What is a Servo Motor?
Servo Motor Introduction: A servo motor is an electric motor that adjusts its position, speed, or torque in response to controller inputs.
The term servo comes from the Latin word servus, meaning servant or slave. This reflects the historical use of servo motors as auxiliary drives that assist the main drive system.
However, modern servo motors are capable of providing high performance and precision as main drives in various applications.
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 either 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 setpoint 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.
The controller employs a closed-loop feedback system, adjusting the motor’s movement to closely align with the desired setpoint, maintaining strict accuracy.
The controller can also implement various control algorithms, such as proportional-integral-derivative (PID) control, fuzzy logic control, adaptive control, etc., to optimize the performance of the servo motor.
Construction of Servo Motor
The construction of a servo motor involves many key components that are used to enable precise control of angular position. A servo motor is similar to a regular motor, but it has more additional parts to facilitate position control.
These essential components include sensors, gears, and a circuit. The motor is guided by a controller, such as Arduino or STM. In industrial applications, AC servo motors utilize an encoder as a position sensor, while DC servo motors employ a potentiometer for this purpose.
A DC servo motor is assembled by combining a DC motor with various components like a gearbox, controller, and potentiometer. On the other hand, an AC servo motor uses an induction motor, complemented by gears and encoders for precise control.
Parts of Servo Motor
Following are the main parts of a servo motor:
#1. Housing.
It is about 1 inch thick coated aluminum housing that surrounds the inner parts of the servo motor so that it protects the motor from external particles. The motor’s housing is designed for quick and easy disassembly and reassembly.
#2. Motor Shaft.
It works similar to a prime mover, whereas the gearbox or belt and pulley system to which it is attached can use that energy to increase the motor’s torque while reducing the motor’s speed. The motor is generally made from cold or hot-rolled steel.
#3. Bearings.
Bearings can provide high accuracy and very low vibration to the motor. The result is a very smooth and cool operation. Bearing life will be improved by using new greases and methods to reduce fret.
#4. Rotor.
The rotor is usually attached to the shaft of the motor and is placed between two bearings. The rotor is the moving part of the servo motor. With the given voltage, the rotor of the motor rotates in the required direction until the error is zero.
#5. Stator.
It is the stationary part of the servo motor. The function of the stator is to create a rotating magnetic field to generate torque efficiently. It is usually made up of 12 individually wrapped winding segments connected by a single copper wire.
#6. Brake.
Brakes are used to hold things when the machine is turned off or the E-stop is activated, it is made up of only a few parts. Keep in mind that the spring will let go when voltage is applied, so care should be taken when releasing the brakes as the motor will fall.
#7. Snap Ring.
Using a snap ring minimizes damage to the motor while maintaining the shaft position after a direct hit or nudge from an unwanted force. Without it, the shaft could easily slide back into the housing.
#8. O Ring.
An O-ring is placed between the two parts to form a seal to stop fluid from entering. O rings are made of plastic polymers and servo motors consist of multiple o-rings.
#9. Bearing Keeper.
A bearing keeper is a handheld plate located close to the pulley end that prevents the bearing from slipping out of place.
#10. Encoder.
An encoder is an electro-mechanical device used to transmit the speed and direction of a motor back to the drive. This allows the operator to observe and adjust certain parameters on demand. These are light in weight and are quite compact.
How Does a Servo Motor Work?
The basic working principle of a servo motor involves the controller receiving two types of input signals:
- A setpoint signal: This is an analog or digital signal that represents the desired position, speed, or torque of the output shaft.
- A feedback signal: This is an analog or digital signal that represents the actual position, speed, or torque of the output shaft measured by the sensor.
The controller compares these two signals and calculates an error signal that represents the difference between them.
The error signal is then processed by a control algorithm (such as PID) that generates a control signal that determines how much voltage or current should be applied to the motor.
The control signal is sent to a power amplifier (such as an H-bridge) that converts it into an appropriate voltage or current level for driving the motor.
The motor then rotates or moves according to the control signal and changes its position, speed, or torque, and sends a new feedback signal to the controller.
The process repeats until the error signal becomes zero or negligible, indicating that the output shaft has reached the desired setpoint.
