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Analysis of accuracy in pointing with redundant hand-held tools: a geometric approach to the uncontrolled manifold method.

ABSTRACT: This work introduces a coordinate-independent method to analyse movement variability of tasks performed with hand-held tools, such as a pen or a surgical scalpel. We extend the classical uncontrolled manifold (UCM) approach by exploiting the geometry of rigid body motions, used to describe tool configurations. In particular, we analyse variability during a static pointing task with a hand-held tool, where subjects are asked to keep the tool tip in steady contact with another object. In this case the tool is redundant with respect to the task, as subjects control position/orientation of the tool, i.e. 6 degrees-of-freedom (dof), to maintain the tool tip position (3dof) steady. To test the new method, subjects performed a pointing task with and without arm support. The additional dof introduced in the unsupported condition, injecting more variability into the system, represented a resource to minimise variability in the task space via coordinated motion. The results show that all of the seven subjects channeled more variability along directions not directly affecting the task (UCM), consistent with previous literature but now shown in a coordinate-independent way. Variability in the unsupported condition was only slightly larger at the endpoint but much larger in the UCM.

SUBMITTER: Campolo D

PROVIDER: S-EPMC3617015 | biostudies-literature | 2013 Apr

REPOSITORIES: biostudies-literature

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Analysis of accuracy in pointing with redundant hand-held tools: a geometric approach to the uncontrolled manifold method.

Campolo Domenico D Widjaja Ferdinan F Xu Hong H Ang Wei Tech WT Burdet Etienne E

PLoS computational biology 20130404 4

This work introduces a coordinate-independent method to analyse movement variability of tasks performed with hand-held tools, such as a pen or a surgical scalpel. We extend the classical uncontrolled manifold (UCM) approach by exploiting the geometry of rigid body motions, used to describe tool configurations. In particular, we analyse variability during a static pointing task with a hand-held tool, where subjects are asked to keep the tool tip in steady contact with another object. In this case ...[more]

PMID: 23592956

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Project description:Human postural sway during stance arises from coordinated multi-joint movements. Thus, a sway trajectory represented by a time-varying postural vector in the multiple-joint-angle-space tends to be constrained to a low-dimensional subspace. It has been proposed that the subspace corresponds to a manifold defined by a kinematic constraint, such that the position of the center of mass (CoM) of the whole body is constant in time, referred to as the kinematic uncontrolled manifold (kinematic-UCM). A control strategy related to this hypothesis (CoM-control-strategy) claims that the central nervous system (CNS) aims to keep the posture close to the kinematic-UCM using a continuous feedback controller, leading to sway patterns that mostly occur within the kinematic-UCM, where no corrective control is exerted. An alternative strategy proposed by the authors (intermittent control-strategy) claims that the CNS stabilizes posture by intermittently suspending the active feedback controller, in such a way to allow the CNS to exploit a stable manifold of the saddle-type upright equilibrium in the state-space of the system, referred to as the dynamic-UCM, when the state point is on or near the manifold. Although the mathematical definitions of the kinematic- and dynamic-UCM are completely different, both UCMs play similar roles in the stabilization of multi-joint upright posture. The purpose of this study was to compare the dynamic performance of the two control strategies. In particular, we considered a double-inverted-pendulum-model of postural control, and analyzed the two UCMs defined above. We first showed that the geometric configurations of the two UCMs are almost identical. We then investigated whether the UCM-component of experimental sway could be considered as passive dynamics with no active control, and showed that such UCM-component mainly consists of high frequency oscillations above 1 Hz, corresponding to anti-phase coordination between the ankle and hip. We also showed that this result can be better characterized by an eigenfrequency associated with the dynamic-UCM. In summary, our analysis highlights the close relationship between the two control strategies, namely their ability to simultaneously establish small CoM variations and postural stability, but also make it clear that the intermittent control hypothesis better explains the spectral characteristics of sway.

