Leg Module Research Articles

Dynamic modeling of wheeled biped robot and controller design for reducing chassis tilt angle

Abstract The wheeled-legged robot combines the advantages of wheeled and legged robots, making it easier to assist people in completing repetitive and time-consuming tasks in their daily lives. This paper presents a study on the kinematic and dynamic modeling, as well as the controller design, of a wheeled biped robot with a parallel five-bar linkage mechanism as its leg module. During the motion of the robot, the robot relies on the tilt angle of the inverted pendulum, and this angle often results in the tilting of the chassis of the robot, presenting challenges for the installation of upper-body payloads and sensor systems. The controller proposed in this paper, which is developed by decoupling the primary motions of the robot and designing a multi-objective, multilevel controller, addresses this issue. This controller employs the pendulum pitch angle of the equivalent inverted pendulum model as the control variable and compensates for the chassis tilt angle (CTA). This control method can effectively reduce the CTA of such robots and eliminate the need for additional counterweights. It also provides a more spacious structural design for accommodating upper-body devices. The effectiveness of this control framework is verified through variable height control, walking on flat ground, and carrying loads over rough terrain and slopes.

A Systematic Methodology for Parasitic Capacitance Estimation and Validation of Multichip Modules

This paper proposes a method for extracting parasitic capacitances from die terminals to baseplate in a multi-chip-module (MCM). The parasitic capacitors constitute the common mode (CM) equivalent circuit model enabling filter design. While traditionally simple open module die area measurements are used to calculate capacitance from concerned nodes to baseplate, such methods result in breaking the module or contamination, rendering the module useless. This is especially concerning for high voltage (HV) rated modules (> 10 kV) where cost can be a deciding factor. Hence, a non-intrusive double pulse test method is developed to extract the parasitic capacitance from specific nodes to ground without physical damage to the module. Consequently, the proposed method is verified using a series of tests and open module measurements. The distributed capacitors can be transformed into lumped capacitors for electromagnetic compatibility (EMC) simulations and filter design. The proposed method is analyzed on a Three-Level Neutral Point Clamped (3L-NPC) phase leg module and compared against traditional method. Finally, the impact of estimation errors on the proposed method are discussed.

Design of preamplifier circuit for ECG circuit of wearable devices

In this study, a wearable electrocardiogram (ECG) acquisition system with high performance instrumentation amplifier is presented. It adopts a 3-op-amp circuit and utilizes 180nm CMOS technology to achieve large input impedance. Furthermore, a drive-right leg module is used to configure the input’s common-mode range, increasing the common-mode rejection rate. Simulations in standard 180nm CMOS technology show bandwidths ranging from 0.1Hz to 251Hz. The front-end circuit operates on a 0.8V power supply. At the same time, using LTspice to conduct a preliminary test on the performance of the circuit, the total integrated input-referred noise of the circuit is 3.98 µVRMS , and the power consumption is 5.059 µ W . This satisfies the need for an ECG circuit with low power and noise requirements for wearable technology. The preliminary research findings presented in this paper have established a solid theoretical framework for the amplifier used in the measuring of ECG signals.

Torque-Based Control of a Bio-Inspired Modular Climbing Robot

This article presents a generalizable, low computational cost, simple, and fast gravity compensation method for legged robots with a variable number of legs. It is based on the static problem, which is a reduction in the dynamic model of the robot that takes advantage of the low velocity of climbing robots. To solve it, we propose a method that computes the torque to be applied by each actuator to compensate for the gravitational forces without using the Jacobian matrix for the forces exerted by the end-effector and without using analytical methods for the gravitational components of the model. We compare our method with the most popular method and conclude that ours is twice as fast. Using the proposed gravity compensator, we present a torque-based PD controller for the position of the leg modules, and a body velocity control without dynamic compensation. In addition, we validate the method with both hardware and a simulated version of the ROMERIN robot, a modular legged and climbing robot. Furthermore, we compare our controller with the usual kinematic inverse controllers, demonstrating that the mean angular and linear error is significantly reduced, as well as the power requirements of the actuators.

Thermoelectric and power generation of 2D structured pieces of graphene-nanodiamonds nanocomposite.

