Abstract:
A liquid ejecting head is operable to eject liquid toward a target medium. A light emitter is operable to emit light. A light receiver is adapted to receive the light emitted from the light emitter, and operable to output a signal in accordance with an amount of the received light, thereby detecting a position of the liquid ejecting head. A transparent member is disposed between the light emitter and the light receiver. A first line pattern is provided with the transparent member so as to oppose the light emitter, and includes first light transmitting sections and first light shielding sections which are alternately arranged in a first direction with a first pitch. A first actuator is operable to move either the light receiver or the transparent member in a second direction perpendicular to the first direction, thereby varying a distance between the transparent member and the light receiver.

Description:
BACKGROUND  
       [0001]     1. Technical Field  
         [0002]     The present invention relates to a position detector and a liquid ejecting apparatus incorporating the same.  
         [0003]     2. Related Art  
         [0004]     In an ink jet printer, a carriage and a printed object such as paper are driven by a motor. Incidentally, in order to perform position control and speed control, an encoder is generally used. The encoder includes a photo sensor and a scale. The photo sensor includes a light emitting element and a light receiving element. the scale includes a light transmitting section which transmits light emitted from the light emitting element, and a light shielding section which shields light emitted from the light emitting element. These light transmitting section and light shielding section are repetitively arranged at a fixed pitch.  
         [0005]     In such the encoder, recently, there is a problem of attachment of ink mist. Namely, recent printers which perform printing with high precision can eject minute ink droplets from a printing head. These minute ink droplets readily become ink mist and drift inside the printer. Therefore, as such the printer is used for a while, solidified ink mist is piled on the scale.  
         [0006]     Japanese Patent Publication No. 2005-81691A (JP-A-2005-81691) teaches that a partition member is arranged between a carriage belt and a scale to prevent the attachment of the ink mist onto the scale. Japanese Patent Publication No. 2004-202963A (JP-A-2004-202963) discloses a configuration for correcting, in a case where duty factor of a signal outputted from a light receiving element decreases due to the attached ink mist, the duty factor of the output signal so as to become 50%.  
         [0007]     In a case where the ink mist is attached onto the light transmitting section of the scale, light which passes through the light transmitting section is diffracted and causes a disadvantageous effect such as an erroneous detection. However, any means for preventing such the disadvantage is not disclosed in the above publications.  
         [0008]     In addition, it is desired to recognize, in advance, when the erroneous detection occurs due to the attachment of the ink mist in view of the degree of dirt. However, any means for detecting the degree of dirt is not disclosed in the above publication.  
       SUMMARY  
       [0009]     It is an advantage of some aspects of the invention to provide a position detector which can detect the degree of dirt in a scale and enhance a detectability based on the detected dirt degree, and to provide a liquid ejecting apparatus incorporating such a position detector.  
         [0010]     According to one aspect of the invention, there is provided a liquid ejecting apparatus, comprising:  
         [0011]     a liquid ejecting head, operable to eject liquid toward a target medium;  
         [0012]     a light emitter, operable to emit light;  
         [0013]     a light receiver, adapted to receive the light emitted from the light emitter, and operable to output a signal in accordance with an amount of the received light, thereby detecting a position of the liquid ejecting head;  
         [0014]     a transparent member, disposed between the light emitter and the light receiver;  
         [0015]     a first line pattern, provided with the transparent member so as to oppose the light emitter, and including first light transmitting sections and first light shielding sections which are alternately arranged in a first direction with a first pitch; and  
         [0016]     a first actuator, operable to move either the light receiver or the transparent member in a second direction perpendicular to the first direction, thereby varying a distance between the transparent member and the light receiver.  
         [0017]     The liquid ejecting apparatus may further comprise a second line pattern, provided with the transparent member so as to oppose the light emitter, and including second light transmitting sections and second light shielding sections which are alternately arranged in the first direction with the first pitch. Each of the first light transmitting sections has a first transmittance and each of the second light transmitting sections has a second transmittance smaller than the first transmittance.  
         [0018]     The first line pattern and the second line pattern may be adjacent to each other in the first direction.  
         [0019]     The first line pattern and the second line pattern may be adjacent to each other in a third direction orthogonal to the first direction and the second direction.  
         [0020]     The liquid ejecting apparatus may further comprise a second actuator, operable to move either the light receiver or the transparent member in the third direction.  
         [0021]     According to one aspect of the invention, there is also provided a method of managing a detection accuracy of the above liquid ejecting apparatus, comprising:  
         [0022]     driving the first actuator so as to increase the distance between the transparent member and the light receiver;  
         [0023]     detecting a change in light receiving condition of the light receiver before or after the driving of the first actuator; and  
         [0024]     judging a degree of dirt on the transparent member based on the detected change.  
         [0025]     The method may further comprise driving the first actuator so as to decrease the distance between the transparent member and the light receiver than the original distance, in accordance with the judged degree of dirt.  
