Patent Application
20150091299
This disclosure relates generally to a connector to reduce a fluid volume when mating with a counterpart.
In anesthesia or in intensive care, the condition of a patient is often monitored e.g. by analyzing the air exhaled by the patient for its carbon dioxide content. For this reason, a small portion of the respiratory gas is delivered to a gas analyzer. The sample is carried along a sampling tube connected at one end of to a respiratory tube adapter and the other end to the gas analyzer. This sampling tube is typically disposable and must have some kind of reliable and tight but simple and cheap connectors. Almost all pneumatic connectors in the respiratory system have tapered conical contact surfaces. Such connectors are simple, easy to connect and cheap to make and they still provide an airtight and reliable connection. The connection such as a well-known fitting called Luer-Lok®, a registered trademark of Becton, Dickinson and Company of Franklin Lakes, N.J. USA, has been in general use for gas sampling but also other similar connectors with differing dimensions can be used. The tapered portion of the connector is nor conical with straight cross section sides because it gives a reliable and tight connection using a large contact area. The tapered portion could in principle also have curved cross section sides or one tapered connector in combination with a suitably designed semi-rigid counterpart. The contact surface responsible for the tightness is always on the tapered portion of the connector. Other possibilities would be cylindrical connectors with either axial or radial gaskets but they are more complicated and expensive and, consequently, not suitable as disposable components. Such connectors are typically used e.g. in pressurized gas lines or gas lines of more permanent nature.
The widely used connector for gas sampling is going to be banned from gas measurement applications in the near future. A new standardized connector is going to be introduced for gas applications. That connector is defined by ISO 80396. It is in principle similar to the widely used connector for gas sampling, but only bigger. The increased size has its flaws. Increased size has a negative effect on the rise time of the measurement and measurement accuracy. The increased size increases dead space inside the connection. Dead space increases mixing of the sampled gas and therefore increases the rise time of the measurement and makes it harder to use low sample flows and to monitor high respiratory rates.
An extra fluid volume such as a dead space is especially inherent in a tapered connection, which are commonly used in patient respiratory circuits. Such a respiratory circuit with a medical gas analyzer 11 is shown in
A gas analyzer designed to measure respiratory gas in real time has to be fast enough to resolve changes in the gas content. This is especially true for carbon dioxide, which varies from close to zero in the inspiratory phase to about 5% in the expiratory phase of the breathing cycle. It is then very important to streamline the complete gas sampling system. Many portions of the system with slowed down response can easily add up to unacceptable performance of the gas analyzer. The reason for an increased rise time of e.g. carbon dioxide is often an extra fluid volume, a dead space in the pneumatic line, where the gas flow is slowed down. The tapered conical connector is susceptible to such dead space, especially if the inner dimensions are significantly larger than those of the bore or sampling line itself. The inherent construction of the conical connector is such that dead space always is introduced and the amount is critically dependent on the tolerance of the conical dimensions. The connectors must allow for axial or longitudinal play in order to avoid the situation of touching axially because then air leak is likely to occur. Therefore, the tolerances always define an axial extra fluid volume in the connection to ensure tightness at the conical surfaces.
For a more or less stable gas composition the extra volume may not have any major impact on the measurement but for fast changes in gas composition the situation is different, especially when using a fast gas analyzer. This is shown in the graph of
Minimal dead space is important also in gas or liquid chromatography. An attempt to make connections with capillaries is well-known. The female part of the connection is slightly tapered. in order to accept the cylindrical capillary tube and make a tight press-fit. This connector fitting is specially designed for conditions encountered in liquid or gas chromatography and is not intended for repeatedly made reliable connections like in gas analyzers. Robustness inevitably adds dead space to the bore of the connection.
