Casing rotator

Abstract

A casing rotator includes control means configured to perform control of leveling a lifting frame, four lifting cylinders are hydraulic cylinders that are arranged at four corners of a virtual quadrilateral defined along an outer edge of the lifting frame in a plan view and that are capable of performing a contracting action and an extending action of applying a press-in force and a pull-out force to a casing, the control means includes a tilt sensor configured to detect a change angle of tilt of the lifting frame with respect to a leveled state, four variable throttle valves forming pairs with the four lifting cylinders and provided in flow passages through which a hydraulic oil flows out from the lifting cylinders in a contracting action state thereof, and a control unit configured to individually adjust throttling degrees of the variable throttle valves based on the detected change angle.

Description

TECHNICAL FIELD

[0001] The present invention relates to a casing rotator, in detail, relates to a casing rotator that press a casing into or pull the casing out from a ground in foundation work in construction or civil engineering.BACKGROUND ART

[0002] A casing rotator used in foundation work is generally configured as follows: a lifting frame is provided above a base frame via four lifting cylinders; a chuck mechanism that can be rotated by a motor is provided on the lifting frame; and a rotating operation by the motor and a lifting operation by the lifting cylinders are transmitted to a casing passing through a penetration hole at the center of each frame in a state where the casing is held by the chuck mechanism (for example, see Patent Literature 1).

[0003] As illustrated in FIG. 10, in each of lifting cylinders 101, a hydraulic circuit is connected to each of a rod-side hydraulic chamber 101a and a head-side hydraulic chamber 101b. When a switching valve 102 is operated to supply a hydraulic oil from a hydraulic pump 103 to the rod-side hydraulic chamber 101a, a chuck mechanism 105 and a lifting frame 106 are integrally lowered, and a casing 104 provided with a drilling bit 104a at the tip is pressed into the ground. Accordingly, in a press-in operation of the casing 104, a sum of the weight Wa of the casing 104 itself, the weight Wb of the chuck mechanism 105 and the lifting frame 106, and press-in forces (outputs in a contracting direction) FA, FB, FC, and FD of the lifting cylinders 101 acts on the drilling bit 104a as a casing press-in force Fcp.

[0004] The press-in force Fi (i=A, B, C, and D) of each lifting cylinder 101 is calculated by using the following Formula 1.Fi=P1×A1−P2×A2   Formula 1

[0005] In Formula 1, Fi is a lifting cylinder press-in force (hereinafter, simply referred to as cylinder press-in force), P1 is a primary pressure, A1 is a primary pressure receiving area, P2 is secondary pressure (back pressure), and A2 is a secondary pressure receiving area. In this case, the hydraulic pressure (primary pressure) P1 supplied to the rod-side hydraulic chamber 101a is adjusted by changing a value of a relief set pressure of a relief valve 107. Accordingly, as illustrated in FIG. 11, the minimum casing press-in force Fcp acting on the drilling bit 104a is substantially equal to a sum of the weight Wa of the casing 104 itself and the weight Wb of the chuck mechanism 105 and the lifting frame 106 even if the value of the relief set pressure of the relief valve 107 is set to 0 (zero).CITATION LISTPatent Literature

[0006] Patent Literature 1: Japanese Patent Application Publication No. 2006-348565SUMMARYTechnical Problem

[0007] The above-mentioned casing rotator has the following problem. When part of the casing tip (drilling bit) comes into contact with an underground obstacle (illustrated while being denoted by reference sign R in FIG. 10) such as a boulder during the press-in operation, a reaction force received by the casing tip in a contact portion differs from that in a non-contact portion, and as a result, the lifting frame tilts. In view of this, control of applying a counter force in the opposite direction to the tilt by activating a leveling jack capable of coming into contact with the ground is conceivable. However, in control in which leveling is directly performed as described above, it is difficult to effectively suppress the tilt of the lifting frame occurring during the press-in operation, and is not sufficient as control means.

