JP7365156B2 - Sewing machine motor control device - Google Patents

Description

The present invention relates to a motor control device for a sewing machine.

2. Description of the Related Art Conventionally, a motor mounted on a sewing machine, for example, a sewing machine motor, has been subjected to PWM (Pulse Width Modulation) control so as to achieve a target rotation speed. That is, when the target rotation speed is set by the sewing machine operator, the driving current of the sewing machine motor is periodically turned on and off, and if the target rotation speed is not reached, the duty ratio is increased to reach the target rotation speed. Then, current control is performed to reduce the duty ratio (for example, see Patent Document 1).

Japanese Patent Application Publication No. 2014-090583

In the above-mentioned conventional motor control device, when an abnormal load that cannot be stopped due to some external factor occurs in the drive system, the motor continues to drive with a large drive current by PWM control.
If such a large current continues to flow, there is a risk that the motor will overheat, be damaged, malfunction, and shorten its lifespan.

An object of the present invention is to provide a sewing machine motor control device that appropriately protects the motor.

The invention according to claim 1 provides a motor control device for a sewing machine, comprising:
a setting input section for setting a target rotation speed for a motor to be controlled;
a detection unit for detecting the operating speed of the motor;
a feedback control unit that performs PWM control so that the operating speed of the motor reaches the target rotation speed;
While the motor is being driven, a count value is added when the length or ratio of the ON period of the drive current to the motor, which is periodically determined by the feedback control unit, is equal to or greater than a predetermined period threshold, and the count value is added to the period threshold. a first load determination unit that subtracts a count value when the count value is less than a specified value, and determines that an overload has occurred in the motor when the count value exceeds a specified value;
and a drive control unit that executes load avoidance control when an overload occurs on the motor ,
The first load determination unit determines whether overload has occurred in the motor when the operating speed or the target rotation speed of the motor detected by the detection unit is less than a predetermined determination threshold. ,
The feedback control unit performs PWM control so that the length or ratio of an on period of a drive current to the motor in the PWM control does not exceed a predetermined limit value;
The operating speed or the target rotational speed of the motor detected by the detection unit is equal to or higher than the determination threshold, and the operating speed of the motor detected by the detection unit periodically with respect to the target rotational speed is A count value is added when the speed is less than a predetermined speed threshold, a count value is subtracted when the speed is greater than or equal to the speed threshold, and when the count value exceeds a specified value, overload of the motor occurs. The present invention is characterized by comprising a second load determining section that determines that .

The invention according to claim 2 is the sewing machine motor control device according to claim 1, comprising:
The first load determination unit is characterized in that the period threshold is determined for each target rotation speed.

The invention according to claim 3 is the motor control device for a sewing machine according to claim 1 or claim 2 ,
The drive control section is characterized by stopping the motor as the load avoidance control.

The invention according to claim 4 is the motor control device for a sewing machine according to any one of claims 1 to 3, comprising:
The drive control section is characterized in that, as the load avoidance control, control is performed to notify an overload state of the motor.

As described above, according to the present invention, it is possible to appropriately detect the overload state of the motor.

1 is a block diagram of a sewing machine that is an embodiment of the invention. FIG. 2 is a diagram showing changes in a motor drive signal and changes in motor current when the sewing machine motor is in a no-load state at a target rotation speed of 200 [spm]. FIG. 2 is a diagram showing changes in a motor drive signal and changes in motor current when the sewing machine motor is under abnormal load at a target rotation speed of 200 [spm]. When the target rotation speed is 200 [spm], 330 [spm], and 420 [spm], the minimum and maximum values of the on-period obtained when the sewing machine motor is under no load and under abnormal load are shown below. This is a chart showing the following. Figure 5 (A) is a graph showing the numerical range of possible on-period values when the sewing machine motor is under no load and under abnormal load at a target rotation speed of 200 [spm], and Figure 5 (B) is a graph showing the numerical range of values of the on-period when the sewing machine motor is under no load and under abnormal load at a target rotation speed of 200 [spm]. The same graph at 330 [spm], and FIG. 5(C) show the same graph at the target rotation speed of 420 [spm]. FIG. 2 is a diagram showing changes in a motor drive signal and changes in motor current when the sewing machine motor is in a no-load state at a target rotational speed of 1500 [spm]. 2 is a chart showing detected rotational speeds when loads of different magnitudes are applied to a sewing machine motor driven at a plurality of target rotational speeds. 8 is a diagram showing the detected rotation speed in FIG. 7. FIG. 5 is a flowchart of control of the sewing machine motor by the motor control device.

