Variable admittance force feedback device and its human-robot interaction stability

In teleoperation, a force feedback device is a medium to build a transparent interaction environment between a human and a remote robotic arm. Using force feedback devices, the users can operate the remote robotic arm intuitively and perceive remote interaction through the force channel, just as if they are in the remote environment. Compared with impedance devices, admittance devices have the advantages of large feedback output, high stiffness, high reverse driving performance, and flexible structure, which are more suitable for the teleoperation of heavy-duty and large-size robotic arms. However, the control of admittance devices is relatively complex and has some inherent limitations such as response delay, instability from high-frequency oscillation, difficulty in achieving constant speed control, etc. Errors in admittance model parameters and human physiological characteristics, such as force application fluctuations, are the root causes of these problems. In this study, we proposed a fuzzy variable damping admittance algorithm, which allows the device to identify the user's movement intention and give respond quickly and accurately. We also established a human-robot interaction (HRI) system model of an admittance master controller device and summarized the principles of the admittance parameter configuration of a stable system. For the device's high-frequency oscillation instability caused by human arm stiffness, we propose an oscillation observation and reduction algorithm. By observing the force signal change characteristics, the algorithm can quickly detect the unstable behavior caused by human hands and perform oscillation reduction. To reduce the influence on upper limb uniform motion caused by fluctuating force application, we proposed a constant velocity intention inference algorithm based on a velocity spherical cone to smooth out the device operating velocity to achieve smooth control. The method proposed in this study achieved stable control in a 6 DOF force feedback device as a master controller, and the effect has been verified by experiments.