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.
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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.
The following figure shows the construction of a standard servo motor.
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 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.
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:
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.
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:
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.
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.
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.
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.
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:
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:
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.
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.
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.
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:
Servo Motor advantages are:
The top Servo Motor disadvantages are:
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.
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.
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.
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?
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.
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.
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 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.
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.
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.
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.
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.
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.
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.
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 EtherNet IP Drives are available in models , , and and can be used on any system that supports EtherNet IP. The SERCOS Interface Models and 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 , 3 Single-Axis Component, and Kinetix 300 provide designers and builders with low-power and single-product flexibility.
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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 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'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 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.
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 W 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.
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 HP, as well as DC drives for heavy industries such as metal, mining, food and beverage, and others. With power ratings as high as kW, ABB's DC drives have the highest power-to-size ratio available. Microdrives are also available for low-power, stand-alone applications.
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.
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.
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.
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.
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.
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:
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.
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.
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:
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.
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:
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;
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.
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.
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.
Choosing the most appropriate type of coupling to use in servo applications can be confusing. This article examines the pros and cons of the various technologies.
Selecting a coupling for a servo application can be a complex process. It involves many different performance factors, including: torque, shaft misalignment, stiffness, rpm, space requirements, and others, that all must be satisfied for the coupling to work properly. Before selecting a coupling, it is helpful to know the specifics of these issues for the application for which the coupling is to be used. Many different types of servo couplings exist with their own individual strong and weak points. This article is designed to introduce end users to the different types of couplings available for servo applications. It also helps the user select the proper coupling for their application by highlighting the factors that should be considered in the decision making process and how they relate to the different product offerings available.
Check out our Servo Coupling Comparison Guide for a performance breakdown of every Ruland servo coupling.
Beam couplings are manufactured from a single piece of material, usually aluminum, and utilize a system of spiral cuts to accommodate misalignment and transmit torque. They generally have good performance characteristics and are an economical choice. For many applications, beam couplings are a good place to start. The single piece design allows the coupling to transmit torque with zero backlash and no maintenance required.
Two basic variations on this theme exist: a single beam style and a multiple beam style. The single beam style has one long continuous cut that usually consists of multiple complete rotations. This results in a coupling that is very flexible and yields light bearing loads. It is able to accommodate all types of misalignment, but works best with angular misalignment and axial motion. Parallel misalignment capabilities are reduced because the single beam is required to bend in two different directions at the same time, creating larger stresses in the coupling that could cause premature failure.
Although the long single beam allows the coupling to bend easily under misalignment conditions, it has the same affect on the rigidity of the coupling under torsional loads. The relatively large amount of windup under torsional loads adversely affects the accuracy of the coupling and reduces its overall performance.
Single beam couplings are an economical option that are best utilized in lower torque applications, especially in connections to
encoders
and other light instrumentation.
Multiple beam couplings, which usually consist of 2 or 3 overlapping beams, attack the problem of low torsional rigidity.
The use of multiple beams allows for the beams to be shorter without sacrificing much of the misalignment capabilities. The shorter beams make the coupling stiffer torsionally and overlapping them so the beams work in parallel increases the allowable maximum torque. This makes them suitable for use in light duty applications with connections such as a servo to a leadscrew. This increase in performance does not come without penalty: bearing loads are increased by a sizeable amount over the single beam variety but, in most cases, remain low enough to protect bearings effectively. Some manufacturers take the multiple beam concept to another level, also. Instead a single set of multiple cuts, two sets of multiple cuts are utilized. The use of multiple sets of cuts gives the coupling additional flexibility and misalignment capability.
It also adds a dimension to the misalignment capability of this type of coupling by more readily accepting parallel misalignment. In constrast to couplings with one beam or a single set of beams, under parallel misalignment, one set of beams bends in one direction and the second set bends in the other direction making the coupling more adaptable to this type of misalignment.
Most commonly, aluminum versions of these couplings are used. However, several manufacturers offer designs available in stainless steel also. The use of stainless steel, in addition to corrosion protection, also increases the torque capacity and stiffness of the coupling to sometimes double that of aluminum parts of the same design. The increase in torque and stiffness is off-set by a dramatic increase in mass and inertia.
Often times the negative affects will outweigh the positives and force the user to look for another type of coupling. In applications using smaller motors, a large percentage of the motor’s torque is used to overcome the inertia of the coupling, seriously reducing the performance of the system.
