The Complete Servo Motor Guide

In this guide, you'll learn everything you need to know about servo motors. We're go over what servo motor is, the different types of servo motors, the advantages and disadvantages of servo motors, and how to pick the right servo motor for your application. We will also learn how servo motors work, and how to troubleshoot them.

Table of Contents

What is a Servo Motor?

A servo motor is a rotational or translational motor that receives power from a servo amplifier and creates torque or force for a mechanical system, such as an actuator or brake. 

Servo motors allow precise control of angular position, acceleration, and velocity. A closed-loop control system is employed with this type of motor. A closed-loop control system considers the current output and modifies it to achieve the desired condition. In these systems, the control action is based on the motor output. A positive feedback system controls the motion and final position of the shaft.

servo motor
Figure 1- Industrial Servo Motor

These motors are constructed for both constant and alternating currents. Since AC servo motors can withstand higher current surges, they are more commonly found in heavy industrial machinery. DC Servo Motors are best suited for smaller applications and have excellent control and feedback. The frequency of the applied voltage and the number of magnetic poles determine the speed of a servo motor.

Servo motors provide versatility in the manufacturing environment. Collaborative robotics, conveyor belts, automatic door openers, CNC turning, radar systems, tracking systems, and automation systems are all typical applications. It also requires a relatively sophisticated controller. The working principle of a servo motor and an electromagnetic motor is the same, except for differences in structure and function. A plastic gear is used in standard servo motors, whereas a metal gear is used in high-power servo motors.

Servo Motor Construction

The following figure shows the construction of a standard servo motor. 

Figure 2- Servo Motor Construction

The servo motor is made up of two windings: stator and rotor. The stator winding is wound on the motor's stationary part, and this winding is also known as the motor's field winding. The rotor winding is wound on the rotating part of the motor, also known as the motor's armature winding. The motor has two bearings on the front and back sides to allow the shaft to move freely. The encoder includes an approximate sensor for determining the motor's rotational speed and revolutions per minute.

Servo motors are widely used in precision control projects in industrial automation. Previously, those who heard of servo motors imagined them only being used in special projects requiring precise torque, speed, and position control. However, its cost has decreased recently, making it an excellent alternative to drives with induction motors and hydraulic and pneumatic actuators.

Hydraulic and pneumatic systems continue to be less expensive than servo motors.

Nonetheless, we can already see servos replacing these in several applications, primarily hydraulic applications that require precision. In these cases, servos are an excellent alternative because they do not have the issues of oil leakage or soil pollution and have the advantage of being more straightforward and precise in actuation than hydraulic actuators. 

Another distinguishing feature of servo motors is their small diameter and long rotor length, unlike conventional motors.

The error signal is generated by comparing the feedback signal to the input command position (desired motor position corresponding to a load) (if there is a difference between them). The error signal output by the error detector is insufficient to start the motor. As a result, the error detector feeds a servo amplifier, which raises the error signal's voltage and power level before rotating the motor shaft to the desired position.

Servo Motor Types

Servo motors are divided into AC (alternating current) and DC (direct current), based on the power supply required for operation.

DC servo motors are brushed permanent magnet motors commonly used in smaller projects due to their low cost, efficiency, and simplicity. AC servos are becoming more popular in the industry because they support applications that require more power while also providing high control accuracy and low maintenance.

Figure 3- Servo Motor Types

AC servos are classified into two types: synchronous and induction. We still have a third type used in smaller applications (the stepper motor). Below is a table that shows the power supported by each type, as well as the main advantages and disadvantages of each type of servo drive:

Table 1- Servo Motor Types' Characteristics

Direct Current Servo Motor

A DC servo motor is made up of a small direct current motor, a feedback potentiometer, a gearbox, and an electronic drive and control loop circuit. A DC servo motor is similar to a standard DC motor in that its stator is a cylindrical structure with a magnet attached to the inside of its frame.

Figure 4- DC Servo Motor

The rotor of a DC servo motor is made up of a brush and a shaft. The outer housing is attached to a commutator and a metal support frame that fits the rotor, and the armature winding is wound on the rotor's metal support frame.

A brush is constructed with an armature coil that supplies current to the commutator. An encoder is built into the rotor on the back of the shaft to detect rotational speed. Because torque is proportional to the amount of current flowing through the armature, designing a controller using simple circuits with this motor construction is easier.

