Patent Publication Number: US-11035355-B2

Title: Tube pump system and method for controlling the tube pump system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. § 119 or 365 to Japanese, Application No. 2018-050828, filed Mar. 19, 2018. The entire teachings of the above application are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a tube pump system and a method for controlling the tube pump system. 
     BACKGROUND ART 
     Conventionally, a tube pump has been known where a tube having flexibility is intermittently compressed by a plurality of rollers so as to supply a liquid in the tube under pressure. The tube pump intermittently supplies the liquid under pressure and hence, pulsation (an operation where an increase and a decrease in flow rate is repeated) is generated in the liquid supplied under pressure. 
     As a device that suppresses pulsation generated in a liquid supplied by a pump under pressure, a damper has been known where a gas chamber and a liquid chamber are formed in the inside of the damper, and a pressure balance between the gas chamber and the liquid chamber is kept thus suppressing pulsation of the liquid introduced into the liquid chamber (see Japanese Unexamined Patent Application, Publication No. 2000-205201 (hereinafter referred to as “JP 2000-205201”), for example). 
     SUMMARY 
     Technical Problem 
     With the provision of the damper disclosed in JP 2000-205201 in a path on the downstream side of a tube pump, pulsation of a liquid can be suppressed. 
     However, the damper disclosed in JP 2000-205201 has a structure including the liquid chamber that stores a fixed amount of liquid and hence, the damper has a space where a liquid which does not flow into the liquid chamber is kept (so-called dead volume). Therefore, various bacteria or the like are generated in the liquid stagnating in the space and hence, there is a possibility that the purity of the liquid is not properly maintained. Further, the damper disclosed in JP 2000-205201 has the gas chamber and the liquid chamber so that a relatively complicated structure and a relatively large volume are required. Accordingly, the device is complicated and large-sized as a whole. 
     The inventors have found the following. That is, when a tube of a tube pump which is compressed by a roller returns to the original shape, a phenomenon occurs where a liquid is drawn back toward the tube pump side from a path on the downstream side of the tube pump, and pulsation is generated due to such a phenomenon. With the suppression or elimination of the phenomenon, pulsation of the liquid can be further suppressed. 
     The present disclosure has been made in view of such circumstances, and an object thereof is to provide a tube pump system where pulsation of a liquid can be suppressed or eliminated without making an apparatus complicated and large-sized, and a method for controlling the tube pump system. 
     Solution to Problem 
     To solve the above-described problem, a tube pump according to the present disclosure employs the following solutions. 
     According to one aspect of the present disclosure, there is provided a tube pump system which includes: a housing unit which has an inner peripheral surface formed into a circular-arc shape around an axis line; a tube having flexibility which is arranged along the inner peripheral surface; a pair of roller units which are housed in the housing unit, and are rotated around the axis line from a contact position to a separate position around the axis line in a state where the pair of roller units compress the tube; a pair of drive units which are configured to rotate the pair of roller units respectively around the axis line in a same direction; and a control unit which is configured to control each of the pair of drive units such that a liquid which flows into the tube from one end of the tube is discharged from the other end of the tube, wherein the control unit controls each of the pair of drive units such that, when one of the pair of roller units passes the separate position, an angular velocity of the other of the pair of roller units toward the separate position is gradually decreased. 
     In a case where the other of a pair of roller units is rotated with a fixed angular velocity after one of the pair of roller units passes a separate position, the distance from a position where the other of the pair of rollers compresses a tube to a separate position is gradually decreased. Consequently, pressure of liquid on the upstream side of the separate position increases as the other of the pair of roller units approaches the separate position, and accompanied with this, the flow rate of fluid discharged from the other end of the tube gradually increases. Accordingly, in a tube pump system according to one aspect of the present disclosure, after one of the pair of roller units passes the separate position, an angular velocity of the other of the pair of roller units toward the separate position is gradually decreased. By doing this, pressure increase of liquid on the upstream side due to approach to the separate position of the other of the pair of roller units can be compensated by pressure decrease of liquid due to decrease of an angular velocity of the other of the pair of roller units. As a result, fluctuation of the flow rate of liquid discharged from the other end of the tube can be inhibited or eliminated, which can inhibit or eliminate pulsation of liquid. 
     In the tube pump system according to one aspect of the present disclosure, a pipe having flexibility is connected to the other end of the tube, the pipe maintaining a pressure of the liquid flowing through the inside of the pipe at a first predetermined pressure higher than an atmospheric pressure, and the control unit may be configured to control each of the pair of drive units such that a pressure of the liquid in the tube which is closed due to a contact of the pair of roller units is increased to a second predetermined pressure having a predetermined pressure difference with respect to the first predetermined pressure when one of the pair of roller units passes the separate position. 
     In the tube pump system according to one aspect of the present disclosure, a static pressure of the liquid in the inside of the pipe is higher than the atmospheric pressure and hence, when the static pressure of the liquid in the pipe is further increased by pulsation of the liquid, the pipe is elastically deformed whereby pulsation of the liquid can be suppressed. 
     Also, in the tube pump according to the present configuration, after one of the pair of roller units passes the separate position, liquid in the tube on the upstream of the separated position and liquid in the tube on the downstream side thereof are in a communicating state with each other. Consequently, when there is the difference in pressure between liquid on the upstream side of the separate position and liquid on the downstream side thereof, the flow rate of liquid discharged from the other end of the tube fluctuates. Accordingly, in the tube pump system according to the present configuration, a pressure of the liquid in the tube which is closed due to a contact of the pair of roller units is increased to a second predetermined pressure having a predetermined pressure difference with respect to the first predetermined pressure when one of the pair of roller units passes the separate position. Therefore, when one of the pair of roller units passes the separate position and the tube compressed by the roller unit returns to the original shape, a pressure difference between a pressure of the liquid on the downstream side of the separate position and a pressure of the liquid on the upstream side of the separate position is reduced thus conforming to a predetermined pressure difference. Accordingly, compared to a case where the pressure difference is larger than the predetermined pressure difference, it is possible to suppress the generation of pulsation of a liquid caused by the fluctuation of the flow rate of the liquid at the separate position when one of the pair of roller units passes the separate position. 
     In the tube pump system according to one aspect of the present disclosure, the control unit may be configured to temporarily increase an angular velocity of one of the pair of roller units when the state where one of the pair of roller units compresses the tube is released. 
     With such a configuration, when the state where one of the pair of roller units compresses the tube is released, one of the pair of roller units can temporarily increase a discharge force for discharging a liquid toward the downstream side of the separate position. Therefore, it is possible to suppress the generation of pulsation of the liquid which is caused by a high pressure liquid on the downstream side of the separate position drawn back toward a low pressure fluid on the upstream side of the separate position. 
     In the tube pump system according to one aspect of the present disclosure, the tube pump system may further include a flowmeter which is configured to measure a flow rate of the liquid discharged from the tube, and the control unit may be configured to control each of the pair of drive units such that the flow rate of the liquid measured by the flowmeter conforms to a target flow rate. 
