Xiumin Diao

Dynamics analysis of a cable-driven parallel manipulator for hardware-in-the-loop dynamic simulation

This paper describes a preliminary study of the dynamics of a 6-DOF cable-driven parallel manipulator for a potential application in a ground-based hardware-in-the-loop simulator of microgravity dynamics and contact-dynamics of spacecraft or robotic systems. Two basic dynamics problems are studied. One is the inverse dynamics problem and the other is the rigidity and vibration problem. The study results support the feasibility of using such a cable-driven manipulator for hardware-in-the-loop simulation of contact dynamics

Workspace Analysis of a 6-DOF Cable Robot for Hardware-in-the-Loop Dynamic Simulation

This paper describes the study of the force-closure workspace of a 6-DOF, cable-driven, parallel robot for the application in a hardware-in-the-loop dynamic simulator, which is used for simulating microgravity contact dynamics of spacecraft or robotic systems. The workspace under study is defined as the set of all end-effector poses satisfying force-closure condition. Force-closure also means that the inverse dynamics problem of the manipulator has a feasible solution. Since there is no limitation on the external wrench and the dynamic motion of the end-effector, such a workspace is the most desirable (or nonrestricted) workspace for the intended application simulating low-speed impact-contact dynamics. A systematic method of determining whether or not a given end-effectors pose is inside the workspace is proposed with mathematical proof. Based on this method, the shape, boundary, dimensions, and volume of the workspace of a 6-DOF cable robot are displayed and discussed

Force-closure analysis of general 6-DOF cable manipulators

This paper proposed a systematic method of verifying the force-closure condition for general 6-DOF cable manipulators with more than seven cables. Without explicitly solving the inverse dynamics problem, the method can determine, by examining the Jacobian matrix of the manipulator, whether a feasible force solution exists. The equivalence (i.e., necessity and sufficiency) of the proposed method to an existing force-closure theorem developed for the robot grasping problem is mathematically proven and hence, this work rigorously shows, for the first time, that the theory for grasping problem is also applicable to cable manipulators. Moreover, a convex-analysis based simplification of the method is discussed.

Dynamics modeling and analysis of inkjet technology-based oligo DNA microarray spotting

Oligo deoxyribonucleic-acid (DNA) microarrays are fabricated through in-situ chemical synthesis. Contact and fluid dynamics contribute to this process. To produce high-quality oligo DNA microarrays, it is important to well understand the dynamics of the fabrication process. Much work has been done in understanding the chemistry principles. However, few studies have been conducted from the mechanics point of view. This paper proposes a contact dynamics model of inkjet technology-based oligo DNA microarray spotting process. The proposed dynamics model can reasonably well explain the dynamics of the oligo DNA microarray spotting process. Note to Practitioners-This research was motivated by the need to develop a dynamics model for analyzing the inkjet technology-based oligo deoxyribonucleic-acid (DNA) microarray spotting process. Modeling techniques for micro/nanoscale dynamics have not been well established in the open literature. This case study shows how this can be done for DNA spotting dynamics. Contact dynamics, electrostatic forces, viscous forces, and van der Waals forces have all been considered in this study. The method may be extended to model and analyze the dynamics of other biological particle spotting processes as well.

Angular-velocity tracking with unknown dynamics for satellite rendezvous and docking

Autonomous satellite on-orbit servicing is a very challenging task when the satellite to be serviced is tumbling and has an unknown dynamics model. This paper addresses an adaptive control approach which can be used to assist the control of a servicing satellite to rendezvous and dock with a tumbling satellite whose dynamics model is unknown. A proximity-rendezvous and docking operation can be assumed to have three steps: 1) pre-dock alignment, 2) soft docking and latching/locking-up, and 3) post-docking stabilization. The paper deals with the first and third steps. Lyapunovbased tracking law and adaptation law are proposed to guarantee the success of the nonlinear control procedures with dynamics uncertainties. A dynamics simulation example is presented to illustrate the application of the proposed control approach. Simulation results demonstrated that the adaptive control method can successfully track any required angular velocity trajectory even when the dynamics model of the target satellite is unknown.

Study of 6-DOF Cable Robots for Potential Application of HIL Microgravity Contact-Dynamics Simulation

[Abstract] This paper first presents a concept of using a 6-DOF cable robot for hardware-in-the-loop (HIL) dynamic simulation of microgravity contact-dynamics behavior of a space system such as a spacecraft or robot. It then addresses three basic problems of the cable robot in order to verify that the cable robot can meet the most critical requirements of such an HIL contact-dynamics simulator. The first problem is whether the dynamic motion of the end-effector being fully controllable under the constraint that all the cables must be in tension during a contact operation, i.e., under what condition the inverse dynamics problem has an all-positive force solution. A systematic method of checking force-closure condition is proposed. The second problem is to make sure that the cable robot can have sufficiently large workspace to simulate the motion of the space system. The force-closure workspace is determined using the systematic method of checking force-closure. The third problem is whether the potential vibration arising from the cable flexibility is acceptable for the intended simulation application. The study results of all the three problems support the feasibility of using such a cable robot for HIL simulation of contact-dynamics.

