JPS639277Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a device in which the speed of a DC motor is controlled using a three-terminal DC motor speed control IC.

A DC motor with a constant magnetic field can be equivalently expressed as an internal resistance and a back electromotive force induced by the rotation of the DC motor connected in series. Therefore, if the DC motor is driven by a constant voltage source having an internal resistance (negative internal resistance) whose absolute value is equal to the internal resistance of the DC motor and takes a negative value, the DC motor will always be The back electromotive force is driven at a rotational speed equal to that of the constant voltage source, and a constant rotational speed that is independent of changes in load or the like can be obtained.

Although this principle is conventionally known, few power supplies having internal resistance as described above have been put into practical use because their circuit configurations are complicated and expensive.

However, with the recent remarkable progress in IC technology, it has become possible to put the above power supply into practical use as an IC for controlling the speed of a DC motor.

Conventionally, many of this type of DC motor speed control ICs have used inexpensive three-terminal packages for transistors, and have been combined with a few external passive circuit elements to form a DC motor speed control device.

Fig. 1 shows the configuration of a conventional DC motor speed control device of this type, in which 1 is a DC motor whose speed is to be controlled, 2 is a speed control IC having terminal pins, 3 and 4 are resistors, and 5 is a speed control IC having terminal pins. is a DC power supply.
In addition, Ia, I _S , _IT , I ₂ , I _K , Ir are the currents flowing through the respective arrow positions, Ra is the equivalent internal resistance value of the DC motor 1, Ea is its back electromotive force, Vref is the reference voltage, V _C represents the power supply voltage.

In the above-mentioned IC, the current distribution circuit is configured so that a current of 1/K of I ₂ always flows through I _K (here, K is the current distribution ratio). 4 are R _T and R _S respectively, the voltage V _O applied to the DC motor 1 is given by the following equation.

V _O =Vref{1+R _T /R _S (1+1/K)} +R _T Ir+R _T /KIa (1) Now, let V _O =V+R _T /KIa (2). (Here, V=Vref{1+R _T /R _S (1+ 1/K)}+R _T Ir.) Here, the first and second terms on the right side of equation (1) are the resistance values.
If R _S and _RT are given, they take constant values regardless of changes in the power supply voltage V _C and load torque (i.e., armature current Ia), but the third value on the right side of equation (1)
The term changes in proportion to the armature current Ia. and,
If we consider the first term on the right side of equation (2) as a voltage source, the resistance (-
R _T /K) is equivalent to being connected in series with this voltage source.

On the other hand, considering the DC motor 1, if the terminal voltage of the DC motor 1 is Vm, it is given by Vm = Ea + RaIa (3), so in Fig. 1, V _O =Vm (4), and V + R _T /KIa. The relationship =Ea+RaIa (5) is obtained. Therefore, the back electromotive force Ea of the DC motor 1 is expressed as Ea=V+( _RT /K-Ra)Ia (6).

From this, if we adjust the resistance R _T and choose R _T = KRa (7), Ea = V, and the DC motor 1 is rotated at such a rotation speed that its back electromotive force Ea is always a constant voltage V. It will be driven. That is, the DC motor 1 is not affected by load torque and maintains a constant rotational speed.

In other words, the rotational speed of the DC motor 1 is N,
When the power generation constant of the DC motor 1 is Ka, Ea=KaN (8) and N=1/Ka[Vref{1+R _T /R _S (1+1/K)} +Ia (R _T /K-Ra)+R _T Ir] (9), and if the resistance value R _T is selected as R _T =K・Ra (10) corresponding to the internal resistance Ra of the DC motor 1, then N=1/Ka[Vref{1+R _T /R _S (1+1/K)} +R _T・Ir】 (11)

In other words, the DC motor 1 is not affected by load torque, etc., and is driven at a constant rotational speed expressed by equation (11).

