Patent Publication Number: US-2022228608-A1

Title: Fluid pressure control device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-006335 filed on Jan. 19, 2021, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a fluid pressure control device configured to control a fluid pressure supplied to a fluid actuator. 
     Description of the Related Art 
     Conventionally, a fluid pressure control device has been known which adjusts the pressure of a pressure fluid from a fluid supply source to a desired pressure, and supplies the fluid to a fluid actuator. For example, JP 2002-243059 A discloses a fluid pressure adjusting device that opens and closes a supply valve element and a discharge valve element by controlling, using an air supply solenoid valve and an air discharge solenoid valve, a pilot pressure that acts on a diaphragm, to displace a rod member provided integrally with the diaphragm. In such a fluid pressure adjusting device, when the supply valve element is placed in an open state, a supply port connected to a fluid supply source and a pressure adjusting port connected to fluid pressure equipment communicate with each other, whereas when the discharge valve element is placed in an open state, the pressure fluid on the side of the pressure adjusting port is discharged to the exterior through a discharge port. 
     Further, a fluid control device that changes a target value of a fluid pressure supplied to a fluid actuator in accordance with an operating state of the fluid actuator is also known. For example, in the specification of U.S. Pat. No. 10,731,679 B2, a fluid control device is disclosed in which, when a decrease of a flow rate in a certain amount or more is detected, a transition is made from a normal operating mode to a standby mode, and at the time of the standby mode, a fluid having a pressure which is set to a lower pressure than at the time of the normal operating mode is supplied to the fluid actuator. Such a fluid control device has a configuration in which a shutoff valve is connected in series to and downstream of a proportional pressure regulating valve. 
     SUMMARY OF THE INVENTION 
     As seen in the fluid pressure adjusting device of JP 2002-243059 A, in order to control the pressure on the port side (secondary port side) that is connected to the fluid pressure equipment from a high pressure to a low pressure, it is common technical knowledge to use a discharge valve element. In this case, it is inevitable that a portion of the pressure fluid from the fluid supply source will end up being discarded without being used in the fluid pressure equipment. The proportional pressure regulating valve disclosed in the specification of U.S. Pat. No. 10,731,679 B2 is also equipped with a port for discharging fluid on the secondary side, and therefore a similar phenomenon occurs. 
     Further, in the fluid control device disclosed in the specification of U.S. Pat. No. 10,731,679 B2, a configuration is required in which a shutoff valve is connected in series to and downstream of a proportional pressure regulating valve, and since the shutoff valve is provided in a flow path having a large flow rate, there is a concern that the size and scale of the device may become large. Furthermore, in the fluid control device disclosed in the specification of U.S. Pat. No. 10,731,679 B2, it is necessary to provide a flow rate sensor in addition to a pressure sensor. 
     The present invention has the object of solving the aforementioned problems. 
     A fluid pressure control device according to the present invention is disposed between a fluid supply source and a fluid actuator, and is configured to transition from a normal mode, in which a fluid pressure supplied to the fluid actuator is set to an operating pressure, to a standby mode, in which the fluid pressure is set to a standby pressure that is lower than the operating pressure. In addition, the fluid pressure control device comprises an inlet port connected to the fluid supply source, an outlet port connected to the fluid actuator, a supply valve configured to adjust an area of a flow path connecting the inlet port and the outlet port, and a diaphragm configured to displace a valve element of the supply valve. 
     A pilot chamber is formed on one side of the diaphragm, and a feedback chamber communicating with the outlet port is formed on another side of the diaphragm. A pilot pressure supply solenoid valve is disposed in a flow path connecting the inlet port and the pilot chamber, and a pilot pressure discharge solenoid valve is disposed in a flow path through which a pressure fluid in the pilot chamber is discharged to an exterior. Furthermore, the fluid pressure control device further comprises a control unit configured to control the pilot pressure supply solenoid valve and the pilot pressure discharge solenoid valve. The fluid pressure control device does not comprise a flow path through which the pressure fluid that has passed through the supply valve is discharged to the exterior. 
     According to the above-described fluid pressure control device, all of the pressure fluid that has passed through the supply valve is supplied to the fluid actuator, and loss of the pressure fluid can be suppressed to a minimum. Further, while performing a control to change a target value (set pressure) of the fluid pressure supplied to the fluid actuator from a high operating pressure to a low standby pressure, the fluid pressure control device does not include a flow path through which the pressure fluid that has passed through the supply valve is discharged to the exterior. Therefore, there is no need to separately provide a shutoff valve, and the device as a whole can be made small in scale. 
     According to the present invention, when transitioning from the normal mode to the standby mode, the fluid pressure control device performs a control to change the target value of the fluid pressure supplied to the fluid actuator from the high operating pressure to the low standby pressure, but the fluid pressure control device does not include a flow path through which the pressure fluid that has passed through the supply valve is discharged to the exterior. Therefore, in addition to enabling a loss of the pressure fluid to be suppressed to a minimum, there is no need to separately provide a shutoff valve, and the device as a whole can be made small in scale. 
