Patent Publication Number: US-11659971-B2

Title: Robot cleaner

Description:
CROSS-REFERENCE TO RELATED THE APPLICATION 
     This application is based on and claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2019-0066239 filed on Jun. 4, 2019 in the Korean Intellectual Property Office, the disclosure of which is incorporated by reference herein in its entirety. 
     BACKGROUND 
     Field 
     The disclosure relates to a robot cleaner. 
     Description of the Related Art 
     A robot cleaner automatically moves an area and cleans the area by suctioning foreign substance such as dust from a floor. 
     The robot cleaner senses a distance to an obstacle, for example, furniture, office supplies, walls, etc. that are installed in the area, and performs mapping the area based on the distance, as the robot cleaner controls driving of wheels to evade the obstacle. In a related art, a sensor that observes a ceiling or floor is used, so that the robot cleaner calculates a distance in which the robot cleaner moves and, based on the moving distance, also calculates the distance to the obstacle. Because the art is an indirect way where the robot cleaner estimates the distance to the obstacle, if the moving distance is not exactly calculated due to a curve of the floor, etc., the distance to the obstacle should also have an error. Specifically, in case of using infrared light or an ultrasonic wave to calculate the distance, a significant error may occur in the distance calculating because the light or wave is scattered from the obstacle. Also, there may be obstacles, for example, a threshold having a protrusion from the floor, a chair or a bed having a space thereunder, and an object spread in both upper and lower directions. However, the robot cleaner cannot completely identify the obstacles. 
     In order to solve the problem, a method is proposed to sense the obstacle by protruding the sensor out of the robot cleaner. As the robot cleaner with a sensor protruding outwards moves, the sensor may happen to be pushed by the obstacle and be forced to get into the robot cleaner. If the sensor is not at a normal position where the sensor properly performs a sensing operation, a connectivity of data collected by the sensor may be broken and there may be loss of the data. 
     SUMMARY 
     According to an embodiment of the disclosure, a robot cleaner includes: a cleaner body configured to move in an area and clean the area; and a sensor unit provided in the cleaner body. The sensor unit includes: a main sensor configured to sense an obstacle in the area; a sensor position changer configured to allow the main sensor to move between a sensing position and a settled position, the main sensor protruding out of the cleaner body at the sensing position and being inside the cleaner body at the settled position; and a stopper configured to restrict the main sensor at the sensing position from moving towards the settled position. 
     The sensor position changer may include: a motor; and a link unit including: a first link member configured to rotate with a rotation axis of the motor; and a second link member, a first end of the second link member hinged to the first link member and a second end of the second link member hinged to the main sensor. 
     The stopper may further include a link member receiver configured to receive the first link member with the main sensor being at the sensing position and to restrict the first link member from overly rotating. 
     The stopper may further include a link member supporter having a flat portion which extends perpendicularly to a direction in which the main sensor moves, the flat portion of the link member supporter supporting the first end of the second link member. 
     The sensor position changer may include: a motor; a pinion coupled with a rotation axis of the motor; and a rack coupled with the main sensor and geared with the pinion. 
     The stopper may further include: a locking member; and a driver configured to allow the locking member to move between a lock state and a unlock state, the locking member in the lock state restricting the rack from moving with the main sensor being at the sensing position. 
     The sensor unit may further include a sensor holder having a space that corresponds to a shape of the main sensor to accommodate the main sensor, and the sensor holder may include: a lower sensor holder holding the main sensor and supported by the sensor position changer; and an upper sensor holder coupled to the lower sensor holder to be movable in a direction where the cleaner body moves within a gap between the lower sensor holder and the upper sensor holder. 
     The sensor unit may further include a sensor holder having a space to accommodate the main sensor. The sensor holder may be supported by the sensor position changer to be movable in every direction where the cleaner body moves. 
     The sensor unit may further include a position restoration member configured to restore the sensor holder which is moved by the obstacle to an initial position. 
     The position restoration member may include: a ring; and a plurality of elastic portions extending from an inner side of the ring inwards in a spiral form. 
     The sensor unit may further include a position restoration guide configured to guide the upper sensor holder to move in a direction where the cleaner body moves and to restore the upper sensor holder to an initial position. 
     The position restoration guide may include: a spring provided between the lower sensor holder and the upper sensor holder; a first guide provided with one of the lower sensor holder and the upper sensor holder; and a second guide provided opposite the first guide. 
     The first guide may include: a guide member having a guide groove that extends perpendicularly to a direction in which the cleaner body moves; and a guide pin supported by one of the lower sensor holder and the upper sensor holder, the guide pin being inserted in the guide groove of the guide member, and the second guide may include: a convex portion protruding from a surface of the upper sensor holder; and a concave portion provided on a surface of the lower sensor holder, a shape of the concave portion corresponding to the convex portion. 
     The sensor unit may further include: a base supporting the motor; and a sensor movement guide provided between the base and the sensor holder, the sensor movement guide being configured to guide the main sensor to move. 
     The sensor unit may further include an auxiliary sensor that is provided at a limit position and senses whether the main sensor reaches the sensing position or is away from the sensing position. 
     The auxiliary sensor may further sense whether the robot cleaner with the main sensor being at the sensing position bumps into the obstacle. 
     The auxiliary sensor may include a pair of auxiliary sensors provided at the limit position opposite to each other in an angle, each of the pair of auxiliary sensors comprising a first terminal and a second terminal, and the sensor unit may further include a pushing switch provided between the pair of auxiliary sensors, the pushing switch being configured to push the second terminal to contact the first terminal. 
     The auxiliary sensor may become off as the main sensor is at the settled position, on as the main sensor is at the limit position, and off as the main sensor is at the sensing position. 
     The sensor unit may further include: a holder cap configured to cover an upper portion of the sensor holder; and a cap supporter having a tension bar that is provided on the upper portion of the sensor holder, the tension bar supporting the holder cap and elastically restore a position of the holder cap. 
     According to an embodiment of the disclosure, a robot cleaner include: a cleaner body configured to move in an area and clean the area; and a sensor unit provided in the cleaner body. The sensor unit includes: a main sensor configured to sense an obstacle in the area; a sensor position changer configured to allow the main sensor to move between a sensing position and a settled position, the main sensor protruding from the cleaner body at the sensing position and being inside the cleaner body at the settled position; and an auxiliary sensor provided at a limit position, the limit position being near the sensing position, the auxiliary sensor sensing whether the main sensor reaches the sensing position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and/or other aspects will become apparent and more readily appreciated from the following description of exemplary embodiments, taken in conjunction with the accompanying drawings, in which: 
         FIG.  1    is a perspective view of a robot cleaner according to an embodiment. 
         FIG.  2    is a perspective bottom view of the robot cleaner. 
         FIG.  3    is an exploded view of the robot cleaner. 
         FIG.  4    is a perspective view of the robot cleaner before a sensor unit ascends. 
         FIG.  5    is a perspective view of the robot cleaner after the sensor unit ascends. 
         FIG.  6    is a block diagram illustrating a configuration of the robot cleaner. 
         FIG.  7    is a perspective view of the sensor unit according to an embodiment. 
         FIG.  8    is an upper exploded view of the sensor unit. 
         FIG.  9    is a lower exploded view of the sensor unit. 
         FIG.  10    is a sectional view of the sensor unit according to a A-A line of  FIG.  7   . 
         FIG.  11    illustrates the sensor holder protruding at the sensing position with a user&#39;s finger caught between the holder cap and the cleaner body. 
         FIG.  12    illustrates a junction feature of the sensor holder and the holder cap. 
         FIG.  13    is a perspective view of the sensor position changer. 
         FIG.  14    illustrates the sensor holder which is at the settled position. 
         FIG.  15    illustrates the sensor holder which is at the sensing position. 
         FIG.  16    illustrates the auxiliary sensor. 
         FIG.  17    illustrates a perspective view of the terminal pushing portion. 
         FIG.  18    is a plane view illustrating arrangement of the auxiliary sensors. 
         FIG.  19    is a sectional view illustrating the auxiliary sensor and the terminal pushing portion with the sensor holder being at the settled position. 
         FIG.  20    is a sectional view illustrating the auxiliary sensor and the terminal pushing portion with the sensor holder being at the limit position. 
         FIG.  21    is a sectional view illustrating the auxiliary sensor and the terminal pushing portion with the sensor holder being at the sensing position. 
         FIG.  22    is a plane view illustrating the auxiliary sensors and the terminal pushing portion with the sensor holder being at the sensing position in a normal operation. 
         FIG.  23    is a plane view illustrating the auxiliary sensors and the terminal pushing portion with the sensor holder being at the sensing position in a situation bumping into an obstacle in a front direction. 
         FIG.  24    is a plane view illustrating the auxiliary sensors and the terminal pushing portion with the sensor holder being at the sensing position in another situation bumping into an obstacle in a right direction. 
