Patent Application
20130343909
1. Field of the Invention
The present invention relates to a liquid feed pump used in a liquid chromatograph or the like, and more particularly to a diaphragm pump that feeds a liquid by deforming a diaphragm.
2. Description of the Related Art
Various liquid feed pumps have been proposed for use in high performance liquid chromatography. Examples of proposed methods for driving the liquid feed pump include a plunger method (Japanese Patent Application Publication No. 2007-292011), a piezoelectric method in which the diaphragm is driven by a piezoelectric element (Japanese Patent Application Publication No. 2006-118397) or the like. The piezoelectric method of driving the diaphragm is advantaged in that a sliding part such as that employed in the plunger method is absent, and therefore particle generation does not occur, meaning that a liquid feed pump having a long life can be provided. The plunger method, on the other hand, is advantaged in that high pressure discharge can be realized by reducing a surface area of an end part of a plunger (corresponding to a surface area of a cylinder end surface of a pump chamber), and a flow rate can be secured by lengthening a stroke of the plunger.
In recent years it has become necessary in high performance liquid chromatography to perform control very small flow rate at a high-pressure during analysis. On the other hand, large flow rate at a low-pressure is required when introducing and replacing an eluent, cleaning a flow passage or the like. In response to these requirements, a method of feeding a liquid at a high-pressure and very small flow rate as well as at a low-pressure and large flow rate using a splitter (a flow divider) that divides a flow of eluent while employing the plunger method, with which high pressure discharge and the flow rate can be secured, has also been proposed (Japanese Patent Application Publication No. 2003-207494).
The following documents are also pertinent to the related art: Japanese Patent Application Publication No. 2006-29314; Japanese Patent Application Publication No. H6-2663; Japanese Patent Application Publication No. H6-2664; and Japanese Patent Application Publication No. S62-159778.
However, although it is possible with the piezoelectric method to provide a long-life liquid feed pump in which particle generation does not occur, a degree of design flexibility in relation to the stroke (displacement) is small, and it is therefore difficult to apply the piezoelectric method to high performance liquid chromatography in which a liquid must be fed at a high-pressure and very small flow rate as well as at a low-pressure and large flow rate.
The present invention has been designed to solve these problems in the related art, and an object thereof is to provide a liquid feed pump that is capable of feeding a liquid at a high-pressure and very small flow rate as well as at a low-pressure and large flow rate while generating substantially no particles.
Manifestations of the present invention for solving the problems described above will be described below while illustrating effects and the like where necessary.
The first manifestation of the invention is a liquid feed pump which comprises a pump housing, a diaphragm, a reciprocating member, a driving member, a seal portion and a diaphragm receiving surface. The pump housing is formed with a columnar hole, a recessed portion surface opposing an opening portion of the hole and a peripheral portion of the hole, an intake passage having an intake port in the recessed portion surface, and a discharge passage having a discharge port in the recessed portion surface. The diaphragm forms a pump chamber together with the recessed portion surface and partitions the pump chamber from the columnar hole. The reciprocating member is reciprocatably inserted into the hole, and configured to reciprocate to press the diaphragm such that the diaphragm deforms. The driving member is configured to displace the reciprocating member periodically in a direction of reciprocation of the reciprocating member and vary a stroke of the reciprocation. The seal portion is configured to sandwich the diaphragm to seal the diaphragm in a position around an outer peripheral side of the recessed portion surface. The diaphragm receiving surface is provided between the seal portion and the opening portion, the diaphragm receiving surface of which a contact area contacting the diaphragm varies in accordance with a displacement and an internal pressure of the pump chamber. In the liquid feed pump, the contact area decreases in response to an increase in the displacement of the reciprocating member to the recessed portion surface side and increases in response to an increase in the internal pressure of the pump chamber.
This manifestation includes the diaphragm receiving surface, the contact area, i.e. the surface area of the surface that contacts the diaphragm, which varies in accordance with the displacement of the reciprocating member that deforms the diaphragm and the internal pressure of the pump chamber. Therefore, support of the diaphragm can be apportioned to the diaphragm receiving surface and the reciprocating member. The contact area between the opening portion into which the reciprocating member is inserted and the seal portion increases in response to an increase in the internal pressure of the pump chamber, and therefore a load apportioned to the diaphragm receiving surface increases in response to an increase in the internal pressure of the pump chamber such that a load apportioned to the reciprocating member can be lightened. Deformation of the diaphragm at this time is limited to the vicinity of the opening portion into which the reciprocating member is inserted, and therefore variation in a volume of the pump chamber accompanying displacement of the reciprocating member is reduced. In other words, displacement of the reciprocating member accompanying variation in the volume of the pump chamber can be increased.
Hence, with the liquid feed pump according to this manifestation, a load exerted on the reciprocating member can be lightened, and an amount by which the reciprocating member displaces in response to variation in the volume of the pump chamber can be increased. Accordingly, a load of the driving member can be reduced, and variation in the volume of the pump chamber accompanying displacement of the reciprocating member can be made very small. As a result, control can be performed at a high-pressure, very small flow rate. A low-pressure, large flow rate, on the other hand, can be realized by separating the diaphragm from the diaphragm receiving surface such that the entire diaphragm is deformed by the piston. Furthermore, at an intermediate pressure, a part of the diaphragm that separates from the diaphragm receiving surface increases in accordance with the transition from a high pressure condition to a low pressure condition. As a result, it is possible to utilize an advantage that the load apportioned to the diaphragm receiving surface is reduced, while the variation in the volume of the pump chamber corresponding to the displacement amount of the reciprocating member increases.
Hence, with this manifestation, a discharge flow rate that corresponds to a discharge pressure can be realized while automatically adjusting a size of a deformation range of the diaphragm in accordance with a pressure of a discharged fluid. As a result, a long-life liquid feed pump in which particle generation does not occur can be provided, and a dynamic range of the flow rate can be enlarged.
