Development of the anthropomorphic robot with carbon fiber epoxy composite materials

The material for the robot structure should have high specific stiffness (stiffness/density) to give positional accuracy and fast maneuverability to the robot. Also, the high material damping is beneficial because it can dissipate the structural vibration induced in the robot structure. This cannot be achieved through conventional materials such as steel and aluminum because these two materials have almost the same specific stiffnesses which are not high enough for the robot structure. Moreover, steel and aluminum have low material dampings.

Composites which usually consist of very high specific modulus fibers and high damping matrices have both high specific stiffnesses and high material dampings. Therefore, in this work, the forearm of an anthropomorphic robot which has 6 degrees of freedom, 70 N payload and 0·1 mm positional accuracy of the end effector was designed and manufactured with high modulus carbon fiber epoxy composite because the magnitudes of the mass and moment of inertia of the forearm of an anthropomorphic robot are most important due to its farthest position from the robot base.

Two power transmission shafts which deliver the power of the motors positioned at the rear of the robot forearm to the wrist and the end effector were also designed and manufactured with high modulus carbon fiber epoxy composite to reduce weight and rotational inertia. The mass reduction of the manufactured composite forearm was 15·9 kg less than the steel forearm.

The natural frequencies and damping capacity of the manufactured composite arm were measured by the fast Fourier transform method and compared to those for the steel arm. From the test, it was found that both the fundamental natural frequency and damping ratio of the composite arm of the robot were much higher than those of the steel arm.     

Composite wrist blocks for double arm type robots for handling large LCD glass panels

Recently, robot structures handling liquid crystal display (LCD) glass panels are increased in size as the size of LCD is increased. In order to handle large LCD panels, the robot structures should have high stiffness to reduce the deflection of robot end effector under the weights of LCD. The LCD manufacturing industries have a trend to employ double arm type robots rather than single arm type robots to increase productivity. Currently, two aluminum wrist blocks that have different configurations not to interfere with each other are mounted on the robot arms. The aluminum wrist block becomes one of the largest deflection sources as the size of the robot structures increases. Since the size of the wrist block can not be increased indefinitely to increase the stiffness due to the limitation of driving motor power, the best way to increase the stiffness of the wrist block is to employ carbon fiber epoxy composite material for structural material of the wrist block because the carbon fiber epoxy composite material has much higher specific stiffness and damping than aluminum. In this work, the two wrist blocks for the double arm type robot for handling large LCD glass panels were designed and manufactured using foam core sandwich structure. Finite element analysis was used along with an optimization routine to design the composite wrist blocks. Box type sandwich structures were employed to reduce shear effect arising from the low modulus of polyurethane foam core. The weight reduction of the composite wrist blocks was more than 50% compared to those of comparable aluminum wrist blocks and found that the composite wrist blocks had much improved performances compared to those of the aluminum wrist blocks from the static and dynamic tests.     

Composite robot end effector for manipulating large LCD glass panels

Recently, the design and the manufacture of light robot end effectors with high stiffness have become important in order to reduce the deflection due to the self-weight and weight of glass panel, a part of LCD, as the size of glass panels as well as robot end effectors increases. The best way to reduce the deflection and vibration of end effectors without sacrificing the stiffness of end effectors is to employ fiber reinforced composite materials for main structural materials because composite materials have high specific stiffness and high damping. In this work, the end effector for loading and unloading large glass panels were designed and manufactured using carbon fiber epoxy composite honeycomb sandwich structures. Finite element analysis was used along with an optimization routine to design the composite end effector. A box type sandwich structure was employed to reduce the shear effect arising from the low modulus of honeycomb structure. The carbon fiber epoxy prepreg was hand-laid up on the honeycomb structure and cured in an autoclave. A special process was used to reinforce the two sidewalls of the box type sandwich structure. The weight reduction of the composite end effector was more than 50% compared to the weight of a comparable aluminum end effector. From the experiments, it was also found that the static and dynamic characteristics of the composite end effector were much improved compared to those of the aluminum end effector.     

