Magnetic Position Sensor Using M-Sequential Code Spread Spectrum
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Solution Overview
Problem
Existing relative position and posture measuring systems, such as the Polhemus sensor, are affected by noise and have delayed response times, making them unsuitable for practical use in virtual reality applications, especially when multiple channels are used for accurate measurements.
Innovation Solution
The implementation of an M-sequential demodulation system that uses a magnetic field generator with orthogonal transmission coils, a magnetic field detector, and a computing unit to compute relative positions and postures based on magnetic field amplitude, employing a clock generator, M-sequential code generators, spread code generators, integrators, and voltage-to-current converters to achieve quick and noise-resistant measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If time division mode is used to drive transmission coils sequentially, then magnetic field detection can be performed, but the response time is delayed and the rate action is slow
Solution Approach 1:
The patent employs periodic square wave signals to simultaneously drive multiple transmission coils, replacing the sequential time-division mode. Each transmission coil is driven by a square wave signal with a specific phase shift, enabling parallel magnetic field generation and detection, thereby significantly improving response speed and reducing detection time.
Solution Approach 2:
The patent pre-generates spread spectrum codes and integrates them before driving the transmission coils. This preliminary processing of signals ensures that the magnetic field detection can be performed directly without additional processing delays, improving the overall response speed of the system.
2Reliability
If carrier wave communication system is used, then magnetic field transmission can be achieved, but the system is weak to noises and detection is limited to short distances
Solution Approach 1:
The patent changes the modulation method from traditional carrier wave to spread spectrum modulation using M-sequential codes. By spreading the signal spectrum and using code division multiplexing, the system achieves superior noise resistance and can accurately detect magnetic fields over longer distances even in noisy environments.
Solution Approach 2:
The patent converts the harmful effect of noise into a beneficial feature by using spread spectrum technology. The wideband spreading signal allows the system to distinguish the desired signal from noise through correlation processing, effectively turning noise resistance into a system advantage that enables long-distance detection.
3Measurement precision
If multiple channels are increased for accurate computation, then measurement precision improves, but noise influence becomes larger
Solution Approach 1:
The patent segments the magnetic field detection into multiple orthogonal transmission channels, each modulated with unique M-sequential codes. This segmentation allows independent processing of each channel's signal, enabling accurate computation of position and posture while maintaining noise resistance through code division multiplexing.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for accurate and rapid computation of relative positions and postures, reducing noise interference and enabling wideband spreading, thus supporting practical applications in virtual reality without the need for time division mode output from transmission coils.
Implementation Method 1
a magnetic field generator including a plurality of transmission coils arrayed orthogonal to each other for transmitting a magnetic signal from each transmission coil
Implementation Method 2
a magnetic field detector for receiving a magnetic field generated in each transmission coil as a magnetic field detection value for each transmission coil
Data Source
AI summary
The present invention provides a relative position and/or posture measuring system for measuring relative positions and relative postures between a magnetic field generator and a magnetic field detector by detecting a change in a magnetic field, in which the magnetic field generator includes a clock generator, a plurality of M-sequential code generators, a plurality of spread code generators, a plurality of integrators, and a voltage to current converter, and transmission coils TX, TY, TZ generate magnetic fields according to driving currents based on spread code obtained by converting code sequences generated by the M-sequential code generators to spread code with the spread code generators. The magnetic field detector reversely spreads received magnetic field detection values to obtain a magnetic field amplitude, and computes relative positions and relative postures of the two from the magnetic field amplitude.