WO2023225852A1

WO2023225852A1 - Device and method for thread drawing

Info

Publication number: WO2023225852A1
Application number: PCT/CN2022/094723
Authority: WO
Inventors: Jibo Yang; Yiming Dong; Qi Lu
Original assignee: Abb Schweiz Ag
Priority date: 2022-05-24
Filing date: 2022-05-24
Publication date: 2023-11-30

Abstract

Embodiments of present disclosure relates to a thread drawing device and a thread drawing method. The thread drawing device comprises: a drive assembly (70) comprising a drive wheel (72) comprising a working platform (722) for supporting a thread (85), the thread (85) comprising a fixed end (852) fixed on an object (90) and a movable end (854) carried by a tool, a pressing assembly (60) comprising a pressing member (62) configured to move between a first position at which the pressing member (62) engages the working platform (722) to clamp the thread to be pulled therebetween and a second position at which the pressing member (62) disengages from the working platform (722) to release the thread to be pulled; and a motor (74) configured to rotate the drive wheel (72) when the pressing member (62) is at the first position so as to move a loose part (855) of the thread at the fixed end from the fixed end to the movable end.

Description

DEVICE AND METHOD FOR THREAD DRAWING

FIELD

Embodiments of the present disclosure generally relate to a field of industrial robots, and more particularly to industrial robots for sewing an object.

BACKGROUND

In automobile industries, more and more cars are manufactured to equip with a leather covered steering wheel. The leather not only improves an outer appearance of the steering wheel but also improves comforts of hand feeling. That is because the leather cover can resist slippery caused by sweat, which means safer drive.

Typically, a leather cover is manually fixed to a blank steering wheel by a manual work. A worker firstly fixes the leather cover to the blank steering wheel for exmaple by gluing and then sews the leather cover to the blank steering wheel stitch by stitch. This is labor intensive and time-consuming. For a single steering wheel, to complete this assembly process, it takes up to one hour even for an experienced operator. There is an increasing need to automate the assembly process by industrial robots.

SUMMARY

Example embodiments of the present disclosure provide a thread drawing device and a thread drawing method which can improve automation degree of a sewing process.

In a first aspect of the present disclosure, it is provided a thread drawing device. The thread drawing device comprises a drive assembly comprising a drive wheel comprising a working platform for supporting a thread, the thread comprising a fixed end fixed on an object and a movable end carried by a tool, a press assembly comprising a pressing member configured to move between a first position at which the pressing member engages the working platform to clamp the thread to be pulled therebetween and a second position at which the pressing member disengages from the working platform to release the thread to be pulled; and a motor configured to rotate the drive wheel when the pressing member is at the first position so as to move a loose part of the thread at the fixed end from the fixed end to the movable end.

According to the present disclosure, for a thread comprising a fixed end fixed on an object and a free end, the loose part of the thread at the fixed end can be easily tensioned. This is particularly advantageous in an automatic sewing operation. This arrangement obviates the need of complex force control mechanism for protecting the thread and the need of complex movement control mechanism due to the changeable length of the thread.

In some embodiments, the thread may be moved from the fixed end to the movable end by a static friction force generated by a pressing force exerted by the pressing member. With this arrangement, movement of the thread can be well controlled by moving the driver wheel. Also, the force for moving the thread can be well controlled by creating a proper contact force between the pressing member and the drive wheel.

In some embodiments, the thread is caused to slide when a drawing force acting upon the thread exceeds a threshold indicative of that the loose part of the thread at the fixed end has been tensioned. The fact that the thread begins to slide indicates that the loose part of the thread at the fixed end has been tensioned. Due to this fact, the thread can be well protected against damage due to excessive drawing force. This is particularly advantageous in an automatic sewing operation.

In some embodiments, the device may further comprise an actuator having a piston, wherein the piston is coupled with the press assembly and the actuator is configured to linearly move the piston so as to move the press assembly. With this arrangement, the press assembly can be moved easily.

In some embodiments, the device may further comprise a frame for supporting the actuator, wherein the frame defines a guide rail for guiding a movement of the press assembly. With this arrangement, the movement of the press assembly can be well controlled and guided.

