Mobile robot and controlling method for the same

Abstract

A mobile robot and a method for controlling the mobile robot are disclosed. Specifically, the mobile robot may include a body forming an exterior; a cutting device mounted on the body for cutting grass; a first wheel and a second wheel coupled to the body for moving the mobile robot; a first motor for driving the first wheel; a second motor for driving the second wheel; a sensor for detecting the rotational speed of at least one of the first motor and the second motor; and a control unit for adjusting the speed of the second motor based on the difference between the commanded speed and the actual speed for the first motor.

Description

Technology Field

[0001] This specification relates to a mobile robot and a method for controlling the same. Background Technology

[0002] Robots were developed for industrial use and have played a role in factory automation. Recently, the fields of robot application have expanded further, with the development of medical and aerospace robots, as well as household robots for general use. Among these robots, those capable of driving under their own power are called mobile robots. A representative example of a mobile robot used in outdoor home environments is the lawnmower robot.

[0003] In the case of mobile robots autonomously navigating indoors, their movable area is limited by walls or furniture, whereas for mobile robots autonomously navigating outdoors, there is a need to pre-set the movable area. Additionally, there is a need to limit the movable area so that the aforementioned lawnmower robot navigates an area where grass is planted. Accordingly, prior art (Korean Published Patent Application No. 2015-0125508) discloses a technology in which a wire defining the working area of ​​a lawnmower robot is embedded, and the lawnmower robot detects a magnetic field formed by an electric current flowing through the wire to move within the working area.

[0004] However, while mobile robots operating autonomously indoors generally have the load applied equally to the left and right wheels to drive straight within the work area, mobile robots operating autonomously outdoors may be unable to drive straight within the work area due to the different loads applied to the left and right wheels.

[0005] U.S. Patent Publication No. 2019-038768A1 discloses a configuration for adaptively adjusting a threshold level recognized as a collision by detecting an incline while a lawnmower robot is driving, and Korean Patent Publication No. 10-2019-0098866 discloses a configuration for controlling a mobile robot to drive as close as possible to the reference path by detecting deviation from the reference path due to sliding when the robot is driving on an incline.

[0006] However, such conventional technology is intended for preventing collisions on slopes, but it has a problem in that it cannot control lawnmower robots that are unable to drive in a straight line due to slopes or different loads to drive in a straight line.

[0007] Furthermore, such conventional technology only discloses configurations such as adaptively adjusting thresholds to prevent collisions on slopes, which can cause user dissatisfaction because the lawnmower robot cannot drive in a straight line.

[0008] As a result, there is a problem where consumer dissatisfaction may arise because the lawnmower robot is unable to control straight-line driving and works on the grass within the work area in an irregular pattern rather than a consistent one.

[0009] In addition, lawn mowing robots that operate in irregular patterns rather than fixed ones have a problem where the lawn mowing service provided by the robot is inferior because they only repeatedly cut the grass in certain areas and fail to cut the grass in other areas. The problem to be solved

[0010] The embodiments of this specification are proposed to solve the aforementioned problems and aim to provide a mobile robot that is controlled to travel in a straight line on a curved slope due to an outdoor environment.

[0011] The embodiment of the present specification aims to provide a mobile robot that is controlled to drive in a straight line by adjusting the speed of motors corresponding to both wheels, which are subjected to different loads due to the outdoor environment.

[0012] The embodiments of this specification aim to provide a mobile robot that can reduce the time required to cut grass within a work area by controlling the speed of the mobile robot traveling in a straight line through the speed adjustment of the motor.

[0013] The embodiments of this specification aim to provide a mobile robot that travels in a straight line so that a lawn mowing service can be provided in a constant pattern rather than an irregular pattern.

[0014] The embodiments of this specification aim to provide a mobile robot that travels in a straight line so that there are no uncut areas of grass within a work area through straight-line travel.

[0015] The technical problems that this embodiment aims to solve are not limited to the technical problems described above, and other technical problems can be inferred from the following embodiments. means of solving the problem

[0016] According to the first embodiment of the present specification, a mobile robot may be provided for controlling the mobile robot to drive in a straight line, comprising: a body forming an exterior; a cutting device mounted on the body for cutting grass; a first wheel and a second wheel coupled to the body for moving the mobile robot; a first motor for driving the first wheel; a second motor for driving the second wheel; a sensor for detecting the rotational speed of at least one of the first motor and the second motor; and a control unit for adjusting the speed of the second motor based on the difference between the commanded speed and the actual speed for the first motor.

[0017] At this time, the control unit can control the speed of the second motor by additionally considering the duty ratio of the control signal for the first motor.

[0018] Preferably, the control unit can control the speed of the second motor to be reduced when the difference between the commanded speed and the actual speed of the first motor is greater than a reference value and the duty ratio of the control signal for driving the first motor is greater than a first value.

[0019] In addition, the control unit can control the speed of the second motor to be reduced at a constant speed in each control cycle when reducing the speed of the second motor.

[0020] Preferably, the speed of the reduced second motor can be controlled to correspond to the actual speed of the first motor.

[0021] At this time, if the difference between the commanded speed and the actual speed of the first motor is smaller than a reference value and the duty ratio of the control signal for driving the first motor is smaller than a second value, it is possible to control the speed of the second motor to accelerate.

[0022] Preferably, the control unit can control the speed of the second motor to accelerate at a constant speed in each control cycle when accelerating the speed of the second motor.

[0023] In addition, the control unit can control the speed of the second motor based on the difference between the commanded speed and the actual speed of the first motor in the interval where the actual speed of the first motor and the actual speed of the second motor correspond to each other.

[0024] In addition, the control unit can change the rotational speed of the third motor driving the cutting device in response to the speed control of the second motor.

[0025] According to a second embodiment of the present specification, a method for controlling a mobile robot to drive in a straight line may be provided, comprising: a step of detecting the rotational speed of a first motor driving a first wheel that moves the mobile robot; a step of detecting the rotational speed of a second motor driving a second wheel that moves the mobile robot; and a step of controlling the speed of the second motor based on the difference between the commanded speed of the first motor and the actual speed.

[0026] At this time, the step of controlling the speed of the second motor may include a step of controlling the speed of the second motor by additionally considering the duty ratio of the control signal for the first motor.

[0027] Preferably, the step of controlling the speed of the second motor may include a step of controlling the speed of the second motor to decelerate when the difference between the commanded speed and the actual speed of the first motor is greater than a reference value and the duty ratio of the control signal for driving the first motor is greater than a first value.

[0028] In addition, the speed of the second motor that has been reduced can correspond to the actual speed of the first motor.

[0029] Preferably, the step of controlling the speed of the second motor may include a step of controlling the speed of the second motor to be decelerated at a constant speed in each control cycle when decelerating the speed of the second motor.

[0030] Preferably, the step of controlling the speed of the second motor may include a step of controlling the speed of the second motor to accelerate when the difference between the commanded speed and the actual speed of the first motor is smaller than a reference value and the duty ratio of the control signal for driving the first motor is smaller than a second value.

[0031] Preferably, the step of controlling the speed of the second motor may include the step of controlling the speed of the second motor to accelerate at a constant speed in each control cycle when accelerating the speed of the second motor.

[0032] Specific details of other embodiments are included in the detailed description and drawings. Effects of the invention

[0033] In the mobile robot according to the proposed embodiment, one or more of the following effects can be expected.

[0034] In a situation where a mobile robot according to an embodiment of the present specification cannot move in a straight line due to different loads on both motors, the convenience of use can be improved by inducing the mobile robot to move in a straight line by adjusting the speed of the relatively faster motor.

[0035] In addition, by additionally considering the duty cycle as well as the difference between the commanded speed and the actual speed, there is an advantage in preventing malfunctions of the mobile robot regarding deviation from the reference path and improving the accuracy of the mobile robot's straight-line driving.

[0036] In particular, by determining situations where the mobile robot cannot drive in a straight line through comparison with a constant value, there is an advantage in being able to cut the grass within the work area more uniformly in a regular pattern.

[0037] In addition, in cases where straight-line driving is not possible, there is an advantage in that the driving stability of the mobile robot can be ensured by decelerating at a constant speed during each control cycle rather than rapidly decelerating the speed of the relatively fast motor.

[0038] In addition, by controlling the speed of the mobile robot to accelerate back up while driving in a straight line through motor speed control, there is an advantage in that the time required to mow the grass within the work area can be shortened.

[0039] The effects of the embodiments are not limited to those mentioned above, and other unmentioned effects will be clearly understood by a person skilled in the art from the description in the claims. Brief explanation of the drawing

[0040] FIG. 1 is a perspective view of a mobile robot according to an embodiment of the present specification. FIG. 2 is an elevation view of a mobile robot in the front direction according to an embodiment. FIG. 3 is an elevation view of a mobile robot according to an embodiment from the right side direction. FIG. 4 is an elevation view of a mobile robot according to an embodiment in the lower side direction. FIG. 5 is a perspective view of a docking device to which a mobile robot docks according to an embodiment. FIG. 6 is an elevation view from the front of a docking device according to an embodiment. FIG. 7 is a block diagram illustrating the function of a mobile robot according to an embodiment. Figure 8 shows an example of a control method for a mobile robot. Figure 9 shows an example of speed control of a wheel of a mobile robot. FIG. 10 shows an example of controlling the driving of a mobile robot that has deviated from a reference path. Figure 11 shows a graph related to the speed control of a motor of a mobile robot according to an embodiment. FIG. 12 shows an example for explaining the work performance of a mobile robot. FIG. 13 is a drawing illustrating a block diagram of a mobile robot according to an embodiment. Specific details for implementing the invention

[0041] The terms used in the embodiments have been selected to be as widely used as possible, taking into account their functions in the present disclosure; however, these may vary depending on the intent of those skilled in the art, case law, the emergence of new technologies, etc. Additionally, in specific cases, terms have been arbitrarily selected by the applicant, and in such cases, their meanings will be described in detail in the relevant explanatory section. Therefore, terms used in the present disclosure should be defined not merely by their names, but based on their meanings and the overall content of the present disclosure.

