These are the three dimensions on which design can be judged,
aesthetics – does it look better?
usability – is it easier to use?
produceability – is it easier or cheaper to make?
Not all design concepts succeed
Not all concepts, no matter how ingenious, prove successful in the market place. What may seem to be an innovative sure-fire hit on paper can, with hindsight, fail to take account of customers’ real needs. Take, for example, the Lawn Ranger, a robotic grass-moving machine devised by an American company. The product concept was an automatic grass-cutting machine which would need only to be shown the perimeter of an area to be cut and then could be left to complete the task while its owner relaxed. All it needed was an initial ‘human-guided’ trip around the outside the lawn. It would then continue to cut round, working its way inwards until it finished the task. The basic technology was indeed ingenious. It included a sensor which would detect the difference between cut and the longer uncut grass as well as sensing potential obstacles in its path. This intriguing concept failed to take account of one important factor, however. People apparently like mowing their grass. It would appear that many people who would have been potential customers for this product prefer to cut the grass themselves because they find it therapeutic.
The stages of design
The text describes in some detail five stages of design which products and services move through as they are designed. These stages are:
- concept generation
- screening
- preliminary design
- evaluation and improvement
- prototyping and final design.
It is worth remembering however that not every product and service moves smoothly between these stages. In practice, the stages could be defined in different ways and the sequence may vary. Most importantly, there will almost certainly be recycling between the stages. So, for example, after the evaluation and improvement stage, it may be that the design must go right back to reconsider the original concept. In fact, at any stage the design could be recycled back to a previous stage.
However, do not dismiss these stages of design. Each of them, or something like them, will generally occur during the design activity. It is important to understand exactly what the product or service concept is. It is important to screen the various alternative design concepts using a broad evaluation technique such as the feasibility, acceptability, vulnerability. Specifying the components in the package using the product structures and bill of materials shown in the chapter is also important. Improvement using techniques such as quality function deployment, value engineering and Taguchi methods must be understood. Finally, the impact of computer-aided design and virtual prototyping, etc. has transformed design in some industries.
Interactive design
The benefits of interactive design are described in the chapter as centring around time and cost. Fast time to market is often the consequence of overlapping the design stage as shown in Figure 5.18, getting objectives clear and resolving conflict early in the process as shown in Figure 5.19, and adopting an organisational structure with relatively heavy project orientation. All this shortens development time which in turn reduces costs (and increases revenue). Also, fast time to market means that products and services can be updated more frequently. However, there is a limit to how often the market will respond positively to updated products and services. There is some evidence from the consumer electronics industry in Japan that excessive updating is unpopular with consumers (because it confuses them) and retailers (because stock becomes obsolete quickly). Because of this it is perhaps relevant to also stress that quality is positively influenced by interactive design. The communication between design stages can pick up problems before they become embedded in the design, early conflict resolution prevents the confusion during the design process which prompts mistakes, and project-based organization structures help the design team to focus on what customers really want.design or group of design projects.
Chapter 10 - The nature of planning and control
What is planning and control?
Planning and control is the reconciliation of the potential of the operation to supply products and services, and the demands of its customers on the operation. It is the set of day-to-day activities that run the operation on an ongoing basis.
What is the difference between planning and control?
A plan is a formalization of what is intended to happen at some time in the future. Control is the process of coping with changes to the plan and the operation to which it relates.
Although planning and control are theoretically separable, they are usually treated together.
The balance between planning and control changes over time. Planning dominates in the long term and is usually done on an aggregated basis. At the other extreme, in the short term, control usually operates within the resource constraints of the operation but makes interventions into the operation in order to cope with short-term changes in circumstances.
How does the nature of demand affect planning and control?
The degree of uncertainty in demand affects the balance between planning and control. The greater the uncertainty, the more difficult it is to plan, and greater emphasis must be placed on control.
This idea of uncertainty is linked with the concepts of dependent and independent demand. Dependent demand is relatively predictable because it is dependent on some known factor. Independent demand is less predictable because it depends on the changes of the market of customer behaviour.
The different ways of responding to demand can be characterized by differences in the P:D ratio of the operation. The P:D ratio is the ratio of total throughput time of goods or services to demand time.
What is involved in planning and control?
In planning and controlling the volume and timing of activity in operations, four distinct activities are necessary:
- Loading, which dictates the amount of work that is allocated to each part of the operation
- Sequencing, which decides the order in which work is tackled within the operation
- Scheduling, which determines the detailed timetable of activities and when activities are started and finished
- Monitoring and control, which involve detecting what is happening in the operation, replanning if necessary, and intervening in order to impose new plans. Two important types are ‘pull’ and ‘push’ control. Pull control is a system whereby demand is triggered by requests from a work centre’s (internal) customer. Push control is a centralized system whereby control(and sometimes planning) decisions are issued to work centres which are then required to perform the task and supply the next workstation. In manufacturing, ‘pull’ schedules generally have far lower inventory levels than ‘push’ schedules.
