Patent Publication Number: US-2012025818-A1

Title: Non-Contacting Position Sensor Using a Rotating Magnetic Vector

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application which claims the benefit of co-pending U.S. patent application Ser. No. 12/816,887 filed on Jun. 16, 2010 which is a continuation application which claims the benefit of U.S. patent application Ser. No. 11/254,574 filed on Oct. 20, 2005 (now U.S. Pat. No. 7,741,839 which issued on Jun. 22, 2010), entitled Non-Contacting Position Sensor Using a Rotation Magnetic Vector, the disclosures of which are explicitly incorporated herein by reference, as are all references cited therein. 
    
    
     BACKGROUND OF THE INVENTION 
     I. Technical Field 
     This invention relates, in general, to non-contacting position sensors. More particularly, this invention relates to the magnetic configuration of a non-contacting position sensor that uses a magnetic flux sensor. 
     II. Background Art 
     Electronic devices are an increasingly ubiquitous part of everyday life. Electronic devices and components are presently integrated in a large number of products, including products traditionally thought of as primarily mechanical in nature, such as automobiles. This trend is almost certain to continue. To successfully integrate electronic and mechanical components, some type of interface between the two technologies is required. Generally, this interface is accomplished using devices such as sensors and actuators. 
     Position sensing is used to electronically monitor the position or movement of a mechanical component. The position sensor produces an electrical signal that varies as the position of the component in question varies. Electrical position sensors are an important part of innumerable products. For example, position sensors allow the status of various automotive parts to be monitored and controlled electronically. 
     A position sensor must be accurate, in that it must give an appropriate electrical signal based upon the position measured. If inaccurate, a position sensor will hinder the proper evaluation and control of the position of the component being monitored. 
     A position sensor must also be adequately precise in its measurement. The precision needed in measuring a position will obviously vary depending upon the particular circumstances of use. For some purposes only a rough indication of position is necessary, for instance, an indication of whether a valve is mostly open or mostly closed. In other applications, more precise indication of position may be needed. 
     A position sensor must also be sufficiently durable for the environment in which it is placed. For example, a position sensor used on an automotive valve will experience almost constant movement while the automobile is in operation. Such a position sensor must be constructed of mechanical and electrical components which are assembled in such a manner as to allow it to remain sufficiently accurate and precise during its projected lifetime, despite considerable mechanical vibrations and thermal extremes and gradients. 
     In the past, position sensors were typically of the “contact” variety. A contacting position sensor requires physical contact to produce the electrical signal. Contacting position sensors typically consist of potentiometers to produce electrical signals that vary as a function of the component&#39;s position. Contacting position sensors are generally accurate and precise. Unfortunately, the wear due to contact during movement of contacting position sensors has limited their durability. Also, the friction resulting from the contact can result in the sensor affecting the operation of the component. Further, water intrusion into a potentiometer sensor can disable the sensor. 
     One important advancement in sensor technology has been the development of non-contacting position sensors. As a general proposition, a non-contacting position sensor (“NPS”) does not require physical contact between the signal generator and the sensing element. As presented here, an NPS utilizes magnets to generate magnetic fields that vary as a function of position and devices to detect varying magnetic fields to measure the position of the component to be monitored. Often, a Hall effect device is used to produce an electrical signal that is dependent upon the magnitude and polarity of the magnetic flux incident upon the device. The Hall effect device may be physically attached to the component to be monitored and move relative to the stationary magnets as the component moves. Conversely, the Hall effect device may be stationary with the magnets affixed to the component to be monitored. In either case, the position of the component to be monitored can be determined by the electrical signal produced by the Hall effect device. 
     The use of an NPS presents several distinct advantages over the use of the contacting position sensor. Because an NPS does not require physical contact between the signal generator and the sensing element, there is less physical wear during operation, resulting in greater durability of the sensor. The use of an NPS is also advantageous because the lack of any physical contact between the items being monitored and the sensor itself results in reduced drag upon the component by the sensor. 
