Patent Publication Number: US-10767292-B2

Title: Sewing machine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of priority of Japanese Patent Application No. 2017-108915, filed on Jun. 1, 2017, the content of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a sewing machine that detects an amount of movement of fabric relative to the sewing machine. 
     BACKGROUND ART 
     A sewing machine has been known which maintains a constant stitch length, by determining the amount of movement of the fabric on a throat plate by an optical sensor fixedly mounted on a frame of a sewing machine, and by controlling the rotational speed of a sewing machine motor so that the stitch is performed with a fixed amount of movement, are known (see, for example, Japanese Patent Application No. 4724938). 
     However, in the sewing machine of the related art, as illustrated in  FIG. 7A , when a sewing needle  112  is positioned above the fabric, a sensor  121  can correctly detect the movement amount m of the fabric C. However, when the sewing needle  112  is stuck into the fabric C, since the movement of the fabric C is restricted, the sensor  121  cannot accurately detect the movement amount of the fabric. 
     In particular, when the sewing needle  112  passes through the bottom dead center and moves upward, as illustrated in  FIG. 7B , since the fabric C is pulled up together with the sewing needle  112 , a movement component mf is generated in the fabric C, and the sensor  121  further degrades the detection precision of the movement amount of the fabric. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a sewing machine that can detect the movement amount of a fabric for avoiding the influence of the stitch of the fabric. The sewing machine of the present invention has the following characteristics (1) to (4). 
     (1) A sewing machine comprising: 
     a movement amount detector which detects a movement amount of fabric; 
     a sewing machine motor serving as a rotary drive source of an upper shaft which applies vertical movement to a needle bar; 
     a shaft angle detector which detects a shaft angle of an output shaft of the upper shaft or the sewing machine motor; and 
     a controller which controls the sewing machine motor based on the detection of the movement amount detector and performs controls of maintaining a constant stitch length, wherein 
     the controller performs controls of maintaining the constant stitch length, by a movement amount of the fabric detected by the movement amount detector in a shaft angle section where a sewing needle is not stuck into a cloth, based on the detection by the shaft angle detector. 
     (2) The sewing machine according to (1), wherein the controller is able to set a range of a predetermined upper shaft angle as a non-detection section, among the shaft angle sections where the sewing needle is not stuck into the cloth, and performs controls of maintaining the constant stitch length, by the movement amount of the fabric detected by the movement amount detector in a section where the sewing needle is excluded from the non-detection section is not stuck into the cloth. 
     (3) The sewing machine according to (1), wherein free motion stitching is performed by manually moving the fabric with respect to a stitch position of the sewing machine. 
     (4) The sewing machine according to (2), wherein free motion stitching is performed by manually moving the fabric with respect to a stitch position of the sewing machine. 
     (5) The sewing machine according to (1), wherein the free motion stitching is performed by manually moving the sewing machine with respect to the fabric. 
     (6) The sewing machine according to (2), wherein the free motion stitching is performed by manually moving the sewing machine with respect to the fabric. 
     In the sewing machine having at least one of the above characteristics (1) to (6), since the controller performs controls of maintaining a constant stitch length based on the movement amount of the fabric detected in the shaft angle section when the sewing needle is not stuck into the cloth, it is possible to more precisely detect the movement amount of the fabric and to perform sewing, while more accurately maintaining the constant stitch length. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a sewing machine according to an embodiment of the present invention; 
         FIG. 2  is a block diagram illustrating a control system of the sewing machine; 
         FIG. 3  is an explanatory view illustrating a range of an upper shaft angle which is the detection section for obtaining the output of each sensor; 
         FIG. 4  is a flowchart illustrating the operation control at the time of sewing by the controller; 
         FIG. 5  is an explanatory view illustrating another example of the detection section; 
         FIG. 6  is an explanatory view illustrating further example of the detection section; and 
         FIG. 7A  illustrates the state of movement of the cloth when the sewing needle is not stuck into the cloth, and  FIG. 7B  is an explanatory view illustrating the state of movement of the cloth when the sewing needle is stuck into the cloth. 
     
    
    
     DETAILED DESCRIPTION 
     Outline of Embodiment of the Invention 
     Hereinafter, a sewing machine according to the present invention will be described with reference to the drawings.  FIG. 1  is a perspective view of the sewing machine  100 , and  FIG. 2  is a block diagram illustrating a control system of the sewing machine  100 . 
     The sewing machine  100  according to the present embodiment is a so-called free motion stitching machine in which a worker freely moves the cloth C as fabric held on a dedicated holding base by a manual operation, and sewing is performed, while relatively positioning the cloth C relative to the stitch position. 
     In the present embodiment, since the illustration of the holding base and the explanation of the structure thereof are the same as well-known holding bases, they will be omitted. 
