Patent Description:
In a hydraulic excavator, a boom, an arm, a bucket, and the like of a work implement (hereinafter, also referred to as "front work implement") are rotatably supported, so that a tip end of the bucket traces out a circular arc locus when the bucket is moved solely. Owing to this, in a case of forming a linear finished surface by the tip end of the bucket by, for example, an arm crowding action, then an operator needs to drive the boom, the arm, and the bucket in a combined fashion so that the tip end of the bucket traces out a linear locus; thus, the operator is required to have expertise.

To address this challenge, there is a technique for applying a function to control actuators to be driven either automatically or semiautomatically by a computer (controller) (hereinafter, referred to as machine control) to excavation work, and moving the tip end of the bucket along a design surface (hereinafter, also referred to as "target excavation surface") during an excavation action (arm or bucket action). As the technique of this type, there is known one for automatically controlling a boom cylinder during the excavation action by operator's operation to add a boom raising action as appropriate, and limiting a tip end position of the bucket onto the design surface.

However, in a case of conducting work for laying earth on a flat or recessed geographical feature to raise a ground level (hereinafter, referred to as "filling work"), a filled upper surface after completion serves as the design surface. The tip end of the bucket is often located below the design surface during the filling work. Owing to this, when the arm crowding action is performed in a state in which the tip end of the bucket is located below the design surface (that is, within a filling range), the machine control to limit the tip end position of the bucket onto the design surface is executed, which possibly results in sudden start of the boom raising action.

To address the problem, Patent Document <NUM>, for example, describes a work vehicle that includes: a design surface information acquiring section acquiring data about a design surface indicative of a target shape of a work object by a work implement; a cutting edge position computing section computing a position of a cutting edge of a bucket; and an action limiting section executing action limiting control by which a boom is forcibly raised in accordance with a relative position of the cutting edge of the bucket to the design surface, and the position of the cutting edge is limited to a region above the design surface, and Patent Document <NUM> describes that, in a state in which the cutting edge is located away from the design surface vertically below by a predetermined distance or longer, the action limiting section does not execute the action limiting control.

Patent Document <NUM> describes a work vehicle that includes a boom, an arm, a bucket, an arm control member, a speed limit determination portion, and a target speed determination portion. The speed limit determination portion determines a speed limit for limiting a speed of a cutting edge of the bucket in accordance with a distance between a cutting edge and a design surface. The target speed determination portion determines a target speed of the boom based on the speed limit. The speed limit determination portion decides on a speed limit calculated based on correlation between the speed limit and the distance between the design surface and the cutting edge when an amount of operation of the arm control member is equal to or greater than a prescribed amount and decides on a speed limit lower than the speed limit calculated based on the correlation when the amount of operation is smaller than the prescribed amount.

According to the work vehicle described in Patent Document <NUM>, the action limiting section does not execute the action limiting control in the state in which the cutting edge of the bucket (tip end of the bucket) is located away from the target excavation surface (design surface) vertically below by a predetermined distance or longer. Owing to this, when the action limiting control (forced boom raising action) is suddenly executed (hereinafter, such a boom action is often referred to as "sudden action") irrespectively of operator's intention in a case of changing the distance of the cutting edge to the target excavation surface from the state of being equal to or larger than the predetermined distance to a state of being smaller than the predetermined distance. As a result, the occurrence of the sudden boom raising action causes the operator who does not desire or expect the boom raising action to feel heavy discomfort. In addition, in a case of the presence of the cutting edge of the bucket near the predetermined distance, the boom raising action under the action limiting control is executed or not executed. In this way, the changeover between on and off of the control irrespective of operator's intention possibly, frequently occurs. Owing to this, there is a concern of increasing operator's discomfort.

An object of the present invention is, therefore, to provide a work machine capable of suppressing sudden occurrence of a boom raising action (occurrence of a sudden action) while a tip end of a work implement is located below a target excavation surface.

While the present application includes a plurality of means for solving the problems which are described by the appended claims. As an example, there is provided a multijoint work machine including: a travel structure; a swing structure swingably attached onto the travel structure; a multijoint work implement that is attached to the swing structure and that includes a boom, an arm, and a bucket; an operation device that outputs an action direction to each of the travel structure, the swing structure, the boom, the arm, and the bucket in response to an operator's operation; and a controller that executes region limiting control to forcibly raise the boom in such a manner that a position of a tip end of the work implement is kept on a target excavation surface and within a region above the target excavation surface if the operation device issues the action direction to the arm or the bucket. The controller includes a target action determination section that determines which is selected as a control mode over a raising speed of the boom at a time of executing the region limiting control, a first mode or a second mode specified by a raising speed lower than a raising speed of the first mode if the tip end of the work implement is located below the target excavation surface, and controls the raising speed of the boom during the region limiting control on the basis of a result of determination.

According to the present invention, it is possible to suppress sudden occurrence of a boom raising action if a tip end of a work implement is located below a target excavation surface; thus, it is possible to suppress an operator from feeling discomfort.

Embodiments of the present invention will be described hereinafter with reference to the drawings. While an example of a hydraulic excavator provided with a bucket <NUM> as an attachment on a tip end of a work implement is described below, the present invention may be applied to a hydraulic excavator provided with an attachment other than the bucket. In the following description, when a plurality of same constituent elements are present, alphabets are often added to reference characters (numbers). However, the plurality of constituent elements are often denoted generically by omitting the alphabets. For example, when three pumps 300a, 300b, and 300c are present, these are often denoted generically by pumps <NUM>.

<FIG> is a configuration diagram of a hydraulic excavator according to a first embodiment of the present invention, and <FIG> is a diagram illustrating a controllercontroller together with a hydraulic drive system in the hydraulic excavator according to the first embodiment of the present invention. In <FIG>, a hydraulic excavator <NUM> is configured with a front work implement 1A and a machine body 1B. The machine body 1B is configured with a lower travel structure <NUM> and an upper swing structure <NUM> swingably attached onto the lower travel structure <NUM>. The front work implement 1A is configured by coupling a plurality of driven members (a boom <NUM>, an arm <NUM>, and a bucket <NUM>) each rotating in a perpendicular direction, and a base end of the boom <NUM> of the front work implement 1A is supported by a front portion of the upper swing structure <NUM>.