     The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings, in which a preferred embodiment of the present invention is shown by way of illustrative example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic drawing of a fluid pressure control device according to an embodiment of the present invention; 
         FIG. 2  is a timing chart showing operations of the fluid pressure control device shown in  FIG. 1 , for a case in which transitioning from a normal mode to a standby mode is automatically performed; 
         FIG. 3  is a graph showing a relationship between a differential pressure (P 1 −P 2 ) and a flow rate Q in the fluid pressure control device shown in  FIG. 1 ; 
         FIG. 4  is a timing chart showing operations of the fluid pressure control device shown in  FIG. 1 , for a case in which transitioning from a normal mode to a standby mode is performed manually; 
         FIG. 5  is a flowchart showing a control by the fluid pressure control device shown in  FIG. 1 , for a case in which transitioning from a normal mode to a standby mode is automatically performed, and returning to the normal mode is performed by a standby release signal; 
         FIG. 6  is a flowchart showing a control by the fluid pressure control device shown in  FIG. 1 , for a case in which transitioning from a normal mode to a standby mode is automatically performed, and returning to the normal mode is automatically performed based on a flow rate; and 
         FIG. 7  is a flow chart showing a control by the fluid pressure control device shown in  FIG. 1 , for a case in which transitioning from a normal mode to a standby mode is performed manually. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     The fluid used in the present invention is a pressure fluid such as compressed air or the like. In the following description, when terms in relation to up and down directions are used, such terms refer to the directions shown in the drawings for the sake of convenience, and the actual arrangement of the constituent members and the like is not necessarily limited to this feature. 
     A fluid pressure control device  10  according to an embodiment of the present invention is disposed between a fluid supply source and a fluid actuator (neither of which is shown). When a flow rate flowing toward the fluid actuator falls continuously below a predetermined value for a predetermined time period, the fluid pressure control device  10  sets the fluid pressure supplied to the fluid actuator to a standby pressure which is lower than an operating pressure. First, a description will be given concerning the configurations and functions possessed by the fluid pressure control device  10  in order to perform such a control. 
     As shown in  FIG. 1 , the fluid pressure control device  10  comprises a valve body  12  in which a supply valve  26  is incorporated, and a control housing  14  in which a pilot pressure supply solenoid valve  36  and a pilot pressure discharge solenoid valve  38  are incorporated. The control housing  14  is connected to an upper part of the valve body  12 . 
     The valve body  12  includes an inlet port  16  connected to a fluid supply source (air compressor), and an outlet port  18  connected to a fluid actuator such as an air cylinder or the like. The inlet port  16  and the outlet port  18  are disposed coaxially. A cylindrical wall portion  22  having a valve seat  22   a  at an end part thereof intersects with a connecting passage  20  that connects the inlet port  16  and the outlet port  18 . At a position facing toward the wall portion  22 , a circular recess  24  that extends downward from the connecting passage  20  is disposed. 
     A valve element  28  constitutes the supply valve  26  together with the valve seat  22   a . The valve element  28  is made up from a disk-shaped plate portion  28   a  capable of abutting against the valve seat  22   a , and a cylindrical guide portion  28   b  that extends downward from a lower surface of the plate portion  28   a . A seal member  28   c  that abuts against the valve seat  22   a  is mounted on an outer circumference of an upper part of the plate portion  28   a . The seal member  28   c  is constituted by an elastic material such as rubber or the like. 
     The guide portion  28   b  of the valve element  28  is supported so as to be capable of sliding in up and down directions in the recess  24  of the valve body  12 . A seal ring  30   a  that is in sliding contact with a wall surface of the recess  24  is mounted on an outer circumference of the guide portion  28   b . In a space on an inner side of the guide portion  28   b , a first spring  32  for biasing the valve element  28  toward the valve seat  22   a  is disposed between the lower surface of the plate portion  28   a  and a bottom surface of the recess  24 . The plate portion  28   a  includes a plurality of holes  28   d  that allows communication between the space on the inner side of the guide portion  28   b  and a space above the plate portion  28   a.    
     In a central portion of the valve body  12 , an elongated rod  40  that extends in the up and down directions is supported so as to be capable of moving in an axial direction thereof. A seal ring  30   b  that is in sliding contact with an outer circumference of the rod  40  is disposed on the valve body  12 . An upper end of the rod  40  integrally includes a disk-shaped flange portion  40   a  that extends in a horizontal direction. A lower end of the rod  40  projects into the connecting passage  20 , and is capable of abutting against an upper surface of the plate portion  28   a  of the valve element  28 . 
