Sorting apparatus

Abstract: A change-over device is provided for a sorting conveyor (100). Projected members of slats (102) forming the sorting conveyor are made of ferromagnetic substance such as iron alloy. Those projected members are guided by a guide rail which is installed on the rear side of the conveyor. The guide rail is made up of a main rail and a branch rail. The side wall of the branch rail is partially omitted near at the inlet of the branching portion of the guide rail where the branch rail branches from the main rail, and instead an upper side wall and a lower side wall are formed there by an electromagnet and a permanent magnet, respectively. When the electromagnet is energized, each projected member is attracted towards the upper side wall, and is then allowed to move along the lower side wall, thus being led into the branch rail. Thus, the articles on the conveyor are suitably sorted while being conveyed to the selected branch conveying path (110).

Description: BACKGROUND OF THE INVENTION This invention relates to classifying or sorting devices, and more particularly to a slat conveyor type sorting device in which an article sorting operation is carried out with a slat conveyor which is suitable for conveying articles different in configuration and in size. There are available a variety of sorting devices in the art; for instance, a sorting device of wheel float type, a sorting device of push-out type, a sorting device of tilt type, a sorting device using obliquely driven belts, and a sorting device using moving shoes on a slat conveyor. The slat conveyor is suitable for conveying articles different in configuration or in size. In the case of the slat conveyor, its sorting device employs moving shoes which are moved along the slats forming the conveying surface (i.e., in a direction perpendicular to the direction of conveyance of the conveyor). Such a sorting device has been disclosed, for instance, by Japanese Patent Application Publication No. 10971/1985 or US Patent Serial No. 4,738,347. The fundamental arrangement of the sorting device incorporated in the slat conveyor is as follows: Each slat has a moving shoe which is slidable longitudinally. The moving shoe is designed as shown in FIG. 10. That is, a projected member 8 extended downwardly from each of the slats (which may be a pin extended downwardly therefrom or a member having a roller) is guided by a main rail 10 or a branch rail 11 of a guide rail 9 installed below the slats. The projected member 8 is moved longitudinally of the slat being guided by the branch rail 11 which is extended obliquely on one side of the conveyor. A conveying-direction change-over device is provided at a predetermined sorting position, and its change-over member, namely, a change-over lever 22 is swung clockwise (in the direction of the arrow C) about a fulcrum 23, as a result of which the projected member moving in a predetermined direction (in the direction of the arrow) is caused to move towards the branch rail 11. In this operation, an article which has reached the sorting position is moved laterally of the conveyor (i.e., in the direction of the branch rail) by tee shoe, thus being classified or sorted. Documents US-A-4,884,677, US-A-5,038,912 and US-A-5,027,939 disclose mechanical systems, wherein the switch of the conveying path is caused by a mechanical switch mechanism and guiding devices connected to the switch mechanism. In addition, a sorting device, which has a conveying direction change-over mechanism utilizing a magnetic attraction force, is known from document US-A-3,731,782. A change-over mechanism disclosed, for instance, by Japanese Patent Application Publication No. 12982/1977 is shown in FIG. 11. That is, permanent magnets 25 are fixedly secured to slide members 24, respectively. Electromagnets 27 arranged at the introducing end and conveying path change-over position of a magnetic guide 26 are so energized as to be equal in polarity to the permanent magnets 25, so that the slide members 24 with the magnetic elements are spaced from the magnetic guide 26 by the force of repulsion, thereby to form an article conveying path, so that an article X is conveyed to the desired one of the branch conveying paths D, E and F. As is apparent from the above description, in the conventional change-over mechanism with the change-over lever, it is necessary to increase the length of the change-over lever 22 in proportion to the diameter (d) of the projected member 8. In addition, when the opening angle  between the main rail 10 and the branch rail 11 is increased, it is also necessary to increase the opening angle α of the change-over lever 22, because it must be substantially equal to the opening angle e. When the length of the change-over lever 22 is increased as was described above, then the rotational moment of the change-over lever 22 is increased, and accordingly it is necessary to increase the force of driving the change-over lever 22 as much. In addition, if the opening angle α of the change-over lever 22 is increased, then the amount of swing of the lever 22 is increased. This means that it takes a relatively long time to accomplish the predetermined operation. In a case where the conveyor driving speed is increased, this difficulty may be eliminated by increasing the speed of operation of a drive system for the change-over lever 22, such as an electromagnetic valve or an air cylinder. However, the method is disadvantageous in the following points: As the drive system is improved in performance, the sorting conveyor is increased in size, or in manufacturing cost. Furthermore, as the length of the change-over lever 22 is increased, the speed of movement of the change-over lever 22, particularly at its end, is increased in proportion to the speed of rotation, as a result of which the lever is greatly shocked when stopped. Hence, in addition to the change-over lever itself, the members around it must be mechanically reinforced. Therefore, if, when it is intended to increase the speed of operation of the change-over lever 22, the opening angle α is decreased to reduce the period of time required for completion of the predetermined operation, then it is not suitable for the case where the projected member 8 is large in diameter and the angle  of the branch rail 11 is large. The mechanism which utilizes the magnetic force of attraction to change the Conveying path, as disclosed by the aforementioned Japanese Patent Application Publication 12982/1977, is high in manufacturing cost, because the permanent magnet 25 must be coupled to each of the number of slide members 24 forming the conveying path. The conveying path in the branching direction is formed by attracting the slide members having the permanent magnets towards the magnetic guide 26. Therefore, the magnetic guide 26 should be extended over the entire length of the conveying path in the branching direction, which increases the manufacturing cost as much. Furthermore, since the conveying path in the branching direction is formed by attracting the slide members towards the magnetic guide 26 as was described above, when it is required to perform a high speed conveyance by moving the slide members 24 at high speed, or when the article X on the slide members 24 is heavy, it is necessary to increase the magnetic force of attraction between the permanent magnets of the slide members and the magnetic guide accordingly. For this purpose, magnets or magnetic substances high in magnetic characteristic must be used, which also increases the manufacturing cost. On the other hand, in the case where the slide members and the magnetic guide are high in magnetic characteristic, the electromagnets must be accordingly high in magnetic performance which are adapted to produce a force of repulsion to space the slide members from the magnetic guide in changing the conveying path. Accordingly, the electromagnets employed are unavoidably bulky. Also, the conventional slat conveyor type sorting device using a moving shoe and a projected member is provided with a cross section portion where two guide rails forming respective guide paths cross each other in order to allow the moving shoe or projected member to go obliquely over the entire width of the conveying surface rightward or leftward selectively. Japanese Patent Application Publication No. 11488/1984 discloses a change-over member used in such cross-section portion as shown in FIG. 14. Pawl-shaped end parts 39a and 39b are pivotally coupled to the end portions (closer to the intersection) of the upstream parts of the guide rails 34a and 34b, respectively. A selected one of the right and left end parts 39a and 39b is swung about the respective fulcrum 40, to switch the conveying paths extended to the downstream parts of the guide rails. In addition a change-over mechanism as shown in FIGS. 12 and 13 has also been disclosed by the afore-mentioned Japanese Patent application Publication No. 11488/1984. In the mechanism, each projected member 32 is made up of a throttle epicyclic wheel 41, and a pair of rollers 42 arranged on both side of the epicydic wheel 41. The projected member 32, being guided by movable boards 43 arranged on the rear side of the conveying surface along both right and left edges, is moved along guide rails 34 in the direction of the arrow which are arranged as shown in FIGS. 