Abstract:
A sewing machine includes a needle bar, a presser bar, a threading device, a processor, and a memory. The needle bar is configured such that a sewing needle is attached thereto. The presser bar is configured such that an accessory device is mounted thereon. The threading device is configured to perform a threading operation in which an upper thread is passed through an eye of the sewing needle attached to the needle bar. The memory is configured to store computer-readable instructions. The computer-readable instructions cause the processor to perform processes that include determining whether a mounted device is a specific accessory device and causing the threading device to perform the threading operation in a case where it is determined that the mounted device is the specific accessory device and a specific condition is satisfied. The mounted device is an accessory device mounted on the presser bar.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2013-068088 filed Mar. 28, 2013, the content of which is hereby incorporated herein by reference. 
     BACKGROUND 
     The present disclosure relates to a sewing machine that includes a threading device. 
     A sewing machine that includes a threading device is known. The threading device includes a threading hook, a thread guide member, a drive mechanism, and an actuator. In a case where a threading key is pressed, the actuator drives the drive mechanism. When the drive mechanism is driven, the threading hook and the thread guide member are operated and an upper thread may be automatically threaded through an eye in a sewing needle. 
     SUMMARY 
     There are cases in which a relatively large accessory device (such as an upper feed device) is mounted on a presser bar of the above-described sewing machine and used. In such a case, when the threading device is operated, a distance between the threading hook and the accessory device may be extremely small. Therefore, the threading hook may come into contact with the accessory device. If the threading hook comes into contact with the accessory device, it is possible that the threading hook may be deformed. 
     Embodiments of the broad principles derived herein provide a sewing machine that is capable of reliably performing a threading operation in a state in which an accessory device is mounted on a presser bar, without contact between a threading hook and the accessory device even when a threading device is operated. 
     Embodiments provide a sewing machine that includes a needle bar, a presser bar, a threading device, a processor, and a memory. The needle bar is configured such that a sewing needle is attached thereto. The presser bar is configured such that an accessory device is mounted thereon. The threading device is configured to perform a threading operation in which an upper thread is passed through an eye of the sewing needle attached to the needle bar. The memory is configured to store computer-readable instructions. The computer-readable instructions cause the processor to perform processes that include determining whether a mounted device is a specific accessory device and causing the threading device to perform the threading operation in a case where it is determined that the mounted device is the specific accessory device and a specific condition is satisfied. The mounted device is an accessory device mounted on the presser bar; 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments will be described below in detail with reference to the accompanying drawings in which: 
         FIG. 1  is a front view of a sewing machine; 
         FIG. 2  is a left side view of the sewing machine; 
         FIG. 3  is a perspective view of an upper feed device; 
         FIG. 4  is a front view of a cloth thickness detection mechanism; 
         FIG. 5  shows longitudinal sectional front views of a threading device in states in which a threading mechanism portion is in a withdrawn position, in a thread laying preparing position, and in a threading operation position; 
         FIG. 6  is a perspective view illustrating an operation of a threading hook in threading; 
         FIG. 7  is a perspective view illustrating an operation of the threading hook in threading; 
         FIG. 8  is a block diagram showing an electrical configuration of the sewing machine and the upper feed device; 
         FIG. 9  is a flowchart showing threading processing; and 
         FIG. 10  is an explanatory diagram of a screen displaying an error message. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, an embodiment of a sewing machine  101  will be explained. 
     Explanation of Sewing Machine  101   
     The external appearance of the sewing machine  101  will be explained with reference to  FIG. 1 . 
     The sewing machine  101  includes a bed  111 , a pillar  112 , an arm  113 , and a head  114 . The bed  111  is a base portion of the sewing machine  101 . The bed  111  includes a flat surface on which a work cloth (not shown in the drawings) may be placed. The pillar  112  extends from the bed  111 . The arm  113  extends from the pillar  112  while facing the bed  111 . The head  114  is provided on a leading end of the arm  113 . 
