Abstract:
A printer includes a position detecting mechanism for detecting and calibrating a position of a carriage on a track, and a print head installed on the carriage for printing a document. The position detecting mechanism has a first portion installed at a calibration position neighboring the track, and a second portion installed on the carriage. The calibration position is positioned within a document printing range of the print head so that the second portion is capable of passing by the first portion during a printing process.

Description:
BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The present invention relates to a printer, and more specifically, the present invention discloses a printer that is capable of setting a calibration position within a range in which a print head is able to print a document. 
     2. Description of the Prior Art 
     Please refer to FIG.  1 . FIG. 1 is a perspective view of a printer  10  disclosed in U.S. Pat. No. 5,861,726. The printer  10  comprises a housing  12 , a carriage  14  installed inside the housing  12  that moves in right and left directions on a horizontal track  16 , an ink container  18  installed on the carriage  14 , a print head  20  set on the ink container  18 , and a step motor  30  for driving the carriage  14 . The printer  10  further comprises a light source  22 , and a light sensor  24  installed outside a printing range of the printer  10 . The carriage  14  further comprises a shield  26  for blocking light transmitted from the light source  22  to the light sensor  24 . 
     The step motor  30  drives the carriage  14  to move left and right along the horizontal track  16 , so that the print head  20  is able to print the document. Before the printer  10  starts to print the document, the printer  10  calibrates a position of the carriage  14  to a zeroed position, i.e. the position that the light source  22  and the light sensor  24  is at, outside of the printing range. The position of the carriage  14  is calibrated by using the step motor  30  to drive the carriage  14  to move until the shield  26  on the carriage  14  blocks the light transmitted from the light source  22  to the light sensor  24 . When starting printing of the document, the step motor  30  drives the carriage  14  to a printing start point, so as to enter the printing range, then prints the document until printing is finished, or the next calibration time, at which time the position of the carriage  14  is zeroed again. 
     In the prior art printing method, the printer  10  is unable to detect immediately if the position of the print head  20  is not accurate, so the print head  20  continues printing on a wrong position, until the whole document is printed, or the next calibration. This wastes time and ink. 
     SUMMARY OF INVENTION 
     It is therefore a primary objective of the claimed invention to provide a printer that is capable of setting the calibration position inside the printing range. While not consuming excess time, the printer is able to detect the position of the print head in the printing process, so as to check whether the position of the print head is correct or not. If the error of the print head position is too large, then the printer is able to stop printing and calibrate the position of the carriage instantly, not wasting printing time and ink. 
     The claimed invention, briefly summarized, discloses a printer including a position detecting mechanism for detecting and calibrating a position of a carriage on a horizontal track, and a print head installed on the carriage for printing a document. The position detecting mechanism has a first portion installed at a calibration position of the horizontal track, and a second portion installed on the carriage. The calibration position is positioned within a document printing range of the print head, so that the second portion is capable of passing by the first portion during a printing process. 
     It is an advantage of the claimed invention that the printer has a position detecting mechanism installed within the printing range of the print head, so that the position of the carriage is detected and calibrated in the printing process. If an error of the print head position exceeds a predetermined range, but is within an acceptable range, the printer can calibrate the position of the carriage after printing the document. In contrast, if the position of the print head has a serious misalignment, then the printer may stop printing the document and calibrate the position of the carriage instantly, to avoid wasting printing time and ink. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a perspective view of a printer according to the prior art. 
     FIG. 2 is a perspective view of a present invention printer. 
     FIG. 3 is a diagram of a relation between an output signal of a light sensor and a position of a light source and the light sensor on a carriage. 
     FIG. 4 is a perspective view of a second embodiment of the present invention printer. 
     FIG. 5 is a perspective view of a third embodiment of the present invention printer. 
     FIG. 6 is another perspective view of the third embodiment of the present invention printer. 
    
    
     DETAILED DESCRIPTION 
     Please refer to FIG.  2 . FIG. 2 is a perspective view of a printer  50  according to the present invention. The printer  50  comprises a housing  52 , a carriage  54  installed within the housing  52  that can move back and forth in left and right directions on a horizontal track  56 , an ink container  58  installed on the carriage  54 , a print head  60  communicated with the ink container  58  for ejecting the ink onto a document while the carriage  54  is moving in left and right directions. The printer  50  further comprises a shield  94  installed on the base of the housing  52  within the printing range in which the print head  60  can print information onto the paper. The shield  94  is used to detect and calibrate the position of the carriage  54 . The printer  50  also has control circuitry  80  for controllings operations of the printer  50 , and a step motor  82  for driving the carriage  54 . The control circuitry  80  comprises a counter  72 , which counts rotational steps of the step motor  82  to record the counted position of a light source  90  and a light sensor  92  disposed on the carriage  54 . 
