Actuator system for work machinery, construction machinery, control device for work machinery, control method for work machinery, and control program for work machinery

Abstract

When a malfunction occurs in the electromagnetic brake, it restricts the movement of the object being braked. [Solution] The actuator system of the work machine includes an electromagnetic brake that brakes the drive shaft of the electric motor when the excitation coil is de-energized and releases the brake on the drive shaft when the excitation coil is energized, and a control device that controls the supply and interruption of power to the electric motor and excitation coil. The control device performs a first process (S10) to interrupt the supply of power to the electric motor and excitation coil, a second process (S20) to acquire the change in the angular position of the drive shaft from the time the first process is completed, a third process (S30) to calculate the amount and direction of rotation of the drive shaft from the initial position which is the angular position at the time the first process is completed, and a fourth process (S50) to control the supply of power to the electric motor so as to apply torque to the drive shaft in the opposite direction to the direction of rotation of the drive shaft when the amount of rotation of the drive shaft exceeds a predetermined value (S40:YES).

Description

Technical Field

[0001] The present invention relates to an actuator system for a work machine, a construction machine, a control device for a work machine, a control method for a work machine, and a control program for a work machine.

Background Art

[0002] The shovel disclosed in Patent Document 1 includes a vehicle body, a boom, an arm, and a bucket. The boom is connected to the front end portion of the vehicle body. The boom is rotatable up and down relative to the vehicle body. The arm is connected to the tip end portion of the boom. The arm is rotatable up and down relative to the boom. The bucket is connected to the tip end portion of the arm. The bucket is rotatable up and down relative to the arm.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in an electric shovel, rotating members such as a boom, an arm, and a bucket may be lifted and held by an electric motor. In this case, a large force is applied to the electric motor due to gravity or the like acting on the rotating members, so it is necessary to operate a brake to hold the positions of the rotating members. However, if an abnormality occurs in the brake when attempting to hold the positions of the rotating members by the brake, there is a risk that the positions of the rotating members will change abruptly due to the force acting on the rotating members.

Means for Solving the Problems

[0005] An actuator system for a work machine to solve the above problems comprises: an electric actuator having a bidirectionally rotatable electric motor and a drive shaft driven by the electric motor; an electromagnetic brake having an excitation coil that brakes the drive shaft when the excitation coil is de-excited and releases the brake on the drive shaft when the excitation coil is excited; a position sensor that detects the angular position of the drive shaft; and a control device that controls the supply and interruption of power to the electric motor and the excitation coil, respectively. The control device performs a first process of interrupting the supply of power to the electric motor and the excitation coil, respectively; a second process of acquiring the transition of the angular position of the drive shaft from the time the first process is completed; a third process of calculating the amount and direction of rotation of the drive shaft from an initial position, which is the angular position of the drive shaft at the time the first process is completed, based on the acquired transition; and a fourth process of controlling the supply of power to the electric motor so as to apply torque to the drive shaft in the opposite direction to the direction of rotation of the drive shaft from the initial position when the amount of rotation of the drive shaft from the initial position exceeds a predetermined value.

[0006] According to the above configuration, if the rotation amount of the drive shaft of the electric motor exceeds a predetermined value without braking the drive shaft by the electromagnetic brake, the power supply to the electric motor is controlled to apply torque to the drive shaft in the opposite direction to the direction of rotation. This makes it possible to restrict the movement of the object being braked when a malfunction occurs in the electromagnetic brake.

[0007] In an actuator system for a work machine, when the control device determines that the amount of rotation of the drive shaft from the initial position has exceeded a predetermined value, and sets the angular position of the drive shaft at that point as the determination position, the control device may, in the fourth process, control the supply of power to the electric motor so as to reduce the difference between a specific target position between the initial position and the determination position and the current angular position of the drive shaft.

[0008] In an actuator system for a work machine, the control device may perform a fifth process during the execution of the fourth process, which calculates the magnitude of the torque applied to the drive shaft based on the current value supplied to the electric motor.

[0009] In an actuator system for a work machine, the electric actuator may drive one of the following: a boom rotatably connected to the body of the construction machine, an arm rotatably connected to the boom, or an attachment rotatably connected to the arm.

[0010] In an actuator system for a work machine, the system further includes a drive circuit having an inverter circuit that converts a DC voltage to an AC voltage and outputs it to the electric actuator, and a converter circuit that converts the AC voltage output by the inverter circuit to a DC voltage and outputs it to the excitation coil, and the control device may control the supply and interruption of power to the electric motor and the excitation coil, respectively, through the control of the drive circuit.

[0011] A construction machine to solve the above problems includes a work machine having a boom rotatably connected to the vehicle body, an arm rotatably connected to the boom, and an attachment rotatably connected to the arm; an electric actuator having a bidirectionally rotatable electric motor and a drive shaft driven by the electric motor, which drives one of the boom, the arm, and the attachment; an electromagnetic brake having an excitation coil which brakes the drive shaft when the excitation coil is de-excited and releases the brake on the drive shaft when the excitation coil is excited; a position sensor which detects the angular position of the drive shaft; and the electric motor and the excitation coil The system includes a control device that controls the supply and interruption of power to each of the following: a first process of interrupting power supply to the electric motor and the excitation coil, a second process of acquiring the change in the angular position of the drive shaft from the time the first process is completed, a third process of calculating the amount and direction of rotation of the drive shaft from an initial position which is the angular position of the drive shaft at the time the first process is completed, based on the acquired change, and a fourth process of supplying power to the electric motor so as to apply torque to the drive shaft in the opposite direction to the direction of rotation of the drive shaft from the initial position if the amount of rotation of the drive shaft from the initial position exceeds a predetermined value.

[0012] According to the above configuration, if the rotation amount of the drive shaft of the electric motor exceeds a predetermined value without braking the drive shaft by the electromagnetic brake, the power supply to the electric motor is controlled to apply torque to the drive shaft in the opposite direction to the direction of rotation. This makes it possible to restrict the movement of the object being braked when a malfunction occurs in the electromagnetic brake.

[0013] A control device for a work machine to solve the above problems is applied to a work machine comprising: an electric motor that can rotate in both directions, an electric actuator having a drive shaft driven by the electric motor, an electromagnetic brake having an excitation coil that brakes the drive shaft when the excitation coil is not excited and releases the brake on the drive shaft when the excitation coil is excited, and a position sensor that detects the angular position of the drive shaft. The control device is capable of controlling the supply and interruption of power to the electric motor and the excitation coil, respectively, and performs the following: a first process of interrupting the supply of power to the electric motor and the excitation coil, respectively; a second process of acquiring the transition of the angular position of the drive shaft from the time the first process is completed; a third process of calculating the amount and direction of rotation of the drive shaft from an initial position, which is the angular position of the drive shaft at the time the first process is completed, based on the acquired transition; and a fourth process of controlling the supply of power to the electric motor so as to apply torque to the drive shaft in the opposite direction to the direction of rotation of the drive shaft from the initial position when the amount of rotation of the drive shaft from the initial position exceeds a predetermined value.

[0014] According to the above configuration, if the rotation amount of the drive shaft of the electric motor exceeds a predetermined value without braking the drive shaft by the electromagnetic brake, the power supply to the electric motor is controlled to apply torque to the drive shaft in the opposite direction to the direction of rotation. This makes it possible to restrict the movement of the object being braked when a malfunction occurs in the electromagnetic brake.

[0015] A control method for a work machine to solve the above problems is applied to a work machine comprising: an electric motor that can rotate in both directions, an electric actuator having a drive shaft driven by the electric motor, an electromagnetic brake having an excitation coil that brakes the drive shaft when the excitation coil is not excited and releases the brake on the drive shaft when the excitation coil is excited, and a position sensor that detects the angular position of the drive shaft. The control device controls the supply and interruption of power to the electric motor and the excitation coil, respectively, and performs: a first process of interrupting the supply of power to the electric motor and the excitation coil, respectively; a second process of acquiring the transition of the angular position of the drive shaft from the time the first process is completed; a third process of calculating the amount and direction of rotation of the drive shaft from an initial position, which is the angular position of the drive shaft at the time the first process is completed, based on the acquired transition; and a fourth process of controlling the supply of power to the electric motor so as to apply a torque to the drive shaft in the opposite direction to the direction of rotation of the drive shaft from the initial position when the amount of rotation of the drive shaft from the initial position exceeds a predetermined value.

[0016] According to the above method, if the rotation amount of the drive shaft of the electric motor exceeds a predetermined value without braking the drive shaft by the electromagnetic brake, the power supply to the electric motor is controlled to apply torque to the drive shaft in the opposite direction to the direction of rotation. This makes it possible to restrict the movement of the object being braked when a malfunction occurs in the electromagnetic brake.

[0017] A control program for a work machine to solve the above problems is applied to a work machine comprising: an electric motor that can rotate in both directions, an electric actuator having a drive shaft driven by the electric motor, an electromagnetic brake having an excitation coil that brakes the drive shaft when the excitation coil is de-excited and releases the brake on the drive shaft when the excitation coil is excited, and a position sensor that detects the angular position of the drive shaft. The control device, which controls the supply and interruption of power to the electric motor and the excitation coil respectively, is made to execute: a first process of interrupting the supply of power to the electric motor and the excitation coil respectively; a second process of acquiring the transition of the angular position of the drive shaft from the time the first process is completed; a third process of calculating the amount and direction of rotation of the drive shaft from an initial position, which is the angular position of the drive shaft at the time the first process is completed, based on the acquired transition; and a fourth process of controlling the supply of power to the electric motor so as to apply torque to the drive shaft in the opposite direction to the direction of rotation of the drive shaft from the initial position if the amount of rotation of the drive shaft from the initial position exceeds a predetermined value.

