Abstract:
In a conveying apparatus wherein a carriage is driven by a linear motor to run along guide rails, the guide rails comprise two parallel guide members, each having a first guide surface that prevents lateral movement of the carriage, and a second guide surface that prevents vertical movement of the carriage. The carriage comprises first wheels disposed between upper and lower surfaces of the carriage for rolling along the first guide surfaces and second wheels disposed spaced apart from the first wheels in the running direction of the carriage to roll along the second guide surfaces.

Description:
This application is a continuation of 07/009,043, filed Jan. 27, 1987, now abandoned, which is a continuation of 06/716,170, filed Mar. 26, 1985, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to conveying apparatus in which a carriage imparted with a propelling force by a linear motor or the like motive means is run under its inertia along guide rails. 
     2. Description of the Prior Arts 
     In a conventional convertion conveying system, the carriage is generally driven by a drive source mounted thereon for running along a predetermined conveying path. With such conveying system, however, due to the installation of the drive source, the size and weight of the carriage is increased. 
     Accordingly, when the carriage runs very fast, there arise problems such that a large centrifugal force is generated at a curved path and energy supply becomes required. 
     On the other hand, there has been proposed a conveying system in which the carriage is not provided with a drive source but imparted with a propelling force from outside thus running the carriage with its own inertia. For example, in a conveying system utilizing a linear induction motor, the carriage is provided with a reaction plate which is supplied with magnetic flux varying with time so as to create in the reaction plate a definite forward or reverse propelling force thereby running or stopping the carriage. This system can miniaturize the carriage, can reduce its weight and can run the carriage at a high speed. 
     When conveying an object by means of a conveying system driven by a linear motor, if it is possible to convey the object, not only in the horizontal direction but also in the vertical direction, it would be possible to provide a three dimensional conveying system efficiently utilizing the space. 
     A prior art system enabling three dimensional conveyance is disclosed in Japanese Patent Application No. 102589/1978 (Japanese Laid Open Patent Specification No. 30726/1980). According to the conveying system disclosed therein, since guide members for limiting the transverse movement of the carriage are provided for the lower surface of the carriage, the guide rails for guiding the carriage and the carriage itself become large and complicated so that it is impossible to decrease the size of the conveying system while ensuring a desired capacity of transportation. 
     Further, when running three dimensionally, the carriage should be restricted in upward movement by upper guide rails. However, since the carriage is provided with only one pair of wheels vertically, there occurs great frictional force between the wheels and the upper guide rail due to the reverse rotation of the wheels. (This Japanese Patent Application does not disclose the three-dimensional running case.) 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to provide an improved carriage driven by a linear motor that can be manufactured compact and can run at high speeds without the danger of derailment. 
     Another object of this invention is to provide an improved carriage driven by a linear motor that can run not only in the horizontal direction but also in the vertical direction. 
     According to this invention, there is provided a conveying apparatus of the type wherein a carriage is run along guide rails, characterized in that the guide rails include two parallel guide members each having a first guide surface that prevents lateral movement of the carriage, and a second guide surface that prevents vertical movement of the carriage and that the carriage includes first guided members positioned between upper and lower surfaces of the carriage for rolling along the first guide surfaces of the guide member, and second guided members longitudinally spaced from the first guided members to move along the second guide surfaces. 
     According to a modified embodiment of this invention the guide rails extend not only in the horizontal direction but also in the vertical direction, thus enabling three dimensional running. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is a perspective view showing a carriage and guide rails embodying the invention; 
     FIG. 2 is a cross-sectional view of the conveying path for the carriage; 
     FIG. 3 is a sectional view taken along a line III--III in FIG. 2; 
     FIG. 4a is a perspective view useful to explain the principle of a linear induction motor; 
     FIG. 4b is a graph showing the relationship between magnetic flux and eddy current; 
     FIG. 5 is a diagrammatic represention of conveying paths; 
     FIG. 6 is a perspective view showing a modified carriage; and 
     FIG. 7 is a cross-sectional view showing a modified conveying path for the carriage. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in FIGS. 1 and 2, a carriage 1 comprises a casing 2 adapted to carry an object, and a reaction plate 3 vertically depending from the bottom of the casing 2. The reaction plate 3 is made of such electric conductor as copper, aluminum or the like material and imparted with forward or reverse propelling force created by the magnetic force generated by the stators 9 to be described later. Two pairs of wheels (guided members) 4 projecting from the side surfaces of the casing 2 are provided on the front and rear sides respectively of the carriage. Furthermore, two pairs of wheels 5 are provided for both ends of each side frame of the carriage. Thus, a total of twelve wheels 4 and 5 are provided. The conveying path 6 for the carriage 1 is formed by a pair of opposed U shaped guide rails 7. The distance a between the confronting inner surfaces 7a of the guide rails 7 is slightly larger than the distance b between the outer peripheries of the wheels 4. The distance c between the upper and lower flanges of each rail is slightly larger than the distance d between the outer peripheries of vertically aligned wheels 5. The inner surfaces 7a, opposing inner surfaces 7b and 7c of the upper and lower flanges act as guide surfaces for the wheels 4 and 5. A linear induction motor 8 is provided beneath the conveying path 6. The linear induction motor 8 is constituted by a reaction plate 3 secured to the bottom of the casing 2 to act as a movable member, and a pair of stators 9 disposed on the opposite sides of the reaction plate 3. As shown in FIGS. 3 and 4a, each stator 9 comprises a lamination of electric sheets punched with teeth and grooves which accommodate coils, not shown. Gaps g of a predetermined width are formed between the reaction plate 3 and the stators 9. 
     The principle of generating the forward or reverse propelling force of the linear induction motor will be described with reference to FIGS. 4a and 4b. FIG. 4a is a perspective view showing a flat plate one side type linear induction motor, while FIG. 4b shows the relationship between the magnetic flux bg and the eddy current. When two or three phase alternating current is passed through the coils of the stators, the instantaneous value bg(T) of the flux density in the gaps 9 is expressed by 
     
