Cartridge with fill level detection

A cartridge (2) with a fill level detection system (10, 10′, 10″), the cartridge comprising a substantially rigid containing wall (4) having a tubular wall portion (12) surrounding a chamber (18) for receiving liquid therein, a plunger or piston (8) mounted inside the chamber and configured to seal one side of the chamber, the plunger or piston being displaceable in the chamber towards an outlet end (14) of the cartridge, characterized in that the fill level detection system comprises a plurality of discrete fixed electrodes (24, 24′) positioned along the tubular wall portion in a juxtaposed manner in a direction of displacement D of the plunger or piston (8), and a mobile electrode member (28) fixed to the plunger or piston and displaceable therewith.

FIELD OF THE INVENTION

The present invention relates to a cartridge for containing fluids, with a fill level detection system. The invention in particular relates to a cartridge for liquid medicinal products, such as insulin, glucagon, and growth hormones, the cartridge comprising a mobile piston or plunger for expelling the liquid or simply allowing a change in volume in the cartridge.

BACKGROUND

Cartridges with a piston or plunger are well-known in insulin pump systems whereby detection of the fill level of the cartridge is important to ensure that the pump system functions correctly and/or that the correct dosage is supplied and/or to signal replacement of the cartridge.

Various cartridge fill level detection systems have been proposed as described in U.S. Pat. No. 5,704,922, U.S. Pat. No. 6,352,523, WO 2007/107558, and DE 102004040441.

In U.S. Pat. No. 5,704,922, a syringe having electrical contacts points for metering doses is disclosed. A disadvantage of this system is the risk of short-circuiting between contacts leading to a false fill level reading. Moreover, in view of the difficulty of providing a large number of contacts, the fill level accuracy of the system is poor. The need to connect the contacts on the plunger requires a connector that is costly and voluminous.

Some of these drawbacks are overcome by contactless fill level detection systems as described for example in U.S. Pat. No. 6,352,523, DE 102004040441 or WO 2007/107558. In these known systems, electrodes are positioned on either side of the cartridge to measure the capacitance which is dependent, inter alia, on the dielectric properties between the electrodes. The dielectric properties depend on the material forming the cartridge walls, the distance separating the electrodes, the material of the plunger, the dielectric value of the liquid in the cartridge and the fill level. As the liquid in the cartridge has a dielectric properties that are different to air and the material of the plunger, the overall capacitance value will vary as the plunger advances and liquid is expelled out of the cartridge. One of the major drawbacks of this measuring system is its sensitivity to interference, and the need to accurately calibrate the system in view of the reliance on many factors affecting the capacitance measurement. The accuracy and reliability of such a system may in many applications be insufficient. Also, the need to adjust calculation of the measurement and to calibrate the cartridge fill level detection as a function of the diameter of the cartridge and the material used for the cartridge as well as the properties of the liquid in the cartridge, is costly.

SUMMARY OF THE INVENTION

In view of the aforegoing, it is an object of this invention to provide a cartridge for fluid storage and delivery, with an accurate and reliable fill level detection system.

It would be advantageous to provide a cartridge with fill level detection that is economical.

It would be advantageous to provide a cartridge with fill level detection that may be implemented in cartridges of different sizes, shapes and materials that is easy to configure and calibrate.

Objects of this invention have been achieved by providing the cartridge with fill level detection according to claim1.

Disclosed herein is a cartridge comprising a substantially rigid containing wall having a tubular wall portion surrounding a chamber for receiving liquid therein, a mobile plunger or piston mounted inside the chamber and configured to seal one side of the chamber, the plunger or piston being displaceable from a plunger end of the tubular wall portion to an outlet end of the tubular wall portion for allowing the liquid to be expelled out of the chamber, and a capacitive fill level detection system, characterised in that the fill level detection system comprises a plurality of discrete fixed electrodes positioned along the tubular wall portion in a juxtaposed manner in the direction of displacement of the plunger or piston, and a complementary mobile electrode member fixed to the plunger or piston and displaceable therewith. The position of the plunger/piston, and thus the fill level of the fluid in the chamber, is determined by reading the capacitance value between each of the plurality of fixed electrodes positioned along the tubular wall portion, and the complementary mobile electrode on the plunger/piston, whereby the fixed electrode that provides the strongest signal indicates the position of the plunger electrode.