     While the use of an NPS presents several advantages, there are also several disadvantages that must be overcome in order for an NPS to be a satisfactory position sensor for many applications. Magnetic irregularities or imperfections may compromise the precision and accuracy of an NPS. The accuracy and precision of an NPS may also be affected by the numerous mechanical vibrations and temperature changes likely to be experienced by the sensor. Because there is no physical contact between the item to be monitored and the sensor, it is possible for them to be knocked out of alignment by such vibrations. A misalignment will result in the measured magnetic field at any particular location not being what it would be in the original alignment. Because the measured magnetic field will be different than that when properly aligned the perceived position will be inaccurate. Linearity of magnetic field strength and the resulting signal is also a concern. 
     Some of these challenges to the use of an NPS have been addressed in existing devices, most notably the devices of U.S. Pat. Nos. 5,712,561 and 6,211,668. 
     There remains, however, a continuing need for an improved position sensor that displays minimal deviations due to changes in temperature and that can be adapted for use over a wide range of measurement distances and angles. 
     SUMMARY OF THE INVENTION 
     A feature of the invention is to provide a sensor that includes a magnet. The magnet has dimensions that include a length, a width and a height. The magnet is adapted to generate a flux field. The flux field has a magnitude of flux and a flux direction. The flux direction changes along at least one of the dimensions. 
     Another feature of the invention is to provide a magnet that provides a rotating magnetic field vector. 
     Yet another feature of the invention is to provide a method for magnetizing a magnet to create a rotating magnetic field vector. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a perspective view of a magnet in accordance with the present invention. 
         FIG. 2  illustrates a front elevation view of  FIG. 1  with a magnetic flux sensor. 
         FIG. 3  illustrates a side elevation view of  FIG. 1 . 
         FIG. 4  illustrates a front elevation view of  FIG. 1  with an alternative magnetic flux sensor location. 
         FIG. 5  illustrates a front elevation view of an alternative embodiment of a magnet and magnetic flux sensor in accordance with the present invention. 
         FIG. 6  illustrates a top plan view of an alternative embodiment of a magnet and magnetic flux sensor in accordance with the present invention. 
         FIG. 7  illustrates a side elevation view of  FIG. 6 . 
         FIG. 8  illustrates a magnetizing fixture and flux vector diagram for the magnet of  FIG. 6  showing the rotating magnetic vector. 
         FIG. 9  illustrates the flux density for the magnet of  FIG. 8  in the plane of the sensor at the nominal airgap between the magnet and sensor. 
         FIG. 10  illustrates a graph of magnetic flux density versus magnet position for the magnet of  FIG. 6 . 
         FIG. 11  illustrates an alternative magnetizing fixture and flux vector diagram for the magnet of  FIG. 6  showing the rotating magnetic vector. 
     
    
    
     It is noted that the drawings of the invention are not to scale. 
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1-4  a non-contacting position sensor  20  is shown. Sensor  20  is adapted for use in monitoring the rotational position of an attached object that moves such as a shaft  22 . Shaft  22  can be connected to any moving object such as a butterfly valve in an engine throttle body. Position sensor  20  includes a magnet  30  and a magnetic flux sensor  50 . Magnet  30  can be rotated through 360 degrees and can measure continuous rotation of an object. 
     As the magnetic field generated by the magnet  30  and detected by flux sensor  50  varies sinusoidally with rotation, an electrical signal is produced by sensor  50  that allows the position of the object to be monitored to be ascertained. 
     Magnet  30  is cylindrical in shape and has an inner surface  32 , an outer surface  34 , end faces  35  and  36  and an interior cavity  38 . Magnet  30  generates a flux field that contains a flux vector that has a relatively constant flux density but a changing direction. A pole piece (not shown) may be used with magnet  30  to further control or direct the flux generated by magnet  30 . Magnetic flux sensor  50  can be a multi-axis hall effect device that is commercially available from Melexis Microelectronic Systems of Concord, N.H. Other multi-axis hall effect devices could also be used. A multi-axis hall effect sensor can measure flux direction by taking the ratio of flux density in 2 orthogonal planes. Magnetic flux sensor  50  has several electrical leads  52  that are used to supply power, ground and an output signal from sensor  50 . Magnetic flux sensor  50  has electrical leads  52 . A printed circuit board or lead frame (not shown) is adapted to hold flux sensor  50  in the proper position spaced from magnet  30  by an air gap  37 . Air gap  37  is located between magnet  30  and flux sensor  50 . Magnetic flux from magnet  30  is established across air gap  37  and is sensed by flux sensor  50 . 
