大学毕业设计（论文）
附录B引用外文文献及其译文
Development of a Novel Drive Topology
for a Five Phase Stepper Motor
Abstract: 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.
1.INTRODUCTION
In 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 th 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 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.
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液体点滴速度监控系统设计
2.CHARACTERISTIC ANALYSIS of MAIN COMPONENTS
The 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 for microcontroller or from external switches. A single IC can drive a 2 phase bipolar permanent magnet motor, a 4 phase 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 polar stepper motor using L297 and L298N ICs
A. CURRENT CONTROL
Small 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),
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大学毕业设计（论文）
Fig. 2. Circuit containing the flip-flop, the oscillator and the comparator used voltage for current control
Fig.3. PWM operation of the 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
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液体点滴速度监控系统设计
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 LOW
III. 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 cycles
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大学毕业设计（论文）
Fig. 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
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