METHOD AND APPARATUS FOR CONTROLLING WORKING UNITS OF POWER SHOVEL

Abstract: PCT No. PCT/JP88/00771 Sec. 371 Date Mar. 30, 1990 Sec. 102(e) Date Mar. 30, 1990 PCT Filed Aug. 2, 1988 PCT Pub. No. WO90/01586 PCT Pub. Date Feb. 22, 1990.A technique relating to automatic excavation by a power shovel is shown. An ideal reference locus of movement of a front edge of a bucket is approximated by a plurality of points, positions of the plurality of points and postures of the bucket at these points are previously set. If the start of automatic excavation is assigned by an operation pedal or the like, the position of the front edge of the bucket at the assigned moment is made a position to start excavation. The positions of the plurality of points set relative to a vehicle are calculated for each of excavation sections divided by the plurality of points according to the position to start excavation, and angles of rotation of respective working machines needed to move the front edge of the bucket to the calculated position and to set the bucket to the posture of the bucket set are calculated for each of the excavation sections, and the respective working machines are automatically driven making the calculated angles of rotation target angles of rotation for each excavation section. The bucket, an arm and a boom are thereby automatically controlled so that the front edge of the bucket moves along the ideal reference locus of movement set and the bucket has the ideal posture set by simple operations. Thus, it is intended to improve operation efficiency. After terminating excavation, dropping of load is reduced by automatically driving the bucket so that the bucket is always horizontally maintained in accordance with manual operations of the arm and boom.

Description: This invention relates to a technique relating to automatic excavation by a power shovel which has a bucket, an arm and a boom as working machines. As is well known, a power shovel has a bucket, an arm and a boom as working machines, which are driven by a bucket cylinder, an arm cylinder and a boom cylinder, respectively. In order to move the bucket in desired locus and posture, it is indispensable to simultaneously control expansion and contraction of the respective cylinders. Accordingly, in order to move the bucket in desired locus and posture, the operator must simultaneously or alternately operate respective operation levers corresponding to the bucket, arm and boom. Hence, skill is needed for their operation. An inexperienced operator causes increase in unnecessary resistance against excavation by, for example, not directing the front edge of the bucket in the direction of movement, or by making the base plate of the bucket interfere with an excavated surface after excavation. On the other hand, there have been proposed various kinds of apparatuses for controlling power shovels in which a moving locus (for example, a straight line, a circular arc or the like) of the front edge of the bucket and the posture of the bucket for the locus have previously been set, and the bucket, arm and boom are automatically controlled so that the front edge of the bucket moves along the locus. However, these conventional automatic excavating apparatuses are in general for finishing operation. Very few apparatuses aim at excavating and loading operations. Furthermore, apparatuses for excavating and loading operations are still incomplete from the viewpoint of operation efficiency, operation capability, time required for excavation, and the like. Hence, the relating technique is still immature for being used in an actual apparatus. Furthermore, in conventional apparatuses, the speed of working machines at the moment of an automatic mode is fixed. No appratuses have existed in which the speeds of working machines can be arbitrarily changed by a simple operation. Moreover, in conventional apparatuses, the locus of excavation is fixed. Hence, there is a problem in that, even when a bucket hits hard earth and sand, an obstacle and the like in the course of excavation, the bucket intends to move along an excavation locus which has previously been set, and as a result, relief loss occurs, and efficiency is therefore reduced. In addition, conventional apparatuses are more or less unsatisfactory from the viewpoint of efficient utilization of pump output. That is, in conventional apparatuses, commands for flow rates for respective working machines are obtained by obtaining the distribution ratio of the flow rate of a pump for respective working machines according to angles of rotation needed for respective working machines, and by distributing the flow rate of the pump determined from actual pump pressure in the distribution ratio. In general, oil supplied from a pump tends to flow toward a working machine having small load. In conventional apparatuses, the values of commands for flow rates calculated from the above-described distribution ratio are input to respective working machines without modification. Hence, oil flows to a working machine having small load in the amount which is more than the amount corresponding to the command for the flow rate, and oil flows to a working machine having large load in the amount which is less than the amount corresponding to the command for the flow rate. As a result, oil is not exactly distributed in accordance with the distribution ratio. Actual flow rates of oil for respective working machines are determined according to relative movement between a pump and valves for working machines, and oil does not flow exactly in the amount corresponding to the values of commands for respective working machines. Hence, the actual values of flow rates become smaller than the sum of the values of commands for flow rates for respective working machines. As a result, relief loss and loss in pump energy are produced, and time for excavation therefore increases. JP-A-59 150 837 describes a controlling device for the power shovel of a working machine, wherein the position of the claw of the bucket is selected and the movement of the bucket is started from the selected position according to a movement program contained in a plurality of memory elements of a memory. To excavate a trench of a given cross-sectional form by repetiting operations, the shovel is positioned at the starting point of excavation and the shovel coordinates are compared with the contents stored in the first memory element containing the nearest position. The shovel is controlled in such a manner that it moves to the stored first position and, thereafter, to the stored second position, etc. No measures are disclosed how the flow rate could be controlled so that the full hydraulic horsepower of the pump can be used to increase the efficiency of the excavating work. JP-A-58 146 119 and JP-A-58 94 879 dislose excavation machines wherein the shovel is moved, in a teaching mode, by manual control. The positions of the bucket obtained in the teaching mode are stored in a memory. During an automatic excavating process, the contents of the memory is read out for obtaining movements of the bucket that are similar to the movements during the teaching process. JP-A-59 131 066 discloses a controlling apparatus for a working machine, wherein the boom, the arm and the bucket are controlled with one lever. The angles of the boom, the arm and the bucket are detected and the speed compositions of the tip of the bucket and the rotational speed of the bucket are given by operation of an operating lever. The rotational direction, low speed and maximum speed command of the bucket are selected by the operating lever which has two switches. The rotational speed of the boom and the arm are found by the operation of the operating lever through an operation apparatus. Thus, the boom and the arm are controlled. It is an object of the present invention to provide a controlling device for a power shovel which improves the excavation efficiency by driving the working machines effectively by utilizing the full pump output. The invention is defined by claim 1. By outputting a command having a value which is larger than the command for a flow rate calculated from the distribution ratio and the relationship between the pump pressure and the flow rate of the pump for a working machine having the largest load (usually the arm) by the second arithmetic means, and by outputting commands having values which are identical to the calculated values of commands for flow rates for other two working machines, the sum of the values of commands for flow rates is made a value which is larger than the flow rate of the pump determined by the pump pressure. As a result, oil flows to the respective working machines in flow rates exactly in the calculated distribution ratio, and relief loss and loss in the output of the pump are reduced. It is thereby possible to effectively utilize the output