Abstract:
A joystick apparatus employs a hermetically sealed load cell having strain gauges placed on flexible beams formed on the load cell. All of the strain gauges are on the same surface of the load cell and therefore wiring is performed on a single side of the load cell. The strain gauges are enclosed in hermetically sealed cavity. The sensing diaphragm consists of a concentric thick inner and outer section joined by thinner diametrically opposed beam elements. The thin beam elements are compliant members which can deflect. Each beam includes strain gauges or sensor elements and the load cell is coupled to a joystick which when moved causes the beams to deflect to cause the sensor elements to produce an electrical output proportional to the force and direction of the joystick. The sensor can yield an output proportional to any angle over the 360° movement of the joystick to provide outputs proportional to the X and Y positions of said joystick. Thus, the joystick arrangement can resolve any angle or force into X and Y components for full directional control.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     Application entitled “Hermetically Sealed Displacement Sensor” filed on Dec. 30, 2005 as Ser. No. 11/322,721 is generally related to this application. This application is a continuation of U.S. patent application Ser. No. 11/824,920 filed Jul. 3, 2007, now U.S. Pat. No. 7,516,675, hereby incorporated in its entirety by reference into this application. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to sensors, in general and more particularly to a joystick sensor which is hermetically sealed. 
     BACKGROUND OF THE INVENTION 
     Joystick sensors have been widely employed and have been known for many years. These devices essentially include an elongated shaft or control rod, which rod is manipulated in the X and Y directions and can provide a 360° movement, whereby the sensor produces an output based on the position of the rod. Such joystick sensors have been used for steering controls for helicopters and other aircraft as well as many other applications. In particular, the most common joystick sensors were made to sense stress and deflection in the X and Y direction. Prior art designs were based on a complex bending beam which was designed to permit easy deflection on a section or portion of the beam in the X direction and on another section of the beam the Y direction. A typical prior art beam is shown in  FIG. 1 . 
     SUMMARY OF THE INVENTION 
     A joystick sensor apparatus, comprising: a load cell having a thick outer peripheral frame with a central thick hub area, the load cell having beams positioned between the central thick area and the outer peripheral frame, a plurality of strain gauges positioned on the beams and having at least a pair of stain gauges on diametrically opposed beams and a joystick coupled to the central hub area and operative when moved to cause the gauges when biased to provide outputs proportional to the X-Y movement of the joystick. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a perspective view of a prior art joystick employing sensor elements or strain gauges. 
         FIG. 2  is a partial cross-sectional view of a joystick sensor apparatus according to this invention. 
         FIG. 3  is a top plan view of a sensor plate employing beams according to this invention. 
         FIG. 4  is a top plan view of the sensor plate of  FIG. 3  further showing an isolation diaphragm. 
         FIG. 5  is a partial cross-sectional view of a beam and sensor arrangement according to this invention. 
         FIG. 6  is a cross-sectional view depicting a sensor plate and a threaded ring aperture plate according to this invention. 
         FIG. 7  is a perspective view of a beam and sensor arrangement according to this invention. 
         FIG. 8  is a top plan view of a sensor patch array according to this invention. 
         FIG. 9  is a perspective plan view of the joystick apparatus. 
         FIG. 10  is top plan view depicting the beam and sensor apparatus according to this invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1  there is shown a prior art joystick sensor. As seen in  FIG. 1 , the sensor has a base  11  which base could be secured to any suitable surface. Attached to the base  11  is a first beam section  12  which essentially is a Y sensing beam section. The beam section  12  has its major surface disposed along the Y axis and has sensors  17  and  18  located on the beam. The other side of the beam has corresponding sensors as  17  and  18 . The sensors  17  and  18  on the front of the beam are wired to the two sensors on the other side of the beam to form a Wheatstone bridge. The beam is separated by a central solid square or rectangular member  20 . Extending from the member  20  is a X axis sensing beam section  15 . As one can ascertain, the sensing beam section  15  has its major surface disposed along the X-axis. Sensing beam  15  has positioned thereon strain gauges  19  and  14  on one side. Two other