[DESCRIPTION]
[Title of Invention]
DEFLECTION CORRECTION DEVICE FOR RAM
[Technical Field]
[0001]
The present invention relates to a deviation correction device for a ram in a
machining tool provided with a saddle moving vertically along a guide of a column
and a ram housing a main shaft unit and fit into the saddle slidably in a horizontal
direction.
[Background Art]
[0002]
A ram of a horizontal boring machine houses the main shaft unit and is fit into
the saddle slidably in the horizontal direction. The ram is supported by the saddle
moving vertically along the guide of the column in a cantilever state. Specifically, as
shown in FIG.ll illustrating the invention of Patent Literature 1, JP62-47125A, the
saddle 13 moves vertically along the guide of the column 14.
In the saddle 13, the ram 1 housing the main shaft unit is fitted slidably in the
horizontal direction.
The saddle 13, the ram I and other parts are connected to balance weights 20
and 21 by a hanger to balance the saddle 13, the ram 1 and other devices with the
balance weights 20 and 21.
[0003]
As described above, the ram of the horizontal boring machine is fitted in the
saddle 13 slidably in the horizontal direction. With one side the ram being supported
by the saddle 13 moving vertically along the guide of the column 14, when the ram 1
is retracted as shown in FIG.12A, there is substantially no deflection of the ram 1.
However, when the ram 1 is extended, the ram moves in a direction of an arrow W in
a cantilever state, causing the ram 1 to bed from a centerline la to a deflection line lb
ofFIG.12B.
Patent Literature 2, JP2003-103434A proposes a solution to the above issue.
[0004]
In Patent Literature 2, JP2003-103434A, a pair of ball screws are provided to
support a main shaft head (saddle) movably in the vertical direction and the main
shaft head supports the ram slidably in the horizontal direction. The ball screw on a
- 1-
front side in a direction of the ram movement is driven by a first servomotor and the
other ball screw is driven by a second servomotor. When the ram extends forward to
the front side, the ball screw on the front side is turned more compared to a main
shaft movement command before correction to lift the main shaft, whereas the other
ball screw is turned less to lower the rear side of the main shaft head, thereby
maintaining a balance of the main shaft head horizontally.
In this manner, a guide surface of the ram is balanced horizontally in the
above manner, preventing a tip of the main shaft head at the tip of the ram from
being displaced.
[0005]
According to Patent Literature 2, JP2003-103434A, there is no need for the
balancing weights of the saddle, the ram and other devices. However, moving the
saddle and the ram requires turning of the pair of the ball screws according to the
main shaft movement data. Thus, the position control of the ram requires
significant power and the devices for turning the ball screws, for setting the main
shaft movement data or the like become expensive.
[Citation List]
[Patent Literature]
[0006]
[Patent Literature l]
JP62-047125A
[Patent Literature 2]
JP2003-103434A
[Summary of Invention]
[Technical Problem]
[0007]
In view of the above issues, it is an object of the present invention is to
provide a machining tool provided with a ram, which has a simple structure and an
inexpensive device cost, and is capable of correcting a deflection of a tip of a main
shaft unit caused by extending the ram.
[Solution to Problem]
[0008]
In view of the above issues, a first aspect of the present invention is a
deflection correction device for a ram in a machining tool which is provided with a
- 2 -
saddle moving vertically along a guide of a column and the ram housing a main shaft
unit and being fitted in the saddle slidably in a horizontal direction, the device
including, but not limited to^
a plurality of hydrostatic bearings via which the saddle is supported by the
column in a longitudinal direction of the column; and
a control unit which controls a hydraulic pressure of the hydrostatic bearing in
accordance with a vertical displacement of the ram to maintain a straightness of the
ram in a direction of a main shaft of the ram so as to correct a misalignment of the
main shaft unit by an inclination of the saddle caused by controlling the hydraulic
pressure.
[0009]
In the first aspect of the present invention, it is preferable that the control
unit controls a hydraulic pressure of one of the plurality of the hydrostatic bearings
supporting the saddle in the longitudinal direction of the column so as to maintain
the straightness of the ram in the direction of the main shaft of the ram, the one of
the hydrostatic bearings being in an extending direction of the ram and below the
main shaft of the main shaft unit.
[0010]
In the first aspect of the present invention, it is also preferable that the control
unit controls a hydraulic pressure of another of the hydrostatic bearings in addition to
the one of the hydrostatic bearings which is arranged in the extending direction of the
ram and below the main shaft of the main shaft unit so as to maintain the
straightness of the ram in the direction of the main shaft of the ram, the another of
the hydrostatic bearings being arranged symmetrically to the one of the hydrostatic
bearings with respect to an intersection of the main shaft of the main shaft unit and a
center line of the column that run at right angles to each other.
[0011]
A second aspect of the present invention is a deflection correction device for a
ram in a machining tool which is provided with a saddle moving vertically along a
guide of a column and the ram housing a main shaft unit and being fitted in the
saddle slidably in a horizontal direction, the device including, but not limited toa
plurality of hydrostatic bearings via which the ram is supported by the
saddle in a longitudinal direction of the ramJ and
a control unit which controls a hydraulic pressure of the hydrostatic bearing in
accordance with a vertical displacement of the ram to maintain a straightness of the
ram in a direction of a main shaft of the ram so as to correct a misalignment of the
• 3 -
main shaft unit by an inclination of the saddle caused by controlling the hydraulic
pressure.
