Drive screw device, liquid delivery mechanism, and liquid delivery method

This drive screw device is provided with: a drive screw; a drive unit which causes the drive screw to rotate; a slider which moves along the drive screw by means of the rotation of the drive screw; and an external load which is provided on the drive screw and applies a rotational load to the drive screw. By this means it is possible to provide a drive screw device with which there is little pressure variation even if a frictional force varies.

TECHNICAL FIELD

The present invention relates to a capillary electrophoresis device and a liquid delivery mechanism suitable for the electrophoresis device. Particularly, the invention relates to an electrophoresis device which fills a capillary or a capillary array with a gel or a fluid polymer solution which is an electrophoretic medium to be a separation medium and a pump mechanism suitable for the electrophoresis device.

BACKGROUND ART

PTL 1 and PTL 2 disclose an electrophoresis device in which a capillary array including sixteen capillaries is used. The capillary is a thin tube of which an inner diameter is tens to hundreds of microns, and the main material is quartz. The outside of the quartz is coated with polyimide of which a thickness is about tens of microns, so as to impart mechanical strength. During electrophoresis, the capillary is used in the state of being filled with a component serving as a sample separation medium.

As the electrophoresis separation medium, a non-fluid crosslinking polymer was used. However, an uncrosslinked fluid polymer solution excellent in productivity and performance stability becomes the mainstream in recent years. PTL 1 discloses a pump mechanism for filling the capillary with gel or polymer which is a sample separation medium. As the pump mechanism, a glass syringe is disclosed. In addition to the glass syringe, an electrophoresis device which includes the pump mechanism driving a plunger is also present.

In the electrophoresis device, the filling is performed at a high pressure to fill the capillary of which an inner diameter is tens to hundreds of microns with a fluid polymer having high viscosity generally. This is because when the pressure is low, it takes time to fill the polymer, and the processing capability of the device is deteriorated. In addition, the polymer is filled at each measurement in order to prevent the variation and deterioration of the performance. The pump mechanism capable of stably generating a high pressure is required in order to shorten an analysis time and improve the processing capability of the device.

In PTL 3, a method of using a spring is disclosed as a method of generating the pressure for polymer filling. In the method, the characteristic of the spring is used such that a force of extending at the time when the spring is compressed is used to feed liquid.

In PTL 2, a method of using a stop torque of a motor is disclosed as a method of generating the pressure for the polymer filling. In the method, the characteristic of a DC motor is used in which as the load torque increases, the number of rotations decreases, and eventually the rotation stops.

Specifically, the pressure is controlled by repeating the following steps. (1) When the pressure in the syringe increases to a desired pressure, the load torque increases, and the DC motor stops. (2) When the polymer advances into the capillary, and the pressure in the syringe decreases, the motor starts to rotate. In this case, the torque characteristic is controlled by adjusting the value of the current flowing in the motor such that the motor stops at a desired pressure. The desired pressure is typically set to such a degree that leakage and damage do not occur in the flow passage system. In addition, an electrophoresis device is also provided in which a method similar to the above method is realized by a stepping motor.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

An object to the invention is to provide a device and a method in which a pressure at a time of filling a capillary array with a phoretic medium is stabilized, and a variation of a liquid delivery amount is reduced.

Solution to Problem

A drive screw device of the invention includes: a drive screw; a drive unit which causes the drive screw to rotate; a slider which moves along the drive screw by means of the rotation of the drive screw; and an external load which is provided on the drive screw and applies a rotational load to the drive screw.

Advantageous Effects of Invention

The pressure at the time of filling the capillary array with the phoretic medium can be stabilized, and the variation of the liquid delivery amount can be reduced.

DESCRIPTION OF EMBODIMENTS

In an electrophoresis device, a capillary of which an inner diameter is tens to hundreds of microns is filled at a high pressure to fill a fluid phoretic medium having high viscosity generally. This is because when the pressure is low, it takes time to fill the phoretic medium, and the processing capability of the device is deteriorated. In addition, the phoretic medium is filled at each measurement in order to prevent the variation and deterioration of the performance. The pump mechanism capable of stably generating a high pressure is required in order to shorten an analysis time and improve the processing capability of the device.

