Patent Publication Number: US-11396424-B2

Title: Handling robot

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 17/385,811 filed on Jul. 26, 2021, which is a continuation of U.S. patent application Ser. No. 15/931,496 filed on May 13, 2020, now patented as U.S. Pat. No. 11,104,514B2, which is a continuation of PCT/CN2018/104654 filed on Sep. 7, 2018, which in turn claims the priority benefits of Chinese Patent Applications No. 201711141498.3 and 201711135812.7, both filed on Nov. 14, 2017. The contents of the above identified applications are incorporated herein by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The present application relates to the field of intelligent warehousing technologies, and in particular, to a handling robot and a method for retrieving an inventory item based on the handling robot. 
     BACKGROUND 
     Intelligent warehousing is a link in the logistics process. The application of intelligent warehousing ensures the speed and accuracy of data input in all aspects of warehouse management of inventory items, thereby ensuring that an enterprise can grasp the real data of the inventory in a timely and accurate manner, and reasonably maintain and control inventory of the enterprise. It is also convenient to manage a batch, a shelf life, etc. of inventory items through scientific coding. Using a location management function of the SNHGES system, it is possible to grasp current location of all inventory items in time, which is conducive to improve an efficiency of warehouse management. 
     A handling robot plays an important role in intelligent warehousing. The handling robot replaces manual handling of the inventory items. However, in the process of implementing the present application, the inventor found that the quantity of the inventory items that can be loaded by an existing handling robot equipped with a shelf is too few and the efficient is low. 
     SUMMARY 
     To solve the above technical problems, embodiments of the present application provide a handling robot and a method for retrieving an inventory item based on the handling robot, which can load a large number of inventory items. 
     In order to solve the above technical problems, the embodiments of the present application provide the following technical solutions. 
     In a first aspect, there is provided a method for retrieving an inventory item based on a handling robot, where the handling robot includes a storage frame; a material handling device that is installed on the storage frame and includes a telescopic arm and a manipulator installed on telescopic arm; and the method for retrieving an inventory item includes: driving, by the telescopic arm, the manipulator to extend to a preset position of a warehouse shelf along a preset horizontal reference line; loading, by the manipulator that is remained on a horizontal plane where the reference line is located, an inventory item located at the preset position; driving, by the telescopic arm, the manipulator loaded with the inventory item to move to the storage frame along the reference line; unloading, by the manipulator that is remained on the horizontal plane where the reference line is located, the inventory item to the storage frame. 
     In some embodiments, the handling robot further includes: a lifting assembly installed between the storage frame and the material handling device; the method for retrieving an inventory item further includes: before the telescopic arm drives the manipulator to extend to the preset position of the warehouse shelf along the reference line, driving, by the lifting assembly, the material handling device to move in a vertical direction so that the manipulator horizontally faces to the preset position. 
     In some embodiments, the storage frame includes: a plurality of storage units distributed in the vertical direction; the method for retrieving an inventory item further includes: before the telescopic arm drives the manipulator loaded with the inventory item to move to the storage frame along the reference line, driving, by the lifting assembly, the material handling device to move in the vertical direction so that the material handling device horizontally faces to a corresponding storage unit. 
     In some embodiments, the handling robot further includes: a movable chassis equipped with the storage frame; the method for retrieving an inventory item further includes: before the lifting assembly drives the material handling device to move in the vertical direction so that the material handling device horizontally faces to the preset position, causing the movable chassis to move to a preset range in front of the warehouse shelf. 
     In some embodiments, the handling robot further includes: a detection device installed on the material handling device; the method for retrieving an inventory item further includes: before the telescopic arm drives the manipulator to extend to the preset position of the warehouse shelf along the reference line, and after the lifting assembly drives the telescopic arm to move in the vertical direction so that the material handling device horizontally faces to the preset position, detecting, by the detection device, position information of the material handling device relative to the inventory item, and adjusting, by the handling robot, a posture of fetching the inventory item according to the position information of the material handling device relative to the inventory item. 
     In some embodiments, the movable chassis can move along its travelling direction; the position information of the material handling device relative to the inventory item includes a first position offset between the inventory item and the reference line in the travelling direction; the adjusting, by the handling robot, a posture of fetching the inventory item according to the position information of the material handling device relative to the inventory item, includes: causing the movable chassis to move along the travelling direction according to the first position offset, so that the first position offset is smaller than a first error value. 
     In some embodiments, the position information of the material handling device relative to the inventory item includes a second position offset between the inventory item and the reference line in the vertical direction, the adjusting, by the handling robot, a posture of fetching the inventory item according to the position information of the material handling device relative to the inventory item, includes: driving, by the lifting assembly, the material handling device to move in the vertical direction according to the second position offset, so that the second position offset is smaller than a second error value. 
     In some embodiments, the position information of the material handling device relative to the inventory item includes a distance between the inventory item and the manipulator along the reference line; the adjusting, by the handling robot, a posture of fetching the inventory item according to the position information of the material handling device relative to the inventory item, includes: adjusting an extension amount of the telescopic arm along the reference line according to the distance, so that the extension amount is larger than the distance. 
     In some embodiments, the detection device includes: an image acquisition device; when the image acquisition device acquires image information of the inventory item, the detection device detects the position information of the material handling device relative to the inventory item. 
     In some embodiments, a surface of the inventory item facing the handling robot is attached with a two-dimensional code label; when the image acquisition device acquires the image information of the inventory item, information provided by the two-dimensional code label is collected, to obtain the position information of the material handling device relative to the inventory item. 
     In some embodiments, the material handling device further includes: a temporary storage unit, the temporary storage unit being provided with the telescopic arm and the detection device; the method for retrieving an inventory item further includes: before the telescopic arm drives the manipulator loaded with the inventory item to move to the storage frame along the reference line, driving, by the telescopic arm, the manipulator loaded with the inventory item to retract to the temporary storage unit along the reference line; unloading, by the manipulator that is remained on the horizontal plane where the reference line is located, the inventory item to the temporary storage unit; and loading, by the manipulator that is remained on the horizontal plane where the reference line is located, the inventory item located on the temporary storage unit. 
     In some embodiments, the material handling device further includes: a fork comprising the telescopic arm, the temporary storage unit, the detection device and the manipulator; a support bracket installed on the storage frame; a rotation assembly installed between the fork and the support bracket; the method for retrieving an inventory item further includes: after the manipulator that is remained on the horizontal plane where the reference line is located loads the inventory item located on the temporary storage unit, and before the telescopic arm drives the manipulator loaded with the inventory item to move to the storage frame along reference line, driving, by the rotation assembly, the telescopic arm to rotate around the vertical direction to a preset angle, so that the material handling device is oriented towards the storage frame. 
     In some embodiments, the position information of the material handling device relative to the inventory item includes: a deflection amount between the inventory item and the reference line in a horizontal direction; the adjusting, by the handling robot, a posture of fetching the inventory item according to the position information of the material handling device relative to the inventory item includes: driving, by the rotation assembly, the fork to rotate around the vertical direction according to the second position offset, so that the deflection amount is smaller than a third error value. 
     In some embodiments, the handling robot further includes: a deflection detection device connected between the fork and the support bracket; the driving, by the rotation assembly, the fork to rotate around the vertical direction includes: when the deflection detection device detects that the fork has not yet rotated to the preset angle, driving, by the rotation assembly, the fork to continue to rotate; when the deflection detection device detects that the fork has rotated over the preset angle, driving, by the rotation assembly, the fork to rotate in a reverse direction; and when the deflection detection device detects that the fork rotates to the preset angle, causing the rotation assembly to stop rotating. 
     In some embodiments, the deflection detection device includes a first sensor provided with a first detection range; a second sensor provided with a second detection range; when the first sensor detects the fork in the first detection range, and the second sensor does not detect the fork in the second detection range, the deflection detection device detects that the fork has not yet rotated to the preset angle; when the first sensor does not detect the fork in the first detection range, and the second sensor detects the fork in the second detection range, the deflection detection device detects that the fork has rotated over the preset angle; and when the first sensor detects the fork in the first detection range, and the second sensor detects the fork in the second detection range, the deflection detection device detects that the fork rotates to the preset angle. 
     In some embodiments, the inventory item includes a first inventory item and a second inventory item; the preset position includes a first preset position and a second preset position, and the first inventory item is located at the first preset position, the second inventory item is located at the second preset position; the storage frame includes a first storage unit and a second storage unit; when there is the second inventory item back behind the first inventory item, the method for retrieving an inventory item further includes: driving, by the telescopic arm, the manipulator to extend to the first preset position of the warehouse shelf along the reference line; loading, by the manipulator that is remained on the horizontal plane where the reference line is located, the first inventory item located at the first preset position; driving, by the telescopic arm, the manipulator loaded with the first inventory item to move to the first storage unit; unloading, by the manipulator that is remained on the horizontal plane where the reference line is located, the first inventory item to the first storage unit; driving, by the telescopic arm, the manipulator to move to the second preset position of the warehouse shelf along the reference line; loading, by the manipulator that is remained on the horizontal plane where the reference line is located, the second inventory item located at the second preset position; driving, by the telescopic arm, the manipulator loaded with the second inventory item to move to the second storage unit along the reference line; and unloading, by the manipulator that is remained on the horizontal plane where the reference line is located, the second inventory item to the second storage unit. 
     In some embodiments, the method for retrieving an inventory item further includes: driving, by the telescopic arm, the manipulator to move to the first storage unit along the horizontal plane where the reference line is located; driving, by the telescopic arm, the manipulator to be remained on the horizontal plane where the reference line is located and to load the first inventory item located at the first storage unit; driving, by the telescopic arm, the manipulator loaded with the first inventory item to move to the first preset position of the warehouse shelf along the reference line; and unloading, by the manipulator that is remained along the reference line, the first inventory item to the first preset position of the warehouse shelf. 
     In an embodiment, the method for retrieving an inventory item further includes: driving, by the telescopic arm, the manipulator to move to the first storage unit along the reference line; driving, by the telescopic arm, the manipulator to be remained on the horizontal plane where the reference line is located, to load the first inventory item located at the first storage unit; driving, by the telescopic arm, the manipulator loaded with the first inventory item to move to the second preset position of the warehouse shelf along the reference line; and unloading, by the manipulator that is remained on the horizontal plane where the reference line is located, the first inventory item to the second preset position of the warehouse shelf. 
     In some embodiments, the method for retrieving an inventory item further includes: uploading current position information of the first inventory item. 
