JP7598034B2 - Method for positioning hydraulic cylinder and hydraulic device - Google Patents

Description

This disclosure relates to a method for positioning a hydraulic cylinder and a hydraulic device.

Patent Document 1 discloses a processing device having a bi-directional hydraulic pump and a hydraulic cylinder that operates with the pressure of oil supplied by the hydraulic pump. The extension and contraction of the piston rod of the hydraulic cylinder is controlled by the rotation direction of the hydraulic pump, so a hydraulic closed circuit without a directional control valve is used. A position detector attached to the piston rod controls the rotation speed and direction of the hydraulic pump, fulfilling the function of controlling the positioning of the piston rod.

Japanese Patent Application Publication No. 09-174300

In the meantime, with the trend towards higher precision in general industrial machinery such as presses, researchers have been exploring the use of one-way pumps and hydraulic open circuits to control cylinder positioning. However, one-way pumps have fixed suction and discharge ports, and the extension and contraction of the piston rod is controlled by operating a directional control valve to change the flow direction of the hydraulic oil, so there was an issue that the ON/OFF switching of the directional control valve did not allow for fine positioning control of the hydraulic cylinder.

The object of the present disclosure is to provide a method for controlling the positioning of a hydraulic cylinder of a hydraulic device equipped with a one-way pump.

The first aspect is
A hydraulic pump (130) that rotates in one direction to transport hydraulic oil;
a motor (140) that drives the hydraulic pump (130);
a hydraulic cylinder (110) driven by hydraulic oil supplied from the hydraulic pump (130);
a pressure sensor (160) for detecting the pressure of the hydraulic oil delivered to the hydraulic cylinder (110);
a pressure control unit (211) that controls the number of revolutions of the motor (140) in order to control the pressure of the hydraulic oil detected by the pressure sensor (160);
a directional control valve (120) provided between the hydraulic pump (130) and the hydraulic cylinder (110) for switching the flow direction of hydraulic oil;
a position sensor (190) for detecting a position of a piston rod (113) of the hydraulic cylinder (110);
a positioning control unit (200) that determines an operation amount of the hydraulic cylinder (110) based on a position of the piston rod (113) detected by the position sensor (190) and a target position, comprising:
The manipulated variable is input to the pressure control unit (211),
The pressure control section (211)
If the piston rod (113) has not reached the target position, the pressure of the hydraulic oil is increased to advance the piston rod (113);
When the piston rod (113) exceeds the target position, the pressure of the hydraulic oil is reduced, and the piston rod (113) is decelerated or retreated by the reaction force of the load pressure generated in the piston rod (113). This is a hydraulic cylinder positioning control method.

In the first embodiment, the amount of operation calculated by the positioning control unit (200) is input to the pressure control unit (211), so that the position of the piston rod (113) can be controlled based on the pressure of the hydraulic oil. For example, when the piston rod (113) has not reached the target position, the pressure of the hydraulic oil is increased based on the amount of operation to advance the piston rod (113), and when the piston rod (113) has passed the target position, the pressure of the hydraulic oil is decreased based on the amount of operation, so that the piston rod (113) can be decelerated to the target position or retracted by the reaction force of the load pressure generated on the rod. By controlling the position of the piston rod (113) based on the pressure rather than the flow rate of the hydraulic oil in this way, it is possible to not only advance the piston rod (113) but also retract it by the reaction force of the load pressure, so that the position of the piston rod (113) can be accurately controlled.

The second aspect is the first aspect,
The hydraulic device (100) further includes a pressure limiter (350) that limits a pressure of the hydraulic oil.
When the pressure based on the input operation amount is equal to or greater than a limit pressure, the limit pressure is output to the pressure control unit (211);
The limiting pressure is variable.

In the second aspect, for example, when depressurizing after the pressing process, the limiting pressure of the pressure limiter (350) is gradually lowered, thereby reducing the pressure of the hydraulic oil without shock. This allows both the positioning control of the hydraulic cylinder (110) in the pressing process and the pressure control of the hydraulic cylinder in the depressurizing process after the pressing process to be performed based on the pressure control of the hydraulic oil. As a result, switching from positioning control to depressurization can be performed continuously. In addition, by making the limiting pressure variable, the pressure reduction gradient (depressurization curve) can be freely adjusted, which contributes to the accuracy and quality of the processed product.

In addition, the hydraulic oil pressure will not rise above the limit pressure, so even if an abnormally high pressure were to occur due to an incorrect target position setting, it would be limited by the pressure limiter (350), allowing the target position and processing material to be safely adjusted or changed.

