JP2006138077A - Device for updating offset value of position sensor of construction machinery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device for updating an offset value of a position sensor of construction machinery, which can easily update the offset value of the position sensor, regardless of the surrounding environment for the installation of the construction machinery. <P>SOLUTION: The position sensor is provided in a hydraulic excavator 1 which is equipped with a boom 5, an arm 6 and a bucket 7, each having two operating limits, and encoders 21-23 for measuring rotational angles of them. The position sensor is equipped with pressure sensors 31 and 32 for detecting the two operating limits of the boom 5, pressure sensors 33 and 34 for detecting the two operating limits of the arm 6, and pressure sensors 35 and 36 for detecting the two operating limits of the bucket 7. An in-vehicle computer 41, which includes a determination means for determining whether or not each of the boom 5, the arm 6 and the bucket 7 is in an operating-limit state, on the basis of the result of detection by the pressure sensors 31-36, performs the offset value updating processing of each of the corresponding encoders 21-23, when the determination means determines that each of the boom 5, the arm 6 and the bucket 7 is in the operating-limit state. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an offset value updating apparatus for a position sensor of a construction machine, which is provided in a construction machine such as a hydraulic excavator and performs a process of updating an offset value of a position sensor that measures the position of a work member.

  A construction machine such as a hydraulic excavator has a front work machine including a plurality of work members such as a boom, an arm, and a bucket, and an operator operates each work member of the front work machine to perform a desired work such as excavation work. Work is to be done.

  In recent years, for example, in order to perform work with a hydraulic excavator more easily, accurately and quickly, a bucket tip position and posture are measured by a position sensor mounted on a joint forming a connecting portion of the working member, and the bucket tip position information And posture information are presented to the operator, and the bucket posture is controlled based on the measurement result.

  In this case, there is a potentiometer as a representative example of the position sensor. Such a potentiometer is mounted on the rotating part of the boom for measuring the angle of the boom with respect to the upper swing body of the excavator, is mounted on the rotating part of the arm for measuring the angle of the arm with respect to the boom, and In order to measure the angle of the bucket with respect to the arm, it is mounted on the rotating part of the bucket and outputs a signal proportional to each angle.

  By the way, when such a position sensor is provided, it is necessary to accurately set the offset value of each position sensor in order to eliminate the influence of individual differences between the position sensors and attachment errors. As a conventional technique for updating the offset value of such a position sensor, there is one disclosed in Patent Document 1.

In this prior art, the design standard value when the working device is set at a predetermined reference position is stored in the ROM, and when the line is attached, the working device is set at the reference position of the working device. The difference between the acquired detection value and the above-mentioned standard value is used as a correction value, that is, an offset value. In this prior art, the reference position of the work device is one of the two operation end positions of the work device.
Japanese Patent Laid-Open No. 3-70001

  For example, when applying the above-described conventional technology to a hydraulic excavator or the like, when updating the offset value of the position sensor, it is necessary to take a posture such as a state where the boom is fully raised, a state where the arm is fully dumped, a state where the bucket is fully dumped, etc. Disappear. However, depending on the surrounding environment where the offset value is updated, the predetermined reference posture as described above may not be obtained due to an obstacle or the like.

  That is, in the prior art, the linear offset value is updated only in one of the two operation limits, so if there is an obstacle near the corresponding one operation limit, the offset value is set. It may not be possible to update. As described above, the conventional technique has a problem that the offset value updating process of the sensor is restricted by the surrounding environment where the hydraulic excavator is installed.

  Also, recently, in order to measure the position with higher accuracy, an encoder is installed on the rotating part of each work member instead of a potentiometer to measure the rotation angle of the corresponding work member, or a stroke composed of a wire encoder. It is also practiced to mount a sensor on the rotating part of each working member and measure the stroke of a hydraulic cylinder that drives the working member. Such an encoder or stroke sensor is highly accurate, but unlike a potentiometer or the like that can measure the absolute position according to the angle, the relative value obtained by outputting a pulse proportional to the amount of change after power-on. In order to measure the position, the offset value must be updated every time when the power is turned on, that is, when the engine such as a hydraulic excavator is started. It has become.

