选择合适的步进电机.doc

SELECTING THE MOTOR THAT SUITS YOUR APPLICATION选择合适的电机Introduction简介Motion control, in its widest sense, could relate to anything from a welding robot to the hydraulic system in a mobile crane. In the field of Electronic Motion Control, we are primarily concerned with systems falling within a limited power range, typically up to about 10HP (7KW), and requiring precision in one or more aspects. This may involve accurate control of distance or speed, very often both, and sometimes other parameters such as torque or acceleration rate. In the case of the two examples given, the welding robot requires precise control of both speed and distance; the crane hydraulic system uses the driver as the feedback system so its accuracy varies with the skill of the operator. This wouldnt be considered a motion control system in the strict sense of the term.Our standard motion control system consists of three basic elements:运动控制，在其最广泛的意义上说，可能与任何移动式起重机中焊接机器人液压系统有关。在电子运动控制领域，我们的主要关切系统范围内的有限功率的大小， 通常高达约10hp （ 7千瓦），并要求在一个或多个方面有严格精密。这可能涉及精确控制的距离或速度，但很多时候是双方的，有时还涉及其它参数如转矩或加速率。在以下所举的两个例子中，焊接机器人，需要精确的控制双方的速度和距离;吊臂液压系统采用驱动作为反馈系统，因此，它的准确度会随着操作者的技能的不同而不同。在严格意义上来说，这将不会被视为一项运动控制系统。 我们的标准运动控制系统由以下三个基本要素组成：Fig. 1 Elements of motion control system图 1运动控制系统的组成元件 混合式步进电机直流伺服无刷电机The motor. This may be a stepper motor (either rotary or linear), a DC brush motor or a brushless servo motor. The motor needs to be fitted with some kind of feedback device unless it is a stepper motor.电机，可能是一个步进电机（要么旋转或线性），也可能是直流无刷电机或无刷伺服马达。电机必须配备一些种回馈装置，除非它是一个步进电机。Fig. 2 shows a system complete with feedback to control motor speed. Such a system is known as a closed-loop velocity servo system.图 2显示了一个完善地反馈控制电机转速的系统。这样一个具有闭环控制系统的速度伺服系统。Fig. 2 Typical closed loop (velocity) servo system图2典型的闭环（速度）伺服系统The drive. This is an electronic power amplifier thatdelivers the power to operate the motor in response to low-level control signals. In general, the drive will be specifically designed to operate with a particular motor type you cant use a stepper drive to operate a DC brush motor, for instance.驱动器是一个电子功率放大器，以提供电力操作电动机来回应低层次的控制信号。一般来说，驱动器将特别设计，其操作与特定电机类型相配合。例如，你不能用一个步进驱动器来操作直流无刷电机。Application Areas of Motor Types不同电机适应的不同领Stepper Motors步进电机：Stepper Motor Benefits步进电机的优点。Stepper motors have the following benefits:步进电机有以下优点： Low cost（1）成本低 Ruggedness（2）耐用 Simplicity in construction（3）结构简单 High reliability（4）高可靠性 No maintenance（5）无维修 Wide acceptance（6）适用广泛 No tweaking to stabilize（7）稳定性很高 No feedback components are needed（8）无需反馈元件 They work in just about any environment（8）适应多种工作环境 Inherently more failsafe than servo motors.（9）相对伺服电机更具有可靠性。There is virtually no conceivable failure within the stepper drive module that could cause the motor to run away. Stepper motors are simple to drive and control in an open-loop configuration. They only require four leads. They provide excellent torque at low speeds, up to 5 times the continuous torque of a brush motor of the same frame size or double the torque of the equivalent brushless motor. This often eliminates the need for a gearbox. A stepper-driven-system is inherently stiff, with known limits to the dynamic position error。因此，几乎没有任何可以想象的失败使步进驱动模块出错。步进电机驱动简单，并且驱动和控制在一个开放的闭环系统内。他们只需要4个驱动器。低速时，驱动器提供良好的扭矩，是有刷电机同一帧大小5倍连续力距，或相当于无刷电机一倍扭矩。这往往不再需要变速箱。步进驱动系统迟缓，在限定的范围内，可以更好的减少动态位置误差。Stepper Motor Disadvantages步进电机缺点。Stepper motors have the following disadvantages:步进电机有下列缺点： Resonance effects and relatively long settling times（1）共振效应和相对长的适应性 Rough performance at low speed unless a microstep drive is used（2）在低速，表现粗糙，除非微驱动器来驱动 Liability to undetected position loss as a result of operating open-loop（3）开环系统可能导致失步 They consume current regardless of load conditions and therefore tend to run hot（4）由于过载，他们消耗过多电流。因此倾向于过热运行。 Losses at speed are relatively high and can cause excessive heating, and they are frequently noisy(especially at high speeds).（5）亏损速度比较高，并可产生过多热量因此，他们噪音很大（尤其是在高速下）。 They can exhibit lag-lead oscillation, which is difficult to damp. There is a limit to their available size, and positioning accuracy relies on the mechanics (e.g., ballscrew accuracy). Many of these drawbacks can be overcome by the use of a closed-loop control scheme.（6）他们的滞后现象导致振荡，这是很难抑制的。