Abstract:
A rotary position sensor featuring a magnetized rotor which produces a magnetic flux density that varies sinusoidally with respect to the angular position of the rotor, which may be either a selectively magnetized ring or disk. The magnetic flux density produced by the rotor is measured by a sensor that responds in a linear fashion to the magnitude of the radial component of the magnetic flux density. Typical embodiments would use magnetic flux density sensors, as for example either linear Hall sensors or magnetoresistive type sensors. The measured magnetic flux densities are then used as in a traditional resolver to compute position or used to directly generate control signals to operate, for example, a motor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation-in-part application of provisional application serial No. 60/153,137, filed on Sep. 9, 1999, which application is currently pending. 
    
    
     TECHNICAL FIELD 
     The present invention relates to rotary magnetic position sensors used to measure angular displacements. 
     BACKGROUND OF THE INVENTION 
     The use of magnetoresistors (MRs) and Hall devices, as position sensors is well known in the art. For example, a magnetically biased differential MR sensor may be used to sense angular position of a rotating toothed wheel, as for example exemplified by U.S. Pat. No. 5,754,042. 
     Position sensors with digital outputs provide discrete position information only, whereas an analog position sensor can provide both position information and outputs that can be used to drive an electric motor or other similar electromechanical devices. Many of these devices are driven by sinusoidal excitations as a function of position. Consequently, an analog position sensor having an output that varies sinusoidally with position could be used to generate absolute angular positions as, for example, for an electrical power steering system to measure the angle of rotation of the steering wheel, and/or reference signals to produce the desired sinusoidal phase drive currents and voltages to drive electric motors and other similar electromechanical devices. 
     Accordingly, what remains needed is a compact inexpensive contactless position sensor having a sinusoidally varying output suitable for specialized sensing schemes. 
     SUMMARY OF THE INVENTION 
     The present invention is a rotary position sensor featuring a magnetized rotor which produces a magnetic flux density that varies sinusoidally with respect to the angular position of the rotor. The magnetic flux density produced by the rotor is measured by a sensor that responds in a linear fashion to the magnitude of the radial component of the magnetic flux density. Typical embodiments would use magnetic flux density sensors, as for example either linear Hall sensors or magnetoresistive type sensors. The measured magnetic flux densities are then used as in a traditional resolver to compute position or used to directly generate control signals to operate, for example, a motor. 
     Magnetized permanent magnet disks or rings can be used as the rotor to generate signals that vary sinusoidally with respect to position for position determination or for phase current or voltage control for electrical machines, such as motors. Normal position information can be obtained by using two linear magnetic flux density sensors in electrical quadrature. Control of three phase currents or voltages requires a minimum of two sensors spaced 120 electrical degrees apart. The third phase signal being derived from the other two. The use of three sensors spaced 120 electrical degrees apart, in this case, provides a measure of redundancy. Multiple equally spaced sensors could also be used as multiple phase commutation sensors for electric drives requiring multiple phases. Additional sensors may also be included for diagnostic or compensation purposes depending on the application. 
     According to a first aspect of the present invention, a rotor made of a homogeneous cylindrical permanent magnetic disk or ring is uniformly magnetized in a parallel fashion (i.e. perpendicular to the axis of the cylindrical disk or ring), and produces a sinusoidal radial magnetic flux density in an external constant length nonmagnetic material, such as an air gap. Properly positioned stationary magnetic flux density sensors detect a sinusoidally varying magnetic flux density as the rotor rotates and output a sinusoidally varying signal in response to the sinusoidally varying magnetic flux density. 
     According to a second aspect of the present invention, a rotor including a continuous cylindrical permanent magnetic ring, or a ring made of discrete magnetic arcuates, is sinusoidally magnetized in a radial fashion (i.e. in a radial direction of a circle perpendicular to the axis of the cylindrical ring or arcuates), and produces a sinusoidal radial magnetic flux density in an external constant length nonmagnetic material, such as an air gap. Properly positioned stationary magnetic flux density sensors detect a sinusoidally varying magnetic flux density as the rotor rotates and output a sinusoidally varying signal in response to the sinusoidally varying magnetic flux density. 
