Patent Publication Number: US-2023160430-A1

Title: Bearing unit with sensorized inner ring

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority to Italian Patent Application No. 102021000029615 filed on Nov. 24, 2021, under 35 U.S.C. § 119, the disclosure of which is incorporated by reference herein. 
     FIELD 
     The present disclosure relates to a bearing unit provided with a sensorized radially inner ring. Such a bearing unit is suitable for applications in the manufacturing sector and especially in the marble cutting industry. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will now be described with reference to the attached drawings, which show non-limiting exemplary embodiments of a bearing unit, in which: 
         FIG.  1    is a partial schematic view of an assembly of a plurality of bearing units for a marble cutting machine; 
         FIG.  2    is a cross-sectional view of a bearing unit according to an exemplary embodiment of the present disclosure; 
         FIG.  3    shows an enlarged cross-sectional view of a radially inner ring of the bearing unit of  FIG.  2   ; 
         FIG.  4    is a partial axial view of the radially inner ring of  FIG.  3   ; 
         FIG.  5    is an axial view of a sensor for the bearing unit of  FIG.  2   ; and 
         FIG.  6    is a cross sectional view of the sensor of  FIG.  5   . 
     
    
    
     DETAILED DESCRIPTION 
     Bearing units of marble cutting machines are subjected to high levels of vibration and high temperatures during the normal course of operation. The vibrations created by the impact of the cutting tools on the blocks of marble to be cut are transmitted to the structure of the machine and to the bearing units causing damage that reduces the operating life of the component parts of the bearing unit and of the bearing unit as a whole. 
     Multiple bearing units are often assembled in a “pack” form that makes it difficult to dissipate the heat produced by friction between wires used to cut the marble and corresponding pulleys that operate the wires. Additional heat is generated by rolling friction from relative rotation of the rings of the bearing unit, particularly on the raceways of the rings. Evidently, heat dissipation is even more difficult in the innermost bearing units of the bearing unit pack, since these central units are more isolated from the external environment. This heat can cause wear that further reduces the operating life of the component parts of the bearing unit and the bearing unit as a whole. 
     In manufacturing, and in particular in the marble cutting industry, known bearing units have very restricted axial dimensions, since they are mounted axially adjacent to each other, forming a “pack” of bearing units. This dimensional limitation makes it necessary to use complex and/or costly technical solutions. Components must have small overall axial dimensions while still providing a high level of performance. 
     Known bearing units have a first component, e.g., a radially outer ring or a radially inner ring, which may be fixed to a rotating element, and a second component, e.g., a radially inner ring or a radially outer ring, which may be fixed to a stationary element. The rotation of one component with respect to the other is allowed by a plurality of rolling bodies that are positioned between a cylindrical surface of the first component and a cylindrical surface of the second component, these surfaces usually being called raceways. The rolling bodies may be balls, cylindrical or tapered rollers, needle rollers, or similar rolling bodies. 
     Users of marble cutting machines often avoid running their machines at more than 110° C., and must therefore control the temperature. Considerable volumes of cooling water are used for this purpose to remove the greatest possible amount of heat. However, it is difficult to determine the exact volume or the correct temperature of the water needed to reduce the temperature of the machine to a safe operating temperature. 
     Accordingly, an object of the present disclosure is to provide a bearing unit that is free of the aforementioned drawbacks. 
     This object may be achieved, for example, by providing a radially inner ring of a bearing unit with a sensor for monitoring the level of vibrations and temperature in the bearing unit. 
       FIG.  1    illustrates an exemplary embodiment of a marble cutting machine  20  suitable for producing marble slabs (known and not illustrated for simplicity of illustration) of a reduced thickness, about 13 mm. 
     Machine  20  may include a plurality of pulleys  22  that enable movement of a plurality of cutting wires (known and not shown for simplicity of illustration) for cutting marble. 
     In various embodiments, pulleys  22  are positioned axially adjacent to each other, and their axial spacing defines a thickness of the marble slabs produced. Rotation of each pulley  22  is allowed by a corresponding bearing unit  10 . 
     A bearing unit  10  may include a radially inner ring  33  and a flanged radially outer ring  31  that rotates relative to inner ring  33  by means of a plurality of rolling bodies  32  interposed between inner ring  33  and outer ring  31 . Outer ring  31  may include a radially outer flange  25 , to which a corresponding pulley  22  is attached by connector  24 , e.g., screws. In various embodiments, bearing unit  10  may further include a cage  34  for containing the plurality of rolling bodies  32  in position in the row of rolling bodies  32 . 
