Work machine

Abstract

To provide a work machine which enables an operator to acquire an operation skill by support from a support engineer while preventing contact with the support engineer.SOLUTION: This work machine comprises: a machine body; a work device supported on the machine body to be operated; a cab in which an operation device and a seat are arranged and which has a door and a window to be supported on the machine body; a seating sensor that detects seating of an operator on the seat; an opening / closing sensor that detects the opened / closed state of the door or the window in the cab; and a controller that controls an operation of the machine body in accordance with an operation of the operation device on the basis of the detection results of the seating sensor and the opening / closing sensor. The controller inhibits the operations of the machine body and the work device when the seating sensor does not detect the seating, and permits the operation of the work device while limiting or inhibiting at least a part of the operation of the machine body when the seating sensor detects the seating and the opening / closing sensor detects the opened state of the door or the window.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a work machine. [Background technology]

[0002] An operator who is trying to learn how to operate a work machine may, for example, practice operating the work machine while talking to a support person standing next to the cab or receiving instructions from the support person. In such cases, it is necessary to prevent the work machine being operated by the operator from coming into contact with the support person.

[0003] Furthermore, Patent Document 1 discloses a technology for restricting the operation of a work machine when a worker carrying a transmitter that transmits its own position is present in a blind spot, in order to prevent the work machine from coming into contact with surrounding workers. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-139312 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the technology of Patent Document 1 restricts the operation of the work machine regardless of whether the person carrying the transmitter is a support person or not. Furthermore, the technology of Patent Document 1 cannot detect people who are not carrying a transmitter.

[0006] The present invention has been made in consideration of the above-described circumstances, and its object is to provide a work machine that allows an operator to learn operating techniques with the support of a support person while avoiding contact with the operator. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention provides a work machine comprising a body, a working device supported on the body and operable by the body, an operating device operated to operate the body and the working device, and a cab supported on the body, with a seat inside for an operator to operate the operating device, the cab having doors and windows, the work machine comprising: a seating sensor that detects when the operator is seated in the seat; an opening / closing sensor that detects the open / closed state of the door or the window in the cab; and a controller that controls the operation of the body in accordance with the operation of the operating device based on the detection results of the seating sensor and the opening / closing sensor, the controller prohibiting the operation of the body and the working device when no operator is seated by the seating sensor, and permitting the operation of the working device and restricting or prohibiting at least a part of the operation of the body when the operator is seated by the seating sensor and the opening / closing sensor detects that the door or the window is open. [Effects of the Invention]

[0008] According to the present invention, the operator can learn the operation technique with the support of the support person while avoiding contact with the support person. Note that the problems, configurations, and effects other than those described above will become clear from the description of the following embodiments. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a side view of a hydraulic excavator. [Figure 2] FIG. 2 is a schematic diagram showing the inside of the cab. [Figure 3] FIG. 2 is a control block diagram of the hydraulic excavator. [Figure 4] 10 is a flowchart of an operation control process. [Figure 5] FIG. 10 is a diagram illustrating an example of a combination of a restrictive action and a non-restrictive action. DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment of a hydraulic excavator 1 as a work machine according to the present invention will be described with reference to the drawings. However, specific examples of the work machine are not limited to the hydraulic excavator 1, and may be any machine having a work implement, such as a wheel loader, a dump truck, or a crane. Furthermore, unless otherwise specified, the terms front, back, left, and right in this specification are based on the viewpoint of an operator H1 who is riding on and operating the hydraulic excavator 1.

[0011] Fig. 1 is a side view of a hydraulic excavator 1. As shown in Fig. 1, the hydraulic excavator 1 includes a lower traveling body 2 and an upper rotating body 3 supported by the lower traveling body 2. The lower traveling body 2 and the upper rotating body 3 are an example of a machine body.

[0012] The lower traveling body 2 is equipped with a pair of left and right crawlers 4L, 4R (the crawler 4R is not shown in FIG. 1) which are endless tracks. The pair of left and right crawlers 4L, 4R rotate independently by driving left and right traveling motors 5L, 5R (see FIG. 3). As a result, the hydraulic excavator 1 travels. However, the lower traveling body 2 may be of a wheeled type instead of the crawlers 4L, 4R.