In some embodiments, the press assembly may comprise: a base for supporting the pressing member; and a spring arranged between the base and the piston for elastically supporting the pressing member. With the spring, the contract force between the pressing member and the drive wheel can be well determined even if a movement distance of the actuator is not accurate.

In some embodiments, the press assembly may further comprise: an adjustment plate coupled to the piston; and a screw rod fixed to the base; wherein the spring is arranged between the base and the adjustment plate, and an elastic force of the spring is adjustable by adjusting a position of the adjustment plate along the screw rod with respect to the base so as to be able to adjust a pressure applied onto the thread. With this arrangement, the contract force between the pressing member and the drive wheel can be easily adjusted.

In some embodiments, the pressing member may be in a form of a roller which is rotatable with respect to the base. This may facilitate the movement of the thread.

In some embodiments, the working platform may comprise a circumferential groove for receiving the thread.

In some embodiments, the circumferential groove comprises a V-shape with a first guide angle.

In some embodiments, the pressing member comprises a convex shape with a second guide angle receivable by circumferential groove, the first guide angle being equal to or larger than the second guide angle.

In some embodiments, a tip of the convex shape is rounded to define a clearance for housing the thread.

In some embodiments, a material of a surface of the pressing member is different from a material of a surface of the working platform.

In a second aspect of the present disclosure, it is provided a robot system for sewing, comprising the thread drawing device of any of the first aspect.

In a third aspect of the present disclosure, it is provided a thread drawing method. The thread drawing method comprises: moving, after a thread being placed on a working platform of a thread drawing device, a pressing member to a first position at which the pressing member engages the working platform to clamp the thread to be pulled therebetween, the thread comprising a fixed end fixed on an object and a movable end carried by a tool; rotating the working platform to a loose part of the thread at the fixed end from the fixed end to the movable end; stopping the rotation of the working platform in response to determining that the thread slides on the working platform; and moving the pressing member to a second position at which the pressing member disengages from the working platform.

DESCRIPTION OF DRAWINGS

Through the following detailed descriptions with reference to the accompanying drawings, the above and other objectives, features and advantages of the example embodiments disclosed herein will become more comprehensible. In the drawings, several example embodiments disclosed herein will be illustrated in an example and in a non-limiting manner, wherein:

Fig. 1 is a schematic view of a robot system according to one example embodiment of the present disclosure;

Fig. 2 is a schematic perspective view of a thread drawing device according to one example embodiment of the present disclosure;

Fig. 3 is a schematic plane view of the thread drawing device according to one example embodiment of the present disclosure, with a pressing member being disengaged from a drive wheel;

Fig. 4 is a schematic sectional view of the thread drawing device according to one example embodiment of the present disclosure, with a pressing member being disengaged from a drive wheel;

Fig. 5 is a perspective view illustrating how a thread is clamped between a pressing of the pressing member and the driving wheel according to one example embodiment of the present disclosure, with the pressing member engaging the drive wheel;

Fig. 6 is a sectional view of Fig. 5; and

Fig. 7 is an enlarged view of a circle portion of Fig 6;

Figs. 8-11 are schematic views illustrating operating principles of the thread drawing device according to example embodiments of the present disclosure; and

Fig. 12 is a flow chart of the thread drawing method according to one example embodiment of the present disclosure.

Throughout the drawings, the same or similar reference symbols are used to indicate the same or similar elements.

DETAILED DESCRIPTION OF EMBODIMENTS

Principles of the present disclosure will now be described with reference to several example embodiments shown in the drawings. Though example embodiments of the present disclosure are illustrated in the drawings, it is to be understood that the embodiments are described only to facilitate those skilled in the art in better understanding and thereby achieving the present disclosure, rather than to limit the scope of the disclosure in any manner.