[Summary of embodiments of the invention]
A sewing machine 100 equipped with a motor control device 90 according to an embodiment of the present invention will be described below.
FIG. 1 is a block diagram showing a control system of sewing machine 100.

[sewing machine]
The sewing machine 100 includes a needle vertical movement mechanism that moves the needle bar that holds the sewing needle up and down, a hook mechanism that twists the lower thread around the upper thread of the sewing needle, a fabric feed mechanism that feeds the fabric on the throat plate, and a mechanism that moves the needle bar that holds the sewing needle up and down. The sewing machine is equipped with well-known components that are generally provided in sewing machines, such as a thread take-up mechanism that tightens the stitches, a thread tension device that applies tension to the upper thread, and a sewing machine frame that stores or holds each of the above components.
The sewing machine 100 includes a motor control device 90 that controls the sewing machine motor 16 that serves as a driving source for the needle vertical movement mechanism.
Note that since the sewing machine 100 has the same configuration as a general sewing machine, a detailed explanation of the well-known configurations other than the motor control device 90 will be omitted.

The sewing machine frame has a sewing machine bed section, a sewing machine arm section, and an upright body section, and a needle plate in which a needle hole is formed is provided at a needle drop position in the sewing machine bed section.

The needle vertical movement mechanism includes an upper shaft rotatably supported inside the sewing machine frame, a sewing machine motor 16 consisting of a servo motor that rotationally drives the upper shaft, an encoder 161 that detects the number of rotations of the sewing machine motor 16, and an upper shaft. The needle bar crank is fixedly mounted on one end of the shaft, and a crank rod is provided to connect the needle bar crank and the needle bar.
With the above configuration, in the needle vertical movement mechanism, the sewing machine motor 16 rotates the upper shaft, and the needle bar moves up and down one round trip per rotation of the upper shaft.

The hook mechanism is provided below the throat plate, and includes an inner hook that holds a bobbin inside, and an outer hook that rotates around the outer periphery of the inner hook using the sewing machine motor 16 as a driving source. Then, a loop of the needle thread of the sewing needle is captured by the tip provided on the outer hook, and the needle thread is entwined with the bobbin thread fed out from the inner hook to form a stitch.

The cloth feed mechanism uses the sewing machine motor 16 as a driving source to rotate a feed dog below the throat plate along the cloth feed direction. At this time, the upper end of the feed dog protrudes and retracts from the opening of the throat plate, contacts the fabric placed on the throat plate from below, and can feed the fabric at a predetermined pitch in the fabric feeding direction.
The thread take-up mechanism includes a thread take-up that rotates back and forth using the sewing machine motor 16 as a driving source, and pulls up and releases the needle thread synchronously with the vertical movement of the sewing needle during the thread path where the needle thread heads toward the sewing needle. Apply appropriate tightening force to the seam formed by the upper and lower threads.
The thread tension device is provided in the middle of the thread path from the needle thread supply source to the take-up thread, and applies appropriate thread tension to the needle thread when forming a seam.

[Motor control device]
As shown in FIG. 1, the motor control device 90 includes a microcomputer 91 and a memory 92, and the microcomputer 91 controls the operation of the sewing machine motor 16, which will be described later, according to various programs and various setting data stored in the memory 92. do.
Further, a pedal 93 serving as a setting input section for inputting the target rotation speed of the sewing machine motor 16 is connected to the microcomputer 91 via an interface 93a.

