Specifications versus Real Needs
It seems self-evident that you should meet the explicit specifications spelled out by the customer and contracted for by your company or called for by your marketing department. However, whether these specifications were written in private by your customer or were negotiated with members of your own organization, they recite not what can best serve the customer but what it thinks it can get and thinks it can afford and therefore asks for. When you work on the inventive phase of design, you may reach some different conclusions. Some of the things asked for may turn out to be much more difficult and costly than anticipated. Conversely, some things not asked for may be features which you can invent and offer, which would be useful to the customer, and which it may be able to afford, yet when the customer wrote the specification it didn't say so and didn't ask for them because it did not know.
You may be able to provide features not asked for at substantially less cost than was anticipated by the customer. You may find that some of the things the customer asked for are really rather more costly than was anticipated. The usual position taken by design engineers is to say that the specification is the law and they must conform rigidly to the law. The alternative is to develop an unsolicited proposal, secure the approval of your management, and offer it to the customer as a proposed revision of the specification. If the attitude of all concerned is constructive and is not controlled by a low innovation index, the customer will get more for its money than it expected, your company will be in a more profitable position, and you yourself will be a hero.
Before you stick your neck out, you must form a judgment and a prediction of the response of both your own people and the customer's people. This is the kind of changing of the world which is within your professional capability and in which you have a reasonable chance of success.
If a program is conducted most cost-efficiently, the specification will evolve with the evolution of the design because the designers will continue to evolve more and better ideas for executing the real purpose of the project. Administratively this is not easy. Even if the specification comes from the marketing department in your own organization, there will be continuous controversy as to what features to add, what features to subtract, what features to change, and what costs to charge. This is an arena in which your own persuasive power has its greatest opportunity.
On the other hand, when you are given an explicit specification by a customer who remains at arm's length for legal reasons (as in competitive bidding) or who is stubborn or when your management insists that no unsolicited proposals be made, then you must conform rigorously to the specification and to the sub-specifications in the specification tree.
Abuse Resistance
Your product and its components will be sized to withstand computed stresses, whether electrical, chemical, or mechanical, with some customary factor of safety. This is not enough.
Your product must withstand some degree of abuse, depending on the nature of the environment into which it is sent. Abuse generates transient peak stresses of many kinds rarely explicitly specified except in some military specifications in which shock and vibration tests are specified. Below are a few examples of real-world abuse which are difficult to quantify:
- A factory machine is run into by a forklift truck.
- An office machine receives a spilled cup of hot coffee.
- A mechanic applies an improper tool such as a hammer instead of a wrench.
- Owner (ignorance, negligence)
- Installer (ignorance, negligence, error)
- Employee (negligence, sabotage)
- Renter (cars, trucks, tools)
- Children
- Hostiles (burglars, vandals)
- Maintainers (negligence, ignorance)
- Public (public telephones, dispensers of gasoline, candy, cigarettes, slot machines, etc.; ignorance, negligence, hostility)
Environment Resistance
The environment can be hostile in many ways. Some of these ways exist in service and some in transportation:
- Heat and cold
- Humidity, high and low
- Liquids (water, oil, chemicals, seawater, coffee spills)
- Vapors (smoke, smog, chemicals, salt air, food)
- Organisms (fungi, bacteria, animals)
- Dust and dirt
- Abrasion
- Burns (cigarettes, soldering irons, cookware, stoves)
- Shock and vibration (in service and in shipment)
- Vacuum (space vehicles)
- Radiation [sunlight, electro-magnetic (radio-frequency interference), nuclear]
- Inversion (turning upside down, usually in shipment)
- Voltage surges, low and high voltage
- Electrical noise
- Pressure surges
- Wet and dirty compressed air
- Improper fuel, dirty fuel
- Environment Protection
If you can arrange to examine products returned by customers for any reason, you will get a degree of enlightenment which no amount of reading can match.
The list is endless if you visualize the environment in the real world where your product will go. As a result of such histories of abuse, conventional styles of construction have been developed in different industries and in different companies. In the truck business the word "trucky" is used to describe devices which appear to be sufficiently robust that truck drivers and maintainers will feel confident in their prolonged satisfactory performance.
Use Preferred Components
It is desirable that you use materials and components which are both standard and preferred in your organization, the customer's organization, or the industry. If you do so, you will please people in each organization and save money for both. If you use uncommon and unconventional materials and components without a need to do so, you will irritate the same people and increase costs.
For aesthetic, functional, and economic reasons, it is desirable to use families of similar components. For example, it is desirable to use the same kind of screwheads or as few variations as possible in a single product.
Maintainability
You should design for maintainability and reliability, whatever those words mean for your product.
In both consumer and industrial products the maintenance question "Shall we fix it, or shall we replace a disposable module?" is always present. This is not a simple question to answer. It depends on the availability of maintenance skills, the availability of a spare-parts distribution network, and business policies of your company. Business considerations such as the profitability of spare parts and sales of spare modules and a service organization may be a determining consideration. Some companies such as IBM and Xerox generate great confidence in their prospective customers because the customers know that if there is a maintenance problem, skilled help will quickly arrive. Here your marketing department and senior management will have opinions with which you may or may not choose to argue.
Suit OEM Components to Automation
The increased use of automatic handling, testing, and assembly machines makes it of value to your customer (and therefore to your own organization) to make components easy for automatic feeding and handling in automatic-assembly machines. Among the things you can do to achieve this end is to make the external shape rigid (no dangling wires, tubes, or chains), provide substantial difference in dimensions so that the part feeder does not confuse length with width, and provide clearly usable gripping features.
Fail-Safe and Fail-Soft
Products should fail safe. Any failure you can imagine happening should result in either a machine stopping or some other situation in which no further damage is done. It is not permissible for a product failure to generate a chain reaction of failures with damage outside the boundaries of the product. Devices such as fuses, circuit breakers, shear pins, slip clutches, and a variety of sensor-initiated shutdowns, and other safety precautions should be provided. Machines should stall safely when overloaded.
Another form of protective design is fail-soft. A product with this characteristic develops failures gradually in such a way that the performance of the product deteriorates slowly, thereby giving warning to its operators that maintenance is needed. An elementary example is a knife which gradually gets dull.
Available skill in maintenance and operating personnel is an important consideration in the design of the product. A design engineer should design the product to suit both the maintainer and the operator. A family car should be designed differently from an earth-moving machine, in part because one is owner-operated and the other is employee-operated.
