Seung-kook Jun

Tension distribution shaping via reconfigurable attachment in planar mobile cable robots

Traditional cable robots derive their manipulation capabilities using spooling winches at fixed base locations. In our previous work, we examined enhancing manipulation capabilities of cable robots by the addition of base mobility to spooling winches (allowing a group of mobile robots to cooperatively manipulate a payload using cables). Base mobility facilitated the regulation of the tension-direction (via active coordination of mobile bases) and allowed for better conditioning of the wrench-feasible workspace. In this paper we explore putting idler pulleys on the payload attachment as alternate means to simplify the design and enable practical deployment. We examine analysis of the system using ellipse geometry and develop a virtual cable-subsystem formulation (which also facilitates subsumption into the previously developed mobile cable robot analysis framework). We also seek improvement of the tension distribution by utilizing configuration space redundancy to shape the tension null space. This tension distribution shaping is implemented in the form of a tension factor optimization problem over the workspace and explored via both simulation and experimental studies.

Stiffness modulation exploiting configuration redundancy in mobile cable robots

In this paper, we investigate the modulation of task space stiffness of mobile cable robots with elastic cables. The elasticity is introduced via springs connected in series with non-extensible cables. The benefit of such series elastic cables include tension control without using force sensors and tension redistribution. However, elasticity also reduces positioning accuracy and makes the system more prone to disturbances. Therefore, careful stiffness modulation is needed for better performance. We exploit the configuration redundancy in mobile cable robots to optimize certain desired task space stiffness criterion. Both simulation and experimental results are presented for validation.

Automation for individualization of Kinect-based quantitative progressive exercise regimen

The Smart Health paradigm has opened up immense possibilities for designing cyber-physical systems with integrated sensing and analysis for data-driven healthcare decision-making. Clinical motor-rehabilitation has traditionally tended to entail labor-intensive approaches with limited quantitative methods and numerous logistics deployment challenges. We believe such labor-intensive rehabilitation procedures offer a fertile application field for robotics and automation technologies. We seek to concretize this Smart Health paradigm in the context of alleviating knee osteoarthritis (OA). Our long-term goal is the creation, analysis and validation of a low-cost cyber-physical framework for individualized but quantitative motor-rehabilitation. We seek build upon parameterized exercise-protocols, low-cost data-acquisition capabilities of the Kinect sensor and appropriate statistical data-processing to aid individualized-assessment and close the quantitative feedback-loop. Specifically, in this paper, we focus our attention on quantitative evaluation of a clinically-relevant deep-squatting exercise. Data for multiple trials with multiple of squatting motions were captured by Kinect system and examined to aid our individualization goals. Principal Component Analysis (PCA) approaches facilitated both dimension-reduction and filtering of the noisy-data while the K-Nearest Neighbors (K-NN) method was adapted for subject classification. Our preliminary deployment of this approach with 5 subjects achieved 95.6% classification accuracy.

Kinetostatic design-refinement of articulated knee braces

Knee bracing has been used to realize a variety of functional outcomes in both sport and rehabilitation application. Much of the literature focuses on the effect of knee misalignment, force reduction and superiority of custom braces over commercial over-the-counter braces. Efforts on developing exoskeletons to serve as knee augmentation systems emphasize actuation of joints, which then adds to bulkiness of ensuing designs. In lieu of this, we would like to employ a semi-active augmentation approach (by addition of springs and dampers). Such an approach serves to redirect power (motions and forces) to achieve the desired functional outcomes from the knee braces. However, the suitable selection of geometric dimensions of the brace and spring parameters to achieve desired motion- and force-profiles at the knee remains a challenge. We therefore introduce a two-stage kinetostatic design process to help customize the brace to match a desired kinematic/static performance.

