BOBBIN WINDING DEVICE OF A SEWING MACHINE AND METHOD FOR CONTROLLING OR REGULATING THE ROTATIONAL SPEED OF THE MOTOR OF A BOBBIN WINDING DEVICE

Description

[0001] The subject of the invention is a bobbin winder of a sewing machine and a method for controlling or regulating the speed (ω) of the motor of a bobbin winder. Sewing machines generally comprise a bobbin winder for winding sewing thread onto a bobbin thread spool. Such bobbins, also called thread spools for short, comprise a cylindrical shaft section that is axially delimited on both sides by a flange. The thread spool is placed onto a motor-driven spindle of the bobbin winder and connected to it in a rotationally fixed manner. By rotating the spindle, the thread or sewing thread is drawn from a thread supply and wound between the flanges onto the shaft section of the thread spool. The outer diameter of the wound sewing thread must not be larger than the outer diameter of the flanges.

[0002] To drive the spindle, bobbin winders can include a dedicated bobbin winder motor. Alternatively, a coupling device can be provided for temporarily coupling the spindle to a drive, particularly the main drive of the sewing machine.

[0003] Various devices are known with which the spindle drive can be stopped when a maximum filling of the thread spool, which is usually adjustable, is reached.

[0004] US2020340159A1 discloses a bobbin winding device comprising a pivotable sensor lever and a switch actuated by this sensor lever. The sensor lever is held in a first pivot position by the force of a spring. A contact element protrudes into the space between the flanges of an empty bobbin when the bobbin is placed on the drivable spindle of the bobbin winding device. When sewing thread is wound onto the bobbin, the diameter of the wound sewing thread increases. As soon as this sewing thread comes into contact with the contact element, it displaces the sensor lever from the first pivot position toward a second pivot position. Upon reaching this predeterminable second pivot position, the sensor lever actuates the switch. As soon as a control system detects this change in state, the bobbin winding motor is switched off.By adjusting the sensor lever arrangement, the switching point can be set so that the bobbin winder motor is stopped when the bobbin reaches its maximum filling level.

[0005] JP2021016398A discloses another bobbin winding device in which a lever is displaced from a first pivot position when winding sewing thread by contact with the sewing thread, counter to the holding force of a first magnet. The pivot position of the lever is detected by a Hall element and another magnet arranged on the lever. As soon as the lever reaches a predetermined second pivot position, the control system specifies a lower setpoint for regulating the speed of the bobbin winding motor. The speed is detected by a rotary encoder. When the bobbin is fully filled, the motor is stopped. A claw formed on the lever then positively engages a corresponding recess on the outside of the motor.

[0006] Such conventional devices for stopping the spindle drive take up comparatively a lot of space and are complex and expensive.

[0007] An object of the present invention is therefore to provide a comparatively simple, space-saving and cost-effective winding device and a suitable method for controlling the motor speed of such a winding device.

[0008] This object is achieved by a spooling device according to the features of patent claim 1 and by a method according to claim 11.

[0009] The bobbin winding device comprises a bobbin winding motor, hereinafter referred to as the motor, and a spindle that can be driven directly or indirectly by means of a transmission device and is designed for the releasable, rotationally fixed fastening of a bobbin thread. The spindle and preferably also the motor are arranged on a support, on which a brake body with a friction surface is also mounted such that the distance between the friction surface and the spindle can be adjusted. The brake body is preferably pivotally mounted on the support.

[0010] If a thread spool is held coaxially on the spindle, the friction surface of the brake body is located at a radial distance from the spindle axis, essentially in the area between the two flanges of the thread spool. The force of a spring presses the brake body or the section of the brake body with the friction surface radially in the direction of the spindle axis. Interacting stops can be arranged on the carrier and on the brake body, which limit the range of movement of the brake body in the direction of the spindle axis. The position of at least one of these stops is preferably adjustable, e.g. by means of an adjusting screw. In this way, an end position can be defined for the brake body, in which it is held by the effect of the spring force. The friction surface of the brake body is then arranged in a reference position at a defined distance from the spindle axis.The reference position is usually specified so that the distance between the friction surface and the spindle axis is slightly smaller than the flange radii of the thread spool. This ensures that the sewing thread comes into contact with the friction surface when wound onto the thread spool, as long as the outer diameter of the wound sewing thread is smaller than or equal to the diameter of the spool flanges. Preferably, the brake body is convexly curved in the area of the friction surface. The curvature or the axes of curvature of the friction surface and the thread spool attached to the spindle can be aligned essentially orthogonally to one another. When the thread spool is placed on the spindle, the spool flange that is at the front in the direction of attachment therefore first hits the brake body in an outer area of the friction surface further away from the spindle axis. The spool flange exerts a radially outward-acting force on the brake body.This is displaced radially outward by the spool flange against the acting spring force, allowing the spool to be pushed further into its desired position and connected to the spindle. As soon as the spool flange has overcome the obstacle or the point on the friction surface radially closest to the spindle axis, the brake body is moved back to its end position defined by the stops by the force of the spring. With such arrangements, thread spools can be simply placed on the spindle and connected to it, and then detached from the spindle in the opposite direction. The friction surface is preferably curved in two dimensions.

