JPS5914801Y2 - Abnormality detection circuit of tacho generator in movable table feeder - Google Patents

Description

[Detailed description of the invention] The present invention is equipped with a servo control device that moves the movable base by driving a servo motor based on the deviation between the speed command voltage and the speed feedback voltage sent out from the tacho generator, and moves the movable base at a rapid traverse speed. This invention relates to an abnormality detection circuit for detecting an abnormality in the tachogenerator in a movable platform feeding device that performs slow feeding after moving from the backward end, and its purpose is to: The purpose is to detect an abnormality in the tachogenerator that causes the movable platform to run out of control, and to prevent the runaway at the initial stage of starting fast forwarding.

Another object of the present invention is to detect an abnormality in the tachogenerator only during fast forwarding when the speed feedback voltage is large, thereby enabling stable abnormality detection without malfunction.

In general, a servo motor control device used in a movable table feeder calculates the deviation between a speed command voltage that commands the speed of a servo motor and a speed feedback voltage sent out from a tachogenerator according to the rotation speed of the servo motor. The servo motor is driven by applying a voltage corresponding to this deviation to a drive device that drives the servo motor.

Therefore, the servo motor is controlled so that the deviation between the speed command voltage and the speed feedback voltage becomes zero, and rotates at a speed according to the speed command voltage.

In such a servo motor control device, if a breakage or short circuit failure occurs in the winding in the tachogenerator or a break or short circuit failure in the speed feedback loop wiring occurs, and the speed feedback voltage becomes zero, the speed command voltage This is directly applied to the drive device as a deviation.

As a result, the rotation speed of the servo motor increases, but since speed feedback is not applied, the deviation does not decrease, and the servo motor continues to increase its rotation speed, causing runaway.

In order to prevent such runaway of the servo motor, a method for detecting an abnormality in the tachogenerator is to constantly measure the speed feedback voltage sent from the tachogenerator and detect an abnormality when the voltage falls below a certain set voltage. It is possible that

However, the speed variable range of a general servo motor is, for example, 1
: 1000, which is very wide.The speed feedback voltage also changes according to the speed of the servo motor, so when the servo motor is rotating at low speed, the speed feedback voltage becomes very small, and the set voltage must be lower than the speed feedback voltage when rotating at the lowest speed. When setting and detecting abnormalities, there are cases where ripples sent out from the tachogenerator, external noise, etc. may cause malfunctions and send an abnormal signal even though there is no abnormality, or no abnormal signal is sent even though there is an abnormality. Reliable abnormality detection cannot be performed.

The present invention has been devised to eliminate such drawbacks, and is characterized by detecting an abnormality in the tachogenerator immediately after the start of fast forwarding of the movable table, and ending the abnormality detection before starting slow forwarding. It is something to do.

Embodiments of the present invention will be described below based on the drawings.

Figure 1 shows the grindstone head 2, which is a movable stand by the servo motor SM.
0 is a block diagram showing the configuration of a servo motor control device that drives the grinding wheel head 20 at preset speeds to perform rapid forward forward movement, grinding forward movement, and backward movement, and a tacho generator abnormality detection circuit according to the present invention. Forward and backward speed settings are made using variable resistors VR1, vR2, and VR3, respectively.
It will be held at

The speed command voltages output from these variable resistors vR1, vR2, and vR3 are respectively applied to gates G1. G2. G3 is applied to the arithmetic unit 10, but gates G1. G2 and G3 are opened in response to a rapid forward command, a grinding forward command, and a backward command, respectively, and a speed command voltage suitable for each feed is applied to the calculator 10.

The arithmetic unit 10 calculates a deviation between a given speed command voltage and a speed feedback voltage sent out from a tacho generator TG, which will be described later. This deviation is amplified by an amplifier 11 and provided to a drive circuit 12.

This drive device 12 changes the voltage applied to the servo motor SM by controlling, for example, the firing phase angle of a thyristor based on a given deviation signal.
The rotational speed of M changes.

The tachogenerator TG outputs a speed feedback voltage according to the rotational speed of the servo motor SM.
A negative speed feedback voltage is output when M rotates forward and the wheel head 20 moves forward, and a positive speed feedback voltage is output when the servo motor SM rotates in the reverse direction and the wheel head 20 moves backward.

