Xianchao Zhao

New kinematic structures for 2-, 3-, 4-, and 5-DOF parallel manipulator designs

In this paper, several types of composite pairs and new kinds of sub-chains (limbs or legs) with specific degrees of freedom are proposed. Based on the special Plucker coordinates for describing the displacement of the output link of a limb, the principle for design of structures of parallel robotic mechanisms is presented. And several new types of 2-, 3-, 4- and 5-DOF parallel robotic mechanisms are obtained.

Use of an orthogonal parallel robot with redundant actuation as an earthquake simulator and its experiments

In this article, an orthogonal 6-degree-of-freedom (DOF) parallel robot with redundant actuation is studied as an earthquake motion simulator. Taking the practical simulation of earthquake waves into consideration, the general characteristics of natural earthquakes are analysed and complexity and variety of seismic waves, three-dimensional and multi-DOF movement, and strong devastating force are regarded as the three obvious features in this article. Based on the characteristics of this orthogonal 6-DOF parallel robot with redundant actuation and the features of earthquakes, the feasibility of using this parallel robot as an earthquake motion simulator is analysed from three aspects: orthogonal 6-DOF structure, decoupling feature, and redundant actuation module. In order to simulate an earthquake motion using this parallel robot, its inverse kinematics and dynamics models are derived. The control system of this earthquake simulator is developed based on the PXIbus development platform. The computed-torque control algorithm based on the inverse dynamics is used in the controller of this equipment. A typical three-directional earthquake motion, the El Centro earthquake, is simulated on the end-effector of this parallel robot by means of its mathematical models and control system. Three main motion parameters of simulated seismic waves, displacements, velocities, and accelerations, are measured, respectively, by laser tracker and acceleration sensors. The experimental results show this equipment is appropriate to be used as an earthquake simulator.

Type synthesis of parallel mechanisms having the first class gf sets and one-dimensional rotation

A method is presented for the type synthesis of a class of parallel mechanisms having one-dimensional (1D) rotation based on the theory of Generalized Function sets (GF sets for short), which contain two classes. The type synthesis of parallel mechanisms having the first class GF sets and 1D rotation is investigated. The Law of one-dimensional rotation is given, which lays the theoretical foundation for the intersection operations of GF sets. Then the kinematic limbs with specific characteristics are designed according to the 2D and 3D axis movement theorems. Finally, several synthesized parallel mechanisms have been sketched to show the effectiveness of the proposed methodology.

A fuzzy-based spatio-temporal multi-modeling for nonlinear distributed parameter processes

Many industrial processes belong to nonlinear distributed parameter systems (DPS) with significant spatio-temporal dynamics. They often work at multiple operating points due to different production and working conditions. To obtain a global model, the direct modeling and experiments in a large operating range are often very difficult. Motivated by the multi-modeling, a fuzzy-based spatio-temporal multi-modeling approach is proposed for nonlinear DPS. To obtain a reasonable operating space division, a priori information and the fuzzy clustering are used to decompose the operating space from coarse scale to fine scale gradually. To get a smooth global model, a three-domain (3D) fuzzy integration method is proposed. Using the proposed method, the model accuracy will be improved and the experiments become easier. A fuzzy-based spatio-temporal multi-modeling approach is proposed for modeling nonlinear distributed parameter processes.To obtain a reasonable operating space division, a priori information and the fuzzy clustering are used to decompose the operating space from coarse scale to fine scale gradually.To get a smooth global model, a three-domain (3D) fuzzy integration method is proposed.Using the proposed method, the model accuracy will be improved and the experiments become easier. Many industrial processes belong to nonlinear distributed parameter systems (DPS) with significant spatio-temporal dynamics. They often work at multiple operating points due to different production and working conditions. To obtain a global model, the direct modeling and experiments in a large operating range are often very difficult. Motivated by the multi-modeling, a fuzzy-based spatio-temporal multi-modeling approach is proposed for nonlinear DPS. To obtain a reasonable operating space division, a priori information and the fuzzy clustering are used to decompose the operating space from coarse scale to fine scale gradually. To reduce the dimension in the local spatio-temporal modeling, the Karhunen-Loeve method is used for the space/time separation. Both multi-modeling and space/time separation can reduce the modeling complexity. Finally, to get a smooth global model, a three-domain (3D) fuzzy integration method is proposed. Using the proposed method, the model accuracy will be improved and the experiments become easier. The effectiveness is verified by simulations.

Calibration of a six-DOF parallel manipulator for chromosome dissection

This article proposes a calibration method for a six-PPPS parallel manipulator which is the macro-part of a dual-drive chromosome dissection system. The calibration model is built with respect to Denavit–Hartenberg notation. Certain adjustment matrices are utilized to provide independent error parameters. The pose of the moving platform as while as relative motion of all prismatic joints and spherical joints are measured by the latest API T3 laser tracker. Other than general methods that need reconstruction of the location and orientation of the platform with point coordinates, these data can be obtained directly within one single measurement in the proposed method. For data processing, a step-by-step calculation method has been presented to select initial error parameters. With this method, partial error parameters can be derived in advance to be substituted into the calibration model providing calculation efficiency superior to simultaneous computation. Simulation based on the geometry of this manipulator shows a decent convergence performance of the calibration model. The experimental results also validate the efficiency and the convenience of the proposed method.

