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A trackball is a pointing device consisting of a ball held by a socket containing sensors to detect a rotation of the ball about two axes—like an upside-down mouse with an exposed protruding ball. The user rolls the ball with the thumb, fingers, or the palm of the hand to move a pointer. Compared with a mouse, a trackball has no limits on effective travel; at times, a mouse can reach an edge of its working area while the operator still wishes to move the screen pointer farther. With a trackball, the operator just continues rolling, whereas a mouse would have to be lifted and re-positioned. Some trackballs have notably low friction, as well as being made of dense material such as glass, so they can be spun to make them coast. The trackball's buttons may be situated to that of a mouse or to a unique style that suits the user. Large trackballs are common on CAD workstations for easy precision. Before the advent of the touchpad, small trackballs were common on portable computers, where there may be no desk space on which to run a mouse. Some small thumbballs clip onto the side of the keyboard and have integral buttons with the same function as mouse buttons. == History == The trackball was invented as part of a post-World War II-era radar plotting system named Comprehensive Display System (CDS) by Ralph Benjamin when working for the British Royal Navy Scientific Service.〔〔 Benjamin's project used analog computers to calculate the future position of target aircraft based on several initial input points provided by a user with a joystick. Benjamin felt that a more elegant input device was needed and invented a ''ball tracker''〔〔 system called the ''roller ball''〔 for this purpose in 1946.〔〔 The device was patented in 1947, but only a prototype using a metal ball rolling on two rubber-coated wheels was ever built〔 and the device was kept as a military secret. The trackball was first built by Tom Cranston, Fred Longstaff and Kenyon Taylor as part of the Royal Canadian Navy's DATAR system in 1952 DATAR was similar in concept to Benjamin's display, but used a digital computer to calculate tracks, and sent the resulting data to other ships in a task force using pulse-code modulation radio signals. This trackball used a Canadian five-pin bowling ball. DATAR's trackball used four disks to pick up motion, two each for the X and Y directions. Several rollers provided mechanical support. When the ball was rolled, the pickup discs spun and contacts on their outer rim made periodic contact with wires, producing pulses of output with each movement of the ball. By counting the pulses, the physical movement of the ball could be determined. Since 1966, the American company ''Orbit Instrument Corporation'' produced a device named ''X-Y Ball Tracker'', a trackball, which was embedded into radar flight control desks.〔〔(【引用サイトリンク】publisher=oldmouse.com )〕 A similar trackball device at the German ' was constructed by a team around ドイツ語:Rainer Mallebrein of Telefunken ドイツ語:Konstanz as part of the development for the Telefunken computer infrastructure around the main frame , process computer TR 86 and video terminal SIG 100-86, which began in 1965.〔 This trackball was called ''ドイツ語:Rollkugel'' (German for "rolling ball"). Somewhat later, the idea of "reversing" this device led to the introduction of the first computer ball mouse (still named ''ドイツ語:Rollkugel'', model RKS 100-86), which was offered as an alternative input device to light pens and trackballs for Telefunken's computer systems since 1968.〔(【引用サイトリンク】title=Telefunken's 'Rollkugel' )〕 In later trackball models the electrical contacts were replaced by a "chopper wheel" which had small slots cut into it in the same locations as the contacts. An LED shone light through the slots to an optical sensor, As the disk rotated the slots alternately lined up and then blocked the light from the LED, causing pulses to be produced in the sensor. The operation was otherwise similar. Mice used the same basic system for determining motion, but had the problem that the ball was in contact with the desk or mousepad. In order to provide smooth motion the balls were often covered with an anti-slip surface treatment, which was, by design, sticky. Rolling the mouse tended to pick up any dirt and drag it into the system where it would clog the chopper wheels, demanding cleanup. In contrast the trackball is in contact only with the user's hand, which tends to be cleaner. The late 1990s replacement of mouseballs by direct optical tracking put trackballs at a disadvantage and forced them to retreat into niches where their distinctive merits remained more important. Most trackballs now have direct optical tracking which follows dots on the ball. As with modern mice, most trackballs now have an auxiliary device primarily intended for scrolling. Some have a scroll wheel like most mice, but the most common type is a “scroll ring” which is spun around the ball. Kensington's SlimBlade Trackball similarly tracks the ball itself in three dimensions for scrolling. two major companies produce consumer trackballs, Logitech and Kensington, although Logitech has narrowed its product line to two models. Other smaller companies occasionally offer a trackball in their product line. Microsoft produced popular models including The Microsoft Trackball Explorer, but has since discontinued all of its products. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Trackball」の詳細全文を読む スポンサード リンク
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