Bearings – Rotary bearing – Fluid bearing
Reexamination Certificate
1999-07-19
2001-03-06
Bonck, Rodney H. (Department: 3681)
Bearings
Rotary bearing
Fluid bearing
C384S100000
Reexamination Certificate
active
06196723
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a dynamic groove bearing comprising an internal bearing part and an external bearing part which can be rotated relatively to each other about an axis of rotation, a bearing surface of one of the bearing parts being provided with two groove patterns for co-operation with a bearing surface of the other bearing part, which groove patterns, viewed parallel to the axis of rotation, are spaced apart, and the groove bearing being provided with a reservoir made from a porous material for holding a lubricant which, in operation, is present between the co-operating bearing surfaces.
The invention further relates to an electric motor comprising a stator and a rotor, which is mounted so a to be rotatable with respect to the stator by means of a dynamic groove bearing.
The invention also relates to a scanning device provided with a support for an information carrier and a scanning unit for scanning the information carrier, said support being rotatable about an axis of rotation by means of an electric motor, while the scanning unit can be displaced with respect to the support at least in a direction transverse to the axis of rotation by means of a displacement device.
A dynamic groove bearing of the type mentioned in the opening paragraph is known from JP-A-08322191. The internal bearing part of the known groove bearing is a shaft, and the external bearing part of the known groove bearing is a bush, the shaft being rotatable in the bush. The groove patterns of the known groove bearing are provided on the shaft. During rotation of the shaft in the bush, the groove patterns generate an overpressure in the lubricant which is present between the co-operating bearing surfaces of the shaft and the bush, so that the shaft is supported in a direction perpendicular to the axis of rotation. The reservoir of the known groove bearing comprises two ring-shaped bodies which are made from a sintered metal and are each secured in the bush near an end of the bush. By using the reservoir, a quantity of a lubricant is present in the known groove bearing, which quantity is much greater than a quantity of lubricant present between the co-operating bearing surfaces. As a result, ageing of the lubricant, which is predominantly caused by a chemical reaction between the lubricant and the bearing metals used in the groove bearing, is retarded considerably, so that the known groove bearing has a much longer service life.
A drawback of the known dynamic groove bearing is that there may be a difference between the quantities of lubricant present in both porous ring-shaped bodies, as a result of which there is a different lubricant supply to both groove patterns, which leads to improper operation of the groove bearing. In addition, the known dynamic groove bearing comprises a relatively large number of parts, which can be attributed to the use of the two porous ring-shaped bodies.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a dynamic groove bearing of the type mentioned in the opening paragraph, which enables the lubricant supply to both groove patterns of the groove bearing to be as uniform as possible, while the number of parts is reduced to a minimum.
To achieve this, the dynamic groove bearing in accordance with the invention is characterized in that, viewed parallel to the axis of rotation, the reservoir is arranged between the two groove patterns. Since, viewed parallel to the axis of rotation, the reservoir is arranged between the two groove patterns, the groove bearing comprises a single centrally arranged reservoir for the lubricant, from which reservoir both groove patterns are provided with lubricant. The central arrangement of the single reservoir between the two groove patterns enables a substantially symmetrical and extremely uniform lubricant supply to the two groove patterns to be obtained, while the number of parts of the groove bearing is limited.
A particular embodiment of a dynamic groove bearing in accordance with the invention is characterized in that the reservoir comprises a ring-shaped body made from the porous material, which body is arranged in the external bearing part. The ring-shaped body can be manufactured in a simple way and can be readily provided in the external bearing part.
A further embodiment of a dynamic groove bearing in accordance with the invention is characterized in that the two groove patterns are provided on an inner wall of, respectively, a first bearing bush and a second bearing bush, which form part of the external bearing part, the ring-shaped body, viewed parallel to the axis of rotation, being retained between the two bearing bushes. The use of the two above-mentioned bearing bushes enables the external bearing part with the ring-shaped body provided therein to be assembled in a simple and practical manner. The ring-shaped body is directly adjacent to the two above-mentioned bearing bushes on which the groove patterns are provided, so that the distance to be bridged by the lubricant from the ring-shaped body to the groove patterns is as short as possible.
Yet another embodiment of a dynamic groove bearing in accordance with the invention is characterized in that the ring-shaped body has an internal diameter which is larger than an internal diameter of the bearing surface of the external bearing part. Since the internal diameter of the ring-shaped body is larger than the internal diameter of the bearing surface of the external bearing part, a lubricant meniscus develops near the interfaces between the ring-shaped body and the co-operating bearing surfaces as a result of capillary liquid forces prevailing between the co-operating bearing surfaces, which lubricant meniscus is fed from the ring-shaped body. In this manner, a reliable, uninterrupted lubricant supply to both groove patterns is obtained.
A particular embodiment of a dynamic groove bearing in accordance with the invention is characterized in that the ring-shaped body is provided with at least one vent duct which extends from an inner wall of the ring-shaped body to an outer wall of the ring-shaped body and opens, near the outer wall of the ring-shaped body, into a vent line of the external bearing part. Said vent duct serves to vent air from the dynamic groove bearing when the groove bearing is being filled with the lubricant. Since the vent duct is provided in the ring-shaped body arranged between the two groove patterns, a necessary mutual decoupling of the pressure profiles generated by the two groove patterns is also provided. In the course of the manufacture of the ring-shaped body, the vent duct can be readily provided in said ring-shaped body, so that a particularly practical construction of the dynamic groove bearing is obtained.
A further embodiment of a dynamic groove bearing in accordance with the invention is characterized in that the ring-shaped body is provided with a first vent duct which, close to one of the two groove patterns, opens into the inner wall of the ring-shaped body, and a second vent duct which, close to the other groove pattern, opens into the inner wall of the ring-shaped body, the two vent ducts opening into a ring-shaped duct of the external bearing part, close to the outer wall of the ring-shaped body, which ring-shaped duct surrounds the ring-shaped body and forms part of the vent line. By using said two vent ducts, air venting of the dynamic groove bearing, when this groove bearing is being filled with the lubricant, is improved. The above-mentioned ring-shaped duct of the external bearing part can be readily provided in the external bearing part and is common to the two above-mentioned vent ducts of the ring-shaped body.
Yet another embodiment of a dynamic groove bearing in accordance with the invention is characterized in that the ring-shaped body is provided with two vent ducts which are diametrically arranged with respect to each other and which open into the inner wall of the ring-shaped body, close to one of the two groove patterns, and with two vent ducts which are diametrically arranged w
Bremer Fridtjof
Hensing Johannes M. M.
Bonck Rodney H.
Treacy David R.
U.S. Philips Corporation
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