[0018] According to the above program, if the rotation amount of the drive shaft of the electric motor exceeds a predetermined value without braking the drive shaft by the electromagnetic brake, the power supply to the electric motor can be controlled to apply torque to the drive shaft in the opposite direction to the direction of rotation. As a result, the above program can restrict the movement of the object being braked when a malfunction occurs in the electromagnetic brake. [Effects of the Invention]

[0019] The above technical concept allows for the restriction of the movement of the object being braked when a malfunction occurs in the electromagnetic brake. [Brief explanation of the drawing]

[0020] [Figure 1] Figure 1 is a schematic side view of an excavator. [Figure 2] Figure 2 is a schematic plan view of an excavator. [Figure 3]Figure 3 is a diagram illustrating the electrical configuration and power transmission path of the excavator. [Figure 4] Figure 4 is a cross-sectional view schematically illustrating the first electric actuator and the first electromagnetic brake. [Figure 5] Figure 5 is a diagram illustrating the configuration of the drive circuit. [Figure 6] Figure 6 is a flowchart illustrating the processing procedure of the braking control. [Mode for Carrying Out the Invention]

[0021] Hereinafter, an embodiment of a working machine will be described taking a construction machine as an example. Note that in the drawings, components may be illustrated in an enlarged scale for easy understanding. In addition, the dimensional ratios of the components may differ from the actual ones or those in other drawings.

[0022] <Overall Configuration> As shown in Figure 1 and Figure 2, an excavator 10 which is a working machine and a construction machine includes a lower traveling body 13 and an upper revolving body 14. The upper revolving body 14 is located on the side opposite to the ground G with respect to the lower traveling body 13. In the present embodiment, the direction in which the upper revolving body 14 is located when viewed from the lower traveling body 13 is the upward direction, and the opposite direction is the downward direction. A specific direction among the directions orthogonal to the upward direction is the forward direction, and the opposite direction is the rearward direction. Further, one of the directions orthogonal to both the upward direction and the forward direction is the left direction, and the other is the right direction. The forward direction and the rearward direction may be collectively referred to as the X direction. The left direction and the right direction may be collectively referred to as the Y direction. The upward direction and the downward direction may be collectively referred to as the Z direction.

[0023] The lower body 13 and the upper body 14 constitute the vehicle body 15. The lower body 13 is, for example, rectangular parallelepiped. The upper body 14 comprises a main housing section 14A and a front housing section 14B. The main housing section 14A is, for example, rectangular parallelepiped. The interior of the main housing section 14A is a hollow storage space. The storage space houses various equipment for operating the excavator 10. The front housing section 14B is located on the front side of the main housing section 14A. The front housing section 14B is located approximately in the center of the main housing section 14A in the Y direction. The front housing section 14B is fixed to the front of the main housing section 14A. The front housing section 14B is, for example, a smaller rectangular parallelepiped than the main housing section 14A. The interior of the front housing section 14B is hollow. Although not shown in the illustration, the upper body 14 includes a cabin in which an operator sits. The cabin is integrally fixed to the main housing section 14A. The upper body 14 is sometimes referred to as the upper rotating body.

[0024] As shown in Figures 1 and 2, the excavator 10 is equipped with a slewing bearing 18. The slewing bearing 18 is located between the lower body 13 and the upper body 14. In Figure 1, the vertical width of the slewing bearing 18 is exaggerated and shown as large with respect to the Z direction. As shown in Figure 2, the slewing bearing 18 comprises an annular inner ring 18A, an annular outer ring 18B, and a plurality of rolling elements. In Figure 2, the rolling elements are not shown. The outer diameter of the inner ring 18A is smaller than the inner diameter of the outer ring 18B. The slewing axis 10J, which is the central axis of the inner ring 18A, approximately coincides with the central axis of the outer ring 18B. The slewing axis 10J extends vertically across the vehicle body 15, i.e., in the Z direction. As shown in Figure 1, the slewing axis 10J passes vertically through both the upper body 14 and the lower body 13. The plurality of rolling elements are located between the inner ring 18A and the outer ring 18B. Multiple rolling elements support the inner ring 18A and the outer ring 18B so that they can rotate relative to each other. As a result, the outer ring 18B is rotatable relative to the inner ring 18A about the pivot axis 10J. The inner ring 18A is fixed to the lower body 13. The outer ring 18B is fixed to the main housing portion 14A of the upper body 14. That is, the upper body 14 is rotatable relative to the lower body 13 about the pivot axis 10J. It can also be said that the upper body 14 rotates relative to the lower body 13.

[0025] As shown in Figures 1 and 2, the excavator 10 is equipped with a pair of running gears 12. The pair of running gears 12 are located on the left and right sides of the lower body 13. Both running gears 12 are connected to the lower body 13. Each pair of running gears 12 includes a crawler for travel and an operating mechanism for rotating the crawler. The crawler is an endless belt shape. The crawler has openings on both the left and right sides. The underside of the crawler is in contact with the ground G. The excavator 10 moves as the crawler rotates. The running gears 12 and the lower body 13 are sometimes collectively referred to as the lower running gear.

[0026] As shown in Figures 1 and 2, the excavator 10 is equipped with a swing bracket 17. The swing bracket 17 is located on the front side of the main housing portion 14A of the upper body 14. The swing bracket 17 comprises a first swing wall 17A and a second swing wall 17B. The first swing wall 17A is located on the upper surface of the front housing portion 14B of the upper body 14. The first swing wall 17A is, for example, disc-shaped. The first swing wall 17A is connected to the front housing portion 14B. The first swing wall 17A is rotatable about a fourth axis 61J relative to the front housing portion 14B. The fourth axis 61J is approximately parallel to the pivot axis 10J. The second swing wall 17B protrudes upward from the upper surface of the first swing wall 17A. The second swing wall 17B is, for example, rectangular plate-shaped.

[0027] <Working equipment> As shown in Figures 1 and 2, the excavator 10 is equipped with a work implement 20. The work implement 20 has a boom 21, an arm 23, and a bucket 25. The boom 21 is the first driven object. The arm 23 is the second driven object. The bucket 25 is the third driven object.

[0028] As shown in Figures 1 and 2, the boom 21 is located on the front side relative to the main housing portion 14A of the upper body 14. The boom 21 is a long, plate-like or columnar shape. As shown in Figure 2, the first longitudinal end 21A of the boom 21 is aligned with the second swing wall 17B of the swing bracket 17 in the direction along the first axis 31J. The first axis 31J is a virtual axis that is approximately perpendicular to the slewing axis 10J. The first end 21A of the boom 21 is rotatably connected to the second swing wall 17B.

[0029] As shown in Figures 1 and 2, the arm 23 extends from the second end 21B of the boom 21, opposite to the first end 21A. The arm 23 is a long, plate-like or columnar shape. As shown in Figure 2, the longitudinal first end 23A of the arm 23 is aligned with the second end 21B of the boom 21 in the direction along the second axis 41J. The second axis 41J is a virtual axis approximately parallel to the first axis 31J. The first end 23A of the arm 23 is rotatably connected to the second end 21B of the boom 21.

[0030] As shown in Figures 1 and 2, the bucket 25 is located near the second end 23B of the arm 23, opposite to the first end 23A. The bucket 25 comprises a bucket body 26, a plurality of claws 27, and a bucket connecting wall 28. The bucket body 26 is box-shaped. That is, as shown in Figure 2, the bucket body 26 has an opening 26A. The claws 27 protrude from one side of the rectangular opening edge of the bucket body 26. The bucket connecting wall 28 protrudes from the outer wall of the bucket body 26, on the opposite side of the opening 26A from the claws 27. As shown in Figure 2, the bucket connecting wall 28 is aligned with the second end 23B of the arm 23 in the direction along the third axis 51J. The third axis 51J is a virtual axis that is substantially parallel to both the first axis 31J and the second axis 41J. The bucket connecting wall 28 is rotatably connected to the second end 23B of the arm 23. Note that Bucket 25 is an attachment.

[0031] <Actuator> As shown in Figure 3, the excavator 10 is equipped with a first electric actuator 31, a second electric actuator 41, and a third electric actuator 51. The first electric actuator 31 drives the boom 21. The second electric actuator 41 drives the arm 23. The third electric actuator 51 drives the bucket 25. The excavator 10 is also equipped with a first inverter circuit 35, a second inverter circuit 45, a third inverter circuit 55, and a DC power supply 19. Although not shown in the figure, the first inverter circuit 35, the second inverter circuit 45, the third inverter circuit 55, and the DC power supply 19 are housed in the main housing 14A of the upper body 14.

[0032] As shown in Figure 2, the first electric actuator 31 is located between the second swing wall 17B of the swing bracket 17 and the first end 21A of the boom 21. As shown in Figures 3 and 4, the first electric actuator 31 comprises a first electric motor 32 and a first reduction gear 33. The first electric motor 32 is a three-phase AC motor. The first electric motor 32 is electrically connected to a DC power supply 19 via a first inverter circuit 35. The first electric motor 32 comprises a housing 32A, a drive shaft 32B, a stator 32C, and a rotor 32D. The stator 32C is located inside the housing 32A. The stator 32C is fixed to the housing 32A. The stator 32C is cylindrical. Although not shown, a coil is wound around the stator 32C. The coil is electrically connected to the DC power supply 19 via the first inverter circuit 35. The rotor 32D is located inside the stator 32C. The rotor 32D is rotatable relative to the stator 32C. The drive shaft 32B is fixed to the rotor 32D. The drive shaft 32B rotates integrally with the rotor 32D. The drive shaft 32B protrudes from the inside to the outside of the housing 32A. The drive shaft 32B is cylindrical. The drive shaft 32B is rotatable relative to the housing 32A about its own central axis, the first axis 31J. That is, the drive shaft 32B outputs torque about the first axis 31J. The drive shaft 32B is driven by the first electric motor 32. The drive shaft 32B is rotatable in both directions about the first axis 31J. As shown in Figure 2, the first axis 31J passes through both the second swing wall 17B of the swing bracket 17 and the first end 21A of the boom 21.

