Download Application of LMD18245 in Two Phase Hybrid Stepping Motor Driver

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-
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