The present invention relates to a work machine endowed with a function by which the driving of a hydraulic actuator is controlled automatically or semi-automatically.
In a hydraulic excavator, a boom, an arm, and a bucket constituting a front work device are rotatably supported, and when the boom, the arm, or the bucket is moved singly, the bucket forward end draws an arcuate locus. Thus, in forming a linear finish surface with the bucket forward end through, for example, an arm drawing operation, it is necessary for the operator to perform a combined operation on the boom, the arm, and the bucket, and great skill is required of the operator.
In this regard, a technique is available according to which a function (machine control) by which the driving of the hydraulic actuators is controlled automatically or semi-automatically by a computer (controller) is applied to excavation work, with the bucket forward end being moved along the design surface (target excavation surface) at the time of excavation operation (at the time of operation of the arm or the bucket) (Patent Document 1).
On the other hand, some conventional hydraulic excavators are equipped with a hydraulic regeneration device which causes the hydraulic fluid in the tank side line of a hydraulic actuator to flow into the pump side line (hydraulic fluid regeneration), thereby increasing the operational speed of the hydraulic actuator (Patent Document 2).
Patent Document 1: Japanese Patent No. 3056254
Patent Document 2: Japanese Patent No. 3594680
In the case where machine control is applied to a hydraulic excavator equipped with a hydraulic regeneration device capable of increasing the expansion/contraction speed of the arm cylinder, hydraulic fluid regeneration is effected in the arm cylinder during the movement of the bucket forward end along the target excavation surface by the machine control, and the arm operational speed fluctuates, whereby there is a fear of the bucket forward end being further engaged in the ground than the target excavation surface.
The present invention has been made in view of the above problem. It is an object of the present invention to provide a work machine in which fluctuation in the speed of the hydraulic actuator due to hydraulic fluid regeneration during the execution of machine control is suppressed, thereby making it possible to improve work efficiency while securing the control accuracy of the machine control.
To achieve the above object, there is provided, in accordance with the present invention, a work machine including: a machine body; a front work device provided on the machine body; a plurality of hydraulic actuators driving the front work device; a hydraulic pump; a plurality of flow control valves controlling a hydraulic fluid flow supplied from the hydraulic pump to the plurality of hydraulic actuators; a plurality of operation devices designating operation of the plurality of hydraulic actuators; a plurality of pilot lines connecting the plurality of operation devices and pilot sections of the plurality of flow control valves; a solenoid proportional valve provided in at least one predetermined pilot line of the plurality of pilot lines; and a controller controlling the solenoid proportional valve to correct pilot pressure of the predetermined pilot line, thereby controlling driving of the front work device, the work machine further including: a regeneration circuit causing the hydraulic fluid in a tank side line of the predetermined hydraulic actuator of the plurality of hydraulic actuators to flow into a pump side line thereof. The controller has an area limiting control section controlling the solenoid proportional valve such that the front work device does not intrude under a target excavation surface, a regeneration control section adjusting flow rate of the hydraulic fluid caused to flow into the pump side line via the regeneration circuit, between zero and a predetermined upper limit value, and a regeneration control switching section that issues an order to the regeneration control section to set the predetermined upper limit value to a first set value when function of the area limiting control section is invalid, and that issues an order to the regeneration control section to set the predetermined upper limit value to a second set value that is smaller than the first set value when the function of area limiting control section is effective.
According to the present invention, fluctuation in the speed of the hydraulic actuator accompanying hydraulic fluid regeneration is suppressed during machine control, whereby it is possible to improve work efficiency while securing the control accuracy of the machine control.
In the following, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same components are indicated by the same reference numerals, and a redundant description will be left out as appropriate. While in the following, a hydraulic excavator equipped with a bucket as the attachment at the distal end of the front work device is taken as an example, the present invention may be applied to a hydraulic excavator equipped with an attachment other than a bucket. Further, while in the following description, in the case where there exist a plurality of similar components, an alphabetical letter may be added to the end of a numeral (number), in some cases, such alphabetic letter is omitted, and the plurality of components are collectively expressed. For example, when there exist four operation levers 23a, 23b, 23c, and 23d, these may be collectively expressed as the operation levers 23.
