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

Abstract

A bobbin winder device of a sewing machine includes a motor (1), which is controlled by a motor controller (21), in order to drive a spindle (7), to which a thread bobbin (9) can be attached in order to wind on sewing thread. A brake device (3) with a brake pad (11), which brakes the bobbin arrangement when the winding radius of the wound sewing thread is greater than a predetermined reference value (C.sub.0), is arranged next to the spindle (7). The motor controller (21) monitors at least one measured variable, which is dependent on the load on the motor (1), in the driving circuit of the motor (1). If this measured variable or the rate of change thereof changes such that it falls below or exceeds an associated stored comparison value, the motor controller (21) causes the motor (1) to be shut down.

Claims

1. A bobbin winder device of a sewing machine, the bobbin winder device comprising: a motor; a spindle mounted on a support and configured to rotate about a spindle axis and which is driveable by said motor, for releasable attachment of a thread bobbin to be filled with sewing thread; a motor controller connected to the motor via electrical conductors and configured to control or regulate a rotational speed of the motor; a brake pad with a friction surface held on the support so as to be movable, wherein a distance between the friction surface and the spindle axis is variable, such that the friction surface is positionable next to the spindle in a reference position with a predeterminable reference distance from the spindle axis 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 with respect to the spindle axis; and the motor controller comprises a sensor configured to detect at least one measured variable, which is dependent on a load of the motor, in a driving circuit of the motor and at least one of a) a stored comparison value for said measured variable or b) a stored comparison value for a rate of change of the measured variable over time.

2. The bobbin winder device as claimed in claim 1, wherein the brake pad comprises a pivot arm mounted on the support next to the motor to pivot about a pivot axis, and the friction surface is spaced apart from the pivot axis on a head protruding on a side of the pivot arm.

3. The bobbin winder device as claimed in claim 2, further comprising a first stop (15a) arranged on the brake pad and a second stop arranged on the support, said first and second stops together limit a freedom of movement of the brake pad in a direction of the spindle axis to define the reference position of the brake pad and the reference distance between the friction surface and the spindle axis.

4. The bobbin winder device as claimed in claim 3, wherein at least one of the first or second stops is moveable in order to adjust the reference position of the brake pad and the reference distance between the friction surface and the spindle axis.

5. The bobbin winder device as claimed in claim 1, wherein the brake pad is convex in a region of the friction surface.

6. The bobbin winder device as claimed in claim 1, wherein the motor controller comprises in at least one of the conductors an electronic switch for interrupting and closing the driving circuit.

7. The bobbin winder device as claimed in claim 1, wherein the sensor of the motor controller comprises at least one voltage sensor for measuring a voltage between the conductors in the driving circuit of the motor.

8. The bobbin winder device as claimed in claim 7, wherein the voltage sensor is arranged between the conductors such that the voltage sensor is connected to the motor even when the driving circuit is interrupted, and the motor controller comprises control specifications for periodically detecting a reverse voltage of the motor, and the motor controller is configured to periodically carry out the following steps: a) interrupting of the driving circuit, b) measuring the reverse voltage using the voltage sensor after a delay time, and c) closing of the driving circuit.

9. The bobbin winder device as claimed in claim 8, wherein the motor controller comprises the control specifications stored in the motor controller for comparing the detected reverse voltage of the motor or a rate of change of the reverse voltage over time with an associated stored comparison value, and the control specifications stored in the motor controller for interrupting the driving circuit if the reverse voltage or the rate of change thereof over time falls below or exceeds the associated comparison value.

10. The bobbin winder device as claimed in claim 9, wherein the motor controller comprises the control specifications for detecting the reverse voltage of the motor in case of a manual rotation of the spindle.

11. A method for controlling or regulating the speed of the motor of the bobbin winder device as claimed in claim 1, the method comprising: winding the sewing thread onto the thread bobbin, which is attached to the spindle, the motor controller monitoring a measured variable, which is dependent on the load on the motor and which is detected by the sensor in the driving circuit of the motor, and causing the motor to shut down as soon as the value of the detected measured variable falls below the associated stored comparison value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The invention is described in more detail in the following text with reference to a number of figures, in which:

[0034] FIG. 1 shows a perspective view of a detail of a bobbin winder device,

[0035] FIG. 2 shows the device of FIG. 1 with a thread bobbin,

[0036] FIG. 3 shows a side view of the device according to FIG. 1,

[0037] FIG. 4 shows a side view of the device according to FIG. 2,

[0038] FIG. 5 shows a block diagram with a motor controller of the bobbin winder device,

[0039] FIG. 6 shows a graph of the time profile of the winding speed when sewing thread is wound in a bobbin winder without speed regulation,

[0040] FIG. 7 shows a graph of the time profile of the motor speed and the rate of change of the motor speed when winding sewing thread in a bobbin winder device with speed regulation, and

[0041] FIG. 8 shows a graph of the time profile of the motor voltage UM in the case of periodic driving with a series of voltage pulses.

