U.S. patent application number 11/291817 was filed with the patent office on 2006-06-22 for grinding machine.
This patent application is currently assigned to TOYODA KOKI KABUSHIKI KAISHA. Invention is credited to Yoshio Wakazono.
Application Number | 20060135044 11/291817 |
Document ID | / |
Family ID | 36596604 |
Filed Date | 2006-06-22 |
United States Patent
Application |
20060135044 |
Kind Code |
A1 |
Wakazono; Yoshio |
June 22, 2006 |
Grinding machine
Abstract
In a cylindrical grinding machine for grinding a rotating
cylindrical workpiece with a rotating grinding wheel, a wheel
spindle for supporting the grinding wheel is divided at its axial
mid portion into first and second spindle components, and
respective ends on the sides opposite to the axial mid portion of
the first and second spindle components are rotatably supported by
a pair of fluid bearings. Each of the first and second spindle
components has at least at its portion supported by a corresponding
one of the fluid bearings a diameter which is determined to secure
a predetermined rigidity at a grinding point between the grinding
wheel and the workpiece, based on a predetermined value obtained
taking into consideration the power consumption by the fluid
bearings or the quantity of energy consumption required from the
beginning to the ending of a grinding operation. Thus, the grinding
machine can be reduced in the energy consumed from the beginning to
the ending of the grinding operation.
Inventors: |
Wakazono; Yoshio;
(Nagoya-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
TOYODA KOKI KABUSHIKI
KAISHA
Kariya-shi
JP
|
Family ID: |
36596604 |
Appl. No.: |
11/291817 |
Filed: |
December 2, 2005 |
Current U.S.
Class: |
451/11 ;
451/49 |
Current CPC
Class: |
B24B 51/00 20130101;
B24B 1/00 20130101 |
Class at
Publication: |
451/011 ;
451/049 |
International
Class: |
B24B 51/00 20060101
B24B051/00; B24B 1/00 20060101 B24B001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 22, 2004 |
JP |
2004-371074 |
Claims
1. A grinding machine for grinding with a grinding wheel a
workpiece of a predetermined length which is carried to be
rotatable together with a work spindle, the grinding machine
comprising: a wheel spindle for supporting the grinding wheel; and
fluid bearing means rotatably supporting the wheel spindle on both
sides of the grinding wheel while securing a predetermined rigidity
at a grinding point defined between the grinding wheel and the
workpiece; wherein the wheel spindle has a diameter determined
based on a set value for the quantity of energy consumption, at
least at portions thereof supported by the fluid bearing means.
2. The grinding machine as set forth in claim 1, wherein the wheel
spindle has the diameter determined based on the set value for the
quantity of energy consumption which value is determined based on a
power consumption by the rotation of the grinding wheel.
3. The grinding machine as set forth in claim 1, wherein the wheel
spindle is divided at its axial mid portion into first and second
spindle components, the grinding machine further comprising;
coupling means provided between the first and second spindle
components for separating or coupling the first and second spindle
components at an axial position where the grinding wheel is
supported on the wheel spindle.
4. A grinding machine for grinding with a grinding wheel a
workpiece of a predetermined length which is carried to be
rotatable together with a work spindle, the grinding machine
comprising: a wheel spindle for supporting the grinding wheel at an
axial mid portion thereof and composed of first and second spindle
components divided at the axial mid portion; coupling means
provided between the first and second spindle components for
separating or coupling the first and second spindle components at
an axial position where the grinding wheel is supported on the
wheel spindle; and a pair of fluid bearings for rotatably
supporting respective ends, on the sides opposite to the axial mid
portion, of the first and second spindle components while securing
a predetermined rigidity at a grinding point defined between the
grinding wheel and the workpiece; wherein each of the first and
second spindle components has a diameter determined based on a set
value for the quantity of energy consumption, at least at a portion
thereof supported by a corresponding one of the fluid bearings.
5. The grinding machine as set forth in claim 4, wherein the
diameter of the first and second spindle components is determined
based on the set value for the quantity of energy consumption which
value is determined based on a power consumption by the rotation of
the first and second spindle components.
Description
INCORPORATION BY REFERENCE
[0001] This application is based on and claims priority under 35
U.S.C. 119 with respect to Japanese Application No. 2004-371074
filed on Dec. 22, 2004, the entire content of which is incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a grinding machine for
grinding a workpiece with a rotating grinding wheel, and in
particular, it relates to an environment-oriented, energy-saving
grinding machine capable of reducing the quantity of energy
consumed from the beginning to the ending of a workpiece
grinding.
[0004] 2. Discussion of the Related Art
[0005] Heretofore, there has been known a grinding machine of the
type that a wheel head on which a grinding wheel is supported by
static pressure bearings in the form of a cantilever to be
drivingly rotatable is mounted on a bed through a slide mechanism
to be movable toward and away from a work head and a foot stock and
that a workpiece which is supported between the work head and the
foot stock to be drivingly rotatable is ground with the grinding
wheel with coolant being showered thereon from a coolant nozzle, as
described, for example, in Japanese unexamined, published patent
application No. 10-118922 (hereafter referred to as Patent Document
1).
[0006] Patent Document 1 discloses a grinding machine which has a
wheel head drivingly rotatably carrying a grinding wheel by static
pressure bearings in the form of a cantilever and a wheel head feed
mechanism for mounting the wheel head through a slide mechanism on
a bed to be movable toward and away from a work head and a foot
stock.
