Optical scanning unit and electro-photographic image forming apparatus including the same

Abstract

An optical scanning unit that includes a first optical device that forms collimated light from light radiated from a light source, a second optical device that focuses the collimated light onto a deflector, and an imaging optical device that focuses light deflected by the deflector onto an exposure object. The optical scanning unit further includes a refraction unit and a diffraction unit, and the power of the refraction unit is φr, the power of the diffraction unit is φd, and the ratio φr/φd is such that 0.5<φr/φd<1.3.

1 . An optical scanning unit comprising:
 a light source to radiate light;   a first optical device comprising a refraction unit and a diffraction unit, to collimate the light radiated from the light source;   a second optical device to focus the collimated light;   a deflector to deflect the focused light; and   an imaging optical device to focus the deflected light onto an exposure object,   wherein a power of the refraction unit is φr, a power of the diffraction unit is φd, and 0.5<φr/φd<1.3.   
   
   
       2 . The optical scanning unit of  claim 1 , wherein 0.6<φr/φd<0.9. 
   
   
       3 . The optical scanning unit of  claim 1 , wherein the first optical device comprises injection molded plastic. 
   
   
       4 . The optical scanning unit of  claim 1 , wherein a variation of the refractive index of the first optical device due to temperature changes is do/dT, and 0.00007<do/dT<0.00012. 
   
   
       5 . The optical scanning unit of  claim 1 , wherein a variation of the wavelength of the light radiated from the light source due to temperature changes is dλ/dT, and dλ/dT<0.3. 
   
   
       6 . The optical scanning unit of  claim 1 , further comprising a supporting unit that supports the first optical device, and
 wherein the focal distance of the first optical device is f 1 , the thermal expansion coefficient of the first optical device is A 1 , the thermal expansion coefficient of the supporting unit is A 2 , the focal distance of the imaging optical device  41  is f 2 , and (1−(f 1 /f 2 ))×0.18<f 1 ×φr×A 2 /A 1 <(1+(f 1 /f 2 ))×0.25.   
   
   
       7 . The optical scanning unit of  claim 6 , wherein 0.6<φr/φd<0.9. 
   
   
       8 . The optical scanning unit of  claim 6 , wherein the first optical device comprises injection molded plastic. 
   
   
       9 . The optical scanning unit of  claim 8 , wherein a variation of the refractive index of the first optical device due to temperature changes is dn/dT, and 0.00007<dn/dT<0.00012. 
   
   
       10 . The optical scanning unit of  claim 8 , wherein the thermal expansion coefficient A 1  of the first optical device is less than 0.0001. 
   
   
       11 . The optical scanning unit of  claim 6 , wherein the variation of the wavelength of the light radiated from the light source due to temperature changes is dλ/dT, and dλ/dT<0.3. 
   
   
       12 . An electro-photographic image forming apparatus comprising:
 a photosensitive body;   an optical scanning unit to form an electrostatic latent image on the photosensitive body by scanning light onto the photosensitive body ; and   a developing unit to develop an electrostatic latent image formed on the photosensitive body by supplying toner to the electrostatic latent image,   wherein the optical scanning unit comprises: a light source to radiate light; a first optical device to collimate the radiated light; a second optical device to focus the collimated light; a deflector to deflect the focused light; and an imaging optical device to focus the deflected light onto the photosensitive body, and   wherein the first optical device comprises a refraction unit and a diffraction unit, and the power of the refraction unit is φr, the power of the diffraction unit is φd, and 0.5<φr/φd<1.3.   
   
   
       13 . The electro-photographic image forming apparatus of  claim 12 , wherein 0.6<φr/φd<0.9. 
   
   
       14 . The electro-photographic image forming apparatus of  claim 12 , wherein the first optical device comprises injection molded plastic. 
   
   
       15 . The electro-photographic image forming apparatus of  claim 12 , wherein a variation of the refractive index of the first optical device due to temperature changes is dn/dT, and 0.00007<dn/dT<0.00012. 
   
   
       16 . The electro-photographic image forming apparatus of  claim 12 , wherein a variation of the wavelength of the radiated light due to temperature changes is dλ/dT, and dλ/dT<0.3. 
   
   
       17 . The electro-photographic image forming apparatus of  claim 12 , further comprising a supporting unit to support the first optical device,
 wherein the focal distance of the first optical device is f 1 , the thermal expansion coefficient of the first optical device is A 1 , the thermal expansion coefficient of the supporting unit is A 2 , the focal distance of the second imaging optical device is f 2 , and (1−(f 1 /f 2 ))×0.18<f 1 ×φr×A 2 /A 1 <(1+(f 1 /f 2 ))×0.25.   
   
   
       18 . The electro-photographic image forming apparatus of  claim 17 , wherein 0.6<φr/φd<0.9. 
   
   
       19 . The electro-photographic image forming apparatus of  claim 17 , wherein the first optical device comprises injection molded plastic. 
   
   
       20 . The electro-photographic image forming apparatus of  claim 19 , wherein a variation of the refractive index of the first optical device due to temperature changes is dn/dT, and 0.00007<dn/dT<0.00012. 
   
   
       21 . The electro-photographic image forming apparatus of  claim 19 , wherein the thermal expansion coefficient A 1  of the first optical device is less than 0.0001. 
   
   
       22 . The electro-photographic image forming apparatus of  claim 17 , wherein, a variation of the wavelength of the radiated light due to temperature changes is dλ/dT, and dλ/dT<0.3. 
   
   
       23 . The optical scanning unit of  claim 1 , wherein a temperature change of the scanning unit of approximately 20° C. produces a focus movement of less than 0.2 mm. 
   
   
       24 . The electro-photographic image forming apparatus of  claim 12 , wherein a temperature change of the scanning unit of approximately 20° C. produces a focus movement of less than 0.2 mm.