This speed feedback voltage is applied to the arithmetic unit 10 as described above, and at the same time, it is also applied to the discrimination circuit 14, which together with the timer 13 constitutes a tachogenerator abnormality detection circuit.

This discrimination circuit 14 compares the speed feedback voltage output from the tachogenerator TG with a set voltage that is smaller than the speed feedback voltage in rapid forward movement during normal operation, and when the speed feedback voltage is lower than the set voltage, It stores and sends an abnormal signal, and is enabled by the time-up signal of the timer 13.

The timer 13 is set to a time longer than the time required for the speed feedback voltage to exceed the set voltage during normal operation after the servo motor starts rotating at high speed, and is started when a fast forward command is given. , is reset when the fast forward forward command is no longer given.

FIG. 2 is a diagram showing a detailed circuit of the discrimination circuit 14, which includes a comparator CP1 that compares the speed feedback voltage and the set voltage, and a comparator CP1 that memorizes that the speed feedback voltage has become smaller than the set voltage and sends out an abnormal signal. It is mainly composed of a flip-flop FF1.

The speed feedback voltage output from the tacho generator TG is applied to the inverting input terminal of the comparator CP1, and the set voltage Vs is applied from the variable resistor R4 to the non-inverting input terminal of the comparator CP1. It will be done.

As described above, this discrimination circuit 14 is effective only during fast forward forward movement, and the speed feedback voltage at this time is negative. voltage is set.

However, this set voltage needs to be set to a value larger than the voltage of ripples outputted from the tachogenerator TG, external noise, etc.

Furthermore, the output terminal of the comparator CP1 is connected to the input terminal of the AND gate via an interface circuit composed of a resistor R1, a zener diode ZD, and an inverter INV, so that the speed feedback voltage is smaller than the set voltage. If so, an "H" signal is output from the inverter INV and applied to the AND gate AND.

The other input terminal of this ant game) AND has a timer 1.
3 time-up signal is given,
When the time-up signal of the timer 13 is applied, this AND gate AND is opened and the operation of the discrimination circuit 14 becomes valid.

The output terminal of the AND gate AND is connected to the set terminal S of the flip-flop FF1, and is set when a signal of °°H is applied from the inverter INV while the AND gate is open.

On the other hand, when a reset signal is applied to the reset terminal R of the flip-flop FF1 from a reset switch (not shown), the flip-flop FF1 is reset.

This flip-flop abnormality signal is output, notifying the abnormality of the tachogenerator and stopping the operation of the servo motor.

The operation of the tachogenerator abnormality detection circuit of the present invention having the above configuration will be described below.

Now, when a fast forward forward command is given to the servo motor control device while the grinding wheel head 20 is stopped at the original position shown in FIG. Given.

As a result, the speed command voltage for rapid forward movement set in the variable resistor VR1 is applied to the calculator 10, and the timer 13 is started.

The calculator 10 calculates and outputs the deviation between the given speed command voltage and the speed feedback voltage sent from the tacho generator TG, but at the time of startup, the servo motor SM is stopped and the speed feedback voltage is zero. Therefore, this computing unit 10
The speed command voltage for fast forward forward movement is directly output as a deviation.

Then, this deviation is amplified by the amplifier 11 and the drive device 1
2, the servo motor SM starts to rotate normally, and the grindstone head 20 starts to move forward rapidly.

When the servo motor SM starts to rotate forward, a negative speed feedback voltage is generated from the tachogenerator TG according to the rotation speed of the servo motor SM as shown in FIG.
given to 0.

Further, this speed feedback voltage is applied to the comparator CP in the discrimination circuit 14.
1 and is compared with the set voltage Vs.

When the servo motor SM is started, the speed feedback voltage is smaller than the set voltage Vs, so the inverter INV outputs a signal of "HI3" and is applied to the AND gate. It is opened when timer 13 times up, so if timer 13 does not time up, the game is opened
Therefore, no "H" signal is output.

As mentioned above, the timer 13 is set to a time TS that is longer than the time measured during normal operation from the start of high-speed rotation until the speed feedback voltage exceeds the set voltage Vs. In this case, the timer 13 does not time up until the speed feedback voltage exceeds the set voltage Vs, and the AND gate AND does not open and becomes “H”.
9? signal is not output.

