Fieldlab UPPS

Smart Sizing System for Electronic Ankle Bracelets



GEOsatis, in collaboration with Fieldlab UPPS and TU Delft, worked on developing an innovative ankle bracelet for offender rehabilitation, aiming for a fit that is both secure and comfortable across a wide range of ankle sizes. Initial sizing was based on an anthropometric study of Swiss subjects, but faced challenges like accommodating large ankles and ensuring comfort at size boundaries. The project leveraged a larger 3D database of the US population, analysing diverse ankle dimensions to refine the bracelet sizing system. A sizing tool was developed and iteratively improved, incorporating factors like ankle circumference, width, and tibia tilt angle, alongside a safety margin for removal. Despite enhancements, differences in size distribution and actual order ratios necessitated additional validation studies, which adjusted the tool based on findings like the optimal fit margin. Future efforts will focus on integrating validation study results, observing the bracelet donning process, and understanding the impact of demographics on size distribution.

Problem definition

The primary challenge was developing a universally fitting ankle bracelet that accommodates the vast diversity in ankle sizes while ensuring both security and comfort. Differences between the sizing tool's predictions and real-world usage highlighted issues in the existing sizing system. GEOsatis and TU Delft collaboratively research new 3D anthropometry techniques for evaluating and optimising bracelet sizing systems.

Workflow description

Collect phase

Analyse phase


The initial step involved analysing a 3D database of the USA population, covering 2384 subjects, to understand variations in ankle dimensions. Essential measurements like minimum ankle circumference, circumference around medial malleoli, width, length, and height were identified and collated into a data file for further examination.


The anthropometric data derived from the study were utilised to construct a preliminary version of the sizing tool. This tool was designed to input bracelet sizes and boundary conditions for fit margins, facilitating the identification of measurement distributions among subjects. Differences between the actual fittings and the model's predictions necessitated multiple iterations to refine the tool, incorporating additional factors such as the tibia's tilt angle and a safety tolerance for removal. 

Design phase

Parametric Modelling

The development of the sizing tool exemplifies the use of parametric modelling, where the design adapts based on the provided data. This approach prevented the need to start from scratch with each iteration, enabling the incorporation of new dimensions and constraints like the tilt angle of the tibia and removal safety tolerance, thus enhancing the tool's accuracy and utility.


Validation testing was a critical component of the design phase, where 3D printed bracelet samples were tested on human subjects to evaluate fit. The tests, which measured the ankle circumference and the minimum distance between the ankle and the bracelet, challenged previous assumptions about the acceptable fit margin. Additionally, physical tests on 3D printed 'extreme' ankles from the database further validated the tool's efficacy, highlighting the impact of ankle shape on perceived fit and necessitating adjustments to the sizing tool.

Produce phase

Use phase


The project, aimed at refining the sizing system for GEOsatis's offender rehabilitation ankle bracelets through advanced 3D anthropometry, has yielded a functional digital sizing tool poised for implementation. Despite challenges, including geographical distances and COVID-19 disruptions, the collaborative effort led to significant advancements in bracelet design. The validation process, although hindered by limited access to prototypes and subjects, brought to light critical insights, particularly the influence of the donning method on sizing discrepancies. The iterative development of the tool, updated six times, underscores the complexity of achieving an optimal fit across a diverse population. Future research will integrate findings from the validation study into the tool and explore the impact of personal demographics on size distribution, addressing remaining gaps such as the unexecuted size fitting from elementary data. This effort highlights the intricate balance between comfort, security, and the vast variability in human anatomy, pointing to a continued need for innovation in wearable technology for offender rehabilitation. The project's outcomes not only enhance GEOsatis's product offerings but also contribute valuable knowledge to the field of wearable device customisation.

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