Structure Design And Stability Research Of Venlo Type Greenhouse General Robot Chassis For Ground And Track Operation

The Venlo greenhouse can create the best growth environment for crops and has become an important part of facility agriculture.The emergence of Venlo greenhouse robots has greatly reduced the work intensity of laborers and improved work efficiency.The chassis is an important part of the robot,and its structural performance has an important impact on the robot’s operating mode,operating efficiency,stability,and flexibility.For the current Venlo greenhouse picking,transportation,and plant protection robots,the chassis has poor versatility,high ground flatness requirements,and slow track switching speed.In this paper,a Venlo greenhouse robot is designed for dual-purpose universal chassis.By adding a shock absorption device,the adaptability to uneven ground is improved.Based on theoretical analysis and dynamics simulation,the chassis steering and obstacle crossing stability are studied,and the steering stability test is carried out.By designing the connecting parts inside the chassis,its universal application is explained.This research can provide a theoretical basis and reference for the design and optimization of the Venlo type greenhouse robot chassis.The main research contents and conclusions are as follows:（1）The overall mechanism design of the chassis.According to the operating environment of the chassis,the overall structure design plan of the robot chassis is determined,which mainly includes:walking device plan,shock absorption device plan,and transmission plan.The selection and calculation of key components such as the motor,damping spring,and chain drive are carried out.Based on the influence of the wheel train layout on the static stability,dynamic stability and driving force of the chassis.By constructing a multi-objective optimization mathematical model and using the artificial bee colony algorithm to solve the problem,the optimal design of the chassis wheel train layout is completed.After optimization,the static stability is improved by 6.54%,the roll angle（?）₁ and the pitch angle（?）₂ in the dynamic stability are reduced by 6.73%and 4.91%,respectively,and the maximum driving force is reduced by2.28%.In the process of chassis movement,statics simulation analysis is carried out on the parts with greater force to ensure that they meet the requirements of use.（2）Steering movement and stability analysis.In order to ensure that the chassis can be turned smoothly on the greenhouse ground,the turning radius of the chassis and the required turning space are analyzed.The results show that the minimum turning space of the chassis is a circular area with a radius of 966mm,which can meet the requirements of the working environment.When the road surface operation is switched to the rail cutting operation,an in-situ 90°steering is required.The side slip and slip of the driving wheel will affect the stability of the steering,and then affect the performance of the upper rail.Based on theoretical analysis,the phenomenon of sideslip and slip is studied,and the factors affecting steering stability are determined as:angular velocity of driving wheels,angular acceleration of driving wheels,static friction coefficient,eccentricity,distance between wheel centers,car body size,load.（3）Dynamic simulation of steering and obstacle crossing.Using ADAMS software to carry out dynamic simulation of in-situ steering stability and obstacle crossing stability.The deviation of the rotation center position of the chassis after steering is used as the stability evaluation index.The factors affecting the stability of the in-situ steering were verified by simulation,and the specific influence trends of each factor on the stability of the steering were determined.Taking the contact force,vertical displacement curve and driving torque of the two driving wheels as performance evaluation indicators,the obstacle crossing stability analysis is carried out.The simulation results show that the two driving wheels will not slip or hang in the air during the obstacle crossing process,and verify that the designed shock absorption device can meet the requirements of the greenhouse environment.（4）Stability test research and general application.Using the Box-Behnken central combination test method,the driving wheel angular velocity,driving wheel angular acceleration,static friction coefficient,and eccentricity are used as test factors.Taking the deviation between the track centerline and the chassis centerline and the steering-track time as evaluation indicators,a four-factor three-level steering stability orthogonal test was carried out.Establish regression models of each test factor and evaluation index,analyze the influence of each test factor,and optimize the test results.The results show that the optimal working parameters of the chassis steering and rail alignment are the angular velocity of the driving wheel 1.3rad/s,the angular acceleration 0.9rad/s²,the static friction coefficient 0.7,and the eccentricity 0mm.The offset between the two centerlines is 7.586mm,and the turning time to track is 4.497s.The offset of the two centerlines of the greenhouse field verification test is 7.46mm,and the turning and alignment time is 4.38s,and the relative error with the predicted value of the model is less than 5%.On the basis of the test prototype,by adding a connecting mechanism inside the chassis,it is connected to the transportation,picking,and plant protection platform.Under different operating conditions,only the operating platform needs to be replaced,realizing the universal application of the chassis.