Stepping motor control procedure for achieving variable rate, quasi-continuous fluid infusion

• US 4,474,309 A
• Filed: 10/22/1981
• Issued: 10/02/1984
• Est. Priority Date: 10/22/1981
• Status: Expired due to Term

• Current Assignee: Oximetrix, Inc.
• Original Assignee: Oximetrix, Inc.
• Inventors: Solomon, Edward G.
• Primary Examiner(s): Rolla, Joseph J.
• Assistant Examiner(s): Handren, Frederick R.
• Application Number:
  US06/314,038
• Time in Patent Office: 1,076 Days
• Field of Search: 222/1, 222/333, 222/63, 604/67, 604/152, 417/12, 417/22, 318/685
• US Class Current: 222/1
• CPC Class Codes: A61M 2205/12 with interchangeable cassettes forming partially or totally the fluid circuit
• CPC Class Codes: A61M 5/14224 Diaphragm type
• CPC Class Codes: A61M 5/172 electrical or electronic A61M5/16804, A61M5/16831 take precedence
• CPC Class Codes: F04B 49/20 by changing the driving speed

Abstract

A control procedure for governing the incremental step operation of a pump stepping motor (74) employed in conjunction with a parenteral fluid metering device (2) is disclosed. The control procedure enables fluid to be pumped from the metering device (2) in non-pulsatile, essentially continuous fashion by suitably adjusting the stepping motor speed to compensate for the interruption of fluid flow which occurs during the refill phase (P_R) of each pumping cycle (C). Adjustment of the stepping motor speed also compensates for non-linearities otherwise introduced into the fluid flow as a result of the camming mechanism (76,78) utilized to convert rotary stepping motor movement into rectilinear pumping movement. Operating power for the stepping motor is conserved by drawing relatively large amounts of current through the stepping motor (74) only at the outset of each incremental step while drawing relatively smaller amounts of current through the stepping motor (74) during the remaining interval between incremental steps.

Claims

1. A method for precise metering of fluids from a metering device, the metering device including a pumping means for providing reciprocal motion to pump fluid from the metering device, a motor means which serves as a source of rotational movement and a camming means which converts the rotational movement of the motor means into the reciprocal motion of the pumping means by rotating with the motor means to move the pumping means through greater and lesser rectilinear displacements as a function of the angular displacement of the motor means, said method comprising the steps of:

operating the motor means at relatively faster rotational speeds during those periods when the camming means moves the pumping means through rectilinear displacements of lesser magnitude; and

operating the motor means at relatively slower rotational speeds during those periods when the camming means moves the piston means through rectilinear displacements of greater magnitude.

2. The method as set forth in claim 1, wherein said motor means includes a stepping motor which operates in incremental steps to rotate the camming means through equal angular displacements, each angular displacement of the camming means producing a greater or lesser rectilinear displacement of the pumping means as a function of the total angular displacement of the motor means, said step of operating the motor means at said relatively faster rotational speeds including the further step of shifting the stepping motor through incremental steps at relatively shorter intervals during those periods when the angular displacements of the camming means produce lesser rectilinear displacements of the pumping means and said step of operating the motor means at said relatively slower rotational speeds includes the further step of shifting the stepping motor through incremental steps at relatively longer intervals during those periods when the angular displacements of the camming means produce greater rectilinear displacements of the pumping means.

3. A pump controller mechanism that drives a pump for metering intravenous fluids to a patient at a predetermined rate in a relatively continous, nonpulsatile fashion, said mechanism comprising

a stepping motor, having a rotatable output shaft,

a plunger for displacing fluid in a pumping chamber,

rotatable camming means driven by the output shaft and operatively connected to the plunger for driving the plunger in incremental linear movements downwardly for expelling fluid from the chamber and upwardly for permitting the refilling of the chamber, said camming means being arranged to be driven through a plurality of incremental equiangular movements providing a linear output drive for the plunger wherein the incremental linear movements of the plunger at the beginning and end of the pumping stroke are substantially shorter in length than those during the rest of the stroke, said incremental movements in said rest of the stroke all being of generally the same length,

and control means for driving said motor so that the camming means is driven at a high rate of speed through those equiangular movements which produce shorter incremental linear movements of the plunger just prior to the completion of its downward movement, during the upward movement of the plunger while the pumping chamber is refilled with fluid, and during the initial downward movement of the plunger and so that the camming means is driven at a lower rate of speed during the remainder of its movement so that the average rate of delivery from the pump over the entire pumping cycle generally equals the delivery rate provided by the lower rate of speed, said high rate of speed accommodating both the time required for refilling the chamber and the shorter incremental movements at the beginning and end of the pumping stroke.

4. A positive displacement intravenous administration pump controller comprising a stepping motor having an incrementally rotatable drive shaft, a plunger operatively connected to said driveshaft for displacing fluid in an intraveous administration pump in a manner such that the plunger is moved in one direction during a filling portion of the operating cycle and in the opposite direction during the pumping portion of the operating cycle, means for driving said drive shaft of the motor through a plurality of equiangular distances, and control circuitry for controlling the rate at which said driving means is operated, said control circuitry including means for operating said driving means at a predetermined high rate during the filling portion and a part of the pumping portion of the operating cycle, and means for operating said driving means at a second rate during the remainder of the pumping portion, said second rate causing the fluid to be delivered at a desired preset rate over the operating cycle, and means for controlling the time that the high rate is maintained during the pumping portion of the cycle so that the average rate over the entire operating cycle equals the desired preset rate, said last named means including a storing means, means for periodically updating the storing means throughout the operating cycle by an incremental value determined by the desired preset rate, means for comparing at the periodic rate the total value in the storing means during the pumping portion of the operating cycle with a second value equivalent to the amount of fluid to be delivered during one incremental movement of the drive shaft, and means for activating said motor to cause it to rotate the drive shaft through one of said equiangular distances when value in the storing means is equal to or greater than said second value.