Compensation of Velocity Divergence Caused by Dynamic Response for Hardware-in-the-Loop Docking Simulator

The hardware-in-the-loop simulation on the ground is effective to test the contact dynamics of the spacecraft in space. However, it is very challenging due to the simulation velocity divergence caused by the time delay. In this study, a compensation approach for the velocity divergence caused by the dynamic response of the motion simulator is proposed. Traditional delay compensation requires the time delay or the delay model to be known. In practice, the dynamic response of the motion simulator is time varying and unknown. This motivates development of the model-free compensation approach. It compensates the contact force from the real-time response error of the motion simulator and the real-time identified contact stiffness and damping. The proposed compensation approach is easy to implement since it does not require the dynamic response model of the motion simulator. Simulations and experiments are used to verify the effectiveness of the proposed compensation approach.

Dynamic characteristics of the scanning system used in online measurement systems for large hot forgings

The scanning system is the core of online measurement systems that are developed for large hot forgings. In this paper, the dynamic characteristics of a scanning system are described and its dynamic performance is improved by complete force balancing. According to the demands of the field environment of large hot forgings, the dynamic characteristics mainly comprise the reduction and amelioration of input torque, and the decrease of shaking force. To these ends, the input torque and the centre of mass (centroid) of the scanning system are derived in succession. Then the complete force balancing conditions are presented. From these conditions, the correlative dynamical parameters are adjusted, the shaking forces to the bearings are eliminated, and the input torques are reduced and ameliorated. Simulations and experiments are also conducted to verify the effect, and the fore-and-aft torques are compared. The results prove the decrease and amelioration of the input torque. This shows that dynamical parameter design is of great significance for the improvement of the dynamic characteristics of scanning systems.The scanning system is the core of online measurement systems that are developed for large hot forgings. In this paper, the dynamic characteristics of a scanning system are described and its dynamic performance is improved by complete force balancing. According to the demands of the field environment of large hot forgings, the dynamic characteristics mainly comprise the reduction and amelioration of input torque, and the decrease of shaking force. To these ends, the input torque and the centre of mass (centroid) of the scanning system are derived in succession. Then the complete force balancing conditions are presented. From these conditions, the correlative dynamical parameters are adjusted, the shaking forces to the bearings are eliminated, and the input torques are reduced and ameliorated. Simulations and experiments are also conducted to verify the effect, and the fore-and-aft torques are compared. The results prove the decrease and amelioration of the input torque. This shows that dynamical parameter...

Design and development of a novel redundant and fault-tolerant actuator unit for heavy-duty parallel manipulators

This paper proposes a novel dual-input/single-output actuator unit, called a redundant and fault-tolerant actuator (RFTA), designed for heavy-load parallel manipulators. After the definitions of redundant and fault tolerance are given, the principle of the proposed RFTA is described using its two working processes. According to the derived kinematics, 12 fault modes caused by two different input velocities are developed and classified, and the physical meanings are represented correspondingly. Mechanical transmitting properties of the proposed RFTA are analysed respectively. On the other hand, RFTA, as a dual-module hot spare architecture to achieve high reliability and safety, with its complete redundant structure can be called Multiple Births Structure (MBS) and is different form the traditional partial redundant structures – Siamesed Births Structure (SBS). The reliability models show that RFTA is more reliable than SBS. Three guidelines – the select guideline, the design guideline, and the operation guideline – are suggested. Those design guidelines are useful to designers and users. A prototype of RFTA and its control system are developed and the relevant experiments are carried out. The experimental results demonstrate that RFTA is able to not only supply double driving force but also tolerate some local faults caused by out-of-syncs. RFTA provides heavy-duty equipment, especially large-scale parallel manipulators, with a new probability in changing their drive mode, from the hydraulic power supply to the motor drive. Furthermore, this paper also demonstrates that RFTA has some potential applicable prospects under heavy-duty environments, such as a large-scale parallel earthquake simulator and an electric press with heavy duty cycles.

Application of a novel 6-DOF parallel robot with redundant actuation for earthquake simulation

In this paper a novel orthogonal 6-DOF (Degree Of Freedom) parallel robot with redundant actuation is studied as an earthquake motion simulator. Taking the practical simulation of earthquake waves into consideration, we firstly analyze the general characteristics of natural earthquakes. Complexity and variety of seismic waves, 3-dimension and multi-DOF movement and strong devastating force are regarded as their three obvious features in this article. Based on the characteristics of this novel orthogonal 6-DOF parallel mechanism with redundant actuation and the features of earthquakes, the feasibility of using this parallel robot as an earthquake motion simulator is analyzed. In order to simulate earthquake motion by using the parallel robot, its unambiguous kinematics and dynamics models are derived in details. The control system of the proposed earthquake simulator is developed based on the PXIbus development platform. A typical three-direction earthquake motion, the El Centro earthquake, is simulated on the end-effector of the parallel robot using its mathematical models and control system. Three main motion parameters of simulated seismic waves, displacements, velocities and accelerations are measured respectively. The experimental results show that this equipment is appropriate for using as an earthquake simulator.

Modeling and experiment of a planar 3-dof parallel micromanipulator

In this paper, a planar 3-DOF XYγ parallel micromanipulator with monolithic structure is presented. The micromanipulator is driven by three piezoelectric (PZT) actuators. To achieve highly accurate control, a new approach investigating the relationship among input-force, payload, stiffness, and displacement (IPSD model) of the XYγ micromanipulator is proposed in analytical style, and the analytical expression of the relationship between driving voltages of PZT actuators and outputs of end-effector is deduced based on the IPSD model. Finally, in order to verify the IPSD model, the simulations by finite element method and experiment are performed. The micromanipulator can be used to do microtasks that need the manipulator perform only planar motion, such as microoperation and microassembly, and the proposed IPSD model is useful for both digital control and design of the XYγ micromanipulator.