     Compared with the prior art, the present application provides a method for retrieving an inventory item based on a handling robot, where the handling robot includes: a storage frame; and a material handling device installed on the storage frame, the material handling device including a telescopic arm and a manipulator installed on the telescopic arm; the method for retrieving an inventory item includes: driving, by the telescopic arm, the manipulator to extend to a preset position of a warehouse shelf along a preset horizontal reference line; loading, by the manipulator that is remained along the reference line, the inventory item located at the preset position; driving, by the telescopic arm, the manipulator loaded with the inventory item to move to the storage frame along the reference line; unloading, by the manipulator that is remained along the reference line, the inventory item to the storage frame. The above method can realize moving the inventory item into the storage frame along the preset horizontal reference line, occupying a small space of the storage frame in the vertical direction, and loading a larger number of inventory items. 
     In a second aspect, there is provided a handling robot, including: a movable chassis; a storage frame, installed on the movable chassis, and provided with a plurality of storage units distributed in a vertical direction, each storage unit being configured to place an inventory item; a material handling device for transporting the inventory item between a warehouse shelf and any one of the storage units, the material handling device having a preset horizontal reference line, and comprising a pusher assembly that is movable relative to the storage frame along the reference line; and a lifting assembly for driving the material handling device to move in the vertical direction, so that any one of the storage units is located on the reference line; when one of the storage units is located on the reference line, the pusher assembly pushes the inventory item to a corresponding storage unit along the reference line, or the pusher assembly pulls the inventory item located at the corresponding storage unit away therefrom 
     In some embodiments, the material handling device further includes a temporary storage unit; the temporary storage unit is configured to temporarily store an inventory item that is to be transported between the warehouse shelf and any one of the storage units, and the temporary storage unit has the reference line; when one of the storage units is located on the reference line, the pusher assembly may push an inventory item located on the temporary storage unit to a corresponding storage unit along the reference line, or the pusher assembly may pull an inventory item on a corresponding storage unit to the temporary storage unit. 
     In some embodiments, the material handling device further includes a telescopic arm. 
     The telescopic arm includes an outer arm section and an inner arm section, the outer arm section is fixedly installed to the temporary storage unit, and the inner arm section is installed to the outer arm section; the pusher assembly is installed to the inner arm section; the inner arm section can move relative to the outer arm section along the reference line, so that the pusher assembly can move relative to the storage frame along the reference line. 
     In some embodiments, the pusher assembly includes a manipulator; the manipulator is installed at an end of the inner arm section, so that the manipulator can move relative to the storage frame along the reference line, and the manipulator can unfold or fold relative to the inner arm section; when the manipulator folds relative to the inner arm section, an end of the inner arm section installed with the manipulator moves to another side from one side of the inventory item on the storage unit or the warehouse shelf that are located on the reference line, so that the manipulator unfolded relative to the inner arm section pulls a corresponding inventory item to the temporary storage unit. 
     In some embodiments, the pusher assembly further includes a fixed push rod; the fixed push rod is installed at an end of the inner arm section away from the manipulator, so that the fixed push rod can move relative to the storage frame along the reference line. 
     The fixed push rod is configured to push the inventory item placed on the temporary storage unit to the storage unit located on the reference line, or to push the inventory item placed on the temporary storage unit to an empty position of the warehouse shelf. 
     In some embodiments, the pusher assembly further includes a push rod driving device; the push rod driving device is connected to the manipulator, and is configured to drive the manipulator to rotate relative to the inner arm section, so that the manipulator can fold or unfold relative to the inner arm section. 
     In some embodiments, the telescopic arm further includes a middle arm section, a flat belt pulley, and an open-loop flat belt; the middle arm section is installed between the inner arm section and the outer arm section, and the middle arm section can move relative to the outer arm section along the reference line, and the inner arm section can move relative to the middle arm section along the reference line; the flat belt pulley is installed on the middle arm section; a middle part of the open-loop flat belt is arranged to be bent and sleeved over the flat belt pulley, so that both ends of the open-loop flat belt are oppositely arranged, one end being fixedly connected to the outer arm section, and the other end being fixedly connected to the inner arm section; when the middle arm section moves at a first speed relative to the outer arm section along the reference line, the inner arm section moves at a second speed relative to the outer arm section along the reference line, and the second speed is twice the first speed. 
     In some embodiments, the material handling device includes a support bracket, a fork, and a rotation assembly; the support bracket is installed on the movable chassis, and the lifting assembly is configured to drive the support bracket to move in the vertical direction; the fork includes the temporary storage unit, the telescopic arm and the pusher assembly; the rotation assembly includes a first rotating member and a second rotating member; the first rotating member is installed to the support bracket; the second rotating member is installed to the temporary storage unit, and can rotate in a vertically set rotation axis relative to the first rotating member, so that the fork can rotate around the rotation axis relative to the support bracket. 
     In some embodiments, the material handling device further includes a detection device; the detection device is configured to detect whether a corresponding warehouse shelf or storage unit is located on the reference line. 
     In some embodiments, the detection device includes an image acquisition device; the image acquisition device is configured to acquire image information of the inventory item to detect whether the corresponding warehouse shelf or storage unit is located on the reference line. 
     Compared with the prior art, in the handling robot of the embodiment of the present application, the handling robot includes: a movable chassis; a storage frame installed on the movable chassis, and provided with a plurality of storage units distributed in a vertical direction, each storage unit being configured to place an inventory item; a material handling device, configured to transport the inventory item between a warehouse shelf and any one of the storage units, having a preset horizontal reference line, and including a pusher assembly, the pusher assembly being movable relative to the storage frame along the reference line; a lifting assembly for driving the material handling device to move in a vertical direction, so that any one of the storage units is located on the reference line; when one of the storage units is located on the reference line, the pusher assembly can push the inventory item to a corresponding storage unit along the reference line, or pull an inventory item located on a corresponding storage unit away. An inventory item can be pushed into or pulled from the storage unit in the above manner, so that a distance between each two adjacent storage units is small, and more storage units can be placed in the handling robot with the same vertical height, increasing the maximum load capacity. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       One or more embodiments are exemplified by drawings corresponding to the embodiments. These exemplary descriptions do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings represent similar elements. Figures in the drawings are not drawn to scale unless otherwise stated. 
         FIG. 1  is a schematic structural diagram of a handling robot according to an embodiment of the present application; 
         FIG. 2  is an exploded schematic diagram of the handling robot shown in  FIG. 1 ; 
         FIG. 3  is an exploded schematic diagram of a movable chassis of the handling robot shown in  FIG. 2 ; 
         FIG. 4  is a schematic structural diagram of a standing frame and a lifting assembly of the handling robot shown in  FIG. 2 ; 
         FIG. 5  is a schematic structural diagram of a driving wheel assembly of the movable chassis shown in  FIG. 3 ; 
         FIG. 6  is a schematic structural diagram of a material handling device of the handling robot shown in  FIG. 2 ; 
         FIG. 7  is an exploded schematic diagram of the material handling device shown in  FIG. 6 ; 
         FIG. 8  is a structural schematic diagram of part of a fork of the material handling device shown in  FIG. 7 ; 
         FIG. 9  is a schematic structural diagram of a middle arm section and an inner arm section driving assembly of the fork shown in  FIG. 8 ; 
         FIG. 10  is a schematic structural diagram of the material handling device shown in  FIG. 6  from another angle, in which part of the structure of the material handling device is omitted; and 
         FIG. 11  is a flowchart of a method for retrieving an inventory item according to another embodiment of the present application. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In order to facilitate understanding of the present application, the present application will be described in more detail below with reference to the drawings and specific embodiments. It should be noted that when an element is expressed as “fixed” to another element, it may be directly on the another element, or there may be existed one or more intermediate elements therebetween. When an element is expressed as “connected” to another element, it may be directly connected to the another element, or there may be existed one or more intermediate elements therebetween. The terms “vertical”, “horizontal”, “left”, “right”, “inner”, “outer”, “first”, “second”, “third”, and similar expressions used in the description of the present application are for illustrative purposes only. The term “connected” has the same meaning as the term “attached” or “coupled”. The term “install” has a same meaning as the term “mount”, including a means of directly or indirectly installing. The term “indirectly installed or connected” means there may be existed one or more intermediate elements therebetween. 
     Unless otherwise defined, all technical and scientific terms used in the description of the present application have the same meaning as commonly understood by a person skilled in the art to which the present application pertains. The terms used in the description of the present application is only for the purpose of description of specific embodiments, and are not intended to limit the present application. The term “and/or” used in the description of the present application includes any and all combinations of one or more related items listed. 
     Referring to  FIGS. 1 and 2 , an embodiment of the present application provides a handling robot  100 , which can be applied to an intelligent warehousing system, an intelligent logistics system, or an intelligent sorting system, etc. In this embodiment, the handling robot  100  applied to the intelligent warehousing system will be taken as an example for detailed description. 
     The intelligent warehousing system is provided with a warehouse shelf, and the warehouse shelf is provided with a preset position for placing an inventory item. 
     It should be noted that the inventory item may be a single object or multiple objects. 
     The handling robot  100  includes a movable chassis  10 , a storage frame  20 , a material handling device  30 , and a lifting assembly  40 . The storage frame  20 , the material handling device  30  and the lifting assembly  40  are all installed to the movable chassis  10 . 
     The movable chassis  10  is configured to realize a moving function of the handling robot  100 . 
     Refer to  FIG. 3  together, the movable chassis  10  includes a bracket assembly  11 , a driven wheel  12 , a driving wheel assembly  13  and a guiding device  14 . The driven wheel  12 , the driving wheel assembly  13  and the guiding device  14  are all installed to the bracket assembly  11 . 
     The bracket assembly  11  is assembled by welding a steel beam, a steel plate and a skin, and the bracket assembly  11  includes a base  110  and a standing frame  111 . The standing frame  111  is installed to the base  110 . There are many ways to install the standing frame  111 . For example, the standing frame  111  may be installed directly or indirectly on the base  110  by fasteners, such as screwed nuts. The standing frame  111  may also be integrally formed with the base  110 , and therefore installing on the base  110 . 
     The base  110  includes a base body  112 , a shaft seat  113 , and a shock absorber bracket  114 . The shaft seat  113  is installed to the base body  112 , and the shock absorber bracket  114  is also installed to the base body  112 . 
     The base body  112  is a horizontally arranged rectangular plate having a symmetrical axis S 1 , and the base body  112  includes a first surface  1120  and a second surface  1121  that are oppositely arranged. It can be seen from  FIG. 3  that the first surface  1120  is a lower surface of the base body  112 , and the second surface  1121  is an upper surface of the base body  112 . 
     The base body  112  is provided with a driven wheel installation socket  1122 , a driving wheel installation socket  1124 , and a guiding device installation socket  1123 . 
     The driven wheel installation socket  1122  is provided on a first surface  1120  of the base body  112 , and is configured to install the driven wheel  12 . 
     The driving wheel installation socket  1124  is arranged as penetrating through the first surface  1120  and the second surface  1121  of the base body  112 , and the driving wheel installation socket  1123  is configured to accommodate the driving wheel assembly  13 . 
     The guiding device installation socket  1123  is arranged as penetrating through the first surface  1120  and the second surface  1121  of the base body  112 , and the guiding device installation socket  1123  is configured to install the guiding device  14 . 
