JP2016078969A - Control circuit of electric hydraulic type grab bucket - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control circuit of an electric hydraulic type grab bucket, driven by a variable type hydraulic pump, and capable of adopting the grab bucket controlled for opening-closing by a pressure switch, without adding a new signal conductor.SOLUTION: A control circuit 14 of an electric hydraulic type grab bucket comprises a first circuit 14a provided in the grab bucket 1 and a second circuit 14b provided in an operation part M. The first circuit 14a comprises a signal output circuit 13 for outputting a detection signal D, while the oil temperature of a hydraulic fluid of the grab bucket 1 exceeds a predetermined temperature value or while delivery pressure of a hydraulic pump 9 for driving the grab bucket 1 exceeds a predetermined pressure value. A part between the signal output circuit 13 and the second circuit 14b is connected by one signal conductor.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a control circuit for an electro-hydraulic grab bucket that opens and closes the grab bucket by remote control.

  Conventionally, an electro-hydraulic grab that opens and closes a grab bucket by driving a hydraulic cylinder with a hydraulic pump by remote operation from an operation unit and switching a supply destination of hydraulic oil between a head side chamber and a rod side chamber of the hydraulic cylinder with a switching valve. Buckets are known (see, for example, Patent Document 1).

  When working using such an electrohydraulic grab bucket, the grab bucket is suspended by a crane or the like via a wire rope. And a hydraulic cylinder is driven with the hydraulic pressure from the hydraulic pump provided in the upper part of the grab bucket, and a grab bucket is opened and closed.

  The operation for opening and closing the grab bucket and the operation of the crane are performed by the controller of the operation unit installed on the ground. The controller and the grab bucket are connected with a cabtyre cable via a control panel.

  In such an electro-hydraulic grab bucket, in order to avoid danger caused by malfunction of the grab bucket and damage of the grab bucket and to enable automatic operation, various sensors are provided in the grab bucket and the detection thereof is performed. A signal is transmitted to the operation unit.

  For example, a signal from an oil temperature sensor that detects the temperature of hydraulic oil that opens and closes the grab bucket, a fall signal that is output from the fall sensor when the grab bucket is tilted more than a predetermined angle, and the like are sent from the grab bucket to the operation unit. Sent. At that time, since the operation unit exists on the ground side, the signal transmitted to the operation unit is transmitted from the grab bucket to the control panel of the operation unit via a cabtire cable, a movable cable, a fixed cable, and the like.

  In the case of an electrohydraulic grab bucket, when the hydraulic cylinder reaches the stroke end when the opening / closing of the grab bucket is completed, the hydraulic pressure of the hydraulic oil increases instantaneously. Therefore, when the grab bucket is opened and closed, it is necessary to detect the completion of the opening and closing, set the switching valve to the neutral position, and promptly shift to the idle circulation state in which the hydraulic oil is returned to the supply source.

  In this regard, when the hydraulic pump is of a fixed type, a relief valve is provided on the discharge side of the hydraulic pump, and the relief pressure is detected based on the overcurrent of the electric motor that drives the hydraulic pump. A method for detecting completion of opening and closing of a bucket is known (see, for example, Patent Document 2).

  On the other hand, if the hydraulic pump is of a variable type that can be expected to save energy, it will instantaneously reach a dead head state when the opening and closing of the grab bucket is completed, and the tilt angle becomes the minimum discharge amount, so it is supplied to the electric motor. The current also decreases instantly. For this reason, it is difficult to detect completion of opening and closing based on the current to the electric motor.

  Therefore, detection of completion of opening / closing of the grab bucket is performed based on the hydraulic pressure of the hydraulic oil discharged from the hydraulic pump. In this case, it is also necessary to send a signal from a pressure switch that operates when the detected value of the hydraulic sensor exceeds a predetermined value to the control panel via a cabtyre cable or the like.

JP 2006-240816 A Japanese Patent Publication No. S58-34623

  However, in the case of an existing crane, the cabtire cable or cable reel that connects the controller and the grab bucket often has no spare. For this reason, in order to additionally secure a signal line from the pressure switch, it is necessary to add a cabtyre cable or a cable reel.

  An object of the present invention is to provide an electro-hydraulic type that can easily employ a grab bucket that is driven by a variable hydraulic pump and is controlled to open and close by a pressure switch without adding a new signal line. It is to provide a control circuit for a grab bucket.

