Hydraulic system

Abstract

To provide a hydraulic device capable of easily attaining reduction of shock in the case of inversion.SOLUTION: A hydraulic device (1) comprises: a hydraulic cylinder (10) including a piston (12) which is reciprocally driven, a first port (10a) and a second port (10b); a hydraulic pump (30) which is rotated unidirectionally for supplying a working oil from an oil tank (20) to the hydraulic cylinder (10); a motor (40) of which the rotation speed is variable and which drives the hydraulic pump (30); a brake valve (50) for controlling a pressure of the working oil returning from the hydraulic cylinder (10) to the oil tank (20); a direction switching valve (60) for switching supply of the working oil to one of the first port (10a) and the second port (10b) and discharge of the working oil from the other of the first port (10a) and the second port (10b); and a control device (80) which controls the motor (40) and the direction switching valve (60).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to hydraulic systems. [Background technology]

[0002] A conventional reciprocating reversing drive system includes a shockless switching valve (see Patent Document 1). In this reciprocating reversing drive system, the moving speed of the spool of the shockless switching valve is adjusted to reduce the shock when the hydraulic cylinder is reversed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 7-158602 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the above-mentioned conventional reciprocating reverse drive system has a problem in that adjustment of the moving speed of the spool in the shockless switching valve is complicated.

[0005] The present disclosure proposes a hydraulic device that can easily reduce shock during reversal. [Means for solving the problem]

[0006] The hydraulic system of the present disclosure comprises: a hydraulic cylinder having a piston that reciprocates, a first port, and a second port that discharges hydraulic oil when hydraulic oil is supplied to the first port and that is supplied with hydraulic oil when hydraulic oil is discharged from the first port; An oil tank for storing hydraulic oil; a unidirectional hydraulic pump for supplying hydraulic oil from the oil tank to the hydraulic cylinder; A motor having a variable rotation speed and driving the hydraulic pump; a brake valve for controlling the pressure of hydraulic oil returning from the hydraulic cylinder to the oil tank; a directional control valve that switches between supply of hydraulic oil to one of the first port and the second port and discharge of hydraulic oil from the other of the first port and the second port; a control device for controlling the motor and the directional control valve; Equipped with.

[0007] The directional control valve according to the present disclosure does not include a shockless control valve, which is a control valve that can change the moving speed of the spool in multiple stages according to the spool position when switching the direction in order to prevent a sudden change in the opening area.

[0008] According to the present disclosure, the driving speed of the piston is controlled by controlling the rotation speed of the motor to adjust the discharge flow rate from the hydraulic pump. The driving direction of the piston is controlled by switching the supply destination of the hydraulic oil from the hydraulic pump using a directional control valve that does not have a shockless function. In this configuration, the shock when the piston reverses can be reduced by appropriately controlling the speed of the piston. This makes it easier to reduce the shock when the piston reverses, compared to when a shockless switching valve is used to reduce the shock when the piston reverses.

[0009] In one embodiment, the control device controls the rotation speed of the motor so that the acceleration of the piston is continuous.

[0010] According to the above embodiment, the acceleration of the piston is continuous, so that the piston accelerates and decelerates smoothly, thereby reducing shock when the piston reverses direction.

[0011] In one embodiment, The control device controls the brake valve. The control device controls the brake valve when the piston decelerates to control the pressure of hydraulic oil returning from the hydraulic cylinder to the oil tank through the brake valve.

[0012] Compared to a system in which the pressure control valve is constantly operated to constantly control the pressure of the hydraulic oil returning from the hydraulic cylinder to the oil tank, according to the above embodiment, the pressure of the hydraulic oil returning from the hydraulic cylinder to the oil tank is controlled by the brake valve when the piston decelerates, thereby reducing losses in the brake valve at times other than when the piston decelerates.

[0013] In one embodiment, The control device is capable of executing flow control for controlling a discharge flow rate of the hydraulic pump by controlling a rotation speed of the motor, and pressure control for controlling a discharge pressure of the hydraulic pump by controlling a rotation speed of the motor, The control device switches the hydraulic pump from flow control to pressure control during a reversal operation in which the drive direction of the piston is reversed.