The third aspect is
A hydraulic pump (130) that rotates in one direction to transport hydraulic oil;
a motor (140) that drives the hydraulic pump (130);
a hydraulic cylinder (110) driven by hydraulic oil supplied from the hydraulic pump (130);
a pressure sensor (160) for detecting the pressure of the hydraulic oil delivered to the hydraulic cylinder (110);
a pressure control unit (211) that controls the number of revolutions of the motor (140) in order to control the pressure of the hydraulic oil detected by the pressure sensor (160);
a directional control valve (120) provided between the hydraulic pump (130) and the hydraulic cylinder (110) for switching the flow direction of hydraulic oil;
a position sensor (190) for detecting a position of a piston rod (113) of the hydraulic cylinder (110);
a positioning control unit (200) that determines an operation amount of the hydraulic cylinder (110) based on a position of the piston rod (113) detected by the position sensor (190) and a target position, comprising:
The manipulated variable is input to the pressure control unit (211),
The pressure control section (211)
If the piston rod (113) has not reached the target position, the pressure of the hydraulic oil is increased to advance the piston rod (113);
This is a hydraulic device that, when the piston rod (113) passes the target position, reduces the pressure of the hydraulic oil, thereby slowing down or retracting the piston rod (113) by the reaction force of the load pressure generated in the piston rod (113).

In the third aspect, the same effect as in the first aspect can be obtained.

The fourth aspect is the third aspect,
The hydraulic device (100) further includes a pressure limiter (350) that limits a pressure of the hydraulic oil.
When the pressure based on the input operation amount is equal to or greater than a limit pressure, the limit pressure is output to the pressure control unit (211);
The limiting pressure is variable.

In the fourth aspect, the same effect as in the second aspect can be obtained.

FIG. 1 is a schematic block diagram of a processing device using a hydraulic device according to an embodiment. FIG. 2 is a diagram for explaining the switching of the directional control valve. FIG. 3 is a graph showing the operation of the processing device.

The following describes embodiments of the present invention with reference to the drawings. Note that the following embodiments are essentially preferred examples and are not intended to limit the scope of the present invention, its applications, or its uses. Furthermore, the configurations of the embodiments, variations, other examples, etc. described below can be combined or partially substituted within the scope of the present invention.

(1) Overall Configuration of the Processing Apparatus As shown in Fig. 1, the processing apparatus (1) of this embodiment is a press machine. A press machine compresses press materials such as metal, rubber, and resin to form them into a predetermined shape and dimensions. In general, high dimensional accuracy is required for the molding of mechanical parts such as machine gears.

The processing device (1) includes a hydraulic device (100), a main machine control unit (300), and a mold (400). The hydraulic device (100) includes a hydraulic cylinder (110), a directional control valve (120), a hydraulic pump (130), a motor (140), a tank (150), a pressure sensor (160), a relief valve (170), a rotation sensor (180), a position sensor (190), a positioning control unit (200), and a pressure flow control unit (210). The hydraulic device (100) includes a circuit (220) configured by oil piping through which hydraulic oil flows. The hydraulic cylinder (110), the tank (150), the hydraulic pump (130), the directional control valve (120), and the relief valve (170) are connected to the circuit (220). The circuit (220) is configured so that hydraulic oil moves back and forth between the tank (150) and the hydraulic cylinder (110). The oil piping includes a first upper piping (221), a second upper piping (222), a first lower piping (223), and a second lower piping (224).

(1-2) Tank The tank (150) stores hydraulic oil. One end of the first lower pipe (223) and one end of the second lower pipe (224) are connected to the tank (150).

(1-3) Hydraulic Pump The hydraulic pump (130) of this embodiment is a one-way pump that rotates in one direction to transport hydraulic oil. The hydraulic pump (130) is connected to the second lower pipe (224). The hydraulic pump (130) pumps oil from the tank (150) and discharges it to the second lower pipe (224).

(1-4) Hydraulic Cylinder The hydraulic cylinder (110) of this embodiment is a single-rod hydraulic cylinder. The hydraulic cylinder (110) is driven by hydraulic oil supplied from a hydraulic pump (130). The hydraulic cylinder (110) includes a cylinder portion (111), a piston (112), and a rod (113). The piston (112) and the rod (113) housed in the cylinder portion (111) move vertically as a unit. The cylinder portion (111) has a first port (P1) to which one end of the first upper pipe (221) is connected, and a second port (P2) to which one end of the second upper pipe (222) is connected.

Hydraulic oil flows in and out of the cylinder section (111) via a first port (P1) and a second port (P2). The first port (P1) is provided in the head side space (S1) of the cylinder section (111). The second port (P2) is provided in the rod side space (S2) of the cylinder. The piston (112) is integrated with the rod (113) and is built into the cylinder section (111).

The piston (112) moves vertically between the first port (P1) and the second port (P2) by sliding on the inner wall of the cylinder section (111). The piston (112) divides the space inside the cylinder section (111) into a head side space (S1) and a rod side space (S2). The spatial volumes of the head side space (S1) and the rod side space (S2) change due to the vertical movement of the piston (112).

One end of the rod (113) is fixed to the piston (112), and the other end is fixed to the upper die (410). The rod (113) moves vertically together with the piston (112). In the following explanation, the downward movement of the rod (113) may be referred to as forward movement, and the upward movement of the rod may be referred to as backward movement. The rod (113) is a piston rod (113).

