JPS63316686A - Current limiting apparatus for dc motor - Google Patents

Abstract

PURPOSE:To prevent torque from being short, by arranging the detecting means of current and internal reference signal, and by comparing both the signals with each other to produce command signal for setting the current of a motor intermittently. CONSTITUTION:So far as a current limiting apparatus is concerned, motor currant Im set intermittently by the limiting of current flows to a current detecting resistor R1, and is turned into a chopping wave by integrating circuits R2, C1, and from a comparator CP1, the output 11 is generated as an artificial chopping wave. The output 11 is turned into the chopping wave at the input section 12 of a comparator CP2, and is compared with internal reference voltage Vref2, and the output 13 of the intermittent command signal of the motor current is generated. Then, by permitting the current limiting apparatus to have dependability on voltage, the function of the current limiting apparatus as a protective apparatus is not spoiled, and the lowering of step-out torque at the time of the lowering of line voltage can be suppressed to be reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a DC motor, and particularly to a DC motor with low loss and high quality.
Concerning constant speed control motors.

[Conventional technology]

As shown in Fig. 7a, Fig. 7b, and Fig. 7C, in the conventional case, when there is no current limiting device, the out-of-synchronization torque when controlling to a constant speed N1 is TD as shown in Fig. 7a.
If the starting current is suppressed to Ist2 by a current limiting device as shown in Fig. 7b, the out-of-synchronization torque becomes Tow.

The value becomes smaller than TDl. Furthermore, as shown in Figure 7C, when the power supply voltage decreases, the starting current also decreases to I.
sts and the out-of-synchronization torque is TD21.
Compared to Toz, the value becomes even smaller, and there are cases where the required torque is not achieved. Note that related technology of this type includes, for example, Japanese Utility Model Application No. 74293/1983.

[Problem that the invention seeks to solve]

Although this current limiting device originally aims to limit the starting current, its action reduces the motor's original maximum torque during servo (hereinafter referred to as out-of-synchronization torque).

As a solution to this problem, the torque constant of the motor can be increased by increasing the number of turns in the winding, increasing the thickness of the core, increasing the amount of magnetic flux of the magnet, etc.
It is conceivable to obtain a larger torque with the same current, but if the motor is already up to the limit of the size limit and these methods are implemented, and if this problem occurs, it is necessary to do something with the current limiting device. You will be asked to take action.

However, by increasing the starting current I sts to I st8' as shown in Fig. 7d without making the current limiting device voltage dependent, the out-of-synchronization torque TD8 can be reduced to
If an attempt is made to increase it to 3', the starting current I sta when the power supply voltage rises will also increase to 15t4', increasing the load on the motor's driving elements, which may lead to breakdown, etc. There is a risk that the current limiting device will no longer function as a current limiting device.

By making the current limiting device voltage dependent when the power supply voltage changes, the present invention minimizes the drop in out-of-synchronization torque when the power supply voltage drops, without impairing the function of the current limiting device as a protection device. ) The purpose is to reduce

[Means for solving problems]

The above object is achieved by making the comparison reference voltage, which is a component of the current limiting device, which has conventionally been a constant value, depend on the power supply voltage.

[Effect]

The current limiting device includes a current detecting means and an internal reference signal, and by comparing the output of the current detecting means and the above-mentioned internal reference signal, generates a command signal to intermittent the motor current, and determines the current value. suppress.

Here, by making the internal reference signal linked to the power supply voltage, when the power supply voltage decreases, the motor current restriction is relaxed, and when the power supply voltage increases, the motor current restriction is strengthened. , it is possible to prevent torque shortage due to motor current limitation, and to also serve as a current limiting device as a protection device.

〔Example〕

An embodiment of the present invention will be described below.

FIG. 1 shows an example of a current limiting device.
Each of the 13 operating waveforms corresponds to 9 to 13 in FIG. That is, the motor current is intermittent due to current limitation.1. teeth,
Flowing into the current detection resistor R1, the voltage waveform of 9 becomes similar to (■), and becomes a triangular wave at the input section 10 of the CPI due to the integrating circuit composed of R2 and 01, and the internal reference voltage V
It is compared with rezl, and the CPI output 11 becomes a pseudo triangular wave. 11 becomes a triangular wave at the input section 12 of the comparator CP2. Note that R3 is a limiting resistance for the discharge current of C2, and is sufficiently smaller than R4. triangle wave 1
2 is the internal reference voltage Vrei2 by the comparator CP2.
The output 13 outputs an intermittent motor current command signal.

Note that here, R5 is a pull-up resistor because the output of the comparator is generally of an open collector type.

In FIG. 1, R1-R5 are resistors, C1 and C2 are capacitors, and vCC is a power supply.

