Telerobotic systems allow a human operator to remotely manipulate an environment. Using telerobo... more Telerobotic systems allow a human operator to remotely manipulate an environment. Using telerobotics, we can remain distant from dangerous or difficult-to-reach locations, or scale our motions and forces to levels beyond normal human abilities. We would like these systems to be capable of the widest possible range of actions, from delicate and gentle to strong and firm, making them more capable tools in the remote environment. Human versatility, in part, comes from our ability to adjust impedance to suit the task we are performing. Humans accomplish this by flexing and relaxing muscles, reorienting the skeletal structure, bracing on nearby objects, and through sensory feedback. In a telerobotic system, the impedance is a combination of the robot impedance, the controllers, position and force scaling, and the human impedance. This multiplicity of contributions limits the operator's ability to affect the overall system behavior directly, ultimately limiting the system's potential abilities. In this research, I have worked to extend the range of telerobotic performance capabilities by incorporating variable impedance actuators and control into the telerobotic system. Their inclusion gives the operator a more direct ability to control the telerobotic impedance and lessens the need for high-bandwidth, transparent controllers. This ultimately lets the operator perform a wider range of tasks. Additionally, the system performance becomes less sensitive to factors such as force feedback level and time delay. In this thesis, I investigate accomplishing impedance control for telemanipulation using variable stiffness actuators and software impedance control. I discuss the need for variable hardware actuators to control short-duration interactions, such as impacts. Based on insights from this work, I design several variable impedance telerobotic control architectures for improved manipulation performance. Results are presented from experiments in one-DOF and multi-DOF, as well as a user study, confirming improved versatile performance and reduced sensitivity to force feedback level. It is my hope that this work will help encourage a design perspective for telerobotic systems which emphasizes the system's versatility and usability over the goal of pure transparency.
Inspired by human physiology, variable impedance actuation has been shown to benefit safety with ... more Inspired by human physiology, variable impedance actuation has been shown to benefit safety with its ability to modulate impact forces. But humans also continually adjust impedance during contact and throughout manipulation tasks. We examine the value and effect of continual impedance variation on quasi-static manipulation. We approach this challenge from the perspective of telerobotics where the operator can explicitly modulate the robotic impedance. Using a three degree of freedom planar teleoperation system we explore two quasi-static tasks: inserting a rigid peg into a tight hole and throwing a switch without overshoot. The work finds that no single impedance can optimally accomplish both tasks. Instead user-controlled impedance variations achieve the desired results, demonstrating the benefits of variable impedance to quasi-static applications in telerobotics.
Variable impedance actuators provide the ability to robustly alter interaction impedances mechani... more Variable impedance actuators provide the ability to robustly alter interaction impedances mechanically, without bandwidth, power, and stability limitations. They can achieve the physical benefits of an elastic transmission and also recover characteristics of traditionally controlled, inelastic motors. We review previously explored benefits of variable impedance actuators for energetic tasks and impact safety. We then focus on benefits in low frequency force interactions. We examine impedance and force dynamic ranges and illustrate how they are significantly increased by physical impedance variation. Theoretical analysis is confirmed by experiments on a 1-DOF testbed with three impedance settings.
Telerobotics fundamentally aims to project human skills into a remote, unstructured environment. ... more Telerobotics fundamentally aims to project human skills into a remote, unstructured environment. A key component of human skills is anticipatory modulation of limb impedances in accordance with task requirements and in expectation of events or disturbances. These adjustments occur continually in human interaction strategies, yet are mostly masked in telerobotics by limited bandwidth controllers and fixed impedance hardware. We propose a telerobotic architecture with user-controlled variable impedance and show a single degree of freedom experimental implementation. The master incorporates a grip force sensor as an additional impedance command channel. Since grip force correlates with the user's own impedance, this input provides an intuitive and natural extension to the regular interface. On the slave, a physically variable clutch actuator is used to adjust both low and high frequency impedance. The additional command channel allows the operator to utilize impedance variation strategies to control impact forces and accomplish varying tasks. These natural interaction strategies are simpler and more robust, leading to superior performance and a telerobot which more effectively represents the operator.
Variable impedance actuation is characterized by the ability to independently set output force an... more Variable impedance actuation is characterized by the ability to independently set output force and output impedance for a robotic device. Adjusting the output impedance in real-time allows a device to better adapt to a variety of tasks, operate in human-like fashion, and support human safety. This paper focuses on a series clutch actuator based on magnetorheological fluid which allows a fast, electrical change of the impedance while maintaining good force tracking. In particular the mechanical clutch can alter the high-frequency impedance, decoupling the motor inertia and thus reducing impact forces. We present the mechanical clutch design and a control system architecture to automatically adjust the fluid magnetization level and leverage the clutch benefits. Experiments verify torque tracking and impact force reduction both in autonomous and telerobotic operation. The actuator was designed and manufactured in collaboration with the Materials Design Institute at Los Alamos National Laboratory, and is tested in a single degree of freedom demonstration.
