Work machine and method for controlling work machine

Abstract

The present invention accurately calculates the weight of a load transported by a work device. This work machine comprises: a work device; a hydraulic cylinder that operates the work device on the basis of hydraulic oil; and a controller that, when the pressure fluctuation of the hydraulic oil supplied to the hydraulic cylinder is less than a prescribed value, calculates the weight of the load to be transported by the work device on the basis of the pressure of the hydraulic oil supplied to the hydraulic cylinder.

Description

Work machine and work machine control method

[0001] The present disclosure relates to a work machine and a method for controlling a work machine.

[0002] As an example of prior art, a work amount detection device for a hydraulic excavator is described in International Publication No. 03 / 033829 (Patent Document 1). In the hydraulic excavator, a load calculation means periodically calculates the weight of the transported load in the bucket while the transported load is being transferred, an average value calculation means calculates an average value of the transported load weight from a predetermined number of times ago to the present, and a standard deviation calculation means calculates a standard deviation of the transported load weight from the predetermined number of times ago to the present based on the average value. Then, a true load value determination means selects the smallest standard deviation from the multiple standard deviations calculated by the standard deviation calculation means during the period from the start to the end of transfer of the transported load to another location, and determines the average value used in calculating the smallest standard deviation as the true value of the transported load weight.

[0003] WO 03 / 033829

[0004] Hydraulic excavators excavate soil and dump it onto dump trucks. In order to manage the amount of soil loaded onto the dump truck, it is necessary to calculate and confirm the weight of the soil in the bucket before discharging it onto the dump truck. The weight of the soil must be calculated while the hoist swings, which raises the work equipment while swinging, from the time excavation is completed until the soil is discharged. However, due to the movement of the vehicle body, the calculated weight value is unstable and sufficient accuracy cannot be obtained.

[0005] The present disclosure proposes a work machine and a method for controlling a work machine that can accurately calculate the weight of a load carried by the work machine.

[0006] According to the present disclosure, a work machine is proposed that includes a work implement, a hydraulic cylinder that operates the work implement based on hydraulic oil, and a controller that calculates the weight of a load carried by the work implement based on the pressure of the hydraulic oil supplied to the hydraulic cylinder when the pressure fluctuation of the hydraulic oil supplied to the hydraulic cylinder is smaller than a specified value.

[0007] According to the present disclosure, a control method for a work machine is proposed. The control method includes the following steps: a first step is to detect the pressure of hydraulic oil supplied to a hydraulic cylinder that operates the work machine; a second step is to calculate pressure fluctuations of the hydraulic oil; and a third step is to calculate the weight of a load carried by the work machine based on the pressure of hydraulic oil supplied to the hydraulic cylinder when the pressure fluctuations are smaller than a specified value.

[0008] According to the work machine and control method disclosed herein, the weight of a load carried by the work machine can be calculated with high accuracy.

[0009] FIG. 1 is a perspective view showing a schematic configuration of a hydraulic excavator. FIG. 2 is a block diagram showing a schematic configuration of the system of the work machine shown in FIG. 1. FIG. 3 is a schematic diagram of a work machine for explaining moment balance. FIG. 4 is a flowchart showing a control method for a work machine in an embodiment. FIG. 5 is a schematic diagram showing a first example of the timing for starting and determining calculation of an average payload value. FIG. 6 is a schematic diagram showing a second example of the timing for starting and determining calculation of an average payload value. FIG. 7 is a schematic diagram showing a third example of the timing for starting and determining calculation of an average payload value. FIG. 8 is a schematic diagram showing a fourth example of the timing for starting and determining calculation of an average payload value. FIG. 9 is a schematic diagram showing a fifth example of the timing for starting and determining calculation of an average payload value. FIG. 10 is a schematic diagram showing a sixth example of the timing for starting and determining calculation of an average payload value. FIG. 11 is a schematic diagram showing a seventh example of the timing for starting and determining calculation of an average payload value. FIG. 12 is a diagram showing the accuracy of payload calculation in Examples and Comparative Examples.

[0010] Hereinafter, the embodiments will be described with reference to the drawings. In the following description, the same parts and components are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed descriptions thereof will not be repeated. In the drawings, configurations may be omitted or simplified for the sake of convenience. It is also intended from the beginning that any configurations may be extracted from the embodiments and arbitrarily combined.

[0011] In the following description, the terms "up," "down," "front," "rear," "left," and "right" refer to directions relative to the operator seated in the driver's seat in the driver's cab 31.

[0012] <Configuration of Work Machine> Fig. 1 is a perspective view that shows a schematic configuration of a hydraulic excavator as an example of a work machine in the embodiment. As shown in Fig. 1, the hydraulic excavator 50 in the embodiment is a large hydraulic excavator. The hydraulic excavator 50 is, for example, a mining hydraulic excavator used in mines. The hydraulic excavator 50 mainly has a running body 35, a revolving body 30, and a work implement 40. The running body 35 and the revolving body 30 form a work vehicle main body.

[0013] The running body 35 has a pair of left and right track devices 36. Each of the pair of left and right track devices 36 has a track. The pair of left and right tracks are rotationally driven to cause the hydraulic excavator 50 to self-propel.

[0014] The rotating unit 30 is installed so as to be freely rotatable relative to the running unit 35. The rotating unit 30 can rotate around a rotation center. The rotating unit 30 mainly includes a cab 31, an engine room 32, a counterweight 33, and an access system 34.

[0015] The operator's cab 31 is disposed on the front left side (vehicle front side) of the revolving unit 30. A driver's seat for an operator is disposed in the internal space of the operator's cab 31.

[0016] The engine room 32 and the counterweight 33 are each located on the rear side (rear side of the vehicle) of the revolving unit 30. The engine room 32 houses an engine unit (engine, exhaust treatment structure, etc.). The upper part of the engine room 32 is covered by an engine hood. The counterweight 33 is located behind the engine room 32.

[0017] The access system 34 is disposed on a side, for example, the left side, of the rotating bed 30. The access system 34 is provided for an operator to enter the cab 31 from the ground and to exit the cab 31 to the ground.

