基于质点-弹簧-阻尼模型的人机接触运动皮肤三维形变仿真

Simulation of three-dimensional deformation of skin in human-robot interaction tasks based on the mass-spring-damper model

人机接触运动中,在接触区域后方和前方皮肤表面分别产生拉伸和堆积形变。针对当前该领域研究的局限性,该文研究了黏滑摩擦下皮肤三维形变仿真模型,为人机作业参数优化、在线轨迹规划和控制提供参考。该文基于皮肤解剖结构,构建皮肤、肌肉脂肪、骨骼3层质点-弹簧-阻尼模型,描述皮肤在拉伸、剪切和弯曲作用下的形变;基于皮肤黏滑摩擦机理,结合改进Kelvin-Voigt黏弹模型,构建皮肤质点-弹簧-阻尼动力学模型,模拟不同作业环境下皮肤的实时三维形变;验证了皮肤质点-弹簧-阻尼模型在Kwiatkowska、Franklin等皮肤拉伸测量试验中的有效性。同时,该文搭建了机器人手臂按摩试验平台和皮肤表面形变测量视觉系统。与试验测量结果对比,皮肤三维形变仿真模型拉伸形变在X和Z方向的平均误差分别为0.295、0.360 mm,标准差分别为0.164、0.085 mm;堆积形变在X、Y和Z方向的平均误差分别为0.317、0.248、0.471 mm,标准差分别为0.090、0、0.232 mm。试验结果表明:该文构建的皮肤三维形变仿真模型误差较小、稳定性较高。

[Objective]In human-robot interaction tasks,where the robot moves tangentially along the skin surface with a specified normal force,stacking and stretching deformations are displayed by the skin ahead of and behind the movement of the end effector.Discomfort,including sensations of compression and pulling on the human body,can be attributed to these deformations.In addition,the anticipated operational trajectory can deviate because of such deformations.Therefore,under stick-slip friction,this paper introduces a three-dimensional skin deformation simulation model.[Methods]First,a three-layered mass-spring-damper(MSD)model,representing the mechanical properties of the skin,muscle fat,and bone layers,is established.Considering the tensile,shear,and bending forces,this model describes the skin deformations.Vision processing methods,including filtering,cropping,uniform sampling,and hand-eye calibration,are employed on the point cloud data obtained from the operation area to establish the particle position of the model.Spring-damper elements,comprising springs and dampers parallelly arranged,are used to connect adjacent particles in the MSD model.Combining modulus of elasticity of various tissue layers helps determine the elastic coefficient of the spring.For the damping properties,a damping algorithm that simulates the viscosity of tissues by reducing the velocity of particles is included in the model.After establishing the simulation model,the stick-slip friction mechanisms between a rigid end effector and a flexible skin surface during tangential sliding in real human-robot interaction tasks are investigated from macroscopic and microscopic perspectives.A particle dynamics equation is established based on the positional dynamics constraints and an improved Kelvin-Voigt dynamic model to facilitate dynamic model simulation under the stick-slip friction.The semi-implicit Euler method is finally employed to solve for the particle position information.The particles of the model are fitted using a cubic spline interpolation surface to obtain three-dimensional deformation information of the skin under various operational environments.[Results]Based on the skin-stretch measurement experimental data,the model displayed vertical and horizontal displacement errors of 0.157 and 0.562 mm,respectively,during a reciprocating linear sliding process with a 17.6 mm travel distance.A robotic arm massage experiment platform and a measurement vision system for skin surface deformation,measuring the stretch deformation of the forearm and the stacking deformation of the upper arm were established to further verify the accuracy of the model.The model simulation produced stretch deformation with average errors of 0.295 and 0.360 mm on the X-axis of tangential movement and the Z-axis of normal loading,respectively,revealing standard deviations of 0.164 and 0.085 mm.The stacking deformation exhibited average errors of 0.317,0.248,and 0.471 mm in the X,Y,and Z-directions,respectively,revealing standard deviations of 0.090,0,and 0.232 mm,respectively.[Conclusions]The proposed simulation model demonstrates minimal error and high stability,enabling an accurate simulation of three-dimensional skin deformations due to various working environments in human-robot interaction tasks.Important references for parameter selection and online trajectory planning and control can be obtained using this model to enhance the comfortable operation experience.