Abstract:
The invention concerns an improvement of a drive system of a color image forming apparatus. The color image-forming apparatus includes a plurality of image-forming elements; a plurality of first driving motors, each of which corresponds to each of the image-forming elements, to drive the plurality of image-forming elements; an intermediate transfer element that is disposed opposite the plurality of image-forming elements; a second driving motor to drive the intermediate transfer element; and a controlling section to control the plurality of first driving motors and the second driving motor. In the color image-forming apparatus, the controlling section controls the plurality of first driving motors and the second driving motor independently of each other, so that a first peripheral speed of each of the image-forming elements coincides with a second peripheral speed of the intermediate transfer element.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an image forming apparatus, and particularly to an improvement of a drive system of a color image forming apparatus. 
     By using a plurality of image forming elements and an intermediate transfer element, in a color image forming apparatus in which a single color toner image formed on the plurality of image forming elements is transferred onto the intermediate transfer element and one full color image is formed, the drive control of the plurality of image forming elements, the control of time of image formation onto the each of image forming elements and the drive control of the intermediate transfer element are very important. When the consistency is insufficient between the respective controls, or there is a difference of peripheral speed between each of image forming elements or between the image forming element and intermediate transfer element, or the time of toner image formation to each of image forming elements is out of the regular time, a color doubling or image disturbance is generated. Therefore, the high accurate control technology is used for each control. 
     Relating to the start stop control of each image forming element and the start stop control of the intermediate transfer element, the time control is conducted, and for the image forming element and the intermediate transfer element which are in contact with each other, the time control which starts simultaneously and stops simultaneously is conducted. 
     However, when the control by only the time is conducted, it has been seen that there are following problems. 
     It is inevitable that, between the image forming element and the intermediate transfer element, the difference of the rising characteristic and the falling characteristic is generated due to the difference of masses of themselves or the difference of inertia of these drive systems. Accordingly, the velocity change at the rising time of the image forming element and the velocity change at the rising time of the intermediate transfer element are different, and these velocity changes at the falling time are different. 
     Therefore, even when the image forming element drive motor and the intermediate transfer element drive motor are simultaneously turned on, the image forming element and the intermediate transfer element reach a predetermined steady state velocity through respectively different changes of velocity. Such different rising characteristics are shown in FIG.  1 . It is defined that the image forming element shows the rising characteristic by a curve A, and the intermediate transfer element has the rising characteristic shown by a curve B. Both are operated at the same steady state velocity V, and in an area a, the peripheral speed of the image forming element is larger than the peripheral speed of the intermediate transfer element, and in an area b, the peripheral speed of the intermediate transfer element is larger than the peripheral speed of the image forming element. Because the image forming element and the intermediate transfer element are in contact with each other, when there is the difference between such the rising characteristics, in the area a, the intermediate transfer element and its drive system act as a load on the image forming element drive motor, and in the area b, the image forming element and its drive system act as a load on the intermediate transfer element dive motor. 
     Such the reverse rotation phenomenon between the peripheral speed of the image forming element and the peripheral speed of the intermediate transfer element or the phenomenon that one side peripheral speed is largely higher than the peripheral speed of the other one, is generated, and an undesirable phenomenon that an excessive load torque is burdened on the drive motor is generated. The phenomenon shown in FIG. 1 is generated not only at the start time, but also at the time of a steady state operation and stop. 
     Accordingly, when the design work of the drive system of the image forming element and the drive system of the intermediate transfer element is conducted, it is necessary that the power of the drive motor and the drive current of the motor are set considering not only original loads but also the above described excessive loads. 
