Development of an artificial muscle linear actuator using ionic polymer–metal composites

We are developing an artificial muscle linear actuator using ionic polymer-metal composites (IPMC)—electro-active polymers that bend in response to electric stimuli—and the goal of our study is applying the actuator to robotic applications, especially to a biped walking robot. In this paper, we will describe the structure of the actuator and an empirical model of the actuator which has two inputs and one output, and whose parameters are identified from input-output data. Based on the empirical model, basic experiments and position control of the linear actuator are demonstrated. Then, we consider walking control of a small-sized biped walking robot. In the application we assume that the developed actuators are connected both in series and in parallel to a joint of the walking robot so that the actuators supply enough torque to the robot, and that they are stretched and compressed enough. It is shown throughout simulations that the biped walking robot with the actuators can walk on level ground with a period synchronized with the period of the input signal.     

基于SMA的关节驱动器的力学分析及控制

分析了一种用于水下微小型仿生机器人的形状记忆合金(SMA)关节驱动器的力学特性,并通过模糊控制的方法对其进行了实验研究。结果表明:对于物理特性呈非线性、温度滞后、时变和受温度影响很大的SMA驱动器来说,采用模糊控制的方法,能够使驱动器稳定、平滑的工作,尽管产生了轻微的超调现象,但收到了令人较为满意的效果。因此,将模糊控制方法应用于SMA驱动器的控制有一定的理论意义和应用价值。     

Micro actuators on the basis of thin SMA foils

Three innovative micro actuator concepts on the basis of the differential SMA principle are presented in this paper: a high adaptive multi-actuator system, which is driven by numerous identical single actuators connected in parallel and in series, a micro gripper for handling and assembling of complex hybrid micro systems and a micro actuator system in medical tools for the percutaneous resection of aortic valves. The SMA material is used in the form of 50 μm thin NiTi foils because of their well-defined properties and high strength. In order to integrate them into micro systems, different manufacturing methods have been applied and improved at the Institute for Microtechnology. Laser cutting and wet chemical etching are used for example to microstructure the actuator elements. Different methods for electrical and mechanical connections of the actuators are employed like soldering by the use of an additional gold layer. A batch fabrication process of SMA actuators is realized by embedding NiTi foil elements into SU-8 structures. To optimize the design of SMA actuator elements according to its application different simulation procedures are used.     

Control of Shape Memory Alloy Actuators with a Neuro-fuzzy Feedforward Model Element

This paper describes development of a motion controller for Shape Memory Alloy (SMA) actuators using a dynamic model generated by a neuro-fuzzy inference system. Using SMA actuators, it would be possible to design miniature mechanisms for a variety of applications including miniature robots for micro manufacturing. Today SMA is used for valves, latches, and locks, which are automatically activated by heat. However it has not been used as a motion control device due to difficulty in the treatment of its highly nonlinear strain-stress hysteresis characteristic. In this paper, a dynamic model of a SMA actuator is developed using ANFIS, a neuro-fuzzy inference system provided in MATLAB environment. Using neuro-fuzzy logic, the system identification of the dynamic system is performed by observing the change of state variables (displacement and velocity) responding to a known input (input voltage to the current amplifier for the SMA actuator). Then, using the dynamic model, the estimated input voltage required to follow a desired trajectory is calculated in an open-loop manner. The actual input voltage supplied to the current amplifier is the sum of this open-loop input voltage and an input voltage calculated from an ordinary PD control scheme. This neuro-fuzzy logic-based control scheme is a very generalized scheme that can be used for a variety of SMA actuators. Experimental results are provided to demonstrate the potential for this type of controller to control the motion of the SMA actuator.     

The Micro Trolley Based on SMA and its Control System

The structure and control system of a micro trolley imitating an insect is introduced. Its movement mechanism is analyzed. The micro trolley imitates the motion of creature muscle using an SMA (Shape Memory Alloy) actuator. An elastic rubber band is put side by side with the SMA actuator so that the velocity of movement increases to almost twice as fast as without the elastic rubber band. The anti-reverse device attached to each wheel successfully prevents the wheels from turning backwards. This paper also analyzes the experiment results of the trolley. The prototype can be applied to the inspection and maintenance of micro pipes and tubes in such specific fields as nuclear power plants or space shuttles.     

