Development of an onsite calibration device for robot manipulators

A novel in-contact three-dimensional(3D)measuring device,called MultiCal,is proposed as a convenient,low-cost(less than US$5000),and robust facility for onsite kinematic calibration and online measurement of robot manipulator accuracy.The device hasμm-level accuracy and can be easily embedded in robot cells.During the calibration procedure,the robot manipulator first moves automatically to multiple end-effector orientations with its tool center point(TCP)constrained on a fixed point by a 3D displacement measuring device(single point constraint),and the corresponding joint angles are recorded.Then,the measuring device is precisely mounted at different positions using a well-designed fixture,and the above measurement process is repeated to implement a multi-point constraint.The relative mounting positions are accurately measured and used as prior information to improve calibration accuracy and robustness.The results of theoretical analysis indicate that MultiCal reduces calibration accuracy by 10%to 20%in contrast to traditional non-contact 3D or six-dimensional(6D)measuring devices(such as laser trackers)when subject to the same level of artificial measurement noise.The results of a calibration experiment conducted on a Staubli TX90 robot show that MultiCal has only 7%to 14%lower calibration accuracy compared to a measuring arm with a laser scanner,and 21%to 30%lower time efficiency compared to a 6D binocular vision measuring system,yielding maximum and mean absolute position errors of 0.831 mm and 0.339 mm,respectively.

A Multi-module Controller for Walking Quadruped Robots

Motion control based on biologically inspired methods,such as Central Pattern Generator(CPG)models,offers a promising technique for robot control.However,for a quadruped robot which needs to maintain balance while performing flexible movements,this technique often requires a complicated nonlinear oscillator to build a controller,and it is difficult to achieve agility by merely modifying the predefined limit cycle in real time.In this study,we tried to solve this problem by constructing a multi-module controller based on CPG.The different parallel modules will ensure the dynamic stability and agility of walking.In the proposed controller,a specific control task is accomplished by adding basic and superposed motions.The basic motions decide the basic foot end trajectories,which are generated by the predefined limit cycle of the CPG model.According to conventional kinematics-based design,the superposed motions are generated through different modules alter the basic foot end trajectories to maintain balance and increase agility.As a considerable stability margin can be achieved,different modules are designed separately.The proposed CPG-based controller is capable of stabilizing a walking quadruped robot and performing start and stop movements,turning,lateral movement and reversal in real time.Experiments and simulations demonstrate the effectiveness of the method.

Dearomative spirocyclization via visible-light-induced reductive hydroarylation of non-activated arenes

A visible-light-induced spirocyclizative hydroarylation via reductive dearomatization of a series of non activated arenes including 2-phenyl indoles and naphthalene derivatives under mild conditions is de scribed.An intriguing chemoselective dearomative hydroarylation of 2-phenyl indoles is presented.Th dearomative hydroarylation protocol rapidly delivers valuable spirocycles with carbon-carbon doub bonds from readily accessible aromatic precursors in a single step.

Untethered quadrupedal hopping and bounding on a trampoline

For quadruped robots with springy legs,a successful jump usually requires both suitable elastic parts and well-designed control algorithms.However,these two problems are mutually restricted and hard to solve at the same time.In this study,we attempt to solve the problem of controller design with the help of a robot without any elastic mounted parts,in which the untethered robot is made to jump on a trampoline.The differences between jumping on hard surfaces with springy legs and jumping on springy surfaces with rigid legs are briefly discussed.An intuitive control law is proposed to balance foot contact forces;in this manner,excessive pitch oscillation during hopping or bounding can be avoided.Hopping height is controlled by tuning the time delay of the leg stretch.Together with other motion generators based on kinematic law,the robot can perform translational and rotational movements while hopping or bounding on the trampoline.Experiments are conducted to validate the effectiveness of the proposed control framework.

Spirocyclizative Remote Arylcarboxylation of Nonactivated Arenes with CO_(2) via Visible-Light-Induced Reductive Dearomatization

Visible-light-induced reductive dearomatization of nonactivated arenes is a very challenging transformation and remains in its infancy.Herein,we report a novel strategy to achieve a visible-light-induced spirocyclizative remote arylcarboxylation of nonactivated arenes including naphthalenyl-and phenyl-bearing aromatics with CO_(2) under mild conditions through a radical-polar crossover cascade(RPCC).This reductive dearomatization protocol rapidly delivers a broad range of spirocyclic and valuable carboxylic acid derivatives from readily accessible aromatic precursors with generally good regioselectivity and chemoselectivity.