Work system and control method

Abstract

A control device generates an operation command for a power cylinder in accordance with a target position of a first element that is one of a plurality of machine elements. When the target position of the first element cannot be achieved, the control device changes the target position of the first element to the position of the first element when the power cylinder has a prescribed stroke length.

Description

Work system and control method

[0001] This disclosure relates to a work system and a control method. This application claims priority to Japanese Patent Application No. 2024-190572, filed in Japan on October 30, 2024, which is incorporated herein by reference.

[0002] Patent Document 1 discloses a technology for automatically operating a hydraulic excavator. In Patent Document 1, the control device for the hydraulic excavator controls the bucket angle to remain constant when the hydraulic excavator automatically rotates toward a transport vehicle while carrying a load, in order to prevent the load from spilling out of the bucket.

[0003] Japanese Patent Publication No. 2019-065661

[0004] In the automated operation described in Patent Document 1, an automatic control signal is generated for a control amount corresponding to the difference between the posture of the work machine and the target posture. Therefore, if the target posture of the work machine exceeds the range of motion of the actuator, a large automatic control signal for a control amount is generated near the stroke end of the power cylinder that drives the work machine, which may cause the rod of the power cylinder to collide strongly with the end of the cylinder, resulting in an impact. In addition, depending on the work machine, the arm and bucket may come into contact at the equivalent of the stroke end of the power cylinder, also resulting in an impact. The object of this disclosure is to provide a work system and control method that can prevent the impact generated in the work machine by the movement of the power cylinder near the stroke end.

[0005] According to one aspect of the present invention, the work system comprises a work machine body, a work machine operable with respect to the work machine body, a power cylinder for driving the work machine, and a control device for controlling the power cylinder, wherein the work machine has a plurality of mechanical elements connected via joints, and the control device generates an operation command for the power cylinder according to a target posture of a first element which is one of the plurality of mechanical elements, and if the target posture of the first element is an unattainable posture, it changes the target posture of the first element to the posture of the first element when the power cylinder has a predetermined stroke length.

[0006] According to the above embodiment, the work system can prevent the generation of impact caused by the power cylinder colliding with the stroke end.

[0007] This is a schematic diagram showing the configuration of the work machine according to the first embodiment. This is a block diagram of the hydraulic circuit of the bucket cylinder according to the first embodiment. This is a diagram showing the internal configuration of the operator's cab according to the first embodiment. This is a schematic block diagram showing the configuration of the control device according to the first embodiment. This is a diagram showing an example of the movement of the work machine during the first rotation according to the first embodiment. This is a diagram showing an example of the movement of the work machine during the second rotation according to the first embodiment. This is a flowchart (Part 1) showing the first rotation control by the control device according to the first embodiment. This is a flowchart (Part 2) showing the first rotation control by the control device according to the first embodiment.

[0008] <First Embodiment> The embodiments will be described in detail below with reference to the drawings.

[0009] 《Configuration of the work machine 100》 Figure 1 is a schematic diagram showing the configuration of the work machine 100 according to the first embodiment. The work machine 100 operates at the construction site, excavates soil and other materials, and loads them as cargo onto the loading platform T of a dump truck or the like. Examples of the work machine 100 include face shovels, backhoe shovels, and rope shovels. The work machine 100 may be electrically driven or hydraulically driven. The work machine 100 according to the first embodiment is a backhoe shovel. The work machine 100 comprises a traveling body 110, a rotating body 120, a work machine 130, and a driver's cab 140. Examples of loading targets T include dump trucks and hoppers.

[0010] The traveling body 110 supports the work machine 100 so that it can move. The traveling body 110 is equipped with two continuous tracks 111 on the left and right sides, and two travel motors 112 for driving each continuous track 111. The slewing body 120 is supported on the traveling body 110 so that it can rotate around a pivot point. The slewing body 120 is an example of the work machine body. The work implement 130 is driven by hydraulics. The work implement 130 is supported on the front of the slewing body 120 so that it can be driven vertically. The operator's cab 140 is a space for the operator to sit in and operate the work machine 100. The operator's cab 140 is located on the left front of the slewing body 120. Here, the part of the slewing body 120 to which the work implement 130 is attached is called the front. Also, with respect to the slewing body 120, the part opposite the front is called the rear, the left side is called the left part, and the right side is called the right part.

[0011] 《Configuration of the Slewing Body 120》 The slewing body 120 comprises an engine 121, a hydraulic pump 122, a control valve 123, and a slewing motor 124. The engine 121 is the prime mover that drives the hydraulic pump 122. The engine 121 is an example of a power source. The hydraulic pump 122 is a variable displacement pump driven by the engine 121. The hydraulic pump 122 supplies hydraulic fluid to each actuator (boom cylinder 131C, arm cylinder 132C, bucket cylinder 133C, travel motor 112, and slewing motor 124) via the control valve 123. The control valve 123 controls the flow rate of hydraulic fluid supplied from the hydraulic pump 122. The slewing motor 124 is driven by the hydraulic fluid supplied from the hydraulic pump 122 via the control valve 123, causing the slewing body 120 to slewing. In other embodiments, the slewing motor 124 may be an electric motor instead of a hydraulic motor.

[0012] 《Configuration of the work machine 130》 The work machine 130 comprises a boom 131, an arm 132, a bucket 133 as a work tool, a boom cylinder 131C, an arm cylinder 132C, and a bucket cylinder 133C. The boom 131, arm 132, and bucket 133 are mechanical elements that constitute the work machine 130. Other examples of work tools include end attachments such as clam buckets, tilt buckets, tilt-rotate buckets, grapples, and lifting magnets.

[0013] The boom 131 is a mechanical element that can operate relative to the slewing body 120. The base end of the boom 131 is rotatably attached to the slewing body 120 via a boom pin, which is an articulation joint. In the working machine 100 shown in Figure 1, the boom 131 is located in the center of the front of the slewing body 120, but it is not limited to this, and the boom 131 may be attached offset in the left-right direction. In this case, the pivot point of the slewing body 120 is not located on the operating plane of the working machine 130. The arm 132 is a mechanical element that can operate relative to the boom 131. The arm 132 connects the boom 131 and the bucket 133. The base end of the arm 132 is rotatably attached to the tip of the boom 131 via an arm pin, which is an articulation joint. The bucket 133 is a mechanical element that can operate relative to the arm 132. The bucket 133 is rotatably attached to the tip of the arm 132 via a pin, which is an articulation joint. The bucket 133 functions as a container for holding excavated soil. The bucket 133 is mounted so that its opening faces the slewing body 120 side (rear). In other words, the backhoe excavator, which is the work machine 100, performs excavation by pulling the bucket 133 towards the front of the slewing body 120.