Furthermore, the sewing machine motor 16 is connected to the microcomputer 91 via a motor driver 16a.
The sewing machine motor 16 is also provided with an encoder 161 as a detection means for detecting its shaft angle, and the encoder 161 is connected to the microcomputer 91 via a motor angle detection circuit 161a.
The encoder 161 outputs pulses at constant minute angular intervals as the shaft angle of the output shaft of the sewing machine motor 16 changes, and the motor angle detection circuit 161a counts the pulses from the encoder 161. Then, the microcomputer 91 calculates the output shaft angle of the sewing machine motor 16 from the count value.
Note that the output shaft angle of the sewing machine motor 16 matches the upper shaft angle. The angle of the upper axis corresponds to one rotation (0 to 360°) of the sewing needle, which moves up and down in one round trip. In the following description, it is assumed that an upper axis angle of 0° corresponds to the top dead center of the sewing needle, and 180° corresponds to the bottom dead center.
The microcomputer 91 acquires the pulse count value of the encoder 161 from the motor angle detection circuit 161a at a constant cycle, and acquires the rotational speed, which is the operating speed of the sewing machine motor 16, from the periodic change in the pulse count value. There is. That is, the encoder 161 and the motor angle detection circuit 161a function as a detection section for detecting the operating speed of the sewing machine motor 16.

The pedal 93 includes a treadle that is stepped on by the operator of the sewing machine, and can set and input the target rotation speed of the sewing machine motor 16 according to the amount of depression of the treadle.

[Sewing machine motor operation control]
The microcomputer 91 functions as a feedback control section 94, a first load determination section 95, a second load determination section 96, and a drive control section 97 by executing various programs stored in the memory 92.
These various functions will be explained below. Note that all specific numerical values mentioned in the following description are merely examples, and are not limited to these numerical values, and all can be adjusted or changed as appropriate depending on the characteristics of the device.

[Feedback control section]
Feedback control section 94 calculates the difference between the target rotation speed input from pedal 93 and the detected rotation speed of sewing machine motor 16 obtained from encoder 161 via motor angle detection circuit 161a, and calculates the difference depending on the magnitude of the difference value. , determines the duty ratio of PWD control performed on the sewing machine motor 16, and inputs it to the motor driver 16a.

FIG. 2 shows changes in the motor drive voltage (referred to as a motor drive signal) and changes in the motor current flowing through the sewing machine motor 16 at a target rotation speed of 200 [spm] and no load on the sewing machine motor 16. It is a line diagram.
In PWM control, as shown in the diagram of the motor drive signal in Figure 2, for example, if the power frequency of the motor power source is 50 [Hz], one period T of the PWM control is 10 [ms], and the period T of the one period T is 10 [ms]. The amount of current flowing through the sewing machine motor 16 is adjusted by switching the power supply on and off during the sewing machine motor 16 and adjusting the magnitude of the ratio (duty ratio) of the on-period T _ON to control the motor output.
Therefore, the feedback control unit 94 repeatedly executes control at the cycle T to increase the duty ratio when the difference value between the detected rotation speed and the target rotation speed becomes large, and to decrease the duty ratio when the difference value becomes small.
In the diagram of the motor drive signal in FIG. 2, a rising portion of the voltage indicates an off period, and a falling portion of the voltage indicates an on period T _ON .

In order to protect the motor, the limit value of the on period T _ON in PWM control is set to a constant value (for example, 8 [ms]) within a range where the off period does not become 0, and the feedback control section 94 , even if the difference value becomes large, the on-period T _ON is controlled so as not to exceed the limit value.

[First load determination section]
The first load determination section 95 determines whether or not the sewing machine motor 16 is overloaded, depending on the length of the ON period T _ON of the drive current to the sewing machine motor 16 in the PWM control executed by the feedback control section 94.
Note that the first load determining unit 95 determines whether or not there is an overload on the sewing machine motor 16 when the target rotational speed of the sewing machine motor 16 is less than a predetermined determination threshold (in a low speed range). If the target rotational speed of the sewing machine motor 16 is equal to or higher than the determination threshold value (in the high speed range), a second load determining section 96, which will be described later, determines whether there is an overload.

