Adjustable Crank Arm With Notched Retention Block
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Solution Overview
Problem
Current variable-length pedal crank systems for rehabilitation are flawed due to vibration, play, and premature component failure, lacking essential features for broad application, and fail to provide a secure and easy-to-adjust mechanism for varying crank lengths to accommodate different knee flexion angles effectively.
Innovation Solution
An adjustable pedal crank assembly with a crank arm featuring notches and a retention block, including a locking pin and clamping body with a resilient member, and a locking mechanism that allows for precise adjustment and secure locking, preventing vibration and loosening, utilizing a locking lever with cam surfaces to apply clamping force and inhibit movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a retractable pin mechanism is used to adjust pedal crank length, then the adjustment is simple and quick, but the system produces vibration, play, and premature component failure
Solution Approach 1:
The crank arm is divided into multiple notched positions along its length, allowing the retention block to lock at discrete intervals. This segmentation provides stable positioning at each adjustment point while maintaining simple operation through the lever mechanism.
Solution Approach 2:
The locking function is extracted from a simple pin mechanism and implemented through a cam-based retention block that positively engages with notches in the crank arm. This removes the harmful play and vibration associated with retractable pins while maintaining ease of adjustment.
2Length of moving object
If a single pin mechanism is used to allow 2-inch crank length, then the crank can reach minimum length, but excess play and vibration occur due to machining tolerances
Solution Approach 1:
Multiple notches are provided at specific locations along the crank arm to provide stable locking positions. This local feature ensures that at each discrete position, the crank is securely held without play or vibration, while still allowing the full range of motion from 2-inch to 6-inch length.
Solution Approach 2:
The notches are pre-positioned at predetermined intervals along the crank arm, establishing stable locking positions before use. This preliminary arrangement of notches ensures that when the retention block engages, the crank is immediately secured without play or vibration.
3Adaptability or versatility
If the pedal crank is made adjustable in length, then it can accommodate different knee flexion angles, but the mechanism becomes complex and difficult to secure without vibration
Solution Approach 1:
The adjustment and locking functions are merged into a single retention block with cam surfaces that simultaneously provides length adjustment through lever movement and secure locking through positive engagement with notches. This integration simplifies the overall mechanism while maintaining adaptability.
Solution Approach 2:
The crank arm length is made dynamically adjustable during operation. The retention block can be moved along the crank arm to change length, and the cam surfaces provide smooth transition between positions while maintaining secure locking at each discrete setting.
4Reliability
If a locking mechanism is used to prevent vibration, then component durability increases, but the adjustment process becomes more complex
Solution Approach 1:
The cam-based retention block automatically engages with the notches in the crank arm when the lever is moved to a locked position. This self-acting mechanism provides secure locking without requiring additional steps or complex procedures, maintaining ease of operation while ensuring component durability.
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 provides a rugged, quick, and easy-to-adjust pedal crank system that ensures secure fixation and prevents vibration, enhancing the rehabilitation process by allowing precise adjustment of crank length to accommodate varying knee flexion angles, thus improving patient and therapist experience and extending equipment lifespan.
Implementation Method 1
a resilient member, such as a spring, that biases the locking pin toward the surface of the crank arm
Implementation Method 2
The locking lever includes a cam surface that abuts the clamping body and provides the downward compressive force to the clamping block when in the locked position
Data Source
AI summary
An adjustable crank assembly is provided. The adjustable crank assembly includes a crank arm having a surface with a plurality of notches, and a retention block that partially houses the crank arm and allows the crank arm to slide along an axis relative to the retention block. The retention block includes a clamping block and a locking pin, both of which being adapted to selectively engage the crank arm when the retention block is placed in a locked position, and a locking lever for transitioning between a locked position and an unlocked position. The locking lever provides a compressive force to the clamping block when placed in a locked position and a retracting force to the locking pin when placed in an unlocked position.