Provided is an autonomous lawn mower including: a movable machine body being movable through unmanned driving with moving devices; at least one lawn mowing work unit mounted on the movable machine body; and a machine body cover that covers an upper surface and a peripheral surface of the movable machine body. The at least one lawn mowing work unit includes: a cutting blade; a prime mover configured to drive the cutting blade; at least one ground-contact member, which is located within an area (WB) between the moving devices in a front-and-rear direction, and is configured to prevent contact of the cutting blade with a ground surface; and an adjustment mechanism configured to allow the lawn mowing work unit to be moved upward and downward with respect to the movable machine body. The ground-contact member and the cutting blade are located inside the machine body cover.

TECHNICAL FIELD

This disclosure relates to an autonomous lawn mower, which is also referred to as a robotic lawn mower.

BACKGROUND ART

As an unmanned self-driving robotic lawn mower, a robotic lawn mower described in Patent Literature 1 below has been known. This robotic lawn mower includes a movable machine body and lawn mowing work units, which are provided inside a casing being open on a bottom. The lawn mowing work units are disposed on a center part of the movable machine body, specifically, between front wheels and rear wheels, which are moving devices. The robotic lawn mower mows a lawn in a field to a predetermined consistent height with use of cutting blades of the lawn mowing work units while automatically performing unmanned driving using the wheels of the movable machine body through the field. The lawn mowing work units are mounted so that their height in an up-and-down direction is adjustable with respect to the movable machine body. Thus, a lawn mowing height can be appropriately set by adjusting the height of the lawn mowing work units in the up-and-down direction with respect to the movable machine body.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

An unmanned self-driving robotic lawn mower does not always drive on a flat ground surface to perform lawn mowing work. It may be required that the unmanned self-driving robotic lawn mower perform lawn mowing work while driving on a ground surface with a slope or unevenness. Also in such a case, unmanned lawn mowing work is required to be automatically performed while dealing with the slope or the unevenness of the ground surface.

According to the related art described above, the lawn mowing work is performed on a lawn below the center part of the movable machine body. When a slope or unevenness of the ground surface is present under an area between the moving devices in a front-and-rear direction, problems are liable to arise in that, for example, a lawn mowing height is varied or the cutting blades strike the ground surface. When the cutting blades strike the ground surface, damage to the cutting blades or the lawn may be brought about. Thus, it is required that the lawn mowing work be performed on the slope or unevenness of the ground surface when the slope or unevenness is present below the area between the moving devices in the front-and-rear direction while maintaining a desired mowing height with reduced damage to the cutting blades of the lawn mowing work units and the lawn in the field.

Solution to Problem

This disclosure has been made in view of the circumstances described above, and has an object to provide an autonomous lawn mower (robotic lawn mower) that allows damage to a cutting blade of a lawn mowing work unit and a lawn in a field to be reduced while maintaining a desired mowing height even when a slope or unevenness of a ground surface is present below an area between moving devices in a front-and-rear direction.

According to this disclosure, there is provided an autonomous lawn mower, including: a movable machine body being movable through unmanned driving with moving devices; at least one lawn mowing work unit mounted on the movable machine body; and a machine body cover that covers an upper surface and a peripheral surface of the movable machine body. The at least one lawn mowing work unit includes: a cutting blade; a prime mover configured to drive the cutting blade; at least one ground-contact member, which is located within an area between the moving devices in a front-and-rear direction, and is configured to prevent contact of the cutting blade with a ground surface; and an adjustment mechanism configured to allow the lawn mowing work unit to be moved upward and downward with respect to the movable machine body. The ground-contact member and the cutting blade are located inside the machine body cover.

According to this disclosure, lawn mowing is performed with the cutting blade of the lawn mowing work unit while the movable machine body is moving through unmanned driving. When the ground-contact member is brought into contact with the ground surface, the cutting blade is held at a desired height above a ground surface. The ground-contact member is located within the area between the moving devices in the front-and-rear direction. Thus, even when a slope or unevenness of the ground surface is present below the area between the moving devices in the front-and-rear direction, the desired mowing height is maintained while the ground-contact member is adapting to the slope or the unevenness. Thus, damage to the cutting blade of the lawn mowing work unit or a lawn in a field can be reduced. The ground-contact member and the cutting blade are located inside the movable body cover. Thus, the ground-contact member and the cutting blade are protected by the machine body cover from foreign matter such as a branch on the ground surface or a branch extending laterally from, for example, a hedge.

As one embodiment of this disclosure, the at least one ground-contact member may be arranged on a front side of the at least one lawn mowing work unit in a traveling direction of the movable machine body. In this manner, the ground-contact member provided on the front side of the lawn mowing work unit can adapt to the slope or the unevenness of the ground surface on the front side in the traveling direction to allow a height (mowing height) of the lawn mowing work unit to be maintained at a desired height and to prevent the cutting blade from striking the ground surface.