An embodiment of the method of intermittent motor current using the motor current intermittent command signal No. 13 is shown in FIGS. 3 and 4.

Figure 3 shows the case of a DC brushed motor, where 13 is H.
At i g h level, TRI is ON.

When TR2 is turned OFF and TR3 is turned OFF, the motor current 1 and 2 are cut off, and when 13 is at a low level, the reverse of the above occurs.

Also, Fig. 4 shows the case of a three-phase full-wave DC brushless motor, and the current intermittent command 13 causes TR13°TR14,T
Turn R15 ON and OFF, transistors TR7 and TR
8. By intermittent base current of TR9, motor current 1. intermittent.

Although the three-phase aftereffect method is taken as an example here, it goes without saying that it is also applicable to other drive methods such as a two-phase aftereffect method. r
It can also be carried out by a combination of a circuit in which the logic level of the current intermittent command 13 is reversed by replacing the e Needless to say, it is possible.

By the way, in order to increase the starting current value and increase the out-of-synchronization torque, it is sufficient to increase the voltage value of Vrefl or decrease the voltage value of vref2 in FIG. 1. To make this respond to changes in power supply voltage,
A configuration as shown in FIGS. 5 and 6 may be adopted.

Figure 5 shows how the power supply voltage E is divided by R20 and R21, and the output of the inverting amplifier, which is composed mainly of the operational amplifier OPI, is set to V.
, ezl, when the power supply voltage decreases, Vre
This configuration increases the voltage value of il.

Figure 6 shows that by setting the voltage obtained by dividing the power supply voltage E by R24 and R25 as V, ez2, the voltage V
This is a configuration that lowers re,2.

By combining Figures 1 and 5, or Figures 1 and 6, the starting current value changes from I sia to I sta' as shown in Figure 8a when the power supply voltage drops, and the out-of-synchronization torque As shown in Figure 8b, from TDll to T o
a' It is possible to increase the current limiter compared to the case where a current limiter having no voltage dependence is used. Conversely, when the power supply voltage increases, as shown in Figures 9a and 9b, compared to using a current limiting device that does not have voltage dependence,
Although the out-of-synchronization torque decreases from TD4 to Toa'', the starting current value decreases from Ist4 to I5t4'', allowing the protection function to work better.

The above is a configuration in which the starting current value changes smoothly in response to changes in the power supply voltage; FIG.

With the configuration shown in FIG. 11, it is also possible to switch the current limit value in stages. CF2 in FIGS. 10 and 11. C.F.
2. CF2. CF2 is a comparator, and each comparator has two comparators, but it goes without saying that by increasing the number of comparators, it is possible to sequentially increase the number of switching stages.

〔Effect of the invention〕

According to the present invention, when the power supply voltage decreases, the starting current can be increased, so the drop in out-of-synchronization torque is kept small, and conversely, when the power supply voltage increases, the increase in the starting current is prevented, and the current limiting device Acts as a protective device.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing one embodiment of the current limiting device of the present invention, Fig. 2 is a voltage waveform diagram of each part for explaining the operation of Fig. 1, and Figs. 3 and 4 are motor current 5 and 6 are block diagrams for changing the starting current value according to changes in the power supply voltage, and Figures 7a, 7b, and 7c.
The figures are explanatory diagrams of the influence of current limitation, power supply voltage drop, and power supply voltage increase, showing a conventional example, FIG. 8a, FIG. 8b, and FIG. 9a. FIG. 9b is an explanatory diagram of the effect, and FIGS. 10 and 11 are circuit diagrams showing a configuration for switching the starting current value in stages according to changes in the power supply voltage. 1... Current-torque characteristic, 2... Speed-torque characteristic, 3... Current-torque characteristic, 4... Speed-torque characteristic, 5... Speed-torque characteristic, 6... Current - Torque characteristic, 7... Speed-torque characteristic, 8... Current-torque characteristic, 9... Current detection point, 10... CPI input part, 11... CPI output part, 12 ...CF2
Input section, 13... Current intermittent command output section, 14...
DC brushed motor, 15... Current-torque characteristics, 16... Speed-torque characteristics, 17... Current-torque characteristics, 18... Speed-torque characteristics.

Claims (1)

[Claims] 1. A driving means for driving a DC motor, a detection means for outputting a signal according to the rotational speed of the DC motor, a reference signal generation means for generating a pulse signal of a predetermined period, a signal from the reference signal generation means and the above-mentioned a phase comparison means for comparing the phases of the signals from the detection means and applying a signal according to the comparison result to the drive means; a means for detecting the current of the DC motor; and a DC motor in response to the output of the current detection means. What is claimed is: 1. A servo control device for a DC motor comprising a current limiting means for limiting the current value of a DC motor, the current limiting device switching or increasing/decreasing the current limiting value in response to changes in power supply voltage.