Patent Publication Number: US-2022213887-A1

Title: Pump system, fluid supply device and method for controlling drive of pump system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority to Japanese Patent Application No. 2020-218021 filed on Dec. 25, 2020. The entire contents of the above-listed application is hereby incorporated by reference for all purposes. 
     TECHNICAL FIELD 
     The present disclosure relates to a pump system, a fluid supply device and a method of controlling drive of the pump system. 
     BACKGROUND 
     For example, patent document 1 discloses a water supply device. In the water supply device of the patent document 1, an optimum value of a rotational frequency of a motor pump changes according to pressure applied to water to be supplied. Thus, it is necessary to adjust a voltage supplied to the motor pump so that the rotational frequency of the motor pump is set at the optimum value for each value of the pressure. Further, patent document 2 discloses a pump control device. The pump control device of the patent document 2 predicts a rotational frequency required for providing a predetermined flow rate based on measurement of a pump performance performed in advance and a measurement result of the pump performance in a state that the pump is attached to a pipe or the like. Further, the pump control device of the patent document 2 calculates and outputs a voltage required for allowing the pump to drive with the required rotational frequency. Patent document 3 discloses a pump unit. The pump unit of the patent document 3 includes two pump portions having different volumes. The pump unit of the patent document 3 can provide either one of a high-pressure mode and a high flow rate mode with a small motor by switching the pump portions according to a pressure state. 
     RELATED ART DOCUMENTS 
     Patent Documents 
     JP 2002-031078A 
     JP 2001-342966A 
     JP 2004-011597A 
     SUMMARY 
     Problems to be Solved by the Invention 
     However, the rotational frequency of the motor pump of the patent document 1 changes according to the supplied voltage and a change of the rotational frequency results in an abnormal noise, a fault and the like caused by a resonance phenomenon of the water supply device. Thus, it is necessary to address the abnormal noise, the fault and the like. Thus, the water supply device should have a complicated configuration. The pump control device of the patent document 2 needs to perform a plurality of calculations to calculate and output the required voltage. Thus, the configuration of the pump control device, particularly, the circuit configuration should be complicated. Further, the pump unit of the patent document 3 needs the plurality of pump portions and a mechanism for switching the pump portions. As a result, a size of the pump unit increases and the configuration of the pump unit becomes complicated. 
     The present disclosure has been made in view of the above-described problems of the conventional arts. Accordingly, it is an object of the present disclosure to provide a pump system which has a superior flow characteristic with a simple configuration, a fluid supply device containing the pump system and a method for controlling drive of the pump system. 
     Means for Solving the Problems 
     The above object is achieved by the present disclosures defined in the following (1) to (7). 
     (1) A pump system, comprising: 
     a vibration actuator which can be electromagnetically driven by applying an alternating-current voltage thereto; 
     a sealed chamber connected to a suction port and a discharge port; and 
     a movable wall for changing a volume of the sealed chamber, 
     wherein the movable wall is displaced due to drive of the vibration actuator to supply fluid in the sealed chamber into a target object, and 
     wherein an effective value of the alternating-current voltage is controlled so that an amplitude of the vibration actuator is constant. 
     (2) The pump system according to the above (1), wherein the effective value is controlled by changing an amplitude of the alternating-current voltage. 
     (3) The pump system according to the above (1), wherein the alternating-current voltage is a rectangular wave, and 
     wherein the effective value is controlled by changing at least one of an amplitude and a duty ratio of the alternating-current voltage. 
     (4) The pump system according to any one of the above (1) to (3), wherein the pump system is configured to detect pressure in the target object to control the effective value based on the detected pressure. 
     (5) The pump system according to any one of the above (1) to (4), wherein the vibration actuator has a resonance frequency which changes according to pressure in the target object. 
     (6) A fluid supply device, comprising: 
     the pump system defined by any one of the above (1) to (5). 
     (7) A method for controlling drive of a pump system containing a vibration actuator which can be electromagnetically driven by applying an alternating-current voltage thereto, a sealed chamber connected to a suction port and a discharge port, and a movable wall for changing a volume of the sealed chamber, wherein the movable wall is displaced due to drive of the vibration actuator to supply fluid in the sealed chamber into a target object, the method comprising: 
     controlling an effective value of the alternating-current voltage so that an amplitude of the vibration actuator is constant. 
     Effects of the Invention 
     The pump system of the present disclosure controls the effective value of the alternating-current (AC) voltage so that the amplitude of the vibration actuator is constant. Therefore, it is possible to prevent the amplitude from reducing when the pressure in the target object increases, and thereby it is possible to provide the pump system which has a superior flow characteristic. 
     The fluid supply device of the present disclosure contains the above-described pump system. Therefore, the fluid supply device can also receive the effect of the pump system, and thereby it is possible to provide the fluid supply device which has the superior flow characteristic. 
     The method for controlling the drive of the pump system of the present disclosure contains controlling the effective value of the alternating-current (AC) voltage so that the amplitude of the vibration actuator is constant. Therefore, it is possible to prevent the amplitude from reducing when the pressure in the target object increases, and thereby it is possible to allow the pump system to have the superior flow characteristic. 
    
