Increasing energy efficiency of high-speed parallel robots by using variable stiffness springs and optimal motion generation

International audienceThe classical approach to decrease the energy consumption of high-speed robots is by lowering the moving elements mass in order to have a lightweight structure. Even if this allows reducing the energy consumed, the lightweight architecture affects the robot stiffness, worsening the accuracy of the mechanism. Recently, variable stiffness actuators (VSAs) have been used in order to reduce the energy consumption of high-speed pick-and-place robots. The idea is to smartly tune online the stiffness of VSA springs so that the robot is put in near a resonance mode, thus considerably decreasing the energy consumption during fast pseudo-periodic pick-and-place motions. However, the serial configuration of springs and motors in the VSA leads to uncontrolled robot deflections at high-speeds and, thus, to a poor positioning accuracy of its end-effector. In order to avoid these drawbacks and to increase the energy efficiency while ensuring the accuracy, this paper proposes the use of parallel arrangement of variable stiffness springs (VSS) and motors, combined with an energy-based optimal trajectory planner. The VSS are used as energy storage for carrying out the reduction of the energy consumption and their parallel configuration with the motors ensure the load balancing at high-speed without losing the accuracy of the robot. Simulations of the suggested approach on a five-bar mechanism are performed and show the increase on energy efficiency. 1 INTRODUCTION It is well-known that in industrial applications, such as high-speed pick-and-place operations, parallel robots are widely used [1, 2]. Repeatability and accuracy are typically the most important criteria to measure their performance. Nevertheless, the design trends to operate at high speeds are shifting to the design of robots with lightweight architectures [3] in order to decrease the energy consumed by the motors, and measure as well the robot performance based on its energy efficiency [4]. For slow motions, gravity-balancing techniques [5-8] have been proposed in order to compensate the input efforts required to move the links of a pick-and-place robot, and thus to avoid consuming energy. Even if these methods have shown their effectiveness at slow speeds, it is not the case for high-speed operations in which the inertial effects are preponderant. A first solution introduced the series elastic actuators (SEAs) [9] to cope with the energy storage issues. The SEAs are compliant actua-tors composed by a motor which is linked to a spring in series that serves as energy storage, and whose stiffness is set by the spring constant. SEAs were first used to absorb contact shocks and to reduce the peak forces due to the impacts in bipedal walking robots [10]. The limitation of the SEAs is that the stiffness is fixed and cannot be altered during motion, thus limiting the level of compliance to adapt for different tasks. Therefore, a recent second solution proposed the use of variable stiffness actuators (VSAs) [11-13] to handle with energy storage issues. VSAs co

Constraint Singularity-Free Design of the IRSBot-2

International audienceThis paper deals with the constraint analysis of a novel two-degree-of-freedom (DOF) spatial translational parallel robot for high-speed applications named the IRSBot-2 (acronym for IRCCyN Spatial Robot with 2 DOF). Unlike most two-DOF robots dedicated to planar translational motions this robot has two spatial kinematic chains that provide a very good intrinsic stiffness. First, the robot architecture is presented and its constraint singularity conditions are given. Then, its constraint singularities are analyzed in its parameter space based on a cylindrical algebraic decomposition. Finally, a deep analysis is carried out in order to determine the sets of design parameters of the IRSBot-2 that prevent it from reaching any constraint singularity. To the best of our knowledge, such an analysis is performed for the first time

Miniaturized modular manipulator design for high precision assembly and manipulation tasks

In this paper, design and control issues for the development of miniaturized manipulators which are aimed to be used in high precision assembly and manipulation tasks are presented. The developed manipulators are size adapted devices, miniaturized versions of conventional robots based on well-known kinematic structures. 3 degrees of freedom (DOF) delta robot and a 2 DOF pantograph mechanism enhanced with a rotational axis at the tip and a Z axis actuating the whole mechanism are given as examples of study. These parallel mechanisms are designed and developed to be used in modular assembly systems for the realization of high precision assembly and manipulation tasks. In that sense, modularity is addressed as an important design consideration. The design procedures are given in details in order to provide solutions for miniaturization and experimental results are given to show the achieved performances

Rapid inversion: running animals and robots swing like a pendulum under ledges.

