Michael French

The spring-and-lever balancing mechanism, George Carwardine and the Anglepoise lamp

Abstract Two short and direct methods of exact analysis of the spring-and-lever balancing mechanism are presented. It is shown that perfect balance can be achieved by the use of a close-coiled spring whose free length is effectively zero and whose stiffness is chosen appropriately. The two-degree-of-freedom balancing mechanism, commonly seen in desk lamps but useful in many other situations, is then analysed. The treatment is extended to allow for the weight of the components of the mechanism itself. The originator of these devices was George Carwardine, whose patents over the period 1931–35 show the evolution of his ideas on this subject. A short biographical note is included as an appendix.

Function Costing: A Potential Aid to Designers

SUMMARY A potential aid to engineering designers is offered by the concept of Junction costing. Many functions can be quantified and the cost associated with that function is often simply related to the quantity or quantities. Obtaining reliable data is difficult, except in the case of components marketed as such, but fortunately there are many of these, such as bearings, reduction gearing and actuators. The problems of modelling cost in terms of function are briefly addressed. The uses of function costing are also discussed, the estimation of cost directly from the specification, the comparison of alternatives, and the detection of areas of potential cost reduction, as in value engineering. An important principle u that the costs used for modelling should be representative of the best (i.e. most economical) practice, wherever found.

The opportunistic route and the role of design principles

This paper describes some aspects of the opportunistic mode of design which, it is held, most designers adopt, particularly for the step from concept to embodiment, or means to form, in which it is most characteristically seen. Simple examples are given which show the operation of constraints in directing the designer, and the strengths and weaknesses of the approach are discussed. Suggestions are made as to the important role design principles can play, and how their systematic introduction could help. Some notes are given on a computer aid which is being developed to prompt the designer in the use of appropriate principles at the appropriate stage in the work.

The exploitation of low-head hydropower by pressure interchange with air, using siphons

Abstract The paper describes and analyses a hydropower system based on siphons in which the pressure of low-head water is converted into air pressure. The analysis suggests that, with careful design of the flow passages to minimize losses, air-pumping efficiencies of 70 per cent or more should be achievable; the overall efficiency of the hydropower system should be better than 60 per cent. Although such values of efficiency are lower than usually found in hydro plant, the economics of the system are likely to be attractive owing to the low capital cost of the system compared with conventional water turbine systems. It is shown that a siphon plant is suitable, in single-stage from, for heads up to about 1.7m. For higher heads the system can be used in two or more stages.

Design Principles Applied to Structural Functions of Machine Components

The functional designer can derive help in his work from various principles, such as the minimization of unsprung mass and the principle of least constraint. This paper lists three groups of such principles which bear upon the structural aspects of design. These are structural design principles proper, general principles bearing upon the structural aspects and principles relating to joints. Some examples from mature technology are given, but the chief use of principles is in cases of evolution or innovation. Some related concepts (efficiencies of use) are given and a brief mention is made of the possible value of such principles in the development of the P-aesthetic sense by which designers recognise good solutions at an early stage.

Analysis of a pitching-and-surging wave-energy converter that reacts against an internal mass, when operating in regular sinusoidal waves

The paper examines the behaviour of a pitching-and-surging wave-energy converter driven by unidirectional waves that exert harmonically varying forces on its hull. The power take-off (PTO) is by means of an inertia that moves either on a straight horizontal rail or on an arm that turns about a horizontal axis. Angular displacements are taken to be small, so that linear analysis is appropriate; these are idealized conditions, but any wave-energy converter must be able to operate effectively in ideal conditions. For good power capture with the least engineering difficulties, it is found that the power take-off inertia should be centred as high as possible above the overall centre of mass G. It is shown that power is captured from the waves by motion of the centre of pressure P relative to the overall centre of mass G. This can only result from motion in pitch and is dependent on the fact that there is a large vertical distance between points P and G. It is found in practical cases that the added mass of water generally brings G closer to P, and this limits the power that can be captured.

Semantic modelling of engineering designs.

The entity-relationship (E-R) approach is a widely used technique for the semantic modelling of commercial database systems. This paper demonstrates that the E-R method can also be applied in the modelling of static design knowledge for knowledge-based engineering design systems. It presents the basic definitions of the E-R data modelling method and describes some extensions which are useful to model the functionality of system components. It demonstrates the use of this method to produce a generic model of a centrifugal hydraulic pump, which is being used in the implementation of an object-oriented intelligent CAD system. Finally, conclusions on the suitability of the entity-relationship for engineering knowledge representation are drawn.

Function Cost of Pressure Vessels and Rolling Element Bearings

The aim of function costing is to provide designers with a technique for estimating costs directly from the specification of a product or system. This paper provides function cost information for pressure vessels and rolling element bearings. It is shown that the cheapest pressure vessels are much longer and thinner than vessels in common use, i.e. pipes. The costs of both roller and ball bearings are approximately proportional to their load capacities. For bearings selected on the basis of their fatigue performance, i.e. when the dynamic load rating is used for selection, the most economic bearing is that with the greatest value for the ratio D/d. The effect of not achieving this optimum ratio of D/d is also shown.

The design of torsion catapults

Abstract This paper briefly describes the Ancient Greek catapults and shows the design to have been sophisticated but poor. It then goes on to show how any of three design principles, properly understood and applied at a high level of abstraction, will lead readily to a much superior design. It is hoped that this strange stematic illustration may help to promote interest in the systematic use of such abstractions and principles in practical design.

Economical conversion of low-head hydropower

Publisher Summary The chapter describes a method of harnessing energy from low heads, without using water turbines. The system is simple and robust. All the major parts are mounted out of the water, and in particular the turbine and alternator can be placed in a convenient dry location. The relatively low cost of this system could make significant amounts of new hydropower economically available in many parts of the world. Proposals for exchanging pressure between water and air have been put forward based on alternating displacement mechanisms but these suffer from the disadvantages of large size and cyclic operation. The hydropower system based on pressure-exchanging siphons offers the prospect of harnessing power economically from the large number of low-head hydro sites that are not viable using water turbines. Efficiencies of 70% or better should be achievable. Although such values of efficiency are lower than usually found in hydro plant, siphon installations should be economic owing to the relatively low capital cost of the system.