[0018] The work implement 40 is supported on the front side of the revolving unit 30. The work implement 40 has, for example, a boom 41, an arm 42, a bucket 43, etc. The base end of the boom 41 is rotatably connected to the revolving unit 30 by a boom foot pin 47 (Figure 3). The base end of the arm 42 is rotatably connected to the tip of the boom 41 by a boom tip pin 48. The bucket 43 is rotatably connected to the tip of the arm 42 by an arm tip pin 49 (Figure 3; the portion where the bucket 43 is supported by the arm 42). The work implement 40 has the bucket 43 at its tip. The bucket 43 is an example of an attachment that is detachably mounted to the tip of the work implement 40.

[0019] The boom 41 can be driven by a boom cylinder 44. The arm 42 can be driven by an arm cylinder 45. The bucket 43 can be driven by a bucket cylinder 46. The boom cylinder 44, the arm cylinder 45, and the bucket cylinder 46 are hydraulic cylinders that operate the work implement 40 using hydraulic oil. The boom 41, the arm 42, and the bucket 43 are each driven by a hydraulic cylinder, thereby driving the work implement 40.

[0020] <Schematic Configuration of Work Machine System> Figure 2 is a block diagram showing a schematic configuration of the work machine system shown in Figure 1. The system in the embodiment is a system for calculating the weight of a load in a bucket 43. The system in the embodiment includes a hydraulic excavator 50 as an example of the work machine shown in Figure 1, and a controller 10 shown in Figure 2. The controller 10 may be mounted on the hydraulic excavator 50, or may be installed in a remote location away from the hydraulic excavator 50.

[0021] The bucket IMU (Inertial Measurement Unit) 11 is attached to a bucket link that connects the bucket cylinder 46 and the bucket 43. The bucket IMU 11 detects the acceleration of the bucket 43 in the front-to-back, left-to-right, and up-to-down directions, and the angular velocity of the bucket 43 around the front-to-back, left-to-right, and up-to-down directions. The angle of the bucket 43 with respect to the arm 42 (bucket angle A3; see FIG. 3 ) is calculated from the detection values ​​of the bucket IMU 11.

[0022] The bucket angle A3 may be detected by an angle sensor attached around the arm tip pin 49. The angle sensor may be a potentiometer or a rotary encoder. Alternatively, a bucket cylinder stroke sensor that detects the amount of displacement of a cylinder rod relative to the cylinder in the bucket cylinder 46 may be attached to the bucket cylinder 46, and the bucket angle A3 may be calculated from the detection value of the bucket cylinder stroke sensor.

[0023] The arm IMU 12 is attached to the arm 42. The arm IMU 12 detects the acceleration of the arm 42 in the front-rear, left-right, and up-down directions, and the angular velocity of the arm 42 around the front-rear, left-right, and up-down directions. The angle of the arm 42 with respect to the boom 41 (arm angle A2; see FIG. 3 ) is calculated from the detection values ​​of the arm IMU 12.

[0024] The arm angle A2 may be detected by an angle sensor attached around the boom tip pin 48. The angle sensor may be a potentiometer or a rotary encoder. Alternatively, an arm cylinder stroke sensor that detects the amount of displacement of the cylinder rod relative to the cylinder in the arm cylinder 45 may be attached to the arm cylinder 45, and the arm angle A2 may be calculated from the detection value of the arm cylinder stroke sensor.

[0025] The boom IMU 13 is attached to the boom 41. The boom IMU 13 detects the acceleration of the boom 41 in the forward / backward, left / right, and up / down directions, and the angular velocity of the boom 41 around the forward / backward, left / right, and up / down directions. From the detection values ​​of the boom IMU 13, the angle of the boom 41 with respect to the revolving unit 30 (boom angle A1; see FIG. 3 ) is calculated.

[0026] The boom angle A1 may be detected by an angle sensor attached to the periphery of the boom foot pin 47. The angle sensor may be a potentiometer or a rotary encoder. Alternatively, a boom cylinder stroke sensor that detects the amount of displacement of the cylinder rod relative to the cylinder in the boom cylinder 44 may be attached to the boom cylinder 44, and the boom angle A1 may be calculated from the detection value of the boom cylinder stroke sensor.

[0027] The rotating unit IMU 14 is attached to the rotating unit 30. The rotating unit IMU 14 measures the acceleration of the rotating unit 30 in the forward / backward, left / right, and up / down directions, and the angular velocity of the rotating unit 30 around the forward / backward, left / right, and up / down directions.

[0028] The boom cylinder bottom pressure sensor 15 is attached to the bottom side of the boom cylinder 44 and detects the pressure (bottom pressure) of the hydraulic oil in the cylinder bottom-side oil chamber of the boom cylinder 44. The boom cylinder head pressure sensor 16 is attached to the head side of the boom cylinder 44 and detects the pressure (head pressure) of the hydraulic oil in the cylinder head-side oil chamber of the boom cylinder 44.

[0029] The left working implement lever 17 and the right working implement lever 18 are disposed inside the cab 31. The left working implement lever 17 and the right working implement lever 18 are operated by an operator sitting in the cab 31. The left working implement lever 17 and the right working implement lever 18 are operated to operate the working implement 40 and the rotating body 30. The left working implement lever 17 and the right working implement lever 18 are, for example, electric operating levers. The left working implement lever 17 and the right working implement lever 18 may also be pilot hydraulic operating levers.

[0030] The left working implement lever 17 is located to the left of the driver's seat. An operator seated in the driver's seat grips the left working implement lever 17 with his left hand and operates the left working implement lever 17. The left working implement lever 17 operates the arm 42 and the rotating structure 30. The left working implement lever 17 receives input from the operator regarding the rotation direction of the rotating structure 30 and the up and down movement of the arm 42. Operation of the left working implement lever 17 in the left and right directions corresponds to the rotation of the rotating structure 30, and left and right rotation operations of the rotating structure 30 are executed in response to the left and right direction operation. Operation of the left working implement lever 17 in the front and rear directions corresponds to the movement of the arm 42, and upward and downward movement of the arm 42 is executed in response to the front and rear direction operation.