[0012]
In the second aspect of the present invention, it is preferable that the control
unit controls a hydraulic pressure of one of the plurality of the hydrostatic bearings
supporting the ram to the saddle so as to maintain the straightness of the ram in the
direction of the main shaft of the ram, the one of the hydrostatic bearings being
arranged in an extending direction of the ram and below a main shaft of the main
shaft unit.
[0013]
In the second aspect of the present invention, it is also preferable that the
control unit controls a hydraulic pressure of another of the hydrostatic bearings in
addition to the one of the hydrostatic bearings which is arranged in the extending
direction of the ram and below the main shaft of the main shaft unit so as to maintain
the straightness of the ram in the direction of the main shaft of the ram, the another
of the hydrostatic bearings being arranged symmetrically to the one of the hydrostatic
bearings with respect to an intersection of the main shaft of the main shaft unit and a
center line of the saddle that run at right angles to each other.
[0014]
The above deflection correction device may further include a restricting device
which regulates an amount of oil supplied to the hydrostatic bearing and a hydraulic
pressure sensor which measures the hydraulic pressure of the oil supplied to each of
the hydrostatic bearings and the control unit may control a restriction amount of the
restricting device so that the hydraulic pressure becomes a target hydraulic pressure
of the hydrostatic bearing based on a hydraulic pressure detected by the hydraulic
pressure sensor.
Further, the above deflection correction device may further include a
restricting device which regulates an amount of oil supplied to the hydrostatic
bearing and the control unit may control a restriction amount of the restricting device
so that the restriction amount of the restricting device becomes a target restriction
amount which is calculated to achieve a target hydraulic pressure of the hydrostatic
bearing.
[Advantageous Effects of Invention]
[0015]
In the present invention, according to the correction process performed by the
control unit, the saddle is supported by the column in a longitudinal direction of the
- 4 -
column via a plurality of hydrostatic bearings and a hydraulic pressure of the
hydrostatic bearing is controlled by the control unit in accordance with a vertical
displacement of the ram to maintain a straightness of the ram in a direction of a main
shaft of the ram so as to correct a misalignment of the main shaft unit by an
inclination of the saddle caused by controlling the hydraulic pressure.
Further, the ram is supported by the saddle in a longitudinal direction of the
ram via a plurality of hydrostatic bearings and a hydraulic pressure of the hydrostatic
bearing is controlled by the control unit in accordance with a vertical displacement of
the ram to maintain a straightness of the ram in a direction of a main shaft of the
ram so as to correct a misalignment of the main shaft unit by an inclination of the
saddle caused by controlling the hydraulic pressure.
Therefore, according to the present invention, it is possible to maintain the
straightness of the ram in the direction of the main shaft by the above correction
method, thereby achieving a high machining accuracy.
Further, by adjusting the hydraulic pressure of the plurality of the hydrostatic
bearings, the balance weights are no longer needed, as was the case of the related art.
It is now possible to achieve the high machining accuracy by the device with a simple
structure and an inexpensive device cost.
[0016]
Among the plurality of the hydrostatic bearings supporting the saddle in the
longitudinal direction of the column, a hydraulic pressure of the one of the hydrostatic
bearings which is arranged in the extending direction of the ram and below the main
shaft of the main shaft unit is controlled by the control unit so as to maintain the
straightness of the ram in the direction of the main shaft of the ram. Therefore, by
inclination of the saddle caused by controlling the hydraulic pressure, the
straightness of the ram in the direction of the main shaft can be maintained.
Among the plurality of the hydrostatic bearings supporting the ram to the
saddle, a hydraulic pressure of the one of the hydrostatic bearings which is arranged
in an extending direction of the ram and below a main shaft of the main shaft unit is
controlled by the control unit so as to maintain the straightness of the ram in the
direction of the main shaft of the ram. Therefore, by inclining the ram in response to
controlling of the hydraulic pressure, the straightness of the ram in the direction of
the main shaft can be maintained.
[0017]
Among the plurality of the hydrostatic bearings supporting the saddle in the
longitudinal direction of the column, a hydraulic pressure of another of the
- 5 -
hydrostatic bearings in addition to the one of the hydrostatic bearings is controlled by
the control unit so as to maintain the straightness of the ram in the direction of the
main shaft of the ram. The another of the hydrostatic bearings being arranged
symmetrically to the one of the hydrostatic bearings with respect to an intersection of
the main shaft of the main shaft unit and a center line of the column that run at right
angles to each other. For instance, it is possible to correct the misalignment of the
main shaft unit by the inclination of the saddle in response to controlling of the
hydraulic pressures of a pair of the hydrostatic bearings 2a and 3a as shown in FIG.2.
The misalignment of the main shaft unit can be corrected more significantly than the
case of using one hydrostatic bearing to correct the misalignment. This allows for a
greater extension amount of the rum.
Further, the load capability of the hydrostatic bearing supporting the tip of the
ram increases and thus, it is possible to withstand the weight increase of the ram
such as addition of attachments.
