Proximity sensor

Abstract

An immersion sensor for use with a cushion or mattress for determining the relative immersion of a person within the cushion or mattress comprising a sensor, a ground and a circuit for measuring capacitance. The sensor comprises a sheet of conductive material, and the ground comprises a second sheet of conductive material. The circuit is adapted to send short bursts of electrical current to the sensor and a capacitor. The circuit is further adapted to measure the length of time the burst of current takes to charge the capacitor. Based upon the measured time, the circuit calculates the proximity of the object based upon the time taken to charge the capacitor. A method that may be implemented with the immersion sensor is also disclosed.

1 . An immersion sensor assembly for use with a cushion or mattress for measuring the depth of immersion of a person within the cushion or mattress comprising:
 a sensor comprising a conductive material;   a ground comprising a second conductive material electrically isolated from the sensor and at least partially surrounding the sensor, the ground electrically connected to and maintained at a ground electrical potential;   a circuit comprising a microprocessor and a reference capacitor, the circuit adapted to send short bursts of electrical current to the sensor and the reference capacitor, the circuit adapted to measure the length of time the burst of current takes to charge the reference capacitor and the circuit adapted to calculate the immersion of the person into the cushion or mattress based upon the time taken to charge the reference capacitor; and   wherein the sensor and the ground when the immersion sensor is laid flat, are nominally coplanar.   
     
     
         2 . The immersion sensor assembly of  claim 1  further comprising at least one layer of nonconductive material disposed over the sensor and the ground. 
     
     
         3 . The immersion sensor assembly of  claim 2  wherein the nonconductive material is foam. 
     
     
         4 . The immersion sensor assembly of  claim 1  wherein the sensor is disposed within a protective encasement of neoprene rubber. 
     
     
         5 . The immersion sensor assembly of  claim 1  wherein the circuit comprises a capacitive sensor. 
     
     
         6 . The immersion sensor assembly of  claim 1  further comprising a driven shield to isolate the sensor from the effect of electromagnetic interference or metallic objects in the direction of the driven shield from the sensor. 
     
     
         7 . The immersion sensor assembly of  claim 1  comprising a plurality of sensors and a plurality of grounds. 
     
     
         8 . The immersion sensor assembly of  claim 7  wherein the circuit is attached to two or more of the plurality of sensors to simultaneously determine the proximity of people to each of the sensors. 
     
     
         9 . The immersion sensor assembly of  claim 8  wherein the circuit is adapted to obtain a proximity measurement from a second sensor to determine a scale of proximity for proximity measurements from a first sensor. 
     
     
         10 . The immersion sensor assembly of  claim 7  wherein the circuit comprises a multiplexer, the multiplexer being attached to two or more of the sensors and also to the circuit and adapted to selectively connect the sensors to the circuit. 
     
     
         11 . An immersion sensor assembly comprising:
 a cushion or mattress having an adjustable depth of immersion of a person on the cushion or mattress;   a sensor comprising a sheet of conductive material;   a grounding plane being in the area around the sensor and allowing a capacitance measurement to be made relative to the distance between a person and the sensor;   a shield comprising a second sheet of conductive material located adjacent to and having generally the same shape and area as the sensor;   a circuit comprising a reference capacitor, the circuit adapted to
 send short bursts of electrical current to the sensor and the reference capacitor, 
 measure the length of time the burst of current takes to charge the reference capacitor and the circuit adapted to calculate the relative proximity of the person based upon the time taken to charge the reference capacitor, 
 drive the shield to electrically isolate the shield from external capacitance or electromagnetic interference, and 
 provide an indication when the person is too deeply immersed within the cushion or mattress. 
   
     
     
         12 . A bed assembly for the support of an individual positioned on the bed, the bed assembly comprising:
 a bed frame, said bed frame comprising metal components;   a mattress on the bed; and   a sensor operatively associated with the mattress, the sensor comprising,
 a microcontroller, 
 a ground layer surrounding the sensor; 
 a shield layer comprising a sheet of conductive material and driving the shield to isolate the sensor from the effect of stray capacitance and electromagnetic interference from the metal bed frame components; 
 a circuit for detecting the capacitive effect of the individual on the mattress and providing a relative output for the microcontroller; 
   wherein the planes formed by the sensor and the shield, when the immersion sensor is laid flat, are nominally parallel; and   wherein the circuit is adapted to provide an indication when the individual is too deeply immersed within the mattress or when the individual is off the mattress.   
     
     
         13 . The bed assembly of  claim 12  wherein the sensor further comprises at least one layer of nonconductive material disposed over the sensor. 
     
     
         14 . The bed assembly of  claim 12  wherein the sensor is integrally formed with a mattress. 
     
     
         15 . The bed assembly of  claim 12  wherein the sensor comprises a plurality of sensors and the shield is sized to isolate the plurality of sensors. 
     
     
         16 . The bed assembly of  claim 15  wherein the circuit comprises a multiplexer, the multiplexer being attached to two or more of the sensors and also to the circuit and adapted to selectively connect the sensors to the circuit. 
     
     
         17 . In a bed assembly comprising a bed frame and a mattress, a method of determining the proper immersion of a person within the mattress comprising the steps of:
 providing a first sensor below mattress comprising a sheet of conductive material;   providing a ground layer comprising a sheet of conductive material that is nominally coplanar and maintained at a ground potential below the cushion or mattress;   providing a shield layer comprising a sheet of conductive material and driving the shield to isolate the sensor from the effect of stray capacitance and electromagnetic interference from the bed frame.   sending short bursts of electrical current to the sensor and a capacitor;   measuring the length of time the burst of current takes to charge the capacitor;   calculating the proximity of the person based upon the time taken to charge the capacitor; and   providing an indication when the person is either over-immersed or under-immersed within mattress.   
     
     
         18 . The method of  claim 17  further comprising the steps of:
 providing a second sensor of smaller area than the first sensor comprising a second sheet of conductive material; 
 sending short bursts of electrical current to the second sensor and the capacitor; 
 measuring the length of time the burst of current takes to charge the capacitor; and 
 calculating the proximity of the person based upon the time taken to charge the capacitor; and 
 determining a scale for the calculation from the first sensor from the calculation obtained from the second sensor.