Alexander Hunt

Portland State University | PSU · Department of Mechanical and Materials Engineering

This study introduces a novel neuromechanical model of rat hindlimbs with biarticular muscles producing walking movements without ground contact. The design of the control network is informed by the findings from our previous investigations into two-layer central pattern generators (CPGs). Specifically, we examined one plausible synthetic nervous s...

This work presents an in-depth numerical investigation into a hypothesized two-layer central pattern generator (CPG) that controls mammalian walking and how different parameter choices might affect the stepping of a simulated neuromechanical model. Particular attention is paid to the functional role of features that have not received a great deal o...

This paper presents experimental test results for joints used in a biomimetic bipedal robot. In this work, MRI and CT scans are utilized to inform the design of joints of similar size and function to the biological counterparts. Three lower body joints, to be actuated by artificial muscles were designed and constructed. Then the range of motion and...

Animal locomotion is influenced by a combination of constituent joint torques (e.g., due to limb inertia and passive viscoelasticity), which determine the necessary muscular response to move the limb. Across animal size-scales, the relative contributions of these constituent joint torques affect the muscular response in different ways. We used a mu...

The domestic dog is interesting to investigate because of the wide range of body size, body mass, and physique in the many breeds. In the last several years, the number of clinical and biomechanical studies on dog locomotion has increased. However, the relationship between body structure and joint load during locomotion, as well as between joint lo...

Modeling muscle-based locomotion in simulation requires reliable interactions between kinematic motion and kinetic forces. Simplifications made in simulation can sometimes obfuscate these interconnections and cause a system to operate in unexpected ways. We present a methodology for calculating muscle parameters that comprise a linear Hill muscle m...

This work presents a biomechanical model of rat hind limbs with biarticular muscles and includes kinematic and kinetic analyses. Our previous model only possessed antagonistic muscle pairs (extensor and flexor) to actuate each joint in the sagittal plane. In this model, we expanded the number of muscles in each limb from 6 to 8, including 3 biartic...

This work demonstrates an algorithm that is able to compute optimal placement for braided pneumatic actuators on a bipedal robot in order to emulate the biology of human legs. The algorithm calculates the torque that muscles are able to generate about a series of joints (back, hip, knee, ankle, subtalar, and metatarsophalangeal) in a human model. I...

Engineering neural networks to perform specific tasks often represents a monumental challenge in determining network architecture and parameter values. In this work, we extend our previously-developed method for tuning networks of non-spiking neurons, the “Functional subnetwork approach” (FSA), to the tuning of networks composed of spiking neurons....

Dogs are an interesting object of investigation because of the wide range of body size, body mass, and physique. In the last several years, the number of clinical and biomechanical studies on dog locomotion has increased. However, the relationship between body structure and joint load during locomotion, as well as between joint load and degenerativ...

This paper presents initial findings that are a stepping stone to creating a sensor suite that monitors human posture with limited inertial measurement units. The focus is on using two inertial measurement units, one on each lower leg, to try to recreate the posture of the lower body. We compare a complementary filter and a biologically inspired fi...

Bipedal robotic leg kinematics and dynamics are a key component in designing biomimetic humanoid robots. This work describes the process of designing artificial muscle attachment locations of the legs of a bipedal robot utilizing pneumatic artificial muscles (PAMs). PAMs offer similar force and activation times to real muscles, while being lightwei...

Legged locomotion is a feat ubiquitous throughout the animal kingdom, but modern robots still fall far short of similar achievements. This paper presents the design of a canine-inspired quadruped robot named DoggyDeux as a platform for synthetic neural network (SNN) research that may be one avenue for robots to attain animal-like agility and adapta...

This work demonstrates a neuromechanical model of rat hindlimb locomotionundergoing nominal walking with perturbations. In the animal, two types of responses toperturbations are observed: resetting and non-resetting deletions. This suggests that the animallocomotor system contains a memory-like organization. To model this phenomenon, we built asynt...

Understanding the kinematics of a hindlimb model is a fundamental aspect of modeling coordinated locomotion. This work describes the development process of a rat hindlimb model that contains a complete muscular system and incorporates physiological walking data to examine realistic muscle movements during a step cycle. Moment arm profiles for selec...

Human balance is achieved using many concurrent control loops that combine to react to changes in environment, posture, center of mass and other factors affecting stability. Though numerous engineering models of human balance control have been tested, no methods for porting these models to a neural architecture have been established. It is our hypo...

This paper details the design, construction, and performance analysis of a biologically inspired knee joint for use in bipedal robotics. The design copies the condylar surfaces of the distal end of the femur and utilizes the same crossed four-bar linkage design the human knee uses. The joint includes a changing center of rotation, a screw-home mech...

This paper presents the design of a novel adjustably damped hip and ankle joint using braided pneumatic actuators. These joints provide a wide range of motion and exhibit the same change in stiffness as flexion increases that human joints exhibit, which should also increase bipedal stability, adaptability, and controllability. The theoretical behav...

We present a synthetic nervous system modeling mammalian locomotion using separate central pattern generator and pattern formation layers. The central pattern generator defines the rhythm of locomotion and the timing of extensor and flexor phase. We also investigated the capability of the pattern formation network to operate using muscle synergies...

This paper presents modelling of a fruit fly’s visual neural system for motion recognition employing non-spiking Hodgkin-Huxley neurons. Motion detection operates based on the Hassenstein-Reichardt correlator principle. An array of motion detectors reveals the velocity field pattern, and an additional summation layer allows calculation of the vanis...