[0007] In the prior art grinding machine, there is taken a
construction that the grinding wheel is drivingly rotatably carried
by the static pressure bearings on the wheel head in the form of
cantilever. Thus, a spindle for the grinding wheel and the diameter
of bearing components have been designed to be large for the
purpose of increasing the rigidity during the grinding operation
thereby to keep the machining accuracy high.
[0008] However, in the prior art grinding machine, since the
bearings for the grinding wheel are arranged to support the
grinding wheel in the form of cantilever wherein the spindle for
the grinding wheel and the diameter of the bearing components have
to be designed to be large for the purpose of increasing the
rigidity during the grinding operation thereby to keep the
machining accuracy high, the friction force generated in each
bearing is large, and hence, a large power is required for idle
rotation of the spindle. With this, the quantity of heat generation
at each bearing is large, and a bearing oil cooler for cooling
lubrication oil supplied to the bearings and a bearing oil pump for
supplying the bearings with the lubrication oil have to be large in
dimension and capacity, so that the power consumption thereby
necessarily becomes large. As a consequence, it has been unable to
reduce the quantity of energy consumed from the beginning to the
ending of the workpiece grinding.
SUMMARY OF THE INVENTION
[0009] It is therefore a primary object of the present invention to
provide an improved grinding machine which is capable of reducing
the power consumption related to a grinding wheel bearing section
including the power for idle rotation at the bearing section, the
power for cooling bearing oil, the power for operating a bearing
oil pump and the like and hence, of reducing the quantity of energy
consumed from the beginning to the ending of a workpiece
grinding.
[0010] Briefly, according to the present invention, there is
provided a grinding machine for grinding with a grinding wheel a
workpiece of a predetermined length which is carried to be
rotatable together with a work spindle. The grinding machine
comprises a wheel spindle for supporting the grinding wheel and
fluid bearing means for rotatably supporting the wheel spindle on
both sides of the grinding wheel while securing a predetermined
rigidity at a grinding point defined between the grinding wheel and
the workpiece. The wheel spindle has a diameter determined based on
a set value of the quantity of energy consumption, at least at each
of portions thereof supported by the fluid bearing means.
[0011] With this configuration, the diameter of the wheel spindle
and the diameter of the bearing means can be determined in terms of
reducing the quantity of energy consumption during the workpiece
grinding. By doing so, the power consumption by the grinding
machine can be reduced throughout the entire time period of the
grinding operation from the beginning to the ending. As a
consequence, it can be realized to provide an environment-oriented,
energy-saving grinding machine capable of reducing the energy
consumption thereby.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[0012] The foregoing and other objects and many of the attendant
advantages of the present invention may readily be appreciated as
the same becomes better understood by reference to the following
detailed description of a preferred embodiment of the present
invention when considered in connection with the accompanying
drawings, wherein like reference numerals designate the same or
corresponding parts throughout several views, and in which:
[0013] FIG. 1 is a schematic plan view of a cylindrical grinding
machine in an embodiment according to the present invention;
[0014] FIG. 2 is a side view of the grinding machine shown in FIG.
1;
[0015] FIG. 3 is an enlarged sectional view of a bearing section
taken along a horizontal plane of the grinding machine shown in
FIG. 1;
[0016] FIG. 4(a) is a further enlarged sectional view showing a
fluid bearing of the bearing section shown in FIG. 3;
[0017] FIG. 4(b) is a cross-sectional view of the fluid bearing
shown in FIG. 4(a);
[0018] FIGS. 5(a) and 5(b) are a graph and an explanatory view for
respectively explaining the relation between the diameter (d) of a
wheel spindle 19 and the friction force at a fluid bearing 35 and
the relation between the spindle diameter (d) and the power for
idle rotation in the fluid bearing 35, wherein FIG. 5(a) shows a
bearing characteristic curve while FIG. 5(b) shows various forces
acting the wheel spindle 19;
[0019] FIG. 6 is a system block diagram of the cylindrical grinding
machine including a computer numerical controller;
[0020] FIG. 7(a) is a graph with the horizontal axis taken as time
axis, showing the power consumption by the cylindrical grinding
machine when a workpiece is machined with respective drive circuits
shown in FIG. 6 generating powers required for the grinding,
wherein a pulse-form line indicated on the lower side represents
the power consumption by the grinding machine according to the
present invention whereas another pulse-form line indicated on the
upper side represents the power consumption by a prior art grinding
machine;
[0021] FIG. 7(b) is an explanatory view showing the shape and
ground areas, as portions to be ground, of a workpiece which is
machined in the grinding operation referred to in connection with
FIG. 7(a);
[0022] FIG. 8(a) is a sectional view of a bearing section taken
along a horizontal plane in the prior art cylindrical grinding
machine;
[0023] FIG. 8(b) is a sectional view of a bearing section taken
along a horizontal plane in a cylindrical grinding machine
practiced according to the present invention;
[0024] FIG. 8(c) is a table showing the diameter of a grinding
wheel, the diameter of the wheel spindle and the entire length of
the wheel spindle for each of the prior art cylindrical grinding
machine and the cylindrical grinding machine practiced according to
the present invention;
[0025] FIG. 9(a) is a graph with the horizontal axis taken as
grinding wheel circumferential speed, showing measured results of
idle rotation powers for the grinding wheels in the cylindrical
grinding machine practiced according to the present invention and
the prior art cylindrical grinding machine;
[0026] FIG. 9(b) is a graph showing power consumption related to
the wheel spindle bearing section including the power for grinding
wheel idle rotation and the powers consumed by a bearing oil supply
device and a bearing oil cooler in each of the cylindrical grinding
machine practiced according to the present invention and the prior
art cylindrical grinding machine;
[0027] FIG. 10(a) is a graph showing the relation between the
machining time and the power consumption on the basis of values
actually measured when a grinding operation is performed in each of
the cylindrical grinding machine practiced according to the present
invention and the prior art cylindrical grinding machine; and
[0028] FIG. 10(b) is an explanatory view of the workpieces used in
grinding operations to gather the actually measured values for the
graph shown in FIG. 10(a).
