Coordinate-capturing apparatus

Abstract

A coordinate-capturing apparatus suitable for inputting handwritten characters or diagrams to a computer or a printer is disclosed. The apparatus includes an ultrasonic transmitter mounted on an input pen for transmitting ultrasonic waves, two ultrasonic receivers for receiving ultrasonic waves transmitted form the ultrasonic transmitter, and a distance calculating device for calculating distances between the input pen and the two ultrasonic receivers in order to determine coordinates representing a position of the input pen on the basis of the calculated distances. The apparatus of the invention can perform coordinate detection smoothly even when the input pen moves fast, and has reduced electric power consumption in the input pen to increase the life-span of a battery included in the input pen.

1 . A coordinate-capturing apparatus comprising: 
 an ultrasonic transmitter mounted on an input pen to be in contact with a medium for transmitting ultrasonic waves;    a first and a second ultrasonic receivers for receiving ultrasonic waves transmitted form said ultrasonic transmitter;    a distance calculating device for calculating distances between said input pen and said first and said second ultrasonic receivers when a specific condition is satisfied;    a coordinate calculating device for calculating coordinates representing a position of said input pen on the basis of said distances calculated by said distance calculating device; and    a distance variation calculating device for calculating variations of said distances between said input pen and said first and second ultrasonic receivers on the basis of time periods between receptions of an ultrasonic wave transmitted from said ultrasonic transmitter at a first time by said first and second ultrasonic receivers respectively and receptions of an ultrasonic wave transmitted from said ultrasonic transmitter at a second time by said first and second ultrasonic receivers respectively;    said distance calculating device calculating, on the basis of said distances calculated when said specific condition is satisfied and said variations of said distances calculated by said distance variation calculating device, distances between said input pen and said first and second ultrasonic receivers when said specific condition is not satisfied.    
     
     
         2 . A coordinate-capturing apparatus according to    claim 1   , in which: 
 said ultrasonic transmitter transmits ultrasonic waves intermittently at regular intervals;    said coordinate-capturing apparatus further includes a clock generator for generating clock pulses continuously; and    said distance variation calculating device includes:    a device for determining first time periods between said first time and said second time for said first and second ultrasonic receivers;    a device for determining second time periods between third times at which ultrasonic waves transmitted from said ultrasonic transmitter at said first time is received by said first and second ultrasonic receivers respectively and fourth times at which ultrasonic waves transmitted from said ultrasonic transmitter at said second time is received by said first and second ultrasonic receivers respectively; and    a device for detecting difference between said first time periods and second time periods to determine said distance variations.    
     
     
         3 . A coordinate-capturing apparatus according to    claim 2   , in which: 
 said ultrasonic transmitter transmits intermittently ultrasonic waves having a first period at a second period;    said device for determining said first time periods includes a device for counting said clock pulses generated during said first period of ultrasonic waves received by said first and second ultrasonic receivers to obtain first count values for said first and second ultrasonic receivers and a device for obtaining, by multiplying said first count values by a ratio of said second period to said first period, count values which are equivalent of said first time periods;    said device for determining said second time periods includes a device for counting said clock pulses generated between said third times and said fourth times respectively to obtain second count values; and    said distance variations are determined on the basis of difference between said first count values and said second count values.    
     
     
         4 . A coordinate-capturing apparatus according to    claim 2   , in which: 
 said input pen includes a timing signal transmitter for transmitting a timing signal of a train of timing pulses having a first period;    said coordinate-capturing apparatus further includes a timing signal receiver for receiving said timing signal;    said ultrasonic transmitter transmits ultrasonic pulses at a second period;    said device for determining said first time periods includes a device for counting said clock pulses generated during said first period of said timing signal received by said timing signal receiver to obtain a first count value, and a device for obtaining count values which are equivalent of said first time periods by multiplying said first count value by a ratio of said second period to said first period;    said device for determining said second time periods includes a device for counting said clock pulses generated between said third times and fourth times to obtain second count values; and    said distance variations are determined on the basis of difference between said first count values and said second count values.    
     
     
         5 . A coordinate-capturing apparatus according to    claim 2   , in which said device for determining said first time periods includes a device for holding a predetermined value corresponding to the number of clock pulses to be generated between said first and second times.  
     
     
         6 . A coordinate-capturing apparatus according to    claim 1   , in which: 
 said ultrasonic transmitter transmits ultrasonic waves continuously while said input pen is in contact with said medium;    said distance variation calculating device calculates said distance variations periodically, and    when said distance variations exceed a predetermined value for any of said first and second ultrasonic receivers, said distance calculating device updates said distances between said input pen and said ultrasonic receivers, and said coordinate calculating device calculates new coordinates.    
     