     When the seal member  28   c  of the valve element  28  is placed in a state of being pressed against the valve seat  22   a  due to the biasing force of the first spring  32 , communication between the inlet port  16  and the outlet port  18  is shut off. On the other hand, as will be discussed later, when a force, which drives the valve element  28  downward against the biasing force of the first spring  32 , acts on the rod  40 , the seal member  28   c  of the valve element  28  separates away from the valve seat  22   a , and the inlet port  16  and the outlet port  18  communicate with each other. In this case, the area of the flow path connecting the inlet port  16  and the outlet port  18  (a degree of opening V of the supply valve  26 ) is adjusted in accordance with the driving force that acts on the rod  40 . 
     The upper part of the valve body  12  includes a diaphragm chamber  46 . In the diaphragm chamber  46 , there are accommodated an upper portion of the rod  40  including the flange portion  40   a , and a diaphragm  44  that is made of a flexible material. An outer circumferential portion of the diaphragm  44  is attached to a groove portion that is formed in the valve body  12 . An inner circumferential portion of the diaphragm  44  is sandwiched between the flange portion  40   a  of the rod  40  and a disc member  42  that is inserted over and fixed to the rod  40 . Consequently, the inner circumferential portion of the diaphragm  44  is fixed to the rod  40 . 
     The diaphragm chamber  46  is partitioned into a pilot chamber  48  and a feedback chamber  50 . The pilot chamber  48  is formed upwardly of the diaphragm  44  and the flange portion  40   a . The feedback chamber  50  is formed downwardly of the diaphragm  44  and the disc member  42 . The feedback chamber  50  communicates with the outlet port  18  via a first passage  52   a  that is formed in the valve body  12 . A second spring  34  is disposed in the feedback chamber  50 . One end of the second spring  34  abuts against the disc member  42 . Another end of the second spring  34  abuts against the valve body  12 . 
     Due to the fluid pressure in the pilot chamber  48  acting on upper surfaces of the diaphragm  44  and the flange portion  40   a , a downward pushing force acts on the rod  40 . Further, due to the fluid pressure in the feedback chamber  50  acting on lower surfaces of the diaphragm  44  and the disc member  42 , and a biasing force of the second spring  34 , an upward pushing force acts on the rod  40 . When the former force exceeds the latter force, the rod  40  drives the valve element  28  downward against the biasing force of the first spring  32 , and displaces the valve element  28  downward to a position balanced with the reaction force of the first spring  32 . If a pressure P 1  in the pilot chamber  48  is increased, the degree of opening V of the supply valve  26  becomes larger. 
     The valve body  12  includes a second passage  52   b  that branches off from the first passage  52   a , and reaches an upper surface of the valve body  12 . Further, the valve body  12  additionally includes a third passage  52   c  and a fourth passage  52   d . A lower end of the third passage  52   c  is connected to the inlet port  16 . An upper end of the third passage  52   c  reaches the upper surface of the valve body  12 . A lower end of the fourth passage  52   d  is connected to the pilot chamber  48 . An upper end of the fourth passage  52   d  reaches the upper surface of the valve body  12 . The control housing  14  includes a fifth passage  52   e  that connects the upper end of the third passage  52   c  and the upper end of the fourth passage  52   d  to each other. The pilot pressure supply solenoid valve  36  is disposed in the fifth passage  52   e . The pilot pressure supply solenoid valve  36  is a normally closed type two-way valve that is capable of being switched between a position to allow communication between the third passage  52   c  and the fourth passage  52   d , and a position to shut off the communication between the third passage  52   c  and the fourth passage  52   d.    
     Accordingly, the pilot pressure supply solenoid valve  36  can be switched between a communicating position to allow the pressure fluid in the inlet port  16  to be introduced into the pilot chamber  48 , and a shutoff position to shut off the pilot chamber  48  from the inlet port  16 . The pilot pressure supply solenoid valve  36  is disposed in a flow path connecting the inlet port  16  and the pilot chamber  48 . Since the pilot pressure supply solenoid valve  36  is not interposed in a flow path having a large flow rate, a small scale solenoid valve is sufficient. 
     The control housing  14  comprises a discharge port  54  that is open to the atmosphere. In order to connect the upper end of the fourth passage  52   d  and the discharge port  54 , the control housing  14  includes a sixth passage  52   f  that branches off from a midway location of the fifth passage  52   e , and reaches the discharge port  54 . The pilot pressure discharge solenoid valve  38  is disposed in the sixth passage  52   f . The pilot pressure discharge solenoid valve  38  is a normally closed type two-way valve that is capable of being switched between a position to allow communication between the fourth passage  52   d  and the discharge port  54 , and a position to shut off the communication between the fourth passage  52   d  and the discharge port  54 . 