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
(Construction of Grinding Machine)
[0029] A grinding machine in an embodiment according to the present
invention will be described hereinafter with reference to the
accompanying drawings. For the convenience in description, the
positional relation regarding the entire construction of the
grinding machine will be explained as viewed by an operator
standing at the front of the grinding machine (i.e., standing on
the left side in FIG. 1). That is, in the following description,
when viewed from the operator side, the operator side will be
referred to as "front", the opposite side will be referred to as
"rear", and the right and left sides will be referred to as "right"
and "left" respectively. Further, the front-rear direction will be
referred as "X-axis direction", and the left-right direction will
be referred to as "Z-direction".
[0030] FIG. 1 is a schematic plan view of a cylindrical grinding
machine in the present embodiment, and FIG. 2 is a side view of the
cylindrical grinding machine shown in FIG. 1. FIG. 3 is an enlarged
sectional view of a bearing section taken along a horizontal plane
of the grinding machine shown in FIG. 1. FIG. 4(a) is a further
enlarged sectional view showing one of fluid bearings of the
bearing section shown in FIG. 3, and FIG. 4(b) is a cross-sectional
view of the fluid bearing shown in FIG. 4(a).
[0031] The cylindrical grinding machine 10 has all drives
controllable by a computer numerical controller (CNC) 100 and is
composed of a grinding machine main body and various attachments or
auxiliary devices (not shown). Main auxiliary devices comprise a
bearing oil supply device for static pressure bearings, a bearing
oil cooler, air supply equipments, a coolant supply device, a mist
collecting device, and duct devices for connecting these devices to
the grinding machine main body.
[0032] The cylindrical grinding machine 10 is composed of a bed 11
constituting a base component of the cylindrical grinding machine
10, a pair of Z-axis rails 12 arranged on the top surface of the
bed 11 to extend in the Z-axis direction, a Z-axis movable member
13 drivingly movable along the Z-axis rails 12 in the Z-axis
direction, a pair of X-axis rails 14 arranged on the top surface of
the Z-axis movable member 13 to extend in the X-axis direction, an
X-axis movable member 15 drivingly movable along the X-axis rails
14 in the X-axis direction, a wheel head 16 mounted on the X-axis
movable member 15 and carrying a grinding wheel (T) to drivingly
rotate the same, and a pair of left and right work heads 17
arranged on the top surface of the bed 11 for carrying a workpiece
W to rotate the same by a work spindle motor 24.
[0033] The Z-axis movable member 13 is constructed to be driven by
a linear motor, and between the pair of Z-axis rails 12, a magnet
21 of the linear motor and a coil 22 of the linear motor are
respectively arranged on the top surface of the bed 11 and the
lower surface of the Z-axis movable member 13. That is, the linear
motor is composed of the coil 22 for generating an electric field
by being electrified and the magnet 21 for generating a power by
the mutual action of the electric field with a magnetic field. The
Z-axis movable member 13 is driven by the linear motor to move in
the Z-axis direction.
[0034] Likewise, the X-axis movable member 15 is constructed to be
driven by a linear motor, and between the pair of X-axis rails 14,
a magnet (not shown) of a linear motor and a coil 23 (the portion
indicated by the hatching in FIG. 1) of the linear motor are
respectively arranged on the top surface of the Z-axis movable
member 13 and the lower surface of the X-axis movable member 15.
The linear motor is composed of the magnet and the coil 23, and the
X-axis movable member 15 is driven by the linear motor to move in
the X-axis direction.
[0035] The X-axis movable member 15 is composed of a base member 25
mounted on the Z-axis movable member 13, a wheel head main body 26
fixedly mounted on the base member 25 and constituting a main
component of the wheel head 16, and a wheel spindle unit 27 having
a wheel spindle19 and removably attached to the wheel head main
body 26. The wheel head main body 26 has a protruding portion 28
protruding forward beyond the front end of the base member 25, and
the wheel spindle unit 27 is attached to a front surface of the
protruding portion 28. Thus, the grinding wheel T is in the state
that it largely protrudes forwardly of the wheel head 16, that is,
in the state of overhanging. In a modified form, the base member 25
may be excluded, so that the wheel head main body 26 may be mounted
directly on the Z-axis movable member 13. In a further modified
form, it may be possible not to provide the wheel spindle 19 on the
wheel spindle unit 27 which is constituted as a unit to be
removably mounted on the wheel head main body 26, but to provide
the wheel spindle 19 on the wheel head main body 26 itself.