     Directions relating to the sewing machine  101  according to the present embodiment will be defined. The direction in which the pillar  112  extends from the bed  111  is the upward direction of the sewing machine  101  and the direction opposite to the upward direction is the downward direction of the sewing machine  101 . The direction in which the arm  113  extends from the pillar  112  is the leftward direction of the sewing machine  101  and the direction opposite to the leftward direction is the rightward direction of the sewing machine  101 . The direction that is orthogonal to the left-right direction and the up-down direction of the sewing machine  101  is the front-rear direction of the sewing machine  101 . A face on which a threading switch  121 , which will be explained below, is arranged is the front face of the sewing machine  101 . 
     A vertically long rectangular liquid crystal display (LCD)  115  is provided on the front face of the pillar  112 . For example, keys to execute various functions necessary to a sewing operation, various messages, various patterns, etc. may be displayed on the LCD  115 . 
     A transparent touch panel  126  is provided on the top surface of the LCD  115 . As a result, it is possible to perform selection of a sewing pattern, various settings, or the like by performing a pressing operation, using a finger or a dedicated touch pen, on a position on the touch panel  126  that corresponds to one of the various keys etc. displayed on the LCD  115 . 
     The threading switch  121  and other operating switches are provided on a lower portion of the front face of the arm  113 . 
     An electrical connections of an upper feed device  104  and the sewing machine  101  will be explained with reference to  FIG. 2 . 
     A presser bar  127  is disposed at the rear of a needle bar  6 . The upper feed device  104  may be detachably mounted on the lower end of the presser bar  127 . The upper feed device  104  may be disposed above the bed  111 . The upper feed device  104  is configured to feed the work cloth in cooperation with a feed dog (not shown in the drawings). Although not shown in the drawings, in addition to the above-described upper feed device  104 , a variety of devices, such as a cloth end cutting device (a side cutter) and a ruffler (a ruffler presser foot) that have known structures, may each be mounted on the sewing machine  101  as an accessory device. 
     An electric board  498  (refer to  FIG. 3 ) is provided inside the upper feed device  104 . A connecting portion  152  is connected to the electric board  498 . The connecting portion  152  includes a lead wire  502  and a connector  503 . The lead wire  502  extends from the electric board  498  to the outside of the upper feed device  104 . The connector  503  is provided on the leading end of the lead wire  502 . The connector  503  may be connected to a connector  141 , which is provided on the head  114  of the sewing machine  101 . The connector  141  is electrically connected to a control portion  60  of the sewing machine  101 , which is shown in  FIG. 7 . A motor  491  (refer to  FIG. 3 ) is provided inside the upper feed device  104 . The motor  491  may be electrically connected to the control portion  60  of the sewing machine  101  via the electric board  498 , the lead wire  502 , and the connector  503 . In other words, the motor  491  and the control portion  60  of the sewing machine  101  may be electrically connected by the connecting portion  152 . A CPU  61 , which is shown in  FIG. 7 , may control the motor  491 . 
     Explanation of Upper Feed Device  104   
     The upper feed device  104  will be explained with reference to  FIG. 3 . 
     The upper feed device  104  may be mounted on and removed from the presser bar  127 . The upper feed device  104  includes a mounting portion  142 , a feed mechanism  143 , a drive mechanism  149 , the connecting portion  152 , and a presser foot  151 . The mounting portion  142  is a portion by which the upper feed device  104  is mounted on the presser bar  127  of the sewing machine  101 . The feed mechanism  143  is configured to feed the work cloth. The drive mechanism  149  is configured to drive the feed mechanism  143 . The connecting portion  152  may electrically connect the motor  491 , which is provided in the drive mechanism  149 , to the control portion  60  of the sewing machine  101 . 
     The mounting portion  142  and the presser foot  151  will be explained. The mounting portion  142  is provided above the feed mechanism  143  in the front end portion of the upper feed device  104 . The mounting portion  142  includes two holding portions  421  and  422 . The holding portions  421  and  422  may be mounted on and fixed to the presser bar  127  by a shoulder screw  423 . The shoulder screw  423  includes a head  425 , a shank  426 , and a threaded portion  424 . The outside diameter of the shank  426  is slightly smaller than the outside diameter of the head  425 . The outside diameter of the threaded portion  424  is slightly smaller than the outside diameter of the shank  426 . The holding portions  421  and  422  are provided on the front end of the upper feed device  104 . The holding portion  421  is provided above the holding portion  422  and is slightly separated from the holding portion  422 . Each of the holding portions  421  and  422  has a recessed portion that is recessed toward the left. The lower end portion of the presser bar  127  may be disposed in the recessed portions. A threaded hole (not shown in the drawings) is provided in the lower end portion of the presser bar  127 . The threaded hole extends through the presser bar  127  in the left-right direction. The threaded portion  424  may be screwed into the threaded hole. A slot (not shown in the drawings) is formed in the left side face of the head  425 . A tool may be fitted into the slot. 