Another feature of this servo motor is that the direction of the torque produced by the motor is determined by the instantaneous polarity of the control voltage. DC servo motors are classified as series motors, control shunt motors, series shunt motors, and permanent magnet shunt motors.

A DC reference voltage is set to the value corresponding to the desired output in the RC servo motor type. Depending on the control circuit, this voltage can be applied to the voltage converter via a potentiometer, a control pulse width (PWM) generator, or timers. Adjusting the potentiometer generates a corresponding voltage, which is then applied to the error amplifier's input. In digital control, a microprocessor or microcontroller generates the PWM pulses to produce more accurate control signals.

A position sensor is used to obtain the feedback signal corresponding to the current position of the load. This sensor is typically a potentiometer that generates a voltage proportional to the absolute angle of the motor shaft via the gear mechanism. The feedback voltage value is then applied to the error amplifier's input (comparator).

The error amplifier is a negative feedback amplifier that reduces the difference between its inputs. It compares the voltage related to the current motor position (as measured by the potentiometer) to the desired voltage related to the desired motor position (as measured by the pulse width to the voltage converter). It outputs the error as a positive or negative voltage.

This error voltage is applied to the armature of the motor. More power is applied to the motor armature when the error is more significant. The amplifier amplifies the error voltage and thus the armature energy as long as the error exists. The motor continues to rotate until the error reaches zero. If the error, on the other hand, is negative, the armature voltage reverses, and the armature rotates in the opposite direction.

Because of the small armature inductive reactance, this motor responds quickly and accurately to begin or end command signals. They are used in a variety of devices and numerically controlled machinery. Its structure is classified into four types:

Series servo motor

Figure 5- Series Servo Motor

The series servo motors have a high starting torque and draw a large current. This motor has very little speed regulation. Turnaround can be accomplished by flipping the field voltage polarity with a split series field winding.

Split series servo motor

Figure 6- Split Series Servo Motor

A split series motor can function as a field-controlled motor that is individually energized. The motor armature provides a constant current supply. This motor has a standard torque speed curve. This specifies a high stall torque and a rapid torque decline by amplifying in speed.

Shunt Control Motor

Figure 7- Shunt Control Servo Motor

The shunt control motor has field and armature windings. Field windings are on the machine's stator, whereas armature windings are on the rotor. The two windings are connected in parallel across the DC source in a DC shunt motor.

Permanent Magnet Shunt Motor

Figure 8-  Permanent Magnet Shunt Motor

It is a permanent excitation motor wherever a stable magnet supplies the field. The motor performance is identical to that of an armature-controlled permanent field motor.

Alternating Current Servo Motor

The squirrel cage induction motor is powered by a motor composed of shortened wire loops on a rotating armature. The voltage in the rotor is "induced" by electromagnetic induction. The main distinction between an induction servo motor and a standard induction motor is that the servo's cage rotor is made of thinner conductor bars, resulting in lower motor resistance.

They are strong, versatile, and capable of delivering significant power. However, they are more commonly found in larger applications due to poor performance at low powers. The synchronous AC servo motor, consisting of a stator and a rotor, is the industry's most common type of servo motor. The stator consists of a cylindrical structure and a core, and the induction coil is wound around the stator core with one end connected to a conductor wire that supplies current to the motor.

Because the rotor is made of a permanent magnet, the type of alternating current induction in the rotor does not affect the servo motor. An AC servo motor is also known as a brushless motor due to its structural characteristics. A schematic diagram of an AC two-phase induction servo motor system is shown in the figure below:

Figure 9- AC Servo Motor

The desired reference input is provided by a theta angle of a synchronous generator's rotor axis. In turn, the synchronous generator's rotor receives constant voltage and frequency. The synchronous generator's three stator terminals are then connected to the control circuit's transformer terminals. As a result, the desired position of the synchronous generator's rotor is transmitted to the control circuit.

Initially, there is a position difference between the generator shaft and the control transformer shaft, which we refer to as an error. The voltage across the control transformer reflects this error, which is amplified before reaching the servo motor phase control. Using the control voltage, the servomotor rotor rotates in the direction required for the error to become zero. This is the fundamental principle that ensures AC servomotor axis position.