[0033] As shown in Figures 3 and 4, the first reduction gear 33 comprises a housing 33A, a reduction mechanism 33B, and a drive shaft 33C. The housing 33A is attached to the housing 32A of the first electric motor 32. The reduction mechanism 33B is located inside the housing 33A. Torque is input to the reduction mechanism 33B from the drive shaft 32B of the first electric motor 32. The reduction mechanism 33B amplifies the torque from the first electric motor 32 at a predetermined ratio and outputs it to the drive shaft 33C. The reduction mechanism 33B is, for example, an eccentric oscillating gear type or a planetary gear type. The drive shaft 33C is cylindrical. The central axis of the drive shaft 33C is approximately coincident with the first axis 31J. The drive shaft 33C is rotatable relative to the housing 33A. The drive shaft 33C rotates about the first axis 31J in accordance with the rotation of the drive shaft 32B of the first electric motor 32. The drive shaft 33C is attached to the first end 21A of the boom 21. That is, the drive shaft 33C inputs torque to the boom 21 around the first axis 31J. The boom 21 receives this torque and rotates around the first axis 31J.

[0034] As shown in Figures 3 and 4, the excavator 10 is equipped with a first electromagnetic brake 81 for the first electric actuator 31. The first electromagnetic brake 81 is located on the opposite side of the first reduction gear 33 from the first electric motor 32. That is, in the direction along the first axis 31J, the first electromagnetic brake 81 is located between the first electric motor 32 and the second swing wall 17B of the swing bracket 17. The first electromagnetic brake 81 is fixed to the housing 32A of the first electric motor 32. The first electromagnetic brake 81 is connected to the drive shaft 32B of the first electric motor 32. The first electromagnetic brake 81 is electrically connected to the DC power supply 19. When the first electromagnetic brake 81 is receiving power from the DC power supply 19, it does not apply braking force to the drive shaft 32B of the first electric motor 32. Therefore, in this case, the drive shaft 32B of the first electric motor 32 can rotate freely. On the other hand, when the power supply from the DC power source 19 is cut off, the first electromagnetic brake 81 applies braking force to the drive shaft 32B. At the same time, the first electromagnetic brake 81 makes the drive shaft 32B of the first electric motor 32 unable to rotate.

[0035] The first electromagnetic brake 81 comprises a housing 81A, an excitation coil 81B, a contact plate 81C, and a movable plate 81D. The housing 81A is cylindrical. The first axis 31J of the housing 81A substantially coincides with the first axis 31J of the housing 32A of the first electric motor 32. One end of the housing 81A in the direction along its first axis 31J is closed. The other end of the housing 81A is fixed to the housing 32A. A portion of the drive shaft 32B of the first electric motor 32 is located inside the housing 81A.

[0036] The contact plate 81C, the movable plate 81D, and the excitation coil 81B are located inside the housing 81A. The contact plate 81C is located closer to the housing 32A in the direction along the first axis 31J of the housing 81A. The contact plate 81C is disc-shaped. The drive shaft 32B of the first electric motor 32 passes through the vicinity of the center of the contact plate 81C. The contact plate 81C rotates integrally with the drive shaft 32B.

[0037] The excitation coil 81B is located on the opposite side of the housing 32A, with the contact plate 81C in between. Although detailed illustrations are omitted, the excitation coil 81B comprises a coil body and a spring. The excitation coil 81B is fixed to the housing 81A. The coil body receives power from the DC power supply 19 and is interrupted by the power supply.

[0038] The movable plate 81D is located between the contact plate 81C and the excitation coil 81B. The movable plate 81D is disc-shaped. There is a hole in the center of the movable plate 81D. The diameter of the hole is larger than the diameter of the drive shaft 32B of the first electric motor 32. The drive shaft 32B is inserted through this hole. The movable plate 81D is movable in a direction along the first axis 31J of the drive shaft 32B. The movable plate 81D receives a biasing force toward the contact plate 81C from the spring of the excitation coil 81B.

[0039] The positional relationship of the movable plate 81D with respect to the contact plate 81C changes depending on whether or not the excitation coil 81B is energized. When the excitation coil 81B is de-energized, the movable plate 81D is pressed against the contact plate 81C by the biasing force of the spring. Consequently, a braking force is applied to the contact plate 81C and, consequently, to the drive shaft 32B of the first electric motor 32, which brakes the rotation of the drive shaft 32B. On the other hand, when the excitation coil 81B is energized, the movable plate 81D is positioned away from the contact plate 81C, against the biasing force of the spring. In this case, the braking force on the contact plate 81C and the drive shaft 32B of the first electric motor 32 is released.

[0040] As shown in Figure 2, the second electric actuator 41 is located between the second end 21B of the boom 21 and the first end 23A of the arm 23. The configuration of the second electric actuator 41 is basically the same as that of the first electric actuator 31, except for details such as dimensions, reduction ratio, and output. Therefore, the configuration of the second electric actuator 41 will be briefly described below.

[0041] As shown in Figure 3, the second electric actuator 41 comprises a second electric motor 42 and a second reduction gear 43. The second electric motor 42 is electrically connected to a DC power supply 19 via a second inverter circuit 45. The drive shaft 42B of the second electric motor 42 outputs torque around its own central axis, the second axis 41J. The drive shaft 42B is driven by the second electric motor 42. The drive shaft 42B is rotatable in both directions around the second axis 41J. As shown in Figure 2, the second axis 41J passes through both the second end 21B of the boom 21 and the first end 23A of the arm 23. The drive shaft 43C of the second reduction gear 43 is attached to the first end 23A of the arm 23. As shown in Figure 3, the drive shaft 43C outputs torque around the second axis 41J. The arm 23 rotates around the second axis 41J in response to the torque from the drive shaft 43C. Furthermore, the functions of the housing 43A and reduction mechanism 43B of the second reduction gear 43 are the same as those of the housing 33A and reduction mechanism 33B of the first reduction gear 33.

[0042] As shown in Figure 3, the excavator 10 is equipped with a second electromagnetic brake 82 for the second electric actuator 41. The configuration of the second electromagnetic brake 82 is basically the same as that of the first electromagnetic brake 81, except for details such as dimensions. Therefore, the configuration of the second electromagnetic brake 82 will be briefly described below. The second electromagnetic brake 82 is located on the opposite side of the second reduction gear 43, with the second electric motor 42 in between. That is, in the direction along the second axis 41J, the second electromagnetic brake 82 is located between the second electric motor 42 and the second end 21B of the boom 21. The second electromagnetic brake 82 is fixed to the housing 42A of the second electric motor 42. The second electromagnetic brake 82 is connected to the drive shaft 42B of the second electric motor 42. The second electromagnetic brake 82 is electrically connected to the DC power supply 19. When the second electromagnetic brake 82 is receiving power from the DC power supply 19, it does not apply braking force to the drive shaft 42B of the second electric motor 42. Therefore, in this case, the drive shaft 42B of the second electric motor 42 can rotate freely. On the other hand, when the power supply from the DC power source 19 is cut off, the second electromagnetic brake 82 applies a braking force to the drive shaft 42B. At the same time, the second electromagnetic brake 82 makes the drive shaft 42B of the second electric motor 42 unable to rotate.

[0043] The second electromagnetic brake 82 comprises a housing 82A and an excitation coil 82B. The housing 82A is cylindrical. The second axis 41J of the housing 82A substantially coincides with the second axis 41J of the housing 42A of the second electric motor 42. One end of the housing 82A in the direction along its second axis 41J is closed. The other end of the housing 82A is fixed to the housing 42A. A portion of the drive shaft 42B of the second electric motor 42 is located inside the housing 82A.

[0044] The excitation coil 82B is located inside the housing 82A. When the excitation coil 82B is not energized, a braking force is applied to the drive shaft 42B of the second electric motor 42, which slows the rotation of the drive shaft 42B. On the other hand, when the excitation coil 82B is energized, the braking force on the drive shaft 42B of the second electric motor 42 is released.

[0045] As shown in Figure 2, the third electric actuator 51 is located between the second end 23B of the arm 23 and the bucket connecting wall 28 of the bucket 25. The configuration of the third electric actuator 51 is basically the same as that of the first electric actuator 31, except for details such as dimensions, reduction ratio, and output. Therefore, the configuration of the third electric actuator 51 will be briefly described below.

[0046] As shown in Figure 3, the third electric actuator 51 comprises a third electric motor 52 and a third reduction gear 53. The third electric motor 52 is electrically connected to a DC power supply 19 via a third inverter circuit 55. The drive shaft 52B of the third electric motor 52 outputs torque around its own central axis, the third axis 51J. The drive shaft 52B is driven by the third electric motor 52. The drive shaft 52B is rotatable in both directions around the third axis 51J. As shown in Figure 2, the third axis 51J passes through both the second end 23B of the arm 23 and the bucket connecting wall 28. The drive shaft 53C of the third reduction gear 53 is attached to the bucket connecting wall 28. As shown in Figure 3, the drive shaft 53C outputs torque around the third axis 51J. The bucket 25 rotates around the third axis 51J in response to the torque from the drive shaft 53C. Furthermore, the functions of the housing 53A and reduction mechanism 53B of the third reduction gear 53 are the same as those of the housing 33A and reduction mechanism 33B of the first reduction gear 33.

[0047] As shown in Figure 3, the excavator 10 is equipped with a third electromagnetic brake 83 for the third electric actuator 51. The configuration of the third electromagnetic brake 83 is basically the same as that of the first electromagnetic brake 81, except for details such as dimensions. Therefore, the configuration of the third electromagnetic brake 83 will be briefly described below. The third electromagnetic brake 83 is located on the opposite side of the third reduction gear 53, with the third electric motor 52 in between. That is, in the direction along the third axis 51J, the third electromagnetic brake 83 is located between the third electric motor 52 and the second end 23B of the arm 23. The third electromagnetic brake 83 is fixed to the housing 52A of the third electric motor 52. The third electromagnetic brake 83 is connected to the drive shaft 52B of the third electric motor 52. The third electromagnetic brake 83 is electrically connected to the DC power supply 19. When the third electromagnetic brake 83 is receiving power from the DC power supply 19, it does not apply braking force to the drive shaft 52B of the third electric motor 52. Therefore, in this case, the drive shaft 52B of the third electric motor 52 can rotate freely. On the other hand, when the power supply from the DC power source 19 is cut off, the third electromagnetic brake 83 applies a braking force to the drive shaft 52B. At the same time, the third electromagnetic brake 83 makes the drive shaft 52B of the third electric motor 52 unable to rotate.