of the pump, and to increase excavation efficiency. FIG. 1 is a block diagram showing a first embodiment of a controlling device that does not belong to the present invention; FIG. 2 is a diagram showing an appearance of a power shovel; FIG. 3 is a diagram used for defining the lengths, angles and the like of working machines; FIG. 4 is a diagram for explaining a method of setting a locus of automatic excavation; FIG. 5 consists of process diagrams for explaining processes of automatic excavation; FIG. 6 is a diagram showing rotating states of a locus of excavation; FIG. 7 is a diagram for explaining a method for obtaining Δα, Δβ and Δγ: FIG. 8 is a diagram showing a curve of constant horsepower; FIG. 9 is a diagram showing an example of the movement of respective working machines at the moment of automatic excavation; FIG. 10 is a diagram schematically showing the calculation of target positions and output states of a command signal; FIG. 11 is a diagram showing a state of excavation when a manual command has been input during excavation; FIG. 12 is a diagram for explaining an initial setting mode for the posture of a bucket; FIG. 13 is a flowchart for explaining the operation of a controller in the first embodiment; FIG. 14 is a diagram showing the relationship between the pump pressure and the set value for determining the moment to start excavation; FIG. 15 is a diagram showing an operation pedal in a second embodiment of the present invention; FIG. 16 is a diagram showing curves of constant horsepower; FIG. 17 is a diagram showing the relationship between the tread force and tread angle of an operation pedal; FIG. 18 is a flowchart for explaining the operation of another controller in the second embodiment not belonging to the present invention; FIG. 19 is a diagram for explaining the relationship between the pump pressure and the set value in a third embodiment not belonging to the present invention; FIG. 20 is a diagram showing variations of the locus when a boom rises in the third embodiment; FIG. 21 is a diagram for explaining an example of excavation in which a section for horizontal excavation is provided in the third embodiment; FIG. 22 is a flowchart for explaining the operation of a controller in the third embodiment; FIG. 23 is a block diagram showing an example of the configuration of control in a fourth embodiment which is designed according to the present invention; FIG. 24 is a diagram for explaining a method for determining commands for flow rates; and FIG. 25 is a flowchart showing the operation of a controller in the fourth embodiment. The present invention will now be explained in detail with reference to the embodiments shown in the accompanying drawings. First, a first embodiment not belonging to the present invention will be explained with reference to FIGS. 1 - 14. FIG. 2 shows the schematic configuration of a power shovel. In FIG. 2, an upper pivoting body 2 is pivotably supported on a running body 1. One end of a boom 3 is pivoted on the pivoting body 2. An arm 4 is pivoted on another end of the boom 3. A bucket 5 is pivoted on another end of the arm 4. The boom 3, the arm 4 and the bucket 5 are rotatably driven by a boom cylinder 6, an arm cylinder 7 and a bucket cylinder 8, respectively. The lengths, angles and the like of the respective working machines are now defined as indicated in FIG. 3. That is, the points of rotation for the boom, arm and bucket and the point of the front-edge of the bucket are represented by points A, B, C and D, respectively, and l₁ ; the length between the points A and B l₂ ; the length between the points B and C l₃ ; the length between the points C and D α ; the angle made by a line segment AB and the vertical axis (the angle of the boom) β ; the angle made by a line segment BC and the production of the line segment AB (the angle of the arm) γ ; the angle made by a line segment CD and the production of the line segment BC (the angle of the bucket) δ ; the angle made by a direction u of excavation and the base plate of the bucket (the angle of excavation) ε ; the angle made by the direction u of excavation and the line segment CD. The posture of the bucket is defined by the angle and the like. First, the method of setting a locus of excavation at the moment of automatic excavation will be explained. In the present embodiment, a locus of excavation for the front edge of the bocket as shown in FIG. 4 is set. This locus is a locus of a circular arc having a radius R centering around a predetermined point O, and the circular-arc locus is approximated by n points P₁, P₂, --- P n . In setting the locus, it is assumed that the amount V of earth in one excavation operation (a hatched region in FIG. 4) is obtained by multiplying the full amount of the bucket by a predetermined number k (= 1 - 3), the depth d of excavation is obtained by multiplying the length of the line segment CD (= l₃) by a predetermined number e (= 0.1 - 1.5), and an angle  is a proper value between 10° - 180°. The values k, e,  and the radius R of the circular arc are determined in accordance with the quality of earth, the form of the bucket, the contents of operation and the like, and a reference locus of excavation is determined by specifying these values. For the locus of excavation thus determined, the n points P₁ - P n are approximated as described above, and these points P₁ - P n are made target positions for the front edge of the bucket for respective unit excavation sections, the positions of the points P₂ - P n are set making the position of the point P₁ to start excavation a reference position. The postures of the bucket, that is, the above-described angles ε₁ - ε n are previoulsy determined for the target positions P₁ - P n , respectively. In determining, the posture ε of the bucket, resistance against excavation is minimized by providing a small excavation angle δ at the moment to start excavation and by providing a small excavation angle δ within a range in which the back portion of the bucket interferes with earth as little as possible during excavation. That is, in this excavation operation, a virtual line OD is rotated by a unit angle Δ (= /n) so that the bucket follows the target positions P₁ - P n with the postures ε₁ - ε n by simultaneously driving the boom, arm and bucket. Automatic excavation in the present embodiment is executed in accordance with the processes shown in FIG. 5. The outline of the processes will now be explained. In the present apparatus, there is provided an operation pedal 10 for instructing an automatic excavation mode in addition to two operation levers 11 and 12 for providing commands for rotation and pivoting motion for the boom, arm and bucket. Automatic excavation along the above-described circular-arc locus is performed by the operation of the operation pedal 10 (by continuing to tread the pedal). First, the operator moves the front edge of the bucket to a desired position to start excavation by operating the operation pedals 11 and 12 (FIG. 5(a)), and then selects the automatic excavation mode and assigns the position to start excavation by treading the operation pedal 10 (FIG. 5(b)). That is, when the operation pedal 10 has been trodden, the position of the front edge of the bucket at that moment is obtained, and the obtained position is made the position to start excavation for the present excavation operation. If the position P₁ to start excavation for the point A of rotation for the boom is expressed by a coordinate (X₁ , Y₁), the position (X₁, Y₁) can be obtained by the following expression using the angle α of the boom, the angle β of the arm and the angle γ of the bucket at the moment when the pedal has been trodden: In the present embodiment, as shown in FIG. 6, a tilt angle ϑ of topography is estimated from the position relationship between the detected position P₁ to start excavation and a predetermined point P a which has previously been set, the above-described circular-arc locus is rotated in accordance with the tilt angle ϑ, and automatic excavation in accordance with the rotated circular-arc locus is performed. The predetermined point P a is set to a proper position in front of the caterpillar 1. It becomes thereby possible to more or less deal with variations in topography. That is, in the present automatic excavation operation, an arithmetic algorithm has previously been set so that the most suitable excavation locus and posture of the bucket at the present excavation operation are determined if the operator assigns only the position to start excavation. In the present embodiment, all positions of the plural points P₁ - P n which have been set relative to the vehicle (the point A of rotation of the boom) are not obtained at the moment to start excavation, but the next target position is obtained each time at each unit section. The storage capacity is thus reduced. When the