[0014] When switching by the directional control valve, the pressure of the hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder may rise excessively, causing vibration in the piston. In response to this, according to the above embodiment, by performing pressure control that controls the pressure during the reversing movement of the piston, the pressure of the hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder when switching by the directional control valve is prevented from rising excessively, and vibration in the cylinder can be prevented. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic block diagram of a large surface grinding machine using a hydraulic device according to a first embodiment of the present disclosure. [Diagram 2] 5 is a graph showing a piston acceleration pattern and a piston velocity pattern according to the present embodiment. [Diagram 3] 4 is a graph for explaining the operation of the hydraulic device according to the first embodiment. [Figure 4] 10 is a graph showing a piston acceleration pattern and a piston velocity pattern in a modified example of the first embodiment. [Diagram 5]10 is a graph illustrating the operation of the hydraulic device according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, a hydraulic device according to an embodiment of the present disclosure will be described with reference to the accompanying drawings.

[0017] [First embodiment] FIG. 1 is a schematic block diagram of a large surface grinding machine using a hydraulic device 1 according to this embodiment.

[0018] Referring to FIG. 1, a hydraulic device 1 of this embodiment reciprocates a movable table 2 having a weight of, for example, 20 to 30 tons.

[0019] The movable table 2 supports a workpiece on its upper surface. As described above, the movable table 2 is reciprocated by the hydraulic device 1. The movable table 2 is provided with a first position detection sensor 3 and a second position detection sensor 4 for detecting the position of the movable table 2. The first position detection sensor 3 is provided at an end of the movable table 2 on one side in the driving direction, and the second position detection sensor 4 is provided at an end of the movable table 2 on the other side in the driving direction. In the following description, the driving direction of the movable table 2 may be referred to as the X direction. Also, the direction from one side to the other side in the X direction may be referred to as the +X direction, and the direction from the other side to one side in the X direction may be referred to as the -X direction.

[0020] The hydraulic device 1 of this embodiment includes a hydraulic cylinder 10, an oil tank 20, a hydraulic pump 30, a motor 40, a brake valve 50, a directional control valve 60, a relief valve 70, and a control device 80.

[0021] The hydraulic cylinder 10 includes a cylinder tube 11, a piston 12 that reciprocates within the cylinder tube 11, and piston rods 13A and 13B that are connected to both end faces of the piston 12. A movable table 2 is connected to the piston rods 13A and 13B. The hydraulic cylinder 10 also includes a first port 10a and a second port 10b. The second port 10b discharges hydraulic oil when the hydraulic oil is supplied to the first port 10a, and receives hydraulic oil from the hydraulic pump 30 when the hydraulic oil is discharged from the first port 10a.

[0022] The hydraulic pump 30 supplies hydraulic oil stored in the oil tank 20 to the hydraulic cylinder 10. The hydraulic pump 30 is a unidirectional hydraulic pump. The hydraulic pump 30 is a fixed displacement pump. The hydraulic pump 30 includes a pressure sensor (not shown) that detects the discharge pressure and a flow rate sensor (not shown) that detects the discharge flow rate.

[0023] The motor 40 is a variable speed motor that drives the hydraulic pump 30. The rotation speed of the motor 40 can be increased or decreased within a certain range by a motor rotation speed control function (not shown) that the control device 80 has.

[0024] The brake valve 50 is provided in a flow path that returns the hydraulic oil discharged from the hydraulic cylinder 10 to the oil tank 20. The brake valve 50 of the present embodiment is an electromagnetic proportional pressure control valve.

[0025] An inlet port 51 of the brake valve 50 is connected to one of the first port 10a and the second port 10b of the hydraulic cylinder 10 via a directional control valve 60. Specifically, the inlet port 51 of the brake valve 50 is connected to one of the first port 10a and the second port 10b of the hydraulic cylinder 10, which discharges hydraulic oil, via the directional control valve 60. In addition, an outlet port 52 of the brake valve 50 is connected to the oil tank 20.

