JPH07328775A - Device for judging deterioration of secondary cable of resistance welding machine - Google Patents

Abstract

PURPOSE:To provide a device for judging the deterioration of the secondary cable of a resistance welding machine dispensing with the cable to detect the current, applicable to the DC power source, capable of appropriately predicting and judging the control limit, and constantly confirm the normal operation. CONSTITUTION:A device for judging the deterioration of a secondary cable is provided with a voltage detecting part 12 of secondary cables 10a, 10b of a resistance welding machine, a deterioration detecting part 14 to compare the measured voltage with the preset limit value to detect the deterioration, and an operation confirming part 16 using the measured voltage. The voltage detecting part consists of input circuits 22a, 22b and rectifying circuits 24a, 24b. The deterioration detecting part is provided with a welding current setting instrument 26, initial resistance setting instruments 28a, 28b of secondary cables, limit value setting instruments 30a, 30b, comparators 32a, 32b to receive the limit voltage and the measured voltage, and alarm counters 34a, 34b to count the result of comparison. The operation confirming part is provided with a trigger level setting instrument 36 below the minimum measured voltagb, comparators 38a, 38k to receive the trigger level and the measured voltage, an AND- gate 40, and an energization display lamp 42 to respond the output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device capable of detecting deterioration of a secondary cable of a resistance welding machine and predicting and determining an appropriate replacement time.

[0002]

2. Description of the Related Art In a resistance welding machine installed on an automobile body assembly line or the like, particularly a spot robot welding machine, a spot welding gun is attached to a robot arm and can be turned over or swung according to a welding portion. Exercise violently. Therefore, the secondary cable connected to the spot welding gun has a structure in which many thin wires are bundled to have flexibility, but it is constantly swung and twisted during welding, and further, thermal fatigue is added, so the disconnection gradually deteriorates. Then, it rapidly progresses to a complete disconnection.

By the way, the power source of the resistance welding machine is broadly divided into a single-phase AC type (50 or 60 Hz) and a three-phase inverter DC type (which converts the frequency to 700 to 1000 Hz for rectification).
There are two types. The single-phase AC type is inexpensive, but it requires a large amount of power supply equipment, so it is almost unused at present except for some simple types. On the other hand, in the three-phase inverter DC type, the main body price is high, but the power supply equipment is inexpensive, and the frequency is high, so the welding transformer can be miniaturized. Further, the direct current type has a higher current density than the alternating current type, which enables higher quality welding. In particular,
Since aluminum and plated materials, which are increasing in number at present, have good conductivity, it is necessary to heat by energization in a shorter time, and the DC method is also excellent in this respect. For this reason, the three-phase inverter DC type is currently the mainstream.

As the secondary cables of the resistance welding machine, there are a two-type cable in which reciprocating cables are housed in separate hoses, and a cable in which reciprocating cables called kickless are housed in the same hose. In kickless, the electromagnetic repulsive force and the attractive force generated during welding energization cancel each other out, and the kicking force is hard to appear to the outside. Therefore, the kickless structure has an advantage that the reciprocating cable is uniformly deteriorated and is easy to manage. However, in most spot robot welding machines, since the reciprocating cables are arranged separately, the two-line type is often used. The cables used vary in length and thickness, and although their nominal resistance values are specified, they vary widely. Therefore, the cable life greatly changes depending on the actual cable used, the usage state, the usage environment, etc., and cannot be set unconditionally.

An example of a secondary cable monitoring device for a resistance welding machine is the device described in Japanese Utility Model Publication No. 54-37780. This is a secondary cable monitoring device that automatically monitors the rate of increase in the impedance of the secondary cable during use with respect to the impedance when it is new and issues an alarm when the preset level of the rate of increase is exceeded. is there. Specifically, the voltage across the secondary cable to be monitored by the welding current is converted into a cable signal voltage E _C , and the voltage E
An alarm level setter that sets the control limit value for the impedance increase in the cable using the output of _C , and a current voltage signal E _I that is proportional to the welding current to generate a cable signal when the secondary cable is new or equivalent. And a comparator for comparing the voltage E _C with the E _I to determine a change in the impedance of the cable. Here, as the welding current signal voltage E _I , a signal from a current transformer inserted on the primary side of the welding machine or a toroidal coil for secondary current detection inserted on the secondary side of the welding machine is used.