[0013] As one example, the traveling motors 5L, 5R rotate in the same direction at the same number of revolutions to move the hydraulic excavator 1 forward or backward (hereinafter referred to as "forward or backward movement"). As another example, the traveling motors 5L, 5R rotate at different rotational speeds (including a state in which one of the traveling motors 5L, 5R is stopped) to change (switch) the direction in which the hydraulic excavator 1 travels to the left or right.

[0014] The upper rotating body 3 is supported on the lower traveling body 2 so as to be rotatable by a swing motor 6. That is, when the swing motor 6 rotates, the upper rotating body 3 swings relative to the lower traveling body 2. The upper rotating body 3 mainly comprises a swing frame 7 serving as a base, a counterweight 9 disposed at the rear of the swing frame 7, a front work machine 10 (working device) attached to the front center of the swing frame 7 so as to be rotatable in the vertical direction, and a cab (operator's seat) 20 disposed on the front left side of the swing frame 7.

[0015] The front work implement 10 includes a boom 11 supported on the upper rotating body 3 so that it can be raised and lowered, an arm 12 supported at the tip of the boom 11 so that it can rotate (crowd, dump), a bucket 13 (attachment) supported at the tip of the arm 12 so that it can rotate (crowd, dump), a boom cylinder 14 that drives the boom 11, an arm cylinder 15 that drives the arm 12, and a bucket cylinder 16 that drives the bucket 13. Note that specific examples of the attachment are not limited to the bucket 13, and may include a grapple, cutter, crusher, breaker, etc. The counterweight 9 is a heavy object that has an arc shape when viewed from above and is used to balance the weight of the front work implement 10.

[0016] The cab 20 is disposed adjacent to the front working implement 10 in the left-right direction (width direction of the machine body). More specifically, the cab 20 is disposed to the left (one side in the left-right direction) of the front working implement 10. However, the location of the cab 20 is not limited to the example described above, and the cab 20 may be disposed on one side of the front working implement 10 in the left-right direction.

[0017] As shown in FIG. 1 , the cab 20 includes a main body 21 and a door 22. The main body 21 is a box-shaped member having an internal space capable of receiving an operator H1. An opening 23 through which the operator H1 can get in and out of the main body 21 is formed on the left side of the main body 21 (the side opposite the side facing the front working implement 10 in the left-right direction of the upper rotating body 3). The door 22 is a plate-shaped member that opens and closes (hereinafter referred to as "opening and closing") the opening 23 of the main body 21. The door 22 may be a pivoting door that pivots about a pivot axis that extends in the vertical direction, or a sliding door that slides in the front-to-rear direction.

[0018] The hydraulic excavator 1 is equipped with a door open / close sensor 24 (see FIG. 3). The door open / close sensor 24 is an example of an open / close sensor that detects the open / closed state of the door 22 and outputs a signal indicating the detection result to the controller 50 (see FIG. 3). For example, the door open / close sensor 24 outputs an open signal when the door 22 is open, and stops outputting the open signal when the door 22 is closed. However, a specific example of the open / close sensor is not limited to the door open / close sensor 24, and may be a window open / close sensor that detects the open / closed state of a window provided on the side of the cab 20.

[0019] Fig. 2 is a schematic diagram showing the interior of the cab 20. As shown in Fig. 2, the interior of the cab 20 (main body 21) is provided with an operating device 25 that is operated to operate the lower traveling body 2, the upper revolving body 3, and the front working implement 10, a seat 26 in which an operator H1 who operates the operating device 25 sits, a seat belt 27 (restraint) that restrains the operator H1 seated in the seat 26, and a display 28. The operator H1 refers to a person who operates the hydraulic excavator 1 by operating the operating device 25 while seated in the seat 26.

[0020] The operating device 25 includes, for example, a pair of left and right operating levers 29, 30 for operating the upper rotating body 3 and the front working implement 10, and a pair of left and right traveling pedals 31, 32 for operating the lower traveling body 2. The operating device 25 outputs an operating signal corresponding to an operation by the operator H1 to the controller 50. When the operator H1 in the cab 20 (more specifically, seated in the seat 26) operates the operating device 25, the lower traveling body 2 travels, the upper rotating body 3 swings, and the front working implement 10 operates.

