Surgery – Means for introducing or removing material from body for... – Treating material introduced into or removed from body...
Patent
1994-04-29
1996-12-31
Mendez, Manuel
Surgery
Means for introducing or removing material from body for...
Treating material introduced into or removed from body...
A61M 516
Patent
active
055889638
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the invention
The invention pertains to a method for measuring a liquid flow and flow rate using optical imaging means and to an apparatus to apply this method.
2. State of the Art
Methods and apparatus for measuring liquid flow rate are well known in the art. U.S. Pat. No. 4,936,828 discloses the use of a camera to measure the volume of falling drops in a liquid flow system and to count the total number of falling drops per unit of time in order to determine the flow rate of the liquid. Under this method, however, the smallest measurable change in the flow rate is limited to the volume of a completed falling drop.
Other known methods for liquid flow determination include measuring the liquid volume or mass per unit of time. Under these methods, the volume or mass of a liquid flowing out of a reservoir during a given period of time is measured to determine the flow over that period of time and the flow rate. The accuracy of such methods depends strongly on the time period over which the measured volume or mass of the liquid is divided, and on the precision of these measurements. These time integration techniques, however, prohibit the real time measurement of the flow in time and flow rate and are particularly unsuited for measuring small flow rates. Furthermore, existing flow measuring devices have a limited operating dynamic range, as it is difficult to combine in one piece of equipment, measurement means for both large and small flows.
Thus the major drawbacks associated with known methods and equipment for measuring the flow and flow rate include the facts that they are time consuming, inaccurate, sensitive to noise, evaporation, vibration, and viscosity, and most importantly, impracticable if real time measurements are desired. Known methods and equipment for measuring flow and flow rate are particularly unsuited for the measurement of especially small flows in medical infusion systems, where deviations from the stipulated flow of very small quantities can have disastrous medical consequences unless corrected or avoided.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to disclose methods for measuring liquid flow and apparatus for practicing these methods.
It is another object of the invention to disclose a method which makes both accurate and real time measurements of relatively small flows.
It is a further object of the invention to disclose a method where optical imaging means are used for measuring the shape and change in shape of a liquid flowing through an outlet.
Another object of the invention is to disclose a method of measuring the meniscus level in a liquid.
It is a further object of the invention to disclose a method of measuring the meniscus level in a liquid collecting container to determine the back-pressure at an outlet of the container.
It is a further object of the invention to disclose a method for controlling and adjusting a flow or flow rate.
The shape of the drop is a function of mass, cohesion, adhesion and construction of the outlet, and represents a volume. This shape can result in a drop that falls from the outlet if the flow or waiting time is long enough. The change in shape in time is a direct measure of the flow. The time dependency of the change is a measure of the flow rate. This is a vital point of the method. Due to the fact that the measurement of volumes of isolated, completed, falling drops is not relevant for the invention, even the yield from a flow over a time so small that a drop will never be formed, can be measured in this way. The method can be simply implemented, requiring only known reliably produced devices.
The use of optical imaging and image processing means enables the measuring of a volume flow rate in real time with a high accuracy and results in a flexible measuring set-up to take into account other relevant parameters like environmental back-pressure. With the use of optical measurement methods, direct contact with the flowing medium is avoided.
In a preferred embodiment, the changing
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patent: 3609379 (1971-09-01), Hildebrandt
patent: 4328801 (1982-05-01), Marx et al.
patent: 4680977 (1987-07-01), Coneno et al.
patent: 4936828 (1990-06-01), Chiang
patent: 5267980 (1993-12-01), Dirr, Jr. et al.
patent: 5331309 (1994-07-01), Sakai
Proceedings Computers in Cardiology, Publ. 1990, Los Alamitos, California, US pp. 405-406, R. Leor, E. A., "A system for the measurement of drop volume of introvenous solutions".
Gordon David P.
Mendez Manuel
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