Therefore, flip-flop FF is not set and no abnormal signal is sent out.

Furthermore, when the tachogenerator TG is normal, the speed feedback voltage exceeds the set voltage Vs and the inverter INV no longer sends out the °H signal before the timer 13 times up, so the timer 13 times up. Even if the Android (game) AND is opened, an "H" signal is not sent from the Android (game) AND, and no abnormal signal is sent.

After the grindstone head 20 is moved forward in this way,
In order to feed the grinding wheel head 20, the sending of the fast forward forward command is stopped, and when the grinding feed command is given, the gate G1
Instead, the gate G2 is opened and the grinding feed speed command voltage set in the variable resistor R2 is applied to the computing unit 10.

At the same time, the timer 13 is reset, thereby closing the game AND and disabling the discrimination circuit 14.

When a speed command voltage for grinding feed is applied to the computing unit 10, the grindstone head 20 moves forward with the grinding feed and grinds the workpiece W.

At this time, the speed feedback voltage has a value smaller than the set voltage Vs as shown in FIG. 3, but since the discrimination circuit 14 is disabled, no abnormality signal is sent out.

When the grinding of the workpiece W is completed and a retreat command is given instead of a grinding feed command, gate G2 is closed and gate G
3 will be opened.

As a result, the negative speed command voltage for retraction set in the variable resistor vR3 is applied to the calculator 10, and the grindstone head 20 is retracted to the original position.

At this time, the speed feedback voltage becomes positive, but as in the case of grinding feed, the discrimination circuit 14 is disabled, so no abnormality signal is sent out.

Next, an explanation will be given of the operation when a failure such as disconnection or short circuit occurs in the tachogenerator TG before the rapid forward movement of the grindstone head 20 is started.

If such a failure occurs, a speed command voltage for rapid forward movement is given to the calculator 10 and the servo motor SM
Even if the high-speed rotation of
Even after lapse of time, the speed feedback voltage does not exceed the set voltage Vs.

Therefore, timer 13 times up and
“H” from inverter INV even when AND is opened
This "H" signal is applied to the set terminal of flip-flop FF1 to set flip-flop FF1.

As a result, an abnormality signal is sent from the output terminal Q, and the operation of the servo motor SM is stopped to prevent runaway of the grindstone head 20 and to notify that the tachogenerator TG is abnormal.

Furthermore, even if the speed feedback voltage does not become completely zero, due to factors such as increased contact resistance of the brushes in a DC tachogenerator, the speed feedback voltage may drop compared to normal operation, as shown by the dashed line in Figure 3. It is also possible to detect abnormalities in cases.

Note that if the set voltage and the set time of the timer 13 are set to V's and T's, respectively, as shown in Fig. 3, the time from startup to the start of abnormality detection can be shortened, and the servo motor SM Even in the case where, after activation, the feed is switched to grinding before the rapid feed speed is completely reached, abnormality detection can be performed reliably.

In the first embodiment of the present invention described above, the timer 1
3 is timed up until the end of the fast forward forward movement, the AND is open, so even though there is no abnormality in the tachogenerator TG, the inverter INV may be “H” due to external noise etc. ” is output, the flip-flop FF1 may be set and an abnormal signal may be sent.

Figure 4 shows a discrimination circuit 14 that detects an abnormality only immediately after the timer 13 times out in order to eliminate such malfunctions.
This shows an example of the comparator CP.

and resistor R0, zener diode ZD, inverter I
Interface circuit and antgame consisting of NV
) AND is the same as in the first embodiment, but the flip-flop that stores that the speed feedback voltage exceeds the set voltage is different.

In this embodiment, the flip-flop FF2 is used as a flip-flop in master-slave operation J-.The flip-flop FF2 is activated by the time-up signal of the timer 13 and is formed by a one-shot multivibrator 15 which outputs an "H" trigger signal with a fixed time width. Triggered.

Since the flip-flop FF2 operates as a master slave, it reads the signals given to the J and K terminals at the rising edge of the trigger signal, and the signals given to the J and K terminals become "H" and "L", respectively. If so, it is set at the fall of the trigger signal, and if it is "L" or "L", the reset state is maintained.

