JPH08265128A - Signal input circuit - Google Patents

Abstract

PURPOSE: To provide an input of a stable signal to a drive system by allowing a filter comprising a resistor and a capacitor to absorb external noise intruded to an input of a photocoupler so that a light emitting element hardly receives the external noise. CONSTITUTION: Since intruded external noise is interrupted by a noise filter 10 in a signal input circuit 5 and only the signal component is charged in a capacitor C, the external noise reaching a light emitting diode D1 of a photocoupler 73 is reduced. Furthermore, the charge charged in the capacitor C by noise absorption is discharged through a resistor R2 when an open collector transistor(TR) 11 is nonconductive, the effect of the filter comprising the capacitor C and the resistor R2 is increased. Since a resistor R1 and the capacitor C are connected in series, no high current flows when the TR 11 is conductive to prevent a damage to the TR 11. Since the capacitor C is connected between signal lines 7, 9, the configuration of the circuit 5 is simplified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal input circuit for inputting a signal from a pulse generator to a drive system via a photocoupler, and more particularly to a photocoupler due to external noise entering the input side of the photocoupler. The present invention relates to a technique for preventing an erroneous signal from being output.

[0002]

2. Description of the Related Art As one of servo position controls, there is "pulse train position control" in which a pulse train is input to a servo driver to perform servo positioning. In this case, a photocoupler is often provided in the signal input circuit in order to electrically disconnect the servo controller side from the servomotor drive system side. In pulse train position control, the command frequency is generally as high as several hundred kilohertz, so a high-speed photocoupler is used to respond to this. FIG. 3 shows a configuration example of a conventional servo controller, servo driver, and servo motor. The servo controller 51 includes a power source 52
A pulse train command generator 53, an amplifier 55, and a transistor Tr ₁₁ are provided. The power source 52 is connected to the outside via the terminal 59 on the positive pole (Vcc potential) side and via the terminal 61 on the negative pole (0 V potential) side. A transistor Tr ₁₁ for open collector output is arranged between the power supply 52 and the terminal 61, and the pulse train from the pulse command generator 53 is input to the base side of the transistor Tr ₁₁ via the amplifier 55.

On the other hand, the servo driver 71 is provided with a signal input circuit 75 having a photo coupler 73.
The signal input circuit 75 includes a signal line 81 provided with an amplifier 79.
, And the signal line 83 to the terminals 85 and 87. The signal line 81 and the signal line 83 are the signal input circuit 75.
Is connected to a signal line 82 and a signal line 84 inside the same, and these signal lines 82 and 84 are connected to the light emitting diode D ₁ of the photocoupler 73. Between the signal line 82 and the signal line 84, in order to prevent the light emitting diode D ₁ when a reverse voltage is applied is from being _damaged, the diode D ₂ is disposed in antiparallel with the light emitting diode D ₁ ing. The terminals 85 and 87 of the servo driver 71 are connected to the terminals 59 and 61 of the servo controller 51 via signal lines 91 and 93. When a signal is output from the pulse command generator 53 in the servo controller 51, the signal is input to the transistor Tr ₁₁ via the amplifier 55. When the transistor Tr ₁₁ is in the open collector state, power is supplied to the servo driver 71 via the signal lines 91 and 93. Inside the servo driver 71, the signal line 8
Power is supplied to the light emitting diode D ₁ of the photocoupler 73 via ₁ , 82, 83, 84, and the light emitting diode D ₁
When the phototransistor Tr ₁₂ receives the output light from the phototransistor Tr ₁₂ , the drive command signal 9 is output to the output side of the photocoupler 73.
5 is output.

