Pressure detection device

Provided is a pressure detection device capable of easy installation and removal of a sensor in/from a diaphragm, measurement of a pressure in a wide rage, and manufacture at a low cost while reducing a size. A sensor part (A) has: a magnet (12) being applied with a load produced by pressing of a diaphragm (8); and a magnet cap (11) covering the magnet (12). The diaphragm (8) has an intra-diaphragm magnetic body (9) buried therein. The intra-diaphragm magnetic body (9) has a protrusion part protruding from the diaphragm (8) so as to be in contact with the magnet (12). The magnet cap (11) has an opening part enabling the protrusion part of the intra-diaphragm magnetic body (9) and the magnet (12) to be joined together.

TECHNICAL FIELD

The present invention relates to a pressure detection device that measures a pressure of a liquid flowing in a tube, without having an air space or a branch tube.

BACKGROUND ART

Conventionally, there have been proposed pressure detection devices that measure a pressure of a fluid flowing in a blood circuit used for dialysis, apheresis, Continuous Renal Replacement Therapy (CRRT), or the like, without having a chamber or a branch tube. Extracorporeal circulation of blood in heart surgery, emergency medical care, or the like needs various treatments, thereby increasing the number of circuits and devices. However, a space where the devices are located and a space where the located devices are used are limited. Therefore, such devices for heart surgery, emergency care, and the like which are utilized especially in emergency cases are desired to be easily handled. From this viewpoint, a diaphragm pressure sensor has been disclosed to easily measure a pressure of a fluid such as blood flowing in an extracorporeal circulation circuit.

For example, a pressure detection device used in devices for extracorporeal blood treatments has been disclosed to (i) be applied with a pressure of a fluid via a diaphragm that is provided at a surface of a tube channel in parallel to a direction of flowing the fluid, and (ii) detect, by a distortion gauge, a vertical movement of a presser pressed on the diaphragm as a power, and (iii) calculates a pressure value from the power based on an area applied with the pressure (refer to Patent Reference 1, for example). This pressure detection device is connected, as a cassette body, to a dedicated device.

Furthermore, a pressure detection station used in apheresis systems has been disclosed to (i) be applied with a pressure of a fluid via a diaphragm that is provided at a surface of a tube channel in parallel to a direction of flowing the fluid, and (ii) detect, by a distortion gauge, a vertical movement of a presser pressed on the diaphragm as a power, and (iii) calculates a pressure value from the power based on the power into a pressure value by calculation based on an area applied with the pressure (refer to Patent Reference 2, for example). This pressure detection station is connected to a dedicated device.

Still further, a liquid pressure detection structure has been disclosed to have (i) a tube body that is expanded and shrunk, (ii) a detection unit that detects an amount of the expanding and shrinking, and (iii) a joining unit that connects the tube body with the detection unit by easily installing and removing the detection unit in/from the tube body (refer to Patent Reference 3).

For these conventional diaphragm pressure sensors, a magnetic joining method has been conceived for easily joining and separating between the diaphragm and the sensor by freely installing and removing the sensor in/from the diaphragm. For examples of the joining method, the Patent Reference 2 and the Patent Reference 3 disclose technologies of joining a sensor to a diaphragm using a magnetic force.

[Patent Reference 2] Japanese Unexamined Patent Application Publication (Japanese Translation of PCT International Application) No. 2002-513321

DISCLOSURE OF INVENTION

Problems that Invention is to Solve

In the meanwhile, measurement of a pressure in a wide range from a negative pressure to a positive pressure needs a strong joint between a diaphragm and a means (sensor) for detecting a displacement of the diaphragm, and continuance of the joint.

However, each structure of the conventional pressure detection devices and the like needs a large magnet to strongly join the diaphragm to the sensor using the magnetic joining method, which fails to reduce a size of the device. In order to realize both of the size reduction and the strong joint between and the diaphragm and the sensor, the conventional pressure detection device or the like needs a plate-shaped magnet having a thin thickness and a large area. In this case, the magnet would easily cause cracks or the like, thereby reducing reliability of a strength.

