1. Research on sensor solutions in the industry
Angle measurement sensors are divided into capacitive, magnetic and optical according to the measurement principle;
1.1 Capacitive Encoder
Principle: The capacitive encoder converts the change of the angle into a capacitance value, and obtains the angle measurement value by measuring the capacitance.
Advantages: large range, high resolution, non-contact measurement method without wear
Disadvantages: Affected by electromagnetic interference, sensitive to environmental humidity; if you choose a capacitive encoder, you need to consider electromagnetic shielding and structural sealing
Manufacturers: capacitive encoder suppliers mainly include SICK, Tamagawa, Yingdong Technology, etc.
1.2 Photoelectric encoder
Principle: By recording the grid on the glass or metal disc, the photoelectric method is used to detect the number of grids and measure the angle
Advantages: high resolution, high precision, non-contact measurement method without wear, anti-electromagnetic interference ability
Disadvantages: The glass code disc is easily affected by vibration and is sensitive to dust and dirt; if you choose a photoelectric encoder, you need to consider the structural buffer and seal
1.3 Magnetic encoding
Principle: There are two measurement principles of magnetic encoding, one is based on magnetoresistance, and the other is Hall-type; magnetoresistance converts magnetic induction into resistance, and Hall-type converts magnetic induction into electricity to realize measurement
Advantages: shock resistance, vibration resistance
Disadvantages: affected by electromagnetic induction, sensitive to temperature, relatively low resolution and accuracy, inferior to optical and capacitive, if you choose a magnetic encoder, you need to accept its low accuracy, and at the same time need to do electromagnetic shielding and temperature compensation.
2. Industry research on sensor parameters
Since our application is at low speed, the response time is not a key consideration; at the same time, our application environment is relatively harsh, so the structure will have a high sealing level. Therefore, accuracy is the main parameter to consider, not resolution.
2.2 Comparison of Magnetic Encoding Parameters
2.2.1 Magneto-resistive angle sensor
Manufacturers mainly include Infineon, TDK, AD, etc., research on the angle sensor chips of three manufacturers:
(1) There are many types of TLE50xx series manufactured by Infineon. For the TLE5014 series with better precision parameters, the manual states that the maximum error of the non-check table is 0.9° in the temperature range [-40°C~+85°C]. The maximum error of the table (correction) is 0.65°; while the maximum error of the non-check table at the temperature [-40°C~+125°C] is 1.0°, and the maximum error of the look-up table (correction) is 0.85°; and this error is at Bz. 0mT, the magnetic field strength is controlled at [33mT~55mT], and it does not include errors such as the eccentricity between the magnetic axis center and the sensor center. Considering the eccentricity between the magnetic axis center and the sensor detection center, the error can be referred to as shown in the following figure:
At the same time, it is necessary to control the gap between the magnet and the sensor. The error of the gap is different. You can refer to the following (the abscissa is the magnetic eccentricity, the ordinate is the angle error, and different colors represent the gap):
Therefore, based on the above error parameters, it is difficult for Infineon’s sensor to ensure a deviation of 1° in the full temperature range, and it is actually impossible to achieve a deviation of less than 10um between the center axis of the magnetic axis and the center of the magnetic sensor.
(2) TDK manufacturer
TDK has several series, among which the best error of TAS series is ±0.6°~0.8° in the whole temperature range; the best error of TDA series is ±0.3° in the whole temperature range (multiple rotation correction), if Without multiple rotation corrections, the optimal error is ±0.7°.
(3) AD manufacturers
The magnetoresistive sensor series of AD manufacturers are mainly ADA series. Before calibration, the maximum error of this kind of products is 5°, and the typical error after single-point calibration is ±0.7°;
(4) According to the descriptions and explanations of the above-mentioned relatively well-known manufacturers, when the magnetoresistive sensor measures the angle to achieve an angle error of ±0.5°, many prerequisites are required, and it is difficult to achieve
2.2.2 Hall-type angle sensor
Manufacturers mainly include ams AMG, Melexis, Allego, Magntec and other factories
(1) ams AMG factory
The 51 series sensors of the ams AMG factory can achieve 12bit resolution in terms of angular resolution, that is, 0.08°, but the nonlinearity error reaches ±1.2° in the full temperature range;
(2) Melexis factory
The nonlinear error of the MLX90xx series from Melexis is ±1.2°
(3) Allego Factory
The A133x series of Allego manufacturer can achieve an error of ±0.6° at an ambient temperature of 25°C, and the error is ±1.75° at a temperature of +150°C
(4) RLS factory
The resolution of AM8192 produced by RLS factory can reach 13bit, and the whole non-linearity is composed of many parts. Combining multiple nonlinear errors, the optimal error is: ±0.7°
The principle error of itself: ±0.15°;
When the deviation between the center of the magnetic axis and the center of the magnetic sensor is 0.15mm, the nonlinear error is: ±0.15°
The nonlinear error caused by the 5V power supply system is: ±0.12°
The difference in height between the magnet and the chip causes an error of: ±0.08°
The error caused by temperature is: ±0.2°;
2.2 Comparison of parameters and indicators of capacitive encoders
(1) CUI Device manufacturers
The accuracy of capacitive encoders from CUI Device can reach 0.2°, and the installation form is as follows:
