欠驱动式柑橘采摘末端执行器设计与试验

Design and Experiment of Underactuated End-effector for Citrus Picking

为实现柑橘采摘的机械化、智能化,设计了一款欠驱动式柑橘采摘末端执行器。该执行器通过三指充分抓握与偏转的融合控制,实现对不同大小及椭圆度的柑橘的稳定采摘。针对不同尺寸柑橘采摘需求,设计了双连杆并联式手指,在抓握直径差异较大的柑橘时,手指能够自动进行抓取或捏取动作,并实现被动柔顺。通过静力学分析,得到抓取力与电机输出力矩间的关系。针对不同椭圆度柑橘采摘需求,为手指根部添加旋转关节。在建立电机驱动控制系统模型的基础上,提出基于电流反馈的主动柔顺控制策略,指根能够旋转合适的角度使指面与柑橘表面紧密贴合,在防止手指棱边刮伤柑橘表皮的同时,增大接触面积、提高摩擦力。仿真结果表明,该末端执行器结构在运动学方面满足设计要求。制作物理样机并在实验室环境下进行了柑橘抓取试验,试验结果表明采摘执行器针对直径30~100 mm的柑橘抓取成功率为98.3%,平均耗时5.3 s。该末端执行器能够针对不同尺寸、不同形状的柑橘实现采摘功能,具有适应性强、抓取稳定、不损伤果实等优点。

Aiming to achieve the development of mechanized and intelligent citrus picking,an underactuated end-effector for citrus picking robot was proposed.Through the fusion control strategy of grip and deflection,the end-effector was able to achieve the stable picking of citrus with different sizes and ovality.According to the needs of picking citrus of different sizes and the analysis of human hands movement patterns,a double-link parallel finger was designed.The double-link parallel finger included two sets of four-link mechanism,which were designed for underactuated finger to enable the end-effector to adapt to different citrus sizes.On the basis of statics analysis,the motors were determined.Besides,a rotatory joint was added to the finger root to fit closely with the citrus.This design can not only protect the orange skin from being scratched by finger edges,but also can increase the contact area and thus increase the friction.In order to ensure the finger rotating correctly,the motor drive control system model was established according to the selected motor characteristics.Laying the establishment of this system model,the servo control strategy based on current feedback was proposed.Finally,the finger movement simulation and the citrus picking experiment using the end-effector were performed.Simulation results showed that the structure can satisfy the design requirements of realizing citrus picking of different sizes and ovality in terms of kinematics.A prototype of the picking end-effector was made and citrus picking experiments were carried out in the experimental environment.The experimental results showed that when the end-effector pinked citrus with diameter ranging from 30 mm to 100 mm,the average success rate was 98.3%and the average time was 5.3 s.It had the advantages of strong adaptability,stable grip,and no damage of the fruit.