[0036] The wheel head 16 is provided with the wheel spindle 19 to
which the grinding wheel T is secured replaceably, and drivingly
rotates the grinding wheel T supported thereon by rotating the
wheel spindle 19.
[0037] The wheel head main body 26 is provided with rotation drive
means 29 for drivingly rotating the wheel spindle 19, and the
rotation drive means 29 is composed of a motor with a drivingly
rotatable spindle and the like. The motor is constituted by a
so-called "built-in motor" whose external housing is formed bodily
with the wheel head main body 26. A drive pulley 30 is secured to
an end of the spindle of the rotation drive means 29 to be
rotatable together with the spindle.
[0038] The wheel head main body 26 is provided with a tension
pulley 31, which is vertically movable in front (on the left side
as viewed in FIG. 2) of the drive pulley 30. The tension pulley 31
is adjustable in its vertical position to make adjustable the
tension of a belt 33 wound between the drive pulley 30 and a wheel
spindle pulley 32 referred to later.
[0039] The wheel spindle unit 27 is composed of a unit base 34
removably attached to the front surface of the protruding portion
28 of the wheel head main body 26, a pair of left and right fluid
bearings 35 provided on a front surface of the unit base 34, the
wheel spindle 19 supported at opposite ends thereof respectively by
the fluid bearings 35 and having the grinding wheel T secured
thereto, and a wheel guard 36 for covering the grinding wheel
T.
[0040] The wheel spindle 19 extends in the Z-axis direction and as
shown in FIG. 3, is composed of a first spindle component 38 which
is provided at its one end with a flange portion 37 for securing
the grinding wheel T thereto, a second spindle component 39 capable
of being coupled with one end of the first spindle component 38,
and coupling means 40 for making the first spindle component 38 and
the second spindle component 39 coupled with, and separated from,
each other selectively. That is, the wheel spindle 19 is axially
divided into the first and second spindle components 38, 39 at its
axial mid portion. Thus, in the coupled state, the wheel spindle 19
takes the construction that it is supported on both sides of the
grinding wheel T, and hence, can attain a rigidity which is the
same to, or more than, that in the prior art grinding machine even
though it is designed to be smaller in its diameter.
[0041] The first spindle component 38 is rotatably supported by the
bearing 35 at a portion adjacent to the flange portion 37 and is
supported by a thrust bearing 41 at its other end. The wheel
spindle pulley 32 is secured to the first spindle component 38
between the bearing 35 and the thrust bearing 41. The belt 33 is
wound between the wheel spindle pulley 32 and the drive pulley 30
on the side of the wheel head main body 26, so that the drive power
from the rotation drive means 29 is transmitted to the wheel
spindle 19 to rotate the wheel spindle 19.
[0042] The second spindle component 39 is provided with moving
means 42 for axially moving the second spindle component 39, at an
end opposite to the side on which it is coupled with the first
spindle component 38, and is movable axially. The second spindle
component 39 is rotatably supported by the bearing 35 arranged
between the moving means 42 and the side for coupling with the
first spindle component 38. In FIG. 3, a numeral 43 denotes an
automatic balancer capable of automatically righting the runout of
the grinding wheel T.
[0043] The first spindle component 38 and the second spindle
component 39 are mutually coupled by the coupling means 40. When
the grinding wheel T is to be replaced with new one, the coupling
of the first spindle component 38 with the second spindle component
39 by the coupling means 40 is released to move the second spindle
component 39 away from the first spindle component 38, whereby a
predetermined space is secured between the first spindle component
38 and the second spindle component 39. The space enables the
grinding wheel T to be detached from, or to be attached to, the
flange portion 37 of the first spindle component 38 by means of
bolts (not shown).
[0044] The bearings 35 of the wheel spindle unit 27 are constituted
by fluid bearings each constructed to operate by utilizing fluid
which is supplied through fluid supply passages formed in the wheel
spindle unit 27 and the wheel head main body 26. Joints means 44
are provided between the wheel spindle unit 27 and the wheel head
main body 26 for making it possible that supply passages provided
in each of them can be joined with, or separated from, each
other.
[0045] As shown in FIG. 4(a) in detail, each of the fluid bearings
35 takes a construction having a bearing member 48 for rotatably
supporting the wheel spindle 19, a first supply pocket or portion
49 for supplying bearing oil (i.e., lubrication oil) between the
bearing member 48 and the wheel spindle 19, a pair of draining
pockets or portions 50 arranged at axially opposite sides of the
first supply portion 49 for draining the bearing oil, and a pair of
second supply pockets or portions 51 arranged axially outsides of
the draining portions 50 for supplying air which is pressurized to
a predetermined pressure. Each fluid bearing 35 is provided with
end members 52 respectively at opposite ends of the bearing member
48, and a clearance of a predetermined width is formed between each
of the end members 52 and a corresponding one of the axial opposite
ends of the bearing member 48 to serve as the second supply
portions 51.
[0046] Each bearing member 48 has its inner diameter which is made
to be slightly larger than the diameter of the wheel spindle 19 and
is formed with the first supply portion 49 and the draining
portions 50 on an internal surface thereof. In each bearing member
48, a clearance (t1) between the wheel spindle 19 and each of
internal surface portions which is defined between the first supply
portion 49 and each draining section 50 in the axial direction is
made to be slightly narrower than another clearance (t2) between
the wheel spindle 19 and each of internal surface portions which is
defined between each draining section 50 and each second supply
portion 51 next thereto.
