Experimental and Statistical Parametric Optimisation of Surface Roughness and Machining Productivity by Lapping

The quality of surfaces machined by lapping depends on numerous variables, some of them controllable and others not. Their existence renders the task of selecting adequate working parameters and their values (set points) such as to obtain the desired response difficult. For this reason, this paper discusses the robust parameter design as an optimisation method for plane lapping. The paper presents the working equipment, the utilized methodology as well as the obtained experimental results. The output quantities selected for describing the lapped surface quality and the machining productivity, respectively, were roughness Ra and the height of the cut layer h

APPLICATIONS OF PNEUMATIC MUSCLES DEVELOPED AT THE FESTO REGIONAL RESEARCH AND TRAINING CENTRE OF BRAŞOV

Compressed air is one of the most important sources of energy in industry, pneumatic actuations tending to hold an increasing share in the conception of modern industrial systems. At present, due to the development of new pneumatic components and systems assemblies of high complexity can be achieved, many of them with applicability in robotics. Such a component is the pneumatic muscle, increasingly deployed in actuation systems, particularly in the field of industrial robots. The paper presents some of the results of research conducted at the Festo Regional Research and Training Centre (FRRTC) at Transilvania University of Braşov

The Rap–RapGAP complex: GTP hydrolysis without catalytic glutamine and arginine residues

The GTP-binding protein Rap1 regulates integrin-mediated and other cell adhesion processes. Unlike most other Ras-related proteins, it contains a threonine in switch II instead of a glutamine (Gln61 in Ras), a residue crucial for the GTPase reaction of most G proteins. Furthermore, unlike most other GTPase-activating proteins (GAPs) for small G proteins, which supply a catalytically important Arg-finger, no arginine residue of RapGAP makes a significant contribution to the GTPase reaction of Rap1. For a detailed understanding of the reaction mechanism, we have solved the structure of Rap1 in complex with Rap1GAP. It shows that the Thr61 of Rap is away from the active site and that an invariant asparagine of RapGAPs, the Asn-thumb, takes over the role of the cis-glutamine of Ras, Rho or Ran. The structure and biochemical data allow to further explain the mechanism and to define the important role of a conserved tyrosine. The structure and biochemical data furthermore show that the RapGAP homologous region of the tumour suppressor Tuberin is sufficient for catalysis on Rheb

Establishing the torsional rigidity of a rotation module responsible for the flexion-extension motions of the elbow

The paper presents and discusses a system devised for the mobilisation of the elbow including a pair of agonist-antagonist pneumatic muscles aimed mainly at ensuring the accuracy of the rotation angle. This system is of SISO type (single input - single output) with the variable Δp (the pressure by that one of the muscles is charged symmetrically in the detriment of the other) as its input value. Further discussed are the dependency of the equilibrium angle on Δp and the possibility of controlling the torsional rigidity by adjusting the sum of the feed pressures

Tribological Behavior of Hydraulic Cylinder Coaxial Sealing Systems Made from PTFE and PTFE Compounds

Current trends concerning hydraulic cylinder sealing systems are aimed at decreasing energy consumption which can be materialized by minimizing leaks and reducing friction. The latest developments in the field of materials and sealing system geometries as well as modern simulation possibilities allow maximum performance levels of hydraulic cylinders. Reducing friction is possible by hydro-dynamic separation of the sliding and sealing points already at very low velocities and by using materials, such as plastomers, from polytetrafluoroethylene (PTFE) (virgin PTFE and filled PTFE). It is within this context that this paper discusses a theoretical and experimental study focused on the tribological behavior of coaxial sealing systems mounted on the pistons of hydraulic cylinders. It presents a methodology for the theoretical determination of the lubricant film thickness between the cylinder piston and the seal. The experimental installation used for measuring fluid film thickness is presented, and the results obtained under various working conditions are compared to the theoretical ones. For the analyzed working conditions related to pressure, speed, and temperature, the paper concludes with a set of criteria for the selection of the optimum seal material so as to maximize energy efficiency

Experimental Research on Polymer-Based Coaxial Sealing Systems of Hydraulic Cylinders for Small Displacement Velocities

Reducing friction in the coaxial sealing systems of hydraulic cylinders is one of the solutions for increasing the energy efficiency of industrial actuations. This is a requirement, particularly in the case of small velocities that carry the risk of eigen-vibrations and/or stick-slip. The authors discuss the experimental research conducted on three coaxial sealing systems made from thermoplastic polymer and polyurethane type materials. The paper presents the equipment and method used for the experimental determination of static and kinematic friction coefficients and discusses the subsequent results obtained to test different working parameters. The experimentally determined friction coefficients yielded a range of materials recommended for coaxial seals such as to minimize the occurrence of jerky operation

Static analysis of a torsion motor generating flexion - extension motions of the elbow

The paper presents the construction and static analysis of a rotation module responsible for conducting flexion-extension motions as part of a medical rehabilitation device of the elbow. The rotation module is actuated by a torsion motor consisting of a pair of agonist-antagonist pneumatic muscles. The study concerning the static behaviour of the rotation module draws upon similarity to the biological model, considering the influence of the neuronal control quantities on the forces developed by the two muscles

Developing an Analytical Model and Computing Tool for Optimizing Lapping Operations of Flat Objects Made of Alloyed Steels

Lapping is a finishing process where loose abrasive grains contained in a slurry are pressed against a workpiece to reduce its surface roughness. To perform a lapping operation, the user needs to set the values of the respective lapping conditions (e.g., pressure, depth of cut, the rotational speed of the pressing lap plate, and alike) based on some material properties of the workpiece, abrasive grains, and slurry, as well as on the desired surface roughness. Therefore, a mathematical model is needed that establishes the relationships among the abovementioned parameters. The mathematical model can be used to develop a lapping operation optimization system, as well. To this date, such a model and system are not available mainly because the relationships among lapping conditions, material properties of abrasive grains and slurry, and surface roughness are difficult to establish. This study solves this problem. It presents a mathematical model establishing the required relationships. It also presents a system developed based on the mathematical model. In addition, the efficacy of the system is also shown using a case study. This study thus helps systematize lapping operations in regard to real-world applications

Fin-Ray effect® based structure for the passive mobilization of the hand joints

In medical rehabilitation and physical therapy practice it has been proved that the passive mobilization of the hand joints as part of rehabilitation exercises improves the recovery period and also diminishes the rehabilitation costs by about 50%. In order to facilitate the practice of passive mobilization exercises in both medical units and patient homes the development of new adequate rehabilitation equipment has become a necessity. It is within the context of this requirement that the paper puts forward and discusses a novel solution of rehabilitation equipment that makes possible the simultaneous exercising of the radiocarpal, metacarpophalangeal and interphalangeal joints. The first novelty proposed by this equipment is using the Fin-Ray effect® in the construction of the hand support and mobilization structure. A further novelty is the utilization of a pneumatic muscle as the motor that drives the equipment. The paper presents the construction of the equipment and discusses range of motion generated by it compared to the corresponding motion limits of the human hand, as identified in literature