         FIG.  25    is a plane view illustrating the auxiliary sensors and the terminal pushing portion with the sensor holder being at the sensing position in further another situation bumping into an obstacle in a left direction. 
         FIG.  26    illustrates a position restoration guide provided in the sensor unit. 
         FIG.  27    is a perspective view of a first guide. 
         FIG.  28    is a sectional view of the first guide according to a B-B line shown in  FIG.  27   . 
         FIG.  29    is a sectional view of the first guide  282  according to a C-C line shown in  FIG.  27   . 
         FIG.  30    is a perspectively sectional view of the upper sensor holder and the lower sensor holder illustrating the first guide and a second guide. 
         FIG.  31    is a diagram illustrating an operation of the auxiliary sensors with the main sensor ascending or descending to the limit position. 
         FIG.  32    is a diagram illustrating an operation of the auxiliary sensors with the main sensor ascending from the limit position to the sensing position. 
         FIG.  33    is a diagram illustrating an operation of the auxiliary sensors with the main sensor at the sensing position moving horizontally. 
         FIG.  34    is a diagram illustrating another example of operations of a first auxiliary sensor and second auxiliary sensors with the main sensor ascending or descending to the limit position. 
         FIG.  35    is a diagram illustrating another example of operations of the first auxiliary sensor and the second auxiliary sensors with the main sensor ascending from the limit position to the sensing position. 
         FIG.  36    is a diagram illustrating another example of operations of the first auxiliary sensor and the second auxiliary sensors with the main sensor at the sensing position moving horizontally. 
         FIG.  37    is a diagram illustrating further another example of operations of a first auxiliary sensor and second auxiliary sensors with the main sensor ascending to the limit position and the sensing position. 
         FIG.  38    is a diagram illustrating further another example of operations of the first auxiliary sensor and the second auxiliary sensors with the main sensor at the sensing position moving horizontally. 
         FIG.  39    is a perspective view of another example of the robot cleaner. 
         FIG.  40    is a perspective view illustrating a bottom of the robot cleaner shown in  FIG.  39   . 
         FIG.  41    is an exploded view of the robot cleaner shown in  FIG.  39   . 
         FIG.  42    is a perspective view of the sensor unit. 
         FIG.  43    is an upper exploded view of the sensor unit. 
         FIG.  44    is a lower exploded view of the sensor unit. 
         FIG.  45    is a sectional view illustrating the terminal pushing portion and the auxiliary sensor. 
         FIG.  46    is a perspective view of the sensor position changer. 
         FIG.  47    is an exploded view of the sensor position changer. 
         FIG.  48    is a sectional view of the sensor position changer and the main sensor at the settled position. 
         FIG.  49    is a sectional view of the sensor position changer and the main sensor moving upwards from the settled position to the sensing position. 
         FIG.  50    is a side view of the terminal pushing portions and the auxiliary sensors with the main sensor being at the settled position. 
         FIG.  51    is a side view of the terminal pushing portions and the auxiliary sensors with the main sensor being at the limit position. 
         FIG.  52    is a side view of the terminal pushing portions and the auxiliary sensors with the main sensor being at the sensing position. 
         FIG.  53    is a plane view of the auxiliary sensors and the main sensor bumping into an obstacle in a direction. 
         FIG.  54    is a plane view of the auxiliary sensors and the main sensor bumping into an obstacle in an opposite direction. 
         FIG.  55    illustrates the position restoration member and the restoration member receiver of the lower sensor holder. 
         FIG.  56    is an exploded view illustrating the sensor holder and the sensor position changer. 
         FIG.  57    illustrates the position restoration member before bumping into an obstacle. 
         FIG.  58    illustrates the position restoration member while bumping into an obstacle. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Below, various embodiments of the disclosure are described with reference to the accompanying drawings. However, these do not intent to limit the disclosure to a specific embodiment form, and it should be understood to include various modifications, equivalents and/or alternatives to the embodiments of the disclosure. Regarding the description of the drawings, like numerals refer to like elements. 
     In the disclosure, terms “have,” “may have,” “include,” “may include,” etc. indicate the presence of corresponding features (e.g. a numeral value, a function, an operation, or an element such as a part, etc.), and do not exclude the presence of additional features. 
     In the disclosure, terms “A or B”, “at least one of A or/and B”, “one or more of A or/and B” or the like may include all possible combinations of elements enumerated together. For example, “A or B”, “at least one of A and B”, or “at least one of A or B” may refer to all of the cases of (1) including at least one A, (2) including at least one B, or (3) including all of at least one A and at least one B. 
     In the disclosure, the terms “a first”, “a second”, “the first”, “the second”, or etc. may use various elements regardless of order and/or importance, and are just used to distinguish an element from another without limiting the elements. For example, a first user device and a second user device may refer to user devices different from each other regardless of the order or importance of the devices. For instance, a first element may be named a second element without departing from the scope of the present disclosure. Likewise, a second element may also be named a first element. 
     In the disclosure, terms “module”, “unit”, “part”, etc. are used to denote an element that performs at least one function or operation, and such an element may be achieved by hardware, software or a combination of hardware and software. Further, a plurality of “modules”, “units”, “parts”, etc. may be integrated into at least one module or chip as at least one processor except a case where it needs to be used as each individual specific hardware. 
     When it is mentioned that a certain element (e.g. a first element) is “(operatively or communicatively) coupled with/to” or “connected to” a different element (e.g. a second element), it will be understood that the certain element may be coupled to the different element directly or through another element (e.g. a third element). On the other hand, when it is mentioned that a certain element (e.g. a first element) is “directly coupled to” or “directly connected to” a different element (e.g. a second element), it will be understood that another elements (e.g. a third element) is not present between the certain element and the different element. 
     The terms used in the disclosure are used to just describe a specific embodiment, and may not intend to limit the scope of another embodiment. Unless otherwise specified clearly in the context, a singular form may include a plural form. The terms used herein including the technological or scientific terms may have the same meanings as those generally understood by a person having ordinary skill in the art. The terms defined in a general dictionary may be construed as having the same or similar meanings as the contextual meanings of the related art, and are not construed as having ideal or excessively formal meanings unless defined clearly in the disclosure. As necessary, even the terms defined in the disclosure may not be construed as excluding embodiments of the disclosure. 
     An aspect of the disclosure is to provide a robot cleaner, which maintains a connectivity of data collected by a sensor and prevents loss of the data. 
     Also, an aspect of the disclosure is to provide a robot cleaner, which identifies whether a main sensor reaches a sensing position or is away from a sensing position. 
     Also, an aspect of the disclosure is to provide a robot cleaner, which senses that a sensor unit bumps into an obstacle and clearly identifies circumstances of the obstacle. 
     Also, an aspect of the disclosure is to provide a robot cleaner, which allows a sensor unit to restore from being moved by an obstacle. 
     Also, an aspect of the disclosure is to provide a robot cleaner, which prevents a user&#39;s finger from being caught by a holder cap when a sensor unit bumps into an obstacle. 
       FIG.  1    is a perspective view of a robot cleaner according to an embodiment.  FIG.  2    is a perspective bottom view of the robot cleaner.  FIG.  3    is an exploded view of the robot cleaner.  FIG.  4    is a perspective view of the robot cleaner before a sensor unit ascends.  FIG.  5    is a perspective view of the robot cleaner after the sensor unit ascends. 
     Referring to  FIG.  1   , the robot cleaner  1  according to an embodiment includes a cleaner body  10  which moves in an area and cleans the area, and a sensor unit  20 . 
     Referring to  FIGS.  2  and  3   , the cleaner body  10  includes a dust suction body  110  which generates suction power and suctions dust in the area, and an upper cover  120  which covers an upper portion of the dust suction body  110 . 
     The dust suction body  110  includes wheels  112  to move in the area, a dust collector  114  to collect the dust from the area, and a sensor housing  116  to accommodate the sensor unit  20 . The dust suction body  110  may further include a motor which generates the suction power to suction the dust in the area. 
     The wheels  112  include a pair of wheels with a plurality of sawtooth in order not to slip on the area. The wheels  112  may further include at least one auxiliary wheel for stable movement of the cleaner body  10 . 
     The dust collector  114  picks up by the suction power the dust in the area into the cleaner body  10 . The dust collector  114  may include a filter to filter the suctioned dust. 
     The sensor unit  20  is provided in the sensor housing  116  of the cleaner body  10 . The sensor unit  20  senses a position of the obstacle or a distance to the obstacle, and whether a position of the sensor unit  20  changes. 
     Referring to  FIG.  4   , the sensor unit  20  is at a settled position where the sensor unit  20  is settled inside the sensor housing  116 . In this state, the robot cleaner  1  may be in a standby state for charging in a charging station. 
     Referring to  FIG.  5   , the sensor unit  20  is changed to a sensing position where the sensor unit  20  protrudes upwards out of the sensor housing  116 . In this state, the robot cleaner  1  may be in a moving state for cleaning, as the sensor unit  20  performs a sensing operation for the obstacle. As to a configuration of the sensor unit  20 , although the position of the sensor unit  20  may be changed in a different way, for example, horizontally or rotatably, a case of change in an ascending and descending way will only be described later. 
