Stair-Climbing Wheelchair Spider Cam Control

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Solution Overview

Problem

Existing stair-climbing wheelchairs face challenges in ascending and descending low-height steps, inadequate traction leading to sliding, and issues with monitoring cam angles for spider crowd engagement, which affect stability and accuracy.

Innovation Solution

The implementation of a skid system with articulated skid runners and multi-directional skid wheels, combined with optical distance sensors and rotary sensors for precise engagement and control, along with a spider system that ensures spider cams move in unison and preload correctly, enhancing traction and stability on stairs and slopes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If large diameter wheels are used to climb stairs, then the ability to climb single low height steps is improved, but the traction required increases and they do not properly load stairs by resting on stair treads

Engineering Contradiction:

Improveability to climb stepsVSAvoidtraction required

Core Design Contradiction:

Adaptability or versatilityVSForce

Solution Approach 1:

The wheelchair is divided into multiple independent wheel assemblies (spiders) with individual control, allowing distributed traction forces across multiple contact points rather than relying on a single large wheel. This segmentation enables proper loading on stair treads while reducing the traction demand on each individual wheel.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Skid runners are introduced as intermediary elements between the wheels and the stairs. These skid runners rest on the stair treads to properly load the stairs, while the wheels provide propulsion. This intermediary system resolves the contradiction by separating the loading function from the propulsion function.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If spring biased cams are used to maintain spider crowd engagement with steps, then control signals are provided, but adjustment slipping occurs and absolute angle measurement is lacking

Engineering Contradiction:

Improvespider crowd engagement controlVSAvoidcam angle measurement

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

Mechanical cam-based angle measurement is replaced with optical or electronic sensors that provide direct absolute angle measurement. This substitution eliminates the adjustment slipping problem inherent in mechanical cam systems while providing precise, reliable angular position data for control.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

A feedback control system is implemented using precise angle sensors to continuously monitor spider crowd engagement and adjust control signals accordingly. This closed-loop feedback replaces the open-loop mechanical cam system, eliminating adjustment drift and providing accurate absolute angle measurement for reliable engagement control.

Inventive Principle:

Principle #23Feedback

3Adaptability or versatility

If the wheelchair is designed to climb stairs, then stair-climbing capability is achieved, but turning around to negotiate low height steps becomes a hindrance

Engineering Contradiction:

Improvestair-climbing capabilityVSAvoidmaneuverability on low steps

Core Design Contradiction:

Adaptability or versatilityVSEase of operation

Solution Approach 1:

The wheelchair employs dynamic wheel assemblies (spiders) that can independently adjust their position and orientation. This dynamic configuration allows the wheelchair to maintain forward-facing orientation while negotiating low steps, eliminating the need to turn around and preserving maneuverability without sacrificing stair-climbing capability.

Inventive Principle:

Principle #15Dynamics

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 enables improved traction and stability for ascending and descending low-height steps, prevents sliding, and provides accurate monitoring of spider crowd engagement, allowing for safer navigation of stairs and slopes.

Implementation Method 1

optical distance sensors

Methodology Applied

Scientific EffectOptical reflection: Reflection

Implementation Method 2

rotary sensors for precise engagement and control

Methodology Applied

Scientific EffectRotational position sensing:

Implementation Method 3

Inadequate coefficient of friction can result in a stair-climbing device sliding down the stairs

Methodology Applied

Scientific EffectFriction: Friction

Data Source

PatentUS10806649B1Enhanced mobility wheelchair

Publication Date: 2020.10.20 COX KENNETH RAY

AI summary

An enhanced mobility wheelchair with semi-autonomous control logic includes criteria for selecting level, stair, and slope modes. Each mode progresses through criteria-invoked phases as the wheelchair travels. Each axis performs an assigned duty for each mode and phase combination to seek a defined target. Control logic invokes stair mode from the level mode when steps are sensed. Criteria restricts negotiating obstacle angles and heights encountered beyond capability and permits reversed travel to exit obstacle. Front and rear support systems include the ability to sense both forward and backward facing steps by adding distance sensors, sensing linkage and rotary sensors. Legrest adjustment raises the feet for forward step climbing and shortens the wheelchair length for tight turns. Steep down slope and steep up slope modes are invoked from a small angle slope mode. Absolute measurement of spider rotation and spider cam engagement does not require adjustment.