Vibration Analysis of Cable-Driven Parallel Manipulators for Hardware-in-the-Loop Contact-Dynamics Simulation

Possible vibration of cable-driven parallel manipulators (called cable manipulators for short) is a concern for some special applications such as hardware-in-the-loop (HIL) contact-dynamics simulation of spacecraft or space robotic systems. A cable manipulator used in HIL simulation is required to be rigid enough to have a high bandwidth to respond its input. This paper provides a vibration analysis of a general 6-DOF cable manipulator. Under an excitation, a cable may deflect in both axial and lateral directions due to its inevitable flexibility. The vibrations of cable manipulators caused by cable flexibility in both axial and lateral directions are analyzed. The study demonstrated that the cable manipulator can provide sufficient rigidity for applications like HIL contact-dynamics simulation of a spacecraft or space robotic system. It is also shown that the vibration of a cable manipulator due to the lateral flexibility of cables can be ignored comparing to that due to the axial flexibility of cables.© 2007 ASME

TU‐C‐AUD C‐03: Teletherapy MicroRT Using a Commercial 192Ir Source

The prototype small‐animal irradiator (microRT) developed at Washington University utilizes the commercial 192Ir high‐dose rate (HDR) remote afterloader source in a teletherapy geometry. The system consists of a set of four Tungstencollimators (5.5 mm diameter hole) mounted to an Aluminum support tube. An HDR catheter is used to transport the source to the collimator and pre‐determined dwell positions center the source at the collimator hole. The mouse is placed on a couch that contains a series of drilled holes that act as fiducial localization marks visible on computed tomography(CT)imaging. For most experiments, the mouse is first anesthetized and placed on a couch. The couch is imaged using a commercial CT scanner (spatial resolution approximately 0.6 mm). The couch geometry is automatically registered in the treatment planningsoftware, which was written in the Computational Environment for Radiotherapy Research (CERR) platform. The treatment planner determines the dose and adjusts the source‐to‐target distance to achieve the required field size and the target dose, coupled with the source strength, determines the irradiation time. The couch is mounted to a computer‐controlled three‐dimensional stage that positions the mouse to submillimeter accuracy. Advantages of the system include its relatively high precision, low fabrication cost, and straightforward and robust operation. Disadvantages include the need for having a commercial HDR source and the associated complexities of scheduling experiments, the relatively poor penumbra, and the steep depth‐dose behavior. The system works very well for parallel‐opposed fields to either the whole brain or hemi‐brain, and tumors grown on the mouse flank.

MO‐E‐AUD C‐07: Modeling Small Animal Micro Irradiator Orthovoltage Sources

Purpose: To model and compute spectral output, intensity, dose fall off, dose rate, and penumbra that can be achieved using industrial orthovoltage x‐rays sources used in small animal micro irradiators. Method and Materials: Using data from commercial sources as input parameters we investigated the performance of orthovoltage sources that can be used in small animal micro irradiators. We developed a pencil beam propagation code which was combined with a mouse digital phantom (MOBY‐John Hopkins Univ.) to simulate a complete small animal delivery system (source + animalmodel). We computed the source spectral output, beam filters, beam penumbra, soft tissue to bone dose ratio, dose fall off, and total dose delivered to the animalmodel. Sources covering the range of 150 to 450kVp with submillimeter focal spot were simulated. Results: We determined that a source of nominal maximum potential output of 320kVp and focal spot of 0.4×0.4 mm2 outperformed other available sources. We designed an optimum Thoraeus‐like filter to obtain a bremsstrahlung spectrum energy greater than 2 mm of Cu to increase skin spare and reduce bone dose. An average beam penumbra of 0.25mm and a dose rate of 40Gy/min were possible using this filtered beam. Higher energy sources would increase cost and shielding thickness. Lower energies sources showed limited intensities when they were aggressively filtered. Conclusion: We developed a numerical model to evaluate the radiation dose delivered by orthovoltage sources typically used in small animal irradiators. We concluded that when radiation quality, skin dose, bone to tissue dose ratio and animal throughput were considered, commercial orthovoltage sources of nominal energy of 320 keV were the best fit for conformal small animal micro irradiators. To obtain high conformality a submillimeter focal spot of 0.5×0.5 mm2 or less must be used. This work supported in part by NIH grant R21CA108677

Simulation of Nanomanipulation Using Compliance-Based Contact Dynamics Modeling Technique

This paper describes dynamics modeling and simulation of AFM-based manipulation of a nano-scale object using the compliance-based contact dynamics modeling technique (also referred to as the penalty method). Such a modeling technique has been well developed and widely applied in macro-scale applications. Its applicability to nano-scale cases is, however, relatively new and thus, requires more investigation. The dynamics model developed in the paper includes the Van der Waals forces, electrostatic forces, contact forces (for modeling repulsion), and friction forces with consideration of contact geometry, stiffness, and friction properties of all the physically interacting objects. The model can simulate the dynamic behavior of interactions between nano-scale objects and its environment. For demonstration, the dynamic simulation results of an AFM-based manipulation process are presented. To provide confidence of the model fidelity, a simulation example which matches some published data is presented.Copyright