The design of motion control systems for legged robots has always been a challenge. This article first proposes a motion control method for legged robots based on the gradient central pattern generator (GD-CPG). The periodic signals output from the GD-CPG neural network are used as the drive signals of each thigh joint of the legged robots, which are then converted into the driving signal of the knee and ankle joints by the thigh–knee mapping function and the knee–ankle mapping function. The proposed control algorithm is adapted to quadruped and hexapod robots. To improve the ability of legged robots to cope with complex terrains, this article further proposes the responsive gradient-CPG motion control method for legged robots. From the perspective of bionics, a biological vestibular sensory feedback mechanism is established in the control system. The mechanism adjusts the robot’s motion state in real time through the attitude angle of the body measured during the robot’s motion, to keep the robot’s body stable when it moves in rugged terrains. Compared with the traditional feedback model that only balances the body pitch, this article also adds the balancing functions of body roll and yaw to balance the legged robot’s motion from more dimensions and improve the linear motion capability. This article also introduces a differential evolutionary algorithm and designs a fitness function to adaptively optimize vestibular sensory feedback parameters. The validity, robustness, and transferability of the method are verified through simulations and physical experiments.

The ability of quadruped robots to overcome obstacles is a critical factor that limits their practical application. Here, a design concept and a control algorithm are presented that aim at enhancing the explosive force of quadruped robots during jumping by utilizing elastic energy storage components. The hind legs of the quadruped robot are designed as energy storage units. Tension springs are utilized as components for storing energy and are installed in a parallel structure on the hind leg. Energy is stored during the compression process of the robot’s torso and released during the jumping phase. The optimal foot force is calculated using a single rigid body model. The mapping relationship between the force applied to the foot and the resulting joint torque is established by developing a dynamic model of the hind legs. Simulation experiments were conducted using the Webots physics engine to compare the impact of varying spring stiffness on joint torque during the jumping process. This study determined the optimal spring stiffness under specific conditions. The hind legs’ torque saving ratio reaches 19%, and the energy-saving ratio reaches 13%, which validates the effectiveness and feasibility of integrating elastic energy storage components.

This article describes a robot walker based on a new single degree-of-freedom six-bar leg mechanism that provides rectilinear, non-rotating, movement of the foot. The walker is statically stable and requires only two actuators, one for each side, to provide effective walking movement on a flat surface. We use Curvature Theory to design a four-bar linkage with a flat-sided coupler curve and then adds a translating link so that walker foot follows this coupler curve in rectilinear movement. A prototype walker was constructed that weighs 1.6 kg, is 180 mm tall, and travels at 162 mm/s. This is an innovative legged robot that has a simple reliable design.

Legged locomotion systems have been effective in numerous robotic missions, and such locomotion is especially useful for providing better mobility over irregular landscapes. However, locomotion capabilities of robots are often constrained by a limited range of gaits and the associated energy efficiency. This paper presents the design of a novel reconfigurable Klann mechanism capable of producing a variety of useful gait cycles. Such an approach opens up new research avenues, opportunities and applications. The position analysis problem that arises when dealing with reconfigurable Klann mechanisms was solved here using a bilateration method, which is a distance-based formulation. By changing the linkage configurations, our aim was to generate a set of useful gaits for a legged robotic platform. In this study, five gait patterns of interest were identified, analysed and discussed that validate the feasibility of our approach and considerably extend the capabilities of the original design.

An optimization model is developed in this paper for the joint trajectories of a hopping robot with a four-bar linkage leg. The dynamic behaviour of the one-legged robot is investigated during the stance and swing phases, and their impacts on gait planning are analysed. Certain constraints characterizing the continuous and cyclic motion of the robot are obtained. The optimization model is solved for the minimum torque and maximum velocity objective functions separately, and the results are compared with those in nature.

Tipping-over and slipping, which are related to zero moment point (ZMP) and frictional constraint respectively, are the two most common instability forms of biped robotic walking. Conventional criterion of stability is not sufficient in some cases, since it neglects frictional constraint or considers translational friction only. The goal of this paper is to fully address frictional constraints in biped walking and develop corresponding stability criteria. Frictional constraints for biped locomotion are first analyzed and then the method to obtain the closed-form solutions of the frictional force and moment for a biped robot with rectangular and circular feet is presented. The maximum frictional force and moment are calculated in the case of ZMP at the center of contact area. Experiments with a 6-degree of freedom active walking biped robot are conducted to verify the effectiveness of the stability analysis.

This paper introduces the design, analysis, and experimental results of a fast mesoscale (12 cm length) quadruped mobile robot that employs unconventional actuators. Four legs of the robot are actuated by two pieces of piezocomposite actuator named LIPCA, which enables the robot to achieve the bounding gait with only one degree of freedom per leg. The forward locomotion is obtained by a creative idea in the design and the speed can be controlled by changing the frequency of actuators. The mechanism of power transfer has been improved in order to use the actuation power more efficiently. Two small RC-servo motors are added to control the locomotion direction. In addition, a small power supply and control circuit is developed that is fit for the robot. Our experiments show that the robot can locomote as fast as about two times its body length per second with the circuit board and a battery installed. The robot is also able to change the heading direction in a controlled way and is capable of continuous operation for 35 min.