Mechanical Leg Research Articles

Stroke impairs the proactive control of dynamic balance during predictable treadmill accelerations.

We maintain balance during gait using both proactive and reactive control strategies. Damage to the brain from a stroke impairs reactive balance, but little is known about how a stroke impacts proactive control during walking. Identifying stroke-related impairments to proactive control could inform the design of interventions to improve balance and reduce fall risk. Therefore, we determined if people with and without stroke differ in their ability to use proactive strategies during predictable treadmill accelerations. Groups of 14 adults with and without stroke walked with single-belt accelerations at random (every one to five strides) and regular (every three strides) intervals. We quantified the effects of the perturbations as changes to center of mass (COM) speed and used mechanical leg work to quantify the proactive strategies to slow the COM. Participants without stroke reduced peak COM speed better than those with stroke when perturbations were at regular intervals (-0.023 versus -0.001 m/s; p=0.007). They also reduced positive leg work more during the perturbation step than the group post-stroke (-7.7% versus -1.9%; p=0.004). Together, these results demonstrate that the sensorimotor impairments resulting from a stroke impair the ability to generate effective proactive adjustments to reduce the destabilizing effects of predictable perturbations.

Modeling and motion analysis of flexible legged robots using the finite particle method

Robotics with flexible legs have attracted significant attention. Engineers often design and analyze the motion of legged robots from kinematic and biomimetic perspective. However, the influence of flexibility of the feet on robot locomotion is often not given sufficient considerations, which is also very crucial to the motion posture of the flexible legged robots, especially as the soft robots design becomes increasingly popular. The mainly difficulties lies in the traditional numerical methods in handling the dynamic motion analysis with both large rigid motion and large deformation. In this paper, the finite particle method (FPM) is used to simulate the motion and deformation coupled problems of the flexible six-legged robot. A shell-based particle model of a six-leg robot and the contact model between legs and ground are built. Without iterative and modification of the FPM analytical framework, structural nonlinearity is efficiently handled after eliminating rigid body motions by a fictitious reverse motion. The motion and deformation of a single leg with varying leg thickness, locomotion speed, and leg-to-ground friction coefficients were simulated. By analyzing the stress distribution in the leg and the number of contact points with the ground, the mechanical leg was optimized in design. Furthermore, the motion and deformation of the entire six-legged robot were simulated using the FPM. The numerical results' feasibility was validated through comparison with experimental data obtained from robot walking tests. The proposed method effectively simulates the motion and deformation of flexible robots, providing significant insights for the design of soft robots.

Reconstruction of mechanical leg axis using non-modular cemented hinged prosthesis in complex primary total knee arthroplasty.

Modular cementless knee arthroplasty systems are capable of precise reconstruction of the mechanical axis. However, they are considered more susceptible to complications. In contrast, non-modular cemented systems are said to be more forgiving and show good long-term results. The aim of this study was to investigate the resulting leg axis after implantation of a non-modular cemented rotating hinged knee prosthesis. Furthermore, potential risk factors for the occurrence of malalignment and complications should be identified. Between 2005 and 2015, 115 patients could be included in this monocentric retrospective cohort study. All patients underwent primary hinged non-modular cemented total knee arthroplasty. Preoperative and postoperative standardized long radiographs were analysed to determine resulting leg axis. Furthermore, epidemiological and intraoperative data as well as perioperative complications were surveyed. Average leg axis was 5.8° varus preoperatively and 0.6° valgus postoperatively. Considering an axis deviation of 3° as the target corridor, 27% of all cases examined were outside the desired range. 21% cases showed a femoral deviation from the target corridor and 15% showed a tibial deviation. There was a significant relationship between the preoperative mLDFA and the mechanical alignment of the femoral component (R = 0.396, p < 0.001) as well as between the preoperative mMPTA and the mechanical alignment of the tibial component (R = 0.187, p = 0.045). The mean operative duration was 96min. No periprosthetic fractures were observed within the study cohort. The main result of the present work is that a non-modular cemented rotating hinged knee arthroplasty system can reconstruct the mechanical leg axis precisely and comparable to modular cementless and unconstrained total knee prostheses. Component malalignment is primarily dependent upon extraarticular deformity preoperatively. Periprosthetic fracture rates and duration of surgery were lower compared with current literature. Level III: Retrospective cohort study.

