Pneumatic Screwdriver Piston Return Mechanism
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Solution Overview
Problem
Conventional pneumatically operated screw drivers face issues with incomplete return of the piston and driver bit to their original positions, especially when the trigger is released before sufficient compressed air is accumulated or if the piston does not reach the bottom dead center due to insufficient screw driving, leading to accidental disengagement of the driver bit from the fastener.
Innovation Solution
The implementation of a main piston and an auxiliary piston configuration, where the auxiliary piston is rotatable and movable, with specific communication holes and a return chamber design, ensures complete return of the piston and driver bit to their original positions without resisting the movement towards the bottom dead center, by controlling the flow of compressed air effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If compressed air accumulation is started when the piston reaches bottom dead center, then the piston can be returned to original position, but the piston may not reach bottom dead center due to insufficient screw driving operation
Solution Approach 1:
The return chamber is designed to accumulate compressed air before the piston reaches bottom dead center, during the downward movement phase. This preliminary accumulation ensures that when the piston needs to return, sufficient compressed air is already available in the return chamber, eliminating the need to wait until bottom dead center and ensuring reliable return even if the screw driving operation is interrupted.
2Speed
If compressed air supply is started before piston reaches bottom dead center, then returning motion is improved, but compressed air resists piston movement toward bottom dead center
Solution Approach 1:
The cylinder is divided into distinct functional zones: a return chamber for compressed air accumulation and a driver bit side for piston movement. The first communication hole selectively connects these zones only during the return phase, preventing compressed air from interfering with the downward piston movement while still enabling efficient return motion when needed.
Solution Approach 2:
The first communication hole acts as an intermediary valve that controls when compressed air from the return chamber can enter the driver bit side. It opens only when the piston needs to return, allowing compressed air to push the piston upward without resisting the downward driving motion, thus mediating between return speed and driving force requirements.
3Loss of time
If the trigger is released before sufficient compressed air is accumulated, then operation time is reduced, but the piston and driver bit do not sufficiently return to original positions
Solution Approach 1:
The return chamber begins accumulating compressed air during the downward movement of the piston, before the trigger is released. This preliminary action ensures that when the trigger is released and the piston needs to return, sufficient compressed air is already accumulated in the return chamber to push the piston and driver bit back to their original positions, eliminating return incomplete issues even with premature trigger release.
Data Source
AI summary
A pneumatically operated screw driver ensuring a complete return of a piston to its top dead center. The screw driver has a compressed air return chamber for returning the piston to its top dead center by applying a compressed air in the return chamber to the piston. The piston includes a main piston and an auxiliary piston. The main piston is first reaches its bottom dead center, and then the auxiliary piston reaches its bottom dead center whereupon screw driving is terminated. Before the auxiliary piston reaches its bottom dead center, and after the main piston moves past a predetermined position, a compressed air is introduced into the return chamber. After the main piston reaches the bottom dead center, application of the compressed air pressure in the return chamber to the auxiliary piston is prevented.