[0021] In this embodiment, the left-right tilting of the operation lever 29 corresponds to the extension and contraction of the bucket cylinder 16 (dumping and crowding of the bucket 13), the front-rear tilting of the operation lever 29 corresponds to the extension and contraction of the boom cylinder 14 (raising and lowering of the boom 11), the left-right tilting of the operation lever 30 corresponds to the rotation of the swing motor 6 (swing of the upper swing body 3), the front-rear tilting of the operation lever 30 corresponds to the extension and contraction of the arm cylinder 15 (raising and lowering of the arm 12), and depression of the travel pedals 31, 32 corresponds to the rotation of the travel motors 5L, 5R (orbiting of the crawlers 4L, 4R). However, the correspondence between the operation direction of the operation device 25 and the operation of the hydraulic excavator 1 is not limited to the example described above.

[0022] The seat belt 27 includes, for example, a belt 33, a buckle 34 (locking portion), and a tongue plate 35 (locked portion). The belt 33 extends in front of the operator H1 seated in the seat 26. The belt 33 according to this embodiment includes a shoulder belt extending from the right shoulder to the left waist of the operator H1, and an abdominal belt extending in the left-right direction along the abdomen of the operator H1. The buckle 34 is fixed to the left side of the seat 26. The tongue plate 35 is attached to the belt 33 and is locked to or unlocked from the buckle 34.

[0023] When the tongue plate 35 is engaged with the buckle 34 (the seat belt 27 is fastened), the operator H1 is restrained in the seat 26. On the other hand, when the tongue plate 35 is released from engagement with the buckle 34 (the seat belt 27 is removed), the operator H1 can leave the seat 26. However, the specific configuration of the restraint is not limited to the example described above.

[0024] The hydraulic excavator 1 is equipped with a seat belt sensor 36 (see FIG. 3 ). The seat belt sensor 36 is an example of a seating sensor that detects that the seat belt 27 is fastened (indirectly detects that the operator H1 is seated in the seat 26) and outputs a restraint signal indicating the detection result to the controller 50. For example, the seat belt sensor 36 outputs a restraint signal to the controller 50 when the seat belt 27 is fastened, and stops outputting the restraint signal when the seat belt 27 is undone. However, a specific example of the seating sensor is not limited to the seat belt sensor 36 that indirectly detects that the operator H1 is seated in the seat 26, and may be a pressure sensor that directly detects that the operator H1 is seated in the seat 26.

[0025] The display 28 is an example of a notification device that notifies information to the operator H1 seated in the seat 26 in accordance with the control of the controller 50. However, specific examples of the notification device are not limited to the display 28, and may be an LED lamp, a speaker, or a combination thereof.

[0026] [Controller 50 Configuration] Fig. 3 is a control block diagram of the hydraulic excavator 1. As shown in Fig. 3, the hydraulic excavator 1 is equipped with a controller 50 having a CPU (Central Processing Unit) 51 and a memory 52. ​​The memory 52 is configured, for example, by a ROM (Read Only Memory), a RAM (Random Access Memory), an HDD (Hard Disk Drive), or a combination of these. The controller 50 realizes the processing described below by having the CPU 51 read and execute program code stored in the memory 52.

[0027] However, the specific configuration of the controller 50 is not limited to this, and may be realized by hardware such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field-Programmable Gate Array).

[0028] The controller 50 controls the overall operation of the hydraulic excavator 1. The controller 50 controls the operation of the hydraulic actuators (travel motors 5L, 5R, swing motor 6, boom cylinder 14, arm cylinder 15, bucket cylinder 16) via a drive circuit 38 in accordance with, for example, an open signal output from the door open / close sensor 24, an operation signal output from the operation device 25, and a restraint signal output from the seat belt sensor 36.

[0029] The drive circuit 38 is a circuit that supplies and discharges hydraulic oil to and from the hydraulic actuator, and includes, for example, a hydraulic oil tank, a hydraulic pump, a directional control valve, an on-off valve, and a relief valve. The configuration of the drive circuit 38 is already well known, so a detailed description will be omitted. Note that the work machine is not limited to being operated by the driving force of a hydraulic actuator, and may also be operated by the driving force of an electric motor (electric actuator). In other words, the work machine may be equipped with a machine body and a work device that are operated by the driving force of an actuator (hydraulic actuator, electric actuator).