     Each bearing unit  10  may be mounted in close axial contact with each axially adjacent bearing unit  10  in order to reduce the axial distance between two adjacent cutting wires for cutting marble slabs of a very low thickness, and in order to avoid any possible axial play between the bearing units. In particular, each radially inner ring  33  may be located in close axial contact to each radially inner ring  33  of an axially adjacent bearing unit  10  and have an axial thickness greater than an axial thickness of a corresponding radially outer ring  31 . 
     To ensure that a thickness of resulting marble slabs is greatly reduced, a bearing unit  10  for a marble cutting machine  20  may have an axial thickness of itself and of its components, that is to say an axial thickness of radially inner ring  33  and flanged radially outer ring  31 , within a range from 18 mm to 30 mm. Bearing unit  10  may further have an inside diameter D of a through hole  30  of radially inner ring  33  of at least 150 mm, and preferably of about 200 mm, so that the ratio between a dimension of the inside diameter “D” and an axial thickness “t” of radially inner ring  33  is between 6.7 and 11.1. This range ensures a suitable axial thickness for obtaining marble slabs of greatly reduced thickness, while maintaining a sufficient stiffness and strength of bearing unit  10 . 
     A bearing unit  10  may further include one or more sealing devices  35  to prevent ingress of contaminants and water. In various embodiments, bearing unit  10  may include two sealing devices  35 , each positioned on opposite axial sides of bearing unit  10 . Sealing device  35  may be particularly useful in applications that produce abrasive dust, e.g., dust from cutting marble or diamond, and in applications that use cooling liquids, e.g., water, to maintain an operating temperature within acceptable limits. Advantageously, sealing device  35  may increase the strength of bearing unit  10  and thus improve a service life of bearing unit  10 . 
     A skilled artisan would appreciate that the terms and expressions recited in the present disclosure, which indicate positions and orientations such as “radial” and “axial” are to be interpreted as relative to an axis of rotation X of bearing unit  10 . 
     For simplicity of illustration, reference  32  may refer to both an individual rolling body of a row of rolling bodies and to the row of rolling bodies. 
     In various embodiments, a sealing device  35  interposed between radially inner ring  33  and radially outer ring  31  may include a shield  40  forming a seal against a support surface  31 ′ of a first seat  31   a  of radially outer ring  31 . Shield  40  may therefore be stably fixed to radially outer ring  31 , and consequently be rotatable together therewith. 
     Advantageously, shield  40  may be made of a composite material. By way of non-limiting example, a composite material that may be used includes a very hard polyurethane or a POM acetal resin. 
     Shield  40  may be held in a stable position by an anchoring element  60 , e.g., a snap ring  60  made of metallic material. In various embodiments, snap ring  60  is interference fitted into a second seat  31   b  of radially outer ring  31 , located in an axially outer position relative to the first seat  31   a , in order to push shield  40  axially towards support surface  31 ′ of outer ring  31 . 
     Radially inner ring  33  may include a seat  33   a  formed by a groove or a recess having a frontal cross section comprising a portion of a circular crown having an amplitude (a) varying from 20° to 22° and a radial depth (h), measured from a radially inner cylindrical surface  33   b  of radially inner ring  33 , ranging from 5.1 mm to 5.3 mm. Radially inner ring  33  may further include a sensor  50  fitted stably in seat  33   a . In various embodiments, sensor  50  may be a temperature sensor and/or a vibration sensor. 
     Seat  33   a  may be provided with an axially inner surface  333  on which sensor  50  bears. Advantageously, seat  33   a  may be open both in a radially inward direction and in an axially outward direction (relative to a transverse axis (Y) of bearing unit  10 ), in order to provide a greater volume of seat  33   a  and consequently for a sensor  50 , or a greater volume which resides in the volume of seat  33   a . It will be appreciated by a person of ordinary skill in the art that a durability and operating life of a sensor  50  may be improved as available space for sensor  50 , and thus a size of sensor  50 , increases. 
     Seat  33   a  may be formed in a relatively load-free area of radially inner ring  33  such that removal of material causes no diminution in load capacity of bearing unit  10 . Furthermore, because seat  33   a  is open in an axial direction, seat  33   a  may be visually inspected more easily during demounting and mounting of sensor  50 . Additionally, a sensor signal of sensor  50  may be sent without passing through a layer of material, improving transmission of the sensor signal. 
     On the other hand, the radially inward opening helps to increase the volume available for sensor  50 . Defining an opening in a radially outward direction increases risk of excessive weakening of radially inner ring  33 . Furthermore, placement of sealing device  35  may be an obstacle to mounting where a radially outward opening is used. 
