JPH0135595B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a DC motor that automatically stops the DC motor by electrically detecting changes in motor load at the end of operation or under abnormal load in a motor drive mechanism using a DC motor. Related to an automatic stop circuit for a motor.

Automatic stopping devices for DC motors using conventional electrical means, in order to absorb the allowable load fluctuations,
The detection level for load fluctuations that require stop control is
The signal-to-noise ratio was obtained by setting it at a position far from the operating load level, and stop control was performed by detecting large load fluctuations such as activation of the lock mechanism at the end of operation or abnormal load. In this case, since the detection level for stop control is fixed, the operating load must be stable in relation to the allowable load fluctuation range. In addition, since the detection level is set far from the usage load level,
It is necessary to have a structure that can obtain large load fluctuations for stop control, but on the other hand, for each stop control operation,
Since a large load will be applied to the motor drive section, structural strength is also required.

Further, an automatic stop device for a DC motor using mechanical means includes a cam disposed in the rotation system of the motor,
By using a combined arrangement with a mechanical switch, stop control is performed by detecting the end of operation position, abnormal load, etc., but in this case, there are restrictions in terms of structure and arrangement.

The present invention is an automatic stopping device for a DC motor using electrical means, and its purpose is to:
It is easy to set the detection level of load fluctuations for stop control, and stable stop control is possible regardless of the size of the load used.Furthermore, the detection level shifts according to load fluctuations, allowing for Since it is possible to prevent the stop control signal from being generated within the range of load fluctuations that occur, and the detection level can be brought closer to the operating load level, automatic stop circuits for DC motors that do not require much structural strength of the motor drive section can be used. This is what we provide.

Embodiments of the present invention will be described in detail below based on the drawings.

First, let's examine the DC motor drive circuit surrounded by the dotted line in Figure 1.

E _S is a battery power source, M is a DC motor, and T is a transistor serving as a power switch.

Here, the collector of transistor T when conducting is
If the voltage between emitters is assumed to be O for convenience, then from the general formula of the motor, V = IR + E _V (1) V: Super voltage of the battery I: Motor current R: Total resistance E _V : Back electromotive force of the motor R = R _S + R _M (2) R _S : Battery internal resistance R _M : Motor armature resistance T = K _T I (3) T: Motor torque = load K _T : Torque constant From (1) and (2) V = I (R _S + R _M ) + K _E N (4) K _E : Power generation constant N: Rotational speed V-IR _S = I R _M +K _E N (5) V-IR _S : Can be expressed as battery voltage.

Therefore, the motor torque (T) is proportional to the motor current (I), that is, the load fluctuation becomes a current fluctuation, which appears as a fluctuation in I, V-IR _S , K _E N from equation (5). Therefore, by detecting either of these, load fluctuations can be detected. In the case of a battery power source, the internal resistance R _S is large, so it is easy to detect the battery voltage V-IR _S .

Therefore, with reference to FIG. 1, an embodiment will be described in which load fluctuations are detected based on fluctuations in battery voltage V-IR _S and the DC motor is automatically stopped.

R ₁ , R ₂ , R ₃ are resistors that divide the battery voltage V- _IRS , R ₄ and C ₁ are resistors and capacitors that constitute the first integrating circuit, and R ₅ and C ₂ are resistors that constitute the second integrating circuit. The resistor and capacitor that make up the circuit, CO is a comparator circuit whose both input terminals are connected to the output terminals of the first and second integrating circuits (connection point of the resistor and capacitor), and FF is a comparator circuit whose reset input terminal is the output of the comparator circuit CO. It is a flip-flop circuit whose output terminal Q is connected to the base of the transistor T.

Note that the time constant of the first integrating circuit is set smaller than the time constant of the second integrating circuit.

Next, its operation will be explained with reference to FIG.

First, as is clear, the potential at point m is always higher than the potential at point n, and points m and n are equal to the battery voltage V-IR _S
is converted into two signals with different levels.

Therefore, when a positive pulse is applied to the set input terminal S of the flip-flop circuit FF, the output terminal Q is inverted to the "H" level. Therefore, the transistor T becomes conductive and power is supplied to the DC motor M.

As the motor M rotates due to this power supply, the motor M stabilizes at a current I and a rotational speed N determined by the operating load level L _U in a steady state.