Experimental test and analysis of impact suppression for hydraulic-driven leg using a new MR damper with multi-channels

When hydraulic-legged robots move under high loads on irregular ground, they are vulnerable to ground impacts. Vibration affects the motion performance of the robot and damages its mechanical structure. This study aims to improve the properties of vibration absorption and impact resistance of hydraulic-legged robots. Because the traditional MR damper (MRD) has small output in finite volume, a novel MRD with a multistage flow channel (MFC-MRD) can output a large damping force designed. First, an MRD prototype was designed for a mechanical leg’s driving joint. Subsequently, the system is analyzed theoretically, and a semi-active control strategy is designed and simulated. Finally, the vibration and impact resistance of the prototype were tested. The experimental results show that in the signal tracking experiment, the maximum overshoot under semi-active control was reduced by 53.0%, and the settling time was reduced by 76.9% compared with the passive control. The impact test reduced the maximum displacement fluctuation by 41.09%, and the buffer time is only 0.24 s.

Neutral to slightly undercorrected mechanical leg alignment provides superior long-term results in patients undergoing matrix-associated autologous chondrocyte implantation.

The aim of this study was to evaluate the role of leg alignment on long-term clinical outcomeafter matrix-associated autologous chondrocyte implantation (M-ACI) and to define an individualized target range to optimize clinical outcome. The present study examined patients who underwent M-ACI of the femoral condyle. The Knee Injury and Osteoarthritis Outcome Score (KOOS) and Magnetic Resonance Observation of Cartilage Repair Tissue (MOCART) were used to assess the results. Clinical outcomes were related to Patient Acceptable Symptomatic State (PASS). For intra- and interobserver reliability of mechanical tibiofemoral angle, mechanical medial proximal tibial angleand mechanical lateral distal femoral angle, we calculated intraclass correlation coefficientsusing a two-way mixed model with absolute agreement. A regression model and receiver-operating characteristics curve were used to identify an individual range of alignment where a favourable clinical outcome could be expected in the long term. Additional osteotomy was performed in 50% of patients with similar clinical outcomes as physiologically aligned patients (p > 0.05). The curve-fitting regression model identified a target range of -2.5° valgus to 4.5° varus for ideal postoperative alignment (R2 = 0.12, p = 0.01). Patients within this range were more likely to achieve PASS (70% vs. 27%, p = 0.001). In medially treated defects, a refined range of -2.5° valgus to 4° varus alignment was found (R2 = 0.15, p = 0.01). These patients were more likely to achieve PASS (67% vs. 30%, p = 0.01) and showed favourable postoperative KOOS and MOCART scores (p = 0.02). Patients with lateral defects were more likely to achieve PASS within a range of -2° valgus and 0.5° varus (90% vs. 45%, p = 0.03) and showed favourable postoperative KOOS and MOCART scores (p = not significant). An individual range of leg alignment-whether achieved by osteotomy or physiologic alignment-should be respected in M-ACI treatment. A neutral to slightly undercorrected alignment favours the postoperative outcome after M-ACI. When planning surgery for patients with focal cartilage defects of the femoral condyle, these ranges should be recognized as critical factors. Level III.

Research on Mechanical Leg Structure Design and Control System of Lower Limb Exoskeleton Rehabilitation Robot Based on Magnetorheological Variable Stiffness and Damping Actuator

During the walking process of lower limb exoskeleton rehabilitation robots, inevitable collision impacts will occur when the swinging leg lands on the ground. The impact reaction force from the ground will induce vibrations in the entire robot’s body from bottom to top. To address this phenomenon, considering the limitations of traditional active compliance and passive compliance methods, a variable stiffness and damping actuator (VSDA) leg structure using a magnetorheological damper (MRD) is proposed. Firstly, experimental methods are used to obtain the ground reaction force (GRF) exerted on a normal person during walking. Then, a mathematical model of the VSDA leg structure is constructed, and its working principle is analyzed. Based on human mass and dimensions, a 3D model is designed and selected. Finally, a simulation model is built in the MATLAB/Simulink environment using the fuzzy switch damping control strategy to simulate the acceleration and displacement of the human body under sinusoidal and random excitations. The results indicate that under sinusoidal excitation, employing fuzzy switch damping control optimizes human displacement by 72.47% compared to the high stiffness and high damping system, and by 16.95% compared to the switch damping system. Human acceleration is optimized by 52.09% compared to the high stiffness and high damping system, and by 25.2% compared to the switch damping system. Under random excitation, adopting fuzzy switch damping control optimizes human displacement by 59.09% compared to the high stiffness and high damping system, and by 21.74% compared to the switch damping system. Human acceleration is optimized by 78.74% compared to the high stiffness and high damping system, and by 31.66% compared to the switch damping system. This validates the VSDA design structure and control method, demonstrating certain advantages in improving the compliance and stability of lower limb exoskeleton rehabilitation robots.