start of excavation has been assigned, the coordinate for the next target position P₂ which advances by the unit angle Δ on the excavation locus determined in accordance with the position to start excavation is obtained. Furthermore, since the posture of the bucket has been determined in accordance with the target position P₂, it is possible to uniquely determine the angle α₂ of the boom, the angle β₂ of the arm and the angle γ₂ of the bucket at the target position P₂. If the target angles α₂, β₂ and γ₂ of the working machines have been determined, it is possible to determine target angles Δα , Δβ and Δγ of rotation for the respective working machines in order to move the front edge of the bucket up to the point P₂ by obtaining deviations from the actual angles of the respective working machines. FIG. 7 is a diagram for explaining the calculation to obtain Δα, Δβ and Δγ , where the symbol ₁ represents the angle made by the horizontal line and the line segment OD, the symbol w₁ represents the angle made by the line segment CD and the line segment OD at the point P₁ to start excavation, and the symbol w₂ represents the angle made by the line segment CD and the line segment OD at the next target position P₂. If the coordinate for the point P₂ is expressed by (X₂, Y₂), we obtain It is also possible to express X₂ by X₂ = X₁ + R · Δ · sin ( ₁ + 0.5Δ ) (3). If the terms in the expression (2) are expressed by l₂cos ( α₁ + β₁ ) + l₃cos (α₁ + β₁ + γ₁) + l a and l₃cos ( α₁ + β₁ + γ₁ ) · Δγ = l b , the following expression holds from the expressions (2) and (3): Y₁ · Δα + l a Δβ + l b Δγ = - R · Δ · sin (₁ + 0.5Δ) (4). Similarly, the following expression holds: = Y₁ - R · Δ · cos ( ₁ + 0.5Δ) (6). If the terms in the expression (5) are expressed by l₂sin ( α₁ + β₁ ) + l₃sin ( α₁ + β₁ + γ₁ ) = l c and l₃sin ( α₁ + β₁ + γ₁ )Δγ = l d , the following expression holds from the expressions (5) and (6): X₁Δα + l c Δβ + l d Δγ = RΔ · cos ( ₁ + 0.5Δ ) (7). Furthermore, since the following expressions hold: ₁ + w₁ = α₁ + β₁ + γ₁ - π/2 (8), and ₁ + Δ + w₂ = α₁ + β₁ + γ₁ + Δα + Δβ + Δγ - π/2 (9), the following expression holds from the expressions (8) and (9): w₂ - w₁ = Δα + Δβ + Δγ - Δ (10). Since all the parameters except Δα, Δβ and Δγ in the above-described expressions (4), (7) and (10) are specified, it is possible to obtain the angles Δα, Δβ and Δγ of rotation for the respective working machines in order to move the front edge of the bucket from the point P₁ to start excavation to the next target point P₂ by solving the expressions (4), (7) and (10). The commands for flow rates for the cylinders of the respective working machines are determined according to the angles Δα, Δβ and Δγ of rotation thus obtained. At that time, the commands for flow rates for the respective working machines are determined so that the sum Q s (= Q bm + Q am + Q bt , where Q bm ; the flow rate for the boom, Q am ; the flow rate for the arm, and Q bt ; the flow rate for the bucket) of flow rates of pressurized oil to be supplied to the respective working machines is equal to the discharge flow rate of the pump at that moment. That is, the distribution ratio of flow rates needed for the respective working machines is determined according to the angles Δα, Δβ and Δγ of rotation, and the flow rate Q d of the pump at the maximum output is obtained from the relationship of constant horsepower between the flow rate Q of the pump and the pump pressure P and the actual pump pressure P d at the present moment. The values of the commands for flow rates for the respective working machines are determined by distributing the flow rate Q d of the pump in the determined distribution ratio. At that time, the actual flow rates to be supplied to the respective working machines are obtained according to the angle of the boom, the angle of the arm and the angle of the bucket at respective moments, and the above-described distribution ratio is occasionally adjusted according to the calculated actual flow rates so that the boom, arm and bucket can simultaneously reach the target angles α₂, β₂, and γ₂. The excavation operation for every unit section ends when the arm has reached the target angle β₂, and the process proceeds to the control for the next section when the angle of the arm has reached the target value β₂. Also in the next section, in the same manner as described above, first, the target position P₃ for the front edge of the bucket and the angle ε₃ for the posture of the bucket are determined. The angles Δα, Δβ and Δγ of rotation are then determined according to the above-described determined values, and the commands for flow rates for the respective working machines are determined according to the distribution ratio of flow rates corresponding to the angles Δα, Δβ and Δγ. The control for this section ends when the arm has reached the target angle β₃, and the process proceeds to the control for the next section. By repeatedly executing such control operations until the end point P n , the front edge of the bucket moves from the initial point P₁ ( α₁, β₁, γ₁ ) along the target positions P₈ ( α₈, β₈, γ₈ ) --- P₁₅ (α₁₅, β₁₅, γ₁₅) --- P₂₀ (α₂₀, β₂₀, γ₂₀) on the circular-arc locus (FIG. 5(c)), as shown in FIG. 9. FIG. 10 shows the schematic configuration of the above-described arithmetic control. That is, in the present automatic excavation operation, it is intended to reduce the memory capacity by calculating the coordinate position of the next target point at the start of each unit section. Furthermore, the commands for flow rates for the respective working machines are occasionally corrected by performing feedback of actual values of flow rates to the commands for flow rates obtained from these target positions with a proper period, and the front edge of the bucket can thus exactly move on the excavation locus which has been set having proper postures. When the operation pedal 10 is returned in the course of excavation, the commands for flow rates for the respective working machines are set to zero, and the respective working machines are immediately stopped as long as manual operation is not performed by the operation levers 11 and 12. When commands by the manual levers 11 and 12 have been input during automatic excavation, priority is given to manual operations for the purpose of security, and automatic excavation is resumed from the point where the lever operation has been stopped. For example, if there has been an input of a manual operation when automatic excavation proceeded to the point P₈, as shown in FIG. 11, automatic excavation toward the next target point P₉ is resumed making the point where the lever operation has been stopped a point to resume excavation. That is, when there has been a manual input during automatic excavation, the automatic excavation is not released, but is temporarily stopped. In this case, it is arranged so that the end of excavation is detected according to the value of the pump pressure of the hydraulic pump, and that the moment when the pump pressure of the hydraulic pump exceeds a predetermined value in the second half of excavation operations in which excavation sections have proceeded to a certain degree is recognized as a moment to end excavation. After the recognition, the boom is raised, the bucket is tilted to a horizontal state, and the excavation operation is thus terminated. As described above, since the end of excavation is detected by detecting load by the pump pressure of the hydraulic pump, it is possible to prevent wasteful excavation. After the end of excavation, the tilt angle of the bucket is shifted to a mode for horizontally holding the bucket in which the tilt angle of the bucket is always maintained at a horizontal state (FIG. 8(d)). That is, in the mode for horizontally holding the bucket, the angle γ of the bucket is automatically controlled so that the relationship α + β + γ = (3/2) π is satisfied in accordance with input commands from the operation lever for the boom and the operation lever for the arm in order to always horizontally maintain the upper surface of the bucket. In the mode for horizontally holding the bucket, the operation of the above-described operation pedal for automatic excavation is made invalid. By such a control operation, it is arranged so that load is not dropped, and the operation during loading work becomes simple (the bucket operation becomes unnecessary). The automatic excavation mode is released when the bucket is rotated to the dump side by a predetermined amount or more by a manual operation in the mode for horizontally holding the bucket. That is, when the operator rotates the bucket to the dump side by the predetermined amount or more for discharging earth in the mode for horizontally holding the bucket, the automatic excavation mode is released (FIG. 5(e)). When the automatic excavation mode has been released, the control