[0042] When a part of a specification is described as “comprising” a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components. Furthermore, terms such as “part” or “module” as used in the specification refer to a unit that processes at least one function or operation, and this may be implemented in hardware or software, or as a combination of hardware and software.

[0043] The expression “at least one of a, b, and c” described throughout the specification may include ‘a alone’, ‘b alone’, ‘c alone’, ‘a and b’, ‘a and c’, ‘b and c’, or ‘a, b, and c all’.

[0044] The "terminal" mentioned below may be implemented as a computer or portable terminal capable of connecting to a server or other terminal via a network. Here, the computer includes, for example, a notebook, desktop, or laptop equipped with a web browser, and the portable terminal may include, for example, a wireless communication device that ensures portability and mobility, and may include all types of handheld-based wireless communication devices such as communication-based terminals like IMT (International Mobile Telecommunication), CDMA (Code Division Multiple Access), W-CDMA (W-Code Division Multiple Access), and LTE (Long Term Evolution), smartphones, tablet PCs, etc.

[0045] Embodiments of the present disclosure are described below with reference to the attached drawings so that those skilled in the art can easily implement them. However, the present disclosure may be embodied in various different forms and is not limited to the embodiments described herein.

[0046] Expressions referring to directions such as “Front (F) / Rear (R) / Left (Le) / Right (Ri) / Up (U) / Down (D)” mentioned below are defined according to their indications in the drawings; however, this is merely for the purpose of explaining the invention so that it can be clearly understood, and it goes without saying that each direction may be defined differently depending on where the reference is placed.

[0047] The use of terms such as 'first, second,' etc., attached to the components mentioned below is intended solely to avoid confusion regarding the components being referred to, and is unrelated to the order, importance, or master-slave relationship between the components. For example, an invention including only the second component without the first component can be implemented, and the first component and the second component may be components of the same type or components of different types.

[0048] In the drawings, the thickness or size of each component may be exaggerated, omitted, or schematically depicted for convenience and clarity of explanation. Additionally, while the size and area of ​​each component do not entirely reflect their actual size or area, the embodiments of this specification may be understood based thereon.

[0049] In addition, angles and directions mentioned in the process of describing the structure of the present invention are based on those described in the drawings. In the description of the structure in the specification, if the reference point and positional relationship for an angle are not clearly mentioned, the relevant drawings should be referenced.

[0050] Referring to FIGS. 1 to 6 below, a lawn mower robot (100) is described as an example, but it is not necessarily limited thereto.

[0051] Referring to FIGS. 1 to 4, the mobile robot (100) includes a body (110) that forms an exterior. The body (110) forms an internal space. The mobile robot (100) includes a driving unit (120) that moves the body (110) with respect to a driving surface. The mobile robot (100) includes a working unit that performs a predetermined task.

[0052] The body (110) includes a frame (111) to which a drive motor module (123), to be described later, is fixed. A blade motor (132), to be described later, is fixed to the frame (111). The frame (111) supports a battery, to be described later. The frame (111) also provides a skeletal structure that supports various other parts. The frame (111) is supported by an auxiliary wheel (125) and a drive wheel (121).

[0053] The body (110) includes lateral blocking portions (111a) to block the user's fingers from entering the blade (131) from both sides of the blade (131). The lateral blocking portions (111a) are fixed to the frame (111). The lateral blocking portions (111a) are positioned to protrude downward relative to the lower side of other parts of the frame (111). The lateral blocking portions (111a) are positioned to cover the upper part of the space between the drive wheel (121) and the auxiliary wheel (125).

[0054] A pair of lateral blocking members (111a-1, 111a-2) are arranged left and right with the blade (131) in between. The lateral blocking member (111a) is arranged at a predetermined distance from the blade (131).

[0055] The front surface (111af) of the lateral blocking part (111a) is formed in a rounded shape. The front surface (111af) forms a surface that bends upward in a rounded shape as it moves forward from the lower side of the lateral blocking part (111a). By utilizing the shape of this front surface (111af), when the mobile robot (100) moves forward, the lateral blocking part (111a) can easily climb over lower obstacles below a predetermined standard.

[0056] The body (110) includes a front blocking portion (111b) to block the user's finger from entering the blade (131) from the front of the blade (131). The front blocking portion (111b) is fixed to the frame (111). The front blocking portion (111b) is positioned to cover a portion of the upper part of the space between a pair of auxiliary wheels (125(L), 125(R)).

[0057] The front blocking portion (111b) includes a protruding rib (111ba) that protrudes downward relative to the lower surface of another part of the frame (111). The protruding rib (111ba) extends in the front-rear direction. The upper end of the protruding rib (111ba) is fixed to the frame (111), and the lower end of the protruding rib (111ba) forms a free end.

[0058] Multiple protruding ribs (111ba) may be spaced apart in the left and right directions. Multiple protruding ribs (111ba) may be arranged parallel to each other. A gap is formed between two adjacent protruding ribs (111ba).

[0059] The front surface of the protruding rib (111ba) is formed in a rounded shape. The front surface of the protruding rib (111ba) forms a surface that bends upward in a rounded shape as it moves forward from the lower surface of the protruding rib (111ba). By utilizing the shape of the front surface of the protruding rib (111ba), when the mobile robot (100) moves forward, the protruding rib (111ba) can easily climb over lower obstacles below a predetermined standard.

[0060] The front blocking section (111b) includes an auxiliary rib (111bb) that assists in rigidity. An auxiliary rib (111bb) is positioned between the upper portions of two adjacent protruding ribs (111ba) to reinforce the rigidity of the front blocking section (111b). The auxiliary rib (111bb) may be formed by protruding downward and extending in a grid pattern.

[0061] A caster (not shown) that rotatably supports an auxiliary wheel (125) is disposed on the frame (111). The caster is rotatably disposed relative to the frame (111). The caster is provided to be rotatable about a vertical axis. The caster is disposed on the lower side of the frame (111). A pair of casters corresponding to a pair of auxiliary wheels (125) is provided.

[0062] The body (110) includes a case (112) that covers the frame (111) from the top. The case (112) forms the upper side and the front / rear / left / right sides of the mobile robot (100).

[0063] The body (110) may include a case connecting part (not shown) that fixes the case (112) to the frame (111). The case (112) may be fixed to the upper part of the case connecting part. The case connecting part may be movably positioned on the frame (111). The case connecting part may be movably positioned only in the up and down direction relative to the frame (111). The case connecting part may be provided to be movable only within a predetermined range. The case connecting part moves integrally with the case (112). Accordingly, the case (112) is movable relative to the frame (111).

[0064] The body (110) includes a bumper (112b) positioned at the front. The bumper (112b) performs the function of absorbing impact when in contact with external obstacles. On the front of the bumper (112b), a bumper groove may be formed that is recessed towards the rear and extends in the left-right direction. Multiple bumper grooves may be spaced apart in the vertical direction. The lower end of the protruding rib (111ba) is positioned lower than the lower end of the auxiliary rib (111bb).

[0065] The bumper (112b) is formed by connecting the front surface and the left and right sides to each other. The front surface and the sides of the bumper (112b) are connected in a rounded manner.

[0066] The body (110) may include a bumper auxiliary part (112c) positioned to wrap around the outer surface of the bumper (112b). The bumper auxiliary part (112c) is coupled to the bumper (112b). The bumper auxiliary part (112c) wraps around the lower part of the front surface and the lower part of the left and right sides of the bumper (112b). The bumper auxiliary part (112c) may cover the lower half of the front surface and the left and right sides of the bumper (112b).

[0067] The front surface of the bumper auxiliary part (112c) is positioned further forward than the front surface of the bumper (112b). The bumper auxiliary part (112c) forms a surface protruding from the surface of the bumper (112b).

[0068] The bumper auxiliary part (112c) can be formed of a material advantageous for shock absorption, such as rubber. The bumper auxiliary part (112c) can be formed of a flexible material.

[0069] The frame (111) may be provided with a movable fixing part (not shown) to which the bumper (112b) is fixed. The movable fixing part may be positioned to protrude upward from the frame (111). The bumper (112b) may be fixed to the upper part of the movable fixing part.

[0070] The bumper (112b) can be positioned to be movable within a predetermined range relative to the frame (111). The bumper (112b) is fixed to a movable fixed part and can move integrally with the movable fixed part.

[0071] The movable fixed part may be movably positioned on the frame (111). The movable fixed part may be rotatably provided within a predetermined range with respect to the frame (111) around a virtual axis of rotation. Accordingly, the bumper (112b) may be rotatably provided integrally with respect to the frame (111) with respect to the movable fixed part.

[0072] The body (110) includes a handle (113). The handle (113) may be positioned on the rear side of the case (112).

[0073] The body (110) includes a battery input section (114) for taking out and taking out a battery. The battery input section (114) may be positioned on the lower side of the frame (111). The battery input section (114) may be positioned on the rear side of the frame (111).

[0074] The body (110) includes a power switch (115) for turning the power of the mobile robot (100) on / off. The power switch (115) may be positioned on the lower side of the frame (111).

