Abstract:
A vehicle body component mounting system is provided with, along a conveyance path for a vehicle body, an upstream component mounting work area using a cell production system, a central component mounting work area in which the vehicle body is conveyed by an overhead conveyor, and a downstream component mounting work area using the cell production system in this order. Components other than principal components are mounted to the vehicle body using the cell production system. The cell production system is adaptable by increasing the number of component boxes, and thus an increase in the length of the line is prevented. The increase in the length of the line is prevented by using a line production system as a base and also using the cell production system as a part thereof.

Description:
TECHNICAL FIELD 
     The present invention relates to a vehicle body component mounting system whereby components are mounted on a vehicle body which is a workpiece. 
     BACKGROUND ART 
     A line production system is a main stream applied in mounting components on a vehicle body, but recently a cell production system comes to be also applied. The line production system is a method whereby components are mounted on the vehicle bodies, which is moving slowly and continuously, by the hands of operators who are waiting on the side of the line. The cell production system is a method whereby component boxes are disposed around a vehicle body and the components taken out from the component boxes are mounted on the vehicle body. So far, various kinds of the cell production system are proposed as disclosed in Patent Literature 1, for example. 
     A working carriage used in the cell production system disclosed in Patent Literature 1 includes: fixed wheels and free wheels at a lower portion of a support pillar; and a working table is disposed at an upper portion of the support pillar. The working carriage can be manually pushed because the fixed wheels and free wheels are provided. 
     Therefore, the working carriage is moved by an operator&#39;s pushing work along a production line from “START” to “END”. During this time, a component manually taken out by the operator from a component shelf is mounted on a mounting target such as a vehicle body. 
     The operator stops the working carriage on the side of a desired component shelf and mounts the component, and then moves the working carriage to a next component shelf. Since the working carriage is repeatedly moved and stopped, a stop period of the working carriage is varied depending on operator&#39;s skill. As a result, production time control becomes difficult. 
     According to the technology disclosed in Patent Literature 1, the working carriage is assumed to be a handcart or the like, and therefore, the mounting target loaded on the working carriage is limited to a small-sized article. On the other hand, manufacturing a vehicle body having a length of about 5 meters is also desired. However, in the case where the mounting target is such a large-sized article, the number of components is vastly increased, thereby expanding the production line and elongating an operator&#39;s walking distance considerably. In other words, it can be hardly said that the cell production system according to Patent Literature 1 is suitable for the large-sized mounting target such as the vehicle body. 
     Considering this, desired are a component mounting system and a conveying technology which are suitable for the large-sized mounting target such as the vehicle body and can keep the production time constant. 
     Additionally, a carriage, a conveyer, etc. may be utilized to convey the workpiece like the vehicle body and the components, but the workpiece and the components can be continuously conveyed by using the conveyer. As a conveyer that conveys the workpiece and components, there is a known conveying technology whereby the workpiece such as the vehicle body is conveyed (see Patent Literature 2, for example.).  FIG. 33  is a diagram illustrating the conveyer disclosed in Patent Literature 2. 
     As illustrated in  FIG. 33 , a conveyer  200  is used for assembling and conveying the vehicle body. On the conveyer  200 , a supporting floor panel  201  having both ends projected arc-shaped and an intermediate floor panel  202  having both ends recessed arc-shaped are arranged such that a projected arc-shaped portion is fitted into a recessed arc-shaped portion. 
     The intermediate floor panel  202  is connected rotatable around a center shaft of the projected arc-shaped portion of the supporting floor panel  201 . At a curve of a vehicle body conveyance passage  203 , the recessed arc-shaped portion moves along the projected arc-shaped portion, and there is no gap generated between the supporting floor panel  201  and the intermediate floor panel  202 . 
     In the case where the workpiece is a vehicle body, components are needed to be mounted on the vehicle body. To mount the components on the vehicle body placed on the conveyer  200 , the components are needed to be mounted on the moving vehicle body. Therefore, mounting the components becomes easy when the components and the vehicle body are placed together on the conveyer  200 . The vehicle body is placed on the conveyer  200  by a lift or the like. 
     However, since the vehicle body conveyance passage  203  is in a closed state, extra work is necessary to place a plurality of components on the conveyer  200  from a different place, and it is difficult to efficiently supply the components to the conveyance passage  203 . 
     Therefore, demanded is a component conveying system that can efficiently convey and supply components to a conveyance passage by which workpieces are continuously conveyed. 
     PRIOR ART LITERATURE 
     Patent Literature 
     Patent Literature 1: JP 2003-251575 A 
     Patent Literature 2: JP 2007-526861 W 
     SUMMARY OF INVENTION 
     Technical Problem 
     An object of the present invention is to provide a component mounting system and a conveying technology which are suitable for a large-sized mounting target such as a vehicle body and can easily keep a constant production time. 
     Further, another object of the present invention is to provide a component conveying system capable of efficiently conveying and supplying the components to a conveyance passage by which the workpieces such as vehicle bodies are continuously conveyed. 
     Solution to Problem 
     According to a first aspect of the invention, provided is a vehicle body component mounting system configured to mount components on a vehicle body of an automobile, including: a center component mounting work area in which the vehicle body is conveyed while being lifted and at least an engine is mounted on the vehicle body during the conveyance; an upstream component mounting work area in which a kind of components needed to be mounted before the engine is mounted is mounted on the vehicle body based on a cell production system; and a downstream component mounting work area in which a kind of components needed to be mounted after the engine is mounted is mounted on the vehicle body based on the cell production system. The upstream component mounting work area, the center component mounting work area, and the downstream component mounting work area are arranged in order along a conveyance passage of the vehicle body. 
     According to a second aspect of the invention, preferably, the upstream component mounting work area in which the cell production system is executed includes a U-shape conveyance passage projected in a lateral direction with respect to the conveyance passage of the center component mounting work area. 
     According to a third aspect of the invention, preferably, the downstream component mounting work area in which the cell production system is executed includes a U-shape conveyance passage projected in a lateral direction with respect to the conveyance passage of the center component mounting work area. 
     According to a fourth aspect of the invention, provided is a conveying carriage unit configured to convey components and a workpiece as a mounting target on which the components are mounted, including: a component carriage configured to convey the components; and a workpiece carriage arranged in front or back of the component carriage, also connected to the component carriage in a separable manner, and configured to convey the workpiece. The component carriage includes a carriage body, a carriage upper floor mounted on the carriage body and also configured such that an operator can ride, and a component housing section disposed at the carriage upper floor and configured to house the components. The workpiece carriage includes a work floor on which the operator rides, and the conveying carriage unit is connected to preceding and following conveying carriage units in a turnable manner. 
     According to a fifth aspect of the invention, preferably, the component housing section includes a first component housing section configured to house components to be mounted on the workpiece, and a second component housing section disposed in front or back of the workpiece and configured to house components to be mounted on the workpiece. The carriage upper floor is a turntable supported by the carriage body in a rotatable manner, and rotation of the turntable is controlled by a rotation angle control section such that a distance from the first component housing section to the workpiece becomes substantially equal to a distance from the second component housing section to the workpiece disposed in front or back. 
     According to a sixth aspect of the invention, preferably, the workpiece carriage is disposed in back of the component carriage, and right and left sub-component carriages are further connected to the component carriage, having the left sub-component carriage disposed on a left side of the workpiece carriage and the right sub-component carriage disposed on a right side of the workpiece carriage. 
     According to a seventh aspect of the invention, provided is a component conveying system in which a floor panel having both ends recessed arc-shaped and configured to load a workpiece and a carriage upper floor having both ends projected arc-shaped and configured to load components to be mounted on the workpiece are arranged such that the projected arc-shaped portion is fitted into the recessed arc-shaped portion, the floor panel is connected to the carriage upper floor in a separable and rotatable manner around a center shaft of the projected arc-shaped portion of the carriage upper floor, and also configured to be conveyed continuously. The component conveying system includes: a U-shape conveyance passage disposed at a conveyance passage for the workpiece and configured to guide the floor panel and the carriage upper floor mutually connected via at least one curved portion; a connect station disposed at an upstream side end portion of the U-shape conveyance passage and configured to connect the floor panel to the carriage upper floor; a release station disposed at a downstream side end portion of the U-shape conveyance passage and configured to release connection of the floor panel from the carriage upper floor, and a component station configured to bring in the carriage upper floor released at the release station, fill the carriage upper floor with the components, and send out the carriage upper floor to the connect station. 
     According to an eighth aspect of the invention, preferably, the component conveying system further includes: a load station whereby the workpiece is loaded on the floor panel before the floor panel reaches the connect station; and an unload station whereby the workpiece is unloaded from the floor panel after the floor panel has passed the release station, wherein the floor panel is conveyed from the unload station to the load station in a circulating manner. 
     According to a ninth aspect of the invention, preferably, the component station includes a collect station configured to collect an emptied component housing section from the carriage upper floor after the carriage upper floor has passed the release station, and a supply station configured to supply the carriage upper floor with the component housing section filled with the components before the carriage upper floor reaches the connect station, and the carriage upper floor is conveyed from the collect station to the supply station in a circulating manner. 
     According to an tenth aspect of the invention, provided is a conveying carriage unit configured to convey components and a workpiece as a mounting target on which the components are mounted, including: a workpiece carriage configured to convey the workpiece; and a component carriage disposed adjacent to the workpiece carriage and configured to convey a part of the components. The workpiece carriage includes a work floor on which an operator rides, the component carriage includes a carriage body, a carriage upper floor mounted on the carriage body, and a component housing section disposed on the carriage upper floor and configured to house a part of the components, and the conveying carriage unit is connected to preceding and following conveying carriage units in a turnable manner. 
