Abstract:
A sewing machine includes at least one detecting portion, a processor, and a memory. The at least one detecting portion is configured to detect an ultrasonic wave that has been transmitted from a transmission source. The memory is configured to store computer-readable instructions that instruct the sewing machine to execute steps including identifying a position of the transmission source of the ultrasonic wave based on information pertaining to the ultrasonic wave that has been detected by the at least one detecting portion, and controlling sewing based on the position of the transmission source that has been identified.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2012-055103 filed Mar. 12, 2012, the content of which is hereby incorporated herein by reference. 
     BACKGROUND 
     The present disclosure relates to a sewing machine, an embroidery unit, and a non-transitory computer-readable medium storing a sewing machine control program that allow sewing in a position specified on a work cloth. 
     A sewing machine is known that can easily set a sewing position and a sewing angle, at which a desired embroidery pattern is to be sewn, on a work cloth. For example, a known sewing machine includes an imaging portion. After a user affixes a marker to a specified position on the work cloth, an image of the marker may be captured by the imaging portion. The sewing machine may automatically set the sewing position and the sewing angle of the embroidery pattern based on the captured image of the marker. 
     SUMMARY 
     However, with the above-described sewing machine, it may be necessary to affix the marker to the work cloth. Further, after the sewing machine has set the sewing position and the sewing angle of the embroidery pattern, the user may need to remove the marker affixed to the work cloth before sewing is performed. Therefore, the operation may be troublesome for the user. 
     Embodiments of the broad principles derived herein provide a sewing machine, an embroidery unit, and a non-transitory computer-readable medium storing a sewing machine control program that enable easily setting a position, on a work cloth, at which sewing is performed. 
     Embodiments provide a sewing machine that includes at least one detecting portion, a processor, and a memory. The at least one detecting portion is configured to detect an ultrasonic wave that has been transmitted from a transmission source. The memory is configured to store computer-readable instructions that instruct the sewing machine to execute steps including identifying a position of the transmission source of the ultrasonic wave based on information pertaining to the ultrasonic wave that has been detected by the at least one detecting portion, and controlling sewing based on the position of the transmission source that has been identified. 
     Embodiments also provide an embroidery unit that can be attached to and detached from a bed of a sewing machine, and to which an embroidery frame can be attached, and that is configured to move the embroidery frame, the embroidery frame being configured to hold a work cloth. The embroidery unit includes at least one detecting portion and a notifying portion. The at least one detecting portion is configured to detect an ultrasonic wave that has been transmitted from a transmission source. The notifying portion is configured to notify the sewing machine of a detection timing at which the ultrasonic wave was detected by the at least one detecting portion. The embroidery unit is configured to move the work cloth based on a position of the transmission source of the ultrasonic wave that has been identified by the sewing machine based on the detection timing that has been notified by the notifying portion. 
     Embodiments further provide a non-transitory computer-readable medium storing a control program executable on a sewing machine. The program includes computer-readable instructions, when executed, to cause the sewing machine to perform the step of identifying, based on information pertaining to an ultrasonic wave that has been detected by at least one detecting portion of the sewing machine, a position of a transmission source of the ultrasonic wave. The at least one detecting portion is configured to detect the ultrasonic wave that has been transmitted from the transmission source. The program further includes computer-readable instructions, when executed, to cause the sewing machine to perform the step of controlling sewing based on the position of the transmission source that has been identified. 
    
    
     
