What Is an Angle Driver?

A stepper motor driver is an actuator that converts electrical pulses into angular displacement. When the stepper driver receives a pulse signal, it drives the stepper motor to rotate a fixed angle (called "step angle") in a set direction, and its rotation runs step by step at a fixed angle. You can control the amount of angular displacement by controlling the number of pulses to achieve the purpose of accurate positioning; at the same time, you can control the speed and acceleration of the motor rotation by controlling the frequency of the pulses to achieve the purpose of speed regulation and positioning.

Stepper motor driver

A stepper motor driver is an actuator that converts electrical pulses into angular displacement. When the stepper driver receives a pulse signal, it drives the stepper motor to rotate a fixed angle (called "

Stepper motors are classified by structure: stepper motors are also called pulse motors, including reactive stepper motors (VR), permanent magnet stepper motors (PM), and hybrid stepper motors (HB).

(1) Reactive stepping motor: Also called induction, hysteresis or reluctance stepping motor. The stator and the rotor are made of soft magnetic material. The large magnetic poles evenly distributed on the stator are equipped with multi-phase exciting windings. The small teeth and slots are evenly distributed around the stator and the rotor. The torque is generated by the change of magnetic flux after power is applied. Generally three, four, five, and six phases; can realize large torque output (large power consumption, current up to 20A, high driving voltage); small step angle (minimum 10 '); power failure When there is no positioning torque; the internal damping of the motor is small, and the single-step operation (referring to the pulse frequency is very low) has a longer oscillation time; the starting and running frequency is higher.

(2) Permanent magnet stepping motor: Usually the motor rotor is made of permanent magnet material. The stator made of soft magnetic material has multi-phase excitation windings. There are no small teeth and slots around the stator and rotor. The stator current and magnetic field interact to generate torque. Generally two-phase or four-phase; small output torque (small power consumption, current is generally less than 2A, driving voltage 12V); large step angle (such as 7.5 degrees, 15 degrees, 22.5 degrees, etc.); a certain amount of power Holding torque; low starting and running frequency.

(3) Hybrid stepping motor: Also called permanent magnet reactive, permanent magnet induction stepping motor, mixing the advantages of permanent magnet and reactive. There is no difference between the stator and the four-phase reactive stepping motor (but the two magnetic poles of the same phase are opposite, and the N and S polarities generated by the windings on the two magnetic poles must be the same), and the rotor structure is more complicated (the inside of the rotor is a cylindrical permanent magnet). Magnet, coated with soft magnetic material at both ends, with small teeth and slots around it). Generally two-phase or four-phase; positive and negative pulse signals must be supplied; output torque is larger than the permanent magnet type (the power consumption is relatively small); the step angle is smaller than the permanent magnet type (generally 1.8 degrees); Positioning torque; higher starting and running frequency; a stepper motor that develops faster. ^[1]

The principle of stepper motor driver is powered by unipolar DC power. As long as the windings of each phase of the stepper motor are energized at the appropriate timing, the stepper motor can be rotated step by step. Figure 1 is a schematic diagram of the working principle of the four-phase reactive stepping motor.

The main structure of stepper motor driver mainly includes the following parts

The stepping motor cannot be directly connected to the power frequency AC or DC power supply to work, but must use a dedicated driver, as shown in the figure, it is composed of a pulse generation control unit, a power drive unit, a protection unit and so on. The two units enclosed by the dotted line in the figure can be realized by microcomputer control. The drive unit must be directly coupled with the drive (anti-electromagnetic interference), and it can also be understood as the power interface of the microcomputer controller, which is briefly introduced here.

1.Single voltage power drive

Practical single-voltage power drive interface and single-step response curve

The circuit is shown in the figure. A resistor Rs is connected in series in the motor winding circuit to make the motor circuit dual voltage power drive interface

The time constant is reduced, the motor can generate large electromagnetic torque at high frequencies, and it can also alleviate the low frequency resonance phenomenon of the motor, but it causes additional losses. In general, Rs is indispensable in simple single-voltage drive circuits. The improvement of Rs stepper motor single-step response is shown in Figure 3 (b).