     In  FIG. 2 , the magnetic flux sensor  50  is mounted in cavity  38  adjacent to inner surface  32 . Alternatively, as shown in  FIG. 4 , sensor  50  can be mounted outside the magnet adjacent outer surface  34 . Magnet  30  can be formed of any suitable magnetic material, such as samarium cobalt, neodymium-iron-boron or ferrite. 
     In another embodiment, shown in  FIG. 5 , only half of the magnet  30  may be used. Semi-cylindrical magnet  40  has an inner surface  44 , an outer surface  42  and end faces  46  and  48 . Magnetic flux sensor  50  can be mounted adjacent interior surface  44 . Magnet  40  can be used to measure up to 180 degrees of rotation of an attached object. 
     Turning to  FIGS. 6 and 7 , another embodiment of a magnet  60  is shown. Magnet  60  has a rectangular shape and is in the form of an elongated bar having outer surfaces  62 ,  64 ,  66 ,  68 ,  70  and  72 . Magnet  60  has dimensions including a length L, a width W and a height H. Magnetic flux sensor  50  can be mounted adjacent surface  62 . Magnet  60  can be used to measure linear travel of an attached object. 
     Alternatively, magnet  60  can be made from thin bonded ferrite and subsequently bent and affixed into a shape similar to magnet  30 . In this manner, magnet  60  can be used to measure the rotary position of an attached object. Further, if magnet  60  is a flexible bonded ferrite magnet material, it can be formed into a ring shape for use in a rotary sensor and may be fitted into a housing. Magnet  60  may also be formed by molding. Magnet  60  can be magnetized in a straight shape and then bent into a circular shape. Alternatively, magnet  60  could also be magnetized after it has been formed into a round shape. 
     Magnet  60  can also be used to make a through-hole sensor in which a shaft extends through a hole along the axis of rotation of the magnet. This design allows the flexibility to place a magnetic flux sensor on the inside or outside of the magnet as needed. 
       FIG. 8  illustrates a more detailed view of bar magnet  60  showing a magnetization pattern  75  and flux vectors generated by magnet  60 . For the convenience of understanding the operation of the present invention, magnet  60  is designated in several adjacent segments or sections  80 A,  80 B,  80 C,  80 D,  80 E,  80 F,  80 G,  80 H,  80 I,  80 J, and  80 K. Sections  80 A-K will be used to illustrate how the flux vectors generated by magnet  60  vary or change with position. In reality, these segments do not exist within magnet  60  and the change in the flux vector is continuous when moving along at least one dimension of magnet  60 . Each segment  80  has an associated flux vector  90 . Flux vectors  90 A,  90 B,  90 C,  90 D,  90 E,  90 F,  90 G,  90 H,  90 I,  90 J and  90 K each have a flux magnitude and a flux direction. 
     The flux direction continuously changes or rotates when moving from segment  80 A towards segment  80 K along length L. A reference axis of X, Y and Z directions are shown in the lower left hand corner of  FIG. 8 . The rotating flux direction is created by rotating the magnetization direction within magnet  60 . The flux direction in  FIG. 8  is shown changing in the X-Z plane. Other planes can also be used as will be discussed later. 
     Referring to  FIG. 9 , the flux vectors  90  for magnet  60  were generated using a computer simulation program. The flux vectors  90  are shown at a distance of 0.1 inch from the magnet surface  62 . A sensing plane  150  was used to simulate the position of flux sensor  50  as magnet  60  is moved along length L. Flux sensor  50  positioned 0.1 inch from the magnet surface would detect this changing flux vector as magnet  60  is moved along length L. 
     It is noted in  FIG. 9  that magnetic vectors  90  have a sizable magnetic field called Bz or a Z axis component as one moves from the bottom surface  72  to the top surface  70  of the magnet. The magnetic field B is measured in Gauss or Tesla. This magnetic field Bz component is parasitic to the magnetic field Bx &amp; By components in the X and Y directions and is minimized near the bottom surface  72  of the magnet  60 . 
     Flux sensor  50  creates three intermediary electrical signals Sx, Sy and Sz that are proportional to the strength of the magnetic field in each direction. Signals Sx, Sy and Sz are internal to and contained in sensor  50 . An electrical output signal is provided on one of the electrical leads  52 . Sensor  50  calculates the output signal by using a proportion of the arctangent of the ratio of these flux densities. This signal has a saw-tooth shape and represents the flux direction that is independent of flux density amplitude variation. For the magnet shown in  FIGS. 8 and 9 , the Sx and Sz signals are of interest because the flux direction is rotating in the X-Z plane. 