Tibiofemoral Subluxation on Radiograph as a Predictor of Location and Size of Osteochondritis Dissecans Lesions of the Knee.

Lower limb malalignment has been associated with osteochondritis dissecans (OCD). However, the location of the OCD lesion often is not concordant with the mechanical leg axis. Other potentially modifiable alignment parameters may influence the propensity for impingement of the femoral condyles. To assess differences in lower limb alignment (LLA) and relative tibiofemoral position between patients with medial (MFC-OCD) or lateral OCD (LFC-OCD) of the femoral condyle. Cohort study; Level of evidence, 3. Patients ≤30 years old who were diagnosed with unicondylar OCD between January 2010 and January 2020 were eligible for this study. Included were 55 patients (age, 20.8 ± 4.5 years)-46 with MFC-OCD and 9 with LFC-OCD. Preoperative standing long-leg radiographs were studied to obtain primary outcomes-including LLA and mechanical alignment analyses-and secondary outcomes-including knee joint obliquity angle; rotation angle; medial, central (c-subluxation), and lateral subluxation (L-subluxation) of the tibia relative to the femur in the coronal plane; and tibiofemoral joint line center distance (TFJCD). With regard to primary outcomes, LLA was significantly different between MFC-OCD (1.7°± 3.1° varus) and LFC-OCD (2.7 ± 3.1° valgus) (P < .001), and 78% (36/46) of patients with MFC-OCD had varus alignment, whereas 78% (7/9) of patients with LFC-OCD had valgus alignment (P < 0.002). With regard to secondary outcomes, patients with MFC-OCD had a more medial tibial position in relation to the femur, with a significantly smaller rotation angle (5.6°± 2.4° vs 9.6°± 3.6°; P < .001), a smaller C-subluxation (7.2 ± 6.6 vs 14.9 ± 8.8 mm; P < .01), a smaller L-subluxation (2.3 ± 2.6 vs 4.4 ± 2.7 mm; P < .05), and reduced TFJCD (3.5 ± 1.7 vs 6.6 ± 1.8 mm; P < .001) compared with the LFC-OCD group. For patients with MFC-OCD, the size of the OCD was significantly correlated with C-subluxation (r = 0.412; P = .006). LLA was significantly different according to OCD location. In patients with MFC-OCD, the tibia was subluxated medially, resulting in a change of joint geometry by approximation of the medial tibial eminence toward the medial femoral condyle, potentially causing excessive pressure overload and microtrauma of the cartilage. Interestingly, the extent of subluxation was correlated with OCD size.

Analysis of a network of FitzHugh-Nagumo neuron circuit coupled to an array of mechanical leg to mimic the locomotion of a multi-legged organism

A bioinspired electromechanical system that employs an array of FitzHugh–Nagumo (FN) neuron circuits designed to drive synchronically an array of mechanical legs is proposed in this paper. The schematic of the electromechanical device is transformed into an equivalent mathematical model thanks to Kirchhoff’s and Newton’s laws. The results of numerical simulations of the model generate an action potential (AP) that follows directly from the excitation of a single block of cell and does not propagate the signal in the neighboring blocks. When the stimulation time is lesser than 3-time units, the AP of the next block is generated during the repolarization of the previous cell, and the instantaneous displacement of the legs of the next block goes operational before the resting state of the previous block of the cell. For stimulation time greater than or equal to 3-time units, the AP is initiated just after the repolarization of the previous block of cells has terminated its activities and the instantaneous displacement of the leg of the next block goes operational, a direct consequence of neuron's communication without loss of amplitude in the permanent regime. Finally, straightforward motion without rotation is achieved.