[0026] The brake valve 50 is an electromagnetic proportional pressure control valve whose set pressure can be changed according to the input current, and controls the pressure of the input port 51 to be approximately constant. As a result, the brake valve 50 adjusts the pressure (back pressure) on the discharge side of the hydraulic oil of the hydraulic cylinder 10 according to the magnitude of the current supplied to the solenoid 53.

[0027] The directional control valve 60 switches the supply destination of the hydraulic oil discharged from the hydraulic pump 30. The directional control valve 60 in this embodiment is an electromagnetic control valve.

[0028] When the first solenoid 61 is energized and the second solenoid 62 is not energized, the directional control valve 60 is in a first switching position on the right side. In the first switching position, the first port 10a of the hydraulic cylinder 10 communicates with the discharge side of the hydraulic pump 30. In addition, in the first switching position, the second port 10b of the hydraulic cylinder 10 communicates with the inlet port 51 of the brake valve 50.

[0029] On the other hand, when the first solenoid 61 is de-energized and the second solenoid 62 is energized, the directional control valve 60 is in the second switching position on the left side. In the second switching position, the second port 10b of the hydraulic cylinder 10 communicates with the discharge side of the hydraulic pump 30. In addition, in the second switching position, the first port 10a of the hydraulic cylinder 10 communicates with the inlet port 51 of the brake valve 50.

[0030] The relief valve 70 is provided downstream (discharge side) of the hydraulic pump 30 and upstream of the directional control valve 60. A portion of the hydraulic oil discharged from the hydraulic pump 30 is not supplied to the hydraulic cylinder 10, but is returned to the oil tank 20 via the relief valve 70.

[0031] The relief valve 70 is a pilot-operated relief valve. An inlet port 71 of the relief valve 70 is connected to the discharge side of the hydraulic pump 30. In addition, an outlet port 72 of the relief valve 70 is connected to the oil tank 20. When the force due to the pressure input to the inlet port 71 of the relief valve 70 exceeds the biasing force of a spring 73, the relief valve 70 opens. In this embodiment, the control device 80 appropriately controls the discharge pressure or discharge flow rate of the hydraulic pump 30, so that the relief valve 70 does not operate.

[0032] The control device 80 receives position detection signals indicating the position of the movable table 2 from the first position detection sensor 3 and the second position detection sensor 4, and outputs a drive signal to drive the motor 40, an excitation signal to excite the first solenoid 61, an excitation signal to excite the second solenoid 62, and an excitation signal to excite the solenoid 53 of the brake valve 50.

[0033] The control device 80 controls the pressure and flow rate of the hydraulic oil supplied from the hydraulic pump 30 to the hydraulic cylinder 10 by controlling the rotation speed of the motor 40. In this way, the control device 80 controls the speed of the piston 12. The control device 80 also switches the switching position of the directional control valve 60 to change the port (first port 10a or second port 10b) through which the hydraulic oil is supplied from the hydraulic pump 30, thereby reversing the drive direction of the piston 12. Furthermore, the control device 80 controls the set pressure of the brake valve 50 so that the pressure (back pressure) on the discharge side of the hydraulic oil of the hydraulic cylinder 10 becomes a predetermined pressure, thereby controlling the pressure (meter-in pressure) on the input side of the hydraulic oil of the hydraulic cylinder 10 not to become negative pressure.

[0034] The control device 80 is capable of performing flow control, which controls the rotation speed of the motor 40 to control the discharge flow rate of the hydraulic pump 30, and pressure control, which controls the rotation speed of the motor 40 to control the discharge pressure of the hydraulic pump 30.

[0035] In the flow rate control, the rotation speed of the motor 40 (the rotation speed of the hydraulic pump 30) is controlled so that the discharge flow rate of the hydraulic pump 30 becomes a flow rate set value. In this embodiment, since the hydraulic pump 30 is a fixed displacement pump, the discharge flow rate of the hydraulic pump 30 is calculated by multiplying the pump capacity (discharge flow rate per rotation) and the rotation speed of the motor 40 per unit time.

