Knowledge of the stepper motor
What is a stepper motor
  Stepper motor is a kind of electrical pulses into angular displacement of the implementing agency. Popular little lesson: When the driver receives a step pulse signal, it will drive a stepper motor to set the direction of rotation at a fixed angle (and the step angle). You can control the number of pulses to control the angular displacement, so as to achieve accurate positioning purposes; the same time you can control the pulse frequency to control the motor rotation speed and acceleration, to achieve speed control purposes.
What kinds of stepper motor sub-
  In three stepper motors: permanent magnet (PM), reactive (VR) and hybrid (HB) permanent magnet stepper usually two-phase, torque, and smaller, step angle of 7.5 degrees or the general 15 degrees; reaction step is generally three-phase, can achieve high torque output, step angle of 1.5 degrees is generally, but the noise and vibration are large. 80 countries in Europe and America have been eliminated; hybrid stepper is a mix of permanent magnet and reactive advantages. It consists of two phases and the five-phase: two-phase step angle of 1.
8 degrees while the general five-phase step angle of 0.72 degrees generally. The most widely used Stepper Motor.
What is to keep the torque (HOLDING TORQUE)
  Holding torque (HOLDING TORQUE) is the stepper motor power but no rotation, the stator locked rotor torque. It is the stepper motor one of the most important parameters, usually when the stepper motor torque at low speed near the holding torque. As the stepper motor's output torque increases with the speed and continuous attenuation, output power increases with the speed change, so keep the torque stepper motor to become a measure of one of the most important parameters. For example, when people say 2N.m the stepper motor in case of no special note is the holding torque of the stepper motor for
What is DETENT TORQUE
  DETENT TORQUE is the stepper motor is not energized, the stator locked rotor torque. DETENT TORQUE translation in the country there is no uniform way, easy to misunderstand us; the reaction is not a permanent magnet stepper motor rotor material, so
it does not DETENT TORQUE.
How much precision stepper motor? Whether the cumulative
  The general accuracy of the stepper motor step angle of 3-5%, and not cumulative.
Stepper motor to allow the minimum amount of surface temperature
Stepper motor causes the motor temperature is too high the first magnetic demagnetization, resulting in loss of torque down even further, so the motor surface temperature should be the maximum allowed depending on the motor demagnetization of magnetic material points; Generally speaking, the magnetic demagnetization points are above 130 degrees Celsius, and some even as high as 200 degrees Celsius, so the stepper motor surface temperature of 80-90 degrees Celsius is normal.
Why is torque stepping motor will decrease with the increase of speed
  When the stepper motor rotates, the motor winding inductance of each phase will form a reverse electromotive force; the higher the frequency the greater the back emf. In its role, the motor with frequency (or speed) increases with the phase current decreases, resulting in decreased torque.
Why is higher than a certain speed stepper motor will not start
  Stepper motor has a technical parameters: no-load starting frequency, ie the stepper motor with no load to start the normal pulse frequency, pulse frequency is higher than the value if the motor does not start, you may lose steps or stall occurs. In the case of a load, start frequency should be lower. If you want the motor to achieve high-speed rotation, the pulse frequency should speed up the process, which started lower frequency, and then rise by a certain acceleration of the desired frequency (motor speed from low rise to high-speed).
How to overcome the two-phase hybrid stepping motor vibration and noisereaction in the shaft
    Low-speed rotation of the stepper motor vibration and noise is an inherent disadvantage of a large, generally can be used to overcome the following programs:
A. If the stepper motor just work in the resonance, by changing the gear ratio can be mechanical transmission to avoid the resonance region;
B. sub-function used with the drive, which is the most common and easiest method;
C. into a smaller step angle stepper motors, such as three or five-phase stepper motor;
D. replace the AC servo motor, can be almost completely overcome the vibration and noise, but the cost is high;
E. increase in the magnetic damper motor shaft, the product already on the market, but a larger change in mechanical structure.