     The shield  94  comprises a first edge  96  and a second edge  98 . The control circuitry  80  records positions of the first edge  96  and the second edge  98  of the shield  94  corresponding to the horizontal track  56 . The position of the first edge  96  of the shield  94  is corresponding to a first calibration position of the horizontal track  56 . The position of the second edge  98  of the shield  94  is corresponding to a second calibration position of the horizontal track  56 . 
     The printing process operated among those components shown in FIG. 2 is further explained below. During movement of the carriage  54  from the end point  97  toward the end point  99  of the horizontal track  56 , when the light source  90  and the light sensor  92  move to the first calibration position (first edge  96 ), the shield  94  starts to block the light transmitted from the light source  90  to the light sensor  92 . Then, the control circuitry  80  compares (a) the first counted position of the light source  90  and the light sensor  92  along the horizontal track  56  (the rotational steps of step motor  82  counted by the counter  72 ), with (b) the first calibration position (the predetermined first rotational step count recorded in the control circuitry  80 ), to obtain a first difference between the two positions. 
     When the light source  90  and the light sensor  92  on the carriage  54  move to the second calibration position (second edge  98 ), the light sensor  92  starts to receive the light transmitted from the light source  90  again. Then, the control circuitry  80  compares (a) the second counted position of the light source  90  and the light sensor  92  along the horizontal track  56  (the rotational steps of step motor  82  counted by the counter  72 ), with (b) the second calibration position (the predetermined second rotational step count recorded in the control circuitry  80 ), to obtain a second difference between the two positions. 
     If (a) the first difference between the first calibration position and the first counted position of the light source  90  and the light sensor  92 , or (b) the second difference between the second calibration position and the second counted position of the light source  90  and the light sensor  92  is less than a first predetermined range, then the control circuitry  80  does not need to calibrate the position of the carriage  54 . This is because the difference is within a permissible error tolerance. 
     If (a) the first difference between the first calibration position and the first counted position of the light source  90  and the light sensor  92 , or (b) the second difference between the second calibration position and the second counted position of the light source  90  and the light sensor  92  is larger than the first predetermined range but less than the second predetermined range, then the control circuitry  80  calibrates the position of the carriage  54  after the on-going document printing process is completed. The control circuitry  80  need not stop printing and calibrate the position of the carriage  54  immediately. In this situation, there does exist certain minor position error of the carriage  54 , but the influence is limited. 
     Otherwise, if a) the first difference between the first calibration position and the first counted position of the light source  90  and the light sensor  92 , or (b) the second difference between the second calibration position and the second counted position of the light source  90  and the light sensor  92  is greater than the second predetermined range, then the control circuitry  80  will instantly stop printing the document and calibrate the position of the carriage  54 . In this situation, there does exist serious position error of the carriage  54  to affect the print out quality. 
     Please refer to FIG.  3 . FIG. 3 is a diagram of a relation between (a) the output signal of the light sensor  92  and (b) the light source  90  and the light sensor  92  moving along the horizontal track  56 . In FIG. 3, F represents the first calibration position corresponding to the first rotational step count recorded in the control circuitry  80 . The first predetermined range corresponding to a smaller tolerance around the first calibration position is defined by the area between F0− and F0+. The second predetermined range corresponding to a larger tolerance around the first calibration position is defined by the area between F1− and F1+. 
     In theory, as shown in FIG. 3, when the light source  90  and light sensor  92  arrive at the position F, then the shield  94  starts to block the light transmitted from the light source  90  to the light sensor  92 . Therefore, when the output signal of the light sensor  92  changes from a high voltage to a low voltage, the counted position (the rotational steps counted by the counter  72 ) should be same as the first calibration position F (the first rotational step count recorded in the control circuitry  80 ). However, in practice, when the transition of the output signal of the light sensor  92  occurs, the rotational steps counted by the counter  72  does not always equal to the first rotational step count recorded in the control circuitry  80  which represents the first calibration position F. 
     If the output signal of the light sensor  92  changes when the light source  90  and the light sensor  92  arrive at the range between F0− and F0+, then the control circuitry  80  does not need to calibrate the position of the carriage  54  because the position of the carriage  54  only has a very minor deviation. If the output signal of the light sensor  92  changes when the light source  90  and the light sensor  92  arrive at the range between F1− and F0−, or at the range between F0+ and F1+, then the control circuitry  80  must calibrate the position of the carriage  54  after the on-going document printing process is completed because the deviation is still tolerable for the on-going document. If the output signal of the light sensor  92  changes while the light source  90  and the light sensor  92  have not reached the position F1−, or when the light source  90  and the light sensor  92  have passed the position F1+, then the control circuitry  80  must instantly stop printing the document and calibrate the position of the carriage  54 . This is because the position of the carriage  54  has a severe deviation. 