[0047] An internal surface portion 54 of each end member 52 is made
to be approximately the same diameter as each internal surface
portion 53b which is defined between each draining portion 50 and
each second supply portion 51 in the axial direction. It is to be
noted that the supporting accuracy and the like of each fluid
bearing 53 is adjustable by properly setting the clearances between
these surface portions and the wheel spindle 19.
[0048] As shown in FIG. 4(b), each fluid bearing 35 is connected
with a unit side supply passage 46a at the first supply portion 49
in the axial direction and over the wheel spindle 19 in the
vertical direction, and is also connected with a unit side draining
passage 46b at each draining portion 50 in the axial direction and
under the wheel spindle 19. As shown in FIG. 3, the unit side
supply passage 46a and the unit side draining passage 46b are
connected by the joint means 44 to a body side supply passage 45a
and a body side draining passage 45b of the wheel head main body
26, respectively. Further, the body side supply passage 45a and the
body side draining passage are connected to a pump and a reservoir
of the bearing oil supply device (all not shown).
[0049] Thus, the bearing oil reserved in the reservoir of the
bearing oil supply device is adjusted by the pump to a
predetermined pressure and is supplied to the first supply portion
49 through the body side supply passage 45a and the unit side
supply passage 46a, while the bearing oil collected at the draining
portions 50 are drained through the unit side draining passage 46b
and the body side draining passage 45b and is cooled by the bearing
oil cooler.
[0050] Further, as best shown in FIG. 3, the second supply portions
51 are connected to an air supply passage 47, and air of a
predetermined pressure supplied from an air supply device (not
shown) is supplied to the second supply portions 51 through the air
supply passage 47. For the wheel spindle unit 27, a CBN (Cubic
Boron Nitride) grinding wheel with a diameter selected in a range
of 100 to 200 mm is used, so that it becomes possible to use a
smaller diameter grinding wheel than those used conventionally.
Although not illustrated in the drawings, the wheel spindle unit 27
and the wheel head main body 26 are secured to each other by
connections using bolts or the like or by suitable lock mechanisms
or the like.
[0051] FIGS. 5(a) and 5(b) are a graph and an explanatory view for
explaining the relation between the spindle diameter (d) of the
wheel spindle 19 and the friction force of each fluid bearing 35 or
the relation between the spindle diameter (d) and the idle rotation
power of each fluid bearing 35 in the present invention, wherein
FIG. 5(b) shows various forces acting on the wheel spindle 19,
whereas FIG. 5(a) represents a bearing characteristic curve.
[0052] In FIG. 5(b), symbol "P" denotes a load such as grinding
force or the like acting on the wheel spindle 19, symbol ".mu.P"
denotes a rotational friction force which is generated through the
bearing oil filled in a clearance between the wheel spindle 19 and
the internal surface of each bearing member 48 of each fluid
bearing 35, symbol "p" a pressure exerted on a bearing projection
area (i.e., the area made by the projection of the wheel spindle
19), symbol ".eta." denotes the viscosity of the bearing oil,
symbol ".mu." denotes friction coefficient, symbol "L" denotes the
length of each fluid bearing 35, symbol "N" denotes the rotational
speed of the wheel spindle 19, and symbol ".eta.N/p" denotes a
bearing constant.
[0053] FIG. 5(a) represents the bearing characteristic curve, in
which three zones including a boundary lubrication zone, a mixed
lubrication zone and a fluid lubrication zone are made depending on
the range of the bearing constant (.eta.N/p). Each fluid bearing 35
in the present invention is designed for use in the fluid
lubrication zone shown in FIG. 5(a), wherein the friction
coefficient (.mu.) is in proportion to the bearing constant
(.eta.N/p).
[0054] Where the circumferential speed and the diameter of the
grinding wheel T are represented respectively as "V" and "D", the
circumferential speed (V) is proportional to a product "ND" and is
expressed as "V.varies.ND" by the use of symbol ".varies." denoting
proportion. Further, the pressure (p) exerted on the bearing
projection area is expressed as "p=P/(dL)" because the projection
area of each bearing 35 is "d". Where symbol (k) is taken to denote
the ratio of the length (L) to the spindle diameter (d) in each
bearing 35, the pressure (p) is expressed as "p=P/(kd2), and hence,
the rotational friction force (.mu.P) of the wheel spindle 19 can
be expressed as follows:
.mu.P.varies.(.eta.N/p)P=.eta.Nkd2.varies..eta.kd2V/D (Expression
1)
[0055] And, the rotational friction force (.mu.P) of the wheel
spindle 19 is a product of the friction force (.mu.P) multiplied by
the radius (d/2) and hence, can be expressed as follows:
.eta.kd3V/2D (Expression 2)
[0056] In this expression, the viscosity (.eta.) of the bearing oil
depends on the property of a bearing oil to be used. In the present
invention, the bearing oil is used as that used in the prior art
cylindrical grinding machine, and the viscosity of the bearing oil
is about 2 cSt (i.g., centi-stokes).
