Arc Foot Research Articles

Mechanical testing of frontal plane adaptability of commercially available prosthetic feet.

IntroductionProsthetic feet have limited adaptability in the frontal plane. Research shows walking on uneven terrain is difficult for many prosthesis users. A new prosthetic foot, the META Arc, was designed with a polycentric ankle joint that allows relatively free movement in the frontal plane to address this limitation. Previous simulations of the polycentric ankle mechanism found potential benefits such as reduced lateral movement of a proximal mass during forward progress and reduced forces being transferred upward from the ground through the foot.MethodsStandard mechanical testing protocols were used to evaluate the Meta Arc prosthetic foot’s performance and six comparable feet commercially available.ResultsThe results found the META Arc prosthetic foot had increased frontal plane adaptability as well as reduced lateral forces, and reduced inversion eversion moment compared to the six comparison feet on 10-degree cross-slope test conditions. All included prosthetic feet had similar results for the percent of energy return and dynamic force in the sagittal plane.ConclusionsThese results suggest the inclusion of the polycentric ankle within the META Arc foot will provide more stability without sacrificing forward walking performance.

Sustainable and homogeneous arc ablation behavior of zirconium cathodes improved by in situ formation of zirconium oxides

Discharge homogeneity is one of the dominant factors affecting cathode lifetime. In this work, the arc ablation behavior of a zirconium cathode is investigated in air and argon atmospheres. Homogeneous discharge processes are observed in air, while poor discharge homogeneity with scattered cathode spots is found in argon. The homogeneous discharge process is related to the layered structure at the discharge center. The surface zirconium oxide layer stabilizes the arc foot and reduces the effective work function. A dual-phase layer underneath, consisting of zirconium oxides and zirconium, enables the transition from the zirconium matrix to the surface oxide layer. The sustainable discharge behaviors are realized by the balance in the cathode, which is created by the ablation of surface zirconium oxides and the oxidization of zirconium in the dual-phase layer.

Homogeneous arc ablation behaviors of CuCr cathodes improved by chromic oxide

Cathode ablation is one of the dominant limitations for extending the maximum operating time of arc heaters. In this work, the arc ablation behaviors and mechanisms of commercial CuCr10, CuCr25, and CuCr50 cathodes were investigated for pure copper and pure chromium cathodes. The discharging homogeneity was improved with the increase of chromium content in the cathodes, which was attributed to the formed chromic oxide layer. The CuCr50 cathodes exhibited the lowest ablation rate with a reduction of 27.0% compared to the copper cathodes. The chromic oxide formed in the pit protected the bottom matrix, leading to a homogeneous ablation process. The mechanism for the improved homogeneous ablation behaviors of the CuCr50 cathodes was proposed and featured by the suppression of deep pits and the dispersion of arc foot. Future attention will be focused on designing composite cathodes with an anti-ablation surface layer and a good conductive matrix.

Real Time Estimation of the Pose of a Lower Limb Prosthesis from a Single Shank Mounted IMU.

The command of a microprocessor-controlled lower limb prosthesis classically relies on the gait mode recognition. Real time computation of the pose of the prosthesis (i.e., attitude and trajectory) is useful for the correct identification of these modes. In this paper, we present and evaluate an algorithm for the computation of the pose of a lower limb prosthesis, under the constraints of real time applications and limited computing resources. This algorithm uses a nonlinear complementary filter with a variable gain to estimate the attitude of the shank. The trajectory is then computed from the double integration of the accelerometer data corrected from the kinematics of a model of inverted pendulum rolling on a curved arc foot. The results of the proposed algorithm are evaluated against the optoelectronic measurements of walking trials of three people with transfemoral amputation. The root mean square error (RMSE) of the estimated attitude is around 3°, close to the Kalman-based algorithm results reported in similar conditions. The real time correction of the integration of the inertial measurement unit (IMU) acceleration decreases the trajectory error by a factor of 2.5 compared to its direct integration which will result in an improvement of the gait mode recognition.

