JPS6211197Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a speed control device for an electric motor, and more particularly to a speed control device for an electric sewing machine that uses a triax to perform phase control to drive the motor.

Conventionally, in order to control the speed of an electric motor, a triax has been used to provide phase-controlled alternating current power. On the other hand, in electric sewing machines,
For example, when the sewing needle sticks to the fabric to be sewn, the electric motor is overloaded and its speed or rotational torque is thereby reduced. For this reason, it has recently been known that in phase control devices using such triaxes, the conduction angle or conduction angle of the triax is controlled by detecting the induced voltage or back electromotive force from the motor. That is, when an electric motor is overloaded, its rotation becomes slower and the induced voltage from the electric motor becomes smaller. Therefore, this induced voltage is detected, and when the voltage becomes small, the conduction angle of the triax is increased to improve torque or rotation. However, all of the conventional devices that control the conduction angle of the triac by detecting the induced voltage from the electric motor have complicated structures and are therefore expensive.

Therefore, the main purpose of this invention is to provide a speed control device for an electric sewing machine that can change the energizing angle of the triax with a simple and inexpensive structure, while eliminating the above-mentioned drawbacks.

In summary, this idea applies bridge rectified direct current to both terminals of the motor, and uses the fact that the voltage between the terminals of this bridge circuit changes depending on the magnitude of the induced voltage of the motor to adjust the speed. A parallel circuit of an ignition capacitor and a feedback resistor is connected between the variable resistor for the triac and one end of the bridge circuit, and a feedback capacitor is connected between this parallel connection point and one end of the triax. Then, when the induced voltage becomes small, the feedback capacitor discharges, the voltage at one end becomes small, and the voltage at the other end of the parallel circuit becomes relatively large, so that when an overload occurs, the feedback capacitor discharges. , a speed control device for a motor, which applies a gate voltage larger than a set state to the gate electrode of the triax.

The above objects and other objects and features of the present invention will become more apparent from the following detailed description with reference to the drawings.

FIG. 1 is a schematic illustration of an electric sewing machine that forms the background of this invention and in which this invention has been implemented. In this structure, a sewing machine arm AM is formed on the upper surface of the sewing machine bed BS, and a sewing machine arm AM that houses various mechanisms therein is provided, and a driving DC motor M is provided below the sewing machine bed BS or outside the sewing machine arm AM. A belt B1 is applied to a pulley MP provided on the rotating shaft of the electric motor M, and the driving force of the belt B1 is transmitted to the belt B2 at a certain speed ratio via an intervening pulley. This belt B
2 further includes a main shaft that serves as a driving source for the various mechanisms described above.
It is hung on a pulley SP formed on SH, and rotationally drives this pulley SP and thus the main shaft SH.

The main shaft SH connects to the needle bar NR via the crank CR.
The needle bar NR is connected to the needle bar NR in the vertical direction according to its rotation. Further, a sewing needle NDL is fitted into the lower end of the needle bar NR, and a lower thread (lower thread bobbin) wound around an inner hook and a bobbin is disposed below the sewing machine bed BS opposite to the position of the sewing needle NDL.
Therefore, the sewing needle NDL stitches the lower thread and upper thread near its bottom dead center, and is then returned to its top dead center, and repeats this operation in accordance with the rotation of the main shaft SH.

Further, in relation to the driving electric motor M, a foot controller unit having, for example, a pedal and controlling the speed of the electric motor M according to the pedal depression is provided.
FCU is provided. And this foot controller unit FCU has a connector
Three lead wires LW3, LW4, LW5 from CNC
Power is supplied by. Power is supplied to this connector CNC from a plug (not shown) through two lead wires LW1 and LW2, and the connector
It is given to electric motor M from CNC.

In addition, the sewing needle is placed at any position on arm AM.
A lighting lamp LP is provided to illuminate the end of the NDL.

It should be noted that in FIG. 1, only the main parts related to this invention are shown, and other parts are omitted.

FIG. 2 is an electrical circuit diagram showing an embodiment of this invention. In the configuration, the plug PL is connected to, for example, a commercial power source, and both ends of the plug PL are connected to two terminals of the connector CNC by lead wires LW1 and LW2.
It is connected to two sockets S1 and S2. This socket S1 is further connected to one side of the foot controller unit FCU by a lead wire LW3, and the socket S3 of this connector CNC is connected to the unit.
Connected to the other side of the FCU. This socket S1
and S3, there is a foot controller unit
Noise prevention check coil CH1, foot switch FSW, triax TRC and noise prevention check coil CH2 as main loop of FCU
series circuit is connected. A lead wire LW is connected between the connection point between the noise prevention choke coil CH1 and the foot switch FSW and the socket S2.
5 connects the noise prevention capacitor C4. If there is no particular need for noise prevention, the lead wire LW5 to which this capacitor C4 should be connected is unnecessary.

