Method and apparatus for detecting object orientation and position
A signal transmitting and receiving system to track the position and orientation of limb segments in order to provide feedback information for the control of the limb movement. The user will generally be seated in a wheelchair that provides a structure upon which orthogonal and/or non-orthogonally oriented coils can be mounted and energized selectively so as to create variously oriented magnetic fields. Multiple wireless sensors injected into the limb detect the local field strength and send information telemetrically to a central controller. The controller extracts information about the position and orientation of each limb segment by combining signals from various sensors according to calibration information and optimal filtering methods for extracting information from multiple nonlinear sensors in mechanically constrained systems.
1. A position and orientation detecting system to measure movement of a limb described with six independent position and orientation variables, comprising:
a) one magnetic field source, comprising an AC source and a transmitter coil energized by an asymmetrical current waveform, configured to be located external to the limb and to generate at least one magnetic field;
b) six physically separated, non-orthogonally oriented capsules configured to be implanted within the limb, each capsule having a sensor configured to sense the magnetic field and to telemetrically transmit at least one signal corresponding to the sensed magnetic field, wherein the transmitted signal comprises phase data; and
c) a controller configured to receive the transmitted signals, to compute the position and orientation of the limb based on the transmitted signals, and to generate information useful in controlling movement of the limb based on the transmitted signals;
wherein the product of the number of the magnetic field source and the capsule is six.
2. The system of claim 1 , wherein the phase data is determined from the sign of the largest signal sensed by the sensor that transmitted the phase data.
3. The system of claim 1 , wherein each sensor includes a sensor coil to sense the magnetic field.
4. The system of claim 3 , wherein each sensor coil is configured to also function as an antenna for a limb stimulator.
5. The system of claim 4 , wherein the transmitter coil is configured to also function as an antenna to transmit data to a limb stimulator.
6. The system of claim 5 , wherein each sensor coil is implanted within the limb at a location that is based on a clinical application.
7. The system of claim 3 , wherein each sensor coil is orientated non-orthogonally relative to the other sensor coils and/or the transmitter coil.
8. The system of claim 7 , wherein the controller comprises a composite optimization algorithm and is configured to solve for a constraint involved in configuring the coils.
9. The system of claim 3 , wherein the controller is configured to apply a global optimization algorithm to minimize local minimum points.
10. The system of claim 9 , wherein the global optimization technique comprises a genetic algorithm.
11. The system of claim 10 , wherein the global optimization technique further comprises a gradient-based optimization technique.
12. The system of claim 3 , wherein the controller comprises a linear approximation technique to cancel muscle deformation.
13. The system of claim 3 , wherein the transmitter coil is positioned at a location that is based on a clinical application.
14. The system of claim 13 , wherein the transmitter coil is placed at a different location.
15. The system of claim 1 , wherein each sensor comprises a single coil wrapped around two ferrite rods, an integrated circuit chip and a micro-PCB board.
16. The system of claim 15 , wherein each capsule includes a stimulator assembly configured to provide stimulation of limb muscle.
17. The system of claim 1 , wherein one of the capsules has a 2-axis MEMS accelerometer to detect the static effects of gravity.
18. The system of claim 1 , wherein the controller is further configured to reduce noise by using an Extended Kalman Filter.