gauges are placed on the other side of the beam  15 . The four sensors are wired in a Wheatstone bridge configuration. The section  16  basically is a joystick handle fitting. In the joystick sensor depicted in  FIG. 1 , a Wheatstone bridge was fabricated separately on each of the two flat surfaces. That is, a Wheatstone bridge is associated with the Y deflection beam  12  as well as a Wheatstone bridge associated with the X deflection beam  15 . In order to obtain proper output, both sides of the thin section required strain gauges which were then wired into the complete Wheatstone bridge. This led to a very complex wiring and assembly technique as the wires had to be directed from one surface of the beam section to the other surface. Thus, as indicated the wiring to complete the bridge connections requires traversing back and forth from one side of the beam to the other side. This complex wiring scheme precludes a simple hermetic structure for the unit. In the prior art, as seen, the strain gauges were positioned to measure the longitudinal stress on the beams. To form a Wheatstone bridge, both tensile and compressive stresses were required. To access both compressive and tensile stresses the gauges were placed on both sides of the beam. Thus, the wiring to complete the bridge would require traversing back and forth, from one side of the beam and then to the other side of the beam. This complex wiring was time intensive requiring complex assembly techniques. This factor precluded the provision of a hermetic structure to enclose the unit. Thus, the prior art device depicted in  FIG. 1  was not hermetically sealed. 
     As seen in  FIG. 1 , an extending longitudinal rod or joystick is coupled to section  16 , which enables one to move the joystick in the X and Y positions at any angle of 360° rotation. The sensors serve to produce outputs based on the position of the joystick. As is known, the beam section  12  as well as beam section  15  will deflect when the joystick is moved by a user. The deflection of the sections  12  and  15  cause the strain gauges which may for example be piezoresistive devices to produce outputs proportional to the movement of the joystick in both the X and Y directions. These voltage outputs are then processed to enable the user to steer the vehicle such as a helicopter or other vehicle and the voltages may further also be used to present a X-Y display indicating to the user where the joystick is in regard to a central position. 
     As one can ascertain, the joystick sensor as depicted in  FIG. 1  has gauges on both sides of the beam section  12  and  15  and the sensors are exposed to the environment and therefore are not hermetically sealed and can be subjected to deleterious substances in the environment. 
     In addition, using the beam structure as depicted in  FIG. 1  made it virtually impossible to obtain a hermetically sealed structure. The prior art design for fabricating joysticks operative in the X and Y direction required complex machining of the structure. In addition the beams would require gauging on both sides of the beams resulting in complex wiring and assembly techniques. As one can see from  FIG. 1  the structure shown which is the prior joystick sensor, has a Y deflection beam section, a X deflection beam section, both beams are separated by a central section  20  the joystick further has a handle accommodating section  16  and a base  11 . Thus, the prior art structure is relatively complex and required a great deal of machining as the structure was usually integrally formed. 
     Referring to  FIG. 2  there is shown a joystick sensor apparatus according to this invention. As seen in  FIG. 2  the joystick  30  basically is capable of operating in a typical fashion. The joystick operates or can be moved in the X-Y plane and as is well known can be rotated through a complete 360°. The purpose of the sensors, is to determine the position of the joystick and to provide X-Y coordinates for control of a motor or other device. The joystick  30  terminates in a bottom flange  31 . The flange is a circular flange and contains apertures which hold mounting screws  33 . The flange  31  is positioned on a threaded adapter ring plate  34 . The adapter ring plate  34  has an extending central tubular section  32 , where section  32  is threaded and which section  32  of the adapter ring plate  34  is inserted into threaded aperture  40 . The adapter ring  34  has threads which engage the threaded aperture  40  of a sensor plate  35 . The adapter ring plate  34  coacts with the sensor plate  35  via the tubular section  32 . As will be explained the sensor plate  35  contains piezoresistive sensors and essentially operates to provide outputs proportional to the X and Y coordinates of the joystick. The sensor plate  35  is mounted on an aluminum adapter plate  36 . In any event, the threaded adapter ring  34  is inserted into the sensor plate  35  via section  32 . The bottom surface of the adapter ring plate  34  overlays the top surface of the sensor plate  35 . The joystick flange which is shown as numeral  31  is bolted to the threaded adapter ring plate  34  which coacts with the top surface of the sensor plate. 