  The control circuit for the electro-hydraulic grab bucket of the present invention is a control circuit for the electro-hydraulic grab bucket that opens and closes the grab bucket by driving the hydraulic cylinder with a variable hydraulic pump by remote operation from the operation unit, The control circuit includes a first circuit provided in the grab bucket, a second circuit provided in the operation unit, and one signal line interposed between the first circuit and the second circuit. The first circuit includes an oil temperature sensor that detects an oil temperature of hydraulic oil in the hydraulic cylinder, a hydraulic sensor that detects a discharge pressure of the hydraulic pump, and a detection temperature of the oil temperature sensor is a predetermined temperature. A signal output circuit that outputs a detection signal to the second circuit via the signal line while the temperature value exceeds or while the detection pressure of the hydraulic sensor exceeds a predetermined pressure value, The control circuit includes the second When the road receives the detection signal, after a predetermined first time has elapsed, the supply of the hydraulic oil to the hydraulic cylinder is stopped and a first control is performed to reduce the hydraulic pressure of the hydraulic oil. When the second predetermined time longer than 1 hour is maintained, the second control is performed to prohibit the opening / closing operation of the grab bucket until the temperature detected by the oil temperature sensor falls below the predetermined temperature value. .

  In the electro-hydraulic grab bucket as in the present invention, the time when the temperature of the hydraulic oil rises and the detected temperature of the oil temperature sensor exceeds a predetermined temperature value is the detected pressure of the hydraulic sensor when the opening and closing of the grab bucket is completed. Is longer than the time over which the predetermined pressure value is exceeded. As the temperature detected by the oil temperature sensor exceeds a predetermined temperature value due to repeated continuous opening and closing operations of the grab bucket, in this case, the opening and closing operation of the grab bucket is prohibited and the temperature of the hydraulic oil is naturally set to a predetermined value. The prohibited state is maintained until the temperature falls below the temperature value.

  Therefore, in the present invention, the first control and the second control by the control circuit described above are performed based on the detection signal output from the signal output circuit.

  Therefore, when the detected signal of the hydraulic sensor exceeds the predetermined pressure value due to the completion of the opening / closing operation of the grab bucket, the first control is performed after the first time has passed and the hydraulic cylinder is turned on. The supply of the hydraulic oil is stopped, and the hydraulic pressure of the hydraulic oil is reduced. Thereafter, the detected pressure of the hydraulic sensor returns to a predetermined pressure value or less. As a result, the output of the detection signal is stopped, so the second control is not performed, and the shift to the open / close prohibited state for prohibiting the open / close operation of the grab bucket is not performed.

  On the other hand, when a detection signal is output because the detected temperature of the oil temperature sensor exceeds a predetermined temperature value, first, after the first time has elapsed, the first control is performed, The supply of hydraulic oil is stopped and the hydraulic pressure of the hydraulic oil is reduced. Thereafter, the detected pressure of the hydraulic sensor returns to a predetermined pressure value or less. As described above, the detected pressure of the hydraulic sensor is a predetermined pressure value during the time when the detected temperature of the oil temperature sensor exceeds the predetermined temperature value. Therefore, the output of the detection signal continues after that. And when said 2nd time passes, 2nd control is started and the opening / closing operation | movement of a grab bucket is prohibited until the detection temperature of an oil temperature sensor falls below the said predetermined temperature value. Note that the prohibition of opening / closing by the second control is performed in a state where the supply of hydraulic oil to the hydraulic cylinder is stopped and the hydraulic pressure of the hydraulic oil is reduced, so that the first control is performed before the second control. There is no.

  Further, the time when the detected pressure of the hydraulic sensor exceeds a predetermined pressure value may overlap with the time when the detected temperature of the oil temperature sensor exceeds a predetermined temperature value. In this case, the detection signal lasts for at least the time when the detected temperature of the oil temperature sensor exceeds the predetermined temperature value, that is, the second time or more, so that the detected temperature of the oil temperature sensor has the predetermined temperature value. As in the case where the detection signal is output due to exceeding, the control circuit performs the first control and the subsequent second control.

  In the above control by the control circuit, the detection signal is transmitted through one signal line as described above. For this reason, as this signal line, a signal line that has been conventionally provided to send a signal that the detected temperature of the oil temperature sensor has exceeded a predetermined temperature value from the first circuit of the grab bucket to the second circuit of the operation unit. Can be used. Therefore, it is necessary to add a new signal line while realizing the first control and the second control necessary for the grab bucket driven by the variable hydraulic pump and controlled to open and close based on the hydraulic pressure of the hydraulic oil. And can be easily adopted.