       FIG.  6    is a block diagram illustrating a configuration of the robot cleaner. Referring to  FIG.  6   , the robot cleaner  1  includes the sensor unit  20 , a driver  30  and a controller  40 . The sensor unit  20  includes a main sensor  21 , a sensor position changer  24  and an auxiliary sensor  27 . 
     The main sensor  21  emits an infrared light, laser light or ultrasonic wave to the area and senses the position of the obstacle or the distance to the obstacle using the infrared light, etc., which is reflected from the obstacle. The main sensor  21  may include a light source to emit the light and a light receiver to receive the light reflected from the obstacle. The light source may include a light emitting device, for example, a light emitting diode to emit an infrared, visible or laser light. The light receiver may include a plurality of pixels arranged in a matrix which is embodied as cadmium sulfite cells, a photo diode, a photo transistor, etc. 
     The sensor position changer  24  is under the control of the controller  40  to allow the main sensor  21  to change from the settled position to the sensing position or vice versa. The auxiliary sensor  27  senses whether the main sensor  21 , of which the position is changed by the sensor position changer  24 , reaches the sensing position or is away from the sensing position. The auxiliary sensor  27  is provided at a limit position through which the main sensor  21  is changed from the sensing position to the sensing position. The auxiliary sensor  27  senses whether the main sensor  21  passes through the limit position while the main sensor  21  ascends or descends. The limit position will be described in more detail later. Also, the auxiliary sensor  27  may further sense whether the sensor unit  20  bumps into the obstacle. 
     The driver  30  is under the control of the controller  40  to drive the pair of wheels  112  (shown in  FIG.  2   ) of the cleaner body  10  to move forward, backward or turn around. The driver  30  may drive the wheels  112  based on information which is received from the sensor unit  20  and represents circumstances regarding the obstacle. 
     The controller  40  generally controls elements of the robot cleaner  1 . The controller  40  controls, for example, the main sensor  21 , the sensor position changer  24  and the driver  30 . 
     The controller  40  controls the sensor position changer  24  so that the sensor unit  20  as illustrated in  FIG.  5    ascends to the sensing position when the robot cleaner  1  shifts from the standby state for charging to the moving state for cleaning. Meanwhile, the controller  40  controls the sensor position changer  24  so that the sensor unit  20  as illustrated in  FIG.  4    descends to the settled position when the robot cleaner  1  shifts to the standby state for charging after cleaning. 
     The controller  40  performs a control operation to provide a visual and/or audible notification to a user if the auxiliary sensor  27  senses that the main sensor  21  passes through the limit position as the main sensor  21  at the sensing position is pushed by the obstacle. The controller  40  controls the driver  30  based on the circumstances information regarding the obstacle which is sensed by the main sensor  21  and the auxiliary sensor  27 . 
     The controller  40  executes a control program (or instructions) which allows the controller  40  to perform control operations. The controller  40  includes a processor which loads at least a part of the control program stored in a non-volatile memory to a volatile memory and executes the loaded control program. The processor may be, for example, a central processing unit (CPU), an application processor (AP), a microprocessor, etc. The processor may be a system-on-chip (SoC) which is mounted on a printed circuit board (PCB) provided in the robot cleaner  1 . 
     The sensor unit  20  may include the sensor position changer  24 ,  64  to change the position of the main sensor. The sensor unit  20  may include a stopper  248 ,  642  which restricts the main sensor  21  at the sensing position from descending by the obstacle other than sensor position changer  24 ,  64 . 
     The sensor unit  20  may include the auxiliary sensor  27 ,  67  to sense whether the main sensor  21  passes the limit position or whether the sensor unit  20  bumps into the obstacle with the main sensor  21  being at the sensing position. 
     The sensor unit  20  may include a position restoration guide  28  and/or a position restoration member  68  to allow a sensor holder  22 ,  62  holding the main sensor  21  at the sensing position to move horizontally and restore from bumping into the obstacle. 
     The sensor unit  20  may include a tension bar  2249  coupling the sensor holder  22 ,  62  with a holder cap  23 ,  63  to prevent a user&#39;s finger from being caught by the holder cap  23 ,  63  being lowered. 
       FIG.  7    is a perspective view of the sensor unit according to an embodiment.  FIG.  8    is an upper exploded view of the sensor unit.  FIG.  9    is a lower exploded view of the sensor unit.  FIG.  10    is a sectional view of the sensor unit according to a A-A line of  FIG.  7   . 
     Referring to  FIGS.  7  through  10   , the sensor unit  20  includes the main sensor  21 , the sensor holder  22 , the holder cap  23 , the sensor position changer  24 , a sensor movement guide  25  and a sensor mounting unit  26 . 
     The main sensor  21  obtains the circumstances information regarding the obstacle which represents the position of the obstacle or the distance to the obstacle by emitting light in all direction and receiving the light reflected from the obstacle. The obtained circumstances information regarding the obstacle is applied to an operation of the robot cleaner  1 . 
     The main sensor  21  includes a case  212  in a cylindrical shape, a sensor provided in the case  212 , a cable  214  connected to the sensor, drawn out of the case  212  and transmitting and receiving a signal, and holder coupling protrusions  217  provided on a surface of the case  212 . 
     The sensor holder  22  includes a lower sensor holder  222  and an upper sensor holder  224 . The lower sensor holder  222  and the upper sensor holder  224  are coupled with each other to accommodate the main sensor  21 . The lower sensor holder  222  and the upper sensor holder  224  accommodating the main sensor  21  are moved by the sensor position changer  24  between the settled position and the sensing position. 
     The lower sensor holder  222  includes a sensor lower portion receiver  2222  having a cylindrical shape to receive a lower portion of the main sensor  21 . The sensor lower portion receiver  2222  includes hinge pin coupling portions  2225  on a bottom of the lower sensor holder  222  where second hinge pins  2468  of the sensor position changer  24  shown in  FIG.  13    are rotatably inserted into the hinge pin coupling portions  2225 . 
     The sensor lower portion receiver  2222  includes lower coupling holes  2227  in  FIG.  9    ( 2327  in  FIG.  8   ) coupled to the holder coupling protrusions  217  of the main sensor  21  and a cable outlet portion  2228  cut to withdraw the cable  222  of the main sensor  21  out of the sensor lower portion receiver  2222 . 
     The upper sensor holder  224  includes a sensor upper portion receiver  2242  having a cylindrical shape to receive an upper portion of the main sensor  21  and a terminal pushing portion  2246  protruding from a surface of the sensor upper portion receiver  2242 , extending radially and bending upwards. 
     The sensor upper portion receiver  2242  includes a sensor opening  2244  provided radially through which light emitted by the main sensor  21  and light reflected from the obstacle pass, and upper coupling holes  2247  in  FIG.  8    ( 2243  in  FIG.  9   ) coupled to the holder coupling protrusions  217  of the main sensor  21 . The holder coupling protrusions  217  of the main sensor  21  is inserted into the upper coupling holes  2247  in  FIG.  8    ( 2243  in  FIG.  9   ) through the lower coupling holes  2227  in  FIG.  9    ( 2327  in  FIG.  8   ) of the lower sensor holder  222 . The sensor upper portion receiver  2242  has a diameter which is wider than that of the sensor lower portion receiver  2222  to accommodate the sensor lower portion receiver  2222 . Also, an inner surface of the sensor upper portion receiver  2242  is apart from an outer surface of the sensor lower portion receiver  2222  by a gap. Accordingly, the sensor upper portion receiver  2242  has a space to move horizontally within the gap against the sensor lower portion receiver  2222  when the sensor unit  20  bumps into the obstacle while moving. 
     The upper sensor holder  224  includes a cap supporter  2248  in a plate shape to support the holder cap  23  over the upper sensor holder  224 . The cap supporter  2248  includes, for example, five tension bars  2249  spirally extending from a center of the cap supporter  2248 . One ends of the tension bars  2249  at the center are integrated and other ends of the tension bars  2249  are acted as free ends  2250 . The free ends  2250  of the tension bars  2249  are joined with joint protrusions  232  provided on an inner side of the holder cap  23 . The free ends  2250  of the tension bars  2249  may be joined with the joint protrusions  232  in a manner of a glue, heat fusion, etc. Alternatively, the tension bars  2249  may be manufactured separately from the cap supporter  2248  and then be coupled to the cap supporter  2248 . Also, the tension bars  2249  may be provided on the holder cap  23  and the joint protrusions  232  on the cap supporter  2248 . 
     The holder cap  23  covers an upper portion of the sensor holder  22 . The sensor position changer  24  allows the sensor holder  22  to move among the settled position, the limit position and the sensing position. At the settled position, the sensor unit  20  is inside the cleaner body  10 . At the limit position, the terminal pushing portion  2246  of the sensor holder  22  corresponds to the pushing switch  276  of the sensor mounting unit  26 . At the sensing position, the sensor holder  22  protrudes out of the cleaner body  10 . 