Recently, the ultrafine 2D structured nanocomposite of graphene (Gr)-nanodiamonds (NDs) produced by a microwave-assisted chemical route was found to have attractive structural properties. This new 2D structured nanocomposite may be employed for a wide spectrum of applications including thermoelectricity (TE) applications. It is well established that TE materials should be highly effective to be used for designing operative devices for powering or cooling small devices. To fulfill such an objective, the functional TE material should possess a high-power factor and low thermal conductivity. In this study, NDs were successfully integrated into Gr with a magnificent structural alteration to the Gr layers/sheets. This structural modification was found to impact the TE final outcome above and below room temperature (RT). The obtained results showed that at 215 K the power factor value was increased from 4 μW m-1 K-2 for the pure Gr to ∼20 μW m-1 K-2 for the Gr-NDs nanocomposite. At higher T, e.g. 365 K, these values slightly decreased, but with clear superiority for the Gr-NDs nanocomposite. The thermal conductivity of the Gr-NDs nanocomposite was significantly reduced to ∼12% of that of the pure Gr, which could reflect a significant enhancement in the value of the figure of merit by >45 times. Furthermore, the output power generated by a single small leg module made of the Gr-NDs nanocomposite was measured and found to be measurable. The obtained values are still relatively low for practical application, but this newly produced material has great potential to be further developed for TE applications.

A three-axis modular horizontal vibration isolation system with adjustable stiffness: Design, analysis and experimental validation

In this study, a modular vibration isolator design is introduced in which the horizontal stiffness of the system can be adjusted in three axes (translational stiffness in the horizontal x and y axes and torsional stiffness about the vertical z-axis) by changing the compressive forces on the leg modules, which are composed of elastic stepped columns and a string. A novel multi-string tensioning mechanism is developed to change the axial compressive forces on all the elastic stepped columns simultaneously, which in turn vary the translational and torsional stiffness of the system. Consequently, the translational and torsional natural frequencies of the system can be tuned to a targeted value by increasing/decreasing the tension forces in the strings for light/heavy payloads. With the use of multiple leg modules in the isolator, the torsional natural frequency can be kept close to the translational natural frequencies at any value of the tension forces in the strings even if the payload masses vary over a wide range. To investigate the relationship between the tension forces and natural frequencies, a leg module is produced. Analytical and finite element models of the leg module are formed, and the results of these models are found to be in good agreement with the experimental results. It is shown that the translational and torsional natural frequencies of the isolator with multiple leg modules can be adjusted to 0.5 Hz and 0.6 Hz, respectively, keeping the lower limits of the isolation bandwidth in the translational and torsional axes less than 1 Hz. Moreover, the upper limit of the isolation bandwidths can be kept above 135 Hz. Therefore, the proposed isolation system has a very wide isolation bandwidth at low frequencies.

Overconstrained coaxial design of robotic legs with omni-directional locomotion

While being extensively researched in literature, overconstrained linkages’ engineering potential is yet to be explored. This study investigates the design of overconstrained linkages as robotic legs with coaxial actuation starting with the simplest case, Bennett linkage, to establish the theoretical foundations and engineering advantages of a class of overconstrained robots. We proposed a parametric design of the spatial links and joints in alternative forms so that one can fabricate these overconstrained limbs via 3D printing and then attach the linkage coaxially to a pair of servo actuators as a reconfigurable leg module. We adopted multi-objective optimization to refine the design parameters by analyzing its manipulability metric and force transmission, enabling omni-directional ground locomotion projected from a three-dimensional surface workspace. The proposed prototype quadruped was capable of omni-directional locomotion and had a minimal turning radius (0.2 Body Length) using the fewest actuators. We further explored the kinematics and design potentials to generalize the proposed method for all overconstrained 5R and 6R linkages, paving the path for a future direction in overconstrained robotics.