As one embodiment of this disclosure, the at least one lawn mowing work unit may include a plurality of lawn mowing work units, each of the plurality of lawn mowing work units may include the ground-contact member and the adjustment mechanism, and each of the lawn mowing work units may be movable upward and downward through intermediation of the adjustment mechanism independently of both of the movable machine body and other lawn mowing work units. In this case, every lawn mowing work unit can adapt to the unevenness of the ground surface based on, as a reference, a height at which the ground-contact member of the lawn mowing work unit is in contact with the ground surface. Thus, the collision between the cutting blade and the ground surface can be automatically prevented in an unmanned manner while the height of each individual lawn mowing work unit is maintained.

As one embodiment of this disclosure, the ground-contact members of the plurality of lawn mowing work units may be located within the area between the moving devices in the front-and-rear direction. In this manner, each of the lawn mowing work units can independently deal with the unevenness of the ground surface, which is present in an area smaller than the area between the moving devices in the front-and-rear direction and thus cannot be dealt with only by the moving devices. Thus, more accurate lawn mowing work can be performed.

As one embodiment of this disclosure, the ground-contact member may be disposed at a position offset from a central line of a work range of the cutting blade in a front-and-rear direction in the lawn mowing work unit. In this case, the ground-contact member can be arranged so as to be offset from the central line extending in the front-and-rear direction of the work range of the cutting blade, where visual quality may be particularly affected. Thus, the ground-contact member is less liable to become an obstacle to the lawn mowing work to thereby achieve mowing for a finely finished lawn.

As one embodiment of this disclosure, the ground-contact members may be disposed on both of a right side and a left side in front of a work range of the cutting blade. In this manner, even when the ground surface has unevenness on any one of the right side and the left side in front of the cutting blade, a mowing height can be maintained at a preset mowing height. Thus, even when the ground surface has a bump, the collision between the cutting blade and the ground surface can be prevented.

As one embodiment of this disclosure, when the adjustment mechanism is in at least one of a plurality of modes for adjusting a mowing height, the ground-contact member may be constantly in contact with the ground surface. According to this embodiment, the ground-contact member is constantly in contact with the ground surface while adjusting its height in accordance with the mowing height. Thus, the ground-contact member is held in contact with the ground surface to thereby enable stable lawn mowing work.

As one embodiment of this disclosure, at least one of the plurality of modes of the adjustment mechanism may be a low lawn mowing work mode. The risk of the contact between the cutting blade and the ground surface becomes highest when the adjustment mechanism is in the low lawn mowing work mode. Thus, when the adjustment mechanism is in the low lawn mowing work mode, the ground-contact member is constantly held in contact with the ground surface. As a result, the contact between the cutting blade and the ground surface can be prevented. Further, the cutting blade is held at the desired height while the lawn mowing work unit is adapting to the unevenness of the ground surface. Thus, the lawn mowing work can be carried out without damaging the cutting blade or a lawn.

As one embodiment of this disclosure, the ground-contact member may be brought into rolling contact with the ground surface. In this manner, friction between the ground-contact member and the ground surface is reduced. Thus, the ground-contact member is less liable to obstruct a thrust force for the movable machine body. Hence, a load on a prime mover for the moving devices during traveling can be reduced.

As one embodiment of this disclosure, the ground-contact member may be brought into sliding contact with the ground surface. This embodiment is dominant over a rolling-type ground-contact member. Specifically, when the ground-contact member is of rolling type, grass may be caught by a bearing portion that allows rolling, resulting in inhibition of smooth rolling of the ground-contact member. In contrast, the sliding contact-type ground-contact member does not cause the problem described above.

As one embodiment of this disclosure, the ground-contact member may be a plate body facing the ground surface and may be brought into contact with the ground surface at a protruding portion that protrudes downward from an outer peripheral portion of the plate body. In this manner, the ground-contact member is more compact and is formed in a simple manner. Thus, the ground-contact member not only contributes to reduction in cost but also suppresses tangling of grass around the ground-contact member.

As one embodiment of this disclosure, the protruding portion may be formed in an annular manner on a lower surface of the plate body. In this manner, the ground-contact member can adapt to unevenness in any direction.

As one embodiment of this disclosure, the ground-contact member may be mounted to a housing configured to support the prime mover. In this manner, the ground-contact member can be fixedly mounted at a desired unrotatable position in proximity to the lawn mowing work unit. Thus, the ground-contact member can adapt to the unevenness of the ground surface with high accuracy. Advantages of this configuration include a high degree of freedom in design of a mounting structure and no additional load on a prime mover for driving the cutting blade.

