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Digital last assessment

Outlining how SATRA is incorporating digital last assessment as part of a comprehensive fit and comfort technical service for both footwear brand owners and last manufacturers.

by Zach Armitage

Image © iStockPhoto.com/Bill Oxford

It has long been accepted that fit and comfort play a vital role in footwear sales and customer loyalty. Assessing the dimensions of a last is, therefore, important – but traditional measurement has its limitations. Digital last assessment, however, overcomes the limitations by being faster and more accurate, without the need for an actual physical last during measurement.

‘Last assessment’ is the analysis of a last for critical dimensions and shape against its marked size. If the last is the wrong shape, has incorrect proportions or dimensions, or is incorrectly marked, the footwear made on it will not provide adequate fit or comfort for the wearer. If the item is uncomfortable, it is unlikely to sell or, if purchased online, will probably be returned. Brand image may then be tarnished, impacting customer loyalty and diminishing future sales.

Precisely defined landmarks and dimensions are measured to determine a last’s suitability. In its simplest form, a last assessment may determine that a last marked as UK size 6 has been labelled incorrectly and is actually an ideal SATRA standard UK size 5. In more complex last assessments, the resulting conclusion may be that a last is an ideal UK size 8 marked correctly with good proportions, but that the sway is excessive, or the fashion allowance and toe shape is insufficient to accommodate the toes. Constriction of the toes is a common characteristic in fashion footwear, and in extreme situations can lead to severe discomfort and several foot ailments.

The advantage of last assessment is that the likely fit and comfort of the finished footwear can be predicted before manufacture and, in cases where modifications are needed, the final comfort of the footwear can be improved without a costly trial-and-error process in making finished samples and performing repeated fit assessments.

The new way to assess a footwear last

Traditional last assessment utilises a sophisticated measurement jig. The precise nature of the measurements and set-up needed to perform an accurate last assessment on a physical last requires significant expertise and time. While great accuracy can be achieved through the traditional method, there is still an opportunity for human error to arise in the 30 to 40-minute process of extensive measurements.

With digital last assessment, the same dimensional analysis can be achieved in a fraction of the time with far less risk of measurement error. In addition, only having a digital file to assess means a saving on physical modelling and remaking costs if working on new designs. Moreover, the digital process removes the risk and time required in sending in a physical object for assessment which, in turn, dramatically speeds up the development processes. Indeed, several iterations of last design, refinement and assessment can be achieved in a single day.

For digital last assessment, SATRA requires a last file that is 3D printable. In addition, a small number of other details are needed: the marked size of the last, the heel pitch, the insock allowance and the plating allowance. If a last is still to be plated and is designed for footwear with an insock to be inserted after lasting, allowances must be made for this both in the last design and the last assessment.

SATRA has incorporated digital last assessment as part of its comprehensive fit and comfort technical service by integrating the algorithms with certain data drawn from its Global Foot Dimensions survey. This work is the culmination of four years of research using three-dimensional (3D) scanning technology to capture and assess thousands of feet in different regions across the world. By bringing the different strands of data together in a way unique to SATRA, the service can provide an indication of the likely population coverage for a particular last.

What this means in more detail is that by comparing the relationship between effective length and joint (ball) girth (the two most important measurements in footwear fit) to the substantial SATRA database of digital 3D foot scans, a report can be produced showing the percentage of the population that could be ideally and adequately fitted on a range of lasts based on the model under assessment. Such a report is valuable in its own right but, as part of its fit and comfort service, SATRA also offers individual companies tailored consultancy – including a deeper analysis of the foot sizing survey (for example, a particular demographic) and how it might relate to and help a specific brand to optimise its last design and the materials and components choices.

Global supply chains and the retail experience are set to evolve at a rapid pace in coming years. It is not that far-fetched to expect ‘virtual fitting rooms’ based on augmented reality, where consumer demand is quickly integrated into product development in a digitally-integrated and more sustainable manufacturing environment. As far as fit and comfort are concerned, SATRA is already looking at the possibility of further enhancing the digital last and foot scan data by linking with consumer data based on brand and size purchasing preferences, powered by artificial intelligence (AI) machine learning.

How can we help?

SATRA members are invited to make contact to start a discussion about any element of our fit and comfort technical service. Please email innovation@satra.com for further details.

Publishing Data

This article was originally published on page 44 of the July/August 2019 issue of SATRA Bulletin.

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