Hand-Held Pneumatic Hammer Drill Air Spring Stiffness Control
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Solution Overview
Problem
High-powered hand-held pneumatic hammer drills face difficulties in controlling the guidance of the tool when pressed against a substrate, leading to excessive loading and potential damage to the percussion mechanism.
Innovation Solution
A hand-held power tool design featuring a pneumatic chamber with a spool valve and check valve system, controlled by a rivet header, which adjusts air pressure to regulate percussive power and stiffness, allowing for easier positioning and targeted reduction of percussive power during chiseling operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the pneumatic chamber increases the quantity of air to reduce percussive power and increase stiffness, then the tool becomes easier to position on the substrate, but the percussive power decreases below the threshold value needed for effective chiseling
Solution Approach 1:
The system dynamically adjusts the quantity of air in the pneumatic chamber based on operational phase. During positioning, air quantity is increased to reduce stiffness and improve ease of positioning. During chiseling, air quantity is reduced to threshold levels to maintain sufficient percussive power. This dynamic adjustment resolves the contradiction between ease of positioning and percussive power availability.
Solution Approach 2:
The system changes the physical parameter of air quantity in the pneumatic chamber to control the stiffness of the air spring. By varying this parameter between two states (higher quantity for positioning, lower quantity for chiseling), the system achieves both easy positioning and adequate percussive power without compromising either function.
2Stability of the object's composition
If the spool valve remains open during chiseling operation to allow air flow, then the pneumatic mechanism maintains flexibility, but the percussive power remains insufficient for effective chiseling
Solution Approach 1:
The spool valve is closed before chiseling operation begins, as a preliminary action to prepare the pneumatic chamber for high-power delivery. This ensures that when chiseling starts, the air quantity is already at the threshold level needed for effective percussive power, eliminating the need for real-time adjustments during the high-power phase.
3Power
If the shut-off valve is closed to prevent air loss during chiseling, then percussive power is maintained at threshold levels, but the system loses adaptability to adjust air quantity for different operational phases
Solution Approach 1:
The air control system is segmented into two independent control paths: a primary shut-off valve that maintains air quantity at threshold levels during chiseling to preserve percussive power, and a secondary spool valve that enables air quantity adjustment during positioning operations. This segmentation allows the system to maintain high percussive power while retaining adaptability for different operational phases through the spool valve's ability to modulate air flow when needed.
Data Source
AI summary
A hand-held machine tool for a striking tool has a motor, an impact mechanism, a spool valve, and a pneumatic chamber. The impact mechanism has an exciter piston moved by the motor, and a hammer coupled to the exciter piston via a pneumatic chamber between the exciter piston and the hammer, and a striker in front of the hammer in the striking direction. In a working position counter to the striking direction, the striker bears on a stop, in a starting position the striker is offset in the striking direction relative to the working position, and in a rest position the striker is offset in the striking direction relative to the starting position. In the starting position, the hammer bearing on the striker closes the spool valve and, in the rest position, the hammer bearing on the striker opens the spool valve.