JPS6230000B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to a constant speed control device for a motor, and more particularly to a constant speed control device for controlling the rotational speed of a motor by an energization duty.

(Prior art) For example, a speed detector such as a tacho generator or rotary encoder is connected to a sewing machine motor, the generated voltage is processed to obtain a finger speed voltage, and this is compared with a target speed voltage to determine the difference between the two. Speed control devices are known that maintain a constant rotational speed of a motor by applying a corresponding voltage to the motor.

Incidentally, speed fluctuations of the sewing machine motor are caused by fluctuations in the motor load, and the motor load includes friction and inertia of the needle drive system, friction between the needle and the cloth, and the like. The main cause of load variation is the friction between the needle and cloth, but at low speeds the load also varies depending on the rotation angle of the cam connected to the needle bar. When the load increases, the speed decreases and the motor back electromotive force voltage decreases, and when the load decreases, the speed increases and the motor back electromotive force voltage increases.
In this way, the back electromotive voltage of the motor is in a corresponding relationship with the motor speed, so the finger speed signal can be obtained by picking up the motor back electromotive voltage, eliminating the need to add speed detection means such as a tacho generator or rotary encoder. No additional torque is consumed to drive these detection means.

Japanese Utility Model Application No. 50-83510 discloses that when a motor is energized in pulses and the duty of this pulse is controlled to perform constant speed control, a back electromotive force of the motor is detected during a period in which the motor is not energized during pulse energization. A constant speed control device is proposed that sets the duty based on . In this case, a triangular wave signal generation circuit generates a triangular wave that gradually increases from the rising point of a pulse generated by a rectangular wave oscillator from a low level L to a high level H, and gradually decreases from a falling point of the pulse from H to L. At the same time as applying it to the Schmitt trigger circuit (comparison circuit), a differential pulse is obtained at the rising point of the pulse from L to H, and while this differential pulse is present, the back electromotive voltage of the motor is supplied to the integrating circuit, and at the target speed voltage, the integrating circuit A voltage is adjusted and applied to the Schmitt trigger circuit, and the output of the Schmitt trigger circuit energizes the motor while the level of the triangular wave exceeds the adjusted voltage.

(Problem to be solved by the invention) The purpose of this constant speed control device is to change the duty of the motor drive current from 0% to 0% according to the rotational speed of the motor.
The above publication states that the purpose is to be able to change up to 100%, but as the duty becomes higher, the rising point of the motor energization pulse (the energization start point) approaches the generation position of the differential pulse, and the duty becomes 100% ( In continuous energization), the differential pulse is used to input the motor drive voltage, not the back electromotive force, into the integrating circuit, and this motor drive voltage does not indicate the motor speed, so constant speed control is disturbed. In addition, this kind of input of the motor drive voltage into the integrating circuit also occurs by adjusting the target speed voltage, and when the target speed voltage is set to a value that causes energization around 100% duty, control is disabled. turbulence and constant speed characteristics are impaired.

Furthermore, if the integration circuit has a large time constant that smooths fluctuations in its integrated voltage in units of one pulse energization, the constant speed control will have a delay time constant that extends over several pulses or more and will have low responsiveness, resulting in low duty cycle control. High responsiveness cannot be obtained, such as detecting the motor speed in the off period following one pulse of energization and setting the energization width (duty) corresponding to the detected value in the next one pulse on period. When the time constant of the integrating circuit is small, the integrated voltage becomes a sawtooth wave that rapidly increases when the differential pulse is applied and then gradually decreases. Thus, at motor speeds where the peak of the sawtooth wave is higher than the peak of the triangular wave, when the rate of taper of the sawtooth wave is smaller than the rate of taper of the triangular wave,
The duty is 50% or more (duty of pulses generated by the square wave oscillator), but when the gradual decrease rate of the sawtooth wave is greater than the gradual decrease rate of the triangular wave, the duty becomes 0%, and the motor speed Due to slight fluctuations in
% or more or 0%, the motor torque fluctuates extremely and stable constant speed control cannot be obtained.