玻璃钢约束阻尼复合结构的阻尼特性

以玻璃纤维增强树脂作为约束层主要材料、丁腈橡胶为阻尼层、钢板为基板制备约束阻尼复合结构, 运用动态黏弹谱仪和悬臂梁共振法, 研究温度、约束层刚度和阻尼层结构对约束阻尼复合结构减振效果的影响。结果表明:自由阻尼复合板的最大阻尼范围落在阻尼层的玻璃化转变区;玻璃钢约束层能将复合结构的阻尼拓展至阻尼层的高弹态区域, 增加阻尼层厚度可以提高约束复合板的阻尼性能;提高孔隙率同样有利于约束复合板阻尼性能提升;铝板约束层提升作用尤为显著, 然而在海洋环境、干湿交替等强腐蚀场合中, 铝板极易腐蚀而丧失约束功能, 因此在这类特殊场合下耐腐蚀的玻璃钢具有优势。      

Experimental evaluation of dynamic behavior of metallic plates reinforced by polymer matrix composites

The applications of composite materials have become common in different industries. These materials introduce lower weight, high strength, and viscoelastic properties. Although composite materials offer many advantages in the designing and manufacturing of structures, they cannot replace the wide range of using metallic materials. Most of the industries especially aerospace try to use composite materials together with metal advantages in order to design a safe and optimized structure. The offshore structure can be reinforced and repaired with composite layers. In this research, the effects of composite reinforcement on the dynamic behavior of metallic plates are studied. Several panels are treated with different lay-ups and the modal testing was conducted to evaluate the effect of such treatments. This reinforcing can change both stiffness and damping properties of structures.

The stiffness properties of such reinforced plates can be influenced by fiber properties, while the damping properties come from the viscoelastic property of the matrix. Modal testing is applied to the specimens and the modal parameters are derived experimentally. This study shows that using composite material can modify both stiffness and damping characteristics.     

助老服务机器人设计及仿人运动研究

针对老年人在日常生活中存在行动不便与认知障碍等问题,设计了一款操作简便、功能丰富的助老服务机器人。为降低助老服务机器人的操作难度,增强用户的体验性,通过建立人体手臂与机器臂的空间关节映射模型,实现了机械臂的仿人运动控制。首先,按照人体手臂与机械臂的结构及自由度分布情况初步建立人机关节映射模型,采用蒙特卡罗方法,对人体手臂和机械臂的工作空间进行仿真分析与对比。然后,针对人体手臂与机械臂在空间结构以及自由度分布上的差异导致的机械臂工作空间较小且无法完全复现人体手臂运动的问题,提出了相应的改进方案,并重新建立了人机关节映射模型;通过Kinect视觉传感器获取人体关节的空间位姿信息,并以人体左肩关节为原点建立人体坐标系,采用空间向量法及基于肘部约束的人臂逆运动学解法求解人体关节的位姿变化。最后,搭建了助老服务机器人仿人运动实验平台,对改进后的人机关节映射模型和相关控制算法的有效性及合理性进行了验证,实验结果表明关节重映射后机械臂能高度还原人体手臂的动作。研究成果对提高机器人的交互能力具有借鉴意义,对降低机器人的操作难度效果明显,也为后续研究更加复杂的仿人运动机器人奠定了基础。     

Design of hybrid steel/composite circular plate cutting tool structures

Substituting composite structures for conventional metallic structures has many advantages because composite materials have both high specific stiffness and damping characteristics compared to conventional metallic materials. In this study, circular plate cutting tools which are used for rough machining of bearing sites in crankshafts or camshafts were designed with the fiber reinforced composite material to reduce tool mass and to improve the dynamic stiffness of circular plate cutting tools. The hybrid steel/composite circular plate cutting tool was analyzed by finite element method with respect to material types such as composite and foam, stacking angles of the composite, adhesive bonding thickness, and dimensions of the cutting tool. Also, the constrained damping characteristics of the tools were experimentally investigated with respect to the adhesive bonding thickness and material type such as composite and PVC foam. From the finite element analysis and experimental results, optimal design parameters for the hybrid steel/composite circular plate cutting tool were suggested.     

