Patent Publication Number: US-10309391-B2

Title: Bellows pump device

Description:
TECHNICAL FIELD 
     The present invention relates to a bellows pump device. 
     BACKGROUND ART 
     In semiconductor production, chemical industries, or the like, a bellows pump may be used as a pump for feeding a transport fluid such as a chemical solution, a solvent, or the like. 
     For example, as disclosed in PATENT LITERATURE 1, in the bellows pump, pump cases are connected to both sides of a pump head in a right-left direction (horizontal direction) to form two air chambers, and a pair of expandable/contractible bellows are provided within the respective air chambers, and the bellows pump is configured such that each bellows is contracted or expanded by alternately supplying pressurized air to the respective air chambers. To the bellows pump, a mechanical regulator is connected which adjusts the pressurized air to be supplied to each air chamber, into an appropriate air pressure. 
     In the pump head, a suction passage and a discharge passage for the transport fluid are formed so as to communicate with the interior of each bellows, and further check valves are provided which permit flow of the transport fluid in one direction in the suction passage and the discharge passage and blocks flow of the transport fluid in another direction in the suction passage and the discharge passage. The check valve for the suction passage is configured: to be opened by expansion of the bellows, to permit flow of the transport fluid from the suction passage into the bellows; and to be closed by contraction of the bellows, to block flow of the transport fluid from the interior of the bellows to the suction passage. In addition, the check valve for the discharge passage is configured: to be closed by expansion of the bellows, to block flow of the transport fluid from the discharge passage into the bellows; and to be opened by contraction of the bellows, to permit flow of the transport fluid from the interior of the bellows to the discharge passage. 
     The pair of bellows are integrally connected to each other by a tie rod. When one of the bellows contracts to discharge the transport fluid to the discharge passage, the other bellows forcedly expands at the same time, so that the transport fluid is sucked from the suction passage. In addition, when the other bellows contracts to discharge the transport fluid to the discharge passage, the one bellows forcedly expands at the same time, so that the transport fluid is sucked from the suction passage. 
     CITATION LIST 
     Patent Literature 
     PATENT LITERATURE 1: Japanese Laid-Open Patent Publication No. 2012-211512 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the bellows pump having the above configuration, when the pressurized air is supplied to the air chamber formed at the outer side of the bellows to cause the bellows to contract, as the contraction proceeds, stress required to cause the bellows to contract increases. Thus, it is necessary to increase the air pressure of the pressurized air to be supplied to the air chamber. However, the mechanical regulator, which adjusts the air pressure of the pressurized air, cannot perform control in which the valve is temporarily opened for increasing the air pressure of the air chamber. Thus, as shown in  FIG. 22 , while each bellows contracts, a phenomenon occurs that the discharge pressure of the transport fluid gradually falls (portions surrounded by dotted lines in the drawing), causing pulsation. 
     The present invention has been made in view of such a situation, and an object of the present invention is to provide a bellows pump device that is able to reduce fall of a discharge pressure of a transport fluid during contraction operation of a bellows. 
     Solution to Problem 
     A bellows pump device of the present invention is a bellows pump device that supplies pressurized air to a hermetic air chamber thereby to cause a bellows disposed within the air chamber to perform contraction operation to discharge a transport fluid, and discharges the pressurized air from the air chamber thereby to cause the bellows to perform expansion operation to suck the transport fluid, the bellows pump device including an electropneumatic regulator configured to adjust an air pressure of the pressurized air to be supplied to the air chamber, such that the air pressure is increased so as to correspond to a contraction characteristic of the bellows during the contraction operation of the bellows. 
     According to the bellows pump device configured as describe above, during contraction operation of the bellows, the air pressure of the pressurized air to be supplied to the air chamber is increased by the electropneumatic regulator so as to correspond to the contraction characteristic of the bellows, so that the air pressure of the pressurized air in the air chamber can be increased as the bellows contracts. Accordingly, fall of the discharge pressure of the transport fluid during contraction of the bellows can be reduced. 
     The electropneumatic regulator preferably adjusts the air pressure every unit time by using the following equation:
 
 P=aX+b,  
 
wherein P denotes the air pressure, a denotes a pressure increase coefficient, X denotes an expansion/contraction position of the bellows, and b denotes an initial air pressure.
 
     In this case, fall of the discharge pressure of the transport fluid during contraction of the bellows can be effectively reduced. 
     In the above bellows pump device, preferably, the bellows includes a first bellows and a second bellows that are expandable/contractible independently of each other, and the bellows pump device further includes: a first driving device configured to cause the first bellows to perform expansion/contraction operation continuously between a most expanded state and a most contracted state; a second driving device configured to cause the second bellows to perform expansion/contraction operation continuously between a most expanded state and a most contracted state; a first detection device configured to detect an expanded/contracted state of the first bellows; a second detection device configured to detect an expanded/contracted state of the second bellows; and a control unit configured to control drive of the first and second driving devices on the basis of each of detection signals of the first and second detection device such that the second bellows is caused to contract from the most expanded state before the first bellows comes into the most contracted state, and the first bellows is caused to contract from the most expanded state before the second bellows comes into the most contracted state. 
     In this case, the first bellows and the second bellows are made expandable/contractible independently of each other, and the control unit is configured to perform drive control such that the second bellows is caused to contract from the most expanded state before the first bellows comes into the most contracted state, and the first bellows is caused to contract from the most expanded state before the second bellows comes into the most contracted state. Thus, at timing of switching from contraction of one bellows (discharge) to expansion thereof (suction), the other bellows has already contracted to discharge the transport fluid. Accordingly, fall of the discharge pressure at the timing of switching can be reduced. As a result, pulsation at the discharge side of the bellows pump device can be reduced. 
     With the above bellows pump device, since the electropneumatic regulator outputs the pressurized air in output cycles such that the air pressure of the pressurized air always has a constant pressure increase coefficient, the following problem may arise. 
     Specifically, for example, in the case a high-temperature transport fluid and a low-temperature transport fluid are fed in this order by the bellows pump device, when switching from feeding of the high-temperature transport fluid to feeding of the low-temperature transport fluid is performed, the bellows may become hard due to a decrease in the temperature of the transport fluid sucked into the bellows. When such a change occurs, the bellows becomes difficult to contract, but the electropneumatic regulator outputs the pressurized air in output cycles such that the air pressure has a constant pressure increase coefficient regardless of the hardness of the bellows. Thus, the discharge pressure of the transport fluid decreases, so that the discharge pressure cannot be maintained constant. 
     When the discharge pressure of the transport fluid cannot be maintained constant, pulsation of the bellows pump device increases, which may have an adverse effect on a semiconductor production process, such as foreign matter flowing in through a filter provided in the middle of a feed pipe for the transport fluid, or collapse of a pattern on a wafer due to pulsation of the transport fluid sprayed from a nozzle end. 
     Therefore, the above bellows pump device preferably further includes: a temperature detection unit configured to detect a temperature of the transport fluid; and a control unit configured to control the electropneumatic regulator such that a pressure increase coefficient used in increasing the air pressure increases as a detection value of the temperature detection unit decreases. 
     In this case, the control unit controls the electropneumatic regulator such that the pressure increase coefficient for the air pressure of the pressurized air to be supplied to the air chamber during the contraction operation of the bellows increases as the temperature of the transport fluid detected by the temperature detection unit decreases. Accordingly, for example, even when the temperature of the transport fluid decreases so that the bellows becomes hard, the bellows can be caused to contract by the air pressure higher than the air pressure prior to the temperature decrease of the transport fluid, since the pressure increase coefficient for the air pressure of the pressurized air to be supplied to the air chamber increases. Therefore, even when the hardness of the bellows changes due to a temperature change of the transport fluid, change of the discharge pressure of the transport fluid during contraction of the bellows can be suppressed. 
     The control unit preferably sets the pressure increase coefficient for the air pressure on the basis of the detection value of the temperature detection unit such that a maximum value of the air pressure does not exceed an allowable withstand pressure of the bellows. 
     In this case, even when the pressure increase coefficient for the air pressure of the pressurized air to be supplied to the air chamber increases, the maximum value of the air pressure does not exceed the allowable withstand pressure of the bellows. Thus, the bellows can be prevented from being deformed or broken due to an increase in the air pressure. 
     Preferably, the control unit has a look-up table in which the pressure increase coefficient is set so as to correspond to each of a plurality of temperature ranges, and controls the electropneumatic regulator on the basis of the look-up table. 
     In this case, the electropneumatic regulator can be easily controlled on the basis of the look-up table. 
     Advantageous Effects of Invention 
     According to the bellows pump device of the present invention, fall of the discharge pressure of the transport fluid during contraction operation of the bellows can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic configuration diagram of a bellows pump device according to a first embodiment of the present invention. 
         FIG. 2  is a cross-sectional view of a bellows pump. 
         FIG. 3  is an explanatory diagram showing operation of the bellows pump. 
         FIG. 4  is an explanatory diagram showing operation of the bellows pump. 
         FIG. 5  is a block diagram showing the internal configuration of a control unit. 
         FIG. 6  is a time chart showing an example of drive control of the bellows pump. 
         FIG. 7  is a cross-sectional view showing a state where a second bellows in a most expanded state has started contracting before a first bellows comes into a most contracted state. 
         FIG. 8  is a cross-sectional view showing a state where the first bellows in a most expanded state has started contracting before the second bellows comes into a most contracted state. 
         FIG. 9  is a graph showing an example of adjustment of an air pressure by first and second electropneumatic regulators. 
         FIG. 10  is a graph showing the discharge pressure of a transport fluid discharged from the bellows pump. 
         FIG. 11  is a schematic configuration diagram showing a modification of the bellows pump device according to the first embodiment. 