The signals from the plurality of fixed electrodes may by read simultaneously or sequentially. Preferably, the plurality of fixed electrodes on the tubular wall portion are connected to a multiplexer configured to activate and read the plurality of electrode sequentially from one end of the tubular wall portion to the other end or in any chosen order.

Advantageously, the fill level detection system according to the invention does not depend on the material properties, shape, and dimensions of the cartridge components and the liquid contained therein and is thus particularly reliable and robust. Also, fill level detection can be easily implemented in cartridges of different sizes, shapes and materials for use with different liquids, easily and with little or no calibration.

Further objects and advantageous aspects of the invention will be apparent from the claims and the following detailed description and annexed drawings.

Referring to the Figures, a cartridge2,2′,2″ comprises a container wall4, an outlet6, a plunger or piston8, and a fill level detection system10,10′,10″.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The container wall4comprises a tubular wall portion12extending from an outlet end14to an opposed plunger end16proximate a starting position of the plunger/piston8when the cartridge is full. The outlet end14, tubular wall portion12and plunger/piston8define a chamber18storing a fluid20that is expelled though the outlet6when the plunger/piston is advanced towards the outlet end14. The tubular wall portion12thus extends in a direction of displacement D of the plunger or piston and preferably has a cylindrical shape.

The cartridge2,2′,2″ may for example be in the general form of a vial for the storage and delivery of a liquid medicine such as insulin, the cartridge being replaceably installed in a delivery system, for instance an insulin pump device. The cartridge may also be non-replaceable and refilled, for example through a valve or a seal, from a separate liquid source.

The outlet end14of the cartridge may for example be in a form of a cap with an aseptic self-sealing membrane that is pierced by a needle that forms the outlet6of the cartridge. The needle6may be connected to a system for delivery of a liquid medicine, such as insulin, to a patient.

The plunger/piston8may comprise a stopper with elastic sealing rings, or a stopper integrally made of an elastic material, for instance silicon rubber.

The cartridge tubular wall portion12may be made of glass, a plastic material or other non-conductive materials suitable for the fluid20that is contained in the cartridge.

The fill level detection system10,10′,10″ comprises a plurality of discrete fixed electrodes24,24′ arranged in a juxtaposed manner along the tubular wall portion12in the direction D of displacement of the plunger8, and a complementary electrode26comprising a conductive mobile discrete electrode member28fixed to the plunger/piston8.

The mobile discrete electrode member28is preferably in a form of a substantially planar disc that has a shape that essentially corresponds to the cross-sectional profile of the chamber18. The mobile discrete electrode member may however be provided in other shapes and sizes without departing from the scope of the invention. The mobile discrete electrode member28may be attached, for example bonded, to a rear side of the plunger/piston opposite the liquid filled side of the chamber. The mobile discrete electrode member may however be mounted within the plunger/piston by overmoulding, assembling in a corresponding cavity in the plunger/piston, or mounted on the liquid contacting side of the plunger/piston8. The mobile discrete electrode member28may be in the form of a metallic disk that is mounted to the plunger/piston, or could be in the form of a conductive layer deposited on a substrate or directly on a surface of the plunger/piston. The mobile discrete electrode member could also be in a form of a conductive material layer that is formed or deposited in an injection molding or casting process during which the plunger or piston is also formed.

The fill level detection system further comprises a signal processing circuit30connected to the plurality of fixed electrodes24,24′ and the complementary mobile electrode member28and configured to send an electrical signal to the electrodes and to read the response thereof. The signal processing circuit, in a preferred embodiment, comprises a signal multiplexer and/or demultiplexer for sending and/or receiving electrical signals to each of the plurality of discrete fixed electrodes24,24′. The fixed electrodes24,24′ can be used either as a receiver or as a sender of the electrical measurement signal whereby the complementary electrode26,26′,26″ may act as a receiver if the discrete plurality of electrodes act as senders, or as a sender if the discrete plurality of electrodes act as receivers.

The multiplexer/demultiplexer30enables an electrical signal to be applied to the plurality of fixed electrodes24,24′ sequentially, i.e. one after the other, and to determine the electrical signal response for each of the fixed electrodes24,24′ whereby the peak signal P will occur for the discrete fixed electrode24m,24m′ positioned closest to the mobile electrode member28as best illustrated inFIG. 1cin conjunction with1a,2cin conjunction with2a, and3bin conjunction with3a. As the signal response strongly depends on the position of the mobile electrode member28, and thus on the plunger/piston position, but not on the dimensions and dielectric properties of the cartridge the fluid, the position of the plunger/piston may be determined reliably and with a high tolerance to external noise, temperature or other factors that may affect reading of a capacitance value.

