Spread Spectrum Clock for Laser Shading Correction EMI
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Solution Overview
Problem
Existing image forming devices face adverse effects of electromagnetic interference (EMI) during high-frequency laser control, particularly when correcting shading characteristics, which can deteriorate print quality.
Innovation Solution
An image forming device that includes a shading characteristic corrector with a PDM signal outputter, a smoothing circuit, and a spread clock outputter, where the spread clock is only activated during initialization to minimize EMI, and the spread clock outputter is selectively enabled for the sub-scanning direction with a constant reference light quantity value to reduce EMI effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a low-pass filter with a reduced time constant is used to improve responsiveness of the analog reference signal, then responsiveness is improved, but electromagnetic interference is not sufficiently suppressed
Solution Approach 1:
The patent introduces a spread spectrum clock generator as an intermediary component that modifies the clock signal before it reaches the PDM circuit. By spreading the clock frequency over a wider bandwidth, the peak electromagnetic interference is reduced while maintaining the fast response capability of the low-pass filter with reduced time constant.
Solution Approach 2:
The patent changes the frequency parameter of the clock signal by applying spread spectrum modulation. This transforms the concentrated high-frequency clock signal into a distributed frequency signal, reducing electromagnetic interference while allowing the low-pass filter to maintain fast response characteristics.
2Manufacturing precision
If the frequency of the reference clock is increased to improve smoothness, then smoothness is improved, but electromagnetic interference deteriorates
Solution Approach 1:
The patent applies spread spectrum modulation to the reference clock signal, changing its frequency characteristics from a concentrated high-frequency signal to a distributed signal across a wider bandwidth. This allows high-frequency operation for smooth shading correction while reducing peak electromagnetic interference through frequency distribution.
Solution Approach 2:
The spread spectrum clock generator acts as an intermediary between the control system and the PDM circuit, providing a high-frequency clock signal with reduced electromagnetic interference characteristics through frequency spreading.
3Object-affected harmful factors
If spread spectrum is applied to the clock signal to reduce electromagnetic interference, then electromagnetic interference is reduced, but print quality deteriorates when the amount of variation of shading per unit time is large
Solution Approach 1:
The patent applies spread spectrum modulation selectively rather than universally. By determining when shading correction is actually needed and applying spread spectrum only in those conditions, the system reduces unnecessary frequency spreading that would degrade print quality while still achieving EMI reduction when required.
Solution Approach 2:
The patent dynamically adjusts the clock signal processing based on operational conditions. The spread spectrum modulation is enabled or disabled according to the shading variation requirements, allowing the system to optimize between EMI reduction and print quality based on real-time conditions.
Data Source
AI summary
An image forming device includes an image data acquirer acquiring image data, a laser source emitting a laser beam, a laser driver forming an electrostatic latent image by irradiating a scanning surface of a charged photoconductor with the laser beam, based on the image data, a shading characteristic corrector correcting light quantity of the laser beam, an image former forming an image based on the electrostatic latent image, and a controller controlling the image data acquirer, the laser driver, the shading characteristic corrector, and the image former. The shading characteristic corrector includes a PDM signal outputter outputting a pulse density modulation signal based on the correction of the light quantity of the laser beam, a smoothing circuit smoothing the pulse density modulation signal to obtain an analog signal to be output, and a spread clock outputter outputting a clock subjected to spread spectrum to the PDM signal outputter.