     When the upper feed device  104  is mounted on the presser bar  127 , the user may adjust the position of the threaded portion  424  to the screw hole portion of the presser bar  127 . In this state, the user may rotate the head  425  using the user&#39;s fingers or fit the tool into the slot to rotate the head  425 . As a result of this, a right side surface of the shank  426  may come into contact with left side surfaces of the holding portions  421  and  422 . Further, if the shoulder screw  423  is rotated and tightened in this state, the holding portions  421  and  422  may be clamped between the shank  426  and the presser bar  127 . In this state, the holding portions  421  and  422  are fixed to the presser bar  127 . The upper feed device  104  may thus be mounted on the presser bar  127 . 
     A presser foot support portion  511 , which supports the presser foot  151 , is provided on the lower edge portion of the holding portion  422 . The presser foot support portion  511  straddles the front end portion of the feed mechanism  143  at the left and right. The presser foot support portion  511  extends obliquely downward and forward. The presser foot  151  is provided on the lower end of the presser foot support portion  511 . The belt positioning portion  512  is provided at the rear of the hole  513  of the presser foot  151 . The belt positioning portion  512  is a rectangular open portion that extends to the rear edge of the presser foot  151 . The front end portion of the belt  435  of the feed mechanism  143  may be disposed on the inner side of the belt positioning portion  512 . The front end portion of the belt  435  may feed the work cloth while pressing downward against the work cloth in the belt positioning portion  512 . 
     The upper feed device  104  may be mounted to the presser bar  127  by the mounting portion  142 . Therefore, when the presser bar  127  is moved upward, the upper feed device  104  is also moved upward and the presser foot  151  is also moved away from the work cloth. When the presser bar  127  is moved downward, the upper feed device  104  is also moved downward and the presser foot  151  also presses downward against the work cloth  100 . 
     Explanation of Cloth Thickness Detection Mechanism  180   
     The cloth thickness detection mechanism  180  will be explained with reference to  FIG. 4 . The cloth thickness detection mechanism  180  is provided to the rear of the needle bar  6 . The cloth thickness detection mechanism  180  includes the presser bar  127 , the presser foot  151 , a presser bar bracket  85 , and a potentiometer  88 . The presser bar  127  is supported by a sewing machine frame such that the presser bar  127  may be moved up and down. The presser foot  151  is mounted on a lower end portion of the presser bar  127 . The presser bar bracket  85  is fixed to substantially the center, in the up-down direction, of the presser bar  127 . The potentiometer  88  is provided on the left side of the presser bar  127 . 
     The potentiometer  88  is a rotary potentiometer. The potentiometer  88  is configured to detect a position in height of the presser bar  127 . An arm  881  extends to the right from a rotating shaft of the potentiometer  88 . A protruding portion  851  protrudes to the left of the presser bar bracket  85 . The arm  881  is in contact with the top face side of the protruding portion  851 . The arm  881  is rotated in accordance with the up/down movement of the presser bar bracket  85 , and a resistance value of the potentiometer  88  changes. The control portion  60  detects the position of the presser bar  127  based on a voltage that corresponds to the resistance value of the potentiometer  88 . 
     Explanation of Threading Device  11   
     The threading device  11  and its peripheral portions will be explained with reference to  FIG. 5 . 