The oldham coupling is a three piece coupling comprised of two hubs and a center member . The center disk, which is usually made of a plastic or, less commonly, a metallic material, is the torque transmitting element. Torque transmission is accomplished by mating slots in the center disk, located on opposite sides of the disk and oriented 90 degrees apart, with drive tenons on the hubs. The slots of the disk fit on the tenons of the hub with a slight press fit. This press fit allows the coupling to operate with zero backlash.
Over time it should be noted that the sliding of the disk over the tenons will create wear to the point the coupling will cease to be zero backlash.The disks, however, are inexpensive items that are easily replaced and a new insert will restore the couplings original performance
In operation, the center element slides on the tenon of the hub to accommodate misalignment. Because the only resistance to misalignment is the frictional force between the hub and disk, oldham couplings have bearing loads that do not increase as misalignment increases. Unlike other types of couplings, there are not any bending members which act as springs, causing bearing loads to increase as the shafts become further misaligned.
However, these ratings can be surpassed at the expense of coupling life. The ability to choose different disk materials is an advantage of this type of coupling. Several manufacturers offer choices of material to meet application needs. Generally. one material is best used zero backlash, high torsional stiffness and torque are required, and another material for applications that have less precise positioning requirements, do not require zero backlash, and can benefit from a coupling that can absorb some vibration and reduce noise. Nonmetallic inserts are also electrically isolating and can act as a mechanical fuse. hen the plastic insert fails, it breaks cleanly and does not allow any transmission of power, preventing other damage from occurring to more expensive machinery components. The area this design is particularly well suited is handling relatively large amounts of parallel misalignment (from .025" to .100" or more depending on coupling size). Coupling manufacturers generally provide smaller misalignment ratings that allow users to obtain maximum life.
There are two general types of jaw couplings: the conventional straight jaw couplings and curved jaw zero backlash jaw couplings. Conventional straight jaw couplings are not typically well suited to servo applications accuracy of torque transmission is required.
Zero backlash jaw couplings are a variation on the same theme, but the differences in design make them well suited to servo applications.The curved jaws help to reduce deformation of the spider, limiting the effects of centrifugal forces during high speed operation.
Zero backlash jaw couplings consist of two metallic hubs and an elastomer insert , which is commonly referred to in the industry as a “spider".The spider is a multiple lobed insert that fits between the drive jaws on the coupling hubs with a jaw from each hub fitted alternately between the lobes of the spider. As in the oldham coupling, there is a press fit between the jaws and the spider that allow the coupling to remain zero backlash. In contrast to the oldham coupling, the torque disk is in shear under torsional loads, the jaw coupling’s spider operates in compression.
When using a zero backlash jaw coupling the user must be careful not to exceed the manufacturer’s rating for maximum torque with zero backlash which can be significantly below the physical limitations of the spider. If this occurs, the spider can be compressed so that there is no longer a preload and backlash will occur, possibly without the user noticing until a problem occurs.
Jaw couplings are well balanced and are able to handle high RPM applications very well ( manufacturers rate speeds up to 40,000 RPM ), but are not able to handle very large amounts of misalignment, especially axial motion. Large amounts of parallel and angular misalignment cause bearing loads that are higher than most other types of servo couplings. Another factor that the user must be aware of is the situation when a jaw coupling fails. If a spider fails, the coupling will not disengage. The jaws from the two hubs will mate similar to teeth on two gears and continue to transmit torque with metal to metal contact which, depending on the application, may be desirable, or could cause problems in the overall system the coupling is installed. An advantage of the jaw coupling is the ability to mix and match spiders based on the application. Manufacturers of zero backlash jaw couplings offer multiple materials with different hardnesses and temperature capabilities that allow the user to choose exactly the insert that meets the application’s performance criteria.
Disc couplings are comprised of, at a minimum, two hubs and a thin metallic or composite disc that is the torque transmitting element. The disc is fastened to the hubs usually with a tight fitting pin that does not allow any play or backlash between the disc and hubs. Some manufacturers offer disc couplings with two discs separated by a rigid center member and attached to a hub at each end.
The difference between the two variations is quite similar to the difference between the single beam style coupling and the multiple beam coupling consisting of two sets of cuts.The is not very adept at accommodating parallel misalignment due to the complex bending of the disc that would be required.The allows each disc to bend in opposite directions to harness the parallel off-set.