  In the present invention, the signal output circuit includes a first break contact that opens while a detected temperature of the oil temperature sensor exceeds a predetermined temperature value, and a detected pressure of the hydraulic sensor exceeds a predetermined pressure value. You may comprise by the series circuit with the open 2nd break contact. According to this, it is possible to easily configure a signal output circuit that outputs a detection signal while the detected temperature exceeds a predetermined temperature value or while the detected pressure exceeds a predetermined pressure value.

  In the present invention, the second circuit starts timing when the detection signal is received, and outputs a first signal indicating a timing for performing the first control when the predetermined first time has elapsed. A first timer, and a second timer that starts timing when the detection signal is received and outputs a second signal indicating a timing for performing the second control when the predetermined second time has elapsed. You may prepare.

  According to this, the control circuit can perform the above-described first control and second control based on the first signal output from the first timer and the second signal output from the second timer.

1 is a schematic configuration diagram of an electrohydraulic grab bucket according to an embodiment of the present invention. It is a figure which shows a part of hydraulic circuit in an electrohydraulic grab bucket. It is a figure which shows a part of control circuit in an electrohydraulic grab bucket.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. As shown in FIG. 1, an electrohydraulic grab bucket 1 to which the control circuit of the embodiment is applied is suspended by a crane 2 or the like via a wire rope 3 or the like. The grab bucket 1 is driven by an operator on the ground operating the controller 4 installed on the ground.

  That is, the grab bucket 1 is driven remotely by a controller 4 to drive a hydraulic cylinder (not shown) with a variable hydraulic pump, and the hydraulic oil is supplied from the hydraulic pump to a head of the hydraulic cylinder by a switching valve. It is opened and closed by switching between the side chamber and the rod side chamber.

  The controller 4 and the grab bucket 1 are connected via a control panel 5 via a cabtire cable 6 and the like. The controller 4 and the control panel 5 constitute an operation unit M. The cabtire cable 6 is adjusted in feeding amount by a cable reel 6a. The grab bucket 1 is opened and closed by the hydraulic pressure of hydraulic oil discharged by a hydraulic pump driven by an electric motor 7 provided on the upper part of the grab bucket 1.

  As shown in FIG. 2, the hydraulic drive circuit 8 of the grab bucket 1 is driven by an electric motor 7, and a variable hydraulic pump 9 that discharges hydraulic oil in an oil tank (not shown) to the oil passage side, a solenoid 10a, And a switching valve 10 for switching the oil passage by 10b.

  The switching valve 10 is a center bypass type and is a four-way, three-position type, and its valve position is switched to the position Pa when the solenoid 10a is excited, and is switched to the position Pb when the solenoid 10b is excited. When neither of the solenoids 10a and 10b is excited, the valve position is set to the neutral position Pc.

  An oil passage 11 from the hydraulic pump 9 to the switching valve 10 is branched into two oil passages 11 a and 11 b in the switching valve 10. The oil passages 11a and 11b are connected to left and right hydraulic cylinders (not shown) that open and close the grab bucket 1, respectively. When the valve position is set to the neutral position Pc, the oil passage 11 is connected to a hydraulic oil supply source and is disconnected from the oil passages 11a and 11b.

  In the grab bucket 1, when the hydraulic pump 9 is driven, an operator remotely operates the solenoids 10 a and 10 b of the switching valve 10 by the controller 4 (FIG. 1), and the hydraulic pressure of the grab bucket 1 through the oil passage 11. It is opened and closed by supplying hydraulic oil to the cylinder. The opening / closing drive of the grab bucket 1 can be stopped by operating the controller 4 to switch the valve position of the switching valve 10 to the neutral position Pc.

  In the oil passage 11 between the hydraulic pump 9 and the switching valve 10, in order to detect the limit of the opening and closing drive of the grab bucket 1, the pressure that is opened when the hydraulic oil pressure exceeds a predetermined pressure value A switch PS is provided. The opening / closing drive of the grab bucket 1 is controlled by the control circuit in accordance with the operation of the controller 4 by the operator. FIG. 3 shows a main part of the control circuit 14.

