NEEDLE PLATE CONSTRUCTION FOR SEWING MACHINE AND SEWING MACHINE

A needle plate has a needle hole and a guide hole communicating with the needle hole. The guide hole is located near a front side of a sewing machine and positionally deviated from an up-down movement trajectory of a sewing needle in a rotating direction of a rotary hook. The needle plate has a groove formed in front of the needle hole and extending from the guide hole in a direction opposite to the rotating direction of the rotary hook. While the groove is open upward and at its portion leading to the guide hole, the other portions of the groove are defined by a bottom surface and side walls. In a sewing operation, depending on a direction in which a member holding a sewing workpiece moves, the lower thread passes through the guide hole to be guided to the front of the needle hole via the groove.

TECHNICAL FIELD

The present invention relates to a needle plate construction for a sewing machine constructed to be able to avoid occurrence of a hitch stitch in forming stitches on a sewing workpiece and also relates to a sewing machine comprising the needle plate construction.

BACKGROUND

There have heretofore been known sewing machines which are provided with: a sewing mechanism that performs sewing on a sewing workpiece (such as a fabric workpiece) by moving vertically or up and down a sewing needle with an upper thread passed therethrough, and rotating a rotary hook, having a lower thread housed therein, in synchronism with the vertical or up-and-down movement of the sewing needle to thereby entwine the upper thread around the lower thread; and a feed mechanism that moves a frame (or holding member), having the sewing workpiece held thereon, relative to a needle drop position, to thereby form a stitch in a desired direction on the sewing workpiece. Such sewing machines can form stitches of various lengths in various directions by performing movement control of the sewing workpiece via the feed mechanism on a stitch-by-stitch basis.

It is known in the art that stitches formed by the sewing machines of the aforementioned type come in different quality, namely perfect stitch quality and hitch stitch quality. The perfect stitch is a stitch formed by entwining an upper thread and a lower thread with each other in a mutually balanced state, while the hitch stitch is a stitch formed by entwining an upper thread and a lower thread with each other in such a manner that only the upper thread draws a spiral shape. It is also known that whether the stitch is formed in the perfect stitch quality or in the hitch stitch quality depends mainly on two factors or causes. The first one of the two factors is behavior of the upper thread; more specifically, in this case, the perfect stitch or the hitch stitch is formed depending on in which of counterclockwise and clockwise directions the upper thread, extending through an eye hole of the sewing needle in a front-to-rear direction to connect to the fabric workpiece when the sewing needle with the upper thread passed therethrough pierces the fabric workpiece, is entwined around the sewing needle in accordance with a moving direction of the fabric workpiece (i.e., stitch forming direction) at the time of stitch formation. It is also known that the hitch stitch is formed by the upper thread being entwined around the sewing needle in the clockwise direction.

Note that throughout this description, the term “front” (“in front of”, “forward”, “front side”, and the like) and the term “rear” (“behind”, “rearward”, “rear side”, and the like) respectively refer to the front and rear (back) of the sewing machine as viewed from the front (or in front view) of the sewing machine, the term “left” and “right” respectively refer to the left and right of the sewing machine as viewed from the front (or in front view) of the sewing machine, and the term “leftward twining direction” and “rightward twining direction” respectively refer to counterclockwise and clockwise directions as viewed in top plan view of the sewing machine.

The second one of the two factors is behavior of the lower thread; more specifically, in this case, the perfect stitch or the hitch stitch is formed depending on a relationship between a path of the lower thread-extending from the rotary hook (lower thread bobbin), provided beneath a needle plate, and passing through a needle hole of the needle plate to connect to the working fabric located above the needle plate— and the needle drop position of the sewing needle. Namely, it is known that the hitch stitch is formed when the path of the lower thread is located to the right of an up-down movement trajectory of the sewing needle (needle drop position) in accordance with the moving direction of the fabric workpiece (stitch forming direction) at the time of stitch formation.

The hitch stitch is undesirable in that it not only looks unattractive as compared to the perfect stitch but also degrades sewing quality (involving, for example, a problem that the stitch easily gets loosened). Thus, there have been proposed a variety of approaches for avoiding occurrence of a hitch stitch. According to one example of such proposed approaches, a determination is made, per stitch to be formed, as to whether the moving direction of the fabric workpiece (i.e., stitch forming direction) is a perfect-stitch forming direction or a hitch-stitch forming (or occurring) direction, and upon determination that the moving direction of the fabric workpiece (stitch forming direction) is the hitch-stitch forming direction, the position of the upper thread or the lower thread relative to the needle drop position is changed by moving the frame or using a given operating piece.

Patent Literature 1 identified below discloses an invention constructed to avoid occurrence of a hitch stitch due to the behavior of the upper thread. According to the invention described in Patent Literature 1, upon determination that the moving direction of the frame holding the fabric workpiece (i.e., stitch forming direction) is a hitch-stitch forming direction in which a hitch stitch is undesirably formed due to the behavior of the upper thread, the frame is caused to detour leftward of the sewing needle and then move to a target needle drop position (target position) for stitch formation before the tip end of the descending sewing needle reaches the upper surface of the fabric workpiece, instead of the frame being moved directly to the target position. Namely, the invention described in Patent Literature 1 intends to avoid occurrence of a hitch stitch due to the behavior of the upper thread, by entwining the upper thread, connecting to the fabric workpiece, counterclockwise around the sewing needle. However, in order to quickly entwine the upper thread counterclockwise around the sewing needle by causing the frame to detour during the descending movement of the sewing needle, this invention requires an exact match between the time of the descending movement of the sewing needle and the time of the detouring movement of the frame. Thus, if there is any time mismatch between the descending movement of the sewing needle and the detouring movement of the frame, this prior art presents a problem of failing to entwine the upper thread around the sewing needle. Therefore, with the technique described in Patent Literature 1, it is difficult to reliably avoid occurrence of a hitch stitch.

Patent Literature 2 identified below discloses an invention constructed to avoid occurrence of a hitch stitch due to behavior of the lower thread. According to the invention described in Patent Literature 2, a recessed portion is formed behind the needle hole of the needle plate in communication with the needle hole, and upon determination that the moving direction of the frame holding the fabric workpiece (i.e., stitch forming direction) is a hitch-stitch forming direction in which a hitch stitch is undesirably formed due to the behavior of the lower thread, the frame is caused to detour along the shape of the recessed portion and then moved to a target needle drop position for stitch formation (target position), instead of the frame being moved directly to the target position. More specifically, the recessed portion has a distal end portion extending in a left-to-right direction. The frame is moved to detour such that the lower thread enters the distal end portion of the recessed portion from the left of the distal end portion to be engaged in the distal end portion, and that the path of the lower thread passes by the left of the needle drop position and is then stopped behind the needle drop position (i.e., such that the sewing needle drops at a position located to the right and in front of the path of the lower thread). Namely, the invention described in Patent Literature 2 intends to avoid occurrence of a hitch stitch due to the behavior of the lower thread by causing the sewing needle to drop at a position located to the right of the path of the lower thread extending upward to connect to the fabric workpiece. However, because the recessed portion formed behind the needle hole in communication with the needle hole has the distal end portion extending in the left-to-right direction, a protrusion (so-called “peninsular portion”) extending in a right-to-left direction is inevitably formed between the distal end portion and the needle hole. Due to the presence of such a protrusion, this prior art may present a problem of causing an unwanted breakage of the upper thread.

As also known in the art, an upper thread loop captured by a hook point of an outer rotary hook is caused to move while slipping between the outer rotary hook and an inner rotary hook and is then lifted up by a thread take-up lever to move upward along the lower thread while twining around the lower thread. With the construction described in Patent Literature 2, however, the upper thread loop moving upward along the lower thread may undesirably get caught on the protrusion (peninsular portion) adjoining the distal end portion of the recessed portion having the lower thread engaged therein, in which case the upper thread may be undesirably cut or broken. Further, because the lower thread is engaged by entering the distal end portion of the recessed portion, there may be encountered a problem that the lower thread remains engaged in the recessed portion depending on the stitching direction of the next stitch and thus takes a lower thread path different from the normal path.

Patent Literature 3 identified below, too, discloses an invention constructed to avoid occurrence of a hitch stitch due to behavior of the lower thread. According to the invention described in Patent Literature 3, a switch mechanism is provided for switching the path of the lower thread, leading to the needle hole of the needle plate after getting out of the rotary hook, between a left-side route for deviating the path to the left of the up-down movement trajectory of the sewing needle and a right-side route for deviating the path to the right of the up-down movement trajectory. Such lower thread path switching by the switch mechanism is performed through driving of an air cylinder. Upon determination that the moving direction of the frame holding the fabric workpiece (i.e., stitch forming direction) is a direction in which a hitch stitch is formed due to the behavior of the lower thread, the switch mechanism switches the path of the lower thread to either the left-side route or the right-side route before the tip end of the descending sewing needle reaches the upper surface of the fabric workpiece, thereby avoiding occurrence of a hitch stitch. However, the invention described in Patent Literature 3 presents a problem that the construction is complicated, because it is necessary to provide the air-cylinder-driven switch mechanism.

Further, Patent Literature 4 identified below discloses an invention constructed to avoid occurrence of hitch stitches due to behavior of the upper thread and the lower thread. The invention described in Patent Literature 4 includes upper thread control means (needle bar pivoting mechanism) that controls a relationship of the upper thread with the sewing needle and lower thread control means (thread drawing mechanism) that controls a relationship of the lower thread with the sewing needle. With such arrangements, this prior art avoids occurrence of hitch stitches by controlling the individual control means in accordance with the moving direction of the fabric workpiece. Because the needle bar pivoting mechanism as the upper thread control means and the thread drawing mechanism as the lower thread control means each have a complicated construction, this prior art presents a problem that the overall construction of the sewing machine is complicated. Furthermore, in a multi-needle sewing machine where one machine head has a plurality of needle bars, such a complicated construction becomes an even more serious problem.

Furthermore, Patent Literature 5 identified below discloses a sewing machine capable of sewing by individually turning a machine head and a rotary hook housing section. This prior art sewing machine is constructed to achieve enhanced sewing quality by appropriately synchronizing the respective operations of the sewing needle and the rotary hook and respective turning of the machine head and rotary hook housing section. However, this sewing machine presents a problem that the construction is complicated because it has to include a mechanism for turning the machine head and the rotary hook housing section and means for synchronizing the respective operations of these components. The construction described in Patent Literature 5 may be suited for linearly sewing in a given direction, such as sewing running stitches; however, with the construction described in Patent Literature 5, synchronization control is very difficult to perform in the case of embroideries, such as a satin stitch embroidery, where the stitching direction may be reversed, because the turning directions of the machine head and the rotary hook housing section have to be reversed stitch by stitch and the stitching direction, too, changes.

PRIOR ART LITERATURE

Patent Literature

SUMMARY

In view of the foregoing prior art problems, it is one of the objects of the present invention to provide a needle plate construction for a sewing machine that is configured to be able to avoid occurrence of a hitch stitch and to provide a sewing machine having such a needle plate construction.

According to a first aspect, the present invention provides a needle plate construction suited for avoiding occurrence of a hitch stitch due to behavior of a lower thread. To accomplish this object, the present invention provides the needle plate construction for the sewing machine, which includes a needle plate having a needle hole for passage therethrough of a sewing needle moving up and down, and is characterized in that the needle plate has a guide hole provided near a front surface of the sewing machine and in communication with the needle hole, the guide hole being located at a position deviated from an up-and-down movement trajectory of the sewing needle substantially in the rotating direction of a rotary hook of the sewing machine, and that the needle plate has a groove portion provided in front of the needle hole and extending from the guide hole in a direction opposite to the rotating direction of the rotary hook, the groove portion opening upward and at a part thereof leading to the guide hole and having a bottom surface and a side wall, wherein a lower thread having moved out of the rotary hook to extend upward is guided to a front of the needle hole through the guide hole via the groove portion.

To be more specific, the rotating direction of the rotary hook is a rotating direction of an outer rotary hook in which a loop of the upper thread is captured (hooked) by a hook point of the rotating outer rotary hook within the rotary hook. Because the rotating direction of the rotary hook is usually the counterclockwise direction, a moving direction of the hook point of the outer rotary hook at the time of capturing the upper thread loop is counterclockwise; such a counterclockwise moving direction of the kook point can be said to be leftward as viewed from the front of the sewing machine. In such a case, the guide hole is located deviated leftward from the up-and-down movement trajectory of the sewing needle (i.e., deviated from the up-and-down movement trajectory substantially in the rotating direction of the rotary hook) and the groove portion extends, in front of the needle hole, rightward from the guide hole (i.e., extends from the guide hole in the direction opposite to the rotating direction of the rotary hook).

As known in the art, in the sewing machine, a holding member (i.e., sewing frame or embroidery frame) for holding a sewing workpiece is disposed above the needle plate and caused to move in a desired direction stitch by stitch to thereby cause a stitch to be formed on the sewing workpiece in the desired direction. As also known in the art, the sewing machine performs sewing on the sewing workpiece by moving up and down the sewing needle with an upper thread passed therethrough and rotating the rotary hook, disposed below the needle plate and having the lower thread housed therein, in synchronism with the up-and-down movement of the sewing needle to thereby entwine the upper thread around the lower thread. In this state, the lower thread, having moved out of the rotary hook to extend upward, is connected to the sewing workpiece with having passed through an opening (namely, the needle hole) of the needle plate. Therefore, the lower thread, having been connected to the sewing workpiece above the rotary hook with having moved out thereof, is also moved by following the movement of the holding member (namely, the sewing workpiece) for forming the stitch. In accordance with a moving direction of the lower thread, a path of the lower thread relative to a trajectory of the up-and-down movement (i.e., the up-and-down movement trajectory) of the sewing needle varies too.

Depending on a moving direction of the sewing workpiece at the time of stitch formation (stitch forming direction), double hitch stitches may occur in some area due to the behavior of the lower thread. Such double hitch stitches are caused by a path of the lower thread, extending from the rotary hook toward the needle hole of the needle plate, being located behind a trajectory of the up-and-down movement (i.e., the up-and-down movement trajectory) of the sewing needle, while the sewing needle drops with the upper thread entwined around the sewing needle in the counterclockwise direction. In view of this point, the needle plate construction according to the present invention is constructed such that it is possible for the path of the lower thread extending from the rotary hook toward the needle hole of the needle plate not to be behind the up-and-down movement trajectory of the sewing needle. Namely, there is provided not only the needle hole but also the guide hole communicating with the needle hole and further provided the groove portion communicating with guide hole. The guide hole is provided near the front surface of the sewing machine and located at a position deviated from the up-and-down movement trajectory of the sewing needle substantially in the rotating direction of the rotary hook (leftward direction), and the groove portion is provided in front of the needle hole and extending from the guide hole in the direction (rightward direction) opposite to the rotating direction of the rotary hook. With this construction, the lower thread causes to pass through the guide hole so that it is possible to guide the lower thread from the guide hole to the front of needle hole via the groove portion. In this way, it is possible to avoid occurrence of double hitch stitches due to the behavior of the lower thread, by structurally forcing the path of the lower thread, extending from the rotary hook toward the needle hole of the needle plate, to be located in front of the up-and-down movement trajectory of the sewing needle.