     
         7 . A coordinate-capturing apparatus according to    claim 6   , in which said coordinate-capturing apparatus further includes a clock generator for generating clock pulses continuously, and said distance variation calculating device includes: 
 a device for determining first time periods between first times and second times for said first and second ultrasonic receivers;    a device for determining second time periods between third times at which ultrasonic waves transmitted from said ultrasonic transmitter at said first times is received by said first and second ultrasonic receivers respectively and fourth times at which ultrasonic waves transmitted from said ultrasonic transmitter at said second times is received by said first and second ultrasonic receivers respectively; and    a device for obtaining differences between said first and second time periods to determine said distance variations.    
     
     
         8 . A coordinate-capturing apparatus according to    claim 7   , in which said device for determining said first time periods includes first counters for counting received ultrasonic waves up to a first value, and said device for determining said second time periods includes second counters for counting said clock pulses until a count of corresponding one of said first counters reaches said first value.  
     
     
         9 . A coordinate-capturing apparatus according to    claim 7   , in which said device for determining said first time periods determines said first time periods by obtaining products of the numbers of ultrasonic waves received by said first and second ultrasonic receivers respectively and ratios of a frequency of said clock pulses to frequencies of ultrasonic waves received by said first and second ultrasonic receivers respectively.  
     
     
         10 . A coordinate-capturing apparatus according to    claim 9   , in which said device for determining said first time periods includes a device for performing multiplication using a predetermined value as said ratios of a frequency of said clock pulses to said frequencies of ultrasonic waves.  
     
     
         11 . A coordinate-capturing apparatus according to    claim 9   , in which said device for determining said first time periods includes a device for measuring actual frequencies of ultrasonic waves received by said first and second ultrasonic receivers, to obtain said ratios on the basis of said actual frequencies.  
     
     
         12 . A coordinate-capturing apparatus according to    claim 11   , in which said device obtaining said ratios obtains said ratios by counting said clock pulses generated during one period of ultrasonic waves received by said first and second ultrasonic receivers respectively.  
     
     
         13 . A coordinate-capturing apparatus according to    claim 11   , in which said input pen has a timing signal transmitter for transmitting a timing signal of a pulse train, and said device determining said ratios obtains said ratios by counting said clock pulses generated during one period of pulses of said timing signal, and by obtaining products of the number of said clock pulses counted during said one period and ratios of a period of said timing signal to periods of ultrasonic waves received by said first and second ultrasonic receivers respectively.  
     
     
         14 . A coordinate-capturing apparatus according to    claim 9   , in which said input pen has a timing signal transmitter for continuously transmitting a timing signal of a pulse train in synchronization with ultrasonic waves, and said device for determining said first time periods counts pulses of said timing signal received by a timing signal receiver to determine said first time periods.  
     
     
         15 . A coordinate-capturing apparatus according to    claim 1   , in which said coordinate calculating device calculates coordinates representing a position of said input pen on the basis of a distance between said first and second ultrasonic receivers and distances between said input pen and said first and second ultrasonic receivers.  
     
     
         16 . A coordinate-capturing apparatus according to    claim 1   , in which said specific condition includes a contact between said input pen and said medium.  
     
     
         17 . A coordinate-capturing apparatus according to    claim 16   , in which said specific condition further includes a transmission of a timing signal at regular time intervals after contact between said input pen and said medium.  
     
     
         18 . A coordinate-capturing apparatus according to    claim 1   , in which said input pen further includes a timing signal transmitter, said coordinate-capturing apparatus further includes a timing signal receiver, and said distance calculating device calculates distances between said input pen and said first and second ultrasonic receivers on the basis of times elapsed between transmission of ultrasonic pulses from said ultrasonic transmitter and receptions of said ultrasonic pulses by said first and second ultrasonic receivers.  
     
     
         19 . A coordinate-capturing apparatus according to    claim 1   , further including a third ultrasonic receiver for receiving ultrasonic waves transmitted from said ultrasonic transmitter, said distance calculating device calculating distances between said input pen and said first and second ultrasonic receivers on the basis of ultrasonic waves received by said first, second, and third ultrasonic receivers when said specific condition is satisfied.  
     
     
         20 . A coordinate-capturing apparatus according to    claim 1   , in which a distance between said first and second ultrasonic receivers is adjustable.