The breakdown of the number of sub-driver is able to represent the precision
    Subdivision stepper motor is essentially an electronic damping (see the literature), its main purpose is to weaken or eliminate low-frequency vibration of the stepper motor to improve the accuracy of the motor running with only one functional subdivision. For example, 1.8 ° step angle of the two-phase hybrid stepping motor, if the number of sub-segments of the drive is set to 4, then the motor running a resolution of each pulse 0.45 °, the precision can motor at or near 0.45 °, also depends on the breakdown of sub-drive current control accuracy and other factors. Breakdown of different manufacturers may vary significantly drive precision; subdivision greater precision the number of difficult control.
Series connection and What is the difference and join law
  Four-phase hybrid stepping motor and driver in series connection and the connection met
hod and what is the difference?
  Four-phase hybrid stepping motor drives are generally two phases to drive, so connection can be used in series connection and the connection method or the four-phase motor connected into a two-phase use. Series connection is generally used where a low motor speed, this time need to drive the motor phase current output current of 0.7 times, so a small motor heating; and join law generally places a higher motor speed to use (also known as high-speed access method), the required drive output current 1.4 times the motor phase current, and thus a larger motor heat.
How to determine the stepper motor driver DC power supply
    A. Determination of the voltage
Hybrid stepping motor driver power supply voltage is generally a wide range (such as the IM483 supply voltage of 12 ~ 48VDC), the supply voltage is usually based on the work of the motor speed and response to the request to choose. If the motor operating speed higher or faster response to the request, then the voltage value is high, but note that the ripple voltage can not exceed the maximum input voltage of the drive, or it may damage th
e drive.
  B. Determination of Current
Power supply current is generally based on the output phase current drive I to determine. If a linear power supply, power supply current is generally preferable 1.1 to 1.3 times the I; if we adopt the switching power supply, power supply current is generally preferable to I, 1.5 to 2.0 times.
Hybrid stepping motor drive signal is FREE to use offline
  FREE off-line signal when low, the drive output to the motor current is cut off, the rotor is in a free state (off state). In some automation equipment, uninterruptible power if the drive directly in cases of motor shaft rotation (manual mode), you can set FREE signal is low, the motor off, the manual operation or adjustment. Manual is completed, then the FREE signal set high, to continue to automatic control.
How to adjust the power of two-phase stepper motor direction of rotation
Just drive the motor wiring and A + and A-(or B + and B-) can be reversed.
The main characteristics of stepping motor
  A stepper motor drive can be added operate pulse drive signal must be no pulse when the stepper motor at rest, such as
If adding the appropriate pulse signal, it will to a certain angle (called the step angle) rotation. Rotation speed and pulse frequency is proportional to.
  2 Dragon step angle stepper motor version is 7.5 degrees, 360 degrees around, takes 48 pulses to complete.
  3 stepper motor has instant start and rapid cessation of superior characteristics.
Change the pulse of the order of 4, you can easily change the direction of rotation.
Therefore, the current printers, plotters, robotics, and so devices are the core of the stepper motor as the driving force.
Stepper motor control example
We use four-phase unipolar stepper motor as an example. The structure shown in Figure 1:
  Four four-phase winding leads (as opposed to phase A1 A2 B1 phase phase B2) and two public lines (to the power of positive). The windings of one phase to the power of the ground. So that the windings will be inspired. We use four-phase eight-beat control, ie, 1 ph
ase 2 phase alternating turn, would enhance resolution. 0.9 ° per step can be transferred to control the motor excitation is transferred in order as follows:
  If the requirements of motor reversal, the transmission excitation signal can be reversed. 2 control scheme
Control system block diagram is as follows
  The program uses AT89S51 as the main control device. It is compatible with the AT89C51, but also increased the SPI interface and the watchdog module, which not only makes the debugging process becomes easy and also more stable. The microcontroller in the program mainly for field signal acquisition and operation of the stepper motor to calculate the direction and speed information. Then sent to the CPLD.
