Infusion pump cassette latch

A tube cassette (22) for receiving infusion tubing is shaped to define a locking surface (26). A pump (20) includes a latch (28) which engages with the locking surface and locks the cassette in a preset position with respect to the pump. A mechanical stop (38) in the pump stops motion of the cassette in a first direction, such that the cassette has moved past the preset position. Until motion of the cassette is stopped by the mechanical stop, the latch allows motion of the cassette past the preset position in the first direction. The latch automatically moves from an open position to a cassette-withdrawal-inhibiting position upon engagement of the latch with the locking surface, and subsequently locks the cassette in the preset position by pushing the cassette in a second direction, from past the preset position to the preset position. Other applications are also described.

FIELD OF THE INVENTION

The present invention relates generally to medical fluid-delivery devices, and more specifically to infusion pumps.

BACKGROUND

Pumps are often used in the medical industry for delivering fluids, e.g., drugs, or diagnostic fluids, to subjects. One type of medical pump is an infusion pump, used to infuse a fluid into a subject's circulatory system via infusion tubing. Some infusion pumps include a valve, or system of valves, that may occlude flow within the infusion tubing by pressing on the outside of the fluid-filled infusion tubing. Often infusion pumps engage with the infusion tubing via a tube cassette.

SUMMARY OF THE INVENTION

Infusion pumps often engage with infusion tubing via a tube cassette that receives the infusion tubing and is subsequently coupled to the infusion pump. The following are some properties and phenomena that may occur in infusion pumps that utilize tube cassettes:In some infusion pumps, the tube cassette has to be inserted in a particular way, e.g., starting from a particular side of the pump and pivoting down towards the opposite side of the pump.In some infusion pumps, the coupling of the tube cassette and the pump may have a region of meta-stability, at which in the absence of any force external to the tube cassette, the tube cassette may be engaged with the pump but in an unstable manner, whereby the tube cassette may pop out at any point.In some infusion pumps, during delivery of the fluid to the subject, if an external force is applied to the tube cassette, pressure may be put on the infusion tubing causing either a bolus delivery to the patient, or inaccuracy of the delivery volume.

In light of these considerations, an infusion pump and tube cassette are provided, in accordance with some applications of the present invention. The tube cassette receives the infusion tubing and is removably couplable to the pump. The pump and tube cassette have a locking system that includes a locking surface on the tube cassette, a latch on the pump, and a mechanical stop disposed within the pump. When the tube cassette is coupled to the pump, the latch lockingly engages with the locking surface in such a way as to ensure that, upon full insertion of the tube cassette into the pump, the latch (a) automatically moves to a cassette-withdrawal-inhibiting position, avoiding a possibly meta-stable connection between the tube cassette and the pump, and (b) locks the tube cassette in a preset position with respect to the pump.

As the tube cassette is inserted into the pump, motion of the tube cassette in a first direction, toward the pump, can continue all the way until the tube cassette is stopped by the mechanical stop. The mechanical stop is positioned to stop the motion of the tube cassette once the tube cassette has “over-traveled,” i.e., has moved past the preset position. The “over-travel” of the tube cassette ensures that the latch fully engages the locking surface, without the latch potentially getting stuck in a meta-stable position. After the latch has achieved a state of making sure the cassette cannot fall out of the pump, the latch then locks the tube cassette in the preset position by pushing the tube cassette back from past the preset position (where it was stopped by the mechanical stop) to the preset position.

There is therefore provided, in accordance with some applications of the present invention, apparatus for delivering a fluid to a subject through infusion tubing, the apparatus including:(A) a tube cassette configured to receive the infusion tubing, the tube cassette shaped to define a locking surface;(B) a pump including a latch,(i) the tube cassette being configured to be removably coupled to the pump, and(ii) the latch being configured to (a) engage with the locking surface and (b) lock the tube cassette in a preset position with respect to the pump when the tube cassette is coupled to the pump; and(C) a mechanical stop disposed within the pump,(i) the mechanical stop being positioned to stop motion of the tube cassette in a first direction, such that when the motion of the tube cassette in the first direction is stopped by the mechanical stop, the tube cassette has moved past the preset position in the first direction, and(ii) the latch being configured to:(a) until the motion of the tube cassette is stopped by the mechanical stop, allow motion of the tube cassette past the preset position in the first direction,(b) automatically move from an open position to a cassette-withdrawal-inhibiting position upon engagement of the latch with the locking surface, and(c) subsequently, lock the tube cassette in the preset position by pushing the tube cassette in a second direction opposite the first direction, from past the preset position to the preset position.

