Haptic joystick with hybrid actuator using air muscles and spherical MR-brake

In this research, a new 2-DOF hybrid actuator concept is explored as a powerful and compact alternative to conventional haptic actuators. The actuator combines a spherical MR-brake and three air muscles and is integrated into a joystick that can apply forces in two degrees-of-freedom. The air muscles are used to create high active forces in a compact volume and the brake compensates for the “spongy” feeling associated with air muscles. To decrease the overall size of the system an inertial measurement unit has been implemented as a position measurement solution. As high as 16 N of total force output could be achieved at the tip of the joystick. Also, up to 16 times improvement in the stable virtual wall stiffness was obtained when the MR-brake was used to compensate for force errors. Experiments with an impedance-based haptic controller with force-feedback gave satisfactory wall following performance. This device can be employed in applications including computer games, military or medical training applications, rehabilitation and in teleoperation of equipment where high force feedback in 2-DOF in a compact work volume may be desirable while interacting with rigid or elastic virtual objects.     

The Rutgers Master II-new design force-feedback glove

The Rutgers Master II-ND glove is a haptic interface designed for dextrous interactions with virtual environments. The glove provides force feedback up to 16 N each to the thumb, index, middle, and ring fingertips. It uses custom pneumatic actuators arranged in a direct-drive configuration in the palm. Unlike commercial haptic gloves, the direct-drive actuators make unnecessary cables and pulleys, resulting in a more compact and lighter structure. The force-feedback structure also serves as position measuring exoskeleton, by integrating noncontact Hall-effect and infrared sensors. The glove is connected to a haptic-control interface that reads its sensors and servos its actuators. The interface has pneumatic servovalves, signal conditioning electronics, A/D/A boards, power supply and an imbedded Pentium PC. This distributed computing assures much faster control bandwidth than would otherwise be possible. Communication with the host PC is done over an RS232 line. Comparative data with the CyberGrasp commercial haptic glove is presented     

Design and Analysis of a Permanent Magnet Spherical Actuator

This paper has proposed a 3-DOF spherical actuator consisting of a ball-shaped rotor with a full circle of permanent- magnet (PM) poles and a spherical-shell-like stator with two layers of circumferential air-core coils. One key feature of this design is the parametrization of PM and coil poles. Based on the torque model of the PM spherical actuator, the relationship between poles' parameters and torque output can be demonstrated. As a result, the actuator design aiming at achieving maximum torque output can be carried out from the relationships. Another advantage of this spherical actuator is its singularity-free workspace, which is verified with the actuator torque model and condition numbers.     

Modeling and control of a curved pneumatic muscle actuator for wearable elbow exoskeleton

A novel curved pneumatic muscle based rotary actuator for the wearable elbow exoskeleton with joint torque control is proposed. Compared to the general utilization of the pneumatic muscle actuator (PMA) in a rotary joint, this novel structure weakens coupling relationship between the output torque/force and contacting displacement of the PMA so that it can be easily utilized in the tele-robotics with torque/force-feedback or the exciting application in rehabilitation for a wide range. By referred to two physical models, namely beam model and membrane model, the mechanics properties of this mechanical structure is analyzed. In addition a hybrid fuzzy controller composed of bang–bang controller and fuzzy controller is employed for output torque control with high accuracy as well as fast response. In a series of experiments, the actuator exhibits both good static and dynamic performances that well validated the models and control strategy.     

A robotic system for blood sampling

A robotic system to take blood samples autonomously from the forearm is presented, and preliminary results are discussed which demonstrate its feasibility. Force/position profiles, while pressing a flat-headed probe against the surface of the skin, enable the determination of a vein's location to within 1 mm on a phantom. When a needle is inserted, the characteristic force/position profile, on puncturing the vein wall, is distinctive enough to implement automatic needle withdrawal to prevent overshoot. Future developments of the project are presented that provide both an autonomous blood sampling robot and a force-feedback surgical trainer     

Hybrid torque modeling of spherical actuators with cylindrical-shaped magnet poles