[0030] [Motion control processing] Fig. 4 is a flowchart of the operation control process. The controller 50 repeatedly executes the operation control process shown in Fig. 4 at predetermined time intervals, for example, while the hydraulic excavator 1 is operating.

[0031] First, the controller 50 determines whether the seat belt 27 is fastened (i.e., whether the operator H1 is fastened to the seat 26) based on the restraint signal of the seat belt sensor 36 (S11). Then, when the controller 50 determines that the seat belt 27 is not fastened (S11: No), it notifies via the display 28 that all operations of the hydraulic excavator 1 (more specifically, the actuators) are prohibited (S12). Then, even if the operating device 25 is operated (an operation signal is output from the operating device 25) while the seat belt 27 is not fastened, the controller 50 prohibits the operation of the hydraulic excavator 1 (actuators).

[0032] Furthermore, when the controller 50 determines that the seat belt 27 is fastened (S11: Yes), it assumes that the operator H1 is seated in the seat 26, and determines whether or not the door 22 is open based on the open signal of the door open / close sensor 24 (S13). Next, when the controller 50 determines that the door 22 is closed (S13: No), it determines whether or not the operating device 25 is being operated based on the operating signal of the operating device 25 (S14).

[0033] When the controller 50 determines that the operating device 25 is being operated (S14: Yes), it controls the operation of the hydraulic excavator 1 (actuator) in accordance with the operation on the operating device 25 (S15). On the other hand, when the controller 50 determines that the operating device 25 is not being operated (S14: No), it does not operate the hydraulic excavator 1 (actuator).

[0034] Furthermore, when the controller 50 determines that the door 22 is open (S13: Yes), it notifies through the display 28 that a restrictive operation, which will be described later, will be restricted (S16). Then, the controller 50 determines whether or not an unrestricted operation is being performed on the operating device 25, based on an operation signal from the operating device 25 (S17).

[0035] When the controller 50 determines that an unrestricted operation is being performed on the operating device 25 (S17: Yes), it controls the unrestricted operation of the hydraulic excavator 1 (actuator) in accordance with the unrestricted operation (S18). On the other hand, when the controller 50 determines that a restricted operation is being performed (S17: No), it restricts or prohibits the operation of the hydraulic excavator 1 (actuator). Furthermore, when the controller 50 determines that the operating device 25 is not being operated (S17: No), it does not operate the hydraulic excavator 1 (actuator). In other words, the controller 50 permits the operation of the front working implement 10 and restricts or prohibits at least a portion of the operation of the machine body.

[0036] Here, "controlling the operation of the hydraulic excavator 1 (actuator) in accordance with the operation of the operating device 25" means that, based on the operation signal output from the operating device 25, the controller 50 causes the actuator to perform an operation in a direction, speed, and amount of operation that corresponds to the direction and amount of operation of the operating device 25 (hereinafter, such an operation will be referred to as "normal operation").

[0037] Furthermore, "prohibiting the operation of the hydraulic excavator 1 (actuator)" means that the controller 50 ignores the operation signal output from the operation device 25 and does not operate the hydraulic excavator 1 (actuator). In other words, even if the operator H1 operates the operation device 25, the hydraulic excavator 1 (actuator) will not operate.

[0038] Furthermore, "restricting the operation of the hydraulic excavator 1 (actuator)" may refer to prohibiting operation, or may refer to the controller 50 causing the hydraulic excavator 1 (actuator) to perform an operation in which at least one of the direction of operation, speed of operation, and amount of operation is restricted from normal operation.

[0039] In steps S16 to S18 of Fig. 4, it is assumed that the operator H1 is practicing operating the hydraulic excavator 1 while receiving support from a support person H2, as shown in Fig. 1. The operator H1 is seated in the seat 26 and wearing a seat belt 27. The support person H2 is standing on the ground or on a platform placed on the ground to the left of the hydraulic excavator 1 (upper rotating body 3) (more specifically, in a position close to the opening 23). Furthermore, the door 22 is in an open state. The operator H1 then talks to the support person H2 through the opening 23 and operates the operating device 25 in response to instructions from the support person H2.

