Bearing assembly

Abstract: A bearing construction has an annular clearance (31) provided between the outer surface of a rotary shaft (2) of a rotatable object (1) and the inner wall of a bearing assembly (3) and a fluid feeding means (44, 71) for filling the clearance (31) with a fluid to form a layer of the fluid. A shaft displacement detecting means (41, 43, 5) detects a displacement of the rotary shaft (2) during rotating action.

Description: The present invention relates to a bearing assembly for supporting a rotary shaft of e.g. a motor and more particularly, to a support mechanism for allowing a rotatable object to rotate smoothly with less friction and thus, to be measured its minimal vibration during rotation. A known support mechamism comprises V-shaped bearing blocks or ball bearing units which are sustained by coil or inverted springs. In action, the V-shaped bearing blocks tend to produce a sliding friction thus causing unwanted vibrations. Hence, a rotatable object to be examined is affected by the vibrations during rotating movement and will cause turbulence. As the result, a minimal vibration on the rotatable object can hardly be measured. Although producing no sliding friction, the ball bearing units also create unwanted vibrations when corresponding to the erratic movement caused by undulation on the surface of a rotary shaft of the rotatable object. Hence, it will be tough to measure a minimal vibration on the rotatable object. As the bearing blocks or units are supported by the coil or inverted springs, a resonant phenomenon determined by an urging coefficient of the springs and a mass of the bearing units is definitely involved and will discourage accurate measurement of vibration. EP-A-0275792 discloses a bearing assembly in which a bearing has an annular clearance provided between a circumferential surface of a rotary shaft of a rotable object and an inner wall of the bearing. A fluid feeding means fills the clearance with fluid to form a layer of the fluid. A shaft detecting means detects displacement of the rotary shaft in a radial direction during rotation of the shaft. It is an object of the present invention to provide a bearing assembly capable of supporting a rotatable object without disturbing its inherent vibration and having a vibration detecting apparatus for detecting a minimal vibration on the rotatable object. According to the present invention, there is provided a bearing assembly comprising: a bearing having an annular clearance provided between a circumferential surface of a rotary shaft of a rotatable object and an inner wall of the bearing and a fluid feeding means for filling the clearance with a fluid to form a layer of the fluid; and a shaft displacement detecting means for detecting a displacement of the rotary shaft in a radial direction during rotation of the shaft, characterised in that the shaft displacement detecting means is a pressure detecting means for detecting a change in a pressure of fluid supplied from the fluid feeding means which has an opening to the clearance formed on the circumferential surface. Using the bearing construction of the present invention, a friction developed between the outer surface of the rotary shaft of the rotatable object and the inner wall of the bearing assembly will be minimised by the action of the fluid layer. As the clearance is filled with the fluid, unfavourable effects will hardly be involved even if the shaft and/or bearing has injury and undulation on the surface. The displacement of the rotary shaft of the rotatable object running on the bearing assembly will be detected by the shaft displacement detecting means for calculation of a degree of vibration caused by unbalance error of the rotatable object. The displacement of the rotary shaft causes a change in the pressure of a fluid flow supplied through the opening of the fluid feeding means to the clearance and will thus be detected through measuring the pressure change with the pressure detecting means. Embodiments of the present invention will now be described with reference to the accompanying drawings in which:- Fig. 1 is a schematic view of the arrangement of a bearing assembly having a vibration detecting means showing one embodiment of the present invention; and Fig. 2 is a schemtic view of the arrangement of a bearing assembly having a vibration detecting means showing another embodiment of the present invention; As illustrated in Fig. 1 there are provided a rotatable object 1 to be examined for unbalance error, a rotary shaft 2 of the object 1, and a bearing assembly 3 supporting the rotary shaft 2 and serving as a rotary shaft support mechamism. The bearing 3 has a groove 31 therein which is shaped semicircular in cross section and slightly greater in the diameter than the rotary shaft 2. Three air passages 41, 42, 43 are arranged open at one end on the wall of the groove 31 and communicating at the other end to an air reservoir 44. The