Volume 2 Issue 8 - December 21, 2007
Design approach for increasing stability and performance of touch pens in screen handwriting tasks
Fong-Gong Wu*, Shuyi Luo


MAR 2006, “Performance Study on Touch-pens Size in Three Screen Tasks,” Applied Ergonomics, 37(2), pp. 149–158 (SCI) (SSCI) NSC93-2213-E-006-078
MAY 2006, “Design and Evaluation Approach for Increasing Stability and Performance of Touch Pens in Screen Handwriting Tasks,” Applied Ergonomics, 37(3), pp. 319–327 (SCI) (SSCI) NSC93-2213-E-006-078
SEP 2006, “Performance of the Five-Point Grip Pen in Three Screen-based Tasks,” Applied Ergonomics, 37(5), pp. 629-639  (SCI) (SSCI) NSC94-2213-E-006-056
Taiwan Patent No.: M273460

The applications of pens are expanding with the development of technologies. The pen-based products increased the opportunities for people to use pens to write on screens. A touch pen used for screen writing is a hand tool and can be considered as an extension of the hand. The proper design of hand tools requires technical, anatomic, anthropometric and physiological considerations. This study investigated the sizes of the touch pens in the current markets to explore the proper length and diameter of a touch pen and observed the user behaviors on the pen-based computers to find natural postures of upper limb (forearm, hand and fingers) and hand gripping. Then the hand anthropometric measurements and the design principles of hand tools were taken into consideration during the touch-pen design for increasing comfort and performance.

The concept of this study was developed from investigations, innovated design and evaluations. The investigations were to survey the sizes of touch pens in the current markets, to explore the behavior of touch-pen used on pen-based computer and to interview the user’s opinions after operations. The results of the observations demonstrated that when a user point-and-clicked on the screen, the forearm hung in the air and did not use their elbow or other hand part for support. Most users held touch pens high on the penholder with a finger grip that appeared loose; that is, the grip pattern was similar to pinching a stick and wielding it. Furthermore, based on observational results and user feedback, this study identified that the loose grip pattern sometimes allowed the pen fall or resulted in incorrect pointing-and-clicking, owing to instability of the pen. For writing task, the feature “using local support” (53.3% using local support, 46.7% not using local support). 6.7% used their wrist (including the side of the hand) for support, 10.0% used their elbow as support, and 36.7% used their little finger for support. Moreover, the users’ fingers appeared to strenuously grip the pen and their fingers become deformed or exert excessive force during screen writing task. While drawing geometric figures on the screen, 63.3% of users did not use support and 30.0% used their little finger for support. Pen holding gestures vary while drawing. Some people use three digits, four digits, or even five digits to hold a pen, whereas others use their little finger for support.

To further understand why people did not write and draw with the forearm supported on a screen, but use their little finger, wrist or elbow for support. This study also collected user opinions by interview. The interview results were as follows:
  • The cause of unnatural gestures was that users could not maintain a straight wrist. For instance, most people write with their wrist resting against the screen or screen edge. While performing tasks, most users had excessive dorsiflexion. When a user’s elbow rested on a table, their hand appeared to have excessive palmar flexion. When the little finger rests against the screen, the finger can easily drift into excessive extension. Although local support can provide support for a user’s hand by grasping the control, the users’ wrists were bent, especially causing palmar flexion or dorsiflexion problems.
  • When writing on paper, people write with their forearm supported on a table or other surface. However, why do users typically use their wrist, elbow or little finger for support when writing on a screen? Interview results indicated that the use of the little finger for support was a habit carried over from past computer use, resulting from user’s fear of scratching or staining the screen. Furthermore, using the wrist, elbow and little finger as local support can also provide considerable stability and facilitate substantial dexterity while writing on a screen.

In terms of ergonomic design, a neutral hand posture is one in which the hand is straight, rather than bent up, down, sideways or twisted. Observational results clearly demonstrated that the key design goal for a touch pen form screenwriting was to eliminate unnatural postures, and increase operational stability and performance.