The properties of this type of coupling are similar to that of bellows couplings. In fact the way the couplings transmit torque in general is very similar. The discs are very thin, allowing them to bend easily under misalignment loading which allows the coupling to accept large amounts of misalignment (up to 5 degrees) with some of the lowest bearing loads available in a servo coupling. Torsionally, the discs are very stiff. The disc coupling has stiffness ratings slightly lower than that of bellows couplings. A downside to these couplings is that they are very delicate and prone to damage if misused or installed improperly. Special care must be taken to insure that the misalignment is within the ratings of the coupling for proper operation.
The bellows coupling is an assembly of two hubs and a thin walled metallic bellows. The assembly is created in most cases by either welding the hubs to the bellows or by using an adhesive of some variety. Although other materials can be and are used, the two most common materials for the bellows are stainless steel and nickel.
Nickel bellows are manufactured using an electrodeposition method. This method involves machining a solid mandrel in the shape of the finished bellows. The nickel is electrodeposited onto the mandrel and the mandrel is then chemically dissolved, leaving behind the finished bellows. This method allows the manufacturer to precisely control the wall thickness of the bellows and also allows for thinner walls than other methods of bellows forming. The thinner walls give the coupling greater sensitively and responsiveness making them ideally suited for extremely precise small instrumentation applications. However, the thinner wall also reduce the torque capacity of the bellows putting a limiton useful applications.
Stainless steel bellows are stronger than nickel versions and are usually manufactured with a process called hydroforming. A thin walled tube is placed into a machine and hydraulic pressure is used to form the convolutions of the bellows around specialized tooling. The characteristics of bellows make them an ideal method for transmitting torque in motion control applications. The uniform thin walls of the bellows allow it to bend easily under loads caused by the three basic types of misalignment between shafts (angular, parallel, axial motion). Generally bellows allow for up to 1-2 degrees of angular misalignment and .010" - .020" of parallel misalignment and axial motion.
The thin, uniform walls result in low bearing loads that remain constant at all points of rotation, without the damaging cyclical high and low loading points found in some other types of couplings. All of this is accomplished while remaining rigid under torsional loads. Torsional rigidity is a key factor in determining the accuracy of the coupling. The stiffer the coupling, the more accurately motion is translated from the motor to the driven component. In the area of servo couplings, bellows type couplings are some of the stiffest available, making them ideal in high performance applications that require a high degree of accuracy and repeatability. Some manufacturers offer bellows couplings with stainless steel hubs, which can be useful in applications corrosion resistance is important. The mass of stainless steel hubs does reduce some of the benefit of this type of coupling. The use of aluminum hubs with a bellows results in a coupling with very low inertia, a feature that is very important in today’s highly responsive systems. Some manufacturers of bellows coupling balance their couplings as a standard offering making them well suited for higher rpm applications (10,000 RPM ) as well.
As the name implies, rigid couplings are torsionally rigid couplings with virtually zero windup under torque loads, but they are also rigid under loads caused by misalignment. If any misalignment is present in the system the forces will cause the shafts, bearings or coupling to fail prematurely. This also means that the couplings cannot be run at extremely high rpm’s since they cannot compensate for any thermal changes in the shafts that can be caused by heat buildup from high speed use. This also means that the couplings cannot be run at extremely high rpm’s since they cannot compensate for any thermal changes in the shafts that can be caused by heat buildup from high speed use. However, in situations misalignment can be tightly controlled rigid couplings offer excellent performance characteristics in servo applications.
Although in the past many people wouldn’t consider using this type of coupling in a servo application, recently smaller sized rigid couplings, especially in aluminum, are increasingly being used in motion control applications due to their high torque capacity, stiffness, and zero backlash.
Choosing the proper servo coupling for an application is a critical part of total system design and greatly affects its overall performance capabilities. For this reason, considering the coupling early in the design process and aligning the coupling performance attributes with the functionality goals of the system can eliminate many problems that typically occur in motion control applications. Each of the couplings discussed have their own individual characteristics that make them ideal for many different uses. A single type of coupling, however, cannot be applied to every application in the field. This leads to the wide variety of couplings currently available and gives the design engineer the ability to select the best possible coupling to maximize system performance and durability
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