PLCs and microprocessors are used in most modern servo drives to generate variable frequency and voltage to drive the motor. This control employs PWM and PID control techniques. A block diagram of an AC servo motor system with programmable logic controllers, position controllers, and servo controllers is shown below:

Figure 10- Typical Servo Motor Block Diagram

Alternating Current Servomotors are available in various sizes and categorized based on how they move.

Positional Rotation Servos feature a 180-degree variation in reference to the zero of its axis and constructive mechanisms (stop gears) that allow it to stop with movement precision.

As its name implies, a continuous rotation servo has no restrictions on the rotation's spatial range. The servo input, in this case, is directly linked to the output speed and direction, allowing the motor to rotate without limits of movement and in both clockwise and counterclockwise directions.

Furthermore, a rack and pinion mechanism allows the linear-type servo to control shaft rotation, translating rotational space variation into linear motion.

Controlling Servo Motors with PWM

Using a quadratic signal oscillation, the control technique known as pulse width modulation (PWM) tries to produce a variable signal. A better resolution signal message is determined by the widths of each pulse or the amount of time each pulse spends at each logic level (low and high). The servo motor's rotational direction and rate are then determined by this signal.

Due to the number of pulses delivered every cycle, the servos are split into Analog and Digital. 

Figure 11- PWM Controlling

Analog servos have PWM power signals while transmitting actions to the servo, causing the reaction time to be delayed when producing torque from inertia.

Digital servos, however, have embedded technology to transmit commands at high frequency per pulse, having about six times more pulses than an analog signal. This high frequency helps minimize motor reaction time and makes motor operation faster and smoother.

Figure 12- Analog VS Digital PWM Control

Applications of Servo Motors

The servo motor is small and efficient, but it has a serious application in some applications, such as precise position control. A pulse width modulator signal drives this motor. Servo motors are used primarily in computers, robotics, toys, CD/DVD players, and other electronic devices. These motors are widely used in applications where a specific task must be performed repeatedly and precisely.

While these cover many applications, there are many more, ranging from toys to complex computer systems. Because they are far more delicate and programmable than other motors, they are required in many industries and manufacturing processes.

The following are some of the most important applications of Servo Motors:

  • In robotics, the servo motor is utilized to initiate movements, giving the arm its exact angle.
  • Robotic cars employ servo motors to operate the wheels, generating enough torque to move the vehicle, start and stop it, and regulate its speed.
  • Conveyor belts that transfer the product through various stages are controlled dynamically by servo motors, which need to start and stop at precise moments. Take product labeling, bottling, and packaging as examples.
  • A servo motor is integrated into the camera to adjust the lens and enhance out-of-focus pictures.
  • Automatic door openers in public locations like supermarkets, hospitals, and theaters use servo motors to operate the door.
  • The servo motor is used in textile manufacturing to operate looms, knitting machines, and spinning and weaving machines.
  • In solar tracking systems, the servo motor is utilized to adjust the panel's tilt so that each solar panel continues to face the sun.
  • To offer precise motion control for milling machines, servo motors are employed in metal forming and cutting equipment.

Advantages Of Servo Motor

Servo Motor advantages are:

  1. It is a very efficient electromechanical energy converter.
  2. Compact  It can deliver more power for its weight and size than its rivals.
  3. Allows high torque and power variability.
  4. It reaches high speed, with fast acceleration and little sound noise.
  5. It has a rotational sensor (encoder) inherent to its construction, ensuring greater accuracy and a closed control loop.
  6. Speed– Servo motors offer high-speed rotation and more torque in a small package.
  7. Translates rotary or linear motion to a digital signal.
  8. Wide range of use for servo motors in a variety of applications.
  9. High durability, above expectations shelf-life, and keeps performance under work overload and high temperatures.

Disadvantages Of Servo Motor

The top Servo Motor disadvantages are:

  1. Servos Motors require tuning to stabilize the feedback loop.
  2. Servo Motor will become unpredictable when something breaks. So, safety circuits are required.
  3. Complex controller requires encoder and electronic support.
  4. Peak torque is limited to a 1% duty cycle. Servo Motors can be damaged by sustained overload.
  5. Gearboxes are often required to deliver power at higher speeds.
  6. Higher overall system cost and the installation cost of a Servo Motor system may be higher than that of a stepper motor due to the requirement for feedback components.