When the target rotation speed of the sewing machine motor 16 is fixed to a constant value, the on-period T _ON becomes longer (the duty ratio becomes larger) in order to maintain the target rotation speed against an increase in the load applied to the sewing machine motor 16. .

FIG. 3 is a diagram showing changes in the motor drive signal and changes in the motor current of the sewing machine motor 16 when the target rotational speed is 200 [spm] and the sewing machine motor 16 is under abnormal load.
In addition, Fig. 4 shows the on-periods obtained when the sewing machine motor 16 is under no load and under abnormal load when the target rotation speed is 200 [spm], 330 [spm], and 420 [spm]. It is a chart showing the minimum value and maximum value of T _ON .
In addition, FIG. 5(A) is a graph showing the numerical range of values of the on-period T _ON that can be taken when the sewing machine motor 16 is under no load and under abnormal load at a target rotation speed of 200 [spm]. B) is the same graph when the target rotation speed is 330 [spm], and FIG. 5(C) is the same graph when the target rotation speed is 420 [spm].
Note that "no load" includes, in addition to no load, a load state that occurs on the sewing machine motor 16 when sewing is being performed properly, and "abnormal load" is a state where sewing is not being performed properly. This refers to a state in which a load is generated that is large enough to deviate from the load generated in one cycle of PWM control of the sewing machine motor 16 when the sewing machine motor 16 is in operation. "Overload" refers to a condition in which continuous abnormal load may cause the motor to overheat, break, malfunction, or shorten its lifespan.

Under the situation where feedback control is performed, in the case of the abnormal load shown in FIG. 3, the on-period T _ON becomes longer and the duty ratio becomes larger than in the case of FIG. 2 described above.
Furthermore, as shown in FIGS. 4 and 5(A) to 5(C), the higher the target rotational speed is, the longer the on-period T _ON becomes.

Therefore, the first load determination section 95 determines a period threshold for the value of the ON period T _ON determined by the feedback control section 94 for each target rotation speed, and when the period threshold is exceeded, an abnormal load is applied to the sewing machine motor 16. It is determined that this has occurred.

More specifically, as shown in FIGS. 5(A) to 5(C), the target rotation speed is 0 to 200 [spm], 200 to 330 [spm], and 330 to 420 [spm], A plurality of bands are set, and a period threshold of the on-period T _ON is set for each band.
For example, in the case of Figure 5 (A), the upper limit of the period threshold is 5.44 [ms] and the lower limit is 4.00 [ms], and in the case of Figure 5 (B), the upper limit of the period threshold is 5.96 [ms], the lower limit In the case of FIG. 5C, the period threshold is set to 6.44 [ms] as the upper limit and 4.52 [ms] as the lower limit, between the lower limit and the upper limit.

Then, in the first load determination unit 95, when the value of the on-period T _ON determined by the feedback control unit 94 is equal to or greater than the period threshold, the count value for determining abnormal load occurrence is added by 1, and the value becomes less than the period threshold. In this case, the count value is subtracted by 1. Then, this counting is repeatedly executed at the PWM control period, and when the count value exceeds a specified value, it is determined that an overload has occurred.
Note that the result of this determination is input to a drive control section 97, which will be described later.

[Second load determination section]
The second load determination unit 96 detects the occurrence of overload from a state in which the detected rotational speed of the sewing machine motor 16 is lower than the target rotational speed in a high speed range where the target rotational speed of the sewing machine motor 16 is equal to or higher than the above-mentioned determination threshold. judge.

FIG. 6 is a diagram showing changes in the motor drive signal and changes in the motor current flowing through the sewing machine motor 16 at a target rotational speed of 1500 [spm] and in a no-load state of the sewing machine motor 16.
Furthermore, FIG. 7 shows the detected rotational speed when loads of different magnitudes are applied to the sewing machine motor 16, which is driven at a plurality of target rotational speeds within the target rotational speed range of 200 to 1500 [spm]. FIG. 8 is a diagram showing the detected rotational speed in FIG. 7.
Note that the load values in FIGS. 7 and 8 are shown in percentages when the load torque at which the sewing machine motor 16 locks at 200 [spm] is 100%.