12 and 13. Each of the guide rails is partially omitted a length shorter than the distance between the two rollers 42 but larger than the diameter of the epicyclic wheel 41; that is, it has a space 38 corresponding to the length. Therefore, the projected member 32 is moved to the following (downstream) guide rail 34 while passing through the space 38. However, the above-described change-over mechanism suffers from various disadvantages. That is, in the mechanism, as shown typically in FIG. 14, the change-over members 39a and 39b are arranged in the cross section portion, so that the guide rails are switched mechanically so as to allow the projected member to move to the following guide rail. Therefore, it is necessary to operate the change-over member 39 whenever it is required to switch the conveying paths. Hence, the mechanism is relatively low in durability, and produces noises whenever operated, thus adversely affecting the working environment. The change-over member 39 is made up of a pair of end parts 39a and 39b as was described above. Hence, in switching the guide rails, it is essential to control the timing of operating (swinging) the end parts 39a and 39b with high accuracy. Accordingly, the mechanism is unavoidably intricate in arrangement. In particular, in order to switch the guide rails at high speed, it is necessary to increase the mechanical strength of the drive system of the change-over member 39, and to operate the control system with higher accuracy. This means an increase in manufacturing cost or in running cost. In addition, it is necessary to provide the change-over member 39 at each of the guide rail cross sections, and therefore, the resultant sorting device is increased in manufacturing cost as much. On the other hand, the change-over mechanism as shown in FIGS. 12 and 13, having no mechanical change-over member as shown in FIG. 14, is free from the above-described difficulties that it is low in durability, produces noises, or it is high in manufacturing cost or running cost. However, it is still disadvantageous in the following point: That is, if the space 38 is not accurately aligned with the adjacent guide rails, then the front end of the projected member collides with the junction 44 of the guide rails, so that the projected member is not smoothly moved over to the following guide rail, which may result in the occurrence of a trouble with the sorting device. This is a serious problem particularly when the conveying speed is high. Accordingly, an object of this invention is to eliminate the above-described difficulties accompanying a conventional sorting device. More specifically, an object of the invention is to provide a sorting device which is able to classify or sort articles on the conveying surface accurately and quickly, and which produces no noises in changing the conveying path, and in which the change-over mechanism is simple in arrangement and low in manufacturing cost. Another object of this invention is to provide a sorting device which is suitable for a high speed conveying operation, thus permitting articles to be classified or sorted positively and quickly. SUMMARY OF THE INVENTION In order to attain the above-noted and other objects, the present invention provides a slat conveyor type sorting apparatus including the features of claim 1. Preferred construction embodiments of the device are defined in the subclaims. BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: FIG. 1 is a perspective view of a sorting conveyor of slat shoe type according to an embodiment of the present invention; FIG. 2 is a top view showing the conveyor shown in FIG. 1; FIG. 3 is a side view showing the conveyor shown in FIG. 1; FIG. 4 is a top view showing essential components of one example of a change-over mechanism in the sorting conveyor according to the invention; FIG. 5 is a top view showing essential components of another example of the change-over mechanism in the sorting conveyor according to the invention; FIG. 6 is a top view showing essential components of yet another example of the change-over mechanism in the sorting conveyor according to the invention; FIG. 7 is a top view showing essential components of an example of a shoe shift mechanism in the sorting conveyor; FIG. 8 is a top view showing essential components of another example of the shoe shift mechanism in the sorting conveyor according to the invention; FIG. 9 is a top view showing essential components of yet another example of the shoe shift mechanism in the sorting conveyor; FIG. 10 is an explanatory diagram for a description of the operation of a lever change-over mechanism in a conventional change-over lever type sorting machine; FIG. 11 is an explanatory diagram showing one example of a sorting machine operating on a magnetic action; FIG. 12 is a perspective view showing one example of a conventional guide rail cross section in a sorting device; FIG. 13 is a top view of the guide rail cross section shown in FIG. 12, for a description of the movement of a projected member in the guide rail cross section; FIG. 14 is a perspective view showing another example of the conventional guide rail cross section; FIG. 15 is a top view showing essential components of another example of the change-over mechanism in the sorting conveyor according to the present invention; FIG. 16 a sectional view taken along line 28-28 of FIG. 15; FIG. 17 is an enlarged view of a major part of FIG 16; FIG. 18 is a sectional view taken along line 30-30 in FIG. 15; FIG. 19 is an enlarged view of a major part of FIG. 18 in a case where a permanent magnet is used as a downstream magnet; FIG. 20 is an enlarged view, each showing a modification of the arrangement shown in FIG. 19; FIGS. 21-24 are top views respectively showing modifications of the change-over mechanism in the sorting conveyor according to the present invention, in which a plurality of change-over devices and a plurality of branch guide rails are provided; FIG. 25 is a top of showing essential components of another example of the change-over mechanism in the sorting conveyor according to the present invention, in which an upstream electromagnet is made up of a plurality of electromagnet elements; FIGS. 26A, 26B, 27, 28A and 28B show modifications for an electromagnet used in the change-over mechanism according to the present invention; FIGS. 29 shows a top view showing essential components of another example of the shoe returning or shifting mechanisms in the sorting conveyor according to the present invention; FIGS. 30 shows a top view showing essential components of further another example of the shoe returning or shifting mechanisms in the sorting conveyor according to the present invention; FIG. 31 shows a perspective view showing a yet another example of the conveying-path change-over mechanism of the present invention; FIG. 32 shows a side view as viewed in a direction of an arrow 45-45 of FIG. 31; FIG. 33 shows a top view showing the example shown in FIG. 31; and FIG. 34 shows a top view showing a modification of the example shown in FIG. 31. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of this invention will be described with reference to the accompanying drawings. A basic construction of a slat conveyor type sorting device according to the present invention will be described hereunder. A slat conveyor 100, as shown in FIG. 1, is made up of a plurality of slats 102 arranged side by side so that articles X are placed on them. Drive chains 108 fixedly coupled to the slats 102 at both ends are driven so that the article X is conveyed in a predetermined direction (i.e., in the direction of the arrow F) together with the slats 102. Articles X are sorted as follows: That is, moving shoes 104 on the slats 102 are moved in a direction (as indicated by the arrow S) perpendicular to the direction of the arrow F by a change-over mechanism (described later) to form a path towards a branch conveying path 110; that is, the article X is moved along the path thus formed into the branch conveying path 110. For example, as shown in FIG. 2, an article X is conveyed from an upstream conveyor A to a sorting conveyor 100, and it is sorted while being on the conveying surface of the sorting conveyor 100 by the moving shoe 104, and delivered to a selected one of the conveyors B and C located downstream of the sorting conveyor and forming respective branch conveying paths 110. FIG. 3 is a side view of the sorting conveyor shown in FIG. 2. The sorting conveyor 100 includes: a conveying region 116 in which an article X is loaded from the conveyor A onto the sorting conveyor 100 and it is classified or sorted while being moved in the direction of the arrow F and delivered to the downstream conveyor B or C; and a returning region 118 which is located on the side which is opposite to the side where the conveying surface is provided, and is moved in the direction of the arrow R. Each of the slats 102 is designed as follows: It has end blocks 107 at both ends, which are suitably coupled to extension pins of the drive chains 108 on both sides of the conveyor. More specifically, the two end blocks 107 are connected through two slat bars 103 to each other, which form a load conveying surface of the slat conveyor 100. The aforementioned moving shoe 104 is mounted on the slat bars 103 in such a manner that it is movable on the slat bars 