[0031] The right work implement lever 18 is located to the right of the driver's seat. An operator sitting in the driver's seat grips the right work implement lever 18 with his right hand and operates the right work implement lever 18. The boom 41 and the bucket 43 are operated by the right work implement lever 18. The right work implement lever 18 receives input from the operator regarding the up and down movement of the boom 41 and the up and down movement of the bucket 43. Operation of the right work implement lever 18 in the forward and backward directions corresponds to the movement of the boom 41, and the boom 41 is raised and lowered in response to the forward and backward operation. Operation of the right work implement lever 18 in the left and right directions corresponds to the movement of the bucket 43, and the bucket 43 is moved downward and upward in response to the left and right operation.

[0032] The above-described operation patterns of the left working implement lever 17 and the right working implement lever 18 are merely examples and are not intended to be limiting. The forward / backward and left / right operation of the left working implement lever 17 and the right working implement lever 18 may correspond to actions different from those described above.

[0033] Detection signals from the IMUs 11 to 14 and the pressure sensors 15, 16 are input to the controller 10. Detection signals indicating the amount of operation of the work implement levers 17, 18 are input to the controller 10. The controller 10 is, for example, a computer, a server, a mobile terminal, or the like, and may also be a CPU (Central Processing Unit).

[0034] <Calculation of Weight of Load in Bucket 43> A method for calculating the weight of a load carried by the work implement 40 will now be described. Figure 3 is a schematic diagram of the work implement 40 for explaining moment balance. As shown in Figure 3, in this embodiment, the current weight value W of the load in the bucket 43 is detected from the balance of each moment about the boom foot pin 47. Here, the balance of each moment about the boom foot pin 47 is expressed by the following equation (1).

[0035]

[0036] In equation (1), Mboomcyl is the moment around the boom foot pin 47 generated by the pressure of the hydraulic oil supplied to the boom cylinder 44. Mboom is the moment around the boom foot pin 47 due to the weight of the boom 41. Marm is the moment around the boom foot pin 47 due to the weight of the arm 42. Mbucket is the moment around the boom foot pin 47 due to the weight of the bucket 43. W is the weight of the current load in the bucket 43. L is the horizontal distance from the boom foot pin 47 to the center of gravity C4 of the load in the bucket 43. Here, the center of gravity C4 of the load when a load of the rated load is loaded in the bucket 43 is stored in the memory unit of the controller 10. W×L is the moment around the boom foot pin 47 due to the load in the bucket 43.

[0037] Mboomcyl is calculated from the load on the boom cylinder 44 (head pressure and bottom pressure; that is, the pressure of the hydraulic oil supplied to the boom cylinder 44). The head pressure of the boom cylinder 44 is detected by a boom cylinder head pressure sensor 16. The bottom pressure of the boom cylinder 44 is detected by a boom cylinder bottom pressure sensor 15. The controller 10 calculates the moment Mboomcyl about the boom foot pin 47 generated by the load on the boom cylinder 44 based on the head pressure and bottom pressure of the boom cylinder 44.

[0038] Mboom is calculated by multiplying the distance r1 between the center of gravity C1 of the boom 41 and the boom foot pin 47 by the weight M1 of the boom 41 (r1 × M1). The position of the center of gravity C1 of the boom 41 is calculated from the boom angle A1, etc. The weight M1 of the boom 41, etc. are stored in the memory unit of the controller 10.

[0039] Marm is calculated as the product (r2 × M2) of the distance r2 between the center of gravity C2 of the arm 42 and the boom foot pin 47 and the weight M2 of the arm 42. The position of the center of gravity C2 of the arm 42 is calculated from the arm angle A2, etc. The weight M2 of the arm 42, etc. are stored in the memory unit of the controller 10.

[0040] Mbucket is calculated as the product (r3 × M3) of the distance r3 between the center of gravity C3 of the bucket 43 and the boom foot pin 47 and the weight M3 of the bucket 43. The position of the center of gravity C3 of the bucket 43 is calculated from the bucket angle A3 and the like. The weight M3 of the bucket 43 and the like are stored in the storage unit of the controller 10.

[0041] In calculating the current weight value W in the bucket 43, the controller 10 calculates the boom angle A1, the arm angle A2, and the bucket angle A3 based on the detected values ​​of the bucket IMU 11, the arm IMU 12, and the boom IMU 13. Based on these boom angle A1, arm angle A2, and bucket angle A3, the controller 10 calculates the positions of the centers of gravity C1, C2, C3, and C4. The controller 10 calculates the distances r1, r2, and r3 between the centers of gravity C1, C2, and C3 and the boom foot pin 47.

[0042] The controller 10 reads out the weight M1 of the boom 41 from the storage unit, and calculates the product of the distance r1 and the weight M1 as the moment Mboom of the boom 41 about the boom foot pin 47. The controller 10 reads out the weight M2 of the arm 42 from the storage unit, and calculates the product of the distance r2 and the weight M2 as the moment Marm of the arm 42 about the boom foot pin 47. The controller 10 reads out the weight M3 of the bucket 43 from the storage unit, and calculates the product of the distance r3 and the weight M3 as the moment Mbucket of the bucket 43 about the boom foot pin 47.

[0043] The controller 10 reads from the storage unit the length of the boom 41, the length of the arm 42, and the center of gravity C4 of the load in the bucket 43 at the rated load. The controller 10 calculates the horizontal distance L from the boom foot pin 47 to the center of gravity C4 of the load based on the boom angle A1, arm angle A2, and bucket angle A3 calculated above, the lengths of the boom 41 and arm 42, and the center of gravity C4 of the load.

[0044] The controller 10 substitutes the moments Mboomcyl, Mboom, Marm, and Mbucket calculated above, and the distance L into the above equation (1). In this way, the controller 10 calculates the weight value W of the load currently loaded in the bucket 43. The weight value W of the load in the bucket 43 is calculated based on the load on the boom cylinder 44 and the attitude of the work implement 40.