         FIG. 12  is a schematic diagram showing the configuration of a fluid feeding system including a bellows pump device according to a second embodiment of the present invention. 
         FIG. 13  is a schematic configuration diagram of the bellows pump device of the second embodiment. 
         FIG. 14  is an example of a look-up table of a control unit of the second embodiment. 
         FIG. 15  is a graph showing change of an air pressure at an electropneumatic regulator controlled by a control unit, corresponding to each of a plurality of temperature ranges in the second embodiment. 
         FIG. 16  is a graph showing a relationship between the temperature of a transport fluid and an allowable withstand pressure of a bellows in the second embodiment. 
         FIG. 17  is a graph showing change of the discharge pressure of the transport fluid discharged from a bellows pump through control of an electropneumatic regulator according to Comparative Example 1. 
         FIG. 18  is a graph showing change of the discharge pressure of the transport fluid discharged from a bellows pump through control of an electropneumatic regulator according to Example 1 of the second embodiment. 
         FIG. 19  is a graph showing change of the discharge pressure of the transport fluid discharged from a bellows pump through control of an electropneumatic regulator according to Comparative Example 2. 
         FIG. 20  is a graph showing change of the discharge pressure of the transport fluid discharged from a bellows pump through control of an electropneumatic regulator according to Example 2 of the second embodiment. 
         FIG. 21  is a graph showing change of the discharge pressure of the transport fluid discharged from a bellows pump through control of an electropneumatic regulator according to Example 3 of the second embodiment. 
         FIG. 22  is a graph showing the discharge pressure of a transport fluid discharged from a conventional bellows pump. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Next, preferred embodiments of the present invention will be described with reference to the accompanying drawings. 
     [First Embodiment] 
     &lt;Entire Configuration of Bellows Pump&gt; 
       FIG. 1  is a schematic configuration diagram of a bellows pump device according to a first embodiment of the present invention. The bellows pump device BP of the present embodiment is used, for example, in a semiconductor production apparatus when a transport fluid such as a chemical solution, a solvent, or the like is supplied in a certain amount. The bellows pump device BP includes: a bellows pump  1 ; an air supply device  2  such as an air compressor or the like which supplies pressurized air (working fluid) to the bellows pump  1 ; a mechanical regulator  3  and two first and second electropneumatic regulators  51  and  52  that adjust the air pressure of the pressurized air; two first and second switching valves  4  and  5 ; and a control unit  6  that controls drive of the bellows pump  1 . 
       FIG. 2  is a cross-sectional view of the bellows pump of the present embodiment. 
     The bellows pump  1  of the present embodiment includes: a pump head  11 ; a pair of pump cases  12  that are mounted at both sides of the pump head  11  in a right-left direction (horizontal direction); two first and second bellows  13  and  14  that are mounted on side surfaces of the pump head  11  in the right-left direction and within the respective pump cases  12 ; and four check valves  15  and  16  that are mounted on the side surfaces of the pump head  11  in the right-left direction and within the respective bellows  13  and  14 . 
     &lt;Configurations of Bellows&gt; 
     The first and second bellows  13  and  14  are each formed in a bottomed cylindrical shape from a fluorine resin such as polytetrafluoroethylene (PTFE), a tetrafluoroethylene-perfluoro alkyl vinyl ether copolymer (PFA), or the like, and flange portions  13   a  and  14   a  are integrally formed at open end portions thereof and are hermetically pressed and fixed to the side surfaces of the pump head  11 . Peripheral walls of the first and second bellows  13  and  14  are each formed in an accordion shape, and are configured to be expandable/contractible independently of each other in the horizontal direction. Specifically, each of the first and second bellows  13  and  14  is configured to expand/contract between a most expanded state where an outer surface of a working plate  19  described later is in contact with an inner side surface of a bottom wall portion  12   a  of the pump case  12  and a most contracted state where an inner side surface of a piston body  23  described later is in contact with an outer side surface of the bottom wall portion  12   a  of the pump case  12 . 
     The working plate  19 , together with one end portion of a connection member  20 , is fixed to each of outer surfaces of bottom portions of the first and second bellows  13  and  14  by bolts  17  and nuts  18 . 
     &lt;Configurations of Pump Cases&gt; 
     Each pump case  12  is formed in a bottomed cylindrical shape, and an opening peripheral portion thereof is hermetically pressed and fixed to the flange portion  13   a  ( 14   a ) of the corresponding bellows  13  ( 14 ). Thus, a discharge-side air chamber  21  is formed within the pump case  12  such that a hermetic state thereof is maintained. 
     An suction/exhaust port  22  is provided in each pump case  12  and connected to the air supply device  2  via the switching valve  4 ( 5 ), the electropneumatic regulator  51  ( 52 ), and the mechanical regulator  3  (see  FIG. 1 ). Accordingly, the bellows  13  ( 14 ) contracts by supplying the pressurized air from the air supply device  2  via the mechanical regulator  3 , the electropneumatic regulator  51  ( 52 ), the switching valve  4 ( 5 ), and the suction/exhaust port  22  into the discharge-side air chamber  21 . 
     In addition, the connection member  20  is supported by the bottom wall portion  12   a  of each pump case  12  so as to be slidable in the horizontal direction, and the piston body  23  is fixed to another end portion of the connection member  20  by a nut  24 . The piston body  23  is supported so as to be slidable in the horizontal direction relative to an inner circumferential surface of a cylindrical cylinder body  25 , which is integrally provided on the outer side surface of the bottom wall portion  12   a , with a hermetic state maintained. Accordingly, a space surrounded by the bottom wall portion  12   a , the cylinder body  25 , and the piston body  23  is formed as a suction-side air chamber  26  of which a hermetic state is maintained. 
     In each cylinder body  25 , a suction/exhaust port  25   a  is formed so as to communicate with the suction-side air chamber  26 . The suction/exhaust port  25   a  is connected to the air supply device  2  via the switching valve  4  ( 5 ), the electropneumatic regulator  51  ( 52 ), and the mechanical regulator  3  (see  FIG. 1 ). Accordingly, the bellows  13  ( 14 ) expands by supplying the pressurized air from the air supply device  2  via the mechanical regulator  3 , the electropneumatic regulator  51  ( 52 ), the switching valve  4  ( 5 ), and the suction/exhaust port  25   a  into the suction-side air chamber  26 . 
     A leakage sensor  40  for detecting leakage of the transport fluid to the discharge-side air chamber  21  is mounted below the bottom wall portion  12   a  of each pump case  12 . 
     In the bellows pump device BP of the present embodiment, a time taken until the suction-side air chamber  26  is fully filled with the pressurized air is shorter than a time taken until the discharge-side air chamber  21  is fully filled with the pressurized air. That is, an expansion time (suction time) for which the bellows  13  ( 14 ) expands from the most contracted state to the most expanded state is shorter than a contraction time (discharge time) for which the bellows  13  ( 14 ) contracts from the most expanded state to the most contracted state. 
     Because of the above configuration, the pump case  12  in which the discharge-side air chamber  21  at the left side in  FIG. 2  is formed, and the piston body  23  and the cylinder body  25  that form the suction-side air chamber  26  at the left side in  FIG. 2 , form a first air cylinder portion (first driving device)  27  that causes the first bellows  13  to perform expansion/contraction operation continuously between the most expanded state and the most contracted state. 
     In addition, the pump case  12  in which the discharge-side air chamber  21  at the right side in  FIG. 2  is formed, and the piston body  23  and the cylinder body  25  that form the suction-side air chamber  26  at the right side in  FIG. 2 , form a second air cylinder portion (second driving device)  28  that causes the second bellows  14  to perform expansion/contraction operation continuously between the most expanded state and the most contracted state. 
     A pair of proximity sensors  29 A and  29 B are mounted on the cylinder body  25  of the first air cylinder portion  27 , and a detection plate  30  to be detected by each of the proximity sensors  29 A and  29 B is mounted on the piston body  23 . The detection plate  30  reciprocates together with the piston body  23 , so that the detection plate  30  alternately comes close to the proximity sensors  29 A and  29 B, whereby the detection plate  30  is detected by the proximity sensors  29 A and  29 B. 
     The proximity sensor  29 A is a first most contraction detection unit for detecting the most contracted state of the first bellows  13 , and is disposed at such a position that the proximity sensor  29 A detects the detection plate  30  when the first bellows  13  is in the most contracted state. The proximity sensor  29 B is a first most expansion detection unit for detecting the most expanded state of the first bellows  13 , and is disposed at such a position that the proximity sensor  29 B detects the detection plate  30  when the first bellows  13  is in the most expanded state. Detection signals of the respective proximity sensors  29 A and  29 B are transmitted to the control unit  6 . In the present embodiment, the pair of proximity sensors  29 A and  29 B form a first detection device  29  for detecting an expanded/contracted state of the first bellows  13 . 
     Similarly, a pair of proximity sensors  31 A and  31 B are mounted on the cylinder body  25  of the second air cylinder portion  28 , and a detection plate  32  to be detected by each of the proximity sensors  31 A and  31 B is mounted on the piston body  23 . The detection plate  32  reciprocates together with the piston body  23 , so that the detection plate  32  alternately comes close to the proximity sensors  31 A and  31 B, whereby the detection plate  32  is detected by the proximity sensors  31 A and  31 B. 