In the first load determination unit 95 described above, as the target rotation speed increases, as shown in FIGS. 5A to 5C, the on-period T _ON gradually becomes longer even in the no-load state. This makes it difficult to select a numerical value for a period threshold that serves as a boundary for determining abnormal load.
On the other hand, in the feedback control section 94, the limit value of the on-period T _ON (8 [ms] in the above example) is determined in order to protect the sewing machine motor 16, as described above.
Therefore, as shown in FIG. 6, when the target rotation speed is increased, the on-period T _ON approaches the upper limit value even under no-load conditions, and there is no room to make the on-period T _ON any longer, so the sewing machine motor 16 is driven. The speed (detected rotation speed) decreases without reaching the target rotation speed.
Therefore, in the high speed range of the target rotational speed, the occurrence of overload can be appropriately determined based on the decrease in the detected rotational speed with respect to the target rotational speed, rather than the value of the on-period T _ON .

Specifically, the second load determination unit 96 sets [target rotation speed - 10%] as the speed threshold value of the detected rotation speed, and when the detected rotation speed is equal to or higher than the speed threshold, a count is set to determine the occurrence of abnormal load. Add 1 to the value, and subtract 1 from the count value if it is less than the speed threshold. Then, this counting is repeatedly executed at the PWM control period, and when the count value exceeds a specified value, it is determined that an overload has occurred.

In FIG. 8, the symbol L is a speed threshold line. As shown in the figure, in the low speed range of the sewing machine motor 16, the load does not fall below line L until the load becomes excessive, but in the high speed range, the rotation speed decreases due to the load before it becomes excessive, so overload is detected immediately. be able to.
Note that the ratio to be subtracted from the target rotation speed as the speed threshold is not limited to 10%, and can be selected as appropriate.
Further, the result of the determination by the second load determining section 96 is also input to a drive control section 97, which will be described later.

[Drive control section]
The drive control section 97 executes load avoidance control based on the determination from the first load determination section 95 or the second load determination section 96 whether overload has occurred on the sewing machine motor 16 .
Specifically, the load avoidance control is to stop driving the sewing machine motor 16. However, the load avoidance control is not limited to this, and for example, the motor control device 90 may be provided with a display device or an audio output device, and the occurrence of an overload may be notified by display or audio. Further, as load avoidance control, the occurrence of an overload may be notified by display or audio, and the driving of the sewing machine motor 16 may be stopped.

[Control of sewing machine motor by motor control device]
Control of the sewing machine motor 16 by the motor control device 90 will be explained based on the flowchart of FIG.
When the operator of the sewing machine depresses the pedal 93, the feedback control section 94 sets a target rotation speed according to the amount of depressing the pedal 93 and starts driving the sewing machine motor 16 (step S1).
Furthermore, when the sewing machine motor 16 starts driving, the abnormal load count values C1 and C2, which determine the occurrence of overload, are reset to 0 in the first load determining section 95 and the second load determining section 96 (step S3).

Next, it is determined whether the current target rotational speed V0 is equal to or higher than a rotational speed determination threshold value V1 for determining whether the current target rotational speed is in a low speed range or a high speed range (step S5).
Then, if the target rotation speed V0 is smaller than the determination threshold value V1 and the sewing machine motor 16 is rotating in a low speed range (step S5: NO), the first load determination unit 95 controls the PWD control of the sewing machine motor 16. It is determined whether the on-period T _ON is greater than or equal to the period threshold T ₁ (step S7).

As a result, if the on-period T _ON is less than the period threshold T ₁ (step S7: NO), the abnormal load count value C1 is subtracted by 1 (step S9). However, C1>0.
On the other hand, if the on-period T _ON is equal to or greater than the period threshold T ₁ (step S7: YES), 1 is added to the abnormal load count value C1 (step S11).
Then, it is determined whether the count value C1 has reached the specified value Cr1 (step S13), and if the count value C1 has reached the specified value Cr1, the process proceeds to step S15, and if it has not reached the predetermined value Cr1, the process returns to step S5. .
Note that the processes from steps S5 to S13 described above are executed in synchronization with one cycle of PWD control.

