Exposure controlling apparatus for electrophotographic copying machine
BACKGROUND OF THE INVENTION 
     The invention relates to an exposure controlling apparatus for an electrophotographic copying machine, and more particularly, to such apparatus in which the exposure value, once adjusted by an operator for a particular copying operation, is automatically reset to a normal value upon completion of that copying operation. 
     One of the factors in obtaining a sharp and clean copy image in an electrophotographic copying machine is the application of a proper exposure to a photosensitive member which has its surface uniformly charged as by corona discharge. An overexposure results in an apparently fair copy free from background smearing (the attachment of toner to non-image areas of the copy) when the electrostatic latent image formed on the surface of the photosensitive member is subsequently developed by a developer which contains toner. However, the density in the image areas diminishes also, with possible consequences that thin lines are not developed in a satisfactory manner or a copy of required legibility is not obtained from an original containing letters and characters of a reduced optical density. Conversely, an underexposure produces a background smearing on the resulting copy. As a result presently available electrophotographic copying machines include some form of sophisticated means which dispenses with the need for close exposure control to assure that a sharp and clean copy is produced from most originals when a copying operation is performed with a given exposure. The use of a developing electrode which is applied with a bias voltage in the developing unit is one example. 
     However, sophistication in the developing unit cannot assure the reproduction of a sharp and clean copy from every kind of those including originals having an extremely high or low contrast between the image and the non-image area, originals having a blackish or a white background, or the like. It follows therefore that an adjustment of the exposure is still necessary with certain originals. However, it is to be noted that such an exposure control is necessary only with special originals such as those having a colored background, for example, which are infrequently used, and it is desirable that the exposure value be maintained at a predetermined value except when these special originals are used. When an operator produces a copy from a special original by making a corresponding exposure control adjustment and leaves the copying machine under the adjusted condition, another operator may want to use the machine to obtain a copy from an ordinary original. If the second operator operates the machine in the usual manner without noticing the exposure control adjustment made by the preceding operator, a satisfactory copy may not be obtained, since an ordinary original should be copied under the normal or preset exposure condition. 
     Therefore, it is desirable that an exposure value, once adjusted by an operator for a particular copying operation, be automatically reset to a normal value or a predetermined constant value upon completion of that copying operation. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an exposure controlling apparatus for an electrophotographic copying machine whereby when an exposure value, is adjusted by an operator for a particular copying operation, the exposure will be automatically reset to a normal value upon completion of that copying operation. 
     It is another object of the invention to provide an exposure controlling apparatus in which when an exposure value other than the normal value is set for a particular copying operation, the exposure is maintained at the set value during the duration of that copying operation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front view of the exposure controlling apparatus constructed in accordance with one embodiment of the invention; 
     FIG. 2 is a similar view to FIG. 1, but showing an exposure controlling, operating member displaced so as to establish an adjusted exposure value; 
     FIG. 3 is a cross section taken along the line III--III shown in FIG. 2, additionally showing a pressure member and a solenoid both not shown in FIG. 2; 
     FIG. 4 is a cross section similar to FIG. 3 but showing the operating member moved from its neutral position to an adjusted exposure position; 
     FIG. 5 is a similar view showing the condition when the solenoid is energized; 
     FIG. 6 is a side elevation of an exposure control member adapted to move into or out of an exposure flux which irradiates a photosensitive member; and 
     FIG. 7 is a front view of a portion of a modified embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, an exposure controlling, operating member 1 has a knob 1a on one end which projects externally of a top cover 3 of a copying machine 2. A resilient blade 4 having a downwardly extending fan-shaped extension 4a is riveted at 1c to the lower end of the operating member 1. The operating member 1 and the blade 4 are both pivotally mounted on a common pin 5 which is secured to a stationary part of the machine, whereby the operating member 1 is rockable or movable between a first or neutral position indicated by a reference character N and a second and a third position, indicated by reference characters D and L, respectively. A pair of return levers 6, 7 each have one end also pivotally mounted on the pin 5, and have their free ends 6a, 7a held in abutting relationship with the opposite sides of the operating member 1 under the resilience of a tension spring 8 which has its opposite ends anchored to the respective levers. 
     At their lower ends, the return levers 6, 7 intersect with each other, and a stop pin 9 is fixedly mounted on the stationary part mentioned above adjacent to the region of such intersection. It will be noted from FIG. 1 that the inner lateral side of both return levers 6, 7 bears against the pin 9 in the neutral position N of the operating member 1. Along its lower periphery, the extension 4a of the reslient blade 4 is formed with a pair of holes 4b, 4c which are selectively engaged by a click-stop ball 11 as the operating member 1 is rocked in either direction. FIG. 3 shows the manner in which the ball 11 operates to retain the operating member 1 in either the second or third position D, L to which it is rocked. Specifically, the ball 11 is loosely received in an opening formed in a stationary plate 12, and partly engages the hole 4b or 4c on one side. On it back side, the extension 4a has a frictional member 13 such as a rubber sheet secured thereto, which is engaged by another frictional member 15 of similar material which is secured to a stationary resilient backup plate 14. 