     Therefore, the motor having the excessive power becomes necessary, and the excessive electric power is necessary, resulting in an increase of cost and increase of the power consumption. 
     SUMMARY OF THE INVENTION 
     To overcome the abovementioned drawbacks in conventional color image forming apparatus employing the intermediate transfer element, it is an object of the present invention to provide a color image-forming apparatus whose cost is low and power consumption is small. 
     Accordingly, to overcome the cited shortcomings, the abovementioned object of the present invention can be attained by image-forming apparatus and methods described as follow. 
     (1) An image-forming apparatus, comprising: a plurality of image-forming elements; a plurality of first driving motors, each of which corresponds to each of the image-forming elements, to drive the plurality of image-forming elements; an intermediate transfer element that is disposed opposite the plurality of image-forming elements; a second driving motor to drive the intermediate transfer element; and a controlling section to control the plurality of first driving motors and the second driving motor; wherein the controlling section controls the plurality of first driving motors and the second driving motor independently of each other, so that a first peripheral speed of each of the image-forming elements coincides with a second peripheral speed of the intermediate transfer element. 
     (2) The image-forming apparatus of item 1, wherein the controlling section performs controlling actions at a rise time of both the plurality of first driving motors and the second driving motor. 
     (3) The image-forming apparatus of item 1, wherein the controlling section performs controlling actions at a steady-state operating time of both the plurality of first driving motors and the second driving motor. 
     (4) The image-forming apparatus of item 1, wherein the controlling section performs controlling actions at a rise time of both the plurality of first driving motors and the second driving motor, so that a moving distance of each of the image-forming elements coincides with that of the intermediate transfer element. 
     (5) The image-forming apparatus of item 1, wherein, when stopping the plurality of first driving motors and the second driving motor, the controlling section turns off the second driving motor preceding to turning off the plurality of first driving motors. 
     (6) The image-forming apparatus of item 1, wherein either a stepping motor or a DC motor is employed for both the plurality of first driving motors and the second driving motor. 
     (7) An image-forming apparatus, comprising: a plurality of image-forming elements; a plurality of first driving motors, each of which corresponds to each of the image-forming elements, to drive the plurality of image-forming elements; an intermediate transfer element that is disposed opposite the plurality of image-forming elements; a second driving motor to drive the intermediate transfer element; and a controlling section to control the plurality of first driving motors and the second driving motor; wherein the controlling section controls the plurality of first driving motors and the second driving motor independently of each other, so that a first peripheral speed of each of the image-forming elements is faster than a second peripheral speed of the intermediate transfer element by a predetermined value. 
     (8) The image-forming apparatus of item 7, wherein the controlling section performs controlling actions at a rise time of both the plurality of first driving motors and the second driving motor. 
     (9) The image-forming apparatus of item 7, wherein the controlling section performs controlling actions at a steady-state operating time of both the plurality of first driving motors and the second driving motor. 
     (10) The image-forming apparatus of item 7, wherein, when stopping the plurality of first driving motors and the second driving motor, the controlling section turns off the second driving motor preceding to turning off the plurality of first driving motors. 
     (11) The image-forming apparatus of item 7, wherein either a stepping motor or a DC motor is employed for both the plurality of first driving motors and the second driving motor. 
     (12) A method for controlling motors equipped in an image-forming apparatus, which includes a plurality of image-forming elements, a plurality of first driving motors to drive the plurality of image-forming elements, an intermediate transfer element disposed opposite the plurality of image-forming elements, and a second driving motor to drive the intermediate transfer element, comprising the step of: controlling the plurality of first driving motors and the second driving motor independently of each other, so that a first peripheral speed of each of the image-forming elements coincides with a second peripheral speed of the intermediate transfer element. 
     (13) The method of item 12, wherein the controlling step is performed at a rise time of both the plurality of first driving motors and the second driving motor. 
