Miniature peristaltic pump

Details Miniature peristaltic pump Miniature peristaltic pump

1999-03-08

2001-03-20

Freay, Charles G. (Department: 3746)

Pumps

Expansible chamber type

Elongated flexible chamber wall progressively deformed

C417S477200, C417S477800, C417S477900

Reexamination Certificate

active

06203296

ABSTRACT:

This invention refers to peristaltic pumps. More specifically, it concerns a miniature peristaltic pump for the injection of drug solutions.
Miniature pumps or micropumps for medical use have been available for several years. Light and of small size, they can be worn discreetly and comfortably by the patient and permit the administration of controlled quantities of drug solutions to said patient, either subcutaneously or intravenously, continuously or according to a specific program, without his having to be confined to bed or hooked up to a cumbersome, costly and noisy machine.
Such pumps are most often of the rotary peristaltic type whose principle consists in having a flexible plastic tubing connected to a reservoir containing the solution and having it pressed locally against a rounded-off support piece by means of pressure rollers mounted on a rotor driven by a motor operating through a gear train. The liquid is thus drawn up from the reservoir and discharged toward the outlet to be injected into the patient.
Patents EP 388 787, EP 447 909, EP 521 184 and WO 94/06491 describe miniature peristaltic pumps of this type.
When designing such pumps, it is particularly important to carefully optimize the coupling between the rollers and the tubing being pressed by the rollers the one after the other against the support piece.
Measurements have shown that the minimum pressure on a roller having a diameter of 5 mm, necessary to make a liquid flow in plastic tubing with an internal diameter of 1.47 mm and an external diameter of 1.96 mm is 95 grams. The corresponding tensile force exerted by the roller is 15 grams. The pressure on the roller may increase up to 150 grams without proportionally increasing the tensile force, which then only increases from 15 to 20 grams. However, beyond that limit, the tensile force increases very rapidly. In fact, it increases to 50 grams for a pressure of 200 grams, after which measurements become impossible.
Such observations are easily explained by the fact that once the flexible tubing has been squeezed until it is completely sealed, any increase in pressure causes deformation of the plastic material and the corresponding tensile force then increases in relation to its elasticity module.
Thus, any variation in the position of the roller in relation to the tubing beyond that which achieves its closure, puts a heavy load on the roller-carrying rotor and its driving motor, which quickly causes jamming and therefore stopping of the pump. The effect is all the more pronounced in the miniature pumps that are obviously equipped with less powerful motors than the nonportable pumps.
Contrary to that, any variation in the position of the roller below the one that enables the complete closure does not permit a sufficient flow of the liquid.
It is thus very important, in order to obtain a reliably functioning pump, that the distance separating the roller from the support piece be perfectly maintained and kept constant in order to avoid jamming or irregular and insufficient output.
Thus, if the support piece and the roller are fixed, extremely strict manufacturing tolerances are necessary and this therefore raises the cost price of the pump quite appreciably.
It is therefore preferable to accept lighter tolerances and to provide a means which automatically adjusts any gap in position between the support piece and the roller.
Patents EP 388 787 and EP 447 909, already referred to, succinctly describe arrangements to resolve this problem.
Patent EP 388 787 shows a support piece which has the shape of a hook articulated at one of its ends by a pin and presses against the tubing by means of a screw-compressed spring. This support piece, being almost always acted upon by two rollers, cannot ensure the correct adjustment of the position gaps for each of the separate rollers.
Patent EP 477 909 shows that the rollers are mounted on their axis with a slight radial play permitting them a certain clearance and that individual leaf springs acting directly on their central part push them towards the outside. Such an arrangement presents the double drawback of complicating the mounting of the rotor and to cause it to slide on the tubing rather than to turn. It is also shown in this document that the springs can be replaced by a unique elastic part, for which no description is supplied, and that they can be definitely omitted because the rollers are then radially displaced by the inherent elasticity of the tubing itself. This shows that the magnitude of the problem has not been fully understood.
Other solutions to compensate the position gaps between the rollers at their support piece have been disclosed in patents U.S. Pat. No. 4,950,136 and CH 562 402. In the described embodiments, each one of the two cylindrical rollers is mounted on a shaft, the ends of which are fitted into oblong openings of the rotor. In the US patent, two semi-circular springs act by their ends upon each end of the shaft to push it toward the outside. In the CH patent, one single semi-circular spring is provided. Such arrangements are however limited to pumps having two rollers.
The so-called cassette pumps are the most common in medical applications. They comprise two parts, on the one hand the actual pump with the motor, the drive electronics, the battery and the pump head formed by the rotor and the pressure rollers and, on the other, the cassette which clips onto the pump and includes the tubing and the support piece. The reservoir is either integrated into the cassette when it is of a small size, or arranged outside when the size is larger.
The pumps in Patents EP 447 909, EP 521 184 and WO 94/06491 are of this variety.
In these three cases, the cassette, which is assembled in a permanent manner, includes the tubing, the support piece and the reservoir. The pumps of the two EP patents are single-use-only because, once connected, the two units cannot be disconnected. At the end of treatment or when the cassette is empty, the entire unit is discarded, including the motor, the pump head, the support piece, the gear train and the circuit which are all still capable of functioning again. As far as the pump in the WO Patent is concerned, its cassette may be discarded at the same time as its reservoir. Thus, in these three pumps, components are being discarded which could still be used as they are because they are not worn out and have never been in contact with the medication injected into the patient.
Documents U.S. Pat. No. 4,817,057 and EP 120 284, moreover, describe peristaltic pumps with large size cassettes, i.e. non-portable ones. Even though the tubing can easily be inserted into, or removed from the cassette, it is fitted with a connecting nozzle to the tubing coming from the reservoir and its part that is subjected to the peristaltic action is specially designed to withstand the prolonged exposure to the compression effect of the rollers. Such a design has drawbacks because, not only does it not permit the re-use of the tubing to administer different drug solutions to different patients, but furthermore, the interconnecting operations of the two tubings increase the risk of bacterial contamination of the circuit.
Another major problem occurs during the design of such pumps. The problem is the discharging of the tubings, i.e. the discharge of the air still contained in the tubings, before inserting the needle into the patient. The rotor's rotation speed being very slow, generally less than 1 rpm, this operation must, in order not to take too much time, be done by making the rotor turn rapidly by external means. Patent EP 388 787 discloses a wheel which is part of the rotor and includes a series of holes into which one can put, for example, the point of a ballpoint pen to turn the wheel rapidly. That solution is certainly an interesting one, but no arrangement has been provided to keep this operation from damaging the gear train.
The object of the invention is to provide an improved miniature peristaltic pump that is free of the drawbacks of pumps known in the prior art.
The miniature p

Affiliated with

Also associated with

Rating

Miniature peristaltic pump does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Miniature peristaltic pump, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Miniature peristaltic pump will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2536876