[0018]
In a similar manner, among the plurality of the hydrostatic bearings supporting the
ram to the saddle, a hydraulic pressure of another of the hydrostatic bearings is
controlled by the control unit in addition to the one of the hydrostatic bearings which
is arranged in the extending direction of the ram and below the main shaft of the
main shaft unit so as to maintain the straightness of the ram in the direction of the
main shaft of the ram. The another of the hydrostatic bearings is arranged
symmetrically to the one of the hydrostatic bearings with respect to an intersection of
the main shaft of the main shaft unit and a center line of the saddle that run at right
angles to each other. Specifically, the misalignment of the main shaft unit is
corrected by the inclination of the ram in response to controlling of the hydraulic
pressures of a pair of the hydrostatic bearings. The misalignment of the main shaft
unit can be corrected more significantly than the case of using one hydrostatic
bearing to correct the misalignment. This allows for a greater extension amount of
the rum.
Further, the load capability of the hydrostatic bearing supporting the tip of the
ram increases and thus, it is possible to withstand the weight increase of the ram
such as addition of attachments.
[0019]
The above deflection correction device is also provided with a restricting device
which regulates an amount of oil supplied to the hydrostatic bearing and a hydraulic
pressure sensor which measures the hydraulic pressure of the oil supplied to each of
- 6 -
the hydrostatic bearings and the control unit controls a restriction amount of the
restricting device so that the hydraulic pressure becomes a target hydraulic pressure
of the hydrostatic bearing based on a hydraulic pressure detected by the hydraulic
pressure sensor. Therefore, the misalignment of the main shaft unit caused by the
deflection of the ram is corrected by performing the feedback control of the measured
pressure of each hydrostatic bearing detected by the hydraulic pressure sensor. As a
result, the pressure of the hydrostatic bearing can be kept at the appropriate value
with high precision.
[0020]
Alternatively, the above deflection correction device is also provided with a
restricting device which regulates an amount of oil supplied to the hydrostatic
bearing and the restriction amount of the restricting device is controlled so that the
restriction amount of the restricting device becomes a target restriction amount which
is calculated to achieve a target hydraulic pressure of the hydrostatic bearing.
Therefore, it is also possible to provide no hydraulic pressure sensor.
[Brief Description of Drawings]
[0021]
[FIG.l] FIG.IA and FIG.IB show structures of a combined unit of a column, a
saddle and a ram in relation to a first embodiment.
[FIG.2] FIG.l shows a structure of the combined unit of the column, the saddle
and the ram in relation to a second embodiment.
[FIG.3] FIG.3 shows a structure of the combined unit of the column, the saddle
and the ram in relation to a third embodiment.
[FIG.4] FIG.4 shows a structure of the combined unit of the column, the saddle
and the ram in relation to a fourth embodiment.
[FIG.5] FIG.5 shows a structure of the combined unit of the column, the saddle
and the ram in relation to a fifth embodiment.
[FIG.6] FIG.6 is a flow chart of a control unit for correcting a position of a main
shaft unit by an inclination of the saddle caused by increasing the hydraulic pressure
in relation to the first embodiment.
[FIG.7] FIG.7 is a flow chart of the control unit for correcting the position of the
main shaft unit by the inclination of the saddle caused by increasing the hydraulic
pressure in relation to the second embodiment.
[FIG.8] FIG.8 is a flow chart of the control unit for correcting the position of the
main shaft unit by an inclination of the ram caused by increasing the hydraulic
- 7 -
pressure in relation to the third embodiment.
[FIG.9] FIG.9 is a flow chart of the control unit for correcting the position of the
main shaft unit by the inclination of the ram caused by increasing the hydraulic
pressure in relation to the fourth embodiment.
[FIG. 10] FIG.IO is a flow chart of the control unit for correcting the position of
the main shaft unit by the inclination of the ram caused by increasing the hydraulic
pressure in relation to the fifth embodiment.
[FIG.ll] FIG.ll is a schematic perspective view of a horizontal boring tool of
related art.
[FIG. 12] FIG. 12 shows an engagement of the ram and the saddle.
[Description of Embodiments]
[0022]
Embodiments of the present invention will now be described in detail with
reference to the accompanying drawings. It is intended, however, that unless
particularly specified, dimensions, materials, shape, its relative positions and the like
shall be interpreted as illustrative only and not limitative of the scope of the present
invention.
[FIRST EMBODIMENT]
[0023]
FIG.IA and FIG. IB show structures of a combined unit of a column, a saddle
and a ram in relation to a first embodiment. The rest of the structure is similar to
the structure shown in FIG.ll except for the balance weights 21 and 22 (the structure
with the part 19 in a dotted area removed from FIG.ll).
FIG.IA and FIG.IB show a column 14, a saddle 13 moving vertically along a
guide of the column 14 and a ram 1 housing a main shaft unit 15 and being slidably
fit in the saddle 13 in a horizontal direction.
The saddle 13 is supported at both sides by four hydrostatic bearings, two
hydrostatic bearings 2a and 2b being arranged on a front side in a extending direction
of the ram 1 and two hydrostatic bearings 3a and 3b being arranged on a root side of
the ram 1.