Human balance is likely achieved using many concurrent control loops that combine to react to changes in environment, posture, center of mass and other factors affecting stability. Though numerous engineering models of human balance control have been tested, no models of how these controllers might operate within the nervous system have yet been es...

To accomplish many useful tasks, robots must be capable of navigating complex, dynamic environments. For this reason, robots often take inspiration from the adaptive responsiveness inherent to living organisms. Our existing model of rat neuromechanics [1] has provided insight into neuromuscular control structures that can generate quadruped locomot...

A dynamical model of an animal's nervous system, or synthetic nervous system (SNS), is a potentially transformational control method. Due to increasingly detailed data on the connectivity and dynamics of both mammalian and insect nervous systems, controlling a legged robot with an SNS is largely a problem of parameter tuning. Our approach to this p...

Braided pneumatic actuators (BPAs) are attractive for use in bio-robots because they offer many muscle-like properties, especially when compared to most other commercially available robotic actuators. Unfortunately, the same properties that make these actuators similar to muscles make them more difficult to control. One such actuator manufactured b...

Human balance control is a complex feedback system that must be adaptable and robust in an infinitely varying external environment. It is probable that there are many concurrent control loops occurring in the central nervous system that achieve stability for a variety of postural perturbations. Though many engineering models of human balance contro...

This paper presents the design and development of a novel biologically inspired knee design for humanoid robots. The robotic joint presented mimics the design of the human knee joint by copying the condylar surfaces of the femur and tibia. The joint significantly reduces the complexity, while preserving the mechanisms of the human knee’s motion, an...

Background Implanted motor system neuroprostheses can be effective at increasing personal mobility of persons paralyzed by spinal cord injuries. However, currently available neural stimulation systems for standing employ patterns of constant activation and are unreactive to changing postural demands. Methods In this work, we developed a closed-loo...

Animals dynamically adapt to varying terrain and small perturbations with remarkable ease. These adaptations arise from complex interactions between the environment and biomechanical and neural components of the animal's body and nervous system. Research into mammalian locomotion has resulted in several neural and neuro-mechanical models, some of w...

We present a serial design process with associated tools to select parameter values for a posture and locomotion controller for simulation of a robot. The controller is constructed from dynamic neuron and synapse models and simulated with the open-source neuromechanical simulator AnimatLab 2. Each joint has a central pattern generator (CPG), whose...

Additive manufacturing with metals is garnering interest for its potential in producing complex parts through near-net shape fabrication, with the potential to significantly reduce waste, cost, and lead-time. Use of the laser hot wire process for additive manufacturing offers relatively superior products when compared with other techniques. However...

A neuromechanical simulation of a planar, bipedal walking robot has been developed. It is constructed as a simplified musculoskeletal system to mimic the biomechanics of the human lower body. The controller consists of a dynamic neural network with central pattern generators (CPGs) entrained by force and movement sensory feedback to generate approp...

A biologically inspired neural control system has been developed that coordinates a tetrapod trotting gait in the sagittal plane. The developed neuromechanical system is used to explore properties of connections in inter-leg and intra-leg coordination. The neural controller is built with biologically based neurons and synapses, and connections are...

A baseline model for testing how afferent muscle feedback affects both timing and activation levels of muscle contractions has been constructed. We present an improved version of the neuromechanical model from our previous work [6]. This updated model has carefully tuned muscles, feedback pathways, and central pattern generators (CPGs). Kinematics...

This work analyzes eigenvalues for a four neuron central pattern generator (CPG) model with slow sodium dynamics. The developed software finds its equilibrium points, characterizes them, and describes the oscillation without running simulations, allowing for rapid system characterization with new parameters. Different regimes have been identified t...

TCERA (Tunable Compliance Energy Return Actuator) is a robotic actuator inspired by properties and behavior of the human knee joint, in that it utilizes antagonistic contraction to vary torsional stiffness and joint angle. The actuator is an electrically activated artificial muscle which uses two constant air-mass pneumatic springs configured antag...

A biologically inspired control system has been developed for coordinating a tetrapod walking gait in the sagittal plane. The controller is built with biologically based neurons and synapses, and connections are based on data from literature where available. It is applied to a simplified, planar biomechanical model of a rat with 14 joints with an a...

� Abstract² A robot is being developed for urban search and rescue missions. USAR Whegs TM implements several new features into Whegs TM robot design. It is the first quadruped Whegs TM robot of this scale. It uses differential steering and the user can rapidly change its running gear to and from tracks and wheel-legs. This is also the first implem...

Animal behavioral, physiological and neurobiological studies are providing a wealth of inspirational data for robot design and control. Several very different biologically inspired mobile robots will be reviewed. A robot called DIGbot is being developed that moves independent of the direction of gravity using Distributed Inward Gripping (DIG) as a...

Animal behavioral, physiological and neurobiological studies are providing a wealth of inspirational data for robot design and control. Several very different biologically inspired mobile robots will be reviewed. A robot called DIGbot is being developed that moves independent of the direction of gravity using Distributed Inward Gripping (DIG) as a...

Successful long-term settlements on the Moon will need a supply of resources such as oxygen and water, yet the process of regularly transporting these resources from Earth would be prohibitively costly and dangerous. One alternative would be an approach using heterogeneous, autonomous robotic teams, which could collect and extract these resources f...

This research developed a robot capable of operating in urban search and rescue conditions. USAR Whegs implements several new features in to Whegs robot design, some more successful than others. It is the first quadruped Whegs robot of this scale. It uses differential steering for control, and is able to switch between tracks and a wheel-leg system...