In a neonatal application, the main ventilation circuit's extra fluid volume has to be as small as possible. There are different solutions to this problem. The connections are also conically tapered even if the dimensions are much larger than what would be used for a gas sampling system. In one solution, there is a sliding internal passage filling the dead space and in another solution a compressible member is used to exclude the extra fluid volume. However, especially for small and disposable connectors like those used in sampling lines of gas analyzers such moving or compressible features would be difficult to implement and would add to the expenses of a disposable accessory.
Since production volumes can be millions per year, the connector is usually made using injection molding. Because of the large volumes, the molds have often multiple cavities to increase productivity. More cavities mean usually also lower part costs. On the other hand, more cavities also complicate the production process making the process harder to control. In the case with conical connectors for example such as described above the important features include for example dimensional accuracy of the sealing surfaces, dimensional accuracy of the lock features, weld line control and sink mark control. There are many variables that are factors contributing in the good or bad end result. These parameters include for example material properties, mold construction, injection point, injection pressure, hold pressure and other known process parameters. All of the parameters can be used in process control, both in single cavity molds and in multi cavity molds. Part geometry and construction becomes more important in multi cavity molds. In other words, bad part construction can be more easily compensated with the process parameters in single cavity molds than in multi cavity molds.
Dimensional accuracy of the connector parts is required to produce leak free seals, to prevent going out of specifications and to minimize the dead space that has to exist at the bottom of the conical connection.
To preserve the integrity of the seal, the sealing surface must not have any significant sink marks, big weld lines or short shots. Therefore the surface thickness of the injection molded parts has to be small enough to avoid shrinkage when the molten material cools down inside the mold after injection but big enough to ensure good confidence of fill. Small shrinkage problems can be adjusted using the process parameters. Adjustment becomes harder to do when the mold cavity number increases and especially when the part geometry is not optimal. Wall thickness of the part has to be preferably uniform around the whole part or gradually shrinking towards fill direction. Therefore bulky features are not desired.
In
According to the specifications of a well-known connector, the inner diameter D3 of the female connector, as shown in
One big contributor to the overall dead space is the extra volume 17 that is left on the bottom of the female connector 12. Due to the conical shape of the connectors the remaining dead space between the male and female connectors is strongly dependent on the size (tolerance) variations of the two parts. For example if the male connector outer diameter was bigger, it would not enter as deep inside the female as it would if the said diameter was smaller. When using standardized conical connectors the minimum distance between the tip of the male connector and the bottom of the female connector is defined by the standards. That feature prevents the connector from bottoming and thus remaining loose and leaking. However, the standard allows significant variations in the insertion depth of the connectors and therefore also in dead space. Tolerances are a result of normal process variation in injection molding and with good part design they can be more easily controlled. With good part design the tolerance variance can be more easily minimized and it can also be directed to a suitable side of tolerance spectrum.
The other big contributor is the dead space inside the male connector. Unlike the dead space between the connectors this is not defined by the standard. When using for example injection molding. which is the most common manufacturing method, the limitations come from the manufacturing process-, quality-, productivity- and price requirements. Some of them are described above.
Another known method to injection mold a conical connector is to increase the wall thickness of the conical part reducing inner diameter D2 inside the conical surface as shown in
The above-mentioned shortcomings, disadvantages and problems are addressed herein which will be understood by reading and understanding the following specification.
In an embodiment a connector to reduce a fluid volume when mating with a counterpart includes a connector body having at least a conical body sector with a sealing surface configured to mate with the counterpart to seal this joint, and a recess inside the connector body and at least partly inside the conical body sector, the recess having a first opening and a second opening. The connector to reduce a fluid volume when mating with a counterpart also includes a tube for a fluid flow, the tube extending through the second opening into the recess towards the first opening. The tube is configured to extend through the second opening at least to such a part of the recess, which is inside the conical body sector.
In another embodiment a connector to reduce a fluid volume when mating with a counterpart includes a connector body having at least a conical body sector with a sealing surface configured to mate with the counterpart to seal this joint, and a recess inside the connector body and at least partly inside the conical body sector, the recess having a first opening and a second opening. The connector to reduce a fluid volume when mating with a counterpart also includes a tube for a fluid flow, the tube extending through the second opening into the recess towards the first opening. The tube is configured to extend through the second opening at least two thirds of a whole length of the recess inside the conical body sector.
