五相步进电机驱动电路开发(论文翻译).doc

一种新的五相步进电机驱动电路开发T.S.维拉孔和T. 萨马拉纳亚克斯里兰卡，佩勒代尼耶大学工程学院，电子与电气工程学院付自刚译摘要本文详细地介绍了一种新的五相步进电机驱动电路。这种新的驱动电路是由商业上现成的，廉价的，标准的步进电机驱动IC搭建，它能实现由内部电流回路驱动的闭环速度和位置控制。经证明，这种驱动电路能推广到任何更多相数的奇数相的步进电机。这种驱动电路具有速度控制和方向控制，包括全步、半步、顺时针、逆时针控制模式。一、 概述在大多数机器人和自动化工程设计中，各种各样步进电机都被广泛应用来得到需要的运动姿态。步进电机倍受人们青睐是因为它不需要频繁的维护并能在苛刻的环境中运行。步进电机及其驱动器的选择要根据具体应用中需要的效果来决定。市场上最常见的是两相和四相步进电机。可是，实际应用中要求高精度，低噪声和低震动，因此五相步进电机得以应用。因为步距角较小，五相步进电机有较高的分辨率，较低的震动和良好的加速与减速特性。因此，确保设计的驱动电路能使步进电机充分发挥这些优点非常重要。因为在机器人应用中是很少见得类型，而且结构很复杂，很难找到它们的驱动IC，只能专门定做。结果导致五相步进电机的驱动电路产品异常昂贵。用普通步进电机如二相与四相步进电机的驱动控制IC来制作其它步进电机的驱动电路是一种经济有效的方法。L297继承了控制单极性和双极性步进电机所需要的所有控制电路系统。L298N双H桥驱动器形成了一个完善的步进电机微处理器接口。在这里，我们通过给L297和L298N加上微处理器和逻辑控制系统研究开发出了一种新的五相步进电机驱动电路。第二部分解释了元器件特性。第三部分介绍了控制逻辑电路设计。第四部分是接口设计，结果在第五部分。最后，第六部分加以总结。二、 主要元器件特性分析如图一所示，集成块L297可以与H桥集成电路一起使用作为步进电机驱动器。在该设计中，H桥的功能用L298N或者L293E实现。这要根据步进电机的额定功率而定。输入L297的控制信号可能来自为控制器或者外部开关。一个IC能驱动一个两相双极性永磁式步进电机，一个四相单极性永磁式步进电机或者一个四相变磁阻式步进电机。因为用到的电子元器件非常少，该设计好处颇多，比如，花费少，可靠性高，占用的空间相对较小。按照接收到的输入信号的不同，L297产生三种不同模式的相位序列，即半步模式，全步模式和波形模式。图一 用L297和L298N构成的驱动一个两相单极性步进电机或一个四相单极性步进电机的电路图A. 电流控制小型步进电机一般小型直流电源来控制绕组电流，它们的绕组电阻也是有限制的。在另一方面，拥有较大额定扭矩值的步进电机具有较小的绕组电阻。因此，它们需要对电流进行控制。L297以两个脉冲宽度调制（PWM）斩波电路的形式提供负载电流控制，每个斩波电路由一个比较器，一个触发器和一个外部感应电阻组成。在该理论中，当电机电流增加时，控制系统将电源电压施加到电机。如图二所示，当电流值达到阈值时，控制系统将通过改变电源电压的占空比来维持电流的期望值。对于每一个斩波电路来说，步进电机电源电压的占空比（D）定义为：D = Ton / (Ton + Toff),其中Ton 和Toff分别是H桥的导通和断开时间。在斩波电路中，触发器由来自振荡器的各个脉冲置位，从而允许输出和允许负载电流增长。感应电阻两端的电压随着负载电流的增长而增长，当电压增长到Vref时，触发器被重置，输出中断直到下次振荡器脉冲到来。在该方法中，Vref决定了负载电流的峰值。图二 包含触发器、振荡器和电压比较器的电流控制电路图三 用于电流控制的PWM操作的电压图三展示了穿过电机的电流是如何被控制的。当电机的电流超过设定值时，施加于电机端得电压将降为零。因此，电流将会衰减，最终电机电流被控制住。L298N是一块包含着两个H桥的单片集成电路。此外，低位晶体管的发射极被引出来作为扩展端子以允许电流敏感电阻的连接。B抑制斩波模式下的电流控制抑制斩波控制模式和相位线斩波控制模式是当今两种最常见的电流控制技术。在后一种方式中，当敏感电阻的电压达到Vref时,只有低端的开关断开。因此这种方法并不适用，我们选用抑制斩波模式。需要的开关序列可以直接来自L297N。抑制斩波模式可以通过将L297N的CONTROL端接地实现。然后斩波作用于INH端来控制通过电机线圈的电流。因此，L297输出的INH信号对创造L298N的使能信号起着非常重要的作用。在敏感电阻的电压达到Vref的情况下，斩波触发器被重置，INH端子被激活并处于低电平状态。然后，所有四个桥电路截止。斩波频率由L2907内部的振荡器决定。在所有的晶体管截止之后，二极管为绕组电流提供转移通路。在下一个振荡周期里，H桥导通。图四说明了当相信号A处于高电平而相信号B处于低电平的时刻的电流控制情况。为了产生和INH1信号相同的激发信号来控制负载电流，这些A和B信号被输入到与L298N中高、低电平开关相连的两个与门。当且仅当INH1为高电平时，与门的输出为高电平。图四 当CONTROL为低电平时的抑制斩波波形三、 逻辑电路设计如图五所示，在任何运行模式下，L297的A,B,C,D相的波形每隔四个时钟周期重复一次。为构建五相步进电机驱动电路，在十个时钟周期之后对相波形进行转换十分重要。图五 在一般工作模式下，L297四相步进电机的两相或者两相步进电机绕组被导通，每四个时钟周期后序列重复图六 五相激励序列通过分析L297的3种工作模式，很明显应该选择一般工作模式，也通常被称作两相导通模式，来产生如图六所示的激励五相步进电机的序列。通过研究五相步进电机所需要的激励序列和L297的A,B,C,D相序列来设计出需要的逻辑电路。按照下列步骤进行。1、 如图六所示，从五相的激励序列中分离出每一相的高低侧晶体管激励模式。2、 从L297的A,B,C,D选出合适的相位来产生高侧激励序列。3、 利用微控制器的A,B,C,D输出信号和相关的与门产生L298N的输入信号。4、 产生L298N的ENA（A使能）和ENB（B使能）信号。将10步的相型分为20步等同于L297输出的四个时钟周期的相型。图七解释了高、低侧激励序列的时钟周期选择。通过选择L297的合适的输出相位，可以产生高侧晶体管的激励序列。已经选择的顺序，即L297的两相导通模式如图八所示。微控制器信号用以产生所需的高侧脉冲模型。有四个输入端的DM74LS08含有两个门，用来将接收到的L297信号和微控制器信号相与。如图九所示，输入信号和使能信号共同决定了高低侧晶体管的开关模式。因此，微控制器提供了使能（EN）信号。但是为了达控制电机电流的目的，INH信号必须与L298N的使能信号衔接，这在下面的电流控制部分会有解释。图十解释了怎样利用由微控制器产生的所需的使能信号和来自L297的抑制（INH）信号来产生L298N的EN信号。这两种信号的与操作产生了L298N相关的EN信号。图七 需要的高低侧晶体管的激励序列图八 L298N输入信号的产生L298N包含两个H桥，其中一个H桥的输出端被用作一相。H桥的两个输入端彼此独立。因此，单独一个H桥的两个输出端都无法使用。为了产生五个相数（的信号），需要使用3个L298N双H桥驱动IC。L298N的输入端与输出端选择将在第四部分的图十三中加以说明。图九 L298N的拉高与接低操作图十 使能信号的产生四、 接口设计用以产生L298N需要的输入信号的逻辑电路和微控制器控制信号在驱动电路中扮演着主要角色。图十一展示了L297的接口，DM74LS08双与门IC和与微控制器PIC16F877A相连的L298N。图十二说明了电路的配置。为了限制通过电机绕组的电流，控制信号必须接地以进入抑制控制模式。微控制器提供了CLOCK信号，HALF/FULL引脚必须接地来进入全步模式（两相导通模式）。ENABLED是用来控制电机运转的。当它处于低电平状态时，INH1, INH2, A, B, C, D都被置于低电平状态。Vref的取值设定了通过电机的电流。这里用到了两个L297，必须使它们同步。这可以通过使用L297的SYNC引脚轻易做到。图十一 系统框图图十三说明了L298N的输入与输出端的使用方法。通常会在Vs 和 Vc 与地之间使用100nF的无感电容。为了避免大电流时的大幅度电压降落，电流敏感电阻器的阻值必须小到0.5。