     The proximity sensor  31 A is a second most contraction detection unit for detecting the most contracted state of the second bellows  14 , and is disposed at such a position that the proximity sensor  31 A detects the detection plate  32  when the second bellows  14  is in the most contracted state. The proximity sensor  31 B is a second most expansion detection unit for detecting the most expanded state of the second bellows  14 , and is disposed at such a position that the proximity sensor  31 B detects the detection plate  32  when the second bellows  14  is in the most expanded state. Detection signals of the respective proximity sensors  31 A and  31 B are transmitted to the control unit  6 . In the present embodiment, the pair of proximity sensors  31 A and  31 B form a second detection device  31  for detecting an expanded/contracted state of the second bellows  14 . 
     The pressurized air generated by the air supply device  2  is alternately supplied to the suction-side air chamber  26  and the discharge-side air chamber  21  of the first air cylinder portion  27  by the pair of proximity sensors  29 A and  29 B of the first detection device  29  alternately detecting the detection plate  30 . Accordingly, the first bellows  13  continuously performs expansion/contraction operation. 
     In addition, the pressurized air is alternately supplied to the suction-side air chamber  26  and the discharge-side air chamber  21  of the second air cylinder portion  28  by the pair of proximity sensors  31 A and  31 B of the second detection device  31  alternately detecting the detection plate  32 . Accordingly, the second bellows  14  continuously performs expansion/contraction operation. At this time, expansion operation of the second bellows  14  is performed mainly during contraction operation of the first bellows  13 , and contraction operation of the second bellows  14  is performed mainly during expansion operation of the first bellows  13 . By the first bellows  13  and the second bellows  14  alternately repeating expansion/contraction operation as described above, suction and discharge of the transport fluid to and from the interiors of the respective bellows  13  and  14  are alternately performed, whereby the transport fluid is transported. 
     &lt;Configuration of Pump Head&gt; 
     The pump head  11  is formed from a fluorine resin such as PTFE, PFA, or the like. A suction passage  34  and a discharge passage  35  for the transport fluid are formed within the pump head  11 . The suction passage  34  and the discharge passage  35  are opened in an outer peripheral surface of the pump head  11  and respectively connected to a suction port and a discharge port (both are not shown) provided at the outer peripheral surface. The suction port is connected to a storage tank for the transport fluid or the like, and the discharge port is connected to a transport destination for the transport fluid. In addition, the suction passage  34  and the discharge passage  35  each branch toward both right and left side surfaces of the pump head  11 , and have suction openings  36  and discharge openings  37  that are opened in both right and left side surfaces of the pump head  11 . Each suction opening  36  and each discharge opening  37  communicate with the interior of the bellows  13  or  14  via the check valves  15  and  16 , respectively. 
     &lt;Configurations of Check Valves&gt; 
     The check valves  15  and  16  are provided at each suction opening  36  and each discharge opening  37 . 
     The check valve  15  (hereinafter, also referred to as “suction check valve”) mounted at each suction opening  36  includes: a valve case  15   a ; a valve body  15   b  that is housed in the valve case  15   a ; and a compression coil spring  15   c  that biases the valve body  15   b  in a valve closing direction. The valve case  15   a  is formed in a bottomed cylindrical shape, and a through hole  15   d  is formed in a bottom wall thereof so as to communicate with the interior of the bellows  13  or  14 . The valve body  15   b  closes the suction opening  36  (performs valve closing) by the biasing force of the compression coil spring  15   c , and opens the suction opening  36  (performs valve opening) when a back pressure generated by flow of the transport fluid occurring with expansion/contraction of the bellows  13  or  14  acts thereon. 
     Accordingly, the suction check valve  15  opens when the bellows  13  or  14  at which the suction check valve  15  is disposed expands, to permit suction of the transport fluid in a direction (one direction) from the suction passage  34  toward the interior of the bellows  13  or  14 , and closes when the bellows  13  or  14  contracts, to block backflow of the transport fluid in a direction (another direction) from the interior of the bellows  13  or  14  toward the suction passage  34 . 
     The check valve  16  (hereinafter, also referred to as “discharge check valve”) mounted at each discharge opening  37  includes: a valve case  16   a ; a valve body  16   b  that is housed in the valve case  16   a ; and a compression coil spring  16   c  that biases the valve body  16   b  in a valve closing direction. The valve case  16   a  is formed in a bottomed cylindrical shape, and a through hole  16   d  is formed in a bottom wall thereof so as to communicate with the interior of the bellows  13  or  14 . The valve body  16   b  closes the through hole  16   d  of the valve case  16   a  (performs valve closing) by the biasing force of the compression coil spring  16   c , and opens the through hole  16   d  of the valve case  16   a  (performs valve opening) when a back pressure generated by flow of the transport fluid occurring with expansion/contraction of the bellows  13  or  14  acts thereon. 
     Accordingly, the discharge check valve  16  opens when the bellows  13  or  14  at which the discharge check valve  16  is disposed contracts, to permit outflow of the transport fluid in a direction (one direction) from the interior of the bellows  13  or  14  toward the discharge passage  35 , and closes when the bellows  13  or  14  expands, to block backflow of the transport fluid in a direction (another direction) from the discharge passage  35  toward the interior of the bellows  13  or  14 . 
     &lt;Operation of Bellows Pump&gt; 
     Next, operation of the bellows pump  1  of the present embodiment will be described with reference to  FIGS. 3 and 4 . In  FIGS. 3 and 4 , the configurations of the first and second bellows  13  and  14  are shown in a simplified manner. 
     As shown in  FIG. 3 , when the first bellows  13  contracts and the second bellows  14  expands, the respective valve bodies  15   b  and  16   b  of the suction check valve  15  and the discharge check valve  16  that are mounted at the left side of the pump head  11  in the drawing receive pressure from the transport fluid within the first bellows  13  and move to the right sides of the respective valve cases  15   a  and  16   a  in the drawing. Accordingly, the suction check valve  15  closes, and the discharge check valve  16  opens, so that the transport fluid within the first bellows  13  is discharged through the discharge passage  35  to the outside of the pump. 
     Meanwhile, the respective valve bodies  15   b  and  16   b  of the suction check valve  15  and the discharge check valve  16  that are mounted at the right side of the pump head  11  in the drawing move to the right sides of the respective valve cases  15   a  and  16   a  in the drawing due to a suction effect by the second bellows  14 . Accordingly, the suction check valve  15  opens, and the discharge check valve  16  closes, so that the transport fluid is sucked from the suction passage  34  into the second bellows  14 . 
     Next, as shown in  FIG. 4 , when the first bellows  13  expands and the second bellows  14  contracts, the respective valve bodies  15   b  and  16   b  of the suction check valve  15  and the discharge check valve  16  that are mounted at the right side of the pump head  11  in the drawing receive pressure from the transport fluid within the second bellows  14  and move to the left sides of the respective valve cases  15   a  and  16   a  in the drawing. Accordingly, the suction check valve  15  closes, and the discharge check valve  16  opens, so that the transport fluid within the second bellows  14  is discharged through the discharge passage  35  to the outside of the pump. 
     Meanwhile, the respective valve bodies  15   b  and  16   b  of the suction check valve  15  and the discharge check valve  16  that are mounted at the left side of the pump head  11  in the drawing move to the left sides of the respective valve cases  15   a  and  16   a  in the drawing due to a suction effect by the first bellows  13 . Accordingly, the suction check valve  15  opens, and the discharge check valve  16  closes, so that the transport fluid is sucked from the suction passage  34  into the first bellows  13 . 
     By repeatedly performing the above operation, the left and right bellows  13  and  14  can alternately suck and discharge the transport fluid. 
     &lt;Configurations of Switching Valves&gt; 
     In  FIG. 1 , the first switching valve  4  switches between supply of the pressurized air from the air supply device  2  to the discharge-side air chamber  21  and the suction-side air chamber  26  of the first air cylinder portion  27  and discharge of the pressurized air from the discharge-side air chamber  21  and the suction-side air chamber  26  of the first air cylinder portion  27 , and is composed of, for example, a three-position solenoid switching valve including a pair of solenoids  4   a  and  4   b . Each of the solenoids  4   a  and  4   b  is magnetized upon reception of a command signal from the control unit  6 . Although the first switching valve  4  of the present embodiment is composed of the three-position solenoid switching valve, the first switching valve  4  may be a two-position solenoid switching valve which does not have a neutral position. 
     When both of the solenoids  4   a  and  4   b  are in a demagnetized state, the first switching valve  4  is maintained at a neutral position, supply of the pressurized air from the air supply device  2  to the discharge-side air chamber  21  (suction/exhaust port  22 ) and the suction-side air chamber  26  (suction/exhaust port  25   a ) of the first air cylinder portion  27  is blocked, and both the discharge-side air chamber  21  and the suction-side air chamber  26  of the first air cylinder portion  27  communicate with and are open to the atmosphere. 
     In addition, when the solenoid  4   a  is magnetized, the first switching valve  4  switches to a lower position in the drawing, and the pressurized air is supplied from the air supply device  2  to the discharge-side air chamber  21  of the first air cylinder portion  27 . At this time, the suction-side air chamber  26  of the first air cylinder portion  27  communicates with and is open to the atmosphere. Accordingly, the first bellows  13  can be caused to contract. 
     Furthermore, when the solenoid  4   b  is magnetized, the first switching valve  4  switches to an upper position in the drawing, and the pressurized air is supplied from the air supply device  2  to the suction-side air chamber  26  of the first air cylinder portion  27 . At this time, the discharge-side air chamber  21  of the first air cylinder portion  27  communicates with and is open to the atmosphere. Accordingly, the first bellows  13  can be caused to expand. 
