Control of multi-dimensional drives with variable pole pitch

Torque control of a spherical machine combining three degrees of freedom in motion is presented. This drive can be used for machine tools and robots to replace conventional rotating or linear machines which are connected in series or parallel. The proposed motor consists of a rotor sphere with permanent magnets and an outer stator core casing with 96 stator poles and windings. The currents of the coils have to be controlled individually because the pole pitch varies during operation. A unique solution to calculate all 96 current commands to produce one desired torque does not exist. Different control algorithms are presented on how to choose the individual phase currents to reach the required torque vector. Simulation showed satisfactory results which are confirmed by experiments. In addition, the controllability of three dimensional motion is demonstrated.

Compared with transmission systems assembled by some single degrees-of-freedom (DOF) electrical motors, three DOF motion can be achieved in a single permanent magnet (PM) spherical motor, which is a new research direction in the field of electrical motors. The structure and operation principle of a novel PM spherical motor are introduced. An effective three dimensional (3-D) electromagnetic torque finite element model of the PM spherical motor is established, and based on the model simulation is made about the torque which can drive the motor spin. The known motor prototype is analyzed and the typical torque characteristics of the motor are derived. Through analyses of torque characteristics, a method is derived which can effectively enhance the output torque of the PM spherical motor. With the results, theoretical guide is provided for configuration optimization and torque control of the PM spherical motor.

We synthesized two kinds of poly(9,9-diochtylfluorene) (PDOF) with different molecular weight distribution. One is PDOF with low weight molecular component (PDOF-l) and the other is PDOF with high molecular component (PDOF-h). The latter showed twice higher PL efficiency than the former. We investigated PL spectra and EL properties of the blended specimens of two PDOFs. The increase in PDOF-l content reduced PL intensity, conduction current at a constant voltage, and EL efficiency. We suggested the model due to excimer formation caused by the degree of freedom in motion of edge groups.

In this paper, Haptic End-effector for Medicine and Manufacturing (HEM2) with five degree of freedom (DoF) motion is developed for safer and more intuitive robotic surgery. In resent years, multi DoF forceps robots have been studied and developed to support surgeons. However, conventional multi DoF forceps robots cannot transmit force sensation to surgeons adequately. Force sensation is important for safe and accurate teleoperation. In this paper, a master-slave five DoF HEM2 is developed as a haptic forceps robot. Five DoF motion corresponds with the motion of human hand which can realize complex tasks. By implementing acceleration based bilateral control, force sensation can be transmitted. Spherical joint driven by parallel link mechanism realizes the bending motion of the end-effector. The coaxial driving power transmission mechanism is used to decrease the weight of movable part and improve backdrivability. Besides, the mechanism is composed of rigid parts. The performance of the five DoF HEM2 is validated by experiments.

To study the effect of food flow rheology on the human esophageal swallowing process, a biologically inspired actuator prototype has been developed. The actuator is made of silicone rubber where smooth and continuous peristaltic motion is generated by inflating air chambers distributed within its body. The soft material gives the actuator intrinsic compliance and infinite degrees of freedom in motion. Thus, it is challenging to model the behavior online by current methods. In order to investigate the large-scale deformation of the soft-bodied actuator in response to the air chamber pressures, a geometrically simplified two-dimensional (2-D) model composed of separated beam-shaped elements is proposed. It considers the mechanical properties of the material, the sophisticated geometry of the actuator as it deforms, and the distributed pressure behavior. Empirical data from the actuator prototype (captured by articulography) and the simulated results are compared to investigate the accuracy of the model. The differences of deformations between the experimental results and the theoretical model are analyzed.

Model-based precision position and force control of SMA actuators with a clamping application

This paper addresses determination of Degrees of Freedom (DOF) in any planar, spatial, or a combined planar-spatial mechanism. The mechanisms under study may have multiple planar and/or spatial closed loops, open chains with links in series, and/or a combination of the two. It is seen that equations available in the literature to calculate the DOF of such general mechanisms with special joint arrangements such as adjacent joints with parallel and/or intersecting axes over-predict the “true” mobility of links. To overcome this difficulty, new concepts as the Degrees of Freedom of Motion (DOFM) and Degrees of Freedom of Workspace (DOFW) have been introduced. The new definition of Degrees of Freedom of Motion yields a tight upper bound on the connectivity between any two links of a mechanism containing neighboring joints with parallel and/or intersecting joint axes.