Referring in particular toFIGS. 1a,1b, the plurality of discrete fixed electrodes24may advantageously comprise electrode portions24athat wrap around the tubular wall portion12of the cartridge partially, for example as shown inFIG. 1b, or completely (not shown). In the case of a cylindrical tubular cartridge as illustrated, the electrode portions24awould thus form partial or complete rings arranged coaxially around the chamber28through which the plunger/piston8is displaced.

The spacing s between adjacent fixed electrodes24,24′ and the width w of each electrode in the direction of displacement D of the plunger/piston may be adjusted to take into account the number of electrodes per unit length of cartridge, the spacing required between adjacent electrodes for electrical insulation or decoupling of capacitive effect, or to take into account the signal strength. In other terms, the geometry of the fixed electrodes may be adjusted to optimize the peak signal P reading. The thickness t of the mobile discrete electrode member28, in the plunger/piston displacement direction D, may be determined empirically for optimal signal accuracy, robustness and strength. Preferably, the thickness t of the mobile electrode member is less than double the spacing s between adjacent fixed electrodes24,24′ more preferably less than 1.5 times the spacing s between adjacent fixed electrodes.

The fixed electrodes24,24′ may be in the form of conductors embedded by overmolding or casting in the material forming the tubular wall portion of the cartridge during formation thereof. The wrap around portions24a,24a′ of the fixed electrodes could also be deposited on a layer inside, or on an outer layer of the tubular wall portion12, by various known metal deposition processes. Fixed electrodes could, in yet another variant, be formed on a separate substrate, for example a flexible substrate or a thermoformable substrate that is wrapped around and bonded or fixed by other means to the cartridge container wall4, whereby the signal processing circuit may also be integrally formed on the substrate or alternatively connected thereto via a connector on the substrate or by other known interconnection means for flexible printed circuits.

The discrete fixed electrodes24,24′ could also be formed on or within a housing with a cavity corresponding to the outer shape of the cartridge so that the housing (not shown) may by inserted over the cartridge as a single piece or assembled therearound by splitting the housing into two pieces or alternatively by having a single housing with essentially U-shape cavity that is mounted in a direction orthogonal to the displacement direction D over the cartridge tubular wall portion12.

Therefore, the fixed electrodes may be formed in or on the tubular wall portion12of the cartridge or on a separate member that is positioned partially or completely around the tubular wall portion12.

In the embodiment ofFIGS. 1ato1c, the mobile electrode member28is connected directly to the signal processing circuit30by means of a conductor lead31which may be an insulated wire conductor. In other variants, the mobile electrode member may be electrically connected to the signal processing circuit30via a plunger push rod made of or comprising a conducting material connected at its other end to the signal processing circuit, or via a piston plunger push spring31′ made of or comprising a conducting material as illustrated in the embodiment ofFIGS. 3a,3b.

Referring toFIGS. 2ato2c, the complementary mobile electrode member28is capacitively coupled to a conductor34of the complementary electrode26′ extending along the cartridge in the direction of displacement D and positioned on an opposite side of the cartridge containing wall4from the discrete fixed electrodes24′, the conductor34being interconnected to the signal processing circuit30. An advantage of this embodiment is that the mobile electrode member28does not require a direct electrical interconnection, whereby the electrical interconnection of the complementary electrode conductor34and the discrete fixed electrodes24′ to the signal processing circuit may be performed without any interconnections to moving parts. The complementary electrode conductor34thus acts as a capacitively coupled electrode with respect to the mobile discrete electrode member28.

It would also be possible, within the scope of this invention, to split the complementary electrode conductor34into a plurality of discrete fixed electrodes arranged opposite the fixed electrodes24′ in order to form juxtaposed pairs of opposing electrodes interconnected to the multiplexer circuit30. In the latter variant, the mobile discrete electrode member28would act as a capacitive coupling element between respective pairs of opposed electrodes arranged either side of the cartridge cavity.

As illustrated in the embodiment ofFIG. 2b, the fixed electrodes24′ and opposed complementary electrode conductor34(or opposed fixed electrodes with reference to the above described variant) may each wrap around less than half the perimeter of the tubular wall portion12of the cartridge.

The complementary electrode conductor34may be mounted or deposited on the cartridge by any of the various techniques mentioned above with respect to the fixed electrodes24,24′.