In this paper, a novel transformable leg-wheel mechanism is proposed. It has three active joints, among which the hip roll joint is directly driven, the hip pitch joint is driven by gear transmission, and the knee joint is driven by synchronous belt transmission. All the actuators are mounted on the body to reduce the weight of the leg-wheel mechanism as possible, so that the motion of the leg-wheel mechanism will be slightly affected by the inertia. The proposed mechanism has two characteristics, the big wheel radius and the reduced actuator. The design and kinematics modeling methods of the leg-wheel mechanism are described. A half-a-heart shape trajectory is proposed to plan the foot motion of the leg-wheel mechanism in the legged locomotion. To make the locomotion mode transition smooth, the transition strategy is designed. Simulation and experimental results verify the feasibility of the proposed leg-wheel mechanism.

High control bandwidth is usually restricted in a photoelectric tracking system (PTS) based on a Charge-Couple Device(CCD) with time delay, which hinders a good tracking performance. Generally, a model-based delay-compensation controller called Smith predictor (SP) can help increase the controller gain to promote the bandwidth by separating delay from the control loop. However, the performance promotion is insufficient because the delay still stays in the forward channel which causes errors between output and input. And the increase of the controller gain is still limited due to the effect of model mismatch on stability. In this paper, to solve the problems, a delay-compound-compensation control (DCCC) based on improved SP by trajectory prediction and velocity feedforward is proposed. The additional trajectory prediction is used to further eliminate the effect of delay existing in the forward channel. The additional velocity feedforward is used to further reform the transfer characteristics limited by the controller gain. A Kalman filter-based design method of trajectory prediction is presented and the optimal design principle of feedback and feedforward controllers is given in the face of model mismatch. Experiments demonstrate that the DCCC is valid and could greatly promote the tracking performance in the low frequency.

In the high-precision optoelectronic tracking system (OTS) based on a charge-coupled device (CCD), the boresight error extracted from the tracking image contains an undeniable delay, which directly limits the control bandwidth of visual tracking. High bandwidth means high response speed and tracking accuracy. Generally, a model-based delay compensation control method called the Smith predictor is utilized to separate time delay from the closed loop to promote the control bandwidth. However, due to the existence of errors between the established model and the real object, the improvement in the bandwidth is still limited to ensure system stability, resulting in insufficient tracking performance. In this paper, to solve the problem, a Smith predictor modified with pseudo feedforward control for the OTS is proposed. The experimental results demonstrate that the proposed method achieves significant improvements in tracking performance, reducing the maximum residual error at 1 Hz from 365 arcseconds (using the classic Smith predictor) to 283 arcseconds, a 22.5% improvement. Across the main frequency band (0.2 Hz to 2 Hz), the residual errors were consistently lower using the proposed method.

Excellent disturbance rejection ability is essential for a photoelectric tracking system (PTS) based on the Charge-Couple Device (CCD) sensor, which is a premise guarantee for obtaining highly accurate tracking, especially under the condition of moving carriers with intense disturbances. The feedforward control method based on disturbance estimated from the system model output and sensor output is currently a commonly used strategy for disturbance compensation due to its ability to directly counteract the disturbances. This disturbance feedforward compensation method behaves sensitively in case of model mismatch caused by internal disturbances, which may lead to a significant reduction in the disturbance compensation effect or even cause system instability. In this paper, unlike disturbance feedforward compensation, a pure disturbance sliding-mode feedback control (DSMFBC) based on disturbance observation without additional sensors is proposed, ensuring faster and precise compensation for disturbance. In case of model mismatch, the observed disturbance is used to build the disturbance feedback control to maintain a more efficient disturbance compensation through the robustness that feedback naturally possesses. To achieve a stronger anti-disturbance capability, a sliding-mode nonlinear control method is used to design the control law. The experimental setup of PTS based on the fast-steering mirror (FSM) demonstrates that the method has better dynamic performance and disturbance rejection ratio.