- The ease with which control can be maintained varies between operations.
- The volume-variety position of an operation has an effect on the nature of its planning and control. Customer responsiveness, the planning horizon, the major planning decisions, the control decision and the robustness of planning and control are especially affected by volume and variety.
Chapter 12 - Inventory planning and control
What is inventory?
Inventory, or stock, is the stored accumulation of the transformed resources in an operation.
Sometimes the words ‘stock’ and ‘inventory’ are also used to describe transforming resources, but terms stock control and inventory control are nearly always used in connection with transformed resources.
Almost all operations keep some kind of inventory, most usually of materials but also of information and customers (customer inventories are normally called queues).
Why is inventory necessary?
Inventory occurs in operations because the timing of supply and the timing of demand do not always match. Inventories are needed, therefore, to smooth the differences between supply and demand.
There are four main reasons for keeping inventory:
- To cope with random or unexpected interruptions in supply or demand(buffer inventory)
- To cope with an operation’s inability to make all products simultaneously(cycle inventory)
- To cope with planned fluctuations in supply or demand(anticipation inventory)
- To cope with transportation delays in the supply network(pipeline inventory)
How much inventory should an operation hold?
This depends on balancing the costs associated with holding stocks against the costs associated with placing an order. The main stock-holding costs are usually related to working capital, whereas the main order costs are usually associated with the transactions necessary to generate the information to place an order.
The most common approach to determining the amount of inventory to order is the economic order quantity (EOQ) formula. The EOQ formula can be adapted to different types of inventory profile using different stock behaviour assumptions.
The EOQ approach, however, has been subject to a number of criticisms regarding the true cost of holding stock, the real cost of placing an order, and the use of EOQ models as prescriptive devices.
When should an operation replenish its inventory?
Partly this depends on the uncertainty of demand. Orders are usually timed to leave a certain level of average safety stock when the order arrives. The level of safety stock is influenced by the variability of both demand and the lead time of supply. These two variables are usually combined into a lead-time usage distribution.
Using re-order level as a trigger for placing replenishment order necessitates the continual review of inventory levels. This can be time-consuming and expensive. An alternative approach is to make replenishment orders of varying size but at fixed time periods.
How can inventory be controlled?
The key issue here is how managers discriminate between the levels of control they apply to different stock items. The most common way of doing this is by what is known as the ABC classification of stock. This uses the Pareto principle to distinguish between the different values of, or significance placed on, types of stock.
Inventory is usually managed through sophisticated computer-based information systems which have a number of functions: the updating of stock records, the generation of orders, the generation on inventory status reports and demand forecasts.
- Chapter 17: Quality planning and control
How can quality be defined?
In several ways. Among the approaches are the transcendent approach which views quality as meaning ‘innate excellence’; the manufacturing-based approach which views quality as being ‘free of errors’; the user-based approach which views quality as ‘fit for purpose’; the product based approach which views quality as a ‘measurable set of characteristics’; and the value-based approach which views quality as a balance between ‘cost and price’.
The definition of quality used in this book combines all these approaches to define quality as ‘consistent conformance to customers’ expectations’.
How can quality problems be diagnosed?
At a broad level, quality is best modeled as the gap between customers’ expectations concerning the product or service and their perceptions concerning the product or service.
Modeling quality this way will allow the development of a diagnostic tool which is based around the perception–expectation gap. Such a gap may be explained by four other gaps:
– the gap between a customer’s specification and the operation’s specification;
– the gap between the product or service concept and the way the organization has specified it;
– the gap between the way quality has been specified and the actual delivered quality;
– the gap between the actual delivered quality and the way the product or service has been described to the customer.
What steps lead towards conformance to specification?
There are six steps:
– define quality characteristics;
– decide how to measure each of the quality characteristics;
– set quality standards for each characteristic;
– control quality against these standards;
– find and correct the causes of poor quality;
– continue to make improvements.
Most quality planning and control involves sampling the operation’s performance in some way. Sampling can give rise to erroneous judgments which are classed as either type I or type II errors. Type I errors involve making corrections where none is needed. Type II errors involve not making corrections where they are in fact needed.
How can statistical process control help quality planning and control?
Statistical process control (SPC) involves using control charts to track the performance of one or more quality characteristics in the operation. The power of control charting lies in its ability to set control limits derived from the statistics of the natural variation of processes. These control limits are often set at ± 3 standard deviations of the natural variation of the process samples.
Control charts can be used for either attributes or variables. An attribute is a quality characteristic which has two states (for example, right or wrong). A variable is one which can be measured on a continuously variable scale.
Process control charts allow operations managers to distinguish between the ‘normal’ variation inherent in any process and the variations which could be caused by the process going out of control.
How can acceptance sampling help quality planning and control?
Acceptance sampling helps managers to understand the risks they are taking when they make decisions about a whole batch of products on the basis of a sample taken from that batch. The risks of any particular sampling plan are shown on its operating characteristic (OC) curve.
However, some of its assumptions make acceptance sampling controversial.
