Journal of Mechanical Engineering 55 (2009)6

SV-JME-6-2009 in digital form »

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Cover plate

Selective Laser Sintering (SLS) is an Additive Manufacturing technology that produces fully functional parts from wide range of different materials. SLS can be used as a rapid prototyping technology, as well as for rapid manufacturing of end-user parts.
On the right side is EOS P100 Formiga SLS machine installed at the Faculty of Mechanical Engineering in Maribor. Figures on top are representing operating procedure with status display of current work on the left and look into sintering procedure on the right side.
Figures on the left side represent some finished products made by SLS technology from polyamide plastic. Image courtesy of: Intelligent Manufacturing Systems Laboratory, Faculty of Mechanical Engineering Maribor.

Author of photography: Bogdan Valentan

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A Reverse Engineering Technique for Creating Virtual Robots

Corresponding author - Simon Brezovnik

Authors - Miran Brezočnik, Simon Klančnik, Ivo Pahole, Karl Gotlih

Abstract

A novel system for out-of-date robotic systems that are not interesting for use any more is introduced. We give a solution for revitalization of these robotic systems with upgrading the programming software from on-line programming to indirect virtual programming and virtual modelling of a production cell equipped with robots. Direct and inverse kinematic models of the robot ACMA XR 701 in the virtual space were developed with reverse engineering technologies.

Keywords - robotics, robot modelling, reverse engineering, robot cell

Paper's information

Strojniški vestnik - Journal of Mechanical Engineering 55(2009)6
UDC 007.52

 A Reverse Engineering Technique for Creating Virtual Robots (pdf)

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Internet Based Teleoperation for Cooperative Navigation and Manipulation

Corresponding author - Ivan Petrović

Authors - Fetah Kolonić, Peter Korondi

Abstract

The Internet is a very fast evolving new technology, allowing people to electronically connect to places that are thousands of miles apart. By combining network technologies with the capabilities of mobile robots and manipulators, Internet users can discover and physically interact with far-away places thereby, creating opportunities of resource sharing, remote experimentation and long-distance learning.
This paper presents a general concept of Internet based teleoperation, which structures a teleoperation system into three layers. The concept was applied in developing a teleoperation system that enables two human operators to safely control two cooperative mobile robots in unknown and dynamic environments from any two PCs connected to the Internet by installing a developed client program on them and by using simple force feedback joysticks. On graphical user interfaces, the operators receive images forwarded by the cameras mounted on robots, and on the joysticks they can feel forces forwarded by developed obstacle prevention algorithm based on the dynamic window approach. To overcome the instability caused by the unknown and varying time delay an event-based teleoperation method is employed to synchronize actions of each robot with commands from its operator. Through experimental investigation it is confirmed that developed teleoperation system enables the operators to successfully accomplish cooperative navigation and manipulation tasks in complex environments.

Keywords - internet, teleoperation, cooperative navigation, manipulation

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 55(2009)6
UDC 007.52

 Internet Based Teleoperation for Cooperative Navigation and Manipulation (pdf)

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A Novel Pelton Turbine Model for Water Hammer Analysis

Corresponding author - Uroš Karadžić

Authors - Anton Bergant, Petar Vukoslavčević

Abstract

This paper presents a novel Pelton turbine model for water hammer analysis. Water hammer phenomena have been investigated in Perućica high-head hydropower plant (HPP), Montenegro. During its first phase of modernisation and refurbishment new distributors (needle valves) have been installed on the first two Pelton turbine units. Closure of the Pelton turbine distributors for the case of emergency shut-down and load rejection under governor control is modelled by two different closing laws i.e. the two-speed closing law and the law that considers actual (measured) needle stroke. Dissipation torques in turbine housing and shaft bearings are considered in the model. Stop procedure of the turbine unit is also investigated. Numerical results using the standard quasi-steady friction model and the convolution based unsteady friction model for different distributor closing laws are compared with the results of measurements. The agreement between computed and measured results is reasonable. It is shown that the effect of unsteady friction on water hammer events in Perućica HPP is of little importance (slow varying transients).