By the way, when the command pulse is sent to the driver side by the open collector output as described above,
When the transistor Tr ₁₁ is off, the signal line 93 is in a floating state. Therefore, external noise easily enters the signal line 93, and an erroneous command pulse is output from the photocoupler 73 due to the external noise, which may cause a problem such as displacement of the servo motor 96. In particular, when the signal line 93 is long, such a problem frequently occurs. As countermeasures against such a problem, for example, Japanese Utility Model Laid-Open No. 55-112868 and Japanese Patent Application Laid-Open No. 5-122044 propose to provide a noise filter before the photocoupler. In the former case, as shown in FIG. 4A, a resistor R _{21 is provided} between the signal generator 103 that generates a signal via the open collector transistor Tr ₂₁ and the photocoupler 105.
And a capacitor C ₂₁ and a noise filter 106. The latter is a photocoupler with a noise filter in which a noise filter consisting of a resistor L ₃₁ and a capacitor C ₃₁ is connected between the input terminal 201 and the photocoupler 203, as shown in FIG. 4B.

[0005]

[SUMMARY OF THE INVENTION Incidentally, in the conventional signal output circuit and the noise photocoupler with filter above must to some extent increase the capacity of the capacitor C _21, C ₃₁ in order to increase the filtering effect against external noise . However, in the case of the signal output circuit shown in FIG. 4A, when the capacitance of the capacitor C ₂₁ increases,
A large current may flow to the signal generation unit 103 side for a long time, and the transistor Tr ₂₁ may be damaged. Similarly, FIG.
When the photocoupler with a noise filter shown in (b) is connected to a signal generator that controls signal output using a transistor, the transistor is damaged when the capacitance of the capacitor C ₃₁ is increased. It's easy to do. Also,
In the above two conventional techniques, it is necessary to separately provide a signal line and a terminal for grounding the capacitor. The present invention
It was devised in light of the actual situation, and its purpose is
To provide a signal input circuit capable of reducing external noise entering the input side of a photocoupler, preventing a large current from flowing to the pulse generator side, and performing stable signal input with a simple configuration. It is in.

[0006]

In order to achieve the above-mentioned object, the first invention is a signal input circuit for inputting a signal from a pulse generator to a drive system via a photocoupler, and the input of the photocoupler is provided. On the side, a filter is connected which is composed of a first resistor connected in series with the light emitting element of the photocoupler and a capacitor connected in parallel with the light emitting element and which absorbs external noise entering the input side. A second resistor is connected in parallel to the light emitting element and the capacitor, which is a signal input circuit. A second invention is a signal input circuit characterized in that a diode for protecting the light emitting element is connected to the light emitting element in series in a forward direction or in parallel in a reverse direction.

[0007]

According to the first aspect of the invention, since the filter including the first resistor and the capacitor absorbs the external noise that has entered the input side of the photocoupler, the external noise reaches the light emitting element of the photocoupler. It gets harder. Moreover, the electric charge charged in the capacitor due to this noise absorption is discharged by the second resistor when the open collector transistor is off, so that the filter effect by the capacitor and the second resistor can be expected. Moreover, since the first resistor and the capacitor are connected in series, a large current does not flow when the open collector transistor is turned on, and damage to the open collector transistor is prevented. According to the second aspect of the present invention, the diode for protecting the light emitting element is connected to the light emitting element in forward series connection or anti-parallel connection, so that the light emitting element can be prevented from being damaged by the reverse voltage. This makes it possible to more stably input the signal from the pulse generator to the drive system.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below with reference to the accompanying drawings for the understanding of the present invention. still,
The following examples are examples embodying the present invention and are not of the nature to limit the technical scope of the present invention.

FIG. 1 is a circuit diagram showing the configuration of a servo driver having a signal input circuit according to an embodiment of the present invention, together with a servo controller and a servo motor. Incidentally, in the figure, those having the same functions as those of the conventional one shown in FIG. 3 are designated by the same reference numerals, and the description thereof will be omitted.