Escaping from predators often demands that animals rapidly negotiate complex environments. The smallest animals attain relatively fast speeds with high frequency leg cycling, wing flapping or body undulations, but absolute speeds are slow compared to larger animals. Instead, small animals benefit from the advantages of enhanced maneuverability in part due to scaling. Here, we report a novel behavior in small, legged runners that may facilitate their escape by disappearance from predators. We video recorded cockroaches and geckos rapidly running up an incline toward a ledge, digitized their motion and created a simple model to generalize the behavior. Both species ran rapidly at 12-15 body lengths-per-second toward the ledge without braking, dove off the ledge, attached their feet by claws like a grappling hook, and used a pendulum-like motion that can exceed one meter-per-second to swing around to an inverted position under the ledge, out of sight. We discovered geckos in Southeast Asia can execute this escape behavior in the field. Quantification of these acrobatic behaviors provides biological inspiration toward the design of small, highly mobile search-and-rescue robots that can assist us during natural and human-made disasters. We report the first steps toward this new capability in a small, hexapedal robot

Using a 3DOF Parallel Robot and a Spherical Bat to hit a Ping-Pong Ball

Playing the game of Ping-Pong is a challenge to human abilities since it requires developing skills, such as fast reaction capabilities, precision of movement and high speed mental responses. These processes include the utilization of seven DOF of the human arm, and translational movements through the legs, torso, and other extremities of the body, which are used for developing different game strategies or simply imposing movements that affect the ball such as spinning movements. Computationally, Ping-Pong requires a huge quantity of joints and visual information to be processed and analysed, something which really represents a challenge for a robot. In addition, in order for a robot to develop the task mechanically, it requires a large and dexterous workspace, and good dynamic capacities. Although there are commercial robots that are able to play Ping-Pong, the game is still an open task, where there are problems to be solved and simplified. All robotic Ping-Pong players cited in the bibliography used at least four DOF to hit the ball. In this paper, a spherical bat mounted on a 3-DOF parallel robot is proposed. The spherical bat is used to drive the trajectory of a Ping-Pong ball.Fil: Trasloheros, Alberto. Universidad Aeronáutica de Querétaro; MéxicoFil: Sebastián, José María. Universidad Politécnica de Madrid; España. Consejo Superior de Investigaciones Científicas; EspañaFil: Torrijos, Jesús. Consejo Superior de Investigaciones Científicas; España. Universidad Politécnica de Madrid; EspañaFil: Carelli Albarracin, Ricardo Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Automática. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Automática; ArgentinaFil: Roberti, Flavio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Automática. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Automática; Argentin

The Penn Jerboa: A Platform for Exploring Parallel Composition of Templates

We have built a 12DOF, passive-compliant legged, tailed biped actuated by four brushless DC motors. We anticipate that this machine will achieve varied modes of quasistatic and dynamic balance, enabling a broad range of locomotion tasks including sitting, standing, walking, hopping, running, turning, leaping, and more. Achieving this diversity of behavior with a single under-actuated body, requires a correspondingly diverse array of controllers, motivating our interest in compositional techniques that promote mixing and reuse of a relatively few base constituents to achieve a combinatorially growing array of available choices. Here we report on the development of one important example of such a behavioral programming method, the construction of a novel monopedal sagittal plane hopping gait through parallel composition of four decoupled 1DOF base controllers. For this example behavior, the legs are locked in phase and the body is fastened to a boom to restrict motion to the sagittal plane. The platform's locomotion is powered by the hip motor that adjusts leg touchdown angle in flight and balance in stance, along with a tail motor that adjusts body shape in flight and drives energy into the passive leg shank spring during stance. The motor control signals arise from the application in parallel of four simple, completely decoupled 1DOF feedback laws that provably stabilize in isolation four corresponding 1DOF abstract reference plants. Each of these abstract 1DOF closed loop dynamics represents some simple but crucial specific component of the locomotion task at hand. We present a partial proof of correctness for this parallel composition of template reference systems along with data from the physical platform suggesting these templates are anchored as evidenced by the correspondence of their characteristic motions with a suitably transformed image of traces from the physical platform.Comment: Technical Report to Accompany: A. De and D. Koditschek, "Parallel composition of templates for tail-energized planar hopping," in 2015 IEEE International Conference on Robotics and Automation (ICRA), May 2015. v2: Used plain latex article, correct gap radius and specific force/torque number