For some applications, the latch is a spring-loaded latch.

For some applications, the latch is configured to, during the coupling of the tube cassette to the pump, sequentially:(a) rotate in a first rotational direction during a transition from (i) an initial position prior to the tube cassette being coupled to the pump to (ii) the open position, during motion of the tube cassette in the first direction,(b) rotate in a second rotational direction, opposite the first rotational direction, in the transition from (i) the open position to (ii) the cassette-withdrawal-inhibiting position, and(c) continue rotation in the second rotational direction during the pushing of the tube cassette in the second direction from past the preset position to the preset position, such that the latch returns to the initial position subsequently to the pushing of the tube cassette in the second direction.

For some applications, the cassette-withdrawal-inhibiting position of the latch is between (a) an initial position of the latch prior to the tube cassette being coupled to the pump and (b) the open position.

For some applications, the pump and the tube cassette are configured such that, in the absence of a sufficient external force maintaining the motion of the tube cassette in the first direction prior to the engagement of the latch with the locking surface, the pump is configured to eject the tube cassette by pushing the infusion tubing which in turn pushes the tube cassette from the pump.

For some applications, the latch includes a lower latch surface, the lower latch surface being configured to engage with the locking surface of the tube cassette, the lower locking surface having a radius of curvature that is substantially equal to a distance between an axis of rotation of the latch and the lower latch surface.

For some applications:the locking surface is a lower locking surface, and the tube cassette is further shaped to define an upper locking surface, opposite the lower locking surface, andthe latch includes a lower latch surface and an upper latch surface, (a) the lower latch surface being configured to engage with the lower locking surface, and (b) the upper latch surface being configured to engage with the upper locking surface when the tube cassette is coupled to the pump, such that:(i) engagement between the lower latch surface and the lower locking surface inhibits cassette withdrawal when the latch moves from the open position to the cassette-withdrawal-inhibiting position, and(ii) subsequently, the upper latch surface pushes the tube cassette in the second direction by pushing on the upper locking surface of the tube cassette.

For some applications, the lower and upper latch surfaces are shaped to define the preset position of the tube cassette, such that subsequently to the upper latch surface pushing the tube cassette in the second direction, (a) movement of the tube cassette in the first direction is inhibited by the upper latch surface, and (b) movement of the tube cassette in the second direction is inhibited by the lower latch surface.

For some applications, the lower locking surface is shaped to define a radius of curvature that is substantially equal to a distance between an axis of rotation of the latch and the lower latch surface.

For some applications:the locking surface is a first locking surface and the tube cassette is shaped to define a second locking surface, andthe latch is a first latch and the pump further includes a second latch, the second latch being configured to (a) lockingly engage with the second locking surface and (b) lock the tube cassette in the preset position with respect to the pump when the tube cassette is coupled to the pump.

For some applications, the first and second latches are disposed on opposite sides of the pump.

The present invention will be more fully understood from the following detailed description of applications thereof, taken together with the drawings, in which:

DETAILED DESCRIPTION

Reference is now made toFIG.1A, which is a schematic illustration of a pump20with a tube cassette22coupled to the pump, in accordance with some applications of the present invention. Pump20is typically an infusion pump, e.g., a volumetric infusion pump, or a peristaltic infusion pump, that delivers fluid, e.g., drugs or diagnostic fluids, to subjects through infusion tubing24. Tube cassette22receives infusion tubing24and is removably couplable to pump20, such that pump20engages with infusion tubing24via tube cassette22.