当IC的输入被截断时，外部桥式二极管提供电流通路。这里通常使用肖特基二极管，因为肖特基二极管容易恢复。五、 结论对步进电机驱动电路的设计方式的理论分析和逻辑分析显示了驱动电路是一种具有几种操作模式和控制模式的简单结构。图十二 L297的配置 图十三 L298N的配置如图十四所示的步进电机驱动电路实物通过了下列性能测试：1. 速度控制性能2. 电流控制性能图十五（a）和（b）展示了在每一相线端得激励信号波形。步进电机五相的激励序列说明它们是按要求工作的。图15（b）显示了橙色的和绿色的激励序列来使黑色的激励序列与其他激励序列相比较。因为流过电机绕组的电流会使电容器充放电，在每一个激励点都会发生突变。通过变换电机五相的激励序列的频率，可以达到控制电机速度的目的。可以明显地看到，在相同的时间分辨率5ms/div下，在图十六（a），（b）中的电压序列的脉冲宽度是图十五（a），（b）中的两倍。可以看出，与图十五所示的激励序列相关的步进电机的转动速度（速度1）是与图十六所示激励序列相关的步进电机转动速度的一半。因此，通过改变由PIC微控制器产生的激励序列的脉冲频率，步进电机的速度也随之改变。图十四 带微控制器的驱动电路图十五（a）在速度1下的蓝、红、橙、绿相电压图15（b） 在速度1下的橙，绿、黑相电压图16（a） 在速度2下的蓝、红、橙绿相电压图16（b） 在速度2下的红、橙、绿、黑相电压图17（a）、（b）、（c）证明了该步进电机驱动电路的电流控制能力。为了达到证明效果，这里只考虑了红色相电压，图17给出了在更高的Vref (=600mV)下的电流波形，该电压高于Vsense。此时，INH信号并未接地来限制通过步进电机的电流。每一相都有正负电流部分，因为相电压从+Vs, +Vs/2变化到 0V，相电流也分别从正、零变为负，相当于后者的电压变化。通过截断L298N的抑制信号（INH信号），电机端子上的电压被限制以控制通过电机绕组的电流。图十七（a） 当Vref = 120 mV时的相电流和INH信号的变化 图十七（b）和（c）给出了当Vref 取两个不同值200mV 和120 mV 时的电流控制能力。图十七（b） 当Vref = 200 mV时的相电流和INH信号的变化图十七（c） 当Vref = 120 mV时的相电流和INH信号的变化六、 总结和市场上的步进电机驱动器相比，这种新提出的五相步进电机驱动器是非常廉价的。由于带有必要的控制能，这款驱动器可用于一般的五相步进电机应用场合。该驱动器简单的结构和坚实的设计使得它具有另外一项优点，那就是它可以应用在机器人上，因为它占用的空间小。最后，该设计还可以作为一种具有许多诸如电流控制，速度控制等附加功能的廉价五相步进电机的雏形。它可以作为一款价廉物美的驱动器推向市场。Development of a Novel Drive Topology for a Five Phase Stepper MotorT.S. Weerakoon and L. SamaranayakeDept. of Electrical and Electronic Engineering, Faculty of Engineering, University of Peradeniya, Sri LankaAbstract-In this paper, a novel drive topology for a five phase stepper motor is described in detail. Commercially off the shelf, low cost, standard stepper motor drive ICs are used to derive a novel drive topology for five phase stepper motors which enables closed loop speed and position control powered by inner current control loop. It is proved that the derived topology can be generalized to any stepper motor with higher odd number of phases. The designed driver consists of full step, half step, clockwise and counter clockwise drive modes with the speed control and current control. I. INTRODUCTIONIn most of the robotics and automation engineering designs various types of stepper motors are used to obtain the required motion profiles. Stepper motors are preferred, as they do not require frequent maintenance and due to their ability to operate in many harsh environments. Selection of the motors and their drive circuits depend on the required performance characteristics of the applications. The two phase and four phase stepper motors are the most common types available in the market.However, for applications requiring high precision, low noise and lower vibration, Five Phase Stepper Motors are used. Due to smaller step angle, five phase stepper motors offer higher resolution, lower vibration and higher accelerations and decelerations. Therefore it is essential to make sure that these motor characteristics can be obtained from the designed drive topology.Because the five phase stepper motors are a rarely used type in the robotic applications and the construction is typically complicated, it is very difficult to find driver ICs, which are manufactured exclusive for them. As a result, the available Driver circuits for five phase stepper motors are very expensive.Using the available drive control ICs manufactured for common kinds of stepper motors such as 2 phased and 4 phased and using them in modeling new driver topology for other stepper motors would be a cost effective approach.The IC L297 integrates all the control circuitry required to control bipolar and unipolar stepper motors. The