Types of Servo Motors
#1. DC Servo Motor.
A DC servo motor consists of essential components like a DC motor, position sensor, gear assembly, and control circuit. This motor allows precise control of speed and position.
To set the desired output, a DC reference voltage is determined using a potentiometer, pulse converter, or timers. In digital control, microprocessors generate PWM pulses for accuracy.
Feedback, obtained through a potentiometer, guides an error amplifier, ensuring precise motor positioning. The amplifier compares current and desired positions, generating an error voltage that powers the motor until the error is zero, facilitating accurate rotation.
#2. AC Servo Motor.
AC servo motors are a specific type of servomotor that converts AC electricity into precise mechanical movements, focusing on accurate angular velocity. Essentially, these motors are two-phase induction motors, featuring specific design distinctions.
They produce mechanical power ranging from a few watts to several hundred watts, operating within a frequency range of 50 to 400 Hz. What sets them apart is their utilization of a closed-loop control system, employing encoders to monitor speed and position.
This feature makes these motors exceptionally adept at precision and control, distinguishing them from others lacking such an advanced feedback system.
#3. Linear Servo Motors.
A linear servo motor is a direct drive solution where the load is directly connected to the moving portion of the motor.
This means that it produces velocity and force based on the actual current and voltage to produce a linear movement along the required axis. For the most part, linear servos use a rack and pinion mechanism to change their output.
Since the linear model features a continuous rotation servo motor, it can move in any direction indefinitely. It will change the required speed, depending on the command signals received.
This happens when the motor offers a quick and accurate response because of the small armature inductive reactance.
#4. Rotary Servo Motors.
A rotary servo motor works by turning something in circles to function. This is different from the linear servo motor that uses a back-and-forth motion.
Rotary servo motors are primarily used in food and beverage processing equipment such as electric food mixers that work by moving in circles.
#5. Brushless Servo Motors.
A brushless servo motor has a permanent magnet shunt control motor that rotates a fixed armature. This armature current eliminates the issues surrounding connecting the current to the moving armature.
Essentially, an electronic controller replaces the brush assembly of a regular DC motor. In many instances, these servo motors are coupled with a type of encoder to activate the supply signal.
Since brushless servo motors are a specific subset of BLDC motors designed for applications that require precise position control as well as high speeds. Because the output is higher there’s much better torque speed and control. They are primarily used in CNC machinery.
#6. Analog Servo Motors.
For the most part, analog servo motors refer to the drives or amplifiers that are designed to operate an analog control circuit. Their control input is usually the conventional +/- 10 voltage signal speed or torque.
A common example of this type of servo motor is the cruise control function in a car. It measures servo motor speed and feeds the information back into a control circuit. This in turn adjusts the accelerator to maintain the chosen speed.
#7. Digital Servo Motors.
Digital servo motors use a small microprocessor to not only receive but also direct action at high-frequency voltage pulses. Typically, a digital servo sends almost six times the amount of pulses an analog signal does.
Faster pulses provide consistent torque which produces faster and smoother response times. It’s worth noting that digital servos are noisier than their analog counterparts.
How to Control a Servo Motor?
The control of a servo motor depends on the type of motor, the feedback mechanism, and the application requirements.
Generally, there are two types of control signals that can be used to control a servo motor: analog and digital.
- Analog control signals are continuous voltage or current signals that vary proportionally to the desired setpoint. They are typically used for simple or low-cost servo systems that do not require high accuracy or resolution. For example, a potentiometer can be used to generate an analog control signal for a hobby servo motor.
- Digital control signals are discrete pulses or bits that represent the desired setpoint in a coded form. They are typically used for complex or high-performance servo systems that require high accuracy, resolution, or communication. For example, a pulse-width modulation (PWM) signal can be used to generate a digital control signal for a brushless DC servo motor.
The controller of a servo motor can be either an external device or an integrated circuit within the motor.
The controller receives the control signals from an external source (such as a computer or a joystick), and the feedback signals from the sensor and generates the appropriate control signals for driving the motor.
The controller can also implement various control algorithms to optimize the performance of the servo motor. Some of the common control algorithms are:
- Proportional-integral-derivative (PID) control: This is a feedback-based control algorithm that adjusts the control signal based on the proportional, integral, and derivative terms of the error signal. It is widely used for servo systems that require a fast and accurate response.