Adaptive Super-Twisting Sliding Mode Control of Underwater Mechanical Leg with Extended State Observer

Underwater manipulation is one of the most significant functions of the deep-sea crawling and swimming robot (DCSR), which relies on the high-accuracy control of the body posture. As the actuator of body posture control, the position control performance of the underwater mechanical leg (UWML) thus determines the performance of the underwater manipulation. An adaptive super-twisting sliding mode control method based on the extended state observer (ASTSMC-ESO) is proposed to enhance the position control performance of the UWML by taking into account the system’s inherent nonlinear dynamics, uncertainties, and the external disturbances from hydrodynamics, dynamic seal resistance, and compensation oil viscous resistance. This newly designed controller incorporates sliding mode (SMC) feedback control with feedforward compensation of the system uncertainties estimated by the ESO, and the external disturbances of the hydrodynamics by fitting the parameters, the dynamic seal resistance, and the compensation oil viscous resistance to the tested results. Additionally, an adaptive super-twisting algorithm (AST) with integral action is introduced to eliminate the SMC’s chattering phenomenon and reduce the system’s steady-state error. The stability of the proposed controller is proved via the Lyapunov method, and the effectiveness is verified via simulation and comparative experimental studies with SMC and the adaptive fuzzy sliding mode control method (AFSMC).

Theoretical investigation of an array of Josephson junction neuron circuits actuating a mechanical leg and the array in mimicking a multi-legged locomotion

Theoretical investigation of an array of Josephson junction neuron circuits actuating a mechanical leg and the array in mimicking a multi-legged locomotion

Periarticular knee osteotomies for pre-arthritic deformities in the frontal plane : Indications and surgical techniques

Currently, periarticular knee joint osteotomies are an integral part of the treatment of early arthritic deformities in the knee joint. Analysis of the deformity is performed with astandardized full-leg standing x‑ray of both legs, as well as alateral x‑ray of the knee joint that includes 2/3 of the proximal tibial shaft. An MRI examination of the knee joint is obtained to assess the articular cartilage, the ligaments and menisci. Torsion angle measurements with the CT/MRT supplement the diagnostics if necessary. Knowledge of normal physiological values and their standard deviations of the mechanical leg axis and the joint angles around the knee is obligatory. The osteotomy is performed as close as possible to the femoral and/or tibial deformity. Postsurgical deformities including pathological patella position or asignificant difference in leg length must be prevented. Adescription of proximal tibia opening or closing wedge osteotomies based on the nomenclature of the joint angles by Paley is presented. The indications for the various osteotomy techniques in the coronary plane are discussed in detail.

Computed torque control and force analysis for mechanical leg with variable rotation axis powered by servo pneumatic muscle

It is difficult for a humanoid leg driven by two groups of antagonistic pneumatic muscles (PMs) to achieve a flexible humanoid gait, and its inherent strong coupling nonlinear characteristics make it hard to achieve good tracking performance in a large range of motion. Therefore, a four-bar linkage bionic knee joint structure with a variable axis and a double closed-loop servo position control strategy based on computed torque control are designed to improve anthropomorphic characteristics and the dynamic performance of the bionic mechanical leg powered by servo pneumatic muscle (SPM). Firstly, the relationship between the joint torque, the initial jump angle and the bounce height of the mechanical leg is established, and then we design a double-joint PM bionic mechanical leg containing a four-bar linkage mechanism of the knee joint. Secondly, a cascade position control strategy is developed, which consists of the outer position loop and the inner contraction force loop, and the mapping relationship is designed between joint torque and antagonistic PM contraction force. Finally, we further project bounce action timing of mechanical leg to realize the periodic jumping movement of the mechanical leg, and simulation and physical experiments of the real-style machine platform have been provided to demonstrate the effectiveness of the designed SPM controller.

Research on Walking Gait Planning and Simulation of a Novel Hybrid Biped Robot

A kinematics analysis of a new hybrid mechanical leg suitable for bipedal robots was carried out and the gait of the robot walking on flat ground was planned. Firstly, the kinematics of the hybrid mechanical leg were analyzed and the applicable relevant models were established. Secondly, based on the preliminary motion requirements, the inverted pendulum model was used to divide the robot walking into three stages for gait planning: mid-step, start and stop. In the three stages of robot walking, the forward and lateral robot centroid motion trajectories and the swinging leg joint trajectories were calculated. Finally, dynamic simulation software was used to simulate the virtual prototype of the robot, achieving its stable walking on flat ground in the virtual environment, and verifying the feasibility of the mechanism design and gait planning. This study provides a reference for the gait planning of hybrid mechanical legged bipedal robots and lays the foundation for further research on the robots involved in this thesis.