     With continued reference to FIG. 3, there is provided a stationary pin 16 on which is pivotally mounted a pressure member 17 having one end connected with a plunger 18a of a solenoid 18 and also engaged with one end of a tension spring 19, the other end of which is secured to a stationary point. The other end of the pressure member 17 is held against the ball 11 under the resilience of the spring 19 unless the solenoid 18 is energized. 
     Referring to FIG. 1, the operating member 1 fixedly carries a pin 1b thereon, to which one end of a wire 21 is anchored, the other end of the wire being secured to a pin 23 on an exposure control member 22 located in the proximity of a photosensitive member 24 as shown in FIG. 6. Referring to FIG. 6, the control member 22 is pivotally mounted at its one end by a pin 25, so as to permit its rocking motion. The free end of the control member 22 is formed with a light shield 22a which is bent to extend toward the path 26 of exposure flux. By a spring, not shown, the control member 22 is biased to rotate clockwise about the pin 25 or in a direction away from the flux 26. The wire 21 extends from the pin 1b on the operating member around stationary pins 28, 29 and around a cam 27 to the pin 23 on the control member 22, as illustrated in FIGS. 1 and 6. The cam 27 is eccentrically secured by a setscrew 27a on a downwardly depending wall 22b of the control member 22 and serves to permit adjustment of the starting and the terminal position of the rocking motion. 
     In operation, when the operating member 1 is turned to the left, as viewed in FIG. 1, about the pin 5 to bring it into the second position D, the ball 11 engages the hole 4b in the resilient blade 4, whereby the operating member 1 is click stopped in this position. During such a rocking motion of the operating member 1, the spring 19 urges, by its resilience, the pressure member 17 against the ball 11, so that the resilient blade 4 flexes resiliently to bring the frictional member 13 thereon into abutting relationship with the other frictional member 15 on the backup plate 14 until the operating member 1 reaches the second position D, whereupon it is click stopped as illustrated in FIG. 3. During such angular movement of the operating member 1, the return lever 6 is driven by it to turn to the left about the pin 5 against the resilience of the spring 8 while the other return lever 7 remains immovable by bearing against the stop pin 9 (see FIG. 2). The magnitude of frictional drag acting between the members 13 and 15 is sufficient to overcome the resilient force exerted by the spring 8 which is thus extended to prevent the operating member 1 from being driven back to the first or netural position N. 
     It will be thus seen that the operating member 1 can be frictionally locked at any position intermediate the neutral position N and the second position D. When the operating member 1 is rocked to the position D, the movement imparted to the wire 21 will be at maximum, and the control member 22 is turned counterclockwise about the pin 25 to advance its light shield 22a into the path of irradiating or exposure light 26, thus producing a minimum exposure of the photosensitive member 24. By interrupting the angular movement of the operating member 1 at a selected position intermediate the positions N and D, the advance of the shield 22a into the light path 26 may be controlled to a desired degree. 
     When the operating member 1 is turned in a direction from the position N toward the position L or in a direction to allow the movement of the wire 21 by a pull exerted by the spring (not shown) which biases the control member 21 clockwise, the shield 22a will be retracted from its neutral position, thereby providing an increased exposure of the photosensitive member 24. Again the degree of increased exposure can be controlled by choosing a suitable position intermediate the positions N and L at which the operating member 1 is locked. 
     It will be seen that the angular movement of the operating member 1 takes place by forcedly turning the knob 1a overcoming the resistance of frictional drag acting between the members 13, 15. On the other hand, as the operating member 1 is moved from the position D to the neutral position N, the return lever 6 turns clockwise under the resilience of the spring 8 until it bears against the stop pin 9. When the operating member 1 is moved from the position N to the position L, the return lever 7 is turned clockwise about the pin 5 against the resilience of the spring 8. 
     The solenoid 18 is adapted to be energized at such a time as the completion of a copying operation or the turning off of a main or master switch occurs in the copying machine. As it is energized, the pressure member 17 is pulled by the plunger 18a to pivot counterclockwise about the pin 16, as shown in FIG. 5. When this happens, the ball 11 which has been forced into the resilient blade 4 is released and the blade is allowed to recover slightly, whereupon the frictional drag acting between the members 13 and 15 reduces rapidly, allowing the operating member 1 to be returned to the neutral position N from a position shown in FIG. 2, for example, by the resilience of the spring 8 which is transmitted thereto through the corresponding return lever which is now return lever 6. Such an automatic resetting or return takes place from any position between and including the opposite extreme positions D and L. The cam 27 shown in FIG. 6 may be moved angularly to effect a fine adjustment of the exposure to an optimum value, thus compensating for any variation in the copying sensitivity. 
     FIG. 7 shows an alternative operating member 30 which is movable between the neutral position N and one other position L. The operating member 30 is pivotally mounted on a stationary pin 31 and is biased by a spring 32 to rotate counterclockwise about the pin 31. In operation, member 30 may be rotated clockwise against the resilience of spring 32 to the position L and stationary stop 33 prevents return rotation beyond neutral position N. In other respects, the arrangement is similar to the embodiment described above.