Further, in step S5 described above, if the target rotational speed V0 of the sewing machine motor 16 is in a high speed range equal to or higher than the determination threshold value V1 (step S5: YES), the second load determination unit 96 detects the rotation speed of the sewing machine motor 16. It is determined whether the rotation speed V is smaller than a speed threshold value set as a coefficient (for example, 0.9) times the target rotation speed V0 (step S17).

As a result, if the detected rotational speed V of the sewing machine motor 16 is equal to or higher than the speed threshold (step S17: NO), the abnormal load count value C2 is subtracted by 1 (step S19). However, C1>0.
On the other hand, if the detected rotational speed V of the sewing machine motor 16 is less than the speed threshold (step S17: YES), 1 is added to the abnormal load count value C2.
Then, it is determined whether or not the count value C2 has reached the specified value Cr2 (step S23). If the count value C2 has reached the specified value Cr2, the process proceeds to step S15, and if it has not reached the predetermined value Cr2, the process returns to step S5.
Note that the processing from steps S5 to S23 described above is executed in synchronization with one cycle of PWD control.

Then, in step S15, the drive control unit 97 executes load avoidance control, and stops driving the sewing machine motor 16 in accordance with the determination that an overload has occurred in the sewing machine motor 16.

[Technical effects of embodiments of the invention]
The motor control device 90 of the sewing machine 100 controls the length (duty ratio) of the ON period T _ON of the drive current for the sewing machine motor 16 in PWM control, which is periodically determined by the feedback control unit 94 while the sewing machine motor 16 is being driven. Accordingly, a first load determining section 95 is provided that determines whether or not the sewing machine motor 16 is overloaded.
When the sewing machine motor 16 is under an abnormal load, the duty ratio increases and the ON period T _ON tends to become longer. Therefore, the first load determination unit 95 appropriately detects the overload of the sewing machine motor 16. This makes it possible to effectively avoid heat generation, damage, malfunction, shortened life, etc. due to overload of the sewing machine motor 16.

In particular, the first load determination unit 95 determines that an abnormal load has occurred on the sewing machine motor 16 when the length or ratio (duty ratio) of the on-period T _ON of the drive current exceeds a predetermined period threshold _T1 . Therefore, overload can be determined more clearly and appropriately.
Further, the first load determination unit 95 determines whether an overload has occurred on the sewing machine motor 16 by increasing or decreasing the count value depending on whether the length of the on-period T _ON of the drive current exceeds the period threshold T ₁ or not. , it is possible to more appropriately detect the occurrence of overload by alleviating the effects of temporary noise and the like.

Further, the first load determining section 95 determines whether or not the sewing machine motor 16 is overloaded when the target rotation speed V is less than a predetermined determination threshold V1.
As the rotational speed of the sewing machine motor 16 increases, the length of the on-period T _ON of the drive current under no load and abnormal load, or the numerical range that is the boundary between the numerical ranges of the duty ratio, becomes narrower, making it difficult to accurately determine these. It becomes difficult. Therefore, the first load determination unit 95 makes the overload determination within the rotation speed range in which the limit value of the target rotation speed V is the determination threshold value V1, making it possible to maintain high determination accuracy.

Further, when the target rotation speed V is equal to or higher than a predetermined determination threshold value V1, and when the detected rotation speed is less than the speed threshold value with respect to the target rotation speed, it is determined that an overload of the sewing machine motor 16 has occurred. The determination is made by the second load determination section.
This makes it possible to detect the occurrence of overload in a wider range of rotational speeds of the sewing machine motor 16.
Also, in the case of the second load determination section 96, the count value is increased or decreased depending on whether the detected rotation speed exceeds the speed threshold value or not, and it is determined that an overload of the sewing machine motor 16 has occurred. Similarly, it is possible to more appropriately detect the occurrence of overload by alleviating the effects of temporary noise and the like.