     A needle bar base  9  extends in the up-down direction. The needle bar base  9  includes support pieces  92  and  93 . The support pieces  92  and  93  extend to the right. The support pieces  92  and  93  are disposed on an upper portion and a lower portion of the needle bar base  9 , respectively. The needle bar  6  is inserted through the support pieces  92  and  93  such that the needle bar  6  may be moved in the up-down direction, and is supported by the support pieces  92  and  93 . A needle bar bracket  24  is positioned between the support pieces  92  and  93 . The needle bar  6  is coupled to a needle bar drive mechanism by the needle bar bracket  24 , and is moved up and down at a specific stroke. When the sewing operation is stopped, the needle bar  6  is stopped at a specific raised position. A positioning member  25  is attached to an upper portion of a coupling portion between the needle bar  6  and the needle bar bracket  24 . The positioning member  25  includes a protruding piece  251  that protrudes to the left. A needle bar thread guide  26  is provided on the lower end of the needle bar  6 . 
     The threading device  11  is mounted on the needle bar base  9 . The threading device  11  is disposed to the left of the needle bar  6 . The threading device  11  includes a first threading shaft  27 , a second threading shaft  28 , a threading mechanism portion  29 , and a rotary mechanism  30 . The threading mechanism portion  29  includes a threading hook  31  (refer to  FIG. 6 ), a thread guide member  32 , and a thread holding member  33 . The threading hook  31  and the thread guide member  32  are provided on the lower end of the first threading shaft  27 . The thread holding member  33  is provided on the lower end of the second threading shaft  28 . The rotary mechanism  30  is configured to rotate the first threading shaft  27  around the shaft center. 
     The first threading shaft  27  is disposed to the left of the needle bar  6 . The first threading shaft  27  extends in the up-down direction. The first threading shaft  27  is supported on the needle bar base  9  such that the first threading shaft  27  may be moved in the up-down direction and may be rotated. The second threading shaft  28  is disposed to the left of the first threading shaft  27 . The second threading shaft  28  is supported on the needle bar base  9  such that the second threading shaft  28  may be moved in the up-down direction. As will be explained in more detail below, the first and second threading shafts  27  and  28  are constantly urged upward with respect to the needle bar base  9  by a compression coil spring  42 . The first and second threading shafts  27  and  28  may be moved integrally in the up-down direction in a state in which positions of the upper ends of the first and second threading shafts  27  and  28  are aligned. A guide shaft  35  is fixed to the needle bar base  9 . The guide shaft  35  is disposed to the left of the second threading shaft  28 . The guide shaft  35  extends in the up-down direction. The guide shaft  35  guides a threading lever  40 . 
     The threading slider  36  is inserted through the upper ends of the first and second threading shafts  27  and  28  such that the threading slider  36  may be moved in the up-down direction. The threading slider  36  is disposed across both the first and second threading shafts  27  and  28 . The threading slider  36  includes a semi-circular wall portion that covers the left half of the upper portion of the first threading shaft  27 . A cam groove  361  extends in a diagonal direction from the wall portion. A sliding pin  37 , which extends horizontally, penetrates through the upper portion of the first threading shaft  27 . The sliding pin  37  is inserted through the cam groove  361 . The rotary mechanism  30  includes the sliding pin  37  and the cam groove  361 . A spring receiving pin  38 , which is positioned below the sliding pin  37 , is provided on the first threading shaft  27 . A compression coil spring  39  is provided between the spring receiving pin  38  and the lower end of the threading slider  36 . 
     The threading lever  40  and a lever plate  41  are fittingly inserted into the guide shaft  35  such that the threading lever  40  and the lever plate  41  may be moved in the up-down direction. The threading lever  40  and the lever plate  41  are used to move the first and second threading shafts  27  and  28  in the up-down direction. The threading lever  40  extends to the left. The threading lever  40  integrally includes a cylindrical portion  401 , which the guide shaft  35  is inserted through. 
     Two sliding ring portions  411  are provided on the lever plate  41 . The guide shaft  35  is inserted into the sliding ring portions  411  such that the guide shaft  35  may be moved in the up-down direction. The two sliding ring portions  411  are disposed on the lever plate  41  such that the two sliding ring portions  411  sandwich the cylindrical portion  401  of the threading lever  40  from above and below. Further, the lever plate  41  integrally includes a plate portion that extends to the right and an operation piece  412  that is positioned on the upper end of the plate portion. The operation piece  412  is configured to come into contact with and depress the top face of the threading slider  36 . The compression coil spring  42  is provided on the guide shaft  35 . The compression coil spring  42  constantly urges the threading lever  40  and the lever plate  41  upward. 