In yet another embodiment a connector to reduce a fluid volume when mating with a counterpart includes a connector body having at least a conical body sector with a sealing surface configured to mate with the counterpart to seal this joint, and a recess inside the connector body and at least partly inside the conical body sector, the recess having a first opening and a second opening. The connector to reduce a fluid volume when mating with a counterpart also includes a tube for a fluid flow, the tube extending through the second opening into the recess towards the first opening. The tube is configured to end at a distance from the first opening, which is less than two times an inner diameter of the tube or, more specifically, less than 1.5 times an inner diameter of the tube, or, even more specifically less than one time an inner diameter of the tube.
Various other features, objects and advantages of the disclosure will be made apparent to those skilled in the art from the accompanying drawings and detailed description thereof.
Specific embodiments are explained in the following detailed description making a reference to accompanying drawings. These detailed embodiments can naturally be modified and should not limit the scope of the invention as set forth in the claims.
A connector for mating with a counterpart to avoid extra fluid volume, such as a dead space, is described. The fluid flow, such as gas flow, can be guided through this connector. With the design explained hereinafter, it would be easier to avoid dead space for example in the ISO 80369 connection bore or any conical/tapered connector facing similar problems advantageously without the drawbacks of the large external size.
One embodiment is shown in
The connector may have a threshold 40 in the recess to prevent the tube extending through the first opening 27. The threshold is situated around the L2 area and at least partly inside the conical body sector 22. Threshold 40 marks a change in the recess 26 diameter. The advantage of this approach is that for example the tube 30 can be assembled against the threshold, in which case an inner diameter D17 of the recess at least partly surrounded by the threshold 40 is less than the inner diameter D11 of the recess for the tube between the second opening 28 and the threshold 40. The threshold may be closer to the first opening 27 than the second opening 28. typically around the recess at the first opening, the threshold may make the assembly easier. The length L7 between the second opening 28 and the threshold 40 can vary to some extent depending on the threshold 40 placement. The recess inner diameter D11 along length L7 may be designed to receive the tube 30, but it can also differ from an outer diameter D10 of the tube 30 to some extent. These are explained in more detail later. Typically an inner diameter of the recess inside the conical body sector is at least as large as the outer diameter D10 of the tube. The threshold 40 is not always present because the recess can be made without the threshold as shown in
The ability to fine tune the wall thickness 110 of the conical body sector 22 without the drawback of adding to the volume such as a dead space results in better dimension and quality control of the sealing surface 23 and therefore resulting in better process accuracy and easier process control to reach better dimensional accuracy from part to part and from batch to batch. Smaller sealing surface diameter D13 is one desired goal that can be achieved in a more constant way with the explained design. That again increases the average insertion depth of the connector 20 corresponding to the sealing area 32 and that results in less volume 36. which is a dead space, between the connector 20 and the counterpart 25. This can be done without breaking the tolerance limits of a standard connector or of a custom conical connector or without bottoming into the opposite end of the counterpart, which would cause leaks.
