Knock-up plate lifting device and image forming apparatus having the same

Abstract

A knock-up plate lifting device for lowering a knock-up plate while inserting and withdrawing a paper feeding cassette, and lifting the knock-up plate when the paper feeding cassette is completely mounted. The knock-up plate lifting device includes a mounting board. A first link is pivotably mounted by a first hinge to the mounting board and has arms extended away from the first hinge. A resilient member is connected to one of the arms of the first link. A second link is pivotably mounted by a second hinge to the mounting board and extends away from the second hinge by a predetermined angle. One arm of the second link is connected with the resilient member and the other arm moves up and down in accordance with the operation of the first hinge.

1 . A knock-up plate lifting device comprising: 
 a mounting board;    a first link pivotably mounted by a first hinge to the mounting board and having first and second arms extending away from the first hinge;    a resilient member connected to the first arm of the first link; and    a second link pivotably mounted by a second hinge to the mounting board and having first and second arms extending away from the second hinge,    wherein the first arm of the second link is connected with the resilient member and the second arm moves up and down in accordance with the operation of the first hinge.    
   
   
       2 . The knock-up plate lifting device of  claim 1 , wherein 
 the second arm of the second link is disposed at a lower position when the first link is vertical to the ground.    
   
   
       3 . The knock-up plate lifting device of  claim 2 , wherein 
 the first and second arms of the second link have different lengths.    
   
   
       4 . The knock-up plate lifting device of  claim 3 , wherein the knock-up plate lifting device further comprises: 
 a guiding projection formed at the second arm of the second link; and    a guiding groove formed at the mounting board to guide the motion of the guiding projection.    
   
   
       5 . The knock-up plate lifting device of  claim 3 , further comprising: 
 an extension member formed at the end of the first arm of the first link and connected to an end of the resilient member.    
   
   
       6 . The knock-up plate lifting device of  claim 1 , wherein 
 the first and second arms of the second link are at a predetermined angle with respect to each other.    
   
   
       7 . An image forming apparatus comprising: 
 a pickup roller mounted to a main body;    a paper feeding cassette removably mounted to the main body under the pickup roller and having a knock-up plate for pushing a printing medium toward the pickup roller;    a first link mounted to a sidewall of the paper feeding cassette by a first hinge and having first and second arms extended in opposite directions from the first hinge;    a resilient member connected to the first arm of the first link;    a second link mounted to the sidewall of the paper feeding cassette by a second hinge and having a first arm connected with the resilient member and a second arm lifting and lowering the knock-up plate in accordance with the operation of the first hinge; and    an operation projection formed on the main body to rotate the first link when the paper feeding cassette is mounted into the main body.    
   
   
       8 . The image forming apparatus of  claim 7 , wherein 
 both sidewalls of the paper feeding cassette include a first link, a resilient member, and a second link, and both sides of the main body includes an operation projection corresponding with the first links.    
   
   
       9 . The image forming apparatus of  claim 7 , wherein 
 the second arm of the second link is disposed at a lower position when the first link is vertical to the bottom of the paper feeding cassette.    
   
   
       10 . The image forming apparatus of  claim 9 , wherein the first and second arms of the second link have different lengths.  
   
   
       11 . The image forming apparatus of  claim 10 , further comprising: 
 a guiding projection formed at the second arm of the second link to lift and lower the knock-up plate; and    a guiding groove formed at the sidewall of the paper feeding cassette to guide motion of the guiding projection.    
   
   
       12 . The image forming apparatus of  claim 7 , further comprising: 
 an extension member formed on the end of the first arm of the first link and connected to an end of the resilient member.    
   
   
       13 . The image forming apparatus of  claim 7 , wherein 
 the first and second arms of the second link are at a predetermined angle with respect to each other.    
   
   
       14 . An image forming apparatus comprising: 
 a pickup roller mounted to a main body;    a paper feeding cassette removably mounted to the main body,    a knock-up plate mounted to the paper feeding cassette for pushing a printing medium toward the pickup roller; and    a first knock-up plate lifting device, comprising: 
 a first link pivotably mounted to a sidewall of the paper feeding cassette, the first link having first and second arms extending away from the first hinge;  
 a resilient member connected to the first arm of the first link;  
 a second link pivotably mounted to the sidewall of the paper feeding cassette, the second link having a first arm connected with the resilient member and a second arm for supporting the knock-up plate; and  
 an operation projection formed on the main body to rotate the first link when the paper feeding cassette is mounted into the main body,  
   wherein when the first link is rotated by the operation projection, the second arm raises the knock-up plate.    
   
   
       15 . An image forming apparatus according to  claim 14 , further comprising: 
 a second knock-up plate lifting device, comprising:    a third link pivotably mounted to a second sidewall of the paper feeding cassette, the third link having first and second arms extending away from the first hinge;    a second resilient member connected to the first arm of the third link;    a fourth link pivotably mounted to the second sidewall of the paper feeding cassette, the fourth link having a first arm connected with the second resilient member and a second arm for supporting the knock-up plate; and    a second operation projection formed on the main body to rotate the third link when the paper feeding cassette is inserted into the main body.    
   
   
       16 . An image forming apparatus according to  claim 14 , further comprising: 
 a guiding projection formed at the second arm of the second link to support the knock-up plate; and    a guiding groove formed on the sidewall of the paper feeding cassette to guide the motion of the guiding projection.    
   
   
       16 . An image forming apparatus according to  claim 14 , wherein 
 the first and second arms of the second link are at a predetermined angle with respect to each other.