No abstract

Droplet manipulation has emerged as a key enabling technology in various scientific and engineering fields with great potentials in advanced applications such as bioanalysis and reagent microreactors. The current strategies generally involve external stimuli or chemical/structural surface gradients to provide the driving force for in plane droplet manipulations, which suffer from low efficiency, poor controllability, and small volume ranges (generally Vmax/Vmin < 10) due to their inherent limitations. Herein, a dynamic gripping based droplet manipulation method is proposed by employing a flexible gripper with a notch covered by superhydrophobic silicon rubber membrane (SRM) between the gripper fingers to dynamically pick up, constrain and release droplets, capable of consecutively manipulating large‐volume‐range (Vmax/Vmin >130) droplets with minimal liquid loss. The robust Cassie‐to‐Wenzel transition (CWT) resistance and mechanical stability of the produced superhydrophobic surface well support the dynamic operations of various droplets, where the superhydrophobic surface presents great water‐repellent performance during stretching and impinging experiments as well as remains superhydrophobicity even after mechanical abrasion against 600 grit SiC sandpaper for 15 m at an applied pressure of 3.2 kPa. Lossless manipulations of 3–180 µL droplets have been experimentally validated, where an application of the proposed method in droplet‐based microreactors for chemical analysis and bioassay is demonstrated.

Sizes and stiffness variations of actively deformable objects pose significant challenges on the design of compliant constant-force gripper. This paper presents a curved-beam based constant force compliant gripper which is composed of the constant force module, the bistable module, the preloading module and the linear guide. A curved-beam constant force mechanism is designed to generate constant force output, the non-constant force motion range of which is further eliminated via curved-based bistable mechanism and preloading module. After a formulation to find the optimal gripper configuration, the design is verified through comparison with simulation results. Finally, a prototype of the proposed gripper is tested to demonstrate its grasping capacity.

Maize seeding is greatly affected by improper seed placement and poor planter performance under a no-tillage mechanisation system. To overcome the issue, we explored the impact of separating board and anti-blocking mechanism (0, 1/4, 1/2, 2/3, 3/4, and 1 type) on maize seeding under different forward speeds (3, 5, 7 km/h) and rotational speeds (260, 400, 530, 740 rpm), where the performance metrics included the mass of straw coiled, seeding height, emergence rate, soil mound depth, straw movement, and straw clearance. The study results show that separating board helps to increase forward and side displacements of the straw, which avoids localized accumulation of straw around the antiblocking mechanism. The straw clearance rate of the anti-blocking mechanism with a separating board is greater than that without the separating board. Therefore, the 2/3 type anti-blocking mechanism with a separating board is recommended for maize seeding at a forward speed of 5 km/h and a rotational speed of 400 rpm.