Optical motion sensor

An apparatus for sensing motion within a sensing region, comprising:

• a first emitting means for emitting a first beam of energy;
• a second emitting means for emitting a second beam of energy complementary to the first beam;
• sensing means for receiving and summing the energies of the first and second beams to produce a corresponding sensing signal having a constant signal portion and while motion is being sensed a time varying signal portion;
• filter means coupled to the sensing means for blocking the constant signal portion of the sum and passing the time varying signal portion;
• detection means for converting the time varying signal portion to a detection signal indicative of motion;
• and
• modulating means responsive to the detection signal for modulating one of the beams to null the time varying signal portion of the sensing signal,
• the detection signal continuing until the modulating means causes the sensing means to produce a constant sensing signal.

An optical motion sensor, comprising:

• a first light emitting diode for emitting a first pulsed beam;
• a second light emitting diode for emitting a second pulsed beam;
• a pulse generator for pulsing the first and second light emitting diodes to produce complementary pulsed beams of energy;
• a photodetector for receiving and summing the energies of the complementary pulsed beams and producing a sensing signal proportional to the sum of the beam energies, the sensing signal having a constant signal portion and a time varying signal portion;
• an amplifier AC coupled to the photodiode for blocking the constant signal portion of the signal current and passing the time varying signal portion;
• sampling means for sampling the time varying signal portion synchronous with the first pulsed beam and converting the amplitude of the signal to a proportional DC detection signal;
• and
• modulating means coupled to the sampling means and responsive to the detection signal for modulating the second pulsed beam at a rate proportional to the value of the detection signal to produce a constant sensing signal in the photodetector by nulling the time varying signal portion thereof, the detection signal continuing until the modulating means causes the photodetector to produce a constant sensing signal.

A method for sensing motion within a region, comprising:

• generating a first beam of energy to reflect off objects within the region;
• generating a second beam complementary to the first pulsed beam;
• sensing the sum of the beam energies at a detection point;
• generating a detection signal proportional to the change in the energy sum if the sum varies over time;
• modulating in response to a detection signal the intensity of one of the pulsed beams to null the time variance in the sum, the modulating thereby preventing further generation of the detection signal after motion within the region has ceased.