     The sensor position changer  24  includes a base  242 , a motor  244  supported by the base  242 , and a link unit  246  coupled to an axis of the motor  244 . 
     The base  242  includes a pair of guide supporters  2422  provided apart from each other, a connector  2424  connecting the guide supporters  2422 , and an axis supporter  2426  supporting the motor  244  to rotate. 
     The sensor movement guide  25  guides the main sensor  21  to stably ascend and descend. The sensor movement guide  25  includes a pair of guide columns  252  extending upwards from the guide supporters  2422 . Meanwhile, the lower sensor holder  222  further includes a pair of guide pipes  254  extending downwards from a bottom of the lower sensor holder  222  to correspond to the pair of guide columns  252 . The sensor movement guide  25  includes springs  256  fitting around the guide columns  252  to elastically float the sensor holder  22 . Alternatively, the guide columns  252  may be provided on the bottom of the lower sensor holder  222  and the guide pipes  254  on the guide supporter  2422 . 
     The sensor mounting unit  26  includes a sensor case  262  which is hollow inside and an auxiliary sensor mounting portion  264  in which the auxiliary sensor  27  is mounted. The sensor case  262  accommodates and supports the sensor holder  22  holding the main sensor  21  and the sensor position changer  24  coupled to the sensor holder  22 . The stopper  248  shown in  FIG.  14    associated with the sensor position changer  24  is provided in the sensor case  262 . In the auxiliary sensor mounting portion  264 , for example, there are a pair of auxiliary sensors  27  provided opposite to each other in an angle and the pushing switch  276  mounted between the pair of auxiliary sensors  27 . 
       FIG.  11    illustrates the sensor holder protruding at the sensing position with a user&#39;s finger caught between the holder cap and the cleaner body.  FIG.  12    illustrates a junction feature of the sensor holder and the holder cap. 
     Referring to  FIG.  11   , the junction feature of the sensor holder  22  and the holder cap  23  helps minimize happening of a situation where a user&#39;s finger is caught between the holder cap  23  and the cleaner body  10  when the sensor holder  22  descends from the sensing position to the settled position. 
     Referring to  FIG.  12   , the cap supporter  2248  includes, for example, the five tension bars  2249  spirally extending from the center of the cap supporter  2248 . The free ends  2250  of tension bars  2249  joined with the junction protrusion  232  of the holder cap  23  has elasticity to be raised upwards easily. Accordingly, if a user&#39;s finger is caught between the holder cap  23  and the cleaner body  10 , it is possible for the finger to be easily taken out of the holder cap  23  as the free ends  2250  of tension bars  2249  is raised upwards from the cap supporter  2248 . 
       FIG.  13    is a perspective view of the sensor position changer. Referring to  FIG.  13   , the sensor position changer  24  includes the motor  244  and the link unit  246  coupled to the axis of the motor  244 . The motor  244  rotates clockwise or counterclockwise. The motor  244  includes a rotation axis  2442 , and a rotating member  2444  provided on the rotation axis  2442  and supporting the link unit  246 . 
     The link unit  246  includes a first link member  2462  and a second link member  2464  which are rotatably coupled with each other. The first link member  2462  includes a pair of first link bars  2462 - 1 ,  2462 - 2 , one ends of which are fixed on a surface of the rotating member  2444  and extend radially. Accordingly, the first link member  2462  rotates together with rotation of the rotating member  2444 . The other ends of the first link bars  2462 - 1 ,  2462 - 2  are provided with first hinge pins  2466  extending parallel with the rotation axis  2442 . 
     The second link member  2464  includes a pair of second link bars  2464 - 1 ,  2464 - 2  which are apart from each other. The second link bars  2464 - 1 ,  2464 - 2  are coupled with a coupling bar  2465 . The second link bars  2464 - 1 ,  2464 - 2  includes at each of one ends of the second link bars  2464 - 1 ,  2464 - 2  hinge pin coupling portions  2463  coupled with the first hinge pins  2466 . The other ends of the second link bars  2464 - 1 ,  2464 - 2  are provided with the second hinge pins  2468 . 
     That is, one end of the second link member  2464  is rotatably coupled with the first link member  2462  via the first hinge pins  2466 , while the other end of the second link member  2464  are rotatably coupled with the hinge pin coupling portion  2225  of the sensor holder  22  shown in  FIG.  9    via the second hinge pins  2468 . The second link member  2464  rotates together with the first link member  2462 . An angle between the first link member  2462  and the second link member  2464  becomes larger or smaller while the first link member  2462  and the second link member  2464  are rotating. That is, a distance between the rotation axis  2442  of the motor  244  and the other end of the second link member  2464  becomes larger or smaller according to the rotation of the first link member  2462  and the second link member  2464 . Accordingly, the sensor holder  22  coupled with the second link member  2464  ascends or descends according to the rotation of the first link member  2462  and the second link member  2464 . 
       FIG.  14    illustrates the sensor holder which is at the settled position.  FIG.  15    illustrates the sensor holder which is at the sensing position. Referring to  FIG.  15   , the first link member  2462  and the second link member  2464  become erected by moving from the settled position to the sensing position according to the rotation of the motor  244  in a first direction. In contrast, referring to  FIG.  14   , the first link member  2462  and the second link member  2464  become folded by moving from the sensing position to the settled position according to the rotation of the motor  244  in a second direction opposite the first direction. 
     The stopper  248  restricts the sensor holder  22  holding the main sensor  21  at the sensing position from moving downwards to the settled position due to an external force caused by, for example, the obstacle. The stopper  248  includes a pair of link member supporters  2482  provided at an end of a rotation path of the link unit  246 . The link member supporters  2482  support the second link member  2464  upwards on lower portions of the second link member  2464  which is erected at the sensing position. Edges of the link member supporters  2482  are apart slightly from the lower portions of the second link member  2464  which is in a state moving close to the sensing position so that the edges of the link member supporters  2482  may not interrupt the rotation of the second link member  2464  due to a contact between the edges of the link member supporters  2482  and the lower portion of the second link member  2464 . 
     The link member supporters  2482  includes flat portions provided on tops of the link member supporters  2482  and extending perpendicularly to a direction in which the sensor holder  22  moves upwards or downwards. The one ends, that is, the lower portions of the second link member  2464  which is erected are positioned on the flat portions of the link member supporters  2482 . Accordingly, the second link member  2464  is restricted from moving downwards as blocked by the flat portions of the link member supporters  2482 . Therefore, even though an external force applies on the sensor holder  22  holding the main sensor  21  to be pushed, it is possible to restrict the sensor holder  22  from forcedly moving downwards. Meanwhile, the sensor holder  22  is allowed to move downwards according to the rotation of the link unit  246  in a normal operation. 
     The stopper  248  includes a link member receiver  2486  accommodating the first link member  2462  of the link unit  246  reaching the sensing position. The link member receiver  2486  has a space between the pair of the link member supporters  2482 . The stopper  248  further includes a wall  2484  restricting the first link member  2462  from overly rotating at the sensing position. The stopper  248  may be integrated in a single body with the base  242  and/or the sensor mounting unit  26 , or be separated from the base  242  and/or the sensor mounting unit  26  and then coupled to the base  242  and/or the sensor mounting unit  26 . 
       FIG.  16    illustrates the auxiliary sensor.  FIG.  17    illustrates a perspective view of the terminal pushing portion.  FIG.  18    is a plane view illustrating arrangement of the auxiliary sensors.  FIG.  19    is a sectional view illustrating the auxiliary sensor and the terminal pushing portion with the sensor holder being at the settled position.  FIG.  20    is a sectional view illustrating the auxiliary sensor and the terminal pushing portion with the sensor holder being at the limit position.  FIG.  21    is a sectional view illustrating the auxiliary sensor and the terminal pushing portion with the sensor holder being at the sensing position.  FIG.  22    is a plane view illustrating the auxiliary sensors and the terminal pushing portion with the sensor holder being at the sensing position in a normal operation.  FIG.  23    is a plane view illustrating the auxiliary sensors and the terminal pushing portion with the sensor holder being at the sensing position in a situation bumping into an obstacle in a front direction.  FIG.  24    is a plane view illustrating the auxiliary sensors and the terminal pushing portion with the sensor holder being at the sensing position in another situation bumping into an obstacle in a right direction.  FIG.  25    is a plane view illustrating the auxiliary sensors and the terminal pushing portion with the sensor holder being at the sensing position in further another situation bumping into an obstacle in a left direction. 
     Referring to  FIG.  16   , the auxiliary sensor  27  has, for example, a hexahedral shape and includes on a side of the auxiliary sensor  27  a first terminal  272  and a second terminal  274 . The first terminal  272  protrudes, for example, in a hemisphere shape from a surface of the auxiliary sensor  27 . The second terminal  274  has, for example, a plate shape with elasticity and is provided over the first terminal  272  in a state of not contacting the first terminal  272 . The auxiliary sensor  27  becomes in an on-state as the second terminal  274  is pressed by an external force to contact the first terminal  272 , while the auxiliary sensor  27  becomes in an off-state as the second terminal  274  is released by the external force to be away from the first terminal  272 . 