     Accordingly, the pilot pressure discharge solenoid valve  38  can be switched between a communicating position to allow the pressure fluid in the pilot chamber  48  to be discharged, and a shutoff position to shut off the pilot chamber  48  from the discharge port  54 . The pilot pressure discharge solenoid valve  38  is disposed in a flow path through which the pressure fluid in the pilot chamber  48  is discharged to the exterior. Since the pilot pressure discharge solenoid valve  38  is not interposed in a flow path having a large flow rate, a small scale solenoid valve is sufficient. Further, since the volume of the pilot chamber  48  is limited and the amount of the pressure fluid in the pilot chamber  48  discharged to the exterior is extremely small, loss of the pressure fluid can be kept to a minimum. 
     A control unit  56  made up from an integrated circuit (IC) is disposed in the control housing  14 . The pilot pressure supply solenoid valve  36  and the pilot pressure discharge solenoid valve  38  are controlled on the basis of signals from the control unit  56 . When the pilot pressure supply solenoid valve  36  is switched to the communicating position and the pilot pressure discharge solenoid valve  38  is switched to the shutoff position, the pressure fluid in the inlet port  16  is introduced into the pilot chamber  48 . Consequently, the pressure P 1  in the pilot chamber  48  increases, and the degree of opening V of the supply valve  26  becomes larger. When the pilot pressure supply solenoid valve  36  is switched to the shutoff position and the pilot pressure discharge solenoid valve  38  is switched to the communicating position, the pressure fluid in the pilot chamber  48  is discharged to the exterior. Consequently, the pressure P 1  in the pilot chamber  48  decreases, and the degree of opening V of the supply valve  26  becomes smaller. 
     In the case that the pilot pressure supply solenoid valve  36  and the pilot pressure discharge solenoid valve  38  are PWM-controlled, the pressure P 1  in the pilot chamber  48  can be finely controlled by controlling the timing at which current is supplied to the solenoid valves  36  and  38 , and therefore, the degree of opening V of the supply valve  26  can be adjusted in a stepless manner. 
     The control housing  14  includes a seventh passage  52   g  that branches off from a midway location of the fifth passage  52   e . A first pressure sensor  58  that detects the pressure P 1  in the pilot chamber  48  is disposed so as to face the seventh passage  52   g . Further, the control housing  14  includes an eighth passage  52   h  connected to the second passage  52   b  of the valve body  12 . A second pressure sensor  60  that detects a pressure P 2  in the outlet port  18  is disposed so as to face the eighth passage  52   h . Signals detected by the first pressure sensor  58  and the second pressure sensor  60  are input to the control unit  56 . 
     An operating pressure Ps 1 , which is a set pressure in a normal mode (at a time of normal operation), a standby pressure Ps 2 , which is a set pressure in a standby mode, a flow rate threshold value L, and a monitoring time period T are stored in the control unit  56 . These values can be arbitrarily set and modified by a user, and are fed into the control unit  56  as input signals G 1 . The operating pressure Ps 1  is a target value (set pressure) of the fluid pressure supplied to the fluid actuator when the fluid actuator is operating. The standby pressure Ps 2  is a target value (set pressure) of the fluid pressure supplied to the fluid actuator when the fluid actuator is in a paused state. The standby pressure Ps 2  is lower than the operating pressure Ps 1 . 
     A standby release signal G 2  for returning from the standby mode to the normal mode is input as a pulse signal to the control unit  56  from the exterior. In the case that a change from the normal mode to the standby mode is made capable of being manually performed, a mode switching signal G 3  is input to the control unit  56  from the exterior. Further, a pressure display unit  62 , which is capable of displaying the set operating pressure Ps 1  and the set standby pressure Ps 2  together with displaying the pressure P 2  in the outlet port  18 , is connected to the control unit  56 . Moreover, the control unit  56  is capable of outputting the pressure P 2  in the outlet port  18  and a later-described estimated flow rate Qe as output signals G 4  to the exterior. 
     The fluid pressure control device  10  according to the present embodiment is provided with the aforementioned configurations and functions. Next, a description will be given with reference to  FIGS. 1 to 3 , concerning a control for a case in which transitioning from the normal mode to the standby mode is automatically performed. A state, in which the fluid actuator is in the operating state and the fluid pressure control device  10  is operating in the normal mode, is regarded as an initial state. Referring to  FIG. 2 , for example, the state at time t 2  corresponds to such an initial state. 
     When the fluid pressure control device  10  is operating in the normal mode, the control unit  56  controls the operations of the pilot pressure supply solenoid valve  36  and the pilot pressure discharge solenoid valve  38 , and thereby adjusts the degree of opening V of the supply valve  26  in a manner so that the pressure P 2  in the outlet port  18 , which is detected by the second pressure sensor  60 , coincides with a target value, which is the operating pressure Ps 1 . Consequently, the pressure P 2  in the outlet port  18  is maintained at the set operating pressure Ps 1 . When the fluid actuator is in the operating state, the pressure P 1  in the pilot chamber  48  significantly exceeds the pressure P 2  in the outlet port  18  that is maintained at the operating pressure Ps 1 , and the degree of opening V of the supply valve  26  is also sufficiently large (from time t 1  to time t 2 ). 