The second manifestation of the invention is the liquid feed pump according to the first manifestation, wherein the seal portion is configured to sandwich the diaphragm between a seal pressurization surface, which is continuously connected to the recessed portion surface, and a seal receiving surface, which is continuously connected to the diaphragm receiving surface. In the second manifestation, the seal receiving surface is connected smoothly to the diaphragm receiving surface.
In the second manifestation, the diaphragm receiving surface is formed as a surface that is connected smoothly to the seal receiving surface, and therefore the diaphragm can be caused to deform smoothly. As a result, wear on the diaphragm caused by excessive deformation of the diaphragm in the vicinity of a boundary region between the diaphragm receiving surface and the seal receiving surface can be suppressed.
The third manifestation of the invention is the liquid feed pump according to the second manifestation, wherein the seal receiving surface is an annular flat surface.
In the third manifestation, the seal receiving surface is an annular flat surface, and therefore excessive damage to the diaphragm caused by a load (a sealing load) exerted on the diaphragm in order to seal the pump chamber can be avoided. As a result, load management when sandwiching the diaphragm within the seal portion can be simplified, and diaphragm attachment by a user can be facilitated.
The fourth manifestation of the invention is the liquid feed pump according to the third manifestation, wherein the diaphragm receiving surface is formed as an annular flat surface, and the opening portion is formed to be concentric with the diaphragm receiving surface.
In the fourth manifestation, the opening portion is formed to be concentric with the diaphragm receiving surface, and therefore the reciprocating member presses a substantially central portion of a region of the diaphragm surrounded by the seal portion. Hence, a load from the reciprocating member acts on the diaphragm substantially evenly such that a large load is prevented from acting locally on the diaphragm.
The fifth manifestation of the invention is the liquid feed pump according to any one of the second to fourth manifestation, wherein the diaphragm receiving surface is formed to be coplanar with the seal receiving surface.
In the fifth manifestation, the diaphragm receiving surface is formed to be coplanar with the seal receiving surface, and therefore the operating range (deformation range) of the diaphragm can be varied smoothly from a high pressure to a low pressure.
The sixth manifestation of the invention is the liquid feed pump according to any one of the first to fifth manifestation, wherein the reciprocating member includes an end portion having a projecting curved surface as a contact surface contacting the diaphragm.
In the sixth manifestation, the reciprocating member includes the end portion having a projecting curved surface as the contact surface that contacts the diaphragm. Therefore, the diaphragm can be supported by the diaphragm receiving surface on the periphery of the opening portion of the cylinder hole while the region of the diaphragm that contacts the piston is varied by the projecting curved surface. Further, the deformation range of the diaphragm increases in accordance with the displacement amount of the piston, and therefore the discharge amount can be adjusted finely at a high pressure.
The seventh manifestation of the invention is the liquid feed pump according to any one of the first to sixth manifestation, wherein the recessed portion surface includes a recessed curved surface, which is recessed in a direction to fit into a shape of the diaphragm when the diaphragm is driven in a discharge direction, and the recessed curved surface includes an intake side groove portion configured to extend in a central direction of the recessed curved surface from the opening portion of the intake passage to communicate with the pump chamber, and a discharge side groove portion configured to extend in the central direction of the recessed curved surface from the opening portion of the discharge passage to communicate with the pump chamber.
In the seventh manifestation, the recessed portion surface that forms the pump chamber together with the diaphragm includes the recessed curved surface that opposes the diaphragm when the diaphragm is driven in the discharge direction, and therefore a large discharge amount can be realized at a low pressure. Meanwhile, the pump housing includes the intake side groove portion that extends in the central direction of the recessed curved surface from the intake port and the discharge side groove portion that extends in the central direction of the recessed curved surface from the discharge port, and therefore intake into and discharge from the pump chamber can be performed smoothly even when the diaphragm deforms greatly to the recessed curved surface side so as to approach the recessed curved surface.
The eighth manifestation of the invention is the liquid feed pump according to any one of the first to seventh manifestation, wherein the driving member includes a piezoelectric actuator configured to drive the diaphragm.
In the eighth manifestation, the driving member includes the piezoelectric actuator configured to drive the diaphragm, and therefore the diaphragm can be driven at a high frequency. As a result, it is possible to realize both a large flow rate and small pulsation.
The ninth manifestation of the invention is a flow control device for controlling a liquid feed pump. The flow control device includes the liquid feed pump according to the eighth manifestation, and a control unit configured to control a discharge flow rate of the liquid feed pump by adjusting a voltage applied to the piezoelectric actuator.
In the ninth manifestation, the discharge flow rate of the liquid feed pump is controlled by adjusting the voltage applied to the piezoelectric actuator, and therefore, by adjusting a voltage waveform, for example, control having a high degree of freedom can be realized.
The tenth manifestation of the invention is the flow control device according to the ninth manifestation, wherein the control unit is configure to apply a pulse voltage, which is a pulse-shaped voltage, to the piezoelectric actuator, and controls the discharge flow rate of the liquid feed pump by adjusting a maximum value of the pulse voltage.
In the tenth manifestation, the discharge flow rate of the liquid feed pump is controlled by adjusting the maximum value of the pulse voltage applied to the piezoelectric actuator, and therefore pulsation variation caused by variation in the discharge flow rate can be suppressed. The present inventors found that pulsation increases when a pulse width lengthens at a small flow rate, for example.
The eleventh manifestation of the invention is the flow control device according to the ninth or tenth manifestation, further includes a pressure sensor configured to measure a discharge pressure of a fluid discharged from the discharge passage, wherein the control unit is configured to restrict the stroke to be smaller than a predetermined value in accordance with the measured discharge pressure.
In the eleventh manifestation, the stroke of the piezoelectric actuator is restricted in accordance with the discharge pressure, and therefore wear on the diaphragm caused by excessive displacement of the piezoelectric actuator when the discharge pressure is high can be prevented.