    
     
       BRIEF DESCRITION OF THE FIGURES 
         FIG. 1  is a perspective view showing an overall configuration of an electronic sphygmomanometer according to a preferred embodiment. 
         FIG. 2  is a cross-sectional view of a pump. 
         FIG. 3  is a cross-sectional view showing a driving principle of the pump shown in  FIG. 2 . 
         FIG. 4  is another cross-sectional view showing the driving principle of the pump shown in  FIG. 2 . 
         FIG. 5  is a schematic diagram showing a spring system of a vibration actuator. 
         FIG. 6  is a graph showing a relationship between a drive frequency and an amplitude. 
         FIG. 7  is a graph showing a relationship between the drive frequency and a flow rate. 
         FIG. 8  is a graph showing a relationship between pressure in a sealed chamber and the amplitude. 
         FIG. 9  is a graph showing a relationship between the pressure in the sealed chamber and the flow rate. 
         FIG. 10  is another graph showing the relationship between the pressure in the sealed chamber and the amplitude. 
         FIG. 11  is another graph showing the relationship between the pressure in the sealed chamber and the flow rate. 
         FIG. 12  is a diagram showing one example of a waveform of an alternating-current (AC) voltage. 
         FIG. 13  is a diagram showing another example of the waveform of the AC voltage. 
         FIG. 14  is a diagram showing yet another example of the waveform of the AC voltage. 
         FIG. 15  is a diagram showing yet another example of the waveform of the AC voltage. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, a pump system, a fluid supply device and a method of controlling drive of the pump system of the present disclosure will be described in detail with reference to a preferred embodiment shown in the accompanying drawings. 
       FIG. 1  is a perspective view showing an overall configuration of an electronic sphygmomanometer according to the preferred embodiment.  FIG. 2  is a cross-sectional view of a pump.  FIG. 3  is a cross-sectional view showing a driving principle of the pump shown in  FIG. 2 .  FIG. 4  is another cross-sectional view showing the driving principle of the pump shown in  FIG. 2 .  FIG. 5  is a schematic diagram showing a spring system of a vibration actuator.  FIG. 6  is a graph showing a relationship between a drive frequency and an amplitude.  FIG. 7  is a graph showing a relationship between the drive frequency and a flow rate.  FIG. 8  is a graph showing a relationship between pressure in a sealed chamber and the amplitude.  FIG. 9  is a graph showing a relationship between the pressure in the sealed chamber and the flow rate.  FIG. 10  is another graph showing the relationship between the pressure in the sealed chamber and the amplitude.  FIG. 11  is another graph showing the relationship between the pressure in the sealed chamber and the flow rate.  FIGS. 12 to 15  are diagrams showing examples of a waveform of an alternating-current (AC) voltage. In the following description, an upper side of the paper on which each of  FIGS. 2 to 4  is illustrated is sometimes referred to as “an upper side” and a lower side of the paper on which each of  FIGS. 2 to 4  is illustrated is sometimes referred to as “a lower side” for convenience of explanation. 
       FIG. 1  shows an electronic sphygmomanometer  1  serving as a fluid supply device. The electronic sphygmomanometer  1  includes a cuff  2 , a main body  3  and a tube  4  for connecting between the cuff  2  and the main body  3  to supply and discharge fluid. The cuff  2  is attached to a measurement target part such as an arm of a user. The cuff  2  has a bladder provided therein. The bladder is inflated when the fluid is supplied from the main body  3  into the bladder to compress the measurement target part. The main body  3  measures pressure in the cuff (target object)  2  to calculate a blood pressure value of the user based on a measurement result. The fluid to be supplied from the main body  3  into the bladder is not particularly limited. Although the fluid may be liquid or gas, it is preferable that the fluid is the gas. For convenience of explanation, the following description will be given with assuming that the fluid is air. 
     When blood pressure is measured according to the general oscillometric method, the following procedure is performed. First, the cuff  2  is wound onto the measurement target part of the user. At the time of measuring the blood pressure, the air is supplied from the main body  3  into the cuff  2  to make the pressure in the cuff  2  (referred to as “cuff pressure”) higher than a maximum blood pressure of the user. After that, the pressure in the cuff  2  is gradually reduced. During this process, the main body  3  detects the pressure in the cuff  2  to obtain a variation of an arterial volume occurring in an artery of the measurement target part as a pulse wave signal. The maximum blood pressure (systolic blood pressure) and a minimum blood pressure (diastolic blood pressure) of the user are calculated based on a change of an amplitude of the pulse wave signal caused by a change of the cuff pressure. More specifically, the maximum blood pressure (systolic blood pressure) and the minimum blood pressure (diastolic blood pressure) of the user are mainly calculated based on a rising edge and a falling edge of the pulse wave signal. However, the blood pressure measurement method is not particularly limited thereto. For example, it is possible to use the Riva-Rocci Korotkoff method commonly used in conjunction with the oscillometric method. 
     As shown in  FIG. 1 , the main body  3  contains a pressure sensor  100  therein. The pressure sensor  100  has a function of detecting the pressure in the cuff  2 . The main body  3  further contains a pump system  10  therein. The pump system  10  includes a pump  5  for supplying the air into the cuff  2  and a control device  6  for calculating (detecting) the pressure in the cuff  2  based on an output signal from the pressure sensor  100  to control drive of the pump  5  based on the calculated pressure in the cuff  2 . 