对他们的可行性，这儿有一个限度，而他们的大小，定位精度主要依靠的是机器（例如，滚珠丝杠的精确度） 。许多这些缺点是可以克服的，通过使用一个闭环控制方案。 Note: The Compumotor Zeta Series minimizes or reduces many of these different stepper motor disadvantages.注： compumotor系列能很多的减小或降低了这些不同的步进电机不利之处。There are three main stepper motor types:主要有3类步进电机： Permanent Magnet (P.M.) Motors（1）永磁式步进电机 ， Variable Reluctance (V.R.) Motors（2）感应式步进电动机， Hybrid Motors（3）混合式步进电机When the motor is driven in its full-step mode, energizing two windings or “phases” at a time (see Fig. 1.8), the torque available on each step will be the same (subject to very small variations in the motor and drive characteristics). In the half-step mode, we are alternately energizing two phases and then only one as shown in Fig. 1.9. Assuming the drive delivers the same winding current in each case, this will cause greater torque to be produced when there are two windings energized. In other words, alternate steps will be strong and weak. This does not represent a major deterrent to motor performancethe available torque is obviously limited by the weaker step, but there will be a significant improvement in low-speed smoothness over the full-step mode.当电动机驱动，在其全步模式，给两个绕组通电时或2相通电的时候（见图 1.8 ） ，扭矩可于每一个步将是相同（除极少数的变异和传动特性）。在半步模式下，我们交替改变两相电流，如图1.9所示。假设该驱动器在每种情况下提供了相同的绕组电流，再通电时，这将导致更大的转矩。换句话说，交替的步进距将时强时若。对电动机表现来说，这并不代表着一个重大的威慑。扭矩明显受制于较弱的一步，但在全步模式时，低速平滑有一个显着的改善。Clearly, we would like to produce approximately equal torque on every step, and this torque should be at the level of the stronger step. We can achieve this by using a higher current level when there is only one winding energized. This does not over dissipate the motor because the manufacturers current rating assumes two phases to be energized the current rating is based on the allowable case temperature). With only one phase energized, the same total power will be dissipated if the current is increased by 40%. Using this higher current in the one-phase-on state produces approximately equal torque on alternate steps (see Fig. 1.10).显然，我们想在每一个步骤实现约相等扭矩对时，这扭矩应该在水平较强的一步。们可以实现这个，当只有一个绕组通电时，通过用高电流水平。这并不过度消耗电机，因为该电机的额定电流假定两个阶段被激活（目前的评级是基于许可的情况温度） 。只有一相通电，如果目前是增加了40 的功率，同样的总功率将会消散 。利用这种更高的电流在一相中产生大致相等的扭矩，在交替的步进距中。（见图1.10 ）Fig. 1.8 Full step current, 2-phase on图1.8 2相供电整步Fig. 1.9 Half step current图1.9 单相半步Fig. 1.10 Half step current, profiled图1.10 单相电流半步图表We have seen that energizing both phases with equal currents produces an intermediate step position half-way between the one-phase-on positions. If the two phase currents are unequal, the rotor position will be shifted towards the stronger pole. This effect is utilized in the microstepping drive, which subdivides the basic motor step by proportioning the current in the two windings. In this way, the step size is reduced and the low-speed smoothness is dramatically improved. High-resolution microstep drives divide the full motor step into as many as 500 microsteps, giving 100,000 steps per revolution. In this situation, the current pattern in the windings closely resembles two sine waves with a 90 phase shift between them (see Fig. 1.11). The motor is now being driven very much as though it is a conventional AC synchronous motor. In fact, the stepper motor can be driven in this way from a 60 Hz-US (50Hz-Europe) sine wave source by including a capacitor in series with one phase. It will rotate at 72 rpm.我们已经看到，给两相都通与平等电流产生的一个中间步进，居于每一相的中间位置。如果两相电流是不平等的， 转子位置将转向更强的一极。这种作用是利用细分驱动，其中细分的大小基于两个绕组中的电流的大小。以这种方式，步长是减少了，而低速平滑度得到大幅度提高。高细分驱动电动机细分整步步进到多达500 个细分步 ，转一圈可细分十万步。在这种情况下，绕组中的电流极为相似的两个正弦波有90 相移。（图1.11 ） 电机被驱动好像转换成了交流同步电机。事实上，步进电机可被驱动，从60赫兹美（50赫兹-欧洲）正弦波源头起，包括电容器系列的一相。它将旋转72转。Fig. 1.11 Phase currents in microstep mode图 1.11步进电机的相电流Standard 200-Step Hybrid MotorThe standard stepper motor operates in the same way as our simple model, but has a greater number of teeth on the rotor and stator, giving a smaller basic step size. The rotor is in two sections as before, but has 50 teeth on each section. The half-tooth displacement between the two sections is retained. The stator has 8 poles each with 5 teeth, making a total of 40 teeth (see Fig. 1.12).标准步进电机运行在同就如同我们的简单模式，但有一个更大的数目齿数在转子和定子中，从而有了一个较小的基本步长。转子有2部分，但每部分有50个齿。该半齿位于两部分之间。