         [0026]     The method may further comprise moving either the transparent member or the light receiver in a third direction orthogonal to the first direction and the second direction, in accordance with the judged degree of dirt. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]      FIG. 1  is a perspective view of a printer incorporating a position detector according to one embodiment of the invention.  
         [0028]      FIG. 2  is a schematic view showing a motor driving control system in the printer.  
         [0029]      FIG. 3  is a schematic section view showing a sheet transporting system in the printer.  
         [0030]      FIG. 4  is a schematic view showing a linear encoder in the printer.  
         [0031]      FIG. 5  is an enlarged plan view of a linear scale in the linear encoder.  
         [0032]      FIG. 6  is a diagram showing a detailed configuration of the linear encoder.  
         [0033]      FIG. 7  is a timing chart showing signals outputted from the linear encoder.  
         [0034]      FIG. 8  is a schematic view showing a modified example of the linear encoder.  
         [0035]      FIG. 9  is a perspective view showing a longitudinal end portion of a linear scale in the linear encoder, and viewed from an inner side of the printer.  
         [0036]      FIG. 10  is a perspective view showing the longitudinal end portion of the linear scale in the linear encoder, and viewed from an outer side of the printer.  
         [0037]      FIG. 11  is a schematic view showing a rotary encoder in the printer.  
         [0038]      FIG. 12  is a flowchart showing a flow including a processing for detecting dirt of the linear scale.  
         [0039]      FIG. 13  is a flowchart showing a detailed flow of the processing for detecting the dirt of the linear scale.  
         [0040]      FIG. 14  is an enlarged schematic view showing a state that ink mist is attached on a dirt detection pattern of the linear scale.  
     
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0041]     A position detector according to one embodiment of the invention and a printer  10  using this position detector will be described below with reference to the accompanying drawings. The printer  10  in the embodiment is an ink jet type printer. However, such the ink jet printer, as long as it can eject ink to perform printing, may adopt any ejection method.  
         [0042]     In the following description, a “downside” indicates a side on which the printer  10  is placed, and an “upside” indicates a side apart from the side on which the printer  10  is placed. A direction where a carriage  31  described later moves is taken as a primary scanning direction, and a direction which is orthogonal to the primary scanning direction and where a printed object P is transported is taken as a secondary scanning direction.  
         [0043]     As shown in  FIG. 1 , the printer  10  comprises a housing  20 , a carriage driving mechanism  30 , a sheet transporting mechanism  40 , a linear encoder  50 , a scale moving mechanism  70  (see  FIG. 9 ), a rotary encoder  80 , and a controller  90 .  
         [0044]     The housing  20  includes a chassis  21  placed on an installation surface, and a supporting frame  22  provide upright which extends from this chassis  21  upward. The carriage driving mechanism  30  includes a carriage  31 , a carriage motor  32 , a belt  33 , a driving pulley  34 , a follower pulley  35 , and a carriage shaft  36 . On the carriage  31 , an ink cartridge  37  can be mounted. As shown in  FIG. 2 , on the lower face of the carriage  31 , a printing head  38  which can eject ink droplets is provided. The belt  33  is an endless belt, and its part is fixed onto the rear face of the carriage  31 . This belt  33  is stretched between the driving pulley  34  and the follower pulley  35 .  
         [0045]     The above printing head  38  is provided with not-shown nozzle arrays corresponding to each color of ink. In nozzles constituting this nozzle array, not-shown piezoelectric elements are arranged. By the operation of this piezoelectric element, the ink droplet can be ejected from the nozzle that is located at the end portion of an ink passage. The printing head  38  is not limited to the piezoelectric type using the piezoelectric element, but may adopt, for example, a heater type which heats ink and utilizes power of the produced bubbles, a magnetostrictive type which uses a magnetostrictive element, or a mist type which controls mist by an electric field. The ink filled into the cartridge  37  may be any kind of ink, for example, dye-based ink or pigment-based ink.  
         [0046]     As shown in  FIG. 3 , the sheet transporting mechanism  40  includes a motor  41  and a sheet feeding roller  42  for feeding a printed object P such as plain paper (refer to  FIG. 2 ). On the downstream side of the sheet feeding roller  42 , a sheet transporting roller pair  43  for transporting the printed object P nipped therebetween is provided. On the downstream side of the sheet transporting roller pair  43 , a platen  44  and the above-mentioned printing head  38  are provided so as to be opposed to each other in the vertical direction. The platen  44  supports, from the downside, the printed object P being transported below the printing head  38  by the sheet transporting roller pair  43 . On the downstream side of the platen  44 , a sheet ejecting roller pair  45  similar to the sheet transporting roller pair  43  is provided.  
         [0047]     The driving force from the motor  41  is transmitted to a driving roller  43   a  in the sheet feeding roller pair  43  and a driving roller  45   a  in the sheet ejecting roller pair  45 .  
