Leng-Feng Lee

Enhanced trajectory tracking control with active lower bounded stiffness control for cable robot

Cable robots have seen considerable recent interest ensuing from their ability to combine a large workspace with significant payload capacity. However, the cables can apply forces to the end-effector only when they are in tension, and thus form a subclass of control problems requiring unilateral control inputs. Furthermore, actuation redundancy occurs when surplus cables are introduced within the system. On one hand, such redundancy needs to be carefully resolved for accurate tracking of the task. On the other hand, it allows the redistribution of the actuation forces to satisfy some secondary criteria. In this paper, we apply such redundancy for enhanced trajectory tracking by actively controlling the task stiffness of the end-effector. The scheme allow us to specify a lower bound of the task stiffness, which is intended to provide improved trajectory tracking and disturbance rejection performance. Finally, we illustrate the improved control performance within a virtual prototype cosimulation framework.

Case Studies of Musculoskeletal-Simulation-Based Rehabilitation Program Evaluation

Variability in motor rehabilitation program outcomes can be attributed not only to individual components (human patient/rehabilitation equipment) but also to their system-level interactions. Thus, effective deployment of a rehabilitation program depends upon: 1) suitable therapist selection of user-device ergonomics; 2) adjustable device settings; and 3) exercise regimen parameters; to achieve desired system-level motor performance. In this paper, we discuss aspects of creation of a virtual design environment, leveraging tools from musculoskeletal analysis, optimization, and simulation-based design, to permit therapists to rapidly evaluate and systematically customize rehabilitation programs. Specifically, this framework is intended to facilitate 1) parametric study of ergonomic/device/regimen settings on musculoskeletal performance; 2) use of design tools such as optimization for decision support in arriving at the best program; and 3) scaffolded examination of linkage between form and function by iterative what-if type of analyses. We use two case studies (bicep-curling and motor rehabilitative driving) to highlight benefits of such simulation-based rehabilitation program evaluation.

Comparison of Alternate Methods for Distributed Motion Planning of Robot Collectives within a Potential Field Framework

In this paper, we evaluate the performance of two candidate formulations for distributed motion planning of robot collectives within an Artificial Potential Field (APF) framework. We exploit the parallel between the formulation of motion planning for group of robots coupled by constraints and the forward dynamics simulation of constrained multibody systems to develop the candidate approaches. We compare and contrast these approaches on the basis of ease of formulation, distribution of computation and overall computational accuracy. Traditionally penalty formulations have enjoyed a prominent position in motion planning of robot collectives due to their ease of formulation, decentralization and scalability. However, the instabilities introduced in the form of “formulation stiffness” at the algorithm development stage have the potential to hinder the subsequent control. Representative results from the distributed motion planning for a group of 3 point-mass robots moving in formation to a desired target location are used to highlight the differences.

Simulation-Based Design of Exoskeletons Using Musculoskeletal Analysis

Exoskeletons are a new class of articulated mechanical systems whose performance is realized while in intimate contact with the human user. The overall performance depends on many factors including selection of architecture, device, parameters and the nature of the coupling to the human, offering numerous challenges to design-evaluation and refinement. In this paper, we discuss merger of techniques from the musculoskeletal analysis and simulation-based design to study and analyze the performance of such exoskeletons. A representative example of a simplified exoskeleton interacting with and assisting the human arm is used to illustrate principal ideas. Overall, four different case-scenarios are developed and examined with quantitative performance measures to evaluate the effectiveness of the design and allow for design refinement. The results show that augmentation by way of the exoskeleton can lead to a significant reduction in muscle loading.© 2010 ASME

Kinematics analysis of in-parallel 5 DOF haptic device

Parallel-architecture haptic devices offer significant advantages over serial-architecture counterparts in applications requiring high stiffness and high accuracy. To this end, many haptic devices have been created and deployed by modularly piecing together several serial-chain arms to form an in-parallel system. However, the overall system performance depends both on the nature of the individual arms as well as their interactions. We build on the rich theoretical background of constrained articulated mechanical systems to provide a systematic framework for formulation of system-level kinematic performance from individual-arm characteristics. Specifically, we develop the system-level kinematic model in a symbolic (yet algorithmic) fashion that facilitates: (i) computational development of pertinent symbolic equations; (ii) generalization to arbitrary architectures; and (iii) combined symbolic/numeric analyses of performance (workspace, singularities, design sensitivities). These various aspects are illustrated using the example of the Quanser High Definition Haptic Device (HD)2 — an in-parallel haptic device formed by coupling two 3-link Phantom 1.5 type serial chain manipulators with appropriate passive joints. We also briefly discuss aspects of ongoing work for design-prototyping and validation, taking advantage of tools from Virtual Prototyping and Hardware-in-the-Loop testing.

