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          Servo motor

1. Servo motor definition 

    Also known as the implementation of the motor servo motor, the automatic control system for the implementation of components to convert signals received from the motor shaft angular displacement or angular velocity output.DC and AC servo motor is divided into two categories, the main feature is that when the signal voltage is zero, no rotation of the phenomenon, the increasing speed with uniform torque decreased.Servo motors to control mechanical servo system in the operation of the engine components. Is a servomotors device.Servo motor can control the speed, position accuracy is very accurate.The voltage signal into a torque and speed to drive the control object.Rotor speed by the input signal control, and can respond rapidly, in the automatic control system for the implementation of components, and has electrical and mechanical time constant, linear and high initiating voltage low.

2. Servo motor works 

   1. Servo mainly rely on impulse to locate, basically can be understood, the servo motor receives a pulse, a pulse will rotate the corresponding point of view, in order to achieve the displacement, because the servo motor itself has issued a pulse function, so the servoEach motor to rotate a point of view, is issued by the corresponding number of pulses, so that the pulse and servo motors to accept the formation of the echo, or called closed-loop, this way, the system will know the number of pulses sent to the servo motor, while the number of receivedpulse came back, so that we can very accurately control the motor rotation, in order to achieve accurate positioning, can reach 0.001mm.DC servo motor into brush and brushless motors.Brush motor low cost, simple structure, starting torque, wide speed range, easy control, need to maintain, but easy to maintain (replacement carbon brushes), generate electromagnetic interference, the environment requirements.So it can be used for cost-sensitive general industrial and civil applications.Brushless motor, small size, light weight, large output, fast response, high speed, small inertia, rotational smoothness, torque and stability.Control complex, easy to implement intelligent, flexible way of their electronic commutation, the commutation can be square wave or sinusoidal commutation.Motor maintenance-free, high efficiency, low operating temperature, electromagnetic radiation is very small, long-life, can be used for a variety of environments.
   2. Brushless AC servo motor is divided into synchronous and asynchronous motors, motion control in the current synchronous motor is generally used, and its power range, can do a lot of power.Large inertia, the maximum rotation speed is low, and with the power increases rapidly decreased.Thus suitable for applications that run on low speed steady.
   3. Servo motor rotor is permanent magnet, the drive control of the U / V / W three-phase power to form fields, the rotor in the magnetic field under the rotation, while the motor comes with encoder feedback signal to the drive, the drive according to the feedback valuecompared with the target value, adjusting the angle of the rotor rotation.Depends on the accuracy of the servo motor encoder accuracy (lines).

Question: AC servo motors and brushless DC servo motor function, what is the difference? A: AC servo better because a sine wave control, torque ripple small.DC servo is a trapezoidal wave.But the DC servo is relatively simple, cheap. 3. Introduction permanent magnet AC servo motor 