[0011] In alternative embodiments, the friction surface could be formed on an elastically deformable portion of the brake body. Preferably, the position of the brake body is adjustable, e.g., by means of an adjusting screw, so that the friction surface can be positioned at the desired reference distance from the spindle axis. An additional spring for adjusting the position of the brake body is possible, but not necessarily required. The elastically deformable portion of the brake body with the friction surface can comprise, e.g., a leaf spring and is preferably not preloaded or only slightly preloaded when the friction surface is at the reference distance from the spindle axis.

[0012] Typically, the motor and spindle are arranged coaxially and directly coupled, so their speeds are identical. The motor is preferably a DC motor. Alternatively, the motor and spindle could be coupled in another way, e.g., via a gear or a drive belt with a specified or specifiable step-up or step-down ratio.

[0013] When sewing thread is wound onto the thread spool, the motor is controlled by a motor controller. The motor controller is usually part of a sewing machine control system, which, in addition to controlling the motor, also controls other functions of the sewing machine. The outer diameter and mass of the wound sewing thread, as well as the moment of inertia of this system, continuously increase. This also applies to the peripheral speed of the wound sewing thread and the frictional resistance of the sewing thread during winding. The driving torque of the motor is counteracted by a braking torque of the sewing thread, which increases with increasing outer diameter. If the motor is controlled at a constant speed or without control, the rotational speed of the spindle decreases slightly when winding the sewing thread due to the increasing load on the motor.

[0014] As soon as the braking torque of the brake body sets in, the rate of decrease in the rotational speed increases. The rotational speed of the motor and / or its temporal rate of change or their amounts can be used as measured variables to detect a fill level of the thread spool defined by the position of the brake body. For this purpose, the brake body is arranged or adjusted in a predeterminable position relative to the spindle axis. In addition, a comparison value for the rotational speed and / or a comparison value for the rate of change of the rotational speed of the spindle or motor is defined in the motor control system. Depending on the design of the spooling device, measured variables and comparison variables for these measured variables can be recorded or specified only in terms of amounts, or alternatively with the respective positive or negative sign.

[0015] If the recorded values or corresponding averaged values fall below or exceed the associated limit values or comparison values, the motor control initiates suitable measures such as the immediate or delayed interruption of the power supply to the motor.

[0016] The rotational speed of the motor and its rate of change are generally parameters whose values change measurably significantly due to the effect of the brake body. Another parameter that changes depending on the load on the motor is the counter electromotive force, also known as CEMF or BEMF for "counter electromotive force" or "back electromotive force". It is essentially proportional to the rotational speed of the spindle driven by the motor and thus represents the rotational speed. The BEMF is proportional to a reverse voltage U BEMF , which is induced in the electrically conductive windings of the motor coil due to the relative movement in the motor's magnetic field. The reverse voltage U BEMF is opposite to the driving control voltage UA of the motor controller. When the motor is almost unloaded, it rotates at its idle speed.The magnitude of the reverse voltage U BEMF is then approximately equal to the control voltage UA , and the effective motor voltage UM , i.e. the difference between the voltage magnitudes UA -U BEMF is small.

[0017] When the motor is not rotating, the reverse voltage U BEMF is zero. The effective motor voltage UM, or the voltage difference UA - U BEMF in the motor's control circuit, essentially determines the motor current IM and thus also the motor's drive power.

[0018] Measured variables such as the source voltage UQ generated by the motor control voltage source, the effective motor voltage UM = UA - U BEMF applied to the motor, and the motor current IM can be recorded, for example, during predefined time intervals in the motor's control circuit. This is relatively simple, e.g., using voltage dividers and / or shunts in a conventional manner. Additional sensors such as Hall sensors or rotary encoders with optical sensors are not required.

[0019] The source voltage UQ is the output voltage provided by the voltage source without a connected load. When a load is connected, the current flowing in the circuit causes a voltage drop due to the internal resistance RQ of the voltage source, so that the actual output voltage or the control voltage UA is lower than the source voltage UQ.

