The essentials of micro DC motor knowledge

There are many micro DC motor applications. Various power tools, toy airplanes, personal care and other daily necessities will use micro motors. Different types of micro motors will be different. Tianfu Micro Motors has focused on the development and production of micro DC motors for many years. , Let’s focus on the important knowledge points of several different types of micro DC motors.

1. Brushless DC motor

1. Speed regulation and control method of brushless DC motor

(1) External analog signal control;

(2) Pulse frequency control;

(3) Built-in potentiometer speed control or external potentiometer control;

(4) PWM control.

2. The principle of speed regulation

In the application of brushless DC motor, the speed control method of DC motor is mostly pulse width speed control, which is the pulse voltage of the supply voltage. When the pulse is widest, the power becomes larger and the speed becomes faster. On the contrary, when the pulse width is reduced, the power And the speed will also decrease. （Note: The pulse width here is not the pulse frequency. The pulse width means that the high level time is long, the low level time is short, and the pulse frequency has not changed. This pulse width modulation does not directly adjust the speed of the DC motor, but adjusts the speed by changing the power or torque of the DC motor.）

3. Judgment method of the number of poles of brushless DC motor

If the driver used is a CD series, you can use the ZERO command to control, so that the driver current flows in from the C terminal of the stator winding and then flows out from the B terminal, which will generate a stator magnetic field with the same number of poles as the rotor magnetic field. In this way, IZERO can be used to set the strength of the magnetic field. We set it to IZERO=5, and then slowly rotate the rotor once. When the magnetic poles of the rotor are aligned with the magnetic poles of the stator, there will be a pause. The number of times can determine the number of poles of the DC motor.

4. Method of obtaining real-time information about the position and speed of the brushless DC motor

Obtain the position and speed signal of the DC motor through the Hall element or the code disc, or use the back-EMF zero-crossing detection method, the third harmonic analysis method and the Kalman prediction method.

Two, stepper motor

1. Determining method of DC power supply current of stepper motor driver

(1) Voltage determination

The power supply voltage range of the stepper motor driver is relatively wide, and the current and voltage are all selected according to the working speed and response of the DC motor. If the speed of the DC motor is faster or the response requirement is faster, the voltage value will be higher. Note: The ripple of the power supply voltage must not exceed the maximum input voltage of the drive, otherwise it will damage the drive;

(2) Current determination

The power supply current is determined by the output phase current I of the driver. If it is a linear power supply, it is generally 1.1-1.3 times I, and 1.5-2 times for a switching power supply.

2. The stepper motor cannot start if it is higher than a certain speed

This is related to the no-load starting frequency parameter of the DC motor. If the pulse frequency is higher than this parameter value, the DC motor will not start normally, and a locked-rotor phenomenon will occur. When there is a load, the starting frequency should be lowered. If the DC motor is to rotate at a high speed, the pulse frequency must have an acceleration process, the starting frequency should be low, and then increase to the required speed according to a certain acceleration (similar to the speed increase of a car, It is impossible to be 100 yards at the start).

3. Brushed DC motor

1. Brushed DC motor voltage regulation and speed change

The brushed DC motor is also the main micro motor product of Tianfu Motor. For the brushed DC motor, if the power supply voltage is changed, the current of the rotor coil can be changed, and then the ampere force received by the stator magnetic field can be changed, and finally the rotor of the brushed DC motor can be changed. The torque changes, the speed of the DC motor increases with the increase of the torque, and vice versa, it decreases with the decrease of the torque. In this case, the pressure is adjusted and the speed is changed.

2. The principle of generating the rotating magnetic field of the armature of the brushed DC motor

The brushed DC motor can generate the armature rotating magnetic field without an external controller. There is a pair of 180° brushes on the miniature DC motor shell. The brushes guide the current to the armature coil through the metal plate of the commutator , Each metal plate covers the armature. When the micro motor is running, the current loop between the power supply, the brushes, the commutator metal plate and the two motor windings will automatically switch every half circle.

The magnetic field of the armature interacts with the magnetic field of the rotor. The magnetic field of the rotor can be generated by a fixed coil on the motor body or by a permanent magnet. When the rotor rotates, the direction of its magnetic field also reverses, so that the motor keeps rotating, because the direction of the magnetic field generated by the coil is always switched and is attracted/repelled by the magnetic field generated by the external coil or permanent magnet.