一种微小型蠕动机器人的步态分析

介绍了一种形状记忆合金(SMA)驱动的微型蠕动机器人的结构和工作原理,并对蠕动机器人的直线运动原理和转弯运动原理分别进行了详细的分析和论述。此外,还通过详细的实验对蠕动机器人步距与SMA驱动器电流的关系、蠕动机器人转弯角度与SMA驱动器电流的关系,以及蠕动机器人响应速度与SMA驱动器电流的关系进行了分析,并确定了SMA驱动器的加热电流。     

Development of a shape memory alloy actuator. Improvement of output performance by the introduction of a σ-mechanism

The driving-force-generating principle of an actuator made of shape memory alloy (SMA) is based on the thermal elastic martensitic transformation, a kind of elastic phenomenon. As a result, conventional SMA actuators which use a circular pulley have tended to exhibit undesirable characteristics such as the maximum generable torque being changed depending on the rotating angle when the robot joint was driven by rotating motion transformed from expansion/contraction of the SMA, so that the servo system to support the torque under a certain load could not have an operable range wide enough for practical application. This paper intends to clarify these problems of SMA actuators and proposes a new joint mechanism using a σ-shaped non-circular pulley, called the σ-mechanism, for joint linkage to overcome the problems. This design enables the maximum generated torque to be kept uniform at all times by reducing the torque-arm-length in inverse proportion when the SMA tension increases corresponding to the rotating angle of the joint. Subsequently, a specifically designing algorithm for the proposed σ-mechanism is discussed. The validity of the new mechanism is demonstrated by an experimental model using an SMA actuator with a σpulley.     

Architecture design of a multiaxis cellular actuator array using segmented binary control of shape memory alloy

A new approach to artificial muscle actuator design is presented, and is implemented using shape memory alloys (SMA). An array of SMA actuators is segmented into many independently controlled, spatially discrete volumes, each contributing a small displacement to create a large motion. The segmented cellular architecture of SMA wires is extended to a multiaxis actuator array by arranging the segments in a two-dimensional (2-D) array. The multiaxis control is streamlined and coordinated using a 2-D segmentation method in order to activate multiple links of a robot mechanism in a coordinated manner. The basic principle of segmented binary control (SBC) is first presented, followed by multiaxis segmentation theory and a design procedure. The method is applied to a five-fingered robotic hand capable of taking a variety of postures. A 10-axis SMA actuator array is built, and SBC is implemented using Peltier-effect thermoelectric devices for selective local heating and cooling. Experiments demonstrate the feasibility and effectiveness of the new method.     

Performance analysis of a new energy-efficient variable supply pressure electro-hydraulic motion control method

Electro-hydraulic actuation is used in many motion control applications due to its high power density, excellent dynamic response and good durability. However fluid power actuation has been shown to be very energy inefficient, with an average efficiency for fluid power systems across all industries of 22% in the USA. This is a very significant problem, given that 3% of the energy used by mankind is transmitted in this way.The key challenge for researchers is to reduce energy losses in hydraulic actuation systems without increasing weight, size, and noise, and without reducing speed of response. Conventional high performance electro-hydraulic motion control systems use a fixed supply pressure with valve-controlled actuators (FPVC). This is inherently inefficient due to the need to use a valve to throttle the flow required by each actuator in the system down to match its load pressure. In this paper, a new load-prediction based method is proposed, in which the supply pressure is varied to track the pressure required by any actuator branch. By implementing this model-based approach using a high response servomotor-driven pump, it is shown that the dynamic response remains excellent. The load model not only allows feedforward control for servomotor speed based on the motion demand, but also feedforward for the control valves to supplement conventional proportional-integral feedback control.The new variable supply pressure valve-controlled (VPVC) method is investigated in simulation and experimentally using a two-axis hydraulic robot arm supplied by an axial piston pump. The performance has been rigorously compared with the same robot arm using a fixed supply pressure and proportional-integral joint position control. Experimental results showed that up to 70% hydraulic power saving was achieved, and that the dynamic tracking errors for VPVC were about half that for FPVC as a result of using feedforward control.     

A new method for actuating parallel manipulators

This paper presents a new technique of actuating a parallel platform manipulator using shape memory alloy (SMA). This is a type of smart materials that can attain a high strength-to-weight ratio, which makes them ideal for miniature application. The work is mainly to develop a new SMA actuator and then incorporating the actuator in building the parallel manipulator prototype. The SMA used in this study is a commercial NiTi wire. The SMA wire provides an actuating force that produces a large bending and end displacement. A 3-UPU (universal–prismatic–universal) parallel manipulator using linear SMA actuators was developed. The manipulator consists of a fixed platform, a moving platform and three SMA actuators. The manipulator workspace was specified based on the restrictions due to actuator strokes and joint angle limits. System identification techniques were used to model both heating and cooling processes. An ON/OFF control was performed and the results showed closeness in simulation and experimental results. This study showed that shape memory alloy actuated beam can successfully be used to provide linear displacement. The built prototype indicates the feasibility of using SMA actuators in parallel manipulators.     