The twelfth manifestation of the invention is the flow control device for controlling a liquid feed pump according to any one of the ninth to eleventh manifestation which further includes a flow rate sensor configured to measure a discharge flow rate of a fluid discharged from the discharge passage, wherein the control unit is configured to restrict a driving period of the reciprocation to be longer than a predetermined value in accordance with the measured discharge flow rate.
In the twelfth manifestation, the driving frequency of the piezoelectric actuator is restricted in accordance with the discharge flow rate, and therefore wear on the pump caused by an excessive driving frequency when the piezoelectric actuator is driven by a large stroke in order to realize a large discharge flow rate can be suppressed.
The thirteenth manifestation of the invention is the flow control device according to any one of the ninth to twelfth manifestation which further includes a flow rate sensor configured to measure a discharge flow rate of a fluid discharged from the discharge passage, wherein the control unit is configured to lengthen a driving period of the reciprocation in response to an increase in the measured discharge flow rate and shorten the driving period of the reciprocation in response to a reduction in the measured discharge flow rate in an operating mode.
The thirteenth manifestation lengthens a driving period of the reciprocation in response to an increase in the measured discharge flow rate and shortens the driving period of the reciprocation in response to a reduction in the measured discharge flow rate in an operating mode. Therefore, efficient driving by a long stroke can be realized when the discharge flow rate increases, and driving in a short driving period, in which pulsation is small, can be realized when the discharge flow rate decreases. The control unit does not have to adjust the driving period in this manner constantly, and either this operating mode may be provided as an operating mode that can be used when needed, or the liquid feed pump may be operated in this operating mode at all times. The driving period may be varied continuously or switched to one of a plurality of preset driving periods.
The fourteenth manifestation of the invention is the flow control device according to any one of the ninth to thirteenth manifestation, wherein the liquid feed pump includes a flow rate sensor configured to measure a discharge flow rate of the liquid feed pump, and the control unit is configured to perform flow rate control by feeding back a discharge flow rate measured at a plurality of measurement timings within respective driving periods of the reciprocation.
In the fourteenth manifestation, the flow rate is controlled by feeding back the discharge flow rate measured (sampled) at the plurality of measurement timings within the respective driving periods of the reciprocation. Therefore, measurement errors caused by timing (or phase) deviation within the driving period can be suppressed, and accurate feedback control can be realized.
The discharge flow rates measured at the plurality of measurement timings may be averaged for use, or the discharge flow rate may be estimated by estimating a waveform of the discharge flow using a representative value obtained at a preset timing. Further, taking into consideration a calculation time of a control law, a feedback value may be reflected in adjusting the pulse voltage that is performed after a plurality of periods from a measured period.
Note that the present invention may be realized not only as a liquid feed pump and a flow control device, but also as a flow control method, a computer program for realizing the flow control method, and a storage medium storing the computer program.
Specific embodiments of the present invention will be described below with reference to the drawings. The embodiments relate to a liquid feed pump used in high pressure gas chromatography.
The liquid feed pump 100 is a diaphragm pump including a pump body 110, check valves 126 and 127, a metallic diaphragm 180, and an actuator 150 that drives the diaphragm 180. An inlet side internal flow passage 122, an outlet side internal flow passage 124, and the check valves 126 and 127 are formed in the pump body 110 as a flow passage through which the eluent flows. The pump body 110 can be manufactured using a metal or a PEEK material, for example.
The check valve 126 allows the eluent to flow only from an inflow port 121 (an IN port) in the direction to the inlet side internal flow passage 122, and prohibits the eluent from flowing in an opposite direction. The check valve 127, meanwhile, allows the eluent to flow only from the outlet side internal flow passage 124 in the direction to a discharge port 125 (an OUT port), and prohibits the eluent from flowing in an opposite direction.
Note that in
The pump body 110 has a columnar shape including a truncated cone-shaped recessed portion surface in a central position on one end surface. As shown in
Opening portions of the inlet side internal flow passage 122 and the outlet side internal flow passage 124 are formed in an outer edge portion of the inclined surface 112 of the recessed portion. The opening portions are disposed in mutually opposing positions on either side of the flat end portion 115. More specifically, the inlet side internal flow passage 122 and the outlet side internal flow passage 124 are disposed in a vertical relationship on either side of a center of the flat end portion 115. An intake side groove portion 113 extending upward in
With this configuration, communication between the inlet side internal flow passage 122 and the outlet side internal flow passage 124 can be secured sufficiently in the pump chamber 123 even when the diaphragm 180 displaces so as to approach the inclined surface 112. Note that the inlet side internal flow passage 122 and the outlet side internal flow passage 124 will also be referred to respectively as an intake passage and a discharge passage.
The pump base 130 takes a donut shape in which a cylinder hole 134 as a columnar hole is formed in a central axis position. Truncated cone-shaped projecting portion surfaces 132, 133 and 135 and an opening portion 136 of the cylinder hole 134 are formed in one end surface of the pump base 130, and a truncated cone-shaped recessed portion surface 131 is formed in another surface. As shown in
The diaphragm 180 is sandwiched between the pump body 110 and the pump base 130. A seal pressurization surface 111 constituted by an annular flat surface is formed on a periphery of the inclined surface 112 of the pump body 110. An inclined surface 116 is formed on an outer periphery of an outer edge of the seal pressurization surface 111, and the seal pressurization surface 111 is formed as an annular projecting portion. The annular flat surfaces 132 and 133 of the pump base 130, meanwhile, form an integrated flat surface having two regions, namely a seal receiving surface 132, which is parallel to the seal pressurization surface 111, and the diaphragm receiving surface 133, which opposes the inclined surface 112. By sandwiching the diaphragm 180 between the seal pressurization surface 111 and the seal receiving surface 132, the pump chamber 123 is sealed from the outside.
Note that the seal pressurization surface 111 and seal receiving surface 132 will also be referred to as a seal portion. Further, a role of the diaphragm receiving surface 133 will be described below.
Hence, the pump chamber 123 is configured as a sealed space that can be varied in volume by displacing the diaphragm 180. With this configuration, the liquid feed pump 100 can function as a pump that performs intake from the check valve 126 and discharge from the check valve 127 by periodically varying the volume of the pump chamber 123. Note that the pump base 130 and pump body 110 will also be referred to as a pump housing.
