832 research outputs found
Design of a High Speed Clutch with Mechanical Pulse-Width Control
Kinetic energy storage via flywheels is an emerging avenue for hybrid vehicle research, offering both high energy and power density compared to more established electric and hydraulic alternatives. However, connecting the high speed flywheel to the relatively low speed drivetrain of the vehicle is a persistent challenge, requiring a transmission with high variability and efficiency. A proposed solution drawing inspiration from the electrical domain is the Switch-Mode Continuously Variable Transmission (SM CVT), which uses a high speed clutch to transfer energy to a torsion spring in discrete pulses with a variable duty cycle. The greatest limitation to the performance of this system is the speed and efficiency of commercial clutch technology. It is the goal of this thesis to develop a novel clutch which meets the actuation speed, controllability, and efficiency requirements of the SM CVT, with potential for reapplication in other rotary mechanical systems with switching functionality.
The performance demands of the clutch were derived via a theoretical design case based on the performance requirements of a typical passenger vehicle, indicating the need for a sub-millisecond engagement and disengagement cycle. This is not met by any conventional clutch. Several concepts were considered across the fluid, electromagnetic and mechanical energy domains. A final concept was chosen which employs a friction disk style architecture, with normal force produced by compressing springs via an axial cam mounted to the flywheel. To control duty cycle, the cam was designed with a radially varying profile such that increasing radial position results in proportionally increasing ratio of high dwell to low dwell. Three synchronized followers are then translated radially on the cam by a control linkage. Analysis of the follower train dynamics and system stiffness were carried out to inform the design of a scaled benchtop prototype. Experimental testing was carried out to characterize the performance of the prototype. It was found that the intended functionality of the design was achieved, with discrete energy transfer accomplished via pulsing of the clutch. However, maximum efficiency was only 33% and torque capacity was only 65% of the intended 70Nm. Significant opportunity exists for improvement of the clutch performance in future research
Redundant actuator development study
Current and past supersonic transport configurations are reviewed to assess redundancy requirements for future airplane control systems. Secondary actuators used in stability augmentation systems will probably be the most critical actuator application and require the highest level of redundancy. Two methods of actuator redundancy mechanization have been recommended for further study. Math models of the recommended systems have been developed for use in future computer simulations. A long range plan has been formulated for actuator hardware development and testing in conjunction with the NASA Flight Simulator for Advanced Aircraft
Optimally Controlling the Timing of Energy Transfer in Elastic Joints: Experimental Validation of the Bi-Stiffness Actuation Concept
Elastic actuation taps into elastic elements' energy storage for dynamic
motions beyond rigid actuation. While Series Elastic Actuators (SEA) and
Variable Stiffness Actuators (VSA) are highly sophisticated, they do not fully
provide control over energy transfer timing. To overcome this problem on the
basic system level, the Bi-Stiffness Actuation (BSA) concept was recently
proposed. Theoretically, it allows for full link decoupling, while
simultaneously being able to lock the spring in the drive train via a
switch-and-hold mechanism. Thus, the user would be in full control of the
potential energy storage and release timing. In this work, we introduce an
initial proof-of-concept of Bi-Stiffness-Actuation in the form of a 1-DoF
physical prototype, which is implemented using a modular testbed. We present a
hybrid system model, as well as the mechatronic implementation of the actuator.
We corroborate the feasibility of the concept by conducting a series of
hardware experiments using an open-loop control signal obtained by trajectory
optimization. Here, we compare the performance of the prototype with a
comparable SEA implementation. We show that BSA outperforms SEA 1) in terms of
maximum velocity at low final times and 2) in terms of the movement strategy
itself: The clutch mechanism allows the BSA to generate consistent launch
sequences while the SEA has to rely on lengthy and possibly dangerous
oscillatory swing-up motions. Furthermore, we demonstrate that providing full
control authority over the energy transfer timing and link decoupling allows
the user to synchronously release both elastic joint and gravitational energy.
This facilitates the optimal exploitation of elastic and gravitational
potentials in a synergistic manner.Comment: 8 pages, 9 figures. Submitted to IEEE Robotics and Automation Letter
非線形弾性要素による内部力補償に基づく無段階変位–力変換機構の創生 ― 微小操作力で強大な磁気力・把持力・制動力・張力を制御可能とするロボット要素 ―
Tohoku University博士(情報科学)thesi
The design and control of an actively restrained passive mechatronic system for safety-critical applications
Development of manipulators that interact closely with humans has been a focus of research in
fields such as robot-assisted surgery and haptic interfaces for many years. Recent introduction
of powered surgical-assistant devices into the operating theatre has meant that robot
manipulators have been required to interact with both patients and surgeons. Most of these
manipulators are modified industrial robots. However, the use of high-powered mechanisms in
the operating theatre could compromise safety of the patient, surgeon, and operating room staff.