       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 according to a first embodiment; 
         FIG. 2  is a perspective view of a receiver; 
         FIG. 3  is a front view of the receiver; 
         FIG. 4  is a cross-sectional view of the receiver taken along a line I-I shown in  FIG. 3 , as seen in an arrow direction; 
         FIG. 5  is a block diagram showing an electrical configuration of the sewing machine and an ultrasonic pen according to the first embodiment; 
         FIG. 6  is a diagram illustrating a calculation method of specified coordinates E according to the first embodiment; 
         FIG. 7  is a flowchart showing main processing according to the first embodiment; 
         FIG. 8  is a front view of the sewing machine according to a second embodiment; 
         FIG. 9  is a plan view of an embroidery unit according to the second embodiment; 
         FIG. 10  is a right side view of the embroidery unit according to the second embodiment; 
         FIG. 11  is a front view of a sewing machine according to a third embodiment; 
         FIG. 12  is a block diagram showing an electrical configuration of the sewing machine and an ultrasonic pen according to the third embodiment; 
         FIG. 13  is a front view of a sewing machine according to a fourth embodiment; 
         FIG. 14  is a diagram illustrating a calculation method of specified coordinates E according to the fourth embodiment; 
         FIG. 15  is a flowchart showing main processing according to the fourth embodiment; 
         FIG. 16  is a front view of a sewing machine according to a fifth embodiment; 
         FIG. 17  is a right side view of a multi-needle sewing machine according to the fifth embodiment; and 
         FIG. 18  is a plan view of an embroidery frame movement mechanism according to the fifth embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     First Embodiment 
     Hereinafter, a first embodiment will be explained with reference to the drawings. A configuration of a sewing machine  1  will be explained with reference to  FIG. 1 . The near side, the far side, the upper side, the lower side, the left side, and the right side of  FIG. 1  are respectively defined as the front side, the rear side, the upper side, the lower side, the left side, and the right side of the sewing machine  1 . Specifically, a direction in which a pillar  12 , which will be described below, extends is the up-down direction of the sewing machine  1 . The longitudinal direction of a bed  11  and an arm  13  is the left-right direction of the sewing machine  1 . A surface on which a plurality of operation switches  21  are arranged is a front face of the sewing machine  1 . 
     The sewing machine  1  includes the bed  11 , the pillar  12 , the arm  13 , and a head  14 . The bed  11  is a base portion of the sewing machine  1  and extends in the left-right direction. The pillar  12  extends upward from the right end of the bed  11 . The arm  13  extends to the left from the upper end of the pillar  12  such that the arm  13  faces the bed  11 . The head  14  is provided on the left end of the arm  13 . A needle plate  34  is disposed on a top surface of the bed  11 . A feed dog, a feed mechanism, a shuttle mechanism (which are not shown in the drawings) and a feed adjustment motor  83  (refer to  FIG. 5 ) are provided below the needle plate  34  (namely, inside the bed  11 ). The feed dog may be driven by the feed mechanism, and may feed a work cloth  100  (refer to  FIG. 6 ) by a specified feed distance. The feed adjustment motor  83  may adjust the feed distance of the feed dog. 
     A needle bar mechanism (not shown in the drawings), a needle bar swinging motor  80  (refer to  FIG. 5 ) and the like are provided on the head  14 . The needle bar mechanism may drive a needle bar  29  in the up-down direction. A sewing needle (not shown in the drawings) may be attached to the needle bar  29 . The needle bar swinging motor  80  may swing the needle bar  29  in the left-right direction. A receiver  94  is provided at the lower left end of the head  14 , on the rear side of a lower surface of the head  14 . A receiver  95  is provided at the lower right end of the head  14 , on the rear side of the lower surface of the head  14 . The receivers  94  and  95  are separated from each other in the left-right direction by the length of the head  14  in the left-right direction. The receivers  94  and  95  are configured to receive (detect) an ultrasonic wave. The receivers  94  and  95  have the same configuration. The receivers  94  and  95  will be described in more detail later. 
     A cover  16  to be opened and closed is provided on an upper portion of the arm  13 . A thread spool (not shown in the drawings) may be accommodated underneath the cover  16 , that is, substantially in a central portion within the arm  13 . An upper thread (not shown in the drawings) may be wound around the thread spool. The upper thread may be supplied from the thread spool, through a thread hook (not shown in the drawings), to the sewing needle attached to the needle bar  29 . The thread hook is provided on the head  14 . The needle bar mechanism, which is provided inside the head  14 , may drive the needle bar  29  such that the needle bar  29  is moved up and down. The needle bar mechanism may be driven by a sewing machine motor  79  (refer to  FIG. 5 ). A presser bar  31  extends downward from the lower end of the head  14 . A presser foot  30  may be detachably attached to the lower end of the presser bar  31 . The presser foot  30  may press down the work cloth  100 . The plurality of operation switches  21  are provided on a lower portion of the front face of the arm  13 . The plurality of operation switches  21  include a start/stop switch. 
     A liquid crystal display (LCD)  15  is provided on the front face of the pillar  12 . The LCD  15  may display images that include various types of items, such as a command, an illustration, a set value, a message, and the like. A touch panel  26  is provided on the front face of the LCD  15 . A user may perform an operation of pressing the touch panel  26  using a finger or a dedicated touch pen. Hereinafter, this operation is referred to as a “panel operation”. The touch panel  26  detects a position pressed by the finger, the dedicated touch pen, or the like, and the sewing machine  1  (more specifically, a CPU  61  that will be described below) determines the item that corresponds to the detected position. In this manner, the sewing machine  1  recognizes the selected item. By the panel operation, the user can select a pattern to be sewn and a command to be executed. 
     Connectors  39  and  40  are provided on a right surface of the pillar  12 . An external storage device (not shown in the drawings), such as a memory card, can be connected to the connector  39 . The sewing machine  1  may read out pattern data and various programs from the external storage device connected to the connector  39 . A connector  916  may be connected to the connector  40 . The connector  916  is coupled to a cable  912  that extends from an ultrasonic pen  91  (which will be described below). The sewing machine  1  may supply electric power to the ultrasonic pen  91  via the connector  40 , the connector  916 , and the cable  912 , and may acquire an electrical signal output from the ultrasonic pen  91 . 
     The ultrasonic pen  91  will be explained. The ultrasonic pen  91  includes a pen body  910  and a pen tip  911 . The pen body  910  has a bar shape. The pen tip  911  is provided at the leading end of the pen body  910 . A point of the pen tip  911  is sharp. Normally, the pen tip  911  is in a protruding position in which the pen tip  911  protrudes slightly to the outside from the pen body  910 . On the other hand, when a force toward the pen body  910  acts on the pen tip  911 , the pen tip  911  is inserted into the pen body  910 . When the force acting on the pen tip  911  is released, the pen tip  911  returns to the original protruding position. 
     The ultrasonic pen  91  includes a switch  913  (refer to  FIG. 5 ), a signal output circuit  914  (refer to  FIG. 5 ), and an ultrasonic transmitter  915  (refer to  FIG. 5 ) inside the pen body  910 . The switch  913  is turned on and off in accordance with the position of the pen tip  911 . The switch  913  may switch output states of the signal output circuit  914  and the ultrasonic transmitter  915 . 
     When no force acts on the pen tip  911  (when the pen tip  911  is in the protruding position), the switch  913  is in an OFF state. When the switch  913  is in the OFF state, the signal output circuit  914  does not output an electrical signal and the ultrasonic transmitter  915  does not output an ultrasonic wave. On the other hand, when the user presses the pen tip  911  against an arbitrary position on the work cloth  100 , a force acts on the pen tip  911 . At this time, the pen tip  911  is inserted into the pen body  910  and the switch  913  is turned on. When the switch  913  is turned on, the signal output circuit  914  outputs an electrical signal to the sewing machine  1  via the cable  912 , and the ultrasonic transmitter  915  transmits an ultrasonic wave. 
     As will be described in detail below, the sewing machine  1  can receive (detect) the ultrasonic wave transmitted from the ultrasonic pen  91  using the receivers  94  and  95 . Based on the detected ultrasonic wave, the sewing machine  1  can identify a transmission source of the ultrasonic wave, namely, the position of the ultrasonic transmitter  915  provided in the ultrasonic pen  91 . The sewing machine  1  can perform sewing based on the identified position. Thus, the user can specify an arbitrary position on the work cloth  100  by pressing the pen tip  911  of the ultrasonic pen  91  on the work cloth  100  (touching the work cloth  100  with the pen tip  911 ). As a result, it is possible to perform sewing in the specified position. 
     The receiver  94  will be explained with reference to  FIG. 2  to  FIG. 4 . The receiver  95  has the same configuration as that of the receiver  94 , so an explanation thereof is omitted. The lower left side, the upper right side, the upper left side, the lower right side, the upper side, and the lower side of  FIG. 2  are respectively defined as the front side, the rear side, the left side, the right side, the upper side, and the lower side of the receiver  94 . 
     As shown in  FIG. 2  and  FIG. 3 , the receiver  94  has a rectangular parallelepiped shape that is slightly longer in the up-down direction. An opening  941  is provided in the center of a lower end portion of the front face of the receiver  94 . The opening  941  has an elliptical shape that is long in the left-right direction. A wall  942  around the opening  941  is a tapered surface (an inclined surface) that becomes narrower from the outer side toward the inner side of a front surface of the receiver  94 . As shown in  FIG. 4 , a substrate  943  and a microphone  944  are provided inside the receiver  94 . The microphone  944  is provided, inside the receiver  94 , behind the opening  941 . A connector  945  is mounted on an upper end of a rear surface of the substrate  943 . The connector  945  may be connected to a connector (not shown in the drawings) that is provided on the sewing machine  1 . An orientation of the receiver  94  is determined by a direction of the opening  941  in relation to the microphone  944 . 
     An electrical configuration of the sewing machine  1  and the ultrasonic pen  91  will be explained with reference to  FIG. 5 . A control portion  60  of the sewing machine  1  includes a CPU  61 , a ROM  62 , a RAM  63 , an EEPROM  64 , and an input/output interface  65 , which are mutually connected via a bus  67 . The ROM  62  stores programs and data etc. that are used by the CPU  61  to execute processing. The EEPROM  64  stores data of various types of sewing patterns that are used for the sewing machine  1  to perform sewing. 
     The operation switches  21 , the touch panel  26 , and drive circuits  71 ,  72 ,  74 ,  75 , and  76  are electrically connected to the input/output interface  65 . The drive circuits  71 ,  72 ,  74 ,  75 , and  76  may respectively drive the feed adjustment motor  83 , the sewing machine motor  79 , the needle bar swinging motor  80 , the LCD  15 , the receiver  94 , and the receiver  95 . The drive circuit  76  includes an amplification circuit. The amplification circuit may amplify ultrasonic signals detected by the receivers  94  and  95 , and may transmit the amplified signals to the CPU  61 . 
     The electrical configuration of the ultrasonic pen  91  will be explained. The ultrasonic pen  91  includes the switch  913 , the signal output circuit  914 , and the ultrasonic transmitter  915 . The switch  913  is connected to the signal output circuit  914  and the ultrasonic transmitter  915 . The signal output circuit  914  can be connected to the input/output interface  65 . The signal output circuit  914  may output an electrical signal to the CPU  61  via the input/output interface  65 . 
     A method of identifying a position on the work cloth  100  specified using the ultrasonic pen  91  will be explained with reference to  FIG. 6 . The user may cause the pen tip  911  of the ultrasonic pen  91  to touch the work cloth  100 , and thereby may specify a position on the work cloth  100  where sewing is to be performed by the sewing machine  1 . Hereinafter, a position on the work cloth  100  that is touched by the pen tip  911  of the ultrasonic pen  91  is also referred to as a specified position. As described below, the sewing machine  1  may identify a specified position by identifying a position of a transmission source of an ultrasonic wave. Therefore, strictly speaking, the position of the ultrasonic transmitter  915  provided in the ultrasonic pen  91  is identified, rather than the position on the work cloth  100  touched by the pen tip  911 . The pen tip  911  and the ultrasonic transmitter  915  are arranged very close to each other. Therefore, the position of the ultrasonic transmitter  915  may be assumed as the position on the work cloth  100  touched by the pen tip  911 , namely, the specified position. Hereinafter, the left-right direction, the front-rear direction, and the up-down direction of the sewing machine  1  are respectively defined as an X direction, a Y direction, and a Z direction. The left-right direction and the up-down direction of  FIG. 6  respectively correspond to the X direction and the Y direction. A direction from the near side to the far side corresponds to the Z direction. 
     The sewing machine  1  identifies the specified position as coordinate information (an X coordinate, a Y coordinate, and a Z coordinate). Here, the coordinate origin (0, 0, 0) is defined as a center point of a needle hole. The needle hole is formed in the needle plate  34  (refer to  FIG. 1 ), and is a hole through which the sewing needle may pass. The center point of the needle hole is a needle drop point, which will be described below. The Z coordinate of a top surface of the needle plate  34  is 0. Coordinates B that indicate the position of the receiver  94  are denoted by (Xb, Yb, Zb). Coordinates C that indicate the position of the receiver  95  are denoted by (Xc, Yc, Zc). Coordinates E that indicate the specified position are denoted by (Xe, Ye, Ze), The Z coordinate of the receivers  94  and  95  indicates the height of the receivers  94  and  95  with respect to the top surface of the needle plate  34 . The coordinates B (Xb, Yb, Zb) and the coordinates C (Xc, Yc, Zc) are stored in advance in the ROM  62 . Hereinafter, the coordinates E are also referred to as “specified coordinates E”. A distance between the specified coordinates E and the coordinates B is referred to as a “distance EB”. A distance between the specified coordinates E and the coordinates C is referred to as a “distance EC”. 
     The distances EB and EC can be expressed by the coordinates B, C, and E based on the Pythagorean theorem. The distance EB and the coordinates B, C, and E satisfy a relationship of Formula (1) below. In a similar manner, the distance EC and the coordinates B, C, and E satisfy a relationship of Formula (2) below.
 