     The shaft seat  113  and the shock absorber bracket  114  are both installed to the second surface  1121  of the base body  112 , and both the shaft seat  113  and the shock absorber bracket  114  are configured to install the driving wheel assembly  13  together. 
     It should be noted that, by providing the driven wheel installation socket  1122  for installing the driven wheel  12  and the driving wheel installation socket  1124  for accommodating the driving wheel assembly  13 , a ground clearance and a centroid height of the movable chassis  10  can be controlled, so that the grip of the movable chassis  10  is improved, and the stability of movement of the movable chassis  10  is improved. 
     Refer to  FIGS. 1 and 2 , the base  110  includes a housing  51  configured to house at least one of the base body  112 , the shaft seat  113 , the shock absorber bracket  114 , and the guiding device  14 . It can be seen from  FIG. 1  that a compartment  511  is formed by an upper surface of the housing  51 , and at least a part of the material handling device  30  can be accommodated in the compartment  511  when the material handling device  30  is lowered to the lowest position. It is obvious from  FIG. 1  that the compartment  511  is provided with a bottom surface. In an embodiment, the compartment  511  is not a through hole. In an embodiment, the compartment  511  is provided with a cavity or a depression, as long as the bottom or lower surface of the compartment  511  is lower than a surrounding area. For example, as shown in  FIG. 1 , when the material handling device  30  is lowered to a particular height (e.g., the lowest height), a part of the bottom of the material handling device  30  is in the compartment  511 . In this way, the material handling device  30  can drop to a lower position. 
     It should be noted that when the material handling device  30  is accommodated in the compartment  511 , it is not required that the material handling device  30  is place on the compartment  511  or supported by the compartment  511 . The lower part of the material handling device  30  is within a space enclosed by the compartment  511  when the material handling device  30  is lowered to the lowest position. 
     Refer to  FIG. 4  together, the standing frame  111  is installed to the second surface  1121  of the base body  112 . The standing frame  111  includes vertical columns  115  and horizontal columns  116  installed to the vertical columns  115 . 
     The vertical columns  115  is vertically arranged and installed to the second surface  1121  of the base body  112 . Two vertical columns are symmetrically distributed relative to a symmetrical axis S 1 . 
     A surface of each vertical column  115  facing another vertical column  115  is provided with a guide rail along a vertical direction. The material handling device  30  is installed to guide rails of the two vertical columns, so that the material handling device  30  can move relative to the vertical columns  115  along the vertical direction. 
     It should be understood that, according to an actual situation, the number of the guide rail is not limited to two. For example, the number of the guide rail may be one, three, or more than three, as long as there is at least one. 
     The horizontal columns  116  are horizontally arranged and are connected between two vertical columns  115 . A plurality of horizontal columns  116  are distributed in a vertical direction. 
     In an embodiment, each of the horizontal columns  116  is integrally formed with the vertical columns  115 . In some other embodiment, each of the horizontal columns  116  is fixedly attached to the vertical columns  115  by a fastener, such as a screwed nut. 
     As shown in  FIG. 4 , the standing frame  111  further includes a top horizontal bar  117  configured to connect the two vertical columns  115 . A wireless communication unit  118  is provided on the top horizontal bar  117 . The wireless communication unit  118  includes an antenna for receiving or sending wireless data. It can be seen from  FIGS. 1 and 2  that the top horizontal bar  117  is, at least in part, enclosed by a housing  53 . 
     As shown in  FIGS. 1 to 4 , each of the two vertical columns  115  is, at least in part, enclosed by a housing  52 . 
     Four driven wheels  12  are distributed in a first rectangle, and one of symmetrical axes of the first rectangle coincides with the symmetrical axis S 1 . The four driven wheels  12  support the bracket assembly  11 . 
     It should be understood that, according to an actual situation, the number of the driven wheel  12  is not limited to four, for example, the number of the driven wheel  12  may also be three, four or more than four, as long as there are at least three. 
     In this embodiment, the driven wheel  12  is a universal wheel. 
     It should be understood that, according to an actual situation, the driven wheel  12  is not limited to a universal wheel. For example, the driven wheel  12  may be a wheel body with a steering bracket (refer to a rear wheel set of an automobile), as long as the driven wheel  12  has a steering function. 
     The driving wheel assembly  13  is configured to drive the movable chassis  10  to move. The driving wheel assembly  13  is installed to the base  110 . Two driving wheel assemblies  13  are symmetrically distributed relative to the symmetrical axis S 1 , and any one of the driving wheel assemblies  13  is located between two driven wheels  12 . 
     Referring to  FIG. 5  together, each driving wheel assembly  13  includes a driving wheel bracket  130 , a driving wheel body  131 , a hub driving device  132 , and a hub reduction device  133 . The driving wheel body  131  is installed to the driving wheel bracket  130 , and the driving wheel body  131  can rotate around a rotation axis S 2  relative to the driving wheel bracket  130 . The rotation axis S 2  is horizontal and perpendicular to the symmetrical axis S 1 , so that the movable chassis  10  can be movable. An output end of the hub driving device  132  is connected to an input end of the hub reduction device  133 , and an output end of the hub reduction device  133  is connected to the driving wheel body  131  by a flange. The hub driving device  132  is configured to provide a first driving force for rotation of the driving wheel body  131  around the rotation axis S 2 . The hub reduction device  133  is configured to transmit the first driving force. 
     It should be understood that, according to an actual situation, the hub reduction device  133  may be omitted. In some embodiments, the output end of the hub driving device  132  is directly connected to the driving wheel body  131  by a flange, so that the driving wheel body  131  can rotate around the rotation axis S 2 . 
     It should be noted that the output end of the hub reduction device  133  or the output end of the hub driving device  132  is connected to the driving wheel body  131  by a flange, which can improve the reliability of the connection to the driving wheel body  131  and realize a stable installation of the driving wheel body  131 , not easy to be detached. 
     The hub driving devices  132  of two driving wheel assemblies  13  are used to perform independent driving controls. Two driving wheel bodies  131  may have different rotational speeds, so that the movable chassis  10  turns toward a side of one driving wheel body  131  with a lower rotational speed, to realize a turning function of the movable chassis  10 . 
     Furthermore, the driving wheel bracket  130  includes a hub bracket  134 , an axle body  135 , and a shock absorber  136 . One end of the driving wheel bracket  130  is arranged near the first axis S 1 , and the other end is arranged away from the first axis S 1 . The driving wheel body  131  is installed to an end of the hub bracket  134  away from the symmetrical axis S 1 . The axle body  135  is connected to the hub bracket  134 , and the axle body  135  is arranged to be parallel to the symmetrical axis S 1 . The axle body  135  is installed to the shaft seat  113  so that the driving wheel assembly  13  can rotate around the axle body  135  relative to the base body  112 . One end of the shock absorber  136  is hinged to an end of the shock absorber bracket  114  away from the base body  112 , so that the shock absorber  136  can rotate around the first axis S 4  that is parallel to the axle body  135 , relative to the base body  112 ; and the other end of the shock absorber  136  is hinged to an end of the hub bracket  134  away from the axle body  135 , so that the shock absorber  136  can rotate around the second axis S 3  that is parallel to the axle body  135 , relative to the hub bracket  134 . The shock absorber bracket  114 , the hub bracket  134 , and the shock absorber  136  form a triangular structure. When the movable chassis  10  turns, the shock absorber  136  can buffer a part of the eccentric force, to further improve the stability of movement of the movable chassis  10 . 
     In this embodiment, the hub driving device  132  is a first motor. 
     It should be understood that, according to an actual situation, the hub driving device  132  is not limited to the first motor. For example, the hub driving device  132  may also be an air motor, a hydraulic transmission system, etc. 
     The guiding device  14  is installed to the second surface  1121  of the base body  131  through a guiding device bracket. In this embodiment, the guiding device  14  is a camera, and a lens of the camera is oriented toward the guiding device installation socket  1124 , for identifying a two-dimensional code attached on the ground so that the movable chassis  10  travels along a preset path. 
     It should be understood that, according to an actual situation, the guiding device  14  is not limited to the camera. For example, the guiding device  14  may be a laser guiding device that travels along a laser beam. For another example, the guiding device  14  is a short wave receiving device, which realizes a guiding function by receiving a specific short wave signal, and so on. 
     Refer back to  FIG. 2 , the storage frame  20  includes a vertical pole  21 , a horizontal pole  22  and a storage unit  23 . The vertical pole  21  is vertically arranged and installed to the second surface  1121  of the base body  112 . Two vertical poles  21  are symmetrically distributed relative to the symmetrical axis S 1 . The horizontal pole  22  is horizontally arranged and is connected between the two vertical poles  21 . Both the number of the horizontal pole  22  and the number of the storage unit  23  correspond to the number of the horizontal column  116 . One horizontal pole  22  and one corresponding horizontal column  116  support one corresponding storage unit  23 , and each storage unit  23  is provided for accommodating an inventory item. 
     A vertical height of any one of horizontal poles  22  is lower than a vertical height of a corresponding horizontal column  116 , so that a corresponding storage unit  23  inclines from a side at which the corresponding horizontal column  116  is located to a side at which a corresponding horizontal pole  22  is located, so that an inventory item placed in the storage unit is not easy to slip off from the side at which the horizontal column  116  is located. 
     Further, each storage unit  23  includes a plate body  24  and a surrounding plate  25 . The plate body  24  are support jointly by the horizontal pole  22  and the horizontal column  116 . The surrounding plate  25  is arranged around an edge of the plate body  24 , and provides an opening  26  at a side near the horizontal column  116 . The surrounding plate  25  can prevent an inventory item sliding off from the plate body  24 , and the inventory item can be pushed into or pulled away from the plate body  24  through the opening  26 . The material handling device  30  is configured to transport an inventory item between the warehouse shelf and any one of the storage units of the storage frame  20 . 
     It should be noted that the number of the opening is not limited. In an embodiment, as shown in  FIGS. 1-2 , the plate body  24  is a plate with a flat upper surface, and each storage unit  23  has a single opening  26 . In some other embodiment, the plate body  24  includes two plates spaced apart from each other. It may be possible that two openings are provided. For example, one opening is provided at a side near the horizontal column  116 , and one opening is provided at a side away from the horizontal column. The inventory item can be pushed into or pulled away from the plate body  24  by the material handling device  30  through the opening near the horizontal column  116 . 
     The structure or shape of the plate body  24  is not limited in the present invention, as long as the plate body  24  can support a weight of the inventory item. In an embodiment, as shown in  FIGS. 1-2 , the plate body  24  includes a flat upper surface. In some other embodiment, the upper surface of the plate body  24  is not flat. For example, the upper surface of the plate body  24  is rough and uneven. 
