Linear actuators are now widely in demand when it comes to various devices for adjusting the position of lighting, opening and closing doors or sashes, and production of retractable designs. They are actively used on an industrial scale in small-sized lifting machines, automatic road barriers and garage doors, and much more.
Actuators can often be found in the automotive industry in mechanisms that open/close the cargo and engine department access. The most prominent and promising field of their application, however, is robotics development where linear drives are a necessity.
An actuator is a specialized drive for control systems. For instance, if we are talking about the development of a robot, the movement of its components is carried out exactly through linear actuators.
A linear actuator is a kind of positioning system where the rotational element of the electric motor is converted into the translational movement of the rod. Often this device includes an engine, gearbox, rotor rotation sensor, and limit switch.
Linear Actuator with Position Feedback
A servo drive is a mechanical device that allows you to perform the task assigned to the input accurately. Accordingly, the input task that came from the control unit can be performed by the system with maximum accuracy at the output.
A linear actuator with feedback has a complex system. A step drive with feedback is considered a motor with a feedback function. This type of stepper motor has high positioning accuracy and improved performance.
If you need to select a linear actuator with feedback, today, there are two main types - a drive with a potentiometer or a drive with an encoder. In total, there are two types of position sensors for linear actuators - ones that employ an optical potentiometer and Hall sensors.
The difference between sensor and actuator is that the sensor must convert the received data, and the actuator is only a motion drive.
Linear Actuators with Potentiometer
A feedback linear actuator potentiometer consists of a flexible wire or tape with a resistance that must be proportional to the distance. There are 3 cleats - 2 control cleats and a wiper cleat. Between the beginning of the tape and the end, there is a connection. The resistance between the ends of the tape and the wiper changes as the wiper potentiometer moves.
When Buying the potentiometer option, don’t forget that it is a variable resistor, the resistance of which depends on the shift between the moving and stationary parts. A reference voltage is applied to the potentiometer, and when the resistance changes, the current strength changes, which becomes the corresponding measuring signal.
A Hall effect potentiometer is an analog sensor. The value of its resistance depends on the movement and positions. In general, it is worth noting what the high-speed linear actuator with potentiometer provides.
Today, a wide variety of potentiometers are produced, with a rated power of maximum 1 W. Such devices are capable of 1 million cycles and can operate both at -45 ° C and +75 ° C.
But keep in mind that a linear potentiometer can only be a method of measuring the position of the drive. It is up to the user to provide a method for reading the signal and its further interpretation, as well as developing a control circuit for each specific application.
How to Control a Linear Actuator Position
There are many products that can use the linear actuator position control ability: these are different control valves, control generators, an engine throttle, gear shifting control on a boat, etc. The control system can set certain positions and return to them at command, as well as allows them to control the linear actuator feedback manually.
We will look at an example using a board with two relays to control a linear drive. We will read the position sensor attached to the linear actuators with position feedback.
All buttons will be using internal pull-up resistors on the microcontroller. Accordingly, it is worth connecting a button between the input contacts and the ground. The relay board connects to the output pins. The linear potentiometer wiring itself should be attached to interrupt contacts.
The next important component is writing the correct code. Such a code mainly uses a button library and encoder library and you can encode these functions yourself. Using two libraries will make the code more readable and accessible.
Do not forget about the constant, in this case - accuracy. If you get into the correct number of pulses of the target position a linear actuator with potentiometer feedback takes, then it will be considered at the target position. If the engine power is turned off, upon reaching the target position, a slight shift may be observed. Accordingly, this can cause the target position to exceed and the controller reverses the drive. This can be repeated until the final target position is obtained again.
Major tasks your code should handle:
- monitoring of buttons’ status,
- manual actuator movement,
- saving of a certain position.
The modern market offers a wide variety of linear and rotary electric drives, which allows us to demonstrate some typical applications.
For example, in agriculture, linear actuators with feedback are often used in adjusting the flow rate and angle of fertilizer flow or in seeders to adjust the amount of seeds for a specific piece of field. In combine harvesters, one can often find a motor accelerator, a fan speed controller, and adjustment of the clearance between the cylinder and concavity.
In the construction industry, you can also often find cars with adjustable hood lift and door opener, stairlift. Even shipbuilding cannot do without actuators, automating capacities of boats small and large.
But linear drives have made a real revolution in healthcare and medicine. After all, customizable stretchers and gynecological tables, X-ray machines and apparatus for mammography, the adjustment of hospital beds and wheelchairs all need actuators to be versatile and high-functioning.
We can observe the regular work of actuators at home, in mixers and oven sensors. Ultimately, you can easily automate the opening and closing of any doors, create a TV lift or allow any drawers to move at command. All you need is a good, sturdy linear actuator and a bit of effort.