[0014] The boom cylinder 131C is a hydraulic cylinder for operating the boom 131. The base end of the boom cylinder 131C is attached to the slewing body 120. The tip end of the boom cylinder 131C is attached to the boom 131. The arm cylinder 132C is a hydraulic cylinder for driving the arm 132. The base end of the arm cylinder 132C is attached to the boom 131. The tip end of the arm cylinder 132C is attached to the arm 132. The bucket cylinder 133C is a hydraulic cylinder for driving the bucket 133. The base end of the bucket cylinder 133C is attached to the arm 132. The tip end of the bucket cylinder 133C is attached to a link mechanism that rotates the bucket 133. The hydraulic cylinder has a bottomed cylindrical cylinder body, a piston that divides the internal space of the cylinder body in two, and a rod connected to the piston and protruding from one end of the cylinder body. The rod is also called a piston rod. Hereinafter, the side of the cylinder body from which the rod protrudes will be referred to as the rod side, and the side with the bottom will be referred to as the cap side. In other words, the cap side is the side of the cylinder from which the piston rod does not protrude. The rod side is the side of the cylinder from which the piston rod protrudes. In the first embodiment, each cylinder is a hydraulic cylinder, but in other embodiments, other powered cylinders such as electric cylinders may be used.

[0015] Figure 2 is a block diagram showing the hydraulic circuit of the bucket cylinder 133C according to the first embodiment. The hydraulic circuit connecting the control valve 123 and the bucket cylinder 133C includes a first oil passage R1 connecting the control valve 123 and the rod side of the bucket cylinder 133C, and a second oil passage R2 connecting the control valve 123 and the cap side of the bucket cylinder 133C. A first pressure sensor P1 is provided in the first oil passage R1. A first bypass oil passage B1 that bypasses to the oil tank is provided in the first oil passage R1. A first relief valve V1 is provided in the first bypass oil passage B1. The first relief valve V1 opens when the internal pressure of the first oil passage R1 exceeds a predetermined relief pressure, bypassing the hydraulic fluid to the oil tank. A second pressure sensor P2 is provided in the second oil passage R2. A second bypass oil passage B2 that bypasses to the oil tank is provided in the second oil passage R2. A second relief valve V2 is provided in the second bypass oil passage B2. The second relief valve V2 opens when the internal pressure of the second oil passage R2 exceeds a predetermined relief pressure, bypassing the hydraulic fluid to the oil tank.

[0016] As a result, the internal pressure of the first oil passage R1 and the second oil passage R2 is kept below the relief pressure. If hydraulic fluid continues to be supplied to the rod side of the bucket cylinder 133C even though the piston of the bucket cylinder 133C has reached the stroke end on the cap side, the internal pressure of the first oil passage R1 reaches the relief pressure, and hydraulic fluid flows from the first relief valve V1 to the oil tank. If hydraulic fluid continues to be supplied to the cap side of the bucket cylinder 133C even though the piston of the bucket cylinder 133C has reached the stroke end on the rod side, the internal pressure of the second oil passage R2 reaches the relief pressure, and hydraulic fluid flows from the second relief valve V2 to the oil tank. Also, when the force acting on the bucket 133 reaches the upper limit of the bucket cylinder 133C while the work machine 130 is in operation, the internal pressure of the passage also reaches the relief pressure. When relief occurs in the bucket cylinder 133C, fuel is consumed even though the cylinder is stopped, so fuel efficiency decreases.

[0017] The relief valve is not limited to the bucket cylinder 133C, but may also be provided in the boom cylinder 131C, arm cylinder 132C, travel motor 112, and slewing motor 124. The relief valve may also be provided between the hydraulic pump 122 and the control valve 123. In this case, the pressure in the oil passage connecting the hydraulic pump 122 and the control valve 123 is kept below the relief pressure. In this case as well, the internal pressure of the first oil passage R1 and the second oil passage R2 can be kept below the relief pressure.

[0018] 《Configuration of the Driver's Cabin 140》 Figure 3 shows the internal configuration of the driver's cab 140 according to the first embodiment. The driver's cab 140 is equipped with a driver's seat 141, an operating terminal 142, and an operating device 143. The operating terminal 142 is located near the driver's seat 141 and serves as a user interface to the control device 160, which will be described later.

[0019] The operating device 143 is a device for driving the traveling body 110, the rotating body 120, and the work equipment 130 by manual operation by an operator. The operating device 143 is equipped with various levers, as well as a start switch 143SW and a teaching switch 143TC.

[0020] The start switch 143SW is provided, for example, on the handle portion of the left operating lever. The start switch 143SW should be positioned near the operator seated in the driver's seat 141. When the start switch 143SW is operated, an automatic control instruction signal is output to the control device 160. When the control device 160 receives the automatic control instruction signal, it starts automatic control. The teaching switch 143TC is provided, for example, on the handle portion of the right operating lever. The teaching switch 143TC is a switch for teaching the control point of the bucket 133. When the teaching switch 143TC is operated, a teaching signal is output to the control device 160. When the control device 160 receives the teaching signal, it identifies the point where the bucket 133 is located at that time as the control point. The teaching switch 143TC may also be a GUI displayed on the display of the control device 160, and the control device 160 may identify the control point by input operation to the teaching switch 143TC displayed on the display.

[0021] Automatic control is the autonomous control by which the work machine 100 controls the drive of the work machine 130 and the slewing body 120 in order to achieve a predetermined operation. In the first embodiment, the automatic control is a control in which the work machine 100 autonomously performs a first slewing, which is a series of operations in which the work machine 100 rotates from a state in which the bucket 133 is positioned to the side of the loading target T due to the excavation of the excavation target, to a position facing the loading target T while raising the boom 131, and a second slewing, which is a series of operations in which the work machine 100 rotates from a state in which the bucket 133 is positioned above the loading target T due to loading, to a predetermined position while lowering the boom 131. The side of the loading target T refers to the outside of the loading platform such as a vessel on which the load is loaded. In addition, in the automatic control according to other embodiments, only the first slewing may be performed. In the first embodiment, the target direction of the slewing body 120 in the first slewing and the second slewing is a direction predetermined by teaching, respectively. In addition, the excavation target is usually at a position lower than the height of the loading target T. Therefore, the work machine 100 controls the drive of the work machine 130 so that the loading object T and the work machine 130 do not come into contact during the first and second rotations. Details of the automatic control will be described later.

