JPS6128000B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control system for a DC motor, and provides a control system that can improve control performance without making the configuration of conventional control systems complicated and expensive.

As is well known, the rotational speed of a DC motor decreases as the load applied to its rotating shaft increases.
It has a so-called drooping characteristic, and when this is used to control the rotation of magnetic recording and reproducing equipment (VTR), etc.
A speed control system was required to keep the rotation speed constant, and was used together with a phase control system that synchronized the phase with an external reference signal, forming the servo system of the VTR. That is, when a DC motor is used in this type of device, there is a major difference from when an AC motor is used in that a speed control system is required.

Conventional speed control methods for DC motors include a method known as an electronic governor that detects the back electromotive force induced in the armature to control the speed, and a method that uses the voltage generated by a generator directly connected to the rotating shaft to control the speed. Methods There were methods that controlled the speed by detecting pulse signals optically, magnetically, or electrostatically. Of these, the generator direct connection method is expensive and is not often used.

The back electromotive voltage detection method cannot maintain the balance of the bridge circuit due to changes in the brush resistance, and in addition to the back electromotive force, a voltage proportional to the armature current is generated, causing an error, so it is not possible to control the speed with high precision. First, although the structure is relatively simple and appears to be inexpensive at first glance, it has the drawback that it requires a highly stable reference voltage source and is expensive.

Two methods of detecting pulse signals to control speed are the so-called FG method, which uses a dedicated frequency generator to detect the rotational speed, and the commonly known PG method, which also doubles as a rotary phase pulse generator used in the phase control system. There is a method called method. Generally, in the FG method, the sampling frequency (speed comparison frequency) is n times the rotation frequency oHz, that is, the speed is controlled by detecting the rotation multiple times per rotation, whereas in the PG method, the speed comparison frequency is n times the rotation frequency oHz. oHz or lower in many cases, the former requires precision machining of the frequency generator and requires a dedicated detector, making it expensive, while the latter can also be used as a detector for phase control. Although it does not require high machining accuracy, it has the drawback of poor control performance due to the low sampling frequency.

The present invention provides an inexpensive control method that has a relatively simple configuration and can improve control performance in order to eliminate the drawbacks of the conventional method. That is, the present invention adds a speed control system based on back electromotive force detection to the speed control system based on the PG method, and provides a novel speed control system configured with a dual speed control system that improves control performance without mutually compensating for the shortcomings of both systems. This provides a control method for a DC motor.

Speed control methods based on the PG method can be classified according to the configuration of the rotational phase pulse detector, and are classified into 1 and 1.
one that detects one pulse signal per rotation;
2. It can be roughly divided into those that detect two pulse signals per rotation.

FIG. 1 shows an example of a waveform diagram of a rotation pulse signal, and A1
corresponds to 1, A2 to A7 correspond to 2,
A8 obtains a signal of one cycle per rotation. In case of 2, it is necessary to distinguish between two pulses,
Consisting of two markers and one detection head, 2a A device that detects two pulses with different polarities A2, A
3, 2b A device that detects two pulses with different amplitudes A4, 2c A device that detects two pulses with different intervals A5, consisting of one marker and two detection heads, 2d Two pulses There is a type A6 that detects each one separately, and there is also a type A6 that detects each one separately, and there is also
There is a type A7, which consists of two markers attached at 180° positions and one detection head, and detects two 2e pulses with substantially equal intervals. Also, A8
is equivalent to one rotation detection in the FG method.

