Electrified Exit Device Latch Dogging Assembly
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing exit devices require large, power-hungry motor actuators to maintain the panic bar in an unlocked position, leading to inefficiencies and the need for a more compact, energy-efficient solution that can be retrofitted into existing systems, while also addressing issues of latch retraction delays due to binding.
Innovation Solution
A modular latch dogging assembly using an electromagnet and actuator that allows the panic bar to be held in an unlocked position without continuous energization, featuring a sensor to adjust actuator parameters for timely latch retraction and a design that reduces the size and power requirements of the actuator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a motor actuator is used to draw the latch from the strike, then the latch can be withdrawn with extra force to overcome internal resisting forces, but the device becomes large in size, requires numerous interconnected moving parts, and consumes large amounts of power
Solution Approach 1:
The patent replaces the motor actuator (electromechanical system) with a solenoid actuator (electromagnetic system). The solenoid uses electromagnetic force to directly move the plunger and retract the latch, eliminating the need for gears, shafts, and other mechanical transmission components. This substitution reduces device size while maintaining sufficient actuating force to overcome internal resisting forces.
Solution Approach 2:
The patent removes the return spring component that was necessary in the motor actuator system to back-drive the gearing and return the actuating shaft to its starting position. The solenoid actuator naturally returns to its extended position when de-energized, eliminating the need for mechanical return mechanisms and reducing overall device complexity and size.
2Reliability
If a motor actuator is used with a large return spring to back-drive the gearing, then the latch can be returned to its locked position, but a larger motor is required to overcome the spring force
Solution Approach 1:
The patent replaces the motor actuator with a solenoid actuator that uses electromagnetic force for both latching and returning operations. The solenoid plunger is extended by electromagnetic force to retract the latch, and naturally returns to its extended position by spring tension (a small internal spring within the solenoid) when de-energized. This eliminates the need for a large return spring and large motor, significantly reducing power consumption while maintaining reliable latch return functionality.
3Reliability
If continuous energizing of the actuator is used to hold the exit device in its unlocked dogged position, then the panic bar remains in the depressed position, but large amounts of power are required to maintain this state
Solution Approach 1:
The patent employs a magnetic hold mechanism that uses a stationary magnet (or electromagnet in holding mode) to attract and hold the armature in the retracted position. Once the solenoid actuator has moved the armature into the magnetic field, the magnetic attraction maintains the unlocked position without requiring continuous actuator energizing. This reduces power consumption from continuous high-power actuator operation to low-power or intermittent magnet energizing.
Solution Approach 2:
The patent implements periodic or intermittent energizing of the magnetic hold mechanism rather than continuous energizing. The actuator is energized briefly to move the armature into position, then the magnetic field is maintained with minimal or periodic energizing to hold the position. This periodic action maintains reliability while dramatically reducing average power consumption compared to continuous actuator energizing.
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 energy-efficient operation by allowing the actuator to be de-energized while maintaining the panic bar in the unlocked position, improves space utilization, and ensures timely latch retraction through parameter adjustments, enhancing the overall efficiency and adaptability of exit devices.
Implementation Method 1
an electromagnet and an actuator in a modular package, wherein an armature fixed to the panic bar is brought into contact with the electromagnet upon energizing of the actuator
Data Source
AI summary
A latch dogging assembly comprises an electromagnet and an actuator mounted on a bracket. A guide slide is pivotally mounted on the bracket with a lead block coupled to the guide slide. A guide pin rides along an inner surface of the bracket causing the guide slide to pivot. A pawl is slidably engaged with the guide slide. A guide link includes a post. An armature is mounted to the panic bar and the post engages the pawl. When the actuator is energized to move the lead block, the pawl engages the post to pivot the armature and thereby cause the panic bar to move from the extended position to the depressed position. When the electromagnet is energized the armature is magnetically held preventing reverse pivoting of the guide link. A method for fully retracting a door latch is also provided.