U.S. patent application number 12/160003 was filed with the patent office on 2009-04-16 for oil pressure unit and speed control method of motor in oil pressure unit.
This patent application is currently assigned to DAIKIN INDUSTRIES, LTD.. Invention is credited to Junichi Miyagi, Tetsuo Nakata, Yasuto Yanagida.
Application Number | 20090097986 12/160003 |
Document ID | / |
Family ID | 39135827 |
Filed Date | 2009-04-16 |
United States Patent
Application |
20090097986 |
Kind Code |
A1 |
Nakata; Tetsuo ; et
al. |
April 16, 2009 |
OIL PRESSURE UNIT AND SPEED CONTROL METHOD OF MOTOR IN OIL PRESSURE
UNIT
Abstract
An oil pressure unit includes an inverter arranged to supply
electric power to a motor; a load sensor arranged to detect a load
of the oil pressure pump; a rotation sensor arranged to detect a
rotation speed of the motor; a current command value calculation
part configured to calculate a current command value so that a
deviation between a speed command value representing a target
rotation speed of the motor and a rotation speed of the motor
converges to zero; a correction part configured to correct the
current command value based on the load of the oil pressure pump;
and a control signal generation part configured to output a control
signal to the inverter based on a corrected current command
value.
Inventors: |
Nakata; Tetsuo; (Shiga,
JP) ; Miyagi; Junichi; (Osaka, JP) ; Yanagida;
Yasuto; (Shiga, JP) |
Correspondence
Address: |
GLOBAL IP COUNSELORS, LLP
1233 20TH STREET, NW, SUITE 700
WASHINGTON
DC
20036-2680
US
|
Assignee: |
DAIKIN INDUSTRIES, LTD.
Osaka-shi, Osaka
JP
|
Family ID: |
39135827 |
Appl. No.: |
12/160003 |
Filed: |
August 27, 2007 |
PCT Filed: |
August 27, 2007 |
PCT NO: |
PCT/JP2007/066559 |
371 Date: |
July 3, 2008 |
Current U.S.
Class: |
417/44.2 |
Current CPC
Class: |
F04B 2203/0201 20130101;
F15B 2211/20576 20130101; F15B 11/0423 20130101; F04B 2205/05
20130101; F04B 49/065 20130101; F15B 2211/6309 20130101; F15B
2211/20538 20130101; F15B 2211/255 20130101; F04B 2203/0209
20130101; F15B 2211/20515 20130101; F15B 2211/6656 20130101; F15B
2211/633 20130101; F15B 2211/6651 20130101; F04B 49/20 20130101;
F15B 11/17 20130101; F04B 2201/1202 20130101 |
Class at
Publication: |
417/44.2 |
International
Class: |
F04B 49/06 20060101
F04B049/06 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 30, 2006 |
JP |
2006-233529 |
Claims
1. An oil pressure unit for supplying oil to an actuator by driving
an oil pressure pump with a motor, the oil pressure unit
comprising: an inverter arranged to supply electric power to the
motor; a load sensor arranged to detect a load of the oil pressure
pump; a rotation sensor arranged to detect a rotation speed of the
motor; a current command value calculation part configured to
calculate a current command value so that a deviation between a
speed command value representing a target rotation speed of the
motor and a rotation speed of the motor converges to zero; a
correction part configured to correct the current command value
based on the load of the oil pressure pump; and a control signal
generation part configured to output control signal to the inverter
based on a corrected current command value.
2. The oil pressure unit according to claim 1, wherein the
correction part corrects the current command value to raise the
rotation speed of the motor with an increase in the load of the oil
pressure pump.
3. The oil pressure unit according to claim 1, wherein the
correction part increases the current command value in response to
an increase in the load of the oil pressure pump.
4. The oil pressure unit according to claim 1, wherein the
correction part acquires a correction value using a correction
coefficient set in advance, and adds the correction value to the
current command value.
5. The oil pressure unit according to claim 3, wherein the
correction part acquires a correction value using a correction
coefficient set in advance, and adds the correction value to the
current command value.
6. The oil pressure unit according to claim 1, wherein the
correction part acquires a correction value using a data table DT
acquired in advance, and adds the correction value to the current
command value.
