millwrights to mechatronics: the merits of multi-disciplinary engineering

Pergamon

0957-4158 (94) E0025-L

Mechatronics Vol. 5, No. 2/3, pp. 95-115, 1995 ~) 1995 Elsevier Science Ltd

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MILLWRIGHTS TO MECHATRONICS: THE MERITS OF MULTI-DISCIPLINARY ENGINEERING*

T I M K I N G

School of Manufacturing and Mechanical Engineering, The University of Birmingham, Edgbaston, Birmingham B15 2TF, U.K.

(Received 14 April 1994; accepted 14 April 1994)

Abstract--In recent years the term "Mechatronics" has come into use to describe a multi-disciplinary approach to engineering (and particularly engineering design) in which a symbiosis of mechanical, electrical, electronic, computer and software engineering is used to create new design solutions to engineering problems. These mechatronic designs can often be more effective than traditional solutions rooted in mono-disciplinary engineering. This paper notes that virtually all engineering was once the province of millwrights and discusses its division into the many currently recognised constituent, and largely separate, disciplines. It is argued that this has followed from the principles of efficiency through division of production which have long been a tenet of capitalist manufacturing. In the closing two decades of the twentieth century there has been a move to return to more integrated production techniques and, with the development of microprocessors and microprocessor controlled systems and products, a need for integration in engineering design and education. The ways in which microprocessors have been applied to, or embedded in, contemporary products, machines and systems are categorised and examples of the design of mechatronic devices, with which the author has been associated, are presented.

M I L L W R I G H T S TO ENGINEERS

The existence and impor tance of millwrights in Britain goes back at least as far as Saxon times; the first doc um e n t a ry record of a water mill dates f rom 726 CE. By 1086 the D o m e s d a y survey was able to record the existence o f 5624 water mills in England. E v e n by this early date not all o f these were for the agricultural purposes of corn milling and irrigation. The s teady deve lopment o f the manufac ture o f wool len cloth during the middle ages made it the count ry ' s greatest source o f wealth. Wate r powered fulling mills for scouring and felting woven cloth were an established technology by the end of the twelfth century enabling the English poe t William Langland to write in the late four teen th century; "Cloth that cometh fro the weaving is naught comeley to wear, Till it is fulled under foot or in the fulling s tocks . . . " [1].

The scope of the millwrights ' craft had become wide reaching and so it was to millwrights tha t the inventors and capitalists o f the late e ighteenth century turned for assistance in developing the new machines on which the industrial revolut ion was founded . Co t ton replaced wool as the principal textile fibre and millwrights built the co t ton mills and their machinery , that so dramatical ly t ransformed the t echnology of manufac ture .

The professions o f the mechanical or civil engineer had not yet been defined or

*Inaugural Lecture, 17 March 1994.

95

96 T.G. KING

differentiated; the millwright was the closest approximation to both. Sir William Fairbairn, a leading civil engineer and himself apprenticed as a millwright, wrote in 1861 [21:

"The millwright o f former days was to a great extent the sole representative of the mechanical art . . . he was an itinerant engineer and mechanic of high reputation. He could handle the axe, the hammer and the plane with equal skill and precision; he could turn, bore or forge with the despatch o f one brought up to these trades and he could set out and cut furrows of a millstone with an accuracy equal or superior to that of the miller himself . . . Generally he was a fair mathematician, knew something of geometry, levelling and mensuration, and in some cases possessed a very competent knowledge of practical mathematics. He could calculate the velocities, strength and power o f machines, he could draw in plan and section and could construct buildings, conduits or water courses in all forms and under all conditions required in his professional practice. He could build bridges, cut canals and perform a variety of work now done by civil engineers. "

It is, then, to millwrights that we should attribute the vital technical steps towards the great changes that were to take place. But their identity as a single trade was to be short lived. According to E. P. Thompson [3] " As late as 1818 the Book of English Trades (a pocket book based mainly on London skills) does not list the trades of engineer, steam engine maker or boiler-maker . . . [but] only ten years later there was published The Operative Mechanic and British Machinist, running to no less than 900 pages, showing the extraordinary diversity of what had once been the mill-wright's craft' '.

The rapid transformation of the British economy brought about by the industrial revolution has been put down by many to the application of the principle of division of labour. Adam Smith's discussion (which pre-dates significant developments in automated machinery) of the manufacturing improvement gained by the separation, between a number of workmen, of the successive steps in the task of pin making has become a celebrated example.

With the development of "self-acting" machines by master mechanics such as the inventor of the lathe slide-rest, Henry Maudslay, it was not long before the principle of division of labour could be seen echoed in systems of machines for serial production. One of the most famous examples is the series of 45 machines (of 22 different kinds) designed by Marc Brunel and built by Maudslay for the manufacture of ships' pulley-blocks. Each of these machines performed a single operation. When installed at the naval dockyard at Portsmouth in 1805 they were said to have been able to satisfy the Royal Navy's requirement for over 100,000 ship's blocks per year, but were operated by only 10 workers compared with the 110 skilled craftsmen previously required [4]. This was the world's first example of a fully mechanised production line [5]. The success of these methods has been so great that for nearly 180 years they have hardly been questioned.