The volume of the pump chamber 123 can be varied by driving the diaphragm 180 to deform using the actuator 150. The actuator 150 includes a driving member 140 having a piston 144 that drives the diaphragm 180, and the pump base 130. Note that the piston 144 will also be referred to as a reciprocating member.
The driving member 140 includes the piston 144, the slide bearing 137b, a biasing spring 145, a laminated piezoelectric actuator 141, an actuator housing 147, an adjuster 143, a steel ball 142, a piezoelectric actuator attachment portion 146, and a double nut N1 and N2. The piston 144 is a columnar member having a flange 144f that extends in a radial direction on one end portion (a left side end portion in
Driving force is applied to the piston 144 from the laminated piezoelectric actuator 141 via the steel ball 142 and the adjuster 143. The steel ball 142 is sandwiched to be capable of sliding between a recessed portion formed in a central position of the adjuster 143, which is attached to a central portion of the flange 144f, and a recessed portion formed in a central position of the laminated piezoelectric actuator 141. As a result, eccentric errors and tilting between the laminated piezoelectric actuator 141 and the piston 144 can be absorbed. The biasing spring 145 biases the piston 144 in a direction for reducing driving force applied to the diaphragm 180 in the flange 144f.
The laminated piezoelectric actuator 141 is stored in a columnar inner hole 149 formed in an interior of the actuator housing 147, and attached to the actuator housing 147 by a position adjustment nut N1 and a fixing nut N2 via the piezoelectric actuator attachment portion 146. By adjusting an amount (a length) by which a male screw S formed on an outer periphery of the actuator housing 147 is screwed to a female screw formed on an inner periphery of the position adjustment nut N1, a relative positional relationship between the laminated piezoelectric actuator 141 and the pump base 130 in a driving direction of the piston 144 can be adjusted.
This adjustment can be absorbed by a clearance CL between the actuator housing 147 and the piezoelectric actuator attachment portion 146. The fixing nut N2 functions as a double nut together with the position adjustment nut N1 so that the position of the piezoelectric actuator attachment portion 146 can be fixed following adjustment of the positional relationship.
During the high pressure operation, the diaphragm 180 is supported by the diaphragm receiving surface 133 and the piston 144. In other words, the diaphragm 180 is capable of transferring a load received from the high-pressure eluent in the pump chamber 123 to the diaphragm receiving surface 133 and the piston 144. More specifically, a circular range having a diameter φB in a central position of the diaphragm 180 is supported by the piston 144, while an annular range obtained by excluding the circular range having the diameter φB from a circular range having a diameter φA is supported by the diaphragm receiving surface 133.
Hence, during the high pressure operation, a deformation range (an operating range) of the diaphragm 180 can be limited to the circular range having the diameter φB, and therefore the diaphragm 180 functions as a small diaphragm substantially including the circular range having the diameter φB. When the diaphragm is small, the diaphragm 180 can be driven appropriately by the laminated piezoelectric actuator 141 against the load applied to the diaphragm 180 even when the pressure of the eluent is high.
Further, deformation of the diaphragm 180 under high pressure is limited to the vicinity of the opening portion 136 into which the piston 144 is inserted, and therefore variation in the volume of the pump chamber 123 accompanying displacement of the piston 144 is reduced. As a result, an amount by which the piston 144 displaces in response to variation in the volume of the pump chamber 123 can be increased, making it clear that the operating condition of the diaphragm 180 corresponds to a deformed condition suitable for control at a high-pressure, very small flow rate.
During the low pressure operation, on the other hand, the diaphragm 180 is supported by the piston 144 alone. During the low pressure operation, the diaphragm 180 separates from the diaphragm receiving surface 133 to be capable of deforming greatly in the interior of the pump chamber 123, and therefore the diaphragm 180 functions as a large diaphragm substantially including the circular range having the diameter φA. When the diaphragm is large, the eluent can be supplied in a large discharge amount by the laminated piezoelectric actuator 141, and therefore the pipes or the like can be cleaned smoothly.
The liquid feed pump 100a according to the first comparative example differs from the liquid feed pump 100 according to the first embodiment in that the diaphragm receiving surface 133 is not provided, and a diameter of the cylinder hole 134 is enlarged to a region of the diaphragm receiving surface 133 such that a cylinder hole 134a is formed. Since the liquid feed pump 100a according to the first comparative example does not include the diaphragm receiving surface 133 of the first embodiment, the diaphragm 180 functions as a large diaphragm during the low pressure operation.
More specifically, as shown in
Hence, during the high pressure operation, the diaphragm receiving surface 133 serves to suppress formation of the unnecessary bend 180k in the diaphragm 180 and prevent an excessive load from being exerted on the laminated piezoelectric actuator 141.
The liquid feed pump 100b according to the second comparative example differs from the liquid feed pump 100 according to the first embodiment in that the diaphragm receiving surface 133 is constituted by a diaphragm receiving surface 133a positioned in a direction (a left side direction in the drawing) separating from the pump chamber 123. The diameter of the piston 144, meanwhile, is identical to that of the liquid feed pump 100 according to the first embodiment.
At a low pressure, as shown in
Hence, a striking effect is obtained by forming the diaphragm receiving surface 133 according to the first embodiment as an annular flat surface connected integrally to the seal receiving surface 132. Note, however, that the diaphragm receiving surface 133 does not necessarily have to be formed as an annular flat surface connected integrally to the seal receiving surface 132, and may be disposed in the vicinity of the seal receiving surface 132 in the displacement direction of the piston 144. For example, the diaphragm receiving surface 133 may be configured to tilt toward a side (the right side in
At a high pressure, the displacement amount (stroke) of the piston 144 is restricted, and therefore a displacement range (also referred to as a deformation range or an operating range) of the diaphragm 180 is limited to the circular range having the diameter φB. The displacement amount of the piston 144 is restricted automatically as an internal pressure of the pump chamber 123 increases, and depending on specifications of the laminated piezoelectric actuator 141, an excessive load may be prevented from acting on the diaphragm 180 by switching a control law to a law used at a high pressure, for example.