     Referring to  FIG. 3  there is shown a top plan view of the sensor plate  35  as depicted in  FIG. 2 . The sensor plate  35  has a central threaded aperture  40  associated with a central hub area  75 . The central hub area  75  has a peripheral flange or rim  70  surrounding aperture  40 . As will be seen the flange  70  is thicker than the thickness of the beams as  45 ,  46 ,  47  and  48 . Extending from the inner surface of the rim  70  are the four beams  45 ,  46 ,  47  and  48 . The beams, as seen, are located at 90° intervals about aperture  40 . For example, beam  46  and  48  are positioned along a common central diameter of aperture  40 , while beams  45  and  47  are positioned along a diameter transverse to the diameter upon which beams  46  and  48  are located. The aperture  40  as depicted in  FIG. 2  is shown and is coaxial with the outer aperture  51 . Thus, as seen, the beams  45 ,  46 ,  47  and  48  emanate from the rim  70  about the central aperture  40  and are symmetrically positioned along the X and Y axes. Inbetween the beams, there are opened area as  49  which depicts the open area between beams  45  and  46 . There is also open area  52  between beams  48  and  47  and open area  53  between beams  46  and  47  and open area  54  between beams  45  and  48 . The sensor plate  35  also contains peripheral apertures such as  50  for mounting purposes. The aperture  50  can accommodate mounting screws or bolts to secure sensor plate  35  to the adapter plate  36 . 
     As will be explained, and is shown in  FIG. 4  the entire beam structure is covered by an isolation diaphragm  61 . The isolation diaphragm  61  is a convoluted diaphragm, as for example, depicted in the top view of  FIG. 4 . The exact nature of the diaphragm will be more clearly explained subsequently. As seen in  FIG. 4 , the inner aperture  40  associated with the sensor plate  35  and the peripheral flange  70  are depicted. The outer aperture  51  is formed in the surface of the rectangular plate  35  and is of relatively the same thickness as the rim  70 . 
     Again, referring to  FIG. 5  there is shown the peripheral flange or rim  70  associated with the inner aperture  40  and surface of plate  35 , the remainder of the plate  35  is not shown. The beam  46  extends from the rim  70  to the plate section  71 . Located on the beam are piezoresistive sensors or gauges as  65 . The gauges are four in number and the orientation of the gauges will be explained. Shown also in  FIG. 5  is that the top portion of the beam is covered by a convoluted isolation diaphragm designated as  61 T, indicative of  61  top. While the bottom of the beam is also covered by a convoluted diaphragm designated  61 B for  61  bottom. As seen the gauges are positioned between the diaphragm  61 B and the bottom surface  72  of the beam  46 . The top surface  73  of the beam has no gauges located thereon. It is also understood that top and bottom are relative and thus, can be interchanged. Also, shown in  FIG. 5 , is the threaded adapter ring  34  which has a surface which coacts with the top surface of the convoluted diaphragm  61 T. While the bottom surface of the threaded adapter ring  34  is above the top surface of the convoluted diaphragm, they do not touch or transmit force. The adapter ring transmits its force to the sensor through the tube section  32 , which acts on the rim  70 , which imparts bending of the beams. The threaded adapter ring  34  is coupled to the joystick flange  31  by fasteners  33  ( FIG. 2 ). Again, referring to  FIG. 5 , the typical beam length designated by L is 0.4 inches, while the width designated by W is 0.190 inches. The dimensions of course are relative and each beam as depicted in  FIG. 3  is of the same dimensions, thus there are four beams where each beam is 0.19 inches wide (W) and approximately 0.4 long (L). Thus, each beam is thinner than the thickness of adapter ring plate  35  and of the rim  70 . The beams as  46  extend an equal distance from the top and bottom surfaces of the plate  35  and rim  70 . Thus, as seen the distance d of the beam  46  from the top surface of the plate  35  and rim  70  is relatively equal to the distance dl from the bottom surface of plate  35  and rim  70 . The equal distances are not required, though they are designed symmetrically here. Other applications may dictate unequal distances. 