The boom <NUM>, the arm <NUM>, the bucket <NUM>, the upper swing structure <NUM>, and the lower travel structure <NUM> configure driven members that are driven by a boom cylinder <NUM>, an arm cylinder <NUM>, a bucket cylinder <NUM>, a swing hydraulic motor <NUM>, and left and right travel motors 3a and 3b, respectively. Action directions to these driven members <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> are output in response to operator's operations on a travel right lever 23a, a travel left lever 23b, an operation right lever 1a, and an operation left lever 1b (which are often generically referred to as operation levers <NUM>, <NUM>) mounted in an operation room on the upper swing structure <NUM>.

An operation device 47a (refer to <FIG>) having the travel right lever 23a, an operation device 47b (refer to <FIG>) having the travel left lever 23b, operation devices 45a and 46a having the operation right lever 1a, and operation devices 45b and 46b having the operation left lever 1b are installed in the operation room. The operation devices <NUM> to <NUM>, which are hydraulic pilot operation devices, supply, as control signals, pilot pressures (often referred to as operating pressures) in response to operation amounts (for example, lever strokes) and operation directions of the operation levers <NUM>, <NUM> operated by an operator to hydraulic drive sections 150a to 155b of flow control valves 15a to 15f (refer to <FIG>) via pilot lines 144a to 149b (refer to <FIG>) to drive these flow control valves 15a to 15f.

A hydraulic fluid delivered from a hydraulic pump <NUM> is supplied to the travel right hydraulic motor 3a, the travel left hydraulic motor 3b, the swing hydraulic motor <NUM>, the boom cylinder <NUM>, the arm cylinder <NUM>, and the bucket cylinder <NUM> via the flow control valves 15a, 15b, 15c, 15d, 15e, and 15f (refer to <FIG>) within a control valve unit <NUM>. The boom cylinder <NUM>, the arm cylinder <NUM>, and the bucket cylinder <NUM> expand and contract by the supplied hydraulic fluid, whereby the boom <NUM>, the arm <NUM>, and the bucket <NUM> rotate and a position and a posture of the bucket <NUM> change. Furthermore, the swing hydraulic motor <NUM> rotates by the supplied hydraulic fluid, whereby the upper swing structure <NUM> swings with respect to the lower travel structure <NUM>. Moreover, the travel right hydraulic motor 3a and the travel left hydraulic motor 3b rotate by the supplied hydraulic fluid, whereby the lower travel structure <NUM> travels.

Meanwhile, a boom angle sensor <NUM>, an arm angle sensor <NUM>, and a bucket angle sensor <NUM> are attached to a boom pin, an arm pin, and a bucket link <NUM> so that rotation angles α, β, γ (refer to <FIG>) of the boom <NUM>, the arm <NUM>, and the bucket <NUM> can be measured, respectively, and a machine body tilt angle sensor <NUM> that detects a longitudinal tilt angle θ of the upper swing structure <NUM> (machine body 1B) with respect to a reference plane (for example, horizontal plane) is attached to the upper swing structure <NUM>.

As illustrated in <FIG>, the hydraulic excavator <NUM> of <FIG> has the hydraulic pump <NUM>, a plurality of hydraulic actuators, which includes the boom cylinder <NUM>, the arm cylinder <NUM>, the bucket cylinder <NUM>, the swing hydraulic motor <NUM>, and the left and right travel motors 3a and 3b driven by the hydraulic fluid supplied from this hydraulic pump <NUM>, the travel right lever 23a, the travel left lever 23b, the operation right lever 1a, and the operation left lever 1b provided to correspond to these hydraulic actuators <NUM> to <NUM>, respectively, the plurality of flow control valves 15a to 15f, which are connected between the hydraulic pump <NUM> and the plurality of hydraulic actuators <NUM> to <NUM>, which are controlled by the control signals output from the operation devices 45a, 45b, 46a, 46b, 47a, and 47b in response to the operation amounts and the operation directions of the operation levers <NUM>, <NUM>, and which control flow rates and directions of the hydraulic fluid supplied to the hydraulic actuators <NUM> to <NUM>, and a relief valve <NUM> opened if a pressure between the hydraulic pump <NUM> and the flow control valves 15a to 15f is equal to or higher than a set value. These elements configure the hydraulic drive system that drives the driven members of the hydraulic excavator <NUM>.

The hydraulic excavator of the present embodiment is provided with a control system assisting an operator's excavation operation. Specifically, the hydraulic excavator <NUM> is provided with an excavation control system that exercises control to forcibly raise the boom <NUM> (often referred to as "region limiting control") on the basis of a position relationship between the target excavation surface and the tip end of the work implement 1A such that a position of a tip end of the work implement 1A (claw tip of the bucket <NUM>) is kept on the target excavation surface and within a region above the target excavation surface in a case of the presence of the action direction issued to the arm <NUM> or the bucket <NUM> from the operation device 45b or 46a. The excavation control system that can execute this region limiting control includes a limiting control switch <NUM> that is installed at a position at which the limiting control switch <NUM> does not obstruct an operator's view such as a position above an operation panel within the operation room and that changes over between validation and invalidation of the region limiting control, pressure sensors 70a and 70b that are provided in pilot lines 144a and 144b of the operation device 45a for the boom <NUM> and that detect a pilot pressure (control signal) as the operation amount of the operation lever 1a, pressure sensors 71a and 71b that are provided in pilot lines 145a and 145b of the operation device 45b for the arm <NUM> and that detect a pilot pressure (control signal) as the operation amount of the operation lever 1b, a solenoid proportional valve 54a that has a primary port side connected to a pilot pump <NUM> and that reduces a pilot pressure from the pilot pump <NUM> to output the reduced pilot pressure, a shuttle valve <NUM> that is connected to a secondary port side of the solenoid proportional valve 54a in the pilot line 144a of the operation device 45a for the boom <NUM>, that selects a higher pressure from between the pilot pressure in the pilot line 144a and the control pressure output from the solenoid proportional valve 54a, and that guides the selected higher pressure to the hydraulic drive section 150a of the flow control valve 15a, a solenoid proportional valve 54b that is installed in the pilot line 144b of the operation device 45a for the boom <NUM> and that reduces the pilot pressure in the pilot line 144b in response to an electrical signal to output the reduced pilot pressure, and a controller <NUM> that is a computer capable of executing the region limiting control.

