Integrated joint actuator for serpentine robots

Serpentine robots, also sometimes called "snake robots," are slender, multisegmented vehicles designed to provide greater mobility than conventional wheeled or tracked robots. Serpentine robots are typically comprised of three or more rigid segments connected by two or three degrees of freedom joints. The segments typically have powered wheels, tracks, or legs to propel the vehicle forward; the joints may be powered or unpowered. We have developed a joint actuator system that is highly optimized for use in serpentine robots. This article first presents an analysis of the particular requirements for joint actuators in serpentine robots. We then compare existing actuators against those requirements and show that pneumatic bellows are ideally suited for this application. Following this analysis, this paper introduces our fully functional, pneumatically operated actuation system that is efficiently integrated in the space occupied by a joint. This system, which we call an "integrated joint actuator," also allows simultaneous proportional control of position and stiffness of the joint. The key advantages of our design over other joint actuation methods are its great strength combined with controllable compliance and minimal space requirements.     

Non-spherical ball-socket joint design for Delta-type robots

Delta-type robots are commonly used for positioning purposes in medical surgery. In such applications, the loading position accuracy of the end effector is of critical importance. However, the positioning accuracy is determined by the loading deflection, which depends in turn on the link flexibility and joint clearance within the system. Importantly, the loading deflection is posture/position dependent. This characteristic greatly complicates the task of improving the positioning accuracy using traditional compensation control methods. Accordingly, the present study proposes a non-spherical ball-socket joint design to improve the loading stiffness of the robot over the entire workspace. An analytical model is derived to quantify the loading deflection as a function of the link flexibility and joint clearance. The experimental results show that the non-spherical ball-socket joint design reduces the total variation in the loading deflection of the end effector by up to 81.04% compared to that of a traditional robot with spherical ball-socket joints when performing positioning over the entire workspace at the assigned height.     

采用锁频环和锁相环联合捕获的载波跟踪

针对传统锁频环-锁相环跟踪算法中环路状态转换过渡中出现频率阶跃的问题,提出了一种采用锁频环和锁相环联合捕获的方式替代单一锁频环进行捕获的改进算法,同时对环路状态转换的门限进行了推导。仿真结果表明,改进的算法在转换过程中更加平稳,环路性能得到了优化。在信噪比为-10 dB且存在加加速度时跟踪环路在转换时没有出现频率阶跃,达到了设计目的。     

Position/force control of uncertain constrained flexible joint robots

This paper addresses the issue of adaptive position/force control of uncertain constrained flexible joint robots (FJRs). The controller is developed without the assumptions of weak robot joint flexibility as adopted in popular singular perturbation (SP) approaches. It relies on the feedback of joint state variables and avoids noisy joint torque measurements found in most controllers developed so far. In addition to the robot inertia parameters, the joint stiffness and the motor inertia are also assumed to be unknown. The proposed approach achieves the position tracking and the boundedness of force errors. The simulation study is conducted to verify the effectiveness of the approach.     

Fault-tolerant schemes for parallel architectures

Fault-tolerance schemes for efficient implementation in parallel VLSI processors are discussed, and a modular approach for tree and mesh-structured architectures is described     

Electromigration-induced failures at Cu/Sn/Cu flip-chip joint interfaces

Various EM-induced failures were observed at a current-stressed Cu/Sn/Cu flip-chip solder joint. At the cathode interface, EM-induced Cu-pad consumption occurred at the current-entry point (maximum current-density) and voiding occurred at the other joint corner away from the current-entry point (minimum current-density). At the anode interface, EM-enhanced Kirkendall voids coalesced into a gap at the Cu₃Sn/Cu interface near the current-exit corner. We believe that the above various EM-induced failure modes were resulted from different current-stressing densities at the joint interfaces.     

Intelligent control of quadruped gallops

In this paper, a new intelligent control approach for high-speed quadruped bounding and galloping gaits is presented. The controller is capable of learning the leg touchdown angles and leg thrusts required to track the desired running height and velocity of a quadruped in only one stride. Training of the controller is accomplished not with a mathematical model, but with simple rules based on a heuristic knowledge of the quadruped mechanics. The result is a controller that produces better velocity and height tracking characteristics than a Raibert-based controller and is robust to modeling errors. Additionally, by making use of the natural dynamics of the system, gait characteristics comparable to biological quadrupeds result. The status of a legged machine being constructed for demonstration of the control approach and further study of the characteristics of galloping is also presented.     