Since expensive fluid polymer is filled generally, desirably, the liquid delivery amount of the phoretic medium is stabilized, and the amount of consumption is suppressed, so as to suppress a running cost. For this reason, it is necessary to stabilize the liquid delivery pressure.

In the plunger actuator of the conventional electrophoresis device, the generated torque of the motor is converted into a thrust by a drive screw, and a pressure is generated in a phoretic medium container by the thrust, so as to feed a liquid. In the process of converting the generated torque into the thrust, as the frictional force specific to the drive screw becomes larger, the generated thrust is affected further by the fluctuation of the frictional force. However, the liquid delivery reaction can be held by the frictional force.

In a device which injects several μL of phoretic medium, a seal diameter of a syringe type phoretic medium container is small. Thus, the generated pressure is largely affected by the fluctuation of the generated thrust. Since the fluctuation of the generated pressure results in the variation of the liquid delivery amount of the phoretic medium, the control of the frictional force is important also in the stabilization of the liquid delivery amount.

The frictional force of the drive screw is fluctuated when the drive screw is used continuously. The frictional force is affected by the surface state. Thus, a countermeasure not to change a machine tool or the like is performed in order to manage the surface state, and a periodic pressure adjustment maintenance is required without the production cost increase or an alternative production method, which is problematic.

Therefore, an object of the invention is to provide an electrophoresis device in which a pressure stabilized at the time of filling the capillary array with the phoretic medium can be obtained, and the variation of the liquid delivery amount is reduced to suppress the running cost and to provide a liquid delivery mechanism in which a high discharge pressure can be generated stably.

First Embodiment

FIG. 1is a view illustrating the configuration of the capillary electrophoresis device into which the invention is applied. This device can be largely divided into two units which are an automatic sampler unit117at the lower portion of the device and an irradiation detection/thermostatic bath unit118at the upper portion of the device.

In the automatic sampler unit117, a Y-axis drive body109is mounted on a sampler base108and can be driven on a Y-axis. In the Y-axis drive body109, a Z-axis drive body110is mounted and can be driven on a Z-axis. A sample tray112is mounted on the Z-axis drive body110, and a phoretic medium container102, an anode side buffer solution container103, a cathode side buffer solution container104, and a sample container105are set on the sample tray112by a user. The sample container105is set on an X-axis drive body111mounted on the sample tray112, and only the sample container105can be driven on an X-axis on the sample tray112. The liquid delivery mechanism106is also mounted in the Z-axis drive body110. The liquid delivery mechanism106is arranged below the phoretic medium container102.

The irradiation detection/thermostatic bath unit118has a thermostatic bath unit113and a thermostatic bath door115, and the inside can be maintained at a constant temperature. An irradiation detection unit116is mounted behind the thermostatic bath unit113, and can perform the detection during the electrophoresis. In the thermostatic bath unit113, the user sets a capillary array101. The electrophoresis is performed while the capillary array101is maintained at a constant temperature by the thermostatic bath unit113, and the detection is performed by the irradiation detection unit116. In addition, an electrode114for dropping the voltage to GND at the time of applying a high voltage for the electrophoresis is also mounted in the thermostatic bath unit113.

As described above, the capillary array101is fixed in the thermostatic bath unit113. The phoretic medium container102, the anode side buffer solution container103, the cathode side buffer solution container104, and the sample container105can be driven on an YZ-axis by the automatic sampler unit117, and only the sample container105can be driven further on X-axis. In the fixed capillary array101, the phoretic medium container102, the anode side buffer solution container103, the cathode side buffer solution container104, and the sample container105can be automatically connected in an arbitrary position by the movement of the automatic sampler unit118.

FIG. 2is a view illustrating the capillary electrophoresis device when viewed from the upper surface. The anode side buffer solution container103set on the sample tray112has an anode side cleaning layer201, an anode side electrophoresis buffer solution layer202, and a sample introduction buffer solution layer203. In addition, the cathode side buffer solution container104has a waste liquid layer204, a cathode side cleaning layer205, and a cathode side electrophoretic buffer liquid layer206.

The phoretic medium container102, the anode side buffer solution container103, the cathode side buffer solution container104, and the sample container105are arranged in the illustrated positional relation. Accordingly, the positional relation of the anode side and cathode side at the time of connection with the capillary array101becomes a positional relation of “the phoretic medium container102and the waste liquid layer204”, “the anode side cleaning layer201and the cathode side cleaning layer205”, “the anode side electrophoresis buffer solution layer202and the cathode side electrophoretic buffer liquid layer206”, and “the sample introduction buffer solution layer203and the sample container105”.