     Referring to  FIG.  17   , the terminal pushing portion  2246  includes an extension portion  2246 - 1  extending from a side of the sensor upper portion receiver  2242  shown in  FIG.  8    and extending upwards, a front pusher  2246 - 2  protruding from an inner surface of the extension portion  2246 - 1  towards the side of the sensor upper portion receiver  2242 , and a pair of side pushers  2246 - 3  protruding from both sides of the extension portion  2246 - 1 . The terminal pushing portion  2246  further includes a pushing switch accommodating portion  2246 - 4  for accommodating the pushing switch  276  shown in  FIG.  18    between the extension portion  2246 - 1  and the side of the sensor upper portion receiver  2242 . 
     The front pusher  2246 - 2  includes a pushing switch guide  2246 - 5  provided on a protruding side of the front pusher  2246 - 2  and having an inwardly curved shape which corresponds to a side of the pushing switch  276  facing the front pusher  2246 - 2 . The pushing switch guide  2246 - 5  guides the pushing switch  276  to allow the front pusher  2246 - 2  to push the pushing switch  276  when the terminal pushing portion  2246  reaches the limit position. 
     The front pusher  2246 - 2  pushes the second terminal  274  of the auxiliary sensor  27  by pushing the pushing switch  276  when the terminal pushing portion  2246  of the sensor holder  22  is moved upwards or downwards by the sensor position changer  24 . Also, the front pusher  2246 - 2  pushes the second terminal  274  of the auxiliary sensor  27  by pushing the pushing switch  276  when the terminal pushing portion  2246  at the sensing position is horizontally moved by bumping into the obstacle. 
     The side pusher  2246 - 3  turns the auxiliary sensor  27  on by pushing the second terminal  274  when the terminal pushing portion  2246  at the sensing position is moved, for example, in a left or right direction by bumping into the obstacle. 
     Referring to  FIG.  18   , the pushing switch  276  is provided between the pair of the auxiliary sensors  27  opposite to each other in an angle in the auxiliary sensor mounting portion  264 . The second terminal  274  is provided between the pushing switch  276  and a body of the auxiliary sensor  27 . 
     The pushing switch  276  has a triangular shape of which two sides face the second terminals  274  of the pair of the auxiliary sensors  27 , respectively. The pushing switch  276  has a lengthwise hole  2762 . A pin  2764  is provided within the lengthwise hole  2762  to be movable in a lengthwise direction. An end of the pin  2764  is fixed to the auxiliary sensor mounting portion  264 . The pushing switch  276  is allowed to move in the lengthwise direction within a range of the lengthwise hole  2762  as the pin  2764  is movable within the lengthwise hole  2762  while the terminal pushing portion  2246  moves upwards or downwards pushing the pushing switch  276  in the lengthwise direction. 
     Referring to  FIG.  19   , when the terminal pushing portion  2246  of the sensor holder  22  is at the settled position, the terminal pushing portion  2246  is apart from the pushing switch  276  at a different height, and the front pusher  2246 - 2  does not push the pushing switch  276  in the lengthwise direction of the lengthwise hole  2762 . Accordingly, the pair of the auxiliary sensors  27  are all off because the second terminals  274  do not contact the first terminals  272 . 
     Referring to  FIG.  20   , when the terminal pushing portion  2246  of the sensor holder  22  is at the limit position by moving upwards, the terminal pushing portion  2246  contacts the pushing switch  276  at a similar height, and the front pusher  2246 - 2  pushes the pushing switch  276  in the lengthwise direction of the lengthwise hole  2762 . Accordingly, the pair of the auxiliary sensors  27  are all on because the second terminals  274  contact the first terminals  272 . 
     Referring to  FIG.  21   , when the terminal pushing portion  2246  of the sensor holder  22  is at the sensing position by moving upwards farther from the limit position, the terminal pushing portion  2246  is apart from the pushing switch  276  at another different height. That is, the pushing switch  276  is away from the front pusher  2246 - 2  and restores to an initial position shown in  FIG.  19   . In this state, the front pusher  2246 - 2  does not push the pushing switch  276  in the lengthwise direction of the lengthwise hole  2762 . Accordingly, the pair of the auxiliary sensors  27  are all off because the second terminals  274  do not contact the first terminals  272 . 
     Referring to  FIG.  22   , when the terminal pushing portion  2246  of the sensor holder  22  is at the sensing position in a normal operation, the front pusher  2246 - 2  does not only push the pushing switch  276  but also the side pushers  2246 - 3  provided on both sides do not push the second terminals  274  of the auxiliary sensors  27 . Accordingly, the main sensor  21  identifies that the sensor unit  20  does not bump into the obstacle because all of the second terminals  274  do not contact the first terminals  272  with the auxiliary sensors  27  being in an off-state. 
     Referring to  FIG.  23   , when the terminal pushing portion  2246  of the sensor holder  22  is at the sensing position with the sensor unit  20  happening to bump into the obstacle in a front direction, the terminal pushing portion  2246  moves backwards and pushes the pushing switch  276 . Accordingly, the main sensor  21  identifies that there is the obstacle in the front direction because all of the second terminals  274  contact the first terminals  272  with the auxiliary sensors  27  being in an on-state. 
     Referring to  FIG.  24   , when the terminal pushing portion  2246  of the sensor holder  22  is at the sensing position with the sensor unit  20  bumping into the obstacle in a right direction, the terminal pushing portion  2246  moves to the left and one of the side pushers  2246 - 3  pushes the second terminal  274  of the auxiliary sensor  27  provided on the left. Accordingly, the main sensor  21  identifies that there is the obstacle in the right direction because the second terminal  274  provided on the left contact the first terminal  272  with the auxiliary sensor  27  being in the on-state. 
     On the other hand, referring to  FIG.  24   , when the terminal pushing portion  2246  of the sensor holder  22  is at the sensing position with the sensor unit  20  bumping into the obstacle in a left direction, the terminal pushing portion  2246  moves to the right and the other of the side pushers  2246 - 3  pushes the second terminal  274  of the auxiliary sensor  27  provided on the right. Accordingly, the main sensor  21  identifies that there is the obstacle in the left direction because the second terminal  274  provided on the right contact the first terminal  272  with the auxiliary sensor  27  being in the on-state. 
       FIG.  26    illustrates a position restoration guide provided in the sensor unit.  FIG.  27    is a perspective view of a first guide.  FIG.  28    is a sectional view of the first guide according to a B-B line shown in  FIG.  27   .  FIG.  29    is a sectional view of the first guide  282  according to a C-C line shown in  FIG.  27   .  FIG.  30    is a perspectively sectional view of the upper sensor holder and the lower sensor holder illustrating the first guide and a second guide. 
     The position restoration guide  28  allows the upper sensor holder  224  to move in every direction against bumping into the obstacle and to restore to an initial position. Referring to  FIG.  26   , the position restoration guide  28  includes the first guide  282  and the second guide  284 . The first guide  282  is provided between the lower sensor holder  222  and the upper sensor holder  224 . The second guide  284  is provided opposite the first guide  282  between the lower sensor holder  222  and the upper sensor holder  224 . 
     Referring to  FIG.  27   , the first guide  282  includes a guide groove  2824  extending perpendicularly to a direction in which the robot cleaner  1  moves, a guide member  2821  having a spring receiver  2825 , a guide pin  2822  inserted in the guide groove  2824 , and a spring  2823  accommodated in the spring receiver  2825 . 
     Referring to  FIG.  28   , the spring  2823  maintains a gap between the lower sensor holder  222  and the upper sensor holder  224 . The spring receiver  2825  is provided at a position of the guide member  2821  above the guide groove  2824 . Referring to  FIG.  29   , the guide groove  2824  has a width corresponding to a thickness of the guide pin  2822  and a depth within which the guide pin  2822  is movable. That is, the guide pin  2822  guides the upper sensor holder  224  to move along a depth direction of the guide groove  2824  or pivot with an axis of the guide pin  2822 . 
     Referring to  FIG.  30   , the second guide  284  includes a convex portion  2842  provided on an outer surface of the lower sensor holder  222  and a concave portion  2844  provided on an inner surface of the upper sensor holder  224  having a shape that corresponds to the convex portion  2842 . The convex portion  2842  and the concave portion  2844  are engaged with each other. When the upper sensor holder  224  moves or pivots as the sensor unit  20  bumps into the obstacle, the upper sensor holder  224  is able to easily restore to the initial position due to elasticity of the spring  2823  and engagement between the convex portion  2842  and the concave portion  2844 . 