     According to an eleventh aspect of the invention, provided is a conveying carriage unit configured to convey components and a workpiece as a mounting target on which the components are mounted, including: a workpiece carriage configured to convey the workpiece; a component carriage disposed adjacent to the workpiece carriage and configured to convey a part of the components, and right and left sub-component carriages pulled by the component carriage or the workpiece carriage and configured to convey a remaining part of the components. The workpiece carriage includes a work floor on which an operator rides, the component carriage includes a carriage body, a carriage upper floor mounted on the carriage body, and a component housing section disposed on the carriage upper floor and configured to house a part of the components, the right and left sub-component carriages are disposed on the sides of a workpiece carriage of a following conveying carriage unit, and the conveying carriage unit is connected to preceding and following conveying carriage units in a turnable manner. 
     According to a twelfth aspect of the invention, preferably, the component housing section includes a first component housing section configured to house components to be mounted on the workpiece, and a second component housing section configured to house components to be mounted on a workpiece disposed in back of the workpiece. The carriage upper floor is a turntable supported by the carriage body in a rotatable manner, and rotation of the turntable is controlled by a rotation angle control section such that a distance from the first component housing section to the workpiece becomes substantially equal to a distance from the second component housing section to the workpiece disposed in back. 
     According to a thirteenth the invention, provided is a component conveying system including: a connection release station disposed on a workpiece conveyance passage and configured to release connection between preceding and following conveying carriage units, and an equipment mounting station whereby equipment is mounted on the workpiece from a side on the following conveying carriage unit when the preceding conveying carriage unit moves forward and the following conveying carriage unit has the side of the workpiece carriage opened. 
     Advantageous Effects of Invention 
     According to the first aspect of the invention, the upstream component mounting work area based on a cell production system, the center component mounting work area in which the vehicle body is conveyed by an overhead conveyer, and the downstream component mounting work area based on the cell production system are arranged along the conveyance passage of the vehicle body in this order. 
     The components to be mounted on the vehicle body conveyed from a coating process are various. However, as for the engine, one engine is mounted on one vehicle body although its size and shape are varied by the displacement. As for a suspension also, four suspensions of front, back, right and left in total are mounted on one vehicle although its size and shape are varied. Thus, the components (such as the engine) having a constant component count are mounted in the center component mounting work area. Additionally, other components to be mounted on a floor bottom surface of the vehicle body are mounted. Since the mounting work is carried out during slow movement by the overhead conveyer, the work based on a line production system is executed in the center component mounting work area. 
     The number of components such as interior trim is increased in a so-called classy car, compared to a typical car. In other words, the number of components other than main components (an engine, etc.) is varied by the kinds of vehicle. In the case where the components other than the main components are mounted based on the line production system, a line length is necessarily elongated because the line length is determined in consideration of a maximum number of the components. 
     According to the present invention, the components other than the main components are mounted based on the cell production system. According to the cell production system, increase of the line length is suppressed because increase of the components can be handled by increasing the number of component boxes. In other words, the present invention is based on the line production system, and concurrently the cell production system is applied in part. Therefore, elongating the line length is suppressed. 
     Further, since the present invention is based on the line production system, variation of a production time can be avoided, and the production time is kept constant. Therefore, according to claim  1 , the present invention is suitable for a large-sized mounting target such as the vehicle body, and capable of easily keeping the constant production time and also reducing the line length. 
     According to the second aspect of the invention, the upstream component mounting work area where the cell production system is executed includes the U-shape conveyance passage laterally projected with respect to the conveyance passage of the center component mounting work area. The number of components needed to be mounted before the engine is mounted can be increased or reduced by adjusting the projected length of the U-shape conveyance passage. Since an apparent line length is determined by a direction of the conveyance passage of the center component mounting work area, the apparent line length is not influenced even though the projected length of the U-shape conveyance passage is increased. Therefore, the apparent line length can be reduced by adopting the U-shape conveyance passage. 
     According to the third aspect of the invention, the downstream component mounting work area where the cell production system is executed includes the U-shape conveyance passage projected in the lateral direction with respect to the conveyance passage of the center component mounting work area. The number of components needed to be mounted after the engine is mounted can be increased or reduced by adjusting the projected length of the U-shape conveyance passage. Since an apparent line length is determined by the direction of the conveyance passage of the center component mounting work area, the apparent line length is not influenced even though the projected length of the U-shape conveyance passage is increased. Therefore, the apparent line length can be reduced by adopting the U-shape conveyance passage. 
     According to the fourth aspect of the invention, since the workpiece carriage and the component carriage can be connected, the workpiece carriage and the component carriage can be continuously conveyed. The operator can work while riding the component carriage or the workpiece carriage. Since there is no need to stop the workpiece carriage for a long time, the production time is kept constant. 
     Also, the conveying carriage unit is connected to the preceding and following conveying carriage units in a turnable manner, and therefore, a conveying traffic line can be meandered. A length of the conveying traffic line can be elongated by such meandering, and expansion of an assembly work area can be avoided. 
     Further, one of the workpiece carriage and the component carriage is made to self-travel, thereby achieving to pull the other one. Consequently, the operator does not need to manually push the carriage, and a heavy article like the vehicle body can be conveyed. Therefore, according to claim  4 , the present invention is suitable for the large-sized mounting target such as the vehicle body, and the production time can be easily kept constant. 
     According to the fifth aspect of the invention, rotation of the turntable is controlled by the rotation angle control section such that the distance from the first component housing section to the workpiece becomes substantially equal to the distance from the second component housing section to the workpiece disposed in front or back. By controlling rotation of the turntable, work efficiency related to the first component housing section and work efficiency related to the second component housing section is equalized. As a result, component mounting work can be leveled. 
     According to the sixth aspect of the invention, the right and left sub-component carriages are additionally connected to the component carriage, having the left sub-component carriage disposed on the left side of the workpiece carriage and the right sub-component carriage disposed on the right side of the workpiece carriage. The moving distance of the component can be shortened, thereby improving operating efficiency. 
     According to the seventh aspect of the invention, the connect station disposed at the upstream side end portion of the U-shape conveyance passage and configured to connect the floor panel to the carriage upper floor, and the release station disposed at the downstream side end portion of the U-shape conveyance passage and configured to release connection of the floor panel from the carriage upper floor are provided. 
     Since the floor panel can be separated from the carriage upper floor, the carriage upper floor released at the release station can be brought into the component station, and the carriage upper floor is filled with the components and then sent out to the connect station. As a result, work efficiency in supplying the components is improved, and the components can be efficiently conveyed and supplied to the conveyance passage by which the workpieces are continuously conveyed. 
     According to the eighth aspect of the invention, the load station whereby the workpiece is loaded on the floor panel before the floor panel reaches the connect station, and the unload station whereby the workpiece is unloaded from the floor panel after the floor panel has passed the release station are provided. 
     The workpiece mounted with the components is unloaded from the floor panel, and the emptied floor panel is promptly conveyed from the unload station to the load station in a circulating manner. Therefore, productivity can be improved. 
     According to the ninth aspect of the invention, the component station includes the collect station configured to collect the emptied component housing section from the carriage upper floor, and the supply station configured to supply the component housing section filled with the components to the carriage upper floor. 
     Since the emptied component housing section is only replaced by the component housing section already filled with a plurality of components, man-hours for supplying the components to the carriage upper floor can be shortened. In addition, since the carriage upper floor is promptly conveyed from the collect station to the supply station in a circulating manner, productivity in supplying the components can be improved. Thus, according to the present invention, supplying the workpiece and supplying the components can be separately and concurrently executed in the workpiece conveyance passage, and therefore, productivity can be more improved. 
     According to the tenth aspect of the invention, the conveying carriage unit includes the workpiece carriage disposed adjacent to the component carriage, and therefore, the workpiece carriage and the component carriage can be continuously conveyed. The operator can work while riding the conveying carriage unit. Since there is no need to stop the conveying carriage unit for a long time while the operator is mounting the components, the production time is kept constant. 
     Further, the conveying carriage unit has the side of the workpiece carriage opened. Since the lifter can be disposed on the side of the workpiece carriage, the heavy article such as the vehicle body can be moved from the workpiece carriage by the lifter. As a result, the lifter can be used while the workpiece carriage is disposed adjacent to the component carriage without separating the component carriage from the workpiece carriage, and productivity can be improved. 
     According to the eleventh aspect of the invention, the component carriage is disposed adjacent to the workpiece carriage in the conveying carriage unit, and therefore, the workpiece carriage and the component carriage can be continuously conveyed. The operator can work while riding the conveying carriage unit. Since there is no need to stop the conveying carriage unit for a long time while the operator is mounting the components, the production time is kept constant. 
     Further, since the conveying carriage unit is connected to the preceding and following conveying carriage units in a turnable manner, the conveying traffic line can be meandered. The length of the conveying traffic line can be elongated by such meandering, and expansion of an assembly work area can be avoided. 
     Furthermore, the operator does not need to manually push the carriage because the conveying carriage unit is self-traveled or moved by being hooked on a chain hook which moves in a circulating manner. Consequently, a large amount of the components can be conveyed and further the heavy article such as the vehicle body can be conveyed. Therefore, according to claim  11 , the present invention is suitable for the large-sized mounting target such as the vehicle body, and the production time can be easily kept constant. 
     Moreover, the components are loaded on the conveying carriage unit and also the operator rides on the same conveying carriage unit, thereby positioning the components near the operator. Therefore, the moving distance of the operator can be shortened and working efficiency can be improved. 
     Additionally, the side of the workpiece carriage of the following conveying carriage unit is opened when connection of the preceding conveying carriage unit is released and is moved forward. Since the lifter can be disposed on the side of the workpiece carriage, the heavy article such as the vehicle body can be moved from the workpiece carriage by the lifter. As a result, the lifter can be used while the workpiece carriage is disposed adjacent to the component carriage without separating the component carriage from the workpiece carriage, and productivity can be improved. 
     According to the twelfth aspect of the invention, rotation of the turntable is controlled by the rotation angle control section such that the distance from the first component housing section to the workpiece becomes substantially equal to the distance from the second component housing section to the workpiece disposed in front or back. By controlling rotation of the turntable, work efficiency related to the first component housing section and work efficiency related to the second component housing section is equalized. As a result, component mounting work can be leveled. 