     As shown in  FIG. 2 , the pump  5  has a housing  7 , a vibration actuator  8  and four pump units  9 . 
     The vibration actuator  8  includes a shaft portion  81 , a movable body  82  supported by the shaft portion  81  so as to be movable with respect to the housing  7  and a pair of coil core portions  85 ,  86  fixed to the housing  7 . 
     The movable body  82  has an elongated shape. The movable body  82  is connected to the housing  7  so that a center portion of the movable body  82  is supported by the shaft portion  81 . Thus, the movable body  82  can perform reciprocating rotation with respect to the housing  7  around the shaft portion  81  like a seesaw. 
     Magnets  83 ,  84  are respectively provided at both end portions of the movable body  82 . The magnets  83 ,  84  are disposed so as to be symmetrical with each other across the shaft portion  81 . The magnets  83 ,  84  respectively have arc-shaped magnetic pole faces  831 ,  841  respectively facing the coil core portions  85 ,  86 . S poles and N poles are alternately arranged on each of the magnetic pole faces  831 ,  841  along its arc direction. Each of the magnets  83 ,  84  is a permanent magnet and composed of an Nd sintered magnet or the like. 
     Pushers  87 ,  88  are provided on the movable body  82  for pushing the pump units  9  when the movable body  82  performs the reciprocating rotation. The pushers  87 ,  88  are disposed so as to be symmetrically with each other across the shaft portion  81 . The pusher  87  is disposed between the shaft portion  81  and the magnet  83  so as to protrude toward both sides in a width direction of the movable body  82  (both sides in the vertical direction in  FIG. 2 ). Further, the pusher  88  is disposed between the shaft portion  81  and the magnet  84  so as to protrude toward both sides in the width direction of the movable body  82  (both sides in the vertical direction in  FIG. 2 ). 
     The coil core portions  85 ,  86  are respectively disposed on both sides of the movable body  82 . The coil core portion  85  faces the magnetic pole face  831  of the magnet  83 . The coil core portion  86  faces the magnetic pole face  841  of the magnet  84 . The coil core portions  85 ,  86  are disposed so as to be symmetrical with each other across the shaft portion  81 . 
     The coil core portion  85  includes a core portion  851  and a coil  859  wound around the core portion  851 . The core portion  851  has a core  852  around which the coil  859  is wound and a pair of core magnetic poles  853 ,  854  respectively extending from both ends of the core  852 . The core magnetic poles  853 ,  854  respectively have magnetic pole faces  853   a,    854   a  facing the magnetic pole face  831  of the magnet  83 . Each of the magnetic pole faces  853   a,    854   a  is curved in an arc shape so as to correspond to a shape of the magnetic pole face  831  of the magnet  83 . The coil  859  is connected to the control device  6 . When an AC (alternating-current) voltage E is applied to the coil  859  from the control device  6 , the core magnetic poles  853 ,  854  are excited. 
     The coil core portion  86  includes a core portion  861  and a coil  869  wound around the core portion  861 . The core portion  861  has a core  862  around which the coil  869  is wound and a pair of core magnetic poles  863 ,  864  respectively extending from both ends of the core  862 . The core magnetic poles  863 ,  864  respectively have magnetic pole faces  863   a,    864   a  facing the magnetic pole face  841  of the magnet  84 . Each of the magnetic pole faces  863   a,    864   a  is curved in an arc shape so as to correspond to a shape of the magnetic pole face  841  of the magnet  84 . The coil  869  is connected to the control device  6 . When the AC voltage E is applied to the coil  869  from the control device  6 , the core magnetic poles  863 ,  864  are excited. 
     The core portions  851 ,  861  are respectively magnetic material which can be respectively excited by supplying the electric power to the coils  859 ,  869 . For example, each of the core portions  851 ,  861  can be formed from electromagnetic stainless steel, sintered material, MIM (metal injection mold) material, a laminated steel sheet, an electrogalvanized steel sheet (SECC) or the like. 
     The four pump units  9  are respectively disposed on an upper left side, an upper right side, a lower left side and a lower right side of the shaft portion  81 . Specifically, two of the pump units  9  are disposed so as to face each other in the vertical direction across the pusher  87 . Further, remaining two of the pump units  9  are disposed so as to face each other in the vertical direction across the pusher  88 . The four pump units  9  have the same configuration as each other. Each of the pump units  9  has a sealed chamber  91  and a movable wall  92 . 
     The sealed chamber  91  is connected to a suction port  98  for sucking the air from the outside into the sealed chamber  91  and a discharge port  99  for discharging the air in the sealed chamber  91  toward the outside. In the present embodiment, two of the sealed chambers  91  located on the upper side of the movable body  82  share one discharge port  99 . Remaining two of the sealed chambers  91  located on the lower side of the movable body  82  share another discharge port  99 . 
     The movable wall  92  constitutes a part of the sealed chamber  91 . The movable wall  92  can be displaced to change a volume in the sealed chamber  91  when the movable wall  92  is pushed by the pusher  87  or  88 . When the volume in the sealed chamber  91  reduces due to displacement of the movable wall  92 , the air in the sealed chamber  91  is discharged from the discharge port  99 . On the other hand, when the volume in the sealed chamber  91  increases due to the displacement of the movable wall  92 , the air flows into the sealed chamber  91  through the suction port  98 . When the above-mentioned reduction and increase of the volume in each of the sealed chambers  91  are repeated, the air is continuously discharged from the discharge ports  99 . The movable walls  92  may be a diaphragm, for example. The movable wall  92  can be formed from elastically deformable material. Each of the movable walls  92  has an insertion portion  921  into which the pusher  87  or  88  should be inserted. Each of the movable walls  92  is connected to the pusher  87  or  88  through the insertion portion  921 . 
