Washing Machine Door Locking Switch for Bounce-Free Door Signals
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Solution Overview
Problem
Existing electromagnetic door locking devices for washing machines suffer from signal disturbances due to contact bounce, which can prevent the machine from starting correctly when the porthole door is open, and lack distinct switching behaviors between blocking and non-activated conditions.
Innovation Solution
A door locking device featuring a contact strip with two parallel, mechanically separate arms to prevent electrical interference, and a design where the differential between closing and opening points of the open-closed door switch is adjusted to prevent incorrect triggering, ensuring a clean signal and increased lifting force with a low-traction solenoid.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-contact door switch is used to detect the open/closed state of the porthole door, then the device structure is simple, but contact bounce causes signal disturbances that prevent reliable machine control
Solution Approach 1:
The single contact strip is divided into two parallel, mechanically separate arms that function as independent contacts. This segmentation eliminates contact bounce because the arms are mechanically independent and close/open simultaneously without relative motion between contact surfaces, providing a clean digital signal for reliable door state detection.
Solution Approach 2:
The two-armed contact strip acts as an intermediary mechanism between the door position and the control electronics. By using the arms as levers that pivot on fixed points, the system converts the door's linear motion into simultaneous contact closure/opening without direct contact between moving parts, eliminating bounce while maintaining signal fidelity.
2Measurement precision
If the opening point of the contact strip is positioned at the theoretical blocking point, then the switching behavior is precise, but incorrect traction on the door can cause premature opening of the contact
Solution Approach 1:
The contact strip arms have different local properties: they are pre-loaded to ensure reliable contact closure, but their opening behavior is controlled by the blocking pawl geometry. The differential positioning creates distinct closing and opening points, where the opening occurs after the blocking point to prevent false triggering during incorrect door operation.
Solution Approach 2:
The contact strip arms are pre-loaded in a closed position before the door reaches the blocking point. This preliminary closure ensures that the contact is already established and latched before the blocking pawl engages, preventing premature opening even if incorrect traction is applied during the blocking process.
3Force
If a high-traction solenoid is used to lift the blocking pawl, then the blocking force is sufficient, but the manufacturing cost increases
Solution Approach 1:
The system uses a spring-loaded mechanism that provides a mechanical advantage to the solenoid. The spring pre-compression creates a counterbalancing force that reduces the actual traction force required from the solenoid to lift the blocking pawl, allowing the use of a lower-cost, lower-force solenoid while maintaining sufficient blocking capability.
Solution Approach 2:
The blocking pawl and contact strip arms are designed with dynamic characteristics that allow the solenoid to operate with reduced force. The lever arms and pivot points create mechanical multiplication of force, and the transient nature of the pawl lifting operation (rather than continuous holding) allows the use of a smaller, more economical solenoid.
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 effectively prevents machine start-up when the porthole door is open, reduces signal disturbances, and provides reliable switching behaviors, while reducing manufacturing costs by using a solenoid with low traction force.
Implementation Method 1
an electromagnet adapted to operate said blocking pawl
Data Source
Figure 1
Figure 2~5
Figure 6~8
AI summary
An electromagnetic door locking device for a washing machine and similar, adapted to lock a sliding cursor (30) cooperating with the end of a hook mounted on the machine porthole door through a blocking pawl (12). The device comprises two preloaded parallel and mechanically separate metal strips (16, 17), accomplishing the closing and the opening of the power circuit and of the open/closed door circuit, respectively, and that are maintained in the open position by said pawl (12) and by an actuator (13) operated by said cursor (30), when said door is open. (Fig. 1).