     With such a configuration, it is possible to control each of the pair of drive units such that the flow rate of the liquid measured by the flowmeter conforms to the target flow rate while the generation of pulsation of the liquid is suppressed. 
     In the tube pump system according to one aspect of the present disclosure, the first predetermined pressure may be equal to or more than 20 kPaG and equal to or less than 250 kPaG. 
     With such a configuration, the first predetermined pressure of the liquid flowing through the pipe becomes sufficiently higher than the atmospheric pressure and hence, further transmission of pulsation of the liquid to the downstream side of the pipe can be suppressed. 
     In a method for controlling a tube pump system according to another aspect of the present disclosure, there is provided a method for controlling a tube pump system which includes: a housing unit which has an inner peripheral surface formed into a circular-arc shape around an axis line; a tube having flexibility which is arranged along the inner peripheral surface; a pair of roller units which are housed in the housing unit, and are rotated around the axis line from a contact position to a separate position around the axis line in a state where the pair of roller units compress the tube; and a pair of drive units which are configured to rotate the pair of roller units respectively around the axis line in a same direction, the method including a controlling step of controlling each of the pair of drive units such that a liquid which flows into the tube from one end of the tube is discharged from the other end of the tube, wherein, in the controlling step, each of the pair of drive units is controlled such that, when one of the pair of roller units passes the separate position, an angular velocity of the other of the pair of roller units toward the separate position is gradually decreased. 
     According to a method of controlling a tube pump system according to one aspect of the present disclosure, after one of the pair of roller units passes the separate position, an angular velocity of the other of the pair of roller units toward the separate position is gradually decreased. By doing this, pressure increase of liquid on the upstream side due to approach to the separate position by the other of the pair of roller units can be compensated by pressure decrease of liquid due to decrease of an angular velocity of the other of the pair of roller units. As a result, fluctuation of the flow rate of liquid discharged from the other end of the tube can be inhibited or eliminated, which can inhibit or eliminate pulsation of liquid. 
     In a method of controlling the tube pump system according to one aspect of the present disclosure, a pipe having flexibility may be connected to the other end of the tube, the pipe maintaining a pressure of the liquid flowing through the inside of the pipe at a first predetermined pressure higher than an atmospheric pressure, and the controlling step may control each of the pair of drive units such that a pressure of the liquid in the tube which is closed due to a contact of the pair of roller units is increased to a second predetermined pressure having a predetermined pressure difference with respect to the first predetermined pressure when one of the pair of roller units passes the separate position. 
     In the method of controlling the tube pump system according to the present configuration, a static pressure of the liquid in the inside of the pipe is higher than the atmospheric pressure and hence, when the static pressure of the liquid in the pipe is further increased by pulsation of the liquid, the pipe is elastically deformed whereby pulsation of the liquid can be suppressed. 
     In the method for controlling a tube pump system according to the present configuration, when one of the pair of roller units passes the separate position, a pressure of the liquid in the tube which is closed due to the contact of the pair of roller units is increased to the second predetermined pressure having a predetermined pressure difference with respect to the first predetermined pressure. Therefore, when one of the pair of roller units passes the separate position and the tube compressed by the roller unit returns to the original shape, a pressure difference between a pressure of the liquid on the downstream side of the separate position and a pressure of the liquid on the upstream side of the separate position is reduced thus conforming to a predetermined pressure difference. Accordingly, compared to a case where the pressure difference is larger than the predetermined pressure difference, it is possible to suppress the generation of pulsation of a liquid caused by the fluctuation of the flow rate of the liquid at the separate position when one of the pair of roller units passes the separate position. 
     In the method for controlling a tube pump system according to another aspect of the present disclosure, in the controlling step, an angular velocity of one of the pair of roller units may be temporarily increased when a state where one of the pair of roller units compresses the tube is released. 
     With such a configuration, when the state where one of the pair of roller units compresses the tube is released, one of the pair of roller units can temporarily increase a discharge force for discharging a liquid toward the downstream side of the separate position. Therefore, it is possible to suppress the generation of pulsation of the liquid which is caused by a high pressure liquid on the downstream side of the separate position drawn back toward a low pressure fluid on the upstream side of the separate position. 
     In the method for controlling a tube pump system according to another aspect of the present disclosure, the method may further include a measuring step of measuring a flow rate of the liquid flowing through the inside of the pipe and, in the controlling step, each of the pair of drive units may be controlled such that the flow rate of the liquid measured in the measuring step conforms to a target flow rate. 
     With such a configuration, it is possible to control each of the pair of drive units such that the flow rate of the liquid measured by the flowmeter conforms to the target flow rate while the generation of pulsation of the liquid is suppressed. 
     In the method for controlling a tube pump system according to another aspect of the present disclosure, the first predetermined pressure may be equal to or more than 20 kPaG and equal to or less than 250 kPaG. 
     With such a configuration, the first predetermined pressure of the liquid flowing through the pipe becomes sufficiently higher than the atmospheric pressure and hence, further transmission of pulsation of the liquid to the downstream side of the pipe can be suppressed. 
     Advantageous Effects 
     According to the present disclosure, it is possible to provide a tube pump system where pulsation of a liquid can be suppressed or eliminated without making an apparatus complicated and large-sized, and a method for controlling the tube pump system. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The foregoing will be apparent from the following more particular description of example embodiments, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments. 
         FIG. 1  is a configuration diagram showing a flow rate control apparatus according to one embodiment of the present disclosure. 
         FIG. 2  is a front view of a tube pump shown in  FIG. 1 . 
         FIG. 3  is a longitudinal cross-sectional view of the tube pump shown in  FIG. 2  taken along a line I-I. 
         FIG. 4  is an exploded perspective view of the tube pump shown in  FIG. 3 . 
         FIG. 5  is a longitudinal cross-sectional view showing a structure in which a first drive unit shown in  FIG. 3  transmits a drive force to a first roller unit. 
         FIG. 6  is a longitudinal cross-sectional view showing a structure in which a second drive unit shown in  FIG. 3  transmits a drive force to a second roller unit. 
         FIG. 7  is a plan view showing the tube pump in a state where a tube is closed. 
         FIG. 8  is a plan view showing the tube pump in a state where the tube starts to open. 
         FIG. 9  is a plan view showing the tube pump in a state where the tube is open. 
         FIG. 10  is a view showing the tube pump in a state where the second roller unit reaches a separate position. 
         FIG. 11  is a partially enlarged view of the tube pump shown in  FIG. 7 . 
         FIG. 12  is a partially enlarged view of the tube pump shown in  FIG. 8 . 
         FIG. 13  is a partially enlarged view of the tube pump shown in  FIG. 9 . 
         FIG. 14  is a partially enlarged view of the tube pump shown in  FIG. 10 . 
         FIG. 15  is a cross-sectional view of the tube shown in  FIG. 11  taken along a line II-II. 
         FIG. 16  is a cross-sectional view of the tube shown in  FIG. 12  taken along a line III-III. 
         FIG. 17  is a cross-sectional view of the tube shown in  FIG. 13  taken along a line IV-IV. 
         FIG. 18  is a cross-sectional view of the tube shown in  FIG. 14  taken along a line V-V. 