2.Dual voltage power drive

The power interface of dual voltage drive is shown in Figure 4. The basic idea of dual voltage drive is to drive with lower voltage UL at lower (low frequency band), and drive with higher voltage UH at high speed (high frequency band). This power interface requires two control signals, Uh is a high-voltage effective control signal, and U is a pulse-width-modulated drive control signal. In the figure, the power tube TH and the diode DL constitute a power conversion circuit. When Uh is low, TH is off, DL is forward biased, and low voltage UL powers the winding. Conversely, Uh is high, TH is on, DL is reverse biased, and high voltage UH supplies power to the winding. This circuit allows the motor to have a larger output in the high frequency band, and the power consumption is reduced when the motor is stationary.

3.High and low voltage power drive

High and low voltage power drive interface is shown in the figure. The design idea of high and low voltage drive is that regardless of the high and low voltage power drive interface of the motor

Regardless of the operating frequency, the high-voltage UH power supply is used to increase the current leading edge of the conducting phase winding, and after the leading edge passes, the low-voltage UL is used to maintain the winding current. This effect also improves the high-frequency performance of the driver, and eliminates the need for series resistor Rs, eliminating additional losses. The high and low voltage drive power interface also has two input control signals Uh and Ul, which should be kept in sync, and the leading edge should change at the same time, as shown in the figure. In the figure, the conduction time t1 of the high-voltage tube VTH cannot be too large or too small. When it is too large, the motor current is overloaded; when it is too small, the dynamic performance improvement is not obvious. It is generally preferred to be 1 ~ 3ms. (It is more appropriate when this value is equivalent to the electrical time constant of the motor).

4.Chopper constant current power drive

The design idea of the constant current drive is to try to keep the current of the phase windings on a fixed value regardless of the lock, low frequency, and high frequency operation. Make the motor have a chopped constant current power drive interface as shown in Figure 6.

Constant torque output characteristics. This is a kind of power interface that is used more and better. Figure 6 is a schematic diagram of a chopped constant current power interface. R in the figure is a small resistance resistor for current sampling, which is called the sampling resistor. When the current is not large, VT1 and VT2 are simultaneously controlled by the walking pulse. When the current exceeds the value given by the constant current, VT2 is blocked and the power supply U is cut off. Because the motor winding has a large inductance, at this time, the diode VD freewheels to maintain the winding current, and the motor generates power by consuming the magnetic field energy in the inductance. At this time, the current will decay according to the exponential curve, and the current sampling value will also decrease. When the current is less than the value given by the constant current, VT2 is turned on and the power is turned on again. Repeatedly, the motor winding current stabilizes at a value determined by a given level, forming a small sawtooth wave, as shown in the figure.

The chopper constant current power drive interface also has two input control signals, where u1 is a digital pulse and u2 is an analog signal. The characteristics of this power interface are: the high frequency response is greatly improved, close to the constant torque output characteristic, the resonance phenomenon is eliminated, but the line is more complicated. Corresponding integrated power modules are available.

5. Up-conversion boost power drive

In order to further improve the high-frequency response of the drive system, an up-frequency boost power drive interface can be used. The voltage provided by this interface to the windings has a linear relationship with the motor's operating frequency. Its main loop is actually a switching regulated power supply. The frequency of the driving pulse is converted to a DC level by using a frequency-to-voltage converter, and this level is used to control the input of the switching regulated power supply, which constitutes frequency feedback. Power drive interface.

6. Integrated Power Drive

A variety of integrated power drive interface circuits for small power stepper motor drivers are available.

The L298 chip is an H-bridge driver designed to accept standard TTL logic level signals and can be used to drive inductive loads. The H-bridge can withstand 46V voltage and phase current up to 2.5A. The logic circuit of L298 (or XQ298, SGS298) uses a 5V power supply, and the power amplifier stage uses a voltage of 5 ~ 46V. The emitter of the lower bridge is led out separately to access the current sampling resistor. L298 (etc.) Adopts 15-pin dual in-line small-wattage package, industrial grade. Its internal structure is shown in Figure 7. The main feature of the H-bridge drive is the ability to energize the motor windings in both forward and reverse directions. L298 is especially suitable for two-phase or

Four-phase stepper motor drive. Stepping electric drive system composed of special chip