     The threading device  11  shown furthest to the left in  FIG. 5  is in a state in which the force to depress the threading lever  40  downward is not acting on the threading lever  40 . In this state, due to the spring force of the compression coil spring  42 , the threading lever  40  and the lever plate  41  are positioned on the upper end of the guide shaft  35 . In the state in which the threading lever  40  and the lever plate  41  are positioned on the upper end of the guide shaft  35 , the threading slider  36  and the first and second threading shafts  27  and  28  are positioned at an uppermost position with respect to the needle bar base  9 . In the uppermost position, the threading mechanism portion  29  that is provided on the lower ends of the first and second threading shafts  27  and  28  is housed inside the head  114 , and this position is a withdrawn position. 
     When the force to depress the threading lever  40  downward acts on the threading lever  40 , the threading lever  40 , the first and second threading shafts  27  and  28 , and the threading mechanism portion  29  descend from the withdrawn position (refer to  FIG. 5 ) by a distance D1. This position is a thread laying preparing position (refer to the threading device  11  in the center of  FIG. 5 ). In the thread laying preparing position, the threading mechanism portion  29  is positioned at a height in the vicinity of a needle bracket  8  of the needle bar  6  that is in a needle up position above a needle. In the thread laying preparing position, a user may perform thread laying, which is an operation in preparation for threading an upper thread T. 
     When the force to depress the threading lever  40  downward further acts on the threading lever  40 , the threading lever  40 , the first and second threading shafts  27  and  28 , and the threading mechanism portion  29  are moved from the thread laying preparing position. Then, at a position at which the threading lever  40 , the first and second threading shafts  27  and  28 , and the threading mechanism portion  29  have been moved from the thread laying preparing position by a distance D2, the sliding pin  37 , which is provided on the first threading shaft  27 , engages with the protruding piece  251  of the positioning member  25 , which is provided on the needle bar  6 . When the sliding pin  37  engages with the protruding piece  251 , the downward movement of the first threading shaft  27  is regulated. This position is a threading operation position (refer to the threading device  11  furthest to the right in  FIG. 5 ). In the threading operation position, the height position of the threading hook  31  is aligned with the height of an eye  71  of a sewing needle  7 . As a result, the threading operation becomes possible. 
     At the time of the threading operation, the threading lever  40  is further depressed by a distance D3 from the position to which the threading lever  40  has been moved by the distance D2. As a result of the downward movement of the threading lever  40 , the threading slider  36  is moved down via the lever plate  41  by the distance D3 with respect to the first and second threading shafts  27  and  28  against the spring force of the compression coil spring  39 . As a result of this, the sliding pin  37  of the first threading shaft  27  is relatively moved up in a diagonal direction inside the cam groove  361  of the threading slider  36 . When the sliding pin  37 , which is the rotary mechanism  30 , is moved up, the first threading shaft  27  and the threading hook  31  are rotated and the threading operation is performed. 
     When the depressing force on the threading lever  40  is released, by the spring force of the compression coil spring  39 , the threading lever  40  and the threading slider  36  are moved up by the distance D3 with respect to the first and second threading shafts  27  and  28 . When the threading slider  36  is moved up, the sliding pin  37  of the first threading shaft  27  is relatively moved down in a diagonal direction inside the cam groove  361  of the threading slider  36 . When the sliding pin  37  descends, the first threading shaft  27  and the threading hook  31  are rotated in a reverse direction. After that, the threading lever  40  is moved up by a distance (D2+D1), and the first and second threading shafts  27  and  28  and the threading mechanism portion  29  are moved up and return to the withdrawn position, as shown by the threading device  11  furthest to the left in  FIG. 5 . 
     The threading mechanism portion  29  (refer to  FIG. 5 ) will be explained with reference to  FIG. 6 . The threading hook  31 , guide members  43  and  43 , and a thread holding wire  44  are provided on the lower end of the first threading shaft  27  (refer to  FIG. 5 ). The threading hook  31  includes a hook portion  311 . The hook portion  311  is provided with a downward orientation on the leading end of the threading hook  31 . The threading hook  31  may be inserted through the eye  71  of the sewing needle  7 . The guide members  43  and  43  are positioned on both sides of the threading hook  31 . At the time of the threading operation, the thread guide member  32 , which is provided on the lower end of the first threading shaft  27 , is configured to hold the upper thread T in a horizontal state in front of the eye  71  of the sewing needle  7 , as shown in  FIG. 6 . 
