On regularity, and the irregularity at surfaces

01. The idea that regularity is a possibility derives directly from the foundations of Euclidean geometry. We allow by it such concepts as the straightness of a straight line, the flatness of a plane, the sphericality of a sphere. We can extend the notion to allow in the imagination such other things as, the exact ellipticality of a plane section through an ellipsoid, or the exact equi-angularity at the apices of some regular polyhedron. Extending the meaning of regularity into the realm of joints, we can envisage if we wish, and please refer to figure 6.01, that the convex conical surface at the joint element on link 1 and the flat plane surface at the joint element on link 2 can make, with one another, continuous line contact. We can similarly imagine that the convex surface of the accurately constructed spherical ball on 2 can make, with the concave surface of the matchingly constructed, equi-radial, spherical socket sunk in 3, continuous surface contact. These and other such imagined, continuous contacts between a pair of joint elements in mechanism – they are not single point contacts or even multiple point contacts but contacts involving ∞1or ∞2 of points – can exist in our imaginations only by virtue of the wholly idealised, but well established concepts due to Euclid.

02. But we know that no mould can ever exactly fit its pattern, that no casting can ever exactly fit its mould, that no welded construction ever matches its production drawing, and that no subsequent machining is ever done on any job accurately.

Some remarks connecting with chapter 6

01. Associated with each set of points of contact and its associated tangent planes and contact normals at a simple joint in mechanism, is a system of motion screws; this is explained in chapter 6. The so-called system of screws or the screw system is simply the set of all of the IS As which are available for relative motion at the joint. It is taken for granted in chapter 6 that the simple joint is considered alone (§ 1.28), and that contact is not being lost at any of the points of contact at the joint (§ 6.15, § 8.12).

02. Provided each one of the contact normals at a joint is projectively independent of the other contact normals at the joint (§ 3.32), the system of motion screws at the joint takes for its numerical name the number six minus the number of points of contact. This matter is thoroughly canvassed in chapter 6; with two points of contact there is discovered and explored the quasigeneral 4-system for example, with three, the quasigeneral 3-system, and so on.

03. It is important to see that in general the systems of screws of which I speak in chapter 6 – they are the systems of motion screws – contain no screws which lie along the contact normals at the points of contact at the joints. The contact normals at any one joint belong as screws of zero pitch to other systems of screws, which are, as we shall see, reciprocal to the mentioned systems.

Transition comment

01. The broad matters discussed in chapter 1, namely those of freedom, mobility and the need for sufficient constraint in mechanism, are of great importance in the wide realm of practical machine design. They are derived however from a somewhat narrow set of assumptions regarding (a) rigidity in the absence of elasticity, (b) crookedness in the absence of accuracy, and (c) direct contact at joints in the absence of lubricated clearances. In chapter 1 there is thus developed what might be seen to be a somewhat simple theory of constraint. It is a simple theory; it is directly applicable; but only in a very rough way is it able to predict, for much of our ordinary machinery, the actual mechanical behaviour of the moving parts.

02. We often see in ordinary working machinery the unhappy effects of friction due to eccentricities of loading (§ 17.24), the consequent continuous likelihood of jamming, chatter, and wear, and the necessity for lavish lubrication at badly affected joints. Such phenomena will be evident whenever the kinematic design for a smooth transmission of the wrenches has been poor (§ 17.26), or, alternatively, whenever the jamming phenomena themselves have been an intended activity of the machine (§ 10.61). Although such matters are important and need to be studied, they are in a curious way irrelevant here. They are not the matters being implied at § 2.01.

Some bases for an argument

01. For the reader already familiar with other discussions about the cylindroid (chapters 6, 15, 16 and elsewhere) it will be clear that a cylindroid is always lurking wherever there is a situation of two degrees of freedom – or wherever there are two forces or wrenches acting (§ 10.14). For the reader unaware as yet of the relevant generalities, the present chapter may be taken as a piece of purposely confusing, preliminary reading. It must be said in the kinematics (and the statics) of mechanism that the simpler a situation appears to be, the more baffling its deeper aspects often are. The science of the relative motion of rigid contacting bodies is bedevilled by degeneracies of its general geometry; these degeneracies, when taken in isolation, have a tendency to render the science a miscellany of unrelated facts and alleged separate theorems for which there appears to be no integrative binding. This chapter deals with some of that miscellany but with almost none of its binding; I shall be dealing here with the kinematics of only a few special cases of two degrees of freedom and I offer no conclusive results at the end of it.