The pilot lines 145a and 145b for the arm <NUM> are provided with the pressure sensors 71a and 71b each detecting the pilot pressure and outputting the pilot pressure to the controller <NUM> and solenoid proportional valves 55a and 55b each reducing the pilot pressure on the basis of a control signal from the controller <NUM> and outputting the reduced pilot pressure. The pilot lines 146a and 146b for the bucket <NUM> are provided with pressure sensors 72a and 72b each detecting the pilot pressure and outputting the pilot pressure to the controller <NUM>, and solenoid proportional valves 56a and 56b each reducing the pilot pressure on the basis of a control signal from the controller <NUM> and outputting the pilot pressure. It is noted that connection lines among the pressure sensors <NUM> and <NUM>, the solenoid proportional valves <NUM> and <NUM>, and the controller <NUM> are not depicted in <FIG> because of space limitations.

Shape information and position information about the target excavation surface stored in a ROM <NUM> or RAM <NUM> to be described later, detection signals of the angle sensor <NUM> to <NUM> and the tilt angle sensor <NUM>, and detection signals of the pressure sensors <NUM> to <NUM> are input to the controller <NUM>. Furthermore, the controller <NUM> outputs electrical signals for correcting the control signals (pilot pressures) for exercising excavation control (region limiting control) to limit a region to the solenoid proportional valves <NUM> to <NUM>.

<FIG> illustrates a hardware configuration of the controller <NUM>. The controller <NUM> has an input section <NUM>, a central processing unit (CPU) <NUM> that is a processor, a read only memory (ROM) <NUM> and a random access memory (RAM) <NUM> that are storage devices, and an output section <NUM>. The signals from the operation devices <NUM> to <NUM>, a signal from a setting device <NUM> that sets the target excavation surface, and the signals from the angle sensors <NUM> to <NUM> and the tilt angle sensor <NUM> are input to the input section <NUM>, and the input section <NUM> performs A/D conversion. The ROM <NUM> is a recording medium that records a control program for executing flowcharts of <FIG> and <FIG> to be described later, various information necessary to execute the flowcharts, and the like, and the CPU <NUM> performs a predetermined computing process on the signals imported from the input section <NUM> and the memories <NUM> and <NUM> in accordance with the control program stored in the ROM <NUM>. The output section <NUM> generates to-be-output signals in response to a computation result of the CPU <NUM>, and outputs the signals to the solenoid proportional valves <NUM> to <NUM> and an informing device <NUM>, thereby driving/controlling the hydraulic actuators <NUM> to <NUM> and displaying images of the machine body 1B, the bucket <NUM>, the target excavation surface, and the like on a display screen of a monitor that is the informing device <NUM>. While the controller <NUM> of <FIG> includes semiconductor memories that are the ROM <NUM> and the RAM <NUM> as the storage devices, another storage device can be provided as an alternative to the semiconductor memories, and the controller <NUM> may be provided with, for example, a magnetic storage device such as a hard disk drive.

<FIG> is a functional block diagram of the controller <NUM> according to the embodiment of the present invention. The controller <NUM> is provided with a work implement posture computing section <NUM>, a target excavation surface computing section <NUM>, a target action computing section <NUM>, a solenoid proportional valve control section <NUM>, and a target action determination section <NUM>. In addition, a work implement posture sensor <NUM>, a target excavation surface setting device <NUM>, an operator's operation sensor <NUM>, the informing device <NUM>, and the solenoid proportional valves <NUM> to <NUM> are connected to the controller <NUM>.

The work implement posture sensor <NUM> is configured with the boom angle sensor <NUM>, the arm angle sensor <NUM>, the bucket angle sensor <NUM>, and the machine body tilt angle sensor <NUM>. The target excavation surface setting device <NUM> is an interface to which information about the target excavation surface (including position information about the target excavation surface) can be input. The information may be input to the target excavation surface setting device <NUM> either by operator's manually inputting the information or by importing the information from outside via a network or the like. Furthermore, a satellite communication antenna is connected to the target excavation surface setting device <NUM>, and the target excavation surface setting device <NUM> may compute excavator global coordinates. The operator's operation sensor <NUM> is configured with the pressure sensors 70a, 70b, 71a, 71b, 72a, and 72b that acquire the operating pressures generated by operator's operating the operation levers <NUM>. The informing device <NUM> is configured with at least one of a display (display device) that displays the position relationship between the target excavation surface and the work implement 1A for the operator and a loudspeaker that informs the operator of the position relationship between the target excavation surface and the work implement 1A by a sound (including a voice). The solenoid proportional valves <NUM> to <NUM> are provided in the pilot pressure (operating pressure) hydraulic lines described with reference to <FIG> and can increase/decrease downstream the operating pressures generated by operator's lever operation. Alternatively, the operating pressures can be generated without the operator's lever operation.

<FIG> illustrates an example of a horizontal excavation action under machine control that is a function to control the work implement 1A either automatically or semiautomatically and to shape the target excavation surface. In a case of conducting horizontal excavation by operator's operating the operation levers <NUM> and an action of crowding the arm <NUM> in an arrow A direction, a boom raising command is output as appropriate so that the tip end (claw tip) of the bucket <NUM> does not penetrate a region below the target excavation surface <NUM>, and the solenoid proportional valve 54a is controlled such that an action of raising the boom <NUM> is automatically carried out. In addition, the solenoid proportional valves <NUM> are controlled to carry out the action of crowding the arm <NUM> so as to realize an excavation speed or excavation accuracy demanded by the operator. At this time, a speed of the arm <NUM> may be reduced by the solenoid proportional valves <NUM> as needed for improvement of the excavation accuracy. Furthermore, the solenoid proportional valves <NUM> may be controlled to cause the bucket <NUM> to automatically rotate in an arrow C direction (dumping direction) so that an angle B of a back surface of the bucket <NUM> with respect to the target excavation surface <NUM> becomes a constant value and leveling work can be easily conducted. In this way, the function to control the actuators either automatically or semiautomatically with respect to the operation amounts of the operation levers <NUM> by the operator, and to actuate the constituent elements of the work implement such as the boom <NUM>, the arm <NUM>, the bucket <NUM>, and the upper swing structure <NUM> is referred to as "machine control. " The region limiting control is one type of machine control.

