stresses under the Ischial Tuberosities in Individuals with Spinal Cord Injury,” Eran Linder-Ganz, Ziva Yizhar, Itzhak Siev-Ner, and Amit Gefen used a Tactilus® pressure mat to determine real-time, sitting interface pressures. These data were fed into a finite element model as pressure boundary conditions. Results from the study are shown in Figures.
Fig 3: Time-dependent Contact Pressure with FE Mesh and Boundary Conditions
In another work entitled, “The Influence of Environmental Temperature on the Response of the Skin to Local Pressure: The Impact of Aging and Diabetes,” Katie McLellan, Ph.D., Jerrold S. Petrofsky, Ph.D., J.D., Granite Zimmerman, Ph.D., Everett Lehmann, D.Sc., P.T., Michelle Prowse, M.S., P.T., Ernie Schwab, Ph.D., and Scott Lee, M.D., of Loma Linda University, used Tactilus® to obtain their pressure data.
Pressure on the skin was measured using a Tactilus® pressure sensor array that contained 500 sensors. The pressure sensors were 7.94 mm × 7.94 mm × 7-mm thick, and they were spaced in intervals of 44.5 × 4.5 mm. The pressure range measured was 0–68 kPa (0–10 psi). The accuracy and reliability were less than 3% error. Calibration was done at the Sensor Products factory as well as randomly throughout the study. The system and software were custom designed for this project to provide a three-dimensional map of pressure distribution. The array was transduced through a 16-bit A/D converter, produced by Sensor Products, with a sample rate of 100 kHz. The three skin sites were the back of the hand (between the second and third metacarpal), the lower back (7 cm lateral of the L3–L4 vertebrae), and over the head of the first metatarsal on the ball of the foot. Figure 4 shows some of the pressure results.
Fig 4: Percentage Increase in Blood Flow versus Temperature and Pressure for Older and Diabetic Patients