This innovation is a sensor technology that can detect pressures, such as ground force reactions, down to 30 g in weight with a minimum resolution of 5 × 5 mm (resolution dictated by the limitations of the resistor grid array). This device uses a commercially available resistor grid array and custom sensing hardware and software. The sensor hardware encompasses an area no greater than 2-3/8 × 2-3/8 in. (≈6 × 6 cm) and, combined with the software, can process more than 900 pressure points at a minimum rate of 72 scans/second (each scan = 900 sensors). The custom hardware and software is, by design, adaptable to all operating systems, as well as custom data protocols and data transfers. In addition to determining relative pressures and center of pressure measurements, the device also uses a sensing system to detect weight (force) within 2% accuracy using a strategic load cell topology. This pressure system, in combination with a force detection system, is called X1 HIDS.

The current hardware contains all of the necessary sensing hardware on a single circuit board. The board contains a microcontroller, several multiplexers, and additional peripheral hardware necessary to detect and measure pressures for the more than 900 sensels. The resistor grid is divided up into 36 rows and 39 columns, each intersection making up a sensel, or variable resistor. As the pressure applied to each sensel increases, the variable resistance changes from very high (megohms) to very low (kilohms to ohms). Each sensel is individually excited one at a time and read before moving on. To eliminate potential wasted scan time, a map file is used to eliminate any row/column combinations that do not produce a physical sensel. As the program continuously loops through each of the variable resistors, the data is stored in local memory on the microcontroller.

Version 1.1 takes the system to a new level of complexity, adding in force detection as well as pressure detection. Version 1.1 is about one-half to two-thirds the size of the original version; however, subsequent versions may be even smaller depending on the number of pressure cells wishing to be sensed, the desired resolution, and the desired streaming data protocol. This design is completely customizable for the desired application.

This work was done by Alex Lanclos and James Holley of Johnson Space Center, and Rochelle Lynn Rea of Oceaneering Space Systems. MSC-25469-1

NASA Tech Briefs Magazine

This article first appeared in the November, 2015 issue of NASA Tech Briefs Magazine.

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