[0020] In some embodiments of the spooling device, the motor controller can, for example, use an electronic switch in the motor's control circuit to interrupt the power supply to the motor periodically, for example every 20 ms, for a short time, for example for a period of approximately 2 ms. In this time window, the voltage component of the motor controller's voltage source drops to zero. A freewheeling diode is generally arranged in parallel with the motor in the reverse direction so that voltages induced in the motor by the switching operations can be neutralized by discharging via this freewheeling diode. Towards the end of each interruption interval, the motor controller can directly measure the value of the reverse voltage U BEMF. In particular, the voltage on the connecting lines to the motor can be recorded, for example on the motor side or downstream of the electronic switch, using an A / D converter. Alternatively, the charging time orThe discharge time of a capacitor can be determined by charging it with the reverse voltage U BEMF via a resistor or discharging it from U BEMF. The time until a specified reference voltage is reached varies depending on the reverse voltage U BEMF. If necessary, the corresponding value of the reverse voltage U BEMF can be determined from this, for example, using a look-up table.

[0021] Detection of the reverse voltage U BEMF is also possible in embodiments of the winding device in which the drive voltage UA for the motor is controlled or regulated by pulse width modulation. The drive frequency is preferably in the range of approximately 16 kHz to approximately 32 kHz, i.e., above the range audible to the human ear and low enough to keep switching losses as low as possible.

[0022] In speed-controlled winding devices, a controlled variable representing the actual rotational speed is generally acquired and processed as a feedback variable, along with a specified target speed as a reference variable, to produce a manipulated variable for controlling the motor. Instead of measured variables acquired by rotary encoders or Hall sensors, the reverse voltage U BEMF can be used as the feedback variable of the control loop. In a motor controller, the reverse voltage U BEMF can be acquired directly in the motor's control circuit and used as an equivalent measured variable to the rotational speed. Winding devices in which the motor speed is determined based on the reverse voltage U BEMF are comparatively simple, small, and cost-effective.

[0023] The motor controller preferably comprises at least one limit or comparison value for the reverse voltage U BEMF , which is stored or predefined in another way, e.g., by means of a voltage divider. With additional monitoring means, such as a monitoring process stored as program code of a control program, the motor controller can detect when the reverse voltage U BEMF rises above or falls below a comparison value and subsequently initiate suitable further process steps, such as interrupting the power supply to the motor.

[0024] For example, the reference value can be set sufficiently low so that the motor control reliably detects only a significant drop in motor speed due to the braking effect of the brake body. However, if the speed drops only slightly when winding sewing thread due to the increasing load on the sewing thread, it remains above the specified reference value.

[0025] The motor control may include means for continuously or stepwise changing the drive voltage UA provided for the motor. In particular, the pulse-to-pause ratio of a clocked voltage source can be gradually or continuously reduced by a control program according to predetermined rules, or directly set to zero as soon as the speed or the reverse voltage U BEMF drops below a predetermined limit.

[0026] Such motor controls, in which the motor speed is monitored using the reverse voltage U BEMF, can detect a drop in the motor speed comparatively easily and reliably and, depending on this speed, for example, interrupt the power supply to the motor or adapt or reduce the setpoint for controlling the motor speed.

[0027] In further embodiments of the winding device, instead of or in addition to the reverse voltage U BEMF, other electrical measured variables of the motor can be measured, in which typical changes occur due to the action of the brake body. Another measured variable is, for example, the motor current IM. The motor control can, for example, measure the motor current IM using a shunt, i.e., a small electrical resistor, in the motor circuit. The shunt voltage is evaluated.

[0028] The motor current IM increases with increasing motor load. Only when the motor is subjected to a significantly higher load due to the effect of the brake body does the motor current IM or a measured variable corresponding to the motor current IM, preferably smoothed using a low-pass filter, exceed a specified reference value. As soon as the motor control detects that the measured variable value is higher than the reference value, it initiates appropriate measures, such as interrupting the power supply to the motor.

[0029] Optionally, the motor controller can store characteristic values of the internal resistance RQ of the voltage source and the source voltage UQ provided by the voltage source. In such motor controllers, the control program can include program code for calculating the magnitude of the reverse voltage U BEMF based on the measured and preferably averaged motor current IM. U BEMF = UA - UM , where UA = UQ - (RQ x I m ).

