Abstract:
An instrumented ball-bearing includes a rotating part, a non-rotating part, and an assembly for detecting rotation parameters. The assembly for detecting rotation parameters includes an encoder and a sensor. The sensor is integrated with the non-rotating part. The sensor includes a sensor unit and at least a microcoil. The microcoil has a substantially planar winding. The microcoil is positioned in the sensor unit of the non-rotating part such that the microcoil is positioned axially opposite the encoder.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to an antifriction bearing in which a rotating member of the bearing supports an encoder and a nonrotating member of the bearing supports a sensor that may be used to determine rotation parameters such as the speed or the angular position of the rotating element supporting the encoder. The present invention also relates to antifriction bearings for use in electric motors, which are required to operate in severe speed and temperature conditions. 
     2. Description of the Relevant Art 
     French Patent No. 2,754,903, describes an antifriction bearing that includes a sensor on the nonrotating track, of the Hall effect probe type, and an encoder on the rotating track moving in rotation with a slight air gap relative to the sensor while being capable of producing in the sensor a periodic signal with a frequency proportional to the rotation speed of rotation of the rotating track. The encoder includes an annular active portion. The annular active portion includes a plastic magnet and an active portion placed opposite the sensor. The active portion may be supplemented by a reinforcement portion that includes two annular elements placed in contact with the active portion on either side of the active zone. 
     This type of antifriction bearing is usually satisfactory, particularly in the field of electric motors. However, this type of encoder cannot operate at temperatures above 120°. In addition, the sensor and the encoder do not operate satisfactorily if they are subjected to high intensity external magnetic fields, for example the magnetic fields induced by the coils of the stator of electric motors and/or by the electromagnetic brake built into the motors. Finally, the axial compactness of this type of antifriction bearing is not optimal and is not easy to incorporate. 
     In high power asynchronous electric motors, control of the motor requires detection of the rotation parameters of the motor. Knowledge of speed and direction of rotation of the rotor may be needed to adapt the frequency and the direction of the current entering the coils of the stator. The use of a multipolar type encoder associated with a Hall effect probe is suitable only for applications in which the power and the control requirements are relatively imprecise, for example for a fan motor that operates at constant speed during use. Optical type sensor encoder systems, such as industrial encoders, require a mechanical interface for driving by the electric motor and are relatively sensitive to impacts and to temperature. Optical type sensor encoder systems are not likely to be built into a motor. 
     The invention aims to remedy these disadvantages. 
     SUMMARY 
     Herein we describe an instrumented antifriction bearing that may be axially compact and may operate at high temperatures while delivering precise detection. The antifriction bearing may also including when they are subjected to intense magnetic fields. 
     In some embodiments, the instrumented antifriction bearing device may include a rotating portion, a nonrotating portion and an assembly for detecting rotation parameters. An assembly for detecting rotation parameters may include an encoder and a sensor. A sensor may be integrated with the nonrotating portion and may include a sensor unit. A sensor may include at least one microcoil with a substantially flat winding. A microcoil may be positioned on a support of a circuit mounted in the sensor unit of the nonrotating portion so that the microcoil may be axially opposite the encoder. This may provide satisfactory axial compactness. 
     In one embodiment, the device may include a plurality of substantially radial coplanar reception microcoils, which may allow substantially precise detection. In certain embodiments, the device may include a plurality of reception microcoils positioned on a plurality of parallel radial planes. An increased number of reception coils may provide enhanced precision. 
     In some embodiments, the device may include a transmission coil positioned in the sensor unit. The transmission coil may also be a microcoil. A microcoil may have a flat winding. In an embodiment, a device may include at least one transmission coil, at least one reception coil, and a data processing circuit positioned on the support. These elements may be used to retain a desired axial compactness. The coils may be made using printed circuit technology. The support may include a printed circuit substrate in the form of a resin circuit board. A sensor may include active and/or passive elements combined in a single module integrated with the nonrotating portion. 
     In some embodiments, the device may include a plurality of microcoils. Microcoils may be coupled in pairs and/or angularly offset in order to generate a differential signal. The encoder may include an encoder wheel. An encoder wheel may include an active zone made of an electrically conducting metal. In certain embodiments, the encoder may include a printed circuit with an annular shaped substrate that includes metallized sectors and nonmetallized sectors. The printed circuit may be mounted on a nonrotating track of the antifriction bearing. 
