Touch Panel Foreign Matter Detection via Dynamic Reference Adjustment
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Solution Overview
Problem
Existing touch type input devices struggle to detect user input when conductive foreign matter, such as water droplets or coins, is present on the touch panel, as it interferes with capacitance changes, leading to inconveniences especially in installations like vehicles where foreign matter cannot be readily removed.
Innovation Solution
The touch type input device employs a control unit that adjusts reference values for capacitors based on the presence of foreign matter, allowing it to differentiate between foreign matter and user input by setting new reference values and detecting changes in capacitance, enabling accurate detection even when foreign matter is present.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a mutual capacitance type touch panel is used to detect multiple touch positions simultaneously, then the quantity of touch positions detected is improved, but the reliability of touch detection deteriorates when conductive foreign matter contacts the operation surface
Solution Approach 1:
The reference value for capacitance is made dynamic rather than fixed. The control unit automatically updates the reference value based on the current state of the touch panel, including the presence of foreign matter. This allows the system to adapt to changing conditions and maintain reliable touch detection even when foreign matter is present on the operation surface.
Solution Approach 2:
The system changes the capacitance parameter by updating the reference value according to the detected capacitance distribution. When foreign matter is detected, the reference value is adjusted to account for the foreign matter's effect, allowing the system to distinguish between foreign matter and actual touch inputs by detecting changes from the updated reference.
2Reliability
If the touch panel requires removal of foreign matter to enable touch detection, then the reliability of touch detection is improved, but the ease of operation deteriorates
Solution Approach 1:
The touch panel system performs self-adjustment by automatically detecting foreign matter and updating its reference value accordingly. The control unit monitors capacitance changes and autonomously adapts to the presence of foreign matter without requiring user intervention to remove it, thus maintaining both reliability and ease of operation.
Solution Approach 2:
The system implements feedback by continuously monitoring capacitance values and using this information to update the reference value. The control unit receives feedback about the capacitance distribution and automatically adjusts the reference to account for foreign matter, enabling the system to maintain accurate touch detection despite the presence of foreign objects.
3Device complexity
If the capacitance reference value is fixed at initial setting, then the device complexity is reduced, but the measurement precision deteriorates when foreign matter is present
Solution Approach 1:
The reference value transitions from a static initial setting to a dynamic value that automatically updates based on detected capacitance conditions. The control unit implements a relatively simple update mechanism that adjusts the reference value when foreign matter is detected, maintaining measurement precision without significantly increasing device complexity.
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 solution allows for reliable detection of user input on the touch panel even when conductive foreign matter is in contact, enhancing convenience by preventing false negatives and accurately recognizing touch and swipe actions, even in scenarios where foreign matter cannot be easily removed.
Implementation Method 1
A projected capacitance type touch panel includes drive electrodes and sensor electrodes that are arranged in a grid-shaped pattern. Capacitors are formed at the intersecting points of the drive electrodes and the sensor electrodes. Touching of the touch panel is detected from the capacitance of each capacitor.
Implementation Method 2
A conductive foreign matter such as a water droplet or a coin may contact or collect on the operation surface of the touch panel. When a foreign matter contacts the operation surface, the capacitance of each capacitor in the area that is in contact with the foreign matter changes toward a second polarity side
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A touch type input device (5) includes a touch panel (11) having a sensor array (14) of drive electrodes (12) and sensor electrodes (13). Capacitors (C) are formed at intersections of the drive electrodes (12) and the sensor electrodes (13). A controller (21) determines whether or not a conductive foreign matter exists on the touch panel (11) from raw data values indicating a change amount in the capacitance of each capacitor (C) from an initial reference value. Further, the controller (21) determines whether or not the touch panel (11) has been touched from control data values indicating a change amount in the capacitance of each capacitor (C) from a control reference value that is changed for each capacitor (C) in accordance with whether or not the foreign matter exists. When the raw data values indicate the existence of the foreign matter, the controller (21) sets the control reference value of each capacitor (C) to a raw data reference value corresponding to the present raw data value.