[0045] The weight value W calculated as described above may be unstable depending on the behavior of the vehicle body, and sufficient accuracy may not be obtained. In this embodiment, a range in which the behavior of the vehicle body is stable is extracted so that the weight value W can be calculated with high accuracy. Figure 4 is a flowchart showing a control method for a work machine in this embodiment.

[0046] 4 , in step S1, the controller 10 calculates the instantaneous value of the weight value W of the load in the bucket 43 (hereinafter also referred to as the “payload”) in accordance with the above-mentioned equation (1). The calculation of the instantaneous value of the payload is always performed regardless of the operating status of the hydraulic excavator 50.

[0047] In step S2, the controller 10 calculates the standard deviation σp of the bottom pressure of the boom cylinder 44. The standard deviation is an example of an index that indicates the distance from the average value. The standard deviation is an index that indicates the degree of dispersion (variation) of numerical values ​​relative to the average. The standard deviation σp of the bottom pressure can be said to be an index that indicates the pressure fluctuation of the hydraulic oil supplied to the boom cylinder 44. The larger the standard deviation σp of the bottom pressure, the greater the variation.

[0048] The boom cylinder bottom pressure sensor 15 constantly detects the bottom pressure of the boom cylinder 44. The detection result of the bottom pressure of the boom cylinder 44 is constantly input from the boom cylinder bottom pressure sensor 15 to the controller 10. The controller 10 constantly calculates the standard deviation σp of the bottom pressure for a predetermined time prior to the current time. In this case, the predetermined time may be, for example, a time corresponding to one cycle of fluctuations in the bottom pressure. The predetermined time may be the period from one peak to the next peak of the fluctuating bottom pressure. The predetermined time may be determined in advance and stored in the controller 10. The controller 10 may also determine the predetermined time in real time.

[0049] The controller 10 may execute the calculation of the standard deviation σp of the bottom pressure while the hydraulic excavator 50 is performing hoist swing. The controller 10 may start the calculation of the standard deviation σp of the bottom pressure when it is determined in step S3 that hoist swing is being performed.

[0050] In step S3, the controller 10 determines whether the hydraulic excavator 50 is performing hoist rotation, in which the boom 41 is raised while the rotating body 30 is rotating. The controller 10 may determine whether hoist rotation is being performed based on the operation details of the left work implement lever 17 and the right work implement lever 18. The controller 10 may determine whether hoist rotation is being performed based on the detection results of the pressure of hydraulic oil supplied to the boom cylinder 44 and the rotation motor. The controller 10 may determine whether hoist rotation is being performed based on the detection results of the rotating body IMU 14 and the boom IMU 13.

[0051] If it is determined that hoist rotation is not being performed (NO in step S3), the determination in step S3 is repeated. The calculation of the average value of the payload is not performed and the process waits until hoist rotation is performed.

[0052] If it is determined that hoist rotation is being performed (YES in step S3), the process proceeds to step S4, where the controller 10 determines whether the standard deviation σp of the bottom pressure of the boom cylinder 44 is smaller than a threshold value. The threshold value of the standard deviation σp is pre-stored in the storage unit of the controller 10. The controller 10 reads out the threshold value from the storage unit. The controller 10 compares the standard deviation σp of the bottom pressure calculated in step S2 with the threshold value read out from the storage unit, and determines whether the standard deviation σp is smaller than the threshold value.

[0053] If it is determined that the standard deviation σp is smaller than the threshold value (YES in step S4), the process proceeds to step S5, where the controller 10 determines whether a certain time has elapsed since it was determined in step S3 that hoist rotation was being performed. The controller 10 has a timer that measures time. The controller 10 stores the time when it was determined in step S3 that hoist rotation was being performed. The controller 10 reads the current time from the timer and calculates the elapsed time from the time when it was determined that hoist rotation was being performed to the current time. The controller 10 reads the threshold value of the elapsed time (the above-mentioned "certain time") from the memory unit. The controller 10 determines whether the elapsed time from the time when it was determined that hoist rotation was being performed to the current time has reached the certain time.

[0054] If the certain time has not yet elapsed (NO in step S5), the process proceeds to step S6, where the controller 10 determines whether the standard deviation σp of the bottom pressure has changed from a value smaller than the threshold value to a value equal to or greater than the threshold value. The controller 10 compares the current standard deviation σp of the bottom pressure with the threshold value read from the memory unit, and determines whether the standard deviation σp is equal to or greater than the threshold value. If the standard deviation σp is smaller than the threshold value (NO in step S6), the controller 10 repeats the determination in step S5 of whether the certain time has elapsed and the determination in step S6 of whether the standard deviation σp is equal to or greater than the threshold value.

[0055] If it is determined that the standard deviation σp of the bottom pressure is equal to or greater than the threshold value before the fixed time has elapsed (YES in step S6), the process proceeds to step S7, where the controller 10 resets the calculation of the payload. If it is determined in step S3 that hoist rotation is being performed, the controller 10 starts calculating the average value of the payload, and stops calculating the average value of the payload in step S7. The controller 10 returns the average value of the payload to the initial value (zero). The process returns to step S4, where it is determined whether the standard deviation σp is smaller than the threshold value.

[0056] In the determination of step S5, if it is determined that a certain time has elapsed and the state in which the standard deviation σp is smaller than the threshold value has continued for the certain time (YES in step S5), the controller 10 determines whether to determine the payload. In step S8, the controller 10 determines whether the standard deviation σp of the bottom pressure has become a value equal to or greater than the threshold value, whether a predetermined time has elapsed since it was determined in step S3 that hoist rotation has started, or whether the bucket 43 has started a dumping operation.

[0057] The controller 10 compares the current standard deviation σp of the bottom pressure with a threshold value read from the storage unit, and determines whether the standard deviation σp is equal to or greater than the threshold value.

[0058] The predetermined time is stored in the memory of the controller 10. The controller 10 stores the time at which it is determined in step S3 that hoist rotation is being performed. The controller 10 reads the current time from the timer and calculates the elapsed time from the time when hoist rotation started to the current time. The controller 10 determines whether the elapsed time from the time when hoist rotation started to the current time has reached the predetermined time.