In order to realize the size reduction for the device, it is also possible to use a permanent magnet as a plate-shaped member buried in the diaphragm. However, such a permanent magnet is buried in the diaphragm, so that the plate-shaped member is exposed to a high temperature during forming the diaphragm. As a result, there is a possibility that the permanent magnet loses or reduces its magnetic force. In addition, the expensive permanent magnet causes a further problem of a high cost of the device.

Furthermore, restriction of a relative position where a diaphragm is joined to a presser is vital to keep an accuracy of the pressure detection. However, if the restriction is to be achieved by adjusting a shape of a magnet, it is necessary to manufacture a magnet having a special shape, which causes a problem of increase of a manufacturing cost.

Thus, the present invention addresses the above problems. It is an object of the present invention to provide a pressure detection device that can realize easiness of installation and removal of a sensor in/from a diaphragm, measurement of a pressure in a wide rage, a size reduction, and a low manufacturing cost.

It is another object of the present invention to provide a pressure detection device that can realize measurement of a pressure with a high accuracy, a size reduction, and a low manufacturing cost.

Means to Solve the Problems

In accordance with an aspect of the present invention for achieving the objects, there is provided a pressure detection device including: a diaphragm provided at a side surface of a tube body that is a transfer channel of a fluid; and a pressure detection part that detects a pressure from the diaphragm, wherein the pressure detection part includes: a magnet that is applied with a load produced by pressing of the diaphragm; and a covering member that is made of a magnetic material and covers the magnet, and the diaphragm includes a plate-shaped member that is made of a magnetic material and buried in the diaphragm, wherein the plate-shaped member includes a protrusion part that protrudes from the diaphragm so as to be in contact with the magnet, and the covering member includes an opening part that enables the protrusion part and the magnet to be joined together.

With the above structure, the pressure detection device according to the present invention can efficiently use magnetic field lines to strongly join the diaphragm to the sensor, while using a magnetic joining method which enables the sensor to be easily installed and removed in/from the diaphragm. As a result, the pressure detection device according to the present invention can measure a pressure in a wide range from a negative pressure to a positive pressure. Furthermore, with the above structure, the present invention can provide a pressure detection device with a small size, having excellent reliability of strength and a high accuracy of pressure detection, without using a large magnet. Still further, since an expensive permanent magnet is not necessary, the pressure detection device according to the present invention can be manufactured at a low cost, while reducing a size. Still further, with the structure, the opening part arranged in the covering member of the magnet restricts a relative position where the diaphragm is joined to the presser. As a result, the pressure detection device according to the present invention can increase an accuracy of pressure detection of the sensor, without increasing a cost.

The pressure detection part may be installed in and removed from the diaphragm reversibly, by magnetic jointing between the magnet and the protrusion part. With the above structure, the pressure detection device according to the present invention can install and remove, by a simple action, the reusable sensor part into/from the diaphragm that will be disposed together with a used blood circuit.

It is preferable that the pressure detection device further includes a pair of wall parts that vertically leads the magnet and the covering member to the diaphragm, wherein a distance between the pair of wall parts is shorter than a distance between two facing edges of a movable part of the diaphragm. In accordance with another aspect of the present invention for achieving the objects, there is provided a pressure detection device including: a diaphragm provided at a side surface of a tube body that is a transfer channel of a fluid; and a pressure detection part that detects a pressure from the diaphragm, wherein the pressure detection part includes a magnet that is applied with a load produced by pressing of the diaphragm, the diaphragm includes a plate-shaped member that is made of a magnetic material and buried in the diaphragm, and the pressure detection device further includes a pair of wall parts that vertically leads the magnet and the covering member to the diaphragm, wherein a distance between the pair of wall parts is shorter than a distance between two facing edges of a movable part of the diaphragm.