[0008] Accordingly, an object of the present invention is to provide a casing rotator including control means capable of effectively suppressing tilt of a lifting frame that occurs during a press-in operation.Solution to Problem

[0009] In order to achieve the above-mentioned object, a casing rotor of the present invention is a casing rotor including: a base frame configured to be installed on a ground; a lifting frame provided above the base frame to be liftable and lowerable via four lifting cylinders; a chuck mechanism configured to be lifted and lowered along with the lifting frame; a rotation transmission mechanism configured to apply a rotating force to a casing held by the chuck mechanism; and control means configured to perform control of leveling the lifting frame, the four lifting cylinders are hydraulic cylinders that are arranged at four corners of a virtual quadrilateral defined along an outer edge of the lifting frame in a plan view and that are capable of performing a contracting action of applying a press-in force to the casing and an extending action of applying a pull-out force to the casing, and the control means includes a tilt sensor configured to detect a change angle of tilt of the lifting frame with respect to a leveled state, four variable throttle valves forming pairs with the four lifting cylinders, respectively, and provided in flow passages through which a hydraulic oil flows out from the respective lifting cylinders in a contracting action state of the lifting cylinders, and a control unit configured to individually adjust throttling degrees of the respective variable throttle valves based on the change angle detected by the tilt sensor.

[0010] Moreover, the control unit adjusts the throttling degrees of the variable throttle valves based on the change angle to increase a flow passage cross-sectional area of the hydraulic oil flowing out from the lifting cylinder located on a tilt upper side out of the two lifting cylinders arranged diagonally to each other in the virtual quadrilateral, and to decrease a flow passage cross-sectional area of the hydraulic oil flowing out from the lifting cylinder located on a tilt lower side.

[0011] Furthermore, the variable throttle valves have an intermediate throttling degree corresponding to an intermediate level of an adjustment range, in an initial state where the contracting action of the lifting cylinders is started.Advantageous Effects

[0012] According to the casing rotator of the present invention, even when the lifting frame tilts during a press-in operation, necessary cylinder press-in forces (outputs in the contracting direction) can be obtained only by performing simple control of individually adjusting the throttling degrees of the respective variable throttle valves to adjust the secondary pressures (back pressures) of the lifting cylinders. Specifically, in correction of the tilt of the lifting frame, indirect control in which adjustment of the cylinder press-in forces is hydraulically achieved is performed to apply a large casing press-in force only to a portion of the casing in contact with an underground obstacle. As a result, the tilt of the lifting frame is corrected to a leveled state, and the press-in operation in which a verticality of the casing is secured can be continued.

[0013] Moreover, the pressure adjustment is performed while focusing on two diagonally-arranged lifting cylinders with the secondary pressures of the respective lifting cylinders considered as a pair (group). Accordingly, the necessary cylinder press-in forces can be obtained at two points (total of four points) on each of the two axes (x axis and y axis) forming the diagonal lines. This has such advantages that the number of control parameters to be taken into consideration is reduced, and setting and checking of values are facilitated.

[0014] Moreover, since the variable throttle valves have the intermediate throttling degree in the initial state, it is possible to secure a maximum change width (increasing width and reducing width) of the necessary cylinder press-in forces in the tilted state while securing the necessary cylinder press-in forces in the leveled state of the lifting frame. Accordingly, press-in operations corresponding to various geological structures on the site can be stably performed.BRIEF DESCRIPTION OF DRAWINGS

[0015] FIG. 1 is a front diagram illustrating a schematic configuration of a casing rotator in one embodiment of the present invention.

[0016] FIG. 2 is a plan diagram of the same embodiment.

[0017] FIG. 3 is a schematic configuration diagram of control means in the same embodiment.

[0018] FIG. 4 is a diagram illustrating a model of four lifting cylinders.

[0019] FIG. 5 is a diagram defining an xyz axis coordinate system on a top surface of a lifting frame in the same embodiment.

[0020] FIG. 6 is a diagram illustrating a tilt (θAC) of the lifting frame in an x axis direction and a tilt (θBD) of the lifting frame in a y axis direction in the same embodiment.

[0021] FIGS. 7A and 7B are diagrams for explaining a method of correcting the tilt of the lifting frame in the same embodiment.