[0022] <Configuration of the measurement system> As shown in Figure 1, the work machine 100 is equipped with a position and orientation calculator 151, an inclination measuring instrument 152, a boom stroke sensor 153, an arm stroke sensor 154, and a bucket stroke sensor 155.

[0023] The position and direction calculator 151 calculates the position of the slewing body 120 and the direction in which the slewing body 120 is facing. The position and direction calculator 151 is equipped with two receivers that receive positioning signals from artificial satellites that constitute the GNSS. The two receivers are installed at different locations on the slewing body 120. Based on the positioning signals received by the receivers, the position and direction calculator 151 detects the position of the representative point of the slewing body 120 in the field coordinate system (the origin of the shovel coordinate system). Using the positioning signals received by the two receivers, the position and direction calculator 151 calculates the direction in which the slewing body 120 is facing as the relationship between the installation position of one receiver and the installation position of the other receiver. The direction in which the slewing body 120 is facing is the direction perpendicular to the front of the slewing body 120. The direction in which the slewing body 120 faces is equal to the horizontal component of the extension direction of the straight line extending from the boom 131 of the work machine 130 to the bucket 133.

[0024] The inclination meter 152 measures the acceleration and angular velocity of the rotating body 120 and detects the attitude (e.g., roll angle, pitch angle) and rotation speed of the rotating body 120 based on the measurement results. The inclination meter 152 is installed, for example, on the underside of the rotating body 120. The inclination meter 152 can be, for example, an inertial measurement unit (IMU).

[0025] The boom stroke sensor 153 is attached to the boom cylinder 131C and detects the stroke length of the boom cylinder 131C. The stroke length of the boom cylinder 131C can be converted into the relative angle of the boom 131 with respect to the slewing body 120. The arm stroke sensor 154 is attached to the arm cylinder 132C and detects the stroke length of the arm cylinder 132C. The stroke length of the arm cylinder 132C can be converted into the relative angle of the arm 132 with respect to the boom 131. The bucket stroke sensor 155 is attached to the bucket cylinder 133C and detects the stroke length of the bucket cylinder 133C. The stroke length of the bucket cylinder 133C can be converted into the relative angle of the bucket 133 with respect to the arm 132. In the first embodiment, the work machine 100 uses the boom stroke sensor 153, the arm stroke sensor 154, and the bucket stroke sensor 155 to determine the angles of each mechanical element of the work machine 130, but other embodiments are not limited to this. For example, in other embodiments, instead of a stroke sensor, a potentiometer for detecting the relative rotation angle of the mechanical elements may be provided, or a tilt sensor such as an IMU for detecting the angle of each mechanical element to the ground may be provided, or an external sensor such as a stereo camera or LiDAR for detecting the external shape of the work machine 130 may be provided to estimate its attitude from its external shape.

[0026] 《Configuration of Control Device 160》 Figure 4 is a schematic block diagram showing the configuration of the control device 160 according to the first embodiment. The work machine 100 is equipped with a control device 160. The control device 160 may be mounted on the operation terminal 142, or it may be provided separately from the operation terminal 142 and receive input and output from the operation terminal 142. The control device 160 receives operation signals from the operation device 143. The control device 160 drives the work machine 130, the slewing body 120, and the traveling body 110 by outputting the received operation signals or operation signals generated for automatic control to the control valve 123. Hereinafter, the operation signals received from the operation device 143 will also be called manual operation signals, and the operation signals generated for automatic control will also be called automatic operation signals. The automatic operation signals include at least operation signals for driving the slewing body 120 and the work machine 130. The automatic operation signals may or may not include operation signals for driving the traveling body 110. If the control device 160 receives a manual operation signal from an operator during automatic control, it may stop the automatic control.

[0027] The control device 160 is a computer comprising a processor 610, main memory 630, storage 650, and interface 670. The storage 650 stores programs. The processor 610 reads programs from the storage 650, loads them into the main memory 630, and executes processing according to the programs.

[0028] Examples of storage 650 include semiconductor memory, magnetic disks, magneto-optical disks, and optical disks. Storage 650 may be an internal medium directly connected to the common communication line of the control device 160, or it may be an external medium connected to the control device 160 via the interface 670. The main memory 630 and storage 650 are tangible, non-temporary storage media.

[0029] The processor 610, upon execution of a program, includes a measurement data acquisition unit 611, an operation signal input unit 612, a posture determination unit 613, a reference determination unit 614, an angle determination unit 615, a movement control unit 616, and an operation signal output unit 617.

[0030] The measurement data acquisition unit 611 acquires measurement data from the measurement system of the work machine 100. Specifically, the measurement data acquisition unit 611 acquires measurement data from the position and orientation calculator 151, the inclination meter 152, the boom stroke sensor 153, the arm stroke sensor 154, the bucket stroke sensor 155, the first pressure sensor P1, and the second pressure sensor P2. The measurement data acquisition unit 611 calculates the angle of the slewing body 120 by integrating the angular velocity of the slewing body 120 measured by the inclination meter 152.

[0031] The operation signal input unit 612 receives operation signals manually operated by the operator from the operation device 143. These operation signals include drive signals for raising and lowering the boom 131, drive signals for raising and lowering the arm 132, drive signals for dumping and digging the bucket 133, drive signals for rotating the slewing body 120 to the right and to the left, drive signals for traveling the traveling body 110, and automatic control instruction signals for the work machine 100.

[0032] The attitude determination unit 613 determines the attitude of the work machine 130 in a vehicle coordinate system with the slewing body 120 as the reference, based on the measurement data acquired by the measurement data acquisition unit 611. Specifically, the attitude determination unit 613 determines the position of the tip P of the arm 132 (Figure 5), the position of the lowest point Q of the bucket 133 (Figure 5), and the angle of the bucket 133 relative to the ground. The lowest point Q of the bucket 133 refers to the point on the outer shape of the bucket 133 that is closest to the ground surface.