The term “comprises” or “includes” and its variants are to be read as open terms that mean “includes, but is not limited to. ” The term “or” is to be read as “and/or” unless the context clearly indicates otherwise. The term “based on” is to be read as “based at least in part on. ” The term “being operable to” is to mean a function, an action, a motion or a state that can be achieved by an operation induced by a user or an external mechanism. The term “one embodiment” and “an embodiment” are to be read as “at least one embodiment. ” The term “another embodiment” is to be read as “at least one other embodiment. ” The terms “first, ” “second, ” and the like may refer to different or same objects. Other definitions, explicit and implicit, may be included below. A definition of a term is consistent throughout the description unless the context clearly indicates otherwise.

There is an increasing need to automate the assembly process for sewing a cover to a steering wheel. The present invention proposes a novel robot system for sewing which can sew a cover to onto a steering wheel. It is to be understood that although the present disclosure takes a steering wheel with a cover as an example to illustrate principles of the present invention, this is merely illustrative, and the inventive concepts are applicable to any other objects that needs to be sewn. The cover may be of various forms, for example, the cover being made of leather, leatherette, fabric and the like.

Fig. 1 shows a robot system 100 for sewing an object. As shown in Fig. 1, the robot system 100 comprises a support 40 for supporting the object to be sewed (in the shown example, a steering wheel 90, a first robotic arm 20, and a second robotic arm 30. The object may a semi-finished product transferred from a previous process and may comprise a cover and a blank steering wheel. The cover may be primarily glued to the blank steering wheel and the cover should be further sewed according to a predetermined sewing pattern so as to tightly fix the cover onto the blank steering wheel. The robot system 100 is configured to perform the above sewing operations.

The robot system 100 may further comprise a controller 10 and the controller 10 can communicate with the first robotic arm 20 and the second robotic arm 30 to control their movements so as to perform sewing operations.

The robot system 100 may further comprise one or

more cameras

52, 54. The

cameras

52 and 54 may be attached to different positions of the robot system so as to obtain images of the object from different perspectives. The images of the object can be sent to the controller 10. In some embodiments, the controller is configured to visually inspect the object based on the image from the cameras and to provide an inspection result indicating a suitability of whether the object can be sewed by the apparatus before the sewing operation. In some embodiments, a sewing quality after the sewing operation can be provided. In some embodiments the controller 10 is configured to identify a plural of positions to be sewed based on the image from the cameras and to generate a sewing path. The sewing path determines a sewing pattern which defines the positions to be sewed in order according to an input rule of lacing pattern based on the identified plural of positions to be sewed. According to the sewing path, the controller controls the first robotic arm 20 and the second robotic arm 30 so as to perform sewing operations. Through the plural of sewing operations, a plural of stitches are automatically formed.

The first robotic arm 20 and the second robotic arm 30 are arranged adjacent to the support 40 and thus can access the steering wheel 90 to perform sewing operations. The first robotic arm 20 and the second robotic arm 30 each comprise a gripper configured to hold the needle 80. The support 40 may comprise a shaft which is rotatable so that positions of the steering wheel 90 can be adjusted according to positions to be sewn of the steering wheel 90.

The sewing operations of the robot system 100 are illustrated as below. The first robotic arm 20 firstly holds the needle 80 and the needle 80 is tied with a length of a thread 85 (referring to Fig. 3) . The second robotic arm 30 is at a standby position. The controller 10 identifies a position to be sewed and instruct the first robotic arm 20 to move to the identified position to be sewed to cause the needle 80 to penetrate a part of the steering wheel 90. Then, the controller 10 instruct the second robotic arm 30 to hold a penetration portion of the needle 80 and pull the whole needle 80 out of the steering wheel 90 after the needle 80 being released by the first robotic arm 20.

Through the above process, the needle 80 is penetrated into the object and the needle 80 is further pulled out of the object by the robot system 100. At this moment, one end of the thread 85 (i.e., a fixed end) is fixed on an object and the other end (i.e., a moveable end) is carried by one of the robotic arm (in shown case, the second robotic arm 30) . There is a large length of the thread which is loose at the fixed end and needs to be penetrated through the object.

