Abstract:
A working machine such as a wheel loader for moving a load measures the weight of the load accurately. While the load is lifted by a boom of the working machine, a boom angle (θ) and a pressure value (P) of a boom cylinder are measured and a boom angular speed (ω) is calculated. A corrected factor (α) is determined according to the boom angular speed (ω), and a corrected pressure value (P′) is calculated from “P′=P−αω.” A predetermined table is referred to and the weight (W) of the load is determined based on the boom angle (θ) and the corrected pressure value (P) of the boom cylinder. Further, calibrations are performed as needed, and each time when a calibration is made, the average value of the calibrated value and the preceding calibrated value is calculated and data is rewritten to this average value.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a working machine that moves a load, and more particularly to a device and method for measuring load weight. 
       DESCRIPTION OF THE RELATED ART 
       [0002]    Conventionally, it is known that a machine used to load dump trucks and other delivery vehicles, such as a wheel loader, employs a load weight measurement device that measures, during boom operation, the weight of the load carried in the bucket and indicates the weight (See Patent Document 1). 
         [0003]    According to the conventional art described in the above document, after the boom begins moving, a prescribed calculation is performed utilizing a numerical table pre-calculated from the boom angle and the difference between the boom cylinder head pressure and bottom pressure, to measure the load weight carried in the bucket. 
         [0004]    Patent Document 1: Japanese Patent Application Laid-open No. 2001-99701 
       BRIEF SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
       [0005]    However, since the conventional art described in the afore-mentioned Patent Document 1 does not take into consideration error factors such as the frictional force generated in the mechanism used to lift the load (hereinafter “lifting mechanism”), or changes in the weight, due to wearing, damage, repair, or replacement of the lifting mechanism components such as bucket or teeth, there is demand to further improve the measurement accuracy. 
         [0006]    Accordingly, an object of the present invention is to improve the measurement accuracy of the load weight moved by a working machine. 
       Means of Solving the Problems 
       [0007]    According to an aspect of the present invention, a working machine for moving a load comprises: a lifting unit for lifting a load; a displacement detection device for detecting the displacement of the lifting unit; an actuator for driving the lifting unit; and a measurement device for measuring the output value or input value of the lifting unit; and further a detection value acquiring means for acquiring, during operation of the lifting unit, the displacement from the displacement detection device and the output value or input value from the measurement device; a speed calculating means for obtaining the movement speed of the lifting unit during operation of the lifting unit; a correcting means for obtaining the corrected value by correcting the output value or input value of the actuator in accordance with the movement speed of the lifting unit; and a means for calculating the load weight based on the corrected value obtained by correcting the output value or input value of the actuator, and the lifting unit displacement obtained from the detection value acquiring means. 
         [0008]    According to this working machine, the input value or output value of the actuator is corrected in accordance with the operation speed of the lifting unit, and the load weight is calculated using this corrected value. This allows the error factors that change depending on the operation speed of the lifting unit, for example forces such as frictional force, to be taken into consideration to obtain measurement results of higher accuracy. 
         [0009]    In an embodiment of the present invention, a hydraulic cylinder is used as an actuator and the pressure difference between the hydraulic cylinder head pressure and bottom pressure is measured to be used as the actuator output value. However, this is just an example, and the present invention can be applied to working machines employing other types of actuators, and an input value can also be measured for use in place of, or together with, the actuator output value. For example, if an electric motor is used as an actuator, the output torque and rotating speed can be measured as the output value of the electric motor, or the input current and input voltage, which are input values, can be detected as well. 
         [0010]    Further, in an embodiment of the present invention, the lifting unit of the working machine has a boom, the actuator includes a hydraulic cylinder for moving the boom, the measurement device includes a pressure detection device for detecting the hydraulic cylinder pressure; and the displacement detection device includes an angle detection device for detecting the angle of the boom. This configuration applies to working machine that raises and lowers a load using a boom, such as a wheel loader, power shovel, or a crane, for example. However, the present invention also applies to working machines that do not have a boom, such as a winch. 
