A Multi-Touch Application for the Automatic Evaluation of Dimensions in Hand-Drawn Sketches

A Multi-Touch Application for the Automatic Evaluation of Dimensions in Hand-Drawn Sketches Ferran Naya, Manuel Contero Instituto de Investigación en Bioingeniería y Tecnología Orientada al Ser Humano (I3BH) Universitat Politècnica de Valencia Valencia, Spain {fernasan, mcontero}@dig.upv.es Jorge Dorribo-Camba Engineering Design Graphics Texas A&M University College Station, TX, USA camba@tamu.edu Abstract Dimensioning plays an important role in the product development process. It is usually learned through sketching exercises where students add the corresponding dimensions to different parts of an engineering drawing. Nevertheless, being able to self-learn proper dimensioning methods is challenging, as a geometric figure requires a specific number of dimensions to be correctly defined. This paper presents an educational software application for multi-touch tablet devices to support dimensioning activities. Our application uses a multi-touch interface where students can create 2D parametric drawings with dimensions using freehand sketches and receive feedback from the system about the quality of their dimensioning exercises. When a student finishes a sketch, the system reports back the correct and incorrect dimensions. Multitouch gestures are also used for basic sketch manipulation (panning, zooming, and rotating), similar to the standard functionality found in modern smart phones and tablets. Preliminary experiences show that multi-touch interfaces provide an effective way to capture students attention. Students found the system very natural, and the time required to learn how to use the application is short. They enjoyed the simplicity of the interface and valued the powerful control of the geometry. Keywords Innovation and technology; multi-touch displays; sketch-based interfaces I. INTRODUCTION Sketching and dimensioning are considered important learning outcomes in the engineering curriculum. The Accreditation Board for Engineering and Technology (ABET) recommends a list of eleven outcomes for assessing engineering students, one of which, criterion 3, states that students must possess the ability to communicate effectively [1]. Many engineering programs interpret this ability as encompassing written, oral, and graphical forms. In 2004, a survey [2] conducted by the Engineering Design Graphics Division of the American Society for Engineering Education (ASEE) identified the ability to sketch engineering objects in the freehand mode as the second most important graphics skill to be learned by engineering students, while the ability to create dimensions was put in the fourth place. In a classroom environment, students typically practice dimensioning through exercises, where they create the orthographic views of an object and add the corresponding dimensions, or just add the missing dimensions to a given drawing. Dimensioning is a common subject in introductory engineering graphics courses. However, self-learning is difficult as dimensioning exercises are open-ended problems. While a geometric figure requires a specific number of dimensions to be properly defined, there are different sets of correct combinations. In this paper, we present an educational software application for multi-touch tablet devices to support dimensioning activities in engineering graphics courses. Our application uses a multi-touch interface where students can create 2D parametric drawings with dimensions using freehand sketches and receive feedback from the system about the quality of their exercises. II. RELATED WORK Different approaches have been taken to teach dimensioning effectively. Some methods are purely methodological. For example, the "Simple Geometry Method (SGM)" developed by [3] involves breaking down a drawing by a process of simplification. A drawing can be understood as complex geometry that is comprised of multiple simple geometric entities such as lines and circles. Students learn to identify these simple geometric forms and provide dimensions for them. Other methods include the integration of dimensioning and tolerancing topics within CAD modeling courses. As reported by [4], some contents that were traditionally offered as standalone courses (e.g. geometric dimensioning, tolerances, and descriptive geometry) can be partially covered in a parametric modeling course, using CAD tools to apply geometric dimensioning and tolerances to 3D models, and drafting and analysis tools to solve descriptive geometry problems. In previous work by [5], educational modules were designed to illustrate geometric dimensioning and tolerancing examples employing a portable Coordinate Measuring Machine (CMM), which interfaced with a parametric solid modeling software package allowing students to visualize tolerance zones. McInnis et al. [6] developed an online working drawing review video and online assessment tool. This tool paid particular attention to dimensioning and ASME ANSI Y14 978-1-4673-5261-1/13/$31.00 2013 IEEE