(Invited) 75 kVA 1kV DC 50 kHz Air-Cooled Inverter with 1.7 Kv SiC Mosfet and 3D-Printed Novel Modular Packaging Structure

In recent years, some air-cooled inverters have been developed and demonstrated for grid applications using SiC power modules. All of these SiC power modules utilize the conventional single-side wire-bonding packaging structure, i.e. only one side of the power module is attached to heat sinks. The potential of silicon carbide (SiC) devices, such as high power density, high frequency and high temperature operation, have not been fully explored yet. To deal with this issue, several research efforts have focused on the development of SiC power modules with double sided-cooling capability, utilizing planar packaging structure . These power modules are able to achieve a comprehensive improvement in overall volume / size, parasitic parameters, as well as thermal impedance. However, some key aspects limit the real application of planar packaging structures. One main reason is that double-side solderable SiC devices are generally not commercially available. Other challenges include interconnection alignment issue, limited choices for die-attach material, complicated fabrication process, etc With the goal of exploring SiC device potential without complicated packaging, an all-SiC air-cooled wire-bonding power module and inverter is developed for grid applications based on 3D printing technology enabling: new packaging structure, optimized heat sink, and more-compact system integration.This paper presents the design and development of an 75 kVA, 50 kHz, 1kV air-cooled Silicon Carbide inverter using advance packaging and additive manufacturing technology. Specifically, an air-cooled power module with a new packaging structure is design, aiming at reduced thermal resistance for high temperature and high-power density operation. The detailed research work involves the design of a new packaging structure, wire-bond SiC power module design and fabrication, as well as associated power stage and control circuit design. The total volume of the power module for the prototype is 99725 mm3 a 48% volume reduction volume compared to previous work reported by the authors. The air-cooled module assembly incorporates three major parts: SiC MOSFET phase leg module with split high side and low side switches, a gate driver with cross-talk and short circuit protection functions, and 3D printed module package. In addition , the thermal performance of the inverter is also evaluated and the results show the maximum junction temperature of the bare die is 103C. Based on the air cool module, a 50-kW three phase inverter is developed and tested to further verify the superior thermal performance of the proposed packaging structure. The experimental results show that the peak efficiency is 99.1% at 1kV,50 KHz switching and 50 kW operating condition. Figure 1

High Performance Solar Thermoelectric Generator Using Asymmetrical Variable Leg Geometries

This paper presents a computational study of the combined effects of variable geometry and asymmetry in the legs of thermocouples of thermoelectric modules used in solar thermoelectric generators (STEGs). Six different models were considered for the thermocouples in each module, namely: rectangular-rectangular legs, rectangular-trapezoidal legs, rectangular-X legs, trapezoidal-trapezoidal legs, trapezoidal-X legs, and X-X legs. Simulations of the six different modules under the same heat flux was carried out in ANSYS 2020 R2 software. Temperature and voltage distributions were obtained for each model and the results indicate significant variations due to the utilization of varying leg geometries. Results show that the X-X leg module generated the highest temperature gradient and electric voltage. In comparison, a temperature gradient and electric voltage of 297 K and 16 V, respectively were achieved with the X-X leg module as against 182 K and 8.4 V, respectively, achieved in a conventional rectangular leg module. This suggests a 63.2% and 90.5% increase in the temperature gradient and electric voltage of the conventional TE module. Therefore, this study demonstrates that X geometry gives the best performance for thermoelectric modules and STEGs.

Thermoelectric properties of oil fly ash-derived carbon nanotubes coated with polypyrrole

Oil fly ash has been reported to be suitable for producing low-cost carbon nanotubes (CNTs). These CNTs exhibit zigzag curved walls with an almost bamboo-like structure. Owing to this structure, these CNTs exhibit very low thermal conductivity as compared to other graphitic carbon materials. They also exhibit relatively low electrical conductivity. However, they exhibit a Seebeck coefficient comparable to that of commercially available CNTs. Therefore, it is of great importance to evaluate the thermoelectric (TE) properties of oil fly ash-derived CNTs. In this study, the TE properties of oil fly ash-derived CNTs were investigated. The CNTs were further coated with polypyrrole (PPy) to enhance their TE performance. PPy was used for the modification because of its attractive TE properties and its suitability as a binder for CNTs. The PPy coating significantly enhanced the electrical conductivity of the CNTs from ∼500 to ∼1300 S/m at room temperature. A small increase in the Seebeck coefficient was also observed. The power factor value increased from 0.1 to 0.6 μW/m K2. At 440 K, the power factor value was 1.4 μW/m K2. The thermal conductivity of the CNTs (∼1 W/m K) decreased significantly by a factor of 10 after the modification with PPy. The power generation characteristics of a single leg module made up of the p-type coated CNTs were investigated under real-time conditions in air. The results demonstrated the potential of the oil fly ash-derived CNTs coated with PPy for applications as TE materials.

