Image forming apparatus, drive mechanism of image forming apparatus and manufacturing method of a worm gear set

Abstract

An image forming apparatus has a plurality of image carriers, a common drive source which drives the plurality of image carriers and a drive shaft that is connected to and driven by the drive source. It also has a plurality of worm gears that are provided corresponding to the plurality of image carriers and are formed coaxially with the drive shaft, and a plurality of worm wheels that are respectively meshed with the respective worm gears and respectively transmit drive forces of the worm gears to the image carriers. The plurality of worm gears are made of a resin material, and the worm gears and the worm wheels drive the plurality of image carries by making use of the elastic deformation of the worm gears when the worm gears and the worm wheels are respectively meshed with each other.

1 . An image forming apparatus comprising: 
 a plurality of image carriers that are arranged in parallel;    a common drive source that drives the plurality of image carriers;    a drive shaft that is connected to and driven by the drive source;    a plurality of worm gears that are provided corresponding to the plurality of image carriers and are formed coaxially with the drive shaft; and    a plurality of worm wheels that are respectively meshed with the respective worm gears and respectively transmit drive forces of the worm gears to the image carriers,    wherein the plurality of worm gears are made of a resin material, and the worm gears and the worm wheels drive the plurality of image carries by making use of the elastic deformation of the worm gears when the worm gears and the worm wheels are respectively meshed with each other.    
   
   
       2 . An image forming apparatus according to  claim 1 , wherein the drive shaft is made of a metal material.  
   
   
       3 . An image forming apparatus according to  claim 2 , wherein the plurality of worm gears are fixed to the drive shaft by forming resin on the drive shaft by molding.  
   
   
       4 . An image forming apparatus according to  claim 3 , wherein the plurality of worm gears are formed by molding such that each preform forming portion where a tooth shape of the worm gear is formed, each gate land having a large wall thickness portion at the time of injecting resin and each film gate having a small wall thickness portion for allowing inflow of resin into each preform forming portion in a squeezed manner are connected.  
   
   
       5 . An image forming apparatus according to  claim 2 , wherein the plurality of worm gears are fixed to the drive shaft by pressfitting molded resin over the drive shaft.  
   
   
       6 . An image forming apparatus according to  claim 5 , wherein the drive shaft differs in a diameter thereof corresponding to positions where the plurality of worm gears are pressfitted.  
   
   
       7 . A drive mechanism of an image forming apparatus comprising: 
 a metal shaft that is used as a drive shaft for simultaneously driving a plurality of constitutional members in the image forming apparatus; and    a plurality of worm gears made of a resin material that are formed over the metal shaft coaxially, transmit a driving force to respective shafts of the plurality of constitutional members, and are formed by insert molding after inserting the metal shaft in a mold,    wherein the plurality of worm gears have helically threaded portions on outer peripheral portions of the resin material.    
   
   
       8 . A drive mechanism of an image forming apparatus according to  claim 7 , wherein the plurality of worm gears are formed by molding, each worm gear including: 
 a preform portion on which the threaded portion is formed;    a gate land that has a gate position for injecting resin; and    a film gate that is formed between the gate land and the preform forming portion while having a thickness smaller than a thickness of the gate land and allows the injected resin to flow into the preform forming portion.    
   
   
       9 . A drive mechanism of an image forming apparatus according to  claim 7 , wherein in the plurality of worm gears, the threaded portion is formed by performing cutting machining after insert molding or by performing insert molding directly.  
   
   
       10 . A drive mechanism of an image forming apparatus according to  claim 7 , wherein the idling prevention treatment is applied to a surface of the metal shaft at positions where the plurality of worm gears are formed by molding.  
   
   
       11 . A drive mechanism of an image forming apparatus comprising: 
 a metal shaft that is used as a drive shaft for simultaneously driving a plurality of constitutional members in the image forming apparatus; and    a plurality of worm gears that are coaxially mounted on the metal shaft and transmit a driving force to respective shafts of the plurality of constitutional members, the plurality of worm gears being made of a resin material which is sequentially pressfitted over the metal shaft,    wherein the plurality of worm gears have helically threaded portions on an outer peripheral portion of the resin material.    
   
   
       12 . A drive mechanism of an image forming apparatus according to  claim 11 , wherein at a plurality of positions where the plurality of worm gears to be sequentially pressfitted are mounted on the metal shaft, the metal shaft has a larger diameter at the positions close to a center portion than at the positions close to both end portions thereof.  
   
   
       13 . A drive mechanism of an image forming apparatus according to  claim 11 , wherein the metal shaft is provided with projection portions having a given height at the plurality of positions thereof where the plurality of worm gears which are sequentially pressfitted are mounted.  
   
   
       14 . A drive mechanism of an image forming apparatus according to  claim 11 , wherein the drive mechanism includes fastening members which prevent the movement of the worm gears in the axial direction of the metal shaft.  
   
   
       15 . A manufacturing method of a worm gear set comprising: 
 a step for inserting a metal shaft in a mold;    a step for filling resin at a plurality of positions that are spaced apart at a given distance in the axial direction of the metal shaft from a gate of the mold; and    a step for coaxially forming a plurality of worm gears on the metal shaft by solidifying the resin and removing the metal shaft and the solidified resin from the mold.    
   
   
       16 . A manufacturing method of a worm gear set according to  claim 15 , wherein the step for forming the plurality of worm gears includes the formation of helically threaded portions by cutting the solidified resin.  
   
   
       17 . A manufacturing method of a worm gear set according to  claim 15 , wherein in the step for filling the resin, the resin is filled until the resin embeds gate lands having large wall thickness portions and, thereafter, by way of film gates having small wall thickness portions and connected to the gate lands, the resin is filled into portions for forming the worm gears which cover the circumference of the metal shaft and are connected to the film gates.  
   
   
       18 . A manufacturing method of a worm gear set for coaxially forming not smaller than three worm gears on a metal shaft, the method comprising: 
 a step for cutting the metal shaft in which out of portions of the metal shaft where the worm gears are formed,    a shaft diameter of the portions at a center side of the metal shaft is large and a shaft diameter of the portions at both end sides of the metal shaft is small; and    a step for sequentially pressfitting resin-made preforms over the cut metal shaft before or after forming helical threads.    
   
   
       19 . A manufacturing method of a worm gear set according to  claim 18 , wherein the manufacturing method further includes a step for forming the helical threads in the resin preforms by cutting when the helical threads are not yet formed in the resin preform to be pressfitted over the metal shaft.  
   
   
       20 . A manufacturing method of a worm gear set according to  claim 18 , wherein the manufacturing method further includes a step for applying a fastening treatment for preventing the displacement of the resin preforms in the axial direction of the metal shaft after pressfitting the resin preforms over the metal shaft.