Exit Pushbar Blocking Arm for Tornado Impact Resistance
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Solution Overview
Problem
Conventional exit devices fail to maintain the door closed during high-energy impacts, such as those from tornado debris, due to the pushbar and mounting rail moving towards each other, causing the latch to open, and increasing the strength of bias springs to prevent this makes the device difficult to operate normally.
Innovation Solution
An exit device with a blocking arm that moves to prevent the pushbar from moving towards the mounting rail during high-energy impacts, using a pivot and blocking arm spring to absorb impact energy and maintain contact with the mounting rail, allowing normal operation after the impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the strength of bias springs is increased to prevent pushbar movement during impact, then the door remains closed during high-energy impact, but the force required for normal operation increases making it difficult to operate
Solution Approach 1:
The invention divides the spring system into two separate functional components: bias springs that maintain normal operational force, and blocking members that prevent pushbar movement during impact. This segmentation allows each component to optimize its function without compromising the other - the bias springs remain weak for ease of operation, while the blocking members provide impact resistance.
Solution Approach 2:
The blocking members act as intermediary elements between the pushbar and the mounting rail. During impact, these blocking members engage to prevent relative movement, while during normal operation they remain disengaged and do not interfere with pushbar operation. This intermediary mechanism resolves the contradiction by providing impact protection without increasing operational force requirements.
2Ease of operation
If conventional exit devices are used, then normal operation is easy, but the device fails to keep the door closed during high-energy impact
Solution Approach 1:
The blocking members are pre-positioned in a retracted state that does not interfere with normal pushbar operation. Before impact occurs, the system is prepared with blocking members ready to engage, but they remain out of the way during normal use. When impact occurs, they automatically engage to prevent door opening, thus providing preliminary preparation that maintains both ease of operation and impact reliability.
Solution Approach 2:
The blocking members are designed to be dynamic rather than static - they can move between a retracted position (during normal operation) and an engaged position (during impact). This dynamic capability allows the system to adapt its behavior based on operational conditions, maintaining ease of use during normal operation while providing automatic protection during impact events.
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 device effectively blocks the pushbar from opening the door during high-energy impacts without increasing the force required for normal operation, ensuring the door remains closed and then returns to normal functionality post-impact.
Implementation Method 1
using a pivot and blocking arm spring to absorb impact energy and maintain contact with the mounting rail
Implementation Method 2
At least one biasing spring acts to bias the pushbar towards the outward position
Data Source
AI summary
An exit device for latching a door in tornado-prone areas keeps the door closed when the door is subjected to tornado debris impact by incorporating a blocking arm that swings outward away from the door as impact energy is transferred through the door to the blocking arm in the exit device. The blocking arm prevents a pushbar actuator from moving towards the door during impact or rebound which would allow the door to open. The blocking arm is biased close to the door in a non-blocking position where it initially receives the transferred impact energy. During the impact event the blocking arm rapidly rotates on a pivot from the non-blocking position to a blocking position away from the door. After the impact event, the blocking arm returns to the non-blocking position so that the exit device operates normally.