     An operation of the threading hook  31  will be explained. The threading mechanism portion  29  may be moved down to the threading operation position and the first threading shaft  27  may be rotated. When the first threading shaft  27  is rotated, the threading hook  31  is moved in the direction of an arrow A and passes through the eye  71  of the sewing needle  7 , as shown in  FIG. 6 . Further, the threading hook  31  hooks the upper thread T that is being held by the thread guide member  32  using the hook portion  311 . After that, the first threading shaft  27  may be rotated in the reverse direction. When the first threading shaft  27  is rotated in the reverse direction, the threading hook  31  is moved in reverse in the direction of an arrow B and the upper thread T passes through the eye  71  along with the threading hook  31 , as shown in  FIG. 7 . The threading is performed in this manner. For example, Japanese Laid-Open Patent Publication No. 2006-158412 discloses a structure and an operation of a threading mechanism portion, the relevant portions of which are incorporated by reference. 
     The sewing machine  101  includes an up-and-down moving mechanism (not shown in the drawings) that is configured to move the threading lever  40  in the up-down direction. The up-and-down moving mechanism is driven by a threading pulse motor  520 , which will be explained below. For example, Japanese Laid-Open Patent Publication No. 2009-165737 discloses a structure and an operation of an up-and-down moving mechanism, the relevant portions of which are incorporated by reference. 
     Electrical Configuration of Sewing Machine  101  and Upper Feed Device  104   
     An electrical configuration of the sewing machine  101  and the upper feed device  104  will be explained with reference to  FIG. 8 . The control portion  60  of the sewing machine  101  includes the CPU  61 , a ROM  62 , a RAM  63 , and an input/output interface  65 . The CPU  61 , the ROM  62 , the RAM  63 , and the input/output interface  65  are electrically connected to each other by a bus  67 . The ROM  62  stores programs for the CPU  61  to execute processing, data, etc. Specifically, the ROM  62  stores a program to execute threading processing shown in  FIG. 8 , a height table  621 , and a maximum cloth thickness table  622 . The height table  621  includes information in which detection values of the potentiometer  88  are associated with heights of the presser foot  151 . The maximum cloth thickness table  622  includes information in which types of accessory devices are associated with maximum cloth thickness values at which threading by the threading device  11  is possible. The RAM  63  stores various temporary data. 
     The threading switch  121 , the touch panel  126 , drive circuits  72 ,  75  and  76 , the potentiometer  88 , and the connector  141  are electrically connected to the input/output interface  65 . The drive circuit  72  may drive a sewing machine motor  79 . The drive circuit  75  may drive the LCD  115 . The drive circuit  76  may drive the threading pulse motor  520 . The threading lever  40  is moved in the up-down direction by the rotation of the threading pulse motor  520 . 
     The connector  141  is connected to one end of the connecting portion  152 . The connecting portion  152  is electrically connected to a connector  504 . The connector  504  is electrically connected to a drive circuit  510 . The connector  504  and the drive circuit  510  are mounted on the electric board  498 , which is provided inside the upper feed device  104 . The drive circuit  510  is electrically connected to the motor  491 . The drive circuit  510  may drive the motor  491 . The CPU  61  controls the drive circuit  510  and may thus control the motor  491 . 
     When the upper feed device  104  is electrically connected to the CPU  61  of the sewing machine  101  via the connector  141 , a Low signal is input to the CPU  61 . When the upper feed device  104  is not electrically connected to the CPU  61 , a High signal is input to the CPU  61 . By detecting the Low signal or the High signal, the CPU  61  can detect whether or not the motor  491  and the control portion  60  of the sewing machine  101  are electrically connected. 