[0033] Hereinafter, a specific method for specifying the posture of the working machine 130 by the posture specifying unit 613 will be described. The posture specifying unit 613 obtains the vertical and horizontal components of the length of the boom 131 based on the relative angle of the boom 131 and the known length of the boom 131 (the distance from the pin at the base end to the pin at the tip end). Similarly, the posture specifying unit 613 obtains the vertical and horizontal components of the length of the arm 132. The posture specifying unit 613 specifies the position of the tip P of the arm 132 as a position that is separated from the position of the working machine 100 by the sum of the vertical components and the sum of the horizontal components of the lengths of the boom 131 and the arm 132 in the direction specified from the orientation and posture of the working machine 100. Further, the posture specifying unit 613 specifies the position of the lowest point Q of the bucket 133 based on the relative angle of the bucket 133 and the known shape of the bucket 133. For example, the posture specifying unit 613 calculates the positions of each of a plurality of points on the outer shell of the bucket 133 based on the relative angle of the bucket 133, and specifies the point with the lowest height among the plurality of points as the lowest point Q. The posture specifying unit 613 calculates the angle of the bucket 133 with respect to the ground by adding the relative angle of the boom 131, the relative angle of the arm 132, and the relative angle of the bucket 133 to the pitch angle of the working machine 100.

[0034] The reference specifying unit 614 receives teaching of the excavation preparation position, interference avoidance position, and loading position of the bucket 133 from the operator as a reference point for automatic control. The reference point for automatic control is an example of a control point. The teaching is performed, for example, according to the following procedure.

[0035] The reference specifying unit 614 causes the operation terminal 142 to display an instruction to move the bucket 133 to the excavation preparation position. The operator operates the operating device 143 to move the bucket 133 to the excavation preparation position, and operates the teaching switch 143TC to output a teaching signal to the control device 160. The reference specifying unit 614 records the posture of the working machine 130 specified by the posture specifying unit 613 as the target posture of the second swing, the position of the tip P of the arm 132 as the target position of the second swing, and the orientation in which the swing body 120 faces as the target orientation of the second swing in the storage 650.

[0036] Next, the reference specifying unit 614 causes the operation terminal 142 to display an instruction to move the bucket 133 to an interference avoidance position that has the height of the upper end of the wall of the vessel of the loading target T and at which the working machine 130 and the loading target T do not overlap in a plan view from above. Note that the wall of the vessel used for teaching may be any of the side wall, the front wall, and the rear wall of the vessel. The operator operates the operating device 143 to move the bucket 133 to the interference avoidance position, and operates the teaching switch 143TC to output a teaching signal to the control device 160. Note that the height of the interference avoidance position may be offset upward by a height with a margin in consideration of control errors and measurement errors. The reference specifying unit 614 records, in the storage 650, the height of the lowest point Q of the bucket 133 specified by the posture specifying unit 613 as the wall height Ht of the loading target T, and the direction in which the revolving body 120 faces as the interference avoidance direction.

[0037] Next, the reference specifying unit 614 causes the operation terminal 142 to display an instruction to move the bucket 133 to a loading position above the loading target T. The operator operates the operating device 143 to move the bucket 133 to the loading position, and operates the teaching switch 143TC to output a teaching signal to the control device 160. The reference specifying unit 614 records, in the storage 650, the posture of the working machine 130 as the target posture of the first turning, the position of the tip P of the arm 132 as the target position of the first turning, and the direction in which the revolving body 120 specified by the posture specifying unit 613 faces as the target direction of the first turning. Also, the height of the lowest point Q of the bucket 133 specified at the loading position may be used as the wall height Ht. Further, in other embodiments, the height of the loading target T does not necessarily have to be the wall height Ht, which is the height of the side wall of the loading platform, and may be the height of the highest point among the entire loading target T.

[0038] The angle determination unit 615 determines the target rotation angle as the angle between the initial direction the slewing body 120 faces when an automatic control instruction signal is input to the operation signal input unit 612 and the target direction recorded in the storage 650. The angle determination unit 615 determines the interference avoidance angle as the angle between the initial direction the slewing body 120 faces when an automatic control instruction signal is input to the operation signal input unit 612 and the interference avoidance direction recorded in the storage 650. The interference avoidance angle is the rotation angle when the work machine 130 and the loading object T do not overlap in a plan view from above. The target rotation angle is the first target rotation angle θ, which is the target rotation angle in the first rotation. ｔ１ And the second target turning angle θ is the target turning angle in the second turn. ｔ２ There is.

[0039] The movement control unit 616 generates an automatic operation signal to implement automatic control when the operation signal input unit 612 receives an automatic control instruction signal. When an automatic control instruction signal is input, the movement control unit 616 executes either an automatic control to implement a first rotation to move the bucket 133 to the loading position, or an automatic control to implement a second rotation to move the bucket 133 to the excavation preparation position. The movement control unit 616 determines whether to execute the first rotation or the second rotation in the automatic control based on whether the bucket 133 is within the range of the loading target T in a plan view from above when the automatic control instruction signal is input. If the bucket 133 is not within the range of the loading target T, the movement control unit 616 executes the first rotation. If the bucket 133 is within the range of the loading target T, the movement control unit 616 executes the second rotation. At this time, the movement control unit 616 controls the slewing body 120 and the working machine 130 so that the loading target T and the working machine 130 do not come into contact, based on the wall height Ht and interference avoidance angle stored in the storage 650.

[0040] The operation signal output unit 617 outputs a manual operation signal input to the operation signal input unit 612, or an automatic operation signal generated by the movement control unit 616, to the control valve 123.

[0041] 《Operation during automatic control》 Here, the movement of the work machine 100 during automatic control according to the first embodiment will be described with reference to the drawings. Figure 5 is a diagram showing an example of the movement of the work machine 100 during the first rotation according to the first embodiment. Figure 6 is a diagram showing an example of the movement of the work machine 100 during the second rotation according to the first embodiment.

