Patent ID: 7746220
Filing Date: 2010-06-29
Classification: G01S

Abstract:
1. Moving object detection apparatus, comprising: a transmitter that emits energy waves with a first frequency to a detection area; a receiver that, when receiving incoming energy waves from the detection area, generates an electric signal corresponding to the incoming energy waves; a detection portion that obtains a detection signal from a reference signal with the first frequency and the electric signal, the detection signal becoming a Doppler shift signal when at least one second frequency different from the first frequency is obtained from the electric signal, the Doppler shift signal being obtained from the first frequency and the at least one second frequency; a binary conversion portion that compares the detection signal with a conversion threshold signal to obtain a binary signal; and a judgment portion that judges whether or not a moving object approaching or leaving the receiver exists in the detection area based on the binary signal, wherein the moving object detection apparatus further comprises an oscillator that generates a first reference signal having the first frequency and supplies the transmitter with the first reference signal to cause the transmitter to emit sine-wave shaped energy waves with the first frequency to the detection area; wherein the detection portion comprises: a phase shifter that shifts the phase of the first reference signal by ¼period to produce a second reference signal; a first detection part that mixes the electric signal generated by the receiver with the first reference signal generated by the oscillator to produce a first detection signal, the first detection signal becoming a first Doppler shift signal that has a frequency of the difference between the first frequency and the second frequency when the second frequency is obtained from the electric signal; and a second detection part that mixes the electric signal generated by the receiver with the second reference signal produced by the phase shifter to produce a second detection signal, the second detection signal becoming a second Doppler shift signal that has a frequency of the difference between the first frequency and the second frequency and is different in phase by ¼ period from the first Doppler shift signal when the second frequency is obtained from the electric signal; wherein the binary conversion portion comprises: a first binary converter that compares the first detection signal with a first conversion threshold signal to obtain a first binary signal; and a second binary converter that compares the second detection signal with a second conversion threshold signal to obtain a second binary signal; wherein the judgment portion comprises: a first judgment part that is configured to: (A) take a transition factor whenever first and second values are respectively set to first and second coordinates in two-dimensional coordinate system in response to the levels of the first and second binary signals, said transition factor being specified by the first and second coordinates; (B) judge that said moving object exists in the detection area if taken each transition factor crosses one coordinate axis in the coordinate system, and otherwise to judge that said moving object does not exist in the detection area; and (C) judge that said moving object approaches the receiver if said each transition factor moves around the origin of the coordinate system in one direction, and to judge that said moving object leaves the receiver if said each transition factor moves in reverse direction to the one direction, in case that said moving object exists in the detection area; a first counter that is configured to: (a) add a first polarity value to a first count value in case that said moving object exists in the detection area and approaches the receiver; and (b) to add a second polarity value to the first count value in case that said moving object exists in the detection area and leaves the receiver, said second polarity value being equal in absolute value to the first polarity value and different in polarity from the first polarity value; a second judgment part that sends out an existence signal when the absolute value of the first count value is larger than that of a judgment threshold value that is equal in polarity to the first polarity value, the existence signal representing that said moving object exists in the detection area.