     Valves  93  are respectively provided between the sealed chambers  91  and the suction ports  98 . Each of the valves  93  allows the air to be suctioned into each of the sealed chambers  91  through the suction port  98  and prevents the air from being discharged from each of the sealed chambers  91  through the suction port  98 . Further, valves  94  are respectively provided between the sealed chambers  91  and the discharge ports  99 . Each of the valves  94  allows the air to be discharged from each of the sealed chambers  91  through the discharge port  99  and prevents the air from being suctioned into each of the sealed chambers  91  through the discharge port  99 . With this configuration, it is possible to more reliably and more efficiently perform the suction and the discharge of the air. 
     As shown in  FIG. 1 , the control device  6  has a drive control unit  61  for controlling the drive of the vibration actuator  8  and a pressure detection unit  62  for detecting the pressure in the cuff  2  based on the output signal from the pressure sensor  100 . The drive control unit  61  is configured to control the drive of the vibration actuator  8  based on the pressure in the cuff  2  detected by the pressure detection unit  62 . The control device  6  is composed of a computer or the like. The control device  6  has a processor (CPU) for processing information, a memory communicatively connected to the processor and an external interface. In addition, the memory stores various programs which can be executed by the processor and the processor can read and execute the various programs or the like stored in the memory. 
     The configuration of the electronic sphygmomanometer  1  has been described. Next, the drive of the pump  5  will be described. In the following description, the four pump units  9  are distinguished from each other by labeling them as the “pump unit  9 A”, the “pump unit  9 B”, the “pump unit  9 C” and the “pump unit  9 D” for convenience of explanation. 
     When the AC voltage E is applied from the drive control unit  61  to the coils  859 ,  869 , the pump  5  is driven by repeatedly alternating between a first state in which the movable body  82  rotates toward one direction as shown in  FIG. 3  and a second state in which the movable body  82  rotates toward another direction as shown in  FIG. 4 . In the first state shown in  FIG. 3 , the core magnetic poles  853 ,  864  are excited with the N pole and the core magnetic poles  854 ,  863  are excited with the S pole. Conversely, in the second state shown in  FIG. 4 , the core magnetic poles  853 ,  864  are excited with the S pole and the core magnetic poles  854 ,  863  are excited with the N pole. 
     In the first state, torque F 1  directed toward an arrow direction illustrated in  FIG. 3  is generated by magnetic force (attractive force and repulsive force) acting between the magnets  83 ,  84  and the coil core portions  85 ,  86 , and thereby the movable body  82  rotates in the direction of the torque Fl. With this movement, the movable walls  92  of the pump units  9 A,  9 D are respectively pushed by the pushers  87 ,  88 , and thereby the volumes in the sealed chambers  91  of the pump units  9 A,  9 D are reduced. As a result, the air in the sealed chambers  91  of the pump units  9 A,  9 D is discharged from the discharge ports  99 . Further, the discharged air is supplied into the cuff  2  through the tube  4 , and thereby the pressure in the cuff  2  increases. On the other hand, since the volumes in the sealed chambers  91  of the pump units  9 B,  9 C increase, the air flows into the sealed chambers  91  of the pump units  9 B,  9 C through the suction ports  98 . 
     In the second state, torque F 2  directed toward a direction opposite to the direction of the torque Fl is generated by the magnetic force (attractive force and repulsive force) acting between the magnets  83 ,  84  and the coil core portions  85 ,  86 , and thereby the movable body  82  rotates in the direction of the torque F 2 . With this movement, the movable walls  92  of the pump units  9 B,  9 C are respectively pushed by the pushers  87 ,  88 , and thereby the volumes in the sealed chambers  91  of the pump unit  9 B,  9 C are reduced. As a result, the air in the sealed chambers  91  of the pump unit  9 B,  9 C is discharged from the discharge ports  99 . Further, the discharged air is supplied into the cuff  2  through the tube  4 , and thereby the pressure in the cuff  2  increases. On the other hand, since the volumes in the sealed chambers  91  of the pump units  9 A,  9 D increase, the air flows into the sealed chambers  91  of the pump units  9 A,  9 D through the suction ports  98 . 
     As described above, when the pump  5  repeatedly alternates between the first state and the second state, it is possible to repeatedly alternate the state in which the air is discharged from the pump units  9 A,  9 D and the state in which the air is discharged from the pump units  9 B,  9 C. As a result, the air can be continuously discharged from the pump  5 . Therefore, it is possible to efficiently supply the air into the cuff  2  and smoothly increase the pressure in the cuff  2 . 
     The drive of the pump  5  has been explained in the above description. Next, a driving principle of the pump  5  will be explained. The vibration actuator  8  is driven according to a motion equation expressed by the following equation (1) and a circuit equation expressed by the following equation (2). 
     
