Matching Items (6)

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Environment Dependent Modulation of Ankle Stiffness During Walking

Description

Advancements in the field of design and control of lower extremity robotics requires a comprehensive understanding of the underlying mechanics of the human ankle. The ankle joint acts as an

Advancements in the field of design and control of lower extremity robotics requires a comprehensive understanding of the underlying mechanics of the human ankle. The ankle joint acts as an essential interface between the neuromuscular system of the body and the physical world, especially during locomotion. This paper investigates how the modulation of ankle stiffness is altered throughout the stance phase of the gait cycle depending on the environment the ankle is interacting with. Ten young healthy subjects with no neurological impairments or history of ankle injury were tested by walking over a robotic platform which collected torque and position data. The platform performed a perturbation on the ankle at 20%, 40%, and 60% of their stance phase in order to estimate ankle stiffness and evaluate if the environment plays a role on its modulation. The platform provided either a rigid environment or a compliant environment in which it was compliant and deflected according to the torque applied to the platform. Subjects adapted in different ways to achieve balance in the different environments. When comparing the environments, subjects modulated their stiffness to either increase, decrease, or remain the same. Notably, stiffness as well as the subjects’ center of pressure was found to increase with time as they transitioned from late loading to terminal stance (heel strike to toe-off) regardless of environmental conditions. This allowed for a model of ankle stiffness to be developed as a function of center of pressure, independent of whether a subject is walking on the rigid or compliant environment. The modulation of stiffness parameters characterized in this study can be used in the design and control of lower extremity robotics which focus on accurate biomimicry of the healthy human ankle. The stiffness characteristics can also be used to help identify particular ankle impairments and to design proper treatment for individuals such as those who have suffered from a stroke or MS. Changing environments is where a majority of tripping incidents occur, which can lead to significant injuries. For this reason, studying healthy ankle behavior in a variety of environments is of particular interest.

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Created

Date Created
  • 2020-05

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Variable Damping Control of the Robotic Ankle Joint to Improve Trade-off between Agility and Stability

Description

This paper presents a variable damping controller that can be implemented into wearable and exoskeleton robots. The variable damping controller functions by providing different levels of robotic damping from negative

This paper presents a variable damping controller that can be implemented into wearable and exoskeleton robots. The variable damping controller functions by providing different levels of robotic damping from negative to positive to the coupled human-robot system. The wearable ankle robot was used to test this control strategy in the different directions of motion. The range of damping applied was selected based on the known inherent damping of the human ankle, ensuring that the coupled system became positively damped, and therefore stable. Human experiments were performed to understand and quantify the effects of the variable damping controller on the human user. Within the study, the human subjects performed a target reaching exercise while the ankle robot provided the system with constant positive, constant negative, or variable damping. These three damping conditions could then be compared to analyze the performance of the system. The following performance measures were selected: maximum speed to quantify agility, maximum overshoot to quantify stability, and muscle activation to quantify effort required by the human user. Maximum speed was found to be statistically the same in the variable damping controller and the negative damping condition and to be increased from positive damping controller to variable damping condition by 57.9%, demonstrating the agility of the system. Maximum overshoot was found to significantly decrease overshoot from the negative damping condition to the variable damping controller by 39.6%, demonstrating an improvement in system stability with the variable damping controller. Muscle activation results showed that the variable damping controller required less effort than the positive damping condition, evidenced by the decreased muscle activation of 23.8%. Overall, the study demonstrated that a variable damping controller can balance the trade-off between agility and stability in human-robot interactions and therefore has many practical implications.

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Created

Date Created
  • 2019-12

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[Detection of Heel-off Initiation Based on the Relationship Between Ground Reaction Forces and Surface Electromyography: Heel-toe, Heel-toe, a Story]

Description

The global population over the age of 60 is estimated to rise to 23% by 2050 only increase the prevalence of functional neurological disorders and stroke. Increase in cases of

The global population over the age of 60 is estimated to rise to 23% by 2050 only increase the prevalence of functional neurological disorders and stroke. Increase in cases of functional neurological disorders and strokes will place a greater burden on the healthcare industry, specifically physical therapy. Physical therapy is vital for a patient’s recovery of motor function which is time demanding and taxing on the physical therapist. Wearable robotics have been proven to improve functional outcomes in gait rehabilitation by providing controlled high dosage and high-intensity training. Accurate control strategies for assistive robotic exoskeletons are vital for repetitive high precisions assistance for cerebral plasticity to occur.

This thesis presents a preliminary determination and design of a control algorithm for an assistive ankle device developed by the ASU RISE Laboratory. The assistive ankle device functions by compressing a spring upon heel strike during gait, remaining compressed during mid-stance and then releasing upon initiation of heel-off. The relationship between surface electromyography and ground reactions forces were used for identification of user-initiated heel-off. The muscle activation of the tibialis anterior combined with the ground reaction forces of the heel pressure sensor generated potential features that will be utilized in the revised control algorithm for the assistive ankle device. Work on this project must proceed in order to test and validate the revised control algorithm to determine its accuracy and precision.

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Date Created
  • 2019-05

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Nonlinear phase based control to generate and assist oscillatory motion with wearable robotics

Description

Wearable robotics is a growing sector in the robotics industry, they can increase the productivity of workers and soldiers and can restore some of the lost function to people with

Wearable robotics is a growing sector in the robotics industry, they can increase the productivity of workers and soldiers and can restore some of the lost function to people with disabilities. Wearable robots should be comfortable, easy to use, and intuitive. Robust control methods are needed for wearable robots that assist periodic motion.

