JPS6345839Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to abnormality detection of a motor, and relates to a device for detecting a decrease in the rotational speed of a motor used, for example, as a cooling fan for a load.

If the rotation speed of a cooling fan motor decreases due to a drop in power supply voltage or a mechanical or electrical accident, the load that is being cooled may overheat and cause a serious accident. I have a problem. Especially when the load to be cooled is a computer, loss of important memory information,
There is a risk that the program will run out of control, so execution must be stopped in response to a detection signal of a decrease in the motor rotation speed, and the power must be turned off after executing the program to transfer memory information to the non-volatile memory.

From these points as well, accurate operation and reliability are required of motor abnormality detection devices.

Conventionally, this type of detection method has been equipped with a mercury switch that oscillates in conjunction with the blades that oscillate due to the wind force of the fan. A system in which the mercury switch is closed or opened depending on the inclination angle of the mercury switch, which stops in conjunction with the blade that stops at the position where the blade stops, and the contact signal is used as a detection signal, or a DC tachogenerator is used to control the motor. There are methods that directly detect the rotational speed, but in the former, dust tends to adhere to the blade pieces and their swing shafts, and this reduces the smoothness of the shaft movement.
Dust adhering to the blades may cause the balance position with the wind force corresponding to the preset rotation speed to be detected to change, causing the mercury switch to malfunction, reducing operational reliability and preventing accurate operation. The disadvantage is that it is difficult to adjust the points. In addition, as is well known, the latter method has a structure with brushes, so the brushes are subject to significant wear and tear.
This has the disadvantage that it is necessary to replace it again and again, and stable detection cannot be maintained over a long period of time, which is time-consuming. In order to improve these drawbacks, a detection method using an AC tacho-generator has been used. Examples of this method are shown in FIGS. 1A and 1B, and these will be explained below. In Fig. 1A, a rectifier DB ₁ with bridge-connected diodes is connected to the output terminal of the AC tachometer generator ACTG, and this rectifier DB ₁
A smoothing capacitor C ₁ and a constant voltage diode ZD ₁ are inserted in parallel between the output terminals of the rectifier DB 1, and an operational amplifier is connected to the (+) output terminal of the rectifier DB ₁ , whose (-) output terminal is grounded to the circuit. Connect the non-inverting input terminal of comparator CP ₁ , and connect the slider of variable resistor VR ₁ inserted between the control power supply V _C and the circuit ground to the inverting input terminal of comparator CP ₁ , and perform the above comparison. When the output voltage of the AC tachogenerator ACTG becomes smaller than the reference voltage set by the variable resistor VR ₁ , the relay X ₁ connected to its output terminal is energized by the device CP ₁ , and its contact signal ( For example, it is detected by opening of normally closed contact X _1b ). Although such a configuration has the advantage of accurate operation, it requires a separate power supply circuit _VD1 for the control circuit, and therefore has the problem of making the device expensive. In Figure 1B, a rectifier DB ₂ is connected to the output terminal of the AC tachogenerator ACTG as described above, and a smoothing capacitor C ₂ and a constant voltage diode ZD ₂ are inserted in parallel between the output terminals of this rectifier DB ₂ . constant voltage diode
Variable resistor VR ₂ and relay X ₂ are inserted in series between the terminals of ZD ₂ , and the contact signal of relay X ₂ (in this example, the open _/ close signal of normally closed contact is. With this configuration, the output of the AC tachogenerator ACTG is directly used as a power source, so the device can be constructed at low cost, but relay X ₂ is a variable resistor.
Since it is designed to be energized through VR ₂ , it will operate at the lowest operating voltage.
Generally, the operating point of a relay is not constant depending on the product.
Even if adjusted using a variable resistor, temperature and aging changes are very large, and due to the characteristics of the relay itself, the repeatability of the operating point is poor, making adjustment difficult, making it difficult to operate accurately and obtaining accurate detection signals. The problem is that it is difficult and has low reliability.

