21-07-2012, 11:50 AM
touch-sensing
![Microsoft Word Document .doc](https://seminarproject.net/images/attachtypes/doc.gif)
ABSTRACT
We can touch things, and our senses tell us when our hands are touching something. But most computer input devices cannot detect when the user touches or releases the device or some portion of the device. Thus, adding touch sensors to input devices offers many possibilities for novel interaction techniques.
We demonstrate the Touch Trackball and the Scrolling TouchMouse, which use unobtrusive capacitance sensors to detect contact from the user’s hand without requiring pressure or mechanical actuation of a switch. We further demonstrate how the capabilities of these devices can be matched to an implicit interaction technique, the On-Demand Interface, which uses the passive information captured by touch sensors to fade in or fade out portions of a display depending on what the user is doing; a second technique uses explicit, intentional interaction with touch sensors for enhanced scrolling.
We present our new devices in the context of a simple tax-onomy of tactile input technologies. Finally, we discuss the properties of touch-sensing as an input channel in general.
Keywords
Input devices, interaction techniques, sensor technologies, haptic input, tactile input, touch-sensing devices.
INTRODUCTION
The sense of touch is an important human sensory channel. In the present context, we use the term touch quite narrowly to refer to the cutaneous sense, or tactile perception [16]. During interaction with physical objects, pets or other human beings, touch (physical contact) constitutes an extremely significant event. Yet computer input devices, for the most part, are indifferent to human contact in the sense that making physical contact, maintaining contact, or breaking contact provokes no reaction whatsoever from most software. As such, touch-sensing input devices offer many novel interaction possibilities.
Touch-sensing devices do not include devices that provide active tactile or force feedback [22]. These are all output modalities that allow a device to physically respond to user actions by moving, resisting motion, or changing texture under software control. Touch sensing is an input channel; touch sensing allows the computer to have greater awareness of what the user is doing with the input device.
Fig. 1 Left: The TouchTrackball (a modified Kensington Expert Mouse) senses when the user touches the ball. Right: The Scrolling TouchMouse (a modified Microsoft IntelliMouse Pro) senses when the user is holding the mouse by detecting touch in the combined palm/thumb areas. It can also sense when the user touches the wheel, the areas immediately above and below the wheel, or the left mouse button.
Of course, certain input devices (such as touchpads, touchscreens, and touch tablets) that require touch as part of their normal operation have been available for many years. In all of these devices, one cannot specify positional data without touching the device, nor can one touch the device without specifying a position; hence touch sensing and position sensing are tightly coupled in these devices. Yet once it is recognized that touch sensing is an orthogonal property of input devices that need not be strictly coupled to position sensing, it becomes clear that there are many unexplored possibilities for input devices such as mice or trackballs that can sense one or more independent bits of touch data (Fig. 1).
We present two examples of interaction techniques that match these new input devices to appropriate tasks. The On-Demand Interface dynamically partitions screen real estate depending on what the user is doing, as sensed by implicit interaction with touch sensors. For example, when the user lets go of the mouse, an application’s toolbars are no longer needed, so we fade out the toolbars and maximize the screen real estate of the underlying document, thus presenting a simpler and less cluttered display. By contrast, we use the touch sensors located above and below the wheel on the Scrolling TouchMouse to support explicit, consciously activated interactions; the user can tap on these touch sensors to issue Page Up and Page Down requests. Touch sensors allow this functionality to be supported in very little physical real estate and without imposing undue restrictions on the shape or curvature of the region to be sensed. We conclude by enumerating some general properties of touch sensors that we hope will prove useful to consider in the design of touch-sensing input devices and interaction techniques.
PREVIOUS WORK
Buxton proposes a taxonomy of input devices [3] that draws a distinction between input devices that operate by touch (such as a touchpad) versus input devices that operate via a mechanical intermediary (such as a stylus on a tablet). Card, Mackinlay, and Robertson [5] extend this taxonomy but give no special treatment to devices that operate via touch. These taxonomies do not suggest examples of touch-sensing positioning devices other than the touchpad, touchscreen, and touch tablet. Buxton et al. provide an insightful analysis of touch-sensitive tablet input [4], noting that touch tablets can sense a pair of signals that a traditional mouse cannot: Touch and Release. Our work shows how multiple pairs of such signals, in the form of touch sensors, can be applied to the mouse or other devices.