DETAILED DESCRIPTION

[0042] FIG. 1 shows a partial view of a bobbin winder device in perspective, with FIG. 3 showing a side view of it.

[0043] The bobbin winder device comprises a bobbin winder motor, henceforth also referred to as motor 1 for short, and a brake device 3, which are secured to a common support 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 connected thereto in a rotationally fixed manner. The spindle axis A and the motor axis A are identical in this embodiment. As an alternative, the spindle 7 could also be coupled or able to be coupled to the motor 1 by means of a transmission device such as, for example, a gearbox (not shown). The spindle 7 is mounted on the support 5 so as to be able to rotate directly or indirectly by means of the motor 1. For example, said spindle can comprise a free end section with a first outer diameter D1 of, for example, about 6 mm for attaching and removing a thread bobbin 9. Adjacent thereto, the spindle 7 can comprise, for example, a step with a larger outer diameter D2. This step is a stop for an end flange 9a of the thread bobbin 9 and defines the axial position thereof when the thread bobbin 9 is attached to the spindle 7 and is releasably connected thereto in a rotationally fixed manner. This is shown in FIGS. 2 and 4, which essentially correspond to FIGS. 1 and 3 with the thread bobbin 9 secured to the spindle 7. The thread bobbin 9 comprises a substantially cylindrical sleeve 9b, at the ends of which two end flanges 9a protrude radially at an axial distance H from one other. Depending on the embodiment of the thread bobbin 9, the axial distance H between the end flanges 9a may be, for example, in the order of magnitude from about 10 mm to about 12 mm. The sleeve 9b can be arranged flush to the outside of the end flanges 9a. As an alternative, the sleeve 9b can slightly overhang the end flanges 9a, for example up to 1 mm on each side. The height of the thread bobbin 9 can therefore be slightly larger than the distance H between the end flanges 9a. In a common embodiment of the thread bobbin 9, the outer diameters of the end flanges are about 20.5 mm and the height is about 11.8 mm.

[0044] The length L of the free end section of the spindle 7 is preferably matched to the height of the thread bobbins 9 to be received, with the result that the length L is in the order of magnitude of 0.5 H to 1.5 H. This saves space and allows easy attachment and removal of thread bobbins 9.

[0045] The brake device 3 comprises a brake pad 11 in the form of a, for example hammer-shaped, lever with a pivot arm, which is mounted on the support 5 next to the motor 1 so as to be able to pivot about a pivot axis B, and with a head which protrudes on the side of the pivot arm at a distance from the pivot axis B. This is shown in FIG. 3 by way of the double-headed arrow P. The pivot axis B of the brake pad 11 and the spindle axis A are arranged substantially orthogonal to one other. The spindle axis A lies in the pivot plane of the brake pad 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 pad 11 could be arranged in an orthogonal plane to the spindle axis A (not shown).

[0046] In a first end region of the pivot arm arranged spaced apart from the pivot axis B, the brake pad 11 comprises a section with a friction surface 13 which protrudes in the direction of the spindle axis A.

[0047] The radial distance C between the friction surface 13 and the spindle axis A can be changed by pivoting the brake pad 11 about the pivot axis B. Generally, the brake pad 11 can be moved in a guided manner, where the distance C between the friction surface 13 and the spindle axis A changes depending on the respective position of the brake pad 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 CO. The bobbin winder device preferably comprises adjusting means for adjusting the reference distance CO. As an alternative, the reference distance CO can also be fixed. As a rule, the reference distance CO is determined by a first stop 15a on the brake pad 11 and a second stop 15b on the support 5, which stops together limit the freedom of movement of the brake pad 11 in the direction of the spindle axis A. The position of at least one of these stops 15a, 15b is preferably variable. In the embodiment according to FIGS. 1 to 4, the first stop 15a is a step protruding on the brake pad 11 and the second stop 15b is the front end of an adjusting screw screwed into a thread on the support 5. The position of the second stop 15b can be easily adjusted by turning the adjusting screw. This second stop 15b defines the reference position of the brake pad 11 by means of attachment to the first stop 15a of said brake pad and thus also defines the reference distance CO between the friction surface 13 and the spindle axis A.

