JP2667735B2 - Motor control method for sewing machine - Google Patents

Description

The present invention relates to a motor control method for a sewing machine,
In particular, the present invention relates to a control method for stabilizing rotation of a motor during a thread cutting operation.

[Conventional technology]

A DC brushless servomotor (hereinafter simply referred to as “motor”) is used as a drive source for rotating the main shaft of the sewing machine, and pulse width modulation (hereinafter “PW
The control method by "M") is often used.

That is, the difference between the speed command value from the sewing machine control unit and the actual motor speed detection value from the motor speed detector is calculated and multiplied by the gain, and the duty PWM according to that value is calculated.
The driver is controlled by the control signal, and the drive current of the motor is controlled.

In such a sewing machine, the thread trimming mechanism of the sewing machine is operated at the time of thread trimming, so that a large load fluctuation occurs as compared with a normal sewing operation.

In the sewing machine head where the load of this thread trimming mechanism is large, when the load increases, the rotation speed of the motor decreases, thereby increasing the deviation from the speed command value, and increasing the drive current to increase the rotation speed. However, when the load exceeds the thread trimming load point, the load suddenly becomes lighter, and the current amount has increased so far, and the speed will increase in reverse, causing the needle up stop position to be exceeded. I got it.

In order to avoid this, conventionally, the speed command value from the sewing machine control unit to the motor control unit is increased (or the gain is increased) at a predetermined timing before the thread trimming mechanism operates, and the rotation speed is increased in advance. At the point where a thread trimming load is applied, the speed variation is reduced (or the gain is reduced) at the point where the thread variation load is applied, thereby controlling the speed to suppress the speed.

[Problems to be solved by the invention]

However, such conventional motor control at the time of thread trimming is speed command or gain predictive control, and is effective for a sewing machine head of the same type (same load). It is difficult to control with the sewing machine head of
There was a problem that the stop position was not stable.

The present invention has been made in view of the above points, and stabilizes the rotation of the motor during the thread trimming operation by using a motor control method that can be easily applied to various sewing machines having different thread trimming loads. An object is to surely stop at a stop position.

[Means for solving the problem]

In order to achieve the above object, a motor control method in a sewing machine according to the present invention provides a method of controlling a drive current of a DC brushless servomotor during driving of a thread trimming mechanism of a sewing machine from other motors. It is characterized by shortening the cycle.

(Operation)

According to the control method of the present invention, during operation of the thread trimming mechanism,
Since the control cycle of the drive current of the motor becomes shorter as the PWM cycle becomes denser, the current ripple is stabilized, and thereby the torque ripple is also stabilized.

〔Example〕

Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.

FIG. 2 is a schematic front view showing the appearance of a sewing machine to which the present invention is applied.

Reference numeral 1 denotes a sewing machine main body (head), which is fixedly mounted on a sewing machine tape 2, and a pulley 4 is attached to a rear end of a sewing machine main shaft 3 provided therein.

A motor 5 is attached to a lower portion of the table 2, and a pulley 6 is mounted on a rotating shaft thereof. A belt 7 is stretched between the pulley 6 on the motor side and the pulley 4 on the sewing machine. 5 is transmitted to the main shaft 3 of the sewing machine via the respective pulleys 6 and 4 and the belt 7.

The motor 5 is provided with a motor speed detector 8 such as a tachogenerator for detecting the rotation speed (number of rotations).

Reference numeral 10 denotes a control circuit box including a sewing machine control unit 10A and a motor control unit 10B, which will be described later, and includes a CPU and a microcomputer including a ROM, a RAM, and the like.

Reference numeral 11 denotes a pedal sensor for detecting the amount of depression of the sewing machine pedal 9. A sewing needle 12 is moved up and down by the rotation of the main shaft 3.

FIG. 3 is a block diagram showing the configuration of a control system according to the present invention in the sewing machine. The same parts as those in FIG. 2 are denoted by the same reference numerals, and their description is omitted.

10A is a sewing machine control unit for controlling the entire sewing machine, and 10B is a motor control unit for controlling the rotation speed of the motor 5 by PWM-controlling the motor driver 12.

Reference numeral 14 denotes a sewing needle position detector for detecting the upper and lower positions of the sewing needle 12, and reference numeral 15 denotes a thread trimming solenoid driving circuit that drives a thread trimming solenoid 16 in accordance with a command from the sewing machine controller 10A.

The motor control unit 10B comprises a deviation calculation circuit 20, an amplifier 21, and a PWM control circuit 22, as shown in FIG. 4, and is provided with a feedback loop by a motor driver 13, a motor 5, and a motor speed detector 8. Is formed.

The motor control unit 10B receives the speed command value from the sewing machine control unit 10A and the actual rotation speed of the motor 5 from the motor speed detector 8 and inputs a deviation calculation circuit 20.
The deviation is calculated by the amplifier 21 and a predetermined gain is calculated by the amplifier 21. According to the value, the PWM control circuit 22
A rectangular pulse as shown by a solid line in FIG.
The PWM control signal is divided into upper and lower PWM control signals PWM1 and
It outputs to the motor driver 13 as PWM2.

The motor 5 and the motor driver 13 are configured as shown in FIG.

The motor 5 is a DC brushless motor, which includes a rotor (not shown) made of permanent magnets and a stator made of three-phase windings U, V, W.

