Paweł Kołodziej

During headland manoeuvres of agricultural tractors, self-propelled machines, and autonomous agricultural vehicles, it is crucial not only to achieve the required working width but also to minimise the number of turns, path length, and time to reach the next field pass. The shortest trajectories can be obtained using Dubins curves or Reeds–Shepp paths. However, traversing such paths at constant velocity is only theoretically feasible. At the junctions between path segments, either the vehicle must stop or the steering angle must change at an infinite rate. These points exhibit abrupt changes in acceleration components, resulting in infinite jerk. This study presents the use of transition curves for executing U-turns and Ω-turns during headland manoeuvres. Implementing curves with gradually varying curvature ensures smooth transitions between trajectory segments, reducing sudden direction changes and improving motion dynamics. The curvature and tangent angle are defined using trigonometric functions. For the designed trajectory, kinematic parameters, including wheel steering angles, were determined for two models of agricultural tractors. The results provide a solid foundation for future research on refining transition curve models and integrating the proposed solutions with agricultural vehicle control systems.

This paper presents the results of quasi-static tests carried out using a texturometer and of impact tests combined with stress relaxation on a stand equipped with a heavy pendulum of the hammer type. The tests were carried out using fresh roots and those stored at 20 °C for 120 h. The impact velocities V_d were 0.001, 0.002, 0.01, 0.02, 0.75, and 1.25 m·s⁻¹. Compiling the relaxation times T₁ for V_d indicated their large drops for both fresh and stored roots. The largest average values T₁ were obtained in the range from 0.197 s to 0.111 s at the small velocities of deformation 0.001–0.02 m·s⁻¹ and the smallest ones in the range from 0.0252 to 0.0228 s at the V_d equal to 0.75 and 1.25 m·s⁻¹. A decrease in T₂ values was observed in the average range of 8.02–4.27 s at V_d = 0.001–0.02 m·s⁻¹ for fresh beets. For the velocities 0.75 m·s⁻¹ and 1.25 m·s⁻¹ and stored roots, the range of average values was smaller and ranged from 6.13 s to 4.54 s. The reaction forces of the F_p sample reached the highest average levels from 168.2 N to 190.8 N for fresh roots and 46.5 to 56.2 N for 5-day-old roots. However, the lowest F_p was recorded at speeds (0.001–0.02 ms⁻¹) 57.5–62.3 N for the fresh roots and 46.5–56.2 N for the 5-day-old roots. For the velocities greater than 0.75 m·s⁻¹ and 1.25 m·s⁻¹, the values of reaction forces increased at the average values 168.2–190.8 N for the fresh roots and 158.2–175.4 N for 5-day-old ones.

This study presents the results of a dynamic two-point bending test and a quasi-static three-point bending test of the quail femurs. Bones from females and males of two genetic strains of Japanese quail belonging to various utility types were analyzed. Mechanical parameters obtained under impact...

Tensile test under quasi-static loads conditions is usually used to determine the mechanical strength of thermoplastic starch films. This kind of test does not fully illustrate the load conditions for packaging films, which, under the conditions of use, are succumb to dynamic loads. Thus, the aim...

Root damages due to mechanical impacts result in deterioration in commercial sugar beet quality. In order to determine the mechanical characteristics of roots, a stand equipped with a pendulum enabling impact investigations of whole beets was used. The roots were stored in a monitored environment for up to 5 days (temperature 15 ± 2 °C, 40 ± 2%). During the tests, the beets were struck against a flat steel resistant surface with the velocities V_imp = 0.5, 1.0 and 1.5 m·s⁻¹. The measurements of local root curvatures in three chosen impact areas and the deformation (d_max) allowed modelling of the volume of contact (CV) by means of the ellipsoid cap. These investigations enabled the determination of the relations between the maximal impact force, F_max, the impact energy, E_imp, and the absorbed energy, E_abs, as well as the contact volume and impact velocity, taking into account the root storage time, S_t. It was found that the maximal impact force increased with increasing impact velocity and decreased with the storage time for each group of roots. With increasing velocity, there were also increases in the following: impact energy, absorbed energy, contact volume and maximal deformation, as well as absorbed energy, referred to as the mass E_abs-v from V_imp. The mean values of the stresses (σ_max), being the quotients of the impact force (F_max) and the surface area of the ellipsoid cap base (A_BE), were 0.81–1.17 MPa, 1.064–1.59 MPa and 1.45–1.77 MPa for the velocities of 0.5, 1.0 and 1.5 m·s⁻¹, respectively. It was confirmed that the statistical significance of the mentioned parameters changes depending on the impact velocity.