     (14) The method of item 12, wherein the controlling step is performed at a steady-state operating time of both the plurality of first driving motors and the second driving motor. 
     (15) The method of item 12, wherein the controlling step is performed at a rise time of both the plurality of first driving motors and the second driving motor, so that a moving distance of each of the image-forming elements coincides with that of the intermediate transfer element. 
     (16) The method of item 12, further comprising the step of: turning off the second driving motor preceding to turning off the plurality of first driving motors, when stopping the plurality of first driving motors and the second driving motor. 
     (17) The method of item 12, wherein either a stepping motor or a DC motor is employed for both the plurality of first driving motors and the second driving motor. 
     (18) A method for controlling motors equipped in an image-forming apparatus, which includes a plurality of image-forming elements, a plurality of first driving motors to drive the plurality of image-forming elements, an intermediate transfer element disposed opposite the plurality of image-forming elements, and a second driving motor to drive the intermediate transfer element, comprising the step of: controlling the plurality of first driving motors and the second driving motor independently of each other, so that a first peripheral speed of each of the image-forming elements is faster than a second peripheral speed of the intermediate transfer element by a predetermined value. 
     (19) The method of item 18, wherein the controlling step is performed at a rise time of both the plurality of first driving motors and the second driving motor. 
     (20) The method of item 18, wherein the controlling step is performed at a steady-state operating time of both the plurality of first driving motors and the second driving motor. 
     (21) The method of item 18, further comprising the step of: turning off the second driving motor preceding to turning off the plurality of first driving motors, when stopping the plurality of first driving motors and the second driving motor. 
     (22) The method of item 18, wherein either a stepping motor or a DC motor is employed for both the plurality of first driving motors and the second driving motor. 
     Further, to overcome the abovementioned problems, other image-forming apparatus and methods, embodied in the present invention, will be described as follow: 
     (23) An image forming apparatus having: a plurality of image forming elements; a plurality of image forming element drive motors which are provided corresponding to each of the plurality of image forming elements, and which drive each of the image forming elements; an intermediate transfer element provided opposed to the plurality of image forming elements; an intermediate transfer drive motor for driving the intermediate transfer element; and a control means for controlling the image forming element driving motors and the intermediate transfer element drive motor, the image forming apparatus is characterized in that the control means controls the image forming element drive motors and the intermediate transfer element drive motor by a method by which they can be independently controlled. 
     (24) An image forming apparatus according to item 23, wherein the control means conducts the control at the rise time of the image forming element drive motors and the intermediate transfer element drive motor so that the peripheral speed of the image forming element and the peripheral speed of the intermediate transfer element become the same. 
     (25) An image forming apparatus according to item 23, or 24, wherein the control means conducts the control at the steady state operation time of the image forming element drive motors and the intermediate transfer element drive motor so that the peripheral speed of the image forming element and the peripheral speed of the intermediate transfer element become the same. 
     (26) An image forming apparatus according to any one of items 23 to 25, wherein the control means conducts the control so that a movement distance of the image forming element and the movement distance of the intermediate transfer element at the rise time of the image forming element drive motors and the intermediate transfer drive motor become the same. 
     (27) An image forming apparatus according to item 23, wherein the control means controls the image forming element drive motors and the intermediate transfer element drive motor so that the peripheral speed of the intermediate transfer element is not higher than the peripheral speed of the image forming elements by a predetermined value. 
     (28) An image forming apparatus according to item 23, or 27, wherein the control means conducts the control at the rise time of the image forming element drive motors and the intermediate transfer element drive motor so that the peripheral speed of the intermediate transfer element is not higher than the peripheral speed of the image forming elements by a predetermined value. 