[0040] It is believed that the support person H2 is in close proximity to the hydraulic excavator 1 in order to communicate with the operator H1 without being overwhelmed by the noise generated by the hydraulic excavator 1. Therefore, it is necessary to prevent the hydraulic excavator 1, which operates in accordance with the operation of the operator H1, from coming into contact with the support person H2.

[0041] Therefore, among the operations of the hydraulic excavator 1 (actuator), an operation with a (high) possibility that the hydraulic excavator 1 will come into contact with the support person H2 is defined as a "restricted operation," and an operation with a (low) possibility that the hydraulic excavator 1 will not come into contact with the support person H2 is defined as an "unrestricted operation." Furthermore, among the operations of the operator H1 on the operating device 25, an operation that instructs the execution of a restricted operation is defined as a "restricted operation," and an operation that instructs the execution of a non-restricted operation is defined as an "unrestricted operation."

[0042] [Combination of restricted and non-restricted movements] Fig. 5 is a diagram showing an example of a combination of restricted and unrestricted operations. As shown in Fig. 5, at least a part of the traveling of the lower traveling structure 2 (i.e., the rotation of the traveling motors 5L, 5R) and the swing of the upper swing structure 3 (i.e., the rotation of the swing motor 6) is a restricted operation. On the other hand, the operation of the front working implement 10 (i.e., the extension and retraction of the boom cylinder 14, arm cylinder 15, and bucket cylinder 16) is an unrestricted operation.

[0043] As in the first embodiment, the controller 50 may permit operation of the front work implement 10 and prohibit all operation of the undercarriage 2 and upper rotating body 3. This allows the operator H1 to practice operating the front work implement 10 while receiving support from the support person H2. On the other hand, it is possible to prevent the traveling undercarriage 2 from coming into contact with the support person H2, prevent soil and sand kicked up by the rotating crawler 4L from hitting the support person H2, and prevent the counterweight 9 or front work implement 10 from coming into contact with the support person H2 due to the rotation of the upper rotating body 3.

[0044] Furthermore, as in the second embodiment, the controller 50 may permit the operation of the front working implement 10, while prohibiting left rotation (rotation of the upper rotating body 3 in which the front working implement 10 faces the door 22) and permitting right rotation (rotation of the upper rotating body 3 in which the front working implement 10 faces the opposite side of the door 22) among the operations of the upper rotating body 3. This allows the operator H1 to practice the operation of rotating the upper rotating body 3 while avoiding the front working implement 10 coming into contact with the support person H2. Other operations in the second embodiment are common to those in the first embodiment.

[0045] Furthermore, as in the third embodiment, the controller 50 may permit the operation of the front working implement 10, and may further limit or prohibit at least one of the swing angle and swing speed of the upper rotating body 3 when swinging to the right, compared to normal operation. More specifically, the controller 50 may permit the upper rotating body 3 to swing to the right, within a range in which the counterweight 9 does not come into contact with the support person H2 (for example, by limiting the swing angle to less than 60°). The controller 50 may also permit the upper rotating body 3 to swing to the right, but at a slower swing speed compared to normal operation. This allows the operator H1 to practice swinging the upper rotating body 3 while avoiding the counterweight 9 from coming into contact with the support person H2. Other operations in the third embodiment are common to those in the second embodiment.

[0046] Furthermore, as in the fourth embodiment, the controller 50 may permit the operation of the front working implement 10, while restricting or prohibiting the operation of changing the traveling direction among the operations of the lower traveling structure 2, and permitting forward and backward movement. This allows the operator H1 to practice the operation of moving the lower traveling structure 2 forward and backward while avoiding the lower traveling structure 2 coming into contact with the support person H2. Other operations in the fourth embodiment are the same as those in the first embodiment.

[0047] Furthermore, as in the fifth embodiment, the controller 50 may permit operation of the front working implement 10 and further restrict the forward and backward travel speed (traveling speed) of the undercarriage 2 compared to normal operation. More specifically, the controller 50 may permit the undercarriage 2 to travel forward and backward at a slower speed compared to normal operation. This allows the operator H1 to practice the operation of moving the undercarriage 2 forward and backward while avoiding the soil kicked up by the crawler 4L from hitting the support person H2. Other operations in the fifth embodiment are common to those in the fourth embodiment.