  As shown in FIG. 3, the control circuit 14 includes a first circuit 14 a that exists in the grab bucket 1 and a second circuit 14 b that exists in the control panel 5. The first circuit 14a and the second circuit 14b are connected by a cabtyre cable 6 (FIG. 1) or the like.

  The first circuit 14 a includes an electric motor 7 that drives the hydraulic pump 9, solenoids 10 a and 10 b of the switching valve 10, a fall detection sensor FS that outputs a fall signal when the grab bucket 1 is tilted by a predetermined angle or more, and a grab bucket A temperature sensor TH that operates when the temperature of one hydraulic oil exceeds a predetermined temperature value, and a pressure switch PS that operates when the hydraulic pressure in the oil passage 11 exceeds a predetermined hydraulic pressure value are included.

  The temperature sensor TH and the pressure switch PS are each configured to include an oil temperature sensor and a hydraulic pressure sensor, and a normally closed switch (break contact) corresponding to each. Each switch forms a series circuit as a first break contact and a second break contact, and when either the temperature sensor TH or the pressure switch PS operates, the series circuit is disconnected.

  That is, by a series circuit of a first break contact that opens while the detected temperature of the oil temperature sensor exceeds a predetermined temperature value and a second break contact that opens while the detected pressure of the hydraulic sensor exceeds a predetermined hydraulic value. The signal output circuit 13 is configured. The signal output circuit 13 is in a disconnected state while the detected temperature of the oil temperature sensor exceeds a predetermined temperature value or while the detected pressure of the oil pressure sensor exceeds a predetermined oil pressure value. A detection signal D is output.

  The second circuit 14b includes an auxiliary relay X11 that operates when the temperature sensor TH or the pressure switch PS operates, a first timer Tp and a second timer Tx that start timing according to the operation of the auxiliary relay X11, and a solenoid. An open switch S1 for energizing 10a to cause the grab bucket 1 to perform an opening operation and a close switch S2 for energizing the solenoid 10b to cause the grab bucket 1 to perform a closing operation are included.

  The first timer Tp starts timing when the detection signal D from the signal output circuit 13 is received, and after that, when a predetermined first time t1 has elapsed, the first timer Tp indicates the timing for performing first control described later. 1 signal A is output.

  The second timer Tx starts timing when it receives the detection signal D from the signal output circuit 13, and then, when a predetermined second time t2 longer than the predetermined first time t1 has elapsed, 2 The second signal B indicating the timing for performing the control is output.

  As the predetermined first time t1, for example, a time of 2 [seconds] or less is selected. For example, 30 [seconds] is selected as the predetermined second time t2.

  The first reason for selecting the second times t1 and t2 in this way is to enable the first signal A and the second signal B to be output according to the duration of the detection signal D. The second reason is that a period during which the temperature detected by the oil temperature sensor exceeds a predetermined temperature value (operation period of the temperature sensor TH) is a period during which the pressure detected by the hydraulic sensor exceeds a predetermined temperature value (pressure switch). This is because the operation period of PS is longer than, for example, 5 [seconds] and exceeds 30 [seconds], for example.

  The period during which the detected temperature of the oil temperature sensor exceeds the predetermined temperature value is so long that the detected temperature rises as the temperature of the hydraulic oil rises due to repeated open / close operation of the grab bucket 1. In this case, the opening / closing operation of the grab bucket 1 is prohibited, and the prohibited state is maintained until the operating oil is naturally cooled by the outside air and the detected temperature falls below a predetermined temperature value. .

  A signal is transmitted between the signal output circuit 13 and the auxiliary relay X11 of the second circuit 14b, indicating that the temperature detected by the oil temperature sensor, which the cabtire cable 6 originally has, exceeds a predetermined temperature value. Are connected through one signal line.

  In this configuration, when the controller 4 is operated by an operator to instruct the opening operation of the grab bucket 1, the opening switch S1 of the control circuit 14 is brought into a connected state. Thereby, the switching valve 10 is energized through the cabtyre cable 6 and the solenoid 10a is excited. Thereby, the valve position of the switching valve 10 becomes the position Pa, and the opening operation of the grab bucket 1 is started.

  When the opening operation is completed, the following control is performed based on the operation of the pressure switch PS of the signal output circuit 13. That is, when the opening operation is completed, the hydraulic pressure in the oil passage 11 is increased, and the discharge amount of the hydraulic pump 9 is minimized. When the hydraulic pressure exceeds a predetermined pressure value, the pressure switch PS of the signal output circuit 13 operates, and the detection signal D is transmitted from the signal output circuit 13 to the auxiliary relay X11 via the cabtyre cable 6.

