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navigation, navigacija, udc:617.3, pedicle, vertebra, model, vretence, prostoročna tehnika, pedikel, and free-hand technique

Izhodišča: Postavitev pedikularnih vijakov s prostoročno tehniko je povezana z znatnim odstotkom predrtja pedikla. To tveganje lahko zmanjšamo z uporabo medoperativne diaskopije ali z navigacijo, ki imata določene pomembne pomanjkljivosti. Obetaven princip, s katerim bi lahko odpravili večino težav, je metoda hitre izdelave prototipov, s katero lahko izdelamo bolniku prilagojene vodilne šablone, ki omogočajo optimalno pozicioniranje vijakov. V zadnjem desetletju je bilo izvedenih nekaj študij, v katerih so predvsem na kadavrih z uporabo šablon relativno uspešno vsadili pedikularne vijake. Pri nas smo izvedli klinično študijo in izdelali šablone, ki omogočajo hkratno vsaditev vijakov na več ravneh. V raziskavo smo prvič vključili tudi križnično hrbtenico. Metode: V prospektivno klinično raziskavo primerov s kontrolami je bilo vključenih 15 oseb. V ledveno in križnično hrbtenico smo vstavili 30 pedikularnih vijakov z uporabo vodilnih šablon, 36 vijakov pa smo vstavili prostoročno pod nadzorom RTG. Na podlagi preoperativnih CT-posnetkov smo s postopkom selektivnega laserskega sintranja izdelali vodilne šablone. V obeh skupinah smo opravili analizo predrtja pediklov glede na pooperativni izvid CT. Rezultati: Incidenca predrtja pedikla je pri uporabi vodilne šablone statistično značilno manjša kot pri kontroli. Zaključki: Uporaba večnivojskih vodilnih šablon se je izkazala kot zanesljiva metoda, ki pomembno zmanjša verjetnost za poškodbo pedikla in s tem povezane zaplete. Kljub temu ima določene pomanjkljivosti, ki so povezane z relativno dolgim časom izdelave vodilnih šablon, z napakami pri izdelavi ali s pozicioniranjem med operacijo. Zaradi omenjenih lastnosti metoda ni nadomestila prostoročne tehnike ali navigacije, vendar je pomembna alternativa v izbranih primerih. Background: Pedicle screw placement using free hand technique has high incidence of pedicle perforation. The said risk can be reduced with intra-operative fluoroscopy or navigation, which have some disadvantages. A promising principle for solving most of the issues is the rapid prototyping technology. By this technique it is possible to manufacture patient specific drill guide templates that enable optimal pedicle screw placement. In the last decade, many studies have featured relatively successful implantations of pedicle screws through the use of drill guide templates, though mostly on cadavers. We performed a similar clinical study involving the manufacture of templates for the lumbar and sacral regions that enable simultaneous multiple-level screw implanting. Methods: A randomized clinical trial was performed in 15 patients. In the lumbar and sacral spine 30 screws were implanted using drill guide template and 36 screws using free hand technique under fluoroscopy supervision. Preoperative CT-scans were taken for drill guide template design and manufacture using selective laser sintering method. According to postoperative CT-scan analysis, pedicle perforation incidence was estimated. Results: The incidence of cortex perforation was significantly reduced in the drill guide template group. Conclusions: Drill guide templates have turned out to be a reliable solution that importantly reduces pedicle perforation incidence and complications related to it. However, there are shortcomings: a relatively lengthy manufacturing process, possible manufacturing faults and incorrect positioning during the operation. Owing to mentioned disadvantages, templates have not replaced free hand and navigation technique yet, but could represent a useful tool in some selected cases.

udc:621.9.048:621.753.5.001.41, sheet-metal forming, nonconventional processes, fast prototyping, and high speed water-jet

V zadnjih desetletjih je tehnologija obdelave s curki z velikimi hitrostnmi dozivela velik razvoj. Od prvih primerov uporabe v zgodnjih sedemdesetih letih prejsnjega stoletja se je uporaba močno povečala. Med vsemi postopki, ki temeljijo na uporabi curkov z velikimi hitrostmi, ima vodilno vlogo rezanje z abrazivnim vodnim curkom (AVC), pri katerem vodni curek z velikimi hitrostmi (VC) pospešuje trde abrazivne delce, ki razjedajo material obdelovanca. Po drugi strani se VC uporablja za rezanje mehkejših materialov, čiščenje, površinsko obdelavo ter za uporabo v medicini in živilski industriji. V zadnjem času se VC uporablja tudi pri preoblikovanju, predvsem za utrjevanje površine izdelka, nekaj raziskav pa je pokazalo, da ima VC velike moznosti kot orodje za postopno preoblikovanje pločevine (PPP). V tej raziskavi smo preučili moznosti uporabe vodnega curka z velikimi hitrostmi kot orodja za PPP. Prikazana je vplivnost postopkovnih parametrov kakor sta tlak in pretok vode, prav tako je definirana najbolj primerna geometrijska oblika vodne sobe za tvorbo curka. Predstavljen je tudi primer postopnega preoblikovanja 0,5 mm debele pločevine iz aluminijeve zlitine v preprosto obliko z VC. Med primerjavo PPP z orodjem z določeno obliko se izkaže, da je predlagana tehnologija ekološko bolj sprejemljiva, saj ni potrebe po uporabi mazalnih sredstev. Prve raziskave nakazujejo, da se izboljša preoblikovalnost pri uporabi VC kot orodja za PPP. High-speed jetting technology has developed quickly over the past few decades.Since its first introduction in the early 1970s the number of applications has rapidly increased. Of the high-speed jet-based processes, cutting with an abrasive water jet (AWJ) is the most common. In this process, hard abrasive particles, which are accelerated by a high-speed water jet (WJ),can erode practically any known material. On the other hand, a plain WJ is used mostly for cutting softer materials, cleaning, surface preparation, applications in medicine and food processing. Recently, WJs have been used in forming, mostly as a tool for surface peening, but some research has shown great potential for a WJ as a tool for incremental sheet-metal forming (ISMF). In this study we analyzed the possibility to apply a high-speed WJ as a tool for ISMF. The importance of process parameters such as water pressure and volume flow were determined, and the most appropriate water-nozzle geometry was defined as well. A case study is included, where a simple geometry was incrementally formed by a WJ in 0.5-mm-thick aluminum-alloy plate. Compared to ISMF with a rigid tool, the proposed technology is more environmentally friendly, since no lubrication is required, and from our firstinvestigation it seems that the formability is increased as well.

udc:658.5:167.7, concurrent engineering, product development, product design, and virtual design

Prispevek je osredotočen na glavne strategije, principe, procese, prakse, tehnologije in ljudi, ki se nanasajo na sočasno inženirstvo. S tem obsega osnovne organizacijske faktorje, orodja, metodologije, računalnisko podprte analize in prototipiranje. Se vedno običajen, zaporeden pristop k razvoju izdelka v veliko proizvodnih podjetjih zamenjuje sodoben sočasen pristop. Za doseganje najboljših učinkov morajo biti vsi glavni prepletajoči elementi od trženja, proizvodnega menedžmenta, nabave, proizvodnje in kakovosti prav tako sočasni. This paper focuses on the main strategies, principles, processes, practices, technologies and people related to concurrent engineering (CE). In this way itdescribes the major CE organizing factors, tools, methodologies, computer-aided analysis and prototyping. The common approach to product development, still used by many manufacturing companies, is based on the sequential principle and is being replaced by the contemporary concurrent approach. To achieve the best results all key cross-functional elements from marketing, product management, purchasing, manufacturing engineering and quality must be concurrent as well.