Umlauffähigkeit räumlicher mechanismenConditions for the complete rotation of spatial mechanisms

For four-membered plane, spherical and spatial mechanisms whose transfer functions are of the same structure, a common theory for the conditions of complete rotation is given. The transfer equation has to allow for the interpretation as the algebraic correspondence of type (1,2) between two conic sections. For this, the theory of conic pencils is required establishing a complete classification of these drives. The reality of the cluster points and the kind of the conic sections supply information on the conditions for complete rotation and the kind of output motion. The conditions for complete rotation are represented independent of the transmission type.     

Type synthesis of spatial mechanisms on the basis of spatial single loop structural groupsTypensynthese räumlicher mechanismen auf der grundlage räumlicher einfach geschlossener strukturgruppen

This paper describes the basis for a new method of type synthesis of spatial mechanisms with the use of single-loop structural groups having zero degrees of freedom. Applying the binary system, the value 0 is used for R (revolute) and 1 is used for P (prismatic) pairs. The five-link spatial groups are described by codes both in the binary and decimal systems. All other groups are reduced to the basis of five-link spatial groups. In these cases two-degree-of-freedom and three-degree-of-freedom kinematic pairs are transformed to one-degree-of-freedom pairs, and these transformations are also described by codes in the binary and decimal systems. This method of coding can be programmed for digital computation and applied towards the automatic type synthesis in the design of spatial mechanisms. The system is equally clear for alphanumeric or for graphical display. To the designer it defines the diagram of the mechanism, pointing out the frame, the mobile links, the types of the kinematic pairs and their mutual disposition in the mechanism configuration.     

Special configurations of spatial mechanisms and robot armsSpezielle konfiguration räumlicher mechanismen und roboterarme

A novel general method is developed for determining special configurations of all single-loop mechanisms. The results are illustrated by means of numerical examples. In addition special configurations of robot arms are investigated, and a simple result which has important practical application is deduced; “when all the screws representing the instantaneous motion of the joints of a robot arm are reciprocal to a common screw or screw then the end effector cannot have free instantaneous movement parallel to the axis or axes of the reciprocal screws”.     

Determination of the condition of existence of complete crank rotation and of the instantaneous efficiency of spatial four-bar mechanismsBestimmung der existenzbedingung einer kurbel und des momentanen wirkungsgrades räumlicher viergliedriger mechanismen

This paper treats the derivation of the general conditions of existence of complete crank rotation in spatial RS_sSR and RS_sSP four-bar mechanisms. These conditions take the form of inequalities which must be satisfied by the coefficients of a quartic equation, with the tangent of the output half-angle as the unknown. Previously derived criteria for special cases (such as the planar four-link mechanism and the 3D-slider-crank) are shown to agree with the new general conditions. The instantaneous quasi-static efficiency of these mechanisms is also presented.     

Mathematical models for analysis and synthesis of spatial mechanisms—IV Seven-link spatial mechanismsMathematische modelle zur analyse und synthese von räumlichen mechanismen. Teil 4: Räumliche mechanismen mit sieben gelenken

In this paper the decomposition method for kinematic synthesis and analysis is extended to 7-link spatial mechanisms. By the way of examples mathematical models for the general 7R mechanism, and RRRPRRR, RRRRPPRR, RRPRPPR 7-link spatial mechanisms are developed whichi are representative of the 42 types of single-loop 7-link spatial mechanisms.     

Mathematical models for analysis and synthesis of spatial mechanisms—I: Four-link spatial mechanismsMathematische modelle zur analyse und synthese von räumlichen mechanismen. Teil 1: Räumliche 4 gliedrige mechanismen

In this paper mathematical models of links connecting all possible combinations of lower kinematic pairs are described simply by determining direction cosines of various joint axes using Plücker line coordinates. These models can be used in conjunction with the decomposition method [4] to analysis and synthesis single and multi-loop spatial mechanisms.     