( Xb−Xe ) 2 +( Yb−Ye ) 2 +( Zb−Ze ) 2 =( EB ) 2   Formula (1)
 
( Xc−Xe ) 2 +( Yc−Ye ) 2 +( Zc−Ze ) 2 =( EC ) 2   Formula (2)
 
     Formula (1) is the same as the equation of a spherical surface (whose radius is the distance EB), the origin of which is the coordinates B and on which the specified coordinates E is. In a similar manner, Formula (2) is the same as the equation of a spherical surface (whose radius is the distance EC), the origin of which is the coordinates C and on which the coordinates E is. 
     The speed at which an ultrasonic wave travels is assumed to be a sonic velocity V. A time required from when the ultrasonic wave is transmitted from the ultrasonic pen  91  at the specified coordinates E to when the ultrasonic wave reaches the receiver  94  is referred to as a propagation time Tb. A time required from when the ultrasonic wave is transmitted from the ultrasonic pen  91  at the specified coordinates E to when the ultrasonic wave reaches the receiver  95  is referred to as a propagation time Tc. In this case, the distances EB and EC are expressed by the following Formulas (3) and (4).
 
 EB=V×Tb   Formula (3)
 
 EC=V×Tc   Formula (4)
 
     The following Formulas (5) and (6) are obtained by substituting Formulas (3) and (4) into Formulas (1) and (2) described above.
 
( Xb−Xe ) 2 +( Yb−Ye ) 2 +( Zb−Ze ) 2 =( V×Tb ) 2   Formula (5)
 
( Xc−Xe ) 2 +( Ye−Ye ) 2 +( Zc−Ze ) 2 =( V×Tc ) 2   Formula (6)
 