Composite heddle frame for high-speed looms

A heddle (or heald) frame is the major part of a loom that produces woven cloth by insertion of weft yarns between warp yarns. Warp yarns are manipulated by many heddles fixed in a heddle frame. Recently, the up and down speed of heddle frames has been increased much for the increase of productivity, which induces higher inertial stresses and vibrations in the heddle frame. Conventional aluminum heddle frames have limits for the speed increase due to their low fatigue flexural strength as well as low bending stiffness. The estimated fatigue life of the aluminum heddle frame was 6 months at 600 rpm and infinite at 400 rpm, which was the same results reported by textile industries. Since carbon fiber epoxy composite materials have high specific fatigue strength (S/ρ), high specific modulus (E/ρ) and high damping capacity, in this paper a composite heddle frame was designed and manufactured. The optimum box type cross-sectional shape of the heddle frame and stacking sequence were determined by finite element analysis. The box type composite structure with several ribs was manufactured with prepregs by the autoclave vacuum bag process. Then the static and dynamic characteristics of the composite heddle frame and the aluminum heddle frame were measured and compared.     

梯形齿环状结构缓冲防护性能研究

目的在高冲击、高过载的环境下,研究高过载测试电子记录器的环阻尼缓冲防护结构的缓冲防护性能。方法从结构和材料上对高过载测试电子记录器中的环阻尼缓冲防护结构进行改进,采用具有梯形齿环状缓冲防护结构,在钢壳内侧壁和内胆盖外侧壁、内胆外侧壁之间装有泡沫铝-聚氨酯或泡沫铜-聚氨酯等复合材料,以更好地起到缓冲防护作用。接着对复合材料结构试样进行Ansys仿真实验,研究泡沫铝-聚氨酯复合材料结构的抗高过载、高冲击性能。结果灌封质量分数为25%的聚氨酯时的泡沫铝-聚氨酯复合材料结构的抗高过载性能较好,灌封质量分数为4.9%聚氨酯时的泡沫铝-聚氨酯复合材料结构的抗冲击性能最好。结论梯形齿环状结构较三角齿螺纹结构有更好的稳定性。     

Development of the composite flexspline for a cycloid-type harmonic drive using net shape manufacturing method

The flexspline for a harmonic drive must be flexible in the radial direction for the elastic deformation, but must be stiff in the torsional direction for accurate transmission of rotational motion. Since these requirements cannot be satisfied simultaneously with conventional metals such as steel or aluminium, in this work the carbon fiber epoxy composite material was employed for the flexspline material in order to increase the torsional stiffness by tailoring the stacking sequence and to improve the manufacturing productivity by moulding rather than machining.

The toothed composite flexspline was manufactured with the elastomeric cascade tooling that is composed of the steel tooth die, the silicon rubber mandrel and the cone-shaped steel core. Also, the steel flexspline with the same dimensions of the composite flexspline was manufactured by CNC wire cutting method.

The static and dynamic performances of the composite flexspline and the steel flexspline were experimentally tested. From the test results, it was found that the developed composite flexspline had better flexibility in the radial direction and high damping capacity at the fundamental natural frequency.     

Control and stabilization of a flexible robot arm

It is shown that a flexible robot arm performing a slewing manoeuvre can be controlled exactly within finite energy states by applying moments at the rotating cylinder the beam is attached to, and shearing forces at the free end of the structure. Furthermore, the use of implementable mechanical damping devices, applied to the base and to the free end of the robot arm, shows that uniform exponential stability holds. A Liapunov function is constructed     

Novel applications of composite structures to robots, machine tools and automobiles

Mechanical design can be classified into stiffness design and strength design. In the stiffness design, the stiffness or deformation of members is concerned, and the enhancement of dynamic characteristics such as natural frequency or damping capacity of members or systems is also important. While, in the strength design, the primary concern is the enhancement of load carrying ability of members or systems.

