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Sometimes when we are creating a project using a linear actuator, we are trying to solve a problem that could not be solved without the advantages that these mechanisms offer. Other times, we are trying to make a certain task easier by automating it. But every now and then, we will create something just because we can. This is one of those projects.
In this article, we will go over how you can use an ultrasonic sensor to measure the linear actuator distance of an object and use it to automatically change the position of the actuator’s stroke. While this was not created with any specific application in mind, the possibilities are endless.
For control, we are using and Arduino Uno with a MegaMoto motor driver. Our actuator is the PA-04-12-400-HS-24VDC. It is important that the actuator has some kind of feedback so that the Arduino is able to monitor its position – any linear actuator feedback control can work, for instance potentiometer feedback would also be effective here. The potentiometer would be less accurate, but would have the advantage of not requiring a homing procedure to be performed after a power loss. The code would also need to be modified.
The wiring for this project is very simple. We will only be making use of one of the two hall effect sensors in the PA-04-HS here – it does not matter which one (pin 4 or 5). The pinout below is for the 6-pin Molex connector that comes with the PA-04-HS:
The code used in the tutorial is a modified version of what we used in another post, Hall Effect Sensors 1: Position Control. Feel free to take a look at this tutorial to better understand how we are using the hall effect sensor for position control! How the ultra-sonic sensor works is by transmitting an ultrasonic ping that is triggered by one of the GPIO pins on the Arduino. That ultrasonic ping is then reflected off an object and detected by the receiver. When the receiver detects the ping, it sends a pulse to the Arduino. Through this, we can conduct an equation to calculate the distance for a linear actuator by measuring the amount of time between transmission and reception, and use a formula to convert that measurement into inches.
How we determine the position of the actuator is by counting the number of pulses output by the Hall effect sensor (this is described in greater detail in the post mentioned above). We can determine the stroke position in inches by finding out how many pulses/inch is output by our specific actuator, and then dividing our pulse count by that number. Having the reading from the ultrasonic sensor and the reading from the Hall effect sensor both converted to inches, makes the coding much cleaner and easier. From there, we are essentially telling the Arduino “if the object is x inches away, extend the actuator x inches.” Uploading the code below will allow you to put in place the linear actuator controlled distance model to one of our PA-04-12-400-HS-24VDC actuators. In the next step we will go over modifications that can be made to the code.
The value of threshold determines how accurately the actuator’s position should match the reading of the ultrasonic sensor. Increasing it will decrease the accuracy, decreasing it will have the inverse effect. By having this value set to 100, we are essentially tell the Arduino not to move the actuator as long as the pulses of the hall effect and ultrasonic sensors are within 100 pulses of eachother. Have this number too low, may result in the actuator moving in frequent jerky motions as it tries to get into the exact correct position.
Change this value to the stroke length of your actuator (or an inch longer). This will tell the Arduino to ignore any values that are too high.
Change this value to the pulses/inch of your actuator.
We sincerely hope you find this project useful – or at least interesting! Please feel free to modify this and make it your own. As always, we would love to see any related projects that you have, whether you use this idea or create something different with our products! You also can reach us by email at firstname.lastname@example.org and by phone at 1-800-676-6123.