Further, because the groove portion has the bottom surface, the upper thread loop, moving upward along the lower thread, can be prevented from getting caught in the groove portion, and thus can be prevented from being cut or broken. Furthermore, because the lower thread is merely received or engaged by the side walls of the groove portion, the lower thread easily comes free or disengage from the groove portion to get back to a normal path as being pulled up in accordance with the upper thread ascending, so that no bad influence is given to the lower thread path at the time of next stitch formation.

According to a second aspect of the present invention, there is provided a sewing machine which includes, in addition to the aforementioned arrangements according to the first aspect, a construction for avoiding occurrence of a hitch stitch due to behavior of the upper thread and thus can avoid occurrence of any types of hitch stitches and can form perfect stitches over an entire range of stitching directions. Namely, according to the second aspect of the present invention, there is provided a sewing machine which can form stitches as perfect stitches over the entire range of stitching directions, namely can achieve “all-perfect-stitch” sewing.

A sewing machine according to a second aspect of the present invention includes: the needle plate construction aforementioned; a sewing mechanism that performs sewing on a sewing workpiece by moving up and down the sewing needle with the upper thread passed therethrough and rotating the rotary hook, disposed below the needle plate and having a lower thread housed therein, in synchronism with the up-and-down movement of the sewing needle to thereby entwine the upper thread around the lower thread; and a feed mechanism that displaces a holding member, having the sewing workpiece held thereon, relative to a needle drop position, to thereby form a stitch in a desired direction on the sewing workpiece. Further, in one embodiment of the present invention, the sewing machine may include; determination means that determines whether or not a next-stitch forming direction belongs to a predetermined area in which a hitch stitch is undesirably formed; and detour control means that, upon determination that the next-stitch forming direction belongs to the predetermined area, moves the holding member via the feed mechanism so as to cause the holding member to detour in a direction corresponding to perfect stitch quality and then move to a target position corresponding to the next stitch.

By such a detouring movement of the holding member via the detour control means, the inventive sewing machine can avoid occurrence of the hitch stitch due to the behavior of the upper thread. In a preferred embodiment of the present invention, as the detour control means moves the holding member, the lower thread moved by following the holding member may be guided into the guide hole of the needle plate, then guided from the guide hole to a front of the needle hole via the groove portion, and then kept located on one of the side walls of the groove portion near the needle hole, whereby the lower thread is prevented from shifting rearward of the up-and-down movement trajectory of the sewing needle. Thus, the inventive sewing machine can avoid occurrence of the double hitch stitches, due to the behavior of the upper thread and the behavior of the lower thread.

Another embodiment of the sewing machine according to the second aspect of the present invention includes a rotary hook as set forth below as a component for avoiding occurrence of a hitch stitch due to the behavior of the lower thread. As well known, the rotary hook of the sewing machine includes a bobbin case rotatably housing a lower thread bobbin having the lower thread wound thereon, an inner rotary hook housing the bobbin case, and an outer rotary hook that rotates around the inner rotary hook in synchronism with the up-and-down movement of the sewing needle, and the inner rotary hook has a needle drop hole formed in an upper front surface portion thereof. The rotary hook disclosed in the present application has a recessed portion formed in the upper front surface portion and at a position deviated from the needle drop hole substantially in the rotating direction of the outer rotary hook, and the recessed portion opens forward and upward and downward and has a rear wall surface. The bobbin case has a thread take-up member provided thereon for directing the lower thread, paid out from the lower thread bobbin, toward the recessed portion of the inner rotary hook, and the lower thread paid out from the lower thread bobbin within the bobbin case is pulled out upward after passing through a hollow space of the recessed portion by way of the thread take-up lever.

With such arrangements, the path of the lower thread, extending from the rotary hook to connect to the sewing workpiece above after passing through the needle hole of the needle plate, is caused to be located to the left of the up-and-down movement trajectory of the sewing needle (needle drop position) after passing through the recessed portion of the rotary hook. Namely, the lower thread paid out from the lower thread bobbin is directed, by the thread take-up member, to the recessed portion of the inner rotary hook and then directed to the needle hole of the needle plate after passing through the recessed portion. Because the recessed portion is formed at the position deviated from the needle drop position substantially in the rotating direction of the outer rotary hook (i.e., at a position to the left of the up-and-down movement trajectory of the sewing needle), the path of the lower thread, extending from the rotary hook toward the needle hole, is located to the left of the up-and-down movement trajectory of the sewing needle. In this manner, it is possible to prevent the path of the lower thread, extending from the rotary hook toward the needle hole, from being located to the right of the up-and-down movement trajectory of the sewing needle and thus reduce occurrence of a hitch stitch.

DETAILED DESCRIPTION

<Area in Which Hitch Stitch Formation Occurs>

First, with reference toFIG.1, a description will be given about a typical example of areas of stitch forming (or occurring) directions in which hitch stitches are formed (or occur).FIG.1is a diagram illustrating relationships between various stitch forming directions and quality of stitches (perfect stitch and hitch stitch) formed in accordance with the stitch forming directions. Note that the relationships between the stitch forming directions and the quality of stitches formed in accordance with the stitch forming directions vary depending on an orientation and type of a rotary hook, andFIG.1illustrates the above-mentioned relationships for a full-rotation vertical rotary hook (so-called “DB type” rotary hook) that is commonly employed in an embroidery sewing machine. Further, it is assumed here that passage of an upper thread through an eye hole of a sewing needle is done by causing the upper thread, paid out downward from an upper thread bobbin, to enter the eye hole from the front side of the sewing needle and then pass backward or rearward through the eye hole to connect to a sewing workpiece (fabric workpiece) as commonly known in the art. The upper thread and a lower thread are entwined with each other as well known, through cooperation between the sewing needle moving up and down and the rotary hook making a full rotation in a counterclockwise direction, so that a stitch is formed on the sewing workpiece (fabric workpiece).

A base point C located at the center of the diagram represents a current needle drop position (i.e., a position of a needle hole of a needle plate in a sewing machine). Several arrows extending from the base point C denote examples of stitching directions from the base point C to next needle drop positions (i.e., next-stitch forming directions). As well known in the art, a stitching direction of each stitch can be set as desired within an angle range of 360°; typically, the stitching direction of each stitch depends on a sewing pattern. For convenience, inFIG.1, the direction of arrow P denotes 0°, and angles from 0° to less than 360° are calibrated in a counterclockwise direction from 0°. Let it be assumed that in the following description, when an area in a particular stitching direction (next-stitch forming direction) is to be identified by an angle, the angle calibration illustrated inFIG.1is followed. InFIG.1, let it be assumed that arrows P and P′ respectively represent leftward and rightward directions of the sewing machine, and, for convenience, the direction represented by arrow P is a positive direction along the X axis (X+) while the direction represented by arrow P′ is a negative direction along the X axis (X−). Directions of the Y axis perpendicularly intersecting the X axis at the base point C represent forward and rearward directions of the sewing machine; the rearward direction that is a direction toward the rear (back) of the sewing machine is a positive direction along the Y axis (Y+), while the forward direction that is a direction toward the front of the machine is a negative direction along the Y axis (Y−). As well known in the art, a moving direction of a holding member (frame) holding a sewing workpiece (fabric workpiece) and a direction of a stitch formed in accordance with the movement of the holding member (frame) are exactly opposite to each other. For example, when a stitch is to be formed in the arrow P direction (0° direction), the holding member (frame) is moved in the arrow P′ direction (180° direction) that is exactly opposite to the arrow P direction.

Further, inFIG.1, pictures of sewing needles, each surrounded by a circle, are illustrated in overlapping relations to the aforementioned arrows. Each of such sewing needle pictures schematically illustrates, together with a picture of the needle hole, a typical example of relationships of upper and lower threads with the sewing needle when a stitch is to be formed in the direction of the corresponding arrow, to help reader's understanding. Note that in each of the sewing needle pictures, the sewing needle in the middle of its descending movement immediately before entry in the needle hole is illustrated, but illustration of the sewing workpiece (fabric workpiece) is omitted for convenience sake.

An entire range of the stitching directions can be divided into several areas α to δ according to quality of stitches that are formed in accordance with the stitching directions. The area α is an area to which the stitching directions in which perfect stitches are formed (i.e., perfect-stitch forming directions) belong, and which covers approximately from about 270° to) 360° (0° and to about 85°. As indicated in the sewing needle pictures depicted in overlapping relations to the arrows in this area α, the sewing needle drops with the upper thread, passing from the eye hole of the sewing needle to the fabric workpiece in response to the movement of the holding member (frame), located to the left of the sewing needle, and thus, stitches formed in this area are the perfect stitches. The areas β to δ other than the area α depicted as a blank or white area inFIG.1are areas to which the stitching directions in which hitch stitches are formed (hitch-stitch forming directions) belong. The hatched area β is an area to which the stitching directions in which hitch stitches are formed due to the behavior of the upper thread belong and which covers approximately from about 85° to about 180°. As indicated in the sewing needle picture depicted in an overlapping relation to the arrow in this area β, the sewing needle drops with the upper thread, passing from the eye hole of the sewing needle to the fabric workpiece in response to the movement of the holding member (frame), located to the right of the sewing needle, and thus, stitches formed in this area are the hitch stitches. The dotted area γ is an area to which the stitching directions in which hitch stitches are formed due to the behavior of both of the upper and lower threads belong and which covers approximately from about 180° to about 210°. The checkered area δ is an area to which the stitching directions in which hitch stitches are formed due to the behavior of the lower thread belong and which covers approximately from about 210° to about 270°. As indicated in the sewing needle picture depicted in an overlapping relation to the arrow in this area δ, the sewing needle drops with the lower thread, passing from the rotary hook to the fabric workpiece in response to the movement of the holding member (frame), located to the right of the sewing needle, and thus, stitches formed in this area are the hitch stitches.

<Fundamental Construction of Sewing Machine>

Now, with reference toFIGS.2to4, a description will be given below about a fundamental construction of a sewing machine to which the present invention is applicable. However, such a fundamental construction itself is well known in the art, and any other desired construction than the illustrated example can be applied to the present invention.FIG.2is a front view of a sewing machine according to one embodiment of the present invention, which, as an example, illustrates the embodiment applied to a multi-head, multi-needle type embroidery sewing machine. A machine frame1is disposed above a table2, and a plurality of machine heads H are disposed on the machine frame1along the length of the machine frame1. Rotary hook bases4, each supporting a respective rotary hook3, are disposed below the machine heads H in corresponding relations to the individual machine heads H. Further, a holding member5for holding a sewing workpiece, such as a fabric, in an extended state is placed on the upper surface of the table2. The holding member5is controllably moved in X-axis and Y-axis directions (i.e., front-rear and left-right directions) via a feed mechanism (not illustrated in the drawings) provided below the table2. The holding member5is one commonly known as an embroidery frame, a fabric-workpiece holding frame, or the like, and the holding member5will hereinafter be referred to as “frame5”. An operation panel6for operating the sewing machine and making various settings is provided to the right of the machine frame1. The operation panel6is, for example, in the form of a touch panel and includes a display section for displaying various information and an input section via which various instructions are given. Note that the above-mentioned feed mechanism operates to displace the frame5, holding the sewing workpiece, relative to a needle drop position and thereby cause a stitch to be formed on the sewing workpiece in a desired direction. Such a feed mechanism itself is well known in the art and thus will not be described in detail here.

FIG.3is a front view of one of the machine heads H, andFIG.4is a side view of the machine head H. A needle bar case8is supported on the front surface of a machine arm7, mounted on the front surface of the machine frame1, in such a manner that the needle bar case8is slidable in the left-right direction along the machine arm7. A plurality of needle bars9are supported in the needle bar case8in such a manner that the bars9are movable up and down, and thread take-up levers10corresponding to the individual needle bars9are pivotably provided in the needle bar case8. Each of the needle bars9is disposed in such a manner that its axis extends in the up-down direction (vertical direction), a sewing needle11is mounted at the lower end of each of the needle bars9. Note that an upper thread T is passed rearward through an eye hole11aof the sewing needle11from the front side of the eye hole11a(seeFIGS.5,20and the like). A slide shaft12extends through the needle bar case8in such a manner that the needle bar case8is slidingly moved in the left-right direction by sliding the slide shaft12laterally via a not-illustrated motor. In response to the sliding movement of the needle bar case8, any one of the plurality of needle bars is selectively positioned at an operating position; in this manner, one needle bar9that should be caused to operate is selected.

A machine shaft13is passed through the machine arm7, and as the main shaft13is rotated via a not-illustrated main shaft motor, a needle bar driving member15is moved up and down along a base shaft16via a not-illustrated cam mechanism, a link14, and the like provided within the machine arm7. The needle bar driving member15is constructed to engage with a locking pin17aof a needle bar connecting stud17fixed to a predetermined position of the needle bar9, and the needle bar driving member15is switchable between a catch position for catching the needle bar9and a non-catch position. In the catch position, the needle bar driving member15engages with the locking pin17aof the needle bar connecting stud17as illustrated inFIG.4. In the non-catch position, the needle bar driving member15is released from the engagement with the locking pin17aof the needle bar connecting stud17, so that the needle bar9is held at an upper position (top dead point) by resilient return force of a tension spring18provided on an upper portion of the needle bar9. When a sewing operation is to be performed by actually moving up and down the needle bar9(and the sewing needle11), the needle bar driving member15is constantly set in the catch position. Control for temporarily stopping the needle bar9(and the sewing needle11) at the top dead point during the sewing operation is commonly known as jump control. When such jump control is to be performed, the needle bar driving member15is temporarily set in the non-catch position. To perform such jump control, a conventionally known jump mechanism is provided in the machine head H. Namely, such a jump mechanism is a mechanism that, when the jump control is to be performed during the sewing operation, holds the sewing needle11at the upper position without causing the sewing needle11to descend or move down. As an example, the jump mechanism includes a jump motor (not illustrated) provided on the arm7, a driving member (not illustrated) that sets the needle bar driving member15in the non-catch position by, in response to driving by the jump motor, pivoting the needle bar driving member15about the base shaft16through a predetermined angle, the abovementioned tension spring18, and the like.

