Wave Energy Buoy PTO Ball Screw Assembly for Low-Friction Conversion
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Solution Overview
Problem
Existing wave energy converter (WEC) buoys face inefficiencies and wear issues in converting wave motion to electricity due to unpredictable movements and significant friction in traditional rack and pinion mechanisms, leading to less than 80% energy conversion efficiency and durability concerns.
Innovation Solution
A power-take-off system utilizing a self-aligning ball screw assembly with a two-axis gimbal and sealed drive tube, which allows for efficient conversion of wave motion to electricity with minimal friction and integration of a brake system, achieving over 95% efficiency and reduced wear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a rack and pinion mechanism is used to convert float movement into rotary motion, then the PTO can generate electrical energy, but the unpredictable lateral movements cause unreliable meshing and significant friction leading to wear and low efficiency
Solution Approach 1:
The patent replaces the traditional rack and pinion mechanical system with a ball screw mechanism. The ball screw uses ball bearings to reduce friction between the screw thread and nut, converting the high-friction sliding contact into low-friction rolling contact. This substitution maintains the ability to convert linear float movement into rotary motion while dramatically reducing energy loss to friction and improving reliability under unpredictable wave conditions
Solution Approach 2:
The patent changes the mechanical parameters of the transmission system by introducing a ball screw with specific pitch and diameter ratios, optimized for the expected range of float movements. The ball screw geometry and bearing arrangement are designed to accommodate lateral movements while maintaining efficient power transmission, transforming the system's mechanical characteristics to better suit the variable wave environment
2Productivity
If a rack and pinion mechanism is used, then the PTO can convert wave motion to electricity, but significant friction causes undesirable wear and reduces efficiency to less than 80%
Solution Approach 1:
The patent replaces the high-wear rack and pinion system with a ball screw mechanism that uses recirculating ball bearings. This substitution changes the contact mechanism from sliding friction (which causes wear) to rolling friction (which minimizes wear). The ball screw assembly is designed with hardened surfaces and proper lubrication channels, further reducing wear and extending component life while improving energy conversion efficiency to above 80%
Solution Approach 2:
The ball screw mechanism incorporates self-lubricating features and recirculating ball bearings that maintain their own lubrication film during operation. The design allows the system to self-regulate friction and wear through the hydrodynamic lubrication effect created by the ball bearings, reducing the need for external maintenance and minimizing material loss over time
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 reliable, durable, and efficient power-take-off system for WEC buoys, capable of maintaining high efficiency and minimizing wear under varying wave conditions, making it suitable for long-term, unattended operation.
Implementation Method 1
A power-take-off system utilizing a self-aligning ball screw assembly with a two-axis gimbal and sealed drive tube
Implementation Method 2
ball screw assembly with a two-axis gimbal and sealed drive tube, which allows for efficient conversion of wave motion to electricity with minimal friction
Implementation Method 3
by means for mounting said PTO for rotational movement about two orthogonal axes substantially perpendicular to an axis of said screw shaft, wherein said means for mounting is a two-axis gimbal
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
A power-take-off system for use in a wave energy converter buoy employs a meshing nut and screw shaft assembly for motion conversion. That is, the motion of the buoy float is coupled to drive the nut along the screw shaft on which it is mounted. The linear movement of the nut along the shaft causes the shaft to rotate and this rotational motion is then coupled to rotate an electrical generator.