     Even when the fluid pressure control device  10  is operating in the normal mode, in the case that the pressure P 2  in the outlet port  18  is greater than the operating pressure Ps 1 , and further, the pressure P 1  in the pilot chamber  48  is less than or equal to a predetermined value, the pilot pressure discharge solenoid valve  38  is set to the shutoff position. The reason therefor is as follows. 
     Depending on the operating condition of the fluid actuator, even if the pilot pressure discharge solenoid valve  38  is maintained at the communicating position, cases may occur in which the pressure P 2  in the outlet port  18  does not become less than or equal to the operating pressure Ps 1 . Further, even if the pilot pressure discharge solenoid valve  38  is maintained at the communicating position, cases may occur in which the pressure P 1  in the pilot chamber  48  is not lowered to atmospheric pressure. Accordingly, a value which is slightly greater than atmospheric pressure (for example, 5 kPa in gauge pressure) is set as a predetermined value Pk, and in the case that the inequalities P 2 &gt;Ps 1  and P 1 ≤Pk are satisfied, the pilot pressure discharge solenoid valve  38  is set to the shutoff position. This is because supplying electrical power to the pilot pressure discharge solenoid valve  38  and maintaining it at the communicating position leads to the electrical power being needlessly consumed. It should be noted that such a situation is not depicted in the timing chart of  FIG. 2 . 
     When the fluid pressure control device  10  is operating in the normal mode, the control unit  56  estimates the flow rate of the fluid flowing toward the fluid actuator (the flow rate Q of the fluid passing through the supply valve  26 ) based on the signals detected by the first pressure sensor  58  and the second pressure sensor  60 . The method of estimating the flow rate Q is as follows. 
     The flow rate Q becomes greater as the differential pressure between the pressure P 1  in the pilot chamber  48  and the pressure P 2  in the outlet port  18  becomes greater. Further, the flow rate Q differs depending on the set pressure, even if the differential pressure between the pressure P 1  in the pilot chamber  48  and the pressure P 2  in the outlet port  18  is the same.  FIG. 3  is a graph showing a relationship between the differential pressure (P 1 −P 2 ) between the pressure P 1  in the pilot chamber  48  and the pressure P 2  in the outlet port  18 , and the flow rate Q, with the set pressure serving as a parameter. More specifically, with the set pressure being set to the two values PsA and PsB (PA&lt;PB), the pressure P 1  in the pilot chamber  48 , the pressure P 2  in the outlet port  18 , and the flow rate Q are actually measured using the pressure sensors and a flow rate sensor, and are shown based on the obtained data. As can be understood from  FIG. 3 , the relationship between the differential pressure (P 1 −P 2 ) and the flow rate Q is approximated by a straight line, and the slope thereof differs depending on the set pressure. 
     Thus, for the flow rate Q of the fluid passing through the supply valve  26 , the estimated flow rate Qe is obtained by the following expression, where K is a constant corresponding to the set pressure (a constant corresponding to the set value of the operating pressure Ps 1 ). 
         Qe=K ( P 1− P 2)
 
     The control unit  56  has stored therein a table relating to the constant K as determined for each of set pressures, and calculates the estimated flow rate Qe based on signals input from the first pressure sensor  58  and the second pressure sensor  60 . 
     In this manner, by including the second pressure sensor  60  in addition to the first pressure sensor  58 , the fluid pressure control device  10  can estimate the flow rate of the fluid flowing toward the fluid actuator. Therefore, the fluid pressure control device  10  does not require a flow rate sensor. In the case of wanting to improve the accuracy with which the flow rate is estimated, a pressure sensor that detects the pressure in the inlet port  16 , and a temperature sensor that detects the temperature of the fluid passing through the supply valve  26  may be added, and in addition to the set pressure, a table relating to a constant (K′) that is set by also taking into consideration the pressure in the inlet port  16  and the temperature of the fluid may be used. 
     When the control unit  56  determines that the estimated flow rate Qe has continuously fallen below the predetermined flow rate threshold value L for the monitoring time period T (predetermined time period) in the normal mode, the control unit  56  considers that the fluid actuator has entered into the paused state, and determines to transition to the standby mode (time t 3 ). In the standby mode, the control unit  56  controls the operations of the pilot pressure supply solenoid valve  36  and the pilot pressure discharge solenoid valve  38 , and thereby adjusts the degree of opening V of the supply valve  26  in a manner so that the pressure P 2  in the outlet port  18 , which is detected by the second pressure sensor  60 , coincides with a target value, which is the standby pressure Ps 2 . Consequently, the pressure P 2  in the outlet port  18  is set to the standby pressure Ps 2 , which is lower than the operating pressure Ps 1 . Transitioning from the normal mode to the standby mode is automatically performed in this manner. 