[0006]

A spot robot welding machine used in an automobile-related assembly process or the like has a teaching function, a spot welding position and a welding current are preliminarily taught, and a full operation is performed for 24 hours. is doing. Therefore, it is necessary to accurately grasp the degree of deterioration of the welding machine secondary cable that may cause disconnection, predict the timing of complete disconnection, and replace immediately before complete disconnection improves operating efficiency and cable economy. It is extremely important in terms of sex.

As mentioned above, the power source of the resistance welding machine is classified into a single-phase AC type and a three-phase inverter DC type.
In particular, it is necessary to develop a secondary cable deterioration determination device that is compatible with the current mainstream DC type.

However, as described above, the structure in which the toroidal coil is inserted on the secondary side of the welding machine to detect the secondary current cannot be applied to the DC power source. Further, in the conventional device, in order to detect the welding current, it is necessary to connect a measurement cable different from that for voltage detection. Since the increase in the number of cables to be connected tends to increase the possibility of connection failure and hinder the welding work, it is important to suppress it as much as possible. In addition, in the conventional device, an alarm is issued only when the increase in the resistance value of the secondary cable exceeds the limit value, but no abnormality is detected until then, so whether the device is operating normally, voltage detection It is not possible to check whether or not the measurement cable for connection has been forgotten or there is a connection failure. Further, since the secondary cable is swung or twisted violently, the measurement cable for voltage detection may be disconnected or broken, and such a situation cannot be accurately grasped.

An object of the present invention is to eliminate the need for a cable for current detection, to support a DC power supply, to appropriately predict and determine a control limit, and to always confirm normal operation. A secondary cable deterioration determination device for a resistance welding machine is provided.

[0010]

SUMMARY OF THE INVENTION According to the present invention, a voltage detecting unit for detecting a voltage drop of each of a pair of secondary cables of a resistance welding machine is compared with a measured voltage and a set limit value to prevent deterioration. A secondary cable deterioration determination device for a resistance welding machine, comprising a deterioration detection unit having a two-channel configuration for detection and an operation confirmation unit for confirming normal operation using the measured voltage. Here, the voltage detection unit includes an input circuit connected between both ends of the pair of secondary cables, and a rectifier circuit that rectifies the amplified output of the input circuit. In addition, the deterioration detection unit has a common welding current setting device that sets the maximum welding current,
An initial resistance setting device that sets the initial resistance value of each secondary cable, a limit value setting device that sets the allowable limit value of each secondary cable at a premium rate, and the limit voltage set by each and the above-mentioned It is provided with a comparator that receives the measured voltage and an alarm counter that counts the comparison result from the comparator when the measured voltage exceeds the limit voltage. Then, the operation confirmation unit includes a trigger level setter that uses a voltage generated in the secondary cable as a trigger level by a current that is equal to or less than the minimum welding current value, and two trigger level setters that receive the trigger level and the two measured voltages. A comparator and an AND gate that ANDs the outputs of both comparators,
A current-carrying indicator lamp is provided for displaying a current-carrying state by the output of the AND gate.

An alarm output section connected to the outputs of the two comparators of the deterioration detection section is provided. The alarm output unit includes a latch circuit connected to the outputs of both comparators and capable of switching between latch and normal operations, an alarm indicator lamp connected to each of the latch circuits, and an OR gate for ORing the outputs of both latch circuits. , A buzzer that operates at the output of the OR gate. It is also desirable to provide a recorder output section connected to the outputs of both rectifier circuits of the voltage detection section. The recorder output section is composed of a smoothing circuit capable of smoothing each rectified output and an output amplifier which amplifies the output of each smoothing circuit by direct current. Each smoothing circuit increases the time constant when the power supply frequency is low. It has a switch mechanism. Furthermore,
It is preferable to connect a dot number counter to the output of the AND gate of the operation confirmation unit.

