The self-locking push switch's mechanical structure achieves a bistable function of "press to lock, press again to release" through the coordinated action of a spring and a locking mechanism. Its core principle can be broken down into three stages: press triggering, locking, and secondary press unlocking, each relying on precise mechanical coordination.
When a finger presses the switch button for the first time, the external force overcomes the return spring's elasticity, pushing the moving part (such as a push rod or slider) downwards. During this process, the hook or cam structure at the end of the moving part moves synchronously. When it reaches the preset position, the hook engages in a slot or groove on the housing or base. This action is similar to inserting a key into a lock cylinder; the engagement of the hook and slot creates a mechanical constraint. Even if the finger is released, the return spring's elasticity cannot cause the moving part to spring back, thus achieving the "press to lock" self-locking state. At this time, the switch's internal contact system (such as metal springs or conductive posts) connects the circuit due to the displacement of the moving part, and the device begins to operate.
Maintaining the self-locking state depends on the stability of the locking mechanism. The latch is typically made of a flexible metal material (such as stainless steel or phosphor bronze), whose deformation capability allows it to bend slightly when inserted into the slot. The edge of the slot is designed with bevels or rounded corners to reduce insertion resistance. Meanwhile, the return spring is compressed in the locked state, with its elastic force perpendicular to the latch's disengagement direction, further preventing accidental unlocking. Some high-end designs also add anti-slip textures or ratchet structures to the contact surface between the latch and the slot, increasing friction to improve locking reliability. The advantage of this mechanical locking mechanism is that it can maintain its state without continuous power supply, making it suitable for scenarios requiring long-term on/off switching.
When unlocking is needed, pressing the button again triggers the release of the latching structure. At this time, the moving part continues to move a short distance under external force. The latch, due to the pressure from the beveled edge of the slot, undergoes elastic deformation and gradually disengages from the slot. Once the latch is fully out of the slot, the return spring immediately pushes the moving part back to its initial position, and the contact system disconnects the circuit, stopping the device from operating. The key to this process lies in the "double-step" design of the latch: the first step locks the latch, while the second step guides the latch out via a ramp, ensuring a smooth unlocking action.
Some designs also add guide grooves or limiting posts between the moving parts and the housing to prevent the latch from jamming due to misalignment during unlocking. The spring is the "power core" of the self-locking push switch, and its performance directly affects the switch's feel and lifespan. The return spring is usually made of stainless steel and provides stable elasticity through a spiral structure. During the locking phase, the spring must withstand the weight of the moving parts and the friction of the latching structure without failing; during the unlocking phase, the spring's elasticity must be sufficient to quickly push the moving parts back to their original position after the latch disengages from the latch. To optimize performance, some switches use a dual-spring design: the main spring handles the reset, while the auxiliary spring (such as a torsion spring) enhances the latch's elastic deformation capability, improving unlocking sensitivity.
The contact system is the key module for the switch to achieve circuit switching. The contacts of a self-locking push switch are usually made of copper alloy or silver alloy; the former is less expensive, while the latter has better conductivity and arc resistance. Contact layouts are divided into two types: single-pole single-throw (controlling a single circuit) and double-pole double-throw (simultaneously controlling two circuits). In the self-locking state, the movement of the moving part drives the contacts to close, forming a conductive path; when unlocking, the contacts open as the moving part resets. Some designs also plate the contact surface with gold or silver to reduce contact resistance and improve conductivity stability.
The mechanical structure of the self-locking push switch achieves convenient "one-press lock, press again release" operation through the precise coordination of springs, locking mechanisms, and the contact system. Its ingenious design lies in transforming simple mechanical motion into a stable bistable state, satisfying the device's on/off control requirements while avoiding the power consumption issues of electronic locking through a purely mechanical structure. From household power supplies to industrial equipment, this structure has become the mainstream solution for push switches due to its high reliability and low cost.