  For this reason, when the arm's reference posture is fixed in a state where the arm is fully dumped, for example, as in the above-described prior art, when the work is started from a state where the arm is parked near the full cloud. In addition, once full dump must be operated. In other words, useless operations must be performed, and there is a concern that work efficiency may be reduced. This is especially true when the arm must always be parked near the full cloud, for example, as described above, due to the surrounding environment or the like.

  The present invention has been made from the above-described prior art, and its purpose is a position sensor for a construction machine that can easily update the offset value of the position sensor regardless of the surrounding environment in which the construction machine is installed. An offset value updating apparatus is provided.

  In order to achieve the above object, the present invention is provided in a work machine having a work member having a plurality of operation limits and a position sensor for measuring the position of the work member, and updates the offset value of the position sensor. In the offset value updating apparatus for the position sensor of the construction machine that performs the processing, a plurality of detection means capable of respectively detecting the plurality of operation limits of the work member, and a detection means of any one of the plurality of detection means Determination means for determining whether the working member is at the operation limit based on a detection result, and when the determination means determines that the work member is at the operation limit, the position sensor offset It is characterized in that processing for updating a value is performed.

  In the present invention configured as described above, the offset value of the position sensor can be updated at any operation limit among the plurality of operation limits of each work member via the plurality of detection means and determination means. When an obstacle or the like exists near one operation limit, the offset value of the position sensor can be updated using the other operation limit. For example, when the construction machine is parked at one operation limit or another operation limit, the position sensor can be updated at that position. That is, the offset value of the position line can be easily updated regardless of the surrounding environment where the construction machine is installed.

  Further, according to the present invention, in the above invention, the construction machine includes a hydraulic excavator including an upper swing body and a boom, an arm, and a bucket that respectively form the work members, and the position sensor is the upper swing A boom position sensor for measuring the relative position of the boom to the body, an arm position sensor for measuring the relative position of the arm with respect to the boom, and a bucket position sensor for measuring the relative position of the bucket with respect to the arm, A boom cylinder bottom pressure sensor for detecting a bottom pressure of a boom cylinder that forms a hydraulic cylinder that drives the boom, and a boom for detecting a rod pressure of the boom cylinder, the detection means being provided corresponding to the boom position sensor Corresponding to the cylinder rod pressure sensor and the above arm position sensor Corresponding to an arm cylinder bottom pressure sensor that detects a bottom pressure of an arm cylinder that forms a hydraulic cylinder that drives the arm, an arm cylinder rod pressure sensor that detects a rod pressure of the arm cylinder, and the bucket position sensor. The determination means includes a bucket cylinder bottom pressure sensor that detects a bottom pressure of a bucket cylinder that forms a hydraulic cylinder that drives the bucket, and a bucket cylinder rod pressure sensor that detects a rod pressure of the bucket cylinder. Is included in the in-vehicle computer, and it is determined whether the bottom pressure or the rod pressure of the corresponding hydraulic cylinder detected by each of the pressure sensors is equal to or higher than the relief pressure, and the position sensor corresponding to each of the pressure sensors It comprises means for determining whether the amount of change in output is less than or equal to a certain value, and when the judgment means determines that the amount of change in output is greater than or equal to the relief pressure and the amount of change in output is less than or equal to a certain value, the corresponding pressure It is characterized in that processing for updating the offset value of the position sensor corresponding to the sensor is performed.

  In the present invention configured as described above, the posture for updating the offset value of the position sensor related to each work member is not fixed to the stroke end on one side of the hydraulic cylinder that drives each work member, and This is possible at the stroke end.

  Further, the present invention is characterized in that, in the above invention, the position sensor comprises an encoder for measuring a relative angle of the working member.