     The second switching valve  5  switches between supply of the pressurized air from the air supply device  2  to the discharge-side air chamber  21  and the suction-side air chamber  26  of the second air cylinder portion  28  and discharge of the pressurized air from the discharge-side air chamber  21  and the suction-side air chamber  26  of the second air cylinder portion  28 , and is composed of, for example, a three-position solenoid switching valve including a pair of solenoids  5   a  and  5   b . Each of the solenoids  5   a  and  5   b  is magnetized upon reception of a command signal from the control unit  6 . Although the second switching valve  5  of the present embodiment is composed of the three-position solenoid switching valve, the second switching valve  5  may be a two-position solenoid switching valve which does not have a neutral position. 
     When both of the solenoids  5   a  and  5   b  are in a demagnetized state, the second switching valve  5  is maintained at a neutral position, supply of the pressurized air from the air supply device  2  into the discharge-side air chamber  21  (suction/exhaust port  22 ) and the suction-side air chamber  26  (suction/exhaust port  25   a ) of the second air cylinder portion  28  is blocked, and both the discharge-side air chamber  21  and the suction-side air chamber  26  of the second air cylinder portion  28  communicate with and are open to the atmosphere. 
     In addition, when the solenoid  5   a  is magnetized, the second switching valve  5  switches to a lower position in the drawing, and the pressurized air is supplied from the air supply device  2  to the discharge-side air chamber  21  of the second air cylinder portion  28 . At this time, the suction-side air chamber  26  of the second air cylinder portion  28  communicates with and is open to the atmosphere. Accordingly, the second bellows  14  can be caused to contract. 
     Furthermore, when the solenoid  5   b  is magnetized, the second switching valve  5  switches to an upper position in the drawing, and the pressurized air is supplied from the air supply device  2  to the suction-side air chamber  26  of the second air cylinder portion  28 . At this time, the discharge-side air chamber  21  of the second air cylinder portion  28  communicates with and is open to the atmosphere. Accordingly, the second bellows  14  can be caused to expand. 
     In  FIG. 1 , a first quick exhaust valve  61  is disposed between the discharge-side air chamber  21  (suction/exhaust port  22 ) of the first air cylinder portion  27  and the first switching valve  4  and adjacently to the discharge-side air chamber  21 . The first quick exhaust valve  61  has an exhaust port  61   a  through which the pressurized air is discharged, and is configured to permit flow of the pressurized air from the first switching valve  4  to the discharge-side air chamber  21  and to discharge the pressurized air flowing out from the discharge-side air chamber  21 , through the exhaust port  61   a . Thus, the pressurized air within the discharge-side air chamber  21  can be quickly discharged through the first quick exhaust valve  61 , not via the first switching valve  4 . 
     Similarly, a second quick exhaust valve  62  is disposed between the discharge-side air chamber  21  (suction/exhaust port  22 ) of the second air cylinder portion  28  and the second switching valve  5  and adjacently to the discharge-side air chamber  21 . The second quick exhaust valve  62  has an exhaust port  62   a  through which the pressurized air is discharged, and is configured to permit flow of the pressurized air from the second switching valve  5  to the discharge-side air chamber  21  and to discharge the pressurized air flowing out from the discharge-side air chamber  21 , through the exhaust port  62   a . Thus, the pressurized air within the discharge-side air chamber  21  can be quickly discharged through the second quick exhaust valve  62 , not via the second switching valve  5 . 
     A quick exhaust valve is not disposed between the suction-side air chamber  26  (suction/exhaust port  25   a ) of each of the air cylinder portions  27  and  28  and the corresponding switching valve  4  or  5 . In the case where quick exhaust valves are mounted at the suction side, the same advantageous effects as those in the case where quick exhaust valves are mounted at the discharge side are obtained, but the effects are not great as compared to those at the discharge side. Thus, in the embodiment, due to the cost, quick exhaust valves at the suction side are not installed. 
     &lt;Configuration of Control Unit&gt; 
     The control unit  6  controls drive of each of the first air cylinder portion  27  and the second air cylinder portion  28  of the bellows pump  1  by switching the respective switching valves  4  and  5  on the basis of detection signals of the first detection device  29  and the second detection device  31  (see  FIG. 2 ). 
       FIG. 5  is a block diagram showing the internal configuration of the control unit  6 . The control unit  6  includes first and second calculation sections  6   a  and  6   b , first and second determination sections  6   c  and  6   d , and a drive control section  6   e.    
     The first calculation section  6   a  calculates a first expansion time from the most contracted state of the first bellows  13  to the most expanded state of the first bellows  13  and a first contraction time from the most expanded state of the first bellows  13  to the most contracted state of the first bellows  13 , on the basis of the respective detection signals of the pair of proximity sensors  29 A and  29 B. Specifically, the first calculation section  6   a  calculates, as the first expansion time, an elapsed time from a time point of end of detection by the proximity sensor  29 A to a time point of detection by the proximity sensor  29 B. In addition, the first calculation section  6   a  calculates, as the first contraction time, an elapsed time from a time point of end of detection by the proximity sensor  29 B to a time point of detection by the proximity sensor  29 A. 
     The second calculation section  6   b  calculates a second expansion time from the most contracted state of the second bellows  14  to the most expanded state of the second bellows  14  and a second contraction time from the most expanded state of the second bellows  14  to the most contracted state of the second bellows  14 , on the basis of the respective detection signals of the pair of proximity sensors  31 A and  31 B. Specifically, the second calculation section  6   b  calculates, as the second expansion time, an elapsed time from a time point of end of detection by the proximity sensor  31 A to a time point of detection by the proximity sensor  31 B. In addition, the second calculation section  6   b  calculates, as the second contraction time, an elapsed time from a time point of end of detection by the proximity sensor  31 B to a time point of detection by the proximity sensor  31 A. 
     On the basis of the calculated first expansion time and first contraction time, the first determination section  6   c  determines a first time difference from a time point at which the first bellows  13  in the most expanded state starts contraction operation to a time point at which the second bellows  14  in the most expanded state starts contraction operation before the first bellows  13  comes into the most contracted state through the contraction operation. 
     The first determination section  6   c  of the present embodiment determines the first time difference, for example, by using the following equation (1).
 
First time difference=(first expansion time+first contraction time)/2  (1)
 
     On the basis of the calculated second expansion time and second contraction time, the second determination section  6   d  determines a second time difference from a time point at which the second bellows  14  in the most expanded state starts contraction operation to a time point at which the first bellows  13  in the most expanded state starts contraction operation before the second bellows  14  comes into the most contracted state through the contraction operation. 
     The second determination section  6   d  of the present embodiment determines the second time difference, for example, by using the following equation (2).
 
Second time difference=(second expansion time+second contraction time)/2   (2)
 
     On the basis of the determined first and second time differences, the drive control section  6   e  controls drive of the first and second driving devices. Specifically, the drive control section  6   e  controls drive of the first and second air cylinder portions  27  and  28  such that: contraction operation of the second bellows  14  in the most expanded state is started at a time point at which the first time difference elapses from a time point at which the first bellows  13  in the most expanded state starts contraction operation; and contraction operation of the first bellows  13  in the most expanded state is started at a time point at which the second time difference elapses from a time point at which the second bellows  14  in the most expanded state starts contraction operation. 
     The bellows pump device BP shown in  FIG. 1  further includes a power switch  8 , a start switch  9 , and a stop switch  10 . 
     The power switch  8  outputs an operation command for powering on/off the bellows pump  1 , and the operation command is inputted to the control unit  6 . The start switch  9  outputs an operation command for driving the bellows pump  1 , and the operation command is inputted to the control unit  6 . The stop switch  10  outputs an operation command for causing a standby state where both the first bellows  13  and the second bellows  14  are in the most contracted state. 
     &lt;Control of Drive of Bellows Pump&gt; 
       FIG. 6  is a time chart showing an example of control of drive of the bellows pump  1  by the control unit  6 . When the power switch  8  is OFF, the first and second switching valves  4  and  5  (see  FIG. 1 ) are maintained at the neutral positions thereof. Therefore, when the power switch  8  is OFF, the air chambers  21  and  26  of the first and second air cylinder portions  27  and  28  of the bellows pump  1  communicate with the atmosphere. Thus, the first bellows  13  and the second bellows  14  are maintained at positions expanded slightly from the standby state, such that the interiors of both air chambers  21  and  26  are balanced with the atmospheric pressure. 
     In starting drive of the bellows pump  1 , the power switch  8  is turned on by an operator, and then the stop switch  10  is turned by the operator to move the first bellows  13  and the second bellows  14  until the standby state. Specifically, the drive control section  6   e  magnetizes the solenoid  4   a  of the first switching valve  4  and the solenoid  5   a  of the second switching valve  5  to cause the first bellows  13  and the second bellows  14  to simultaneously contract until the most contracted state. Accordingly, the first bellows  13  and the second bellows  14  are maintained in the standby state. In the standby state, the proximity sensors  29 A and  31 A are in ON states of detecting the detection plates  30  and  32 , respectively. 
     Next, when the start switch  9  is turned on by the operator, the drive control section  6   e  initially executes control for calculating the first expansion time and the first contraction time of the first bellows  13  and the second expansion time and the second contraction time of the second bellows  14 . 
     Specifically, the drive control section  6   e  demagnetizes the solenoid  4   a  of the first switching valve  4  and also magnetizes the solenoid  4   b  to cause the first bellows  13  to expand from the most contracted state (standby state) to the most expanded state. At the same time with this, the drive control section  6   e  demagnetizes the solenoid  5   a  of the second switching valve  5  and also magnetizes the solenoid  5   b  to also cause the second bellows  14  to expand from the most contracted state (standby state) to the most expanded state. 
     When the first bellows  13  expands from the most contracted state to the most expanded state, the first calculation section  6   a  counts a time from a time point (t 1 ) at which the proximity sensor  29 A becomes OFF to a time point (t 2 ) at which the proximity sensor  29 B becomes ON, to calculate the first expansion time (t 2 −t 1 ) of the first bellows  13 . 