6 in a direction perpendicular to the load conveying direction (i.e., in the direction of the arrow F). Each moving shoe 104, as shown in FIG. 3, includes a projected member 106 comprising a guided member 140 (i.e. a roller, wheel, bearing or the like) mounted on a shaft 135 extended downwardly from the slat 2. A change-over mechanism 200 (described later) is operated to guide the projected member 106 to a main rail 122 or a branch rail 124 of a guide rail 120 installed below the slats. FIG. 4 is a top view showing essential components of a branching section of a conveying path, for a description of one example of the change-over mechanism according to the invention for the conveying path. The guide rail 120, as was described above, comprises: the main rail 122 for conveying an article X straightly (i.e., in a main direction) on the conveyor; and the branch rail 124 for conveying an article X in a sorting direction (i.e., in a branch direction). The branch rail 124 has a side wall 130 which is partially omitted near the inlet of a branching portion of the guide rail where the branch rail 124 branches from the main rail 122, and instead an upper side wall 213a and a lower side wall 251 are formed there by an electromagnet 213 and a permanent magnet 250 or an electromagnet 250', respectively, in such a manner that those upper and lower side walls 213a and 251 are aligned with the side wall 130. Sensors 217 are arranged beside the guide rail 120, upstream of the branching portion, to detect the passage of each projected member 106 moving along the guide rail 120, to provide a passage detection signal. The passage detection signal and sorting data (not shown) are suitably utilized to control the energization of the electromagnet 213. The projected member 106 of each moving shoe 104 includes a roller or bearing 140. In FIG. 4, the projected member 106 is moved downwardly along the guide rail during conveyance. When no sorting operation is carried out; that is, in the case where the articles on the conveyor are moved straightly, the projected member is moved straightly downwardly in FIG. 4, thus moving along the main rail 120 (as a projected member 106a in FIG. 1). In this operation, the electromagnet 213 is not energized; that is, the projected member 106, being not attracted by the electromagnet 213, is moved straightly into the main rail 122. On the other hand, in a sorting operation, the electromagnet is energized so that the projected member 106 is attracted (moved) towards the upper side wall 213a (as a projected member 106b in FIG. 4). Thereafter, it is allowed to moved along the lower side wall 251 formed by the permanent magnet 250 or electromagnet 250' by the virtue of magnetic attraction thereof, so that it is led into the branch rail 124. In the case where the lower side wall 251 is formed by the electromagnet 250', the latter 250' is energized at the same time as the electromagnet 213. FIG. 5 shows another example of the conveying path change-over mechanism according to the invention. Similarly as in the case of the change-over mechanism shown in FIG. 4, a guide rail 120 is made up of a main rail 122 and a branch rail 124. However, in the second example, the guide rail 120 is designed as follows: The width of the rail is smaller towards the portion of the guide rail (hereinafter referred to as "a first portion", when applicable) which is located upstream of the branching portion of the guide rail 120 where the branch rail 124 branches from the main rail 122, being decreased substantially equal to the outer diameter of projected members 126, and in the following portion (hereinafter referred to as "a second portion", when applicable) larger towards the downstream end of the guide rail 120. That is, the guide rail 120 is so designed that the rail width meets L' < L, and L' < L'' as shown in FIG. 5. A pair of electromagnets 223a and 223b are provided on both sides of the second portion of the guide rail 120 where the rail width is larger towards the downstream end of the guide rail as was described above. The arrangement of the electromagnets 223a and 223b are not limited to that which is described above. For instance, the electromagnet may be set as follows: The side walls of the guide rail 120 are partially omitted at the aforementioned second portion where the rail width is gradually increased, and the pair of electromagnets 223a and 223b are set to reform the parts of the side walls thus omitted. As was described above, the rail width is gradually decreased substantially equal to the outside diameter of the projected members 126. Therefore, on the border line between the first portion of the guide rail 120 where the rail width is gradually decreased as described above, and the second portion following the first portion, the distance of the projected member 126 from the electromagnets 223a and 223b is decreased, and the magnetic force of attraction applied to the projected member 126 is increased as much, so that the latter 126 is positively led to the branch rail 124 as required. In addition, in the second example of the change-over mechanism, a part of the side wall 130, near the branching portion of the guide rail 120 where the branch rail 124 branches from the main rail 122, is made of a magnetic substance 260' which is magnetized by a permanent magnet 260. It is not always necessary for the permanent magnet 260 to cover the entire length of the magnetic substance. That is, it may be so positioned as to cover only a part of the magnetic substance which is closer to the branching portion of the guide rail. In FIG. 5, the permanent magnet 260 is rectangular in section; however, the invention is not limited thereto or thereby; that is, it is not limited in configuration; and all that is necessary for the permanent magnet is able to magnetize the magnetic substance 260'. Sensors 217 for detecting the passage of each projected member 126 are provided upstream of the pair of electromagnets 223a and 223b, to output a detection signal. The detection signal and sorting data are utilized to control the energization of the electromagnets 223a and 223b. The projected member 126 of each moving shoe 104 is made up of a roller or bearing, and it is moved downwardly, in FIG. 5, along the guide rail 120 during conveyance. When no sorting operation is carried out; that is, articles on the conveyor are to be moved straightly, only the left electromagnet 223b is energized, so that the projected member 126 passing through the second portion of the guide rail where the rail width is gradually increased is attracted (moved) towards the electromagnet 223b (as a projected member 126a in FIG. 5). Thereafter, the projected member 126 is allowed to move along the left side wall of the guide rail (as a projected member 126b in FIG. 5), thus being led into the main rail 122 (as a projected member 126c). In order that the projected member 126 which has been attracted towards the electromagnet 223b may be more positively moved along the left side wall of the guide rail, the part of the side wall may be formed of a magnetic substance magnetized by a permanent. On the other hand, in a sorting operation, only the right electromagnet 223a is energized, so that the projected member 126 is attracted (moved) towards the electromagnet 223a (as a projected member 126d. Thereafter, the projected member 126 is allowed to move along the part 260' of the side wall of the branch rail, which is made of a magnetic substance (as projected members 126e and 126f in FIG. 5), thus being led into the branch rail 124 (as a projected member 126g in FIG. 5). As the projected members 126 are moved in the above-described manner, the moving shoes 104 are accordingly moved longitudinally of the slats. As a result, the article X on the conveyor is pushed in the direction of the arrow S in FIG. 1, thus being moved into the branch conveying path extended laterally of the conveyor. Thus, the article X has been classified. FIG. 6 shows yet another example of the conveying path change-over mechanism 200 according to the present invention. The change-over mechanism 200 includes an electromagnet 233 and a switch 236 for controlling the energization of the electromagnet 233, and is located in a branch section of the guide rail 120 where the branch rail 124 branches from the main rail 122. A side wall 130 of the branch rail 124 is partially omitted at an inlet portion of the branch rail 124, and a core 233a of the electromagnet 233 is located on that portion along the extension of the side wall 130 in place of the omitted side wall. Although the configuration of the core 233a is not limited as far as the core 233a forms a part of the side wall of the branch rail 124, it is preferable that the core 233a is slightly bent at its upper end portion so as to smoothly merge to the guide rail 120 in order to surely and smoothly guide the projected member 106 toward the branch rail 124 during the conveying path change-over operation. Sensors 217 are located at upstream of the branch section of the guide rail 120 so as to detect the passing of the projected member 106 which moves along the guide rail 120. A detection signal fed out from the sensors 217 are amplified by the amplifier 235 and supplied to the switch 236. The switch 236 controls the current supply to the electromagnet 233 through the appropriate