1,2Dept. of Computing & Information Science
3Dept. of Physics
University of Guelph
Guelph, Ontario, Canada N1G 2W1
We describe a prototype two-ball mouse containing the electronics and mechanics of two mice in a single chassis. Unlike a conventional mouse, which senses x-axis and y-axis displacement only, our mouse also senses z-axis angular motion. This is accomplished through simple calculations on the two sets of x-y displacement data. Our mouse looks and feels like a standard mouse, however certain primitive operations are performed with much greater ease. The rotate tool - common in most drawing programs - becomes redundant as objects are easily moved with three degrees of freedom. Mechanisms to engage the added degree of freedom and different interaction techniques are discussed.
Keywords: pointing devices, multi-degree-of-freedom input, rotation
Figure 2 illustrates the dimensions and degrees of freedom for several "mouse-type" devices. As a standard mouse is manoeuvred on a mouse pad, only its x and y displacement are sensed, as indicated in the "Mouse" column. This is sufficient for most tasks using, for example, word processors or spreadsheets. However, within drawing packages and other graphics programs, a common task is to move an object to a new location and with a neworientation. This is a full two dimensional task and it requires three degrees of freedom. Since mouse angular motion is not sensed, a rotate tool or a manipulator handle is usually required. Although other schemes can be devised to control the orientation of objects , they are unnatural and violate the basic perceptual structure of interaction .
Figure 1. A mouse pad is a two-dimensional surface with three degrees of freedom: x, y, and THETA-z.
Figure 2. Dimensions vs. degrees of freedom. Grey dots indicate degrees of freedom sensed for several types of input devices. (See text for discussion)
With some simple arithmetic in the interface software, the z-axis or rotational component of the mouse's motion is easily computed from the two streams of x-y positional data. The result is a mouse that senses all three degrees of freedom in a two-dimensional surface. ("2-ball Mouse" column in Figure 2).
Figure 3. Two-ball mouse (a) bottom view. (b) top view with cover and balls removed.
The Owl by Pegasus Technologies and the AeroDuet by Creative Labs are 3df pointing devices that are held in the air. They sense x, y, and z position so, again, they are distinctly different from our device ("A" column in Figure 2). There are also a variety of 6df devices, such as the InsideTrak by Polhemus ("B" column in Figure 2). Devices that sense z-axis position are operated in the air and are suited to games, virtual reality and other non-mainstream applications. In our view, such devices are not likely to garner the support of users of desktop systems, even if the application leans toward 3D interactive graphics. Current systems that combine a mouse with rotate tools or manipulation handles are familiar and there will be resistance to change unless the benefits are substantial and immediate. Since our device is a mouse, it does not impose a major new technique on the user. And it will work with existing tools as new techniques gain acceptance.
An interesting new device is the Rockin'Mouse . It looks like a mouse except it has a curved bottom allowing it to "rock" on the desktop. The rocking motion yields THETA-x an THETA-y data ("C" column in Figure 2). It is operated without lifting from the desktop, so it also has that special mouse-like appeal. Finally, column "D" in Figure 2 identifies a hypothetical 5df device. It would sense rocking motion about the x and y axes (like the Rockin'Mouse) as well as z-axis angular motion (like our mouse). And it would not require lifting from the desktop. Such a device could be very appealing to users who are reluctant to change their ways.
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