     Similarly, when the second bellows  14  expands from the most contracted state to the most expanded state, the second calculation section  6   b  counts a time from a time point (t 1 ) at which the proximity sensor  31 A becomes OFF to a time point (t 2 ) at which the proximity sensor  31 B becomes ON, to calculate the second expansion time (t 2 −t 1 ) of the second bellows  14 . 
     Next, after a predetermined time (t 3 −t 2 ) elapses, the drive control section  6   e  demagnetizes the solenoid  4   b  of the first switching valve  4  and also magnetizes the solenoid  4   a  to cause only the first bellows  13  to contract from the most expanded state to the most contracted state. 
     At this time, the first calculation section  6   a  counts a time from a time point (t 3 ) at which the proximity sensor  29 B becomes OFF to a time point (t 4 ) at which the proximity sensor  29 A becomes ON, to calculate the first contraction time (t 4 −t 3 ) of the first bellows  13 . 
     Then, at the first determination section  6   c , the first time difference is determined on the bases of the calculated first expansion time and first contraction time. In the present embodiment, the first determination section  6   c  calculates the first time difference by using the following equation (3).
 
First time difference=(first expansion time+first contraction time)/2=(( t 2− t 1)+( t 4− t 3))/2  (3)
 
     Next, at the same time as a time point (t 4 ) at which the first bellows  13  contracts to the most contracted state, the drive control section  6   e  demagnetizes the solenoid  5   b  of the second switching valve  5  and also magnetizes the solenoid  5   a  to cause the second bellows  14  to contract from the most expanded state to the most contracted state. 
     At this time, the second calculation section  6   b  counts a time from a time point (t 4 ) at which the proximity sensor  31 B becomes OFF to a time point (t 6 ) at which the proximity sensor  31 A becomes ON, to calculate the second contraction time (t 6 −t 4 ) of the second bellows  14 . 
     Then, at the second determination section  6   d , the second time difference is determined on the basis of the calculated second expansion time and second contraction time. In the present embodiment, the second determination section  6   d  calculates the second time difference by using the following equation (4). 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           
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                                         expansion 
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                                         time 
                                       
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     Thereafter, each time the first bellows  13  performs a one-round-trip operation, the first expansion time and the first contraction time are calculated by the first calculation section  6   a , and the first time difference is determined on the basis of the calculated first expansion time and the first contraction time by the first determination section  6   c , as described above. 
     Similarly, each time the second bellows  14  performs a one-round-trip operation, the second expansion time and the second contraction time are calculated by the second calculation section  6   b , and the second time difference is determined on the basis of the calculated second expansion time and second contraction time by the second determination section  6   d , as described above. 
     Meanwhile, the drive control section  6   e  starts drive of the first bellows  13  before the second bellows  14  comes into the most contracted state. Specifically, at a time point (t 5 ) before the second bellows  14  comes into the most contracted state, the drive control section  6   e  demagnetizes the solenoid  4   a  of the first switching valve  4  and also magnetizes the solenoid  4   b . Accordingly, the first bellows  13  starts expansion operation from the most contracted state. 
     After a predetermined time (t 6 −t 5 ) from the time point at which the first bellows  13  starts expansion operation, the second bellows  14  comes into the most contracted state, and the proximity sensor  31 A is switched from OFF to ON, but the drive control section  6   e  continues to maintain the second bellows  14  in the most contracted state for a while. 
     Thereafter, when the proximity sensor  29 B is switched from OFF to ON at a time point (t 7 ) at which the first bellows  13  comes into the most expanded state, the drive control section  6   e  demagnetizes the solenoid  4   b  of the first switching valve  4  and also magnetizes the solenoid  4   a  after a predetermined time (t 8 −t 7 ) elapses. Accordingly, the first bellows  13  starts contraction operation from the most expanded state. 
     In addition, from a time point (t 8 ) at which the solenoid  4   a  is magnetized, the drive control section  6   e  start counting the first time difference determined above. 
     Then, when a predetermined time (t 9 −t 8 ) elapses from the time point at which the first bellows  13  starts contraction operation, the drive control section  6   e  demagnetizes the solenoid  5   a  of the second switching valve  5  and also magnetizes the solenoid  5   b . Accordingly, while the first bellows  13  performs contraction operation, the second bellows  14  expands from the most contracted state to the most expanded state. 
     At this time, at a time point (t 10 ) at which the second bellows  14  comes into the most expanded state, the proximity sensor  31 B is switched from OFF to ON, but the drive control section  6   e  continues to maintain the second bellows  14  in the most expanded state. 
     Next, when the first time difference (t 11 −t 8 ) elapses, the drive control section  6   e  demagnetizes the solenoid  5   b  of the second switching valve  5  and also magnetizes the solenoid  5   a . Accordingly, before the first bellows  13  comes into the most contracted state, the second bellows  14  starts contraction operation from the most expanded state (see  FIG. 8 ). 
     In addition, at a time point (t 11 ) at which the solenoid  5   a  is magnetized, the drive control section  6   e  starts counting the second time difference determined above. 
     After the second bellows  14  starts contraction operation, when the proximity sensor  29 A is switched from OFF to ON at a time point (t 12 ) at which the first bellows  13  comes into the most contracted state, the drive control section  6   e  demagnetizes the solenoid  4   a  of the first switching valve  4  and also magnetizes the solenoid  4   b . Accordingly, while the second bellows  14  performs contraction operation, the first bellows  13  expands from the most contracted state to the most expanded state. 
     At this time, at a time point (t 13 ) at which the first bellows  13  comes into the most expanded state, the proximity sensor  29 B is switched from OFF to ON, but the drive control section  6   e  continues to maintain the first bellows  13  in the most expanded state. 
     Next, when the second time difference (t 14 −t 11 ) elapses, the drive control section  6   e  demagnetizes the solenoid  4   b  of the first switching valve  4  and also magnetizes the solenoid  4   a . Accordingly, before the second bellows  14  comes into the most contracted state, the first bellows  13  starts contraction operation from the most expanded state (see  FIG. 7 ). 
     In addition, from a time point (t 14 ) at which the solenoid  4   a  is magnetized, the drive control section  6   e  starts counting the first time difference determined immediately before. The first time difference determined immediately before is a time difference determined on the basis of the first expansion time (t 7 −t 5 ) and the first contraction time (t 12 −t 8 ) calculated as a result of an immediately-previous one-round-trip operation of the first bellows  13 . 
     After the first bellows  13  starts contraction operation, when the proximity sensor  31 A is switched from OFF to ON at a time point (T 15 ) at which the second bellows  14  comes into the most contracted state, the drive control section  6   e  demagnetizes the solenoid  5   a  of the second switching valve  5  and also magnetizes the solenoid  5   b . Accordingly, while the first bellows  13  performs contraction operation, the second bellows  14  expands from the most contracted state to the most expanded state. 
     At this time, at a time point (t 16 ) at which the second bellows  14  comes into the most expanded state, the proximity sensor  31 B is switched from OFF to ON, but the drive control section  6   e  continues to maintain the second bellows  14  in the most expanded state. 
     Next, when the above first time difference (t 17 −t 14 ) determined immediately before elapses, the drive control section  6   e  demagnetizes the solenoid  5   b  of the second switching valve  5  and also magnetizes the solenoid  5   a . Accordingly, before the first bellows  13  comes into the most contracted state, the second bellows  14  starts contraction operation from the most expanded state. 
     In addition, from a time point (t 17 ) at which the solenoid  5   a  is magnetized, the drive control section  6   e  starts counting the second time difference determined immediately before. The second time difference determined immediately before is a time difference determined on the basis of the second expansion time (t 10 −t 9 ) and the second contraction time (t 15 −t 11 ) calculated as a result of an immediately-previous one-round-trip operation of the second bellows  14 . 
     After the second bellows  14  starts contraction operation, when the proximity sensor  29 A is switched from OFF to ON at a time point (t 18 ) at which the first bellows  13  comes into the most contracted state, the drive control section  6   e  demagnetizes the solenoid  4   a  of the first switching valve  4  and also magnetizes the solenoid  4   b . Accordingly, while the second bellows  14  performs contraction operation, the first bellows  13  expands from the most contracted state to the most expanded state. 
     At this time, at a time point (t 19 ) at which the first bellows  13  comes into the most expanded state, the proximity sensor  29 B is switched from OFF to ON, but the drive control section  6   e  continues to maintain the first bellows  13  in the most expanded state. 
     Next, when the above second time difference (t 20 −t 17 ) determined immediately before elapses, the drive control section  6   e  demagnetizes the solenoid  4   b  of the first switching valve  4  and also magnetizes the solenoid  4   a . Accordingly, before the second bellows  14  comes into the most contracted state, the first bellows  13  starts contraction operation from the most expanded state. 
     Thereafter, the drive control section  6   e  controls drive of the bellows pump  1  such that, as described above, on the basis of the first and second time differences determined immediately before, the first bellows  13  is caused to contract from the most expanded state before the second bellows  14  comes into the most contracted state, and the second bellows  14  is caused to contract from the most expanded state before the first bellows  13  comes into the most contracted state. 
     Therefore, even when the first and second contraction time (discharge times) and the first and second expansion times (suction times) vary due to a discharge load of the transport fluid or the like, drive of the bellows pump  1  can be controlled at optimum timing so as to follow the variation. 
     In the present embodiment, although the first and second time differences determined immediately before are used, drive of the bellows pump  1  may be controlled by using the first and second time differences initially determined immediately after start of operation, when there is no variation in the above discharge times and suction times. In this case, switching between the expansion operation and the contraction operation of the first and second bellows  13  and  14  may be performed every predetermined time by using a timer or the like, not by using the proximity sensors  29 A,  29 B,  31 A, and  31 B. 
