Grinding method and grinding apparatus

A work W is rotated on a lower grinding wheel 13 provided on a work support base 11. Both surfaces of the work W are simultaneously subjected to grinding process by an upper grinding wheel 24 provided on a grinding shaft 22 of a grinding head 21 and the lower grinding wheel 13. The work W is applied with a pressure force of a primary load through the grinding shaft 22 by a piston rod 36 of a primary pneumatic cylinder 35 which is operated by a first air pressure. The work W is also applied with a pressure force of a secondary load through a lever member 43 by a piston rod 46 of the secondary pneumatic cylinder 45 which is operated by a second air pressure higher than the first air pressure. By adjusting the second air pressure, the pressure force is controlled.

BACKGROUND OF THE INVENTION 
The present invention relates to a grinding technique in which a pressure 
force is applied to the surface of a work so as to grind the work by a 
grinding tool. 
In case of flatly grinding the surface of a work to be processed while 
rotating a grinding wheel, the outer circumferential surface of the 
grinding wheel is brought into contact with the work or an end surface of 
the grinding wheel is brought into contact with the work. Therefore, the 
work to be processed is set on a fixed table or a rotation table. 
In case where both surfaces of an aluminum substrate for a magnetic disk, 
as a work, are simultaneously ground, for example, an apparatus disclosed 
in the Publication of Japanese Patent No. 2556605 is used. This apparatus 
has a lower platen having an upper surface where a ring-like lower 
grinding wheel is provided, and an upper platen having a lower surface 
where a ring-like upper grinding wheel is provided so as to face the lower 
grinding wheel. The work is set in a holding hole formed in a plurality of 
carriers provided on the lower grinding wheel. Each carrier is engaged 
with a sun gear provided rotatably at the rotation center portion of the 
lower platen and is also engaged with an inner-toothed gear provided 
outside the lower platen. In this manner, both surfaces of the work held 
by the carriers are ground by the upper and lower grinding wheels, by 
rotating the upper and lower level disks in a state in which the sun gear 
is rotated and the work is revolved while rotating about the sun gear. 
In the grinding process of a work with use of a grinding wheel, it is 
necessary that the pressure force applied to the work from a grinding 
wheel is set to a predetermined value. Therefore, developments have been 
made for a technique in which the pressure force applied to the grinding 
wheel is detected by a sensor and an air pressure supplied to a pneumatic 
cylinder which applies the pressure force to the grinding wheel is 
controlled based on a detection value by a sensor and a reference value 
depending on the air pressure (for example, see Japanese Patent Laid-Open 
Publication No. 63-22266). 
However, in case where the pressure force is set by controlling the air 
pressure supplied to the pneumatic cylinder for moving the grinding wheel 
close to and apart from the work, it is difficult to control the load with 
high precision such that the pressure force becomes equal to the target 
load. In case of processing a work with use of a grinding wheel, it has 
been found that the pressure force applied to the work from the grinding 
wheel greatly influences the processing precision of the work, so it is 
significant to control the pressure force to an optimum condition. 
SUMMARY OF THE INVENTION 
An object of the present invention is to enable highly precise control of 
the pressure force to the work from a grinding tool in a grinding 
apparatus. 
The grinding method according to the present invention comprises steps of: 
rotating and driving a grinding tool in contact with a work, by a grinding 
shaft; supplying a first fluid pressure to a primary fluid pressure 
cylinder having a first piston rod connected with the grinding shaft, 
thereby to apply a primary load to the grinding shaft; supplying a second 
fluid pressure higher than the first fluid pressure, to a secondary fluid 
pressure cylinder having a second piston rod connected between both end 
portions of a lever member connected to the first piston rod, the lever 
member having a swing center portion at one of the end portions, and the 
other one of the end portions being connected with the first piston rod; 
controlling the second fluid pressure to adjust the secondary load; and 
grinding the work by the grinding tool under condition that the primary 
load and the secondary load adjusted are applied to the grinding shaft. 