Copper Cathode’s Ablated Structure Operated in a 50 Megawatt Arc Heater

An oxygen-free high-conductivity copper cathode was tested in a 50 MW arc heater with working currents up to 2600 A and power up to 13.6 MW by using air as the test gas. After testing, the structure of the ablated cathode was measured and analyzed. The erosion rate of the cathode was . An arc foot area and an oxide layer area appeared and were located at the end of the cathode. The arc foot area was covered with molten signs, ablated pits, and deformations. The oxide layer was composed of parallel traces that were generated by melted liquid. The grain size at the cathode’s thinnest wall thickness was refined from the original to due to recrystallization. The grain size increased and the phenomenon of abnormal grain growth appeared, with an increase of the distance from the arc foot. The Vickers hardness agreed well with the grain size. The erosion mass loss includes not only vaporization removal but also melting removal via shear force generated by swirl air, considering the erosion rate and ablated phenomena. A modified particle ejection model is proposed to describe the erosion mechanism that agrees with the ablated phenomena of the test.

Dynamic characteristics and safety criterion of deep rock mine opening under blast loading

The blasting vibration in deep mining affects the safety of the adjacent roadways. To estimate the stability of a deep rock mass opening during blasting excavation, the dynamic responses of the deep rock mass subjected to blast loading are investigated in this study. The relationships between the blasting vibration velocity and the frequency over time, horizontal distance, and depth are analyzed, and the stress distribution of the surrounding rock mass is depicted through field tests and numerical simulation. The failure mechanism of deep rock mass is thus revealed, and a new safety criterion regarding the blasting vibration of the deep rock mass is put forward. The results indicate that the vertical vibration velocity is higher than the horizontal vibration velocity and that the vertical tension of the seismic wave of the blast is larger than that of the shearing action in the near-blasting field, which contrasts that of the far field. Both the vibration velocity and frequency decrease with an increase in time, distance, and depth, and the range of influence of the blasting vibration in terms of depth is larger than that for the horizontal direction. Therefore, the deep rock mass is more vulnerable to damage than the shallow rock mass under blast loading. In addition, the surrounding rock stress tends to transfer from the arc foot on the blasting side to the straight wall on the rear side, and the shear stress is ahead of the tensile stress. It was verified through a case calculation that the new criterion has practical value and can be used as a guide for evaluating the blasting vibration effects of the deep rock mass.

Influencing the arc and the mechanical properties of the weld metal in GMA-welding processes by additive elements on the wire electrode surface

Under the premise of an increasing scarcity of raw materials and increasing demands on construction materials, the mechanical properties of steels and its joints are gaining highly important. In particular high- and highest-strength steels are getting in the focus of the research and the manufacturing industry. To the same extent, the requirements for filler metals are increasing as well. At present, these low-alloy materials are protected by a copper coating (<1μm) against corrosion. In addition, the coating realizes a good ohmic contact and good sliding properties between the welding machine and the wire during the welding process. By exchanging the copper with other elements it should be possible to change the mechanical properties of the weld metal and the arc stability during gas metal arc welding processes and keep the basic functions of the coating nearly untouched. On a laboratory scale solid wire electrodes with coatings of various elements and compounds such as titanium oxide were made and processed with a Gas Metal Arc Welding process. During the processing a different process behavior between the wire electrodes, coated and original, could be observed. The influences ranges from greater/shorter arc-length over increasing/decreasing droplets to larger/smaller arc foot point. Furthermore, the weld metal of the coated electrodes has significantly different mechanical and technological characteristics as the weld metal from the copper coated ground wire. The yield strength and tensile strength can be increased by up to 50%. In addition, the chemical composition of the weld metal was influenced by the application of coatings with layer thicknesses to 15 microns in the lower percentage range (up to about 3%). Another effect of the coating is a modified penetration. The normally occurring “argon finger” can be suppressed or enhanced by the choice of the coating. With the help of the presented studies it will be shown that Gas Metal Arc Welding processes are significantly affected by thin film coatings on solid wire electrodes for Gas Metal Arc welding. The influences are regarding the stability of the arc, the properties of the weld metal in terms of geometric expression, chemical composition and mechanical properties, the composition of the arc-plasma and the dynamics of the molten metal.

受動歩行機の円弧足を参考とした足部着用型歩行補助器

受動歩行機の円弧足を参考とした足部着用型歩行補助器

Level-Ground Walking for 3D Quasi-Passive Walker with Flat Feet - Lateral-plane Input using McKibben-Type Artificial Muscle -

Currently, many bipedal robots have been proposed to realize the high energy efficiency walking. The passive dynamic walking does not require control input. Generally, a foot of passive dynamic walking robot is an arc foot. In this paper, it is intended to establish a control method and control mechanism to achieve energy efficient and stable gate. Therefore, we developed 3D quasi-passive walker with flat feet driven by an antagonistic pneumatic artificial muscle. An antagonistic mechanism is constituted by a pair of McKibben muscle. And an antagonistic pneumatic system is used as joint actuators of linkage mechanisms which control the torque, joint stiffness and position simultaneously. Finally, this report shows that the 3D quasi-passive walking in the level ground can realize by the swinging (simple) input of the frontal direction, and the stride of the robot is proportional to lateral-plane input.