In order to improve this point, it is also possible to form it as shown in FIG. This will be explained. 1 is an AC tachometer generator (hereinafter abbreviated as ACTG). This includes, for example, a rotor magnet that is disk-shaped, magnetized with multiple poles on its outer periphery, and drivingly connected to the rotor of a motor (not shown), and a ring-shaped detection device that is fitted concentrically around the outer periphery of the rotor magnet. A coil, and upper and lower yokes that clamp and support this detection coil from above and below and are provided with the same number of teeth as the number of magnetized poles facing the outer periphery of the rotor magnet, and magnetic flux interlinks with the detection coil as the rotor rotates. It is designed to generate electricity by utilizing the change in the detection coil, and send out an AC output according to the rotation speed of the rotor from both ends of the detection coil. 2 is ACTG1 above
This is a control circuit that is connected to the AC output and sends out a detection signal in response to the AC output. This is the above
A rectifier DB ₃ with bridge-connected diodes is connected to both ends of the detection coil (not shown) of ACTG 1, and a constant voltage diode ZD ₃ for relay overexcitation prevention and a smoothing capacitor are connected between the output terminals of the rectifier DB ₃ .
Insert C ₃ and variable resistor VR ₃ in parallel,
The base of a transistor Q ₁ is connected to the slider of the variable resistor VR ₃ via a detection voltage regulator diode ZD ₄ , and the collector of this transistor Q ₁ is connected to the (+) of the rectifier DB ₃ via a relay X ₃ . ) side output terminal, and the emitter is connected to the (-) side output terminal of rectifier DB ₃ , and both ends of _{the normally closed contact X 3b of the} above relay , the transistor _Q1 is turned on to excite the relay _X3 , its normally closed contact _X3b is opened, and the contact signal of the relay _X3 is sent out from the output end as a detection signal.

Regarding ACTG1, the voltage e induced in the detection coil is expressed as e=-ndΦ/dt (1), where n is the number of turns of the detection coil and Φ is the interlinking magnetic flux. When the number of poles is 2P and the rotation speed of the rotor is N (r・p・m), the magnetic flux Φ changes sinusoidally, so the magnetic flux Φ is Φ=Φ _O sin2π・P・N・t/60 …( 2) However, t: Time (seconds) Φ _O : Maximum value of magnetic flux Φ, which can be expressed as a constant. Now, by substituting the above equation (2) into (1), e=-nΦ _O d sin2π・P・N・t/60/dt =−nΦ _O・2π・P・N/60・Cos2π・P・N・t/60...(3) where the frequency and angular frequency ω are =
If we set PN/60・ω=2π, the above equation (3) becomes e=−nΦ _O 〓・cosωt …(4), and this equation (4) expresses the AC waveform of the angular frequency ω (frequency), and its The peak value is proportional to (ω) (the - sign indicates that the phase is shifted). have such characteristics
Looking at the case where a load resistor RL is connected to ACTG1, the equivalent circuit is as shown in Figure 3.
ACTG to the generated voltage (AC effective value) E of ACTG1
It can be shown as a circuit in which a self-inductance Lo of 1 and a load resistance RL are inserted in series. Note that the coil resistance of ACTG1 is smaller than the load resistance R _L , so it will be ignored.

Here, if the above equation (4) is expressed as an AC effective value and the proportionality constant is K, then the generated voltage E of ACTG1 is
It is shown as E=K・ω (5). Also, the reactance Xo of the self-inductance Lo is expressed as Xo=ω・Lo (6). Therefore, the output current I is Then, finding the voltage V _L across the load resistance R _L , we get: becomes. Now, if R _L is larger than ω Lo (R _L > ω Lo), equation (8) is It can be shown that if the load resistance R _L is large,
The output voltage of ACTG1 is proportional to ω, that is, the rotation speed. This characteristic is shown in FIG. 4 using the load resistance R _L parameter. Therefore, it is common practice to select a large value for the load resistance _RL .

From this relationship between ACTG and load resistance, the second
The operation of the device constructed as shown in the figure will be explained with reference to FIG. Note that the resistance value of variable resistor VR ₃ is R _V
Let us explain by assuming that the coil resistance value of relay X ₃ is R _X. When the motor (not shown) starts and the rotational speed increases, the output voltage of ACTG1 starts to rise, but since its value is low, the constant voltage diode _ZD4 is non-conductive, so the transistor _Q1 is turned off. Therefore, the load of ACTG1 is a variable resistance.
VR becomes only ₃ , and the output voltage of ACTG1 increases according to the curve shown by the dashed line. Next, when the rotation speed increases to the detection set rotation speed N _p ,
Constant voltage diode ZD ₄ becomes conductive and transistor Q ₁ turns on. This ON causes relay X ₃ to be energized and its normally closed contact X _3b to open, this contact signal is sent as a detection signal to a protection device (not shown), and the object to be cooled, such as a computer, is powered on. However, by turning on the transistor _Q1 , the load on ACTG1 becomes variable resistor _VR3 and coil resistance of relay _X3 in parallel, that is, R _L = R _V R _X , and the output voltage is expressed by the curve R _L = It follows R _{V R} Therefore, the transistor Q ₁ turns off, and the output voltage rises again according to the curve R _L = R _V and turns on again. Due to this turning on, the output voltage decreases because it follows the curve R _L = R _V RX. The same operation as when the transistor _Q1 is turned off is repeated as shown by the _arrow until the output voltage shown by the curve R _L = _{R V R} This results in unstable operation, resulting in the disadvantage that accurate detection corresponding to the motor rotation speed cannot be performed between the rotation speed N ₀ and _{N 1} . The same can be said because the same operation occurs even when the rotational speed decreases (N ₁ →N ₀ ). To solve this problem, it is possible to increase the size of the ACTG to lower the output impedance, or add a bleeder resistance that is smaller than the relay, but this would add an extra load to the motor, and the ACTG However, the problem is that the device becomes large and expensive.