[0042] When automatic control for the first rotation is initiated, as shown in Figure 5, the control device 160 first starts driving the work machine 130 (boom 131, arm 132, and bucket 133), and moves the bucket 133 upward by raising the boom 131. At this time, the control device 160 controls the bucket 133 so that its angle to the ground becomes the target holding angle. The target holding angle may be, for example, the angle at which the opening surface of the bucket 133 is horizontal (angle to the ground 0 degrees). For example, the target holding angle is one example of the target posture of the bucket 130. Also, the posture in which the opening surface is horizontal is one example of the cradle posture. In other embodiments, the cradle posture of the bucket 130 may be a posture that is slightly tilted towards the dump side from horizontal. In this case, the control device 160 may shorten the bucket soil discharge time. After a delay, the control device 160 starts rotating the rotating body 120. The control device 160 sets the rotation angle of the rotating body 120 to the first interference avoidance angle θ ａ１ The timing of the start of the rotation is adjusted so that the posture of the work machine 130 becomes the target posture for the first rotation until it matches the target posture. The rotation angle of the rotating body 120 is the first interference avoidance angle θ. ａ１ If the posture of the work implement 130 is in the target posture for the first rotation by the time it matches, that is, if the height of the lowest point Q of the bucket 133 is higher than the wall height Ht of the loading target T, the work implement 130 will not come into contact with the loading target T due to the rotation of the rotating body 120. In addition, if the work implement 130 is driven simultaneously with the rotation, the rotation angle will be the first interference avoidance angle θ ａ１ If the posture of the work implement 130 reaches the target posture in the first rotation by the time it matches the first interference avoidance angle θ, the control device 160 may start driving and rotating the work implement 130 simultaneously. ａ１When it exceeds this value, the control device 160 turns the revolving body 120 without moving the working machine 130. When the turning angle of the revolving body 120 reaches the first target turning angle θ ｔ１ that is, when the bucket 133 reaches the loading position, the control device 160 performs a dumping operation to turn the bucket 133 in the dumping direction and ends the automatic control.

[0043] When the automatic control related to the second turn is started, the control device 160 starts turning the revolving body 120. The control device 160 turns the revolving body 120 without moving the working machine 130 until the turning angle of the revolving body 120 exceeds the second interference avoidance angle θ ａ２ and maintains the height of the lowest point of the bucket 133. When the turning angle of the revolving body 120 exceeds the second interference avoidance angle θ ａ２ the control device 160 drives the boom 131, the arm 132, and the bucket 133. When the turning angle of the revolving body 120 reaches the second target turning angle θ ｔ２ the control device 160 ends the drive of the revolving body 120. Also, when the posture of the working machine 130 becomes the target posture at the start of excavation, the control device 160 ends the drive of the working machine 130.

[0044] Note that FIGS. 5 and 6 show an example where the positional relationship between the excavation position and the loading target T is about 90 degrees centered on the revolving body 120, but other embodiments are not limited to this. For example, in other embodiments, the positional relationship between the excavation position and the loading target T may be at other turning angle positions, such as about 180 degrees centered on the revolving body 120.

[0045] 《Operation of the control device 160》 When the start switch 143SW is operated by the operator, the operation signal input unit 612 of the control device 160 receives the input of an automatic control instruction signal. When an automatic loading instruction signal is input, the control device 160 determines whether to execute the first turn or the second turn based on whether the bucket 133 is within the range on the loading platform of the loading target T in a plan view from above.

[0046] Figure 7 is a flowchart (Part 1) showing the first rotation control by the control device 160 according to the first embodiment. Figure 8 is a flowchart (Part 2) showing the first rotation control by the control device 160 according to the first embodiment. When performing the first rotation, the control device 160 performs the first rotation control shown in Figure 6. First, the measurement data acquisition unit 611 acquires measurement data of the orientation of the work machine 100 (step S1). The movement control unit 616 reads the target orientation (orientation facing the loading target T), target posture, wall height Ht of the loading target T, and interference avoidance orientation of the rotating body 120 from the storage 650 (step S2). The angle determination unit 615 determines the first target rotation angle θ based on the orientation of the rotating body 120 determined in step S1 and the target orientation and interference avoidance orientation read in step S2. ｔ１ and the first interference avoidance angle θ ａ１ Identify (Step S3).

[0047] Next, the measurement data acquisition unit 611 acquires measurement data of the position and orientation of the work machine 100, the tilt angle, the slewing speed, and the stroke length of each cylinder (step S4). The posture determination unit 613 determines the posture of the work machine 130 based on the measurement data (step S5). In other words, the posture determination unit 613 determines the position of the tip P of the arm 132, the position of the lowest point Q of the bucket 133, and the angle of the bucket 133 relative to the ground.

[0048] The movement control unit 616 takes the target orientation, target attitude, and wall height Ht read out in step S2, and the first interference avoidance angle θ identified in step S3, and processes them. ａ１ Based on this, an automatic operation signal is generated to move the bucket 133 above the loading target T. That is, the movement control unit 616 determines that the lowest point Q of the bucket 133 is moved from the position of the lowest point Q at the start of the first swing control by the wall height Ht and the first interference avoidance angle θ. ａ１ Automatic operation signals are generated to reach the loading position, represented by the target bearing and target attitude, via the interference avoidance position represented by the symbol. At this time, the movement control unit 616 generates automatic operation signals for the bucket 133 so that the angle of the bucket 133 relative to the ground becomes the target holding angle.

[0049] Specifically, the movement control unit 616 generates an automatic operation signal in the following procedure. First, the movement control unit 616 determines a target value for the relative angle of the bucket 133 based on the relative angle of the boom 131 and arm 132 and the target holding angle identified from the measurement data acquired in step S4 (step S6). The target value for the relative angle of the bucket 133 is also called the angle related to the target posture. Next, the movement control unit 616 determines whether the target value for the relative angle of the bucket 133 determined in step S6 exceeds the range of motion of the bucket 133 determined from the range of motion of the bucket cylinder 133C (step S7). In other words, the movement control unit 616 determines whether the target value for the relative angle of the bucket 133 is greater than the upper limit of the range of motion of the bucket 133, and whether the target value for the relative angle of the bucket 133 is less than the lower limit of the range of motion of the bucket 133.

[0050] If the target value of the relative angle of bucket 133 exceeds the movable angle range of bucket 133 (step S7: YES), the movement control unit 616 changes the target value of the relative angle of bucket 133 to the upper or lower limit of the movable angle range of bucket 133 (step S8). In other words, if the target value of the relative angle of bucket 133 is greater than the upper limit of the movable angle range of bucket 133, the movement control unit 616 changes the target value of the relative angle of bucket 133 to the upper limit of the movable angle range. The posture of bucket 133 related to the target value of the relative angle at this time is the posture of bucket 133 when the bucket cylinder 133C reaches the stroke end on the rod side. Also, if the target value of the relative angle of bucket 133 is less than the lower limit of the movable angle range of bucket 133, the movement control unit 616 changes the target value of the relative angle of bucket 133 to the lower limit of the movable angle range. The posture of bucket 133 related to the target value of the relative angle at this time is the posture of bucket 133 when the bucket cylinder 133C reaches the stroke end on the cap side. Furthermore, if the target value of the relative angle of the bucket 133 does not exceed the movable angle range of the bucket 133 (step S7: NO), the movement control unit 616 does not change the target value of the relative angle of the bucket 133.