  Furthermore, the present invention is characterized in that, in the above invention, the position sensor comprises a stroke sensor for detecting a stroke of the hydraulic cylinder that drives the working member.

  In the present invention, the offset value of the position sensor can be updated at each of the plurality of operation limits of the work member via the plurality of detection means and determination means. Regardless of this, it is possible to easily update the offset value of the position sensor, and it is possible to relax restrictions on the update of the offset value of the position sensor due to the surrounding environment as compared with the related art. In addition, the work can be started quickly after the offset value is updated, and the work efficiency can be improved as compared with the conventional case.

  The best mode for carrying out an offset value updating apparatus for a position sensor of a construction machine according to the present invention will be described below with reference to the drawings.

[Construction machine provided with this embodiment]
FIG. 1 is a perspective view showing a hydraulic excavator cited as an example of a construction machine provided with an embodiment of an offset value updating apparatus for a position sensor according to the present invention.

  The construction machine shown in FIG. 1 is a hydraulic excavator 1, and the hydraulic excavator 1 is provided on a lower traveling body 2, an upper revolving body 3 that is turnable on the lower traveling body 2, and an upper revolving body 3. The front work machine 4 is made up of. The front work machine 4 includes a work member, that is, a boom 5 that is provided on the upper swing body 3 so as to be rotatable in the vertical direction, and a work member, that is, an arm 6 that is provided at the tip of the boom 5 so as to be rotatable in the vertical direction. The arm 6 includes a working member, that is, a bucket 7 provided at the tip of the arm 6 so as to be rotatable in the vertical direction. These boom 5, arm 6, and bucket 7 are driven by expanding and contracting the boom cylinder 8, arm cylinder 9, and bucket cylinder 10. The upper swing body 3 is provided with a cab 11.

  In addition, the hydraulic excavator 1 is a boom position sensor that detects a boom angle that is a relative rotation angle between the upper swing body 3 and the boom 5, that is, between the boom encoder 21 and the boom 5 and the arm 6. Are provided with an arm encoder 22 having a relative rotation angle and a bucket encoder 23 having a relative rotation angle between the arm 6 and the bucket 7.

[Principal configuration of this embodiment]
FIG. 2 is a block diagram showing the main configuration of the present embodiment. As shown in FIG. 2, the hydraulic excavator 1 shown in FIG. 1 is provided corresponding to a boom position sensor, that is, a boom encoder 21, and detects a bottom pressure of a boom cylinder 8 that drives the boom 5. A sensor 31 and a boom cylinder rod pressure sensor 32 for detecting the rod pressure of the boom cylinder 8 are provided. Further, an arm cylinder bottom pressure sensor 33 that detects the bottom pressure of the arm cylinder 9 and an arm cylinder rod pressure sensor that detects the rod pressure of the arm cylinder 10 are provided corresponding to the arm position sensor, that is, the arm encoder 22. 34 is provided. A bucket cylinder bottom pressure sensor 35 that detects the bottom pressure of the bucket cylinder 10 that drives the bucket 7 and detects the rod pressure of the bucket cylinder 10 is provided corresponding to the bucket position sensor, that is, the bucket encoder 23. Pressure sensor 36.

  These pressure sensors 31 to 36 constitute a plurality of detection means capable of detecting a plurality of operation limits of the boom 5, the arm 6, and the bucket 7, that is, two operation limits, respectively.

  Furthermore, this embodiment is provided with the vehicle-mounted computer 41 including the determination means which determines whether each of the boom 5, the arm 6, and the bucket 7 is in an operation limit, and each position sensor, ie, the boom encoder 21, mentioned above, The arm encoder 22 and the bucket encoder 23 and the above-described detection means, that is, the pressure sensors 31 to 36 are connected to the in-vehicle computer 41. The in-vehicle computer 41 has a function of calculating the position of the tip of the bucket 7 and controlling the bucket 7 based on the detection results of the encoders 21 to 23 and the pressure sensors 31 to 36.

