This letter introduces a novel anti-skid foot design consisting of two different types of foot pads, a cylindrical foot covered with rubber and a complementary foot with an array of spine mechanisms. The primary foot is designed to provide contact during movements that do not require excessive friction forces. On the other hand, the complementary foot is specialized to provide larger traction for dynamic motions. A passive slip detection and lock and release mechanisms are also designed to enable conditional switching to the complementary foot pad if slip occurs while the primary foot is in use. Experimental results demonstrated that the anti-skid foot can sustain 1.9 times of tangential load on a concrete block, compared with the maximum tangential load that a rubber foot pad can sustain on the same surface. Using this enhanced tangential load capability, a two-legged planar robot equipped with the novel foot was able to jump, land, and attach to the surface of a concrete block with a slope of 50°.
Tau, a microtubule associated protein, is the main component of the aberrant paired helical filaments found in Alzheimer’s Disease (AD). Tau is present in phosphorylated and aggregated form not only in AD, but in other pathologies.However, the mechanisms by which tau induces neuronal death remain unclear. In this experiment, for study of mechanism induced by tau, the tau binding proteins of hippocampus were isolated by immunoprecipitation and SDS-PAGE. The proteins were compared between transgenic mice expressing neuron-specific anolase(NSE)-controlled human wild-type tau (NSE/tau23) and NSE-controlled mouse. We confirmed several important proteins, which are related to AD mechanism.
A scanning tunneling microscope has been built, which can resolve atomic arrangements of conductors and semiconductors in ultra high vacuum below Torr. Its background and operational principles are reviewed and the guide lines in building the scanning tunneling microscope are shown. The results of measurements for highly oriented pyrolytic graphite and Si(111) surface are presented.
This paper presents the design and implementation of a bounding controller for the MIT Cheetah 2 and its experimental results. The paper introduces the architecture of the controller along with the functional roles of its subcomponents. The application of impulse scaling provides feedforward force profiles that automatically adapt across a wide range of speeds. A discrete gait pattern stabilizer maintains the footfall sequence and timing. Continuous feedback is layered to manage balance during the stance phase. Stable hybrid limit cycles are exhibited in simulation using simplified models, and are further validated in untethered three-dimensional bounding experiments. Experiments are conducted both indoors and outdoors on various man-made and natural terrains. The control framework is shown to provide stable bounding in the hardware, at speeds of up to 6.4 m/s and with a minimum total cost of transport of 0.47. These results are unprecedented accomplishments in terms of efficiency and speed in untethered experimental quadruped machines.
This paper presents a contact-implicit model predictive control (MPC) framework for the real-time discovery of multi-contact motions, without predefined contact mode sequences or foothold positions. This approach utilizes the contact-implicit differential dynamic programming (DDP) framework, merging the hard contact model with a linear complementarity constraint. We propose the analytical gradient of the contact impulse based on relaxed complementarity constraints to further the exploration of a variety of contact modes. By leveraging a hard contact model-based simulation and computation of search direction through a smooth gradient, our methodology identifies dynamically feasible state trajectories, control inputs, and contact forces while simultaneously unveiling new contact mode sequences. However, the broadened scope of contact modes does not always ensure real-world applicability. Recognizing this, we implemented differentiable cost terms to guide foot trajectories and make gait patterns. Furthermore, to address the challenge of unstable initial roll-outs in an MPC setting, we employ the multiple shooting variant of DDP. The efficacy of the proposed framework is validated through simulations and real-world demonstrations using a 45 kg HOUND quadruped robot, performing various tasks in simulation and showcasing actual experiments involving a forward trot and a front-leg rearing motion.
This paper presents a method for achieving high-speed running of a quadruped robot by considering the actuator torque-speed operating region in reinforcement learning. The physical properties and constraints of the actuator are included in the training process to reduce state transitions that are infeasible in the real world due to motor torque-speed limitations. The gait reward is designed to distribute motor torque evenly across all legs, contributing to more balanced power usage and mitigating performance bottlenecks due to single-motor saturation. Additionally, we designed a lightweight foot to enhance the robot's agility. We observed that applying the motor operating region as a constraint helps the policy network avoid infeasible areas during sampling. With the trained policy, KAIST Hound, a 45 kg quadruped robot, can run up to 6.5 m/s, which is the fastest speed among electric motor-based quadruped robots.
This paper describes selected issues with the commissioning and implementation of a real-time control system for an experimental bipedal robot platform named MABEL at the University of Michigan. Real world issues with printed circuit board layout and manufacturing, replacement of third party components, and communication issues associated with the computer control system are discussed. Control system implementation issues such as cable stretching in the hip and knee joint drivetrains, sensor resolution issues, and problems with software implementation related to computer processing speed for control system throughput are also presented. We illustrate solutions to each of these specific issues. In addition to standard troubleshooting processes, several complex concepts that may aid any commissioning and implementation effort are noted. A summary and discussion of future work with the robot conclude the paper.
This paper presents a bio-inspired quadruped controller that allows variable-speed galloping. The controller design is inspired by observations from biological runners. Quadrupedal animals increase the vertical impulse that is generated by ground reaction forces at each stride as running speed increases and the duration of each stance phase reduces, whereas the swing phase stays relatively constant. Inspired by this observation, the presented controller estimates the required vertical impulse at each stride by applying the linear momentum conservation principle in the vertical direction and prescribes the ground reaction forces at each stride. The design process begins with deriving a planar model from the MIT Cheetah 2 robot. A baseline periodic limit cycle is obtained by optimizing ground reaction force profiles and the temporal gait pattern (timing and duration of gait phases). To stabilize the optimized limit cycle, the obtained limit cycle is converted to a state feedback controller by representing the obtained ground reaction force profiles as functions of the state variable, which is monotonically increasing throughout the gait, adding impedance control around the height and pitch trajectories of the obtained limit cycle and introducing a finite state machine and a pattern stabilizer to enforce the optimized gait pattern. The controller that achieves a stable 3 m s(-1) gallop successfully adapts the speed change by scaling the vertical ground reaction force to match the momentum lost by gravity and adding a simple speed controller that controls horizontal speed. Without requiring additional gait optimization processes, the controller achieves galloping at speeds ranging from 3 m s(-1) to 14.9 m s(-1) while respecting the torque limit of the motor used in the MIT Cheetah 2 robot. The robustness of the controller is verified by demonstrating stable running during various disturbances, including 1.49 m step down and 0.18 m step up, as well as random ground height and model parameter variations.
This paper describes design of tracked vehicle which can adapt rough terrain using passive link mechanism. The vehicle has two track modules at both sides which have four-bar link mechanism with passive spring elements. The passive spring elements of the link mechanism provide the restoring force which helps the vehicle to be changed to stable configuration when overcoming uneven terrains. The two track modules are connected with rotary joint so that it provides adaptability to laterally located terrain roughness. Simulating under various conditions, we verify our design concept and determine critical design parameter. We manufactured prototype vehicle with determined design parameters from simulation results. The vehicle has size of 295 mmtimes210 mmtimes105 mm, and weight of the vehicle is 1.31 kg. The prototype equips two 2.17 W DC motors as driving motors. We conducted experiments with manufactured prototype under various terrain conditions. The terrain conditions include steps, stairs, trench, and unstructured terrain. In experiments, this vehicle shows good overcoming ability for the tested terrain conditions
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