The motor driver 13 includes two power transistors Q1 and Q2 connected in series between the positive and negative lines of a 280V DC power supply.
2. Connect three sets of Q3 and Q4, Q5 and Q6 in parallel, and connect the connection points of the two power transistors of each set to the other ends of the windings U, V, and W in which one end of the motor 5 is star-connected. Each is connected.

The base of each upper power transistor Q1, Q3, Q5
Gate circuit G in which any one of them is selectively opened
A gate control signal for the upper stage is applied via 1, G3, G5, and a gate circuit G2, G4, G6 in which any one is selectively opened at the base of each of the lower power transistors Q2, Q4, Q6.
, A lower stage PWM control signal is applied.

The ON / OFF timing of each power transistor is controlled by each gate signal of U +, V +, W + and U-, V-, W-, and each of the power transistors is controlled by upper and lower PWM control signals. The motor 5 is driven by controlling the amount of current flowing through the power transistor.

The magnitude of this current amount is determined by the duty (pulse width / period) of the PWM control signal, that is, the ratio of the ON time of each power transistor controlled by t / T in FIG. 6 (a), and the ON time is long. As the drive current of the motor 5 increases, the rotation speed increases.

The PWM control circuit 22 shown in FIG.
The PWM control signal P to be output in response to the cycle switching signal S from
The periods of WM1 and PWM2 can be switched between 500 μS shown in FIG. 6A and 250 μS shown in FIG. However, to keep the duty unchanged, set the cycle to 1/2
When set to, the pulse width is also halved.

Next, a motor control method for thread trimming in the sewing machine of this embodiment will be described with reference to the timing chart of FIG.
The description will be made also with reference to the flow chart in the figure.

When the pedal 9 (FIG. 2) of the sewing machine is depressed, the pedal sensor 11 detects this and generates a thread cutting request signal shown in FIG. 7 (a).

Accordingly, the sewing machine control unit 10A drives the motor 5 by the motor control unit 10B, and the sewing machine needle position detector 14 detects the needle down signal shown in FIG. A thread cutting solenoid signal shown in FIG. 4D is output to 15 to excite the thread cutting solenoid 16 and operate a thread cutting mechanism (not shown).

Then, by the rotation of the sewing machine main shaft 3 by the motor 5,
While the sewing machine needle 12 is moving from the lower position to the upper position, the thread is cut by the thread cutting mechanism. During this thread cutting operation, the motor load is normal as shown in FIG. 7 (d). It becomes bigger and more unstable.

Therefore, the sewing machine control unit 10A
At the same time as turning the cycle switching signal S to "1",
As shown in the flowchart, the period of the PWM signal is 250
μS and the pulse width is calculated value / 2. At the same time as turning off the thread trimming solenoid 16,
Set to μS and the pulse width to the calculated value / 1.

That is, when the thread trimming solenoid 16 is not ON, that is, in the case of normal sewing, as shown in FIG. 6 (a), the PWM cycle is set to a rough state of 500 μS, and To control the rotation speed of the motor 5,
The heat generation of the power transistors Q1 to Q6 and the generation of radio noise are suppressed.

During the thread trimming operation in which the thread trimming solenoid 16 is ON, as shown in FIG. 6 (b), the PWM cycle is reduced to 1/2, that is, 250 μS, and the pulse width is also switched to 1/2 of the calculated value.

By this switching, the ripple of the motor drive current as shown by a broken line in FIG.
As shown by the broken line in FIG. 2, the torque ripple is also stabilized, so that the rotational torque of the motor 5 is stabilized and the thread cutting mechanism can be operated stably.

Thereby, the stop position of the sewing needle 12 after thread trimming is also stabilized, so that the performance of the sewing machine is improved.

〔The invention's effect〕

As described above, by applying the motor control method according to the present invention, the rotation of the motor during the thread trimming operation in the sewing machine can be stabilized, and the sewing machine needle can be reliably stopped at the upper stop position.

Moreover, it can be easily applied to various sewing machines having different thread cutting loads.

[Brief description of the drawings]

FIG. 1 is a flow chart showing a PWM switching operation by the control system shown in FIG. 3, FIG. 2 is a schematic front view showing an appearance of a sewing machine to which the present invention is applied, and FIG. FIG. 4 is a block diagram showing the motor control unit 10B and its feedback loop shown in FIG. 3, FIG. 5 is a circuit diagram showing details of the motor 5 and the motor driver 13, and FIG. FIG. 6 is a waveform diagram of two types of PWM control signals to be switched and a motor drive current, and FIG. 7 is a timing chart showing signal waveforms at the time of a thread trimming operation. 1 ... sewing machine body (head), 2 ... sewing machine table 3 ... DC brushless motor 8 ... motor speed detector, 9 ... pedal 10 ... control circuit box 10A ... sewing machine controller, 10B ... motor Control unit 11 Pedal sensor 12, Sewing needle 13 Motor driver 14 Sewing needle position detector 15 Thread trimming solenoid drive circuit 16 Thread trimming solenoid 20 Deviation calculation circuit 22, 22 PWM control circuit

Claims (1)

(57) [Claims] 1. A sewing machine in which a DC brushless servomotor is used as a drive source and a drive current of the motor is controlled by a pulse width modulation signal. A motor control method, wherein the period of the pulse width modulation signal is made shorter than at the time of driving.