     According to the thirteenth aspect of the invention, the connection release station and the equipment mounting station are provided. When connection between the preceding and following conveying carriage units is released and the preceding conveying carriage unit is moved forward, the side of the workpiece carriage of the following conveying carriage unit is opened. An assist device configured to assist in lifting the equipment can be disposed on the side of the workpiece carriage. As a result, the large equipment such as a sheet can be mounted on the workpiece like the vehicle body on the following conveying carriage unit, and operating efficiency can be improved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a plan view illustrating a conveying carriage unit according to a first embodiment of the present invention. 
         FIG. 2  is a perspective view illustrating a workpiece carriage illustrated in  FIG. 1 . 
         FIG. 3  is a perspective view illustrating the workpiece carriage illustrated in  FIG. 2 , viewed from a bottom surface. 
         FIG. 4  is an exploded perspective view illustrating a component carriage illustrated in  FIG. 1 . 
         FIG. 5  is a cross-sectional view taken along a line  5 - 5  in  FIG. 4 . 
         FIG. 6  is a diagram viewed from an arrow  6  in  FIG. 5 . 
         FIG. 7  is a diagram illustrating operation of a rotary sensor illustrated in  FIG. 6 . 
         FIGS. 8( a ) and 8( b )  are diagrams illustrating operation of the conveying carriage unit. 
         FIG. 9  is a perspective view illustrating the conveying carriage unit illustrated in  FIG. 1 . 
         FIG. 10  is a diagram illustrating arrangement of lifters selected from component mounting facility. 
         FIG. 11  is a diagram illustrating arrangement of overhead conveyers selected from the component mounting facility. 
         FIG. 12  is a diagram illustrating arrangement of workpiece conveyance passages selected from the component mounting facility. 
         FIG. 13  is a diagram illustrating a detail plan of the component mounting facility. 
         FIG. 14  is an explanatory diagram illustrating the component conveying system illustrated in  FIG. 13 . 
         FIG. 15  is a diagram illustrating a modified example of an upstream component mounting work area illustrated in  FIG. 13 . 
         FIG. 16  is a plan view illustrating a conveying carriage unit according to a second embodiment of the present invention. 
         FIG. 17  is a perspective view illustrating a workpiece carriage illustrated in  FIG. 16 . 
         FIG. 18  is a perspective view illustrating the workpiece carriage illustrated in  FIG. 16 , viewed from a bottom surface. 
         FIG. 19  is an exploded perspective view illustrating a component carriage illustrated in  FIG. 16 . 
         FIG. 20  is a cross-sectional view taken along a line  20 - 20  in  FIG. 19 . 
         FIG. 21  is a diagram viewed from an arrow  21  in  FIG. 20 . 
         FIG. 22  is a diagram illustrating operation of a rotary sensor illustrated in  FIG. 21 . 
         FIGS. 23( a ) and 23( b )  are diagrams illustrating operation of the conveying carriage unit. 
         FIG. 24  is a perspective view illustrating the conveying carriage unit illustrated in  FIG. 16 . 
         FIG. 25  is a diagram illustrating arrangement of overhead conveyers selected from the component mounting facility. 
         FIG. 26  is a diagram illustrating arrangement of workpiece conveyance passages selected from the component mounting facility. 
         FIG. 27  is a diagram illustrating a detail plan of the component mounting facility. 
         FIG. 28  is an explanatory diagram illustrating the component conveying system illustrated in  FIG. 27 . 
         FIG. 29  is a diagram illustrating operation of an assist device. 
         FIG. 30  is a diagram illustrating operation of a lifter. 
         FIG. 31  is a diagram illustrating operation of a hanger. 
         FIG. 32  is a diagram illustrating a modified example of an upstream component mounting work area illustrated in  FIG. 28 . 
         FIG. 33  is a schematic diagram illustrating a conveying technology for a vehicle body or the like in a related art. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Preferred embodiments according to the present invention will be described below in detail based on the attached drawings. 
     First Embodiment 
     A system for mounting vehicle body components and conveying the components according to the present invention is implemented by a “component mounting facility”. A “conveying carriage unit” is an important element among elements constituting the component mounting facility. Accordingly, the “conveying carriage unit” will be described first, and later the “component mounting facility” will be described. 
     As illustrated in  FIG. 1 , a conveying carriage unit  10  includes a workpiece carriage  20  configured to convey a vehicle body  12  as a workpiece (mounting target), a component carriage  40  disposed in front of the workpiece carriage  20  and configured to convey a component  13 , and right and left sub-component carriages  70 L,  70 R pulled by the component carriage  40  and disposed on the sides of the workpiece carriage  20 . A reference sign  40   r  indicated by an imaginary line is a component carriage following behind. 
     The carriages  20 ,  40 ,  70 L, and  70 R will be individually described in detail. 
     As illustrated in  FIG. 2 , main elements of the workpiece carriage  20  are a frame body  21  formed by assembling steel material in a lattice shape, a floor panel  22  laid over the frame body  21 , and four workpiece receiving bases  23  placed on the floor panel  22 . The floor panel  22  includes recessed arc-shaped portions  22   a ,  22   a  formed by cutting front and rear portions in a recessed arc-shape. Additionally, the floor panel  22  includes work floors  24 L,  24 R applied with non-slip work on right and left side portions of the floor panel. A first operation post  25  is disposed at a rear portion of the one work floor  24 R. 
     Positioning pins  26 ,  26  are erected on the workpiece receiving bases  23 ,  23  respectively. The vehicle body  12  ( FIG. 1 ) is positioned in a horizontal direction by these positioning pins  26 ,  26 . Then, the vehicle body is supported by the four workpiece receiving bases  23 . 
     Two right and left eye plates  27 L,  27 R are provided at a front portion of the frame body  21 . The eye plates  27 L,  27 R are the plates having open holes  28  respectively. Further, a long arm  29  is extended rearward from a rear portion of the frame body  21 , and a first locking mechanism  31  is provided at a tip of the long arm  29 . The first locking mechanism  31  is, preferably, a cylinder unit having a pin  32  protruded upward. The cylinder unit may be any one of an air cylinder, a hydraulic cylinder, and an electric cylinder. The pin  32  can be vertically moved by operating an operating element  25   a  of the first operation post  25 . The operating element  25   a  may be any one of a push button, a lever, and a touch sensor, regardless of types. 
     As illustrated in  FIG. 3 , a plurality of universal wheels  33  is provided at a lower surface of the frame body  21 . The universal wheel  33  is also referred to as a caster, and does not prevent the carriage from turning by the universal wheel itself turning. Additionally, a drive box  34  is provided at a center of the lower surface of the frame body  21 . The drive box  34  includes a motor and a drive source inside thereof, and right and left drive wheels  35 L,  35 R are driven by the drive source. The drive wheels  35 L,  35 R contact a track (or road surface) and cause the workpiece carriage  20  to self-travel. Further, a guide wheel  36  is protruded from the drive box  34 . The guide wheel  36  plays a role of determining a traffic line of the workpiece carriage  20  by being fitted into a U-shape conveyance passage later described. The guide wheel  36  may be a non-rotational guide shoe. 
     As illustrated in  FIG. 4 , main elements of the component carriage  40  are a carriage body  41  formed by assembling steel material in a lattice shape, a plurality of universal wheels  42  attached to a lower surface of the carriage body  41 , a plurality of rollers  43  attached to an upper surface of the carriage body  41 , a circular carriage upper floor  44  mounted on the carriage body  41  in a manner placing on the rollers  43 , a roof-type frame  45  disposed at the carriage upper floor  44 , a first component housing section  46  and a second component housing section  47  provided at the roof-type frame  45 . The carriage upper floor  44  is provided with a second operation post  48  including two operating elements  48   a ,  48   b.    
     On the circular carriage upper floor  44 , an area surrounding the first component housing section  46  and second component housing section  47  is set as a work floor  44   a , and an operator works on this work floor  44   a . Meanwhile, according to the embodiment, the shape of the carriage upper floor  44  has been described to be circular, but not limited thereto, the shape of the carriage upper floor  44  may be other shapes, such as an oval, as long as projected arc-shaped portions  44   b ,  44   b  each having a projected arc-shape are formed in front and back of the carriage upper floor  44 . 
     Further, right and left plates  51 L,  51 R are extended rearward from a rear portion of the carriage body  41 , and second locking mechanisms  52 L,  52 R are provided at the plates  51 L,  51 R respectively. The second locking mechanisms  52 L,  52 R are, preferably, cylinder units having pins  53  protruded upward in the same manner as the first locking mechanism  31  ( FIG. 2 ). The cylinder unit may be any one of an air cylinder, a hydraulic cylinder, and an electric cylinder. The pins  53 ,  53  can be vertically moved by operating an operating element  48   a  of the second operation post  48 . 
     The pins  53 ,  53  are fitted into the eye plates  27 L,  27 R on the workpiece carriage  20  side from below, and therefore, the component carriage  40  travels together with the workpiece carriage  20  without laterally swinging and turning. 
     Also, side arms  54 L,  54 R are extended from right and left sides of the carriage body  41 , and third locking mechanisms  55 L,  55 R are provided at the side arms  54 L,  54 R respectively. The third locking mechanisms  55 L,  55 R are, preferably, cylinder units having pins  56 ,  56  protruded upward in the same manner as the second locking mechanisms  52 L,  52 R. The cylinder unit may be any one of an air cylinder, a hydraulic cylinder, and an electric cylinder. The pins  56 ,  56  can be vertically moved by operating an operating element  48   b  of the second operation post  48 . 
     As illustrated in  FIG. 5 , a perforated plate  57  is provided at a lower center portion of the carriage body  41  and a shaft bearing block  58  is provided at an upper center portion thereof. A center shaft  59  is extended downward from a center of the carriage upper floor  44 , and a tip of the center shaft  59  is fitted into the shaft bearing block  58 . Since the carriage upper floor  44  is supported by the plurality of rollers  43 , no downward load is applied to the shaft bearing block  58 . The shaft bearing block  58  exerts an effect of guiding the center shaft  59  in a rotatable manner. 