Keywords - water hammer, Pelton turbine, high-head HPP, turbine speed change, unsteady friction

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 55(2009)6
UDC 621.22

 A Novel Pelton Turbine Model for Water Hammer Analysis (pdf)

 

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Availability Management of Complex Technical Systems

Corresponding author - Dejan Vidojevic
Authors - Branislav Jeremic, Miroslav Babic

Abstract

This work presents basic elements of availability management methodology in complex technical systems according to the business and user perspectives. The methodology primarily relates to Information Technology (IT) systems, and the presented availability perspectives are based on parameters resulted from the exploitation conditions, according to analysis of the Tax Administration Information System of the Republic of Serbia – DIS 2003. The result of the implemented technology enhances the availability level through the clear identification and elimination of critical elements that affect the stability of IT infrastructure and ensures a continuing service provided by the system. The criteria of the optimization applied within the implementation of the availability enhancing process present a relation between the cost price of service provided by the system and expenditures of investments in improvements. Considering the established business requirements through the system, the availability management process should be given an appropriate level of service.

Keywords - maintenance, reliability, availability, it system, it infrastructure, it service, user

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 55(2009)6
UDC 658.5

 Availability Management of Complex Technical Systems (pdf)

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Variation of Normal Anisotropy Ratio „r” during Plastic Forming

Corresponding author - Srbislav Aleksandrović

Authors - Milentije Stefanović, Dragan Adamović, Vukić Lazi

Abstract

Cold rolled thin sheet metals are typical anisotropic materials as a consequence of the production process of rolling. Anisotropy is usually described from two aspects: as plane anisotropy and as a normal one. Most frequently used anisotropy parameter is the normal anisotropy ratio or the r value, which represents strains ratio in sheet metal plane and along its thickness. It is determined experimentally, usually as mean constant numeric valu, without testing the possible variation in dependence on realized plastic strain.
Accurate defining of the r value has great significanc, since it is not only the formability parameter, but also the crucial anisotropy parameter in software for simulation of the plastic forming process.
The paper presents the results of experimental investigation of three typical materials: low carbon Al killed steel DC04 sheet metal, alloy AlMg4.5Mn0.7 sheet metal and stainless steel X5CrNi18-10 sheet metal. Particular attention is given to defining the dependence of the r value on plastic strain during the forming process. The experiment requires sophisticated devices and accurate calculations. In the actual case, the computerized measuring system Zwick/Roell Z 100 was used. In addition, the paper contains the proposal on how to take into account variations of the r values during the plastic forming process.

Keywords - sheet metal, anisotropy, r value

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 55(2009)6
UDC 621.983.3

 Variation of Normal Anisotropy Ratio „r” during Plastic Forming (pdf)

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Research on the Influence of the Cutting Speed on the Specific Cutting Force During Turning

Corresponding author - Stefan Velchev

Avtorji - Ivan Kolev, Кrassimir Ivanov

Abstract

A hypothetical graphical dependence showing the cutting speed influence on the specific cutting force when cutting ductile materials is proposed on the basis of the physical nature. Some hypothetical mathematical models for the approximation of that dependence when changing the cutting speed are shown. Trough experimental study when turning different kinds of processed material and mathematical modelling of the experimental data, new mathematical models approximating the dependence of the specific cutting force and cutting speed have been received. A new, better empiric mathematical model when referred to the structure, adequacy and accuracy is recommended.

Keywords - specific cutting force, thickness of cut, hypothetical models

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 55(2009)6
UDC 621.91

 Research on the Influence of the Cutting Speed on the Specific Cutting Force During Turning (pdf)

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STEP-NC: A New Programming Code for the CNC Machines

Corresponding author - Primoz Kržič

Authors - Antun Stoic, Janez Kopač

Abstract
The paper deals with the newest advances in standardization of manufacturing data management. The overview of previous work and projects and the latest developments on introducing the ISO 10303- 238 and ISO 14649 standards is presented. The advantages of the new data models are shown and the plans on future work are presented.

Keywords - manufacturing machines, CNC programming, ISO standards

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 55(2009)6
UDC 621.9

 STEP-NC: A New Programming Code for the CNC Machines (pdf)

 

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