COMPUTING DEVICE AND COMPUTING METHOD

A hydraulic excavator includes a vehicular body, a boom bottom pin supported by the vehicular body, a boom rotatably coupled to the vehicular body by the boom bottom pin, a boom top pin attached to a tip end of the boom, an arm rotatably coupled to the boom by the boom top pin, an arm top pin attached to a tip end of the arm, and a bucket rotatably coupled to the arm by the arm top pin. The computing device calculates a weight of a load conveyed by a work implement based on any two equilibrium equations of an equation of moment equilibrium around the boom bottom pin, an equation of moment equilibrium around the boom top pin, and an equation of moment equilibrium around the arm top pin.

TECHNICAL FIELD

The present disclosure relates to a computing device and a computing method to calculate a weight of a load conveyed by a work implement.

BACKGROUND ART

Japanese Patent Laying-Open No. 10-245874 (PTL 1) discloses a computing device that calculates a load weight in a bucket based on a condition for equilibrium of force around a bucket support shaft in a hydraulic excavator including the bucket.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

The literature describes experimentally finding a position of a center of gravity of a load in a bucket. The position of the center of gravity of the load in the bucket, however, is not necessarily constant. Therefore, it has been difficult to enhance accuracy of a load weight with a technique to calculate the load weight based on the experimentally found position of the center of gravity.

The present disclosure proposes a computing device capable of accurately calculating a weight of a load conveyed by a work implement.

Solution to Problem

According to one aspect of the present disclosure, a computing device in a work machine including a work implement, the computing device calculating a weight of a load conveyed by the work implement, is proposed. The work machine includes a vehicular body, a boom bottom pin supported by the vehicular body, a boom rotatably coupled to the vehicular body by the boom bottom pin, a boom top pin attached to a tip end of the boom, an arm rotatably coupled to the boom by the boom top pin, an arm top pin attached to a tip end of the arm, and an attachment rotatably coupled to the arm by the arm top pin. The computing device calculates the weight of the load based on any two equilibrium equations of an equation of moment equilibrium around the boom bottom pin, an equation of moment equilibrium around the boom top pin, and an equation of moment equilibrium around the arm top pin.

According to one aspect of the present disclosure, a computing device in a work machine including a work implement, the computing device calculating a weight of a load conveyed by the work implement, is proposed. The work machine includes a vehicular body, a boom bottom pin supported by the vehicular body, a boom rotatably coupled to the vehicular body by the boom bottom pin, a boom top pin attached to a tip end of the boom, an attachment rotatably coupled to the boom by the boom top pin, and a pivot member supported by the boom and being rotatable with respect to the boom together with the attachment. The computing device calculates the weight of the load based on two equilibrium equations of an equation of moment equilibrium around the boom bottom pin and an equation of moment equilibrium around a center of rotation of the pivot member.

According to one aspect of the present disclosure, a computing device of a work machine including a work implement, the computing device calculating a weight of a load conveyed by the work implement, is proposed. The work machine includes a vehicular body, a boom bottom pin supported by the vehicular body, a boom having one end rotatably coupled to the vehicular body by the boom bottom pin, a boom top pin attached to the other end of the boom, an arm having one end rotatably coupled to the other end of the boom by the boom top pin, an arm top pin attached to the other end of the arm, an attachment having one end rotatably coupled to the other end of the arm by the arm top pin, a boom hydraulic cylinder that drives the boom to rotationally operate, an arm hydraulic cylinder that drives the arm to rotationally operate, an attachment hydraulic cylinder that drives the attachment to rotationally operate, a pressure sensor, and a position sensor. The pressure sensor includes at least two sensors of a boom pressure sensor that is attached to the boom hydraulic cylinder and outputs hydraulic oil pressure information of the boom hydraulic cylinder, an arm pressure sensor that is attached to the arm hydraulic cylinder and outputs hydraulic oil pressure information of the arm hydraulic cylinder, and an attachment pressure sensor that is attached to the attachment hydraulic cylinder and outputs hydraulic oil pressure information of the attachment hydraulic cylinder. The position sensor includes a boom position sensor that outputs boom information for obtaining a position of the boom with respect to the vehicular body, an arm position sensor that outputs arm information for obtaining a position of the arm with respect to the boom, and an attachment position sensor that outputs attachment information for obtaining a position of the attachment with respect to the arm. The computing device calculates the weight of the load in conveyance of the load based on any two relational expressions of a first relational expression generated from the hydraulic oil pressure information of the boom hydraulic cylinder and the boom information, a second relational expression generated from the hydraulic oil pressure information of the arm hydraulic cylinder and the arm information, and a third relational expression generated from the hydraulic oil pressure information of the attachment hydraulic cylinder and the attachment information. The pressure sensor includes at least two sensors corresponding to the two relational expressions.

According to one aspect of the present disclosure, a computing method of calculating a weight of a load conveyed by a work implement, for a work machine including the work implement, is proposed. The work implement includes as members, a boom that pivots around a first center of rotation, an arm that pivots around a second center of rotation, and an attachment that pivots around a third center of rotation. The computing method includes processing below. First processing is to establish, for the members, relational expressions of a motion around any two centers of rotation of the first center of rotation, the second center of rotation, and the third center of rotation. Second processing is to obtain a weight and a position of a center of gravity of each of the members. Third processing is to obtain positions of the members in conveyance of the load. Fourth processing is to obtain thrust corresponding to the motion in the relational expressions. Fifth processing is to compute horizontal distances between the positions of the centers of gravity of the members in conveyance of the load and corresponding ones of the first center of rotation, the second center of rotation, and the third center of rotation based on the positions of the centers of gravity and the positions of the members, respectively. Sixth processing is to compute the weight of the load conveyed by the work implement based on the relational expressions, the obtained information, and the computed information.

Advantageous Effects of Invention

According to the computing device and the computing method according to the present disclosure, a weight of a load conveyed by a work implement can accurately be calculated.

DESCRIPTION OF EMBODIMENTS

An embodiment will be described below with reference to the drawings. In the description below, the same components have the same reference characters allotted and their labels and functions are also identical. Therefore, detailed description thereof will not be repeated.

First Embodiment

<Construction of Work Machine>

FIG.1is a side view schematically showing a construction of a hydraulic excavator100as an exemplary work machine based on a first embodiment of the present disclosure. As shown inFIG.1, hydraulic excavator100in the present embodiment mainly includes a traveling unit1, a revolving unit2, and a work implement3. A vehicular body of hydraulic excavator100is constituted of traveling unit1and revolving unit2.

Traveling unit1includes a pair of left and right crawler belt apparatuses1a. Each of the pair of left and right crawler belt apparatuses1aincludes a crawler belt. As a pair of left and right crawler belts is rotationally driven, hydraulic excavator100travels.

Revolving unit2is provided as being revolvable with respect to traveling unit1. Revolving unit2mainly includes an operator's cab (cab)2a, an operator's seat2b, an engine compartment2c, and a counterweight2d. Operator's cab2ais arranged, for example, on the forward left (on a front side of a vehicle) of revolving unit2. Operator's seat2bwhere the operator takes a seat is arranged in an internal space in operator's cab2a.

Each of engine compartment2cand counterweight2dis arranged on a rear side (on a rear side of the vehicle) of revolving unit2with respect to operator's cab2a. An engine unit (an engine, an exhaust treatment structure, and the like) is accommodated in engine compartment2c. An engine hood covers the top of engine compartment2c. Counterweight2dis arranged in the rear of engine compartment2c.