The effect of morphological modification on the thermoelectric properties of ZnO nanomaterials

At present, huge research efforts are dedicated to improve the efficiency of thermoelectric (TE) materials. Nanostructuring is one of the suggested methods to improve their TE performance. However, the morphology of a nanomaterial might play a significant role on its TE properties. In this work, we demonstrated this effect by producing zinc oxide (ZnO) in two different morphologies using the microwave assisted chemical route. Nanoparticles (NPs) and nanorods (NRs) were synthesised by changing the molar ratios of the starting precursors. The obtained results show that the NRs have improved TE properties compared to those of the NPs, particularly at high temperature. At 673 K the Seebeck coefficient, electrical conductivity and power factor values of the ZnO NRs reached −1020 μV/K, 22 S/m and 23 μW/m.K2, respectively. The NPs have only recorded −850 μV/K, 3 S/m and 2.4 μW/m.K2 of these factors. Moreover, the thermal conductivity of the NRs was found to be three times lower than that of the NPs. As a result of these differences the Figure of Merit (zT) value of the NRs is around 0.012, while that of the NPs is only 0.001. Power generation characteristics of single leg modules made of the ZnO NPs and NRs, measured under the conditions of actual applications in an air atmosphere were also investigated. The output power of the ZnO NRs is found to be several times higher than that of the NPs. These results have clearly demonstrated the effect of nanostructures morphology on the TE performance, which might be important for future TE generators.

Improved Gait of Persons With Multiple Sclerosis After Rehabilitation: Effects on Lower Limb Muscle Synergies, Push-Off, and Toe-Clearance.

Introduction: Persons with MS (PwMS) have markedly reduced push-off and toe-clearance during gait compared to healthy subjects (HS). These deficits may result from alterations in neuromotor control at the ankle. To optimize rehabilitation interventions for PwMS, a crucial step is to evaluate if and how altered neuromotor control, as represented by muscle synergies, improves with rehabilitation. In this study we investigated changes in ankle motor control and associated biomechanical parameters during gait in PwMS, occurring with increase in speed after gait rehabilitation.Methods: 3D motion and EMG data were collected while 11 PwMS (age 50.3 + 11.1; EDSS 5.2 + 1.2) walked overground at self-selected speed before (T0) and after 20 sessions (T1) of intensive treadmill training. Muscle synergies were extracted using non-negative matrix factorization. Gait parameters were computed according to the LAMB protocol. Pearson's correlation coefficient was used to evaluate the similarity of motor modules between PwMS and HS. To assess differences in distal module activations representing neuromotor control at the ankle [Forward Propulsion (FPM) and Ground Clearance modules (GCM)], each module's activation timing was integrated over 100% of the gait cycle and the activation percentage index (API) was computed in six phases.Ten age matched HS provided two separate speed-matched normative datasets for T0 and T1. For speed independent comparison for the PwMs Z scores were calculated for all their gait variables.Results: In PwMS velocity increased significantly from T0 to T1 (0.74–0.90 m/s, p < 0.05). The activation profiles (API) of FPM and GCM of PwMS improved in pre-swing (p < 0.05): FPM (Mean [95% CI] [%]: T0: 12.5 [5.7–19.3] vs. T1: 9.0 [2.7–15.3]); GCM (T0: 26.7 [18.2–35.3] vs. T1: 24.5 [18.2–30.7]). This was associated with an increase in toe clearance (80.3 to 103.6 mm, p < 0.05) and a higher ankle power peak in pre-swing (1.53–1.93 W/kg, p < 0.05).Conclusion: Increased gait speed of PwMS after intensive gait training was consistent with improvements in spatio-temporal gait parameters. The most important finding of this study was the re-organization of distal leg modules related to neurophysiological changes induced by rehabilitation. This was associated with an improved ankle performance.