     In Formulas (5) and (6), the coordinates B (Xb, Yb, Zb), the coordinates C (Xc, Yc, Zc) and the sonic velocity V are known values and stored in advance in the ROM  62 . The propagation time Tb and the propagation time Tc are each identified by calculating a difference between a transmission timing T 1  and a detection timing T 2 . The transmission timing T 1  is a timing at which the ultrasonic wave is transmitted from the ultrasonic transmitter  915  of the ultrasonic pen  91 . The detection timing T 2  is a timing at which the ultrasonic wave is detected by each of the receivers  94  and  95 . The thickness of the work cloth  100  is small enough to be ignored, in comparison to the values Xe and Ye. Therefore, the value Ze of the specified coordinates E (Xe, Ye, Ze) can be deemed to be zero. Thus, the values Xe and Ye can be calculated by solving the simultaneous equations represented by Formulas (5) and (6). Here, taking orientations of the receivers  94  and  95  into account, the specified coordinates E (Xe, Ye, Ze (=0)) on the work cloth  100  that are specified using the ultrasonic pen  91  can be determined. 
     It is preferable that the receivers  94  and  95  be provided in positions of the sewing machine  1  that satisfy the following conditions (A) to (E). In an explanation of the conditions (A) to (E), the receivers  94  and  95  are referred to as receivers  93  for convenience of the explanation. 
     (A) An object is unlikely to enter between the ultrasonic pen  91  and the receivers  93 . 
     (B) The receivers  93  are separated from each other to some extent. 
     (C) The distance, in the X direction and the Y direction, from the needle hole (the origin) of the needle plate  34  to the receivers  93  is large. 
     (D) The distance from the needle hole (the origin) to the receivers  93  is not extremely large. 
     (E) The receivers  93  are provided above the top surface of the bed  11 . Specifically, the receivers  94  are provided above the work cloth  100  placed on the bed  11 . 
     The reasons are as follows. 
     The condition (A) is set because if an object enters between the ultrasonic pen  91  and the receivers  93 , the receivers  93  may not receive the ultrasonic wave transmitted from the ultrasonic pen  91 . The object may be, for example, a hand or an arm of the user. For example, there is a possibility that the hand or the arm enters between the pen tip  911  and the receivers  93  when the user who holds the ultrasonic pen  91  in the user&#39;s hand is specifying the specified position. In this case, the ultrasonic wave transmitted from the ultrasonic pen  91  may be shielded by the hand or the arm. Therefore, a case may occur in which the receivers  93  cannot receive the ultrasonic wave. For that reason, it is preferable that the receivers  93  be provided in positions where the hand or the arm of the user does not enter between the ultrasonic pen  91  and the receivers  93  when the user is performing an operation using the ultrasonic pen  91 . 
     The reason for setting the condition (B) is as follows. When the simultaneous equations represented by Formulas (5) and (6) are solved, if the difference between the coordinates B and C is small, the results of Formulas (5) and (6) are close to each other. In this case, an error of the calculated specified coordinates E may become large. 
     The reason for setting the condition (C) is as follows. As the distance from the origin to the receivers  93  in the X direction and the Y direction increases, the Z-coordinate values of the coordinates B and C become relatively smaller than the X-coordinate values and the Y-coordinate values of the coordinates B and C. Therefore, it is possible to reduce an influence on a calculation result caused by the thickness of the work cloth  100 . 
     The reason for setting the condition (D) is as follows. If the distance from the origin to the receivers  93  is extremely large, the ultrasonic wave transmitted from the ultrasonic pen  91  may be attenuated before the ultrasonic wave reaches the receivers  93 . Therefore, it is difficult for the receivers  93  to accurately receive the ultrasonic wave. 
     The reason for setting the condition (E) is that the pen tip  911  of the ultrasonic pen  91  may come into contact with the top surface of the work cloth  100  that is placed on the bed  11 . It is preferable that the receivers  93  can accurately receive the ultrasonic wave transmitted from the ultrasonic pen  91  that is in contact with the top surface of the work cloth  100 , Therefore, it is preferable that the receivers  93  be provided above the top surface of the bed  11 . 
     In the first embodiment, as shown in  FIG. 1 , the receiver  94  is provided at the lower left end of the head  14  and the receiver  95  is provided at the lower right end of the head  14 . The position on the work cloth  100  that can be easily specified by the user while the user is holding the ultrasonic pen  91  in the user&#39;s hand may be a position on the front side with respect to the needle hole. Thus, the condition (A) is substantially satisfied. The distance between the receivers  94  and  95  is almost the same as the length of the head  14  in the left-right direction. Therefore, the receivers  94  and  95  are sufficiently separated from each other, and the condition (B) is satisfied. The receivers  94  and  95  are provided on the rear side of the lower surface of the head  14 . Thus, the distances from the origin to the receivers  94  and  95  in the X direction and the Y direction are larger than when the receivers  94  and  95  are provided substantially in the center, in the front-rear direction, of the lower surface of the head  14 . Thus, the condition (C) is satisfied. The distances from the origin to the receivers  94  and  95  are not extremely large. Thus, the condition (D) is satisfied. The receivers  94  and  95  are provided above the top surface of the bed  11 . Thus, the condition (E) is satisfied. In this manner, in the first embodiment, the positions in which the receivers  94  and  95  are provided satisfy all the conditions (A) to (E). Therefore, the sewing machine  1  can calculate the specified coordinates E more precisely. 
     Processing that is performed by the CPU  61  of the sewing machine  1  to identify the specified position will be specifically explained with reference to  FIG. 7 . Main processing is performed by the CPU  61  in accordance with the program stored in the ROM  62 . For example, when a command to perform sewing is input by a panel operation, the CPU  61  may start the main processing. 
     The CPU  61  determines whether an electrical signal output from the signal output circuit  914  of the ultrasonic pen  91  has been detected via the cable  912  (step S 11 ). If the electrical signal has not been detected (NO at step S 11 ), the processing returns to step S 11 . It is assumed that the user specifies an arbitrary position on the work cloth  100  using the ultrasonic pen  91  and the pen tip  911  of the ultrasonic pen  91  comes into contact with the work cloth  100 . The pen tip  911  of the ultrasonic pen  91  may be inserted into the pen body  910  and the switch  913  may be turned on. The signal output circuit  914  may output an electrical signal. The CPU  61  may detect the electrical signal (YES at step S 11 ). In a case where the switch  913  of the ultrasonic pen  91  is turned on, the ultrasonic transmitter  915  transmits an ultrasonic wave at the same time as when the signal output circuit  914  outputs the electrical signal. However, the propagation speed of the electrical signal is significantly higher than the propagation speed of the ultrasonic wave, and the electrical signal reaches the CPU  61  substantially at the same timing as the timing at which the switch  913  is turned on. 
     If the CPU  61  has detected the electrical signal output from the signal output circuit  914  of the ultrasonic pen  91  (YES at step S 11 ), the CPU  61  identifies a time at which the electrical signal is detected. The CPU  61  acquires the identified time as the transmission timing T 1  of the ultrasonic wave (step S 13 ). The CPU  61  stores the acquired transmission timing T 1  in the RAM  63 . 
     The CPU  61  determines whether the ultrasonic wave transmitted from the ultrasonic pen  91  has been detected via at least one of the receivers  94  and  95  (step S 15 ). If the ultrasonic wave has not been detected via at least one of the receivers  94  and  95  (NO at step S 15 ), the CPU  61  determines whether or not a predetermined time period (for example, one second) has elapsed (step S 35 ). If the predetermined time period has not elapsed (NO at step S 35 ), the processing returns to step S 15 . The CPU  61  stands by for the predetermined time period until at least one of the receivers  94  and  95  detect the ultrasonic wave. 
     Here, it is assumed that the ultrasonic wave transmitted from the ultrasonic transmitter  915  of the ultrasonic pen  91  is shielded by, for example, the hand or the arm of the user, the work cloth  100 , or the like and does not reach the receivers  94  and  95 . In this manner, if the predetermined time period has elapsed without detecting the ultrasonic wave by at least one of the receivers  94  and  95  (YES at step S 35 ), the CPU  61  displays on the LCD  15  an error message indicating that the ultrasonic wave has not been detected (step S 37 ). In a case where the user sees the error message, the user may once again specify an arbitrary position on the work cloth  100  using the ultrasonic pen  91 . The processing returns to step S 11  to re-detect the electrical signal output from the signal output circuit  914  of the ultrasonic pen  91 . 
     If the CPU  61  detects the ultrasonic wave via at least one of the receivers  94  and  95  within the predetermined time period from the detection of the electrical signal (YES at step S 15 ), the CPU  61  identifies a time at which the ultrasonic wave is detected. The CPU  61  acquires the identified time as the detection timing T 2  (step S 17 ). The CPU  61  stores the acquired detection timing T 2  in the RAM  63 . 
     The CPU  61  determines whether both the receivers  94  and  95  have detected the ultrasonic wave (step S 19 ). If one of the receivers  94  and  95  has not detected the ultrasonic wave (NO at step S 19 ), the processing returns to step S 15 . If both the receivers  94  and  95  have detected the ultrasonic wave (YES at step S 19 ), the CPU  61  calculates the propagation time Tb and the propagation time Tc (step S 21 ). The CPU  61  calculates the propagation time Tb and the propagation time Tc by subtracting the transmission timing T 1  from the detection timing T 2 . 