[0075] The body (110) includes a blade protection portion (116) that covers the lower side of the central portion of the blade (131). The blade protection portion (116) is provided such that the edge of the centrifugal portion of the blade (131) is exposed, while the central portion of the blade (131) is covered.

[0076] The body (110) includes a first opening / closing part (117) that opens and closes the portion where the height adjustment part (156) and the height display part (157) are arranged. The first opening / closing part (117) is hinged to the case (112) to enable opening and closing operations. The first opening / closing part (117) is arranged on the upper side of the case (112).

[0077] The first opening / closing part (117) is formed in a plate shape and covers the upper side of the height adjustment part (156) and the height display part (157) when closed.

[0078] The body (110) includes a second opening / closing part (118) that opens and closes the portion where the display module (165) and the input part (164) are located. The second opening / closing part (118) is hinge-coupled to the case (112) and is configured to enable opening and closing operations. The second opening / closing part (118) is positioned on the upper side of the case (112). The second opening / closing part (118) is positioned behind the first opening / closing part (117).

[0079] The second opening / closing part (118) is formed in a plate shape and covers the display module (165) and the input part (164) when closed.

[0080] The opening angle of the second opening / closing part (118) is set to be smaller than the opening angle of the first opening / closing part (117). This allows the user to easily open the first opening / closing part (117) even when the second opening / closing part (118) is in an open state, and allows the user to easily operate the height adjustment part (156). In addition, it allows the user to visually check the contents of the height display part (157) even when the second opening / closing part (118) is in an open state.

[0081] For example, the opening angle of the first opening / closing part (117) may be configured to be approximately 80 to 90 degrees based on the closed state. For example, the opening angle of the second opening / closing part (118) may be configured to be approximately 45 to 60 degrees based on the closed state.

[0082] The first opening / closing part (117) opens by lifting the rear end upward with the front end as the center, and the second opening / closing part (118) opens by lifting the rear end upward with the front end as the center. Through this, the user can open and close the first opening / closing part (117) and the second opening / closing part (118) from the rear of the lawn mower robot (100), which is a safe area, even when the lawn mower robot (100) moves forward. In addition, through this, the opening operation of the first opening / closing part (117) and the opening operation of the second opening / closing part (118) can be prevented from interfering with each other.

[0083] The first opening / closing part (117) may be provided to be rotatable with respect to the case (112) around a rotation axis extending in the left / right direction from the front end of the first opening / closing part (117). The second opening / closing part (118) may be provided to be rotatable with respect to the case (112) around a rotation axis extending in the left / right direction from the front end of the second opening / closing part (118).

[0084] The body (110) may include a first motor housing (119a) that accommodates a first drive motor (123(L)) inside, and a second motor housing (119b) that accommodates a second drive motor (123(R)) inside. The first motor housing (119a) may be fixed to the left side of the frame (111), and the second motor housing (119b) may be fixed to the right side of the frame. The right end of the first motor housing (119a) is fixed to the frame (111). The left end of the second motor housing (119b) is fixed to the frame (111).

[0085] The first motor housing (119a) is formed as a cylindrical shape with height extending from left to right. The second motor housing (119b) is formed as a cylindrical shape with height extending from left to right.

[0086] The driving unit (120) includes a driving wheel (121) that rotates by the driving force of a driving motor module (123). The driving unit (120) may include at least one pair of driving wheels (121) that rotate by the driving force of a driving motor module (123). The driving wheels (121) include a first wheel (121(L)) and a second wheel (121(R)) that are each provided on the left and right sides so as to rotate independently. The first wheel (121(L)) is positioned on the left side, and the second wheel (121(R)) is positioned on the right side. The first wheel (121(L)) and the second wheel (121(R)) are spaced apart from each other on the left and right sides. The first wheel (121(L)) and the second wheel (121(R)) are positioned on the lower rear side of the body (110).

[0087] The first wheel (121(L)) and the second wheel (121(R)) are each provided to rotate independently so that the body (110) can rotate and advance relative to the ground. For example, when the first wheel (121(L)) and the second wheel (121(R)) rotate at the same rotational speed, the body (110) can advance relative to the ground. For example, when the rotational speed of the first wheel (121(L)) is faster than the rotational speed of the second wheel (121(R)), or when the rotational direction of the first wheel (121(L)) and the rotational direction of the second wheel (121(R)) are different from each other, the body (110) can rotate relative to the ground.

[0088] The first wheel (121(L)) and the second wheel (121(R)) may be formed larger than the auxiliary wheel (125). The shaft of the first drive motor (123(L)) may be fixed to the center of the first wheel (121(L)), and the shaft of the second drive motor (123(R)) may be fixed to the center of the second wheel (121(R)).

[0089] The drive wheel (121) includes a wheel outer portion (121b) that contacts the ground. For example, the wheel outer portion (121b) may be a tire. A plurality of protrusions may be formed on the wheel outer portion (121b) to increase friction with the ground.

[0090] The drive wheel (121) may include a wheel frame (not shown) that fixes the outer periphery of the wheel (121b) and receives power from a motor (123). The shaft of the motor (123) is fixed to the center of the wheel frame so that rotational force can be received. The outer periphery of the wheel (121b) is arranged to wrap around the circumference of the wheel frame.

[0091] The drive wheel (121) includes a wheel cover (121a) that covers the outer surface of the wheel frame. The wheel cover (121a) is positioned in the opposite direction to the direction in which the motor (123) is positioned relative to the wheel frame. The wheel cover (121a) is positioned in the center of the outer periphery (121b) of the wheel.

[0092] The driving unit (120) includes a driving motor module (123) that generates driving force. It includes a driving motor module (123) that provides driving force to a driving wheel (121). The driving motor module (123) includes a first driving motor (123(L)) that provides driving force to a first wheel (121(L)) and a second driving motor (123(R)) that provides driving force to a second wheel (121(R)). The first driving motor (123(L)) and the second driving motor (123(R)) may be spaced apart to the left and right. The first driving motor (123(L)) may be positioned to the left of the second driving motor (123(R)).

[0093] The first drive motor (123(L)) and the second drive motor (123(R)) may be positioned on the lower side of the body (110). The first drive motor (123(L)) and the second drive motor (123(R)) may be positioned on the rear side of the body (110).

[0094] The first drive motor (123(L)) may be positioned to the right of the first wheel (121(L)), and the second drive motor (123(R)) may be positioned to the left of the second wheel (121(R)). The first drive motor (123(L)) and the second drive motor (123(R)) are fixed to the body (110).

[0095] The first drive motor (123(L)) may be positioned inside the first motor housing (119a) and configured so that the motor shaft protrudes to the left. The second drive motor (123(R)) may be positioned inside the second motor housing (119b) and configured so that the motor shaft protrudes to the right.

[0096] In this embodiment, the first wheel (121(L)) and the second wheel (121(R)) are each directly connected to the rotation axis of the first drive motor (123(L)) and the rotation axis of the second drive motor (123(R)), respectively, but parts such as shafts may be connected to the first wheel (121(L)) and the second wheel (121(R)), and the rotational force of the motor (123(L), ​​123(R)) may be transmitted to the wheels (121a, 120b) by means of gears or chains.

[0097] The driving unit (120) may include an auxiliary wheel (125) that supports the body (110) together with a driving wheel (121). The auxiliary wheel (125) may be positioned in front of the blade (131). The auxiliary wheel (125) is a wheel that does not receive driving force from a motor and serves to support the body (110) in an auxiliary manner against the ground. A caster supporting the rotation axis of the auxiliary wheel (125) is coupled to the frame (111) so as to be rotatable about a vertical axis. A first auxiliary wheel (125(L)) positioned on the left and a second auxiliary wheel (125(R)) positioned on the right may be provided.

[0098] The work unit is configured to perform a predetermined task. The work unit is positioned in the body (110).

[0099] For example, the work unit may be equipped to perform tasks such as cleaning or mowing the lawn. As another example, the work unit may be equipped to perform tasks such as transporting or finding objects. As yet another example, the work unit may perform security functions such as detecting external intruders or dangerous situations in the surroundings.

[0100] In this embodiment, the work unit is described as performing lawn mowing, but there may be various examples of the types of work performed by the work unit, and it is not necessary to be limited to the examples described herein.

[0101] The working part may include a blade (131) rotatably equipped for mowing grass. The working part may include a blade motor (132) that provides rotational force to the blade (131).

[0102] The blade (131) is positioned between the drive wheel (121) and the auxiliary wheel (125). The blade (131) is positioned on the lower side of the body (110). The blade (131) is provided to be exposed on the lower side of the body (110). The blade (131) rotates around a rotation axis extending in the vertical direction to cut grass. In the embodiment, the means for cutting grass is described as a blade (131), but is not limited thereto, and a circle blade type, a reel type, a line or strand type where the cutter is formed as a string, or other well-known cutter means for cutting grass may be configured.

[0103] The blade motor (132) may be positioned in front of the first wheel (121(L)) and the second wheel (121(R)). The blade motor (132) is positioned on the lower side of the central portion within the internal space of the body (110).

[0104] The blade motor (132) may be positioned at the rear of the auxiliary wheel (125). The blade motor (132) may be positioned at the lower part of the body (110). The rotational force of the motor shaft is transmitted to the blade (131) using a structure such as a gear.

[0105] The mobile robot (100) includes a battery that supplies power to a drive motor module (123). The battery provides power to a first drive motor (123(L)). The battery provides power to a second drive motor (123(R)). The battery may supply power to a blade motor (132). The battery may provide power to a control unit (190), an azimuth sensor (176), and an output unit (165). The battery may be placed on the lower side of the rear portion within the internal space of the body (110).

