Closed-form inverse kinematics of 6R milling robot with singularity avoidance

For a 6R milling robot, it is necessary to convert the postprocessing cutter locations (CL) into the robot’s revolute joint variables. This paper introduces an algorithm for calculating the forward and inverse kinematics of a 6R robot according to the CL data generated by conventional CAD/CAM systems. A redundant mechanism is analyzed to avoid the singular configurations and joint limits. The Denavit–Hartenberg (D–H) convention is referred to for developing the forward kinematics, and a closed-form solution of the inverse kinematics is presented by means of kinematic decoupling. A fundamental approach with modifying factor for avoiding singularity are developed with regard to three-axis and five-axis CL data. A gap bridging strategy is applied to reduce the jerk motion caused by tool retraction and cut paths connection. Finally, the result is conducted to simulation and machining test to verify the algorithms.     

Development of a novel piezoresistive thin film sensor system based on hydrogenated carbon

Thin film sensor systems based on hydrogenated carbon have the advantage to combine two very important characteristics in order to be used in measurement engineering: Firstly, the sensory layer demonstrates piezoresistive behavior and secondly its good properties related to hardness and wear resistance lead in a tribologically stable system. Therefore, the thin film sensor systems can be applied into the main distribution of force within machine parts or used for universal interchangeable sensor systems, e.g. sensory washers. In this article the deposition of a self-contained thin film sensor system on a large technical component (spindle shaft) is shown. The spindle shaft with a length of 480 mm and an outer diameter of 90 mm is part of a belt driven machining spindle for planing machines in woodworking industries. In order to establish a measurement system, which allows monitoring the clamping force of the tool holder and the imbalance of the mounted tool, the thin film sensor system was directly applied to the front surface of the spindle shaft. For this application a novel self-contained thin film sensor system was developed, which consists of an alumina layer for electrical isolation, a chromium layer to establish internal sensor electrodes, a piezoresistive hydrogenated carbon layer (1 μm) and a second covering wear resistance and insulation layer (silicon and oxygen modified carbon layer). The piezoresistive sensor layer and the top layer are part of the diamond like carbon layer family (Robertson, Diam Relat Mater 12:79–84, 2003; Bewilogua et al. DLC based coatings for tribological applications, pp. 67–75, 2006; Biehl et al. Thin Solid Films 515(3):1171–1175, 2006, Novel measurement and monitoring system for forming processes based on piezoresistive thin film systems. Springer Verlag, pp. 879–883, 2010).     

Combinatorial preparation and characterization of thin-film multilayer electro-optical devices

In this article we present a setup for the combinatorial vapor deposition of thin-film multilayer devices as well as methods for the fast and efficient analytic screening of the libraries obtained. The preparation setup is based on a commercially available evaporation chamber equipped with various evaporation sources for both organic and metallic materials. The combinatorial approach is realized by the combination of a rotation stage for the substrate, a five-mask sampler, and an additional mask whose position can be deliberately varied along one axis during the evaporation process. The latter is used to evaporate linear as well as step gradients by continuous or stepwise movement of a shutter mask. The mask sampler allows to define the sectors of the library and to evaporate more complex structures, e.g., an electrode layout. Finally, the simultaneous evaporation of two or more materials enables us to produce layers of varying composition ratio in general and doped materials, in particular. For the control of the evaporation process we have developed an automation software, which is particularly helpful for complex library designs and which grants excellent repeatability of experiments. Efficient and fast characterization of the obtained libraries is realized by (i) a purely optical setup and (ii) an electro-optical setup. (i) The UV/vis reader FLASHScan 530 permits to map out the UV/vis absorbance or fluorescence of the whole library. The UV/vis absorbance is primarily used to determine layer thicknesses and to confirm thickness uniformity across larger regions. The fluorescence measurements are used to determine the composition of layers containing fluorescent dyes. (ii) For a detailed short- and long-term electro-optical analysis we have developed an automated measurement system, which allows the characterization of 8x8 optoelectronic devices and to study their degradation behavior. Both solar cells and organic light-emitting diodes can be tested. Finally, we have developed a data analysis software to extract characteristic values from the huge amount of data and with this facilitate the finding of systematic dependencies.     

Electro-conductive adhesives for high density package and flip-chip interconnections

Dispensable isotropic conductive adhesives (ICA) and snap-curing anisotropic conductive adhesives (ACA) are developed through the EC funded Brite EuRam project DACTEL #BE95-1503. They show very promising capabilities for high-density applications when compared to benchmark electro-conductive adhesives.As first high-density application, assemblies of ceramic and plastic ball grid array/land grid array (LGA) on FR4 with DAC3-102/14 ICA are realized. Mixed assemblies solder/ICA show poor results, especially during aging. Full polymer LGA assemblies are built successfully. Daisy chains with hundreds of transitions component/substrate present resistances as low as 4 Ω. After comparison with benchmark products, CLGAs show themselves to be particularly reliable under moisture conditioning.Secondly, flip-chip assemblies on board, of medium sized chips bumped with electroless NiAu and using DAC2-143/02 ACA, are performed. Contact resistances as low as 10 mΩ are produced. For this application, reliability results are succinct.Finally, flip-chip assemblies on glass of slim chips with NiAu bump pitch down to 80 μm, by means of the newly developed DAC2-143/02 ACA, are demonstrated. The material shows better performances than a benchmark anisotropic conductive film, where measurements reveal contact resistances lower than the sheet resistance of the transparent indium tin oxide metallization used in display applications. Thermal cycling and temperature storage reveal good behavior of the ACA paste.     

Semiquantitative method for the evaluation of grease barrier coatings

Many tests are known for testing the grease barrier performance of coatings in paper or paperboard. Some are manifested in standard procedures such as TAPPI, ASTM, or ISO, but as many procedures were developed and modified by companies and research groups. Mainly the test methods are based on visually detecting the amount of oil, which is in most cases dyed for better contrast, penetrating through the coating, meaning the procedures are based on a subjective visual evaluation and thus often not linked for instance to a statistical meaningful physical value. We found that by using a slightly modified ASTM D 722 test the L*a*b* color coordinates determined with a commercial handheld spectrophotometer are related to the grease barrier performance of an organic coating. By applying this new method the penetration time of an oil/dye mixture could be correlated to the lightness L* and chromaticity b* and fitted by an exponential function. Furthermore, the coating was slightly modified and an improvement or worsening of the grease barrier could be detected clearly outside of the statistical scatter of a control series. We call this method semiquantitative, since the level of grease barrier of a coating is not measured directly by a quantitative value, but color coordinates are correlated in a series to the effectiveness of the grease barrier.     

Synthesis and characterization of ABA-triblock copolymers with poly(ethylene glycol) segments and LC-segments

This paper describes the synthesis of ABA-triblock copolymers with poly(ethylene glycol) A-blocks and a liquid crystalline polyester B-block. Three block copolymer series are presented with different block length of A- and B-blocks. The block copolymers show thermotropic liquid crystalline behavior up to a content of poly(ethylene glycol) segments of 50 wt%. Depending on their composition and chain length, the block copolymers are microphase separated or non-microphase separated. In the microphase separated block copolymers the poly(ethylene glycol) segments are able to crystallize. The degree of crystallinity and the spherulite diameter is strongly influenced by the length of the poly(ethylene glycol) segment itself as well as by the length of the incorporated polyester segment. Received: 19 December 1997/Revised version: 22 December 1997/Accepted: 22 December 1997