The successes of this form of manufacture have, during this period, had a profound effect on the organisation of our society. Ivor Tiefenbrun, the founder and Managing Director of the innovative hi-fi company, Linn Products Ltd, expressed it well [6]: "As a tool wielding animal, man's ideas are shaped by his technology. The ideas and techniques o f the production line spread to every sphere o f human endeavour from

Millwrights to mechatronics 97

religion to philosophy and even included the administrative process . . , the production line approach dominates in almost every field of endeavour. Indeed the serial production line approach may jeopardise future human progress."

Tiefenbrun goes on to argue for an alternative people-centred manufacturing approach, but as he himself suggests these ideas are wider than just manufacturing. In company with the production line model, the division and re-division of skills has proceeded unabated since Adam Smith's time. Millwrights divided into mechanical and civil engineers and those disciplines have themselves sub-divided into the myriad specialisations that we recognise today. Electrical engineering, coming later on the scene in the late nineteenth century, has likewise been fragmented into heavy and light current specialisms, analogue and digital, radio and audio, and so on. In more recent times the relatively new skills relating to digital computation have divided into specialisations concerned with hardware and software respectively. Software production has been further sub-divided into systems analysis, programming and coding. Even industrial design, which might be considered in many ways a unifying multi- disciplinary activity, has been described by one of its principal proponents, Sir Misha Black, as "a specialised engineering discipline . . . " [7]. The fragmentation of all these disciplines has serious consequences for design activities, where the creativity of the designer can be limited by the narrower perspective afforded by a high degree of specialism.

WHAT IS MECHATRONICS?

Precisely who coined the term "mechatronics" will, perhaps, never be resolved, but it is clear that it came into relatively common use in Japan in the mid 1980s and started to be used in Europe and the USA shortly afterwards. Even in the relatively short lifespan of the term it has been used and interpreted in many ways, but the various definitions generally agree that Mechatronics differs from "traditional" engineering by encompassing or integrating the previously separately considered disciplines of mechanical, electrical, electronic, computer and software engineering. Beyond this general idea, however, definitions diverge. Some very general definitions stress only the importance of the cross-disciplinary nature of mechatronics. Propo- nents of this view would probably include optical engineering and chemical engineering as legitimate parts of mechatronics. This school of thought sees the term as the flagship of a new, more integrated approach to engineering and engineering education. At the other end of the spectrum of definitions there are those that would limit "true mechatronics" to those computer-controlled mechanical systems which employ advanced software control strategies to enable previously unattainable ends to be met. Some manufacturing engineers would alternatively define mechatronics in a more global sense in terms of the unity of the product and the manufacturing system which produces it.

So why do we need to define mechatronics? One could argue that to attempt to define it at all is contrary to the spirit of mechatronics in rejecting compartmentalisa- tion of engineering into separate disciplines. Unfortunately, there are many occasions when it is necessary to have a reasonably concise and well agreed definition to hand. This is very much the case, for example, when one is arguing for mechatronics,

98 T.G. KING

whether for funding for multi-disciplinary engineering education or for the merits of a new approach to designing your company's "next generation" product. In these situations you need a word which, at least approximately, defines the concept. A formal definition has been proposed by the European Community:

"Mechatronics is the synergistic integration of mechanical engineering with electronics and intelligent computer control in the design and manufacture of products and processes."

It is, perhaps, a little unfortunate that this definition presupposes an adequate definition of machine intelligence, but this may not be a problem in most practical situations, where a rather loose interpretation of intelligence will probably be appropriate. A broader definition of mechatronics in the context of machine and product design is more in line with the author's approach:

"Mechatronics is the design and manufacture of products and systems possessing both a mechanical functionality and an integrated algorithmic control."

It would be presumptuous, of course, to suppose that the coining of the term mechatronics suggests that the mechatronic approach is entirely new. Multi-disciplinary engineering involving the mechanical, electronic and control fields has been going on for a long time in some areas such as the aviation industry, to name but one example. It could be argued to be the inheritor of the spirit of the eighteenth century millwrights whose qualities have been alluded to here. It is to be hoped that the term "mechatronics" will be of benefit in highlighting the existence of this type of engineering and attracting more engineers to try it and to experience its advantages first-hand.

Since the most recent addition to the technical armoury of engineering designers is the ability to incorporate (embed) microprocessor control into their designs it is useful to look at the objectives for doing this in the creation of products and systems which may be considered mechatronic.

DESIGN OBJECTIVES FOR EMBEDDED MICROPROCESSORS

Three categories of application of embedded microprocessors can be distinguished, with differing objectives [8], as follows,

(1) Enhancement - - the addition of a microprocessor adds features or improves performance, but the underlying (existing) design of the product or system is little altered. The addition of the microprocessor might, however, improve accuracy, operating speed or flexibility of use, reduce maintenance requirements or increase reliability.

A very positive example of this type of application would be an engine manage- ment system for a motor vehicle, providing greater economy, smoother idling and longer service intervals. Many less valuable instances exist where the microprocessor is not much more than a "fashion accessory" adding little to the system which could not have been achieved in other ways.


