Washing Machine Door Lock With Bell Crank Stroke Amplification
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Solution Overview
Problem
Existing door blocking devices for electric household appliances, such as front-loading washing machines, require a longer stroke for the blocking element to enhance safety and reliability while maintaining low production and assembly costs, without increasing bulk.
Innovation Solution
The blocking device employs electrically operated actuator means and a bell crank mechanism with a metallic foil and bi-metallic bi-stable knee-pad device, allowing the catch to move between extracted and retracted positions, providing a longer stroke independent of the actuator means used, and ensuring compactness and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the stroke of the blocking element (striker) is increased to enhance safety and reliability, then the blocking performance is improved, but the bulk of the device is increased
Solution Approach 1:
The bell crank mechanism transforms the linear movement of the bi-metallic spring into a rotational oscillating movement, and then converts it back into linear movement with extended stroke for the catch. This dimensional transformation allows achieving a longer stroke without proportionally increasing the overall device volume, as the motion is redirected through a different spatial dimension (rotation vs. linear translation).
Solution Approach 2:
The bell crank acts as an intermediary mechanism between the bi-metallic spring actuator and the catch. It receives the limited stroke movement from the spring and transforms it into a longer stroke movement for the catch through its lever arm geometry, where the ratio between the two arm lengths determines the stroke multiplication factor.
2Reliability
If a longer stroke for the blocking element is implemented, then the safety is improved, but the production and assembly cost increases
Solution Approach 1:
The control means are divided into distinct functional segments: the bi-metallic spring actuator, the bell crank mechanism, and the catch assembly. This segmentation allows each component to be manufactured independently using standard processes, facilitating modular production and assembly while maintaining the overall functionality of achieving a longer stroke.
Solution Approach 2:
By using the bell crank to convert linear motion to rotational motion and back to linear motion with extended stroke, the system achieves a longer catch stroke without requiring a longer actuator stroke. This allows the use of compact, cost-effective actuators while still achieving the desired safety performance through geometric motion transformation rather than simply scaling up all components.
3Reliability
If the stroke of the catch is extended, then the blocking reliability is improved, but the dimensions of the device are increased
Solution Approach 1:
The bell crank mechanism introduces a rotational dimension to the system, allowing the catch to achieve an extended stroke through oscillating rotation rather than direct linear extension. The catch moves in an arc path during operation, and its effective blocking stroke is determined by the bell crank's lever arm ratio, not by the linear distance from the actuator.
Solution Approach 2:
The bell crank serves as a motion transformation intermediary that decouples the actuator stroke length from the catch stroke length. The bi-metallic spring only needs to provide a limited actuating movement, while the bell crank's geometry (ratio between its two arm lengths) determines the final catch stroke, allowing independent optimization of actuator size and catch stroke.
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
This configuration results in a lightweight, cost-effective, and highly reliable blocking device with a longer stroke for the catch, ensuring secure door closure and efficient operation, independent of the type of control means used, while maintaining a compact layout.
Implementation Method 1
the electric supply current heats the resistive tablet, which heats the bi-metallic spring
Implementation Method 2
a bi-metallic spring arranged in proximity of a positive temperature coefficient (PTC) resistive tablet; when the electric household appliance is working, the electric supply current heats the resistive tablet, which heats the bi-metallic spring, making it snap in position
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
A blocking device (1) including a striker (5) in the form of a striker plate (5) sliding perpendicularly to the door (2) and adapted to cooperate in use with a notch (3) of the door (2), and a safety device (6) including a catch (7) blocking the sliding of the striker (5) and control means (8) including electrically operated actuating means (10) for selectively moving the catch (7) between an extracted position and a retracted position from/into its seat (11) in the safety device, in which positions the catch (7) is adapted to respectively intercept/not intercept the striker (5); wherein the control means (8) include a first element (12) actuated by the actuator means so as to be mobile between a first and a second limit stop positions in a direction (P) perpendicular to that of movement (S) of the catch (7); and a bell crank (14) restrained so as to be oscillating on a plane parallel to direction (S) of movement of the catch (7), operatively connected with its first shorter arm (15) to the first element and with its second longer arm (16) to the catch, to receive from the first element (12) an oscillating movement so to shift the catch (7) between said extracted and retracted positions in response to a movement of the first element (12) between said second and first limit stop positions.