Rapid changes in the wall thickness T10 of the conical body sector 22, for example step-like changes or gradual changes, are not desired, but the design could still work even with the changes in the wall thickness 110 present in the design. Changes that are less than 10% of the wall thickness T10 or around 10% of the wall thickness T10 might not have a severe impact on quality. These might be for example changes in the recess draft angle or slight chamfers on the recess surface. Changes around 25% of the wall thickness T10 might already cause some problems especially in multi cavity molds. Changes around 50% of the wall thickness T10 of the conical body sector 22 might cause severe problems for example if the changes occur around the length L3 of the sealing area 32 along a longitudinal axis of the recess 26 or especially the sealing area 32. Rapid or gradual changes in the inner diameter D11 of the recess 26 occurring outside of the sealing area 32 would cause less problems in injection molding, but might still have some negative effect on the tube to the connector interface depending on other parameters. In other words, the connection between the parts might be compromised. This is if the change causes large material clusters. If the rapid changes do not cause large material clusters the change might not have significant impact on quality. A good example of this is the thickness of intersecting wall having the thickness T12, that for example creates the threshold 40. It is a wall that is intersecting with the conical body sector 22 with the wall thickness T10. A general rule is that intersecting wall, whose thickness in this case is T12, can be 0.5 times the thickness of the wall, in this case conical body sector 22, in order to have a sink mark free surface on the wall. So, if T12 is less than 0.5 times T10, there are no major problems in sealing surface 23 quality around the intersection area. If T12 is more than 0.5 times T10, there might be problems with sealing surface 23 quality around the intersection area. Quality problems on surface 23 increase when T12 increases in relation with T10. Problem area is usually situated around the intersection area, so they should especially be avoided around the sealing area 32. The same applies if a similar step or steps or intersecting wall or -walls are situated anywhere else around the conical body sector area 22 inside the recess 26. Step height is less critical than the distance of the area having a changed diameter along the longitudinal axis of the recess 26.
This embodiment hereinbefore also reduces dramatically the volume 36 found in some of the prior art designs caused by diameter D2 inside the conical surface and the whole conical. connection between the connector 20 and the counterpart 25 by helping to minimize the length between the tip 34 of the connector 20 and the opposite end 35 of the counterpart 25 and therefore volume 36. This can be done without the drawbacks of the prior art designs. In the preferred designs it removes the dead space inside the connector 20 totally. In order to get full benefits out of the design the tube 30 is assembled into the recess 26, filling this recess inside the connector 20 and making the fluid flow path. 38 through the whole connector free of any cavities that would cause dead spaces. The tube 30 can be attached for example by gluing or by using solvent to melt the parts together and to seal the connection. Using glue helps to fill cavities that might be between the mated parts because of design or dimensions. Using solvent helps to equalize slight overlapping differences in diameters.
The tube 30 may extend through the second opening 28 of the connector 20 into the recess 26, which means that tube depth L5 can vary to some extent. There is no need to use the whole conical body sector 22 for sealing i.e. the length L3 of the sealing area 32 along the axis of the recess 26 is usually less than the length L2 of the conical body sector 22, such as the conical surface length, along the axis of the recess 26. Therefore the tube may extend through the second opening 28 of the recess 26 to at least such part of the recess which is inside the conical body sector. The tube may extend at least one third of the whole length of the recess inside the conical body sector 22. It is even better if the tube can extend into the recess at least half of the whole length of the recess inside the conical body sector or at least two thirds of the whole length of the recess inside the conical body sector. Better results can be achieved if the tube may extend through the second opening at least to such part of the recess which is besides inside the conical body sector 22 but also inside the sector where the sealing area 32 will mate with the counterpart 25 to make a sealed joint. Typically tube is configured to extend through the second opening 28 and through the recess 26 inside the conical body sector 22 towards the first opening 27 ending at a distance from the first opening, which is less than two times an inner diameter of the tube or, more specifically, 1,5 times an inner diameter of the tube, or, even more specifically less than one time an inner diameter of the tube. The tube may also extend through the second opening all the way through the recess 26 inside the conical body sector 22 to the first opening 27, which may be at a tip 34 of the connector 20.