Development and control of a micro artificial muscle cell using electro-conjugate fluid

As a man–machine interaction increases its importance in the robotic and mechatronic fields, a soft robot, which is inspired from natural systems, becomes one of the most important research trends. There are several research topics related to soft robots such as soft structures or artificial skins, compliance control, soft actuators or artificial muscles, and so on. For the natural muscle potentially has great flexibility, the authors believe that the artificial muscle actuator must be a promising technology for soft robots. Hence in this study, we develop a new type of micro artificial muscle cell, which is an element of an integrated artificial muscle, using electro-conjugate fluid (ECF) and measure its driving performances. In addition, position control characteristics are also clarified by experiments. Experimental results show the micro artificial muscle cell using electro-conjugate fluid has a quite good control performance.     

Batch fabrication of micro grippers with integrated actuators

In this paper we present improvements in the field of batch fabricated micro grippers with shape memory alloy (SMA) actuators or pneumatic drives. In this context we illustrate two methods of structuring SMA foils. Moreover, it is shown how the processed SMA elements can be embedded into monolithic SU-8 grippers. We also describe actuator elements for silicon/SU-8 hybrid micro grippers. Furthermore, we report on the advantages of pneumatic micro grippers and how this alternative actuation principle can be fabricated in batch technology. In this regard, a thermoplastic adhesive electrodepositing process is presented.     

仿生“蚯蚓”机器人的SMA 执行器实现

虽然从生物学角度来说,蚯蚓的波浪式运动机制已经相当清楚,但在小尺寸下人工蚯蚓的实现仍然是极具挑战性的工作.采用记忆合金材料(SMA),设计实现了用于仿生蚯蚓机器人的执行器,并通过该执行器的动作循环模仿,实现了蚯蚓的波浪式运动.实现的人工蚯蚓共有四单元,每一单元都有可独立驱动的执行器.执行器由一根或三根SMA弹簧构成,其波动式运动的最高频率为0.6 Hz.每一单元人工蚯蚓,都被覆特定形状的软硅胶皮,该硅胶皮提供了SMA执行器的对抗力,同时也是安装微型腿的平台,从而进一步提高了人工蚯蚓的运动效率.初步的测试显示该执行器工作有效,人工蚯蚓的运动速度可达2.5mm/s,与真实的蚯蚓运动速度相近.     

A multilink active catheter with polyimide-based integrated CMOSinterface circuits

This paper describes an active catheter with flexible polyimide-based integrated CMOS interface circuits for communication and control (C&C IC) to be used for applications in biomedicine. The active catheter has a multilink structure. Distributed micro shape memory alloy (SMA) coils are utilized as actuators for multidegree of freedom movement. The C&C IC's, which are incorporated on the links, require three common lead wires to address all the links and control the selected SMA actuators in the active catheter. An MOS transistor with large channel width is used for switching the SMA actuator. To reduce the system size and simplify the assembly work, the C&C circuit and three lead wires are fabricated on the same substrate using CMOS-compatible polyimide-based process. The outer diameter of the fabricated active catheter is approximately 2.0 mm. The fabricated active catheter has a four-link structure and six degrees of freedom of movement per one link. A simple bending model of one unit is presented and compared with the experiments. The fabricated C&C IC measures 1.0 mm×3.35 mm×0.2 mm. The link addressing and the actuator switching functions of the fabricated chip were confirmed. The minimum access time for addressing and actuating a single unit was 6.4 μs. The active catheter was actuated by the fabricated C&C IC chip with flexible interconnect leads in response to the C&C signals from the outside controller     

An Operator-based Nonlinear Vibration Control System Using a Flexible Arm with Shape Memory Alloy

