Patent Application
20070217919
The present invention relates generally to peristaltic pumps and more specifically to peristaltic pumps used in ophthalmic surgical equipment.
Peristaltic pumps work by compressing or squeezing a length of flexible tubing (sometimes between a fixed race) using a rotating roller head. As the roller head rotates, the rollers stretch and pinch off a portion of the tubing and push any fluid trapped in the tubing between the roller in the direction of rotation. Peristaltic pumps are widely used in medical applications because of their predictable flow properties.
Many factors influence the efficiency of peristaltic pumps, for example, pump motor torque, pump speed and pump tube flexibility. The efficiency of a peristaltic pump is also dependent on how tightly the pump rollers crush the tubing against the pump race. If the tubing is not collapsed completely by the rollers, not all of the fluid will be pushed further down the tube. One characteristic of peristaltic pumps is that flow rate varies in a cyclical manner. As a roller begins to pinch off the pump tubing, flow rate is reduced to minimum and then is accelerated to a maximum as the roller continues to sweep along the pump tubing segment. The pressure moves in an inverse relationship to the flow (Pressure ⇑ as Flow ⇓ or Pressure ⇓ as Flow ⇑). As the next roller begins to pinch off the pump tubing, the cycle starts again. This cyclical variation in flow rate causes a cyclical variation in pressure within the fluid path, the effects of which can be observed as pressure pulsations at the operative site. Prior art peristaltic pumps have reduced the effects of these pulsations by increasing the number of pump rollers and/or by tapering the tubing, by introducing capacitance/compliance chambers into the aspiration line or by variable radius pumps. Increasing the number of rollers and/or the use of variable radius pumps increases the cost and complexity of the pumping mechanism. Compliance or capacitance chamber negatively affect the performance (such as vacuum rise time) of the pump.
Accordingly, a need continues to exist for a method of reducing pulsations in a peristaltic pump that can be implemented without adding unnecessary complexity or compliance to the pumping system.
The present invention improves upon prior art peristaltic pumps by providing a peristaltic pump having an adaptive pulsation profile.
Accordingly, one objective of the present invention is to provide a high efficiency peristaltic pump.
Another objective of the present invention is to provide a peristaltic pump that reduces pump pulsations.
Yet another objective of the present invention is to provide a peristaltic pump having an adjustable, adaptive pulsation profile.
These and other advantages and objectives of the present invention will become apparent from the detailed description, drawings and claims that follow.
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With respect to cassette 18, sheet 20 contains molded fluid channel 26 that is generally planar, arcuate in shape (within the plane) and having a radius approximating that of rollers 16 about shaft 24. Sheet 20 may be made of any suitably flexible, easily molded material such as silicone rubber or thermoplastic elastomer. Sheet 20 is attached or bonded to substrate 22 by any suitable technique such as adhesive, heat fusion or mechanical crimping. Substrate 22 preferably is made of a material that is rigid with respect to sheet 20, such as a rigid thermoplastic, and may be made by any suitable method, such as machining or injection molding.
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Pump 10 of the present invention has an adaptive variable speed control to accelerate rotation of rollers 16 on roller head 14 through known minimum flow (maximum pressure) points, and slow down rotation of rollers 16 on roller head 14 through known maximum flow (minimum pressure) points. This acceleration/deceleration profile can be adaptive; in other words, can vary depending upon cassette 18 and/or the surgical parameters set by the user. For example, a set of pressure data versus roller 16 position can be recorded by surgical console 112 using sensor 126 and encoder 25 during initial priming or other pre-operational tests of cassette 18. This data can be can be used to derive a pump speed profile required to achieve a desired pressure/flow profile. The derived profile can be used to control the speed of pump 10 during use. In addition, pressure data and position of roller 16 can be continually monitored during use, and this data can be can be used adaptively to vary the pump speed to achieve and maintain a desired pressure/flow profile during surgery. Further, console 112 can be programmed with a variety of pressure/flow profiles previously generated so as to optimize the pressure/flow profile for a particular cassette type or surgical technique. The proper pressure/flow profile can be manually selected by the user, or console 118 may automatically boot up such optimum pressure/flow profile by automatic identification of the cassette (e.g. barcode or RFID). All of these features can be implemented on commercially available surgical equipment using software commands well within a person skilled in the art.
Alternatively, sensor 126 may be used to predict minimum and maximum flow/pressure points based on the speed of motor shaft 12 so that encoder 25 is not necessary.
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This description is given for purposes of illustration and explanation. It will be apparent to those skilled in the relevant art that modifications may be made to the invention as herein described without departing from its scope or spirit. For example, the present invention is also applicant to more conventional peristaltic pumps that stretch a length of tubing over the roller head.