This dissertation studies a phase based oscillator constructed with a second order dynamic system and a forcing function based on the phase angle of the system. This produces a bounded control signal that can alter the damping and stiffens properties of the dynamic system. It is shown analytically and experimentally that it is stable and robust. It can handle perturbations remarkably well. The forcing function uses the states of the system to produces stable oscillations. Also, this work shows the use of the phase based oscillator in wearable robots to assist periodic human motion focusing on assisting the hip motion. One of the main problems to assist periodic motion properly is to determine the frequency of the signal. The phase oscillator eliminates this problem because the signal always has the correct frequency. The input requires the position and velocity of the system. Additionally, the simplicity of the controller allows for simple implementation.

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Created

Date Created
  • 2016

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A Study on the Analysis of Treadmill Perturbation Data for the Design of Active Ankle Foot Orthosis to Prevent Falls and Gait Rehabilitation

Description

According to the Center for Disease Control and Prevention report around 29,668 United States residents aged greater than 65 years had died as a result of a fall in 2016.

According to the Center for Disease Control and Prevention report around 29,668 United States residents aged greater than 65 years had died as a result of a fall in 2016. Other injuries like wrist fractures, hip fractures, and head injuries occur as a result of a fall. Certain groups of people are more prone to experience falls than others, one of which being individuals with stroke. The two most common issues with individuals with strokes are ankle weakness and foot drop, both of which contribute to falls. To mitigate this issue, the most popular clinical remedy given to these users is thermoplastic Ankle Foot Orthosis. These AFO's help improving gait velocity, stride length, and cadence. However, studies have shown that a continuous restraint on the ankle harms the compensatory stepping response and forward propulsion. It has been shown in previous studies that compensatory stepping and forward propulsion are crucial for the user's ability to recover from postural perturbations. Hence, there is a need for active devices that can supply a plantarflexion during the push-off and dorsiflexion during the swing phase of gait. Although advancements in the orthotic research have shown major improvements in supporting the ankle joint for rehabilitation, there is a lack of available active devices that can help impaired users in daily activities. In this study, our primary focus is to build an unobtrusive, cost-effective, and easy to wear active device for gait rehabilitation and fall prevention in individuals who are at risk. The device will be using a double-acting cylinder that can be easily incorporated into the user's footwear using a novel custom-designed powered ankle brace. The device will use Inertial Measurement Units to measure kinematic parameters of the lower body and a custom control algorithm to actuate the device based on the measurements. The study can be used to advance the field of gait assistance, rehabilitation, and potentially fall prevention of individuals with lower-limb impairments through the use of Active Ankle Foot Orthosis.

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Created

Date Created
  • 2020

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Human Activity Recognition and Control of Wearable Robots

Description

Wearable robotics has gained huge popularity in recent years due to its wide applications in rehabilitation, military, and industrial fields. The weakness of the skeletal muscles in the aging population

Wearable robotics has gained huge popularity in recent years due to its wide applications in rehabilitation, military, and industrial fields. The weakness of the skeletal muscles in the aging population and neurological injuries such as stroke and spinal cord injuries seriously limit the abilities of these individuals to perform daily activities. Therefore, there is an increasing attention in the development of wearable robots to assist the elderly and patients with disabilities for motion assistance and rehabilitation. In military and industrial sectors, wearable robots can increase the productivity of workers and soldiers. It is important for the wearable robots to maintain smooth interaction with the user while evolving in complex environments with minimum effort from the user. Therefore, the recognition of the user's activities such as walking or jogging in real time becomes essential to provide appropriate assistance based on the activity.

This dissertation proposes two real-time human activity recognition algorithms intelligent fuzzy inference (IFI) algorithm and Amplitude omega ($A \omega$) algorithm to identify the human activities, i.e., stationary and locomotion activities. The IFI algorithm uses knee angle and ground contact forces (GCFs) measurements from four inertial measurement units (IMUs) and a pair of smart shoes. Whereas, the $A \omega$ algorithm is based on thigh angle measurements from a single IMU.

This dissertation also attempts to address the problem of online tuning of virtual impedance for an assistive robot based on real-time gait and activity measurement data to personalize the assistance for different users. An automatic impedance tuning (AIT) approach is presented for a knee assistive device (KAD) in which the IFI algorithm is used for real-time activity measurements. This dissertation also proposes an adaptive oscillator method known as amplitude omega adaptive oscillator ($A\omega AO$) method for HeSA (hip exoskeleton for superior augmentation) to provide bilateral hip assistance during human locomotion activities. The $A \omega$ algorithm is integrated into the adaptive oscillator method to make the approach robust for different locomotion activities. Experiments are performed on healthy subjects to validate the efficacy of the human activities recognition algorithms and control strategies proposed in this dissertation. Both the activity recognition algorithms exhibited higher classification accuracy with less update time. The results of AIT demonstrated that the KAD assistive torque was smoother and EMG signal of Vastus Medialis is reduced, compared to constant impedance and finite state machine approaches. The $A\omega AO$ method showed real-time learning of the locomotion activities signals for three healthy subjects while wearing HeSA. To understand the influence of the assistive devices on the inherent dynamic gait stability of the human, stability analysis is performed. For this, the stability metrics derived from dynamical systems theory are used to evaluate unilateral knee assistance applied to the healthy participants.

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Created

Date Created
  • 2018