L298N dual H bridge drive forms a complete microprocessor to stepper motor interface. Here, novel drive topology is investigated and developed for five phase stepper motors by adding a microprocessor and logical control system with L297 and L298N. The complete topology is described in this paper.Section II explains the component characteristics. Section III is on the control logic circuit design phenomena. The interface design is given in Section IV with results in Section V. Finally the conclusions are presented in Section VI.II. CHARACTERISTIC ANALYSIS OF MAIN COMPONENTSThe IC L297 can be used with an H bridge driver IC for motor drive applications as shown in Fig.1. In this design H bridge function is achieved from the L298N or L293E. This may change depending on the power rating of the motor. The control signals to the L297 may be received from microcontroller or from external switches. A single IC can drive a 2 phase bipolar permanent magnet motor, a 4 phase unipolar permanent magnet motor or a 4 phase variable reluctance motor. Because very few electronic components are used, it has many advantages such as lower cost, higher reliability and the ability to house in a comparatively smaller space. The L297 generates three modes of phase sequences, namely half step mode, full step mode and wave mode depending on the input signals it receives. Fig. 1. Circuit diagram to drive a 2 phase bipolar or 4 phase unipolar stepper motor using L297 and L298N ICsA. CURRENT CONTROLSmall stepper motors generally need small DC supplies that control the winding currents and they are limited by the winding resistances. On the other hand, motors with the larger rated torque values have windings with smaller resistances. Therefore, they require a controlled current supply.The L297 provides load current control in the form of two Pulse Width Modulation (PWM) chopper circuits and each chopper circuit consists of a comparator, a flip-flop and an external sensing resistor.In this method, while the motor current is increasing, the control system applies the supply voltage to the motor. When the current is reached up to the threshold, the control system tries to maintain the current at the desired value by changing the duty ratio of the voltage supply as shown in Fig.2. For each chopper circuit, the duty ratio (D) of the voltage supply to the motor is defined as:D = Ton / (Ton + Toff),where the Ton and Toff are switch on and off durations respectively of the H bridge.In the chopper circuit, the flip-flop is set by each pulse from the oscillator, enabling the output and allowing the load current to increase. As it increases the voltage across the sensing resistor increases and when this voltage reaches Vref the flip-flop is reset, disabling the output until the next oscillator pulse arrives. In this method Vref determines the peak load current.Fig. 2. Circuit containing the flip-flop, the oscillator and the comparator used Fig.3. PWM operation of the voltage for current control for current controlling Fig.3 shows how the current through the motor is controlled. When the motor current goes beyond the set point, the voltage applied to the motor terminal will be grounded. Therefore the current will decay and finally the motor current can be controlled. The L298N is a monolithic circuit contains two H bridges. In addition, the emitter connections of the lower transistors are brought out to external terminals allowing the connection of current sensing resisters.B. CURRENT