In
The boom 2, the arm 3, the bucket 4, the upper swing structure 6, and the lower track structure 5 constitute driven members driven by a boom cylinder 11, an arm cylinder 12, a bucket cylinder 13, a swing hydraulic motor 8, and left and right traveling hydraulic motors 7a and 7b. Operational designation to these driven members 2 through 6 is outputted in accordance with the operation by the operator of a left traveling lever 23c, a right traveling lever 23d, a left operation lever 23a, and a right operation lever 23b mounted in a cab on the upper swing structure 6 (These are sometimes generally referred to as the operation levers).
Installed in the cab are an operation device 33a (shown in
The hydraulic fluid delivered from the hydraulic pump 21 is supplied to the left traveling hydraulic motor 7a, the right traveling hydraulic motor 7b, the swing hydraulic motor 8, the boom cylinder 11, the arm cylinder 12, and the bucket cylinder 13 via the flow control valves 51 through 56 (shown in
In order that the rotational angles α, β, and γ (shown in
As shown in
The hydraulic excavator 1 of the present embodiment is equipped with a control system (hereinafter referred to as the “excavation control system”) aiding the excavation operation of the operator. The excavation control system performs, for example, a control (hereinafter referred to as “area limiting control”) to forcibly raise the boom 2 such that the bucket forward end (the claw tip of the bucket 4) is not engaged deeper in the ground than a target excavation surface 200 (shown in
The excavation control system of the present embodiment is equipped with: an area limiting switch 34 installed at a position where it does not interfere with the field of vision of the operator, such as above an operational panel in the cab and switching between effective/invalid of the area limiting control; pressure sensors 71a and 71b provided in pilot lines 41a and 41b of the operation device 31a for the boom 2 and detecting a pilot pressure (control signal) as the operation amount of the boom raising direction or the boom lowering direction of the operation lever 23a; pressure sensors 72a and 72b provided in pilot lines 42a and 42b of the operation device 31b for the arm 3 and detecting a pilot pressure (control signal) as the operation amount in the arm drawing direction or the arm pushing direction of the operation lever 23b; pressure sensors 73a and 73b provided in pilot lines 43a and 43b of the operation device 32a for the bucket 4 and detecting a pilot pressure (control signal) as the operation amount in the bucket crowding direction or the bucket dumping direction of the operation lever 23a; a solenoid proportional valve 81a a primary port side of which is connected to a pilot pump 24 and which reduces and outputs a pilot pressure from the pilot pump 24; a shuttle valve 26 connected to a pilot line 41a of the operation device 31a for the boom 2 and a secondary port side of the solenoid proportional valve 81a, selecting the higher of the pilot pressure in the pilot line 41a and a control pressure outputted from the solenoid proportional valve 81a, and guiding it to a pilot section 51a of the flow control valve 51; a solenoid proportional valve 81b installed in a pilot line 41b of the operation device 31a for the boom 2 and reducing and outputting the pilot pressure in the pilot line 41b in accordance with an electric signal; solenoid proportional valves 82a and 82b installed in pilot lines 42a and 42b of the operation device 31b for the arm 3 and reducing and outputting the pilot pressure in the pilot lines 42a and 42b in accordance with an electric signal; solenoid proportional valves 83a and 83b installed in pilot lines 43a and 43b of the operation device 32b for the bucket 4 and reducing and outputting the pilot pressure in the pilot lines 43a and 43b in accordance with an electric signal; and a controller 100 consisting of a computer or the like capable of executing various computations.
The controller 100 performs various computations based on a switching signal from the area limiting switch 34, configuration information and positional information on the target excavation surface 200 set by a target excavation surface setting device 35 described below, detection signals from the angle sensors 61 through 63 and the inclination angle sensor 64, and detection signals from the pressure sensors 71 through 73, and outputs an operation signal for correcting the pilot pressures of the pilot lines 41 through 43 to the solenoid proportional valves 81 through 83.
The work implement posture sensor 60 is composed of a boom angle sensor 61, an arm angle sensor 62, a bucket angle sensor 63, and a machine body inclination angle sensor 64.
The target excavation surface setting device 35 is an interface capable of inputting information related to the target excavation surface 200 (including positional information on the target excavation surface). The input to the target excavation surface setting device 35 may be manually effected by the operator, or the information may be taken in from the outside via a network or the like. Further, a satellite communications antenna may be connected to the target excavation surface setting device 35 to compute global coordinates of the excavator.