The grinding apparatus according to the present invention comprises: a 
support base for supporting a work; a grinding head provided with a 
grinding shaft for rotating and driving a grinding tool for grinding the 
work, the grinding head being provided to be opposed to the support base; 
a primary fluid pressure cylinder operated by the first fluid pressure, 
the primary fluid pressure cylinder having a first piston rod connected to 
the grinding shaft; a lever member having end portions, one of which 
portions is set on the grinding head such that the lever member can swing, 
and the other of which portions is connected with the first piston rod; a 
secondary fluid pressure cylinder operated by a second fluid pressure 
higher than the first fluid pressure, the secondary fluid pressure 
cylinder having a second piston rod connected between both end portions of 
the lever member; and a fluid pressure regulation means for controlling 
the second fluid pressure applied to the secondary fluid pressure 
cylinder, wherein a primary load depending on the primary fluid pressure 
cylinder is applied to the grinding shaft and a secondary load depending 
on the secondary fluid pressure cylinder is applied to the grinding shaft 
through the lever member. A pressure receiving area of the secondary fluid 
pressure cylinder may be set to be smaller than a pressure receiving area 
of the primary fluid pressure cylinder. 
According to the present invention, a fluid pressure higher than the fluid 
pressure applied to the primary fluid pressure cylinder is applied to the 
secondary fluid pressure cylinder, and the pressure force applied to the 
grinding shaft is adjusted by controlling the fluid pressure applied to 
the secondary fluid pressure cylinder. Therefore, the pressure force can 
be controlled with high precision. If the pressure receiving area of the 
secondary fluid pressure cylinder is set to be smaller than the pressure 
receiving area of the primary fluid pressure cylinder, the second fluid 
pressure can be set to a value higher than the first fluid pressure.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In the following, the embodiments of the present invention will be 
specifically explained on the basis of the drawings. 
FIG. 1 is a cross-sectional view showing a grinding apparatus as an 
embodiment of the present invention. This grinding apparatus comprises a 
work support base 11 for supporting a work W, and a grinding head 21 
provided above and opposed to the work support base 11. 
The work W is an aluminum substrate for a magnetic disk as described above, 
and the support base 11 is arranged as shown in FIG. 2. The work support 
base 11 has a lower platen 12 of a rotation table type which is rotatable 
in the direction indicated by an arrow in FIG. 2, and a ring-like lower 
grinding wheel 13 is set on the upper surface of the lower platen 12. A 
sun gear 14 having an outer diameter smaller than the inner diameter of 
the lower grinding wheel is provided at the rotation center portion of the 
lower platen, to be rotatable in the same direction as the lower platen 
12, as indicated by an arrow. A ring-like inner-toothed gear 15 having a 
diameter larger than the outer diameter of the lower grinding wheel 13 is 
fixed to a base seat 16, so as to surround the lower platen 12. 
In the case of the figure, ten carriers 17 are provided between the sun 
gear 14 and the inner-toothed gear 15, and circular five holding holes 18 
for containing works W are formed in each of the carriers 17, and the 
thickness of the carrier 17 is formed to be smaller than that of the work 
W. 
When the sun gear 14 is rotated in such a state that each carrier 17 is 
engaged between the sun gear 14 and the inner-toothed gear 15, each 
carrier 17 revolves around the sun gear 14 with rotating about its own 
axis since the inner-toothed gear 15 is fixed. Therefore, the works W 
moves in the horizontal direction, drawing a cycloidal curve or a trochoid 
curve, in contact with the lower grinding wheel 13 in the horizontal plane 
by the carriers 17. 
The grinding head 21 is movable in the vertical direction and the 
horizontal direction by a drive means, which is not shown. The upper 
platen 23 is set on the lower end portion of a grinding shaft 22 provided 
rotatably on the grinding head 21, and an upper grinding wheel 24 having a 
ring-like shape corresponding to the lower grinding wheel 13 is fixed to 
the upper platen 23. 
The grinding shaft 22 is engaged with a drive sleeve 25 provided rotatably 
on the grinding head 21, at the portion of the direct acting guide portion 
26 provided for the grinding shaft 22, such that the grinding shaft 22 is 
vertically movable. The grinding shaft 22 is movable in the axial 
direction with a predetermined stroke in relation to the drive sleeve 25 
and is also rotatable integrally with the drive sleeve 25. To drive and 
rotate the grinding shaft 22, a timing belt 32 is tensioned between a 
pulley 27 fixed to the drive sleeve 25 and a pulley 31 fixed to a shaft 29 
of a grinding shaft rotation motor 28. 