       
         
           
             
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     J 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       
                         
                           d 
                           2 
                         
                         ⁢ 
                         
                           θ 
                           ⁡ 
                           
                             ( 
                             t 
                             ) 
                           
                         
                       
                       
                         dt 
                         2 
                       
                     
                   
                   = 
                   
                     
                       
                         K 
                         t 
                       
                       ⁢ 
                       
                         i 
                         ⁡ 
                         
                           ( 
                           t 
                           ) 
                         
                       
                     
                     - 
                     
                       
                         K 
                         sp 
                       
                       ⁢ 
                       
                         θ 
                         ⁡ 
                         
                           ( 
                           t 
                           ) 
                         
                       
                     
                     - 
                     
                       D 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         
                           d 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           θ 
                           ⁢ 
                           
                             ( 
                             t 
                             ) 
                           
                         
                         dt 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     J: Inertial moment [Kg*m 2 ] 
     θ(t): Displacement angle [rad] 
     K t : Torque constant [Nm/A] 
     i(t): Current [A] 
     K sp : Spring constant [N/m] 
     D: Damping coefficient [Nm/(rad/s)] 
     
       
         
           
             
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     e 
                     ⁡ 
                     
                       ( 
                       t 
                       ) 
                     
                   
                   = 
                   
                     
                       Ri 
                       ⁡ 
                       
                         ( 
                         t 
                         ) 
                       
                     
                     + 
                     
                       L 
                       ⁢ 
                       
                         
                           di 
                           ⁡ 
                           
                             ( 
                             t 
                             ) 
                           
                         
                         dt 
                       
                     
                     + 
                     
                       
                         K 
                         e 
                       
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         
                           dx 
                           ⁡ 
                           
                             ( 
                             t 
                             ) 
                           
                         
                         dt 
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     e(t): Voltage [V] 
     R: Resistance [Ω] 
     L: Inductance [H] 
     K e : Counter-electromotive force constant [V/(m/s)] 
     As described above, the inertial moment J [Kg*m 2 ], the displacement angle (rotational angle) θ(t) [rad], the torque constant K t [Nm/A], the current i(t) [A], the spring constant K sp [N/m], the damping coefficient D [Nm/(rad/s)] and the like of the movable body  82  can be appropriately set as long as they satisfy the equation (1). Similarly, the voltage e(t) [V], the resistance R [Ω], the inductance L [H] and the counter-electromotive force constant K e [V/(m/s)] can be appropriately set as long as they satisfy the equation (2). 
     Further, a flow rate of the pump  5  is determined by the following equation (3) and pressure of the pump  5  is determined by the following equation (4). 
       [Equation  3 ] 
         Q=Axf* 60   (3)
 
     Q: Flow rate [L/min] 
     A: Piston area [m 2 ] 
     x: Piston displacement [m] 
     f: Drive frequency [Hz] 
     
       
         
           
             
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     4 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   P 
                   = 
                   
                     
                       P 
                       0 
                     
                     ⁡ 
                     
                       ( 
                       
                         
                           
                             V 
                             + 
                             
                               Δ 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               V 
                             
                           
                           
                             V 
                             - 
                             
                               Δ 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               V 
                             
                           
                         
                         - 
                         1 
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     P: Increased pressure [kPa] 
     P 0 : Atmospheric pressure [kPa] 
     V: Sealed chamber volume [m 3 ] 
     ΔV: Changed volume [m 3 ] 
     ΔV=Ax 
     A: Piston area [m 2 ]x: Piston displacement [m] 
     As described above, the flow rate Q [L/min], the piston area A [m 2 ], the piston displacement x [m], the drive frequency f [Hz] and the like of the pump  5  can be appropriately set as long as they satisfy the equation (3). Similarly, the increased pressure P [kPa], the atmospheric pressure P 0  [kPa], the sealed chamber volume V [m 3 ], the changed volume ΔV [m 3 ] and the like can be appropriately set as long as they satisfy the equation (4). 
     Next, a resonance frequency of the vibration actuator  8  will be explained. As shown in  FIG. 5 , the vibration actuator  8  has a spring mass system structure for supporting the movable body  82  by magnetic springs B 1  formed by the magnetic force acting between the coil core portions  85 ,  86  and the magnets  83 ,  84  and air springs (fluid springs) B 2  formed by elastic force of compressed air in the sealed chambers  91 . Thus, the movable body  82  has a resonant frequency f r  expressed by the following equation (5). 
     
       
         
           
             
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     5 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     f 
                     r 
                   
                   = 
                   
                     
                       1 
                       
                         2 
                         ⁢ 
                         π 
                       
                     
                     ⁢ 
                     
                       
                         
                           K 
                           sp 
                         
                         J 
                       
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     f r : Resonance frequency [Hz] 
     K sp : Spring constant [N/m] 
     J: Inertial moment [kg*m 2 ] 
     Further, the spring constant K sp  can be expressed by a sum of a spring constant KACT of the vibration actuator  8  itself, which contains the effects of the magnetic springs B 1  and elastic force B 3  of the movable walls  92 , and a spring constant K Air  of the air springs B 2  as expressed by the following equation (6). 
       [Equation 6] 
         K   sp   =K   ACT   +K   Air    (6)
 