Typically, tube cassette22is shaped to define at least one locking surface26, e.g., a first locking surface26′ and a second locking surface26″ respectively on either side of tube cassette22. Typically, pump20comprises at least one latch28, e.g., a first latch28′ and a second latch28″ disposed respectively on either side of pump20. As tube cassette22is coupled to pump20, e.g., inserted into pump20by being pushed into pump20in a first direction toward pump20, latch28lockingly engages a locking surface26of tube cassette22. Typically, such as is shown inFIG.1A, first latch28′ engages with first locking surface26′ and second latch28″ engages with second locking surface26″.

Subsequently to the latch28engaging with locking surface26, latch28(e.g., latches28′ and28″) locks tube cassette22in a preset position with respect to pump20, as further described hereinbelow with reference toFIGS.2and3.FIG.1Ashows tube cassette22already locked in the preset position after having been coupled to pump20. For some applications, as further described hereinbelow, each latch28has a lower latch surface30and an upper latch surface32.

Reference is now made toFIG.1B, which is a schematic illustration of latch28, in accordance with some applications of the present invention. For some applications, latches28are spring-loaded latches. As further described hereinbelow, tube cassette22is coupled to pump20typically by a user pushing tube cassette22into pump20. In turn, tube cassette22pushes latch to rotate, in a first rotational direction, represented by curved arrow36. Spring29spring-loads latch28, such that as latch28rotates in the first rotational direction, spring29biases latch28to return to its initial position by rotating in a second rotational direction, opposite the first rotational direction (represented by curved arrows42inFIGS.2and3).

Reference is now made toFIG.2, which is a schematic illustration showing various different positions of latch28during coupling of tube cassette22to pump20, in accordance with some applications of the present invention.FIG.2shows a transition of the latch position from position (A), prior to tube cassette22being coupled to pump20, through to position (E), in which tube cassette22is locked in the preset position with respect to pump20.

Coupling of tube cassette22to pump20is typically done by pushing tube cassette22in a first direction, toward pump20. For some applications, latches28′ and28″ may be engaged one after the other, i.e., tube cassette22is coupled to pump20by engaging one of the latches and then pivoting tube cassette22in a direction toward pump20to engage the other latch. Typically, latches28′ and28″ are identical in shape and disposed in a generally mirror-image orientation with respect to each other so it does not matter which latch is engaged first and which latch is engaged after pivoting tube cassette22toward pump20. Thus, tube cassette22may alternatively or additionally be pushed toward pump20such that both latches are engaged simultaneously.

Position (A) of latch28represents an initial position of latch28, prior to tube cassette22being coupled to pump20. As described hereinabove, coupling of tube cassette22to pump20is via movement of tube cassette22in a first direction, toward pump20. Arrow34represents motion of tube cassette22in the first direction. As tube cassette22moves in the first direction (e.g., due to a user pushing tube cassette22into pump20), tube cassette22pushes latch28to rotate, in a first rotational direction from the initial position (A) to an angular position (B) (that is, the angular position is at a non-zero angle from the initial position). As tube cassette22continues to move further in the first direction, latch28continues its rotation in the first rotational direction until position (C) is reached, representing an open position of latch28. Curved arrow36in positions (B) and (C) represents the first rotational direction in which latch28rotates in the transition from position (A) to position (B) and subsequently from position (B) to position (C), i.e., to the open position of latch28.

As shown in position (C), latch28, e.g., lower latch surface30, has not yet engaged with locking surface26. Typically, prior to engagement of latch28, e.g., lower latch surface30, with locking surface26, in the absence of a sufficient external force maintaining the motion of tube cassette22in the first direction, pump20ejects tube cassette22by pushing infusion tubing24, which in turn pushes tube cassette22from pump20. If tube cassette22is released prior to reaching a threshold position, pump20will eject tube cassette22. In order to not be ejected by pump20, tube cassette22has to move, in the first direction, past the threshold position.