         [0011]    Further, in an embodiment of the present invention, the correcting means may calculate the correction factor from the movement speed of the lifting unit and the output value or input value of the actuator and correct the output value or input value of the actuator based on the correction factor and the lifting unit movement speed. According to this configuration, error factors that change in response to the output value or input value of the actuator or the movement speed of the lifting unit can be taken into consideration. 
         [0012]    Further, in an embodiment of the present invention, the correcting means may comprise a speed correction table defining the correlation among the output value and input value of the actuator, the lifting unit movement speed, and the correction factor, that is used to calculate the correction factor. A constant can also be used as a correction factor. 
         [0013]    For the working machine having a boom, the boom angular speed, for example, can be used as the above-mentioned movement speed, but this is nothing more than just an illustration. For example, a variety of movement speeds related to the movement of the lifting unit, including the boom hoisting speed, bucket hoisting speed, movement speed of the hydraulic cylinder piston that moves the lifting unit, or the rotational speed of the hydraulic or electric motor that moves the lifting unit, can be used for the above-mentioned correcting process. 
         [0014]    According to another aspect of the present invention, a working machine comprises a lifting unit for lifting a load; a displacement detection unit for detecting displacement of the lifting unit; an actuator for driving the lifting unit; and a measurement unit for measuring the output value and input value of the actuator; and further comprises a load weight calculating means having a load weight calculation table defining the correlations among the output value or input value of the actuator, the displacement of the lifting unit, and the load weight; that acquires, during operation of the lifting unit, the displacement from the displacement detecting device and the output value or input value from the measurement device; and that calculates the load weight referring to said load weight calculation table, based on said displacement acquired from said displacement detecting device and said output value or input value acquired from said measurement device; and a calibrating means that inputs the specified load weight value; acquires, during calibration operation of the lifting unit, the displacement from the displacement detection device and the output value or input value from the measuring device; and calibrates the load weight calculation table based on the displacement acquired from the displacement detecting device, the output value or input value acquired from the measurement device, and the specified load weight. 
         [0015]    According to this working machine, the load weight specification is input, and during the calibration operation the displacement is acquired from the displacement detection device and the output value or input value is acquired from the measuring device, and the load weight calculation table is calibrated based on the displacement acquired from the displacement detection device, the output value or input value acquired from the measuring device, and the specified load weight. Occasionally executing this type of calibration eliminates error factors due to changes in the weight of the lifting unit resulting from wearing, damage, corrosion, etc., of the components of the lifting unit to make measurement of greater accuracy possible. 
         [0016]    An embodiment of the present invention is a working machine further comprising a speed calculating means for obtaining the movement speed of the lifting unit during movement of the lifting unit; and a correcting means for obtaining a corrected value by correcting the output value or input value of the actuator according to the speed, wherein the load weight calculation table records the corrected value for the output value or input value of the actuator and the numerical value for obtaining the load weight based on the displacement of the lifting unit; and wherein the load weight calculating means calculates the load weight referring to the load weight calculation table, based on the corrected value from the correcting means and the acquired load lifting unit displacement, and calibrates the load weight calculation table numerical values. This makes it possible to take into consideration the error factors (frictional force for example) that change depending on the movement speed of the lifting unit to obtain measurement results of greater accuracy. 
         [0017]    Further, in an embodiment of the present invention, the calibrating means calculates, during calibration execution, the average value of the numerical value acquired from the current calibration and the numerical value currently registered in the load weight calculation table, and then uses the calculated average value as the post-calibration numerical value for calibrating the load weight calculation table. According to this configuration, the data acquired from the calibration during calibration of the load weight calculation table is not used to update the load weight calculation table but rather the average value of the data acquired from the calibration and the existing data of the load weight calculation table is obtained and this average value is used to update the load weight calculation table so that in the event the data received from the calibration is not a correct value, the effect of this error will not be 100%. 