- Fuzzy logic control: This is a rule-based control algorithm that adjusts the control signal based on fuzzy sets and linguistic variables. It is useful for servo systems that deal with uncertainty or nonlinearities.
- Adaptive control: This is a self-tuning control algorithm that adjusts the control parameters based on the changing conditions of the servo system. It is beneficial for servo systems that face disturbances or variations.
Advantages of Servo Motor
Servo motors offer substantial benefits across various industries due to their superior technology compared to traditional motors.
Below, we explore each advantage, illustrating how servo motors are often the best choice.
#1. High Efficiency.
Servo motors are designed to operate at high efficiencies, often reaching up to 90% under light load conditions. This efficiency is crucial in reducing energy consumption and operational costs, making servo motors a preferred choice in industries focusing on sustainability and cost-efficiency.
Compared to traditional motors, such as AC or DC motors, which may operate at lower efficiencies, especially under variable loads, servo motors maintain optimal performance, minimizing energy waste.
#2. High Output Power Relative to Their Size.
Despite their compact size, servo motors deliver a high power output, making them ideal for applications where space is at a premium but high performance is demanded.
This characteristic allows them to be used effectively in robotic arms and precision assembly machines, where large, bulky motors cannot be accommodated.
In contrast to stepper motors, which also offer compact size but typically lower power outputs, servo motors provide a better power-to-size ratio, enhancing the capability of compact systems.
#3. More Constant Torque at Higher Speed.
Servo motors excel in maintaining consistent torque at higher speeds, a significant advantage for applications requiring stable power through varying operational speeds.
They are capable of delivering 2-3 times more continuous power and 5-10 times more rated torque for short periods compared to many conventional motors.
This feature is particularly important in applications such as CNC machining and automated material handling, where precise torque control is necessary to maintain accuracy and prevent errors.
Unlike brushless motors, which may experience torque fluctuations under similar conditions, servo motors ensure a smoother operation and better performance consistency.
#4. Closed-loop Control.
Closed-loop control is a fundamental feature of servo motors, allowing for precise and accurate performance. This system uses feedback to constantly adjust the motor’s operation to meet the desired position, speed, or force requirements.
Unlike open-loop systems, such as those found in stepper motors, closed-loop control prevents error accumulation and ensures high accuracy and repeatability in operations.
This makes servo motors particularly effective in applications requiring precise motion control, such as in robotic arms and CNC machines.
#5. Quiet Operation.
One of the significant advantages of servo motors is their ability to operate quietly at high speeds. This quiet operation is essential in environments where noise reduction is critical, such as in laboratory or medical equipment.
Compared to other motors like AC induction motors, which can generate considerable noise under similar conditions, servo motors maintain a lower sound profile, enhancing the comfort and usability of the equipment they power.
#6. Short Period Management.
Servo motors excel in managing high-performance demands over short periods. They can quickly ramp up to high speeds and manage sudden stops with minimal wear and tear, thanks to their robust design and precise control features.
This ability is crucial in sectors like packaging, where machinery must often start and stop rapidly during operation.
While traditional motors may struggle with heat accumulation and mechanical stress under these conditions, servo motors handle these conditions with ease, ensuring longevity and reliability.
#7. Highly Reliable.
Servo motors are celebrated for their high reliability, which ensures minimal downtime and maintenance costs. This reliability stems from their sophisticated design, which includes durable materials and advanced engineering techniques.
The feedback mechanism integral to servo systems continuously monitors and adjusts the motor’s performance, reducing wear and tear and preventing common failures seen in less advanced motors.
This makes servo motors particularly valuable in critical applications like medical devices and aerospace technology, where failure can have severe consequences.
#8. High Ratio of Torque to Inertia.
The high ratio of torque to inertia in servo motors allows for extremely responsive and agile performance. This ratio is crucial for applications requiring rapid start and stop motions with high precision, such as in robotics and CNC machinery.
Servo motors can quickly reach desired speeds and precisely control movements, outperforming other motors like AC induction motors, which may struggle with lag and inertia in similar scenarios.