[0012]

First, the welding current and the initial value of the secondary cable are set, this product is set as the initial voltage, and the allowable limit value of the voltage increase rate due to the deterioration of the secondary cable is set as the condition for determining the quality. The setting of the welding current is common to the two channels, and the initial resistance value and the limit value are set independently. When the judgment result exceeds the limit value, the number of times is independently counted in two channels. The replacement value of the secondary cable is predicted based on this count value. Also, each time welding is performed, the logical product of the voltages detected from both secondary cables is taken and the current indicator lamp is turned on to confirm that the operation is normally performed.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing the overall structure of a secondary cable deterioration determining device for a spot robot welding machine according to the present invention. The present apparatus includes a voltage detection unit 12 that detects the voltage drop of each of the pair of secondary cables 10a and 10b of the spot robot welding machine, and two channels that detect deterioration by comparing their measured voltages with a set limit value. The deterioration detecting section 14 and the operation confirming section 16 for confirming the normal operation by using the measured voltage. Here, the power source of the resistance welding machine is an AC type, and the secondary cables 10a and 10b are connected to the secondary side of the welding transformer 18, and the spot welding gun 19 is connected thereto. The spot welding gun 19 is moved by a robot arm so as to be inverted or swiveled, and spot welding is performed at a desired welding site. This device has a two-channel configuration because in the case of the two-type cable that is often used in spot robot welding machines, the length of the secondary cable differs between the forward and return paths, and the use of the secondary cable Because the state is different, the degree of deterioration is different, and it is preferable from the economical point of view to replace them separately when they approach the control limit.

A detection cable 20 is connected between both ends of each of the pair of secondary cables 10a and 10b and is guided to the voltage detection section 12. The voltage detector 12 includes an input circuit 22 that differentially amplifies voltage drops in both secondary cables.
a, 22b, and rectifier circuits 24a, 24b for rectifying the amplified outputs of both input circuits 22a, 22b, respectively. As a result, a measured voltage obtained by amplifying and rectifying the voltage drop of each of the secondary cables 10a and 10b is obtained.

The deterioration detecting unit 14 includes a common welding current setting device 26 for setting a welding current (in the case of multi-spot welding, a maximum welding current) and an initial resistance setting for setting an initial resistance value of each secondary cable. 28a, 28b, limit value setters 30a, 30b for setting the limit value of each secondary cable at an additional rate, and comparators for inputting both limit voltages set by them and the above-mentioned both measured voltages, respectively. 32a and 32b, and an alarm counter 34 for counting the results when the measured voltage exceeds the limit voltage.
a, 34b. The welding current setting device 26 is common, but other than that, it has a two-channel structure in which two similar circuits are provided for each.

The operation confirmation section 16 includes a trigger level setter 36 for setting a trigger level to a voltage generated in a secondary cable when a new product is produced by a current equal to or lower than a welding current (minimum welding current in the case of multi-spot welding), and its trigger. Two comparators 38, each of which inputs the level and the above-mentioned both measured voltages
a and 38b, an AND gate 40 that takes the logical product of the outputs of both comparators 38a and 38b, and an energization indicator lamp 42 that performs energization display in response to the output of the AND gate 40. The output of the AND gate 40 is also input to the dot number counter 44.

Further, in this embodiment, the output of both the comparators 32a and 32b of the deterioration detecting unit 14 is used to generate various alarm outputs, and the measured voltage from the voltage detecting unit 12 is output to the outside. A recorder output unit 48 for outputting to a recorder or the like is provided.

Now, in the spot robot welding machine, usually, a work of sequentially welding a plurality of different points (multi-spot welding) is performed in one stroke. In that case, the welding current to be set differs depending on the condition of the welding site, etc., and the welding site and welding current are stored in the spot robot welder in advance (teaching function), and the welding is performed according to that. A specific example of welding 6 points in one stroke shown in FIG. 2 will be described. The spot welding gun attached to the robot arm is supposed to sequentially perform spot welding at six points from point to point in one stroke. In this example, the point has the largest welding current. Therefore, this maximum welding current value is set in the welding current setting device 26. Also, the initial resistance setters 28a and 28b
Is set to the initial resistance value of the secondary cables 10a and 10b (resistance value when new). In FIG. 2, the vertical axis represents the measurement voltage, but if the resistance is constant (initial value), the voltage is proportional to the current, so the magnitude of the measurement voltage can be viewed as the magnitude of the welding current.

