Petar Todorovic

Locating and clamping of complex geometry workpieces with skewed holes in multiple-constraint conditions

Purpose – The purpose of this paper is to propose a general model for locating and clamping workpieces of complex geometry with two skewed holes under multiple constraints. Design/methodology/approach – Numerous constraints related to application of the proposed model are discussed as prerequisite to design of fixture solution. Based on theoretical model, a fixture was designed and successfully tested in experimental investigation. Experimental results were also verified using FEM simulations. Findings – This study showed that, opposed to conventional approach, novel solution results in significantly smaller fixture dimensions, while providing greater stability. Insertion of mandrels and supports element sub-assemblies into the workpiece holes significantly increases workpiece stiffness through an increased moment of inertia, while the internal support elements largely diminish the problem of thin wall deformation in the workpiece. Practical implications – The fixture designed in this case was actually us...

Towards continuous and real-time attention monitoring at work: reaction time versus brain response

Abstract Continuous and objective measurement of the user attention state still represents a major challenge in the ergonomics research. Recently available wearable electroencephalography (EEG) opens new opportunities for objective and continuous evaluation of operators’ attention, which may provide a new paradigm in ergonomics. In this study, wearable EEG was recorded during simulated assembly operation, with the aim to analyse P300 event-related potential component, which provides reliable information on attention processing. In parallel, reaction times (RTs) were recorded and the correlation between these two attention-related modalities was investigated. Negative correlation between P300 amplitudes and RTs has been observed on the group level (p < .001). However, on the individual level, the obtained correlations were not consistent. As a result, we propose the P300 amplitude for accurate attention monitoring in ergonomics research. On the other hand, no significant correlation between RTs and P300 latency was found on group, neither on individual level. Practitioner Summary: Ergonomic studies of assembly operations mainly investigated physical aspects, while mental states of the assemblers were not sufficiently addressed. Presented study aims at attention tracking, using realistic workplace replica. It is shown that drops in attention could be successfully traced only by direct brainwave observation, using wireless electroencephalographic measurements.

An implementation of infrared thermography in maintenance plans within a world class manufacturing strategy

The objective of the paper is to show the implementation of infrared thermography within World Class Manufacturing (WCM) maintenance strategy. The results from infrared thermography inspections in a food processing and packaging solutions company were presented. Applicability of the infrared thermography, during a two-year period, caused a substantial reduction the potential breakdown in the pilot area. Upon feasibility confirmation, the proposed method was spread to other production equipment of the company.

Static Friction at High Contact Temperatures and Low Contact Pressure

The problem of measuring static friction at high temperatures and low contact pressures is theoretically analyzed, as well as the instruments for the accurate determination of the coefficient of static friction at high temperatures for contact pairs made of steel and bronze. The results of experimental investigation show that at low contact pressure and temperature above 120°C coefficient of static friction dramatically increases. This increase in the coefficient of friction can be of great practical value with regard to the load capacity of contacts where external forces are balanced with friction forces.

Continuous controllable balloon dilation: a novel approach for cervix dilation

BackgroundCervical dilation using mechanical dilators is associated with various complications, such as uterine perforation, cervical laceration, infections and intraperitoneal hemorrhage. To achieve safe and painless cervical dilation, we constructed a new medical device to achieve confident mechanical cervical dilation: a continuous controllable balloon dilator (CCBD).MethodsControlled pumping of incompressible fluid into the CCBD increases the pressure and outer diameter of the CCBD, continuously dilating the cervical canal. The reliability of the CCBD was confirmed in vitro (testing for consistency and endurance, with no detected risk for breakage) and in vivo. A multi-center clinical study was conducted,with 120 pregnant women randomly assigned to one of three groups: Group I,control group, no dilation;Group II,mechanical dilation, Hegar dilator (HeD); and Group III,CCBD. The tissue material for histological evaluation was obtained from the endocervical mucosa before and after dilation using the HeD or CCBD.ResultsThe CCBD dilations were successful and had no complications in all 40 patients of Group III. The cervical tissue was markedly less damaged after CCBD dilation compared with HeD dilation (epithelium damage: 95% (HeD) vs. 45% (CCBD), P <0.001; basal membrane damage: 82.5% (HeD) vs. 27.5% (CCBD), P <0.001; stromal damage: 62.5% (HeD) vs. 37.5% (CCBD), P <0.01). Cervical hemorrhagia was observed in 90% of the patients after HeD dilation versus in 32.5% of the patients after CCBD dilation.ConclusionsThe CCBD should be used as a replacement for mechanical dilators to prevent uterine and cervical injury during cervical dilation.Trial registrationISRCTN54007498

Occupational safety and health education under the lifelong learning framework in Serbia

Serbia is aligning with European Union requirements and the occupational safety and health (OSH) administration is one of the most representative sectors of this alignment. Many efforts were made in this field, by introducing new laws and regulations, but it turned out to be insufficient. OSH professionals need to renovate and strengthen their knowledge in accordance with continuous, updated and improved OSH standards and regulation. Lifelong learning (LLL) programmes can contribute to forming professionals who are always up to date. This paper presents an implemented LLL programme, over the duration of two academic years, dedicated to OSH professionals, and investigates whether this programme will be helpful and accepted by professionals. The results from the study show that the given LLL programme had indeed a positive influence on the professional careers of the participants and that the LLL presents the future trend in OSH education.

A Tool for Neuroergonomic Study of Repetitive Operational Tasks

The objective of the present work in progress, in the field of neuroergonomics, is to find psychophysiological correlates for vigilance decrement and mental fatigue in industrial environments as well as the measurements of postural loads using multimodal system. This system is composed of (wirelessly obtained) electroencephalographic measurements (EEG), electrodermal activity (EDA) and commercial 3D motion capture sensor kinect™. The aim of this study is to decrease potential operational error due to slips in attention and mental fatigue of a worker and consequently lead to more reliable and safer production. Further, postural loads could be assessed on-line, thus preventing the over-load of the workers and, consequently, possible work-related MSDs.

Static coefficient of rolling friction under heating

The effect of heating, the normal load, and the radii of the members in contact on the static coefficient of rolling friction is considered. The design of a new apparatus for measuring the parameters of rolling friction over an inclined plane at elevated temperatures is presented. A need to specify the effect of the type of the materials in contact, as well as the roughness and contact geometry, on the static coefficient of rolling friction is emphasized.