The operator operation sensor 70 is composed of the pressure sensors 71 through 73 gaining an pilot pressure generated through the operation of the operation levers 23 by the operator.
The area limiting control section 110 includes a work implement posture computing section 111, a target excavation surface computing section 112, a target operation computing section 113, and a solenoid proportional valve control section 114.
The work implement posture computing section 111 computes the posture of the front work device 1A based on the information from the work implement posture sensor 60. The posture of the front work device 1A can be defined based on the excavator reference coordinates of
Referring back to
Next, the regeneration circuit 90 of
In
The regeneration circuit 90 is controlled by a regeneration control section 120 (shown in
In
Next, the operation of the regeneration circuit 90 will be described.
In
At this time, while the pump delivery pressure Pd detected by the pressure sensor 94 is lower than the first set pressure Pd1 of the relational function 121a (shown in
As described above, when, from the state where the regeneration flow rate is maximum, the load on the arm cylinder 12 increases due to the resistance of earth and sand or the like abutting the bucket forward end, the delivery pressure Pd of the hydraulic pump 21 increases. When the value of this pump delivery pressure Pd is between the first set pressure Pd1 and the second set pressure Pd2 of the relational function 121a of
When the claw tip of the bucket 4 is engaged in the earth and sand, and the value of the pump delivery pressure Pd becomes equal to or more than the second set pressure Pd2 of the relational function 121a (shown in
As shown in
In the hydraulic excavator 1 constructed as described above, in the case, for example, where hydraulic fluid regeneration is effected in the arm cylinder 12 during the horizontal excavation operation under area limiting control, the operational speed of the arm 3 fluctuates, so that there is a fear of the claw tip of the bucket 4 being engaged deeper in the ground than the target excavation surface 200. In view of this, in order to suppress fluctuation in the speed of the arm cylinder 12 accompanying the hydraulic fluid regeneration during the execution of the arm limiting control, the controller 100 of the present embodiment is equipped with a regeneration control switching section 130 for restricting the regeneration flow rate in the arm cylinder 12.
In
First, the regeneration control switching section 130 determines whether or not the area limiting switch 34 is at the ON position (step S10).
In the case where it is determined in step S10 that the area limiting switch 34 is at the ON position (YES), designation is given to the regeneration control section 120 so as to set the upper limit value of the regeneration flow rate to the second set value F2 (shown in
On the other hand, in the case where it is determined in step S10 that the area limiting switch 34 is not at the ON position (NO), designation is given to the regeneration control section 120 so as to set the upper limit value of the regeneration flow rate to the first set value F1 (step S20). As a result, during non-execution of the area limiting control, the regeneration flow rate in the arm cylinder 12 is not limited.
In the present embodiment, the case where the area limiting switch 34 is at the OFF position (that is, during non-execution of the area limiting control) is defined as “the case where the function of the area limiting control section 110 is invalid,” and the case where the area limiting switch 34 is at the ON position (that is, during execution of the area limiting control) is defined as “the case where the function of the area limiting control section 110 is effective.”
In the hydraulic excavator 1 according to the present embodiment, in the case where the function of the area limiting control section 110 is effective (that is, during execution of the area limiting control), the regeneration flow rate in the arm cylinder 12 is limited, whereby the fluctuation in the speed of the arm cylinder 12 is suppressed, so that it is possible to secure the control accuracy in the area limiting control. On the other hand, in the case where the function of the area limiting control section 110 is invalid (that is, during non-execution of the area limiting control), the expansion/contraction speed of the arm cylinder 12 is increased, with the regeneration flow rate not being limited, so that it is possible to improve work efficiency in a work not involving the area limiting control.
The hydraulic excavator 1 according to the second embodiment of the present invention will be described with reference to
In the hydraulic excavator 1 according to the first embodiment, in the case where the area limiting switch 34 is at the ON position (that is, during the execution of the area limiting control), the regeneration flow rate in the arm cylinder 12 is limited. However, even during the execution of the area limiting control, in the case where the bucket 4 is greatly spaced away from the target excavation surface 200, there is no fear of the claw tip of the bucket 4 being engaged deeper in the ground than the target excavation surface 200 even if the operational speed of the arm 3 fluctuates with the hydraulic fluid regeneration in the arm cylinder 12.