Further, if the torque of the DC motor 1 is T _M and the torque constant of the DC motor 1 is Kt, then T _M = Kt・Ia (12), and N=1/Ka[Vref{1+R _T /R _S (1+1 /K)} +T _M /Kt(R _T /K-Ra)+R _T・Ir] (13) It is given by:

This is the operating principle of the DC motor speed control device shown in FIG.

By the way, as mentioned above, in the DC motor speed control device, it is conventional to use fixed carbon film resistors, etc., whose resistance value changes little with temperature changes, for the resistors 3 and 4 as external passive circuit elements of the IC 2. It was the ordinary way.

Now, if there is a temperature change around the speed control device including the DC motor 1, how will the rotational speed change with respect to the load torque change (the change in rotational speed per unit load torque is μ)? I decided to think about what would happen.

FIG. 2 shows the characteristics of the conventional example, in which the change in rotational speed with respect to the change in load torque is smaller on the low temperature side and larger on the high temperature side compared to room temperature.

When this increases, positive feedback is applied to the control circuit on the low temperature side, making the control system unstable, causing oscillation, uneven rotation, and other negative effects. Furthermore, on the high temperature side, the rotational speed changes significantly in response to changes in load torque, which is undesirable.

This is because the armature winding of DC motor 1 is usually a copper winding, and the temperature coefficient of its resistance value is 0.4%/℃, whereas resistor 3 has a carbon film fixed resistor (temperature coefficient) with a small temperature coefficient. This is because a coefficient of about -0.05%/°C) is used.

In order to solve the above-mentioned problems, the present invention uses a resistance element having a positive temperature coefficient as the resistor 3, such as a metal film resistor whose temperature coefficient can be arbitrarily selected. Changes in the resistance value of the child winding are canceled out so that changes in rotational speed (load characteristics) in response to changes in load torque remain approximately constant even if the ambient temperature changes.

Figure 3 shows the characteristics of an embodiment of the present invention, in which a metal film resistor with a temperature coefficient of 0.36%/°C is used as the resistor 3, and the rate of change in the load characteristic μ with respect to temperature changes is almost zero. I can do it.

This will be explained in more detail below using mathematical formulas.

Changes in rotational speed with respect to changes in load torque, that is, load characteristics μ, can be calculated by partially differentiating Equation (13) with respect to torque T _M , and calculating μ=∂・μ／∂・T∂M=1/Ka・Kt (R _T / K-Ra) (
14) becomes.

Considering the temperature change of the load characteristic μ (T is the absolute temperature), Δμ/ΔT = (Δμ/ΔT) Ka + (Δμ/ΔT) K _T + (
Δμ/ΔT) Ra+(Δμ/ΔT)R _T +(Δμ/ΔT)K (15) Now, if R _T =KRa (16) then Δμ/ΔT=−Ra/Ka・Kt (1/RaΔRa/ΔT− 1/R _T ΔR _T /ΔT+1/KΔK
/ΔT) (17) Therefore, from equation (17), in order to make the temperature characteristic of the load characteristic μ zero, 1/RaΔRa/ΔT−1/R _T ΔR _T /ΔT+1/KΔK/ΔT
Must be =0(18). Here, the temperature characteristic of the current distribution ratio K in IC2 is configured to be very small (approximately 0.004%/°C) due to its operating principle.
It can almost be ignored.

Therefore, by making the temperature coefficient of the armature winding resistance Ra and the temperature coefficient of the resistance value R _T of the resistor 3 equal, temperature changes in the load characteristic μ can be almost eliminated.

However, in such a speed control device, since the resistance 3 changes as the ambient temperature changes, the influence of the temperature characteristics of the magnetic flux of the stator magnet of the DC motor 1 appears in fluctuations in the rotational speed. Therefore, it is conceivable to connect a diode in series with the resistor 3 to offset the temperature change of the resistor 3 to improve the temperature fluctuation of the rotation speed. Considering the temperature change of the stator magnetic flux, generally speaking, barium ferrite etc.
For F _XD magnets, it is 0.18%/℃, and the temperature change range is
If the temperature is 60°C, the magnetic flux will change by 10.8%. In order to reduce this change to zero, if varistor diodes are used as diodes, 10 or more varistor diodes are required.