At an intermediate pressure, the displacement amount (stroke) of the piston 144 is increased such that the operating range of the diaphragm 180 increases to a circular range having a diameter φC. The operating range of the diaphragm 180 increases as the pressure of the eluent decreases. At a low pressure, the displacement amount (stroke) of the piston 144 is increased further, and the operating range of the diaphragm 180 is increased to an entire region, or in other words the circular range having the diameter φA.
Hence, with the liquid feed pump 100 according to the first embodiment, the operating range of the diaphragm 180 can be varied automatically in accordance with a discharge pressure of the eluent. More specifically, the operating range of the diaphragm 180 narrows as the internal pressure of the pump chamber 123 rises and widens as the internal pressure of the pump chamber 123 falls.
The liquid feed pump 100 can be controlled by a control system in which a measured value of a discharge flow rate is used as a feedback amount and an operating amount is set as a voltage applied to the laminated piezoelectric actuator 141, for example. In this control system, when the measured value of the discharge flow rate is smaller than a target value, an operation is performed in a direction for increasing the displacement amount of the piston 144, and when the measured value of the discharge flow rate is larger than the target value, an operation is performed in a direction for reducing the displacement amount of the piston 144. Note that a specific configuration of the control system according to this embodiment will be described below.
Hence, with the liquid feed pump 100 according to the first embodiment, the diaphragm 180 can be driven as a diaphragm having an appropriate operating range substantially corresponding to the discharge pressure of the eluent. As a result, the liquid feed pump 100 can be caused to function as a diaphragm pump having a wide dynamic range extending from high pressure/small amount discharge to low pressure/large amount discharge.
The operating restriction relating to the discharge pressure is set on the basis of following knowledge and analysis results obtained by the present inventors. As described above, the liquid feed pump 100 has a favorable characteristic whereby the operating range of the liquid feed pump 100 is varied automatically in accordance with the discharge pressure of the eluent.
However, the present inventors found that, depending on settings of the specifications of the laminated piezoelectric actuator 141 (excessive driving force, for example), the diaphragm 180 may become worn due to excessive displacement of the diaphragm 180 (substantially displacement of the piston 144). More specifically, the present inventors found that when the operating condition of
The operating restriction relating to the discharge flow rate is set on the basis of following experiments and analysis conducted by the present inventors. As described above, the liquid feed pump 100 has a favorable characteristic whereby the displacement amount of the diaphragm 180 is varied automatically in accordance with the discharge pressure of the eluent. In other words, the displacement amount (stroke) of the diaphragm 180 decreases automatically in response to an increase in the discharge pressure of the eluent.
However, the present inventors found that a pulsation effect increases as the discharge flow rate decreases. The reason for this is that when the discharge flow rate decreases, a pulsation rate increases, making pulsation apparent. Further, in high performance liquid chromatography, measurement is performed during the high pressure operation, in which the discharge flow rate is small, and it is therefore desirable to reduce pulsation. On the other hand, the present inventors found that when pump operations (operations of the laminated piezoelectric actuator 141 and the check valves) are reduced by reducing the discharge flow rate, the driving frequency can be increased.
In the high pressure operation mode, on the other hand, as shown in
Hence, with the liquid feed pump 100 according to the first embodiment, the driving frequency of the diaphragm 180 can be switched in accordance with the discharge flow rate. In so doing, pulsation can be suppressed by increasing the driving frequency at the small discharge flow rate Q2 while keeping the driving frequency of the diaphragm within the operating range at the large discharge flow rate Q1. The discharge flow rate Q2 of the high pressure operation is the flow rate used during measurement, and it is therefore very important to reduce pulsation.
Note that the driving frequency of the diaphragm does not necessarily have to be adjusted in response to a switch between the low pressure operation mode and the high pressure operation mode, and may be adjusted in response to modification of a set flow rate during the high pressure operation, for example. The set flow rate is a discharge flow rate set by a user in accordance with a measurement subject, a measurement aim, or the like, and serves as a target value in the control system to be described below.
By increasing the driving frequency of the diaphragm 180, the discharge flow rate can be increased while both reducing pulsation and maintaining the stroke of the diaphragm 180, and as a result, a range of the set flow rate of the liquid feed pump 100 during the high pressure operation can be enlarged. In other words, pulsation during measurement can be reduced even further, leading to an improvement in measurement precision, and moreover, the dynamic range of the discharge flow rate of the liquid feed pump 100 during the high pressure operation can be enlarged.
At a time t1, the liquid feed pump 100 starts to drive the piston 144 using the laminated piezoelectric actuator 141 in response to the rise of the driving voltage W1. Accordingly, the piston 144 starts to displace the diaphragm 180 such that the volume of the pump chamber 123 begins to decrease, and as a result, the internal pressure of the pump chamber 123 rises. When the internal pressure of the pump chamber 123 exceeds a pressure in the discharge port 125, the check valve 127 opens, whereby chemical discharge begins.
At a time t2, movement of the piston 144 in response to the rise of the driving voltage W1 ends such that the piston 144 stops. Accordingly, the volume of the pump chamber 123 stops varying, and therefore chemical discharge from the pump chamber 123 ceases and the check valve 127 closes.
At a time t3, the liquid feed pump 100 starts to drive the piston 144 in an opposite direction using the laminated piezoelectric actuator 141 in response to the fall of the driving voltage W1. Accordingly, the internal pressure of the pump chamber 123 falls. When the internal pressure of the pump chamber 123 falls below a pressure in the inflow port 121, the check valve 126 opens, whereby chemical inflow begins.
The discharge flow rate C3 is a flow rate supplied to a measurement instrument prepared on the user side, such as an injector or a column. The discharge flow rate C3 is a value measured by the flow rate sensor 50 downstream of a volume damper 80 and an orifice 51, to be described below. Pulsation in the discharge flow rate C3 is reduced by the volume damper 80 and the orifice 51.
