Abstract:
A web transporting mechanism of a printing apparatus has a buffer mechanism section for absorbing a fluctuation of the web length from a transporting section to a fixing section generated by a difference between a speed of transporting a web in the transporting section and a speed of transporting a web in the fixing section. The web transporting mechanism includes at least one brake member suppressing a motion of a movable buffer. The brake member has a drive means.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a web transporting mechanism of a printing apparatus for forming an image on a web continuously transported. More particularly, relates to the web transporting mechanism of the printing apparatus having a buffer mechanism for absorbing a fluctuation of a web length between a transporting section and a fixing section. 
     2. Description of the Related Art 
     In a printing apparatus for forming an image on a continuous web, the web is transported in such a manner that a pin member of a tractor mechanism mounted on the printing apparatus is engaged in a sprocket hole of the web of paper and the web is transported when the tractor mechanism is driven. In the case where the web having the sprocket holes is used, it is necessary to cut off both end portions of the web, in which the sprocket holes are formed, after the completion of printing. Therefore, a printing apparatus has been put into practical use in which a web having no sprocket holes is used and the web is transported by a transporting roller mechanism instead of the tractor mechanism so that the work of cutting both end portions of the web can be avoided. 
     The above printing apparatus includes: a transporting section for recording and forming an image on a web; and a fixing section for fixing the image onto the web by heating and pressurizing toner which has been transported onto the web in the transporting section, wherein the web is discharged from the fixing section. However, in this structure, a transporting member (Hereinafter, referred to as transporting means,) for transporting the web in the transporting section and the transporting means for transporting the web in the fixing section are independently driven. Accordingly, it is difficult to perfectly make the web transporting speed in the transporting section coincide with the web transporting speed in the fixing section. 
     When the web transporting speed in the transporting section is higher than that in the fixing section, looseness of the web is caused between the transporting section and the fixing portion. When the web is continuously transported by the transporting section and the fixing section, the degree of looseness is increased. On the contrary, when the web transporting speed in the fixing section is higher than that in the transporting section, a sufficiently long web cannot be supplied from the transporting section to the fixing section. In order to solve the above problems, a buffer mechanism absorbs a fluctuation in the web length between the transporting section and the fixing section caused by a difference in the web transporting speed generated between the transporting section and the fixing section. 
     An example of the buffer mechanism of a conventional printing apparatus is shown in  FIG. 3  and explained as follows. 
     There is provided a movable buffer  4 , the position of which is changed according to the length (referred to as a web length L hereinafter) of the web  3  between the transporting section  1  and the fixing section  2 . The movable buffer  4  is pushed to the web  3  by the twist coil spring  5 , and a position of the movable buffer  4  is changed according to the web length L. The position of the movable buffer  4  is detected by the sensor  6 . According to the detection signal, the web transporting speed in the fixing section  2  is controlled. Explanations will be made into a case in which the web transporting speed of the fixing section  2  is controlled by the rotating speed of the heat roller  7  and that of the pressure roller  8 . In the case where it is detected that a position of the movable buffer  4  is higher than the target position (the wab length L is longer than the target value), the rotating speed of the heat roller  7  is increased so that the web length L can be shortened. On the contrary, in the case where it is detected that a position of the movable buffer  4  is lower than the target position (the wab length L is shorter than the target value), the rotating speed of the heat roller  7  is decreased so that the web length L can be extended. In this case, the explanations are made into the case in which the web transporting speed in the fixing section  2  is changed. However, it should be noted that the present invention is not limited to the above specific system. When a difference between the rotating speed of the web transporting rollers  9   a ,  9   b , which determines the web transporting speed of the transporting section  1 , and the rotating speed of the heat roller  7 , which determines the web transporting speed in the fixing section  2 , is made to be variable by the web transporting speed control circuit  10  according to the detection signal of the sensor  6  to detect the position of the movable buffer  4 , the same effect can be provided. (See JP-A-9-146316.) 
     SUMMARY OF THE INVENTION 
     Due to the above constitution, even if the web transporting speed in the transporting section and the web transporting speed in the fixing section are not made to perfectly coincide with each other, it is possible to continuously transport the web at high speed. 
