Heater Temperature Sensing Element Inversion for Thermal Efficiency
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Solution Overview
Problem
In image forming apparatuses, temperature sensing elements on the heater's surface reduce heat transfer efficiency and thermal responsiveness when thick protective layers or wider substrates are used to ensure withstand voltage, leading to increased apparatus size.
Innovation Solution
A temperature sensing element is placed on the surface of the heater opposite to the heating element, with a separate insulation circuit to prevent reduction in thermal responsiveness and heat transfer efficiency, and to avoid increasing the heater's size by using a thinner surface protective layer and optimizing substrate width.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the thermistor is formed on the surface of the heater on the side of the nip portion, then the temperature sensing is achieved, but it is necessary to form the thermistor such that the thermistor has a thick surface protective layer or increase the width of the substrate of the heater to secure adequate withstand voltage
Solution Approach 1:
The temperature sensing element is positioned on the back surface of the heater substrate opposite to the nip portion side, rather than on the conventional front surface. This inversion allows the sensing element to be electrically isolated from the high-voltage heating circuit, eliminating the need for thick protective layers that would impede heat transfer. The sensing element contacts the film directly through the thin substrate, maintaining high heat transfer efficiency while achieving accurate temperature sensing.
2Reliability
If the thickness of the surface protective layer of the thermistor is increased to secure adequate withstand voltage, then the electrical insulation is improved, but the heat transfer efficiency of the heater and accuracy in sensing the nip temperature are reduced
Solution Approach 1:
By inverting the position of the temperature sensing element to the back surface of the substrate, the electrical insulation requirement is satisfied through the substrate itself rather than requiring a thick protective layer on the heat-transfer surface. This eliminates the trade-off between insulation thickness and heat transfer efficiency.
Solution Approach 2:
The heater substrate acts as an intermediary that provides both mechanical support and electrical insulation. By positioning the sensing element on the back surface, the substrate mediates between the high-voltage heating circuit and the low-voltage sensing circuit, allowing thin protective layers on the front surface while maintaining adequate withstand voltage capability.
3Reliability
If the width of the substrate of the heater is increased to secure adequate withstand voltage, then the electrical insulation is improved, but the size of the apparatus is increased
Solution Approach 1:
Inverting the sensing element position to the back surface allows the use of a narrower substrate width. The electrical insulation is achieved through the substrate thickness and configuration rather than requiring excessive width, thus reducing the overall heater and apparatus size while maintaining adequate withstand voltage capability.
4Measurement precision
If the temperature sensing element is disposed on the sliding surface of the heater which slides on the film, then the temperature sensing is achieved, but it reduces the thermal responsiveness and heat transfer efficiency of the heater
Solution Approach 1:
The temperature sensing element is inverted to the back surface of the substrate, away from the film-contacting sliding surface. This eliminates the thermal resistance introduced by protective layers on the sliding surface, maintaining high thermal responsiveness and heat transfer efficiency to the film while still enabling accurate temperature sensing through the substrate.
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 configuration allows for effective temperature sensing while maintaining high heat transfer efficiency and preventing size increases, ensuring accurate temperature control and reduced material costs.
Implementation Method 1
a heating element provided on the substrate
Implementation Method 2
a temperature sensing element provided on a surface of the substrate opposite to a surface on which the heating element is provided
Data Source
Figure 1
Figure 2
Figure 3(A)~3(B)
AI summary
Provided is an image forming apparatus including a temperature sensing circuit to which a temperature sensing element is electrically connected, wherein a surface of a heater on a side where the temperature sensing element is provided is in contact with the inner surface of a film, a heating element is provided in a primary side circuit which is electrically connected to a commercial power supply, and between the primary side circuit and the temperature sensing circuit, basic insulation or reinforced insulation or double insulation in which additional insulation is added to the basic insulation is provided, and between a secondary side circuit which is reinforced insulated or double insulated with respect to the primary side circuit and the temperature sensing circuit, the basic insulation or the reinforced insulation or the double insulation is provided, and the temperature sensing circuit is a circuit different from the primary side circuit and the secondary side circuit.