7. The oil pressure unit according to claim 3, wherein the
correction part acquires a correction value using a data table DT
acquired in advance, and adds the correction value to the current
command value.
8. The oil pressure unit according to claim 1, wherein the load
sensor is a pressure sensor arranged to detect a pressure of oil in
a discharge line of the oil pressure pump.
9. The oil pressure unit according to claim 3, wherein the load
sensor is a pressure sensor arranged to detect a pressure of oil in
a discharge line of the oil pressure pump.
10. The oil pressure unit according to claim 4, wherein the load
sensor is a pressure sensor arranged to detect a pressure of oil in
a discharge line of the oil pressure pump.
11. The oil pressure unit according to claim 5, wherein the load
sensor is a pressure sensor arranged to detect a pressure of oil in
a discharge line of the oil pressure pump.
12. The oil pressure unit according to claim 6, wherein the load
sensor is a pressure sensor arranged to detect a pressure of oil in
a discharge line of the oil pressure pump.
13. A speed control method of a motor in an oil pressure unit for
supplying oil to an actuator by driving an oil pressure pump with
the motor, which is controlled by an inverter comprising: detecting
a load of the oil pressure pump; detecting a rotation speed of the
motor; calculating a current command value so that a deviation
between a speed command value representing a target rotation speed
of the motor and a rotation speed of the motor converges to zero;
correcting the current command value based on the load of the oil
pressure pump; and outputting a control signal to the inverter
based on a corrected current command value.
14. The oil pressure unit according to claim 2, wherein the
correction part increases the current command value in response to
an increase in the load of the oil pressure pump.
15. The oil pressure unit according to claim 2, wherein the
correction part acquires a correction value using a correction
coefficient set in advance, and adds the correction value to the
current command value.
16. The oil pressure unit according to claim 2, wherein the
correction part acquires a correction value using a data table
acquired in advance, and adds the correction value to the current
command value.
17. The oil pressure unit according to claim 2, wherein the load
sensor is a pressure sensor arranged to detect a pressure of oil in
a discharge line of the oil pressure pump.
18. The oil pressure unit according to claim 7, wherein the load
sensor is a pressure sensor arranged to detect a pressure of oil in
a discharge line of the oil pressure pump.
Description
TECHNICAL FIELD
[0001] The present invention relates to an oil pressure unit for
driving an oil pressure pump with a motor.
BACKGROUND ART
[0002] Conventionally, in an oil pressure unit having an oil
pressure pump directly connected to a motor as a drive source, a
speed control (PI control) calculation is executed to calculate a
current command value through comparison of a speed command value
of the motor and a current rotation speed, and a current control
based on the current command value is realized by an inverter. The
motor controlled by the inverter is then driven so that pressure
oil is discharged from the oil pressure pump (e.g., patent document
1).
[0003] Patent document 1: Japanese Laid-Open Patent Publication No.
2004-162860
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0004] In such oil pressure unit, the pressure of oil (oil
pressure) becomes larger as a total amount of the oil discharged
from the oil pressure pump by a drive of the oil pressure pump
increases. An increase in the oil pressure leads to an increase in
a load of the oil pressure pump in discharge, and causes a load
torque of the motor to become larger.
[0005] Thus, in such oil pressure unit, in a case where a stepwise
speed command value is provided, if a rotation speed of the motor
drastically rises in response to the speed command value, the load
of the oil pressure pump drastically increases and the load torque
of the motor drastically becomes large. If the load torque of the
motor drastically becomes large, the speed control constituted by
the PI control cannot follow, and the rotation speed of the motor
might lower.
[0006] A method of preventing lowering of the rotation speed of the
motor includes a method of improving a response of the control by
shortening a control period of the PI control by improving a
processing speed of a microcomputer that performs the PI control.
However, a cost of the microcomputer increases if such method is
adopted. Furthermore, since the improvement of the processing speed
of the microcomputer has physical limitations, lowering in the
rotation speed of the motor cannot be effectively prevented with
such method.
[0007] Another method includes a method using the load torque for
the speed control in which the load torque is estimated from
acceleration information obtained by differentiating the rotation
speed of the motor. However, since the rotation speed is discrete
information, a noise component increases by differentiation. Thus,
there is a possibility a behavior will become unstable if the speed
control is executed using the load torque.