     Referring to  FIG. 6 , there is shown the sensor plate  35  having beam sections  46  and  48  in conjunction with the adapter ring plate  34 . Thus, as clearly shown in  FIG. 6 , the threaded adapter ring  34  has the tubular section  32  inserted into aperture  40  and beams as  46  and  48  on the sensor plate  35  and are contacted via the diaphragms by the extending surface portions of the threaded aperture ring  34 . As shown clearer in  FIG. 2 , the joystick flange  31  is positioned on the threaded aperture ring and is secured thereto. Therefore, any movement of the joystick  30  causes a movement or a deflection of the threaded aperture ring plate  35  which coacts with the convoluted isolation diaphragms as  61 T and  61 B, depicted in  FIG. 5 . While the bottom surface of the threaded adapter ring  34  is above the top surface of the convoluted diaphragm, they do not touch or transmit force. The adapter ring transmits its force to the sensor through the tube section  32 , which acts on the rim  70 , which imparts bending of the beams. 
     Referring to  FIG. 7  there is shown a perspective view of the sensor plate  35 . In most instances the same reference numerals have been utilized to depict corresponding parts from the other figures. Thus, as seen in  FIG. 7 , the sensor plate has a central aperture  40  which is essentially surrounded by the peripheral flange or rim  70 . Also shown is the aperture  51  whereby the beams  45 ,  46 ,  47  and  48  extend from the peripheral surface of aperture  51  to the peripheral flange  70  surrounding aperture  40 . The aperture  51  is coaxial with aperture  40  and has the beams emanating from the outer periphery and below the surface of plate  35 . The beams are symmetrically disposed, as seen in  FIG. 6 , about the periphery of the outer coaxial aperture  51  and aperture  40 . As shown in  FIG. 5 , the reference numeral  71  refers to the spaces d and dl of the top and bottom surfaces of plate  35 . As seen in  FIG. 5  and  FIG. 7 , each beam as  46  depicted in  FIG. 5  is symmetrically located between the circular flange  70  and the outer aperture  51 . The spaces between each of the beams as depicted in  FIG. 3  are clearly shown in  FIG. 7  and the same reference numerals again have been indicated to depict space  49 ,  51 ,  52  and  54 . Thus, the construction and nature of the sensor plate  35  should be clearer from the perspective diagram depicted in  FIG. 7 . Also shown in  FIG. 7  is that each of the beams have a gauge configuration or gauge patch positioned thereon. Thus, beam  47  contains a gauge or patch configuration  80 , while beam  46  contains the gauge configuration  81 , beam  45  contains gauge configuration  82  and beam  48  contains gauge configuration  83 . The gauges are typically piezoresistive gauges which are fabricated from silicon and have metallized contacts. It is immediately noted that all the gauge configurations associated with the beams are located on the same beam surface and therefore can be easily wired and accessed. It is also noted that the convoluted diaphragm which would enclose the top as well as the bottom of the beams, is not shown. The convoluted diaphragms  61  are positioned over the top and bottom surfaces of the beams and one can therefore hermetically seal the strain gauge patches associated with each of the beams. 
     Referring to  FIG. 8 , there is shown a typical strain gauge patch configuration employed. Essentially the patch contains a silicon substrate  92 . Located on the silicon substrate  92  are piezoresistive sensors responding to axial tension/compression stresses as well as Poisson gauges. Referring to  FIG. 8 , gauge  90  or sensor  90  is a Poisson gauge, while gauge  93  can operate in a tension/compression mode. This mode is also indicative of gauge  96  as well as gauge  97 . Thus, as shown in  FIG. 8 , there are four gauges located on the silicon substrate which consists of gauges  90 ,  93 ,  96  and  97 . Also positioned between gauges are metallized contacts as contact  91 . As seen the gauge configuration is open and has two contacts at the bottom depicted as contacts  100  and  101 . Each of these contacts is a metallized contact. Thus, the configuration of gauges as shown in  FIG. 8  can be wired whereby one can utilize the gauges as part of a bridge circuit in conjunction with other gauges located on other beams. Each beam as indicated above, and as shown in  FIG. 7  has a gauge patch, which includes the gauge configuration depicted in  FIG. 8 . Thus, the present joystick sensor uses the strain gauge patch  95 . The patch incorporates 4 gauges in a preconfigured bridge arrangement. One employs silicon and the silicon is selected to be oriented in the &lt;110&gt; orientation to maximize the piezoresistive coefficient in mutually orthogonal axes. The patch incorporates the axial and Poisson gauges in a single piece or single silicon part. Installation of the patch requires only access to one side of the beam as depicted in  FIG. 7  resulting in a far simpler assembly technique as compared to those techniques existing in the prior art. In any event, the crystal orientation is selected as above and operation is indicated in the following mathematical analysis proves the operation of the sensor arrangement as depicted in  FIG. 8  to determine X-Y and Z positioning. 
     Crystal Orientation 
     The Poisson&#39;s stress is related to the compressive stress by Poisson&#39;s ration v. In silicon, v is typically 0.3.
 
