News Column

Patent Issued for Compact and Robust Load and Moment Sensor

June 26, 2014



By a News Reporter-Staff News Editor at Computer Weekly News -- According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventor Palmer, Michael L. (Ladera Ranch, CA), filed on January 27, 2011, was published online on June 10, 2014.

The assignee for this patent, patent number 8746080, is Freedom Innovations, L.L.C. (Irvine, CA).

Reporters obtained the following quote from the background information supplied by the inventors: "This disclosure relates to sensors for detecting loads and moments applied to the sensor, and more specifically to a compact and robust sensor for detecting loads applied to the sensor in a single direction and moments applied to the sensor in a single plane.

"Modern, computer-controlled prosthetic devices have many advantages over conventional prosthetic devices. For example, computer-controlled prosthetic devices can allow the amputees to walk with limited fear of stumbling or falling, allow amputees to lead a more active lifestyle, and improve the likelihood that amputees can realize their full economic potential. It is desirable to extend these benefits to as many as is possible of the thousands of new amputees each year, and the millions of existing amputees.

"A load and moment sensor that is both compact and robust would extend the benefits of the modern, computer-controlled prosthetic device to a broader cross section of the amputee population. Since the prosthetic device must be the same length as the intact limb of the amputee, a more compact sensor allows the prosthetic device to be used by amputees that are shorter in height, especially children. Furthermore, a more robust sensor allows the prosthetic device to be used both in harsher environments and in more aggressive activities such as construction, hiking, and various sports.

"In addition, designing a single, compact sensor to measure both an applied load and an applied moment presents a difficult challenge. The need to have a usable load output and the need to have a compact sensor may be opposing requirements. For example, when a force is applied to the sensor at a point off center, it typically generates not only an applied load on the sensor, but also an applied moment on the sensor. The applied load and moment create strains in the sensor. As the force is shifted further off center, the strain induced by the applied moment increases while the strain induced by the applied load remains constant. At a certain point, the strain induced by the applied load will be so small relative to the strain induced by the applied moment that it will become very difficult to measure both strains in the same sensor. One solution to maintain balance between load-induced strain and moment-induced strain is to increase the physical size of the sensor in the plane of the applied moment thereby sacrificing compactness.

"Thus, there is a need for a compact and robust load and moment sensor for detecting loads applied to the sensor in a single direction and moments applied to the sensor in a single plane."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventor's summary information for this patent: "The present invention relates to a compact and robust load and moment sensor for detecting loads applied to the sensor in a single direction and moments applied to the sensor in a single plane. This allows for load and moment detection in a compact sensor which can be modular. The modularity of the load and moment sensor allows for it to be replaced easily if it is damaged. Furthermore, the modularity allows for the load and moment sensor to be formed from a high strength material such as steel with minimal impact on the device's overall weight. The high strength material can improve the functional life of the load and moment sensor.

"The load and moment sensor of the present invention includes a plurality of strain gauges placed on specific locations of a sensing element of the sensor. The plurality of strain gauges are wired together into resistor circuits such as two Wheatstone bridges. The output of one Wheatstone bridge is proportional to the applied load while the output of the other is proportional to the applied moment. While the strain gauges can be located, for example, on a single sensing element, some of the resistive elements of the Wheatstone bridges can be located elsewhere on the prosthetic leg. By intelligently placing the strain gauges on the single sensing element, and by using the Wheatstone bridges, more accurate information regarding the load in the single direction and the load in the single plane is received. That is, the combination of the location of the strain gauges and the use of the Wheatstone bridges allows for good side load rejection (which is load and/or moment not in the single direction or the single plane), good noise rejection, and good temperature compensation.

"The good side load rejection, noise rejection, and temperature compensation can allow the prosthetic leg to more accurately mimic a human gait. Furthermore, the use of one Wheatstone bridge for applied load and another for applied moment improves performance of the prosthetic leg since a processor does not need to calculate the load and moment. The load and moment are measured directly from the outputs of the Wheatstone bridges.

"In addition, the use of a single sensing element can reduce an amount of components utilized by the prosthetic leg. Since components are prone to be damaged, reducing a number of components also reduces an amount of objects which can be potentially damaged. This translates to a lower cost and greater reliability because there are less components that are prone to being damaged and which need to be replaced.

"Also, the strain gauges can be semiconductor strain gauges which tend to have a smaller size while having a higher gauge factor. The higher gauge factor allows for the load and moment sensor to provide accurate results using low strains, which increases fatigue life and resistance to overloading of the load and moment sensor.

"These improvements in the sensor can improve the functionality of the prosthetic leg such that it may have application to a broader cross section of the amputee population. The compact feature of the load and moment sensor of the present invention allows the prosthetic device to be used by amputees that are shorter in height, especially children, since the prosthetic device must be the same length as the intact limb of the amputee. Furthermore, the robustness of the load and moment sensor of the present invention allows the prosthetic device to be used both in harsher environments and in more aggressive activities such as construction, hiking, and various sports.

"In one embodiment, the present invention is a load and moment sensor including a sensing element, a first Wheatstone bridge including a first plurality of strain gauges located on the sensing element, wherein the first Wheatstone bridge detects a moment in a single plane, and a second Wheatstone bridge including a second plurality of strain gauges located on the sensing element, wherein the second Wheatstone bridge detects a load in a single direction.

"In another embodiment, the present invention is a load and moment sensor including a sensing element including a mounting surface, a first Wheatstone bridge including a first strain gauge, a second strain gauge, a third strain gauge, and a fourth strain gauge, wherein the first strain gauge, the second strain gauge, the third strain gauge, and the fourth strain gauge are located on the sensing element in a first plane parallel to the mounting surface, and the first Wheatstone bridge detects a moment in a single plane. The load and moment sensor can also include a second Wheatstone bridge including a fifth strain gauge, a sixth strain gauge, a seventh strain gauge, and an eighth strain gauge, wherein the fifth strain gauge, the sixth strain gauge, the seventh strain gauge, and the eighth strain gauge are located on the sensing element in a second plane perpendicular to the mounting surface, and the second Wheatstone bridge detects a load in a single direction.

"In yet another embodiment, the present invention is a method for determining a load and a moment applied to a load and moment sensor including using a first set of strain gauges located on a sensing element to measure a moment applied to the load and moment sensor, and using a second set of strain gauges located on the sensing element to measure a load applied to the load and moment sensor."

For more information, see this patent: Palmer, Michael L.. Compact and Robust Load and Moment Sensor. U.S. Patent Number 8746080, filed January 27, 2011, and published online on June 10, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8746080.PN.&OS=PN/8746080RS=PN/8746080

Keywords for this news article include: Freedom Innovations L.L.C..

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Source: Computer Weekly News


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