     K ACT : Spring constant of vibration actuator itself 
     K Air : Spring constant of air spring 
     In the vibration actuator  8 , the spring constant K Air  of each air spring B 2  changes according to the pressure in each sealed chamber  91  (the pressure in the cuff  2 ) and thus the resonant frequency f r  of the movable body  82  changes according to the change of the spring constant K Air  as is clear from the above equations (5) and (6). 
     Next, description will be given to a change of an amplitude Y of the vibration actuator  8  and a change of the flow rate Q of the air discharged from the pump  5  which are caused by the change of the resonance frequency f r . The following description will be given to a representative example in which the pump  5  can increase the pressure in the cuff  2  up to 50 kPa at the maximum for convenience of explanation. It is noted that the maximum value of the pressure in the cuff  2  is not particularly limited and can be appropriately set so as to meet required conditions. Further, since the cuff  2  is connected to the sealed chambers  91  through the tube  4  as described above, the pressure in the cuff  2  is equal to the pressure in each sealed chamber  91 . Thus, the meaning of the “pressure in the sealed chamber(s)  91 ” and the meaning of the “pressure in the cuff  2 ” are synonymous with each other. 
       FIG. 6  shows a relationship between the drive frequency f and the amplitude Y when the pressure in the cuff  2  falls within the range between 0 kPa to 50 kPa. Further,  FIG. 7  shows a relationship between the drive frequency f and the flow rate Q when the pressure in the cuff  2  falls within the range between 0 kPa to 50 kPa. The drive frequency f is a frequency of the AC voltage E. Further, in  FIGS. 6 and 7 , a voltage value and a waveform of the AC voltage E are constant and only the drive frequency f is changed. In  FIG. 6 , the resonance frequency f r  at each pressure substantially coincides with a value of the drive frequency f at which the amplitude Y becomes the largest. Further, in  FIG. 7 , the resonance frequency f r  at each pressure substantially coincides with a value of the drive frequency f at which the flow rate Q becomes the largest. As is also clear from  FIGS. 6 and 7 , it should be understood that the resonant frequency f r  changes according to the pressure in the cuff  2 . However, it should be noted that the relationships shown in  FIGS. 6 and 7  are merely examples and thus the present disclosure is not necessarily limited to these relationships. 
       FIG. 8  shows a relationship between internal pressure of the sealed chamber  91  and the amplitude Y when the drive frequency f is set to a frequency f n (f=f n ). Further,  FIG. 9  shows a relationship between the internal pressure of the sealed chamber  91  and the flow rate Q of the sealed chamber  91  when the drive frequency f is set to the frequency f n (f=f n ). As is clear from  FIGS. 8 and 9 , the amplitude Y changes according to the pressure in the cuff  2  and the flow rate Q changes according to the change of the amplitude Y which is caused by the change of the pressure in the cuff  2 . Specifically, the amplitude Y reduces as the pressure in the cuff  2  increases and the flow rate Q also reduces together with the reduction of the amplitude Y. This indicates the following two phenomena caused while the resonance frequency f r  is shifted to the higher side due to the increase of the pressure in the cuff  2 . One of the two phenomena is that the amplitude Y increases and the flow rate Q also increases as the drive frequency f approaches the resonance frequency f r . The other one of the two phenomena is that the amplitude Y reduces and the flow rate Q also reduces as the drive frequency f moves away from the resonance frequency f r , on the contrary. 
     When the flow rate Q reduces as the pressure in the cuff  2  increases as described above, the flow rate Q is not stabilized and thus it becomes impossible to supply a sufficient amount of air into the cuff  2  in a high-pressure region. Thus, the pressure in the cuff  2  cannot be smoothly increased. As described above, the method of applying the constant AC voltage E whose effective value is not changed regardless of the pressure in the cuff  2  cannot allow the pump  5  to have a superior flow characteristic. 
     On the other hand, if it is possible to suppress the reduction of the amplitude Y caused when the pressure in the cuff  2  increases and allow the vibration actuator  8  to always vibrates with the amplitude Y which is sufficiently large when the pressure in the cuff  2  falls within the range between 0 kPa and 50 kPa, it becomes possible to suppress the above-mentioned reduction of the flow rate Q and stabilize the flow rate Q. As a result, it becomes possible to supply the sufficient amount of air into the cuff  2  even in the high-pressure region. Therefore, in the present embodiment, the effective value of the AC voltage E is controlled so that the amplitude Y is kept to be sufficiently large when the pressure in the cuff  2  takes any value in the range between 0 kPa to 50 kPa. Hereinafter, description will be given to this control method. 
     First, it is noted that the control method is premised on that the drive frequency f is constant (the drive frequency f does not change) during the drive of the pump  5 . Although the drive frequency f is not particularly limited to a specific value, the drive frequency f can be determined as follows, for example. As described above, the amplitude Y increases and the flow rate Q also increases as the drive frequency f approaches the resonance frequency f r . Further, a drive mode of the pump  5  approaches resonance drive as the drive frequency f approaches the resonance frequency f r . The resonance drive can allow the vibration actuator  8  to perform power saving drive. Thus, it is preferable to set the drive frequency f to a frequency located between a minimum value and a maximum value of the resonance frequency f r  when the pressure in the cuff  2  falls within the range between 0 kPa and 50 kPa. Namely, in the example shown in  FIGS. 6 and 7 , it is preferable to set the drive frequency f to a frequency located between the resonance frequency f r  when the pressure in the cuff  2  is 0 kPa and the resonance frequency f r  when the pressure in the cuff  2  is 50 kPa. By setting the drive frequency f according to the above-mentioned concept, it is possible to suppress a difference between the drive frequency f and the resonance frequency f r  when the pressure in the cuff  2  falls within the range between 0 kPa and 50 kPa to be small, and thereby the above-described effects can be easily obtained. For this reason, the drive frequency f is set to the frequency f n  located within the range between the resonance frequency f r  when the pressure in the cuff  2  is 0 kPa and the resonance frequency f r  when the pressure in the cuff  2  is 50 kPa (f=f n ). 