     Threading Processing 
     The threading processing will be explained with reference to  FIG. 9 . The threading processing is executed by the CPU  61  of the sewing machine  101  in accordance with the program stored in the ROM  62 . The threading processing may be executed, for example, when the user presses the threading switch  121 . Each of the steps shown in the flowchart indicates the processing of the CPU  61 . 
     At step S 12 , the CPU  61  outputs a control signal that instructs the potentiometer  88  to detect the thickness of the work cloth. When the potentiometer  88  receives the control signal from the CPU  61 , the potentiometer  88  detects the thickness of the work cloth. More specifically, the CPU  61  detects a height of the presser foot  151  (a cloth thickness) that corresponds to a detection voltage, based on the height table  621  that is stored in the ROM  62 . The RAM  63  stores the height of the presser foot  151  (the cloth thickness) in response to a control signal from the CPU  61 . 
     At step S 14 , the CPU  61  determines whether or not a specific accessory device is mounted on the presser bar  127 . The specific accessory device may be, for example, the upper feed device  104 . More specifically, the CPU  61  may detect the Low signal from the upper feed device  104  via the connector  141 . When the upper feed device  104  is not electrically connected to the CPU  61 , the CPU  61  may detect the High signal. When the CPU  61  detects the Low signal (yes at step S 14 ), the CPU  61  advances the processing to step S 15 . When the CPU  61  detects the High signal (no at step S 14 ), the CPU  61  advances the processing to step S 25 . 
     At step S 15 , the CPU  61  determines whether or not the cloth thickness detected at step S 12  is larger than a maximum cloth thickness value that corresponds to a type of the accessory device and at which the threading is possible. More specifically, the CPU  61  reads the cloth thickness stored in the RAM  63  at step S 12 . Further, the CPU  61  reads the maximum cloth thickness table  622  stored in the ROM  62 . The CPU  61  determines whether or not the cloth thickness stored in the RAM  63  is larger than the maximum cloth thickness value stored in the ROM  62 . The maximum cloth thickness value may be, for example, a maximum value at which threading is possible when the upper feed device  104  is mounted on the presser bar  127 . The maximum cloth thickness value may be, for example, 2.5 mm. When the CPU  61  determines that the detected cloth thickness is larger than the maximum cloth thickness value (yes at step S 15 ), the CPU  61  advances the processing to step S 16 . When the CPU  61  determines that the detected cloth thickness is not larger than the maximum cloth thickness value (no at step S 15 ), the CPU  61  advances the processing to step S 25 . 
     At step S 16 , the CPU  61  prohibits execution of the threading operation by the threading device  11 . More specifically, the CPU  61  does not drive the threading pulse motor  520 . When the CPU  61  does not drive the threading pulse motor  520 , the threading mechanism portion  29  is in the withdrawn position shown in  FIG. 5  due to the spring force of the compression coil spring  42 . 
     At step S 17 , the CPU  61  performs notification that it is not possible to perform the threading operation by the threading device  11 . More specifically, the CPU  61  causes the LCD  115  to display an error message  261  shown in  FIG. 10 . The error message  261  may be, for example, a message instructing the user to remove the work cloth. Specifically, the CPU  61  outputs a control signal to the LCD  115  in order to display the error message  261 . The LCD  115  displays the error message  261  in response to the control signal received from the CPU  61 . More specifically, the CPU  61  reads image information representing the error message  261  from the ROM  62  and transmits an image signal to the LCD  115 . 
     The user may see the error message  261  displayed on the LCD  115 , and may remove the work cloth. At step S 19 , in a similar manner to the processing at step S 12 , the CPU  61  outputs a control signal that instructs the potentiometer  88  to detect the thickness of the work cloth. 
     At step S 21 , in a similar manner to the processing at step S 15 , the CPU  61  determines whether or not the cloth thickness detected at step S 19  is larger than the maximum cloth thickness value that corresponds to the type of the accessory device and at which the threading is possible. If, for example, the user has not yet removed the work cloth, the CPU  61  determines that the cloth thickness is larger than the maximum cloth thickness value (yes at step S 21 ) and returns the processing to step S 16 . On the other hand, for example, when the user has removed the work cloth, the CPU  61  determines that the cloth thickness is not larger than the maximum cloth thickness value (no at step S 21 ) and advances the processing to step S 23 . 
