US20240183092A1

US20240183092A1 - Bobbin winder device of a sewing machine and method for controlling or regulating the speed of the motor of a bobbin winder device

Info

Publication number: US20240183092A1
Application number: US18/530,498
Authority: US
Inventors: Daniel Rupp; Roland Beer; Alain Capt; Ulrich Bareis; Giovanni Pederzoli
Original assignee: BERNINA International AG
Current assignee: BERNINA International AG
Priority date: 2022-12-06
Filing date: 2023-12-06
Publication date: 2024-06-06

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 (C₀), 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.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from Swiss Patent Application No. 001455/2022, filed Dec. 6, 2022, which is incorporated herein by reference as if fully set forth.

TECHNICAL FIELD

The invention relates to a bobbin winder device of a sewing machine and to a method for controlling or regulating the speed (w) of the motor of a bobbin winder device.

BACKGROUND

Sewing machines usually include a bobbin winder device for winding sewing thread onto a bobbin thread coil. Such bobbin thread spools, also known as thread bobbins for short, comprise a cylindrical shaft section which is axially bounded on both sides by a flange. The thread bobbin is attached to a motor-driven spindle of the bobbin winder device and connected to it in a rotationally fixed manner. By rotating the spindle, the thread or the sewing thread is drawn from a thread supply and wound between the flanges on the shaft section of the thread bobbin. The outer diameter of the wound sewing thread may not be greater than the outer diameter of the flanges.
Bobbin winder devices may include a separate bobbin winder motor to drive the spindle. As an alternative, a coupling device for temporary coupling of the spindle to a drive, in particular to the main drive of the sewing machine, may be provided.
Different devices which can be used to stop the drive of the spindle when a generally adjustable maximum filling of the thread bobbin is reached are known.
US2020340159A1 discloses a bobbin winder device which comprises a pivotable sensor lever and a switch which can be actuated by said sensor lever. The sensor lever is held in a first pivot position by the force of a spring. In this case, a contact element protrudes into the gap between the flanges of an empty bobbin when it is attached to the drivable spindle of the bobbin winder 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 in the direction of a second pivot position. When this second predeterminable pivot position is reached, the sensor lever actuates the switch. As soon as a controller detects this change in state, the bobbin winder motor is switched off. By adjusting the sensor lever arrangement, the switching point can be set in such a way that the bobbin winder motor is stopped when the bobbin reaches a maximum fill level.
JP2021016398A discloses another bobbin winder device in which, during winding of sewing thread, a lever is displaced from a first pivot position counter to the holding force of a first magnet by attachment to the sewing thread. The pivot position of the lever is detected by means of a Hall element and a further magnet arranged on the lever. As soon as the lever reaches a predetermined second pivot position, the controller specifies a lower setpoint for regulating the speed of the bobbin winder motor. The speed is detected by means of a rotary encoder. The motor is stopped when the bobbin reaches maximum filling. A claw formed on the lever then engages in a positively locking manner in a corresponding recess on the outside of the motor.
Such conventional devices for stopping the spindle drive take up a comparatively large amount of space and are complex and expensive.