     The sewing machine  100  includes a needle bar up-down moving mechanism for vertically moving the needle bar  13  for holding the sewing needle  12  at the lower end portion, a shuttle mechanism for catching needle thread passed through the sewing needle  12  and tangling with the needle thread, a thread take-up lever mechanism for pulling up the upper thread to form a nodule, a thread tensioner for applying a predetermined tension to the upper thread, a sewing machine frame  11  for storing or holding the thread tensioner, and a controller  90  as a control unit for controlling the operation of each portion. 
     Since the shuttle mechanism, the thread take-up lever mechanism and the thread tensioner are the same as well-known configurations in the sewing machine, a detailed explanation will be omitted. 
     The sewing machine frame  11  includes a sewing machine bed portion located at the lower portion of the sewing machine body, a standing portion standing from one end portion of the sewing machine bed portion, and a sewing machine arm portion extending from the standing portion in the same direction as the sewing machine bed portion. 
     In the following description, a direction along a longitudinal direction of the sewing machine bed portion  111  in a horizontal direction is defined as an X axis direction, a direction orthogonal to the X axis direction in the horizontal direction is defined as a Y axis direction, and a vertical direction orthogonal to the X axis direction and the Y axis direction is defined as a Z axis direction. 
     The needle bar up-down moving mechanism includes a sewing machine motor  30  serving as a driving source of the sewing operation, an upper shaft (not illustrated) which is rotationally driven by the sewing machine motor  30 , and a clutch mechanism (not illustrated) which converts the torque of the upper shaft into upper and lower reciprocating motions and applies to the needle bar  13 . 
     An output shaft of the sewing machine motor  30  is equipped with an encoder  31  as a shaft angle detector, and performs a pulse output according to the shaft angle change amount of the output shaft. 
     The transmission ratio from the output shaft of the sewing machine motor  30  to the upper shaft is known, and the controller  90  calculates the shaft angle of the output shaft of the sewing machine motor  30  from the pulse output of the encoder  31 , and can further calculate the shaft angle of the upper shaft from the transmission ratio. 
     Further, an encoder may be provided on the upper shaft to directly detect the shaft angle of the upper shaft. 
     Further, the sewing machine  100  is provided with an intermediate presser  14  which presses the cloth C so that it can smoothly escape from the cloth C when the sewing needle  12  rises. The intermediate presser  14  is supported by the lower end portion of the intermediate bar  141 . The intermediate presser  14  is formed as a small frame body capable of loosely inserting the sewing needle  12 , obtains power from a sewing machine motor  30  (see  FIG. 2 ) which is a drive source for vertically moving the needle bar  13  via a well-known transmission mechanism, and moves up and down with an amplitude smaller than that of the needle bar  13 . It should be noted that the intermediate presser  14  is out of phase with the needle bar  13 , and the intermediate presser  14  descends when the sewing needle  12  ascends. Further, the intermediate presser  14  is set so that a certain gap is formed between the throat plate  16  and at the bottom dead center position so as not to hinder the movement of the cloth C. 
     Further, as illustrated in  FIG. 2 , the sewing machine  100  includes a thread trimmer  43  for cutting thread at the time of completion of sewing. The thread trimmer  43  includes a movable knife capable of performing a reciprocating rotation so as to pass under an eye on the lower side of the throat plate  16 , a fixed knife for cutting the sewing the thread by cooperation with the moving knife (both are not illustrated), a thread trimming motor  431  for reciprocally rotating the moving knife, and a driving circuit  432  for driving the thread trimming motor  431  in accordance with a command from the controller  90 . 
     In the sewing machine bed portion  111 , on the both sides of the eye (not illustrated) of the throat plate  16  in the X axis direction, in the vicinity of the stitch position of the sewing machine  100  with respect to the cloth C manually fed, first and second sensors  21  and  22  serving as a movement amount detector for detecting the relative movement amount in the horizontal plane (X-Y plane) are provided, respectively. 
     These first and second sensors  21  and  22  are two-dimensional image sensors fixedly mounted in a state of being directed upward from the upper surface of the throat plate  16 . 
     Further, the first and second sensors  21  and  22  are arranged so that their optical axes are parallel to the Z axis direction and are symmetrical with respect to a plane including the center line of the needle bar  13 . 
     The resolution of these sensors  21  and  22  is 3 [μm]. In addition, the respective sensors  21  and  22  detect the lower surface of the cloth C on the throat plate  16  as needed, and input the detection data to the adjoining processer  23 . 
     The numerical values of the resolutions of the sensors  21  and  22  are merely examples and are not limited to the above numerical values. 
     The processer  23  attached to the first and second sensors  21  and  22  inputs the pulse signal to the controller  90  whenever a change of resolution of 3 [μm] is generated with respect to the movement amount of the cloth C, from continuous detection signals that are input from time to time from each of the sensors  21  and  22 . 