In the hydraulic excavator 1 according to the present embodiment, in the case where the area limiting control is being executed and where the distance from the claw tip position of the bucket 4 to the target excavation surface 200 is equal to or more than a predetermined distance (in the case where the claw tip of the bucket 4 is outside, for example, the finishing area to be excavated), the expansion/contraction speed of the arm cylinder 12 is increased without limiting the regeneration flow rate, thereby improving work efficiency in a work involving the area limiting control while securing the control efficiency of the area limiting control.
In
In
In the present embodiment, the case where the area limiting switch 34 is at the OFF position or the case where the area limiting switch 34 is at the ON position and where the distance from the claw tip position of the bucket 4 to the target excavation surface 200 is not smaller than the predetermined distance D0 (that is, the case where the effect of the area limiting control is not conspicuous) is defined as “the case where the function of the area limiting control section 110 is invalid,” and the case where the area limiting switch 34 is at the ON position and where the distance from the claw tip position of the bucket 4 to the target excavation surface 200 is smaller than the predetermined distance D0 (that is, the case where the effect of the area limiting control is conspicuous) is defined as “the case where the function of the area limiting control section 110 is effective.”
Also in the hydraulic excavator 1 according to the present embodiment, it is possible to attain the same effect as that of the first embodiment.
Further, in the hydraulic excavator 1 according to the present embodiment, in the case where the function of the area limiting control section 110 is effective (that is, in the case where the area limiting control is being executed and where the distance from the claw tip position of the bucket 4 to the target excavation surface 200 is equal to or more than the predetermined distance D0 (the case where the claw tip of the bucket 4 is, for example, outside the finishing area to be excavated)), the expansion speed of the arm cylinder 12 is increased without limiting the regeneration flow rate. As a result, it is possible to improve work efficiency in a work involving the area limiting control while securing the control accuracy of the area limiting control.
The hydraulic excavator 1 according to the third embodiment of the present invention will be described with reference to
In the hydraulic excavator 1 according to the first embodiment, in the case where the area limiting switch 34 is at the ON position (that is, during the execution of the area limiting control), the regeneration flow rate in the arm cylinder 12 is limited. Here, in the case where the distance from the claw tip position of the bucket 4 to the target excavation surface 200 is small during the execution of the area limiting control, in order to secure the control accuracy, pressure reduction (correction) is effected via the solenoid proportional valves 82a and 82b such that the pilot pressure of the pilot lines 42a and 42b (the arm pilot pressure) is lower than a predetermined pilot pressure, and the operational speed of the arm 3 is limited. That is, the arm pilot pressure corrected by the solenoid proportional valves 82a and 82b (referred to, in the following, as the “corrected arm pilot pressure”) is equal to or more than a predetermined pilot pressure only in the case where the bucket 4 is greatly spaced away from the target excavation surface 200. Thus, in the case where the area limiting control is being executed and where the corrected arm pilot pressure is equal to or more than the predetermined pilot pressure, even if the operational speed of the arm 3 fluctuates with the hydraulic fluid regeneration in the arm cylinder 12, there is no fear of the claw tip of the bucket 4 being engaged deeper in the ground than the target excavation surface 200.
In the hydraulic excavator 1 according to the present embodiment, in the case where the area limiting control is being executed and where the corrected arm pilot pressure is equal to or more than a predetermined pilot pressure, the expansion/contraction speed of the arm cylinder 12 is increased without limiting the regeneration flow rate, whereby improving work efficiency of a work involving the limiting control while securing the control accuracy due to the area limiting control.
In
In
In the present embodiment, the case where the area limiting switch 34 is at the OFF position or the case where the area limiting switch 34 is at the ON position and where the corrected arm pilot pressure is not lower than the predetermined pilot pressure PA0 (that is, the case where the effect of the area limiting control is not conspicuous) is defined as “the case where the function of the area limiting control section 110 is invalid,” and the case where the area limiting switch 34 is at the ON position and where the corrected arm pilot pressure is lower than the predetermined pilot pressure PA0 (that is, the case where the effect of the area limiting control is conspicuous) is defined as “the case where the function of the area limiting control section 110 is effective.”
