A spring actuator is a spring-loaded switching device used to electrically activate or control secondary devices in automated or manual systems. Also know as a spring limit switch, these devices typically consist of a moving, spring-loaded mechanical arm of various designs and lengths. The arm is connected via a linkage to a set of electrical contacts through which the relevant control circuit is routed. When the arm moves, it activates the contacts which either cut or activate the control circuit. The spring actuator is commonly used as a limit detector and safety device on moving devices such as sliding gates, cranes, and machine parts.
Most moving machinery operates within clearly defined, set parameters in terms of the range of movement of which they are capable. This is true of both automated and manually-controlled systems. Good examples of this are automated gates and overhead cranes. The gate will slide along its tracks until it reaches the end of its travel, at which point the drive motor must shutdown. An overhead crane will also travel along its tracks until it reaches its end where it will stop.
In all of these situations, the end of the safe travel for the device will, in the majority of cases, be indicated by a limit sensor such as a spring actuator. This is a type of switch that has a protruding, spring-loaded arm that activates an internal electric contact. The gate, for instance, will be equipped with two actuators, one on either end of its travel range through which the gate motors control circuit will pass. When the gate is opened, it will travel to the end of the track where a plate or rod mounted on the gate pushes the spring actuator arm over against its internal spring pressure, thereby switching off the gate motor. This switching also signals the gate controller to reverse the direction of the motor when the gate is next activated.
Many spring actuator types feature bi-directional operation with two sets of internal contacts. This allows the actuator to respond to the movement of a device in both directions of its travel. The spring actuator allows automated systems such as the security gate, to operate safely without an operator being physically present to check for over-travel. In the case of manual systems, such as the overhead crane for example, the limits are generally used as safety mechanisms to ensure that machine operators do not exceed operational limits.