The work implement posture computing section <NUM> computes a posture of the work implement 1A on the basis of information from the work implement posture sensor <NUM>. The posture of the work implement 1A can be defined on the basis of excavator reference coordinates of <FIG>. The excavator reference coordinates of <FIG> are coordinates set to the upper swing structure <NUM>, a base of the boom <NUM> rotatably supported by the upper swing structure <NUM> is assumed as an origin, and Z-axis is set in a vertical direction of the upper swing structure <NUM> and an X-axis is set in a horizontal direction thereof. It is assumed that a tilt angle of the boom <NUM> with respect to the X-axis is a boom angle α, a tilt angle of the arm <NUM> with respect to the boom is an arm angle β, and a tilt angle of the claw tip of the bucket with respect to the arm is a bucket angle γ. It is also assumed that a tilt angle of the machine body 1B (upper swing structure <NUM>) with respect to the horizontal plane (reference plane) is a tilt angle θ. The boom angle α is detected by the boom angle sensor <NUM>, the arm angle β is detected by the arm angle sensor <NUM>, the bucket angle γ is detected by the bucket angle sensor <NUM>, and the tilt angle θ is detected by the machine body tilt angle sensor <NUM>. The boom angle α becomes maximum when the boom <NUM> is raised to a maximum level (highest level) (when the boom cylinder <NUM> is at a stroke end in a raising direction, that is, when a boom cylinder length is the largest), and becomes minimum when the boom <NUM> is lowered to a minimum level (lowest level) (when the boom cylinder <NUM> is at a stroke end in a lowering direction, that is, when the boom cylinder length is the smallest). The arm angle β becomes minimum when an arm cylinder length is the smallest, and becomes maximum when the arm cylinder length is the largest. The bucket angle γ becomes minimum when a bucket cylinder length is the smallest (as depicted in <FIG>), and becomes maximum when the bucket cylinder length is the largest.

The target excavation surface computing section <NUM> computes the target excavation surface <NUM> on the basis of information from the target excavation surface setting device <NUM>. The target action computing section <NUM> computes a target action of the work implement 1A so that the bucket <NUM> moves on the target excavation surface and within the region above the target excavation surface, on the basis of information from the work implement posture computing section <NUM>, the target excavation surface computing section <NUM>, the target action determination section <NUM>, and the operator's operation sensor <NUM>. The solenoid proportional valve control section <NUM> computes commands to the solenoid proportional valves <NUM> to <NUM> on the basis of commands from the target action computing section <NUM>. The solenoid proportional valves <NUM> to <NUM> are controlled on the basis of the commands from the solenoid proportional valve control section <NUM>. Furthermore, the informing device <NUM> informs the operator of various information related to the machine control on the basis of information from the target action computing section <NUM>.

The commands output from the target action computing section <NUM> to the solenoid proportional valve control section <NUM> include a boom raising command. The boom raising command is a command output to the solenoid proportional valve control section <NUM> at a time of forcibly raising the boom <NUM> so that the position of the tip end of the bucket <NUM> is kept on the target excavation surface <NUM> and within the region above the target excavation surface <NUM> at a time of executing the region limiting control. When the boom raising command is input to the solenoid proportional valve control section <NUM>, then the solenoid proportional valve control section <NUM> outputs a valve opening command (command current) to the solenoid proportional valve 54a, and a hydraulic fluid (hereinafter, referred to as secondary pressure) generated in the solenoid proportional valve 54a is supplied to the hydraulic drive section 150a to drive the control valve 15a. The hydraulic operating fluid is thereby guided into a bottom-side hydraulic chamber of the boom cylinder <NUM> from the hydraulic pump <NUM> to raise the boom <NUM>. A raising speed of the boom <NUM> (boom raising speed) at that time is controllable by a value of a secondary pressure of the solenoid proportional valve 54a, that is, a command from the solenoid proportional valve control section <NUM> to the solenoid proportional valve 54a.

The target action determination section <NUM> determines which is more preferably selected, a first mode (normal boom raising control) or a second mode (deceleration boom raising slow action control) as a control mode over the raising speed of the boom <NUM> during execution of the region limiting control if the tip end of the work implement 1A is located below the target excavation surface, and outputs a result of determination to the target action computing section <NUM>. The target action computing section <NUM> outputs a command computed on the basis of this result of the determination to the solenoid proportional valve control section <NUM>. The solenoid proportional valve control section <NUM> outputs the command to the solenoid proportional valve 54a on the basis of this command, and the boom raising speed is finally controlled in the control mode selected by the target action determination section <NUM>.

In the present embodiment, the target action determination section <NUM> makes the determination on the basis of a downward penetration amount of the tip end of the work implement 1A (claw tip of the bucket <NUM>) into the target excavation surface <NUM>, selects the second mode (deceleration boom raising slow action control) if the penetration amount is equal to or higher than a predetermined value, and selects the first mode (normal boom raising control) if the penetration amount is lower than the predetermined value. Details of the target action determination section <NUM> will be described with reference to <FIG>.

<FIG> illustrates a control flowchart by the target action determination section <NUM> of the present embodiment. First, in Step <NUM>, the target action determination section <NUM> computes the distance between the target excavation surface <NUM> and the tip end of the bucket <NUM> on the basis of the position of the tip end of the bucket <NUM> in the excavator reference coordinates input from the work implement posture computing section <NUM> and the position of the target excavation surface (abbreviated as "target surface" in <FIG>) <NUM> in the excavator reference coordinates input from the target excavation surface computing section <NUM>. In addition, it is assumed that the distance is a penetration amount D of the work implement 1A into the target excavation surface <NUM> and the penetration amount D of the work implement 1A is the penetration amount D of the tip end of the bucket <NUM> in a case in which the tip end of the bucket <NUM> is located below the target excavation surface <NUM>. If the penetration amount D is equal to or higher than a predetermined value D1 (for example, <NUM>), a process goes to Step <NUM>.