[0059] The dumping operation of the bucket 43 is an operation of lowering the cutting edge of the bucket 43. When the bucket 43 performs the dumping operation, the load in the bucket 43 is discharged from the bucket 43. The controller 10 determines whether the operation of discharging the load from the bucket 43 has started.

[0060] The controller 10 may determine whether the bucket 43 has started the dumping operation based on the operation details of the right work implement lever 18. The controller 10 may determine whether the bucket 43 has started the dumping operation based on the detection result of the pressure of the hydraulic oil supplied to the bucket cylinder 46. The controller 10 may determine whether the bucket 43 has started the dumping operation based on the detection result of the bucket IMU 11.

[0061] If the standard deviation σp of the bottom pressure is smaller than the threshold value, a predetermined time has not yet elapsed since the start of hoist rotation, and the dumping operation of the bucket 43 has not started (NO in step S8), the determination of whether or not to determine the payload in step S8 is repeated.

[0062] In the judgment of step S8, if it is determined that the standard deviation σp has reached a value equal to or greater than the threshold value, or if it is determined that the bucket 43 has started a dumping operation, or if it is determined that a predetermined time has elapsed since the start of hoist rotation (YES in step S8), processing proceeds to step S9.

[0063] In step S9, the controller 10 determines the average value of the payload during the period in which the standard deviation σp of the bottom pressure is smaller than the threshold value as the final value of the payload. As described in step S1, calculation of the instantaneous value of the payload is constantly performed. The controller 10 determines the average value of the instantaneous values ​​of the payload calculated from the time when it is determined in step S4 that the standard deviation σp is smaller than the threshold value to the time when the determination in step S8 is YES as the final value of the payload.

[0064] If it is determined in step S4 that the standard deviation σp of the bottom pressure is greater than or equal to the threshold value (NO in step S4), the processing proceeds to step S10, and the controller 10 determines whether the bucket 43 has started a dumping operation or whether a predetermined time has elapsed since it was determined in step S3 that hoist rotation had started.

[0065] If the bucket 43 has not started the dumping operation and the predetermined time has not yet elapsed since the start of hoist rotation (NO in step S10), the process returns to step S4, where it is determined whether the standard deviation σp is smaller than the threshold value.

[0066] In the determination of step S10, if it is determined that the bucket 43 has started a dumping operation or if it is determined that a predetermined time has elapsed since the start of hoist rotation (YES in step S10), the process proceeds to step S11. The controller 10 sets the average value of the payload during hoist rotation as the final payload value. As described in step S1, calculation of the instantaneous value of the payload is constantly performed. The controller 10 sets the average value of the instantaneous values ​​of the payload calculated from the time it is determined in step S3 that hoist rotation has started to the time it is determined as YES in step S10 as the final payload value.

[0067] In this way, the series of processes for calculating the weight value W of the load in the bucket 43 is completed ("END" in FIG. 4).

[0068] 4, if it is determined in step S5 that the standard deviation σp has remained smaller than the threshold for a certain period of time, a determination is made in step S8 as to whether or not to determine the payload. The process of determining whether or not to determine the payload in step S8 does not necessarily have to be performed. If it is determined in step S5 that a certain period of time has elapsed, the process of determining the payload in step S9 may be performed subsequently.

[0069] In the example shown in Fig. 4, if it is determined in step S3 that hoist rotation is being performed, calculation of the average value of the payload is immediately started. A waiting time may be set when it is determined in step S3 that hoist rotation is being performed. A processing flow in which the determination in step S4 is made after the waiting time has elapsed may also be used. The timing at which calculation of the load weight is started may be delayed from the timing at which hoist rotation is started.

[0070] In the example shown in Fig. 4, in step S3, it is determined whether hoist rotation is being performed, in which the boom 41 is raised while the rotating body 30 is rotating. In addition to hoist rotation, even when the rotating body 30 is always only rotating, it is possible to accurately calculate the weight value W according to the processing flow shown in Fig. 4.

[0071] FIG. 5 is a schematic diagram showing a first example of the timing for starting calculation of the payload average value and determining the payload average value. The horizontal axis of the graphs shown in FIG. 5 and the subsequent FIGS. 6 to 11 represents time, and the vertical axis of the graphs represents the standard deviation σp of the bottom pressure of the boom cylinder 44. The dashed lines extending parallel to the horizontal axis in the graphs represent the threshold value of the standard deviation σp. The open circles in the graphs represent the timing for starting calculation of the payload average value. The closed circles in the graphs represent the timing for determining the payload. "Time X" in the graphs represents the "predetermined time" described in step S8 of FIG. 4. "Time Y" in the graphs represents the "fixed time" described in step S5 of FIG. 4.

[0072] In the example shown in Fig. 5, the standard deviation σp becomes smaller than the threshold value before it is determined that hoist rotation is being performed. At the time when it is determined that hoist rotation is being performed, the standard deviation σp is smaller than the threshold value.

[0073] In Fig. 5, the state in which the standard deviation σp is smaller than the threshold value continues for a certain period of time Y or more (YES in step S5 in Fig. 4), so a determination is made in step S8 as to whether to finalize the payload. The state in which the standard deviation σp is smaller than the threshold value continues until the bucket 43 starts the dumping operation or a predetermined period of time X has elapsed since the start of hoist rotation. In this case, the controller 10 determines the finalized payload value to be the average value obtained by averaging the instantaneous values ​​of the payload from the time the hoist rotation starts until the time the bucket 43 starts the dumping operation or the predetermined period of time X has elapsed since the start of hoist rotation (steps S8 and S9 in Fig. 4).

[0074] 6 is a schematic diagram showing a second example of the timing for starting and determining the payload average value. In the example shown in Fig. 6, when it is determined that hoist rotation is being performed, the standard deviation σp is greater than the threshold. After hoist rotation starts, the standard deviation σp changes from a value equal to or greater than the threshold to a value smaller than the threshold.