[0106] The mobile robot (100) is equipped with a blade (131) that can change the height relative to the ground, thereby allowing the grass cutting height to be changed. The mobile robot (100) includes a height adjustment unit (156) for a user to change the height of the blade (131). The height adjustment unit (156) includes a rotatable dial, so that the height of the blade (131) can be changed by rotating the dial.

[0107] The mobile robot (100) includes a height display unit (157) that displays the height level of the blade (131). When the height of the blade (131) is changed according to the operation of the height adjustment unit (156), the height level displayed by the height display unit (157) is also changed. For example, the height display unit (157) may display the expected height of the grass after the mobile robot (100) performs lawn mowing with the current blade (131) height state.

[0108] When the mobile robot (100) is docked to the docking device (200), it includes a docking insert (158) that is connected to the docking device (200). The docking insert (158) is provided to be recessed so that the docking connection (210) of the docking device (200) can be inserted. The docking insert (158) is positioned on the front of the body (110). By connecting the docking insert (158) and the docking connection (210), the mobile robot (100) can be guided to an accurate position when charging.

[0109] The mobile robot (100) may include a charging corresponding terminal (159) positioned in a location where it can contact a charging terminal (211) to be described later, while the docking insertion part (158) is inserted into the docking connection part (210). The charging corresponding terminal (159) may include a pair of charging corresponding terminals (159a, 159b) positioned in a location corresponding to a pair of charging terminals (211) (211a, 211b). The pair of charging corresponding terminals (159a, 159b) may be positioned left and right with the docking insertion part (158) in between.

[0110] A terminal cover (not shown) that can open and close the docking insertion part (158) and a pair of charging terminals (211) (211a, 211b) may be provided. When the mobile robot (100) is in motion, the terminal cover may cover the docking insertion part (158) and a pair of charging terminals (211) (211a, 211b). When the mobile robot (100) is connected to the docking device (200), the terminal cover may be opened to expose the docking insertion part (158) and a pair of charging terminals (211) (211a, 211b).

[0111] Meanwhile, referring to FIGS. 5 and 6, the docking device (200) includes a docking base (230) placed on the floor and a docking support (220) protruding upward from the front part of the docking base (230).

[0112] The docking base (230) defines a plane parallel to the horizontal direction. The docking base (230) is plate-shaped so that the mobile robot (100) can be placed on it. The docking support (220) extends from the docking base (230) in a direction intersecting the horizontal direction. Additionally, at least a portion of the mobile robot (100) may be positioned on the docking base (230) when docked.

[0113] When charging the mobile robot (100), it includes a docking connection part (210) that is inserted into the docking insertion part (158). The docking connection part (210) may protrude rearward from the docking support part (220).

[0114] The docking connection part (210) may be formed such that its vertical thickness is smaller than its horizontal width. The horizontal width of the docking connection part (210) may be formed to become narrower towards the rear. When viewed from the top, the docking connection part (210) is generally trapezoidal. The docking connection part (210) is formed with a left-right symmetrical shape. The rear portion of the docking connection part (210) forms a free end, and the front portion of the docking connection part (210) is fixed to the docking support part (220). The rear portion of the docking connection part (210) may be formed with a rounded shape.

[0115] When the docking connection part (210) is fully inserted into the docking insertion part (158), charging can be performed by the docking device (200) of the mobile robot (100).

[0116] The docking device (200) includes a charging terminal (211) for charging the mobile robot (100). The charging terminal (211) and the charging corresponding terminal (159) of the mobile robot (100) come into contact, so that power for charging can be supplied from the docking device (200) to the mobile robot (100).

[0117] The charging terminal (211) includes a contact surface facing the rear, and the charging corresponding terminal (159) includes a contact corresponding surface facing the front. By the contact surface of the charging terminal (211) and the contact corresponding surface of the charging corresponding terminal (159) coming into contact, the power of the docking device (200) is connected to the mobile robot (100).

[0118] The charging terminal (211) may include a pair of charging terminals (211) (211a, 211b) forming a positive pole and a negative pole. The first charging terminal (211) (211a) is provided to be in contact with the first charging corresponding terminal (159a), and the second charging terminal (211) (211b) is provided to be in contact with the second charging corresponding terminal (159b).

[0119] A pair of charging terminals (211) (211a, 211b) may be positioned with the docking connection (210) in between. A pair of charging terminals (211) (211a, 211b) may be positioned on the left and right sides of the docking connection (210).

[0120] The docking base (230) includes a wheel guard (232) on which the drive wheel (121) and auxiliary wheel (125) of the mobile robot (100) stand. The wheel guard (232) includes a first wheel guard (232a) that guides the movement of the first auxiliary wheel (125) and a second wheel guard (232b) that guides the movement of the second auxiliary wheel (125). A central base (231) that is convex upward is disposed between the first wheel guard (232a) and the second wheel guard (232b). The docking base (230) includes a slip prevention part (234) to prevent the first wheel (121(L)) and the second wheel (121(R)) from slipping. The slip prevention part (234) may include a plurality of protrusions that protrude upward.

[0121] Meanwhile, a boundary wire may be implemented to set the boundary of the driving area where the mobile robot (100) travels or the work area for mowing the lawn. Meanwhile, in the embodiment, the boundary wire may be referred to as a wire. The boundary wire may generate a signal that the mobile robot (100) can detect, and the mobile robot (100) may detect such a signal to identify at least one of the driving area and the work area, and may perform driving and work based on the identified result. In the embodiment, the driving area and the work area may be the same area. Additionally, the mobile robot (100) may detect the distance to the boundary wire through a boundary signal transmitted from the boundary wire. More specifically, the distance to the boundary wire may be identified by identifying the direction and strength of the magnetic field generated according to the current flow of the boundary wire, and a driving path may be determined based on this. More specifically, when adjacent to the boundary wire, the magnetic field strength of the vertical component of the ground is strong, and as it moves further away from the wire, the magnetic field strength of the vertical component decreases. In the case of the horizontal magnetic field component, it is strongest near the wire, and its strength may decrease as it moves further away from the wire. The mobile robot (100) can detect the magnetic fields in the vertical and horizontal directions and determine the distance from the wire based on this. The mobile robot (100) of the embodiment can detect a signal generated from the wire through at least one sensor, and the specific arrangement of the sensor will be described later.

[0122] For example, a magnetic field can be generated around the boundary wire by allowing a predetermined current to flow along the boundary wire. Here, the generated magnetic field may be a constant of the boundary signal. By allowing an alternating current with a predetermined change pattern to flow through the boundary wire, the magnetic field generated around the boundary wire may change with a predetermined change pattern. The mobile robot (100) can detect the distance to the boundary wire by using a boundary signal detection unit (177) that detects the magnetic field, and thereby can drive and perform work within the boundary set by the boundary wire.

[0123] The boundary wire can receive current through a connection with a docking device (200). The docking device (200) may include a wire terminal (250) connected to the boundary wire. Both ends of the boundary wire may be connected to a first wire terminal (250a) and a second wire terminal (250b), respectively. Through the connection between the boundary wire and the wire terminal (250), the power of the docking device (200) can supply current to the boundary wire.

[0124] The wire terminal (250) may be positioned at the front (F) of the docking device (200). That is, the wire terminal (250) may be positioned on the side opposite to the direction in which the docking connection part (210) protrudes. The wire terminal (250) may be positioned on the docking support part (220). The first wire terminal (250a) and the second wire terminal (250b) may be positioned spaced apart to the left and right.

[0125] The docking device (200) may include a wire terminal opening / closing part (240) that covers the wire terminal (250) so as to be openable and closable. The wire terminal opening / closing part (240) may be positioned at the front (F) of the docking support part (220). The wire terminal opening / closing part (240) may be hinge-coupled to the docking support part (220) and configured to open / close through rotational movement.

[0126] Meanwhile, a reference wire may be implemented in the docking device (200) to allow the mobile robot (100) to recognize the position of the docking device (200). The reference wire may generate a predetermined docking position signal. The mobile robot (100) detects the docking position signal, recognizes the position of the docking device (200) by the reference wire, and can return to the recognized position of the docking device (200) when a return command or charging is required. Such a position of the docking device (200) may serve as a reference point for the mobile robot (100)'s driving.

[0127] For example, a magnetic field can be generated around the reference wire (270) by allowing a predetermined current to flow along the reference wire. Here, the generated magnetic field is a docking position signal. By allowing an alternating current with a predetermined change pattern to flow through the reference wire, the magnetic field generated around the reference wire can change with a predetermined change pattern. The mobile robot (100) can recognize that it has approached the reference wire (270) within a predetermined distance by using a boundary signal detection unit (177) that detects the magnetic field, and thereby can return to the position of the docking device (200) set by the reference wire.

[0128] The reference wire can generate a magnetic field in a direction distinct from the boundary wire. For example, the reference wire can be extended in a direction intersecting the horizontal direction. Preferably, the reference wire can be extended in an up-and-down direction orthogonal to the horizontal direction.

[0129] The reference wire can be installed in the docking device (200), and the reference wire can be placed at various locations in the docking device (200).

[0130] FIG. 7 is a block diagram illustrating the function of a mobile robot according to an embodiment.

[0131] The mobile robot (100) may include an input unit (164) capable of inputting various instructions from a user. The input unit (164) may include buttons, a dial, a touch-type display, etc. The input unit (164) may include a microphone (not shown) for voice recognition. In this embodiment, a plurality of buttons are arranged on the upper part of the case (112).

[0132] The mobile robot (100) may include an output unit (165) that outputs various information to a user. The output unit (165) may include a display module that outputs visual information. The output unit (165) may include a speaker (not shown) that outputs auditory information.