Work implement3is pivotably supported on the front side of revolving unit2, and for example, on the right of operator's cab2a. Work implement3includes, for example, a boom3a, an arm3b, a bucket3c, a boom cylinder4a, an arm cylinder4b, and a bucket cylinder4c. Boom3ahas a base end (one end) rotatably coupled to revolving unit2by a boom bottom pin5a. Arm3bhas a base end (one end) rotatably coupled to a tip end (the other end) of boom3aby a boom top pin5b. (One end of) bucket3cis rotatably coupled to a tip end (the other end) of arm3bby an arm top pin5c.

In the present embodiment, positional relation of portions of hydraulic excavator100will be described with work implement3being defined as the reference.

Boom3aof work implement3rotationally moves around boom bottom pin5awith respect to revolving unit2. A trace of movement of a specific portion of boom3a, for example, the tip end of boom3a, that pivots with respect to revolving unit2is in an arc shape, and a plane including the arc is identified. When hydraulic excavator100is two-dimensionally viewed from above, the plane is shown as a straight line. A direction of extension of this straight line is defined as a forward/rearward direction of the vehicular body of hydraulic excavator100or the forward/rearward direction of revolving unit2, and it is also simply referred to as the forward/rearward direction below. A lateral direction (direction of a vehicle width) of the vehicular body of hydraulic excavator100or the lateral direction of revolving unit2is a direction orthogonal to the forward/rearward direction in a plan view and it is also simply referred to as the lateral direction below. An upward/downward direction of the vehicular body of hydraulic excavator100or the upward/downward direction of revolving unit2is a direction orthogonal to the plane defined by the forward/rearward direction and the lateral direction and it is also simply referred to as the upward/downward direction below.

In the forward/rearward direction, a side where work implement3protrudes from the vehicular body is defined as the forward direction and a direction opposite to the forward direction is the rearward direction. A right side and a left side in the lateral direction when one faces the forward direction are defined as a right direction and a left direction, respectively. A side where the ground is located and a side where the sky is located in the upward/downward direction are defined as a lower side and an upper side, respectively.

The forward/rearward direction refers to the forward/rearward direction of an operator who sits in operator's seat2bin operator's cab2a. The lateral direction refers to the lateral direction of the operator who sits in operator's seat2b. The upward/downward direction refers to the upward/downward direction of the operator who sits in operator's seat2b. A direction in which the operator sitting in operator's seat2bfaces is defined as the forward direction and a direction behind the operator sitting in operator's seat2bis defined as the rearward direction. A right side and a left side at the time when the operator sitting in operator's seat2bfaces front are defined as the right direction and the left direction, respectively. A foot side of the operator who sits in operator's seat2bis defined as the lower side and a head side is defined as the upper side.

Boom3acan be driven by boom cylinder (boom hydraulic cylinder)4a. As a result of this drive, boom3acan pivot around boom bottom pin5ain the upward/downward direction with respect to revolving unit2. Arm3bcan be driven by arm cylinder (arm hydraulic cylinder)4b. As a result of this drive, arm3bcan pivot around boom top pin5bin the upward/downward direction with respect to boom3a. Bucket (attachment)3ccan be driven by bucket cylinder (attachment hydraulic cylinder)4c. As a result of this drive, bucket3ccan pivot around arm top pin5cin the upward/downward direction with respect to arm3b. Work implement3can thus be driven.

Boom bottom pin5ais supported by the vehicular body of hydraulic excavator100. Boom bottom pin5ais supported by a pair of vertical plates (not shown) of a frame of revolving unit2. Boom top pin5bis attached to the tip end of boom3a. Arm top pin5cis attached to the tip end of arm3b. Each of boom bottom pin5a, boom top pin5b, and arm top pin5cextends in the lateral direction. Boom bottom pin5ais also called a boom foot pin.

Work implement3includes a bucket link3d. Bucket link3dincludes a first link member3daand a second link member3db. A tip end of first link member3daand a tip end of second link member3dbare coupled to each other as being rotatable relative to each other with a bucket cylinder top pin3dcbeing interposed. Bucket cylinder top pin3dcis coupled to a tip end of bucket cylinder4c. Therefore, first link member3daand second link member3dbare coupled to bucket cylinder4cwith the pin being interposed.

First link member3dahas a base end rotatably coupled to arm3bwith a first link pin3ddbeing interposed. Second link member3dbhas a base end rotatably coupled to a bracket at a root of bucket3cwith a second link pin3debeing interposed.

A pressure sensor6ais attached to a head side of boom cylinder4a. Pressure sensor6acan detect a pressure (a head pressure) of hydraulic oil within a cylinder-head-side oil chamber40A of boom cylinder4a. A pressure sensor6bis attached to a bottom side of boom cylinder4a. Pressure sensor6bcan detect a pressure (a bottom pressure) of hydraulic oil within a cylinder-bottom-side oil chamber40B of boom cylinder4a. Pressure sensors6aand6boutput hydraulic oil pressure information defined by the head pressure and the bottom pressure to a controller10which will be described later.

A pressure sensor6cis attached to a head side of arm cylinder4b. Pressure sensor6ccan detect a pressure (a head pressure) of hydraulic oil within a cylinder-head-side oil chamber of arm cylinder4b. A pressure sensor6dis attached to a bottom side of arm cylinder4b. Pressure sensor6dcan detect a pressure (a bottom pressure) of hydraulic oil within a cylinder-bottom-side oil chamber of arm cylinder4b. Pressure sensors6cand6doutput hydraulic oil pressure information defined by the head pressure and the bottom pressure to controller10which will be described later.

A pressure sensor6eis attached to a head side of bucket cylinder4c. Pressure sensor6ecan detect a pressure (a head pressure) of hydraulic oil within a cylinder-head-side oil chamber of bucket cylinder4c. A pressure sensor6fis attached to a bottom side of bucket cylinder4c. Pressure sensor6fcan detect a pressure (a bottom pressure) of hydraulic oil within a cylinder-bottom-side oil chamber of bucket cylinder4c. Pressure sensors6eand6foutput hydraulic oil pressure information defined by the head pressure and the bottom pressure to controller10which will be described later.

Boom3a, arm3b, and bucket3care provided with respective position sensors for obtaining information on positions and attitudes thereof. The position sensors output boom information, arm information, and attachment information for obtaining the respective positions of boom3a, arm3b, and bucket3cto controller10which will be described later.

A stroke sensor7ais attached to boom cylinder4aas a position sensor. Stroke sensor7adetects an amount of displacement of a cylinder rod4abwith respect to a cylinder4aain boom cylinder4aas boom information. A stroke sensor7bis attached to arm cylinder4bas a position sensor. Stroke sensor7bdetects an amount of displacement of a cylinder rod in arm cylinder4bas arm information. A stroke sensor7cis attached to bucket cylinder4cas a position sensor. Stroke sensor7cdetects an amount of displacement of a cylinder rod in bucket cylinder4cas attachment information.