     In stopping drive of the bellows pump  1 , first, the stop switch  10  is turned on by the operator. The drive control section  6   e  that has received this operation signal moves the first bellows  13  and the second bellows  14  into the standby state. At this time, when either one of the first bellows  13  and the second bellows  14  is performing expansion operation, the drive control section  6   e  stops the expansion operation and immediately causes the either one of the first bellows  13  and the second bellows  14  to start contraction operation. Then, when the first bellows  13  and the second bellows  14  come into the standby state, the power switch  8  is turned off by the operator. 
     Before one bellows  13  ( 14 ) comes into the most contracted state, the control unit  6  of the present embodiment causes the other bellows  14  ( 13 ) to contract from the most expanded state. However, the control unit  6  may perform control such that, when the one bellows  13  ( 14 ) comes into the most contracted state, the other bellows  14  ( 13 ) is caused to contract from the most expanded state. From the standpoint of reducing pulsation at the discharge side of the bellows pump  1 , control is preferably performed as in the present embodiment. 
     &lt;Configurations of Electropneumatic Regulators&gt; 
     In  FIGS. 1 and 2 , the first electropneumatic regulator  51  is disposed between the mechanical regulator  3  and the first switching valve  4 . In addition, the second electropneumatic regulator  52  is disposed between the mechanical regulator  3  and the second switching valve  5 . Each of the electropneumatic regulators  51  and  52  has a function to steplessly adjust the air pressure outputted from an output port (not shown), on the basis of a set pressure that is externally preset. 
     During contraction of the first bellows  13 , the first electropneumatic regulator  51  of the present embodiment adjusts the air pressure of the pressurized air to be supplied to the discharge-side air chamber  21  of the first air cylinder portion  27 , such that the air pressure is increased so as to correspond to the contraction characteristic of the first bellows  13 . 
     In addition, during contraction operation of the second bellows  14 , the second electropneumatic regulator  52  adjusts the air pressure of the pressurized air to be supplied to the discharge-side air chamber  21  of the second air cylinder portion  28 , such that the air pressure is increased so as to correspond to the contraction characteristic of the second bellows  14 . 
     &lt;Control of Electropneumatic Regulators&gt; 
       FIG. 9  is a graph showing an example of adjustment of the air pressure by the first and second electropneumatic regulators  51  and  52 . In  FIG. 9 , during an expansion time T 1  when the first bellows  13  is expanding (during expansion operation), the first electropneumatic regulator  51  adjusts the air pressure of the pressurized air such that the air pressure is always a constant air pressure c. The air pressure c is instructed from the control unit  6 . Then, during a contraction time T 2  when the first bellows  13  is contracting (during contraction operation), the first electropneumatic regulator  51  adjusts the air pressure of the pressurized air in accordance with an instruction from the control unit  6  such that the air pressure is an air pressure calculated by the control unit  6  every unit time (e.g., 10 ms) using the following equation (5).
 
 P=aX+b   (5)
 
     P denotes the air pressure of the pressurized air outputted from the output port, a denotes a pressure increase coefficient, X denotes an expansion/contraction position of the first bellows  13 , and b denotes the initial air pressure. In the present embodiment, the pressure increase coefficient a indicates the contraction characteristic of the first bellows  13 , and the initial air pressure b is set at a value higher than the air pressure c. In addition, for example, where the most expanded state of the first bellows  13  is X 0  (=0 mm) as shown in  FIG. 3  and the most contracted state of the first bellows  13  is X max  as shown in  FIG. 4 , the expansion/contraction position X is set as a displacement from X 0 . 
     Similarly, during an expansion time T 3  when the second bellows  14  is expanding (during expansion operation), the second electropneumatic regulator  52  adjusts the air pressure of the pressurized air such that the air pressure is always a constant air pressure c. The air pressure c is instructed from the control unit  6 . Then, during a contraction time T 4  when the second bellows  14  is contracting (during contraction operation), the second electropneumatic regulator  52  adjusts the air pressure of the pressurized air in accordance with an instruction from the control unit  6  such that the air pressure is an air pressure calculated by the control unit  6  every unit time (e.g., 10 ms) using the above equation (5). In this case, X denotes an expansion/contraction position of the second bellows  14 , and the pressure increase coefficient a indicates the contraction characteristic of the second bellows  14 . 
     By using the expansion/contraction position of the bellows  13  ( 14 ) as X in the above equation (5) as described above, for example, even when the discharged fluid resistance increases so that the discharge time increases, the value of the pressure increase coefficient a in a look-up table in a second embodiment described later can be used as a fixed value. 
     In addition, the present expansion/contraction position of the bellows  13  ( 14 ) can be calculated, for example, on the basis of a time difference taken from the most expanded state of the bellows  13  ( 14 ) to the most contracted state of the bellows  13  ( 14 ) and obtained through position measurement in advance. As a matter of course, the present expansion/contraction position of the bellows  13  ( 14 ) also can be detected by a displacement sensor or the like. 
     In the present embodiment, each of the pressure increase coefficient a and the initial air pressures b and c that are used when the air pressure into which adjustment is made by each of the electropneumatic regulators  51  and  52  is calculated in the control unit  6  is set at the same value, but may be set at values different between the respective electropneumatic regulators. 
       FIG. 10  is a graph showing the discharge pressure of the transport fluid discharged from the bellows pump  1 . As shown in  FIG. 10 , by the first and second electropneumatic regulators  51  and  52  adjusting the air pressure of the pressurized air as described above, fall of the discharge pressure of the transport fluid discharged from the bellows pump  1  can be reduced while each of the bellows  13  and  14  is contracting alone (at portions surrounded by dotted lines in the drawing). 
     Furthermore, by the drive control section  6   e  controlling drive of the bellows pump  1  on the basis of the first and second time differences as described above, at timing of switching from contraction of one bellows (discharge) to expansion thereof (suction) (at portions surrounded by solid lines in the drawing), the other bellows has already contracted to discharge the transport fluid. Thus, great fall of the discharge pressure at the timing of switching can be reduced. 
     Therefore, by combining the control by the first and second electropneumatic regulators  51  and  52  and the control by the drive control section  6   e , pulsation at the discharge side of the bellows pump  1  can be effectively reduced. 
     As described above, according to the bellows pump device BP of the present embodiment, during contraction operation of the bellows  13  ( 14 ), the air pressure of the pressurized air supplied to the discharge-side air chamber  21  is increased by the electropneumatic regulator  51  ( 52 ) so as to correspond to the contraction characteristic of the bellows  13  ( 14 ), so that the air pressure of the pressurized air in the discharge-side air chamber  21  can be increased as the bellows  13  ( 14 ) contracts. Accordingly, fall of the discharge pressure of the transport fluid during contraction of the bellows  13  ( 14 ) can be reduced. 
     In addition, since the electropneumatic regulator  51  ( 52 ) adjusts the air pressure every unit time by using the aforementioned equation (5), fall of the discharge pressure of the transport fluid during contraction of the bellows  13  ( 14 ) can be effectively reduced. 
     In addition, the first bellows  13  and the second bellows  14  are made expandable/contractible independently of each other, and the control unit  6  is configured to perform drive control such that the second bellows  14  is caused to contract from the most expanded state before the first bellows  13  comes into the most contracted state, and the first bellows  13  is caused to contract from the most expanded state before the second bellows  14  comes into the most contracted state. Thus, the following advantageous effects are achieved. Specifically, at timing of switching from contraction of one bellows (discharge) to expansion thereof (suction), the other bellows has already contracted to discharge the transport fluid. Thus, great fall of the discharge pressure at the timing of switching can be reduced. As a result, pulsation at the discharge side of the bellows pump  1  can be reduced. 
     In addition, the bellows pump device BP of the present embodiment does not need to ensure a space for installing another member (accumulator) other than the bellows pump, as compared to a bellows pump device having an accumulator mounted at the discharge side of a bellows pump. Thus, a substantial increase in an installation space can be suppressed. Furthermore, since the bellows pump device BP of the present embodiment discharges the transport fluid by using a pair of the bellows  13  and  14  similarly to a conventional bellows pump having a pair of bellows connected to each other by a tie rod, the amount of the fluid discharged does not decrease. 
     The control unit  6  is able to perform drive control so as to use the first time difference determined on the basis of the first expansion time and the first contraction time of the first bellows  13 , to cause the second bellows  14  in the most expanded state to contract before the first bellows  13  comes into the most contracted state, and also so as to use the second time difference determined on the basis of the second expansion time and the second contraction time of the second bellows  14 , to cause the first bellows  13  in the most expanded state to contract before the second bellows  14  comes into the most contracted state. Accordingly, the second bellows can be assuredly caused to contract before the first bellows comes into the most contracted state, and also the first bellows can be assuredly caused to contract before the second bellows comes into the most contracted state. 
     Immediately after start of operation of the bellows pump  1 , the control unit  6  calculates the expansion times and the contraction times of the first and second bellows  13  and  14  beforehand, and performs drive control. Thus, even when these expansion times and these contraction times are not known before start of operation, the second bellows  14  (first bellows  13 ) can be assuredly caused to contract before the first bellows  13  (second bellows  14 ) comes into the most contracted state. 
     The control unit  6  performs drive control on the basis of the first and second time differences determined immediately before. Thus, even when the first expansion time and the first contraction time of the first bellows  13  (the second expansion time and the second contraction time of the second bellows  14 ) vary, the second bellows  14  (first bellows  13 ) can be assuredly caused to contract so as to follow the variation, before the first bellows  13  (second bellows  14 ) comes into the most contracted state. 