     (29) An image forming apparatus according to item 23, 27 or 28, wherein the control means conducts the control at the steady state operation time of the image forming element drive motors and the intermediate transfer element drive motor so that the peripheral speed of the intermediate transfer element is not higher than the peripheral speed of the image forming elements by a predetermined value. 
     (30) An image forming apparatus according to any one of items 23 to 29, wherein the control means turns off the intermediate transfer element drive motor not later than the image forming element drive motor at the stop time. 
     (31) An image forming apparatus according to any one of items 23 to 30, wherein a stepping motor or a DC motor is used as the image forming element drive motor and the intermediate transfer element drive motor. 
     (32) A control method of a motor in an image forming apparatus characterized in that the image forming element drive motor and the intermediate transfer element drive motor are controlled by a method by which they can be controlled independently of each other. 
     (33) A control method of a motor in an image forming apparatus according to item 32, wherein the image forming element drive motor and the intermediate transfer element drive motor are controlled so that the peripheral speed of the image forming element and the peripheral speed of the intermediate transfer element drive motor at the rise time are the same. 
     (34) A control method of a motor in an image forming apparatus according to either one of item 32 or 33, wherein the image forming element drive motor and the intermediate transfer element drive motor are controlled so that the peripheral speed of the image forming element and the peripheral speed of the intermediate transfer element drive motor at the steady state operation time are the same. 
     (35) A control method of a motor in an image forming apparatus according to any one of items 32 to 34, wherein the image forming element drive motor and the intermediate transfer element drive motor are controlled so that the movement distance of the image forming element and the movement distance of the intermediate transfer element at the rise time are the same. 
     (36) A control method of a motor in an image forming apparatus according to item 32, wherein the image forming element drive motor and the intermediate transfer element drive motor at the rise time are controlled so that the peripheral speed of the intermediate transfer element drive motor is not higher than the peripheral speed of the image forming element by a predetermined value. 
     (37) A control method of a motor in an image forming apparatus according to either one of item 32 or 36, wherein the image forming element drive motor and the intermediate transfer element drive motor at a steady state operation time are controlled so that the peripheral speed of the intermediate transfer element drive motor is not higher than the peripheral speed of the image forming element by a predetermined value. 
     (38) A control method of a motor in an image forming apparatus according to any one of items 32 to 37, wherein the intermediate transfer element drive motor is turned off not later than the image forming element drive motor at the stop time. 
     (39) A control method of a motor in an image forming apparatus according to any one of items 32 to 38, wherein a stepping motor or a DC motor is used as the image forming element drive motor and the intermediate transfer element drive motor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and advantages of the present invention will become apparent upon reading the following detailed description and upon reference to the drawings in which: 
     FIG. 1 is a view showing rise characteristics of an image forming element and an intermediate transfer element; 
     FIG. 2 is a view showing an overall structure of a color image forming apparatus according to the embodiment of the present invention; 
     FIGS.  3 ( a ) and  3 ( b ) are views showing drive systems of a photoreceptor and the intermediate transfer element; 
     FIG. 4 is a block diagram of a control system of the color image forming apparatus according to the embodiment of the present invention; and 
     FIGS.  5 ( a ) and  5 ( b ) are graphs showing changes of peripheral speeds of the photoreceptor and the intermediate transfer element in the embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 2, a color image forming apparatus according to the embodiment of the present invention will be described below. FIG. 2 shows a whole structure of the color image forming apparatus according to the embodiment of the present invention. 
     The color image forming apparatus shown in the drawing forms a full color toner image onto an intermediate transfer element  10  by a yellow image forming section  1 Y forming a yellow toner image, a magenta image forming section  1 M forming a magenta toner image, a cyan image forming section  1 C forming a cyan toner image and a black image forming section  1 K forming a black toner image, and the full color toner image is transferred onto a recording sheet P from the intermediate transfer element  10  and the full color toner image is formed on the recording sheet P. 