   80 years since the 20th century, with the integrated circuits, power electronics and AC variable speed drive technology, permanent magnet AC servo drive technology with outstanding development, national electrical manufacturers have launched their own well-known AC servo motor and servo drive seriesand continue to improve and update products.AC servo system has become a contemporary high-performance servo systems the main development direction, so that the original DC servo facing the crisis of being eliminated.90 years later, the world has been commercialized by AC servo digital control system is a sine wave motor servo drive.AC servo drive the rapid development of the field in the transmission.Permanent magnet AC servo motor compared with DC servo motor, the main advantages are: ⑴ without brush and commutator, it is reliable and maintenance requirements for maintenance and low.⑵ cooling the stator winding more convenient.⑶ inertia is small, easy-to improve the system fast.⑷ adapted to high-speed high torque working condition.⑸ under the same power, smaller size and weight.Since the German MANNESMANN of Rexroth Indramat division in the company's Hanover Trade Fair 1978 was officially launched MAC permanent magnet AC servo motor and drive system, which marks this new generation of AC servo technology has entered the practical stage.To the late 20th century, 80 years, the company has a complete line of products.The servo-device market are turning to the exchange system.Early analog systems such as zero-drift, interference, reliability, accuracy and flexibility in areas such as lack of motion control is still not fully meet the requirements, in recent years with the microprocessor, the new digital signal processor (DSP) applicationsthe emergence of digital control system, the control section can be carried out entirely by the software, called Jiang hazy or Tuan Shen Jing only fresh coarse hempen fabric, valiant only Shen of the permanent magnet AC servo system.So far, high-performance servo systems mostly use electrical permanent magnet synchronous AC servo motor, control the drive to use more fast, accurate positioning of the all-digital servo system.Typical manufacturers such as Siemens of Germany, the United States and Japan Kollmorgen companies such as Panasonic and Yaskawa.Yaskawa Electric has launched a small-scale production of AC servo motors and drives, in which D series for CNC machine tools (maximum speed of 1000r/min, torque is 0.25 ~ 2.8Nm), R series is suitable for the robot (the highest speed of 3000r/min, torque is 0.016 ~ 0.16Nm).Launched after the M, F, S, H, C, G six series.90 20th century, has introduced a new D-series and R series.Rectangular wave drive from the old series, 8051 to control the sine wave drive, 80C, 154CPU and gate array chip control, torque ripple from 24% to 7%, and improved reliability.Thus, the formation of only a few years, eight series (power range of 0.05 ~ 6kW) more complete system to meet the working machinery, transportation agencies, welding robots, assembly robots, electronic components, processing machinery, printing presses, high speed winding machine, winding machines for different needs.CNC equipment to produce the famous Japanese law that g (Fanuc) company, in the 20th century has introduced the mid-80s S series (13 specifications), and L series (5 specifications) of the permanent magnet AC servo motor.L Series has a smaller moment of inertia and the mechanical time constant, particularly for applications that require fast response servo system.Other Japanese manufacturers, such as: Mitsubishi Motors (HC-KFS, HC-MFS, HC-SFS, HC-RFS and HC-UFS series), Toshiba Seiki (SM series), Okuma Iron Works (BL series), Sanyo Electric(BL series), standing stones motor (S series) and many other manufacturers have entered the permanent magnet AC servo system fray.Germany Rexroth (Rexroth) The MAC Indramat Division Series AC servo motor Total 7 Frame 92 specifications.Germany's Siemens (Siemens)'s IFT5 series three-phase permanent magnet AC servo motor standard and short form is divided into two categories, a total of 98 species of 8 frame size specifications.Allegedly the same series AC servo motor and DC servo motor output torque compared IHU series, which weighs only 1 / 2, supporting the transistor PWM drive 6SC61 series, the most for 6-axis motor control.Bosch (BOSCH) ferrite magnets produced the SD series (17 standard) and rare earth permanent magnet of the SE series (8 specs) AC servo motor and drive controller Servodyn SM series.American production companies Gettys servo device as Gould Electronics, once a division of (Motion Control Division), production of M600 series A600 series AC servo motor and servo drives.After the merger to the AEG, Gettys name restored, the introduction of A700 all-digital AC servo system.U.S. AB (ALLEN-BRADLEY) 1326-based production company driver division ferrite permanent magnet AC servo motor and servo controller PWM AC 1391.Frame size motors including 3 of 30 specifications.ID (Industrial Drives) is a famous Cole Morgan (Kollmorgen) of industrial drives division, has produced BR-210, BR-310, BR-510 a total of 41 specifications of the three series of brushless servo motor and servo BDS3drive.Since 1989, launched a new series designed solely doped Jian Pirates (Goldline) permanent magnet AC servo motor, including the B (small inertia), M (Middle Inertia) and EB (explosion proof) three categories, 10,20,40,60,80 five frame sizes, each of 42 categories of specifications, all using NdFeB permanent magnet, torque range of 0.84 ~ 111.2Nm, a power range of 0.54 ~ 15.7kW.Supporting the drive has BDS4 (analog), BDS5 (digital type, with position control) and the Smart Drive (digital type) of three series, the maximum continuous current of 55A.Goldline Series represents contemporary art in permanent magnet AC servo technology.Ireland's Inland formerly a division of Kollmorgen abroad, now merged into the AEG, the production of DC servo motors, DC torque motor and servo amplifier is known.Production BHT1100, 2200,3300 three frame sizes of 17 kinds of specifications of SmCo permanent magnet AC servo motor and eight controllers.French Alsthom Group factory in Paris Parvex LC series (long form) and GC series (short) 14 AC servo motor specifications, and production AXODYN series of drives.The former Soviet Union for the CNC machine tools and robots servo control developed two series of AC servo motor.One ДBy series uses ferrite magnets, there are two frame sizes, frame sizes are 3 for each core length, each with two winding data, a total of 12 specifications, a continuous torque range of 7 ~ 35N.m.2ДBy series uses rare earth permanent magnet, 6 frame size 17 specifications, the torque range is 0.1 ~ 170N.m, supporting the 3ДБ controller.In recent years, Panasonic has introduced the all-digital AC servo system based MINAS series, in which permanent magnet AC servo motor with MSMA series of small inertia-type, power from 0.03 ~ 5kW, a total of 18 kinds of specifications; the inertia type with MDMA, MGMA, MFMA threeseries, the power from 0.75 ~ 4.5kW, 23 kinds of specifications, MHMA series of large inertia motor power range from 0.5 ~ 5kW, 7 kinds of specifications.Samsung developed in recent years, all-digital AC servo motor and drive system, which FAGA AC servo motor series of CSM, CSMG, CSMZ, CSMD, CSMF, CSMS, CSMH, CSMN, CSMX a variety of models, the power from 15W ~ 5kW.Now often used (Powerrate) This comprehensive index as the servo motor quality factor, measuring a variety of AC and DC servo motor contrast and dynamic response performance stepper motor.Continuous motor power, said the rate of change (rated) torque and rotor inertia ratio.Change rate is calculated by power analysis, the permanent magnet AC servo motor technology indicators for the United States ID, Goldline Series is the best, followed by Germany's Siemens in IFT5 series. 
                   