         [0018]    Further, an embodiment of the present invention further comprises a clearing means that initializes the load weight calculation table numerical values to the specified initial values. By performing this initialization process, the load weight calculation table returns to the state it was in at the time it was shipped from the factory. When calibration has been repeated many times to date, or when the lifting unit of the working machine has been significantly repaired or replaced, there are cases when there is some concern about the reliability of the numerical values in the current load weight calculation table. In such a case, it is effective to newly conduct calibration after conducting the afore-mentioned initialization process. 
         [0019]    Another aspect of the present invention provides a device and means for measuring the weight of the load transported by a working machine in accordance with the afore-mentioned principles. Further, another aspect of the present invention provides a computer program that commands a computer to perform the load weight measurement method. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a configuration drawing of an external view of a wheel loader relating to the present embodiment; 
           [0021]      FIG. 2  is a configuration drawing of a load weight measurement system; 
           [0022]      FIG. 3  is a flow chart showing the flow of the overall control relating to a controller  11  of the present invention; 
           [0023]      FIG. 4  is a function block diagram of the part of the controller  11  that performs the load weight measurement; 
           [0024]      FIG. 5  is a table that shows an example of a load weight calculation table; 
           [0025]      FIG. 6  is a table that shows an example of a speed correction table; 
           [0026]      FIG. 7  is a flow chart showing details of the load weight measurement operation flow; 
           [0027]      FIG. 8  is a flow chart showing the process for the load weight table calibration operation. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]    The following describes details of an embodiment of the present invention with reference to the drawings. 
         [0029]    The embodiments shown below apply the present invention to a wheel loader as an example of a working machine to make this explanation easy to understand, but in addition to a wheel loader the present invention can be applied to a variety of working machines having a lifting function including but not limited to power shovels, cranes, and winches. 
         [0030]      FIG. 1  is a configuration drawing of an external view of a wheel loader  1 . 
         [0031]    The wheel loader  1  is provided with, as the lifting unit, a boom  2  that freely rotates around a boom pin  3  attached to a rear anchor unit, and a bucket  4  that freely rotates around a bucket pin  5  attached to an end of boom  2 . In the vicinity of the boom pin  3  is provided a boom angle detection device  6 , such as a potentiometer, that detects the displacement of the boom  2 , for example, the lift angle (θ) (hereinafter “boom angle”). As shown in  FIG. 1 , the boom angle (θ) is measured in the counterclockwise direction, the angle between the perpendicular line  18  passing through the boom pin  3  and the straight line  19  that connects the boom pin  3  to the bucket pin  5  that attaches the end of the boom  2  to the bucket  4 . In addition, when the straight line  19  that connects the boom pin  3  to the bucket pin  5  is horizontal, the boom angle (θ) is defined as “boom angle (θ)=0 degrees.” Further, the wheel loader  1  is provided with a hydraulic cylinder (hereinafter “boom cylinder”)  7  that raises the boom  2 , and the boom cylinder  7  is provided with a head pressure detection device  8  and a bottom pressure detection device  9  that detect the head pressure and bottom pressure, respectively. The substantial output pressure value and input pressure value of the boom cylinder  7  is the pressure difference (P) between the afore-mentioned head pressure and bottom pressure. Here, this pressure difference (P) is called the boom cylinder pressure value (P). 
         [0032]      FIG. 2  is a configuration drawing of a load weight measurement system installed in the wheel loader  1 . 
         [0033]    As shown in  FIG. 2 , the wheel loader  1  is provided with a controller  11  comprising a microprocessor or the like that is electrically connected to the afore-mentioned boom angle detection device  6 , head pressure detection device  8 , and bottom pressure detection device  9  as well as a keyboard  30  and a data storage section  31 . The keyboard  30  is installed in a driver&#39;s cabin  14  and is used for inputting, among other data, the hereafter-mentioned calibration signal for specifying the start of calibration operation and the load weight value that specifies the weight of the load that can be lifted. In addition, the data storage section  31  stores in advance the hereafter-mentioned load weight calculation table  63  and a speed correction table  64 . 