定子每5个齿有8个极，完整的共有40个齿（见图1.12 ）Fig. 1.12 200-step hybrid motor图1.12 200步混合标准电机If we imagine that a tooth is placed in each of the gaps between the stator poles, there would be a total of 48 teeth, two less than the number of rotor teeth. So if rotor and stator teeth are aligned at 12 oclock, they will also be aligned at 6 oclock. At 3 oclock and 9 oclock the teeth will be misaligned. However, due to the displacement between the sets of rotor teeth, alignment will occur at 3 oclock and 9 oclock at the other end of the rotor.如果我们想象一个齿，是摆在2个定子极点每一齿隙中，假设定子共有48个齿，少于转子齿数两个。因此，如果转子和定子的齿排列一整圈，他们同样也可以排列半圈。1/4和3/4圈也同样可以排列。 然而，由于转子齿排列位置，在另一端的转子，排列将发生在1/4和3/4位置处。The windings are arranged in sets of four, and wound such that diametrically-opposite poles are the same. So referring to Fig. 1.12, the north poles at 12 and 6 oclock attract the south-pole teeth at the front of the rotor; the south poles at 3 and 9 oclock attract the north-pole teeth at the back. By switching current to the second set of coils, the stator field pattern rotates through 45. However, to align with this new field, the rotor only has to turn through 1.8. This is equivalent to one quarter of a tooth pitch on the rotor, giving 200 full steps per revolution.绕组4个一组，并对角线方向的极性相反。如图1.12所示 ，北极在转子前面的12点和6点位置，吸引着在在背面3时和9时的南极。通过开关第二组线圈的电流，定子场模式旋转45 。不过，要配合这个新的领域，转子只转过1.8 。相当于转子，这只转过了四分之一齿间距，每一次旋转要200个全步。Note that there are as many detent positions as there are full steps per rev, normally 200. The detent positions correspond with rotor teeth being fully aligned with stator teeth. When power is applied to a stepper drive, it is usual for it to energize in the “zero phase” state in which there is current in both sets of windings. The resulting rotor position does not correspond with a natural detent position, so an unloaded motor will always move by at least one half step at power-on. Of course, if the system was turned off other than in the zero phase state, or the motor is moved in the meantime, a greater movement may be seen at power-up.注意到，每一次旋转全部时这儿有很多定位点位置，通常是200个 。该定位点的位置与转子齿全面接轨定子齿时相对应。当通电给步进驱动器时， 它通常是零阶段状态时最活跃，也就是两套绕组都通电。因此产生的转子位置并不符合转子自然定位点的位置。因此，空载时，一旦通电电机将至少步进半步。当然，如果系统关机，或在零相位位置，电机一旦通电将步进一大步。Another point to remember is that for a given current pattern in the windings, there are as many stable positions as there are rotor teeth (50 for a 200-step motor). If a motor is de-synchronized, the resulting positional error will always be a whole number of rotor teeth or a multiple of 7.2. A motor cannot “miss” individual steps position errors of one or two steps must be due to noise, spurious step pulses or a controller fault.另一点要注意的是，对于一个给定电流的绕组，有很多稳定的位置，正如转子齿（200步进电机有50个齿）。如果电机是同步电机，导致位置误差将永远是一个整体倍转子齿或能被7.2 整除 。电机不能细分，如个别一个或两个位置误差，是由于噪声，错误脉冲或控制器故障造成的。Fig. 2.19 Digital servo drive图2.19数字伺服驱动Digital Servo Drive OperationFig. 2.19 shows the components of a digital drive for a servo motor. All the main control functions are carried out by the microprocessor, which drives a D-to-A convertor to produce an analog torque demand signal. From this point on, the drive is very much like an analog servo amplifier.图2.19显示为伺服电机的数控驱动。所有的主控制功能是微处理器，驱动为D A模拟转换器，以产生一个模拟扭矩需求信号。从这个角度上，这台机器非常很像一个模拟伺服放大器。Feedback information is derived from an encoder attached to the motor shaft. The encoder generates a pulse stream from which the processor can determine the distance travelled, and by calculating the pulse frequency it is possible to measure velocity.反馈的信息是来自隶属该电机轴的一个编码器。编码器生成脉冲流可确定传输路程，并通过计算脉冲频率，是可以测定转速的。The digital drive performs the same operations as its analog counterpart, but does so by solving a series of equations. The microprocessor is programmed with a mathematical model (or “algorithm”) of the equivalent analog system. This model predicts the behavior of the system. In response to a given input demand and output position. It also takes into account additional information like the output velocity, the rate of change of the input and the various tuning settings.数码驱动通过求解一系列的方程式，履行同样类似的功能。微处理器是与数学模型（或“算法 ）的等效的编程模拟系统。这模型预测系统的行为。它响应一个给定输入的信号并产生速度。它同样也考虑到额外信息如输出速度，速率转变中的投入和各种调校设定。To solve all the equations takes a finite amount of time, even with a fast processor this time is typically between 100ms and 2ms. During this time, the torque demand must remain constant at its pr