     According to a third aspect of the present invention, a rotor made of a cylindrical permanent magnetic disk, a continuous magnetic ring or a ring made of discrete magnetic arcuates is sinusoidally magnetized in a tangential fashion (i.e. tangential to a circle perpendicular to the axis of the cylindrical disk or ring), and produces a sinusoidal radial magnetic flux density in an external constant length nonmagnetic material, such as an air gap. Properly positioned stationary magnetic flux density sensors detect a sinusoidally varying magnetic flux density as the rotor rotates and output a sinusoidally varying signal in response to the sinusoidally varying magnetic flux density. 
     Accordingly, it is an object of the present invention to provide a rotary position sensor according to the first, second, and third aspects of the present invention which is capable of producing and detecting a sinusoidally varying magnetic flux density used to determine angular position of the rotor and/or to provide sinusoidal signals to drive multiple phase electric machines, wherein the rotary position sensor according to the second and third aspects of the present invention are capable of providing sinusoidal signals to drive multiple phase electric machines which require more than two magnetic poles for their operation. 
     This and additional objects, features and advantages of the present invention will become clearer from the following specification of a preferred embodiment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a schematic representation of magnetic disk according to a first aspect of the present invention. 
     FIG. 1B is a schematic representation of magnetic ring according to the first aspect of the present invention. 
     FIG. 2A is a first example of a rotary position sensor according to the first aspect of the present invention. 
     FIG. 2B is a second example of a rotary position sensor according to the first aspect of the present invention. 
     FIG. 3 is an example of a rotary position sensor according to a second aspect of the present invention. 
     FIG. 4A is a first example of a rotary position sensor according to a third aspect of the present invention. 
     FIG. 4B is a second example of a rotary position sensor according to the third aspect of the present invention. 
     FIG. 5A is an example of a multipole rotary position sensor according to the second aspect of the present invention. 
     FIG. 5B is an example of a multipole rotary position sensor according to the third aspect of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1A is a schematic representation of a magnetic disk  10  used in accordance with a first aspect of the present invention. The length  12  and radius  14  are, typically, approximately 10 mm. However, the exact dimensions of the length  12  and radius  14  depend upon the particular application. The disk is rotatable about a rotation axis R. 
     FIG. 1B is a schematic representation of magnetic ring  10 ′ used in accordance with a first aspect of the present invention. The length  12 ′ and radius  14 ′ are, typically, approximately 10 mm. The thickness of the ring  16 ′ is, typically, 3 to 10 mm depending upon the number of magnetic poles and the particular application. The exact dimensions of the length  12 ′ and radius  14 ′ depend upon the particular application, as well. The ring  10 ′ is rotatable about a rotation axis R a . 
     FIG. 2A is a first example of a rotary position sensor  20  according to the first aspect of the present invention. The rotary position sensor  20  consists of a magnetic disk  10  rotatable about the rotation axis R, the disk forming a rotor  10   a  that is homogeneously magnetized in a parallel fashion  22  as shown by the magnetic flux density  24  in FIG. 2A, a stationary core  26  made of a ferromagnetic (also referred to as “soft” magnetic) material, and a stationary annulus  28  made of a nonmagnetic material with two or more magnetic flux density sensors  30  (ie., Hall sensors or magnetoresistors) which are appropriately positioned, not necessarily in quadrature, within the annulus to detect the magnetic flux density  24  to meet specific sensing requirements. As is well known in the art, the homogeneous cylindrical permanent magnet  10  will produce a sinusoidal radial flux density  24  in a constant length nonmagnetic gap  32  when uniformly magnetized in a parallel fashion  22  as shown in FIG.  2 A. As the rotor  10   a  rotates, the magnetic flux density sensors  30  detect a sinusoidal magnetic flux density  24  and output a corresponding sinusoidal signal. The signal outputs of the magnetic flux density sensors  30  may be used to detect the absolute angular position of the rotor  10   a  or to provide sinusoidal signals to drive multiple phase electric machines. 