     The yellow image forming section  1 Y is composed of a drum-like photoreceptor  2 Y as an image forming element, and a scorotron charger, and has a charging apparatus  3 Y to provide a uniform charging potential onto the photoreceptor  2 Y, an exposure apparatus  4 Y to dot-exposure the photoreceptor  2 Y by a light beam from a laser light source, a developing apparatus  5 Y to develop an electrostatic latent image formed by the charge and exposure on the photoreceptor  2 Y and to form the yellow toner image, a transfer apparatus  6 Y composed of the scorotron charger to transfer the toner image on the photoreceptor  2 Y onto the intermediate transfer element  10 , and a cleaning apparatus  7 Y to clean the photoreceptor  2 Y. 
     The magenta image forming section  1 M has a photoreceptor  2 M as the image forming element having a function which is the same as the above description in the yellow image forming element  1 Y, charging apparatus  3 M, exposure apparatus  4 M, developing apparatus  5 M, transfer apparatus  6 M, and cleaning apparatus  7 M, and the cyan image forming section  1 C has a photoreceptor  2 C as the image forming element having a function which is the same as the above description in the yellow image forming section  1 Y, charging apparatus  3 C, exposure apparatus  4 C, developing apparatus  5 C, transfer apparatus  6 C, and cleaning apparatus  7 C, and the black image forming section  1 K has a photoreceptor  2 K as the image forming element having a function which is the same as the above description in the yellow image forming section  1 Y, charging apparatus  3 K, exposure apparatus  4 K, developing apparatus  5 K, transfer apparatus  6 K, and cleaning apparatus  7 K. 
     The intermediate transfer element  10  is stretched over a drive roller  11 A, driven roller  11 B, and driven roller  11 C, and is rotated in the arrowed direction. In the periphery of the intermediate transfer element  10 , the yellow image forming section  1 Y, magenta image forming section  1 M, cyan image forming section  1 C, black image forming section  1 K, a transfer apparatus  12  composed of a corotron charger to transfer a toner image on the intermediate transfer element  10  onto the recording sheet P, separation apparatus  13  composed of corotron charger to separate the recording sheet P from the intermediate transfer element  10 , and cleaning apparatus  14  to clean the intermediate transfer element  10 , are arranged. 
     The recording sheet P is accommodated in a sheet feed cassette  20 , and is conveyed by a sheet feed roller  21  from the sheet feed cassette  20 , and by a register roller  22 , the sheet is fed onto a position of the transfer apparatus  12  in timed relationship with the toner image formation on the intermediate transfer element  10 . Numeral  23  is a fixing apparatus having a belt, which is a heat source, and pressure roller, and while the recording sheet P is conveyed, the toner image is fixed on the recording sheet P. The recording sheet P passed through the fixing apparatus  23  is delivered on a sheet delivery tray  27  through conveyance rollers  24 ,  25  and  26 . 
     A  28 Y,  28 M,  28 C, and  28 K are toner containers to respectively accommodate a yellow toner, magenta toner, cyan toner, and black toner, and each of color toners is supplemented to the developing apparatus  5 Y,  5 M,  5 C, and  5 K to which each color toner corresponds, from these toner containers. 
     According to the arrowed rotation of the photoreceptor  2 Y, the charge by the charger  3 Y, exposure by the exposure apparatus  4 Y, and development by the developing apparatus  5 Y are conducted, and the yellow toner image is formed on the photoreceptor  2 Y, and respectively, by the same charge, exposure, and development, the magenta toner image is formed on the photoreceptor  2 M, and by the same charge, exposure, and development, the cyan toner image is formed on the photoreceptor  2 C, and by the same charge, exposure, and development, the black toner image is formed on the photoreceptor  2 K. The timing control is conducted so that these color toner images are superimposed on and transferred onto the intermediate transfer element  10 , and a full color toner image is formed. 
     The full color toner image on the intermediate transfer element  10  is transferred onto the recording sheet P by the transfer apparatus  12 . After the full color toner image is fixed on the recording sheet P by the fixing apparatus  23 , the recording sheet P is delivered onto a sheet delivery tray  27 . 
     The photoreceptors  2 Y,  2 M,  2 C, and  2 K are respectively cleaned by cleaning apparatus  7 Y,  7 M,  7 C, and  7 K after the transfer, and are in the condition that the next image formation can be conducted. The intermediate transfer element  10  is cleaned by the cleaning apparatus  14  after the full color toner image is transferred, and in the condition that the next image formation can be conducted. The toner consumed by the development is respectively supplemented from the toner containers  28 Y,  28 M,  28 C, and  28 K, to the corresponding developing apparatus  5 Y,  5 M,  5 C, and  5 K. 