                      Principle of the servo motor

1. AC servo motor 

    AC servo motor stator phase structure is essentially single-phase capacitor induction motor similar. The stator is equipped with 90 ° difference between the two locations each winding, one field winding Rf, it is always connected to the AC voltage Uf; anotheris the control winding L, link control signal voltage Uc.Therefore, the two AC servo motor servo motors, also known as.AC servo motors are usually made of squirrel-cage rotor, but in order to make the servo motor has a wide speed range, the mechanical properties of the linear, no "rotation" phenomenon and the rapid response of the performance, it is compared with ordinary motor should bewith the rotor resistance and a small moment of inertia of these two characteristics.Rotor structure is currently used more often in two forms: one is the use of high resistivity conductive material made of high resistivity conducting bar of squirrel cage rotor, in order to reduce the rotational inertia of the rotor, rotor do slender; otherOne is made of aluminum alloy hollow cup-shaped rotor, Beibi thin, only 0.2-0.3mm, in order to reduce the reluctance of magnetic circuit, to be placed inside the hollow cup-shaped rotor fixed stator. hollow cupRotor moment of inertia is small, responsive, and smooth operation, so it is widely used.AC servo motor in the absence of control voltage, the stator field windings, only the magnetic field pulse generated by the rotor stationary.When a control voltage, the stator generates a rotating magnetic field, rotating magnetic field along the direction of the rotor rotation, in the case of constant load, the motor speed with the size of the control voltage changes, when the control voltage of the opposite phase, the servo motorwill be reversed.The working principle of AC servo motor with split phase single phase induction motor although similar, but the former is much greater than the latter of rotor resistance, so the induction motor servo motor, compared with stand-alone, there are three significant features: 1, high starting torqueAs a large rotor resistance, the torque curve shown in Figure 3, curve 1, with ordinary asynchronous motor torque curve than 2, a marked difference.It will enable the critical slip S0> 1, so that not only the torque characteristics (mechanical properties) is closer to linear, and has a larger starting torque.Therefore, when one has control of stator voltage, rotor turning once, that has a quick start, high sensitivity.2, 3, wide operating range, no rotation of the phenomenon, the normal operation of the servo motor, as long as the loss of control voltage, the motor stop running.When the voltage of the servo motor control is lost, it is running single-phase, due to a large rotor resistance, stator rotating in the opposite direction of the role of rotating magnetic field generated by the rotor torque characteristics of the two (T1-S1, T2-S2 curves) and the synthesis of torque characteristics (T-S curve) AC servo motor output power is generally 0.1-100W.When the power frequency is 50Hz, voltage 36V, 110V, 220,380 V; when the power frequency is 400Hz, voltage 20V, 26V, 36V, 115V and other.AC servo motor to run smoothly, low noise.However, non-linear control characteristics, and because a large rotor resistance, loss, low efficiency, and is therefore compared with the capacity of DC servo motor, bulky, heavy weight, it applies only to a small 0.5-100W power control system.

