System for adjusting output current of discharge electrode for electrophotographic copying machines

A system for adjusting the output current of a discharge electrode for electrophotographic copying machines comprising the step of adjusting the output current of the discharge electrode in the electrophotographic copying machine by selecting a selector switch which corresponds to a class of photosensitive members, such that the discharge electrode produces an output current which is suited for the photosensitive members of the class.

BACKGROUND OF THE INVENTION 
The present invention relates to an improvement in a system for adjusting 
an output current of a discharge electrode for electrophotographic copying 
machines (hereinafter simply referred to as copying machines). 
In the conventional copying machines, the output of a discharge electrode 
is adjusted to suit for the charging characteristics of a photosensitive 
member after each replacement of the photosensitive member. Particularly, 
when the photosensitive member contains a sensitizing agent composed of a 
selenium compound, the output current must be adjusted after each 
replacement. When the charging characteristics of the photosensitive 
member have not been known, the output of the discharge electrode must be 
adjusted while checking the charging characteristics, requiring a 
specially designed device. Therefore, it is difficult to quickly perform 
the adjustment in a site where the copying machine is installed. Or even 
when the charging characteristics of the photosensitive member have been 
known, the adjustment must be effected while observing the output current 
by an ammeter, requiring very clumsy operation and a lot of time. 
FIG. 1 is a diagram of a power supply circuit for a discharge electrode 
incorporating an adjusting circuit, which is used for a conventional 
copying machine. According to this power supply circuit, constant current 
characteristics and constant voltage characteristics are obtained by 
feeding back an output current and an output voltage to an oscillation 
circuit, relying upon a high-voltage power supply of an inverter type. 
Namely, with the conventional copying machines, an ammeter is inserted 
between an output terminal P and a discharge electrode or a voltmeter is 
inserted between the output terminal P and the ground, and a variable 
resistor VR inserted in a feedback path to the oscillation circuit is 
manipulated to vary the output current or the output voltage while viewing 
the ammeter or the voltmeter to find an optimum output value. 
SUMMARY OF THE INVENTION 
The inventors of the present invention have forwarded research in an 
attempt to easily carry out the adjustment when the photosensitive member 
is to be replaced, and have found the fact that if the photosensitive 
members are suitably divided into several classes depending upon their 
charging characteristics, the power supply can be so adjusted that the 
discharge electrode gives an optimum output current for a representative 
charging characteristic within a range of each class, making it possible 
to obtain satisfactory copying results even though the charging 
characteristics of the photosensitive members may slightly differ within 
the range of the same class, and have thus accomplished the present 
invention. 
In effect, the object of the present invention is to provide a system for 
adjusting an output current of a discharge electrode for copying machines 
comprising classifying photosensitive members depending upon their 
charging characteristics, selecting a circuit for adjusting the output 
current of the discharge electrode in the copying machine by a selector 
switch depending upon a class of photosensitive members, and selecting a 
selector switch which corresponds to a new class when the photosensitive 
members are to be replaced by a different class of photosensitive members, 
such that the discharge electrode produces an output current which is 
suited for the photosensitive members of the new class.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 2 illustrates an example of a power supply circuit which includes a 
circuit for adjusting the output current of a discharge electrode, and 
which corresponds to the case in which the charging characteristics of the 
photosensitive members are divided into six classes. 
Symbols S.sub.1 to S.sub.6 denote selector switches which consist of a 
double-circuit rotary switch having 6 contacts or push-button switches of 
the charge-over type. When the selector switch S.sub.1 is selected to 
correspond to the charging characteristics of the photosensitive members 
of a first class, a circuit S.sub.1 including resistors R.sub.1, Ra is 
closed permitting a constant output current i.sub.1 to flow into a 
discharge electrode which is connected across the output terminal P and 
the ground. When the selector switch S.sub.2 is selected to correspond to 
the charging characteristics of the photosensitive members of a second 
class, a circuit S.sub.2 including resistors R.sub.2, Ra is closed and the 
circuit S.sub.1 is opened, so that a constant output current i.sub.2 is 
allowed to flow to the discharge electrode. Similarly, a constant output 
current i.sub.3 flows when the selector switch S.sub.3 is selected, a 
constant output current i.sub.4 flows when the selector switch S.sub.4 is 
selected, a constant output current i.sub.5 flows when the selector switch 
S.sub.5 is selected, and a constant output current i.sub.6 flows when the 
selector switch S.sub.6 is selected. 
Symbols VR.sub.1 to VR.sub.3 denote variable resistors for finely adjusting 
the output current of the discharge electrode to suit for the 
representative charging characteristic of each class, and symbol FV 
denotes a variable resistor for effecting fine adjustment to cope with the 
shape of the discharge electrode or mounting errors. These variable 
resistors will be adjusted during or after inspection of the copying 
machine in the factory, and need not be adjusted by the users in replacing 
the photosensitive members. 
A relation between the resistance of the variable resistor in a feedback 
path to the oscillation circuit and the output current, varies as shown in 
FIG. 3. Therefore, with the copying machine being adjusted by the variable 
resistor FV to suit for the photosensitive members having high charging 
characteristics which require a reduced output current as denoted by A, if 
the selector switch is changed to process the photosensitive members 
having low charging characteristics which require an increased output 
current as denoted by B, the adjustment may often become excessive or, 
conversely, insufficient. To preclude such an inconvenience according to 
the present invention, resistors Ra, Rb and Rc (Ra&gt;Rb&gt;Rc in this 
embodiment) are commonly inserted in the circuits which correspond to the 
charging characteristics of the neighbouring two classes and are connected 
to the variable resistor FV in parallel with the resistors R.sub.1 to 
R.sub.6 of each of the circuits which correspond to each of the classes. 
Accordingly, the output current can be adjusted to suit well for the 
charging characteristics of each of the classes. Each of the variable 
resistors VR.sub.1 to VR.sub.3 is also commonly connected to two circuits 
corresponding to the charging characteristics of the neighbouring two 
classes as shown in FIG. 2, in order to assure sufficient accuracy for 
each of the classes. 
With the copying machine of the present invention which has been adjusted 
as mentioned above, when the photosensitive members are replaced by the 
photosensitive members having different charging characteristics, the 
selector switch needs be simply selected to suit for the class of charging 
characteristics. Then, the discharge electrode is so set as to discharge 
an output current which is suited for sensitizing the photosensitive 
members, enabling the copying operation to be stably carried out. 
The present invention is by no means limited to the aforementioned 
embodiment only, but can also be applied to the photosensitive members 
which use sensitizing agents other than selenium compounds, and to the 
sheet-like photosensitive members in addition to the drum-like 
photosensitive members. Furthermore, the photosensitive members may be 
more finely classified or coarsely classified depending upon a variance in 
the charging characteristics. Moreover, an adjusting circuit employing a 
variable resistor which is not directly related to the replacement of the 
photosensitive members may be modified or eliminated.