[0030] The invention is described in more detail below with reference to some figures. Figure 1 shows a detail of a spooling device in a perspective view, Figure 2 shows the device from Figure 1 with a thread spool, Figure 3 a side view of the device according to Figure 1 , Figure 4 a side view of the device according to Figure 2 , Figure 5 is a block diagram with a motor control of the bobbin winding device, Figure 6 is a diagram of the time course of the bobbin speed when winding sewing thread in a bobbin winding device without speed control, Figure 7 is a diagram of the time course of the motor speed and the rate of change of the motor speed when winding sewing thread in a bobbin winding device with speed control, Figure 8 is a diagram of the time course of the motor voltage UM when periodically controlled with a series of voltage pulses.

[0031] Figure 1shows a perspective partial view of a spooling device, Figure 3 a side view of it.

[0032] The bobbin winding device comprises a bobbin winding motor, hereinafter also referred to as motor 1 for short, and a braking device 3, which are fastened to a common carrier 5. A spindle 7, which can be driven by the motor 1, is arranged coaxially to the motor axis A or to the drive shaft of the motor 1 and is connected to it in a rotationally fixed manner. The spindle axis A' and the motor axis A are identical in this embodiment. Alternatively, the spindle 7 could also be coupled or coupleable to the motor 1 by means of a transmission device such as a gear (not shown). The spindle 7 is rotatably mounted on the carrier 5 directly or indirectly by means of the motor 1. It can, for example, comprise a free end section with a first outer diameter D1 of, for example, approximately 6 mm for inserting and removing a thread spool 9. Adjacent to this, the spindle 7 can, for example, comprise a shoulder with a larger outer diameter D2.This shoulder serves as a stop for an end flange 9a of the thread spool 9 and defines its axial position when the thread spool 9 is placed on the spindle 7 and detachably connected to it in a rotationally fixed manner. This is shown in the . Figures 2 and 4 which essentially represent the Figures 1 and 3with thread spool 9 attached to spindle 7. Thread spool 9 comprises a substantially cylindrical sleeve 9b, at the ends of which two end flanges 9a project radially at an axial distance H from one another. Depending on the design of thread spool 9, the axial distance H between end flanges 9a can be, for example, in the order of magnitude of approximately 10mm to approximately 12mm. Sleeve 9b can be arranged flush with the end flanges 9a on the outside. Alternatively, sleeve 9b can project slightly beyond the end flanges 9a, for example by up to 1mm on each side. The height of thread spool 9 can therefore be somewhat greater than the distance H between end flanges 7a. In a common design of thread spool 9, the outer diameters of the end flanges are approximately 20.5mm and the height approximately 11.8mm.

[0033] Preferably, the length L of the free end section of the spindle 7 is matched to the height of the thread spools 9 to be accommodated, so that the length L is in the range of 0.5 H to 1.5 H. This saves space and allows for easy insertion and removal of thread spools 9.

[0034] The braking device 3 comprises a braking body 11 in the form of a hammer-shaped lever, for example, with a pivoting arm which is mounted on the support 5 next to the motor 1 so as to be pivotable about a pivot axis B, and with a head which projects laterally from the pivoting arm at a distance from the pivot axis B. This is shown in Figure 3represented by the double arrow P. The pivot axis B of the brake body 11 and the spindle axis A' are arranged essentially orthogonally to each other. The spindle axis A' lies in the pivot plane of the brake body 11. In alternative embodiments, the pivot axis B could also be aligned parallel to the spindle axis A' and the pivot plane of the brake body 11 could be arranged in a plane orthogonal to the spindle axis A' (not shown).

[0035] In a first end region of the pivot arm arranged at a distance from the pivot axis B, the brake body 11 comprises a section projecting in the direction of the spindle axis A' with a friction surface 13.

[0036] By pivoting the brake body 11 about the pivot axis B, the radial distance C of the friction surface 13 from the spindle axis A' can be changed. In general, the brake body 11 can be moved in a guided manner, whereby the distance C of the friction surface 13 from the spindle axis A' changes depending on the respective position of the brake body 11. In an end position, which is also referred to as the reference position, this distance C is minimal. This minimum distance C is also referred to as the reference distance C 0. Preferably, the spooling device comprises setting means for adjusting the reference distance C 0 . Alternatively, the reference distance C 0 can also be fixed. As a rule, the reference distance C 0 is determined by a first stop 15a on the brake body 11 and a second stop 15b on the carrier 5, which together limit the range of movement of the brake body 11 in the direction of the spindle axis A'. Preferably, the position of at least one of these stops 15a, 15b is variable.In the embodiment according to the . Figures 1 to 4 The first stop 15a is a shoulder protruding from the brake body 11 and the second stop 15b is the front end of an adjusting screw that is screwed into a thread on the carrier 5. By turning the adjusting screw, the position of the second stop 15b can be easily adjusted. This second stop 15b defines, by contact with the first stop 15a of the brake body 11, its reference position and thus also the reference distance C 0 of the friction surface 13 from the spindle axis A'. The brake body 11 is held in the reference position by the force of a restoring means, for example a spring 17. The spring 17 can, for example, be a helical spring that is held tensioned between the carrier 5 and the lever arm of the brake body 11. In the reference position, the spring 17 is slightly pretensioned so that it can hold the brake body 11 in the reference position. In the illustrations in the Figures 1 to 4The hook-shaped end of the spring 17 is loose. To use the spooling device, the spring 17 is tensioned by hooking this end into an adjacent hole 18 on the brake body 11.

