Flexible Payload Research Articles

NON-LINEAR DIRECT JOINT CONTROL FOR MANIPULATOR HANDLING A FLEXIBLE PAYLOAD WITH INPUT CONSTRAINTS

In this paper, we propose a non-linear control strategy for a robotic manipulator handling a flexible payload in the presence of input constraints and input disturbances, which does not require end-point boundary control.

Cooperative Aerial Load Transport with Force Control

We consider a group of aerial manipulators (AM) collaboratively transporting a flexible payload. Each AM is a combination of an Unmanned Aerial Vehicle (UAV) with a two-degree-of-freedom robotic manipulator (RM) attached to it. Contact forces between the agents (AMs) and the payload are modeled as the gradient of nonlinear potentials that describe the deformation of the payload. We develop an adaptive decentralized control law for transporting a payload with an unknown mass without explicit communication between the agents. The algorithm guarantees that all the agents converge to a desired velocity and the contact forces are regulated. The sum of the estimates of the unknown mass from all the agents converge to the true mass. Using the inverse kinematics of the AM, we implement the developed algorithm at the kinematic level for the AMs and demonstrate its effectiveness in simulations.

Measuring water level in rivers and lakes from lightweight Unmanned Aerial Vehicles

The assessment of hydrologic dynamics in rivers, lakes, reservoirs and wetlands requires measurements of water level, its temporal and spatial derivatives, and the extent and dynamics of open water surfaces. Motivated by the declining number of ground-based measurement stations, research efforts have been devoted to the retrieval of these hydraulic properties from spaceborne platforms in the past few decades. However, due to coarse spatial and temporal resolutions, spaceborne missions have several limitations when assessing the water level of terrestrial surface water bodies and determining complex water dynamics. Unmanned Aerial Vehicles (UAVs) can fill the gap between spaceborne and ground-based observations, and provide high spatial resolution and dense temporal coverage data, in quick turn-around time, using flexible payload design. This study focused on categorizing and testing sensors, which comply with the weight constraint of small UAVs (around 1.5kg), capable of measuring the range to water surface. Subtracting the measured range from the vertical position retrieved by the onboard Global Navigation Satellite System (GNSS) receiver, we can determine the water level (orthometric height). Three different ranging payloads, which consisted of a radar, a sonar and an in-house developed camera-based laser distance sensor (CLDS), have been evaluated in terms of accuracy, precision, maximum ranging distance and beam divergence. After numerous flights, the relative accuracy of the overall system was estimated. A ranging accuracy better than 0.5% of the range and a maximum ranging distance of 60m were achieved with the radar. The CLDS showed the lowest beam divergence, which is required to avoid contamination of the signal from interfering surroundings for narrow fields of view. With the GNSS system delivering a relative vertical accuracy better than 3–5cm, water level can be retrieved with an overall accuracy better than 5–7cm.

Separable data hiding in encrypted image based on compressive sensing and discrete fourier transform

Reversible data hiding in encrypted images has become an effective and popular way to preserve the security and privacy of users’ personal images. Recently, Xiao et al. firstly presented reversible data hiding in encrypted images with use of the modern signal processing technique compressive sensing (CS). However, the quality of decrypted image is not great enough. In this paper, a new method of separable data hiding in encrypted images are proposed by using CS and discrete fourier transform, which takes full advantage of both real and imaginary coefficients for ensuring great recovery and providing flexible payload. Compared with the original work, the proposed method can obtain better image quality when concealing the same embedding capacity. Furthermore, image decryption and data extraction are separable in the proposed method, and the secret data can be extracted relatively accurately.

Efficient wet paper embedding for steganography with multilayer construction

This work proposes an efficient data hiding scheme for wet paper channel by using a multilayer construction, in which a number of node-bits in different layers are derived from all cover bits and used to carry the secret data. By applying the wet paper coding method to the node-bits and altering the changeable cover bits, the node-bits are modified into their desired values and the secret data are embedded in a layer-by-layer manner. An equilibration mechanism is also introduced to flip the denser changeable cover bits with higher probability. This way, paper folding method is equivalent to a special case of the proposed scheme, and a family of data hiding methods with more flexible relative payload and higher embedding efficiency can be generated.