Project description:The brain must coordinate with redundant bodies to perform motion tasks. The aim of the present study is to propose a novel control model that predicts the characteristics of human joint coordination at a behavioral level. To evaluate the joint coordination, an uncontrolled manifold (UCM) analysis that focuses on the trial-to-trial variance of joints has been proposed. The UCM is a nonlinear manifold associated with redundant kinematics. In this study, we directly applied the notion of the UCM to our proposed control model called the "UCM reference feedback control." To simplify the problem, the present study considered how the redundant joints were controlled to regulate a given target hand position. We considered a conventional method that pre-determined a unique target joint trajectory by inverse kinematics or any other optimization method. In contrast, our proposed control method generates a UCM as a control target at each time step. The target UCM is a subspace of joint angles whose variability does not affect the hand position. The joint combination in the target UCM is then selected so as to minimize the cost function, which consisted of the joint torque and torque change. To examine whether the proposed method could reproduce human-like joint coordination, we conducted simulation and measurement experiments. In the simulation experiments, a three-link arm with a shoulder, elbow, and wrist regulates a one-dimensional target of a hand through proposed method. In the measurement experiments, subjects performed a one-dimensional target-tracking task. The kinematics, dynamics, and joint coordination were quantitatively compared with the simulation data of the proposed method. As a result, the UCM reference feedback control could quantitatively reproduce the difference of the mean value for the end hand position between the initial postures, the peaks of the bell-shape tangential hand velocity, the sum of the squared torque, the mean value for the torque change, the variance components, and the index of synergy as well as the human subjects. We concluded that UCM reference feedback control can reproduce human-like joint coordination. The inference for motor control of the human central nervous system based on the proposed method was discussed.

Project description:BackgroundThis study assessed surgical accuracy and functional outcomes using hand-held accelerometer-based navigation following total knee arthroplasty (TKA).Question(1) Does hand-held navigation (the iAssist system) improve surgical accuracy (assessed with five parameters commonly used to evaluate surgical alignment: the hip-knee-ankle angle (HKA), femoral coronal angle (FCA), tibial coronal angle (TCA), femoral sagittal angle (FSA), and tibial slope angle (TSA)) compared to conventional instruments in TKA? (2) Which surgical alignment parameters among HKA, FCA, TCA, FSA, and TSA can obtain the most advantage from the iAssist system? (3) Does the iAssist system lead to better functional outcomes at two years of follow-up after TKA?MethodsThis parallel-group double-blinded randomized controlled trial recruited 60 patients (30 patients each in the iAssist and conventional group) with osteoarthritis who underwent primary TKA by a single surgeon at Siriraj Hospital. There was no loss to follow-up in the study. All procedures in both groups were performed using similar surgical exposure, prosthesis implant, perioperative and postoperative protocols. Participants in the iAssist group received the iAssist system as an assistive technique, while those in the conventional group only had conventional instruments. Surgical alignments (HKA, FCA, TCA, FSA, and TSA) were recorded using CT scan at six weeks post-operation. Functional outcomes were assessed with knee ROM, KSS, and EQ-5D at 6 months, 1 year and 2 years post-operation. Baseline characteristics including age, sex, the affected knee side, and body mass index were comparable between the two groups, similar to preoperative ROM, KSS, and EQ-5D.ResultsThe mean operative time was relatively longer in the iAssist than the conventional group, although not statistically significant (88.1 ± 13.7 versus 83.4 ± 21.3; p = 0.314). Among the surgical alignment parameters evaluated, FCA was the only radiographic parameter with a statistically significant difference between the two groups and was closer to 90º in the iAssist group (89.4 ± 2.2 in the iAssist versus 87.2 ± 2.1 in the conventional group; p = 0.003). Also, there was a higher proportion of outliers in the conventional than the iAssist group (23.3% versus 10%; p = 0.086). Nonetheless, HKA and TCA did not differ between the two groups (p = 0.25 and 0.096, respectively), although the percentages of outliers were higher in the conventional than the iAssist group (HKA: 26.7% vs. 13.3%; p = 0.101 and TCA: 6.7% versus 0%; p = 0.078). Likewise, we observed other radiographic parameters had no significant group differences, including FSA and TSA. Furthermore, at two years post-operation, we found no differences between the iAssist and the conventional group in knee ROM (106.7 ± 14.6 versus 108.2 ± 12.7; p = 0.324), KSS (82.5 ± 6.4 versus 83.8 ± 3.4; p = 0.324), and EQ-5D (0.9 ± 0.2 versus 1.0 ± 0.1; p = 0.217). All functional outcomes were also comparable at 6 months and 12 months of follow-up postoperatively.ConclusionThe iAssist technology increase surgical precision by allowing for a more precise FCA with fewer outliers than conventional equipment. iAssist had longer operative time. Functional outcomes and quality of life were not different.Level of evidenceI.

Dataset Information

Analysis of accuracy in pointing with redundant hand-held tools: a geometric approach to the uncontrolled manifold method.

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Analysis of accuracy in pointing with redundant hand-held tools: a geometric approach to the uncontrolled manifold method.

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