The technical problem is how to draw the loose thread through the object. There are a number of challenges for drawing the loose part of the thread through the object. One of the problems is that the thread is typically very thin and cannot withstand a large force. Thus, a force for drawing the loose part of the thread should not be too large so as to ensure that the thread does not break after each drawing operation and function well. Another problem is a length of the loose part of the thread is changeable since its length reduces after each sewing operation. Accordingly, a distance for drawing the loose part of the thread should be changeable. If the second robotic arm 30 that now carries the needle directly pulls the needle away to draw the loose part of the thread to penetrate the object, the second robotic arm should meet at least the above two requirements, which is overwhelming difficult.

To solve the above technical problem, as shown in Fig. 1, the robot system 100 may further comprise a thread drawing device 200 which is configured to draw the loose part of the thread to penetrate the object. The thread drawing device 200 may be arranged at any proper position that can be accessed by the robotic arms, for example, by robotic arm 30. With the thread drawing device 200, the loose part of the thread can be pulled through the object. In some embodiments, the thread is made of chemical fiber, cotton, or any other proper material for sewing. It is to be understood that this is merely illustrative and the thread may be made of any other proper material.

Figs. 2-4 show schematic views of a thread drawing device 200 according to one example embodiment of the present disclosure.

As shown in Figs. 2-4, the thread drawing device 200 comprises a drive assembly 70 and a pressing assembly 60. The drive assembly 70 comprises a drive wheel 72 and a motor 74. The motor 74 may be controlled by the controller 10. For example, the motor may receive instructions from the controller 10 to rotate the drive assembly 70 or to stop rotating the drive assembly 70. In some embodiments, a gear box 78 (or reducer) may be arranged between the drive wheel 72 and the motor 74 such that rotation of the drive wheel 72 may be properly designed. As shown in Fig. 4, an output shaft 76 of the motor 74 is coupled to a gear box 78 which further couples to the drive wheel 72.

The drive wheel 72 may comprise a working platform 722 for supporting a thread 85. The pressing assembly 60 may comprise a pressing member 62 configured to move between a first position and a second position. At the first position, the pressing member 62 engages the working platform 722 to clamp the thread to be pulled therebetween. When the thread 85 is clamped between the pressing member 62 and the working platform 722, the motor 74 drives to rotate the drive wheel 72 and the thread 85 is thus pulled from the fixed end 852 toward the movable end 854. With this arrangement, a loose part 855 of the thread 85 can be from the fixed end 852 toward the movable end 854 conveniently.

In some embodiments, the thread 85 is moved from the fixed end 852 to the movable end 854 by a static friction force generated by a pressing force exerted by the pressing member 62. Since the drawing force for moving the thread 85 is due to the static friction force, the force acting on the thread 85 can be well controlled. In this way, the thread 85 can be well protect to avoid being subject to an excessive force to break the thread 85. Moreover, it makes it possible to adjust the static friction force by adjusting the pressing force. In this way, the force acting on the thread 85 can be easily adjusted according to requirements.

In some embodiments, the thread 85 is configured to slide when a drawing force acting upon the thread exceeds a threshold indicative of that the loose part of the thread at the fixed end has been tensioned. This threshold can be determined in association with a material of the thread. Due to this arrangement, it is unnecessary to provide additional force control sensors to control the force acting on the thread.

In some embodiments, as shown in Figs. 2 and 3, an actuator 64 is provided for moving the pressing assembly 60. The actuator 64 may takes any proper forms as long as it ca move the pressing assembly 60 between the first and second positions. For example, the actuator may pneumatic actuator, electromagnetic actuator, or any other proper actuators. In the shown example, a pneumatic actuator 64 is shown and comprises a cylinder 69 and a piston 67 arranged therein. The piston 67 is coupled to the pressing assembly 60. This piston 67 can perform a linear movement in response to an action of the actuator 64.

In some embodiments, as shown in Fig. 4, a frame 66 is provided for supporting the actuator 64 and the frame 66 defines a guide rail 662 for guiding a movement of the pressing assembly 60. Due to the guide rail 662, the movement of the pressing assembly 60 can be well guided.