As explained hereinbefore, it is advantageous to have the tube 30 close to the tip 34 of the connector, for example at a distance of around 0.5 mm-1 mm from the tip depending on the connector size. Or alternatively at a distance of similar scale as the wall thickness T10 of the conical body sector 22. This approach helps the assembly, as the tube can be pressed against the threshold 40 of the recess 26, if such threshold exist, but naturally the recess can be without the threshold in which case the tube may extend to the tip 34 of the connector. However, the thickness T12 of the intersecting wall, which creates for example the threshold 40, can be also anything between 0 mm and 0.5 mm. This results in less bulky features around the sealing area 32 and results therefore into longer length L3 of the sealing area that is free of sink marks. The threshold 40 can also be anywhere in the recess 26. inside the sealing area 32 or better two thirds of the length L3 of the sealing area from the tip 34 of the connector or still better one third of the length L3 of the sealing area away from the tip 34 of the connector or even better less than one third away from the tip 34 of the connector. The more sealing area 32 there is intact, the better seal there is. If the recess 26 goes through the whole connector 20 without the threshold 40, the tube 30 can be positioned for example by an assembly jig.
These embodiments discussed hereinbefore having less bulky features help also the injection molding, especially when trying to reach dimensional accuracy and the sealing surface diameter D13 that is as close to the minimum tolerance of the diameter. The sink marks caused by the bulky features or intersecting walls can be compensated using a large hold pressure. That may result in slightly increased part dimensions, for example the sealing surface diameter D13, resulting in the increased volume 36 described above. Because of the conical sealing surfaces 23, even really small. dimensional changes result in large differences in insertion depth and thus the length of L3 of the sealing area 32. The embodiments also help to control the leakage caused by sink marks around the tip 34 of the connector 20 or connector body 21.
The sampling line can be assembled into the bottom surface 40 of the recess 26 which is a good option, but it can be also assembled at an offset from the bottom surface 40, resulting in an additional dead space inside the connector 20. However, both alternatives would remove or reduce respectively all the problems from the steps or changes in diameter in the flow path 38 that are necessary in the prior art as shown in
The recess 26—along length L7 having the inner diameter D11 that is designed to receive the tube 30, may also go through the whole connector 20 as explained hereinbefore and as shown in
If the recess 26 along length L7 having diameter D11 that is designed to receive the tube 30, is not situated inside the sealing area 32, it may not help to improve the injection molding, therefore causing the problems described above. The same situation can occur if the length L7 of the recess between the threshold 40 and the second opening 28 is not entirely extending into the sealing area 32. In these cases at least one hollow 42 at the tip 34 of connector 20 around the recess 26 or between the recess and the sealing surface 23 as shown in
In a cylindrical injection molded connector an advantageous option would be to have a cylindrical hollow shape around the flow path 38, which hollow may be for example apart from the recess 26. The smaller inner diameter D16 of the hollow 42 has to be big enough to leave a tubular channel for the sampled gas to flow through. In the preferred option this feature can have the same diameter as the inner diameter D12 of the tube 30. The size of the hollow 42 and the recess 26 can be used to adjust the surface thickness of the first shot in areas around the flow path 38 between the first opening 27 and the second opening 28 of the connector 20, both along distance L7 and around the hollow 42. It results in the same benefits described above. Maximum outer diameter D15 of the hollow 42 may be less than the conical sealing surface diameter D13. The assembly steps are shown in
The filler material for at least one hollow 42 can be the same as the first shot or it can be other material as well. It can be injection molded, transfer molded or tilled using a separate method, for example gluing. There is no need to use the whole sealing surface 23 along the length L2 of the conical body sector 22 for sealing. Therefore the minimum depth of the hollow 42 has to be within the range of the sealing area 32 of the connector pair. The maximum depth of the hollow 42 is less than the length L2 of the conical body sector 22, i.e. the hollow 42 plus the recess 26 along length L7 having diameter D11, that is designed to receive the tube 30, is max. the length L6 of the conical body 21.
An alternative method of avoiding the shrinkage issue on the sealing surface 23 while having a small inner diameter D12 of the tube 30 is to have a similar hollow 42 that
The embodiments of this application help to develop a connector that is relatively large in scale for easy handling and good mechanical strength, but still having a small enough flow path 38 and the volume 36 to ensure fast and accurate measurement. The connector is also easy to produce with accurate dimensions in large production volumes.
The written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