[0008] Moreover, if a gain of the speed control is increased to
improve a response to the load variation, an oscillation might
occur when the stepwise speed command value is provided.
[0009] In view of the above problems, it is an object of the
present invention to provide a technique capable of improving a
followability of the rotation speed of the motor with respect to
the variation of the load of the oil pressure pump.
Means for Solving the Problems
[0010] A first aspect of an oil pressure unit according to the
present invention relates to the oil pressure unit for supplying
oil to an actuator by driving an oil pressure pump (16A) with a
motor (15), characterized in that it comprises an inverter (14) for
supplying power to the motor (15), a load sensor (17) for detecting
a load of the oil pressure pump (16A), a rotation sensor (21) for
detecting a rotation speed of the motor (16), a current command
value calculation means (12) for calculating a current command
value so that a deviation between a speed command value
representing a target rotation speed of the motor (15) and a
rotation speed of the motor (15) converges to zero, a correction
means (18A; . . . ; 18D) for correcting the current command value
based on the load of the oil pressure pump (16A), and a control
signal generation means (13) for outputting a control signal to the
inverter (14) based on a corrected current command value.
[0011] According to a second aspect of the oil pressure unit, in
the first aspect, it is characterized in that said correction means
(18A; . . . ; 18D) corrects the current command value to raise the
rotation speed of said motor (15) with an increase in the load of
said oil pressure pump (16A).
[0012] According to a third aspect of the oil pressure unit, in the
first or the second aspect, it is characterized in that said
correction means (18A; . . . ; 18D) increases the current command
value with an increase in the load of said oil pressure pump
(16A).
[0013] According to a fourth aspect of the oil pressure unit, in
any one of the first to the third aspects, it is characterized in
that said correction means (18A) acquires a correction value (If)
using a correction coefficient (Kf) set in advance, and adds said
correction value (If) to said current command value.
[0014] According to a fifth aspect of the oil pressure unit, in any
one of the first to the third aspects, it is characterized in that
said correction means (18B; 18C; 18D) acquires a correction value
(If) using a data table DT acquired in advance, and adds said
correction value (If) to said current command value.
[0015] According to a sixth aspect of the oil pressure unit, in any
one of the first to the fifth aspects, it is characterized in that
said load sensor (17) is a pressure sensor (17) for detecting a
pressure of oil in a discharge line (19) of said oil pressure pump
(16A).
[0016] A seventh aspect of the oil pressure unit relates to a speed
control method of a motor (15) in the oil pressure unit for
supplying oil to an actuator by driving an oil pressure pump (16A)
with the motor (15) controlled by an inverter (14) and,
characterized in that it comprises the steps of: a) detecting a
load of said oil pressure pump (16A); b) detecting a rotation speed
of said motor (15); c) calculating a current command value so that
a deviation between a speed command value representing a target
rotation speed of said motor (15) and a rotation speed of said
motor (15) converges to zero; d) correcting the current command
value based on the load of said oil pressure pump (16A); and e)
outputting a control signal to said inverter (14) based on the
corrected current command value.
THE EFFECT OF THE INVENTION
[0017] According to the first aspect to the seventh aspect of the
oil pressure unit of the present invention, the followability of
the rotation speed of the motor with respect to the variation of
the load (load oil pressure) of the oil pressure pump can be
improved since the current command value is corrected based on the
load of the oil pressure pump.
[0018] In particular, according to the second aspect of the oil
pressure unit of the present invention, lowering in rotation speed
of the motor involved in an increase of the load of the oil
pressure pump can be prevented since the current command value is
corrected to raise the rotation speed of the motor with an increase
in the load of the oil pressure pump.
[0019] The objects, features, aspects, and advantages of the
present invention will become apparent from the following detailed
description and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 It is a schematic view showing a configuration of an
oil pressure unit according to an embodiment.
[0021] FIG. 2 It is a schematic view showing a configuration of an
oil pressure unit without a correction part.
[0022] FIG. 3 It is a view showing a state of an operation when a
stepwise speed command is provided in the oil pressure unit
according to the embodiment.
