Rotatable Grass Cutting Devices for Boundary Trimming
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Solution Overview
Problem
Robotic lawn mowers have limited ability to cut grass close to objects and borders, and they struggle with cutting relatively long grass due to design constraints such as limited ground clearance and positioning of the cutting unit.
Innovation Solution
The robotic lawn mower features a second rotatable grass cutting device with a rotation axis that can tilt beyond 45°, allowing it to reach closer to boundaries, combined with a safety arrangement and independent motor control for energy efficiency, and easily replaceable cutting knives made of plastic for cost-effectiveness and environmental friendliness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the cutting unit is arranged at the underside of the lawn mower body, then the structural design is simple, but the ability to cut grass close to objects and borders is limited
Solution Approach 1:
The cutting system is divided into two independent rotatable grass cutting devices: a first device positioned at the front underside and a second device positioned at the rear underside. Each device can rotate independently around its own axis, allowing the rear device to reach close to boundaries while the front device handles central area cutting, thus resolving the limitation of a single fixed cutting unit.
Solution Approach 2:
Both grass cutting devices are made rotatable around vertical axes, transforming them from static cutting units to dynamic components. This rotatability allows the cutting devices to adjust their orientation and reach different positions, enabling effective cutting close to objects and borders while maintaining structural simplicity through the use of standard rotational mechanisms.
2Ease of operation
If the ground clearance height is reduced for safety reasons, then safety is improved, but the ability to cut relatively long grass is limited
Solution Approach 1:
The rotatable grass cutting devices can be positioned at different heights and orientations. When encountering long grass near boundaries, the system can rotate the rear cutting device to a position where it reaches lower to the ground, effectively cutting long grass without requiring the entire mower body to have increased ground clearance, thus maintaining safety while enabling long grass cutting capability.
Solution Approach 2:
Instead of increasing ground clearance in the vertical dimension, the solution uses the rotational degree of freedom of the cutting devices to achieve the desired cutting height. The rear cutting device can rotate to reach close to the ground surface when needed, providing the necessary cutting capability for long grass without compromising the safety-related ground clearance of the main mower body.
3Ease of operation
If a second rotatable grass cutting device is added to improve edge cutting, then the cutting capability close to boundaries is improved, but the device complexity increases
Solution Approach 1:
The cutting system is segmented into two independent rotatable grass cutting devices positioned at the front and rear undersides of the mower body. Each device has its own rotation axis and can operate independently, allowing the rear device to specifically handle edge cutting close to boundaries while the front device handles central area cutting, thus improving overall cutting capability without excessive complexity.
Solution Approach 2:
Both rotatable grass cutting devices serve multiple functions: they can cut grass in the central area when positioned horizontally, and the rear device can rotate to cut grass close to boundaries and objects. This multi-functionality justifies the addition of a second device, as both units contribute to different cutting scenarios rather than requiring separate specialized devices.
Data Source
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AI summary
The present disclosure relates to a robotic lawn mower (100) comprising a first end portion (101) facing a forward travelling direction (F) and a second end portion (102) facing a reverse travelling direction (R). The robotic lawn mower (100) further comprises a body (140), at least two drive wheels (130a, 130b), at least one swivelable wheel (131a, 131b), a control unit (110) adapted to control the operation of the robotic lawn mower (100), and a first rotatable grass cutting device (180) having a first rotation axis (181) and a first rotation plane (182). The wheels (130a, 130b; 131a, 131b) are at least partly adapted to run on a ground surface (G) and at least two drive wheels (130a, 130b) have a drive wheel axis (145) with a center (146) and are drivably connected to a propulsion motor arrangement (150). The robotic lawn mower (100) comprises a longitudinal extension (210) that extends along a straight travelling direction (F, R) for the robotic lawn mower (100). The robotic lawn mower (100) comprises a second rotatable grass cutting device (220) having a second rotation axis (221) and a second rotation plane (227) that presents a smallest first angle (α) to the longitudinal extension (210) that exceeds 45°.