AZIMUT-3 is an omnidirectional non-holonomic (or pseudo-omnidirectional) robotic platform intended for safe human-robot interaction. In its wheeled configuration, shown in Fig. 1, AZIMUT-3 uses eight actuators for loc...
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AZIMUT-3 is an omnidirectional non-holonomic (or pseudo-omnidirectional) robotic platform intended for safe human-robot interaction. In its wheeled configuration, shown in Fig. 1, AZIMUT-3 uses eight actuators for locomotion: four for propulsion and four for steering the wheels, which can rotate 180 degrees around their steering axis. Propulsion is done using standard DC brushless motors (Bayside K064050-3Y) with optical encoders (US Digital E4-300-157-HUB, 0.3 deg of resolution), capable of reaching 1.47 m/s. The platform uses steerable wheels motorized using differential elastic actuators (DEA), which provide compliance, safety and torque control capabilities. AZIMUT-3's hardware architecture consists of distributed modules for sensing and low-level control, communicating with each other through a 1 Mbps CAN bus. A Mini-ITX computer equipped with a 2.0 GHz Core 2 duo processor running Linux with real-time patches (RT-PREEMPT) is used on-board for high-level control modules. Nickel-metal hydride batteries provide power to the platform for up to 3 hours of autonomy. A passive vertical suspension mechanism (Rosta springs) is used to connect the wheels to AZIMUT-3's chassis, allowing them to keep contact with the ground on uneven surfaces. The platform has a 34 kg payload capacity and weights 35 kg.
Robots are usually built using stiff actuators that can provide impressive motion performances. However, they struggle to control the force, they do not handle collisions graciously and are generally bad at interactin...
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Robots are usually built using stiff actuators that can provide impressive motion performances. However, they struggle to control the force, they do not handle collisions graciously and are generally bad at interacting significantly with partially unknown or kinematically constrained environments. One solution is to add a force sensor in the closed-loop control of backdrivable actuators [1], but this is limited in terms of stability, safety and robustness [2] [3]. One of the foremost initiatives using this method was undertaken by the German Aerospace Center (DLR) and resulted in three generations of extensively optimized lightweight robotic arms [4] that can physically interact with people. Performances are impressive but robustness is still an issue.
For complex robotic tasks (e.g., manipulation, locomotion), the lack of knowledge of precise interaction models, the difficulties to precisely measure the task associated physical quantities (e.g., position of contact...
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For complex robotic tasks (e.g., manipulation, locomotion), the lack of knowledge of precise interaction models, the difficulties to precisely measure the task associated physical quantities (e.g., position of contact points, interaction forces) in real-time, the finite sampling time of digital control loops and the non-collocation of sensors and transducers have negative effects on performance and stability of robots when using simple force or simple movement controllers. To cope with these issues, a new compact design for high performance actuators specifically adapted for integration in robotic mechanisms is presented. This design makes use of a mechanical differential as its central element. Results shown that differential coupling between an intrinsically high impedance transducer and an intrinsically low impedance mechanical spring provides the same benefits as serial coupling, but in a more compact and simple design. This new actuator, named Differential Elastic Actuator (DEA), provides interesting design implementations, especially for rotational actuators used for mobile robot locomotion.
The most common ground locomotion method to make a mobile robot move is to use two-wheel drive with differential steering and a rear balancing caster. Controlling the two motors independently makes the robot non-holon...
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The most common ground locomotion method to make a mobile robot move is to use two-wheel drive with differential steering and a rear balancing caster. Controlling the two motors independently makes the robot non-holonomic in its motion. Such robots can work well indoor on flat surfaces and in environments adapted for wheelchairs. But the benefit of providing mobility to a robot directly relies on its locomotion capability, for handling different types of terrains (indoors or outdoors) and situations such as moving slowly or rapidly, with or without the presence of moving objects (living or not), climbing over objects and potentially having to deal with hazardous conditions. It is with this objective in mind that we designed AZIMUT. AZIMUT is a legged tracked wheeled robot capable of changing the orientation of its four articulations. Each articulation has three degrees of freedom (DOF): it can rotate 360deg around its point of attachment to the chassis, can change its orientation over 180deg, and rotate to propulse the robot.
This video shows the functionalities of a 3 serial DOF robotic arm. Each DOF is actuated with a patent pending differential elastic actuator (DEA) [1,2]. Compared to the abundantly studied series elastic actuator [3,4...
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ISBN:
(纸本)9781424420575
This video shows the functionalities of a 3 serial DOF robotic arm. Each DOF is actuated with a patent pending differential elastic actuator (DEA) [1,2]. Compared to the abundantly studied series elastic actuator [3,4], DEA uses a differential coupling between a high impedance mechanical speed source and a low impedance mechanical spring. Possible implementations of a mechanical differential include the use of a standard gearbox, harmonic drive, cycloidal gearbox, bar mechanism, cable mechanism and all other mechanism that implement a differential function between three mechanical ports. For the implementation reported in this video, we used a harmonic drive for a very compact design. A passive torsion spring (thus the name elastic), with a known impedance characteristic corresponding to the spring stiffness, is used, with an electrical DC brushless motor. A non-turning sensor connected in series with the spring measures the torque output of the actuator.
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