[0048] The brake pad 11 is held in the reference position by the force of a restoring means, for example a spring 17. The spring 17 may be, for example, a coil spring which is held tensioned between the support 5 and the lever arm of the brake pad 11. In the reference position, the spring 17 is slightly preloaded so that it can hold the brake pad 11 in the reference position. In the illustrations in FIGS. 1 to 4, the one end of the spring 17 that is bent in a hook-shaped manner is loose. In order to use the bobbin winder device, the spring 17 is tensioned by hooking this end into an adjacent hole 18 on the brake pad 11.

[0049] When a thread bobbin 9 is attached to the spindle 7, the section of the brake pad 11 with the friction surface 13 is substantially between two planes which are defined by the parallel end flanges 9a of the thread bobbin 9.

[0050] The friction surface 13 of the brake pad 11 may be convex at least in sections. In such brake pads 11, the reference position can be predetermined such that at least one section of the friction surface 13 slightly dips into the region between the end flanges 9a of the thread bobbin 9. The reference distance CO of the friction surface 13 is then slightly smaller than the outer radius R (FIG. 4) of each of the end flanges 9a. For example, the reference distance CO can be in the order of magnitude of from 85% to 100% of the outer radius R of the end flanges 9a. When sewing thread is wound onto the thread bobbin 9, this causes the sewing thread which is 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.

[0051] In such arrangements, the lower end flange 9a of a thread bobbin 9 displaces the brake pad 11 counter to the acting spring force outward when the thread bobbin 9 is attached to the spindle 7 or is removed from the spindle 7. The spring constant of the spring 17 is dimensioned such that the force required for displacing the brake pad 11 from the reference position into a passing position, in which the distance C between the friction surface 13 and the spindle axis A corresponds to the radius R of the bobbin flanges 9a, is rather low, for example about 0.5 N to about 5 N.

[0052] However, the coefficient of friction of the friction surface 13 with conventional sewing threads is sufficiently large so that at least one electrical characteristic variable in the driving circuit of the motor 1 changes significantly or in a way that can be clearly measured 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 bobbin 9.

[0053] By further winding of sewing thread, the diameter of the wound sewing thread increases further, whereby the brake pad 11 is displaced from the reference position counter to the force of the spring 17. In this case, the braking force which is exerted by the brake pad 11 on the thread bobbin 9 with the wound sewing thread increases more and more. This additional load on the motor 1 can be detected by means of electrical measured variables in the driving circuit of the motor 1.

[0054] The brake pad 11 is preferably made of a dimensionally stable plastic. In particular, it may include an injection-molded part made of plastic. As an option, the brake pad 11 in the region of the friction surface 13 may be made of another material, which is, for example, abrasion-resistant and/or has a higher coefficient of friction, according to the braking effect to be achieved. In addition or as an alternative, the friction surface 13 can include structures such as ribs, for example.

[0055] As an option, the brake pad 11 may comprise an integrated blade 14 for easy cutting of the sewing thread after the winding process has been completed.

[0056] The motor 1 or at least one coil of the motor 1 is connected to a motor controller 21 via two electrical conductors 22. The motor controller 21 comprises a voltage source 23, as shown in FIG. 5, which usually generates a source voltage UQ in a manner controlled by a microcontroller 25. Due to the internal resistance RQ of the voltage source 23, the output voltage or driving voltage UA for driving the motor 1 is dependent on the load and is thus lower than or equal to the source voltage UQ. The voltage source 23 is connected to the motor 1 via the electrical conductors 22 so as to form a driving circuit.

[0057] At least one of these conductors 22 preferably comprises in the motor controller 21 an electronic switch 27 for interrupting and closing this circuit. In such switches 27, the motor controller 21 may include means on the voltage source side and/or on the motor side for detecting the voltage between the conductors 22. In particular, a voltage divider consisting of two high-resistance resistors can be arranged, for example, between the conductors 22 and can be 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 wires 22 in relation to the resistance values. As a rule, a freewheeling diode, diode for short, 24 is arranged in the reverse direction between the conductors 22. A discharge current of the motor coil can flow via this diode 24 when the circuit is disconnected.

[0058] If the circuit is interrupted by the switch 27, the motor controller 21 can identify the source voltage UQ on the side of the voltage source 23. On the motor side 1, the motor controller 21 can identify the instantaneous reverse voltage UBEMF of the motor 1 shortly after the circuit has been interrupted, that is to say after a decay time of about 1 to 3 ms. This instantaneous reverse voltage is proportional to the speed of the motor.