     By limiting amplitude (a) of the portion of a circular crown to between 20° and 22°, it is possible to occupy less than 6% of an annular axial surface  33   c  of radially inner ring  33 . This characteristic facilitates axial clamping of bearing unit  10  without creating excessively unbalanced contact forces. Indeed, if amplitude (a) of seat  33   a  were 180°, then half of axial annular surface  33   c  would be in contact with an adjacent bearing unit (and would therefore be subject to loading) and half would not be. In this case, axial clamping of bearing unit  10  would create a moment acting on bearing unit  10 , significantly shortening the service life of bearing unit  10 . 
     By designing a seat  33   a  in the shape of a portion of a circular crown with an amplitude (a) of the portion of circular crown in a range of 20° to 22°, it is possible to mitigate the occurrence of such moments, as 94% of axial annular surface  33   c  of radially inner ring  33  may be in contact with an adjacent bearing unit  10 . In other words, when bearing units  10  are axially clamped, the forces tend to balance out and distribute, and transmit uniformly from one bearing unit  10  to an adjacent bearing unit  10 . 
     Additionally, designing seat  33   a  as a portion of a circular crown with an amplitude of 20° helps maintain sufficient strength in the structure of radially inner ring  33 . 
     As illustrated in  FIGS.  5  and  6   , a sensor  50  may be axially defined by two semi-annular surfaces,  53  and  55 , transverse to an axis A and extending around axis A through an arc of circumference subtended by an angle (β). Sensor  50  may be radially defined by a radially outer cylindrical surface  51  and a radially inner cylindrical surface  54  facing axis A. To assist in mounting sensor  50  in a correct orientation, sensor  50  may include a protrusion  52  formed in an asymmetrical position on outer cylindrical surface  51  and extending radially outwards from surface  51 . Protrusion  52  may be asymmetrical such that it is positioned axially closer to semi-annular surface  53  than to semi-annular surface  55 , provided that a sensing element of sensor  50  is also positioned inside sensor  50  closer to semi-annular surface  53  than to semi-annular surface when sensor  50  is mounted. 
     Dimensions of sensor  50  may be sized such that a whole of seat  33   a  is occupied when sensor  50  is mounted. In particular, sensor  50  may have a frontal cross section in a shape of a portion of a circular crown having an angle (β) varying from 18° to 20°, and a substantially square transverse cross section having a side measurement L from 4.7 mm to 4.9 mm. 
     In various embodiments, sensor  50  transmits data via radio waves and may be a Wi-Fi compatible device. By using Wi-Fi technology, it is possible to avoid design complications that would be caused by having to run a wire into a center of a bearing unit pack that may contain as many as 108 adjacent bearing units. Moreover, since radially outer ring  31  may rotate, using a wired connection would require modifying the shaft to allow a wire to run inside it to a central bearing unit of the bearing unit pack. This solution is inconvenient and costly to produce. 
     In alternative embodiments, sensor  50  may transmit a signal via Bluetooth. A Wi-Fi signal may be preferable to a Bluetooth signal because Bluetooth may have a lower range than a Wi-Fi signal (e.g., 10 m range for Bluetooth compared to a 100 m range for a Wi-Fi signal). Additionally, a Wi-Fi sensor may sustain multiple connections to multiple devices, whereas a Bluetooth sensor may only connect to a single device at a time. 
     In various embodiments, sensor  50  may be stably fixed in seat  33   a  of radially inner ring  33 , by gluing for example. Advantageously, an adhesive used for gluing sensor  50  in seat  33   a  may be compatible with both the material of radially inner ring  33  and the composite material of sensor  50 . An example of an adhesive may be one that becomes fully cured on steel in a short time (e.g., six hours at an ambient temperature of 22° C.) while also being suitable for plastic materials. It may also withstand high temperatures, e.g., having a heat resistance at 110° C. or more than 75% at an ambient temperature. 
     The adhesive may be inserted into seat  33   a  of radially inner ring  33 , while ensuring that a thickness of the adhesive is such that it does not allow sensor  50 , when fitted into the seat, to project beyond a maximum dimensions of seat  33   a . For the purpose of demounting, the adhesive may be removed by a solvent. 
     Sensor  50  may be positioned as near to a point of greatest heat generation in radially inner ring  33 , e.g., a radially inner raceway  33 ′. In various embodiments, a minimum distance “d” between raceway  33 ′ and seat  33   a  may be less than 3 mm. Because radially inner ring  33  may be made of steel, a temperature detected by sensor  50  may be practically the same as a temperature of raceway  33 ′, which may be regarded as a temperature of bearing unit  10 . 
     To ensure that the sensing element of sensor  50  is always in a position nearest raceway  33 ′, seat  33   a  may be provided with a chamfer  332  formed on a corresponding radially outer surface  331  to define an axial stop for protrusion  52 , which, by engaging with chamfer  332 , ensures that sensor  50  is correctly mounted. 