Irving Paul Girsang Jaspreet Singh Dhupia School of Mechanical and Aerospace Engineering Nanyang Technological University Singapore, 639798 irving1@e.ntu.edu.sg , djaspreet@ntu.edu.sg ABSTRACT Wind turbine s commonly operat e in an uncertain and noisy environment . Disturbance accommodating controller (DAC) has shown promis ing results in dealing with changing wind speed to regulate generator speed at its rated speed in above rated wind speed condition . However, it has been reported that the number of considered system modes (or degrees of freedom) in design of DAC affects th e system performance. Simulation using high order model, higher than that is considered in the control design, showed unstable response due to effect from the unmodeled structural dynamic s. In this study, DAC with Kalman estimator is designed for variable pitch wind turbines to take into account the unmodeled dynamics and noise measurement . The control performance is simulated using high order FAST model that ha s active generator, drive -train, blade, and tower dynamics in Simulink environment. Simulation re sults show that DAC with Kalman estimator gives best performance in terms of speed regulation and control cost, compared to two other linear controllers: Gain Scheduled Proportional Integral (GSPI) controlle r and DAC with linear estimator . INTRODUCTION Var iable speed variable pitch w ind turbine operates in four major operating regions. Region 1 lies below the cut -in wind speed, below which the wind speed is too low for energy production. Region 2 lies between the cut -in wind speed and the rated wind speed. In this region, the turbine operates to capture as much wind energy as possible. Region 3 , which is considered in this paper, lies between the rated wind speed and the cut -out wind speed. In this region, the turbine operates to produce constant power outpu t at its rated power. This constant rated power can be achieved by operating the turbine at constant generator torque and constant generator speed through feedback control and pitchable blades. The last region, Region 4, lies above the cut -out wind speed , above which the turbine is parked to prevent damage on wind turbine structure due to enormous loads coming from the extremely high wind speed . The p redominant methods of regulating constant generator speed in Region 3 are linear control methods utilizing blade pitch actuation. Common controller types are the model -based Proportional ±Integral -Derivative (PID) controller and Disturbance Accommodating Controller (DAC) [1 -6]. DAC using linear estimator approach has been shown to be effective in attenuating win d disturbances that act as the process noise on wind turbine s [3 -7]. However, this approach is sensitive to mode ling error s, as reported by Wright [6] , that DAC simulation with the activated unmodeled turbine ¶VV WUXFWXUDO dynamics, i.e. turbine with higher order dynamics, can le ad to unstable system response . Moreover, when measurement noise is present, which is not considered in the controller design, additional low pass filter is required to prevent noisy control signal , which can cause problems such as c hattering and controller saturation . This paper presents a robust control approach based on disturbance accommodating control concept for variable pitch wind turbines that compensates for both unmodel ed dynamics, i.e. model ing errors, and external disturba nces , i.e. wind speed input and measurement noise. This approach utilizes Kalman estimation in the feedback loop to estimate both system and disturbance states from noisy measurement signal. Comprehensive formulation and analysis of disturbance accommodati ng controllers using Kalman estimat or can be found in [ 8]. S ome practical advantages of implementing the Kalman estimator in DAC include easy tuning of the estimator parameters, i.e. the noise covariance ASME 2012 5th Annual Dynamic Systems and Control Conference joint with theJSME 2012 11th Motion and Vibration ConferenceDSCC2012-MOVIC20121 Copyright © 2012 by ASME

There are many tasks which require robotic manipulators interaction with environment. It consists of three control problems, i.e., position control, impact control and force control. The position control means the way of reaching to the environment. The moment of touching to the environment yields the impact control problem and the force control is to maintain the desired force trajectory after the impact with the environment. These three control problems occur in sequence, so each control algorithm can be developed independently. Especially for redundant manipulators, each of these three control problems has been important independent research topic. For example, joint torque minimization and impulse minimization are typical techniques for such control problems. The three control problems are considered as a single task in this paper. The position control strategy is developed to improve the performance of the task, i.e., minimization of the individual joint torques and impulse. Therefore, initial conditions of the impact control problem are optimized at the previous position control algorithm. Such a control strategy yields improved result of the impact control. Similarly, the initial conditions for the force control problem are indirectly optimized by the previous position control and impact control strategies. The force control algorithm uses the individual joint torque minimization concept. It also minimizes the force disturbances. The simulation results show the proposed control strategy works well.

Autonomous underwater vehicles (AUVs) are poised to become an indispensable tool for ocean exploration, underwater research and development, and military activities. One of the key elements of these vehicles is dependability; there must be some form of fault recovery/fault tolerance in the control system. In this work, we use an approach involving synthesis of motions in degrees of freedom (DOF) that are unactuated, by combining motions in DOF that are actuated. The objective is to determine the usefulness of the method for a typical streamlined vehicle which is controlled by control surfaces rather than thrusters. We find that the method has difficulties in its present form because of the righting moment designed into the vehicle, but it is functional on a modified model of the vehicle.

