Toward Unified Control of a Powered Prosthetic Leg: A Simulation Study

Quintero, David; Martin, Anne E.; Gregg, Robert D.

doi:10.1109/tcst.2016.2643566

Cited by 38 publications

(29 citation statements)

References 37 publications

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“…The virtual constraints define joint angles as polynomial functions of a perfectly linear phase variable [16]. Thus, nonlinear regions in the phase trajectory will cause excessively slow or fast progression through the joint patterns [11]. …”

Section: Methodsmentioning

confidence: 99%

“…The horizontal hip position served as a phase variable in separate controllers for the stance and swing periods (i.e., two finite states for the gait cycle) in the simulations of [10]. Because the hip position is monotonic over the entire gait cycle, this “unified” phase variable enabled a single controller in the prosthetic leg simulations of [11]. Piecewise monotonic phase variables like the global hip angle can separately control the stance and swing periods [12] or be converted into unified phase variables during rhythmic motion [13], [14].…”

Section: Introductionmentioning

confidence: 99%

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Piecewise and unified phase variables in the control of a powered prosthetic leg

Villarreal¹,

Quintero²,

Gregg

2017

2017 International Conference on Rehabilitation Robotics (ICORR)

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Many control methods have been proposed for powered prosthetic legs, ranging from finite state machines that switch between discrete phases of gait to unified controllers that have a continuous sense of phase. In particular, recent work has shown that a mechanical phase variable can parameterize the entire gait cycle for controlling a prosthetic leg during steady rhythmic locomotion. However, the unified approach does not provide voluntary control over non-rhythmic motions like stepping forward and back. In this paper we present a phasing algorithm that uses the amputee’s hip angle to control both rhythmic and non-rhythmic motion through two modes: 1) a piecewise (PW) function that provides users voluntary control over stance and swing in a piecewise manner, and 2) a unified function that continuously synchronizes the motion of the prosthetic leg with the amputee user at different walking speeds. The two phase variable approaches are compared in experiments with a powered knee-ankle prosthesis used by an above-knee amputee subject.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Piecewise and unified phase variables in the control of a powered prosthetic leg

Villarreal¹,

Quintero²,

Gregg

2017

2017 International Conference on Rehabilitation Robotics (ICORR)

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“…Identifying a sufficiently accurate model of the prosthetic leg is very difficult, and measuring interaction forces requires expensive multi-axis load cells. Therefore, we utilize a model-free torque control method in this application, specifically output PD control [20], [25]. …”

Section: Control Methodsmentioning

confidence: 99%

“…In particular, virtual constraints defined with the Discrete Fourier Transform (DFT) encapsulate the property of periodicity [19], which respects the repetitive nature of the gait cycle. The conceptual design of DFT virtual constraints was studied in simulations of an amputee biped model in [20], demonstrating that the unified controller can produce stable walking across various walking speeds.…”

Section: Introductionmentioning

confidence: 99%

Preliminary experiments with a unified controller for a powered knee-ankle prosthetic leg across walking speeds

Quintero

Villarreal

Gregg

2016

2016 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS)

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This paper presents the experimental validation of a novel control strategy that unifies the entire gait cycle of a powered knee-ankle prosthetic leg without the need to switch between controllers for different periods of gait. Current control methods divide the gait cycle into several sequential periods each with independent controllers, resulting in many patient-specific control parameters and switching rules that must be tuned for a specific walking speed. The single controller presented is speed-invariant with a minimal number of control parameters to be tuned. A single, periodic virtual constraint is derived that exactly characterizes the desired actuated joint motion as a function of a mechanical phase variable across walking cycles. A single sensor was used to compute a phase variable related to the residual thigh angle’s phase plane, which was recently shown to robustly represent the phase of non-steady human gait. This phase variable allows the prosthesis to synchronize naturally with the human user for intuitive, biomimetic behavior. A custom powered knee-ankle prosthesis was designed and built to implement the control strategy and validate its performance. A human subject experiment was conducted across multiple walking speeds (1 to 3 miles/hour) in a continuous sequence with the single phase-based controller, demonstrating its adaptability to the user’s intended speed.

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“…While details are not provided here, the simulation is able to walk at a wide range of speeds and with varying degrees of biomimicry. As a result, prosthesis controllers can be designed systematically, either via optimization [23] or by systematically transforming known joint angle trajectories into virtual constraints [49]. …”

Section: Simulationmentioning

confidence: 99%

Stable, Robust Hybrid Zero Dynamics Control of Powered Lower-Limb Prostheses

Martin

Gregg²

2017

IEEE Trans. Automat. Contr.

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To improve the quality of life for lower-limb amputees, powered prostheses are being developed. Advanced control schemes from the field of bipedal robots, such as hybrid zero dynamics (HZD), may provide great performance. HZD-based control specifies the motion of the actuated joints using output functions to be zeroed, and the required torques are calculated using input-output linearization. For one-step periodic gaits, there is an analytic metric of stability. To apply HZD-based control on a powered prosthesis, several modifications must be made. Because the prosthesis and amputee are only connected via the socket, the prosthesis controller does not have access to the full state of the biped, which decentralizes the form of the input-output linearization. The differences between the amputated and contralateral sides result in a two-step periodic gait, which requires the orbital stability metric to be extended. In addition, because human gait is variable, the prosthesis controller must be robust to continuous moderate perturbations. This robustness is proved using local input-to-state stability and demonstrated with simulations of an above-knee amputee model.

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Toward Unified Control of a Powered Prosthetic Leg: A Simulation Study

Cited by 38 publications

References 37 publications

Piecewise and unified phase variables in the control of a powered prosthetic leg

Piecewise and unified phase variables in the control of a powered prosthetic leg

Preliminary experiments with a unified controller for a powered knee-ankle prosthetic leg across walking speeds

Stable, Robust Hybrid Zero Dynamics Control of Powered Lower-Limb Prostheses

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