     The drive control unit  61  stores a target amplitude Y t  which is a target value of the amplitude Y. Although the target amplitude Y t  is not particularly limited to a specific value, it is preferable that the target amplitude Y t  is larger. By setting the target amplitude Y t  as large as possible, a larger flow rate Q can be provided and thus it is possible to improve the flow rate characteristic of the pump  5 . The target amplitude Y t  may be set with keeping a margin for avoiding a risk of failure or the like with respect to a maximum amplitude which can be provided by the vibration actuator  8 . For example, the target amplitude Y t  can be set to fall within the range between about 80% to 95% of the maximum amplitude of the vibration actuator  8 . By setting the target amplitude Y t  according to the above-mentioned concept, it is possible to sufficiently drive the pump  5  with sufficient power while ensuring the life and the long-term reliability of the pump  5 . 
     The drive control unit  61  has (stores) a control program for keeping the amplitude Y at the target amplitude Y t  when the pressure in the cuff  2  falls within the range between 0 kPa and 50 kPa. The control program is not particularly limited to a specific kind. Examples of the control program contain a table in which values of the pressure in the cuff  2  are respectively associated with effective values of the AC voltage E for allowing the amplitude Y to be the target amplitude Y t  when the pressure in the cuff  2  takes at each value, a calculation formula to which a value of the pressure in the cuff  2  is substituted to calculate an effective value of the AC voltage E for allowing the amplitude Y to be the target amplitude Y t  when the pressure in the cuff  2  takes this value, and the like. 
     The drive control unit  61  obtains the effective value of the AC voltage E corresponding to the pressure in the cuff  2  detected by the pressure detection unit  62  from the control program as a “target effective value” to control the AC voltage E so that the effective value of the AC voltage E coincides with the obtained target effective value. The control method is not particularly limited to a specific kind. For example, it is possible to use a feedback control method as the control method. In this feedback control method, the AC voltage E is controlled so that an actual effective value of the AC voltage E approaches the target effective value, for instance, the actual effective value of the AC voltage E coincides with the target effective value with comparing the actual effective value of the AC voltage E with the target effective value. 
     According to the above-described control method, it is possible to keep the amplitude Y at the target amplitude Y t  when the pressure in the cuff  2  falls within the range between 0 kPa and 50 kPa as shown in  FIG. 10 . Namely, it is possible to keep the amplitude Y constant. As a result, it is possible to suppress the reduction of the amplitude Y described with reference to  FIG. 8  when the pressure in the cuff  2  increases. Further, since the reduction of the amplitude Y is suppressed, the degree of the reduction of the flow rate Q when the pressure in the cuff  2  increases becomes smaller than that in the case shown in  FIG. 9  as shown in  FIG. 11 . Therefore, the pump system  10  can have the superior flow rate characteristic as compared with the case where the AC voltage E is kept constant. In this regard, the language of “the amplitude Y is constant” means not only a state that the amplitude Y is always kept at the target amplitude Y t  but also a state that the amplitude Y fluctuates in the vicinity of the target amplitude Y t  due to a device configuration, a circuit configuration or the like. 
     Further, according to the pump system  10 , it is possible to prevent the control method from being complicated unlike the configuration of the patent document  2  and it is not required to provide a plurality of pump portions having different volumes unlike the configuration of the patent document  3 . Therefore, the pump system  10  can provide the superior flow rate characteristic with the simple configuration. Further, the resonant frequency f r  of the vibration actuator  8  is determined by the inertial moment J and the spring constant K sp  as described above and does not change depending on the effective value of the AC voltage E. Therefore, it becomes unnecessary to address the abnormal noise, the fault and the like caused by the resonance phenomenon of the pump  5  or it becomes easier to address the abnormal noise, the fault and the like as compared with the case of using the motor as disclosed in the patent document  1 , even if necessary. From these points of view, the pump system  10  can provide the superior flow rate characteristic with the simple configuration. 
     In this regard, the waveform of the AC voltage E is not particularly limited to a specific form. For example, the waveform of the AC voltage E may be a sinusoidal wave as shown in  FIG. 12 , a triangular wave as shown in  FIG. 13 , a sawtooth wave as shown in  FIG. 14  or a rectangular wave as shown in  FIG. 15 . Among these waveforms, the waveform of the AC voltage can be the sinusoidal wave as shown in  FIG. 12  because the sinusoidal wave tends not to cause noises or the like. On the other hand, a waveform generation circuit for generating the sinusoidal wave is likely to be more expensive than waveform generation circuits for the other waveforms. Thus, if it is desired to configure the pump system  10  with a low cost, the waveform of the AC voltage E can be the triangular wave, the sawtooth wave or the rectangular wave. 
