Novel infinitely Variable Transmission allowing efficient transmission ratio variations at rest

Recent studies showed that Continuously Variable Transmissions (CVT) and Infinitely Variable Transmissions (IVT) can considerably improve the locomotion efficiency in legged robot. A CVT is a transmission whose ratio can be continuously varied and an IVT is a transmission whose ratio can be continuously varied from positive to negative values. However, efficient use of such transmissions in walking applications requires changing the transmission ratio at a minimal energy cost, even at rest, i.e. when the input shaft is not rotating. This contribution proposes a novel CVT and IVT principle which can achieve such ratio variations at rest. The presented CVT is a modified planetary gear, whose planets are conical and mounted on inclined shafts, and whose ring is made of contiguous diabolo-shaped rollers. This configuration enables the control of the transmission ratio by adjusting the point of contact between the cones and rollers that comprise the ring. A traditional planetary gear system can be added to the CVT to form an IVT

MASSART-PIÉRARD, Françoise. La langue : Vecteur d'organisation internationale. Louvain-la-Neuve, Éditions d'Acadie, 1995, 194 v.

Gait and balance training is an essential ingredient for locomotor rehabilitation of patients with neurological impairments. Robotic overhead support systems may help these patients train, for example by relieving them of part of their body weight. However, there are only very few systems that provide support during overground gait, and these suffer from limited degrees of freedom and/or undesired interaction forces due to uncompensated robot dynamics, namely inertia. Here, we suggest a novel mechanical concept that is based on cable robot technology and that allows three-dimensional gait training while reducing apparent robot dynamics to a minimum. The solution does not suffer from the conventional drawback of cable robots, which is a limited workspace. Instead, displaceable deflection units follow the human subject above a large walking area. These deflection units are not actuated, instead they are implicitly displaced by means of the forces in the cables they deflect. This leads to an underactuated design, because the deflection units cannot be moved arbitrarily. However, the design still allows accurate control of a three-dimensional force vector acting on a human subject during gait. We describe the mechanical concept, the control concept, and we show first experimental results obtained with the device, including the force control performance during robot-supported overground gait of five human subjects without motor impairments

Design and study of a new continuously variable transmission with potential application to lower limb prosthesis

Series elastic actuators (SEA) are very popular in rehabilitation robotics. Among other advantages, elastic elements between the actuator and the load permit to store and release energy during the task completion, such that the energy balance is improved and the motor power peak is decreased. In rhythmic tasks like walking, this reduces to design the spring stiffness such that it works at resonance. To comply with different gaits and cadences, it is therefore necessary to design Variable Stiffness Actuators (VSA). The first part of the thesis investigates lower limb prostheses concepts. A particular concept of VSA is applied to active transtibial and transfemoral prostheses. The model of an original actuation concept is reported, relying on the combination of a power motor, a compliant element (a spring), a mechanical differential, and Continuously Variable Transmissions (i.e. a mechanical transmission whose ratio can be continuously varied). It allows to manage the mechanical power flows through the device in both directions (i.e. when energy should be produced or absorbed by the knee and/or ankle), so that the power motor does not face the sharp load power fluctuations. A preliminary approach to synthesize a closed-loop controller for this device, and simulation results of this closed-loop behavior are reported. These results illustrate the capacity of this actuation principle to filter the load power profile, and further highlight the necessity to maximize the mechanical efficiency of each part of this actuation scheme. The second part investigates a new kind of Continuously Variable Transmissions (CVT) principle which can achieve ratio variations at rest, i.e. with zero velocity of the shaft. This feature is mandatory for the concept developed in the first part. The presented design is a modified planetary gear, whose planets are conical and mounted on inclined shafts, and ring is made of contiguous diabolo-shaped rollers. This configuration allows moving the contact point radius on the cones and then modifying the transmission ratio. Importantly, this movement relies on rolling and not on sliding, such that it requires virtually no actuation energy. Two prototypes have been designed and experiments were conducted and showed that the CVT transmission ratio can indeed continuously vary by keeping an efficiency between 70,% and 90,%. This proved the possibility to embed the design in a transfemoral prosthesis. In sum, this thesis deals about a new design of Continuously Variable Transmission allowing ratio variations at rest. This design aimed to be integrated in a new actuation system for transfemoral prosthesis.(FSA - Sciences de l'ingénieur) -- UCL, 201