The servo driver 1 has a signal input circuit 5.
Get Input to servo driver 1 via signal lines 91, 93
The applied pulse command is_,Signals via signal lines 81 and 83
It is input to the input circuit 5. In addition, the servo driver 1
Is a conventional amplifier 79 and pull-up resistor R₁₁What
Be prepared. Inside the signal input circuit 5, there is a photo coupler.
73 is provided. Light emitting diode of photo coupler 73
Code D₁Is connected to the signal line 7 connected to the signal line 81.
Controller via signal line 9 connected to signal line 83
The signal from 51 is sent. Between signal line 7 and signal line 9
Is a diode D₂Is a light emitting diode D₁Opposite to
It is connected in parallel. This diode D ₂Is the signal line
Light emitting diode when reverse voltage is applied via 7, 9
De D₁It is to prevent the damage. Belief
Line 7 has a light emitting diode D₁In series with resistor R₁Is distributed
It is set up. This resistance R₁In series with the light emitting die
Aether D₁And a capacitor C is connected in parallel with. This
These resistance R₁And low pass that combines the capacitor C
A filter is used to remove external noise.
The filter 10 is constructed. In addition, the capacitor C and
Photo diode D₁In parallel with R₂Are connected.
This resistance R₂Discharges the electric charge stored in the capacitor C
It is for doing.

As described above, the open collector transition
Star Tr₁₁When is OFF, the signal line 93 is
It becomes a swinging state and external noise easily enters,
In the signal input circuit 5 of this embodiment, the invading external noise is
The noise is blocked by the noise filter 10 and charged in the capacitor C.
Since it is charged, the light emitting diode D of the photocoupler 73 ₁
It is possible to reduce the external noise reaching the. Only
Was also charged in the capacitor C by this noise absorption
The charge is the open collector transistor Tr₁₁When off
And the resistance R₂Is discharged by the capacitor C and
Resistance R₂The filter effect by can be expected. Moreover,
Anti-R₁And the capacitor C are connected in series,
Open collector transistor Tr₁₁When turn on
The current does not flow and the open collector
Langista Tr₁₁Damage is prevented. Also, the conden
The C is similar to the conventional circuit shown in FIGS. 4 (a) and 4 (b).
Connect between signal line 7 and signal line 9 without grounding
Therefore, connect the signal line and terminal for grounding the capacitor C.
Since it is not necessary to provide it separately, the signal input circuit 5
Simpler configuration.

[Second Embodiment] Next, a second embodiment of the present invention will be described. FIG. 2 is a block diagram showing the configuration of a signal input circuit 25 which is a modification of the signal input circuit 5. In this signal input circuit 25, a diode D ₃ is connected in series to the light emitting diode D ₁ instead of the diode D ₂ .
When it is inconvenient for some reason to provide a protective diode in reverse parallel to the light emitting diode D ₁ of the photocoupler 73, as in this embodiment, the light emitting diode D 1 is used.
_A protective diode D ₃ may be connected in series with ₁ .
As a result, as in the case of the first embodiment described above, the light emitting diode D ₁ is not affected even when a reverse voltage is applied to the signal lines 7 and 9.
Is less likely to be damaged, and a command signal can be stably input to the servo motor 96. The embodiments of the present invention have been described above. The characteristic configuration of the above-described embodiment will be described below. With the above noise filter 10,
External noise that has entered the input side and is composed of a first resistor connected in series to the light emitting element of the photocoupler and a capacitor connected in parallel to the light emitting element and in series with the first resistor. Is configured to absorb. Here, the resistor R ₁ corresponds to a first resistor connected in series to the light emitting element of the photocoupler, the capacitor C is parallel to the light emitting element, and
Equivalent to a capacitor connected in series with the resistor. Also,
The resistor R ₂ constitutes a second resistor connected in parallel with the light emitting element and the capacitor. The light emitting diode D ₁ corresponds to a light emitting element of a photo coupler.