The needle bar9selected to be positioned at the operating position is moved up and down, in response to ascending and descending movement of the needle bar driving member15, while being caught by the needle bar driving member15. In the course of the up-down movement of the needle bar9positioned at the operating position, the sewing needle11mounted at the distal end of the needle bar9is passed through a needle hole19aof a needle plate (or throat plate)19, so that the sewing operation is performed in the well-known manner. Once the above-mentioned jump mechanism is actuated by being driven by the jump motor (not illustrated), the needle bar driving member15is set in the non-catch position in such a manner that the needle bar9is shifted to a jumped state and held at the top dead point as noted above without being caught by the needle bar driving member15.

A lifting rod20is provided, behind a respective one of the needle bars9, in the needle bar case8in such a manner that the rod20is movable up and down. The lifting rod20has an axis extending in the up-down direction (vertical direction) similarly to the needle bar9, and a presser foot device21is provided at the lower end of each of the lifting rods20. Such a presser foot device21functions to press and hold down the sewing workpiece in place from above in response to the descending movement of the sewing needle11, and the presser foot device21includes a pressing member22and a guide member23as will be set forth in detail later. The pressing member22is mounted to the lower end of the lifting rod20, and the guide member23is mounted to the lower end of the pressing member22. One of the lifting rods20that corresponds to the needle bar9selectively set at the operating position is driven by a fabric pressing motor24provided on the machine frame7, and a link mechanism25is connected to the fabric pressing motor24. As the fabric pressing motor24is reciprocatively rotated, a fabric pressing driving member provided on the machine frame7is moved up and down via the link mechanism25. The fabric pressing driving member26is constructed to engage with a locking pin27aof a lifting rod connecting stud27fixed to a predetermined position of the lifting rod20. The locking pin27aof one of the lifting rods20, provided in the needle bar case8, that corresponds to the needle bar9selectively set at the operating position engages with the fabric pressing driving member26, and thus, the lifting rod20is moved up and down in its axial direction, together with the presser foot device21(the pressing member22and the guide member23), in response to the ascending/descending movement of the fabric pressing driving member26. When the needle bar is to be jumped by the above-mentioned jump mechanism, the fabric pressing motor24is de-actuated in such a manner that the presser foot device21(the pressing member22and the guide member23) is stopped at the predetermined upper portion (top dead point).

A combination of the machine head H and the rotary hook3corresponding to the machine head H constitutes a sewing mechanism that moves up and down the sewing needle11with an upper thread passed therethrough and rotates the rotary hook3, having a lower thread housed therein, in synchronism with the up-and-down movement of the sewing needle11to thereby entwine the upper thread around the lower thread for performing sewing on the sewing workpiece.

<Construction of Presser Foot Device>

FIG.5is an enlarged front view of an embodiment of the presser foot device21. A mounting member28is provided at the lower end of the lifting rod20, and the pressing member22of the presser foot device21is detachably mounted on the mounting member28by use of a screw. A lower end portion of the pressing member22extends downward to a position immediately below the needle bar9and has a through-hole22afor passage therethrough of the sewing needle11. Thus, when the pressing member22descends, in response to the descending movement of the needle bar9, to hold down the sewing workpiece in place from above, the sewing needle11descends further to pass through the through-hole22aand pierce the sewing workpiece, so that sewing is performed on the sewing workpiece. The aforementioned construction of the presser foot device21is similar to the construction of the well-known fabric presser foot device. The presser foot device21provided in the present embodiment is characterized in that the guide member projecting downward is provided at the lower end of the pressing member22. Note that the constituent components22,23and the like of the presser foot device21may be formed of a suitable material, such as metal.

The guide member23, which is of a substantially cylindrical shape, has a hollow portion (opening extending in the vertical direction) communicating with the through-hole22aof the pressing member22in such a manner that the sewing needle11having passed through the through-hole22acan pass through the hollow portion of the guide member23vertically or in the up-down direction. The guide member23is not of a complete cylindrical shape and has an opening section (recessed section)29that opens to the lower end of the guide member23and extends over an area from a position opposed to the front left of the sewing needle11, passing through the opening section29, to a position opposed to the left side surface of the sewing needle11, as viewed in front view (see alsoFIG.8). Of course, the opening section (recessed section)29is in communication with the hollow portion of the guide member23in such a manner that a portion of the upper thread, having been passed through the eye hole11aof the sewing needle11passing through the hollow portion, (i.e., a portion of the upper thread connecting to the sewing workpiece) can move out of the guide member23via the opening section29depending on in which direction the frame5is moved. Because the counterclockwise rotating direction of the rotary hook3is, in other words, a generally leftward direction as viewed in top plan view, it may be said that the opening section29formed generally to the left of the sewing needle11as viewed in front view is formed to allow or enable the upper thread to pass therethrough substantially in the rotating direction of the rotary hook3. Because the presser foot device21is constructed to enable the upper thread to move out of the guide member23via the opening section29, the upper thread can be entwined around the sewing needle11in the counterclockwise direction (i.e., in the rotating direction of the rotary hook3) in accordance with any one of the moving directions of the frame5which vary over a wide range as will be set forth in detail later.

In the guide member23, the front edge and rear edge of the opening section29formed generally to the left of the sewing needle11correspond respectively to front and rear edge portions23aand23bof the guide member23. Namely, the opening section29is demarcated by the above-mentioned front and rear edges, and when the upper thread takes a detour to move in another direction after having moved out the opening of the guide member23, such detouring movement of the upper thread is restricted by the front or rear edge portion23aor23bof the guide member23. Such a restricting action by the front edge portion23aplays an important role to avoid occurrence of a hitch stitch due to the behavior of the upper thread. Therefore, a wall portion of the guide member23extending forward from the front edge (i.e., front edge portion23a) of the opening section29will hereinafter be referred to as “restricting section23a”. In the present embodiment, the movement of the upper thread in a direction away from the front edge of the opening section29, formed generally to the left of the sewing needle11, which is to be restricted by the restricting section23a, namely by the front edge portion23a, is generally rightward movement. Stated differently, the upper thread's movement to be restricted by the restricting section23ais movement in a direction opposite to the rotating direction (counterclockwise direction) of the rotary hook3. Therefore, it may be said that the restricting section23aof the guide member23is provided in such a manner as to restrict the movement of the upper thread in the direction opposite to the rotating direction of the rotary hook3.

As noted above, the opening section29is provided to open to the lower end of the guide member23. Thus, the restricting section23adefining the front edge of the opening section is provided in such a manner as to restrict the movement of the upper thread, passing through the opening section29, in the direction opposite to the rotating direction of the rotary hook3until the upper thread reaches the lower end of the guide member23. Thus, the upper thread in the state of being restricted by the restricting section23ais caused to move along the restricting section23ato the lower end of the guide member23in response to the descending of the sewing needle11. Then, by passing downward through the opening section29, the upper thread is released from the restriction by the restricting section23a. Once the upper thread is released from the restriction by the restricting section23a, the upper thread twines around the sewing needle11in the counterclockwise direction (i.e., in the rotating direction of the rotary hook3). As an example, the restricting section23aof the guide member23is provided to extend over a suitable area extending forward from the front edge of the opening section29. As will be described in detail later, the restricting section23aof the guide member23is provided for preventing the upper thread from being located to the right of the sewing needle11(in other words, for causing the upper thread to twine around the sewing needle11in the counterclockwise direction) when the sewing needle11pierces the sewing workpiece, in order to avoid occurrence of a hitch stitch due to the behavior of the upper thread. InFIG.5, reference character V denotes a vertical or up-and-down movement trajectory of the sewing needle11. Note that for the purpose of preventing the upper thread from being located to the right of the sewing needle11when the sewing needle11pierces the sewing workpiece, the restricting section (front edge portion)23aof the guide member23or at least the lower end of the restricting section23a(that abuts against the sewing workpiece) is located to the left of the up-and-down movement trajectory V of the sewing needle11. Namely, the restricting section23ais provided so as to restrict the movement of the upper thread at a position deviated from the movement trajectory V of the sewing needle11substantially in the rotating direction of the rotary hook3(or deviated leftward of the trajectory V).

In the embodiment illustrated inFIG.5(orFIG.8), the front edge of the opening section29, namely the restricting section (front edge portion)23aof the guide member23, has a shape recessed obliquely from an upper part of the member23toward a left lower end of the member23. Because of such a slantingly recessed shape, an upper or central open area of the opening section is somewhat wider in the forward direction than a lower open area of the opening section29. Thus, when some slackness has occurred in a portion of the upper thread restricted by the restricting section23aafter moving out of the opening section29during the descending movement of the sewing needle11and the pressing member22, the slackness can be absorbed by the wider open area of the opening section29; thus, appropriate holding of the upper thread by the restricting section23acan be maintained as long as possible, so that it is possible to prevent as effectively as possible the upper thread from undesirably coming off the restricting section23abefore the sewing needle11pierces the sewing workpiece. However, such slanting of the restricting section is not necessarily essential, and the front edge of the opening section29, namely the restricting section (front edge portion)23aof the guide member23, may be formed to extend in the vertical direction.

Note that the guide member23may be of any suitable outer shape without being limited to the substantially cylindrical shape as described above.FIG.6illustrates a modification of the guide member23, of which (a) is a bottom perspective view, (b) is a top plan view, and (c) is a front view. The guide member23-1illustrated inFIG.6has two side wall surfaces interconnected at a suitable angle (for example, about) 90°, and a hollow space defined by these side surfaces and an adjoining hollow space function as a hollow space for allowing passage therethrough of the sewing needle11(this space corresponds to the above-mentioned hollow portion) and as a hollow space of the opening section29for allowing passage therethrough of the upper thread substantially in the rotating direction of the rotary hook3. The front side wall surface of the two side wall surface of the guide member23-1functions as the restricting section23a.

FIG.7illustrates another modification of the guide member23, of which (a) is a bottom perspective view, (b) is a top plan view, and (c) is a front view. The guide member23-2illustrated inFIG.7has three side wall surfaces interconnected at a suitable angle (for example, about) 90°, and a hollow space defined by the three side wall surfaces and an adjoining hollow space function as a hollow space for allowing passage therethrough of the sewing needle11(this space corresponds to the above-mentioned hollow portion) and a hollow space of the opening section29for allowing passage therethrough of the upper thread substantially in the rotating direction of the rotary hook3. The front side wall surface of the three side wall surfaces of the guide member23-2functions as the restricting section23a.

Whereas the guide members23illustrated inFIGS.5to7each have the front side wall surface and the front edge portion of the front side wall surface functions as the restricting section23a, the present invention is not so limited, and the restricting section23amay be in the form of a pin-shaped or line-shaped thin pole member having no side wall surface. For example, two such thin pole members may be provided in such a manner as to form a hollow space as the opening section29between the two pole members, and one of the pole members located in front of the other pole member may be made to function as the restricting section23a. In such a case, an arc-shaped connecting foot portion may be provided opposite to the opening section29so as to interconnect the respective lower ends of the two thin pole members. As still another modification, one or more other thin pole members may be provided to be surrounded by the arc-shaped connecting foot portion. As yet another modification, the guide member23may be in the form of only one thin pole member functioning as the restricting section23a.

FIG.8is a perspective view illustrating another modification of the presser foot device21, in which a cover30is provided beneath the pressing member22for covering the guide member23. The presser foot device21illustrated inFIG.8is constructed in the same manner as the presser foot device21illustrated inFIG.5except for elements pertaining to the cover30. The cover30has a bottom portion with a smoothly rounded, downwardly convex curved bottom surface (bowl-like bottom surface), and a through-hole of a relatively large diameter is formed in the bottom portion in such a manner as to loosely receive therein the guide member23. The cover30is also recessed in an upper inner surface portion thereof for fitting engagement with the pressing member22. By attaching the cover30to the guide member23from below and fastening the cover30to the guide member23by a screw, the cover30is assembled and fixed to the pressing member22so as to cover the outer peripheral surface of the guide member23. Because the guide member23is loosely received in the cover30with some gap therebetween, the aforementioned function of the guide member23is never impaired. Because a lower end portion of the guide member23is surrounded by the convexly convex curved (bowl-like) bottom surface of the cover30, it is possible to prevent the guide member23from undesirably catching on a stitch on the moving sewing workpiece, even if, for example, an up-and-down stroke of the presser foot device21is reduced in order to prevent fluttering of the sewing workpiece.

In the present embodiment, a novel construction is employed, in relation to the needle hole19aof the needle plate19, for avoiding occurrence of a hitch stitch due to the behavior of the lower thread.FIG.9is a sectional perspective view illustrating an embodiment of such a novel needle plate construction.FIG.10illustrates at an enlarged scale the needle hole19aand portions around the needle hole19a, of which (a) is a top plan view, (b) is a perspective view illustrating a section taken along line A-A of (a), and (c) is a fragmentary perspective view illustrating a path of the lower thread D. As in the conventionally known construction, the needle hole19ais a substantially simple circular hole as illustratively denoted with a dotted line inFIG.10(a). The vertical or up- and -down movement trajectory (denoted by V inFIG.5) of the sewing needle11passes through a substantial center of the circle.

In the needle plate construction according to the present embodiment, a guide hole31and a groove portion32are provided in the needle plate19in relation to the needle hole19a. The guide hole31formed through the needle plate19is located near the front of the sewing machine and is in communication with the needle hole19a. Further, the guide hole31is located at a position deviated from the up-and-down movement trajectory of the sewing needle11substantially in the rotating direction of the rotary hook3(i.e., deviated leftward from the up-and-down movement trajectory inFIG.10(a)). Further, the groove portion32of the needle plate19is located in front of the needle hole19aand extends from the guide hole31in a direction opposite to the rotating direction of the rotary hook3(i.e., extends rightward from the guide hole31inFIG.10(a)). While the groove portion32opens upward and opens laterally at its part communicating with the guide hole31, the remaining part of the groove portion32is defined by a bottom surface32and side walls32b(FIG.10(b)). As well known, during the sewing operation, the lower thread D having moved out of the rotary hook3passes through the needle hole19ato extend upward and thereby forms a stitch on the sewing workpiece. The needle plate19in the embodiment is constructed in such a manner that the lower thread D having moved out of the rotary hook3passes through not only the needle hole19abut also the guide hole31communicating with the needle hole19a. When the lower thread D passes through the guide hole31, a portion of the lower thread D having moved upward from the guide hole31can be guided via the groove portion32to a position located in front of the needle hole19aas illustrated inFIG.10(c), depending on a moving direction of the frame5. Because the groove portion32has the bottom surface32a, an upper portion of the lower thread D is bent upward and guided to an upper hollow space of the groove portion32via the bottom surface32awith a lower portion of the lower thread D remaining in the guide hole31.