Ka 대역 위성 출력 전력 제어 기술 연구

Ka 대역 위성통신 시스템에서 강우 감쇠 보상을 위해서는 위성 탑재체에서 강우 지역의 출력 전력을 높일 수 있는 시스템이 요구된다. Ka 대역 출력 전력 제어 기술은 위성 탑재체에서 하향 링크(19.8 ~ 22.2 GHz)의 출력 전력 조정을 가능하게 한다. 본 논문에서는 다중 빔 안테나와 다중 입출력 증폭기를 이용한 Ka 대역 위성 출력전력 제어 기술에 대하여 소개한다. 한반도 상에 8개의 빔을 형성하기 위해 배열 급전 소자와 반사판으로 구성된 다중 빔 안테나가 설계되었다. 빔 당 목표 EIRP는 59 dBW 이상이며, 강우 감쇠 보상을 위한 전력 제어 기능은 강우 지역에 비 강우 지역 대비 최대 6 dB의 EIRP 상승이 가능하도록 설계하였다. 다중 입출력 증폭기는 다중 빔 안테나와 함께 구성될 때 위성 출력 전력 제어를 위해 효과적으로 사용될 수 있다. <TEX>$4{\times}4$</TEX> 다중 입출력 증폭기가 기술 검증을 위해 제작되었으며 Ka 대역 위성 송신 주파수 대역에서 24 dB 이상의 격리도 성능을 나타낸다. For Ka-band satellite communication system, a new flexible payload technologies which can compensate rain attenuation have to be developed. The Ka-band satellite output power control technology enables to adjust downlink output power of satellite payload in Ka-band (19.8 ~ 22.2 GHz). In this paper, we introduce multi-beam antenna with multi-port amplifiers for Ka-band flexible output power allocation system. We have designed multi-beam antenna with array-fed reflector to form 8 beams on the Korean Peninsula. The target EIRP per beam is more than 59 dBW. The system is designed to present 6 dB boost beams for rainfall areas. Individual beams were optimized by the excited amplitude and phase of feed elements of the feed cluster. The multi-port amplifier(MPA) is one of effective approaches for flexible power allocation in combination with multi-beam antenna. In case of using MPA in multi-beam system, the inter-port isolation characteristic of MPA is important parameter to avoid interference among the output ports. In this paper, we propose a new MPA structure that consists of two <TEX>$4{\times}4$</TEX> Buttler matrixes and phase/amplitude controllable power amplifier modules.

Neutron Sensitivity of High-Speed Networks

Recently, engineers have been studying on-payload networks for fast communication paths. Using intrasystem networks as a means to connect devices together allows for a flexible payload design that does not rely on dedicated communication paths between devices. In this manner, the data flow architecture of the system can be dynamically reconfigured to allow data routes to be optimized for the application or configured to route around devices that are temporarily or permanently unavailable. To use intrasystem networks, devices will need network controllers and switches. These devices are likely to be affected by single-event effects, which could affect data communication. In this paper, we will present radiation data and performance analysis for using a Broadcom network controller in a neutron environment.

Cooperative Load Transport: A Formation-Control Perspective

We consider a group of agents collaboratively transporting a flexible payload. The contact forces between the agents and the payload are modeled as gradients of nonlinear potentials that describe the deformations of the payload. The load-transport problem is then treated in a similar fashion to the formation-control problem. Decentralized control laws are developed such that without explicit communication, the agents and the payload converge to the same constant velocity; meanwhile, the contact forces are regulated. Experimental results illustrate the effectiveness of our designs.