As one embodiment of this disclosure, the movable machine body may include a controller, and after the controller acquires information regarding unevenness of the ground surface, the controller may reduce a speed of the movable machine body. In general, the ground-contact member has higher adaptability to the unevenness of the ground surface when the movable machine body moves at a lower speed than when the movable machine body moves at a higher speed. For example, when the movable machine body is driven to move at a high moving speed on the ground surface having unevenness, the movable machine body may skip and the lawn mowing work unit may be separated from the ground surface, making it difficult to achieve a desired mowing height. In such a case, similarly to the lawn mowing work unit, the ground-contact member is separated from the ground surface. Thus, the adaptability to the ground surface is lowered. In contrast, according to this embodiment, after acquiring the information regarding the unevenness of the ground surface, the controller decreases the moving speed of the movable machine body. Thus, the adaptability of the ground-contact member to the unevenness of the ground surface is improved to thereby enable maintaining the mowing height at the desired height.

DESCRIPTION OF EMBODIMENTS

Now, with reference to the accompanying drawings, an embodiment of this disclosure is described.

An autonomous lawn mower1illustrated inFIG.1according to one embodiment of this disclosure is also referred to as a robotic lawn mower. The autonomous lawn mower1mows a lawn in a field to a predetermined consistent height while performing unmanned self-driving through the field. The lawn mower1ofFIG.1includes a machine body cover1A being open on a bottom. A movable machine body2and at least one lawn mowing work unit3, which are described later, are disposed inside the machine body cover1A. The machine body cover1A covers an upper surface and a peripheral surface of the movable machine body2. The machine body cover1A prevents contact of obstacles such as a branch on a lawn or a branch extending laterally from, for example, a neighboring hedge with the movable machine body2or the lawn mowing work unit3.

FIG.2is a plan view of the lawn mower1ofFIG.1with the machine body cover1A removed, in which an internal structure of the lawn mower1is illustrated. A right side inFIG.2corresponds to a front side F in a traveling direction of the movable machine body2, and a left side inFIG.2corresponds to a rear side R in the traveling direction of the movable machine body2. The lawn mower1includes the movable machine body2and at least one lawn mowing work unit3. The movable machine body2has front wheels4fand rear wheels4r, which correspond to moving devices4, and is movable through unmanned driving. The lawn mowing work unit3is mounted on the movable machine body2. The movable machine body2includes a machine body frame5. For example, a pair of right and left driving wheels4r,4rcorresponding to the rear wheels, an electric drive motor6, a rechargeable battery7, a pair of right and left steered wheels4f,4fcorresponding to the front wheels, and a steering adjustment section8(seeFIG.3) are mounted on the machine body frame5. The drive motor6serves as a drive source for the driving wheels4r,4r. The rechargeable battery7serves as a power source for the drive motor6. The steering adjustment section8controls the steered wheels4f,4f. Any of a set of the front wheels4fand a set of the rear wheels4rmay be determined to be the driving wheels, and another one of the sets may be determined to be the steered wheels. Further, only one wheel may be provided as any of the front wheels4for the rear wheels4r. The drive motor6and the steering adjustment section8are automatically controlled by a controller9including a microcomputer. In place of the moving devices4corresponding to the front wheels4fand the rear wheels4r, a crawler-type moving device including a pair of right and left track belts may be used.

In an example illustrated inFIG.2, five lawn mowing work units3are mounted on the movable machine body2. The number of lawn mowing work units3to be disposed and positions at which the lawn mowing work units3are disposed can be appropriately set. As one example thereof, three lawn mowing work units3on the front side are disposed at equal intervals within a width of the movable machine body2in a right-and-left direction and two lawn mowing work units3on the rear side are disposed behind the three lawn mowing work units3in the illustrated example. The lawn mowing work units3on the rear side are disposed just behind spaces between the lawn mowing work units3on the front side. All the lawn mowing work units3are arranged inside the machine body cover1A so as to be located within an area with a wheel base WB (distance between the front wheels and the rear wheels) of the movable machine body2. When the moving device4is a crawler-type one, the lawn mowing work units3are arranged inside the machine body cover1A so as to be located within an area having a length of right and left track belts in the front-and-rear direction.

As illustrated inFIG.3, a lower edge of at least a front part1Af of the machine body cover1A is in proximity to a ground surface G. The front part1Af of the machine body cover1A inhibits foreign matter such as a branch or dust on the ground surface G or a branch extending laterally from entering the lawn mowing work units3. As a result, the lawn mowing work units3can be protected from foreign matter.