     FIG. 2B is a second example of a rotary position sensor  20 ′ according to the first aspect of the present invention. The rotary position sensor  20 ′ consists of a magnetic ring  10 ′ which is rotatable about the rotation axis R a , the ring being homogeneously magnetized in a parallel fashion  22 ′ as shown by the magnetic flux density  24 ′ in FIG.  2 B. The rotary position sensor  20 ′ further consists of a stationary outer core  26 ′ made of a magnetic material, a stationary annulus  28 ′ made of a nonmagnetic material with two or more magnetic flux density sensors  30   a  (ie., Hall sensors or magnetoresistors) which are appropriately positioned, not necessarily in quadrature, within the annulus to detect the magnetic flux density  24 ′ to meet specific sensing requirements, and a inner core  34  made of a ferromagnetic material rotating in conjunction with the magnetic ring  10 ′, wherein the magnetic ring and the inner core collectively form a rotor  36 . As is well known in the art, the homogeneous cylindrical permanent magnet  10 ′ will produce a sinusoidal radial flux density  24 ′ in a constant length nonmagnetic gap  32 ′ when uniformly magnetized in a parallel fashion  22 ′ as shown in FIG.  2 B. As the rotor  36  rotates, the magnetic flux density sensors  30   a  detect a sinusoidal magnetic flux density  28 ′ and output a corresponding sinusoidal signal. The signal outputs of the magnetic flux density sensors  30   a  may be used to detect the absolute angular position of the rotor  36  or to provide sinusoidal signals to drive multiple phase electric machines. 
     FIG. 3 is an example of a rotary position sensor  40  according to a second aspect of the present invention. The rotary position sensor  40  consists of a magnetic ring  42  rotatable about a rotation axis R b , wherein the ring is sinusoidally magnetized in a radial fashion  54  as shown by the magnetic flux density  50  in FIG.  3 . The rotary position sensor  40  further consists of a stationary outer core  44  made of a magnetic material, a stationary annulus  46  made of a nonmagnetic material with two or more magnetic flux density sensors  30   b  (ie., Hall sensors or magnetoresistors) which are appropriately positioned, not necessarily in quadrature, within the annulus to detect the magnetic flux density  50  to meet specific sensing requirements, and an inner core  52  made of a magnetic material rotating in conjunction with the magnetic ring  42 , wherein the magnetic ring and the inner core collectively form a rotor  38 . The sinusoidal magnetized cylindrical permanent magnet  42  will produce a sinusoidal radial flux density  50  in a constant length nonmagnetic gap  56  when sinusoidally magnetized in a radial fashion  54  as shown in FIG.  3 . As the rotor  38  rotates, the magnetic flux density sensors  30   b  detect a sinusoidal magnetic flux density  50  and output a corresponding sinusoidal signal. The signal outputs of the magnetic flux density sensors  30   b  may be used to detect the absolute angular position of the rotor  38  or to provide sinusoidal signals to drive multiple phase electric machines. 
     FIG. 4A is a first example of a rotary position sensor  60  according to a third aspect of the present invention. The rotary position sensor  60  consists of a rotor  62   a  rotatable about a rotation axis R c , consisting of a cylindrically-shaped magnetic disk  62  which is sinusoidally magnetized in a tangential fashion  64  as shown by the magnetic flux density  66  in FIG.  4 A. 
     The rotary position sensor  60  further consists of an outer core  68  made of a ferromagnetic material, and a stationary annulus  70  made of a nonmagnetic material with two or more magnetic flux density sensors  30   c  (ie., Hall sensors or magnetoresistors) which are appropriately positioned, not necessarily in quadrature, within the annulus to detect the magnetic flux density  66  to meet specific sensing requirements. The sinusoidally magnetized disk permanent magnet  62  will produce a sinusoidally radial flux density  66  in a constant length nonmagnetic gap  74  when sinusoidally magnetized in a tangential fashion  64  as shown in FIG.  4 A. As the rotor  62   a  rotates, the magnetic flux density sensors  30   c  detect a sinusoidal magnetic flux density  66  and output a corresponding sinusoidal signal. The signal outputs of the magnetic flux density sensors  30   c may be used to detect the absolute angular position of the rotor  62   a  or to provide sinusoidal signals to drive multiple phase electric machines. The cylindrically-shaped magnetized disk  62  may be a multipole magnetized, as shown by the dashed magnetic flux density  66 ′ to provide magnetic poles P a , P b , P c, P   d . 