By the way, when a diode is connected, the rotation speed N is calculated from equation (11) as N=1/Ka [Vref{1+R _T /R _S (1+1/K)} +R _T Ir+V _D ] (19) (Here, V _D is the terminal voltage of the diode). Therefore, in this type of speed control device, the lowest rotational speed that can be set is when R _S becomes infinite, and the lowest rotational speed Nmin is Nmin = 1/Ka (Vref + R _T Ir + V _D ) (20) becomes. Therefore, when the number of diodes increases,
V _D becomes large and the required rotation speed cannot be produced. Therefore, in order to improve temperature fluctuations in rotational speed, it is necessary to further perform temperature compensation.

Therefore, by using a resistance element having a positive temperature coefficient as the resistor 4, temperature fluctuations in the rotation speed can be made zero. FIG. 5 shows the characteristics of an embodiment of the present invention, in which a metal film resistor with a temperature coefficient of 0.36%/° C. is used as the resistor 3.

Hereinafter, an embodiment of the present invention will be explained with reference to FIG.
Elements having the same functions as those shown in FIG. 1 are designated by the same figure numbers, and their explanations will be omitted.

The resistor 5 shown in FIG. 4 is a carbon film resistor, and the resistor 6 is a resistance element having a positive temperature coefficient. The resistor 5 and the resistor 6 form the resistor 3 in FIG. The combined value of the resistors 5 and 6 performs temperature compensation for changes in rotational speed (load characteristics) with respect to changes in load torque. However, the resistance 5 may have an infinite value depending on the characteristics of the DC motor. Resistor 8 is a carbon film variable resistor, and resistor 9 is a resistance element having a positive temperature coefficient. The resistor 8 and the resistor 9 form the resistor 4 in FIG. A diode 7 and a resistor 9 perform temperature compensation for the rotational speed.

As described above, according to the present invention, with a simple configuration, it is possible to set the rotation speed down to low speeds, and it is also possible to compensate for fluctuations in load characteristics and rotation speed due to temperature changes, and it can be mass-produced at low cost. This is possible and has great practical effects.

[Brief explanation of the drawing]

Fig. 1 is an electrical circuit configuration diagram of a DC motor speed control device having a 3-terminal DC motor speed control IC, Fig. 2 is a characteristic diagram showing the temperature change of conventional load characteristics when using the same device, Fig. 3 is a characteristic diagram showing temperature changes in load characteristics according to the embodiment of the present invention, Fig. 4 is an electrical circuit diagram of the speed control device for a DC motor according to the embodiment of the present invention, and Fig. 5 is a diagram of the same device. FIG. 3 is a characteristic diagram showing changes in rotational speed with respect to changes in ambient temperature. 1...Small DC motor, 2...3-terminal DC motor speed control IC, 3, 4, 5, 8...Resistor, 6,
9... Resistance element having a positive temperature coefficient, 7... Diode.

Claims (1)

[Scope of utility model registration request] Equipped with a 3-terminal DC motor speed control IC configured to generate a reference voltage between two terminals, ground the remaining terminal, and so that a current proportional to the current flowing through the terminal always flows through the terminal, A DC motor is connected between the DC power supply positive terminal and the terminal, and a resistor 5 and a resistor 6 are connected between the power supply positive terminal and the terminal as external passive circuit elements of the IC.
A diode 7 is connected in series to the parallel connection circuit of the motor, and a resistor 8 and a resistor 9 are connected between the terminals to operate as a constant voltage source having a negative internal resistance whose absolute value is equal to the internal resistance of the DC motor. and controlling the rotational speed of the DC motor to be constant, characterized in that the resistor 6 and the resistor 9 are composed of resistance elements having a positive temperature coefficient. Motor speed control device.