     When the sinusoidal wave, the triangle wave or the sawtooth wave as shown in  FIGS. 12, 13 and 14  is used as the AC voltage E, it is possible to use a method of changing a maximum voltage value Emax of the AC voltage for controlling the effective value of the AC voltage E. As the maximum voltage value Emax of the AC voltage E becomes larger, the effective value of the AC voltage E also becomes larger. On the contrary, as the maximum voltage value Emax of the AC voltage E becomes smaller, the effective value of the AC voltage E also becomes smaller. 
     On the other hand, when the rectangular wave shown in  FIG. 15  is used as the AC voltage E, it is possible to use the method of changing the maximum voltage value Emax of the AC voltage E or a method of changing a duty ratio (=a/b) of the AC voltage E for controlling the effective value of the AC voltage E. As is the case with using the other waveforms as the AC voltage E, as the maximum voltage value Emax of the AC voltage E becomes larger, the effective value of the AC voltage E also becomes larger. On the contrary, as the maximum voltage value Emax of the AC voltage E becomes smaller, the effective value of the AC voltage E also becomes smaller. Further, as the duty ratio of the AC voltage E becomes larger, the effective value of the AC voltage E also becomes larger. On the contrary, as the duty ratio of the AC voltage E becomes smaller, the effective value of the AC voltage E also becomes smaller. The drive control unit  61  may control both or either one of the maximum voltage value Emax and the duty ratio of the AC voltage E. In a case of using the method of controlling both of the maximum voltage value Emax and the duty ratio of the AC voltage E, it is possible to control the effective value of the AC voltage E more accurately as compared with a case of using the method of controlling either one of the maximum voltage value Emax and the duty ratio of the AC voltage E. In the case of using the method of controlling either one of the maximum voltage value Emax and the duty ratio of the AC voltage E, the control of the pump  5  becomes simpler as compared with the case of using the method of controlling both of the maximum voltage value Emax and the duty ratio of the AC voltage E, and thereby it becomes possible to simplify the circuit configuration and the like. 
     The method for controlling the drive of the pump  5  performed by the drive control unit  61  has been described in the above description. Although the pressure detection unit  62  detects the pressure in the cuff  2  based on the output signal of the pressure sensor  100  and the drive control unit  61  controls the effective value of the AC voltage E based on the detection result of the pressure detection unit  62  in the above-described method for controlling the drive of the pump  5 , the method of controlling the drive of the pump  5  is not particularly limited thereto as long as it can control the pump  5  so that the amplitude Y is constant. 
     For example, the following method can be used. First, an increased amount of the pressure in the cuff  2  per unit time is obtained in advance from an experiment, a simulation or the like based on the volume in the cuff  2  and the flow rate Q provided when the amplitude Y coincides with the target amplitude Y t . Based on the increased amount of the pressure in the cuff  2  per unit time, it is possible to predict a relationship between an elapsed time from a drive start time of the pump  5  and the pressure in the cuff  2  at that elapsed time. Thus, the drive control unit  61  may have (store) a control program containing a table (timing table) in which the elapsed time from the drive start time of the pump  5  is associated with the effective value of the AC voltage E for allowing the amplitude Y to be the target amplitude Y t  at that elapsed time, a calculation formula into which the elapsed time from the drive start time of the pump  5  is substituted for calculating the effective value of the AC voltage E for allowing the amplitude Y to be the target amplitude Y t  at that elapsed time, or the like. Further, the drive of the pump  5  may be controlled based on this control program. According to this method, since it becomes unnecessary to feed back the pressure in the cuff  2 , it is possible to make the circuit configuration simpler. 
     Although the pump system, the fluid supply device and the method for controlling the drive of the pump system of the present disclosure have been described based on the illustrated embodiment, the present disclosure is not limited thereto. The configuration of each part can be replaced with any configuration having a similar function. Further, other optional component(s) may also be added to the present disclosure. 
     In addition, although the pump system and the fluid supply device are applied to the electronic sphygmomanometer  1  in the above-described embodiment, the present invention is not limited thereto. For example, the pump system and the fluid supply device can be applied to any device which requires the supply of fluid. Further, although the pump  5  has the four pump units  9  in the above-described embodiment, the present disclosure is not limited thereto. For example, the present disclosure involves an aspect in which the pump  5  has at least one pump unit  9 . 
     Further, the configuration of the vibration actuator  8  is not particularly limited as long as the configuration of the vibration actuator  8  allows the amplitude Y of the vibration actuator  8  to change according to the pressure in the sealed chamber(s)  91 . For example, although the magnets  83 ,  84  are provided on the movable body  82  and the coil core portions  85 ,  86  are provided on the housing  7  in the above-described embodiment, the present disclosure is not limited thereto. The present disclosure involves an aspect in which the arrangement of the magnets  83 ,  84  and the arrangement of the coil core portions  85 ,  86  are reversed. Namely, the coil core portions  85 ,  86  may be provided on the movable body  82  and the magnets  83 ,  84  may be provided on the housing  7 . Further, the magnets  83 ,  84  may be replaced with electromagnets.