Before the innovated design, this study firstly examines the size effects on the performance of various touch-pens in the current markets. Three different lengths (80, 110 and 140mm) and four different diameters (5.5, 8, 11 and 15mm) were tested in three screen tasks for determining the ideal dimensions of the pen-based products. The sizes of 140mm x 8mm were suitable for three tasks using. Following, the innovated design of touch pen was created depending on the results of the proper sizes, behavior observations, as well as the theories of hand motion and design principles. Several studies proposed several methods for increasing hand stability. Handle should be designed to have large content surface to distribute the force and to direct it to less-sensitive areas, such as the tough tissue between thumb and index finger, or to change tool shapes to reduce the wrist angle, minimize hand disorders, and increase user performance. The use of the cleft between the thumb and index finger as an extra contact point that can improve handle holding or griping. These design cases illustrated the following findings: (1) the safest forces are those applied to the parts of the hand which contain fat pads and thick muscles, such as finger segments and areas below the thumb; and, (2) the palm touch is the most complete touch, involving some or the entire inner surface of the hand. Consequently, this study integrated the previous findings with observational results and arrived at the idea of adding an extra contact point under the tough tissues of the thumb cleft to diminish the need of using wrist, little finger and elbow for local support while operating a touch pen. The tripod grip, the most common gripping method, uses four contact points: thumb; index finger; middle finger; and, an additional point made by the thumb cleft. In addition to the fourth contact point, a fifth contact point was added to the proposed pen below the thumb cleft to minimize unnatural gestures and slipping. The position of fifth point is located on the tough tissues of the thumb between the muscles of flexor pollicis brevis and adductor pollicis, and stretches across the thumb cleft. This novel pen is called the five-point grip pen (FPGP).

To further understand the usability of the FPGP, the final stage was design evaluations. In the first place, to understand whether the FPGP is superior to the normal touch pen on performance and upper limb postures. The performing times and error rates were the dependent variables. The upper limb postures and the grip patterns were surveyed and evaluated. The experimental and observational results showed: (1) the performance of the FPGP is superior (with fewer error rates) than the common touch pen in three screen tasks. (2) Although the touch pens with or without a brace did not differ in terms of time performance, fewer errors occurred in the writing and pointing-and-clicking tasks when a touch pen with a brace was used. This study recommends that tasks required high degree of accuracy, a touch-pen with a brace should be helpful. When drawing on a screen people can use the FPGP to improve hand stability and save time. (3) The advantages of the FPGP include: increased hand stability, improved unnatural postures, and provided adjustability. The disadvantages of the FPGP were the limits of gripping patterns and the pen could not be twirled by users.

The FPGP was superior to a normal touch pen in performance and hand postures. Thus, the further evaluation stage was considered to verify the performance of various handbreadths, brace shapes, and brace sizes. Nine braces with three shapes (ball, ball-and-brick, and natural) and three brace sizes (large, medium and small). The experimental results indicated that: (1) the subjective ranking results were consistent with the results of performance measures in all three tasks. (2) All measures were affected by brace shape and brace size but differently for each task. (3) The natural shape was the best brace for all tasks. (4) The small brace was best for all users during the writing task; the large size was the best brace during pointing-and-clicking task; the large and medium braces were suitable for all users during drawing task.

This study proposed FPGPs that added the brace to a touch pen to increase the stability in screen tasks. The idea and results can be applied to those that needed higher accuracy or continuous freehand without supporting control tasks, such as wall-painting, surgery operation, and other required aiming tasks. Moreover, for choosing a brace size, the findings suggested that (1) for performing tasks that required prompt or accurate position-based movements and stable tracing movements the large braces were appropriate, (2) for tasks that required detailed operation in various directions the small braces were preferred.
The concise design processes of the Five Point Grip Pen (FPGP)
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