What Is The Difference Between Induction and Servo Motor?

Induction motors are open-loop systems, whereas servo motors are closed-loop systems. Induction motors have high inertia, whereas servo motors have very low inertia. As a result, servo motors are used in applications where instant and precise load positioning is required.

How to choose a Servo Drive vs. a VFD?

Servo Drives and VFDs are used in machines to drive motors and control motion.  They seem to do the same thing, so why choose a servo drive vs. a VFD?

VFDs are used with induction motors in applications that require velocity control. The ability to control velocity by varying the frequency of the voltage delivered to the motor distinguishes VFD systems. Another significant difference is that they do not use feedback on the motor, resulting in open-loop velocity control. This means that if there is a stall or if the load changes, VFDs will not compensate, resulting in less precise velocity control than servos. VFDs can be set to ramp up to a specific speed and then drive at that speed for extended periods.

Figure 13- SINAMICS VFD, From Siemens Automation

As with many engineering decisions, there are no hard and fast rules, and there are numerous examples of servo drives and VFDs having capabilities beyond their traditional roles. For example, technological advancements and the constant need to provide more features make it no longer difficult to find servo drives that can power induction motors - both with and without feedback. Similarly, numerous VFDs can power motors with feedback (an induction motor with feedback is commonly referred to as a Closed Loop Vector motor or CLV). As a result, some areas overlap the capabilities of servo drives and VFDs.

In most cases, the choice is obvious based on the application's needs, but it can become uncertain when both can do the job. We'll start with the simple situations and then go over what happens when both are appropriate.

When coordinated motion between multiple axes is required, servo drives are unquestionably the best option. Or when quick acceleration and deceleration are required, as with pick-and-place gantries. Or when exact sub-micrometer positioning is required for semiconductor applications or when precise velocity control is required to grow a silicon ingot.

When the velocity of a conveyor belt must be set to a specific speed, VFDs are the obvious choice. Alternatively, hydraulic pumps and air blowers can be used. Or in the case of some electric vehicles, where precise control is not required.

When both can do the job, the middle ground is reached. For example, in velocity mode and position mode applications, the precision would be considered a little loose for a servo but well within the capabilities of a VFD.

Conveyor systems are an excellent example. On the one hand, a simple conveyor application may only need to turn on in the morning and run at the same speed throughout the day. A variable frequency drive (VFD) would be an excellent choice. A servo system would be a better choice for a more demanding conveyor system that needed to start, stop, go forward, backward, match speed with another conveyor, and more.

There is a wide range of conveyor systems with varying requirements, some of which fall within the overlapping capabilities of both servos and VFDs. When there is no clear choice, the analysis boils down to performance, features, and price.

Performance and Features

When deciding on a system, consider the lower cost of a VFD system versus the superior features and performance of a servo drive system. Consider systems with the features you require or desire. What motion does the system need to perform, and what features will improve or make the final product more convenient?

Cost

After you've narrowed down your candidate pool based on performance, consider the costs. Servo systems are generally more expensive than VFD systems because the servo motor accounts for a large portion of the cost. Unlike induction motors, servo motors use permanent magnets, raising material and manufacturing costs. Furthermore, because they have more features, servo drives frequently cost more than VFDs. When you get to this point, it's a cost-performance tradeoff.

Efficiency

Because they cannot be plugged into a wall, many mobile applications rely on batteries for power. When batteries are used as a power source, efficiency becomes a top priority for system designers. This is because increasing efficiency allows machines to run for longer periods between charges, increasing system uptime.

Remember that servos employ permanent magnet motors, whereas VFDs employ induction motors. Permanent magnet motors are much more efficient than induction motors, so servo systems have a clear advantage when efficiency is required.

Size

Servo Drives are much smaller and more tightly integrated than VFDs. The size of the components becomes an important consideration for smaller mobile applications for two reasons. Smaller parts, for starters, make it easier for system designers to integrate the components into their designs. Second, smaller components weigh less, lowering the machine's overall weight.