shifts to a bucket posture automatic setting mode in which the bucket is always controlled in the most suitable posture at the moment to start excavation (FIG. 5(f)). That is, in the bucket posture automatic setting mode, the bucket cylinder is controlled so that the most suitable bucket posture at the moment to start excavation is maintained in accordance with the position of a bucket pin (the point C in FIG. 3) which is determined by the positions of the boom and the arm after discharging earth. To put it concretely, if the bucket posture is defined by the angle λ (the angle made by a line segment connecting the position of the front edge of the bucket to the above-described set point P a and the upper surface of the bucket), as shown in FIG. 12, and the angle made by the horizontal line and the above-described line segment is represented by τ, the angle γ of the bucket is controlled so that the following expression is satisfied: ∝ + β + γ + λ + τ = (3/2) π (11). That is, in the above-described expression, the angle λ is a predetermined value, and the angle τ can be obtained from the angles α, β and the like. Hence, the angle γ of the bucket is controlled so that the expression (11) is satisfied in accordance with the angle α of the boom and the angle β of the arm provided by manual operations. The bucket posture setting mode is stopped when the operation lever 11 for the bucket is manually operated. Subsequently, the respective working machines including the bucket are driven in accordance with commands from the operation levers 11 and 12. In the case when the operator has arbitrarily changed the posture of the bucket at the moment of initial automatic excavation or the bucket posture setting mode, and the like, the bucket is not necessarily maintained in the most suitable posture at the moment to start excavation. In such cases, the bucket posture is not abruptly corrected to the most suitable posture until the next section, but sections are provided in an appropriate number, and the bucket is gradually corrected to the most suitable angle in these sections. FIG. 1 shows an example of the configuration of the control for realizing the above-described respective fuctions. In FIG. 1, whether or not an automatic excavation mode assigning pedal 10 has been trodden is detected by a pedal operation detector 17, and the detected signal is input to a controller 20. The direction and amount of operation of the bucket/boom operation lever 11 are detected by a lever position detectors 13 and 15. A bucket rotation command γ ˙ r and a boom rotation command α ˙ r are input from these detectors 13 and 15 to switches 30 and 32, respectively. The direction and amount of the operation of the arm operation lever 12 are detected by a lever position detector 14, and an arm rotation command β ˙ r which is the detected signal thereby is input to a switch 31. The command signals α ˙ r , β ˙ r and γ ˙ r by the operation levers 11 and 12 are also input to the controller 20. The switches 30, 31 and 32 performs switching operations according to switching control signals SL₁, SL₂ and SL₃ input from the controller 20, respectively, and selectively switch command signals γ ˙ c , β ˙ c and α ˙ c at the moment of automatic excavation input from the controller 20 and command signals γ ˙ r , β ˙ r and α ˙ r at the moment of manual excavation input from the lever position detectors 13, 14 and 15. A bucket control system 40 consists of an angle sensor 41 for detecting the angle γ of the bucket, a differentiator 42 for detecting the actual rotation speed γ ˙ of the bucket by differentiating the angle γ of the bucket, an addition point 43 for obtaining a deviation between a target value and a signal indicating the actual rotation speed γ ˙ of the bucket, and a flow rate control valve 44 for supplying a bucket cylinder 4 with pressurized oil having a flow rate in accordance with a deviation signal from the addition point 43 so as to make the deviation signal 0. Similarly to the bucket control system 40, an arm control system 50 and a boom control system 60 includes angle sensors 51 and 61, differentiators 52 and 62, addition points 53 and 63, and flow rate control valves 54 and 64, respectively, and control the rotation of the arm and boom so as to coincide with command values. The angle γ of the bucket, the angle β of the arm and the angle α of the boom detected by the angle sensors 41, 51 and 61 in these fow rate control systems, respectively, are also input to the controller 20. The pump pressure in a pump (not shown) for the working machines is detected by an oil pressure sensor 70, and the value of the detected pressure is input to the controller 20. The function of such a configuration will be explained with reference to the flowchart shown in FIG. 13. When the operation pedal 10 has been trodden, the tread is detected by a pedal operation detector 17. The detected signal is input to the controller 20, which starts the control by the automatic excavation mode (step 100). For the purpose of security, it is arranged so that the automatic mode can be operated only when manual operations by the operation levers 11 and 12 are performed and at the moment of the bucket posture automatic setting mode shown in FIG. 5(f), and the controller 20 does not start the automatic mode even if the operation pedal 10 has been trodden in other cases. When the automatic mode has been started, the controller 20 obtains the position P₁ of the front edge of the bucket at the moment of start according to the outputs γ , β and α from the angle sensors 41, 51 and 61 (see expression (1)). Subsequently, the controller 20 puts the calculated position P₁ to start excavation into an arithmetic program made from the expressions (4), (7) and (10), and calculates angles Δα, Δβ and Δγ of rotation for the respective working machines needed to set the bucket to the posture ε₂ of the bucket at the next target position P₂ and to move the front edge of the bucket from the position P₁ to the position P₂ (step 110). The controller 20 then determines the distribution ratio of oil to be supplied to the respective working machines from these angles Δα, Δβ and Δγ of rotation (step 120), further obtains the pump pressure P d from the output of the oil pressure sensor 70 at this moment, and obtains the flow rate Q d of the pump at the maximum output corresponding to the pump pressure P d from the relationship of constant horsepower shown in FIG. 8. The controller 20 then obtains the command signals α ˙ c , β ˙ c and γ ˙ c for the respective working machines by distributing the flow rate Q d of the pump in the above-described distribution ratio, and outputs the command signals α ˙ c , β ˙ c and γ ˙ c to the switches 32, 31 and 30, respectively (step 130). When the automatic mode has been selected, respective contacts of the switches 30, 31 and 32 are switched to the side of the controller 20 by the switching control signals SL₁, SL₂ and SL₃ of the controller 20, and the above-described command signals α ˙ c , β ˙ c and γ ˙ c from the controller 20 are input to the boom control system 60, the arm control system 50 and the bucket control system 40 via the switches 32, 31 and 30, respectively. At the next step 140, the controller 20 determines whether or not the pedal 10 is trodden according to the output from the pedal operation detector 17. When the return of the pedal 10 has been detected, the command signals α ˙ c , β ˙ c and γ ˙ c to be input to the respective flow rate control systems are immediately made zero (step 150). At step 160, it is determined whether or not one of manual commands γ ˙ r , β ˙ r and α ˙ r has been input by the operation of the operation levers 11 and 12. When one of the manual commands has been input, priority is given to the input manual command (step 170). That is, when one of the manual commands have been input, the switch of the working machine corresponding to the input manual command among the switches 30, 31 and 32 is switched to the side of the operation lever, so that the command signal from the side of the operation lever is supplied to the corresponding flow rate control system. Thus, the command signal α ˙ c , β ˙ c or γ ˙ c (these signals are zero when the operation pedal is switched off) from the controller 20 or the command signals α ˙ r , β ˙ r or γ ˙ r from the manual levers 11 and 12 are input to the corresponding flow rate control systems 60, 40 and 50 in accordance with the operation state of the operation pedal 10 and the operation levers 11 and 12, and the bucket, arm or boom are thereby rotated (step 180). It is arranged so that the controller 20 obtains the actual flow rates of oil to be supplied to the respective cylinders 8, 7 and 6 according to the outputs from the angle sensors 41, 51 and 61, respectively, and successively adjusts the above-described distribution ratio in accordance