[0024]
A hydraulic pump 8 supplies the oil to the hydrostatic bearing 2a via a variable
restricting device 6. A controller 10 controls a restriction amount of the restricting
device 6. Among the hydrostatic bearings 2a, 2b, 3a and 3b supporting the saddle 13
in the longitudinal direction of the column 14, the hydrostatic bearing 2a is arranged
- 8 -
in an extending direction of the ram 1 and below the main shaft of the main shaft unit
15. The hydraulic pressure of the hydrostatic bearing 2a is controlled.
[0025]
From a stop state (or an almost-stop state) as shown in FIG.lA to an operation
state as shown in FIG. IB, the ram 1 moves in a direction of an arrow Y. As shown in
FIG. IB, the ram 1 supported by the saddle 13 at one side, moves leftward from the
saddle 13, increasing a projection amount from a support position.
At the same time, the controller 10 increases a pressure of the hydrostatic
bearing 2 by regulating the restriction amount of the variable restricting device 6 and
the saddle is lifted in a direction of an arrow Z of FIG. IB by means of the hydrostatic
bearing 2a.
By this, the saddle 13 inclines, thereby lifting a side of the ram 1, which is on
the main shaft unit side 15 in a direction of an arrow Z of FIG.IB. A line l u shown
in FIG.IB indicates a horizontal line.
In this manner, a straightness of the ram 1 in a direction of the main shaft
unit 15 is maintained.
[0026]
In order to maintain the straightness in the direction of the main shaft Is of
the ram 1, the controller 10 performs such control to increase the hydraulic pressure
Pr2a of the hydrostatic bearing 2a in accordance with a vertical displacement of the
ram 1, i.e. a deflection 6, thereby correcting the deflection 5 by the inclination of the
saddle caused by the increased hydraulic pressure Praa as shown in FIG.6.
[0027]
FIG.6 is a flow chart of a control unit for correcting a position of the main shaft
unit by the inclination of the saddle caused by increasing the hydraulic pressure.
In FIG.6, in a step SI, an extending amount X of the ram 1, and based on the
detected value, the following correction is performed.
In a step S2, the amount of deflection, 5 is estimated from a formula (l).
8=(WaX3/3EI)+(wX4/8EI) (l)
where Wa is a weight of an attachment, w is a uniformly distributed load, E is a
longitudinal elastic modulus (self-weight) and I is a second moment of area of the ram
1.
In order to correct the amount of deflection 6, in a step S3, an angle 9 of the
upward inclination of the ram 1 is estimated from a formula (2).
e=tani(y/x) (2)
where y and x are angles of inclination.
- 9 -
[0028]
In a step S4, a flow coefficient Ki of the hydrostatic bearing i is estimated.
In a step S5, a pressure Pn of the hydrostatic bearing i (the hydrostatic
bearings 2b, 3a and 3b excluding the controlled hydrostatic bearing 2a) at the
inclination angle 9, is obtained from a formula (3).
Pri=(l/(1+Ki/Kci))- Psi (3)
where Kci is a flow coefficient of a variable restricting device i and Psi is a supply pressure
of the hydrostatic bearing i.
[0029]
In a step S6, a load weight Wi of the hydrostatic bearing i at the inclination angle 0,
is obtained from a formula (4).
Wi=Ai- Pri (4)
where Ai is an effective area of the hydrostatic bearing i.
In a step S7, a load weight W2a of the hydrostatic bearing 2a is obtained. The
symbols that are not explained herein are shown in FIG. IB.
M+W3bL3b+W2bL2b=W2aL2a+W3aL3a (5)
where M is a rotation moment acting to turn the saddle by self-weights of the ram,
the attachment, and the saddle.
In a step S8, a pressure Pr2a of the hydrostatic bearing 2a is obtained from a
formula (6).
Pr2a=W2a/A2a (6)
In steps S9 and SIO, a flow coefficient Kc2a of the variable restricting device 6
to achieve the pressure Pr2a, is obtained, and the restriction amount of the variable
restricting device 6 is adjusted to a restriction length Se to achieve the flow coefficient
Kc2a. The restriction length is an adjustment amount of restriction of the restricting
device 6.
[0030]
In order to achieve the obtained hydraulic pressure of the hydrostatic bearing,
the restriction amount is controlled in accordance with the flow coefficient. Thus,
the control configuration can be simplified without a hydraulic pressure sensor.
[0031]
According to the above correction process by the controller 10, the
misalignment of the main shaft unit 15 can be corrected by an inclination 9 of the
saddle 13 caused by increasing the hydraulic pressure Pr2a in accordance with the
vertical displacement of the ram 1, i.e. the deflection 8, so as to maintain the
straightness of the ram 1 in the direction of the main shaft Is.
• 10-
[0032]
According to the first embodiment, it is possible to maintain the straightness
of the ram 1 in the direction of the main shaft Is by the above correction method,
thereby achieving a high machining accuracy.
Further, by adjusting the hydraulic pressure of the hydrostatic bearings and a
state of the variable restricting device, unlike the case of the related art, the balance
weights (the parts in the dotted area 19 of FIG.ll) are no longer needed. It is now
possible to achieve the high machining accuracy by the device with a simple structure
and an inexpensive device cost.
[SECOND EMBODIMENT]
[0033]
A second embodiment of the present invention is explained in reference to
FIG.2.