     &lt;Modification&gt; 
       FIG. 11  is a schematic configuration diagram showing a modification of the bellows pump device according to the above embodiment. In the bellows pump device BP according to the present modification, similarly as in the conventional art, a pair of right and left bellows are integrally connected to each other by a tie rod, which is not shown, and only the discharge-side air chamber  21  and the suction/exhaust port  22  are formed in each of the air cylinder portions  27  and  28 . 
     Accordingly, when the pressurized air is supplied to one discharge-side air chamber  21 , the corresponding bellows contracts, so that the transport fluid is discharged. At the same time, the other bellows forcedly expands, so that the transport fluid is sucked from the suction passage. In addition, when the pressurized air is supplied to the other discharge-side air chamber  21 , the other bellows contracts, so that the transport fluid is discharged. At the same time, the one bellows forcedly expands, so that the transport fluid is sucked. 
     Each suction/exhaust port  22  is connected to the air supply device  2  via a single switching valve  54 , a single electropneumatic regulator  53 , and the mechanical regulator  3 . 
     The switching valve  54  switches between supply and discharge of the pressurized air by magnetizing or demagnetizing a pair of solenoids that are not shown, such that the pressurized air is supplied to one of the discharge-side air chambers  21  of both air cylinder portions  27  and  28  and the pressurized air is discharged from the other of the discharge-side air chambers  21 . 
     During contraction operation of each bellows, the electropneumatic regulator  53  adjusts the air pressure of the pressurized air to be supplied to the corresponding discharge-side air chamber  21 , such that the air pressure is increased so as to correspond to the contraction characteristic of the bellows that contracts. The details thereof are the same as in the above embodiment, and thus the description thereof is omitted. 
     [Second Embodiment] 
     &lt;Entire Configuration of System&gt; 
       FIG. 12  is a schematic diagram showing the configuration of a fluid feeding system including a bellows pump device according to the second embodiment of the present invention. The fluid feeding system feeds a transport fluid such as a chemical solution, a solvent, or the like in a certain amount, for example, in a semiconductor production apparatus. The fluid feeding system includes: a tank  70  for storing the transport fluid; a circulation passage  71  through which the transport fluid stored in the tank  70  is fed to the outside and returned to the tank  70 ; a plurality of supply passages  72  that branch from a middle portion of the circulation passage  71  and through which the transport fluid is supplied to a wafer that is not shown; and a bellows pump device BP that feeds the transport fluid from the tank  70 . 
     On the circulation passage  71 , a filter  73  is provided at the downstream side of the bellows pump device BP. In addition, on the circulation passage  71 , an opening/closing valve  74  for opening/closing the circulation passage  71  is provided at the downstream side with respect to branch points with the supply passages  72 . 
     Each supply passage  72  is provided with a plurality of nozzles  75  for spraying the transport fluid. 
     The fluid feeding system further includes a temperature sensor  76  for detecting the temperature of the transport fluid within the tank  70  and a plurality of (two in the illustrated example) heaters  77  disposed at the middle portion of the circulation passage  71 . 
     The heaters  77  heat the transport fluid within the circulation passage  71  on the basis of the temperature of the transport fluid detected by the temperature sensor  76 . Accordingly, the temperature of the transport fluid sprayed from the nozzles  75  via the supply passages  72  from the circulation passage  71  can be maintained at an appropriate temperature. 
     The temperature sensor  76  is provided at the tank  70 , but may be provided at the middle portion of the circulation passage  71  or at a middle portion of each supply passage  72 . 
     &lt;Control of Electropneumatic Regulators&gt; 
       FIG. 13  is a schematic configuration diagram of the bellows pump device BP of the second embodiment. 
     In  FIG. 13 , the control unit  6  of the present embodiment controls the respective electropneumatic regulators  51  and  52  on the basis of the temperature of the transport fluid detected by a temperature detection unit  7 . In the present embodiment, the above temperature sensor  76  (see  FIG. 12 ) for adjusting the temperature of the transport fluid within the circulation passage  71  is used as the temperature detection unit  7 . Therefore, the control unit  6  of the present embodiment controls the respective electropneumatic regulators  51  and  52  on the basis of a detection value of the temperature sensor  76 . 
     In the present embodiment, the temperature sensor  76  for adjusting the temperature of the transport fluid within the circulation passage  71  is used as the temperature detection unit  7  for controlling the electropneumatic regulators  51  and  52 , but a temperature sensor dedicated for detecting the temperature of the transport fluid may be provided to the bellows pump  1 . 
     The control unit  6  of the present embodiment controls the respective electropneumatic regulators  51  and  52  such that, as the detection value of the temperature sensor  76  decreases, the pressure increase coefficient a used in increasing the air pressure of the pressurized air increases. Specifically, the control unit  6  has a look-up table in which the pressure increase coefficient a is set so as to correspond to each of a plurality of temperature ranges, and instructs an air pressure into which adjustment is made by each of the electropneumatic regulators  51  and  52 , with respect to each of the electropneumatic regulators  51  and  52  on the basis of the look-up table. 
       FIG. 14  is an example of a look-up table  6   f  of the control unit  6 . The look-up table  6   f  of the present embodiment indicates pressure increase coefficients a 1 , a 2 , and a 3  corresponding to three temperature ranges, that is, a low temperature range (10 to 20° C.), an intermediate temperature range (20 to 60° C.), and a high temperature range (60 to 80° C.), respectively. Each of the pressure increase coefficients a 1  to a 3  is a coefficient determined experimentally, and is set so as to meet a relationship of a 1 &gt;a 2 &gt;a 3 . 
     The control unit  6  of the present embodiment controls the respective electropneumatic regulators  51  and  52  by using the look-up table method, but may calculate a pressure increase coefficient by using a calculation formula from the detection value of the temperature sensor  76  or the like. In addition, four or more temperature ranges may be set. 
       FIG. 15  is a graph showing change of the air pressure at the electropneumatic regulator  51  ( 52 ) controlled by the control unit  6 , corresponding to each of the plurality of temperature ranges. As shown in  FIG. 15 , start air pressures Ps 1 , Ps 2 , and Ps 3  at a time point of start of contraction of the bellows  13  ( 14 ), corresponding to the low temperature range, the intermediate temperature range, and the high temperature range, respectively, are set at an initial air pressure b that is the same value. 
     Then, regarding the air pressures corresponding to the respective temperature ranges, as the bellows  13  ( 14 ) contracts, the pressure differences therebetween increase due to the differences between the pressure increase coefficients a 1  to a 3  (the gradients of increase straight lines), and the air pressure has a higher value as the temperature range is lower. 
     The start air pressures Ps 1  to Ps 3  corresponding to the respective temperature ranges may be set at values different from each other, for example, a higher value is set as the temperature range is lower. 
       FIG. 16  is a graph showing a relationship between the temperature of the transport fluid and an allowable withstand pressure of the bellows  13  ( 14 ). The “allowable withstand pressure” of the bellows  13  ( 14 ) is a pressure difference between the pressure at the outer side of the bellows  13  ( 14 ) (in the discharge-side air chamber  21 ) and the pressure at the inner side of the bellows  13  ( 14 ), and is a maximum pressure difference with which the bellows  13  ( 14 ) is not deformed/broken. 
     As shown in  FIG. 16 , the allowable withstand pressure of the bellows  13  ( 14 ) is found to decrease as the temperature of the transport fluid increases. Thus, for protecting the bellows  13  ( 14 ), the start air pressures Ps 1  to Ps 3  (the initial air pressure b in the present embodiment) or the pressure increase coefficients a 1  to a 3  of the air pressure in the look-up table  6   f  (see  FIG. 14 ) are set such that the maximum value of the air pressure (a gauge pressure not including the atmospheric pressure) corresponding to each temperature range does not exceed the allowable withstand pressure of the bellows  13  ( 14 ). 
     That is, as shown in  FIG. 15 , the start air pressures Ps 1  to Ps 3  or the pressure increase coefficients a 1  to a 3  are set such that end air pressures Pe 1 , Pe 2 , and Pe 3  at a time point of end of contraction of the bellows  13  ( 14 ) that are maximum values of the air pressure corresponding to the low temperature range, the intermediate temperature range, and the high temperature range, respectively, do not exceed the allowable withstand pressures of the bellows  13  ( 14 ) corresponding to the highest temperatures of the respective temperature ranges. 
     For example, in the case of the high temperature range (60 to 80° C.), the start air pressure Ps 3  or the pressure increase coefficient a 3  is set such that the end air pressure Pe 3  does not exceed the allowable withstand pressure (about 0.6 MPa in  FIG. 16 ) of the bellows  13  ( 14 ) corresponding to 80° C. which is the highest temperature of the high temperature range. 
     The electropneumatic regulator  51  ( 52 ) is controlled by the control unit  6  as follows. 
     When the control unit  6  acquires the detection value of the temperature sensor  76 , the control unit  6  refers to the look-up table  6   f  (see  FIG. 14 ) and selects the temperature range in which the detection value is included. 
     For example, when the detection value of the temperature sensor  76  is 15° C., the control unit  6  refers to the look-up table  6   f  and selects the low temperature range (10 to 20° C.) as the temperature range in which the detection value is included. 
     Next, the control unit  6  refers to the look-up table  6   f  and determines the pressure increase coefficient a corresponding to the selected temperature range. For example, when the selected temperature range is the low temperature range, the control unit  6  refers to the look-up table  6   f  and determines the pressure increase coefficient a 1  corresponding to the low temperature range, as the pressure increase coefficient a. 
