Bias Current Control for Laser Array in Image Forming Apparatus
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Solution Overview
Problem
In electrophotographic image forming apparatuses with multiple light emitting elements, setting the bias current value accurately is challenging due to interference from multiple light sources, leading to degradation in light emission response and image quality issues.
Innovation Solution
The apparatus includes a photosensitive member, a charging unit, a light source with multiple light emitting elements, a current supply unit, and a potential detection unit. It calculates a correction value based on detected potential to adjust the bias current, ensuring it is set close to the threshold current value, thereby improving light emission response and image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a bias current is supplied to the semiconductor laser to improve light emission response, then the light emission delay is reduced, but the laser beam intensity becomes unstable and may change the surface potential of the photosensitive member
Solution Approach 1:
The patent implements a feedback control mechanism where a photodiode detects the intensity of the laser beam and the control unit adjusts the bias current based on the detected intensity to maintain stability. This closed-loop feedback system ensures that the laser beam intensity remains constant even when operating conditions change, resolving the contradiction between fast response and stable intensity.
Solution Approach 2:
The patent dynamically changes the bias current parameter based on operating conditions such as temperature and drive current variations. By adjusting the bias current within a controlled range rather than using a fixed value, the system maintains both fast light emission response and stable laser beam intensity across different operating conditions.
2Speed
If the bias current value is set close to the threshold current value to improve light emission response, then the response speed increases, but the measurement precision of the photodiode decreases due to interference from multiple light emitting elements
Solution Approach 1:
The patent divides the measurement process into separate time slots for each light emitting element. During the measurement period for a specific element, only that element is activated while others are turned off. This temporal segmentation eliminates interference from multiple light sources, allowing the photodiode to accurately detect the laser beam intensity even when the bias current is set close to the threshold value for fast response.
Solution Approach 2:
The patent employs periodic activation of individual light emitting elements during the measurement phase. Each element is turned on and off in a periodic sequence, allowing the photodiode to measure the intensity of one element at a time without interference from others. This periodic action enables both fast response operation and precise measurement by separating the measurement events in time.
3Productivity
If multiple light emitting elements are used to increase productivity, then the image forming speed increases, but the bias current control becomes complex and measurement precision deteriorates
Solution Approach 1:
The patent segments the control and measurement processes for multiple light emitting elements into distinct time slots. Each element is controlled and measured independently in sequence rather than simultaneously, which simplifies the control logic despite having multiple elements. This segmentation approach maintains high productivity by enabling rapid sequential operation while reducing control complexity compared to simultaneous multi-element control.
Solution Approach 2:
The patent uses periodic activation and measurement of each light emitting element in a cyclic sequence. This periodic action allows the system to handle multiple elements efficiently by repeating the control-measure-adjust cycle for each element, maintaining high image forming speed while keeping the control mechanism relatively simple and measurement precision high through time-separated operations.
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
This approach allows for precise control of the bias current for each light emitting element, reducing light emission delay and overshooting, and maintaining consistent image density, thus enhancing the overall image forming process.
Implementation Method 1
forms electrostatic latent images by scanning the surfaces of photosensitive members such as photosensitive drums by using laser beams emitted from a semiconductor laser
Implementation Method 2
a potential detection unit configured to detect a potential of an electrostatic latent image formed on the photosensitive member exposed to the light beam
Data Source
AI summary
Since a photodiode (PD) is disposed in the vicinity of the plurality of light emitting elements and, therefore, the PD also receives a laser beam emitted only by a bias current during the APC period, setting a bias current based on a result of light amount detection by the PD does not result in a bias current setting with sufficient accuracy. To solve this issue, an electrophotographic image forming apparatus forms an electrostatic latent image pattern on a photosensitive drum, and controls the value of the bias current set for a first light emitting element based on the potential of the electrostatic latent image pattern and a detecting result of the PD.