2A1-I04 受動歩行機の円弧足を参考とした足部着用型歩行補助器

2A1-I04 受動歩行機の円弧足を参考とした足部着用型歩行補助器

Mechanisms and processes of arc propagation over an ice-covered surface

The general objective of this paper is to investigate the physical mechanisms and processes involved in the propagation of arc over the surface of ice. In the present research work, high-speed imaging and optical emission spectroscopy techniques were synchronized with the electrical measurements to study the various parameters of arc on an ice surface, i.e. channel radius, propagation velocities, arc column temperature and electron density. These results, together with observation of the propagation patterns and arc foot geometries, calculation of arc energy and the examination of the state of thermal equilibrium provide background information for understanding the ice-covered insulator flashover phenomenon. Arc root structure, current profile, propagation pattern and velocity were investigated under different type of applied voltage and different polarities. Water film conductivity and thickness, relative air humidity and the direction of arc propagation were also analyzed as influencing parameters of arc propagation. The effects of different possible mechanisms, e.g. collision and thermal ionization, buoyancy force and electrostatic force, on different stages of arc propagation has been discussed.

胴体の傾きによる推力を利用した2足歩行について

An attempt to extend passive dynamic walking from a slope to a horizontal surface have begun since the late 80's about the same time as the research on passive dynamic walking. A method using inclination of an upper body has been originally examined by McGeer, which enables a biped with the upper body to walk on the horizontal surface using counter torque of the torque generating to maintain the body inclination. However there are no deep insight into properties of the method such as stability against the inclination and robustness. Moreover, no researchers could achieve a real biped using the body inclination, and then the method would be sensitive against uncertainties (e.g., the ground undulation and small obstacles), accordingly. In this paper, we introduce an upper body and circular arc feet to a compass model biped and achieve various dynamic walking gait using thrust via the upper body inclination through numerical simulations. Stability of the walking gait is also analyzed using the Poincaré method. Moreover, a geometric tracking control using a cyclic motion of the biped walking is introduced in order to achieve more robust gait. Stability of the controlled walking is also analyzed using a Poincaré map of HZD. In addition, we discuss the difference between the walking using the upper body inclination and the geometric tracking controlled walking.

Mechanical and energetic consequences of rolling foot shape in human walking

During human walking, the center of pressure under the foot progresses forward smoothly during each step, creating a wheel-like motion between the leg and the ground. This rolling motion might appear to aid walking economy, but the mechanisms that may lead to such a benefit are unclear, as the leg is not literally a wheel. We propose that there is indeed a benefit, but less from rolling than from smoother transitions between pendulum-like stance legs. The velocity of the body center of mass (COM) must be redirected in that transition, and a longer foot reduces the work required for the redirection. Here we develop a dynamic walking model that predicts different effects from altering foot length as opposed to foot radius, and test it by attaching rigid, arc-like foot bottoms to humans walking with fixed ankles. The model suggests that smooth rolling is relatively insensitive to arc radius, whereas work for the step-to-step transition decreases approximately quadratically with foot length. We measured the separate effects of arc-foot length and radius on COM velocity fluctuations, work performed by the legs and metabolic cost. Experimental data (N=8) show that foot length indeed has much greater effect on both the mechanical work of the step-to-step transition (23% variation, P=0.04) and the overall energetic cost of walking (6%, P=0.03) than foot radius (no significant effect, P>0.05). We found the minimum metabolic energy cost for an arc foot length of approximately 29% of leg length, roughly comparable to human foot length. Our results suggest that the foot's apparently wheel-like action derives less benefit from rolling per se than from reduced work to redirect the body COM.

Experimental investigation of the process of Arc propagation over an ice surface

In this paper, some of the characteristics of an arc propagating over an ice-covered insulator surface were investigated. Special attention was paid to the arc root and channel characteristics. All experiments were performed on a simplified physical model to simulate real ice-covered insulators. From the obtained results, based on a set of time-resolved measurements of a surface discharge, some important characteristics, namely arc foot geometry and channel diameter were observed. Possible mechanisms controlling these variations are discussed. An empirical model, accounting for arc propagation pattern on an ice surface, is proposed. The paper contains a substantial amount of new material with a view of closing some major gaps in the present state of knowledge of ice surface flashover.