As is clear from the above examples, there are various configurations of rotational phase pulse detectors in the PG method, and therefore the circuit configurations at the front stage that amplify and separate pulse signals are somewhat different. However, the configuration of the signal processing circuit for obtaining the speed error signal at the subsequent stage is common. That is, a speed reference circuit that creates a speed reference signal with a constant time width that is synchronized with one of the two pulses separated in the above example 2, and a slope signal that is synchronized with the trailing edge of the output of the speed reference circuit A. A first waveform conversion circuit that creates a sampling pulse that is synchronized with the other separated pulse, and a first waveform conversion circuit that creates a slope signal that is synchronized with the other separated pulse. A conversion circuit, a second waveform conversion circuit that creates a sampling pulse synchronized with the trailing edge of the speed reference circuit output, and a speed comparison that samples and holds the first waveform conversion circuit output with the second waveform conversion circuit output. The speed comparison circuit amplifies the output of the speed comparison circuit and controls the drive of the DC motor to form a speed control system. The difference between A and B is whether a slope signal or a sampling pulse is created using the speed reference circuit output, and since the polarity is opposite, in this case, of course, the polarity of the slope signal or the driving amplifier Select the polarity and configure it to become a negative feedback loop. Next, in the case of 1, since there is only one pulse, it can be realized by combining two pulses in the case of 2. However, the constant time width of the speed reference circuit needs to be approximately equal to the rotation period.

The above is a general explanation of the speed control method using the PG method.
There is JP-A-48-7218, an example of using A2 is JP-A-49-57822, and an example of using A5 is JP-A-51.
-104520, as an example of using A6 is JP-A-51-
124406, an example of using A8 is JP-A-51-104519
However, the present invention mutually compensates for the decrease in control performance due to the low sampling frequency of the PG method by adding a back electromotive voltage detection method speed control system.
This provides a new control system with improved control performance, and is applicable to any of the PG speed control systems using rotation pulse signals as illustrated in FIG.

FIG. 2 shows an example of the configuration of the control system of the present invention to which A2 in FIG. 1 is applied, and FIG. 3 shows an example of a waveform diagram.

In Figures 2 and 3, 1 is a DC motor, 2
is a rotating disk directly connected to the rotating shaft of the DC motor 1, markers 3 and 4 are fixed to the disk 2 with opposite polarities, and a detection head is mounted opposite the rotating surface of the markers 3 and 4. 5 is provided. The detection head 5
The rotation pulse signal S1 is obtained by the separation amplification circuit 6.
Separates the positive pulse and negative pulse at output S2,
Obtain S3. The next speed reference circuit 7 is triggered by one output S2 of the separation amplifier circuit 6 to generate a speed reference signal S4 having a constant time width τ _S. The output S4 of the speed reference circuit 7 is inputted to the next first waveform conversion circuit 8 to create a slope signal S5 with a negative slope synchronized with the trailing edge. On the other hand, the other output S3 of the separation amplifier circuit 6
is input to the second waveform conversion circuit 9 to create a sampling pulse S6. A speed comparison circuit 10 samples the slope portion of the output S5 of the first waveform conversion circuit 8 using the output S6 of the second waveform conversion circuit and holds it to obtain a speed error signal. 12 is a reference voltage input terminal; 13, 14, and 15 are bridge resistors that constitute a bridge circuit together with the armature resistance of the DC motor 1; 16 is a power operational amplifier;
12 to 16 constitute a back electromotive voltage detection type speed control system. The speed error signal is inverted and amplified by an amplifier 11, and is used as a reference voltage source for a reference voltage input terminal 12.

On the other hand, for the phase control system, the external reference signal input terminal 17
The external reference signal S7 inputted into the circuit is passed through a third waveform conversion circuit 18 and converted into a positive slope signal S8, and one output S2 of the separation amplifier circuit 6 is passed through a fourth waveform conversion circuit 19 and converted into a sampling pulse S9. The phase comparison circuit 20 converts the slope portion of the third waveform conversion circuit output S8 into the fourth waveform conversion circuit output S.
9 and hold to obtain a phase error signal. Phase control can be performed by adding the phase error signal to the speed reference circuit 7 or the speed error signal through the gain adjuster 21 to perform speed modulation.