     FIG. 3 shows a drive system of the photoreceptor and intermediate transfer element. The photoreceptor  2  commonly showing the photoreceptors  2 Y,  2 M,  2 C and  2 K, is driven by a photoreceptor drive motor MP which is commonly showing photoreceptor drive motors in the same manner, through gears g 1 -g 4 . The intermediate transfer element  10  is driven by an intermediate transfer element drive motor MT through gears g 5 -g 8 . 
     FIG. 4 is a block diagram of the control system of the color image forming apparatus according to the embodiment of the present invention. 
     A photoreceptor drive motor MY to drive the photoreceptor  2 Y, photoreceptor drive motor MM to drive the photoreceptor  2 M, photoreceptor drive motor MC to drive the photoreceptor  2 C, photoreceptor drive motor MK to drive the photoreceptor  2 K, and intermediate transfer element drive motor MT to drive the intermediate transfer element  10 , are driven by respective drive circuits DY, DM, DC, DK, and DT, and these drive circuits individually connected to a control means CR composed by a microcomputer by control lines. For photoreceptor drive motors MY, MM, MC, MK, and the intermediate transfer element drive motor MT, a stepping motor or DC motor can be used. 
     The photoreceptors  2 Y,  2 M,  2 C, and  2 K are in contact with the intermediate transfer element  10  as shown in FIG. 2, and these photoreceptors  2 Y,  2 M,  2 C, and  2 K and the intermediate transfer element  10  are driven so that they are moved at the same steady state peripheral speed. Further, at the time of start and at the time of stop, the synchronous control to almost simultaneously start and stop them is conducted on the photoreceptors  2 Y,  2 M,  2 C, and  2 K and the intermediate transfer element  10 . 
     The reversal phenomenon of the peripheral speed of the photoreceptor and the intermediate transfer element at the start time shown in FIG. 1 or the phenomenon that the large speed difference is generated, is generated because only the on/off time of the photoreceptor and the intermediate transfer element is synchronized, and the speed control corresponding to the characteristics at the rise time of both is not independently conducted on both of them. 
     In the present embodiment, when the photoreceptor drive motors MY, MM, MC, MK, to drive the photoreceptor  2  and the intermediate transfer element drive motor MT to drive the intermediate transfer element  10  are controlled by a method by which they can be controlled independently, as described below, the undesirable phenomenon generated in the reversal phenomenon of the speed at the start time shown in FIG. 1, is surely prevented. Such the undesirable phenomenon as described above, is generated not only at the rise time but also at the steady state operation time to be operated at the steady state speed, and the stop time, however, these undesirable phenomena are surely prevented by the present embodiment. 
     Particularly, because the intermediate transfer element  10  is in contact with 4 photoreceptors  2 Y,  2 M,  2 C and  2 K, when the peripheral speed of the intermediate transfer element  10  is higher than the peripheral speed of the photoreceptors  2 Y,  2 M,  2 C and  2 K, the very large reduction torque is loaded on the intermediate transfer element drive motor MT. In the present embodiment, such the excessive load loaded on the intermediate transfer element drive motor is surely prevented. 
     In the present embodiment, specifically, by the following 2 methods, the generation of the excessive load is prevented. In this connection, in the following description, the description is made in such a manner that the photoreceptors  2 Y,  2 M,  2 C and  2 K are defined as the photoreceptor  2 , and the photoreceptor drive motors MY, MM, MC, and MK are defined as the MP. The content described in the following, is applied for the respective of the photoreceptors  2 Y,  2 M,  2 C and  2 K, and the photoreceptor drive motors MY, MM, MC, and MK. 
     (1) The peripheral speed of the photoreceptor and the peripheral speed of the intermediate transfer element make the same. 
     FIG.  5 ( a ) shows the speed changes of the both when the peripheral speed of the photoreceptor  2  and the intermediate transfer element  10  is made the same. In FIG.  5 ( a ), Lab shows the peripheral speed of the photoreceptor  2  and the peripheral speed of the intermediate transfer element  10 . As shown by the drawing, the peripheral speed of both is the same as shown by the Lab, in the rise time to the time t1 at which the peripheral speed of both reaches from the start time t0 to the steady state speed V, and in the steady state operation time after the time t1. 
     The control by which the speed becomes the peripheral speed shown in FIG.  5 ( a ), is conducted when the photoreceptor drive motor MP and the intermediate transfer element drive motor MT are controlled by the control means CR. 
     Next, an example of the control when a stepping motor is used as the photoreceptor drive motor MP and the intermediate transfer element drive motor MT, will be described. 
     When parameters shown in Table 1 are used, 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
             
