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| Solenoids Used in Medical (Applied to a Autotransfusion Type Machine) |
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A manufacturer of medical equipment expressed the need for a method to control the flow of blood and blood by-products to a patient.
Due to the high bio-hazard now associated with the handling and use of whole blood and blood by-products, the interested company devised what they refer to as an "Autotransfusion" type system. Using this system, the attending medical staff in operating theaters, emergency rooms, and recovery or intensive care units can now salvage the shed blood of a patient for re-use by that same patient. This machine recovers this shed blood, removes particulate matter and performs functions such as cell washing and platelet-rich plasma sequestration. In addition to the obvious benefits to the patient (by using the patient's own blood and blood by-products, the bio-hazard presented by the disposal of human blood is reduced and the exposure to the attending staff is likewise reduced because any spilled or un-used fluids are transferred directly into a bio-hazard waste bag.)
Patient and operator safety has been designed into the autotransfusion equipment. Some of the safety features include a bubble detector (senses gaseous bubbles in the system before they can be introduced into the patient), automatic level sensor and a certrifuge cover lock. In addition the control of the various functions is achieved by a touch sensitive screen which can be locked out to prevent accidental changes in operation. Pre-programmed functions are set to automatically concentrate red cells and wash them for reinfusion to the patient in just minutes. The actual plumbing of this machine consists of three color coded disposable I.V. tubes. These tubes are routed from the patient thru poppet type pinch mechanisms which when the system is operating, are held open. When the system is powered down, or a particular function is desired to be "OFF", the poppet type mechanisms pinch the affected I.V. tube off. This is also a safety feature, in case of power interruption, all the I.V. tubes are to be pinched off.
In the prototype system, the I.V. tube pinch-off was accomplished using small D.C. gear motors. The motors rotated a cam which opened the affected poppet valve. This mechanism worked well except for the cost and the inability of the gear motor to allow the poppets to close in case of an electrical interruption. This situation with the power interrupt prompted the designers of this instrument to seek another method.
The requirements for the operation of the poppet were: .250" stroke and 8 lbs. Force. Each poppet must be capable of remaining in the open position during the entire medical procedure. The device has the sophistication to be able to either drop the applied voltage to a predetermined level or produce a P.W.M. type output to the drive device.
For this application, the size 6EC solenoid was suggested. At .250" stroke, 20°C ambient, _ duty cycle, the force of this device is greater than 15 lbs. Allowing 30° derating for higher than 20° ambient temperature and coil heating, plenty of solenoid was still available to do the job. The customer will be able to energize this unit at full _ duty, allow it to make its full .250" stroke and, either by a mechanical method or by electronic method, they step the voltage down to a level less than continuous duty (12 VDC) which will provide the holding force necessary to hold the poppet devices open throughout the entire medical procedure. By going to a voltage lower than continuous, the customer is assured of minimal coil heating and power consumption of the autotransfusion machine.
By using the #6 EC solenoid, we offer:
1. Performance with standard life on this solenoid is 1-5 million cycles.
2. Greatly reduced design complexity. The first existing design used gear motors and cams for a high part count to accomplish the job. The Low Profile Solenoid does the same job with one moving part and much less part count.
3. Elimination of fail safe problem, this device will apply force in an in-line configuration of the poppet mechanism. The return spring of the poppet will supply the force to pinch the I.V. tube, the solenoid will supply the force to keep the poppet open during the procedure. Any possible failure of the solenoid or power failure will result in the solenoid going to the de-energized condition, resulting in the pinching off of the affected I.V. tube.
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