Patent Publication Number: US-8121811-B2

Title: Systems and methods for detecting angular position

Description:
I. BACKGROUND 
     The invention relates generally to the field of detecting angular positions of a rotating device. 
     II. SUMMARY 
     In one respect, disclosed is a method for detecting angular position of a rotating device, the method comprising: sensing and counting high-resolution transitions of a high-resolution digital sensor in response to the rotating device rotating; sensing low-resolution transitions of a low-resolution digital sensor in response to the rotating device rotating, the low-resolutions transitions being spaced apart at uneven angles; determining an angular position of the rotating device in response to determining a number of high-resolution transitions between pairs of low-resolution transitions. 
     In another respect, disclosed is a system for detecting an angular position of a rotating device, the system comprising: a high-resolution digital sensor positioned such that the high-resolution digital sensor senses rotation of the rotating device; a low-resolution digital sensor positioned such that the low-resolution digital sensor senses rotation of the rotating device; a control circuit electrically coupled to the digital sensor; the control circuit being configured to: receive and count high-resolution transitions from the high-resolution digital sensor in response to the rotating device rotating; receive low-resolution transitions from the low-resolution digital sensor in response to the rotating device rotating, the low-resolution transitions being spaced apart at uneven angles; determine an angular position of the rotating device in response to determining a number of high-resolution transitions between pairs of low-resolution transitions. 
     In yet another respect, disclosed is an electric motor comprising: a rotor configured to produce a magnetic field; one or more stator coils rotatively coupled to the rotor; a high-resolution digital sensor positioned such that the high-resolution digital sensor senses rotation of the rotating device; a low-resolution digital sensor positioned such that the low-resolution digital sensor senses rotation of the rotating device; a control circuit electrically coupled to the digital sensor; the control circuit being configured to: receive and count high-resolution transitions from the high-resolution digital sensor in response to the electric motor rotating; receive low-resolution transitions from the low-resolution digital sensor in response to the electric motor rotating, the low-resolution transitions being spaced apart at uneven angles; determine an angular position of the rotating device in response to determining a number of high-resolution transitions between pairs of low-resolution transitions. 
     Numerous additional embodiments are also possible. 
    
    
     
       III. BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects and advantages of the invention may become apparent upon reading the detailed description and upon reference to the accompanying drawings. 
         FIG. 1  is a block diagram illustrating a system for detecting an angular position of a rotating device, in accordance with some embodiments. 
         FIG. 2  is a block diagram illustrating digital sensors used in the determination of the angular position of a rotating device, in accordance with some embodiments. 
         FIG. 3  is a graphical representation illustrating signals received from digital sensors used in the determination of the angular position of rotating device, in accordance with some embodiments. 
         FIG. 4  is a graphical representation illustrating example signals returned from the stator coils of an electric motor indicating a position of the electric motor, in accordance with some embodiments. 
         FIG. 5  is a flow diagram illustrating a method for detecting the angular position of a rotating device, in accordance with some embodiments. 
     
    
    