In the past, arms used in the fields of industry and robotics have been designed not to vibrate by increasing their mass and stiffness. The weight of arms has tended to be reduced to improve speed of operation, and decrease the cost of their production. Since the weight saving makes the arms lose their stiffness and therefore vibrate more easily, the vibration suppression control is needed for realizing the above purpose. Incidentally, the use of various smart materials in actuators has grown. In particular, a shape memory alloy (SMA) is applied widely and has several advantages: light weight, large displacement by temperature change, and large force to mass ratio. However, the SMA actuators possess hysteresis nonlinearity between their own temperature and displacement obtained by the temperature. The hysteretic behavior of the SMA actuators affects their control performance. In previous research, an operator-based control system including a hysteresis compensator has been proposed. The vibration of a flexible arm is dealt with as the controlled object; one end of the arm is clamped and the other end is free. The effectiveness of the hysteresis compensator has been confirmed by simulations and experiments. Nevertheless, the feedback signal of the previous designed system has increased exponentially. It is difficult to use the system in the long-term because of the phenomenon. Additionally, the SMA actuator generates and radiates heat because electric current passing through the SMA actuator provides heat, and strain on the SMA actuator is generated. With long-time use of the SMA actuator, the environmental temperature around the SMA actuator varies through radiation of the heat. There exists a risk that the ambient temperature change dealt with as disturbance affects the temperature and strain of the SMA actuator. In this research, a design method of the operator-based control system is proposed considering the long-term use of the system. In the method, the hysteresis characteristics of the SMA actuator and the temperature change around the actuator are considered. The effectiveness of the proposed method is verified by simulations and experiments.

     

Heavy material handling by cooperative robot control

Multifingered dextrous robot hands can perform more complex tasks than simpler end effectors. Teleoperation, in which a robot mimics the motion of a remote operator, provides a convenient method for controlling these robot hands. Damage to the object being manipulated by the robot hand may result in the case of open-loop control if there is no force-feedback sensation to the operator from the robot hand. The need arises for new actuator technology to provide force feedback to the hand master. These actuators have to meet the tight space and light weight requirements of a dextrous master. One candidate is the shape memory alloy (SMA) actuator. SMAs, such as Nitinol, are materials with a unique 'mechanical memory' and high force/weight ratio. A prototype SMA actuator and its hardware interface were designed and tested. Results showed that the actuator met the space and weight limitations of the master (Exos DHM?) and provided adequate reactive force feedback to the operator. However, the actuator had a low bandwidth of operation, due to relatively slow engagement and disengagement motions. This makes it unusable in real-time control situations.     

基于多级多路径控制的无线传感器电源管理方法

无线传感器通常长期在野外工作,其电源能耗一直是受业界关注的技术问题.针对采用低压锂电池供电的无线传感器,提出采用多级多路径控制的电源管理方法,实现超低压降、电源超低功耗和大电流输出.采用本电源管理方法的无线传感器不仅能充分利用电池电能量,还能兼容多种供电电源(如锂电池、锂亚电池、干电池、铅酸电池等)的应用场景.     

Impact Analysis of a Dual-Crawler-Driven Robot

This paper presents the impact analysis of a new dual-crawler-driven robot. This dual-crawler-driven robot is realized by connecting rigidly two crawler modules. In this newly proposed crawler module, a planetary gear reducer is deployed as the power transmission device to give two different outputs with just one actuator. Compared with the crawler driven by two actuators, our crawler module driven by one actuator could show good impact absorption when the robot collides with an obstacle due to the fact that there exists an output redundancy in each module. To determine what the advantage of our mechanism to the impact absorption is, impact analysis of the robot is conducted from the external components of the robot to its internal transmission parts while the robot encounters a collision with obstacles. The results of impact effect to the actuators in our mechanism are correspondingly derived in comparison with that in the conventional mechanism where each output is provided by one actuator. Numerical results are used to demonstrate the advantage of our mechanism on impact absorption.     

SMA驱动的微型平面关节机器人的研究

近年来，利用形状记忆合金（ＳＭＡ）的形状记忆效应原理制作的驱动器已在机器人领域中得到应用，ＳＭＡ驱动器以其重量轻、结构紧凑、易控制等优点，大大推动了微型机器人的发展．本课题使用所研制的推挽式直线位移型和旋转关节型ＳＭＡ驱动器代替传统的伺服驱动系统，研制了一台三自由度（两个旋转自由度和一个直线自由度）且带末端夹持器的微型平面关节机器人．本文将介绍该机器人的结构设计，控制系统及其软件设计．     

Global output-feedback tracking and load disturbance rejection for electrically-driven robotic manipulators with uncertain dynamics

In this paper the tracking problem for rigid robot manipulators with uncertain parameters and unmodelled torque actuators (DC motors) is addressed and solved by combined first/second-order sliding mode control methodology. The robot is electrically-driven through a pulse-width modulated actuator supply voltage. The proposed controller does not require the availability of the joint velocity, is insensitive to smooth load disturbances and guarantees a global domain of attraction. Computer simulations confirm the feasibility of the proposed approach.