A three-point bending test under quasi-static load conditions is usually used in studies on the bones' mechanical properties. On its basis, the bone strength is determined, corresponding to the maximum force required for the fracture. In natural conditions, bone fractures most often occur as a...

This paper presents planning of smooth trajectories using the asymmetric profiles of displacement, velocity, acceleration and jerk of described higher degree polynomials. The presented way of determination of polynomial and asymmetry coefficients as well as motion time includes the procedure at both constraints of single kinematic quantities, i.e., velocity, acceleration, jerk and introducing a few constraints simultaneously. Moreover, the paper presents a method of planning trajectories with intermediate points consisting in concatenation of the analyzed polynomials. The proposed method of trajectory planning was compared to that of using the S-curve. The results in the form of kinematic quantity courses are presented graphically. The discussed method guarantees continuity of displacement, velocity, acceleration and jerk. It can be used for planning trajectories of various technical objects (e.g., manipulators, mobile robots, CNC machine tools, optical disk drives, autonomous vehicles, etc.).

Non-thermal endovenous ablations, due to the lowest probability of complications, are the new method of treating chronic venous insufficiency—one of the most common diseases globally. The Flebogrif system (Balton Sp. z o.o., Warsaw, Poland) is a new mechano-chemical ablation system causing the mechanical damage of endothelium that allows for better sclerosant penetration into its wall. The purpose of the article is to provide mechanical characteristics in the form of force–displacement dependence for a single cutting element, and a bundle of cutting elements of Flebogrif as a whole for different levels of protrusion of the bundle of cutting elements. A TA.HD plus (Stable Micro Systems, Godalming, UK) analyzer equipped with special handles, was used for characteristics testing. The head movement speed used was 5 mm·s⁻¹. The Flebogrif system was tested for three cutting element protrusion levels: L = L_max, L = 0.9·L_max, and L = 0.8·L_max. Before testing, geometric measurement of the spacing of the cutting elements for three proposed protrusions was performed. It was established that decreasing the working length of the cutting elements will increase their rigidity, and, as a result, increase the force exerted on the internal surface of the vein wall. The obtained characteristics will allow for specifying contact force variability ranges and the corresponding diameter ranges of operated veins.

The investigations on the response of bone tissue under different loading conditions are important from clinical and engineering points of view. In this paper, the influence of nesfatin-1 administration on rat humerus mechanical properties was analyzed. The classical three-point bending and impact tests were carried out for three rat bone groups: control (SHO), the humerus of animals under the conditions of established osteopenia (OVX), and bones of rats receiving nesfatin-1 after ovariectomy (NES). The experiments proved that the bone strength parameters measured under various mechanical loading conditions increased after the nesfatin-1 administration. The OVX bones were most susceptible to deformation and had the smallest fracture toughness. The SEM images of humerus fracture surface in this group showed that ovariectomized rats had a much looser bone structure compared to the SHO and NES females. Loosening of the bone structure was also confirmed by the densitometric and qualitative EDS analysis, showing a decrease in the OVX bones’ mineral content. The samples of the NES group were characterized by the largest values of maximum force obtained under both quasi-static and impact conditions. The energies absorbed during the impact and the critical energy for fracture (from the three-point bending test) were similar for the SHO and NES groups. Statistically significant differences were observed between the mean F_{i max} values of all analyzed sample groups. The obtained results suggest that the impact test was more sensitive than the classical quasi-static three-point bending one. Hence, F_{i max} could be used as a parameter to predict bone fracture toughness.