     While the invention is subject to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and the accompanying detailed description. It should be understood, however, that the drawings and detailed description are not intended to limit the invention to the particular embodiments. This disclosure is instead intended to cover all modifications, equivalents, and alternatives falling within the scope of the present invention as defined by the appended claims. 
     IV. DETAILED DESCRIPTION 
     One or more embodiments of the invention are described below. It should be noted that these and any other embodiments are exemplary and are intended to be illustrative of the invention rather than limiting. While the invention is widely applicable to different types of systems, it is impossible to include all of the possible embodiments and contexts of the invention in this disclosure. Upon reading this disclosure, many alternative embodiments of the present invention will be apparent to persons of ordinary skill in the art. 
     In some embodiments, the angular position of a rotating device is to be determined. In some embodiments, one or more high resolution transitions of a high-resolution digital sensor are sensed and counted in response to the rotating device rotating. Similarly, low-resolution transitions of a low-resolution digital sensor are sensed in response to the rotating device rotating, the low-resolutions transitions being spaced apart at uneven angles. 
     In some embodiments, the angular position of the rotor may be determined by counting the number of high-resolution transitions between the low-resolution transitions. Since the low resolution transitions are spaced apart at uneven angles, an angular position of the rotating device may be identified by counting and distinguishing the high resolution transition between pairs of low resolution transitions. 
     In some embodiments, a direction of rotation may also be determined by comparing successive numbers of high resolution transitions between successive pairs of low resolution transitions. The sequence of the numbers of high-resolution transitions may then indicate the direction of rotation. 
     In some embodiments, an additional high-resolution digital sensor may be used. In some embodiments, the digital sensor and the additional digital sensor may be in quadrature with each other. A direction of rotation of the rotating device may be determined by comparing the low resolution transitions to the high resolution transitions and the other high resolution transitions. 
     In some embodiments, the rotating device may be an electric motor comprising stator coils and one or more rotors. In some embodiments, the electric motor may be a three-phase AC electric motor comprising three or more stator coils. The rotor of the electric motor may be a single pair north-south power magnet. The rotor may also consist of additional power magnet pairs. In such embodiments, each mechanical revolution of the electric motor may correspond to multiple effective electrical revolutions depending on the pairs of power magnets used. Electromagnets using coils may also be used in place of the power magnets. 
     In some embodiments, an approximate angular position of the electric motor may be determined by sending an electric pulse through one or more of the stator coils of the electric motor. The timing of the returning pulse, among other factors, is affected by the current position of the rotor (power magnet, in some embodiments) of the electric motor though the interaction of the magnetic flux from the rotor and the magnetic flux generated by the pulse travelling through the one or more stator coils. Thus, an approximate position of the rotor may be determined in response to detecting the timing of a returning electrical pulse from the stator coil. 
     In some embodiments, the rotating device may be calibrated such that a specific transition of the digital sensor is known to a high degree of accuracy. In such embodiments, once the calibrated transition occurs, the angular position of the rotating device may be determined to a great degree of accuracy. 
       FIG. 1  is a block diagram illustrating a system for detecting an angular position of a rotating device, in accordance with some embodiments. 
     In some embodiments, the rotating device may be an electric motor. It should be noted, however, that the methods and systems described herein may be applied to other rotating devices whose angular position is to be determined. 
     In some embodiments, electric motor  110  is configured to receive electrical power and to convert the electrical power to mechanical energy, which may be transferred to a load through axle  120 . The motor may be a three-phase electric motor and may include three stator coils  150  configured to receive AC current through electric lines  145 . The changing magnetic field generated by stator coils  150  generates a torque on rotor  115  and axle  120 . In some embodiments, rotor  115  may include one or more pairs of north-south power magnets. In other embodiments, rotor  115  may include electromagnets that generate magnetic fields using coils and DC current. In some embodiments, control circuit  140  is configured to generate appropriate currents to supply to stator coils  150  through electrical lines  145 . Depending on the rotational speed, direction of the rotational speed, and position of the rotor, currents having an appropriate amplitude and phase must be supplied to the stator coils to generate optimal rotation of the rotor. 
     Electric motor  110  may also include one or more digital sensors that are coupled to control circuit  140  using electrical line  135 . In some embodiments, the digital sensors may include detectors  130  that may be stationary and transition rings  125  containing high and low signal information that may be detected by detectors  130  while transition rings  125  rotate relative to detectors  130 . 
     The digital sensor may be any suitable device that can generate a series of low and high signals while the transition ring rotates in relation to the detector. For example, the digital sensor may be a laser that is either reflected or not by the transition ring; a Hall sensor rotating over north and south magnets, a reluctance sensor, etc. 
       FIG. 2  is a block diagram illustrating digital sensors used in the determination of the angular position of a rotating device, in accordance with some embodiments. 
     A low resolution digital monitor may include detector  220  and transitions ring  210 . In some embodiments, detector  220  may be mounted such that detector  220  rotates relative to transitions ring  220  when the rotating device rotates. For example, transition ring  210  may be connected to the rotating portion of the rotating device, and detector  220  may be mounted to a stationary portion or vice versa. 
     Any suitable digital sensor may be used that can generate low and high type signals. In some embodiments, a hall sensor may be used as the detector and magnets may be used for the transition rings. A south magnet, for example, may indicate a low value (hashed portion of the ring) and a north magnet may be used to indicate a high value. Other similar digital sensors may be used such a laser light as the detector and reflective/non-reflective surfaces as the transition ring. A reluctance type sensor may also be used. 