     Immediately after transitioning from the normal mode to the standby mode and at least while the pressure P 2  in the outlet port  18  falls from the operating pressure Ps 1  to the standby pressure Ps 2  (from time t 3  to immediately before time t 4 ), the supply valve  26  is controlled so as to be maintained in the closed position, and communication between the inlet port  16  and the outlet port  18  is shut off. This is because the pressure P 2  in the outlet port  18 , which is detected by the second pressure sensor  60 , continues to remain higher than the standby pressure Ps 2 , which is the target value. Accordingly, the pressure fluid is not newly supplied from the fluid supply source toward the fluid actuator, and consumption of the pressure fluid becomes zero. At this time, the fluid that is accumulated in the fluid actuator gradually escapes. 
     The standby mode is a mode for preparing return of the fluid actuator in the paused state to the operating state. The fluid actuator does not need to be supplied with the pressure fluid in the paused state, however, by supplying the fluid at the standby pressure Ps 2  beforehand, it is possible for the fluid actuator to be quickly and smoothly returned to the operating state. Moreover, while the fluid, which is at the standby pressure Ps 2 , is being supplied to the fluid actuator in the paused state, a constant leakage of the fluid occurs in the fluid actuator. The amount of such leakage is smaller than the amount of leakage that occurs in the case that the fluid, which is at the operating pressure Ps 1 , is supplied to the fluid actuator in the paused state. 
     Even when the fluid pressure control device  10  is operating in the standby mode, in the case that the pressure P 2  in the outlet port  18  is greater than the standby pressure Ps 2 , and further, the pressure P 1  in the pilot chamber  48  is less than or equal to the predetermined value, the pilot pressure discharge solenoid valve  38  is set to the shutoff position. This is because, similar to when operating in the normal mode, even if the pilot pressure discharge solenoid valve  38  is maintained at the communicating position, cases may occur in which the pressure P 2  in the outlet port  18  does not become less than or equal to the standby pressure Ps 2 . Further, since the pressure P 1  in the pilot chamber  48  is not lowered to atmospheric pressure, unnecessary operation of the pilot pressure discharge solenoid valve  38  is suppressed. It should be noted that such a situation is not depicted in the timing chart of  FIG. 2 . 
     Returning from the standby mode to the normal mode is performed in accordance with the standby release signal G 2  (time t 5 ). The standby release signal G 2  is a pulse signal that is input to the control unit  56  from the exterior, in order to return the fluid actuator, which is in the paused state, to the operating state. For example, the signal may be a signal which is input by an operation performed by the user on a touch panel, or may be a signal which is automatically input at a time that is set by the user for resuming operation of the fluid actuator. When returning from the standby mode to the normal mode, in order to realize a soft start, the set pressure may be changed in a stepwise manner from the standby pressure Ps 2  to the operating pressure Ps 1 . Further, returning to the normal mode need not necessarily be performed in accordance with the standby release signal G 2 , but may be performed at a time that the estimated flow rate Qe has become greater than the flow rate threshold value L. 
     Incidentally, in the fluid pressure control device  10 , when transitioning from the normal mode to the standby mode, the set pressure of the outlet port  18  is changed from the high operating pressure Ps 1  to the low standby pressure Ps 2 . However, the fluid pressure control device  10  is not provided with a valve that controls the change from the high pressure to the low pressure (a valve for discharging fluid from the outlet port  18 ). This is because, when the fluid actuator enters into the paused state, there is no need to rapidly cause the pressure P 2  in the outlet port  18  to decrease to the standby pressure Ps 2 , and it is satisfactory to wait for the pressure P 2  in the outlet port  18  to decrease naturally to the standby pressure Ps 2  by allowing the fluid accumulated in the fluid actuator to escape to a certain extent. In the foregoing manner, since the fluid pressure control device  10  is not provided with a valve for discharging the fluid from the outlet port  18 , loss of the pressure fluid can be suppressed. 
     Next, a description will be given with reference to  FIG. 4 , concerning a control for a case in which transitioning from the normal mode to the standby mode is manually performed. 
     Similar to the case in which transitioning from the normal mode to the standby mode is automatically performed, when the fluid pressure control device  10  is operating in the normal mode, the control unit  56  calculates the estimated flow rate Qe. In addition, at time t 3 , when the control unit  56  determines that the estimated flow rate Qe has continuously fallen below the flow rate threshold value L for the monitoring time period T, the control unit  56  waits for a change in the mode switching signal G 3  which is manually input from the exterior. At time t 3 ′, when the mode switching signal G 3  changes from OFF to ON, the control unit  56  determines to transition from the normal mode to the standby mode. Returning from the standby mode to the normal mode is performed in accordance with changing of the mode switching signal G 3  from ON to OFF (time t 5 ′). 
