Auto winding mechanism for window blind

An auto winding mechanism for a window blind, comprising:

• an upper seat;
• a lower seat connected with the upper seat;
• two guide rollers pivotally mounted between the upper seat and the lower seat;
• two pull cords wound around the two guide rollers in two opposite directions;
• and
• an S-shaped elastic winding tape;
• wherein:
• each of the two guide rollers has an upper end connected with the S-shaped elastic winding tape and a lower end connected with a respective one of the two pull cords;
• each of the two guide rollers has a periphery provided with a gear, with the S-shaped elastic winding tape located intermediate the gear and the upper seat;
• the gears of the two guide rollers mesh with each other, with the two guide rollers rotated in concert with each other;
• each of the two guide rollers has a bottom provided with a bottom disk;
• the upper seat has a surface provided with two pivot holes;
• the lower seat has a surface facing the upper seat, with two annular grooves extending from the surface to a depth away from the upper seat and receiving the bottom disk of each of the two guide rollers, with the lower seat provided with two shafts extending through the two guide rollers and aligning with the two pivot holes of the upper seat;
• each of the two shafts of the lower seat is located in a respective one of the two annular grooves of the lower seat;
• the two guide rollers are pivotally mounted on the two shafts of the lower seat with the gears of the two guide rollers meshing with each other;
• the bottom disk of each of the two guide rollers is pivotally mounted in a respective one of the two annular grooves of the lower seat;
• each of the two guide rollers is limited between the respective shaft and the respective annular groove of the lower seat, with each of the two guide rollers rotatable on the lower seat smoothly and stably without producing vibration or deflection;
• the upper seat is mounted on the lower seat, with the two pivot holes of the upper seat aligning with the two shafts of the lower seat;
• the two pivot holes of the upper seat and the two shafts of the lower seat are connected with the upper seat combined with the lower seat;
• the gear of each of the two guide rollers is disposed above the bottom disk of each of the two guide rollers;
• each of the two pull cords is disposed under the gear of each of the two guide rollers and is disposed above the bottom disk of each of the two guide rollers;
• each of the two pull cords is limited between the upper seat and the bottom disk of a respective one of the two guide rollers and between the surface of the lower seat and the gear of the respective one of the two guide rollers;
• the bottom disk of each of the two guide rollers has a thickness equal to a depth of the respective annular groove of the lower seat;
• the bottom disk of each of the two guide rollers limits and prevents each of the two pull cords from being moved downward away from the gear;
• and
• the bottom disk of each of the two guide rollers is received in and has a diameter flush with that of the respective annular groove of the lower seat and without a clearance between the bottom disk of each of the two guide rollers and the respective annular groove of the lower seat to prevent each of the two pull cords from being jammed between the bottom disk of each of the two guide rollers and the respective annular groove of the lower seat.