[0075] In Fig. 6, the state in which the standard deviation σp is smaller than the threshold value continues for a certain period of time Y or more (YES in step S5 in Fig. 4), so a determination is made in step S8 as to whether to finalize the payload. The state in which the standard deviation σp is smaller than the threshold value continues until the bucket 43 starts a dumping operation or a predetermined period of time X has elapsed since the hoist started swinging. In this case, the controller 10 determines the finalized value of the payload to be the average value obtained by averaging the instantaneous values ​​of the payload from the time when the standard deviation σp changes from a value equal to or greater than the threshold value to a value smaller than the threshold value until the bucket 43 starts a dumping operation or the predetermined period of time X has elapsed since the hoist started swinging (steps S8 and S9 in Fig. 4).

[0076] 7 is a schematic diagram showing a third example of the timing of starting calculation of the payload average value and determining the payload average value. In the example shown in Fig. 7, the standard deviation σp becomes smaller than the threshold value before it is determined that hoist rotation is being performed. At the time when it is determined that hoist rotation is being performed, the standard deviation σp is smaller than the threshold value.

[0077] In Fig. 7, the state in which the standard deviation σp is smaller than the threshold value continues for a certain time Y or more (YES in step S5 in Fig. 4), so a determination is made in step S8 as to whether to finalize the payload. The standard deviation σp changes from a value smaller than the threshold value to a value equal to or greater than the threshold value before the bucket 43 starts a dumping operation or before the predetermined time X has elapsed since the start of hoist rotation. In this case, the controller 10 determines the finalized payload value to be the average value obtained by averaging the instantaneous values ​​of the payload from the time when hoist rotation starts to the time when the standard deviation σp changes from a value smaller than the threshold value to a value equal to or greater than the threshold value (steps S8 and S9 in Fig. 4).

[0078] 8 is a schematic diagram showing a fourth example of the timing for starting and determining the calculation of the payload average value. In the example shown in Fig. 8, when it is determined that hoist rotation is being performed, the standard deviation σp is greater than the threshold. After hoist rotation starts, the standard deviation σp changes from a value equal to or greater than the threshold to a value smaller than the threshold.

[0079] In Fig. 8, the state in which the standard deviation σp is smaller than the threshold value continues for a certain period of time Y or more (YES in step S5 in Fig. 4), so a determination is made in step S8 as to whether to finalize the payload. The standard deviation σp changes from a value smaller than the threshold value to a value equal to or greater than the threshold value before the bucket 43 starts its dumping operation or before the predetermined period of time X has elapsed since the hoist started swinging. In this case, the controller 10 determines the finalized value of the payload to be the average value obtained by averaging the instantaneous values ​​of the payload from the time when the standard deviation σp changes from a value equal to or greater than the threshold value to the time when the standard deviation σp changes from a value smaller than the threshold value to a value equal to or greater than the threshold value (steps S8 and S9 in Fig. 4).

[0080] 9 is a schematic diagram showing a fifth example of the timing for starting and determining the calculation of the payload average value. In the example shown in FIG. 9, the standard deviation σp is greater than the threshold value when it is determined that hoist rotation is being performed. After hoist rotation starts, the standard deviation σp changes from a value equal to or greater than the threshold value to a value smaller than the threshold value, but before the fixed time Y has elapsed, the standard deviation σp returns to the threshold value or greater. In this case, the calculation of the payload average value is reset (steps S4 to S7 in FIG. 4).

[0081] In Fig. 9, the state in which the standard deviation σp is smaller than the threshold value continues for a certain time Y or more (YES in step S5 in Fig. 4), so a determination is made in step S8 as to whether to finalize the payload. The standard deviation σp changes from a value smaller than the threshold value to a value equal to or greater than the threshold value before the bucket 43 starts a dumping operation or before the predetermined time X has elapsed since the hoist started swinging. In this case, the controller 10 determines the final value of the payload to be the average value obtained by averaging the instantaneous values ​​of the payload from the point in time when the standard deviation σp changes from a value equal to or greater than the threshold value to the point in time when the standard deviation σp changes from a value smaller than the threshold value to a value equal to or greater than the threshold value (steps S8 and S9 in Fig. 4).

[0082] FIG. 10 is a schematic diagram showing a sixth example of the timing for starting calculation and determining the payload average value. In the example shown in FIG. 10, the standard deviation σp is greater than the threshold value when it is determined that hoist rotation is being performed. After hoisting is started, the standard deviation σp does not become smaller than the threshold value until the bucket 43 starts its dumping operation or a predetermined time X has elapsed since the start of hoist rotation (NO in step S4 in FIG. 4). In this case, the controller 10 determines the average value of the payload during hoist rotation as the determined payload value. The controller 10 determines the determined payload value as the average value obtained by averaging the instantaneous values ​​of the payload from the start of hoist rotation until the bucket 43 starts its dumping operation or the predetermined time X has elapsed since the start of hoist rotation (steps S10 and S11 in FIG. 4).

[0083] 11 is a schematic diagram showing a seventh example of the timing for starting and determining the calculation of the payload average value. In the example shown in FIG. 11, the standard deviation σp is greater than the threshold value when it is determined that hoist rotation is being performed. After hoist rotation starts, the standard deviation σp changes from a value equal to or greater than the threshold value to a value smaller than the threshold value, but before the fixed time Y has elapsed, the standard deviation σp returns to the threshold value or greater. In this case, the calculation of the payload average value is reset (steps S4 to S7 in FIG. 4).

[0084] 11, the state in which the standard deviation σp is smaller than the threshold value does not continue for a certain time Y or more from the start of hoist rotation until the bucket 43 starts its dumping operation or a predetermined time X has elapsed since the start of hoist rotation. In this case, the controller 10 sets the average value of the payload during hoist rotation as the final value of the payload. The controller 10 sets the average value of the instantaneous values ​​of the payload from the start of hoist rotation until the bucket 43 starts its dumping operation or until the predetermined time X has elapsed since the start of hoist rotation as the final value of the payload (steps S10 and S11 in FIG. 4).

[0085] <Functions and Effects> Although some of the description overlaps with the above description, the characteristic configuration and functions and effects of this embodiment can be summarized as follows.