Wrench Reconfigurability via Attachment Point Design in Mobile Cable Robots

In our previous paper [1], we examined enhancing manipulation capabilities of cable robots by addition of base mobility to the spooling-winches. Base mobility facilitated the regulation of the tension-direction (via active repositioning of the mobile bases) and allowed for better conditioning of the wrench feasible workspace. In this paper, we explore design-modifications on the attachment to the common payload (merging multiple cables, attachment via pulleys) as alternate means to improve quality of the wrench-feasible workspace. Specifically we systematically examine the role played by attachment-modality and location, focusing on the benefits/drawbacks of the ensuing natural mechanical averaging behavior. Further, by using the notion of virtual cable subsystems, we illustrate the subsumption of this case into our previous mobile-cable-robot analysis framework. We seek improvement of the overall tension distribution by utilizing configuration space redundancy to shape the tension null-space. This is implemented computationally within the framework of a Tension Factor optimization problem over the workspace and explored via both simulation and experiments.Copyright

Planar Cable Robot with Variable Stiffness

Variable stiffness modules add significant robustness to mechanical systems during forceful interactions with uncertain environments. Traditionally, most existing variable stiffness modules tend to be bulky by virtue of their use of solid components making them less suitable for mobile applications. In recent times, pretensioned cable-based modules have been proposed to reduce weight. While passive, these modules depend on significant internal tension to provide the desired stiffness and their stiffness modulation capability tends to be limited. In this paper, we present a planar 2DOF cable robot formed by three active variable stiffness modules that we developed which decouples tension from stiffness. Controlled changes in structural parameters (independent of cable actuation) now permits independent modulation of the perceived stiffness. By varying each module’s stiffness, the overall Cartesian stiffness of the robot can be modulated. We show that this approach is more effective than by increasing internal tension only. It is also easier than varying configuration to achieve variable stiffness. Further, thanks to the added active stiffness adjustment motor, it is able to independently vary stiffness and internal tension. Therefore such active module can achieve same Cartesian stiffness as passive modules but with much lower internal tension, which is more efficient. We present the analysis of the system and verified via both simulation and experimental results for the effectiveness of the Cartesian stiffness varying capability of the planar cable robot.

A Cable Based Active Variable Stiffness Module With Decoupled Tension

Variable-stiffness modules add significant robustness to mechanical systems during forceful interactions with uncertain environments. Traditionally, most existing variable stiffness modules tend to be bulky by virtue of their use of solid components making them less suitable for mobile applications. In recent times, pretensioned cable-based modules have been proposed to reduce weight. While passive, these modules depend on significant internal tension to provide the desired stiffness and stiffness modulation capability tends to be limited. In this paper, we present design, analysis and testing of a cable based active variable stiffness module that can be realized to achieve a large stiffness range. Controlled changes in structural parameters (independent of cable length actuation) now permits independent modulation of the perceived stiffness with desired tension. This capability is now systematically evaluated on a hardware-in-the-loop experimental setup and results are analyzed.Copyright

Compliant Knee Exoskeleton Design: Parallel Coupled Compliant Plate (PCCP) Mechanism and Pennate Elastic Band (PEB) Spring

Recent research in exoskeletons has examined ways for improving flexibility, wearability as well as reducing weight of overall system. Compliant mechanisms offer a class of articulated multi-body systems that allow relatively stiff but lightweight solution for exoskeleton/brace.Copyright

Quantitative Methodology for Knee Exoskeleton Design

Traditionally, the design of exoskeletons (from choice of configuration to selection of parameters) as well as the process of fitting this exoskeleton (to the individual user/patient) has largely depended on intuition and/or practical experience of a designer/physiotherapist. However, improper exoskeleton design and/or incorrect fitting can cause buildup of significant residual forces/torques (both at joint and fixation site). Performance can be further compromised by the innate complexity of human motions and need to accommodate the immense individual variability (in terms of patient–geometries, motion–envelopes and musculoskeletal–strength). In this paper, we propose a systematic and quantitative methodology to evaluate various alternate exoskeleton designs using twist- and wrench-based modeling and analysis. This process is applied in the context of a case-study for developing optimal configuration and fixation of a knee brace/exoskeleton. An optimized knee brace is then prototyped using 3D printing and instrumented with 6–DOF force-torque transducer. Knee brace is then physically tested together with a saw-bones knee model in a scaled knee bracing test. Preliminary results of the physical testing of the knee brace show promise and are discussed.© 2014 ASME