Image forming apparatus and image write start position adjusting method for the same

Abstract

A high-quality image forming apparatus that is capable of accurately adjusting the size and position of an image during image formation on a second surface of a transfer material, even when there has been expansion/contraction of the transfer material due to thermal fixing after image formation on a first surface thereof, to thereby avoid image displacement during two-sided image formation and multiple image formation. A pulse adjusting section sets a second number of pulses of the image clock corresponding to a distance from BD signal detector to the write start position of the latent image during image formation on the second surface, to a number of pulses different from a first number of pulses of the image clock corresponding to a distance from the horizontal synchronization signal detecting device to the write start position of the latent image during image formation on the first surface, based on the first number of pulses of the image clock during image formation on the first surface, in accordance with an expansion/contraction ratio of the transfer material after fixing of the image on the first surface.

1 . An image forming apparatus capable of successively forming images on a first surface and a second surface of a transfer material and fixing the images, comprising: 
 at least one image carrier;    a plurality of light scanning devices that respectively form latent images on said at least one image carrier by scanning a light beam based on image data and in accordance with an image clock;    a plurality of horizontal synchronization signal detecting devices that detect from the light beam horizontal synchronization signals for controlling respective write start positions of the respective latent images on the at least one image carrier;    a plurality of pulse adjusting devices that adjust the respective numbers of pulses of the image clock during image formation on the second surface in accordance with numbers of pulses of the image clock corresponding respectively to distances from respective ones of the plurality of horizontal synchronization signal detecting devices to write start positions of the respective latent images and an expansion/contraction ratio of the transfer material after fixing of the images on the first surface;    a belt-shaped member;    an in-surface image positioning device that detects at least one mark provided on said belt-shaped member and adjusts the respective numbers of pulses separately for respective ones of said image forming devices; and    a control device that causes said in-surface image positioning device to adjust the respective numbers of pulses for the respective ones of said image forming devices separately when image formation is carried out on the first surface, and causes a corresponding one of said pulse adjusting devices to adjust the image write start position of one of said image forming devices used as a reference separately when image formation is carried out on the second surface.    
   
   
       2 . An image forming apparatus as claimed in  claim 1 , wherein said belt-shaped member comprises a transfer material conveying member disposed to successively pass said image forming devices such that the respective latent images formed on said at least one image carrier are transferred onto the transfer material conveyed by said transfer material conveying member.  
   
   
       3 . An image forming apparatus as claimed in  claim 1 , wherein said belt-shaped member comprises an intermediate transfer device that primarily transfers visible images formed on said at least one image carrier onto said intermediate transfer device, and then secondarily transfers the visible images onto the transfer material.  
   
   
       4 . An image forming apparatus as claimed in  claim 1 , comprising a clock frequency correcting device that corrects a size of the image formed on the second surface to a size of the image formed on the first surface after fixing by modulating a frequency of the image clock during image formation on the second surface.  
   
   
       5 . An image forming apparatus according to  claim 1 , comprising a transfer material positioning device that positions one end edge of the transfer material in a light beam scanning direction before image formation, and wherein: 
 said transfer material positioning device is disposed on an image write start side and displaceable in accordance with a length of the transfer material in the light beam scanning direction; and    the imager forming apparatus is configured such that when the transfer material passes said image forming device for image formation, a center of the transfer material in the light beam scanning direction passes an approximate center of said image forming device.    
   
   
       6 . An image write start position adjusting method for an image forming apparatus that is capable of successively forming images on a first surface and a second surface of a transfer material and fixing the images and includes a light scanning device that forms a latent image on an image carrier by scanning a light beam based on image data and in accordance with an image clock, a horizontal synchronization signal detecting device that detects from the light beam a horizontal synchronization signal for controlling a write start position of the latent image on the image carrier, the method comprising: 
 a pulse adjusting step of adjusting a number of pulses of the image clock during image formation on the second surface in accordance with a number of pulses of the image clock corresponding to a distance from said horizontal synchronization signal detecting device to the write start position of the latent image and an expansion/contraction ratio of the transfer material after fixing of the image on the first surface.    
   
   
       7 . An image write start position adjusting method for an image forming apparatus that is capable of successively forming images on a first surface and a second surface of a transfer material and fixing the images and includes a plurality of light scanning devices that respectively form latent images on at least one image carrier by scanning a light beam based on image data and in accordance with an image clock, a plurality of horizontal synchronization signal detecting devices that detect from the light beam horizontal synchronization signals for controlling respective write start positions of the respective latent images on the at least one image carrier, the method comprising: 
 a pulse adjusting step of adjusting the respective numbers of pulses of the image clock during image formation on the second surface in accordance with numbers of pulses of the image clock corresponding respectively to distances from respective ones of the plurality of horizontal synchronization signal detecting devices to write start positions of the respective latent images and an expansion/contraction ratio of the transfer material after fixing of the images on the first surface;    an in-surface image positioning step of detecting at least one mark provided on a belt-shaped member and adjusting the respective numbers of pulses separately for respective ones of the image forming devices; and    a control step of causing said in-surface image positioning step to adjust the respective numbers of pulses for the respective ones of the image forming devices separately when image formation is carried out on the first surface, and causing said pulse adjusting step to adjust the image write start position of one of the image forming devices used as a reference separately when image formation is carried out on the second surface.    
   
   
       8 . An image write start position adjusting method for an image forming apparatus as claimed in  claim 6 , comprising an image size adjusting step of adjusting a size of the image formed on the second surface to a size of the image formed on the first surface after fixing by modulating a frequency of the image clock during image formation on the second surface.