Also in the hydraulic excavator 1 according to the present embodiment, it is possible to achieve the same effect as that of the first embodiment.
Further, in the hydraulic excavator 1 according to the present embodiment, in the case where the function of the area limiting control section 110 is effective (that is, in the case where the area limiting control is being executed and where the corrected arm pilot pressure is equal to or more than the predetermined pilot pressure PA0 (in the case where the bucket 4 is to be regarded as greatly spaced away from the target excavation surface 200)), the expansion speed of the arm cylinder 12 increases without the regeneration flow rate being limited. As a result, it is possible to improve work efficiency in a work involving the area limiting control while securing the control accuracy in the area limiting control.
While in the present embodiment the corrected arm pilot pressure is gained from the target operation computing section 113, pressure sensors may be provided between the solenoid proportional valve 82a of the pilot line 42a and the pilot section 52a and between the solenoid proportional valve 82b of the pilot line 42b and the pilot section 52b, thereby detecting the corrected arm pilot pressure.
The hydraulic excavator 1 according to the fourth embodiment of the present invention will be described with reference to
In the hydraulic excavator 1 according to the first embodiment, in the case where the area limiting switch 34 is at the ON position (that is, during execution of the area limiting control), the regeneration flow rate in the arm cylinder 12 is limited. Here, in the case where, during the execution of the area limiting control, the distance from the claw tip position of the bucket 4 to the target excavation surface 200 is small, the corrected boom raising pressure generated by the solenoid proportional valve 81a and the corrected boom lowering pressure generated by the solenoid proportional valve 81b are both equal to or less than a predetermined pilot pressure. Thus, in the case where the area limiting control is being executed and where the corrected boom raising pilot pressure or the corrected boom lowering pilot pressure (hereinafter collectively referred to as “the corrected boom pilot pressure”) is equal to or more than a predetermined pilot pressure, even if the operational speed of the arm 3 fluctuates with the hydraulic fluid regeneration in the arm cylinder 12, there is no fear of the claw tip of the bucket 4 being engaged deeper in the ground than the target excavation surface 200.
In the hydraulic excavator 1 according to the present embodiment, in the case where the area limiting control is being executed and where the corrected boom pilot pressure is equal to or more than a predetermined pilot pressure, the expansion/contraction speed of the arm cylinder 12 is increased without limiting the regeneration flow rate, whereby it is possible to improve work efficiency in a work involving the area limiting control while securing the control accuracy of the area limiting control.
In
In
In the present embodiment, the case where the area limiting switch 34 is at the OFF position or the case where the area limiting switch 34 is at the ON position and where the corrected boom pilot pressure is not lower than the predetermined pilot pressure PB0 (that is, the case where the effect of the area limiting control is not conspicuous) is defined as “the case where the function of the area limiting control section 110 is invalid,” and the case where the area limiting switch 34 is at the ON position and where the corrected boom pilot pressure is lower than the predetermined pilot pressure PB0 (that is, the case where the effect of the area limiting control is conspicuous) is defined as “the case where the function of the area limiting control section 110 is effective.”
Also in the hydraulic excavator 1 according to the present embodiment, it is possible to achieve the same effect as that of the first embodiment.
Further, in the hydraulic excavator 1 according to the present embodiment, in the case where the function of the area limiting control section 110 is effective (that is, in the case where the area limiting control is being executed and where the corrected boom pilot pressure is equal to or more than the predetermined pilot pressure PB0 (in the case where the bucket 4 is to be regarded as greatly spaced away from the target excavation surface 200), the expansion speed of the arm cylinder 12 increases without the regeneration flow rate being limited. As a result, it is possible to improve work efficiency in a work involving the area limiting control while securing the control accuracy in the area limiting control.
While in the present embodiment the corrected boom pilot pressure is gained from the target operation computing section 113, pressure sensors may be provided between the shuttle valve 26 of the pilot line 41a and the pilot section 51a and between the solenoid proportional valve 81b of the pilot line 41b and the pilot section 51b, thereby detecting the corrected boom pilot pressure.
