Dual-Mode Force Sensing Resistor for Light Tap Detection
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Solution Overview
Problem
Force sensing resistors (FSRs) are unable to detect light taps and touches effectively due to their quiescent state operating as an open circuit, limiting their ability to perform force sensing in response to minor inputs.
Innovation Solution
Implementing a method that allows the FSR to switch between capacitive sensing mode and resistive sensing mode, where it operates in capacitive mode when no external forces are applied and transitions to resistive mode when a threshold force is applied, enabling detection of a continuum of user inputs including light taps and forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If FSR operates in quiescent state as open circuit, then it can detect threshold forces effectively, but it cannot detect light taps and touches
Solution Approach 1:
The FSR system dynamically switches between capacitive sensing mode and resistive sensing mode based on the applied force magnitude. In capacitive mode, the system detects light taps and touches through capacitance changes. When force exceeds a threshold, the system transitions to resistive mode where the FSR contacts the resistive substrate and measures resistance changes. This dynamic mode switching enables the system to adapt to different input intensities, resolving the contradiction between detecting light inputs and threshold forces.
Solution Approach 2:
The system changes the sensing parameter from capacitance to resistance based on the applied force. For light taps, capacitance changes are measured; for threshold forces, resistance changes are measured. This parameter change allows the FSR to effectively detect across the full range of input forces, from light taps to firm presses.
2Measurement precision
If FSR uses resistive sensing only, then it can measure force magnitude, but it requires threshold force to activate
Solution Approach 1:
The system dynamically selects the sensing mode based on force magnitude. For forces below the threshold, capacitive sensing is used to detect light taps and touches reliably. When force exceeds the threshold, the system switches to resistive sensing for accurate force magnitude measurement. This dynamic adaptation ensures both reliable detection across all force levels and accurate measurement when force is applied.
Solution Approach 2:
Capacitive sensing acts as an intermediary mechanism that detects light forces before the FSR makes contact with the resistive substrate. This intermediary detection method ensures that light taps are not missed, while still allowing the primary resistive sensing mechanism to accurately measure larger forces.
3Stability of the object's composition
If FSR acts as open circuit in quiescent state, then it maintains stable baseline, but it cannot detect light inputs
Solution Approach 1:
The system transitions from a static open-circuit state to a dynamic dual-mode sensing approach. In the quiescent state, capacitive sensing maintains a stable baseline by measuring capacitance without requiring physical contact. When light inputs occur, the system detects capacitance changes without needing the FSR to contact the resistive substrate, thus maintaining baseline stability while enabling light input detection.
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
Enables the detection of user inputs such as light taps, initial contact, and applied forces, enhancing the sensitivity and functionality of FSRs in input devices by leveraging existing circuitry for both capacitive and resistive sensing.
Implementation Method 1
When operating in the first mode, the processing circuitry is configured to detect a capacitance of the sensor apparatus
Implementation Method 2
When operating in a second mode, the processing circuitry is configured to detect a resistance of the sensor apparatus
Data Source
AI summary
An input device includes a sensor apparatus coupled to a sensing region. The sensor apparatus is operable in at least a first mode or a second mode. When operating in the first mode, the input device is configured to detect a capacitance of the sensor apparatus. When operating in a second mode, the input device is configured to detect a resistance of the sensor apparatus. The input device is further configured to process user inputs in the sensing region based at least in part on the detected capacitance or resistance of the sensor apparatus. In some implementations, the input device may be configured to switch between the first mode and the second mode based at least in part on the detected capacitance or resistance of the sensor apparatus.