calculation based on the detection signal from the sensors 217 and the sorting data appropriately inputted. The projected member 106 of the moving shoe 104 is made up of a roller or bearing and travels along the guide rail 120 downwardly of FIG. 6 during the conveyance of the object or article. When the sorting operation is not performed (i.e. the article on the conveyor is merely conveyed straightly), the current is not supplied to the electromagnet 233 so that the projected member 106 is not attracted to the electromagnet 233 and is moved straightly and downwardly toward the main rail 122 as shown by the reference numeral 106''. On the other hand, when the sorting operation is performed, by supplying the current to the electromagnet 233 the projected member 106 is attracted to the electromagnet 233 so as to be moved along the core 233a of the electromagnet 233, as a result of which the projected member is introduced into and guided along the branch rail 124. Depending on the successive movement of the projecting members 106, the respective moving shoes 104 are moved longitudinally of the slats so that the article X on the conveyor is forced in a direction of arrow S in FIG. 1 toward a branch conveying path, thereby enabling the desired sorting operation. While there has been described in connection with the preferred embodiments of the conveying-path change-over device, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention. For example, as shown in Fig. 15, the electromagnet 213 and the magnet 250 or electromagnet 250' of the embodiment shown in Fig. 4 may be united to each other through a yoke. In the change-over mechanism shown in Fig. 15, an electromagnet 213 and a plurality of permanent magnets 250 or electromagnets 250' are untied together though a yoke 280. A lateral end, i.e. the left-hand side end of the yoke 280 forms a part of the side wall 130a of the branch rail 124. The lateral end of the yoke 280 has substantially the same dimension as the thickness of the guide wheel 140 as shown in Fig. 16 and connects the side wall 131a to side wall 130a with no gap, so as to smoothly guide the guide wheel or rotary member 140 of the projected member 106 therealong. As shown in Fig. 16, the yoke 280 includes a first yoke member 280a connected to a magnetic pole 213a of the electromagnet 213, and bent into a L-shaped to be directed toward the guide rail 132b and laid over a coil of the electromagnet 213, and a second yoke member 280b connected to the other magnetic pole 213b and similarly bent toward the guide rail 132b. Distal ends of the first and second yoke member 280a, 280b constitute the aforementioned lateral end of the yoke 280 and are positioned to correspond to a level of the rotary member 140 suspended from the moving shoe 104 through the shaft 135. As best shown in Fig. 17, the first and second yoke members 280a, 280b are spaced from each other with a predetermined gap so that the closed loop M of the magnetic circuit is formed between the rotary member 140 and the yoke 280 when the rotary member 140 is brought into contact with the yoke 280 in a state where the electromagnet 213 is energized. This yoke arrangement can concentrate and strengthen the magnetic force of the electromagnet 213 so as to surely attract the rotary member 140 thereto in the sorting operation. Additionally, the gap may be filled with a spacer if desired. The first and second yoke members 218a, 218b are elongated to the upstream end of the side wall 130a of the branch guide rail 124 to cover all of the permanent magnet 250 or electromagnet 250'. In a case where permanent magnets 250 are used in this mechanism, each of the permanent magnets 250 having the same thickness as that of the gap is interposed and held between the first and second yoke members 280a and 280b as shown in Fig. 18 In this case, also, the closed loop M of the magnetic circuit is formed between the permanent magnet 250 and the rotary member 140 through the yoke 280, as best shown in Fig. 19. In addition, the permanent magnet 250 is so arranged as to magnetize each of the first and second yoke members in the same polarity as the magnet 250 and the electromagnet 213 does. That is, if the first yoke member 280a is magnetized in S polarity by the electromagnet 213, the permanent magnet 250 is so arranged as to magnetize the first yoke member 280a in S polarity. Various arrangement may be applicable in stead of the arrangement in which a single permanent magnet 250 is vertically interposed between two yoke members 280a and 280b. For example, as shown in Fig. 20 it is possible to arrange a plurality of yoke members (three yoke members 280a, 280b and 280c are shown in the drawing) and a plurality of permanent magnets (two permanent magnet 280b and 280c are shown in the drawing) alternately in order to form a plurality of closed magnetic loops corresponding in number to the permanent magnets. If the magnet located downstream of the electromagnet 213 is constituted by an electromagnet 250', the cross-sectional view taken along line 30-30 is substantially the same view as that shown in Fig. 16. Returning to Fig. 15, a slit 290 is formed between the electromagnet 213 and a most upstream one of the permanent magnet 250 or electromagnet 250' so as to pass through the each of the first and second yoke members 280a and 280b. The slit 290 functions so as to effectively prevent the heat generated in conjunction with the energization of the electromagnet 213 from being transmitted to the permanent magnet 250 or electromagnet 250' through the yoke 18 resulting in a thermal damage that the magnitude of the attractive force of downstream magnets is decreased. This slit 290 also functions so as to prevent the unwanted magnetization of the yoke 280 near the electromagnet 213 due to the downstream magnets 250, 250'resulting in the undesired attraction that the rotary member 140 is attracted to the yoke 280 due to the magnetic force of the downstream magnet 250, 250' although the electromagnet 213 is not energized. This slit arrangement is particularly effective in a case where each downstream magnet is made up of the permanent magnet 250 since the permanent magnet is likely to be thermally damaged and yoke 280 is always magnetized by the permanent magnet 250. In order to achieve these two effects, other various arrangements may be applicable to the yoke. For example, a plurality of perforate holes may be formed though the yoke 280 in stead of the aforementioned slit 290. The yoke 280 may be divided into two sections, one corresponding to the electromagnet 213 and the other corresponding to the downstream magnets 250, 250'. Further, a non-magnetic material, antimagnetic material, thermally insulative material or the like may be provided in or filled into the divided part between the two sections. A support shaft guide member 150a for guiding the support shaft 135 of the moving shoe 104 therealong may be provided on the side wall 132b of the guide rail 120 upstream of the electromagnet 213. The support shaft guide member 150a functions to move the projected member 106 laterally toward the side wall 131a through the support shaft 135 and bring the rotary member 140 into contact with the side wall 131a before the rotary member 140 approaches the electromagnet 213. Consequently, the rotary member 140 is surely brought into contact with the yoke 280. As shown in Fig. 16, a lower portion of the support shaft 135 projecting below the rotary member 140 is guided by and along a side face of the support shaft guide member 150a. Another support shaft guide member 150b may be provided on the guide rail 120 upstream of a common junction 160 between the main rail 122 and the branch rail 124. The support shaft guide member 150b is in the form of a triangular shape as viewed from above, where an apex is located at the most upstream and two sides are respectively extending from the apex substantially along the main rail 122 and the branch rail 124. As shown in Fig. 18, the lower portion of the support shaft 135 projecting below the rotary member 140 is guided by and along the side face of the support shaft guide member 150b. This support shaft guide member 150b functions so as to surely guide the projected member 106 toward the branch rail 124 when the electromagnet 213 is activated for sorting operation, and further to advance the completion of the sorting operation depending only on the magnetic attraction in the conveying-path change-over mechanism from the position shown by reference numeral 106d to the position shown by reference numeral 106c. It is preferable that the support shaft guide member 150b is arranged as shown in Figs. 31-33 in order to positively prevent an accidental stoppage and/or damage of the sorting conveyor due to the collision of the projected member 106 against the support shaft guide member 150b. The support shaft guide member 150b shown in Figs. 31-33 is chamfered between the upper surface 150b 4 and each of the side faces 150b 2 and 150b 3 to provide tapered guide surfaces T1 and T2 having a common edge line 150b 5 which extends obliquely downward from the upper surface 150b 4 of the support shaft guide member 150b to the apex 150b 1 . The common edge line 140b 5 is parallel with an center line C of the main rail 122 in a plane view as shown in Fig. 33. The tapered guide surfaces T1 and T2 is also slanted