(1-5) Mold The mold (400) is disposed below the hydraulic cylinder (110). The mold (400) has an upper mold (410) and a lower mold (420). The upper mold (410) is connected to the rod (113). This allows the upper mold (410) to move in the vertical direction. The lower mold (420) is fixed below the upper mold (410). The press material is pressed between the upper mold (410) and the lower mold (420).

1, the directional control valve (120) is provided between the hydraulic pump (130) and the hydraulic cylinder (110) to switch the flow direction of the hydraulic oil. One end of each of the first upper pipe (221), the first lower pipe (223), the second upper pipe (222), and the second lower pipe (224) is connected to the directional control valve (120).

As shown in FIG. 2, the directional control valve (120) can be switched among a first state, a second state, and a stop state. In the first state, the second upper pipe (222) and the first lower pipe (223) communicate with each other, and the first upper pipe (221) and the second lower pipe (224) communicate with each other (FIG. 2(a)). In the second state, the first upper pipe (221) and the first lower pipe (223) communicate with each other, and the second upper pipe (222) and the second lower pipe (224) communicate with each other (FIG. 2(b)). In the stop state, the first upper pipe (221), the second upper pipe (222), and the first lower pipe (223) communicate with each other (FIG. 1), and the second lower pipe (224) is blocked from within the circuit (220).

In the first state, the hydraulic oil pumped up from the tank (150) to the second lower pipe (224) flows into the head side space (S1) via the first upper pipe (221), and at the same time, the hydraulic oil in the rod side space (S2) flows into the tank (150) via the second upper pipe (222), the relief valve (170), and the first lower pipe (223). As a result, the pressure of the hydraulic oil acts downward on the piston (112), so that the piston (112) and the rod (113) move downward.

On the other hand, in the second state, the hydraulic oil pumped up from the tank (150) to the second lower pipe (224) flows into the rod side space (S2) via the check valve (CV) and the second upper pipe (222), and at the same time, the hydraulic oil in the head side space (S1) flows into the tank (150) via the first upper pipe (221) and the first lower pipe (223). As a result, the pressure of the hydraulic oil acts upward on the piston (112), causing the piston (112) and the rod (113) to move upward.

(1-7) Relief Valve The relief valve (170) is provided in the second upper pipe (222). Specifically, the relief valve (170) is provided so as to bypass the check valve (CV) provided in the second upper pipe (222). The relief valve (170) is set to a minimum pressure that can prevent the piston (112) from descending due to its own weight caused by the weight of the upper die (410). The check valve (CV) allows the hydraulic oil in the second upper pipe (222) to flow toward the rod side space (S2) and restricts the reverse flow. As a result, when the piston (112) tries to move downward, the hydraulic oil in the second upper pipe (222) flows through the relief valve (170). The check valve (CV) and the relief valve (170) are integrated to function as a counterbalance valve.

(1-8) Motor The motor (140) drives the hydraulic pump (130). The motor (140) is a servo motor and is controlled by a rotation command output from the selection control unit (213). The motor (140) normally rotates to cause the hydraulic oil in the second lower pipe (224) to flow toward the hydraulic cylinder (110). However, when an operation is performed to reduce the pressure of the hydraulic oil in the second lower pipe (224), the motor (140) can temporarily rotate in the reverse direction to cause the hydraulic oil in the second lower pipe (224) to flow back into the tank (150).

(1-9) Rotation Sensor The rotation sensor (180) detects the number of rotations of the motor (140). The rotation sensor (180) transmits the detected value of the number of rotations of the motor (140) to the flow rate control unit (212).

(1-10) Pressure Sensor The pressure sensor (160) detects the pressure of the hydraulic oil of the hydraulic device (100). Specifically, the pressure sensor (160) is connected to the second lower pipe (224), and detects the pressure of the hydraulic oil being conveyed to the hydraulic cylinder (110) while the directional control valve (120) is operating. In the pressing process, it reflects the pressure value applied to the press material. In the rod lifting process, it reflects the weight of the die itself. Hereinafter, the pressure of the hydraulic oil may be simply referred to as "pressure".

(1-11) Position Sensor The position sensor (190) detects the current position of the rod (113). At the bottom dead center of the press process, the machining dimensions of the material can be ascertained by detecting the current position of the rod. The position sensor (190) inputs position information of the rod (113) to the positioning control unit (200), and at the same time, the information is also fed back to the part generating process command values on the main machine side, and is used for switching the machining process.

(1-12) Positioning Control Unit The positioning control unit (200) determines an amount of operation based on the current position of the rod (113) detected by the position sensor (190) and a target position input from a position command unit. The target position of the rod (113) is continuously set by the position command unit (310) throughout the entire pressing process.