     In an embodiment, the plate body  24  is integrally formed with the horizontal column  116  supporting the plate body  24 . In some other embodiments, the plate body  24  is fixedly attached on the horizontal column  116  supporting the plate body  24  by fasteners, such as screwed nuts. 
     In an embodiment, the vertical pole  21  and the horizontal pole  22  can be omitted. In an embodiment, each storage unit  23  is wholly supported by the corresponding horizontal column  116 . In an embodiment, a storage unit  23  disposed at a lowest height is supported by both the horizontal column  116  and the housing  51 , and other storage units  23  are wholly supported by the horizontal column  116 . 
     The material handling device  30  can move along the vertical direction so that a position of the material handling device  30  is horizontally opposite to any one of the storage units. The material handling device  30  is configured to transport the inventory item between a preset position of the warehouse shelf and any one of the storage units. 
     It can be seen from  FIGS. 1-4  that the storage frame  20  and the material handling device  30  are disposed at different sides of the vertical columns  115 . For example, as shown in  FIGS. 1-2 , the two vertical columns  115  form a vertical plane. The material handling device  30  is disposed at a left side of the vertical plane, and the storage frame  20  is disposed at a right side of the vertical plane. 
     Refer to  FIGS. 6 and 7  together, the material handling device  30  includes a support bracket  31 , a fork  32 , a rotation assembly  33 , and a detection device  34 . The rotation assembly  33  is installed between the support bracket  31  and the fork  32 , so that the fork  32  can rotate around a vertically set rotation axis S 5  relative to the support bracket  31 . The detection device  34  is configured to detect position information of the material handling device  30  relative to the inventory item. 
     The support bracket  31  is assembled by welding a steel beam and a steel plate, and is a horizontal arranged plate structure. An end of the support bracket  31  near the standing frame  111  is provided with a slide  310 . Two slides  310  are symmetrically distributed relative to the symmetrical axis S 1 . Each slide  310  is installed to a corresponding guide rail, and moves along the guide rail. The fork  32  installed to the support bracket  31  moves along the vertical direction relative to the storage frame  20 . 
     The fork  32  is configured to transport the inventory item between the preset position of the warehouse shelf and any one of the storage units. The fork  32  includes a temporary storage unit  35 , a telescopic arm  36 , and a pusher assembly  37 . The temporary storage unit  35  has a reference line S 6 . The telescopic arm  36  is installed to the temporary storage unit  35 , and is separated from the reference line S 6  by a preset distance. The pusher assembly  37  is installed to the telescopic arm  36 . The telescopic arm  36  drives the pusher assembly  37  to move in a direction parallel to the reference line S 6 . 
     When the fork  32  moves along the vertical direction, any one of the storage units may locates on the reference line S 6 . That is, the fork  32  can move to a same height as any one of the storage units. 
     When one of the storage units is located on the reference line S 6 , the pusher assembly  37  may push the inventory item located on the temporary storage unit  35  to the corresponding storage unit  23  along the reference line S 6 , or the pusher assembly  37  may pull the inventory item on the corresponding storage unit  23  to the temporary storage unit  35 . 
     In an embodiment, the pusher assembly  37  is further configured to pull the inventory item located on the warehouse shelf to the temporary storage unit  35 , or push the inventory item located on the temporary storage unit  35  to a preset position of the warehouse shelf. 
     It should be understood that, according to an actual situation, in the process of transporting the inventory item on the warehouse shelf to the temporary storage unit  35 , the fork  32  is not limited to using the pusher assembly  37  to pull the inventory item on the warehouse shelf to the temporary storage unit  35 , or to push the inventory item on the temporary storage unit  35  to a preset position on the warehouse shelf. In some embodiments, the fork  32  further includes a pickup component for transporting the inventory item on the warehouse shelf to the temporary storage unit. For example, the pickup component clamps the inventory item on the warehouse shelf to the temporary storage unit  35  by clamping. For another example, the pickup component lifts the inventory item from the warehouse shelf to the temporary storage unit  35  by lifting, and so on. 
     The temporary storage unit  35  is a horizontally arranged rectangular plate structure with the reference line S 6 . The temporary storage unit  35  is configured to temporarily store an inventory item to be transported between the warehouse shelf and any one of the storage units  23 . 
     For example, in the process of transporting the inventory item from the warehouse shelf to the storage frame  20 , the fork  32  first transports the inventory item on the warehouse shelf to the temporary storage unit  35 , and then the fork  32  transports the inventory item on the temporary storage unit  35  to any one of the storage units  23  of the storage frame  20 . And vice versa, and due to word limitations, no description is repeated here. 
     It should be noted that, for the provision of the temporary storage unit  35 , in a first aspect, it can transport an inventory item on one storage unit  23  to another storage unit  23 , having a wide range of applications. In a second aspect, it can be realized that any storage unit  23  does not need to be located on the reference line S 6  with the warehouse shelf at the same time, and there is no need for adaptive adjustment between the warehouse shelf and the storage frame  20 , which makes the handling robot  100  has strong compatibility and can be adapted to different environments. Since there is no need to modify the warehouse shelf and the storage frame  20 , the economy is better. In a third aspect, the temporary storage unit  35  can also store the inventory item for a long time, so that the maximum load capacity of the handling robot  100  is expanded. 
     Two telescopic arms  36  are symmetrically distributed relative to the reference line S 6 . 
     It should be understood that, according to an actual situation, the number of the telescopic arms  36  is not limited to two, for example, the number of the telescopic arm  36  may be one. 
     Each telescopic arm  36  includes an outer arm section  360 , a middle arm section  361 , an inner arm section  362 , a middle arm section driving assembly  363 , and an inner arm section driving assembly  364 . The outer arm section  360  is installed to the temporary storage unit  35 , and the middle arm section  361  is installed to the outer arm section  360 . The middle arm section  361  can move relative to the outer arm section  360  along the reference line S 6 . The inner arm section  362  is installed to the middle arm section  361 , and the inner arm section  362  can move relative to the middle arm section  361  along the reference line S 6 . The middle arm section driving assembly  363  is configured to drive the middle arm section  361  to move relative to the outer arm section  360  along the reference line S 6 , and the inner arm section driving assembly  364  is configured to drive the inner arm section  362  to move relative to the middle arm section  361  along the reference line S 6 . 
     When the telescopic arm  36  is compressed, the inner arm section  362  overlaps with the outer arm section  360 . 
     When the telescopic arm  36  extends, the inner arm section  362  is separated from the outer arm section  360  in a direction along the reference line S 6 . 
     It should be understood that, according to an actual situation, the middle arm section  361  and the inner arm section driving assembly  364  may be omitted. In some embodiments, the inner arm section  362  is installed to the outer arm section  360 , and the inner arm section  362  can move relative to the outer arm section  360  along the reference line S 3 . The middle arm section driving assembly  363  is configured to drive the inner arm section  362  to move relative to the outer arm section  360  along the reference line S 6 . 
     The middle arm section driving assembly  363  includes a sprocket wheel mechanism  3630  and a middle arm section driving device  3631 . An output end of the middle arm section driving device  3631  is connected to a driving sprocket wheel of the sprocket wheel mechanism  3630 . The middle arm section driving device  3631  is configured to drive the driving sprocket wheel to rotate. The middle arm section  361  is fixedly connected to a roller chain of the sprocket wheel mechanism  3630 , and the sprocket wheel mechanism  3630  can drive the middle arm section  361  to move relative to the outer arm section  360  along the reference line S 6 . 
     As shown in  FIG. 8 , the middle arm section  361  includes a connecting plate  3611 . The connecting plate  3611  is fixedly connected to a roller chain of the sprocket wheel mechanism  3630 . The sprocket wheel mechanism  3630  can drive the middle arm section  361  through the connecting plate  3611  to move relative to the outer arm section  360 . 
     It should be understood that, according to an actual situation, the sprocket wheel mechanism  3630  may be replaced with a pulley mechanism or the like. 
     The middle arm section driving device  3631  is a second motor. 
     It should be understood that, according to an actual situation, the middle arm section driving device  3631  is not limited to a motor. For example, the middle arm section driving device  3631  may also be an air motor, a hydraulic transmission system, or the like. 
     Refer to  FIG. 9  together, the inner arm section driving assembly  364  includes a movable pulley  3640  and a strop  3641 . The movable pulley  3640  is installed to the middle arm section  362 . A middle part of the strop  3641  is arranged to be bent so that two ends of the strop  3641  are oppositely arranged, that is, the strop  3641  is U-shaped, and the middle part of the strop  3641  is sleeved over the movable pulley  3640 . One end of the strop  3641  is fixedly connected to the outer arm section  360 , and the other end of the strop  3641  is fixedly connected to the inner arm section  362 . The movable pulley  3640  and the strop  3641  form a movable pulley structure. When the middle arm section  361  moves at a first speed relative to the outer arm section  360  along the reference line S 6 , the inner arm section  362  moves at a second speed relative to the outer arm section  360  along the reference line S 6 , the second speed is twice the first speed. 
     In this embodiment, the movable pulley  3640  is a flat belt pulley, and the strop  3641  is an open-loop flat belt. 
     It should be understood that, according to an actual situation, the movable pulley  3640  and the strop  3641  are not limited to the flat belt pulley and the open-loop flat belt. In some embodiments, the movable pulley  3640  is a sprocket wheel, and strop  3641  is a roller chain. 
     The pusher assembly  37  includes a fixed push rod  370 , a manipulator  371 , and a push rod driving device  372 . In an embodiment, two ends of the fixed push rod  370  are respectively fixedly installed at opposite ends of the two inner arm sections  362 , and two manipulators  371  are respectively installed at ends of the inner arm sections  362  away from the fixed push rod  370 . The manipulators  371  can fold or unfold relative to the inner arm sections  362 . The push rod driving device  372  is configured to drive the manipulators  371  to fold or unfold relative to the inner arm sections  362 . 
     In some other embodiment, the pusher assembly  37  includes two fixed push rods symmetrically disposed relative to the reference line S 6 , and each fixed push rod is fixedly installed to a corresponding inner arm section  362 . 
     When the telescopic arm  36  is in a compressed state, the temporary storage unit is located between the two ends of the inner arm section  362  in a direction along the reference line S 6 . 
     When the telescopic arm  36  is in an extension state, an end of the inner arm section  362  installed with the fixed push rod  370  is close to the temporary storage unit, and an end of the inner arm section  362  installed with the manipulator  371  is away from the temporary storage unit. 
     In an embodiment, the push rod driving device  372  includes a third motor, and an end of the manipulator  371  is installed at an output end of the third motor. The third motor is configured to drive the manipulator  371  to rotate relative to the inner arm section  362  around the third axis S 7  that is parallel to the reference line S 6 , so that the manipulator  371  unfolds or folds relative to the inner arm section  362 . 