     A position detection method when the light source  90  and the light sensor  92  on the carriage  54  arrive the second calibration position is similar to the position detection method when the light source  90  and the light sensor  92  on the carriage  54  arrive the first calibration position. 
     In the present invention, the printer  50  detects the difference between the first and second counted positions of the light source  90  and the light sensor  92  and the first and second calibration positions at the horizontal track  56 , recorded by the control circuitry  80 . The printer  50  detects the above difference once whenever the light source  90  and the light sensor  92  pass through the first or second calibration position once in either process: (a) the carriage  54  moving from the end point  97  towards the end point  99 , or (b) the carriage  54  moving from the end point  99  towards the end point  97 . 
     Moreover, the printer  50  is also capable of detecting the difference between the position of the light source  90  and the light sensor  92 , corresponding to the horizontal track  56 , and the position which the first or second calibration position at the horizontal track  56 , recorded by the control circuitry  80 . This difference will be measured when the light source  90  and the light sensor  92  pass through the first or second calibration position. 
     Please refer to FIG.  4 . FIG. 4 is a perspective view of a second embodiment of a present invention printer  100 . The difference between the printer  100  of the second embodiment and the printer  50  of the first embodiment is the shield  94  of the printer  100  is installed on the carriage  54 , and the light source  90  and the light sensor  92  of the printer  100  are installed on the housing  52  within a range in which the print head  60  is capable of printing the document. The position of the light source  90  and the light sensor  92  of printer  100  corresponds to the calibration position of the horizontal track  56 , for detecting the position of the carriage  54 . 
     In the process of the print head  60  printing the document shown in FIG. 4, the first edge  96  of the shield  94  moves towards the end point  99  of the horizontal track  56  to a position in which the shield  94  starts to block the light transmitted from the light source  90  to the light sensor  92 . When this happens, the control circuitry  80  compares (a) the first counted position of the first edge  96  of the shield  94  represented by the rotational steps counted by the counter  72 , with (b) the predetermined calibration position recorded in the control circuitry  80 , and obtains a difference between the two positions. 
     Later, the shield  94  further moves and makes the second edge  98  of the shield  94  move to a position in which the light sensor  92  starts to receive the light transmitted from the light source  90  again. When this occurs, the control circuitry  80  compares (a) the second counted position of the second edge  98  of the shield  94  represented by the rotational steps counted by the counter  72 , with (b) the predetermined calibration position recorded in the control circuitry  80 , and obtains a difference between the two positions. 
     If the difference between the counted position of the first edge  96  or the second edge  98  of the shield  94  and the calibration position at the horizontal track  56  exceeds a first predetermined range but within a second predetermined range, then the control circuitry  80  calibrates the position of the carriage  54  after the on-going printing process is completed. 
     If the difference between the counted position of the first edge  96  or the second edge  98  of the shield  94  and the calibration position at the horizontal track  56  exceeds the second predetermined range, then the control circuitry  80  instantly stops printing the document and calibrates the position of the carriage  54  immediately. 
     Similarly, the printer  100  detects the above difference once whenever the first edge  96  or the second edge  98  passes through the calibration position once in either process: (a) the carriage  54  moving from the end point  97  towards the end point  99 , or (b) the carriage  54  moving from the end point  99  towards the end point  97 . 
     Please refer to FIG.  5  and FIG.  6 . FIG.  5  and FIG. 6 are perspective views of a third embodiment of a present invention printer  110 . The difference between the printer  110  and the printer  50  is the printer  110  uses a DC motor  114  to drive the carriage  54 . The printer  110  further comprises an optics ruler  112  installed on the housing  52 . The carriage  54  further has a light source  108  installed for transmitting the light towards the optics ruler  112 , and a light sensor  106  for detecting the light transmitted from the light source  108  and through the optics ruler  112  and generating the corresponding position signal. The counter  72  is used, according to the position signal generated by the light sensor  106 , to indicate the position of the light source  90  and the light sensor  92 , corresponding to the horizontal track  56 . 
     Similarly, the printer  110  is also able to use the DC motor  114  to drive the carriage  54 . The printer  110  is able to use the optics ruler  112 , light source  108 , and the light sensor  106  to generate the position signal. Based on the position signal generated from the optical ruler  112 , the counter  72  is able to record the first counted position of the first edge  96  or the second counted position of the second edge  98 , corresponding to the horizontal track  56 . 
     In contrast to the prior art, the present invention printer is able to stop printing the document and calibrate the position of the carriage instantly when the position of the print head has a serious error, not wasting printing time and ink. If the error of the print head position exceeds a predetermined range but is still tolerable, the printer can calibrate the position of the carriage after printing the document. This avoids wasting the printing document, and ensures the printing quality of the next document. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only be the metes and bounds of the appended claims.