With the above structure, a pair of wall parts vertically leading the sensor part to the diaphragm serves as a stopper restricting a displacement of the diaphragm. As a result, the pressure detection device according to the present invention can prevent that the diaphragm is expanded, for example, and thereby being damaged, when the diaphragm in which the pressure detection part is not installed is applied with a sudden strong positive pressure.

Furthermore, since the pair of wall parts restricts a movement of the magnet, the pressure detection device according to the present invention can detect a pressure with a high accuracy.

The plate-shaped member may have a plurality of holes along a circle that is inside an outer circumference of the plate-shaped member and that has a same center as a center of the outer circumference, and the plurality of holes may be provided with a member to join the plate-shaped member to the diaphragm, thereby integrating the plate-shaped member to the diaphragm.

It should be noted that the present invention can be realized not only as the pressure detection device, but also as a pressure detection method. That is, in accordance with still another aspect of the present invention for achieving the objects, there is provided a pressure detection method of detecting a pressure from a diaphragm provided at a side surface of a tube body that is a transfer channel of a fluid, the pressure detection method including detecting a load using a magnet, the load being produced by pressing of the diaphragm, wherein the magnet is covered with a covering member made of a magnetic material, a plate-shaped member made of a magnetic material is buried in the diaphragm and has a protrusion part protruding from the diaphragm so as to be in contact with the magnet, the covering member includes an opening part that enables the protrusion part and the magnet to be joined together, and the detecting includes joining the protrusion part to the magnet, so as to detect the pressure from the diaphragm. In accordance with still another aspect of the present invention for achieving the objects, there is provided a pressure detection method of detecting a pressure from a diaphragm provided at a side surface of a tube body that is a transfer channel of a fluid, the pressure detection method including detecting a load using a magnet, the load being produced by pressing of the diaphragm, wherein a plate-shaped member made of a magnetic material is buried in the diaphragm, a movement of the magnet is restricted by a pair of wall parts to vertically lead the magnet to the diaphragm, and a distance between the pair of wall parts is shorter than a distance between two facing edges of a movable part of the diaphragm, and the detecting includes: restricting the movement of the magnet; and thereby joining the diaphragm to the magnet, so as to detect the pressure from the diaphragm.

Effects of the Invention

The pressure detection device according to the present invention can efficiently use magnetic field lines to strongly join a diaphragm to a sensor, while using the magnetic joining method. As a result, the pressure detection device enables the sensor to be easily installed and removed in/from the diaphragm, and can measure a pressure in a wide range. In addition, the pressure detection device according to the present invention that can perform correct pressure detection can be manufactured at a low cost, while reducing a size. Furthermore, the pressure detection device according to the present invention can prevent damage on the diaphragm, thereby detecting a pressure with a high accuracy.

Accordingly, the present invention is highly suitable for practical use, in recent days the importance of the extracorporeal blood treatments such as dialysis has been increased.

NUMERICAL REFERENCES

BEST MODE FOR CARRYING OUT THE INVENTION

The following describes a preferred embodiment according to the present invention with reference to the drawings.

Firstly, an overall structure of the pressure detection device according to the present embodiment is described with reference toFIGS. 1 and 2.

FIG. 1is a perspective external view of the pressure detection device according to the present embodiment.FIG. 2is a cross-sectional view of the pressure detection device according to the present embodiment.

The pressure detection device according to the present embodiment includes a sensor part A and a disposable part B. The sensor part A is inserted into and engaged with the disposable part B in a direction shown by an arrow inFIG. 1. The sensor part A is a sensor structure that detects a pressure. The sensor part A includes a load cell1, a sensor chassis2, a presser3, a spring4, a magnet cap11, and a magnet12. The disposable part B is a structure included in a blood circuit for which a pressure of flowing blood is detected. The disposable part B includes a disposable-part upper chassis5, a disposable-part lower chassis6, a diaphragm8, an intra-diaphragm magnetic body9, and a ring10.

The load cell1is a pressure detector that converts a load transmitted via the presser3, into an electric signal using a distortion gauge.

