COMET 5 / 50 and 400 mm3 field of view on a portable multiaxis stand and rotary table for automated object positioning
University of Bremen - Faculty of Production Technology Bremen Institute for Metrology, Automation and Quality Science
A historical illustrated book from the 100 year company history (1806 to 1906) of the Bremer Melchers Group is among the exhibits of the Übersee Museum in Bremen. In the scope of contract work, the elaborate and valuable book cover had to be measured by the Bremer Institute for Metrology, Automation and Quality Science (BIMAQ) in high-resolution 3D using a fringe projection system. Since the object to be measured is an especially valuable exhibit, tactile measurement was ruled out entirely in order to protect the delicate book cover from damage. In addition, the large-format object has a multitude of details which all had to be scanned and measured. For this reason, only an optical, contact-free, non-destructive measuring technology with the possibility of extensive surface detection came into consideration.
SOLUTION AND PRODUCT
The Bremer Institute for Metrology, Automation and Quality Science (BIMAQ) is an engineering research institute at the Faculty of Production Technology at the University of Bremen which was established in 2007 after the federation of two research institutions. Committed to the transfer of knowledge, BIMAQ scientists work in both fundamental research and in application-based projects: From the development of new production or measuring methods to the optimization of production processes or the development of prototypes. The BIMAQ collaborates with international research institutions and companies, and employees a staff of around 40. The teams work in national research and industry projects, are involved in comprehensive EU projects, and play a key role in a special Bremen research field of the Deutsche Forschungsgemeinschaft (German Research Foundation). The BIMAQ's core competence is measuring technology with the supplemental fields of automation, quality science, and energy systems.
The leather cover of the historical illustrated book and the gravures on the binding had to be digitized. For this purpose, a COMET 5 fringe projection system was procured in the scope of a project subsidized by the BMU (Federal Ministry for the Environment, Nature Conversation, Building, and Nuclear Safety), which includes establishing a laboratory for large gear systems. In addition to a conventional tactile coordinate measuring device for large-format gears with diameters of up to 3 metres, a suitable measuring device was procured in the innovative fringe projection system from ZEISS Optotechnik. Since the University of Bremen is a public institution, the purchase of the fringe projection system was regulated by means of a public call for tenders.
In addition to the price, the low probing and sphere spacing deviations, the Matlab interface, the low weight, and the adjustable measuring mode (maximum resolution / maximum measuring speed) were the deciding criteria. The extreme flexibility in combination with the mobility of the system, in particular, drove the decision to procure the ZEISS Optotechnik system. With the possibilities for adapting the field of measurement, objects ranging in size from a few centimetres to several metres can be measured. The measurements can also take place under the widest range of environmental conditions. The introduction of the system proceeded smoothly and quickly. A selection of staff members visited the introductory training in Neubeuern and shared their knowledge with other staff members.
The metal clasp of the book was initially measured separately and served as the successful test run. The pointcloud consisting of millions of coordinates that were taken during single measurement shots was linked to a surface (triangular) model by means of the system software. With manual preparation of the measuring data, measuring errors were recognized and corrected. Additional automatic post-processing smoothed and optimized the final data. The Esprit CAM software generated the CNC code from the reworked data for an ORI SEIKI 5-axis CNC mill, which was used to reproduce the book cover first as a plastic model and then as an aluminium model. The high level of precision during the preparation now enables the further use of the duplicate as an exhibition piece and opens up further application possibilities for the measuring technology, as well as the production possibilities in the BIMAQ and the faculty at the University of Bremen.
RESULT / BENEFIT FOR THE CUSTOMER
The COMET 5 measuring system is used by multiple departments in the institute for the widest range of measuring tasks. The and the handling of optical measurement systems are also a component of several lectures and labs. Before the ZEISS Optotechnik fringe projection system was procured, there were two antiquated fringe projectors at the BIMAQ which could no longer meet the requirements of the institute. On the one hand, the fields of view of the systems were too small for research currently conducted at the BIMAQ, and on the other hand, the hardware/software components were no longer up to date. Optical geometric measuring technology is an important supplement to conventional tactile geometric measuring technology and is thus used within the research, instruction, and service spectrum of the institute.
Only a few trained staff members were capable of using the previous fringe projection devices due to their complexity. On the other hand, a number of staff members are familiar with the ZEISS Optotechnik system, thanks to its simple operability. This enables flexible use of the system without necessitating the expertise of only a few staff members. In addition, collaboration with students has been simplified considerably. The results of measurements are available more quickly, so the students can perceive the direct benefits of this measuring technology. With the new system, it is much easier to create interest in fringe pro-jection, which can then lead to new ideas for measuring tasks and is reflected both in the course of the lectures and labs, as well as in the students' written results.
“Thus far, the collaboration with ZEISS Optotechnik has always run smoothly. The company's technical support has saved us a great deal of time and frustration on more than one occasion, and the sales department is always ready to help and more than willing to adapt to our special requirements as an institute or university”, says the user. The measuring system is currently used in a few research projects and will serve as a reference method for newly developed measuring approaches for wind power systems, in particular. For this reason, an expansion of the field of view is planned, which should offer possibilities for measuring large-volume components. In addition, preparations are being made for the acquisition of a robot for instructional purposes, which could also be used as a positioning device for the measuring system.
ADVANTAGES / STATEMENT
• Optical geometric measuring technology as an important supplement to conventional tactile geometric measuring technology
• User-friendly, flexible, and mobile system
• High precision with minimal probing and sphere spacing deviations
• Adjustable measuring mode (maximum resolution / maximum scanning speed)
Dipl.-Ing. Michael Sorg, Head of Energy Systems and Material Testing Department, BIMAQ - University of Bremen