Further, the guide hole31is located deviated from the up-and-down movement trajectory of the sewing needle11substantially in the rotating direction of the rotary hook3(i.e., deviated leftward from the up-and-down movement trajectory) and the groove portion32extends, in front of the needle hole19a, from the guide hole31in the direction opposite to the rotating direction of the rotary hook3(i.e., extends rightward from the guide hole31), as noted above. Thus, as the frame5is moved generally leftward by later-described detouring movement control (or detour control) of the frame5, the lower thread D is guided into the guide hole31. Then, as the frame5is moved generally rightward to the needle drop position (target position), the lower thread D is guided from the guide hole31generally rightward along the groove portion32. Because both side surfaces of the groove portion32are defined by the side walls32b, the lower thread D is received or engaged by a rear side surface of the side walls32b(namely, rear side wall32b) and kept in front of the up-and-down movement trajectory of the sewing needle11without shifting rearward of the up-and-down movement trajectory of the sewing needle11. Because the path of the lower thread D extending from the rotary hook3toward the needle hole19aof the needle plate19is kept in front of the up-and-down movement trajectory of the sewing needle11without shifting rearward of the up-and-down movement trajectory of the sewing needle11in the aforementioned manner, it is possible to avoid occurrence of a hitch stitch (particularly, double hitch stitches). Further, because the groove portion32has the bottom surface32a, a loop of the upper thread (upper thread loop), passing through the needle hole19ato go upward along the lower thread D while reducing the size of the loop, can be prevented from undesirably getting caught in the groove portion32, and thus, it is possible to avoid occurrence of breakage of the upper thread. Furthermore, because the lower thread D is merely received or engaged by the rear side wall32b, the lower thread D can readily separate from, or is readily separated or disengaged from, the groove portion32to return to a normal path (i.e., a path passing through the needle hole19a) as the lower thread D is pulled up in response to the upward movement of the upper thread, and thus, formation of the path of the lower thread D at the time of next stitch formation will not be adversely influenced.

In a portion where the guide hole31connects to the needle hole19a, as illustrated by way of example in the top plan view ofFIG.10(a), a rear side wall surface31aof the guide hole31slants from its rear end portion forward substantially in the rotating direction of the rotary hook3(i.e., slants in a diagonally forward left direction). Namely, this wall surface31aslants in the diagonally forward left direction from its rear end in such a manner that the rearmost end of the surface31ais located nearest to the up-and-down movement trajectory of the sewing needle11and the frontmost end of the surface31ais located to the left of and farthest from the up-and-down movement trajectory of the sewing needle11. When the path of the lower thread D is to be shifted from the needle hole19ato the guide hole31at the time of the detouring movement control of the frame5, the slanting of the wall surface31ain the connecting portion effectively contributes to a smooth shift of the lower thread path from the needle hole19ato the guide hole31. However, the present invention is not so limited, and the configuration of the connecting portion may be designed in any other desired suitable manner.

In the present embodiment, a novel construction is provided, in relation to the rotary hook3, for avoiding occurrence of a hitch stitch due to the behavior of the lower thread.FIG.11is a front view illustrating an embodiment of such a novel construction of the rotary hook, andFIG.12is a top plan view of the novel construction of the rotary hook.FIG.13(a)andFIG.13(b)are respectively a left side view and a right side view of the novel construction of the rotary hook. As well known in the art, the rotary hook3is disposed beneath the needle plate19. As an example, the rotary hook3is a full-rotation vertical rotary hook (“DB type” rotary hook). The rotary hook includes a bobbin case40that rotatably houses a lower thread bobbin (not illustrated) having a lower thread wound thereon, an inner rotary hook50that houses the bobbin case40, and an outer rotary hook60that rotates around the inner rotary hook50in synchronism with the up-and-down movement of the sewing needle11. As known in the art, the inner rotary hook50is fixed to a rotary hook base4via a rotary hook support70, and the bobbin case40is fixed within the inner rotary hook50. The outer rotary hook60is fixed to a lower shaft (not illustrated) that rotates in synchronism with the up-and-down movement of the sewing needle11, and thus, the outer rotary hook60rotates together with the lower shaft. In the full-rotation vertical rotary hook (“DB type” rotary hook), a rotating direction R of the outer rotary hook60is counterclockwise. In an upper front surface portion of the inner rotary hook50, a needle drop hole51is provided to avoid interference with the sewing needle11.

Further, in an upper front surface portion of the inner rotary hook50, a recessed portion is formed at a position deviated from the needle drop hole51in the rotating direction R of the outer rotary hook60. The recessed portion52opens forward and upward and downward and has a rear wall surface52athat is formed to be located at a substantial limit position where the rear wall surface52adoes not interfere with a movement trajectory of a hook point61of the outer rotary hook60. Because the rear wall surface52aof the recessed portion52is located at the substantial limit position as noted above, the lower thread path leading from the recessed portion52to the sewing workpiece (i.e., changing positions of the lower thread from the recessed portion52toward the needle hole19a) can be set as far rearward as possible of the needle drop position (up-and-down movement trajectory of the sewing needle), and thus, a range over which occurrence of a hitch stitch due to the behavior of the lower thread can be avoided can be expanded as much as possible. Left and right side wall surfaces of the recessed portion52are respectively surfaces of an upstream side wall52blocated upstream in the rotating direction R of the outer rotary hook60and a downstream side wall52clocated downstream in the rotating direction R of the outer rotary hook60.

On a predetermined position of the bobbin case40near the upper end of the bobbin case40(preferably, beneath the recessed portion52), a thread take-up member41is provided for directing (guiding) the lower thread, paid out from the lower thread bobbin, toward the recessed portion52of the inner rotary hook50. As will be described in detail later, the lower thread, paid out from the lower thread bobbin within the bobbin case40, is pulled upward after passing through a hollow space of the recessed portion52of the inner rotary hook50via the thread take-up member41. The lower thread having passed through the recessed portion52is entwined with the upper thread loop in response to the rotation of the outer rotary hook60as conventionally known and then moved upward through the needle hole19ain response to the ascending movement of the sewing needle11, thereby forming a stitch. In the aforementioned manner, the recessed portion52formed in the inner rotary hook50functions to form the path of the lower thread.

With the above-described rotary hook construction, the path of the lower thread leading from the rotary hook3to the sewing workpiece, located above the rotary hook3, through the needle hole19aof the needle plate19is caused to be located to the left of the up-and-down movement trajectory of the sewing needle11(needle drop position) after passing through the recessed portion52provided in the upper front surface portion of the inner rotary hook50. Namely, the lower thread paid out from the lower thread bobbin is directed by the thread take-up member41to the recessed portion52of the inner rotary hook50and then directed to the needle hole19aof the needle plate19after passing through the recessed portion52. Because the recessed portion52is formed at the position deviated from the needle drop hole51in the rotating direction R of the outer rotary hook60(i.e., located to the left of the up-and-down movement trajectory of the sewing needle11) and the rear wall surface52aof the recessed portion52is formed at the substantial limit position where the rear wall surface52adoes not interfere with the movement trajectory of the hook point61of the outer rotary hook60as noted above, the path of the lower thread leading from the rotary hook3toward the needle hole19ais located to the rear left of the up-and-down movement trajectory of the sewing needle11. In this way, it is possible to prevent the path of the lower thread, leading from the rotary hook3toward the needle hole19a, from being located to the right of the up-and-down movement trajectory of the sewing needle11and thereby reduce occurrence of hitch stitches.

A further description will be given about the aforementioned arrangements with reference toFIG.1. In the area δ to which the stitching directions in which hitch stitches are formed due to the behavior of the lower thread belong, the frame5is moved in a rearward right direction that is 180° opposite to the stitching direction. Thus, in a conventionally known rotary hook of a type where the lower thread is fed from below the up-and-down movement trajectory of the sewing needle, the sewing needle drops with the path of the lower thread located to the right of the up-and-down movement trajectory of the sewing needle by the lower thread being pulled by a sewing workpiece, which undesirably results in occurrence of a hitch stitch. By contrast, in the present embodiment, when the frame5is moved in the rearward right direction for stitching in the area δ, the lower thread extending from the rotary hook3toward the needle hole19aabuts against the rear wall surface52aof the recessed portion52, and rightward movement of the lower thread is restricted by the upstream side wall52b. Because the lower thread having moved out of the rotary hook3is directed to move to the needle hole19aby way of the left of the up-and-down movement trajectory of the sewing needle11, the needle drops to a position located to the right of the lower thread, and thus, it is possible to reduce occurrence of a hitch stitch.

For example, in a case where the stitching direction belongs to the area δ ofFIG.1and the frame5is moved in a direction of about 70°, the path of the lower thread can be reliably caused to be located to the left of the needle drop position (the up-and-down movement trajectory of the sewing needle11). Thus, in this case, even if the position of the rear wall surface52aof the recessed portion52is shallower than, namely located somewhat in front of, the above-mentioned substantial limit position, occurrence of a hitch stitch can be avoided. On the other hand, in a case where the frame5is moved, for example, in a direction of about 40° and if the position of the rear wall surface52aof the recessed portion52is shallower than the above-mentioned substantial limit position, the path of the lower thread is located to the right, rather than to the left, of the needle drop position (the up-and-down movement trajectory of the sewing needle11) by way of the front of the movement trajectory, and thus, occurrence of a hitch stitch cannot be avoided. However, by setting the position of the rear wall surface52aof the recessed portion52at the above-mentioned substantial limit position, the path of the lower thread can be caused to be located to the left of the needle drop position (the up-and-down movement trajectory of the sewing needle11) in such a manner as to avoid occurrence of a hitch stitch, even in the case where the frame5is moved, for example, in the direction of about 40°. Namely, by setting the position of the rear wall surface52amore rearward, it is possible to expand the area in which occurrence of a hitch stitch can be avoided by the construction of the rotary hook employed in the present embodiment. Further, by positioning the rear wall surface52aat the above-mentioned substantial limit position, it is possible to maximize the area for which detour control (detouring movement control) of the frame is not required.

Preferably, a construction for locking the lower thread at the time of thread cutting may be provided on the downstream side wall52cof the recessed portion52. As illustrated inFIG.12, the downstream side wall52cprojects forward more than the upstream side wall52band has a projecting part52dformed at its front end. A thread cutting device (not illustrated) is provided above the rotary hook3as known in the art. When a thread cutting operation is to be performed by the thread cutting device, a portion of the lower thread extending from the rotary hook toward the needle hole19ais captured and guided leftward to a cutting position where the portion of the lower thread is cut by the cutting device. When the lower thread is moved leftward for such a thread cutting operation as noted above, the lower thread abuts against the downstream side wall52cin such a manner that it is movable in the front-rear direction along the downstream side wall52cas appropriate. If the front edge of the downstream side wall52cis in the same plane as the front surface of the side wall, the lower thread may undesirably easily come off the front edge of the downstream side wall52c. In such a case, the lower thread reaches the thread cutting device after having moved a shorter distance from the rotary hook3; if the lower thread is cut by the cutting device in such a state, the length of the lower thread remaining after the cutting becomes shorter, and some problem or inconvenience may occur in a next operation. In order to avoid such an inconvenience, the above-mentioned projecting part52dis provided at the front end of the downstream side wall52cin such a manner as to somewhat project beyond the front surface of the side wall52c. Thus, when the lower thread abutting against the downstream side wall52cmoves forward during the thread cutting operation, the lower thread is engaged by the projecting part52dand thus is prevented from coming off the front edge of the downstream side wall52c. With such arrangements, it is possible to ensure or secure a necessary and sufficient remaining length of the lower thread after the cutting operation and prevent a problem or inconvenience from occurring in the next operation.

Next, a description will be given about examples of further improvements of the inner rotary hook50and the outer rotary hook60. As known in the art, the outer rotary hook60has, on its outer periphery, the hook point61for capturing a loop of the upper thread pulled out of the eye hole11aof the sewing needle11. Further, a thread dividing spring (i.e., upper spring part)62is fixed to the outer peripheral surface of the outer rotary hook60by use of a screw. A distal end portion62aof the thread dividing spring62is formed in a claw shape for guiding the upper thread loop captured by the hook point61. Further, a front end edge (i.e., front side edge)62bof the thread dividing spring62is formed to be located behind the rear wall surface52aof the recessed portion52in the inner rotary hook50, as illustrated inFIG.13(b). In other words, the front end edge62bof the thread dividing spring62is formed so as not to project forward beyond the front side edge (i.e., side edge located in front of the movement trajectory) of the hook point61of the outer rotary hook60.

The conventionally known thread dividing spring is shaped to have a projecting portion (fin portion) which extends in the rotating direction of the outer rotary hook and whose front edge end projects forward for pushing forward the upper thread loop captured in response to the rotation of the outer rotary hook. With the front edge end of the thread dividing spring projecting forward like this, the lower thread, directed from the rotary hook toward the needle hole, is also pushed forward, and thus, slackness may occur in the lower thread.

By contrast, in the present embodiment, no such projecting portion (fin portion) is formed on the front end edge62bof the thread dividing spring62, therefore, the thread dividing spring62does not contact the lower thread guided by the recessed portion52and thus slackness does not occur in the lower thread. Namely, in the present embodiment, the thread dividing spring does not push forward the upper thread loop, and thus, the thread dividing spring62is referred to more generically as “upper spring part”.

Instead of providing a projecting (fin) portion on the front end edge62bof the thread dividing spring (upper spring part)62, the inner rotary hook50in the present embodiment has an improved construction as described hereinbelow. As illustrated inFIG.11,FIG.13(a), and the like, a raised portion53protruding forward is formed on a front outer peripheral surface of the inner rotary hook50over a range of about one-quarter arcuate angle (i.e.,) 90°, particularly over a range less than one-quarter arcuate angle (i.e.,) 90°, and more particularly, as in the illustrated example, over a range of about 80° from the recessed portion52downstream in the rotating direction of the rotary hook. More specifically, the raised portion53, which has a generally mountain-like sectional shape, has a guide surface53aslanting forward in such a manner that the slanting angle gradually increases in a downstream-to-upstream direction of the rotation of the rotary hook, and that a protruding height of the raised portion53gets smaller in an upstream-to-downstream direction of the rotation of the rotary hook. Such a protruding portion53functions to push forward the upper thread loop captured by the hook point61of the outer rotary hook60. As the outer rotary hook60rotates, the upper thread loop is pushed forward while moving upward from below the raised portion53(in a rear-to-front direction)) and passes around the inner rotary hook50while moving along the front surface of the bobbin case40. In this manner, the raised portion53of the inner rotary hook50can be caused to function as a substitute for the fin portion of the conventionally known thread dividing spring.

As denoted by two-dot chain lines inFIGS.11and12, the rotary hook support70fixed to the rotary hook base4has a projection71that is fittable in the recessed portion52of the inner rotary hook52. The inner rotary hook50is fixed to the rotary hook base4with the projection71fitted in the recessed portion52in such a manner that the inner rotary hook50is prevented from rotating together with the outer rotary hook60. Further, with the projection71fitted in the recessed portion52, a suitable hollow space is formed between the rear wall surface52aof the recessed portion52and the distal end of the projection71, and the lower thread guided to the recessed portion52passes through this hollow space to move on to the needle hole19a.

