The stepper motor is a discrete motion device, which has an essential connection with modern digital control technology. In the current domestic digital control system, the stepper motor is widely used. With the emergence of all-digital AC servo systems, AC servo motors are also increasingly used in digital control systems. In order to adapt to the development trend of digital control, most of the motion control systems use stepping motors or all-digital AC servo motors as execution motors. Although the two in the control mode is similar (pulse string and direction signal), but in the use of performance and application occasions there are large differences. Now on the use of the two performance for a comparison of stepper motor and AC servo motor performance comparison of stepper motor and AC servo motor performance comparison c. First, the control accuracy of different two-phase hybrid stepper motor step angle is generally 3.6 °, 1.8 °, five-phase hybrid stepper motor step angle is generally 0.72 °, 0.36 °. There are also some high-performance stepper motor step angle is smaller. For example, a stepping motor for slow-feeding machine tools produced by Si-Tong, its step angle of 0.09 °; Germany's BERGER LAHR company (BERGER LAHR) production of three-phase hybrid stepping motor step angle can be set by the dipswitch for 1.8 °, 0.9 °, 0.72 °, 0.36 °, 0.18 °, 0.09 °, 0.072 °, 0.036 °, compatible with the step angles of two-phase and five-phase hybrid stepper motors. The control accuracy of the AC servo motor is ensured by the rotary encoder at the rear of the motor shaft. In the case of a Panasonic all-digital AC servo motor, for example, for a motor with a standard 2500-line encoder, the pulse equivalent is 360°/10,000 = 0.036° due to the quadruple-frequency technology used inside the driver. For a motor with a 17-bit encoder, the drive receives 217 = 131072 pulses per motor turn, that is, its pulse equivalent of 360 ° / 131072 = 9.89 seconds. Is the step angle of 1.8 ° of the stepper motor pulse equivalent of 1 / 655. Second, the low-frequency characteristics of different stepper motor at low speeds prone to low-frequency vibration phenomenon. Vibration frequency and load conditions and driver performance related to the general view that the vibration frequency for the motor no-load starting frequency of half. This low-frequency vibration phenomenon determined by the operating principle of the stepper motor is very unfavorable to the normal operation of the machine. When the stepper motor works at low speed, generally should be used to damping technology to overcome the low-frequency vibration phenomenon, such as adding a damper on the motor, or the driver using subdividing technology and so on. AC servo motors run very smoothly and do not vibrate even at low speeds. AC servo system with *** vibration suppression function, can cover the lack of mechanical rigidity, and the system has an internal frequency analysis function (FFT), can detect the mechanical *** vibration point, easy to adjust the system. Third, the moment frequency characteristics of different stepper motor output torque with the increase in speed and decline, and at higher speeds will fall sharply, so its maximum operating speed is generally in the 300 ~ 600 RPM. AC servo motor for constant torque output, that is, in its rated speed (generally 2000 RPM or 3000 RPM) within the rated torque can be output, in the rated speed above the constant power output. Fourth, different overload capacity stepper motor generally does not have overload capacity. AC servo motor has a strong overload capacity. Panasonic AC servo system, for example, it has speed overload and torque overload capacity. Its maximum torque is three times the rated torque, which can be used to overcome the moment of inertia of inertial loads at the moment of starting. Stepper motor because there is no such overload capacity, in order to overcome this moment of inertia in the selection, often need to select a larger torque motor, and the machine does not require so much torque during normal operation, there will be a waste of torque phenomenon. Fifth, different operating performance stepper motor control for open-loop control, start too high a frequency or load is too easy to lose step or blocking the phenomenon of stopping too high a speed is easy to overshoot the phenomenon, so in order to ensure the accuracy of its control, should be dealt with to raise and lower the speed problem. AC servo drive system for closed-loop control, the driver can be directly on the motor encoder feedback signal sampling, the internal composition of the position loop and speed loop, generally does not appear stepper motor loss of step or overshoot phenomenon, the control performance is more reliable. Six, speed response performance is different stepper motor accelerated from standstill to the working speed (generally a few hundred revolutions per minute) takes 200 to 400 milliseconds. AC servo system acceleration performance is better, to Panasonic MSMA 400W AC servo motor, for example, from standstill to accelerate to its rated speed of 3000RPM only a few milliseconds, can be used for the requirements of rapid start-stop control occasions. In summary, AC servo systems are superior to stepper motors in many performance aspects. However, stepper motors are also often used as actuating motors in some less demanding applications. Therefore, in the process of control system design to consider the control requirements, cost and other factors, select the appropriate control motor. The person who wrote this post is selling AC servo motors, right? The content is basically correct, however, not comprehensive. The owner used to compare several parts, some of which can be viewed from another perspective. 