Identification of dynamic and friction parameters of a parallel manipulator with actuation redundancy

The dynamic model is formulated in the joint space for a parallel manipulator with actuation redundancy. The established model is expressed in its linear matrix form with respect to the dynamic and friction parameters, and then the Weighted Least Square (WLS) method is applied to estimate the parameters. In order to get satisfying estimated results, the filters of joint angle and actuated torque are designed for the parallel manipulator. A simple and effective method is presented to design the excitation trajectory by analyzing the mechanism structure characteristics of the actual parallel manipulator. Another type of trajectory which is different from the excitation trajectory is adopted to verify the estimated parameters. The dynamic control experiments based on the identified model with the estimated parameters are implemented on an actual 2-DOF parallel manipulator with actuation redundancy, and the tracking accuracy of the identified model is compared with the result of the so-called nominal model.     

Performance comparison of three planar 3-DOF parallel manipulators with 4-RRR, 3-RRR and 2-RRR structures

This paper presents a comparison study on the conditioning, velocity, payload and stiffness performance of three planar 3-DOF parallel manipulators with 4-RRR, 3-RRR and 2-RRR structures, respectively. The conditioning, velocity, payload and stiffness indices are developed to compare the performance of the three parallel manipulators. An optimum region is investigated. A comparison of the results indicates that the conditioning performance, payload performance and stiffness performance of the 4-RRR manipulator is the best, and those performances of the 2-RRR one is the worst. The three manipulators have different output velocity performance. The 4-RRR and 2-RRR manipulators have the largest and smallest optimum region, respectively.     

A dexterity comparison for 3-DOF planar parallel manipulators with two kinematic chains using genetic algorithms

In this research work, a dexterity comparison is performed for seven three-degree-of-freedom (3-DOF) Planar Parallel Manipulators with two kinematic chains (PPM2KCs) using genetic algorithms. Introducing a new design approach, one of the three kinematic chains of seven possible fully planar parallel manipulators (FPPMs) is disconnected in order to design the new seven PPM2KCs, and one active actuator is added to the first leg to maintain the 3-DOF. These manipulators are designed on the basis of two purposes: (i) increasing the workspace area, and (ii) reducing the chance of interference since the three independent kinematic chains not only cause interference among the mechanical components but also reduce the workspace, which are the major challenges for parallel manipulators. Afterwards base distances are optimized using genetic algorithms (GAs) to compute the performance indices κ and GDI for the PPM2KCs. The results have been examined regarding especially two objectives: (i) selecting the best possible architecture among the seven new designed configurations for a specific task, and (ii) analyzing the correlation between joint types (prismatic or revalue) and dexterous maneuverability for PPM2KCs. It has been concluded that the PPR (prismatic–prismatic–revolute) planar parallel manipulator is the best configuration, providing the best dexterous maneuverability among the others.     

Optimum cycle redundancy-check codes with 16-bit redundancy

Optimal binary cyclic redundancy-check codes with 16 parity bits (CRC-16 codes) are presented and compared to those in existing standards for minimum-distance, undetected-error probability on binary symmetric channels (BSCs) and properness. The codes in several cases are seen to be superior at block lengths of practical interest when they are used on low-noise BSCs. The optimum minimum distance obtainable by some CRC-16 codes is determined for all block lengths. For several typical low-noise BSCs the minimum undetected error probability achievable with some CRC-16 codes is given for all block lengths     

A built-in self-repair design for RAMs with 2-D redundancy

This brief presents a built-in self-repair (BISR) scheme for semiconductor memories with two-dimensional (2-D) redundancy structures, i.e., spare rows and spare columns. The BISR design is composed of a built-in self-test module and a built-in redundancy analysis (BIRA) module. The BIRA module executes the proposed RA algorithm for RAM with a 2-D redundancy structure. The BIRA module also serves as the reconfiguration unit in the normal mode. Experimental results show that a high repair rate (i.e., the ratio of the number of repaired memories to the number of defective memories) is achieved with the BISR scheme. The BISR circuit has a low area overhead-about 4.6% for an 8 K /spl times/ 64 SRAM.     

Development of 6-dof parallel seismic simulator with novel redundant actuation

This paper presents the prototype of the 6-dof parallel seismic simulator developed by Shanghai Jiao Tong University. Inverse kinematics analysis is carried out by the simulation. In the prototype building, the novel redundant actuation is adopted. The contribution of the novel redundantly actuated interface is that it makes possible for the motors to drive a much large load and expand the age of the lead screw. The spherical joint is also replaced by the combination of Hooke joint and rotation joint. In these ways, it is feasible for the 6-dof parallel seismic simulator with novel redundant actuation to be used for the application of large load requirement.     

Analysis of a two-unit parallel redundancy with an imperfect switch

A parallel redundant system of two identical units is studied when the switchover from repair to on-line is defective. It is assumed that there is a single repair facility and that either unit has priority over the switching device while queuing for repair. The reliability and availability functions are obtained explicitly when the units have a constant failure rate. The method of extension to cover the case of dissimilar units with non-constant failure rates is also indicated.     