Fiber reinforced composite materials offer a combination of strength and modulus that are either comparable to or better than many traditional metallic materials. Because of their low specific gravities, the strength-weight ratios, and modulus-weight ratios of these composite materials are much superior to those metallic materials. Composite materials can be tailored to meet the specific requirements of each particular design. Available design parameters are the choice of materials (fiber, matrix), the volume fraction of fiber and matrix, fabrication method, number of layers in a given direction, thickness of individual layers, type of layer (unidirectional or fabric), and the layer stacking sequence.

The greatest disadvantages of composite materials are the costs of the materials and the lack of well-defined design rules, therefore, composite materials should be applied in the right place with appropriate design rules. Up to now, the fiber reinforced composite structures are mainly employed in the strength design such as aircraft, spacecraft and vehicles.

In this paper, the novel application examples of composite structures to components for the robots, machine tools and automobiles are addressed considering the stiffness design issues of composite structures.     

Characteristics of joining inserts for composite sandwich panels

Composite sandwich constructions are widely employed in various light weight structures, because composite sandwich panels have high specific stiffness and high specific bending strength compared to solid panels. Since sandwich panels are basically unsuited to carry localized loads, the sandwich structure should provide joining inserts to transfer the localized loads to other structures.In this work, the load transfer characteristics of the partial type insert for composite sandwich panels were investigated experimentally with respect to the insert shape. The static and dynamic pull out tests of the composite sandwich panels composed of an aluminum honeycomb core, two laminates of carbon fiber/epoxy composite and aluminum insert, were performed. From the experiments, the effect of the insert shape on the mechanical characteristics of composite sandwich panels was evaluated.     

Adhesively bonded lap-joints for the composite-steel shell structure of high-speed vehicles

Recently the design and manufacture of lightweight train structures have become important in order to increase speed. Composite train structures have many advantages over conventional steel or aluminum train structures because of their high specific strength, modulus and high damping capacity, which is beneficial for NVH (noise, vibration and harshness).

From the structures of high-speed trains, the upper car-body is a good candidate for composite structures which increase the stability of trains due to the low gravity center of vehicles.

If the side body of the train is made of steel plates, then joining of composite structures to the steel structures is required.

In this work, the adhesive joining method between the composite upper car-body structure and the steel side plates was investigated. A 1/10-size model of a real train subjected to internal pressure was developed and tested statically and dynamically.     

Parametric study on design of composite–foam–resin concrete sandwich structures for precision machine tool structures

In this paper, sandwich structures for micro-EDM machines are optimized by using parametric study varying composite geometries and parameters like stacking sequence, thickness and rib geometry. The structures are composed of fibre reinforced composites for skin material and resin concrete and PVC foam (Closed cell, Divinycell) for core materials. Column structure was designed by a beam with cruciform rib and performance indices such as static bending stiffness (EI) and specific bending stiffness (EI/ρ) for dynamic stability are examined by controlling the thickness and stacking sequence of composites. For the machine tool bed, which usually has a plate shape, was designed to have high stiffness in two directions at the same time controlling stacking sequence and rib geometry; that is, rib thickness and number of ribs. The sensitivity of design parameters like rib thickness and composite skin thickness was examined and the optimal condition for high stiffness structure was suggested. Finite element analysis was also performed to verify the static and dynamic robustness of the machine structure. L-shaped joint for combining bed and column of the micro-EDM machine was proposed and fabricated using adhesive bonding. The dynamic performance such as damping characteristics was investigated by vibration tests. From the results optimal configuration and materials for high precision micro-EDM machines are proposed.     

Thrust bearing design for high-speed composite air spindles

The air spindles whose shafts are made of carbon fiber composite are appropriate for high-speed and high-precision machining such as small hole drilling of printed circuit board (PCB) or wafer cutting for manufacturing semiconductors because the carbon fiber composite shaft has low rotational inertia, high damping ratio and high fundamental natural frequency.

The axial load capability and stiffness of air spindles for drilling operation are dependent on thrust bearings that are composed of air supply part mounted on the housing and rotating part mounted on the rotating shaft of spindle.