obliquely downward from the common edge line 150b 5 toward respective side faces 150b 2 and 150b 3 so as to forcibly guide the support shaft 140 toward respective guide rail 122 and 124. The height of the apex 150b 1 of the support shaft guide member 150b is so selected as to be coincident with to that of the axial end 135a of the support shaft 135 as best shown in Fig. 32. The apex 150b 1 may be located slightly below the axial end 135a. End points P1 and P3 of the tapered guide surfaces T1 and T2 are located downstream relative to an end point P3 of the edge line 150b 5 in Fig. 31, but may be located upstream relative to the end point P3 of the edge line. The apex 150b 1 is located upstream relative to the common junction 160 between the guide rails 122 and 124 and deviated from the center line C of the main rail 122 toward the branch rail 124. The position of the apex 150b 1 is appropriately determined based on the branching angle between the main rail 122 and branch rail 124, the conveying speed of the sorting conveyor or the like. The support shaft guide member 150b thus constructed functions as follows: When the projected member 106 is not sufficiently attracted toward the branch rail 124 by the electromagnet 213, the support shaft 135 of the projected member 106 rides on either one of the tapered guide surfaces T1 and T2, so that the support shaft 135 is slid along and guided by the tapered guide surface T1 or T2. Accordingly, the projected member 106 is surely guided toward either the main rail 122 or the branch rail 124 without any collision of the support shaft 135 against the support shaft guide member 150b. Even if the support shaft 135 is moved on a prolongation of the edge 150b 5 toward the support shaft guide member 150b, the support shaft 135 rides on the guide member 150b at the apex 150b 1 , slid obliquely downward on one of the tapered guide surface T1 and T2, and then delivered to corresponding one of the main rail 122 and branch rail 124, which faces the tapered guide surface on which the support shaft 135 is slid, as shown in Fig. 32. Thus, the tapered guide surfaces T1 and T2 of the support shaft guide member 150b function so as to forcibly guide the support shaft 135 toward either one of the main rail 122 and the branch rail 124 surely, and to positively prevent the accidental stoppage and/or damage of the sorting conveyor due to the collision of the support shaft 135 against the apex 150b 1 of the support shaft guide member 150b. The support shaft guide member 150b may be arranged so that the apex 150b 1 is located closer to the center line C of the main rail 122 as shown in Fig. 34 in comparison with the embodiment shown in Figs. 31-33. In this case, the edge 150b 6 of the support shaft guide member 150b is not parallel to the center line C and extends from the apex 150b 1 toward the branch rail 124 so that the support shaft 135 ride on the guide member 150b at the apex 150b 1 is guided by the tapered guide surface T1 toward the main rail 122. As illustrated in Fig. 34, a notch portion 150b 7 may be formed in the support shaft guide member 150b so that the support shaft 150 which exceeds the tapered guide surface T1 and rides on the upper surface 150b 4 of the guide member 150b (arrow H) because of the high speed conveyance is delivered to the main rail 122. The projected member 106 whose support shaft 135 falls down from the upper surface 150b 4 to the main rail 122 through the notch portion 150b 7 , is subsequently guided by the side wall of the main rail 122. The notch portion 150b 7 may be formed in the support shaft guide member 150b at a side where the branch rail 124 is provided. Also, the apex 150b 1 and the edge 150b 6 may be arranged so that the support shaft 135 which rides on the support shaft guide member 150b at the apex 150b 1 is forcibly guided to the branch rail 124. Further, many modifications for reducing the load of the electromagnet can be applied to the conveying-path change-over device of the present invention. For example, a plurality of change-over mechanisms may be provided in the sorting conveyor in order to sort a conveyed package to a single downstream conveyor. Fig. 21 shows a sorting conveyor to which such modification is applied utilizing the change-over device or mechanism shown in Fig. 4. The sorting conveyor shown in Fig. 21 includes first and second conveying-path change-over mechanisms 200 1 and 200 2 provided on inlet portions of first and second branch rails 124 1 and 124 2 , respectively. The same or similar reference numerals are denoted to the parts corresponding functionally or equivalent to those shown in Fig. 4, so that detailed description is omitted here. In addition, reference numeral 122' designates another main rail for guiding projected members which have been already moved from left hand side to right hand side to sort a package to a right hand side downstream conveyor before reaching the sorting position shown in Fig. 21, projected members which are to be moved from the right hand side to the left hand side to sort a package to a left hand side downstream conveyor after passing through the sorting position shown in Fig. 21, or the like. Operation of this sorting conveyor is as follows: When a package conveyed together with the slat 102 is not to be sorted in the sorting position as shown in Fig. 21, neither the first change-over mechanism 200 1 nor the second change-over mechanism 200 2 is activated so that the projected member 106 is moved straightly along the main rail 122 as indicated by reference numerals 106, 106e and 106a. When the conveyed package is to be sorted to the right hand side downstream conveyor B, one of the change-over mechanism (for example, a first change-over mechanism 200 1 ) is activated while keeping the other change-over mechanism (i.e. the second change-over mechanism 200 2 ) resting so that the projected member 106 is moved toward the first branch rail 124 1 by the first change-over mechanism 200 1 and guided along the first branch rail 124 1 as indicated by the reference numerals 106, 106b, 106c, 106d and 106i to sort the package to the downstream conveyor B. Thereafter, when the next package to be sorted is conveyed to the sorting position as shown in Fig. 21, the operation is shifted through a switching means (not shown in the drawing) so that the second change-over mechanism 200 2 is activated whereas the first change-over mechanisms 200 1 is kept resting. Therefore, the projected member 106 in this case is moved to the second branch rail 124 2 by the second change-over mechanism 200 2 and guided along the second branch rail 124 2 as indicated by the reference numerals 106, 106e, 106f, 106g 106h and 106j so that the package is sorted to the downstream conveyor B. As is apparent from the above-description, the packages conveyed to the sorting position as shown in Fig. 21 can be sorted to the downstream conveyor B by utilizing alternately the first and second change-over mechanisms 200 1 and 200 2 . Therefore, it is possible to prevent thermal damage caused on the change-over mechanism due to the continuous energization applied to the electromagnets 213 and/or 250' since one change-over mechanism can be rested when the other change-over mechanism is activated. In the above-noted modification, the first and second change-over mechanisms 200 1 and 200 2 are utilized alternately one by one of the packages. However, the modification should not be restricted thereto or thereby. For example, it is also possible in the above-noted modified example that the first change-over mechanism 200 1 continues to sort a predetermined number of packages toward the downstream conveyor B and thereafter the sorting operation is shifted from the first change-over mechanism 200 1 to the second change-over mechanism 200 2 by the switching means so that the second change-over mechanism 200 2 continues to sort the predetermined packages toward the downstream conveyor B. Further, the shifting of the sorting operation between the first and second change-over mechanisms can be performed every predetermined time period. Furthermore, thermal sensors are respectively provided for the change-over mechanism 200 1 and 200 2 so that the sorting operation is shifted by the switching means depending on the detected value of the thermal sensors, thereby preventing the thermal damage. Moreover, it is possible that the first change-over mechanism 200 1 is used as a main change-over device whereas the second change-over mechanism is used as a secondary change-over device. That is, if a package to be sorted to the downstream conveyor B is not accidentally sorted by the first change-over mechanism 200 1 , then such circumstance is detected, for instance by a sensor provided on the main rail 122 between the two branch rails, upon which the second change-over mechanism 200 2 is activated to sort the package to the downstream conveyor B surely. Also, if one of the first and second change-over devices 200 1 and 200 2 must be repaired or replaced with a new one, then such repair and replacement for one change-over device can be performed without stoppage of the conveyor since the other change-over device can perform the desired sorting operation. Fig. 22 shows a similar modification in which a plurality of change-over mechanisms and a plurality of branch rails are provided for one