SUMMARY

An object of the present invention is therefore to provide a comparatively simple and space-saving bobbin winder device which can be produced in a cost-effective manner and a suitable method for controlling the motor speed of such a bobbin winder device.
This object is achieved by a bobbin winder device having one or more of the features described herein as well as by a method also having one or more of the features described herein.
The bobbin winder device comprises a bobbin winder motor, henceforth also referred to as motor for short, and a spindle which can be driven by said motor directly or indirectly by means of a transmission apparatus, the spindle being designed for the releasable rotationally fixed attachment of a bobbin thread spool. The spindle and preferably also the motor are arranged on a support, on which a brake pad with a friction surface is also held so that the distance between the friction surface and the spindle is variable. The brake pad is preferably pivotably mounted on the support.
When a thread bobbin is held coaxially on the spindle, the friction surface of the brake pad is radially spaced apart from the spindle axis essentially in the area between the two flanges of the thread bobbin. The force of a spring presses the brake pad or the section of the brake pad with the friction surface radially in the direction of the spindle axis. Interacting stops, which limit the freedom of movement of the brake pad in the direction of the spindle axis, may be arranged on the support and on the brake pad. The position of at least one of these stops is preferably adjustable, for example by means of an adjusting screw. It is thus possible to define an end position for the brake pad, in which it is held by the action of the spring force. The friction surface of the brake pad is then arranged in a reference position at a defined distance from the spindle axis. The reference position is generally specified in such a way that the distance between the friction surface and the spindle axis is slightly smaller than the flange radii of the thread bobbin. This ensures that the sewing thread comes into contact with the friction surface during winding onto the thread bobbin as long as the outer diameter of the wound sewing thread is smaller than or equal to the diameter of the bobbin flanges. The brake pad is preferably convex in the region of the friction surface. The curvature or the axes of curvature of the friction surface and the thread bobbin attached to the spindle can be aligned substantially orthogonally to one other. Therefore, when the thread bobbin is attached to the spindle, the bobbin flange at the front in the insertion direction first hits the brake pad in an outer area of the friction surface further away from the spindle axis. The bobbin flange in this case exerts a radially outward force on the brake pad. The brake pad is pushed radially outward by the bobbin flange counter to the acting spring force, such that the bobbin can be pushed further into its target position and connected to the spindle. As soon as the bobbin flange has overcome the obstacle or the point of the friction surface radially closest to the spindle axis, the brake pad is moved by the force of the spring back to its end position defined by the stops. In such arrangements, thread bobbins can simply be attached to the spindle and connected to it, and also separated from the spindle again in the opposite direction. The friction surface is preferably curved in two dimensions.
In alternative embodiments, the friction surface could be formed on an elastically deformable section of the brake pad. The position of the brake pad is preferably adjustable, for example by means of an adjusting screw, such that the friction surface can be positioned at the desired reference distance to the spindle axis. An additional spring for adjusting the position of the brake pad is possible, but not necessarily required. The elastically deformable section of the brake pad with the friction surface may comprise, for example, a leaf spring and is preferably not or only slightly prestressed if the friction surface is at the reference distance from the spindle axis.
As a rule, the motor and the spindle are arranged coaxially with respect to one another and are coupled directly to one other, with the result that their speeds are identical. The motor is preferably a DC motor. As an alternative, the motor and the spindle could also be coupled to one another in other ways, for example via a gearbox or a drive belt with a predetermined or predeterminable transmission or reduction ratio.
When sewing thread is wound onto the thread bobbin, the motor is driven in a manner controlled by a motor controller. The motor controller is generally part of a sewing machine controller which controls other functions of the sewing machine in addition to controlling the motor. The outer diameter and the mass of the wound sewing thread as well as the moment of inertia of this system increase continuously. This also applies to the circumferential speed of the wound sewing thread and to the friction 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 as the outer diameter increases. If the motor is driven continuously or not in a regulated manner, the rotational speed of the spindle will decrease slightly when the sewing thread is wound due to the increasing load on the motor.
As soon as the braking torque of the brake pad is applied, the reduction rate of the rotational speed increases. The rotational speed of the motor and/or the rate of change thereof over time or the magnitudes thereof can be used as measured variables for detecting a fill level of the thread bobbin which is defined by the position of the brake pad. For this purpose, the brake pad 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 are defined in the motor controller. Depending on the embodiment of the bobbin winder device, measured variables and comparison variables for these measured variables can only be detected or specified in terms of magnitude or alternatively with the respective positive or negative sign.
If the detected values or corresponding averaged values fall below or exceed the associated limit values or comparison values, the motor controller initiates appropriate measures such as the immediate or delayed interruption of the power supply to the motor, for example.
The rotational speed of the motor and the rate of change thereof are generally parameters whose values change significantly due to the effect of the brake pad in a manner that can be measured.
Another parameter which changes depending on the load on the motor is the back electromotive force, also known as CEMF or BEMF for “counter electromotoric force” or “back electromotoric force”. This force is essentially proportional to the rotational speed of the motor-driven spindle and thus represents the rotational speed. The BEMF is proportional to a reverse voltage UBEMF induced in the electrically conductive windings of the motor coil due to the relative movement in the magnetic field of the motor. The reverse voltage UBEMF is directed counter to the actuating driving voltage UA of the motor controller. When the motor is almost unloaded, it rotates at its idle speed. The magnitude of the reverse voltage UBEMF is then approximately the same as the driving voltage UA, and the effective motor voltage UM, that is to say the difference between the voltage magnitudes UA-UBEMF, is small.