[0048] The third electromagnetic brake 83 comprises a housing 83A and an excitation coil 83B. The housing 83A is cylindrical. The third axis 51J of the housing 83A substantially coincides with the third axis 51J of the housing 52A of the third electric motor 52. One end of the housing 83A in the direction along its third axis 51J is closed. The other end of the housing 83A is fixed to the housing 52A. A portion of the drive shaft 52B of the third electric motor 52 is located inside the housing 83A.

[0049] The excitation coil 83B is located inside the housing 83A. When the excitation coil 83B is not energized, a braking force is applied to the drive shaft 52B of the third electric motor 52, which slows the rotation of the drive shaft 52B. On the other hand, when the excitation coil 83B is energized, the braking force on the drive shaft 52B of the third electric motor 52 is released.

[0050] As shown in Figure 3, the excavator 10 is equipped with a fourth electric actuator 61 and a fourth inverter circuit 65. As shown in Figure 1, the fourth electric actuator 61 is housed in the front part 14B of the housing of the upper body 14. Although not shown in the figure, the fourth inverter circuit 65 is housed in the main part 14A of the housing of the upper body 14. The configuration of the fourth electric actuator 61 is basically the same as that of the first electric actuator 31, except for details such as dimensions, reduction ratio, and output. Therefore, the configuration of the fourth electric actuator 61 will be briefly described below.

[0051] As shown in Figure 3, the fourth electric actuator 61 comprises a fourth electric motor 62 and a fourth reduction gear 63. The fourth electric motor 62 is electrically connected to a DC power supply 19 via a fourth inverter circuit 65. The drive shaft 62B of the fourth electric motor 62 outputs torque around its own central axis, the fourth axis 61J. The drive shaft 62B is driven by the fourth electric motor 62. The drive shaft 62B is rotatable in both directions around the fourth axis 61J. The drive shaft 63C of the fourth reduction gear 63 is attached to the first swing wall 17A of the swing bracket 17. The drive shaft 63C outputs torque around the fourth axis 61J. The swing bracket 17 rotates around the fourth axis 61J in response to the torque from the drive shaft 63C. The functions of the housing 63A and reduction mechanism 63B of the fourth reduction gear 63 are the same as those of the housing 33A and reduction mechanism 33B of the first reduction gear 33.

[0052] As shown in Figure 3, the excavator 10 is equipped with a fourth electromagnetic brake 84 for the fourth electric actuator 61. The configuration of the fourth electromagnetic brake 84 is basically the same as that of the first electromagnetic brake 81, except for details such as dimensions. Therefore, the configuration of the fourth electromagnetic brake 84 will be briefly described below. The fourth electromagnetic brake 84 is located on the opposite side of the fourth reduction gear 63, with the fourth electric motor 62 in between. That is, in the direction along the fourth axis 61J, the fourth electromagnetic brake 84 is located between the fourth electric motor 62 and the first swing wall 17A of the swing bracket 17. The fourth electromagnetic brake 84 is fixed to the housing 62A of the fourth electric motor 62. The fourth electromagnetic brake 84 is connected to the drive shaft 62B of the fourth electric motor 62. The fourth electromagnetic brake 84 is electrically connected to the DC power supply 19. When the fourth electromagnetic brake 84 is receiving power from the DC power supply 19, it does not apply braking force to the drive shaft 62B of the fourth electric motor 62. Therefore, in this case, the drive shaft 62B of the fourth electric motor 62 can rotate freely. On the other hand, when the power supply from the DC power source 19 is cut off, the fourth electromagnetic brake 84 applies a braking force to the drive shaft 62B. At the same time, the fourth electromagnetic brake 84 makes the drive shaft 62B of the fourth electric motor 62 unable to rotate.

[0053] The fourth electromagnetic brake 84 comprises a housing 84A and an excitation coil 84B. The housing 84A is cylindrical. The fourth axis 61J of the housing 84A substantially coincides with the fourth axis 61J of the housing 62A of the fourth electric motor 62. One end of the housing 84A in the direction along its fourth axis 61J is closed. The other end of the housing 84A is fixed to the housing 62A. A portion of the drive shaft 62B of the fourth electric motor 62 is located inside the housing 84A.

[0054] The excitation coil 84B is located inside the housing 84A. When the excitation coil 84B is not energized, a braking force is applied to the drive shaft 62B of the fourth electric motor 62 to control its rotation. Conversely, when the excitation coil 84B is energized, the braking force on the drive shaft 62B of the fourth electric motor 62 is released.

[0055] As shown in Figure 3, the excavator 10 is equipped with a fifth electric actuator 71 and a fifth inverter circuit 75. As shown in Figure 2, the fifth electric actuator 71 is housed in the main housing 14A of the upper body 14. The configuration of the fifth electric actuator 71 is basically the same as that of the first electric actuator 31, except for details such as dimensions, reduction ratio, and output. Therefore, the configuration of the fifth electric actuator 71 will be briefly described below.

[0056] As shown in Figure 3, the fifth electric actuator 71 comprises a fifth electric motor 72 and a fifth reduction gear 73. The fifth electric motor 72 is electrically connected to the DC power supply 19 via a fifth inverter circuit 75. The drive shaft 72B of the fifth electric motor 72 outputs torque around its own central axis, the fifth axis 71J. The drive shaft 72B is driven by the fifth electric motor 72. The drive shaft 72B is rotatable in both directions around the fifth axis 71J. Multiple teeth are formed on the drive shaft 73C of the fifth reduction gear 73. These teeth mesh with the teeth formed on the inner ring 18A of the slewing bearing 18. The drive shaft 73C outputs torque around the fifth axis 71J. In response to this torque, the upper body 14 rotates with the housing 72A of the fifth electric motor 72 relative to the inner ring 18A and, consequently, the lower body 13. In other words, the fifth electric actuator 71 rotates the upper body 14 relative to the lower body 13. The functions of the housing 73A and reduction mechanism 73B of the fifth reduction gear 73 are the same as those of the housing 33A and reduction mechanism 33B of the first reduction gear 33.

[0057] The excavator 10 is equipped with a fifth electromagnetic brake 85 for the fifth electric actuator 71. The configuration of the fifth electromagnetic brake 85 is basically the same as that of the first electromagnetic brake 81, except for details such as dimensions. Therefore, the configuration of the fifth electromagnetic brake 85 will be briefly described below. The fifth electromagnetic brake 85 is located on the opposite side of the fifth reduction gear 73, with the fifth electric motor 72 in between. The fifth electromagnetic brake 85 is fixed to the housing 72A of the fifth electric motor 72. The fifth electromagnetic brake 85 is connected to the drive shaft 72B of the fifth electric motor 72. The fifth electromagnetic brake 85 is electrically connected to the DC power supply 19. When the fifth electromagnetic brake 85 is receiving power from the DC power supply 19, it does not apply braking force to the drive shaft 72B of the fifth electric motor 72. Therefore, in this case, the drive shaft 72B of the fifth electric motor 72 can rotate freely. On the other hand, when the power supply from the DC power source 19 is cut off, the fifth electromagnetic brake 85 applies braking force to the drive shaft 72B. At the same time, the fifth electromagnetic brake 85 makes the drive shaft 72B of the fifth electric motor 72 unable to rotate.

[0058] The fifth electromagnetic brake 85 comprises a housing 85A and an excitation coil 85B. The housing 85A is cylindrical. The fifth axis 71J of the housing 85A substantially coincides with the fifth axis 71J of the housing 72A of the fifth electric motor 72. One end of the housing 85A in the direction along its fifth axis 71J is closed. The other end of the housing 85A is fixed to the housing 72A. A portion of the drive shaft 72B of the fifth electric motor 72 is located inside the housing 85A.

[0059] The excitation coil 85B is located inside the housing 85A. When the excitation coil 85B is not energized, a braking force is applied to the drive shaft 72B of the fifth electric motor 72, which slows the rotation of the drive shaft 72B. On the other hand, when the excitation coil 85B is energized, the braking force on the drive shaft 72B of the fifth electric motor 72 is released.

[0060] <Sensor> As shown in Figure 3, the actuator system for the excavator 10 includes a first position sensor 38, a second position sensor 48, a third position sensor 58, and a fourth position sensor 68. The first position sensor 38 detects the angular position 38S of the drive shaft 32B of the first electric motor 32. The second position sensor 48 detects the angular position 48S of the drive shaft 42B of the second electric motor 42. The third position sensor 58 detects the angular position 58S of the drive shaft 52B of the third electric motor 52. The fourth position sensor 68 detects the angular position 68S of the drive shaft 62B of the fourth electric motor 62. The angular position detected by each position sensor is a value in the range of "0 degrees to 360 degrees", with a predetermined reference position being "0 degrees". In other words, each angular position indicates the absolute angle of the drive shaft of each electric motor. Each position sensor repeatedly outputs a signal corresponding to the information it has detected to the control device 100, which will be described later.

[0061] Although not shown in the diagram, the excavator 10 is equipped with various sensors necessary for its operation, in addition to the sensors mentioned above. For example, the excavator 10 is equipped with sensors that detect the current values ​​flowing through each of the electric motors 32, 42, 52, 62, and 72, and sensors that detect the temperature of the DC power supply 19. In Figure 3, the current sensor 91 that detects the current value 91S supplied to the first electric motor 32 is shown as a representative example. The current value 91S detected by the current sensor 91 indicates a positive or negative value depending on the rotation direction of the drive shaft 32B of the first electric motor 32. In addition, the excavator 10 is equipped with various operating devices 90 that are operated by the operator. In the drawing, the various operating devices 90 are shown together as a group. The various operating devices 90 are located in the cabin. The various operating devices 90 transmit signals 90S corresponding to the operator's operations to the control device 100, which will be described later.

