Patent Application
20090028727
This invention pertains to diluter pumps for use in chemistry analyzers.
Chemistry analyzers perform automated chemical analysis tasks on a sample, such as a blood sample. Many of these tasks require dilution fluid to achieve appropriate reagent concentrations. This fluid is usually supplied by a pump known as a diluter pump or diluter. One prior art design for a diluter uses two pistons of different diameters that move in a metal cylinders defined in a metal block. Each piston bears a seal to keep water in the pump's compression chambers.
Chemistry analyzers are very important health care tools. They can detect imbalances in a number of chemical species in bodily fluids, such as cholesterol, glucose, enzymes, iron, magnesium, protein, uric acid, chlorine, lithium, potassium, or sodium. This information can help to diagnose a variety of conditions, such as high cholesterol, abnormal liver function, or diabetes, to name only a few. Improvements to the quality of measurements performed by chemistry analyzers could therefore have a positive effect on the care of a very large number of patients.
A chemistry analyzer is also a relatively expensive item for a health care provider, such as a hospital, and this cost is usually passed on to health care consumers. The cost passed on to consumers can be affected by the initial cost of the analyzer, the cost of reagents and reaction vessels, and the cost of maintaining and servicing the analyzer. Improvements that lead to a reduction in cost of chemistry analyzers and their maintenance could therefore have a positive effect on the overall cost of health care. And the overall health care savings resulting from even a relatively small reduction in the costs associated with an analyzer could be substantial in view of the large number of patients served by these analyzers.
The cost savings could also help make the technology available to more patients, as well. In developing countries and remote or less affluent regions of developed countries, cost may prevent health care providers from having easy access to a chemistry analyzer. They might thus need to send samples to remote facilities, recommend that patients travel to those facilities, or even diagnose conditions without the benefits of automated chemical analysis. Improvements that lead to a reduced cost of chemistry analyzers and their maintenance could therefore have a significant effect on the availability of health care as well as the promptness and efficiency with which it can be delivered.
In one general aspect, the invention features a chemistry analyzer precision pump with a pump block that defines a first pump chamber with a fluid port at a first end, an opening for a piston at a second end, and a seal mount located between the opening and the port. A second, smaller, pump chamber has a fluid port at a first end, an opening for a piston at a second end, and a seal mount located between the opening and the port. A first seal is mounted at the first seal mount and a second seal is mounted at the second seal mount. A first piston is mounted to reciprocate in the first pump chamber, past the first seal, and a second, smaller piston is mounted to reciprocate in the second pump chamber, past the second seal.
In preferred embodiments, the first and second seals include a flouropolymer, such as polytetrafluoroethylene. The first and second seals can each include a first spring positioned to bias them against their respective pistons. The first and second springs can be circular. The first seal mount can be defined at least in part by a portion of the pump block in the first pump chamber and centered around a longitudinal axis of the first pump chamber proximate its piston opening, with the second seal mount being defined at least in part by a portion of the pump block in the second pump chamber and centered around a longitudinal axis of the second pump chamber proximate its piston opening. The first and second seals can be O-ring seals. The first and second pump chambers can be parallel chambers defined in the pump block. The pump block can be made of plastic, with the pump chambers being defined by machined bores in the plastic pump block. The pump block can be made of polycarbonate or acrylonitrile butadiene styrene. The pump block can be at least partially transparent to visible light. The pump can further include a linear drive mechanism coupled to both the first and second pistons. The linear drive mechanism can include a stepper motor and a lead screw. The first and second pistons can be made of a ceramic material. The first piston can have a conical head defined by a first conic surface, with the first pump chamber having a conical head defined by a third conic surface that has an aperture that is substantially the same as an aperture of the first conic surface, whereby the conical head of the first piston mates with the conical head of the first pump chamber at the top of its stroke, and the second piston can have a conical head defined by a second conic surface, with the second pump chamber having a conical head defined by a fourth conic surface that has an aperture that is substantially the same as an aperture of the second conic surface, whereby the conical head of the second piston mates with the conical head of the second pump chamber at the top of its stroke. The first pump chamber can include a first bushing mount area, with a first bushing mounted in the first bushing mount area to constrain motion of the first piston, and the second pump chamber can include a second bushing mount area, with a second bushing mounted in the second bushing mount area to constrain motion of the second piston. The pistons can have portions with different cross sections at different distances from their heads, with an outer surface of a first of these portions interacting with a working surface of a respective bushing and an outer surface of a second of these portions interacting with a respective seal. A bore of the first pump chamber can be related to a bore of the second chamber by a ratio of about 4:1. A first intake two-way valve and a first outlet two-way valve can bye hydraulically connected to the first chamber and a second intake two-way valve and a second outlet two-way valve can be hydraulically connected to the second chamber.
