System and method for loose nut detection

Abstract

One illustrative embodiment includes an apparatus for detecting if a fastener moves from a first position to a different second position. The apparatus includes a first connector for connecting a first side of a contact bridge to the fastener for movement in response to movement of the fastener, and a second connector for connecting a second side of the contact bridge to an object to remain stationary relative to the object. One of the first and second sides of the contact bridge includes first and second spaced apart electrical conductors; the other side includes a third electrical conductor. The third electrical conductor is positionable to contact the first and second electrical conductors when the fastener is in the first position, and the third electrical conductor may be spaced apart from at least one of the first and second electrical conductors when the fastener is in the second position.

What is claimed is: 
     
         1 . Apparatus for detecting rotation of a fastener relative to an object; the apparatus comprising:
 a first part having an aperture configured to receive and non-rotationally engage a part of the fastener that is rotatable relative to the object;   a second part between the first part and the object, the second part comprising a base configured to non-rotationally engage the object;   an electrical current path extending between first and second electrical conductors on the second part wherein the electrical current path extends from the second part into the first part, through the first part and back into the second part wherein rotation of the first part relative to the second part results in a varying electrical characteristic of the current path, the variable electrical characteristic having distinct values for each of multiple different relative angular positions of the first and second parts.   
     
     
         2 . Apparatus according to  claim 1  wherein the first part is rotatably coupled to the second part for rotation relative to the second part about an axis and the second part is apertured on the axis to receive the fastener. 
     
     
         3 . Apparatus according to  claim 1  comprising a monitoring circuit connected to monitor the value of the electrical characteristic of the circuit path. 
     
     
         4 . Apparatus according to  claim 3  wherein the electrical characteristic comprises at least one of: a varying electrical resistance; a varying electrical impedance and a varying capacitance. 
     
     
         5 . Apparatus according to  claim 4  comprising a data store and a processor configured to compare the value of the electrical characteristic determined by the monitoring circuit to a reference value stored in the data store and to generate a signal if the value of the electrical characteristic determined by the monitoring circuit differs by more than a threshold amount from the reference value. 
     
     
         6 . Apparatus according to  claim 4  comprising a data store containing a table relating different values of the electrical characteristic to different relative angles between the first and second parts. 
     
     
         7 . Apparatus according to  claim 6  comprising a processor configured to compare the value of the electrical characteristic determined by the monitoring circuit to a reference value stored in the data store and to generate a signal if the value of the electrical characteristic determined by the monitoring circuit differs by more than a threshold amount from the reference value. 
     
     
         8 . A sensor assembly comprising:
 the apparatus of  claim 1 ; and   a detector in electrical communication with the first and second electrical conductors and configured to generate a notification in response to a change in electrical conductivity of the current path.   
     
     
         9 . The sensor assembly of  claim 8  wherein the notification comprises a radio frequency signal. 
     
     
         10 . The sensor assembly of  claim 9  comprising a wireless transmitter connected to transmit a signal comprising the notification to a communication module. 
     
     
         11 . The sensor assembly of  claim 10  comprising a data processor configured to periodically operate the detector, cache data representing an output of the detector and transmit the cached data periodically in periodic operational property signals a the communication module by way of the wireless transmitter. 
     
     
         12 . Apparatus according to  claim 1  wherein the current path comprises a contact bridge having a first side supported on the first part and a second side supported on the second part wherein one of the first and second sides of the contact bridge includes first and second spaced-apart electrically-conductive bodies and the other one of the first and second sides of the contact bridge includes a third electrically-conductive body arranged to bridge between the first and second electrically-conductive bodies for a range of angles of relative rotation of the first and second parts. 
     
     
         13 . Apparatus for detecting movement of a fastener away from a first position relative to an object, the apparatus comprising:
 a contact bridge having first and second sides wherein one of the first and second sides of the contact bridge includes first and second spaced-apart electrically-conductive bodies and the other one of the first and second sides of the contact bridge includes a third electrically-conductive body dimensioned to bridge between the first and second electrically-conductive bodies;   a first connector operative to couple the first side of the contact bridge to move together with the fastener if the fastener moves relative to the object;   a second connector operative to connect the second side of the contact bridge to remain stationary relative to the object;   
       wherein, when the first connector couples the first side to the fastener in the first position and the second connector couples the second side to the object, the third electrically-conductive body is positionable to bridge between the first and second electrically-conductive bodies and motion of the fastener relative to the object causes change in a value of an electrical characteristic of a current path extending through the first, second and third electrically-conductive bodies. 
     
     
         14 . Apparatus according to  claim 13  wherein the third electrically-conductive body is spaced apart from at least one of the first and second electrically-conductive bodies when the fastener is moved to a second position different from the first position. 
     
     
         15 . Apparatus according to  claim 13  further comprising a detector in electrical communication with the current path, the detector configured to determine the value of the electrical characteristic. 
     
     
         16 . Apparatus according to  claim 15  further comprising a data store operative to store a reference value;
 a monitor configured to periodically compare the reference value to a present value of the electrical characteristic determined by the detector; and 
 a warning indicator, wherein the monitor is operative to operate the warning indicator if an absolute difference between the present value and the reference value exceeds a predetermined threshold. 
 
     
     
         17 . Apparatus according to  claim 13  wherein the electrical characteristic comprises a varying electrical resistance, electrical impedance or variable capacitance. 
     
     
         18 . Apparatus according to  claim 13  wherein the fastener comprises a bolt or nut and the motion of the fastener relative to the object comprises rotary motion. 
     
     
         19 . Apparatus according to  claim 13  wherein the fastener comprises a linearly-movable fastener and the first, second and third electrically-conductive bodies are configured to be co-linear along a line of movement of the fastener. 
     
     
         20 . Apparatus according to  claim 13  comprising a data store accessible to a processor, the data store containing a table relating different values of the electrical characteristic to different relative positions of the first and second sides of the contact bridge.