Zhu Songqing

Hopping movement simulation of elastic actuator

In this paper, we presented a multimodal elastic actuator which combining the motor, spring, brake and clutch that produces several modes of operation. The operation modes including stiff position control, series elastic actuation as well as the possibility to store and release energy were analyzed. A prototype of multimodal elastic actuator was constructed, dynamics equations of elastic actuator were established, and hopping movements with harmonic excitation were studied. Hopping movement was analyzed using receding horizon policy, the elastic actuator was controlled with preloaded hopping, and the hopping simulations with different ground trajectories were studied. The hopping movement simulation study of multimode elastic actuator provides important theoretical basis for the understanding of motion mechanism of bionic actuator and control implementation of hopping movement.

The study of multimodal series elastic actuator

An elastic actuator is proposed for meeting the knee power-assisted exoskeleton effective drive demand under different walking pattern. The actuator can achieve different motion of power-assisted knee exoskeleton through the motor driving the screw nut, series with spring and combing with the corresponding brake pads, and the motion modes are analyzed. The kinematics equations of elastic actuator were established, and the effects of spring stiffness and damping for the properties of elastic actuator are studied. The prototype of actuator is designed and tested, and braking force and motion following experiments are implanted. The results of experiments showed that the elastic actuator can realize effective braking force and favorable motion following. The study of multi-mode elastic actuator provides important theoretical basis for the understanding of motion mechanism of bionic actuator.

The Energy Amplification Characteristic Research of a Multimodal Actuator

A multimodal actuator is proposed to fulfil the different walking patterns of a power-assisted knee exoskeleton. With this actuator, the exoskeleton leg can realize several modes of operation, including series elastic actuation, stiff position control and energy storage and release. The energy amplification characteristics of the multimodal actuator in the series elastic mode are analysed. A dynamics model was established to study how series elasticity and the equivalent mass of transmission influence a power source, such as an electric motor. The results, in both simulation and experiment, show that series elasticity can amplify actuator power output, and the power output of a multimodal actuator is greater when the equivalent mass of the transmission mechanism is smaller. This research into multimodal actuator energy amplification supplies important insights into the design of artificial systems that can more closely approximate the performance of biological systems.

Noise-insensitive and edge-preserving resolution upconversion scheme for digital image based on the spatial general autoregressive model

This study proposes an edge-preserving image interpolation algorithm for both clean images and polluted images. First, the structure of an image window is learnt adaptively by using a spatial general autoregressive (SGAR) model that is a uniform expression for both linear and non-linear autoregressive (AR) models. Parameters of the SGAR model are estimated in a moving window in the input low-resolution image by using the robust generalised M-estimator. Next, the interpolation model is established from the learnt model and a new feedback mechanism in accordance with the residual sum of squares minimisation principle. Finally, the gradient simulated annealing algorithm is used to solve the interpolation model, which can rapidly converge to the global optimum in probability with the help of gradient information. Experiments have been performed using worldwide datasets to evaluate the performance of the authors method. The results demonstrate that their method is superior to a recent AR model-based method and is bicubic, especially when images are polluted by noise such as Gaussian noise, Poisson noise, impulse noise, or a combination of these.

The muscle activation patterns of lower limb during stair climbing at different backpack load

Stair climbing under backpack load condition is a challenging task. Understanding muscle activation patterns of lower limb during stair climbing with load furthers our understanding of the factors involved in joint pathology and the effects of treatment. At the same time, stair climbing under backpack load requires adjustments of muscle activations and increases joint moment compared to level walking, which with muscle activation patterns are altered as a result of using an assistive technology, such as a wearable exoskeleton leg for human walking power augmentation. Therefore, the aim of this study was to analyze lower limb muscles during stair climbing under different backpack load. Nine healthy volunteers ascended a four-step staircase at different backpack load (0 kg, 10 kg, 20 kg, 30 kg). Electromyographic (EMG) signals were recorded from four lower limb muscles (gastrocnemius, tibialis anterior, hamstring, rectus femoris). The results showed that muscle activation amplitudes of lower limb increase with increasing load during stair climbing, the maximum RMS of gastrocnemius are greater than tibialis anterior, hamstring and rectus femoris whether stair climbing or level walking under the same load condition. However, the maximum RMS of hamstring are smaller than gastrocnemius, tibialis anterior and rectus femoris. The study of muscle activation under different backpack load during stair climbing can be used to design biomechanism and explore intelligent control based on EMG for a wearable exoskeleton leg for human walking power augmentation.