The electric motor transforms electrical energy into kinetic energy which has been one of the most impactful inventions for society over the last 200 years. They are used in an uncountable number of applications from mundane to intricate and generate billions of dollars in value every year. This class of human invention has been the subject of continued innovation since its inception, and today, partnered with modern semiconductors, sensor technologies, and a growing ability to optimize magnetics, the electric motor is the focus of some of the richest people and most brilliant engineers. Take the Tesla Model 3’s IPM-SynRM electric motor for example.
A subset of the electric motor, the linear electric motor, serves the world quietly on the factory floor, in the laboratory, at the physiotherapist, and in a handful of other places most folks don’t regularly think about. With that said, this “unrolled” version of the rotary electric motor is making our industries cleaner and more sophisticated by supplanting power-hungry and unreliable pneumatics with precision and efficiency.
Modern linear electric motors are evolving to serve a smarter world.
In the linear actuator game there are many players, with the goal being to convert energy into linear force and motion. Common methods employ compressed air, hydraulics, or electricity as the energy source, as seen below.
Single Double Acting
When compressed gasses are utilized, valves and pressure regulators serve as the means to control linear motion or forces. In hydraulic systems, valves and pumps are employed. In cases where electricity is used, an electric motor is utilized to convert electrical energy into linear force or motion, with a motor driver responsible for its control.
Among electric linear actuators, there are several methods of creating linear action, including gears, pulleys, and screws. Today we’re looking at Linear Motors - a subset of electric linear actuators - which produce force and motion using only magnetic interaction, and require no mechanical force transmission.
There are many traditional devices that today’s society has started calling “smart.” The smart watch, a smart home, smart TVs, smartphones…even smart toasters. When society starts labeling a technology as smart, it means that the tech knows something about its world. A smart watch can assess sleep quality, smartphones listen to conversation and can deliver targeted advertisements, and the smart toaster learns its user’s preferences for toasting bagels. These smart technologies have all had sensors and programmed logic built into them, and all of them know how to communicate. The concept is that this intelligence, borne from sensing, logic, and connectivity, enhances the life of the user and creates a smarter society.
And as toasters get smarter, so too do linear motors. Like smart devices, there are three primary things that set the smart linear motor apart from traditional linear motors: sensors, logic, and language.
The first notable difference between typical linear actuators and smart linear motors is their sensors. A smart linear motor can measure its force generation, position, speed, acceleration, temperatures, and voltage. While this is normally done with external sensors, the smart linear motor packages and protects these senses within its body.
A few notable advantages that onboard sensors bring to a device:
In order to utilize sensor information gathered, on board logic is required.
Smart devices take the sensor information they collect, and combine it into something useful. In the case of a smart linear motor, the onboard logic can accomplish various tasks as the application requires:
Watch how these logic functions perform in the following videos:
Sensors and logic need to communicate within a system, using a shared language to function.
Traditional motors do not communicate. These devices are simple coils of wire and magnets. All the sensing, logic, and communication is handled by external components including motor drivers, sensor amplifiers, and controllers.
Smart linear motors are different. Having these components integrated, they contain some kind of communication protocol which accepts commands for the motor’s behaviors, and reports information from its sensors.
Smart linear motor languages are typically some kind of serial communication, though it could also be a more primitive analog method, like the 4-20 mA current loop or digital voltage triggers. Whatever the communication method, there are often SDKs available that allow software developers to talk to the motor without having to fully understand all the details.
Understanding the role that sensors, logic and language broadly play in a feedback loop, we can more easily define what a smart linear motor is not.
Every tool has a purpose but no tool solves all problems. While a lack of mechanical force transmission makes a linear motor fast, quiet, and smooth, it also poses challenges.
For instance, a linear motor moves freely when unpowered. For applications that require things to stay relatively rigid when powered off, this could be a problem. A related issue is that a linear motor requires a control loop to become ‘rigid’ or to very closely hold a position. While a screw drive can absorb disturbances in the mechanical transmission, and a hydraulic piston will absorb disturbances due to the incompressibility of the fluid, a linear motor typically must sense at least some position error before it can correct.
That said, smart linear motors have their own limits.
While smart linear motors have very high control loop frequencies and ultra low latency due to the locality of all the sensors and drivers, they can still not achieve as rigid a holding force as other technologies.
Another challenge of the linear motor is its need to draw power in order to hold a load against gravity or other sustained forces. The smart linear motor is no different in this regard. So when large sustained loads are present, other technologies or external compensation like springs are often needed.
The following table provides a general comparison between the most common motor types and how they measure against each other.
It becomes clear that smart linear motors are superior in the majority of categories mentioned above, but this doesn’t mean they are the best choice for every linear motor application. So, what are the ideal circumstances and for which professionals are smart linear motors best suited?
Unlike traditional linear motors, a smart linear motor can be used by designers and programmers who do not have traditional electrical engineering skills. They just require a good idea of what they need the device to do, and are comfortable communicating using its language or SDK. Compared to the excessive wiring, component mounting, and tuning required for a traditional linear actuator, the smart linear motor requires much less knowledge and training to become quickly proficient.
Essentially, the smart linear motor reduces the skill barrier requirement so that a mechanical engineer can get the results that were previously reserved for professionals with an electrical engineering background. However, just because it can be used by a wider range of professionals, doesn’t necessarily mean it’s the best choice for every linear motion application.
Are you interested to learn if a smart linear motor makes sense for your project application? Book a free consultation with our Applications Engineer and find out now!