In the previous article, I wrote about the PID control algorithm, which everyone recognizes, and then I want to combine the PID algorithm to tell you about some practical projects, such as PID control motor speed, etc., to improve everyone's practical application ability. But before controlling the motor, let's learn how the motor works and how we control it through this article.
Motors can be found almost everywhere in our lives, from electric toothbrushes to new energy electric vehicles. The electric motor is the power engine, the source of power, and is used in any system that requires power output. So it's up to us to understand how it works and how to control it. This article will use the vernacular way, taking the DC brush motor as an example, so that you can understand the basic working principle of the motor, easy to understand, one article is enough, you must read it!
The evolution of the motor - from magnets to motors
When it comes to motors, we must start with magnets, because motors actually use the characteristics of magnets to achieve rotation.
magnet
Speaking of magnets, we all know that there are two poles, an S pole (South Pole) and an N pole (North Pole), as shown in the picture above, our earth is a huge magnet.
Magnets can absorb a lot of metallic things, and magnets also have a very important characteristic: the same poles repel each other, and the opposite poles attract each other.
Opposite poles attract each other
The same poles are mutually exclusive
In the vernacular, two magnets are close to each other, and if they are close to the same pole at both ends, such as both N or both S, then there will be a repulsive force between the two magnets and push each other away. Conversely, if there are different poles near the two ends, i.e. N and S, then there will be an attraction between the two magnets and they will be drawn together.
Rotatable magnets
As shown in the figure above, if we add a rotation axis to one of the magnets, fix it, and then take another magnet to get close to it, because this end close to the rotatable magnet is the S pole, and the rotatable magnet N pole attracts and repels the S pole, so that the rotatable magnet will rotate clockwise until it becomes parallel to the two magnets below, and the rotatable magnet has rotated 1/4 turn.
Parallel state
Then if we turn the right near the magnet, the NS poles are reversed, as shown in the following figure,
NN排斥
In this way, because the N pole is relatively close to the rotatable magnet, it will be repelled by NN, and the rotatable magnet will rotate 1/4 turn clockwise.
Then, because of the NS attraction, the rotatable magnet will continue to rotate 1/4 turn, as shown below:
NS attracts
Finally, the following parallel state is reached, and the rotatable magnet has been rotated 3/4 of the time.
parallel
At this time, if we continue to switch the poles near the right side of the magnet, then the SS same pole will produce a repulsive force, so the rotatable magnet continues to rotate clockwise, as shown in the following figure, so that the rotatable magnet continues to rotate 1/4 turn, so that it has rotated once.
SS rejection
This also returns to the original state, and then because of the attraction of NS, it continues to rotate clockwise, and a new circle of selection begins, and if we continue to periodically switch the poles close to the magnet as above, then the left rotatable magnet will rotate periodically.
Electromagnets
How, when you see this, you can find out if this rotating magnet is the prototype of the motor, but how does it connect with electricity, isn't the motor rotating with electricity? Then continue to look down.
Electromagnets
As shown in the picture above, we know that ordinary screws are not magnetic because they are ordinary iron metal. But if we wrap a coil around the screw and energize the coil, then the coil and the screw will generate a magnetic field, just like the rod magnet above, which is the so-called electromagnet. Electromagnets use electric current to generate magnetic force, which is a non-permanent magnet, which means that there is no magnetic force when the power is off. The magnet used in the magnet rotation experiment above does not require electricity, it is a permanent magnet. When an electric current is passed through a wire, a magnetic field is generated, and when it is passed through a conductor made into a solenoid, a magnetic field similar to a rod magnet is generated. Add a ferromagnetic material (here we are a screw) to the center of the solenoid, and the magnetic material will be magnetized to strengthen the magnetic field. When we switch the direction of the current, the electromagnet is the pole and also switches.
The magnetic field strength generated by the electromagnet is related to the size of the direct current, the number of coils and the magnetic material in the center, and the distribution of the coil and the selection of the magnetic material will be paid attention to when designing the electromagnet, and the magnitude of the direct current will be used to control the magnetic field strength.
