Air Spring Power Tool Torque Protection With Elastomeric Damping
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Solution Overview
Problem
Air spring systems in power tools experience torsional shock loads, known as 'jam shocks', which can lead to stress fractures and catastrophic failure due to incomplete piston strokes and subsequent collisions between the pinion gear and rack, especially when a nail becomes jammed.
Innovation Solution
Incorporation of a lifter gear with elastomeric dampers and a one-way needle bearing clutch to absorb and manage the shock loads, using a hub and lifter gear configuration with elastomeric pads positioned between bearing elements to absorb impact forces and prevent reverse rotation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the motor continues to rotate the pinion gear for one complete rotation after piston release, then the piston is fully retracted and the system is ready for the next operation, but the pinion gear teeth collide with the rack causing torsional shock loads when the piston does not travel to the designed extent
Solution Approach 1:
A torque limiter is introduced as an intermediary component between the motor and the pinion gear. This torque limiter allows the pinion gear to rotate freely when excessive torque is detected, preventing the harmful collision between pinion teeth and rack while still enabling the motor to complete its rotation cycle for operational readiness.
Solution Approach 2:
The system changes the torque parameter dynamically by incorporating a torque limiter that allows slip or disengagement when a predetermined torque threshold is exceeded. This parameter change prevents the transmission of harmful shock loads to the rack while maintaining normal torque transmission during legitimate operation.
2Strength
If stronger materials are used to withstand jam shock, then the drive mechanism can resist stress fractures, but the weight of the portable tool increases
Solution Approach 1:
The torque limiter acts as a beforehand cushioning mechanism by preventing excessive torque from being transmitted to the drive mechanism in the first place. Rather than relying on strong materials to withstand the shock, the system proactively limits the torque to prevent harmful shock loads, avoiding the need for heavy reinforcement materials.
3Ease of operation
If the pinion gear is rotated to allow piston movement by compressed gas, then the fastener is driven into the workpiece, but the continued rotation forces pinion teeth to disengage and re-engage causing forceful impact
Solution Approach 1:
The torque limiter serves as a mediator that decouples the motor's continuous rotation from the pinion gear's engagement with the rack. When the piston completes its stroke and the pinion teeth would normally collide with the rack, the torque limiter allows the pinion to rotate freely without transmitting force to the rack, eliminating the forceful impact while maintaining ease of piston release.
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 effectively reduces and eliminates shock loads, protecting the drive mechanism from damage and extending the tool's lifespan by absorbing impact forces and maintaining smooth operation.
Implementation Method 1
A first elastomeric damper is positioned within the first receptacle between the first bearing element and a bearing element defined portion of the first receptacle
Implementation Method 2
The solution effectively reduces and eliminates shock loads, protecting the drive mechanism from damage and extending the tool's lifespan by absorbing impact forces
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
A power tool includes an air spring cylinder. A piston is movably positioned within the cylinder and a driver blade and a rack are attached to the piston. The power tool includes a lifter gear including a lifter gear wheel portion, and a plurality of teeth extending radially from the lifter gear wheel portion and configured to engage the rack. A hub includes a first end operably connected to a motor output and a second end including a hub wheel portion. A first receptacle is provided in one of the lifter gear and the hub and a first bearing element extends from the other of the lifter gear and the hub into the first receptacle. A first elastomeric damper is positioned within the first receptacle between the first bearing element and a bearing element defined portion of the first receptacle.