An experimental investigation of the data delivery performance of a wireless sensing unit designed for structural health monitoring

This study explores the reliability of a wireless sensing unit by testing it in a real-world university laboratory environment. The unit employs off-the-shelf products for their key components, while a flexible payload scheme was adopted for radio packet transmission to maximize throughput and minimize latency. The testing consists of two main parts: (1) a series of loopback tests using two off-the-shelf radio components with carrier frequencies of 900 MHz and 2.4 GHz, respectively, and (2) wireless transmission of a shake table response to a periodic swept sine excitation. The performance of the wireless channel is examined in each part of the study. Through this experimental investigation, it is validated that a loopback test may be used as a fast prototyping approach to characterize the complex transmitting environment of a structure in which a wireless monitoring system is installed. Various factors leading to signal attenuation are ranked according to their effects on packet delivery performance. Transmitting range and building materials are among the leading factors causing packet loss (and therefore data loss) in this specific testing environment. The severity of interference from 802.11b wireless systems in close proximity to the wireless sensing unit was investigated. Some preliminary results on the influence of operating rotating machinery and human activities are to wireless sensors were investigated. The results presented herein offer a guideline for applying wireless sensing within real-world structures so that the reliability of the wireless monitoring system is maximized. Due to uncertainties associated with the reliability of wireless communications, statistical analysis is performed on the collected time histories to reveal the underlying patterns associated with data loss. Temporal correlations of data loss were measured and found to be related to the adopted radio. A statistical distribution of the size of consecutive lost data points was further derived from the collected data. Such results have identified the need to further develop: (1) reliable communication protocols to reduce these losses in data and information, and (2) robust data processing and system identification tools to anticipate and explicitly handle any data loss. Copyright © 2007 John Wiley & Sons, Ltd.

UAV Payload and Mission Control Hardware/Software Architecture

This paper presents an embedded hardware/software architecture specially designed to be applied on mini/micro unmanned aerial vehicles (UAV). A UAV is a low-cost non-piloted airplane designed to operate in D-cube (Dangerous-Dirty-Dull) situations [8]. Many types of UAVs exist today; however with the advent of UAV's civil applications, the class of mini/micro UAVs is emerging as a valid option in a commercial scenario. This type of UAV shares limitations with most computer embedded systems: limited space, limited power resources, increasing computation requirements, complexity of the applications, time to market requirements, etc. UAVs are automatically piloted by an embedded system named "Flight Control System." Many of those systems are commercially available today, however no commercial system exists nowadays that provides support to the actual mission that the UAV should perform. This introduces a hardware/software architecture specially designed to operate as a flexible payload and mission controller in a mini/micro UAV. Given that the missions UAVs can carry on justify their existence; we believe that specific payload and mission controllers for UAVs should be developed. Our architectonic proposal for them orbits around four key elements: a LAN-based distributed and scalable hardware architecture, a service/subscription based software architecture and an abstraction communication layer.

GUIDANCE, ONBOARD SIGNAL PROCESSING AND ROBUST CONTROL OF AGILE FLEXIBLE REMOTE SENSING SPACECRAFT

Problems on guidance, onboard signal processing and robust gyromoment motion control of agile spacecraft (SC) for the Earth remote sensing and for the flexible payload transportation, are considered. Elaborated methods for dynamic research of the SC angular motion at principle modes under external and parametric disturbances, partial discrete measurement of the state, multiple filtering and digital control by the gyro moment cluster, are presented

DYNAMIC MODELLING OF FLEXIBLE PAYLOADS MANIPULATED BY A SMART GRIPPER IN ROBOTIC ASSEMBLY

During robotic assembly of flexible payloads, gravity and inertial forces acting on these payloads may induce both static shape deformation and vibration of the thin-walled payloads. Static deformations, which arise from deformation of the part due to its own weight under the influence of gravity, lead to misalignment of mating points of the part. Unwanted vibrations, arising from inertial forces acting on the part as it is positioned for assembly, must be damped out before it can be mated with other parts. This paper investigates the development of dynamic models of arbitrarily shaped flexible thin-walled payloads grasped by a smart gripper, comprised of multiple linearly actuated fingers with non-contact proximity sensors. Such an actuated gripper allows both part-reshaping and active damping of unwanted vibrations of the part. Finite element modelling techniques are used to generate dynamic models of these arbitrarily shaped parts. Component mode synthesis methods are used to combine the dynamics of the actuated gripper with the dynamics of the thin-walled parts. The resultant dynamic model, developed with finite element modelling, is of high order, and hence model order reduction methods are employed to reduce the model order but retain the essential dynamics of the thin-walled payload gripper system. Using a two time-scale modelling technique, an integrated closed-loop modal truncation and control design procedure is used to design a shape and vibration controller for thin-walled payload. Simulation results modelling thin-walled sheet metal parts manipulated by an industrial robot confirm the validity of the proposed modelling approach.