[0037] When a thread spool 9 is attached to the spindle 7, the section of the brake body 11 with the friction surface 13 lies essentially between two planes defined by the parallel end flanges 9a of the thread spool 9. The friction surface 13 of the brake body 11 can be convex, at least in sections. With such brake bodies 11, the reference position can be specified such that at least a section of the friction surface 13 slightly extends into the area between the end flanges 9a of the thread spool 9. The reference distance C 0 of the friction surface 13 is then somewhat smaller than the outer radius R ( Fig. 4) of each of the end flanges 9a. The reference distance C 0 can, for example, be in the order of 85% to 100% of the outer radius R of the end flanges 9a. When winding sewing thread onto the thread spool 9, this causes the sewing thread wound onto the sleeve 9b to come into contact with the friction surface 13 before the maximum winding radius of the sewing thread reaches the value of the outer radius R of the end flanges 9a.

[0038] In such arrangements, the lower end flange 9a of a thread spool 9 displaces the brake body 11 outwardly against the acting spring force when the thread spool 9 is placed onto the spindle 7 or removed from the spindle 7. The spring constant of the spring 17 is dimensioned such that the force required to displace the brake body 11 from the reference position into a passing position, in which the distance C of the friction surface 13 to the spindle axis A' corresponds to the radius R of the spool flanges 9a, is rather small, for example, approximately 0.5N to approximately 5N.

[0039] However, the friction coefficient of the friction surface 13 with conventional sewing threads is sufficiently large so that at least one electrical characteristic in the control circuit of the motor 1 changes significantly or clearly measurably as soon as the friction surface 13 comes into contact with the wound sewing thread during the winding process and exerts a braking force or a braking torque on the wound thread spool 9.

[0040] As the sewing thread is further wound, the diameter of the wound sewing thread increases further, displacing the brake body 11 from its reference position against the force of the spring 17. This progressively increases the braking force exerted by the brake body 11 on the thread spool 9 containing the wound sewing thread. This additional load on the motor 1 can be detected using electrical measurement variables in the control circuit of the motor 1.

[0041] The brake body 11 is preferably made of a dimensionally stable plastic. It can, in particular, comprise an injection-molded plastic part. Optionally, the brake body 11 can be made of a different material in the area of the friction surface 13, depending on the desired braking effect, such as abrasion-resistant material and / or having a higher coefficient of friction. Additionally or alternatively, the friction surface 13 can comprise structures such as ribs.

[0042] Optionally, the brake body 11 can include an integrated blade 14 for easy cutting of the sewing thread after completion of the winding process.

[0043] The motor 1 or at least one coil of the motor 1 is connected to a motor control 21 via two electrical conductors 22. The motor control 21 comprises, as in Figure 5Shown is a voltage source 23, which generates a source voltage UQ, usually controlled by a microcontroller 25. Due to the internal resistance RQ of the voltage source 23, the output voltage or control voltage UA for controlling the motor 1 is load-dependent and thus less than or equal to the source voltage UQ. The voltage source 23 is connected to the motor 1 via the electrical conductors 22 to form a control circuit.

[0044] Preferably, at least one of these conductors 22 in the motor controller 21 comprises an electronic switch 27 for interrupting and closing this circuit. With such switches 27, the motor controller 21 can comprise means on the voltage source side and / or the motor side for detecting the voltage between the conductors 22. In particular, for example, a voltage divider comprising two high-value resistors can be arranged between the conductors 22 and connected to a measuring device of the motor controller 21 for measuring the center voltage (not shown). The center voltage is proportional to the voltage between the conductors 22 in the ratio of the resistance values. As a rule, a freewheeling diode (diode 24 for short) is arranged in the blocking direction between the conductors 22. A discharge current from the motor coil can flow through this diode 24 when the circuit is interrupted.

[0045] If the circuit is interrupted by switch 27, motor control 21 can determine the source voltage UQ on the voltage source 23 side. On the motor 1 side, motor control 21 can determine the instantaneous reverse voltage U BEMF of motor 1 shortly after the circuit is interrupted, i.e., after a decay time of approximately 1 to 3 ms. This is proportional to the motor speed.