[0023] FIG. 4 It is a view showing a state of an operation when a
stepwise speed command is provided in the oil pressure unit oil
pressure unit not including a correction part.
[0024] FIG. 5 It is a schematic view showing an oil pressure unit
including a correction part capable of acquiring a correction value
using a data table.
[0025] FIG. 6 It is a schematic view showing an oil pressure unit
in which two oil pressure pumps are driven with one motor.
[0026] FIG. 7 It is a schematic view showing an oil pressure unit
in which two oil pressure pumps are connected in series.
BEST MODE FOR CARRYING OUT THE INVENTION
[0027] An embodiment of the present invention will now be described
with reference to the drawings.
<Configuration>
[0028] FIG. 1 is a schematic view showing a configuration of an oil
pressure unit 10A according to the embodiment of the present
invention. The oil pressure unit 10A is connected to a molding
machine etc., and supplies oil as working fluid to an actuator (not
shown) having the oil pressure as the power source.
[0029] As shown in FIG. 1, the oil pressure unit 10A includes a
controller 20, an inverter unit 14, a motor 15, an oil pressure
pump 16A, a pressure sensor 17, and a pulse generator 21. In the
oil pressure unit 10A having such configuration, the oil is taken
in from a tank (not shown) by the oil pressure pump 16A driven by
the motor 15, and the oil is discharged. The discharged oil is
supplied to the actuator such as an oil pressure cylinder or an oil
pressure motor through a discharge line 19.
[0030] The pressure sensor 17 serves as a load sensor for detecting
the load of the oil pressure pump. The pressure sensor 17 also
detects the pressure (also referred to as "present pressure" or
"load oil pressure") of the oil in the discharge line 19 of the oil
pressure pump.
[0031] The pulse generator 21 serves as a rotation sensor for
outputting a pulse signal for detecting the rotation speed of the
motor to the controller 20 (speed detection part 22).
[0032] The inverter unit 14 controls the rotation number of the
motor 15 by performing switching based on a control signal from the
controller 20.
[0033] The controller 20 includes a P-Q control part 11, a current
command value calculation part 12, a correction part 18A, a control
signal generation part 13, and a speed detection part 22. The
controller 20 outputs a control signal for driving the
inverter.
[0034] The P-Q control part 11 generates discharge
pressure-discharge flow rate characteristics (P-Q characteristics)
based on a set pressure and a set flow rate from a higher level
system such as a molding machine. The P-Q control part 11 outputs a
speed command value based on the present pressure from the pressure
sensor 17 as an input.
[0035] The current command value calculation part (also referred to
as "PI control part") 12 performs a proportional-integral (PI)
control with the speed command value and the current speed as
inputs, and outputs a current command value. More specifically, the
PI control part 12 calculates the current command value so that the
deviation between speed command value representing the target
rotation speed of the motor 15 and the rotation speed of the motor
15 converges to zero.
[0036] The correction part 18A corrects the current command value
based on the present pressure from the pressure sensor 17. The
details will be hereinafter described.
[0037] The control signal generation part 13 generates a control
signal for controlling the inverter part 14 based on the corrected
current command value.
<Correction Unit>
[0038] The correction part 18A will now be described in detail.
[0039] FIG. 2 is a schematic view showing a configuration of a
general oil pressure unit 10B. The oil pressure unit 10B has the
same configuration as the oil pressure unit 10A other than that the
correction part 18A is not equipped.
[0040] A high response is demanded on the molding machine to which
the oil pressure unit 10B is connected from the standpoint of mass
production. Thus, in the oil pressure unit 10B for driving the
molding machine, a stepwise speed command is provided in a short
cycle.
[0041] As the total amount of the oil discharged from the oil
pressure pump 16A increases, the oil pressure (load oil pressure)
in the discharge line 19 of the oil pressure pump 16A becomes
larger. As the load oil pressure becomes larger, the load of the
oil pressure pump 16A in discharge increases. That is, the load oil
pressure and the load torque of the motor 15 are more or less in a
proportional relationship, where the load torque of the motor 15
becomes larger as the load oil pressure becomes larger.