In addition, each socket S1, S of the connector CNC
2, S3 have corresponding pins P1, P2,
P3 is inserted. The pin P1 is connected to one end of the illumination lamp LP, and the other end of the lamp LP is connected to a relay terminal T included in the connector CNC. A power switch PSW is inserted between pin P2 and terminal T. A motor circuit M is connected between pin P3 and terminal T. A noise prevention capacitor C5 is connected between pins P1 and P2.
However, a noise prevention capacitor C6 is connected in parallel between pins P2 and P3.

The motor circuit M is configured as a series commutator motor including a series connection of a noise prevention coil CH3, an armature A, a noise prevention coil CH4, and a field coil FC. A diode bridge circuit consisting of diodes D1 to D4 is connected between the pin P3 and the terminal T at both ends of this series connection. Furthermore, the field coil FC has
A diode D5 for freewheeling is connected in parallel.

The foot controller unit FCU includes a foot switch FSW that is linked to a foot controller pedal (not shown), and a variable resistor VR that has a slider that is displaced depending on the amount of depression of the foot switch FSW. This variable resistor VR has one end connected to the foot switch FSW and the triax via the current limiting resistor R1.
It is connected to the connection point y with the TRC, and the other end is connected to the connection point between the triac TRC and the choke coil CH2 via a semi-fixed resistor R3 and a capacitor C1 for fine speed adjustment. Furthermore, a semi-fixed resistor R2 for correction is connected in parallel to both ends of the variable resistor VR. The series connection point between the semi-fixed resistor R3 and the capacitor C1 is connected to the diagonal via the resistor R4.
Connected to point x of one electrode of DIC. The other electrode of this diac DIC is connected to the gate electrode of the triac TRC.

A feedback capacitor C2, which is one feature of this invention, is connected between the point x and one electrode of the triac TRC, that is, the point y.

Between the point x and the other electrode of the triax TRC, there is a capacitor C for feedback (and a capacitor C), which is one of the features of this invention, at the point z.
A resistor R5 (acting for reducing the hysteresis of 3) is connected. An ignition capacitor C3 is further connected in parallel to the resistor R5. In addition,
It will be appreciated that the capacitor C1 serves to reduce the hysteresis of the capacitor C3, and that the resistor R4 constitutes a charging/discharging path for this capacitor C1.

In operation, when the power switch PSW is turned on, the motor circuit M is energized and enters a standby state. Then, when the foot controller pedal is depressed, the foot switch FSW is turned on, and the foot controller unit FCU is energized. When the foot controller pedal is depressed, the slider of the variable resistor VR is displaced, and a voltage corresponding to the amount of depression is derived from the variable resistor VR. Therefore, the capacitor C3 is charged through the path of resistor R1 - variable resistor VR (semi-fixed resistor R2) - semi-fixed resistor R3 - resistor R4. This capacitor C3
When charged to a certain level, it is discharged,
The discharged charge is applied from point x to one electrode of the dielectric DIC. Therefore, this diac DIC
conducts at a conduction angle depending on the discharge charge of the capacitor C3 and therefore the voltage applied from the variable resistor VR via the resistors R3 and R4. Therefore, the triac TRC conducts at an energization angle that corresponds to the amount of pedal depression. Therefore, the plug PL−
Lead wire LW1-Socket S1-Lead wire LW3
-Chiyoke coil CH1 -Foot switch FSW-
Triac TRC - York coil CH2 - Lead wire LW4 - Socket S3 - Pin P3 - Motor circuit M - Terminal T - Power switch PSW - Pin P2 -
A driving current for the motor circuit M flows through the path of the socket S2, the lead wire LW2, and the plug PL, causing the motor circuit M to rotate. The capacitor C2 is also charged at the same time.

At this time, the potential Vy at point y is approximately 100V, which approximates the power supply voltage, and the potential Vz at point z is the sum of the driving voltage of the motor circuit M and its induced voltage. The potential difference between points y and z remains constant and balanced, and the motor circuit M continues to rotate.

Let us now assume that the load on the motor circuit M suddenly increases, as in the case where the sewing needle NDL (Fig. 1) sticks to the cloth at low speed rotation. in this case,
The rotation of the motor circuit M becomes smaller, and its induced voltage also becomes smaller. Therefore, the potential at point z also decreases. Therefore, if the voltage (voltage drop) across the resistor R5 is constant, that is, the amount of depression of the foot controller pedal is constant, Vy-Vz increases, and Vx increases. Therefore, the dial
The DIC and therefore the triac TRC will conduct at a larger conduction angle.