[0133] In this embodiment, the display module (165) outputs an image in an upward direction. The display module (165) is positioned on the upper side of the case (112). As an example, the display module (165) may include a liquid crystal display (LCD) panel. In addition, the display module (165) may be implemented using various display panels, such as a plasma display panel or an organic light emitting diode display panel.

[0134] The mobile robot (100) includes a storage unit (166) for storing various information. The storage unit (166) records various information necessary for controlling the mobile robot (100) and may include a volatile or non-volatile recording medium. The storage unit (166) may store information input from the input unit (164) or received from the communication unit (167). The storage unit (166) may store a program for controlling the mobile robot (100).

[0135] The mobile robot (100) may include a communication unit (167) for communicating with external devices (terminals, etc.), servers, routers, etc. For example, the communication unit (167) may be implemented to communicate wirelessly using wireless communication technologies such as IEEE 802.11 WLAN, IEEE 802.15 WPAN, UWB, Wi-Fi, Zigbee, Z-wave, Blue-Tooth, etc. The communication unit may vary depending on the communication method of the other device or server to be communicated.

[0136] The mobile robot (100) includes a sensing unit (170) that detects information related to the state of the mobile robot (100) or the environment outside the mobile robot (100). The sensing unit (170) may include at least one of a remote signal detection unit (171), an obstacle detection unit (172), a rain detection unit (173), a case flow sensor (174), a bumper sensor (175), an azimuth sensor (176), a boundary signal detection unit (177), a GPS detection unit (178), and a cliff detection unit (179). The sensing unit (170) may include various additional sensors in addition to the sensors shown in FIG. 7.

[0137] The remote signal detection unit (171) receives an external remote signal. When a remote signal is transmitted by an external remote controller, the remote signal detection unit (171) can receive the remote signal. For example, the remote signal may be an infrared signal. The signal received by the remote signal detection unit (171) can be processed by the control unit (190).

[0138] A plurality of remote signal detection units (171) may be provided. The plurality of remote signal detection units (171) may include a first remote signal detection unit (171a) disposed in the front portion of the body (110) and a second remote signal detection unit (171b) disposed in the rear portion of the body (110). The first remote signal detection unit (171a) receives a remote signal transmitted from the front. The second remote signal detection unit (171b) receives a remote signal transmitted from the rear.

[0139] The obstacle detection unit (172) detects obstacles around the mobile robot (100). The obstacle detection unit (172) can detect obstacles in front. A plurality of obstacle detection units (172a, 172b, 172c) may be provided. The obstacle detection unit (172) is positioned on the front surface of the body (110). The obstacle detection unit (172) is positioned above the frame (111). The obstacle detection unit (172) may include an infrared sensor, an ultrasonic sensor, an RF sensor, a PSD (Position Sensitive Device) sensor, etc.

[0140] The rain detection unit (173) detects rain when it rains in the environment where the mobile robot (100) is placed. The rain detection unit (173) can be placed in the case (112).

[0141] The case flow sensor (174) detects the flow of the case connection part. When the case (112) is lifted upward relative to the frame (111), the case connection part moves upward, and the case flow sensor (174) detects the lifting of the case (112). When the case flow sensor (174) detects the lifting of the case (112), the control unit (190) can control the operation of the blade (131) to stop. For example, when a user lifts the case (112) or when a situation occurs where a lower obstacle of a significant size lifts the case (112), the case flow sensor (174) can detect this.

[0142] The bumper sensor (175) can detect the rotation of the movable fixed part. For example, a magnet may be placed on one side of the lower part of the movable fixed part, and a sensor that detects a change in the magnetic field of the magnet may be placed on the frame (111). When the movable fixed part rotates, the sensor detects a change in the magnetic field of the magnet, thereby enabling the implementation of a bumper sensor (175) that detects the rotation of the movable fixed part. When the bumper (112b) collides with an external obstacle, the movable fixed part rotates in conjunction with the bumper (112b). By detecting the rotation of the movable fixed part, the impact of the bumper (112b) can be detected.

[0143] The sensing unit (20) includes a tilt information acquisition unit that acquires tilt information regarding the inclination of the driving surface (S). The tilt information acquisition unit can acquire tilt information regarding the inclination of the driving surface (S) on which the body (110) is placed by detecting the tilt of the body (110). For example, the tilt information acquisition unit may include a gyro sensing module (176a). The tilt information acquisition unit may include a processing module (not shown) that converts the detection signal of the gyro sensing module (176a) into tilt information. The processing module may be implemented as an algorithm or program as part of the control unit (190). As another example, the tilt information acquisition unit may include a magnetic field sensing module (176c) to acquire tilt information based on detection information regarding the Earth's magnetic field. The gyro sensing module (176a) can acquire information regarding the rotational angular velocity with respect to the horizontal plane of the body (30). Specifically, the gyro sensing module (176a) can detect rotational angular velocity centered on the X-axis and Y-axis, which are parallel to the horizontal plane and mutually orthogonal. Through a processing module, the rotational angular velocity with respect to the X-axis (roll) and the rotational angular velocity with respect to the Y-axis (pitch) can be combined to calculate the rotational angular velocity with respect to the horizontal plane. Through the processing module, the rotational angular velocity can be integrated to calculate the inclination value. Additionally, in the embodiment, the gyro sensing module (176a) can detect rotational angular velocity with respect to yaw.

[0144] The gyro sensing module (176a) can detect a predetermined reference direction. The tilt information acquisition unit can acquire tilt information based on the reference direction.

[0145] The azimuth sensor (AHRS) (176) may be equipped with a gyro sensing function. The azimuth sensor (176) may further be equipped with an acceleration sensing function. The azimuth sensor (176) may further be equipped with a magnetic field sensing function.

[0146] The azimuth sensor (176) may include a gyro sensing module (176a) that performs gyro sensing. The gyro sensing module (176a) can detect the horizontal rotational speed of the body (110). The gyro sensing module (176a) can detect the tilt speed of the body (110) relative to the horizontal plane.

[0147] The gyro sensing module (176a) may be equipped with a gyro sensing function for three axes of a mutually orthogonal spatial coordinate system. The information collected by the gyro sensing module (176a) may be roll, pitch, and yaw information. The processing module can calculate the direction angle by integrating the rolling, pitch, and yaw angular velocities.

[0148] The azimuth sensor (176) may include an acceleration sensing module (176b) that performs acceleration sensing. The acceleration sensing module (176b) may be equipped with acceleration sensing functions for three axes of a mutually orthogonal spatial coordinate system. A predetermined processing module may calculate velocity by integrating acceleration and calculate distance traveled by integrating velocity.

[0149] The azimuth sensor (176) may include a magnetic field sensing module (176c) that performs magnetic field sensing. The magnetic field sensing module (176c) may be equipped with magnetic field sensing functions for three axes of a mutually orthogonal spatial coordinate system. The magnetic field sensing module (176c) can detect the Earth's magnetic field.

[0150] The boundary signal detection unit (177) detects the boundary signal of the boundary wire (290) and / or the docking position signal of the reference wire (270).

[0151] A boundary signal detection unit (177) may be positioned in the front part of the body (110). This allows the boundary of the driving area to be detected early while moving forward, which is the main driving direction of the mobile robot (100). The boundary signal detection unit (177) may be positioned in the inner space of the bumper (112b).

[0152] The boundary signal detection unit (177) may include a first boundary signal detection unit (177a) and a second boundary signal detection unit (177b) spaced apart from each other. The first boundary signal detection unit (177a) and the second boundary signal detection unit (177b) may be positioned in the front part of the body (110).

[0153] For example, the boundary signal detection unit (177) includes a magnetic field sensor. The boundary signal detection unit (177) may be implemented using a coil to detect changes in the magnetic field. The boundary signal detection unit (177) may detect a magnetic field in at least the horizontal direction. The boundary signal detection unit (177) may detect a magnetic field for three axes that are orthogonal to each other in space.

[0154] Specifically, the first boundary signal detection unit (177a) can detect a magnetic field signal in a direction orthogonal to the second boundary signal detection unit (177b). The first boundary signal detection unit (177a) and the second boundary signal detection unit (177b) detect magnetic field signals in directions orthogonal to each other, and by combining the detected magnetic field signal values, they can detect magnetic fields for three axes that are orthogonal to each other in space.

[0155] When the boundary signal detection unit (177) detects a magnetic field for three mutually orthogonal axes in space, it determines the direction of the magnetic field with the sum vector value for the three axes, and if the direction of the magnetic field is close to the horizontal direction, it recognizes the docking position signal, and if it is close to the vertical direction, it recognizes it as a boundary signal.

[0156] Additionally, the boundary signal detection unit (177) can distinguish between the boundary signal and the docking position signal by the difference in magnetic field direction. Specifically, when the first boundary wire corresponding to the first driving area and the second boundary wire corresponding to the second driving area overlap at least partially or entirely with each other and current is applied in the same direction, a magnetic field having a greater strength than the magnetic field generated at each first boundary wire and second boundary wire is generated, and each signal can be distinguished by the difference in magnetic field strength.

[0157] As another example, the boundary signal detection unit (177) can distinguish between adjacent boundary signals and boundary signals of the first driving area and the second driving area based on differences in magnetic field distribution. Specifically, when a portion of the first boundary wire of the first driving area and the second boundary wire of the second driving area are placed within a certain distance from each other and current is applied in the same direction or in a different direction, the boundary signal detection unit (177) can detect that the magnetic field strength has multiple peaks within a preset distance on the planar coordinates and recognize them as adjacent boundary signals.