CONTROL IN INHIBIT CHOPPER MODE Inhibit chopper control mode and phase line chopper control mode are two of the most common types of current control techniques available. In the latter case when the voltage across the sensing resistor reaches to Vref, only the low side switch is made off. Hence this method is not suitable and inhibit chopper control mode has to be used. The required switching sequences for this can be taken directly from L297. Inhibit chopper mode can be selected by pulling down (grounded) the CONTROL input signal of L297. Then chopper acts on INH to control the current through the motor coils. Therefore the contribution of INH signal generated from L297 is very important to create ENABLE signal for L298N. In the case when the voltage across the sensing resister reaches to Vref, the chopper flip-flop is reset and INH is activated and is brought to low. Then it turns off all four switches of the bridge. The chopping frequency is determined by the internal oscillator of the L297. After switching off all transistors, the diodes provide a path to divert the winding current. The switches of the H bridge are made on in the next oscillator cycle. Fig.4 explains current control phenomena at an instant when phase signal A is high and B is low. These A and B signals are fed to two AND gates connected to low and high side switches in the L298N to generate excitation signal with the same INH1 signal in order to control the load current. The AND gate output will become high only if and only if the INH1 is high.Fig. 4. Inhibit chopper waveform when CONTROL is LOWIII. LOGIC CIRCUIT DESIGNING In any mode of operations, wave patterns of A, B, C and D phases of the L297 repeat after four clock cycles as shown in Fig.5. Translation of the repetition of the phase waveform after the ten clock cycles is essential to derive the drive topology for the five phase stepper motor.Fig. 5. In the normal operation, L297 two phases of a 4 phase stepper motor or two ends of a 2 phase stepper motor winding are made ON at a time and the sequence repeats after every 4 clock cyclesFig. 6. Five phase excitation sequence By analyzing the three modes of operations of the L297, it is clear that in the normal drive mode, which is usually called as two-phase-on drive mode, should be selected to achieve the required excitation sequence for a 5 phase stepper motor as shown in the Fig.6. By studying the required excitation sequence for 5 phase stepper motor and A, B, C, D phase sequences of the L297, the required logic circuit was designed. The procedure mentioned below was followed.(i) Separation of High and Low side transistor excitation pattern for each phase from five phase excitation sequences as shown in Fig.6.(ii) Selection of suitable phases from A, B, C and D of L297 to generate the high side excitation sequences.(iii) Generating input signals to the L298N using A, B, C, D output signals of the microcontroller and the relevant AND gates.(iv) Create ENA (enable A) and ENB (enable B) signals for L298N By dividing ten (10) steps of required phase pattern in to twenty (20) steps can be equated to the four clock cycles of output wave pattern generated by the L297. The Fig.7 explains the clock cycle selection for required high and low side excitation sequence. High side transistor excitation sequence can be generated from L297 by selecting suitable output phases of the L297. The selected order, which is the two-phase-on mode of L297 is shown in the Fig.8. The