CPLD with EPM7128SLC84-15, EPM7128 programmable logic device of large-scale, for the ALTERA company's MAX7000 family. High impedance, electrically erasable and other characteristics, can be used for the 2500 unit, the working voltage of +5 V. CPLD receives information sent from the microcontroller after converted to the corresponding control signal output to the stepper motor drive. Put the control signal drives the motor windings after the
input, to achieve effective control of the motor.      2.1 The hardware structure of the motor drive
Motor drive using the following circuit:
    R1-R8 in which the resistance value of 320Ω. R9-R12 resistance value 2.2KΩ. Q1-Q4 as Darlington D401A, Q5-Q8 for the S8550. J1, J2 and the stepper motor connected to the six-lead。
Advantages and disadvantages of stepper motor
Advantages
  1. The motor rotation angle is proportional to the number of pulses;
  2. When the motor stopped with a maximum torque (when the winding excitation time);
  3. Since the accuracy of each step in the three per cent to five per cent, and the error will not accumulate to the next step and thus has better positional accuracy and repeatability of movement;
  4. Excellent response from the stop and reverse;
  5. In the absence of brush, high reliability, it just depends on the life of the motor bearing li
fe;
  6. Motor response only determined by the number of input pulses, which can be used open loop control, which makes the motor and control structure can be relatively simple
System cost
  7. Just load directly connected to the motor shaft can also be extremely slow synchronous rotation.
  8. Speed ​​is proportional to the pulse frequency, and thus a relatively wide speed range.
Shortcomings
1. If not properly controlled prone to resonance;
2. Difficult operation to a higher speed.
3. Difficult to obtain high torque
4. There is no advantage in terms of volume weight, low energy efficiency.
5. Over load will destroy the synchronization, the work will be issued when high-speed vibration and noise.
Stepper motor drive method
Stepper motor can not be directly connected to AC or DC power supply frequency on the work, and must use a dedicated stepper motor driver, as shown in Figure 2, which consists of pulse control units, power drive unit, protection unit and other components. Fig crossed the midpoint of the two units can be surrounded by computer control to achieve. Stepper motor drive unit and the direct coupling, can also be interpreted as the power stepper motor computer controller interface, to be brief here.
Figure 2 stepper motor driver controller
Figure 2 stepper motor driver controller
1, single-voltage power driver interface
Practical circuit shown in Figure 3. Strings in the motor winding circuit with resistance Rs, the motor circuit time constant decreases, the motor can produce more high-frequency electromagnetic torque, but also alleviate the low-frequency electrical resonance phenomenon, but it caused an additional loss. Under normal circumstances, the simple single-voltage drive circuit, Rs is indispensable. Rs step on the stepper motor to improve the response shown in Figure 3 (b).
Figure 3 Single-voltage power-driven interface and single-step response curves
Figure 3 Single-voltage power-driven interface and single-step response curves

Figure 4 dual voltage power driver interface
  2, dual voltage power driver interface
Dual voltage-driven power interface shown in Figure 4. The basic idea of ​​dual-voltage drive is low (low frequency) with a low voltage UL-driven, and in the high-speed (high frequency) is driven with higher voltage UH. This power interface requires two control signals, Uh control signals for the high-pressure, U is the control pulse width modulated drive signals. Figure, the power tube constitutes TH and DL diode power conversion circuit. When Uh Low, TH shutdown, DL is the bias, low voltage UL on the winding power. High contrast Uh, TH conduction, DL reverse bias, on the winding high voltage power supply UH. This circuit allows the motor at high frequencies also have higher output, reduced power consumption and static locking.
    3, the high and low voltage power driver interface


Figure 5, high and low voltage power driver interface

Figure 5, high and low voltage power driver interface
High and low voltage power driver interface in Figure 5.

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