At the same time, when the induced voltage from the motor circuit M decreases, the potential at point z decreases as described above.
Correspondingly, the potential difference across the capacitor C2 increases, and the charge stored in the capacitor C2 is discharged as described above. This capacitor C
The discharged charge of 2 flows as a charging current of the capacitor C3 and is applied to one side of the diode DIC, that is, the point x. Therefore, this diac DIC has a voltage depending on the amount of depression of the controller pedal given by the variable resistor VR, the resistor R1, and the semi-fixed resistors R2 and R3.
This discharge voltage of capacitor C2 is applied in a superimposed manner. Therefore, this dialogue
The conduction angle of the DIC, that is, the triac TRC, is determined by the superimposed voltage due to the discharged charge of the capacitor C2, which is larger than the conduction angle depending on the pedal position of a normal foot controller.

In this way, the feedback capacitor C2
Due to the cooperation between the motor circuit M and the feedback resistor R5, a drive current larger than the current set by the foot controller pedal flows through the motor circuit M, and its rotational torque or rotation is maintained at a large level even under overload conditions. be able to. Such cooperative circuits are particularly effective in the case of small motor circuits.

Note that the effect of capacitor C2 is variable resistor VR
This becomes more noticeable in the low speed rotation range where the resistance values of the resistor R1 and the semi-fixed resistors R2 and R3 are large. This is because in such a low speed rotation range, the variable resistor connected in parallel to capacitor C2
The series resistance value of VR etc. becomes relatively large, and therefore, in such a state, a large amount of current from the plug PL flows through the circuit of the capacitor C2. Therefore, the charge charged to this capacitor C2 becomes large, and the discharged charge accordingly becomes large, causing the dielectric to become
DIC has a larger conduction angle. At the same time,
This is because during low speed rotation, the ratio of the induced (feedback) voltage from the motor circuit to the drive voltage is relatively large, and its influence on the resistance R5 is large.

Note that when the voltage applied to one end (point This is to reduce hysteresis due to residual charge in the capacitor C3.

Further, for the above-described effect, the capacitor C2 is selected depending on the correlation with the series resistance value of the variable resistor VR or the like. That is, this capacitor C
The larger the capacitance of capacitor C2, the greater the torque improvement performance during overload.However, it is necessary to select a value such that the dielectric DIC will not conduct due to the discharge current of capacitor C2 alone.

As described above, according to this invention, since a capacitor and a resistor are provided to feed back changes in the induced voltage of the motor to the gate electrode of the triax, the amount of feedback can be extremely large, and as a result, the amount of feedback can be extremely large. A reduction in the torque or rotation of the motor under load can be largely compensated for.

In the above-described embodiment, a sewing machine using an electric motor was used as an example, but such a speed control circuit can be applied to other rotating equipment having a similar circuit configuration.

[Brief explanation of the drawing]

FIG. 1 is a schematic illustration of an electric sewing machine that forms the background of this invention and in which this invention can be implemented. Second
The figure is an electrical circuit diagram showing an embodiment of this invention. In the figure, M is the motor (motor circuit), NDL
is a sewing needle, DIC is a diac, TRC is a triac, C1, C2, and C3 are capacitors, VR is a variable resistor, R1, R4, and R5 are resistors, and R2 and R3 are semi-fixed resistors.

Claims (1)

[Claims for Utility Model Registration] (1) AC power source, electric motor, for supplying the AC power source to the electric motor,
and a current path including a triax for phase control, a variable resistance circuit that receives the alternating current power at one end and generates a control voltage for speed adjustment of the motor, and the other end of the variable resistance circuit and the gate of the triax. a series circuit of a first resistor and a diac inserted between the electrode, a series connection point between the first resistor and the diac, and one conductive electrode of the triac of the current path; a first capacitor for feeding back changes in the induced voltage of the motor to the gate electrode of the triax via the diagonal; a series connection point between the first resistor and the diac; and the other conductive electrode of the triac in the current path; and the electric motor, and the first
a second resistor for feeding back changes in the induced voltage of the motor to the gate electrode of the triax via the diagonal in cooperation with the capacitor; A speed control device for a motor, comprising a second capacitor for igniting said triac via a second capacitor. (2) a third capacitor connected in parallel to the series connection circuit of the first resistor and the second capacitor in the current path, and for reducing hysteresis of the second capacitor; A speed control device for an electric motor according to claim 1, further comprising a utility model registered claim. (3) The speed control device for an electric motor according to claim 1 or 2, wherein the capacitance of the first capacitor is selected such that the discharge charge of the capacitor alone does not energize the triax. .