     The CPU  61  multiplies the calculated Tb and Tc by the sonic velocity V and thereby calculates the distances EB and EC (step S 23 ) (refer to Formulas (3) and (4)). The CPU  61  substitutes the coordinates B (Xb, Yb, Zb), the coordinates C (Xc, Ye, Ze), and the distances EB and EC into Formulas (5) and (6), and solves the simultaneous equations. Thus, the CPU  61  calculates the specified coordinates E (Xe, Ye, Ze (=0)). In this manner, the CPU  61  identifies the position specified using the ultrasonic pen  91 , namely, the specified position (step S 25 ). 
     The CPU  61  displays, on the LCD  15 , a display image that shows a relationship between the specified position, which is indicated by the specified coordinates E (Xe, Ye, Ze), and the work cloth  100  (step S 27 ). The CPU  61  determines whether the start/stop switch, which is one of the operation switches  21 , has been pressed (step S 29 ). If the start/stop switch has not been pressed (NO at step S 29 ), the processing returns to step S 29 . If the start/stop switch has been pressed (YES at step S 29 ), the CPU  61  drives the feed dog and moves the work cloth such that the position indicated by the X-coordinate “Xe” and the Y-coordinate “Ye” of the specified coordinates E calculated at step S 25  matches the needle drop point (step S 31 ). Then, the CPU  61  starts sewing (step S 33 ). In this manner, sewing is started from the position on the work cloth  100  specified using the ultrasonic pen  91 , namely, the specified position. When the sewing is complete, the main processing ends. The needle drop point is a point at which the sewing needle may penetrate the work cloth  100 , namely, the center point of the needle hole formed in the needle plate  34 . 
     As explained above, in a case where the user specifies an arbitrary position on the work cloth  100  using the ultrasonic pen  91 , the sewing machine  1  can identify the specified position and start sewing. In this manner, the user can easily and appropriately specify a position on the work cloth  100  using the ultrasonic pen  91 . The sewing machine  1  can detect the ultrasonic wave using the plurality of receivers  94  and  95 , and calculate the specified coordinates E based on the transmission timing T 1  and the detection timings T 2 . Thus, the sewing machine  1  can accurately identify the specified position. 
     The present disclosure is not limited to the first embodiment and various modifications may be made. The positions in which the receivers  94  and  95  are provided are not limited to the head  14  of the sewing machine  1 . For example, the receivers  94  and  95  may be provided on at least one of the presser foot  30  and the presser bar  31 . More specifically, the receiver  94  may be provided on the left side of the presser foot  30  or the presser bar  31  and the receiver  95  may be provided on the right side of the presser foot  30  or the presser bar  31 . 
     For example, the receiver  94  may be provided on one of the head  14 , the presser foot  30 , and the presser bar  31 , and the receiver  95  may be provided on the arm portion  13  side of the pillar  12 , namely, on any part of a left surface  17  (refer to  FIG. 1 ) of the pillar  12 . In this case, the opening  941  of the receiver  95  is provided such that the opening  941  faces to the left. In this case, the distance between the receivers  94  and  95  is larger than when the receiver  95  is provided on the head  14  (refer to condition (B)). The distance, in the X direction and the Y direction, from the needle hole (the origin) of the needle plate  34  to the receiver  95  also increases (refer to condition (C)). Further, the receivers  94  and  95  are provided above the top surface of the bed  11  (refer to condition (E)). In this manner, the positions in which the receivers  94  and  95  are provided satisfy a plurality of conditions included in the conditions (A) to (E), in a similar manner to the first embodiment. Therefore, the sewing machine  1  can precisely calculate the specified coordinates E. Further, particularly in this case, it is possible to increase the distance between the receivers  94  and  95 . 
     The combinations of the positions of the receivers  94  and  95  are not limited to those of the first embodiment and the modified examples described above. In a case where the receivers  94  and  95  are provided on the head  14 , the positions of the receivers  94  and  95  are not limited to the rear side of the lower surface of the head  14 . For example, the receivers  94  and  95  may be provided on the front side of the lower surface of the head  14 , substantially in the center in the front-rear direction of the lower surface of the head  14 , or the like. In a case where the receiver  95  is provided on the left surface  17  of the pillar  12 , the height at which the receiver  95  is disposed is not particularly limited. However, it is preferable that the receiver  95  be disposed in a lower position in order to reduce an influence caused by approximating the value Ze in Formulas (5) and (6) to zero. 
     The receivers  94  and  95  may be provided on a part other than the head  14 , the presser foot  30 , the presser bar  31 , and the left surface  17  of the pillar  12 . For example, the receivers  94  and  95  may be provided on a lower side surface of the arm  13 , a front surface or a rear surface of the head  14 , or an upper surface of the bed  11  at the left end of the bed  11 . The ultrasonic pen  91  need not necessarily be attached to the sewing machine  1 . The sewing machine  1  may detect an ultrasonic wave output from a known device configured to output an ultrasonic wave, and may identify a position of the transmission source of the ultrasonic wave as the specified position. 
     Second Embodiment 
     A second embodiment will be explained. In the second embodiment, as shown in  FIG. 8  to  FIG. 10 , receivers  84  and  85  are provided not on the sewing machine  1 , but on an embroidery unit  2 , which can be attached to and detached from the bed  11  of the sewing machine  1 .  FIG. 9  and  FIG. 10  show the embroidery unit  2  that is not attached to the sewing machine  1 . The embroidery unit  2  includes a body portion  51  and a carriage  52 . 
     As shown in  FIG. 9  and  FIG. 10 , a connection portion  54  is provided on a right surface of the body portion  51  of the embroidery unit  2 . In a state in which the embroidery unit  2  is attached to the sewing machine  1 , the connection portion  54  is connected to a connection receiving portion (not shown in the drawings) of the sewing machine  1 , and thus the embroidery unit  2  and the sewing machine  1  are electrically connected. 
     The carriage  52  is provided on the upper side of the body portion  51 . The carriage  52  has a rectangular parallelepiped shape that is long in the front-rear direction. The carriage  52  includes a frame holder  55 , a Y axis movement mechanism (not shown in the drawings), and a Y axis motor (not shown in the drawings). The frame holder  55  is a holder to which an embroidery frame (not shown in the drawings) can be detachably attached. The holder  55  is provided on a right surface of the carriage  52 . The embroidery frame is a known frame that includes an inner frame and an outer frame. The embroidery frame may clamp and hold the work cloth  100 . The work cloth  100  held by the embroidery frame may be arranged on the top surface of the bed  11  and below the needle bar  29  and the presser foot  30 . The Y axis movement mechanism may move the frame holder  55  in the front-rear direction (the Y direction). Along with the movement of the frame holder  55  in the front-rear direction, the work cloth  100  held by the embroidery frame may be moved in the front-rear direction. The Y axis motor may drive the Y axis movement mechanism. The CPU  61  (refer to  FIG. 5 ) controls the Y axis motor. 
     An X axis movement mechanism (not shown in the drawings) and an X axis motor (not shown in the drawings) are provided inside the body portion  51 . The X axis movement mechanism may move the carriage  52  in the left-right direction (the X direction). Along with the movement of the carriage  52  in the left-right direction, the work cloth  100  held by the embroidery frame may be moved in the left-right direction. The X axis motor may drive the X axis movement mechanism. The CPU  61  controls the X axis motor. 
     The receiver  84  is provided at the front end of an upper surface of the carriage  52 . The receiver  85  is provided at the rear end of the upper surface of the carriage  52 . The receivers  84  and  85  receive are configured to an ultrasonic wave. The receivers  84  and  85  have the same configuration as the receivers  94  and  95 . The embroidery frame attached to the frame holder  55  is located at the right of the right surface of the carriage  52 , Therefore, the receivers  84  and  85  are located above the position of the carriage  52  where the embroidery frame can be attached. Thus, the receivers  84  and  85  are located above the body portion  51  of the embroidery unit  2 . When the embroidery unit  2  is attached to the bed  11  of the sewing machine  1 , the receivers  84  and  85  are located above the bed  11 . Openings of the receivers  84  and  85  are directed to the right. In a case where the receivers  84  and  85  receive an ultrasonic wave, the receivers  84  and  85  each transmit an electrical signal to the sewing machine  1 . The CPU  61  may receive the electrical signals from the receivers  84  and  85 , and thereby may detect the ultrasonic wave transmitted from the ultrasonic pen  91 . 
     Processing that is performed by the CPU  61  of the sewing machine  1  to identify the specified position will be explained with reference to  FIG. 7 . In a case where the CPU  61  detects an electrical signal output from the signal output circuit  914  of the ultrasonic pen  91  via the cable  912  (YES at step S 11 ), the CPU  61  acquires the transmission timing T 1  (step S 13 ). In a case where the CPU  61  receives the electrical signal from each of the receivers  84  and  85  (YES at step S 15 ), the CPU  61  identifies a time at which the electrical signal is received from the receiver  84  and a time at which the electrical signal is received from the receiver  85 , and acquires the identified times as the detection timings T 2  (step S 17 ). The CPU  61  calculates the specified coordinates E and identifies the specified position (steps S 21  to S 25 ). The CPU  61  controls the X axis motor and the Y axis motor, and thereby moves the embroidery frame such that the position of the specified coordinates E on the work cloth  100  matches the needle drop point (step S 31 ). Next, the CPU  61  starts sewing on the work cloth  100 . The CPU  61  drives the needle bar  29  and the shuttle mechanism (not shown in the drawings) simultaneously with the embroidery frame being moved in the left-right direction (the X direction) and the front-rear direction (the Y direction). The sewing needle attached on the needle bar  29  sews an embroidery pattern on the work cloth  100  held by the embroidery frame. In this manner, the embroidery pattern is sewn in the specified position on the work cloth  100  (step S 33 ). 