Effect of circular arc feet on a control law for a biped

SUMMARYThe purpose of our research is to study the effects of circular arc feet on the biped walk with a geometric tracking control. The biped studied is planar and is composed of five links and four actuators located at each hip and each knee thus the biped is underactuated in single support phase. A geometric evolution of the biped configuration is controlled, instead of a temporal evolution. The input-output linearization with a PD control law and a feed forward compensation is used for geometric tracking. The controller virtually constrains 4 degrees of freedom (DoF) of the biped, and 1 DoF (the absolute orientation of the biped) remained. The temporal evolution of the remained system with impact events is analyzed using Poincaré map. The map is given by an analytic expression based on the angular momentum about the contact point. The effect of the radii of the circular arc feet on the stability is studied. As a result, the speed of convergence decreases when the radii increases, if the radius is larger than the leg length the cyclic motion is not more stable. Among the stable cyclic motion, larger radius broadens the basin of attraction. Our results agree with those obtained for passive dynamic walking on stability, even if the biped is controlled through the geometric tracking.

621 受動歩行における踵・足首・足趾を有する足の有効性

Many studies of passive dynamic walking use a circular arc foot. However, a circular arc foot is constrained the walking movement because the transmission of power to ground is difficult. To take a passive dynamic walking in biped walking, the foot which can transmit power to the ground and can perform a passive walk is required. So, we propose the foot that contains circular arc heel, the ankle joint, the toe joint as a foot that takes place of a circular arc foot and verify the effectiveness of this proposed foot by the simulation

受動歩行の脚運動に対する円弧足の力学的効果

The passive walker with knees can naturally execute the leg motion, which is essential to take a step forward, by the dynamics of legs under the gravity only. On the other hand, an inadequate dynamics causes an undesirable leg motion, such that the stance leg bends at the knee joint, the swing leg unsuitably strikes its foot on the slope and the walker falls backward by the negative gravitational moment. Though an arc foot is very important for the leg motion, its dynamical effects and mechanism have never been clarified, and a useful design framework of its shape has never been established. In this study, for the sake of simplicity and clarity, the linearized simplest walking model is used. In this paper, the dynamical effects of the arc foot, which can keep the knee joint of stance leg straight only by the stopper and can enhance the flexion of knee joint of swing leg, are discussed. Also, its geometrical negative effect is examined. Furthermore, the forward-falling condition of the walker is derived based on the energy analysis. Finally, the desired arc foot is designed and the actual effects are confirmed by a walking experiment.

Arc Feet Effects on Stability Based on a Simple Oscillator-Driven Walking Model

Lower-extremity movement in bipedal walking is characterized by a foot-rolling motion that includes heel-strike and toe-off. We investigated the dynamical influence of this movement on walking stability using a simple walking model that has a circular arc at the end of each leg. The leg is driven by a rhythmic signal from an internal oscillator to generate walking. We focused on stability characteristics due to the arc foot based on (1) the stability region for parameters such as mass distribution and walking speed, in which the circular arc radius is optimal when it is almost the same length as the leg to maximize the stable region and (2) the rate of convergence to stable walking, which is maximized by a circular arc radius of zero. These two conflicting results imply that the optimal radius of a circular arc for local stability is a trade-off between the two criteria, reflecting a dynamic feature of bipedal walking that should be considered in biped robot design.

1P1-B04 圧力中心軌跡の解析に基づく平面足を持つ二足ロボットのリミットサイクル歩行(受動歩行ロボット)

Since most of traditional biped walkers based on Passive Dynamic Walking (PDW) have arc feet and locked ankle joint, they cannot realize multimodal locomotion except walking (e.g. keeping standing posture, running). In this paper, we consider how we can substitute the flat feet with the arc feet. We hypothesize that the arc feet correspond to a circular Roll Over Shape (ROS), which is a shape of trajectory of center of pressure in human walking. We found that this circular ROS was generated by ankle joint driven by flexible muscles antagonistically. Measuring ROS with various tensions of muscles and equilibrium positions of ankle joint, we investigate the relationship between ROS and walking behavior.

1P1-B09 受動歩行機の円弧足の力学的役割とそのメカニズム(受動歩行ロボット)

1P1-B09 受動歩行機の円弧足の力学的役割とそのメカニズム(受動歩行ロボット)