In another general aspect, the invention features a chemistry analyzer precision pumping method that includes driving a first piston through a first pump chamber, driving a second piston through a second pump chamber, wherein the first piston has a larger diameter than the second piston and wherein the first pump chamber has a larger diameter than the second pump chamber, holding a first seal between the first piston and an outer wall of the first pump chamber at a first seal mounting location, and holding a second seal between the second piston and an outer wall of the second pump chamber at a second seal mounting location.
In a further general aspect, the invention features a chemistry analyzer precision pump, including means defining a first pump chamber and a second pump chamber that has a smaller capacity than does the first pump chamber, means for displacing fluid in the first pump chamber, means for displacing fluid in the second pump chamber, first sealing means, second sealing means, means for holding the first sealing means between the first means for displacing and a surface of the first pump chamber at a first mounting location in the first pump chamber, and means for holding the second sealing means between the second means for displacing and a surface of the second pump chamber at a second seal mounting location in the second pump chamber.
In another general aspect, the invention features a chemistry analyzer precision pump that includes a first pump chamber having a fluid port at a first end, and an opening for a piston at a second end, with the first pump chamber including a first head tapered from the first end to the second end. A second pump chamber has a fluid port at a first end, and an opening for a piston at a second end, with the second pump chamber including a second head tapered from the first end to the second end of the second pump chamber. A first piston is mounted to reciprocate in the first pump chamber and has a first tapered piston head, and at least a portion of the first tapered piston head has a taper portion that matches at least a portion of the first tapered pump chamber head, such that the first tapered piston head portion mates with the first tapered pump chamber head portion at the top of its stroke. A second piston is mounted to reciprocate in the second pump chamber and has a second tapered piston head, and at least a portion of the second tapered piston head of the second piston has a second taper portion that matches at least a portion of the second tapered pump chamber head, such that the second tapered piston head portion mates with the second tapered pump chamber head portion at the top of its stroke.
In preferred embodiments, the first and second pumps can be made of a ceramic material. The first and second pistons and the first and second pump chambers all have a circular right conical shape. The first and second pump chambers can have different bores, with the first and second pistons having different diameters. The tapered cross-section of the pistons in diluter pumps according to the invention can improve the precision and accuracy with which diluter fluid is dispensed in a chemistry analyzer. This can lead to more accurate and/or precise readings. It may also allow an analyzer to be used with reagents having less precise concentrations, which may reduce their cost.
The pump blocks of the diluter pumps according to the invention can also be built less expensively because of looser tolerances for the cylinder bores and the use of seals in the cylinders instead of on the pistons. This can, in turn, reduce the cost of the chemistry analyzer.
Referring to
Referring also to
The distal ends 44, 54 (heads) of the pistons 12, 14 preferably each have a conical cross-section. This cross-section is designed to closely match the conical cross-section of the compression chambers 46, 48. The use of these cooperating cross-sections tends to discourage the formation of bubbles in the dilution fluid, allowing the pump to dispense it more precisely. Note that while the presently preferred embodiment employs a right circular cone (i.e., a cone that has its apex aligned directly above the center of its circular base), other tapered shapes, such as hemispheres, oval right cones, oblique cones, or otherwise distorted cones, might also be used in some situations.