[0057] Further, the ratio (k) of the length (L) to the spindle
diameter (d) in each bearing 35 is generally determined in
dependence on the purpose of use (e.g., the ration L/d is a value
in a range of 2 to 4 or so), and the cylindrical grinding machine
according to the present invention was designed to have
approximately the same value as used in the prior art grinding
machine, that is, to take a value k=1.5. Further, the
circumferential speed (V) of the grinding wheel T was designed to
120 m/s (meters per second) which is the same value as used in the
prior art grinding machine.
[0058] From the foregoing, the power consumption by the grinding
wheel T can be considered to exclude the constants in the
expression .eta.kd3V/2D and hence, is proportional to d3/D. That
is, since the power consumption by the grinding wheel T does not
depend on the load such as a grinding force exerted on the wheel
spindle 19 and since it is proportional to the cube of the spindle
diameter (d) of the bearing component, but is inversely
proportional to the diameter (D) of the grinding wheel T, it is
understood that the diameter (D) of the bearing prevails over other
parameters.
[0059] Accordingly, based on results of the foregoing analysis, the
diameter (d) of each bearing 35 is determined based on a set value
for the quantity of energy consumption in terms of reducing the
quantity of energy consumption by reducing the power consumption by
the rotation of the grinding wheel T and in particular, the idle
rotation power which influences largely upon the quantity of energy
consumption from the beginning to the ending of a workpiece
grinding as well as by reducing the accompanying power consumption
related to the wheel spindle including the power for bearing oil
cooling, the power for the bearing pump and so forth.
Alternatively, the set value for the quantity of energy consumption
is determined based on a reduction target for the quantity of
energy consumption during a workpiece grinding in the prior art
cylindrical grinding machine, and the diameter (d) of each bearing
35 is determined to satisfy such a reduction target. In this case,
in taking into consideration design parameters such as, for
example, the ratio (k) of the length (L) to the spindle diameter
(d) in each bearing 35, the viscosity (.eta.) of the bearing oil,
the diameter (D) of the grinding wheel T, the circumferential speed
(V) of the grinding wheel T and the like on the basis of the power
consumption by each bearing 35 or the quantity of energy
consumption from the beginning to the ending of a workpiece
grinding, the diameter (d) of each bearing 35 is determined so that
a predetermined rigidity can be secured at the grinding point
(i.e., a point where the grinding wheel T contacts the workpiece
W).
(Operation of System)
[0060] FIG. 6 shows a system including a computer numerical
controller according to the present invention. The system including
the computer numerical controller according to the present
invention is composed of the cylindrical grinding machine 10, the
computer numerical controller 100, a drive circuit (DU_Z) 201 for
driving the Z-axis movable member 13, a drive circuit (DU_X) 202
for driving the X-axis movable member 15, a drive circuit (DU_T)
203 for driving the rotation drive means 29, a drive circuit (DU_C)
204 for driving the coolant supply device 20 and a drive circuit
(DU_S) 205 for driving the work spindle motor 24.
[0061] The computer numerical controller 100 executes program
controls of the drive circuit (DU_Z) 201, the drive circuit (DU_X)
202, the drive circuit (DU_T) 203, the drive circuit (DU_C) 204 and
the drive circuit (DU_S) 205 through an interface 103 in accordance
with NC data 102 defining machining data.
[0062] The drive circuit (DU_Z) 201 drives the Z-axis movable
member 13 in the Z-axis direction by the linear motor composed of
the coil 22 and the magnet 21 by electrifying the coil 22 to
generate an electric field and by generating a power through the
mutual operations of a magnetic field of the magnet 21 with the
electric field.
[0063] Likewise, the drive circuit (DU_X) 202 drives the X-axis
movable member 15 in the X-axis direction by the linear motor
composed of the coil 23 and the magnet by electrifying the coil 23
to generate an electric field and by generating a power through
mutual operations of a magnetic field of the magnet with the
electric field.
[0064] The drive circuit (DU_T) 203 rotationally drives the
rotation drive means 29 being a built-in motor and rotates the
wheel spindle 19 and the grinding wheel T by transmitting the drive
power from the drive pulley 30 to the wheel spindle pulley 32
through the belt 33.
[0065] The drive circuit (DU_C) 204 drives the coolant supply
device 20 to make coolant ejected toward the grinding point.
[0066] The drive circuit (DU_S) 205 rotationally drives the work
spindle motor 24 at a predetermined rotational speed to drive the
workpiece W set on the work heads 17.
[0067] FIG. 7(a) is a graph with the horizontal axis taken as time
axis, showing the power consumption of the cylindrical grinding
machine when a workpiece is machined while the aforementioned
respective drive circuits generate powers required for the
grinding, wherein a pulse-form line indicated on the lower side
represents the power consumption by the grinding machine according
to the present invention whereas another pulse-form line indicated
on the upper side represents the power consumption by the prior art
grinding machine. Further, FIG. 7(b) is an explanatory view showing
the shape and ground areas, as portions to be ground, of a
workpiece W which is machined in the grinding operation referred to
in connection with FIG. 7(a). Where the ground areas of the
workpiece W are determined as three portions marked A, B and C as
shown in the drawing, the pattern of the power consumption in
grinding these three portions is indicated in FIG. 7(a) to
correspond respectively to periods or segments marked A', B' and C'
in the grinding machine according to the present invention and to
periods or segments marked A'', B'' and C'' in the prior art
grinding machine.
