JPH04355249A - Bearing unit with sleeve and production thereof - Google Patents

Abstract

PURPOSE:To facilitate the set working of the outer periphery of the sleeve of the bearing unit with the sleeve to be used for a magnetic recording and reproducing device, etc., and to improve the finishing accuracy of the outer peripheral surface of the bearing with respect to a revolving shaft as well as to reduce the cost of production. CONSTITUTION:An inner race 11 is provided on the revolving shaft 6 and a bearing outer ring 13 is mounted via a sliding ball 12 thereto. A plating layer 31 consisting of NiCr, Cu, etc., is formed on the sleeve 30 and the bearing outer ring 13 is fitted therein. The outer peripheral surface of the sleeve 30 is cut by the set working, by which the sleeve 30 having the improved accuracy of coaxiality and cylindricity is obtd. The changeover from the grinding to the cutting is possible in this way and the bearing unit with the sleeve which can improve the reliability and shorten the working time is obtd.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bearing unit with a sleeve used for a rotating shaft of a magnetic recording/reproducing device and a method for manufacturing the same.

0002

[Prior Art] Video tape recorders (hereinafter referred to as VTR) and digital audio tape recorders (hereinafter referred to as DA)
Rotating cylinder (referred to as T) and tape running guide post,
Furthermore, precision bearings are used in spindles and the like of computer hard disk drives. As these electronic devices become smaller and have higher performance, bearings are required to have higher precision. For example, an example of a bearing structure for a DAT rotary head device is shown on page 36 of the September 1990 issue of Radio Technology.

Next, the reason why such a high-precision bearing structure is necessary will be explained using a DAT rotating head device as an example. FIG. 2 shows a pattern of recording tracks on a magnetic tape in a DAT. Originally, the magnetic tape 1 should be formed in a straight line as shown by a track 2 shown by a solid line, but in reality, it is recorded in a curved state as shown by a track 3 shown by a broken line. One of the factors for this is the perpendicularity of the rotating surface of the magnetic head in the rotating cylinder with respect to the rotating axis. FIG. 3 is a sectional view showing the main structure of the DAT rotary head device. In this figure, a rotating shaft 6 is attached to a fixed cylindrical lower cylinder 4 via a sleeved bearing unit including a sleeve 5. As shown in FIG. An upper cylinder 7 is rotatably attached to a rotary shaft 6 projecting upward from the fixed lower cylinder 4, and a pair of magnetic heads 8 are provided at an outer peripheral position facing the lower cylinder 4. The magnetic tape 1 is connected to this upper cylinder 7 and lower cylinder 14.
The magnetic head 8 is wound around and travels, and is recorded and reproduced by the magnetic head 8.

[0004] Therefore, the perpendicularity of the rotating shaft 6 to the cylinder end faces of the lower cylinder 4 and the upper cylinder 7, indicated by A, is a very important factor. This verticality is the lower cylinder 4
The rotating shaft 6 protruding from both sides of the cylinder is supported horizontally by, for example, a V block, and when the lower cylinder 4 is rotated, it is measured as the surface runout of the cylinder end face, and the maximum value of this surface runout is taken as the verticality. This verticality is usually 0.001 to 0.00
An accuracy of 2 mm is required. Therefore, it is important to ensure the runout accuracy of the outer circumferential surface of the sleeve 5 with respect to the rotating shaft 6. Hard disk spindle and VTR
The same applies to the case of the tape running guide post.

Next, the structure of a conventional bearing with a sleeve will be explained using FIG. 4. In FIG. 4(a), for example, D
FIG. 2 is a cross-sectional view of a sleeved bearing unit used in the upper and lower cylinders of an AT. Bearing unit with sleeve 1
Inner races 11 are provided at two locations on the rotating shaft 6 of No. 0, the inner races 11 being cut along the outer periphery so as to have an arcuate cross section. The plurality of balls 12 fitted into the inner race 11 and the bearing outer ring 13 constitute a pair of upper and lower bearings for the rotating shaft 6. A sleeve 14 is fitted onto the outer periphery of each bearing outer ring 13 with a preload applied so that each bearing outer ring 13 approaches each other. This preload is intended to reduce thrust play of the sleeve 14 with respect to the rotating shaft 6. In this case, the material of the sleeve 14 is selected so that the magnitude of the preload applied to the rotating shaft 6 of the bearing outer ring 13 does not change depending on the temperature of the usage environment. Generally, the rotating shaft 6 and the ball 12
, bearing steel is used for the bearing outer ring 13 and sleeve 14, and stainless steel is used for the traveling guide post and the like which are required to be non-magnetic.