Static Shape and Vibration Control of Flexible Payloads With Applications to Robotic Assembly

This paper addresses the simultaneous control of vibration and static shape deformation of arbitrarily shaped thin-walled flexible payloads. During robotic assembly of these thin-walled parts, gravity and inertial forces acting on the parts may induce both static shape deformation and vibrations in the part sufficiently large that accurate and high speed assembly of these parts is hindered. Static deformations, which arise due to deformation of the part caused by its own weight under the influence of gravity, lead to misalignment of mating points of the parts. Unwanted vibrations, arising from inertial forces acting on the thin-walled parts as they are positioned for assembly, must damp out before parts can be mated, further hindering the process. In this work, a smart gripper with actuated contact points to grasp the flexible thin-walled parts is proposed to solve this problem. The smart gripper is capable of both part reshaping and active damping of unwanted vibrations of the part. It is fixed to a robotic manipulator and is comprised of multiple linearly actuated fingers with laser-based noncontact proximity sensors, and associated signal processing and controllers. In this paper, a simultaneous vibration and static shape controller is developed. The proposed controller is a composite modal controller in conjunction with a quasi-static modal filter and a bias Kalman filter, which is synthesized based on the reduced-order dynamic model of the flexible payload. A near industrial practice demonstration of the feasibility of the proposed approach is carried out using a proof-of-concept smart gripper to manipulate an automotive fender. Experimental results indicate that unwanted vibrations are successfully damped out, allowing faster cycle times for an assembly process, and static shape deformations are corrected, allowing accurate positioning of parts for assembly.

3314 宇宙ロボットアームの手先微小速度操作実験(S85-1 宇宙ロボットと制御技術(1),S85 宇宙ロボットと制御技術)

We generally move the end-effector (EE) of the robotic arm in very low velocity around the target position when we transport payloads in orbit. The joints of the arm also must be rotated very slowly in such circumstance. However, the joint rotates discontinuously in very low velocity because an influence of friction at reduction gears is dominant. The discontinuous rotation of joints possibly causes vibration when the arm is operated on a flexible base or it handles a flexible payload. We investigate operation methods to avoid the discontinuous rotation by utilization of a redundant arm. The redundant arm can maintain over a certain minimum velocity although the EE moves in very low velocity. In addition, we apply Input Shaping to suppress a residual vibration of the arm induced by the operation method of maintaining the minimum velocity. In this paper, we report the experiment results of the minimum velocity maintaining operation and Input Shaping application.

Study of deployed and modular active phased-array multibeam satellite antenna

A deployed, self-cooled and modular (tile-based) active phased array for multibeam applications has recently been proposed in the literature. This novel antenna facilitates the implementation of large array antennas in space with many beams from the same aperture, offering a flexible payload with the potential for high traffic capacity. However, the configuration also raises some questions about degradation in antenna performance, due to constraints such as non-circular aperture, frame gap, uniform amplitude excitation, and a calibration boom deployed in front of the array. Methods dealing with these issues are discussed in this paper. It is shown that a phase-only optimization technique can effectively reduce interference between same-frequency spatially reused beams, and can compensate for EIRP and C/I degradation for tile-correlated errors and failures.

Six-degree-of-freedom hexapods for active damping and active isolation of vibrations

Abstract : As future astronomic missions will require more and more stringent resolution requirements, the high demand for an environment clean of vibrations and disturbance appears. This also leads to the need for high precision steering devices for fine pointing of sensitive optics with the highest possible accuracy. Several methods exist to reduce vibration levels: the first consists in isolating the sensitive system from the perturbation and the second in damping the structure vibration modes. Therefore, two Stewart platforms have been designed, manufactured and tested. The first is a soft hexapod that provides 6 degree-of-freedom (DOF) active isolation and the second is a stiff hexapod that provides active damping to whatever flexible payload attached/mounted to it. In addition, both hexapods have steering capabilities. 1. INTRODUCTION The two robots presented in this paper are based on the cubic configuration of Stewart platform [9], more details about cubic configuration are shown in [1]. The legs of the soft hexapod consist in soft electro-dynamic actuators. This hexapod consists mainly of two plates connected to each other by six legs. Each leg of the soft Stewart platform contains a voice coil electro-dynamic linear actuator, a force sensor and two flexible joints. This Stewart platform is aimed to be used in active vibration isolation. Only active control can achieve simultaneously high isolation performances (–40