         bg=Bg cos(wt-πx/τ) 
    
     where 
     Bg: crest value of the flux density, 
     w=2πf: angular frequency of source voltage (red/s) 
     f: frequency (Hz) 
     t: time (s) 
     x: distance (m) along the stator surface, 
     τ: pole pitch 
     The pole pitch τ represents the length of one half period of the flux density bg. Since the magnetic flux generated by the stators 9 is an alternating flux, eddy current is induced in the reaction plate 3, that is, the movable member according to Len&#39;s law. Symbols • and x applied to the section of the reaction plate 3 shown in FIG. 4a represents the magnitude and direction of the eddy current. The instantaneous value jr of the eddy current is expressed by 
     
         jr=Jr sin(wt-πX/τ-φ) 
    
     where 
     Jr: crest value of eddy current 
     φ: phase difference caused by the impedance of reaction plate 3. 
     Since the flux density bg in the gaps forms a shifting field the product of the flux density bg and the instantaneous value of the eddy current produces a continuous thrust F according to the lefthand law of Fleming. Although this thrust F is produced in the left and right directions as viewed in FIG. 4a, since bg x jr in the left region shown in FIG. 4b is larger than that in the right region, the reaction plate 3 would be moved toward left. To apply a reverse propelling force to the reaction plate 3, reverse phase alternating current should be passed through the coils of the stators 9. The magnitude of the thrust F can be varied by varying the frequency f or amplitude of the alternating current. 
     The conveying path 6 for guiding the carriage 1 imparted with the propelling force as above described will be described with reference to FIG. 5. The conveying path 6 shown in FIG. 5 comprises a switch 10 which selects the carriage 1 running in the direction shown in arrow A to proceed along an upper conveying path 6a or a lower conveying path 6b which are spaced from the path 6a in the vertical direction. Beneath the path 6, 6a and 6b are disposed stators 9 which impart forward or reverse propelling force to the reaction plate 3 of the carriage 1. 
     The apparatus constructed as above described operates as follows. Application of the propelling force to the carriage 1 can be done by passing 2 or 3 phase alternating current through the coils of the stators so as to generate magnetic flux, thereby inducing eddy current. The product of the flux and the eddy current produces a continuous thrust F according to the lefthand law of Fleming. When the carriage 1 is imparted with the thrust in this manner, wheels 4 and 5 secured to the casing 2 would be caused to run by its inertia while being guided by the U shaped guide rails 7. The guide rails 7 are provided with guide surfaces 7a that prevent transverse movement of the carriage 1. Moreover, the guide rails 7 are provided with guide surfaces 7b and 7c which prevent vertical movement of the carriage 1. On the other hand, the carriage 1 is provided with wheels 4 rolling along the guide surfaces 7a and wheels 5 rolling along the guide surfaces 7b and 7c. Consequently, the carriage can run only in the direction A and prevented from moving in the other directions. For this reason, even when the conveying path 6 guiding the carriage 1 is bent in the horizontal and vertical directions, the carriage 1 can move in three dimensional directions without derailment. Although the conveying path shown in FIG. 5 is bent only in the vertical direction, the path can be bent in a horizontal plane. In this embodiment, wheels 4 and 5 provided for the carriage 1 decrease the frictional resistance with respect to the guide surfaces 7a, 7b and 7c, whereby high speed running of the carriage can be ensured even when it runs under its inertia. Since the wheels 4 for preventing the lateral movement of the carriage 1 are secured to the front and rear ends of the carriage 1, it is possible to decrease the lateral dimension of the carriage 1 while maintaining the capacity of loading object of the casing 2 at a constant value, thereby miniaturizing the carriage 1. 
     It should be understood that the invention is not limited to the specific embodiment described above and that various changes and modifications will be obvious to one skilled in the art without departing from the true spirit and scope of the invention as defined in the appended claims. For example, as shown in FIG. 6, four wheels 5 engaging the upper and lower flanges 7b and 7c of each guide rail may be provided for the side surfaces of the carriage 1 so as to decrease the number of parts. Furthermore, as shown in FIG. 7, opposing guide rails may be shaped to have a letter L cross-section for clamping respective rails between wheels 5. In FIG. 7, parts corresponding to those shown in FIG. 6 are designated by the same reference numerals. Although in the foregoing embodiments, a linear induction motor was used for imparting the propelling force, other types of linear motor, for example, a linear step motor or a linear direct current can also be used.