A ball-joint-like three-degree-of-freedom (3-DOF) spherical actuator which features a ball-shaped rotor with multiple permanent magnet (PM) poles and a spherical-shell-like stator with air-core coils is proposed to achieve omni-directional smooth motion in only one joint. Unlike previous study in which dihedral-shaped PMs are employed as the rotor poles, this paper utilizes cylindrical-shaped PMs to facilitate the fabrication and reduce the system cost significantly. Torque output of the spherical actuator is formulated with a hybrid method, i.e., using both analytical and experimental methodologies. Specifically, the analytical torque model of spherical actuator with dihedral-shaped PM poles is derived. Then a research prototype with cylindrical-shaped PM poles is developed, and a torque measurement testbed is built up to conduct experiment on the prototype. As the torque variation trend of actuators using two different types of PM poles with respect to the rotor orientation is similar, parameters in the analytical model are adjusted to fit with the experimental measurements. The resulting torque model can be employed for real-time motion control of the actuator. The cylindrical-shaped PM poles also reduce the inertial moment of the rotor by 60%, which is favorable for achieving better dynamic performance of the spherical actuator.     

Design,fabrication, modeling and control of a fabric-based spherical robotic arm

In this paper we present a spherical soft robotic arm made from fabric. The inflatable arm has a small mass and is pneumatically actuated. A configuration is employed with only three actuators controlling the two rotational degrees of freedom of a spherical joint. This differs from the commonly employed antagonistic pairs, including four actuators for two degrees of freedom. The fabrication procedure of the lightweight and compliant system is discussed in detail and uses commonly available materials and tools. The capability of the robotic arm to adjust the joint stiffness as a function of the actuator pressures is investigated and characterized for different deflection directions. The static mapping from the actuator pressures to the orientation of the robotic arm is identified from data and the inverse mapping is employed in a position controller. The modeling and controller derivation are performed for three different stiffness levels demonstrating the ability of the spherical robotic arm to change the joint stiffness independently of controlling the position. The position tracking performance is experimentally evaluated by tracking a square trajectory. A comparison of the tracking performance for the different stiffness levels shows that accurate tracking is more challenging for the smallest joint stiffness. A gray-box model capturing the interactions of the two degrees of freedom is used in a learning scheme that is applied for the smallest stiffness level. The learning approach reduces interactions between the two degrees of freedom and demonstrates the control performance achievable with the system developed.     

Multi-Level Balanced Isolated Floating Difference Amplifier

An innovative amplifier is proposed for applications involving high capacitive load and large voltage output swing, such as piezoelectric (PZT) actuator drivers. This amplifier is configured in a multi-level arrangement with floating amplifiers, yielding a high voltage gain as a sum of all individual gains from its operational amplifiers. The merits of such an amplifier also include a wide bandwidth and high potential power. Experiments using a six-level arrangement demonstrate a 100 kHz bandwidth with $ pm 200~{hbox{V}}$ output swing for different capacitive loadings.      

Design and hybrid control of the pneumatic force-feedback systems for Arm-Exoskeleton by using on/off valve

This article models a pneumatic force-feedback system consisting of the double-acting cylinder and a set of high-speed on–off valves, and its fuzzy controller in order to provide an insight into pneumatic system design and force-feedback control requirements of the Arm-Exoskeleton, which is applied in robot-teleoperation and robotics. In modeling, effects of nonlinear flow through the valves, air compressibility in cylinder chambers, and time delay and attenuation of the pressure input in the connecting tubes are considered. Based on this mathematical model, the hybrid fuzzy control method for the precise force-feedback control is proposed and the fuzzy controllers are realized with the Mega8 MCUs as the units of the distributed control system in the Arm-Exoskeleton. At last a series of experiments validated the models and control method.     

中国天眼-“Fast“天体信号反射系统设计

本文通过分析天体位置,综合考虑反射面上相邻节点距离变幅度、促动器径向伸缩范围,建立电磁波反射面板调节的线性规划模型,并进行优化设计。首先介绍发射面板调节的工作原理,并论证调整反射面板使之成为可聚焦电磁波信号至焦点的理想抛物面的可行性。利用坐标旋转的方法,针对天体的位置调整反射面板,使接收器尽可能收到多的电磁波信号。利用促动器拉伸主索节点以调整反射面板,借助于球坐标系和坐标旋转的方法得到理想的抛物面,有效的控制整个天体信号反射系统。     

Assessment of multi-layer piezoelectric actuator technology for middle-ear implants

