Aykut Cihan Satici

Design of a reconfigurable ankle rehabilitation robot and its use for the estimation of the ankle impedance

This paper presents the design, analysis, and a clinical application of a reconfigurable, parallel mechanism based, force feedback exoskeleton for the human ankle. The device can either be employed as a balance/proprioception trainer or configured to accommodate range of motion (RoM)/strengthening exercises. The exoskeleton can be utilized as a clinical measurement tool to estimate dynamic parameters of the ankle and to assess ankle joint properties in physiological and pathological conditions. Kinematic analysis and control of the device are detailed and a protocol for utilization of the exoskeleton to determine ankle impedance is discussed. The prototype of the device is also presented.

Passive velocity field control of a forearm-wrist rehabilitation robot

This paper presents design, implementation and control of a 3RPS-R exoskeleton, specifically built to impose targeted therapeutic exercises to forearm and wrist. Design of the exoskeleton features enhanced ergonomy, enlarged workspace and optimized device performance when compared to previous versions of the device. Passive velocity field control (PVFC) is implemented at the task space of the manipulator to provide assistance to the patients, such that the exoskeleton follows a desired velocity field asymptotically while maintaining passivity with respect to external applied torque inputs. PVFC is augmented with virtual tunnels and resulting control architecture is integrated into a virtual flight simulator with force-feedback. Experimental results are presented indicating the applicability and effectiveness of using PVFC on 3RPS-R exoskeleton to deliver therapeutic movement exercises.

Assist On-Ankle: a reconfigurable ankle exoskeleton with series-elastic actuation

We present the kinematics, optimal dimensional synthesis, series-elastic actuation, control, characterization and user evaluation of AssistOn-Ankle, a reconfigurable, powered exoskeleton for ankle rehabilitation. AssistOn-Ankle features reconfigurable kinematics for delivery of both range of motion (RoM)/strengthening and balance/proprioception exercises. In particular, through lockable joints, the underlying kinematics can be configured to either a self-aligning parallel mechanism that can naturally cover the whole RoM of the human ankle, or another parallel mechanism that can support the ground reaction forces/torques transferred to the ankle. Utilizing a single device to treat multiple phases of treatment is advantageous for robotic rehabilitation, since not only does it decrease the device cost and help with the space requirements, but also shorten the time it takes for patients to familiarize with the device. Bowden cable-based series-elastic actuation of AssistOn-Ankle allows for a remote placement of the motors/drivers to result in a compact design with low apparent inertia, while also enabling high-fidelity force/impedance control and active backdriveability of the device.

Design optimization, impedance control and characterization of a Modified Delta Robot

Optimal dimensional synthesis, impedance control and experimental characterization a Modified Delta Mechanism based haptic interface are presented. In particular, a multi-criteria design optimization problem is formulated to maximize the transparency of the device. Kinetostatic and dynamic performance indices are optimized simultaneously to reveal design trade-offs between these metrics and an optimal solution is selected from the non-dominated solution set by studying these design trade-offs and considering primary design criteria. A prototype Modified Delta Robot with the optimal dimensions is constructed. A high fidelity model of the robot is formulated and the device is controlled using open-loop impedance control. Finally, the performance of the device is tested and experimental characterization results are presented.

Optimal Design of Haptic Interfaces

Haptic interfaces are computer-controlled motorized devices that physically interact with human operators to render presence of computationally mediated environments. Ideal haptic devices are desired to withstand human applied forces with very high stiffness and be capable of displaying a full range of impedances down to the minimum value humans can perceive. The performance of a haptic interface under closed loop control is measured by the transparency of the display, that is, by quantifying the correspondence between the desired and actually rendered impedance values. During haptic rendering, the haptic interface is coupled to the control system and its existence results in parasitic effects on the displayed impedances, deteriorating the perfect transparency. Therefore, independent of the control algorithm, both the kinematic and dynamic performance of the haptic device have an impact on the overall performance of the haptic display. Robotic manipulators with parallel kinematic chains are popular among haptic interfaces due to their inherent advantages in satisfying requirements of haptic applications with respect to their serial counterparts. Parallel mechanisms offer compact designs with high stiffness and have low effective inertia since their actuators can be grounded in many cases. In terms of dynamic performance, high position and force bandwidths are achievable with parallel mechanisms thanks to their light, but stiff structure. Besides, parallel mechanisms do not superimpose position errors at joints; hence, can achieve high precision. Despite these favorable characteristics of parallel mechanisms, optimal design of such mechanisms with closed kinematic chains is significantly more challenging. Parallel mechanisms have smaller workspace with possible singularities within the workspace and their kinematic, dynamic, and singularity analysis are considerably harder than that of serial manipulators. Due to the additional complexities involved, the dimensional synthesis of parallel mechanisms is still an active area of research. Optimum design of parallel mechanisms, even for a single objective function, is challenging due to the nonlinear, large scale nature of such mechanisms (Lee & Kim, 2006) and nonconvex properties of performance indices with respect to the design variables (Qi & Womersley, 1996). Many different optimization approaches applicable to nonlinear, non-convex optimization problems such as genetic algorithms (Lee et al., 2001; Lee & Kim, 2006; Stuckman & Easom, 1992; Zheng & Lewis, 1994), simulated annealing (Risoli et al., 1999), Bayesian techniques (Stuckman & Easom, 1992; Stuckman et al., 1991), Monte-Carlo simulations (Stuckman & Easom, 1992; Zheng & Lewis, 1994), controlled randomized searches (Lou et al., 2008), performance charts (Liu & Wang, 2007), workspace atlases (Liu et al., 2006), and branch and 12