The positioning control unit (200) calculates an amount of manipulation to make the current position follow the target position. This amount of manipulation is input to the pressure control unit (211) after being limited in upper limit by the pressure limiter (350) described below. The pressure control unit (211) controls the rotation of the motor (140) so that the current pressure from the pressure sensor (160) matches the above amount of manipulation. As a result, the amount of manipulation is calculated to maintain a constant thickness of the processed material at the bottom dead center of the press. In other words, the pressure manipulation amount is calculated so that the current position of the rod maintains the target value. In this embodiment, the maximum flow rate is input to the flow rate control unit (212), and the selection control unit (213) always selects the pressure control unit (211).

(1-13) Pressure and Flow Control Unit The pressure and flow control unit (210) includes a pressure control unit (211), a flow control unit (212), and a selection control unit (213).

The pressure control unit (211) controls the pressure based on the detection value of the pressure sensor (160) and the pressure command value output from the pressure limiter (350).

The flow control unit (212) controls the flow rate in the discharge direction of the pump based on the detection value of the rotation sensor (180) and the flow rate command value output from the flow rate command unit (340). In this embodiment, the maximum flow rate is input to the flow rate control unit (212), and the selection control unit (213) always selects the pressure control unit (211). The movement speed of the rod (113) is controlled by continuously moving the position command.

The selection control unit (213) has a function of selecting either the output value from the pressure control unit (211) or the output value from the flow control unit (212) and outputting the selected output value as a rotation command value to the motor (140). In this embodiment, the maximum flow rate is input to the flow control unit (212), and the selection control unit (213) always selects the pressure control unit (211).

The pressure and flow control unit (210) acts as a limiter for the hydraulic oil pressure and flow rate, and reduces the motor rotation when either one exceeds the command value, so that either the pressure or the flow rate becomes equal to the command value. The pressure and flow control unit (210) incorporating the selection control unit (213) of this embodiment is a commonly used controller that is commonly used in combination with a pump and a motor as a control controller for a one-way pump.

(2) Main Machine Control Unit The main machine control unit (300) is composed of a programmable logic controller (PLC). The main machine control unit (300) has a process command unit (370), a pressure limiter (350), an interlocking switching unit (380), and a positive/negative reversal unit (360). The process command unit (370) has a position command unit (310), a switching command unit (320), a pressure command unit (330), and a flow rate command unit (340). Each of the process command units (370) is built in as software, for example.

The position command unit (310) sets a target position for the rod (113) and outputs a command for the target position to the positioning control unit (200). In this embodiment, the origin is the point (upper end) where the rod (113) is furthest back, and the downward direction is the positive direction.

The switching command unit (320) supplies current to the solenoid of the directional control valve (120) via a relay switch to switch between the first state, the second state, and the stopped state.

The pressure command unit (330) outputs a predetermined pressure value to the pressure limiter (350).

The flow rate command unit (340) outputs a predetermined flow rate command to the flow rate control unit (212). In this embodiment, it is fixed to a maximum value.

The pressure limiter (350) limits the pressure of the hydraulic oil by software. If the pressure value input to the pressure limiter (350) is equal to or greater than the limit pressure value, the pressure limiter (350) outputs the limit pressure value to the pressure control unit (211). For example, if the pressure based on the operation amount input from the positioning control unit (200) is equal to or greater than the limit pressure value, the pressure limiter (350) outputs the limit pressure value to the pressure control unit (211).

The limit pressure value is determined, for example, based on a user setting. The limit pressure value is variable. The limit pressure value is set to a value equal to or higher than the required pressure while the rod (113) is moving, but is set to gradually decrease over time during the depressurization process after pressing. For example, the operation amount input to the pressure limiter (350) will not exceed the limit pressure value, and the operation amount gradually decreases as the limit pressure value decreases. As a result, the pressure command value output to the pressure control unit (211) also changes to gradually decrease.

The interlocking switching unit (380) receives a control (switching) signal for the directional control valve (120) from the switching command unit (320). The interlocking switching unit (380) also receives an operation amount from the positioning control unit (200). The function of the interlocking switching unit (380) will be described later.

The positive/negative reversing unit (360) reverses the sign of the operating force applied to the hydraulic cylinder (110) in synchronization with the directional control valve (120). Specifically, when the rod (113) advances, a positive operating amount is input from the positioning control unit (200) to the pressure control unit (211), whereas when the rod (113) retreats, a negative operating amount is generated from the positioning control unit (200) because the upper end is the origin and the downward direction is the positive direction. However, the positive/negative reversing unit (360) works in conjunction with the directional control valve (120) to reverse the negative value to a positive value, so that a positive operating amount is input to the pressure control unit (211) even when the rod (113) retreats. This allows the positioning control of the rod (113) to be performed in the same way when the rod (113) retreats as when it advances.