(2) Simplification--the microprocessor system replaces one or more complex mechanisms. An example of this type of application could be given in the re-design of the screw-cutting lathe. In traditional mechanical designs descended from the concepts embodied in Leonardo da Vinci's (c. 1500) sketch of a screw-cutting machine, or Henry Maudslay's practical implementation of c. 1800, the tool is moved relative to the longitudinal axis of the workpiece by a leadscrew so that a helical path can be cut. The relative rates of rotation of leadscrew and spindle/workpiece must be controlled to enable screws of different pitches to be produced. This has been achieved by the use of change-gears, initially loose gear-wheels which could be assembled to the machine to provide the desired ratio, and later by more convenient multi-ratio gearboxes. These components add significantly to the complexity and expense of the machine. The mechatronic approach is to provide an entirely separate motor drive for the leadscrew which is then synchronised electronically to the rotation of the spindle. The gearbox is now redundant--electronic control of the relative rates of rotation allows an infinity of pitches to be cut with greater convenience. The physical construction of the lathe is simplified, its component layout made more flexible and cost savings can be effected. A similar approach has been used on gear manufacturing machines to replace the gear train between cutter (hob) and gear blank. In this case the replacement of a complex gear train by appropriate separately controlled drives actually enabled a stiffer coupling to be achieved between hob and blank, thereby significantly improving the quality of the gears produced as well as simplifying machine construction.

(3) Innovation--the application of the microprocessor makes possible the creation of previously unrealisable products or systems. Most robotic devices fall into this category and so do machines which use advanced sensor technologies such as machine vision.

The first two categories are not, of course, mutually exclusive. In many instances the application of microprocessors increases value both by improving performance and by reducing cost but generally, in mechanical systems, design objectives of enhancement have historically preceded those of simplification. This is certainly true in textile machinery where patterning systems were implemented in the early 1970s using minicomputer systems. Since these data processors were then very expensive, significant product enhancement was the only practical objective for their application, even to complex high-cost machines. This approach provided a precedent for "enhancement mode" applications of the increasingly affordable microprocessor systems which started to become available in the late 1970s. More interesting from an engineering point of view are simplification and innovation modes of application.

The following sections provide some examples of simplification and innovation through the author's application of mechatronic design in textile machinery.

A MECHATRONIC TENSION COMPENSATOR FOR CONE WINDING

This example illustrates a mechatronic system in which embedded microprocessor control serves to simplify what would otherwise be an extremely mechanically complex system.

In many situations in the textile industry packages of yarn are unwound to feed into

100 T .G. KING

processing machinery. Often it is more convenient to draw the (low inertia) yarn supply over the end of the stationary package rather than rotate the (high inertia) package to unwind the yarn. This is commonly the case in knitting machines. In order that the yarn can be drawn off smoothly it is, therefore, wound into conical packages during its production. Whilst advantageous for the yarn user, this can present a problem for the yarn manufacturer. In those spinning processes which produce yarn at a constant rate (such as the modern open-end processes) winding the yarn onto a cone, as illustrated in Fig. 1, presents a cyclically varying mismatch between supply and take-up because of the difference in surface speed between large and small ends of the cone. Unless some kind of tension compensator is provided the resulting tension variations will cause a poorly wound package, yarn breakage, or both. At low production speeds the problem can be resolved by the use of a simple spring compensator, using a low-rate spring to maintain an adequately constant tension. Such a system is illustrated in Fig. 2; the two bollards around which the yarn passes are mounted on a disc which can oscillate back and forth to take in and let out yarn, thereby evening out the tension fluctuations as the yarn is wound from the small end to the large end of the cone. At low winding rates this passive compensator arrangement is perfectly adequate, but increased production speeds on modern machines have required manufacturers to develop positive compensator mechanisms. At first sight this seems straightforward. One might imagine from the simple geometry of the cone that the required compensator motion would be easily mechanically derived. In practice this is by no means the case. Firstly, because the helix angle at which the yarn is wound varies in a complex manner, partly because of the practical limitations of manufacturing the traverse cam which distributes the yarn along the cone, and secondly because the compensation required changes as the

package being wound

(

,rav e,se . - S \ guiae

delivery roller

Fig. 1. Fixed delivery rate cone winding.

Millwrights to mechatronics

• ~ a ~ r ~ . . . . .

fixed b a r ~ ~ \"k::::~

Fig. 2. Winding system with a passive mechanical compensator.

101

winding operation progresses and the package increases in size (Fig. 3). These problems have not prevented purely mechanical solutions from being engineered but they are complex and costly and generally contain sliding contact surfaces (e.g. cams) which need to be carefully shielded from the fibres and dust of the spinning mill.

The mechanics of a mechatronic positively driven tension compensator can be much simpler. Figure 4 shows such a device [9]. The simple two-bollard principle of the passive spring compensator is retained, but the bollard disc is now positively driven by a small stepping motor, the motion of which is controlled by a single-chip microprocessor of the 8051 family. An open-loop control strategy is dictated currently in this case by the non-availability of any cheap and reliable method of sensing tension in the running yarn. The control system is illustrated in Fig. 5. The motion of the disc is synchronised with the oscillation of the yarn traverse-guide using an optical

0 ) v

l

Fig. 3. Changing ratio of diameters during winding.