     A driven gear  61  is provided halfway at the center shaft  59 . A servo motor  62  is disposed near the driven gear  61 , and the driven gear  61  is rotated by a drive gear  63  driven by the servo motor  62 . As a result, the carriage upper floor  44  horizontally turns around the center shaft  59 . In other words, the carriage upper floor  44  is a turntable. 
     The servo motor  62  is provided with an encoder  64  configured to detect a rotation angle and a rotary direction of a motor center shaft  59 . Further, the carriage body  41  is provided with a rotary sensor  65  and a rotation angle control section  66  in addition to the servo motor  62 . Operation of the rotary sensor  65  will be described later. Note that angle information from the rotary sensor  65  and angle information from the encoder  64  are input to the rotation angle control section  66 . The rotation angle control section  66  controls the servo motor  62  based on the angle information. 
     The pin  32  is positioned at the center shaft  49  of the projected arc-shaped portion  44   b  (carriage upper floor  44 ). The pin  32  is vertically moved by operating the operating element  25   a  illustrated in  FIG. 2 , thereby connecting the workpiece carriage  20  to the component carriage  40 . In other words, the floor panel  22  is connected to the carriage upper floor  44  via the pin  32  in a separable manner. 
     The workpiece carriage  20  is rotatably connected to the position of the center shaft  49  of the projected arc-shaped portion  44   b  by the pin  32 . In other words, the floor panel  22  is rotatably connected to the carriage upper floor  44  at the position of the center shaft  49 . 
     A front portion of the component carriage  40  is connected to the workpiece carriage  20  on the front side via the pin  53 , and a rear portion of the component carriage  40  is connected to the workpiece carriage  20  on the rear side via the pin  32 . In other words, the floor panel  22  and the carriage upper floor  44  are alternately and continuously conveyed. 
     As illustrated in  FIG. 6 , the tip of the long arm  29  is fitted into a fork-shaped arm  67  extending from the rotary sensor  65 . In  FIG. 6 , the fork-shaped arm  67  is not tilted because the long arm  29  is not tilted. 
     As illustrated in  FIG. 5 , the long arm  29  is horizontally rotatable around the pin  32  of the first locking mechanism  31 . As a result, the long arm  29  may rotate around the pin  32  by only an angle 2θ as illustrated in  FIG. 7 . The rotation angle 2θ is detected by the rotary sensor  65 . 
     As illustrated in  FIG. 8( a ) , the vehicle body  12  is placed in back of the component carriage  40  and further a preceding vehicle body  12   f  is placed in front of the component carriage  40 . As shown by an arrow ( 1 ), a component is taken out from the first component housing section  46  and mounted on the vehicle body  12 . Also, as shown by an arrow ( 2 ), a component is taken out from the second component housing section  47  and mounted on the preceding vehicle body  12   f.    
     In the case where the preceding workpiece carriage  20   f  is turned by the angle 2θ with respect to the workpiece carriage  20 , the carriage upper floor  44  is rotated by the angle θ as illustrated in  FIG. 8( b ) . This operation is executed by the rotation angle control section  66  ( FIG. 5 ). 
     As a result, rotation of the turntable (carriage upper floor  44 ) is controlled by the rotation angle control section  66  such that a distance L from the first component housing section  46  to the vehicle body  12  becomes substantially equal to a distance Lf from the second component housing section  47  to preceding vehicle body  12   f  (describing by the angle, the angles of the component housing section with respect to the preceding and following vehicle bodies become equal). By controlling rotation of the turntable (carriage upper floor  44 ), work efficiency related to the first component housing section  46  and work efficiency related to the second component housing section  47  are equalized. As a result, component mounting work can be leveled. 
     More specifically, as illustrated in  FIG. 8( a ) , conveyance is continuously executed at a constant speed without stop in normal operation. As illustrated in  FIG. 8( b ) , when coming at a corner, the turntable on the component carriage is rotated so as to adjust the angles of the component housing section with respect to the preceding and following vehicle bodies to become equal, thereby minimizing moving distances of operators riding the preceding and following carriages to reach the component. 
     A turning center of the turntable  44  is the pin  32  illustrated in  FIG. 5 . The turning center and rotary center (center shaft  59 ) of the turntable (carriage upper floor  44 ) is the same axis. More specifically, since the turning center of the conveying carriage unit and the rotary center of the turntable are the same axis, relative positions of the component housing sections  46 ,  47  with respect to the vehicle body  12  are easily controlled. 
     As illustrated in  FIG. 9 , the right and left sub-component carriages  70 L,  70 R are pulled by the component carriage  40 . A pin  56  of the third locking mechanism  55 L can be moved down by operating the operating element  48   b  provided at the second operation post  48 . As a result, the sub-component carriage  70 L is separated from the component carriage  40 . The sub-component carriage  70 R can be separated in the same manner. By operating the operating element  48   b , connecting the sub-component carriages  70 L,  70 R to the component carriage  40  and separating the sub-component carriages  70 L,  70 R from the component carriage  40  can be optionally executed. 
     In  FIG. 1 , the right and left sub-component carriages  70 L,  70 R are additionally connected to the component carriage  40 , having the left sub-component carriage  70 L disposed on the left side of the workpiece carriage  20  and the right sub-component carriage  70 R disposed on the right side of the workpiece carriage  20 . The moving distance of the component can be shortened, thereby improving operating efficiency. 
     However, the sub-component carriages  70 L,  70 R can be omitted. Therefore, the necessary elements of the conveying carriage unit  10  are the workpiece carriage  20  and the component carriage  40  placed in front of the workpiece carriage  20 . The component carriage  40  may also be placed in back of the workpiece carriage  20  as illustrated by the imaginary line in  FIG. 1 . Therefore, the component carriage  40  is placed in front or back of the workpiece carriage  20 . 
     More specifically, in  FIG. 1 , the conveying carriage unit  10  includes the component carriage  40  configured to convey the components, and the workpiece carriage  20  placed in front or back of the component carriage  40 , and configured to be connected to the component carriage  40  in a separable manner and convey the workpiece (vehicle body  12 ). As illustrated in  FIGS. 8( a ) and ( b ) , the component carriage  40  is connected to the front and back of the workpiece carriage  20  in a turnable manner. 
     Since the workpiece carriage  20  and the component carriage  40  are connectable, the workpiece carriage  20  and the component carriage  40  can be continuously conveyed. The operator can work while riding on the component carriage  40  or workpiece carriage  20 . Since there is no need to stop the workpiece carriage  20  for a long time, the production time is kept constant. 
     Further, the conveying carriage unit  10  is connected to the preceding and following conveying carriage units  10  in a turnable manner, and therefore, a conveying traffic line can be meandered. The meandered conveying traffic line can elongate the conveying traffic line, and expansion of an assembling area can be avoided. 
     Further, one of the workpiece carriage  20  and the component carriage  40  is made to self-travel, thereby achieving to pull the other one. Consequently, the operator does not need to manually push the carriage, and a heavy article like the vehicle body can be conveyed. 
     The component conveying system adopted with the above-described conveying carriage unit  10  will be described below. The component mounting facility  80  for operating the component conveying system is illustrated in  FIG. 13 . A description will be first provided for each of categories extracted in  FIGS. 10 to 12  since the facility configuration is complex. 
       FIG. 10  is a diagram illustrating arrangement of lifters, and a discharge line  83  extends from a coating process  81  to a first lifter  82 . The discharge line  83  is substantially an L-shaped to change directions. An assembly line  85  extends from the first lifter  82  to an inspection process  84 . The first lifter  82 , a second lifter  86 , a third lifter  87 , a fourth lifter  88 , and a fifth lifter  89  are arranged on the assembly line  85 . The assembly line  85  corresponds to the “conveyance passage” in the present invention. 
       FIG. 11  is a diagram illustrating arrangement of overhead conveyers, and a first overhead conveyer  91  is arranged along the discharge line  83 . The vehicle body  12  finished with coating is hung by a hanger  92  of the first overhead conveyer  91  and carried to above the first lifter  82 . 
     Further, a second overhead conveyer  93  is arranged along the assembly line  85 . The second overhead conveyer  93  conveys the vehicle body  12  being hung by the hanger  94 , and components to be mounted on the floor bottom surface of the vehicle body, such as an engine, is mounted on the vehicle body  12  while conveying the vehicle body  12 . 
     Additionally, a third overhead conveyer  96  is provided, whereby a door  95  is received between the first overhead conveyer  91  and the second overhead conveyer  93 , a window regulator or the like is built in the door  95 , and the door is transferred to an entrance side of the inspection process  84 . 
       FIG. 12  is a diagram illustrating arrangement of the conveyance passages for a workpiece, and an upstream component mounting work area  97  is positioned between the first lifter  82  and the second lifter  86 , and a U-shape conveyance passage  98  orthogonally or obliquely projected in a lateral direction from the assembly line  85  is disposed between the first lifter  82  and the second lifter  86 . The conveying carriage unit  10  loaded with the vehicle body  12  moves along the U-shape conveyance passage  98  having a curved portion  99 . Additionally, component-only conveyance passages  101 ,  102  are connected at a leg portion of the U-shape conveyance passage  98  as indicated by a dash line, and in a component station  110  the component carriage  40  filled with the components is fed to the U-shape conveyance passage  98  from the component-only conveyance passage  101 . Further, the emptied component carriage  40  is sent back to the component-only conveyance passage  102  from the U-shape conveyance passage  98 . The sub-component carriages  70 L,  70 R are pulled by the component carriage  40 . 
     A downstream component mounting work area  103  is positioned between the third lifter  87  and the fourth lifter  88 , and the U-shape conveyance passage  98  projected in a lateral direction from the assembly line  85  is disposed between the third lifter  87  and the fourth lifter  88 . A description for others will be omitted here for being same as the upstream component mounting work area  97 . 