The present invention simplifies the circuit configuration of the constant speed control system by omitting mechanical additional means such as a tacho generator and rotary encoder, and provides a constant speed control device that has high responsiveness for correcting speed fluctuations and high stability of speed control. The purpose is to provide.

[Structure of the invention]

(Means for Solving the Problems) The constant speed control device of the present invention includes a switching element connected between one end of the motor and a motor energizing power source;
a sample and hold circuit connected to the one end of the motor; a constant frequency oscillator; a timing device that resets the sample and hold circuit in synchronization with the output signal of the constant frequency oscillator; and a timing device that resets the sample and hold circuit at the same time as the sample and hold circuit is reset. a waveform generating circuit that generates a sawtooth wave whose level is gradually increased from the base level after being reset; A comparison device is provided that makes the switching element conductive while the switching element is turned.

(Function) According to this, by resetting the sample-and-hold circuit in synchronization with the output signal of the constant-frequency oscillator by the timing device (updating the signal pull signal), the holding voltage of the sample-and-hold circuit is adjusted to the period of the constant-frequency oscillator, and the holding voltage of the motor is This is a sample of the voltage appearing at one end. On the other hand, the waveform generation circuit generates a sawtooth wave whose level reaches the base level at the same time as the sample and hold circuit is reset, and whose level gradually increases from the base level after the reset. ). That is, the sample and hold circuit is reset (the sample signal is updated) when the sawtooth wave is at the base level. The comparator then compares the holding voltage of the sample and hold circuit with the level of the sawtooth wave, and while the latter exceeds the former, the switching element is made conductive, thereby resetting the sample and hold circuit (updating the sample signal). When , the sawtooth wave is at the base level and is lower than the holding voltage of the sample and hold circuit.The comparator makes the switching element non-conductive at this time, so the voltage generated by the motor, that is, the back electromotive force corresponding to the motor speed, is sampled and held. Updated and maintained in the circuit. That is, the motor drive current is not taken in while the switching element is conducting (motor current is being applied). Even if the sample and hold circuit has a discharge time constant and generates a voltage that sharply rises and then gradually decreases at the time of reset, the sawtooth wave is a sawtooth wave that rapidly decreases to the base level at the reset and then gradually increases. The rate of decrease in voltage in the sample-and-hold circuit will never exceed the rate of decrease in the sudden drop in the sawtooth waveform, and therefore, at a certain point in motor speed, the motor's energization duty will cut to a large value and 0%. The duty does not change, the duty changes smoothly, and stable constant speed control is obtained.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

(Embodiment) FIG. 1 shows an embodiment of the present invention, and FIG. 2 shows electrical signals of various parts of the circuit shown in FIG. 1. In FIG. 1, reference numeral 1 denotes a sewing machine motor, and when a switching transistor 2 is turned on, 24V from a motor power supply circuit (not shown) is applied to the rotor winding of the motor 1. The transistor 2 is controlled on/off by a comparison circuit 3. A sample and hold circuit 4 is connected to the rotor winding of the motor 2 via a variable resistor VR for speed setting. Pulse oscillator 5 is 2KHZ
A pulse a is generated and applied to the timing circuit 6.

In the timing circuit 6, the transistor 6
a conducts during the high level H section of the pulse, its collector voltage becomes an inverted waveform of the output pulse a of the oscillator 5, and the capacitor 6b differentiates the collector voltage,
This produces a differential pulse b in the resistor R1 at the falling point of the pulse a. This differential pulse b is applied to the transistor 7a of the waveform generating circuit 7, and the transistor 7a becomes conductive in synchronization with the differential pulse b. Due to conduction of the transistor 7a, in the sample hold circuit 4, the reset transistor 3 is turned on.
4a becomes non-conductive. That is, the transistor 4a of the sample and hold circuit 4 becomes non-conductive due to the differential pulse b. When the transistor 4a is non-conductive, the back electromotive force of the motor 1 is applied to the capacitor 4b via the resistor VR and the diode D1 (reset: sampling and updating of the held value). Since the series circuit of the resistor R2 and the diode D2 is connected in parallel to the capacitor 4b, a voltage of approximately Vi·R2/(R2+R3+VR) is applied to the capacitor 4b. That is, Vi is the back electromotive force of the motor 1, and a fraction thereof is applied. When the differential pulse b disappears, the transistor 4a becomes conductive and connects the anode of the diode D1 to ground. During this conduction of transistor 4a, capacitor 4b gradually discharges through resistor R2 and diode D2. Therefore, the voltage d of the sample and hold circuit 4 suddenly rises to a value corresponding to the motor back electromotive voltage at the time of reset, and then gradually decreases to form a sawtooth waveform.