     In the second embodiment, the receivers  84  and  85  are respectively provided at the front end and the rear end of the carriage  52 , as shown in  FIG. 9  and  FIG. 10 . Therefore, when the embroidery unit  2  is attached to the bed  11 , all the above-described conditions (A) to (E) are satisfied. The ultrasonic wave transmitted from the ultrasonic pen  91  when the pen tip  911  is in contact with the work cloth  100  may be not shielded by the hand or the arm of the user (refer to condition (A)). The distance between the receivers  84  and  85  is separated by a length, in the front-rear direction, of the carriage  52 . As a result, the receivers  84  and  85  are sufficiently separated from each other (refer to condition (B)). The distances, in the X direction and the Y direction, from the needle hole (the origin) of the needle plate  34  to the receivers  84  and  85  are larger than when the receivers  84  and  85  are provided on the head  14 , the presser foot  30  or the presser bar  31  of the sewing machine  1  (refer to condition (C)). The distances from the origin to the receivers  84  and  85  are not extremely large (refer to condition (D)). The receivers  84  and  85  are provided above the body portion  51  of the embroidery unit  2 . Therefore, the receivers  84  and  85  are located above the bed  11  (refer to condition (E)). Specifically, the receivers  84  and  85  are provided above the work cloth  100  held by the embroidery frame. Therefore, the sewing machine  1  can calculate the specified coordinates E more precisely and perform sewing on the work cloth  100 . Further, the height from the top surface of the bed  11  to the receivers  84  and  85  is low. If the height from the top surface of the bed  11  to the receivers  84  and  85  is high, there is a possibility that the influence on a calculation result caused by the thickness of the work cloth  100  increases. If the height from the top surface of the bed  11  to the receivers  84  and  85  is low, the influence caused by approximating the value Ze in Formulas (5) and (6) to zero may decrease. Therefore, the error of the calculated specified coordinates E may become small. 
     In the second embodiment, the receivers  84  and  85  may be provided on a part other than the top surface of the carriage  52 . For example, the receiver  84  may be provided on a front surface of the carriage  52  and the receiver  85  may be provided on a rear surface of the carriage  52 . For example, the receiver  84  may be provided at the front side of the right surface of the carriage  52 , and the receiver  85  may be provided at the rear side of the right surface of the carriage  52 . 
     Third Embodiment 
     A third embodiment will be explained. As shown in  FIG. 11 , the sewing machine  1  of the third embodiment is different from the sewing machine  1  of the first embodiment in that the sewing machine  1  is provided with an ultrasonic pen  92  that is not connected to the sewing machine  1  via a cable. Instead of the signal output circuit  914  (refer to  FIG. 5 ), an electromagnetic wave output circuit  921  (refer to  FIG. 12 ) is provided inside the ultrasonic pen  92 . The ultrasonic pen  92  accommodates a battery (not shown in the drawings). The ultrasonic pen  92  may be driven by the battery. The electromagnetic wave output circuit  921  may output an electromagnetic wave signal of a predetermined frequency. When the switch  913  (refer to  FIG. 12 ) is in an OFF state, the electromagnetic circuit  921  does not output the electromagnetic wave signal. When the switch  913  is turned on, the electromagnetic wave output circuit  921  outputs the electromagnetic wave signal. The CPU  61  may receive the electromagnetic wave signal output from the electromagnetic wave output circuit  921  using an electromagnetic wave detector  97  (refer to  FIG. 12 ). The electromagnetic wave detector  97  is provided inside the sewing machine  1 . The position of the electromagnetic detector  97  is not limited to the inside of the sewing machine  1  as long as the sewing machine  1  can receive the electromagnetic wave signal. 
     An electrical configuration of the sewing machine  1  and the ultrasonic pen  92  according to the third embodiment will be explained with reference to  FIG. 12 . The third embodiment is different from the first embodiment in that the ultrasonic pen  92  includes the electromagnetic wave output circuit  921  and in that the sewing machine  1  includes the electromagnetic wave detector  97 . The electromagnetic wave output circuit  921  is connected to the switch  913 . The electromagnetic detector  97  is connected to the input/output interface  65 . When the electromagnetic wave detector  97  receives the electromagnetic wave signal output from the electromagnetic wave output circuit  921  of the ultrasonic pen  92 , the electromagnetic wave detector  97  outputs a signal to the CPU  61  via the input/output interface  65 . 
     Main processing according to the third embodiment will be explained with reference to  FIG. 7 . At step S 11 , the CPU  61  determines whether the electromagnetic wave detector  97  has detected the electromagnetic wave signal output from the electromagnetic wave output circuit  921  of the ultrasonic pen  92 , instead of detecting the electrical signal output from the signal output circuit  914  of the ultrasonic pen  91  (step S 11 ). If the electromagnetic wave detector  97  has not detected the electromagnetic wave signal (NO at step S 11 ), the processing returns to step S 11 . If the electromagnetic wave detector  97  has detected the electromagnetic wave signal (YES at step S 11 ), the CPU  61  identifies a time at which the electromagnetic wave signal has been detected. The CPU  61  acquires the identified time as the transmission timing T 1  of the ultrasonic wave (step S 13 ). The CPU  61  stores the acquired transmission timing T 1  in the RAM  63 . Processing from steps S 15  to S 33  is performed in the same manner as in the first embodiment, and an explanation thereof is omitted here. 
     As explained above, in the third embodiment, the sewing machine  1  can identify the transmission timing of the ultrasonic wave by detecting the electromagnetic wave signal output by the ultrasonic pen  92 . In other words, there is no need to provide a cable to connect the ultrasonic pen  92  and the sewing machine  1 . As a result, there is no way the cable can be an obstruction to the operation. Thus, the user can easily specify the specified position on the work cloth  100  using the ultrasonic pen  92 . 
     In the third embodiment, the ultrasonic pen  92  may be provided with a known timer circuit and the timer circuit may be connected to the electromagnetic wave output circuit  921 . In this case, the electromagnetic wave output circuit  921  of the ultrasonic pen  92  may output an electromagnetic wave signal that notifies the CPU  61  of the time at which the switch  913  is turned on. The CPU  61  may receive the electromagnetic wave signal via the electromagnetic wave detector  97  and may identify the time notified by the electromagnetic wave signal. The CPU  61  may acquire the identified time as the transmission timing of the ultrasonic wave. 
     The electromagnetic wave signal output from the electromagnetic wave output circuit  921  may be an electromagnetic wave signal of an arbitrary frequency. For example, the electromagnetic wave signal may be a microwave or infrared light. 
     Fourth Embodiment 
     A fourth embodiment will be explained. As shown in  FIG. 13 , the fourth embodiment is different from the third embodiment in that the sewing machine  1  is provided with a receiver  96  in addition to the receivers  94  and  95  and in that the ultrasonic pen  92  is not provided with the electromagnetic wave output circuit  921 , as will be described below in detail. The receiver  96  is provided on the left surface  17  of the pillar  12 . The receiver  96  has the same configuration as the receivers  94  and  95 . The receiver  96  is provided such that an opening (not shown in the drawings) of the receiver  96  is directed to the left. The CPU  61  may detect the ultrasonic wave using the receivers  94 ,  95  and  96  and may calculate the specified coordinates E based on the detection timings T 2  of the receivers  94 ,  95  and  96 . Unlike the first embodiment to the third embodiment, the CPU  61  does not acquire the transmission timing T 1  of the ultrasonic wave, and does not use the transmission timing T 1  when calculating the specified coordinates E. An electrical configuration of the sewing machine  1  according to the fourth embodiment is a configuration obtained by removing the electromagnetic wave detector  97  and the electromagnetic wave output circuit  921  from the block diagram shown in  FIG. 12  that shows the electrical configuration of the sewing machine  1  according to the third embodiment. 
     A method for identifying a position on the work cloth  100  specified by the ultrasonic pen  92  will be explained with reference to  FIG. 14 . The may user specify the specified position on the work cloth  100  by causing the pen tip  911  of the ultrasonic pen  92  to touch the work cloth  100 . The left-right direction and the up-down direction of  FIG. 14  respectively correspond to the X direction and the Y direction. A direction from the near side to the far side of  FIG. 14  corresponds to the Z direction. Coordinates D of the receiver  96  are denoted by (Xd, Yd, Zd). A distance between the specified coordinates E and the coordinates D of the receiver  96  is referred to as a “distance ED”. 
     The distance ED can be expressed by the coordinates B, C, D, and E based on the Pythagorean theorem. The distance ED and the coordinates D and E satisfy a relationship of the following Formula (7).
 