         FIG. 19  is a graph showing angular velocities of the first roller unit and the second roller unit with respect to a rotation angle of the first roller unit. 
         FIG. 20  is a graph showing a comparative example of angular velocities of the first roller unit and the second roller unit with respect to the rotation angle of the first roller unit. 
         FIG. 21  is a graph showing a flow rate of a liquid measured by a flowmeter of a tube pump system according to this embodiment. 
         FIG. 22  is a graph showing a flow rate of a liquid measured by a flowmeter of the tube pump system. 
     
    
    
     DETAILED DESCRIPTION 
     A description of example embodiments follows. 
     Hereinafter, a tube pump system and a method for controlling the tube pump system according to one embodiment of the present disclosure are explained with reference to drawings. 
     Hereinafter, a tube pump system  700  according to one embodiment of the present disclosure will be explained with reference to drawings. 
     The tube pump system  700  of this embodiment is an apparatus that supplies a liquid under pressure from an inflow end  701  to an outflow end  702  and, at the same time, controls a flow rate of the liquid supplied under pressure by a tube pump  100 . 
     As shown in  FIG. 1 , the tube pump system  700  of this embodiment includes: the tube pump  100  that supplies a liquid under pressure; a pipe  200  through which the liquid is conveyed from the tube pump  100  to a needle valve  500 ; a pressure sensor  300  that detects a pressure of the liquid flowing through the pipe  200 ; a flowmeter  400  that measures a flow rate of the liquid flowing through the pipe  200 ; a needle valve  500  that adjusts a pressure of the liquid flowing through the pipe  200  arranged on the upstream side of the needle valve  500 ; and a control unit  600  that controls a discharge amount of the liquid discharged from the tube pump  100 . 
     Hereinafter, respective configurations of the tube pump system  700  of this embodiment are explained. 
     The tube pump  100  is a device that supplies a liquid under pressure from the inflow end  701  to the outflow end  702 . The tube pump  100  supplies the liquid under pressure by repeating an operation where rollers are moved in a state where a tube having flexibility is compressed by the rollers. The liquid discharged from the tube pump  100  to the pipe  200  passes through the flowmeter  400  and the needle valve  500 , and reaches the outflow end  702 . 
     The tube pump  100  will be mentioned later in detail. 
     The pipe  200  is a pipe through which a liquid is conveyed from the tube pump  100  to the needle valve  500 . The pipe  200  is made of a resin material (for example, a silicone resin) having flexibility that is elastically deformed due to a pressure of the liquid supplied under pressure by the tube pump  100 . The pipe  200  can maintain a pressure of the liquid flowing through the inside of the pipe  200  at a first predetermined pressure Pr 1  which is higher than an atmospheric pressure by adjusting an opening degree of the needle valve  500  mentioned later. 
     A flow path length L of the pipe  200  is desirably set to approximately 1000 mm, for example. 
     The pressure sensor  300  is a device that detects a pressure of the liquid flowing through the inside of the pipe  200 . The pressure sensor  300  is arranged on the pipe  200  through which the liquid is introduced from the tube pump  100  to the needle valve  500 , at a position on the upstream side of the flowmeter  400 . The pressure sensor  300  transmits the detected pressure to the control unit  600 . 
     The flowmeter  400  is a device that measures a flow rate of the liquid flowing through the inside of the pipe  200 . The flowmeter  400  is arranged on the pipe  200  through which the liquid is introduced from the tube pump  100  to the needle valve  500  at a position on the downstream side of the pressure sensor  300 . The flowmeter  400  transmits the measured flow rate to the control unit  600 . 
     The needle valve  500  is a device that adjusts a flow rate of a fluid flowing through the needle valve  500  from the pipe  200  to the outflow end  702  by adjusting an insertion amount of a needle-shaped valve body (illustration is omitted) with respect to a valve hole (illustration is omitted). The needle valve  500  forms a region having a minimum flow path cross sectional area in a path through which the liquid is introduced from the tube pump  100  to the outflow end  702 . 
     The needle valve  500  is made to have a minimum flow path cross sectional area in order to allow the needle valve  500  to have a highest pipe resistance in the path through which the liquid is introduced from the tube pump  100  to the outflow end  702 . Therefore, the liquid in the pipe  200  on the upstream side of the needle valve  500  is maintained at a high static pressure. In this embodiment, the opening degree of the needle valve  500  is adjusted such that a pressure of a liquid flowing through the inside of the pipe  200  conforms to the first predetermined pressure Pr 1  which is higher than an atmospheric pressure. 
     In this embodiment, the first predetermined pressure Pr 1  is desirably set to a value which falls within a range of equal to or more than 20 kPaG and equal to or less than 250 kPaG. Particularly, the first predetermined pressure Pr 1  is desirably set to a value which falls within a range of equal to or more than 90 kPaG and equal to or less than 110 kPaG. Reference character “G” denotes a gauge pressure. 
     The pipe  200 , where a liquid is maintained in the inside of the pipe  200  with a high static pressure, is made of a flexible resin material. This is because when a static pressure in the pipe  200  is further increased by pulsation of the liquid, the pipe  200  is elastically deformed and hence, transmission of pulsation of the liquid to the downstream side can be suppressed. 
     As described above, in the path through which a liquid is introduced from the tube pump  100  to the outflow end  702 , the pipe  200  made of a flexible resin material is arranged on the upstream side of the needle valve  500  having the highest pipe resistance and hence, pulsation of the liquid supplied under pressure from the tube pump  100  can be suppressed. 
     The control unit  600  is a device that controls a first drive unit  50  and a second drive unit  60  mentioned later respectively such that a liquid which flows into a flexible tube  101  of the tube pump  100  from one end of the tube  101  is discharged from the other end of the tube  101 . 
     The control unit  600  controls each of the first drive unit  50  and the second drive unit  60  such that the pressure transmitted from the pressure sensor  300  agrees with the first predetermined pressure Pr 1 . The control unit  600  also controls each of the first drive unit  50  and the second drive unit  60  such that a flow rate measured by the flowmeter  400  conforms to a predetermined target flow rate. A method for controlling the first drive unit  50  and the second drive unit  60  by the control unit  600  will be mentioned later in detail. 
     Next, the tube pump  100  of the tube pump system  700  will be explained. 
     The tube pump  100  of this embodiment shown in  FIG. 2  is a device where a first roller unit  10  (first contact member) and a second roller unit  20  (second contact member) are rotated around an axis line X 1  (first axis line) in the same direction so as to make a fluid in a tube  101  which flows into the tube  101  discharge from an inflow-side end portion  101   a  to an outflow-side end portion  101   b . The pipe  200  is connected to the outflow-side end portion  101   b.    
       FIG. 2  shows the tube pump  100  in a state where a cover  83  shown in  FIG. 3  is removed. 
     As shown in  FIG. 2  which is a front view, in the tube pump  100 , the tube  101  is arranged in a circular-arc shape around the axis line X 1  along an inner peripheral surface  82   b  of a recess  82   a  of a roller housing unit  82  that houses the first roller unit  10  and the second roller unit  20 . As shown in  FIG. 2 , the first roller unit  10  and the second roller unit  20  housed in the roller housing unit  82  are rotated around the axis line X 1  along a counter-clockwise rotation direction (a direction shown by an arrow in  FIG. 2 ) while being in contact with the tube  101 . 