[In-vehicle computer processing overview]
FIG. 3 is a flowchart showing an outline of processing executed by the in-vehicle computer provided in the present embodiment.

  As shown in FIG. 3, in the in-vehicle computer 41, first, in step S1, processing for turning off the boom offset flag, the arm offset flag, the bucket offset flag, and the position calculation flag is performed. Next, an offset value update process is performed in step S2. Next, angle calculation processing is performed in step S3, and position calculation processing is performed in step S4. Thereafter, the process returns to step S3, and the processes of steps S3 and S4 are repeatedly performed.

[Overview of offset value update processing]
FIG. 4 is a flowchart showing the offset value update process of step S2 in the process shown in FIG.

  In the offset value update process, first, in step S21, it is determined whether or not the boom offset flag is OFF. If the determination result is YES, the process proceeds to step S22, and boom offset value update processing is executed. If the determination result of step S21 is NO, the process proceeds to step S23.

  In step S23, it is determined whether the arm offset flag is OFF. If the determination result is YES, the process proceeds to step S24, and an arm offset value changing process is executed. If the determination result of step S23 is NO, the process proceeds to step S25.

  In step S25, it is determined whether the bucket offset flag is OFF. If the determination result is YES, the process proceeds to step S26, and bucket offset value change processing is executed. If the determination result of step S25 is NO, the process proceeds to step S27.

  Next, in step S27, it is determined whether all the offset flags of the boom 5, the arm 6, and the bucket 7 are ON. If the determination result is yes, the position calculation flag is turned on in step S28. If the determination result of step S27 is NO, the process proceeds to step S29.

  In step S29, it is determined whether or not the position calculation flag is ON. If the determination result is YES, the offset value update process is terminated. If the determination result is NO, the process returns to step S21, and all the encoders 21 to 23 are returned. Repeat until the offset value update process is completed.

[Boom offset value update processing]
FIG. 5 is a flowchart showing the boom offset value update process of step S22 in the offset value update process shown in FIG.

  First, in step S211, it is determined whether or not the boom cylinder bottom pressure is equal to or greater than a threshold value, and whether the boom encoder output change (difference between the current value and the previous value) is equal to or less than the threshold value. Here, it is determined whether or not the boom 5 has reached the stroke end of the raising operation. Therefore, for example, the relief pressure is set as the threshold value of the boom cylinder bottom pressure, and the threshold value of the output change of the boom encoder 21 is set to, for example, zero or a value corresponding to the resolution.

  If the determination result is YES, that is, if the boom 5 has reached the stroke end of the raising operation, the process proceeds to step S222, where the maximum raising angle BMANGup of the boom 5 is substituted for the origin angle BMANGorg of the boom 5, and the boom encoder offset value is set. The current value of the boom encoder output is substituted into BMCNToffset, and the boom offset flag is turned ON. Thereby, the offset value update process of the boom encoder 21 is completed. Here, the maximum raising angle BMANGup of the boom 5 and the maximum lowering angle BMANdown of the boom 5, which will be described later, are the values shown in FIG. 9, and the stroke ends of the upper revolving unit 2, that is, the boom 5 raising and lowering operations with respect to the horizontal line, respectively. The angle at.

  If the determination result in step S221 is NO, the process proceeds to step S223, in which whether or not the rod pressure of the boom cylinder 8 is equal to or greater than the threshold value and the boom encoder output change (difference between the current value and the previous value) is equal to or less than the threshold value. judge. Here, it is determined whether or not the boom 5 has reached the stroke end of the lowering operation.

  If the determination result is YES, that is, if the stroke end of the lowering operation of the boom 5 has been reached, the process proceeds to step S224, and the maximum lowering angle BMANdown of the boom 5 is substituted into the origin angle BMANG0rg of the boom 5, and the boom encoder offset The current value of the boom encoder output is substituted for the value BMCNToffset, and the boom offset flag is turned ON. Thereby, the offset value update process of the boom encoder 21 is completed.