[0086] As shown in Fig. 3, the controller 10 calculates the weight of the load carried by the work implement 40 based on the pressure of the hydraulic oil supplied to the boom cylinder 44. As shown in Figs. 4 to 9, the controller 10 calculates the weight of the load carried by the work implement 40 when the pressure fluctuation of the hydraulic oil supplied to the boom cylinder 44 is smaller than a specified value.

[0087] The pressure of the hydraulic oil supplied to the boom cylinder 44 has a large effect on the weight of the load carried by the work implement 40. Focusing on the pressure fluctuations of the hydraulic oil, the standard deviation σp is used as an index of pressure variation. If the variation in hydraulic pressure is small, the fluctuation in the calculated value of the load weight is also small, so the load weight can be calculated stably. By calculating the load weight when the hydraulic oil pressure is stable, the weight of the load carried by the work implement 40 can be calculated with high accuracy.

[0088] 4, the controller 10 may constantly calculate the instantaneous weight of the load and calculate the weight of the load by averaging the instantaneous values. By calculating the weight of the load as an average value that smooths out the temporal variation of the instantaneous weight values, the weight of the load can be calculated more accurately.

[0089] 4 to 9, the controller 10 may determine whether to determine the weight of the load when the pressure fluctuation of the hydraulic oil remains smaller than a specified value for a certain period of time. In this way, the weight of the load can be determined when the pressure of the hydraulic oil is stable.

[0090] As shown in Figures 4 and 9, the controller 10 may reset the calculation of the load weight if the hydraulic oil pressure fluctuation exceeds a specified value before a certain period of time has elapsed. If the hydraulic oil pressure fluctuation becomes smaller than the specified value and then increases to the specified value again in a short period of time, the load weight calculated up to that point is not used. When the hydraulic oil pressure fluctuation again becomes smaller than the specified value, the load weight calculation is restarted. An unstable calculation result from a short period of time is not determined as the load weight. In this way, the load weight can be calculated reliably and accurately.

[0091] 4 and 7 to 9, the controller 10 may determine the weight of the load when the pressure fluctuation of the hydraulic oil changes from a value smaller than a specified value to a value equal to or greater than the specified value. By calculating the weight of the load when the pressure fluctuation of the hydraulic oil is smaller than the specified value and determining the weight of the load when the pressure fluctuation of the hydraulic oil increases to a value equal to or greater than the specified value, the weight of the load can be calculated with high accuracy when the pressure of the hydraulic oil is stable.

[0092] 4, 6, 8-9, the controller 10 may start calculating the weight of the load when the pressure fluctuation of the hydraulic oil changes from a value equal to or greater than a specified value to a value smaller than the specified value, thereby ensuring that the weight of the load can be calculated when the pressure of the hydraulic oil is stable.

[0093] 4 to 11 , the controller 10 may calculate the weight of the load during hoist rotation in which the rotating body 30 rotates and the work machine 40 rises. By calculating the weight of the load during hoist rotation from the time when the hydraulic excavator 50 completes excavation to scoop the load into the bucket 43 until the time when the load is unloaded onto a loading machine such as a dump truck, the weight of the load can be calculated with high accuracy.

[0094] 4 to 5 and 7, the controller 10 may start calculating the weight of the load when the hoist starts rotating. In this way, it is possible to reliably calculate the weight of the load while the hoist is rotating.

[0095] 4 to 11, the controller 10 may determine the weight of the load when a predetermined time has elapsed since the start of hoist rotation. By setting the timing for determining the weight of the load in this manner, the weight of the load can be determined early and the weight of the load can be calculated in a short time.

[0096] 4 to 11 , the controller 10 may determine the weight of the load in the bucket 43 when starting the operation of unloading the load from the bucket 43. When the load starts to be unloaded from the bucket 43, the weight of the load in the bucket 43 fluctuates. By determining the weight of the load in the bucket 43 for the period up to the time the load is unloaded from the bucket 43, excluding the time period in which the weight of the load fluctuates, the weight of the load can be calculated more accurately.

[0097] In the embodiment, an example has been described in which the hydraulic excavator 50 is equipped with a bucket 43 as an attachment at the tip of the work implement 40, and the weight of a load in the bucket 43 is calculated. The attachment is not limited to the bucket 43, and other types of attachments may be attached to the tip of the work implement 40 depending on the type of work. For example, the attachment may be a lifting magnet, and in this case, the load carried by the work implement 40 may be a magnetic body that is attracted to and held by the lifting magnet.

[0098] In the embodiment, an example has been described in which the work machine is a hydraulic excavator 50. The work machine is not limited to the hydraulic excavator 50, and may be another type of work machine that has a work implement capable of transporting a load and a hydraulic cylinder that operates the work implement. For example, the work machine may be a loading shovel, a tire-powered excavator, a wheel loader, a skid steer loader, or the like.

[0099] <Additional Notes> The above description includes the following additional features.

[0100] (Supplementary Note 1) A work machine comprising: a work machine; a hydraulic cylinder that operates the work machine based on hydraulic oil; and a controller that calculates the weight of a load carried by the work machine based on the pressure of the hydraulic oil supplied to the hydraulic cylinder when pressure fluctuations of the hydraulic oil supplied to the hydraulic cylinder are smaller than a specified value.

[0101] (Supplementary Note 2) The work machine according to Supplementary Note 1, wherein the controller constantly calculates an instantaneous value of the weight and calculates the weight by averaging the instantaneous values.

[0102] (Supplementary Note 3) The work machine according to Supplementary Note 1 or Supplementary Note 2, wherein the controller determines whether to confirm the weight when a state in which the pressure fluctuation is smaller than the specified value continues for a certain period of time.

[0103] (Supplementary Note 4) The work machine according to Supplementary Note 3, wherein the controller resets the calculation of the weight if the pressure fluctuation becomes equal to or greater than the specified value before the fixed time period has elapsed.

[0104] (Supplementary Note 5) The work machine according to any one of Supplementary Note 1 to Supplementary Note 4, wherein the controller determines the weight when the pressure fluctuation changes from a value smaller than the specified value to a value equal to or greater than the specified value.