Less weight means less mass to push around, which means better acceleration and longer battery life. As with efficiency, servo drives have a distinct advantage in terms of size compared to VFDs. A servo motor will be smaller than an induction motor for the same amount of power. The most recent servo designs have also been miniaturized and optimized for mobile applications. For these reasons, servos are the clear choice when smaller sizes are required. Because AC induction motors can be built much larger than servo motors, VFDs are the default choice for high-power systems.

Power

Power is essential for large machines. Servo systems are limited to a few hundred kilowatts, whereas induction systems can reach megawatts. As power requirements increase, servo systems eventually lose to induction motors and VFDs, though this transition occurs at a much higher power level than most applications require.

More Powerful and Compact

The most obvious advantage of synchronous motors over induction motors is their higher torque density. A servo motor of comparable physical size to an induction motor typically produces 40-60% more torque. This means that a servo motor must be smaller and lighter than its induction counterparts to achieve the required torque, speed, or power. As a result, a PM motor is ideal for applications with limited space and/or weight.

Servo motors, for example, excel in many robotics applications that require compact, lightweight motors with high power, accuracy, and speed. The exceptional power output that servo motors provide, especially given their size and weight, provides a significant advantage for robotics machine builders, resulting in more dependable, space-efficient solutions. This is also true for renewable energy applications such as wind power, where motor performance and efficiency are critical.

Low Inertia for High Dynamic Response

Because servo motors are smaller, they have less inertia than comparable induction motors. Because of its low inertia, the synchronous motor can accelerate and decelerate much faster to and from its rated speed. It also allows for much more precise acceleration and deceleration from full speed. Synchronous motors are thus ideal for highly dynamic or motion-control applications.

Regarding motion control, servo motors are ideal for packaging applications. These low-inertia motors provide precise, coordinated motion when combined with EtherCAT Motion Controls. From tracking to sorting and forming, this adaptable setup works well in almost any part of the packaging line.

Full Torque at Zero Speed

Another significant advantage of the PM motor is that it can indefinitely maintain full torque at zero speed. This is in stark contrast to most induction motors, which have limited low-speed torque and stability. VFD adjustments (e.g. Voltage Boost) can be made for low-speed operation, but this increases motor heating and limits performance. If a holding torque at zero speed is required, or if the application requires a low-speed operation, a servo motor (with feedback) is required.

Higher IP Rated Protection

In addition to benefits for motor control, servo motors frequently have advantages in their housing designs. Most servo synchronous motors do not require a cooling fan, allowing them to be IP65-rated. Induction motors, on the other hand, are typically rated IP44 or IP54. Therefore, if the motor operates in a harsh environment, a servo motor may be advantageous to avoid premature failure.

Figure 14- Servo Motor Design

Servo motors have a brushless design that makes them ideal for harsh environments and applications. This includes the food and beverage industries, where machines may be subjected to drastic temperature changes and washdowns. A servo motor can be useful in various industrial applications involving high pressure or temperature levels. 

Increasingly Economical

Finally, as servo motors have so many advantages over induction motors, you may be wondering why anyone would choose an induction motor. Traditionally, servo motors have been significantly more expensive than induction motors. While servo motors are still more expensive, the price difference is narrowing.

Synchronous motors with similar power specifications to induction motors are now available for only 10-20% more money. Previously, the servo motor could cost twice as much as the induction motor. This price disparity should continue to narrow as servo motors become more common.

Servo Drive Manufacturers in Industrial Automation

All variables encountered by service systems – torque, position, and velocity – are components of a complex motion control system that affects safety, efficiency, and equipment condition. As a result, having the proper servo system components is critical. Without the proper components, servo systems can overheat and shorten the motor's lifespan.

There are numerous OEM servo drive manufacturers worldwide. Many manufacture interchangeable components, while others design drives specifically for specific applications. Here are the top ten servo drive manufacturers in the industrial automation space.

Allen Bradley

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Figure 15- Allen Bradley Servo Hardware

Allen Bradley EtherNet IP Drives are available in models 5500, 5700, and 6500 and can be used on any system that supports EtherNet IP. The SERCOS Interface Models 6000 and 6200 are designed for low and high-power applications and are ideal for integration with their food-grade motors. Finally, for standalone and low-power applications, the Kinetix 5100, 3 Single-Axis Component, and Kinetix 300 provide designers and builders with low-power and single-product flexibility.