The voltage d of the capacitor 4b is applied to the negative phase input terminal (-) of the comparator OP1.

On the other hand, in the waveform generation circuit 7, a voltage of 5V is applied to the capacitor 7b via the resistor R4, but since the resistor R4 is grounded via the diode D3 and the transistor 7a, the transistor 7a is When conductive by differential pulse b, capacitor 7b discharges through diode D3 and transistor 7a. Therefore, capacitor 7b charges up when differential pulse b disappears and transistor 7a is non-conductive. As a result, the voltage c of the capacitor 7b becomes a sawtooth wave c, which reaches the base level at the falling point of the pulse a (differential pulse b) and gradually increases in level thereafter, in synchronization with the pulse a. This sawtooth wave c is the comparator
Applied to the positive phase input terminal (+) of OP1.

The comparator OP1 generates a voltage e at a high level H while the voltage level of the positive phase input terminal (+) exceeds the voltage level of the negative phase input terminal (-), and the transistor 3a
to be applied. The transistor 3a is at this high level H.
conducts to make the switching transistor 2 conductive. Therefore, 24V from the motor power supply circuit is applied to the motor 2 while the voltage e is at the high level H.

Note that in the waveform generation circuit 7, the transistor 7
Since the diode D3 is connected in series with the capacitor 7b, the residual potential of the capacitor 7b is connected to the diode D3.
The forward voltage drop is Vd. As a result, when motor 1 is energized to rotate from a stop, the voltage at the positive phase input terminal (+) of comparator OP1 is always higher than the voltage at the negative phase input terminal (-) (in this case, the ground level), and comparator OP1 A high level H output is always produced.
If diode D3 is omitted, when the motor 1 is energized to rotate from a stop, no voltage is applied to the motor M1 during the pulse width of the differential pulse b, and the speed increase of the motor 1 is slow. However, it is necessary to provide circuit means for applying a bias to the positive phase input terminal (+) of the comparator OP1.

Therefore, when starting the motor from a stopped state, the level of the sawtooth wave c is higher than the voltage d of the sample and hold circuit 4 over the entire period of the pulse a, and the energization duty of the motor 1 becomes 100%. When the motor 1 starts rotating, the voltage d becomes higher than the base level of the sawtooth wave c, so the energization duty of the motor 1 becomes less than 100%, and when the sample and hold circuit 4 is reset, the voltage d becomes higher than the base level of the sawtooth wave c.
There is no 24V applied to sample and hold circuit 4.
The back electromotive force of the motor 1 is taken in.

Resistor R5 is connected to the negative phase input terminal (-) of comparator OP1.
A voltage of 5V is applied through the diode D4, and in this state where 5V is applied, the output of the comparator OP1 is at a low level L, and the transistor 2 remains off. The anode of the diode D5 is connected between the resistor R5 and the anode of the diode D4, and a rotation instruction signal is applied to the cathode of the diode D5. When the rotation instruction signal is at a high level H = 5V, the output of comparator OP1 is at a low level L and the motor 1 is stopped. When the rotation instruction signal is at a low level L = ground, the diode D
Since the anode of No. 4 becomes low level L = earth,
The output of comparator OP1 becomes high level H, and motor 1 starts. As the speed of motor 1 increases, the voltage of capacitor 4b increases, so comparator OP1
The output of the motor 1 is periodically reversed to H/L, and the motor 1 is pulse-energized.