To move the grinding shaft 22 vertically with a predetermined stroke and to 
apply a primary load to the grinding shaft 22, a primary pneumatic 
cylinder 35 is attached to the grinding head 21. A first piston rod 36 
which is moved forward and backward by the pneumatic cylinder 35 is 
connected with the grinding shaft 22 through a thrust bearing 37. To 
detect the pressure force applied to the grinding shaft 22, the first 
piston rod 36 is provided with a load sensor 38. 
A lever member 43 is attached to a bracket 41 fixed to the grinding head 21 
by a pin 42 such that the lever member 43 can swing freely in the vertical 
direction at an end portion of the lever member 43, and the other end 
portion of the lever member 43 is connected with a first piston rod 36 
through a pin 44 fixed to the first piston rod 36. A secondary pneumatic 
cylinder 45 is attached to the grinding head 21, and the second piston rod 
46 which moves forward and backward by the pneumatic cylinder 45 is 
connected with the lever member 43, at the portion between both end 
portions of the lever member 43. 
FIG. 3 is a schematic view showing the connection between the lever member 
43 and two pneumatic cylinders 35 and 45. Supposing that the position of 
the pin 42 is a fulcrum and the position of the pin 44 is an action point, 
the dimension between these positions is L.sub.1. Supposing that the 
position of the pin 47 is a load point, the dimension between the fulcrum 
and the load point is L.sub.2. In the case of the figure, the ratio of 
L.sub.1 to L.sub.2 is approximately set to 5:1. Where the pressure 
receiving area of the piston 36a of the primary pneumatic cylinder 35 is 
A.sub.1 and the pressure receiving area of the piston 46a of the secondary 
pneumatic cylinder 45 is A.sub.2, the ratio of A.sub.1 :A.sub.2 is 
approximately set to 5:1. Where the air pressure supplied from a supply 
port 35a into the primary pneumatic cylinder 35 is P.sub.1 and the air 
pressure supplied from the supply port 45a into the secondary pneumatic 
cylinder port 45a is P.sub.2 when the first piston rod 36 is pushed down 
to apply a pressure force to the upper grinding wheel 24, the ratio of 
P.sub.1 :P.sub.2 is approximately set to 1:25. 
In this manner, the difference between the pressure force of the primary 
load applied to the grinding shaft 22 by the primary pneumatic cylinder 35 
and the pressure force of the secondary load applied to the grinding shaft 
22 from the action point by the secondary pneumatic cylinder 45 becomes 
small. Therefore, the ratios of the air pressures, the pressure receiving 
areas, and the lengths to the load points can be set to arbitrary ratios, 
as far as the secondary load can be controlled within a range within which 
the target pressure force can be set by adding the pressure force applied 
to the grinding shaft, to the primary load, with this primary load used as 
a reference. 
In the case of the figure, according to the ratio of the lengths of the 
lever member 43, a load which is five times larger than the secondary load 
applied to the grinding shaft 22 from the position of the action point of 
the pin 44 can be applied to the secondary pneumatic cylinder 45 at the 
load point of the pin 47, so the pressure force can be controlled by 
controlling the high air pressure applied to the cylinder 45. 
By supplying an air with a constant first pressure P.sub.1, which is set 
previously, from the supply/exhaust port 35a of the primary pneumatic 
cylinder 35, the pressure force of the primary load applied to the 
grinding shaft 22 by the first piston rod 36 is set to be constant. In 
contrast, the second pressure P.sub.2 supplied from the supply/exhaust 
port 45a of the secondary pneumatic cylinder 45 can be controlled. By 
controlling this second pressure, an adjusted pressure force of the 
secondary load is applied to the grinding shaft 22. 
For example, suppose that the first pressure P.sub.1 is 0.126 kg/cm.sup.2, 
the second pressure P.sub.2 is 3.304 kg/cm.sup.2, and the target pressure 
force applied to the upper grinding wheel 24 through the grinding shaft 22 
is about 10 kgf. To control the tolerable range of the target pressure 
force to be 5% or less, the pressure tolerable value of the pressure 
P.sub.1 must be within .+-.0.0021 kg/cm.sup.2 if the pressure force is 
controlled only by the pressure P.sub.1. In contrast, in case where the 
first pressure P.sub.1 is kept constant and the pressure P.sub.2 higher 
than the pressure P.sub.1 is controlled, the tolerable range of the target 
pressure force can sufficiently be set to be 5% or less if the pressure 
P.sub.2 is controlled with the range of .+-.0.0551 kg/cm.sup.2, as in the 
present invention. 