As described above, the secondary cable has a structure in which a large number of fine wires are bundled in order to have flexibility, and the wire gradually deteriorates during use, and then rapidly progresses to complete wire breakage. That is, the resistance value gradually increases with the deterioration, and the measurement voltage also increases. The amount of voltage increase due to this deterioration (increase in resistance value) is shown by the hatched portion in FIG. Therefore, as the control limit determination condition, the limit value setters 30a and 30b set the allowable limit of the voltage increase rate due to the deterioration of the secondary cable as a percentage with the initial value being zero.

The comparators 32a and 32b compare the measured voltage obtained by the secondary cables 10a and 10b with the allowable limit value obtained as described above, and output when the measured voltage exceeds the allowable limit value. Is generated, and each of the alarm counters 34a and 34b counts it separately. The count value of the alarm counters 34a and 34b predicts the replacement time of the secondary cable. The measured voltage of the secondary cable may happen to exceed the permissible limit voltage depending on the operating conditions or due to noise or the like, but it does not mean that the secondary cable cannot be used immediately. As the deterioration progresses, the numerical values of the alarm counters 34a and 34b rapidly increase, so that the appropriate replacement time is determined.

FIG. 3 shows a circuit example (for one channel) of the welding current setting device 26, the initial resistance setting devices 28a and 28b, and the limit value setting devices 30a and 30b of the deterioration detecting section 14.
Welding current setting device 26, initial resistance setting devices 28a, 28b,
Each of the limit value setters 30a and 30b is composed of an adder including an operational amplifier, which are connected in cascade. Then, the digital switches S _{1 to} S ₇ are provided to the respective setting means.
Is used to facilitate the setting. The reference voltage V _REF is input to the welding current setting device 26, and the output voltage is added to this reference voltage at the ratio of the input resistance R _i and the feedback resistance R _f according to the set values of the digital switches S _{1 to} S ₃ . The output voltage of the welding current setting device 26 is set to a value corresponding to the maximum welding current in the case of multi-spot welding as described above. Initial resistance setting unit 28a, the output voltage from the welding current setting device 26 is inputted to 28b, and outputs a voltage corresponding to the setting value of the digital switches S _4, S _5. This output voltage is set to be equal to the measured voltage (initial value) when the secondary cable is new. Limit value setting unit 30a, 30b is adapted to set a premium rate for the initial value, the digital switch S _6, S ₇ for the limit value set in the output voltage corresponding to the initial value when zero percent A fixed resistor R _c is connected to the input so that is always added. When a certain numerical value is set to the digital switches S ₆ and S ₇ , the voltage increased in proportion to the numerical value is used as the limit value setter 30a,
30b outputs.

Next, in the operation confirming section 16, the trigger level setter 36 sets the trigger level so that all 6 points can be detected in the case of the multi-spot welding operation of 6 points per stroke in FIG. 2, for example. That is, the trigger level is set to a level lower than the measured voltage at the point of the minimum welding current value. However, if it is too low, a malfunction due to the influence of noise or the like may occur, so a value slightly lower than the measured voltage (initial value) by the minimum welding current value is set.
This trigger level and each measured voltage are compared with each other by the comparators 38a, 38a.
Comparing in b, the output occurs when the measured voltage is large. The AND gate 40 takes the logical product of the outputs of both comparators to drive the current indicator lamp 42 and the dot number counter 44. As a result, the fact that welding is in progress
It is possible to always notify by lighting the lamp, and at the same time, the total number of weldings (operation status of the resistance welding machine) can be grasped by the dot number counter 44.

In this type of device, from its original purpose,
The alarm is issued only when the deterioration of the secondary cable progresses and the limit value is exceeded. Since no alarm is naturally issued while the deterioration of the secondary cable is small, the prior art has no means for confirming whether or not the device is operating normally. Also, if the measurement cable, which should have been connected to the secondary cable, is disconnected for some reason, the alarm will not be activated, so the user should wait until the secondary cable is completely disconnected. It is possible that you may not notice any abnormality in the measurement cable. On the other hand, in the apparatus of the present invention, the current-carrying indicator lamp 42 is turned on every time welding is performed, so that it can be always confirmed that the apparatus or the like is operating normally. It should be noted that since the current-carrying indicator lamp 42 lights only when the outputs of the two channels of the AND gate 40 match, the lamp does not light even if one of the measurement cables is disconnected, and the abnormality can be detected early.