with these actual flow rates. Subsequently, the controller 20 determines whether or not the arm has reached the target angle β₂ according to the detected output β from the angle sensor 51 (step 190). When the arm has not reached the target angle β₂, the process returns to step 120, where the same control as described above is repeated. When the arm has reached the target angle β₂, it is determined whether or not excavation has ended (step 200). When excavation has not ended, the process returns to step 110, where the arithmetic control to move the position of the front edge of the bucket to the next target position P₃ is performed in the same manner as described above. Subsequently, the front edge of the bucket is moved along the target positions P₄, P₅, --- until it is determined that excavation has ended at step 200, in the same manner as described above. In this case, it is arranged so that the moment when the output value from the oil pressure sensor 70 has exceeded a predetermined value in the second half of the excavation sections is detected as the moment to terminate excavation. When a manual command has been input during automatic excavation, the controller 20 returns the process to step 110 at the moment when the manual command has been stopped, switches the switch corresponding to the working machine for which the manual command has been input to the side of the controller 20, and redrives all the working machines by command signals from the controller 20 making the point where the manual operation has been stopped a point to resume the process. When the end of excavation has been determined at step 200, the controller 20 shifts to the mode for horizontally holding the bucket which horizontally controls the tilt angle of the bucket (step 210). In the mode for horizontally holding the bucket, the switches 31 and 32 are switched to the side of the manual levers 11 and 12, the switch 30 continues to be connected to the side of the controller 20, and the boom and arm are driven according to manual commands. As for the bucket, the command signal γ ˙ c is output from the controller 20 so that the relationship α + β + γ = (3/2) π is satisfied, and the tilt angle of the bucket is always maintained in a horizontal state even if the boom and arm are arbitrarily subjected to manual operations. If the bucket has been rotated toward the dump side by a predetermined angle or more during the mode for horizontally holding the bucket, the controller 20 releases the automatic mode (step 220), and shifts the process to a bucket posture initial setting mode (step 230). In this mode, initially, the switches 31 and 32 are connected to the side of the manual levers 11 and 12 and the switch 30 is connected to the side of the controller 20, so that manual commands are input to respective control systems only for the boom and arm. As for the bucket, the command signal γ ˙ c from the controller 20 is output so that the above-described expression (11) is satisfied, and hence the bucket always has the most suitable initial posture in accordance with the height of the bucket. This automatic setting mode is stopped when a manual command for the bucket has been input. In the above-described embodiment, the moment when the pump pressure exceeds a predetermined set value in the second half of excavation operations, that is, when the load on the working machines exceeds a constant value is made the end of excavation, and the process is then shifted to the mode for horizontally holding the bucket. However, the number of divided sections may merely be counted, and the moment when excavation for a predetermined number of sections has ended may be made the end of excavation. Furthermore, the absolute posture of the bucket may be determined, and the moment when the absolute posture of the bucket nearly approaches a horizontal state may be made the end of excavation. Moreover, although, in the above-described embodiment, the moment when the operation pedal 10 has been trodden is made the moment to start excavation and the position of the front edge of the bucket at that moment is made the position to start excavation, the load may be detected according to the pump pressure and the moment when the pump pressure has exceeded a predetermined set value J may be made the moment to start automatic excavation, as shown in FIG. 14, in order to more exactly set the point to start excavation. That is, in the case in which the moment when the operation pedal 10 has been trodden is made the start of excavation, it is difficult to make the moment when the front edge of the bucket has reached earth completely coincide with the moment when the operation pedal has been trodden, and variations therefore arise in the position to start excavation. This causes variations in the amount of excavated earth, which may further cause inferior excavation efficiency. Accordingly, if the condition for determining the moment to start excavation is set to the moment when the pump pressure after the operation pedal has been trodden reaches the set value J or more, it becomes possible to more exactly determine the point to start excavation. That is, if it is assumed that the front edge of the bucket is separated from earth at the moment when the operation pedal has been trodden, the respective working machines are automatically moved in the direction of reaching earth from the moment when the operation pedal has been trodden to the moment when the bucket reaches earth even if the manual operation is stopped. Subsequently, since there is a change in load at the moment when the bucket has reached earth, the change is detected by the pump pressure. To put it concretely, the set point J for detecting the moment to start excavation is set for the pump pressure, the moment when the pump pressure has exceeded the set point J is made the actual moment to start excavation, and the position of the front edge of the bucket is made the position to start excavation, in this case, if separate pumps are provided for the respective working machines, the moment to start excavation may be detected by the pump pressure of a working machine having a large detection value. In this detection method, since the load detection is performed by the pump pressure, the method has the advantage that only one pressure gauge is needed in the case of using one pump. Furthermore, the following function to prevent wasteful excavation may be added to the above-described embodiment. As described above, in the present apparatus, automatic excavaton is performed so that the excavation angle δ always becomes small. In such an excavation operation, if it is assumed that conditions, such as the quality of earth and the like, are identical, the amount of work necessary for scooping and pushing aside the same amount of earth is constant. In addition, in the present apparatus, since the control of the pump is performed along the curve of constant horsepower shown in FIG. 8, it is estimated that the time necessary to perform the above-described amount of work can be nearly constant. Accordingly, one automatic excavation operation is first tried at a location having a horizontal surface of earth, and the excavation time at that moment, that is, the time from the moment when the bucket touches the surface of earth to the moment to start scooping (the boom is raised and the bucket is tilted) is measured and stored. For automatic excavation from the next excavation operation, scooping is started from the moment when the stored time has lapsed from the moment to start excavation. Wasteful excavation is thus prevented. In order to perform the above-described timing and storing operations, an appropriate operation button may, for example, be provided, and the measuring and storing operation for the excavation time may be performed when this button has been pushed before the assignment to start automatic excavation by the operation pedal 10. If such a function is supplemented, it is possible to securely prevent wasteful excavation and to shorten the excavation time even if topography has changed due to a change in the number of excavation operations, the locus of excavation and the like. Next, an explanation will be provided of a second embodiment in which the following additional functions are provided for the operation pedal 10. (1) The automatic mode is selected and the moment to start excavation is indicated by treading the operation pedal 10 (this function is also provided in the preceding embodiment). (2) The speeds of the respective working machines can be changed in accordance with the tread angle. (3) Automatic excavation is terminated by treading the pedal 10 by a predetermined angle or more during automatic excavation. (4) At the moment of discharging earth (at the moment of releasing the automatic mode), the angle of the arm and the angle of the boom at that time