A small multi-layer piezoelectric actuator, which contains a stack of piezoelectric crystals in a thin-layered compact structure, was evaluated for its suitability as a stimulator in middle ear hearing implants. Using laser Doppler vibrometry for non-contact vibration measurement, the actuator was found to have a useful bandwidth spanning the range of audio frequencies. During simulated surgical implantation on human temporal bones, one side of the actuator was cemented to the medial wall of the attic of the middle ear and the other side was cemented to the body of the incus. Stapes displacement from actuator excitation at 3.5V_rms was equivalent to that from acoustic stimulation at 90 dB SPL below 1 kHz, increasing to 120 dB at 8 kHz, which is more than adequate stimulation of the ossicular chain. The total harmonic distortion (THD) was less than 2.5% over the audio frequency range. The corresponding power consumption was 0.7 mW per volt of excitation at 1 kHz, which is low enough for the actuator to be used in a partially implantable hearing implant. The surgical implantation and positioning of this type of actuator are straightforward due to the simple linear motion it provides.     

An interactive framework for personalized computer-assisted neurorehabilitation.

This paper presents the implementation of a framework for computer-assisted neurorehabilitation that intends to address the need for more personalized healthcare technologies. This framework called UniTherapy is applied to home neurorehabilitation for individuals with stroke-induced disability. It supports interactive upper limb assessment and therapy that makes use of mass-marketed force-reflecting joysticks and wheels, as well as some customized therapeutic devices. A novel service-oriented technical infrastructure is presented, which includes a rich menu of performance assessment capabilities and support features that include telerehabilitation links, protocol design, and data analysis tools. Results are presented that demonstrate its potential as a sensor-based assessment tool. User feedback is summarized.     

Design and Characterization of a Novel Hybrid Actuator Using Shape Memory Alloy and DC Micromotor for Minimally Invasive Surgery Applications

The end-effectors in the state-of-the-art robotic tools for minimally invasive surgery (MIS) are actuated by actuator packs located outside the patient's body, with the power transmitted from the actuator pack to the end-effector by means of sliding link or tendon-driven mechanisms. This method of power transmission limits the number of degrees-of-freedom (DOFs) in these systems, as the design of a spherical wrist gets complicated. The design of the spherical wrists can be simplified, and the number of DOFs increased, if local actuation is used for the end-effector. However, there are no suitable actuation systems available in the literature. In this paper, a novel design idea for developing a millimeter-scale actuator is presented for locally actuating the end-effector (5-mm-diameter laparoscopic needle driver) for a robot performing MIS. This actuator is designed by combining a dc micromotor and a shape memory alloy actuator in series. The designed actuator is 5.14 mm in diameter (including casing) and 40 mm in length, and is used to actuate a 20-mm-long needle driver assembly, while generating a force of 24 N, resulting in a gripping force of 8 N. The total stroke length of the actuator is 1 mm, which results in a 45 opening of the needle driver jaw with a gap of 8 mm in between the jaws.     

The effect of actuator saturation on the performance of PD-controlled servo systems

Perhaps the most often utilized means of closed-loop control of a servo system is proportional-derivative (PD) control. Linear analysis methods suggest the best tracking performance is achieved at maximum possible proportional and derivative gains. Maximum gains, however, drive the actuators into saturation, which renders the system nonlinear and the linear analysis invalid. This paper investigates the effect of actuator saturation on servo system tracking performance by formulating a frequency-based tracking performance measure roughly equivalent to the linear system −3 dB bandwidth. The proposed measure utilizes a series of band-limited pseudo-random tracking inputs to characterize the ‘bandwidth’ of the (nonlinear) saturating system. Numerical simulations based on this measure show that, for a servo system that exhibits actuator saturation, the best tracking performance is not achieved at maximum gain. Instead, performance improves up to a given gain, then begins to recede as the gain is increased further. The simulations also show that avoiding actuator saturation to ensure linear behavior significantly sacrifices tracking performance. The measure of tracking performance is compared with the −3 dB bandwidth utilized in linear analysis techniques, and the two are shown to be well correlated.     