This capability ensures that servo motors provide consistent performance under varying load conditions, enhancing their utility in dynamic environments.
#9. High Acceleration.
Servo motors are capable of high acceleration rates, enabling them to reach high speeds in very short intervals. This feature is essential for sectors where speed and efficiency are paramount, such as in packaging and printing industries.
High acceleration allows for faster cycle times and increased productivity, significantly boosting throughput.
Unlike stepper motors, which may experience loss of torque at high speeds, servo motors maintain consistent torque levels throughout their operational range, ensuring stable and efficient performance.
#10. High-speed Performance.
Servo motors are renowned for their ability to operate at high speeds while maintaining precision and efficiency.
This high-speed performance is crucial in applications like packaging lines and assembly processes where the speed of operation directly correlates with productivity levels.
Unlike traditional motors, which may lag in response and struggle with speed consistency under varying load conditions, servo motors provide swift responses with minimal speed fluctuation.
This capability ensures that processes remain fast and consistent, reducing cycle times and increasing throughput.
#11. Torque Control.
Exceptional torque control is another significant advantage of servo motors. With advanced algorithms and feedback systems, servo motors can precisely control the amount of torque applied, adjusting dynamically to the task requirements.
This precise torque control is vital in applications requiring intricate manipulation of materials, such as in CNC machining or robotics, where precise movement and force are critical.
The ability to adjust torque on the fly differentiates servo motors from stepper motors and other less sophisticated systems that might provide less accuracy, leading to increased wear and potential errors in sensitive operations.
#12. Smooth Running.
The smooth operation of servo motors is essential for applications that require stability and precision. Servo motors are designed to operate without the vibrations and noise associated with many other motor types, such as DC or stepper motors.
This smooth running is particularly important in sectors such as medical device manufacturing and optical technology, where vibrations can compromise the quality of production or the accuracy of sensitive instruments.
By ensuring smooth operation, servo motors enhance the overall reliability and quality of the systems they power, contributing to longer machine life and reduced maintenance needs.
#13. High Accuracy.
The precision of servo motors is one of their most significant advantages, making them indispensable in fields where accuracy is paramount.
With advanced feedback systems that continuously adjust for positional accuracy, servo motors can achieve exceptional levels of precision.
This feature is crucial in applications such as CNC machining and robotics, where even the slightest deviation can lead to errors.
Unlike stepper motors, which can lose position without feedback, servo motors maintain accuracy through continuous monitoring and adjustment, ensuring operations are consistently precise and reliable.
#14. Small in Size.
One of the appealing features of servo motors is their compact size relative to their power output. This small footprint allows for greater flexibility in design and application, especially in space-constrained environments such as automated medical devices and compact assembly lines.
The compact size of servo motors does not compromise their performance, making them a preferred choice over larger, bulkier motors that require more space and often do not provide proportional power increases.
#15. Well Suited to Varying Load Applications.
Servo motors excel in applications that involve varying loads, adapting seamlessly to changes without losing performance. This adaptability is due to their sophisticated control systems, which adjust the motor’s power output to match the load requirements dynamically.
Whether the application involves lifting heavy loads or manipulating delicate components, servo motors maintain steady performance, unlike conventional motors that might struggle with fluctuation in load, potentially leading to wear and inefficiency.
This capability makes servo motors ideal for industries like packaging, where load conditions can change rapidly and frequently.
Disadvantages of Servo Motor
While servo motors are highly valued for their precision, efficiency, and versatility, they do possess certain limitations that may make other technologies more suitable in specific use cases. Understanding these limitations is crucial for selecting the right motor type for each application.
#1. High Cost.
For many, one of the primary disadvantages of servo motors is their cost. Servo systems, including motors and their required controllers and encoders, are generally more expensive than simpler systems like stepper motors.
This higher initial investment can be a significant barrier, especially for small businesses or applications where cost is a critical factor. In cases where precision and speed are not paramount, more cost-effective alternatives may be advisable.
#2. Complexity of Setup and Maintenance.
Servo motors require sophisticated control systems and precise feedback mechanisms, which can complicate their setup and maintenance.