opening of the air passage 42 is located at the bottom of the groove 31 so as to be just beneath the rotary shaft 2. The two other openings of the air passages 41 and 43 are disposed symmetrical about the air passage 42. Also, a pressure detector 5 is provided for measuring a change in the pneumatic pressure of the air reservoir 44 and feeding its corresponding signal through a converter 51 having a built-in amplifier to an unbalance measuring circuit 6. An amount of compressed air to be supplied to the air reservoir 44 is produced by a compressor 71, stabilized in pressure by a pressure stabilizer 72, and controlled by a flow controller 73 to a specific flow of supply required for slightly lifting up the rotary shaft 2. Denoted by 8 is a driving system for rotating the object 1, which is provided with a driving motor 81 controlled for actuation by a controller circuit 82. In action, the driving system 8 when receiving a signal from the controller circuit 82 actuates the object 1 to rotate at a high speed required for measuring a degree of unbalance error and upon detection of an unbalance point, decelerates it while measuring a phase data of the unbalance point before stopping the unbalance point at a desired angle. For the purpose, the driving motor 81 is preferably a stepping or servo motor. A procedure of the measuring action of the unbalance detecting apparatus of the present invention starts with setting of the object 1 onto the bearing assembly 3. The rotary shaft 2 of the object 1 is lifted up by a flow of air supplied through the three air passages 41,42,43 and then, the object 1 is driven by the driving system 8 for rotation at a speed of as high as more than several hundreds of revolutions per minute. The opening of each air passage is as small as about 0.5 mm in diameter for ease of detecting a pressure change. The rotary shaft 2 vibrates as the unbalance point denoted by the letter A is turned at high speed. When the angular position of the unbalance point A becomes in alignment with the opening of any air passage, the rotary shaft 2 is radially displaced by a centrifugal force developed on the point A so as to decrease its distance from the wall of the groove 41. Accordingly, the resistance against the outward flow of air is increased thus causing the pressure in the air passage to rise up. The increase of pressure is detected by the pressure detector 5 in the air reservoir 44 and translated to a degree of upward and downward or vertical oscillation of the rotating object 1. A resultant unbalance signal of the pressure detector 5 is analyzed with the unbalance measuring circuit 6 to calculate a phase data of the unbalance point and a magnitude of the unbalance error on the object 1. However, horizontal displacement of the unbalance point A or the rotary shaft 2 causes two opposite pressure changes of their respective air passages 41,43 to offset each other while the pressure in the air passage 42 remains unchanged. Hence, no pressure change is involved in the air reservoir 44. The vertical or upward and downward oscillation of the unbalance point A causes a change in the pressure of the outward flow of air from the air passage 42 which in turn varies the pressure in the air reservoir 44. The vertical oscillation of the rotary shaft 2 is detected by the pressure detector 5 and its signal is transmitted through the converter 51 to the unbalance measuring circuit 6 where a phase data of the unbalance point A and a magnitude of the unbalance error are calculated from the signal. In the embodiment shown in Fig.1, the bearing assembly 3 has a bearing construction and a shaft displacement detecting means arranged integral with each other. The advantages of the unbalance detecting apparatus of the embodiment will now be explained. The rotary shaft 2 is sustained on a thin layer of air and can thus rotate with a quite lower rate of friction. Also, unwanted vibration resulting from undulation and roughness on both the surface of the rotary shaft 2 and the wall of the groove 31 of the bearing assembly 3 can largely be absorbed by the layer of air, thus affecting by minimum degrees on the oscillation caused by the unbalance error of the object 1. As the oscillation of the object 1 is minimum affected, it can successfully be measured and converted into an unbalance signal when the object 1 being rotated at a lower speed. As the measurement of unbalance error is executed during the lower speed rotation, the object 1 can be stopped at a higher accuracy and within a shorter duration for desired positioning after the measurement. Also, as the measurement of unbalance error is carried out during the rotation at a lower speed, a repeat action for checking that the unbalance error is eliminated can be executed just after application of e.g. an amount of balance-weight paste which remains not completely cured. Accordingly, the overall unbalance error detecting and correcting procedure will be