The sensor chassis2is a member having a hollow therein. In the hollow, there is the load cell1, the presser3, and the spring4.

The presser3has one end connected to the load cell1and the other end connected to the magnet cap11. The presser3is a member that moves upwards and downwards inside of the sensor chassis2, and transmits the load from the magnet cap11to the load cell1.

The spring4is an elastic member, such as a spring, that moves the presser3to apply the load onto the load cell1.

The magnet cap11is a member made of a magnetic material and covers the magnet12. The magnet cap11has one surface connected to the other end of the presser3, and another surface having an opening for engaging the magnet12with the intra-diaphragm magnetic body9in the diaphragm8.

The magnet12is engaged with the intra-diaphragm magnetic body9to be applied with the load from the diaphragm8. The magnet12may be an electromagnet or the like.

The disposable-part upper chassis5is a member used to install the sensor part A into the disposable part B. The disposable-part upper chassis5leads the magnet cap11to be vertically contact with the diaphragm8.

The disposable-part lower chassis6is a member included in a tube that is a fluid channel7. The disposable-part lower chassis6has an opening part on a part of a side surface facing the disposable-part upper chassis5of the tube. In the opening part, the diaphragm8is provided.

The diaphragm8is a plate-shaped member that seals the opening part of the disposable-part lower chassis6and is displaced according to variations of a pressure of fluid flowing in the fluid channel7, thereby applying load to the magnet12. There is another case where the diaphragm8applies load to the magnet12by pressing, without being displaced. The diaphragm8is made of a synthetic rubber such as silicone or an isoprene rubber. As shown in the top view ofFIG. 3(B), the diaphragm8includes a central part8aand a peripheral part8b. The central part8ais harder than the peripheral part8b. In the diaphragm8, the intra-diaphragm magnetic body9is buried.

The intra-diaphragm magnetic body9is a plate-shaped member that is made of a magnetic material and buried in the diaphragm8. A part of the intra-diaphragm magnetic body9vertically protrudes to contact the sensor part A. The intra-diaphragm magnetic body9has a plate-shaped part9aof a disk shape as shown inFIG. 4with eight holes9dtherein. The holes9dare arranged equally spaced apart along a concentric circle9chaving the same center as a center of an outer circumference9b. This plate-shaped part9aof the intra-diaphragm magnetic body9is covered with a synthetic rubber material such as liquid silicone or an isoprene rubber, and the synthetic rubber material is hardened to integrate the plate-shaped part9ato the diaphragm8. Here, the synthetic rubber material located on and under the plate-shaped part9aand the synthetic rubber material in the eight holes9drealize strong integration of the intra-diaphragm magnetic body9to the diaphragm8.

The ring10is a ring-shaped member that is gripped between the disposable-part upper chassis5and the disposable-part lower chassis6, and fixes the diaphragm8by pressing the diaphragm8towards the disposable-part lower chassis6. An end part of the ring10close to the protrusion part of the intra-diaphragm magnetic body9has a tapering shape tapering towards the wall parts5bof the disposable-part upper chassis5. A lower edge of the end part matches a periphery of a part of the diaphragm8vibrating in parallel to the fluid channel7. The matching of the end part of the ring10and the periphery of the part (movable part) of the diaphragm8restricts a horizontal movement of the diaphragm8.

The above dimensions (shape) can prevent outer projection (protrusion) of the diaphragm and damages due to the projection (protrusion), even if something causes a large positive pressure on a lumens of the blood circuit in which the pressure detection part is not installed. It should be noted that it is also possible in the pressure detection device, mechanism, or method according to the present invention that the pressure detection part ofFIG. 1Ais removed when pressure detection is not necessary, and installed as shown inFIG. 2only when the pressure detection is performed. In the above case, the pressure detection part can be installed in the diaphragm (the protrusion part of the buried magnetic body9) by a simple action, which is convenient.

Next, the features of the pressure detection device according to the present embodiment are described with reference toFIG. 5.