Further, a description will be given about an example of the bobbin case40with reference toFIG.14. Note that the lower thread bobbin housed within the bobbin case40is not illustrated inFIG.14. As illustrated inFIG.14(a), a body42of the bobbin case40has an opening42aformed in its upper front surface portion for avoiding interference with the sewing needle11having dropped to the needle drop position. In a central part (central outer peripheral surface portion) of the bobbin case body42, a pull-out hole42bis formed for pulling out the lower thread from the lower thread bobbin housed within the bobbin case. Further, on the outer peripheral surface portion of the bobbin case body42, a thread tension spring43is mounted for imparting constant tension to the lower thread. Furthermore, a guide groove42cfor regulating a passing position of the lower thread is formed above the pull-out hole42b. An upper portion of the central part of the bobbin case body42is also open, and this upper opening of the central part of the bobbin case body42is in communication with the above-mentioned opening42a.

The thread take-up member41is provided on an upper front surface portion of the bobbin case40, and more specifically, the thread take-up member41is located at a position beneath the opening42aand deviated a little to the left of the bobbin case40. As a preferred example, the thread take-up member41is in the form of a spring so as to impart tension to the lower thread paid out from the lower thread bobbin and directed toward the hollow space of the recessed portion52. For this reason, the thread take-up member41will hereinafter be referred to also as “thread take-up spring”. The thread take-up spring (thread take-up member)41has a ring portion41aof an annular or curved shape for passing therethrough (or catching) the lower thread paid out from the lower thread bobbin, and the lower thread passed through the ring portion41ais directed toward the hollow space of the recessed portion52of the inner rotary hook50. The tension imparted by the thread take-up spring41functions to not only appropriately guide the lower thread, which is on its way to the needle hole19a, to pass through the recessed portion52(i.e., regulates the path of the lower thread so as to pass through the recessed portion52) but also absorb slackness occurring in the lower thread. The thread take-up spring41, which extends generally horizontally on and along the front surface of the bobbin case40, is fixed at one end (right end), opposite from the above-mentioned ring portion41a, to the bobbin case40, and the ring portion41aconstitutes a free end of the thread take-up spring41. The ring portion41ais located substantially immediately below the recessed portion52of the inner rotary hook50and is swingable in the up-down and left-right directions by resilient restoring force of the spring in response to movement of the lower thread passed through the ring portion41a. In one implementation, a length from the fixed end (right end) of the thread take-up spring41to the other end adjoining the ring portion41a(left end) is relatively long as illustrated in the figures. Thus, a swing range (stroke range) of the thread take-up spring41can be made relatively large, so that relatively large slackness of the lower thread can be absorbed. The thread take-up member41constituted by a spring member as set forth above can not only function to reliably guide the lower thread toward the recessed portion52of the inner rotary hook50but also function to prevent slackness of the lower thread under various conditions by imparting tension to the lower thread.

The lower thread pulled out of the pull-out hole42bof the bobbin case40abuts against the thread tension spring43, passes through the guide groove42c, passes through the ring portion41aof the thread take-up lever41to move upward, then passes through the recessed portion52of the inner rotary hook50, and then moves out of the rotary hook toward the needle hole19a. However, the present invention is not so limited, and the lower thread pulled out of the pull-out hole42bof the bobbin case40may be passed through the ring portion41aof the thread take-up spring by way of the thread tension spring43without being passed through the guide groove42c.

As an option, a guide member44may be provided in the bobbin case40in front of the thread take-up spring (thread take-up member)41as shown inFIG.14(b). The guide member is removably mounted by a screw to an upper front left surface portion of the bobbin case body42. The guide member44has a guide surface44aprotruding forward from its mounted position, and this guide surface44ais formed to connect generally continuously to the front surface of the bobbin case40(i.e., extend in the substantially same plane as the front surface of the bobbin case40). By the provision of such a guide member44, the upper thread loop, moving to the front surface of the bobbin case40and then moving upward along the front surface as the rotary hook3rotates, can be guided smoothly along the front surface of the bobbin case40.

Further, the guide member44has an opening44bformed in the guide surface44aso as to extend through the guide member44in the front-rear direction in such a manner as to enable a distal end of a picker of a well-known construction (not illustrated) to be inserted therein. The well-known picker is a member that, at the time of cutting of the upper thread by a thread cutting device (not illustrated), holds a portion of the upper thread on the sewing needle and thereby ensures a predetermined remaining length of the upper thread so as to prevent the upper thread from slipping out of the eye hole of the sewing needle. The well-known picker has a pair of left and right distal end portions, and at the time of the thread cutting operation, the two distal end portions are inserted into the opening42aof the bobbin case40to catch and hold the upper thread, passing through the rotary hook3, and thereby ensure a predetermined (after-cutting) remaining length of the upper thread, so that the upper thread can be prevented from slipping out of the eye hole of the sewing needle. Such a picker can be applied to the present embodiment, too. In the picker (not illustrated) to be applied to the present embodiment, one of the picker's distal end portions must be formed into a length somewhat shorter than that of the conventionally known picker in order to prevent interference to the thread take-up spring41. The guide surface44aand the opening44bof the guide member44provide a construction suited for such a special picker. Namely, with the picker set at a predetermined position in the present embodiment, the shorter distal end portion (the left distal end portion) of the picker enters the opening44bin the guide surface44aof the guide member44but does not abut against the thread take-up spring41. Thus, when the upper thread loop moves upward along the guide surface44aof the guide member44protruding forward of the thread take-up spring41, the upper thread loop is reliably caught on the two distal end portions (i.e., caught on the shorter distal end portion as well) of the picker; in this way, it is possible to ensure a predetermined remaining length of the upper thread and thereby prevent the upper thread from slipping out of the eye hole11aof the sewing needle11. Note that such a guide member44is not necessarily essential and may be dispensed with if the sewing machine is of a type that does not include a picker.

In the present embodiment, in order to avoid occurrence of a hitch stitch due to the behavior of the upper thread, not only the guide member23is provided in the presser foot device21as set forth above, but also detour control of the frame5(frame detour control) is performed. This frame detour control is performed by an electric/electronic control system.FIG.15is a block diagram illustrating an example of a control system (i.e., control device or controller) of the inventive sewing machine. As known, this control system includes: a CPU (Central Processing Unit)102that controls various processing and driving operations of the sewing machine; a RAM (Random Access Memory)102that is a working area of the CPU101; and a storage device103(ROM or Read-Only Memory and/or a readable/writable memory, such as a flash memory or a hard disk) that has prestored therein in a non-volatile manner pre-programmed embroidery data (sewing data) of one or more patterns, program control data related to such embroidery data (sewing data), and various processing programs and data. The control system further includes: a driver104for the main shaft motor for rotating the main shaft13; drivers105and106for X-axis and Y-axis motors for respectively moving the frame5in X-axis and Y-axis directions; a driver107for the jump motor for jumping the needle bar9; and a driver108for the fabric pressing motor24for moving the presser foot device21up and down. The individual drivers are connected to the respective motors. The control system further includes an input/output interface109including the above-mentioned operation panel6. The operation panel6is in the form of a touch panel for displaying images and receiving user's input operations as noted above, and various setting and controlling screens are displayed on the touch panel. A user of the sewing machine can perform various operations and make various settings by, for example, touching images and the like displayed on the screen of the touch panel. Further, the control system may include a communication interface (not illustrated) for communication with external devices and/or internal or external communication networks.

As known in the art, the sewing data of a desired pattern selected by the user are read out from the storage device103under the control of the CPU101and the drivers104to108and the like are controlled in accordance with the stitch-by-stitch sewing data, so that a sewing operation is performed to form stitches in a sequential manner. On the basis of the sewing data, a determination can be made as to whether or not a direction in which a next stitch is to be formed, namely a next-stitch forming direction, belongs to any one of the predetermined hitch-stitch forming (occurring areas) (for example, areas β to δ illustrated inFIG.1). This determination can be made by the CPU101executing a predetermined program. Namely, the CPU101and the predetermined program function as determination means that determines, on the basis of the sewing data read out from the storage device103, whether or not a direction in which a next stitch is to be formed, namely a next-stitch forming direction, belongs to any one of the predetermined hitch-stitch forming areas.

In the present embodiment, upon determination that the next-stitch forming direction belongs to any one of the predetermined hitch-stitch forming areas, detour control for moving the frame5in a detouring manner is performed when the frame5is to be moved to a target position corresponding to the next stitch, in order to avoid occurrence of a hitch stitch due to the behavior of the upper thread. Such detour control can be performed by a given program executed by the CPU101. Namely, the CPU101and the given program function as means (i.e., detour control means) that, upon determination by the determination means that the next stitch forming direction belongs to any one of the predetermined hitch-stitch forming areas, performs the jump control via the jump mechanism (driver107and the like) and performs the detour control of the frame5by activating the aforementioned feed mechanism (drivers105,106and the like) to perform detouring movement of the frame5. Here, the detouring movement of the frame5includes moving, with the sewing needle11jumped upward to a predetermined upper position, the frame5in a particular direction such that the upper thread extending downward from the sewing needle11moves out of the opening section29of the guide member23of the presser foot device21and then further moving the frame5to the target position corresponding to the next stitch in such a manner that the upper thread, having moved out of the opening section29, abuts against the restricting section23a. Such movement of the frame5that causes the upper thread, having moved out of the opening section29, to abut against the restricting section23aof the guide member23is nothing but detouring movement of the upper thread where the upper thread, having moved out of the opening section29, takes such a detour as to go by way of the restricting section23a. Namely, the detouring movement is such movement where, with the sewing needle11jumped upward, the frame5is temporarily moved in such a direction as to cause the upper thread to move out of the opening section29, then caused to take a detour such that the upper thread, having moved out of the opening section29, abuts against (i.e., goes by way of) the restricting section23aand finally moved to reach the target position corresponding to the next stitch, instead of the frame5being moved directly to the target position corresponding to the next stitch.

As illustrated as the typical example inFIG.1, the areas to which the stitching directions in which hitch stitches are formed (occur) due to the behavior of the upper thread belong are the areas β and γ. Of the area β, a partial area around 90° (i.e., an area in which the stitching directions are toward the rear of the sewing machine) is an area in which occurrence of hitch stitch formation can be avoided by causing the frame5to make detouring movement of a relatively small detour amount, and this partial area will hereinafter be referred to as “first area S1” for convenience sake. As a reference, an example of the first area S1is illustrated inFIG.16. InFIG.16, the base point C located at the center of the diagram represents a current needle drop position (i.e., current position of the eye hole19aof the needle plate19) as inFIG.1, and let it be assumed that a stitching direction from the base point C to a next needle drop position (i.e., next-stitch forming direction) is identified by an angle within a range from 0° to less than 360° calibrated in the counterclockwise direction. Moving directions of the frame5corresponding to the first area S1of the stitching directions around 90° belong to an area around 270° that is exactly opposite (180 degrees opposite) to the first area S1. As a reference, an example of a movement target position of the frame5corresponding to a stitch in a stitching direction belonging to the first area S1is denoted by T1inFIG.16. As may be seen from the figure, the target position T1corresponding to the next stitch is relatively near the position to which frame5has been temporarily moved, at the time of the detouring movement, in such a direction as to cause the upper thread to move out of the opening section29of the guide member23(i.e., toward the front left). Therefore, the target position T1can be reached by the frame5being caused to make a relatively small amount of detouring movement. InFIG.16, the first area S1is illustrated as having a range from angle a to angle b, for example, from 85° to less than 112°; however, such a range of the first area S1may be variably set as appropriate as will be described later.

The remaining partial area of the areas β and γ to which the stitching directions in which hitch stitches are formed due to the behavior of the upper thread belong is an area in which occurrence of hitch stitch formation is avoided by causing the frame5to make detouring movement of a relatively large detour amount. This partial area will hereinafter be referred to as “second area S2” for convenience sake. This second area S2includes the remaining portion of the area β and the entirety of the area γ illustrated inFIG.1. Moving directions of the frame5corresponding to the second area S2belong to an area that is exactly opposite (180 degrees opposite) to the second area S2. An example of a movement target position of the frame5corresponding to a stitch of a stitching direction belonging to the second area S2is denoted by T2inFIG.16. As may be seen from the figure, at the time of the detouring movement of the frame5, the target position T2corresponding to the next stitch is relatively far from the position to which the frame5has been temporarily moved in such a direction as to cause the upper thread to move out of the opening section29of the guide member23(i.e., toward the front left), and this target position T2tends to be near the rear of the sewing machine. Therefore, in order to reach the target position T2, it is necessary for the frame5to make detouring movement of a relatively large detour amount. InFIG.16, the second area S2is illustrated as having a range from angle b to angle c, for example, from about 112° to about 210°; however, such a rang of the second area S2, too, may be variably set as appropriate as will be described later. Note that the areas for which the detour amount of the frame5differs are not limited to the above-mentioned two areas S1and S2and may be three or more areas. Further, inFIG.16, reference character S0denotes an area for which no detouring movement of the frame5is performed, and the areas α and δ illustrated inFIG.1are included in this area S0.

In one embodiment of the present invention, the aforementioned control means may perform the above-mentioned jump control once (i.e., one time), two times or more during the detouring movement of the frame5. In one implementation, in a case where the next-stitch forming direction belongs to the above-mentioned first area S1, the control means performs the jump control once (one time) during the detouring movement. Further, in a case where the next-stitch forming direction belongs to the above-mentioned second area S2, the control means performs the jump control two times during the detouring movement.

FIG.17is a diagram illustrating several trajectories of the detouring movement of the frame5performed by the frame detour control by the control means. InFIG.17, as inFIG.16, reference character C denotes a (current) needle drop position (base point) at the beginning of the detouring movement, and reference characters T1and T2denote needle drop positions (target positions) at the end of the detouring movement.FIG.18is a sectional plan view illustrating relationships between the upper thread T and the guide member23of the presser foot device21during the detouring movement of the frame5and more particularly illustrating in a horizontal sectional view the guide member23, the sewing needle11, and a portion of the upper thread T entering the eye hole11aof the sewing needle11. Note, however, that because the sewing needle in the jumped state is located at a position higher than the guide member23, the respective sections of the guide member23and the sewing needle11(and the section of the portion of the upper thread T entering the eye hole11a) are not at the same height.