microcontroller signals are used to generate the required high side pulse patterns. The DM74LS08 Quad 2-Input AND Gates are used to AND microcontroller signals and signals received from L297. As shown in Fig.9, the input signals and Enable signals determine the high side and low side transistor switching patterns. Therefore ENABLED (EN) signals are fed from the microcontroller. But to achieve current control of the motor INH signal must engaged with the Enabled signal to the L298N as explained under current control section. The Fig.10 explains how the EN signal to L298N is generated using the required Enable signal created by the microcontroller and Inhibit (INH) signal from L297. An AND operation of these two signals generates the relevant EN signal for L298N.Fig. 7. Required High and Low side transistor excitation sequencesFig. 8. Generation of Input signals to the L298N The L298N consists with H-bridges and one output of a bridge was used for a phase. Two inputs of one H bridge is dependent each other. Therefore both outputs of a single bridge cannot be used. To generate five phases, it is required to have three numbers of L298N dual full bridge driver ICs. The selection of inputs and outputs of L298N are shown in Fig.13 of Section IV.Fig. 9. Pull up and Pull down operation of L298NFig.10. Generation of ENABLED signalIV. INTERFACE DESIGNING The logic circuitry used to generate required input signals for L298N and microcontroller control signals play a major role in the driver circuit. The Fig.11 shows interface of L297, DM74LS08 Quad 2-Input AND Gates ICs and L298N with the microcontroller PIC16F877A. The circuit configuration for L297 is shown in Fig.12. The control signal has to be grounded to obtain the inhibit control mode in order to limit the current through the motor windings. The CLOCK signal is supplied by the microcontroller and HALF/FULL pin should always to be low for full mode (two-phase-on) of operation. The ENABLED signal is used to control the motion of the motor. When it is low, all INH1, INH2, A, B, C, D pins are brought to low. The Vref value sets the current flowing through the motor. There are two L297 ICs used and it is necessary to synchronize them. It can be done easily by using the SYNC pin of L297.Fig. 11. Block diagram of the system The Fig.13 shows how the input and output terminals are used in L298N. Usually 100nF non-inductive capacitors are used between both Vs and Vc with the ground. The value of the current sensing resistor has to be as small as 0.5 in order to avoid large voltage drops at large currents. External diode bridges provide current circulating paths when the inputs of the IC are chopped. Usually Schottky diodes are used here because they are faster in recovery.V. RESULTS The theoretical and logical analysis of the stepper drive circuit design approach shows that it is a simple construction having several modes of operation and control.Fig. 12. Configuration of L297 Fig.13. Configuration of L298N The performance of the stepper drive circuit shown in the Fig.14 was tested for the following capabilities: 1. Speed control capability 2. Current control capability The Fig.15 (a) and (b) show the excitation wave forms at each phase terminal. The excitation sequences for all five phases reveal that they are working according to the requirement. Fig.15 (b) shows additional orange and green phase excitation sequences to compare the black phase excitation with the others. Due to the charging and the d