Lightweight Legs Research Articles

A Low-Inertia and High-Stiffness Cable-Driven Biped Robot: Design, Modeling, and Control

In this paper, a biped robot system for dynamic walking is presented. It has two 2-degree-of-freedom (DOF) lightweight legs and a 6-DOF hip. All the joint pulleys of the legs are driven by motors that are placed at the hip using steel cables. Since all the heavy motors are mounted at the hip, the biped robot has remarkably low-mass legs beyond the hip, which guarantees low inertia during walking at high speeds. Utilizing cable-amplification mechanisms, high stiffness and strength are achieved, resulting in better control performance compared to conventional direct-driven methods. Techniques are developed to estimate joint-angle errors caused by the elastic deformation of the cables. To achieve smooth control, we introduce the concept of a virtual leg, which is an imaginary leg connecting the hip joint and the ankle joint. A robust control approach based on the “virtual leg” is presented, which considers the variances of the virtual leg length during walking. Experiments are conducted to validate the effectiveness of the mechanical design and the proposed control approach.

Design and analysis of a concentrated-driven bionic-leg capable of omnidirectional legged locomotion based on 3-Dimensional dual-parallelogram-linkages

The Flexible, fast and lightweight leg mechanism is the key to improve legged robot’s mobility, efficiency and adaptability on complex terrain. Inspired by the motion mechanism of legged animals, we report a concentrated-driven omnidirectional legged locomotion bionic leg – OmniLeg. All the motor actuators are centrally installed in the hip plate of the proposed leg to reduce the rotational inertia. Meanwhile, the special 3-Dimensional dual-parallelogram-linkages transmission mechanism enables it to have the ability of omnidirectional legged locomotion in 3-Dimensional space and makes the posture of leg’s endpoint does not change with the motion of the leg mechanism which simplifying the motion control. In this paper, firstly the theoretical model, including mobility, kinematics model, inverse kinematics model, dimension parameters and workspace model, have been derived, analyzed and verified with the design and control of the real prototype. Next, to demonstrate the ability of omnidirectional legged locomotion intuitively, we manufacture a single-legged omnidirectional mobile robot and design a quadruped robot, and the simulation and experiment result illustrate that the design and analytical mode of OmniLeg is feasible and correct, which could be widely applied in the field of legged robot.

Generate an Optimum Lightweight Legs Structure Design Based on Critical Posture in A-FLoW Humanoid Robot

Lightweight construction and energy efficiency play an important role in humanoid robot development. The application of computer-aided engineering (CAE) in the development process is one of the possibilities to achieve the appropriate reduction of the weight. This paper describes a method to generate an optimum lightweight legs structure design based on critical posture during walking locomotion in A-FLoW Humanoid robot.The criticalposture can be obtained from the highest forces and moments in each joint of the robot body during walking locomotion. From the finite element analysis (FEA) result can be realized leg structure design of A-FLoW humanoid robot with a maximum displacement value of 0.05 mmand weight reduction about 0.598 Kg from the thigh structure and a maximum displacement value of 0,13 mmand weight reduction about 0.57 kg from the shin structure.

Combination Therapy of Hyaluronic Acid Mesotherapic Injections and Sclerotherapy for Treatment of Lower Leg Telangiectasia Without Major Venous Insufficiency

