Abstract:
A multi-turn non-contacting rotary shaft position sensor that determines a positional parameter of a rotating shaft. The sensor converts the rotational movement of an input shaft to a linear translational movement of a magnetic element. A magnetically sensitive sensor is provided in a fixed location in close proximity to the magnetic element within the flux field of that magnetic element. As the input shaft rotates, the magnetic element moves along that linear path toward or away from the magnetically sensitive sensor so that the sensor detects the change in the magnetic flux imposed by the magnetic element. That change in magnetic flux is used to determining a positional parameter of the input shaft.

Description:
RELATED APPLICATIONS 
     The present application is based upon and claims the benefit of U.S. Provisional Application Ser. No. 60/183,270 filed Feb. 17, 2000. 
    
    
     FIELD OF THE INVENTION 
     The invention generally relates to position sensors, and more particularly, to a magnetically sensitive sensor that detects a positional parameter of a rotating element. 
     BACKGROUND 
     Rotary sensors using contacting technology, such as potentiometers, suffer from various disadvantages that have limited their use. In applications requiring prolonged use over many years or requiring many cycles, the contacting sensors develop dead zones and non-uniform electrical behavior. Additionally, contacting sensors, even when in good condition, exhibit a relatively high degree of electrical noise during operation. This noise is a problem in sensitive electronic circuits. 
     It has been suggested to use non-contacting angular sensors to overcome the disadvantages of contacting sensors. Such sensors are not as susceptible to wear and exhibit reduced electrical noise. One barrier to the widespread use of non-contacting transducers, however, is the restricted angular range of those devices. Examples of such devices are shown in the U.S. Pat. Nos. 3,777,273; 3,988,710; 4,425,557 and 5,789,917. All of these devices have an angular operating range of less than one-half turn. 
     Another barrier to the widespread use of non-contacting sensors is the use of magnetic devices in such sensors. Magnetic fields are short acting, thus magnetic sensors have limited range and they exhibit undesirable signal-to-noise ratios (SNR) due to outside magnetic disturbances. The problems with non-linearity and SNR have been somewhat offset by the use of pole pieces, or flux directors. Flux directors attempt to extend the usable linear range of a magnetic field by advantageously shaping the field. The need to improve the SNR has been cited in various publications, including U.S. Pat. Nos. 5,444,369; 5,789,917; and 5,757,179. 
     There are contacting rotary sensors that exhibit extended range, but these sensors suffer from the disadvantages discussed above and are generally too complex and too costly for commercial acceptance. Moreover, these multi-turn sensors provide only a relative position indication, having no absolute reference. 
     SUMMARY OF THE INVENTION 
     The advantages of magnetic, non-contacting sensors over contacting potentiometric types include virtually unlimited operating life, owing to the fact that there are no physical contacts. Non-contacting sensors according to the principles of the invention do not suffer from the wear degradation and electrical noise exhibited by contacting sensors. A sensor according to the principles of the invention also offers a useful range of many full revolutions. Such a range makes the present invention a suitable replacement for absolute rotary encoders, angular sensors, potentiometers, tuners, and robotic joint sensors. A sensor according to the principles of the invention reduces SNR by converting a relatively large rotational mechanical input to a smaller linear mechanical translation of the magnet in the measurement circuit. This technique allows the sensor to use a very small portion of the magnetic field that is close to the magnet. This field portion offers the highest magnetic flux density for a given magnet and thus results in improved SNR. Also, the small size of this field portion reduces dependence on linearity. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     A more complete understanding of the invention may be obtained from consideration of the following description in conjunction with the drawing in which: 
     The FIGURE is a perspective view, partially cut away, showing the rotary shaft position sensor constructed in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, there is shown a perspective view, partially cut away, of a rotary shaft position sensor  10  constructed in accordance with the present invention. As can be seen, there is a housing  12  that may be of any variety of materials, such as metals or plastic compositions. Within the housing  12 , there is formed a specially configured pocket  14  within which is located a magnetic element  16 . The magnetic element  16  may be a permanent magnetic that emits a magnetic flux therefrom and the purpose of the magnetic field flux will be later appreciated. The exterior portion  18  of the magnetic element  16  is also specially configured, and as shown, that exterior portion  18  may be formed in a prismatic shape, it being of importance that the exterior portion  18  of the magnetic element  16  be specially configured so as to fit with the pocket  14  such that the magnetic element  16  is prevented from rotating with respect to housing  12  but can move along a linear path within the housing  12  indicated by the arrow A. 
     Extending outwardly from the magnetic element  16  is threaded shaft  20 , shown as externally threaded and the threaded shaft  20  extends external of the housing  12 . The threaded shaft  20  may be a separately formed part that is inserted into the magnetic element  16  or insert molded in the production of the magnetic element  16 , however, in any event, the threaded shaft  20  is firmly affixed to that magnetic element  16 . 
     An input shaft  22  is threadedly affixed to the threaded shaft  20  external of the housing  12  by means of internal threads  24 . Thus, the input shaft  22  and the threaded shaft  20  are threadedly engaged together and, as stated, in the preferred embodiment, the threaded shaft  20  has external threads and the input shaft  22  has internal threads  24 . The threaded shaft  20  and the input shaft  22  are threadedly engaged together and, as can be seen, the external and internal locations of the respective threads on each of those components could readily be reversed and the rotary shaft position sensor  10  still function in the manner to be explained. 