         [0048]     As shown in  FIG. 4 , the linear encoder  50  includes a linear scale  51  and a photo sensor  60 . The linear scale  51  is formed of an elongated transparent member  52  made of a transparent material such as PET (polyethylene terephthalate). However, other various materials can be applied as the transparent member. As shown in  FIG. 9 , holes  51   a  are formed at both longitudinal ends of the linear scale  51 , and hooks  712  (described later) are respectively inserted into the holes  51   a , so that the linear scale  51  is suspended between the hooks  712 .  
         [0049]     For convenience of description, of the transparent member  52 , a surface facing a light emitter  61  (described later) will be described below as a front surface  52   a , and a surface facing a light receiver  63  (described later) will be described as a back surface  52   b.    
         [0050]     As shown in  FIG. 5 , position detecting patterns  53  and dirt detecting patterns  54  are formed on the linear scale  51 . The position detecting patterns  53  include first light transmitting sections  53   a  transmitting light and first light shielding sections  53   b  shielding light. The first light shielding sections  53   b  are sections formed by performing a black print with such a thickness not to transmit light on the front surface of the transparent member  52 . The first light transmitting sections  53   a  are portions to which the black print is not performed and can transmit light emitted from the light emitters  61  to be described later.  
         [0051]     In the embodiment, the dirt detecting patterns  54  are not necessarily required and a configuration from which the dirt detecting patterns  54  are omitted may be employed.  
         [0052]     Here, in the embodiment, the first light transmitting sections  53   a  and the first light shielding sections  53   b  have the same width, that is, the same pitch. The widths of the first light transmitting sections  53   a  and the first light shielding sections  53   b  are not necessarily equal to each other, but the pitch with which the first light transmitting sections  53   a  and the first light shielding sections  53   b  are alternately disposed (hereinafter, referred to as a mask pitch M) must be constant all over the circumference.  
         [0053]     The dirt detecting patterns  54  are provided in a position closer to the longitudinal end of the linear scale  51  than a portion that the position detecting patterns  53  are provided. The position is outer than one end of a printing region. Similarly to the position detecting patterns  53 , the dirt detecting patterns  54  include second light transmitting sections  54   a  transmitting light and second light shielding sections  54   b  shielding light.  
         [0054]     Here, the second light transmitting sections  54   a  of the dirt detecting patterns  54  have a light transmitting area and a light transmittance which are smaller than those of the first light transmitting sections  53   a  of the position detecting patterns  53 . In order to decrease the light transmittance of the light transmitting sections  53   a , a light shielding pattern  54   k  may be provided in the second light transmitting sections  54   a . Here, the light shielding pattern  54   k  includes a plurality of hatched light shielding sections  54   m  which are tilted about the tangential direction of the rotary scale  51 . The light transmitting area and the light transmittance of the second light transmitting sections  54   a  are smaller than the light transmitting area and the light transmittance of the first light transmitting sections  53   a  due to existence of the light shielding sections  54   m . The light intensity of the light passing through the second light transmitting sections  54   a  is smaller than the light intensity of the light passing through the first light transmitting sections  53   a.    
         [0055]     The mask pitch Mm formed by the second light transmitting sections  54   a  and the second light shielding sections  54   b  is equal to the mask pitch M formed by the first light transmitting sections  53   a  and the first light shielding sections  53   b . However, the mask pitch Mm may be different from the mask pitch M. The dirt detecting patterns  54  are not limited to the structure in which they are disposed on the end of the linear scale  51  in the longitudinal direction (i.e., the position detecting patterns  53  and the dirt detecting patterns  54  are horizontally arranged). For example, the position detecting patterns  53  and the dirt detecting patterns  54  may be vertically arranged.  
         [0056]     As shown in  FIGS. 4 and 6 , the photo sensor  60  comprises a light emitter  61 , a collimator lens  62 , and a light receiver  63 . These light emitter  61  and light receiver  63  are opposed to each other through the linear scale  51  located between the collimator lens  62  and the light receiver  63  in a non-contact manner. The light emitter  61  comprises light emitting element  610  such as a light emitting diode, and the light generated by this light emitting element  610  is emitted toward the linear scale  51 .  
         [0057]     The light receiver  63  comprises a substrate  64 , and a first light receiving element array  65  and a second light receiving element array  66  which are provided on this substrate  64 . In the first light receiving element array  65 , plural light receiving elements  65   a  and  65   b  are arrayed. Similarly, in the second light receiving element array  66 , plural light receiving elements  66   a  and  66   b  are arrayed. Each of the light receiving elements  65   a ,  65   b ,  66   a , and  66   b  can convert the received light into an electric signal according to the quantity of the received light. A phototransistor, a photodiode, a photo-IC or the like may be adopted as the light receiving element. These light receiving elements are arranged such that two elements are provided in every one segment (corresponding to the mask pitch M) constituted by a pair of the light transmitting section  53   a  ( 54   a ) and  53   b  ( 54   b ). Further, the first light receiving element array  65  and the second light receiving element array  66  are shifted from each other in the extending direction thereof by one fourth of the mask pitch M so that a phase difference between the arrays  65  and  66  becomes  90  degrees.  