The liquid feed pump 100 can reduce pulsation in the discharge flow rate by increasing a pulse frequency of the driving voltage W1. The laminated piezoelectric actuator 141 can be driven at several kHz, for example. Note, however, that when a limit on a responsiveness of the check valves 126 and 127 is lower than the driving frequency of the laminated piezoelectric actuator 141, the driving frequency of the laminated piezoelectric actuator 141 may be set on the basis of the responsiveness of the check valves 126 and 127.
The liquid feed pump 100 suctions the eluent from the solvent storage jar 60, and supplies the suctioned eluent to the load 30 via the volume damper 80, the orifice 51, and the flow rate sensor 50, in that order. The volume damper 80 and the orifice 51 serve to reduce pulsation. The flow rate of the eluent supplied to the load 30 is measured by the flow rate sensor 50, and a resulting measurement value is transmitted to the control circuit 10. The pressure sensor 40 measures a pressure of the eluent between the volume damper 80 and the orifice 51. Note that the control circuit 10 and the driver circuit 20 will also be referred to as a control unit. The control unit, the pressure sensor 40, and the flow rate sensor 50 will also be referred to as a control device.
The control circuit 10 adjusts a voltage value of the driving voltage by operating the driver circuit 20 in accordance with a flow rate command signal and the measurement value of the flow rate sensor 50, and performs feedback control for bringing the measurement value of the flow rate sensor 50 close to the flow rate command signal. This feedback control is performed within a range of allowable displacement amounts (allowable driving voltages) and allowable driving frequencies (voltage pulse frequencies) set in advance on the basis of the operating restrictions (see
When eluent is to be introduced into the high performance chromatography device 90 or the eluent is to be replaced, liquid is discharged into the waste liquid jar 70 by opening the waste liquid valve 71. At this time, the liquid feed pump 100 is required to perform discharge at a low-pressure, large flow rate.
A one-part elastic adhesive having modified silicone resin or epoxy modified silicone resin as a main component or a two-part elastic adhesive constituted by a base resin (epoxy resin) and a hardener (modified silicone resin), for example, may be used to form the elastic adhesion layer 183.
In the diaphragm 180b according to the comparative example, the laminated first metal plate 181 and second metal plate 182 respectively have a thickness t, and therefore pressure resistance is doubled. The reason for the increase in pressure resistance is that the pressure resistance is dependent on a tensile strength in the in-plane direction (an expansion direction) of the first metal plate 181 and others, and therefore the diaphragm 180a has substantially equal pressure resistance to a metal plate material having twice the thickness on each layer.
Meanwhile, since the first metal plate 181 and the second metal plate 182 are simply laminated together in the diaphragm 180b according to the comparative example, a bending rigidity of them is obtained by adding together the respective bending rigidity values of the first metal plate 181 and the second metal plate 182. In other words, the bending rigidity of the diaphragm 180b according to the comparative example is twice the bending rigidity of the first metal plate 181.
However, since the diaphragm 180b according to the comparative example is not adhered, the diaphragm 180b is dismantled during diaphragm cleaning. Hence, the present inventors found that a lamination condition of the diaphragm 180b varies when the diaphragm 180b is reassembled following cleaning. Moreover, the present inventors found that during assembly of the diaphragm, foreign matter becomes trapped between the first metal plate 181 and the second metal plate 182, causing a durability of them to deteriorate.
The diaphragm 180a according to the second embodiment differs in that the first metal plate 181 and the second metal plate 182 are adhered to each other. Since the pressure resistance is dependent on the tensile strength in the in-plane direction (a lengthwise direction) of the first metal plate 181 and others, the pressure resistance can be doubled regardless of whether or not the layers are adhered.
Meanwhile, in the diaphragm 180a according to this embodiment, the first metal plate 181 and the second metal plate 182 are adhered to each other, and therefore, assuming that deviation and deformation does not occur between the layers, the bending rigidity of the diaphragm 180a is increased eightfold. The reason for this increase is that the first metal plate 181 and the second metal plate 182 behave as a single plate material having twice the thickness.
In the diaphragm 180a, however, the first metal plate 181 and the second metal plate 182 are adhered to each other by the elastic adhesion layer 183 possessing elasticity in a direction for displacing the first metal plate 181 and the second metal plate 182 relative to each other in the in-plane direction of them, and therefore this excessive bending rigidity can be avoided. The reason for this is that since the first metal plate 181 and the second metal plate 182 are adhered to each other by the elastic adhesion layer 183 that possesses elasticity in a direction for displacing the first metal plate 181 and the second metal plate 182 relative to each other in the in-plane direction of them, the bending rigidity of the diaphragm 180a is close to that of the diaphragm 180b according to the comparative example.
By constructing the diaphragm 180a such that the first metal plate 181 and the second metal plate 182 are adhered to each other, the diaphragm need not be dismantled during cleaning and other maintenance. As a result, the diaphragm 180a can be improved in maintainability, and the problem of variation in the lamination condition of the diaphragm 180a during reassembly following maintenance can be solved. Hence, calibration of the diaphragm 180a following dismantling and maintenance such as cleaning can be simplified or eliminated.
Further, during assembly of the diaphragm, the problem of a reduction in durability due to foreign matter becoming trapped between the first metal plate 181 and the second metal plate 182 can be suppressed. Moreover, a maximum distortion of the first metal plate 181 and the second metal plate 182 can be reduced, enabling an improvement in the durability of the diaphragm 180a.
Note, however, that a thickness of the elastic adhesion layer 183 is preferably no greater than 10 μm. The reason for this is that the elastic adhesion layer 183 may be deformed in an out-of-plane direction (a thickness direction) of the diaphragm 180a by the pressure of the pump chamber 123 such that the volume of the pump chamber 123 varies, and as a result, the discharge amount may become unstable.