FIG. 5is a partial cross-sectional view showing that the sensor A is being installed into the disposable part B.

As described above, the sensor part A is inserted into the disposable part B in a direction shown by the arrow inFIG. 5. Here, the engagement part2aof the sensor chassis2of the sensor part A is engaged with the engagement part5aof the disposable-part upper chassis5of the disposable part B, thereby locking the sensor part A together with the disposable part B. This structure enables the sensor part A to be easily installed into the disposable part B.

Here, on a surface of the magnet cap11covering the magnet12where the magnet cap11contacts the diaphragm8, a guide13that is an opening part for joining the protrusion part of the intra-diaphragm magnetic body9to the magnet12is provided. A diameter of the guide13is adjusted according to a diameter of the protrusion part of the intra-diaphragm magnetic body9, so that the protrusion part can join with the diameter of the guide13.

A distance between two facing wall parts5bof the disposable-part upper chassis5is adjusted according to a shape and dimensions of the magnet cap11, so that the wall parts5bcan lead the magnet cap11to be vertically contact with the diaphragm8. Furthermore, the distance between the two facing wall parts5bis adjusted to be shorter than a distance between facing edges (namely, facing edges of a part where the intra-diaphragm magnetic body9is buried, inFIG. 5) of the part (movable part) of the diaphragm8where the diaphragm8vibrates in a direction perpendicular to the fluid channel7.

As described above, the magnet12is covered by the magnet cap11, and only part of the magnet cap11where the magnet12contacts with the protrusion part of the intra-diaphragm magnetic body9is opened to form the guide13. With this structure, magnetic field lines of the magnet12are converged in a cross section of the guide13. Thereby, it is possible to improve a joining force joining the magnet12to the intra-diaphragm magnetic body9. This means that, with the structure, magnetic field lines of the magnet12are efficiently used to exert a strong joining force on a limited contact area where the magnet12contacts the intra-diaphragm magnetic body9, which makes it possible to measure a pressure in a wide range from a negative pressure to a positive pressure. In addition, with the above structure, since the magnet12does not need to be large to obtain the strong joining force, a size reduction of the pressure detection device can be achieved without reducing reliability of strength and an accuracy of pressure detection. Furthermore, with the simple structure of covering the magnet12with the magnet cap11, the size reduction of the pressure detection device can be achieved at a low cost, without using an expensive material such as a permanent magnet.

In addition, the guide13in the magnet cap11can restrict a relative position between the magnet12and the intra-diaphragm magnetic body9being joined together. That is, this structure can prevent a displacement of the relative position between the magnet12and the diaphragm8, and can keep a high accuracy of pressure detection of the sensor part A. Thereby, it is possible to realize a size reduction of the pressure detection device at a lower cost in comparison with the device using a magnet having a special shape, without reducing the accuracy of the pressure detection.

Furthermore, the distance between the two facing wall parts5bof the disposable-part upper chassis5is adjusted to be shorter than the distance between the facing edges of the displacing part of the diaphragm8. Thereby, the pair of the wall parts5bserves as a stopper when the diaphragm8is displaced (more particularly, vibrates along the disposable-part lower chassis6). As a result, an unexpected displacement of the diaphragm8can be restricted thereby further increasing an accuracy of the pressure detection.

It should be noted that appropriate selection of a material and a shape of the magnet cap11makes it possible to arbitrarily set a range of a measurable pressure, especially, a range of a measurable negative pressure.

Here, an effect of the use of the magnet cap11is described with reference toFIG. 6.

FIG. 6shows a graph plotting a difference in the joining force joining the magnet12to the intra-diaphragm magnetic body9, between when the magnet cap11is used and when the magnet cap is not used.