The basic structure is the same as that of the first embodiment. The saddle
13 is supported at both sides by four hydrostatic bearings, two hydrostatic bearings
2a and 2b being arranged on the front side in the extending direction of the ram 1 and
two hydrostatic bearings 3a and 3b being arranged on the root side of the ram 1.
[0034]
The hydraulic pump 8 supplies the oil to the hydrostatic bearing 2a via the
variable restricting device 6 and to the hydrostatic bearing 3a via a variable
restricting device 7. The controller 10 controls the restriction amount of the
restricting device 6 and a restriction amount of the restricting device 7.
Among the hydrostatic bearings 2a, 2b, 3a and 3b supporting the saddle 13 in
the longitudinal direction of the column 14, the hydrostatic bearing 2a is arranged in
the extending direction of the ram 1 and below the main shaft of the main shaft unit
15. The hydraulic pressure of the hydrostatic bearing 2a is controlled and the
hydrostatic bearing 3a is arranged symmetrically to the hydrostatic bearing 2a with
respect to an intersection Cl of the main shaft of the main shaft unit 15 and a center
line of the column 14 that run at right angles to each other. The controller 10
controls the hydraulic pressures of the hydrostatic bearings 2a and 3a.
[0035]
From a stop state (or an almost-stop state) as shown in FIG.2 to an operation
state, the ram 1 moves in the direction of an arrow Y and the ram 1 supported by the
saddle 13 at one side moves leftward from the saddle 13, causing a center line A to
deflect to a center line B.
Meanwhile, the controller 10 regulates the restriction amount of the variable
- 11-
restricting device 6 to increases the pressure of the hydrostatic bearing 2a and also
regulates the restriction amount of the variable restricting device 7 to increase the
pressure of the hydrostatic bearing 3a.
[0036]
Then, the saddle 13 is lifted in a direction of an arrow F of FIG.2 by means of
the hydrostatic bearing 2a on the front side in the extending direction of the ram 1.
At the same time, the saddle is lowered in a direction of an arrow F2 of FIG.2 by
means of the hydrostatic bearing 3a on a side opposite to the front side.
By this, a position of a tip of the ram 1 changes onto a center axis of the ram 1
in a non-deflection state as indicated by an arrow S in FIG.2, thereby maintaining the
straightness of the ram 1 in the direction of the main shaft unit 15.
[0037]
In order to maintain the straightness of the saddle 13 in the direction of the
main shaft Is, the controller 10 performs the control to increase the hydraulic
pressures Pr2a and Pr3a of the hydrostatic bearings 2a and 3a in accordance with a
vertical displacement of the saddle 13, i.e. a deflection 6, thereby correcting the a
misalignment of the main shaft unit 15 by the inclination angle 9 of the saddle 13
caused by the increased hydraulic pressures Pr2a and Prsa as shown in FIG.7.
FIG.7 is a flow chart of the control unit for correcting the position of the main
shaft unit according to the second embodiment.
In FIG.7, a flow coefficient Kcsa of the variable restricting device 7 of the
hydrostatic bearing 3a is obtained from a database obtained beforehand in accordance
with the amount of deflection 8 of the tip of the saddle 13 calculated in a step S12.
The flow coefficient Kc3a of the variable restricting device 7 is used to calculate
Pri in a step S15 and also to calculate a restriction length S? of the restriction amount
in a step S20.
The rest of the process is substantially the same as that of the first
embodiment.
[0038]
According to the correction method performed by the controller 10, it is
possible to maintain the straightness of the saddle 13 in the direction of the main
shaft Is by means of the hydrostatic bearings 2a and 3a. The misalignment of the
main shaft unit 15 caused by the deflection 5 of the saddle 13 can be corrected more
significantly than the first embodiment. This allows for a greater extension amount
of the rum 1.
Further, the load capability of the hydrostatic bearing supporting the tip of the
• 12-
ram 1 increases and thus, it is possible to withstand the weight increase of the ram 1
such as addition of attachments.
[THIRD EMBODIMENT]
[0039]
FIG.3 shows a structure of the combined unit of the column, the saddle and the
ram in relation to a third embodiment.
FIG.3 shows the saddle 13 moving vertically along the guide of the column 14
(see FIG. 11) and the ram 1 housing the main shaft unit 15 and being slidably fit in
the saddle 13 in a horizontal direction.
The ram 1 is supported by four hydrostatic bearings at upper and lower sides
in a longitudinal direction of the ram 1. A pair of hydrostatic bearings 20a and 20b
are arranged on the lower side and another pair of hydrostatic bearings 30a and 30b
are arranged on the upper side.
[0040]
The hydraulic pump 8 supplies the oil to the hydrostatic bearing 20a via a
variable restricting device 61. The controller 10 controls a restriction amount of the
restricting device 61. Among the hydrostatic bearings 20a, 20b, 30a and 30b
supporting the ram 1 to the saddle 13, the hydrostatic bearing 20a is arranged in the
extending direction of the ram 1 and below the main shaft of the main shaft unit 15.
The hydraulic pressure of the hydrostatic bearing 2a is controlled.