[0036] In the flow rate control, the discharge flow rate of the hydraulic pump 30 is controlled so that the piston 12 operates according to a speed pattern generated in advance. That is, in the flow rate control, the rotation speed of the motor 40 (the rotation speed of the hydraulic pump 30) is controlled so that the piston 12 operates according to the above speed pattern. The above speed pattern is data that represents the speed at which the piston 12 moves from the time it starts to move until it stops. The speed pattern of the piston 12 is calculated from the acceleration pattern of the piston 12. The above acceleration pattern is data that represents the acceleration at which the piston 12 moves from the time it starts to move until it stops.

[0037] In the pressure control, the rotation speed of the motor 40 (the rotation speed of the hydraulic pump 30) is controlled so that the discharge pressure of the hydraulic pump 30 becomes a pressure setting value.

[0038] Hereinafter, the operation of the hydraulic device 1 of this embodiment will be described with reference to FIGS.

[0039] Fig. 2 is a graph showing an acceleration pattern of piston 12 and a velocity pattern of piston 12 according to this embodiment. In Fig. 2, the horizontal axis is time and the vertical axis is an arbitrary scale. Fig. 2 shows, from the top, an acceleration pattern, a trapezoidal velocity pattern obtained by integrating the acceleration pattern, and a first-order lag velocity pattern obtained by applying a first-order lag filter to the trapezoidal velocity pattern.

[0040] Referring to FIG. 2, the control device 80 generates a speed pattern by integrating a pre-planned acceleration pattern. In this embodiment, an acceleration pattern in which the acceleration changes stepwise is used as the acceleration pattern. That is, in this embodiment, a discontinuous acceleration pattern is used as the acceleration pattern. By integrating the acceleration pattern, a trapezoidal speed pattern in which an acceleration portion, a constant speed portion, and a deceleration portion are repeated is obtained. In addition, a first-order lag filter is applied to the trapezoidal speed pattern to obtain a first-order lag speed pattern. In the first-order lag speed pattern, sudden changes in speed between the acceleration portion and the constant speed portion and between the deceleration portion and the constant speed portion are mitigated compared to the trapezoidal speed pattern.

[0041] FIG. 3 is a graph showing the operation of the hydraulic device 1 of this embodiment. In FIG. 3, the horizontal axis is time, and the vertical axis is an arbitrary scale. In FIG. 3, from the top, the excitation state of the first solenoid 61, the excitation state of the second solenoid 62, the control of the control device 80, the discharge flow rate of the hydraulic pump 30, the discharge pressure of the hydraulic pump 30, the set pressure of the brake valve 50, the speed of the piston 12, and the acceleration of the piston 12 are shown. The acceleration of the piston 12 is shown by overlapping it with a two-dot chain line. Times t1 to t7 shown in FIG. 3 correspond to times t1 to t7 shown in FIG. 2. In addition, in FIG. 3, the speed of the piston 12, the acceleration of the piston 12, and the acceleration of the movable table 2 show simulation results calculated based on the excitation state of the first solenoid 61, the excitation state of the second solenoid 62, the control of the control device 80, the discharge flow rate of the hydraulic pump 30, the discharge pressure of the hydraulic pump 30, and the set pressure of the brake valve 50.

[0042] 3 shows the operation of the hydraulic device 1 when the piston 12 is driven in the +X direction, and then the driving direction of the piston 12 is reversed and the piston 12 is driven in the -X direction. Specifically, the piston 12 is driven in the +X direction from time t1 to t4, and then the driving direction of the piston 12 is reversed at time t4, and the piston 12 is driven in the -X direction from time t4 to t7.

[0043] In this embodiment, the control device 80 executes flow rate control from time t1 to t7. In the flow rate control, the control device 80 controls the rotation speed of the motor 40 (the rotation speed of the hydraulic pump 30), the brake valve 50, and the directional control valve 60 so that the piston 12 operates according to a first-order lag speed pattern (shown in FIG. 2).

[0044] 3, during times t1 to t4, the first solenoid 61 of the directional control valve 60 is on and the second solenoid 62 is off. At this time, hydraulic oil is supplied from the hydraulic pump 30 to the first port 10a of the hydraulic cylinder 10, and hydraulic oil is discharged from the second port 10b of the hydraulic cylinder 10. As a result, the piston 12 is driven in the +X direction.