An angle sensor may be employed as the position sensor. An angle sensor9ais attached around boom bottom pin5a. An angle sensor9bis attached around boom top pin5b. An angle sensor9cis attached around arm top pin5c. Angle sensors9a,9b, and9cmay each be implemented by a potentiometer or a rotary encoder. Angle sensors9a,9b, and9coutput information on an angle of rotation of boom3aand the like (boom information, arm information, and attachment information) to controller10which will be described later.

As shown inFIG.1, in a side view, an angle formed between a straight line (shown with a chain double dotted line inFIG.1) that passes through boom bottom pin5aand boom top pin5band a straight line (shown with a dashed line inFIG.1) that extends in the upward/downward direction is defined as a boom angle θb. Boom angle θb is normally an acute angle. Boom angle θb represents an angle of boom3awith respect to revolving unit2. Boom angle θb can be calculated from a result of detection by stroke sensor7aor a measurement value from angle sensor9a. In a side view, an angle formed between the straight line that passes through

boom bottom pin5aand boom top pin5band a straight line (shown with a chain double dotted line inFIG.1) that passes through boom top pin5band arm top pin5cis defined as an arm angle θa. Arm angle θa represents an angle of arm3bwith respect to boom3ain an area where arm3bpivots in the side view. Arm angle θa can be calculated from a result of detection by stroke sensor7bor a measurement value from angle sensor9b.

In a side view, an angle formed between the straight line that passes through boom top pin5band arm top pin5cand a straight line (shown with a chain double dotted line inFIG.1) that passes through arm top pin5cand a cutting edge of bucket3cis defined as a bucket angle θk. Bucket angle θk represents an angle of bucket3cwith respect to arm3bin an area where bucket3cpivots in the side view. Bucket angle θk can be calculated from a result of detection by stroke sensor7cor a measurement value from angle sensor9c.

An inertial measurement unit (IMU) may be employed as the position sensor. IMUs8a,8b,8c, and8dare attached to revolving unit2, boom3a, arm3b, and first link member3da, respectively. IMU8ameasures an acceleration of revolving unit2in the forward/rearward direction, the lateral direction, and the upward/downward direction and an angular velocity of revolving unit2around the forward/rearward direction, the lateral direction, and the upward/downward direction. IMUs8b,8c, and8dmeasure accelerations of boom3a, arm3b, and first link member3dain the forward/rearward direction, the lateral direction, and the upward/downward direction and angular velocities of boom3a, arm3b, and first link member3daaround the forward/rearward direction, the lateral direction, and the upward/downward direction, respectively.

Based on a difference between the acceleration measured by IMU8aattached to revolving unit2and the acceleration measured by IMU8battached to boom3a, an acceleration in extension and contraction of boom cylinder4a(an amount of change in speed of extension and contraction of boom cylinder4a) can be obtained. Boom angle θb, arm angle θa, and bucket angle θk may be calculated based on results of detection by IMUS8b,8c, and8d, respectively.

Though a stroke sensor of each hydraulic cylinder, an angle sensor of each link such as boom3a, and the IMU are given as exemplary position sensors, the position sensor may be a six-axis acceleration sensor. Some of the sensors may together be used as the position sensor. In addition to the sensors above, a global navigation satellite system (GNSS) may be used together as the position sensor.

<Schematic Configuration of System of Work Machine>

A schematic configuration of a system of the work machine will now be described with reference toFIG.2.FIG.2is a block diagram showing a schematic configuration of a system of the work machine shown inFIG.1.

As shown inFIG.2, the system in the present embodiment is a system for determining a load weight which is a weight of a load L (FIG.1) conveyed by work implement3. The system in the present embodiment includes hydraulic excavator100representing an exemplary work machine shown inFIG.1and controller10shown inFIG.2. Controller10may be mounted on hydraulic excavator100. Controller10may be provided outside hydraulic excavator100. Controller10may be arranged at a worksite of hydraulic excavator100or at a remote location distant from the worksite of hydraulic excavator100.

Engine31is, for example, a diesel engine. Output from engine31is controlled by control of an amount of injection of fuel into engine31by controller10.

A hydraulic pump33is coupled to engine31. As rotational drive force from engine31is transmitted to hydraulic pump33, hydraulic pump33is driven. Hydraulic pump33is a variable displacement hydraulic pump that includes, for example, a swash plate and varies a delivery capacity as an angle of tilt of the swash plate is varied. Some of oil delivered from hydraulic pump33is supplied as hydraulic oil to a direction control valve34. Some of oil delivered from hydraulic pump33is reduced in pressure by a pressure reduction valve and used as pilot oil.

Direction control valve34is a spool type valve that switches a direction of flow of hydraulic oil, for example, by moving a rod-shaped spool. As the spool moves in an axial direction, an amount of supply of hydraulic oil to an actuator40is regulated. Direction control valve34is provided with a spool stroke sensor that detects a distance of movement of the spool (spool stroke).

As supply and release of a hydraulic pressure to actuator40is controlled, an operation of work implement3, revolution of revolving unit2, and a traveling operation of traveling unit1are controlled. Actuator40includes boom cylinder4a, arm cylinder4b, and bucket cylinder4cshown inFIG.1and a travel motor and a not-shown revolution motor.

In the present example, oil supplied to actuator40for activating actuator40is referred to as hydraulic oil. Oil supplied to direction control valve34for activating direction control valve34is referred to as pilot oil. A pressure of pilot oil is referred to as a pilot hydraulic pressure.

Hydraulic pump33may deliver both of hydraulic oil and pilot oil as above. Hydraulic pump33may separately include a hydraulic pump (a main hydraulic pump) that delivers hydraulic oil and a hydraulic pump (pilot hydraulic pump) that delivers pilot oil.

An operation apparatus25is arranged in operator's cab2a. Operation apparatus25is operated by an operator. Operation apparatus25accepts an operation by the operator for driving work implement3. Operation apparatus25accepts an operation by the operator for revolving revolving unit2. Operation apparatus25provides an operation signal in response to an operation by the operator.

Operation apparatus25includes a first control lever25R and a second control lever25L. First control lever25R is arranged, for example, on the right of operator's seat2b. Second control lever25L is arranged, for example, on the left of operator's seat2b. Operations in front, rear, left, and right directions onto first control lever25R and second control lever25L correspond to biaxial operations.

For example, boom3aand bucket3care operated by operating first control lever25R. An operation onto first control lever25R in the forward/rearward direction corresponds, for example, to an operation of boom3a, and an operation to lower boom3aand an operation to raise boom3aare performed in accordance with the operation in the forward/rearward direction. An operation onto first control lever25R in the lateral direction corresponds, for example, to an operation of bucket3c, and an operation in a direction of excavation (upward) and a direction of dumping (downward) of bucket3cis performed in accordance with the operation in the lateral direction.

For example, arm3band revolving unit2are operated by operating second control lever25L. An operation in the forward/rearward direction onto second control lever25L corresponds, for example, to revolution of revolving unit2, and a right revolution operation and a left revolution operation of revolving unit2are performed in accordance with an operation in the forward/rearward direction. An operation onto second control lever25L in the lateral direction corresponds, for example, to an operation of arm3b, and the operation of arm3bin the direction of dumping (upward) and the direction of excavation (downward) is performed in accordance with the operation in the lateral direction.

Pilot oil delivered from hydraulic pump33and reduced in pressure by the pressure reduction valve is supplied to operation apparatus25. The pilot hydraulic pressure is regulated based on an amount of operation onto operation apparatus25.