[0041]
From a stop state (or an almost-stop state) as shown in FIG.3 to an operation
state, the ram 1 moves in the direction of an arrow Y and the ram 1 supported by the
saddle 13 at one side moves leftward from the saddle 13, causing a center line A to
deflect to a center line B.
Meanwhile, the controller 10 regulates the restriction amount of the variable
restricting device 61 to increases the pressure of the hydrostatic bearing 20a. Thus,
a side of the ram 1 which is on the side of the main shaft unit 15, is lifted in a
direction of an arrow F of FIG.3 by means of the hydrostatic bearing 20a.
By this, a position of a tip of the ram 1 changes onto the center axis of the ram
1 in a non-deflection state as indicated by an arrow S in FIG.3, thereby maintaining
the straightness of the ram 1 in the direction of the main shaft unit 15.
[0042]
In order to maintain the straightness of the ram 1 in the direction of the main
shaft Is, the controller 10 performs a control to increase the hydraulic pressure Pr20a
of the hydrostatic bearing 20a in accordance with a vertical displacement of the ram 1,
- 13-
i.e. a deflection 5, thereby correcting a misalignment of the main shaft unit 15 by the
inclination of the ram 1 caused by the increased hydraulic pressure Pr20a as shown in
FIG.8.
In a step S37 of FIG.8, a load weight W20a of the hydrostatic bearing 20a is
obtained from a formula (5).
W20a=W+W30b+W30a-W20b (S)
where W is a weight of the ram 1 and the attachment. The symbols that are not
explained herein are already described in FIG.3.
The rest of the structure is substantially the same as the first embodiment.
[0043]
According to the correction method performed by the controller 10, it is
possible to maintain the straightness of the ram 1 in the direction of the main shaft
Is. The misalignment of the main shaft unit 15 can be corrected by increasing the
hydraulic pressure Pr20a of the hydrostatic bearing 20a in accordance with the vertical
displacement of the ram 1, i.e. the deflection 6.
[FOURTH EMBODIMENT]
[0044]
FIG.4 shows a structure of the combined unit of the column, the saddle and the
ram in relation to a fourth embodiment.
FIG.4 shows the saddle 13 moving vertically along the guide of the column 14
(see FIG.ll) and the ram 1 housing the main shaft unit 15 and being slidably fit in
the saddle 13 in the horizontal direction.
The ram 1 is supported by four hydrostatic bearings at upper and lower sides
in the longitudinal direction of the ram 1. Two hydrostatic bearings 20a and 20b are
arranged on the lower side and two hydrostatic bearings 30a and 30b are arranged on
the upper side.
[0045]
The hydraulic pump 8 supplies the oil to the hydrostatic bearing 20a via a
variable restricting device 32 and to the hydrostatic bearing 30a via a variable
restricting device 33. The controller 10 controls a restriction amount of the
restricting device 32 and a restriction amount of the restricting device 33. Among
the hydrostatic bearings 20a, 20b, 30a and 30b supporting the ram 1 to the saddle 13,
the hydrostatic bearing 20a is arranged in the extending direction of the ram 1 and
below the main shaft of the main shaft unit 15 and the hydrostatic bearing 30a is
arranged symmetrically to the hydrostatic bearing 20a with respect to an intersection
C2 of the main shaft of the main shaft unit 15 and a center line of the saddle 13 that
- 14-
run at right angles to each other. The controller 10 controls the hydraulic pressures
of the hydrostatic bearings 20a and 30a
[0046]
From a stop state (or an almost-stop state) as shown in FIG.4 to an operation
state, the ram 1 moves in the direction of an arrow Y and the ram 1 supported by the
saddle 13 at one side moves leftward from the saddle 13, causing a center line A to
deflect to a center line B.
Meanwhile, the controller 10 regulates the restriction amount of the variable
restricting device 32 to increases the pressure of the hydrostatic bearing 20a and also
regulates the restriction amount of the variable restricting device 33 to increase the
pressure of the hydrostatic bearing 30a.
[0047]
Therefore, a side of the ram 1, which is on the main shaft unit side 15, is lifted
by means of the hydrostatic bearing 20a in a direction of an arrow F l of FIG.4 and
simultaneously the ram 1 is pushed downward in a direction of an arrow F2 by means
of the hydrostatic bearing 30a which is on the side opposite to the extending direction.
By this, a position of a tip of the ram 1 changes onto a center axis of the ram 1
in a non-deflection state as indicated by an arrow S in FIG.3, thereby maintaining the
straightness of the ram 1 in the direction of the main shaft unit 15.
[0048]
In order to maintain the straightness of the ram 1 in the direction of the main
shaft Is, the controller 10 performs a control to increase the hydraulic pressures Pr20a
and Praoa of the hydrostatic bearings 20a and 30a in accordance with a vertical
displacement of the ram 1, i.e. the deflection 6, thereby correcting the a misalignment
of the main shaft unit 15 by the inclination angle 9 of the ram 1 caused by the
increased hydraulic pressures Pr20a and Praoa as shown in FIG.9.
FIG.9 is a flow chart of a control unit for correcting a position of the main shaft
unit.
In FIG.9, a flow coefficient Kcsoa of the variable restricting device 33 of the
hydrostatic bearing 30a is calculated from a database obtained beforehand in
accordance with the amount of deflection 8 of the tip of the ram 1 calculated in a step
S52.