( Xd−Xe ) 2 +( Yd−Ye ) 2 +( Zd−Ze ) 2 =( ED ) 2   Formula (7)
 
     In the same manner as Formulas (1) and (2) described above, Formula (7) is the same as the equation of a spherical surface (whose radius is the distance ED), the origin of which is the coordinates D and on which the specified coordinates E is. 
     A time required from when the ultrasonic wave is transmitted from the ultrasonic pen  92  at the specified coordinates E to when the ultrasonic wave reaches the receiver  96  is referred to as a propagation time Td. In this case, the distance ED can be expressed by the following Formula (8).
 
 ED=V×Td   Formula (8)
 
     Further, Formulas (4) and (8) can be transformed into the following Formulas (9) and (10).
 
 EC=V×Tc=V ×( Tc−Tb )+ V×Tb   Formula (9)
 
 ED=V×Td=V ×( Td−Tb )+ V×Tb   Formula (10)
 
     A propagation time difference (Tc−Tb) in Formula (9) is the same as the difference between the detection timing T 2  at which the ultrasonic wave is detected via the receiver  95  and the detection timing T 2  at which the ultrasonic wave is detected via the receiver  94 . In a similar manner, a propagation time difference (Td−Td) in Formula (10) is the same as the difference between the detection timing T 2  at which the ultrasonic wave is detected via the receiver  96  and the detection timing T 2  at which the ultrasonic wave is detected via the receiver  94 . Accordingly, Formulas (9) and (10) can be transformed into the following Formulas (11) and (12). Detection timings at which the ultrasonic wave is detected via the receivers  94 ,  95 , and  96  irrespectively referred to as T 2   b , T 2   c  and T 2   d.  
 
 EC=V ×( T 2 c−T 2 b )+ V×Tb   Formula (11)
 
 ED=V ×( T 2 d−T 2 b )+ V×Tb   Formula (12)
 
     Following Formulas (13), (14), and (15) can be obtained by substituting Formulas (3), (11), and (12) into Formulas (1), (2), and (7).
 
( Xb−Xe ) 2 +( Yb−Ye ) 2 +( Zb−Ze ) 2 =( V×Tb ) 2   Formula (13)
 
( Xc−Xe ) 2 +( Ye−Ye ) 2 +( Zc−Ze ) 2   ={V ×( T 2 c−T 2 b )+ V×Tb}   2   Formula (14)
 
( Xd−Xe ) 2 +( Yd−Ye ) 2 +( Zd−Ze ) 2   ={V ×( T 2 d−T 2 b )+ V×Tb}   2   Formula (15)
 
