Liquid Surface Detector Using Capacitance Error Correction
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Solution Overview
Problem
Existing liquid surface detectors for image forming apparatuses face inaccuracies in detecting liquid surface height due to changes in detection environments, leading to increased manufacturing costs when multiple sensors are used, and inaccuracies when relying on stored capacitance values that may not account for stray capacitance differences.
Innovation Solution
A liquid surface detector with an electrode pad, coil, and memory that senses resonance frequency to determine capacitance, storing initial and error values to correct capacitance measurements, allowing for accurate liquid surface level determination by subtracting error values from sensed capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If three sensors (upper limit sensor, lower limit sensor, and capacitance sensor) are used to accurately detect liquid surface height, then detection accuracy is improved, but manufacturing cost increases
Solution Approach 1:
The patent combines multiple sensing functions into a single capacitance sensor system. By measuring capacitance at different liquid surface levels (upper limit, lower limit, and current level) using one sensor, the system eliminates the need for separate sensors while maintaining detection accuracy across the full range of liquid levels.
Solution Approach 2:
The capacitance sensor is designed to perform multiple functions: detecting upper limit, lower limit, and current liquid surface levels. This multi-functional approach allows a single sensor to replace what would traditionally require three separate sensors, reducing manufacturing cost while maintaining comprehensive detection capability.
2Ease of manufacture
If capacitance values are stored in memory for later use to reduce sensor quantity, then manufacturing cost is reduced, but detection accuracy deteriorates due to environmental changes
Solution Approach 1:
The system dynamically adjusts the capacitance reference values stored in memory based on the actual detection environment. By measuring and storing the actual upper limit and lower limit capacitance values in the specific operating environment, the system compensates for environmental variations such as stray capacitance changes, ensuring accurate liquid surface level detection despite environmental differences from the calibration phase.
3Ease of manufacture
If a single capacitance sensor is used instead of multiple sensors, then manufacturing cost is reduced, but detection accuracy deteriorates due to stray capacitance variations
Solution Approach 1:
The system continuously monitors capacitance changes and uses feedback to compensate for stray capacitance variations. By comparing measured capacitance values against stored reference values and adjusting for environmental factors, the system maintains accurate liquid surface level detection using only a single sensor, effectively eliminating the accuracy loss that would normally result from stray capacitance variations.
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 enables accurate detection of liquid surface height by accounting for environmental changes and reducing manufacturing costs by using a single sensor setup, ensuring reliable operation of image forming apparatuses.
Implementation Method 1
The coil L1 is connected to the electrode pad 93 and is a part of a first resonance circuit 91. The detection control circuit 90 senses a resonance frequency of the first resonance circuit 91
Implementation Method 2
The detection control circuit 90 determines a first capacitance as a capacitance of the first resonance circuit 91. The tank with the attached electrode pad 93 is used as a capacitor
Implementation Method 3
Dielectric constant between the electrodes changes along with the height of liquid in the container. Capacitance changes in accordance with the degree that the electrode is soaked in the liquid
Data Source
AI summary
A liquid surface detector includes an electrode pad, a coil, a memory, and a detection control circuit. The electrode pad is attached to an outer side surface of a tank of the image forming apparatus. The coil is connected to the electrode pad. The memory stores initial values. The detection control circuit determines a capacitance (first capacitance) of a first resonance circuit including the coil and the tank with the electrode pad. When determining a liquid surface level value, the detection control circuit subtracts an error value from the first capacitance so as to determine a first corrected capacitance, and determines the liquid surface level value based on the first corrected capacitance and the initial value.