     When the manipulator  371  folds to the inner arm section  362 , and an inventory item is located on the reference line S 6 , the end of the inner arm section  362  installed with the manipulator  371  can move from a side of the corresponding inventory item facing the temporary storage unit to a side of the inventory item away from the temporary storage unit along the reference line S 6 , so that the manipulator  371  relative to the inner arm section  362  may pull the inventory item to the temporary storage unit along the reference line S 6 . 
     It should be noted that an inventory item is located on the reference line S 6 , where the so-called inventory item may be an inventory item on the warehouse shelf or an inventory item on the storage unit, as long as the inventory item is located on the reference line S 6 . 
     When the warehouse shelf is located on the reference line S 6 , the fixed push rod  370  can push the inventory item located on the temporary storage unit  35  to a preset position of the warehouse shelf. It should be noted that when the warehouse shelf is located on the reference line S 6 , the material handling device  30  is at a same height as the warehouse shelf. 
     Similarly, when one storage unit  23  is located on the reference line S 6 , the fixed push rod can push the inventory item that is temporarily stored on the temporary storage unit  35  to a corresponding storage unit  23  along the reference line S 6 . It should be noted that when one storage unit  23  is located on the reference line S 6 , the material handling device  30  is at a same height as the storage unit  23 . 
     It should be understood that, when the fixed push rod  370  pushes the inventory item, the manipulator  371  can fold relative to the inner arm section  362  or unfold relative to the inner arm section  362 . When the fixed push rod  370  completes the pushing of the inventory item and is reset, the manipulator  371  folds relative to the inner arm section  362 . 
     It should be understood that, according to an actual situation, the temporary storage unit  35  can be omitted. The temporary storage unit  35  has basically the same structure as the storage unit  23  or the warehouse shelf, and at the position of the temporary storage unit  35 , the temporary storage unit  35  can be directly replaced with the storage unit  23 . In some embodiments, each storage unit  23  is located on the same horizontal plane as a corresponding warehouse shelf. When one storage unit  23  and the preset positions of one warehouse shelf are both on the reference line S 6 , the fixed push rod  370  may push the inventory item placed on the corresponding storage unit  23  to the preset position of the corresponding warehouse shelf, or the manipulator  371  unfolded relative to the inner arm section  362  pulls the inventory item located on the corresponding warehouse shelf to the corresponding storage unit  23 . 
     In some embodiments, the fixed push rod  370  may be omitted. Specifically, the manipulator includes a pushing surface and a pulling surface, which are oppositely arranged. The pushing surface is oriented toward one end of the reference line, and the pulling surface is oriented toward the other end of the reference line. The inner arm section  362  installed with the manipulator  371  can move to either side of the inventory item (located on the temporary storage unit, the storage unit, or the warehouse shelf) by the manipulator  371  folded relative to the inner arm section  362 , and the manipulator  371  unfolded relative to the inner arm section  362  can push the inventory item to the temporary storage unit  35 , the storage unit  23  or the preset position of the warehouse shelf via the pushing surface, or pull the inventory item to the temporary storage unit  35 , the storage unit  23  or the preset position of the warehouse shelf via the pulling surface. 
     The rotation assembly  33  is configured to rotate the fork  32  relative to the storage frame  20  around a vertical direction, so that any two or three of any storage unit  23 , the warehouse shelves and the reference line S 6  may not be located in the same vertical plane. 
     Refer to  FIG. 10  together, the rotation assembly  33  includes a rotation mechanism  330 , a rotation driving mechanism  331 , a deflection detection device, and a rotation limit device. The rotation mechanism  330  is installed between the fork  32  and the support bracket  31 . The rotation mechanism  330  can rotate around the rotation axis S 5 , and the rotation driving mechanism is configured to drive the rotation mechanism  330  to rotate around the rotation axis S 5 . The deflection detection device is configured to control the rotation driving mechanism  331 . 
     The rotation mechanism  330  includes a first rotation member  3300  and a second rotation member  3301 . The first rotation member  3300  is installed to a surface of the support bracket  31  facing the fork  32 . The second rotation member  3301  is installed to the first rotation member  3300 , and the second rotation member  3301  can rotate around the rotation axis S 5  relative to the first rotation member  3300 . The fork  32  is installed to the second rotation member  3301 . 
     In this embodiment, the first rotation member  3300  is a slewing bearing inner ring, and a center line of the slewing bearing inner ring is coaxial with the rotation axis S 5 . The second rotation member  3301  is a slewing bearing outer ring, and the slewing bearing outer ring is sleeved on the slewing bearing inner ring, so that the slewing bearing outer ring can rotate around the rotation axis S 5  relative to the slewing bearing inner ring, and the slewing bearing outer ring and the slewing bearing inner ring support the fork  32  together. 
     It should be understood that, according to an actual situation, the first rotation member  3300  and the second rotation member  3301  are not limited to a combination of the slewing bearing inner ring and the slewing bearing outer ring. 
     The rotation driving mechanism  331  includes an outer ring gear  3310 , a rotation driving gear  3311 , and a rotation driving device. The outer ring gear  3310  is fixedly connected to the second rotation member  3301 , and the outer ring gear  3310  is coaxial with the rotation axis S 5 . An output end of the rotation driving device is connected to the rotation driving gear  3311 , and the rotation driving device is configured to drive the rotation driving gear  3311  to rotate, so that the outer ring gear  3310  that is engaged with the rotation driving gear  3311  rotates around the rotation axis S 5 , and drives the second rotation member  3301  fixedly connected to the outer ring gear  3310  to rotate around the rotation axis S 4 . 
     In this embodiment, the outer ring gear  3310  is integrally formed with the slewing bearing outer ring. 
     It should be understood that, according to an actual situation, the rotation driving mechanism  331  is not limited to the outer ring gear  3310  and the rotation driving gear  3311 . For example, the rotation driving mechanism is a worm gear mechanism, a gear set, or a planetary gear mechanism. 
     In this embodiment, the rotation driving device is a fourth motor. It should be understood that, according to an actual situation, the rotation driving device may also be a linear motor, an air motor, a hydraulic drive system, etc. 
     The rotation limit device includes a first limit post  3320 , a second limit bar  3321 , and a limit block  3322 . The first limit bar  3320  and the second limit bar  3321  are both installed to the surface of the support bracket  31  facing the fork  32 , and the first limit bar  3320  and the second limit bar  3321  are circumferentially distributed around the rotation axis S 5 . The limit block  3322  is installed to a surface of the fork  32  facing the support bracket  31 . The limit block  3322  can abut against the first limit bar  3320  and the second limit bar  3321 , respectively, enabling the rotation mechanism  330  to rotate around the rotation axis S 5  within a preset angle range, to drive the fork  32  to rotate to a preset angle, so that the preset angle is within the preset angle range. 
     The deflection detection device is configured to detect whether the fork  32  rotates to the preset angle. 
     When the deflection detection device detects that the fork has not yet rotated to the preset angle, the deflection detection device controls the rotation assembly to drive the fork to continue to rotate. 
     When the deflection detection device detects that the fork rotates over the preset position, the deflection detection device controls the rotation assembly to drive the fork to rotate in a reverse direction. 
     When the deflection detection device detects that the fork rotates to the preset angle, the deflection detection device controls the rotation assembly to stop rotating. 
     The deflection detection device includes a first sensor  3330 , a second sensor  3331  and a rotation controller. The first sensor  3330  and the second sensor  3331  are both connected to the rotation controller. 
     The first sensor  3330  is provided with a first detection range. The first sensor  3330  is configured to detect the fork  32  within the first detection range. 
     The second sensor  3331  is provided with a second detection range. The second sensor  3331  is configured to detect the fork  32  within the second detection range. 
     The rotation controller is connected to the rotation driving device, and is configured to control the fork  32  to rotate around the rotation axis S 5  through the rotation driving device. 
     When the first sensor  3330  detects the fork  32  in the first detection range, and the second sensor  3331  does not detect the fork  32  in the second detection range, the fork  32  has not yet rotated to the preset angle. 
     When the first sensor  3330  does not detect the fork  32  in the first detection range, and the second sensor  3331  detects the fork  32  in the second detection range, the fork  32  has rotated over the preset angle. 
     When the first sensor  3330  detects the fork  32  in the first detection range, and the second sensor  3331  detects the fork  32  in the second detection range, the fork  32  rotates to the preset angle. 
     In this embodiment, the first sensor  3330  is a first proximity switch, and the first proximity switch is installed to the surface of the fork  32  facing the support bracket  31 . The second sensor  3331  is a second proximity switch, the second proximity switch and the first proximity switch are installed to the surface of the support bracket  31 . The first proximity switch and the second proximity switch are circumferentially distributed around the rotation axis S 5 . The rotation controller further includes a detection board  3333 . The detection board  33  is installed to the surface of the support bracket  31  facing the fork  32 , and the detection board  3333  is arranged to be bend around the rotation axis S 5 . 
     When the fork  32  rotates into a first preset angle range and does not rotate into a second preset angle range, the first proximity switch faces the detection board  3333 , and the second proximity switch does not face the detection board  3333 . 
     When the fork  32  does not rotate into the first preset angle range but rotates into the second preset angle range, the first proximity switch does not face the detection board  3333 , but the second proximity switch faces the detection board  3333 . 
     When the fork  32  rotates to a benchmark angle, the first proximity switch faces one end of the detection board  3333 , and the second proximity switch faces the other end of the detection board  3333 . 
     In some embodiments, the rotation assembly  33  may be omitted, and the material handling robot may adjust a horizontal orientation of the fork  32  by the movable chassis  10  to replace the function of the rotation assembly, as long as a storage unit  23  and a corresponding warehouse shelf are located on the reference line S 6  at the same time. For example, when the movable chassis  10  and the lifting assembly  40  work so that a storage unit  23  and a corresponding warehouse shelf are located at the reference line S 6 , one end of the inner arm section  362  installed with the manipulator  371  first passes the corresponding storage unit  23 , and then the manipulator  371  unfolded relative to the inner arm section  362  pulls the inventory item to the corresponding storage unit, and then continues to pull to the temporary storage unit  35 . And the fixed push rod  370  pushes the inventory item located on the temporary storage unit  35  to the corresponding storage unit  23 , and then continues to push the inventory item located on the corresponding storage unit  23  to the preset position of the corresponding warehouse shelf. Since the inventory item first passes through the corresponding storage unit  23  or the corresponding warehouse shelf, then reaches the temporary storage unit  35 , the temporary storage unit  35  may be omitted in this embodiment. 
     Refer back to  FIG. 6 , the detection device  34  is configured to detect the position information of the material handling device  30  relative to the inventory item, i.e., to determine whether the storage unit  23 , the preset position of the warehouse shelf, or the inventory item is located on the reference line S 6 . 
     Specifically, the position information of the material handling device relative to the inventory item includes a first position offset between the inventory item and the reference line in the travelling direction, and a second position offset between the inventory item and the reference line in the vertical direction, the distance between the inventory item and the manipulator along the reference line, and the deflection amount between the inventory item and the reference line in the horizontal direction. These position information will be described in detail below. 