As illustrated inFIG.3, the lawn mowing work units3are mounted so that their height in an up-and-down direction can be adjusted with respect to the machine body frame5. In the illustrated example, each of the lawn mowing work units3is coupled to the machine body frame5through intermediation of pivotable parallel links10so as to be movable upward and downward. Thus, each of the lawn mowing work units3is movable upward and downward while maintaining a horizontal state. All the lawn mowing work units3are coupled to a relay shaft11. When the relay shaft11is pivoted in both of a forward direction and a reverse direction, all the lawn mowing work units3are moved vertically at the same time. A height of the lawn mowing work units3in the up-and-down direction is appropriately adjusted and set in accordance with a lawn mowing height. Details of a vertical movement mechanism for the lawn mowing work units3are described later. InFIG.3, for simplification of illustration, only the lawn mowing work units3on the front side inFIG.2are illustrated, and an illustration of the lawn mowing work units3on the rear side is omitted.

As illustrated inFIG.4, each of the lawn mowing work units3includes a work-unit housing12. The work-unit housing12includes a horizontal frame13having a circular shape and a motor cover14. The motor cover14is firmly fixed onto an upper surface of the horizontal frame13. An electric cutting-blade drive motor15serving as a prime mover is arranged on the horizontal frame13, and the motor cover14is firmly fixed onto the horizontal frame13so as to cover the cutting-blade drive motor15. The cutting-blade drive motor15is driven by using the rechargeable battery7as a power source. Proximal end portions10aof the parallel links10are pivotably supported on the machine body frame5, and swingable distal end portions10bof the parallel links10are pivotably supported on the motor cover14.

An output shaft15aof the cutting-blade drive motor15passes through the horizontal frame13to extend directly downward. A blade disc16is firmly fixed to a lower end portion of the output shaft15a. The blade disc16rotates in a plane of rotation orthogonal to the output shaft15aand is rotationally driven under a state in which the plane of rotation of the blade disc16is facing the field.

At least one cutting blade17is swingably mounted to a lower surface of an outer peripheral portion of the blade disc16. The cutting blade17is removably mounted to the blade disc16with use of an appropriate mounting member20so as to be swingable in a horizontal plane. The mounting member20includes, for example, a bolt18such as a stepped bolt and a nut19. Although the number of cutting blades is not limited, it is preferred that a plurality of cutting blades be provided to the blade disc16at equal angular intervals.

A protective disc21having a thin plate-like shape that protects the cutting blade17from, for example, collision against the ground surface G is provided below the blade disc16so as to face the ground surface G. The protective disc21is disposed concentrically with the blade disc16, and is rotatable independently of the blade disc16. A diameter of the protective disc21is smaller than a diameter of a rotation area defined by the cutting blade17when the blade disc16is rotated. Lawn mowing work is substantially performed by a blade portion17aof the cutting blade17. The blade portion17ais located on a radially outer side of the protective disc21. A holding member22that supports the protective disc21is firmly fixed at a center of a lower surface of the protective disc21. The holding member22also functions as a ground-contact member to be brought into sliding contact with the ground surface G at the time of low lawn mowing work. However, the holding member22is not necessarily required to be in contact with the ground surface at the time of low lawn mowing work.

The cutting blade17is pointed in a radial direction of the blade disc16by centrifugal force generated through the rotation of the blade disc16and protrudes outward beyond the blade disc16. This protruding orientation illustrated inFIG.4corresponds to a lawn mowing orientation of the cutting blade17. During the lawn mowing work, the cutting blade17constantly moves within a micro-angular range under resistance of grass and the centrifugal force generated through the rotation of the blade disc16. Further, when the cutting blade17gets high resistance during the work, the cutting blade17is retracted in a direction opposite to a rotating direction of the blade disc16so as to avoid the resistance. When the resistance is lost, the cutting blade17is returned to an initial lawn mowing orientation by the centrifugal force generated through the rotation of the blade disc16.

The above-mentioned structure of the cutting blade17is merely an example. As another simple example, an elongated rectangular cutting blade or a circular cutting blade may be firmly fixed to the output shaft15aof the cutting-blade drive motor15at a central portion of the cutting blade so as to be rotated in a horizontal plane.

Each of the lawn mowing work units3includes at least one ground-contact member23and is located together with the ground-contact member23inside the machine body cover1A. With this configuration, obstacles such as a branch on the ground surface or a branch extending laterally from, for example, a hedge can be prevented from entering the machine body cover1A and coming into contact with the lawn mowing work units3or the ground-contact member23. When the ground-contact member23is in contact with the ground surface G as illustrated inFIG.4, each of the lawn mowing work units3is located at a low lawn mowing work height position LP. When the lawn mowing work units3are located at the low lawn mowing work height position LP, the cutting blade17is held at a low height (for example, from 10 mm to 20 mm) above the ground surface, which is suitable for low lawn mowing work. When the lawn mowing work units3are located at the low lawn mowing work height position LP, each of the lawn mowing work units3is moved upward and downward independently of both of the movable machine body2and the other lawn mowing work units3so as to adapt to the unevenness of the ground surface G.