standards with the objective of improving the quality of the working drawings required in final design project reports. There is practically no computer software specifically designed to support students with dimensioning activities. Martinez and Félez [7] developed a methodology based on a computer application that uses variational geometry, which allows students to draw a simple shape and obtain the different alternative dimensions, according to the ISO-129 standard. Their system consists of a sketching module that supports the creation of shapes. These shapes are created by combining lines, circles, and arcs. A calculation module outputs a complete set of dimensions for the sketch that are consistent with the rules established by the ISO-129 standard. Although the most suitable set of dimensions is provided, the application is flexible. If the student wants to replace a specific dimension, the algorithm automatically reconfigures the complete dimensioning set and proposes a different one. III. DIMENSIONING TECHNICAL DRAWINGS Before an object can be built, complete information about both size and shape must be provided. The process of adding size information to a drawing is known as dimensioning. Dimensioning technical drawings is used to provide a complete description of an object so it can be built and defined. If a part is dimensioned properly, then the intent of the designer is clear to both the person making the part and the inspector checking it. Additionally, proper dimensioning improves the quality of the 3D models created with parametric CAD packages, since students can also learn to use geometric and dimensional constraints efficiently. If students know how to add dimensions properly, they also understand the concept of degrees of freedom and the fully-constrained sketch paradigm (a fullyconstrained sketch is a sketch with zero degrees of freedom, i.e. a sketch in which all degrees of freedom of each geometric element are defined using geometric and dimensional constraints). The main challenges for students when adding dimensions to a drawing are the following: How many dimensions are needed to define an accurate and complete object? In general, dimensions should not be duplicated. Also, only the minimum number of dimensions required to produce or inspect the part should be provided. Over- and under-dimensioned sketches are common errors in students work. Therefore, many exercises need to be done in order to learn how to fully-dimension a drawing. What set of dimensions should be used? There are different sets of dimensions that define a part, but not all of them are correct. A typical selection criterion involves analyzing what information is necessary to manufacture the object. For example, to drill a hole, the manufacturer needs to know the diameter of the hole, the location of the center of the hole, and the depth to which the hole needs to be drilled. These three dimensions describe the hole in complete detail for the feature to be made [8]. Selecting a correct set of dimensions for a drawing requires the correct control and use of the following items: Size dimensions (indicate the overall sizes of the object and the sizes of the features). Location dimensions (locate features of an object from a specified datum, surface or other feature). Dimensions of chamfers, fillets, and rounds. Dimensioning of symmetrical parts. Dimensions of arcs. Dimensions of revolved solids. Inclined surfaces. Dimensions of standard features and shapes (prism, cylinder, hole, etc). With the educational objective of assisting engineering students in learning proper dimensioning practices and standards, a computer aided sketching application called eparsketch has been designed. It is described in detail in the next section. IV. METHODOLOGY A. Software Application for Learning Dimensioning Our application for learning dimensioning, called eparsketch, is a version of a research application for managing 2D parametric freehand sketches [9] adapted for educational purposes. The application eparsketch uses a multi-touch tablet where students can create 2D parametric drawings by using freehand sketches to define the geometric elements (line, arc, circle and ellipse). Combined shapes, which are automatically broken down into basic elements, are also supported. These sketches are automatically recognized by the software and converted to parametric entities, such as those usually employed in modern 3D CAD systems. The drawn shapes can be controlled using a set of gestures (symbolic codes) representing geometric constraints (parallel, perpendicular, tangent, vertical, horizontal or concentric), dimensional constraints (linear, diameters or radii) and delete command. Fig. 1. Inking mode operation: drawing a dimensional constraint.

The application eparsketch uses a single-touch and multitouch gesture alphabet to distinguish between the two basic modes of operation: inking and visualization. Inking allows the creation of drawing entities, supporting both thick and thin lines. This mode follows technical drawing conventions where thick lines are related to edges and object contours, and thin lines are used for dimensions and other types of annotations. In the context of our application, drawing with a finger on the screen means thin (Fig. 1) and putting two or more fingers together means thick. The whole hand is used to delete elements. Fig. 3. Sketching sequence in exercise to learn how many dimensions are needed (II): students dimension a given shape (dimensional control). Visualization mode is controlled by a set of multi-touch gestures where several fingers (pan function) can be used, or two hands at the same time (zoom and rotation). This is similar to the functionality found in modern multi-touch smartphones and tablets. The sketching methodology that is supported by the application follows the typical steps employed by engineers for creating technical sketches. This is an important point, as students do not need to learn any special sketching tools or program commands. They can apply the rules they have learnt previously. We conducted a pilot study of our application with freshman engineering students to test the usability of the software. We used two types of exercises in this study. The first group of exercises was defined to assist students in finding how many dimensions are needed to fully-define a drawing, and a second group was used to select what set of dimensions is appropriate. Fig. 2. Sketching sequence in exercise to learn how many dimensions are needed (I): students define, constrain and edit a shape. B. Exercises to learn how many dimensions are needed The first type of exercise is based on drawing creation and dimensioning. As the user is editing, constraining and dimensioning the corresponding sketch, the system reports the current number of degrees of freedom, which is indicative of the number of missing dimensions. The sketching sequences presented in Fig. 2, Fig. 3 and Fig. 4 illustrate the process. In this type of exercise, the student defines the geometry of the 2D shape (the strokes made by the user are interpreted as geometric entities) which is automatically corrected, adjusted, and connected to other existing elements in the drawing (Fig. 2). Once the user has entered the complete sketch outline, the shape can be edited, dimensioned, and constrained. The user can manage the geometric entities and the geometric constraints using a set of gestures (where the strokes are interpreted as commands). Therefore, if the user wants to generate design alternatives, or adjust some sketch features to reach a specific dimensional condition, the system provides parametric capabilities and handwritten dimensional control to the two-dimensional freehand sections (Fig. 3). The majority of gestures are inspired by the conventional symbols used in technical drafting. During the sketching process, the system