Further, the apparatus of this embodiment has an alarm output section 46 connected to the outputs of the two comparators 32a and 32b of the deterioration detecting section 14. The details of the alarm output unit 46 are shown in FIG. The alarm output unit 46 includes latch circuits 50a and 50b, which are connected to the outputs of both comparators 32a and 32b, respectively, and are capable of switching between latch and normal operations, and latch circuits 50a and 5b.
Alarm indicators 52a and 52b respectively connected to 0b
And an OR gate 54 that ORs the outputs of both latch circuits 50a and 50b, a buzzer 56 that operates by the output of the OR gate 54, an AC100V output terminal 58, and a relay contact 60. In the latch mode, after the alarm is issued, the alarm indicator lights 52a and 52b continue to be lit, and at the same time, the buzzer 56 also continues to ring. In the normal mode, when an alarm is issued (only during energization), the alarm indicators 52a and 52b are turned on and the buzzer 56 sounds. The alarm indicator lamps 52a and 52b indicate which channel has an alarm, and since the buzzer 56 is common to two channels, it sounds when an alarm is issued to either channel. The output of the AC100V output terminal 58 can be used for driving a rotation warning lamp, and the relay contact 60 can be used for controlling other control devices and measuring devices.

The alarm indicators 52a and 52b can also be used for setting the initial resistance by the above-mentioned initial resistance setters 28a and 28b. First, the limit value setters 30a and 30b
Set the limit value (%) by the digital switches S ₆ and S ₇ of 0
%, And while actually operating the resistance welding machine, for example, if CH (channel) 1 is being set, set the digital switches S ₄ and S ₅ to the limit point of whether the CH1 alarm indicator lamp 52a is lit or not. Set. For multi-spot welding, make this setting at the maximum current. Thereby, the initial resistance value of the secondary cable can be easily set.

Further, the present apparatus has a recorder output section 48 connected to the outputs of both the rectifier circuits 24a and 24b of the voltage detection section 12. As shown in FIG. 5, the recorder output unit 48 includes smoothing circuits 62a and 62b capable of smoothing both rectified outputs, and output amplifiers 64a and 64b amplifying the outputs of both smoothing circuits 62a and 62b, respectively. The smoothing circuits 62a and 62b are smoothed by a smoothing circuit having a small time constant when the power supply frequency is high, and reduce the ripple of the rectified output when the power supply frequency is low.
It has a switch 66 for increasing the time constant of the smoothing circuit. This allows the welding current to be monitored externally using a recorder, etc.
Since it can be recorded, analysis data of the deterioration status can be obtained and used for determining the judgment standard. The level of the frequency by the switch 66 is switched depending on the type of the welding machine power source when the direct current output from the recorder output section 48 is used in an external monitoring device such as a recorder. When the power supply frequency is normal, the value is "low", and when the frequency of the inverter type is high, the value is "high".

An example of a three-phase inverter DC type welding machine power source is shown in FIG. The three-phase AC input is rectified by the rectifier circuit 70, smoothed by the capacitor 72, and switched by the inverter 74. The switching frequency is currently about 1 kHz. The switching is controlled by the control circuit 76. This is transmitted to the secondary side through the welding transformer 78, rectified by the diode 80, and the spot welding gun 84 is energized through the secondary cable 82 to perform welding. The device of the present invention can be applied to such a DC power supply. A measurement cable for voltage detection may be connected between both ends of both the secondary cables 82. Since the device of the present invention is provided with a rectifier circuit in the measurement system, it can be used in the conventional AC type as well as in the case of the three-phase inverter DC type as described above. In this case, it is not necessary to consider the polarity.

[0028]

Since the apparatus of the present invention sets the welding current by the welding current setting device, a measuring cable for detecting the welding current is not required, and the number of measuring cables is reduced, so that it is easy to handle, and there is no disconnection of the cable. The trouble can be avoided as much as possible. In addition to AC type, it can also be used with DC type welding machine power supplies. In the present invention, the additional value of the secondary cable resistance value is set by the limit value setting device, and the deterioration is determined by counting the number of times the measured voltage exceeds the measured voltage, and thus the appropriate management limit is predicted and determined. Since it is possible to eliminate the improper work such as exchanging the secondary cable which is still usable, it is excellent in economical efficiency such as material saving and improvement of welding machine operating efficiency. Further, in the present invention, during welding energization, since the energizing indicator light is turned on, it is possible to confirm normal operation, it is possible to quickly detect trouble occurrences such as equipment malfunctions and disconnection of the measurement cable, and suddenly the secondary cable It is possible to avoid the occurrence of abnormal situations such as complete disconnection and the welding machine stopping.