     As can be seen from the figure, transition ring  210  is configured to generate low and high signals at uneven angles. More details of these signals are provided in  FIG. 3 . The distribution of the signals may be used to determine the angular position of the rotating device as well as the direction of rotation. It should be noted that in some embodiments, only one high resolution signal may be used. 
     One or two or more high resolution digital sensors may also be used. In some embodiments, detector  225  and  230  may be used in combination with transitions ring  215 . The hashed surfaces may indicate the high values of the signal, for example. In some embodiments, the two high-resolution sensors may be in quadrature with each other—90 degrees out-of-phase with each other. 
     Example signals generated by the digital sensors are provided in  FIG. 4 . 
     Additional low resolution sensors may be used (not shown here) for increased accuracy and reliability. 
       FIG. 3  is a graphical representation illustrating signals received from digital sensors used in the determination of the angular position of rotating device, in accordance with some embodiments. 
     As shown in the figure, signal  310  (L) may be generated from detector  220  and transition ring  210 , signal  315  (H 1 ) may be generated from detector  230  and transition ring  215 , and signal  320  (H 2 ) may be generated using detector  225  and again transition ring  215 . In some embodiments, only one high resolution signal may be generated (H 1 , for example). 
     An angular position of rotating device may be determined by counting the number of high resolution transitions (H 1  and H 2 ) that occur between low resolution transitions (L). For example, if 6 transitions first occurs followed by 10 transitions, then it may be determined that the rotating device is at approximately the transition at 150 degrees. Furthermore, it may be determined that the rotating device is rotating clockwise. 
     It should be noted that alternative spacing between the low resolution transitions may be used to more efficiently determine angular position. 
     An angular position of the electric motor may also be determined when a transition in signal  310  occurs and compared to signals  315  and  320 . The transitions may be calibrated to correspond to known angular positions. A transition may be identified by examining high resolution signals  315  and  320 . For example, if a rising transition is detected in signal  310  and a rising transition is detected in signal  320 , the transition corresponds to the angular position at 90 degrees. If on the other hand a falling transition is detected on signal  320 , the transition corresponds to the angular position at 270 degrees. 
     Similarly, the direction of rotation may be determined. In the example above, the first scenario would correspond to a clockwise rotation and the second scenario would correspond to counter-clockwise rotation. 
       FIG. 4  is a graphical representation illustrating example signals returned from the stator coils of an electric motor indicating a position of the electric motor, in accordance with some embodiments. 
     In an embodiment where the rotating device is an electric motor, an initial angular position of the electric motor may be determined by sending electrical pulses to stator coils  150  using control circuit  140  (shown in  FIG. 1 ). Shown in this figure are the times the electric pulses return to control circuit  140  for different positions of rotor  115 . Graphs  410 ,  415 , and  420  correspond to each of stator coils  150 . The timing of the returning pulses from each of the stator coils depends on the angular position of the rotor. In some embodiments, a single pulse from a single stator coil may be used to determine an initial position of the rotor. In other embodiments, for increased accuracy, additional pulses may be sent through the single stator coil and then averaged. For additional accuracy pulses may be sent through one or more additional stator coils (or more multiple averaged pulses). The results from all stator coils may then be compared to determine a more accurate angular position for the rotor. 
     A more detailed explanation of how to obtain an initial angular position of the electric motor is given in a paper by Marco Tursini, Member, IEEE, Roberto Petrella, Member, IEEE, and Francesco Parasiliti, titled “Initial Rotor Position Estimation Method for PM Motors”, IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 39, NO. 6, NOVEMBER/DECEMBER 2003, which is incorporated herein by reference. 
       FIG. 5  is a flow diagram illustrating a method for detecting the angular position of a rotating device, in accordance with some embodiments. 
     Processing begins at  500  whereupon, at block  510 , high-resolution transitions of a high-resolution digital sensor are sensed and counted in response to a rotating device rotating. 
     At block  515 , low-resolution transitions of a low-resolution digital sensor are sensed in response to the rotating device rotating, the low-resolutions transitions being spaced apart at uneven angles. 
     At block  520 , an angular position of the rotating device is determined in response to determining a number of high-resolution transitions between pairs of low-resolution transitions. 
     Processing subsequently ends at  599 . 
       FIG. 1  shows an example of a system that may be used to perform the method described here. 
     Those of skill will appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Those of skill in the art may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention. 
     The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. 
     The benefits and advantages that may be provided by the present invention have been described above with regard to specific embodiments. These benefits and advantages, and any elements or limitations that may cause them to occur or to become more pronounced are not to be construed as critical, required, or essential features of any or all of the claims. As used herein, the terms “comprises,” “comprising,” or any other variations thereof, are intended to be interpreted as non-exclusively including the elements or limitations which follow those terms. Accordingly, a system, method, or other embodiment that comprises a set of elements is not limited to only those elements, and may include other elements not expressly listed or inherent to the claimed embodiment. 
     While the present invention has been described with reference to particular embodiments, it should be understood that the embodiments are illustrative and that the scope of the invention is not limited to these embodiments. Many variations, modifications, additions and improvements to the embodiments described above are possible. It is contemplated that these variations, modifications, additions and improvements fall within the scope of the invention as detailed within the following claims.