The flow coefficient Kcaoa of the variable restricting device 33 is used in the
formula for the pressure Pri in a step S55 and also to calculate the adjustment
amount of restriction S33 of the restriction amount in a step S60.
The rest of the process is substantially the same as that of the third
- 15-
embodiment.
[0049]
According to the correction method performed by the controller 10, it is
possible to maintain the straightness of the ram 1 in the direction of the main shaft
Is by means of the hydrostatic bearings 20a and 30a. The misalignment of the main
shaft unit 15 caused by the deflection 6 of the ram 1 can be corrected more
significantly than the third embodiment. This allows for a greater extension amount
of the rum 1.
Further, the load capability of the hydrostatic bearing supporting the tip of the
ram 1 increases and thus, it is possible to withstand the weight increase of the ram 1
such as addition of attachments.
[FIFTH EMBODIMENTl
[0050]
FIG.5 shows a structure of the combined unit of the column, the saddle and the
ram in relation to a fifth embodiment.
FIG.5 shows the saddle 13 moving vertically along the guide of the column 14
(see FIG. 11) and the ram 1 housing the main shaft unit 15 and being slidably fit in
the saddle 13 in the horizontal direction.
The ram 1 is supported by four hydrostatic bearings at upper and lower sides
in a longitudinal direction of the ram 1. Two hydrostatic bearings 20a and 20b are
arranged on the lower side and two hydrostatic bearings 30a and 30b are arranged on
the upper side.
[0051]
The hydraulic pump 8 supplies the oil to the hydrostatic bearing 20a via a
variable restricting device 32 and to the hydrostatic bearing 30a via the variable
restricting device 33. Further, the hydraulic pump 8 is connected to the hydrostatic
bearing 20b via the variable restricting device 34 and to the hydrostatic bearing 30b
via the variable restricting device 35.
[0052]
The controller 10 controls the restriction amounts of the variable restricting
devices 32 and 33. Further, the controller 10 controls the restriction amounts of the
variable restricting devices 34 and 35.
In the oil path of each of the hydrostatic bearings 20a, 20b, 30a and 30b, a
hydraulic pressure sensor 37, 38, 39, 40 is provided to measure the hydraulic pressure
of the oil in each oil path. The measured pressure is inputted from the hydraulic
pressure sensor 37, 38, 39, 40 to the controller 10.
- 16-
[0053]
From a stop state (or an almost-stop state) as shown in FIG.5 to an operation
state, the ram 1 moves in the direction of an arrow Y and the ram 1 supported by the
saddle 13 at one side moves leftward from the saddle 13, causing a center line A to
deflect to a center line B.
Meanwhile, the controller 10 regulates the restriction amount of the variable
restricting device 34 to increases the pressure of the hydrostatic bearing 20a and also
regulates the restriction amount of the variable restricting device 35 to increase the
pressure of each of the hydrostatic bearings 20a, 20b, 30a and 30b at an appropriate
value based on the measured pressure inputted from the
[0054]
The controller 10 adjusts the pressure of the hydrostatic bearing 20a, 20b, 30a,
30b based on the measured pressure inputted from the hydraulic pressure sensor 37,
38, 39, 40. Specifically, based on the measured pressure inputted from the hydraulic
pressure sensor 37, 38, 39, 40, the pressure of the hydrostatic bearings 20a and 20b
and the pressure of the hydrostatic bearings 30a and 30b can be kept at the
prescribed appropriate value.
Therefore, a side of the ram 1, which is on the main shaft unit side 15, is lifted
by means of the hydrostatic bearing 20a in a direction of an arrow Fl of FIG.5 and
simultaneously the ram 1 is pushed downward in a direction of an arrow F2 by means
of the hydrostatic bearing 30a which is on the side opposite to the extending direction.
By this, a position of a tip of the ram 1 changes onto a center axis of the ram 1
in a non-deflection state as indicated by an arrow S in FIG.5, thereby maintaining the
straightness of the ram 1 in the direction of the main shaft unit 15.
[0055]
In order to maintain the straightness of the ram 1 in the direction of the main
shaft Is, the controller 10 performs a control to increase the hydraulic pressures Pr20a
and Praoa of the hydrostatic bearings 20a and 30a in accordance with the vertical
displacement of the ram 1, i.e. the deflection 6, thereby correcting the a misalignment
of the main shaft unit 15 by the inclination angle 9 of the ram 1 caused by the
increased hydraulic pressures Pr20a and Praoa as shown in FIG. 10.
FIG. 10 is a flow chart of a control unit for correcting a position of the main
shaft unit.
In FIG. 10, a flow coefficient Kcaoa of the variable restricting device 33 of the
hydrostatic bearing 30a is calculated from a database obtained beforehand in
accordance with the amount of deflection 5 of the tip of the ram 1 calculated in a step
- 17-
S72.
The flow coefficient Kcsoa of the variable restricting device 33 is used in the
formula for the pressure Pn in a step S75 and also to calculate the adjustment
amount of restriction S33 of the restriction amount in a step S80.
[0056]
After the step S80 of FIG. 10, the hydraulic pressure of each of the hydrostatic
bearing is detected by the pressure sensor 37, 38, 39, 40 in a step S81.