Operation apparatus25and direction control valve34are connected to each other through a pilot oil channel450. Pilot oil is supplied to direction control valve34through pilot oil channel450. A spool of direction control valve34is thus moved in the axial direction to regulate a direction of flow and a flow rate of hydraulic oil supplied to boom cylinder4a, arm cylinder4b, and bucket cylinder4c, so that operations in the upward/downward direction of boom3a, arm3b, and bucket3care performed.

A pressure sensor36is arranged in pilot oil channel450. Pressure sensor36detects the pilot hydraulic pressure. A result of detection by pressure sensor36is provided to controller10. An amount of increase in pilot hydraulic pressure is different depending on an angle of tilt of each of control levers25L and25R from a neutral position. Contents of the operation onto operation apparatus25can be determined based on a result of detection of the pilot hydraulic pressure by pressure sensor36.

Detection signals from stroke sensors7ato7c, IMUs8ato8d, angle sensors9ato9c, and pressure sensors6ato6fare also provided to controller10.

Controller10may electrically be connected to each of stroke sensors7ato7c, IMUs8ato8d, angle sensors9ato9c, and pressure sensors6ato6fand36through wires, or may wirelessly communicate therewith. Controller10may be implemented, for example, by a computer, a server, or a portable terminal, or by a central processing unit (CPU).

Though operation apparatus25has been described above as being of a pilot hydraulic type, operation apparatus25may be an electrical operation apparatus. When operation apparatus25is electrical, an amount of operation onto each of first control lever25R and second control lever25L is detected, for example, by a potentiometer. The potentiometer is a displacement sensor that obtains an electrical (voltage) output in proportion to a mechanical position. A result of detection by the potentiometer is provided to controller10. Contents of operation onto operation apparatus25can be determined based on a result of detection by the potentiometer.

<Functional Block in Controller10>

A functional block in controller10will now be described with reference to FIG.3.FIG.3is a diagram showing a functional block within controller10shown inFIG.2.

As shown inFIG.3, a boom cylinder thrust calculator10aobtains a result of sensing by pressure sensors6aand6b. Specifically, boom cylinder thrust calculator10aobtains the head pressure of boom cylinder4asensed by pressure sensor6a. Boom cylinder thrust calculator10aobtains the bottom pressure of boom cylinder4asensed by pressure sensor6b. Boom cylinder thrust calculator10acalculates boom cylinder thrust Fboom based on the head pressure and the bottom pressure of boom cylinder4a.

Thrust is defined as force that moves an object in a direction of motion, and boom cylinder thrust Fboom is thrust generated by boom cylinder4athat rotates boom3arelatively to the vehicular body. Boom cylinder thrust Fboom is force applied in the direction of extension of boom cylinder4a. Boom cylinder thrust calculator10aoutputs calculated boom cylinder thrust Fboom to a load weight calculator10i.

An arm cylinder thrust calculator10bobtains a result of sensing by pressure sensors6cand6d. Specifically, arm cylinder thrust calculator10bobtains the head pressure of arm cylinder4bsensed by pressure sensor6c. Arm cylinder thrust calculator10bobtains the bottom pressure of arm cylinder4bsensed by pressure sensor6d. Arm cylinder thrust calculator10bcalculates arm cylinder thrust Farm based on the head pressure and the bottom pressure of arm cylinder4b.

Arm cylinder thrust Farm is thrust generated by arm cylinder4bthat rotates arm3brelatively to boom3a. Arm cylinder thrust Farm is force applied in the direction of extension of arm cylinder4b. Arm cylinder thrust calculator10boutputs calculated arm cylinder thrust Farm to load weight calculator10i.

A bucket cylinder thrust calculator10cobtains a result of sensing by pressure sensors6eand6f. Specifically, bucket cylinder thrust calculator10cobtains the head pressure of bucket cylinder4csensed by pressure sensor6e. Bucket cylinder thrust calculator10cobtains the bottom pressure of bucket cylinder4csensed by pressure sensor6f. Bucket cylinder thrust calculator10ccalculates bucket cylinder thrust Fbucket based on the head pressure and the bottom pressure of bucket cylinder4c.

Bucket cylinder thrust Fbucket is thrust generated by bucket cylinder4cthat rotates bucket3crelatively to arm3b. Bucket cylinder thrust Fbucket is force applied in the direction of extension of bucket cylinder4c. Bucket cylinder thrust calculator10coutputs calculated bucket cylinder thrust Fbucket to load weight calculator10i.

A boom angle calculator10dobtains information on boom angle θb from at least one sensor of stroke sensor7a, IMU8b, and angle sensor9a. Boom angle calculator10dcalculates boom angle θb based on the obtained information. Boom angle calculator10doutputs calculated boom angle θb to a gravity center position calculator10g.

An arm angle calculator10eobtains information on arm angle θa from at least one sensor of stroke sensor7b, IMU8c, and angle sensor9b. Arm angle calculator10ecalculates arm angle θa based on the obtained information. Arm angle calculator10eoutputs calculated arm angle θa to gravity center position calculator10g.

A bucket angle calculator10fobtains information on bucket angle θk from at least one sensor of stroke sensor7c, IMU8d, and angle sensor9c. Bucket angle calculator10fcalculates bucket angle θk based on the obtained information. Bucket angle calculator10foutputs calculated bucket angle θk to gravity center position calculator10g.

Various types of information such as a dimension, a weight, and a position of the center of gravity of each member that makes up work implement3are stored in a storage10j. Such various types of information may be inputted from an input portion11outside controller10into storage10j. Storage10jmay be arranged outside controller10, instead of being included in controller10.

Gravity center position calculator10gcalculates a position relative to boom bottom pin5a, of the center of gravity of each member that makes up work implement3such as boom3a, cylinder4aaof boom cylinder4a, or first link member3da. Gravity center position calculator10gcalculates the relative position of each member that makes up work implement3based on boom angle θb calculated by boom angle calculator10d, arm angle θa calculated by arm angle calculator10e, bucket angle θk calculated by bucket angle calculator10f, and the position of the center of gravity of each member that makes up work implement3, the position of the center of gravity being stored in storage10j.

Gravity center position calculator10gcalculates attitudes of boom3a, arm3b, and bucket3cwith boom bottom pin5abeing defined as the reference, based on boom angle θb, arm angle θa, and bucket angle θk. Gravity center position calculator10gcalculates a state (attitude and stroke) of other constituent members of work implement3based on the calculated attitudes. Gravity center position calculator10gcalculates the relative position of each member that makes up work implement3, with boom bottom pin5abeing defined as the reference, based on the result of calculation and the stored position of the center of gravity of each member.

A moment distance calculator10hcalculates a distance in a horizontal direction from boom bottom pin5ato the center of gravity of each member that makes up the work implement. Specifically, moment distance calculator10hcalculates a distance Xboom in the horizontal direction from boom bottom pin5ato the center of gravity of boom3a. Moment distance calculator10hcalculates a distance Xarm in the horizontal direction from boom bottom pin5ato the center of gravity of arm3b. Moment distance calculator10hcalculates a distance Xbucket in the horizontal direction from boom bottom pin5ato the center of gravity of bucket3c.

Moment distance calculator10hcalculates a distance XboomC in the horizontal direction from boom bottom pin5ato the center of gravity of a cylinder portion (cylinder4aa) of boom cylinder4a. Moment distance calculator10hcalculates a distance XboomCR in the horizontal direction from boom bottom pin5ato the center of gravity of a cylinder rod portion (cylinder rod4ab) of boom cylinder4a.

