Text-to-image generative models have increasingly been used to assist designers during concept generation in various creative domains, such as graphic design, user interface design, and fashion design. However, their applications in engineering design remain limited due to the models' challenges in generating images of feasible designs concepts. To address this issue, this paper introduces a method that improves the design feasibility by prompting the generation with feasible CAD images. In this work, the usefulness of this method is investigated through a case study with a bike design task using an off-the-shelf text-to-image model, Stable Diffusion 2.1. A diverse set of bike designs are produced in seven different generation settings with varying CAD image prompting weights, and these designs are evaluated on their perceived feasibility and novelty. Results demonstrate that the CAD image prompting successfully helps text-to-image models like Stable Diffusion 2.1 create visibly more feasible design images. While a general tradeoff is observed between feasibility and novelty, when the prompting weight is kept low around 0.35, the design feasibility is significantly improved while its novelty remains on par with those generated by text prompts alone. The insights from this case study offer some guidelines for selecting the appropriate CAD image prompting weight for different stages of the engineering design process. When utilized effectively, our CAD image prompting method opens doors to a wider range of applications of text-to-image models in engineering design.

翻译：文本到图像生成模型已日益应用于创意领域的概念生成阶段，以辅助设计师进行图形设计、用户界面设计和时装设计等工作。然而，由于现有模型在生成可行设计概念图像方面存在挑战，其在工程设计中的应用仍较为有限。为解决这一问题，本文提出一种通过可行CAD图像提示生成以提升设计可行性的方法。本研究以自行车设计任务为例，采用现成的文本到图像模型Stable Diffusion 2.1，通过七种不同CAD图像提示权重的生成设置，产出多样化的自行车设计方案，并评估其感知可行性与新颖性。结果表明，CAD图像提示能有效帮助Stable Diffusion 2.1等文本到图像模型生成视觉上更可行的设计图像。虽然观察到可行性与新颖性之间存在普遍权衡关系，但当提示权重保持在0.35左右时，设计可行性得到显著提升，同时其新颖性仍与纯文本提示生成的设计保持相当水平。本案例研究的发现为工程设计不同阶段选择合适CAD图像提示权重提供了指导原则。若有效运用，本研究所提出的CAD图像提示方法将为文本到图像模型在工程设计中的更广泛应用开启新的可能。