[0059] The motor controller 21 preferably comprises in one of the conductors 22 a shunt 29 or a resistor RS with a low value in the order of magnitude of, for example, one ohm, which enables the identification of the motor current IM based on the voltage drop US=IM?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 by way of a measuring apparatus (not shown). This voltage drop is proportional to the motor current IM.

[0060] The load on the motor 1 increases when sewing thread is wound due to the increasing moment of inertia of the bobbin arrangement and the increasing sewing thread resistance. As soon as the brake pad 11 exerts an additional braking force on the bobbin arrangement, the load suddenly increases more significantly. This has an effect on electrical parameters such as the motor current IM, the driving voltage UA, the motor voltage UM and the reverse voltage UBEMF. The motor controller 21 is designed to monitor at least one of these parameters by detecting its values by means of a sensor apparatus in the driving circuit of the motor 1 and comparing these with a comparison value which is predetermined for this parameter. If the determined parameter value exceeds or falls below the comparison 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 driving circuit by way of 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 by way of 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.

[0061] In FIG. 6, the bold line L1 shows the time profile of the speed ? of a spindle 7 in revolutions per minute (rpm) when sewing thread is wound, where the motor 1 is driven by way of an unregulated DC voltage. As soon as the motor 1 is connected to the voltage source 23, the speed increases to a maximum value and then decreases continuously due to the increasing load on the motor 1. The braking effect of the brake pad 11 starts at point P1. The speed ? then decreases significantly more sharply and shortly thereafter falls below a predefined comparison value ?S at point P2. The motor controller 21 detects this and can cause the motor 1 to be switched off.

[0062] In FIG. 7, the bold line L2 shows in an analogous manner the time profile of the speed ? of the spindle 7, where the motor controller 21 regulates the speed ? to a predetermined setpoint ?0. The reverse voltage UBEMF of the motor 1 is used here as the feedback variable. In addition, the thin solid line L3 shows the time derivative of the speed or the time profile of the change in speed ?.

[0063] During the winding of sewing thread, the motor controller 21 regulates the driving voltage UA for the motor 1 so that its speed ? essentially corresponds to the setpoint ?0. Once the braking effect of the brake pad 11 has been applied at point P1, the motor power is no longer sufficient to maintain the setpoint speed ?0. The speed ? drops rapidly until it drops below the specified comparison value ?S at point P2.

[0064] In an analogous manner, it is possible to define a comparison value ?S for the change in speed ?, the motor controller 21 being able to initiate the interruption of the power supply to the motor 1 when said comparison value is undershot.

[0065] In some embodiments of the bobbin winder device, the sensor apparatus of the motor controller 21 comprises a current sensor for detecting the motor current IM and/or a voltage sensor for detecting the driving voltage UA. These measured variables can easily be detected in the driving circuit during operation of the motor 1 and, if necessary, can also be smoothed, for example using a low-pass filter.

[0066] In some embodiments of the bobbin winder device, the source voltage UQ which is provided by the voltage source 23 is variable. This can be achieved, for example, by an electronic switching element with a high switching frequency of about 16 kHz to about 20 kHz periodically establishing and interrupting a connection to a provided operating voltage. The electronic switches 27 in the connecting conductors 22 to the motor 1 can also be used as switching elements.

[0067] The pulse-pause ratio determines the value of the motor voltage UM which is provided in this way. By increasing or decreasing this pulse-pause ratio, the motor controller 21 can increase or decrease the motor power and thus the speed ? of the motor 1. The motor controller 21 preferably comprises predetermined rules, for example rules stored in the microcontroller 25, for controlling the pulse width ratio. By means of such specifications, it is possible to influence the speed ? of the spindle 7 depending on the elapsed winding time and/or the detected motor current IM, for example when winding sewing thread onto an empty thread bobbin 9. In particular, the speed ? of the spindle 7 can be reduced as the fill level of the thread bobbin 9 increases.

[0068] In some embodiments of the bobbin winder device, the motor controller 21 can regulate, for example, the motor voltage UM or the reverse voltage UBEMF during the winding of sewing thread to a predetermined setpoint by detecting this voltage as a measured variable and adjusting the pulse-pause ratio so that the motor voltage UM or the reverse voltage UBEMF corresponds to the setpoint.

[0069] In an analogous manner, the motor voltage UM and/or the reverse voltage UBEMF can be detected and regulated to a predetermined value.