[0046] Preferably, the motor controller 21 includes a shunt 29 or a resistor RS with a small value in the order of magnitude of, for example, one ohm in one of the conductors 22, which enables the determination of the motor current IM based on the voltage drop US = IM x RS. The shunt 29 is arranged in series with the motor 1 between the conductors 22 of the motor circuit. The voltage drop across the shunt 29 can be measured using a measuring device (not shown). This is proportional to the motor current IM.

[0047] The load on the motor 1 increases when winding up sewing thread due to the increasing moment of inertia of the spool assembly and the increasing sewing thread resistance. As soon as the brake body 11 exerts an additional braking force on the spool assembly, the load suddenly increases. This affects electrical parameters such as the motor current IM , the control voltage UA , the motor voltage UM and the reverse voltage U BEMF . The motor controller 21 is designed to monitor at least one of these parameters by detecting its values using a sensor device in the control circuit of the motor 1 and comparing it with a reference value predetermined for this parameter. If the determined parameter value exceeds or falls below the reference value due to the increasing load on the motor 1, the motor controller 21 initiates suitable measures such as, for example,the interruption of the control circuit with one of the switches 27 and / or the reduction of the source voltage UQ in one or more steps to 0 V. This is particularly possible with a clocked voltage source 23, in which the source voltage UQ can be changed by changing the duty cycle or the pulse-pause ratio of voltage pulses.

[0048] At Figure 6The bold line L1 shows the temporal progression of the rotational speed ω of a spindle 7 in revolutions per minute (rpm) when winding sewing thread, wherein the motor 1 is controlled by an unregulated direct voltage. As soon as the motor 1 is connected to the voltage source 23, the rotational speed increases to a maximum value and then decreases continuously due to the increasing load on the motor 1. At point P1, the braking effect of the brake body 11 begins. The rotational speed ω then decreases significantly more sharply and shortly thereafter falls below a predetermined comparison value ω S at point P2. The motor control 21 detects this and can cause the motor 1 to be switched off.

[0049] At Figure 7The bold line L2 shows, in an analogous manner, the time course of the speed ω of the spindle 7, whereby the motor control 21 regulates the speed ω to a predetermined setpoint ω 0 . The reverse voltage U BEMF of the motor 1 is used as the feedback variable. In addition, the solid thin line L3 shows the time derivative of the speed or the time course of the speed change ω'.

[0050] During the winding of sewing thread, the motor control 21 regulates the control voltage UA for the motor 1 such that its speed ω essentially corresponds to the setpoint value ω 0 . After the braking effect of the brake body 11 begins at point P1, the motor power is no longer sufficient to maintain the setpoint speed ω 0 . The speed ω drops rapidly until it drops below the specified comparison value ω S at point P2.

[0051] In an analogous manner, a comparison value ω' S can be defined for the speed change ω', below which the motor control 21 can interrupt the power supply to the motor 1.

[0052] In some embodiments of the winding device, the sensor device of the motor controller 21 comprises a current sensor for detecting the motor current IM and / or a voltage sensor for detecting the drive voltage UA. These measured variables can be easily detected in the drive circuit during operation of the motor 1 and, if necessary, additionally smoothed, e.g., using a low-pass filter.

[0053] In some embodiments of the winding device, the source voltage UQ provided by the voltage source 23 is variable. This can be achieved, for example, by an electronic switching element periodically establishing and interrupting a connection to a provided operating voltage at a high switching frequency of approximately 16 kHz to approximately 20 kHz. The electronic switches 27 in the connecting conductors 22 to the motor 1 can also be used as switching elements. The mark-to-space ratio determines the value of the motor voltage UM thus provided. By increasing or decreasing this mark-to-space ratio, the motor controller 21 can increase or decrease the motor power and thus the speed ω of the motor 1. Preferably, the motor controller 21 comprises predetermined rules, e.g. stored in the microcontroller 25, for controlling the pulse width ratio. By means of such specifications, for example,When winding sewing thread onto an empty thread spool 9, the speed ω of the spindle 7 can be influenced depending on the elapsed winding time and / or the detected motor current IM. In particular, the speed ω of the spindle 7 can be reduced as the fill level of the thread spool 9 increases.

[0054] In some embodiments of the bobbin winding device, the motor controller 21 can, for example, regulate the motor voltage UM or the reverse tension U BEMF to a predetermined setpoint during the winding of sewing thread by detecting this tension as a measured variable and adjusting the pulse / pause ratio so that the motor voltage UM or the reverse tension U BEMF corresponds to the setpoint. In an analogous manner, the motor voltage UM and / or the reverse tension U BEMF can also be detected and regulated to a predetermined value.