     In  FIG. 2  which is a front view, a contact position Po 1  indicates a position around the axis line X 1  at which a state of the first roller unit  10  or the second roller unit  20  changes over from a state where the first roller unit  10  or the second roller unit  20  is separated from the tube  101  to a state where the first roller unit  10  or the second roller unit  20  is in contact with the tube  101 . Further, a separate position Po 2  indicates a position around the axis line X 1  at which a state of the first roller unit  10  or the second roller unit  20  changes over from a state where the first roller unit  10  or the second roller unit  20  is in contact with the tube  101  to a state where the first roller unit  10  or the second roller unit  20  is separated from the tube  101 . Broken lines shown in  FIG. 2  indicate the first roller unit  10  and the second roller unit  20  arranged at the contact position Po 1  and the separate position Po 2 . 
     Until the first roller unit  10  and the second roller unit  20  reaches the separate position Po 2  from the contact position Po 1 , the first roller unit  10  and the second roller unit  20  are rotated around the axis line X 1  independently in a state where the first roller unit  10  and the second roller unit  20  compress the tube  101  in cooperation with the inner peripheral surface  82   b.    
     As shown in a longitudinal cross-sectional view of  FIG. 3  and an exploded perspective view of  FIG. 4 , the tube pump  100  of the embodiment includes: the first roller unit  10  and the second roller unit  20  that rotate around the axis X 1  while being in contact with the tube  101 ; a drive shaft  30  (a shaft member) that is arranged on the axis X 1  and is coupled to the first roller unit  10 ; a drive cylinder (a cylindrical member)  40  that is coupled to the second roller unit  20 ; a first drive unit  50  that transmits a drive force to the drive shaft  30 ; a second drive unit  60 ; and a transmission mechanism  70  (a transmission unit) that transmits a drive force of the second drive unit  60  to the drive cylinder  40 . 
     The first roller unit  10  has: a first roller  11  that rotates around an axis parallel to the axis X 1  while being in contact with the tube  101 ; a first roller support member  12  coupled to the drive shaft  30  so as to integrally rotate around the axis X 1 ; and a first roller shaft  13  both ends of which are supported by the first roller support member  12 , and to which the first roller  11  is rotatably attached. 
     The second roller unit  20  has: a second roller  21  that rotates around an axis parallel to the axis X 1  while being in contact with the tube  101 ; a second roller support member  22  coupled to the drive cylinder  40  so as to integrally rotate around the axis X 1 ; and a second roller shaft  23  both ends of which are supported by the second roller support member  22 , and to which the second roller  21  is rotatably attached. 
     As shown in  FIG. 3 , the first drive unit  50  and the second drive unit  60  are housed inside a casing (a housing member)  80 . A gear housing unit  81  for housing the transmission mechanism  70 , and a support member  90  that supports the first drive unit  50  and the second drive unit  60  are attached to an inside of the casing  80 . In addition, the roller housing unit  82  for housing the first roller unit  10  and the second roller unit  20  is attached to an upper part of the casing  80 . 
     The roller housing unit  82  has the recess  82   a  that houses the first roller unit  10  and the second roller unit  20 . The recess  82   a  has the inner peripheral surface  82   b  formed into a circular-arc shape around the axis line X 1 . 
     As shown in  FIG. 3 , the tube  101  is arranged in a circular-arc shape around the axis line X 1  along the inner peripheral surface  82   b.    
     A first through hole  91  that extends along the axis X 1  and a second through hole  92  that extends along an axis X 2  are formed in the support member  90 . The first drive unit  50  is attached to the support member  90  by a fastening bolt (illustration is omitted) in a state where a first drive shaft  51  is inserted into the first through hole  91  formed in the support member  90 . Similarly, the second drive unit  60  is attached to the support member  90  by a fastening bolt (illustration is omitted) in a state where a second drive shaft  61  is inserted into the second through hole  92  formed in the support member  90 . As described above, each of the first drive unit  50  and the second drive unit  60  is attached to the support member  90 , which is the integrally formed member. 
     Here, with reference to  FIG. 5 , there will be explained a structure in which the first drive unit  50  transmits a drive force to the first roller unit  10 . In  FIG. 5 , a portion shown by continuous lines is the portion included in the structure of transmitting a drive force of the first drive unit  50  to the first roller unit  10 . 
     As shown in  FIG. 5 , the first drive unit  50  has the first drive shaft  51  that is arranged on the axis X 1  and is coupled to the drive shaft  30 . The first drive shaft  51  is attached to a lower end of the drive shaft  30  in a state where a pin  51   a  that extends in a direction perpendicular to the axis X 1  is inserted into the first drive shaft  51 . The drive shaft  30  is fixed to the first drive shaft  51  by the pin  51   a  so as not to relatively rotate around the axis X 1 . Therefore, when the first drive unit  50  rotates the first drive shaft  51  around the axis X 1 , a drive force of the first drive shaft  51  is transmitted to the drive shaft  30 , and the drive shaft  30  rotates around the axis X 1 . 
     The first drive unit  50  has; the first drive shaft  51 ; the first electric motor  52 ; and a first reducer  53  that reduces a velocity of rotation of a rotation shaft (illustration is omitted) rotated by the first electric motor  52 , and transmits the rotation to the first drive shaft  51 . The first drive unit  50  rotates the first drive shaft  51  around the axis X 1  by transmitting a drive force of the first electric motor  52  to the first drive shaft  51 . 
     A position detecting member  51   b  that rotates around the axis X 1  together with the first drive shaft  51  is attached to the first drive shaft  51 . In the position detecting member  51   b , in an annularly formed outer peripheral edge, a slit (illustration is omitted) for detecting a rotation position of the first roller unit  10  around the axis X 1  is formed in a peripheral direction around the axis X 1 . 
     As shown in  FIG. 5 , a position detection sensor  54  is arranged so as to sandwich an upper surface and a lower surface of the outer peripheral edge of the position detecting member  51   b . The position detection sensor  54  is the sensor in which a light-emitting element is arranged on one of an upper surface side and a lower surface side, and in which a light-receiving element is arranged on the other of the upper surface side and the lower surface side. The position detection sensor  54  detects a rotation position indicating which position the first roller unit  10  is arranged around the axis X 1  by detecting by the light-receiving element through the slit that light emitted by the light-emitting element passes through in connection with the rotation of the position detecting member  51   b  around the axis X 1 , and transmits it to a control unit  600 . 
     The lower end of the drive shaft  30  is coupled to the first drive shaft  51 , and an upper end thereof is inserted into an insertion hole formed in the cover  83 . A third bearing member  33  that rotatably supports a tip of the first drive shaft  51  around the axis X 1  is inserted into the insertion hole of the cover  83 . 
