Apple submitted a patent for a button-less pan & zoom ability on a mouse :
Patent Application number 20070080945 details a mouse having a button-less pan and scroll switch. [..] the mouse would sense different hand positions and act in different ways according to how it is being held.
“In one embodiment, the first mode of operation of the mouse may be a cursor control mode and the first operations on the display screen may be cursor movements on the display screen. Additionally, the second mode of operation of the mouse may be a pan and/or scroll control mode and the second operations on the display screen may be scrolling and/or panning movements on the display screen.”
So maybe this means if you hold the mouse normally you move the mouse; if you hold it a different way — maybe close to the bottom — it scrolls and pans.
How about this alternative as a design to steal: Hold the mouse the usual way all the time, but tilt it to scroll in a given direction. Tilt left and right to scroll horizontally or tilt to the top or bottom edge to scroll vertically. The more you tilt, the faster it scrolls.
One advantage here is you wouldn’t have to lift & shift the mouse to keep scrolling down a long page. You could just tilt the mouse up at the right steepness to scroll down the page and lift again to keep scrolling. Plus, you don’t have to shift your hand to start scrolling.
I think this idea is different than the patent application. The patent seems focused on detecting the user’s grip and in having different modes of operation, interpreting the mouse motion in different ways. This idea is about adding extra sensory input to the mouse and allowing it to remain modeless.
How might this be implemented? There are probably a number of ways… Accelerometers may be tricky as regular mouse motions accelerate the mouse. Presumably if the mouse was moving, it wouldn’t be scrolling or panning. Alternatively, multiple distance sensors under the mouse would be able to measure the height of different edges of the mouse and from this, tilt angles can be computed.
The sensitivity would have to be done right to avoid excessive wrist twisting. A little motion should go a long way. It should be possible to lift the edges of the mouse only by lifting fingers while keeping the wrist flat. Some rebalancing of the mouse may be in order to shift the center of mass closer to the center of the mouse.
Another consideration is the case of the mouse reaching the edge during normal mouse motions. We need to reliably distinguish between tilting to scroll and tilting while shifting a mouse back into range. One possible way would be to detect mouse movement while tilted. (The sensors on the edge of the mouse would be full-fledged mouse position sensors.) Another way would be to require the angle to pass a threshold before it’s interpreted as a scroll. The user would snap an edge of the mouse up in one direction and then reduce the angle for finer control. This topic calls for some research, starting with an analysis of how mice are brought back in-range.
Alternative: Press and drag the heel to scroll
If this tilting thing is too expensive or difficult to implement an alternative design is to construe pressure on the heel of the mouse to indicate scrolling. Dragging the mouse while pressing the heel scrolls in either direction. You can think of this as another button on the heel of the mouse that just happens to be used to initiate scrolling.
It would probably be better to interpret these movements as changes in scrolling velocity rather than in absolute scrolling position, to avoid having to shift the mouse back in range. The further from the “heel down” location the mouse moves, the faster the scroll. Releasing the heel stops the scroll.
This feels pretty good on my old, lightweight Logitech mouse: it’s easy to add pressure on the ball of the hand to press the heel. Unlike the Apple patent this avoids having to shift the hand on the mouse.
[One other thought: would it be possible to add detection for yaw? Say the tip of the mouse is lifted off the desk and the mouse pivoted clockwise and counter-clockwise on its heel. Could multiple optical mouse sensors detect the direction of the twisting? Perhaps a nice research topic.]
There is a precedent for this idea, something called the tilt mouse. However this device is modal and has a peculiar mechanism where the top of the mouse separates from the bottom.