Variable step rate precision pumping apparatus
First Claim
1. Apparatus for dispensing liquids using a stepper motor pump that has first and second windings which, upon being energized, step the pump by a predetermined angular step the quantity of liquid dispensed by the pump being determined by the angular step size, the apparatus comprising a controller for generating first and second digital signals in response to an input indicating a predetermined liquid dispense rate;
- means for converting the first and second digital signals to corresponding first and second analog signals; and
means for driving the first and second windings of the stepper motor pump at a selected rate within a predetermined range of rates with the first and second analog signals to dispense liquid, the controller having means for varying the first and second digital signals to vary the step size of the pump to control the amount of liquid dispensed.
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Accused Products
Abstract
A method and apparatus for controlling a low volume, low rate precision dispensing pump for photochemicals and the like comprises generating constant current signals having magnitudes related by sin and cos values to the angular step size of the stepper motor pump, and varying the magnitudes smoothly over an incremental range of angles to vary the quantity of liquid dispensed. The step size and step rate can be varied to provide a desired liquid dispense rate. The magnitude of the current applied to the motor is ramped up and down while maintaining constant the relative relationships in the magnitudes of the currents applied in order to smoothly step the motor over a desired step angle.
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Citations
18 Claims
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1. Apparatus for dispensing liquids using a stepper motor pump that has first and second windings which, upon being energized, step the pump by a predetermined angular step the quantity of liquid dispensed by the pump being determined by the angular step size, the apparatus comprising a controller for generating first and second digital signals in response to an input indicating a predetermined liquid dispense rate;
- means for converting the first and second digital signals to corresponding first and second analog signals; and
means for driving the first and second windings of the stepper motor pump at a selected rate within a predetermined range of rates with the first and second analog signals to dispense liquid, the controller having means for varying the first and second digital signals to vary the step size of the pump to control the amount of liquid dispensed. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
- means for converting the first and second digital signals to corresponding first and second analog signals; and
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9. An apparatus for dispensing liquids using a stepper motor pump of the type that dispenses a predetermined quantity of liquid for a predetermined angular step of a motor that drives the pump, the apparatus comprising means for inputting a dispense rate for a liquid to be dispensed as a specified quantity of liquid in a specified time;
- first means for selecting from a predetermined range of times an update step rate corresponding to a rate at which the pump is stepped;
second means for selecting a step angle for the selected update step rate;
means for comparing the selected step angle to a predetermined range of angles;
means responsive to the comparing means determining the step angle to be outside the predetermined range of angles for varying the update rate and step angle to achieve the input liquid dispense rate; and
means for controlling the pump at said update rate and said step angle to dispense liquid at said input dispense rate. - View Dependent Claims (10, 11, 12, 13)
- first means for selecting from a predetermined range of times an update step rate corresponding to a rate at which the pump is stepped;
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14. A method of controlling a stepper motor pump of the type which dispenses a predetermined quantity of liquid for a predetermined angular rotation of the motor, comprising selecting, for a desired liquid dispense rate, an angular step size of the motor to dispense a predetermined quantity of liquid;
- determining an update step rate at which the motor must be stepped to provide the desired dispense rate;
comparing the determined update step rate to a predetermined range of step rates, and, upon the determined update step rate falling outside of said predetermined range of step rates, selecting a new step size, determining a new update step rate, and comparing the new update step rate to the predetermined range of step rates; and
repeating said selecting, determining and comparing until a combination of step size and update step rate is determined which provides the desired dispense rate for an update step rate within the predetermined range of step rates. - View Dependent Claims (15, 16, 17, 18)
- determining an update step rate at which the motor must be stepped to provide the desired dispense rate;
Specification