     In addition, the drive shaft  30  is rotatably supported around the axis X 1  on an inner peripheral side of the drive cylinder  40  by a cylindrical first bearing member  31  inserted along the outer peripheral surface, and a cylindrical second bearing member  32  formed independently from the first bearing member  31 . 
     As described above, in the drive shaft  30 , the outer peripheral surface of a lower end side is supported by the first bearing member  31 , the outer peripheral surface of a central portion is supported by the second bearing member  32 , and the outer peripheral surface of a tip side is supported by the third bearing member  33 . Therefore, the drive shaft  30  smoothly rotates around the axis X 1  in a state of holding a central axis on the axis X 1 . 
     Here, a reason why the first bearing member  31  and the second bearing member  32  are arranged in the axis X 1  direction in a state of being separated from each other as shown in  FIG. 5  is that an endless annular projection part  40   a  that extends around the axis X 1  is formed at an inner peripheral surface of the drive cylinder  40 . 
     The first roller support member  12  of the first roller unit  10  is coupled to the tip side of the drive shaft  30  so as to integrally rotate around the axis X 1 . 
     As described above, the drive force by which the first drive unit  50  rotates the first drive shaft  51  around the axis X 1  is transmitted from the first drive shaft  51  to the first roller unit  10  through the drive shaft  30 . 
     As shown in  FIG. 5 , the lower end of the drive shaft  30  is supported by an upper surface of an annularly formed thrust bearing  35 , and a lower surface of the thrust bearing  35  is supported by the support member  90 . Therefore, in a case where a downward thrust force is added to the drive shaft  30  along the axis X 1 , the thrust force is supported by the thrust bearing  35  without being transmitted to the first reducer  53  and the first electric motor  52 . 
     Therefore, in the case where the downward thrust force is added to the drive shaft  30  along the axis X 1 , it is suppressed by the thrust force that impact is added to the first reducer  53  and the first electric motor  52 . 
     Next, with reference to  FIG. 6 , there will be explained a structure in which the second drive unit  60  transmits a drive force to the second roller unit  20 . In  FIG. 6 , a portion shown by continuous lines is the portion included in the structure of transmitting the drive force of the second drive unit  60  to the second roller unit  20 . The structure shown in  FIG. 6  has: the second roller unit  20 ; the drive cylinder  40 ; the second drive unit  60 ; and the transmission mechanism  70 . 
     The transmission mechanism  70  shown in  FIG. 6  has: a first gear unit  71  that rotates around the axis X 2  (a second axis) parallel to the axis X 1 ; and a second gear unit  72  to which a drive force of the second drive shaft  61  is transmitted from the first gear unit  71 . The transmission mechanism  70  transmits the drive force of the second drive shaft  61  around the axis X 2  to the outer peripheral surface of the drive cylinder  40 , and rotates the drive cylinder  40  around the axis X 1 . 
     As shown in  FIG. 6 , the second drive unit  60  has; the second drive shaft  61  arranged on the axis X 2 ; a second electric motor  62 ; and a second reducer  63  that reduces a velocity of rotation of a rotation shaft (illustration is omitted) rotated by the second electric motor  62 , and transmits the rotation to the second drive shaft  61 . The second drive unit  60  rotates the second drive shaft  61  around the axis X 2  by transmitting a drive force of the second electric motor  62  to the second drive shaft  61 . 
     The second drive shaft  61  is inserted into an insertion hole formed in a central portion of the first gear unit  71  formed in a cylindrical shape around the axis X 2 . The first gear unit  71  is fixed to the second drive shaft  61  by fastening a fixing screw  71   a  in a state where the second drive shaft  61  is inserted into the first gear unit  71 , and making a tip of the fixing screw  71   a  abut against the second drive shaft  61 . In a manner as described above, the first gear unit  71  is coupled to the second drive shaft  61 , and rotates around the axis X 2  together with the second drive shaft  61 . 
     A first gear  71   b  of the first gear unit  71  formed around the axis X 2  is engaged with a second gear  72   b  of the second gear unit  72  formed around the axis X 1 . Therefore, a drive force by rotation of the first gear unit  71  around the axis X 2  is transmitted as the drive force that rotates the second gear unit  72  around the axis X 1 . 
     A position detecting member  71   c  that rotates around the axis X 1  together with the second drive shaft  61  is formed at the first gear unit  71 . In the position detecting member  71   c , in an annularly formed outer peripheral edge, a slit (illustration is omitted) for detecting a rotation position of the second roller unit  20  around the axis X 1  is formed in a peripheral direction around the axis X 2 . 
     As shown in  FIG. 6 , a position detection sensor  64  is arranged so as to sandwich an upper surface and a lower surface of an outer peripheral edge of the position detecting member  71   c . The position detection sensor  64  is the sensor in which a light-emitting element is arranged on one of an upper surface side and a lower surface side, and in which a light-receiving element is arranged on the other of the upper surface side and the lower surface side. The position detection sensor  64  detects a rotation position indicating which position the second roller unit  20  is arranged around the axis X 1  by detecting by the light-receiving element through the slit that light emitted by the light-emitting element passes through in connection with the rotation of the position detecting member  71   c  around the axis X 2 , and transmits it to the control unit  600 . 
     The drive cylinder  40  is inserted into an insertion hole formed in a central portion of the second gear unit  72  formed in a cylindrical shape around the axis X 1 . The insertion hole is a hole having an inner peripheral surface coupled to the outer peripheral surface of the drive cylinder  40 . 
     The second gear unit  72  is fixed to the drive cylinder  40  by fastening a fixing screw  72   a  in a state where the drive cylinder  40  is inserted into the second gear unit  72 , and making a tip of the fixing screw  72   a  abut against the drive cylinder  40 . In a manner as described above, the second gear unit  72  is coupled to the drive cylinder  40 , and rotates around the axis X 1  together with the drive cylinder  40 . 
     As shown in  FIG. 6 , the drive cylinder  40  is arranged in a state of sandwiching the first bearing member  31  and the second bearing member  32  on an outer peripheral side of the drive shaft  30 . Therefore, the drive cylinder  40  can be rotated around the axis X 1  independently from the drive shaft  30 . The drive shaft  30  rotates around the axis X 1  by the drive force by the first drive unit  50 , and the drive cylinder  40  rotates around the axis X 1  by the drive force by the second drive unit  60  in a state of being independent from the drive shaft  30 . 
     The second roller support member  22  of the second roller unit  20  is coupled to a tip side of the drive cylinder  40  so as to integrally rotate around the axis X 1 . 
     As described above, the drive force by which the second drive unit  60  rotates the second drive shaft  61  around the axis X 2  is transmitted to the outer peripheral surface of the drive cylinder  40  by the transmission mechanism  70 , and is transmitted from the drive cylinder  40  to the second roller unit  20 . 
     Next, discharging of a liquid performed by the tube pump system  700  of this embodiment will be explained with reference to drawings. 