         [0058]     In a case where the width dimension of the light transmitting section  53   a ,  54   a  is the same as that of the light shielding section  53   b ,  54   b  as in this embodiment, one light receiving element is associated with each of the light emitting sections  53   a  ( 54   a ) and the light shielding sections  53   b  ( 54   b ).  
         [0059]     As shown in  FIG. 6 , the plural light receiving elements  65   a ,  65   b ,  66   a ,  66   b  are connected to a signal amplifier  67 . Analog waveform signals outputted from the light receiving elements, after being amplified by this signal amplifier  67 , are outputted to a first comparator  68   a  and a second comparator  68   b . The first comparator  68   a  and the second comparator  68   b  output pulse waveform digital signals on the basis of the analog signals outputted through the signal amplifier  67  from the respective light receiving element arrays  65  and  66 .  
         [0060]     Here, the light receiving element  65   a  in the first light receiving element array  65  is connected to a positive terminal of the first comparator  68   a , and the light receiving element  65   b  in the first light receiving element array  65  is connected to a negative terminal of the first comparator  68   a . The light receiving elements  66   a  and  66   b  in the second light receiving array  66  are similarly connected to the second comparator  68   b . For example, in a case where the level of the analog signal inputted to the positive terminal is higher than the level of the analog signal inputted to the negative terminal, a high-level signal is outputted. In the contrary case, a low-level signal is outputted. Hereby, it is possible to output pulse signals (ENC-A, ENC-B) as shown in  FIG. 7 , corresponding to detection by the light transmitting section  53   a ,  54   a  and the light shielding section  53   b ,  54   b.    
         [0061]     A pulse signal ENC-A is outputted from the first comparator  68   a  corresponding to the first light receiving element array  65 , and a pulse signal ENC-B in which the phase is shifted by 90 degrees is outputted from the second comparator  68   b  corresponding to the second light receiving element array  66  shifted by one fourth of the mask pitch M relative to the first light receiving element array  65 .  
         [0062]     Here, as shown in  FIG. 8 , there may be adopted a configuration in which a single light receiving element array  650  is provided. In this case, a light receiving element  650   a  is connected to either a positive terminal or a negative terminal of the first comparator  68   a , and a light receiving element  650   b  is connected to either a positive terminal or a negative terminal of the second comparator  68   b.    
         [0063]     Next, the scale moving mechanism  70  will be described with reference to  FIGS. 9 and 10 . As shown in  FIG. 9 , the scale moving mechanism  70  includes a supporting plate  71 , a guide pin  72 , a spring  73 , an eccentric cam  74 , and a gear train  75 .  
         [0064]     The supporting plate  71  is formed by a bending process. A bent portion  711  is extended from an upper end of a base portion  71   a . A hook  712  is provided at a portion of the bent portion  711  away by a predetermined distance from the base portion  71   a . A tip end of the hook  712  bent toward the base portion  71   a  from a joint of the hook  712 . The hook  712  engages with the hole  51   a  of the linear scale  51 . The linear scale  51  can be supported in a suspended state by the engagement.  
         [0065]     A pair of guide slots  713  are formed in the base portion  71   a . The guide pins  72  are inserted into the guide slots  713 . The guide pins  72  are members protruding from a side face  22   a  of the support frame  22 . By inserting the guide pins  72  into the guide slots  713 , the supporting plate  71  can slide in the sheet transporting direction (as represented by an arrow in  FIG. 3 ).  
         [0066]     Here, the end of one guide pin  72   a  of the guide pins  72  has a hook shape protruding toward the sheet ejecting direction from the joint of the guide pin  72   a . One end of the spring  73  is hooked and fixed to the guide pin  72   a . The hook-shaped guide pin  72   a  is also referred to as a spring engagement pin  72   a  in the following description.  
         [0067]     A spring engagement member  714  is projected from the base portion  71   a  at a position in the sheet supply side of the guide slot  713  so as to correspond to the spring engagement pin  72   a . The other end of the spring  73  is hooked and fixed to the spring engagement member  714  so that the spring  73  is suspended between the spring engagement pin  72   a  and the spring engagement member  714 . Accordingly, an elastic bias force directed to the sheet ejecting side is given to the supporting plate  71 .  
