JPH0632901B2 - Grinding wheel fine contact detection device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grinding wheel fine contact detection device for detecting a contact between a grinding wheel of a grinding machine and a workpiece during processing and outputting a contact detection signal.

<Prior art> In the grinding machine, when starting to grind a work, the grindstone micro-contact detection device monitors whether or not the grindstone contacts the work, and the feed speed of the grindstone during idle grinding until the grindstone contacts the work. When the grindstone comes into contact with the work and the grindstone fine contact detection device outputs a contact detection signal, the grindstone feed speed is reduced to a predetermined speed based on this detection signal so that the grinding of the work can be started. , The idle grinding time is shortened to shorten the cycle time.

Conventionally, there is a grindstone fine contact detection device for a grinding machine used as described above as shown in FIG. This grindstone micro-detection device has an acoustic emission sensor (hereinafter referred to as an AE sensor) 3 attached to a work table 2 and detects ultrasonic energy generated when a grindstone 10 of a grinder contacts the work 1 by the AE sensor 3. Then, the detection signal is amplified by the preamplifier 4. Further, the discriminator 5 removes noise noise from the amplified signal and passes only the contact sound, the detector 6 converts the amplified signal to a DC level, and the variable amplifier 7 changes the amplification level (detection sensitivity) of the contact level. Then, the comparator 8 compares the detection signal from the variable amplifier 7 with the contact level signal,
When the level of the detection signal becomes higher than that of the contact level signal, the AND gate 9 outputs the contact signal, and when the AND gate 9 receives the signal indicating that the contact signal is being measured, it outputs the contact detection signal.

<Problems to be Solved by the Invention> However, the above-mentioned conventional grindstone fine contact detection device for a grinding machine has a detection signal from the AE sensor 3 and one threshold value.
(Contact level signal) is compared by the comparison unit 8 and the contact detection signal is output when the level of the detection signal becomes higher than the threshold value, so that it is similar to the detection signal at the initial stage of grinding. A sudden noise signal (water or noise from the work piece) causes a malfunction, and the feed speed of the grindstone is reduced to the specified speed during grinding before the grindstone still contacts the work. Therefore, there is a problem that the idle grinding time becomes long.

Therefore, an object of the present invention is to provide two thresholds, a high level threshold and a low level threshold, so that the level of a detection signal falls below the low level threshold after exceeding the high level threshold. It is an object of the present invention to provide a grindstone fine contact detection device for a grinding machine, which can output only a correct contact detection signal without being affected by a noise signal by determining the persistence until the time.

<Means for Solving the Problems> In order to achieve the above object, the present invention is based on the fact that the contact signal of the grindstone is longer than a noise signal for a certain level or longer. That is, the grindstone fine contact detection device of the grinding machine of the present invention, a sensor for detecting a signal generated immediately before the grindstone of the grinder contacts the work and when the grindstone of the grinder contacts the work,
Based on the signal from the sensor, the high level threshold, which is the threshold between the normal level of the signal at the initial stage of grinding and the level of sudden noise generated immediately before the start of grinding, and the grindstone contact the workpiece. A variable threshold circuit that outputs a low level threshold value that is the threshold value of the signal level when the grindstone is away from the workpiece and the set state is maintained. Comparing the signal from the sensor with the high level threshold, and when the level of the signal is higher than the high level threshold, the signal for setting the state holding means is set. The output from the first comparator is compared with the signal from the sensor and the low level threshold, and when the level of the signal becomes lower than the low level threshold, the state holding means is reset. A second comparator for outputting a signal for resetting, and whether or not the duration of the set state of the state holding means has exceeded a predetermined time, and when the duration of the set state exceeds the predetermined time, It is characterized in that a contact determination means for outputting a contact detection signal is provided.

<Operation> When a sensor detects a signal generated immediately before the grindstone of the grinder contacts the work and when the grindstone of the grinder contacts the work, the normality of the above signal at the initial stage of grinding is based on this signal. Level and the level of the above-mentioned signal when the grindstone is in contact with the workpiece and the grindstone is far from the workpiece. A low level threshold value, which is a threshold value with respect to the level of the signal at that time, is output from the variable threshold circuit. Then, the signal from the sensor and the high level threshold value are compared by the first comparator, and when the level of the signal becomes higher than the high level threshold value, a signal for setting the state holding means is issued, while The signal from the sensor and the low level threshold value are compared by the second comparator, and when the level of the signal becomes lower than the low level threshold value, a signal for resetting the state holding means is output.

