History of Servo Motors
Frequently Asked Questions
The steam engine governor is considered the first powered feedback system that used a gain value, so it is considered the firstservo mechanism. The word servo motors originated from the French phrase "Le Servomoteur" or the "slave motors". The first known record of its use was by JJL Farcot in 1868 to describe steam engines and hydraulics for use in steering a vessel.
What are Servo Motors
Anaheim Automation provides an extensive variety of customary and Servo Motors. Occasionally, OEM customers with mid to large quantity requirements prefer to have Servo Motors that are custom or modified to meet their accurate design requirements. Most of the time the customization is as effortless as shaft modification, brake, oil seal for an IP65 rating, mounting dimensions, wire colors, or label. Other times, a customer might require that Servo Motors meet an ideal requirement such as, speed, torque, and/or voltage. Engineers appreciate that Anaheim Automationís Servo Motors product line can answer their desire for creativity, flexibility and system efficiency. Buyers appreciate the simplicity of the "1-stop shop," and the price savings of custom Servo Motors design, while engineers are pleased with Anaheim Automation's dedicated involvement in their particular servo motor system.
Anaheim Automationís average Servo Motors products are a price -effective solution, in that they are known for their rugged construction and superior performance. A considerable size of its sales growth has resulted from dedicated engineering, friendly customer service and professional application assistance, often surpassing the customer's expectations for fulfilling their custom requirements. While a acceptional portion of Anaheim Automation's Servo Motors sales involves unique, custom, or private-labeling requirements, the company takes pride in its average stock base located in Anaheim, California, USA. To make customization of Servo Motors affordable, a minimum quantity and/or a Non-Recurring Engineering (NRE) fee is required. Contact the factory for details, should you require custom Servo Motors in your design.
All Sales for customized or modified Servo Motors are Non-Cancelable-Non-Returnable, and a NCNR Agreement should be signed by the customer, per each request. All Sales, including customized Servo Motors, are made pursuant to Anaheim Automationís average Terms and Conditions, and are in lieu of any other expressed or implied terms, including but not limited to any implied warranties.
Anaheim Automation's customers for the Servo Motors products are divergent: companies operating or designing automated machinery or processes that involve food, cosmetics or medical packaging, labeling or tamper-evident requirements, cut-to-length applications, assembly, conveyor, material handling, robotics, unique filming and projection effects, medical diagnostics, inspection and security apparatuses, pump flow control, metal fabrication (CNC machinery), and equipment upgrades. Numerous OEM customers request that we ďprivate-labelĒ the Servo Motors, so that their customers stay loyal to them for servicing, replacements and repairs.
Tech Tip - AC Motors Advantages and Disadvantages
The most customary and basic industrial motor is the 3-phase AC induction motor, sometimes shortened to AC Motor. Pertinent detailed information can be found about AC motors by checking the nameplate.
Advantages of Using AC Motors
• AC Motors are of a basic design
• The basic design AC motors: Simply stated, a series of 3 windings in the exterior stator section with a basic rotating section (rotor). The changing field caused by the 50 or 60 Hertz AC line voltage causes the AC motor rotor to rotate around the axis of the motor.
• The speed of AC motors will depend upon these 3 variables:
1. The fixed number of winding sets (poles) built into AC motors, which determines the motor's base speed.
2. The frequency of the AC line voltage. Variable speed drives change this frequency to change the speed of AC motors.
3. The amount of torque loading on AC motors, causes slipping.
• AC Motors are of a low cost construction
AC motors have the advantage of being the lowest cost motor. AC motors are perfect for applications requiring more than about 1/2 hp (325 watts) of power. This is due to the basic design of AC motors. For this reason, AC motors are commonly chosen for fixed-speed applications, such as in industrial applications and for commercial and domestic applications where AC line power can be easily attached. Over 90% of all motors are AC induction motors. They are found in air conditioners, washers, dryers, industrial machinery, fans, blowers, vacuum cleaners, and several other applications.
• AC Motors operate reliably
The basic design and construction of AC motors casue them to be intensely certain and are thought to be low maintenance. Unlike DC Brush Motors, there are no brushes to replace. If AC Motors are used in the applicable environment, protected by an enclosure, AC motors can expect to replace the bearings after several years of continuous operation. If the application is well designed in a guarding environment, AC motors may not require the bearings to be replaced for more than 10 years.
• Easily Found Replacements
The extensive use of AC motors in several contrasting industries has resulted in easily found replacements for existing equipment repairs and/or upgrades. Several manufacturers adhere to either European (metric) or American (NEMA) standards.
• AC Motors are made by several manufacturers , so it is relatively easy to obtain replacements (for basically the same motor)
• AC Motors are designed in a variety of mounting styles (dependent upon the motor manufacturer). Foot Mount, C-Face, Large Flange, Vertical and Specialty.