[0022] FIG. 8 is a graph illustrating a relationship between a primary pressure and a cylinder press-in force in the same embodiment.

[0023] FIG. 9 is a block line diagram illustrating a flow of control by a control unit in the same embodiment.

[0024] FIG. 10 is a hydraulic system diagram for explaining a press-in operation of a casing in a conventional technique.

[0025] FIG. 11 is a graph illustrating a relationship between a relief set pressure and a casing press-in force in the conventional technique.DESCRIPTION OF EMBODIMENTS

[0026] FIGS. 1 to 9 are diagrams illustrating one embodiment of a casing rotator of the present invention. As illustrated in FIGS. 1 to 3, the casing rotator 11 is roughly configured to include a base frame 12 configured to be installed on a ground, a lifting frame 14 provided above the base frame 12 to be liftable and lowerable via four lifting cylinders 13A, 13B, 13C, and 13D, a chuck mechanism 16 configured to be lifted and lowered along with the lifting frame 14 and supported to be movable in an up-down direction by four chuck cylinders (only one chuck cylinder is illustrated) 15 standing upright on the lifting frame 14, a rotation transmission mechanism 18 configured to hydraulicly apply a rotating force to a casing 17 held by the chuck mechanism 16, and control means 19 configured to perform control of leveling the lifting frame 14. Moreover, casing insertion holes 20 penetrating the base frame 12, the lifting frame 14, and the chuck mechanism 16 in the vertical direction are formed, respectively, in center portions of the base frame 12, the lifting frame 14, and the chuck mechanism 16.

[0027] The four lifting cylinders 13A to 13D are each a double-acting hydraulic cylinder including a hydraulic oil supply-discharge port in each of a rod-side hydraulic chamber 13a and a head-side hydraulic chamber 13b, and are arranged at four corners of a virtual quadrilateral VR defined along an outer edge of the lifting frame 14 in a plan view as illustrated in FIG. 2. Moreover, the four lifting cylinders are configured to be connected in parallel in terms of hydraulic circuit such that a hydraulic pressure (primary pressure) P1 based on a value of a relief set pressure evenly acts on the four lifting cylinders. Reference can be made to FIG. 10 and the conventional configuration of Patent Literature 1 regarding this point.

[0028] In a press-in operation in which a press-in force is applied to the casing 17, the hydraulic oil is supplied to the rod-side hydraulic chambers 13a of the respective lifting cylinders 13A to 13D to cause the lifting cylinders 13A to 13D to simultaneously perform a contracting action. In this case, in each of the lifting cylinders 13A to 13D, movement of a piston causes the hydraulic oil in the head-side hydraulic chamber 13b to be pushed out and flow out to a head-side flow passage 21. This hydraulic oil returns to a tank (not illustrated) while merging in the way. This causes the chuck mechanism 16 and the lifting frame 14 to be integrally lowered, and the casing 17 including a drilling bit 17a at a tip is pressed into the ground.

[0029] Meanwhile, in a pull-out operation in which a pull-out force is applied to the casing 17, the hydraulic oil is supplied to the head-side hydraulic chambers 13b of the respective lifting cylinders 13A to 13D to cause the lifting cylinders 13A to 13D to simultaneously perform an extending action. In this case, in each of the lifting cylinders 13A to 13D, movement of the piston causes the hydraulic oil in the rod-side hydraulic chamber 13a to be pushed out and flow out to a rod-side flow passage 22. This hydraulic oil returns to the tank while merging in the way. This causes the chuck mechanism 16 and the lifting frame 14 to be integrally lifted, and the casing 17 is pulled out from the ground.