         [0034]    Further, the controller  11  is connected to a display  12  installed in the driver&#39;s cabin  14 . The display  12  is provided with a load weight display section  21  that shows the load weight (W) in the bucket  4  and a cumulative load weight display section  22  that shows the cumulative weight that has been loaded to date. In addition, the controller  11  is connected to a printer  13  that prints out the load weight and cumulative load weight in accordance with the instruction from a print switch  20 . Also, a lever  23  and a buzzer  17  are electrically connected to the controller  11 . The lever  23  is provided in the driver&#39;s cabin  14  and is operated by the operator of the wheel loader  1  (hereinafter “operator”) to move the boom  2  and the bucket  4 . In addition, the buzzer  17  is provided in the driver&#39;s cabin  14  and buzzes to warn the operator when the load weight loaded in the bucket  4  is an overload. 
         [0035]    Next,  FIG. 3  is used to explain the load weight (W) measurement flow processed by the controller  11 . In the following flow charts, “Step” is abbreviated as “S.” 
         [0036]    As shown in  FIG. 3 , the controller  11  determines whether or not a calibration signal is being input (S 50 ). The calibration signal is input by the operator using the keyboard  30 . When the controller  11  determines that a calibration signal has been input, it performs the hereafter-mentioned calibration operation (S 53 ), and if it determines that a calibration signal has not been input, it determines whether or not it is necessary to perform load weight measurement using the specified determination conditions each time the boom  2  is moved (S 51 ). Then, when the controller  11  determines that it is necessary to perform load weight measurement, it performs the load weight measurement that is described in detail hereafter (S 52 ). 
         [0037]      FIG. 4  shows a function block diagram of the part of the controller  11  that measures the load weight. 
         [0038]    As shown in  FIG. 4 , the controller  11  has an angular speed calculation section  60 , a pressure correction section  61 , and a load weight calculation section  62 , and, further, the data storage section  31  contains a load weight calculation table  63  and a speed correction table  64 . 
         [0039]    The angular speed calculation section  60  repeatedly inputs the boom angle (θ) several times at a fixed interval during operation of the boom  2  and calculates the angular speed of the boom  2  (ω) at the time of each input (hereinafter “boom angular speed”). Here, the boom angular speed (ω) is the rotational speed per unit time of the boom  2 . 
         [0040]    The pressure correction section  61  repeatedly inputs the boom cylinder pressure value (P) detected from the afore-mentioned head pressure detection device  8  and the bottom pressure detection device  9  at a fixed interval during operation of the boom  2  while also inputting the boom angular speed (ω) at the time of each input calculated by the angular speed detection section  60 . Next, the pressure correction section  61  refers to the speed correction table  64  based on the boom cylinder pressure value (P) and the boom angular speed (ω) at the time of each input and calculates a correlation factor (α) in accordance with the combination of the boom cylinder pressure value (P) and the boom angular speed (ω). In the afore-mentioned speed correction table  64  is recorded the various correction factors (α) corresponding to the boom cylinder pressure value (P) and boom angular speed (ω) values. This correction factor (α) value is a value included in the boom cylinder pressure value (P), used to correct the error factors that change in accordance with the boom angular speed (ω), such as friction for example. Then, the pressure correction section  61  utilizes the calculated correction factor (α), boom cylinder pressure value (P), and the boom angular speed (ω) to calculate the speed corrected pressure value (hereinafter “corrected pressure value”) (P′) in accordance, for example, with the formula “P′=P−αω.” 
         [0041]    The load weight calculation section  62  enters the corrected pressure value (P′) and the boom angle (θ) at the time of each input for each of the afore-mentioned set intervals, refers to the load weight calculation table  63 , and calculates the load weight (W) corresponding to the corrected pressure value (P′) and boom angle (θ) combination. In addition, the afore-mentioned load weight calculation table  63  records the correlation among various corrected pressure values (P′), the boom angle (θ), and the load weight (W). Based on the numerical values recorded in the afore-mentioned load weight calculation table  63 , the load weight (W) corresponding to the corrected pressure value (P′) and boom angle (θ) combination is calculated at the time of each input, and then the most accurate load weight (W) is calculated based on load weight (W) at a plurality of inputs. 