• There are several environmental styles available for AC Motors, to include a all-inclusive range of applications and industries, called Specialty AC Motors by most. Because of the all-inclusive range of environments in which people want to use AC motors, manufacturers have adapted by providing a all-inclusive range of packaging/enclosure designs, such as Open Drip Proof (ODP), Completely Enclosed/Fan-Cooled (TEFC), Completely Enclosed/Air-Over (TEAO), Completely Enclosed/Blower-Cooled (TEBC), Completely Enclosed/Non-Ventilated (TENV), and Completely Enclosed/Water-Cooled (TEWC) versions.
Disadvantages of Using AC Motors
• High-priced speed control - Speed controllers can be high-priced. The electronics required to handle an AC inverter driver are considerably more high-priced than those required to handle a DC motor. However, if performance requirements can be met ~meaning that the required speed range is over 1/3rd of base speed ~ AC inverters and AC motors are usually more cost-effective overall, than are DC motors and DC drives. This is especially valid for applications larger than 10 horsepower, because of cost savings in the AC motor.
• Inability to operate at low speeds - Standard AC motors should not be operated at speeds less than about 1/3rd of the base speed, due to thermal considerations. A DC motor should be thought to be for these applications.
• Exhaused positioning control - Positioning drivers and controllers can be high-priced and crude. Even a vector drive is exceptionally crude when controlling a standard AC motor. Stepper motors and Servo Motors are more applicable for applications wherein positioning and speed control is crucial.
Accessories of Servo Motors
Anaheim Automation provides several different accessories for our servo motors. These accessories include a brake, encoder, connector, cable and a handheld interface unit.
The brakes for our servo motors are a 24vdc system. The brakes used with the servo motors are adept for any holding applications. They are available on all of the servo motors Anaheim Automation has to offer, and are already attached to the rear of the servo motors. The brakes for the servo motors have a low voltage design for applications that are susceptible to delicate batter, brown out, or lengthy wiring runs. When electric power is adjusted to the brake of the servo motors the armature is pulled by the electromagnet force in the magnet body assembly, which overcomes the spring action. This allows the friction disc to rotate freely. When electrical power is interrupted, the electromagnetic force is removed and the pressure spring mechanically forces the armature plate to clamp the friction disc between itself and the pressure plate.
Anaheim Automation's servo motors are built with a 2500 counts per revolution quadrature encoder, with a resolution of 10,000 pulses per revolution.
Anaheim Automation's servo motors come with all the mandatory connectors to connect to another company's servo driver or an Anaheim Automation servo driver. These connectors for servo motors can additionally be purchased separately if they are lost. Please refer to the user's guide for a particular part number.
The cables for servo motors can be made with the supplied servo motor connector, or can be purchased from Anaheim Automation. The cable for use with servo motors comes with a regular length of 5M but can be adjusted to any length required.
Customizing Servo Motors
We offer a variety of options to customize servo motors. This list includes: brake, shaft, oil seal for an IP65 rating, mounting dimensions, torque, speed, and voltage. Please give us a call for any custom applications where servo motors may be used.
Feedback of Servo Motors
There are 2 options for feedback controls on Servo Motors. These options include either a servo resolver or a servo encoder. A servo resolver and a servo encoder provide the same solution in various applications, but are vastly different. They are both used to sense direction, sped, and position of the output shaft on servo motors.
The resolver on servo motors uses a secondary set of rotor and stator coils called the transformer to induce rotor voltages across an air gap. The resolver does not use any electronic components, accordingly it's very robust with a high temperature range, and is inherently shock resistance due to its design. A resolver is most often used in harsh environments.
The optical encoder on servo motors uses a rotating shutter to interrupt a beam of light across an air gap midway between a light source and a photodetector, over time the errosion associated with the rotating shutter reduces the longevity and reliability of the encoder.
The application will determine whether an encoder or a resolver is needed. Encoders are more accurate and are much easier to implement so they should be the first choice for nearly any application. The only reason to choose a resolver is if logenvity and enviroment requires it.
Types of Servo Motors
There are two major types of servo motors - Linear and Rotary.
Rotary Servo Motors
Rotary servo motors are what people think of when they think of servo motors. The three different types of rotary servo motors are: AC Servo Motors,Brushless DC Servo Motors, and Brush DC Servo Motors . The motion of rotary servo motors is often converted into linear motion by the use of a screw thread (leadscrew or ball screw), or with the use of pulleys and belts.
Rotary AC Servo Motors are an AC type motor that is used with a feedback mechanism. These are generally only used in smaller application because big AC Servo Motors are typically too inefficient when compared to its Brushless or DC counterparts.
Linear Servo Motors
Linear servo motors are flattened out servo motors where the rotor is on the inside, and the coils are on the outside of a flexable u-channel. Both types of servo motors are becoming more preffered as the prices for servo motors continue to come down.
