Image Forming Apparatus Charge Control Voltage Suppression
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Solution Overview
Problem
Image forming apparatuses face a challenge in suppressing the increase of applying voltage when no load is attached, leading to potential abnormal discharge and increased costs due to the need for higher withstand voltage components.
Innovation Solution
An image forming apparatus is designed with an attachment unit, an applying circuit, a voltage detection circuit, a current detection unit, and a control device that switches from constant current control to constant voltage control when the load current is below a threshold and the applying voltage exceeds a certain value, thereby maintaining the output voltage within a target range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If constant current control is applied to ensure the load current reaches the target value, then the charge amount for the photosensitive drum is sufficient, but the applying voltage rapidly increases when no load is attached, potentially causing abnormal discharge
Solution Approach 1:
The control device continuously monitors both the load current and applying voltage, using feedback from voltage detection circuit 160 to detect no-load conditions and adjust control strategy accordingly. The feedback mechanism compares detected voltage against predetermined thresholds to trigger appropriate control modes.
Solution Approach 2:
The control device dynamically switches between constant current control mode and constant voltage control mode based on real-time detection of load conditions. When no-load is detected (voltage ≥ threshold and current < determination value), the system transitions from constant current to constant voltage control to prevent abnormal discharge.
2Power
If the applying voltage is increased to ensure the load current reaches the target value, then the charge voltage is sufficient, but components require higher withstand voltage, increasing cost
Solution Approach 1:
The control device changes the operating parameters of applying circuit 150 by switching control modes. In constant voltage control mode, the applying voltage is limited to a predetermined threshold value, preventing excessive voltage buildup that would require high-withstand-voltage components, while still providing sufficient charge voltage when load is present.
3Reliability
If constant current control is used to maintain stable operation, then the load current is controlled accurately, but the applying voltage may exceed safe limits when no load is attached
Solution Approach 1:
The voltage detection circuit 160 continuously monitors the applying voltage in advance, detecting no-load conditions before the voltage can reach dangerous levels. This preliminary detection allows the control device to switch to constant voltage control proactively, preventing voltage from exceeding safe limits.
Data Source
AI summary
An image forming apparatus, comprising: an attachment unit to which a load for image formation is attached; an applying circuit configured to apply an applying voltage to the load; a voltage detection circuit configured to detect the applying voltage; a current detection unit configured to detect a load current; and a control device, wherein the control device is configured to: subject the applying circuit to constant current control in accordance with a detected value of the current detection unit so that the load current becomes a target current; and switch to a constant voltage control by which the applying voltage is controlled to become a target voltage when an absolute value of the load current is smaller than a determination value and an absolute value of the applying voltage is larger than or equal to a threshold during execution of the constant current control.