Further, since the drive control unit 97 stops the sewing machine motor 16 as load avoidance control, it is possible to reduce and avoid driving the sewing machine motor 16 under overload, and it is possible to effectively protect the sewing machine motor 16. It is.
Further, if the motor control device 90 is provided with a display section and an audio output section, and the drive control section 97 is configured to perform control to notify the overload state of the sewing machine motor 16 as load avoidance control, it is possible to operate the sewing machine. It is possible to immediately notify the operator of an overload on the sewing machine motor 16, and it is possible to take countermeasures according to the situation at that time.

[others]
In the motor control device 90, the various functions of the feedback control section 94, first load determination section 95, second load determination section 96, and drive control section 97 are realized by the microcomputer 91 executing programs in the memory 92. Although the configuration is illustrated, some or all of these various functions may be configured by hardware such as a chip or a circuit.

Furthermore, in the motor control device 90, a case has been exemplified in which the target rotation speed is compared with a determination threshold value to determine which of the first load determination section 95 and the second load determination section 96 should perform overload determination. Processing may be performed such that the detected rotational speed instead of the target rotational speed is compared with a determination threshold value to determine which of the first load determination section 95 and the second load determination section 96 should perform the overload determination.

Further, although an example has been shown in which the speed threshold value of the second load determination unit 96 is multiplied by a coefficient less than 1 of the target rotation speed, the present invention is not limited thereto.
For example, the speed threshold of the second load determination unit 96 may be set to a rotation speed obtained by subtracting a predetermined number from the target rotation speed. In this case, the predetermined number to be subtracted from the target rotation speed may be determined individually for each size of the target rotation speed (may be for each fixed band).

Further, the object to be controlled by motor control device 90 is not limited to sewing machine motor 16.
For example, if the sewing machine 100 includes a motor other than the sewing machine motor, the other motor is controlled to determine overload using the same configuration as the motor control device 90 of the sewing machine motor 16 described above. The device may be mounted on a sewing machine.

16 Sewing machine motor (motor)
16a Motor driver 90 Motor control device 91 Microcomputer 92 Memory 93 Pedal (setting input section)
94 Feedback control section 95 First load determination section 96 Second load determination section 97 Drive control section 100 Sewing machine 161 Encoder (detection section)
161a Motor angle detection circuit (detection section)
T ₁ period threshold T _{ON ON} period V Detected rotation speed V0 Target rotation speed V1 Judgment threshold

Claims (4)

a setting input section for setting a target rotation speed for a motor to be controlled;
a detection unit for detecting the operating speed of the motor;
a feedback control unit that performs PWM control so that the operating speed of the motor reaches the target rotation speed;
While the motor is being driven, a count value is added when the length or ratio of the ON period of the drive current to the motor, which is periodically determined by the feedback control unit, is equal to or greater than a predetermined period threshold, and the count value is added to the period threshold. a first load determination unit that subtracts a count value when the count value is less than a specified value, and determines that an overload has occurred in the motor when the count value exceeds a specified value;
and a drive control unit that executes load avoidance control when an overload occurs on the motor ,
The first load determination unit determines whether an overload has occurred in the motor when the operating speed or the target rotation speed of the motor detected by the detection unit is less than a predetermined determination threshold. ,
The feedback control unit performs PWM control so that the length or ratio of an on period of a drive current to the motor in the PWM control does not exceed a predetermined limit value;
The operating speed or the target rotational speed of the motor detected by the detection unit is equal to or higher than the determination threshold, and the operating speed of the motor detected by the detection unit periodically with respect to the target rotational speed is A count value is added when the speed is less than a predetermined speed threshold, a count value is subtracted when the speed is equal to or higher than the speed threshold, and when the count value exceeds a specified value, overload of the motor occurs. A motor control device for a sewing machine , comprising a second load determination section that determines that . 2. The motor control device for a sewing machine according to claim 1, wherein the first load determination section determines the period threshold value for each of the target rotation speeds. 3. The motor control device for a sewing machine according to claim 1 , wherein the drive control section stops the motor as the load avoidance control. The motor control device for a sewing machine according to any one of claims 1 to 3, wherein the drive control unit performs control to notify occurrence of overload of the motor as the load avoidance control. .

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