Computer simulation of an adaptive control system for a free-flying space robotic module with flexible payload’s transportation

The synthesis and computer simulation of a control system for a free-flying space robotic module (SRM) are considered. It is assumed that the control system includes relay actuators. The mode of flexible payload transportation is analyzed. The control system is designed on the base of an adaptive coordinate-parametric control principle. The procedure of computer synthesis for a three-dimensional modal–physical dynamics model of the SRM plus a non-rigid payload (SRM-P) is described. The synthesis is made in MATLABs and MAPLEs computer systems. On the basis of numerical analyses of the space module’s dynamic portrait, we have obtained the intensity dependence of the oscillations excited by relay control moments on the coordinates of the payload capture point. This dependence is represented by a multi-extremal function. Its global extremum (minimum) in the domain of admissible values for the argument is considered as the criterion in the task of choosing the optimal values of the payload capture point coordinates. The results of this task are used in the tuning of the capture point that makes it possible to avoid the resonance swing of the flexible payload and SRM-P as a whole.

Command Shaping Nonlinear Inputs Using Basis Functions

Manufacturing operations exist which require robotic repositioning of flexible payloads. Product quality or throughput can be adversely affected if payload vibration is not controlled. Using command shaped inputs can prevent excitation of payload dynamics, however, most of the literature has focused on linear, single input systems. General robotic repositioning typically involves simultaneous motion of multiple degrees of freedom resulting in the payload excitation function being a nonlinear combination of the robot input states. Under these conditions, removal of the individual input’s frequency content in the vicinity of the payload’s resonances does not guarantee that the nonlinear combination of the inputs will be free of detrimental frequency content. Presented in this paper is a method for trajectory design of point-to-point flexible payload maneuvers with multiple inputs nonlinearly driving payload dynamics. Simulation and experimental results are provided for the coordinated maneuver of a flexible beam. Using this trajectory generation approach, the residual oscillation is reduced by a factor of 20 as compared to the worst case maneuver, without a reduction in total maneuver time.

3306 大型柔軟構造物操作のための双腕ロボットの制御

It is expected that autonomous space robots conduct many on-orbit servicings, for example the construction and maintenance of large space structures as well as the capture and recovery of damaged satellites. In order to realize these missions, robot manipulators mounted on a satellite can be useful. During the capturing operation of a floating target, it may be difficult for a manipulator to grapple it directly because of target nutation or tumbling. In order to damp the angular momentum of target, the method using a cushion type damper has been proposed. After grappling the target, it is necessary to handle the payload suppressing the vibration. We will analyze the handling operation of the flexible payload by dual manipulator. In this paper, we report the results of the ground experiment and the numerical simulation, and discuss the validity and feasibility of this operation.

PC-based control of robotic and mechatronic systems under MS-Windows NT workstation

A method is proposed to perform control using Intel/sup (R)/ based PCs operated by Windows NT/sup TM/ directly. The software package developed is called WinRec v.1 (Windows real-time control). This low cost method keeps all the advantages of Windows NT without attaching any other kernels and avoids switching different operating systems between experimentation and control design/analysis. A thorough description of the method to set up the multimedia timer provided by Microsoft Development Network Library is presented. Self-customized algorithms based on advanced control techniques can be implemented with the standard protocol that is established here. The proposed protocol is evaluated using two different systems in control experiments. In the first system, an industrial robot manipulator is controlled by applying an independent joint PID control scheme. Results are also shown from experiments where LQR and H/sub 2/ controllers are applied to suppress vibrations of a flexible payload carried by the robot manipulator. In the second system, position, force, temperature, voltage and current data are simultaneously recorded in order to evaluate the performance of a shape-memory-alloy wire bundle actuator in open loop control experiments.