# US 7,612,708 B2 · RF system for tracking objects > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,612,708 B2 - Document ID: US7612708B2 - Status: Granted - Kind: B2 - Application number: 11/957,826 - Filed: 2007-12-17 - Published: 2008-04-24 - Granted: 2009-11-03 - Earliest claimed: 2005-05-06 - Assignees: Orthosoft Inc. - Inventors: Jean-Louis Laroche - Web page: https://patentgrep.com/patent/US7612708B2 ## CPC - G01S 13/874: {Combination of several systems for attitude determination (in general G01C, control of attitude G05D1/49)} - A61B 34/20: Surgical navigation systems; Devices for tracking or guiding surgical instruments, e.g. for frameless stereotaxis - A61B 90/36: {Image-producing devices or illumination devices not otherwise provided for} - A61B 2034/2051: {Electromagnetic tracking systems} - A61B 2090/3975: {active} - G01S 7/4004: {of parts of a radar system} - G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES - A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D) ## Abstract A system for tracking an object in space for position, comprises a transponder device connectable to the object. The transponder device has one or several transponder aerial(s) and a transponder circuit connected to the transponder aerial for receiving an RF signal through the transponder aerial. The transponder device adds a known delay to the RF signal thereby producing an RF response for transmitting through the transponder aerial. A transmitter is connected to a first aerial for transmitting the RF signal through a first aerial. A receiver is connected to the first, a second and third aerials for receiving the RF response of the transponder device therethrough. A position calculator is associated to the transmitter and the receiver for calculating a position of the object as a function of the known delay and the time period between the emission of the RF signal and the reception of the RF response from the first, second and third aerials. A method is also provided. ## Claims ### Claim 1 A system for tracking an object in space for position, comprising: a transponder device connectable to the object, the transponder device having a transponder aerial and a transponder circuit connected to the transponder aerial for receiving an RF signal through the transponder aerial, the transponder device for adding a known delay to the RF signal for thereby producing an RF response for transmitting through the transponder aerial; first, second and third aerials; a transmitter connected to the first aerial for transmitting the RF signal through the first aerial; a receiver connected to the first, second and third aerials for receiving the RF response of the transponder device therethrough; a position calculator associated to the transmitter and the receiver for calculating a position of the object as a function of the known delay and the time period between the emission of the RF signal and the reception of the RF response from the first, second and third aerials; and an obstruction detector for producing obstruction data, wherein the position calculator is for calculating the position of the object as a function of the known delay, the time period and the obstruction data. ### Claim 2 (depends on 1) The system according to claim 1, wherein the transponder aerial comprises three orthogonally oriented transponder aerials whereby an orientation of the transponder device is calculated by the position calculator as a function of the RF response of the three transponder aerials. ### Claim 3 (depends on 1) The system according to claim 1, wherein the position calculator has a clock to measure the time period, the clock actuated by the transmitter. ### Claim 4 (depends on 2) The system according to claim 2, wherein the clock of the position calculator comprises a cycle counter and a phase comparator. ### Claim 5 (depends on 1) The system according to claim 1, wherein the position calculator has value data associating a distance between at least two of the first, second and third aerial to a time value, whereby the position calculator is for calculating the position as a function of the known delay, the time period and the distance between at least two of the first, second and third aerial. ### Claim 6 (depends on 1) The system according to claim 1, further comprising a fourth aerial connected to the receiver for receiving the RF response therethrough, with the time period including the reception of the RF response from the fourth aerial. ### Claim 7 (depends on 1) The system according to claim 1, wherein the transponder device is for amplifying the RF response, such that the obstruction detector identifies reflective obstructions. ### Claim 8 (depends on 1) The system according to claim 1, further comprising a fourth aerial connected to the receiver for receiving the RF response therethrough, the obstruction detector for considering the RF response received through all of the four aerials to identify obstruction, whereby the obstruction data filters the RF response received through one of the four aerials upon detection of obstruction for said one aerial. ### Claim 9 (depends on 1) The system according to claim 1, wherein the obstruction detector has a sensor device for visually detecting obstructions. ### Claim 10 (depends on 1) The system according to claim 1, wherein the transponder device has a portable power source. ### Claim 11 (depends on 1) The system according to claim 1, wherein said transponder device is switched between three transponder aerials and a transponder circuit is connected to the transponder aerials for receiving RF signals through the transponder aerials, the transponder devices for adding a known delay to the RF signal for thereby producing RF pulses for transmitting through the transponder aerials, further wherein the three transponder aerials are orthogonally oriented. ### Claim 12 A method for tracking an object in space for position, comprising the steps of: emitting an RF signal from a fixed position; receiving the RF signal with a transponder device on the object; emitting from the transponder device an RF return signal consisting of the RF signal with a known time delay; receiving the RF signal with at least three aerials associated to the fixed position; detecting obstruction; and calculating a position of the object from a distance between each of the at least three aerials and the transponder device as a function of the known delay and the time period between the emission of the RF signal and the reception of the RF response from the first, second and third aerials and obstruction data. ### Claim 13 (depends on 12) The method according to claim 12, wherein the step of receiving the RF signal is performed in three orthogonal axes, such that the step of calculating also involves calculating an orientation of the object. ### Claim 14 (depends on 12) The method according to claim 12, wherein the step of receiving the RF signal is performed with four aerials, such that the position is calculated as a function of the known delay and the time period between the emission of the RF signal and the reception of the RF response from the first, second, third and fourth aerials.