       FIG.  31    is a diagram illustrating an operation of the auxiliary sensors with the main sensor ascending or descending to the limit position.  FIG.  32    is a diagram illustrating an operation of the auxiliary sensors with the main sensor ascending from the limit position to the sensing position.  FIG.  33    is a diagram illustrating an operation of the auxiliary sensors with the main sensor at the sensing position moving horizontally. 
     The auxiliary sensors  27  become in the on-state or the off-state according to whether the first terminals  272  and the second terminals  274  contact with each other. Referring to  FIGS.  31  and  32   , the main sensor  21  ascends from the settled position P 1  to the limit position P 2  or descends from the sensing position P 3  to the limit position P 2 . Accordingly, the terminal pushing portion  2246  pushes the second terminals  274  towards the first terminals  272 , and the auxiliary sensors  27  become in the on-state because the first terminals  272  and the second terminals  274  contact with each other. In this state, the auxiliary sensors  27  identify whether the main sensor  21  reaches the sensing position P 3  or is away from the sensing position P 3 . 
     Referring to  FIG.  32   , the main sensor  21  ascends from the limit position P 2  farther to the sensing position P 3 . Accordingly, the second terminals  274  restore to the initial position, the auxiliary sensors  27  become in the off-state because the first terminals  272  and the second terminals  274  are apart from each other. In this state, the auxiliary sensors  27  are in a standby state to sense whether the sensor unit  20  bumps into the obstacle. 
     Referring to  FIG.  33   , the main sensor  21  at the sensing position P 3  moves horizontally with the sensor unit  20  bumping into the obstacle. Accordingly, one of the auxiliary sensors  27  becomes in the on-state because one of the first terminals  272  and one of the second terminals  274  contact with each other. In this state, the auxiliary sensor  27  in the on-state shown on the left in  FIG.  33    senses that the sensor unit  20  bumps into the obstacle and identifies that the obstacle exists at a position on the right in  FIG.  33   . In a similar manner, if the auxiliary sensor  27  on the right in  FIG.  33    would be in the on-state, the auxiliary sensor  27  might identify that the obstacle exists at a position on the left in  FIG.  33   . 
     When the main sensor  21  is at the settled position P 1 , the two auxiliary sensors  27  are all in the off-state. When the main sensor  21  is at the limit position P 2 , the two auxiliary sensors  27  are all in the on-state. When the main sensor  21  is at the sensing position P 3  without bumping into the obstacle, the two auxiliary sensors  27  are all in the off-state. On the other hand, when the main sensor  21  is at the sensing position P 3  bumping into the obstacle, the main sensor  21  moves horizontally and one of the two auxiliary sensors  27  is in the on-state, of which the situation is applied to the operation of the robot cleaner  1 . 
     Meanwhile, referring back to  FIGS.  31  and  32   , when the main sensor  21  is at the sensing position P 3 , the main sensor  21  may be moved from the sensing position P 3  to the limit position P 2  without the controller  40  controlling the sensor position changer  24 . For example, when the sensor unit  20  at the sensing position P 3  bumps into the obstacle, the main sensor  21  may be forcedly moved downwards to the limit position P 2  by an external force caused by the obstacle. In this state, the auxiliary sensors  27  turns from the off-state into the on-state. Then, the controller  40  may control the sensor position changer  24  to move the sensor holder  22  upwards so that the main sensor  21  is restored to the sensing position P 3 . Optionally, the controller  40  may also perform an alert operation, for example, notifying a user of bumping into the obstacle. 
       FIG.  34    is a diagram illustrating another example of operations of a first auxiliary sensor and second auxiliary sensors with the main sensor ascending or descending to the limit position.  FIG.  35    is a diagram illustrating another example of operations of the first auxiliary sensor and the second auxiliary sensors with the main sensor ascending from the limit position to the sensing position.  FIG.  36    is a diagram illustrating another example of operations of the first auxiliary sensor and the second auxiliary sensors with the main sensor at the sensing position moving horizontally. 
     The sensor unit  20  of this embodiment includes a single first auxiliary sensor  27  and a pair of second auxiliary sensors  29 . The first auxiliary sensor  27  and the second auxiliary sensors  29  are provided at different height from each other. The first auxiliary sensor  27  is provided below the second auxiliary sensors  29 . The first auxiliary sensor  27  becomes in the on-state or the off-state according to whether the first terminal  272  and the second terminal  274  contact with each other. The second auxiliary sensors  29  become in the on-state or the off-state according to whether third terminals  292  and fourth terminals  294  contact with each other. 
     Referring to  FIGS.  34  and  35   , the main sensor  21  ascends from the settled position P 1  to the limit position P 2  or descends from the sensing position P 3  to the limit position P 2 . Accordingly, the first auxiliary sensor  27  becomes in the on-state because the first terminal  272  and the second terminal  274  contact with each other. In this state, the first auxiliary sensor  27  identifies whether the main sensor  21  reaches the sensing position P 3  or is away from the sensing position P 3 . 
     Referring to  FIG.  35   , the main sensor  21  ascends from the limit position P 2  farther to the sensing position P 3 . Accordingly, the first auxiliary sensor  27  becomes in the off-state because the first terminal  272  and the second terminal  274  are apart from each other. In this state, the third terminals  292  and the fourth terminals  294  are apart from each other and the second auxiliary sensors  29  are in the standby state to sense whether the sensor unit  20  bumps into the obstacle. 
     Referring to  FIG.  36   , the main sensor  21  at the sensing position P 3  moves horizontally with the sensor unit  20  bumping into the obstacle. Accordingly, one of the second auxiliary sensors  29  becomes in the on-state because one of the third terminals  292  and one of the fourth terminals  294  contact with each other. In this state, the second auxiliary sensor  27  in the on-state shown on the right in  FIG.  36    senses that the sensor unit  20  bumps into the obstacle and identifies that the obstacle exists at a position on the left in  FIG.  36   . 
     When the main sensor  21  is at the settled position P 1 , the first auxiliary sensor  27  and the two second auxiliary sensors  29  are all in the off-state. When the main sensor  21  is at the limit position P 2 , the first auxiliary sensor  27  is in the on-state and the two second auxiliary sensors  29  are in the off-state. When the main sensor  21  is at the sensing position P 3  without bumping into the obstacle, the first auxiliary sensor  27  and the two second auxiliary sensors  29  are all in the off-state. On the other hand, when the main sensor  21  is at the sensing position P 3  bumping into the obstacle, the main sensor  21  moves horizontally and one of the two second auxiliary sensors  29  is in the on-state, of which the situation is applied to the operation of the robot cleaner  1 . 
     Meanwhile, similarly to the embodiment illustrated in  FIGS.  31  through  33   , when the sensor unit  20  at the sensing position P 3  bumps into the obstacle without the controller  40  controlling the sensor position changer  24 , the main sensor  21  may be forcedly moved downwards to the limit position P 2 . In this state, the first auxiliary sensor  27  turns from the off-state into the on-state. Then, the controller  40  may control the sensor position changer  24  to move the sensor holder  22  upwards so that the main sensor  21  is restored to the sensing position P 3 . Alternatively, before the first auxiliary sensor  27  turns into the on-state, the two second auxiliary sensors  29  may turn all from the off-state into the on-state without the controller  40  controlling the sensor position changer  24 . In this state, the controller  40  may first perform an alert operation, for example, notifying a user of bumping into the obstacle. And then, if the first auxiliary sensor  27  turns into the on-state, the controller  40  may control the sensor position changer  24  to move the sensor holder  22  upwards. 
       FIG.  37    is a diagram illustrating further another example of operations of a first auxiliary sensor and second auxiliary sensors with the main sensor ascending to the limit position and the sensing position.  FIG.  38    is a diagram illustrating further another example of operations of the first auxiliary sensor and the second auxiliary sensors with the main sensor at the sensing position moving horizontally. 
     The sensor unit  20  of this embodiment includes a single first auxiliary sensor  27  and a pair of second auxiliary sensors  29 . The first auxiliary sensor  27  and the second auxiliary sensors  29  are provided at different height from each other. In this embodiment, the first auxiliary sensor  27  is provided above the second auxiliary sensors  29 . Also, a pair of terminal pushing portions  2246  are provided at different heights corresponding to the first auxiliary sensor  27  and the second auxiliary sensors  29 , respectively. 
     The first auxiliary sensor  27  becomes in the on-state or the off-state according to whether the first terminal  272  and the second terminal  274  contact with each other. The second auxiliary sensors  29  become in the on-state or the off-state according to whether third terminals  292  and fourth terminals  294  contact with each other. 
     Referring to  FIG.  37   , the main sensor  21  ascends from the settled position P 1  to the limit position P 2  and the sensing position P 3 . Accordingly, the first auxiliary sensor  27  becomes in the on-state because the first terminal  272  and the second terminal  274  contact with each other, whereas the second auxiliary sensors  29  are in the off-state because the third terminals  292  and the fourth terminals  294  are apart from each other. Then, when the main sensor  21  descends, the first auxiliary sensor  27  becomes in the off-state. That is, the first auxiliary sensor  27  in the on-state identifies that the main sensor  21  reaches the sensing position P 3 , and in the off-state identifies that the main sensor  21  is away from the sensing position P 3 . When the main sensor  21  is at the limit position P 2  and the sensing position P 3 , the second auxiliary sensors  29  are in the off-state and the standby state to sense whether the sensor unit  20  bumps into the obstacle. 
