Alternating Transfer Voltage for Coarse Paper Image Density
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Solution Overview
Problem
Existing image forming apparatuses face challenges in maintaining adequate image density on recording media with coarse surfaces, such as Japanese paper, due to inadequate toner transfer, resulting in patterns of light and dark patches and white spots.
Innovation Solution
An image forming apparatus that includes an image bearing member, a transfer member, a power source, and a controller, where the power source outputs alternating voltages with a time-averaged value greater than the midpoint voltage, and the controller adjusts the duty ratio based on the recording medium's roughness, temperature, humidity, or electrical resistance to ensure effective toner transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a DC voltage is applied as secondary transfer bias, then the toner image can be transferred onto the recording medium, but white spots appear in recessed portions of coarse surfaces
Solution Approach 1:
The patent applies an AC voltage superimposed on the DC secondary transfer bias voltage. This periodic AC component causes the toner to oscillate within the transfer nip, enabling it to reach recessed portions of coarse recording medium surfaces that would otherwise be inaccessible with DC voltage alone, thereby eliminating white spots while maintaining image density uniformity
Solution Approach 2:
The patent modifies the electrical parameters of the transfer bias by introducing an AC voltage component with specific frequency and amplitude characteristics. This parameter change transforms the static DC field into a dynamic composite field that can effectively transfer toner to both projecting and recessed portions of the recording medium surface
2Object-affected harmful factors
If an AC voltage superimposed on DC voltage is applied as secondary transfer bias, then white spots are suppressed, but image density becomes inadequate on coarse surfaces
Solution Approach 1:
The patent optimizes the parameters of the superimposed AC voltage, including its amplitude, frequency, and duty cycle, to achieve the right balance. By carefully controlling these parameters, the AC component provides enough energy to move toner into recessed portions without being so strong as to prevent adequate transfer to projecting portions, thus achieving both white spot suppression and sufficient image density
3Manufacturing precision
If the secondary transfer bias voltage is increased to improve transfer to recessed portions, then image density improves, but white spots appear due to excessive voltage
Solution Approach 1:
Instead of increasing the DC voltage level which causes white spots, the patent uses a superimposed AC voltage with controlled amplitude and frequency. This periodic action provides the necessary energy to reach recessed portions through oscillatory motion of toner particles, while the time-averaged voltage remains at a level that prevents excessive force and white spot formation
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
The solution ensures consistent image density across both recessed and projecting portions of the recording medium, reducing white spots and enhancing image quality by optimizing the transfer process.
Implementation Method 1
a power source which outputs a voltage having a first voltage in a transfer direction in which the toner image is transferred from the image bearing member to the recording medium and a second voltage having a polarity opposite to that of the first voltage, which alternate when the toner image is transferred from the image bearing member onto the recording medium
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
An image forming apparatus includes a power source (39) to output a voltage having an alternating waveform to transfer a toner image from an image bearing member (31) to a recording medium. A time-averaged value (Vave) of the voltage has a polarity in a transfer direction, in which the toner image is transferred from the image bearing member (31) to the recording medium, and an absolute value of the time-averaged value is greater than a midpoint value (Voff) of the voltage intermediate between a maximum value and a minimum value of the voltage. As a roughness of the recording medium increases, a duty ratio (Duty) expressed by A / (A+B) is reduced, where A is an area of the waveform of the voltage in a return direction opposite the transfer direction relative to the midpoint value in one cycle and B is an area in the transfer direction relative to the midpoint value.