FIG. 3is a sectional view taken along line A-A ofFIG. 2. The phoretic medium container102is set to be inserted into a guide301embedded in the sample tray112. In addition, in the liquid delivery mechanism106, a plunger601built in the liquid delivery mechanism106is arranged below the phoretic medium container102.

At the time of the electrophoresis, the right side of the capillary array101inFIG. 3indicates the cathode side, and the left side indicates the anode side. The automatic sampler unit117moves to the position of “the anode side electrophoresis buffer solution layer202and the cathode side electrophoretic buffer liquid layer206”, and the high voltage is applied to the capillary array101on the cathode side to flow to GND to the electrode114through the cathode side buffer solution container104and the anode side buffer solution container103, such that the electrophoresis is performed.

FIG. 4is a detail view illustrating the capillary array101. The capillary array101has a capillary401which is a glass tube of which an inner diameter is about ϕ50 μm, and a detection part402is attached to the capillary401. The detection part402is detected by the irradiation detection unit116. A load header406and SUS pipes407are attached to the cathode side end portion of the capillary401. As a material of the load header406, for example, a PBT resin which is a resin having a high insulating property and a high comparison tracking index is desirable. A component which attains conducting of all the SUS pipes407is built in the load header406, and a high voltage is applied to the component to apply the high voltage to all the SUS pipes407. The capillaries401penetrate and are fixed to the SUS pipes407, respectively. On the anode side, a plurality of capillaries401are tied together by a capillary head403. The capillary head403includes a capillary head distal end405which has a needle shape at an acute angle and a capillary head boss404which is a portion of which an outer diameter is larger than that of the capillary head distal end405. As a material of the capillary head403, a PEEK resin or the like which is a resin having stiffness to be hardly broken and high stability against chemicals and analysis is desirable.

Although not illustrated in the drawings, when the capillary array101is fixed in the thermostatic bath unit113, each of the detection part402, the load header406, and the capillary head403is fixed. The detection part402is positioned with high accuracy so as to be detected by the irradiation detection unit. The load header406is fixed to be conducted with a part to which a high voltage is applied at the time of being fixed. In the capillary head403, the capillary head distal end405is directed directly downward, and the capillary head is firmly fixed to withstand a load. In the positional relation of the cathode side and the anode side at the time of fixing, the plurality of capillaries401are arranged not to overlap with each other at the time of being set in the device.

FIG. 5is a detail view illustrating the phoretic medium container102. In the phoretic medium container102, a seal502having a recessed shape is built in a syringe501, and the container is sealed with a cap504by placing a rubber stopper503from above. The upper portion of the cap504is further sealed with a film505. The material of the syringe501is desirably a PP resin or the like which is a resin which can be thinly molded. The material of the seal502is desirably an ultrahigh molecular PE resin or the like which is frequently used for the sealing of liquid in a sliding portion and has an excellent sliding property. The material of the rubber stopper503is desirably a silicon rubber or the like which is stable with respect to analysis. The material of the cap504is desirably a PC resin or the like in order to be uniform with the film505of each container. In the phoretic medium container102, the phoretic medium506is enclosed, and air507which enters during enclosing is enclosed so as to be accumulated at the upper portion. The phoretic medium506is enclosed in an amount with which the analysis can be performed a plurality of times. When a load is applied from the outside, the seal502can operate the inner portion of the syringe501.

FIG. 6is a schematic view illustrating the liquid delivery mechanism106in this embodiment. A stepping motor613rotates in response to the number of input pulses to rotate a drive screw602and to move a lead screw604straight. The driving method of the stepping motor613is one-or-two phase excitation, for example. The lead screw604is coupled with a slider603, and the slider603is coupled with the plunger601. The position of the plunger601is controlled by a rotary encoder614integrated with the stepping motor613. The slider603is connected with a linear guide609and is movable in the axial direction of the drive screw602. The slider603is coupled with a detection plate610and is detected by a sensor611fixed in a liquid delivery mechanism base612. The detection position of the sensor611is the origin position of the plunger601.