     Referring to  FIG.  38   , the main sensor  21  at the sensing position P 3  moves horizontally with the sensor unit  20  bumping into the obstacle. Accordingly, one of the second auxiliary sensors  29  becomes in the on-state because one of the third terminals  292  and one of the fourth terminals  294  contact with each other. In this state, the second auxiliary sensor  27  in the on-state shown on the right in  FIG.  38    senses that the sensor unit  20  bumps into the obstacle and identifies that the obstacle exists at a position on the left in  FIG.  38   . 
     When the main sensor  21  is at the settled position P 1 , the first auxiliary sensor  27  and the two second auxiliary sensors  29  are all in the off-state. When the main sensor  21  is at the limit position P 2  and the sensing position P 3  without bumping into the obstacle, the first auxiliary sensor  27  is in the on-state and the two second auxiliary sensors  29  are in the off-state. When the main sensor  21  is at the sensing position P 3  bumping into the obstacle, the main sensor  21  moves horizontally and one of the two second auxiliary sensors  29  is in the on-state, of which the situation is applied to the operation of the robot cleaner  1 . 
     Meanwhile, similarly to the embodiments illustrated in  FIGS.  31  through  36   , when the sensor unit  20  at the sensing position P 3  bumps into the obstacle without the controller  40  controlling the sensor position changer  24 , the main sensor  21  may be forcedly moved downwards and away from the sensing position P 3 . In this state, the first auxiliary sensor  27  turns from the on-state into the off-state. Then, the controller  40  may control the sensor position changer  24  to move the sensor holder  22  upwards so that the main sensor  21  is restored to the sensing position P 3 . Optionally, the controller  40  may also perform an alert operation, for example, notifying a user of bumping into the obstacle. 
     Here, the auxiliary sensor  27  may be of a non-contact type because the auxiliary sensor  27  continues being in the on-state at the limit position P 2 , which affects a life span of the auxiliary sensor  27  or hinders the movement of the main sensor  21 . 
       FIG.  39    is a perspective view of another example of the robot cleaner.  FIG.  40    is a perspective view illustrating a bottom of the robot cleaner shown in  FIG.  39   .  FIG.  41    is an exploded view of the robot cleaner shown in  FIG.  39   . 
     Referring to  FIGS.  39  through  41   , the robot cleaner  2  includes a cleaner body  50  which moves in an area and cleans the area, and a sensor unit  60 . 
     The cleaner body  50  includes a dust suction body  510  which generates suction power and suctions dust in the area, and an upper cover  520  which covers an upper portion of the dust suction body  510 . 
     The dust suction body  510  includes wheels  512  to move in the area, a dust collector  514  to collect the dust from the area, and a sensor housing  516  to accommodate the sensor unit  60 . The dust suction body  510  may further include a motor which generates the suction power to suction the dust in the area. 
     The wheels  512  include a pair of wheels with a plurality of sawtooth in order not to slip on the area. The wheels  512  may further include at least one auxiliary wheel for stable movement of the cleaner body  50 . 
     The dust collector  514  picks up by the suction power the dust in the area into the cleaner body  50 . The dust collector  514  may include a filter to filter the suctioned dust. 
     The sensor housing  516  includes a sensor mounting unit  5162  accommodating the sensor unit  60  and an auxiliary sensor mounting portion  5164  in which auxiliary sensors  67  is mounted. 
     The sensor unit  60  is mounted in the sensor housing  516 . The sensor unit  60  senses the position of the obstacle or the distance to the obstacle, and whether the position of the sensor unit  60  changes. 
       FIG.  42    is a perspective view of the sensor unit.  FIG.  43    is an upper exploded view of the sensor unit.  FIG.  44    is a lower exploded view of the sensor unit. 
     Referring to  FIGS.  42  through  43   , the sensor unit  60  includes a main sensor  61 , a sensor holder  62 , a holder cap  63 , a sensor position changer  64 , the auxiliary sensors  67 , a position restoration member  68 , and a coupling member  69 . 
     The main sensor  61  has a cylindrical shape and obtains the circumstances information regarding the obstacle which represents the position of the obstacle or the distance to the obstacle by emitting light and receiving the light reflected from the obstacle. The obtained circumstances information regarding the obstacle is applied to an operation of the robot cleaner  2 . 
     The sensor holder  62  includes a lower sensor holder  622  and an upper sensor holder  624 . The lower sensor holder  622  and the upper sensor holder  624  are coupled with each other to accommodate the main sensor  61 . The lower sensor holder  622  and the upper sensor holder  624  accommodating the main sensor  61  are moved by the sensor position changer  64  between the settled position and the sensing position. 
     The lower sensor holder  622  accommodates a sensor lower portion receiver  6222  having a cylindrical shape to receive a lower portion of the main sensor  61 . 
     The sensor lower portion receiver  6222  includes a pair of terminal pushing portions  6224  opposite to each other on outer sides of the sensor lower portion receiver  6222  and a restoration member receiver  6226  having an opening of a clover shape on a bottom of the sensor lower portion receiver  6222 . The terminal pushing portions  6224  protrude from the outer sides of the sensor lower portion receiver  6222 , extend upwards, and protrude outwards at ends of the terminal pushing portions  6224 . 
     The upper sensor holder  624  includes a sensor upper portion receiver  6242  having a cylindrical shape to receive an upper portion of the main sensor  61 . 
     The sensor upper portion receiver  6242  includes a sensor opening  6244  provided radially through which light emitted by the main sensor  61  and light reflected from the obstacle pass, and a cap supporter  6248  in a plate shape to support the holder cap  63  over the upper sensor holder  624 . 
     The cap supporter  6248  includes, for example, five tension bars  6249  spirally extending from a center of the cap supporter  6248 . The tension bars  6249  may be manufactured by cutting a top of the cap supporter  6248  in a depth direction. One ends of the tension bars  6249  at a center of the top of the cap supporter  6248  are integrated and other ends of the tension bars  6249  are acted as free ends  6250 . The free ends  6250  of the tension bars  6249  are joined with joint protrusions  632  provided on an inner side of the holder cap  63 . 
     The holder cap  63  covers an upper portion of the sensor holder  62 . The holder cap  63  includes the joint protrusions  632  provided on the inner side of the holder cap  63 . The free ends  6250  of the tension bars  6249  may be joined with the joint protrusions  632  in a manner of a glue, heat fusion, etc. 
     The sensor position changer  64  allows the sensor holder  62  to move among the settled position, the limit position and the sensing position. The sensor position changer  64  includes a motor  642 , a pinion  644  coupled with an axis of the motor  642 , a rack  646  geared with the pinion  644 , and a rack pinion mounting unit  648 . 
     The motor  642  rotates clockwise or counterclockwise. 
     The pinion  644  is coupled with the axis of the motor  642  and includes a circular gear with a plurality of tooth around a side of the circular gear. 
     The rack  646  includes a linear gear  6462  having a plurality of tooth geared with the circular gear of the pinion  644 . The rack  646  also includes a rack flange  6464  with a clover shape to support the sensor holder  62 . 
     As the pinion  644  rotates clockwise or counterclockwise according to the rotation of the motor  642  with the rack  646  reciprocally moving upwards or downwards, the main sensor  61  is allowed to move reciprocally between the settled position and the sensing position. 
     A pair of the auxiliary sensors  67  are provided on a path along which the pair of terminal pushing portions  6224  move. The auxiliary sensors  67  are mounted in the auxiliary sensor mounting portion  5164  shown in  FIG.  41   . The auxiliary sensors  67  have a similar configuration of the auxiliary sensors  27  illustrated in  FIG.  17    and include first terminals  672  and second terminals  674 . The auxiliary sensors  67  become in the on-state when the main sensor  61  is at the limit position while moved upwards or downwards by the sensor position changer  64 . The auxiliary sensors  67  in the on-state sense the position of the obstacle when the sensor unit  60  bumps into the obstacle. 
     The position restoration member  68  is provided within the opening of the restoration member receiver  6226  of the lower sensor holder  622 . Also, the position restoration member  68  is provided between the rack flange  6464  of the sensor position changer  64  and the coupling member  69 . The position restoration member  68  has elasticity to allow the lower sensor holder  622  to move horizontally when bumping into the obstacle and then to restore an initial position. 
     The coupling member  69  has a clover shape fixing to the rack flange  6464  with the restoration member receiver  6226  being interposed therebetween and the position restoration member  68  being provided therein. Accordingly, the lower sensor holder  622  ascends or descends together with the rack  646 . 