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optical encoder

traverse cam

package traverse guide

=~" hall effect ~ - sensor

inductive proximity probe

optimised curved bar

stepper ~ : ~ motor

lightweight bollard disc

end break detector

delivery miler

reflective opto-switch

yam guide

Fig. 4. Mechatronic tension compensator.

~ ' ~ ( ~ cone size pulses

optical ehcoder

clock sync pulses J]J1JLPJ1JI_ ~ _ L _ L angle (timing) pulses

l e~er ROM IoI~III I I i i,'o port l

,o=u: ~ l cPo ,o,.,'T I"I"I'I ,Toc, s.ns_ ,__

Fig. 5. Control system schematic.


encoder mounted on the traverse cam-shaft. The output pulses from this encoder are counted and the bollard disc rotated by small increments (of one four-hundredth of a rotation) whenever an appropriate number of pulses has been counted. The numbers of pulses required to be seen before each successive step in the cycle are stored in a data table in the microprocessor controller's memory. This provides, in effect, a kind of "electronic cam" function. Unlike a mechanical cam, however, it can be a function of as many variables as we wish--simple rotational cams are a function of a single variable and space-cams are limited to two. In this case the effect of the cone size increasing is accommodated by making the data table two-dimensional so that it can contain data for a number of successive increments of cone diameter. Giving it a third dimension enables allowance to be made for the further complicating effects of the anti-patterning mechanisms usually employed in winding systems to avoid ridges forming in the package if successive layers are too precisely superimposed. This would be virtually impossible to effect with a mechanical system.

Although system simplification, relative to a mechanical positively driven compensator, is the primary objective of the design described here, it also has a number of other important advantages, some of which exhibit common characteristics of mechatronic solutions. In particular, it is extremely flexible--changing the angle of the cone (various angles are used in the textile industry) can be easily accommodated by altering the data table information. Likewise, other changes in the machine configura- tion are simple, e.g. changes to the yarn path. For the mechanical solution merely altering the position of one yarn guide requires re-engineering the whole compensator! The mechatronic system also has the considerable benefit of being able to co-operate easily with human operators or automation systems on the spinning machine. For example, it can "park" the bollard disc in a suitable position for threading the yarn, a task which is accomplished by robotic piecers on the latest machines. Again, this is difficult to achieve with a mechanical solution.

A MECHATRONIC LINKING MACHINE FOR GARMENT ASSEMBLY

This example illustrates the use of a mechatronic design approach to innovating a new product which could not otherwise have been produced.

The main body panels of fully-fashioned outerwear garments are knitted on one type of machine, whilst the "trims", e.g. collars, facings and ribbed waist bands, are usually knitted on different types of machines. The highest quality method of joining these components together is a process termed "linking", in which the knitted loops of one component are matched one-for-one with those of the component with which it is to be joined and a chain stitch is used to sew them together. This provides a flexible joint, with minimum bulkiness in the seam, although care must be taken that no loops are missed in the process or the garment can unravel. The process is therefore used for the more expensive products and is performed by hand with the aid of simple machines. These comprise a series of grooved points onto which the loops are loaded and which serve to guide the needle of the machine's sewing head, as illustrated in Fig. 6. The operators of these machines need skill, concentration and good eye-sight.

A mechatronic system has been developed to help to automate the linking process

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Iol iper

~ ~ g r o o v e d ~\ points

Fig. 6. Linking with a single chain stitch.

[10-14]. Collars and other ribbed garment components are knitted in bulk; each joined to the next by waste courses of knitting which enable them to be separated before linking. The row of loops on each trim to be used for linking is termed the "slack course" since it is knitted with slightly larger loops than the other rows. The most arduous part of the manual linking process is identifying these loops and loading them onto the points. This part of the process was therefore selected for automation by the use of a machine vision technique.

Since the fabric is deformable and, indeed, this very deformability must be exploited to gently stretch the components to bring their loops into register with the pitch of the linking points, it was not considered useful to image an area of the fabric and attempt to determine the positions of multiple loops in the slack course. Instead, an approach based on progressive sensing and insertion of the linking points into the loops was adopted. This was implemented by using a low-cost line-scan CCD sensor to build up an image of the area of fabric under consideration at any one time, allowing the fabric to be progressively distorted to bring a single loop into alignment with the next sequential point, which is then inserted. This process is continued until all loops in the slack course have been dealt with. In this way the amount of data to be handled is kept to a minimum and the changes in the geometry of the fabric caused by the insertion of one point can be taken into account when inserting the next.

The vision system has to be able to identify which loops are to be used for linking. Figure 7 depicts the construction of plain knitting. The system uses a knowledge base of different knitted constructions to assist it in finding the correct loops in plain and different types of ribbed fabrics.

The sensor head (camera) and the fabric positioning mechanism are mounted on a carriage which moves in front of the trims as illustrated in Fig. 8. Another carriage, behind the trims, carries the point insertion mechanism and a fibre optic bundle for back-illuminating the fabric. The front and rear carriages are moved together, their alignment being maintained by two ball-screws, rotationally coupled by a timing belt at the end of the machine.

