Series Switch Encoding Circuit for Aircraft Joystick Reliability
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Solution Overview
Problem
Existing devices for encoding the state of multiple switches on movable levers, such as aircraft joysticks, face challenges in reliability due to electromagnetic interference and require numerous conductive wires, limiting freedom of movement and causing confusion when multiple switches are actuated simultaneously.
Innovation Solution
A device with a series connection of normally closed switches and resistors, where each switch has a priority node and a measuring line connected through a bottom resistor, allowing for prioritization and redundancy, reducing the number of wires needed and enhancing reliability by defining a hierarchy of switch actuation and providing redundant measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple conductive wires are used to connect switches to control device, then each switch state can be detected independently, but the freedom of movement of the lever is limited and cable passing at articulations becomes problematic
Solution Approach 1:
Multiple switch states are merged into a single digital signal transmitted through one wire. The patent connects n switches in series between a voltage line and reference line, with each switch having a parallel resistor, and reads their combined state through a single measuring line, eliminating the need for n+1 separate wires.
Solution Approach 2:
A single wire serves multiple functions by carrying information about the state of multiple switches simultaneously. The measuring line not only provides a return path for current but also serves as the information carrier for detecting the state of all switches through voltage measurement.
2Device complexity
If digital electronic multiplexing is used to reduce wire count, then fewer wires are needed, but reliability deteriorates in environments with electromagnetic radiation
Solution Approach 1:
The patent uses simple, robust analog voltage measurement instead of complex digital electronics. The solution employs basic electrical components (resistors, switches, voltage source) that are inherently resistant to electromagnetic interference, avoiding the vulnerability of digital signals while maintaining wire reduction benefits.
3Device complexity
If analog solutions with resistor arrays are used, then wire count is reduced, but identification of actuated switches becomes difficult when multiple switches are open
Solution Approach 1:
The patent segments the circuit into distinct switch-resistor units connected in series, where each switch Pi has its own parallel resistor Ri. This segmentation allows the control device to identify which specific switches are actuated by measuring the voltage at intermediate nodes between switches, enabling precise identification even when multiple switches are open.
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
The solution effectively encodes switch states with improved reliability, allowing for clear prioritization and error-free determination of actuated switches, even in environments with electromagnetic interference, while minimizing wire complexity and maintaining free movement of the lever.
Implementation Method 1
each switch being associated with a single resistor and connected by a first terminal to a first terminal of said resistor at a common point, named priority node... a second terminal of each resistor is connected to the measuring line... the measuring line is connected to the reference line by an additional resistor, named bottom resistor
Data Source
AI summary
The invention relates to a device (1) for encoding information between a plurality of normally closed switches (P1 . . . Pn) arranged on an operating lever (2) and a control device (9), said switches being connected in series between a voltage line (3) and a measuring line (5), each switch (Pi) being associated with a single resistor (Ri) connected between the terminal of the switch closest to a voltage source (Vcc) and the measuring line. The encoding device thus allows a hierarchy of the switches to be obtained.