     It is to be noted that the processer  23  previously determines one of the first and second sensors  21  and  22  as the main and the other as the sub, inputs the pulse signal based on the detection of the main sensor to the controller  90 , and inputs a pulse signal based on the detection of the sub sensor to the controller  90  when an error occurs in the main sensor. 
     Control System of Sewing Machine 
     The sewing machine  100  includes the controller  90  that controls the operation of each component, and the sewing machine motor  30  and the encoder  31  thereof are connected to the controller  90  via a drive circuit  32 . 
     Further, the thread cutting motor  431  of the above-described thread trimmer  43  is connected to the controller  90  via a drive circuit  432 , and the first and second sensors  21  and  22  are connected via the processer  23 . 
     An operation panel  41  serving as an operation unit for an operator of the sewing machine to input an operation to the sewing machine, a start button  42  for starting sewing, and a pedal  44  for driving the sewing machine motor  30  are connected to the controller  90 , respectively via an interface (not illustrated). 
     From the operation panel  41 , for example, the stitch length which is a seam length for each stitch is set. Further, a display unit is provided on the operation panel  41 , and various kinds of information are displayed. 
     The controller  90  mainly includes a CPU  91  for controlling the sewing machine motor  30 , a RAM  92  serving as a work area of the CPU  91 , a ROM  93  for storing a program processed by the CPU  91 , and an EEPROM  94  as a storage unit in which data used for calculation processing is stored and which is configured to be capable of rewriting the data. 
     Operation Control When Sewing 
     Next, a sewing operation control performed by the controller  90  of the sewing machine  100  will be described. 
     As described above, in the sewing machine  100 , sewing is performed, while the sewing worker moves the cloth C arbitrarily with respect to the stitch position. 
     When the cloth C is arbitrarily moved by the hand of the sewing machine operator, the controller  90  controls the rotational speed of the sewing machine motor  30  such that the sewing is performed while maintaining the set stitch length set from the operation panel  41 . 
     That is, the controller  90  calculates the movement speed of the cloth C from the time interval (referred to as a pulse interval) of the pulse inputted based on the detection of the first or second sensors  21  and  22 , and further calculates the rotational speed of the sewing machine motor  30  for the upper shaft to make one rotation until the movement by the set stitch length at the movement speed is performed, and controls so as to achieve the rotational speed. The calculation of the rotational speed of the sewing machine motor  30  based on the detection by the first sensor  21  or the second sensor  22  is repeatedly executed at a minute time period 
     By the way, during the period from when the sewing needle  12  sticks the cloth C until it is completely removed, the movement of the cloth C is restrained by the sewing needle  12 , making it difficult to obtain the movement speed of the cloth C accurately. 
       FIG. 3  is an explanatory view illustrating the upper shaft angle until the descending the sewing needle  12  reaches the throat plate  16  and the sewing needle  12  rising while passing through the needle bar bottom dead center reaches the throat plate  16 , the upper shaft angle as the needle bar top dead center is 0° and the upper shaft angle as the needle bar bottom dead center is 180°. 
     As illustrated in the drawing, the upper shaft angle at which the descending sewing needle  12  reaches the throat plate  16  is 90°, and the upper shaft angle at which the sewing needle  12  rising through the needle bar bottom dead center reaches the throat plate  16  is 270°. 
     Therefore, the controller  90  avoids the shaft angle section (a non-detection section N) of the upper shaft angle of not less than 90° and not more than 270°, which makes it difficult to accurately obtain the movement speed of the cloth C, and determines the movement speed of the cloth C from the time interval of the pulse input from the processer  23  of the first sensor  21  or the second sensor  22  in a shaft angle section (a detection section S) of the upper shaft angle of more than 270° and less than 90°. 
     The “detection section” means an upper shaft angle section for controlling the rotational speed of the sewing machine motor  30  based on the detection by the first sensor  21  or the second sensor  22 , and the “non-detection section” means an upper shaft angle section that controls the rotational speed of the sewing machine motor  30  without being based on the detection of the first sensor  21  or the second sensor  22 . 
     In this case, the movement speed of the cloth C cannot be obtained during the non-detection section N of the upper shaft angle. Therefore, the controller  90  controls the rotational speed of the sewing machine motor  30 , regarding that the cloth C is moving at the movement speed of the cloth C in the non-detection section N and the movement speed obtained just before entering the non-detection section N. 
     It should be noted that the movement speed of the cloth C in the non-detection section N may not be the movement speed of the cloth C just before entering the non-detection section N, but other reasonable values may be adopted. For example, an average value of movement speeds of a plurality of cloth C calculated in the detection section S may be adopted. 
     Furthermore, the speed obtained by multiplying the movement speed of the cloth C just previously obtained or the movement speed of the averaged cloth C by a predetermined coefficient may be used as the movement speed of the cloth C in the non-detection section N, thereby controlling the rotational speed of the sewing machine motor  30 . 