1, different control accuracy Obviously, the owner does not know the stepper motor driver has a "subdivision" concept. Two-phase stepper motor stepping angle is 1.8 degrees yes, but now 64 subdivided drive is also very common. Note that, at this time, the motor is 200 * 64 = 12800 pulses turn a circle. And the common AC servo on the market, the encoder is just 2048 or 2500 lines. Of course, there are motors with 17-bit encoders, but there are also stepper drivers with 256 subdivisions. In terms of resolution, AC servo is still a little higher, but far from the owner wrote so exaggerated. Moreover, since it is said that the control accuracy, then, people who have used the servo should know that the dynamic reproducibility of the servo is how many times the resolution. As far as conventional design is concerned, when selecting a model, multiply the reproducibility index by 5 as the resolution of the servo feedback. In this way, the control accuracy of the servo is really better than the servo? 2, low-frequency characteristics are different When the stepper motor fine fraction reaches 32 or more, there is basically no low-frequency vibration problems. Servo want to maintain an accurate, stable low speed, with people should know how difficult to adjust the parameters (as long as the speed, do not want to position, then, okay to do a little bit) 3, the moment characteristics of different For the torque, need to add that the servo itself does not have to keep the torque, and stepper motors have to keep the torque. The difference is that the so-called stationary servo motor, in fact, is a dynamic balancing process, the motor will not really stop in the specified position (so AC servo reproducibility to be set to the feedback resolution of 3-5 times, and stepper motor reproducibility can be higher than the resolution). 4, different overload capacity There is nothing to say about this, but for the torque waste statement, or a little opinion. Many stepper drivers provide a half-current function, when the full torque output is not required, you can reduce the current, reduce the torque. 5, different operating performance Step loss is indeed the fatal flaw of the stepper motor, but the servo can not take into account the acceleration and deceleration curve? You really give a step signal to try, the motor will have how much jitter. However, the jitter will eventually stop in the correct position, which is indeed better than a stepper. If the positioning control, this jitter does not matter, if the process control, who dares to use this? 6, speed response performance is different because the AC servo can have instantaneous high torque output, so the acceleration performance may be stronger than the stepper, but the Panasonic added to 3000RPM with a few milliseconds, first tried to speak again, OK? And when it comes to response, it is impossible not to talk about the essential flaw of AC servo - hysteresis. General motor, speed loop response of 2 milliseconds, position loop response is rarely seen data, generally considered to be 8 milliseconds. When it comes to fast start and stop, servo always hand its response frequency limitations, while the stepper motor basically do not have to consider the problem of response time. With a stepper motor can be very simple to do a second to start and stop 100 times, each time to move 20 microns, with a servo you can try. Stepper and servo, it does not matter whether the advantages and disadvantages, each applicable occasions, in general, large loads, high speed applications, do not use stepper motors, but low loads, low-speed occasions, high subdivision of the stepper performance than the AC servo to be better. - By: motioncontrol Saturday, April 16, 2005 19:44 Reply (1) | Cite (0) Join Bozai The debugging of the basic parameters of the frequency converter (reproduced) Keywords: frequency converter, parameter debugging The frequency converter has a lot of functional parameters, and generally there are dozens or even hundreds of parameters for the user to choose. In practical application, it is not necessary to set and debug each parameter, most of which can be used as long as the factory settings. However, some parameters and the actual use of the situation has a great relationship, and some are also interrelated, so according to the actual setting and debugging. Because the function of each type of inverter is different, and the name of the same function parameters are not consistent, for the convenience of the narrative, this paper to Fuji inverter basic parameter name as an example. As the basic parameters are almost all types of inverters, it can be done completely bypassed. Keywords: inverter parameter debugging Inverter function parameters are many, generally there are dozens or even hundreds of parameters for users to choose. In the actual application, it is not necessary to set and debug each parameter, and most of them can be used as long as the factory setting value. However, some parameters and the actual use of the situation has a great relationship, and some are also interrelated, so according to the actual setting and debugging. Because the function of each type of inverter is different, and the name of the same function parameters are not consistent, for the convenience of the narrative, this paper to Fuji inverter basic parameter name as an