FIG.17(a)illustrates a trajectory of the detouring movement in the case where the next-stitch forming direction belongs to the aforementioned first area S1; in this case, the jump control is performed once during the detouring movement. The needle bar9(and hence the sewing needle11) having moved upward at the base point C is set in the jumped state to be held at the upper position by the jump mechanism. Further, the fabric pressing motor24is de-actuated, and the presser foot device21is stopped at a predetermined upper position. Simultaneously, the frame5is controlled to move in such a direction as to cause the upper thread T, extending downward from the sewing needle11, to move out of the opening section29of the guide member23. The movement of the frame5at that time is denoted by A1inFIG.17(a). An end point of the movement A1(i.e., a mid-point m1of the detouring movement) of the frame5may be set as an appropriate X-Y coordinate value. In order to perform the detouring movement of the frame5in an efficient (compact) manner, the end point of the movement A1of the frame5may be set in such a manner that the movement A1is executed in a diagonally forward left direction as illustrated. However, the present embodiment is not so limited, and the end point of the movement A1(i.e., the mid-point m1) of the frame5may be set in any other appropriate manner as long as such a modification does not depart from the scope and spirit of the present invention.FIG.18(a)illustrates a state in which the upper thread T has moved out of the opening section29of the guide member23in the diagonally forward left direction in response to the movement A1of the frame5. Once the frame5reaches the mid-point m1, the jump control for one stitch is brought to an end.

Next, the frame5is moved from the mid-point m1to the target position T1corresponding to the next stitch. Such movement of the frame5is denoted by A2inFIG.17(a). The movement A2of the frame5is executed in the diagonally forward right direction as illustrated, and during the course of the movement A2, the upper thread T, having moved out of the opening section29of the guide member23, abuts against (or is received by) the restricting section23aof the guide member23, and thus, rightward movement of the upper thread T is restricted by the restricting section23a.FIG.18(b)illustrates the state in which the upper thread T has abutted against the restricting section23ain response to the movement A2of the frame5. In this state, the upper thread T having moved out of the eye hole11aof the sewing hole11is located to the left of the sewing needle11. While the frame5is moving from the mid-point m1toward the target position T1, the needle bar9(and the sewing needle11) and the presser foot device21descend. Of course, appropriate operating time adjustment is made in such a manner that the frame5reaches the target position T1to complete the detouring movement before the descending sewing needle11and presser foot device21contact the upper surface of the sewing workpiece.

FIG.17(b)illustrates a trajectory of the detouring movement in the case where the next-stitch forming direction belongs to the second area S2; in this case, the jump control is performed two times (for two stitches) during the detouring movement of the frame5. The needle bar9(and hence the sewing needle11) having moved upward at the base point C is set in the jumped state and held at the upper position through the jump mechanism. Further, the fabric pressing motor24is de-actuated, and the presser foot device21is stopped at a predetermined upper position (top dead point). Simultaneously, the frame5is controlled to move in such a direction as to cause the upper thread T, extending downward from the sewing needle11, to move out of the opening section29of the guide member23. The movement of the frame5at that time is denoted by A1inFIG.17(b)as inFIG.17(a). Similarly to the aforementioned, the end point of the movement A1(i.e., the first mid-point m1of the detouring movement) of the frame5may be set as an appropriate X-Y coordinate value. Similarly to the aforementioned, in order to perform the detouring movement of the frame5in an efficient (compact) manner, the end point of the movement A1(i.e., the first mid-point m1) may be set in such a manner that the movement A1of the frame5is executed in a diagonally forward left direction as illustrated. The state in which the upper thread T has moved out of the opening section29of the guide member23in the diagonally forward left direction in response to the movement A1of the frame5is illustrated inFIG.18(a). Although the first jump control for one stitch (first stitch) ends once the frame5reaches the first mid-point m1, the second jump control for another one stitch (second stitch) is performed immediately following the first jump control in order to keep the jumped state of the sewing needle9(the sewing needle11).

Then, with the sewing needle9kept in the jumped state, the frame5is moved from the first mid-point m1to a second mid-point m2. Such movement of the frame5is denoted by A2inFIG.17(b). The movement A2of the frame5is executed in the diagonally forward right direction as illustrated, and during the course of the movement A2, the upper thread T, having moved out of the opening section29of the guide member23, abuts against (or is received by) the restricting section23aof the guide member23, and thus, rightward movement of the upper thread T is restricted by the restricting section23a. Such a state in which the upper thread T abuts against the restricting section23ais similar to the state illustrated inFIG.18(b). In this state, the upper thread T having moved out of the eye hole11aof the sewing needle11is located to the left of the sewing needle11. An end point of the movement A2(i.e., the second mid-point m2) of the detouring movement of the frame5may be set as an appropriate X-Y coordinate value. In order to enable the upper thread T to reliably reach the target position T2and to abut against (to be received by) the restricting section23a, the end point of the movement A2(i.e., the second mid-point m2) of the frame5may be set such that the movement A2is executed in an appropriate diagonally forward right direction as illustrated. Once the frame5reaches the second mid-point m2, the second jump control is brought to an end. Note that when the frame5reached the end point of the movement A2(the second mid-point m2), the upper thread T has been entwined counterclockwise around the restricting portion23a.

Then, the frame5is moved from the second mid-point m2toward the target position T2corresponding to the next stitch. Such movement of the frame5is denoted by A3inFIG.17(b)and is executed in the diagonally rearward right direction as illustrated. In response to the movement A3of the frame5, the upper thread T is further entwined counterclockwise around the restricting section23ato move further in the diagonally rearward right direction. However, the upper thread T having moved out of the eye hole11aof the sewing needle11is still located to the left of the sewing needle11, as in the state illustrated inFIG.18(b). While the frame5is moving from the second mid-point m2toward the target position T2, the needle bar9(and hence the sewing needle11) and the presser foot device21descend. Similarly to the aforementioned, appropriate operating time adjustment is made in such a manner that the frame5reaches the target position T12to complete the detouring movement before the descending sewing needle11and presser foot device21contact the upper surface of the sewing workpiece.

In the above-described frame detour control illustrated inFIGS.17(a) and (b), the detouring movement of the frame5is performed in an intermittent manner. For example, stitch-by-stitch sewing data (frame moving data) and jump control codes may be pre-programmed in combination, and the detouring movement by the one-time jump control may be performed on the basis of a combination of the sewing data of the first one stitch (i.e., frame moving data for moving the frame5to the mid-point m1) and the jump control code and the sewing data of the next one stitch (frame moving data for moving the frame5to the target position T1). Further, the detouring movement by the two-time jump control may be performed on the basis of a combination of the sewing data of the first one stitch (frame moving data for moving the frame5to the mid-point m1) and the jump control code, a combination of the sewing data of the next one stitch (frame moving data for moving the frame to the second mid-point m2) and the jump control code, and the sewing data of the last one stitch (frame moving data for moving the frame5to the target position T2). Note that the number of times the jump control is performed in the frame detour control is not limited to one or two as noted above and may be three or more or only one.

The detouring movement of the frame5may be performed continuously rather than intermittently as noted above.FIG.17(c)illustrates an example in which the detouring movement of the frame5is performed continuously. In the example ofFIG.17(c), the target position is denoted by T2as inFIG.17(b), and the detouring movement of the frame5is performed continuously along the trajectories A1, A2, and A3as inFIG.17(b). For example, a parameter prescribing that the frame5is to be moved continuously when the jump control codes are read out successively, and the detouring movement of the frame5to the target position T2may be performed continuously on the basis of such a parameter with the needle bar9kept in the jumped state.

<Prevention of Upper Thread Slackening>

In one embodiment of the present invention, it is preferable to take measures for preventing slackening of the upper thread during the detouring movement control (or detour control) of the frame5. For that purpose, an upper thread slackening preventing section200is provided in a lower portion of the needle bar case8. Such an upper thread slackening preventing section200is disposed above an upper thread locking device400of a well-known construction, and opposite end portions of a base plate201of the slackening preventing section200are fixed by screws to brackets that are mounted to left and right side surfaces of the needle bar case8. Pressing pieces203are fastened to positions of the base plate201, which correspond to the individual needle bars9, by screws202each having a spring fitted over its stem portion. The upper surface T (not illustrated inFIG.3) hanging down from the thread take-up lever10is passed between the base plate201and the pressing piece203. Thus, by adjusting a screw-in amount of the screw202to vary the resiliency of the spring, slight tension is imparted by contact resistance to the upper thread T passing between the base plate201and the pressing piece203. The upper thread T having passed through the upper thread slackening preventing section200is passed through the upper thread locking device400and then passed through the eye hole11aof the corresponding sewing needle11. The tension imparted to the upper thread T by the screw202and pressing piece203of the upper thread slackening preventing section200may be of such a strength that can prevent the upper thread T, having been caught on (entwined around) the guide member23at the time of the detouring movement control of the frame5, from undesirably slipping down from the guide member23due to its slackening. With the above-described upper thread slackening preventing section200, even if slackening occurs in a portion of the upper thread T located above the preventing section200at the time of the descending of the thread take-up lever10that moves up and down even during the jumping of the needle bar9, slackening that may occur in a portion of the upper thread T located below the preventing section200can be avoided by the contact resistance in the preventing section200. Thus, it is possible to prevent the upper thread T, caught on (entwined around) the guide member23during the detouring movement control of the frame5, from slipping down from the guide member23due to the slackness of the upper thread T. Note that the construction of the upper thread slackening preventing section200is not limited to the illustrated construction and may be any other suitable construction as long as it can prevent slackening of the upper thread T. Alternatively, the upper thread locking device400of the well-known construction may be used as a substitute for the upper thread slackening preventing section200, without the upper thread slackening preventing section200being provided. Because the above-described upper thread slackening preventing section200constantly imparts tension to the upper thread T, even slight contact resistance might adversely influence tightness of stitches. Thus, as a modification of the invention, the upper thread slackening preventing section200may be constructed as a movable type, similarly to the upper thread locking device400, in such a manner as to impart tension to the upper thread T only during the detouring movement control of the frame5.

<Sewing Control for Achieving All Perfect Stitches>

The above-described sewing machine of the present invention can avoid occurrence of hitch stitches due to the behavior of the upper thread and lower thread and thereby achieve all-perfect-stitch sewing in which all stitches are formed as perfect stitches over the entire range of the stitching directions.FIG.19is a flow chart illustrating an example of a computer program for performing sewing control to achieve such all-perfect-stitch sewing in accordance with an embodiment of the present invention. This computer program is stored, for example, in the storage device103illustrated inFIG.15and executed by the CPU101.

The computer program illustrated inFIG.19is started when a sewing operation is to be started for sewing a user-selected pattern (embroidery pattern or other sewing pattern) of a plurality of stitches. At step St1, a stitch counter n indicative of a particular position in a stitch formation order is set at an initial value of “1”. At step St2, stitch movement amount data Pn (X-Y moving data of the frame5) for forming a stitch of a particular position in the stitch formation order designated by a current value of the stitch counter n (i.e., nth stitch) is obtained. At next step St3, a needle moving direction (i.e., next-stitch forming direction) of the obtained stitch movement amount data Pn is calculated by using the current needle drop position as the base point C. At next step St4, a determination is made as to whether or not the calculated needle moving direction (next-stitch forming direction) belongs to the area S0(for which the frame detour control is not to be performed) illustrated inFIG.16. With a YES determination at step St4, the program goes to step St5, while with a NO determination, the program branches to step St8.

At step St5, a sewing operation for one stitch is performed by moving the frame5to a target position corresponding to the stitch movement amount data Pn and causing the needle bar9to descend. The detouring movement of the frame5is not performed in the sewing operation of step St5. As noted above, the area S0illustrated inFIG.16includes the areas α and δ illustrated inFIG.1. If the calculated needle moving direction (next-stitch forming direction) belongs to the area α, it is possible to form a perfect stitch by merely performing a normal sewing operation. If, on the other hand, the calculated needle moving direction (next-stitch forming direction) belongs to the area δ, it is possible to avoid occurrence of a hitch stitch due to the behavior of the lower thread and thereby form a perfect stitch by using the above-described unique rotary hook construction of the sewing machine of the present invention. Details of such perfect stitch formation will be given below.

<Avoidance of Hitch Stitch Occurrence in Area δ>

FIG.20is a view explanatory of a mechanism for, by use of the rotary hook construction of the inventive sewing machine, avoiding occurrence of a hitch stitch due to the behavior of the lower thread, of which (a) is a front view of the rotary hook construction and (b) is a top plan view illustrating at an enlarged scale a relationship between the sewing needle and the lower thread in the inner rotary hook50. Note that the rotary hook3illustrated inFIG.20is similar to the rotary hook3described above with reference toFIGS.11to14. In the case where the next-stitch forming direction belongs to the area δ, the frame5is moved in the rearward right direction toward the target position corresponding to the next stitch. The lower thread D extending from the rotary hook3toward the needle hole19ais pulled in the rearward right direction in response to the movement of the frame5, during which time the lower thread D abuts against the rear wall surface52aof the recessed portion52of the inner rotary hook50and the rightward movement of the lower thread D is restricted by the upstream side wall52bof the recessed portion52as illustrated inFIGS.20(a) and (b). The lower thread D having moved out of the rotary hook3moves toward the needle hole19aby way of the rear left of the up-and-down movement trajectory of the sewing needle11and connects to the sewing workpiece W located above; thus, when the ascending/descending sewing needle11is located beneath the needle plate19, the lower thread D is always located to the rear left (i.e., behind and to the left of) of the sewing needle11and never located to the right of the sewing needle11. In this way, occurrence of a hitch stitch in the area δ due to the behavior of the lower thread D can be avoided structurally, and entwining between the upper thread T and lower thread D achieved in the rotary hook3can form a perfect stitch.

Note that when the sewing needle11passes through the sewing workpiece (fabric workpiece) W, the sewing workpiece may flutter in the up-down direction; thus, undesired slackening may occur in the lower thread D, and the slackened lower thread D may undesirably move rightward beyond the tip of the sewing needle11. However, the thread take-up member41in the present embodiment performs a spring action as noted above; thus, even when the lower thread D has slackened due to the fluttering of the sewing workpiece W or the like, the spring action of the thread take-up member (thread take-up spring)41located substantially immediately below the recessed portion52of the inner rotary hook50quickly absorbs the slackness of the lower thread D. In this way, it is possible to keep the lower thread D in an appropriately taut state and thereby prevent the lower thread D from moving rightward beyond the tip of the sewing needle11. Further, because the front end edge62bof the upper spring part (thread dividing spring)62of the outer rotary hook60is located behind the rear wall surface52aof the recessed portion52of the inner rotary hook50as noted above, the front end edge62bdoes not push forward the lower thread D by abutting against the lower thread D. Thus, no slackening occurs in the lower thread D due to the behavior of the upper spring part (thread dividing spring)62of the outer rotary hook60. In the above-described manner, the present embodiment takes all possible measures of eliminating a possibility of occurrence of a hitch stitch due to slackness of the lower thread D as well.