If the motor does not rotate, the reverse voltage UBEMF is equal to zero. The effective motor voltage UM or the voltage difference UA-UBEMF in the driving circuit of the motor essentially determines the motor current IM and thus also the drive power of the motor.
Measured variables such as, for example, the source voltage UQ generated by the voltage source of the motor controller, the motor voltage UM=UA−UBEMF applied effectively to the motor and the motor current IM can be detected, for example, during predeterminable time intervals in the driving circuit of the motor. This is possible in a comparatively simple manner, for example by means of voltage dividers and/or shunts in a known manner. Additional sensors such as, for example, Hall sensors or rotary encoders with optical sensors are not required.
The source voltage UQ is the output voltage provided by the voltage source without a connected load. When the load is connected, the current flowing in the circuit causes a voltage drop due to the internal resistance RQ of the voltage source, with the result that the actual output voltage or the driving voltage UA is lower than the source voltage UQ.
In some embodiments of the bobbin winder device, the motor controller can use, for example, an electronic switch in the driving circuit of the motor to interrupt the power supply to the motor periodically, for example every 20 ms, briefly, for example for about 2 ms in each case. During this time window, the voltage component of the voltage source of the motor controller drops to zero. A freewheeling diode in the reverse direction is generally arranged in parallel with the motor so that voltages induced in the motor by the switching processes can be neutralized by discharge via said freewheeling diode. Towards the end of each interruption interval, the motor controller can directly measure the value of the reverse voltage UBEMF. In particular, the voltage on the connecting lines to the motor can be detected, for example on the motor side or downstream of the electronic switch, by means of an A/D converter. As an alternative, it is possible to determine, for example, the charging time or the discharge time of a capacitor that is charged with the reverse voltage UBEMF or discharged starting from UBEMF via a resistor. The time until a specified reference voltage is reached varies depending on the reverse voltage UBEMF. If required, the corresponding value of the reverse voltage UBEMF can be determined from this, for example via a look-up table.
The detection of the reverse voltage UBEMF is also possible in embodiments of the bobbin winder device in which the driving voltage UA for the motor is controlled or regulated by pulse width modulation. The driving frequency is preferably in the range of about 16 kHz to about 32 kHz, that is to say below the range audible by the human ear and low enough to keep switching losses as low as possible.
In the case of speed-regulated bobbin winder devices, a controlled variable which represents the actual rotational speed is generally detected and processed as a feedback variable together with a specified setpoint speed as a guide variable to a manipulated variable for actuating the motor. Instead of measured variables which are detected by means of rotary encoders or Hall sensors, the reverse voltage UBEMF can be used as the feedback variable of the control loop. In the case of a motor controller, the reverse voltage UBEMF can be detected directly in the driving circuit of the motor and used as an equivalent measured variable of the rotational speed. Bobbin winder devices in which the speed of the motor is determined based on the reverse voltage UBEMF are comparatively simple, small and cost-effective.
The motor controller preferably comprises at least one limit value or comparison value which is stored or specified in another manner, for example by means of a voltage divider, for the reverse voltage UBEMF. With additional monitoring devices, such as, for example, a monitoring process stored as a program code of a control program, the motor controller can identify when the reverse voltage UBEMF rises above or falls below a comparison value and subsequently can initiate suitable further process steps, such as, for example, the interruption of the power supply to the motor.
For example, the comparison value can be set to be sufficiently low so that the motor controller reliably detects only a sharp drop in the motor speed due to the braking effect of the brake pad. However, if the speed when winding sewing thread only decreases slightly due to the increasing load of the sewing thread, it remains above the specified comparison value.
The motor controller can include means for continuously or gradually changing the supplied driving voltage UA for the motor. In particular, the pulse-pause ratio of a clocked voltage source can be gradually or continuously reduced or set directly to zero by a control program according to specified rules as soon as the speed or the reverse voltage UBEMF drops below a specified limit value.
Such motor controllers in which the motor speed is monitored by means of the reverse voltage UBEMF can detect a decrease in the motor speed comparatively easily and reliably and, depending on this speed, can, for example, interrupt the power supply to the motor or adapt or reduce the setpoint for regulating the motor speed.
In further embodiments of the bobbin winder device, other electrical measured variables of the motor where typical changes occur due to the action of the brake pad can be detected instead of or in addition to the reverse voltage UBEMF. Another measured variable is, for example, the motor current IM. The motor controller can detect, for example, the motor current IM in the motor circuit by means of a shunt, that is to say a small electrical resistor. The shunt voltage is evaluated in this case.
The motor current IM increases as the load on the motor increases. Only when the motor is subjected to significantly more load by the action of the brake pad does the motor current IM or a measured variable corresponding to the motor current IM, which is preferably smoothed by means of a low-pass filter, exceed a predetermined comparison value. As soon as the motor controller identifies that the value of the measured variable is higher than the comparison value, it initiates appropriate measures such as interrupting the power supply to the motor.
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 UBEMF based on the detected and preferably averaged motor current IM. The following holds true: UBEMF=UA−UM, where UA=UQ−(RQ×IM).

BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

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

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

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

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,

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

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

FIG. 1 shows a partial view of a bobbin winder device in perspective, with FIG. 3 showing a side view of it.
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 9 a 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 9 b, at the ends of which two end flanges 9 a 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 9 a may be, for example, in the order of magnitude from about 10 mm to about 12 mm. The sleeve 9 b can be arranged flush to the outside of the end flanges 9 a. As an alternative, the sleeve 9 b can slightly overhang the end flanges 9 a, 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 9 a. 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.
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.
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).
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′.
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 15 a on the brake pad 11 and a second stop 15 b 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 15 a, 15 b is preferably variable. In the embodiment according to FIGS. 1 to 4 , the first stop 15 a is a step protruding on the brake pad 11 and the second stop 15 b is the front end of an adjusting screw screwed into a thread on the support 5. The position of the second stop 15 b can be easily adjusted by turning the adjusting screw. This second stop 15 b defines the reference position of the brake pad 11 by means of attachment to the first stop 15 a of said brake pad and thus also defines the reference distance CO between the friction surface 13 and the spindle axis A′.
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.
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 9 a of the thread bobbin 9.
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 9 a 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 9 a. 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 9 a. When sewing thread is wound onto the thread bobbin 9, this causes the sewing thread which is wound onto the sleeve 9 b 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 9 a.
In such arrangements, the lower end flange 9 a 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 9 a, is rather low, for example about 0.5 N to about 5 N.
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.
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.
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.
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.
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.
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.
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.
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.
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.
In FIG. 6 , the bold line L1 shows the time profile of the speed ω 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 ω then decreases significantly more sharply and shortly thereafter falls below a predefined comparison value ωS at point P2. The motor controller 21 detects this and can cause the motor 1 to be switched off.
In FIG. 7 , the bold line L2 shows in an analogous manner the time profile of the speed ω of the spindle 7, where the motor controller 21 regulates the speed ω to a predetermined setpoint ω0. 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 ω′.
During the winding of sewing thread, the motor controller 21 regulates the driving voltage UA for the motor 1 so that its speed ω essentially corresponds to the setpoint ω0. 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 ω0. The speed ω drops rapidly until it drops below the specified comparison value ωS at point P2.
In an analogous manner, it is possible to define a comparison value ω′S for the change in speed ω′, the motor controller 21 being able to initiate the interruption of the power supply to the motor 1 when said comparison value is undershot.
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.
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.
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 ω 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 ω 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 ω of the spindle 7 can be reduced as the fill level of the thread bobbin 9 increases.
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.
In an analogous manner, the motor voltage UM and/or the reverse voltage UBEMF can be detected and regulated to a predetermined value.
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 ω of the motor 1.
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.
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.
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.
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.
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 ω 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 ω, for example in order to wind sewing thread onto a thread bobbin 9 in the shortest possible time. The speed ω 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.
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 9 a, 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.
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.
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.

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 (15 a) 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.