Footstep Sensing Spring Mechanism for Position-Independent Load Detection
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Solution Overview
Problem
Existing footstep sensing devices for vehicle extendable step plates face challenges in accurately sensing a minimum load of 15 kg independently of the treadle's position, due to changing force ratios and lever effects during extension and retraction, leading to errors in movement stopping.
Innovation Solution
The device employs secondary spring elements that are switched on during extension and off during retraction, with main spring elements providing counteracting forces adjusted by roller blocks and spacer elements to reduce dependency on treadle position, using inductive switches and coordinated secondary spring elements to improve interaction and reduce extension path dependency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If spring elements are adjusted to sense minimum load at the start of extension, then load sensing accuracy is improved at retraction position, but load sensing accuracy deteriorates at extended position due to changed lever ratios
Solution Approach 1:
The patent applies dynamics by making the spring element configuration changeable during operation. Secondary spring elements are selectively engaged or disengaged based on the treadle's extension position, allowing the system to adapt its mechanical properties dynamically. This resolves the contradiction by enabling the system to optimize for position-specific lever ratio changes rather than being fixed throughout the entire range of motion.
Solution Approach 2:
The patent changes the physical parameters of the spring system by introducing secondary spring elements that modify the overall spring constant and force characteristics. By adjusting which spring elements are active (main only, or main plus secondary), the system compensates for position-dependent parameter changes in lever ratios, maintaining consistent load sensing accuracy across different extension positions.
2Adaptability or versatility
If secondary spring elements are switched on during extension, then position dependency is reduced, but device complexity increases
Solution Approach 1:
The patent segments the spring system into distinct main spring elements and secondary spring elements, each serving specific functions at different positions. This segmentation allows independent optimization and control of each spring group, managing complexity through modular organization rather than a single complex spring mechanism.
Solution Approach 2:
The patent implements preliminary action by pre-configuring the secondary spring elements to be engaged or disengaged at specific extension positions. The spacer element is pre-positioned to automatically activate the secondary springs at the appropriate moment, eliminating the need for complex active control systems and reducing operational complexity.
3Measurement precision
If the treadle extends further, then the counteracting force from spring elements must be increased to maintain sensing accuracy, but this requires additional spring force
Solution Approach 1:
The patent applies counterweight by introducing secondary spring elements that provide additional counteracting force specifically when needed at extended positions. These secondary springs compensate for the reduced mechanical advantage at extended positions, balancing the force requirements across the full range of motion without over-designing the entire system for maximum extension.
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 ensures more accurate sensing of the minimum load required to stop the treadle movement, minimizing errors by adjusting counteracting forces based on the treadle's position, thereby maintaining consistent load detection across different extension states.
Implementation Method 1
The roller blocks are connected to spring elements which are supported on a frame that does not move together with the treadle. If the footplate is stepped on, the footplate lowers against the spring force of the spring elements
Implementation Method 2
An inductive switch can advantageously be used as the switching element
Implementation Method 3
The step is designed similar to a pressure switch, if it is loaded from above, a switch is actuated
Data Source
Figure 1~3
Figure 4~6
Figure 7~9
AI summary
The device has a primary spring element (2) with a switch element (13) i.e. inductive switch, and arranged such that spring force of the element represents a counter acting force working against the force acting on a top side of a footboard (1). The control element senses whether the force is larger than the counter acting force, and a signal i.e. a stop signal is generated for movement of the footboard. A secondary spring element (3) increases the counter acting force during extension of the footboard, and reduces the counter acting force during retraction of the footboard.