Referring now back toFIG.19, at step St8, a further determination is made as to whether or not the needle moving direction (next-stitch forming direction) calculated at step St3above belongs to the first area S1(a part of the area β) illustrated inFIG.16. With a YES determination at step St8, the program goes to step St9. At step St9, the frame detouring movement control for the first area S1is performed by using a small or short detouring movement trajectory as illustrated inFIG.17(a). A NO determination at step St8means that the needle moving direction (next-stitch forming direction) calculated at step St3above belongs to the second area S2(i.e., the area including the remaining part of the area β and the area γ) illustrated inFIG.16; in this case, the program goes to step St10to perform the frame detouring movement control for the second area S2by using a large or long detouring movement trajectory as illustrated inFIG.17(b).

<Avoidance of Hitch Stitch Occurrence in Area S1>

The frame detouring movement control for the first area S1(one-time jump control) performed at step St9includes moving the frame5to the mid-point m1with the needle bar9kept in the jumped state, then moving the frame5to the target position T1, and dropping the sewing needle11onto the sewing workpiece W. Details of such control will be given below with reference toFIG.21as well.FIG.21is a perspective view explanatory of functions of the guide member23of the presser foot device21during the detouring movement control of the frame5.

By moving the frame5to the mid-point m1with the needle bar9kept jumped to hold the sewing needle11at the upper position, the frame5is moved as denoted by A1inFIG.17(a), and thus, the upper thread T is placed in a state where a portion of the thread T projects in the diagonally forward left direction out of the opening section29of the guide member23of the presser foot device21as illustrated inFIG.18(a);FIG.21(a)illustrates such a state of the upper thread T in a perspective view. Next, by moving the frame5from the mid-point m1to the target position T1, the frame5is moved as denoted by the trajectory A2ofFIG.17(a), and thus, the upper thread Tis placed in a state where it abuts against (or is received by) the restricting section23aof the guide member23to be restricted by the restricting section23aas illustrated inFIG.18(b). Simultaneously, the needle bar9is released from the jumped state, so that the sewing needle11and the presser foot device21descend.

FIG.21(b)illustrates a state immediately before the descending sewing needle11enters the through-hole22aformed in the pressing member22of the presser foot device21. As seen from the figure, the upper thread T connecting to the sewing workpiece W from the rear portion of the eye hole11aof the sewing needle11is caught on the restricting section23aof the guide member23(more specifically, received in a recessed portion of the restricting section23a), and thus, movement of the upper thread T rightward beyond the up-and-down movement trajectory of the sewing needle11is restricted by the restricting section23a, so that the upper thread T is held located to the left of the sewing needle11.

FIG.21(c)illustrates a state in which the sewing needle11has further descended to enter the guide member23of the pressing member22immediately before the needle11pierces the sewing workpiece W. The sewing needle11descending within the guide member23passes by the right of a portion of the upper thread T having moved out from the rear portion of the eye hole11aof the sewing needle11to connect to the sewing workpiece W while being restricted by the restricting section23a. Once the guide member23of the presser foot device21reaches its bottom dead point, the descending movement of the presser foot device21is stopped, after which only the sewing needle11descends further.

FIG.21(d)illustrates a state in which the tip of the further descending sewing needle has sticked into the sewing workpiece W after having passed through the guide member23. As the sewing needle11descends, the portion of the upper thread T, connecting to the sewing workpiece W from the rear portion of the eye hole11aof the sewing needle11, descends along the restricting section23awhile being kept located to the left of the sewing needle11by the rightward movement of the upper thread portion being restricted by the restricting section23aof the guide member23.

FIG.21(e)illustrates a state in which the portion of the upper thread T, connecting to the sewing workpiece W from the rear portion of the eye hole11aof the sewing needle11, has reached a position beneath the lower end of the guide member23as the sewing needle11descends further. In this state, the portion of the upper thread T, connecting to the sewing workpiece W from the rear portion of the eye hole11aof the sewing needle11, is released from the restricting section23aand starts to twine around the sewing needle11in the counterclockwise direction.

When the eye hole11aof the further descending sewing needle11has reached a position below the needle plate19by the further descending sewing needle11passing through the sewing workpiece W and the needle hole19aof the needle hole19, the portion of the upper thread T, connecting to the sewing workpiece W from the rear portion of the eye hole11aof the sewing needle11, extends upward along the left side of the sewing needle11to reach the sewing workpiece W after passing through the needle hole19aof the needle plate19. In the state where the sewing needle11has descended to the rotary hook3in the aforementioned manner, the path of the upper thread T leading from the rear portion of the eye hole11ato the sewing workpiece W (needle hole19a) above, is held located to the left of the sewing needle11. In the state where the sewing needle has descended into the rotary hook3, the upper thread T having moved out from the rear portion of the eye hole11ato extend upward is captured by the hook point61of the outer rotary hook60and moved together with the hook point61, so that a loop of the upper thread is formed (pulled out). Then, the upper thread loop is entwined with the lower thread D through a combination of the rotation of the rotary hook3, ascending movement of the sewing needle11, and movement of the thread take-up lever10; in this manner, a stitch is formed. Because the upper thread T having moved out from the rear portion of the eye hole11aenters the rotary hook3while being located to the left of the sewing needle11(entwined counterclockwise around the sewing needle11), the above-mentioned stitch is formed as a perfect stitch. In the above-described manner, it is possible to avoid occurrence of a hitch stitch in the first area S1(a part of the area β).

<Avoidance of Hitch Stitch Occurrence in Area S2>

The frame detouring movement control for the second area S2(two-time jump control) performed at step St10includes moving the frame5to the first mid-point m1with the needle bar9jumped for one stitch, then moving the frame5to the second mid-point m2with the needle bar9jumped for another one stitch, and finally moving the frame5to the target position T2and then causing the sewing needle11to drop onto the sewing workpiece W. Details of such control will be given below with reference toFIG.21(a)andFIG.22as well.

By moving the frame5to the first mid-point m1with the needle bar9jumped for one stitch to hold the sewing needle11at the upper position, the frame5is moved at denoted by A1inFIG.17(b), and the upper thread T, extending downward from the rear portion of the eye hole11aof the sewing needle11held at the upper position, moves in the diagonally forward left direction out of the opening section29of the guide member23of the presser foot device21as illustrated inFIG.18(a). Such a state is illustrated in the perspective view ofFIG.21(a).

Next, by moving the frame5from the first mid-point m1to the second mid-point m2with the needle bar9still kept jumped (jumped for another one stitch), the frame5is moved generally rightward as denoted by the trajectory A2ofFIG.17(b). Once the frame5reaches the second mid-point m2, the jump control is brought to an end. When the end point of the movement A2(i.e., second mid-point m2) has been reached, the upper thread T has been entwined around the restricting section23aof the guide member23in the counterclockwise direction. Such a state is illustrated in the perspective view ofFIG.22. In this state, as seen from the figure, the upper thread T, extending downward from the sewing needle11to connect to the sewing workpiece W, has been deeply entwined around the restricting section23aof the guide member23in the counterclockwise direction. Because the detouring movement of the frame5by the two-time jump control enables the upper thread T to be reliably entwined around or caught on the restricting section23ain the aforementioned manner, it is possible to reliably prevent an upper thread entwining mistake.

Finally, by moving the frame5from the second mid-point m2to the target position T2, the frame5is moved as denoted by the trajectory A3ofFIG.17(b). In response to such movement A3, the upper thread T is further entwined around the restricting section23ain the counterclockwise direction to go in the diagonally rearward right direction. In this manner, the upper thread T, extending from the rear portion of the eye hole11aof the sewing needle11to the sewing workpiece W, is deeply entwined counterclockwise around the restricting section23aof the guide member23and thus restricted from moving rightward beyond the up-and-down movement trajectory of the sewing needle11, so that the upper thread T is held located to the left of the sewing needle11. Because the jump control has already ended by that time, the needle bar9(and thence he sewing needle11) and the presser foot device21descend while the frame5is being moved from the second mid-point m2toward the target position T2.

During the course of the movement of the further descending sewing needle11to the rotary hook3through the sewing workpiece W and the needle hole19a, the upper thread Tis placed in various states similar to those described above with reference toFIGS.21(c) to (e). Namely, the portion of the upper thread T, having moved out from the rear portion of the eye hole11aof the sewing needle11, enters the rotary hook3while being kept located to the left of the sewing needle (entwined around the sewing needle11in the counterclockwise direction), and thus, it is possible to form stitches while avoiding occurrence of a hitch stitch due to the behavior of the upper thread. Particularly, in the remaining part of the area β of the second area S2, a perfect stitch is formed by avoiding occurrence of a hitch stitch due to the behavior of the upper thread as described above. In the area γ of the second area S2, a hitch stitch due to the behavior of the upper thread and a hitch stitch due to the behavior of the lower thread occur in a mixture. Thus; as for the area γ, it is not sufficient to only avoid occurrence of a hitch stitch due to the behavior of the upper thread, and it is necessary to avoid occurrence of a hitch stitch due to the behavior of the lower thread as well. More specifically, occurrence of a hitch stitch due to the behavior of the lower thread need be avoided; because, double hitch stitches occur if the lower thread is located behind the up-and-down movement trajectory of the sewing needle11, even though the upper thread is entwined counterclockwise around the sewing needle11by the frame detour control. Occurrence of such a hitch stitch due to the behavior of the lower thread can be avoided by use of the unique needle plate construction related to the needle hole19aof the needle plate19, as described above. Details of such avoidance of a hitch stitch due to the behavior of the lower thread will be given below.

<Avoidance of Hitch Stitch Occurrence in Area γ Due to Behavior of Lower Thread>

As described above with reference ofFIGS.9,10and other figures, the needle plate19has the guide hole31and the groove portion32formed therein in relation to the needle hole19a. FIG. is a perspective view illustrating a mechanism for, by use of the construction of the needle plate having the guide hole31and the groove portion32, avoiding occurrence of a hitch stitch due to the behavior of the lower thread. To ease understanding of the figure, illustration of the frame5and the sewing workpiece W present between the presser foot device21and the needle plate19is omitted in the figure, and accordingly, illustration of a lower portion of the upper thread T and an upper portion of the lower thread D is also omitted in the figure. Further, a distance between guide member23of the presser foot device21and the needle plate19(needle hole19a) is illustrated as if it is constant for convenience sake; actually, however, this distance varies as the presser foot device21moves up and down.

FIG.23(a)illustrates a state when the frame5has been moved almost to the first mid-point m1(in the diagonally forward left direction) in the frame detouring movement control (two-time jump control) for the second area S2performed at step St10. In this state, the upper thread T, extending downward from the rear portion of the eye hole11aof the sewing needle11located at the upper position, has moved in the diagonally forward left direction out of the opening section29of the guide member23of the presser foot device21as noted above. The lower thread D, extending upward from the rotary hook3to connect to the sewing workpiece W, has been passed through the needle hole19ain accordance with the needle drop position before the movement of the frame5; then, the lower thread D is guided from the needle hole19ato the guide hole31in response to the movement of the frame5to the first mid-point m1(in the diagonally forward left direction).

FIG.23(b)illustrates a state when the frame5has been moved almost to the second mid-point m2(generally in the rightward direction) in the frame detouring movement control (two-time jump control) for the second area S2performed at step St10. In this state, the upper thread T, extending downward from the rear portion of the eye hole11aof the sewing needle11located at the upper position, is received by or caught on the restricting section23aof the guide member in such a manner that right movement of the upper thread T beyond the up-and-down movement trajectory of the sewing needle11is restricted by the restricting section23and the upper thread T is entwined around the restricting section23ain the counterclockwise direction. In response to the movement of the frame5from the first mid-point m1to the second mid-point m2(generally in the rightward direction), the lower thread D is bent upward by an edge of the guide hole31to enter the upper hollow space of the groove portion32and is then guided generally rightward along the groove portion32.

FIG.23(c)illustrates a state when the frame5has been moved almost to the target position T2(generally in the diagonally rearward right direction) in the frame detouring movement control (two-time jump control) for the second area S2performed at step St10. In this state, the upper thread T, extending downward from the rear portion of the eye hole11aof the sewing needle located at the upper position, has been entwined further around the restricting section23aof the guide member23in the counterclockwise direction, as noted above. In response to the movement of the frame5from the second mid-point m2to the target position T2(generally in the diagonally rearward right direction), the lower thread D is received by the rear side wall32b(near the needle hole19a) of the groove portion32(seeFIG.10(b)) and held in front of the up-and-down movement trajectory of the sewing needle11without shifting rearward beyond the up-and-down movement trajectory of the sewing needle11. This means that the path of the lower thread D pulled out upward from the rotary hook3to lead to the needle plate19is kept located in front of the up-and-down movement trajectory of the sewing needle11.

With the frame5located at the target position T2, the sewing needle11descends further and then ascends, during the course of which a stitch is formed by the loop of the upper thread T twining around the lower thread D in response to the rotation of the rotary hook3as noted above. At this stage, the upper thread T having moved out from the rear portion of the eye hole11aenters the rotary hook3with the upper thread T located to the left of the sewing needle11(entwined around the sewing needle11in the counterclockwise direction), and the path of the lower thread D pulled out of the lower thread bobbin to extend to the needle plate19is kept located in front of the up-and-down movement trajectory of the sewing needle11. With such arrangements, it is possible to achieve desired sewing where occurrence of both a hitch stitch due to the behavior of the upper thread and a hitch stitch due to the behavior of the lower thread (i.e., double hitch stitches) is avoided.

Note that although the lower thread D is also pulled out in response to the detouring movement of the frame5, slackness of the pulled-out lower thread D is absorbed promptly by the aforementioned spring action of the thread take-up member41. Namely, in the present embodiment, even though the lower thread D is pulled out in response to the detouring movement of the frame5, the spring action of the thread take-up member (thread take-up spring)41provided in the rotary hook3promptly absorbs slackness of the pulled-out lower thread D, and thus, the lower thread D can be kept in a taut state. Therefore, in the present embodiment, the lower thread D can be avoided from getting slackened to come off the receiving or engaging portion (groove portion32) of the needle plate19. Namely, in the present embodiment, the thread take-up member (thread take-up spring)41functions also as tension imparting means provided below the needle plate19for imparting tension to the lower thread pulled out upward from the rotary hook3to go toward the needle hole19aor the guide hole31of the needle plate19.

As well known in the art, the loop of the upper thread T captured by the hook point61of the outer rotary hook60passes through the inner rotary hook50and is then pulled by the thread take-up lever10(FIG.4) upward along the lower thread D while reducing the size of the loop. Further, in the present embodiment, where the groove portion32is formed to have the bottom surface32a, the loop of the upper thread T, passing upward through the needle hole19atogether with the lower thread D while reducing the size of the loop, without getting caught in the groove portion32, so that an unwanted upper thread breakage can be avoided. Further, because the lower thread D is only received or engaged by the rear side wall32b(FIG.10(b)), the lower thread easily comes free from the groove portion32to return to the normal path (i.e., to the path along which the lower thread D passes through the needle hole19a) when the sewing needle drops at the target position T2, as the lower thread D is pulled upward in response to the ascending movement of the upper thread T. Thus, no adverse influence is given to path formation of the lower thread D at the time of next stitch formation.