In some embodiments, as shown in Figs. 2 and 4, the pressing assembly 60 comprises a base 61 for supporting the pressing member 62 and a spring 68 arranged between the base 61 and the piston 67 for elastically supporting the pressing member 62. During action of the actuator 64, the piston 67 firstly presses the spring 68 and then the pressing member 62 is moved by the spring 68. Accordingly, even if a movement distance of the piston 68 is not precise, the pressing force that the pressing assembly 60 presses the thread 85 can be well controlled. Since the thread’s pulling force depends on an elastic force of spring. The elastic force of the spring can be adjusted by replacing different types of springs, for example changing spring’s compressing length, or tuning the pressure of compressing air of cylinder.

In some embodiments, as shown in Figs. 2-4, the pressing assembly 60 further comprises an adjustment plate 65 coupled to the piston 67 and a screw rod 614 fixed to the base 61. The spring 68 is arranged between the base 61 and the adjustment plate 65. An elastic force of the spring is adjustable by adjusting a position of the adjustment plate 65 along the screw rod 614 with respect to the base 61. When the piston 67 moves, the adjustment plate 65 is firstly moved by the piston 67. The movement of the adjustment plate 65 compresses the spring 38 which in turns moves the pressing member 62. The adjustment plate 65 may be arranged on the screw rod 614 which further engages a nut 616. By moving the nut 616 along the screw rod 614, the elastic force of the spring 68 can be easily adjusted without changing spring’s compressing length, or tuning the pressure of compressing air of cylinder.

In some embodiments, the pressing member 62 can be fixedly attached to the base 61. In some embodiments, the pressing member 62 is rotatable with respect to the base 61. This can improve a smooth movement of the thread.

In some embodiments, as shown in Fig. 4, the pressing member 62 can be supported on a shaft 611. The pressing member 62 includes a central hole through which the shaft 611 extends. In some embodiments, a bearing may be arranged between the pressing member 62 and the shaft 611.

Figs. 5-7 show structural details of the pressing member 62 and the drive wheel 72 according to one example embodiment of the present disclosure. As shown in Fig. 5, The pressing member 62 is in a form of a roller which is rotatable with respect to the base 61. The working platform 722 comprises a circumferential groove for receiving the thread 85. The thread 85 can be placed on the circumferential groove and held in the circumferential groove.

In some embodiments, as shown in Figs. 6 and 7, the circumferential groove comprises a V-shape with a first guide angle. It is to be understood that the shape of the circumferential groove is merely illustrative. The circumferential groove may be of any proper shape as long as it can receive the thread 85.

In some embodiments, as shown in Figs. 6 and 7, the pressing member 62 comprises a convex shape. The convex shape may fit the circumferential groove. In this way, the pressing member 62 can be reliably fit in the circumferential groove. In some embodiments, the convex shape is provided with a second guide angle. The first guide angle is equal to or larger than the second guide angle so that the pressing member 62 can fit the circumferential groove.

In some embodiments, as shown in Fig. 7, a tip of the convex shape of the pressing member 62 is rounded to define a clearance 725 for housing the thread. With this arrangement, there is always a space left to holding the thread 85 such that the thread 85 will not be over-pressed to destroy or damage the thread 85.

In some embodiments, some measures may be taken to further increase the static friction force while the smooth movement of the thread would not be affected. In some embodiments, a material of a surface of the pressing member 62 is different from a material of a surface of the working platform 722. Experiment tests show that different materials of the contact surfaces may contribute to increase of the static friction force.

Next, operating principles of the thread drawing device 200 according to one example embodiment of the present disclosure are illustrated by with reference to Figs. 8-11.

Fig. 8 shows an initial state of the thread drawing device 200. As shown by the arrow, the pressing member 62 moves up and disengages from the drive wheel 72 and a room is left for passage of the needle. At the initial state, the thread 85 with one end tied to the needle 80 is placed onto the working platform 722 of the drive wheel 72, for example by a robotic arm 30. The working platform 722 is shaped to hold the thread 85. One end of the thread, i.e., the fixed end 852, is fixed to the object 90 supported on the support 40 (referring to Fig. 1) . The other end of the thread 85, the movable end 854, is movable or free and can be moved by the robotic arm 30. A loose part 855 of the thread is adjacent to the fixed end 852 and this loose part 855 of the thread is corresponding to a portion of the thread which needs to pass through the object to form a stitch. It is to be understood that in the shown example, the motor 74 is configured to drive the drive wheel 72 by a belt-arrangement, this is merely illustrative and any other proper drive means can be used.