     In some embodiments, the encoder may include an encoder wheel with windows and/or teeth attached to a rotating track of the antifriction bearing. The encoder may be a substantially solid block. The encoder may be pressed sheet metal. An encoder may operate at high temperatures. For the purposes of this application, windows refer to holes formed in the encoder between two circumferentially continuous portions. For the purposes of this application, teeth refer to portions of material that are integrated with a circumferentially continuous portion of the encoder. The encoder may include an axial portion positioned on a cylindrical bearing surface of the rotating track and a radial portion directed towards the other track and in which the windows or the teeth are formed. 
     To increase compactness, at least one portion of the encoder may be positioned in the space situated between the antifriction bearing tracks. For example, a portion of the encoder may be positioned radially between the cylindrical surfaces of the tracks which extend between the bearing raceways and the frontal surfaces delimiting said tracks and axially, at right angles to the cylindrical surfaces, between the rolling elements and the frontal radial surfaces of the antifriction bearing tracks. In certain embodiments, the encoder may be positioned outside the space situated between the antifriction bearing tracks. 
     In some embodiments, the sensor unit may be annular. In another embodiment, the sensor unit may occupies an angular sector of less than 360°, for example approximately 120°. In certain embodiments, the data processing circuit may be an application-specific integrated circuit (ASIC). 
     In some embodiments, an electric motor may include a rotor, a stator, at least one antifriction bearing supporting the rotor, and a sensor assembly including an encoder and a sensor. The sensor may include at least one microcoil with a substantially flat winding positioned on a support of a circuit that is mounted in the sensor unit and integrated with the stator such that the microcoil is positioned axially opposite the encoder. In an embodiment, a winding may include an outer track integral with the stator and supporting the sensor unit and an inner rotating track integral with the rotor and supporting the encoder. The motor may be of the high power asynchronous type in which precise control may be required and facilitated by measuring the rotation parameters precisely. For the purposes of this application, a microcoil refers to a coil with a winding formed on a circuit. For example, a microcoil may include a copper coil on a printed circuit substrate. The thickness of the card and the microcoil may be approximately 1 mm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features and advantages of the methods and apparatus of the present invention will be more fully appreciated by reference to the following detailed description of presently preferred but nonetheless illustrative embodiments in accordance with the present invention when taken in conjunction with the accompanying drawings in which: 
         FIG. 1  depicts a view of an axial section of an embodiment of an instrumented antifriction bearing; 
         FIG. 2  depicts a partial view of the sensor of  FIG. 1 ; 
         FIG. 3  depicts a frontal view in elevation of the encoder of  FIG. 1 ; 
         FIG. 4  depicts a frontal view in elevation of an embodiment of an encoder variant; 
         FIG. 5  depicts a view of an axial section of an embodiment of an instrumented antifriction bearing; 
         FIG. 6  depicts a frontal view in elevation of the encoder of  FIG. 5 ; and 
         FIG. 7  depicts a wiring diagram of an embodiment of a sensor. 
     
    
    
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF EMBODIMENTS 
     As illustrated in  FIG. 1 , the rolling bearing  1  may include an outer track  2 ; an inner track  3 ; a row of rolling elements  4 , such as balls, placed between the outer track  2  and the inner track  3  and retained by a cage  5 ; a seal  6  on one of its sides; on the opposite side a speed sensor  5  integrated with the outer track  2 ; and an encoder  8  integrated with the inner track  3 . In an embodiment, the outer track may be nonrotating and the inner track may be rotating. In an embodiment, the outer track may be rotating and the inner track may be rotating. 
     In some embodiments, a sensor  7  may include a detection portion  9  as depicted in greater detail in  FIG. 2 . A sensor may include a support unit  10  made of a synthetic material and a metal element  11  fitted onto a bearing surface of the outer track  2 . A groove in a track may be used to attach the seal provided in noninstrumented antifriction bearings. A cable  12  may be coupled to the detection portion  9  and may be used to transmit information about speed, position, and/or or rotation parameters. Information may be transmitted to any unit that are capable of exploiting the data. 
     In some embodiments, an encoder  8 , as depicted in  FIGS. 1 and 3 , may include a support portion  13  and an operational portion  14 . The support portion  13  may tubular in shape. The support portion  13  may be positioned on a cylindrical bearing surface  3   a  of the inner track  3  formed between the trackway  3   b  which is coupled with the rolling elements  4  and a radial surface  3   c  which forms the end of the inner track  3  in the axial direction on the side of the sensor. The operational portion  14  may be radial and may include a plurality of windows  15 . Windows may have a rectangular shape and may be elongated radially at the large diameter end of the operational portion  14 , allowing a continuous circular portion  16  to remain. The operational portion  14  and the support portion  13  may be a solid unit and may provide an economic and particularly robust construction. The encoder  8  may be a metal sheet formed by means of pressing and punching steps. The operational portion  14  may be slightly recessed relative to the radial surface  3   c  of the inner track  3 . The encoder  8  may be particularly compact and positioned in the space defined radially between the tracks  2  and  3  of the rolling bearing and axially between the rolling elements  4  and the radial plane through which the end surfaces  2   c ,  3   c  of said tracks  2  and  3  pass. 
