Bias Power Supply Frequency Control for Image Banding Reduction
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Solution Overview
Problem
Image forming apparatuses face challenges in preventing banding due to interference between the harmonic of the AC output signal and the modulation signal, which affects image quality by causing uneven charging biases on the photoconductor drum.
Innovation Solution
A bias power-supply device that includes a transformer with a first and second winding, a switch circuit, and a modulation circuit to generate an alternating-current output signal with a specific frequency setting and modulation signal, ensuring the interval of stripes with different densities on the transfer material is smaller than a predetermined interval, thereby minimizing banding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the frequency of the modulation signal and the frequency of the alternating-current output signal are set to cause interference, then banding is generated on the transfer material, but image quality deteriorates
Solution Approach 1:
The patent applies parameter changes by carefully selecting and adjusting the frequency parameters of the modulation signal and alternating-current output signal. Specifically, it sets the modulation signal frequency to be an integer multiple of the AC output signal frequency, which changes the frequency relationship parameter to prevent interference patterns that cause banding, thereby maintaining image quality while eliminating the harmful banding effect.
Solution Approach 2:
The patent converts the potential harmful interference between signals into a beneficial relationship by establishing a specific frequency ratio (integer multiple relationship). This transforms what would normally be a harmful interference pattern into a synchronized relationship where the modulation signal's harmonics align with the AC output signal, preventing banding while maintaining the necessary signal functions for image formation.
2Manufacturing precision
If the frequency relationship between modulation signal and AC output signal is not controlled, then banding interval becomes large and visible, but image quality is maintained only by coincidence
Solution Approach 1:
The patent establishes a precise parameter relationship where the modulation signal frequency is set to an integer multiple of the AC output signal frequency. This parameter setting ensures that the interval of stripes with different densities remains smaller than a predetermined interval, making banding imperceptible while consistently maintaining high image quality across different operating conditions.
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 effectively reduces banding by controlling the interference frequency, maintaining image quality and preventing deterioration caused by uneven charging biases.
Implementation Method 1
a transformer that includes a first winding and a second winding, and outputs an alternating-current output signal from the second winding when the first winding is supplied with current
Implementation Method 2
an interval of stripes with different densities generated on the transfer material by interference between the modulation signal and a harmonic of the alternating-current output signal
Data Source
AI summary
A bias power-supply device of an image forming apparatus includes a transformer that includes a first winding and a second winding, and outputs an alternating-current output signal from the second winding when the first winding is supplied with current; a switch circuit that includes a switching element, and supplies the first winding of the transformer with the current by switching the switching element in accordance with a received modulation output signal; and a modulation circuit that receives a frequency setting signal of setting a frequency of the alternating-current output signal and a modulation signal, and generates the modulation output signal having a modulated pulse width. A frequency of the modulation signal and a frequency of the alternating-current output signal are set to cause an interference frequency between the modulation signal and a harmonic of the alternating-current output signal is higher than a predetermined frequency.