The first decade of the DGOU's cartilage register-insights for clinical practice

Registry data provide valuable epidemiological insights that help to further improve process and outcome quality in patient care. The German Cartilage Registry (KnorpelRegister DGOU) was established in 2013 as an instrument for quality assurance after surgical cartilage regenerative procedures on hip, knee and ankle joints. Participation in the German Cartilage Registry is optional for hospitals and practices. Currently, more than 160institutions in Germany, Austria and Switzerland participate in the data collection. The implementation of PROMs ("patient related outcome measurement"), as well as the recording of surgery-related influencing factors, enable adifferentiated scientific analysis and represent akey quality feature of the registry. Initial analyses of the registry data have already provided clinically relevant findings for immediate patient care. For example, patients who underwent focal cartilage therapy prior to ACT show aclinically relevant, significantly worse outcome than patients who underwent primary ACT. First conclusions could also be drawn regarding the relevance of concomitant cartilage therapy. For example, in patients with focal cartilage damage of the medial knee joint compartment, registry data indicate that leg axis correction is indicated even in cases of mild deviation of the mechanical leg axis. The data and findings obtained from the Cartilage Registry represent an important aspect of clinical care research and serve as acomplement to well-designed, clinically prospective cohort studies, RCTs, and meta-analyses.

A New Single-Leg Lower-Limb Rehabilitation Robot: Design, Analysis and Experimental Evaluation

Conventional lower-limb rehabilitation robots are large, complicated to wear, and require moving the patient to a designated position. To solve these problems, a new single-legged lower-limb rehabilitation robot (S-LLRR) that is easy to move and suitable for different height carriers was proposed. The mechanical leg has a variable working space, and its rotating joints are designed with mechanical limiters. The series configuration of the S-LLRR was analyzed, and trajectory planning was performed based on continuous linear motion training. Meanwhile, an active training control method based on the sand model was proposed to enhance the motion sensation of patients, and an active participation degree evaluation model was designed based on human physiological information. The simulation and experimental results showed that S-LLRR had a large workspace and good motion accuracy, and the accuracy of the active participation degree evaluation model could reach more than 85%. This research could provide a theoretical basis for improving the standardization and compliance of lower-limb robot rehabilitation training.

Design Scheme of Intelligent Robot Based on Crawler Sports Chassis

The chassis structure design of mobile robots is currently separated into four categories: wheel type, mechanical leg type, McNair wheel type, compound type, and crawler type, with wheel leg type, common crawler type, and wheel crawler type being under compound type. A formula Complex application scenarios frequently limit the robot's passibility throughout the actual application process. A new robot design plan is offered to overcome this problem: an intelligent robot built on a crawler-type moving chassis. To achieve the robot's astute observation of the surrounding environment, the advantages of wheeled and legged robots will be organically merged, and intelligent control terminals will be included in the hardware design. The mechanical framework will be built on a traditional crawler chassis, with leg guiding added. The crawler actuator of the structure will drive the crawler actuator of the leg-guided design to enable the robot to get out of problems in the face of challenging terrain conditions such as stairs, steps, and steep slopes. This work proposes an intelligent robot design strategy based on crawler motion chassis with high practicability, novelty, and broad applicability.

PREDICTING MECHANICAL LEG ALIGNMENT FROM KNEE X-RAY IMAGES BY UTILIZING DEEP-LEARNING NEURAL NETWORKS

Several studies have linked leg malalignment to early onset and progression of knee OA. Detecting abnormalities in mechanical alignment before radiographic evidence of knee OA is present, might increase the rate of early detection. Hence, conservative joint preserving interventions or even osteotomies could reduce the need or delay full joint replacement. In addition, medical trials often face high dropout rates, consequently, AI based support could improve the recruitment process. Detecting mechanical leg malalignment: 1) before the malalignment is immediately obvious to the clinician and 2) excluding/including patients recruited for medical trials. This study utilized a dataset of 8,878 digital radiographs ((I) 6,181 AP/PA full-leg x-rays, (II) 2,292 AP/PA knee x-rays with SynaFlexer positioning frame, (III) 405 AP/PA knee x-rays captured without SynaFlexer). The images were obtained from a diverse range of sources, including the OAI study, the University for Continuing Education Krems (AT), and five additional sites in Austria and the US. All knee images in the dataset were accompanied by their corresponding full-leg images, obtained on the same day. To determine the ground-truth hip-knee-ankle angle (HKA), the full-leg images were processed using IB Lab LAMA (ImageBiopsyB Lab, Vienna, Austria), a commercial software that automatically determines clinical measurements from full-leg radiographs. These images were used to train the AI algorithm. The algorithm produced binary outputs for HKA threshold values of 5° (clinically relevant) and 7.5° (clinical trial relevant). The algorithm reached MAE rates of 0.98° (cropped full-leg), 1.56° (SynaFlexer knee) and 2.10° (non-SynaFlexer knee). Summarizing all image modalities, the overall performance for the 5° threshold was 74-86% Sensitivity and 79-90% Specificity. Following, 7.5° threshold performance reached 81-92% Sensitivity and 85-92% Specificity. While this study primarily focused on absolute HKA threshold values of 5° and 7.5° for varus/valgus classification, this threshold determination process is highly adaptable to accommodate specific use cases, such as the desired angle threshold for classification or the preferred balance between sensitivity and specificity. In addition, overestimated HKA have an elevated angle above the normal range and could proceed towards or above mentioned thresholds. Chen K. PhD funding “LowerAustria Society for Scientific Research” (LSC20-020). Salzlechner C. and Lepenik C. are employees of ImageBiopsy Lab. Ljuhar R. is a shareholder of ImageBiopsy Lab. This manuscript was prepared using an OAI public use data set and does not necessarily reflect the opinions or views of the OAI investigators or the NIH. Lepenik C. thanks Avelar C. for comments on an early version of this article. CORRESPONDENCE ADDRESS: [email protected]

