Research Group Projects and Descriptions

We know from early Roman mosaics that physical rehabilitation and amplification technologies have been used during much of recorded history. Although the goal of constructing such technologies is not new, great scientific and technological hurdles still remain. Even today, permanent assistive devices are viewed by the physically challenged as separate, lifeless mechanisms and not intimate extensions of the human body—structurally, neurologically, and dynamically. The Biomechatronics group seeks to advance technologies that promise to accelerate the merging of body and machine, including device architectures that resemble the body’s own musculoskeletal design, actuator technologies that behave like muscle, and control methodologies that exploit principles of biological movement.

In state-of-the-art commercial prosthetic knees, there is no mechanism or actuator that exploits elasticity in addition to the generation of positive mechanical work (non-conservative motive output). Such behavior is essential to replicate the muscle-like actuation properties of biological joints. Using the biomechanics of the human knee, we are exploring a novel architecture for a powered external knee prosthesis. This prosthesis employs agonist-antagonist actuated series elasticity in order to provide generation of positive mechanical work. The objective of this adaptive powered prosthetic device is to improve gait and metabolic energy consumption of above-knee amputees, on variant terrain conditions.

We are designing a powered hip-knee-ankle orthosis to assist individuals suffering from neuromuscular disorders. In contrast to mechanically passive, commercially available orthoses, we are adding actuation and control to enhance movement of hip, knee, and ankle joints. We motivate our control scheme with kinematic gait data measured from unimpaired humans walking at slow, moderate, and fast speeds. However, instead of simply tracking biological trajectories, our controller enforces a particular whole-body, angular momentum partition (how the angular momentum of individual body segments contributes to total-body angular momentum). In our current work, orthosis hardware systems are being designed and biomimetic controllers are being evaluated using morphologically realistic, humanoid walking simulations.

We are designing an active ankle-foot orthosis for the treatment of ankle pathologies resulting from disease or traumatic injury. Muscle-like actuators are being advanced to control both joint impedance and motive force during inversion and eversion as well as plantar and dorsi flexion movements. In addition to this work, we are developing global orientation sensors to send ankle angle and ground reaction force measurements from the unaffected leg to the controller on the affected side. Using these sensory signals, the actuators move the affected limb to mimic the unaffected side, thereby restoring gait symmetry.

We are developing a control architecture for bipedal locomotion devices such as robots and powered orthotics. Advanced nonlinear control techniques, including feedback linearization, sliding control, and multivariable optimization, are utilized in this control architecture, yielding a highly stable and tunable controller for a highly unstable and nonlinear plant. Tests—using a 3-D, 12-degree-of-freedom humanoid model—include a variety of disturbed initial states and of control goals for the center of mass, swing foot, and other points being controlled. An interesting property of this controller is the emergence of appropriate non-contact limb behavior in response to disturbances. Also, due to its large range of operation, this control architecture can reject significant disturbances more easily than simpler controllers, and requires a less-detailed reference trajectory than simpler controllers. This has the additional benefit of reducing the computational workload of a motion planner in an integrated motion planning and control system. Such control architectures will find use in assistive devices for the elderly and handicapped.

Motivated by applications in rehabilitation and robotics, we are developing methodologies to control muscle-actuated systems via electrical stimulation. As a demonstration of such potential, we are developing centimeter-scale robotic systems that utilize muscle for actuation and glucose as a primary source of fuel. This is an interesting control problem because muscles: a) are mechanical state-dependent actuators; b) exhibit strong nonlinearities; and c) have slow time-varying properties due to fatigue-recuperation, growth-atrophy, and damage-healing cycles. We are investigating a variety of adaptive and robust control techniques to enable us to achieve trajectory tracking, as well as mechanical power-output control under sustained oscillatory conditions. To implement and test our algorithms, we developed an experimental capability that allows us to characterize and control muscle in real time, while imposing a wide variety of dynamical boundary conditions.

This research aims to extract a potentially small set of underlying principles that govern human movement and to apply that set of principles to biomimetic control systems. Using a morphologically realistic human model and kinematic gait data, we find that spin angular momentum in human walking is highly regulated, and that there exists a nonlinear coupling between center of mass transverse forces, center of mass position, and center of pressure location. Using an open loop optimization strategy, we show that biologically realistic leg joint kinematics emerge through the minimization of spin angular momentum and the sum of the joint torques squared. This suggests that both angular momentum and energetic factors are important considerations for biomimetic controllers.

