Design of experimental prototype of flexible chassis used in greenhouse

Abstract: A novel general power-output chassis system for agricultural vehicles been used in facility agriculture was proposed in this study, and named as Flexible Chassis. An initial prototype had been developed previously for basic theoretical research of four-wheel independent drive and four-wheel independent steering which was based on a simplified model. To study the kinematic and dynamic characteristics of the Flexible Chassis under practical operating conditions, the second prototype named as the experimental prototype has been developed. The mechanical structure of the flexible chassis consisted of the chassis frame, power battery pack, and single-wheel running system. The four single-wheel running systems were symmetrically distributed on both sides of the chassis frame, which was the only source of driving force for maintaining and transforming the driving attitude of the flexible chassis. The power battery pack included four maintenance-free lead-acid batteries, and was placed in the chassis frame with a cross distribution. This allocation was helpful to reduce the whole machine size and prevented interference with the four single-wheel running systems. The single-wheel running system was the core part of the Flexible Chassis. It was made up of offset-axle knuckle mechanic, wheel hub motor, and electromagnetic locking device. Through the interaction between the four single-wheel running systems, the chassis frame, and the ground, the Flexible Chassis can achieve lengthways, horizontal, and slant linear movement, two-wheel or four-wheel steering movement, and revolving movement. The rated traction of the flexible chassis was 2 400 N, and the rated traction power was 8 kW. Therefore, it can work for more than one hour when equipped with a single furrow reversible plough. The technical parameters of the flexible chassis were that the total weight was 750 kg; and the length, width and height were 1 715, 1 475, and 1 135 mm, respectively. The tread was 1 320 mm, the wheel base was 1 200 mm, and the minimum ground clearance was 235 mm. The speed of plowing operation was 5 km/h and the maximum speed was 28 km/h. The control system of the Flexible Chassis was formed by one chassis central control subsystem (CCCS) which was composed of control handle (CH), core data processing module (CDPM), and posture monitoring module (PMM). The four single-wheel running control subsystems (SRCS) were composed of control module (CM), actuator module (AM), and state monitoring module (SMM). All the subsystems communicated through the CANBUS. When the Flexible Chassis started, the CDPM calculated the current state parameters of the Flexible Chassis through accepting and analyzing the sensors data from PMM and SMMs. When the control signal of CH was accepted, the expected state parameters of every single-wheel running system were calculated and sent to SRCSs by CDPM. The CMs, through the analysis of the expected state parameters, calculated and outputted the corresponding control signals to the AMs. Every output torque of wheel hub motors and locking torque of electromagnetic locks were adjusted in real time by AMs for realizing the expected state parameters of every single-wheel running systems, thus accomplishing the expected driving attitude of the Flexible Chassis. The adaptive fuzzy PID control theory was used to SRCSs. The steering response angle (SRA) and steering response time (SRT) of single-wheel running systems were measured. Compared to the theoretical prototype, the experimental prototype was significantly improved in terms of machine power, mechanical structure, control system and other aspects. The mean value of SRA was between 89.84° and 90.11°. The maximum value was 90.880°, and the minimum value was 89.208°. The mean value of SRT was between 4.24 and 4.28 s. The maximum value was 4.495 s, and the minimum value was 4.054 s. The results indicated that the control was relatively stable and there was no major fluctuation. The acceleration pulse of the Flexible Chassis' barycenter was measured in vertical, horizontal, oblique linear, and rotational motion experiment. All values of acceleration pulse were less than 0.007 g. The results showed that the Flexible Chassis could operate stably in basic running attitude.