[0045] From time t1 to t4, the control device 80 controls the discharge flow rate of the hydraulic pump 30 (the flow rate of hydraulic oil supplied to the first port 10a) and the set pressure of the brake valve 50 so that the piston 12 operates according to a preset first-order lag speed pattern (shown in FIG. 2).

[0046] During the period from time t1 to time t2 when the speed is increasing according to the first-order lag speed pattern, the control device 80 controls the rotation speed of the motor 40 so as to generally increase the discharge flow rate of the hydraulic pump 30. As a result, the piston 12 is driven in the +X direction while being accelerated during the period from time t1 to t2.

[0047] Between time t2 and time t3 when the speed is constant in the first-order lag speed pattern, the control device 80 controls the rotation speed of the motor 40 so that the discharge flow rate of the hydraulic pump 30 becomes approximately constant. As a result, the piston 12 is driven in the +X direction at a constant speed between times t2 and t3.

[0048] During the period from time t3 to time t4 when the speed is decreasing according to the first-order lag speed pattern, the control device 80 controls the rotation speed of the motor 40 so as to generally decrease the discharge flow rate of the hydraulic pump 30. As a result, the piston 12 is driven in the +X direction while being decelerated during the period from time t4 to t5.

[0049] The control device 80 increases the set pressure of the brake valve 50 at time t3' before the reversal of the drive direction of the piston 12 (time t4). By increasing the set pressure of the brake valve 50, the pressure (back pressure) on the discharge side of the hydraulic oil of the hydraulic cylinder 10 of the piston 12 increases, and the piston 12 is decelerated. In other words, from time t3' to t4, the discharge flow rate of the hydraulic pump 30 is reduced and the set pressure of the brake valve 50 is increased, thereby decelerating the piston 12 while keeping the pressure (meter-in pressure) on the input side of the hydraulic cylinder 10 in a state where it does not become negative pressure.

[0050] At time t4, the control device 80 controls the directional control valve 60 to switch from the first switching position to the second switching position. That is, the first solenoid 61 of the directional control valve 60 switches from on to off at time t4, and the second solenoid 62 switches from off to on at time t4. As a result, the supply of hydraulic oil to the first port 10a and the discharge of hydraulic oil from the second port 10b are switched to the supply of hydraulic oil to the second port 10b and the discharge of hydraulic oil from the first port 10a, respectively, and the driving direction of the piston 12 is reversed.

[0051] From time t4 to t7, the first solenoid 61 of the directional control valve 60 is off, and the second solenoid 62 is on. At this time, hydraulic oil is supplied from the hydraulic pump 30 to the second port 10b of the hydraulic cylinder 10, and hydraulic oil is discharged from the first port 10a of the hydraulic cylinder 10. As a result, the piston 12 is driven in the -X direction.

[0052] From time t4 to t7, the control device 80 controls the discharge flow rate of the hydraulic pump 30 (the flow rate of hydraulic oil supplied to the second port 10b) and the set pressure of the brake valve 50 so that the piston 12 operates according to a preset first-order lag speed pattern (shown in FIG. 2).

[0053] During the period from time t4 to time t5 when the speed is decreasing in the first-order lag speed pattern, the control device 80 controls the rotation speed of the motor 40 so as to generally increase the discharge flow rate of the hydraulic pump 30. As a result, the piston 12 is driven in the -X direction while being accelerated during the period from time t4 to t5.

[0054] Between time t5 and time t6 when the speed is constant in the first-order lag speed pattern, the control device 80 controls the rotation speed of the motor 40 so that the discharge flow rate of the hydraulic pump 30 is approximately constant. As a result, the piston 12 is driven in the -X direction at a constant speed from time t5 to t6.

[0055] During the period from time t6 to time t7 when the speed is increasing in accordance with the first-order lag speed pattern, the control device 80 controls the rotation speed of the motor 40 so as to generally decrease the discharge flow rate of the hydraulic pump 30. As a result, the piston 12 is driven in the -X direction while being decelerated during the period from time t6 to t7.