Moment distance calculator10hcalculates a distance XarmC in the horizontal direction from boom bottom pin5ato the center of gravity of the cylinder portion of arm cylinder4b. Moment distance calculator10hcalculates a distance XarmCR in the horizontal direction from boom bottom pin5ato the center of gravity of the cylinder rod portion of arm cylinder4b.

Moment distance calculator10hcalculates a distance Xboomtop in the horizontal direction from boom bottom pin5ato boom top pin5b. Moment distance calculator10hcalculates a distance Xarmtop in the horizontal direction from boom bottom pin5ato arm top pin5c.

Moment distance calculator10hcalculates a distance hboom from boom bottom pin5ato boom cylinder4ain a direction orthogonal to the direction of extension of boom cylinder4a. Moment distance calculator10hcalculates a distance harm from boom top pin5bto arm cylinder4bin a direction orthogonal to the direction of extension of arm cylinder4b. Moment distance calculator10hcalculates a distance hbucket from arm top pin5cto bucket cylinder4cin a direction orthogonal to the direction of extension of bucket cylinder4c.

Moment distance calculator10houtputs these calculated distances to load weight calculator10i.

Load weight calculator10icalculates a weight Mpayload of load L loaded in bucket3c. A method of calculating weight Mpayload will be described later. Load weight calculator10ioutputs calculated weight Mpayload to a display12outside controller10. Display12may be arranged, for example, in operator's cab2a(FIG.1) or at a remote location distant from hydraulic excavator100. Display12shows calculated weight Mpayload on a screen. An operator who operates hydraulic excavator100in operator's cab2a, an operator who operates hydraulic excavator100at a remote location, or a monitoring person who monitors an operation of hydraulic excavator100can recognize weight Mpayload of load L loaded in bucket3cby looking at display12.

Each of input portion11and display12may be connected to controller10through a wire or wirelessly.

<Calculation of Weight of Load L>

Details of the method of calculating weight Mpayload of load L loaded in bucket3cwill be described below. Weight Mpayload of load L is calculated based on any two of three relational expressions set up from information from the position sensors and information from the pressure sensors during conveyance of load L, in connection with three respective links (boom3a, arm3b, and bucket3c) that make up work implement3. With attention being paid below to boom3aand bucket3cas the links, moment equilibrium equations are set up as relational expressions to explain the method of calculating weight Mpayload of load L.

Load weight calculator10ishown inFIG.3reads an equation of moment equilibrium around boom bottom pin5afrom storage10j.FIG.4is a schematic diagram showing moment equilibrium around boom bottom pin5a. The equation of moment equilibrium around boom bottom pin5ais expressed in an equation (1) below.

The left side of the equation (1) expresses the moment resulting from boom cylinder thrust Fboom. In the first term in the right side of the equation (1), Mpayload represents the weight of load L loaded in bucket3c. Xpayload represents a distance in the horizontal direction from boom bottom pin5ato the position of the center of gravity of load L loaded in bucket3c. The first term in the right side of the equation (1) expresses the moment resulting from load L loaded in bucket3c.

MXwe in the second term in the right side of the equation (1) represents a moment resulting from a self-weight of work implement3. Moment MXwe is calculated in an equation (2) below.

In the equation (2), Mboomrepresents a weight of boom3a. MboomCrepresents a weight of the cylinder portion of boom cylinder4a. MboomCRrepresents a weight of the cylinder rod portion of boom cylinder4a. Marmrepresents a weight of arm3b. MarmCrepresents a weight of the cylinder portion of arm cylinder4b. MarmCRrepresents a weight of the cylinder rod portion of arm cylinder4b. Mbucketrepresents a weight of bucket3c.

Each of these weights Mboom, MboomC, MboomCR, Marm, MarmC, MarmCR, and Mbucketis stored in storage10j, for example, as a result of an operation for input into storage10jwith the use of input portion11shown inFIG.3.

Load weight calculator10ithen reads the equation of moment equilibrium around arm top pin5cfrom storage10j.FIG.5is a schematic diagram showing moment equilibrium around arm top pin5c. The equation of moment equilibrium around arm top pin5cis expressed in an equation (3) below.

The left side of the equation (3) represents the moment resulting from thrust Fbucketof bucket cylinder4c. The first term in the right side of the equation (3) represents the moment resulting from load L loaded in bucket3c. MXwebucket in the second term in the right side of the equation (3) represents a moment resulting from a self-weight of bucket3c.

Based on the simultaneous equations of the equation (1) and the equation (3), an equation (4) below not dependent on distance Xpayload can be established as an equation for calculating load weight Mpayload.

The equation (1) includes distance Xpayload and the equation (3) also includes distance Xpayload. By solving the two equilibrium equations as the simultaneous equations, the equation (4) not including distance Xpayload is derived. Load weight Mpayload can be calculated based on the equation (4). More accurate load weight Mpayload can thus be calculated without being affected by displacement of the position of the center of gravity of load L loaded in bucket3c.

By substituting load weight Mpayload calculated in accordance with the equation (4) into the equation (1) or the equation (3), distance Xpayload can be calculated. An equation (5) below not dependent on load weight Mpayload can be established as an equation for calculating distance Xpayload from the simultaneous equations of the equation (1) and the equation (3).

The position of the center of gravity of load L loaded in bucket3ccan be corrected in accordance with calculated distance Xpayload.

In summary, a computing method of calculating weight Mpayload of load L conveyed in bucket3cincludes processing below.FIG.11is a diagram showing a flowchart of the computing method in the present disclosure.

Processing performed in step S1shown inFIG.11is to establish, for the members of work implement3, relational expressions of a motion around any two centers of rotation of boom bottom pin5a(first center of rotation), boom top pin5b(second center of rotation), and arm top pin5c(third center of rotation). In the present embodiment, the relational expressions of the motion around the first center of rotation and the third center of rotation are established. The relational expression of the motion may be an equation of moment equilibrium around the center of rotation of the motion. The establishment of the equation may be to obtain information on the relational expression stored in storage10j. The information on the relational expression obtained from storage10jmay be one relational expression organized about load weight Mpayload based on the relational expressions of the motion around the two centers of rotation.

Processing performed in step S2is to obtain the weight and the position of the center of gravity of each of members that are boom3a, arm3b, and bucket3c(attachment). Information on the center of gravity and the position of the center of gravity of each member may be obtained from storage10j.

Processing performed in step S3is to obtain a position of each member while load L is conveyed. The position of each member may be obtained by obtaining an angle of rotation of each member which represents the attitude of each member and computing the position based on the angle of rotation.

Processing performed in step S4is to obtain thrust corresponding to the motion of the member in the relational expression of the motion of each member. In the present embodiment, thrust is obtained by measuring pressures of hydraulic oil in the hydraulic cylinders that operate boom3aand bucket3c. Thrust may be obtained from the head pressure and the bottom pressure of the hydraulic cylinder that pivots each of members that are boom3a, arm3b, and bucket3c(attachment).

Processing performed in step S5is to compute the distances in the horizontal direction (moment distance) between the positions of the centers of gravity of the members while load L is conveyed and respective ones of the first center of rotation, the second center of rotation, and the third center of rotation that are the centers of rotation of the members, based on the positions of the centers of gravity of the members and the positions of the members while load L is conveyed.