The pair of keyholes K1h and K2h are disposed in opposing positions (positions located on a straight line) relative to a central position of the diaphragm 180c. The pair of keyholes K1h and K2h are disposed thus so that a large distance is secured between the pair of keyholes K1h and K2h, enabling an increase in a positioning precision obtained with the pair of keyholes K1h and K2h. The keyholes K1h and K2h are provided respectively with biasing portions K1s and K2s. The biasing portions K1s and K2s are formed as a plurality of elastic projections provided on an inner edge of the keyholes K1h and K2h. When keys (parts of a fluid instrument) K1 and K2 projecting from the pump body 110 are inserted into the keyholes K1h and K2h, the biasing portions K1s and K2s respectively engage with the keys K1 and K2. As a result, the diaphragm 180c is prevented from falling out of the pump body 110, and assembly is facilitated. In a condition where the biasing portions K1s and K2s are engaged with the keys K1 and K2, the biasing portions K1s and K2s bias the respective keys K1 and K2 such that reaction force generated by the respective engagements is canceled out.
The through holes dh1 to dh6, meanwhile, are disposed in an annular shape at an uneven pitch. More specifically, an angle α between the through hole dh1 and the through hole dh6 is set at a different angle to an angle β between the through hole dh1 and the through hole dh2. As a result, the keys K1 and K2 can be prevented from being attached to the respective keyholes K1h and K2h in reverse. Note, however, that the through holes dh1 to dh6 do not necessarily have to be arranged in an annular shape. In other words, a shape (in this case, a hexagon) formed by linking central positions of the through holes dh1 to dh6 may be any shape that is asymmetrical relative to a line segment in any direction in the plane of the diaphragm 180c. Thus, erroneous attachment of the diaphragm 180c can be suppressed.
Further, detachment holes R1 and R2 are formed in the pump body 110. The detachment holes R1 and R2 are holes for inserting rods (not shown) used to detach the diaphragm 180c from the pump body 110 during dismantling. Thus, the user can detach the diaphragm 180c easily during dismantling by inserting the rods (not shown) into the detachment holes R1 and R2 in the pump body 110 from an opposite side of the diaphragm 180c.
More specifically, the metal plates 186 and 187 are adhered to either side of the attachment plate material 189 formed of a stainless steel metal plate via elastic adhesion layers 186a and 187a, whereupon the metal plates 185 and 188 are adhered respectively to the metal plates 186 and 187 via elastic adhesion layers 185a and 188a. Hence, in this embodiment, an equal number of the four nickel/cobalt alloy metal plates 185 to 188 are attached to both surfaces of the stainless steel attachment plate material 189. Note that silicone film of several μm or the like, for example, may be used as the elastic adhesion layers 185a, 186a, 187a and 188a. Further, the metal plate 188 forms a surface opposing the pump chamber 123, and is therefore preferably polished.
Nickel/cobalt alloy exhibits superior elasticity, strength, corrosion resistance, thermal resistance, and constant elasticity. Moreover, nickel/cobalt alloy is non-magnetic and exhibits superior durability. Hence, nickel/cobalt alloy is a suitable material for a metal diaphragm. Stainless steel, meanwhile, is highly workable and exhibits superior corrosion resistance, tenacity, and ductility. In particular, the workability of the stainless steel serving as the material of the attachment plate material 189 facilitates work for forming the keyholes K1h and K2h and the through holes dh1 to dh6.
The attachment plate material 189 is used to reattach the diaphragm 180c following dismantling of the liquid feed pump 100a for cleaning. The four nickel/cobalt alloy metal plates 185 to 188, meanwhile, are members that function as the diaphragm. The four nickel/cobalt alloy metal plates 185 to 188 and the stainless steel attachment plate material 189 are sandwiched between the seal pressurization surface 111 and the seal receiving surface 132.
Hence, with the multilayer diaphragm according to this embodiment, the number of laminated layers can be set freely in consideration of the pressure resistance and operability of the diaphragm.
The embodiments described in detail above have the following advantages.
(1) According to the above embodiments, a long-life liquid feed pump in which particle generation does not occur can be realized.
(2) According to the above embodiments, a liquid feed pump that feeds liquid at both a high-pressure, very small flow rate and a low-pressure, large flow rate (i.e. that has a wide dynamic range) can be realized.
(3) In the liquid feed pump according to the above embodiments, the diaphragm receiving surface is formed to be coplanar with the seal receiving surface, and therefore the operating range (deformation range) of the diaphragm can be varied smoothly from a high pressure to a low pressure.
(4) In the liquid feed pump according to the above embodiments, the opening portion of the cylinder hole is formed to be concentric with the diaphragm receiving surface, and therefore the piston presses a substantially central portion of the region of the diaphragm surrounded by the seal pressurization surface and the seal receiving surface. Hence, the load from the piston acts on the diaphragm substantially evenly such that a large load can be prevented from acting locally on the diaphragm.
(5) In the liquid feed pump according to the above embodiments, the center of the opening portion of the cylinder hole is aligned with the center of the recessed portion surface in the axial direction of the cylinder hole. When the diaphragm deforms, therefore, the central portion of the pump chamber varies in volume, and as a result, the pressure in the pump chamber varies in a balanced manner such that the eluent can be fed smoothly.
(6) In the control device according to the above embodiments, the displacement amount of the piezoelectric actuator is restricted in accordance with the discharge pressure, and therefore damage to the diaphragm caused by excessive displacement of the piezoelectric actuator at a high pressure can be prevented.
(7) With the multilayer diaphragm according to the above embodiments, both superior pressure resistance and flexibility can be achieved.
(8) With the multilayer diaphragm according to the above embodiments, erroneous attachment is suppressed, enabling an improvement in maintainability.
(9) With the multilayer diaphragm according to the above embodiments, calibration following dismantling and cleaning can be simplified or eliminated.
The present invention is not limited to the above embodiments and may be implemented as follows, for example.
(1) In the above embodiments, the two keyholes K1h and K2h are used for positioning, but for example, three or more keyholes may be provided, as in a diaphragm 180d according to a first modified example.