[0062] <Control device> As shown in Figure 3, the actuator system of the excavator 10 includes a control device 100. The control device 100 controls the supply and interruption of power to the electric motors 32, 42, 52, 62, 72 and the excitation coils 81B, 82B, 83B, 84B, 85B, respectively. The control device 100 is a computer equipped with a processing circuit. The processing circuit includes a CPU 101 and a memory 102. The memory 102 includes three types: RAM, ROM, and electrically rewritable non-volatile memory. In this embodiment, these three types are collectively referred to as memory 102. The memory 102 pre-stores various control programs 102A that describe the processing to be executed by the CPU 101. The memory 102 pre-stores various data 102B necessary for the CPU 101 to execute the control programs 102A. The processing circuit includes a communication circuit for wireless communication with the outside.

[0063] <Drive Circuit> As shown in Figure 5, the actuator system of the excavator 10 further includes a drive circuit 110. Here, for ease of understanding, we will describe the drive circuit 110 that controls the drive of the first electric motor 32 and the first electromagnetic brake 81, but the same applies to the drive circuits that control the drive of the electric motors 42, 52, 62, 72 and the electromagnetic brakes 82-84.

[0064] Specifically, the drive circuit 110 includes a motor drive circuit 111 and a brake drive circuit 112. The motor drive circuit 111 is equipped with a DC power supply 19 and a capacitor 114. The DC power supply 19 has the function of supplying power to the first inverter circuit 35. The positive terminal of the capacitor 114 is connected to the positive terminal of the DC power supply 19. The negative terminal of the capacitor 114 is connected to the negative terminal of the DC power supply 19. The capacitor 114 has the function of stabilizing the voltage of the DC power supply 19 by supplying current to the DC power supply 19 when the DC power supply 19 becomes unstable due to the large current flowing through the motor drive circuit 111.

[0065] <Inverter Circuit> Furthermore, the motor drive circuit 111 has a first inverter circuit 35. The first inverter circuit 35 has a positive-side supply line 115 connected to the positive terminal of the DC power supply 19 and a negative-side supply line 116 connected to the negative terminal of the DC power supply 19.

[0066] Furthermore, the first inverter circuit 35 is equipped with six switching elements 121, 122, 123, 124, 125, and 126. In this embodiment, the switching elements 121 to 126 used are IGBTs (Insulated Gate Bipolar Transistors). The collector terminals of switching elements 121, 123, and 125 are electrically connected to the positive side supply line 115. The emitter terminal of switching element 121 is electrically connected to the first motor power line 127 of the first electric motor 32. The emitter terminal of switching element 123 is electrically connected to the second motor power line 128 of the first electric motor 32. The emitter terminal of switching element 125 is electrically connected to the third motor power line 129 of the first electric motor 32. The collector terminal of switching element 122 is electrically connected to the first motor power line 127 and the emitter terminal of switching element 121. The collector terminal of switching element 124 is electrically connected to the second motor power line 128 and the emitter terminal of switching element 123. The collector terminal of switching element 126 is electrically connected to the third motor power line 129 and the emitter terminal of switching element 125. The emitter terminals of switching elements 122, 124, and 126 are electrically connected to the negative electrode supply line 116. Furthermore, the gate terminals of switching elements 121 to 126 are electrically connected to the CPU 101 of the control device 100.

[0067] <Operation of the Inverter Circuit> The first inverter circuit 35 shown in Figure 5 converts the DC voltage from the DC power supply 19 into an AC voltage and outputs it to the first electric motor 32 of the first electric actuator 31. The CPU 101 controls the supply and interruption of power to the first electric motor 32 through the control of the inverter circuit 35. Specifically, the first inverter circuit 35 drives the first electric motor 32 when a gate signal generated by the CPU 101 is input to the switching elements 121 to 126. The CPU 101 controls the on and off states of the switching elements 121 to 126. For example, the CPU 101 inputs the gate signal to the gate terminals of the switching elements 121 and 124, switching the switching elements 121 and 124 to the ON state. In this case, a current is generated that flows in the following order: positive side supply line 115 → switching element 121 → first motor power line 127 → U-phase coil C1 → V-phase coil C2 → second motor power line 128 → switching element 124 → negative side supply line 116. Next, the CPU 101 inputs gate signals to the gate terminals of switching elements 122 and 125, switching switching elements 122 and 125 to the ON state. In this case, a current is generated that flows in the following order: positive side supply line 115 → switching element 125 → third motor power line 129 → W-phase coil C3 of the first electric motor 32 → U-phase coil C1 → first motor power line 127 → switching element 122 → negative side supply line 116. Furthermore, the CPU 101 inputs gate signals to the gate terminals of switching elements 123 and 126, switching switching elements 123 and 126 to the ON state. In this case, a current is generated that flows in the following order: positive side supply line 115 → switching element 123 → second motor power line 128 → V-phase coil C2 → W-phase coil C3 → third motor power line 129 → switching element 126 → negative side supply line 116. As a result, a magnetic force is generated in the following order: U-phase coil C1 → V-phase coil C2 → W-phase coil C3 → U-phase coil C1 → V-phase coil C2 → W-phase coil C3 →… and the rotor of the first electric motor 32 rotates accordingly. That is, the first electric motor 32 is a three-phase AC motor equipped with a U-phase coil C1, a V-phase coil C2, and a W-phase coil C3.

[0068] <Converter Circuit> As shown in Figure 5, the brake drive circuit 112 is provided with a capacitor 117 and a first electromagnetic brake 81. The brake drive circuit 112 also has a converter circuit 130. The converter circuit 130 has a positive-side output line 118 connected to the positive side of the first electromagnetic brake 81 and a negative-side output line 119 connected to the negative side of the first electromagnetic brake 81. The positive terminal of the capacitor 114 is connected to the positive-side output line 118. The negative terminal of the capacitor 114 is connected to the negative-side output line 119. The capacitor 114 has the function of suppressing pulsations in the current flowing through the converter circuit 130.

[0069] Furthermore, the converter circuit 130 includes six diodes 131, 132, 133, 134, 135, and 136. The cathode terminals of diodes 131, 133, and 135 are electrically connected to the positive side output line 118. The anode terminal of diode 131 is electrically connected to the cathode terminal of diode 132. The anode terminal of diode 133 is electrically connected to the cathode terminal of diode 134. The anode terminal of diode 135 is electrically connected to the cathode terminal of diode 136. The anode terminals of diodes 132, 134, and 136 are electrically connected to the negative side output line 119.

[0070] Furthermore, a first wiring 141 for the first electromagnetic brake 81 branches off from the first motor power line 127 of the first electric motor 32. The first wiring 141 is connected in the converter circuit 130 between the anode terminal of diode 131 and the cathode terminal of diode 132. Also, a second wiring 142 for the first electromagnetic brake 81 branches off from the second motor power line 128 of the first electric motor 32. The second wiring 142 is connected in the converter circuit 130 between the anode terminal of diode 133 and the cathode terminal of diode 134. In addition, a third wiring 143 for the first electromagnetic brake 81 branches off from the third motor power line 129 of the first electric motor 32. The third wiring 143 is connected in the converter circuit 130 between the anode terminal of diode 135 and the cathode terminal of diode 136.

[0071] <Operation of the converter circuit> Furthermore, the converter circuit 130 shown in Figure 5 converts the AC voltage output by the first inverter circuit 35 into a DC voltage and outputs it to the excitation coil 81B of the first electromagnetic brake 81. The CPU 101 of the control device 100 controls the supply and interruption of power to the excitation coil 81B through the control of the first inverter circuit 35. Specifically, a portion of the current flowing through the first motor power line 127 flows in the order of first wiring 141 → diode 131 → positive side output line 118 → first electromagnetic brake 81. Also, a portion of the current flowing through the second motor power line 128 flows in the order of second wiring 142 → diode 133 → positive side output line 118 → first electromagnetic brake 81. In addition, a portion of the current flowing through the third motor power line 129 flows in the order of third wiring 143 → diode 135 → positive side output line 118 → first electromagnetic brake 81. Furthermore, since the current flows continuously in the order of first wiring 141 → second wiring 142 → third wiring 143 → first wiring 141 → second wiring 142 → third wiring 143 →…, the AC current output by the first inverter circuit 35 is converted to DC.

[0072] <Switching Regulator> As shown in Figure 5, in the brake drive circuit 112, a switching regulator 150 is provided between the converter circuit 130 and the first electromagnetic brake 81. The switching regulator 150 comprises a switching element 151, a coil 152, and a capacitor 153. The switching element 151 is provided on the positive side output line 118. The coil 152 is provided downstream of the switching element 151 on the positive side output line 118. The positive terminal of the capacitor 153 is connected to the positive side output line 118. The negative terminal of the capacitor 153 is connected to the negative side output line 119.

[0073] The switching regulator 150 turns the switching element 151 on and off based on the drive signal output from the CPU 101. This controls the supply period of the voltage input to the first electromagnetic brake 81, and adjusts the voltage input to the first electromagnetic brake 81. However, when the switching element 151 is turned on and off, the rapid changes in voltage and current cause ringing, which introduces noise into the output voltage. Therefore, in this embodiment, the coil 152 and capacitor 153 are used to reduce this noise.

[0074] <Braking control> The CPU 101 is capable of performing braking control. Braking control is a control system designed to address abnormalities that occur in the electromagnetic brakes 81-83. For ease of understanding, this explanation focuses on braking control for the first electromagnetic brake 81 and the first electric motor 32, but similar braking control is performed for electromagnetic brakes 82 and 83 and electric motors 42 and 52. The CPU 101 performs each braking control individually or in parallel, for example, in response to signals from the operating device 90. The following describes a series of processes performed by the CPU 101 during braking control.