Siemens

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Figure 16- SINAMICS Drives Family

Siemens sells servo drives under the SINAMICS brand for a variety of low and medium-voltage DC drive applications. Siemens provides standard performance models ranging from the V20, which can produce up to 30kW, to the G150/150, which can produce up to 2700 kw. This standard performance line also includes two mid-range models, the G120 and G120C, with capacities of 250 and 125 kW, respectively.

Siemens also manufactures industry-specific drives, such as the G120X and G180, for complex systems requiring a wide range of communication and operating frames and special safety applications. Conveyance, processing, pumps, and compressors are examples of industrial applications.

They provide energy-efficient S120 and S120CM for low-voltage applications. They provide highly scalable and adaptable modularity that can be combined with various other components. They also offer a diverse set of communication protocols.

The modular S150 SINAMICS high performance drive can recover energy from the system and improve energy efficiency. This modular system is adaptable to larger control systems and a wide range of communication protocols. The SINAMICS DCM is compact yet delivers high power ratings when needed, for more straightforward, cost-effective, and high-performance needs.

Schneider Electric

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Figure 17- Schneider Lexium Easy 26

Schneider's Lexium family is divided into several groups based on power and functionality. The Lexium 32, 23 Plus, and 28 models are available in various single and three-phase drive configurations. The Lexium 32 has a maximum power rating of 11kW, while the Lexium 23 has a maximum power rating of 7.5kW, and the Lexium 28 has a maximum power rating of 4.5kW.

Schneider's PacDrive LMC controller family controls the Lexium 52 standalone drive. They have a high power density and are ideal for self-contained single axis applications. 

Industries requiring economical yet scalable automation can work in industry-specific environments with Schneider's stainless steel motor line.

The Lexium 62 is a modular multi-axis drive that takes up half the cabinet space of comparable models. This saves money on cabling and mounting. The 62 is compatible with PacDrive controllers and is available in safe versions that allow management via the SERCOS interface.

Omron

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Figure 18- Omron Servo Drive Family

Omron servo drives are available in EtherCat, ML-II, and Analog/Pulse versions. All models include an encoder and offer advanced tuning options via vibration, anti-torque, and disturbance algorithms. All models have advanced functions such as load inertia detection, dynamic braking and regeneration, and over-travel protection.

Emerson/GE

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Figure 19- PACMotion Servo Family

All of Emerson's PACMotion servo drives are plug-and-play compatible with servo motors. PACMotion servo drives have a low profile and are compact. They all use EtherCat controllers but can be used with third-party components. Each drive has closed-loop control over speed, torque, and position.

Emerson PACMotion servo drives are available in eight models ranging from 1100W to 16,000W. There are four models, each with a 120/240V AC and a 240/480V AC rating. Multiple drives with up to 50 coordinated control axes can be added to the system to scale for more extensive system builds, and all come standard with Safe Torque Off. 

ABB

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Figure 20- ABB Servo Motors and Drives

Depending on the application, ABB offers a wide range of drive sizes, frames, and power ratings. They manufacture low-voltage AC drives for systems with capacities of up to 7500 HP, as well as DC drives for heavy industries such as metal, mining, food and beverage, and others. With power ratings as high as 24000 kW, ABB's DC drives have the highest power-to-size ratio available. Microdrives are also available for low-power, stand-alone applications.

Mitsubishi Electric

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Figure 21- MItsubishi Servo Motors and Drive

The Mitsubishi MELSERVO line has fewer options compared to other manufacturers.  To keep system components in sync and in real-time, all offer EtherNet-based optical communication. It provides the MR-J4-GF Family for small applications, the MR-J4XX-B Family for 2 and 3-axis applications, and the MR-J4-A Family for general-purpose applications.

Servo Motor Troubleshooting

Any piece of hardware or equipment will eventually develop problems, but the more common ones are usually manageable if you know how to deal with them. Some of the more common issues will occur regardless of maintenance or upkeep and may even result in a motor failure during an operation. Before you start disassembling the servo to inspect the components, check to see if there's a quick fix. Next, we’ll cover a quick rundown of issues you might face and what they can do about them.