In the above configuration, the operation of the PG speed control system is such that when the rotation speed of the DC motor 1 increases (decreases), the frequency of the rotation pulse signal S1 increases (decreases), and the interval between the positive pulse and the negative pulse becomes short. Since the sampling pulse S6 that samples the slope part of the slope signal S5 created from the speed reference signal S4 samples a high (low) voltage, the speed error signal obtained becomes high (low) and is inverted amplified. The output voltage of the amplifier circuit 11 becomes lower (higher). As a result, a command to lower (increase) the rotational speed can be given to the DC motor 1, and the speed can be controlled to reach the reference speed. However, the rotational speed becomes stable at the slope sampling position _P1 of the slope signal S5, which coincides with the reference speed. In addition, in the back electromotive voltage detection method speed control system, the armature resistance of the DC motor 1 is Ra, the bridge resistance 13, 1
4 and 15 as R ₁ , R ₂ , and R ₃ respectively, R ₁ /R _a =R ₂
/R ₃ , the output is determined so that the potential difference between the positive-phase input and the negative-phase input of the power operational amplifier 16 becomes O [V], so the input voltage of the reference voltage input terminal 12
Since Ei [V] and the back electromotive force Ea [V] of the DC motor 1 can be controlled to match, the rotation speed Ω [rad/sec] is as follows: Ω=KΩ・Ea (1) However, , KΩ is the back electromotive force constant [V·sec/rad].

It is constant from equation (1). That is, the reference voltage Ei
If [V] is stable, the rotation speed can be kept constant.

Furthermore, in the phase control system, the slope portion of the slope signal S8 created using the external reference signal S7 is converted into a rotation pulse signal S.
Sampling is performed using the sampling pulse S9 created from 1, and speed modulation is applied based on the held phase error signal. When the rotational phase advances (lags), a low (high) voltage is generated and control is made to match the reference phase. are doing. However, in a state in which phase synchronization is established, approximately one point _P2 of the slope portion of the slope signal S8 is sampled and stabilized.

Next, in order to further clarify the present invention, the present invention will be explained using block diagrams.

FIG. 4 is a block diagram of the DC motor 1,
FIG. 5 is an example of a block diagram of the control system of the present invention.

In Figure 4, Eo _(s) is the input voltage [V], Q _(s)
is load torque [gr ^- cm], Ra is armature resistance Ω, K
τ is a torque constant [A/gr ^- cm], J is a moment of inertia [gr ^- cm·sec ² /rad], S is a Laplace transform operator, and Ωo _(s) is a rotational speed [rad/sec]. However, armature inductance La [H], viscous resistance D
[grem·sec/rad] is omitted because its value is small compared to Ra and J. However, the general formula for Ωo _(s) is However, Tm=Ra・Kτ・J/KΩ [sec].

It is expressed as

In Figure 5, Ao is the gain of the power operational amplifier, Ωi _(s) is the reference speed [rad/sec], Kd is the speed comparison gain [V・sec/rad], Gs1 _(s) is the transfer function of the speed control system sampler, H _1(s) is the transfer function of the holder, _K1 is the gain of the inverting amplifier circuit, θo _(s) is the rotational phase [rad], θi _(s) is the reference phase [rad], and Kc is the phase comparison gain [V/ rad], Gs2 _(s) is the transfer function of the phase control system sampler, H _{2 (s)} is the transfer function of the same holder, and Kv is the velocity modulation gain [rad/sec·V].

First, Ω due to only the back electromotive force detection method and speed control system.
The general formula for o _(s) is and 1-R ₃ /R ₂ /R _a /R ₁ >0, that is, R
The system is stable if _a /R ₁ >R ₃ /R ₂ , but if 1-R ₃ /R ₂ /R _a /R ₁ <0
That is, if R _a /R ₁ <R ₃ /R ₂ , the system becomes unstable. 1
-R ₃ /R ₂ /R _a /R ₁ = 0, that is, if R _a /R ₁ = R ₃ /R ₂ , it is a critical state, and at this time, the influence of the load torque Q _(s) can be completely eliminated.

Next, when adding the PG speed control system, Ωo _(s)
The general formula is: Ωo _(s) = G _1(s)・We _(s)・Ωi _(s) +Wq
_(s)・Q _(s) /1+G _1(s)・We _(s) (4) However, G _1(s) = Kd・Gs _1(s)・H _1(s)・K ₁ ,
From equation (3), We _(s) and Wq _(s) are We _(s) = Ωo _(s) /Ei
_(s) , Wq _(s) = Ωo _(s) /Q _(s) .