Brushless Motors Encoder Feedback
For low-speed applications we recommend use of an encoder for the feedback rather than Hall sensors. The Hall sensor count per revolution can only be as great as a number of polls times the number of Hall Sensors. The brushless motor controller can use this higher count to its advantage when operating the brushless motors. With more counts per revolution at its disposal, the brushless motor controller can use this additional information to more precisely control the velocity of the brushless motors. The higher the resolution on the encoder to more finely the brushless motor controller can control the brushless motor. Even though the cost is much greater for encoders when compared to Hall sensors this fee can be justified as it can result in very precise control for a much lower cost than other technologies such as Servo motors were AC motors or synchronous motors.
Basics of Servo Motors
The elementary definition for servo motors is an automatic instrument that uses an error-correction routine to correct the motion of the servo motors. The general term servo can be applied to systems other than servo motors that use a feedback apparatus such as an encoder or other feedback instrument to control the motion parameters. Commonly when the term servo is used it applies to 'servo motors' but this term is also used as a general control term with the meaning of a feedback loop to position whatever the item is including servo motors.
Servo Motors are different from other controlled motors in that it is controlled by a time-based derivative ordinaryly referred to as the PID loop. Servo motors that are used to control position must be capable of changing the velocity of the output shaft because the time-based derivative, or the rate of change of position, is velocity.
Costs of Servo Motors
Servo Motors are thought to be one of the more costly motors when compared to AC, Brushless, DC, Stepper, and other motor types. The reason for the cost of Servo Motors is the precision required to make the servo motors and the costly components that go along with servo motors.
Generally speaking servo motors are intended to be a greatly accurate positioning or speed control device. The motion of servo motors should be smooth and greatly accurate. To accomplish these features, servo motors are manufactured under greatly snug control parameters. Along with the cost of the servo motors are the case, bearings, connectors, and feedback devices. The case is usually industrial grade, often sealed to achieve an IP65 rating or better. The bearings are high quality to make sure that the servo motors can run at the speeds aimed and can handle the appropriate axial and radial loads. The connectors are typically mil-style connectors that can be detached at the servo motors themselves, but are still greatly reliable and industrial grade. The Feedback devices are typically differential encoders and or resolvers. The devices are greatly costly and add cost to servo motors.
Servo Drivers Basics
Servo Drivers are electronic amplifiers which are used to power servo motors. The servo Drivers tracks the feedback signals from a servo motor and regularly adjusts for deviations in speed, position, and torque from its presumed behavior. There are two ways that servo Drivers attain their desired motion. First, a "PID" (Proportional, Integral, and derivative position loop) and a "PIV" (Proportional position loop, Integral and proportional Velocity loop) are used to detect and correct any inconsistencies on the servo Drivers speed, position, or torque. Second, "Feed forward control," used to track how well the actual motion follows commands on the servo Drivers. Servo Drivers incorporate both types of control to achieve the greatest performance.
Servo Drivers PID loop are made up of the proportional, the integral, and the derivative values. The proportional value tests for the reaction to the current error, the integral value determines the reaction according to the sum of recent errors, and the derivative value determines the reaction by the rate at which the error has been changing.
Servo Drivers Proportional gain - For a quicker response time, boost the servo Drivers proportional gain. Exceedingly large value of proportional gain leads to instability and oscillation.
Servo Drivers Integral gain - The bigger the servo Drivers integral gain value, the faster the steady state errors are eliminated, which also creates a larger overshoot.
Servo Drivers Derivative gain - The greater the value of the servo Drivers derivative gain reduces overshoot, but slows down transient response and can lead to instability due to signal noise amplification in the differentiation of error.
What is the efficiency of AC Servo Motors?
Usually the efficiency of AC Servo Motors is about 95%.
What is the difference between a servo motor and a regular motor?
"Servo" indicates that there is a feedback loop, which adjusts one (or more) operating parameters of the motor, such as velocity, position, motion, and/or torque. Servo motors are employed in closed-loop systems, where repetition and accuracy are important. "Regular" motors (those without feedback) are run in open-loop systems, where positional accuracy is not quite so important.
What are the differences between Step and Servo motors?
Step motors are permanant magnet motors that 'Step' one increment each time the computer gives its control electronics one pulse. These motors do not need position feed back (if run within their limits). When stopped they automatically hold their position. Servo motors are DC motors with an encoder feedback loop. The computer reads the position of the motor and controls the power that is applied to the motor. Servo's move faster point to point and are better at accelerating heavy machinery. They have more power at high speeds than a stepper motor, and can spin much faster, generally 3000-6000 rpm. A step motor has lots of low speed power, however it should not be run faster than 800 rpm since torque falls off quickly. A Servo system knows where the machine is while cutting, and knows whether the motor is under heavy load or an axis has jammed and will stop the machine. A stepper system does not have feedback and does not know whether or not it has jammed or lost position. In this aspect, a servo is more reliable. Step motors are just as accurate as Servo and, additionally, are simpler and maintance free in harsh and/or dusty applications. The Servo motor's encoder, however, is succeptable to dirt and vibration causing problems.
autonics online distributor