Towards the goal of developing stable humanoid robots and leg prostheses/othoses, we are developing a biologically motivated control system for walking where system angular momentum is explicitly controlled. Using human kinematic walking data, we find that spin angular momentum is highly regulated in walking. In addition, our analysis shows that the distribution of angular momentum throughout the human body, or the angular momentum partition, is invariant with walking speed. Motivated by these biomechanical results, we conduct numerical simulations of walking using a morphologically realistic human model. Our control system searches for joint reference trajectories that minimize the error between the model's angular momentum partition and the biologically determined partition. In order to understand motor control in humans, we are experimenting with biological time delays (order 100 ms) and correlating our simulation results with human behavior.

We are developing a robust, low-power, stable, and lightweight leg orthosis designed to dramatically increase the locomotory endurance of humans. Instead of the biological leg actively stiffening to support body weight throughout each locomotory step, the orthosis, running parallel to the leg, will offer that support, deactivating leg muscles and dramatically lowering metabolic demands. The proposed transportation technology promises to dramatically reduce the human effort required to traverse rough terrains in urban and natural environments.

Alumni Contributor(s): Andrew Valiente

A large percentage of the work done at the knee during normal walking is dissipative. A rotary magnetorheological damper along the knee axis can exert high damping forces with only minimal electrical power. This method has distinct advantages over conventional, fully passive, and modern hydraulic transfemoral prostheses. Biologically realistic control of the MR prosthesis can reduce the metabolic rate of the user and improve biological cosmesis.

People on the autism spectrum face a number of challenges, including motor movement issues that can cause limbs to cease activity. Circumstantial evidence suggests that autonomic nervous system influences related to stress and overload may arise from and contribute to these problems. We propose to allow individuals to monitor several physiological parameters to see if there are patterns that recognize or predict the onset of their individual motor problems. We plan to develop new, wearable technology to treat these problems via the use of tiny, vibrotactile devices carefully placed at the joints. We hypothesize that some methods of touch-feedback and vibration at the joints may enable individuals to recover motor functioning during episodes of intermittent loss. We are also exploring the development of personally controlled devices that facilitate finer motor movement for augmenting communication as needed for assisting in typing or pointing.

The human ankle provides a significant amount of net positive work during the stance period of walking, especially at moderate to fast walking speeds. On the contrary, conventional ankle-foot prostheses are completely passive during stance, and consequently, cannot provide net positive work. Clinical studies indicate that transtibial amputees using conventional prostheses experience many problems during locomotion including a high gait metabolism, a low gait speed, and gait asymmetry. Researchers believe the main cause for the observed locomotion is due to the inability of conventional prostheses to provide net positive work during stance. The objective of this project is to develop a powered ankle-foot prosthesis that is capable of providing net positive work during the stance period of walking. To this end, we investigate the mechanical design and control system architectures for the prosthesis. We also conduct a clinical evaluation of the proposed prosthesis on different amputee participants.

Human walking neuromechanical models show how each muscle works during normal, level-ground walking. They are mainly modeled with clutches and linear springs, and are able to capture dominant normal walking behavior. This suggests us to use a knee-flexor spring for below-knee amputees. We have developed the powered ankle prosthesis, which generates enough force to enable a user to walk "normally." However, amputees still have problems at the knee joint due to the lack of gastrocnemius, which works as a ankle-knee flexor as well as a plantarflexor. We hypothesize that metabolic cost and EMG patterns of an amputee with our powered ankle and virtual gastrocnemius will dramatically improve.

Studies of human walking have been largely centered on developing an accurate model of straight level-ground walking. These models drive humanoid robots and other prosthetic devices. However, more dynamic models of walking involving turns are largely understudied, and few forward dynamics models of human turning exist. It is our goal in this project to understand the critical biomechanical features of turning. We hope to use these insights to develop a neurodynamic model of turning and develop more robust control for humanoid robotics and powered prosthetics.