The necessity for regular calibration and the potential need for specialized knowledge to troubleshoot and repair these systems can increase operational costs and downtime.
For simpler applications, this level of complexity might not be justified, making simpler motor systems more appealing due to their ease of use and maintenance.
#3. Sensitivity to Environmental Factors.
Servo motors are sensitive to environmental factors such as dust, vibrations, and heat, which can affect their performance and durability.
This sensitivity requires that servo motor systems be installed in well-controlled environments, potentially increasing the cost for suitable infrastructure.
In rugged or variable environments, more robust motor types, such as AC induction motors, might be preferable due to their ability to withstand harsh conditions without significant degradation.
#4. Application-Specific Suitability.
While servo motors excel in applications requiring high precision, speed, and torque, they may not be the best choice for all scenarios.
In applications where load requirements are consistently high and speed variation is minimal, other motor types, such as direct drive motors, may offer better efficiency and lower operational costs.
Additionally, for very high-speed, low-torque applications, other specialized motors might achieve better performance outcomes.
Applications of Servo Motors
#1. Robotics.
Servo motors are used in robot arms, legs, joints, fasteners, etc. to provide important instructions and force for the robot to perform tasks such as picking, placing, welding and assembly.
Servo motors plays a very important role in the field of robots. They are used in robotic arms, to perform tasks, such as picking and placing object, welding, painting, and even surgery. Good control ensures easy movement and high precision, which is very important in difficult tasks.
#2. Industrial Automation.
Servo motors are used to control the movement and position of various parts and equipment in production. Servo motors are in conveyors, feeders, loaders, unloaders, etc. to automate the system to deliver better quality and increase the productivity of manufacturing.
In industrial automation, servo motors drive robotic arms and other automated systems. These motors allow controlled movement required for operations such as assembly, welding and painting.
The precision and repeatability of servo motors increases the efficiency and quality of the production process.
#3. Printing And Scanning.
Servo motors are used in printing machines to managing the printing panel up and down for heat press the ink on the material.
Scanners and printers use servo motors to control the movement of the print head or scanner head. This precise control ensures that text and images are printed or printed accurately and maintains high resolution and clarity. Servo motors help ensure consistency in printing and printing output.
#4. CNC Machines.
Servo motors are used to control the axes of CNC machine tools. CNC Machine tools includes lathe, milling machine, etc. uses Servo Motors. CNC machines use Servo Motor to complete sensitive and difficult tasks such as: Cutting, drilling, engraving, etc.
Servo motors provide precisely control the position and speed of the tool used in CNC machine, which is essential for tasks such as milling, turning and 3D printing, where even small deviations can affect the quality of the product.
Servo motors make the same thing repeatable, which is important for the production of good products.
#5. Aerospace.
Devices used in spaces needs electronic controller, servo motors are used to provide angular controller for motion control and other required features as well.
In aviation, servo motors control the control functions of aircraft components such as flaps, ailerons, and rudders.
This precise control is required for stable and effective management. Servo motors on aircraft help position solar panels and antennas for proper operation and communication.
#6. Medical Devices.
Servo Motors are also used in the fields of health and care devices. Servo motors are used in various medical devices and equipments. Some of the major uses cases are in: surgical robots, scanners, pumps, ventilators, etc.
Servo motors are used to provide precise and controllable movement in medical equipment. For example, in robotic surgery, servo motors are used to perform delicate operations with high precision. Diagnostic equipment such as MRI or CT scanners use these to produce clear and precise images.
#7. Conveyor Belts.
Servo motors in conveyor systems provide the speed and position control necessary to ensure synchronized operation of production lines.
For example, on a packaging or sorting line, the product must move at a similar speed and be positioned correctly for the next process, such as labeling or routing.
#8. Camera and Surveillance Systems.
In surveillance systems, servo motors control the digital camera’s pan and tilt feature, allowing for accurate adjustments.
This option is essential for tracking gadget movement, covering large areas, and focusing the camera on specific points of interest.
#9. Antenna Positioning.
In communications, especially in satellite and radar systems, servo motors adjust the position of antennas to ensure the antennas are aligned to send and receive signals.
This precise control is necessary to manage the communication network, especially when tracking the movement of objects or paying attention to the environment.