         [0068]     A bracket  715  is projected from the base portion  71   a  so as to extend in the vertical direction. A cam face  74   a  of the eccentric cam  74  comes in contact with the bracket  715 . Here, the bracket  715  always comes in contact with the cam face  74   a  by the elastic bias force of the spring  73 . Accordingly, when the eccentric cam  74  rotates, the supporting plate  71  can slide in the sheet transporting direction along the shape of the cam face  74   a  and the shape of the guide slot  713 . The eccentric cam  74  is disposed on a rotary shaft  74   b . The read end gear of the great train  75  is provided on the rotary shaft  74   b.    
         [0069]     Here, the motor for rotating the eccentric cam  74  may be a motor independent of the motors  32  and  41  described above and may employ a configuration for distributing the driving force of the motor  41 . In such a configuration, it is necessary to employ a configuration that the eccentric cam  74  does not rotate at the time of carrying the printed object P using a mechanism for switching engagement and disengagement of some gears of the gear train  75 .  
         [0070]     Only one side end of the printer  10  is shown in  FIGS. 9 and 10 . However, the above-mentioned configuration is provided at the opposite side end of the printer  10  and the linear scale  51  can move uniformly in the sheet transporting direction.  
         [0071]     As shown in  FIG. 11 , the rotary encoder  80  comprises a disc-shaped scale  81  rotated by the motor  41 , and a photo sensor  82  similar to the photo sensor  60  of the linear encoder  50 . This rotary encoder  80  has the same constitution as that of the linear encoder  50  except that the scale  81  is formed in the shape of a disc. Therefore, the detailed description of the rotary encoder  80  is omitted.  
         [0072]     As shown in  FIG. 2 , an encoder signal outputted from the linear encoder  50  or the rotary encoder  80 , a print signal from a computer  100 , and various output signals are inputted to a controller  90 . More specifically, the controller  90  includes CPU, ROM, RAM, ASIC, a DC unit, and a driver to control the carriage motor  32 , the printing head  38 , the motor  41 , and the like.  
         [0073]     When the printer  10  is operated under the above constitution, the operation performed by the linear encoder  50  will be described below.  
         [0074]     When the linear encoder  50  is activated and the light emitter  61  emits the light toward the linear scale  51 , the emitted light passes through the collimator lens  62 , so that the light emergent from the collimator lens  62  becomes parallel light. A part of the emergent light to be incident on the light receiving elements  65   a  to  66   b  located on the longitudinal end portions of the light receiving element arrays  65 ,  66  travels in the transparent member  52  without being reflected by the front surface  52   a . The light emitted from the back surface  52   b  of the transparent member  52  reaches the first light transmitting sections  53   a  or the first light shielding sections  53   b.    
         [0075]     Here, when minute ink droplets are ejected from the printing head  38  to the printed object P, the ink mist floats inside the printer  10  and is accumulatively attached as dirt to the linear scale  51 . In this case, in the printer  10 , the dirt of the linear scale  51  is detected at predetermined timings. Hereinafter, a series of operations of the printer  10  at the time of detecting the dirt of the linear scale  51  will be described.  
         [0076]     As shown in  FIG. 12 , first, the controller  90  judges whether it is the timing to detect the dirt of the linear scale  51  (S 10 ). The timing to detect the dirt of the linear scale  51  may be a timing, for example, after the printing work is completely performed to a print sheet or predetermined number of print sheets P, or when the printer  10  is activated. The timing to detect the dirt of the linear scale  51  may be a timing when a predetermined time period t 1  has been passed since the printer  10  is activated, or whenever a predetermined time period t 2  has been passed thereafter. The timing to detect the dirt of the linear scale  51  may be a timing when the printing work is completely performed to a predetermined number n 1  of printed objects P after the printer is activated, or whenever the printing work is completely performed to a predetermined number n 2  of printed objects P thereafter.  
         [0077]     When it is judged in step S 10  that it is not the timing for detection (NO in S 10 ), the dirt of the linear scale  51  is not detected, but the printer  10  is in a standby state or performs the printing work to the next printed object P. On the other hand, when it is judged in step S 10  that it is the timing for detection (YES in S 10 ), a predetermined pre-processing is performed (S 11 ). Here, the pre-processing means a processing of driving the carriage motor  32  to move the carriage  31  to a position (for example, a home position) suitable for detecting the dirt and an activation of the scale moving mechanism  70  to be described later, but processes other than the above-mentioned processes may be included in the pre-processing.  
         [0078]     Here, the pre-processing may include an operation of activating the scale moving mechanism  70 . In this case, the scale moving mechanism  70  moves the linear scale  51  to approach the light emitter  61 . Then, the linear scale  51  is spaced apart from the light receiver  63 . Here, when the ink mist is attached to the first light transmitting sections  53   a , the light passing through the first light transmitting sections  53   a  is often diffracted due to the ink mist. The effect of the diffraction becomes stronger as the distance between the first light transmitting section  53   a  and the light receiver  63  increases. Accordingly, when the linear scale  51  comes away from the light receiver  63 , the light is diffracted and the light is incident on the light receiving elements  65   a  to  66   b  which are originally covered with the light shielding sections  53   b  and  54   b  to block the incidence of light thereto. Accordingly, the detection precision of the light emitted from the light emitter  61  is deteriorated. As a result, when the first light transmitting sections  53   a  come away from the light receiver  63 , it is possible to find out the detection limit of the first light transmitting sections  53   a  in advance. It is also possible to sense the detection lifetime on the basis of the distance by which the linear scale  51  comes away from the light receiver  63 .  
