Datasheet

Thursday, 17 July 2003 MiniProject: Design Aspects Colin K McCord
EEE512J2 – Electronic Product Design Page 30 Chapter 6: Physical Design
6.0. PHYSICAL DESIGN
The shape, form, aesthetics, styling, tactile qualities / human interaction surfaces and visual interaction of the
ECG monitor could determine if the product is a commercial success or a failure.
Figure 6.0a shows the shape of traditional ECG monitor; clearly it’s a square
box. If engineers had their way everything would simply be put into a square
box, but in terms of attracting customers the dull old square has no chance.
The attraction of the design could be improved by simply rounding the edges.
The controls, display, and sockets should be layouted in a logical and neat
manor. Styling of the product is extremely important, it should have unique
style that sets it apart form any other product on the market, and colour should
be chosen wisely for example bright colours may attract someone’s attention.
Human interaction surfaces and tactile qualities, must be right, as certain
textures feel bad (e.g. cheap plastic feel), while others give the impression of
quality.
Plastics are characterised by high strength-to-density ratios, excellent thermal and electrical insulation
properties, and good resistance to acids, alkalis, and solvents. The giant molecules of which they consist
may be linear, branched, or cross-linked, depending on the plastic. Linear and branched molecules are
thermoplastic (soften when heated), whereas cross-linked molecules are thermosetting (harden when
heated).
The ECG monitor should be ergonomically efficient and packaged in ABS-type plastic. As this is a low
volume product a vacuum mode solution would be the most viable. ABS-type plastic was chosen because it
is a tough, heat-resistant thermoplastic making it ideal for this project.
The manufacture of the plastic case will be carried by a plastic specialist company charging an agreed price
for each case. Generally the larger the quality to be manufactured the lower the production cost, but there
are high tooling costs involved with the large production method of manufacture which are no viable for low
volume products (like this ECG monitor).
6.1. ABS Plastic (Acrylonitrile Butadiene Styrene)
ABS is a graft copolymer made by dissolving styrene-butadiene copolymer in a mixture of acrylonitrile and
styrene monomers, then polymerizing the monomers with free-radical initiators in an emulsion process.
Grafting of acrylonitrile and styrene onto the copolymer chains occurs by chain-transfer reactions. ABS was
patented in 1948 and introduced to commercial markets by the Borg-Warner Corporation in 1954.
ABS is a tough, heat-resistant thermoplastic. The three structural units provide a balance of properties, the
butadiene groups (predominantly trans-1,4) imparting good impact strength, the acrylonitrile affording heat
resistance, and the styrene units giving rigidity. ABS is widely used for appliance and telephone housings,
luggage, sporting helmets, pipe fittings, and automotive parts.
6.2. Manufacture of Plastics
The manufacture of plastic and plastic products involves procuring the raw materials, synthesising the basic
polymer, compounding the polymer into a material useful for fabrication, and moulding or shaping the plastic
into its final form.
Most plastics today are derived from petrochemicals. These oil-based raw materials are more widely
available and less expensive than other raw materials. However, because the world supply of oil is limited,
other sources of raw materials, such as coal gasification, are being explored.
Figure 6.0a. ECG Monitor