Then, the contact determination means determines whether or not the duration of the set state of the state holding means exceeds a predetermined time, and as a result, when the duration of the set state exceeds the predetermined time, contact detection is performed. The signal is output. Therefore, it is possible to detect only the contact signal from the signal including the noise signal output from the sensor and output only the correct contact detection signal.

<Example> Hereinafter, the present invention will be described in detail with reference to illustrated examples.

FIG. 1 is a block diagram showing an embodiment of the present invention.
The AE sensor 21 detects ultrasonic energy generated when a grindstone (not shown) contacts the work and outputs a detection signal, and is attached to a work table (not shown). The detection signal output from the AE sensor is amplified by the amplifier 22, one of which is input to the first filter 23 and the other of which is input to the second filter 24. The first filter is inputted to the first envelope detector circuit 25 through only a frequency band with strong levels during grinding of the input signal (50KH _z hereinafter). Further, the second filter is inputted through only the frequency band level increases as the grinding of the input signal proceeds (around 200KH _z) to the second envelope detector circuit 26. This second envelope detection circuit 26
The second envelope detection signal output from the second envelope detection signal is added by the adder 27 together with the first envelope detection signal output from the first envelope detection circuit 25, and the added detection signal a is a fluctuation threshold circuit. 28, the first comparator 29, and the second comparator 30.

The fluctuation threshold circuit 28 adds the output signal from the first reference value setting circuit 28a to the average value signal obtained by integrating the detection signal a input from the adder 27 in the integrating circuit to obtain a high level signal. The threshold value V _H is output, and similarly, the adder 27
The output signal of the second reference value setting circuit 28b is added to the average value signal obtained by integrating the detection signal a input from the integrator circuit to output the low level threshold value VL.

Here, the high level threshold value V _H is a threshold value between the normal detection signal a at the initial stage of grinding and the level of a sudden noise signal generated immediately before the start of grinding. The low level threshold value VL is a threshold value of the detection value a when the grindstone is in contact with the work and the level of the detection signal a when the grindstone is far from the work.

The detection signal a from the adder 27 is compared with the high level threshold value VH by the first comparator 29. If the level of the detection signal a becomes higher than the high level threshold value, immediately before the start of grinding. Since a sudden noise is generated, a signal for setting the flip-flop 31 which is the state holding means is output. In addition, the detection signal a from the adder 27
Is compared with the low level threshold value VL by the second comparator 30, and when the level of the detection signal a becomes lower than the low level threshold value, it means that the grindstone has moved away from the work. A signal for setting the one-shot circuit to "H" is output.

The flip-flop 31 is set when the level of the terminal S becomes "H" by the signal from the first comparator 29, the terminal Q outputs the signal b of "H", and the second one-shot circuit 33 outputs "H". The signal d of "is output. Then, the AND gate 34 outputs the touch detection signal e of "L". Further, the second one-shot circuit 33 can arbitrarily set the duration of the level "H", and outputs the signal d of "L" when the set duration has elapsed. Then, the AND gate 34 outputs the touch detection signal e of "H". On the other hand, the flip-flop 31 is reset when the terminal R becomes "H" by the "c" signal c of "H" from the first one-shot circuit 32, the terminal Q outputs a signal b of "L", and the AND gate 34 The contact detection signal e of "L" is output.

FIG. 2 shows the waveforms of the output signals a, b, c, d, e of the respective parts in FIG. The operation of the grindstone contact microscopic detection device of the grinding machine will be described below with reference to FIG. FIG. 2a shows the waveform of the detection signal output from the adder 27 of FIG. 1. When the level of the detection signal a becomes higher than the high level threshold VH, the operation of the first comparator 29 causes the operation of FIG. The flip-flop 31 is set as shown in b. On the other hand, when the level of the detection signal a becomes lower than the low level threshold value VL, the flip-flop 31 is reset by the output signal c of the first wasshot circuit 32 (FIG. 2c) by the operation of the second comparator 30. .

At the same time as the flip-flop 31 is set, FIG. 2d
As shown in FIG. 5, the output signal d of the second one-shot circuit 33 becomes "H", and when the set duration time has passed, the signal d is "L" because it is over the period in which sudden noise occurs immediately before the start of grinding. "It becomes. Therefore, the AND gate 34 is "H" only when the output signal b of the flip-flop 31 is "H" and the output signal d of the second one-shot circuit 33 is "L" as shown in FIG. 2e. The contact detection signal e is output.

In other words, the level of the detection signal a is the high level threshold VH.
When the contact time from when the contact time exceeds the low level threshold value VL exceeds the contact time set by the second one-shot circuit 33, the "H" contact detection signal e is output. is there.