     The position information of the material handling device relative to the inventory item includes the first position offset between the inventory item and the reference line in travelling direction. 
     The detection device includes a camera device  340 , a primary lighting equipment  341 , and a secondary lighting equipment  342 . The camera device  340  is installed to a surface of the temporary storage unit  35  facing the support bracket  31 , and a lens of the camera device  340  is in the same direction as the direction of the extension of the telescopic arm  36 . The camera device  340  is configured to acquire image information, such as, shooting the two-dimensional code on the warehouse shelf or the two-dimensional code attached on the inventory item, so as to determine whether the storage unit, the preset position of the warehouse shelf, or the inventory item is on the reference line S 6 . Alternatively, the camera device  340  is configured to determine the position of the inventory item relative to the warehouse shelf and the position of the inventory item relative to the storage frame  20  through an image difference algorithm, and so on. 
     It should be understood that, according to an actual situation, the camera device  340  may be replaced with a laser guiding device, an infrared sensor, and etc. 
     The primary lighting equipment  341  is installed to the temporary storage unit  35 , and is located on one side of the primary lighting equipment  341  away from the camera device  340 . The primary lighting equipment  341  and the lens of the camera device  340  have the same orientation. The primary lighting equipment  341  is configured to compensate for light, so that the camera device  340  can clearly shoot the two-dimensional code on the warehouse shelf or the inventory item. 
     The secondary lighting equipment  342  is installed on the support bracket  31 , two secondary lighting equipments  342  are distributed relative to the symmetrical axis S 1 , and the orientation of each secondary lighting equipment  342  is inclined upward, and is arranged back to the other lighting equipment  342 . The fork rotates around the rotation axis S 5  until the camera device  340  is located above one secondary lighting equipment  342 , and then the one secondary lighting equipment  342  can further perform light compensation on the camera device  340 , so that the handling robot  100  can be adapted to different lighting environments, such as day and night. The secondary lighting equipment  342  is arranged to be inclined, so that the light emitted by the secondary lighting equipment  342  is not easily all reflected to the lens of the camera device  340 , resulting in excessive light compensation. 
     As shown in  FIGS. 1-2, and 6-7 , the fork  32  further includes a housing  38 . The housing  38  is installed around the temporary storage unit  35  and configured to prevent the inventory item on the temporary storage unit  35  from falling off. At least a part of the temporary storage unit  35  and the telescopic arm  36  is in the housing  38 . For example, as shown in  FIGS. 1-2 and 6-7 , at least a part of the telescopic arm  36  and at least a part of the temporary storage unit  35  are housed in the housing  38 . 
     As shown in  FIGS. 1-2 and 6-7 , the housing  38  is U-shaped. The housing  38  includes a left housing member  381 , a right housing member  382 , and a rear housing member  383 . The left housing member  381  is configured to house at least a part of one telescopic arm  36 , and the right housing member  382  is configured to house at least a part of another telescopic arm  36 . 
     It is not limited to the ways to make and install the housing member  38 . In an embodiment, the left housing member  381 , the right housing member  382  and the rear housing member  383  are integrally formed into one piece. In some other embodiments, the left housing member  381 , the right housing member  382  and the rear housing member  383  are separate components. Both the left housing member  381  and the right housing member  382  may be connected to the rear housing member  383  via fasteners, such as screwed nuts. However, it may be also possible that one of the left housing member  381  and the right housing member  382  is integrally formed with the rear housing member  383 , and another of the left housing member  381  and the right housing member  382  is connected to the rear housing member  383  by fasteners. 
     In an embodiment, the left housing member  381  may be integrally formed with one telescopic arm  36 , and the right housing member  382  may be integrally formed with another telescopic arm  36 . 
     It is not limited to the shape and structure of each of left housing member  381 , the right housing member  382  and the rear housing member  383 , as long as the housing  38  is U-shaped as a whole. In an embodiment, the rear housing member  383  includes an arcuate outer surface. And in some other embodiments, the rear housing member  383  includes a flat outer surface. If the left housing member  381  and the right housing member  382  are symmetrically disposed relative a reference line, and the rear housing member  383  connects to both an end of the left housing member  381  and an end of the right housing member  382 , a U-shaped housing  38  is formed. 
     As shown in  FIGS. 1-2 and 6-7 , a compartment  39  configured to accommodate the inventory item is provided in the fork  32 . In an embodiment, the elements including at least the housing  38  and the temporary storage unit  35  form the compartment  39 . The compartment  39  is provided with a single opening  391  in a direction parallel to the direction of extension or retraction of the telescopic arm  36 . 
     It can be seen from  FIGS. 1-2 and 6-7  that the single opening  391  is formed in the fork  32  in the direction parallel to the direction of extension or retraction of the telescopic arm  36 . In an embodiment, as shown in  FIGS. 1-2 and 6-7 , the U-shaped housing  38  is provided with the single opening  391  at the front side of the fork  32 , which is away from the rear housing member  383 . 
     The single opening  391  is located at a side opposite to the rear housing  383 . It is obvious that the inventory item can only be pushed away or pulled into the temporary storage unit  35  through the single opening  391 . Because there is only one opening in the direction of extension or retraction of the telescopic arm  36 , the telescopic arm  36  cannot extend in two directions. It is obvious from  FIGS. 1-2 and 6-7  that the telescopic arm  36  can only extend in a single direction through the single opening  391 . That is, the telescopic arm  36  can only extend in the direction towards the opening  391 , and the telescopic arm  36  cannot extend in a reverse direction. For example, the telescopic arm  36  cannot extend in a direction towards the rear housing member  383 . 
     The lifting assembly  40  is configured to drive the material handling device  30  to move relative to the storage frame  20  in the vertical direction. The lifting assembly  40  includes a lifting transmission mechanism and a lifting drive mechanism  42 . The lifting drive mechanism  42  is configured to provide a second driving force for movement of the material handling device  30  relative to the storage frame  20  in the vertical direction, and the lifting transmission mechanism is configured to transmit the second driving force to the material handling device  30 . 
     The lifting transmission mechanism includes two sets of synchronous wheel mechanisms  43 . The two sets of synchronous wheel mechanisms  43  are installed to two opposite surfaces of the two vertical columns  115 , respectively. Each set of synchronous wheel mechanism  43  includes a driving synchronous wheel  430 , a tension wheel  431  and a synchronous belt  432 . The driving synchronous wheel  430  is installed at one end of the vertical columns  115  near the base body  112 , and the tension wheel  431  is installed at one end of the vertical columns  115  away from the base body  112 . The tension wheel  431  and the driving synchronous wheel  430  are sleeved on the synchronous belt  432 . The lifting drive mechanism  42  is connected to the driving synchronous wheel  430 , and is configured to drive the driving synchronous wheel  430  to rotate. The driving synchronous wheel  430  drives the synchronous belt  432  to move in the vertical direction, so that the support bracket  31  fixedly connected to the synchronous belt  432  synchronously moves in the vertical direction. 
     The synchronous belt  432  of each synchronous wheel mechanism  43  is connected with a counterweight  433 . Each counterweight  433  has a certain mass, and is installed on a counterweight rail of a corresponding vertical column  115 . Each counterweight  433  can move relative to the corresponding vertical column  115  in the vertical direction. When the material handling device  30  moves in the vertical direction, the counterweight  433  can act as a buffer, and reduce the load of the lifting drive mechanism  42 . 
     It should be understood that, on one hand, according to an actual situation, the number of the synchronous wheel mechanisms  43  is not limited to two. For example, the number of the synchronous wheel mechanisms  43  may be one, two or more, as long as there is at least one. On the other hand, according to an actual situation, the lifting transmission mechanism is not limited to the synchronous wheel mechanism  43 . For example, the lifting transmission mechanism may also be a sprocket wheel mechanism, or a gear rack mechanism, a turbine worm mechanism, a lifting screw mechanism, and so on. 
     Since the support bracket  31  supports the fork, the lifting drive mechanism has a large load during the transport of the inventory item. In order to ensure that the material handling device can smoothly lift, two synchronization wheel mechanisms have a high synchronization rate. 
     The lifting drive mechanism  42  includes a lifting driving device  420 , a driving shaft  421 , a driving gear, and a driven gear (both the driving gear and the driven gear are installed in the gearbox  422  in the figure). Two ends of the driving shaft  421  are connected to two driving synchronous wheels  430  of the two synchronous wheel mechanisms  43  through flat keys. The driving shaft  421  transmits a torque to the driving synchronous wheel  430  through the flat keys, so that the driving synchronous wheels  430  of the two synchronous wheel mechanisms  43  can rotate synchronously, which allows the material handling device  30  to smoothly move in the vertical direction. The driven gear is sleeved between two shafts of the driving shaft  421 , and the driving gear engages with the driven gear to transmit the driving force of the lifting driving device  420 . 
     It should be understood that, according to an actual situation, the synchronous wheel mechanism  43  may be replaced with a sprocket wheel mechanism, or a gear rack set, or the like. 
     In some embodiments, short shafts at both ends of the driving shaft  421  are coaxially connected by a coupling. One end of one short shaft facing away from the coupling is connected to the driving synchronous wheel  430  of one synchronous wheel mechanism  43 , and one end of the other short shaft facing away from the coupling is connected to the driving synchronous wheel  430  of the other synchronous wheel mechanism  43 , which can further ensure the synchronization rate of the two driving synchronous wheels  430 . 
     In this embodiment, the lifting driving device  420  is a fifth motor. It should be understood that, according to an actual situation, the lifting drive device is not limited to the fifth motor. For example, the lifting driving device may also be an air motor, hydraulic transmission system, etc. 
     When the handling robot  100  is in a work state, the handling robot  100  specifically involves the following several processes: 
     The handling robot  100  transports the inventory item on the warehouse shelf to the temporary storage unit. In step  1 , the movable chassis  10  drives the handling robot  100  to move to a warehouse shelf where an inventory item is placed. The movable chassis  10  is guided by the guiding device  14  so that the movable chassis  10  travels along a specified path, and when reaching the warehouse shelf where the inventory item is placed, the movable chassis  10  is stationary relative to the warehouse shelf. The movable chassis  10  moves in a travelling direction. In step  2 , the lifting assembly  40  drives the fork  32  to move relative to the warehouse shelf in the vertical direction, so that the reference line S 6  of the fork  32  is on the same horizontal plane as the inventory item. In an embodiment, the fork  32  moves sideways relative to the travelling direction to pull or push the inventory item. For example, the fork  32  may be rotated so that the horizontal orientation of the fork is perpendicular to the travelling direction. In step  3 , the fork  32  rotates around the vertically set rotation axis S 5  so that the inventory item is on the reference line S 6 . In step  4 , the telescopic arm  36  extends along the reference line. The manipulator  371  installed at one end of the inner arm section  362  folds relative to the inner arm section  362 , and the one end of the inner arm section  362  installed with the manipulator  371  moves from a side of the inventory item facing the temporary storage unit  35  to a side of the inventory item facing away the temporary storage unit  35 . In step  5 , the manipulator  371  unfolds relative to the inner arm section  362 , and then the telescopic arm  36  is retracted so that the manipulator  371  pulls the inventory item into the temporary storage unit  35 . 
