1. Field of the Invention
The present invention relates to character input device usable for a mobile phone, PC, mobile terminal, word processor, household electrical appliance, etc., more particularly relates to a character input device designed to enable easy key input by few keys, primarily the directional keys, with less movement of the fingers and line of sight.
2. Description of the Related Art
In the mobile type character input devices of mobile phones etc., there is little area for disposition of the keys, so it is only possible to provide a limited number of keys.
Therefore, a large number of key operations were necessary to input a character. Here, “character” includes alphanumerics, symbols, and phonetic syllabaries or ideographs of different languages.
Take, for example, the case of inputting characters of the Japanese language hiragana phonetic syllabary in conventional mobile phones in use in Japan. The hiragana phonetic syllabary consists of 50 characters arranged in 10 groups of five characters each as follows:                a () i () u () e () o ()        ka () ki () ku () ke () ko ()        sa () si () su () se () so ()        ta () ti () tu () te () to ()        na () ni () nu () ne () no ()        ha () hi () hu () he () ho ()        ma () mi () mu () me () mo ()        ya () (i) yu () (e) yo ()        ra () ri () ru () re () ro ()        wa () wi () u () we () wo ()        
The practice has been to assign one of the 10 rows of characters to each of the “0” to “9” keys, select one of the rows by pressing one of the keys, and select one of the five characters of the corresponding row by successively pressing that key.
Since the different rows of characters were assigned to separate keys in this way, a large amount of finger movement was involved. Beginners had to move their line of sight back and forth between the display and keys, so the efficiency of input was extremely poor.
Further, for example, if pressing the key assigned the row a (), i (), u (), e (), o () once, a () was input, if pressing it twice, i () was input, and similarly if pressing it three times, u (), four times, e (), and five times, o () was input. Therefore, to input o (), it was necessary to press the key five times. Further, if intending to input i (), but mistakenly pressing the key three times, it was necessary to repeatedly press the key until that character was again returned to. This led to increased stress to the user. In recent years, mobile phones provided with “return” keys to return to the previous character and thereby eliminate this problem have been seen, but since these basically add another key, they cannot be said to be effective in terms of input efficiency.
Further, as an alternative means, it may be considered to use a virtual keyboard enabling character selection by a mouse in a PC etc., but since the display units are small in size, this had the problem of over half of the screen being taken up by the virtual keyboard.
Japanese Unexamined Patent Publication (Kokai) No. 2001-265501 and Japanese Unexamined Patent Publication (Kokai) No. 2000-155643 disclose to solve this problem by adopting simplified character input systems.
Japanese Unexamined Patent Publication (Kokai) No. 2001-265501, however, discloses to arrange a specific character of each of the rows (for example, a (), ka (), sa (), ta (), na (), ha (), ma (), ya (), ra (), wa () on one row when inputting for example characters of the hiragana phonetic syllabary, so the visibility would probably become poor in a small display unit such as that of a mobile phone. Further, when focusing on the a () row, movement to the ha () row required five key strokes by either of the “right” key or the “left” key.
Japanese Unexamined Patent Publication (Kokai) No. 2000-155643 also suffered from the above problem and also the inability to display all of the rows due to making them cyclic. Therefore, in this case as well, the problem of poor visibility arose.