Overheating

Most servos are susceptible to heat, especially when running for extended periods. While maintenance crews report a higher call volume for overheating during the summer months, it can occur at any time.

Servos can overheat for various reasons, including rising indoor and outdoor temperatures, extended operating times, inadequate ventilation, or even the state of your company's equipment. As their internals wear out, older machines overheat more frequently.

Overheating servos is never good because high temperatures can damage your equipment and even destroy other parts of your connected system. Of course, any good servo will have a failsafe and shut down if the temperature exceeds a dangerous level. That doesn't It changes the fact that it can cause significant damage to company equipment and waste a substantial amount of time for your team.

Ensure your plant is climate-controlled and the temperature is as stable as possible. You don't have to keep it cold inside your plant, but you want to keep temperatures from rising too high.

Additionally, never try to cool the servo while it is running by opening the cabinet door or placing a fan nearby. This strategy will only put additional strain on the system. Excess dust and dirt can and will get inside, causing damage to the components.

If the overheating equipment is old, have it serviced and ensure all major components are in good working order. When dealing with an older motor, you may need to replace a few — or several — parts.

Finally, always turn off an overheating system and allow it to cool down for a reasonable amount of time. If this occurs regularly, and the equipment is idle more than it is operational, you may want to consider replacing it.

Servo Motor Won’t Turn

Now and then, you might notice that your motor isn't moving. This discovery may appear bad news because a servo motor has so many components making it difficult to pinpoint the exact problem. That is not the case if you know this quick tip.

Simply look at the controller's Digital-Analog-Converter output. If you find a DAC parameter value of zero or close to it, this is why the drive is not moving. There is a problem with the controller, and you may need to replace it. If that number is greater, the controller is functioning properly, and you can proceed.

If the drive causes the problem, you should be able to run a self-test. This test causes the motor to run at a low efficiency so you can see if it's working properly. If nothing happens, you'll know the issue is with the drive.

Servo Making Abnormal Noises

It is natural for a servo motor to make a small amount of noise. During normal operation, the most common noise produced by a servo drive or motor is humming. However, it should never be so loud that it becomes obnoxious. If the servo makes unusual noises, the issue is likely incorrect wiring or electrical problems. Check that the servo is properly grounded and receiving the appropriate power. Ensure the servo is turned off before working on the electrical circuits.

Servo Motor Producing Reduced Torque

The amount of muscle, energy, or power required to rotate and move a mechanism is referred to as torque. It is caused by three primary sources: friction, external forces such as fighting gravity, and accelerating the inertia of a mechanism. Motors have a limited It has a certain amount of torque by design, so if you choose the wrong one, it may not be able to handle the workload your team requires. You may also experience a servo motor malfunction, which stops producing enough torque. Some of the most popular servos are 4.8v to 6.0v, or 130.5 oz-in and 152.8 oz-in, respectively.

Aside from the motor's lack of power, here are some other things to consider:

  • The servo amplifier rating.
  • The servo’s workload limits.
  • Low voltage or voltage drops within the system.
  • Bad capacitors.
  • Inadequate or improper connections.

Servo Smells Bad or Produces Smoke

If your servo emits a strong odor, it is most likely reminiscent of something burning. If you notice this or see any kind of smoke, it means your system is overheating.

Examine the cooling system or airflow to ensure that it is not obstructed in any way. If your servo is already exposed, make sure no dirt or dust particles have made their way inside. If neither of these steps solves the problem, check to see if the bearings are in good working order. They can have a variety of problems, including excessive lubrication, worn bearings, and overheating. You may also smell ozone, which indicates that windings or wiring are on fire. If this is the case, you must ensure that the wires are contactless and that the system is properly grounded.

Servo Motor Stops Upon Reaching High Speed Ranges

Analyzing the exact issue is highly challenging due to the multiplicity of factors that may cause motor stalling under high speed demands. The servo motor should be examined for any abnormalities in operation as well as any physical component malfunctions, such as quick overheating, weak bearings, faulty capacitors, velocity sensor issues, poorly maintained wiring, or noisy readings. Additionally, some subsystems provide undesirable results, such as issues with the overload protection system, voltage fluctuations, insufficient motor specifications, and improper control design. 