     A center component mounting work area  104  is positioned between the second lifter  86  and the third lifter  87 , and components to be mounted on the floor bottom surface of the vehicle body, such as the engine, are mounted in the center component mounting work area  104 . 
     The component mounting facility  80  illustrated in  FIG. 13  is completed by combining the above-described configurations. The component mounting facility  80  includes the upstream component mounting work area  97 , center component mounting work area  104 , and downstream component mounting work area  103 . 
     In the center component mounting work area  104 , the components to be mounted on the floor bottom surface of the vehicle body, such as the engine, are mounted on a vehicle body  12 C to be conveyed while being hung at the second overhead conveyer  93 . More specifically, the components mounted in the work area are an engine front suspension assembly (assembly preliminarily assembled with constituting components of the engine and a front suspension), a rear suspension assembly (assembly preliminarily assembled with constituting components of the a rear suspension), and other components to be mounted on the floor bottom surface of the vehicle body (components that can be mounted on the vehicle body only in a upward moving state). Further, the engine front suspension assembly and rear suspension assembly are respectively conveyed to a mounting station in an assembled state, and lifted by an automatic mounting machine from below the vehicle body, and fastened with a bolt in a docked state with the vehicle body. In this work area, stop-and-go conveyance is executed at least in this station. 
     In the upstream component mounting work area  97 , components needed to be mounted on the vehicle body before the engine is mounted, namely, the components that cannot be mounted after the engine is mounted are mounted based on a cell production system. Examples of such components are members to be mounted on an engine room wall surface (e.g., a radiator, a pedal assembly, a steering column, a brake hose, etc.). Additionally, other components are suitably mounted in the upstream component mounting work area  97 . 
     More specifically, in the upstream component mounting work area  97 , a plurality of operators ride on one carriage, and the components are mounted during the time of conveyance from a start point to an end point of this work area. This work corresponds to the work based on the cell production system. In the normal operation, conveyance is continuously executed at a constant speed without stop. When coming at a corner, the turntable on the component carriage is rotated such that angles of the component housing section with respect to the preceding and following vehicle bodies are adjusted to be equal, thereby minimizing the moving distance of the operators riding on the preceding and following carriages to reach the component. 
     The work based on the cell production system is also executed in the downstream component mounting work area  103  in the same manner. In the downstream component mounting work area  103 , components needed to be mounted on the vehicle body after the engine is mounted, namely, the components that can be mounted only after the engine is mounted are mounted based on the cell production system. Examples of such components are a battery, an air cleaner filter, an engine mount side bracket, an engine fastening bolt, and so on. Further, fuel injection work or oil injection work are executed in the area  103 . Furthermore, other components are suitably mounted in the downstream component mounting work area  103 . 
     Next, general operation will be described. A vehicle body  12 A finished with coating (coat-finished vehicle body) is transferred from the hanger  92  to the first lifter  82 . An underbody harness is set on the vehicle body  12 A. Below the first lifter  82 , only the workpiece carriage  20  separated from the component carriage  40  is waiting. The vehicle body  12 A is transferred to the workpiece carriage  20  by lowering the first lifter  82 . A load station  111  to load the vehicle body  12 A as the workpiece on the floor panel  22  of the workpiece carriage  20  is disposed below the first lifter  82 . 
     The workpiece carriage  20  loaded with the vehicle body  12 A moves forward. A door is removed at a door removing stage  105 . The vehicle body without the door is denoted by the reference sign  10 B. Further, the removed door is carried by the third overhead conveyer  96 . The workpiece carriage  20  moves forward, advances to an entrance of the U-shape conveyance passage  98 , and waits at the entrance. On the other hand, a component carriage filled with the components (see  FIG. 12 ) is waiting at the workpiece-only conveyance passage  101 . 
     Then, the component carriages  40  and the workpiece carriages  20  are alternately made to advance to the U-shape conveyance passage  98  in the order, and the component carriage  40  is connected to the preceding workpiece carriage  20   f  and subsequently the workpiece carriage  20  is connected to the component carriage  40 . In this manner, the component carriages  40  and the workpiece carriages  20  are connected bumper-to-bumper. A connect station  112  to connect the floor panel  22  of the workpiece carriage  20  to the carriage upper floor  44  of the component carriage  40  is disposed at an upstream side end portion of the U-shape conveyance passage  98 . 
     Note that the component carriage  40  may be preliminarily connected to the workpiece carriage  20  at the entrance of the U-shape conveyance passage  98 , and then the workpiece carriage  20  in such a set state may be connected to the preceding component carriage  40 . 
     In the above-described manner, the plurality of conveying carriage units  10  mutually connected is arranged in series. The conveying carriage unit  10  continuously moves forward at the constant speed on the U-shape conveyance passage  98 . Since there is a sufficient distance from the entrance to an exit of the U-shape conveyance passage  98 , the components are mounted on the vehicle body  12 B during the conveyance. The vehicle body finished with mounting the components is denoted by the reference sign  12 C. Since the relative positions between the component housing section and the vehicle body do not change in the upstream component mounting work area  97 , the cell production system is executed. 
     At the exit of the U-shape conveyance passage  98 , the head component carriage  40  is separated from the workpiece carriage  20  on which the vehicle body  12 C is loaded. Then, the component carriage  40  is returned to the component-only conveyance passage  102 . The workpiece carriage  20  is also separated from the following component carriage  40 . A release station  113  to release connection between the carriage upper floor  44  of the component carriage  40  ( FIG. 4 ) and the floor panel  22  of the workpiece carriage  20  is disposed at a downstream end portion of the U-shape conveyance passage  98 . 
     The released workpiece carriage  20  is made to advance to below the second lifter  86 . The vehicle body  12 C is picked up by the second lifter  86 , and hung by the hanger  94  of the second overhead conveyer  93 . An unload station  114  configured to pick up the vehicle body  12 C as the workpiece from the floor panel  22  of the workpiece carriage  20  and unload the same is disposed below the second lifter  86 . 
     The emptied workpiece carriage  20  is returned to the load station  111  below the first lifter  82 , passing a workpiece carriage circulation passage  115 . Thus, the floor panel  22  of the workpiece carriage  20  is conveyed in a circulating manner along the U-shape conveyance passage  98  and the workpiece carriage circulation passage  115 . The workpiece carriage  20  emptied at the unload station  114  is promptly returned to the load station  111 , thereby improving productivity. 
     In the center component mounting work area  104 , the components to be mounted on the floor bottom surface of the vehicle body, such as the engine, are mounted on the vehicle body  12 C hung by the hanger  94 . The second overhead conveyer  93  repeats advancing and stopping operations, but since a component box is fixed on the ground, the line production system is to be executed. 
     Operation in the downstream component mounting work area  103  is same as the operation in the upstream component mounting work area  97 . More specifically, a vehicle body  12 D is transferred to the workpiece carriage  20  by the third lifter  87 , a vehicle body denoted by a reference sign  12 E is completed by mounting the components in the downstream component mounting work area  103 . 
     A vehicle body  12 E being lifted is mounted with tires at the fourth lifter  88 . A vehicle body  12 F being lifted is mounted with a bumper at the fifth lifter  89 . Next, a vehicle body  12 G is mounted with the door at a door mounting station  106 , and made to advance to the inspection process  84 . 
     The number of components needed to be mounted before (or after) the engine is mounted can be increased or reduced by adjusting the projected length of the U-shape conveyance passage  98 ,  98 . Since an apparent line length is determined by the direction of the conveyance passage in the center component mounting work area, the apparent line length is not influenced even though the projected length of the U-shape conveyance passage  98  is increased. Therefore, the apparent line length can be reduced by adopting the U-shape conveyance passage  98 . 
     Next, the component station will be described. 
     As illustrated in  FIG. 14 , the component station  110  includes collect stations  116 ,  116  configured to collect the emptied sub-component carriages  70 L,  70 R, first component housing section  46 , and second component housing section  47  from the component carriage  40 , and supply stations  117 ,  117  configured to supply the sub-component carriages  70 L,  70 R, first component housing section  46 , and second component housing section  47  which are filled with components  13 . 
     The component carriage  40  having connection released at the release station  113  moves along the component-only conveyance passage  102 . The emptied sub-component carriages  70 L,  70 R are removed from the component carriage  40  at the collect station  116  configured to collect the sub-component carriages  70 L,  70 R. Subsequently, the sub-component carriages  70 L,  70 R filled with the components  13  are mounted on the component carriage  40  at the supply station  117  configured to supply the sub-component carriages  70 L,  70 R. 
     Since the sub-component carriages  70 L,  70 R are preliminarily filled with the components  13  in a component yard, man-hours for replacing the emptied sub-component carriages  70 L,  70 R with the sub-component carriages  70 L,  70 R filled with the components  13  can be saved with respect to the component carriage  40 . 
     After that, the component carriage  40  moves forward and the emptied first component housing section  46  and second component housing section  47  are removed from the carriage upper floor  44  of the component carriage  40  at the collect station  116  configured to collect the first component housing section  46  and second component housing section  47 . Then, the first component housing section  46  and second component housing section  47  filled with the components  13  are supplied to the carriage upper floor  44  at the supply station  117  configured to supply the first component housing section  46  and second component housing section  47 . 
     Since the first component housing section  46  and second component housing section  47  are preliminarily filled with the components  13  in the component yard, the man-hours for replacing the emptied first component housing section  46  and second component housing section  47  with the first component housing section  46  and second component housing section  47  filled with the components  13  can be saved with respect to the carriage upper floor  44  of the component carriage  40 . 
     The component carriage  40  having left the component station  110  moves along the component-only conveyance passage  101 , and is connected to the workpiece carriage  20  at the connect station  112 . Thus, the carriage upper floor  44  of the component carriage  40  is conveyed in a circulating manner along the U-shape conveyance passage  98  and the component-only conveyance passages  101 ,  102  because the component carriage  40  can be separated from the workpiece carriage  20 . Since the component carriage  40  filled with the components  13  is returned to the connect station  112  via the component station  110  which is a different place of the workpiece conveyance passage  85 , work efficiency in supplying components  13  and unloading is improved. 