[0030] The control means 19 is additionally installed as a component of a main body of the casing rotator 11 or as a component of a hydraulic unit (hydraulic pressure source device) of the casing rotator 11, and, as illustrated in FIG. 3, is roughly configured to include a tilt sensor 23 configured to detect a change angle of tilt of the lifting frame 14 with respect to a leveled state, four variable throttle valves 24 forming pairs with the respective four lifting cylinders 13A to 13D and provided in the respective head-side flow passages 21, a control unit (CPU) 25 configured to individually adjust throttling degrees of the respective variable throttle valves 24 based on the change angle detected by the tilt sensor 23, and a storage unit (memory and the like) 26 that stores a control program to be executed in the control unit 25. The control unit 25 and the storage unit 26 are, for example, incorporated in a controller 27 including various I / O interfaces.

[0031] The tilt sensor 23 is, for example, a two-axis tilt sensor installed in the lifting frame 14, and detects the tilt of the lifting frame 14 with respect to the leveled state as an absolute angle. In the present embodiment, as illustrated in FIGS. 4 to 6, intersections between a top surface of the lifting frame 14 and the center axes of the four lifting cylinders 13A to 13D that exert cylinder press-in forces (outputs in a contracting direction) FA, FB, FC, and FD are referred to as A, B, C, and D, respectively, an x axis is defined on a diagonal line connecting the two points of A and C as a first pair, a y axis is defined on a diagonal line connecting the two points of B and D as a second pair, and a z axis is defined to extend in the vertical direction from an intersection of the x axis and the y axis (FIGS. 4 and 5).

[0032] The tilt sensor 23 detects a tilt angle of the z-axis direction in the z-axis direction of the lifting frame 14 as θAC, and detects a tilt angle of the z-axis direction in the y axis direction as θBD, based on an xyz axis coordinate system defined on the top surface of the lifting frame 14 as described above (FIG. 6). The change angles (actual angles) θAC and θBD detected by the tilt sensor 23 are transmitted to the controller 27, and are used in hydraulic control for correcting the tilt of the lifting frame 14 in the control unit 25.

[0033] Each of the variable throttle valves 24 is, for example, incorporated in an electromagnetic proportional control valve in which a throttling degree is changed depending on an electric control signal from the controller 27. When the throttling degree is increased, a flow passage cross-sectional area (throttle diameter) decreases, and a flow rate of the passing hydraulic oil decreases. Meanwhile, when the throttling degree is reduced, the flow passage cross-sectional area (throttle diameter) increases, and the flow rate of the passing hydraulic oil increases. In the present embodiment, a value of an electric current supplied to an attached solenoid is adjusted such that the variable throttle valves 24 have an intermediate throttling degree corresponding to an intermediate level of an adjustment range (state where the flow passage area is throttled to an intermediate level), in an initial state where the contracting action of the lifting cylinders 13A to 13D is started, that is at start of the press-in operation of the casing 17. Meanwhile, the variable throttle valves 24 have the minimum throttling degree (state where the flow passage area is increased to a maximum level and is not throttled), in an initial state where the extending action of the lifting cylinders 13A to 13D is started, that is at start of the pull-out operation of the casing 17.

[0034] In the casing rotator 11 configured as described above, when part of the tip (drilling bit 17a) of the casing 17 comes into contact with an underground obstacle (see reference sign R in FIG. 10) such as a boulder during the press-in operation, a reaction force received by the tip of the casing 17 in a contact portion differs from that in a non-contact portion. This disrupts drilling in a portion of the tip of the casing 17 where the resistance acting on the drilling bit 17a is large, and causes the drilling to progress in a portion on the opposite side where the resistance acting on the drilling bit 17a is relatively small. As a result, as illustrated in FIG. 7A, the lengths (strokes) of the four lifting cylinders 13A to 13D become uneven, and the lifting frame 14 tilts.