In Step <NUM>, the target action determination section <NUM> determines whether the operator causes the operation device 45b or 46b to issue the action direction to the arm <NUM> or the bucket <NUM>, that is, whether the operation input is performed on the operation lever 1b or 1a on the basis of an output from the operator's operation sensor <NUM>. If determining in Step <NUM> that the operation input is performed on the arm <NUM> or the bucket <NUM>, the target action determination section <NUM> selects the deceleration boom raising slow action control as the control mode in Step <NUM>. The target action determination section <NUM> thereby outputs a control mode command in the second mode to the target action computing section <NUM>, and the boom raising speed during the boom raising control is controlled in the second mode by the solenoid proportional valve 54a.

Now, the normal boom raising control (first mode) and the deceleration boom raising slow action control (second mode) will be described. Normally, when the region limiting control described above is executed, then the boom raising command is output from the target action computing section <NUM>, and the boom raising action is controlled in such a manner that the tip end of the bucket does not penetrate the target excavation surface <NUM> on the basis of the command. It is assumed that the control mode over the boom raising speed at this time is the normal boom raising control (first mode). On the other hand, the deceleration boom raising slow action control (second mode) is a control mode that is not intended to prevent the penetration of the tip end of the bucket into the target excavation surface <NUM> but that is selected to mitigate operator's discomfort, and the boom raising speed at that time is always set lower than the speed during the normal boom raising control in the same condition. For example, the speed in the second mode can be set to a value obtained by multiplying the speed in the first mode by a predetermined rate (for example, <NUM>%). The speed in the second mode can be kept to a predetermined value in such a manner that the speed in the second mode is always controlled to be equal to or lower than the speed in the first mode. As the predetermined value in this case, a minimum value of the boom raising speed, that is, the boom raising speed while a minimum pilot pressure that enables the control valve 15a to move from a neutral position is acting on the hydraulic drive section 150a can be selected.

The boom speed control based on the deceleration boom raising slow action control can be exercised continuously until the bucket tip end is located above the target excavation surface <NUM>. In other words, in this case, once the deceleration boom raising slow action control is selected, the deceleration boom raising slow action control is continuously selected while the bucket tip end is penetrating into the target excavation surface <NUM> even if the penetration amount of the bucket tip end into the target excavation surface <NUM> becomes lower than the predetermined value. It is noted that this is also applicable to other embodiments.

Furthermore, if the deceleration boom raising slow action control is selected in Step <NUM>, the target action determination section <NUM> issues a command to the informing device <NUM> to inform the operator of the selection of the deceleration boom raising slow action control in Step <NUM>. At this time, operator's changing over the limiting control switch <NUM> to a region limiting control invalid position stops the selection of the deceleration boom raising slow action control and the execution of the region limiting control.

On the other hand, if determining in Step <NUM> that the operation input is not performed on the arm <NUM> or the bucket <NUM>, the target action determination section <NUM> does not execute the boom raising control (Step <NUM>).

Moreover, if determining in Step <NUM> that the penetration amount of the bucket tip end into the target excavation surface is equal to or lower than the predetermined value, the process goes to Step <NUM>. In and after Step <NUM>, the target action determination section <NUM> executes the normal region limiting control. First, if the target action determination section <NUM> determines that the arm <NUM> or the bucket <NUM> is operated on the basis of an output from the operator's operation sensor <NUM> in Step <NUM>, the process goes to Step <NUM>.

In Step <NUM>, the target action determination section <NUM> determines whether the boom raising command is issued from the target action computing section <NUM> on the basis of an input signal from the target action computing section <NUM>. If determining in Step <NUM> that the boom raising command is issued, the target action determination section <NUM> selects the normal boom raising control to execute boom raising in Step <NUM>. In other words, the target action determination section <NUM> issues a control mode command in the first mode to the target action computing section <NUM>, and the boom raising speed during the boom raising control is controlled in the first mode by the solenoid proportional valve 54a.

If determining in Step <NUM> that the boom raising command is not output, or determining in Step <NUM> that the operation input is not performed on the arm <NUM> or the bucket <NUM>, the target action determination section <NUM> does not execute the boom raising control.

After the process goes up to "RETURN" in the flowchart, the process returns to Step <NUM> and the target action determination section <NUM> repeats the process described above.

Effects by the present configuration will be described with reference to <FIG> illustrates a position relationship between the hydraulic excavator and the target excavation surface <NUM>. The hydraulic excavator can travel on a ground <NUM> in a current geographical feature. The target excavation surface <NUM> is indicated by a broken line and this indicates a surface that is now subjected to the filling work and to be finally shaped.

As indicated by an arrow E, it is assumed herein that the hydraulic excavator travels on the ground <NUM> from left to right and that the tip end of the bucket <NUM> penetrates into a region below the target excavation surface <NUM>. The hydraulic excavator normally travels without operating the front work implement 1A (front operation). In other words, the boom raising control is not executed by presence of Step <NUM> or <NUM> of <FIG> because of no operation on the arm <NUM> or the bucket <NUM>, and the tip end of the bucket <NUM> penetrates into the region below the target excavation surface <NUM> as the hydraulic excavator travels. A reference character D denotes the distance between the target excavation surface <NUM> and the tip end of the bucket <NUM> (penetration amount), and reference character D1 denotes the predetermined value in Step <NUM>.