are stored by treading the pedal 10 by a predetermined angle or more. At the moment of excavation after the next excavation operation, if the pedal 10 is trodden after the end of excavation, the arm and boom automatically move to positions corresponding to the angle of the arm and the angle of the boom which have been stored as described above while maintaining the bucket in a horizontal state. This is for discharging earth at an identical position. First, as for the above-described function (2), by changing the sum Q s (= Q bm + Q am + Q bt , where Q bm ; the flow rate for the boom, Q am ; the flow rate for the arm, Q bt ; the flow rate for the bucket) of flow rates of pressurized oil to be supplied to the respective working machines in accordance with the tread angle of the operation pedal 10, the speeds of the working machines are changed in accordance with the tread angle. That is, in the present embodiment, the process is identical to the process in the preceding embodiment in that the angles Δα, Δβ and Δγ of rotation for the respective working machines for moving the front edge of the bucket from a certain target point to the next target point are obtained by solving the expressions (4), (7) and (10) described before, and the distribution ratio (Q bm : Q am : Q bt ) for flow rates needed for the respective working machines is determined according to the obtained andgles Δα, Δβ and Δγ. At that time, however, the tread angle ϑ of the operation pedal 10 is detected (see FIG. 15), and a suitable curve of constant horsepower in accordance with the detected value ϑ is selected (see FIG. 16). In this case, as shown in FIG. 16, a plurality of curves of constant horsepower consisting of the relationship between the flow rate Q for the pump and the pump pressure P are set in accordance with the tread angle ϑ of the pedal , and a curve of constant horsepower which corresponds to the detected tread angle ϑ of the pedal is selected. The values of the commands for flow rates for the respective working machines are determined by obtaining the flow rate Q d of the pump which corresponds to the actual pump pressure P d according to the selected curve of constant horsepower, and by distributing the flow rate Q d of the pump in the determined distribution ratio. That is, in this case, although the total flow rate Q s is changed in accordance with the tread angle ϑ of the pedal, the distribution ratio determined as described above is never changed. Next, the above-described function (3) will be explained. When the operation pedal 10 has been trodden by a predetermined angle or more during excavation, scooping (in which the bucket is rotated toward the tilt side and the boom is raised) is performed and automatic excavation is forcibly terminated, even if the excavation section has not been completed to the end, in order to prevent wasteful excavation. That is, the relationship between the tread force and the tread angle ϑ of the operation pedal 10 is provided in two stages, as shown in FIG. 17. The operator strongly treads the pedal 10 by the angle ϑ₁ or more in the case when he determines that the bucket sufficiently scoops earth and sand during excavation, and the like. When the pedal 10 has been trodden by the angle ϑ₁ or more during excavation, tilting of the bucket and raising of the boom are performed from that moment, and automatic excavation is forcibly terminated. Hence, it is possible to favorably prevent wasteful excavation by the determination of the operator. Next, the above-described function (4) will be explained. If the operation pedal 10 has been trodden by the predetermined angle ϑ or more in the same manner as described above (see FIG. 17) when the automatic mode explained with reference to FIG. 5(e) is released, the angle α m of the boom and the angle β m of the arm are stored in a memory 21 within the controller 20. At the moment of excavation after the next excavation operation, when the operation pedal is trodden within the angle range of 0 - 0₁ after terminating automatic excavation, the boom and arm automatically move to positions corresponding to the angle α m of the boom and the angle β m of the arm which have been stored as described above while maintaining a horizontal state of the bucket at the moment of the mode for horizontally holding the bucket. Thus, earth and sand are discharged at an identical position at the moment of respective excavation operations. During this control operation, if manual commands have been input for the boom and arm, the automatic operations for the boom and arm are stopped, and the boom and arm are thereafter driven in accordance with the manual commands. The bucket is thereafter automatically driven so that the upper surface of the bucket is always maintained in a horizontal state in accordance with the manual commands for the boom and arm. Thus, in the second embodiment, since the operation pedal 10 is provided with the above-described four functions, it is arranged so that the pedl operation detector 17 shown in FIG. 1 detects the tread angle ϑ of the operation pedal 10, and the detected signal ϑ is input to the controller 20. If the operation pedal 10 has been trodden by the angle ϑ or more when the automatic mode was released, the angle α m of the boom and the angle β m of the arm at that moment are stored in the memory 21 within the controller 20. FIG. 18 shows such a concrete example of the operation of the second embodiment. In FIG. 18, steps 161, 171, 250 and 260 are added to the flowchart shown in FIG. 13, and step 130 shown in FIG. 13 is replaced by step 131. In FIG. 18, like steps as those shown in FIG. 13 are indicated by like step numbers, and an explanation thereof will be omitted. That is, at step 131, the controller 20 takes in the detected value ϑ by the pedal operation detector 17, selects a curve of constant horsepower corresponding to the detected value ϑ, obtains the pump pressure P d from the output from the oil pressure sensor 70 at this moment, and obtains the flow rate Q d of the pump which corresponds to the pump pressure P d from the selected curve of constant horsepower. The controller 20 then obtains the command signals α ˙ c , β ˙ c and γ ˙ c for the respective working machines by distributing the pump pressure Q d in the distribution ratio described before, and outputs the command signals α ˙ c , β ˙ c and γ ˙ c to the switches 32, 31 and 30, respectively. At step 180, it is determined whether or not the operation pedal 10 has been trodden to an angle exceeding the angle 0₁. If the result is affirmative, excavation is terminated by scooping the bucket to a horizontal state and raising the boom (step 190). Subsequently, the bucket is shifted to the mode for horizontally holding the bucket (step 210). Thus, wasteful excavation is prevented. When releasing the automatic mode (step 220), it is determined whether or not the operation pedal 10 has been trodden to an angle exceeding the angle ϑ₁ (step 250). If the result is affirmative, the controller 20 takes in the outputs β m and α m from the angle sensors 51 and 61, and stores the angle β m of the arm and the angle α m of the boom which have been taken in in the memory 21 (step 260). At the moment of excavation after the next excavation operation, when the operation pedal 10 has been trodden within the angle range of 0 - ϑ₁ after terminating automatic excavation, the boom and arm automatically move to positions corresponding to the angle α m of the boom and the angle β m of the arm which have been stored as described above while maintaining a horizontal state of the bucket at the moment of the mode for horizontally holding the bucket described before. Thus, earth and sand are discharged at an identical position at the moment of respective excavation operations. During this control operation, if manual commands have been input for the boom and arm, the controller 20 switches the switches 31 and 32 to the side of the operation levers, and the boom and arm are driven in accordance with the manual commands. Although, in the present embodiment, the tread up to the second step of the operation pedal is detected by detecting that the operation pedal 10 has been trodden deeper than the predetermined angle ϑ₁, the tread up to the second step may be determined by detecting that the operation pedal has been trodden up to the angle ϑ₂ shown in FIG. 17. Furthermore, the method for changing the sum of commands for flow rates for the respective working machines in accordance with the tread angle of the pedal is not limited to that shown in the above-described embodiment, but a predetermined curve of constant horsepower shown in FIG. 8 may be shifted by a calculation in accordance with the tread angle of the pedal. Any method may be used, provided that the sum of the commands for flow rates for the respective working machines is eventually changed while