Heater Control Waveform for Current Detection Accuracy
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Solution Overview
Problem
Conventional image forming apparatuses face challenges in accurately detecting current due to distortion in current detection transformers, especially with increasing power supply and stringent regulations regarding flicker and harmonic current control, particularly when combining phase control and wave number control.
Innovation Solution
The proposed solution involves a control method that combines phase control and wave number control by devising a specific control wave form to cancel errors caused by distortion in current detection transformers, improving current detection precision by adjusting the power supply pattern to the heater, including specific patterns for different power ratios and using a current detection circuit that rectifies and amplifies the transformer output to peak-hold values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If phase control is used to suppress flicker, then flicker is reduced, but harmonic current and switching noise increase
Solution Approach 1:
The patent divides the control period into multiple sub-periods and applies different control strategies (phase control or wave number control) to different sub-periods. This segmentation allows the system to suppress flicker during certain periods while minimizing harmonic current and switching noise during others, thereby resolving the contradiction between these harmful factors.
Solution Approach 2:
The patent dynamically switches between phase control and wave number control based on the instantaneous power supply voltage. When voltage is within a predetermined range, phase control is used to suppress flicker; when voltage exceeds the range, wave number control is used to minimize harmonic current and switching noise. This dynamic adaptation resolves the contradiction by selecting the optimal control method for each operating condition.
2Object-generated harmful factors
If wave number control is used to suppress harmonic current and switching noise, then harmonic current and switching noise are reduced, but flicker increases
Solution Approach 1:
The control period is segmented into multiple sub-periods, and wave number control is applied to specific sub-periods when voltage conditions require minimization of harmonic current and switching noise, while phase control is applied to other sub-periods for flicker suppression. This segmentation resolves the contradiction by time-multiplexing different control strategies.
Solution Approach 2:
The system dynamically selects between wave number control and phase control based on real-time voltage monitoring. When voltage exceeds a predetermined threshold, wave number control is activated to minimize harmonic current and switching noise; when voltage is within the threshold, phase control is used to suppress flicker. This dynamic selection resolves the contradiction by adapting the control method to instantaneous operating conditions.
3Measurement precision
If current detection transformer is used for current detection, then current can be detected, but distortion occurs in the detection signal
Solution Approach 1:
The patent uses a feedback mechanism where the detected current information is fed back to the control circuit to adjust the heater control signals. The control circuit compensates for transformer distortion by incorporating correction factors or alternative detection methods, thereby maintaining current detection accuracy despite the inherent distortion in the transformer output.
Solution Approach 2:
The patent introduces an intermediary processing stage between the current detection transformer and the control circuit. This intermediary includes signal conditioning circuits that rectify, amplify, and filter the distorted transformer output signal, converting it into an accurate representation of the actual current for use in control decisions.
4Power
If power supply voltage increases, then heating performance improves, but harmonic current and switching noise increase
Solution Approach 1:
The patent dynamically adjusts the control method based on the power supply voltage level. When voltage is high (providing better heating performance), the system switches to wave number control to minimize harmonic current and switching noise. When voltage is low, phase control is used to suppress flicker. This dynamic adaptation allows the system to maintain optimal heating performance while minimizing harmful factors under each voltage condition.
Solution Approach 2:
The patent changes the control parameters (phase angle or wave number) based on the power supply voltage level. By adjusting these parameters dynamically, the system optimizes heating performance at high voltages while minimizing harmonic current and switching noise through wave number control, and suppresses flicker through phase control at lower voltages.
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 enhances current detection accuracy and precision, allowing for precise control of the power supplied to the heater, thereby improving temperature control and compliance with regulatory standards while reducing the influence of distortion from current detection transformers.
Implementation Method 1
distortion in current detection transformers
Implementation Method 2
a current detection circuit that rectifies and amplifies the transformer output
Implementation Method 3
a current detection circuit that rectifies and amplifies the transformer output
Implementation Method 4
a heater connected to an AC power supply via a switching element
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
A wave form corresponding to at least one power ratio among a plurality of power ratios set according to a temperature of a fixing part include a first group wherein a negative half-wave to at least partially turn on a half-wave and a positive-half-wave to at least partially turn on a half-wave continue in order after a half-wave to entirely turn off an one half-wave, and a second group wherein a positive-half-wave to at least partially turn on a half-wave continues just after a -half-wave to entirely turn off an one half-wave, thereby an accuracy of current detection can be improved.