[Arm offset value update processing]
FIG. 6 is a flowchart showing the arm offset value update process of step S24 in the offset value update process shown in FIG.

  First, in step S241, it is determined whether the arm cylinder rod pressure is equal to or greater than a threshold value and the arm encoder output change (difference between the current value and the previous value) is equal to or less than the threshold value. Here, it is determined whether or not the arm 6 has reached the stroke end of the dump operation. Therefore, for example, the relief pressure is set as the threshold value of the arm cylinder bottom pressure, and for example, zero or a value corresponding to the resolution is set as the threshold value of the output change of the arm encoder 22.

  If the determination result is YES, that is, if the arm 6 has reached the stroke end of the dump operation, the process proceeds to step S242, and the maximum dump angle AMANGup of the arm 5 is substituted for the origin angle AMANGorg of the arm 6, and the arm encoder offset value The current value of the arm encoder output is substituted into AMCNToffset, and the arm offset flag is turned ON. Thereby, the offset value update process of the arm encoder 22 is completed. Here, the maximum dump angle AMANGup of the arm 6 and the maximum cloud angle AMANGdown of the arm 6 to be described later are values shown in FIG. 10, and the arm 6 relative to the line connecting the pivoting portion of the boom 5 and the pivoting portion of the arm 6. This is the angle at the stroke end of each dump operation.

  If the determination result in step S241 is NO, the process proceeds to step S243, and it is determined whether or not the bottom pressure of the arm cylinder 9 is equal to or greater than the threshold value and the arm encoder output change (difference between the current value and the previous value) is equal to or less than the threshold value. judge. Here, it is determined whether or not the arm 6 has reached the stroke end of the cloud operation.

  If the determination result is YES, that is, if the stroke end of the cloud operation of the arm 6 has been reached, the process proceeds to step S244, where the maximum cloud angle AMANGdown of the arm 6 is substituted for the origin angle AMANG0rg of the arm 6, and the arm encoder offset The current value of the arm encoder output is substituted into the value AMCNToffset, and the arm offset flag is turned ON. Thereby, the offset value update process of the arm encoder 22 is completed.

[Bucket offset value update processing]
FIG. 7 is a flowchart showing the bucket offset value update process in step S26 in the offset value update process shown in FIG.

  First, in step S261, it is determined whether or not the bucket cylinder rod pressure is equal to or greater than a threshold value and the bucket encoder output change (difference between the current value and the previous value) is equal to or less than the threshold value. Here, it is determined whether or not the bucket 7 has reached the stroke end of the dump operation. Accordingly, for example, the relief pressure is set as the threshold value of the bucket cylinder bottom pressure, and for example, zero or a value corresponding to the resolution is set as the threshold value of the output change of the bucket encoder 23.

  If the determination result is YES, that is, if the bucket 75 has reached the stroke end of the dump operation, the process proceeds to step S262, and the maximum dump angle BKANGup of the bucket 7 is substituted for the origin angle BKANGorg of the bucket 7, and the bucket encoder offset value Substitute the current value of the bucket encoder output in BKCNToffset, and turn on the bucket offset flag. Thereby, the offset value update process of the bucket encoder 23 is completed. Here, the maximum dump angle BKANGup of the bucket 7 and the maximum cloud angle BMANGdown of the bucket 7 to be described later are values shown in FIG. 10, and the bucket 7 has a line with respect to a line connecting the rotating part of the arm 6 and the rotating part of the bucket 7. This is the angle at the stroke end of each dump operation and cloud operation.

  If the determination result in step S261 is NO, the process proceeds to step S263, and whether or not the bottom pressure of the bucket cylinder 9 is equal to or higher than the threshold value and the bucket encoder output change (difference between the current value and the previous value) is equal to or lower than the threshold value. judge. Here, it is determined whether or not the bucket 7 has reached the stroke end of the cloud operation.