maintaining the distribution ratio. Next, a third embodiment not belonging to the present invention will be explained. In the third embodiment, load detection is performed by detecting the pump pressure of the working machines during automatic excavation as shown in FIGS. 4 and 9, and two different set values C₁ and C₂ are set for the pump pressure, as shown in FIG. 19. It is arranged so that the set value C₁ is a value which is a little smaller than relief pressure, and the set value C₂ is a value which is smaller than the value C₁ by about several - several tens of kgf/cm². During automatic excavation, when the above-described pump pressure for the working machines becomes larger than the set value C₁, the boom is raised until the pump pressure becomes the set value C₂ or less. The raising of the boom is stopped at the moment when the load becomes equal to the set value C₂. At the moment of the raising operation of the boom, the arm and bucket are rotated until both the arm and bucket reach the target angles Δβ and Δγ calculated at the start of the proper excavation section, respectively. Subsequently, the position of the front edge of the bucket for stopping the boom and rotating the bucket and arm to the target angles Δγ and Δβ as described above is calculated, and automatic excavation for remaining sections is resumed making the calculated position a point to resume excavation. To put it concretely, as shown in FIG. 20, the point to resume excavation after performing the raising of the boom is represented by a symbol P g , the target position is calculated making the point P g a point to start excavation for the present excavation section. Accordingly, the center of the circular-arc locus moves from point O to point O', and the locus after resuming excavation becomes a locus made by shifting the locus at the moment of the initial excavation operation upwardly by a length corresponding to the raised amount of the boom. Thus, also after resuming excavation, automatic excavation is performed so that a virtual line OD is rotated centering around the point O' successively by a unit angle Δ. When the locus is corrected as described above, it is considered that the amount of excavated earth becomes smaller than in the case of not correcting the locus. Hence, in the present embodiment, a horizontal excavation section I shown by cross hatching in FIG. 21 is provided so that the amount of excavated earth is always constant. That is, if it is assumed that excavation sections have proceeded up to an intermediate point after correcting the locus by raising the boom, the volume VA which the front edge of the bucket has cut away up to the present moment and the volume VB which the bucket intends to subsequently cut away when the horizontal excavation section is not provided are calculated. If the excavated volume according to the reference locus when the locus is not corrected is represented by the symbol V and the volume of the horizontal excavation section I is represented by the symbol VI, it is possible to determine the volume VI by the following expression because the volume V can previously be obtained: VI = V - (VA + VB). If the volume VI is thus determined, the depth d of excavation can be obtained from the position of the front edge of the bucket at that moment. Hence, it is possible to obtain the length l = (VI/D) of the horizontal excavation section. By inserting the horizontal excavation section having the calculated length l before the remaining sections, it is arranged so that the amount of excavated earth is always constant. FIG. 22 shows a concrete example of the operation of the third embodiment. This flowchart is made by inserting steps 162 and 172 between step 160 and step 180 in the flowchart shown in FIG. 13 and steps 191 - 194 between step 190 and step 200. In FIG. 22, like steps having identical functions as those in FIG. 13 are indicated by like step numbers, and an explanation thereof will be omitted. That is, at step 162 during automatic excavation, the controller 20 determines whether or not the prump pressure detected by the oil pressure sensor 70 has exceeded the set value C₁ (step 162). Since the determination seldom becomes "YES" at an initial stage of excavation, the process generally proceeds to step 180. However, if the pump pressure detected by the oil pressure sensor 70 has exceeded the set value C₁ during such automatic excavation operation (step 162), the controller 20 corrects the locus by raising the boom until the pump pressure is reduced down to the set value C₂ as shown in FIGS. 19 and 20 (step 172). At the moment of rasing the boom, the arm and bucket are rotated by the angles Δβ and Δγ of rotation calculated at the start of the excavation section, and the boom is stopped at the moment when the pump pressure is reduced down to the set value C₂. Subsequently, automatic excavation is resumed making this point the point to resume excavation. Subsequently, the controller 20 determines whether or not the arm has reached the target angle β₂ according to the output β detected by the angle sensor 51 (step 190). If the arm has not reached the target angle β₂, the process returns to step 120. When the arm has reached the target angle β₂, it is then determined whether or not the excavation has proceeded to an intermediate point (step 191). If the excavation has not proceeded to an intermediate point, the process returns to step 110, where the arithmetic control to move the position of the front edge of the bucket to the next target position is performed in the same manner as described above. Subsequently, in the same manner, the front edge of the bucket is sequentially moved along target positions until it is determined that the excavation has proceeded to an intermediate point at step 191. When it has been determined that the excavation ended up to an intermediate point (step 191), it is determined whether or not the locus has been corrected (step 192). When the locus has been corrected, the horizontal excavation section which has been explained with reference to FIG. 21 is added, and the working machines are driven by the horizontal excavation (step 193). That is, the controller 20 has stored the positions of the front edge of the bucket calculated from outputs from the angle sensors 41, 51 and 61 at respective moments. Hence, the controller 20 obtains the volume VA cut away by the front edge of the bucket from the start of excavation to the intermediate point according to the stored data, and further obtains the volume VB for the remaining sections from the reference locus of movement which has previously been set and the actual position of the front edge of the bucket. The controller 20 then obtains the volume VI for the horizontal excavation section I by subtracting the added value of the excavation volume VA and VB from the excavation volume V when the locus is not corrected, and determines the length l of the section by dividing the volume VI by the actual depth d of excavation calculated from the outputs from the angle sensors 41, 51 and 61. When the horizontal excavation has ended (step 194), it is determined whether or not the excavation has ended (step 200). Subsequently, the process returns to the mode for horizontally holding the bucket described before (step 210). In the present embodiment, when the locus is corrected by raising the boom, the bucket and arm are rotated until both the bucket and arm reach the target angles and the point of the front edge of the bucket at that moment is made a point to resume excavation. However, the position of the front edge of the bucket at the moment when the arm has reached the target angle after raising of the boom was stopped may be made a point to resume excavation. Furthermore, the horizontal excavation is not limited to an indermediate point, but may be performed at an arbitrary excavation point. Moreover, the horizontal excavation may be properly added even when the correction of the locus by raising the boom is not performed. Next, the present invention will be explained with respect to the fourth embodiment. FIG. 23 shows the configuration of the control according to the fourth embodiment, wherein a filter 80 is added to the configuration of FIG. 1. That is, the respective command signals α ˙ c , β ˙ c and γ ˙ c output from the controller 20 are input to the control systems 60, 50 and 40 via the filter 80, respectively, and hence abrupt variations in the command signals are suppressed by the filter 80. In the present embodiment, the following control is performed when the commands Q am , Q bm and Q bt for flow rates for the respective working machines are determined. That is, the controller 20 obtains the angles Δα, Δβ and Δγ of rotation of the respective working machines for moving the front edge of the bucket from a certain point to start excavation to the next target point