     As shown in  FIG. 1 , the tube pump system  700  of this embodiment detects a pressure of the liquid discharged from the tube pump  100  to the pipe  200  by the pressure sensor  300 , and transmits the pressure of the liquid to the control unit  600 . The tube pump system  700  also measures a flow rate of the liquid flowing through the pipe  200  by the flowmeter, and transmits the flow rate of the liquid to the control unit  600 . The control unit  600  controls angular velocities of the first roller unit  10  and the second roller unit  20  around the axis line X 1  such that the flow rate of the liquid flowing through the pipe  200  agrees with a target flow rate. An operator of the tube pump system  700  adjusts an opening degree of the needle valve  500  such that a pressure of a liquid detected by the pressure sensor  300  agrees with the first predetermined pressure Pr 1 . 
     In the tube pump system  700  shown in  FIG. 1 , a control signal for controlling the first drive unit  50  and the second drive unit  60  of the tube pump  100  is transmitted from the control unit  600  to the tube pump  100 . 
     The tube pump  100  may be formed as a device in which the control unit  600  is incorporated. In this case, the control unit  600  incorporated in the tube pump  100  generates a control signal for controlling the first drive unit  50  and the second drive unit  60 , and transmits the control signal to the first drive unit  50  and the second drive unit  60 . 
     An example shown in  FIG. 7  to  FIG. 18  is an example where a liquid in which pulsation is not generated (a liquid in which the fluctuation of the flow rate is not generated) flows into the tube  101  from the inflow-side end portion  101   a  of the tube  101 , and the liquid is discharged from the outflow-side end portion  101   b  in a state where pulsation is not generated in the liquid. 
       FIG. 7  to  FIG. 10  are plan views showing the tube pump  100 , and chronologically show states where the second roller unit  20  approaches the separate position Po 2 .  FIG. 11  to  FIG. 14  are partially enlarged views of the second roller  21  of the tube pump  100  shown in  FIG. 7  to  FIG. 10  and an area in the vicinity of the second roller  21 . Each of  FIG. 15  to  FIG. 18  is a longitudinal cross-sectional view of the tube  101  shown in  FIG. 11  to  FIG. 14 . 
       FIG. 7  is a plan view showing the tube pump  100  in a state where the tube  101  is closed. The state where the tube  101  is closed means a state where, as shown in  FIG. 11  and  FIG. 15 , the second roller  21  of the second roller unit  20  compresses the tube  101 . At this point of time, a flow path cross sectional area of the tube  101  shown in  FIG. 15  becomes zero. 
       FIG. 8  is a plan view showing the tube pump  100  in a state where the tube  101  starts to open. The state where the tube  101  starts to open means a state where, as shown in  FIG. 12  and  FIG. 16 , the release of a state where the second roller  21  of the second roller unit  20  compresses the tube  101  is started. At this point of time, a flow path cross sectional area of the tube  101  shown in  FIG. 16  assumes a value larger than zero. 
       FIG. 9  is a plan view showing the tube pump  100  in a state where the tube  101  is open. The state where the tube  101  is open means a state where, as shown in  FIG. 13  and  FIG. 17 , the state where the second roller  21  of the second roller unit  20  compresses the tube  101  is released. At this point of time, a flow path cross sectional area of the tube  101  shown in  FIG. 17  is substantially equal to the flow path cross sectional area of the tube  101  in a state where the second roller  21  is not brought into contact with the tube  101 . 
       FIG. 10  is a plan view showing the tube pump  100  in a state where the second roller unit  20  reaches the separate position Po 2 . The state where the second roller unit  20  reaches the separate position Po 2  means a state where, as shown in  FIG. 14  and  FIG. 18 , deformation of the tube  101  caused by the second roller unit  20  is released. At this point of time, a flow path cross sectional area of the tube  101  shown in  FIG. 18  is substantially equal to the flow path cross sectional area of the tube  101  shown in  FIG. 17 . This means that after the second roller unit  20  reaches a position shown in  FIG. 9 , although deformation of the tube  101  is gradually released, a flow path cross sectional area of the tube  101  does not change. 
       FIG. 19  is a graph showing angular velocities (rad/s) of the first roller unit  10  and the second roller unit  20  with respect to a rotation angle Ra (°) of the first roller unit  10 . In this embodiment, the rotation angle Ra of the first roller unit  10  means an angle around the axis line X 1  by assuming respective positions shown in  FIG. 7  as 0°, 90°, 180° and 270°. 
     The control unit  600  shown in  FIG. 1  transmits a control signal to the tube pump  100  for controlling the first drive unit  50  and the second drive unit  60  such that the first roller unit  10  and the second roller unit  20  are rotated at angular velocities shown in  FIG. 19  when the second roller unit  20  passes the separate position Po 2 . 
     Next, with reference to  FIG. 19 , there will be explained a method for controlling the tube pump  100  by the control unit  600  when the second roller unit  20  passes the separate position Po 2 . Hereinafter, the method for controlling the first roller unit  10  is explained. A method for controlling the second roller unit  20  is substantially equal to the method for controlling the first roller unit  10 . Accordingly, hereinafter, the explanation of the method for controlling the second roller unit  20  is omitted. 
     As shown in  FIG. 7 , the separate position Po 2  exists within a range where the rotation angle Ra around the axis line X 1  is more than 270° and less than 360° (0°). Hereinafter, an operation executed by the tube pump  100  while the rotation angle is from 0° to 360° will be explained. 
     As shown in  FIG. 7 , the rotation angle Ra 1  corresponds to a state where the tube  101  is closed due to contact to the second roller unit  20 . Also, as shown in  FIG. 8 , the rotation angle Ra 2  corresponds to a state where the tube  101  contacted to the second roller unit  20  starts to open. Also, as shown in  FIG. 9 , the rotation angle Ra 3  corresponds to a state where the tube  101  is opened. Also, as shown in  FIG. 10 , the rotation angle Ra 4  corresponds to a state where the second roller unit  20  reaches the separate position Po 2 . 
     The rotation angle Ra 5  corresponds to a state where the tube  101  is closed due to contact to the first roller unit  10 . Also, the rotation angle Ra 6  corresponds to a state where the tube  101  contacted to the first roller unit  10  starts to open. Also, the rotation angle Ra 7  corresponds to a state where tube  101  is opened. Also, the rotation angle Ra 8  corresponds to a state where the first roller unit  10  reaches the separate position Po 2 . 
     The control unit  600  maintains an angular velocity V 1  until the first roller unit  10  rotates from the rotation angle of 0° to the rotation angle Ra 1 , and when the first roller unit  10  reaches the rotation angle Ra 1 , the control unit  600  increases the angular velocity V 1  to an angular velocity V 4 . Here, the angular velocity V 4  may be an arbitrary angular velocity which is larger than the angular velocity V 1  in accordance with property of each portion of the tube pump  100  so that no fluctuation (pulsation) occurs in a flow rate measured by the flowmeter  400 . For example, the control unit  600  sets the angular velocity V 4  to be proportional to a first predetermined pressure Pr 1  detected by the pressure sensor  300 . Due to this, a pressure of liquid which is closed in the inner portion of the tube  101  can be made to agree with the first predetermined pressure Pr 1  of liquid in the pipe  200 . 