[0075] The CPU 101 starts braking control when the start condition is met. An example of a start condition is when the CPU 101 receives a hold request signal. The hold request signal is a signal requesting that the boom 21 be held in place. The hold request signal is transmitted, for example, from the control device 90 in response to the operator's operation. If the CPU 101 receives a release request signal while repeating steps S20 to S40 described later, it terminates the braking control at that point. The release request signal is a signal requesting that the hold on the boom 21 be released. The release request signal is transmitted, for example, from the control device 90 in response to the operator's operation.

[0076] As shown in Figure 6, when the CPU 101 starts braking control, it first executes the process in step S10. In step S10, the CPU 101 performs a first process. In the first process, the CPU 101 switches the excitation coil 81B of the first electric motor 32 and the first electromagnetic brake 81 from energized to disconnected. That is, the CPU 101 cuts off the power supply to the first electric motor 32 and the excitation coil 81B that it had been supplying up to that point. The CPU 101 can cut off the power supply to the first electric motor 32 and the excitation coil 81B by turning off all the switching elements in the inverter circuit 35. Once the CPU 101 has cut off the power supply to the first electric motor 32 and the excitation coil 81B, it proceeds to step S20.

[0077] In step S20, the CPU 101 obtains the latest angular position 38S of the drive shaft 32B of the first electric motor 32. Once the CPU 101 obtains the latest angular position 38S, it stores the obtained angular position 38S in memory 102. After storing the angular position 38S in memory 102, the CPU 101 proceeds to step S30. If the determination in step S40, described later, is NO, the CPU 101 returns to step S20 and performs step S20 again. The CPU 101 repeats the process of step S20 as long as the determination in step S40 remains NO. In this case, the CPU 101 obtains a new angular position 38S each time it performs the process of step S20. Once the CPU 101 obtains a new angular position 38S, it stores the obtained angular position 38S over time. In other words, by repeating the process of step S20, the CPU 101 obtains the change in the angular position 38S of the drive shaft 32B from the time the first process is completed. The process of repeating the process in step S20 in this way is the second process.

[0078] In step S30, the CPU 101 performs a third process. In the third process, the CPU 101 calculates the rotation angle, which is the amount of rotation of the drive shaft 32B from the initial position, and the rotation direction of the drive shaft 32B from the initial position. The initial position is the angular position 38S of the drive shaft 32B at the time the first process is completed. The initial position is the first angular position 38S among the transitions of angular positions 38S stored in memory 102. When the process proceeds to step S30, the CPU 101 calculates the amount of rotation and the rotation direction of the drive shaft 32B based on the transitions of angular positions 38S over the period stored in memory 102. After step S30, the CPU 101 proceeds to step S40.

[0079] In step S40, the CPU 101 determines whether the amount of rotation of the drive shaft 32B from the initial position is greater than or equal to a predetermined value. The memory 102 stores this predetermined value in advance. This predetermined value is determined, for example, through experimentation or simulation, as a value that allows the system to determine whether the drive shaft 32B is not being braked by the first electromagnetic brake 81. If the amount of rotation is less than the predetermined value (step S40: NO), the CPU 101 determines that the position of the boom 21, which is rotated by the drive shaft 32B, is being maintained, and returns to the process in step S20. On the other hand, if the amount of rotation is greater than or equal to the predetermined value (step S40: YES), the CPU 101 determines that the position of the boom 21 is not being maintained, and proceeds to the process in step S50.

[0080] In step S50, the CPU 101 starts the fourth process. The fourth process is the process of controlling the power supply to the first electric motor 32 so as to apply a torque to the drive shaft 32B in the opposite direction to the rotation direction of the drive shaft 32B from the initial position. In step S50, the CPU 101 first identifies the initial position and the determination position related to the angular position 38S from the transition of the angular position 38S stored in the memory 102. As described above, the initial position is the angular position 38S of the drive shaft 32B at the time the execution of the first process is completed. The determination position is the angular position of the drive shaft 32B at the time it is determined that the amount of rotation of the drive shaft 32B from the initial position has exceeded a predetermined value. The determination position is the last angular position 38S in the transition of the angular position 38S. Once the CPU 101 has identified the initial position and the determination position, it sets a specific angular position between these initial position and determination position as the target position. After this, the CPU 101 starts feedback control of the first electric motor 32 based on this target position. The above describes the processing in step S50. Feedback control controls the power supply to the first electric motor 32 so that the difference between a specific target position between the initial position and the determination position and the current angular position of the drive shaft 32B is minimized. In this embodiment, the CPU 101 controls the power supply to the first electric motor 32 so that the current angular position of the drive shaft 32B coincides with the initial position. That is, the specific target position in this embodiment is the same as the initial position. In this case, the drive shaft 32B rotates until it returns to the initial position, and the angular position of the drive shaft 32B is maintained at the initial position. When the CPU 101 starts feedback control, it proceeds to step S60. From here on, the CPU 101 continues feedback control and, consequently, the fourth process until the determination in step S70 described later becomes YES.

[0081] In step S60, the CPU 101 notifies that the rotation amount of the drive shaft 32B is abnormal. The CPU 101 displays, for example, the words "Brake abnormality" or "Return boom to initial position" on the display. Alternatively, the CPU 101 may notify the abnormality by outputting an audio message from a speaker or by illuminating a warning light. The display, speaker, and warning light are installed, for example, in the cabin. After issuing the notification, the CPU 101 proceeds to step S70. The CPU 101 may continue the notification until the braking control is terminated.

[0082] In step S70, the CPU 101 determines whether the termination condition has been met. The termination condition is, for example, when the CPU 101 receives a release request signal. The release request signal is transmitted from the control device 90, for example, when an operator who has noticed the notification operates the control device 90. If the termination condition has not been met (step S70: NO), the CPU 101 performs the process of step S70 again. On the other hand, if the termination condition has been met (step S70: YES), the CPU 101 terminates the fourth process. At the same time, the CPU 101 terminates the braking control. After this, the CPU 101 controls the power supply to the first electric motor 32 in response to the operator's operation of the control device 90, etc.

[0083] <Operation of the Embodiment> The following is an overview of the overall process performed by the CPU 101. Here, for the sake of ease of understanding, we will explain the control of the first electromagnetic brake 81 and the first electric motor 32, but the same applies to the control of the electromagnetic brakes 82, 83 and the electric motors 42, 52.

[0084] For example, during excavation work, the CPU 101 rotates the boom 21 by driving the drive shaft 32B of the first electric motor 32. After rotating the boom 21 to scoop up heavy objects such as soil, the CPU 101 may maintain the angular position of the boom 21. For example, the CPU 101 rotates the upper body 14 while maintaining that angular position. Here, if the CPU 101 wants to maintain a constant angular position of the boom 21, it de-energizes the excitation coil 81B to maintain the current angular position of the drive shaft 32B of the first electric motor 32 (step S10). Suppose that at this time there is a malfunction in the first electromagnetic brake 81, and even though the first electromagnetic brake 81 is de-energized, the movable plate 81D remains separated from the contact plate 81C. And as a result, braking force cannot be applied to the drive shaft 32B. In this case, the boom 21 rotates downward due to gravity acting on the scooped heavy object and the weight of the boom 21 itself. Simultaneously, the drive shaft 32B of the first electric motor 32 rotates. When the amount of rotation of the drive shaft 32B due to this rotation exceeds a predetermined value (step S40: YES), the CPU 101 controls the power supply to the first electric motor 32 so as to apply a torque to the drive shaft 32B in the opposite direction to the rotation direction of the drive shaft 32B (step S50).

[0085] <Effects of the Embodiment> (1) As described in the operation of the embodiment, the drive shaft 32B may rotate as a result of the first electromagnetic brake 81 being unable to apply braking force to the drive shaft 32B. In this case, the CPU 101 controls the power supply to the first electric motor 32 so as to apply torque to the drive shaft 32B in the opposite direction to the rotation direction of the drive shaft 32B. As a result, the CPU 101 can restrict the movement of the boom 21, which is the object to be braked, in relation to the rotation direction of the drive shaft 32B, and prevent the boom 21 from falling. The same effect can be obtained even when the electromagnetic brakes 82 and 83 are malfunctioning.

[0086] (2) When the CPU 101 applies torque to the drive shaft 32B in the opposite direction to the rotation direction of the drive shaft 32B, it uses the angular position of the drive shaft 32B at the time the power supply to the first electric motor 32 is cut off as the target position and provides feedback control to the first electric motor 32. As a result, the CPU 101 can maintain the angular position of the drive shaft 32B and, consequently, the boom 21, at approximately the same position as at the time the power supply to the first electric motor 32 is cut off. The same effect can be obtained for the arm 23 and the bucket 25.

[0087] (3) In step S60 shown in Figure 6, when the first electromagnetic brake 81 malfunctions, the first electric motor 32 holds the boom 21 in place and notifies the operator of the malfunction of the first electromagnetic brake 81. This allows the operator to check the notification and repair the first electromagnetic brake 81, thereby preventing the situation in which the first electromagnetic brake 81 does not operate from continuing. The same effect can be obtained in the event of malfunctions in the electromagnetic brakes 82 and 83.

[0088] (4) In construction machinery such as excavators 10, the working equipment 20 may be used to lift heavy objects such as soil and maintain its position. Therefore, the configuration of this embodiment, which uses electric motors 32, 42, and 52 to maintain the positions of the boom 21, arm 23, and bucket 25, is particularly effective for the working equipment 20 of construction machinery.

[0089] (5) In this embodiment, the operating state of both the first electric motor 32 and the first electromagnetic brake 81 can be switched by operating or stopping the switching elements 121 to 126 of the first inverter circuit 35. This simplifies the circuit configuration and control of the drive circuit 110. The same effect can be obtained when switching the operating states of the electric motors 42 and 52 and the electromagnetic brakes 82 and 83.

[0090] (6) In this embodiment, the wiring 141 to 143 for the first electromagnetic brake 81 is branched from the first inverter circuit 35. In this case, the wiring for the first electromagnetic brake 81 is shorter compared to when the wiring for the first electromagnetic brake 81 is routed from the DC power supply 19, so the space required for wiring storage can be reduced. The same effect can be obtained when the wiring for electromagnetic brakes 82 and 83 is branched from the first inverter circuit 35.