[0056] The control device 80 increases the set pressure of the brake valve 50 at time t6' before the reversal of the drive direction of the piston 12 (time t7). By increasing the set pressure of the brake valve 50, the pressure (back pressure) on the discharge side of the hydraulic oil in the hydraulic cylinder 10 of the piston 12 increases, and the piston 12 decelerates. In other words, from time t6' to t7, the discharge flow rate of the hydraulic pump 30 is reduced and the set pressure of the brake valve 50 is increased, thereby decelerating the piston 12.

[0057] As described above, the control device 80 controls the rotation speed of the motor 40 (the rotation speed of the hydraulic pump 30), the brake valve 50, and the directional control valve 60, so that the speed of the piston 12 operates according to a first-order lag speed pattern (shown in FIG. 2). Also, the acceleration of the piston 12 is continuous, unlike the pre-planned discontinuous acceleration pattern (shown in FIG. 2). The acceleration being continuous means that there are no discontinuous points in the acceleration. Also, in this simulation, the movable table 2 is driven with its own natural vibration. Therefore, the acceleration of the movable table 2 oscillates compared to the acceleration of the piston 12.

[0058] The hydraulic device 1 according to this embodiment has the following functions.

[0059] The drive speed of the piston 12 is controlled by controlling the rotation speed of the motor 40 to adjust the discharge flow rate from the hydraulic pump 30. The drive direction of the piston 12 is controlled by switching the port to which hydraulic oil is supplied from the hydraulic pump 30 using the directional control valve 60 that does not have a shockless function. In this configuration, the shock caused when the piston 12 reverses can be reduced by appropriately controlling the speed of the piston 12. This makes it easier to reduce the shock caused when the piston 12 reverses, compared to when a shockless switching valve is used to reduce the shock caused when the piston 12 reverses.

[0060] In addition, since the acceleration of the piston 12 is continuous, the piston 12 smoothly accelerates and decelerates, thereby reducing the shock when the piston 12 reverses direction.

[0061] There is a system in which the pressure control valve is constantly operated so as to constantly control the pressure of the hydraulic oil returning from the hydraulic cylinder 10 to the oil tank 20. In contrast, the pressure of the hydraulic oil returning from the hydraulic cylinder 10 to the oil tank 20 is controlled by the brake valve 50 when the piston 12 decelerates, and the brake valve 50 is opened when the piston 12 is accelerated or driven at a constant speed, so that loss in the brake valve 50 can be reduced except when the piston 12 decelerates.

[0062] [Variations] Fig. 4 is a graph showing an acceleration pattern of the piston 12 and a velocity pattern of the piston 12 according to a modified example of this embodiment. In Fig. 4, the horizontal axis is time and the vertical axis is an arbitrary scale. Fig. 2 shows, from the top, an acceleration pattern and an S-shaped velocity pattern obtained by integrating the acceleration pattern.

[0063] Referring to Fig. 4, the control device 80 generates a speed pattern by integrating a pre-planned acceleration pattern. In the modified example shown in Fig. 4, a trapezoidal acceleration pattern in which the acceleration changes continuously is used as the acceleration pattern. By integrating the acceleration pattern, an S-shaped speed pattern in which acceleration, constant speed, and deceleration are smoothly repeated is obtained. In flow rate control, the control device 80 controls the rotation speed of the motor 40 (the rotation speed of the hydraulic pump 30), the brake valve 50, and the directional control valve 60 so as to operate according to the S-shaped speed pattern.

[0064] [Second embodiment] The second embodiment is similar to the first embodiment except for the operation of the hydraulic device 1, and Figures 1 and 2 are referenced. In the second embodiment, detailed description of the same configuration as the first embodiment will be omitted.

[0065] Fig. 5 is a diagram for explaining the operation of the hydraulic device 1 according to this embodiment. Fig. 5 shows, from the top, the excitation state of the first solenoid 61, the excitation state of the second solenoid 62, the control of the control device 80, the discharge flow rate of the hydraulic pump 30, the discharge pressure of the hydraulic pump 30, the set pressure of the brake valve 50, the speed of the piston 12, and the acceleration of the piston 12. Fig. 5 also shows the simulation results of the speed of the piston 12, the acceleration of the piston 12, and the acceleration of the movable table 2 calculated based on the excitation state of the first solenoid 61, the excitation state of the second solenoid 62, the control of the control device 80, the discharge flow rate of the hydraulic pump 30, the discharge pressure of the hydraulic pump 30, and the set pressure of the brake valve 50.

