Fixing Unit Overheating Protection via Contactless Sensor
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Solution Overview
Problem
Conventional image forming apparatuses lack a hardware-based power shut-off mechanism to prevent overheating of the fixing unit, relying solely on contact sensors, which are prone to errors due to surface irregularities and pollutant accumulation, and cannot directly utilize contactless sensors for protection.
Innovation Solution
An image forming apparatus with a contactless-sensing protector that uses a pair of contactless sensors to output sensing and compensating voltages, comparing them against a temperature characteristic table to shut off power if either voltage exceeds set limits, ensuring the fixing unit is protected from overheating and control errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a contact sensor is used to sense temperature of the fixing unit, then the temperature can be sensed, but the sensing accuracy deteriorates due to surface irregularities and pollutant accumulation on the contact part
Solution Approach 1:
The patent replaces the contact-based mechanical sensing system with a contactless optical sensing system. The optical sensor detects temperature through infrared radiation without physical contact, eliminating the problem of surface irregularities and pollutant accumulation affecting measurement accuracy.
Solution Approach 2:
The patent introduces an intermediary optical field to transfer temperature information. Instead of direct contact between sensor and heat roller, the optical sensor detects thermal radiation as an intermediary carrier of temperature information, enabling non-contact measurement.
2Reliability
If only a contact sensor is used for temperature sensing, then the device complexity is low, but the reliability deteriorates due to contact sensor limitations
Solution Approach 1:
The patent segments the temperature sensing function into two independent parts: a contact sensor for primary temperature detection and a contactless optical sensor for auxiliary detection and protection. This segmentation allows each sensor to perform its specific function without interfering with the other, improving overall system reliability.
Solution Approach 2:
The patent implements beforehand cushioning by using the contactless optical sensor as a backup protection mechanism. If the contact sensor fails or provides inaccurate readings, the optical sensor can independently trigger protection, cushioning against potential damage before it occurs.
3Reliability
If a contact-sensing protector is used to protect the fixing unit, then the fixing unit is protected from overheating, but the protection cannot be directly applied to contactless sensors
Solution Approach 1:
The patent creates a universal protection mechanism that can work with both contact and contactless sensors. The protection circuit is designed to accept temperature signals from either sensor type and provide appropriate protection responses, making the protection system adaptable to different sensing methods.
Solution Approach 2:
The patent implements feedback mechanisms where both the contact sensor and contactless optical sensor provide temperature information to the control system. The system uses this feedback to make informed protection decisions, adjusting protection actions based on real-time temperature readings from either or both sensors.
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
Effectively prevents overheating and control errors by comparing sensor voltages against a temperature characteristic table, providing a hardware-based power shut-off mechanism that enhances protection of the fixing unit, even when contactless sensors detect abnormal temperatures.
Implementation Method 1
a contactless sensor which includes a pair of sensors sensing temperature of the fixing unit by a contactless method and respectively outputting a sensor-sensing voltage and a sensor-compensating voltage
Implementation Method 2
the contactless sensor includes two sensors, i.e., a thermo-sensitive device for sensing infrared and a thermo-sensitive device for compensating temperature
Data Source
AI summary
An image forming apparatus including: an image forming unit which forms an image; a fixing unit which fixes the image transferred to a printing medium; a power supply which supplies operation power to the fixing unit; a contactless sensor sensing a temperature of the fixing unit and respectively outputting a sensor-sensing voltage and a sensor-compensating voltage; and a contactless-sensing protector which shuts off the power if the sensor-sensing voltage is higher than the sensor-compensating voltage. The fixing unit can be protected from overheating and control error through the contactless-sensing protector for sensing the fixing temperature and shutting off the power.