         [0042]    Next, the load weight calculation table  63  and speed correction table  64  are explained. 
         [0043]      FIG. 5  shows an example of the load weight calculation table  63 . 
         [0044]    As shown in  FIG. 5 , the load weight calculation table  63  shows the correlation among the load weight (W), the boom angle (θ), and the corrected pressure value (P′). More specifically, when there are several representative values for the load weight (W) in the load weight calculation table  63 , for example, W=0 t (status when there is no load), 4.625 t (intermediate rated load), 9.25 t (maximum rated load), and 18.5 t (overload), the corrected pressure value (P′) for the various values within the boom angle (θ) variable range, for example −40 degrees to +45 degrees, is recorded. 
         [0045]      FIG. 6  shows an example of the speed correction table  64 . 
         [0046]    As shown in  FIG. 6 , the speed correction table  64  shows the correlation among the correction factor (α), the boom cylinder pressure value (P), and the boom angular speed (ω). More specifically, the speed correction table  64  records the correction factor (α) values “a 11  to a 99 ” corresponding to the various combinations of the boom cylinder pressure values (P) “P 1  to P 9 ” and the various boom angular speeds (ω) “ω 1  to ω 9 .” Note that in this embodiment the correction factor (α) is used as a function of the boom angular speed (ω) and the boom cylinder pressure value (P), but depending on the working machine the correction factor (α) can be a constant, either the boom angular speed (ω) or the boom cylinder pressure value (P) alone can be a variable of a function, or a different variable, such as the boom angle (θ) can be used as a variable of a function. The configuration of the speed correction table  64  can change depending on the circumstances, or, if the correction factor α is a constant, the speed correction table  64  is not necessary. 
         [0047]    Next,  FIG. 7  will be used to explain the load weight measurement operation (S 52  of  FIG. 3 ) process flow. 
         [0048]    As shown in  FIG. 7 , this process is conducted during the movement of the boom  2 , or more specifically while the load is being lifted. The controller  11  detects the current boom angle (θ) value of the boom  2  based on the output signal of the boom angle detection device  6  (S 1 ). Next, the controller  11  inputs the head pressure and bottom pressure detected from the head pressure detection device  8  and the bottom pressure detection device  9  and calculates the difference to calculate the current boom cylinder pressure value (P) (S 2 ). Next, the controller  11  utilizes the afore-mentioned current boom angle (θ) value and the boom angle (θ) value detected before the first cycle to calculate the boom angular speed (ω) using the prescribed calculation method (S 3 ). Next, the controller  11  refers to the speed correction table ( FIG. 6 ) to determine the correction factor (α) corresponding to the combination of the current boom angular speed (ω) and the boom cylinder pressure value (P) (S 4 ). Next, the controller  11  substitutes the current boom angular speed (ω), the boom cylinder pressure value (P), and the correction factor (α) into the formula “P′=P−αω” to calculate the corrected pressure value (P′) (S 5 ). The corrected pressure value (P′) is a value that subtracts the error components such as the frictional force, etc., that change according to the boom angular speed (ω), from the boom cylinder pressure value (P). Next, the controller  11  refers to the load weight calculation table  63  and calculates the load weight (W) corresponding to the combination of the current boom angle (θ) and corrected pressure value (P′) (S 6 ). The load weight calculation table  63  only records numerical values for the load weight (W) representative values, so interpolation calculation is performed using these numerical values to calculate the current load weight (W). 
         [0049]    The afore-mentioned Steps  1  (S 1 ) to Step  6  (S 6 ) are repeatedly executed a plurality of times at a constant interval using a repeat loop (L 1 ). This is used to calculate the load weight (W) at a plurality of points during the movement of the boom  2 . Also, the controller  11  averages the load weight (W) at a plurality of points to obtain the most accurate load weight (W) value (S 7 ), and stores this in the data storage section  31 , displays it on the display  12 , and, further, checks if this value exceeds the overload value, and if it does, sounds the buzzer  17  to warn the operator (S 8 ). 
