How does a magnetic encoder work

If you have the opportunity to disassemble a magnetic rotary encoder, you will usually see an internal structure. Compared with ordinary encoders ( resolvers), magnetic encoders have the same mechanical shaft housing structure, but at the same time its position detection mechanism is very simple. It only needs to install a small magnet at the end of the mechanical shaft to follow the rotation of the shaft. A PCB circuit board at the end of the encoder.

So, how does the magnetic encoder measure the rotational position feedback?

Let us first look at a classic physical phenomenon (electromagnetism to be precise).

A voltage is applied to both ends of a flat rectangular conductor to generate current in one direction (such as the long direction). At this time, if another magnetic field perpendicular to the conductor plane acts on the charged conductor, the electric charge flowing through the conductor will be cancelled due to the Lorentz force induced by the magnetic field.

According to the left-hand law learned in the middle school physics class, it is possible to determine the direction of the offset when the charge flows, the direction of the offset when the positive negative charges circulate in the magnetic field. This means that when a current flows through a flat conductor in a magnetic field, its positive negative charges will pass along the left right paths respectively.

At this time, there will be a potential difference on both sides of the conductor, that is, in the direction perpendicular to the current flow.

This is the Hall effect, discovered in 1879 by the physicist Edwin Herbert Hall.

When an electric current passes through a conductor in a magnetic field, the magnetic field will generate a force perpendicular to the direction of movement of the electrons in the conductor, thereby generating a potential difference in the direction perpendicular to the conductor the lines of magnetic force.

Next, if the magnetic field applied to the conductor rotates in the direction indicated by the arrow above with the current flow path as the axis, the Hall potential difference will change due to the change in the angle between the magnetic field the conductor. The change trend of this potential difference is the same as the change trend of the output voltage of the secondary coil in the previous "Resolver", which is a sinusoidal curve. Therefore, according to the voltage on both sides of the charged conductor, the magnetic field rotation angle can be inversely calculated.

This is the basic working principle of the magnetic encoder to measure the rotational position feedback.