     Next, a modified example of the component mounting facility  80  illustrated in  FIG. 13  will be described. 
     As illustrated in  FIG. 15 , the conveyance passage in the upstream component mounting work area  97  may be W-shaped. By forming the conveyance passage  107  in the W-shape, the larger number of components can be mounted. Further, a projecting length y from the assembly line  85  is shortened although a distance x between the first lifter  82  and the second lifter  86  is elongated. The same shall apply in the downstream component mounting work area  103  ( FIG. 13 ). 
     The workpiece carriage  20  is a self-traveling carriage including the drive source, but may be moved by being hooked on a chain hook that moves in a circulating manner, or may be moved by being pushed by the operator. 
     Connection and separation between the workpiece carriage  20  and component carriage  40  and connection and separation between the component carriage  40  and sub-component carriages  70 L,  70 R may be executed by manually inserting or pulling out a pin. More specifically, use of the overhead conveyer  93  is essential in the center component mounting work area  104 , but movement of the carriages  20 ,  40  in the upstream and downstream component mounting work areas  97 ,  103  may be any one of self-traveling, traveling by external force, and traveling by hand-pushing. 
     The conveying carriage unit according to the present invention may convey the vehicle body and also may convey other articles other than the vehicle body. Additionally, the carriage upper floor may be a non-rotational floor laid over the carriage body, and the component housing section may be one housing section without divisions of the first and second component housing sections. 
     Second Embodiment 
     Next, a conveying technology according to a second embodiment will be described, and elements same as the conveying technology according to a first embodiment will be described by denoting the elements with same reference signs. 
     As illustrated in  FIG. 16 , conveying carriage unit  10  according to the second embodiment includes a workpiece carriage  20  configured to convey a vehicle body  12  as a workpiece (mounting target), a component carriage  40  disposed adjacent to the workpiece carriage  20 , and right and left sub-component carriages  70 L,  70 R pulled by the component carriage  40  and disposed on the sides of a following workpiece carriage  20   r . The reference sign  20   r  indicated by an imaginary line is the following workpiece carriage, and the reference sign  40   r  indicated by an imaginary line is a following component carriage. The carriages  20 ,  40 ,  70 L, and  70 R will be individually described in detail. 
     As illustrated in  FIG. 17 , main elements of the workpiece carriage  20  are a frame body  21  formed by assembling steel material in a lattice shape, a floor panel  22  laid over the frame body  21 , and four workpiece receiving tables  23  placed on the floor panel  22 . A front portion and a rear portion of the floor panel  22  are cut in an arc shape. Additionally, the floor panel  22  includes work floors  24 L,  24 R applied with non-slip work on right and left side portions thereof. A first operation post  25  is disposed at a front portion of one of the work floors  24 L. 
     Positioning pins  26 ,  26  are erected on the workpiece receiving bases  23 ,  23  respectively. The vehicle body  12  ( FIG. 1 ) is positioned in a horizontal direction by these positioning pins  26 ,  26 . Then, the vehicle body  12  is supported by the four workpiece receiving bases  23 . 
     Two right and left eye plates  27 L,  27 R are provided at a rear portion of the frame body  21 . The eye plates  27 L,  27 R are the plates having open holes  28  respectively. Further, a long arm  29  is extended frontward from a front portion of the frame body  21 , and a first locking mechanism  31  is provided at a tip of the long arm  29 . The first locking mechanism  31  is, preferably, a cylinder unit having a pin  32  protruded upward. The cylinder unit may be any one of an air cylinder, a hydraulic cylinder, and an electric cylinder. The pin  32  can be vertically moved by operating an operating element  25   a  of the first operation post  25 . The operating element  25   a  may be any one of a push button, a lever, and a touch sensor, regardless of types. 
     As illustrated in  FIG. 18 , a plurality of universal wheels  33  is provided at a lower surface of the frame body  21 . The universal wheel  33  is also referred to as a caster, and does not prevent the carriage from turning by the universal wheel itself turning. A drive box  34  is provided at a center of the lower surface of the frame body  21 . The drive box  34  includes a motor and a drive source inside thereof, and drive wheels  35 L,  35 R are driven by the drive source. The drive wheels  35 L,  35 R contact a track (or road surface) and cause the workpiece carriage  20  to self-travel. Further, a guide wheel  36  is protruded from the drive box  34 . The guide wheel  36  plays a role of determining a traffic line of the workpiece carriage  20  by being fitted into a U-shape conveyance passage later described. The guide wheel  36  may be a non-rotational guide shoe. 
     As illustrated in  FIG. 19 , main elements of the component carriage  40  are a carriage body  41  formed by assembling steel material in a lattice shape, a plurality of universal wheels  42  attached to a lower surface of the carriage body  41 , a plurality of rollers  43  attached to an upper surface of the carriage body  41 , a circular carriage upper floor  44  mounted on the carriage body  41  so as to be placed above the rollers  43 , a roof-type frame  45  provided at the carriage upper floor  44 , a first component housing section  46  and a second component housing section  47  provided at the roof-type frame  45 . The carriage upper floor  44  is provided with a second operation post  48  including two operating elements  48   a ,  48   b.    
     On the circular carriage upper floor  44 , an area surrounding the first component housing section  46  and second component housing section  47  is set as a work floor  44   a , and an operator works on this work floor  44   a . A component housing section  50  includes the roof-type frame  45 , first component housing section  46 , and second component housing section  47 . The component housing section  50  is detachably provided on the carriage upper floor  44 . 
     Further, plates  51 L,  51 R are extended frontward from the rear portion of the carriage body  41 , and second locking mechanisms  52 L,  52 R are respectively provided at the plates plates  51 L,  51 R. The second locking mechanisms  52 L,  52 R are also, preferably, cylinder units having pins  53  protruded upward. The cylinder unit may be any one of an air cylinder, a hydraulic cylinder, and an electric cylinder. The pins  53 ,  53  can be vertically moved by operating an operating element  48   a  of the second operation post  48 . 
     The pins  53 ,  53  are fitted into the right and left eye plates  27 L,  27 R on the workpiece carriage  20  side from below, and therefore, the component carriage  40  travels together with the workpiece carriage  20  without laterally swinging and turning. 
     Also, side arms  54 L,  54 R are extended from right and left sides of the carriage body  41 , and third locking mechanisms  55 L,  55 R are respectively provided at the side arms  54 L,  54 R. The third locking mechanisms  55 L,  55 R are also, preferably, cylinder units having pins  56 ,  56  protruded upward. The cylinder unit may be any one of an air cylinder, a hydraulic cylinder, and an electric cylinder. The pins  56 ,  56  can be vertically moved by operating an operating element  48   b  of the second operation post  48 . 
     As illustrated in  FIG. 20 , a perforated plate  57  is provided at a lower center portion, and a shaft bearing block  58  is provided at an upper center portion of the carriage body  41 . A center shaft  59  is extended downward from a center of the carriage upper floor  44 , and a tip of the center shaft  59  is fitted into the shaft bearing block  58 . Since the carriage upper floor  44  is supported by the plurality of rollers  43 , no downward load is applied to the shaft bearing block  58 . The shaft bearing block  58  exerts an effect of guiding the center shaft  59  in a rotatable manner. 
     A driven gear  61  is provided halfway at the center shaft  59 . A servo motor  62  is disposed near the driven gear  61 , and the driven gear  61  is rotated by a drive gear  63  driven by the servo motor  62 . As a result, the carriage upper floor  44  horizontally turns around the center shaft  59 . In other words, the carriage upper floor  44  is a turntable. 
     The servo motor  62  is provided with an encoder  64  configured to detect a rotation angle and a rotary direction of a motor center shaft  59 . Further, the carriage body  41  is provided with a rotary sensor  65  and a rotation angle control section  66  in addition to the servo motor  62 . Operation of the rotary sensor  65  will be described later. Note that angle information from the rotary sensor  65  and angle information from the encoder  64  are input to the rotation angle control section  66 . The rotation angle control section  66  controls the servo motor  62  based on the angle information. 
     As illustrated in  FIG. 21 , the tip of the long arm  29  is fitted into a fork-shaped arm  67  extending from the rotary sensor  65 . In the drawing, the fork-shaped arm  67  is not tilted because the long arm  29  is not tilted. 
     As illustrated in  FIG. 20 , the long arm  29  is horizontally rotatable around the pin  32  of the first locking mechanism  31 . As a result, the long arm  29  may rotate around the pin  32  by only an angle 2θ as illustrated in  FIG. 22 . The rotation angle 2θ is detected by the rotary sensor  65 . 
     As illustrated in  FIG. 23( a ) , the vehicle body  12  is placed in front of the component carriage  40  and further a following vehicle body  12   r  is placed in back of the component carriage  40 . As shown by the arrow ( 1 ), a component is taken out from the first component housing section  46  and mounted on the vehicle body  12 . Also, as shown by the arrow ( 2 ), a component is taken out from the second component housing section  47  and mounted on the following vehicle body  12   r.    
     In the case where the following workpiece carriage  20   r  is turned by the angle 2θ with respect to the workpiece carriage  20 , the carriage upper floor  44  is rotated by the angle θ as illustrated in  FIG. 23( b ) . This operation is executed by the rotation angle control section  66  ( FIG. 20 ). 
     As a result, rotation of the turntable (carriage upper floor  44 ) is controlled by the rotation angle control section  66  such that a distance L from the first component housing section  46  to the vehicle body  12  becomes substantially equal to a distance Lr from the second component housing section  47  to vehicle body  12   r  (describing in terms of the angle, the angles of the component housing section with respect to the preceding and following vehicle bodies become equal). By controlling rotation of the turntable (carriage upper floor  44 ), work efficiency related to the first component housing section  46  and work efficiency related to the second component housing section  47  are equalized. As a result, component mounting work can be leveled. 