In the diaphragm 180d according to the first modified example, a third keyhole K3h is formed in addition to the keyholes K1h and K2h. In so doing, a situation in which the diaphragm 180d is rotated 180 degrees about a central axis thereof such that the key K1 and the key K2 are inserted into the wrong keyholes K1h and K2h (the opposite keyholes) can be prevented. In other words, a situation in which the key K1 and the key K2 are inserted respectively into the keyhole K2h and the keyhole K1h can be prevented.
Further, the third keyhole K3h is formed in a position deviating from a vertical bisector of a line linking central positions of the keyholes K1h and K2h. In other words, the keyholes K1h, K2h and K3h are arranged in the diaphragm 180d in an annular shape at an uneven pitch. In so doing, a situation in which the keys K1 and K2 are inserted into the keyholes K2h and K1h in reverse after the diaphragm 180d has been reversed and rotated 180 degrees can be prevented.
Hence, by providing the keys and keyholes in the diaphragm 180d according to the first modified example, various types of erroneous attachment possibly occurring when the diaphragm 180d is rotated 180 degrees or reversed and rotated 180 degrees can be prevented. The keys K1, K2 and K3 and keyholes K1h, K2h and K3h will also be referred to as positioning portions. The keys K1, K2 and K3 will be referred to as positioning projecting portions. The keyholes K1h, K2h and K3h will be referred to as positioning holes. Note that the keyholes K1h, K2h and K3h do not necessarily have to be arranged in a ring shape. In other words, a shape (in this case, a triangle) formed by linking the central positions of the keyholes K1h, K2h and K3h may be any shape that is asymmetrical relative to a line segment in any direction in the plane of the diaphragm 180d. Thus, erroneous attachment of the diaphragm 180d can be suppressed.
(2) In the above embodiments, the diaphragm 180c is prevented from becoming detached from the pump body 110 by the biasing portions K1s and K2s attached to the keyholes K1h and K2h. For example, however, biasing portions for preventing detachment may be provided in a location other than the keyholes K1h and K2h, as in a diaphragm 180e according to a second modified example.
(3) In the above embodiments, the diaphragm receiving surface is formed to be coplanar with the seal receiving surface, but the diaphragm receiving surface does not necessarily have to be coplanar. When the diaphragm receiving surface is formed to be coplanar, however, the operating range (deformation range) of the diaphragm can be varied smoothly from a high pressure to a low pressure. The diaphragm receiving surface 133 may be configured as desired as long as a contact area of the diaphragm receiving surface 133, which is a surface area of a surface that contacts the diaphragm 180, varies in accordance with the internal pressure of the pump chamber 123.
(4) The seal receiving surface is flat in the above embodiments, but may be curved. When the seal receiving surface is flat, however, excessive damage to the diaphragm caused by a load (a sealing load) exerted on the diaphragm in order to seal the pump chamber can be avoided. As a result, the sealing load can be managed more easily, and therefore torque management of the bolts B1 to B6 on the user side can be facilitated during reattachment of the diaphragm.
(5) The surface of the piston that contacts the diaphragm is a projecting curved surface in the above embodiments, but may be a flat surface. When the contact surface with the diaphragm is a projecting curved surface, however, the diaphragm can be supported by the diaphragm receiving surface on the periphery of the opening portion 136 of the cylinder hole 134 while the region of the diaphragm that contacts the piston is varied by the projecting curved surface. Further, the deformation range of the diaphragm increases in accordance with the displacement amount of the piston, and therefore the discharge amount can be adjusted finely at a high pressure. The projecting curved surface may be formed in a workable spherical surface shape, for example.
(6) The intake port and the discharge port are disposed in opposing positions in the above embodiments, but may be disposed otherwise. When the intake port and the discharge port are disposed in opposing positions, however, the liquid feed pump can be disposed such that the intake port and the discharge port are provided respectively on a lower side and an upper side in a vertical direction, for example, and in so doing, liquid retention can be eliminated, making it easier to replace the liquid and remove air bubbles.
(7) The diaphragm is driven by a piezoelectric actuator in the above embodiments, but may be driven using another driving method. When the diaphragm is driven by a piezoelectric actuator, however, the diaphragm can be driven at a high frequency such that the discharge amount can be secured by a small displacement of the diaphragm, and pulsation can be reduced.
(8) In the above embodiments, the entire diaphragm receiving surface contacts the diaphragm when driving is not underway. However, at least a part of the diaphragm receiving surface may be separated from the diaphragm when the discharge pressure is low, for example, or this condition may be set as a permanent deformation during an operation. The diaphragm receiving surface may be configured as desired as long as the diaphragm is supported thereby when the internal pressure of the pump chamber increases so that the load exerted on the piston is lightened.
When the internal pressure of the pump chamber increases, the diaphragm receiving surface may lighten the load exerted on the piston by bearing a load obtained by multiplying the internal pressure of the pump chamber by a surface area of a contact surface between the diaphragm and the diaphragm receiving surface. Note that the surface area of the contact surface between the diaphragm and the diaphragm receiving surface will also be referred to as a contact area.
(9) In the above embodiments, the diaphragm is not connected to the piston, and the diaphragm is deformed when pressed by the piston. However, the diaphragm may be connected to the piston. Note that when the diaphragm and the piston are connected, the diaphragm and an apex of the piston are preferably connected by a single point (or a sufficiently small region).
(10) In the above embodiments, the multilayer diaphragm is used in a liquid feed pump, but the multilayer diaphragm may be used in a flow control valve, for example. The multilayer diaphragm may be used widely in fluid instruments employing diaphragms.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-100011 | Apr 2011 | JP | national |
This application is a Continuation of International Patent Application No. PCT/JP2012/059254, filed on Apr. 4, 2012, which claims priority to Japanese Patent Application No. 2011-100011, filed on Apr. 27, 2011, each of which is hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2012/059254 | Apr 2012 | US |
| Child | 14012820 | US |
