Stepper Motor Drive based on DRV8825

Article excerpt from: http://bbs.21ic.com/forum.php?mod=viewthread&tid=279798&fromuid=835218

1.introduction of main parameters of stepping motor
Phase Number: The phase number of the stepper motor refers to the number of coils. There are two-phase, three-phase, four-phase, five-phase respectively. Pass
constant condition, high phase number, small step angle and high precision.
rated current: The current size of the motor during normal operation.
Step Angle: It represents the angle at which the motor rotates with each step pulse signal of the control system. This parameter is reversed
the actual accuracy of the stepper motor is reflected.
Holding torque : refers to the torque of the stator that locks the rotor when the stepper motor is energized but not rotated.
Braking torque: Refers to the moment when the stepper motor does not have power, the stator locks the rotor.
Maximum temperature: Stepper motor temperature is too high first will make the magnetic material of the motor demagnetization, resulting in torque drop and loss
The maximum temperature allowed on the surface of the motor shall be determined by the demagnetization point of the magnetic materials of different motors;
in other words, the demagnetization point of magnetic materials are above the degree of Celsius, and some even up to a degree Celsius,
so the stepping motor outside temperature in Celsius 80-90 degree completely normal.



2.DRV8825 Performance Introduction
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3.1 Chip introduction
The DRV8825 can drive a two four-wire stepper motor and can also drive two DC brushed motors, input
pressure 8-45v, maximum current 1.7A, can withstand the instantaneous voltage of 2.5A. Driven by a PWM input. Can be
by avref/bvref to adjust the electric current on the motor winding resistance, the current size should be the motor rated current;
with mode0/mode1/mode2, three corners to configure the subdivision drive mode, you can configure the 2/4/8/16/32
subdivision. Nhome feet, starting from power on the motor turned over $ the position of the ° is home state. Motor Go to Home State
the nhome pin will output a low level.

3.2 driver steps
Stepper motor to start must be in a fixed start frequency range, after starting can be increased by increasing the frequency of the driving pulse to speed up, the frequency should be slowly increased, the motor in the acceleration of inertia resistance will be relatively large. Stepping motor active load is divided into two types: inertia load, friction load, motor in the process of acceleration is mainly inertia load, the speed is stable after the main friction load.


3.Breakdown of Stepper motors
Introduction to 4.1 Subdivision:
The subdivision control of the stepping motor is realized by the phase currents of the stepper motor, taking the two-phase motor as an example, if the rated phase current of the motor is 3a 0 3a or from 3a mutation to Span style= "font-family: ' Times New Roman ';" >0 10 The motor is driven in a subdivision state, and the current in its windings changes only 0.3a 3a


The principle of 4.2 subdivision :
The subdivision principle is essentially the control of the current in the excitation winding of the motor, so that a uniform rotating magnetic field is formed inside the motor.

the role of 4.3 subdivision:
1. The subdivision allows the motor to operate more smoothly.
2. the torque is increased.
3. solve the noise problem when the motor is working at low frequency. Stepper motor in the low-frequency operation, there will be large vibration, large noise
's shortcomings. If the use of subdivision, it can be a good solution to this problem, Stepper motor subdivision control, from the
by controlling the current in the excitation winding of stepping motor, the synthetic magnetic field inside the stepping motor is homogeneous .
Circular rotating magnetic field, which realizes the subdivision of stepping motor step angle.

4.modulation of stepping motor

Different stepper motor in different subdivision mode has different effects, experiment to get a little experience, choose different subdivision mode, the motor speed can reach the fastest when the subdivision mode to drive the motor the best effect, the concrete will be reflected in the noise is small, the driving torque is large, the calorific value is small.

5. LAYOUT considerations for DRV stepper motor Drivers
DRV Cloth Board should pay attention to the treatment of heat dissipation, power (ldo,dc-dc) from the DRV as far as possible, the surrounding line does not matter around the DRV, Set aside a certain amount of space, the route has an impact on heat dissipation. the 0 foot of DRV is a heat sink, preferably on a weld board, and perforated to the back of the board to dissipate heat.

Stepper Motor Drive based on DRV8825