Widerstand gegen abrasiven verschleiss und dynamische bruchzähigkeit weisser vanadingusseisen

The wear behaviour under abrasive sliding loading, the structure and dynamic fracture toughness of white cast iron containing (4 – 6)% V are considered in this paper. In wear systems containing hard abrasive particles (silicon carbide), the dynamic fracture toughness and wear resistance increase with increasing austenite content in the structure. In systems with less hard abrasive particles (e.g. flint, garnet) these alloys exhibit a combination of high fracture toughness and high wear resistance. The vanadium-alloyed white cast irons with a predominantly austenitic matrix show more favourable values with respect to both dynamic fracture toughness and wear resistance in comparison with a simultaneously tested chromium white cast iron.     

Die ermittlung selbstanpressungsfähiger zwischenräder-anordnungen für Reibrädergetriebe mit hilfe von graphen

Friction drives with intermediate wheels are in many ways advantageous compared with those without. Intermediate wheels can generate the correct pressure-force relationship automatically. However, a designer must know all the ways in which forces can act upon such a wheel. In this paper, these ways are described for amorphous wheels. Graphs are then formed, in which vertices represent the loci of the forces acting on the wheels, and which yield the same vertex-induced permutation group as do the loci of the wheels. In any of these graphs, one can find all configurations of two-colored vertices not mappable onto each other. The technical interpretations of the vertex-colored graphs can then easily be followed.     

Mathematical models for analysis and synthesis of spatial mechanisms—III Six-link spatial mechanismsMathematische modelle zur analyse und synthese von räumlichen mechanismen. Teil 3: räumliche mechanismen mit sechs gelenken

In this paper the decomposition method for kinematic synthesis and analysis is extended to all 6-link, single-loop spatial mechanisms. This is accomplished by solving sets of equations which can be used to describe mathematical models of all 6-link spatial mechanisms. These sets of equations are solved sequentially in an organised way by subdividing the sets of equations into groups of equations which describe the intersection of two planes with a unit radius sphere (computer programme PREB3), and the intersection of a plane and a unit radius sphere (computer programme PREB2). By way of examples mathematical models for RRRTRR, RRPRTR, RTRPRP, RRPPRC spatial mechanisms are described which are representative of the 130 distinct 6-link spatial mechanisms.     

A closed-form linear multi-step algorithm for the steady-state response of high-speed flexible mechanismsEin schlie ungsformiger linearer mehrschrittalgorithmus zur bestimmung stationarer erzwungener schwingungen von schnell-aufenden elastischen mechanismen

Based on the general form of linear multi-step methods, a closed-form algorithm for the steady-state solution of periodically time-dependent vibrating systems—high-speed flexible mechanisms with uniform rotation input can be taken as a special case—is developed. The algorithm is tested by three examples and verified by comparing the computational responses with the previously published experimental results. Besides, the computational results also show that this algorithm, compared with Fourier series method, is of higher accuracy and far higher computational efficiency.     

4×4电容式触摸键盘的设计与实现

随着电子技术的发展,触摸按键作为一种接口技术在电子产品中得到了广泛的应用,由于电容式触摸按键具有寿命长、无机械磨损、易清洁、防水防污等特点,深受用户欢迎。该文结合电容触摸按键的原理,利用STM32单片机通用定时器的输入捕获功能,设计实现了4×4电容式触摸键盘系统。经测试,电路具有较高的可靠性。     

Mechanismen für die gleichmässige teilung der ellipse

Die gleichmäßige Teilung der Ellipse in eine Anzahl n gleichlanger Bogenstücke ist ein analytisch nicht lösbares Problem. Numerisch kann diese Aufgabe ohne weiteres gelöst werden. Technische Bedeutung hat die Lösung für die gleichmäßige Anordnung von Elementen auf dem Umfang eines elliptischen Werkstückes. Für die Teilung von Ellipsen an Werkstücken, die auf Unrund-Drehmaschinen (Oval- oder Ellipsendrehmaschinen) gefertigt werden, bieten sich nichtlinear geteilte Ellipsen-Teilscheiben an. Einem historischen Vorbild folgend, und zwar dem Compensating Index Mechanismus von J. J. Holtzapffel, werden Mechanismen untersucht, die die Teilung der Ellipse mit hinreichender Annäherung erreichen, eine einfache technische Lösung darstellen und möglichst stufenlos auf das Achsenverhältnis der zu teilenden Ellipse einstellbar sind.     