[0042] Therefore, in the oil pressure unit 10B, when the stepwise
speed command is provided, the rotation speed of the motor 15
drastically rises in response to the speed command value. The load
oil pressure drastically increases with rise in rotation speed of
the motor 15. The load torque drastically becomes larger with an
increase in the load oil pressure. Thus, the speed control by the
PI control cannot be followed, and the rotation speed of the motor
15 lowers.
[0043] In order to prevent the lowering in the rotation speed of
the motor 15 by an increase in load torque, the generated torque of
the motor 15 needs to become larger with the increase in load
torque. The generated torque of the motor 15 and the motor current
are in proportional relationship, and thus the motor current, that
is, the current command value merely needs to become large for the
generated torque of the motor 15 to become large.
[0044] In brief, the followability of the rotation speed of the
motor 15 with respect to variation of the load oil pressure can be
improved by changing the current command value with variation of
the load oil pressure. Furthermore, the lowering in the rotation
speed of the motor 15 can be prevented by increasing the current
command value with the increase in load oil pressure.
[0045] In the oil pressure unit 10A according to the present
embodiment, the correction part 18A for correcting the current
command value based on the load oil pressure is equipped. In the
correction part 18A, the correction value (current correction
value) If is acquired using the present pressure (pressure detected
value) Pd detected by the pressure sensor 17 and a correction
coefficient Kf acquired in advance. The correction value If is
added to the current command value output from the current command
value calculation part 12.
[0046] According to the correction part 18A, the current command
value is corrected based on the load of the oil pressure pump 16A,
that is, the pressure (load oil pressure) of the oil in the
discharge line 19. Therefore, the followability of the rotation
speed of the motor 15 with respect to the variation of the load
(load oil pressure) of the oil pressure pump 16A can be enhanced
(improved).
[0047] The coefficient acquired through tests in advance is used as
the correction coefficient Kf. Specifically, the correction
coefficient Kf is set so that the current command value necessary
for preventing lowering in the rotation speed of the motor 15 and
following the speed command can be acquired in the correction part
18A. The correction coefficient Kf can also be represented as being
set so that the lack of current command value necessary for
preventing lowering in the rotation speed of the motor 15 and
following the speed command can be acquired as the correction
value.
[0048] Through the use of the correction coefficient Kf set so that
the lack of the current command value can be acquired as the
correction value, the rotation speed of the motor 15 can be
controlled to the rotation speed given by the speed command
value.
[0049] The correction value If acquired using the correction
coefficient Kf becomes larger with rise in load oil pressure. Thus,
in the correction part 18A, the current command value can be
corrected so as to raise the rotation speed of the motor 15 with
the increase in load oil pressure, and lowering in rotation speed
of the motor 15 involved in rise of the load oil pressure is
prevented.
[0050] The operation in a case where a stepwise speed command SC is
provided in the oil pressure unit 10A will now be specifically
described. FIG. 3 is a view showing a state of an operation when a
stepwise speed command SC is provided in the oil pressure unit 10A
according to the present embodiment.
[0051] As shown in FIG. 3(a), when the stepwise speed command SC is
provided in the oil pressure unit 10A, the rotation speed Rs1 of
the motor 15 drastically rises in response to the speed command SC.
The pressure Pd1 of the oil discharged from the oil pressure pump
16A then drastically increases, and the load torque of the motor 15
becomes larger.
[0052] However, in the oil pressure unit 10A, the correction value
If which value becomes larger with the increase in the load oil
pressure Pd1 is acquired in the correction part 18A. The correction
value If is added to the output from the current command value
calculation part 12, and the corrected current command value Ic1 is
acquired (see FIG. 3(b)). The current command value Ic1 becomes
larger following the increase in the load oil pressure Pd1, and
thus the lowering in the rotation speed Rs1 of the motor 15 by the
increase in load torque is prevented. The rotation speed Rs1 of the
motor 15 thus can follow the rotation speed given by the speed
command SC.
[0053] There will be compared the operation in a case where the
stepwise speed command SC is provided in the oil pressure unit 10A
with the operation in a case where the stepwise speed command SC is
provided in the oil pressure unit 10B not including the correction
part 18A. FIG. 4 is a view showing a state of an operation when the
stepwise speed command SC is provided in the oil pressure unit
10B.