Meanwhile, when the ground-contact member23is separate from the ground surface G and the lawn mowing work units3are in midair, the lawn mowing work units3are located at a high lawn mowing work height position HP (seeFIG.8A). A plurality of different height-level positions may be set as the high lawn mowing work height position HP. In this case, all the thus set height-level positions are collectively referred to as the high lawn mowing work height positions HP in terms of contrast from the low lawn mowing work height position LP.

The ground-contact member23illustrated inFIG.4is a rolling-type (for example, wheel-type, roller-type, or caster-type) ground-contact member, which is to be brought into rolling contact with the ground surface G. The rolling-type ground-contact member23has low friction against the ground surface G. Thus, the ground-contact member23is less liable to become an obstacle to a thrust force for the movable machine body2. The ground-contact member23is supported by the horizontal frame13of the work-unit housing12through intermediation of an arm25having a bearing portion24. The ground-contact member23is disposed on the front side F in the traveling direction of the movable machine body2with respect to at least a work range of the cutting blade17(rotation area defined by the cutting blade17when the blade disc16is rotated). With the configuration described above, when the ground surface G has unevenness on the front side F of the work range of the cutting blade17, each of the lawn mowing work units3is moved upward and downward while adapting to the unevenness of the ground surface G. Thus, the cutting blade17is automatically prevented from striking the ground surface G in an unmanned manner.

As illustrated inFIG.5, the ground-contact members23are located within an area WB between the front wheels4fand the rear wheels4r, which are the moving devices of the movable machine body2, in the front-and-rear direction. The positions at which the ground-contact members23are disposed are specifically determined as described above for the following reason. Some lawn mowing work requires accuracy for a lawn mowing height in accordance with visual quality to be achieved or a purpose of mowing. Specifically, low lawn mowing work for mowing a lawn to a significantly short consistent height may be required not only for improvement of a view of a ball game ground such as a golf course or a soccer field after lawn mowing but also for other purposes, for example, for allowing easier finding of balls in the field and for allowing smoother rolling of balls. For the low lawn mowing work, the lawn mowing work unit3is required to be set at a low height in the up-and-down direction with respect to the movable machine body2so that the cutting blade17of the lawn mowing work unit3is located closer to the ground surface G.

When the low lawn mowing work is performed, however, the lawn mowing work unit3is close to the ground surface G. Thus, when the ground surface G has fine unevenness, the cutting blade17of the lawn mowing work unit3may strike a bump after the front wheel4fof the movable machine body2passes over the bump. When the cutting blade17strikes the ground surface G, the cutting blade17or the lawn may be damaged. Thus, the collision is not preferred for the lawn mower1and in view of maintenance of visual quality of the lawn or conservation of roots of grass. In particular, a working condition of the unmanned self-driving robotic lawn mower1is not supposed to be constantly monitored by a human. Thus, it is highly important to autonomously avoid the contact of the cutting blade17with a bump on the ground surface G.

Thus, in this embodiment, as illustrated inFIG.5, the ground-contact members23are disposed so as to be located within the area WB between the front wheels4fand the rear wheels4rin the front-and-rear direction, which are the moving devices of the movable machine body2. Thus, even when a slope or unevenness of the ground surface G is present under the area between the front wheels4fand the rear wheels4rduring the low lawn mowing work, a desired mowing height is maintained while the ground-contact members23are adapted to the slope or unevenness. At the same time, the cutting blade17is prevented from striking the ground surface G.

Although the arrangement of the ground-contact members23is not limited, two ground-contact members23on the front side are arranged on the right side and the left side in front of a work range26of the cutting blade17, and one ground-contact member23on the rear side is arranged at a central position behind the work range26of the cutting blade17for each of the lawn mowing work units3in the example illustrated inFIG.5. The ground-contact members23on the front side are arranged at positions offset from a center line C of the work range26of the cutting blade17, which extends in the front-and-rear direction. Thus, the ground-contact members23are less liable to obstruct the lawn mowing work. Further, the ground-contact members23are disposed on the right side and the left side in front of (on the front side F of) the work range26of the cutting blade17. Thus, even when a bump on the ground surface G is present on any of the right side and the left side in front of (on the front side F of) the cutting blade17, the collision between the cutting blade17and the ground surface G can be prevented.

As a modification example of the ground-contact member23, as illustrated inFIG.6, a ground-contact member27to be brought into sliding contact with the ground surface G may be used. This modification example is similar to, for example, a ground-contact member of a sleigh. The modification example has superiority over the rolling type ground-contact member23. Specifically, when the ground-contact member is of rolling type, grass may be caught by the bearing portion24(seeFIG.4) that allows rolling, resulting in inhibition of smooth rolling of the ground-contact member23. In contrast, when the sliding-contact type ground-contact member27is used, the problem described above does not occur.