The signal line 7 and the signal line 9 correspond to the input current signal line and the output current signal line of the light emitting element, respectively. In the above embodiment, the capacitor C is the signal line 7.
And the signal line 9 are connected.
Further, the above-mentioned embodiment is characterized in that the light emitting element is connected to an open collector transistor for controlling pulse output provided on the pulse generator side. Furthermore, in the first embodiment, the diodes D ₂ and D ₃ are connected in parallel with the light emitting element, and in the second embodiment, the diodes D ₂ and D ₃ are connected in series with the light emitting element. In the above embodiment, when the servo controller 51 is provided with a transistor for open emitter output on the Vcc side of the power supply 52 instead of the transistor Tr ₁₁ for open collector output, the signal line 91 is likely to be in a floating state. The same applies when a relay that operates in response to the output from the pulse train command generator 53 is used instead of the transistor. The present invention can be applied to any of these cases, and external noise that has entered the photocoupler can be reduced by blocking external noise that has entered when the signal line is in a floating state. . Moreover, the electric charge charged in the capacitor due to this noise absorption is discharged by the second resistor when the open collector transistor is off, so that the filter effect by the capacitor and the second resistor can be expected. Moreover, since the first resistor and the capacitor are connected in series, a large current does not flow when the open collector transistor is turned on, and damage to the open collector transistor is prevented.

[0014]

As described above, according to the present invention, the external noise that has entered the input side of the photocoupler is absorbed by the filter, and the charge stored in the capacitor due to this noise absorption causes the open collector transistor to turn off. Since it is sometimes discharged by the second resistor, a filter effect by the capacitor and the second resistor can be expected. Moreover, since the first resistor and the capacitor are connected in series, a large current does not flow when the open collector transistor is turned on, and damage to the open collector transistor is prevented. Further, since the filter capacitor is connected to the light emitting element of the photocoupler, that is, between the input current signal line and the output current signal line of the light emitting element, it is necessary to connect the capacitor to the ground as in the conventional case. No signal lines or terminals are required, and the configuration of the signal input circuit is simplified accordingly. In particular, when the light emitting element of the photocoupler is connected to the open collector transistor provided on the pulse generator side, external noise is likely to enter, and this open collector transistor is easily damaged by a large current. The invention absorbs the external noise that has entered in such a case by the filter,
In addition, it is possible to prevent the open collector transistor from being damaged because a large current does not flow from the noise absorbing capacitor to the pulse generator. Furthermore, in series with the light emitting element of the photocoupler in the forward direction or in antiparallel,
Since the diode for protecting the light emitting element was connected,
Even when a reverse voltage is applied to the photocoupler, the light emitting element is less likely to be damaged and a signal can be stably input.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a servo driver including a signal input circuit according to an embodiment of the present invention, together with a servo controller and a servo motor.

FIG. 2 is a circuit diagram showing a modified example of a signal input circuit.

FIG. 3 is a circuit diagram showing a connection configuration example of a conventional servo driver, servo controller, and servo motor.

FIG. 4 is a circuit diagram showing a conventional circuit configuration example for reducing external noise.

[Explanation of symbols]

1 ... servo driver 5 ... signal input circuit 7,9,81,83,91,93 ... signal line 51 ... controller 52 ... power supply 53 ... pulse train command generator 73 ... photo coupler 96 ... servomotor C ₁ ... capacitor D ₁ ... Light-emitting diode D ₂ , D ₃ ... Diode R ₁ , R ₂ ... Resistor Tr ₁ ... Phototransistor Tr ₁₁ ... Open collector transistor

Claims (2)

[Claims] 1. A signal input circuit for inputting a signal from a pulse generator provided with an open collector transistor for controlling pulse output to a drive system through a photocoupler,
On the input side of the photocoupler, a first resistor connected in series to the light emitting element of the photocoupler and a capacitor parallel to the light emitting element and connected in series to the first resistor are provided. A signal input circuit, characterized in that a filter for absorbing external noise that has entered the input side is connected, and a second resistor is connected in parallel to the light emitting element and the capacitor. 2. The signal input circuit according to claim 1, wherein a diode for protecting the light emitting element is connected in series in the forward direction or in parallel in the reverse direction with respect to the light emitting element.