Magnetic sensor system for fast-response, high resolution, high accuracy, three-dimensional position measurements

• US 6,789,043 B1
• Filed: 09/23/1999
• Issued: 09/07/2004
• Est. Priority Date: 09/23/1998
• Status: Expired due to Fees

• Current Assignee: Johns Hopkins University
• Original Assignee: Johns Hopkins University
• Inventors: Nelson, Carl V., Jacobs, Bryan C.
• Primary Examiner(s): Wachsman, Hal
• Assistant Examiner(s): TSAI, CAROL S W
• Application Number:
  US09/401,701
• Time in Patent Office: 1,811 Days
• Field of Search: 367/128, 702/36, 702/37, 702/38, 702/57, 702/65, 702/66, 702/67, 702/94, 702/95, 702/92, 702/93, 702/115, 702/127, 702/150, 702/153, 702/183, 702/190, 702/197, 702/FOR.103, 702/FOR.104, 702/FOR.105, 702/FOR.106, 702/FOR.110, 702/FOR.124, 702/FOR.130, 702/FOR.134, 702/FOR.135, 702/FOR.144, 702/FOR.155, 702/FOR.164, 702/FOR.170, 702/FOR.171, 324/207.2, 324/207.21, 324/207.25, 324/173, 324/174, 324/202, 700/63, 700/69, 700/85, 700/258
• US Class Current: 702/152
• CPC Class Codes: G01B 7/004 for measuring coordinates of points
• CPC Class Codes: G01V 15/00 Tags attached to, or associated with, an object, in order to enable detection of the object record carriers for use with machines having a detectable tag or marker G06K19/00

Abstract

The position, orientation, velocity and acceleration of remote sensors is determined using magnetic fields. Multiple, arbitrarily oriented magnetic field transmitters are placed in one reference frame (source reference frame), and multiple, arbitrarily oriented magnetic field receivers are placed in a second reference frame (body reference frame). The spatially varying magnetic fields of the transmitters in the source reference frame are sensed by the magnetic field receivers in the body reference frame. The computer algorithm uses a physics-based extended Kalman filter to resolve the position; orientation, velocity and acceleration of the body relative to the source reference frame. The physics-based extended Kalman filter can accommodate the effects of metal in the source and body reference frames and thus allow the system to measure position, orientation, velocity and acceleration under conditions where eddy currents would normally hinder other magnetic position measuring systems. The Kalman filter also allows the use of multiple transmitters and receivers distributed over an arbitrarily large sensing volume, thereby extending the useful range and accuracy of the system. Further, the Kalman filter allows the use of high-speed measurements with minimal signal averaging, thus extending the useful dynamic response of the system. Moreover, the Kalman filter allows the use of arbitrarily oriented transmitters and receivers, thus increasing the flexibility of the system in many applications.

Claims

1. A method for determining the position, velocity and acceleration of an object, comprising:

providing a three dimensional fixed reference frame of known dimensions;

providing an object, the position, velocity and acceleration of which are to be measured;

generating electrical current from an oscillator;

delivering said current from said oscillator to a power amplifier;

directing said amplified current firm said amplifier to a plurality of transmitters;

generating a magnetic field from said transmitters in said reference frame;

receiving said magnetic field signal from said transmitters into at least one receiver;

demodulating and amplifying said received magnetic field signal into magnetic field components from said receiver signal, wherein said output from said amplifier is proportional to said magnetic field components;

applying an extended Kalman filter utilizing a mathematical algorithm to said demodulated and amplified signal to calculate the position, velocity and acceleration of said object.

2. A method as in claim 1, wherein said electrical current is selected from the group consisting of an alternating current source, a direct current source, a pulsed direct current source, and combinations thereof.

3. A method as in claim 1, wherein said mathematical algorithm mathematically models said transmitters as dipoles, said algorithm further uses total field and vector magnetic field mathematical components to calculate said three-dimensional position of said object.

4. A method as in claim 1, further comprising placing calibrated magnetic field receivers at a known location in an uncalibrated transmitter geometry, wherein said algorithm determines the location of said transmitter in said fixed reference frame.

5. A method as in claim 1, wherein said algorithm mathematically averages said signals from said receivers.

6. A method as in claim 1, wherein said algorithm mathematically treats eddy currents generated in metal surfaces and objects nearby said transmitters as virtual magnetic field transmitters, said algorithm further calculating the position and orientation of said virtual magnetic field transmitters.