       FIG. 10  is a graph of magnetic field strength as a function of linear position along magnet length L.  FIG. 10  shows the output signals Sx and Sz from sensor  50  corresponding to the Bx and Bz flux vectors for magnet  60 . The Sy signal is not shown in  FIG. 10  as it is not needed in order to determine the position of magnet  60 . 
     The arctangent of the ratio for a line down the vertical midpoint of the sensing plane is shown in  FIG. 10  and is labeled Arctan. It is noted that the Arctan line is linear and has a period P. The length of period P corresponds to the Length L of the magnet. 
       FIG. 8  also shows a magnetization fixture  100  that is needed to create the magnetization pattern  75  in magnet  60 . Magnetization  FIG. 100  includes a wire  101  that has ends  102  and  104 . Wire  101  can be a copper wire that is connected to a source of electrical power (not shown). Current  110  flowing through wire  101  causes a magnetic field corresponding to magnetization pattern  75  to be imposed upon and imparted to magnet  60 . It is noted that the distance between wire ends  102  and  104  and the distance between the magnet and wire allows for tailoring of the period of the vector rotation or how fast the flux vector rotates along the length of the magnet. 
     The present invention has several advantages. One advantage is that the flux density of flux vectors  90 A-K results in the output signal sensed by flux sensor  50  being independent of all amplitude related variations of the magnet, temperature variation being one of the variations. Therefore, additional temperature compensation devices and circuits are not needed. Another advantage is that the sensing period of sensor  20  can easily be changed. The period of the vector rotation or how fast the flux vector rotates along the length of the magnet can be changed by adjusting magnetization fixture  100 . The period can be changed by selecting the physical dimension and spacing of wire  101 . 
     It should be appreciated that the present invention may be readily adapted for use in measuring rotations of any angular dimension or in measuring any linear movements. The invention may be used to measure rotations of three hundred and sixty degrees or more, using an electronic counter for multiple revolutions. 
     Referring to  FIG. 11 , an alternative magnetizing fixture  200  and flux vector diagram for magnet  60  is shown.  FIG. 11  illustrates a magnetization pattern  275  and flux vectors generated by magnet  60 . For the convenience of understanding the operation of the present invention, magnet  60  is designated in several adjacent segments or sections  80 A,  80 B,  80 C,  80 D,  80 E,  80 F,  80 G,  80 H,  80 I,  80 J,  80 K,  80 L and  80 M. Sections  80 A-M will be used to illustrate how the flux vectors generated by magnet  60  vary or change with position. In reality, these segments do not exist within magnet  60  and the change in the flux vector is continuous when moving along at least one dimension of magnet  60 . Each segment  80  has an associated flux vector  290 . Flux vectors  290 A,  290 B,  290 C,  290 D,  290 E,  290 F,  290 G,  290 H,  290 I,  290 J,  290 K,  290 L and  290 M each have a flux magnitude and a flux direction. 
     The flux direction continuously changes or rotates when moving from segment  80 A towards segment  80 M along length L. A reference axis of X, Y and Z directions are shown in the lower left hand corner of  FIG. 11 . The rotating flux direction is created by rotating the magnetization direction within magnet  60 . The flux direction in  FIG. 11  is shown changing in the X-Y plane. Other planes can also be used such as the Y-Z plane. 
       FIG. 11  also shows a magnetization fixture  200  that is needed to create the magnetization pattern  275  in magnet  60 . Magnetization fixture  200  includes a wire  202  that has ends  204  and  206  and U-shaped portions  254  and  256 . Wire  202  can be a copper wire that is connected to a source of electrical power (not shown). Current  252  flowing through wire  201  causes a magnetic field corresponding to magnetization pattern  275  to be imposed upon and imparted to magnet  60 . It is noted that the distance between wire ends  204  and  206  and the distance between U-shaped sections  256  and  258  and the distance between the magnet and wire allows for tailoring of the period of the vector rotation or how fast the flux vector rotates along the length of the magnet. 
     Although the invention has been taught with specific reference to these embodiments, someone skilled in the art will recognize that many other changes can be made in form and detail without departing from the spirit and the scope of the invention. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.