     In this case, in order to ensure the stability of continuously transporting the web, the spring constant of the twist coil spring for giving a reaction force to the movable buffer is set at a high value, so that a tension given to the web can be increased. However, when the spring constant of the twist coil spring is set at the high value, a transporting blurring is caused immediately after the start of transporting operation, and quality of printing is deteriorated as described as follows. That is, in the case where the timing of starting to transport the web in the fixing section is earlier than the timing of starting to transport the web in the transporting section, the web located in the buffer mechanism pushes down the movable buffer, and the movable buffer falls down by inertia. At this time, the web and the movable buffer are separated from each other, and a gap is formed between them. After that, the movable buffer is raised by a repulsion of the twist coil spring and comes into contact with the web again. At this time, the web slips on the web transporting roller by the shock generated at this time, and the web transporting speed fluctuates and transporting blurring is caused. On the contrary, in the case where the timing of starting to transport the web in the fixing section is later than the timing of starting to transport the web in the transporting section, the web sent out from the transporting section loosens on the buffer mechanism. At this time, the web and the movable buffer are separated from each other and a gap is formed between them. After that, the movable buffer is raised by the repulsion of the twist coil spring and comes into contact with the web again. At this time, the web slips on the web transporting roller by the shock generated at this time, and the web transporting speed fluctuates and transporting blurring is caused. 
     As described above, the following incompatible problems are caused, which will be explained in more detail as follows. When the spring constant of the twist coil spring is increased high so that the stability of continuously transporting the web can be enhanced, an intensity of the shock is increased at the time when the movable buffer comes into contact with the web immediately after the transporting operation has started. Therefore, the transporting blurring is deteriorated, and the quality of printing is deteriorated immediately after the start of transporting the web. The printing speed of the printing apparatus has been recently increased. Accordingly, there is a stronger demand of stabilizing the operation of transporting the web. Therefore, it has become difficult to reduce a difference between the speed of transporting the web in the transporting section and the speed of transporting the web in the fixing section. As a result, a fluctuation of the web length between the transporting section and the fixing section is increased. Due to the foregoing, a remarkable phenomenon is caused in which the web located on the movable buffer is separated from the movable buffer immediately after the transporting operation has started. As a result, the degree of the transporting blurring is deteriorated by the shock caused when the movable buffer comes into contact with the web again, and the quality of printing is deteriorated immediately after the transporting operation has started. However, there is a strong demand of customers for higher quality these days. Therefore, it can be said that the importance of solving this problem is very high. 
     It is an object of the invention to enhance a quality of printing immediately after the operation of transporting a web has been started by reducing the transporting blurring by decreasing a shock at the time when the movable buffer comes into contact with the web immediately after the operation of transporting the web has been started without deteriorating the stability of continuously transporting the web. 
     In order to solve the above problems, there is provided with a web transporting mechanism of a printing apparatus including a movable buffer for absorbing a fluctuation of the web length from the transporting section to the fixing section which is generated by a difference between the speed of transporting the web in the transporting section and the speed of transporting the web in the fixing section, wherein at least one brake member for suppressing a motion of the movable buffer are provided and a drive means is provided in the brake member. 
     By thus configuration, a printing apparatus of high printing quality in which the quality of printing is enhanced immediately after the operation of transporting a web has been started by reducing the transporting blurring by decreasing a shock at the time when the movable buffer comes into contact with the web immediately after the operation of transporting the web has been started without deteriorating the stability of continuously transporting the web. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing the buffer mechanism section according to an embodiment of the invention; 
         FIG. 2  is a perspective view showing the buffer mechanism section of the embodiment of the invention; and 
         FIG. 3  is an arrangement view showing an outline of the related art. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An object of suppressing a transporting blurring immediately after transporting a web has been started is realized without deteriorating the stability of continuously transporting the web. 
     Embodiment 1 
     Embodiment 1 of the buffer mechanism section of the present invention will be explained below referring to  FIG. 1 . 
