Models & Prototypes

Putting plastic, metal and silicon in your hands

Protomodels960d

In the course of a design project we usually produce a number of physical and virtual models or prototypes, ranging from improvised models for quick sanity checks through to Engineering Prototypes. Some of these we make ourselves—I’ve got a well-equipped workshop with milling machine, lathe, 3D-printer and SMD reflow oven. For some, parts are produced externally on the basis of our CAD-files and specifications. Below is an overview of the various types of models we make and use—what the most appropriate one is depends on what we want to proof, try or illustrate with the model.

Proof-of-principle/Proof-of-concept model

I make a distinction between Proof-of-Concept and Proof-of-Principle. To me the latter proves the physical principles behind a technology, while the former demonstrates the feasibility of a particular embodiment. Take for example the Inscentinel VASOR (top right in the image above): The principle is: “Bees predictably extend their proboscis when exposed to a target odour they’ve been conditioned for”. That was proven on a lab bench by observation. The design concept behind the VASOR is to detect the proboscis extension of an immobilised bee by measuring the obscuration of an IR beam.

Proof-of-Concept models are not intended for repeated use—they’re made up of sticky tape, blu-tack, cannibalised parts and whatever else is at hand. In many cases there is some imagination required to see what the model actually proves. The model on the left was made to see if we could detect chemiluminescense with a photodiode. We could.

Breadboard

This to me is a distributed physical model build to run a series of experiments on design parameters for the intended product. It is primarily a test bench where elements of the design can easily be adjusted or exchanged, not a representation of the intended product. A breadboard is often of modular construction, and some effort is spent on making adjustments and measurements easy and repeatable.

Breadboards model only those product elements for which operating parameters need to be determined early on in the design process—especially where these parameters are inter-related. An example is an airflow model where the effect of a number of choices for fans, filters and channel geometry impact the design choices. The example shown left is for a diagnostic reader where detector, optics, and illumination could be quickly exchanged and adjusted.

Handling model

This is a non-functional model of representative dimensions and shape, intended to collect user feedback on ergonomics and styling. Concept-phase handling models are typically improvised from wood, card and everyday objects—like the “medical imager” on the left. In later phases blue foam models or rapid prototyped parts are used.

Under handling models I include user-interface mock-ups on tablets or PCs—PowerPoint can be used to good effect here.

Lab model

A Lab Model (LM) is an integrated functional model intended to test and demonstrate how sub-functions interact in the intended product. It is functionally but not necessarily geometrically representative of production intent—but it will typically be of a similar size and general layout. A lab model is intended to operate within a narrower set of parameter values then a breadboard and will therefore be much less adaptable. Functions with low technical risk will often still be implemented using off-the-shelf items, e.g. power supplies, microcontroller evaluation boards, RC-servos.

Presentation model

This is a non-functional model that is representative in appearance – intended to convey the look and feel of the intended product. In that sense you can call it a “tangible rendering”. We make presentation models by rapid prototyping or by machining from modeling boards, finished to a high cosmetic standard. They may include dummy functionality—the presentation model of a laboratory instrument shown left contained the innards of a digital photo frame—showing a number of possible user interface approaches. Presentation models are primarily used to get early user feedback and to pre-sell products that are still in development.

Product demonstrator

This is a model that looks like and works like a production version, but where the design was not detailed taking into account all the limitation of series production—in that sense they differ from Engineering Prototypes. This means that a product demonstrator can be made at a fraction of the cost of a true engineering prototype.

A product demonstrator is like a functional concept car. They are excellent in allowing potential users to gain first-hand experience at an early stage—this will allow the incorporation of their feedback in the production versions. They can show end-users or marketing partners that your technology can be succesfully implemented in a feasible product.

Engineering prototype

The difference between an Engineering Prototype, lab models and product demonstrators is that in the former all parts and modules are made to not only be functionally representative, but are made according to production intent—taking into account constraints imposed by the intended production process. If a part is to be injection moulded it will have draft, even wall thickness and take into account the mould geometry (e.g. side actions).

3-D CAD model

I use Geomagic Design Expert to create a 3-D CAD model—a computer model that describes the geometry of parts, and the hierarchy of their relationships in assemblies. All products contain a mix of catalogue parts (existing parts that can be bought on specification such as fasteners, motors, electronic components, springs etc.) and custom parts that are unique to the product we’re designing. In the latter case we need to model every detail of the part’s geometry, allowing parts to be produced directly from our 3-D files. In the former case we might not model all details, just those that are relevant for the part’s relationships with other parts (or in the case of subsequent rendering for added realism).

The image on the left shows a screen capture of a CAD model for a programming tool we built to speed up the production of 2,000 semi-disposable test cartridge prototypes. To share 3-D CAD models with clients for review and input we can create a 3-D PDF file—requiring only the free Adobe PDF reader for viewing.

The 3-D CAD model is also used as input for Finite Element Analysis and photo-realistic rendering.

Finite Element Model

I use LISA-FEA for finite element analysis of linear problems. These include stresses/strains in solid parts, vibration, heat and fluid flow and a number of electro-magnetic phenomena. LISA can import 3-D CAD geometry, and within the LISA program I can apply material properties, loads and constraints. Both steady-state and transient problems can be modelled.

FEA modelling with LISA is surprisingly straightforward, but it does require considerable insight to make sure that the model is appropriate to the question that needs to be answered.

Presentation render

I use KeyShot for photo-realistic rendering from 3-D CAD data. In KeyShot I can assign materials and textures to parts, apply graphic labels and create a virtual studio where I can manipulate lights, camera and backgrounds to take virtual pictures of virtual models. Once we detailed the virtual product and set up the virtual studio we can use it to take pictures just as we would use a physical studio.

The virtual studio is a 3-D model, each “picture” (render) is a 2-D image (still or animated). The render on the left shows a concept design for a baby monitor.

Our clients have found these renders very useful in communicating product concepts to potential users, investors or partners.