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Application of LMD18245 in Two Phase Hybrid Stepping Motor Driver 1 Pu Ji1, Xiuhe Wang1, Feng Lin2, Rong Zhang1, Shiyong Liu1 Department of Electrical Engineering, Shandong University, Jinan 250061, China 2 Shenyang Institute of Aeronautical Engineering, Shenyang, 110034,China Abstract—This paper proposed a PWM control circuit for two-phase hybrid stepping motor based on LMD18245. The circuit uses two pieces of EPROMs and DACs to achieve 1/5 microstepping. Choosing different address of EPROM by selecting the coding switch, it can output different current and number of subdivision. The driver system has quite good characteristic and is quite simple, reliable and versatile. I. INTRODUCTION Stepping motor is a kind of electromechanical component that is driven in step angle or line displacement by electric pulse signal. Because of having the advantage of easy open-loop control and no accumulating error, stepping motor is being applied widely in many fields. It plays an important role in manufacture, transportation, etc. In order to meet the requirement of high-precision orientation and moving smoothness, subdivision driving of stepping motor is adopted. Microstepping is a relatively new stepping motor technology that controls the current in the motor winding to a degree that further subdivides the number of positions between poles. In this paper a micro-stepping driver for two-phase hybrid stepping motor is designed. Commonly the logic control circuits of stepping motor is made of the circular impulse distributor. According to the need of stepping motor excitation which store in ROM sequentially in the form of binary, we get the circular impulse distributor. The output current of circular impulse distributor is very small, which can't drive the stepping motor directly , so all connect with the power amplification circuit. This kind of driver circuit has such shortcomings as bad dependability and complexity. This paper proposed one hb stepping motor driver based on memory technology. In designing of the micro-stepping driver, two pieces of EPROMs and D/As are used. All the technology made the overall circuit has a higher running performance, fast switching time, small power dissipation and volume. II. THE TWO PHASE HB STEPPING MOTOR DRIVER SYSTEM crostepping function comprises of an adder/subtractor, EPROM and a digital to analog converter with its voltage reference. The operational amplifiers are used such that one amplifies the actual stator current signal and the other compares the required amount of current and the actual current measured. The required amount of current is obtained from the DAC. The voltage reference determines the maximum amount of stator current that the motor can handle at sustained operations. Fig.1 .two phase HB step motor driver system This scheme provides a digital path for controlling the motor current and 1/5 microstepping. In this paper we use an external digital-to-analog converter(DAC) to provide voltage reference, use LMD18245 to achieve bipolar chopper drive. The two input signals (voltage reference) for LMD18245 are sinusoidal and 90°out of phase. This may be accomplished by using two look-up tables stored in ROM and DACs. An up/down counter may be used to generate the appropriate address locations for the ROMs and the data outputs used to control the DACs. We can change speed of the motor by adjust the frequency of clock pulse and this circuit can also make stepping motor rotating in both direction change direction by adjusting the UP/DOWN level. The counter can be preset to any binary number present on the jam inputs by a high level on the PRESET line. We can achieve different micro-step by change the preset binary number. The experimental results demonstrated that this control method can effectively improve the performance of two phase hybrid stepping motor systems. III. THE PRINCIPLE OF LMD18245 The LMD18245 full-bridge power amplifier incorporates all the circuit blocks required to drive and control current in a brushed type DC motor or one phase of a bipolar stepper motor. The LMD18245 controls the motor current via a fixed off-time chopper technique. An all DMOS H-bridge power stage delivers continuous output currents up to 3A (6A peak) at supply voltages up to 55V. The DMOS power switches feature low RDS for high efficiency, and a diode intrinsic to the DMOS body structure eliminates the discrete diodes typically required to clamp bipolar power stages. An innovative current sens- One of the most important considerations in the motor applications is the design of appropriate drive circuits. The dynamic performance of a step motor is heavily dependent on the drive circuits. Based on analysis on driving technology of stepping motors, a new stepping motor driver system is developed in this paper as shown in Figure 1.It has quite good characteristic and is quite simple, reliable and versatile. The portion of the block diagram which implements the microstepping function comprises of an 706 ing method eliminates the power loss associated with a sense resistor in series with the motor. A four-bit digitalto-analog converter (DAC) provides a digital path for controlling the motor current, and, by extension, simplifies implementation of full, half and microstep stepping motor drives. For higher resolution applications, an external DAC can be used. plifier can control current in one phase of a bipolar stepper motor. The stepping motor driver system consists of EPROM and digital-to-analog converter(DAC) that generate