A New Method for Measuring the Rotational Angles of a Precision Spherical Joint Using Eddy Current Sensors

Do Magnets Have the Potential to Serve as a Stabilizer for the Shoulder Joint in Massive Rotator Cuff Tears?: A Biomechanical Cadaveric Study

Background

Disruption of the rotator cuff muscles compromises concavity compression force, which leads to superior migration of the humeral head and loss of stability. A novel idea of using the magnetic force to achieve shoulder stabilization in massive rotator cuff tears (MRCTs) was considered because the magnets can stabilize two separate entities with an attraction force. This study aimed to investigate the biomechanical effect of the magnetic force on shoulder stabilization in MRCTs.

Methods

Seven fresh frozen cadaveric specimens were used with a customized shoulder testing system. Three testing conditions were set up: condition 1, intact rotator cuff without magnets; condition 2, an MRCT without magnets; condition 3, an MRCT with magnets. For each condition, anterior-posterior translation, superior translation, superior migration, and subacromial contact pressure were measured at 0°, 30°, and 60° of abduction. The abduction capability of condition 2 was compared with that of condition 3.

Results

The anterior-posterior and superior translations increased in condition 2; however, they decreased compared to condition 2 when the magnets were applied (condition 3) in multiple test positions and loadings (p < 0.05). Abduction capability improved significantly in condition 3 compared with that in condition 2, even for less deltoid loading (p < 0.05).

Conclusions

The magnet biomechanically played a positive role in stabilizing the shoulder joint and enabled abduction with less deltoid force in MRCTs. However, to ensure that the magnet is clinically applicable as a stabilizer for the shoulder joint, it is necessary to thoroughly verify its safety in the human body and to conduct further research on technical challenges.

The Influence of Magnetic Field of AMB on Eddy-Current Sensor Operation

This paper presents laboratory results on the influence of the magnetic field of an active magnetic bearing (AMB) on the eddy-current sensor operation. The magnetic suspension technology enables continuous diagnostics and monitoring of a rotary machine and eliminates drawbacks of classical bearing properties. The magnetic bearing system usually consists of two radial and one axial magnetic bearing. It is combined with a control unit, amplifiers and sensors for measuring the instantaneous position of the shaft. For this purpose, eddy-current sensors are frequently used. They operate in close proximity to the electromechanical actuators; therefore, the question arises whether the actuators do not interfere with the correct operation of these sensors. In the paper, the test rig and research plan prepared for that investigation are delivered. Measurement signals were registered from four control channels for different configurations of power supplies for system elements, e.g., with sensors and AMBs turned off, with sensors turn on and at normal work. Recorded time courses are presented and discussed in the paper. For the prepared test rig and AMB/eddy-current sensor configuration, no significant influence of the generated magnetic field from the support is found for the eddy-current sensor output.

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

The ball joint is a multi-degree-of-freedom transmission pair, if it can replace the inner frame in the aviation photoelectric pod to carry the optical load, which will greatly simplify the system structure of the photoelectric pod and reduce the space occupied by the inner frame. However, installation errors in ball joint siting introduce nonlinear errors that are difficult to correct and two degree of freedom angular displacement of the ball joint is difficult to detect, which limits application in the precision control of two degrees of freedom systems. Studies of spherical capacitive sensors to date have not tested sensors for use in an inner frame stabilisation mechanism nor have they analysed the influence of installation error on sensor output. A two-axis angular experimental device was designed to measure the performance of a ball joint capacitive sensor in a frame stabilisation mechanism in an aeronautical optoelectronic pod, and a mathematical model to compensate for ball joint capacitive sensor installation error was created and tested. The experimental results show that the resolution of the capacitive sensor was 0.02° in the operating range ±4°, the repeatability factor was 0.86%, and the pulse response time was 39 μs. The designed capacitive sensor has a simple structure, high measurement accuracy, and strong robustness, and it can be integrated into ball joint applications in the frames of aeronautical photoelectric pods.

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

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.