Processing performed in step S6is to compute the weight (load weight Mpayload) of load L conveyed by work implement3by input of the obtained information and the computed information into the relational expressions of the motion of the members. The obtained information refers to the weight and the position of the center of gravity of each member of work implement3and thrust of the hydraulic cylinder that pivots each member while load L is conveyed. The computed information refers to the distance in the horizontal direction between the position of the center of gravity of each member while load L is conveyed and the center of rotation of each member.

Second Embodiment

In the first embodiment, an example in which weight Mpayload of load L loaded in bucket3cis calculated based on the two equilibrium equations of the equation of moment equilibrium around boom bottom pin5aand the equation of moment equilibrium around arm top pin5cis described. Without being limited to this example, controller10can calculate weight Mpayload of load L loaded in bucket3cbased on any two equilibrium equations of the equation of moment equilibrium around boom bottom pin5a, the equation of moment equilibrium around boom top pin5b, and the equation of moment equilibrium around arm top pin5c. In a second embodiment, an example in which weight Mpayload is calculated based on the two equilibrium equations of the equation of moment equilibrium around boom bottom pin5aand the equation of moment equilibrium around boom top pin5bwill be described.

The construction of hydraulic excavator100, the system configuration, and the functional block in controller10in the second embodiment are as described in the first embodiment with reference toFIGS.1to3.

In the second embodiment, load weight calculator10ireads the equation of moment equilibrium around boom top pin5bfrom storage10j.FIG.6is a schematic diagram showing equilibrium of the moment around boom top pin5b. The equation of moment equilibrium around boom top pin5bis expressed in an equation (6) below.

The left side of the equation (6) expresses the moment resulting from arm cylinder thrust Farm. The first term in the right side of the equation (6) expresses the moment resulting from load L loaded in bucket3c. MXwe_arm in the second term in the right side of the equation (6) represents the moment resulting from the self-weight of work implement3on a tip end side of work implement3relative to boom top pin5b. Moment MXwe_arm is calculated based on the equilibrium equation similar to the equation (2).

From the simultaneous equations of the equation (1) and the equation (6), an equation (7) below not dependent on distance Xpayload can be established as an equation for calculating load weight Mpayload.

The equation (1) includes distance Xpayload and the equation (6) also includes distance Xpayload. By solving the two equilibrium equations as the simultaneous equations, the equation (7) not including distance Xpayload is derived. Load weight Mpayload can be calculated based on the equation (7). More accurate load weight Mpayload can thus be calculated without being affected by displacement of the position of the center of gravity of load L loaded in bucket3c.

By substituting load weight Mpayload calculated in accordance with the equation (7) into the equation (1) or the equation (6), distance Xpayload can be calculated. An equation not dependent on load weight Mpayload can be established as an equation for calculating distance Xpayload from the simultaneous equations of the equation (1) and the equation (6). The position of the center of gravity of load L loaded in bucket3ccan be corrected in accordance with calculated distance Xpayload.

In the description of the first and second embodiments, an example in which load weight Mpayload which is the weight of load L loaded in bucket3cis calculated is described. Without being limited thereto, for example, the weight of a suspended load can accurately be calculated by applying the concept in the embodiments, for example, to hydraulic excavator100of arm crane specifications in which a hook is attached to second link pin3deto lift up and down load L.

In hydraulic excavator100shown in the first and second embodiments, three links (boom3a, arm3b, and bucket3c) of work implement3include position sensors9a,9b, and9cand corresponding pressure sensors6a,6b, and6c, respectively, however, the construction is not limited as such. The pressure sensor may be provided only in links associated with two relational expressions used for calculation of load weight Mpayload.

Third Embodiment

In the first and second embodiments, hydraulic excavator100including bucket3cas the attachment at the tip end of work implement3is described. The attachment is not limited to bucket3c, and the attachment may be changed to a grapple, a lifting magnet, or the like depending on a type of works. In a third embodiment, hydraulic excavator100including a lifting magnet103as the attachment will be described.

FIG.7is a side view schematically showing a construction of hydraulic excavator100as an exemplary work machine based on the third embodiment. Hydraulic excavator100based on the third embodiment is substantially identical in construction to hydraulic excavator100in the first embodiment shown inFIG.1, and different in including lifting magnet103instead of bucket3cat the tip end of work implement3.

Lifting magnet103includes a main body portion105and a support portion104. Main body portion105is made of a magnet that generates magnetic force. Main body portion105is made, for example, of an electromagnet. Main body portion105can hold and convey a magnetic material by magnetic force. Support portion104supports main body portion105. Support portion104is rotatably coupled to the tip end of arm3bby arm top pin5c. Second link member3dbhas the base end rotatably coupled to a bracket at a root portion of support portion104by second link pin3de.

In hydraulic excavator100including lifting magnet103, it is difficult to keep a constant position of load L conveyed by work implement3, that is, the magnetic material attracted and held by main body portion105, relative to main body portion105and a constant attitude of the magnetic material. Therefore, the position of the center of gravity of the magnetic material tends to be displaced. As shown inFIG.7, a more accurate weight of load L can be calculated without being affected by displacement of the position of the center of gravity of load L held by lifting magnet103by establishing an equation for calculating the weight of load L not dependent on displacement of the position of the center of gravity of load L, based on two equilibrium equations of the equation of moment equilibrium around boom bottom pin5aand the equation of moment equilibrium around arm top pin5c.

In hydraulic excavator100shown in the first to third embodiments, the weight of load L can more accurately be calculated by calculating the weight of load L during revolution of revolving unit2with respect to traveling unit1.

Fourth Embodiment

In the first to third embodiments, an example in which hydraulic excavator100is defined as the work machine is described. Without being limited to hydraulic excavator100, the weight of load L conveyed by work implement3can accurately be calculated by applying the concept of the embodiments to a work machine including work implement3with a multiple-link mechanism that conveys load L. For example, the work machine may be a wheel loader, a back hoe loader, or a skid steer loader.

FIG.8is a side view schematically showing a construction of a wheel loader200as an exemplary work machine based on a fourth embodiment. As shown inFIG.8, wheel loader200includes a vehicular body frame202, a work implement203, a traveling apparatus204, and a cab205.

A vehicular body of wheel loader200is composed of vehicular body frame202and cab205. In cab205, a seat where an operator sits and an operation apparatus are arranged. Work implement203and traveling apparatus204are attached to the vehicular body of wheel loader200. Work implement203is arranged in front of the vehicular body and a counterweight206is provided at a rearmost end of the vehicular body.

Vehicular body frame202includes a front frame211and a rear frame212. A steering cylinder213is attached to front frame211and rear frame212. Steering cylinder213is a hydraulic cylinder. Steering cylinder213extends and contracts by hydraulic oil from a steering pump (not shown). As steering cylinder213extends and contracts, front frame211and rear frame212can swing with respect to each other in the lateral direction. A direction of travel of wheel loader200can thus laterally be changed.

