Measurement of the damped oscillation of a section of the UK East Coast Main Line (ECML) catenary/contact wire system was undertaken, and the natural frequency and mechanical damping were found to be 1.4Hz and 0.05 respectively. This information was used to assess the effect of increasing the mechanical damping ratio on the susceptibility of the system to an aerodynamic galloping instability. The section of line tested was known to gallop at wind speeds of approximately 40 mile/h, and theoretical and experimental work verified this. A friction damper arm was designed and three units were fitted to the section of line affected. The introduction of increased mechanical damping was found to raise the mechanical damping coefficient of the line to between 0.095 and 0.18, and the mathematical analysis produced a theoretical wind speed for galloping oscillation of between 75 and 141 mile/h respectively. For over a year since the units were fitted, no problems with galloping instability have been observed
Air motors, having inherently low cost, good power to weight ratio and intrinsically safe operation, can be utilised to control industrial robots. This paper describes the research carried out on the characterisation and control of a pneumatic system to provide actuation for a three-degrees-of-freedom (3 DO F) robot. The actuator which is used as a drive is a mechanically robust piston air motor constructed of aluminium, utilising a proportional spool valve to allow air-flow control. The dynamics of the air motor in conjunction with a solenoid valve have been experimentally determined using a single-degree-of-freedom robot system. A microprocessor, combined with a position sensor and a sensitive proportional valve allows the pneumatic robot system to be controlled, Numerous control strategies have been proposed rece~ly to control a 3DOF revolute robot arm. As such systems are nonlinear and result in coupled equations of motion it has been found necessary to employ advanced adaptive control theory to achieve satisfactory control. These approaches involve considerable on-line computation which can restrict the applicability of the control algorithm and requires the use of high powered (and expensive) computers. Four adaptive strategies have been extended to a 3DOF robot system and compared to a relatively simple modified PID approach which is not computationaUy intensive. From simulations the performance of the modified PID approach was found to be almost as good as the adaptive strategies considered.
With recent developments in N. C. manufacturing processes it is relatively straightforward to produce a journal bearing with spherical surfaces. Such a bearing offers two main advantages over a conventional bearing: it can tolerate much larger misalignment and it can resist axial forces. In this paper, the steady state performance of a spherical journal bearing is studied by using a finite bearing theory. The dynamic characteristics of the bearing are represented by eight displacement and velocity force coefficients and the boundary of bearing stability is determined. The effect of superlaminar flow upon the bearing performance is also studied, and typical bearing design charts are provided. In comparison, the behavior of the spherical journal bearing is found to be similar to that of an equivalent cylindrical bearing.
A shaft failure in a 634 kW diesel generator after 4000 hours of operation required investigation, especially when similar sets began to show signs of excessive bearing housing wear. The failure was found to be due to torsional fatigue caused by operation at an unforeseen resonant condition. The damage to the bearing housing of this type of set was also attributed to this behaviour. Replacement of the bearings and housings and redesign of the flexible coupling has been undertaken to prevent further failures. Modifications to design procedures are now being adopted to ensure similar problems do not occur in other existing or new machines
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