DEVICE FOR ENTERING SIGNS INTO A CELLULAR TELEPHONE
TECHNICAL FIELD
The invention concerns a device for character input in a mobile telephone. It replaces a set of buttons or keyboard and, for example, makes it possible to reduce the size of mobile telephones.
BACKGROUND
In mobile telephony it is becoming increasingly common to send text messages and E-mail. Coinciding with telephones becoming smaller, it is becoming increasingly difficult to make space for a text-input keyboard. The invention in question provides the possibility of text input without a keyboard.
SUMMARY OF THE INVENTION
For the purpose described above, the invention provides a device for character input in a mobile telephone, in accordance with the following patent claim.
The invention is thus based on the signals from an accelerometer being decoded and the characters being identified by means of algorithms for pattern recognition. The device is part of the mobile telephone or sends signals to the mobile telephone via a line or cordlessly.
DESCRIPTION OF PREFERRED EMBODIMENTS
By fitting objects such as a mobile telephone or another tangible object with a sensitive accelerometer, the accelerometer can be made to send signals when the object is used in the same way as a pen. When the signals are decoded, patterns in them can be linked to various characters or commands. In this way, a computer can be programmed to recognise the movement patterns of various hand-written characters. In practice, this can then be employed in a mobile telephone, for example, in such a way that the entire telephone is used like a pen.
To achieve the best possible degree of efficiency, the accelerometer should be located as far away as possible from the object's centre of gravity, such as in one of its corners or on the tip of a mobile telephone's antenna. When the object, e.g. the telephone, is then used like a "pen", the part of the telephone that contains the accelerometer can be held against the writing surface. This is because the tip of a pen is the part that moves the most when the pen is used for writing.
The accelerometer can even be fitted into a separate object that could be similar to a pen in shape. Then the signals from the accelerometer, either before or after processing/interpretation/decoding to characters/commands, could be sent via a line or cordlessly to the telephone.
In accordance with the invention, the accelerometer can be uni-, di- or triaxial.
Basic principle for decoding signals Decoding of the acceleration signals is based on pattern recognition. It is not necessary to integrate the signals so that the written characters are visible in order for them to be recognised. Character recognition can be performed either on the direct acceleration signals or following time integration of the position signals.
Advantages
Compared to decoding of speech, the decoding of hand movements means processing significantly (at least by a factor of ten) smaller quantities of information. To further limit the quantity of information that needs to be processed, higher and lower frequencies can be filtered out when the accelerations that are generated by normal handwriting fall within a fairly narrow frequency range. Discernment of character sequences within the movement pattern The device must be able to discern movements that correspond to a character or a command from the movements to which it is subjected. First, it must be able to identify the start and end of a character. The following methods can be used to decide which parts of a movement pattern should be decoded.
Contact with the surface, contact sensor or pressure sensor A pressure sensor or contact sensor in the tip of the device signals when the device comes into contact with the (writing) surface. From this point on the acceleration signals are decoded on the horizontal plane until the device is lifted from the surface, i.e. the contact sensor signals that contact with the surface has been broken.
Surface contact - acceleration pattern
When the device is brought into contact with the surface, powerful acceleration at right angles to the surface arises. If a triaxial accelerometer is used, this signal can be used to identify the start of the characters/commands. From this juncture, the acceleration signals are decoded on the horizontal plane until the device is lifted from the surface, which is recognised by the resulting acceleration that arises when the pen is lifted from the surface.
Surface contact - vibration patterns
If the device is used on an uneven surface, such as paper, the vibrations that arise during the writing process are detected by means of the accelerometer and used as a signal that contact with the surface is taking place.
Movement to the left
If all the characters are written on the same spot, the device must be moved back between two characters. This movement, in conjunction with a downward movement, could be used to mark the start of a character. In the same way, a movement upwards could be used to recognise the end of a character. 4 Discernment of commands from within the movement pattern
It is also possible to allow movements, other than those that correspond to written characters, to match various commands. For example, movements in three dimensions can be used for this. The command movements are essentially recognised in the same way as characters, i.e. by means of algorithms for pattern recognition.
Other uses
The device can also be used to recognise people's initials or signatures. By decoding and registering the acceleration pattern, it will in practice be impossible to forge signatures. The principle described for decoding handwriting movement patterns, interpreted by means of an accelerometer, can also be used for character input in a computer. The advantages of this are evident, such as when the computer is so small there is no space for a keyboard; or for people who have difficulties in using a normal keyboard.