σ p =vσ c   [1]
 
For a piezoresistive gage, the resistance equation is
 
Δ R/R=σ   x π x +σ y π y +σ z π z   [2]
 
This relates the change in gage resistance ΔR divided by the unstressed resistance R, to the stresses σ in the subscripted directions, and the piezoresistive coefficients applicable to the piezoresistor. This applicability is governed by basic crystal species, crystallographic orientation, doping species, doping level, and current direction related to stress direction.
 
For a gauge with the current in the same direction as the force (gage C)
         (1) The x direction is associated with compressive stress. The stress is transverse to the current flow in the gauge so the π x  coefficient becomes −π 44 /2   (2) The y direction is associated with Poisson&#39;s ratio stress. The stress is longitudinal to the current flow in the gauge so the π y  coefficient becomes π 44 /2   (3) The z direction is associated with out of plate stress. The stress is transverse to the current flow in the gauge so the π z  coefficient becomes 0.
 
Δ R/R=σ   c (−π/2)+σ p π 44 /2+σ z 0  [3]
 
Inserting the Poisson ration [1], this [3] becomes
 
Δ R/R=−σ   c (π 44 /2)1+ v )  [4]
 
For a gauge with the current in the orthogonal direction as the force (gage P)
   (4) The x direction is associated with compressive stress. The stress is longitudinal to the current flow in the gauge so the π x  coefficient becomes π 44 /2   (5) The y direction is associated with Poisson&#39;s ration stress. The stress is transverse to the current flow in the gauge so the π y  coefficient becomes −π 44 /2   (6) The z direction is associated with out of plate stress. The stress is transverse to the current flow in the gauge so the π z  coefficient becomes 0.
 
Δ R/R=σ   c (π 44 /2)+σ p (−π 44 /2)+σ z 0  [5]
 
Inserting the Poisson ration [1], this [5] becomes
 
Δ R/R=σ   c (π 44 /2)(1+ v )  [6]
       

