Apparatus and control method for accurate rotary peristaltic pump filling

Abstract

A filling machine with a rotary peristaltic dispenser that compensates for the nonlinear flow rate characteristic of the dispenser to increase product fill accuracy is disclosed. A computer processor including associated electronic circuitry and programs is provided for defining, digitizing and storing the real pulsating flow rate characteristic of the dispenser. In order to ensure a precise delivery of the filled product, the computer calculates the angular rotation of the rotor needed to deliver the desired fill weight for each filling cycle. The angular rotation needed to maintain a uniform fill weight is generally different for each filling cycle. The current position of the rotor is first established prior to each filling cycle and then located on a stored look-up table containing the flow rate characteristic as a starting point for digital integration of the characteristic over the angular distance of the driver. The computer then integrates the digitized flow characteristic based on the look-up table in the computer memory, starting from the current rotor position one step at a time. Each step represents a small regular angular increment of the dispense rotor. After each step of integration, the subtotal of the calculated amount is compared to the calibrated set-point until the desire set-point fill weight is reached. When the integrated subtotal reaches the set-point the integration stops. The number of steps used during the integration establishes the target distance of the system driver. The system then advances the driver by the calculated angular distance, thus ensuring the delivery of the required product weight with high precision. As a result, the apparatus and control method of the present invention takes into account the pulsating nature of the rotary peristaltic dispenser.