Electricity: measuring and testing – Electrostatic field – Using modulation-type electrometer
Reexamination Certificate
2001-09-27
2003-12-02
Le, N. (Department: 2858)
Electricity: measuring and testing
Electrostatic field
Using modulation-type electrometer
Reexamination Certificate
active
06657434
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a surface potential detection apparatus and a surface potential detection method in which a surface potential is measured through a non-contact method.
2. Discussion of Background
A surface potential detection apparatus of this type, which may be employed to detect the surface potential of a photosensitive drum in a photocopier, laser beam printer or the like through a non-contact method, for instance, utilizes a surface potential sensor that generates an AC signal corresponding to the surface potential of the photosensitive drum by using a tuning fork to mechanically interrupt the electrical field between a detection electrode and the photosensitive drum as disclosed in Japanese Examined Patent Publication No. 6467/1991 and the like. The AC signal is then amplified at a pre-amplifier and the amplified signal is guided to a synchronous detection circuit via an isolator, where the signal wave is detected with a signal that is synchronized with the mechanical interruption. The synchronous detection output signal output from the synchronous detection circuit is converted to a DC signal at an integrating circuit. The DC signal obtained at the integrating circuit is input to a high-voltage amplifier.
The individual circuits share a common ground line. The high-voltage amplifier controls the potential at the common ground line in conformance to the input DC signal so as to equalize the potential at the common ground line to the potential at the surface of the photosensitive drum which is the measurement target surface. By extracting the potential at the common ground line via an attenuator, a buffer amplifier and the like, a surface potential signal is obtained. The common ground line achieves a floating relationship with a ground potential or the frame ground potential.
The greatest advantage achieved through this method is that even when the distance between the surface potential sensor that includes the tuning fork and the detection electrode and the surface of the photosensitive drum constituting the measurement target surface changes, a highly accurate surface potential detection signal manifesting a very low degree of distance dependency is obtained.
The surface potential detection apparatus described above normally includes two units, i.e., a surface potential sensor and a signal processing device. The surface potential sensor is constituted as a type of probe which includes a detection electrode, a tuning fork, a drive circuit, a pre-amplifier and the like. The signal processing device includes the remaining circuit portion that is needed to achieve the function as a surface potential detection apparatus.
Numerous tandem type high-speed photocopiers and laser printers have been proposed and put into practical use in recent years. In these image generating apparatuses utilizing four photosensitive drums (cyan, magenta, yellow and black), the surface potentials at the four photosensitive drums must be measured.
Since it is necessary to provide one surface potential sensor and one signal processing device in conjunction with each photosensitive drum in the prior art, four sets each having a surface potential sensor and a signal processing device must be provided for the four photosensitive drums. Each signal processing device constituting a surface potential detection apparatus has a complicated circuit structure and includes two transformers, which is bound to cause increases in the size, the weight and the production cost of the device. Accordingly, in the prior art, the size, the weight and the production cost of the surface potential detection apparatus itself are notably significant since the signal processing device must be provided for each of the four photosensitive drums, posing a critical problem to be addressed.
In addition, since the surface potential sensor in the prior art, which obtains an AC signal corresponding to the surface potential at the photosensitive drum by mechanically interrupting the electrical field between the detection electrode and the photosensitive drum with a tuning fork, has a complicated structure that includes a mechanically movable part, a great deal of time and work must be expended to manufacture, assemble, adjust, maintain and inspect the surface potential sensor.
SUMMARY OF THE INVENTION
It is a first object of the present invention to provide a surface potential detection apparatus that achieves simplification in the circuit, miniaturization and reductions in the weight and the production cost.
It is a second object of the present invention to provide a new and improved surface potential detection method which makes it possible to detect a surface potential with a high degree of reliability through a simple structure and a surface potential detection apparatus and a surface potential detection sensor that may be directly utilized to implement the method.
It is a third object of the present invention to provide a new and improved surface potential detection method which greatly facilitates the processes of production, assembly, adjustment, inspection, maintenance and the like and a surface potential detection apparatus and a surface potential detection sensor that may be directly utilized to implement the method.
In order to achieve the first object, the surface potential detection apparatus according to the present invention includes a plurality of surface potential sensors, a switching circuit and a signal processing circuit. The plurality of surface potential sensors are provided independently of one another. The switching circuit individually selects and outputs signals provided by the surface potential sensors with varied timing for each surface potential sensor. The signal processing circuit is connected to the plurality of surface potential sensors via the switching circuit to serve the plurality of surface potential sensors.
Since the surface potential detection apparatus according to the present invention is provided with the plurality of surface potential sensors which function independently of one another, the surface potential sensors may be utilized in conjunction with four photosensitive drums (cyan, magenta, yellow and black) in an image generating apparatus such as a tandem type high-speed photocopier or a tandem type high-speed laser beam printer to individually detect the surface potentials at the four photosensitive drums.
The switching circuit individually selects and outputs the signals provided by the plurality of surface potential sensors with varied timing for each surface potential sensor. Thus, the signals that are output from the plurality of surface potential sensors can be extracted separately from one another over time.
Since the signal processing circuit is connected to the plurality of surface potential sensors via the switching circuit, it receives the signals from the surface potential sensors separately over time. Then, it implements necessary signal processing within time frames allocated to the individual surface potential sensors.
The signal processing circuit is shared by the plurality of surface potential sensors. Thus, only a single signal processing circuit is required. This greatly simplifies the circuit structure and also greatly reduces the size, the weight and the production cost compared to the surface potential detection apparatus in the prior art which necessitates four sets each constituted of a surface potential sensor and a signal processing device to be provided in conjunction with the four photosensitive drums.
Each of the plurality of surface potential sensors may assume a structure adopted in the known art. Typically, the surface potential sensors each generate an AC signal corresponding to the surface potential at the measurement target surface by interrupting the electrical field between the detection electrode and the measurement target surface. In this case, the switching circuit individually selects and outputs the detection signal and a synchronous signal which is in synchronization with
Urano Takashi
Yamamoto Takashi
He Amy
Le N.
TDK Corporation
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