As disclosed in <CIT>, in a case of configuring the hydraulic excavator in such a manner that the region limiting control is not executed when the penetration amount D is equal to or higher than the predetermined value (which is assumed as D1 similarly to the present embodiment), the boom raising control is not executed while the work is conducted in a range in which the penetration amount D is equal to or higher than D1 even with the operator's operating the arm <NUM> in a state of the hydraulic excavator on a right side of <FIG>. Owing to this, a probability increases that the operator forgets the execution of the region limiting control when the penetration amount D is lower than D1 or falsely understand that the region limiting control does not work at all irrespectively of the penetration amount D. In addition, if the filling work then proceeds to reduce the penetration amount D and the tip end of the bucket <NUM> reaches D1, the boom raising control is suddenly executed at the normal speed specified in the first mode. The occurrence of this sudden action causes the operator who does not expect or desire the boom raising action to feel heavy discomfort. Furthermore, in the work in circumstances where the penetration amount D continues to be a value near D1, the changeover between on and off of the boom raising control frequently occurs in response to a change in the penetration amount D; thus, there is a concern that the operator desired action cannot be smoothly carried out to disturb the progress of the work.

In the present embodiment configured as described above, by contrast, when the arm <NUM> is operated in the state of the hydraulic excavator on the right side of <FIG>, the boom raising control is executed at the low speed specified in the second mode. The boom raising speed at this time is lower than the normal speed (that is, lower than that when the penetration amount D is lower than D1); thus, it is possible to suppress anxiety of the operator about the sudden boom raising action by the machine control. Furthermore, the forgetting or misunderstanding described above does not occur since the operator can perceive that the region limiting control functions by expression of the boom raising action. Moreover, the operator spontaneously suspends the region limiting control by the region limiting control switch <NUM> on an occasion of a case in which the region limiting control is unnecessary; thus, it is possible to prevent the execution of the operator unintended machine control. Therefore, according to the present embodiment, if the tip end of the work implement is located below the target excavation surface, it is possible to suppress the sudden occurrence of the boom raising action and, therefore, possible to suppress the operator from feeling discomfort.

Moreover, in the embodiment described above, if the second mode is selected, the controller <NUM> is configured to inform the operator of the selection through the informing device. This can further accelerate the operator's recognition of the region limiting control, so that it is possible to further suppress the occurrence of the forgetting or misunderstanding described above.

Furthermore, as mentioned above, in a case of configuring the controller <NUM> in such a manner that the boom speed control based on the deceleration boom raising slow action control (second mode) is continuously carried out until the tip end of the bucket is located above the target excavation surface <NUM>, the boom raising control based on the deceleration boom raising slow action control is carried out while the bucket tip end is penetrating into the target excavation surface <NUM> even if the penetration amount D of the bucket tip end into the target excavation surface <NUM> is lower than the predetermined value D1. Owing to this, the speed of automatic boom raising does not suddenly change until the bucket tip end reaches the target excavation surface <NUM>; thus, it is possible to mitigate operator's discomfort.

An example useful for understanding the present invention (briefly: example) will next be described. It is noted that a hardware configuration of a hydraulic excavator in the present example is the same as that in the first embodiment and, therefore, not described and that functions overlapping those in the first embodiment are not sometimes described.

In the present example, "determination" by the target action determination section <NUM> differs from that in the first embodiment, and the target action determination section <NUM> is configured to change the control mode over the boom raising speed during the boom raising control in the light of a reason for penetration into the target excavation surface. In other words, the target action determination section <NUM> changes the control mode over the boom raising speed, depending on the reason for the penetration into the target excavation surface such as the penetration due to travel or swing, the penetration due to a forward posture of the excavator, and the penetration due to other unexpected reasons (for example, the penetration due to deteriorated control accuracy during excavation).

Specifically, the target action determination section <NUM> determines which is preferably selected to control the boom speed during the boom raising control, the first mode or the second mode, on the basis of the action direction to the lower travel structure <NUM> or the upper swing structure <NUM> from the operation devices 46b, 47a, and 47b (operation levers 1b, 23a, and 23b) and the position relationship between the target excavation surface <NUM> and the tip end of the work implement 1A. In addition, the target action determination section <NUM> selects the second mode (deceleration boom raising slow action control) if the tip end of the work implement 1A moves below the target excavation surface <NUM> by the action direction to the lower travel structure <NUM> or the upper swing structure <NUM> from the operation devices 46b, 47a, and 47b (operation levers 1b, 23a, and 23b), and selects the first mode (normal boom raising control) if the action direction to the lower travel structure <NUM> or the upper swing structure <NUM> from the operation devices 47a and 47b or the operation device 46b is not present and if the tip end of the work implement 1A is located above the target excavation surface <NUM>. Details of the target action determination section <NUM> will be described with reference to <FIG>.

<FIG> is a control flowchart by the target action determination section <NUM> in the present example. It is noted that the present flowchart is carried out per control cycle.

First, in Step <NUM>, the target action determination section <NUM> determines whether the penetration of the bucket tip end into the target excavation surface <NUM> was present in a control cycle just before a current control cycle. If determining that the penetration of the bucket tip end into the target excavation surface <NUM> was not present, the target action determination section <NUM> regards the current bucket tip end as being located above the target excavation surface <NUM> and a process goes to Step <NUM>.

In Step <NUM>, the target action determination section <NUM> determines whether a travel operation or a swing operation is present via the operation levers 23a and 23b or the operation lever 1b. If the target action determination section <NUM> determines herein that the travel operation or the swing operation is present, the process goes to Step <NUM>.

In Step <NUM>, the target action determination section <NUM> determines whether the penetration of the bucket tip end into the target excavation surface <NUM> is present on the basis of the position of the tip end of the bucket <NUM> input from the work implement posture computing section <NUM> and the position of the target excavation surface <NUM> input from the target excavation surface computing section <NUM>. If determining in Step <NUM> that the penetration into the target excavation surface <NUM> is present, then the target action determination section <NUM> determines that a cause for the penetration is the travel or swing operation, and the process goes to Step <NUM>.

In Step <NUM>, the target action determination section <NUM> determines whether an operation input is performed on the arm <NUM> or the bucket <NUM> from the operation lever 1b or 1a. If determining herein that the operation input is performed on the arm <NUM> or the bucket <NUM>, the target action determination section <NUM> selects the deceleration boom raising slow action control (second mode) as the control mode over the boom raising speed in Step <NUM>. In addition, in Step <NUM>, the target action determination section <NUM> issues a command to the informing device <NUM> to inform the operator of the selection of the deceleration boom raising slow action control due to the presence of the swing or travel. It is noted that the deceleration boom raising slow action control may be executed until the work implement 1A is located above the target excavation surface <NUM> similarly to the first embodiment.