As the carriages traverse the width of a trim, the sensor scans the fabric, providing data to identify the slack course, selects the loops to be loaded onto points and calculates the movements required to position the loops correctly.


direction of

knitting

Fig. 7. Large-scale diagram of knitted fabric. +: centres of loops to be selected; 0 : "inverted" loops which must not be selected.

TRIM SEPARATION DEVICE "-~ f " TRANSFER

LENS AND ~ ( SYSTEM LINEAR ARRAY ' ~ POINT |

SENS0~ .,

I ~ ~POtNT c:RONT z ~ I t ~[ iNSERTION

LOOP MECHANISM

1 I SUPPLY

Fig. 8. Automatic linking machine (side view).

The fabric is held between a smooth face on the rear carriage and a pair of rubber rollers which are driven so that they normally roll on the fabric as the carriage traverses. By "advancing" or "retarding" the rotation of these rollers with respect to the carriage movement they can exert a force to bring the slack course loop of current interest into alignment with the points in the traverse direction. In the vertical direction, alignment is achieved by driving the pair of rollers axially. Figure 9 shows the mechanism which achieves this. The camera is in the right foreground. The fine pitch timing belt drive running across the top of the carriage advances and retards the rollers (when the belt is stationary they just roll on the fabric as the carriage moves; a small stepping motor, not visible in the picture but mounted to the machine frame,

106 T .G . KING

Fig. 9. Automatic linking machine head.

provides the advance and retard action). Vertical motion of the rollers is produced by the small stepping motor on the front carriage, visible just to the rear of the camera lens.

The very small incremental motions required of the stepping motors to "coax" the loops into alignment required special motor controllers since, typically, each motor moves only a few steps in each direction, but is required to do so at high speed. This was achieved by providing each of the axis motors with its own purpose built 8085 based microprocessor controller. These are co-ordinated by a supervisory computer which also processes the vision data.

Although based on low cost sensing and utilising relatively low performance eight-bit microprocessors, this machine demonstrates that, given an appropriate mechatronic approach, the deformability of fabrics is not an insurmountable obstacle to automation in garment assembly.

A MECHATRONIC LACE SCALLOPING MACHINE

This final example illustrates another textile mechatronic system in which embedded microprocessor control is used for innovating an otherwise impossible system.

Lace is manufactured by a specialised knitting process in broad webs up to 3.3 m wide. Each web contains many pattern repeats across its width which must be


separated into individual lengths of lace. This involves cutting along the edges of the pattern to separate the pieces from one another and, in most cases, to remove unwanted knitted background mesh as illustrated in Fig. 10. This process is termed scalloping and is currently performed by human operatives using simple machines employing rotary or band knives, or even scissors for some particularly difficult and elasticated designs. This is obviously a labour intensive process and it would be most desirable to automate it fully using machine vision. Unfortunately the path to be cut can bear a complex or arbitrary relationship to the pattern features (at least at the detailed scale) which makes implementation of a system based on simple line-following approaches untenable. The task is made more difficult by the requirements of high-resolution imaging, necessary to record the fine detail of the lace figuring and the relatively large image width needed to contain the cutting path. To achieve good process economics a web speed of 1 ms -1 is desirable, which demands very rapid processing of the image data to provide real-time control. Further difficulties are caused by the deformable nature of the lace whose dimensions vary with tension and manufacturing conditions and the changes in the pattern caused by the release of tension in the lace structure as it is cut.

Using a laser for scalloping offers several advantages. Cutting with the laser can produce an advantageously finished edge in which the (mainly thermoplastic) fibres comprising the yarns from which the lace is knitted can be lightly locally fused together. This helps to prevent fraying without creating a hard edge which would be uncomfortable when worn against the skin and could snag hosiery. Other advantages of laser cutting include the elimination of cutter sharpening, the very small diameter of the focused beam which allows intricate profiles to be cut, and the high cutting speeds which can be achieved without stressing the material. This last point is especially important since it makes it possible to cut more than one edge at a time.

100 mm

Fig. 10. Small section of lace web. a: lace; b: edges to be cut; c: waste mesh.

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Using knife cutting the interaction between the cutting forces would render this virtually impossible.

The prototype system is illustrated in Fig. 11. The cutting position is on the right of the diagram. To its left is an optical encoder running on the surface of the lace web which is used for lace to camera synchronisation. Later versions of the machine have two cutting beams, independently tracked and individually controlled by two galvanometers. The machine can be divided into the following principal functional blocks.

• Supervisory system: a computer system to co-ordinate the operation of the following functional blocks.

• Vision system: hardware and software to acquire the image data from the moving web of lace.

• Tracking system: which computes from the image data the required instantaneous position of the cutting point as the web moves past the laser.

• Cutting system: comprising laser, beam-delivery and beam deflection hardware to deliver the laser energy to the point determined by the tracking system.

• Transport system: responsible for presenting the lace to the imaging and cutting systems.