When the motor starts, a large starting current I _S flows to accelerate the motor (the voltage at this time drops to V-I _S R), and then the battery voltage V-I _S
The potential at point m is higher than the potential at point n, and the time constant of resistor R ₄ and capacitor C ₁ is smaller than the time constant of resistor R ₅ and capacitor C ₂ . As a result, the potential at point m' remains higher than the potential at point n', so the output terminal of comparator circuit CO continues to be at the "L" level.

Therefore, if this DC motor M is used as a drive source for winding film in a camera, for example, and a mechanical lock mechanism is activated after a predetermined amount of winding operation is completed, the motor is forcibly stopped. Then, the motor load M _L suddenly increases to a heavy load L _E state. In other words, when the motor M stops, the back electromotive force
When _EV decreases, motor current I relatively increases, so battery voltage V-IR _S decreases.

Therefore, since the time constants of resistor R ₄ and capacitor C ₁ are smaller, a situation occurs where the potential at point m′ is lower than the potential at point n′, and in that state, the output terminal of comparator circuit CO becomes Inverted to "H" level. As a result, the flip-flop circuit FF is reset and the output terminal Q is inverted to the "L" level, so that the transistor T is cut off. Therefore,
The DC motor M is electrically stopped as the power supply is cut off.

The above embodiment is a case where an abnormal state in which the load of the motor M changes from a working load level to a heavy load side is detected.

For example, a film drive motor built into a camera can be used to advance the film one frame at a time, or to rewind the film (winding it into the pyrone). In the operating state, the film comes off from the drive shaft system of the motor, resulting in an abnormal state in which the load on the motor M changes from the operating load level to the light load side.

Therefore, with reference to FIGS. 3 and 4, an embodiment will be described in which the load change toward the light load side is detected and the power supply to the DC motor M is cut off to stop the motor M.

The added elements in this example are the one-shot multivibrator circuit OSM and the AND gate circuit AG, and the changed conditions are the resistance
The time constant of the second integrating circuit formed by R ₅ and capacitor C ₂ is set smaller than the time constant of the first integrating circuit formed by resistor R ₄ and capacitor C ₁ .

Similarly to the above, when a positive pulse is applied to the set input terminal S of the flip-flop circuit FF, the motor M receives power and starts rotating, and the operating load level
The current I becomes stable after increasing to the rotational speed N determined by L _U. At this time, due to the rise in battery voltage V-IR _S , the potential at point n' is temporarily higher than the potential at point m' because the time constant due to resistor R ₅ and capacitor C ₂ is smaller. occurs, and in this state, the output terminal of the comparator circuit CO is inverted to the "H" level.

However, when the previous positive pulse arrived, the one-shot multivibrator circuit OSM had also started operating, and its output was inverted to the "L" level for a predetermined period of time, so the output terminal of the AND gate circuit AG was " It remains at the "L" level, and the flip-flop circuit FF is not reset.

Then, when the motor load M _L changes to a light load L _F state, the rotational speed N of the motor M increases and the back electromotive force E _V value increases, and when the motor current I relatively decreases, the battery voltage V- Since _IRS will further increase,
A situation in which the potential at point n' becomes higher than the potential at point m' occurs again, and the output terminal of comparator circuit CO is again inverted to the "H" level. At this time, since the output of the one-shot multivibrator circuit OSM has already returned to the "H" level, the output terminal of the AND gate circuit AG is inverted to the "H" level.
The flip-flop circuit FF is reset and power supply to the motor M is stopped.

Note that the potentials at points m' and n' are the battery voltage V-IR _S
The level relationship can be prevented from reversing within a certain range of variation, and the load variation within that range is the permissible load variation within the usage load.

In any case, if the motor stop control signal is not generated for some reason even after the set working time (the time required to rotate the specified amount) has elapsed, the motor will be stopped. As a measure to ensure that the circuit stops after a predetermined period of time, the output terminal of the comparator circuit CO or the AND gate circuit AG is connected to one input terminal, and the output terminal is connected to the reset input terminal R of the flip-flop circuit FF. It is sufficient to provide an OR gate circuit and apply an overtime control signal to the other input terminal of the OR gate circuit.The overtime control signal generating circuit can be a one-shot multi-channel circuit whose inversion time is set to the overtime time. A vibrator circuit etc. can be used.