     Referring to  FIG. 9  there is shown a perspective view of the joystick sensor according to this invention. Essentially  FIG. 9  employs the same reference numerals as used in  FIG. 2  to denote corresponding parts. As seen in  FIG. 9  the joystick  320  and the bottom flange member  31  are bolted to the threaded adapter ring  34 . The adapter ring  34  is positioned on the sensor plate as depicted in  FIG. 2 . The sensor plate  35  as indicated contains the beams as well as the gauge patch associated with each beam. There is an aluminum adapter module  36  depicted and a, motor mount  37 . The movement of the joystick determines X-Y coordinates for activating the motor according to the X-Y coordinates. It is understood that the joystick can be utilized to determine X-Y directions in many applications which do not necessarily include motors and the operation will suffice for any application where a-joystick is employed. Thus the stress profile of the disclosed joystick designs include tensile, compression, Poisson, and torsional stresses. As the joystick is subjected to a force along one axis, the beams in that axis will be subjected to the moment at the free end at the inner hub. This moment will include a tensile and compressive stress in the beams along the associated axis. The positive/negative stress will be opposite on the opposing surface of the beam as well as on the opposite side of the central hub. In addition as the beam is bending a Poisson stress will be experienced perpendicular to the bending axis. The beams in the orthogonal axis will experience a torsional stress as they will see a twist which is perpendicular to their central axis. The design of the beams is such that the tensile and compressive stresses are maximized while the torsional stresses are minimized. The axial stresses, which are the major stresses will provide about 500 microstrain for the formation of the Wheatstone bridge and voltage output for the unit. The Poisson stresses are the next major stress in the structure. These stresses will allow the formation of the Wheatstone bridge on a single side of the beam which thereby simplifies assembly of the unit and allows a simple hermetic structure to enclose the unit. The torsional stresses on the orthogonal beam set are at least an order of magnitude smaller than the tensile stresses. They are on the order of 15 microstrain for the above noted dimensions. This will allow cross axis signals to be very small thus not affecting position or measurement of the joystick. Using the tensile and compressive axial stresses, as well as the Poisson stresses will allow the strain gages to be placed on one side of the beam. The tensile, compressive and Poisson strains are all accessible from a single side, eliminating the cross wiring of the prior art to access the opposite side of the beam. In addition cross wiring to the other side of the central hub is eliminated as all strains can be accessed on one beam. The four strain gauges can be incorporated on a single strain patch as shown for example in  FIG. 8  using the properties of silicon to advantage. Using a silicon with 110 crystal directions, orthogonal to each other will allow the piezoresistive coefficients to be maximized for both the tensile/compressive and Poisson gauges. In addition, the strain gauge patches minimize space and wiring allowing multiple patches to be place on the beams resulting in a simple multiple redundant system. 
     Referring to  FIG. 10  there is shown a top plan view of the beam arrangement according to this invention. As seen the beams  45 ,  46 ,  47  and  48  are directed from the central hub area  75  containing rim  70  associated with aperture  40 . The beams again are symmetrically directed from the central hub area  75  to the outer peripheral edge  71 . The beams shown in  FIG. 10  utilize the same reference numerals as depicted above. In any event, as one can see, beams  46  and  48  are directed along the X axis while beams  45  and  47  are directed along the Y axis. The beams are symmetrically disposed along each of the central X and Y axes which as indicated above, are transverse to each other. The joystick sensing structure can detect and measure positions in a full 360° around the joystick axis which is the center point of the structure designated as CP. As the joystick is moved from a major axis, as for example the X or Y axis, the beams will experience as stress proportional to the vector resolution of the position. For example, for a joystick position at 45° between the X and Y axes, the beam will experience stresses proportional to the vector resolution, as indicated on the diagram by the X and Y equations where X=F cos θ while Y=F sin θ. As seen in  FIG. 10  the force F is shown with the angle θ. In any event, the X and Y coordinates are the force components in each orthogonal direction and θ is the angle as measured from the X axis. At 45° each axis will experience √2/2 or 0.707 times the force applied to the joystick. The stress and output of each axis will be proportional, reflecting this intermediate position. Thus, the joystick as shown above, is hermetically sealed thus protecting the sensors in all types of environment where the joystick as indicated is simple to utilize and simple to wire using various bridge configurations. The sensor patch as indicated can be redundant and multiple patches can be placed on each beam. 
     It should be apparent to one skilled in the art that there are many modifications and alternative configurations that can be employed. All of which are deemed to be encompassed with the spirit and scope of the claims appended hereto.