[0158] A GPS detection unit (178) may be provided to detect a Global Positioning System (GPS) signal. The GPS detection unit (178) may be implemented on a PCB, but is not limited thereto, and may be implemented by being included in a processor included in the mobile robot (100).

[0159] The cliff detection unit (179) detects whether there is a cliff on the driving surface. The cliff detection unit (179) is positioned at the front of the body (110) so as to detect whether there is a cliff in front of the mobile robot (100).

[0160] The sensing unit (170) may include an opening / closing detection unit (not shown) that detects whether at least one of the first opening / closing unit (117) and the second opening / closing unit (118) is opened or closed. The opening / closing detection unit may be placed in the case (112).

[0161] The mobile robot (100) includes a control unit (190) that controls autonomous driving. The control unit (190) can process a signal from the sensing unit (170). The control unit (190) can process a signal from the input unit (164).

[0162] The control unit (190) can control the driving of the first driving motor (123(L)) and the second driving motor (123(R)). The control unit (190) can control the driving of the blade motor (132). The control unit (190) can control the output of the output unit (165).

[0163] The control unit (190) includes a main board (not shown) placed in the internal space of the body (110). The main board can be implemented via a PCB.

[0164] The control unit (190) can control the autonomous driving of the mobile robot (100). The control unit (190) can control the driving of the driving unit (120) based on a signal received from the input unit (164). The control unit (190) can control the driving of the driving unit (120) based on a signal received from the sensing unit (170).

[0165] Additionally, the control unit (190) can process the signal from the boundary signal detection unit (177). Specifically, when a docking position signal is detected by the boundary signal detection unit (177), the control unit (190) can set the location where the docking position signal was detected as a reference point. When a return command is input to the reference point determined by the docking position signal, the control unit (190) can drive the mobile robot (100) to the reference point.

[0166] Additionally, when a boundary signal is detected by the boundary signal detection unit (177), the control unit (190) can set the location where the boundary signal was detected as the boundary of the driving area. The control unit (190) can drive the mobile robot (100) within the boundary of the driving area.

[0167] Additionally, when an adjacent boundary signal is detected by the boundary signal detection unit (177), the control unit (190) can set the location where the adjacent boundary signal was detected as an adjacent boundary area (295). The control unit (190) can return the mobile robot (100) along the adjacent boundary area (295).

[0168] Figure 8 shows an example of a control method for a mobile robot.

[0169] Referring to FIG. 8, in step S810, the rotational speed of the first motor driving the first wheel that moves the mobile robot can be detected. In step S820, the rotational speed of the second motor driving the second wheel that moves the mobile robot can be detected. Meanwhile, in the embodiment, the first wheel and the second wheel may each correspond to one of the left wheel and the right wheel of the mobile robot. In the embodiment, the first wheel and the second wheel are described as corresponding to the wheel where a difference occurs between the commanded speed and the actual speed, and the wheel that adjusts the corresponding speed, respectively; however, it is obvious that the first wheel may correspond to the left wheel or the right wheel of the mobile robot.

[0170] The mobile robot can move via the mounted first and second wheels. The mobile robot can cut grass using a cutting device while moving within a work area. At this time, the mobile robot can cut grass while moving within the work area according to a preset pattern. Alternatively, the mobile robot can detect a signal formed on a wire defining the work area and use it to cut grass while moving within the work area. Here, the cutting device can correspond to a blade, and the motor driving the cutting device can correspond to a blade motor.

[0171] A mobile robot can control the rotation of a first motor and a second motor based on a commanded speed. Specifically, the mobile robot can cut grass within a work area by driving the first motor and the second motor based on the same commanded speed. At this time, the first motor and the second motor can rotate based on the same rotational speed based on the commanded speed. Based on straight-line driving by the first wheel and the second wheel rotating according to the same rotational speed, the mobile robot can cut grass within the work area. Here, the rotational speed is information that can be detected through a sensor and may include the speed at which the motor actually rotated. For example, the mobile robot can control the first motor based on a commanded speed 1 and control the second motor based on a commanded speed 1. The first wheel of the mobile robot can rotate at a rotational speed 1 by the first motor, and the second wheel can also rotate at a rotational speed 1 by the second motor. The mobile robot can move in a straight line by rotating the first wheel and the second wheel at a rotational speed of 1, and thus can cut the grass inside the work area.

[0172] At this time, the mobile robot can monitor the rotational speed of the first motor driving the first wheel and the rotational speed of the second motor driving the second wheel. In addition, the mobile robot can detect the difference between the commanded speed and the rotational speed based on the monitored information.

[0173] Considering the environment within the work area where the mobile robot travels, the loads applied to the first motor and the second motor may differ, and consequently, the rotational speeds of the first motor and the second motor may differ. For example, if the grass within the work area is unevenly distributed and a relatively larger load is applied to the first motor than to the second motor, the rotational speeds of the first motor and the second motor may differ despite having the same commanded speed. Specifically, the control unit of the mobile robot instructed the first motor and the second motor to operate according to commanded speed 1, but due to the unbalanced load, the first motor may rotate according to rotational speed 1 and the second motor may rotate according to rotational speed 2. In this case, if the rotational speeds of the first motor driving the first wheel and the second motor driving the second wheel are different, the mobile robot may not be able to travel straight within the work area due to the difference in rotational speeds. For example, due to an unbalanced load, the first motor has a difference of Vx between the commanded speed 1 and rotational speed 1, and the second motor has a difference of Vy between the commanded speed 2 and rotational speed 2. In this case, if Vx > Vy, the mobile robot cannot move in a straight line because the second motor is relatively faster than the first motor. As another example, in the case of the first motor, due to the load, the commanded speed 1 > rotational speed 1, but in the case of the second motor, the commanded speed 1 = rotational speed 2, the mobile robot cannot move in a straight line because the second motor is relatively faster than the first motor.

[0174] Alternatively, the rotational speeds of the first motor and the second motor may differ due to the curved slope within the work area where the mobile robot travels. For example, due to the curved slope within the work area, the rotational speeds of the first motor and the second motor may differ despite having the same commanded speed. Specifically, the control unit of the mobile robot instructed the first motor and the second motor to operate according to commanded speed 1, but due to the curved slope, the first motor may rotate according to rotational speed 1 and the second motor may rotate according to rotational speed 2. In this case, if the rotational speeds of the first motor driving the first wheel and the second motor driving the second wheel are different, the mobile robot may not be able to travel straight within the work area due to the difference in rotational speeds. For example, due to a curved slope, the first motor has a difference of Vx between the commanded speed 1 and rotational speed 1, and the second motor has a difference of Vy between the commanded speed 2 and rotational speed 2. In this case, if Vx > Vy, the mobile robot cannot move in a straight line because the second motor is relatively faster than the first motor. As another example, due to a curved slope, the first motor has a commanded speed 1 > rotational speed 1, but the second motor has a commanded speed 1 = rotational speed 2. In this case, the mobile robot cannot move in a straight line because the second motor is relatively faster than the first motor.

[0175] Meanwhile, in such a situation, the commanded speed of a motor rotating at a speed lower than the commanded speed can be increased; however, if the commanded speed is greater than a certain ratio of the maximum commanded speed, the actual rotational speed may not increase even if the commanded speed is increased.

[0176] In step S830, the speed of the second motor can be controlled based on the difference between the commanded speed and the actual speed for the first motor. Here, the actual speed may represent the speed at which the motor actually rotated.

[0177] When the rotational speed 1 of the first motor is smaller than the rotational speed 2 of the second motor due to an unbalanced load or a curved slope, the mobile robot can control the commanded speed 2 of the second motor based on the difference between the commanded speed 1 of the first motor and the rotational speed 1. When driving straight, the commanded speed 1 of the first motor and the commanded speed 2 of the second motor may be the same, but when driving straight, the commanded speed 1 of the first motor and the commanded speed 2 of the second motor may be different. For example, regarding the first motor of a mobile robot driving straight, the commanded speed 1 is greater than the rotational speed 1 by Vx, and regarding the second motor, the commanded speed 1 is greater than the rotational speed 2 by Vy, and Vx > Vy, the commanded speed of the second motor may be lowered by taking into account the relatively slower rotational speed 1 of the first motor. That is, the mobile robot can lower the command speed of the second motor by considering Vx, or the mobile robot can lower the command speed of the second motor by considering the difference between Vx and Vy. With respect to the second motor, the command speed can be controlled from command speed 1 to command speed 2, and the mobile robot can drive straight by rotating the second motor based on command speed 2. As another example, with respect to the first motor of a mobile robot driving straight, the command speed 1 is greater than rotation speed 1 by Vx, and with respect to the second motor, the command speed 1 and rotation speed 2 are the same, so the command speed of the second motor can be lowered by considering the rotation speed 1 of the relatively slower first motor. That is, the mobile robot can lower the command speed of the second motor by considering Vx. With respect to the second motor, the command speed can be controlled from command speed 1 to command speed 2, and the mobile robot can drive straight by rotating the second motor based on command speed 2.When the mobile robot travels in a straight line due to the speed control of the second motor, the commanded speed of the mobile robot can be increased to the existing commanded speed, and the mobile robot can cut the grass inside the work area at the increased speed.

[0178] The mobile robot can control the speed of the second motor by additionally considering the duty ratio of the control signal for the first motor. The duty ratio is the ratio of the on and off states of the control signal; when the duty ratio is maximum (100%), the motor moves with maximum torque, and when the duty ratio is minimum (0%), the mobile robot may remain stationary without moving.