Fig. 9 shows a subsequent state of the thread drawing device 200 following the initial state. As shown by the arrow, the pressing member 62 moves down and engage the drive wheel 72. At the state, the thread 85 is clamped between the pressing member 62 and the drive wheel 72 and is subject to a pressure force from the pressing member 62. In some embodiments, this pressure force forms the static friction force for moving the thread. In some embodiments, the pressure force can be properly selected or designed by designing the structures of the pressing assembly. In some embodiments, the pressure force can be adjusted according to a require force for moving the thread.

Fig. 10 shows a subsequent state of the thread drawing device 200 following the state of Fig. 9. As shown by the arrow, the pressing member 62 keeps pressing and engaging the drive wheel 72. Thus, the pressure force is continuously applied onto the thread. At this state, the motor 74 receives instructions from the controller 10 and starts to draw the thread 85. As the motor 74 rotates, the drive wheel 72 also rotates. When the drive wheel 72 rotates, the thread 85 keeps affixed to the drive wheel 72 due to the static friction force and thus also rotates. The loosed part 85 of the thread 85 is gradually pulled toward the movable end 854. As the motor 74 rotates, the whole loosed part 85 of the thread 85 is tensioned which means the whole loosed part 85 are completely removed.

At this state, as the motor 74 continues rotating, there is relative movement between the thread 85 and the drive wheel 72. In particular, the thread 85 begins sliding between the pressing member 62 and the drive wheel 72. This generally means that the whole loosed part 85 of the thread 85 has been tensioned. In response to the sliding movement of the thread 85, the motor 74 stops rotation. With this arrangement, the thread 85 can be tensioned in an easy way.

Fig. 11 shows a subsequent state of the thread drawing device 200 following the state of Fig. 10. When the motor 74 stops rotation, as shown by the arrow, the pressing member 62 moves up and disengages from the drive wheel 72 and a room is left for passage of the needle. The robotic arm 30 may take the needle to a proper position to perform the next sewing cycle.

Fig. 12 is a flow chart of a thread drawing method 300 according to one example embodiment of the present disclosure.

As shown in Fig. 12, the method 300 comprises the following actions. At a block 302, after a thread being placed on a working platform 722 of a thread drawing device, a pressing member 62 is moved to a first position. At the first position, the pressing member 62 engages the working platform 722 to clamp the thread to be pulled therebetween. The thread comprises a fixed end fixed on an object for example, a steering wheel, and a movable end carried by a tool, for example, by a robotic arm. At a block 304, the working platform 722 is rotated so as to move a loose part of the thread at the fixed end from the fixed end to the movable end.

At a block 306, the thread is caused to slide when a drawing force acting upon the thread exceeds a threshold indicative of that the loose part of the thread at the fixed end has been tensioned. The fact that the thread slides on the working platform 722 indicates that the loose part of the thread is tensioned. The relative movement between the thread and the working platform ensures that the thread cannot be damaged due to over large pulling force. In some embodiments, rotation of the working platform 722 may be stopped at a proper time after the thread slides relative to the working platform. At a bock 308, the pressing member 62 is moved to a second position. At the second position, the pressing member 62 disengages from the working platform 722 to release the thread to be pulled. Also, a space between the pressing member and the working platform 722 can be formed and thus the thread can be placed on the working platform 722 to start another sewing operation.

With the thread drawing device and the thread drawing method of the present disclosure, the loose part of the thread can be tensioned easily without reliance of complex force control mechanisms. Also, the thread can be well protected against damage due to over large pulling force.