[0055] Motor controllers 21 can be designed to repeatedly interrupt the power supply to motor 1 for short intervals at least long enough for the motor inductance to be discharged via diode 24 or for the voltage induced by the respective switching operation to be reduced. The duration t 2 of the time intervals depends on the motor inductance and the respective motor current. It is usually in the order of magnitude of approximately 1 ms to approximately 3 ms, in particular approximately 2 ms. Within these time intervals, the motor voltage UM drops to the value of the reverse voltage U BEMF , which is caused by self-induction in the coil windings of motor 1 and is proportional to the speed ω of motor 1.

[0056] As in Figure 8 As shown, a motor controller 21 can be designed to determine the reverse voltage U BEMF even in the case of clocked motors 1.

[0057] The motor 1 is periodically controlled with a series of rectangular voltage pulses for a duration t 1 , which is, for example, in the order of magnitude of approximately 10 ms to approximately 100 ms, in particular approximately 18 ms to 20 ms. The motor controller 21 generates a corresponding control signal U PWM with a specific pulse / pause ratio. In accordance with the rhythm of this control signal U PWM, an electrical switching element is connected to a provided operating voltage in order to generate a control voltage UA, the value of which is determined by the pulse / pause ratio.

[0058] In a subsequent measuring interval, the duration t 2 of which is preferably in the range of approximately 1 ms to approximately 3 ms, the motor controller 21 interrupts the control circuit. The motor voltage UM measurable on the connecting lines 22 to motor 1 drops to the value of the reverse voltage U BEMF during this measuring interval. After a delay time t 4 , the motor controller 21 records the value of this reverse voltage U BEMF at point P4 shortly before the end of the measuring interval.

[0059] This cycle, whose duration t 3 corresponds to the sum of t 1 + t 2, is then repeated. Preferably, the period t 3 is in the range of approximately 15 ms to approximately 30 ms, in particular approximately 20 ms.

[0060] Such motor controls 21 can include a speed control. In this case, U BEMF is detected as a measured variable in the control circuit of the motor 1, and the pulse / pause ratio when controlling the motor 1 is controlled such that U BEMF assumes a predetermined value. When winding sewing thread onto a thread spool 9, the speed of the spindle 7 can, for example, be kept constant or adjusted as a function of time according to a function predetermined in the motor control 21. The motor control 21 can, for example, include two or more different default values for the speed ω, which are activated at predetermined times during or after the start of the winding process. For example, it is possible to reduce the speed ω of the spindle 7 in steps. This can prevent the amount of thread wound up per unit of time from constantly increasing due to the increasing outer diameter of the wound sewing thread.In particular, the peripheral speed of the wound sewing thread can be reduced before the friction surface 13 of the brake body 11 comes into contact with the sewing thread. The spindle 7 can thus be driven at optimized speeds ω, for example, to wind sewing thread onto a thread spool 9 in the shortest possible time. The speed ω can be reduced in good time before the friction surface 13 of the brake body 11 comes into contact with the wound sewing thread, in order to enable gentle braking by the brake body 11.

[0061] The delay time until the speed is reduced or the corresponding duration after starting the winding process can be predefined in the motor control 21, for example. Since the time at which the friction surface 13 hits the wound sewing thread depends on various parameters, one or more different times for reducing the speed can optionally be specified depending on at least one of these parameters. Such parameters are, for example, the thread or sewing thread thickness, the average thread length wound per unit of time, dimensions of the thread spool 9, such as e.g. the sleeve diameter, the radius R or the mutual distance H of the coil flanges 9a, the reference distance C 0 of the friction surface 13 to the spindle axis A' and, if applicable, the outer diameter of wound sewing thread or the degree of filling of the thread spool 9 at the beginning of the winding process.

[0062] The detection of the reverse voltage U BEMF is particularly advantageous because it can be performed at time intervals in which the control circuit of motor 1 is interrupted. Interference from the voltage source 23 is therefore negligible.

[0063] Furthermore, the motor controller 21 can include stored control rules for detecting the reverse voltage U BEMF for further purposes. In particular, the motor controller 21 can be designed to detect the reverse voltage U BEMF even when the spindle 7 and thus also the drive shaft of the motor 1 are rotated manually, wherein the voltage source 23 is inactive and / or the motor circuit is interrupted. Depending on the direction of rotation of the spindle 7, a reverse voltage U BEMF with a positive or negative sign is then generated, which is detected by a voltage sensor of the motor controller 21. The spindle 7 or the drive shaft of the motor 1 can thus be used as a user interface for controlling the bobbin winder or other parts of the sewing machine. For example,The state of a visual or acoustic display or representations on a graphical user interface can be changed to support required user actions for winding sewing thread onto the thread spool 9 as soon as the spindle 7 is manually rotated. In particular, the motor controller 21 can include stored control rules to check the direction of rotation of the motor 1 during manual winding of the first turns of sewing thread and to issue an alarm signal if this does not match the direction of rotation of the motor 1.