Since the stresses induced in the rotating part of thrust bearing by centrifugal force are very high at high-speed rotation, the axial stiffness and load capability of an air spindle should be designed considering the stresses induced by the centrifugal force as well as the natural frequency of rotating shaft to avoid the resonant whip vibration of the spindle.

In this work, the air supply part of a thrust air bearing for a high-speed composite air spindle was designed considering its axial stiffness and load capability. The rotating part of the thin thrust bearing was designed through finite element analysis considering the static and dynamic characteristics under axial load and the centrifugal force during high-speed rotation.     

Development of guide rollers using electroplated carbon fiber-epoxy composite for thin polymer film processing

Since thin polymer films can not sustain the large tension generated from the rotational inertia of a guide roller during start and stop periods of film processing and can be easily damaged by the rough surface of the guide roller, the guide roller should have low rotational inertia, low friction coefficient, high bending stiffness and fine surfaces.

The carbon fiber-epoxy composite material electroplated with chromium has excellent properties for the structure of the guide roller due to its high specific modulus and high damping, which reduces induced vibrations.

In this paper, the design and manufacturing methods as well as the static, dynamic and frictional characteristics of the carbon fiber-epoxy composite rollers electroplated with chromium were investigated using analytical and experimental methods to improve the performance of the high speed guide roller.     

Uncertainty analysis and allocation of joint tolerances in robot manipulators based on interval analysis

Many uncertain factors influence the accuracy and repeatability of robots. These factors include manufacturing and assembly tolerances and deviations in actuators and controllers. The effects of these uncertain factors must be carefully analyzed to obtain a clear insight into the manipulator performance. In order to ensure the position and orientation accuracy of a robot end effector as well as to reduce the manufacturing cost of the robot, it is necessary to quantify the influence of the uncertain factors and optimally allocate the tolerances. This involves a study of the direct and inverse kinematics of robot end effectors in the presence of uncertain factors. This paper focuses on the optimal allocation of joint tolerances with consideration of the positional and directional errors of the robot end effector and the manufacturing cost. The interval analysis is used for predicting errors in the performance of robot manipulators. The Stanford manipulator is considered for illustration. The unknown joint variables are modeled as interval parameters due to the inherent uncertainty. The cost-tolerance model is assumed to be of an exponential form during optimization. The effects of the upper bounds on the minimum cost and relative deviations of the directional and positional errors of the end effector are also studied.     

泡沫材料动刚度及阻尼系数的声阻抗管测量方法研究

提出了泡沫材料动刚度和阻尼系数的声学测量分析模型,建立了相应的实验测量系统。对2种铝板泡沫缓冲结构的动刚度和阻尼系数进行了实验测量和计算分析,结果表明:可以根据声阻抗的测量结果,分析计算得到泡沫材料的动刚度和阻尼系数;铝板泡沫缓冲结构中铝板的质量越大,相应的共振频率越低,共振峰值也越高;对于泡沫材料相同、铝板质量不同的铝板泡沫缓冲结构,通过声阻抗曲线得到的动刚度及阻尼系数分别基本相同;考虑泡沫材料质量的影响,可以得到更准确的计算结果。     

Optimum design of the co-cured double lap joint composed of aluminum and carbon epoxy composite

Since the co-cured joint composed of composite and metallic structures has been widely used in joining process due to its simple and easy manufacturing process, the optimum design of the co-cured joint is important because the joint is usually the weakest part among the components of assembled structures.

In this work, the effect of design parameters for co-cured joint, such as fiber stacking sequence, stiffness ratio of composite to aluminum on the static tensile load capabilities and dynamic fatigue characteristics of the co-cured double lap joint composed of aluminum and carbon epoxy composite were experimentally investigated. Also, the stress distribution and energy release rate of the co-cured joint were calculated using finite element analysis with respect to design parameters.

From the experimental and finite element analysis results, the optimum values for each design parameters were obtained. Also, the optimum stiffness ratio for each stacking sequence of the carbon epoxy composite was obtained.