     The handling robot  100  transports an inventory item in the temporary storage unit  35  to a storage pallet. In step  1 , the fork  32  rotates relative to the storage frame  20  around the rotation axis S 5  until the reference line S 6  of the fork  32  is on the same vertical plane as the storage unit (in an embodiment provided by the present application, when the reference line S 6  of the fork  32  is on the same vertical plane as the storage unit, the fork  32  is at a benchmark angle relative to the support bracket  31 ). In step  2 , the lifting assembly  40  drives the fork  32  to move in the vertical direction, so that one storage unit is located on the reference line S 6 . In step  3 , the telescopic arm  36  extends along the reference line S 6  so that the fixed push rod  370  installed at an end of the inner arm section  362  facing away from the manipulator  371  pushes the inventory item located in the temporary storage unit  35  into a corresponding storage unit  23 . 
     The handling robot  100  transports an inventory item in a storage pallet to the temporary storage unit  35 . In step  1 , the fork  32  rotates relative to the storage frame  20  around the rotation axis S 5  until the reference line S 6  of the fork  32  is on the same vertical plane as the storage unit. In step  2 , the lifting assembly  40  drives the fork  32  to move in the vertical direction so that one storage unit is located on the reference line S 6 . In step  3 , the telescopic arm  36  extends along the reference line. The manipulator  371  installed at one end of the inner arm section  362  folds relative to the inner arm section  362 , and one end of the inner arm section  362  installed with the manipulator  371  moves from the side of the inventory item facing the temporary storage unit to the side of the inventory item facing away the temporary storage unit. In step  5 , the manipulator  371  unfolds relative to the inner arm section  362 , and then the telescopic arm  36  is retracted so that the manipulator  371  pulls the inventory item into the temporary storage unit. 
     The handling robot  100  transports the inventory item in the temporary storage unit to the warehouse shelf. 
     In step  1 , the movable chassis  10  drives the handling robot  100  to move to a preset position of the warehouse shelf. The movable chassis  10  is guided by the guiding device  14  to allow the movable chassis  10  to travel along a specified path. When reaching the warehouse shelf, the movable chassis  10  is stationary relative to the warehouse shelf. In step  2 , the lifting assembly  40  drives the fork  32  to move relative to the warehouse shelf in the vertical direction, so that the reference line S 6  of the fork  32  is on the same horizontal plane as the preset position. In step  3 , the fork  32  rotates around the vertically set rotation axis S 5  so that the preset position is on the reference line S 6 . In step  4 , the telescopic arm  36  extends along the reference line S 6 , so that the fixed push rod  370  installed at an end of the inner arm section  362  facing away the manipulator  371  pushes the inventory item located in the temporary storage unit to the preset position of the warehouse shelf. 
     An embodiment of the present application provides a handling robot  100 . The handling robot  100  includes: a movable chassis  10 ; a storage frame  20 , installed on the movable chassis  10 , and provided with a plurality of storage units  23  distributed in a vertical direction, each storage unit  23  being configured to place an inventory item; a material handing device  30 , configured to transport an inventory item between a warehouse shelf and any one of the storage units  23 , where the material handling device  30  has a preset horizontal reference line S 6 , and the material handling device  30  includes a pusher assembly, the pusher assembly can move relative to the storage frame along the reference line; and a lifting assembly, configured to drive the material handling device to move in a vertical direction so that any one of the storage units is located on the reference line. When one of the storage units is located on the reference line, the pusher assembly can push the inventory item to a corresponding storage unit along the reference line, or the pusher assembly can pull the inventory item located on the corresponding storage unit away therefrom. By the above method, the handling robot  100  equipped with the storage frame  20  can load a large number of inventory items. 
     Additionally, it can be realized that an inventory item is pushed into or pulled away a storage unit, so that a distance between each two adjacent storage units is small, and more storage units can be placed in the handling robot with the same vertical height, increasing the maximum load capacity. 
     In addition, for such push-pull method for transporting an inventory item, there is no requirement for the shape of the inventory item, as long as the inventory item can be pushed by a push rod, which allows the handling robot has a wide range of applications. 
     Moreover, for such push-pull method for transporting an inventory item, the inventory item transported by the material handling device  30  each time may be a single object or several separated objects. For example, when the material handling device  30  transports the inventory item from the warehouse shelf, a plurality of objects on the warehouse shelf are sequentially arranged along the reference line S 6 . One end of the inner arm section  362  installed with the manipulator  371  moves from the front side of the closest object to the back side of the farthest object, and then the manipulator  371  pulls the plurality of objects together away the warehouse shelf. 
     Refer to  FIG. 11  together, another embodiment of the present application provides a method for retrieving an inventory item based on the handling robot  100  above. The method for retrieving an inventory item includes the following steps. 
     Step  201 : driving, by the telescopic arm, the manipulator to extend to the preset position of the warehouse shelf along the preset horizontal reference line. 
     The manipulator at one end of the telescopic arm extends to the preset position of the warehouse shelf along the reference line. 
     Step  202 : loading, by the manipulator that is remained on the horizontal plane where the reference line is located, an inventory item located at the preset position. 
     In this embodiment, the manipulator is configured to pull the inventory item. According to an actual situation, the manipulator may be in various forms. For example, the manipulator may be in the form of clip or pallet, but is not limited thereto. In this embodiment, the manipulator drags the inventory item. In some embodiments, according to an actual situation, the manipulator can clamp the inventory item, or support the inventory item, etc., as long as the manipulator can drive the inventory item to move along the reference line. 
     Step  203 : driving, by the telescopic arm, the manipulator loaded with the inventory item to move to the storage frame along the reference line. 
     Step  204 : unloading, by the manipulator that is remained on the horizontal plane where the reference line is located, the inventory item to the storage frame. 
     It should be noted that whether the manipulator moves, loads or unloads the inventory item is carried out on the preset horizontal reference line, having a high utilization rate in the vertical space, and a reasonable utilization of the vertical space. 
     Since the position of the inventory item on the warehouse shelf, i.e., the preset position, may not be on the same horizontal plane as the reference line, a lifting assembly is added to drive the material handling device to move in the vertical direction. During the lifting process of the material handling device, the reference line can be on the same horizontal plane with the inventory item located at any height. 
     In some embodiments, before step  201 , the method for retrieving an inventory item further includes: 
     Step  2005 : driving, by the lifting assembly, the material handling device to move in the vertical direction, so that the manipulator is horizontally opposed to the preset position. 
     Due to an economic factor in terms of land occupation in the warehouse, the value of horizontal space is higher than that of vertical space. Therefore, a preferred option is that the storage frame is provided with a plurality of storage units distributed in a vertical direction. Under the condition of providing the lifting assembly, the lifting assembly can also be fully utilized. 
     In some embodiments, before step  203 , the method for retrieving an inventory item further includes: 
     Step  2025 : driving, by the lifting assembly, the material handling device to move in the vertical direction, so that the material handling device is horizontally opposed to a corresponding storage unit and is therefore at a same height as the corresponding storage unit. 
     The material handling device is opposed to any corresponding storage unit through the lifting assembly, and then the inventory item can be stored in the corresponding storage unit. 
     The handling robot is equipped with the movable chassis, and can move between different warehouse shelves, so that the handling robot can realize the function of transporting the inventory item between different warehouse shelves. 
     In some embodiments, before step  2005 , the method for retrieving an inventory item further includes: 
     Step  2004 : moving the movable chassis to a preset range in front of the warehouse shelf. 
     The movable chassis carries the storage frame, the material handling devices, etc. to move to a preset range in front of the warehouse shelf. The warehouse shelf here may be a warehouse shelf in which an inventory item to be transported is placed, or a warehouse shelf in which an inventory item to be transported needs to be placed. 
     Since the material handling device needs to be aligned with the inventory item, i.e., keeping the inventory item on the reference line, it needs to perform alignment by the lifting assembly in the vertical direction, and perform adjustment by the movable chassis in the horizontal direction, so that the inventory item is located on the reference line in the horizontal direction, improving an accuracy of the manipulator for loading the inventory item. 
     The material handling device is provided with a detection device for detecting a position of the material handling device relative to the inventory item, i.e., detecting whether the inventory item is on the reference line. 
     In some embodiments, before step  203  and after step  2025 , the method for retrieving an inventory item further includes: 
     Step  2026 : detecting, by the detection device, position information of the material handling device relative to the inventory item, and adjusting, by the handling robot, a posture of fetching the inventory item according to the position information of the material handling device relative to the inventory item. 
     In an actual situation, an adjustment of the position of the reference line only by the movable chassis has a low efficiency. This is due to a low efficiency of turning of the present movable chassis on one hand, and a high load of the handling robot and not high accuracy of the movement of the handling robot on the other hand, thereby the adjustment of the position of the reference line only by the movable chassis having a low efficiency. 
     Therefore, it is necessary to perform a joint adjustment in various aspects, to improve the efficiency and accuracy of the posture of fetching the inventory item by the handling robot. 
     Specifically, the movable chassis is provided with a travelling direction, and the movable chassis has the highest efficiency when moving in the travelling direction. 
     The position information of the material handling device relative to the inventory item includes a first position offset between the inventory item and the reference line in the travelling direction. A skilled person in the art knows that the reference line represents the material handling device and that the first position offset is actually a relative position between the material handling device and the inventory item in the travelling direction. In other words, the first position offset actually represents an amount of positional deviation of the material handling device with respect to the inventory item in the travelling direction. 
     In step  2026 , the adjusting, by the handling robot, a posture of fetching the inventory item according to the position information of the material handling device relative to the inventory item includes: 
     Step  2026 A: causing the movable chassis to move in the travelling direction according to the first position offset, so that the first position offset is smaller than a first error value. 
     Since it is difficult to move the movable chassis to a position with a determined value during the adjustment of the movable chassis, the first error value is set. As long as an actual error, i.e., the first position offset, is smaller than the first error value, it can be considered that the movable chassis moves to a desired place. A person skilled in the art can set the first error value in the handling robot in advance according to an actual situation. 
     Further, the position information of the material handling device relative to the inventory item includes a second position offset between the inventory item and the reference line in the vertical direction. A skilled person in the art knows that the second position offset is actually a relative position between the material handling device and the inventory item in the vertical direction. In other words, the second position offset actually represents an amount of positional deviation of the material handling device with respect to the inventory item in the vertical direction. 