[0066] 5, the control device 80 of this embodiment alternately executes flow control, which controls the rotation speed of the motor 40 to control the discharge flow rate of the hydraulic pump 30, and pressure control, which controls the rotation speed of the motor 40 to control the discharge pressure of the hydraulic pump 30. The control device 80 of this embodiment executes pressure control during the reversal movement of the piston 12, that is, before and after times t4 and t7. By this control, before and after the spool of the directional control valve 60 passes through the midpoint, the control device 80 limits the discharge pressure of the hydraulic pump 30 so that the discharge pressure of the hydraulic pump 30 does not become excessively high. Also, in this embodiment, in order to improve the vibration suppression effect by the pressure control, a limit value that changes stepwise in conjunction with the switching timing of the directional control valve 60 is set for the discharge pressure of the hydraulic pump 30.

[0067] In this embodiment, the same effects as those of the first embodiment are achieved.

[0068] If the pressure of the hydraulic oil supplied from the hydraulic pump 30 to the hydraulic cylinder 10 rises excessively when the directional control valve 60 is switched in a reversing operation that reverses the drive direction of the piston 12, vibrations may occur in the piston 12. In this embodiment, by performing pressure control that controls the discharge pressure of the hydraulic pump 30 during the reversing operation of the piston 12, an excessive rise in the pressure of the hydraulic oil supplied from the hydraulic pump 30 to the hydraulic cylinder 10 when the directional control valve 60 is switched is suppressed, and vibrations in the piston 12 can be suppressed.

[0069] Although the embodiments have been described above, it will be understood that various changes in form and details are possible without departing from the spirit and scope of the claims. [Explanation of symbols]

[0070] 1 Hydraulic system 2 Movable table 3. First position detection sensor 4 Second position detection sensor 10 Hydraulic cylinder 10a 1st port 10b 2nd port 11 Cylinder tube 12 Piston 13A, 13B Piston rod 20 Oil Tank 30 Hydraulic Pump 40 Motor 50 Brake valve 51 Inlet Port 52 Exit Port 53 Solenoid 60 Directional valve 61 First solenoid 62 Second solenoid 70 Relief valve 71 Inlet Port 72 Exit Port 73 Spring 80 Control device

Claims

1. a hydraulic cylinder (10) having a piston (12) for reciprocating motion, a first port (10a), and a second port (10b) for discharging hydraulic oil when hydraulic oil is supplied to the first port (10a) and for receiving hydraulic oil when hydraulic oil is discharged from the first port (10a); An oil tank (20) for storing hydraulic oil; a unidirectional hydraulic pump (30) for supplying hydraulic oil from the oil tank (20) to the hydraulic cylinder (10); a motor (40) whose rotation speed is variable and which drives the hydraulic pump (30); a brake valve (50) for controlling the pressure of hydraulic oil returning from the hydraulic cylinder (10) to the oil tank (20); a directional control valve (60) that switches between supplying hydraulic oil to one of the first port (10a) and the second port (10b) and discharging hydraulic oil from the other of the first port (10a) and the second port (10b); a control device (80) for controlling the motor (40) and the directional control valve (60); Equipped with the control device (80) controls the number of revolutions of the motor (40) so that the acceleration of the piston (12) is continuous; The control device (80) controls the brake valve (50), The control device (80) controls the brake valve (50) when the piston (12) decelerates, thereby controlling the pressure of the hydraulic oil returning from the hydraulic cylinder (10) to the oil tank (20) through the brake valve (50).

2. the control device (80) is capable of executing flow control for controlling a discharge flow rate of the hydraulic pump (30) by controlling a rotation speed of the motor (40), and pressure control for controlling a discharge pressure of the hydraulic pump (30) by controlling the rotation speed of the motor (40); 2. The hydraulic system (1) according to claim 1, wherein the control device (80) switches the hydraulic pump (30) from flow control to pressure control during a reversal operation in which a driving direction of the piston (12) is reversed.

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