Microwave Irradiation to Produce High Performance Thermoelectric Material Based on Al Doped ZnO Nanostructures

Microwave irradiation is found to be effective to provide highly crystalline nanostructured materials. In this work, this technique has been used to produce highly improved thermoelectric (TE) material based on aluminum (Al) doped zinc oxide (ZnO) nanostructures (NSs). The effect of Al dopant at the concentration range 0.5–3 mol % on the structural and TE properties has been investigated in more details. The optimum concentration of Al for better TE performance is found to be 2 mol %, which could significantly increase the electrical conductivity and reduce the thermal conductivity of ZnO NSs and thus enhance the TE performance. This concentration showed almost metallic conductivity behavior for ZnO NSs at low temperatures, e.g., below 500 K. The electrical conductivity reached 400 S/m at room temperature, which is around 200 times greater than the value recorded for the pure ZnO NSs. Remarkably, the measured room temperature thermal conductivity of the microwave synthesized ZnO NSs was very low, which is around 4 W/m·K. This value was further reduced to 0.5 W/m·K by increasing the Al doping to 3 mol %. The figure of merit recorded 0.028 at 675 K, which is 15 times higher than that of the pure ZnO NSs. The output power of a single leg module made of 2 mol % Al doped ZnO NSs was 3.7 µW at 485 K, which is higher by 8 times than that of the pure sample. These results demonstrated the advantage of the microwave irradiation rout as a superior synthetic technique for producing and doping promising TE nanomaterials like ZnO NSs.

Hybrid Pulse Width Modulation Strategy of a High-Frequency Link Three-Phase Four-Leg Matrix Converter Based on Compensation Theory

A high-frequency link (HFL) three-phase four-leg matrix converter (MC) can output three-phase balanced voltage for unbalanced load conditions. It is an inverter with great development potential. This paper presents a hybrid pulse width modulation (HPWM) strategy for a four-wire matrix converter based on the fourth bridge leg compensation method. Firstly, the rear-stage topology of a high-frequency link three-phase four-leg matrix converter is decoupled into two sets of ordinary three-phase four-wire inverters. Then the compensation strategy is applied to separate the fourth bridge leg from the coupling of the ordinary inverter and realize its independent control. Under the theory of compensation, the fourth bridge leg plays a role in compensating the deviation of the neutral point potential when the load is unbalanced, the fourth bridge leg does not need to work when the load is balanced. Finally, the fourth bridge leg modulation wave obtained by the compensation method is combined with the front three bridge leg modulation waves to perform the coupling control using the hybrid pulse width modulation strategy. It has changed the problem that the previous hybrid pulse width modulation strategy cannot be directly applied to the four-wire matrix converter. This strategy is simple to control, without adding any auxiliary commutation detection circuitry, can effectively solve the inherent commutation problem in the bidirectional switch tube of the four-wire matrix converter. It simplifies the complexity of the system, reduced control cost, and high switching loss caused by high switching frequency. The fast adjustment function of compensation strategy makes the dynamic response performance of system under load fluctuation state more prominent, the harmonic distortion rate is smaller. The perfect combination of two strategies allows the high-frequency link three-phase four-leg matrix converter with any form of load to give full play to its structural advantages. The related work verifies the feasibility and effectiveness of the modulation method and control logic.

A 50-kW Air-Cooled SiC Inverter With 3-D Printing Enabled Power Module Packaging Structure and Genetic Algorithm Optimized Heatsinks

This article presents a systematic power stage design approach for a high-power density air-cooled inverter, which involves the utilization of emerging 1.7 kV silicon carbide (SiC) mosfet bare die engineering samples, heatsinks optimized with genetic algorithm, and built using three-dimensional printing technology and integrated power modules with a novel packaging structure. The developed air-cooled inverter assembly is mainly composed of the SiC mosfet phase leg modules with split high-side and low-side switch submodules, which are attached to two separate heatsinks for increased heat dissipation area and reduced thermal resistance. The heatsink is designed using a co-simulation environment with finite element analysis in COMSOL and genetic algorithm in MATLAB. The primary design procedure, including bare die device characterization, loss calculation, thermal evaluation, and power module development, is elaborated. The proposed design approach is verified and validated through experiments at each stage of development. The experimental results show that the inverter California Energy Commission efficiency is 98.4%, and a power density of 75 W/in3 is achieved with a sufficient junction temperature margin for semiconductor long-term reliability.