If the target action determination section <NUM> determines in Step <NUM> that the travel operation or the swing operation is not present, the process goes to Step <NUM>.

In Step <NUM>, the target action determination section <NUM> determines whether the machine body tilt angle θ is greater than a predetermined angle θ1 in a forward tilting direction, on the basis of an output from the machine body tilt angle sensor <NUM>. If the target action determination section <NUM> determines in Step <NUM> that the machine body tilt angle θ is greater than the predetermined angle θ1, the process goes to Step <NUM>.

In Step <NUM>, the target action determination section <NUM> determines whether the penetration of the bucket tip end into the target excavation surface <NUM> is present on the basis of the position of the tip end of the bucket <NUM> input from the work implement posture computing section <NUM> and the position of the target excavation surface <NUM> input from the target excavation surface computing section <NUM>. If determining in Step <NUM> that the penetration into the target excavation surface <NUM> is present, then the target action determination section <NUM> determines that a cause for the penetration is a forward tilt posture of the machine body, and the process goes to Step <NUM>.

In Step <NUM>, the target action determination section <NUM> determines whether the operation input is performed on the arm <NUM> or the bucket <NUM>. If the target action determination section <NUM> determines in Step <NUM> that the operation input is performed on the arm <NUM> or the bucket <NUM>, the process goes to Step <NUM>.

In Step <NUM>, similarly to Step <NUM> of <FIG>, the target action determination section <NUM> determines whether the boom raising command is issued. If determining in Step <NUM> that the boom raising command is issued, the target action determination section <NUM> determines not to execute the boom raising control (that is, cancels the boom raising command in Step <NUM>) since the machine body tilt angle θ is great, and issues a command to the informing device <NUM> to inform the operator that the boom raising control is not executed in Step <NUM>.

If the target action determination section <NUM> determines that the penetration was present in Step <NUM>, if the target action determination section <NUM> determines that the penetration into the target excavation surface <NUM> is not present in Step <NUM> or <NUM>, or if the target action determination section <NUM> determines that the machine body tilt angle θ is equal to or less than a predetermined angle θ1 in Step <NUM>, the process goes to Step <NUM>. It is noted that cases of going to Step <NUM> include a case in which the penetration is not due to the travel, the swing, or the forward tilt posture but for some reason during the excavation work (for example, the deteriorated control accuracy during excavation).

The target action determination section <NUM> selects the normal boom raising control (first mode) in Step <NUM> if determining that the arm <NUM> or the bucket <NUM> is operated and the boom raising command is issued at that time in Steps <NUM> and <NUM>. In addition, it is assumed that the target action determination section <NUM> does not execute the boom raising control in Step <NUM> if determining that the arm or bucket operation is not present in Step <NUM>, <NUM>, or <NUM> or if the boom raising command is not output in Step <NUM> or <NUM>.

Effects of the present example will be described. A case in which the tip end of the work implement 1A moves below the target excavation surface <NUM> due to the travel of the lower travel structure <NUM> or the swing of the upper swing structure <NUM> does not necessarily indicate that the bucket tip end penetrates into the target excavation surface <NUM> during the excavation work. In the present example, therefore, the boom raising control is executed in the second mode lower in speed than the first mode in such a case, and the operator is informed that the control different from normal control is functioning. By doing so, if the boom raising action at the low speed occurs after the travel or the swing, it is possible to cause the operator to easily recognize that movement of the bucket tip end below the target excavation surface <NUM> is due to the travel or the swing. Therefore, if the operator does not desire to execute the region limiting control (boom raising control), the operator can easily and spontaneously suspend the region limiting control by the region limiting control switch <NUM>.

Furthermore, if the bucket tip end penetrates into the target excavation surface <NUM> due to the bad geographical features and the tilting of the machine body, then the excavator has an unstable posture in many cases, and there is a concern of the deteriorated excavation accuracy under such circumstances. In the present example, therefore, even with the penetration into the target excavation surface <NUM> without the action direction to the lower travel structure <NUM> or the upper swing structure <NUM>, the target action determination section <NUM> is configured to regard the tilting of the machine body as the cause for the penetration and to suspend the boom raising control (region limiting control) if the machine body tilt angle θ is greater than the predetermined angle θ1 in the forward tilting direction. With this configuration, it is possible to avoid execution of the boom raising control with the excavator in the unstable posture and continue stable work.

Furthermore, in the present example, the target action determination section <NUM> is configured to execute Step <NUM> if a determination result is NO in Steps <NUM> and <NUM>; thus, even if the bucket tip end penetrates into the target excavation surface <NUM> for the cause other than the above causes (the travel, the swing, and the tilting of the machine body), the target action determination section <NUM> can control the boom speed in the first mode. With this configuration, if the bucket tip end penetrates into the region below the target excavation surface <NUM> for some cause (for example, the deteriorated control accuracy over the bucket tip end) during the excavation work, the bucket tip end can be promptly moved back to the target excavation surface <NUM>; thus, it is possible to prevent deterioration of work efficiency for the excavation work.

Therefore, according to the present example, it is possible to carry out appropriate boom raising control, depending on the various circumstances described above.

A second embodiment of the present invention will next be described. The present embodiment is a modification of the first embodiment. It is noted that a hardware configuration of a hydraulic excavator in the present embodiment is the same as that in the first embodiment and, therefore, not described and that functions overlapping those in the first embodiment are not described.

<FIG> is a flowchart by the target action determination section <NUM> in the third embodiment. As obvious from this figure, the target action determination section <NUM> makes determination on the basis of the machine body tilt angle θ of the excavator in Step <NUM>. In addition, the target action determination section <NUM> (<NUM>) selects the second mode if the penetration amount D is equal to or higher than the predetermined value D1 (if the process passes through Step <NUM>), (<NUM>) suspends the region limiting control if the penetration amount D is lower than the predetermined value D1 and the machine body tilt angle θ is equal to or greater than the predetermined angle θ1 (if the process passes through Step <NUM>), and (<NUM>) selects the first mode if the penetration amount D is lower than the predetermined value D1 and the machine body tilt angle θ is less than the predetermined angle θ1 (if the process passes through Step <NUM>).