     Next, the control unit  6  calculates an air pressure from the above equation by using the determined pressure increase coefficient a, and instructs the electropneumatic regulator  51  ( 52 ) to perform adjustment to the calculated air pressure. For example, when the determined pressure increase coefficient a is the pressure increase coefficient a 1  for the low temperature range, the control unit  6  instructs an adjustment air pressure with respect to the electropneumatic regulator  51  ( 52 ) such that a pressure change corresponding to the low temperature range as shown by a solid line in  FIG. 15  is achieved. 
     &lt;Effect Verification by Examples and Comparative Examples&gt; 
     A verification test conducted by the present inventors in order to verify the effects obtained by the bellows pump device BP of the present embodiment, will be described. In the verification test, the effects were verified by comparing and evaluating examples with control of the electropneumatic regulator in the present embodiment and comparative examples with control of the electropneumatic regulator in the conventional art, for change of the discharge pressure of the transport fluid discharged from the bellows pump. 
       FIG. 17  is a graph showing change of the discharge pressure of the transport fluid discharged from the bellows pump through control of the electropneumatic regulator according to Comparative Example 1. 
     Specifically,  FIG. 17  is a graph showing the discharge pressure of the transport fluid discharged from the bellows pump when the electropneumatic regulator is controlled by using the pressure increase coefficient corresponding to the intermediate temperature range in the case where the temperature of the transport fluid is included in the low temperature range, in Comparative Example 1. 
     In Comparative Example 1 shown in  FIG. 17 , as shown by an arrow in the drawing, the discharge pressure of the transport fluid decreases while the bellows contracts. The reason for the decrease of the discharge pressure is thought to be that, even though the bellows becomes hard to be difficult to contract due to the temperature decrease of the transport fluid, the pressurized air having the air pressure corresponding to the intermediate temperature range which is lower than the air pressure corresponding to the low temperature range is supplied to the air chamber during contraction operation of the bellows, so that the air pressure acting on the bellows is insufficient. 
       FIG. 18  is a graph showing change of the discharge pressure of the transport fluid discharged from the bellows pump through control of the electropneumatic regulator according to Example 1. 
     Specifically,  FIG. 18  is a graph showing the discharge pressure of the transport fluid discharged from the bellows pump when the electropneumatic regulator is controlled by using the pressure increase coefficient corresponding to the low temperature range in the case where the temperature of the transport fluid is included in the low temperature range, in Example 1. 
     In Example 1 shown in  FIG. 18 , the discharge pressure of the transport fluid almost does not change while the bellows contracts. Therefore, when Comparative Example 1 in  FIG. 17  and Example 1 in  FIG. 18  are compared to each other, it is found that, in the case where the temperature of the transport fluid is included in the low temperature range, change of the discharge pressure of the transport fluid discharged from the bellows pump can be suppressed more by controlling the electropneumatic regulator using the pressure increase coefficient corresponding to the low temperature range, than using the pressure increase coefficient corresponding to the intermediate temperature range. 
       FIG. 19  is a graph showing change of the discharge pressure of the transport fluid discharged from the bellows pump through control of the electropneumatic regulator according to Comparative Example 2. 
     Specifically,  FIG. 19  is a graph showing the discharge pressure of the transport fluid discharged from the bellows pump when the electropneumatic regulator is controlled by using the pressure increase coefficient corresponding to the intermediate temperature range in the case where the temperature of the transport fluid is included in the high temperature range, in Comparative Example 2. 
     In Comparative Example 2 shown in  FIG. 19 , as shown by an arrow in the drawing, the discharge pressure of the transport fluid increases while the bellows contracts. The reason for the increase of the discharge pressure is thought to be that, even though the bellows becomes flexible to be easy to contract due to the temperature increase of the transport fluid, the pressurized air having the air pressure corresponding to the intermediate temperature range which is higher than the air pressure corresponding to the high temperature range during contraction operation of the bellows, so that an excessive air pressure acts on the bellows. 
       FIG. 20  is a graph showing change of the discharge pressure of the transport fluid discharged from the bellows pump through control of the electropneumatic regulator according to Example 2. 
     Specifically,  FIG. 20  is a graph showing the discharge pressure of the transport fluid discharged from the bellows pump when the electropneumatic regulator is controlled by using the pressure increase coefficient corresponding to the high temperature range in the case where the temperature of the transport fluid is included in the high temperature range, in Example 2. 
     In Example 2 shown in  FIG. 20 , the discharge pressure of the transport fluid almost does not change while the bellows contracts. Therefore, when Comparative Example 2 in  FIG. 19  and Example 2 in  FIG. 20  are compared to each other, it is found that, in the case where the temperature of the transport fluid is included in the high temperature range, change of the discharge pressure of the transport fluid discharged from the bellows pump can be suppressed more by controlling the electropneumatic regulator using the pressure increase coefficient corresponding to the high temperature range, than using the pressure increase coefficient corresponding to the intermediate temperature range. 
       FIG. 21  is a graph showing change of the discharge pressure of the transport fluid discharged from the bellows pump through control of the electropneumatic regulator according to Example 3. 
     Specifically,  FIG. 21  is a graph showing the discharge pressure of the transport fluid discharged from the bellows pump when the electropneumatic regulator is controlled by using the pressure increase coefficient corresponding to the intermediate temperature range in the case where the temperature of the transport fluid is included in the intermediate temperature range, in Example 3. 
     In Example 3 shown in  FIG. 21 , the discharge pressure of the transport fluid almost does not change while the bellows contracts. Therefore, it is found that change of the discharge pressure of the transport fluid discharged from the bellows pump can be suppressed more when the pressure increase coefficient corresponding to the intermediate temperature range is used in the case where the temperature of the transport fluid is included in the intermediate temperature range, than when the pressure increase coefficient corresponding to the intermediate temperature range is used in the case where the temperature of the transport fluid is included in the low temperature range or the high temperature range as in Comparative Example 1 in  FIG. 17  or Comparative Example 2 in  FIG. 19 . 
     As described above, according to the bellows pump device BP of the present embodiment, the control unit  6  controls the electropneumatic regulator  51  ( 52 ) such that the pressure increase coefficient a for the air pressure of the pressurized air to be supplied to the discharge-side air chamber  21  during contraction operation of the bellows  13  ( 14 ) increases as the temperature of the transport fluid detected by the temperature sensor  76  decreases. Accordingly, for example, even when the temperature of the transport fluid decreases so that the bellows  13  ( 14 ) becomes hard, the bellows  13  ( 14 ) can be caused to contract by the air pressure higher than the air pressure prior to the temperature decrease of the transport fluid, since the pressure increase coefficient for the air pressure of the pressurized air to be supplied to the discharge-side air chamber  21  increases. Therefore, even when the hardness of the bellows  13  ( 14 ) changes due to a temperature change of the transport fluid, change of the discharge pressure of the transport fluid during contraction of the bellows  13  ( 14 ) can be suppressed. 
     The start air pressures Ps 1  to Ps 3  or the pressure increase coefficient a for the air pressure of the pressurized air is set on the basis of the detection value of the temperature sensor  76  such that the maximum value of the air pressure does not exceed the allowable withstand pressure of the bellows  13  ( 14 ). Thus, even when the pressure increase coefficient a for the air pressure increases, the maximum value of the air pressure does not exceed the allowable withstand pressure of the bellows  13  ( 14 ). Therefore, the bellows  13  ( 14 ) can be prevented from being deformed or broken due to an increase in the air pressure. 
     Since the control unit  6  has the look-up table  6   f  in which the pressure increase coefficient a is set so as to correspond to each of the plurality of temperature ranges, the control unit  6  can easily control the electropneumatic regulator  51  ( 52 ) on the basis of the look-up table  6   f.    
     The points of which the description is omitted in the second embodiment are the same as in the first embodiment. 
     &lt;OTHERS&gt; 
     The present invention is not limited to the above embodiments, and changes may be made as appropriate within the scope of the present invention described in the claims. For example, other than the above embodiments, the bellows pump  1  is also applicable to other bellows pumps such as a bellows pump having a pair of right and left bellows integrally connected to each other by a tie rod, a bellows pump in which one of a pair of bellows is replaced with an accumulator, or a single-type bellows pump configured with only one bellows of a pair of bellows. 
     The electropneumatic regulators  51  to  53  are disposed at the upstream sides of the switching valves  4 ,  5 , and  54 , but may be disposed at the downstream sides of the switching valves  4 ,  5 , and  54 . However, in this case, impact pressures generated when the switching valves  4 ,  5 , and  54  are switched act at the primary sides of the electropneumatic regulators  51  to  53 . Thus, the electropneumatic regulators  51  to  53  are preferably disposed at the upstream sides of the switching valves  4 ,  5 , and  54 , from the standpoint of preventing breakdown of the electropneumatic regulators  51  to  53 . 
     The first and second detection device  29  and  31  in the above embodiment are composed of proximity sensors, but may be composed of other detection device such as limit switches or the like. In addition, the first and second detection device  29  and  31  detect the most expanded states and the most contracted states of the first and second bellows  13  and  14 , but may detect other expanded/contracted states thereof. Furthermore, the first and second driving devices  27  and  28  in the present embodiment are driven by the pressurized air, but may be driven by another fluid, a motor, or the like. 
     REFERENCE SIGNS LIST 
       6  control unit 
       6   f  look-up table 
       7  temperature detection unit 
       13  first bellows (bellows) 
       14  second bellows (bellows) 
       21  discharge-side air chamber (air chamber) 
       27  first air cylinder portion (first driving device) 
       28  second air cylinder portion (second driving device) 
       29  first detection device 
       31  second detection device 
       51  first electropneumatic regulator (electropneumatic regulator) 
       52  second electropneumatic regulator (electropneumatic regulator) 
       53  electropneumatic regulator