Positioning Error Compensation of a Flexible Track Hybrid Robot for Aircraft Assembly Based on Response Surface Methodology and Experimental Study

With the development of aviation industry, more stringent demands are put forward for the performance and manufacturing level of aircraft. Moreover, the automation and precision of aircraft assembly determine the efficiency and quality of aircraft production. In order to improve the positioning precision of the flexible track hybrid robots which are applied to the flexible automatic assembly of aircraft, a precision compensation method based on response surface methodology was proposed in this paper. Firstly, the global positioning error model, optimized by characteristics of error data, was constructed to predict the positioning errors of the flexible track hybrid robot. Secondly, the predicted errors are utilized to realize the compensation of the target points at drilling workspace on nose and front fuselage assembly areas. Finally, a series of experiments of the flexible track hybrid robot with no-load and drilling scenarios are implemented to validate the proposed precision compensation method. The experiment of a hybrid robot for aircraft assembly shows that the mean value of the absolute positioning precision of the end-effector was promoted from 0.081 mm to 0.025 mm, maximum error reduced from 0.143 mm to 0.039 mm., respectively, which means that the position accuracy of the robot is increased by 69.1% and 72.7% for two experimental conditions.

Effect of unsupported sleepers on dynamic behavior of running vehicles and ride comfort index

Nowadays, with various advancements in the railway industry and increasing speed of trains, the design of railway tracks and vehicles has become vitally important. One of the frequent problems of ballasted tracks is the existence of unsupported sleepers. This phenomenon occurs due to the lack of ballast underneath the sleepers. Here, a model is presented, in which a flexible track model in a multibody dynamics program is developed, in order to study the dynamic behavior of a vehicle. By utilizing the model, it is feasible to simulate unsupported sleepers on the flexible track including rail, sleeper, and ballast components. In order to verify the results of numerical model, a field test is performed. Findings indicate that, in the case of a single unsupported sleeper through the track, the ride comfort index increased by 100% after increasing the train speed from 30 to 110 km/h. Moreover, when it is needed to have ride comfort index improvement over the uncomfortable level, the vehicle speed should be less than 70 km/h and 50 km/h for tracks with one unsupported sleeper and two unsupported sleepers, respectively.

Determination of wheel loading reduction in railway track with unsupported sleepers and rail irregularities

This study investigates the simultaneous effects of unsupported sleepers and rail random irregularities on track displacement and wheel load reduction, by means of numerical simulations with vehicle-track coupling. Vehicles are simulated as multibody systems comprising the major vehicle masses and suspension systems with nonlinear stiffness and damping. Flexible track with rail, sleeper and ballast components is considered using finite element and multibody programs. Numerical results of the simulations are in good agreement with field test measurements. Findings show that in tracks with less than four unsupported sleepers the vehicle is able to move at a speed of 110 km/h; with a higher number of unsupported sleepers the vehicle is vulnerable to derailment. The vehicle speed has no effect on the maximum rail displacement in tracks with less than four unsupported sleepers.

Influence of out-of-round wheels on the vehicle–flexible track interaction at rail welds

The dynamic analysis of the vehicle–flexible track interaction involves the study of vehicle motion and its dynamic impact transmitted to the track structure. This paper studies the influence of the out-of-round vehicle wheels running over rail welds on a flexible ballast track. The rails are modeled as an Euler-Bernoulli beam discretely supported by a spring-damper force element that represents the flexibility of the track structure. The dynamic behavior of the vehicle–flexible track interaction is studied using the combination of the finite element method and the multi-body system. In this paper, the simulation of the vehicle with the out-of-roundness wheel running over rail welds on a flexible ballast track in the high-frequency range and the vehicle–track interaction is coupled by a non-linear wheel–rail contact model. The effects of the out-of-roundness wheel on the vehicle–flexible track interaction at rail welds are investigated by comparing the effects of the round wheel under different vehicle speeds. Results indicate that the out-of-roundness wheel at rail welds creates a high magnitude dynamic effect on the vehicle and track components. The obtained simulation results were used to set a safety limitation for the wheel and rail irregularity size.

An Analytical Model for Predicting Ground Pressure under a Rigid-Flexible Tracked Vehicle on Soft Ground

Ground pressure is a significant parameter for the mobility, tractive performance, and soil compaction. In this study, an analytical model for predicting ground pressure distribution under a rigid-flexible tracked vehicle on soft ground was developed. The model considered the primary design parameters of the tracked vehicle, soil characteristics, and soil shear. The ground pressure was not uniform, and its maximum values under the roadwheels were 90.20, 103.57, and 150.14 kPa. The ground pressure was inversely proportional to the ratio of the lengths of the flexible track and rigid grouser. An experiment was conducted to verify the analytical model. The maximum error between the measured and simulated results was smaller than 8%, thereby verifying the analytical model.