Dry and oil-lubricated sliding wear of Si<Subscript>3</Subscript>N<Subscript>4</Subscript> and Si<Subscript>3</Subscript>N<Subscript>4</Subscript>/BN fibrous monoliths

A high-temperature ball-on-flat tribometer was used to investigate dry and oil-lubricated friction and wear of sintered Si₃N₄ and Si₃N₄/hexagonal boron nitride (H-BN) fibrous monoliths. The friction coefficients of base Si₃N₄ flats sliding against Si₃N₄ balls were in the range of 0.6–0.8 for dry and 0.03–0.15 for lubricated sliding, and the average wear rates of Si₃N₄ were 10^–5 mm³ N^–1 m^–1 for dry sliding and 10^–10–10^–8 mm³ N ^–1m^–1 for lubricated sliding. The friction coefficients of Si₃N₄ balls against composite fibrous monoliths were 0.7 for dry sliding and 0.01–0.08 for lubricated sliding. The average specific wear rates of the pairs were of the same order as those measured for the conventional Si₃N₄ pairs. However, the fibrous monoliths, in combination with sprayed dry boron nitride, resulted in reduction in the lubricated friction coefficients of the test pairs and significant reduction in their wear rates. The most striking result of this study was that the coefficients of friction of the Si₃N₄/H-BN fibrous monolith test pair were 70–80 lower than those of either roughened or polished Si₃N₄ when tests were performed under oil-lubricated sliding conditions over long distances (up to 5000 m). The results indicated that Si₃N₄/H-BN fibrous monoliths have good wear resistance and can be used to reduce friction under lubricated sliding conditions.     

Wechselbiegeapparatur für die in situ-Untersuchung von Zerrüttungsvorgängen im Rasterelektronenmikroskop

An SEM stage (Fig. 1 and 2) is described which allows bending fatigue of metallic specimens in the vacuum of the specimen chamber. With the aid of inductive displacement pick-ups the angle of bending can be measured (Fig. 3) as well as the momentum of bending (Fig. 4). Thus the mechanical hysteresis can be registrated and the fatigue of the specimen can be controlled. Fig. 5 shows the geometry of the fatigue specimen, which has an electrolytically polished surface area of about 6 × 3 mm² on which the development of deformation topography can be studied during the fatigue experiment. The main advantages of the new fatigue apparatus are:

• 1 No interruption of cyclic straining is necessary for the investigation of the specimen surface.
• 2 The specimen is in vacuum during the complete experiment so that environmental influences are reduced.
• 3 The development of surface topography can be monitored continuously.
• 4 Differences of the topography (e. g. fatigue cracks) in the phase of tension and compression can be detected.

In the case of fatigue of polycrystalline metals, fatigue cracks often start at the surface of the specimen in slipbands produced by the cyclic straining. Fig. 6 shows typical fatigue slipbands with extrusions and intrusions for pure Al. A slipband crack in a later stage of fatigue is shown in Fig. 7. For the investigation of the distribution of fatigue cracks at the surface the possibility of watching the surface in different phases of bending is a great help. The cyclic crack opening – which depends on the crack depth – can be seen by eye on the TV-screen and can be recorded on video tape when the frequency of bending is about 1 cycle/s or can be photographed from the record display at very low frequencies of bending. Fig. 8 gives an example of the difference in crack opening in the phase of tension and compression of the specimen surface respectively.     

Studying kinetics of scintillation process in a CaMoO<Subscript>4</Subscript> crystal

The kinetics of scintillation process in Czochralski-grown CaMoO₄ crystals excited by α particles and γ rays from ²³⁸Pu and ¹³⁷Cs radioactive isotopes, respectively, is investigated. Kinetics of scintillations is shown to be complex and multicomponent in character. Fast and slow scintillation components are observed, and their relative contributions to the total light yield in the scintillator are determined. The possibility is demonstrated of discriminating between scintillator signals due to α particles and γ rays.     