Control of Internal Dynamics of Grid-Connected Modular Multilevel Converter Using an Integral Backstepping Controller

The modular multilevel converter (MMC) has significant applications in power systems due to its promising features, such as modularity, reliability, scalability, and low harmonic distortion. One of the challenges in the operation of MMC is to regulate the circulating current in its phase leg and sub module (SM) capacitor voltage. This paper presents the control of internal dynamics, i.e., circulating current and submodule capacitor voltage, of the MMC using an integral backstepping algorithm. The design of the controller is based on Lyapunov stability function. The backstepping control ensures the convergence of the error signal to zero. Additionally, the integral action in the control law increases the robustness and reliability of the system against the external disturbances and model uncertainties. Moreover, the integral term in the controller eliminates the residual steady-state error. The Lyapunov function-based design of the backstepping controller guarantees the convergence of circulating current as well as submodule capacitor voltage for any possible initial condition. Moreover, the performance of the proposed integral backstepping controller is compared with the proportional resonant (PR) controller. The proposed backstepping control scheme for three-phase MMC has been implemented in MATLAB/Simulink.

30-kW All-SiC Inverter with 3D-Printed Air-Cooled Heatsinks for Plug-In and Full Electric Vehicle Applications

This paper presents the design and development of a 30-kW 3D printed based air-cooled silicon carbide (SiC) inverter for electric vehicle application. Specifically, an all-SiC air-cooled power module is designed, aiming at reduced thermal resistance for high temperature and high power density operation. The module assembly incorporates three major parts: an optimized 3D printed heat sink, a SiC MOSFET phase leg module, and a two-channel gate driver. The electrical and thermal performance of the power module is evaluated through double pulse test and continuous operation. Based on the air-cooled power module, a three-phase half-bridge voltage source inverter with 3D-printed air duct is built and tested to further verify the performance of the power module.

Simplified Triped Robot for Analysis of Three-Dimensional Gait Generation

[abstFig src='/00290003/08.jpg' width='230' text='The tripedal robot “Martian petit”' ] Significant efforts to simplify the body structure of multi-legged walking robots have been made over the years. Of these, the Spring-Loaded-Inverted-Pendulum (SLIP) model has been very popular, therefore widely employed in the design of walking robots. In this paper, we develop a SLIP-based tripedal walking robot with a focus on the geometric symmetry of the body structure. The proposed robot possesses a compact, light-weight, and compliant leg modules. These modules are controlled by a distributed control law that consists of decoupled oscillators with only local force feedback. As demonstrated through experiments, the simplified design of the robot makes possible the generation of high-speed dynamic locomotion. Despite the structural simplicity of the proposed model, the generation of several gait-patterns is demonstrated. The proposed minimalistic design approach with radial symmetry simplifies the function of each limb in the three-dimensional gait generation of the robot.

Theoretical Design of a Leg Module for a Hexapod Underwater Robot

In this paper a theoretical design of two degrees of freedom (single leg module) of a hexapod underwater robot is carried out. The length of the two links together is (30 cm) and the motor for the joint 2 is mounted inside the robot. In addition, forward kinematics analysis is performed to specify angle of movement for each joint by applying Denavit- Hartenberg notation. Furthermore, 3d drawings show the leg implementation. Finally, MATLAB Simulink is used to design PID controller and examine the control signal.

アクティブサスペンション型脚モジュールを用いた4脚走行ロボットの走行制御

Four-legged animals achieve high speed and high efficiency movement by changing their gait according to speed and terrain. Consequently, it can be assumed that such movement is possible by a four-legged running robot based on reproducing the various gaits of four-legged animals. We are developing an active-suspension mechanism consisting of a spring and a DC motor on the leg module to imitate the legs of animals and studying the high-speed running of a four-legged running robot. This mechanism strengthens the instantaneous power of jumping and controls dumping at landing, although the springs and motors are mutually constrained and it is difficult for them to demonstrate maximum force. In this study, we examined the optimal spring for an active suspension leg module. Furthermore, we evaluated the running speed and power consumption of a trot and a bound gaits using the selected spring.