Closed-loop magnetic bearing and angular velocity control of a reaction sphere actuator

This article presents the first closed-loop magnetic bearing and angular velocity experimental results of a reaction sphere actuator for satellite attitude control. The proposed reaction sphere is a permanent magnet spherical actuator whose rotor is supported by magnetic bearing and can be torqued electronically about any desired axis. The spherical actuator is composed of an 8-pole permanent magnet spherical rotor and of a 20-pole stator with electromagnets. The electromechanical model of the reaction sphere is summarized together with procedures to estimate the rotor magnetic state, the back-EMF voltage, and the rotor angular velocity, which are all fundamental ingredients for controller design. Dynamic controllers are developed to levitate the rotor inside the stator (magnetic bearing) and to control the rotor angular velocity. The magnetic bearing is based on a state-space controller with reduced-order displacement velocity estimator whereas the angular velocity controller is a simple proportional controller with a dedicated angular velocity estimator. The developed control algorithms are experimentally validated using the developed laboratory prototype showing the ability of simultaneously levitating the rotor while rotating it about a given arbitrary axis.     

Precision positioning using MEMS based microactuator

The critical factor for the hard disk manufacturers when designing the new generation of high capacity hard disks is ‘areal density'. Although linear density has increased dramatically increases in track density are limited by servo bandwidths, which are controlled by the actuator resonance. An approach, which is currently being investigated by the researchers, is the use of a second high bandwidth actuator at the end of the conventional voice-coil actuator. After theoretical analysis and discussions with industry electrostatic design in which the microactuator will sit on the slider between the suspension and the read/write head is selected. The design factors are: higher servo bandwidth, higher resonant frequency and low voltage supply. To microfabricate such microactuator we propose to use the latest technology called microelectromechanical systems technology. After schematic drawing layout design is made, it has been tested for electrical connections in the electrical layout model and the optimized design parameters are obtained. Finally it is shown that the design will satisfy the required specifications.     

An Unconstrained Architecture for Systematic Design of Higher Order $SigmaDelta$ Force-Feedback Loops

Nowadays, $SigmaDelta$ -modulation is a widely used technique for analog-to-digital (A/D) conversion, especially when aiming for high resolutions. While being applied initially for purely electrical A/D converters, its application has been expanded to mixed mechanical–electrical systems. This has led to the use of $SigmaDelta$ force-feedback for digital readout of high-performance inertial sensors. However, compared with their electrical counterpoint, $SigmaDelta$ force-feedback loops often have to deal with three additional issues: 1) an increased stability problem due to phase-lag occurring in the sensor; 2) the injection of relatively high levels of readout noise in the loop; and 3) the lack of degrees-of-freedom of many $SigmaDelta$ force-feedback architectures for implementing an arbitrary noise transfer function. As a result, $SigmaDelta$ force-feedback loops found in literature are designed in a much less systematic way as compared with electrical $SigmaDelta$ modulators. In this paper, we address these issues and propose a new unconstrained architecture. Based on this architecture, we are able to present a systematic approach for designing $SigmaDelta$ force-feedback loops. Additionally, the main strengths and weaknesses of different $SigmaDelta$ force-feedback architectures are discussed.      

边缘驱动双腔可变形透镜的设计及制备

针对基于边缘驱动的可变形透镜无法进行球差像差的问题,该文提出了一种边缘驱动双腔可变形透镜结构。上腔体压电圆环32个致动器,校正除球差外的其余低阶像差,主要包括离焦、像散及慧差的校正。下腔体压电圆环1个致动器,通过与上腔致动器的相互作用,实现球差的校正。搭建了可变形透镜性能测试平台并进行了实验。实验结果表明,该可变形透镜能重构前4阶Zernike像差。     

基于电流与电压复合控制的压电陶瓷驱动器

针对电压控制型压电陶瓷驱动器存在动态性能差的问题,及电流控制型压电陶瓷驱动器存在在静态下易充电饱和、难以获得稳定输出的问题,该文设计了基于电流与电压控制的复合型压电陶瓷驱动器.该驱动器具有电流电压双闭环反馈,使驱动器可兼具良好的静态和动态特性.在此基础上,分析了复合型驱动器的性能特点和各参数对其性能的影响,通过调整参数可改变驱动器性能,以满足不同需求.实验结果表明,该驱动器驱动行程为10 μm的压电陶瓷时,0～100 V阶跃信号响应时间小于400 μs,满行程带宽可达1.5 kHz,给定直流信号下可获得良好的稳定输出.