Fault-tolerant designs for 256 Mb DRAM

This paper describes fault-tolerant designs, which have been used to boost the yield of a 286 mm² 256 Mb DRAM with x32 both-ends DQ. The 256 Mb DRAM consists of sixteen 16 Mb units, each containing one 128 Kb row redundancy block. This row redundancy block architecture allows flexible row redundancy replacement, where random faults, clustered faults, and grouped faults can be efficiently repaired. Flexible column redundancy replacement with interchangeable master DQ's (MDQ) is used to allow a 256 b data compression without causing a data conflict, while improving the column access speed by 2 ns. A depletion NMOS bitline-precharge-current-limiter suppresses the current flow which occurs as a result of a wordline-bitline short-circuit to only 15 μA per cross fail, avoiding a standby current fail. Consequently, the hardware results show a significant yield enhancement of 16 times relative to the intra-block/segment replacement. Detailed simulation results show that this 256 Mb DRAM allows 275 random faults to be repaired with 5.5% silicon area overhead for 80% chip yield     

Fault-tolerant control for automated highway systems

Increasing highway traffic congestion and real estate costs that limit the building of new highways has brought about a renewed interest in an automated highway system (AHS) where the vehicle steering task (“lateral control”) and the braking/throttle tasks (“longitudinal control”) are taken over by computers to increase the throughput of existing highways. Since safety plays a key role in the development of an AHS, fault-tolerant control is vital. In this paper, we develop a robust longitudinal sliding-mode control algorithm and prove that this control algorithm is stable for a certain class of faults. In addition, we show that intervehicle spacing errors will not become amplified along the AHS in the event of a loss of lead vehicle information. The performance of the sliding-mode controller is demonstrated through a series of simulations incorporating various vehicle and AHS faults     

Connectors for self-reconfiguring robots

Connectors for self-reconfiguring robots are difficult to design because of the wide range of requirements. We describe the DRAGON connector, whose most distinctive features are its ability to self-align and its strength-to-weight ratio. It weighs 170 g, but holds over 70-kg load. It is able to self-align /spl plusmn/15 mm (O/5) lateral offsets and /spl plusmn/45/spl deg/ directional and rotational offsets. It allows autonomous docking and reconfiguration in a fraction of a second, without any complex control.     

液压四足机器人伺服阀驱动电路设计

随着机器人应用的扩展,液压四足机器人作为一种特种机器人,因其高度的机动性和大负载能力而受到人们的高度重视。在液压系统中,阀控动力系统通过控制伺服阀来调节流入执行元件中的液压油流量,从而控制液压执行元件。事实上,由于控制输入信号一般比较微弱,因此控制输入信号需要利用控制放大器处理和功率放大后才能用于控制伺服阀工作。提出了一种伺服阀驱动电路的设计方案,该驱动电路同时驱动一条腿的三个伺服阀工作,通过Multisim进行仿真分析后,研制了电路板。最后利用半实物仿真设备搭建测试系统的控制模型,并经该驱动板进行功率放大,结果表明该驱动电路运行稳定可靠,满足了设计要求。     

Fault-tolerant multicasting in MINs for ATM switches

This article proposes a fault-tolerant multicast routing algorithm in multistage interconnection networks (MINs) for ATM switch architectures. It employs both region and cube encoding schemes as the header encoding scheme. A multicast packet can be routed to its destinations in only two phases through the MIN having a single faulty element     

Distributed fault detection for modular and reconfigurable robots with joint torque sensing: A prediction error based approach

A distributed fault detection scheme for modular and reconfigurable robots (MRRs) with joint torque sensing is proposed in this paper. With the proposed scheme, the joint torque command is filtered and compared with a filtered torque estimate derived from the nonlinear dynamic model of MRR with joint torque sensing. Common joint actuator faults are considered with fault detection being performed independently for each joint module. The proposed fault detection scheme for each module does not require motion states of any other module making it an ideal modular approach for fault detection of modular robots. Experimental results have confirmed the effectiveness of the proposed fault detection scheme.     

Reliable gait planning and control for miniaturized quadruped robot pet

This paper proposes a gait planning and control algorithm for the quadruped robot pet commercialized by Dasarobot, Korea. Reliable motion and online characteristics are the key requisites for the motion planning algorithm of a commercialized robot. At joint control level of the proposed gait control, sample-based interpolation makes joint trajectory tractable for small motor and controller of the miniaturized robot. Centroid body sway ensures walking stability to achieve reliability of the proposed gaits at the motion planning level. By using ground coordinates representation, it is possible to integrate several online gaits and realize a compact and efficient gait planning algorithm. Experimental results are presented to verify the proposed gait planning and control algorithm.     

