Dynamic thickness adaptation for an in-line scale

摘要

Methods and apparatus for weighing an article, such as a mail piece, while the article is moving at high speed. An article (900) is received from an intake transport (1200), and gripped in a weighing station (1310), in between a capstan roller and a pinch roller (1316), which are synchronized to minimize slipping. A first precision servo system (1252, 1250) alters the speed of the article, and in the process acquires torque data for storage and analysis (1212, 1282). A second precision servo system (1260,1330) applies a constant force, via a tension arm (1320), urging the pinch roller (1316) against the capstan roller, independently of the thickness of the mail piece. Active electronic damping (1900) reduces oscillation when an inconsistency in thickness of the article is encountered during weighing. The damping force is subtracted from the capstan motor torque data for improved accuracy (FIG. 20B).

主权项

1. A method for weighing a moving article on the fly, comprising:
receiving an incoming article having a first velocity; without stopping the article, gripping the article between a capstan roller and an opposed pinch roller; synchronizing rotation of the pinch roller and the capstan roller to avoid slippage of the article gripped between them; providing a capstan servo motor having a shaft operatively coupled to the capstan roller and opposed pinch roller; providing a first servo amplifier coupled to the capstan servo motor so as to form a first closed-loop servo system for driving the capstan servo motor and for monitoring torque applied by the capstan servo motor; in the first servo amplifier, commanding the capstan servo motor to a predetermined command speed that is different from the first velocity of the article in order to cause an acceleration of the article; beginning after the article is gripped between the pinch roller and the capstan roller, weighing the article on the fly by acquiring a series of capstan servo motor torque sample data as the article moves between the pinch roller and capstan roller, so that the captured torque data reflects the torque applied by the capstan servo motor to change the article speed from the first velocity to the command speed; storing the acquired torque sample data in a memory; providing a second closed-loop servo system arranged for controllably repositioning the pinch roller relative to the capstan roller to apply a controllable gripping force on the article as the article moves between the pinch roller and capstan roller, wherein the second closed-loop servo system provides an indication of a current position of the pinch roller as the article moves between the pinch roller and capstan roller; detecting a change in the current position of the pinch roller responsive to a change in thickness of the article as it moves along still gripped between the pinch roller and the capstan roller; correcting the stored capstan servo motor torque data to remove a torque error caused by the change in thickness of the article; and processing the corrected torque data to determine a weight of the article independently of the actual speed of the article.