Key Technology Research And Development On Compliant Assembly System With Force Sensing

Assembly process is an important process in the industrial production,which consumes a lot of manpower and time.Driven by the demand for automatic assembly,more and more production enterprises choose robotic assembly instead of manual assembly.However,the traditional assembly line method can only achieve large-scale assembly of the same product.In assembly scenario with fast product iteration,such as 3C product assembly,assembly line method cannot replace manual assembly.At present,robots have low environmental perception ability and intelligence,and assembly systems with flexible characteristics such as high versatility and low assembly force are rarely applied in industrial field.Therefore,taking irregular objects such as 3C electronic products as assembly object,relevant researches on flexible assembly based on force perception is carried out in this paper,and a compliant assembly system with low cost and high versatility is achieved.The main research contents are as follows:(1)A compliant assembly system based on 6-axis collaborative robot is implemented,and its overall framework design is described,including five software modules: jog module,positioning module,multi-segment trajectory planning module,security module and state monitoring module,which can meet the basic functions of users in assembly task development,such as debugging,execution and monitoring.(2)Aiming at the problem that most force control methods in compliant assembly systems require accurate dynamic model,a robot dynamic identification method based on Lagrange dynamic equation and QR decomposition method is implemented.It adopts the fifth-order Fourier series as the dynamic excitation trajectory,and selects the least square method as the system identification method.(3)Based on the dynamic parameter identification algorithm of 6-axis collaborative robot,a joint impedance control strategy based on sinusoidal friction compensation is proposed without force sensor.This method solves the problem that it is difficult to accurately compensate the joint static friction in the force control algorithm without a force sensor,resulting in poor estimation accuracy of the external force when the joint is stationary.This method can implement the estimation of the external force and hybrid force/position control without force sensor.In addition,a hybrid force/position control strategy based on admittance control is implemented for compliant assembly scenarios using 6-axis force/torque sensor.(4)For the assembly scenario of irregular objects such as remote controller,an assembly strategy design method based on degrees-of-freedom constraints is proposed,which solves the problems of difficulty in obtaining assembly states and designing assembly strategies in the assembly scenarios with multiple surface geometric features.This method can analyze the geometric features and possible contact states of the irregular shape object surface,and design a series of assembly actions to constrain the relative degrees-of-freedom between two objects,and finally make the coordinate system of the two objects coincide.(5)Based on the assembly system and related algorithms designed in this paper,practical assembly experiments are carried out to verify the effectiveness of the assembly strategy.Experimental results show that the success rate of the designed assembly strategy reaches 94% in the irregular shape object assembly scenario,and the manipulator end force of the assembly process is less than 20 N.It can ensure that the assembly can be completed with high success rate under the condition of small assembly force.