  If the determination result is YES, that is, if the stroke end of the cloud operation of the bucket 7 has been reached, the process proceeds to step S264, where the maximum cloud angle BKANGdown of the bucket 7 is substituted for the origin angle BKANG0rg of the bucket 7, and the bucket encoder offset The current value of the bucket encoder output is substituted for the value BKCNToffset, and the bucket offset flag is turned ON. Thereby, the offset value update process of the bucket encoder 23 is completed.

[Angle calculation processing]
FIG. 8 is a flowchart showing the angle calculation process of step S3 in the process shown in FIG.

  First, in step S231, the boom angle BMANG is calculated using the function Fbm from the boom origin angle BMANGorg, boom encoder offset value BMCNToffset, and boom encoder output current value BMCNT set in the boom offset value update process. Here, the function Fbm is an expression showing the relationship between the count value of the encoder and the rotation angle.

  Next, in step S232, the arm angle AMANG is calculated using the function Fam from the arm origin angle AMANGorg, arm encoder offset value AMCNToffset, and arm encoder output current value AMCNT set in the arm offset value update processing. Here, the function Fam is an expression showing the relationship between the count value of the encoder and the rotation angle.

  Next, in step S233, the bucket angle BKANG is calculated using the function Fkm from the bucket origin angle BKANGorg, bucket encoder offset value BKCNToffset, and bucket encoder output current value BKCNT set in the bucket offset value update process. Here, the function Fkm is an expression showing the relationship between the count value of the encoder and the rotation angle.

  As described above, in this embodiment, the posture for updating the offset value of the position sensor related to each work member can be made at the stroke end on both sides without being fixed to the stroke end on one side of the corresponding hydraulic cylinder. Therefore, for example, when the work is started from a parking posture as shown in FIG. 12, the offset value update process can be completed by raising the boom 5, operating the arm 6 in the cloud, and operating the bucket 7 in the cloud direction. . When the work is started from the parking posture as shown in FIG. 13, the offset value update process can be completed by raising the boom 5, the arm 6 in the dump, and the bucket 7 in the dump direction. .

[Effect of this embodiment]
As described above, according to the present embodiment, the offset value update process can be easily realized regardless of the surrounding environment where the excavator 1 is installed, and the restriction on the offset value update process due to the surrounding environment can be relaxed. . Further, if the hydraulic excavator 1 is positioned at one of the operation limits, a desired work can be started immediately after the offset value update process, and the work efficiency can be improved.

[Other Embodiments of the Present Invention]
In addition, in the said embodiment, although the encoders 21-23 which measure a rotation angle are provided as a position sensor, it replaces with these encoders 21-23, and uses the wire-type encoder which measures the stroke of each cylinder 8-10. You may make it the structure which provided the stroke sensor which consists of. In this case, the strokes of the cylinders 8 to 10 are set as values corresponding to the rotation angles of the working members at the stroke ends shown in FIGS. Fbm, Fam, and Fbk are set as strokes for the count value of the stroke sensor, and calculation for obtaining the rotation angle of each working member from the obtained strokes of the respective cylinders 8 to 10 may be performed.