         [0079]     After the pre-processings are completed, the degree of dirt of the linear scale  51  (position detecting patterns  53 ) is detected (S 12 ) while moving the carriage  31  in the primary scanning direction by driving the carriage motor  32 . The detection is performed on the basis of the process flow shown in  FIG. 13 .  
         [0080]     When the detection is completed in step S 12 , a necessary processing is performed (S 13 ) in accordance with the detected degree of dirt of the linear scale  51 . In step S 13 , a variety of processes can be considered and the processes will be described below.  
         [0081]     An example of such processes can include a processing of activating the scale moving mechanism  70  to bring the linear scale  51  close to the light receiver  63 . In this case, it is possible to reduce the effect of diffraction due to the attachment of the ink mist to the first light transmitting sections  53   a  and thus to decrease the possibility of the erroneous detection. Since this process is finished only with movement of the linear scale  51  and does not accompany increase in power consumption, it is simple and economical.  
         [0082]     Another example of such processes can include a processing of setting the driving voltage of the carriage motor  32 . More specifically, the driving voltage is set so that the movement speed of the photo sensor  60  is slower than that when the ink mist is not attached. In this case, when a predetermined amount of ink mist is attached to the linear scale  51  and thus there is possibility of the erroneous detection in the linear encoder  50 , it is possible to reduce the possibility of the erroneous detection.  
         [0083]     Another example of such processes can include a processing of checking whether the detection limit of the linear scale  51  can be reached by performing the printing work to which number of printed objects P. More specifically, the number of print sheets or the print time until the linear scale  51  reaches the detection limit is calculated by the controller  90 . By performing the check and calculation, it is possible to be aware of the number of print sheets or the print time until the linear scale  51  is contaminated.  
         [0084]     Another example of such processes can -include a processing of displaying a predetermined message on a display device (not shown) such as a liquid crystal display provided in the printer  10 . The predetermined message includes a notice indicating that the linear scale  51  comes close the detection limit or almost reaches the detection limit, an error message resulting from the dirt of the linear scale  51 , and a message indicating that it is necessary to clean the linear scale  51 . It is possible to inform a user that the linear scale  51  is contaminated by displaying the messages and to prevent operation failure of the printer  10  due to the erroneous detection of the linear scale  51 .  
         [0085]     Another example of such processes can include a processing of stopping the operation of the printer so as not to use the printer when the degree of dirt is great. By not allowing the use of the printer  10 , it is possible to prevent the operation failure of the printer  10  due to the erroneous detection of the linear scale  51  and to prevent damage or the like on the printer  10  due to the transporting failure of the printed object. Another example can include a processing of allowing the controller  90  to control the printer so that the printer  10  is stopped after the printing work is performed for a predetermined time period or to a predetermined number of sheets after detecting the dirt.  
         [0086]     Another example can include a processing of setting the upper limit of the rotation speed of the carriage motor  32  to regulate the rotation speed of the linear scale  51 . In this case, the rotation speed of the linear scale  51  is lowered and thus it is possible to prevent the erroneous detection of the photo sensor  60  even when the linear scale  51  is contaminated to some extent. By preventing such erroneous detection, it is possible to allow the printer  10  to perform a print work to a predetermined number of sheets or for a predetermined time.  
         [0087]     Another example can include a processing of perform the control for increasing the amount of light emitted from the light emitting element  610  by providing a variable resistor  611  in the light emitter  61  (see  FIG. 6 ) and adjusting the variable resistor  611 . When the linear scale  51  is contaminated more or less but the degree of dirt is not great, the printer  10  can perform the printing work in a predetermined number of sheets or for a predetermined time period by increasing the amount of light emitted from the light emitting element  610 . The amount of light emitted from the light emitting element  610  may be increased gradually by the use of the variable resistor  611  with such an increasing rate to perform the printing work in a predetermined number of sheets or for a predetermined time period. In this case, it is possible to reduce the power consumption of the light emitter  61 .  
         [0088]     Another example can include a processing of deviating the detection position in the position detecting patterns  53  by activating a scale lifting mechanism in a case where the printer  10  is provided with such a mechanism. For example, since the ink mist can be easily attached to the lower portions of the position detecting patterns  53  and thus the detection precision can be easily deteriorated, the scale lifting mechanism may be activated to detect the upper portion of the linear scale  51 .  
         [0089]     Another example can include a processing of removing the dirt of the linear scale  51  by wiping with a cleaning member such as a sponge.  