Now, as a method for ensuring the coaxiality and cylindricity of the sleeve 14 with respect to the rotating shaft 6 with a predetermined accuracy, the sleeve 14 is inserted through the bearing outer ring 13 while the rotating shaft 6 is fixed.
An assembly process is used in which the outer peripheral surface of the sleeve 14 is finished by rotating the sleeve 4. This assembly process is a precision cutting process, and when machining hard materials such as bearing steel and stainless steel, extreme care must be taken to prevent grinding debris from entering the bearing race surface where the internal balls 12 slide. Grinding is performed while brushing. FIG. 4(b) is an explanatory diagram showing processing conditions for the conventional sleeved bearing unit 10. Here, the rotating shaft 6 is fixed by a support of a grinding machine, and the roller 20 is brought into contact with the outer periphery of the sleeve 14 to rotate the sleeved bearing unit 10, which is the workpiece. The sleeve 14 was then ground by bringing the grinding wheel 21 into contact with the grinding wheel 21 while rotating it from a different direction.

[0007]

[Problems to be Solved by the Invention] However, when such a sleeve is ground, fine grinding powder is scattered and easily enters the inside of the sleeved bearing unit 10, causing grinding on the sliding surface of the ball 12, etc. Powder may adhere. Therefore, the sleeved bearing unit 10 must be cleaned during manufacturing. However, if cleaning is not sufficient and grinding powder remains, abnormal noise may be generated as the rotating shaft 6 rotates when the sleeved bearing unit 10 is used. Furthermore, since the life of the bearing unit is abnormally shortened, cleaning must be repeated, which takes a lot of time and effort. Furthermore, since the grinding process is used, the process takes a long time, leading to an increase in the price and deterioration of the quality of the bearing.

The present invention has been made in view of these conventional problems, and is easy to process and inexpensive to manufacture.
It is an object of the present invention to provide a bearing unit with a sleeve and a method for manufacturing the same that can ensure highly accurate coaxiality and cylindricity between the rotating shaft and the outer peripheral surface of the sleeve.

[0009]

[Means for Solving the Problems] The invention according to claim 1 of the present application includes a rotating shaft, a bearing portion that rotatably holds the rotating shaft, and a cylindrical sleeve that fits on the outer peripheral surface of the bearing portion. This is a bearing unit with a sleeve, which is characterized in that a surface layer made of a material that is easier to cut than the material of the sleeve is formed on the outer peripheral surface of the sleeve.

[0010] The invention according to claim 4 of the present application includes a rotating shaft;
A method for manufacturing a bearing unit with a sleeve, which includes a bearing portion that rotatably holds the rotating shaft, and a cylindrical sleeve that fits on the outer circumferential surface of the bearing portion, the sleeve having an outer circumferential surface made of a material of the sleeve. A surface layer of a material that is easier to cut is formed, and the sleeve is rotated by holding the rotation axis of the sleeve unit, and a cutting tool is brought into contact with the sleeve to perform assembly processing by cutting. This is a characteristic feature.

[0011]

[Operation] According to the invention of claims 1 and 4 of the present application having such characteristics, a sleeve is provided so as to fit on the outer circumferential surface of the rotating shaft and at least one bearing portion, and the sleeve material is coated on the outer circumferential surface. By forming a surface layer that is easier to cut, the outer circumferential surface of the sleeve can be finished with coaxiality and cylindricity with the rotating shaft at a predetermined accuracy by cutting.

According to the invention of claims 2, 3, 5, and 6 of the present application, the surface layer of the sleeve is formed of NiCr plating or Cu plating, so that cutting can be easily performed.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing the structure of a sleeved bearing unit in one embodiment of the present invention. Note that the same parts as those in FIG. 4 showing the conventional example are given the same reference numerals and detailed explanations are omitted. Inner race 1 on rotating shaft 6
1 are formed at two locations separated by a specific interval. A plurality of balls 12 are rotatably held in each inner race 11 by a bearing outer ring 13. The sleeves 30 are arranged so that each bearing outer ring 13 is pressurized in a direction in which they approach each other.
is fitted onto the outer peripheral surface of each bearing outer ring 13. sleeve 30
The material is, for example, bearing steel, which is the same material as the rotating shaft 6, and is configured so that changes in pressurization due to temperature fluctuations do not occur. A surface layer is formed on the outer peripheral surface of the sleeve 30 before it is fitted to the bearing outer ring 13. This surface layer is, for example, a NiCr plating layer 31, and its thickness is, for example, about 0.005 to 0.01 mm.

Now, as post-processing of the sleeved bearing unit, in order to ensure the coaxiality and cylindricity of the sleeve 30 with respect to the rotating shaft 6 at a predetermined accuracy, the rotating shaft 6 is fixed to a support of a cutting machine and plated. Cutting of the layer 31 is performed. FIG. 1(b) is an explanatory diagram showing processing conditions for the sleeved bearing unit of this embodiment. With the rotating shaft 6 fixed by the support of the cutting machine, the roller 40 is attached to the plating layer 31.
The workpiece, ie, the sleeve 30, is rotated while being brought into contact with the outer periphery of the sleeve 30. On the other hand, a cutting tool such as a cutting tool 41 is provided at a position opposite to the roller 40 of the cutting machine, and is moved parallel to the rotating shaft 6 to finish the plating layer 31.