Overall operation of the system proceeds as follows. The web of lace is transported continuously past the imaging system and the cutting position, which is slightly downstream. The image data acquired is continually processed to derive a control signal which is used to drive a galvanometer to deflect the laser beam. The image data acquisition and galvanometer control output are synchronised to the web movement to allow for the separation between imaging and cutting positions. The separation between these two positions is, however, kept as small as possible in order to minimise any errors due to gross positional change or localised pattern distortion in the lace between imaging and subsequent cutting.

Overall control of the machine is performed by a Motorola 68020 microprocessor system. This monitors the whole machine and provides user interface via a VDU and high resolution video output for setting-up and diagnostic purposes. Figure 12 shows the general arrangement of the supervisory and other computing hardware.

J

~ ~ Jfocusing ~line-jcan ~ F / ~ Lens

cam'l l i fO" encoder ~,~ I. f-\ lace motion

" ~ r '

source beam ~

Fig. 11. Laser lace scalloping machine.


S T A R T LINE-IICJ~ i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

rl I I CAMERA CONTROL

& DATA ACQUISITION

GALVANOMETERS

OPERATOR INTERFACE

HI-RES VIDEO DISPLAY

Fig. 12. Control system schematic.

The tasks of the vision system are to acquire image data and extract the cutting path information in real-time. Because the lace is in a continuous moving web a line-scan camera is more appropriate than area-scan types. Processing the image on an incremental basis, as each new line of information becomes available, is also essential to the quasi-continuous real-time control strategy adopted to deal with distortion of the lace in transportation and cutting. The vision system therefore consists of a high-speed, high resolution, line-scan camera coupled by a specially designed interface to a digital signal processor (DSP) board with multiple DSPs. The DSP board is connected to the supervisory 68020 microprocessor. A fuller description of the development of the DSP system has been given elsewhere [15,16].

The lace is locally back-lit, where it passes under the line-scan camera, using a fluorescent tube driven by a high frequency electronic ballast. The electronic ballast is run from a D.C. supply which provides further mains frequency rejection. The resulting illumination is extremely uniform and flicker free.

The camera is connected by a specially designed interface card to one of the DSPs. The interface thresholds the video data, at a level which can be optimised automatic- ally. After thresholding the binary image data is placed in shared memory for access by the DSPs performing the tracking process.

The system tracks the cutting path on the lace by a reference map based technique. Reference maps for each pattern to be cut are created by scanning one pattern repeat, on the machine, and defining the required cutting path on the visual display using a mouse and pointer. The pattern and cutting data are then processed to match

110 T.G. KING

the ends of the pattern repeat to one another and extract the information in a band centred on the cutting line. This information then forms the reference map for tracking. This procedure is required the first time any new pattern is to be scalloped, but the information can be stored for subsequent re-use. The cutting path can be arbitrarily defined with respect to the lace pattern so that its placement is a design decision. This offers considerable flexibility.

During scalloping, the current position of the web is continually computed by matching with the reference map. The web is deformable, and also has quite large tolerances on manufacturing dimensions. The matching process tolerates this, and achieves high processing speed by using a specially developed incremental algorithm [17]. The algorithm avoids re-calculating an area-based pattern match for each new line of image data, but instead performs centre-weighted line matching using a cross-correlation technique. The line matching result is then combined with previous line matching information, using a filtering process, to give the stability of an area-based matching approach but with much reduced computation. The centre- weighting of the line match and the decaying impulse response of the filters give most weight to image matching close to the current tracking point so that the algorithm is robust against distortion and scale errors of greater than + 10%, both along and across the web.

The CO2 laser used in the prototype machine is a 240 W continuous wave (CW) unit. The laser beam is delivered by a series of fixed mirrors through an enclosed tube to a focusing lens. The converging beam issuing from the lens is directed onto a lightweight front-silvered mirror mounted on a galvanometer whose position is controlled by the tracking process. A beam-splitter and a second set of optical components allow two cuts to be made at once.

The prototype system described here has been successfully tested in scalloping trials, and produces well scalloped edges. Figure 13 shows samples of lace cut using the system. The DSP system alone is only capable of tracking at a maximum of around 0.3ms -1 but scalloping at the target web of 1 ms -1 will be achieved by incorporation of purpose designed circuitry which implements the first stages of the tracking algorithm in dedicated hardware; this has been built and tested and will be assembled to the rig soon. A prototype machine which independently tracks two scalloping paths and cuts them simultaneously is working in the laboratory and will soon undergo factory trials.

Summarising this example, it should be noted that the mechatronic system described successfully demonstrates pattern cutting .in registration with the features of a deformable material. The use of a mechatronic approach has enabled a highly productive machine to be constructed which can finish both edges of the lace simultaneously--a hitherto unrealisable target--and which can scallop complex curves previously only attainable by the use of scissors.

LIMITATIONS AND FUTURE REQUIREMENTS OF MECHATRONICS

A danger which has become evident in product enhancement applications of microprocessors lies in the temptation to the designer to add extra features to the product just because this becomes easy to do. The presence of an embedded

112 T.G. KING

microprocessor is invariably seen as a marketable attribute and for it to fulfil its marketing potential it must show its presence by providing a panoply of "extra functions" or customer definable choices. So far it has been rare for manufacturers to consult customers and users as to what features they actually want. Some products have reached levels of complexity where the users choose to ignore almost all of their enhanced features--most telephones are now capable of remembering ten or more telephone numbers; how many ever get taught even one?