         [0090]     Next, the processing for detecting the degree of dirt of the linear scale  51  (position detecting patterns  53 ) in S 12  will be described with reference to  FIG. 13 . In the process flow shown in  FIG. 13 , the degree of dirt is detected all over the longitudinal direction of the linear scale  51  while the photo sensor  60  moves along the linear scale  51  by driving the carriage motor  32 . However, the degree of dirt of the linear scale  51  may be detected only by operating the scale moving mechanism  70  without driving the carriage motor  32 . In this case, the degree of dirt is detected by only a part of the linear scale  51 .  
         [0091]     First, as shown in  FIG. 13 , a driving voltage of the carriage motor  32  is set (S 20 ). More specifically, in response to a command from the controller  90 , a driving voltage corresponding to a rotation speed for the dirt detection is applied to the carriage motor  32 . Subsequently, a driving time period of the carriage motor  32  is set (S 21 ).  
         [0092]     Next, the carriage motor  32  is driven with the set driving voltage for the set driving time period (S 22 ). The carriage  31  moves with the driving of the carriage motor  32  and the photo sensor  60  fixed to the carriage  31  moves relative to the linear scale  51 . With the relative movement, the linear encoder  50  outputs, for example, an A-phase signal ENC-A and a B-phase signal ENC-B with a cycle T The A-phase signal ENC-A and the B-phase signal ENC-B which are the output signals of the linear encoder  50  are input to the controller  90 . That is, the controller  90  acquires the output signals of the linear encoder  50  (S 23 ).  
         [0093]     Thereafter, the controller  90  judges whether the degree of dirt of the linear scale  51  is greater than a predetermined value (S 24 ). This judgment may be performed by comparing the pulse signals ENC-A and ENC-B with each other in a state in which the light receiver  63  is normal. The judgment on whether the degree of dirt is greater than a predetermined value may be performed using the dirt detecting patterns  54  provided in the linear scale  51 . By bringing the linear scale  51  away from the dirt detecting patterns  54 , this is because it can be earlier judged for the dirt detecting patterns  54  in the state in which the detection precision of the light receiver  63  is deteriorated whether the degree of dirt is greater than a predetermined degree.  
         [0094]     When a predetermined amount of ink mist is accumulated on the linear scale  51  and the accumulated ink mist grows to a predetermined size, for example, as shown in  FIG. 14 , stains D 1 , D 2 , and D 3  are made by the ink mist is attached in the second light transmitting section  54   a . The light passing through the second light transmitting section  54   a  is blocked by the stains D 1  and D 2  and the light shielding section  54   m . When the stains (portions shielding the light) are generated, the period of the A-phase signal. ENC-A or the B-phase signal ENC-B output from the linear encoder  50  is varied. In the embodiment, when a predetermined variation occurs in the cycle of the A-phase signal ENC-A or the B-phase signal ENC-B output from the linear encoder  50 , it is judged that the stains (portions shielding the light) are generated in the dirt detecting patterns  54 . In this state, it is judged that a degree of dirt greater than a predetermined degree occurs in the linear scale  51 .  
         [0095]     More specifically, in step S 24 , it is judged whether the cycle (or the frequency) of the A-phase signal ENC-A or the B-phase signal ENC-B when the photo sensor  60  passes through the dirt detecting patterns  54  deviates from the range of ±×% (for example, ±15%) of the basic cycle T (or frequency). When it is judges that it does not deviate from the range of ±×% (NO), it is subsequently judged whether the phases of the A-phase signal ENC-A and the B-phase signal ENC-B are inverted (S 25 ).  
         [0096]     When NO is judged in S 25 , the detected period does not deviate from the range of ±×% and the inversion of the phase does not occur. Accordingly, it is judged that the accurate position detection in the linear encoder  50  is possible (that is, the accurate detection is possible) with the dirt detecting patterns  54  (step S 26 ). That is, since a sufficient size or amount of stains (portions shielding light) are not formed in the second light transmitting sections  54   a , it is judged that the degree of dirt is within the allowable range and thus the position detection in the linear encoder  50  is possible.  
         [0097]     Subsequently, it is judged whether the driving time period of the carriage motor  32  is greater than the set time (step S 27 ). When it is judged that the driving time period of the carriage motor  32  is less than the set time, the judgment and process subsequent to S 23  is performed again in S 23 . When the driving time period of the carriage motor  32  is greater than the set time period, the carriage motor  32  is stopped (step S 28 ). By activating the scale moving mechanism  70  after stopping the carriage motor  32 , the linear scale  51  is restored to the original position. With the movement, the linear scale  51  is in the state in which general position detection is possible.  
         [0098]     In this way, the detection of dirt is completed and then the position detection of the linear encoder  50  becomes possible.  