As a solution to the safety problem, the use of actively restrained passive arms has been
proposed. Clutches or brakes at each joint are used to restrict the motion of the end-effector to
restrain it to a pre-defined region or path. However, these devices have only had limited success
in following pre-defined paths under human guidance.
In this research, three major limitations of existing passive devices actively restrained are
addressed. [Continues.
A portable elbow exoskeleton for three stages of rehabilitation
Patients suffering from stroke need to undergo a standard and intensive rehabilitation therapy. The rehabilitation training consists of three sequential stages: the first stage is controlled joint movement under external actuator, the second stage deals with supporting the movements by providing assistive force, and the last stage provides variety and difficulty to exercises. Most of the exoskeletons developed so far for rehabilitation are restricted to a particular type of activity. Although a few exoskeletons incorporate different modes of rehabilitation, those are software controlled requiring sensory data acquisition and complex control architecture. To bridge this gap, a portable elbow exoskeleton has been developed for delivering three stages of rehabilitation in a single structure without affecting the range of motion and safety features. Use of electric motor and springs have been arranged in the actuation mechanism to minimize the energy consumption. The developed exoskeleton enhances torque to weight ratio compared to existing models, and all the three modes of rehabilitation have been controlled using a single motor
Design of a Haptic Interface for Medical Applications using Magneto-Rheological Fluid based Actuators
This thesis reports on the design, construction, and evaluation of a prototype two degrees-of-freedom (DOF) haptic interface, which takes advantage of Magneto-Rheological Fluid (MRF) based clutches for actuation. Haptic information provides important cues in teleoperated systems and enables the user to feel the interaction with a remote or virtual environment during teleoperation. The two main objectives in designing a haptic interface are stability and transparency. Indeed, deficiencies in these factors in haptics-enabled telerobotic systems has the introduction of haptics in medical environments where safety and reliability are prime considerations. An actuator with poor dynamics, high inertia, large size, and heavy weight can significantly undermine the stability and transparency of a teleoperated system. In this work, the potential benefits of MRF-based actuators to the field of haptics in medical applications are studied. Devices developed with such fluids are known to possess superior mechanical characteristics over conventional servo systems. These characteristics significantly contribute to improved stability and transparency of haptic devices. This idea is evaluated and verified through both theoretical and experimental points of view. The design of a small-scale MRF-based clutch, suitable for a multi-DOF haptic interface, is discussed and its performance is compared with conventional servo systems. This design is developed into four prototype clutches. In addition, a closed-loop torque control strategy is presented. The feedback signal used in this control scheme comes from the magnetic field acquired from embedded Hall sensors in the clutch. The controller uses this feedback signal to compensate for the nonlinear behavior using an estimated model, based on Artificial Neural Networks. Such a control strategy eliminates the need for torque sensors for providing feedback signals. The performance of the developed design and the effectiveness of the proposed modeling and control techniques are experimentally validated. Next, a 2-DOF haptic interface based on a distributed antagonistic configuration of MRF-based clutches is constructed for a class of medical applications. This device is incorporated in a master-slave teleoperation setup that is used for applications involving needle insertion and soft-tissue palpation. Phantom and in vitro animal tissue were used to assess the performance of the haptic interface. The results show a great potential of MRF-based actuators for integration in haptic devices for medical interventions that require reliable, safe, accurate, highly transparent, and stable force reflection
Numerical and experimental investigation of a semi-active vibration control system by means of vibration energy conversion
A vibration control concept based on vibration energy conversion and storage with respect to a serial-stiffness-switch system (4S) has previously been proposed. Here, we first present a rotational electromagnetic serial-stiffness-switch system as a novel practical vibration control system for experimental validation of the concept and, furthermore, an improved control strategy for higher vibration suppression performance is also proposed. The system consists of two spring-switch elements in series, where a parallel switch can block a spring. As an alternating mechanical switch, the experimental system uses two electromagnets with a shared armature. By connecting the armature to the rotating load or the base, the electromagnets decide which of the two spiral springs is blocked, while the other is active. A switching law based on the rotation velocity of the payload is used. Modelling and building of the experimental system were carried out. The corresponding experiment and simulation were executed and they matched well. These results prove that our serial-stiffness-switch system is capable of converting vibration energy and realizing vibration reduction under a forced harmonic disturbance. The effects of disturbance frequency, disturbance amplitude and sampling frequency on the system performance are shown as well. A position feedback control-based switching law is further put forward and experimentally verified to improve the repositioning accuracy of the disturbed system
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