Motion stereo for mobile robots

A method allowing a mobile robot to measure accurately its distance from external objects is introduced. It only requires a single uncalibrated camera and a dynamic vision system. The method was evaluated in an optical laboratory and also in outdoor-experiments. Even in outdoor-experiments with a vehicle moving at a speed of 30 km/h, errors of less than 1% of the true distance were achieved in real time. The accuracy achievable with the method depends on the nature of the image features used as a basis for the measurement. Laboratory experiments have been performed to investigate quantitatively the characteristics of the feature detectors under conditions of reduced lighting and, consequentially, reduced SNR, and with image features not matching the feature detectors perfectly. The best results can be achieved by using edge-like features. Point-like features do have certain desirable characteristics, but point detectors are more sensitive to noise than edge detectors. Hence, the accuracy achieved with corner detectors was less than the one achieved with edge detectors. Nevertheless, even with corner detectors the resulting error was less than 1%, despite the fact that the image of the target object did not contain good corners     

Self-replicating robots for lunar development

In this paper, the concept of self-replicating robots (SRRs) is reviewed, and the feasibility of a particular kind of minimalistic SRR is analyzed in the context of lunar resource development. The key issue that will determine the feasibility of this approach is whether or not an autonomous robotic factory can be devised such that it is light enough to be transported to the moon, yet complete in its ability to self-replicate with no other inputs than those resources available on the lunar surface. Self-replication leads to exponential growth, and would allow as few as one initial factory to spawn lunar production of materials and energy on a massive scale. Such capacity would dramatically impact man's ability to explore and colonize space and collect solar energy for terrestrial applications. Our concept of a self-replicating robotic factory consists of four subsystems: 1) multifunctional robots for digging and transportation of materials, and assembly of components during the replication process; 2) materials refining and casting facility; 3) solar energy conversion, storage and transmission; and 4) electromagnetic rail guns for long-distance transportation (for example, for sending materials to low-earth orbit (LEO), or transporting replicated factories to distal points on the moon). Each of these subsystems is described in the context of current technologies, with an emphasis on 1). We build on previous concepts for self-replicating systems, present a simple prototype that demonstrates active mechanical replication, and develop an analytical model of how the proliferation of such systems on the lunar surface would occur.     

Reliability bounds for dependent failures

Upper and lower bounds are obtained for the reliability of a series system with statistically dependent component failures. The method can be applied to series subsystems when these are obtained by decomposing a complex system. Numerical examples illustrate the use of the method     

Sequential tests for integrated-circuit failures

We propose a sequential probability ratio test (SPRT) based on a 2-parameter Weibull distribution for integrated-circuit (IC) failure analysis. The shape parameter of the Weibull distribution characterizes the decreasing, constant, or increasing failure rate regions in the bath tub model for IC. The algorithm (SD) detects the operating region of the IC based on the observed failure times. Unlike the fixed-length tests, the SD, due to its sequential nature, uses the minimum average number of devices for the test for fixed error tolerances in the detection procedure. We find that SD is, on average, 96% more statistically efficient than the fixed-length test. SD is highly robust to the variations in the model parameters, unlike other existing sequential tests. Since the accuracy of the tests and the test length are conflicting requirements, we also propose a truncated SD which allows a better control of this tradeoff. It has both the sequential nature of examining measurements and the fixed-length property of guaranteeing that the tolerances be met approximately with a specified number of available measurements     

Fuzzy error governor: A practical approach to counter actuator saturation on flexible joint robots

In this paper, a practical method to counter actuator saturation based on a fuzzy error governor is developed and a complete case study is considered. In addition to good performance, the method has two attracting properties: It does not change the structure of the main controller, and therefore, the theoretically proven characteristics of the system are untouched, and it is simply implementable in practice. The proposed controller structure is applied on a flexible joint robot (FJR). The robust stability of the closed loop system for an n-DOF FJR is thoroughly analyzed and the proposed controller is implemented on a laboratory setup to show the ease of implementation and the resulting closed-loop performance. The main controller used for the n-DOF FJR consists of a composite structure, with a PD controller on the fast dynamics and a PID controller on the slow dynamics. The bandwidth of the fast controller is decreased during critical occasions with the fuzzy logic supervisor, which adjusts the loop gain to a proper level. Using Lyapunov direct method, the robust stability of the overall system is analyzed in presence of modeling uncertainties, and it is shown that if the PD and the PID gains are tuned to satisfy certain conditions, the closed loop system becomes UUB stable.     

Fault-tolerant communications for wafer-scale integration of a processor array

This paper describes schemes for introducing fault-tolerance into a two-dimensional orthogonal array of cells with nearest neighbour communication paths. The schemes are designed to tolerate a large number of faults and are therefore applicable to the yield-enhancement of large-area VLSI circuits. Simulation results are presented which show the superiority of the schemes over previous proposals and indicate that the nearest neighbour interconnections need not be a barrier to the desirable goal of integrating an array computer onto a whole-wafer circuit.