     In step  2026 , the adjusting, by the handling robot, a posture of fetching the inventory item according to the position information of the material handling device relative to the inventory item includes: 
     Step  2026 B: driving, by the lifting assembly, the material handling device to move in the vertical direction according to the second position offset, so that the second position offset is smaller than a second error value. 
     It should be noted that, in step  2025 , the material handling device has achieved a preliminary lifting, but the inventory item has not been accurately positioned on the reference line, and by fine-tuning, the reference line can be located near the middle of the inventory item, to improve the accuracy of retrieving the inventory item. A person skilled in the art can set the second error value in the handling robot in advance according to an actual situation. 
     Further, the position information of the material handling device relative to the inventory item includes a distance between the inventory item and the manipulator along the reference line. A skilled person in the art knows that the direction along the reference line represents the direction of extension of telescopic arm and that the distance between the inventory item and the manipulator along the reference line is a distance between the inventory item and the manipulator in a direction of extension of the telescopic arm. 
     In step  2026 , the adjusting, by the handling robot, a posture of fetching the inventory item according to the position information of the material handling device relative to the inventory item includes: 
     Step  2026 C: adjusting an extension amount of the telescopic arm along the reference line according to the distance, so that the extension amount is larger than the distance. 
     It should be understood that by setting the extension amount of the telescopic arm, the time for the telescopic arm to extend to the preset position can be minimized, and the efficiency of retrieving an inventory item can be improved. A person skilled in the art may set the distance in the handling robot in advance according to an actual situation. 
     In this embodiment, the detection device is an image acquisition device. It should be understood that, according to an actual situation, the detection device can also be in other forms. For example, the material handling device is provided with a laser transmitter and a laser receiver, and the inventory item is provided with a reflective surface, and the positioning of the material handling device relative to the inventory item can be realized by the laser transmitter emitting a laser to the reflective surface, and the laser reflected by the reflective surface entering the laser receiver. Alternatively, the material handling device is provided with a radio frequency transmitter, and the inventory item is attached with an electronic label, and the position relationship between the material handling device and the inventory item can be determined by radio frequency identification. 
     Further, when the image acquisition device acquires image information of the inventory item, the detection device detects the position information of the material handling device relative to the inventory item. 
     Further, a surface of the inventory item facing to the handling robot is attached with a two-dimensional code label. When the image acquisition device acquires the image information of the inventory item, the image acquisition device collects the information provided by the two-dimensional code label, and obtain the position information of the material handling device relative to the inventory item. 
     In an actual situation, it may happen that a height of the warehouse shelf and a height of the storage frame are not on the same horizontal plane. At this time, the inventory item cannot be directly transported from the preset position of the warehouse shelf to the storage frame. Installing a temporary storage unit on the material handling device can realize transportation of the inventory item in the case that the height of the warehouse shelf and the height of the storage frame are not on the same horizontal plane. 
     In some embodiments, before step  203 , the method for retrieving an inventory item further includes: 
     Step  2026 : driving, by the telescopic arm, the manipulator loaded with the inventory item to retract to the temporary storage unit along the reference line. 
     Step  2027 : unloading, by the manipulator that is remained on the horizontal plane where the reference line is located, the inventory item to the temporary storage unit. 
     Step  2028 : loading, by the manipulator that is remained on the horizontal plane where the reference line is located, the inventory item located on the temporary storage unit. 
     The inventory item on the warehouse shelf is first transported to the temporary storage unit, and then the lifting assembly lifts or lower to make the temporary storage unit and one storage unit located at the same height, transporting the inventory item to the corresponding storage unit. 
     Since inventory items are solid and mostly cuboid, and in an actual situation, retrieving an inventory item requires a high accuracy when directly facing the inventory item. It is difficult for the reference line to pass through the inventory item and be orthogonal to one surface of the inventory item by movement of the movable chassis in only one horizontal dimension. Therefore, a horizontal dimension is supplemented to increase the flexibility of the adjustment of the posture of fetching the inventory item, which can more quickly adjust the posture of fetching the inventory item and improve accuracy of retrieving the inventory item at the same time. 
     In some embodiments, after step  2028  and before step  203 , the method for retrieving an inventory item further includes: 
     Step  2029 : driving, by the rotation assembly, the telescopic arm to rotate to a preset angle around a vertical direction, so that the material handling device is oriented towards the storage frame. 
     In some embodiments, the position information of the material handling device relative to the inventory item includes a deflection amount between the inventory item and the reference line in the horizontal direction. A skilled person in the art knows that the deflection amount is an amount of angle deviation of the material handling device with respect to the inventory item in the horizontal plane. 
     In step  2026 , the adjusting, by the handling robot, a posture of fetching the inventory item according to the position information of the material handling device relative to the inventory item includes: 
     Step  2026 D: driving, by the rotation assembly, the fork to rotate around a vertical direction according to the deflection amount, so that the deflection amount is smaller than a third error value. 
     A person skilled in the art may set the third error value in the handling robot in advance according to an actual situation. 
     The rotation requires a high precision and requires a high speed to improve efficiency, but it is difficult for the fork to stop at a preset angle due to the inertia during the rotation. 
     In some embodiments, the driving, by the rotation assembly, the fork to rotate around a vertical direction includes: when the deflection detection device detects that the fork has not yet rotated to the preset angle, driving, by the rotation assembly, the fork to continue to rotate; when the deflection detection device detects that the fork has rotated over the preset angle, driving, by the rotation assembly, the fork to rotate in a reverse direction; and when the deflection detection device detects that the fork rotates to the preset angle, causing the rotation assembly to stop rotating. 
     The deflection detection device controls the rotations of the fork, and makes the fork to rotate to the preset angle. 
     Specifically, the deflection detection device includes: a first sensor provided with a first detection range; and 
     a second sensor provided with a second detection range. 
     When the first sensor detects the fork in the first detection range, and the second sensor does not detect the fork in the second detection range, the deflection detection device detects the fork has not yet rotated to the preset angle. 
     When the first sensor does not detect the fork in the first detection range, and the second sensor detects the fork in the second detection range, the deflection detection device detects the fork has rotated over the preset angle. 
     When the first sensor detects the fork in the first detection range, and the second sensor detects the fork in the second detection range, the deflection detection device detects the fork rotates to the preset angle. 
     In order to improve the utilization of the warehouse in the horizontal space, inventory items are placed in positions at two different depths of the warehouse shelf, which may decrease an aisle for the handling robot and improve the utilization rate of the warehouse in the horizontal space. 
     In some embodiments, the inventory item includes a first inventory item and a second inventory item. 
     The preset position includes a first preset position and a second preset position. 
     The first inventory item is located at the first preset position, and the second inventory item is located at the second preset position. 
     The storage frame includes a first storage unit and a second storage unit. 
     When there is the second inventory item behind the first inventory item, the method for retrieving an inventory item further includes: 
     Step  301 : driving, by the telescopic arm, the manipulator to extend to the first preset position of the warehouse shelf along the reference line. 
     Step  302 : loading, by the manipulator that is remained on the horizontal plane where the reference line is located, the first inventory item located at the first preset position. 
     Step  303 : driving, by the telescopic arm, the manipulator loaded with the first inventory item to move to the first storage unit along the reference line. 
     Step  304 : unloading, by the manipulator that is remained on the horizontal plane where the reference line is located, the first inventory item to the first storage unit. 
     Step  305 : driving, by the telescopic arm, the manipulator to move to the second preset position of the warehouse shelf along the reference line. 
     Step  306 : loading, by the manipulator that is remained on the horizontal plane where the reference line is located, the second inventory item located at the second preset position. 
     Step  307 : driving, by the telescopic arm, the manipulator loaded with the second inventory item to move to the second storage unit along the reference line. 
     Step  308 : unloading, by the manipulator that is remained on the horizontal plane where the reference line is located, the second inventory item to the second storage unit. 
     The first inventory item is transported to the first storage unit, and then the second inventory item is transported to the second storage unit. 
     In an actual situation, there may be a case where only the second inventory item is needed and the first inventory item is not needed. 
     In some embodiments, the method for retrieving an inventory item further includes: 
     Step  309 : driving, by the telescopic arm, the manipulator to move to the first storage unit along the reference line. 
     Step  3010 : driving, by the telescopic arm, the manipulator to remain on the horizontal plane where the reference line is located to load the first inventory item located on the first storage unit. 
     Step  3011 : driving, by the telescopic arm, the manipulator loaded with the first inventory item to move to the first preset position of the warehouse shelf along the reference line. 
     Step  3012 A: unloading, by the manipulator that is remained on the horizontal plane where the reference line is located, the first inventory item to the first preset position of the warehouse shelf. 
     In an actual situation, it is not the best choice to place the unwanted first inventory item in the first preset position, because the second preset position is empty, and the second preset position is behind the first preset position, it is still necessary to take out the inventory item in the first preset position when an inventory item needs to be placed in the second preset position, thereby having a low efficiency. 
     In some other embodiments, alternatively, the method for retrieving an inventory item further includes: 
     Step  309 : driving, by the telescopic arm, the manipulator to move to the first storage unit along the reference line. 
     Step  3010 : driving, by the telescopic arm, the manipulator that is remained on the horizontal plane where the reference line is located, to load the first inventory item located on the first storage unit. 
     Step  3011 : driving, by the telescopic arm, the manipulator loaded with the first inventory item to move to the second preset position of the warehouse shelf along the reference line. 
     Step  3012 B: unloading, by the manipulator that is remained on the horizontal plane where the reference line is located, the first inventory item to the second preset position of the warehouse shelf. 
     The inventory items correspond to positions of the warehouse shelf one by one. 
     In some embodiments, the method for retrieving an inventory item further includes: 
     Step  3013 : uploading current position information of the first inventory item. 
     Compared with the prior art, the present application provides a method for retrieving an inventory item based on a handling robot, where the handling robot includes: a storage frame; a material handling device installed on the storage frame and including a telescopic arm and a manipulator installed to the telescopic arm; the method for retrieving an inventory item includes: driving, by the telescopic arm, the manipulator to extend to a preset position of a warehouse shelf along a preset horizontal reference line; loading, by the manipulator that is remained on the reference line, the inventory item in the preset position; driving, by the telescopic arm, the manipulator loaded with the inventory item to move to the storage frame along the reference line, and unloading, by the manipulator that is remained on the reference line, the inventory item to the storage frame. By the above method, the inventory item can be moved to the storage frame along the preset horizontal reference line, the occupied space of the storage frame in the vertical direction is less and a larger number of inventory items can be loaded. 
     Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, not to limit them; based on the idea of the present application, the technical features in the above embodiments or different embodiments may also be combined, the steps can be implemented in any order, and there are many other variations in different aspects of the present application as described above. For simplicity, they are not provided in detail; although the present application has been described in detail with reference to the aforementioned embodiments, a person having ordinary skill in the art should understand that they may still modify technical solutions described in the aforementioned embodiments, or equivalently replace some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.