The monostable linear electromagnet is activated by electrical pulses. After activation, its armature remains in the end position and can be maintained without continuous power supply. An electric pulse of opposite polarity activates the reset spring, causing the armature to return to its initial position.
The monostable linear electromagnet is an ideal choice for applications with strict energy consumption requirements. They are particularly suitable for applications without a mains connection, as they can be powered by batteries or solar energy.
The monostable electromagnet is a widely used electro-mechanical conversion device, whose core feature is that it can automatically stabilize the moving core (or armature) in a preset position (i.e., "steady state") using a permanent magnet or mechanical spring after power is cut off.
Its working principle can be decomposed into two distinct stages:
Action and holding phase (energized): When the coil is energized, the electromagnetic force generated overcomes the spring force or magnetic resistance, driving the moving core to another working position and completing the designated work task at this position.
Reset stage (power off): Once the coil is powered off, the electromagnetic force disappears. At this point, the moving iron core is no longer constrained by the electromagnetic force. Under the elastic force of the reset spring or the magnetic force of the permanent magnet, it automatically and quickly returns to its initial stable position, ready for the next action.
Based on the force that is relied upon for resetting after power loss, there are primarily two designs for monostable electromagnets:
Spring return type: This is the most common type. Its steady-state position is determined by the preload force of the spring. When powered on, electromagnetic force overcomes the spring force to attract the armature; when powered off, the spring force pushes the armature back to its original position. The structure is simple and reliable, and it is widely used in various relays and contactors.
Permanent magnet holding type: This design utilizes permanent magnets to stably maintain the moving iron core in a specific position (such as the closed position). When action is required, a current in a specific direction is passed through the coil to generate a counteracting magnetic field that cancels out the permanent magnetic force, allowing the iron core to move away from its stable position under the influence of another force (such as the opening spring force). Its advantage lies in the fact that it does not consume electrical energy during stable holding, resulting in high energy efficiency, and it can provide a substantial holding force (up to 3500N or more for some models).
Drive Type
The drive circuit design for a monostable electromagnet is flexible and can be selected according to application requirements:
Simple DC drive: Apply a constant voltage directly to enable the electromagnet to quickly attract and maintain its position. This method is simple, but the coil will continue to heat up during the holding phase, resulting in high power consumption.
PWM (Pulse Width Modulation) drive: By generating PWM signals through a microcontroller or similar device to control the switch transistor, the average voltage and current of the coil can be adjusted. This method allows for:
Low power consumption maintenance: After actuation, the position is maintained through a PWM signal with a low duty cycle, significantly reducing coil heating and energy consumption.
Dynamic performance optimization: By employing complex driving strategies (such as rapid driving with high voltage in the initial stage, followed by switching to low voltage or PWM maintenance), both rapid response and low power consumption requirements can be met.
Pulse drive (for permanent magnet retention type): Only a brief forward or reverse current pulse is required to "trigger" a state change, after which the permanent magnet maintains the state on its own, without the need for continuous power supply.
