Three-Position Latching Solenoid

February 25, 2022

Latching solenoids have been available for many years, and they are receiving renewed attention because of their reputation for being energy efficient and their adaptability to a wide variety of applications. Latching solenoids do not need constant power to maintain a commanded state. As a result, they use very little power and generate very little heat. The most common type of latching solenoid provides only two armature positions: fully extended or fully retracted. But some applications require a solenoid with three positions.

Before discussing the design and function of the three-position latching solenoid, it is important to review the basics of latching solenoid technology. Latching solenoids are ideal for applications with a low cycle rate because only a short pulse of power is needed to move the armature into either the latched or de-latched position. A pulse of power of one polarity is used to move the armature into the latched position. The armature is then held in position either by a permanent magnet or residual magnetism (depending on the solenoid’s design). A pulse of power of the opposite polarity cancels the magnetic hold, and the armature is driven back to its base position by a spring, although other means can be used as required by the application.

The three-position latching solenoid works on the same principle. But instead of the armature being either fully extended or retracted, the armature can also be actuated to a center position. The typical three-position latching solenoid will use a spring located on both sides of the armature assembly to hold the armature in the center position. But this design requires that the opposing forces of these two springs be adjusted during assembly. TLX Technologies’ three-position latching solenoid is more refined and utilizes just one spring. This provides a tighter tolerance for the center position and eliminates the need for adjusting opposing spring forces. The spring in TLX’s design expands against hard stops to achieve the center position and compresses with the movement of the armature in either direction.

This solenoid is commanded in much the same manner as a traditional latching solenoid but with one key difference. The three-position latching solenoid has two coils, one on each side of the armature. A pulse of power of one polarity to one coil extends the armature, and a pulse of power to the other coil fully retracts the armature. To command the armature to the middle position, a pulse of power of the opposite polarity is sent to both coils simultaneously, canceling the magnetic hold on the armature and moving it to the center position.

TLX’s three-position latching solenoid can utilize a patented shunt ring to improve the solenoid’s pull-in force. The shunt ring is located next to either pole and greatly increases the amount of pull the pole exerts on the armature. This allows for a smaller solenoid for a given amount of voltage and current compared to a solenoid without a shunt ring

This article was originally published by TLX Technologies in February 2022

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