Servo Motor Repair 

It is recommended to get in touch with the particular vendor or technical support for the drive based on the preliminary analysis. On the other hand, once you've located the problem, you can continue  making the fixes. Make sure you have the proper testing equipment and meters before doing any repairs. It should be noted that because this technology is more complicated, it won't be offered in standard retail stores.

Before turning the device on, check the electronics of the servo drive for broken or burnt components (MOSFETs, inputs, outputs, IGBT relays, feedback circuits, power supplies, and capacitors).

Once the machine or main breaker has been turned on, check the LED or readout display. Make sure the screen is powered on if there is one and it does not illuminate. If the alarm goes off before any other lights come on, the servo drive is probably at fault. If the drive begins to function before the alert rings, you can rule it out. 

Check the servo drive and motor for any damaged, missing, or deformed components. Check the cable or motor plugs. These parts may require replacement if you spot any anomalies. Check the diagnostic or lead meters to see whether the motor axis has any excessive friction. 

Even though friction is a rare concern, it can and frequently does happen when there is not enough lubrication. Examine the airflow system or the coolant in the motor box. Examine all wires, clean or remove any debris, and dry out any plugs. Examine the axis for binding and the condition of the DC motor's brushes. Use a voltmeter to check for an incoming power source. The servo drive should be tested first to make sure the voltage is correct.

Some of the important questions you should ask yourself after the initial analysis are:

  • Is there an alarm, does the servo motor have problems feeding or moving swiftly, or does it emit a loud hum? There might be a catch.
  • Does it make a loud growl or other sound when moving quickly? The bearings could be broken.
  • Does the motor sluggishly stop or stop all at once? It's possible that you have an electrical issue. Make sure that neither the electrical box nor one of the axes has received any coolant.

After completing a repair or replacement of parts, you should test the servo motor before resuming normal operation. This can be accomplished by plugging it into a universal tester, which will provide feedback, phases, rotation, speeds, and direction under load. Also, don't put it through a lot of work right away. Start slowly to ensure everything is in working order before resuming operation.

Servo Motor Hardware Overview

Industrial servo motor control systems are composed by a group of devices responsible for actuating the servomotor under the project specifications in order to attend the process needs. The system is often segmented on the following device modules:

Figure 23- Siemens’ Controllers; S120 (left) and PLC S7-1500 (right)

Control System: the control system is responsible for reading the plant status and executing automation algorithms that will provide the necessary instructions for the servo system to execute. PLCs and CU (Control Units) are the brains of the operation; it is where bits and bytes will tell the hardware what to do;

Power System: Since we are dealing with the most diverse power specifications when it comes to industrial motors, Power Systems are responsible for treating the Power into the project specifications in all aspects, from power filtering, power isolations, power AC-DC/DC-DC/DC-AC conversion and finally delivering the final power specification directly to the motor. Reactors, Line Filters and Motor Modules make up the power group;

Figure 24- SINAMICS Power System

Motor and Data Exchange: Once the control system has run the control algorithms and the power has been transformed into the necessary specifications, this energy will now be converted in a physical actuation of the motor axis. The motor, in some advanced control systems, does not even need to be, necessarily, servo motors. Many servo controllers also support common induction motors + encoders as the mechanical output of the system. However, of course, the convenient equipment (servo or induction motor) should be specified according to the proper application needs. Some industrial servomotors, from Siemens automation for example, also have integrated data exchange protocols (DriveCliq, in Siemens) with the control system. This defines a system that is simpler to maintain, operate and develop.

Figure 25- Siemens’ Servo Motor and Drive

Commissioning a Sinamics Servo Drive from Siemens Automation

Now that we have learned plenty about servo motors, it’s time to see how the Servo Motor actually works in a practical way, by commissioning a Sinamics servo motor.

Sinamics Starter is the leading software from SIEMENS Automation for driver and servo driver configuration, parametrization, and control development. The proper commissioning of drivers is vital in ensuring secure and error-free operation of process control and machine operations. 

Conclusion

Servo motor systems are a widely used approach to mechanical interventions in machines and processes throughout Industrial Automation. Properly specifying, installing, commissioning, programming, implementing, and maintaining these systems is not an easy task, though. Many aspects should be taken into consideration in these steps, but they will most certainly reward those who own this kind of expertise with high efficiency and accuracy among the most varied automation tasks.

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