Position regulation in Cartesian space of a class of inextensible soft continuum manipulators with pneumatic actuation

This work investigates the position regulation in Cartesian space of a class of inextensible soft continuum manipulators with pneumatic actuation subject to model uncertainties and to unknown external disturbances that act on the tip. Soft continuum manipulators are characterised by high structural compliance which results in a large number of degrees-of-freedom, only a subset of which can be actuated independently or instrumented with sensors. External disturbances, which are common in many applications, result in uncertain dynamics and in uncertain kinematics thus making the control problem particularly challenging. We have investigated the use of integral action to model the uncertain kinematics of the manipulators, and we have designed a new control law to achieve position regulation in Cartesian space by employing a port-Hamiltonian formulation and a passivity-based approach. In addition, we have compared two adaptive laws that compensate the effects of the external disturbances on the system dynamics. Local stability conditions are discussed with a Lyapunov approach and are related to the controller parameters. The performance of the controller is demonstrated by means of simulations and experiments with two different prototypes.     

Dynamics and control of redundantly actuated parallel manipulators

It has been shown that redundant actuation provides an effective means for eliminating singularities of a parallel manipulator, thereby improving its performance such as Cartesian stiffness and homogeneous output forces. Based on this concept, several high-performance parallel manipulator prototypes have been designed. A major difficulty that prevents application of the vast control literature developed for the serial counterparts to redundantly actuated parallel manipulators is the lack of an efficient dynamical model for real-time control. In this paper, using the Lagrange-D'Alembert formulation, we propose a simple scheme for computing the inverse dynamics of a redundantly actuated parallel manipulator. Based on this approach, four basic control algorithms, a joint-space proportional derivative (PD) control, a PD control in generalized coordinates, an augmented PD control, and a computed-torque control, are formulated. A two-degrees-of-freedom redundantly acutated parallel manipulator designed for a high-speed assembly task is used to verify the simplicity of the proposed approach and to evaulate the performance of the four control algorithms.     

Static balancing of 3-DOF planar parallel mechanisms

The static balancing of planar 3-DOF parallel mechanisms is addressed in this paper. Static balancing is defined as the set of conditions on mechanism dimensional and inertial parameters which, when satisfied, ensure that the weight of the links does not produce any torque (or force) at the actuators for any configuration of the mechanism, under static conditions. For the mechanisms studied here, conditions for static balancing are obtained, and it is shown that balancing is generally possible, even when the dimensional parameters are imposed, which is a useful property since dimensional parameters are usually obtained from kinematic design or optimization. Then, the conditions for the static balancing of the same mechanisms are derived for designs in which elastic elements are included. Finally, examples of balanced mechanisms are given. A dynamic study is performed     

Torque minimisation of the 2-DOF serial manipulators based on minimum energy consideration and optimum mass redistribution

This paper deals with the analytically tractable solution for input torques minimisation of two degrees of freedom serial manipulators based on minimum energy control and optimal redistribution of movable masses. The minimisation problem is carried out in two steps: at first, the optimal trajectory of the manipulator is defined as a function, which leads to the minimisation of energy consumption. Then, by introducing the obtained trajectory into dynamic equations, the torques are reduced by using the optimal redistribution of movable masses, which is carried out via an adaptive counterweight system. For this purpose, the torques due to the dynamic loads of the counterweights are presented as a function of the counterweight positions. The conditions for optimal dynamic balancing are formulated by minimisation of the root-mean-square value of the input torque including the dynamic loads of the unbalanced manipulator and counterweights. The suggested approach is illustrated by numerical simulations carried out using ADAMS software.     

A motion base with 6-DOF by parallel cable drive architecture

This paper proposes a new type of motion base for virtual sensation of acceleration by applying a parallel cable drive architecture. It has outstanding advantages in comparison with conventional Stewart platforms. Especially, 1) rotational motion range is large; 2) the motion platform can be grounded on the floor; 3) scene projection to all the walls is possible; and 4) its redundancy of cables improves safety for cut of cables. Optimal fundamental mechanical design is performed from the viewpoint of kinematics. Simulation results show that a 3-3-2 cable configuration is one of the best designs as a motion base. The prototype developed has the maximum motion range of translation ±0.45 m × ±0.4 m × 1.1 m and that of rotation ±45° in roll angle, ±45° in pitch, and ±35° in yaw. It can produce acceleration 1 G for 0.8 s at its maximum, even if gravity is not used. A trajectory planning method for longer-term sensation utilizing gravity is proposed. Low-frequency component of acceleration is realized by rotational motion and high frequency is produced by translational motion. Experimental results to create virtual acceleration of a roller coaster demonstrated effectiveness of this new design     