     Also, for example, it is acceptable that the control unit  600  applies a fixed angular velocity V 4  which is not proportional to the first predetermined pressure Pr 1 , and sets the range of a rotation angle from the rotation angle Ra 1  to the rotation angle Ra 3  to be proportional to the predetermined pressure Pr 1 . In this case, the rotation angle Ra 3  may be increased without fluctuation of the rotation angle Ra 1 , or the rotation angle Ra 1  may be decreased without fluctuation of the rotation angle Ra 3 . Further, the rotation angle Ra 1  may be decreased and the rotation angle Ra 3  may be increased. By doing this, a pressure of the liquid which is closed in the inner portion of the tube  101  can be made to agree with the first predetermined pressure Pr 1  of liquid in the pipe  200 . 
     The control unit  600  increases the angular velocity of the first roller unit  10  from the rotation angle Ra 1  in order to reduce an angular difference around the axis line X 1  between the first roller unit  10  and the second roller unit  20 . 
     As shown in  FIG. 7  and  FIG. 8 , at the rotation angle Ra 1  and the rotation angle Ra 2 , the tube  101  is brought into a state where portions of the tube  101  are compressed due to the contact of the first roller unit  10  and the second roller unit  20  thus being closed. Therefore, when an angular difference around the axis line X 1  between the first roller unit  10  and the second roller unit  20  is reduced, an inner volume of the closed tube  101  is reduced so that a pressure of the liquid in the tube  101  is increased. 
     The control unit  600  controls the first drive unit  50  and the second drive unit  60  such that, at the rotation angle Ra 2  at which the tube  101  starts to open, a pressure of a liquid in the tube  101  is increased to a second predetermined pressure Pr 2  having a predetermined pressure difference with respect to the first predetermined pressure Pr 1  which is a pressure of a liquid in the pipe  200 . 
     In this embodiment, the predetermined pressure difference is desirably set to a value within 0.2 times that of the first predetermined pressure Pr 1 . That is, it is desirable that the second predetermined pressure Pr 2  satisfies the following conditional expression (1).
 
0.8Pr1≤Pr2≤1.2Pr1  (1)
 
     The control unit  600  increases the pressure of the liquid in the tube  101  so as to allow the liquid to have the second predetermined pressure Pr 2  which satisfies the conditional expression (1). With the increase of the pressure, when the tube  101  is brought into the state where the tube  101  starts to open, a difference in pressure of a liquid between the upstream side of the position at which the tube  101  starts to open and the downstream side of the position at which the tube  101  starts to open is reduced. Therefore, it is possible to suppress a drawback that a forward and reverse flow of a liquid is generated between the upstream side and the downstream side of the position at which the tube  101  starts to open thus generating pulsation. 
     The control unit  600  maintains the angular velocity V 4  as an angular velocity of the first roller unit  10  after the first roller unit  10  passes the rotation angle Ra 2  in a state that the tube  101  starts to open until it reaches the rotation angle Ra 3 . This is because a flow route cross-sectional area of the tube  101  increases even when the first roller unit  10  passes the rotation angle Ra 2  until it reaches the rotation angle Ra 3  in a state that the tube  101  is open. The control unit  600  maintains an angular velocity of the first roller unit  10  higher than that of the second roller unit  20  to prevent inflow and outflow of liquid between the upstream side and the downstream side of an opening position of the tube  101  when the flow route cross-sectional area of the tube  101  increases. 
     The control unit  600  decreases from the angular velocity V 4  to the angular velocity V 2  after the first roller unit  10  passes the rotation angle Ra 3  where the tube  101  is in state of open. As shown in  FIG. 19 , the angular velocity V 2  is higher than the angular velocity V 1 . 
     In an example shown in  FIG. 19 , the angular velocity of the first roller unit  10  is gradually decreased with a fixed inclination from the angular velocity V 4  to the angular velocity V 2 ; however, other aspects may be applied. For example, it is acceptable to previously measure a waveform of a flow rate in time series variation measured by the flowmeter  400  when the first roller unit  10  and the second roller unit  20  are rotated around the axis line X 1  with a fixed velocity, and decrease the angular velocity from the angular velocity V 4  to the angular velocity V 2  to obtain a waveform which is opposite of the waveform of a flow rate in time series variation. By doing this, the angular velocity of the first roller unit  10  can be decreased from the angular velocity V 4  to the angular velocity V 2  to compensate for the time series variation of the flow rate when the first roller unit  10  and the second roller unit  20  are rotated around the axis line X 1  with a fixed velocity. 
     The control unit  600  gradually decreases the angular velocity V 2  to the angular velocity V 1  after the first roller unit  10  reaches the rotation angle Ra 4  until it reaches the rotation angle Ra 5 . That is, the control unit  600  controls each of the first drive unit  50  and the second drive unit  60  such that the angular velocity of the first roller unit  10  toward the separate position Po 2  is gradually decreased after the second roller unit  20  passes the separate position Po 2 . 
     Here, the angular velocity V 2  may be an arbitrary angular velocity which is larger than the angular velocity V 1  in accordance with property of each portion of the tube pump  100  so that no fluctuation (pulsation) occurs in a flow rate measured by the flowmeter  400 . For example, the control unit  600  sets the angular velocity V 2  to be proportional to a first predetermined pressure Pr 1  detected by the pressure sensor  300 . Due to this, a pressure of liquid in the inner portion of the tube  101  can be made to agree with the first predetermined pressure Pr 1  of liquid in the pipe  200 . 
     The control unit  600  increases the angular velocity V 1  of the first roller unit  10  to the angular velocity V 3  with a fixed acceleration after the first roller unit  10  passes the rotation angle Ra 5  until it reaches the rotation angle Ra 6 . Here, the rotation angle Ra 6  corresponds to a state where the first roller unit  10  starts to open while cancelling a state that the first roller unit  10  compresses the tube  101 . Accordingly, the control unit  600  temporarily increases an angular velocity of the first roller unit  10  when the state that the first roller unit  10  compresses the tube  101  is cancelled. By doing this, a discharge force that the first roller unit  10  discharges liquid toward the downstream side of the separate position Po 2  can be temporarily enhanced when the state that the first roller unit  10  compresses the tube  101  is cancelled. 
     This is because a volume in the inner portion of the tube  101  which is closed by the first roller unit  10  and the second roller unit  20  gradually increases when the tube  101  is changed from a state where a flow route cross-sectional area shown in  FIG. 15  is 0 to a state where a flow route cross-sectional area shown in  FIG. 16  is larger than 0. Accompanied with increase of the volume in the inner portion of the tube  101 , a flow rated of liquid discharged from the tube pump  100  is decreased. As described above, by temporarily enhancing a discharge force of the first roller unit  10 , the flow rate of liquid discharged from the tube pump  100  is decreased, whereby occurrence of pulsation of liquid can be inhibited. 
     Here, the angular velocity V 3  may be an arbitrary angular velocity which is larger than the angular velocity V 1  in accordance with property of each portion of the tube pump  100  so that no fluctuation (pulsation) occurs in a flow rate measured by the flowmeter  400 . For example, the control unit  600  sets the angular velocity V 3  to be proportional to the first predetermined pressure Pr 1  detected by the pressure sensor  300 . Due to this, a pressure of liquid in the tube  101  can be made to agree with the first predetermined pressure Pr 1  of liquid in the pipe  200 . 