example. As the basic parameters are almost all types of inverters, it can be done completely by touch. A acceleration and deceleration time acceleration time is the output frequency from 0 up to the maximum frequency time required, deceleration time is from the maximum frequency down to 0 time required. The acceleration and deceleration times are usually determined by the rise and fall of the frequency setting signal. The rate of rise of the frequency setting must be limited to prevent overcurrent when the motor is accelerated, and the rate of fall must be limited to prevent overvoltage when it is decelerated. Acceleration time setting requirements: the acceleration current is limited to below the overcurrent capacity of the frequency converter, so as not to cause the frequency converter to trip; deceleration time setting points are: to prevent the smoothing circuit voltage is too large, so as not to regenerate the overvoltage stall and make the frequency converter trip. Acceleration and deceleration time can be calculated according to the load, but in the debugging is often taken according to the load and experience first set a longer acceleration and deceleration time, through the starting and stopping motor to observe whether there is overcurrent, over-voltage alarm; and then acceleration and deceleration set time is gradually shortened to the operation of the alarm does not occur in the principle of repeating the operation a few times, you can determine the optimal acceleration and deceleration time. The torque boost, also called torque compensation, is a method to increase the low frequency range f/V to compensate for the reduced torque at low speed caused by the resistance of the motor stator winding. When set to automatic, the voltage during acceleration can be automatically increased to compensate for the starting torque so that motor acceleration can be carried out smoothly. If manual compensation is used, a better curve can be selected by test according to the load characteristics, especially the starting characteristics of the load. For the load with variable torque, if it is not selected properly, the output voltage will be too high at the low speed, which will waste the electric energy, and even the phenomenon that the motor will have a high current when starting with the load, and the rotating speed will not be able to go up. Electronic thermal overload protection This function is set to protect the motor from overheating, it is the CPU in the inverter calculates the temperature rise of the motor according to the value of the running current and the frequency, so as to carry out overheating protection. This function is only applicable to the occasion of "one towing one", but in the case of "one towing many", a thermal relay should be installed on each motor. Electronic thermal protection set value (%) = [motor rated current (A) / inverter rated output current (A)] × 100%. IV Frequency limitation That is, the upper and lower limit amplitude of inverter output frequency. Frequency limit is to prevent misoperation or external frequency setting signal source failure, and cause the output frequency is too high or too low, in order to prevent damage to the equipment of a protective function. It can be set according to the actual situation in the application. This function can also be used as a speed limit, such as belt conveyor, due to the transport of materials is not too much, in order to reduce the wear and tear of machinery and belts, can be driven by a frequency converter, and the upper frequency converter frequency is set to a certain frequency value, so that the belt conveyor can be run at a fixed, lower working speed. V Bias frequency Some are also called deviation frequency or frequency deviation setting. Its use is when the frequency is set by an external analog signal (voltage or current), this function can be used to adjust the frequency setting signal is the lowest when the output frequency of the high and low, such as Figure 1. some frequency converters when the frequency setting signal is 0%, the deviation value can be acted on in the range of 0 ~ fmax, and some frequency converters (such as Ming Denshuo, Sanken) can also be set on the bias polarity. Such as in the debugging when the frequency setting signal is 0%, the frequency converter output frequency is not 0Hz, but xHz, then the bias frequency is set to negative xHz can make the frequency converter output frequency is 0Hz. six Frequency Setting Signal Gain This function is effective only when the frequency is set with external analog signal. It is used to make up for the inconsistency between the external set signal voltage and the voltage inside the frequency converter (+10v); at the same time, it is convenient to select the analog set signal voltage, when setting, when the analog input signal is the maximum (such as 10v, 5v or 20mA), find out the frequency percentage of the output f/V graph and set it with this parameter; such as the external set signal is 0~5v, if the frequency converter output is 0~50Hz, the frequency is 0~50Hz. If the external setting signal is 0～5v, if the frequency of inverter output is 0～50Hz, then set the gain signal to 200%. Torque limitation can be divided into driving torque limitation and braking torque limitation. It is based on the output voltage and current value of the inverter, and the CPU carries out torque calculation, which can significantly improve the shock load recovery characteristics during acceleration/deceleration and constant speed operation. The torque limiting function