Furthermore, as mentioned above, when the detection direction of motor load fluctuations is switched from heavy load side to light load side, such as when one motor is used as a film drive source for a camera, The configuration of the detection circuit may be switched in conjunction with the switching operation.

This will be explained using drawings.

FIG. 5 is a circuit diagram showing this embodiment. This embodiment consists of a voltage dividing circuit composed of R ₁ , R ₂ , and R ₃ in the embodiment shown in FIG. 3 and two integrating circuits composed of R ₄ , R ₁ , R ₅ , and C _{2 .} An interlocking switch S for switching the connection state of the two integrating circuits is inserted between the two integrating circuits and the comparator circuit CO. That is, when the DC motor automatic stop circuit of this embodiment is used for detecting load fluctuations on the heavy load side among motor load fluctuations,
Switch S connects an integrator circuit with a small time constant consisting of a resistor _R4 and a capacitor _C1 to point m, which has a high potential among the voltage dividing points of the voltage divider circuit, and outputs the integrator circuit with a small time constant. the comparator circuit
Connected to input to the inverted side input terminal of CO. In addition, a resistor is placed at the n point where the potential of the voltage dividing point is low.
An integrating circuit with a large time constant consisting of R ₅ and a capacitor C ₂ is connected, and the output of the integrating circuit is connected to be input to the non-inverting input terminal of the comparator circuit CO. That is, when the switch S is used for detecting a load change toward the heavy load side, the switch S is placed in the state shown in FIG.

Further, when used for detecting a load change toward the light load side, the switch S is switched to a state opposite to that shown in FIG. 5. That is,
An integrating circuit with a large time constant consisting of a resistor R ₅ and a capacitor C ₂ is connected to the voltage dividing point m, and the output terminal n' of the integrating circuit is connected to the inverting input terminal of the comparator circuit CO. Further, an integrating circuit with a small time constant consisting of a resistor R ₄ and a capacitor C ₁ is connected to the voltage dividing point n, and the output terminal m' of the integrating circuit is connected to the non-inverting input terminal of the comparator circuit CO.

The switching operation of switch S is performed in conjunction with the switching operation when the motor load fluctuation detection direction is switched from the heavy load side to the light load side, or vice versa, depending on the switching of the usage mode. It's fine. In this way, an automatic stop circuit for a DC motor is obtained in which the switch S is automatically switched depending on the mode of use and the motor can be stopped with optimum accuracy at all times.

Furthermore, the above-described embodiments have the advantage that the battery voltage V-IR _S
This method detects changes in the motor load by detecting changes in the motor's load, but as mentioned above, it detects the motor current I or the element _KEN related to the rotational speed and converts it into voltage. However, it is possible to detect motor load fluctuations.

As described above, since the automatic stop circuit of the present invention does not require any mechanical elements, it is not subject to structural or layout restrictions, and the abnormal load detection level changes to follow the operating load level. , within the set range, the level relationship will not be reversed, so the level difference can be made relatively small,
Detection performance can be improved, stable operation can be obtained, and restrictions on the strength of the motor drive section can be reduced.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing one embodiment of the present invention, Fig. 2 is an explanatory diagram of the operation of the circuit shown in Fig. 1, Fig. 3 is a circuit diagram showing another embodiment of the invention, and Fig. 4 is FIG. 3 is an explanatory diagram of the operation of the circuit. FIG. 5 is a circuit diagram showing a third embodiment of the present invention. E _S ...Battery power supply, M...DC motor, _R1 to _R5 ...Resistor, _C1 , _C2 ...Capacitor, CO...Comparator circuit, FF...Flip-flop circuit, OSM...One-shot multivibrator circuit, AG...AND gate circuit , S...Switch.

Claims (1)

[Claims] 1. A voltage divider circuit that detects the load voltage of a DC motor and divides the detected load voltage into two voltage components of different magnitudes, and each voltage divided by the voltage divider circuit. Two integrating circuits each having a different time constant that integrates each component, the magnitude of the output voltage of the two integrating circuits being reversed by a change in the load voltage accompanying a load fluctuation of the DC motor. an integrating circuit, a comparing circuit that compares the output voltages of the two integrating circuits, a flip-flop circuit that is reset when the output of the comparing circuit is inverted, and a reset state output of the flip-flop circuit to An automatic stop circuit for a DC motor, comprising a transistor switch that cuts off power supply to the motor.