초록 ▼

A color image forming apparatus comprises photoconductor drums on which toner images of each color are developed and formed; an endless intermediate transfer belt arranged in a contactable state with the photoconductor drums to run; first bias transfer rollers which perform first bias transfer in wh

A color image forming apparatus comprises photoconductor drums on which toner images of each color are developed and formed; an endless intermediate transfer belt arranged in a contactable state with the photoconductor drums to run; first bias transfer rollers which perform first bias transfer in which the toner images of each color are transferred from the photoconductor drums onto the intermediate transfer belt; a second bias transfer roller which performs second transfer in which the toner images on the intermediate transfer belt are transferred onto paper; and a separation unit which, when a maximum print length of an image is below a length from a transfer point A to a transfer point B, separates the photoconductor drums and the intermediate transfer belt from each other after all first bias transfer of the toner images to be transferred on the last paper in a first print job has been completed, before second bias transfer onto the last paper is started and after second bias transfer onto paper immediately before the last paper has been completed.

대표청구항 ▼

1. A color image forming apparatus comprising:a plurality of photoconductors arranged in a line so that their rotary center shafts become parallel with one another and rotating in the peripheral direction, on which electrostatic latent images corresponding to toner images of each color are formed re

1. A color image forming apparatus comprising:a plurality of photoconductors arranged in a line so that their rotary center shafts become parallel with one another and rotating in the peripheral direction, on which electrostatic latent images corresponding to toner images of each color are formed respectively; developing units provided respectively correspondingly to said photoconductors and making said electrostatic latent images formed on said photoconductors visible to form toner images; an endless intermediate transfer member arranged in a contactable state with said photoconductors to run; first bias transfer rollers which are arranged in a loop of said intermediate transfer member correspondingly to each photoconductor, and bring said intermediate transfer member into pressure contact with said photoconductors thereby to transfer the toner images of each color on said photoconductor onto said intermediate transfer member, that is, to perform first bias transfer; a second bias transfer roller which presses a recording medium against said intermediate transfer member thereby to transfer the toner image transferred on said intermediate transfer member onto said recording medium, that is, to perform second bias transfer; and a separation mechanism which, when a maximum print length of an image to be printed on one recording medium is below a length from a transfer point of the first bias transfer located on the most downstream side in the moving direction of said intermediate transfer member to a transfer point of second bias transfer in the moving direction of said intermediate transfer member, separates said photoconductor and said intermediate transfer member from each other during a period after all first bias transfer of the toner image to be transferred on a last recording medium in a first print job has been completed, before second bias transfer onto the last recording medium is started and after second bias transfer onto a recording medium immediately before the last recording medium has been completed. 2. The color image forming apparatus according to claim 1, wherein said separation unit separates said intermediate transfer member and said photoconductor from each other by at least any one of a first operation in which said first bias transfer roller is moved in a direction separating from said intermediate transfer member, and a second operation in which said photoconductor is moved in a direction separating from said intermediate transfer member.3. The color image forming apparatus according to claim 2, wherein said photoconductor stops its rotation after it has separated from said intermediate transfer member.4. The color image forming apparatus according to claim 1, wherein said photoconductor stops its rotation after it has separated from said intermediate transfer member.5. A color image forming apparatus comprising:a plurality of photoconductors arranged in a line so that their rotary center shafts become parallel with one another and rotating in the peripheral direction, on which toner images of each color are formed respectively; an endless intermediate transfer member arranged in a contactable state with said photoconductors to run; a plurality of first bias transfer rollers which are respectively arranged in a loop of said intermediate transfer member correspondingly to each photoconductor, and bring said intermediate transfer member into pressure contact with said photoconductors thereby to transfer the toner images of each color on said photoconductors onto said intermediate transfer member; guide grooves into which rotary shafts of said first bias transfer rollers are fitted, which can move said first bias transfer roller to two positions comprising a contact position where said intermediate transfer member is brought into pressure contact with said photoconductors and a separation position where said intermediate transfer member is separated from said photoconductors; and a lift drive section which is provided so that it can reciprocate linearly in the arrangement direction of the plural first