InContacts: Tracking Microsurface Interactions Using Modular Optical Flow Sensor Systems

Tracking fine-grained surface interactions such as sliding, pressing, and deformation is essential for enriching tangible interaction design. However, existing systems often require external infrastructures, markers, or controlled environments, limiting their deployment in everyday contexts. We present InContacts, a compact, wireless module equipped with an optical flow sensor that enables the detection of microsurface interactions without the need for external setup or special tracking objects. By leveraging both positional data and image quality (IQ) data, InContacts enables robust relative sensing of interaction states and intensity trends, rather than precise absolute measurement, across a wide range of materials and configurations. We modularize the sensing mechanism and provide a visual programming graphical user interface (GUI) and code generation tools to enable rapid prototyping, supporting rapid prototyping and system integration. We technically characterize the sensing capabilities and limitations of the proposed system through a series of benchmarks, including motion tracking behavior, material-dependent responses, and deformation-related signals. In addition, we report a hands-on workshop as qualitative, deployment-oriented evidence, illustrating how the proposed sensing primitives can be appropriated and combined in practical interaction scenarios. The results show that modular optical flow sensors can function as versatile surface interaction sensors beyond their conventional device-centric use cases, supporting scalable and practical deployment in real-world environments.