(3) Issues with rod positioning control In hydraulic equipment equipped with a bi-directional hydraulic pump, the direction of the hydraulic pump's discharge flow rate is controlled by switching the rotation direction of the motor between positive and negative. For this reason, the pump and the hydraulic cylinder must be directly connected to form a closed hydraulic circuit. A closed hydraulic circuit is generally a circuit that is combined with a hydraulic motor.

When connected to equipment such as hydraulic cylinders, where the oil balance changes significantly when the cylinder expands or contracts, the pressure loss at the check valve installed in the closed circuit increases, making it easier for negative pressure to occur in the hydraulic circuit, adversely affecting the operation and lifespan of the hydraulic equipment.

For this reason, hydraulic circuits in general industrial machinery are generally configured with a one-way pump and hydraulic open circuit, with a directional control valve used to control the direction of movement of the hydraulic cylinder. Also, because the discharge and suction ports of bi-directional hydraulic pumps are interchangeable, the structure makes it difficult to take measures to suppress fluid noise, resulting in high noise levels. As their use is specialized for driving construction machinery, there are also issues with availability and cost.

In light of this, cylinder positioning control using one-way pumps and hydraulic open circuits has been explored as precision increases in general industrial machinery such as presses. However, one-way pumps have fixed suction and discharge ports, and the extension and contraction of the rod is controlled by operating a directional control valve to change the flow direction of the hydraulic oil, so there was an issue that fine positioning control of hydraulic cylinders was not possible using ON/OFF switching with a directional control valve.

Specifically, controllers for one-way pumps only have positive values for both flow rate and pressure, and ignore negative values. As a result, the direction of pump operation cannot be changed by a flow rate command, and a rod that has passed the target position cannot be retracted to the target position. In this case, the rod can be retracted by switching the directional control valve. However, with ON/OFF control using a directional control valve, it is difficult to perform fine position control (for example, a few micrometers) to return a piston rod that has advanced beyond the target position to the target position.

Furthermore, while the method of replacing ON/OFF switching with servo valves has been partially put to practical use, there are issues with energy conservation and safety associated with the use of accumulators.

In response to this, the hydraulic device (100) of this embodiment is equipped with a positioning control unit (200) that controls the positioning of the rod. The position of the rod (113) is controlled based on the amount of operation output from the positioning control unit (200). The following describes a method for controlling the positioning of the hydraulic cylinder (110) of this embodiment.

(4) Operation of the Hydraulic Device The operation of the hydraulic device (100) will be described with reference to FIG. 3. The operation of the hydraulic device (100) is performed in the following order: standby step, high-speed lowering step, low-speed lowering step, positioning step, depressurization step, high-speed rising step, and standby step. One press material is molded by this series of operations (pressing process). When multiple press materials are molded continuously, the pressing process is repeated. The positioning control of the rod (113) operates in all processes except the standby step. In the hydraulic device (100) of this embodiment, only the pressure control unit (211) of the pressure and flow control unit (210) is used, and the flow control unit (212) is fixed to the maximum flow rate. In the pressure and flow control unit (210), the selection control unit (213) receives only the output value from the pressure control unit (211) and outputs a rotation command value based on the output value to the motor (140). Therefore, in the following description, it is assumed that the pressure control section (211) controls the number of revolutions of the motor (140) in order to control the pressure of the hydraulic oil detected by the pressure sensor (160).

(4-1) Standby Step In the standby step, the rod (113) is maintained in the most retracted position (highest position). Specifically, the main engine control unit (300) stops the directional control valve (120). This prevents hydraulic oil from flowing through the circuit (220). The positioning control unit (200) sets the same value as the current position as the position command value so as not to output the manipulated variable, and the pressure control unit (211) controls the number of rotations of the motor (140) to zero. This causes the rod (113) to remain stationary in the most retracted position.

(4-2) High-speed descent step In the high-speed descent step, the main machine control unit (300) switches the directional control valve (120) from the stopped state to the first state. At the same time, the position command unit (310) inputs a position command value that changes to the descent side to the positioning control unit (200). The positioning control unit (200) calculates an operation amount so as to follow the position command value by comparing it with the current position from the position sensor (190). When this operation amount is input to the pressure control unit (211), the pressure control unit (211) increases and adjusts the rotation speed of the motor (140) so as to generate a current pressure equal to the operation amount by comparing it with the current pressure from the pressure sensor (160). As a result, the current position follows the change in the position command, and the speed of the rod is indirectly maintained at a high speed. At the start of the high-speed descent step, the pressure limiter (350) is set to a pressure higher than the pressure required for this process.

When the motor (140) rotates, the hydraulic oil in the tank (150) flows into the head side space (S1) via the second lower pipe (224) and the first upper pipe (221), and the hydraulic oil in the rod side space (S2) flows into the tank (150) via the second upper pipe (222) and the first lower pipe (223).

As a result, the piston (112) moves downward and the rod (113) descends. The load pressure generated in the piston (112) rises to the value of the operation amount of the positioning control unit (200).