[0051] Next, the movement control unit 616 determines whether the posture of the work machine 130, as identified in step S5, has reached the target posture (step S9). For example, the movement control unit 616 determines that the posture of the work machine 130 has reached the target posture if the difference between the measured relative angles of the boom 131, arm 132, and bucket 133 and the target value is less than or equal to a predetermined value. If the posture of the work machine 130 has not reached the target posture (step S9: NO), the movement control unit 616 generates an automatic operation signal to bring the boom 131, arm 132, and bucket 133 closer to the target relative angle (step S10).

[0052] At this time, the movement control unit 616 generates an automatic operation signal based on the relative angles of the boom 131, arm 132, and bucket 133, which are identified from the measurement data acquired in step S4. Specifically, the movement control unit 616 determines the control amount, i.e., the angular velocity, of the automatic operation signal for the boom 131 by substituting the difference between the measured value of the relative angle of the boom 131 and the target value of the relative angle of the boom 131 related to the target posture into a predetermined control variable function. The control variable function is a function in which the control amount increases as the difference in relative angles increases. Similarly to the boom 131, the movement control unit 616 determines the control amount of the automatic operation signal for the arm 132 and bucket 133 based on the measured values ​​of the relative angles of the arm 132 and bucket 133 and the control variable function.

[0053] The movement control unit 616 determines whether the slewing body 120 is slewing or not (step S11). The movement control unit 616 determines that the slewing body 120 is slewing if, for example, the slewing speed of the slewing body 120 is equal to or greater than a predetermined speed. If the work machine 130 is not slewing (step S11: NO), the movement control unit 616 calculates the completion time until the work machine 130 reaches the target posture based on the control amounts of the boom 131 and arm 132 generated in step S10 (step S12). Also, when the slewing body 120 starts to slewing, the movement control unit 616 determines that the slewing angle is equal to the first interference avoidance angle θ identified in step S3. ａ１The movement control unit 616 calculates the time it will take to reach the first interference avoidance angle θ. The movement control unit 616 determines whether the completion time calculated in step S12 is less than the time it will take to reach the first interference avoidance angle θ. ａ１ When it reaches the target position, it is determined whether the work machine 130 will be in the target position.

[0054] If the completion time is greater than or equal to the arrival time (step S14: NO), i.e., the turning angle is the first interference avoidance angle θ ａ１ If the work machine 130 does not reach the target posture by the time it arrives, the movement control unit 616 does not generate a rotation operation signal for the rotating body 120. On the other hand, if the completion time is less than the arrival time (step S14: YES), i.e., the rotation angle is the first interference avoidance angle θ ａ１ If the work machine 130 reaches the target posture before reaching the target, the movement control unit 616 generates a rotation operation signal for the rotating body 120 (step S15). This allows the control device 160 to prevent the work machine 130 from rotating while its height is low and coming into contact with the loading target T.

[0055] The operation signal output unit 617 outputs the generated automatic operation signal to the control valve 123 (step S16). This drives the work machine 100. The control device 160 then returns the process to step S4 and continues control.

[0056] On the other hand, if it is determined in step S11 that the work implement 130 is rotating (step S11: YES), the movement control unit 616, based on the rotation speed of the work implement 130 identified in step S4, stops the rotation operation signal, and the rotation angle becomes the first target rotation angle θ due to rotation by inertia. ｔ１ It is determined whether or not the target is reached (step S17). In a turn due to inertia, the turning angle is the first target turning angle θ. ｔ１ If the target is not reached (step S17: NO), the movement control unit 616 generates a rotation operation signal in step S15, and the operation signal output unit 617 outputs the rotation operation signal to the control valve 123 in step S16.

[0057] On the other hand, the turning angle due to inertia becomes the first target turning angle θ ｔ１ If it is determined that the target angle has been reached (step S17: YES), the movement control unit 616 determines whether the rotation angle has reached the target rotation angle and whether the posture of the work machine 130 is in the target posture (step S18). ｔ１ If the target position is not reached, or if the posture of the work machine 130 is not the target posture (step S18: NO), the control device 160 returns the process to step S4.

[0058] On the other hand, the turning angle is the first target turning angle θ ｔ１ When the target position is reached and the posture of the work machine 130 is in the target position (step S18: YES), the movement control unit 616 generates an automatic operation signal to bring the boom 131, arm 132 and bucket 133 closer to the target value of the relative angle related to the loading position (step S19). The loading position of the work machine 130 may be, for example, a position in which the bucket 133 has been rotated in the dumping direction from the target position in the first rotation. The loading position may also be a position in which the boom 131 has been further rotated in the pushing direction and the arm 132 has been rotated in the downward direction. The movement control unit 616 determines the control amount of the automatic operation signal for the boom 131, arm 132 and bucket 133 based on the measured relative angle and the control amount function. The operation signal output unit 617 outputs the generated automatic operation signal to the control valve 123 (step S20). This drives the work machine 100.

[0059] Next, the measurement data acquisition unit 611 acquires measurement data of the position and orientation of the work machine 100, the tilt angle, the slewing speed, and the stroke length of each cylinder (step S21). The posture identification unit 613 identifies the posture of the work machine 130 based on the measurement data (step S22). Next, the movement control unit 616 determines whether the posture of the work machine 130 identified in step S22 is the loading posture (step S23). If the posture of the work machine 130 is not the loading posture (step S23: NO), the control device 160 returns to step S19. On the other hand, if the posture of the work machine 130 is the loading posture (step S23: YES), the control device 160 terminates the first slewing process related to the first slewing control.

[0060] 《Operation and Effects》 As described above, the control device 160 according to the first embodiment generates an operation command for the bucket cylinder 133C according to the target posture of the bucket 133, and if the target posture of the bucket 133 is a posture that cannot be achieved within the movable range of the bucket cylinder 133C, it changes the target posture of the bucket 133 to the posture of the bucket 133 when the bucket cylinder 133C reaches the stroke end. As a result, the control device 160 according to the first embodiment can prevent an impact from occurring due to the bucket cylinder 133C colliding with the stroke end. The work machine 100 according to the first embodiment is an example of a work system. The bucket 133 according to the first embodiment is an example of a first element.