     The input shaft  22  is rotatable affixed to the housing  12  such that the input shaft  22  can freely rotate with respect to the housing  12  but is restrained from any axial movement with respect thereto. In the Figure, the mounting of the input shaft  22  is accomplished by means of a mounting bushing  26  that is fitted to the housing  12  and that mounting bushing  26  has an inner end  28 , an outer end  30  and an exterior flange  32  that seats against the housing  12 . Mounting bushing  26  thus surrounds the input shaft  22  and provides a seal against the input shaft  22  while allowing the input shaft  22  to freely rotate within the mounting bushing  26 . 
     To prevent the input shaft  22  from moving axially with respect to the housing  12 , there is formed an inner flange  34  at the inner end of the input shaft  22  and which rotatably engages the inner end  28  of the mounting bushing  26  to prevent the input shaft  22  from moving axially outwardly from the housing  12 . A further device, such as a C-clip, not shown, can be inserted into a groove  36  formed in the input shaft  22  just proximate the outer end  30  of the mounting bushing  26  such that the axial movement of the input shaft  22  toward the housing  12  is also prevented, thus restraining the input shaft  22  with respect to the housing  12  along either axial direction while, at the same time, allowing the input shaft  22  to freely rotate within the housing  12 . 
     A magnetically sensitive sensor  38  is mounted proximate the magnetic element  16  and that mounting is preferably by means of a recess  40  that is formed in the housing  12  and into which the sensor  38  is fitted, thus retaining that sensor  38  firmly in a fixed position with respect to the housing  12  so that the finite distance between the magnetically sensitive sensor  38  and the magnetic element  16  is affected only by the movement of the magnetic element  16 . As can be noted, however, it is important that the magnetically sensitive sensor  38  be positioned within the magnetic field of the magnetic element  16  and the precise finite distance from that magnetic element  16  is dependent, of course, on the strength of the magnetic field of that magnetic element  16 . 
     The actual magnetically sensitive sensor  38  may be of a variety of sensors provided that such sensors are capable of detecting the changing magnetic field of the magnetic element  16  as the distance between the magnetic element  16  and the sensor changes. Typical of such magnetically sensitive sensors is a Hall Effect sensor or a Giant Magneto Resistive (GMR) sensor, however other sensors sensitive to magnetic flux may be used consistent with the principles of the invention. 
     Accordingly, with the elements of the present invention described, the operation of the rotary shaft position sensor  10  can be described. As the input shaft  22  is rotated, that rotation causes the magnetic element  16  to translate in the direction along the axis of the threaded shaft  20  and thus the magnetic element  16  moves axially within the housing  12  dependent upon the amount of angular rotation of the input shaft  22 . The amount of such translational movement per angular rotation of the input shaft  22  is, of course, dependent upon the threads per inch, thread pitch or other parameter of the threaded interengagement between the input shaft  22  and the threaded shaft  20  of the magnetic element  16 . In the design of a particular rotating shaft position sensor  10 , therefore, the amount of linear translation of the magnetic element  16  per the amount of angular rotation of the input shaft  22  can be designed in accordance with the particular rotation of the input shaft  22  depending upon the particular use of the device such that the use of the rotary shaft position sensor  10  is applicable to a wide variety of differing applications. 
     In any event, as the input shaft  22  is rotated, the magnet element  16  is linearly translated by the interengement of the threaded shaft  20  and the internal threads  24  of the input shaft  22  to change the distance between that magnetic  16  and the magnetically sensitive sensor  38  such that the effect of the magnetic flux field on sensor  38  changes in proportion thereto and that change in magnetic field can be measured in order to determine the rotation of the input shaft  22 . 
     It should be noted here that the rotation of the input shaft  22  being measured by this invention is not limited to a 90, 180 or even 360 degree rotation of the input shaft  22  but may be applicable readily to multiple full rotations of the input shaft  22 . 
     As indicated, the magnetically sensitive sensor  38  experiences the change in the magnetic field flux radiated by the magnet element  16  and the sensor itself may be any one of a variety of sensors, among such typical sensors is a Linear Hall Effect sensor where the sensor produces an electrical change in a voltage signal analogous to the angular position of the input shaft  22 , or, alternatively, the sensor  38  may be a Giant Magneto Resistive (GMR) sensor that experiences a change in internal resistance responsive to the change in the magnetic field and, in such case, that change of resistance can be measured and which is also analogous to the angular position of the input shaft  22 . Other sensors may also be utilized as long as the particular sensor is sensitive to a changing of the magnetic flux field emitted by the magnetic element  16 . In this way, a varying magnetic influence is imposed upon the magnetically sensitive sensor, the magnetic influence being dependent on the angular position of the input shaft. 
     As can now be seen, the rotary shaft position sensor  10  according to the principles of the invention can be used to detect and measure various parameters of the rotational movement of the input shaft  22  including, but not limited to, the angular position of that input shaft  22 , the amount of rotation of the input shaft  22  and even the angular velocity of the rotation by means of the sensing and interpretation of the changing effect of the magnetic field upon the magnetically sensitive sensor  38 . The present invention can even be used to determine the direction of rotation of the input shaft  22 , that is, whether it is moving in the clockwise or counterclockwise directions by determining whether the influence of the magnetic flux is increasing or decreasing upon the magnetically sensitive sensor  38 . 
     It is to be understood that the invention is not limited to the illustrated and described forms of the invention contained herein. It will be apparent to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not considered limited to what is shown in the drawing and described in the specification.