When the position sensor (190) detects that the lower end of the rod (113) has reached a predetermined position, the position command unit (310) slows down the rate of change of the position command. Here, the predetermined position is the position immediately before the upper die (410) comes into contact with the press material.

(4-3) Slow descent step In the slow descent step, the position command value changes slowly, so the positioning control unit (200) calculates a lower manipulated variable compared to the fast descent step. When this manipulated variable is input to the pressure control unit (211), the pressure control unit (211) reduces and adjusts the rotation speed of the motor (140) so that a current pressure equal to the manipulated variable is generated in comparison with the current pressure from the pressure sensor (160). As a result, the current position follows the change in the position command, and the moving speed of the rod (113) indirectly slows down. The pressure limiter (350) is set to a pressure higher than the pressure required for this process.

When the upper die (410) comes into contact with the press material, processing pressure is generated (point a in Figure 3). As the load pressure rises, the rotation speed of the motor (140) decreases and the descending speed of the rod (113) begins to decrease, but since the positioning control unit (200) is feeding back the position change, it immediately increases the operation amount and issues a command to the pressure control unit (211). As a result, the load pressure rises and the motor rotation is maintained at the speed of the low-speed process. The position command stops when the specified bottom dead center is reached, so the process moves to the positioning and pressure holding step.

(4-4) Positioning and Pressure Holding Step In the positioning and pressure holding step, the position command unit (310) stops the target position for a certain period of time. The positioning control unit (200) calculates the amount of operation so that the rod (113) stops at the target position during this time. This amount of operation is input to the pressure control unit (211) as a pressure command value for holding the rod (113) at the target position. The pressure control unit (211) adjusts the number of revolutions of the motor (140) so that a current pressure equal to the amount of operation is generated by comparing it with the current pressure from the pressure sensor (160). Since the position command is stopped, the number of revolutions of the motor (140) is maintained at almost zero as a result. However, since a reaction force (upward force) from the press material acts on the upper die (410), the rod (113) is pushed by the press material and tries to move backward. Therefore, the number of revolutions of the motor (140) is not simply stopped, but a torque is generated to maintain the target position against the load pressure.

In the positioning and pressure-holding step, the position of the rod (113) is controlled to an accuracy of several micrometers near the target position based on such an operation amount. In this embodiment, when the rod (113) has not reached the target position, the pressure control unit (211) advances the rod (113) by increasing the pressure of the hydraulic oil, and when the rod (113) has exceeded the target position, the pressure control unit (211) decreases the pressure of the hydraulic oil to cause the rod (113) to retreat by the reaction force of the load pressure generated in the rod (113). In this way, in this embodiment, the positioning control of the rod (113) is performed using the pressure of the hydraulic oil as the operation amount. If the operation amount calculated by the positioning control unit (200) is input to the flow control unit (212) that directly controls the rotation speed of the motor (140), the input value of the flow control unit (212) is limited to a positive value, so the rod (113) can be advanced toward the target value, but cannot be retreated when the target value is exceeded. Therefore, precise positioning control of the rod (113) is not possible. In the positioning and pressure-maintaining step, the required flow rate is zero, so the number of rotations of the motor (140) must be finely adjusted positively or negatively around zero to maintain the position. In contrast, in this disclosure, the pressure of the hydraulic oil is a positive value even in the positioning and pressure-maintaining step, so precise positioning control of the rod (113) is achieved by controlling this as the manipulated variable.

(4-5) Depressurization Step In the depressurization step, the pressure command unit (330) gradually reduces the limit pressure value until it becomes zero. The operation amount input to the pressure limiter (350) is forcibly gradually reduced in accordance with the reduction in the limit pressure value. As a result, the pressure command value output from the pressure limiter (350) also gradually reduces. In the pressure control unit (211), since the pressure command value becomes smaller than the detection value input from the pressure sensor (160), a negative operation amount is calculated, and the motor rotation is reversed. As a result, the oil compressed to the cylinder head side is returned to the tank (150) by the hydraulic pump (130) rotating in the reverse direction, thereby reducing the pressure. That is, although the input to the pressure control unit (211) is limited to a positive value, the calculation result can be reversed to positive or negative. In other words, in the positioning and pressure holding step, the rotation speed of the motor (140) is maintained at approximately zero while a predetermined positive current pressure is generated, and then, in the depressurization step, the current positive pressure decreases until it becomes zero, and the rotation speed of the motor (140) also decreases, but since the rotation speed decreases from a state of approximately zero, the motor (140) ends up rotating in the reverse direction. In this way, when the pressure is decreased, the hydraulic pump (130) can be temporarily operated as a bidirectional pump.

Specifically, in the depressurization step, the rotation speed of the motor (140) decreases from zero to a negative value, causing the motor (140) to rotate in the reverse direction, decreasing the load pressure on the press material. When the limit pressure value and the current pressure both reach zero, the rotation speed of the motor (140) is returned to zero by the pressure control unit (211), and the depressurization step ends. At the end of the depressurization step, the directional control valve (120) is switched to a stopped state and temporarily put into a standby state in preparation for the next step.