       FIG.  45    is a sectional view illustrating the terminal pushing portion and the auxiliary sensor. Referring to  FIG.  45   , the terminal pushing portion  6224  includes an extension portion  6224 - 1  protruding from the outer side of the sensor lower portion receiver  6222  and extending upwards, and a pushing protrusion  6224 - 2  protruding outwards at an end of the extension portion  6224 - 1 . The pushing protrusion  6224 - 2  pushes the second terminal  674  of the auxiliary sensor  67  to contact the first terminal  672  when the terminal pushing portion  6224  ascends or descends to the limit position. Also, the extension portion  6224 - 1  pushes the second terminal  674  of the auxiliary sensor  67  to contact the first terminal  672  when the terminal pushing portion  6224  is at the sensing position horizontally bumping into the obstacle. 
       FIG.  46    is a perspective view of the sensor position changer.  FIG.  47    is an exploded view of the sensor position changer. Referring to  FIGS.  46  and  47   , the motor  642  includes a rotation axis  6422 . The pinion  644  includes a circular gear  6442  with a plurality of tooth around a side of the circular gear  6442 , and a first axis coupling portion  6444  fixing to the rotation axis  6422  of the motor  642  at a center of the pinion  644 . 
     The rack pinion mounting unit  648  accommodates the motor  642 , the rack  646  and the pinion  644 . The rack pinion mounting unit  648  includes a first case  6482  supporting the motor  642 , and a second case  6484  coupled with the first case  6482  proving a space to accommodate the rack  646  and the pinion  644 . The first case  6482  includes a hole  6483  through which the rotation axis  6422  of the motor  642  passes. The second case  6484  includes a second axis coupling portion  6485  supporting an axis of the pinion  644  rotatable. 
       FIG.  48    is a sectional view of the sensor position changer and the main sensor at the settled position.  FIG.  49    is a sectional view of the sensor position changer and the main sensor moving upwards from the settled position to the sensing position. Referring to  FIGS.  48  and  49   , the sensor unit  60  further includes a stopper  70  to restrict the main sensor  61  at the sensing position from moving downwards by an external force. The stopper  70  includes a locking member  72  and a driver  74  allows the locking member to move between a lock state and a unlock state. The stopper  70  may be, for example, a solenoid valve. The rack pinion mounting unit  648  includes a hole  6487  through which the locking member  72  passes. 
     Referring to  FIG.  48   , at the settled position, because the locking member  72  is in the unlock state and does not protrude through the hole  6487 , the rack  646  is not prevented from moving. On the other hand, referring to  FIG.  49   , at the sensing position, the locking member  72  is in the lock state protruding through the hole  6487  and supporting upwards on a lower end of the rack  646 . Accordingly, the main sensor  61  is restricted from moving downwards due to an external force. Optionally, the controller  40  may control the stopper  70  to operate in the unlock state with the locking member  72  restoring and the pinion  644  and the rack  646  to allow the main sensor  61  to move downwards to the settled position. The stopper  70  may be in the lock state when the main sensor  61  is at the sensing position, for example, during cleaning, and be in the unlock state before the main sensor  61  moves to the settled position, for example, when the cleaning ends to be in the standby state for charging in the charging station. 
       FIG.  50    is a side view of the terminal pushing portions and the auxiliary sensors with the main sensor being at the settled position.  FIG.  51    is a side view of the terminal pushing portions and the auxiliary sensors with the main sensor being at the limit position.  FIG.  52    is a side view of the terminal pushing portions and the auxiliary sensors with the main sensor being at the sensing position. 
     Referring to  FIG.  50   , when the main sensor  61  is at the settled position, the pair of auxiliary sensors  67  are all in the off-state apart from the terminal pushing portions  6224  at different heights. 
     Referring to  FIG.  51   , when the main sensor  61  is at the limit position moving upwards, the pair of auxiliary sensors  67  are all in the on-state with the second terminals  674  being pushed by the pushing protrusions  6224 - 2  of the terminal pushing portions  6224 . In this state, the pair of auxiliary sensors  67  identify whether the main sensor  61  reaches the sensing position or is away from the sensing position. 
     Referring to  FIG.  52   , when the main sensor  61  is at the sensing position moving farther upwards, the pair of auxiliary sensors  67  are all in the off-state with the second terminals  674  not being pushed by the pushing protrusions  6224 - 2  of the terminal pushing portions  6224 . In this state, the pair of auxiliary sensors  67  are in the standby state to sense whether the sensor unit  60  bumps into the obstacle. 
       FIG.  53    is a plane view of the auxiliary sensors and the main sensor bumping into an obstacle in a direction.  FIG.  54    is a plane view of the auxiliary sensors and the main sensor bumping into an obstacle in an opposite direction. Referring to  FIG.  53   , for example, when the sensor unit  60  bumps into the obstacle in a range of 180 degrees from south-east to north-west in a counterclockwise direction, the main sensor  61  moves in an opposite direction shown as arrows. Accordingly, a first auxiliary sensor  67 - 1  becomes in the on-state because a first extension portion  6224 - 1  pushes the second terminal  674 - 1  of the first extension portion  6224 - 1 . In this way, the first auxiliary sensor  67 - 1  identifies circumstances of the obstacle as positioned in the range of 180 degrees from south-east to north-west in the counterclockwise direction. 
     Referring to  FIG.  54   , for example, when the sensor unit  60  bumps into the obstacle in a range of 180 degrees from south-east to north-west in a clockwise direction, the main sensor  61  moves in another opposite direction shown as arrows. Accordingly, a second auxiliary sensor  67 - 2  becomes in the on-state because a second extension portion  6224 - 2  pushes the second terminal  674 - 1  of the second extension portion  6224 - 2 . In this way, the second auxiliary sensor  67 - 2  identifies circumstances of the obstacle as positioned in the range of 180 degrees from south-east to north-west in the clockwise direction. Therefore, the first auxiliary sensor  67 - 1  and the second auxiliary sensor  67 - 2  can identify circumstances of the obstacle in a range of 360 degrees around the main sensor  61 . 
       FIG.  55    illustrates the position restoration member and the restoration member receiver of the lower sensor holder  620 . Referring to  FIG.  55   , the position restoration member  68  includes a ring  682 , supporting protrusions  684  provided around a side of the ring  682 , a hole portion  686  ( 680  in  FIG.  57   ) provided at a center of the position restoration member  68 , and a plurality of elastic portions  688  connected between the ring  682  and the hole portion  686 . The elastic portions  688  have a spiral shape for effective deformation. The restoration member receiver  6226  of the lower sensor holder  622  includes a positioning portion  6226 - 1  having a circular shaped opening into which the position restoration member  68  is inserted. Inner sides of the positioning portion  6226 - 1  contact the side of ring  682  positioning the position restoration member  68 . The restoration member receiver  6226  further includes grooves  6226 - 2  provide on the inner sides of the positioning portion  6226 - 1  engaged with the supporting protrusions  684  of the position restoration member  68  inserted in the positioning portion  6226 - 1 . 
       FIG.  56    is an exploded view illustrating the sensor holder and the sensor position changer.  FIG.  57    illustrates the position restoration member before bumping into an obstacle.  FIG.  58    illustrates the position restoration member while bumping into an obstacle. 
     Referring to  FIG.  56   , the coupling member  69  includes a column  692  passing through the hole portion  688  of the position restoration member  68  with the rack flange  6464  of the rack  646  coupled with the coupling member  69 . Accordingly, the coupling member  69  and the rack  646  have a common axis with the hole portion  688  of the position restoration member  68 . The lower sensor holder  622  is able to move in all horizontal direction due to the elasticity of the position restoration member  68  relatively to the common axis of the hole portion  688  of the position restoration member  68 , the coupling member  69  and the rack  646 . Also, the lower sensor holder  622  is able to restore to an initial position. 
     Referring to  FIG.  57   , the lower sensor holder  622  is in a state of being at the initial position when not bumping into the obstacle. At this time, the position restoration member  68  maintains an initial form. 
     Referring to  FIG.  58   , the lower sensor holder  622  is in another state of moving horizontally in a direction shown as an arrow when bumping into the obstacle. At this time, the position restoration member  68  is deformed from the initial form. When the state bumping into the obstacle is over, the position restoration member  68  restores the initial form. 
     According to the disclosure, it is possible for the robot cleaner to maintain a connectivity of data collected by a sensor and prevent loss of the data by restricting a sensor unit from moving downwards by an external force due to an obstacle. 
     Also, it is possible for the robot cleaner to identify whether a main sensor reaches a sensing position or is away from a sensing position. 
     Also, it is possible for the robot cleaner to sense that a sensor unit bumps into an obstacle and clearly identify circumstances of the obstacle. 
     Also, it is possible for the robot cleaner to allow a sensor unit to restore from being moved by an obstacle. 
     Also, it is possible for the robot cleaner to prevent a user&#39;s finger from being caught by a holder cap when a sensor unit bumps into an obstacle. 
     Although a few exemplary embodiments have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these exemplary embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.