OUTPUT SYNCHRONIZATION FOR TELEOPERATION OF WHEEL MOBILE ROBOT

The potential for use of robotic systems in remote applications arenas has long motivated development of robust and stable means of teleoperated control of slave systems. However, telerobotic systems face challenges stemming from the devices themselves, environmental factors, communication and control complexities. To address these challenges, we will adopt the passivity based synchronization framework [1] and study its applicability to safely synchronize two heterogeneous Lagrangian systems. Within this framework, an adaptive controller identifies and stabilizes the dynamics of the master and slave systems and renders the dynamics passive to a secondary coupling input. The passive mapping used to couple the output states of the master and slave systems and is made insensitive to lossy and delayed communication medium. Specifically, an adaptive passive synchronization teleoperation controller is developed between an Omni haptic device that serves as our master and a differentially driven nonholonomic Wheel Mobile Robot (WMR) as the slave system. A battery of hardware-in-the-loop simulations are used to verify the proposed controller.

Web-Based Self-Paced Virtual Prototyping Tutorials

By permitting designers to realistically, accurately and quantitatively prototype and test multiple intermediate models within virtual environment, Virtual Prototyping (VP), also known as Simulation-Based Design (SBD), has rapidly gained popularity and become a crucial part of most engineering design processes. While there is a significant demand from industry for students trained in this methodology, currently there is not much room in engineering curriculum to permit widespread adoption in the lecture-based classroom. In this paper, we describe the rationale and the stages in the development of a series of web-based and self-paced VP tutorials targeted at students of a course in machine and mechanism design. These undergraduate seniors are permitted to: (1) interactively explore the process of creating engineering analysis models in integrated VP environment; (2) develop skills for interactive SBD of models; and (3) develop their engineering judgment by interactive exploration of a spectrum of examples. The outcome of a phased introduction of these exercises and our experience based on the first successful course offering are also discussed.Copyright

Virtual musculoskeletal scenario-testing case-studies

Doctors, dentists, nurses, athletic trainers, occupational therapists and allied health-care professionals are expected to learn the linkage between anatomy, physiology and ultimately functional-performance of muscles i.e. how muscles affect movement or which sets of muscles carry various loads. However the extent of understanding of functional-performance that can be imparted in a didactic-lecture or cadaver-lab setting of a ldquoGross Anatomyrdquo class is limited. Hence we seek to create the architecture and algorithms for scaffolded interaction with human musculoskeletal simulation models (virtual prototypes) that can make varied ldquowhat-ifrdquo type analyses and hypothesis-testing possible. This is very pertinent in the context of the target audience of healthcare professionals who may lack prior exposure to such virtual computational scenario testing tools. Providing such access is vital to training of the next generation of health care professionals to leverage ubiquitous computing and the quantitative-paradigm.

Musculoskeletal simulation-based parametric study of optimal gait frequency in biped locomotion

Researchers have hypothesized that animal locomotory patterns seen are consistent with the resonant frequencies endowed by their musculoskeletal structures. Further it is posited that systems succeed in minimizing their energy expenditure by moving at this resonant frequency. We choose to systematically study this hypothesis in the specific context of bipedal locomotion. Researchers have sought to correlate the preferred strike frequency with the resonant frequencies of the model or used indirect measurement such as oxygen consumption, electromyography (EMG) to assess expended effort. In our study, we employed virtual prototyping with a capable musculoskeletal simulation model to study the same hypothesis. We benchmark against the available literature and demonstrate that valuable insights can be obtained that can complement the current knowledge-base in biped locomotion.

An Engineering Approach to Utilizing Bio-Inspiration in Robotics Applications

As an interdisciplinary field lying at the intersection of biology and robotics, bio-inspired robotics has seen considerable interest from a research, education, and ultimately application perspective. The scope of this interest has ranged from creating and operating walking, crawling, and flying robots based on biological counterparts; to evaluating biological algorithms for potential engineering applications; to deconstructing the functioning of living organisms from the macro- to the microlevels; and ultimately to constructing the next generation of bio-inspired robots from the bottom up. Significant synergies are forthcoming from such an approach, but numerous limitations still exist. We begin with the discussion of general principles behind taking inspiration from a biological source and converting it into implementable engineering concepts using case studies of bird-inspired robots, snake-inspired robots, and mastication robots. These case studies describe how useful features of the biological creatures were selected and simplified so that they can be implemented using the existing technologies.