Here, there is a difference as shown in FIG. 3 between the waveform of the contact signal and the waveform of the noise signal when the grindstone contacts the work. FIG. 3A shows a waveform of a noise signal due to the coolant or the like before the grindstone contacts the work when the grindstone is driven and the work table is moved forward by using the coolant during grinding. . The pulse shown on the lower side of the figure is a pulse of the upper noise waveform at a predetermined level. Similarly, FIG. 3B shows the waveform of the contact signal when the grindstone contacts the work during grinding and performs grinding. From FIG. 3, the waveform of the noise signal due to coolant or the like has a pulse width of several 100 μsec, whereas the waveform of the contact signal during grinding has a pulse width of several msec. That is, if the duration of the second one-shot circuit 33 in FIG. 1 is set to be longer than the pulse width based on the noise signal waveform and shorter than the pulse width based on the contact signal waveform, the noise signal is detected as the detection signal a. When input, the duration from when the level of the detection signal a exceeds the high level threshold VH to when it falls below the low level threshold VL exceeds the duration set by the second one-shot circuit 33. Therefore, the contact detection signal e is not output.

Thus, the high level threshold and the low level threshold 2
Two thresholds are provided, and the contact of the grindstone with the work is detected by the duration from when the level of the detection signal a exceeds the high level threshold VH to when it falls below the low level threshold VL. It is possible to detect only the contact signal from the included detection signal a and output the correct contact detection signal e.

In the above embodiment, the first comparator 29, the second comparator 30, the first one-shot circuit 32, the second one-shot circuit 33,
Although the level determination and the duration determination of the detection signal a are performed using the flip-flop 31 and the AND gate 34, the present invention is not limited to this, and may be performed by a clock counter and determination means.

<Effects of the Invention> As is clear from the above, the grindstone fine contact detection device for a grinding machine according to the present invention provides a normal level of the signal at the initial stage of grinding and a level of sudden noise generated immediately before the start of grinding. High level threshold value which is a threshold value and low level threshold value which is a threshold value of the signal level when the grindstone is in contact with the work and the signal level when the grindstone is away from the work , A first comparator for setting the state holding means when the level of the signal from the sensor becomes higher than the high level threshold, and the level of the signal from the sensor A second comparator that resets the state holding means when the value becomes lower than the low level threshold value, and a contact judgment signal that outputs a contact detection signal when the state holding means is in the set state for a predetermined time or more. Since another means is provided, only the correct touch detection signal can be obtained without being affected by noise based on the duration from when the level of the signal from the sensor exceeds the high level threshold to when it falls below the low level threshold. Can be output. Therefore, by using the grindstone fine contact detection device of this grinding machine, the idle grinding time does not become longer than necessary due to a malfunction due to a noise signal during grinding, and the cycle time can be shortened.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing output signal waveforms of respective portions in FIG. 1, and FIG. 3 is a contact signal when a grindstone during grinding comes into contact with a work. FIG. 4 is an explanatory diagram of a noise signal due to the coolant, and FIG. 4 is a block diagram of a conventional example. 21 ... AE sensor, 22 ... Amplifier, 23, 24 ... Filter, 25, 26 ... Envelope detection circuit, 27 ... Adder, 28 ... Fluctuation threshold circuit, 29 ... First comparator , 30 ... second comparator, 31 ... flip-flop, 32, 33 ... one-shot circuit, 34 ... AND gate.

Claims (1)

[Claims] 1. A sensor for detecting a signal generated immediately before the grindstone of the grinder contacts the work and when the grindstone of the grinder contacts the work, and based on the signal from the sensor, at the initial stage of grinding. The high level threshold, which is the threshold between the normal level of the signal and the level of sudden noise that occurs immediately before the start of grinding, and the level of the above signal when the grindstone is in contact with the workpiece and the grindstone from the workpiece A variable threshold circuit that outputs a low level threshold value that is a threshold value with respect to the level of the signal when separated, state holding means that holds the set state, a signal from the sensor, and If the level of the signal is higher than the high level threshold value by comparing with the high level threshold value, the first comparator for outputting the signal for setting the state holding means and the sensor. And a second comparator which outputs a signal for resetting the state holding means when the level of the signal becomes lower than the low level threshold by comparing the signal from the above and the low level threshold. A contact determination means is provided for determining whether or not the duration of the set state of the state holding means exceeds a predetermined time, and outputting a contact detection signal when the duration of the set state exceeds the predetermined time. A grindstone fine contact detection device for a grinding machine.