(4-6) High Pressure Rising Step In the high pressure rising step, the rod (113) is retracted to the standby position. First, the switching command unit (320) switches the directional control valve (120) from the stopped state to the second state (b) using the interlocking switching unit (380). The position command unit (310) quickly decreases the position command toward the home standby position. The positioning control unit (200) compares the value of the position sensor (190) to calculate the manipulated variable, but since the standby position value is smaller than the current position, the manipulated variable is calculated as a negative value. This is converted to a positive value by the interlocking switching unit (380) and the positive/negative reversal unit (360) and is output to the pressure control unit (211). The pressure limiter (350) is set to a pressure higher than the pressure required in this process.

Specifically, the main engine control unit (300) switches the directional control valve (120) from the stopped state to the second state at the end of the depressurization step. At the same time, the interlocking switching unit (380) inverts the manipulated variable output from the positioning control unit (200) by the positive/negative reversing unit (360). The positioning control unit (200) calculates the manipulated variable as a negative value because the standby position value is smaller than the current position. This is converted to a positive value by the interlocking switching unit (380) and the positive/negative reversing unit (360) and input to the pressure control unit (211). The pressure control unit (211) increases the rotation speed of the motor (140) based on the input pressure command value to increase the load pressure to the pressure command value. As a result, the current position follows the position command value until the rod (113) reaches the standby position, and the third rotation speed is maintained. This makes it possible to control the speed and stop the rod (113) by positioning control even when the rod (113) is retreating.

At this time, the hydraulic oil in the head side space (S1) flows into the tank (150) via the first upper pipe (221) and the first lower pipe (223), while the hydraulic oil in the tank (150) flows into the rod side space (S2) via the second lower pipe (224) and the second upper pipe (222). As a result, the piston (112) rises together with the rod (113). A load pressure is generated on the piston (112) mainly due to the weight of the upper die, but the pressure control unit (211) controls this to maintain the rising speed of the rod (113).

When the rod (113) reaches the standby position, the standby step is executed again. Specifically, the main engine control unit (300) sets the flow command value and pressure command value to zero, and switches the directional control valve (120) to a stopped state. As a result, the rod stops and the motor rotation speed is controlled to zero. In addition, because the pressure command value is zero, the motor rotation torque and hydraulic oil pressure also become zero.

(5) Features (5-1) Feature 1
In the positioning method of the hydraulic cylinder (110) of this embodiment, the pressure control unit (211), to which the operation amount calculated by the positioning control unit (200) is input, moves the rod (113) forward by increasing the pressure of the hydraulic oil if the rod (113) has not reached the target position, and decreases the pressure of the hydraulic oil if the rod (113) has passed the target position, thereby slowing down or retracting the rod (113) by the reaction force of the load pressure generated in the rod (113).

This makes it possible to control the position of the rod (113) by inputting the manipulated variable calculated by the positioning control unit (200) into the pressure control unit (211) and manipulating the pressure value of the hydraulic oil. Even if the rod (113) exceeds the target value, the pressure can be reduced, and the rod (113) can be decelerated or retreated to the target position by the reaction force of the load pressure generated in the rod (113).

In this way, even in the case of a one-way pump in which the flow rate command value cannot be used to reverse the rotation of the motor (140) by inputting a negative value, by using the positioning operation amount as the pump pressure command value, it is possible to inexpensively and precisely control the position of the rod (113) with an open circuit using a general-purpose one-way pump, without using a special bidirectional pump or closed circuit.

Furthermore, when the rod (113) moves backward, the positioning control can be performed by simply reversing the positioning operation amount in conjunction with the directional control valve (120), and the load pressure can be controlled by the pressure command value, just as when the rod moves forward.

(5-2) Feature 2
In the method for positioning the hydraulic cylinder (110) of the present embodiment, the pressure limiter (350) that limits the pressure of the hydraulic oil outputs the limit pressure to the pressure control section (211) when the pressure based on the input operation amount is equal to or higher than the limit pressure. The limit pressure is variable.

According to this, the pressure limiter (350) reduces the limiting pressure during the positioning step, thereby lowering the pressure command value input to the pressure control unit (211). This allows the depressurization step to be performed.

In this way, by controlling the positioning of the hydraulic cylinder (110) based on the pressure control of the hydraulic oil, the control state can be automatically switched by simply manipulating the command values for position control and pressure control, without having to switch the control state from the outside.

In addition, by making the limit pressure value variable, the pressure drop gradient (pressure release curve) can be freely adjusted, which contributes to the precision and quality of pressed products.

In addition, the hydraulic oil pressure will not rise above the limit pressure, so even if an abnormally high pressure were to be generated, for example, by incorrectly setting the target position, it will be limited by the pressure limiter (350), allowing the target position and processing material to be adjusted or changed safely.