     As noted previously, transitioning from the normal mode to the standby mode is performed on the condition that the mode switching signal G 3  undergoes a change after the estimated flow rate Qe has continuously fallen below the flow rate threshold value L for the monitoring time period T. However, transitioning from the normal mode to the standby mode may be performed only on the condition that the mode switching signal G 3  undergoes a change. 
     Flowcharts for realizing the aforementioned controls are shown in  FIGS. 5 to 7 .  FIG. 5  is a flowchart for a case in which transitioning from the normal mode to the standby mode is automatically performed, and returning to the normal mode is performed in accordance with the standby release signal G 2 .  FIG. 6  is a flowchart for a case in which transitioning from the normal mode to the standby mode is automatically performed, and returning to the normal mode is automatically performed based on a flow rate.  FIG. 7  is a flowchart for a case in which transitioning from the normal mode to the standby mode is performed manually. 
     In step S 1  shown in  FIG. 5 , the control unit  56  reads the latest signals input from the first pressure sensor  58  and the second pressure sensor  60 , and thereby acquires the pressure P 1  in the pilot chamber  48  and the pressure P 2  in the outlet port  18 . Then, the control unit  56  compares the pressure P 2  in the outlet port  18  with the operating pressure Ps 1 . When the pressure P 2  in the outlet port  18  is less than the operating pressure Ps 1 , the control unit  56  controls the pilot pressure supply solenoid valve  36  and the pilot pressure discharge solenoid valve  38 , and thereby increases the degree of opening V of the supply valve  26 . When the pressure P 2  in the outlet port  18  is greater than the operating pressure Ps 1 , the control unit  56  controls the pilot pressure supply solenoid valve  36  and the pilot pressure discharge solenoid valve  38 , and thereby decreases the degree of opening V of the supply valve  26 . 
     Next, upon proceeding to step S 2 , the control unit  56  determines whether or not the pressure P 2  in the outlet port  18 , which has been acquired in step S 1 , is greater than the operating pressure Ps 1 , and further, whether or not the pressure P 1  in the pilot chamber  48 , which has been acquired in step S 1 , is less than or equal to the predetermined value Pk. In the case that such a determination result is YES, the control unit  56  outputs, to the pilot pressure discharge solenoid valve  38 , a signal for switching to the shutoff position, and then the process proceeds to step S 3 . In the case that the determination result is NO, the process immediately proceeds to step S 3 . 
     In step S 3 , the control unit  56  obtains the estimated flow rate Qe based on the pressure P 1  in the pilot chamber  48  and the pressure P 2  in the outlet port  18 , which have been acquired in step S 1 , while referring to the table relating to the constant K, and then the process proceeds to step S 4 . In step S 4 , the control unit  56  compares the estimated flow rate Qe obtained in step S 3  with the flow rate threshold value L, and in the case that the estimated flow rate Qe is less than or equal to the flow rate threshold value L, the process proceeds to step S 5 . In the case that the estimated flow rate Qe is greater than the flow rate threshold value L, the process returns to step S 1 . 
     In step S 5 , the control unit  56  determines whether or not a time period of greater than or equal to the monitoring time period T has elapsed since the estimated flow rate Qe has become less than or equal to the flow rate threshold value L. More specifically, the control unit  56  determines whether or not the state in which the estimated flow rate Qe is less than or equal to the flow rate threshold value L has continued for a time period of greater than or equal to the monitoring time period T. If the state in which the estimated flow rate Qe is less than or equal to the flow rate threshold value L has continued for a time period of greater than or equal to the monitoring time period T, the process proceeds to step S 6 . If the state in which the estimated flow rate Qe is less than or equal to the flow rate threshold value L has not continued for a time period of greater than or equal to the monitoring time period T, the process returns to step S 1 . In step S 6 , in order to transition from the normal mode to the standby mode, the control unit  56  changes the set pressure from the operating pressure Ps 1  to the standby pressure Ps 2 , and then the process proceeds to step S 7 . 
     In step S 7 , the control unit  56  reads the latest signals input from the first pressure sensor  58  and the second pressure sensor  60 , and thereby acquires the pressure P 1  in the pilot chamber  48  and the pressure P 2  in the outlet port  18 . Then, the control unit  56  compares the pressure P 2  in the outlet port  18  with the standby pressure Ps 2 . When the pressure P 2  in the outlet port  18  is less than the standby pressure Ps 2 , the control unit  56  controls the pilot pressure supply solenoid valve  36  and the pilot pressure discharge solenoid valve  38 , and thereby increases the degree of opening V of the supply valve  26 . When the pressure P 2  in the outlet port  18  is greater than the standby pressure Ps 2 , the control unit  56  controls the pilot pressure supply solenoid valve  36  and the pilot pressure discharge solenoid valve  38 , and thereby decreases the degree of opening V of the supply valve  26 . 