             
               
                   
                 N 
                 Number of steps of photoreceptor drive motor MP up to 
               
               
                   
                   
                 the time when photoreceptor 2 reaches the final speed. 
               
               
                   
                 B 
                 Number of steps of intermediate transfer element 
               
               
                   
                   
                 drive motor MT up to the time when intermediate 
               
               
                   
                   
                 transfer element 10 reaches the final speed. 
               
               
                   
                 R1 
                 Diameter of photoreceptor 2 
               
               
                   
                 R2 
                 Diameter of drive roller 11A to drive the 
               
               
                   
                   
                 intermediate transfer element 10. 
               
               
                   
                 G1 
                 Gear ratio of drive system to drive the photoreceptor 2. 
               
               
                   
                 G2 
                 Gear ratio of drive system to drive the intermediate 
               
               
                   
                   
                 transfer element 10. 
               
               
                   
                 Vs 
                 Initial peripheral speed. 
               
               
                   
                 Ve 
                 Final peripheral speed. 
               
               
                   
                   
               
             
          
         
       
     
     The number of steps at the rise time of the photoreceptor drive motor MP, the number B of steps at the rise time of the intermediate transfer element drive motor MT, peripheral speed V1 (n) of the photoreceptor  2 , peripheral speed V2 (m) of the intermediate transfer element  10 , and the movement distance D1 at the rise time of the photoreceptor  2  and the movement distance D2 at the rise time of the intermediate transfer element  10 , are expressed by the following expressions (1) to (6). 
     (1) The number of steps of the photoreceptor drive motor MP=N. 
     [Expression 1] 
     (2) The number of steps of the intermediate transfer element drive motor MT.              B   =         R2                 π   ×   G2       R1                 π   ×   G1       ×   N             [     Expression                 2     ]                                
     (3) The photoreceptor peripheral speed                  V1        (   n   )       =       Vs   +         Ve   -   Vs     N     ×   n                 n       =   1       ,   2   ,     3                 …             [     Expression                 3     ]                                
     (4) The intermediate transfer element peripheral speed                  V2        (   m   )       =       Vs   +         Ve   -   Vs     B     ×   m                 m       =   1       ,   2   ,     3                 …             [     Expression                 4     ]                                
     (5) The movement distance of the photoreceptor              D1   =       ∫     n   =   0     N            (     Vs   +         Ve   -   Vs     N     ×   n       )             n                 [     Expression                 5     ]                                
     (6) The movement distance of the intermediate transfer element        D2   =       ∫     m   =   0     B            (     Vs   +         Ve   -   Vs     B     ×   m       )             m                                
     In the example of the present embodiment, the photoreceptor drive motor MP and the intermediate transfer element drive motor MT are controlled so that the photoreceptor peripheral speed V1 (n)=the intermediate transfer element peripheral speed V2 (m), and the photoreceptor movement distance D1=the intermediate transfer element movement distance D2 are satisfied. For the condition that the photoreceptor peripheral speed and the intermediate transfer element peripheral speed are made the same, the control to maintain the above condition throughout the rise time and the steady state operation time of them is conducted. 
     Such the control is attained when the control of the control pulse frequency by the divider which the control means CR has, is independently conducted of the photoreceptor drive motor MP and the intermediate transfer element drive motor MT. By the control shown in FIG.  5 ( a ), it can be prevented that the excessive load due to the drive system of the photoreceptor  2  is loaded onto the intermediate transfer element drive motor MT. 
     (2) The peripheral speed of the intermediate transfer element is made lower than the peripheral speed of the photoreceptor by a predetermined value. 
     In another example of the present embodiment, the control that the difference between the photoreceptor peripheral speed V1 (n) and the intermediate transfer element peripheral speed V2 (m), that is, the difference ΔV shown by the following expression (7) becomes a predetermined value K, is conducted. Such the control is also attained when the control pulse of the photoreceptor drive motor MP and the intermediate transfer element drive motor MT is independently controlled. 