voltage reference, which provide a digital path for controlling the motor current and LMD18245 which is a H-bridge power amplifier. The 20 k Ω resistor and 2.2 nF capacitor connected between RC and ground set the offtime at about 48 μ s, and the 2.2 k Ω resistor connected between CS OUT and ground sets the gain at about 1A per volt of the threshold for chopping. Digital signals control the thresholds for chopping, the directions of the winding currents, and, by extension, the driver type (full step, half step, etc). Fig.2 function block and connection diagram of LMD18245 Chopper amplifiers employ feedback driven switching of a power bridge to control and limit current in the winding of a motor (Figure 2). The bridge consists of four solid state power switches and four diodes connected in an H configuration. Control circuitry monitors the winding current and compares it to a threshold. While the winding current remains less than the threshold, a source switch and a sink switch in opposite halves of the bridge force the supply voltage across the winding, and the winding current increases rapidly towards VCC/R. As the winding current surpasses the threshold, the control circuitry turns OFF the sink switch for a fixed period or offtime. During the off-time, the source switch and the opposite upper diode short the winding, and the winding current recirculates and decays slowly towards zero. At the end of the off-time, the control circuitry turns back on the sink switch, and the winding current again increases rapidly towards VCC/R. The above sequence repeats to provide a current chopping action that limits the winding current to the threshold. Chopping only occurs if the winding current reaches the threshold. During a change in the direction of the winding current, the diodes provide a decay path for the initial winding current. Since the bridge shorts the winding for a fixed period, this type of chopper amplifier is commonly referred to as a fixed off-time chopper. Fig. 3. Typical application circuit for driving bipolar stepper motors. To make the motor take 1/5 steps, the windings can also be energized with sinusoidal currents. The motor takes one 1/5 step each time the level of either winding current changes. IV. THE TYPICAL APPLICATION OF LMD18245 This paper proposed a PWM control circuit for two phase hybrid stepping motor based on LMD18245 as shown in Figure 3. It has quite good characteristic and is quite simple, reliable and versatile. In this scheme, we leave the interior DACs unused, M1 to M4 connect to +5Vand impose the two external input signals on DAC REF. Thus we can divide the winding current into 20 equivalent portions. The LMD18245 H-bridge power am- 707 Fig.4 winding currents and lookup table for 1/5 step drive Along with the obvious advantage of increased step resolution, microstepping reduces both full step oscillations and resonances that occur as the motor and load combination is driven at its natural resonant frequency or subharmonics thereof. Both of these advantages are obtained by replacing full steps with bursts of microsteps. When compared to full step drive, the motor runs smoother and quieter. Figure 4 shows the lookup table for this application of the typical application circuit. Dividing 90°electrical per full step by five microsteps per full step yields 18° electrical per microstep as is shown in Figure 5. α , therefore, increases from 0 to 342° in increments of 18°. Each full 360° cycle comprises twenty half steps. Rounding |cosa| to five bits gives DA, the decimal equivalent of the binary number applied at DAC reference. DIRECTION A controls the polarity of the current in winding A. Fig.7 two phase voltage reference Fig.5 .current vector after subdivision V. EXPERIMENTAL RESULTS The proposed control scheme was validated for experiment. A 24V 1A 0.46-mm-pole-pitch two phase hb stepping motor was used in these experiments. The sampling rate was approximately 3.3 kHz. Since the driver fulfill 1/5 subdivision, one cycle voltage reference corresponds with 20 pulses as is shown in Fig 6. At the same time one cycle direction signal corresponds to 20 pulses. Fig 7 shows the two phase voltage references which phases difference 90°electrical. Fig.8 .direction signal and pulse Fig.9 .direction signal and voltage reference Fig.6 voltage reference and pulse 708 per. This circuit can also make stepping motor roatting in both direction, speed adjust and brake control as well. The capabilities of the system have been investigated and a typical application successfully implemented and demonstrated. REFERENCES [1] T. Kenjo and A. Sugawara, Stepping Motors and Their Microprocessor Controls, 2nd ed. London, U.K.: Oxford Univ. Press, 1994. [2] D. W. Novotny and T. A. Lipo, Vector Control and Dynamics of ac Drives. London, U.K.: Oxford Univ. Press, 1996.. [3] Rahman, M.F. Poo, A.N. “An application oriented test proce dure for designing microstepping step motor controllers”,1988,IEEE Trans. pp,542-546. [4] Layer H.P.,”Digital sine cosine mine stepping drive”, Proc, 6th annual symposium on IMCSD 1977, USA, pp.179-184. [5] S. M. Yang, F. C. Lin, and M. C. Chen, “Control of a two-phase linear stepping motor with three-phase voltage source inverter,” in Proc. IEMDC’03, June 2003, pp. 1720–1725. [6] Middleton ,et al. Electronmagnetic damping for stepper motors with chopper drivers, IEEE Transaction on industry electronics, 1986, 33(3): 241~246. Fig.10 .one phase winding voltage VI. CONCLUSION Based on the memory technology, a stepping motor drive system has been successfully developed in this pa- 709