     More specifically, as illustrated in  FIG. 23( a ) , conveyance is continuously executed at a constant speed without stop in normal operation. As illustrated in  FIG. 23( b ) , when coming at a corner, the turntable on the component carriage is rotated such that the angles of the component housing section with respect to the preceding and following vehicle bodies are adjusted to be equal, thereby minimizing the moving distance of the operators riding on the preceding and following carriages to reach the component. 
     A turning center of the conveying carriage unit  10  is the pin  32  illustrated in  FIG. 20 . The turning center and rotary center (center shaft  59 ) of the turntable (carriage upper floor  44 ) is the same axis. More specifically, since the turning center of the conveying carriage unit and the rotary center of the turntable are the same axis, relative positions of the component housing sections  46 ,  47  with respect to the vehicle body  12  are easily controlled. 
     As illustrated in  FIG. 24 , the right and left sub-component carriages  70 L,  70 R are pulled by the component carriage  40 . A pin  56  of the third locking mechanism  55 R can be moved down by operating the operating element  48   b  provided at the second operation post  48 . As a result, the right sub-component carriage  70 R is separated from the component carriage  40 . The left sub-component carriage  70 L can be separated in the same manner. By operating the operating element  48   b , connecting the right and left sub-component carriages  70 L,  70 R to the component carriage  40  and separating the right and left sub-component carriages  70 L,  70 R from the component carriage  40  can be optionally executed. 
     In  FIG. 16 , the right and left sub-component carriages  70 L,  70 R are additionally connected to the component carriage  40 , and the left sub-component carriage  70 L is placed on the left side of the workpiece carriage  20   r  and the right sub-component carriage  70 R is placed on the right side of the workpiece carriage  20   r . The moving distance of the component can be shortened, thereby improving operating efficiency. 
     However, the sub-component carriages  70 L,  70 R can be omitted. Therefore, the necessary elements of the conveying carriage unit  10  are the workpiece carriage  20  and the component carriage  40  placed in back of the workpiece carriage  20 . The component carriage  40  may also be placed in front of the workpiece carriage  20   r  of a following conveying carriage unit  10   r  as illustrated by the imaginary line in  FIG. 16 . Therefore, the component carriage  40  is placed in front and back of the workpiece carriage  20 . 
     More specifically, in  FIG. 16 , the conveying carriage unit  10  includes the workpiece carriage  20  configured to convey the workpiece (vehicle body  12 ), and the component carriage  40  disposed in back of the workpiece carriage  20 , also connected to the workpiece carriage  20  in a separable manner and configured to convey the components. The conveying carriage unit is connected to preceding and following conveying carriage units in a turnable manner as illustrated in  FIG. 23 . 
     Since the workpiece carriage  20  and the component carriage  40  are connectable, the workpiece carriage  20  and the component carriage  40  can be continuously conveyed. The operator can work while riding on the component carriage  40  or workpiece carriage  20 . Since there is no need to stop the workpiece carriage  20  for a long time, the production time is kept constant. 
     Further, the conveying carriage unit  10  is connected to the preceding and following conveying carriage units  10  in a turnable manner, and therefore, a conveying traffic line can be meandered. A length of the conveying traffic line can be elongated by such meandering, and expansion of an assembly work area can be avoided. 
     Moreover, one of the workpiece carriage  20  and the component carriage  40  is made to self-travel, thereby achieving to move the other one integrally. Consequently, the operator does not need to manually push the carriage, and a heavy article such as the vehicle body can be conveyed. 
     A vehicle body component mounting system adopted with the above-described conveying carriage unit  10  will be described below. The component mounting facility  80  for operating the vehicle body component mounting system is illustrated in  FIG. 27 . A description will be first provided for each of categories extracted in  FIGS. 25 and 26  since the facility configuration is complex. 
     Arrangement of the coating process, lifters, a discharge line, an assembly line is same as the embodiment illustrated in  FIG. 10 . 
       FIG. 25  is a diagram illustrating arrangement of overhead conveyers, and a first overhead conveyer  91  is arranged along the discharge line  83 . The vehicle body  12  finished with coating is hung by a hanger  92  of the first overhead conveyer  91  and carried to above the first lifter  82  ( FIG. 10 ). 
     Further, a second overhead conveyer  93  is arranged along the assembly line  85 . The second overhead conveyer  93  conveys the vehicle body being hung by the hanger  94 , and components to be mounted on the floor bottom surface of the vehicle body, such as an engine, are mounted on the vehicle body  12  while being conveyed. 
     Additionally, a third overhead conveyer  96  is provided, whereby a door  95  is received between the first overhead conveyer  91  and the second overhead conveyer  93 , a window regulator or the like is built in the door  95 , and the door is transferred to an entrance side of the inspection process  84 . 
       FIG. 26  is a diagram illustrating arrangement of upstream and downstream component mounting work areas, the upstream component mounting work area  97  is positioned between the first lifter  82  and the second lifter  86 , and a U-shape conveyance passage  98  orthogonally or obliquely projected in a lateral direction from the assembly line  85  is disposed between the first lifter  82  and the second lifter  86 . The conveying carriage unit  10  on which the vehicle body  12  is loaded moves along the U-shape conveyance passage  98 . Additionally, component-only conveyance passages  101 ,  102  indicated by a dash line are connected at a leg portion of the U-shape conveyance passage  98 , and the conveying carriage unit  10  filled with the components is fed to the U-shape conveyance passage  98  from the component-only conveyance passage  101 . Further, the emptied conveying carriage unit  10  is sent back to the component-only conveyance passage  102  from the U-shape conveyance passage  98 . Note that the sub-component carriages  70 L,  70 R are pulled by the component carriage  40  of the conveying carriage unit  10 . 
     Additionally, a downstream component mounting work area  103  is positioned between the third lifter  87  and the fourth lifter  88 , and the U-shape conveyance passage  98  projecting sideways from the assembly line  85  is disposed between the third lifter  87  and the fourth lifter  88 . A description for others will be omitted for being same as the upstream component mounting work area  97 . 
     A center component mounting work area  104  is positioned between the second lifter  86  and the third lifter  87 , and components to be mounted on the floor bottom surface of the vehicle body, such as the engine, are mounted in the center component mounting work area  104 . 
     The component mounting facility  80  illustrated in  FIG. 27  is formed by combining the above-described configurations. The component mounting facility  80  includes the upstream component mounting work area  97 , center component mounting work area  104 , and downstream component mounting work area  103 . 
     In the center component mounting work area  104 , the components to be mounted on the floor bottom surface of the vehicle body, such as the engine, are mounted on a vehicle body  12 C to be conveyed while being hung at the second overhead conveyer  93 . More specifically, the components mounted in the work area are an engine front suspension assembly (assembly preliminarily assembled with constituting components of the engine and a front suspension), a rear suspension assembly (assembly preliminarily assembled with constituting components of the a rear suspension), and other components to be mounted on the floor bottom surface of the vehicle body (components that can be mounted to the vehicle body only in a upward moving state). Further, the engine front suspension assembly and rear suspension assembly are respectively conveyed to a mounting station in an assembled state, and lifted by an automatic mounting machine from below the vehicle body, and fastened with a bolt in a docked state with the vehicle body. In the work area, stop-and-go conveyance is executed at least in this station. 
     In the upstream component mounting work area  97 , components needed to be mounted on the vehicle body before the engine is mounted, namely, the components that cannot be mounted after the engine is mounted are mounted based on the cell production system. Examples of such components are members to be mounted on an engine room wall surface (e.g., a radiator, a pedal assembly, a steering column, a brake hose, etc.). Additionally, other components are suitably mounted in the upstream component mounting work area  97 . 
     More specifically, in the upstream component mounting work area  97 , a plurality of operators ride on one conveying carriage, and the components are mounted during the time of conveyance from a start point to an end point of this work area. This work corresponds to the work based on a cell production system. In the normal operation, conveyance is continuously executed at a constant speed without stop. When coming at a corner, the turntable on the component carriage is rotated such that the angles of the component housing section with respect to the preceding and following vehicle bodies are adjusted to be equal, thereby minimizing the moving distance of the operators riding on the preceding and following carriages to reach the component. 
     The work based on the cell production system is also executed in the downstream component mounting work area  103  in the same manner. In the downstream component mounting work area  103 , components needed to be mounted on the vehicle body after the engine is mounted, namely, the components that can be mounted only after the engine is mounted are mounted based on a cell production system. Examples of such a component are a battery, an air cleaner filter, an engine mount side bracket, an engine fastening bolt, and so on. Further, fuel injection work or oil injection work are executed in the area  103 . Furthermore, other components are suitably mounted in the downstream component mounting work area  103 . 
     Next, general operation will be described. 
     A coating-finished vehicle body  12 A is moved to the first lifter  82  from the hanger  92 . An underbody harness is set on the vehicle body  12 A. The workpiece carriage  20  of the conveying carriage unit  10  filled with the components is waiting below the first lifter  82 . 
     The vehicle body  12 A is transferred to the workpiece carriage  20  by lowering the first lifter  82 . Further, the place where the first lifter  82  is arranged is a vehicle body load station  111  whereby the vehicle body  12 A is loaded on the conveying carriage unit  10 . 
     A door is removed at a door removing stage  105 . The vehicle body without the door is denoted by a reference sign  12 B. The vehicle body  12 B is loaded on the workpiece carriage  20  and the conveying carriage unit  10  moves forward. Further, the removed door is carried by the third overhead conveyer  96 . The conveying carriage unit  10  advances to a connect station  112  whereby the conveying carriage units  10  are mutually connected. The conveying carriage unit  10  having advanced is connected to a rear portion of the preceding conveying carriage unit  10  already waiting at the connect station  112 . 
     More specifically, the workpiece carriage  20  of the advancing conveying carriage unit  10  is connected to the preceding component carriage  40  of the conveying carriage unit  10  already waiting. In the same manner as connecting the component carriage  40  to the workpiece carriage  20 , a plurality of conveying carriage units  10  is connected bumper-to-bumper. 