     While stable mounting of sensor  50  on radially inner ring  33  is preferable, e.g., by gluing, it is not critical. In embodiments in which radially inner ring  33  is stationary, risk of detachment is low, since the radially inner ring in this application is not rotatable but is locked against the shaft. Furthermore, because each bearing unit  10  is locked in a bearing unit pack, each sensor  50  is forced to remain in each seat  33   a  of each radially inner ring  33 . 
     In various embodiments, seat  33   a  may be positioned opposite an application point “P” of a force “F” acting on radially inner ring  33 , relative to transverse axis Y of bearing unit  10 . This positioning may be achieved during mounting of bearing unit  10 , during operation, or by adjusting marble cutting machine  20 . 
     For example, if a direction of force F transmitted to radially inner ring  33  is radially inward and axially outward (i.e., from the right to the left in  FIG.  2   ), it is advantageous to use bearing unit  10  with a sensor  50  mounted in an axially inner position (i.e., on the right according to  FIG.  2   ). Radially inner ring  33  may thus be under load in a portion where seat  33   a  is not present (i.e., a portion where there is no absence of material resulting from formation of a seat  33   a ). This arrangement avoids possible problems caused by truncation or cracking of radially inner ring  33 . 
     Preliminary tests have demonstrated the feasibility of this solution: a sensor was glued stably to the shield of the bearing unit, and the standard test (at 750 r.p.m. for 8 hours) for checking a new bearing unit design for marble cutting machines was conducted. The outcome of the test was positive, since it allowed the temperature of the shield, and therefore of the bearing unit, to be monitored throughout the duration of the test. 
     The solution with the sensorized bearing unit has considerable advantages. It allows checking of the temperature of the bearing unit in any position by fitting a sensorized bearing unit in any specific position in the bearing unit pack (e.g., the center of the bearing unit pack). Thus the temperature of the whole bearing unit pack can be monitored and checked. By enabling a user of a marble cutting machine  20  to check a temperature and a vibration of a bearing unit  10  during operation, the user may, in real-time, stop the machine or increase a flow of cooling water when a temperature or vibration exceeds operating limits without incurring a risk of burning out one or more of bearing units  10  in a bearing unit pack. Furthermore, since the user is directly checking the temperature, a flow rate and/or temperature of cooling water may be modified so as to increase an amount of heat that can be dissipated by the water. This improves performance of marble cutting machine  20  and does not require marble cutting machine  20  to be stopped in order to make such modifications. 
     A manufacturer of a marble cutting machine  20  may supply an end user with a machine that is already optimized for a best flow of cooling water, so as to improve performance of machine  20  as far as possible while reducing a temperature of a bearing unit pack during operation. 
     By implementing a sensor  50  that may check vibrations of a bearing unit pack, a user may set correct operating limits of marble cutting machine  20 . 
     Dimensions of seat  33   a  for sensor  50  allows for use of sensors of different types to be housed within seat  33   a . A volume available for sensor  50  may be of the order of thousands of cubic centimeters. In various embodiments, the volume of seat  33   a  may be between 1000 mm 3  and 1100 mm 3 . A sensor  50  may therefore be selected on the basis of its service life, the type of measurement, its size, etc. 
     Finally, by gluing sensor  50  to seat  33   a  as described herein, sensor  50  may be mounted and dismounted easily and may therefore be replaced in case of breakage without loss of the whole bearing unit  10 . 
     Using a sensorized shield in this way allows for easy alterations in configuration of a bearing unit  10 . A sensorized radially inner ring may be supplied on request together with sensor  50  for measuring the temperature and vibration, and a user may use these sensorized bearing units wherever necessary. 
     A bearing unit  10  sensorized in this way may be fitted in a median position relative to a bearing unit pack for purposes of monitoring the highest temperature levels of the bearing unit pack. 
     Real-time knowledge of the temperature of a bearing unit  10  enables an operator, during the optimization or use of marble cutting machine  20 , to increase or reduce a flow rate of water within a shaft. This makes it possible to avoid always using the greatest possible amount of water, which would clearly be an uneconomical and inefficient solution in terms of consumption and waste. 
     In addition to the embodiments of the disclosure as described herein, it is to be understood that numerous other variants exist. It is also to be understood that said embodiments are provided solely by way of example and do not limit the object of the disclosure, its applications, or its possible configurations. On the contrary, although the descriptions herein enable one of ordinary skill in the art to implement the present disclosure according to at least one exemplary embodiment, it is to be understood that numerous variations of the components described may be envisaged without thereby departing from the scope of the disclosure as defined in the appended claims, interpreted literally and/or according to their legal equivalents.