As another modification example of the ground-contact member23,27, a ground-contact member (protective disc)40illustrated inFIG.7may be used. The protective disc40illustrated inFIG.7is a modification example of the protective disc21ofFIG.4. The protective disc40ofFIG.7is different from the protective disc21ofFIG.4in that the protective disc40has a protruding portion42protruding downward from an outer peripheral portion of a circular plate body41facing the ground surface G. The protective disc40is brought into sliding contact with the ground surface G at the protruding portion42. Otherwise, the protective disc40is similar to the protective disc21ofFIG.4. InFIG.7, as in the case of the holding member ofFIG.4, the holding member22is not necessarily required to be brought into contact with the ground surface during the low lawn mowing work.

In the example illustrated inFIG.7, the downwardly protruding portion42being in contact with the ground surface G extends in an annular manner from a lower surface of an outer peripheral portion of the circular plate body41. In this case, the protruding portion42having an annular shape is located concentrically with the output shaft15aof the cutting-blade drive motor15, which serves as a center of rotation of the cutting blade17. Although not shown, the protruding portion42may be formed intermittently on the outer peripheral portion of the circular plate body41as another modification example of the formation of the downwardly protruding portion42. Further, only one downwardly protruding portion42may be formed. When only one downwardly protruding portion42is formed or the downwardly protruding portion42is formed intermittently, a specific position at which the downwardly protruding portion42is formed is only required to be set to an appropriate position on the outer peripheral portion of the plate body41.

With the protective disc (ground-contact member)40having the outer peripheral portion on which the downwardly protruding portion42is formed, the ground-contact member40is more compact and is formed in a simpler manner than the ground-contact member23,27described above. Thus, the protective disc40not only contributes to reduction in cost but also suppresses tangling of grass around the ground-contact member40. Further, the protective disc40illustrated inFIG.7, which has the downwardly protruding portion42extending in an annular manner from the lower surface of the outer peripheral portion of the plate body41, also has an advantage in that the protruding portion42is always located in the vicinity of the cutting blade17so that the ground-contact member40can deal with unevenness that is present in any direction. When a single downwardly protruding portion42is formed or the downwardly protruding portion42is intermittently formed on the outer peripheral portion of the plate body41having a circular shape, friction against the ground surface G is smaller than friction of the protective disc40ofFIG.7against the ground surface G. Thus, the ground-contact member is less liable to obstruct the thrust force for the movable machine body2. Thus, a load on a prime mover for the moving devices4during traveling can be reduced. Further, an increase in weight of the ground-contact member can also be suppressed.

When a protective disc (ground-contact member) having an outer peripheral portion from which the protruding portion42downwardly extends, such as the protective disc40ofFIG.7, is used, the ground-contact member23ofFIG.4or the ground-contact member27ofFIG.6is not required to be provided. However, the above-mentioned protective disc may be used in combination with the ground-contact member23,27.

Next, with reference toFIG.2,FIG.3, andFIGS.8, an example of an adjustment mechanism28(vertically moving mechanism for the lawn mowing work unit) which allows the lawn mowing work unit3to be moved upward and downward with respect to the movable machine body2is described. InFIGS.8, there is illustrated a coupling relationship among a drive pulley32, a drive belt30, a relay pulley29, a relay shaft11, driven pulleys33, driven belts34, which form the adjustment mechanism28, and the lawn mowing work unit3.

As illustrated inFIG.2, the relay shaft11of the adjustment mechanism28is horizontally supported on the movable machine body2so as to extend in the right-and-left direction of the movable machine body2. The relay shaft11is arranged between the lawn mowing work units3on the front side and the lawn mowing work units3on the rear side. The relay pulley29is firmly fixed to the relay shaft11. The relay pulley29is coupled through intermediation of the drive belt30to the drive pulley32for an electric motor31for vertical movement serving as a prime mover. The electric motor31for vertical movement is mounted onto the movable machine body2and is actuated by using the rechargeable battery7as a power source as in the case of the electric drive motor6. The driven pulley33is firmly fixed to the relay shaft11for each lawn mowing work unit3.

As illustrated inFIG.2andFIG.3, the adjustment mechanism28that allows the lawn mowing work unit3to be moved upward and downward is located inside the machine body cover1A. This arrangement is effective to prevent foreign matter such as a branch on the ground surface or a branch extending laterally from entering the machine body cover1A so as to enable maintaining a desired mowing height while preventing damage to the adjustment mechanism28.

