For a lot of people, motors and actuators may seem like the same thing. Movement is involved, they may well sound the same, there’s some kind of energy source going in, and there’s no way your facility will function without both of them. In principal, they both use the same technologies, they can even look the same, but they’re different beasts.
The Easy Difference
The easiest way to tell a motor and actuator apart is by how they’re being used. A motor is designed to spin at a relatively high RPM for significant spans of time. Think of the motor in your AC Compressor, a fuel pump, the mixer or coffee grinder sitting on your kitchen counter. If you turned it on and left it to function forever, there would be no consequences except for the motor failing.
By contrast, an actuator has a linear output, instead of a continuous output. It moves a damper, valve, elevator, or some other device that has a limited range. Think about your car door, it can be all the way open, half open, closed, or anywhere in between. If you wanted to mechanically open it, that’d be an ideal job for an actuator. If you used a simple motor, you’d run the risk of going over 100% open or over 100% closed, and damage/destroy the door. If you used a device that isn’t intended to stop at an exact position, you’d break the thing it actuates. This is where an actuator comes in. It works exactly enough and more or less stops.
This begs the question, how do you make something into an actuator? Inside there must be something we see elsewhere, some form of electrical, hydraulic, or pneumatic motor. In large part, that is the case. There’s either something that spins or some form of piston or ram device that pushes outwards. In both cases, it’d be bad to simply leave them on all the time. We use a control-signal to track how much actuation we have achieved and how much more is needed before the device stops moving and locks into position.
The Control Signal can be achieved numerous ways. It can be a pneumatic system that compares two pressures, moving the actuator until they’re equal. It can use electrical traces to record the actuator’s position and apply power until the desired trace is active (this system is used to control the transfer case actuator on many cars and trucks). This sort of control can even be done by inferring the actuator position from very precise input voltages and ‘homing’ the actuator, as has been done on some 3D printers.
This all comes back to the big question. Why do we need these anyway? Are there that many places where something only needs to move a little bit? Well, the purpose is for automation. These are the sort of devices that control your air ducts. They can increase efficiency in your HVAC system by mixing air of different temperatures or cutting off cold airflow to rooms that don’t need it. They can open windows, control valves, and allow you to automate parts of a facility in a field called Process Controls. In that setting, actuators allow massive factories to function with minimal human input, increasing their productivity and safety.
Perhaps the biggest examples of this technology are factory-scale bakeries, petroleum, and nuclear plants. In these settings, you want precise amounts of ingredients constantly flowing into your batter mixing system. You want your workers to be safe a few hundred feet away from the potentially explosive vat of fuel you’re cooking up should anything go wrong. And for any chemical and nuclear plant, you want to remove the possibility of human error. A person might open a valve too much, but an actuator will always be precise.
This precision has trickled down to small businesses and even residential settings across the world. You can buy 3D printers for mere hundreds of dollars. You can have a zoned hvac system in your home. And these wonderful actuators are what make it possible.