基于高斯混合-隐马尔科夫融合算法识别奶牛步态时相

奶牛步态时相是反映奶牛健康及跛行严重程度的重要指标。为准确自动识别奶牛步态时相，本研究提出一种融合高斯混合模型 （Gaussian Mixture Model，GMM） 和隐马尔科夫模型 （Hidden Markov Model，HMM）的无监督学习奶牛步态时相识别算法 GMM-HMM。使用惯性测量单元采集奶牛后肢加速度和角速度信号，通过卡尔曼滤波消除噪声，筛选并提取特征值，构建GMM-HMM模型，实现奶牛静立相、连续步态中的站立相和摆动相等3种步态时相的自动识别。结果表明，静立相识别的准确率、召回率和F₁分别为89.28%、90.95%和90.91%，连续步态中的站立相识别的准确率、召回率和F₁分别为91.55%、86.71%和89.06%，连续步态中的摆动相识别的准确率、召回率和F₁分别为86.67%、91.51%和89.03%。奶牛步态分割的准确率为91.67%，相较于基于事件的峰值检测法和动态时间规整算法准确率分别提高了4.23%和1.1%。本研究可为下一步基于穿戴式步态分析的奶牛跛行特征提取提供技术参考。

Gait Phase Recognition of Dairy Cows based on Gaussian Mixture Model and Hidden Markov Model

The gait phase of dairy cows is an important indicator to reflect the severity of lameness. IThe accuracy of available gait segmentation methods was not enough for lameness detection. In this study, a gait phase recognition method based on Gaussian mixture model (GMM) and hidden Markov model (HMM) was proposed and tested. Firstly, wearable inertial sensors LPMS-B2 were used to collect the acceleration and angular velocity signals of cow hind limbs. In order to remove the noise of the system and restore the real dynamic data, Kalman filter was used for data preprocessing. The first-order difference of the angular velocity of the coronal axis was selected as the eigenvalue. Secondly, to analyze the long-term continuous recorded gait sequences of dairy cows, the processed data was clustered by GMM in the unsupervised way. The clustering results were taken as the input of the HMM, and the gait phase recognition of dairy cows was realized by decoding the observed data. Finally, the cow gait was segmented into 3 phases, including the stationary phase, standing phase and swing phase. At the same time, gait segmentation was achieved according to the standing phase and swing phase. The accuracy, recall rate and F₁ of the stationary phase were 89.28%, 90.95% and 90.91%, respectively. The accuracy, recall rate and F₁ of the standing phase recognition in continuous gait were 91.55%, 86.71% and 89.06%, respectively. The accuracy, recall rate and F₁ of the swing phase recognition in continuous gait were 86.67%, 91.51% and 89.03%, respectively. The accuracy of cow gait segmentation was 91.67%, which was 4.23% and 1.1 % higher than that of the event-based peak detection method and dynamic time warping algorithm, respectively. The experimental results showed that the proposed method could overcome the influence of the cow's walking speed on gait phase recognition results, and recognize the gait phase accurately. This experiment provides a new method for the adaptive recognition of the cow gait phase in unconstrained environments. The degree of lameness of dairy cows can be judged by the gait features.