2. Servo motor selection method 1. And compare the performance of the stepper motor 

    As an open-loop stepper motor control system, and modern digital control technology are intrinsically linked.In the current domestic digital control system, the stepper motor is widely used.With the all-digital AC servo-systems, AC servo motor also increasingly used in digital control systems.In order to meet the development trend of digital control, motion control systems they use digital stepper motors or AC servo motor as the implementation of the motor.While both are similar in the control (pulse train and direction signal), but in applications where performance and there are big differences.Performance of both is to make a comparison.

Control accuracy are different: two-phase hybrid step motor step angle is generally 1.8 °, 0.9 °, five-phase hybrid stepping motor step angle is usually 0.72 °, 0.36 °.There are also some high-performance stepper motor through after the breakdown of a smaller step angle.Such as Sanyo (SANYO DENKI) production of two-phase hybrid step motor step angle by its DIP switch is set to 1.8 °, 0.9 °, 0.72 °, 0.36 °, 0.18 °, 0.09 °, 0.072 °, 0.036 °compatible with the two-phase and five-phase hybrid stepping motor step angle.Precision AC servo motor control back from the motor shaft rotary encoder guarantee.To Sanyo all-digital AC servo motor, for example, the standard for the 2000 line encoder with the motor, since the internal drive, four-frequency technology using a pulse equivalent to 360 ° / 8000 = 0.045 °.For the encoder with the motor 17, the driver receives 131 072 pulses per motor revolution, that is, a pulse equivalent to 360 ° / 131072 = 0.0027466 °, a step angle of 1.8 ° stepper motor pulse equivalent1 / 655. Different frequency characteristics, the stepper motor at low speeds prone to low frequency vibration.Vibration frequency and load conditions and drive performance, generally considered no-load off the motor frequency half the frequency.This works by the stepper motor vibration frequency determined by the normal operation of the machine is very negative.When the stepper motor in low speed, generally should be used to overcome the low frequency vibration damping phenomena, such as additional damper on the motor, or drive with subdivision techniques.AC servo motor is running very smoothly, even if it does not appear in the low-speed vibration.AC servo system with resonance suppression, can cover the lack of mechanical stiffness, and function within the system has a frequency analysis (FFT), can detect mechanical resonance point, easy system tuning. The different torque-frequency characteristics, the stepper motor output torque decreases with speed increases, and at higher speeds would drop dramatically, so its maximum operating speed is generally at 300 ~ 600RPM.AC servo motor for constant torque output, which in its rated speed (typically 2000RPM or 3000RPM) or less, can output rated torque above the rated speed constant power output.Fourth, generally do not overload with various stepper motor overload.AC servo motor with a strong overload.AC servo system to Sanyo, for example, it has the speed and torque overload overload.Its maximum torque is two to three times the rated torque can be used to overcome the inertia of the load moment of inertia at the start moment.Stepper motor because there is no such overload, in the selection order to overcome this moment of inertia, often need to select a larger motor torque, while the machine during normal operation and does not require so much torque, giving rise to a torquewasting phenomenon. Five different operating performance stepper motor control for the open-loop control, start frequency is too high or too prone to lose the load step or the phenomenon of stall, stop rotating speed is too high when the phenomenon prone to overshoot, so as to ensure their controlaccuracy, should handle up, spin-down problem.AC servo drive system for closed loop control, the drive can be directly on the motor encoder feedback signal is sampled, the internal structure of the position loop and speed loop, generally will not be lost step or stepper motor overshoot phenomenon, the control performance more reliable.Six-speed response performance of different stepper motors to accelerate from standstill to operating speed (typically several hundred per minute, rpm) 200 ~ 400 ms.AC servo system is better acceleration performance to Sanyo 400W AC servo motor, for example, accelerates from zero to its rated speed of 3000RPM is only a few milliseconds, fast start and stop can be used to control the situation requires.In summary, the AC servo system is superior in many performance stepper motor.But in some less demanding situations are often to do with the implementation of the stepper motor motor.Therefore, the control system design process control requirements to be taken into account, costs, and many other factors, the choice of the appropriate motor control. 