bias transfer rollers and which has cam noses supporting said rotary shafts of said first bias transfer rollers, and raising and letting down said first bias transfer rollers along said guide grooves thereby to move the first bias transfer roller to said contact position or said separation position, wherein said lift drive section includes a first drive portion for raising and letting down said first bias transfer rollers respectively corresponding to said photoconductors on which toner images of yellow, magenta, and cyan are formed, and a second drive portion for raising and letting down said first bias transfer roller corresponding to said photoconductor on which a toner image of black is formed; and said second drive portion raises and lets down said first bias transfer roller independently of said first drive portion, and when said first drive portion moves so as to move said first bias transfer roller to said contact position, said second drive portion is moved by the first drive portion and moves said first bias transfer roller to said contact position. 6. A image forming apparatus comprising:a photoconductor on which a toner image is formed; a loop-like intermediate transfer member which is arranged in a contactable state with said photoconductor to run; a first bias transfer roller which brings said intermediate transfer member into pressure contact with said photoconductor and transfers the toner image formed on said photoconductor onto said intermediate transfer member thereby to perform first bias transfer; and a separation mechanism which separates said intermediate transfer member and said photoconductor from each other immediately after a transferring an image for a final page in a multiple-page single print job from said photoconductor to said intermediate transfer member. 7. The image forming apparatus according to claim 6, wherein plural photoconductors and plural first bias transfer rollers are provided, and said separation mechanism separates said intermediate transfer member and said photoconductor from each other immediately after a final transferring of said image from the photoconductors to said intermediate transfer member.8. The image forming apparatus according to claim 7, further comprising a second bias transfer roller which transfers said toner image formed on said intermediate transfer member onto a recording medium, that is, performs second bias transfer, wherein said intermediate transfer member and said photoconductor are separated from each other after second bias transfer onto a page that is immediately before said final page has been completed and after said first bias transfer for said final page has been completed.9. A color image forming apparatus comprising:a plurality of photoconductors arranged in a line so that their rotary center shafts become parallel with one another and rotating in the peripheral direction, on which toner images of each color are formed respectively; an endless intermediate transfer member arranged in a contactable state with said photoconductors to run; a plurality of first bias transfer rollers which are respectively arranged in a loop of said intermediate transfer member correspondingly to each photoconductor, and bring said intermediate transfer member into pressure contact with said photoconductors thereby to transfer the toner images of each color on said photoconductors onto said intermediate transfer member; guide grooves into which rotary shafts of said first bias transfer rollers are fitted, which can move said first bias transfer roller to two positions comprising a contact position where said intermediate transfer member is brought into pressure contact with said photoconductors and a separation position where said intermediate transfer member is separated from said photoconductors; and a lift drive section which is provided so that it can reciprocate linearly in the arrangement direction of the plural first bias transfer rollers and which has cam noses supporting said rotary shafts of said first bias transfer rollers, and raising and letting down said first bias transfer rollers along said guide grooves thereby to move the first bias transfer roller to said contact position or said separation position wherein said lift drive section separates said intermediate transfer member and said photoconductor from each other immediately after first bias transfer on the last recording medium in a first print job has been completed. 10. The image forming apparatus according to claim 9 further comprising a second bias transfer roller which transfers said toner image formed on said intermediate transfer member onto a recording medium, that is, performs second bias transfer, wherein said intermediate transfer member and said photoconductor are separated from each other after second bias transfer onto a recording medium immediately before said last recording medium has been completed and after said first bias transfer on said last recording medium has been completed,wherein said lift drive section includes a first drive portion for raising and letting down said first bias transfer rollers respectively corresponding to said photoconductors on which toner images of yellow, magenta, and cyan are formed, and a second drive portion for raising and letting down said first bias transfer roller corresponding to said photoconductor on which a toner image of black is formed; and said second drive portion raises and lets down said first bias transfer roller independently of said first drive portion, and when said first portion moves so as to move said first bias transfer roller to said contact position, said second drive portion is moved by the first drive portion and moves said first bias transfer roller to said contact position.