[0091] <Example of changes> The above embodiment can be implemented with the following modifications. The above embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0092] The switching regulator 150 may be omitted from the drive circuit 110 shown in Figure 5. The configuration of the circuit that supplies power to the first electromagnetic brake 81 is not limited to the example of the embodiment described above. As long as the power supply to the first electromagnetic brake 81 can be turned on and off, the configuration of the circuit that supplies power to the first electromagnetic brake 81 is not limited. For example, the DC power supply 19 and the first electromagnetic brake 81 may be directly connected by a power line. A switch for switching the power supply to the first electromagnetic brake 81 on and off may be provided in the middle of the power line. Power may also be supplied to the first electromagnetic brake 81 from a DC power supply separate from the DC power supply 19 that supplies power to the first electric motor 32. The same applies to the other electromagnetic brakes 82 to 85.

[0093] The electromagnetic brakes 81 to 85 in the above embodiment were configured to apply braking force to the drive shafts 32B, 42B, 52B, 62B, and 72B of the electric motors 32, 42, 52, 62, and 72. However, the electromagnetic brakes 81 to 85 may also be configured to apply braking force to the drive shafts 33C, 43C, 53C, 63C, and 73C of the reduction gears 33, 43, 53, 63, and 73. The rotation of the drive shafts 33C, 43C, 53C, 63C, and 73C is obtained by reducing the rotation of the drive shafts 32B, 42B, 52B, 62B, and 72B with the reduction gears 33, 43, 53, 63, and 73. Therefore, the torque of drive shafts 33C, 43C, 53C, 63C, and 73C becomes greater than the torque of drive shafts 32B, 42B, 52B, 62B, and 72B. Thus, as in the above embodiment, by using electromagnetic brakes 81-85 to brake drive shafts 32B, 42B, 52B, 62B, and 72B, the drive shafts can be braked with a small braking force.

[0094] The shape of the drive shafts 32B, 42B, 52B, 62B, 72B of the electric motors 32, 42, 52, 62, 72, and the drive shafts 33C, 43C, 53C, 63C, 73C of the reduction gears 33, 43, 53, 63, 73 is not limited to a cylindrical shape. Each drive shaft only needs to be shaped to transmit torque to the mating component.

[0095] In the above embodiment, the CPU 101 of the control device 100 calculated the rotation angle as the amount of rotation of the drive shafts 32B, 42B, and 52B from the initial position, which is the angular position at the time of completion of the first process. However, the CPU 101 may also calculate the rotation speed of the drive shafts 32B, 42B, and 52B as the amount of rotation of the drive shafts 32B, 42B, and 52B.

[0096] • In the control processing, the following fifth processing may be performed while the fourth processing is being executed. That is, while the fourth processing is being executed, the CPU 101 calculates the load of the heavy object loaded into the bucket 25 based on the driving force required to brake the boom 21. Specifically, in the fifth processing, the CPU 101 acquires the latest current value detected by the current sensor 91. Then, the CPU 101 calculates the magnitude of the torque applied to the drive shaft 32B based on the acquired current value. Then, the CPU 101 calculates the load of the heavy object based on the calculated magnitude of the torque. The memory 102 has in advance stored various conversion information necessary for the CPU 101 to execute the fifth processing. For example, the memory 102 stores first conversion information that represents the relationship between the current value supplied to the first electric motor 32 and the torque applied to the drive shaft 32B. In this first conversion information, the larger the absolute value of the current value, the larger the torque. The memory 102 also stores second conversion information that represents the relationship between the torque applied to the drive shaft 32B and the load of the heavy object. The CPU 101 uses this conversion information to detect the magnitude of the torque applied to the drive shaft 32B and, consequently, the load of the heavy object, based on the current value supplied to the first electric motor 32. This concludes the fifth process.

[0097] In the fourth process, the CPU 101 maintains the angular position of the drive shaft 32B of the first electric motor 32 at approximately a constant value by performing feedback control of the first electric motor 32. The current value supplied to the first electric motor 32 at this time reflects the torque required to maintain the angular position of the drive shaft 32B at approximately a constant value. Therefore, in the fifth process, the CPU 101 can accurately calculate the torque applied to the drive shaft 32B based on the current value during feedback control. The torque applied to the drive shaft 32B is the force required to support the load of the heavy object loaded into the bucket 25. In other words, the torque applied to the drive shaft 32B reflects the load of the heavy object loaded into the bucket 25. Therefore, the CPU 101 can accurately calculate the load of the heavy object based on the torque applied to the drive shaft 32B.

[0098] Furthermore, the CPU 101 may use the information on the load of the heavy object calculated in the fifth process to calculate the current value supplied to the first electric motor 32. For example, after the braking control is completed, until the electromagnetic brake 81 is maintained and returned to its normal state, the rotation and braking of the drive shaft 32B will be performed solely through the control of the first electric motor 32, without using the electromagnetic brake 81. For example, when braking the drive shaft 32B, if the current value supplied to the first electric motor 32 is calculated taking into account the load of the heavy object, the accuracy of the angular position and other parameters of the drive shaft 32B will be improved.

[0099] • For the purpose of calculating the load of heavy objects, the fourth and fifth processes may be performed under conditions where there is no abnormality in the first electromagnetic brake 81. That is, as described in the above example of circuit modification, a configuration is adopted in which the DC power supply 19 and the first electromagnetic brake 81 are directly connected by a power line. Furthermore, feedback control of the first electric motor 32 is performed so that the position of the boom 21 can be maintained while the first electromagnetic brake 81 is energized by this power line, that is, with the braking force by the first electromagnetic brake 81 intentionally released. Then, based on the current value 91S supplied to the first electric motor 32 at that time, the torque applied to the drive shaft 32B and, consequently, the load of heavy objects may be calculated.

[0100] Regarding the fourth braking process, the target position when feedback-controlling the first electric motor 32 is not limited to the example of the above embodiment. The target position can be anywhere between the initial position and the determination position. Note that "between the initial position and the determination position" includes the initial position. Similarly, "between the initial position and the determination position" includes the determination position.

[0101] Regarding the fourth process, it is not essential to control the power supply to the first electric motor 32 to maintain the drive shaft 32B in the target position. The fourth process only needs to apply a torque to the drive shaft 32B in the opposite direction to the rotation direction of the drive shaft 32B. For example, in the fourth process, a torque may be applied to the drive shaft 32B in the opposite direction to the rotation direction of the drive shaft 32B so that the falling speed of the boom 21 decreases.

[0102] The configuration of the first electric actuator 31 is not limited to the examples of the above embodiment. The first electric actuator 31 only needs to include an electric motor and be able to drive the rotation of the boom 21. For example, the first reduction gear 33 may be omitted from the first electric actuator 31. Furthermore, the first electric actuator 31 is not limited to outputting torque coaxial with the drive shaft of the electric motor to the outside.

[0103] The mounting configuration of the first electric actuator 31 to the boom 21 and swing bracket 17 is not limited to the example of the above embodiment. Any mounting configuration is acceptable as long as the boom 21 can be rotated by the first electric actuator 31. For example, the orientation of the first electric actuator 31 between the second swing wall 17B of the swing bracket 17 and the boom 21 may be reversed. That is, the first electric actuator 31 may be mounted to the boom 21 and swing bracket 17 such that the first reduction gear 33 is located closer to the second swing wall 17B and the first electric motor 32 is located closer to the boom 21.

[0104] Similar to the above-described examples of modifications to the first electric actuator 31, the configuration and mounting of the second electric actuator 41 are not limited to the examples of the above embodiments. The second electric actuator 41 only needs to include an electric motor and be able to drive the rotation of the arm 23.

[0105] Similar to the above-described examples of modifications to the first electric actuator 31, the configuration and mounting of the third electric actuator 51 are not limited to the examples of the above embodiments. The third electric actuator 51 only needs to include an electric motor and be able to drive the rotation of the bucket 25.

[0106] Similar to the above-described examples of modifications to the first electric actuator 31, the configuration and mounting of the fourth electric actuator 61 are not limited to the examples of the above embodiments. The fourth electric actuator 61 only needs to include an electric motor and be able to drive the rotation of the swing bracket 17.

[0107] Similar to the above-described examples of modifications to the first electric actuator 31, the configuration and mounting of the fifth electric actuator 71 are not limited to the examples of the above embodiments. The fifth electric actuator 71 includes an electric motor and only needs to be able to drive the rotation of the upper body 14 relative to the lower body 13.

[0108] The attachment is not limited to the bucket 25. Appropriate devices, mechanisms, tools, etc. may be used as attachments depending on the work. If an attachment that does not require rotation is used, the third electric actuator 51 may be eliminated and the attachment may be directly connected to the arm 23.

[0109] The overall configuration of the work machine 20 is not limited to the examples of the above embodiment. For example, the bucket 25 may be eliminated. If the bucket 25 is eliminated, the third electric actuator 51 may also be eliminated accordingly. Alternatively, the arm 23 may be eliminated, and the bucket 25 may be connected to the boom 21 without using the arm 23. If the arm 23 is eliminated, the second electric actuator 41 may also be eliminated accordingly. The work machine 20 may be configured by adopting appropriate components depending on the work.

[0110] In the above embodiment, when the rotational amount of the drive shafts 32B, 42B, and 52B of the electric motors 32, 42, and 52 exceeded a predetermined value, the CPU 101 performed control to apply torque in the opposite direction to the rotational direction of the drive shafts 32B, 42B, and 52B. However, the CPU 101 may also perform control to apply torque in the opposite direction to the rotational direction of the drive shaft 62B when the rotational amount of the drive shaft 62B of the fourth electric motor 62 that rotates the swing bracket 17 exceeds a predetermined value. Furthermore, the CPU 101 may also perform control to apply torque in the opposite direction to the rotational direction of the drive shaft 72B when the rotational amount of the drive shaft 72B of the fifth electric motor 72 that rotates the upper body 14 of the vehicle body 15 exceeds a predetermined value. In other words, the objects to which the electric motors are driven, and therefore the objects to which the braking control is applied, are not limited to the boom 21, arm 23, and bucket 25. The braking control may be applied to one or more of the boom 21, arm 23, and bucket 25, or to other components.