In the fourth embodiment, a direction in which wheel loader200travels straight is herein referred to as a forward/rearward direction of wheel loader200. In the forward/rearward direction of wheel loader200, a side on which work implement203is arranged with respect to vehicular body frame202is defined as a forward direction, and a side opposite to the forward direction is defined as a rearward direction. A lateral direction of wheel loader200is a direction orthogonal to the forward/rearward direction in a plan view. When looking in the forward direction, a right side and a left side in the lateral direction are a right direction and a left direction, respectively. An upward/downward direction of wheel loader200is a direction orthogonal to a plane defined by the forward/rearward direction and the lateral direction. In the upward/downward direction, a side on which the ground is present is a lower side and a side on which the sky is present is an upper side.

Traveling apparatus204includes running wheels204aand204b. Each of running wheels204aand204bis a wheel and includes a tire made of rubber. Running wheel (front wheel)204ais rotatably attached to front frame211. Running wheel (rear wheel)204bis rotatably attached to rear frame212. Wheel loader200can be self-propelled as running wheels204aand204bare rotationally driven.

Work implement203serves to do such works as excavation. Work implement203is attached to front frame211. Work implement203includes a bucket214, a boom215, a bell crank216, a tilt rod217, a boom cylinder218, and a bucket cylinder219.

Boom215has a base end rotatably attached to front frame211by a boom bottom pin221. Boom215is thus rotatably attached to the vehicular body. Bucket214is rotatably attached to a tip end of boom215by a boom top pin222. Boom bottom pin221is supported by the vehicular body of wheel loader200. Boom top pin222is attached to the tip end of boom215. Boom bottom pin221and boom top pin222extend in the lateral direction.

Boom cylinder218drives boom215. Boom cylinder218has one end rotatably attached to front frame211of the vehicular body by a pin223. Boom cylinder218is thus rotatably attached to the vehicular body. Boom cylinder218has the other end rotatably attached to boom215by a pin224.

Boom cylinder218is, for example, a hydraulic cylinder. Boom cylinder218extends and contracts by hydraulic oil from a work implement pump (not shown). Boom215is thus driven and bucket214attached to the tip end of boom215is moved upward and downward.

Bell crank216is rotatably supported on boom215by a support pin229. Bell crank216has a first end located on one side of support pin229and a second end located opposite to the first end with respect to support pin229. Bell crank216has the first end connected to bucket214with tilt rod217being interposed. Bell crank216has the second end connected to front frame211of the vehicular body with bucket cylinder219being interposed.

Tilt rod217has one end rotatably attached to the first end of bell crank216by a pin227. Tilt rod217has the other end rotatably attached to bucket214by a pin228.

Bucket cylinder219drives bucket214with respect to boom215. Bucket cylinder219has one end rotatably attached to front frame211of the vehicular body by a pin225. Bucket cylinder219has the other end rotatably attached to the second end of bell crank216by a pin226.

Bucket cylinder219is, for example, a hydraulic cylinder. Bucket cylinder219extends and contracts by hydraulic oil from a work implement pump (not shown). As bucket cylinder219extends and contracts, bell crank216is driven to rotate with respect to boom215. As rotation of bell crank216is transmitted to bucket214through tilt rod217, bucket214is driven and pivots upward and downward with respect to boom215. Bell crank216corresponds to the pivot member in the embodiment that can rotate with respect to boom215together with bucket214.

Wheel loader200further includes a sensor that senses information on thrust Fboomof boom cylinder218and a sensor that senses information on thrust Fbucketof bucket cylinder219.

The sensor that senses information on thrust Fboomof boom cylinder218is, for example, pressure sensors231band231h. Each of pressure sensors231band231hsenses a cylinder pressure of boom cylinder218. Pressure sensor231bsenses a bottom pressure of boom cylinder218. Pressure sensor231hsenses a head pressure of boom cylinder218.

The head pressure means a pressure on a cylinder rod side with respect to a piston of a hydraulic cylinder and the bottom pressure means a pressure on a tube side with respect to the piston.

The sensor that senses information on thrust Fbucketof bucket cylinder219is, for example, pressure sensors232band232h. Each of pressure sensors232band232hsenses a cylinder pressure of bucket cylinder219. Pressure sensor232bsenses a bottom pressure of bucket cylinder219. Pressure sensor232hsenses a head pressure of bucket cylinder219.

Wheel loader200further includes a sensor that senses information on an attitude of work implement203. The sensor that senses information on the attitude of work implement203includes, for example, a first sensor that senses information on a boom angle and a second sensor that senses information on a bucket angle with respect to the boom.

The information on the attitude of work implement203includes distance hboomand distance hbucket(FIG.10). Distance hboomis a distance between boom bottom pin221and pin223in a direction orthogonal to a direction of extension of boom cylinder218. Distance hbucketis a distance between support pin229and pin226in a direction orthogonal to a direction of extension of bucket cylinder219.

The boom angle refers to an angle of boom215with respect to front frame211of the vehicular body. The bucket angle refers to an angle of bucket214with respect to boom215.

The first sensor that senses information on the boom angle is, for example, a potentiometer233. Potentiometer233is attached as being concentric with boom bottom pin221. Instead of potentiometer233, a stroke sensor235of boom cylinder218may be employed as the first sensor that senses information on the boom angle.

An inertial measurement unit (IMU)237may be employed as the first sensor that senses information on the boom angle. IMU237is attached, for example, to boom215.

The second sensor that senses information on the bucket angle is, for example, a potentiometer234. Potentiometer234is attached as being concentric with support pin229. Instead of potentiometer234, a stroke sensor236of bucket cylinder219may be employed as the second sensor that senses information on the bucket angle.

An IMU238may be employed as the second sensor that senses information on the bucket angle. IMU238is attached, for example, to tilt rod217.

Potentiometers233and234, stroke sensors235and236, and IMUs237and238may be used as a sensor that senses information on a position of a center of gravity GC1of work implement203. Information on the position of center of gravity GC1of work implement203is a distance Xwe.

Distance Xwe represents a distance between center of gravity GC1and boom bottom pin221along the forward/rearward direction of wheel loader200. Distance Xwe represents a distance along the horizontal direction between center of gravity GC1and boom bottom pin221while wheel loader200is placed on a horizontal ground.

Potentiometers233and234, stroke sensors235and236, and IMUs237and238may be used as the sensor that senses information on a position of a center of gravity GC2of a load within bucket214. Information on the position of center of gravity GC2of the load within bucket214is distance Xpayload.

Distance Xpayload represents a distance between center of gravity GC2and boom bottom pin221along the forward/rearward direction of wheel loader200. Xpayload represents a distance along the horizontal direction between center of gravity GC2and boom bottom pin221while wheel loader200is placed on the horizontal ground.

FIG.9is a diagram showing a functional block in a controller250in the fourth embodiment. The system in the present embodiment is a system for determining a load weight which is a weight of a load conveyed by work implement203. The system in the present embodiment includes wheel loader200representing an exemplary work machine shown inFIG.8and controller250shown inFIG.9. Controller250may be mounted on wheel loader200. Controller250may be provided outside wheel loader200. Controller250may be arranged at a worksite of wheel loader200or at a remote location distant from the worksite of wheel loader200.

As shown inFIG.9, a boom cylinder thrust calculator250aobtains a result of sensing by pressure sensors231band231h. Specifically, boom cylinder thrust calculator250aobtains the head pressure of boom cylinder218sensed by pressure sensor231h. Boom cylinder thrust calculator250aobtains the bottom pressure of boom cylinder218sensed by pressure sensor231b. Boom cylinder thrust calculator250acalculates boom cylinder thrust Fboombased on the head pressure and the bottom pressure of boom cylinder218.