As illustrated inFIGS.8, one end30aof the drive belt30is firmly fixed to the drive pulley32, and another end30bof the drive belt30is firmly fixed to the relay pulley29. The driven pulleys33are coupled to the lawn mowing work units3through intermediation of the driven belts34, respectively. One end34aof each of the driven belts34is firmly fixed to the driven pulley33, and another end34bof each of the driven belts34is firmly fixed to a corresponding one of the lawn mowing work units3. The electric motor31for vertical movement, the drive pulley32, the drive belt30, the relay pulley29, the relay shaft11, the driven pulleys33, and the driven belts34form the adjustment mechanism28for each of the lawn mowing work units3.

Similarly to the lawn mowing work unit3illustrated inFIG.3andFIG.4, the lawn mowing work unit3illustrated inFIG.8corresponds to the lawn mowing work unit3on the front side illustrated inFIG.2. As illustrated inFIG.2, the lawn mowing work unit3on the front side is located in front of the relay shaft11. Thus, an alignment coupling plate35extending to the rear side R is firmly fixed to an upper surface of the motor cover14of each of the lawn mowing work units3on the front side. The another end34bof the driven belt34is firmly fixed to a rear end of the alignment coupling plate35. Meanwhile, for the lawn mowing work units3on the rear side illustrated inFIG.2, an alignment coupling plate (not shown) extending to the front side is firmly fixed to the upper surface of the motor cover14, and the another end34bof the driven belt34is firmly fixed to a front end of the alignment coupling plate.

The adjustment mechanism28has a plurality of modes for adjustment of the mowing height. When the adjustment mechanism28is in a low lawn mowing work mode corresponding to at least one of the modes, the ground-contact members23are constantly in contact with the ground surface G. Specifically, the drive pulley32for the electric motor31for vertical movement (seeFIG.2) is pivotable in both of a forward direction and a reverse direction between, for example, a predetermined high lawn mowing work angular position HAP illustrated inFIG.8Aand a low lawn mowing work angular position LAP illustrated inFIG.8B. The drive pulley32can be stopped steplessly or in a step-by-step manner between the angular position HAP and the angular position LAP. The drive pulley32is pivoted and stopped by controlling the electric motor31for vertical movement with use of the controller9(seeFIG.2for both of the electric motor31and the controller9).

When the drive pulley32is stopped at the high lawn mowing work angular position HAP, the relay pulley29and all the driven pulleys33are also stopped at the predetermined high lawn mowing work angular position HAP ofFIG.8Aunder tension of the drive belt30. Further, all the lawn mowing work units3are brought up into the air and held at the high lawn mowing work position HP under tension of the driven belts34(high lawn mowing work mode). At this time, a rotational force in a counterclockwise direction acts on the relay shaft11under own weight of all the lawn mowing work units3. When the rotational force and a stopping force for the drive pulley32are balanced out, the rotation of the relay shaft11is blocked.

When the electric motor31for vertical movement is actuated in a state ofFIG.8Ato pivot the drive pulley32in a clockwise direction to the predetermined low lawn mowing work angular position LAP ofFIG.8B, the drive belt30is released by the amount corresponding to a pivot angle. Thus, the relay pulley11and all the driven pulleys33are pivoted in the counterclockwise direction by the rotational force acting on the relay shaft11in the counterclockwise direction. As a result, all the lawn mowing work units3are moved downward under their own weight, and the lawn mowing work units3reach the low lawn mowing work height position LP at which the ground-contact members23are brought into contact with the ground surface G (low lawn mowing work mode). At this time, a range of the pivot angle of the drive pulley32is set in advance so that the drive belt30and the driven belts34have a predetermined amount of looseness. The looseness of the drive belt30and the driven belts34allows each of the lawn mowing work units3to adapt to a recessed portion in the ground surface G independently of both of the movable machine body2and the other lawn mowing work units3. Further, it is apparent that, when the lawn mowing work unit is located at the low lawn mowing work height position LP illustrated inFIG.8B, each of the lawn mowing work units3can also adapt to a bump on the ground surface G independently of both of the movable machine body2and the other lawn mowing work units3.

The following adjustment mechanism may be used as a modification example of the adjustment mechanism28. Specifically, the drive pulley32, the drive belt30, the relay pulley29, and the relay shaft11are eliminated from the configuration described above. In place of the relay shaft11, a drive shaft that is pivotable in both of the forward direction and the reverse direction and is stoppable within a predetermined angular range is arranged horizontally. The drive shaft is rotationally driven by the electric motor31for vertical movement. The driven pulleys33, which correspond to the lawn mowing work units3, respectively, are firmly fixed to the drive shaft. As in the case of the adjustment mechanism ofFIG.4, the another end34bof the driven belt34having the one end34afirmly fixed to each of the driven pulleys33is connected to a corresponding one of the lawn mowing work units3. In this case, when the drive shaft is rotationally driven by the electric motor31for vertical movement, the lawn mowing work units3can be displaced to the high lawn mowing work height position HP and the low lawn mowing work height position LP. When the lawn mowing work units3are located at the low lawn mowing work height position LP, a range of a pivot angle of the drive shaft is set in advance so that the driven belts34have looseness. In this manner, the lawn mowing work units3can be moved upward and downward so as to adapt to unevenness of the ground surface G independently of both of the movable machine body2and the other lawn mowing work units3. Further, the arrangement of the adjustment mechanisms28inside the machine body cover1A prevents foreign matter such as a branch from entering the machine body cover1A to thereby enable preventing damage to the adjustment mechanisms28.