     FIG. 4B is a second example of a rotary position sensor  60 ′ according to the third aspect of the present invention. The rotary position sensor  60 ′ consists of a magnetic ring  62 ′ rotatable about a rotation axis R d , which is sinusoidally magnetized in a tangential fashion  64 ′ as shown by the magnetic flux density  66 ′ in FIG.  4 B. The rotary position sensor further consists of a stationary outer core  68 ′ made of a ferromagnetic material, a stationary annulus  70 ′ made of a nonmagnetic material with two or more magnetic flux density sensors  30   d  (ie., Hall sensors or magnetoresistors) which are appropriately positioned, not necessarily in quadrature, within the annulus to detect the magnetic flux density  66 ′ to meet specific sensing requirements, and an inner core  72 , made of either a ferromagnetic material or nonmagnetic material depending upon the application, rotating in conjunction with the magnetic ring  62 ′, wherein the magnetic ring and the inner core collectively form a rotor  76 . The sinusoidally magnetized permanent magnet ring  62 ′ will produce a sinusoidal radial flux density  66 ′ in a constant length nonmagnetic gap  74 ′ when sinusoidally magnetized in a tangential fashion  64 ′ as shown in FIG.  4 B. As the rotor  76  rotates, the magnetic flux density sensors  30   d ′ detect a sinusoidal magnetic flux density  66 ′ and output a corresponding sinusoidal signal. The signal outputs of the magnetic flux density sensors  30   d  may be used to detect the absolute angular position of the rotor  76  or to provide sinusoidal signals to drive multiple phase electric machines. 
     FIG. 5A is an example of a multipole rotary position sensor  80  according to the second aspect of the present invention. The multipole rotary position sensor  80  consists of a magnetic ring  82  rotatable about a rotation axis R e , wherein the ring is sinusoidally magnetized in a radial fashion  84  as shown by the magnetic flux density  86  such as to produce a magnetic ring having multiple magnetic poles P 1 , P 2 , P 3 , P 4 , as shown in FIG.  5 A. The multipole rotary position sensor  80  further consists of a stationary outer core  88  made of a ferromagnetic material, a stationary annulus  90  made of a nonmagnetic material with two or more magnetic flux density sensors  30   e  (ie., Hall sensors or magnetoresistors) which are appropriately positioned, not necessarily in quadrature, within the annulus to detect the magnetic flux density  86  to meet specific sensing requirements, and an inner core  94  made of a ferromagnetic material rotating in conjunction with the magnetic ring  82 , wherein the magnetic ring and the inner core collectively form a rotor  92 . The multiple sinusoidally magnetized permanent magnet ring  82  will produce multiple sinusoidally radial flux densities  86  in a constant length nonmagnetic gap  96  when sinusoidally magnetized in a radial fashion  84  as shown in FIG.  5 A. As the rotor  92  rotates, the magnetic flux density sensors  30   e detect a sinusoidal magnetic flux density  86  and output a corresponding sinusoidal signal. The signal outputs of the magnetic flux density sensors  30   e  may be used to detect the absolute angular position of the rotor  92  or to provide sinusoidal signals to drive multiple phase electric machines, especially electric machines with more than two phases. 
     While the magnetic ring  82  may be in the form of a continuous multi-pole magnetized magnetic material, as shown by dashed lines  98 , the ring may be composed of discrete magnetic arcuates  98 ′ mutually connected by magnetic or nonmagnetic material  98 ″ to collectively form the ring. 
