Keeping track of shop floor production by PETER THORNTON

If information from factory shop floors was more readily available, planning production would b e easier. This article describes the various data collection methods that have been used to date.

T o the uninitiated the provision of timely and accurate information on which to base production con-

trol decisions may seem a minor problem which can easily be rectified.

In reality the collection of data, upon which shop floor planning and control is so critically dependent, is far more com- plex. Even in small and medium sized manufacturing companies the number of events to be monitored combined with the rate of change can quickly create enormous data collection and analysis difficulties.

A basic requirement for the success of any shop floor data gathering and analysis system is that it be at least as dynamic as the activities which it attempts to monitor and control. This has been the fundamental problem. Manual, paper-based systems have found it extremely difficult, even accept- ing cost considerations, to achieve the response time demanded. Conse- quently, these systems have not been able to provide managers with the detailed and timely information required to properly control the manu- facturing environment.

Early computer-based data collection systems which attempted to rectify these

Peter Thornton is a consultant with DL Associates.

deficiencies were not only too expensive for most companies but continue to suf- fer from many of the problems inherent in the manual systems they were intended to supersede. Recent micro- electronic developments, however, appear to offer a large number of com- panies a more responsive, less error- prone and cost-effective solution to their data gathering and analysis problems.

Shop floor data collection systems fall into two distinct generations. The first includes those which are essentially paper-based and manual, and the second those relying on varying degrees of com- puter support.

The paper-based systems, of which there are several, all suffer from a com- bination of drawbacks: inflexibility, inaccuracy, slowness and the need for manual transcription.

Early attempts to improve on manual, paper-based systems in the late 1960s and early 1970s centred on the use of shop floor data collection terminals usu- ally linked into computer-based produc- tion control packages. In theory, the computer could perform the required calculations rapidly and accurately, while the shop floor terminals enabled machine operatives to directly enter job progress and machine availability. As data could be made immediately avail- able to the central computer, master production files could be updated as fre- quently as required. Furthermore, the computer could go through a validation routine before accepting data entered at the terminals, thereby substantially reducing the error rate.

The reality, however, was often very

different. Many of these early systems had cost drawbacks, practical deficien- cies and technical limitations.

For all but the largest manufacturing organisation such systems involved a prohibitively high level of investment. Even in many large firms cost factors restricted the number of shop floor ter- minals to perhaps one to every 20-25 employees, necessitating some workers to make round trips of up to 50 yards to enter data.

More significantly, however, this approach continued to suffer from a number of the deficiencies associated with manual paper-based systems. In particular, these systems could not pro- vide visible evidence of exceptional cir- cumstances while corrective action was still possible. For technical and cost reasons they did not, for the most part, operate interactively in real-time. And, as a consequence of operating in batch mode, some of the drawbacks of paper systems were simply reproduced by an expensive computer-based system.

Attempts to overcome the problems created by batch mode operation on the one hand and data integrity on the other centred on the use of real-time com- puters and pre-recorded input media respectively. During the 1970s the fall- ing cost of computing power made economic the wider use of real-time operation and the development of badge reading type data terminals improved data integrity. Together these two developments made possible the partial automation of shop floor data collection.

Systems currently available from IBM, ICL, Hewlett-Packard, NCR and

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APPLICATIONS Shop floor data collection

others, improve the level of data integ- rity by removing from the operator the need to enter his personal details and any fLxed data relating to the job and opera- tion - this data being supphed in the form of a badge and pre-punched card respectively. Variable data is entered by the operative by means of a keyboard. In addition, data is automatically trans- mitted to an on-line data collection centre which, in most cases, will now take the form of a real-time computer capable of being accessed for up-to- the-minute enquiries.

These systems have, to a large extent, automated the procedures for the collec- tion of fLxed shop floor data.

However, these systems continue to possess a number of undesirable fea- tures. The operator still has full respon- sibility for initiating data transfer, enter- ing variable data and ensuring that data entry media is maintained in acceptable condition. Furthermore, data entry con- tinues to interrupt workflow as, in most cases, multi-function data entry stations are still too expensive for each operator to have his own.

While developments in the field of microelectronics have been instrumental in reducing the cost of multi-function data collection terminals, allowing a higher ratio of data entry stations to workers, the same technology is making this approach to shop floor data gather- ing obsolete.

