GRAPHICS TABLETS

GRAPHICS TABLTES
Graphics Tablet also called pen pad consists of a flat surface upon which the user may draw an image using an attached stylus, a pen-like drawing apparatus. The image generally does not appear on the tablet itself but, rather, is displayed on the computer monitor. Some tablets however, come as a functioning secondary computer screen that you can interact with directly using the stylus. Some tablets are intended as a general replacement for a mouse as the primary pointing and navigation device for desktop computers. It also a common tool of experimental electronic performances where drawn shapes and lines along with position, velocity and direction can be measured by software patches which are designed to interpret these variables and convert them into sounds, projected colours, etc.
The first electronic handwriting tablet was the Telautograph. Styalator was the first graphic tablet resembling contemporary tablets and used for handwriting recognition by a computer. The RAND Tablet also known as the Grafacon for Graphic Converter employed a grid of wires under the surface of the pad that encoded horizontal and vertical coordinates in a small magnetic signal. The stylus would receive the magnetic signal, which could then be decoded back as coordinate information.
Summagraphics also made an OEM version of its BitPad which was sold by Apple Computer as an accessory to their Apple II. These tablets used a magnetostriction technology which used wires made of a special alloy stretched over a solid substrate to accurately locate the tip of a stylus or the center of a digitizer cursor on the surface of the tablet. This technology also allowed Proximity or Z axis measurement.
There have been many attempts to categorize the technologies that have been used for graphics tablets. Some of the categories used include; Passive Tablets, Active Tablets, Optical tablets, Acoustic tablets, Electromagnetic tablets, Capacitative tablets. Let us know if what are those categories mean.
The Passive Tablets make use of electromagnetic induction technology, where the horizontal and vertical wires of the tablet operate as both transmitting and receiving coils as opposed to the wires of the RAND Tablet which only transmit. The tablet generates an electromagnetic signal, which is received by the LC circuit in the pen. The wires in the tablet then change to a receiving mode and read the signal generated by the pen. Modern arrangements also provide pressure sensitivity and one or more switches (similar to the buttons on a mouse), with the electronics for this information present in the pen itself, not the tablet. On older tablets, changing the pressure on the pen nub or pressing a switch changed the properties of the LC circuit, affecting the signal generated by the pen, which modern ones often encode a digital data stream onto the signal. By using electromagnetic signals, the tablet is able to sense the stylus position without the stylus having to even touch the surface, and powering the pen with this signal means that devices used with the tablet never need batteries. The Active tablets differ in that the stylus used contains self-powered electronics that generate and transmit a signal to the tablet. These pens rely on an internal battery rather than the tablet for their power, resulting in a bulkier pen. Eliminating the need to power the pen means that such tablets may listen for pen signals constantly, as they do not have to alternate between transmit and receive modes, which can result in less jitter. Optical tablets operate by a very small digital camera in the pen, and then doing pattern matching on the image of the paper. The Acoustic tablets early models were described as spark tablets a small sound generator was mounted in the stylus, and the acoustic signal picked up by two microphones placed near the writing surface. Electromagnetic tablets the Wacom is one example of a graphics tablet that works by generating and detecting an electromagnetic signal in the Wacom design, the signal is generated by the pen, and detected by a grid of wires in the tablet. Other designs such as those by Pencept generate a signal in the grid of wires in the tablet, and detect it in the pen. Capacitative tablets have also been designed to use an electrostatic or capacitative signal. Scriptel's designs are one example of a high-performance tablet detecting an electrostatic signal. Unlike the type of capacitative design used for touch screens, the Scriptel design is able to detect the position of the pen while it is in proximity to the tablet.






] References
^ About.com - Before You Buy a Graphics Tablet
^ Gray, Elisha (1888-07-31), Telautograph, United States Patent 386,815, http://rwservices.no-ip.info:81/pens/biblio70.html#Gray1888b
^ Dimond, Tom (1957-12-01), Devices for reading handwritten characters, Proceedings of Eastern Joint Computer Conference, pp. 232–237, http://rwservices.no-ip.info:81/pens/biblio70.html#Dimond57, retrieved on 2008-08-23
^ An Historical Timeline of Computer Graphics and Animation,
^ Pencept Penpad (TM) Manual, Pencept, Inc., 1983-06-15, http://rwservices.no-ip.info:81/pens/biblio83.html#Pencept83
^ GP-10 SAC Two-dimensional Sonic Digitizer, Science Accessories Corporation, 1988-06-15, http://users.erols.com/rwservices/pens/biblio85.html#Pencept88
^ AirPen Storage Notebook: PC NoteTaker, www.pegatech.com, 2005-06-15, http://users.erols.com/rwservices/pens/biblio05.html#Pentel05
^ Hyperspace 3-D Digitizer, Mira Imaging, Incorporated, 1989-04-15, http://users.erols.com/rwservices/pens/biblio90.html#Mira89
^ Scriptel Corporation, http://www.scriptel.com, retrieved on 2008-08-24
^ New Products: CAD Graphics Tablet, IEEE Communications, Vol 22 No 4, 1984-04-15, http://users.erols.com/rwservices/pens/biblio85.html#Scriptel84
^ Kable, Robert G. (1986-07-15), Electrographic Apparatus, United States Patent 4,600,807 (full im