Telerobotic systems allow a human operator to remotely manipulate an environment. Using telerobo... more Telerobotic systems allow a human operator to remotely manipulate an environment. Using telerobotics, we can remain distant from dangerous or difficult-to-reach locations, or scale our motions and forces to levels beyond normal human abilities. We would like these systems to be capable of the widest possible range of actions, from delicate and gentle to strong and firm, making them more capable tools in the remote environment. Human versatility, in part, comes from our ability to adjust impedance to suit the task we are performing. Humans accomplish this by flexing and relaxing muscles, reorienting the skeletal structure, bracing on nearby objects, and through sensory feedback. In a telerobotic system, the impedance is a combination of the robot impedance, the controllers, position and force scaling, and the human impedance. This multiplicity of contributions limits the operator's ability to affect the overall system behavior directly, ultimately limiting the system's potential abilities. In this research, I have worked to extend the range of telerobotic performance capabilities by incorporating variable impedance actuators and control into the telerobotic system. Their inclusion gives the operator a more direct ability to control the telerobotic impedance and lessens the need for high-bandwidth, transparent controllers. This ultimately lets the operator perform a wider range of tasks. Additionally, the system performance becomes less sensitive to factors such as force feedback level and time delay. In this thesis, I investigate accomplishing impedance control for telemanipulation using variable stiffness actuators and software impedance control. I discuss the need for variable hardware actuators to control short-duration interactions, such as impacts. Based on insights from this work, I design several variable impedance telerobotic control architectures for improved manipulation performance. Results are presented from experiments in one-DOF and multi-DOF, as well as a user study, confirming improved versatile performance and reduced sensitivity to force feedback level. It is my hope that this work will help encourage a design perspective for telerobotic systems which emphasizes the system's versatility and usability over the goal of pure transparency.
Inspired by human physiology, variable impedance actuation has been shown to benefit safety with ... more Inspired by human physiology, variable impedance actuation has been shown to benefit safety with its ability to modulate impact forces. But humans also continually adjust impedance during contact and throughout manipulation tasks. We examine the value and effect of continual impedance variation on quasi-static manipulation. We approach this challenge from the perspective of telerobotics where the operator can explicitly modulate the robotic impedance. Using a three degree of freedom planar teleoperation system we explore two quasi-static tasks: inserting a rigid peg into a tight hole and throwing a switch without overshoot. The work finds that no single impedance can optimally accomplish both tasks. Instead user-controlled impedance variations achieve the desired results, demonstrating the benefits of variable impedance to quasi-static applications in telerobotics.
Variable impedance actuators provide the ability to robustly alter interaction impedances mechani... more Variable impedance actuators provide the ability to robustly alter interaction impedances mechanically, without bandwidth, power, and stability limitations. They can achieve the physical benefits of an elastic transmission and also recover characteristics of traditionally controlled, inelastic motors. We review previously explored benefits of variable impedance actuators for energetic tasks and impact safety. We then focus on benefits in low frequency force interactions. We examine impedance and force dynamic ranges and illustrate how they are significantly increased by physical impedance variation. Theoretical analysis is confirmed by experiments on a 1-DOF testbed with three impedance settings.
Telerobotics fundamentally aims to project human skills into a remote, unstructured environment. ... more Telerobotics fundamentally aims to project human skills into a remote, unstructured environment. A key component of human skills is anticipatory modulation of limb impedances in accordance with task requirements and in expectation of events or disturbances. These adjustments occur continually in human interaction strategies, yet are mostly masked in telerobotics by limited bandwidth controllers and fixed impedance hardware. We propose a telerobotic architecture with user-controlled variable impedance and show a single degree of freedom experimental implementation. The master incorporates a grip force sensor as an additional impedance command channel. Since grip force correlates with the user's own impedance, this input provides an intuitive and natural extension to the regular interface. On the slave, a physically variable clutch actuator is used to adjust both low and high frequency impedance. The additional command channel allows the operator to utilize impedance variation strategies to control impact forces and accomplish varying tasks. These natural interaction strategies are simpler and more robust, leading to superior performance and a telerobot which more effectively represents the operator.
Variable impedance actuation is characterized by the ability to independently set output force an... more Variable impedance actuation is characterized by the ability to independently set output force and output impedance for a robotic device. Adjusting the output impedance in real-time allows a device to better adapt to a variety of tasks, operate in human-like fashion, and support human safety. This paper focuses on a series clutch actuator based on magnetorheological fluid which allows a fast, electrical change of the impedance while maintaining good force tracking. In particular the mechanical clutch can alter the high-frequency impedance, decoupling the motor inertia and thus reducing impact forces. We present the mechanical clutch design and a control system architecture to automatically adjust the fluid magnetization level and leverage the clutch benefits. Experiments verify torque tracking and impact force reduction both in autonomous and telerobotic operation. The actuator was designed and manufactured in collaboration with the Materials Design Institute at Los Alamos National Laboratory, and is tested in a single degree of freedom demonstration.
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Papers by Daniel Walker