The hydraulic excavator 1 according to the fifth embodiment of the present invention will be described with reference to
The area limiting control section 110 according to the present embodiment is capable of being switched between a normal control mode in which priority is given to the control accuracy of the front work device 1A (hereinafter referred to as “the accuracy priority mode”) and a control mode in which priority is given to the operational speed of the front work device 1A (hereinafter referred to as “the speed priority mode”). Further, as mode switching means issuing an order to the area limiting control section 110 to switch from the accuracy priority mode to the speed priority mode, the hydraulic excavator 1 according to the present embodiment is equipped with a rough excavation switch 36 (shown in
When, during the execution of the area limiting control, it is determined that the excavation surface 201 (shown in
In the hydraulic excavator 1 according to the present embodiment, when it is determined that the distance from the excavation surface 201 to the target excavation surface 200 is small, the operator operates the rough excavation switch 36 to the OFF position to effect switching from the speed priority mode to the accuracy priority mode. That is, the rough excavation switch 36 is at the ON position only in the case where the excavation surface 201 is greatly spaced away from the target excavation surface 200. Thus, in the case where the area limiting control is being executed and where the rough excavation switch 36 is at the ON position, even if the operational speed of the arm 3 fluctuates with the hydraulic fluid regeneration in the arm cylinder 12, there is no fear of the claw tip of the bucket 4 being engaged in the ground deeper than the target excavation surface 200.
In the hydraulic excavator 1 according to the present embodiment, in the case where the area limiting control is being executed and where the rough excavation switch 36 is at the ON position, the expansion/contraction speed of the arm cylinder 12 is increased without limiting the regeneration flow rate, whereby improving work efficiency involving the area limiting control while securing the control accuracy of the area limiting control.
In
In
In the present embodiment, the case where the area limiting switch 34 is at the OFF position or the case where the area limiting switch 34 is at the ON position and where the rough excavation switch 36 is at the ON position (that is, the case where the effect of the area limiting control is not conspicuous) is defined as “the case where the function of the area limiting control section 110 is invalid,” and the case where the area limiting switch 34 is at the ON position and where the rough excavation switch 36 is at the OFF position (that is, the case where the effect of the area limiting control is conspicuous) is defined as “the case where the function of the area limiting control section 110 is effective.”
Also in the hydraulic excavator 1 according to the present embodiment, it is possible to achieve the same effect as that of the first embodiment.
Further, in the hydraulic excavator 1 according to the present embodiment, in the case where the function of the area limiting control section 110 is effective (that is, in the case where the area limiting control is being executed and where the rough excavation switch 36 is at the ON position (in the case where the excavation surface 201 is to be regarded as greatly spaced away from the target excavation surface 200)), the expansion speed of the arm cylinder 12 is increased without the regeneration flow rate being limited. As a result, it is possible to improve efficiency in a work involving the area limiting control while securing the control accuracy of the area limiting control.
The present invention, embodiments of which have been described in detail above, is not restricted to the above embodiments but includes various modifications. For example, the above embodiments have been described in detail in order to facilitate the understanding of the present invention, and are not always restricted to constructions equipped with all the components mentioned above. Further, to the construction of a certain embodiment, a part of the construction of another embodiment may be added, or a part of the construction of a certain embodiment may be deleted or replaced by a part of another embodiment.
Number | Date | Country | Kind |
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2016-134408 | Jul 2016 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2017/007996 | 2/28/2017 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
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WO2018/008190 | 1/11/2018 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
5442912 | Hirata | Aug 1995 | A |
5835874 | Hirata et al. | Nov 1998 | A |
5918527 | Haga | Jul 1999 | A |
5960378 | Watanabe | Sep 1999 | A |
6076029 | Watanabe | Jun 2000 | A |
9725874 | Meguriya | Aug 2017 | B2 |
10280948 | Vigholm | May 2019 | B2 |
20170101761 | Wu | Apr 2017 | A1 |
Number | Date | Country |
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06-081375 | Mar 1994 | JP |
08-128065 | May 1996 | JP |
11-021941 | Jan 1999 | JP |
11-101202 | Apr 1999 | JP |
3056254 | Jun 2000 | JP |
3594680 | Dec 2004 | JP |
2015194601 | Dec 2015 | WO |
Entry |
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International Preliminary Report on Patentability received in corresponding International Application No. PCT/JP2017/007996 dated Jan. 17, 2019. |
International Search Report of PCT/JP2017/007996 dated Jun. 6, 2017. |
Number | Date | Country | |
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20190106861 A1 | Apr 2019 | US |