For the case of the mouse, we have already introduced one version of such a device, called the TouchMouse, in previous work [10]. This particular TouchMouse incorporated a pair of contact sensors, one for the thumb/palm rest area of the mouse, and a second for the left mouse button. This TouchMouse was used in combination with a touchpad (for the nonpreferred hand) to support two-handed input. The present paper demonstrates the TouchTrackball and a new variation of the TouchMouse, matches these devices to new interaction techniques, and discusses the properties of touch-sensing devices in general.
Balakrishnan and Patel describe the PadMouse, which is a touchpad integrated with a mouse [1]. The PadMouse can sense when the user’s finger touches the touchpad. The TouchCube [12] is a cube that has touchpads mounted on its faces to allow 3D manipulations. Rouse [21] uses a panel with 4 control pads, surrounding a fifth central pad, to implement a “touch sensitive joystick.” Rouse’s technique only senses simultaneous contact between the thumb on the central pad and the surrounding directional pads. Fakespace sells Pinch Gloves (derived from ChordGloves [17]), which detect contact between two or more digits of the gloves.
Harrison et al. [7] detect contact with handheld displays using pressure sensors, and demonstrate interaction techniques for scrolling and for automatically detecting the user’s handedness. Harrison et al. also draw a distinction between explicit actions that are consciously initiated by the user, versus implicit actions where the computer senses what the user naturally does with the device.
The Haptic Lens and HoloWall do not directly sense touch, but nonetheless achieve a similar effect using cameras. The Haptic Lens [23] senses the depression of an elastomer at multiple points using a camera mounted behind the elastomer. The HoloWall [18] uses an infrared camera to track the position of the user’s hands or a physical object held against a projection screen. Only objects close to the projection surface are visible to the camera and thus the HoloWall can detect when objects enter or leave proximity.
Pickering [20] describes a number of technologies for touchscreens (including capacitive, infrared (IR) detection systems, resistive membrane, and surface acoustic wave detection); any of these technologies could potentially be used to implement touch-sensing input devices. For example, when a user grabs a Microsoft Sidewinder Force Feedback Pro joystick, this triggers an IR beam sensor and enables the joystick’s force feedback response.
Looking beyond direct contact sensors, a number of non-contact proximity sensing devices and technologies are available. Sinks in public restrooms activate when the user’s hands reflect an IR beam. Burglar alarms and outdoor lights often include motion detectors or light-level sensors. Electric field sensing devices [26][24] can detect the capacitance of the user’s hand or body to allow deviceless position or orientation sensing in multiple dimensions. Our touch-sensing input devices also sense capacitance, but by design we use this signal in a contact-sensing role. In principle, an input device could incorporate both contact sensors and proximity sensors based on electric fields or other technologies.
The following taxonomy organizes the various tactile input technologies discussed above. The columns are divided into contact and non-contact technologies, with the contact category subdivided into touch-sensing versus pressure or force sensing technologies. The rows of the table classify these technologies as either discrete (providing an on / off signal only) or continuous if they return a proportional signal (e.g., contact area, pressure, or range to a target). A technology is single-channel if it measures touch, pressure, or proximity at a single point, or multi-channel if it includes multiple sensors or multiple points of contact. The table omits the position and orientation-sensing properties of input devices as these are handled well by previous taxonomies [3][5]. The table also does not attempt to organize the various technologies listed within each cell.
Table 1
TOUCH SENSING: HOW IT WORKS
The touch-sensing input devices described in this paper employ the circuitry shown in Fig. 2, which senses contact from the user’s hand– no pressure or mechanical actuation of a switch is necessary to trigger the touch sensor. The “touch sensors” are conductive surfaces on the exterior of the device shell that are applied using conductive paint (available from Chemtronics [6]). The conductive paint is then connected internally to the touch sensing circuitry.
The internal circuitry generates a 30 Hz square wave that is present on the conductive paint pad. The parasitic capacitance of the user’s hand induces a slight time delay in this square wave. When this time delay passes a critical threshold, a Touch or Release event is generated. A potentiometer (shown in the circuit diagram) allows adjustment of this threshold to accommodate conductive surfaces of various sizes; this only needs to be set once when the circuit is constructed (no calibration step is required for individual users).