         [0050]    Next,  FIG. 8  is used to explain the calibration operation (S 53  of  FIG. 3 ) process. 
         [0051]    As shown in  FIG. 8 , the controller  11  determines whether or not an all clear signal has been entered by the operator using the keyboard  30  (S 11 ). If an all clear signal has been entered (S 11 : Yes), the controller  11  clears all of the data in the load weight calculation table  63  and returns it to the previously provided initial values (S 20 ). This action changes the contents of the load weight calculation table  63  to the same contents as at the time of factory shipment. In addition, if the all clear signal has not been input, the controller  11  determines if no-load calibration has been selected by the operator using the keyboard  30  (S 12 ). If no-load calibration has been selected (S 12 : Yes), the controller  11  moves the boom  2  through the entire variable range of the boom angle (θ) (S 13 ). In addition, in this case the bucket  4  is left empty. 
         [0052]    Then, the controller  11  repeats the same process as Step  1  (S 1 ) to Step  6  (S 6 ) shown in  FIG. 7  during the operation throughout the variable range of the boom to calculate the corrected pressure value (P′) corresponding to the values for the boom angle (θ) recorded in the load weight calculation table  63  (S 14 ). Then, the controller  11  takes the average value of the corrected pressure value (P′) at each boom angle (θ) during the currently performed calibration and the corrected pressure value (P′) corresponding to the column when the load weight (W) of the load weight calculation table  63  is zero (no load) (S 15 ), and then uses this average value to overwrite the corrected pressure value (P′) corresponding to the no-load column of the load weight calculation table  63  (S 21 ). 
         [0053]    In addition, in the afore-mentioned Step  12  (S 12 ), when no-load calibration was not selected, the controller waits in the meantime for the operator to use the keyboard  30  to specify the load weight (S 16 ). Here, the load weight that can be specified is either the intermediate rated load, the maximum rated load, or the overload recorded in the load weight calculation table  63 . Together with this, the operator loads a load having the exact same weight as the afore-mentioned specified weight into the bucket  4 . Then, after the afore-mentioned load has been loaded, the controller  11  moves the boom  2  through the entire variable range of the boom angle (θ) (S 17 ). Then, the controller  11  repeatedly conducts the same process as for Steps  1  (S 1 ) to Step  6  (S 6 ) as shown in  FIG. 7  while the boom is moving through the entire variable range and then calculates the corrected pressure value (P′) corresponding to the values for the boom angle (θ) recorded in the load weight calculation table  63  (S 18 ). Then, the controller  11  takes the average value of the corrected pressure value (P′) at each boom angle (θ) during the currently performed calibration and the corrected pressure value (P′) corresponding to the column when the load weight (W) of the load weight calculation table  63  is zero (no load) (S 19 ), and then uses this average value to overwrite the corrected pressure value (P′) corresponding to the no-load column of the load weight calculation table  63  (S 21 ). 
         [0054]    As explained above, according to this embodiment, occasionally executing this calibration eliminates the error factors due to changes in the weight of the lifting unit resulting from wearing, damage, corrosion, etc., of the bucket, bucket attachment/removal teeth, bucket pin, boom pin, etc., to make measurement with good accuracy possible. 
         [0055]    In addition, the data acquired from the calibration during calibration of the load weight calculation table is not used to update the load weight calculation table but rather the average value of the data acquired from the calibration and the existing data of the load weight calculation table is obtained and this average value is used to update the load weight calculation table so that in the event the data received from the calibration is not a correct value, the effect of this error will not be 100%. 
         [0056]    Embodiments of the present invention were explained above, but these embodiments are merely examples used to explain the present invention and these embodiments are not intended to limit the scope of the present invention. The present invention can perform a variety of other embodiments without deviating from this summary. 
         [0057]    For example, the afore-mentioned embodiments only perform calibration on the load weight calculation table, but calibration can also be performed on the speed correction table.