Thrust is defined as force that moves an object in the direction of motion, and boom cylinder thrust Fboomis thrust generated by boom cylinder218that rotates boom215relatively to the vehicular body. Boom cylinder thrust calculator250aoutputs calculated boom cylinder thrust Fboomto a load weight calculator250i.

A bucket cylinder thrust calculator250cobtains a result of sensing by pressure sensors232band232h. Specifically, bucket cylinder thrust calculator250cobtains the head pressure of bucket cylinder219sensed by pressure sensor232h. Bucket cylinder thrust calculator250cobtains the bottom pressure of bucket cylinder219sensed by pressure sensor232b. Bucket cylinder thrust calculator250ccalculates bucket cylinder thrust Fbucketbased on the head pressure and the bottom pressure of bucket cylinder219.

Bucket cylinder thrust Fbucketis thrust generated by bucket cylinder219that rotates bucket214relatively to boom215. Bucket cylinder thrust calculator250coutputs calculated bucket cylinder thrust Fbucketto load weight calculator250i.

A boom angle calculator250dobtains information on a boom angle from at least one sensor of stroke sensor235, IMU237, and potentiometer233. Boom angle calculator250dcalculates the boom angle based on the obtained information. Boom angle calculator250doutputs the calculated boom angle to a gravity center position calculator250g.

A bucket angle calculator250fobtains information on a bucket angle from at least one sensor of stroke sensor236, IMU238, and potentiometer234. Bucket angle calculator250fcalculates the bucket angle based on the obtained information. Bucket angle calculator250foutputs the calculated bucket angle to gravity center position calculator250g.

Various types of information such as a dimension and a weight of each member that makes up work implement203and a position of center of gravity GC1of work implement203are stored in a storage250j. Such various types of information may be inputted from an input portion251outside controller250into storage250j. Storage250jmay be arranged outside controller250, instead of being included in controller250.

Gravity center position calculator250gcalculates a position of center of gravity GC1of work implement203relative to boom bottom pin221. Gravity center position calculator250gcalculates the relative position of center of gravity GC1of work implement203based on the boom angle calculated by boom angle calculator250d, the bucket angle calculated by bucket angle calculator250f, and the position of center of gravity GC1in work implement203stored in storage10j.

A moment distance calculator250hcalculates a distance in the horizontal direction from boom bottom pin221to center of gravity GC1of work implement203. Specifically, moment distance calculator250hcalculates distance Xwe in the horizontal direction from boom bottom pin221to center of gravity GC1of work implement203.

Moment distance calculator250hcalculates distance Xbucket in the horizontal direction from boom bottom pin221to a center of gravity GC3(FIG.10) of bucket214. Moment distance calculator250hcalculates a distance Xtiltrod in the horizontal direction from boom bottom pin221to the center of gravity of tilt rod217.

Moment distance calculator250hcalculates a distance Xpin in the horizontal direction from boom bottom pin221to support pin229.

Moment distance calculator250hcalculates distance hboomfrom boom bottom pin221to boom cylinder218in a direction orthogonal to the direction of extension of boom cylinder218. Moment distance calculator250hcalculates distance hbucketfrom support pin229to bucket cylinder219in a direction orthogonal to the direction of extension of bucket cylinder219.

Moment distance calculator250houtputs these calculated distances to load weight calculator250i.

Load weight calculator250icalculates weight Mpayload of a load loaded in bucket214. Load weight calculator250ioutputs calculated weight Mpayload to a display252outside controller250. Display252may be arranged, for example, in cab205(FIG.8) or at a remote location distant from wheel loader200. Display252shows calculated weight Mpayload on a screen. An operator who operates wheel loader200in cab205, an operator who operates wheel loader200at a remote location, or a monitoring person who monitors an operation of wheel loader200can recognize weight Mpayload of the load loaded in bucket214by looking at display252.

Each of input portion251and display252may be connected to controller250through a wire or wirelessly.

Details of the method of calculating weight Mpayload of the load loaded in bucket214in the fourth embodiment will be described below. Load weight calculator250ishown inFIG.9reads an equation of moment equilibrium around boom bottom pin221from storage250j. The equation of moment equilibrium around boom bottom pin221is expressed in an equation (8) below.

The left side of the equation (8) expresses the moment resulting from boom cylinder thrust Fboom. In the equation (8), Mpayload represents the weight of the load loaded in bucket214. Xpayload represents the distance in the horizontal direction from boom bottom pin221to center of gravity GC2of the load loaded in bucket214. The first term in the right side of the equation (8) expresses the moment resulting from the load loaded in bucket214.

MXwein the second term in the right side of the equation (8) represents the moment resulting from the self-weight of work implement203. Moment MXweis calculated as a product of a sum M1(FIG.8) of weights of members that make up work implement203and distance Xwe in the horizontal direction from boom bottom pin221to center of gravity GC1of work implement203.

Load weight calculator250ithen reads the equation of moment equilibrium around support pin229from storage250j.FIG.10is a schematic diagram showing moment equilibrium around support pin229. The equation of moment equilibrium around support pin229is expressed in an equation (9) below.

The left side of the equation (9) represents the moment resulting from bucket cylinder thrust Fbucket. The first term in the right side of the equation (9) represents the moment resulting from the load loaded in bucket214. MXwe_pin in the second term in the right side of the equation (9) represents the moment resulting from the self-weight of work implement203on the tip end side of work implement203relative to support pin229. Moment MXwe_pin is calculated in an equation (10) below.

In the equation (10), Mbucketrepresents the weight of bucket214. Mtiltrod represents the weight of tilt rod217. Each of these weights Mbucketand Mtiltrod is stored in storage250j, for example, by an operation for input into storage250jthrough input portion251shown inFIG.9.

Based on the simultaneous equations of the equation (8) and the equation (9), an equation (11) below not dependent on distance Xpayload can be established as an equation for calculating load weight Mpayload.

The equation (8) includes distance Xpayload and the equation (9) also includes distance Xpayload. By solving the two equilibrium equations as the simultaneous equations, the equation (11) not including distance Xpayload is derived. Load weight Mpayload can be calculated based on the equation (11). More accurate load weight Mpayload can thus be calculated without being affected by displacement of the position of the center of gravity of the load loaded in bucket214.

By substituting load weight Mpayload calculated in accordance with the equation (11) into the equation (8) or the equation (9), distance Xpayload can be calculated. An equation not dependent on load weight Mpayload can be established as an equation for calculating distance Xpayload from the simultaneous equations of the equation (8) and the equation (9). The position of the center of gravity of the load loaded in bucket214can be corrected in accordance with calculated distance Xpayload.

In wheel loader200shown in the fourth embodiment, by calculating the weight of the load during loaded rearward travel in which wheel loader200travels rearward while the load is loaded in bucket214, the weight of the load can more accurately be calculated.

In the embodiments, controller10uses two equilibrium equations of moment equilibrium equations for a plurality of links provided in the work implement, as the relational expressions for calculation of the weight of the load. The relational expression is not limited to the moment equilibrium equation, and a motion equation for each of the plurality of links may be employed. The motion equation may be set up based on information from the pressure sensor and the position sensor as in the case of the equilibrium equation.

REFERENCE SIGNS LIST