[0061] Here, we will describe an example in which the bucket cylinder 133C reaches its stroke end during the first rotation process. For example, if the target holding angle is close to horizontal and the first rotation process begins with the working machine 100 in a position where the boom 131 and arm 132 are greatly extended forward, the target position of the bucket 133, determined based on the target holding angle, exceeds the range of motion of the bucket 133. That is, the target position of the bucket cylinder 133C becomes a position beyond the stroke end on the rod side. Since the control device 160 controls the bucket cylinder 133C based on the difference between the measured relative angle of the bucket 133 and the target relative angle, it instructs the supply of hydraulic fluid to the cap side of the bucket cylinder 133C with a large control amount, even though the bucket cylinder 133C is located near the stroke end on the rod side. As a result, the piston of the bucket cylinder 133C collides with the stroke end on the rod side, causing an impact. In contrast, the control device 160 according to the first embodiment suppresses the amount of control when the bucket cylinder 133C is located near the stroke end on the rod side by setting the target holding angle of the bucket 133 to an angle corresponding to the relative angle of the bucket 133 at the stroke end when the bucket cylinder 133C reaches the stroke end, thereby suppressing the occurrence of impact. In other embodiments, the target holding angle may be an angle that corresponds to a predetermined stroke length prior to the stroke end, rather than the angle at the stroke end.

[0062] <Other Embodiments> Although one embodiment has been described in detail above with reference to the drawings, the specific configuration is not limited to that described above, and various design changes are possible. That is, in other embodiments, the order of the above-described processes may be changed as appropriate. Also, some processes may be executed in parallel.

[0063] The control device 160 according to the above embodiment may be composed of a single computer, or the configuration of the control device 160 may be divided among multiple computers, and the multiple computers may cooperate with each other to function as the control device 160. In this case, some of the computers constituting the control device 160 may be mounted inside the work machine 100, while the other computers may be provided outside the work machine 100.

[0064] The control device 160 according to the above-described embodiment changes the target value of the relative angle in accordance with the stroke end of the bucket cylinder 133C during the first rotation process, but is not limited to this. For example, if the control device 160 according to another embodiment controls the bucket 133 to maintain the angle of the bucket 133 at a target holding angle during the second rotation process, the control device 160 may change the target value of the relative angle in accordance with the stroke end of the bucket cylinder 133C during the second rotation process.

[0065] In another embodiment, the control device 160 may change the target value of the relative angle according to the stroke end of the bucket cylinder 133C in control of maintaining the angle of the bucket 133 at a constant angle for leveling. In another embodiment, the control device 160 may change the target value of the relative angle according to the stroke end of the bucket cylinder 133C in control of changing the target angle of the bucket 133, such as in automatic excavation or automatic soil removal.

[0066] In another embodiment, the control device 160 may change the target value of the relative angle not only for the bucket 133 but also for the arm 132 in accordance with the stroke end of the arm cylinder 132C. In another embodiment, the control device 160 may change the target value of the relative angle for the boom 131 in accordance with the stroke end of the boom cylinder 131C. In yet another embodiment, if the bucket 133 has a tilt function and the control device 160 controls the bucket 133 according to a target value of the tilt angle, the control device 160 may change the target value of the tilt angle in accordance with the stroke end of the power cylinder for driving the tilt of the bucket 133.

[0067] The target posture, target orientation, interference avoidance orientation, and wall height Ht according to the above-described embodiment are recorded in the storage 650 by teaching, but are not limited to this. For example, the work machine 100 according to another embodiment may recognize the position and shape of the loading target T by equipping it with external sensors such as a stereo camera or LiDar, and determine the target posture, target orientation, interference avoidance orientation, and wall height Ht based on this. In other words, the reference identification unit 614 may determine the target posture, target orientation, interference avoidance orientation, and wall height Ht based on the shape data of the loading target T. In another embodiment, the position, posture, and orientation of the loading target T may be received by communication with the loading target T, and the target posture, target orientation, interference avoidance orientation, and wall height Ht may be determined based on this and the known shape of the loading target T. In other embodiments, when the loading target T travels automatically by communication with a control device, the control device may receive the position and orientation of the loading target T from the control device and determine the target attitude, target orientation, interference avoidance orientation, and wall height Ht based on this and the known shape of the loading target T. In other embodiments, the reference identification unit 614 may determine the target attitude, target orientation, interference avoidance orientation, and wall height Ht based on input from the operator to the operation terminal 142. In other embodiments, the work machine 100 may separately determine the target attitude, target orientation, and interference avoidance orientation, and the wall height Ht. In other embodiments, the control device 160 may separately include a first reference identification unit that determines the target attitude, target orientation, and interference avoidance orientation, and a second reference identification unit that determines the wall height Ht. For example, the work machine 100 may determine the target attitude, target orientation, and interference avoidance orientation by teaching, and determine the wall height Ht by operator input. Alternatively, the operator may determine the wall height Ht, which is the height of the loading target, by inputting the type of machine used for the work. In other words, the control device 160 determines the wall height Ht by reading the height associated with the input machine type from a table that has been pre-associated with the machine type and wall height Ht.

[0068] Furthermore, the control device 160 according to the above embodiment identifies the posture of the work machine 130 based on measurement data from a sensor that measures the posture of the work machine 130, but is not limited to this. For example, in another embodiment, if the work machine 100 is equipped with external sensors such as a stereo camera or LiDar, the posture of the work machine 130, particularly the height of the lowest point Q of the bucket 133, may be recognized based on measurement data from the external sensors, and automatic control may be performed based on this.

[0069] Furthermore, while the target holding angle in the above-described embodiment is predetermined, for example, to be the angle at which the opening surface of the bucket 133 becomes horizontal, the target holding angle may also be set by the operator. For example, the reference identification unit 614 in another embodiment may accept the setting of the target holding angle of the bucket 133. In this case, the reference identification unit 614 displays an input screen for the target holding angle of the bucket 133 on the operation terminal 142, for example, and records the target holding angle entered by the operator in the storage 650. In another embodiment, the reference identification unit 614 may set the target holding angle by teaching.

[0070] The control device 160 according to the above embodiment calculates the angle of the slewing body 120 by integrating the angular velocity of the slewing body 120 measured by the inclination measuring instrument 152, but is not limited to this. For example, the control device 160 according to another embodiment may calculate the angle of the slewing body 120 based on the difference in direction measured by the position and direction calculator 151. In yet another embodiment, the angle of the slewing body 120 may be determined using the detected value of a rotation angle sensor provided on the slewing motor 124.