The present invention was developed in view of the above points, and its purpose is to provide a device that can be constructed at a low cost, is easy to adjust, operates accurately, and improves reliability. Our goal is to provide the following.

Embodiments of the present invention will be described below with reference to FIGS. 6 and 7. Incidentally, since only a part of the configuration of the control circuit 2 shown in FIG. 2 is different, parts corresponding to those in FIG. 2 will be given the same reference numerals and redundant explanation will be avoided. In Figure 6, 3 is ACTG1
This is a control circuit connected to the output terminal of the The differences from the control circuit 2 shown in FIG. 2 will be explained as follows.
Connect the base of transistor Q ₂ through the base resistor R ₁ to the collector of transistor Q 1, and this transistor _{Q 2 connects} its collector to the above relay X ₃
The collector resistance R has the same value as the coil resistance _{of 2}
Connect the emitter to the (+) side output terminal _{of rectifier DB 3 through} the (+) side output terminal of rectifier DB ₃ , and connect the normally _closed contact The contact signal is sent out as a detection signal through the contact signal.

Next, its operation will be explained with reference to FIG.
As mentioned above, the resistance value of variable resistor VR ₃ is R _V ,
The coil resistance value of relay X ₃ will be explained as R _X. When the motor (not shown) starts and the rotation speed increases, the output voltage of ACTG1 starts to rise, but since its value is low, the voltage regulator diode is used as described above.
Since ZD ₄ is non-conducting, transistor Q ₁ is off. As a result of this turning off, the base potential of the transistor _Q2 rises, and the transistor Q2 is turned on. By turning on, the load of ACTG1 becomes variable resistor VR ₃ and collector resistor R ₂ in parallel, that is, R _L = R _V R ₂ , and ACTG
1's output voltage rises according to the curve R _L =R _V R ₂ in FIG. Next, when the rotation speed increases and reaches the detection set rotation speed N ₀ , the constant voltage diode ZD ₄ becomes conductive and the transistor Q ₁ turns on. As a result of this turning on, transistor _Q2 is turned off as its base potential decreases, and relay _X3 is energized.
The load of ACTG1 is variable resistor VR ₃ and relay X ₃ coil resistance R _X in parallel, that is, R _L = R _V R _X ,
The output voltage of ACTG1 increases according to the curve R _L =R _V R _X in FIG. At this time, the normally closed contact X _3b is opened by the excitation of the relay X ₃ , and this contact signal is sent as a detection signal to a protection device (not shown), and the power of a load such as a computer to be cooled is turned on. Then, the rotation speed increases further and the output voltage of ACTG1 becomes R _L = R _V as shown in Figure 7.
It rises according _to the curve _{of R}
Even if the output voltage of relay X ₃ increases, the voltage applied to relay X 3 is suppressed to the Zener voltage VZ ₃ ,
Overexcitation of X ₃ is prevented.

The rotation speed of the motor (not shown) decreases and ACTG1
When the output voltage drops below the Zener voltage VZ ₃ of the voltage _regulator diode ZD ₃ , the output voltage drops according to the curve R _L = R _{V R} When reached, the constant voltage diode
ZD ₄ becomes non-conductive, transistor Q ₁ turns off, relay X ₃ becomes de-energized, its normally closed contact X _3b returns, or closes, and this contact signal is sent as a detection signal to a protection device (not shown). The protection device shuts off the power of a load to be cooled, such as a computer, in a timely manner. At this time, transistor Q ₂ is turned on by turning off transistor Q ₁ , and the load of ACTG1 is variable resistor VR _3.
and the collector resistor R ₂ are connected in parallel (R _L = R _V R ₂ ), and the output voltage of ACTG1 is R _L = R _V R ₂ in Figure 7.
descends according to the curve of In _{this way , the} coil resistance value R _{X of} relay By being selected,
The load on ACTG1 is constant, and as shown in Figure 7, the output voltage characteristics are constant regardless of whether transistor _Q1 is on or off. A detection signal is obtained. Also, transistor
Constant voltage diode ZD ₄ serves as a detection for Q ₁
If the change in the Zener voltage VZ ₄ due to temperature changes is small (for example, the output voltage V ₀ corresponding to the detection setting rotation speed N ₀ and the voltage division ratio β of the variable resistor VR ₃ is V ₀ · β ≒ 5V ), the error in the detected rotational speed due to temperature changes can be made extremely small. Furthermore, the Zener voltage VZ ₃ of the constant voltage diode ZD ₃ suppresses the output voltage of ACTG ₁ to prevent overexcitation of the _relay It is assumed that a large current flows through (7) above.
When ω→∞ according to the formula, the output current I of ACTG1 is Therefore, there is no need to use a constant voltage diode that has a constant value and has a large current withstand capacity.
The load on the motor is also reduced.