downstream conveyor. Difference of the arrangement shown in Fig. 22 from that shown in Fig. 21 is that a plurality of the branch rails are jointed together as a common branch rail 124 com near the downstream conveyor B. According to this arrangement, the projected member 106 is guided to the rail 122' at the same position regardless of whether the first change-over mechanism 200 1 or the second change-over mechanism 200 2 is utilized for sorting operation, so that it is possible to reduce the width of the downstream conveyor along the conveying direction F. These modifications shown in Fig. 21 and 22 can be applied to the various embodiments of the present invention in order to reduce the load of the electromagnets. The cases where these modifications are applied to the embodiment shown in Fig. 5, are illustrated in Figs. 23 and 24 as examples. Moreover, another modification can be made to the electromagnet 213 itself in order to prevent the thermal damage caused on the change-over mechanism of the present invention due to the excessive continuous energization. For example, as shown in Fig. 25, the electromagnet 213 in the change-over mechanism 200 may be made up of first and second independent electromagnet elements 213 1 and 213 2 which are alternately used by the action of a switching means for the sorting operation as similarly to the first and second electromagnets 213 1 and 213 2 of the sorting conveyor shown in Fig. 21. That is, when a package conveyed together with the slat 102 is not to be sorted in the sorting position as shown in Fig. 21, neither the first electromagnet element 213 1 nor the second electromagnet element 213 2 is activated so that the projected member 106 is moved straightly along the main rail 122 as indicated by reference numerals 106 and 106a. When the conveyed package is to be sorted to the downstream conveyor, one of the electromagnet elements (for example, a first electromagnet element 213 1 ) is activated while keeping the other electromagnet element (i.e. the second electromagnet element 213 2 ) resting so that the projected member 106 is moved toward the branch rail 124 by the action of the first electromagnet element 213 1 and guided along the branch rail 124 as indicated by the reference numerals 106, 106b, 106c and 106d to sort the package to the downstream conveyor. Thereafter, when the next package to be sorted is conveyed to the sorting position as shown in Fig. 25, the operation is shifted through the switching means (not shown in the drawing) so that the second electromagnet element 213 2 is activated whereas the first electromagnet element 213 1 is kept resting. Therefore, the projected member 106 in this case is also moved to the branch rail 124 by the action of the second electromagnet element 213 2 and guided along the branch rail 124 as indicated by the reference numerals 106, 106b, 106c and 106d so that the package is sorted to the downstream conveyor. Since the packages conveyed to the sorting position as shown in Fig. 25 can be sorted to the downstream conveyor by utilizing alternately the first and second electromagnet elements 213 1 and 213 2 , it is possible, as similarly to the arrangement shown in Fig. 21, to prevent thermal damage caused on the change-over mechanism 200 due to the continuous energization applied to the electromagnets 213. In addition, if the first and second electromagnet elements 213 1 and 213 2 are simultaneously activated, then the electromagnet 213 can produce a larger magnetic attractive force per a unit current in comparison with that having a single windings. Similar modification can be applied to the downstream electromagnets 250'. An importance of this modification is that the electromagnet 213 is made up of a plurality of electromagnet elements so that one of electromagnet elements can be rested even under a condition that the projected member 106 must be sorted to the branch rail 124. Therefore, the disposition and the number of the electromagnet elements should not be restricted to those shown in Fig. 25. The electromagnet elements 213 1 and 213 2 may be disposed to be juxtaposed along the guide rail, i.e. the branch rail 124 in an upstanding manner as can be seen from Fig. 26A, and to be juxtaposed perpendicularly relative the extending direction of the branch rail 124 in the upstanding manner as can be seen in Fig. 26B. Further, as illustrated in Fig. 27, it is possible that a pair of upper and lower coils are wound around a common central core 215 to constitute the first and second electromagnet elements 213 1 and 213 2 . In this case, the entire electromagnet 213 can be miniaturized to increase the freedom of design for the branch portion. Yoke members 280a and 280b of magnetic or ferromagnetic material may be respectively attached to the pole ends of the electromagnet 213 made up of the first and second electromagnet elements 213 1 and 213 2 so as to constitute a part of the side wall of the branch guide rail 124 and form the closed magnetic loop or circuit M. The yoke members 280a and 280b may be arranged to extend in parallel relation to each other to constitute the part of the side wall. In addition, an inclined arrangement that one of distal portions of the yoke members 280a and 280b is arranged in an inclined manner (i.e., the lower yoke member 280b extends with an angle relative to the upper horizontal yoke member 280a in Fig. 27), can enhance the effective generation of the magnetic flux from the yoke members 280a and 280b. Furthermore, as shown in Figs. 28A and 28B, the common core 215 having therearound a pair of coil windings constituting the first and second electromagnet elements 213 1 and 213 2 , may be processed so that the closed magnetic loop or circuit M is formed between the core 215 and the rotary member 140 through both ends of the core 215. In this case, also, an inclined arrangement that one of end portions of the core 215 is arranged in an inclined manner (i.e., the lower end portion of the core 215 extends with an angle relative to the upper horizontal end portion of the core 215 in Fig. 28A and 28B, can enhance the effective generation of the magnetic flux from the core 215. As was described above, in the conveying-path change-over device of the invention, the part of the side wall of the branch rail which part is located near the inlet of the branching portion of the guide rail where the branch rail branches from the main rail is made up of the side wall provided by the electromagnet, so that the projected members of magnetic substance are led to the branch rail as the electromagnet providing the upper side wall is energized. That is, the change-over device of the invention, being simple in arrangement and in construction, is able to smoothly switch the directions of conveyance of articles on the conveyor as desired; that is, it is able to move the articles straightly in the main direction, or laterally of the conveyor in the branch direction. Hence, with the change-over device of the invention, the article sorting operation can be achieved merely by controlling the energization of the electromagnet, and the article conveying directions can be positively switched, and the time required for switch the article conveying directions can be greatly reduced. Furthermore, in the change-over device of the invention, the moving shoes on the slats, unlike the conventional ones, can be manufactured at lower cost, because it is unnecessary all the moving shoes to have magnets. The change-over mechanism, operating on the energization of the electromagnet, is simple in arrangement, and small in the number of components. Therefore, it is advantageous in the reduction of manufacturing cost and in the scale of arrangement. With the change-over mechanism, the article conveying directions or paths are switched electrically (not mechanically). Hence, the change-over mechanism is less troubled in operation, and produces only low noises when operated. Furthermore, each of the projected members is made up of a roller or bearing. Therefore, the projected members are smoothly moved along the guide rail, and when the article conveying paths are switched, noises are less produced. The above-noted arrangements and modifications for the change-over mechanism according to the present invention can be used for a shoe returning or shifting mechanism 300 in the sorting device. This case will be described hereunder. After the sorting operation as mentioned above, each slat 102 is moved to the returning region 118 located opposite to the conveying surface, and in the returning region 118 it is moved in the direction (of the arrow R) opposite to the direction of conveyance (i.e., the direction of the arrow F) on the conveying surface. In the case where the article X is to be moved to the right-handed side in FIG. 2 (i.e., towards the conveyor B), in the conveying region 116 the moving shoes 104 of the slats 102 on the conveying surface are moved towards the right ends of the slats 104 which are on the right-handed side in the longitudinal direction of the latter; whereas in the case where the article X is to be moved to the left-handed side in FIG. 2 (i.e., towards the conveyor C), in the conveying region 116 the moving shoes 104 of the slats 102 are moved towards the left ends of the slats 102, thus reaching the downstream end 114 of the sorting conveyor. After reaching