An external load for applying the rotational load is attached in the drive screw602. In this embodiment, a torque limiter615is used. The torque limiter615has a structure in which an inner ring607and an outer ring606are fitted coaxially. The inner ring607of the torque limiter615has a hollow structure. In addition, the inner ring607and the outer ring606can be rotated separately. A constant rotational resistance is present between the inner ring607and the outer ring606. As a method for applying the rotational resistance, a magnet type which is hard to be affected by abrasion is preferable. The drive screw602penetrates the hollow portion of the inner ring607to be fitted with the inner ring607by a parallel pin608vertically penetrating the drive screw602, whereby the drive screw602and the inner ring607are rotated synchronously. The outer ring60is fixed so as not to be rotated by a torque limiter outer ring presser605fixed in the liquid delivery mechanism base612. By such a structure, the resistance can be given to the drive screw602. For example, the torque limiter615requiring a torque of 45 mN·m at the time of fixing the outer ring606and rotating the inner ring607is used.

Then, the description will be given about a procedure for the injection of the phoretic medium506. In addition,FIGS. 7 to 10illustrate the positional relation of the plunger601, the phoretic medium container102, and the capillary head103at each point. Incidentally, in the description, a direction of pushing the plunger601to the phoretic medium container506is set as a normal rotation of the stepping motor613, and a direction of pulling out the plunger601is set as an inverse rotation of the stepping motor613.

FIG. 7is a view illustrating an initial state which is a series of movements of an injecting operation of the phoretic medium506. As described above, the phoretic medium container102is set by being inserted into the guide301embedded in the sample tray112. At this time, the plunger601of the liquid delivery mechanism106is arranged directly under the phoretic medium container102, and the seal502in the phoretic medium container102can be operated by the movement of the plunger601.

FIG. 8is a view illustrating an injection starting state of the phoretic medium506which is a series of movements of the injecting operation of the phoretic medium506. After the capillary head403is connected, the plunger601is driven by the liquid delivery mechanism106so as to operate the seal502, and the volume in the phoretic medium container102is changed such that the liquid is fed. At this time, the inside of the phoretic medium container102is highly pressurized, and each component of the phoretic medium container102expands. Since the phoretic medium container102has low stiffness at this time, the amount of expansion is large, and the container becomes unstable. For this reason, the expansion of the phoretic medium container102makes a large effect on the sealing property of the phoretic medium506.

In this regard, the guide301suppresses the expansion of the syringe501. In addition, the capillary head403suppresses the expansion of the rubber stopper503. Further, since the seal502has a recessed shape, when the seal502expands due to the internal pressure, the shape becomes more sealed. The seal502is formed to have a shape or strength easy to expand compared to the syringe501, and the effect of the expansion of the syringe501can be reduced. Specifically, the thickness of the syringe501is set to 1 mm, and the thickness of the seal502is set to about 0.6 mm, such that a difference is provided in expansion factors. Accordingly, the effect of the expansion on the sealing property is reduced. However, no matter how much the expansion amount is reduced, the expansion amount cannot be removed. The expansion amount is varied so as to affect the management of an amount of liquid delivery.

In this regard, the stepping motor613is driven by a driving current which is a pressure required to feed the liquid, so as to drive the plunger601. The pressure required to feed liquid at this time is set to 3 MPa, and in order to generate the pressure, the driving current of the stepping motor613is adjusted such that the thrust of the plunger601becomes 75 N. Accordingly, the inside of the phoretic medium container102expands, but the stepping motor613performs stepping-out when the internal pressure increases as much as needed.

Herein, the stepping-out of the stepping motor613is defined. During the injection of the phoretic medium, the stepping motor613becomes in a state of being driven at a specified current and a pulse rate. In the plunger601, the internal pressure of the phoretic medium container102is increased to generate the thrust of 75 N. During the liquid delivery, in the phoretic medium container102, the internal pressure of 3 MPa is generated, and thus in the seal502, the liquid delivery reaction is generated in a direction of pushing back the plunger601. Herein, when the thrust for driving the plunger601and the liquid delivery reaction are balanced, the rotation of the drive screw602stops. When the rotation of the drive screw602stops, a constant pulse rate is given to the stepping motor613, but the stepping motor is not rotated by the pulse rate. The state at this time is referred to as the stepping-out. The stepping-out state of the stepping motor613is detected by the rotary encoder614.