Therefore, in the discrimination device of this embodiment, the timer 1
3 is time up and one shot multivibrator 1
When a trigger signal is sent from 5, at the rising edge of this trigger signal, the signal output from the AND gate and the "L" level of the terminal are read into the terminal 5, and at the falling edge of the trigger signal, it is set or reset. hold.

If the tachogenerator TG is normal and the AND gate AND is sending out an "L" signal when the timer 13 times up, it will go "L" at the rise of the trigger signal.
, "Since the signal of L91 is read, it is not set at the fall of the trigger signal, but maintains the reset state.

After this, no trigger signal is given to the flip-flop FF2, so the ant game will be interrupted due to foreign noise, etc.
) Even if a HI3 signal is output from AND, it will not be set by mistake.

Further, if the tachogenerator TG is out of order when the timer 13 times up, the signal of &4L91 is read "H" at the rising edge of the trigger signal, and is set at the falling edge of the trigger signal.

As a result, an abnormality signal is sent from the output terminal Q, the rotation of the servo motor SM is stopped, and the abnormality of the tachogenerator TG is notified.

In this manner, the discrimination circuit 14 of this embodiment effectively operates to detect an abnormality only immediately after the timer 13 times up, so malfunctions due to external noise with a high peak value are less likely to occur.

In the above two embodiments, abnormality detection was performed only during rapid forward movement, but if it is desired to perform abnormality detection during backward movement, the set voltage may be made positive and the inverter INV may be eliminated.

In addition, if you want to perform abnormality detection both during rapid forward movement and during backward movement, switch the set voltage Vs and turn on the inverter IN.
A switching circuit for enabling and disabling V may be provided.

In the above two embodiments, the time-up signal of the timer 13 is used to enable the discrimination circuit 14, but if the origin of the start of fast forwarding is always constant, fast forwarding will start during normal operation. The determination circuit 14 may be enabled by a signal from a limit switch that is pressed after the speed feedback voltage exceeds the set voltage.

As described above, the tachogenerator abnormality detection circuit of the present invention detects an abnormal decrease in the tachogenerator output, which causes the movable platform to run out of control, at the start of fast forwarding.
Since it has the effect of preventing the start of runaway itself, the safety effect is further enhanced and there is an effect of safety.

In addition, the abnormality detection circuit for the tachogenerator according to the present invention detects abnormalities using the speed feedback voltage during fast forwarding when the voltage is high, so that malfunctions will not occur due to ripples generated by the tachogenerator and external noise. It has the advantage of being able to detect abnormalities.

Furthermore, a device in which abnormality detection is performed only when the timer times out has the advantage that malfunctions are less likely to occur due to large noise voltages generated during high-speed rotation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the servo motor control device and the tacho generator abnormality detection circuit of the present invention, and FIG.
The figure shows a detailed circuit diagram of the discrimination circuit 14 in Figure 1, and
The figure shows a temporal change in the speed feedback voltage, and FIG. 4 is a circuit diagram showing a second embodiment of the discrimination circuit 14. DESCRIPTION OF SYMBOLS 10... Arithmetic unit, 11... Amplifier, 12... Drive device, 13... Timer, 14... Discrimination circuit, 15...
...One-shot multivibrator, AND...And gate, CPl...Comparator, FF1. FF2
...Flip-flop, G1-G3...Gate, S
M... Servo motor, TG... Tacho generator,
VR1 to VR4...Variable resistor, Vs...Setting voltage.

Claims (1)

[Scope of utility model registration request] The deviation between the speed command voltage and the speed feedback voltage sent out from the tacho generator according to the rotational speed of the servo motor is applied to a drive device that drives the servo motor, thereby causing the movable base driven by the servo motor to be fast-forwarded. and a setting means for setting a set voltage smaller than the speed feedback voltage and larger than the external noise signal during fast forwarding during normal operation in the feeding device of the movable platform which is configured to move at a slow forwarding speed lower than the fast forwarding speed; A discrimination circuit that compares the speed feedback voltage output from the tacho generator with the set voltage and sends an abnormal signal if the speed feedback voltage is smaller than the set voltage, and a discrimination circuit that responds to a fast-forward command for the movable base. and a control means that is energized by the controller, activates the determining means immediately after the speed feedback voltage exceeds the set voltage under normal conditions, and disables the determining means before sending the transport command. Features: Abnormality detection circuit for the tacho generator in the movable table feeder.