Web guidance mechanism for automatically centering a web during movement of the web along a curved path

摘要

A web guidance mechanism (14) for automatically centering a web (12) in a thermal printer has an elongated base member (22) with first and second end portions each defining a slot (24,26). A crank (28) is rotatably mounted on the base member (22) and has slider arms (30,34) attached thereto. Web guides (32,36) are mounted on the distal end portions of the slider arms (30,34) and are engagable with the slots (24,26) for lateral movement. A coil spring (38) biases the web guides (32,36) towards one another to create two normally equal but opposite centering edge forces (F1,F2) so that lateral movement of the web (12) does not occur until twice the nominal edge force is applied to the web (12).