Abrading – Precision device or process - or with condition responsive... – With feeding of tool or work holder
Reexamination Certificate
2002-12-16
2004-12-07
Nguyen, George (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
With feeding of tool or work holder
C451S243000, C451S246000, C451S231000, C082S018000, C082S148000, C409S165000
Reexamination Certificate
active
06827631
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a center support grinding method, a center support grinding machine, and a centering method for centers thereof in which a cylindrical workpiece to be subjected to outer diameter machining is held by the two centers and fed to a grinding wheel while being rotated, in particular, to a center support grinding method, a center support grinding machine, and a centering method for centers thereof which are suitable for the grinding of the peripheral surface of a cylindrical workpiece with a small diameter and in which it is easy to miniaturize the grinding machine for grinding per se.
DESCRIPTION OF THE PRIOR ART
In the grinding of the cylindrical surface of a cylindrical workpiece of minute size, for example, in the grinding of the cylindrical surface of a Zr ferrule for an optical connector, an optical fiber insertion hole of 0.125 mm is formed at the center of a cylinder with an outer diameter of 2.5 mm to 1.25 mm concentrically with the outer diameter, and a concentricity on the order of submicrons is required between the insertion hole and the outer diameter.
In today's world, where the markets of automobiles and household electrical appliances have reached saturation and where the demand for computers and information equipment has increased, the technical field is expanding where there is a requirement for precision grinding of the cylindrical surface of a cylindrical workpiece of minute size constituting a mechanical part (a rotation shaft in a hard disk apparatus, a recording head rotation shaft in a video camera, a bearing therefor, etc.) for use in such products as are in increasing demand.
Incidentally, a conventional grinding machine has been used for precision grinding of such a cylindrical-surface of minute size, the grinding machine having on a base of great mass and high rigidity heavy and robust tables for moving a workpiece and a grinding wheel, there being provided on these tables a heavy and robust workpiece retaining spindle and a grinding wheel retaining spindle. Usually, the main body of this conventional grinding machines for minute workpieces has a floor area of 1 m
2
and a weight of close to 1 ton. In an example, a workpiece having a diameter of 4 mm, a length of 10 mm, and a weight of 1 g is machined by a machine one million times as heavy as that.
On the other hand, in the case of grinding the cylindrical surface of a general mechanical part, for example, a workpiece having a diameter of 4 cm, a length of 10 mm, and a weight of 1 kg, it is machined by a machine tool with a floor area and a weight of not more than 10 m
2
and 10 tons, which means the ratio of the weight of the machine to the weight of the workpiece is approximately 10 thousand.
Thus, the grinding machine for machining a workpiece of minute size occupies and exhibits a large floor area and a large weight which are out of proportion to the workpiece. This excessively large grinding machine is based on the idea of “The larger serves for the smaller”. That is, the grinding machine for machining a workpiece of minute size is endowed with the ability to machine a relatively large workpiece, and the grinding wheel driving motor is large and heavy and exhibits an accordingly large output. The grinding wheel base on which the large and heavy driving motor is placed is inevitably large and heavy. Further, the table on which the workpiece and the grinding wheel are to be placed is also larged and heavy. Further, the feed screw for moving these heavy tables is thick, and the driving motor for the feed screw is large and heavy.
It is to be assumed that this tendency of the grinding machine for machining a workpiece of minute size to be excessively large and heavy is attributable to the following conventional circumstances:
(1) No machine tool dedicated to minute parts has been commercially produced.
(2) In purchasing a machine tool, it is generally believed that the larger the size and capacity, the better.
However, in machining a minute size workpiece, such as a ferrule, the rotation shaft of a hard disk apparatus, the recording head rotation shaft of a video camera, and the bearings thereof, the volume of the portion removed by machining is small, and the requisite power for machining is also small.
Thus, for the machining of a minute size workpiece, running a large and heavy machine tool by a high power motor, constructing a large building of high load capacity for installing the large and heavy machine tool, and providing a wide air conditioning facilities for accommodating the machine tool, are superfluous and wasteful.
By using a motor of an output, weight, and size suitable for the machining of a minute size workpiece and appropriately reducing the size and weight of the spindle stock, table, etc. it is possible to machine a minute size workpiece without involving an excessively large machine tool, excessive energy consumption, or excessive plant facilities.
After studying this possibility, the present inventor has found out that it is possible to reduce the size and weight of a machine tool so as to realize a machine which is approximately 20 to 30 kg in weight and 20 to 30 cm across in size and which can be raised and moved by hand.
If such a miniaturized machine is realized, it would provide the following advantages from the economical viewpoint. It is possible to reduce the requisite power for the machine tool itself. It is also possible to reduce the price of the machine, the plant facility cost, and the plant running cost, such as the air conditioning cost. Further, when the machine is out of order, instead of depending on the conventional in-field services, which involve a high cost and a long downtime, it is possible to obtain a substitute from the maker by using courier service, thereby recovering the failure in a short time and at low cost.
Specifically speaking, in realizing a reduction in the weight and size of a grinding machine for machining a minute part, the following are to be taken into account: supply and discharge of a minute workpiece, rotary drive, feed, in-process sizing, etc.
In cylindrically grinding a cylindrical workpiece, a chuck-drive/center-support system is widely used, in which the forward end of a workpiece chuck gripped by a main shaft chuck is center-supported. Further, in a known lathe using the chuck-drive/center-support system, the centers are rotated in synchronism with the chuck to eliminate relative rotation between the workpiece and the centers to thereby achieve an improvement in rotation accuracy (See, for example, patent document 1).
Patent Document 1
JP 2000-71104 A (See Paragraphs 0019 and 0020, and
FIGS. 1 and 2
)
In the chuck-drive/center-support system, however, the chuck has a rather large outer size and requires much space, with the result that the arrangement space for the workpiece supply/discharge device, the rotary drive device, the feed device, the in-process sizing device, etc. is rather small. Further, grinding is performed on an outer configuration basis, and not on a center-hole basis.
Generally speaking, to machine a cylindrical workpiece on a center-hole basis with high concentricity, the optimum method to be adopted is a two-center support type machining system, in which the cylindrical workpiece is held, with the forward ends of a pair of centers being inserted into center holes provided in the end surfaces of the cylindrical workpiece. However, in machining a small diameter cylindrical workpiece, such as a Zr ferrule, it is necessary to arrange a machining tool such as a grinding wheel, a workpiece supply/discharge device, a sizing device, etc. close to each other in a small space around the workpiece, which results in a poor operability if ordinary “carriet turning” is adopted, thereby hindering a reduction in size and weight.
Instead of “carriet turning”, patent document 2 discloses a ferrule rotating method using a rubber roller as shown in FIG.
11
. In
FIG. 11
, a ferrule
1
constituting a cylindrical workpiece is elastically supported between a stationary center
10
Nakamura Yukimasa
Tomotaki Katsura
Adams & Wilks
Nguyen George
Seiko Instruments Inc.
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