Actual Arm Research Articles

Control properties induced by the existence of antagonistic pairs of bi-articular muscles — Mechanical engineering model analyses

In order to reveal control properties induced by antagonistic pairs of bi-articular muscles, we performed theoretical simulation analyses as well as actual arm robotic analyses utilizing two-joint link models equipped with pneumatic artificial rubber actuators. The previously reported EMG patterns of human movements were well explained from activating level patterns of the actuators in terms of mechanical control engineering. Results obtained in the present studies strongly suggest that the existence of the antagonistic pair of bi-articular muscles could positively contribute to the compliant properties of the multi-articular extremity, and to independently control position and force at the endpoint of the extremity, leading to smooth, fine and precise movements.

Perceptual distortion contributes to the curvature of human reaching movements.

Unconstrained point-to-point human arm movements are generally gently curved, a fact which has been used to assess the validity of models of trajectory formation. In this study we examined the relationship between curvature perception and movement curvature for planar sagittal and transverse arm movements. We found a significant correlation (P < 0.0001, n = 16) between the curvature perceived as straight and the curvature of actual arm movements. We suggest that subjects try to make straight-line movements, but that actual movements are curved because visual perceptual distortion makes the movements appear to be straighter than they really are. We conclude that perceptual distortion of curvature contributes to the curvature seen in human point-to-point arm movements and that this must be taken into account in the assessment of models of trajectory formation.

A Hierarchical Distributed Path Planning for Redundant Manipulators Based on Virtual Arm

This paper proposes a collision-free path planning algorithm in the task space based on virtual arms. The virtual arm has the same kinematic structure as the actual arm except that its end-point is located at the joint or link of the actual arm. Therefore, the configuration of the actual arm can be represented as a set of end-points of the virtual arms, and the path planning for multi-joint manipulators can be performed only in the task space. Our method adopts a hierarchical strategy which consists of the global level, the intermediate level, and the local level. The global level plans the collision-free endpoint trajectory of the actual arm based on the global representation of the task space. The intermediate level generates the subgoals for the actual and virtual endpoints based on the current positions and the actual endpoint trajectory specified by the global level. The local level moves each end-point to the corresponding subgoal, avoiding the close obstacles based on the local informations of the task space. The effectiveness of the method is verified by computer simulations using a planar manipulator with redundant joint degrees of freedom.

Modelling and Control of an Elastic Robot Arm with Rotary and Prismatic Joints

The application of industrial robots to advanced manufacturing tasks requires highly accurate position and/or force control. Actual limitations to these requirements are mainly caused by elasticity, Coulomb friction and backlash in the system. Conventional control algorithms do not consider these effects and can hardly provide sufficient control accuracy or yield limit cycles. In this paper the common multibody approach of models of industrial robots is extended to derive more realistic models including elasticity of both joints and links, Coulomb friction and backlash. For the rotatory motion of an elastic robot arm with a revolute joint an algorithm for a highly accurate position control is developed based on (i) multi-layer control to damp quickly the elastic motions "separately" from the rigid-body motion of the robot, and (ii) compensation of Coulomb friction and backlash by the method of disturbance rejection control. In contrast to the very successful results in case of rotatory motion, the modelling and a suitable design of a control system for the translational motion of an elastic arm with a prismatic joint is a much more difficult Problem. A complex control system is obtained represented approximately by a set of ordinary linear time-variant differential equations of vanable order depending on the actual arm length driven out. Certam approaches of designing a feedback control are discussed.

Anorexia in cancer patients: Prevalence and impact on the nutritional status

One hundred and eightysix cancer patients with different types, site and stage of disease, consecutively admitted to the Istituto Nazionale Tumori, Milan, were examined. The purpose of the study was to assess the prevalence of subjective anorexia and to determine whether some nutrition-related indices are different within homogeneous categories of cancer patients, anorectic and non-anorectic. Anorexia was measured on the basis of an appetite score, evaluated with a visual analogue rating scale. Nutritional intake was evaluated by a computerised programme of the habitual food consumption. Nutritional assessment included anthropometric evaluations (triceps skinfold, arm circumference, arm muscle circumference) and biochemical indices (serum albumin, and total iron binding capacity). A nutritional index was then calculated: GNS = P + I + M × 100, where P: actual weight/premorbid weight; I: actual weight/ideal weight; M: actual arm muscle mass circumference/ideal arm muscle mass circumference. The evaluation of the data showed that: (1) The prevalence of subjective anorexia ranged from 1 3 to 2 5 of the patients depending on the type and site of tumour, and stage of disease. (2) Most of the nutritional-related variables were significantly worse in anorectic compared with non-anorectic patients. (3) Within groups of patients with different tumour location, but homogeneous for the presence or absence of subjective anorexia, there is no difference with respect to nutritional indices; except for patients with cancer of the oesophagus and stomach who were always more depleted. (4) Anorexia did not seem to influence the nutritional status in patients with cancer at an early stage (except in cancer of oesophagus and stomach) but it was associated to malnutrition as the disease progressed to more advanced stages.

The control of hand equilibrium trajectories in multi-joint arm movements.

According to the equilibrium trajectory hypothesis, multi-joint arm movements are achieved by gradually shifting the hand equilibrium positions defined by the neuromuscular activity. The magnitude of the force exerted on the arm, at any time, depends on the difference between the actual and equilibrium hand positions and the stiffness and viscosity about the equilibrium position. The purpose of this paper is to test the validity and implications of this hypothesis in the context of reaching movements. A mathematical description of the behavior of an arm tracking the equilibrium trajectory was developed and implemented in computer simulations. The joint stiffness parameters used in these simulations were derived from experimentally measured static stiffness values. The kinematic features of hand equilibrium trajectories which were derived from measured planar horizontal movements gave rise to the suggestion that the generation of reaching movements involves explicit planning of spatially and temporally invariant hand equilibrium trajectories. This hypothesis was tested by simulating actual arm movements based on hypothetical equilibrium trajectories. The success of the predicted behavior in capturing both the qualitative features and the quantitative kinematic details of the measured movements supports the equilibrium trajectory hypothesis. The control strategy suggested here may allow the motor system to avoid some of the complicated computational problems associated with multi-joint arm movements.

Arthrokinetic nystagmus and ego-motion sensation.

A compelling illusion of body rotation and nystagmus can be induced when the horizontally extended arm of a stationary subject is passively rotated about a vertical axis in the shoulder joint. Lateral nystagmus with the fast phase beating in the opposite direction to the arm movement was found consistently; the mean slow phase velocity increased with increasing actual arm velocity and reached about 15 degrees/sec; the mean position of the eyes was deviated towards the fast phase as in optokinetic nystagmus, and the nystagmus continued after the cessation of stimulation (arthrokinetic after-nystagmus). The existence of an arthrokinetic circularvection and nystagmus indicates a convergence of vestibular and somatosensory afferents from joint receptors. It is concluded that information about joint movements plays an important role within the multisensory processes of self-motion perception.