     In Formulas (13), (14), and (15), the coordinates B (Xb, Yb, Zb), the coordinates C (Xc, Ye, Zc), the coordinates D (Xd, Yd, Zd), and the sonic velocity V are known values and are stored in advance in the ROM  62 . The detection timings T 2   b , T 2   c  and T 2   d  respectively correspond to times at which The CPU  61  detects the ultrasonic wave via the receivers  94 ,  95 , and  96  (step S 43 , refer to  FIG. 15 ). The value Ze of the specified coordinates E (Xe, Ye, Ze) is deemed to be zero. Based on the above, the values Xe, Ye, and Tb can be calculated by solving the simultaneous equations represented by Formulas (13), (14), and (15). In this manner, the specified coordinates E (Xe, Ye, Ze (=0)) on the work cloth  100  that are specified using the ultrasonic pen  92  are calculated. 
     Processing that is performed by the CPU  61  of the sewing machine  1  to identify the specified position will be explained with reference to  FIG. 15 . The main processing is performed by the CPU  61  in accordance with the program stored in the ROM  62 . The CPU 61  may start the main processing when, for example, a command to perform sewing is input by a panel operation. 
     The CPU  61  determines whether at least one of the receivers  94 ,  95 , and  96  has detected the ultrasonic wave transmitted from the ultrasonic pen  92  (step S 41 ). If none of the receivers  94 ,  95 , and  96  has detected the ultrasonic wave (NO at step S 41 ), the CPU  61  determines whether the ultrasonic wave has been detected by at least one of the receivers  94 ,  95 , and  96  after the main processing has been started (step S 61 ). If none of the receivers  94 ,  95  and  96  has detected the ultrasonic wave after the main processing has been started (NO at step S 61 ), the processing returns to step S 41 . If the ultrasonic wave has been detected by at least one of the receivers  94 ,  95 , and  96  after the main processing has been started (YES at step S 61 ), the CPU  61  determines whether a predetermined time period (for example, one second) has elapsed from when the ultrasonic wave has been detected for the first time after the start of the main processing (step S 63 ). If the predetermined time period has not elapsed (NO at step S 63 ), the processing returns to step S 41 . If the predetermined time period has elapsed (YES at step S 63 ), the CPU  61  displays an error message, on the LCD  15 , indicating that the ultrasonic wave has not been detected (step S 65 ). The processing returns to step S 41 . 
     If at least one of the receivers  94 ,  95 , and  96  has detected the ultrasonic wave within the predetermined time period (YES at step S 41 ), the CPU  61  identifies a time at which the ultrasonic wave has been detected. The CPU  61  acquires the identified time as the detection timing T 2  (step S 43 ). The CPU  61  stores the acquired detection timing T 2  in the RAM  63 . 
     The CPU  61  determines whether all the receivers  94 ,  95 , and  96  have detected the ultrasonic wave (step S 45 ). If at least one of the receivers  94 ,  95 , and  96  has not detected the ultrasonic wave (NO at step S 45 ), the processing returns to step S 41 . If all the receivers  94 ,  95 , and  96  have detected the ultrasonic wave (YES at step S 45 ), the CPU  61  calculates differences “T 2   c -T 2   b ” and “T 2   d -T 2   b ” between the detection timings (step S 47 ). The CPU  61  calculates the distances EB, EC, and ED based on the calculated differences and the propagation time Tb (step S 49 ) (refer to Formulas (3), (11), and (12)). The CPU  61  substitutes the coordinates B (Xb, Yb, Zb), the coordinates C (Xc, Ye, Zc), the coordinates D (Xd, Yd, Zd), and the distances EB, EC, and ED into Formulas (13), (14), and (15), and solves the simultaneous equations. Thus, the CPU  61  calculates the specified coordinates E (Xe, Ye, Ze (=0)). In this manner, the CPU  61  identifies the position specified using the ultrasonic pen  92 , namely, the specified position (step S 51 ). Processing from steps S 27  to S 33  is performed in the same manner as in the first embodiment to the third embodiment (refer to  FIG. 7 ) and an explanation thereof is thus omitted here. 
     As explained above, in the fourth embodiment, the sewing machine  1  can calculate the specified coordinates E using only the detection timings T 2  without using the transmission timing T 1 , unlike the first embodiment to the third embodiment. Therefore, there is no need to provide structural elements that are necessary to identify the transmission timing T 1 , such as the signal output circuit  914  (refer to  FIG. 5 ) in the first embodiment, or the electromagnetic wave detector  97  and the electromagnetic wave output circuit  921  in the third embodiment. As a result, in the fourth embodiment, the specified coordinates E can be calculated with a simpler configuration than the configurations of the first embodiment to the third embodiment. 
     In the fourth embodiment, the three positions in which the receivers  94 ,  95 , and  96  are provided are not limited to the lower left end and the lower right end of the head  14  of the sewing machine  1  and the left surface  17  of the pillar  12 . For example, all the receivers  94 ,  95 , and  96  may be provided on the head  14 . For example, the receiver  94  may be provided on the rear side of the lower left end of the head  14 , the receiver  95  may be provided on the rear side of the lower right end of the head  14 , and the receiver  96  may be provided at substantially the center of the front side of the lower end of the head  14 . 
     The receivers  94  and  95  may be provided on the left and right sides of the presser bar  31  or the presser foot  30 , and the receiver  96  may be provided on the left surface  17  of the pillar  12 . The receiver  96  may be provided on the lower surface of the arm  13 . 
     The receivers  94  and  95  may be provided on the left and right sides of the presser bar  31  or the presser foot  30 , and the receiver  96  may be provided at substantially the center, in the left-right direction, of the front side of the lower end of the head  14 . 
     As explained above, the receivers  94 ,  95 , and  96  may be provided on any of the head  14 , the presser foot  30 , the presser bar  31 , the left surface  17  of the pillar  12  and the lower surface of the arm  13 . The combinations of the portions of the receivers  94 ,  95 , and  96  are not limited to those of the above-described fourth embodiment and the modified examples. 
     In a case where the embroidery unit  2  is attached to the sewing machine  1  and used, the receivers  94 ,  95 , and  96  may be provided on the carriage  52  (refer to  FIG. 8  to  FIG. 10 ). In this case, the receivers  94  and  95  may be respectively provided at the front end and the rear end of the top surface of the carriage  52 , and the receiver  96  may be provided at substantially the center, in the front-rear direction, of the top surface of the carriage  52 . The receivers  94  and  95  may be respectively provided at the front end and the rear end of the top surface of the carriage  52 , and the receiver  96  may be provided on the rear side of the lower right end of the head  14 . The receivers  94  and  95  may be respectively provided at the front end and the rear end of the top surface of the carriage  52 , and the receiver  96  may be provided on the left surface  17  of the pillar  12 . 
     Fifth Embodiment 
     A fifth embodiment will be explained. As shown in  FIG. 16 , a multi-needle sewing machine  3  (hereinafter referred to as a sewing machine  3 ) according to the fifth embodiment includes a plurality of needle bars. The sewing machine  3  is provided with receivers  131  and  132 . A configuration of the sewing machine  3  will be explained with reference to  FIG. 16  to  FIG. 18 . In the explanation below, it is defined that the upper side, the lower side, the left side, the right side, the near side, and the far side of  FIG. 16  are respectively defined as the upper side, the lower side, the left side, the right side, the front side, and the rear side of the sewing machine  3 . That is, the direction in which a pillar  103 , which will be described below, extends is the up-down direction of the sewing machine  3 . The direction in which an arm  104  extends is the front-rear direction of the sewing machine  3 . 
     As shown in  FIG. 16  and  FIG. 17 , a main body  120  of the sewing machine  3  includes a support portion  102 , the pillar  103 , and the arm  104 . The support portion  102  is formed in an inverted U shape in a plan view and supports the whole of the sewing machine  3 . A left and right pair of guide grooves  125  are provided on a top surface of the support portion  102 . The guide grooves  125  extend in the front-rear direction. The pillar  103  extends upward from the rear end of the support portion  102 . The arm  104  extends forward from the upper end of the pillar  103 . A needle bar case  121  is mounted on the leading end (the front end) of the arm  104  such that the needle bar case  121  can be moved in the left-right direction. Ten needle bars (not shown in the drawings) that extend in the up-down direction are provided inside the needle bar case  121  such that the needle bars are arranged at equal intervals in the left-right direction. One of the ten needle bars that is in a sewing position may be slidingly moved in the up-down direction by a needle bar drive mechanism (not shown in the drawings) that is provided inside the needle bar case  121 . A sewing needle  135  can be attached to and detached from the lower end of each of the needle bars. 
     An operation portion  106  is provided on the right side of a central portion, in the front-rear direction, of the arm  104 . The operation portion  106  includes a liquid crystal display (LCD)  107 , a touch panel  108 , and an operation switch  141 . The LCD  107  may display various types of information, such as an operation image that is used for the user to input a command, for example. The touch panel  108  is used to accept a command from the user. The user may perform an operation of pressing the touch panel  108  using a finger or a dedicated touch pen. Hereinafter, this operation is referred to as a “panel operation”. The touch panel  108  detects a position pressed by the finger, the dedicated touch pen, or the like, and the sewing machine  3  determines the item that corresponds to the detected position. In this manner, the sewing machine  3  recognizes the selected item. By the panel operation, the user can select or set a pattern to be sewn and various types of conditions, such as sewing conditions. The operation switch  141  is used to command the start or stop of the sewing. 
     A cylinder bed  110  is provided below the arm  104 . The cylinder bed  110  extends forward from the lower end of the pillar  103 . A shuttle (not shown in the drawings) is provided inside the leading end (the front end) of the cylinder bed  110 . The shuttle may house a bobbin (not shown in the drawings) around which a lower thread (not shown in the drawings) is wound. A shuttle mechanism (not shown in the drawings) is provided inside the cylinder bed  110 . The shuttle mechanism (not shown in the drawings) may drive the shuttle. A needle plate  116 , which has a rectangular shape in a plan view, is provided on a top surface of the cylinder bed  110 . A needle hole (not shown in the drawings), through which the sewing needle  135  may pass, is formed in the needle plate  116 . 
     A left and right pair of thread spool stands  112  are provided at the rear side of a top surface of the arm  104 . Ten thread spools (not shown in the drawings), the number of which is the same as the number of the needle bars, can be placed on the pair of thread spool stands  112 . A upper thread (not shown in the drawings) may be supplied from a thread spool placed on one of the thread spool stands  112 . The upper thread may be supplied to an eye (not shown in the drawings) of the sewing needle  135  that is attached to the lower end of each of the needle bars, via a thread guide  117 , a tensioner  118 , a thread take-up lever  119 , and the like. The ultrasonic pen  91  may be connected to the sewing machine  3  via the cable  912 , in the same manner as in the first embodiment. 
     An embroidery frame movement mechanism  111  (refer to  FIG. 18 ) is provided below the arm  104 . The embroidery frame movement mechanism  111  may detachably support an embroidery frame  184  (refer to  FIG. 18 ). Various types of embroidery frames can be used as the embroidery frame  184 . The embroidery frame  184  may hold the work cloth  100 . The embroidery frame movement mechanism  111  may be driven by an X axis motor (not shown in the drawings) and a Y axis motor (not shown in the drawings), and may move the embroidery frame  184  in the front-rear direction and in the left-right direction. 
     The embroidery frame movement mechanism  111  will be explained with reference to  FIG. 18 . The embroidery frame movement mechanism  111  includes a holder  124 , an X carriage  122 , an X axis drive mechanism (not shown in the drawings), a Y carriage  123 , and a Y axis movement mechanism (not shown in the drawings). The holder  124  may detachably support the embroidery frame  184 . The X carriage  122  is a plate member that is long in the left-right direction. A part of the X carriage  122  protrudes forward from the front face of the Y carriage  123 . The holder  124  is attached to the X carriage  122 . The X carriage  122  may move in the left-right direction (the X axis direction) using the X axis motor as a driving source. 
     The Y carriage  123  has a box shape that is long in the left-right direction. The Y carriage  123  supports the X carriage  122  such that the X carriage  122  can be moved in the left-right direction. The Y axis movement mechanism (not shown in the drawings) is provided with a left and right pair of moving members (not shown in the drawings). The moving members are coupled to lower portions of the left and right ends of the Y carriage  123 . The moving members pass through the guide grooves  125  (refer to  FIG. 16 ) in the up-down direction. The moving members may be moved in the front-rear direction (the Y axis direction) along the guide grooves  125 , using the Y axis motor as a driving source. The Y carriage  123  coupled to the moving members and the X carriage  122  supported by the Y carriage  123  may be moved in the front-rear direction (the Y axis direction) along with the movement of the moving members. In a state in which the embroidery frame  184  that holds the work cloth  100  is attached to the holder  124 , the work cloth  100  is arranged between one of the needle bars and the needle plate  116 . 
     As shown in  FIG. 16  to  FIG. 18 , the receiver  131  is provided at the left end of a top surface of the Y carriage  123 , and the receiver  132  is provided at the right end of the top surface of the Y carriage  123 . The receivers  131  and  132  are configured to receive an ultrasonic wave. The receivers  131  and  132  have the same configuration as the receiver  94 . The embroidery frame  184  attached to the folder  124  is located at the front of the Y carriage  123 . Therefore, the receivers  131  and  132  are located above the work cloth  100  held by the embroidery frame  184 . Openings provided in the receivers  131  and  132  are directed forward. 
     Processing that is performed by a CPU (not shown in the drawings) of the sewing machine  3  to identify the specified position will be briefly explained with reference to  FIG. 7 . In a case where the CPU detects an electrical signal output from the signal output circuit  914  of the ultrasonic pen  91  via the cable  912  (YES at step S 11 ), the CPU acquires the transmission timing T 1  (step S 13 ). In a case where the CPU detects the ultrasonic wave transmitted from the ultrasonic pen  91  via the receivers  131  and  132  (YES at step S 15 ), the CPU identifies a time at which the ultrasonic wave is detected by the receiver  131  and a time at which the ultrasonic wave is detected by the receiver  132 , and acquires the identified times as the detection timings T 2  (step S 17 ). The CPU calculates the specified coordinates E and identifies the specified position (steps S 21  to S 25 ), In a case where a panel operation is performed to start sewing (YES at step S 29 ), the CPU controls the X axis motor and the Y axis motor and thereby moves the embroidery frame  184  such that the position of the specified coordinates E on the work cloth  100  matches a needle drop point (step S 31 ). The CPU starts sewing on the work cloth  100 . The CPU drives the needle bar and the shuttle mechanism simultaneously with the embroidery frame being moved in the left-right direction (the X direction) and the front-rear direction (the Y direction). The sewing needle attached to the needle bar sews an embroidery pattern on the work cloth  100  held by the embroidery frame. In this manner, the embroidery pattern is sewn in the specified position on the work cloth  100  (step S 33 ). 
     The receivers  131  and  132  are provided on the Y carriage  123 . Therefore, the ultrasonic wave that is transmitted from the ultrasonic pen  91  when the pen tip  911  is in contact with the work cloth  100  is unlikely to be shielded by a hand or an arm of the user who uses the ultrasonic pen  91  (refer to condition (A)). The distance between the receivers  131  and  132  is separated by a length, in the left-right direction, of the Y carriage  123 . Therefore, the receivers  131  and  132  are sufficiently separated from each other (refer to condition (B)). The distances, in the X direction and the Y direction, from the needle hole (the origin) of the needle plate  116  to the receivers  131  and  132  are large (refer to condition (C)). The distances between the origin and the receivers  131  and  132  are not extremely large (refer to condition (D)). The receivers  131  and  132  are provided above the cylinder bed  110  (refer to condition (E)). 
     As described above, in the fifth embodiment, the sewing machine  3  is provided with the receivers  131  and  132 . The sewing machine  3  can identify the specified position by detecting the ultrasonic wave by each of the receivers  131  and  132 . The positions in which the receivers  131  and  132  are provided satisfy all the above-described conditions (A) to (E). Therefore, the sewing machine  3  can calculate the specified coordinates E more precisely and can perform sewing on the work cloth  100 . Further, the height from the cylinder bed  110  to the receivers  131  and  132  is sufficiently small. As a result, the influence caused by approximating the value Ze in Formulas (5) and (6) to zero may decrease. Therefore, the error of the calculated specified coordinates E may become small. 
     In the above-described fifth embodiment, the sewing machine  3  may be provided with the ultrasonic pen  92  that may output an electromagnetic wave signal, instead of the ultrasonic pen  91 . The receivers  131  and  132  may be provided in positions other than the Y carriage  123 . For example, the receivers  131  and  132  may be provided on a front surface of the pillar  103  and a lower surface of the arm  104 . 
     The sewing machine  3  may be provided with three receivers as in the fourth embodiment. The sewing machine  3  may identify the specified position based only on the detection timings. In this case, the receivers may be provided on any positions on the sewing machine  3 , without being limited to the Y carriage  123 . For example, the receivers may be provided on the front surface of the pillar  103  and the lower surface of the arm  104 . 
     Sixth Embodiment 
     The number of the receivers may be one. For example, it is assumed that the one receiver is the receiver  94  that is provided on the left lower end of the head  14 . Then, with respect to the coordinates B indicating the position of the receiver  94 , specified coordinates indicating the specified position specified by the ultrasonic pen  91  are referred to as coordinates F. At this time, the X coordinates of the coordinates B and the coordinates F are assumed to be the same. To simplify an explanation, Z coordinates are omitted in the following explanation. In other words, the coordinates B are assumed to be (Xb, Yb) and the coordinates F are assumed to be (Xb, Yf). In this case, it is possible to calculate a distance FB between the coordinates F and the coordinates B in the Y direction, based on the propagation time required for the ultrasonic wave transmitted from the ultrasonic pen  91  that is at the coordinates F of the specified position to reach the receiver  94 . The coordinates B are known values. Thus, with respect to the needle drop point that is the origin, the Y coordinate “Yf” of the coordinates F of the specified position can be calculated. 
     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.