In the present embodiment configured as described so far, similarly to the example useful for understanding the invention, it is possible to avoid execution of the boom raising control with the excavator in the unstable posture and continue stable work.

Examples of the first mode and the second mode that are the control modes over the boom raising speed during the execution of the region limiting control will be described with reference to <FIG>.

In <FIG>, a boom raising speed VB in the first mode is specified by a straight line and a speed VB in the second mode is specified by a curve. If the first mode and the second mode are smoothly connected at the predetermined value D1 and the penetration amount D changes from a state of being equal to or higher than D1 to a state of being lower than D1, a case of changing over between the modes before and after the predetermined value D1 is supposed. It is noted that the first mode may be similarly specified by a curve or the second mode may be similarly specified by a straight line.

In <FIG>, the speed VB in the second mode is specified by a constant value irrespective of the penetration amount D. In <FIG>, if the penetration amount D changes from the state of being equal to or higher than D1 to the state of being lower than D1, a case of keeping the second mode until the penetration amount D becomes zero without changeover of the mode even with the penetration amount D reaching the predetermined value D1 (a case of continuously executing the boom speed control based on the second mode until the bucket tip end is located above the target excavation surface <NUM>) is supposed.

While the penetration amount D is associated with the boom raising speed VB for the brevity of description in the examples of <FIG>, the boom raising speed VB in each mode can be made independent of the penetration amount. Any pattern of the first mode and the second mode is applicable to cases other than the examples of <FIG> as long as the speed in the second mode takes on a value equal to or lower than the speed in the first mode with the same penetration amount.

Meanwhile, while the penetration of the work implement 1A into the target excavation surface <NUM> has been described while taking the penetration amount of the bucket tip end by way of example in each of the embodiments described above, an object to be controlled is not limited to the bucket tip end. For example, not the bucket tip end but an arbitrary point on the bucket such as the back surface of the bucket may be set as the object to be controlled.

While the angle sensors are used for detecting the angles of the boom, the arm, and the bucket for information about the posture, stroke sensors detecting stroke lengths of the boom cylinder, the arm cylinder, and the bucket cylinder may be used to calculate the information about the posture of the excavator as an alternative to the angle sensors.

In the flowcharts of <FIG>, <FIG>, and <FIG>, Steps <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> can be omitted.

While various types of control is exercised by setting the bucket tip end and the target excavation surface to a two-dimensional coordinate system (excavator coordinate system) set to the hydraulic excavator, the bucket tip end and the target excavation surface may be set to a three-dimensional coordinate system (world coordinate system) set to the ground (Earth) as an alternative to the two-dimensional coordinate system.

In the first embodiment, if a determination result is YES in Step <NUM>, then the same determination (determination whether the boom raising command is output) as that in Step <NUM> may be additionally executed, and the process may go to Step <NUM> if a determination result is YES in the additional step and go to Step <NUM> if the determination result is NO in the additional step.

In the example useful for understanding the invention, if a determination result is NO in Step <NUM> (travel operation/swing operation is not present), the process may go not to Step <NUM> but to Step <NUM>. In other words, Steps <NUM>, <NUM>, <NUM>, and <NUM> can be omitted.

While it is determined whether the travel or swing operation is present in Step <NUM>, determination may be made only on the basis of the presence of the travel operation. Furthermore, if the bucket tip end is to penetrate into the target excavation surface by the swing on the assumption that the machine control is executed with objects to be controlled including the swing, the swing may be controlled or interrupted.

Moreover, while a determination condition of Step <NUM> is that the machine body tilt angle θ is equal to or greater than the predetermined angle θ1 in the forward tilting direction, the determination condition is not necessarily limited to the forward tilting direction. For example, the determination condition according to a backward tilting direction or a roll tilting (roll angle) may be used.

Various patterns are available for determination of the penetration into the target excavation surface due to the travel or the swing. For example, as an alternative to the above example, the target action determination section <NUM> may be configured to monitor the position relationship between the bucket tip end and the target surface during the travel operation or swing operation, and to execute the process of Step <NUM> upon confirmation of the movement of the bucket tip end from above the target excavation surface to below the target excavation surface.

Claim 1:
A work machine comprising:
a travel structure (<NUM>);
a swing structure (<NUM>) swingably attached onto the travel structure (<NUM>);
a multijoint work implement (1A) that is attached to the swing structure (<NUM>) and that includes a boom (<NUM>), an arm (<NUM>), and a bucket (<NUM>);
an operation device (<NUM>, <NUM>, <NUM>) configured to output an action direction to each of the travel structure (<NUM>), the swing structure (<NUM>), the boom (<NUM>), the arm (<NUM>), and the bucket (<NUM>) in response to an operator's operation; and
a controller (<NUM>) configured to execute region limiting control to forcibly raise the boom (<NUM>) in such a manner that a position of a tip end of the work implement is kept on a target excavation surface and within a region above the target excavation surface when the operation device (<NUM>, <NUM>) issues an action direction to the arm (<NUM>) or the bucket (<NUM>), wherein
the controller (<NUM>)
includes a target action determination section (<NUM>) configured to determine which is selected, as a control mode over a raising speed of the boom (<NUM>) at a time of executing the region limiting control, a first mode or a second mode specified by a raising speed lower than a raising speed of the first mode when the tip end of the work implement (1A) is located below the target excavation surface, and
to control the raising speed of the boom (<NUM>) during the region limiting control based on a result of determination by the target action determination section (<NUM>),
characterized in that
the target action determination section (<NUM>) configured to make the determination based on a penetration amount of the tip end of the work implement (1A) into the target excavation surface, to select the second mode when the penetration amount is equal to or higher than a predetermined value, and to select the first mode when the penetration amount is lower than the predetermined value.