     In some embodiments, a detection portion  9  of the sensor  7  may include a support  17 , a transmission microcoil  19 , and at least four reception microcoils  20 . An integrated circuit  18 , such as an ASIC type, may be mounted on a support  17  and may be used to process data. A transmission microcoil  19  may include an excitation coil. The circuit may include a predetermined number of filtering elements such as capacitors, resistors, etc., which are not shown. The detection portion  9  may be positioned axially at a slight distance from the operational portion  14  of the encoder  8  and may occupy an angular sector of approximately 120° while being inserted into the support unit  10 , which may be substantially circular. In an embodiment, a continuous angular sector of 360° may be provided for insertion of the detection portion into the support unit. The detection portion  9  may include a face, oriented facing the encoder  8 , that is not substantially covered by the material of the support unit  10 . 
     In some embodiments, microcoils  19  and  20  may be flat winding types of microcoils. Microcoils may be printed circuits or integrated circuits. The flatness of the windings may provide the sensor  7  with excellent axial compactness. In addition, the reception coils  20  may have a square outer contour. Reception coils may be positioned one after the other on the arc of a circle formed by the support  17 , while the transmission coil  19  substantially surrounds the reception coils  20  and is shaped like an arc of a circle. The coils  19  and  20  may be coupled to the data processing circuit  18 . The coils  19  and  20  may be coupled to the cable  12 . 
     A metal element  11  may include a portion that forms a hook  11   a  bent into a groove of the outer track  2  that may be used for fastening a sealing element which, in a noninstrumented antifriction bearing, may be substantially symmetrical with the seal  6 . The metal element  11  may be supplemented by a short radial portion directed outward from the portion  11   a  and an axial portion  11   c  extending from the free end of the radial portion  11   b . A short radial portion may be in contact on one side with the end radial surface  2   c  of the outer track  2  and on the other side with the support unit  10  of the sensor  7 . An axial portion  11   c  may radially surround the support unit  10 , with the exception of the cable outlet zone  12  where the support unit  10  may extend outward forming a protuberance  21  surrounding the cable  12  and protecting its outlet. 
     In some embodiments, a support unit  10  may be made of a synthetic material and may have a generally annular shape with the protuberance  21  projecting over its periphery. A support unit may have an axial hollow on its radial face on the side of the antifriction bearing that constitutes a housing for the detection portion  9  while covering the detection portion on its face opposite the rolling bearing and over its thickness in the radial direction. The support unit  10  and the detection portion  9  may be integrated. In one embodiment, the support unit  10  could be metallic. 
       FIG. 4  depicts an embodiment of an encoder in which the support portion  13  is similar to  FIG. 3 . The operational portion  14  may be oriented radially outward from the support portion  13 . A support portion may be formed by a plurality of teeth  22 , which may be substantially rectangular in shape, elongated radially, whose periphery is circular, and crenellations  23  of slightly trapezoidal shape. The reception coils  20  may be electrically excited by the transmission coil  19  connected to an oscillating circuit. The transmission coil  19  may generate by induction an electric signal in the reception coils  20 . During the rotation of the encoder  8 , the windows and the full portions of the operational portion  14  passing before the microcoils may produce a variation of the metal mass situated in front of each reception microcoil  20 . In the reception coils  20 , this may result in a variation of the phase of the electric signal induced due to losses by eddy currents. These variations of the electric signal emitted by the various reception coils  20  and processed by the circuit  18  may be the basis of the generation of signals representative of the parameters of rotation of the encoder  8 , such as the speed of rotation. 
     In some embodiments, a sensor with microcoils may allow the instrumented antifriction bearing to deliver reliable information, even when magnetic fields of high intensity are present. The encoder may be made of an electrically conducting and magnetic metal material, such as steel, or electrically conducting and nonmagnetic material, such as aluminum or copper. 
     Reception microcoils  20  may operate in pairs to deliver a differential signal. The reception microcoils  20  of a pair may be angularly offset by an angle represented by β. An angular pitch of the windows is represented by φ. For the signal to be out of phase, one of these angles may not be a multiple of the other. This therefore gives β≠a*φ where a is any integer, the angle β usually being greater than φ. For example this could be β=(a+0.5)*φ or β=(a+0.25)*φ. 
