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When a multi-degree-of-freedom manipulator operates in underground coal mines, its communication signal is easily affected by external factors such as pulses and electromagnetic interference. It reduces the reliability of signal transmission and affects the flexibility and control precision of the multi-degree-of-freedom manipulator. To improve the communication signal quality of underground multi-degree-of-freedom manipulator, a filtering method for underground manipulator communication signal based on improved time-frequency peak filtering is proposed. The method extracts carrier features based on the carrier nodes of the manipulator communication signal, and extracts transmission period features based on Hilbert transform theory. The method uses wavelet decomposition to solve the wavelet transform coefficient of each level, obtains the disturbance frequency of communication signals, and completes the classification of communication signal features. The method introduces phase compensation factors to improve time-frequency peak filtering. The reduction threshold is calculated according to the scaling factor and reduction factor, so as so adjust the fixed window length. The improved time-frequency peak filtering is used to filter the noise in communication signals. Thus the noise suppression of the multi-degree-of-freedom manipulator communication signal is achieved. A 3-degree-of-freedom manipulator is taken as the experimental object. The pulse width is set to be 8 μs. The Baud rate is 120 bit/s, the communication signal transmission interval is 2 ms, and the signal amplitude is 1. 30 dB Gaussian white noise is added to the communication signal. The experimental results show that the output signal-to-noise ratio of the communication signal processed by the filtering method for underground manipulator communication signal based on improved time-frequency peak filtering is 94 dB. The bit error rate is basically stable at 0.6%, and the average frame loss rate is reduced from 2.9% before filtering to 0.8%. The method effectively improves the communication signal quality and transmission reliability of the multi-degree-of-freedom manipulator.

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In the field of aerial robotics, physical interaction with the surrounding environment is currently receiving a considerable attention. One of the key challenges is to control not only the position, but also the force exerted by the end-effector while performing complex tasks such as object manipulation, inspection, and assembly/disassembly. To meet these demands, this paper proposes a dynamic hybrid position/force controller for a quadrotor-borne multi-degree-of-freedom manipulator. The system is modeled under the situation that the constraints on the end-effector are described by a set of hypersurfaces, and system dynamics are then developed while taking into account the redundancy of the system. To verify the effectiveness of the proposed hybrid controller, we carried out numerical simulations for two different application scenarios which include (1) placement of a sensor unit on a vertical wall and (2) inspection with contact on a curved-shape wall. The results show that the system is able to maintain the desired force and position simultaneously in both cases. [ABSTRACT FROM AUTHOR]