Drive transmission mechanism, image forming apparatus including drive transmission mechanism and assembly method of drive transmission mechanism

An assembling method of a drive transmission mechanism,

• wherein the drive transmission mechanism includes a drive input gear part, an output side coupling, a coil spring, a slide pin and a coupling retracting mechanism, wherein
• the drive input gear part includes:
• a cylindrical boss formed on a rotational center;
• a slide hole formed so as to penetrate the boss;
• a protrusion formed on an outer circumferential surface of the boss;
• a rim formed concentrically with the boss on an outer side in a radial direction of the boss, and around which gear teeth are formed;
• and
• a web coupling between the boss and the rim,
• the drive input gear part is coupled to a drive side input gear,
• the output side coupling is formed into a cylindrical shape, has an engagement groove which is formed on an inner circumferential surface and is engageable with the protrusion, has an annular flange part protruding outward formed around an outer circumferential surface of an axial end portion, inserted on an outer circumference of the boss, and rotated together with the drive input gear part around a same rotational axis as the drive input gear part to output a drive force of the drive input gear part to a driven member,
• the coil spring biases the output side coupling to a direction separate from the drive input gear part along the rotational axis,
• the slide pin is inserted into the slide hole, and
• the coupling retracting mechanism retracts the output side coupling in a direction approaching the drive input gear part against biasing force of the coil spring, the assembling method comprising:
• a first step to fit the coupling retracting mechanism in a guide hole formed in a frame placed horizontally;
• a second step to dispose the drive input gear part and the output side coupling from above the coupling retracting mechanism with their rotating centers coincident with the rotational center and then to dispose the drive input gear at a position where the drive input gear part is capable of being meshed with a gear disposed adjacent to the drive input gear part;
• a third step to insert the coil spring into the slide hole of the drive input gear part;
• and
• a fourth step to insert the slide pin fixed on a drive sheet metal in the slide hole and to fix the drive sheet metal to the frame.