Innovative Mechanical Engineering

AGAR: DESIGN AND CONTROL SYNTHESIS FOR A NEXT-GENERATION AGRICULTURAL GROUND ROBOT

Miloš Simonović — 2025-12-24

Unmanned ground vehicles (UGVs) emerge as practical enablers of automation for labor-intensive agricultural operations, but real deployment is still constrained by a persistent design tension: machines that are versatile enough to justify investment often become too heavy/rigid for uneven terrain, while lightweight robots typically sacrifice implement compatibility and slope stability. This paper first synthesizes recent advances in agricultural UGV mechanical architectures and autonomy stacks, with emphasis on drivetrain choices, suspension/levelling concepts, energy supply, perception, and hierarchical control. It then presents AgAR (Agriculture Autonomous Robot) as an integrated design-and-control solution that deliberately couples mechanical modularity with a layered autonomy framework. AgAR combines a lightweight modular chassis with four independently actuated wheel-leg modules forming a hybrid suspension/active levelling system, enabling dynamic ground-clearance control and improved stability on rough and sloped fields. A swappable battery concept supports long duty cycles, while optional modules-including a Category-I three-point hitch and an electric PTO-enable direct use of standard tractor implements and higher-power attachments. A multimodal sensor suite (RTK-GNSS, IMU, stereo vision, 3D LiDAR, ultrasonics) feeds a ROS-centered architecture that separates localization, perception, planning, and safety, supported by industrial control hardware for deterministic low-level actuation and fail-safe stops. Comparative analysis against representative contemporary platforms highlights AgAR’s distinctive combination of terrain adaptability, interoperability with conventional implements, and extensible autonomy.

EXPERIMENTAL SETUP FOR EFFICIENCY EVALUATION OF LASER-CUT SPUR GEARS USING A MODULAR GEARBOX

Andjela Perović — 2025-10-02

This paper presents the preparation and methodology for investigating the feasibility of using laser-cut spur gears in functional, low-load transmission systems. Six gear pairs with different transmission ratios, but identical center distances, were designed and manufactured using a laser cutting process. The focus was on achieving acceptable geometric accuracy and reliable meshing through a simplified and cost-effective production method. Each gear pair was mounted in a dedicated test module and prepared for future experimental testing using the GUNT AT200 apparatus. The test setup provides the capability for precise measurement of torque and rotational speed under controlled conditions, with multiple load levels and repeated trials planned to ensure data consistency. The main goal of this study is to establish a structured methodology and framework for evaluating the mechanical efficiency of laser-cut gears and to explore how gear ratio and geometry may influence performance. The study does not aim to directly compare laser-cut gears with conventional or industrial models, but rather to assess the potential applications of these simply manufactured gears as a cost-effective solution in suitable areas. This research lays the groundwork for future testing and analysis and is expected to contribute to the broader use of laser-cut gears in applications such as prototyping, education, and light-duty mechanical systems.

EVALUATION AND THERMAL MODELING OF A HIGH-POWER GEARBOX

Vojkan Nojner — 2025-11-18

This paper presents an evaluation of a high-power gearbox intended for driving belt conveyors in open-pit mining, with a particular focus on thermal modeling and stability under continuous heavy-duty operation. To improve thermal performance and ensure long-term reliability, thermal Finite Element Analysis (FEA) was conducted to optimize the geometry and cooling characteristics of the gearbox housing. Based on the simulation results, a prototype was manufactured and subjected to experimental validation on a test bench, simulating real operating conditions. Key performance parameters, including temperature distribution, structural integrity, and operational efficiency, were monitored and analyzed. The test results demonstrated that the optimized gearbox design successfully meets the thermal and mechanical requirements for demanding industrial applications. The study confirms the effectiveness of using thermal FEA in the early design phase and highlights the importance of integrated simulation and testing in the development of reliable power transmission systems.

INTEGRATED APPLICATION OF LEAN TOOLS FOR PROCESS OPTIMIZATION IN SME MANUFACTURING: A CASE STUDY OF REFRIGERATION EQUIPMENT PRODUCTION

Dragan Pavlović — 2025-12-24

Small and medium-sized enterprises (SMEs) often operate with resource constraints, high product variety, and informal processes that hinder systematic efficiency improvements. This paper presents a single-case study of an SME that manufactures customized refrigeration aggregates for industrial cooling applications and applies an integrated set of Lean tools for process optimization. The research follows an action-oriented approach and combines SIPOC (Suppliers-Inputs-Process-Outputs -Customers), process flowcharting, value stream mapping, eight-waste analysis, Pareto analysis, Ishikawa diagrams, and 5S-based proposals. The current-state Value Stream Mapping (VSM) reveals a total non-value-added time of 24 days and 170 minutes and a value-added time of 615 minutes, with major wastes arising from waiting, motion, inventory accumulation, and rework. Pareto analysis shows that waiting for chassis components and unnecessary operator movement account for more than 60% of recorded disruptions, while the Ishikawa diagram highlights structural causes linked to manpower, methods, materials, machinery, measurement, and the working environment. A future-state VSM, built on targeted improvements, reduces non-value-added time (NVAT) to 15 days and 170 minutes and increases value-added time (VAT) to 650 minutes, and an ideal-state design suggests further reductions to 6 days and 140 minutes. The paper demonstrates that a coordinated application of Lean tools can provide SMEs in specialized manufacturing sectors, such as refrigeration equipment production, with a practical roadmap for diagnosing inefficiencies and designing coherent, high-impact improvement strategies.

