SYSTEMS AND METHODS FOR ADAPTIVE CANCELLATION OF A MOVING METAL OBJECT'S EFFECT ON RECEIVED SIGNALS
Metal detection process includes calibration operations to determine a plurality of gain settings and a plurality of model parameters, each corresponding to a region through which a moving metal door travels as it traverses a predefined motion path. Thereafter, a corresponding one of the plurality of gain settings is selected, and a corresponding set of the model parameters are selected. The selected gain setting control AFE gain so as to maintain the output of the AFE within a predetermined valid operating range. The model parameters are used to cancel the influence of the moving metal door from output controlled AFE signal.
1 . A method for adaptive cancellation of a moving metal object's effect on received signals, comprising:
performing calibration operations comprising
detecting, by a system controller of a metal detection system, an effect of a moving metal object of non interest (MMONI) upon on a first signal received at the metal detection system;
determining a plurality of gain settings for an Analog Front End (“AFE”) of a receiver circuitry associated with the metal detection system, each of said plurality of gain settings corresponding to one of a plurality of regions through which the MMONI travels along a predefined motion path;
selecting each of said plurality of gain settings to maintain an output of the AFE within a predetermined valid operating range while moving through each said region;
after selecting said plurality of gain settings, determining a model comprising a set of model parameters to characterize the influence of the moving metal object on the first signal, said model relating a position of the MMONI to a predicted received signal amplitude; and
following completion of the calibration operations
determining a MMONI position as it traverses the predefined motion path;
selecting for each region through which the MMONI travels a corresponding one of the plurality of gain settings, and a corresponding set of the model parameters applicable to the region;
using the selected gain setting for each region to control AFE gain so as to maintain the output of the AFE within the predetermined valid operating range and thereby produce a gain controlled AFE output signal; and
cancelling the effects of the moving metal object on the gain controlled signal by applying the model parameters to determine a modeled influence of the MMONI at each door position, and subtracting the modeled influence from the gain controlled AFE output signal.
2 . The method according to claim 1 , further comprising selecting each of the plurality of gain settings to maintain the AFE output within a predetermined input range of an A/D converter to which the AFE is connected.
3 . The method according to claim 1 , wherein the model is determined using a linear regression method.
4 . The method according to claim 1 , wherein the model is determined using a non-linear curve fitting method.
5 . The method according to claim 1 , wherein the MMONI is a moving door comprised of metal.
6 . The method according to claim 1 , wherein the metal detection system also performs operations to detect one or more electronic article surveillance (EAS) tags.
7 . The method according to claim 6 , wherein the EAS tags are acouto-magnetic tags.
8 . The method according to claim 1 , wherein the set of model parameters for each said region facilitates prediction of the gain controlled signal produced in response to the MMONI.
9 . The method according to claim 8 , wherein the set of model parameters define a linear equation.
10 . The method according to claim 9 , wherein the model parameters for each said region include a slope value and an intercept value defined in accordance with a Cartesian coordinate system.