By performing the operations of steps St5, St9, and St10in accordance with the needle moving direction (i.e., the next-stitch forming direction) of the stitch movement amount data Pn, the inventive arrangements achieve desired all-perfect-stitch sewing where occurrence of hitch stitches due to the behavior of the upper thread and due to the behavior of the lower thread (i.e., all types of hitch stitches) is avoided.

Now describing the remaining steps illustrated inFIG.19, the program goes to step St6after execution of the operations at step St5, St9, or step St10and increments the value n of the stitch counter by one at step St6. At step St7, a determination is made as to whether or not the value n incremented by one at step St6is greater than the “total number of stitches” of the pattern for which the sewing operation is being performed currently. With a NO determination at step St7, the program reverts to step St2above to repeat the operations at and after step St2for that incremented-by-one value n (i.e., for the next stitch). Once the sewing of the pattern for which the sewing operation is performed currently is completed, a YES determination is made at step St7, and thus the program ofFIG.19is brought to an end.

<Setting of Frame Detour Control Data>

According to one embodiment, the inventive sewing machine may be constructed in such a manner that various data related to the frame detour control (i.e., various conditions for the detour control) can be set and changed or modified as desired by the user.FIG.24illustrates an example of a screen display via which various data related to the frame detour control (i.e., various conditions for the detour control) can be set and changed or modified as desired by use of the operation panel (seeFIG.2). The operation panel6includes a touch-enabled display screen, and necessary images, data, and the like are displayed on the display screen in accordance with various operation modes. When the operation mode is a setting mode, a parameter setting screen110as illustrated in the figure is displayed on the display screen of the operation panel6. As an example, setting items of Nos. 21 to 30 for the frame detour control are displayed with their respective current setting values. Alternatively, instead of the plurality of setting items of Nos. 21 to 30 being displayed simultaneously on the parameter setting screen110, at least one of such setting items may be displayed on the screen110at a time, and the displayed setting item may be switched to another by a scroll operation or the like.

If the user touches and thereby selects a desired one of the setting items of Nos. 21 to displayed on the parameter setting screen110, the current setting value of the selected one setting item is displayed on a display section111. By the user operating a setting value change key112, the current setting value of the selected setting item can be changed to increase or decrease, and the thus-varied setting value is displayed on the display section111. By the user depressing an ENTER key113after the change of the setting value, the changed setting value is made effective.

The setting item “All Perfect Stitch (Apfs) Use” of No. 21 corresponds to setting means for setting whether performing the frame detouring movement control should be made valid or not. Whether performing the frame detouring movement control should be made valid or not may be set, for example, by setting “Yes” or “No”. The illustrated example denotes a state in which the setting item is set at “Yes”. In an alternative, this setting value “Yes/No” may be replaced with “ON/OFF”.

In order to actually control the validation/invalidation of the detouring movement control of the frame5in according with the setting of the No. 21 setting item, it is only necessary to modify a part of the flow ofFIG.19as shown inFIG.25. Namely, step St11is inserted between steps St3and St4, and a determination is made at this step St11as to whether or not the setting item “All Perfect Stitch (Apfs) Use” is currently set at “YES” (i.e., as to whether performing the detouring movement control of the frame5is currently made valid or not). With a YES determination at step St11, the program goes to step St4above, where the detouring movement control of the frame5is performed in the aforementioned manner. With a NO determination at step St11, however, the program jumps over step St4to step St5; thus, in this case, the detouring movement control of the frame5is not performed.

By enabling such setting as to whether performing the frame detouring movement control should be made valid or not as noted above, the sewing operation can be performed in a variety of manners and with an enhanced efficiency. Although the inventive sewing machine can avoid occurrence of a hitch stitch due to the behavior of the upper thread and enhance the sewing quality by performing the detouring movement of the frame5as described above, an overall production efficiency of the sewing tends to inevitably decrease because extra time is required for the detouring movement of the frame5. Depending on an intended or desired sewn product, it may sometime be more preferable to avoid a decrease of the production efficiency than to avoid degradation of the sewing quality resulting from occurrence of a hitch stitch. For example, in a case where a hidden part of a product invisible on the outer surface of the product is to be sewn, it may be considered to be more preferable to give priority to the production efficiency over the avoidance of occurrence of a hitch stitch. Further, the user may sometimes want to select whether or not to perform the detouring movement control of the frame5, depending on a type of the sewing workpiece (fabric workpiece), a type of the upper thread, or the like. Furthermore, a degree of demand for avoiding occurrence of a hitch stitch may differ between simple straight sewing and complicated embroidery sewing. For these various possible cases, it is useful and beneficial to provide the function of selecting validation (Yes or ON) or invalidation (No or OFF) of the detouring movement of the frame5.

The setting items of Nos. 22 to 24 are means for setting parameters a, b, and c prescribing a needle moving direction (stitch forming direction) for the frame detour control and more particularly correspond to setting means for variably setting respective ranges of the aforementioned first and second areas S1and S2(seeFIG.16). Boundary angles a and b that define the range of the first area S1are variably set in accordance with setting of the items of Nos. 22 and 23. The boundary angle b of the angles b and c defining the range of the second area S2is variably set in accordance with setting of the item of No. 23, and the boundary angle c is variably set in accordance with setting of the item of No. 24. As an example, predetermined values (for example, a=85°, b=112°, and c=) 210° may be initially set in advance as the boundary angles a, b, and c; then, these initially set predetermined values a, b, and c may be increased or decreased, by user's manual operations, in such a manner that the thus-changed values are set as the boundary angles a, b, and c. Then, the determinations about the areas S0and S1at steps St4and St8of FIG. are made on the basis of such variably-set values (i.e., values of the boundary angles a, b, and c).

Generally, it is difficult to precisely demarcate an area in which a hitch stitch is undesirably formed, and thus, to be on the safe side, it may be preferable to perform the frame detouring movement control after setting the areas S1and S2, for which the frame detouring movement control is to be performed, to somewhat wider ranges. However, if the areas S1and S2are set to somewhat wider ranges like this, the overall production efficiency may undesirably decrease as the number of times the frame detouring movement control is performed increases. Further, depending on a desired or intended sewn product, there may arise a case in which the user desires to avoid a decrease of the production efficiency as much as possible by allowing or tolerating occurrence of a hitch stitch in sewing of a sewing workpiece portion for which it is not necessary to give high priority to the quality of stitches. Further, there may arise a case in which the user desires to variably set the ranges of the areas S1and S2, for which the frame detour control is to be performed, in accordance with a type of the sewing workpiece (fabric workpiece), a type of the upper thread, or the like, without fixing the ranges of the areas S1and S2. For these various possible cases, it is useful and beneficial to provide the function of variably setting the ranges of the predetermined areas S1and S2(values of the individual boundary angles a, b, and c) for which the detouring movement control of the frame5is to be performed.

The setting items of Nos. 25 and 26 are means for setting parameters X1 and Y1 that define a first moving direction in the frame detour control (i.e., setting means for variably setting a detouring path of the frame5); more particularly, the setting items of Nos. 25 and 26 correspond to setting means for variably setting an X-Y displacement coordinate position of the first mid-point m1(seeFIG.17) (i.e., a coordinate position relative to the base position C). The setting items of Nos. 27 and 28 are means for setting parameters X2 and Y2 that define a second moving direction in the frame detour control (i.e., setting means for variably setting a detouring path of the frame5); more particularly, the setting items of Nos. 27 and 28 correspond to setting means for variably setting an X-Y displacement coordinate position (i.e., a coordinate position relative to the first mid-point m1) of the second mid-point m2(seeFIG.17). For these parameters X1, Y1, X2, and Y2, too, predetermined values may be initially set in advance, and then these predetermined values may be increased or decreased, by response to user's manual operations, in such a manner that the thus-changed values are set as the parameters X1, Y1, X2, and Y2. Note that respective current values (2.5 mm, 2.5 mm, −3.8 mm, and 1.1 mm) of the parameters X1, Y1, X2, and Y2 illustrated in the figure are each denoted in an X-Y coordinate expression of stitches denoted inFIG.1. For example, the X-Y displacement coordinate position of X1=2.5 mm and Y1=2.5 mm for defining the first mid-point m1indicates a stitch position belonging to a quadrant of X+ and Y+ in the X-Y coordinate expression of stitches denoted inFIG.1. Because the moving direction of the frame5corresponding to that stitch position is 180° opposite to the stitch position and hence belongs to a quadrant of X− and Y−, the moving direction of the frame5corresponds to the movement of the frame5from the base point C to the first mid-point m1located to the left of and in front of the base point C inFIG.17. Further, the X-Y displacement coordinate position of X2=−3.8 mm and Y2=1.1 mm for defining the second mid-point m2indicates a stitch position belonging to a quadrant of X− and Y+ in the X-Y coordinate expression of stitches denoted inFIG.1. Because the moving direction of the frame5corresponding to that stitch position is 180° opposite to the stitch position and hence belongs to a quadrant of X+ and Y−, the moving direction of the frame5corresponds to the movement of the frame5from the first mid-point m1to the second mid-point m2located to the right of and in front of the first mid-point m1inFIG.17. The detouring movement control of the frame5of steps St9and St10ofFIG.19is performed on the basis of the settings set here (i.e., the set values of the parameters X1 and Y1 and the parameters X2 and Y2 respectively defining the first and second mid-points m1and m2).

By enabling variable setting of the parameters X1, Y1, X2, and X2 defining the moving directions in the detour control of the frame5as described above, the detouring path of the frame5can be modified as necessary, If a relatively long detouring path of the frame5is set, for example, the upper thread can be reliably entwined around the guide member23of the presser foot device21; however, because extra time is required for the detouring movement of the frame5in such a case, the overall production efficiency of the sewing decreases. If a relatively short detouring path of the frame5is set, on the other hand, the detouring movement of the frame5does not take much time, and thus, the overall production efficiency of the sewing can be enhanced. Therefore, the aforementioned setting means of the inventive sewing machine are useful and beneficial because they enable setting of an appropriate detouring path of the frame5in consideration of to which of the sewing quality and the production efficiency should be given priority.

Further, the setting items of Nos. 29 and 30 are means for setting an effective minimum stitch length and an effective maximum stitch length that are applied to the above-described frame detour control. The effective minimum stitch length is a minimum value of the stitch length that is applicable to the frame detour control, while the effective maximum stitch length is a maximum value of the stitch length that is applicable to the frame detour control. As an example, 0.0 mm is initially set as the effective minimum stitch length, and 36.0 mm is initially set as the effective maximum stitch length. By increasing or decreasing a desired one of these initially-set values as necessary, it is possible to set a user-desired effective minimum stitch length or maximum stitch length. In a case where such setting is to be applied to the frame detour control, the frame detour control may be performed if the length of a stitch to be formed next (next stitch length) is within a range between the set effective minimum stitch length and effective maximum stitch length. For example, a step of determining whether the length of the stitch to be formed next is within the range between the set effective minimum stitch length and effective maximum stitch length may be inserted between step St3and step St4ofFIG.19(or between step St11and step St4ofFIG.25). With a YES determination at such a determination step, the program goes to step St4, while with a NO determination at such a determination step, the program jumps to step St5.

It should be noted that the construction (or configuration) for enabling the setting of various data related to the frame detour control (i.e., various conditions for the detour control) in the inventive sewing machine is not limited to the above-described construction or configuration where various data are set by user's manual operations via the operation panel6of the sewing machine as described above. Namely, an alternative construction may be employed such that at the time of making a desired sewing pattern program or embroidery pattern program, various data related to the frame detour control may be set as desired as detour controlling program data and prestored together with the sewing pattern program or embroidery pattern program. Such a construction in which the various data related to the frame detour control (i.e., conditions for the detour control) are supplied as such programmed data may also be employed in an embodiment of the setting means for variably setting the various data related to the frame detour control (conditions for the detour control).

Note that whereas the above-described embodiments are constructed in such a manner that when the detour control of the frame5is to be performed, the needle bar jump control by the jump mechanism is performed together with the frame detour control, the present invention is not so limited, and the present invention may also be practiced in a type of sewing machine that is not provided with the jump mechanism that performs the jump control of the needle bar. In order to perform the detour control of the frame5in such a sewing machine not provided with the jump mechanism, it is only necessary to control the operation of the needle bar in such a manner that the sewing needle does not drop during the detouring movement of the frame5. For example, by reducing the rotation speed of the main shaft13during the detouring movement of the frame5, the needle bar can be controlled in such a manner as to prevent the sewing needle from dropping during the detouring movement of the frame5.

The embodiments of the present invention have been described above in relation to the case where the present invention is applied to a multi-head and multi-needle type sewing machine. However, the present invention should not be construed as being so limited, and the present invention may also be applied to a single-head type sewing machine or a single-needle type sewing machine. Furthermore, the present invention is applicable to both an embroidery sewing machine and an ordinary sewing machine. In addition, the holding member (or frame) for holding the sewing workpiece in the present invention is not limited to a flat plate type and may be a rotary type like a hat/cap frame. What is more, the rotary hook in the present invention is not limited to a full-rotation vertical rotary hook (DB type) and may be of any other desired type, such as a horizontal rotary hook or a half rotary hook. Furthermore, depending on the type, rotating direction and the like of the rotary hook employed, the areas in which a hitch stitch is undesirably formed may differ from the areas described above in relation to the embodiments of the present invention. In order to deal with such an area difference, it is only necessary to make appropriate modifications that may include making area determinations corresponding to the different areas, modifying the needle bar construction according to the different areas (for example, changing the positions of the guide hole31and the groove portion32), or modifying the rotary rook construction (for example, changing the position of the recessed portion52) according to the different areas.

What is more, the operation panel6employed in the present invention may be either mounted fixedly to the sewing machine or mounted removably to the sewing machine. As a modification, the above-described setting means (i.e., setting device) for manually setting various conditions for the detour control may be implemented by a portable-type operation panel (such as a mobile computer or a mobile terminal) constructed to enable manual setting of various conditions for the detour control as described above with reference toFIG.24. In such a modification, the setting means (i.e., setting device) implemented by such a portable-type operation panel is provided with a communication function for enabling communication with the control device of the sewing machine and is constructed to enable transmission and receipt of setting information and data between the operation panel and the control device of the sewing machine. Needless to say, the inventive sewing machine may be constructed in such a manner that both of the operation panel6mounted fixedly or removably on the sewing machine and the portable-type operation panel can be used in combination as the setting means (i.e., setting device) for manually setting various conditions for the detour control.