PM4Robot: A Scriptable Parametric Modeling Interface for Conceptual Robot Design Using PM4VR

The increasing complexity of robot design, driven by advancements in human-centered computing [5], automation [4], AI [23], optimization [24], and robotics hardware [20], requires conceptual design tools that offer flexibility, rapid iteration, and seamless integration with hardware and software development pipelines. While current modeling tools are powerful, they often struggle to strike a balance between ease of use and the technical precision necessary for early-stage robotic design. Traditional CAD tools for robot design [19] tend to be rigid, making it difficult to modify a design once it is created. Conversely, existing parametric modeling systems may lack essential robotics-specific features needed for quickly prototyping articulated systems that include actuators, sensors, and mechanical joints. This presents a challenge in creating adaptable and efficient tools for the conceptual design phase.

Various robotics design platforms, such as CoppeliaSim(V-REP) [2] and ROS-based robot architectures [18], provide simulation and visualization capabilities for robot design. However, these platforms tend to focus on behavior and control systems rather than the geometric modeling required for early design stages. Parametric modeling [22] has been widely used in design industries, allowing designers to create models defined by a set of adjustable parameters. Tools like Rhino/Grasshopper [3] and Autodesk's Fusion 360 [21] provide users with flexible parameter-based design workflows. However, these tools are often specialized for architectural or industrial design rather than robotic systems. PM4VR was initially developed to address the gap between parametric modeling and immersive VR environments [7]. By offering a scriptable VR system, PM4VR's extensions enable users to manipulate complex models within VR for various types of applications [8, 9, 10, 11, 12, 13, 14, 15, 16, 17]. As shown in Fig. 1, PM4Robot extends PM4VR for robotic applications, enabling the prototyping of robot geometry design in a creative way.

Overview.Fig. 2 provides an overview of our proposed PM4Robot-based solution for parametric conceptual robot design. Starting with the NURBS shapes for different parts of the robot's geometry, designed using the Unity NURBS editor originally developed by Li et al.[9], the robot designer creates a Java^♭ script as input. After executing on PM4VR which is extended into Robot4VR, this Java^♭ script automatically loads the NURBS shapes and their symmetric counterparts for all robot parts using a for loop. Robot4VR then stores the model in *.obj format, utilizing a custom texture mapping technique we developed to preserve material color. Next, the object file is uploaded to Adobe Mixamo's auto-rigger tool [1] and downloaded in *.fbx format, containing the bone information necessary for the animation creation. After adding bones using Mixamo's auto-rigger tool, the *.obj file is automatically converted to an *.fbx format. The robot is then animated in Unity using the Animator Controller, with the settings shown in Fig. 6. Finally, the robot can be animated in an immersive virtual environment using Unity's Animator Controller [6] tool.

Symmetric NURBS Surface.As the robot's geometry is symmetric given a center line, therefore, in Robot4VR, we extend the PM4VR by implementing a new Java^♭ method called addNURBSSymmetry("name", q, f(u, v), u₀ : u₁, v₀ : v₁). Mathematically, we construct the surface by loading the NURBS geometry from "name".NURBS file as s(u, v); Then, deforming NURBS surface along normal direction at (u, v) with distance of parametric function f(u, v), where we get a new parametric surface g(u, v). And then, after flipping along axis q, we get g_q(u, v) which is calculated with this equation:

To highlight the unique capabilities of PM4Robot, we conducted a series of case studies aimed at illustrating its rapid prototyping potential, emphasizing creativity and flexibility in robotic form development. PM4Robot was designed as an interactive interface that empowers users to conceptualize and animate robotic forms swiftly, adjusting various parameters to explore a broad range of design possibilities. As shown in Fig. 3, seven distinct conceptual robots were created using the PM4Robot interface, each exhibiting a unique shape while all being animated with the same gesture. This uniformity in animation allows a clear focus on the variations in robotic design, underscoring PM4Robot's versatility in handling diverse shapes and configurations. In addition, Figs. 4 and 5 demonstrate the adaptability of PM4Robot by presenting the same set of robot designs animated with different gestures. Each figure includes the Java^♭ script parametric functions at the bottom, giving insight into the modularity and customization potential of the PM4Robot framework. These parametric functions allow for quick adjustments, enabling a seamless exploration of animation and design variations, which is crucial in PM4Robot's iterative design workflows.

User Study. Fig. 8 provides a glimpse into a preliminary user study conducted within a virtual robot showcase, where participants had the opportunity to engage directly with PM4Robot's interface by adjusting parameter values on a conceptual robot through the VR hardware of Oculus Quest 2. This hands-on engagement allowed users to explore PM4Robot's flexibility, gaining a deeper understanding of how parameter adjustments impact the final design and behavior of the robot. Such interactive user studies aim to gather feedback on usability and functionality, contributing to the ongoing refinement of PM4Robot and offering a comprehensive demonstration of these case studies in action, This preliminary user study showcases the dynamic prototyping process, highlighting PM4Robot's extensive design flexibility. For a more detailed understanding of PM4Robot's user interaction under the VR settings, please refer to this link: https://youtu.be/fbHEywZAlcw

This paper presents PM4Robot, a parametric modeling interface specifically designed for conceptual robot design. Built on the PM4VR, PM4Robot introduces specialized tools tailored to the unique challenges of robotic form design. PM4Robot introduces a new way to approach conceptual robot design, combining parametric modeling and VR for an interactive, flexible design process. By merging parametric modeling with VR, PM4Robot offers an interactive, flexible platform for designing robotic appearance. A case study demonstrates the effectiveness and efficiency of PM4Robot in designing a variety of conceptual robots. The results indicate that PM4Robot enhances the creativity of conceptual robot designers, offering a promising avenue for future research in the field of parametric modeling for conceptual robot design. Future improvements for PM4Robot aim to incorporate real-time physics simulations and task-based simulations. Adding real-time physics will allow users to see how robots interact with their environment in a realistic way. Task-based simulations will further enhance PM4Robot by enabling users to simulate specific tasks, such as grasping objects, navigating obstacles, or performing complex maneuvers, which will be valuable for refining robot functionality for real-world applications.