(6) Other Embodiments The above-described embodiment may be configured as follows.

The hydraulic device (100) need only have a pressure control section (211), and does not necessarily have to have a pressure flow control section (210).

The main machine control unit (300) does not need to be equipped with a positive/negative reversal unit (360). Generally, processing machines perform processing work by advancing a cylinder, and positional accuracy may be required, but when retracting, the cylinder often only needs to return to its original position and does not require high-precision positioning control, so retraction can be controlled by only the normal pressure and flow control unit (210).

In this embodiment, the positioning control unit (200) uses a general-purpose controller, but it is also possible to incorporate position control calculations (generally PID control) into a programmable logic controller (PLC) using software.

Although the embodiments and modifications have been described above, it will be understood that various modifications of form and details are possible without departing from the spirit and scope of the claims. Furthermore, the above embodiments and modifications may be combined or substituted as appropriate as long as the functionality of the subject matter of this disclosure is not impaired. The descriptions "first," "second," etc. described above are used to distinguish the words to which these descriptions are attached, and do not limit the number or order of the words.

As described above, the present disclosure is useful for a method for controlling the positioning of a hydraulic cylinder and a hydraulic device.

100 Hydraulic system
110 Hydraulic cylinder
120 Directional valve
130 Hydraulic pump
140 Motor
160 Pressure Sensor
190 Position Sensor
211 Pressure control section
350 Pressure limiter

Claims (4)

A hydraulic pump (130) that rotates in one direction to transport hydraulic oil;
a motor (140) that drives the hydraulic pump (130);
a hydraulic cylinder (110) driven by hydraulic oil supplied from the hydraulic pump (130);
a pressure sensor (160) for detecting the pressure of the hydraulic oil delivered to the hydraulic cylinder (110);
a pressure control unit (211) that controls the number of revolutions of the motor (140) in order to control the pressure of the hydraulic oil detected by the pressure sensor (160);
a directional control valve (120) provided between the hydraulic pump (130) and the hydraulic cylinder (110) for switching the flow direction of hydraulic oil;
a position sensor (190) for detecting a position of a piston rod (113) of the hydraulic cylinder (110);
a positioning control unit (200) that determines an operation amount of the hydraulic cylinder (110) based on a position of the piston rod (113) detected by the position sensor (190) and a target position, comprising:
The manipulated variable is input to the pressure control unit (211),
The pressure control section (211)
If the piston rod (113) has not reached the target position, the pressure of the hydraulic oil is increased to advance the piston rod (113);
When the piston rod (113) exceeds the target position, the pressure of the hydraulic oil is reduced, and the piston rod (113) is decelerated or retreated by a reaction force of the load pressure generated on the piston rod (113) ;
When the piston rod (113) coincides with the target position, the current pressure of the hydraulic oil is maintained.
A method for controlling the positioning of a hydraulic cylinder. The hydraulic device (100) further includes a pressure limiter (350) that limits a pressure of the hydraulic oil.
the pressure limiter (350) functions to output the limit pressure to the pressure control section (211) when the pressure based on the input operation amount is equal to or greater than a limit pressure;
The method for controlling the positioning of a hydraulic cylinder according to claim 1 , wherein the limit pressure is variable. A hydraulic pump (130) that rotates in one direction to transport hydraulic oil;
a motor (140) that drives the hydraulic pump (130);
a hydraulic cylinder (110) driven by hydraulic oil supplied from the hydraulic pump (130);
a pressure sensor (160) for detecting the pressure of the hydraulic oil delivered to the hydraulic cylinder (110);
a pressure control unit (211) that controls the number of revolutions of the motor (140) in order to control the pressure of the hydraulic oil detected by the pressure sensor (160);
a directional control valve (120) provided between the hydraulic pump (130) and the hydraulic cylinder (110) for switching the flow direction of hydraulic oil;
a position sensor (190) for detecting a position of a piston rod (113) of the hydraulic cylinder (110);
a positioning control unit (200) that determines an operation amount of the hydraulic cylinder (110) based on a position of the piston rod (113) detected by the position sensor (190) and a target position, comprising:
The manipulated variable is input to the pressure control unit (211),
The pressure control section (211)
If the piston rod (113) has not reached the target position, the pressure of the hydraulic oil is increased to advance the piston rod (113);
When the piston rod (113) exceeds the target position, the pressure of the hydraulic oil is reduced, and the piston rod (113) is decelerated or retreated by a reaction force of the load pressure generated on the piston rod (113) ;
When the piston rod (113) coincides with the target position, the current pressure of the hydraulic oil is maintained.
Hydraulic system. The hydraulic device (100) further includes a pressure limiter (350) that limits a pressure of the hydraulic oil.
the pressure limiter (350) functions to output the limit pressure to the pressure control section (211) when the pressure based on the input operation amount is equal to or greater than a limit pressure;
The hydraulic system of claim 3 , wherein the limit pressure is variable.