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1、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
2、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 generali
3、zed 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
4、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
5、 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 resolu
6、tion, 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
7、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 phase
8、d 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
9、 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 th
10、e 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
11、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,
12、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 sequence
13、s, 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 win
14、ding 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 (P
15、WM) 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
16、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 respectiv
17、ely 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 th
18、e 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
19、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
20、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 a
21、vailable. 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 chopp
22、er 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
23、 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 pro
24、vide 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
25、 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
26、 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 pha
27、se 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 a
28、s 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
29、 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
30、 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
31、 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 mod
32、e 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 h
33、igh 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 si
34、gnal 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 Inpu
35、t 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 bri
36、dge 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
37、 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
38、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 pi
39、ns 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
40、 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
41、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 L2
42、97 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 sequenc
43、es 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 discharging of the capacitors by the current flowing through th
44、e windings of the motor, there are some transients at each excitation points. The speed control of the motor has been achieved by varying the frequency of the excitation sequence of the five terminals. It is clearly shown that the pulse width of the voltage sequences of Fig.15 (a), (b) gets doubled
45、in the Fig.16 (a), (b) in same time scale of 5ms/div. It is observed that the rotating speed (speed 1) of the motor relevant to the excitation sequence shown in Fig.15 is half that of the speed (speed 2) of the excitation sequence shown in Fig.16. Hence by varying the pulse frequency of the excitati
46、on sequence generated by the PIC microcontroller, the speed of the motor can be varied.Fig. 14. Drive circuit with microcontrollerFig. 15(a). Voltages of the Blue, Red, Orange and Green phases at speed 1Fig. 15(b). Voltages of the Orange, Green and Black phases at speed 1Fig. 16 (a). Voltages of Blu
47、e, Red, Orange and Green phases at speed 2Fig. 16 (b). Voltages of the Red, Orange, Green and Black phases at speed 2 The current controlling capability of the motor drive circuit has been demonstrated in the Fig.17(a), (b), (c). For the sake of demonstration, only the RED phase has been considered
48、and Fig.17(a) shows the current wave at higher Vref (=600mV) which is greater than the Vsense. Then the INH signal does not pull down to limit the current absorb by the motor. Each phase has positive and negative current components, because the phase voltage varies from +Vs, +Vs/2 to 0V and current to the phase varies from positive, zero to negative respectively, corresponding to the latter voltage variation. By chopping the inhibit (INH) signal to the L298N, the voltage at the motor terminals is limited to control the current through each winding.Fig. 17(a). Phase Current and INH