[0179] According to an embodiment, if the difference between the commanded speed and rotational speed of the first motor is greater than a reference value and the duty ratio of the control signal for driving the first motor is greater than a first value, the mobile robot can control the commanded speed of the second motor to decrease from commanded speed 1 to commanded speed 2. In this case, an example of the reference value and the first value may be a statistical value determined in advance through experiment. For example, a mobile robot that travels in a straight line based on commanded speed 1 for the first motor and the second motor may experience a difference between the commanded speed and the actual speed of the first motor due to a curved slope. In this case, if the difference between the commanded speed and the actual speed is greater than a reference value (e.g., 15 mm / s) and the duty ratio of the control signal for driving the first motor is greater than a first value (e.g., 96%), the mobile robot can control the commanded speed of the second motor to decrease from commanded speed 1 to commanded speed 2. At this time, the commanded speed of the motor can be reduced to a constant speed (e.g., 25 mm / s per cycle) during the control cycle and can be reduced until the mobile robot moves in a straight line. At this time, the commanded speed of the mobile robot can be reduced to a minimum commanded speed (e.g., 250 mm / s) considering whether a malfunction is suspected. Specifically, the commanded speed for the second motor of the mobile robot can be reduced by 25 mm / s per control cycle from 400 mm / s until it moves in a straight line, and the mobile robot can move in a straight line when the commanded speed is 300 mm / s. At this time, the commanded speed of the reduced second motor may be the same as the actual speed of the first motor. Specifically, if the commanded speed of the reduced second motor is 300 mm / s and is the same as the rotational speed of the second motor, the commanded speed of the reduced second motor may be the same as the actual speed of the first motor.

[0180] More specifically, the mobile robot can control the command speed of the second motor to decrease from command speed 1 to command speed 2 when the average value of the difference between the command speed and rotational speed of the first motor is greater than a reference value and the duty ratio of the control signal for driving the first motor is greater than a first value. In this case, an example of the reference value and the first value may be a statistical value determined in advance through experiments. For example, a mobile robot that travels in a straight line based on command speed 1 for the first motor and the second motor may experience a difference between the command speed and the actual speed of the first motor due to a curved slope. In this case, the mobile robot can control the command speed of the second motor to decrease from command speed 1 to command speed 2 when the average value of the difference between the command speed and the actual speed is greater than a reference value (e.g., 15 mm / s) and the duty ratio of the control signal for driving the first motor is greater than a first value (e.g., 96%). For example, if the average value of the difference between the commanded speed and the actual speed during five control cycles is greater than a reference value and the duty ratio of the control signal for driving the first motor is greater than the first value, the commanded speed of the second motor can be controlled to be reduced. At this time, the commanded speed of the motor can be reduced to a constant speed (e.g., 25 mm / s per cycle) during the control cycle and can be reduced until the mobile robot travels in a straight line. At this time, the commanded speed of the mobile robot can be reduced to a minimum commanded speed (e.g., 250 mm / s) considering whether a malfunction is suspected. Specifically, the commanded speed for the second motor of the mobile robot can be reduced by 25 mm / s per control cycle from 400 mm / s until it travels in a straight line, and the mobile robot can travel in a straight line when the commanded speed is 300 mm / s. At this time, the reduced commanded speed of the second motor can be the same speed as the actual speed of the first motor.Specifically, if the commanded speed of the decelerated second motor is 300 mm / s, which is the same as the rotational speed of the second motor, the commanded speed of the decelerated second motor may be the same as the actual speed of the first motor. Meanwhile, in the embodiment, the control cycle may be determined according to the characteristics of at least one of the control unit and the motor, and may be determined based on the switching frequency for controlling the motor. Meanwhile, when the unit of the motor speed is described as mm / s, it may be a speed set based on the distance the mobile robot advances when the motor rotates at that speed and the wheel connected to the motor rotates.

[0181] At this time, the rotational speed of the motor driving the cutting device may be changed based on the difference between the commanded speed and the rotational speed of the first motor. Alternatively, the rotational speed of the motor driving the cutting device may be changed based on the speed control of the second motor.

[0182] According to another embodiment, the mobile robot can control the command speed of the second motor to accelerate from command speed 1 to command speed 2 when the difference between the command speed and rotational speed of the first motor is smaller than a reference value and the duty ratio of the control signal for driving the first motor is smaller than a second value. This is a case where the load applied to the first motor and the second motor is reduced, and the mobile robot can accelerate the decelerated speed. In this case, examples of the reference value and the second value may be statistical values ​​determined in advance through experiments. The mobile robot can control the command speed of the second motor to accelerate from command speed 1 to command speed 2 when the difference between the command speed and the actual speed is smaller than a reference value (e.g., 15 mm / s) and the duty ratio of the control signal for driving the first motor is smaller than a second value (e.g., 90%). In this case, the command speed of the motor may be accelerated at a constant speed (e.g., 25 mm / s per cycle) during the control cycle. At this time, the command speed of the mobile robot can be accelerated up to the maximum command speed (e.g., 500 mm / s). Specifically, the command speed for the second motor of the mobile robot can be accelerated from 300 mm / s by 25 mm / s per control cycle. This represents a case where the speed of the motor corresponding to the other wheel is accelerated so that the load on the motor corresponding to one wheel is reduced, allowing it to rotate at a speed corresponding to the command speed, and in response, the mobile robot can drive in a straight line.

[0183] More specifically, the mobile robot can control the command speed of the second motor to accelerate from command speed 1 to command speed 2 when the average value of the difference between the command speed and the rotational speed of the first motor is smaller than a reference value and the duty ratio of the control signal for driving the first motor is smaller than a second value. This is a case where the load applied to the first motor and the second motor is reduced, and the mobile robot can accelerate the decelerated speed. In this case, examples of the reference value and the second value may be statistical values ​​determined in advance through experiments. For example, during five control cycles, the mobile robot can control the command speed of the second motor to accelerate from command speed 1 to command speed 2 when the average value of the difference between the command speed and the actual speed is smaller than a reference value (e.g., 15 mm / s) and the duty ratio of the control signal for driving the first motor is smaller than a second value (e.g., 90%). At this time, the commanded speed of the motor can be accelerated to a constant speed (e.g., 25 mm / s per cycle) during the control cycle. At this time, the commanded speed of the mobile robot can be accelerated up to a maximum commanded speed (e.g., 500 mm / s). Specifically, the commanded speed for the second motor of the mobile robot can be accelerated from 300 mm / s by 25 mm / s per control cycle.

[0184] According to an embodiment, the speed of the second motor can be controlled based on the difference between the commanded speed and the actual speed of the first motor in a section where the actual speed of the first motor and the actual speed of the second motor correspond to each other. Specifically, in a section where the actual speed of the first motor and the actual speed of the second motor are the same, the commanded speed of the second motor can be controlled based on the difference between the commanded speed and the actual speed of the first motor. For example, when driving straight because the actual speeds of the first motor and the second motor are the same, the commanded speed of the second motor, which was decelerated, can be accelerated based on the difference between the commanded speed and the actual speed of the first motor.

[0185] Figure 9 illustrates an example of controlling the speed of a wheel of a mobile robot. Figures 910 and 920 illustrate different methods for controlling the speed of the wheel for a mobile robot that cannot drive in a straight line, where the right wheel in the reference direction rotates at a speed lower than the commanded speed and the left wheel rotates at a speed corresponding to the commanded speed.

[0186] Referring to FIG. 9, the mobile robot can drive in a direction of movement (913) different from the reference direction (911) in FIG. 910. At this time, the reference direction (911) is a direction along a virtual line where work is expected to be performed by the mobile robot through straight driving, for example, a direction where the mobile robot's driving is expected according to a pre-set pattern. The mobile robot can detect the difference between the reference direction (911) and the direction of movement (913). When a difference between the reference direction (911) and the direction of movement (913) occurs as in FIG. 910, the mobile robot can drive straight by decelerating the speed VL of the left wheel and accelerating the speed VR of the right wheel. Specifically, the mobile robot can decelerate the speed VL of the left wheel by α as in Equation 1 and accelerate the speed VR of the right wheel by α as in Equation 2. In the following mathematical formulas 1 and 2, α may be a speed to compensate for the difference between the reference direction (911) and the direction of movement (913).

[0187] [Mathematical Formula 1]

[0188]

[0189] [Mathematical Formula 2]

[0190]

[0191] In Figure 920, the mobile robot can travel in a direction of movement (923) different from the reference direction (921). At this time, the reference direction (921) is a direction along a virtual line where work is expected to be performed by the mobile robot through straight driving, for example, it may be a direction where the mobile robot's driving is expected according to a pre-set pattern. The mobile robot can detect the difference between the reference direction (921) and the direction of movement (923). When a difference between the reference direction (921) and the direction of movement (923) occurs as in Figure 920, the mobile robot can drive straight by decelerating the speed VL of the left wheel and maintaining the speed VR of the right wheel. Specifically, the mobile robot can decelerate the VL speed of the left wheel by 2α as in Equation 3, and maintain the VR speed of the right wheel as in Equation 4. That is, by decelerating the speed of the wheel with relatively less load by 2α, it can be controlled to match the speed of the wheel with relatively more load. α may be a speed to compensate for the difference between the reference direction (921) and the direction of movement (923).

[0192] [Mathematical Formula 3]

[0193]

[0194] [Mathematical Formula 4]

[0195]

[0196] According to the embodiment, when the speeds of the left and right wheels are varied by -α and +α as in Figure 910, the direction can be changed so that the mobile robot can drive straight in the reference direction more quickly when the speed of the left wheel is varied by -2α as in Figure 920. In this way, in the embodiment of Figure 920, if the actual speed of the right wheel is lower than the commanded speed, the commanded speed of the left wheel can be reduced while maintaining the commanded speed of the right wheel. By controlling in this way, the mobile robot can be controlled so that it can drive effectively in the reference direction (921) even when the commanded speed of the right wheel corresponds to the maximum commanded speed.