     FIG. 5B is an example of a multipole rotary position sensor  100  according to a third aspect of the present invention. The multipole rotary position sensor  100  consists of a magnetic ring  102  rotatable about a rotation axis R f , wherein the ring is sinusoidally magnetized in a tangential fashion  104  as shown by the magnetic flux density  106  such as to produce a magnetic ring having multiple magnetic poles P 1 ′, P 2 ′, P 3 ′, P 4 ′, as shown in FIG.  5 B. The multipole rotary position sensor  100  further consists of a stationary outer core  108  made of a ferromagnetic material, a stationary annulus  110  made of a nonmagnetic material with two or more magnetic flux density sensors  30   f  (ie., Hall sensors or magnetoresistors) which are appropriately positioned, not necessarily in quadrature, within the annulus to detect the magnetic flux density  106  to meet specific sensing requirements, and an inner core  114  made of either a ferromagnetic material or nonmagnetic material depending upon the application rotating in conjunction with the magnetic ring  102 , wherein the magnetic ring and the inner core collectively form a rotor  112 . The multiple sinusoidally magnetized cylindrical permanent magnet  102  will produce multiple sinusoidally radial flux densities  106  in a constant length nonmagnetic gap  116  when sinusoidally magnetized in a radial fashion  104  as shown in FIG.  5 B. As the rotor  112  rotates, the magnetic flux density sensors  30   f  detect a sinusoidal magnetic flux density  106  and output a corresponding sinusoidal signal. The signal outputs of the magnetic flux density sensors  30   f  may be used to detect the absolute angular position of the rotor  112  or to provide sinusoidal signals to drive multiple phase electric machines, especially electric machines with two or more pole pairs. Machines with one pole pair would use the sensor configurations of FIGS. 2A and 2B. 
     It is to be noted that while FIGS. 5A and 5B depict multipoles in the form of two pairs of magnetic poles, any number of pairs of magnetic poles may be provided. Further, the magnetic ring of FIG. 5B may be continuous or may be composed of discrete arcuate magnets as shown at FIG. 5A; indeed, any of the magnetic disks or rings may be discretely constructed. 
     Several comments concerning the rotary position sensor according to the present invention will be addressed hereinbelow. 
     The rotary position sensor according to the present invention is a low cost, analog position sensor comprising, in one form, a rotating, parallel magnetized disk-type magnet, a nonmagnetic annulus containing two or more linear magnetic flux density sensors (magnetoresistor or Hall sensor), and a ferromagnetic (also referred to as a “soft” magnetic) stationary core. The nonmagnetic annulus provides support for the magnetic flux density sensors and serves as a bearing surface for the rotating magnet, it also maintains the concentricity between the various elements of the sensor. However, embodiments without this annulus are also possible. The two-pole structure of the magnet allows for the maximum thickness of the annulus (or air gap) for a given magnet diameter, thus minimizing eccentricity effects. 
     A modified embodiment of the rotary position sensor according to the present invention is applicable to brushless motor applications, where the sensor permits direct control of the commutation by employing one sensor for each of the m-phases. In this case, the number of poles in the machine must match the number of poles of the sensor magnet. For applications with four or more poles, the magnetization must be modified from the parallel to either sinusoidal tangential or radial. In the radially magnetized case, either ring magnets or arcuates combined with a ferromagnetic core are required. The tangentially magnetized magnets do not need this core as the flux is contained almost entirely in the magnet. 
     Another modified embodiment of the rotary position sensor according to the present invention uses a ring magnet and ferromagnetic (soft magnetic) core in place of the magnet disk. In this embodiment, the ring magnet can be mounted directly over the shaft of a motor or any other device requiring similar rotary position monitoring. 
     Another embodiment of the rotary position sensor according to the present invention employs the sum of the outputs of a set of phase commutation sensors as a means for calibration and diagnostics. This is achieved by summing all output and checking for any deviation from a zero sum (ideal case). 
     Yet another embodiment of the rotary position sensor according to the present invention is where an m-phase brushless motor is operated using any set of (m−1) flux sensors. The output of the faulted flux density sensor is equal to the negative sum of the outputs of the remaining (m−1) flux density sensors. A fault tolerant sensor can therefore be constructed which can operate with the loss of any one of the (m) flux sensors. 
     It should be noted that while two magnetic flux density sensors are depicted in each shown embodiment, this is merely by way of example; one, two, or more magnetic flux density sensors may be used with any embodiment. 
     To those skilled in the art to which this invention appertains, the above described preferred embodiment may be subject to change or modification. Such change or modification can be carried out without departing from the scope of the invention, which is intended to be limited only by the scope of the appended claims.