Electric Pole Pruner Gear Locking for Low-Resistance Return Stroke
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Solution Overview
Problem
Existing electric pole pruners face inefficiencies in drive systems, such as low screw drive efficiency and increased complexity, and handling issues due to top-heavy designs, particularly when cutting thicker branches.
Innovation Solution
An electric pole pruner with an epicyclic gear assembly that includes a selectively lockable ring gear using a brake rotor and caliper, allowing efficient power transmission during the cutting stroke and decoupling for a light return stroke, reducing resistance and enabling higher cutting capacity with reduced power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a reciprocating screw drive is used, then the cutting mechanism can be actuated, but the drive efficiency is low (around 50%) and the device complexity increases due to controlled back-and-forth motion requirements
Solution Approach 1:
The patent replaces the reciprocating screw drive with a drum and string element mechanism. The electric motor rotates the drum, which winds the string element to pull the cutting mechanism, eliminating the need for controlled back-and-forth screw motion and associated control electronics.
Solution Approach 2:
The patent extracts the return stroke function from the motor-driven system by using a spring element to automatically return the cutting mechanism. This separates the power transmission function (motor to drum) from the return motion function (spring), simplifying the overall control system.
2Ease of operation
If the electric motor is placed in the immediate vicinity of the blades, then the cutting mechanism can be directly actuated, but the arrangement becomes top-heavy with poor handling properties
Solution Approach 1:
The patent segments the drive system into two parts: a compact drum mechanism integrated near the cutting head for direct actuation, and a separate electric motor mounted on the pole shaft. This allows the motor weight to be positioned lower on the pole, improving balance and handling while maintaining direct mechanical connection to the cutting mechanism.
3Reliability
If a planetary gear with one-way clutch is used, then the spring-biased return motion can be facilitated, but the one-way clutch is prone to premature wear particularly when cutting thicker branches
Solution Approach 1:
The patent removes the one-way clutch from the system entirely. Instead of using a planetary gear with clutch, it employs a simple drum and string element mechanism where the string element naturally prevents reverse rotation of the drum during the power stroke, eliminating the wear-prone clutch component.
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 enhances cutting capacity, decreases power consumption, and provides improved handling properties by allowing a lightweight construction with reduced resistance during the return stroke, suitable for cutting thicker branches.
Implementation Method 1
a brake caliper (16) configured to selectively lock the ring gear (11) by frictionally engaging the brake pads (16a, 16b) with the brake rotor (15), when actuated
Data Source
Figure 1
AI summary
An electric pole pruner (1) having a spring returned cutting head (3) and equipped with a drive unit (6) comprising an electric motor (7) coupled to a drum (8) via an epicyclic gear assembly configured to reduce rotation speed and to increase torque. A string element (13) is coupled to the drum (8) of the drive unit (6), and to the cutting head (3) so as to actuate the latter. The pole pruner (1) further comprises a locking arrangement (14) configured to selectively lock or release a ring gear (11) of the gear assembly (9) so as to convert rotation of the electric motor (7) into rotation of the drum (8) when the ring gear (11) is locked, and to convert rotation of the drum (8) into rotation of the ring gear (11) when the ring gear (11) is released.