Thus, for some applications, pump20and tube cassette22are designed so as to allow “over-travel” of tube cassette22in the first direction, thus ensuring that tube cassette22moves past the threshold position, allowing latch28, e.g., lower latch surface30, to engage locking surface26. A mechanical stop38is disposed within pump20and positioned to stop the motion of tube cassette22in the first direction. Thus, the external force pushing tube cassette22in the first direction is able to continue pushing until motion of tube cassette22in the first direction is stopped by mechanical stop38. When the motion of tube cassette22in the first direction is stopped by mechanical stop38, tube cassette22has moved past the preset position with respect to pump20, i.e., has “over-traveled” in the first direction. The preset position with respect to pump20is represented by dashed line40inFIG.2.

The “over-travel” position where the motion of tube cassette22is stopped by mechanical stop38is represented by position (D) inFIG.2. As described hereinabove, latch28, e.g., latches28′ and28″, lock tube cassette22in the preset position with respect to pump20. However, until the motion of tube cassette22is stopped by mechanical stop38, latch28allows motion of tube cassette22past the preset position in the first direction.

Upon engagement of latch28, e.g., lower latch surface30, with locking surface26, latch28, being typically spring-loaded, automatically moves from its open position, position (C), to a cassette-withdrawal-inhibiting position, position (D). During this transition from the open position to the cassette-withdrawal-inhibiting position, latch28switches direction and rotates in a second rotational direction, opposite the first rotational direction, represented by curved arrow42in position (D).

Typically, the cassette-withdrawal-inhibiting position of latch28is between the initial position of latch28prior to tube cassette22being coupled to pump20(position (A)) and the open position of latch28(position (C)), i.e., latch28inhibits cassette-withdrawal even before latch28returns to its initial position. The combination of the following three characteristics of the coupling of tube cassette22to pump20results in substantially no chance of a meta-stable coupling between tube cassette22and pump20, i.e., where tube cassette22is coupled to pump20but in an unstable manner:(a) in the absence of sufficient force to keep tube cassette22moving, pump20ejecting tube cassette22prior to engagement of latch28and locking surface26,(b) allowing “over-travel” to ensure engagement of latch28and locking surface26as tube cassette22is pushed toward pump20, and(c) latch28automatically moving to the cassette-withdrawal-inhibiting position (prior to latch28finishing closing), upon engagement of latch28with locking surface26.

Subsequently to latch28moving to the cassette-withdrawal-inhibiting position, latch28locks tube cassette22in the preset position by pushing tube cassette22(further described hereinbelow) in a second direction, opposite the first direction, e.g., away from pump20, such that tube cassette22moves from past the preset position to the preset position, at dashed line40. Arrow44represents motion of tube cassette22in the second direction as tube cassette22is pushed by latch28, e.g., by latches28′ and28″, back to the preset position. During this pushing of tube cassette22in the second direction, latch28continues its rotation in the second rotational direction, such that latch28returns to the initial position of latch28subsequently to the pushing of tube cassette22in the second direction, such as is shown in position (E) ofFIG.2.

For some applications, latch28pushes tube cassette22in the second direction via engagement between upper latch surface32of latch28and an upper locking surface46of tube cassette22(i.e., locking surface26is a lower locking surface26and tube cassette22is shaped to define an upper locking surface46as well). Subsequently to the motion of tube cassette22being stopped by mechanical stop38, the external force that was maintaining the motion of tube cassette22in the first direction (e.g., the external force being generated by the user pushing the tube cassette into pump20) is typically terminated. In the absence of the external force, latch28, being typically spring-loaded, continues its rotational motion back towards the initial position of latch28. During this continued rotational motion in the second rotational direction, upper latch surface32pushes upper locking surface46in the second direction, e.g., away from pump20.

Typically, lower latch surface30and upper latch surface32are shaped to define the preset position of tube cassette22, such that subsequently to latch28pushing tube cassette22into the preset position, (a) movement of tube cassette22in the first direction is inhibited by upper latch surface32, and (b) movement of tube cassette22in the second direction is inhibited by lower latch surface30. As used in the present application including in the claims, movement being prohibited is taken to mean that movement of larger than 20 microns is inhibited. The preset position of tube cassette22, in turn, defines a preset distance D1between tube cassette22and mechanical stop38, and a preset distance between a pressing surface inside pump20(not shown) that repeatedly presses on infusion tubing24to deliver the fluid to the subject.