The influence of the load torque Q _(s) is further reduced, and the rotational speed Ωo _(s) is controlled to match the reference speed.

Furthermore, when a phase control system is added, θ _p(s) , Ωo
The general formula for _(s) is θ _p(s) = G _2(s)・W _1(s)・θ _i(s) +W ₁ ′ _(s)
・Q _(s) /1+G _2(s)・W _1(s) /S×1/S
(5) However, G _2(s) = K _c・G _s2(s)・H _2(s)・K _v , W _1
(s) and W ₁ ′ _(s) are obtained from equation (4) as W _1(s) =Ωo _(s) /Ω
i _(s) , W ₁ ' _(s) = Ωo _(s) /Q _(s) .

Ωo _(s) = S·θ _p(s) (6), and the influence of Q _(s) is further reduced.

As is clear from the above explanation, the PG method uses sample value control, and can only perform one speed comparison per rotation, and has a control effect only in the frequency range below 1/2 of the speed comparison frequency. The electromotive voltage detection method is continuous value control, and has a control effect continuously over one rotation and over the entire frequency range. In addition, the reference voltage of the back electromotive voltage detection method is
Stable supply is possible using the PG method speed error signal. In this way, the drawbacks of the PG method are not compensated for by the back electromotive force detection method, and the drawbacks of the back electromotive voltage detection method are compensated for by the PG method.

Note that there is no significant difference in the number of parts between when the back electromotive force detection method speed control is used in the PG method speed control system and when it is not used, and the features of the PG method can be utilized in terms of cost. Further, the power operational amplifier 16 can be replaced with a low-power operational amplifier equipped with a current booster and can be constructed at low cost.
Furthermore, the present invention is not limited to the PG method;
Needless to say, this method can also be applied to the FG method.

Furthermore, the present invention is not limited to the control method of a VTR, but can also be applied to other electronic devices (for example, record players, tape recorders, video discs, etc.).
Needless to say, it is applicable to

As is clear from the above explanation, in the control system using the DC motor of the present invention, in addition to the conventional PG or FG speed control system and phase control system, a back electromotive force detection system is also used. By adding a speed control system, it is configured with a double speed control system.
The control performance can be significantly improved without compensating for the shortcomings of the PG method and the back electromotive voltage detection method. Further, there is a small difference in the number of parts between the speed control circuit using the back electromotive force detection method and the conventional drive amplifier circuit, and the speed control circuit has features such as being able to be constructed at low cost.

[Brief explanation of the drawing]

Fig. 1 is a waveform diagram of a rotation pulse signal, Fig. 2 is a block diagram showing an embodiment of the control method of the present invention, Fig. 3 is a waveform diagram of each part of Fig. 2, and Fig. 4 is a block diagram of a DC motor. , FIG. 5 is a block diagram of the control system of the present invention. DESCRIPTION OF SYMBOLS 1... DC motor, 2... Rotating disk, 5... Detection head, 6... Separation amplifier, 7... Speed reference circuit, 8, 9, 18, 19... Waveform conversion circuit, 10
... Speed comparison circuit, 11 ... Amplifier, 12 ... Reference voltage input terminal, 16 ... Operational amplifier, 17 ...
External reference signal input terminal, 20...phase comparison circuit.

Claims (1)

[Claims] 1. A DC motor having one end connected to a common ground and the other end connected to the negative phase input terminal of the operational amplifier, and a first resistor having one end connected to the output terminal of the operational amplifier and the other end connected to the negative phase input terminal. , one end is connected to the output end,
a second resistor whose other end is connected to the positive phase input terminal of the operational amplifier; and a third resistor whose one end is connected to the reference voltage input terminal and the other end is connected to the positive phase input terminal of the operational amplifier. an electromotive voltage detection method speed control system; and a rotation detection method speed control system that detects at least one rotation pulse signal per rotation of the DC motor, obtains a speed error signal from the rotation pulse signal, and inputs it to the reference voltage input terminal. and a phase control system that obtains a phase error signal by comparing the phases of the rotation pulse signal and an external reference signal, and speed-modulates the rotation detection type speed control system based on the phase error signal. Characteristic control method for DC motors.