It is a perspective view which shows the hydraulic excavator mentioned as an example of the construction machine with which one Embodiment of the offset value update apparatus of the position sensor which concerns on this invention is provided. It is a block diagram which shows the principal part structure of this embodiment. It is a flowchart which shows the outline | summary of the process implemented with the vehicle-mounted computer with which this embodiment is equipped. It is a flowchart which shows the offset value update process of step S2 among the processes shown in FIG. It is a flowchart which shows the boom offset value update process of step S22 among the offset value update processes shown in FIG. It is a flowchart which shows the arm offset value update process of step S24 among the offset value update processes shown in FIG. It is a flowchart which shows the bucket offset value update process of step S26 among the offset value update processes shown in FIG. It is a flowchart which shows the angle calculation process of step S3 among the processes shown in FIG. It is a figure which shows the attitude | position in each stroke end of the boom with which the hydraulic shovel shown in FIG. 1 is equipped. It is a figure which shows the attitude | position in each stroke end of the arm with which the hydraulic shovel shown in FIG. 1 is equipped. It is a figure which shows the attitude | position in each stroke end of the bucket with which the hydraulic shovel shown in FIG. 1 is equipped. It is a figure which shows an example of the parking attitude | position of the hydraulic shovel shown in FIG. It is a figure which shows the other example of the parking attitude | position of the hydraulic shovel shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hydraulic excavator 2 Lower traveling body 3 Upper turning body 4 Front work machine 5 Boom (working member)
6 Arm (working member)
7 Bucket (working material)
8 Boom cylinder (hydraulic cylinder)
9 Arm cylinder (hydraulic cylinder)
10 Bucket cylinder (hydraulic cylinder)
11 cab 21 boom encoder (boom position sensor)
22 Arm encoder (arm position sensor)
23 Bucket encoder (bucket position sensor)
31 Boom cylinder bottom pressure sensor (detection means)
32 Boom cylinder rod pressure sensor (detection means)
33 Arm cylinder bottom pressure sensor (detection means)
34 Arm cylinder rod pressure sensor (detection means)
35 Bucket cylinder bottom pressure sensor (detection means)
36 Bucket cylinder rod pressure sensor (detection means)
41 Onboard computer

Claims (4)

An offset value of a position sensor of a construction machine that is provided in a work machine having a work member having a plurality of operation limits and a position sensor that measures the position of the work member, and that performs a process of updating the offset value of the position sensor. In the update device,
A plurality of detecting means capable of respectively detecting the plurality of operation limits of the working member;
Determination means for determining whether the working member is at the operation limit based on a detection result of any one of the plurality of detection means,
An offset value updating apparatus for a position sensor of a construction machine, which performs a process of updating an offset value of the position sensor when the determining means determines that the working member is at the operation limit. In the invention of claim 1,
The construction machine is composed of a hydraulic excavator including an upper swing body and a boom, an arm, and a bucket that form the working member,
The position sensor measures a relative position of the boom relative to the upper swing body, an arm position sensor that measures a relative position of the arm relative to the boom, and a relative position of the bucket relative to the arm. Including a bucket position sensor,
The detection means is
A boom cylinder bottom pressure sensor that detects a bottom pressure of a boom cylinder that is provided corresponding to the boom position sensor and forms a hydraulic cylinder that drives the boom, and a boom cylinder rod pressure sensor that detects a rod pressure of the boom cylinder When,
An arm cylinder bottom pressure sensor that detects a bottom pressure of an arm cylinder that is provided corresponding to the arm position sensor and forms a hydraulic cylinder that drives the arm, and an arm cylinder rod pressure sensor that detects a rod pressure of the arm cylinder When,
A bucket cylinder bottom pressure sensor for detecting a bottom pressure of a bucket cylinder provided corresponding to the bucket position sensor and forming a hydraulic cylinder for driving the bucket, and a bucket cylinder rod pressure sensor for detecting a rod pressure of the bucket cylinder Including
The determination means is included in the in-vehicle computer and determines whether or not the corresponding bottom pressure of the hydraulic cylinder or the rod pressure detected by each of the pressure sensors is equal to or higher than the relief pressure, and corresponds to each of the pressure sensors. Comprising means for determining whether the change in the output of the position sensor is below a certain value,
When it is determined by the determination means that the pressure is equal to or higher than the relief pressure and the change amount of the output is equal to or lower than a certain value, the offset value of the position sensor corresponding to the corresponding pressure sensor is updated. An offset value updating device for a construction machine position sensor. In the invention of claim 1,
The position sensor comprises an encoder that measures a relative angle of the working member, and an offset value update device for a position sensor of a construction machine. In the invention of claim 1,
The position sensor comprises a stroke sensor that detects a stroke of the hydraulic cylinder that drives the work member.

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