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How Actuators and Limit Switch Feedback work?

Linear actuators are quite common to various applications, coming in the form of an electro-mechanical component that can create motion in a straight line. Often found in industrial machinery, valves, computer peripherals, and more, linear actuators create the necessary linear motion for different processes through the use of mechanics, hydraulics, or pneumatics. In some instances, feedback controls may be necessary, and such characteristics may be managed with the use of sensors and limit switch features.

Many linear actuators may feature a limit switch, a mechanical component that constrains the range at which the device can extend or retract from its typical mechanical dimensions. For an electric linear actuator, as an example, movement is achieved by the spinning of the motor. With the motor, an acme screw is driven, pushing the shaft rod in or out of the assembly. The direction that the shaft rod moves is dependent upon the direction that the motor is spinning, and the mechanical limit switch guarantees a stopping point on either side. It is important to know that the motor may continue to run even when the switch limitation is reached. If the motor can no longer rotate and begins to stall, a high current draw may occur which can potentially burn out the motor. To prevent such situations, some actuators implement mechanical limit switches or hall effect sensors that shut off the motor when the actuator reaches its limit of travel.

In other instances, the limit switch feedback signals may be used to control the system. In such cases, rather than utilizing a trigger for motor shut off operations, an analog signal is provided as a part of an integrated control system. For limit switch feedback, such features may come in one of two different configurations. The first configuration is to have both signals separated from one another. With the extended limit switch and the retracted limit switch, separate signals can be provided to the operator to convey normally open and closed operations. These signals are then taken by the control system, used for the means of positioning the actuator by driving the motor as necessary.

The second configuration is fairly similar to the first, albeit having a shared signal for the extended limit switch and retracted limit switch. While the second configuration is capable of enacting similar open and closed states, less wiring is involved. Using either configuration for a particular application, the user will always be notified when the actuator has reached its limit through the use of an indicator light. This is important as the operator of the system will not always be in an area where they can witness the movement of the actuator itself, instead relying on control panel indicators to dictate operational characteristics. While this can simplify procedures, it can also act as a redundancy in a control loop for the means of bolstering safety.

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