Further, since the welding current setting device, the initial resistance setting device, and the limit value setting device can be composed of an operational amplifier and a digital switch, anyone can easily use them. Further, various alarms can be generated by the alarm output unit, deterioration status of the secondary cable can be monitored by the recorder output unit, and necessary data can be collected.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a secondary cable deterioration determination device according to the present invention.

FIG. 2 is an explanatory diagram showing an example of measured voltage in the case of 6 points per stroke.

FIG. 3 is a partial detailed circuit diagram of a deterioration determination unit.

FIG. 4 is a block diagram of an alarm output unit.

FIG. 5 is a block diagram of a recorder output unit.

FIG. 6 is a block diagram showing an example of a three-phase inverter DC welding machine power supply.

[Explanation of symbols]

 10a, 10b Secondary cable 12 Voltage detection part 14 Deterioration detection part 16 Operation confirmation part 18 Welding transformer 19 Spot welding gun 20 Detection cable 22a, 22b Input circuit 24a, 24b Rectification circuit 26 Welding current setting device 28a, 28b Initial resistance setting Units 30a, 30b Limit value setters 32a, 32b Comparators 34a, 34b Alarm counter 36 Trigger level setters 38a, 38b Comparator 40 AND gate 42 Energized indicator light 44 Hitting point counter 46 Alarm output unit 48 Recorder output unit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hisao Kojima 2-453 Chuo, Honjo City, Saitama Prefecture Honjo Factory, Fuji Kiko Co., Ltd. (72) Saburo Onuma 2-453 Chuo, Honjo, Saitama Prefecture No. Fuji Kiko Co., Ltd. Honjo Factory

Claims (4)

[Claims] 1. A voltage detection unit for detecting a voltage drop of each of a pair of secondary cables of a resistance welding machine, and a deterioration detection unit for detecting deterioration by comparing their measured voltages with a set limit value. An operation confirmation unit that confirms normal operation using the measured voltage is provided, and the voltage detection unit includes an input circuit connected between both ends of the pair of secondary cables, and a rectifier that rectifies an amplified output of the input circuit. The deterioration detection part consists of a common welding current setting device that sets the maximum welding current, an initial resistance setting device that sets the initial resistance value of each secondary cable, and the allowable limit value of each secondary cable. From the comparator when the measured voltage exceeds the limit voltage, and the limit value setter that sets each at a premium rate, the comparator that inputs each limit voltage set by them and each of the above-mentioned measured voltage, respectively. The comparison result An alarm counter that counts each of them is provided, and the operation confirmation unit has a trigger level setter that uses a voltage generated in the secondary cable by a current below the minimum welding current value as a trigger level, and the trigger level and both of the above. It is provided with two comparators each having a measured voltage as an input, an AND gate for taking a logical product of the outputs of both comparators, and an ON indicator lamp for displaying an ON state in response to the output of the AND gate. A secondary cable deterioration determination device for a resistance welding machine. 2. A latch circuit having an alarm output section connected to the outputs of two comparators of the deterioration detecting section, wherein the alarm output section is connected to the outputs of both comparators and is capable of switching a latch / normal operation. 2. An apparatus according to claim 1, further comprising: an alarm indicator lamp connected to each of the latch circuits, an OR gate for ORing outputs of the latch circuits, and a buzzer operated by an output of the OR gate. 3. A recorder output section connected to the outputs of both rectification circuits of the voltage detection section, wherein the recorder output section has a smoothing circuit capable of smoothing each rectified output and an output of both smoothing circuits, respectively. The device according to claim 1 or 2, comprising an output amplifier for DC amplification, and each smoothing circuit having a switch mechanism for increasing a time constant when the power supply frequency is low. 4. The apparatus according to claim 1, further comprising a dot number counter connected to the output of the AND gate of the operation confirmation unit.