[0197] FIG. 10 shows an example of controlling the driving of a mobile robot that has deviated from a reference path.

[0198] The mobile robot can cut the grass in the work area by driving along a reference path (1010) according to a preset pattern. However, if the mobile robot moves along a movement path (1020) instead of the reference path (1010) due to a curved slope or an unbalanced load, the mobile robot can check the difference dt between the reference path (1010) and the movement path (1020). At this time, the mobile robot can use dt to confirm that it has deviated from the preset pattern. Specifically, if dt is greater than a certain value, the mobile robot recognizes that it has deviated from the preset pattern and can change the tracking direction of the mobile robot by considering the difference dt between the reference path (1010) and the movement path (1020). Specifically, the mobile robot can determine the tracking angle through Equation 5. In mathematical formula 5, θ represents the tracking angle, dt represents the difference between the reference path (1010) and the moving path (1020), KP represents the error proportional gain, and KI represents the error integral gain.

[0199] [Mathematical Formula 5]

[0200]

[0201] FIG. 11 shows a graph related to the speed control of a motor of a mobile robot according to one embodiment.

[0202] Referring to FIG. 11, the mobile robot can move in a straight line at a speed of V1 mm / s with both the first wheel and the second wheel in the T1 section, and the commanded speed and the actual speed of the first wheel and the second wheel can correspond to each other. At this time, in the T2 section, due to the load applied to the first motor, the rotational speed of the first wheel can be decelerated from V1 to V2 even if the control signal to the first motor corresponding to the first wheel is controlled at the maximum duty ratio. In the T2 section, the mobile robot can recognize the deviation between the actual speeds of the first wheel and the second wheel, and by detecting such a deviation in actual speed, the mobile robot can recognize that it has deviated from the reference path in the T2 section. In the T3 section, the mobile robot can decelerate the commanded speed of the second motor from V1 to V2 based on the difference between the commanded speed V1 and the actual speed V2 for the first motor. In the T4 section, the first motor of the mobile robot has a commanded speed of V1 but an actual rotational speed of V2, and the second motor may have a commanded speed and an actual rotational speed of V2. If the mobile robot travels straight at a speed of V2 in the T4 section, the mobile robot may accelerate to a commanded speed of V1 again in the T5 section. Descriptions that overlap with the foregoing are omitted.

[0203] FIG. 12 shows an example for explaining the work performance of a mobile robot.

[0204] Referring to FIG. 12, the mobile robot (1200) can cut grass while traveling along an ideal path, which is a reference path according to a preset pattern. However, if the mobile robot (1200) deviates from the reference path, the work performance for cutting grass within the work area may be degraded. Accordingly, the mobile robot (1200) needs to ensure that the difference between the work performance according to the reference path and the work performance according to the actual path is within the value according to Equation 6. Here, C (1230), B (1120), and A (1110) in Equation 6 can be seen in FIG. 12. In Equation 6, θ may be an angle corresponding to the difference between the ideal path and the actual path. For example, θ may be an angle within 2 degrees to satisfy the work performance.

[0205] [Mathematical Formula 6]

[0206]

[0207] According to an embodiment, even if the mobile robot travels along a path different from the reference path due to a load, the mobile robot can control the speed applied to the motor so that the error between the reference path and the actual path remains within a certain range. Specifically, the commanded speed of the motor can be adjusted to be relatively fast so that the error remains within a certain range. For example, if the allowable error range is relatively small, the commanded speed of the motor can be decelerated more quickly, and if the allowable error range is relatively large, the commanded speed of the motor can be decelerated more slowly.

[0208] FIG. 13 is a drawing illustrating a block diagram of a mobile robot according to one embodiment. Although the block diagram of FIG. 13 may have some overlapping components with the block diagram of FIG. 7, it is not limited thereto, and it is obvious that the embodiment of the present specification can be implemented as a mobile robot comprising at least one of the components corresponding to the block diagram of FIG. 13 and the components corresponding to FIG. 7.

[0209] Referring to FIG. 13, the mobile robot (1300) may include at least one of an input unit (1310), an output unit (1320), a control unit (1330), a storage unit (1340), a communication unit (1350), a sensor (1360), a first motor (1370), a second motor (1380), and a third motor (1390). The mobile robot (1300) illustrated in FIG. 13 is illustrated only with components related to the present embodiment. Therefore, it can be understood by those skilled in the art related to the present embodiment that other general-purpose components may be included in addition to the components illustrated in FIG. 13. Since the mobile robot (1300) may include the aforementioned mobile robot, explanations regarding redundant content are omitted.

[0210] The first motor (1370) corresponds to a motor that drives the first wheel, the second motor (1380) corresponds to a motor that drives the second wheel, and the third motor (1390) corresponds to a motor that drives the cutting device. The sensor (1360) can monitor and detect the rotational speed of at least one of the first motor (1370) and the second motor (1380). For example, the sensor (1360) may be a Hall sensor.

[0211] The control unit (1330) can control the overall operation of the mobile robot (1300) and process data and signals. The control unit (1330) may be composed of at least one hardware unit. Additionally, the control unit (1330) may operate by one or more software modules generated by executing program code stored in memory. The control unit (1330) may include a processor and memory, wherein the processor can control the overall operation of the mobile robot (1300) and process data and signals by executing program code stored in memory. The control unit (1330) can adjust the speed of the second motor (1380) based on the difference between the commanded speed and the actual speed of the first motor (1370). If a difference between the commanded speed and the actual speed of the first motor (1370) occurs due to a load, the control unit (1330) can control the commanded speed of the second motor (1380) to be reduced for straight-line driving. As a result, the control unit (1330) can maintain a constant work performance of the mobile robot (1300).

Claims

Claim 1 A mobile robot comprises: a body forming an exterior; a cutting device mounted on the body for cutting grass; a first wheel and a second wheel coupled to the body for moving the mobile robot; a first motor for driving the first wheel; a second motor for driving the second wheel; and a sensor for detecting the actual speed of at least one of the first motor and the second motor. The control unit includes a control unit that adjusts the command speed of the second motor based on the difference between the command speed and the actual speed of the first motor and the duty ratio of the control signal for driving the first motor. The control unit, when the command speed of the first motor and the command speed of the second motor are the same, if the actual speed of the first motor is lower than the command speed of the first motor and the actual speed of the second motor, and the difference between the command speed and the actual speed of the first motor is greater than a reference value and the duty ratio of the control signal for driving the first motor is greater than a first value, adjusts the command speed of the second motor to the same speed as the actual speed of the first motor; and if it is determined that the actual speed of the first motor and the adjusted command speed of the second motor have become the same, and the difference between the command speed and the actual speed of the first motor is smaller than a reference value and the duty ratio of the control signal for driving the first motor is smaller than a second value, adjusts the command speed of the second motor to the same speed as the first motor. A mobile robot that adjusts at the same speed as the command speed. Claim 2 delete Claim 3 delete Claim 4 A mobile robot according to claim 1, wherein the control unit controls the second motor to decelerate at a constant speed in each control cycle when decelerating the second motor's commanded speed. Claim 5 delete Claim 6 delete Claim 7 A mobile robot according to claim 1, wherein the control unit controls the second motor to accelerate the commanded speed at a constant speed in each control cycle when accelerating the commanded speed of the second motor. Claim 8 A mobile robot according to claim 1, wherein the control unit controls the commanded speed of the second motor based on the difference between the commanded speed and the actual speed of the first motor in a section where the actual speed of the first motor and the actual speed of the second motor correspond to each other. Claim 9 A mobile robot according to claim 1, wherein the control unit changes the rotational speed of a third motor driving the cutting device in response to the command speed control of the second motor. Claim 10 A method for controlling a mobile robot comprises: a step of detecting the actual speed of a first motor that drives a first wheel that moves the mobile robot; a step of detecting the actual speed of a second motor that drives a second wheel that moves the mobile robot; and a step of controlling the commanded speed of the second motor based on the difference between the commanded speed of the first motor and the actual speed and the duty ratio of a control signal for driving the first motor, wherein the step of controlling the commanded speed of the second motor comprises, when the commanded speed of the first motor and the commanded speed of the second motor are the same, the actual speed of the first motor becomes lower than the commanded speed of the first motor and the actual speed of the second motor, the difference between the commanded speed of the first motor and the actual speed is greater than a reference value, and the duty ratio of the control signal for driving the first motor is greater than a first value, the step of adjusting the commanded speed of the second motor to the same speed as the actual speed of the first motor. A control method comprising the step of adjusting the command speed of the second motor to be the same as the command speed of the first motor when it is determined that the actual speed of the first motor and the adjusted command speed of the second motor have become the same, and when the difference between the command speed and the actual speed of the first motor is smaller than a reference value and the duty ratio of the control signal for driving the first motor is smaller than a second value. Claim 11 delete Claim 12 delete Claim 13 delete Claim 14 A control method according to claim 10, wherein the step of controlling the command speed of the second motor includes the step of controlling the command speed of the second motor to be decelerated at a constant speed in each control cycle when decelerating the command speed of the second motor. Claim 15 delete Claim 16 A control method according to claim 10, wherein the step of controlling the command speed of the second motor includes the step of controlling the command speed of the second motor to accelerate at a constant speed in each control cycle when accelerating the command speed of the second motor.

Images