Stepped Planetary Gear Drive for High-Speed Oscillating Cutters
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Solution Overview
Problem
Existing tool drive units for handheld cutting tools face challenges in achieving high performance, ergonomics, and compactness due to limitations in gear ratios, weight, and centrifugal forces, particularly in oscillating cutting tools with high drive speeds.
Innovation Solution
A single-stage planetary gear design with stepped planets and a flywheel connected to the drive pinion, allowing for increased gear ratio and reduced centrifugal forces, combined with a lightweight and compact construction using a coaxial arrangement of the electric motor and planetary gear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a multi-stage planetary gearbox is used to achieve high gear ratio, then the reduction ratio is sufficient, but the weight increases significantly making the tool less ergonomic
Solution Approach 1:
The planetary gear set is segmented into two functional sections: a first circumferential section for engaging with the drive pinion and a second circumferential section for engaging with the ring gear. This segmentation allows each section to be optimized independently, achieving high gear ratio in a single stage without the weight penalty of multi-stage designs.
Solution Approach 2:
The invention transitions from a single-diameter planet design to a stepped planet design with two different circumferential sections of different diameters. This dimensional change enables the planets to engage with two different gear elements (pinion and ring gear) simultaneously, achieving high reduction ratio in one stage rather than requiring multiple stages.
2Speed
If the drive speed is increased to improve cutting performance, then the cutting energy increases, but the centrifugal forces on planet bearings increase causing potential planet detachment
Solution Approach 1:
The planet is segmented into two circumferential sections with different diameters. The first section (larger diameter) engages with the drive pinion, while the second section (smaller diameter) engages with the ring gear. This segmentation reduces the orbital speed at which planets rotate around the pinion, thereby reducing centrifugal forces on the planet bearings and preventing planet detachment at high drive speeds.
Solution Approach 2:
The invention changes the geometric parameters of the planets by creating a stepped design with two different circumferential sections. By adjusting the diameters of these sections, the orbital speed of the planets is optimized to reduce centrifugal forces while maintaining high drive speed operation, thus improving reliability.
3Weight of moving object
If a single-stage planetary gearbox is used to reduce weight, then the gearbox is lighter and more ergonomic, but the gear ratio is insufficient to ensure material enters the gearbox at high drive speeds
Solution Approach 1:
The invention introduces a stepped planet design with two circumferential sections of different diameters, adding a dimensional feature to the traditional single-diameter planet. This allows the single-stage gearbox to achieve a sufficiently high gear ratio by engaging the planets with both a drive pinion and a ring gear at different diameters, ensuring material enters the gearbox even at high drive speeds.
4Use of energy by moving object
If the rotational speed of rotating masses is increased to store more energy, then the cutting performance improves, but the centrifugal forces increase requiring reinforced planet bearings
Solution Approach 1:
The planet is segmented into two circumferential sections where the first section (larger diameter) engages with the drive pinion and the second section (smaller diameter) engages with the ring gear. This segmentation allows the system to store more energy through higher rotational speeds while simultaneously reducing the centrifugal forces on the planet bearings, as the planets rotate at a lower orbital speed around the pinion.
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 enables higher drive speeds with reduced centrifugal forces, increased storable energy, and a lighter, more ergonomic tool design, enhancing the tool's performance and handling.
Implementation Method 1
A planetary gear set (30) is arranged in the gearbox mounting chamber (18). The planetary gear set (30) has a first circumferential section (41) and a second circumferential section (42). The first circumferential section (41) is engaged with the drive pinion (10). The second circumferential section (42) is engaged with a ring gear (36).
Implementation Method 2
The drive pinion (10) has a third circumferential section (43) and a fourth circumferential section (44). The fourth circumferential section (44) is engaged with the planetary gear (30). The third circumferential section (43) has a larger diameter than the fourth circumferential section (44) and is designed as a flywheel (7).
Implementation Method 3
The first diameter (d1) of the first circumferential section (41) is larger than the second diameter (d2) of the second circumferential section (42). Because the planets (32) each have a first circumferential section (41) and a second circumferential section (42), and the first diameter of the first circumferential section is larger than the second diameter of the second circumferential section, and the first circumferential section is exclusively engaged with the drive pinion and the second circumferential section is exclusively engaged with the ring gear, the orbital speed at which the planets run in the ring gear is reduced compared to a design in which either there is no first circumferential section and the drive pinion is engaged with the second circumferential section, or there is no second circumferential section and the ring gear is engaged with the first circumferential section.
Data Source
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AI summary
A tool drive unit (1) for a cutting blade (131, 132) of a handheld tool (100) is specified, comprising an electric motor (3) configured to rotate a drive pinion (10) at a drive speed, a gearbox housing (14), a planetary gear (30) arranged in the gearbox housing (14) with a single ring gear (36), a single planet carrier (34) and planets (32) driven by the drive pinion (10), an eccentric shaft (50) driven by the planetary gear (30) at an output speed and configured to drive at least one cutting tool (131, 132) in an oscillating manner, wherein the planets (32) each have a first circumferential section (41) and a second circumferential section (42), wherein a first diameter (d1) of the first circumferential section (41) is larger than a second diameter (d2) of the second circumferential section (42).wherein the first circumferential section (41) engages exclusively with the drive pinion (10) and the second circumferential section (42) engages exclusively with the ring gear (36), and the tool drive unit (1) has a flywheel (7) which is rotationally fixed to the drive pinion (10). Furthermore, a handheld working device (100) comprising the tool drive unit (1) is specified.