COMPARATIVE ANALYSIS OF JOB PRIORITY RULES IN SINGLE-MACHINE SCHEDULING UNDER UNCERTAINTY

Aleksandar Stanković — 2025-12-24

The sequencing of operations represents a critical component of production scheduling, directly influencing system performance, throughput, and delivery reliability. Among the numerous scheduling strategies, job priority rules provide a structured and analytically transparent mechanism for determining the order of task execution. Their effectiveness, however, depends strongly on the production environment, variability of processing times, and the selected performance criterion. This paper presents a comparative study of several well-established job priority rules within the context of a single-machine scheduling problem under uncertainty. The analysis focuses on five rules commonly employed in manufacturing and service systems: First-In-First-Out (FIFO), Shortest Processing Time (SPT), Weighted Shortest Processing Time (WSPT), Earliest Due Date (EDD), and Critical Ratio Rule (CRR). Each rule is examined through its mathematical formulation, decision logic, and operational implications. The comparative evaluation highlights how different rules perform under varying system conditions and uncertainty levels. The findings emphasize that the efficiency of a given rule is context-dependent and that its suitability must be assessed in relation to process variability, load intensity, and scheduling objectives. The results provide a comprehensive overview and practical guidelines for selecting appropriate priority rules in stochastic production environments.

LIQUID DESICCANT SYSTEM; EVAPORATIVE COOLING SYSTEM; HEAT RECOVERY; AIR CONDITIONING; ROTARY DEHUMIDIFIER

Ehsan Kianpour — 2025-11-18

The rise in global temperatures caused by both natural and human factors—particularly the widespread use of fossil fuels—poses a serious threat to the environment and human health. Alongside environmental challenges, conventional air conditioning systems have proven inefficient due to high energy consumption and low performance in humidity control, especially in hot and humid regions. One innovative approach to reducing energy consumption and increasing efficiency is the use of absorption cooling systems, which absorb air moisture using liquid or solid sorbents and regenerate them using renewable heat sources such as solar energy. In this study, the performance and modeling of absorption cooling systems with different configurations of flat membrane and shell-and-tube heat exchangers were investigated. The main goal is to identify the best sorbent and system configuration to achieve maximum efficiency under similar climatic conditions. Predicted simulations show that the absorption cooling system provides an average total cooling capacity of 2.12 kW, with an overall coefficient of performance (COP) of 0.44 and a collector efficiency of 49% (based on absorber surface area).

SCHOOL OF ELASTICITY AND FRACTURE MECHANICS AT THE FACULTY OF MECHANICAL ENGINEERING, NIŠ: RESEARCH AND GLOBAL COLLABORATION

Katica (Stevanović) Hedrih — 2025-12-24

This paper presents a part of the scientific results in elasticity theory and fracture mechanics achieved through projects at the Department of Mechanics, Faculty of Mechanical Engineering, Niš. It recalls the doctoral dissertation of Prof. Dr Danilo Rašković on rectangular rod torsion, partly included in Jakov Hlitčijev’s Theory of Elasticity. Under Rašković’s guidance and through nine project cycles, numerous defended doctorates contributed to founding the Serbian School of Nonlinear Oscillations and Hybrid Systems Dynamics. Special focus is on parallel research in elasticity and fracture mechanics. Notable results include Dragan Jovanović’s master’s thesis on elasticity and photoelasticity and his doctoral work in fracture mechanics, as well as Ljubiša Perić’s research on stress, deformation, and polarisation in piezoelectric ceramics. Both were mentored by Prof. Katica (Stevanović) Hedrih. International collaborations include Prof. Emanuel Gdoutos (University of Xanthi and Chicago), honorary doctorate recipient and guest editor of a Facta Universitatis special issue on fracture mechanics; Prof. Jerzy Pinder (Waterloo University); Prof. Stjepan Jecic (Zagreb); and Prof. Rastko Čukić (Belgrade). Key fracture mechanics results by Dragan Jovanović were recognised at the World Conference on Experimental Mechanics. Recent advances (2024–2025) include new fractional-order rheological models and dynamic systems by Katica Hedrih, Anđelka Herdrih, and Julijana Simonović. The paper also reviews the textbook-monograph Strength of Materials and Resistance of Structures by Dragan Jovanović and Julijana Simonović. References include works by Hlitčijev, Rašković, Hedrih, Jovanović, and Simonović, forming the knowledge base for generations of mechanical engineers. This paper emphasises the continuity of knowledge transfer and scientific ideas at the University of Niš since its founding in 1960.