the downstream end 114 of the sorting conveyor, the moving shoe 104 of each slat 102 from which the article X has been delivered to the conveyor B is moved to the returning region 118 while being kept on the right-handed portion of its slat 102; whereas the moving shoe 104 from which the article X has been delivered to the conveyor C is moved to the returning region 118 while being kept on the left-handed portion of its slat 102. In order to classify or sort articles X on the sorting conveyor 100 which are successively delivered thereto from the upstream conveyor A, the moving shoes 104 moving through the returning region 118 while being kept on the right-handed or left-handed portions of the slats 102 should be shifted right or left ends of the slats at the upstream end 112 of the sorting conveyor 100 according to the given sorting data. For thus purposes, a shoe shifting mechanism 300 is provided on the rear side of the slat surface in the returning region 118 of the sorting conveyor 100. Fig. 7 shows an example of a shoe shifting device 300 not within the scope of the present invention, which partially utilizes the arrangement of the present invention as shown in Fig. 5. The shoe shifting mechanism 300 comprises: a shoe centering guide rail 303 including a pair of side walls 130a and 130b; branch guide rails 124a and 124b which branch right and left (in the directions of the arrows D and E) from the shoe centering guide rail 303; and a pair of electromagnets 313a and 313b disposed near the branching point of the branch guide rails 124a and 124b. The guide wheel 140 of the projected member 106 of the moving shoe 104 moving through the returning region in the direction of the arrow R is first guided by the shoe centering guide rail 303 of the shoe shifting mechanism 300, and then led to one of the branch guide rails 124a and 124b which is on the side where one of the electromagnets 313a and 313b is provided which is energized in response to a shoe shifting signal. Sensors 317 are provided at the upstream end of the shoe centering guide rail 303, to detect the passage of each of the projected member 106, thereby to control the energization of the electromagnets 313a and 313b. Thus, as the projected member 106 moves, the moving shoe 104 is moved in the direction of the arrow D or E. As a result, the moving shoe 104 is moved to the conveying region 116 after being shifted to either end of the slat 102 as desired. According to the shoe shifting mechanism 300, before the article X on the conveyor A upstream of the sorting conveyor 100 reaches the upstream end 112 of the latter 100, the moving shoes 104 can be shifted to the right or left end of conveying surface of the sorting conveyor 100 according to the sorting data. In addition, the position of installation of the shoe shifting mechanism 300 may be suitably adjusted according to the speed of movement of the article X on the conveyor A. In a shoe shifting mechanism 300 not covered by the scope of protection of the invention and shown in FIG. 7, the common end (or junction) 307 of the branch guide rails 124a and 124b is on the central axis Y of the shoe centering guide rail 303. Hence, when power failure occurs, or when the power switch is turned off at the end of the article sorting operation, or when the electrical system of the mechanism becomes out of order, the electromagnets 313a and 313b cannot be energized, and therefore there is an adverse possibility that the projected member 106 moving along the shoe centering guide rail 303 is caused to strike against the common end 307 by its inertia. In order to increase the article sorting speed, it is necessary to move the slats 102 forming the conveying surface to move in the conveying direction quickly. However, when the speed is increased, then the inertia of the projected member 106 is also increased, and therefore, when the projected member 106 strikes against the common end 307, the amount of shock given to the latter 307 is increased as much. Thus, the common end 307 may be broken in the long use of the shoe shifting mechanism. For these reasons, it is necessary that the modification that the projected member 106 is prevented from striking against the common junction 307 of the branch guide rails 124a and 124b is applied to the above-mentioned arrangements of the shoe shifting mechanism. FIG. 8 shows another example of the shoe shifting mechanism according to the invention, which utilizes the arrangement shown in FIG. 4. The shoe shifting mechanism 300 comprises: a shoe centering guide rail 303 made up of a pair of right and left side walls 130b and 130a the distance between which is slightly larger than the outside diameter of the projected members 106 (the wheel 140); and branch guide rails 124a and 124b extended right and left from the shoe centering guide rail 303. The side wall 130a includes an upper side wall 130c which is bent outwardly at a given point on the shoe centering guide rail, and provided with an electromagnet 323; and a lower side wall 130d which is extended from the upper side wall 130c, thus forming part of a side wall of the branch guide rail 124a. The lower side wall 130d is provided with a permanent magnet or electromagnet 350, 350'. The branch guide rails 124a and 124b have a common junction 307. The common junction 307 is on the prolongation of the side wall 130a which is located at a side where the upper side wall 130c and the lower side wall 130d are provided; more specifically, it is shifted as much as a distance L from the central axis Y of the shoe centering guide rail 303. Each projected member 106 is guided downwardly (in the direction of the arrow R) in the shoe shifting mechanism 300 in FIG. 8. First, it passes through the shoe centering guide rail 303, thus being led to the branch guide rail 124a or 124b. Hence, the moving shoes 104, while moving through the returning region 118 (in FIG. 3), are shifted on the respective slats 102 to one side so as to be ready for the next sorting operation, and then moved towards the upstream end 112 of the sorting conveyor 100. Sensors 317 for detecting the passage of each projected member 106 are disposed beside the shoe centering guide rail 303 at the upstream end, to output a projected member passage detection signal. This detection signal, and sorting data are utilized for control of the electromagnet 323 provided on the upper side wall 130c. In the case where, after the sorting operation, each shoe 104 is to be shifted to the right end of the respective slat 102 at the upstream end (or the upper end) of the sorting conveyor 100 in FIG. 2, the electromagnet 323 on the upper side wall 130c of the shoe shifting mechanism 300 is energized, so that the projected member 106 moving along the shoe centering guide rail 303 is caused to move along the upper side wall 130c while being attracted by the electromagnet 323. Thereafter, the projected member 106 is allowed to move along the lower side wall 130d while being attracted by the electromagnet 350' or permanent magnet 350, so that it is led to the branch guide rail 124a merging with the lower side wall. Thus, the moving shoe 104 coupled to the projected member 106 is moved in the direction of the arrow D. On the other hand, in the case where each shoe 104 is to be shifted to the left end of the respective slat 102, the electromagnet 323 is not energized. Hence, the projected member 106 moving along the shoe centering guide rail 303 is allowed to move downwardly without being attracted towards the upper side wall 130c, so that it is led to the branch guide rail 124b; that is, it is guided in the direction of the arrow E. The width of the shoe centering guide rail 303 is slightly larger than the outside diameter of the projected member 106. Therefore, the projected members 106 are allowed to move downwardly along the central line Y of the shoe centering guide rail 303. As was described above, the common junction 307 of the branch guide rails 124a and 124b is shifted towards the branch guide rail 124a as much as the distance L from the central axis Y. Hence, the projected member 106 moving along the central axis Y towards the common junction 307 is caused to go along the side wall 307a of the branch guide rail 124b without striking against the common junction 307, thus being led into the branch guide rail 124b. As was described above, when, in the shoe shifting mechanism, the electromagnet provided for the upper side wall is not energized, the projected members are led to the branch guide rail on the side which is opposite to the side where the upper side wall is located, without striking against the common junction of the two branch guide rails. The electromagnet is not energized for instance in the following cases: the energization is controlled according to the sorting data, the energization is accidentally suspended because of power failure, the power switch of the conveyor is turned off after the sorting operation, and the electrical system of the conveyor becomes out of order. Even in those cases, the projected member moving by its own inertia is led into the branch guide rail without striking against the common junction of the branch guide rails. Hence, in the invention, the guide rail will not be damaged. As a result, the guide rails, being prevented from damage, are increased in service life, whereby the maintenance