The solution to many of the problems which have continually dogged attempts to develop effective shop floor data gathering lies in a system which can automatically capture data from the environment and which operates in real-time at the individual machine level. In other words, an effective system has two critical features: the use of equipment which can capture data with- out the need for operator intervention and the distribution of intelligent data entry points throughout the factory.

The reasons for suggesting that a sys- tem with these two characteristics would overcome many of the deficiencies pre- viously associated with shop floor data collection systems are as follows.

Data capture Data capture implies the transfer of

data from the environment to a compu- ter system without, or with the very minimum of, human involvement. The data is obtained by means of sensors automatically in computer sensible form.

This contrasts with data collection which depends primarily on human involvement at both the data gathering and entry stages, with all the attendant problems that this can create. While badge and pre-punched card readers represent a move towards data capture, it could be argued that these systems are best regarded as data collection because of the key role played by the operator in initiating and managing the data transfer sequence.

Examples of the main types of equip- ment providing each of the two modes of data entry are:

Data collection keyboards touch-pad telephones card, badge and tag readers Data capture machine sensors bar codes.

Data capture has a number of advan- tages over conventional data collection. First and foremost, any data gathered by this method will possess the important qualities of accuracy and timeliness. Consequently, any exceptional circum- stances relating to machines, such as breakdowns or lengthy stoppages, which tended to remain invisible to trad- itional data collection systems, will be automatically notified to the system in real-time.

Secondly, while the use of data cap- ture equipment will not in the majority of cases completely eliminate the need for operator involvement in data gather- ing, it can, nevertheless, help improve operator efficiency in the performance of this task.

As the system is not passive, simply waiting for the operator to initiate a data transaction, it can cue the operator when data is expected and can also indicate the type of input which is required. This facility can also be usefully employed to alert operators and maintenance staff to the need for their attention at particular machines.

Distributed terminals The distribution of data entry points

to individual machines has a number of important implications for the level of data integrity achieved by a data gather- ing system. Data accuracy is in fact improved for three reasons: (a) since the identity of each terminal is known to the system fLxed data concern- ing such factors as operator details and machine identification does not usuaUy need to be entered.

(b) again, as the terminal is machine specific the data entry keys used for vari- able data can be customised. This reduces the data error rate in two ways: fzrstly there are fewer keys so that mis- takes are proportionally less likely, and secondly a given amount of data can be entered with fewer key strokes. (c) the location of the terminal at the machine effectively eliminates the prob- lems associated with the need to go to a communal data entry station to input data.

This last factor also has the added advantage of improving labour and machine utilisation, if only marginally, as the work is less severely disrupted by data entry procedures.

Only a few years ago a system with similar characteristics to that described above would not have been feasible on technical and economic grounds for all but large companies with special requirements. Today, as a result of technological developments which have substantially improved the reliability, and reduced the size and cost of the elec- tronic components and sensors upon which distributed data capture systems are based, it is now practicable for even fairly small firms to actually install sim- ple but effective data capture networks.

Due to its technological basis and direct interface with the machine, par- ticularly as presently implemented, data capture is in many ways more closely akin to process control than data collec- tion. As the majority of data capture sys- tems in use are essentially concerned with monitoring machine activity and performance, data capture could almost be regarded as the input side of process control. While it is true that a few sys- tems do possess a rudimentary ability to progress individual jobs, this is a secon- dary feature only achievable in certain circumstances.

Unlike the majority of process Control applications, however, the vast majority of data logging systems require no com- plex algorithms and are not particularly time critical by computing standards. This means that the technology required is comparatively simple.

Standard microprocessors and related chips, with all that this implies for cost and reliability, are consequently usually more than adequate. Indeed, the logging may be so non-time critical as to allow a microcomputer programmed in a high- level language like Basic to perform the job. In the few applications where speed is a problem the difficulty can often be

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APPLICATIONS Shop floor data collection

overcome by either using dedicated counting chips or taking average figures. This latter solution is possible because the same level of accuracy is not required as in process control.

In addition to complexity and speed, t h e other major consideration determin- hag the type of technology employed is the number of systems to be built. In low quantities the choice is essentially bet- ween configuring systems from standard cards (sometimes referred to as micro- modules) to meet particular require- ments or using a general purpose micro- computer. The Pet with its IEEE 488 general purpose interface bus (GPIB) is widely used, as is the Apple.

For larger volumes, the more cost- effective approach, which improves effi- ciency and minimises redundancy, is to use custom-built systems designed spec- ifically to perform data logging tasks. In sufficient quantities this approach can lead to the development of very efficient and inexpensive systems. This type of system is offered by Dextralog.