     At step S 23 , the CPU  61  cancels the error. Specifically, the CPU  61  deletes the display of the error message  261 , and outputs a control signal to the LCD  115  to display a menu screen. The LCD  115  displays the menu screen in response to the control signal from the CPU  61 . More specifically, the CPU  61  reads image information representing the menu screen from the ROM  62  and transmits an image signal to the LCD  115 . 
     At step S 25 , the CPU  61  outputs a control signal to the threading pulse motor  520  to perform the threading operation, as explained with reference to  FIGS. 5 to 7 . More specifically, the threading pulse motor  520  rotates by a specific amount in response to the control signal from the CPU  61 . When the threading pulse motor  520  rotates, the threading lever  40  is depressed. When the threading lever  40  is depressed, the threading mechanism portion  29  is moved down from the withdrawn position to the threading operation position. The first threading shaft  27  and the threading hook  31  are rotated by the rotary mechanism  30  and the threading operation is performed. After that, the threading pulse motor  520  is rotated in the reverse direction, thus returns the threading mechanism portion  29  to the withdrawn position. After ending the processing at step S 25 , the CPU  61  ends the threading processing. 
     Effects of Present Embodiment 
     When the CPU  61  determines that the cloth thickness detected at step S 15  is larger than the maximum cloth thickness value that corresponds to the type of the accessory device and at which the threading is possible, the CPU  61  prohibits the execution of the threading operation. Thus, it is possible to reliably avoid the threading hook  31  from coming into contact with the presser foot support portion  511  of the upper feed device  104 . 
     At step S 17 , the LCD  115  displays the error message  261  instructing the user to remove the work cloth. By displaying the error message  261  on the LCD  115 , the user can know that it is necessary to remove the work cloth in order to perform the threading operation. 
     Modified Examples 
     Hereinafter, modifications that can be added to the above-described embodiment will be exemplified. 
     In the present embodiment, the explanation is made in which the specific accessory device is the upper feed device  104 . However, the specific accessory device is not limited to the upper feed device  104  and may be another accessory device or various presser members for which there is a possibility of contact with the threading hook  31 . 
     In a case where there are a plurality of types of the specific accessory device or the presser member, the following control may be performed. At step S 14  of the threading processing shown in  FIG. 9 , the CPU  61  may identify the accessory device or the presser member that is mounted on the presser bar  127 . More specifically, a camera may be provided on the head  114  of the sewing machine  101 . The camera may perform image capture of the accessory device or the presser member. The CPU  61  may identify the type of the accessory device or the presser member by a known pattern matching method using the captured image. The ROM  62  may store the maximum cloth thickness table  622  in which the accessory device or the presser member is associated with the maximum cloth thickness value. At step S 15 , the CPU  61  may read the maximum cloth thickness table  622  and may determine whether or not the cloth thickness is larger than the maximum cloth thickness value that corresponds to the type of the accessory device or presser member identified at step S 14 . 
     In the present embodiment, in order to perform notification that the threading operation by the threading device  11  is not possible, the CPU  61  displays the error message  261  on the LCD  115 . However, the sewing machine  101  may be provided with a speaker or a buzzer and may output an error sound. 
     The above-described program may be recorded on a computer-readable storage medium, such as a hard disk, a flexible disk, a CD-ROM, or a DVD, and may be executed by being read from the storage medium by a computer. The program may be a transmission medium that can be distributed via a network such as the Internet. 
     In the present embodiment, the processing to determine whether or not the accessory device mounted on the presser bar  127  is the specific accessory device, the processing to determine whether or not the detected cloth thickness is larger than the maximum cloth thickness value, the processing to prohibit the execution of the threading operation, and the processing to notify that the execution of the threading operation is not possible are performed by software executed by the CPU  61 , but each of the above processing may be performed by hardware. 
     The apparatus and methods described above with reference to the various embodiments are merely examples. It goes without saying that they are not confined to the depicted embodiments. While various features have been described in conjunction with the examples outlined above, various alternatives, modifications, variations, and/or improvements of those features and/or examples may be possible. Accordingly, the examples, as set forth above, are intended to be illustrative. Various changes may be made without departing from the broad spirit and scope of the underlying principles.