[0035] Accordingly, for the x axis direction, for example, the control unit 25 adjusts the throttling degrees of the respective variable throttle valves 24 based on the change angles θAC and θBD detected by the tilt sensor 23 to increase the flow passage cross-sectional area of the hydraulic oil flowing out from the lifting cylinder 13A located on the tilt upper side where the casing 17 is desired to be firmly pressed in out of the two lifting cylinders 13A and 13C (two lifting cylinders arranged on one diagonal line of the virtual quadrilateral VR), and to decrease the flow passage cross-sectional area of the hydraulic oil flowing out from the lifting cylinder 13C located on the tilt lower side where the casing 17 does not have to be pressed in so much. Similarly, for the y axis direction, the control unit 25 adjusts the throttling degrees of the respective variable throttle valves 24 to increase the flow passage cross-sectional area of the hydraulic oil flowing out from the lifting cylinder 13D located on the tilt upper side where the casing 17 is desired to be firmly pressed in out of the two lifting cylinders 13B and 13D (two lifting cylinders arranged on the other diagonal line of the virtual quadrilateral VR), and to decrease the flow passage cross-sectional area of the hydraulic oil flowing out from the lifting cylinder 13B located on the tilt lower side where the casing 17 does not have to be pressed in so much.

[0036] For example, focusing on the lifting cylinder 13A on the tilt upper side, as illustrated in FIG. 3, the throttling degree of the variable throttle valve 24 is controlled to be reduced from the intermediate throttling degree. As a result, the flow passage area through which the hydraulic oil flowing out to the head-side flow passage 21 passes increases, and a secondary pressure (back pressure) P2 of the lifting cylinder 13A decreases. Then, as described in the calculation formula of the cylinder press-in force FA (see Formula 1 in explanation of Background Art), the cylinder press-in force (output in the contracting direction) FA increases due to the decrease of the secondary force (P2×A2) that hinders a primary force (P1×A1). This allows a large casing press-in force Fcp to be applied to the portion in contact with the underground obstacle, and allows the casing 17 to be firmly pressed in.

[0037] Moreover, focusing on the lifting cylinder 13C on the tilt lower side, the throttling degree of the variable throttle valve 24 is controlled to be increased from the intermediate throttling degree. As a result, the flow passage area through which the hydraulic oil flowing out to the head-side flow passage 21 passes decreases, and a secondary pressure (back pressure) P2 of the lifting cylinder 13C increases. Then, as described in the calculation formula of the cylinder press-in force FC, the cylinder press-in force (output in the contracting direction) FC decreases due to the increase of the secondary force (P2×A2) that hinders a primary force (P1×A1). This allows a small casing press-in force Fcp to be applied to the portion not in contact with the underground obstacle, and allows the casing 17 not to be pressed in so much.

[0038] As described above, the lifting cylinders 13A and 13C located on one diagonal line and the lifting cylinders 13B and 13D located on the other diagonal line are considered as pairs, a control target of setting (leveling) the tilt of the lifting frame 14 to 0 (zero) is given, the tilt of the lifting frame 14 is detected by the tilt sensor 23, and the control of individually adjusting the variable throttle valves 24 provided in the head-side flow passages (secondary flow passages) 21 of the respective lifting cylinders 13A to 13D depending on the tilt is performed. In this case, as illustrated in FIG. 8, the hydraulic pressure (primary pressure) P1 supplied to the rod-side hydraulic chambers 13a of the respective lifting cylinders 13A to 13D are fixed, but P2 change depending on the throttling degrees of the variable throttle valves 24. As a result, the cylinder press-in forces FA, FB, FC, and FD change to increase or decrease within a predetermined range depending on the throttling degrees of the variable throttle valves 24.

[0039] For example, for the tilt of the lifting frame 14 as illustrated in FIG. 7A, the control unit 25 executes the control program and adjusts the throttling degree of the variable throttle valve 24 paired with the lifting cylinder 13A to “small”, the throttling degree of the variable throttle valve 24 paired with the lifting cylinder 13C to “intermediate”, the throttling degree of the variable throttle valve 24 paired with the lifting cylinder 13B to “large”, and the throttling degree of the variable throttle valve 24 paired with the lifting cylinder 13D to “minimum (zero)”. In this case, magnitude relationships of the cylinder press-in forces FA, FB, FC, and FD are such that relationships of FD>FA>FC>FB are established as illustrated in FIG. 8. An increase of the cylinder press-in force FD of the lifting cylinder 13D thereby mainly contributes to the press-in operation of the casing 17, and the large casing press-in force Fcp is applied only to the portion of the casing 17 in contact with the underground obstacle. As a result, the forces are applied such that the tilt of the lifting frame 14 is decreased, that is leveled as illustrated in FIG. 7B.

