# US 2018/0023940 A1 · Position sensing system with an electromagnet > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2018/0023940 A1 - Document ID: US20180023940A1 - Status: Published application - Kind: A1 - Application number: 15/657,407 - Filed: 2017-07-24 - Published: 2018-01-25 - Earliest claimed: 2016-07-22 - Assignees: Regents of the University of Minnesota - Applicants: Regents of the University of Minnesota - Inventors: Ryan Madson; Rajesh Rajamani - Web page: https://patentgrep.com/patent/US20180023940A1 ## CPC - G01B 7/003: {for measuring position, not involving coordinate determination (coordinate measuring G01B7/004)} - G01D 5/145: {influenced by the relative movement between the Hall device and magnetic fields (see G01R33/06)} - G01D 5/147: {influenced by the movement of a third element, the position of Hall device and the source of magnetic field being fixed in respect to each other} - G01D 5/2013: {by a movable ferromagnetic element, e.g. a core (G01D5/2033 takes precedence)} - G01V 3/10: using induction coils - G01V 3/12: operating with electromagnetic waves {(operating with millimetre waves G01V8/005)} - H02J 50/10: using inductive coupling - G01B 7/30: for measuring angles or tapers; for testing the alignment of axes - G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS - G01D: MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR - G01V: GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS (means for indicating the location of accidentally buried, e.g. snow-buried, persons A63B29/02) - H02J: ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY ## Abstract A position sensing system for measuring a position of a moving object includes an electromagnet configured to generate an alternating magnetic field, and a magnetic sensor configured to measure an intensity of a first magnetic field that is based on the alternating magnetic field. A controller is configured to estimate a position of the moving object based on the measured intensity of the first magnetic field. ## Claims ### Claim 1 A position sensing system for measuring a position of a moving object, comprising: an electromagnet configured to generate an alternating magnetic field; a magnetic sensor configured to measure an intensity of a first magnetic field that is based on the alternating magnetic field; and a controller configured to estimate a position of the moving object based on the measured intensity of the first magnetic field. ### Claim 2 (depends on 1) The position sensing system of claim 1, wherein the controller is configured to estimate the position of the moving object based further on a nonlinear model of a magnetic field produced by the electromagnet as a function of position around the electromagnet. ### Claim 3 (depends on 1) The position sensing system of claim 1, wherein the moving object is a piston positioned within a cylinder. ### Claim 4 (depends on 3) The position sensing system of claim 3, wherein the electromagnet is positioned on the piston, and the magnetic sensor is positioned on the cylinder. ### Claim 5 (depends on 3) The position sensing system of claim 3, wherein the electromagnet is positioned on the cylinder, and the magnetic sensor is positioned on the piston. ### Claim 6 (depends on 5) The position sensing system of claim 5, wherein the magnetic sensor on the piston is powered by a battery, and wherein no wires are connected to the piston. ### Claim 7 (depends on 3) The position sensing system of claim 3, wherein the electromagnet and the magnetic sensor are positioned on the cylinder. ### Claim 8 (depends on 7) The position sensing system of claim 7, and further comprising: a permanent magnet positioned on the piston. ### Claim 9 (depends on 8) The position sensing system of claim 8, wherein the first magnetic field is based on both the alternating magnetic field and a magnetic field produced by the permanent magnet. ### Claim 10 (depends on 7) The position sensing system of claim 7, and further comprising: an inductive coil positioned on the piston. ### Claim 11 (depends on 10) The position sensing system of claim 10, wherein the electromagnet is configured to induce an alternating current in the inductive coil during on portions of an on-off duty cycle of the electromagnet. ### Claim 12 (depends on 11) The position sensing system of claim 11, wherein the magnetic sensor is configured to measure the intensity of the first magnetic field only during off portions of the on-off duty cycle of the electromagnet. ### Claim 13 (depends on 3) The position sensing system of claim 3, wherein the electromagnet is positioned on the cylinder and the magnetic sensor is positioned on a piston rod of the piston, wherein the electromagnet and the magnetic sensor are external to the cylinder, and wherein no components of the position sensing system are located inside of the cylinder. ### Claim 14 (depends on 13) The position sensing system of claim 13, wherein the magnetic sensor on the piston rod is battery-powered with a rechargeable battery, and wherein the battery is recharged inductively each time the piston rod is fully retracted and stationary. ### Claim 15 (depends on 1) The position sensing system of claim 1, wherein a frequency of the alternating magnetic field is much higher than a frequency of motion of the moving object and is also much higher than a frequency of motion of any unexpected disturbances from other nearby moving magnetic or ferromagnetic objects. ### Claim 16 (depends on 1) The position sensing system of claim 1, wherein the controller includes a high-pass or band-pass filter that extracts only an intensity of the first magnetic field at a specific known alternating frequency of the alternating magnetic field. ### Claim 17 (depends on 1) The position sensing system of claim 1, wherein the moving object has rotational motion and wherein relative rotational motion between the electromagnet and the magnetic sensor is used to compute a relative rotational angle of the moving object. ### Claim 18 A method of measuring a position of a moving object, comprising: generating an alternating magnetic field with an electromagnet; measuring an intensity of a first magnetic field that is based on the alternating magnetic field; and estimating a position of the moving object based on the measured intensity of the first magnetic field. ### Claim 19 (depends on 15) The method of claim 15, and further comprising: estimating the position of the moving object based further on a nonlinear model of a magnetic field produced by the electromagnet as a function of position around the electromagnet. ### Claim 20 (depends on 15) The method of claim 15, wherein the moving object is a piston positioned within a cylinder.