2. Selection method First, the speed and encoder resolution of confirmation. Second, the motor shaft load torque conversion and processing gear torque calculations. Third, calculate the load inertia, inertia of the match, Yaskawa servo motors, for example, some products match up to 50 times the inertia, but the actual smaller the better, so good on the accuracy and response speed. Fourth, the calculation of resistance and choice of regeneration, for the server, usually more than 2kw to external configuration. Fifth, cable selection, the encoder cable shielded twisted pair, and for other Japanese Yaskawa servo system product is 6-cell absolute encoder, incremental is 4 core. 3. Servo Motor Installation Notes 1, the servo motor oil and water conservation A: servo motor can be used in water or oil droplets will be affected by the invasion of the place, but it is not fully waterproof or anti-oil.Therefore, the servo motor should not be placed or used in water or oil intrusion in the environment.B: If the servo motor connected to a reduction gear, use the servo motor fuel should be sealed to prevent the reduction gear oil into the servo motor C: servo motor cable not immersed in oil or water. 2, servo motor cable to reduce stress → A: Make sure the cable is not due to external bending moment, or by their own weight or vertical load, especially in the cable outlet or connection.B: In the case of the servo motor moves, should the cable (that is configured with the motor Flanagan) is firmly fixed to a stationary part of the (relative motor), and should be installed in the cable with a bearing in the attached cables to extendit, so the bending stress can be minimized .C: cable bend radius be as large as possible. 3, the servo motor allows the shaft load A: make sure when you add in the installation and operation of the servo motor shaft in radial and axial load control within the specified value for each model.B: When installing a rigid coupling to be cautious, especially over the curved shaft and bearing load may cause damage or wear C: best to use a flexible coupling, so that the radial load below the allowable value,This material is designed for high mechanical strength of the servo motor design.D: axial load on the permit, please refer to the "permissible axle load table" (Manual). 4, the servo motor is installed Note A: In the install / remove components to the servo motor shaft coupling, do not directly tap with a hammer shaft.(Direct beat hammer shaft, the other side of the servo motor shaft encoder to be knocked bad) B: strive to align the shaft to the best state (on a bad vibration or bearing damage may result.) 4. DC servo motor characteristics First, the DC brushless motor features: 1. A small moment of inertia, low starting voltage, load current is small; 2. Disposable contact change to the system, greatly improving the motor speed, maximum speed up to 100 000rpm; 3. Brushless servo motor servo control in the implementation, the encoder can also be achieved without the speed, position, torque control; 4. There is no brush wear, in addition to high speed, but also has a long life, low noise, electromagnetic interference and other characteristics; Second, the DC brush servo motor characteristics: 1. The volume is small, the fast response quick, overloading capacity, wide speed range; 2. Low-speed torque, and fluctuations in small, smooth; 3 .. low noise, high efficiency; 4. Backend encoder feedback (optional) constitute the advantages of the DC servo; 

    Use: DC servo motor can be used in a spark machine, robot, precise machinery.Can also configure the 2500P / R analysis of the degree of high standard encoder and tachometer, with gear box plus more, so that the accuracy of machinery and equipment to bring reliable and high torque.Speed is good, unit weight and volume, the output power of the highest, more than AC motors, and much higher than the stepper motor.Multi-level structure of the torque ripple small.

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