As shown inFIG. 6, when the magnet cap11is used, approximately two times stronger joining force is exerted between the magnet12and the intra-diaphragm magnetic body9, in comparison with when the magnet cap is not used. This means that the use of the magnet cap11to converge the magnetic field lines of the magnet12into the cross section of the guide13dramatically increases a joining force joining the magnet12to the intra-diaphragm magnetic body9. Here, this graph shows a relationship between existence of the magnet cap11and the joining force, assuming that a thickness of the magnet cap11is 0.8 mm, a thickness of the magnet12is 5 mm, and a thickness of the protrusion part of the intra-diaphragm magnetic body9is 2.5 mm. It should be noted that these values are merely examples, and even different thicknesses result in the same difference in the effect of the existence of the magnet cap11.

Moreover, the thickness of the protrusion part of the intra-diaphragm magnetic body9influences the joining force joining the magnet12to the intra-diaphragm magnetic body9.

FIG. 7is a graph showing an effect of the thickness of the protrusion part of the intra-diaphragm magnetic body9onto a strength of the magnetic joining force.FIG. 7shows a relationship between the thickness of the protrusion part of the intra-diaphragm magnetic body9and the joining force, assuming that a thickness of the magnet12is 5 mm.

As shown inFIG. 7, the increase of the thickness of the protrusion part of the intra-diaphragm magnetic body9increases the joining force joining the magnet12to the intra-diaphragm magnetic body9, up to 2 mm of the thickness. However, after exceeding 2 mm, the joining force is appropriately constant, even if the thickness is increased. This shows that the thickness of the protrusion part of the intra-diaphragm magnetic body9is preferably equal to or more than 2 mm, when the thickness of the magnet12is 5 mm.

It should be noted that the thickness of the protrusion part of the intra-diaphragm magnetic body9may be arbitrarily set depending on a desired joining force and a desired removing force.

Furthermore, a diameter of the protrusion part of the intra-diaphragm magnetic body9influences the joining force joining the magnet12to the intra-diaphragm magnetic body9. Increase of the diameter of the protrusion part, in other words, increase of an area where the magnet12contacts the intra-diaphragm magnetic body9, can increase the joining force joining the magnet12to the intra-diaphragm magnetic body9. However, the increase of the area where the magnet12contacts the intra-diaphragm magnetic body9reduces sensitivity of the magnet12, thereby reducing an accuracy of pressure detection. Therefore, the diameter of the protrusion part of the intra-diaphragm magnetic body9is arbitrarily set depending on a desired joining force and a desired accuracy of the pressure detection.

As described above, the pressure detection device according to the present embodiment, which has a simple structure in which the magnet12is covered with the magnet cap11, efficiently uses magnetic field lines of the magnet12to strongly join the diaphragm8to the sensor part A. Thereby, the pressure detection device according to the present embodiment can measure a pressure in a wide range from a negative pressure to a positive pressure. In addition to the advantages of the magnetic joining method for the easiness in installing and removing the sensor part in/from the disposable part, there are other advantages of size reduction of the pressure detection device with a low cost while keeping a reliability of strength and a high accuracy of pressure detection. Still further, the magnet cap11has a shape to restrict a relative position between the magnet12and the diaphragm8, which makes it possible to prevent damage on the diaphragm8, and keep an accuracy of pressure detection of the sensor part without increasing a cost.

Although the exemplary embodiment of the pressure detection device according to the present invention has been described in detail above, those skilled in the art will be readily appreciate that many modifications are possible in the exemplary embodiment without materially departing from the novel teachings and advantages of the present invention. Accordingly, all such modifications are intended to be included within the scope of the present invention.

For example, it has been described in the present embodiment that the presser3is separated from the magnet cap11, but the presser3may be integrated with the magnet cap11.

Furthermore, it has been described in the present embodiment that the diaphragm8applies load onto the load cell1, but it is also possible that the load cell1applies load to the diaphragm8. In this case, the presser3and the spring4operate in an opposite direction to the direction in the embodiment.

INDUSTRIAL APPLICABILITY

The pressure detection device according to the present invention can be used as a device that measures a pressure of a fluid flowing in a blood circuit. The pressure detection device is suitable for measurement of a pressure of a fluid in a blood circuit used for dialysis, apheresis, or the like.