Thus, according to the present invention, the pressure force of the primary 
load is applied directly to the grinding shaft 22 by the primary pneumatic 
cylinder 35, and the pressure force generated by the secondary pneumatic 
cylinder 45 applied with the second air pressure P.sub.2 higher than the 
first air pressure P.sub.1 applied to the primary pneumatic cylinder 35 is 
converted through the lever member 43 into a small secondary load, which 
is indirectly applied to the grinding shaft 22. As a result of this, the 
secondary load can be controlled by controlling the second pressure 
applied to the secondary pneumatic cylinder 35 which generates a large 
load, so the pressure force applied to the works W through the grinding 
shaft 22 can be adjusted with high precision. If the target load is 
adjusted by controlling the second pressure which is higher than the first 
pressure, the control can be achieved over a large pressure range, so that 
fine control of the secondary load can be performed relatively, i.e., 
control can be performed with high precision. Accordingly, the pressure 
force applied to the grinding shaft 22 can be controlled with high 
precision. 
In particular, if the pressure receiving area of the secondary pneumatic 
cylinder 45 is set to be smaller than the pressure receiving area of the 
primary pneumatic cylinder 35, as described above, the second pressure can 
be set to be much larger than the first pressure, so the error of the 
control target load can be reduced to be small. 
To supply compressed air to each of the pneumatic cylinders 35 and 45, the 
tank 52 connected to the air pressure pump 51 is connected with air 
pressure pipes 53a, 53b and 54. The air pressure pipe 53a is connected to 
the supply-exhaust port 35a of the primary pneumatic cylinder 35, and the 
air pressure pipe 53a is provided with a regulating valve 55a for setting 
the first pressure for applying the primary load to the grinding shaft 22. 
The air pressure pipe 53b is connected to the supply-exhaust port 35b of 
the primary pneumatic cylinder 35, and the air pressure pipe 53b is 
provided with a regulating valve 55b for setting a higher pressure than 
the first pressure to move upward the grinding shaft 22 together with the 
upper platen 23 and the upper grinding wheel 24. 
Meanwhile, the air pressure pipe 54 is provided with a pressure regulator 
56 for adjusting the pressure of the compressed air to be supplied to the 
secondary pneumatic cylinder 45. An electropneumatic regulator or the like 
is used as the pressure regulator 56, and the air pressure applied to the 
secondary pneumatic cylinder 45 is controlled by an electric signal 
supplied from a control circuit. 
To switch the supply and exhaustion of air with respect to the cylinder 
through the supply-exhaust ports 35a and 35b of the primary pneumatic 
cylinder 35, a switch valve 57a is provided for the air pressure pipe 53a, 
and a switch valve 57b is provided for the air pressure pipe 53b. Further, 
to perform supply/exhaustion of the air with respect to the cylinder 
through the supply-exhaust ports 45a and 45b of the secondary pneumatic 
cylinder 45, a switch valve 58 is provided for the air pressure pipe 54. 
Electromagnetic valves are used as the 57a, 57b and 58, and switching 
operation is performed by an electric signal. Note that the first air 
pressure P.sub.1 may be changed by using an electropneumatic regulator in 
place of the regulating valve 55a. 
FIG. 4 is a block diagram showing a control circuit for controlling the 
operation of the grinding apparatus, and the control section 61 including 
a CPU (central processing unit) or the like is inputted with signals 
through an input key for instructing start of the apparatus, a key for 
inputting the pressure force, and a load sensor 38. The control section 61 
supplies operation signals to a head elevation motor 63 for moving up and 
down the grinding head 21, to a sun gear rotation motor 65 for driving and 
rotating the sun gear 14, and to a grinding shaft rotation motor 28 for 
driving and rotating the grinding shaft 22. Further, the control section 
61 also supplies operation signals to the pressure regulator 56 and the 
switch valves 57a, 57b and 58. 
The control section 61 is provided with an amplifier for amplifying analog 
signals from the load sensor 38 and the like, an A/D converter for 
converting the analog signals into digital signals, a D/A converter for 
converting digital signals outputted to the pressure regulator 56, into 
analog signals, and the like. Also, the control section 61 is connected 
with ROMs 66 and 67 which store calculation formulas and map data 
concerning correspondences to the voltage values to be outputted to the 
pressure regulator 56 in accordance with signals from the load sensor 38. 
