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Biped robots possess higher capabilities than other mobile robots for moving on uneven environments. However, due to natural postural instability of these robots, their motion planning and control become a more important and challenging task. This article presents a Cartesian approach for gait planning and control of biped robots without the need to use the inverse kinematics and the joint space trajectories, thus the proposed approach could substantially reduce the processing time in both simulation studies and online implementations. It is based on constraining four main points of the robot in Cartesian space. This approach exploits the concept of Transpose Jacobian control as a virtual spring and damper between each of these points and the corresponding desired trajectory, which leads to overcome the redundancy problem. These four points include the tip of right and left foot, the hip joint, and the total center of mass (CM). Furthermore, in controlling biped robots based on desired trajectories in the task space, the system may track the desired trajectory while the knee is broken. This problem is solved here using a PD controller which will be called the Knee Stopper. Similarly, another PD controller is proposed as the Trunk Stopper to limit the trunk motion. Obtained simulation results show that the proposed Cartesian approach can be successfully used in tracking desired trajectories on various surfaces with lower computational effort.

Implementation of haptic feedback in minimally invasive surgical teleoperator systems may lead to improved performance in many common surgical procedures; however, most of the currently available surgical teleoperators do not provide force feedback, mainly because of the associated stability issues. In this paper, we study the effect of a special type of the force reflection algorithms, called projection-based force reflection (PBFR) algorithms, on the stability and performance of a dual-arm haptic-enabled teleoperator system for minimally invasive surgical applications. The performance of different algorithms is experimentally compared in the presence of negligible as well as nonnegligible communication delays. In particular, the teleoperator system's performance is experimentally evaluated in three common surgical tasks, which are knot tightening, pegboard transfer, and object manipulation. The results obtained indicate that, in almost all cases, the PBFR algorithms demonstrate statistically significant improvement of performance in comparison with the conventional direct force feedback.

Stability fulfilment for biped robots is drastically essential. Thus, to predict and maintain a dynamic stable status of biped robots defining an accurate stability measure is required which can represent dynamic equilibrium condition. Several postural stability metrics have been proposed so far. In this article, the Moment-Height stability (MHS) measure which has been previously proposed for wheeled mobile robots is developed for biped robot control. The responses of this criterion for stability monitoring of a biped robot is compared with the well known stability criterion Zero-Moment Point (ZMP). To this end, two common case studies of robot's motion including standing up and walking are considered and the results of application of the MHS are compared with those of the ZMP. The obtained results reveal the merits of MHS over ZMP in terms of its higher sensitivity to walking height (overall height of the robot's center of mass) and indicating the direction of foot rotation. The MHS metric is able not only to monitor the state of postural stability of a biped robot during the entire gait cycle, but also it does reliably indicate the severity of instability of the gait.