[0068] Next, detailed description with reference to FIG. 7(a) will
be made regarding the power consumption which depends on the power
consumptions by the respective drive circuits in grinding the
workpiece W shown in FIG. 7(b) by each of the grinding machine
according to the present invention and the prior art grinding
machine. First of all, the pattern of power consumption will be
described in the case that the grinding operation is performed by
the grinding machine according to the present invention.
[0069] The time when all the preparations required for the
machining of the workpiece W have been completed with the same
being set on the work heads 17 is set as machining time "0" on the
horizontal axis and as power consumption "0" on the vertical axis.
By the time "s1", the work spindle motor 27 is driven by the drive
circuit (DU_S) 205 to rotate the workpiece W at the predetermined
rotational speed and the grinding wheel T is driven by the drive
circuit (DU_T) 203. The power consumption at this time is indicated
as "L1" inclusive of those consumptions by the bearing oil supply
device and the bearing oil cooler. Then, by the time "s2", the
coolant supply device 20 is driven by the drive circuit (DU_C) 204
to make the coolant ejected toward the grinding point. The power
consumption at this time is indicated as "L2".
[0070] Thereafter, by the time "s3", the drive circuit (DU_Z) 201
electrifies the coil 22 to drive the Z-axis movable member 13 by
the linear motor in the Z-axis direction. Further, the drive
circuit (DU_X) 202 electrifies the coil 23 to drive the X-axis
movable member 15 by the linear motor in the X-axis direction. The
time period from "s2" to "s3" is the time period for positioning
the grinding point by the linear motors in the Z-axis direction and
the X-axis direction. These positioning operations are performed to
move the grinding wheel T between the ground areas and are called
as "index operations". The power consumption at this time is
indicated as "L5". Although in the pattern of power consumption
shown in FIG. 7(a), the power consumption "L5" during the index
operation in the Z-axis direction is made larger than the power
consumption "L4" during the index operation in the X-axis
direction, they may be reverse in the relation of their magnitudes.
In addition, the index operations in the Z-axis direction and the
X-axis direction may be performed simultaneously at least in a part
of the sections. The present invention features that the power
consumption during the index operation is larger than the power
consumption "L3" during a grinding period referred to later. This
means that it is suffice that the power consumption during the
index operation at least in the Z-axis direction or the X-axis
direction is larger than the power consumption "L3" during the
grinding period.
[0071] Subsequently, the time period from "s3" to "s4" is the time
period in which the grinding wheel T on the X-axis and Z-axis
movable members 15, 13 having been positioned by the aforementioned
index operations enters into a grinding stage while gradually
increasing the infeed amount from a position adjacent to the
grinding point, and this infeed of the grinding wheel T is called
as an "approach stage". The power consumption at this stage is the
same as that in the time period from "s1" to "s2".
[0072] The time period for the grinding stage begins upon
completion of the approach stage and ends at the time "s5". The
power consumption at this grinding stage increases from "L2" to
"L3" with the increase of the load by grinding. Then, until the
time "s6", that is, during the time period from the termination of
the infeed of the grinding wheel T to the extinction of sparks, the
grinding wheel T is caused to remain as it is in the X-axis
direction for a spark-out grinding.
[0073] The aforementioned time period from "s2" to "s6" is the
machining segment A' corresponding to the ground area A of the
workpiece W, and in this machining example, the same machining as
aforementioned is performed in turn in the machining segments
marked B' and C', whereby the grinding operation is terminated at
the time period "s7". Thereafter, by the time "s8", the operation
of the coolant supply device 20 by the drive circuit (DU_C) 204 is
discontinued to let the power consumption go down to "L1". Further,
by the time "s9", the Z-axis movable member 13 and the X-axis
movable member 15 are returned to a predetermined original position
by being driven by the drive circuit (DU_Z) 201 and the drive
circuit (DU_X) 202 respectively in the Z-axis direction and the
X-axis direction.
[0074] Since at this time, the grinding of the workpiece W is
terminated, the work spindle motor 24 is stopped by the drive
circuit (DU_S) 205 to discontinue the rotation of the workpiece W,
and the rotation of the grinding wheel T is discontinued by the
drive circuit (DU_T) 203. Further, the operations of the bearing
oil supply device and the bearing oil cooler are also stopped to
complete the grinding operation, whereby the power consumption is
returned to "0".
[0075] Next, description will be made regarding the grinding
performed by the prior art grinding machine, wherein the operations
overlapping those described above will be described simply.
[0076] Upon completion of the machining preparations, by the time
"s1", the workpiece W is rotated at the predetermined rotational
speed and the grinding wheel T is rotated in the same manner as
that described with respect to the present invention. The power
consumption at this time is indicated as "M1", which is larger than
the power consumption "L1" in the present invention. This is
because in the prior art grinding machine, the diameters of the
grinding wheel T and the wheel spindle 19 are larger, which
requires an in crease in the power consumption. Then, by the time
"s2", coolant is ejected toward the grinding point. The power
consumption at this time is indicated as "M2".
[0077] Next, description will be made regarding the machining
segment A'' corresponding to the ground area A of the workpiece W.
With respect to the approach time period (s3 to s4), the grinding
time period (s4 to s5) and the spark-out grinding time (s5 to s6)
as explained in the foregoing machining example in the present
invention, the same is applied to the prior art grinding machine,
and respective power consumptions during these time periods are
indicated as "M2", "M5" and "M2", respectively. The same machining
as that in the machining segment A'' is performed in each of
machining segments B'' and C'', and after the operation of the
coolant supply device is stopped, the grinding wheel T is returned
to an original position, whereby the grinding operation is
completed at the time "s10".
