Development Voltage Switching Circuit for Drum Startup Toner Control
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Solution Overview
Problem
Existing power supply systems for electrophotographic image forming apparatuses fail to prevent toner adhesion to the photosensitive drum during the initial rotation phase due to the surface potential being 0 V, leading to potential marking on the back surface of the sheet.
Innovation Solution
A power supply apparatus with a boost circuit and a control unit (CPU) that adjusts the development voltage to a positive polarity immediately after drum rotation starts, followed by gradual transitions to the target negative voltage during image formation, using a simple circuit configuration to manage voltage polarity changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the development voltage is applied immediately after drum rotation starts, then the image formation process can begin without delay, but toner adhesion occurs on the photosensitive drum surface because the surface potential is 0 V
Solution Approach 1:
The patent applies a positive polarity voltage to the developing roller before the photosensitive drum surface potential becomes negative, as a preliminary action to prevent toner adhesion. This preliminary voltage application occurs during the initial rotation phase when the drum surface potential is still 0 V or becoming negative, thereby preventing unwanted toner transfer before the actual image formation begins.
Solution Approach 2:
The patent changes the voltage polarity parameter from positive to negative on the developing roller during different operational phases. Specifically, a positive polarity voltage is applied during the initial rotation phase to prevent toner adhesion, and then the voltage polarity is switched to negative when the drum surface potential becomes sufficiently negative for proper image formation.
2Reliability
If a complex voltage control system is used to prevent toner adhesion, then toner transfer can be controlled accurately, but the device complexity increases
Solution Approach 1:
The patent employs a transistor switch to dynamically change the voltage polarity applied to the developing roller based on the operational phase. The transistor is turned on during the initial rotation phase to apply positive polarity voltage, and turned off when the drum surface potential becomes negative, allowing the system to adapt its voltage characteristics dynamically without complex control circuitry.
Solution Approach 2:
The patent uses a transistor as an intermediary switching element to control the voltage polarity change. This simple semiconductor device acts as a mediator between the power supply and the developing roller, enabling reliable voltage polarity switching through a single control signal from the control unit, thereby avoiding the need for complex voltage control systems.
3Device complexity
If the development voltage transitions directly to target negative voltage, then the voltage control is simple, but excessive voltage stress damages low-cost transistors
Solution Approach 1:
The patent applies a positive polarity voltage to the developing roller beforehand during the initial rotation phase, cushioning the subsequent voltage transition. This preliminary positive voltage application prevents excessive voltage stress during the transition to negative voltage, thereby protecting low-cost transistors from damage while maintaining simple voltage control.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively prevents toner adhesion to the photosensitive drum and reduces back surface marking by ensuring the development voltage is sufficiently higher than the drum's surface potential, protecting low-cost transistors from excessive voltage stress.
Implementation Method 1
a boost circuit for boosting a voltage supplied from a first power supply to generate a first power supply voltage
Implementation Method 2
a first transistor Tr1 with a base, a collector, and an emitter; the emitter of the first transistor Tr1 is connected to the output of the boost circuit; the collector of the first transistor Tr1 is connected to the emitter of a second transistor Tr2
Data Source
Figure 1
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AI summary
A power supply (10) apparatus generates an output voltage. Boost means (700) boosts a voltage supplied from a reference voltage source and generates a first power supply voltage. Processing means (300) controls switching the boost means on and off. A first transistor (Trl) is connected to the first power supply voltage. A second transistor (Tr2) is connected to a collector of the first transistor. A resistance element (R0) is connected to a collector of the second transistor. A voltage source (VPR) is connected to the resistance element and generates a second power supply voltage. A collector voltage, which is an output voltage, of the second transistor is controlled by controlling an amount of base current of the first transistor.