Servo Motor – An Introduction
Published on : Friday 15-09-2023
What is a servo motor? This article explains the concept and the benefits.
A servo motor is a self-contained electrical device that moves parts of a machine with high efficiency and great precision. In simpler terms, a servo motor is a BLDC motor with a sensor for positional feedback. This allows the output shaft to be moved to a particular angle, position, and velocity that a regular motor cannot do. However, a servo motor is only one part of a closed-loop motion control system. A complete motion system includes an amplifier, control circuit, drive gears, potentiometer, shaft, and an encoder or resolver as well as the servo motor.
A servo motor consists of three main components:
A motor: This can be either a DC motor or an AC motor depending on the power source and the application requirements. The motor provides the mechanical power to rotate or move the output shaft.
A sensor: This can be a potentiometer, an encoder, a resolver, or another device that measures the position, speed, or torque of the output shaft and sends feedback signals to the controller.
A controller: This can be either an analog or a digital circuit that compares the feedback signals from the sensor with the desired set point signals from an external source (such as a computer or a joystick) and generates control signals to adjust the motor’s voltage or current accordingly.
How does a servo motor work?
Servo motors are used to control position and speed very precisely, but in a simple case, only position may be controlled. Mechanical position of the shaft can be sensed by using a potentiometer, which is coupled with the motor shaft through gears. The current position of the shaft is converted into an electrical signal by the potentiometer, and compared with the command input signal. In modern servo motors, electronic encoders or sensors are used to sense the position of the shaft.
Command input is given according to the required position of the shaft. If the feedback signal differs from the given input, an error signal is generated. This error signal is then amplified and applied as the input to the motor, which causes the motor to rotate. And when the shaft reaches to the required position, error signal becomes zero, and hence the motor stays standstill holding the position.
The command input is given in the form of electrical pulses. As the actual input applied to the motor is the difference between feedback signal (current position) and applied signal (required position), speed of the motor is proportional to the difference between the current position and the required position. The amount of power required by the motor is proportional to the distance it needs to travel.
Advantages of servo motor
Higher output power: A servo motor produces a high output power. If you are into intense mathematical problems, you can calculate the output independently, but you can also let a servo drive do the job for you.
Efficient & accurate: Ensuring accuracy is something everyone strives for, which is a specialty for the servo motor. It attains its precision by a rotating motor that relays a signal back to its position and speed drive. Encoder accuracy guarantees that everything comes out smoothly.
Accelerated torque: Looking at the differences between a servo and a stepping motor, you will find that a servo motor can speed up loads due to its high torque ratio. It gets the increased torque from using gearboxes along with the engines to provide a reliable speed.
Short period management: An excellent detail about a servo motor is that it uses as much power as necessary, meaning it won’t exert any extra energy, allowing for efficient power and torque usage for shorter periods.
Servo motor applications
Servo motors are used in a wide range of industrial and commercial applications that require precise control of motion, including:
Robotics: Servo motors are commonly used in robotics for precise control of joint movements, as well as for grippers and end effectors.
CNC machines: Servo motors are widely used in computer numerical control (CNC) machines for precision positioning and motion control of cutting tools.
Packaging machinery: Servo motors are used in packaging machinery to control the movement of conveyor belts, as well as for the precise positioning and movement of packaging materials.
Aerospace: Servo motors are used in aerospace applications for precise control of aircraft components, such as flaps and landing gear.
Autonomous guided vehicles: Servo motors are used to power and steer the wheels in autonomous guided vehicles.
Medical equipment: Servo motors are used in medical equipment for precise control of medical devices, such as surgical robots, prosthetics, and other medical devices.
Printing and paper processing: servo motors are used in printing and paper processing equipment for precise control of paper feeding, cutting, and folding.
Industrial automation: Servo motors are used in a wide range of industrial automation applications, including conveyor systems, material handling, and assembly lines.
How to select a servo motor?
There are several considerations when selecting a servo motor for a specific application, such as the required speed, torque or force, motion profile, available physical envelope, and environmental factors. This means that the chosen motor solution must produce the load torque and speed requirements, fit in the available space, and perform as required under the subjected environmental conditions of the application.
A servo motor is part of a total mechanism that provides motion to a load – to move it, machine it, lift it, inspect it, etc. The servo motor is the muscle that provides the necessary torque, force, and speed (required load point) to perform a given function. The fastest and most reliable way to determine these needs is with a motor sizing tool that calculates the load points required by a motor and analyses information about the load, transmission elements, and motion profile to select a motor from the motor database that matches the load parameters. As the initial load points are determined, the sizing tool checks for the optimum solution and narrows the motor choices based on the required torque, speed, inertial ratio, and associated margins acquired from the motor ratings.
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