Through the teachings provided herein in the above description and relevant drawings, many modifications and other embodiments of the disclosure given herein will be appreciated by those skilled in the art to which the disclosure pertains. Therefore, it is understood that the embodiments of the disclosure are not limited to the specific embodiments of the disclosure, and the modifications and other embodiments are intended to fall within the scope of the disclosure. In addition, while exemplary embodiments have been described in the above description and relevant drawings in the context of some illustrative combinations of components and/or functions, it should be realized that different combinations of components and/or functions can be provided in alternative embodiments without departing from the scope of the disclosure. In this regard, for example, it is anticipated that other combinations of components and/or functions that are different from the above definitely described will also fall within the scope of the disclosure. While specific terms are used herein, they are only used in a general and descriptive sense rather than limiting.

Claims

A thread drawing device, comprising

a drive assembly (70) comprising a drive wheel (72) comprising a working platform (722) for supporting a thread (85) , the thread (85) comprising a fixed end (852) fixed on an object (90) and a movable end (854) carried by a tool,

a pressing assembly (60) comprising a pressing member (62) configured to move between a first position at which the pressing member (62) engages the working platform (722) to clamp the thread to be pulled therebetween and a second position at which the pressing member (62) disengages from the working platform (722) to release the thread to be pulled; and

a motor (74) configured to rotate the drive wheel (72) when the pressing member (62) is at the first position so as to move a loose part (855) of the thread at the fixed end from the fixed end to the movable end.
The device according to claim 1, wherein the thread is moved from the fixed end to the movable end by a static friction force generated by a pressing force exerted by the pressing member (62) .
The device according to claim 1, wherein the thread is caused to slide when a drawing force acting upon the thread exceeds a threshold indicative of that the loose part of the thread at the fixed end has been tensioned.
The device according to claim 1, further comprising an actuator (64) for moving the pressing assembly (60) having a piston (67) , wherein the piston is coupled to the pressing assembly (60) and the actuator (64) is configured to linearly move the piston so as to move the pressing assembly (60) .
The device according to claim 4, further comprising a frame (66) for supporting the actuator (64) , wherein the frame (66) defines a guide rail (662) for guiding a movement of the pressing assembly (60) .
The device according to any of claims 1-5, wherein the pressing assembly (60) comprises:

a base (61) for supporting the pressing member (62) ; and

a spring (68) arranged between the base (61) and the piston for elastically supporting the pressing member (62) .
The device according to claim 6, wherein the pressing assembly (60) further comprises:

an adjustment plate (65) coupled to the piston; and

a screw rod (614) fixed to the base (61) ;

wherein the spring (68) is arranged between the base and the adjustment plate, and an elastic force of the spring is adjustable by adjusting a position of the adjustment plate along the screw rod with respect to the base so as to be able to adjust a pressure applied onto the thread.
The device according to claim 6, wherein the pressing member (62) is in a form of a roller which is rotatable with respect to the base.
The device according to any of claims 1-5, 7, and 8, wherein the working platform (722) comprises a circumferential groove for receiving the thread.
The device according to claim 9, wherein the circumferential groove comprises a V-shape with a first guide angle.
The device according to claim 10, wherein the pressing member (62) comprises a convex shape with a second guide angle receivable by circumferential groove, the first guide angle being equal to or larger than the second guide angle.
The device according to claim 11, wherein a tip of the convex shape is rounded to define a clearance (725) with respect to the working platform (722) for housing the thread.
The device according to any of claims 1-5, 7, 8, and 10-12, wherein a material of a surface of the pressing member (62) is different from a material of a surface of the working platform (722) .
A robot system for sewing, comprising the thread drawing device of any of claims 1-13.
A thread drawing method, comprising

moving, after a thread being placed on a working platform (722) of a thread drawing device, a pressing member (62) to a first position at which the pressing member (62) engages the working platform (722) to clamp the thread to be pulled therebetween, the thread comprising a fixed end fixed on an object and a movable end carried by a tool;

rotating the working platform (722) to move a loose part of the thread at the fixed end from the fixed end to the movable end;

causing the thread to slide when a drawing force acting upon the thread exceeds a threshold indicative of that the loose part of the thread at the fixed end has been tensioned; and

moving the pressing member (62) to a second position at which the pressing member (62) disengages from the working platform (722) .