Remote haptic sensing using sliding‐mode assist disturbance observer as force detector

Abstract

Bilateral controlled master-slave robot system is an important intermediary to realise remote haptic sensing. This study proposes a sliding-mode assist disturbance observer (SMADO) to detect force information in wider bandwidth without force sensors by making use of the fast switching of sliding-mode control values. Moreover, a bilateral control law is proposed based on the SMADO. The proposal tolerates the presence of disturbances and uncertainties in the robots. The influence of these factors is degraded by using the net forces to design the bilateral control rather than employing a robust compensation. This design shows such a feasibility that high performance haptic sensing can be achieved using the SMADO as a wide bandwidth force detector without any robust compensators. The validity of the proposal is confirmed by experiments in practice. The proposal realises the position tracking and action-reaction law between the two robots, which makes the operator vividly feel the remote object. IntroductionTransmitting the haptic sense is a challenging technology to extend and enhance human hands with many potential applications, such as space exploration, nuclear engineering and telesurgery [1]. This technology can be traced back to the teleoperation with bilateral control law in past decades. In a bilateral control system, there is a master robot and a slave robot, which transmit the motion and the forces between the human operator and the environment object. Therefore bilateral control system plays a role of an intermediary between the human operator and the environment object [2][3][4][5].Human beings sense an environment object through the mechanical distortion of the object and the reaction forces [6]. Therefore, in bilateral control system, a correspondence of positions and action-reaction forces between the master and the slave is always desired [7]. To achieve satisfactory performance, many efforts were reported in the literature. The most effective and famous one is Lawrence's four-channel control framework [8]. This method uses local and remote information of positions and forces in the control of each robot. However, there are two main problems in the algorithm. One is the requirement of force sensors. The other is the influence of disturbances and uncertainties.The force sensors increase system cost, hardware mounting difficulty and spatial requirements [9]. Besides, the bandwidth of force sensor always limits the practical performance of a bilateral control algorithm. On the other hand, the forces from the operator and the environment are not only inputs to the bilateral control but also disturbances to the master and slave robots [10]. Moreover, uncertainties of the robots also influence the performance of traditional bilateral control. Therefore the bilateral control system with disturbance rejection and without force sensors are investigated by more and more researchers.Sumiyoshi and Ohnishi [11] introduced the disturbance observer (DOB) [12] into the four-channel control, and successfully improved t...

Bilateral force sensorless control based on finite‐time adaptive sliding‐mode‐assisted disturbance observer

“…For another control objective, the experimental results of the resultants of forces on the master and slave are shown in Figure 8(b). This shows that the resultants of forces using the proposed method and PD+DOB method are similar and closer to zero compared with the method in [25]. The chattering phenomenon under the method reported in [25] is caused by the sign function and fixed switching gain of SMC.…”

“…Figure 6 shows the experimental results obtained using the method reported in [25]. Figure 6(a) shows the position tracking curves of the master and slave actuators.…”

“…Figure 8(a) shows the position errors of the master and slave actuators using the three different methods. It can be seen that the position error using the PD+DOB method is larger than the errors using the another two methods, and the error using the method [25] is almost the same as that of the proposed method, which is because the assistant parts of the SMADO and ASMADO can compensate for the residual‐disturbance estimation error of the DOB. This confirms the effectiveness of the SMADO and ASMADO.…”

“…In this section, the experiments are carried out on bilateral realtime brushless DC motors to verify the effectiveness of the proposed method. To demonstrate that the proposed method provides a system with good transparency, it is compared with the proposed SMADO method reported in [25] and the conventional method PD+DOB for a bilateral teleoperation system. Moreover, the essence of DOB is the same as in [20] and [21], and the DOB is a low-pass filter, and is a typical comparison method.…”

“…To detect force information in a wider bandwidth and achieve good transparency in real‐time, a sliding‐mode‐assisted disturbance observer (SMADO) was proposed in [25], which achieved good transparency of the bilateral control system. The method the authors in [25] proposed used sliding mode control (SMC) to assist the DOB in detecting the residual forces in high‐frequency by using the fast switching of SMC values. It is worth noting that the disturbances and dynamic uncertainties were tolerated and remained in the system as they had little influence on the performance of haptic sensing.…”