     In the above-described manner, the plurality of mutually connected conveying carriage units  10  is arranged in series. The conveying carriage unit  10  continuously moves forward at the constant speed on the U-shape conveyance passage  98 . Since there is a sufficient distance from the entrance to an exit of the U-shape conveyance passage  98 , the components are mounted on the vehicle body  12 B during the conveyance. 
     The conveying carriage unit  10  advances to a connection release station  113  immediately before the exit of the U-shape conveyance passage  98 . In the connection release station  113 , the preceding conveying carriage unit  10  is separated. The following conveying carriage unit  10  has a side of the workpiece carriage  20  opened. The following conveying carriage unit  10  having the side opened is also sequentially separated. 
     An equipment mount station  114  whereby equipment is mounted on the vehicle body  12 B is disposed between the connection release station  113  and the second lifter  86 . In the equipment mount station  114 , an assist device  121  configured to lift relatively heavy equipment such as a sheet is disposed. 
     The conveying carriage unit  10  separated at the connection release station  113  advances to the equipment mount station  114 . The equipment such as the sheet is lifted by the assist device  121 , and the equipment is mounted on the vehicle body  12 B from the side of the workpiece carriage  20 . The vehicle body finished with mounting the components and equipment is denoted by the reference sign  12 C. Since the relative positions between the component housing section and the vehicle body do not change in the upstream component mounting work area  97 , the cell production system is executed. 
     The conveying carriage unit  10  loaded with the vehicle body  12 C is advanced to below the second lifter  86 . The vehicle body  12 C is picked up by the second lifter  86 , and hung by the hanger  94  of the second overhead conveyer  93 . Further, the place where the second lifter  86  is arranged is a vehicle body discharge station  115  whereby the vehicle body  12 C is discharged from the conveying carriage unit  10 . 
     The emptied conveying carriage unit  10  is advanced to the component-only conveyance passage  102 . The component-only conveyance passage  102  is connected to the component station whereby the components are loaded on the emptied conveying carriage unit  10 . 
     In the center component mounting work area  104 , the components to be mounted on the floor bottom surface of the vehicle body, such as the engine, are mounted on the vehicle body  12 C hung by the hanger  94 . The second overhead conveyer  93  repeats advancing and stopping operations, but since a component box is fixed on the ground, the line production system is to be executed. 
     Operation in the downstream component mounting work area  103  is same as the upstream component mounting work area  97 . More specifically, a vehicle body  12 D is transferred to the workpiece carriage  20  by the third lifter  87 , a vehicle body denoted by a reference sign  12 E is completed by mounting the components at the downstream component mounting work area  103 . 
     A vehicle body  12 E being lifted is mounted with tires at the fourth lifter  88 . A vehicle body  12 F being lifted is mounted with a bumper at the fifth lifter  89 . Next, a vehicle body  12 G is mounted with the door at a door mounting station  106 , and made to advance to the inspection process  84 . 
     The number of components needed to be mounted before (or after) the engine is mounted can be increased or reduced by adjusting the projected length of the U-shape conveyance passages  98 ,  98 . Since an apparent line length is determined by the direction of the conveyance passage in the center component mounting work area, the apparent line length is not influenced even though the projected length of the U-shape conveyance passage  98  is elongated. Therefore, the apparent line length can be shortened by adopting the U-shape conveyance passage  98 . 
     Next, the component station will be described. As illustrated in  FIG. 28 , the component station  110  includes a collect station  116  configured to collect the emptied component housing section  50  and right and left sub-component carriages  70 L,  70 R from the conveying carriage unit  10 , and supply stations  117 ,  117  configured to supply the component housing section  50  and sub-component carriages  70 L,  70 R filled with the components to the conveying carriage unit  10 . 
     The conveying carriage unit  10  from which the vehicle body  12  is discharged at the vehicle body discharge station  115  advances to the component-only conveyance passage  102 . The emptied component housing section  50  and sub-component carriages  70 L,  70 R are removed from the component carriage  40  at the collect station  116 . The conveying carriage unit  10  moves along the component-only conveyance passage  102 , and the component housing section  50  filled with the components is loaded on the component carriage  40  at the supply station  117 , and then the sub-component carriages  70 L,  70 R filled with the components are connected to the component carriage  40 . 
     Since the component housing section  50  and the sub-component carriages  70 L,  70 R are preliminarily filled with the components in a component yard, man-hours for replacing the emptied component housing section  50  and sub-component carriages  70 L,  70 R with the component housing section  50  and sub-component carriages  70 L,  70 R filled with the components  13  can be saved with respect to the component carriage  40 . 
     The conveying carriage unit  10  having left the supply station  117  moves to the component-only conveyance passage  101 , and the vehicle body  12  is loaded on the vehicle body load station  111 . Thus, while the workpiece carriage  20  and component carriage  40  are integrally connected, the vehicle body  12  can be loaded and discharged and further the component housing section  50  and sub-component carriages  70 L,  70 R can be collected and connected, thereby achieving to improve productivity. 
     Moreover, only one passage is necessary for the conveying carriage unit  10  in the upstream component mounting area, thereby achieving to reduce the facility cost. 
     Next, operation of the assist device will be described. As illustrated in  FIG. 29 , the assist device  121  is disposed at the equipment mount station  114 . The assist device  121  includes a support pillar  122 , a beam portion  123  disposed at an upper portion of the support pillar  122 , and an equipment supporting portion  124  movably disposed at the beam portion  123 . 
     In the equipment mount station  114 , the conveying carriage unit  10  has the side of the workpiece carriage  20  opened. Accordingly, the assist device  121  can be disposed on the side of the workpiece carriage  20 . Further, since the assist device  121  supports a sheet  125  as the equipment by the equipment supporting portion  124 , an operator  126  can easily mount the heavy article like the sheet  125  on the vehicle body  12 . 
     As illustrated in  FIGS. 30 and 31 , the conveying carriage unit  10  has the side of the workpiece carriage  20  opened in the vehicle body discharge station  115  ( FIG. 28 ). Therefore, an arm portion  94   a  of the hanger  94  is carried close to the vehicle body  12  from the side and can support the vehicle body  12 . Since the hanger  94  can be used without separating the workpiece carriage  20  from the component carriage  40  ( FIG. 28 ), and man-hours can be reduced, productivity in an entire assembly line can be improved. 
     Further, the conveying carriage unit  10  has the side of the workpiece carriage  20  opened. Therefore, the second lifter  86  can be disposed on the side of the workpiece carriage  20 , and can lift the vehicle body  12 . Since the second lifter  86  can be used without separating the workpiece carriage  20  from the component carriage  40  ( FIG. 28 ) and the man-hours can be reduced, productivity in the entire assembly line can be improved. 
     Next, a modified example of the component mounting facility  80  according to the second embodiment illustrated in  FIG. 27  is illustrated in  FIG. 32 . As illustrated in  FIG. 32 , the conveyance passage in the upstream component mounting work area  97  may be W-shaped. By forming the conveyance passage  107  in the W-shape, the larger number of components can be mounted. Further, a projecting length y from the assembly line  85  is shortened although a distance x between the first lifter  82  and the second lifter  86  is elongated. The same shall apply in the downstream component mounting work area  103 . 
     Meanwhile, the workpiece carriage  20  is a self-traveling carriage including the drive source, but may be moved by being hooked on a chain hook that moves in a circulating manner, or may be moved by being pushed by the operator. 
     Connection and separation between the workpiece carriage  20  and component carriage  40  and connection and separation between the component carriage  40  and sub-component carriages  70 L,  70 R may be executed by manually inserting or pulling out a pin. More specifically, use of the overhead conveyer  93  is essential in the center component mounting work area  104 , but movement of the carriages  20 ,  40  in the upstream and downstream component mounting work areas  97 ,  103  may be any one of self-traveling, traveling by external force, and traveling by hand-pushing. 
     Further, the conveying carriage unit according to the present invention may convey the vehicle body, and also may convey other articles other than the vehicle body. Additionally, the carriage upper floor may be a non-rotational floor laid over the carriage body, and the component housing section may be one housing section without divisions of the first and second component housing sections. Further, the conveying carriage unit is applied in the cell production system according to the embodiment, but not limited thereto, the conveying carriage unit may also be used in a normal production line. 
     Additionally, according to the embodiment, the sub-component carriages  70 L,  70 R are hooked on the pins  56  of the side arms  54 L,  54 R, but not limited thereto, the sub-component carriages  70 L,  70 R may be connected to pins or the like provided at other portions of the conveying unit as long as the sub-component carriages can be connected to the workpiece carriage  20  or the component carriage  40 . 
     INDUSTRIAL APPLICABILITY 
     The present invention is suitable for a component mounting line whereby components are mounted on a vehicle body. 
     REFERENCE SIGNS LIST 
     
         
           10  Conveying carriage unit 
           12  Mounting target (workpiece, vehicle body) 
           13  Component 
           20  Workpiece carriage 
           22  Floor panel 
           22   a  Recessed arc-shaped portion 
           24 L,  24 R Work floor 
           40  Component carriage 
           41  Carriage body 
           44  Carriage upper floor (turntable) 
           44   a  Work floor 
           44   b  Projected arc-shaped portion 
           46  Component housing section (first component housing section) 
           47  Component housing section (second component housing section) 
           49  Center shaft of projected arc-shaped portion 
           50  Component housing section 
           66  Rotation angle control section 
           70 L,  70 R Sub-component carriage 
           85  Workpiece conveyance passage (assembly line) 
           93  Overhead conveyer (second overhead conveyer) 
           97  Upstream component mounting work area 
           98  U-shape conveyance passage 
           99  Curved portion 
           101 ,  102  Component-only conveyance passage 
           103  Downstream component mounting work area 
           104  Center component mounting work area 
           110  Component station 
           111  Load station 
           112  Connect station 
           113  Connection release station 
           114  Equipment mount station 
           116  Collect station 
           117  Supply station