On the increase of system reliability by parallel redundancy

Adding parallel redundancy to different components generally yields different system reliability improvements. The effect of such parallel redundancy upon system reliability when applied at various places and in various systems is investigated. The problem of how to choose components for parallel redundancy is studied, and some results are given. Some examples are presented to illustrate the approach     

Efficient built-in redundancy analysis for embedded memories with 2-D redundancy

A novel redundant mechanism is proposed for embedded memories in this paper. Redundant rows and columns are added into the memory array as in the conventional approaches. However, the redundant rows and columns are divided into row blocks and column blocks, respectively. The reconfiguration is performed at the row (column) block level instead of the conventional row (column) level. Based on the proposed redundant mechanism, we first show that the complexity of the redundancy allocation problem is NP-complete. Thereafter, an extended local repair-most (ELRM) algorithm suitable for built-in implementation is proposed. The complexity of the ELRM algorithm is O(N), where N denotes the number of memory cells. According to the simulation results, the hardware overhead for implementing this algorithm is below 0.17% for a 1024/spl times/2048-b SRAM. Due to the efficient usage of the redundant elements, the manufacturing yield, repair rate, and reliability can be improved significantly.     

Gait simulation via a 6-DOF parallel robot with iterative learning control

We have developed a robotic gait simulator (RGS) by leveraging a 6-degree of freedom parallel robot, with the goal of overcoming three significant challenges of gait simulation, including: 1) operating at near physiologically correct velocities; 2) inputting full scale ground reaction forces; and 3) simulating motion in all three planes (sagittal, coronal and transverse). The robot will eventually be employed with cadaveric specimens, but as a means of exploring the capability of the system, we have first used it with a prosthetic foot. Gait data were recorded from one transtibial amputee using a motion analysis system and force plate. Using the same prosthetic foot as the subject, the RGS accurately reproduced the recorded kinematics and kinetics and the appropriate vertical ground reaction force was realized with a proportional iterative learning controller. After six gait iterations the controller reduced the root mean square (RMS) error between the simulated and in situ; vertical ground reaction force to 35 N during a 1.5 s simulation of the stance phase of gait with a prosthetic foot. This paper addresses the design, methodology and validation of the novel RGS.     

Optimal design and development of a five-bar finger with redundant actuation

In order to develop a human hand mechanism, a five-bar finger with redundant actuation is designed and implemented. Each joint of the finger is driven by a compact actuator mechanism having an ultrasonic motor and a gear set with a potentiometer, and controlled by a VME bus-based control system. Optimal sets of actuator locations and link lengths for cases of a minimum actuator, one-, two-, and three-redundant actuators are obtained by employing a composite design index which simultaneously considers several performance indices, such as workspace, isotropic index, and force transmission ratio. According to the optimization result, several finger-configurations optimized for a special performance index are illustrated, and it is concluded that the case of one redundant actuator is the most effective in comparison to the cases of more redundant actuators, and that the case of two redundant actuators is the most effective in multi-fingered operation in which the force characteristic is relatively important, as compared to the kinematic isotropy and the workspace of the system.     

Optimum noise-source reflection-coefficient design with feedbackamplifiers

The issue of designing a low-noise microwave feedback amplifier for a given optimum noise-source coefficient Γ_Sopt is addressed and a set of original formulas is presented. These expressions define a new procedure which does not rely on computer optimization in order to get the required noise performance of the low-noise amplifier stage. The technique permits the design of a circuit which is simultaneously noise and power matched at its input port without an input matching circuit. This method can be used to screen devices for an optimum noise performance and it provides the essential mathematical tool for designing the core of a feedback amplifier     

Application of a 3-DOF parallel manipulator for earthquake simulations

In this paper a formulation and experimental results are presented for a novel application of a 3-degree of freedom (DOF) parallel manipulator to simulate point seismograms and three-dimensional (3-D) earthquake motion. The rigid body acceleration is analyzed to simulate real 3-D earthquakes. Furthermore, first experimental results are reported to analyze earthquake effects on scaled civil structures.     

随机均衡器的计算机辅助最优化设计

本文提供了一种实用的随机均衡器的计算机辅助设计方法.以二元件均衡器为链接模型,以非线性最小二乘法为最优化方式,解决了多节均衡器链接中初始参数值的选取问题.讨论了0.618法在非单一极值区间的应用.并且通过实例计算说明这一方法的有效性和实用性.     

并行冗余网络中高效信息采集策略设计

基于并行冗余网络结构提出一种带宽占用率小的网络状态参数采集策略。采用线性预测的方法,自适应的调整信息采集的时间间隔,通过获取少量网络状态数据样本,进而能够获得整个网络样本空间的主要性能状态指标的精确估计。最后通过OMNET＋＋网络仿真软件对高效信息采集策略进行了仿真验证,仿真结果表明：提出的高效信息采集策略相比传统的信息采集方法的带宽占用率减小了约69%。