Claims

1. A bobbin winder device of a sewing machine, comprising a motor (1); a spindle (7) mounted on a support (5) and configured to rotate about a spindle axis (A') and which is driveable by said motor (1), for releasable attachment of a thread bobbin (9) to be filled with sewing thread; and a motor controller (21) connected to the motor (1) via electrical conductors (22) and configured to control or regulate the rotational speed (ω) of the motor (1), characterized in that a brake body (11) with a friction surface (13) is movably held on the support (5), wherein the distance (C) between the friction surface (13) and the spindle axis (A') is variable; that the friction surface (13) can be positioned next to the spindle (7) in a reference position with a predeterminable reference distance (C0) from the spindle axis (A') corresponding to a maximum winding radius of the sewing thread to be wound and is displaceable radially outwards from the reference position counter to a force of a restoring element, in particular a spring (17), with respect to the spindle axis (A'); and that the motor controller (21) comprises a sensor means for detecting at least one measured variable, which is dependent on a load of the motor (1), in a driving circuit of the motor (1) and a stored comparison value for the measured variable and / or a stored comparison value for the rate of change of the measured variable over time.

2. A bobbin winder device according to claim 1, characterized in that the brake body (11) comprises a pivot arm mounted on the support (5) next to the motor (1) to pivot about a pivot axis (B), and that the friction surface (13) is spaced apart from the pivot axis (B) on a head protruding on a side of the pivot arm.

3. A bobbin winder device according to claim 2, characterized in that a first stop (15a) is arranged on the brake body (11) and a second stop (15b) is arranged on the support (5), said first and second stops together limiting a freedom of movement of the brake body (11) in a direction of the spindle axis (A'), thereby defining the reference position of the brake body (11) and the reference distance (C0) between the friction surface (13) and the spindle axis (A').

4. A bobbin winder device according to claim 3, characterized in that at least one of the stops (15a, 15b) is moveable for adjusting the reference position of the brake body (11) and the reference distance (C0) between the friction surface (13) and the spindle axis (A').

5. A bobbin winder device according to any one of claims 1 to 4, characterized in that the brake body (11) is convex in a region of the friction surface (13).

6. A bobbin winder device according to any one of claims 1 to 5, characterized in that the motor controller (21) comprises in at least one of the conductors (22) an electronic switch (27) for interrupting and closing the driving circuit.

7. A bobbin winder device according to any one of claims 1 to 6, characterized in that the sensor means of the motor controller (21) comprises at least one voltage sensor for measuring a voltage between the conductors (22) in the driving circuit of the motor (1).

8. A bobbin winder device according to claim 7, characterized in that the voltage sensor is arranged between the conductors (22) such that the voltage sensor is connected to the motor (1) even when the driving circuit is interrupted, and that the motor controller (21) comprises control specifications for periodically detecting the reverse voltage (UBEMF) of the motor (1), wherein the following steps are periodically carried out: a) interrupting the driving circuit b) measuring the reverse voltage (UBEMF) using the voltage sensor after a delay time (t4) c) closing the driving circuit.

9. A bobbin winder device according to claim 8, characterized in that the motor controller (21) comprises stored control specifications for comparing the detected reverse voltage (UBEMF) of the motor (1) or a rate of change of the reverse voltage (UBEMF) over time with an associated stored comparison value, and stored control specifications for interrupting the driving circuit if the reverse voltage (UBEMF) or the rate of change thereof over time falls below or exceeds the associated comparison value.

10. A bobbin winder device according to claim 8 or 9, characterized in that the motor controller (21) comprises the control specifications for detecting the reverse voltage (UBEMF) of the motor (1) in case of a manual rotation of the spindle (7).

11. A method for controlling or regulating the speed (ω) of the motor (1) of a bobbin winder device as claimed in claim 1, whereby sewing thread is wound onto a thread bobbin (9) attached to the spindle (7), characterized in the motor controller (21) monitors a measured variable, which is dependent on the load on the motor (1) and which is detected by the sensor means in the driving circuit of the motor (1), and causes the motor to shut down as soon as the value of the detected measured variable falls below the associated stored comparison value.