When the stepping motor613is stepped out, the phoretic medium container102expands, and the internal pressure increases to a set value. Although the stepping-out is detected, the stepping motor613continues to drive while stepping out. The phoretic medium506gradually feeds the liquid into the capillary401, and thus the plunger601is gradually driven. Further, after it is detected that the phoretic medium container102expands, a driven amount of the plunger601is detected by the rotary encoder614, and a required amount of the phoretic medium506is sent to the capillary401. By such a liquid delivery method, the liquid delivery amount can be managed without being affected by the expansion of the phoretic medium container102.

When the stepping motor613is used while stepping out, a moment when there is no driving force occurs. In addition, in this embodiment, the pressure fluctuation with time up to the service life of the device is reduced. Thus, the drive screw602is formed such that although the frictional force is fluctuated, the pressure fluctuation, that is, the fluctuation of the thrust is small. This is because the surface of the drive screw602is changed with time, and the frictional force, that is, a holding force or the thrust is fluctuated. For example, a sliding screw having a long lead length or a ball screw is used as the drive screw602in which the pressure fluctuation with time can be reduced. The drive screw602has a linear-rotational motion converting action, and a force to reverse the drive screw602is generated by the liquid delivery reaction. When an external load more than the force generated by a linear-rotational motion is applied to the axis, the drive screw602is not reversed, and thus the liquid can be fed with suppressing the pressure fluctuation. Therefore, the liquid delivery mechanism can be realized such that the thrust fluctuation of the drive screw602with time is reduced, and a constant pressure can be obtained during the liquid delivery.

FIGS. 10(a) and 10(b)are views schematically illustrating the change of the pressure over time at the time of filling the phoretic medium506with this method.FIG. 10(a)illustrates the pressure from the start of the injection to the completion of the injection, andFIG. 10(b)illustrates the position of the plunger601. The liquid delivery pressure is a constant pressure from the start to the completion. The position of the plunger601is in conjunction with the injection amount of the phoretic medium, and the liquid delivery pressure is almost constant. Thus, the plunger moves at a constant speed. It is detected by the rotary encoder614that the plunger601moves by a set amount from the injection starting position, and the liquid delivery ends. The phoretic media506for plural times of operations are put in the phoretic medium container102in advance, and the liquid delivery is repeated as many times as required for filling the capillary401.

Second Embodiment

A friction type may be used in addition to the magnet type as the method for applying the external load to the drive screw602by the torque limiter615. The external load may be applied not only by the torque limiter615, but also by a method in which the resistance is applied by applying pressure with the drive screw602as the ball screw, the resistance is applied by applying pressure to the linear guide609, the resistance is applied by the stepping motor613with an electromagnetic brake, the surface state of the drive screw602is roughened, and a gear ratio is raised in a state where the drive screw602and the stepping motor613are connected by a gear.

Third Embodiment

The driving method of the stepping motor613may be one-phase excitation, two-phase excitation, or microstep in addition to the one-or-two phase excitation.

Fourth Embodiment

The stepping motor613and the drive screw602may be separate bodies and be connected by coupling. Alternatively, the gear may be connected with both of the stepping motor613and the drive screw602, and the stepping motor613may be connected to be folded.

Fifth Embodiment

A solvent such as water and a washing liquid is sealed in the phoretic medium container102and is fed to the capillary401by the liquid delivery mechanism106, so as to wash the capillary401.

REFERENCE SIGNS LIST

103: anode side buffer solution container

104: cathode side buffer solution container

105: sample container

106: liquid delivery mechanism

112: sample tray

113: thermostatic bath unit

115: thermostatic bath door

116: irradiation detection unit

117: automatic sampler unit

201: anode side cleaning layer

202: anode side electrophoresis buffer solution layer

203: anode side sample introduction buffer solution layer

204: waste liquid layer

205: cathode side cleaning layer

206: cathode side electrophoretic buffer liquid layer

402: detection part

404: capillary head boss

405: capillary head distal end

406: load header

602: ball screw

605: torque limiter outer ring fixing device

606: torque limiter outer ring

607: torque limiter inner ring

608: parallel pin

609: linear guide

610: detection plate

611: origin sensor

612: liquid delivery mechanism base