School of Instrument Science and Opto-electronic Engineering, Hefei University of Technology, Hefei 230009, China.
Sensors (Basel). 2020 Jul 20;20(14):4020. doi: 10.3390/s20144020.
Precision spherical joint is a spherical motion pair that can realize rotation with three degrees of freedom. This joint is widely used in robots, parallel mechanisms, and high-end medical equipment, as well as in aerospace and other fields. However, the rotation orientation and angle cannot be determined when the joint is in passive motion. The real-time determination of the rotation orientation and angle is crucial to the improvement of the motion control accuracy of the equipment where the joint is installed in. In this study, a new measurement method that utilizes eddy current sensors is proposed to identify the special features of the joint ball and realize angle measurements indirectly. The basic idea is to manufacture the specific shape features on the ball without affecting its movement accuracy and mechanical performance. An eddy current sensor array is distributed in the ball socket. When the ball head rotates, the features on the ball opposite to the sensor, as well as the output signal of every eddy current sensor, change. The measurement model that establishes the relationship between the output signal of the eddy current sensor array and the rotation direction and angle of the ball head is constructed by learning and training an artificial neural network. A prototype is developed using the proposed scheme, and the model simulation and feasibility experiment are subsequently performed. Results show that the root mean square angular error of a single axis within a range of ±14° is approximately 20 min, which suggests the feasibility of the proposed method.
精密球面关节是一种能够实现三个自由度旋转的球面运动副。该关节广泛应用于机器人、并联机构和高端医疗设备以及航空航天等领域。然而，在被动运动时，该关节无法确定旋转方向和角度。实时确定旋转方向和角度对于提高安装该关节的设备的运动控制精度至关重要。在本研究中，提出了一种利用电涡流传感器的新测量方法，通过识别关节球的特殊特征来间接实现角度测量。基本思想是在球上制造特定的形状特征，而不影响其运动精度和机械性能。在球窝中分布有电涡流传感器阵列。当球头旋转时，与传感器相对的球上的特征以及每个电涡流传感器的输出信号都会发生变化。通过学习和训练人工神经网络，构建了一个建立电涡流传感器阵列输出信号与球头旋转方向和角度之间关系的测量模型。使用提出的方案开发了一个原型，并随后进行了模型仿真和可行性实验。结果表明，在±14°范围内的单个轴的均方根角误差约为 20 分钟，表明了该方法的可行性。