according to the expressions (4), (7) and (10) described before, and then determines the distribution ratio of flow rates of pressurized oil needed for the respective working machines according to the obtained angles Δα, Δβ and Δγ of rotation. The controller 20 then obtains the flow rate Q d of the pump at the moment of the maximum output from the relationship between the flow rate Q of the pump and the pump pressure P indicated by a dotted line in FIG. 24 and the actual pump pressure P d which has been detected. The commands for flow rates for the respective working machines are determined from the flow rate Q d of the pump thus obtained and the above-described distribution ratio. As for the command Q am for the flow rate for the arm the load of which is considered to be largest, a value which is larger than the value of the command determined from the flow rate Q d of the pump and the distribution ratio, for example the maximum value, is assigned. As for the commands Q bm and Q bt for the flow rates for the remaining two working machines (the boom and bucket), the values of the commands determined from the flow rate of the pump and the distributaion ratio described above are output. Thus, it is arranged so that the sum Q s (= Q bm + Q am + Q bt , where Q bm ; the command for the flow rate for the boom, Q am ; the command for the flow rate for the arm, Q bt ; the command for the flow rate for the bucket) of the commands for the flow rates for the respective working machines becomes larger than the flow rate Q d of the pump which has been obtained. By outputting the commands for flow rates via the filter 80, variations of the values of the commands with time are reduced so that the machine can operate following the values of the commands. FIG. 25 is a flowchart showing such function of the fourth embodiment. In this flowchart, step 130 in the flowchart shown in FIG. 13 is replaced by step 132. That is, at step 132, when determining the commands for flow rates for the respective working machines from the obtaianed flow rate Q d of the pump and the above-described distribution ratio, the controller 20 assigns a value which is larger than the value of the command determined from the flow rate Q d of the pump and the distribution ratio, for example the maximum value, for the command Q am for the flow rate for the arm the load of which is considered to be largest. As for the commands Q bm and Q bt for the flow rates for the remaining two working machines (the boom and bucket), the values of the commands which are determined from the flow rate of the pump and the distribution ratio described above are output. Thus, the controller 20 obtains the command signals α ˙ c , β ˙ c and γ ˙ c for the respective working machines, and outputs the command signals α ˙ c , β ˙ c and γ ˙ c to the switches 32, 31 and 30 via the filter 80, respectively. As described above, in the present embodiment, at the moment of automatic excavation, a value which is larger than the command for the flow rate obtained from the distribution ratio and the pump pressure, for example the maximum value, is assigned for the command for the flow rate for the working machine having large load, and the commands for flow rates obtained from the distribution ratio and the pump pressure are output for the boom and bucket which have small load. Hence, the actual flow rates for the respective working machines are distributed exactly in the calculated distribution ratio, and the sum of the actual flow rates of oil flowing for the respective working machines coincides with the flow rate of the pump at the moment of the maximum output which is obtained from the pump pressure. Accordingly, relief loss and loss in the output of the pump are reduced. As a result, it becomes possible to effectively utilize the output of the pump, and to increase excavation efficiency. Furthermore, since it is arranged so that the commands for flow rates are output via the filter 80, abrupt variations in the values of the commands are suppressed. As a result, it is possible to reduce loss in the output of the pump.

Claims: A controlling device for a power shovel of a vehicle which includes a boom (3) pivoted to a vehicle body (2), an arm (4) pivoted to a front edge of the boom (3), a bucket (5) pivoted to a front edge of the arm (4), a boom cylinder (6) for driving the boom (3), an arm cylinder (7) for driving the arm (4), a bucket cylinder (8) for driving the bucket (5), a first flow rate control valve (64) for controlling pressurized oil supplied to the boom cylinder (6), a second flow rate control valve (54) for controlling pressurized oil supplied to the arm cylinder (7), a third flow rate control valve (44) for controlling pressurized oil supplied to the bucket cylinder (8), a hydraulic pump for supplying pressurized oil into the first to third flow rate control valves (64,54,44), a boom angle detector (61) for detecting an angle of rotation of the boom (3), an arm angle detector (51) for detecting an angle of rotation of the arm (4), a bucket angle detector (41) for detecting an angle of rotation of the bucket (5), and controlling means (20) being utilized for initially setting a reference locus of movement of a front edge of the bucket (5) approximated by a plurality of points, the plurality of points subdividing an overall excavation run into a plurality of discrete excavation sections, the controlling means (20) being further utilized for setting respective postures of the bucket (5) when the front edge of the bucket (5) is situated at the plurality of points, and for driving the bucket (5), arm (4) and boom (3) so that the front edge of the bucket (5) moves from an assigned position to start excavation along the plurality of points while the bucket (5) maintains the initially set postures at the plurality of points, characterized in that the controlling device comprises: pump pressure detecting means (70) for detecting the pump pressure of the hydraulic pump; assigning means (10) for assigning an automatic excavation mode, first arithmetic means, when the automatic excavation mode is assigned by the assigning means (10), for taking in detected values of the boom angle detector (61), arm angle detector (51) and bucket angle detector (41) to obtain an excavation start position relative to the vehicle on the basis of the detected values; second arithmetic means for calculating positions of the plurality of points set relative to the vehicle on the basis of the excavation start position obtained by the first arithmetic means and for obtaining an angle of rotation of the boom (3), an angle of rotation of the arm (4) and an angle of rotation of the bucket (5) needed to move the front edge of the bucket (5) to the calculated positions and to set the bucket (5) to the posture of the bucket (5) set for a proper point for each of excavation sections; third arithmetic means for obtaining the distribution ratio of flow rates of pressurized oil to be supplied to the boom cylinder (6), arm cylinder (7) and bucket cylinder (8) according to the angle of rotation of the boom (3), angle of rotation of the arm (4) and angle of rotation of the bucket (5) for each of the excavation sections obtained by the second arithmetic means; flow rate command arithmetic means for setting the relationship between the pump pressure for obtaining a predetermined horsepower and the flow rate of the pump and for obtaining commands for flow rates for the first, second and third control valves (64,54,44) by distributing the flow rate of the pump calculated from the relationship set and from the pump pressure detected by the pump pressure detecting means (70); and flow rate command correcting means (135) for outputting a command for flow rate which is larger than the flow rate of the obtained command for a cylinder having the largest load, and for correcting the command for flow rate from the flow rate command arithmetic means to output the obtained commands for the other two cylinders. The controlling device for a power shovel according to claim 1, wherein the flow rate command correcting means outputs a command for a flow rate fixed to the maximum value for the cylinder having the largest load. The controlling device for a power shovel according to claim 1 or 2, further including a low-pass filter (80) for outputting the commands for flow rates outputted from the flow rate command correcting means by reducing variations of the commands for flow rates with time. The controlling device for a power shovel according to one of claims 1-3, wherein the flow rate command correcting means uses the arm cylinder (6) as the cylinder having the largest load.

Inventors: HANAMOTO TADAYUKI, TAKASUGI SHINJI, HANAMOTO, TADAYUKI, TAKASUGI, SHINJI
Applicants: KOMATSU MFG CO LTD, KABUSHIKI KAISHA KOMATSU SEISAKUSHO
Application year: 1988
Main classification: E02F3
IPC codes: E02F3