  As a result, the auxiliary relay X11 operates and the first timer Tp and the second timer Tx start timing. The first timer Tp outputs a first signal A when measuring a predetermined first time t1. In response to this, the excitation of the solenoid 10a is stopped, the switching valve 10 is returned to the neutral position Pc, and the oil passage 11 is connected to the hydraulic oil supply source. That is, the control circuit 14 performs the first control for stopping the supply of the hydraulic oil to the hydraulic cylinder and reducing the hydraulic pressure of the hydraulic oil. By performing such control, an increase in the temperature of the hydraulic oil is suppressed.

  Note that when the oil passage 11 is connected to the hydraulic oil supply source, the oil pressure in the oil passage 11 is lowered, so that the pressure switch PS returns after a few seconds. The time from the start of the operation of the pressure switch PS to the return is within about 5 [seconds].

  The control circuit 14 operates in the same manner as the above-described opening operation of the grab bucket 1 even when the controller 4 performs an operation of closing the grab bucket 1. That is, when the grab bucket 1 is closed, the pressure switch PS and the auxiliary relay X11 are operated, and after the predetermined time t1 is counted by the first timer Tp, the switching valve 10 is returned to the neutral position Pc.

  However, the predetermined time t1 set in the first timer Tp in this case is slightly longer than in the case of the opening operation of the grab bucket 1. This is because the switching valve 10 is returned to the neutral position Pc later than in the opening operation, and the force is applied to the grab bucket 1 by the hydraulic cylinder for a longer time, so that the grab bucket 1 is securely closed.

  On the other hand, when the temperature of the hydraulic oil that drives the grab bucket 1 exceeds a predetermined temperature value and the temperature sensor TH operates, the control circuit 14 similarly detects that. That is, when the temperature sensor TH operates, the detection signal D is transmitted from the signal output circuit 13 to the auxiliary relay X11 through the cabtyre cable 6.

  In response to this, the auxiliary relay X11 operates, and the first timer Tp and the second timer Tx start timing. When the temperature sensor TH is operated, the operation state is considerably long and continues for, for example, 30 [seconds] or more. Therefore, the operation of the second timer Tx is stopped until a predetermined second time t2, for example, 30 [second]. It can be timed without any problems.

  The second timer Tx outputs the second signal B when measuring a predetermined second time t2. Based on the second signal B, the control circuit 14 performs the second control for prohibiting the opening / closing operation of the grab bucket 1 until the temperature of the hydraulic oil decreases. To prohibit the opening / closing operation, even when the operator instructs the controller 4 to open / close the grab bucket 1, the opening / closing operation of the grab bucket 1 is not performed, or the operator is prohibited from opening / closing the grab bucket 1. Display and sound output to indicate that there is. Only display and sound output may be used.

  In this case, since the first timer Tp also outputs the first signal A when the predetermined first time t1 is measured, the first control described above is performed before the second control. Note that the prohibition of opening / closing by the second control is performed in a state where the supply of hydraulic oil to the hydraulic cylinder is stopped and the hydraulic pressure of the hydraulic oil is reduced, so that the first control is performed before the second control. There is no.

  In addition, when duplication occurs in the operation period of the temperature sensor TH and the pressure switch PS, the first one according to the detection signal D output based on the operation of the temperature sensor TH and the pressure switch PS that has been operated first. The timer Tp and the second timer Tx start timing. Thereafter, the detection signal D lasts for a predetermined second time t2 or more set in the second timer Tx.

  Accordingly, in this case as well, as in the case where only the temperature sensor TH is operated, the first control is performed when a predetermined short time t1 has elapsed from the time when the detection signal D is output, and the predetermined long time is reached. The second control is started when t2 has elapsed.

  According to the present embodiment, the detection signal D is a signal line for transmitting a signal that the cabtyre cable 6 originally has that the temperature detected by the oil temperature sensor exceeds a predetermined temperature value. And transmitted instead of the signal. Based on the detection signal D, the control circuit 14 performs the first control to be performed when the opening / closing of the grab bucket 1 is completed and the second control to be performed when the temperature of the hydraulic oil rises to a predetermined temperature value or more. It can be carried out.