       FIG. 4  is a flowchart illustrating processing executed by the CPU  91  of the controller  90  during sewing. Based on this, the process executed by the CPU  91  at the time of sewing will be described in detail. 
     Initially, the CPU  91  first detects a depression of the pedal  44  (step S 1 ). If it is not detected, the CPU  91  detects the depression of the pedal  44  again (step S 1 : NO). When detecting the depression of the pedal  44  (step S 1 : YES), driving of the sewing machine motor  30  is started (step S 3 ). 
     The CPU  91  determines from the output of the encoder  31  whether or not the upper shaft angle is within the detection section S (step S 5 ). When the upper shaft angle is within the detection section S (step S 5 : YES), the CPU  91  calculates the movement speed of the cloth C from the time intervals of the pulses of the first and second sensors  21  and  22  (step S 7 ), and calculates the rotational speed of the sewing machine motor  30  corresponding to the movement speed (step S 9 ). Further, the CPU  91  controls the sewing machine motor  30  so as to achieve the calculated rotational speed (step S 11 ). 
     Thereafter, the process proceeds to step S 15 . 
     On the other hand, when determining that the output of the encoder  31  is out of the detection section S (step S 5 : NO), the CPU  91  controls the sewing machine motor  30  so as to obtain the latest rotational speed calculated within the detection section S (step S 13 ). 
     Thereafter, the process proceeds to step S 15 . 
     In step S 15 , the depression of the pedal  44  is detected. When the depression of the pedal  44  is continued (step S 15 : NO), the process returns to step S 5  and whether or not the upper shaft angle is within the detection section S is determined again. 
     Further, when the depression of the pedal  44  is released (step S 15 : YES), the CPU  91  stops the sewing machine motor  30  and the operation control ends. 
     Technical Effect of Embodiment of the Invention 
     In the sewing machine  100 , based on the detection by the encoder  31  serving as the shaft angle detector, the controller  90  performs controls of maintaining the constant stitch length, by the movement amount of the cloth C detected by the first or second sensor  21 ,  22  as the movement amount detector in the detection section S which is the shaft angle section when the sewing needle  12  is not stuck into the cloth C. 
     For this reason, it is possible to control the sewing machine motor  30  by reducing the influence of the inaccurate movement amount of the cloth C detected in the non-detection section N which is the shaft angle section when the sewing needle  12  sticks the cloth C, and it is possible to perform sewing by more accurately maintaining the target stitch length. 
     Therefore, in the case of performing free motion stitching by manually moving the cloth C like the sewing machine  100 , it is possible to improve particularly the sewing quality. 
     Regarding the Range of Detection Section of Upper Shaft Angle 
     The setting of the detection section S is not limited to the section between 90° and 270° illustrated in  FIG. 3 , and may be a narrower range. In the present embodiment, the upper shaft angle range in which the sewing needle  12  is located below the throat plate  16  is defined as the section after the sewing needle  12  sticks the cloth C until the complete removal, but as illustrated in  FIG. 5 , for example, the range of the upper shaft angle where the sewing needle  12  is higher than the throat plate  16  may be set as the detection section S in consideration of the thickness of the cloth C. 
     In addition, the number of detection section S is not limited to one, and a plurality of detection section S may be set. For example, when the upper shaft angle at which the detection accuracy of the movement speed of the cloth C decreases is known, for example, theoretically or empirically, other than the range of the upper shaft angle in which the sewing needle  12  is sticking the cloth C, such a range of the upper shaft angle may be set as a new non-detection section, and a plurality of detection sections may be provided accordingly. 
     For example, when it is known that disturbance occurs in the detection movement speed of the cloth C around the top dead center of the sewing needle  12 , as illustrated in  FIG. 6 , the upper shaft angle at which the sewing needle  12  sticks the cloth C is set as the first non-detection section N 1 , and the periphery of the top dead center of the sewing needle  12  is set as the second non-detection section N 2 . The upper shaft angle between the first non-detection section N 1  and the second non-detection section N 2  may be set as the first detection section S 1  and the second detection section S 2 . 
     As a result, sewing can be performed while controlling the sewing machine motor  30  by reducing the influence of an incorrect movement amount of the cloth, and maintaining the target stitch length more accurately. 
     Further, the range of an arbitrary upper shaft angle may be set as the non-detection section within the range of the upper shaft angle at which the sewing needle  12  is not stuck into the cloth C by the setting means such as the operation panel  41 . Also, the number of detectors may be arbitrarily set. 
     Others 
     A case where the above-mentioned sewing machine  100  manually moves the cloth C relative to the sewing machine  100 , but it is needless to say that a sewing machine that performs free motion stitching by manually moving the sewing machine  100  with respect to the cloth C may be adopted.