02. However with no more than a primitive understanding of the relationship c + f= 6, where c is the number of constraints upon a body and/is its number of freedoms (§ 1.52), we can begin a useful argument here about the matter of two degrees of freedom.

Introduction

The origin and at the very core of lean enterprise lies the design of the Toyota production system (TPS) and its ability to flow products through a low buffered manufacturing process (Womack et al., 1990). On first encountering the approach to systematically designing a high-performance production system, it appears counter-intuitive to many and a long way away from the Western traditions that have been dominated by mass production thinking (Womack and Jones, 1996). However, the ‘system’ design combines a number of key features which support customer service and the compression of time between receiving goods and receiving payment for the conversion process (Mather, 1988). This chapter will examine the basic elements of the ‘pull’ systems of a lean enterprise and explore alternatives for businesses that do not conform to the ‘high volume–standard product’ environment of automotive component manufacturing and assembly.

Production scheduling

The history of production scheduling in the West began with the use of clerical workers to schedule manually the complex products and the manufacturing/assembly processes so that products were outputted into the finished good stores just as customer due dates for orders were reached. In essence these planners attempted to launch production in time for when the customer expected delivery, but there were many aspects of traditional and mass production approaches which complicated even the most simple of manufacturing processes. These features included a core belief that batch production was the answer to cost efficiency (and therefore profit maximisation).

Introduction

The ‘art’ of designing a fully effective lean production system requires attention to detail and a keen eye on the standardisation of processes in a manner that makes working life simpler and better for those who work in the factory (Grief, 1991). On first encounter with a system that has been implemented with full visual management practices, observers find it a contradiction, the almost-clinical approach to the design of the workplace seems to conflict with the high premium lean manufacturers place upon team autonomy. In reality, there is no contradiction because visual management creates a standard which allows ‘abnormality’, in whatever form, to be detected quickly and frees the worker from thinking about the basics of good management in favour of applying thought processes to more important matters of improvement. It looks simple in operation but visual management is an art in itself and a lesson that is well worth learning as it provides a path for problem-solving and improvement activities in a way that can be sustained due to its simplicity and ‘ease of doing’ on a daily basis.

Examples of good visual management surround us all – the red markings on the rev counter on the dashboard of your car and the level markings on the side of your kettle to avoid overfilling, and even the different colours of fire extinguishers are just a few.

Getting started

The first stage in the ‘hands-on’ element of the lean journey is to orientate people's thoughts and interest through awareness raising and promotional activities. The purpose of awareness-raising seminars is to provide key personnel with knowledge of what to expect from CANDO activities and to understand why these activities take place. The seminars consist of an outline of the principles of lean, a business game to illustrate lean principles and a review of CANDO activities. The lean business approach looks to change the system, but also to drive the change with the workforce by including them in the decision-making and change process. As a result, it is important that the whole organisation is aware of the lean business approach, and gradually the training in the application of lean principles will cascade down throughout the organisation and out into the supply chain (Dimancescu et al., 1996).

CANDO is the most common starting point for the beginning of all change aimed at creating a lean production organisation and commences with the promotion of visible change within the workplace. Years of failed initiatives have resulted from good ideas that had little in them for those that were the subjects of the changes – the shop-floor teams. To create a positive management–employee relationship requires a clear signal from management that they are seriously focusing on lean as a business approach and not as a short-term initiative.

We have addressed the subject of lean holistically, though our discussion has by no means been exhaustive. Indeed there are endless aspects of lean implementation we could have tackled: the application of lean into the new product process, supply chain management or translation of lean into a service environment, to name just a few. However, for the purposes of focus and keeping our target readership, we have limited our discussions to lean implementation in a manufacturing environment. In this chapter we do allow ourselves a little latitude, and cast our thoughts to what we believe are some of the major challenges facing our target readership today. An awareness of these issues is a sound starting point for solving them. Key to this is the prime driving force of lean – that of delivering value to customers. Before we continue, however, we offer the reader a brief summary of this journey through the book so far. For those that have read the book from end to end, this will act as a review and reminder; for those that have dipped in and out, this will offer a useful overview.

Brief review of the book

In our Introduction we present our research sponsors and dismiss the myth that lean is just an automotive or Japanese phenomenon. We identify our target readership and set our aims and objectives in writing this book.