Regardless of the hardware used, the final systems developed can be expected to possess some combination of the fol- lowing technical features: - physically compact to allow position- ing on the machine. - low voltage requirements to minimise installation and networking costs. - sufficiently impervious to factory floor conditions. - modularity to facilitate maintenance, removal and re-configuration.

This last factor, which might be gen- erally termed serviceability, is important since despite the high level of reliability (one company quotes a mean-time-to- failure for its systems of 48 weeks) breakdowns are inevitable, and at some- time changing the layout of facilities on t h e shopfloor may be needed. In this respect serviceability not only includes such factors as the simplicity of the wir- ing but also the scope for re-configuring and the ability to "tap-into" the network so that data transactions on the highway can be monitored as an aid to fault diag- nosis.

Making use of low-cost microelectron- ics technology and the flexibility pro- vided by microprocessors, data capture systems can be configured in a variety of ways. Generally speaking there are three main configurations: • stand-alone modules operating inde- pendently and used to monitor the per- formance of individual machines. • dedicated networks which monitor a

number of machines and analyse the data gathered. • integrated networks consisting of a data logging network with a degree of local in te l l igence l inked in to a computer-based production control sys- tem.

A stand-alone, microprocessor-based monitoring device can be obtained for around £600 for a standard application. Complex sensors or interfaces will raise this basic price.

These devices usually provide an automatic logging facility for a limited number of basic machine functions (perhaps three to five) and can normally be interfaced without technical prob- lems. Another device is a simple micro- terminal which has a single line display and a keypad enabling the operator to enter variable data.

A central microcomputer for a dedi- cated factory data capture network, capable of handling up to 15 micro- terminals will cost approximately £3,000-£4,000. In addition, each micro- terminal together with sensors will cost from £250 upwards.

Systems of this type, with various upgrades to the central microcomputer, can be expanded to handle over 100 machines.

Future shop floor data gathering sys- tems will probably incorporate com- plementary elements from both data capture and data collection systems. The aim will be to provide a facility capable of locating individual jobs on the shop floor (information concerning progress) and identifying activity levels at work- centres (machine status monitoring). The system would operate in real-time.

A system meeting these requirements is likely to have the following charac- teristics: • cheap micro-terminals distributed to each workstation. • sensors which directly moni tor machine function and performance. • some means of automatically captur- ing fixed job details. • some means of catering for variable data, e.g. a customised keypad.

C a s e s t u d y

The following case history shows what can be achieved by taking an integrated approach towards data gathering.

A major vehicle mafiufacturer has set-up a sophisticated network of data collection and data capture systems to monitor the flow and level of production at one of its Midlands sites.

In all, the system has 202 data entry points distributed about the shop floor linked into a universal plant cabling sys- tem. This system enables all the com- puters, data collection equipment and production monitoring and control devices to be plugged into a common data transmission medium.

Although there is a common data highway, production planning and con- trol within the factory depends upon the input from three information systems. (i) Body routeing and recording. This sys- tem records the movement of car bodies as they pass selected points in the pro- duction cycle, thus enabling production achievement to be compared against the plant production program on a continu- ous basis. The system also maintains a record of the work-in-progress content at each phase in the production cycle. The standard report gives a complete breakdown of production achieved to date together with a full work-in- progress listing. (ii) Facilities monitoring. A second sys- tem comprises stoppage sensors linked to facility control devices. The sensors are polled at regular intervals by the cen- tral computer. When a stop is recorded, the nature of the stoppage is identified by referring to a table of failure condi- tions held in memory. The automatic location and analysis of stoppages speeds up corrective action from service engineers and also aids preventative maintenance. (iii) Vehicle tracking. The progress of individual vehicles is monitored by a third system. Data for this system is obtained from two sources. Either it is fed in automatically from the vehicle scheduling system or it is entered from bar codes via light-pen stations.

The provision of up-to-the-minute information on vehicle progress assists in vehicle scheduling, so that production and sales orders can be matched more accurately. Essentially, product ion scheduling staff can react faster and re- schedule build mixes in the event of equipment malfunctions or changes in sales priorities.

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For further information circle the follow- ing numbers on the enquiry card. IBM 130 ICL 131 Hewlett-Packard 132 NCR 133 Pet 134 Apple 135 Dextralog 136

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