As another example of the adjustment mechanism28, a mechanism for driving the parallel links10upward may be used. In this case, when the adjustment mechanism28is in the low lawn mowing work mode, downward movement of the parallel links10is limited with a margin. As a result, the lawn mowing work units3can adapt to a recessed portion in the ground surface G. Even in this example, the adjustment mechanisms28are arranged inside the machine body cover1A. Thus, foreign matter such as a branch does not enter the machine body cover1A from an outside, and hence damage to the adjustment mechanisms28can be prevented.

As a modification example, as illustrated inFIG.2andFIG.3, a detection device36for detecting unevenness of the ground surface G may be disposed on the movable machine body2. In this case, the controller9ofFIG.2is configured to reduce a speed of the movable machine body2after acquiring information regarding the unevenness of the ground surface G, which has been detected by the detection device36. Thus, the lawn mowing work units3can more precisely adapt to the unevenness of the ground surface G. In particular, in order to detect the unevenness of the ground surface G, which is present on the front side in the traveling direction, it is preferred that the detection device36be disposed on the movable machine body2so as to be located on the front side in the traveling direction. With the configuration described above, the detection device36can detect unevenness of the ground surface G before the lawn mowing work units3reach the unevenness, and the controller9can reduce the moving speed of the movable machine body2to a moving speed that allows the ground-contact members23to be always reliably brought into contact with the ground surface G. More preferably, the detection device36is able to acquire ground-surface information over a distance of at least 5 meters from a front end portion of the movable machine body2. This specific distance is determined in consideration of application of a brake.

Further, a plurality of detection devices36may be provided. In this case, pieces of information acquired from the detection devices36are combined and output as single information to the controller9to thereby enable enhancing detection accuracy. Examples of the detection device36include a tilt sensor, an infrared sensor, a photoelectric sensor, a millimeter-wave radar sensor, other sensors, and a camera. When the plurality of detection devices36are provided, a detection error can be reduced by using a plurality of detection devices36of the same kind. Further, when a plurality of different kinds of detection devices36are used, detection accuracy can be enhanced regardless of, for example, an environment by setting the detection devices36so that, under a detection environment in which one detection device36is not capable of performing detection with high accuracy, another detection device36functions supplementarily to or dominantly over the one detection device36. For example, a camera can detect the unevenness of the ground surface G over a broad range. However, the camera has low detection ability for a ground surface with a shade. In this case, when a combination of broad-range detection means such as a camera and short-range detection means such as an infrared sensor is used, features of both of the means can be maximumly utilized.

Further, the information regarding the unevenness of the ground surface G may be acquired without the detection device36provided to the movable machine body2. The controller9acquires information by comparing, for example, topographical information and positional information of a field, which are stored in advance, and positional information of the lawn mower1with each other and then estimating a position of the unevenness of the ground surface G. The detection device36that detects the unevenness of the ground surface G for each time may fail to perform detection due to a failure of the detection device36or may have a time lag in outputting the information detected by the detection device36to the controller9. With the above-mentioned configuration, the information regarding the unevenness of the ground surface G can be reliably acquired without being affected by a state and accuracy of the detection device36or a time lag. It is apparent that at least one of the topographical information and the positional information associated with the topographical information may be used together with a method of detecting the unevenness of the ground surface for each time in order to enhance the detection accuracy. This configuration allows the topographical information and the positional information of the field, which are stored in advance, to be corrected. Thus, more precise ground-surface information can be constructed.

At least one of the topographical information and the positional information of the field may be stored in a memory of the lawn mower1. Further, the information may be stored in a server so that the lawn mower1receives the information via the server. In this manner, costs can be reduced by reducing memory capacity mounted on the lawn mower1or an unnecessary amount of memory capacity is allowed to be used by another function. One example of the positional information of the lawn mower1includes information acquired from a global navigation satellite system (GNSS) sensor, which receives a radio signal emitted from a satellite in a GNSS such as a GPS.

The embodiments of this disclosure have been described in detail. However, a specific configuration is not limited to those of the embodiments described above. For example, changes in design without departing from the scope of this disclosure are encompassed in this disclosure. Further, technologies in the above-mentioned embodiments described above may be used in combination as long as there is no particular contradiction or problem in, for example, purpose and configuration.