[0054] As shown in FIG. 4(a), when the stepwise speed command SC is
provided in the oil pressure unit 10B, the rotation speed Rs2 of
the motor 15 lowers by influence of an increase in the load oil
pressure Pd2 due to drastic rise in the rotation speed Rs2 of the
motor 15.
[0055] Comparing FIG. 3(b) with FIG. 4(b), the magnitude of the
current command value is different in zone BT. The difference in
magnitude of the current command value indicates that the
appropriate current command value necessary for following the
rotation speed of the motor 15 to the speed command SC is not
acquired (calculated) in the oil pressure unit 10B (FIG. 4(b)).
[0056] Therefore, when the rapid speed command like the stepwise
speed command SC is provided, the rotation speed of the motor 15
cannot be followed to such speed command with only the speed
control constituted by the PI control.
[0057] In the present embodiment, the correction value If that
becomes larger with the increase in the load oil pressure Pd is
acquired using the load oil pressure Pd detected by the pressure
sensor 17 and the correction coefficient Kf previously acquired in
the correction part 18A. The relevant correction value If is added
to the current command value output from the current command value
calculation part 12.
[0058] As described above, the current command value Ic1 can be
increased following the increase in the load oil pressure Pd1 by
adding the correction value If acquired based on the load oil
pressure Pd1 to the current command value output from the current
command value calculation part 12 in a feedforward manner. The
lowering in the rotation speed Rs1 of the motor 15 by the increase
in load torque thus can be prevented.
<Modification>
[0059] The embodiment of the present invention has been described,
but the present invention is not limited to the content described
above.
[0060] For instance, in the above embodiments, the correction value
If is acquired using the correction coefficient Kf previously
acquired in the correction part 18A, but is not limited thereto.
FIG. 5 is a schematic view showing an oil pressure unit 10C
including a correction part 18B capable of acquiring the correction
value If using a data table DT.
[0061] Specifically, the correction value If may be acquired
(calculated) using a data table DT showing a relationship between
the load oil pressure (pressure detected value) Pd acquired in
advance and the correction value If in the correction part 18B, as
shown in FIG. 5.
[0062] An appropriate correction value If thus can be acquired with
respect to the load pressure Pd from the pressure sensor 17 even if
the load pressure and the correction value necessary for following
the speed command are not in a proportional relationship.
[0063] Furthermore, the oil pressure unit 10A is driven using one
oil pressure pump 16A in the above embodiment, but is not limited
thereto.
[0064] Specifically, the oil pressure unit may be driven using a
plurality of oil pressure pumps. FIG. 6 is a schematic view showing
an oil pressure unit 10D in which two oil pressure pumps 16A, 16B
are driven with one motor.
[0065] For instance, as shown in FIG. 6, information (pump drive
information) indicating which oil pressure pump is being driven is
output to the correction part 18C from the P-Q control part 11
according to the switching of the pump when configuring the oil
pressure unit 10D with two oil pressure pumps 16A, 16B. In the
correction part 18C, the data table for acquiring the correction
value If is switched according to the pump drive information, and
the correction value If corresponding to the driven pump is
acquired.
[0066] When simultaneously driving the two oil pressure pumps 16A,
16B, the data table showing a relationship between the load oil
pressure (pressure detected value) Pd and the correction value If
in a case where the two oil pressure pumps 16A, 16B are
simultaneously driven is used to acquire the correction value
If.
[0067] The two oil pressure pumps 16A, 16B do not need be connected
in parallel. FIG. 7 is a schematic view showing an oil pressure
unit in which two oil pressure pumps are connected in series. As
shown in FIG. 7, when the two oil pressure pumps are connected in
series such that the oil discharged from one oil pressure pump 16B
is taken in by the other oil pressure pump 16A, the pressure of the
oil discharged form the oil pressure pump 16A on the downstream
side is detected by the pressure sensor (17). The current command
value is corrected based on the oil pressure discharged by the oil
pressure pump 16A on the downstream side.
[0068] Although the present invention has been described in detail
above, the above description is merely illustrative in all aspects
and the present invention should not be limited by the description.
It should be recognized that an infinite number of modifications
that are not illustrated can be contrived without deviating from
the scope of the invention.
* * * * *