Runjie Shen

An Analytic Method for the Kinematics and Dynamics of a Multiple-Backbone Continuum Robot

Continuum robots have been the subject of extensive research due to their potential use in a wide range of applications. In this paper, we propose a new continuum robot with three backbones, and provide a unified analytic method for the kinematics and dynamics of a multiple-backbone continuum robot. The robot achieves actuation by independently pulling three backbones to carry out a bending motion of two-degrees-of-freedom (DoF). A three-dimensional CAD model of the robot is built and the kinematical equation is established on the basis of the Euler-Bernoulli beam. The dynamical model of the continuum robot is constructed by using the Lagrange method. The simulation and the experiments validation results show the continuum robot can exactly bend into pre-set angles in the two-dimensional space (the maximum error is less than 5% of the robot length) and can make a circular motion in three-dimensional space. The results demonstrate that the proposed analytic method for the kinematics and dynamics of a continuum robot is feasible.

Real-time Walking Pattern Generation for a Biped Robot with Hybrid CPG-ZMP Algorithm

Biped robots have better mobility than conventional wheeled robots. The bio-inspired method based on a central pattern generator (CPG) can be used to control biped robot walking in a manner like human beings. However, to achieve stable locomotion, it is difficult to modulate the parameters for the neural networks to coordinate every degree of freedom of the walking robot. The zero moment point (ZMP) method is very popular for the stability control of biped robot walking. However, the reference trajectories have low energy efficiency, lack naturalness and need significant offline calculation. This paper presents a new method for biped real-time walking generation using a hybrid CPG-ZMP control algorithm. The method can realize a stable walking pattern by combining the ZMP criterion with rhythmic motion control. The CPG component is designed to generate the desired motion for each robot joint, which is modulated by phase resetting according to foot contact information. By introducing the ZMP location, the activity of the CPG output signal is adjusted to coordinate the limbs’ motion and allow the robot to maintain balance during the process of locomotion. The numerical simulation results show that, compared with the CPG method, the new hybrid CPG-ZMP algorithm can enhance the robustness of the CPG parameters and improve the stability of the robot. In addition, the proposed algorithm is more energy efficient than the ZMP method. The results also demonstrate that the control system can generate an adaptive walking pattern through interactions between the robot, the CPG and the environment.

Swimming Behavior Analysis Based on Bacterial Chemotaxis in Solution

Microrobots is playing more and more important roles for medical applications, such as targeting tumoral lesions for therapeutic purposes, Minimally Invasive Surgery (MIS) and highly localized drug delivery. However, energy efficient propulsion system poses significant challenges for the implementation of such mobile robots. Flagellated chemotactic bacteria can be used as an effective integrated propulsion system for microrobots. In this paper, we proposed a new type of propulsion method that is inspired by the motility mechanism of flagellated chemotactic bacteria in different pH gradients. The pH gradient field was established in solution through electrolysis method. The distribution of the pH values in solution was measured with pH indicator and analyzed with image processing technology, and the mechanism by which the pH values changed was also discussed. The swimming speed and direction of the bacteria were studied experimentally. Through analyzing the key parameters, such as stabilization time and electrode voltage, the optimal design of propulsion mechanism based on bacteria motion in the pH gradient field was proven.

A long-stroke horizontal electromagnetic vibrator for ultralow-frequency vibration calibration

A novel long-stroke horizontal electromagnetic vibrator with maximum stroke of 1?m is proposed. To reply to the strong nonlinearity arising from long stroke, a closed double-magnetic circuit with optimal air gap, an electro-viscoelastic-suspension device and a track following device are adopted in the vibrator. Also, a compact moving component with a higher first-order natural frequency is designed to increase the operating frequency of the vibrator. Finally, experimental results show that the vibrator could output low distortion acceleration on its working platform from 0.002?Hz to 100?Hz, which verifies the validity of the proposed technologies and the applicability of the vibrator for an ultralow-frequency vibration calibration system.

A novel vibration-level-adjustment strategy for ultralow-frequency vibration calibration based on frequency-shifted method

Aimed at the time-consuming process of an ultralow-frequency vibration calibration, a strategy of rapid vibration-level-adjustment for ultralow-frequency vibration exciters is put forward. First, an ultralow-frequency vibration exciter system based on a displacement feedback control technique is analyzed, whose frequency response function between its input voltage and output displacement is established and calculated based on MATLAB. It is found that the output displacement of the system is only dependent on the input voltage rather than the input signal frequency. Then, a novel rapid vibration-level-adjustment strategy on the basis of the frequency-shifted method is proposed, whose process is that the vibration exciter is first adjusted to the target vibration level at a higher pre-adjustment frequency and then the input signal frequency is gradually decreased from the pre-adjustment frequency to the target ultralow frequency. The method is applied in an ultralow-frequency vibration automatic calibration system. The experimental results indicate that the new strategy can obviously reduce the time of the vibration-level adjustment of ultralow-frequency vibration exciters, and improve the efficiency of the calibration system. The study is helpful for the widespread use of ultralow-frequency vibration calibration.

Contact impact inhibition strategy for biped robot walking based on central pattern generator

Biped robot has exceptional obstacle negotiation capability and great potential applications in military, rescue and space exploration. However, an instantaneous impact will happen when the swing foot of the biped robot contacts with the ground, which easily causes damage to the drive mechanism and robot instability. This paper proposes a rhythmic control method based on central pattern generation (CPG) to overcome the contact impact and improve the locomotion stability of the robot. The dynamic model of a seven-link planar biped robot is established. And the discontinuous contact constraint and contact impact process of the foot are analyzed. A CPG network with joint angle velocity feedback signal is put forward to control the robot to achieve stable walking. Simulation studies show that the proposed method can effectively reduce the impact of foot contact and improve the robot locomotion stability. The results are promising for the design of the biped robot control strategy.

Erratum to: Swimming Behavior Analysis Based on Bacterial Chemotaxis in Solution

AbstractFig. 6 of Ref. [1] (page 317) should be replaced by the figure in the right, in which the words “cathode” and “anode” are exchanged. Also on the same page the following corrections should be made: (a)Left column, line 7 from the bottom, “cathode anode” should be replaced by “anode and cathode”;(b)Right column, line 5 from the top, “anode” should be replace by “cathode”, and “cathode” should be replace by “anode”.Fig. 6Circular electrolysis device (On actual PCB board, anode and cathode at different layer on the board). The authors apologize for the mistakes in their original manuscript.