[0078] In the grinding machine according to the present invention,
the power consumption by the idle rotation of the grinding wheel T
and by the bearing oil supply device and the bearing oil cooler
which are required to be operated in connection therewith is at the
level "L1" indicated in FIG. 7(a), and the power at this level is
required throughout the entire time period (0 to s9) from the
beginning to the ending of the workpiece grinding operation.
Effects of the Embodiment
[0079] As described above, in the present embodiment, the power
consumption by the bearing section 27 or the quantity of energy
consumption from the beginning to the ending of a workpiece
grinding operation is set to a predetermined quantity, in
dependence on which the diameter of each bearing 35 is determined
so that a predetermined rigidity can be secured at the grinding
point. Consequently, as shown in FIG. 7(a), the power consumption
at the level "M1" by the prior art grinding machine is lowered to
that at the level "L1" by the cylindrical grinding machine in the
present embodiment, so that the power consumption or the quantity
of energy consumption can be reduced throughout the entire time
period (0 to s9) from the beginning to the ending of the workpiece
grinding operation. The quantity of energy consumption which can be
reduced in the present embodiment can be indicated as that covered
by the hatched area in FIG. 7(a). Accordingly, it can be realized
in the present embodiment to provide the environment-oriented,
energy-saving grinding machine capable of reducing the quantity of
energy consumption.
Example practiced
[0080] FIG. 8(a) is a sectional view of a bearing section taken
along a horizontal plane in the prior art cylindrical grinding
machine, FIG. 8(b) is a sectional view of a bearing section taken
along a horizontal plane in a cylindrical grinding machine
practiced according to the present invention, and FIG. 8(c) is a
table showing the diameter of the grinding wheel T, the diameter of
the wheel spindle 19 and the entire length of the wheel spindle 10
in each of the respective grinding machines. In the practiced
example, the power consumption related to the grinding wheel
bearing was determined with the aim of lowering the idle rotation
power for the grinding wheel T, and the diameter of the wheel
spindle 19 was designed so that a predetermined rigidity of 100
N/.mu.m (newtons per micrometer) was able to be secured as that at
the grinding point of the grinding wheel T.
[0081] FIG. 9(a) is a graph with grinding wheel circumferential
speed on the horizontal axis, showing measured results of idle
rotation power for the grinding wheel in each of the cylindrical
grinding machine according to the present invention and the prior
art cylindrical grinding machine. FIG. 9(b) is a graph showing the
power consumption related to the wheel spindle bearing including
the power for grinding wheel idle rotation and the powers consumed
by the bearing oil supply device and the bearing oil cooler in each
of the cylindrical grinding machine practiced according to the
present invention and the prior art cylindrical grinding
machine.
[0082] As demonstrated in FIG. 9(a), the idle rotation power for
the grinding wheel T in the cylindrical grinding machine practiced
according to the present invention was about one fourth (1/4) of
that in the prior art cylindrical grinding machine. In the case
that the circumferential speed of the grinding wheel T was set to
120 m/s (meters per second) which has been wide use in terms of
machining efficiency, the idle rotation power in the cylindrical
grinding machine practiced according to the present invention was 1
kW. Further, as demonstrated in FIG. 9(b), with the decrease of the
idle rotation power for the grinding wheel T, the power consumption
related to the grinding wheel bearing including the powers consumed
by the bearing oil supply device and the bearing oil cooler was
also reduced at a similar rate and was able to be greatly reduced
to 2.3 kW in the cylindrical grinding machine practiced according
to the present invention thought that in the prior art cylindrical
grinding machine was 9 kW.
[0083] FIG. 10(a) is a graph showing the relation between the
machining time and the power consumption on the basis of the values
which were actually measured values when a workpiece W shown in
FIG. 10(b) was ground in each of the cylindrical grinding machine
practiced according to the present invention and the prior art
cylindrical grinding machine. The workpiece W was a stepped shaft
with five stepped portions and had five ground areas. The total
machining time in the cylindrical grinding machine practiced
according to the present invention was reduced by the high speed
driving using the linear motors to 44 seconds which was 12% shorter
than 50 seconds taken by the grinding in the prior art cylindrical
grinding machine. Further, in the cylindrical grinding machine
wherein the diameter of the fluid bearings 35 for the grinding
wheel T was designed on the basis of the quantity of power
consumption by the bearing section 27 or the energy consumption
from the beginning to the ending of the workpiece grinding
operation, the power consumption related to the grinding wheel
bearing including the idle rotation power for the grinding wheel T
and the powers consumed by the bearing oil supply device and the
bearing oil cooler was able to be reduced by about 7 kW at all the
time points from the beginning to the ending of the workpiece
grinding operation, in comparison with that in the prior art
cylindrical grinding machine. The reduction of about 7 kW in the
power consumption corresponds to the reduction of about 0.1 kWh per
workpiece when converted into the quantity of energy
consumption.
[0084] Obviously, numerous modifications and variations of the
present invention are possible in light of the above teachings. It
is therefore to be understood that within the scope of the appended
claims, the present invention may be practiced otherwise than as
specifically described herein.
* * * * *