     Next, upon proceeding to step S 8 , the control unit  56  determines whether or not the pressure P 2  in the outlet port  18 , which has been acquired in step S 7 , is greater than the standby pressure Ps 2 , and further, whether or not the pressure P 1  in the pilot chamber  48 , which has been acquired in step S 7 , is less than or equal to the predetermined value Pk. In the case that such a determination result is YES, the control unit  56  outputs, to the pilot pressure discharge solenoid valve  38 , a signal for switching to the shutoff position, and then the process proceeds to step S 9 . In the case that the determination result is NO, the process immediately proceeds to step S 9 . 
     In step S 9 , the control unit  56  determines whether or not the standby release signal G 2  for returning from the standby mode to the normal mode has been input from the exterior. In the case that the standby release signal G 2  has been input from the exterior, the process returns to step S 1 . In the case that the standby release signal G 2  has not been input from the exterior, the process returns to step S 7 . 
     As shown in  FIG. 6 , the flowchart for a case in which returning to the normal mode is performed based on the flow rate is a flowchart in which step S 91  and step S 92  are provided instead of step S 9  in the flowchart of  FIG. 5 . Hereinafter, a description will be given focusing on the changed portions. 
     In step S 91 , the control unit  56  obtains the estimated flow rate Qe based on the pressure P 1  in the pilot chamber  48  and the pressure P 2  in the outlet port  18 , which have been acquired in step S 7 , while referring to the table relating to the constant K, and then the process proceeds to step S 92 . In step S 92 , the control unit  56  compares the estimated flow rate Qe obtained in step S 91  with the flow rate threshold value L. In the case that the estimated flow rate Qe is greater than the flow rate threshold value L, the process returns to step S 1 . In the case that the estimated flow rate Qe is less than or equal to the flow rate threshold value L, the process returns to step S 7 . 
     As shown in  FIG. 7 , the flowchart for a case in which transitioning from the normal mode to the standby mode is performed manually is a flowchart in which, in the flowchart of  FIG. 5 , step SA is added between steps S 5  and S 6 , and step S 9  is changed to step S 9 ′. Hereinafter, a description will be given focusing on the added and changed portions. 
     In step S 5 , the control unit  56  determines whether or not the state in which the estimated flow rate Qe is less than or equal to the flow rate threshold value L has continued for a time period of greater than or equal to the monitoring time period T. If the state in which the estimated flow rate Qe is less than or equal to the flow rate threshold value L has continued for a time period of greater than or equal to the monitoring time period T, the process proceeds to step SA. If the state in which the estimated flow rate Qe is less than or equal to the flow rate threshold value L has not continued for a time period of greater than or equal to the monitoring time period T, the process returns to step S 1 . 
     In step SA, the control unit  56  determines whether or not the mode switching signal G 3  has been changed from OFF to ON. In the case that the mode switching signal G 3  has been changed from OFF to ON, the process proceeds to step S 6 . In the case that the mode switching signal G 3  remains OFF, the process returns to step S 1 . In step S 6 , in order to transition from the normal mode to the standby mode, the control unit  56  changes the set pressure from the operating pressure Ps 1  to the standby pressure Ps 2 , and then the process proceeds to step S 7 . 
     In step S 9 ′, the control unit  56  determines whether or not the mode switching signal G 3  has been changed from ON to OFF. In the case that the mode switching signal G 3  has been changed from ON to OFF, the process returns to step S 1 . In the case that the mode switching signal G 3  remains ON, the process returns to step S 7 . 
     In accordance with the fluid pressure control device  10  according to the present embodiment, when transitioning from the normal mode to the standby mode, a control is performed to change the target value of the fluid pressure supplied to the fluid actuator from the high operating pressure Ps 1  to the low standby pressure Ps 2 , but there is not included a flow path through which the pressure fluid that has passed through the supply valve  26  is discharged to the exterior. Therefore, in addition to enabling a loss of the pressure fluid to be suppressed to a minimum, there is no need to separately provide a shutoff valve, and the device as a whole can be made small in scale. Further, based on the detection signals of the first pressure sensor  58  that detects the pressure P 1  in the pilot chamber  48 , and the detection signals of the second pressure sensor  60  that detects the pressure P 2  in the outlet port  18 , the flow rate flowing toward the fluid actuator is estimated. Therefore, there is no need to provide a flow rate sensor, and the device as a whole can be made small in scale. 
     The present invention is not limited to the embodiment described above, and various configurations may be adopted therein without deviating from the essence and gist of the invention.