NiCr of the plating layer 31 is easier to micro-fabricate than the bearing steel of the sleeve 30, and the outer dimensions of the sleeve 30 can be finished while maintaining a predetermined surface roughness. Since the surface of the sleeve 30 is coaxially machined with the rotating shaft 6 fixed to a cutting machine, coaxiality with the rotating shaft 6 is ensured. Furthermore, since the cutting tool 41 is also fed parallel to the main axis of the cutting machine, cylindricity is also ensured. Therefore, the runout of the outer circumferential surface of the sleeve 30 can be suppressed to a predetermined value or less, and the machining time is shortened compared to conventional grinding. In addition, the chips produced by cutting the sleeve 30 do not turn into dust like they do during grinding, but instead become continuous or relatively large chips, making it difficult for these chips to get into the balls 12 and inner race 11 . Therefore, the cleaning process can be simplified. In addition, this bearing unit with sleeve is
When used as a tape running guide post for TR or DAT, the surface of the sleeve 30 must be made of a non-magnetic material. In this case, the same effect can be obtained by applying, for example, Cu plating as the surface layer.

Next, when the sleeved bearing unit of this embodiment is press-fitted into the inner circumferential surface of the lower cylinder 4 shown in FIG. 4 and the upper cylinder 7 is fitted to one end of the rotating shaft 6, A rotating cylinder whose perpendicularity to the axis 6 is ensured with a predetermined accuracy is realized. Further, although a ball bearing unit with a bearing outer ring 13 is used in this embodiment, the outer circumferential surface of the sleeve can be maintained at a predetermined accuracy even in other bearing units in which the sleeve and the bearing outer ring are integrally formed.

[0017]

As described above, according to the invention described in claims 1 and 4, the surface of the sleeve that fits on the outer peripheral surface of the bearing portion is formed of a surface layer of a material that is easier to process than the material of the sleeve. . Therefore, by holding the rotating shaft and assembling the outer circumferential surface of the sleeve by cutting, the coaxiality and cylindricity of the rotating shaft and the outer circumferential surface of the sleeve can be ensured with high precision. Furthermore, by using the cutting process, the cutting debris is much larger than the grinding powder during the grinding process, and it is difficult for it to enter the inside of the bearing unit. For this reason, this bearing unit with a sleeve is less likely to generate abnormal noise during use, and has the effect of extending its life. In addition, since it is manufactured using cutting processing, processing time can be shortened.
This also has the effect of lowering the price of the bearing unit.

Furthermore, according to the invention as set forth in claims 2, 3, 5, and 6, the surface layer of the sleeve is plated with NiCr, thereby making it easier to cut the sleeve. Furthermore, by plating the surface layer of the sleeve with Cu, even if the sleeve is made of magnetic material such as bearing steel, the surface becomes non-magnetic, so it can be used as a guide post for magnetic tape. to be born.

[Brief explanation of the drawing]

FIG. 1(a) is a sectional view showing the structure of a sleeved bearing unit according to an embodiment of the present invention, and FIG. 1(b) is an explanatory diagram showing processing conditions for the sleeved bearing unit of this embodiment.

FIG. 2 is a recording track pattern of a magnetic tape in a rotary head type magnetic recording/reproducing device.

FIG. 3 is a sectional view of a rotating cylinder in the magnetic recording/reproducing device.

FIG. 4(a) is a sectional view showing the structure of a conventional bearing unit with a sleeve, and FIG. 4(b) is an explanatory view showing processing conditions for the conventional bearing unit with a sleeve.

[Explanation of symbols]

6 Rotation axis 11 Inner lace 12 Ball 13 Bearing outer ring 30 Sleeve 31 Plating layer

Claims (6)

[Claims] 1. A bearing unit with a sleeve, comprising a rotating shaft, a bearing portion that rotatably holds the rotating shaft, and a cylindrical sleeve that fits on the outer peripheral surface of the bearing portion,
A bearing unit with a sleeve, characterized in that a surface layer made of a material that is easier to cut than the material of the sleeve is formed on the outer peripheral surface of the sleeve. 2. The sleeved bearing unit according to claim 1, wherein the surface layer is made of NiCr plating. 3. The sleeved bearing unit according to claim 1, wherein the surface layer is made of Cu plating. 4. A method for manufacturing a bearing unit with a sleeve, which includes a rotating shaft, a bearing portion that rotatably holds the rotating shaft, and a cylindrical sleeve that fits on the outer peripheral surface of the bearing portion, the method comprising: A surface layer of a material that is easier to cut than the material of the sleeve is formed on the outer circumferential surface of the sleeve, and the rotation axis of the sleeve unit is held to rotate the sleeve, and a cutting tool is brought into contact with the sleeve. A method for manufacturing a bearing unit with a sleeve, characterized in that assembly is performed by cutting. 5. The method of manufacturing a sleeved bearing unit according to claim 4, wherein the surface layer is formed of NiCr plating. 6. The method of manufacturing a sleeved bearing unit according to claim 4, wherein the surface layer is formed of Cu plating.