Abstract:
The force sensing switch comprising a housing and a movable member movable relative to the housing upon having a predetermined force applied thereagainst by an adjacent moving structure when the structure becomes misaligned, the movable member engaging circuitry within the housing which will produce an alarm signal and will stop the adjacent structure from moving.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a force sensitive switch. More particularly, the switch, when force is applied against a section thereof, is operative to stop a machine or the like until a structure of the machine producing the force on the switch, is repositioned. 
     2. Prior Art 
     The existing art for such devices uses roller switches or rubbing blocks for force detection. The roller switch, when contacted by a misaligned belt, for example, has a spring loaded arm which rotates about a pivot, when the arm has rotated beyond a predetermined point, the switch gives a signal by closure of contacts or the like. The roller mounted upon the pivoted arm is free to rotate about its own axis so that contact with the moving belt will not cause undue wear. 
     When a belt is partially misaligned, sufficient to contact the roller but insufficient to cause machine stoppage, the roller rotates continuously, generating heat, and becoming a maintenance hazard. 
     An alternative type of detector, known generally as a rub block or rubbing block, is made from substantially rigid material containing, embedded therewithin, a temperature detector. When used in the above described application, when the moving belt contacts the rubbing block applying force thereagainst, the rubbing block becomes heated and when the preset temperature is reached, the temperature sensor generates a signal to stop the machine. This type of detector is hazardous as heat must be generated for the device to operate. 
     SUMMARY OF THE INVENTION 
     According to the invention there is provided a force sensing switch comprising a housing and a movable member movable relative to the housing upon having a predetermined force applied thereagainst by an adjacent moving structure when the structure becomes misaligned, the movable member engaging circuitry within the housing which will produce an alarm and will stop the adjacent structure from moving. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross sectional view through the switch of the present invention. 
     FIG. 2 is a diagram showing switch circuitry. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Perusing the Figures in greater detail, it will be understood that the force sensitive switch made in accordance with the teachings of the present invention and generally identified by the reference numeral  10 , comprises a body  12  made up of a rigid housing  14  made from metal or other substantially rigid material and a movable member  13  which is movable toward and away from the rigid housing  14 , with a suitable flexible seal  16  engaged therebetween. 
     Within the housing  14  is mounted a load cell assembly  17  consisting of a bending beam  18  of elastic material fixed at one end  19  to a support base  21  therefor and upon which are bonded strain gauges  20 . Acting on the bending beam  18  is one end  22  of a rod  23  suitably guided by a guide beam  24  to permit force to act on the bending beam  18  in one direction only. The other end  25  of the rod  23  is also suitably guided via a port  26  in a wall  28  of the housing  14  and restrained from movement in directions other than the direction of action on the beam  18 . Attached to this end  25  of the rod  23  is the movable member  13  which may comprise a suitable button, plate, disc, arm, or sphere which may be hardened to resist the action of wear. The end  25  of the rod  23  also incorporates a shoulder  29  which will not allow the rod  23  to disconnect from the housing  14 , the shoulder  29  being of a greater extent than the port  26 . 
     When a force acts on the member  13 , it is transmitted via the rod  23  to the bending beam  18  where strain on the beam  18  is measured by the strain gauges  20 . The rod  23  is so dimensioned that when the bending beam  18  has been bent to the design limits, and well before the elastic limit is exceeded, the end  22  of the rod  23  contacts a rigid stop  30  which may be a wall  30  of the housing  14  itself, and prevents further force on the movable member  13  from over-stressing the bending beam  18 . An amplifier  32  converts the strain on the bending beam  18  to a voltage, substantially proportional to the force applied to the movable member  13 . This voltage may be compared in a voltage comparator  34  with a fixed voltage set on an adjustable potentiometer  44  which fixed voltage may be set through manipulation of a set screw  45  such that when the voltage produced by the strain gauge amplifier  32  exceeds the preset potentiometer voltage  44  setting, an output signal is generated by the comparator  34 . This output signal is provided to an output device such as an indicator light  46  and/or a normally energized relay coil  47  to signal that the force acting on the movable member  13  had exceeded the setting on the potentiometer  44 , turning off the indicator light  46  and deenergizing the relay coil  47  to cause an alarm indication and/or stoppage of a machine part producing the force on the movable member  13 , to be described further below. 
     When the rigid housing  14  of the switch  10  is mounted solidly to one part of a machine (not shown), misaligned motion of another part of the machine (not shown), adjacent the movable member  13 , will cause a force to be applied to the movable member  13 . Therefore the switch  10  can be used to detect relative displacement or misalignment between two parts of a machine. 
     This detection is particularly applicable, but not limited, to machines such as belt conveyors or belt elevators (not shown) where it is necessary to detect that movement of a belt of the machine into an undesirable or misaligned position has occurred. In such application, the switch  10  would be mounted to a rigid part of a machine in such a position that if the moving belt of the machine was misaligned laterally, it would generate a force onto and against the movable member  13  of the switch  10 . In such application, the force sensing switch  10  may be arranged to warn of, or control, such an “out of bounds” condition. 
     The heart of the touch switch  10  may be in the form of either a Wheatstone full bridge  50  consisting of resistive-type strain gauges  20 A,  20 B,  20 C and  20 D, fed by voltage V+ as shown in FIG. 2 or may be a Wheatstone half bridge  50  consisting of resistive-type strain gauges  20 B and  20 D and fixed resistors  20 A and  20 C, as will be understood by those skilled in the art. If no force is applied to movable member  13 , no bending of beam  18  occurs and the resistance on all gauges  20 A,  20 B,  20 C and  20 D is equal. In this condition, the voltages at the left and right arms of the bridge  50  which feed differential amplifier  32  are equal fractions of V+ and relay coil  47  is maintained in its normally energized state. 
     When force is applied to movable member  13  it transmits this force downward on rod  23  which in turn causes bending of beam  18  mounting strain gauges  20 , when connected as a full bridge, the resistance of  20 A and  20 D increases and the resistance of  20 B and  20 C decreases. When connected as a half bridge, the resistance of  20 B decreases and the resistance of  20 D increases. Either case causes the output voltage of amplifier  32  to increase substantially proportionally with increasing force. If this force increases to the point where the voltage at the output of amplifier  32  and therefore at the A input of comparator  34  exceeds the voltage at the B input of comparator  34 , then the output of comparator  34  goes high, deenergizing the output device, shown in this embodiment to comprise the relay coil  47 . The signal can produce a visual indication through the preferred LED  46 , and can pass through a cable  55 , suitably attached to the machine in known manner, to cause motion of the adjacent structure, such as the belt, to cease, upon misalignment. 
     It will also be understood by those skilled in the art that various structures of the circuitry described above may be mounted on a circuit board  57 , if desired. 
     As described above, the force sensing switch  10  provides a number of advantages, some of which have been described above and others of which are inherent in the invention. Also, modifications may be proposed to the switch  10  without departing from the teachings herein. As an example, all equivalent structures, such as use of a Wheatstone quarter bridge in place of a half or full bridge, etc., should be considered within the scope of the teachings herein. Accordingly, the scope of the invention is only to be limited as necessitated by the accompanying claims.