Technical Resources

Angle Sensors

Application Note for Off-Axis configuration

Application Note of Angle Sensors

This is a technical document that describes conditions for use and layout examples when constructing an Off-Axis magnetic encoder system.

An Off-Axis is a configuration where the sensor center is not located on the rotational axis as shown in the figure 1. The AKM angle sensor (AK745x) is a non-contact rotary angle sensor that supports Off-Axis configuration in addition to the Shaft-End configuration. It corresponds to the Off-Axis configuration, so that a thinner motor system, through-axis and hollow-axis motor can be configured.

This document provides the information about the magnetic condition for use in Off-Axis, the magnet example available to be used in Off-Axis and recommended layouts using the magnet.

In this document, two layouts are introduced. One is where the IC is put on the side of magnet as shown in figure 2, and the other is where the IC is put diagonally below the magnet as shown in figure 3.

Figure1: Off-Axis configuration
Figure2: Off-Axis configuration where the IC is put on the side of magnet
Figure3: Off-Axis configuration where the IC is put diagonally below the magnet

Magnet Selection Guideline for Shaft-End configuration

Application Note of Angle Sensors

The AKM angle sensor (AK74xx) enables the measurement of magnetic fields (Bx, By) parallel to the chip surface and can detect the absolute angle of the magnetic field over the full range of 0 to 360 degrees.

A non-contact rotary angle sensor can be easily built with only a magnet and a sensor. However, for those who have never used a magnetic-based sensor until now or are considering AKM's rotation angle sensor for the first time, it is not easy to select the optimal magnet and determine the sensor arrangement. This document is a guideline for magnet selection when constructing a magnetic encoder system in the Shaft-End Configuration

The Shaft-End Configuration is where the magnet center and sensor center are aligned on the axis of rotation as shown in Figure 1. Figure 2 shows the magnetic fields (Bx, By) with respect to the rotation angle for the Shaft-End Configuration.

Figure 1: Shaft-End Configuration
Figure 2: Magnetic Field (Bx, By) vs. angle

*Bz=0 if there is no misalignment in the Shaft-End

Examples 1 and 2 are taken from the example data in this document. It is published that the data such as the installable range of the sensor and the angle error due to the misalignment when using our recommended magnet. The verification data is caliculated by the magnetic field simulation. 

In addition to the characteristics when using the recommended magnet, the following verification results are also available:

  • Installable range of the sensor and the angle error when the magnet size varies slightly from the recommended magnet.
  • Installable range of the sensor and the angle error when changing magnet shape and material from the recommended magnet.
Example 1: Range for Gap Between Sensor and Magnet (Recommended Magnet)
Example 2: Misalignment vs. Angle Error (Recommended Magnet)