Note that the present invention is not limited to the embodiments, and without changing the gist, for example, a resistor may be inserted in series with the constant voltage diode ZD ₄ , or a resistor may be inserted in parallel with the base and emitter of transistors Q ₁ and Q ₂ . or a capacitor, adding a flywheel diode or surge absorber to the relay coil, replacing transistors Q ₁ and Q ₂ with other semiconductor elements (e.g. field effect transistors), etc.
It goes without saying that the relay contact signal may be derived from a normally open contact, or the relay may be replaced with a semiconductor relay such as a photocoupler.

According to the present invention, since the control circuit is made to respond to the output voltage of the AC tachometer generator, there is no need to provide a separate control power supply circuit, and the configuration can be simplified. A variable resistor and a first transistor connected to a relay are connected in parallel to the output terminal where the output voltage is rectified and smoothed, and the slider of the variable resistor is connected to the base of the first transistor via a detection voltage regulator diode. The voltage dividing ratio of the variable resistor is set so that when the output voltage of the AC tachogenerator corresponds to the detected rotational speed of the motor, the detection constant voltage diode is made conductive to turn on the first transistor. Therefore, the operating point of the relay can be stabilized, and the second transistor, which turns on and off complementary to the first transistor, can be connected via a collector resistor having the same value as the coil resistance of the relay. Since the load of the AC tachometer generator is connected to the rectified and smoothed output end to be constant regardless of whether the first transistor is on or off, the output voltage characteristics of the AC tachometer generator can be kept constant, and the motor rotation The detection signal can be accurately detected according to the number of rotations, and the sensitivity can be easily adjusted by simply adjusting the voltage division ratio of the variable resistor according to the detection rotation speed. Since it is possible to select the
It has significant practical effects, such as being able to perform accurate detection without temperature and aging changes, and making the device simpler and cheaper.

[Brief explanation of the drawing]

Figure 1 is a block diagram illustrating a conventional device using an AC tachometer generator. Figure A shows one in which a control power source is provided separately, and Figure B shows one in which the output of the AC tachometer generator is directly used as a control power source. It is something. Fig. 2 is a block diagram showing another conventional embodiment, Fig. 3 is an equivalent circuit diagram explaining the load characteristics of an AC tachometer generator, and Fig. 4 shows the load characteristics of Fig. 3 using load resistance parameters. 5 is an output voltage characteristic diagram explained with reference to the operation of FIG. 2, FIG. 6 is a block diagram showing an embodiment of the present invention, and FIG. 7 is an output voltage characteristic diagram of FIG. 6. 1: AC tachometer generator, 2, 3: Control circuit, X ₃ : Relay, ZD ₃ : Constant voltage diode for relay overexcitation prevention, VR ₃ : Variable resistance, ZD ₄ : Constant voltage diode for detection, Q ₁ : First transistor,
Q ₂ : Second transistor, R ₂ : Collector resistance,
DB ₃ : Rectifier, C ₃ : Smoothing capacitor.

Claims (1)

[Scope of utility model registration request] A constant voltage diode for preventing relay overexcitation, a smoothing capacitor, and a variable resistor are inserted in parallel between the output terminal of an AC tachometer generator connected to the rotor of the motor and the output terminal of a rectifier connected to the output terminal of an AC tachometer generator connected for driving. The base of the first transistor is connected to the actuator via a constant voltage diode for detection,
The collector and emitter of this first transistor are inserted between the output terminals of the rectifier via a relay, and the base of the second transistor whose emitter is commonly connected to the emitter of the first transistor is connected to a base resistor. and the collector of this second transistor is commonly connected to the relay via a collector resistor having the same value as the coil resistance of the relay to keep the load of the AC tachogenerator constant. 1. A motor abnormality detection device, characterized in that the motor abnormality detection device detects a decrease in the rotational speed of the motor.