     [Expression 6] 
     (7) The difference between peripheral speed V1and peripheral speed V2          Δ                 V     =             Ve   -   Vs     N     ×   n     -         Ve   -   Vs     B     ×   m       =   K                            
     The control according to the expression (7) is shown in FIG.  5 ( b ). As shown in FIG.  5 ( b ), the peripheral speed Lb of the intermediate transfer element  10  is always lower than the peripheral speed Lb of the photoreceptor  2  by a predetermined value K at the rise time of t0−t1 and at the steady state operation time after t1. As the predetermined value K, a minute value of about 0.2-0.5% of the speed V1or V2 is preferable. 
     As described above, the control that the intermediate transfer element peripheral speed is made lower than the photoreceptor peripheral speed by a predetermined value is conducted throughout at the rise time and the steady state operation time of the intermediate transfer element  10  and the photoreceptor  2 . 
     By the control satisfying the condition shown by the expression (7), it can be avoided that the load of the drive system of the photoreceptor  2  becomes a load torque of the intermediate transfer element drive motor MT. 
     In the present embodiment, at the time of completion of an image forming process, that is, at the stop time of the photoreceptor  2  and the intermediate transfer element  10 , the control so that an excessive load is not burdened on the intermediate transfer element, is conducted. Specifically, the control that the timing at which the control means CR turns off the intermediate transfer element drive motor MT, is made slightly earlier than the timing at which the control means CR turns off the photoreceptor drive motor MP, is conducted. By this control, the excessive lord burdened on the intermediate transfer element drive motor MT is eliminated. 
     According to the present invention, the following effects can be obtained. 
     (1) Because the photoreceptor and intermediate transfer element can be independently controlled, the control corresponding to the rise characteristic or fall characteristic at the start time, steady state operation or stop time of them can be conducted, and it is prevented that the excessive load torque is burdened on the image forming element drive motor or intermediate transfer element drive motor. As the result, the motors having the necessary minimum power as these motors can be used, and the electric power consumption can be reduced, and the cost reduction and consumption energy reduction can be realized. In a color image forming apparatus using a plurality of image forming elements and intermediate transfer element, all the load of the drive systems of the image forming elements are burdened on the intermediate transfer element drive motor, and there is a case where the load torque of the intermediate transfer element drive motor is increased, however, according to the present invention, in the color image forming apparatus, the excessive load burdened on the intermediate transfer element can be surely avoided, and the cost reduction and energy consumption reduction can be surely realized. 
     (2) Because the peripheral speed of the photoreceptor and the peripheral speed of the intermediate transfer element are controlled so that they become the same, the excessive load burdened on the intermediate transfer element drive motor at the rise time can be very finely removed. 
     (3) Because the peripheral speed of the photoreceptor and the peripheral speed of the intermediate transfer element are controlled so that they become the same, the excessive load burdened on the intermediate transfer element drive motor at the steady state operation time can be very finely removed. 
     (4) Because the movement distance of the photoreceptor and the movement distance of the intermediate transfer element are controlled so that they become the same, the excessive load burdened on the intermediate transfer element drive motor at the rise time can be very finely removed. 
     (5) The excessive load burdened on the intermediate transfer element drive motor at the stop time can be very finely removed. 
     (6) Because the control is conducted so that the peripheral speed of the intermediate transfer element does not always exceed the peripheral speed of the photoreceptor, the excessive load burdened on the intermediate transfer element at the rise time can be very finely removed. 
     (7) Because the control is conducted so that the peripheral speed of the intermediate transfer element does not always exceed the peripheral speed of the photoreceptor, the excessive load burdened on the intermediate transfer element at the steady state operation time can be very finely removed. 
     (8) The excessive load burdened on the intermediate transfer element drive motor at the stop time is eliminated, and the load burdened on the intermediate transfer element drive motor is decreased. 
     Disclosed embodiment can be varied by a skilled person without departing from the spirit and scope of the invention.