Pole Pruner Gear Locking for Low-Resistance Return Strokes
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Solution Overview
Problem
Existing electric pole pruners face inefficiencies in drive systems, such as low screw drive efficiency and premature wear of one-way clutches, leading to increased complexity and poor handling properties.
Innovation Solution
An electric pole pruner with an epicyclic gear assembly that uses a locking arrangement with a brake rotor and caliper to transmit power for cutting strokes and decouple the cutting mechanism for return strokes, allowing a lighter biasing member and reduced power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a reciprocating screw drive is used to achieve cutting motion, then the cutting mechanism can be actuated, but the drive efficiency is low (around 50%) and additional control electronics are required increasing complexity
Solution Approach 1:
The patent replaces the reciprocating screw drive mechanism with a drum and string element system. The electric motor rotates the drum, winding the string element to pull the cutting head forward for cutting, while the return stroke is achieved passively through spring biasing and gravity, eliminating the need for complex reciprocating screw mechanisms and associated control electronics.
Solution Approach 2:
The patent extracts the power transmission function from the cutting head assembly and places it in a separate drive unit mounted on the pole. This separation allows the cutting mechanism to be lighter and improves handling properties, while the motor and gear assembly are positioned optimally for efficient power delivery.
2Use of energy by moving object
If a one-way clutch is used in the planetary gear to facilitate spring biased return motion, then the return stroke can be achieved without motor work, but the one-way clutch is prone to premature wear especially when cutting thicker branches
Solution Approach 1:
The patent removes the one-way clutch component entirely from the system. Instead, the return motion is achieved through a simple spring biasing mechanism that pushes the cutting head back to its starting position after cutting, eliminating the wear-prone one-way clutch while maintaining energy efficiency.
Solution Approach 2:
The spring biasing system provides automatic return motion without requiring motor intervention or complex clutch mechanisms. The system uses the stored elastic energy in the spring to naturally return the cutting head to its initial position, creating a self-service mechanism that is both reliable and energy-efficient.
3Ease of operation
If the electrical drive is placed in the immediate vicinity of the blades (attached to the handles) to achieve cutting motion, then the cutting mechanism can be directly actuated, but the arrangement becomes top-heavy having poor handling properties
Solution Approach 1:
The patent divides the pruner into distinct functional segments: a lightweight cutting head assembly for easy handling and a separate drive unit containing the motor and gear assembly mounted on the pole. This segmentation allows optimal weight distribution with the heavier components positioned higher on the pole where they balance the tool, improving overall handling properties.
Solution Approach 2:
The patent extracts the heavy motor and gear assembly from the cutting head and places it in a separate drive unit mounted on the pole. This separation creates a top-heavy configuration that actually improves handling by positioning the counterweight (motor assembly) higher up, balancing the tool and reducing wrist strain during operation.
4Productivity
If a locking arrangement with brake rotor and caliper is used to selectively lock the ring gear, then power transmission for cutting stroke is enabled, but the device complexity increases
Solution Approach 1:
The patent uses an electromagnetic brake mechanism that changes the friction parameter between the brake pads and rotor to achieve locking and releasing of the ring gear. By controlling the electromagnetic force, the system can selectively engage or disengage the brake to lock or release the ring gear, providing simple binary control for power transmission during cutting strokes.
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
This design enhances cutting capacity, reduces power consumption, and improves handling by enabling a lightweight construction with reduced resistance during return strokes.
Implementation Method 1
a brake caliper (16) configured to selectively lock the ring gear (11) by frictionally engaging the brake pads (161) with the brake rotor (15)
Implementation Method 2
a biasing member (5) configured to return the knife (4) form the cutting position to the starting position
Data Source
AI summary
An electric pole pruner having a spring returned cutting head and equipped with a drive unit having an electric motor coupled to a drum via an epicyclic gear assembly is configured to reduce rotation speed and to increase torque. A string element is coupled to the drum of the drive unit, and to the cutting head so as to actuate the cutting head. The pole pruner further includes a locking arrangement to selectively lock or release a ring gear of the gear assembly so as to convert rotation of the electric motor into rotation of the drum when the ring gear is locked, and to convert rotation of the drum into rotation of the ring gear when the ring gear is released.