         [0099]     In S 24 , when the period T 1  of the A-phase signal ENC-A or the B-phase signal ENC-B deviates from the range of ±×% from the cycle T (YES) or when the phases of the A-phase signal ENC-A and the B-phase signal ENC-B are inverted (YES), it is judged that a sufficient size or amount of stains (portions shielding light) are formed in the second light transmitting section  54   a  and thus the corresponding processes are performed. That is, it is judged that the accurate position detection with the linear encoder  50  is not possible (S 29 ). In this case, the carriage motor  32  is stopped in S 28 .  
         [0100]     According to the printer  10  having the above-mentioned configuration, the linear scale  51  can move between the light emitter  61  and the light receiver  63  by the scale moving mechanism  70 . Accordingly, the linear scale  51  can come close to and away from the light emitter  61  and the light receiver  63 .  
         [0101]     On the contrary to the above-described case, when the linear scale  51  moves to come close to the light receiver  63 , it is possible to enhance the detection precision of the light receiver  63 . That is, even when the ink mist is attached to the linear scale  51  and the light is diffracted by the portions to which the ink mist is attached, the linear scale  51  is not much affected by the diffraction by coming close to the light receiver  63 . Accordingly, even when a predetermined amount of ink mist is attached thereto, it is possible to maintain the detection precision of the light receiver  63 , thereby elongating the detection lifetime of the linear scale  51 .  
         [0102]     A driving force for sliding is given to the supporting plate  71  from the motor through the eccentric cam  74  and the gear train  75 . Specifically, in the embodiment, the eccentric cam  74  is provided and thus by converting the driving force of the motor into the rotary motion of the eccentric cam  74 , it is possible to allow the supporting plate  71  to smoothly slide. Accordingly, the linear scale  51  can be brought close to the light emitter  61  or the light receiver  63 , thereby easily accomplishing the detection of the degree of dirt and the elongation of the lifetime of the linear scale  51 .  
         [0103]     In the embodiment, the position detecting patterns  53  and the dirt detecting patterns  54  are provided in the linear scale  51 . Accordingly, it is possible to detect the degree of dirt in the linear scale  51  using the dirt detecting patterns  54 , as well as to detect the dirt with the movement of the linear scale  51  using the scale moving mechanism  70 . As a result, it is possible to further accurately judge the degree of dirt in the linear scale  51 . When it is judged from the detection result that the degree of dirt greater than a predetermined degree is generated in the linear scale  51 , the linear scale  51  comes close to the light receiver  63  under the controlling of the motor by the controller  90 . Even when the light is diffracted by the portions of the linear scale  51  to which the ink mist is attached, the linear scale  51  is not much affected by the diffraction by coming close to the light receiver  63  and thus it is possible to enhance the detection precision of the light receiver  63 . In addition, it is possible to elongate the detection lifetime of the linear scale  51 .  
         [0104]     In this embodiment, the scale moving mechanism  70  for moving the linear scale  51  is provided. However, instead of the scale moving mechanism  70 , there may be provided a sensor moving mechanism for moving the photo sensor  60  in the sheet transporting direction. Even in such a configuration, the distance of the linear scale  51  relative to the light emitter  61  or the light receiver  63  can be varied. Accordingly, the same advantages can be obtained.  
         [0105]     In this embodiment, the supporting plate  71  can slide in the sheet transporting direction with the rotation of the eccentric cam  74 . However, the supporting plate  71  may be allowed to slide using an additional structure without providing the eccentric cam  74 . For example, a rack gear is fitted to the lower side of the supporting plate  71  and a pinion gear is provided at the final stage of the gear train  75 . Here, when the pinion gear is disposed at a fixed portion, the linear scale  51  can move to come close to and away from the light emitter  61  and the light receiver  63 .  
         [0106]     In this embodiment, the linear encoder  50  is used as the position detector. However, the same advantages can be obtained by applying the same concept with respect to the rotary encoder  80 .  
         [0107]     In the above embodiment, the printer  10  is exemplified as the liquid ejecting apparatus. However, the liquid ejecting apparatus may be any apparatus such as a color filter manufacturing apparatus, a dyeing machine, a micromachine, a semiconductor processing machine, a surface processing machine, a three-dimensional molding machine, a liquid vaporizing apparatus, an organic EL manufacturing apparatus (particularly, polymer EL manufacturing apparatus), a display manufacturing apparatus, a film coating system, and a DNA chip manufacturing apparatus. Here, liquid ejected from the apparatus is changed according to its purpose. For example, metal material, organic material, magnetic material, conductive material, wiring material, film coating material, and various processing liquid may be adopted.  
         [0108]     Although only some exemplary embodiments of the invention have been described in detail above, those skilled in the art will readily appreciated that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of the invention. Accordingly, all such modifications are intended to be included within the scope of the invention.  
         [0109]     The disclosure of Japanese Patent Application No. 2005-295967 filed Oct. 11, 2006 including specification, drawings and claims is incorporated herein by reference in its entirety.