The signal generation timing shown in FIG. 2 indicates a state in which the rotation instruction signal becomes a low level L and the motor 1 is started, and then the motor 1 is stabilized at a certain speed. In this case, if the speed of motor 1 now decreases, motor 1
Since the back electromotive voltage of the capacitor 4b decreases, the charge-up voltage of the capacitor 4b during the pulse b period becomes low, so the H output period Pt of the comparator OP1 widens, thereby accelerating the motor 1. Conversely, when the speed of the motor 1 increases, the back electromotive voltage of the motor 1 increases, and the charge-up voltage of the capacitor 4b in the pulse b section becomes higher, so the H output period Pt of the comparator OP1 becomes narrower, and as a result, the motor 1 decelerates. In this way, the speed of the motor 1 is controlled to a constant speed determined by the setting of the variable resistance VR. If the resistance value of VR is increased, the speed of the motor 1 will be decreased, and if it is decreased, it will be increased.

〔Effect of the invention〕

As described above, in the present invention, the back electromotive force of the motor is extracted as a command speed signal and the motor is controlled at a constant speed by feedback pulse width control. Means are omitted, there are fewer mechanical elements,
Moreover, the electrical processing circuit has become simpler. Particularly in sewing machine motors, large load fluctuations occur during one vertical movement of the needle, and therefore it is necessary to quickly compensate for the fluctuations.According to the present invention, however, the current value at that point in each cycle of pulse a is Since compensation is performed according to the speed, there is an advantage that the motor speed is stabilized at a constant speed during one vertical movement of the needle.
In this way, the feedback delay is extremely small.

Further, according to the present invention, by resetting the sample and hold circuit in synchronization with the output signal of the constant frequency oscillator by the timing device (updating the sample signal),
The holding voltage of the sample and hold circuit is obtained by sampling the voltage appearing at one end of the motor at the period of the constant frequency oscillator. On the other hand, since the waveform generation circuit generates a sawtooth wave that reaches the base level at the same time as the sample and hold circuit is reset, and whose level gradually increases from the base level after the reset,
The sawtooth wave is synchronized with the reset of the sample and hold circuit (sample signal update). That is, the sample and hold circuit is reset (the sample signal is updated) when the sawtooth wave is at the base level. The comparing device compares the holding voltage of the sample and hold circuit with the level of the sawtooth wave, and while the latter exceeds the former, the switching element is made conductive, and the sample and hold circuit is reset (sample signal update). At this time, the sawtooth wave is at the base level and is lower than the holding voltage of the sample and hold circuit.The comparator makes the switching element non-conductive at this time, so the voltage generated by the motor, that is, the back electromotive force corresponding to the motor speed, is sampled and held. Updated and maintained in the circuit. That is, the motor drive current is not taken in while the switching element is conducting (motor energizing). Even if the sample-and-hold circuit has a discharge time constant and generates a voltage that sharply rises and then gradually decreases at the time of reset, the sawtooth wave is a sawtooth wave that rapidly decreases to the base level at the time of reset and then gradually increases. The rate of decrease in voltage in the sample-and-hold circuit will never exceed the rate of decrease in the sudden drop in the sawtooth waveform, and therefore, at a certain point in motor speed, the motor's energization duty will cut to a large value and 0%. The duty does not change, the duty transition is smooth, and stable constant speed control can be obtained.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram showing an embodiment of the present invention;
FIG. 2 is a time chart showing the electrical signals of each part. 1: sewing machine motor, 2: transistor (switching element), 3: comparison circuit, 4: sample hold circuit, 5: pulse oscillator, 6: timing circuit, 7: waveform generation circuit.

Claims (1)

[Claims] 1. A switching element connected between one end of the motor and a motor energizing power source; A sample hold circuit connected to the one end of the motor; A constant frequency oscillator; a timing device that resets the sample and hold circuit; a waveform generating circuit that generates a sawtooth wave that is reset to a base level by the timing device simultaneously with the reset of the sample and hold circuit, and whose level gradually increases from the base level after the reset; and a comparison device that compares the holding voltage of the sample and hold circuit with the level of the sawtooth wave and makes the switching element conductive while the latter exceeds the former.