The pressure forces applied to the grinding shaft 22 can be displayed on 
the display section 68. 
Next, procedure of grinding the works with use of the grinding apparatus 
described above will be explained below. Under condition that the works W 
are set in the holding holes 18 of the carrier 17, at first, the grinding 
head 21 is moved up and down by the elevation motor 63, so the upper 
grinding wheel 24 is positioned to be opposed to the lower grinding wheel 
13 through the works W. By operating the switch valve 57a in this state, a 
compressed air at a predetermined pressure is supplied to the primary 
pneumatic cylinder 35. In this manner, the upper grinding wheel 24 is 
brought into contact with the surfaces of the works W. 
The pressure force applied to the works W through the grinding shaft 22 is 
detected by the load sensor 38. If there is a deviation from the preset 
pressure force, a signal corresponding to the deviation is outputted to 
the pressure regulator 56, and an operation signal is supplied to the 
switch valve 58, so the pressure force is corrected by the lever member. 
Thus, the works W are applied with a primary load depending on the primary 
pneumatic cylinder 35 applied with a first air pressure P.sub.1, and a 
secondary load depending on the secondary pneumatic cylinder 45 applied 
with a secondary air pressure P.sub.2, which loads are combined with each 
other, so the pressure force is controlled with high precision by 
controlling the secondary load depending on the secondary pneumatic 
cylinder 45 applied with a high pressure. 
In case where the ratio of L.sub.1 :L.sub.2 is set to 5:1 as shown in the 
figure, the load which is five times larger than the secondary load 
applied to the position of the action point depending on the pin 44 is 
controlled, as for the load applied to the portion of the load point at 
the pin 47 by the piston rod 46. Thus, since control of a large load is 
performed, the pressure force applied to the grinding shaft 22 can be 
controlled with high precision. 
By rotating and driving the upper grinding wheel 24 and the lower grinding 
wheel 13 under condition that a predetermined pressure force is applied, 
both surfaces of each work W are simultaneously processed. After 
completion of the processing, conduction through the switch valve 57a is 
stopped and the conduction to the switch valve 57b is made, so the 
grinding shaft 22 is moved up by a predetermined stroke. The grinding head 
21 is moved up by the head elevation motor 63, and the works W are picked 
out from the grinding apparatus. 
In the present embodiment, explanations has been made of a case where 
grinding wheels as grinding tools are respectively set on the upper platen 
23 and the lower platen 12, to perform the process of grinding the works. 
However, the grinding apparatus shown in the figures is applicable to the 
case where polishing process is performed. The grinding process and the 
polishing process are totally called grinding-polishing process. The 
polishing process includes lapping for adjusting dimension errors of works 
and for improving the surface finish, and includes polishing for forming a 
mirror surface with high precision. A buff or the like is used as a 
polishing tool in each case. In case of the lapping, alumina powder, 
silicon carbide powder, glass powder, diamond powder, or the like is used 
as abrasive grains for lapping. In case of the polishing, abrasive grains 
having much smaller grains than those for the lapping are used. 
The present invention should not be limited to the embodiment described 
above, and may be variously modified within the scope of the invention not 
departing from the gist. 
For example, although the embodiment has been explained with reference to 
the case of grinding both surfaces of each work, the present invention is 
applicable to a case where only one surface of each work is ground. In 
this case, works are not provided on the lower grinding wheel but are 
directly provided on a rotation table or a fixed table. Also, the present 
invention is applicable not only to the case where a plurality of works 
are processed simultaneously but also to the case where works are 
processed one after another. Although the pneumatic cylinders 35 and 45 
are used in the case shown in the figures, any fluid can be used as long 
as the cylinders are of a type such as a hydraulic cylinder that uses 
fluid as its operation medium. The work is not limited to an aluminum 
substrate but a glass substrate can be ground and/or polished. 
According to the present invention, a pressure force depending on a primary 
load is directly applied to a grinding shaft by a primary fluid pressure 
cylinder applied with a first fluid pressure, and a pressure force 
depending on a secondary load is indirectly applied to the grinding shaft 
through a lever member as for a secondary fluid pressure cylinder applied 
with a second pressure higher than the first fluid pressure. Therefore, 
the secondary load can be controlled with high precision, so the pressure 
force applied to the grinding shaft can be controlled with high precision. 
As a result, the ground surfaces of the works are applied with a pressure 
force with fewer errors, and the works can be ground with high precision.