We still have a long way to go in developing user friendly systems, partly, I suspect, because of the point of sale appeal of "more features". Purchasers have long had difficulties in assessing the inherent quality of mechanical and electro-mechanical products. Industrial designers have sought to convey the qualities of products by styling, often using forms and motifs borrowed from elsewhere; their aim being to imply the underlying quality of a product which the purchaser can only assess from its exterior appearance. This problem of conveying product quality can be even more extreme with a microprocessor based product. Much of the quality inherent in a microprocessor-embedded product may exist only in the quality of its programming-- directly visible to no-one but the most determined practitioners of "reverse-engineering" and appreciated indirectly only once the user is familiar with the operation of the product--usually long after the point of purchase. Obvious external manifestation of the processor's presence--the "feature glut" -- therefore takes on a formidable marketing importance.

Persuading the customer that "less-is-more" is difficult, but there are signs that simplicity may be becoming a sales asset as customers for microprocessor-embedded products become more seasoned.

A different and more serious problem lies in the relationship between mechatronic devices and humans. As our machines become more capable they appear more "intelligent". Some of the operations they can perform would stretch the mental capabilities of most humans, their response times are often quicker than ours and their sensory capabilities can, admittedly in limited ways at present, be superior. It is, therefore, sometimes very difficult for us to decide whether such machines are in complete control and performing correctly, and conversely when they should not be trusted! Even when functioning correctly from a programming point of view the most impressive mechatronic systems currently only have a very limited sensory perspective. They can, therefore, be quite unaware of problems or fault conditions which a human being could hardly fail to notice. How many mechatronic cameras, for example, are quite happy to auto-focus on the inside of the aircraft window rather than the interesting scene you wanted to record, 10,000 metres below? When the "smart" photocopier reports that it has detected a paper feed problem part way through a long double-sided, collated print run should you believe its confident assertion that it can sort out the problem? Clearly, major safety implications are possible in some other applications and these are not necessarily related to "failure" modes, only, perhaps, to estimates of appropriate behaviour based on insufficient sensory data. Humans make these kinds of mistakes too; we may need to incorporate some aspects of human factors and the psychology of perception into their programming.

The "cognitive" potentialities of our machines have been dramatically increased in the past decade by rapid developments in the fields of microprocessor architectures


and programming techniques. Almost as startling have been the improvements in sensory systems, many of them based on visual imaging, which are now enabling machines to experience our world more fully. The area which now appears to be lagging behind is the one which 20 years ago appeared the most advanced--the provision of suitable actuator technologies.

For many years almost all electro-mechanical actuation techniques have been electromagnetic; electric motors, electromagnets and solenoids have usually been the only options. We need new actuator technologies if our mechatronic devices are to be as dextrous and as energy efficient as their potential applications demand. Some progress has been made in this area. One possibility lies in the application of piezoelectric materials [18]. These offer the attractive possibilities of generating large forces very rapidly, and can be highly energy efficient--requiring virtually no power to maintain a holding force, for example. Unfortunately currently available piezoelectric actuators require relatively high operating voltages (typically 100 V or more) and produce minute displacements. Research and development will soon produce a new generation of devices with significantly lower operating voltages. The author and co-workers are investigating efficient ways of mechanically amplifying the output displacements of piezoelectric actuators to enable their use in the faster, more

OUTPUT ~ ~ PRE-LOAD

~ PIEZO

Fig. 14. Perspective view of a piezoelectric single stage amplifier device producing 200/an displacement.

Structure Perspective

Tamlon S ~

Fig. 15. Piezoelectric strip dutch; principle of operation and perspective view.

114 T. G. KING

A M P U F I E R S

. . . . . R O T O R ~ , ~ .-~

Fig. 16. View of a quarter section of a piezo-harmonic motor.

dextrous mechatronic systems of the future. Specific designs and appropriate design techniques have been produced [19-22] and work is ongoing. Figures 14 and 15 illustrate two of these mechanically amplified actuators, based on flexure hinged structures, whilst Fig. 16 shows a piezoelectrically actuated motor concept, currently being researched, capable of very fine increments of rotation, again employing flexure hinged displacement amplifying techniques.

CONCLUSIONS

The examples of mechatronic systems in textile machinery presented in this paper are, I believe, very much in keeping with the multi-disciplinary spirit of the millwrights whose textile and other machinery first transformed the industrial scene. Without specialisation we would quite possibly not have developed the microprocessor and other technologies essential to these new designs but without generalists our design perspectives are unacceptably narrowed. Britain's past success has been based on manufacturing: the innovative design of manufactured goods and hardware systems for their manufacture. Our future as a developed nation will depend on our performance in fiercely competitive markets. A primary resource will be our creative skills. We cannot afford to allow traditional divisions between engineering disciplines to dull our creativity either in industry or in education.