The locking of tube cassette22in the preset position by latch28, e.g., latches28′ and28″, inhibits any external forces that may act on tube cassette22during delivery of the fluid from affecting the delivery of the fluid, by affecting the distance between the pressing surface and infusion tubing24. For example, in the absence of latch28(e.g., latches28′ and28″) locking tube cassette22in the preset position, if an external force pushes on tube cassette22in the first direction, e.g., towards pump20, the distance between the pressing surface inside pump20and infusion tubing24will decrease, which in turn may cause a bolus of fluid to be delivered to the subject and/or an inaccuracy in the volume of fluid delivered to the subject. Similarly, for example, in the absence of latch28(e.g., latches28′ and28″) locking tube cassette22in the preset position, if an external force pulls tube cassette22in the second direction, e.g., away from pump20, the distance between the pressing surface and infusion tubing24may increase, resulting in potential under-delivery of the fluid to the subject.

Reference is now made toFIG.3, which is a schematic illustration showing various different positions of latch28, in accordance with some applications of the present invention. It is desirable that as soon as latch28(e.g., upper latch surface32) has pushed tube cassette22into the preset position, any continued rotational movement of latch28in the second rotational direction (i.e., as latch28returns to its initial position) not change preset distance D1between tube cassette22and mechanical stop38. This is advantageous, for example, if latch28does not return to its initial position, tube cassette22is still (a) inhibited from falling out of pump20due to latch28having automatically moved to the cassette-withdrawal-inhibiting position, and (b) locked in the preset position due to latch28not changing the distance between tube cassette22and mechanical stop38during its rotational motion in the second direction subsequent to pushing tube cassette22into the preset position. (Although pump20is not shown inFIG.3, distance D1inFIG.3represents the same preset distance D1shown inFIG.2between tube cassette22and mechanical stop38when latch28is in position (E).).

For some applications, this is achieved by lower locking surface26having radius of curvature R that is substantially equal to a distance D2between an axis of rotation48of latch28and lower latch surface26, such that, subsequently to upper latch surface32pushing tube cassette22into the preset position, as lower latch surface30continues to swing rotationally inwards towards pump20the motion of lower latch surface30follows the radius of curvature R of lower locking surface26. Typically, the radius of curvature R being substantially equal to distance D2ensures that as latch surface30continues to swing rotationally inwards, towards pump20, a distance of typically no more than 20 microns is maintained between lower latch surface30and lower locking surface26. Thus, at no point between (a) when tube cassette22is pushed into the preset position and (b) when latch28returns to the initial position, does lower latch surface30push on lower locking surface26in the first direction, e.g., toward pump20. Yet, at substantially every point during the continued rotation in the second direction, if latch28were to stop its motion, lower latch surface30would still inhibit movement of tube cassette22in the second direction, as described hereinabove.

Reference is now made toFIGS.4A and4B, which are schematic illustration of tube cassette22, in accordance with some applications of the present invention. For some applications, tube cassette22is shaped to define an orientation key to ensure that tube cassette22can only be inserted into pump20in one orientation of tube cassette22with respect to pump20. For example, a first cavity50in tube cassette22may engage with a corresponding protrusion on pump20(or vice versa) such that if a user tried to insert tube cassette22into pump20in a different orientation, the protrusion on pump20would inhibit the insertion. For some applications, a side-to-side positioning key ensures that once tube cassette22is locked in the preset position with respect to pump20, not only is the distance between the pressing surface inside pump20and infusion tubing24tightly defined, but also the longitudinal site along infusion tubing24at which the pressing surface presses on infusion tubing24. For example, a second cavity52in tube cassette22may engage with a corresponding protrusion on pump20(or vice versa) to ensure that tube cassette22cannot move from side-to-side with respect to pump20when tube cassette22is coupled to pump20.