Speed Tracking Control for Unmanned Driving Robot Vehicle Based on Fuzzy Adaptive Sliding Mode Control

To achieve accuracy and stable speed tracking under different conditions, a speed tracking method for the unmanned driving robot vehicle with sliding mode gains adjusted by a fuzzy adaptive system is proposed. Using the complex vector method and equivalent substitution method, kinematics and dynamics models of driving mechanical legs are established. Combined with models of driving and brake systems of manipulated vehicles, the longitudinal dynamics model is built. Then the longitudinal manipulation strategy is established. Based on the dynamics model of the mechanical leg, the sliding mode controller's control law is deduced. In addition, the fuzzy adaptive approximation is constructed and the fuzzy adaptive law is designed. Furthermore, the stability of the fuzzy sliding mode controller is proven using the Lyapunov function. Finally, through simulation and experiment, a comparison among the proposed method and several existing control methods demonstrates the effectiveness of the proposed method.

Clutch Mechanical Leg Neural Network Adaptive Robust Control of Shift Process for Driving Robot With Clutch Transmission Torque Compensation

In order to improve the motion accuracy and robustness of the clutch mechanical leg for driving robot (CMLDR), and to improve the shift performance of the driving robot vehicle (DRV) for the engagement operation of CMLDR, a neural network adaptive robust control method of shift process for CMLDR with clutch transmission torque compensation is proposed. First, the dynamics model of the driving robot is established considering an external interference force and dynamic modeling error of the mechanical leg. Second, the upper clutch controller including a two-parameter shift module, a switch controller, and a finite-time linear quadratic regulator of the clutch transmission torque is designed. Third, the estimator of clutch engagement torque through a Kalman filter in the process of shift is constructed. Then, the neural network adaptive robust (NNAR) controller of the mechanical leg is designed. Finally, the proof of stability analysis for NNAR controller is conducted. Experiment and simulation results show that the designed controller of the mechanical leg has a strong antiinterference ability. And the DRV accurately tracks the target speed after compensating for the transmission torque.

Design and locomotion analysis of a close-chain leg-wheel mobile platform

PurposeTo take the advantages of terrain-adaptive capability of legged platform and fast-moving ability of wheeled platform, this paper aims to design a leg-wheel mobile platform for obstacle surmounting and analyze the feasibility and locomotivity of different moving modes.Design/methodology/approachThe platform consists of six leg-wheel units. Each of the units has a close-chain mechanical leg and an actuated wheel at the end of the leg. The platform moves with two modes: legged mode and leg-wheel composite mode. The legged mode achieves high mobility driven by crank motors, while the leg-wheel composite mode achieves obstacle-surmounting ability actuated by crank motors and pitch link motors and obtains high efficiency with the hub motors. The gait planning in different modes has been carried out and the obstacle-surmounting capacity has been analyzed.FindingsBased on the results of kinematic analysis and gait planning of the close-chain leg-wheel platform, the high mobility and efficiency obstacle-surmounting ability are demonstrated with the two movement modes. The feasibility of the design and the performance of the mobile platform is verified with the prototype experiment. The results of this paper show that the platform possesses good obstacle-surmounting capability.Originality/valueThe work presented in this paper is a novel exploration to design a close-chain leg mechanism and with an actuated wheel in series. The close-chain leg mechanism has the advantages of high leg lift and single degree of freedom characteristics, which makes the platform obtain the ability of obstacle-surmounting.