Acknowledgements--The work described in this paper includes the joint efforts of many colleagues, all of whom deserve credit. I would like to particularly thank (in alphabetical order): Eddie Baker, Paul Green, Mike Jackson, Brian Murphy, Mike Preston, Ron Sims, Liguo Tao, John Thornley, Ray Vitols, Gordon Wray, Ian Wright, Wei Xu and Sen Yang who have each made significant contributions.

REFERENCES

1. Reynolds J., Windmills and Watermills, p. 115. Evelyn, London (1970). 2. Fairbairn W., Treatise on Mills and Millwork, 4th edn (1878); preface to 1st edn, (1861), quoted in

Jefferys J. B., The Story o f the Engineers, 1800-1945. Lawrence and Wishart, London (1945).


3. Thompson E. P., The Making o/the English Working Class, pp. 270-271. Pelican, Harmondsworth, U.K. (1968).

4. Gilbert K. R., Machine Tools, Catalogue of the Science Museum Collection, p. 90. HMSO, London (1966).

5. Rolt L. T. C., Great Engineers, p. 97. G. Bell & Sons, London (1962). 6. Tiefenbrnn I., Manufacturing in the future. Roy. Soc. Arts Jnl CLXI(5441), 549-557 (July 1993). 7. Black M., Engineering and industrial design. Proc Inst. Mech. Engrs 186(74/72), 897-912 (1972). 8. King T. G. and Sims R., Mechanical design in the microprocessor era--illustrations from the textile

industry. IMechE Engineering Design '86 Congress, NEC, Birmingham, U.K. (1986). 9. King T. G. and Yang S., Tension compensation for fixed delivery cone winding: a mechatronic

approach. In Mechatronic Design in Textile Engineering (Edited by Acar M.), NATO ASI Series E: Applied Sciences, Volume 279, pp. 179-190. Kluwer Academic, Dordrecht, ISBN 0-7923-3024-0 (1995).

10. King T. G., Murphy B. J. M. and Vitols R., Low cost, high speed sensing of knitted fabrics. Sensor Rev. 5(3), 119-123 (1985).

11. Vitols R., Wray G. R., Murphy B. J. M., Baker J. E. and King T. G., Computer controlled machinery for garment manufacture. Proc. Textile Inst. Conf. "Computers in the World of Textiles", pp. 284-296, Hong Kong, September. Textile Institute, Manchester, ISBN 0-0900739 69 X (1984).

12. Vitols R., Murphy B. J. M., Wray G. R., Baker J. E. and King T. G., The development of computer- controlled machinery for the making up of garments, lEE Proc. 132, Part D, No. 4, 178-182 (1985).

13. Preston M. E., King T. G., Wray G. R., Vitols R. and Murphy B. J. M., Mechatronics apphed to the manufacture of knitted garments. Mechatronics 89--Mechatronics in products and Manufacturing, University of Lancaster, 11-13 September (1989).

14. Preston M. E., King T. G., Vitols R. and Murphy B. J. M., A mechatronic system for knitted fabric handling. Proc. 1MechE/IEE Conference "Mechatronics: Designing Intelligent Machines", pp. 17-22, Cambridge. Mechanical Engineering Publications, London, ISBN 0 85298 722 6 (1990).

15. King T. G., Tao L. G., Jackson M. R., Preston M. E. and Yang S., Computer-vision controlled high-speed laser cutting of lace. Proc. 2nd Int. Conf. on Computer Integrated Manufacturing (ICC1M '93), Vol. 2, pp. 929-936, Singapore. World Scientific Publishing, Singapore, ISBN 981-02-1947-4 (1993).

16. King T. G., Tao L. G., Jackson M. R. and Preston M. E., Real-time tracking of patterns on deformable materials using DSP. lEE SERTA '93, pp. 178-183, Cirencester, U.K. IEE, London, ISBN 0-85296-5931 (1993).

17. King T. G. and Tao L., An incremental real-time pattern tracking algorithm for line-scan camera applications. Mechatronics 4,503-516 (1994).

18. King T. G., Preston M. E., Murphy B. J. M. and Cannell D. S., Piezoelectric ceramic actuators: a review of machinery applications. Precision Engng 12(3), 131-136 (1990).

19. Thornley J. K., Preston M. E. and King T. G., Piezoelectric and electrostrictive actuators: device selection and application techniques. 1MechE "Eurotech Direct-Machine Systems", paper C414/057, pp. 115-119, NEC, Birmingham, U.K., 2-4 July (1991).

20. Thornley J. K., King T. G. and Preston M. E., The design of mechanical amplifiers using piezoelectric multilayer devices for use as fast actuators. Proc. 1MechE Conf. "Mechatronics--The Integration of Engineering Design", Dundee. Mechanical Engineering Publications, London, ISBN 0852988400 (1992).

21. Thornley J. K., Preston M. E. and King T. G., A very high speed piezoelectrically actuated clutching device. Mechatronics 3,295-304 (1993).

22. Thornley J. K., King T. G. and Xu W., Piezoceramic actuators for mechatronic applications. Proc. Int. Conf. on Machine Automation (ICMA '94), pp. 569-583, Tampere, Finland. Tampere University of Technology, Tampere, Finland, ISBN 951-722-107-X (1994).

millwrights to mechatronics: the merits of multi-disciplinary engineering

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