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In most industrial applications, whether it is the food industry, textile, plastics, or even health care, servo motors play a major role in how we automate our surroundings. While it is easy to take them at face value, there is a lot of engineering that went into how these motors were designed, how they function, and how they are controlled. The ecosystem of servo motors may be small compared to the likes of PLCs, but there is quite a bit to know before stepping into the wonderful world of automation.
The term “Servo motor” dates back to the 1860s under the French name “Le servomoteur”, translating to slave motor, and was used to describe hydraulic and steam engines upon boats by a French gentleman named Joseph Farcot. He used it to describe “a power amplifying machine under precise control as to position by a human operator”. Fast forward to the 1800s with the inventions of the battery, electromagnet, and the discovery of a magnetic field, the first electric motor was built and introduced by Mortiz Jacobi in 1834. While it was only a single-phase, single-direction weak motor, it still showed its potential. The 1880s is when the three-phase motor began to emerge from different inventors and in the 1950s is when automation began to grow within the United States. While factories at the time were using pneumatic and hydraulic-controlled machines, they proved to be unreliable, imprecise, and prone to leaks. The servo motor then began to be adopted as a more precise and user-friendly alternative. Now they control some of the most advanced robotics in automation.
Servo motors convert electricity into precise, bidirectional rotational movements. Controlled by either a PLC or a dedicated controller, they take input data and rotate based on the commands given by the controller. This rotation is then applied to the machine or system that the motor is attached to through the shaft, whether it is to roll a conveyer belt, control the joints of a robotic arm, or power a CNC mill.
The secret ingredient for precise motor function is an encoder. These devices are connected to both the motor and the controller to observe the position of the actuator shaft, the change of position, and the rate of change. They also convert the mechanical input into electrical impulses to feed into the controller in the form of quadrature signals. There are two types of encoders:
Mechanical encoders work by using a sensor to identify the change in the magnetic field of a rotating magnetized wheel. The wheel has a series of magnetic poles around its circumference, and they output a predictable response to the sensing circuit to determine its position. Likewise, increasing the number of magnetic poles will increase the resolution and accuracy of the encoder. These types of encoders are more suitable for contaminated environments where excessive shock, moisture, and dust are prevalent.
Optical encoders use a similar method, but instead of a magnetized wheel, they use a light, a disk, and a sensor. While the magnetized encoder uses magnets, the optical encoder uses slits in a disk where light from its attached LED can pass through to the sensor on the other side. When the disk, or code wheel, is spun, the light from the LED will shine through one slit at a time to pass the light to the photo sensor to read its position. Instead of shining through, optical encoders can also reflect light from a LED to a sensor off of the disk. Both of these methods are reliable and accurate, and like the magnetic encoders, can increase in resolution based on the number of slits in the code wheel. They are also easier to improve accuracy and resolution compared to a magnetic encoder and can also be miniaturized to fit into smaller motors. These encoders are better suited for applications with a much higher magnetic field, such as in larger motors
Alternatively, encoders can be substituted for potentiometers, resolvers, or Hall effect transducers though may show a decrease in responsiveness and reliability.
The most common types of motors found in industrial applications are AC and DC motors. The main difference between the two is how they are powered. DC motors use DC power to operate and its speed is directly proportional to the voltage being supplied while AC motors use AC power and are controlled by the frequency of the applied voltage.
To set up a servo motor or multiple motors in any application, it is important to understand how this operation works. To have a successful setup, three main items are mandatory. While further research will be needed to match the correct drives, controllers, and motors, here is how they operate:
Like everything with moving parts, servo motors do require maintenance. A faulty motor can lead to unexpected downtime in an industrial setting while it is getting replaced when it could have been prevented with regularly scheduled maintenance. Not only will it cost money to replace that motor, but it will also render the part it is attached to inoperable, which also costs money due to downtime.
Thankfully, preventative maintenance isn’t difficult with intermediate mechanical knowledge. This requires separating the motor’s face plate from its main body to reach the internals. This allows the technician to perform a wear check on the internal parts, such as bearings, seals, and the brake. Bearings are one of the parts that require extra maintenance as they are worn quite often, leading to servo breakdowns with high repair costs. Seals prevent unwanted dust, water, oil, and debris from working their way into the motor to cause internal damage. The breaks on the motor can fail if oil is present on its mechanical parts. Lack of maintenance can also cause the brake to block and produce metallic dust in its system.
Servo motors play a role in a variety of applications. Due to their precision and reliability, they can tackle tasks that demand repetitive yet precise movements. Some real-world applications are as follows:
Servo motors provide an efficient and reliable way to control our modern industrial plants. These motors save an exponential amount of manpower and have significantly improved production and economical growth. While understanding how these motors function may seem like a daunting task to some people, this guide has been written to help everyone understand just how simple these machines truly are and how they can impact the daily lives of everyone around them.
This entry was posted on January 23rd, 2023 and is filed under Uncategorized. Both comments and pings are currently closed.
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