Next, in a step S82, it is determined if the pressure Pn is at the target
pressure. If the pressure Pn is not at the target pressure, the restriction amount of
each variable restriction device is adjusted.
The rest is substantially the same as that of the fourth embodiment.
[0057]
According to the correction method performed by the controller 10, the
misalignment of the main shaft unit 15 is corrected by performing the feedback
control of the measured pressure of each hydrostatic bearing detected by the
hydraulic pressure sensor 37, 38, 39, 40 so as to maintain the straightness of the ram
1 in the direction of the main shaft Is. As a result, the misalignment of the main
shaft unit 15 can be corrected with high precision.
[0058]
It is, of course, possible to combine the inclination correction of the saddle 13
with respect to the column 14 in relation to the first and second embodiments with
the inclination correction of the ram 1 with respect to the saddle 13 in relation to the
third to fifth embodiments so as to overall control the inclination correction of the
saddle 13 with respect to the column 14 and the inclination correction of the ram 1
with respect to the saddle 13.
[Industrial Applicability]
[0059]
According to the present invention, it is now possible to provide a machining
tool provided with a ram, which has a simple structure and an inexpensive device cost,
and is capable of correcting a deflection of a tip of a main shaft unit caused by
extending the ram.

[CLAIMS]
1. A deflection correction device for a ram in a machining tool which is provided
with a saddle moving vertically along a guide of a column and the ram housing a main
shaft unit and being fitted in the saddle slidably in a horizontal direction, the device
comprising:
a plurality of hydrostatic bearings via which the saddle is supported by the
column in a longitudinal direction of the column! and
a control unit which controls a hydraulic pressure of the hydrostatic bearing in
accordance with a vertical displacement of the ram to maintain a straightness
of the ram in a direction of a main shaft of the ram so as to correct a
misalignment of the main shaft unit by an inclination of the saddle caused by
controlling the hydraulic pressure.
2. The deflection correction device for the ram according to claim 1,
wherein the control unit controls a hydraulic pressure of one of the plurality of
the hydrostatic bearings supporting the saddle in the longitudinal direction of
the column so as to maintain the straightness of the ram in the direction of the
main shaft of the ram, the one of the hydrostatic bearings being in an
extending direction of the ram and below the main shaft of the main shaft unit.
3. The deflection correction device for the ram according to claim 2,
wherein the control unit controls a hydraulic pressure of another of the
hydrostatic bearings in addition to the one of the hydrostatic bearings which is
arranged in the extending direction of the ram and below the main shaft of the
main shaft unit so as to maintain the straightness of the ram in the direction of
the main shaft of the ram, the another of the hydrostatic bearings being
arranged symmetrically to the one of the hydrostatic bearings with respect to
an intersection of the main shaft of the main shaft unit and a center line of the
column that run at right angles to each other.
- 19-
4. A deflection correction device for a ram in a machining tool which is provided
with a saddle moving vertically along a guide of a column and the ram housing a main
shaft unit and being fitted in the saddle slidably in a horizontal direction, the device
comprising:
a plurality of hydrostatic bearings via which the ram is supported by the saddle
in a longitudinal direction of the ram; and
a control unit which controls a hydraulic pressure of the hydrostatic bearing in
accordance with a vertical displacement of the ram to maintain a straightness
of the ram in a direction of a main shaft of the ram so as to correct a
misalignment of the main shaft unit by an inclination of the saddle caused by
controlling the hydraulic pressure.
5. The deflection correction device for the ram according to claim 4,
wherein the control unit controls a hydraulic pressure of one of the plurality of
the hydrostatic bearings supporting the ram to the saddle so as to maintain the
straightness of the ram in the direction of the main shaft of the ram, the one of
the hydrostatic bearings being arranged in an extending direction of the ram
and below a main shaft of the main shaft unit .
6. The deflection correction device for the ram according to claim 5,
wherein the control unit controls a hydraulic pressure of another of the
hydrostatic bearings in addition to the one of the hydrostatic bearings which is
arranged in the extending direction of the ram and below the main shaft of the
main shaft unit so as to maintain the straightness of the ram in the direction of
the main shaft of the ram, the another of the hydrostatic bearings being
arranged symmetrically to the one of the hydrostatic bearings with respect to
an intersection of the main shaft of the main shaft unit and a center line of the
saddle that run at right angles to each other.
-20-
7. The deflection correction device for the ram according to any one of claims 1 to
6, further comprising^
a restricting device which regulates an amount of oil supplied to the hydrostatic
bearing," and
a hydraulic pressure sensor which measures the hydraulic pressure of the oil
supplied to each of the hydrostatic bearings,
wherein the control unit controls a restriction amount of the restricting device so
that the hydraulic pressure becomes a target hydraulic pressure of the
hydrostatic bearing based on a hydraulic pressure detected by the hydraulic
pressure sensor.
8. The deflection correction device for the ram according to any one of claims 1 to
6, further comprising:
a restricting device which regulates an amount of oil supplied to the hydrostatic
bearing,
wherein the control unit controls a restriction amount of the restricting device so
that the restriction amount of the restricting device becomes a target
restriction amount which is calculated to achieve a target hydraulic pressure of
the hydrostatic bearing.
Dated" this 11/01/2012