[0048] [Effects of the embodiment] According to the above embodiment, when the seat belt 27 is fastened and the door 22 is open (S11: Yes & S13: Yes), it is determined that the operator H1 is practicing operating the hydraulic excavator 1 with the support of the support person H2. In this case, by permitting the operation of the front working implement 10 and restricting or prohibiting at least a portion of the operation of the lower traveling body 2 and the upper rotating body 3, it is possible to allow the operator H1 to learn operating techniques with the support of the support person H2 while avoiding contact with the support person H2.

[0049] Furthermore, the effects of the variations (Examples 2 to 5) in the permitted, restricted, and prohibited operations of the lower traveling body 2 and the upper rotating body 3 are as described above. Note that Examples 1 to 5 can be combined in any combination.

[0050] The above-described embodiments are merely illustrative examples of the present invention, and are not intended to limit the scope of the present invention to these embodiments. Those skilled in the art can implement the present invention in various other forms without departing from the spirit of the present invention. [Explanation of symbols]

[0051] 1: Hydraulic excavator (work machine) 2: Undercarriage (airframe) 3: Upper rotating body (aircraft) 4L, 4R: Crawler 5L, 5R: Travel motor 6: Swing motor 7: Swivel frame 9: Counterweight 10: Front work equipment (working device) 11: Boom 12: Arm 13: Bucket 14: Boom cylinder 15: Arm cylinder 16: Bucket cylinder 20: Cab 21: Main body 22: Door 23 :Aperture 24: Door open / close sensor (open / close sensor) 25: Operating device 26: Sheet 27: Seat belt (restraint) 28: Display 29,30: Control lever 31, 32: Travel pedal 33: Belt 34: Buckle 35: Tongue plate 36: Seat belt sensor (seating sensor) 38: Drive circuit 50: Controller 51: CPU 52: Memory H1: Operator H2: Support personnel

Claims

1. The aircraft and a working device that operates while being supported by the machine body; a cab having doors and windows, and in which an operating device that is operated to operate the machine body and the work device and a seat in which an operator that operates the operating device is seated are disposed, the cab having doors and windows and supported on the machine body, a seating sensor that detects when an operator is seated on the seat; an opening / closing sensor for detecting an opening / closing state of the door or the window in the cab; a controller that controls the operation of the machine body in accordance with the operation of the operation device based on the detection results of the seating sensor and the opening / closing sensor, The controller prohibiting the operation of the machine body and the working device when no seat is detected by the seat sensor; a work machine that permits operation of the work device and restricts or prohibits at least a portion of the operation of the machine body when the seating sensor detects that a person is seated and the open / close sensor detects that the door or the window is open.

2. 2. The work machine according to claim 1, The airframe is a lower running body; an upper rotating body rotatably supported on the lower traveling body and supporting the working device and the cab, The controller permits operation of the work device and restricts or prohibits the rotation of the upper rotating body when the seating sensor detects a seated person and the open / close sensor detects that the door or the window is open.

3. 3. The work machine according to claim 2, the controller permits operation of the work device and further restricts at least one of the rotation angle and rotation speed of the upper rotating body when the seating sensor detects a seated person and the open / close sensor detects that the door or the window is open.

4. 2. The work machine according to claim 1, The controller permits operation of the work device and restricts or prohibits operation to change the direction in which the machine body travels when the seating sensor detects a seated person and the open / close sensor detects that the door or the window is open.

5. 5. The work machine according to claim 4, When the seating sensor detects that a person is seated and the open / close sensor detects that the door or the window is open, the controller permits operation of the work device and further limits the travel speed at which the machine body moves forward and backward.

6. 2. The work machine according to claim 1, An alarm device is provided in the cab to notify information, The controller When the seating sensor does not detect a seating position, the notification device notifies the user that the operation of the machine body and the working device is prohibited; a notification device that notifies the operator that operation of the work device is permitted and that at least a portion of the operation of the machine body is restricted or prohibited when the seating sensor detects that the operator is seated and the open / close sensor detects that the door or the window is open.

7. 2. The work machine according to claim 1, The seating sensor detects whether a seat belt that restrains an operator in the seat is fastened, thereby assuming that the operator is seated.

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