[0070] Motor controllers 21 may be designed to repeatedly interrupt the power supply to the motor 1 during short intervals at least for so long that the motor inductance can be discharged via the diode 24 or the voltage which is induced by the respective switching process can be reduced. The duration t2 of the time intervals is dependent on the motor inductance and on the respective motor current. Said duration is usually in the order of magnitude of about 1 ms to about 3 ms, in particular about 2 ms. Within these time intervals, the motor voltage decreases UM reduces to the value of the reverse voltage UBEMF, which is caused by self-induction in the coil windings of the motor 1 and is proportional to the speed ? of the motor 1.

[0071] As shown in FIG. 8, a motor controller 21 may be designed to determine the reverse voltage UBEMF even with motors 1 that are driven in a clocked manner.

[0072] In this case, the motor 1 is actuated periodically for a duration t1, for example in the order of magnitude of about 10 ms to about 100 ms, in particular about 18 ms to 20 ms, with a series of square-wave voltage pulses. The motor controller 21 in this case generates a corresponding control signal UPWM with a specific pulse-pause ratio. In the rhythm of this control signal UPWM, an electrical switching element is connected to a supplied operating voltage in order to generate a driving voltage UA, the value of which is determined by the pulse-pause ratio.

[0073] In a subsequent measurement interval, the duration t2 of which is preferably in the order of magnitude of about 1 ms to about 3 ms, the motor controller 21 interrupts the driving circuit. The motor voltage UM which can be measured at the connecting lines 22 to the motor 1 decreases to the value of the reverse voltage UBEMF during this measuring interval. After a delay time t4, the motor controller 21 detects the value of this reverse voltage UBEMF shortly before the end of the measuring interval at point P4.

[0074] This cycle, the duration t3 of which is the sum of t1+t2, is then repeated. The period t3 is preferably in the range of about 15 ms to about 30 ms, in particular about 20 ms.

[0075] Such motor controllers 21 may include speed regulation. In this case, UBEMF is detected as a measured variable in the driving circuit of the motor 1 and, when the motor 1 is driven, the pulse-pause ratio is regulated in such a way that UBEMF assumes a predetermined value. When sewing thread is wound onto a thread bobbin 9, the speed of the spindle 7 may, for example, be kept constant or adjusted depending on the time according to a function specified in the motor controller 21. By way of example, the motor controller 21 may comprise two or more different specified values for the speed w, which are activated at specified times during or after the start of the winding process. For example, it is thus possible to gradually reduce the speed ? of the spindle 7. This can prevent the amount of thread wound per unit of time from steadily 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 pad 11 comes into contact with the sewing thread. The spindle 7 can thus be driven with optimized speeds ?, for example in order to wind sewing thread onto a thread bobbin 9 in the shortest possible time. The speed ? can be reduced in good time before the friction surface 13 of the brake pad 11 comes into contact with the wound sewing thread in order to allow gentle braking by the brake pad 11.

[0076] The delay time until the speed is reduced or the corresponding duration after the winding process has started may, for example, be fixed in the motor controller 21. Since the time of impact of the friction surface 13 on 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 thickness of the thread or sewing thread, the average thread length wound per unit of time, dimensions of the thread bobbin 9, such as, for example, the sleeve diameter, the radius R or the mutual distance H between the bobbin flanges 9a, the reference distance CO between the friction surface 13 and the spindle axis A and, if applicable, the outer diameter of the wound sewing thread or the fill level of the thread bobbin 9 at the beginning of the winding process.

[0077] The detection of the reverse voltage UBEMF is therefore particularly advantageous because it can be carried out at time intervals in which the driving circuit of the motor 1 is interrupted. Disturbances caused by the voltage source 23 are therefore negligible.

[0078] In addition, the motor controller 21 may include stored control instructions for detecting the reverse voltage UBEMF for further purposes. In particular, the motor controller 21 may be designed to detect the reverse voltage UBEMF even when the spindle 7 and thus also the drive shaft of the motor 1 are rotated manually, where 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 UBEMF with a positive or negative sign is then generated and detected by means of a voltage sensor of the motor controller 21. The spindle 7 or the drive shaft of the motor 1 can be used in this way as a user interface for controlling the bobbin winder device or other parts of the sewing machine. For example, the state of an optical or acoustic display or representations on a graphical user interface can be changed in order to support required user actions for winding sewing thread onto the thread bobbin 9 as soon as the spindle 7 is rotated manually. In particular, the motor controller 21 may include stored control instructions in order to check the direction of rotation of the motor 1 when the first turns of sewing thread are wound manually and to output an alarm signal if this does not match the direction of rotation of the motor 1.