can realize automatic acceleration and deceleration control. Assuming that the acceleration and deceleration time is less than the load inertia time, it also ensures that the motor automatically accelerates and decelerates according to the torque setting value. The drive torque function provides powerful starting torque, and during steady state operation, the torque function will control the motor torque difference and limit the motor torque to the maximum setting value, so that it will not cause the inverter to trip when the load torque suddenly increases, even when the acceleration time is set too short. When the acceleration time is set too short, the motor torque will not exceed the maximum setting value. A large driving torque is favorable for starting, and it is more appropriate to set it at 80-100%. The smaller the setting value of braking torque is, the larger the braking force is, which is suitable for the occasions of rapid acceleration and deceleration, if the setting value of braking torque is set too large, there will be over-voltage alarm phenomenon. If the braking torque is set to 0%, it can make the total amount of regeneration added to the main capacitor close to 0, which makes the motor decelerate to a standstill without using the braking resistor when decelerating without tripping. However, in some loads, such as braking torque set to 0%, when decelerating, there will be a short idling phenomenon, resulting in repeated starting of the inverter, the current fluctuates greatly, and in severe cases, the inverter will be tripped, which should be noted. Eight acceleration and deceleration mode selection is also called acceleration and deceleration curve selection. General inverter has linear, non-linear and S three curves, usually most of the linear curve; non-linear curve for variable torque loads, such as fans, etc.; S curve for constant torque loads, its acceleration and deceleration changes more slowly. Setting can be based on the load torque characteristics, select the appropriate curve, but there are exceptions, the author in the debugging of a boiler induced draft fan frequency converter, the first acceleration and deceleration curve to choose a nonlinear curve, together with the start-up operation of the inverter on the trip, adjusting the change of many parameters have no effect, and then changed to the S curve after the normal. The reason is: before the start of the induced draft fan due to the flue gas flow and self-rotation, and reverse and become a negative load, so that the selection of the S-curve, so that the frequency of just starting a slower rise in frequency, thus avoiding the occurrence of frequency inverter tripping, of course, this is for the frequency inverter does not have a starting DC braking function of the method used. IX Torque vector control Vector control is based on the theory that: asynchronous motors and DC motors have the same torque generating mechanism. The vector control method is to decompose the stator current into a prescribed magnetic field current and torque current and control them separately, while outputting the stator current synthesized from both to the motor. Therefore, the same control performance as that of a DC motor can be obtained in principle. With the torque vector control function, the motor can output the maximum torque under various operating conditions, especially when the motor is in the low-speed operating region. Nowadays, almost all inverters adopt no-feedback vector control, because the inverter can compensate the rotational difference according to the load current size and phase, so that the motor has very hard mechanical characteristics, which can satisfy the requirements for most of the occasions, and there is no need to set up the speed feedback circuit outside the inverter. This function can be set according to the actual situation in the effective and ineffective in the choice of a can. The function related to it is the rotary compensation control, whose function is to compensate for the speed deviation caused by the load fluctuation, and the rotary frequency corresponding to the load current can be added. This function is mainly used for positioning control. Energy-saving control Fan and pump belong to reduced torque load, i.e., as the rotational speed decreases, the load torque decreases proportionally to the square of the rotational speed, and the inverter with energy-saving control function is designed with a special V/f mode, which improves the efficiency of motor and inverter, and automatically reduces the output voltage of the inverter according to the load current to achieve the purpose of energy-saving, and can be set as effective or ineffective according to the specific conditions. The mode can be set as effective or invalid according to the specific situation. To illustrate, nine, ten of these two parameters is very advanced, but some users in the equipment transformation, simply can not enable these two parameters, that is, after enabling the frequency converter trips frequently, deactivated after all normal. The reasons are: (1) the original motor parameters and inverter requirements with the motor parameters are too different. (2) The function of the set parameters do not know enough, such as energy-saving control function can only be used in the V / f control mode, can not be used in the vector control mode. (3) Vector control mode is enabled, but there is no manual setting and automatic reading of motor parameters, or the reading method is improper.
Reference:
.
/?url=/showtopic.aspx?id=86