At this point, let's think about it, if we replace the rotatable magnet in the above rotation experiment with this electromagnet, will everything be controlled. As shown in the figure below, if we electrify the electromagnet wire, then it has a magnetic force, NN repulsion, and the electromagnet will rotate clockwise.
NN排斥
If we continue to change the direction of the current in the rotatable solenoid wire, is it easy to change the two poles of the electromagnet NS, and whether the electromagnet can continue to rotate, which is the same as the rotation of the permanent magnet above.
Well, in order to increase the magnetic force and rotation speed, you can symmetry the magnet on the left side of the rotating electromagnet and put a permanent magnet on the right side, which is close to the polarity of the electromagnet and the polarity of the right near the magnet is opposite, which is S, and the right side is N. In this way, both sides of the rotatable electromagnet are subjected to magnetic force, so the rotation will be more powerful. As shown below:
Permanent magnets on both sides
armature
We continued to optimize and replaced the magnets on both sides with curved permanent magnets that were more magnetic. As shown below:
Bend the permanent magnet
Then, the rotatable screw ring wire in the middle is replaced with a metal ring loop with better conductivity, and the metal loop is energized to produce magnetism, like a flat electromagnet. As shown in the figure below, the toroidal circuit in the motor is called the armature.
armature
In the same way as the rotating screw electromagnet above, if we energize the armature and continuously switch the direction of the current periodically, can we achieve continuous rotation of the armature?
Commutators and brushes
As shown in the figure below, we connect two arc-shaped discs to both ends of the rotating armature, they rotate with the armature, and there is a gap between the two arc-shaped discs, which is called a commutator.
commutator
The commutator needs to be combined with brushes to be effective. Two elastic and retractable conductive structures are placed on both sides of the commutator, which are connected to the external circuit, remain motionless during the rotation of the commutator, and are connected with the external circuit to ensure the supply of power to the armature. As shown below:
brushes
How does the combination of brushes and commutators achieve automatic polarity reversal of the rotatable armature?
Automatic reversing
As shown in the figure above, if the left brush is connected to the positive pole of the power supply, and the right brush is connected to the negative pole of the power supply, the left brush is in contact with the A commutator piece of the armature, and the right brush is connected to the armature B commutator piece. However, if the armature continues to rotate half a turn, the left brush and the armature's B commutator piece will be conducted, and the right brush and the A commutator piece will be turned on, so that the positive and negative poles of the armature will be reversed, the current direction will be reversed, and the NS polarity will be reversed, so that the motor will rotate continuously, as above.
Multi-circuit
Modern motors generally have many armature circuits and multiple commutators, so as to ensure that the rotation of the motor is smoother. As shown in the picture above.
As we have already mentioned above, the magnetic force of the electromagnet is related to the density of the coil, so modern motors generally increase the number of turns of the brush circuit to make the rotation faster and the rotation force greater. As shown below:
匝数
At the same time, the coil is wound around the electromagnet, so that the magnetic force will be stronger and rotate faster. As shown below:
electromagnet
With the addition of the shell and the connection terminals, you see, the complete DC motor is probably the following structure, which is similar to our actual motor.
Complete motor structure
Physical motors
After the motor is energized, the middle rotating part (rotor) will generate magnetic force, and the action with the fixed magnet next to it will rotate, and the rotor will drive the rotating shaft to rotate, and the rotating shaft can output power through other transmission structures, and the general rotating force is called torque.
So far, we have finished talking about the working principle of the motor.
How to control motor speed and torque?
Generally speaking, the rotational speed of a DC motor is proportional to the electromotive force of the winding (the voltage applied to the winding minus the resistance voltage drop of the winding), and its torque is proportional to the current. The control of the rotation speed can generally be achieved by controlling the input voltage of the motor. The higher the voltage, the faster the rotational speed.
Therefore, for a given DC motor, because the physical parameters of the motor itself have been fixed, we cannot change it, such as the rotor moment of inertia, the number of coil turns, etc., but what the controller can do is to control the speed of the motor by adjusting the voltage at both ends of the input motor, and control the force torque by adjusting the input current.
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