A Novel Method for Detecting the Two-Degrees-of-Freedom Angular Displacement of a Spherical Pair, Based on a Capacitive Sensor

Abstract

The spherical pair has an important role in the inner frame of the stabilization mechanism of the aviation optoelectronic pod. However, its two-degrees-of-freedom (2-DOF) angular displacement signal is difficult to detect, seriously restricting its application in aviation optoelectronic pods. Therefore, this study proposes a new method to measure a spherical pair’s 2-DOF angular displacement using a spherical capacitive sensor. The capacitive sensor presented by this method realizes the measurement of the 2-DOF angular displacement of the spherical pair by integrating the spherical electrode groups in the ball head and the ball socket of the spherical pair. First, based on the geometric structure of the spherical pair, the structure of the capacitive sensor is designed, and the mathematical model for the capacitive sensor is deduced. Then, the sensor’s output capacitance, in different directions, is simulated by Ansoft Maxwell software. Finally, an experiment device is built for the measurement experiments. The simulation analysis and experimental results show that the spherical capacitive sensor has an approximately linear output in different directions, and the measured output capacitance is as high as 89.7% of the theoretical value. Compared with the existing sensors that measure the 2-DOF angular displacement signal of the ball pair, the sensor proposed in this study has an integrated structure, which can be integrated into the spherical pair. That makes it possible to apply the spherical pair to the inner frame of the aviation optoelectronic pod.

Analysis and Correction of Measurement Error of Spherical Capacitive Sensor Caused by Assembly Error of the Inner Frame in the Aeronautical Optoelectronic Pod

“…Ignoring the edge effect, the differential output capacitances and of the sensor can be written as a matrix ( ) [ 9 ]: where is the air dielectric constant, and H is .…”

“…The sensor’s parameters are listed in Table 1 [ 9 ], and the 3D finite element simulation model is shown in Figure 3 .…”

“…Equation ( 12 ) shows that only the electrode gap d can induce a slope offset error in the capacitive sensor. Thus, measurement error is mainly governed by installation error [ 9 ].…”

“…These features make it suitable for use in applications where precise measurements are required, such as spherical pairs, CNC machine tools, and noncontact force–distance measurement [ 5 , 6 , 7 , 8 ]. These advantages over other sensing methods have ensured that the capacitive angle sensor has been researched in great depth [ 9 ]. This type of capacitive sensor detects 2-DOF angular displacement by calculating change in capacitance due to joint rotation.…”

Codes coupling optimization for absolute measurement

“…Currently, there are primarily two solutions for precision measurement: optical and electrical solutions. Electrical solutions, such as inductance and capacitance displacement sensors [1,2], have achieved relative maturity in small range applications due to their high accuracy and low cost advantages. These electrical solutions are commonly utilized in piezoelectric ceramic displacement stages and equipment.…”