  Therefore, the grab bucket 1 driven by the variable hydraulic pump 9 and controlled to open and close based on the hydraulic pressure of the hydraulic oil can be easily adopted without the need to add a new signal line.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to this. For example, the signal output circuit 13 described above is not configured by a series circuit of break contacts (normally closed switches), but instead of a make contact (normally open) that is closed when an oil temperature sensor or a hydraulic sensor detects a value exceeding a predetermined pressure value. You may comprise by the parallel circuit of a switch.

  Also,

  DESCRIPTION OF SYMBOLS 1 ... Grab bucket, 9 ... Hydraulic pump, 10 ... Switching valve (solenoid valve), 14 ... Control circuit, 14a ... 1st circuit, 14b ... 2nd circuit, 13 ... Signal output circuit, 6 ... Cabtyre cable, M ... Operation unit, TH ... temperature sensor (oil temperature sensor, first break contact), PS ... pressure switch (hydraulic sensor, second break contact), Tp ... first timer, Tx ... second timer.

The control circuit for the electro-hydraulic grab bucket of the present invention is a control circuit for the electro-hydraulic grab bucket that opens and closes the grab bucket by driving the hydraulic cylinder with a variable hydraulic pump by remote operation from the operation unit, The control circuit includes a first circuit provided in the grab bucket, a second circuit provided in the operation unit, and one signal line interposed between the first circuit and the second circuit. The first circuit includes an oil temperature sensor that detects an oil temperature of hydraulic oil in the hydraulic cylinder, a hydraulic sensor that detects a discharge pressure of the hydraulic pump, and a detection temperature of the oil temperature sensor is a predetermined temperature. during exceeds the temperature value, or while the pressure detected by the oil pressure sensor exceeds a predetermined pressure value, and a signal output circuit which outputs a detection signal via the signal line to said second circuit, wherein Signal output circuit is conductive The signal line that is in a disconnected state is disconnected while the predetermined temperature value is exceeded or the predetermined pressure value is exceeded, or the signal line that is in a disconnected state is While the temperature value is exceeded or the predetermined pressure value is exceeded, the detection signal is output by being in a conductive state, and the control circuit is configured such that the second circuit is the detection signal. Is received after a lapse of a predetermined first time, the first control is performed to stop the supply of hydraulic oil to the hydraulic cylinder to reduce the hydraulic pressure of the hydraulic oil, and the detection signal is longer than the first time. The second control for prohibiting the opening / closing operation of the grab bucket is performed until the temperature detected by the oil temperature sensor falls below the predetermined temperature value when the second temperature is maintained.

Claims (3)

An electric hydraulic grab bucket control circuit that opens and closes the grab bucket by driving a hydraulic cylinder with a variable hydraulic pump by remote operation from an operation unit,
The control circuit includes a first circuit provided in the grab bucket, a second circuit provided in the operation unit, and one signal line interposed between the first circuit and the second circuit. Consists of
The first circuit includes an oil temperature sensor that detects an oil temperature of hydraulic oil in the hydraulic cylinder, a hydraulic sensor that detects a discharge pressure of the hydraulic pump, and a detection temperature of the oil temperature sensor exceeds a predetermined temperature value. A signal output circuit that outputs a detection signal to the second circuit via the signal line while the detection pressure of the hydraulic sensor exceeds a predetermined pressure value,
When the second circuit receives the detection signal, the control circuit performs a first control to stop the supply of hydraulic oil to the hydraulic cylinder and to reduce the hydraulic pressure of the hydraulic oil after a predetermined first time has elapsed. And when the detection signal lasts for a predetermined second time longer than the first time, the grab bucket opening and closing operation is prohibited until the temperature detected by the oil temperature sensor falls below the predetermined temperature value. A control circuit for an electro-hydraulic grab bucket characterized by performing control.   The signal output circuit includes a first break contact that opens while the detected temperature of the oil temperature sensor exceeds a predetermined temperature value, and a second break that opens while the detected pressure of the hydraulic sensor exceeds a predetermined pressure value. 2. The control circuit for an electro-hydraulic grab bucket according to claim 1, comprising a series circuit with a contact.   The second circuit starts timing when the detection signal is received, and outputs a first signal indicating a timing for performing the first control when the predetermined first time has elapsed. And a second timer that starts timing when the detection signal is received and outputs a second signal indicating a timing for performing the second control when the predetermined second time has elapsed. The control circuit for the electrohydraulic grab bucket according to claim 1 or 2.

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