Centerless grinding machine

Details Centerless grinding machine Centerless grinding machine

2002-05-30

2004-05-04

Morgan, Eileen P. (Department: 3723)

Abrading

Precision device or process - or with condition responsive...

With feeding of tool or work holder

C451S242000, C451S243000, C451S407000

Reexamination Certificate

active

06729938

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a centerless grinder which comprises a grinding wheel spindle stock and a regulating wheel spindle stock disposed in opposed relation, and a work rest disposed between the grinding wheel spindle stock and the regulating wheel spindle stock.
BACKGROUND ART
One exemplary centerless grinder of the aforesaid type is shown in FIG.
9
.
FIG. 9
is a front view illustrating the centerless grinder partly in section. As shown in
FIG. 9
, the centerless grinder
100
includes a bed
108
, a grinding wheel spindle stock
101
disposed on the bed
108
and having a grinding wheel
101
a
, a regulating wheel spindle stock
102
disposed in opposed relation to the grinding wheel spindle stock
101
and having a regulating wheel
102
a
, a work rest
103
disposed between the grinding wheel spindle stock
101
and the regulating wheel spindle stock
102
and having a blade
103
a
for supporting a workpiece W, feed devices
104
,
104
for moving the grinding wheel spindle stock
101
and the regulating wheel spindle stock
102
, and the like. By the operations of the feed devices
104
,
104
, the grinding wheel spindle stock
101
and the regulating wheel spindle stock
102
are moved toward and away from each other.
The feed devices
104
,
104
include feed screws
105
,
105
respectively disposed as extending in the directions of the movements of the grinding wheel spindle stock
101
and the regulating wheel spindle stock
102
, driving motors
106
,
106
for respectively rotating the feed screws
105
,
105
about axes thereof, nuts
107
,
107
respectively fixed to the grinding wheel spindle stock
101
and the regulating wheel spindle stock
102
in threading engagement with the feed screws
105
,
105
, and the like.
Brackets
109
,
109
fixed to opposite sides of the bed
108
respectively hold the feed screws
105
,
105
so as to restrict the axial movements thereof and permit the rotational movements thereof about the axes thereof. The feed screws
105
,
105
are respectively rotated by the driving motors
106
,
106
, whereby the grinding wheel spindle stock
101
and the regulating wheel spindle stock
102
are moved toward and away from each other.
Thus, the feed devices
104
,
104
are respectively driven to properly move the grinding wheel spindle stock
101
and the regulating wheel spindle stock
102
, so that the workpiece W is supported by the grinding wheel spindle stock
101
, the regulating wheel spindle stock
102
and the work rest
103
, and the workpiece W has a predetermined depth of grinding. Then the workpiece W is thrown between the grinding wheel
101
a
and the regulating wheel
102
a
which are now rotating. Thus, the workpiece W is ground by the grinding wheel
101
a.
When the workpiece W is ground by the centerless grinder
100
, a grinding liquid is supplied to a grinding part so as to cool the grinding part. Heat generated during the grinding is absorbed by the grinding liquid to increase the temperature of the grinding liquid. Where the temperature of the grinding liquid is 20° C. immediately after the start of the machining, for example, the grinding liquid is heated up to about 35° C. to about 40° C. after a lapse of 20 to 30 minutes from the start of the machining.
The grinding liquid supplied to the grinding part generally drops on the bed
108
, and then is collected in a storage tank. Therefore, the temperature of an upper portion of the bed
108
is increased by the grinding liquid having dropped on the bed
108
. On the other hand, a lower portion of the bed
108
is less susceptible to the increase in the temperature of the grinding liquid. Hence, the upper portion of the bed
108
is more liable to be thermally deformed than the lower portion of the bed
108
as shown in FIG.
10
. In
FIG. 10
, the thermal deformation of the bed
108
is exaggerated for purpose of illustration, and an initial state immediately after the machining and a thermally deformed state are indicated by a continuous line and a chain double-dashed line, respectively.
As shown, the upper portion of the bed
108
is thermally deformed to be convexly curved upward. Since the grinding wheel spindle stock
101
and the regulating wheel spindle stock
102
disposed on the bed
108
are upwardly offset and the feed screws
105
are held on the opposite sides of the bed
108
, the grinding wheel spindle stock
101
and the regulating wheel spindle stock
102
are displaced away from each other by the thermal expansion of the upper portion of the bed
108
. Therefore, the centerless grinder
100
having the aforesaid construction conventionally suffers from a problem such that the grinding dimensional accuracy is remarkably reduced by the thermal deformation.
In view of the foregoing, it is an object of the present invention to provide a centerless grinder which can minimize the reduction in machining accuracy even if the bed is thermally deformed by the heat generated during the grinding.
DISCLOSURE OF THE INVENTION
In accordance with the present invention, there is provided a centerless grinder, which comprises: a bed; a grinding wheel spindle stock and a regulating wheel spindle stock disposed on the bed in opposed relation; a work rest fixed on the bed between the grinding wheel spindle stock and the regulating wheel spindle stock for supporting a workpiece between the grinding wheel spindle stock and the regulating wheel spindle stock; at least one of the grinding wheel spindle stock and the regulating wheel spindle stock serving as a feedable wheel spindle stock which is movable in a direction toward and away from the other wheel spindle stock; and a feed device for moving the feedable wheel spindle stock in the direction, wherein the feed device comprises: a feed screw having one end fixed onto the bed between the grinding wheel spindle stock and the regulating wheel spindle stock, and disposed as extending in the direction of the movement; a nut retained in the feedable wheel spindle stock in threading engagement with the feed screw so that an axial movement thereof along the feed screw is restricted and a rotational movement thereof about an axis thereof is permitted; and a driving motor for rotating the nut about the axis thereof.
In the centerless grinder, the one end of the feed screw is fixed onto the bed and, when the nut is rotated about the axis thereof by the driving motor, the nut threadingly engaged with the feed screw and the feedable wheel spindle stock retaining the nut are moved along the feed screw. The one end of the feed screw is thus fixed onto the bed between the grinding wheel spindle stock and the regulating wheel spindle stock and, therefore, even if the bed is thermally expanded by heat generated during the grinding, the nut threadingly engaged with the feed screw and the feedable wheel spindle stock retaining the nut are kept in a proper positional relationship with respect to the feed screw by the threading engagement with the feed screw irrespective of the thermal expansion of the bed. As a result, the positional relationship between the grinding wheel spindle stock and the regulating wheel spindle stock is properly maintained.
The inventive centerless grinder is free from a significant change in the positional relationship between the grinding wheel spindle stock and the regulating wheel spindle stock, which often occurs due to the thermal deformation of the bed in the conventional centerless grinder in which the feed screws are retained on the sides of the bed. Therefore, the inventive centerless grinder provides an effect of minimizing the reduction in the machining accuracy of the workpiece which may occur due to the thermal deformation of the bed.
The centerless grinder may be constructed such that the grinding wheel spindle stock and the regulating wheel spindle stock respectively serve as feedable wheel spindle stocks which are movable in a direction toward and away from each other, wherein the feed device comprises: a single feed screw disposed as extending in the direction o

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