[0105] (Supplementary Note 6) The work machine according to any one of Supplementary Note 1 to Supplementary Note 5, wherein the controller starts calculating the weight when the pressure variation changes from a value equal to or greater than the specified value to a value smaller than the specified value.

[0106] (Supplementary Note 7) The work machine according to any one of Supplementary Note 1 to Supplementary Note 6, further comprising a rotating body that rotates about a rotation center and supports the work implement, wherein the controller calculates the weight during hoist rotation in which the rotating body rotates and the work implement is raised.

[0107] (Supplementary Note 8) The work machine according to Supplementary Note 7, wherein the controller starts calculating the weight when the hoist rotation starts.

[0108] (Supplementary Note 9) The work machine according to Supplementary Note 7 or Supplementary Note 8, wherein the controller determines the weight when a predetermined time has elapsed since the start of the hoist rotation.

[0109] (Supplementary Note 10) The work machine according to any one of Supplementary Note 1 to Supplementary Note 9, wherein the work implement has a bucket at a tip, and the controller determines the weight of the load in the bucket when starting an operation to discharge the load from the bucket.

[0110] An example will be described below. Fig. 12 is a diagram showing the accuracy of payload calculation in an example and a comparative example. The horizontal axis of the three graphs shown in Fig. 12 is time. The vertical axis of the upper graph is the instantaneous value of payload. The vertical axis of the middle graph is the average value of payload. The vertical axis of the lower graph is the standard deviation σp of the bottom pressure of the boom cylinder 44.

[0111] As explained in steps S1 and S2 of Fig. 4, the calculation of the instantaneous value of the payload and the calculation of the standard deviation σp of the hydraulic pressure are always performed. As shown in Fig. 12, the calculation of the instantaneous value of the payload and the calculation of the standard deviation σp of the hydraulic pressure are performed before the hydraulic excavator 50 starts hoist swing, and the calculation of the instantaneous value of the payload and the calculation of the standard deviation σp of the hydraulic pressure are also performed when the bucket 43 starts the dumping operation or after the predetermined time X has elapsed since the start of hoist swing.

[0112] In the example, the final payload value was calculated as an average value obtained by averaging the instantaneous values ​​of the weight of the load carried by the work implement 40 during a period in which the pressure fluctuation of the hydraulic oil supplied to the boom cylinder 44 was smaller than a specified value, according to the flowchart shown in Fig. 4. In the comparative example, the final payload value was calculated as an average value obtained by averaging the instantaneous values ​​of the weight of the load from the time when hoist swing started until the time when the bucket 43 started its dumping operation or until a predetermined time X had elapsed since the start of hoist swing. The open and closed circles in Fig. 12 indicate the timing for starting calculation of the average payload value and the timing for determining the payload, respectively, as in Figs. 5 to 11.

[0113] As shown in Figure 12, the deviation between the confirmed value and the true value of the payload was smaller in the example and larger in the comparative example. In the time period immediately before the bucket 43 starts its dumping operation or the predetermined time X has elapsed since the start of hoist rotation, the standard deviation σp of the hydraulic pressure exceeds the threshold value, causing the calculated instantaneous value of the payload to decrease. In the comparative example, the average payload value was calculated including this time period, resulting in a large error. In contrast, in the example, the average payload was calculated only during time periods when the standard deviation σp of the hydraulic pressure was stable, excluding the above time period, thereby reducing the error and enabling more accurate calculation of the payload.

[0114] The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0115] 10 Controller, 11 Bucket IMU, 12 Arm IMU, 13 Boom IMU, 14 Swing unit IMU, 15 Boom cylinder bottom pressure sensor, 16 Boom cylinder head pressure sensor, 17 Left work implement lever, 18 Right work implement lever, 30 Swing unit, 31 Operator's cab, 35 Traveling unit, 40 Work implement, 41 Boom, 42 Arm, 43 Bucket, 44 Boom cylinder, 45 Arm cylinder, 46 Bucket cylinder, 47 Boom foot pin, 48 Boom tip pin, 49 Arm tip pin, 50 Hydraulic excavator.

Claims

1. A work machine comprising: a work machine; a hydraulic cylinder that operates the work machine based on hydraulic oil; and a controller that calculates the weight of a load carried by the work machine based on the pressure of the hydraulic oil supplied to the hydraulic cylinder when pressure fluctuations of the hydraulic oil supplied to the hydraulic cylinder are smaller than a specified value.

2. A work machine according to claim 1, wherein the controller constantly calculates an instantaneous value of the weight and calculates the weight by averaging the instantaneous values.

3. A work machine as set forth in claim 1, wherein said controller determines whether or not to confirm said weight when a state in which said pressure fluctuation is smaller than said specified value continues for a certain period of time.

4. A work machine according to claim 3, wherein said controller resets the calculation of said weight if said pressure fluctuation becomes equal to or exceeds said specified value before said fixed time has elapsed.

5. The work machine according to claim 1, wherein said controller determines said weight when said pressure fluctuation changes from a value smaller than said specified value to a value equal to or greater than said specified value.

6. A work machine according to claim 1, wherein the controller starts calculating the weight when the pressure fluctuation changes from a value equal to or greater than the specified value to a value smaller than the specified value.

7. The work machine according to claim 1, further comprising a rotating body that rotates about a rotation center and supports the work machine, wherein the controller calculates the weight during hoist rotation in which the rotating body rotates and the work machine is raised.

8. The work machine according to claim 7, wherein the controller starts calculating the weight when the hoist rotation starts.

9. The work machine of claim 7, wherein the controller determines the weight when a predetermined time has elapsed since the start of the hoist rotation.

10. The work machine of claim 1, wherein the work machine has a bucket at a tip, and the controller determines the weight of the load in the bucket when initiating an operation to unload the load from the bucket.

11. A method for controlling a work machine, comprising: detecting the pressure of hydraulic oil supplied to a hydraulic cylinder that operates a work machine; calculating the pressure fluctuation of the hydraulic oil; and, when the pressure fluctuation is smaller than a specified value, calculating the weight of a load carried by the work machine based on the pressure of the hydraulic oil supplied to the hydraulic cylinder.

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