provides feedback with the remaining number of degrees of freedom that need to be constrained. This is used to inform the student if the sketch is over- or under-defined (Fig. 4). C. Exercises to learn what set of dimensions to use In this type of exercises, a drawing without dimensions is presented to the student (Fig. 5 and Fig. 6). The student is asked to add dimensions. When the student finishes the sketch, the system reports the correct dimensions (in green color), the incorrect dimensions (in red color), and adds the dimensions that were missed by the student (in orange). The application has successfully solved all proposed exercises, and the dimensions drawn by the user are compared with the correct set dimensions of the solution. a) Sketch presented to the student b) Dimensions created by the student c) eparsketch correction Fig. 5. Sketching sequence in exercise to select the correct set of dimensions to use (I): dimensioning symmetrical parts. Fig. 4. Sketching sequence in exercise to learn how many dimensions are needed (III): students dimension a given shape. D. Preliminary studies Our preliminary experience with students shows that multitouch interfaces are a powerful tool to capture students attention. They stimulate and build positive attitudes in students toward dimensioning tasks. Initial tests have revealed encouraging results. Students with an engineering background find the system very natural and the learning process very effective. They enjoy the simplicity of the interface and value the powerful control of the sketched geometry. We have tested our application in multiple Tablet-PC s running Microsoft Windows 7, supporting pen-input using a stylus. The parametric engine used to power the system, Siemens 2DCM, is only available for the Windows platform, which is a limitation in terms of portability to Android and ios tablets.

Although some manufacturers have decided to exclude pen input from their current models of tablet devices, our experience in the context of this work suggests that, for sketching and technical work, users can greatly benefit from the precision offered by a stylus instead of a pure touch-based drawing. a) Sketch presented to the student ACKNOWLEDGMENTS This work was partially supported by the Spanish Ministry of Economy and Competitiveness (Project ref. TIN2010-21296-C02-01). b) Dimensions created by the student c) eparsketch correction Fig. 6. Sketching sequence in exercise to select the correct set of dimensions to use (II): rounds and location dimensions. From a usability standpoint, preliminary tests show that a pure tactile management system is not as effective as the combination of pen-input (for sketching) and multi-touch gestures (for visualization tasks, such as zoom, pan and rotate). The screen size is a limiting factor for using a pure multi-touch operation, as users feel less precise in the drawing tasks. REFERENCES [1] ABET. Criteria for accrediting engineering programs, Accreditation Board for Engineering and Technology. Baltimore, Maryland., 2011. [2] Barr, R. E. (2004). The Current Status of Graphical Communication in Engineering Education. Proceedings of 34th ASEE/IEEE Frontiers in Education Conference (pp. S1D8-13). Savannah, GA. [3] Latif, N., & Graham, D. (1999). Dimensioning through understanding geometry. 1999 ASEE Annual Conference Proceedings, pp. 1831-1837. [4] Irwin, J. (2007). Embedded design in parametric modeling and CAM. 2007 ASEE Annual Conference and Exposition, Conference Proceedings. [5] Hewerdine, K. P., Leake, J. M., & Hall, W. B. (2011). Linking CAD and metrology to explain, demonstrate, and teach geometric dimensioning and tolerancing. 2011 ASEE Annual Conference and Exposition, Conference Proceedings. [6] McInnis, J., Sobin, A., Bertozzi, N., & Planchard, M. (2010). Online Working Drawing Review and Assessment. Engineering Design Graphics Journal, 74(1), 1-7. [7] Martínez, M. L., & Félez, J. (2006). An Oriented Constraint Solving- Based Methodology Approach to Learn Dimensioning. International Journal of Engineering Education, 22(2), 359-372. [8] Bertoline, G. R., Wiebe, E. N., Miller, C. L., & Nasman, L. O. (1995). Engineering Graphics Communication. Burr Ridge, IL: Richard D. Irwin. [9] Naya, F., Contero, M., Aleixos, N., Company, P. (2007). ParSketch: A Sketch-Based Interface for a 2D Parametric Geometry Editor. In: Jacko, J.A. (ed.) Human-Computer Interaction. Interaction Platforms and Techniques. LNCS, vol. 4551, pp. 115 124. V. CONCLUSIONS In this paper, an educational software application for dimensioning is presented. It was designed for multi-touch tablet devices to assist engineering students in learning proper dimensioning practices and standards. Our application allows students to create freehand sketches, apply dimensions, and receive immediate feedback about the completeness and correctness of their work. The interface was intentionally designed to simulate a traditional sketching environment, and it offers a promising alternative for self-learning complex topics such as dimensioning. Preliminary results from our tests show that multi-touch interfaces are an effective way to stimulate students, capture their attention, and build a positive attitude toward dimensioning tasks. Participants found the application intuitive and very easy to learn.