     When an encoder passes in rotation before the sensor, the discontinuities of material of the operational portion  14  may cause periodic variations of the metal mass that is opposite the reception microcoils  20 . If there is metal material before each of the coils of a pair of reception coils, the phase difference between the two differential coils may be zero. If there is metal material before at least one of the two reception coils forming a pair and the metal material is distributed differently before each coil, the losses due to the eddy currents in the metal material may generate a phase difference of the currents. This phase difference may then be processed and extracted adequately by the processing circuit  18 , in order to obtain desired information, such as angular speed, direction of rotation, position, etc. 
     In some embodiments, generation of an electronic signal may not depend on the level or the direction of a magnetic field sensed by the microcoils, but on the modification of the currents induced by the excitation coil  19  in the reception coils  20  in the presence of the variations of the electrically conducting metal masses passing before said microcoils. The signal may be therefore very insensitive to external magnetic fields, which makes the device according to the invention extremely suitable for operating in an environment subjected to strong magnetic fields such as electric motors. The reception coils  20  may be distributed on the support  17  with a radial position and angular pitch suitable for cooperating with the operational portion  14  of the encoder  8  and/or delivering the required signals. In an embodiment, the number of reception coils  20  may be increased in the circumferential direction and/or several coils may be stacked in the axial direction in order to obtain higher powered signals. 
     In some embodiments, since the microcoils and/or processing circuit  18  may be extremely thin, the sensor  7  may have extremely small axial dimensions, which may allow integration into a sensor unit  10 . Likewise, the encoder may be, due to its structure, thin axially and may be easily integrated into the space between the bearing tracks, such that the encoder does not affect the external dimensions of the instrumented antifriction bearing. 
       FIGS. 5 and 6  depict and embodiment of an encoder  8  made with a printed circuit technique. From a conventional printed circuit substrate coated with a thin metal layer, such as copper, a disk may be made including metallized sectors  8   a  and nonmetallized sectors  8   b . The substrate may be electrically nonconducting and the metallized sectors  8   a  may be electrically conducting. 
     A disk may be coupled (e.g., by appropriate means, such as fitment and/or bonding) onto an axial portion  3   d  the rotating track  3  of the bearing  1 . The axial portion  3   d  may be configured to be coupled to the disk. This type of encoder wheel has little inertia, great axial compactness, and the contours of the active portions may be made with great precision. The aggregate signal may be particularly weak. 
       FIG. 7  depicts in greater detail the electrical functions of an embodiment of the system. Reception coils  20  may be grouped in two pairs numbered  24  and  25  and framed by dashed lines. For clarity of the drawing, the pairs of reception coils  24  and  25  are shown outside the exciting transmission coil whereas in reality they are inside said transmission coil  19 . The coils  19  and  20  may be coupled to the processing circuit  18 . The processing circuit  18  may include an oscillator  26 , whose output is connected to the transmission coil  19 , and two phase demodulators  27  and  28  coupled to the output of each of the reception coils  20 . In an embodiment, the circuit  18  may include two interpolating comparators  29 ,  30 , positioned at the output of the phase demodulators  27  and  28 . At the output, the processing circuit  18  may transmit a digital signal representative of at least one parameter of rotation of the antifriction bearing, such as speed, position, direction of rotation, acceleration, etc. 
     In some embodiments, an instrumented antifriction bearing may be produced that can be easily integrated into a mechanical assembly due to its small bulk. The instrumented antifriction bearing may operate at high temperatures, such as those existing in an electric motor, and/or operate in an environment subjected to strong magnetic fields. Through these qualities, the instrumented antifriction bearing according to the invention has worthwhile capabilities for use in a high power asynchronous electric motor. The instrumented antifriction bearing may fulfill both the mechanical function of a bearing and the electronic functions of detection necessary to control the motor. 
     In this patent, certain U.S. patents, U.S. patent applications, and other materials (e.g., articles) have been incorporated by reference. The text of such U.S. patents, U.S. patent applications, and other materials is, however, only incorporated by reference to the extent that no conflict exists between such text and the other statements and drawings set forth herein. In the event of such conflict, then any such conflicting text in such incorporated by reference U.S. patents, U.S. patent applications, and other materials is specifically not incorporated by reference in this patent. 
     Further modifications and alternative embodiments of various aspects of the invention will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein are to be taken as the presently preferred embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description of the invention. Changes may be made in the elements described herein without departing from the spirit and scope of the invention as described in the following claims.