A first fluid outlet 48 is located at the peak of the larger conical compression chamber 46 and a second fluid outlet 58 is located at the peak of the smaller conical compression chamber 56. A first three-way solenoid valve 32 has a common port hydraulically connected to the first fluid outlet 48, and a second three-way solenoid valve 34 has a common port hydraulically connected to the second fluid outlet 58. Each of the valves has a normally (open) port hydraulically connected to a pump fluid inlet 36 and a normally (closed) port hydraulically connected to a pump outlet 38. In this embodiment, the valves are connected to the pump's inlet and outlet via inlet and outlet channels defined by the pump block. Suitable solenoid valves are available from the Lee Company, of Essex Connecticut (e.g., part number LHDA2421111H).
Referring also to
Referring to
The use of precisely dimensioned pistons in connection with seals mounted in the pump block allows the cylinder bores to be defined with relatively loose tolerances, so that the block can be manufactured relatively inexpensively. In this embodiment, the pump block is made of acrylic, and the larger cylinder, the smaller cylinder, and the inlet and outlet channels are bored into the block. The block is screwed onto a two-part aluminum frame that also supports the actuation mechanism.
The pump 10 is capable of aspiring and expelling fluid, and it can use these capabilities to provide both a transfer mode and a dispensing mode. In its transfer mode, the pump can cause a probe on a moving arm to draw in samples or reagents and then expel them into a reaction vessel. In its dispensing mode, the pump can dispense dilution fluid from a supply line to the probe to dilute the reaction mixture or to clean the probe. Other modes, such as a reverse pumping mode, are also possible, but these modes are not currently used in the presently preferred embodiment.
Referring to
The pistons end their descent when the desired quantity of diluent has been drawn into the selected part of the pump. The three-way valve of the selected cylinder is then switched from its inlet position to its outlet position (step 104), but the three-way valve of the unselected cylinder is left in its inlet position (step 114). The actuator can then be energized in reverse to cause the pistons to ascend in their respective cylinders in an outlet stroke (step 106, 116). During the outlet stroke, the selected cylinder dispenses the desired quantity of diluter fluid and the unselected cylinder dumps its charge back into the supply line.
Referring to
The pistons end their descent when the desired quantity of fluid has been aspirated by the selected part of the pump. The three-way valve of the selected cylinder is then left in its outlet position (step 124), the three-way valve of the unselected cylinder is left in its inlet position (step 134), and the actuator is energized in reverse to cause the pistons to ascend in their respective cylinders in an outlet stroke (step 126, 136). During the outlet stroke, the selected cylinder expels the fluid that was aspired during the aspiration stroke and the unselected cylinder dumps its charge back into the supply line.
The pump can use either one of the cylinders, or even both, to transfer or dispense fluid. These different modes of operation can be applied to different tasks in particular applications. In one embodiment in which the pump is used in a chemical analyzer, for example, the larger and smaller cylinders are used for different kinds of transfer tasks, the larger cylinder is used in dispensing mode for washing and dilution tasks, and the smaller cylinder is used only in a diagnostic dispensing mode to confirm that the pump is working properly. Overall, the sequencing methods described above allow fluid to be dispensed and transferred with just two relatively inexpensive three-way valves, but other types of valves and sequencing arrangements might also be suitable in some instances.
In this application the relative terms such as “above” and “below” have been used in a manner that is intended to refer to a reference orientation of the pump in which the compression chambers are located at the top of the pump. But in some instances the pump might be located in another position.
The present invention has now been described in connection with a number of specific embodiments thereof. However, numerous modifications which are contemplated as falling within the scope of the present invention should now be apparent to those skilled in the art. For example, the pistons could have portions with different cross sections at different distances from their heads, with an outer surface of a first of these portions interacting with a working surface of a respective bushing and an outer surface of a second of these portions interacting with a respective seal. It is therefore intended that the scope of the present invention be limited only by the scope of the claims appended hereto. In addition, the order of presentation of the claims should not be construed to limit the scope of any particular term in the claims.