[0071] The control device 160 according to the above-described embodiment performs automatic control based on a comparison of the slewing angle and the interference avoidance angle, but is not limited thereto. For example, the control device 160 according to another embodiment may perform automatic control based on a comparison of the position of the bucket 133 and the rearmost point of the slewing body 120 in the slewing direction of the outer shape of the loading target T. For example, the control device 160 according to another embodiment may adjust the slewing start timing so that the bucket 133 is located in a region near the rearmost point of the slewing body 120 in the slewing direction. In another embodiment, the control device 160 may generate automatic control signals for each mechanical element and the slewing body 120 so that the bucket 133 follows a predetermined trajectory. The trajectory may be determined, for example, by fitting with a predetermined curve function, or by teaching by manual operation. The trajectory may be represented by a time series arrangement of the attitude of the bucket 133, the attitudes of each mechanical element and the slewing body 120, or operation signals.

[0072] The work machine 100 according to the above-described embodiment is operated directly by an operator who is seated in the driver's cab 140, but is not limited to this. For example, the work machine 100 according to another embodiment may be operated by remote control. The remote control system according to another embodiment includes, for example, an operating device 143 located remotely from the work machine 100, a display device that displays an image of the environment of the work machine 100, and a remote control device that communicates with the work machine 100. When the operator operates the operating device 143 of the remote control system, the remote control device transmits an operation signal to the control device 160 by communication. In this case, the functions of the control device 160 may be implemented in the remote control device, or they may be implemented separately in the work machine 100 and the remote control device, respectively. The remote control system is an example of a work machine system.

[0073] The automatic control according to the above embodiment performs a first rotation to move the bucket 133 from the position at the completion of excavation to the loading point, and a second rotation to move it to the position for starting the next excavation, but is not limited to this. For example, in another embodiment, the control device 160 may perform fully automatic control that automatically executes a series of operations including the first rotation, soil removal, and the second rotation. Also, for example, in another embodiment, the control device 160 may perform only the second rotation and not the first rotation. Furthermore, the automatic control according to the above embodiment is started by triggering the operation of the start switch 143SW by the operator, but is not limited to this. For example, in another embodiment, the control device 160 may autonomously determine the start timing of the automatic control and start the automatic control without operation of the start switch 143SW.

[0074] The work machine 100 according to the above-described embodiment is a backhoe shovel, but is not limited thereto. For example, the work machine 100 according to another embodiment may be a face shovel. In a face shovel, the bucket 133 may come into contact with the arm 132 near the end of the stroke of the bucket cylinder 133C. Also, the cylinder length at which the bucket 133 comes into contact with the arm 132 may change depending on the posture of the work machine 130. For this reason, in a face shovel, the range of motion of the bucket cylinder 133C may be determined by the relative angle between the bucket 133 and the arm 132. A target posture in which the bucket 133 and the arm 132 interfere with each other can be said to be an unattainable posture.

[0075] According to the above embodiment, the work system can prevent the generation of impact caused by the power cylinder colliding with the stroke end.

[0076] 100...Working machine 110...Traveling body 111...Continuous track 112...Travel motor 120...Slewing body 121...Engine 122...Hydraulic pump 123...Control valve 124...Slewing motor 130...Working machine 131...Boom 131C...Boom cylinder 132...Arm 132C...Arm cylinder 133...Bucket 133C...Bucket cylinder 140...Operator's cab 141...Driver's seat 142...Operation terminal 143...Operation device 143SW...Start switch 143TC...Teaching switch 151...Position and orientation calculator 152...Incline measuring instrument 153...Boom stroke sensor 154...Arm stroke sensor 155...Bucket stroke sensor 160...Control device 610...Processor 630...Main memory 650...Storage 670...Interface T...Loading target 611...Measurement data acquisition unit 612...Operation signal input unit 613...Attitude determination unit 614...Reference determination unit 615...Angle determination unit 616...Movement control unit 617...Operation signal output unit R1...First oil passage R2...Second oil passage P1...First pressure sensor B1...First bypass oil passage V1...First relief valve P2...Second pressure sensor B2...Second bypass oil passage V2...Second relief valve

Claims

1. A work system comprising: a work machine body; a work implement that can be operated relative to the work machine body; a power cylinder that drives the work implement; and a control device that controls the power cylinder, wherein the work implement has a plurality of mechanical elements connected via joints, and the control device generates an operation command for the power cylinder according to a target posture of a first element which is one of the plurality of mechanical elements, and sets the power cylinder to a predetermined stroke length if the target posture of the first element is an unattainable posture.

2. The work system according to claim 1, wherein the predetermined stroke length is the stroke length when the power cylinder reaches the stroke end.

3. The work system according to claim 1 or claim 2, wherein the first element is a bucket having an opening, and the target posture of the first element is the bucket-holding posture.

4. The work system according to claim 3, wherein the holding position of the bucket is such that the opening of the bucket is horizontal.

5. The work system according to claim 4, wherein the control device identifies a loading position for loading the load held in the bucket onto the loading target, and generates an operation command for moving the bucket to the loading position while maintaining the bucket's posture in the target posture.

6. The work system according to claim 5, wherein the control device generates an action command to move the bucket into a loading position after the bucket is positioned at the target position and the bucket's posture has reached the target posture.

7. The work system according to claim 1 or 2, wherein the plurality of mechanical elements include a boom that is movable relative to the work machine body, an arm that is movable relative to the boom, and a bucket that is the first element and is movable relative to the arm, and the control device acquires measured values ​​of the angle of the boom relative to the work machine body and the angle of the arm relative to the boom, and determines the target posture of the bucket based on the measured values ​​of the angles of the boom and the arm.

8. The work system according to claim 7, wherein the control device changes the angle relating to the target posture of the bucket to the lower limit of the movable angle range if the angle relating to the target posture of the bucket is smaller than the lower limit of the movable angle range of the bucket with respect to the arm.

9. The work system according to claim 7, wherein the control device changes the angle relating to the target posture of the bucket to the upper limit of the movable angle range if the angle relating to the target posture of the bucket is greater than the upper limit of the movable angle range of the bucket with respect to the arm.

10. A control method for a work machine comprising: a work machine body; a work machine that can be operated relative to the work machine body; a power cylinder that drives the work machine; and a control device that controls the power cylinder, wherein the work machine has a plurality of mechanical elements connected via joints, the control device generates an operation command for the power cylinder according to a target posture of a first element which is one of the plurality of mechanical elements, and sets the power cylinder to a predetermined stroke length when the target posture of the first element is an unattainable posture.

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