     Temporarily enhancing the discharge force of the first roller unit  10  is especially effective when the first predetermined pressure Pr 1  which is a pressure of liquid circulating in the inner portion of the pipe  200  is relatively low (for example, 90 kPa or less). This is because a pressure fluctuation due to decrease of the flow rate of liquid discharged from the tube pump  100  becomes relatively large with respect to the first predetermined pressure Pr 1  when the first predetermined pressure Pr 1  is relatively low. 
     Next, a flow rate of liquid to be controlled by a tube pump system  700  according to this embodiment will be explained with comparison to a comparative example. 
       FIG. 20  is a graph showing a comparative example of an angular velocity (rad/s) of the first roller unit  10  and the second roller unit  20  to a rotation angle Ra (°) of the first roller unit  10 . In a comparative example, the control unit  600  decreases the angular velocity V 4  to the angular velocity V 1  after the first roller unit  10  passes the rotation angle Ra 3  where the tube  101  is in a state of open. Also, in a comparative example, the control unit  600  maintains the angular velocity V 1  until the first roller unit  10  reaches the rotation angle Ra 3 . 
       FIG. 21  is a graph showing a flow rate of liquid measured by the flowmeter  400  of the tube pump system  700  according to this embodiment.  FIG. 22  is a graph showing a flow rate of liquid measured by the flowmeter  400  of a tube pump system of a comparative example. 
     As shown in  FIG. 22 , in the tube pump system of the comparative example, periodic pulsation with the amplitude of about 2 ml/min with an interval of approximately 3 seconds occurs in a flow rate of liquid measured by the flowmeter  400 . In a period in which a flow rate decreases, the first roller unit  10  passes the rotation angle Ra 3  and the tube  101  is in an open state, and thus it is estimated that the flow rate of liquid discharged from the tube pump  100  decreases in accordance with increase of an inner volume of the tube  101 . Also, in a period in which a flow rate increases, the distance between a position where the first roller unit  10  compresses the tube  101  and the separated position Po 2  is shortened as the first roller unit  10  approaches the separated position Po 2 , and thus it is estimated that a pressure of liquid on the downstream side of the first roller unit  10  increases. In this way, in the comparative example, fluctuation of the flow rate of liquid measured by the flowmeter  400  occurs after the first roller unit  10  and the second roller unit  20  pass the separate position Po 2 , whereby a periodic fluctuation (pulsation) of the flow rate occurs. 
     On the other hand, as shown in  FIG. 21 , in the tube pump system  700  according to this embodiment, no periodic pulsation occurs in the flow rate of liquid measured by the flowmeter  400 . It is estimated that this is because, even when the first roller unit  10  passes the rotation angle Ra 3  and the tube  101  is in an open state, the angular velocity of the first roller unit  10  is decreased only to the angular velocity V 2  which is higher than the angular velocity V 1 , which inhibits decrease of a discharge rate of liquid from the tube pump  100  in accordance with increase of an inner volume of the tube  101 . Also estimated is that this is because the angular velocity of the first roller unit  10  is gradually decreased as the first roller unit  10  approaches the separated position Po 2 , which inhibits pressure increase of liquid on the downstream side of the first roller unit  10 . 
     There will be explained actions and effects exerted by the tube pump system  700  according to this embodiment explained above. 
     According to the tube pump system  700  according to this embodiment, after one of the first roller unit  10  and the second roller unit  20  passes the separate position Po 2 , an angular velocity of the other of the first roller unit  10  and the second roller unit  20  toward the separate position Po 2  is gradually decreased. By doing this, pressure increase of liquid on the upstream side due to approach to the separate position Po 2  by the other of the first roller unit  10  and the second roller unit  20  can be compensated by pressure decrease of liquid due to decrease of an angular velocity of the other of the first roller unit  10  and the second roller unit  20 . As a result, fluctuation of the flow rate of liquid discharged from the outflow-side end portion  101   b  of the tube  101  can be inhibited or eliminated, which can inhibit or eliminate pulsation of liquid. 
     According to the tube pump system  700  according to this embodiment, when one of the first roller unit  10  and the second roller unit  20  passes the separate position Po 2 , a pressure of the liquid in the tube  101  which is closed due to the contact of the first roller unit  10  and the second roller unit  20  is increased to the second predetermined pressure Pr 2  having a predetermined pressure difference with respect to the first predetermined pressure Pr 1 . Therefore, when one of the first roller unit  10  and the second roller unit  20  passes the separate position Po 2  and the tube  101  compressed by the first roller unit  10  or the second roller unit  20  returns to the original shape, a pressure difference between a pressure of the liquid on the downstream side of the separate position Po 2  and a pressure of the liquid on the upstream side of the separate position Po 2  is reduced thus conforming to a predetermined pressure difference. Accordingly, compared to a case where the pressure difference is larger than the predetermined pressure difference, it is possible to suppress the generation of pulsation of a liquid caused by the fluctuation of the flow rate of the liquid at the separate position Po 2  when one of the first roller unit  10  and the second roller unit  20  passes the separate position Po 2 . 
     Further, the tube pump system  700  according to this embodiment includes the flowmeter  400  which measures a flow rate of the liquid flowing through the inside of the pipe  200 , and the control unit  600  controls each of the first drive unit  50  and the second drive unit  60  such that the flow rate of the liquid measured by the flowmeter  400  conforms to a target flow rate. 
     With such a configuration, it is possible to control each of the first drive unit  50  and the second drive unit  60  such that the flow rate of the liquid measured by the flowmeter  400  conforms to the target flow rate while the generation of pulsation of the liquid is suppressed. 
     In the tube pump system  700  according to this embodiment, an opening degree of the needle valve  500  is desirably adjusted such that the first predetermined pressure Pr 1  is equal to or more than 20 kPaG and equal to or less than 250 kPaG. 
     With such a configuration, the first predetermined pressure Pr 1  of the liquid flowing through the pipe  200  becomes sufficiently higher than the atmospheric pressure and hence, further transmission of pulsation of the liquid to the downstream side of the pipe  200  can be suppressed. 
     Other Embodiments 
     In the above explanation, the tube pump system  700  is provided with the needle valve  500  having a minimum flow path cross sectional area in the path through which a liquid is introduced from the tube pump  100  to the outflow end  702 . However, another aspect may be employed. For example, an orifice or the like having a minimum flow path cross sectional area in the path through which a liquid is introduced from the tube pump  100  to the outflow end  702  may be provided in place of the needle valve  500 . 
     In the above explanation, in the tube pump system  700 , the control unit  600  controls the tube pump  100  such that a flow rate of a liquid measured by the flowmeter  400  conforms to a target flow rate. However, another aspect may be employed. For example, an aspect where a flow rate measured by the flowmeter  400  is not controlled by the tube pump  100 , or an aspect where the flowmeter  400  is not provided may be employed. 
     While example embodiments have been particularly shown and described, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the embodiments encompassed by the appended claims.