Measuring the light yield in a CaMoO<Subscript>4</Subscript> scintillating crystal

The light yield in CaMoO₄ scintillating crystals irradiated with α particles and γ rays from ²⁴¹Am and ¹³⁷Cs radioactive isotopes, respectively, have been measured. It is shown that the light yield in this crystal for γ rays, measured in the wavelength range of 400–700 nm at room temperature (22°C), is ～3000 photons/MeV, and the ratio α/β is ～0.25.     

Ungenutzte möglichkeiten der nichtumlauffähigen (totalschwingenden) gelenkvierecke

Possibilities of non-rotatable four bars have not yet been used, up to now. To produce periodic motions four bars are still having members which are able to ratate. Totally oscillating mechanisms do not allow rotating motions at all. After having found methods to drive mechanisms of this kind by an additional rotating crank, it should be shown that there are advantages to their use in practical application.     

Evaluation of cyanoacrylate glues for making attached living-leaves epidermis replicas and its scanning electron microscopy observations (evaluación de pegamentos de cianoacrilato para hacer réplicas epidérmicas en hojas vivas adheridas y su observación al MEB)

Six brands of cyanoacrylate glue were tested to make inverse replicas of a leaf's epidermis. All of them gave satisfactory results for observations up to 8000x with a Philips XL-20 scanning electron microscope (SEM), working at 10 kV. Genus of plants used were Xanthosoma sp., Psidium sp., Melicocca sp., Sorghum sp., and Stenotaphrum sp. The main limitations were that the epicuticular wax gets embedded within the glue. Spindle- or oval-shaped artifacts are produced by stomatal apertures. This paper confirms previous findings related to the fact that cyanoacrylate glues are an alternative method for making fast, inexpensive, and sturdy epidermis replicas for scanning electron microscopy observation.     

A low cost,one-piece nitrogen burst processing rack for 3¼× 4 inches and 4×5 inches TEM and SEM negatives

A processing rack designed with a built-in nitrogen burst plenum to accommodate 3¼ × 4 in. and 4 × 5 in. negative can be inexpensively constructed from plexiglass.     

Progression of fretting fatigue damage in Ti–6Al–4V

An investigation was conducted to explore the nature of fretting fatigue damage in the stages prior to crack formation. In the unique experimental apparatus employed in this study, where total slip never occurs, several locations on each test specimen exist where cracks can develop due to local contact conditions. Under the test conditions used, not all of the sites had cracks upon test completion. This study evaluated the condition of non-cracked sites on several fretted specimens in an effort to identify differences between these and sites where small cracks were observed.A single test condition of 620 MPa average applied static clamping stress and 250 MPa applied axial fatigue stress for R=0.5 was selected, which corresponds to a fretting fatigue life of 10⁷ cycles based on prior work. For specimens tested to 10⁶ cycles, or 10% of life, several destructive and non-destructive characterization methods were chosen: scanning electron microscopy (SEM), residual stress measurement and transmission electron microscopy (TEM). Each site at which crack nucleation could be expected was inspected in the SEM and was then characterized using surface X-ray diffraction to quantify the residual stresses field near that location. Then TEM foils were cut from one area on a specimen with tiny cracks and dislocation densities were observed. A novel technique was used which permitted TEM samples to be obtained from regions in close proximity on the original specimen.Comparisons were made between as-received (AR) and stress-relief annealed (SRA) specimens, on which the stress-relief was applied prior to fretting fatigue testing. SEM inspection was useful for qualitative analysis of wear debris and identification of cracks as small as 20 μm, but was unable to provide quantitative data on the level of fretting fatigue damage beyond crack size. Although differences were noted in the residual stresses for the SRA versus the AR specimens, no residual stress peaks were noted in the edge of contact regions where cracks would eventually develop. TEM observations in the vicinity of the crack nucleation region showed that the dislocation structure decayed rapidly into the specimen thickness. The cause of the dislocations was attributed to plastic deformation caused by the clamping stresses.