[0111] The configuration of the upper body 14 is not limited to the example of the upper embodiment. For example, the cabin may be eliminated from the upper body 14. The shape of the main housing portion 14A and the front housing portion 14B may be other than a rectangular parallelepiped. The upper body 14 only needs to be configured to realize the necessary functions, such as housing various equipment.

[0112] As shown in the above example of modification, the operating equipment 90 may be removed from the upper body 14 in conjunction with the removal of the cabin from the upper body 14. At the same time, various signals, such as request signals or command signals for the operation of the excavator 10, may be transmitted wirelessly from equipment outside the vehicle body 15 to the control device 100.

[0113] The overall configuration of the vehicle body 15, and by extension the excavator 10, is not limited to the examples of the above embodiments. For example, the overall shape of the vehicle body 15 may be changed from the examples of the above embodiments in conjunction with changing the shape of the upper body 14, as in the modified example above. It is sufficient that the excavator 10 as a whole is configured to perform the required work, such as excavation.

[0114] • The work machine is not limited to the excavator 10. The work machine may be any construction machine other than the excavator 10. Furthermore, the work machine is not limited to construction machines. Examples of work machines other than construction machines include machines used in forestry, quarrying, industrial waste treatment, and agriculture.

[0115] The processing circuit of the control device 100 may have any of the following configurations (a) to (c). (a) The processing circuit comprises one or more processors that perform various processes according to a computer program. The processor includes a CPU 101 and memory 102 such as RAM and ROM. Memory 102 stores program code or instructions configured to cause the CPU 101 to perform the processes. Memory 102, i.e., computer-readable media, includes any available media that can be accessed by a general-purpose or dedicated computer.

[0116] (b) The processing circuit comprises one or more dedicated hardware circuits that perform various processing tasks. Examples of dedicated hardware circuits include application-specific integrated circuits, i.e., ASICs or FPGAs.

[0117] (c) The processing circuit comprises a processor that executes a portion of the various processes according to a computer program, and a dedicated hardware circuit that executes the remaining parts of the various processes.

[0118] In the above embodiment, a structure composed of multiple objects may be integrated, or conversely, a structure composed of a single object may be divided into multiple objects. Whether or not the objects are integrated, the structure should be configured in a way that achieves the objective of the invention.

[0119] In the above embodiment, if multiple functions are provided in a distributed manner, some or all of those multiple functions may be consolidated and provided together. Conversely, if multiple functions are consolidated and provided together, some or all of those multiple functions may be distributed and provided together. Regardless of whether the functions are consolidated or distributed, it is sufficient that the device is configured to achieve the objective of the invention. [Explanation of Symbols]

[0120] 10... Excavator 15... Vehicle body 20…Work equipment 21... Boom 23... Arm 25… Bucket 31…First electric actuator 32…First electric motor 32B, 42B, 52B, 62B, 72B… Drive shaft 35…First Inverter Circuit 38…First position sensor 41…Second electric actuator 42…Second electric motor 45...Second inverter circuit 48...Second position sensor 51…Third electric actuator 52…Third electric motor 55...Third inverter circuit 58...Third position sensor 61...Fourth electric actuator 62…Fourth electric motor 65…Fourth inverter circuit 68...Fourth position sensor 71…5th electric actuator 72…5th electric motor 75... Fifth inverter circuit 81...First electromagnetic brake 81B, 82B, 83B, 84B, 85B… Excitation coils 82... Second electromagnetic brake 83...Third electromagnetic brake 84…Fourth electromagnetic brake 85... Fifth electromagnetic brake 100...Control device 102A... Control program 110…Drive circuit 130... Converter circuit

Claims

1. A motor capable of rotating in both directions, and an electric actuator having a drive shaft driven by the electric motor, An electromagnetic brake having an excitation coil, which brakes the drive shaft when the excitation coil is de-excited and releases the brake on the drive shaft when the excitation coil is excited, A position sensor for detecting the angular position of the drive shaft, A control device that controls the supply and interruption of power to the electric motor and the excitation coil, respectively, is provided. The control device is A first process of interrupting the power supply to the electric motor and the excitation coil, respectively, A second process to obtain the change in the angular position of the drive shaft from the time the first process is completed, A third process calculates the amount and direction of rotation of the drive shaft from its initial position, which is the angular position of the drive shaft at the time the first process is completed, based on the acquired transitions. If the amount of rotation of the drive shaft from the initial position exceeds a predetermined value, a fourth process is performed in which the power supply to the electric motor is controlled to apply a torque to the drive shaft in the opposite direction to the rotation direction of the drive shaft from the initial position. Actuator systems for industrial machinery.

2. When the angular position of the drive shaft at the time it is determined that the amount of rotation of the drive shaft from the initial position has exceeded the predetermined value is defined as the determination position, In the fourth process, the control device controls the power supply to the electric motor so as to reduce the difference between a specific target position between the initial position and the determination position and the current angular position of the drive shaft. The actuator system for a work machine according to claim 1.

3. During the execution of the fourth process, the control device performs a fifth process to calculate the magnitude of the torque applied to the drive shaft based on the current value supplied to the electric motor. The actuator system for a work machine according to claim 2.

4. The electric actuator drives one of the following: a boom rotatably connected to the body of the construction machine, an arm rotatably connected to the boom, or an attachment rotatably connected to the arm. An actuator system for a work machine according to any one of claims 1 to 3.

5. The drive circuit further comprises an inverter circuit that converts a DC voltage to an AC voltage and outputs it to the electric actuator, and a converter circuit that converts the AC voltage output by the inverter circuit to a DC voltage and outputs it to the excitation coil. The control device controls the supply and interruption of power to the electric motor and the excitation coil, respectively, through the control of the drive circuit. The actuator system for a work machine according to claim 1.

6. A work machine having a boom rotatably connected to the vehicle body, an arm rotatably connected to the boom, and an attachment rotatably connected to the arm, An electric actuator having a bidirectionally rotatable electric motor and a drive shaft driven by the electric motor, which drives one of the boom, the arm, and the attachment, An electromagnetic brake having an excitation coil, which brakes the drive shaft when the excitation coil is de-excited and releases the brake on the drive shaft when the excitation coil is excited, A position sensor for detecting the angular position of the drive shaft, A control device that controls the supply and interruption of power to the electric motor and the excitation coil, respectively, is provided. The control device is A first process of interrupting the power supply to the electric motor and the excitation coil, respectively, A second process to obtain the change in the angular position of the drive shaft from the time the first process is completed, A third process calculates the amount and direction of rotation of the drive shaft from its initial position, which is the angular position of the drive shaft at the time the first process is completed, based on the acquired transitions. If the amount of rotation of the drive shaft from the initial position exceeds a predetermined value, a fourth process is performed in which the electric motor is energized to apply torque to the drive shaft in the opposite direction to the rotation direction of the drive shaft from the initial position. Construction machinery.

7. A motor capable of rotating in both directions, and an electric actuator having a drive shaft driven by the electric motor, An electromagnetic brake having an excitation coil, which brakes the drive shaft when the excitation coil is de-excited and releases the brake on the drive shaft when the excitation coil is excited, This is applied to a work machine equipped with a position sensor that detects the angular position of the drive shaft, It is possible to control the supply of power to the electric motor and the excitation coil, respectively, and to cut off the power supply. A first process of interrupting the power supply to the electric motor and the excitation coil, respectively, A second process to obtain the change in the angular position of the drive shaft from the time the first process is completed, A third process calculates the amount and direction of rotation of the drive shaft from its initial position, which is the angular position of the drive shaft at the time the first process is completed, based on the acquired transitions. If the amount of rotation of the drive shaft from the initial position exceeds a predetermined value, a fourth process is performed in which the power supply to the electric motor is controlled to apply a torque to the drive shaft in the opposite direction to the rotation direction of the drive shaft from the initial position. Control device for industrial machinery.

8. A motor capable of rotating in both directions, and an electric actuator having a drive shaft driven by the electric motor, An electromagnetic brake having an excitation coil, which brakes the drive shaft when the excitation coil is de-excited and releases the brake on the drive shaft when the excitation coil is excited, A position sensor for detecting the angular position of the drive shaft, Applied to a work machine equipped with, a control device that controls the supply and interruption of power to the electric motor and the excitation coil, A first process of interrupting the power supply to the electric motor and the excitation coil, respectively, A second process to obtain the change in the angular position of the drive shaft from the time the first process is completed, A third process calculates the amount and direction of rotation of the drive shaft from its initial position, which is the angular position of the drive shaft at the time the first process is completed, based on the acquired transitions. If the amount of rotation of the drive shaft from the initial position exceeds a predetermined value, a fourth process is performed in which the power supply to the electric motor is controlled to apply a torque to the drive shaft in the opposite direction to the rotation direction of the drive shaft from the initial position. A method for controlling industrial machinery.

9. A motor capable of rotating in both directions, and an electric actuator having a drive shaft driven by the electric motor, An electromagnetic brake having an excitation coil, which brakes the drive shaft when the excitation coil is de-excited and releases the brake on the drive shaft when the excitation coil is excited, A position sensor for detecting the angular position of the drive shaft, Applicable to a work machine equipped with, a control device that controls the supply and interruption of power to the electric motor and the excitation coil, respectively, A first process of interrupting the power supply to the electric motor and the excitation coil, respectively, A second process to obtain the change in the angular position of the drive shaft from the time the first process is completed, A third process calculates the amount and direction of rotation of the drive shaft from its initial position, which is the angular position of the drive shaft at the time the first process is completed, based on the acquired transitions. If the amount of rotation of the drive shaft from the initial position exceeds a predetermined value, a fourth process is performed to control the power supply to the electric motor so as to apply torque to the drive shaft in the opposite direction to the rotation direction of the drive shaft from the initial position. Control program for industrial machinery.

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