Continuously Variable Planetary Transmission

Transmission (10) comprising a sun (1), a planet carrier (4), a first planet (21) having a first axis of revolution (41) and a first lateral surface (31) that is nonparallel to it, and a ring (3). When there is a relative movement between said first planet (21) and said ring (3) for a constant transmission ratio, a force of power transmission, Formula (I), between said first planet (21) and said ring (3) defines a plane (55). The transmission (10) comprises rolling means (15) for allowing a movement of translation between said ring (3) and said first planet (21) along a direction of translation (65) that is perpendicular to said plane (55) such that different transmission ratios can be obtained, corresponding to different coupling points (8) between said first lateral surface (31) and said ring (3) along said direction of translation (65)

Modeling and control of a transfemoral prosthesis embedding two infinitely variable transmissions

In this paper, we report the model of an original actuation concept for a transfemoral prosthesis, relying on the combination of a single power motor, a compliant element (a spring), a mechanical differential, and two infinitely variable transmissions. It allows to manage the mechanical power flows through the device in both directions (i.e. when energy should be produced or dissipated by the knee and ankle), so that the power motor does not face the sharp load power fluctuations. The paper further reports a preliminary approach to synthesize a closed-loop controller for this device, and simulation results of this closed-loop behavior for three locomotion tasks: level-ground walking and stair ascent/descent. These results illustrate the capacity of this actuation principle to filter the load power profile, and further highlight the necessity to maximize the mechanical efficiency of each part of this actuation scheme

Variable Stiffness Actuator Based on Infinitely Variable Transmission: Application to an Active Ankle Prosthesis

Abstract — Series elastic actuators are very popular in rehabilitation robotics. Among other advantages, elastic elements between the actuator and the load permit to store and release energy during the task completion. To comply with different gaits and cadences, it is necessary to modify the stiffness and thus to design Variable Stiffness Actuators (VSA). This contribution proposes to apply a particular concept of VSA to an active ankle prosthesis. We establish that a promising approach is simply to control the amount of energy stored in the elastic element. This contribution surveys a paper recently accepted to the IROS conference 2012 [1]. I

[Downloaded 2013/05/15 at 12:19:52] Variable Stiffness Actuator Applied to an Active Ankle Prosthesis: Principle, Energy-Efficiency, and Control

Series elastic actuators are very popular in rehabilitation robotics. Among other advantages, elastic elements between the actuator and the load permit to store and release energy during the task completion, such that the energy balance is improved and the motor power peak is decreased. In rhythmic tasks like walking, this reduces to design the spring stiffness such that it works at resonance. To comply with different gaits and cadences, it is therefore necessary to design Variable Stiffness Actuators (VSA). This paper proposes three contributions: (i) we apply a particular concept of VSA to an active ankle prosthesis; (ii) we discuss the relevance of using VSA to change the stiffness also within the gait cycle; and (iii) we elaborate some control strategies for this device. Our guideline is to track a mechanical design and a controller maximizing energy efficiency. We establish that a promising approach is simply to control the amount of energy stored in the elastic element. Référence bibliographiqu

Adaptive Position Anticipation in a Support Robot for Overground Gait Training

Rehabilitation robots being developed nowadays rely on force and/or impedance control. The simplest mode of force control is when the robot has to be transparent. This contribution proposes a method to improve transparency on a support robot for overground training and surveys a paper presented to the ICORR conference 201

Variable Stiffness Actuator Based on Infinitely Variable Transmission: Application to an Active Ankle Prosthesis

Series elastic actuators are very popular in rehabilitation robotics. Among other advantages, elastic elements between the actuator and the load permit to store and release energy during the task completion. To comply with different gaits and cadences, it is necessary to modify the stiffness and thus to design Variable Stiffness Actuators (VSA). This contribution proposes to apply a particular concept of VSA to an active ankle prosthesis. We establish that a promising approach is simply to control the amount of energy stored in the elastic element. This contribution surveys a paper recently accepted to the IROS conference 201

Variable Stiffness Actuator applied to an active ankle prosthesis: Principle, energy-efficiency, and control

Series elastic actuators are very popular in rehabilitation robotics. Among other advantages, elastic elements between the actuator and the load permit to store and release energy during the task completion, such that the energy balance is improved and the motor power peak is decreased. In rhythmic tasks like walking, this reduces to design the spring stiffness such that it works at resonance. To comply with different gaits and cadences, it is therefore necessary to design Variable Stiffness Actuators (VSA). This paper proposes three contributions: (i) we apply a particular concept of VSA to an active ankle prosthesis; (ii) we discuss the relevance of using VSA to change the stiffness also within the gait cycle; and (iii) we elaborate some control strategies for this device. Our guideline is to track a mechanical design and a controller maximizing energy efficiency. We establish that a promising approach is simply to control the amount of energy stored in the elastic element