Telangiectasia is the dilation of dermal capillaries mainly due to hypertension and vein insufficiency. Treatments of choice for this condition are sclerotherapy with foam liquid or intradermal fiber optic laser energy delivery. The aim of this study was to assess the efficacy of a new therapeutic approach consisting in the use of polymerized hyaluronic acid mesotherapic injections following sclerotherapy in the areas of the skin affected by telangiectasia in patients without major vein insufficiency. A total of 20 women, aged between 19 and 64 years, affected by recurrent lower leg telangiectasia, were included in this study. Patients were preliminarily submitted to echo color Doppler sonography to rule out severe saphenofemoral valve and lower limb major vein insufficiency. All patients underwent 3 sessions a month of polidocanol 1% capillary injections for 2 months. This was followed by 0.1 ml cross-linked hyaluronic acid introduction in the polidocanol 1% needle track. A total of 50 mesotherapic injections (0.05 ml each) were performed on the skin surface where an ice pack was previously applied for 4 to 5 minutes. A follow-up visit was performed at 3 months. The results, based on photographic examination, were rated as follows: poor improvement (0%-50%), good improvement (51%-75%), and very good improvement (76%-100%). The side effects of the clinical procedure, in terms of pain, itching, paresthesia, ecchymosis, and relapse of telangiectasia over the treated skin surface, as well as a persisting pigmentation in the injection spots and induced benefits related to leg heaviness and comfort, were recorded. In total, 6 patients displayed a slight venous insufficiency, 3 patients displayed patent venous insufficiency, and 11 patients did not show any venous insufficiency. Before treatment, itching was present in 18 out of 20 patients, paresthesia in 15 out of 20 patients, ecchymosis in 16 out of 20 patients, and leg heaviness in 15 out of 20 patients. At the 3-month follow-up, an improvement of 0% to 50% was observed in 4 patients who had a relapse in telangiectasia. A 51% to 75% improvement was observed in 3 patients and a 76% to 100% improvement occurred in 13 patients. At the 3-month follow-up, itching persisted only in 4 patients; paresthesia was absent in 12 patients, while 3 patients still presented this symptom; ecchymosis was absent in 16 patients; 15 patients reported a feeling of lightweight legs. Among the patients with relapsing telangiectasia, 2 patients reported pigmentation due to hemosiderin deposit in the skin at the 3-month follow-up. The slight venous insufficiency, observed at the beginning of the study, improved in 5 out of 6 patients. The patients' compliance with the procedure was high and 16 out of 20 patients declared their willingness to repeat the whole clinical procedure, if necessary. This pilot clinical study supports the use of hyaluronic acid mesotherapic injections following sclerotherapy for treatment of lower leg telangiectasia without major venous insufficiency. We propose that the prolonged persistence of cross-linked hyaluronic acid, across the microvascular venous areas, is able to induce a stronger stromal tissue, thus preventing relapse. Further clinical studies, comparing this new approach with existing clinical procedures, are needed in a larger number of patients.

Tools for understanding and optimizing robotic gait training

This article reviews several tools we have developed to improve the understanding of locomotor training following spinal cord injury (SCI), with a view toward implementing locomotor training with robotic devices. We have developed (1) a small-scale robotic device that allows testing of locomotor training techniques in rodent models, (2) an instrumentation system that measures the forces and motions used by experienced human therapists as they manually assist leg movement during locomotor training, (3) a powerful, lightweight leg robot that allows investigation of motor adaptation during stepping in response to force-field perturbations, and (4) computational models for locomotor training. Results from the initial use of these tools suggest that an optimal gait-training robot will minimize disruptive sensory input, facilitate appropriate sensory input and gait mechanics, and intelligently grade and time its assistance. Currently, we are developing a pneumatic robot designed to meet these specifications as it assists leg and pelvic motion of people with SCI.

Experimental study of biped dynamic walking

An experimental study of a biped robot is presented. A new scheme named the "linear inverted pendulum mode" is utilized for controlling a biped walking on rugged terrain. The authors developed a six-DOF biped robot, "Meltran II," which has lightweight legs and moves in a two-dimensional vertical plane. To investigate the effects not well discussed in the theory, the authors carried out two experiments, the support phase experiment and the support exchange experiment. The support phase experiment was carried out to check the actual dynamics of a biped walking under the proposed control. It was shown that the dynamics of the robot can be regarded as linear even though the mass of the legs, which was neglected in the theory, exists. The support exchange experiment was performed to check leg support exchange. The authors found that a smooth leg support exchange is achieved by making the foot contact with a certain vertical speed and holding two-leg support for a certain short period. Based on these results, a whole biped control system was implemented. In the authors' experiment the robot walked over a box of 3.5 cm height at a speed of 20 cm/s.