     In  FIG. 1 , reference numeral  3  is a web. In many cases, the web  3  is usually made of paper used for a printing apparatus. However, the web  3  is not necessarily limited to paper. In some cases, a plastic film is used as the web  3 . 
     The brake plate  11  is provided in the movable buffer  4  located between the transporting section  1  and the fixing section  2 . The support member  13  for supporting a pushing force of the brake member  12  is arranged at a position opposed to the brake member  12  while the brake plate  11  is being interposed between the brake member  12  and the support member  13 . Due to this structure, the brake plate  11  is given a frictional force. Therefore, the original reaction force F 1  given to the movable buffer  4  by the twist coil spring  5  is canceled by the frictional load, so that the reaction force F 1  can be reduced. The brake member  12  is arranged so that it can be made to be variable between the position, at which the brake member  12  is contacted with the brake plate  11  by a drive member  14  (referred to as a drive means  14 ), and the position at which the brake member  12  is separated from the brake plate  11 . In this embodiment, the drive means  14  is a solenoid by which a position of the brake member  12  can be linearly changed. Due to this structure, the reaction force of the movable buffer  4  can be changed between the original reaction force F 1  and the reaction force F 2  (F 1 &gt;F 2 ) which is a reaction force in the case where the brake member  12  is pushed to the brake plate  11 . 
     The frictional load given to the brake plate  11  by the brake member  12  and the support member  13  depends upon a pushing force generated by the drive means  14 . This pushing force can be adjusted when the interval S between the brake member  12  and the support member  13  is changed. That is, when the interval S is extended, the pushing force (frictional load) is reduced. As a result, the reaction force F 2  is increased. On the contrary, when the interval S is reduced, the pushing force (frictional load) is increased. As a result, the reaction force F 2  is decreased. In this way, when the interval S is changed, the reaction force F 2  can be set at an arbitrary value from 0 to F1 (0≦F2≦F1). 
     The drive means  14  can drive the brake member  12  by a control signal sent from the drive means control circuit  15  according to the state of transporting the web. That is, before the transporting of the web is started, the brake member  12  and the support member  13  are pushed to the brake plate  11 . Immediately after the start of transporting the web, in order to reduce a shock given from the movable buffer to the web  3 , the reaction force of the movable buffer  4  is made to be the reaction force F 2  so as to suppress the transporting blurring. In this way, the printing quality can be enhanced. After that, the brake member  12  is retracted by the drive means  14  to a position separate from the brake plate  11  so that the reaction force of the movable buffer  4  can be made to be the original reaction force F 1  generated by the coil spring  5 . In this way, the stability of continuously transporting the web can be ensured. The drive timing of the drive means  14 , that is, the timing at which the reaction force of the movable buffer  4  is changed over from F 2  to F 1  (or from F 1  to F 2 ) is determined while consideration is being given to the transporting blurring and the stability of transporting the web. Therefore, the timing at which the reaction force of the movable buffer  4  is changed over from F 2  to F 1  (or from F 1  to F 2 ) is determined by making experiments. Even in the structure in which the support member  13  is not provided, as long as it is a system in which the brake member  12  is pushed to the brake plate  11  so as to give a brake force and suppress a motion of the movable buffer  4 , the same setting can be made. 
     Embodiment 2 
     Embodiment 2 is shown in  FIG. 2 . In this embodiment, the spring  16  is arranged at the rear of the support member  13  of Embodiment 1. In the case of the brake mechanism of the present invention, as the brake mechanism is frequently used, the contact faces of the brake plate  11 , the brake member  12  and the support member  13  are abraded and the pushing force (frictional load) is decreased. Accordingly, there is a possibility that the reaction force F 2  of the movable buffer immediately after the start of transporting the web is changed with time. However, when the pushing force is further given by the spring  16  and the spring constant of the spring  16  is set at a value as low as possible, it is possible to reduce a change in the pushing force (frictional load) relying on the pushing stroke which has changed by the abrasion of the contact faces described above. In this embodiment, the spring  16  is arranged on the support member  13  side. However, the spring  16  may be attached to the brake member  12  side. Alternatively, the spring  16  may be attached to the brake plate  11  side.