executed at higher efficiency. Fig.2 shows another embodiment of the present invention in which a bearing construction which acts as a supporting means for supporting the load of a rotatable object is arranged separately of the shaft displacement detecting means. As shown, a bearing unit 32 for supporting the load of a rotatable object 1 has an air passage 42 therein. Also, two shaft displacement detecting means or air blower units 33,34 are provided having air passages 41,43 therein respectively for supply of pressured air. The bearing unit 32 is spaced by distances 46,45 from the air blower units 33,34 respectively so that the flow of air from its air passage 42 can rarely affect the pneumatic pressure in the air passages 41,43. More particularly, the flow of air from the air passage 42 is passed between the rotary shaft 2 and the bearing unit 32 and discharged to the clearances 46,45 while the pressure in the air passages 41,43 of their respective air blower units 33,34 remain unaffected. The flow of air to be supplied through the air passage 42 is controlled by a flow controller 73 to a specific rate needed for lifting up the rotary shaft 2 slightly from the bearing unit 32 during rotation. Also, the flow of air to be supplied through the air passages 41,43 is controlled by another flow controller 74 to a predetermined rate and then, supplied into an air reservoir 44 which has a couple of air chambers 4A and 4B. When the rotary shaft 2 is displaced to the left by the action of an unbalance point A of the rotating object 1, its clearance from the air blower unit 33 becomes smaller and the pressure of the air flow in air passage 41 of the air blower unit 33 is increased. Hence, the pressure in the air chamber 4A rises up. Simultaneously, its clearance from the air blower unit 34 becomes greater causing the pneumatic pressure in the air passage 43 and thus, in the air chamber 4B to be lowered. As the two air chambers 4A,4B in the air reservoir 44 are increased and decreased in the pressure respectively, a resultant pressure difference causes a diaphragm mounted to a partition therebetween to deflect. The deflection of the diaphragm is then detected by a distortion gage 52 which is consisted mainly of a piezoelectric sensor and resistors and directly mounted to the diaphragm, and measured as a correct value of the pressure difference in the air reservoir 44. A resultant pressure difference signal of the distortion gage 52 is transferred through a converter 51 having a built-in amplifier to an unbalance measuring circuit 6 which in turn calculates a phase data of the unbalance point A and a magnitude of the unbalance error from the signal. The unbalance point A can be stopped at any desired position through controlling a driving system 8 by the phase data fed through a controller circuit 82. As described above, accuracy in the measurement is increased because a pressure change in the air reservoir 44 caused by the horizontal oscillation of the rotary shaft 2 is detected as the pressure difference between the two chambers 4A, 4B. The same effect will be given by detecting the two pressures of their respective air passages 41, 43 and amplifying them with a differential amplifier for ease of comparison. Also, the pressure change detecting means may be replaced with a pair of means for detecting the velocity of an air flow. The two air velocity detecting means are preferably disposed within or adjacent to the air blower unit 33, 34 for higher accuracy and quicker response. In any case, the rotatable object 1 to be examined is supported by the rotary shaft support mechanism of the present invention having a fluid layer arrangement. Although the layer of air is used for no-contact support of the rotary shaft 2 on the bearing assembly or unit, other fluids will be employed with equal success.

Claims: A bearing assembly comprising: a bearing (3) having an annular clearance provided between a circumferential surface of a rotary shaft (2) of a rotatable object (1) and an inner wall of the bearing (3) and a fluid feeding means (71, 72, 73) for filling the clearance with a fluid to form a layer of the fluid; and a shaft displacement detecting means for detecting a displacement of the rotary shaft (2) in a radial direction during rotation of the shaft, characterised in that the shaft displacement detecting means is a pressure detecting means (5) for detecting a change in a pressure of fluid supplied from the fluid feeding means which has an opening to the clearance formed on the circumferential surface. A bearing assembly according to claim 1, wherein the pressure detecting means detects a change in the difference in pressures in the clearance at opposite sides of the rotary shaft (2).

Inventors: OKUMURA HIROMITSU, OKUMURA, HIROMITSU
Applicants: DENSHI SEIKI KOGYO KABUSHIKI K, DENSHI SEIKI KOGYO KABUSHIKI KAISHA
Application year: 1992
Main classification: F16C32
IPC codes: G01H1, F16C32, G01M1, G01M13