[0040] In this case, as illustrated in FIG. 9, the cylinder press-in forces FA, FB, FC, and FD are calculated by using Formulae 2 to 7 described below, with the control targets for leveling the lifting frame 14 being θAC0=0 and θBD0=0.FA=(PAC+KAC)F0   Formula 2FC=(PAC−KAC)F0   Formula 3KAC=kAC(θAC0−θAC)   Formula 4FB=(PBD+KBD)F0   Formula 5FD=(PBD−KBD)F0   Formula 6KBD=kBD(θBD0−θBD)   Formula 7F0: cylinder press-in force in case where there is no throttlingPAC: proportion of press-in forces of two lifting cylinders 13A and 13C in case where tilt is 0(0<PAC<1)PBD: proportion of press-in forces of two lifting cylinders 13B and 13D in case where tilt is 0(0<PBD<1)kAC: control parameter in diagonal AC direction(value satisfying kAC>0 and PAC−KAC>0)kBD: control parameter in diagonal BD direction(value satisfying kBD>0 and PBD−KBD>0)

[0048] θAC0: target angle (0) in diagonal AC direction

[0049] θBD0: target angle (0) in diagonal BD direction

[0050] As an example, assume that F0=1000 N, PAC=0.5 and kAC=0.05, and the casing rotator 11 is in a state where the diagonal line AC (x axis) is tilted by 5 deg (θAC=5 deg) in the lifting frame 14 during the press-in operation, the lifting cylinder 13C is located on the tilt upper side, and the lifting cylinder 13A is located on the tilt lower side. In this case, PAC=0.5 is a setting value in the case where press-in is desired to be performed at force of ½×F0 when the tilt of the lifting frame 14 is 0, that is leveled, and PAC is set as desired by an operator. A press-in force of 500 N is thereby exhibited by each lifting cylinder in the press-in operation in a uniform geological layer. KAC is a setting value of a magnitude of force of response based on the change angle θAC, and is set in advance based on specifications of the casing rotator 11, construction conditions, and the like.

[0051] When the values are substituted into Formula 4, calculation of KAC=0.05×(0−5)=−0.25 can be performed. Moreover, when the values are substituted into Formulae 2 and 3, calculation of FA=(0.5−0.25)×1000=250 N and FC=(0.5+0.25)×1000=750 N can be performed. FA and FC thereby change (increase and decrease) in conjunction with each other depending on the tilt of the lifting frame 14 with the press-in force of ½×F0 being a reference, and the forces are applied such that the tilt of the lifting frame 14 decreases.

[0052] When the tilt of the diagonal line BD (y axis) is taken into consideration in addition to the tilt of the diagonal line AC (x axis) in this case, FB and FD are calculated by using Formulae 5 to 7 (for example, FB=300 N and FD=700 N), and change (increase and decrease) in conjunction with each other depending on the tilt of the lifting frame 14 with the press-in force of ½×F0 being a reference, and the forces are applied such that the tilt of the lifting frame 14 decreases. The throttling degrees of the respective variable throttle valves 24 are thereby adjusted such that the cylinder press-in forces FA, FB, FC, and FD of the respective lifting cylinders 13A to 13D match the calculation results (FA=250 N, FC=750 N, FB=300 N, and FD=700 N) obtained by using Formulae 2 to 7, and the press-in operation of the casing rotator 11 is performed based on this control.

[0053] As described above, according to the casing rotator 11 of the present invention, even when the lifting frame 14 tilts during the press-in operation, the necessary cylinder press-in forces (outputs in the contracting direction) FA, FB, FC, and FD can be obtained only by performing simple control of individually adjusting the throttling degrees of the respective variable throttle valves 24 to adjust the secondary pressures (back pressures) of the lifting cylinders 13A to 13D. Specifically, in the correction of the tilt of the lifting frame 14, indirect control in which the adjustment of the cylinder press-in forces FA, FB, FC, and FD is hydraulically achieved is performed to apply a large casing press-in force Fcp only to a portion of the casing 17 in contact with an underground obstacle. As a result, the tilt of the lifting frame 14 is corrected to a leveled state, and the press-in operation in which the verticality of the casing 17 is secured can be continued.