DragonFlex – Smart Steerable Laparoscopic Instrument

The purpose of this research is to simulate high degree of freedom motions with low degree of freedom motions. It breaks the rule of using high degree of freedom to simulate high degree of freedom motions. Besides, except for using expensive servo slider, the study uses cables to control the simulator to reach the purpose of simulating unlimited space with limited space of the simulator and it also reach the demands of low cost. In the research, the operator’s tactile sense in body is simulated; the “visual helmet” is also added. Compared with the traditional infrared transmission, it is faster and the changes of the produced environments are more immediate. This makes the operator feels more realistic in the variation of the virtual scenes. The combination of the cable controlled simulator and the visual helmet with the software of virtual reality games makes the operator obtain more actual simulating effects in visual, audio feedback and tactile, motion feedback. It makes operator feel as if s/he is in the real world.

In this paper, model-based precision force and position control of an ionic polymer metal composite (IPMC) is presented. A 23.8 mm × 3.4 mm × 0.16 mm IPMC strip was used as an actuator in a cantilever configuration. Open-loop force and position responses of an IPMC are not repeatable, and hence closed-loop precision control is of critical importance to ensure proper functioning, repeat-ability and reliability. After feedback controllers were designed and implemented with empirically obtained fourth-order plant transfer functions, the overshoot decreased from 460 to 2.8 per cent and the settling time was reduced from 37.5 to 3.22 s in force control. In position control the overshoot decreased from 333 to 20.3 per cent and the settling time was reduced from 21.5 to 2.56 s. Microscale precision force and position control capabilities of the IPMC actuator were also demonstrated experimentally. An 8 μN force resolution was achieved with a force noise of 0.5μN r.m.s., and the position resolution was 6 μm with a position noise of 2.5 μm r.m.s. The maximum force and tip displacement achieved with the IPMC actuator under closed-loop control were 2 mN and 5 mm respectively. The IPMC actuator could follow various commanded force and position trajectories such as sinusoidal and trapezoidal position profiles, and a velocity profile with a 3 mm/s maximum velocity. A novel hybrid force and position control strategy demonstrated its utility in practical micromanipulalion applications where the actuator force must be limited to prevent damaging micro-objects. High-precision control of the IPMC at low force level proved its potential for micromanufacturing and micromanipulation applications such as robotic and biomedical microgrippers.

This paper presents the design, fabricate and evaluation of a Magnetic Resonance compatible finger rehabilitation device, which could not only be used as a finger rehabilitation training tool after stroke, but also to study the brain's recovery process during the rehabilitation therapy (ReT). The mechanics of this device are designed to be adjustable to different persons' finger phalanges, and also the gap between one finger to another can be easily changed. By using an ultrasonic motor as its actuator, the device has been designed to be portable, with a high torque output. In addition, the mechanical has been developed into two working models (passive and active) in order to overcome the intrinsic shortage of non-back drivability in ultrasonic motor. The result system enables the client to do extension and flexion rehabilitation exercises in two degrees of freedom (DOF) for each finger as well as one DOF motion on the thumb. Finally, experiment has been carried out to evaluate the performance of the device.

This paper is the first in a two-part series analyzing human arm and hand motion during a wide range of unstructured tasks. The wide variety of motions performed by the human arm during daily tasks makes it desirable to find representative subsets to reduce the dimensionality of these movements for a variety of applications, including the design and control of robotic and prosthetic devices. This paper presents a novel method and the results of an extensive human subjects study to obtain representative arm joint angle trajectories that span naturalistic motions during Activities of Daily Living (ADLs). In particular, we seek to identify sets of useful motion trajectories of the upper limb that are functions of a single variable, allowing, for instance, an entire prosthetic or robotic arm to be controlled with a single input from a user, along with a means to select between motions for different tasks. Data driven approaches are used to discover clusters and representative motion averages for the wrist 3 degree of freedom (DOF), elbow-wrist 4 DOF, and full-arm 7 DOF motions. The proposed method makes use of well-known techniques such as dynamic time warping (DTW) to obtain a divergence measure between motion segments, Ward's distance criterion to build hierarchical trees, and functional principal component analysis (fPCA) to evaluate cluster variability. The emerging clusters associate various recorded motions into primarily hand start and end location for the full-arm system, motion direction for the wrist-only system, and an intermediate between the two qualities for the elbow-wrist system.