Knee Walker Steering System with Tie Rod Linkage
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Solution Overview
Problem
Existing knee walkers require users to push the device with their good leg and lean their body to change direction, leading to increased effort and risk of balance loss and falling due to static handlebars and swiveling wheels.
Innovation Solution
A knee walker design with a steering system that includes a rotatable handlebar connected to a steering gear, a steering arm, and a tie rod linkage, allowing for controlled directional movement without the need for body lean or excessive effort, with front wheels spaced wider than rear wheels for enhanced stability and a mechanism to prevent oversteering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If static handlebars are used with swiveling wheels, then the device structure is simple, but the user must push the device with their good leg and lean their body to change direction, increasing effort and risk of balance loss
Solution Approach 1:
The handlebar is changed from a static structure to a dynamic steering system. The handlebar shaft rotates to control the steering arm, which pivots the front wheels through the steering rod and tie rod linkage. This dynamic system allows the user to change direction by simply turning the handlebar without pushing or leaning, resolving the contradiction between structural simplicity and ease of directional control.
Solution Approach 2:
A steering arm is introduced as an intermediary component between the handlebar shaft and the front wheels. The steering arm receives rotational input from the handlebar shaft and transmits it to the front wheels through the steering rod and tie rod linkage, enabling smooth directional control without requiring the user to push or lean the device.
2Adaptability or versatility
If swiveling wheels are used, then the device can change direction, but the user must push the device with their good leg, increasing physical effort
Solution Approach 1:
The steering arm acts as an intermediary that translates small rotational movements of the handlebar shaft into controlled pivoting of the front wheels. This mechanical advantage system reduces the force the user needs to apply compared to directly pushing the device, while maintaining full directional movement capability.
Solution Approach 2:
The manual pushing action is replaced by a mechanical steering system. Instead of using the user's good leg to push the device for directional changes, the system uses the handlebar shaft, steering arm, and tie rod linkage to mechanically control wheel pivoting, significantly reducing the required user effort.
3Ease of operation
If the front wheels are allowed to pivot freely, then the device is highly maneuverable, but the user may oversteer and lose balance
Solution Approach 1:
The tie rod linkage is designed to prevent the front wheels from pivoting beyond a certain degree. This preliminary constraint counteracts the potential harmful effect of oversteering before it can occur, allowing high maneuverability within safe limits while preventing balance loss from excessive wheel rotation.
Solution Approach 2:
The tie rod linkage provides mechanical feedback that limits the range of wheel pivoting. As the wheels approach the maximum safe pivot angle, the tie rod geometry naturally resists further rotation, providing passive feedback that prevents oversteering and maintains user balance while preserving maneuverability within the safe operating range.
Data Source
AI summary
A knee walker includes a frame; a cushion; a front crossmember; two rear wheels; two front spindles and two front wheels each pivotally connected to one of the two front spindles. Positive steering is provided by a handlebar rotatably connected to the front end of the frame; a steering gear responsively engaged with the rotatably connected handlebar shaft; a steering arm actuated by the steering gear responsive to the handlebar; a steering rod connecting the steering arm and one of the two front spindles, so as to pivot one associated front wheel responsive to the steering arm; and a tie rod linking the two front spindles responsively to the steering rod.