[0054] Moreover, the pressure adjustment is performed while focusing on two diagonally-arranged lifting cylinders (13A and 13C or 13B and 13D) with the secondary pressures of the respective lifting cylinders considered as a pair (group). Accordingly, the necessary cylinder press-in forces FA, FB, FC, and FD can be obtained at two points (total of four points) on each of the two axes (x axis and y axis) forming the diagonal lines. This has such advantages that the number of control parameters to be taken into consideration is reduced, and setting and checking of values are facilitated.

[0055] Moreover, since the variable throttle valves 24 have the intermediate throttling degree in the initial state, it is possible to secure a maximum change width (increasing width and reducing width) of the necessary cylinder press-in forces FA, FB, FC, and FD in the tilted state while securing the necessary cylinder press-in forces FA, FB, FC, and FD in the leveled state of the lifting frame 14. Accordingly, press-in operations corresponding to various geological structures on the site can be stably performed.

[0056] Note that the present invention is not limited to the above-mentioned embodiment. The control means only needs to be configured to be mainly incorporated in an existing system, and may be changed as appropriate depending on the specifications of the casing rotator, and the parts may be arranged as desired. For example, the tilt sensor and the variable throttle valves may have any configurations, arrangement, setting conditions (for example, adjustment of throttling degrees), and the like, and the specifications of the control program may be any specifications.REFERENCE SIGNS LIST11 casing rotator

[0058] 12 base frame

[0059] 13 lifting cylinder

[0060] 13a rod-side hydraulic chamber

[0061] 13b head-side hydraulic chamber

[0062] 14 lifting frame

[0063] 15 chuck cylinder

[0064] 16 chuck mechanism

[0065] 17 casing

[0066] 17a drilling bit

[0067] 18 rotation transmission mechanism

[0068] 19 control means

[0069] 20 casing insertion hole

[0070] 21 head-side flow passage

[0071] 22 rod-side flow passage

[0072] 23 tilt sensor

[0073] 24 variable throttle valve

[0074] 25 control unit

[0075] 26 storage unit

[0076] 27 controller

Claims

1. A casing rotator comprising:a base frame configured to be installed on a ground;a lifting frame provided above the base frame to be liftable and lowerable via four lifting cylinders;a chuck mechanism configured to be lifted and lowered along with the lifting frame;a rotation transmission mechanism configured to apply a rotating force to a casing held by the chuck mechanism; andcontrol means configured to perform control of leveling the lifting frame, whereinthe four lifting cylinders are hydraulic cylinders that are arranged at four corners of a virtual quadrilateral defined along an outer edge of the lifting frame in a plan view and that are capable of performing a contracting action of applying a press-in force to the casing and an extending action of applying a pull-out force to the casing, andthe control means includesa tilt sensor configured to detect a change angle of tilt of the lifting frame with respect to a leveled state,four variable throttle valves forming pairs with the four lifting cylinders, respectively, and provided in flow passages through which a hydraulic oil flows out from the respective lifting cylinders in a contracting action state of the lifting cylinders, anda control unit configured to individually adjust throttling degrees of the respective variable throttle valves based on the change angle detected by the tilt sensor.

2. The casing rotator according to claim 1, wherein the control unit adjusts the throttling degrees of the variable throttle valves based on the change angle to increase a flow passage cross-sectional area of the hydraulic oil flowing out from the lifting cylinder located on a tilt upper side out of the two lifting cylinders arranged diagonally to each other in the virtual quadrilateral, and to decrease a flow passage cross-sectional area of the hydraulic oil flowing out from the lifting cylinder located on a tilt lower side.

3. The casing rotator according to claim 2, wherein the variable throttle valves have an intermediate throttling degree corresponding to an intermediate level of an adjustment range, in an initial state where the contracting action of the lifting cylinders is started.

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