cost or running cost is reduced as much. In addition, with the shoe shifting mechanism of the invention, the projected members will never collide with the common junction of the right and left branch guide rails. Hence, the projected member can be smoothly and positively led to the right or left branch guide rail, which makes it possible to classify the articles at higher speed. FIG. 9 shows a further shoe shifting mechanism 300 not within the scope of the invention. The shoe shifting mechanism 300, similarly as in the case of the mechanism shown in FIG. 8, includes: a shoe centering guide rail 303 made up of a pair of right and left side walls 130a and 130b, the distance between which is slightly larger than the diameter of the projected member 106 (the wheel 140); and branch guide rails 124a and 124b which are extended from the shoe centering guide rail 303. The shoe shifting mechanism 300 further includes an upper side wall 130c, an intermediate side wall 130e, and a lower side wall 130d. The upper side wall 130c is extended outwardly from the shoe centering guide rail 303 at a given point to a distance M from the central axis Y of the shoe centering guide rail 13, and has an electromagnet 323. The intermediate side wall 130e is extended downwardly (towards the branch guide rail 124a) from the upper side wall 130c. The lower side wall 130d is extended from the intermediate side wall 130e, thus forming part of a side wall of the branch guide rail 124a. The lower side wall 130d is provided with a permanent magnet 360a. The opposite side wall 130b is provided with a permanent magnet 360b in such a manner that the latter 360b is laid over the shoe centering guide rail 303 and the branch guide rail 124b. Each of the projected member 106 is allowed to move downwardly (in the direction of the arrow R) in the shoe shifting mechanism 300 thus constructed. The projected member 106 passes through the shoe centering guide rail 303 first, and then led to the branch guide rail 124a or 124b. Hence, the moving shoes 104, while passing through the returning region 118 shown in FIG. 3, are shifted on the respective slats 102 to one side so as to be ready for the next sorting operation, and then moved to the upstream end 112 of the sorting conveyor 100. Sensors 317 for detecting the passage of each projected member 106 are arranged beside the shoe centering guide rail 303 at the upper end, to output a guide wheel passage detection signal. The passage detection signal, and sorting data are utilized to control the electromagnet 333 provided on the upper side wall 130c. In the case where, after the sorting operation, the moving shoes 104 are to be shifted to the right ends of the respective slats 102 at the upstream end (or the upper end in FIG. 2) of the sorting conveyor 100, the electromagnet 333 provided for the upper side wall 130c in the shoe shifting mechanism 300 is energized. As a result, each projected member 106 moving down the shoe centering guide rail 303 is first caused to move along the upper side wall 130c while being attracted by the electromagnet 333, and then to move along the intermediate side wall 130e and the lower side wall 130d while being attracted by the permanent magnet 360a, whereby it is led to the branch guide rail 124a. Thus, the moving shoe coupled to the projected member 106 is guided in the direction of the arrow D. In the case where the moving shoes 104 are to be shifted to the left ends of the respective slats 102, the electromagnet 333 is not energized. Hence, each projected member 106 moving down the shoe centering guide rail 303 is allowed to move downwardly as it is, without being attracted towards the upper side wall 130c, and then move along the side wall 130f on which the permanent magnet 360b is arranged, thus being led to the branch guide rail 124b. That is, the moving shoe 104 is guided in the direction of the arrow E. More specifically, when the projected member 106 moving straightly along the central axis Y of the shoe centering guide rail 303 without being attracted towards the upper side wall 130c, comes near the intermediate side wall 130e, it is attracted towards the side wall 130f by the magnetic force of the permanent magnet 360b, because the latter 360b is located above the permanent magnet 360a to apply a stronger magnetic attraction force to the projected member 106. Hence, even when the projected member 106 comes near the common junction 307 of the branch guide rails 124a and 124b, it will not strike against the junction 307; that is, it is led along the side wall 130f into the branch guide rail 124b. According to the invention, the common junction 307 of the branch guide rails 124a and 124b is shifted from the central axis Y towards the upper side wall 130c, so that the shoes are more smoothly guided into the branch guide rail 124b. While there has been described in connection with the preferred embodiments of the shoe returning or shifting mechanism, the invention should not be restricted thereto or thereby. Various changes and modifications may be made therein without departing from the spirit of the invention. For example, as shown in Fig. 29, the arrangement shown in Fig. 8 may be modified to have first and second shoe returning or shifting mechanisms 300 1 and 300 2 which are alternately used to prevent the thermal damage caused on the electromagnet 323 and the electromagnet 350' due to the excessive continuous energization thereof. Also, the arrangement shown in Fig. 8 may be modified, as shown in Fig. 30, to include a plurality of independent electromagnet elements 323 1 and 323 2 which are alternately used to prevent the thermal damage and a yoke 380 having a slit 390 to attain the smooth guide of the projected member 106 therealong and produce the close-looped magnetic flux therefrom. Moreover, the support shaft guide member 150b described in connection with Figs. 15, and 31-34 may be provided upstream of the common junction 307. Furthermore, one of the branch rail 124a and 124b may be arranged linearly with respect to the shoe centering guide rail 303. Thus, with the cross section of the guide rails according to the invention, the articles on the conveying surface can be classified positively, smoothly and quickly.

Claims: Slat conveyor type sorting apparatus comprising a change-over device, a plurality of slats (102) arranged side by side to form a conveying surface on which articles (X) are loaded, drive means (108) for moving said slats in a direction substantially perpendicular to a longitudinal direction of said slats (102) to convey said articles (X) together with said slats and moving shoes (104) mounted on corresponding slats (102) and movable in said longitudinal direction for sorting said articles (X), said change-over device comprising: a projecting member (106) protruding from each of said moving shoes (104) below said conveying surface; first, second and third guide rails (122, 124, 122) each having two side walls and being installed below and substantially parallel with respect to said conveying surface for guiding said projecting member (106) together with said moving shoe (104) when said slats (102) are moved by said drive means (108), wherein said second and third guide rails (124, 122) branch from said first guide rail (122) such that said projecting member (106) moving along said first guide rail (122) is selectively introduced into said second rail (124) or said third rail (122) and a magnet means (250, 250'), which is actuated for attracting said ferromagnetic projecting member (106) by means of a magnetic force toward said second guide rail (124), said magnet means is provided at a first side wall (130; Fig. 15: 130a) of said second guide rail, said magnet means including a yoke (280) forming a closed loop of magnetic flux generated by said magnet means (213, 250', 250) when being in contact with said projecting member (106), and wherein said first guide rail (122) defines a central axis, and said second (124) and third (122) guide rails include respective further side walls (Fig. 27: 130b) which are jointed together at a common junction area, and wherein said common function area is laterally deviated from said central axis . The sorting apparatus according to claim 1, wherein said magnet means is constituted by an electromagnet (213, 250') or a permanent magnet (250). The sorting apparatus according to claim 1 or 2, wherein said first and said third guide rail (122) extend linearly with respect to each other such that said projecting member (106) moving along said first guide rail (122) is introduced into said third guide rail (122) when said electromagnet (213, 250') is not energized. The sorting apparatus according to claim 1 or 2, wherein said second guide rail (124) includes a fixed side wall (130) along which said projecting member (106) is guided, said magnet means (213, 250, 250') constituting a part of said fixed side wall (2.3a, 251). The sorting apparatus according to anyone of claims 2 to 4, wherein said electromagnet (213, 250') includes a plurality of electromagnetic elements (250') which are selectively actuated to attract said projecting member (106) to said electromagnet (213, 250'). The sorting apparatus according to anyone of claims 1 to 5, further comprising: a second magnet means (223b) for operatively attracting said projected member (106) towards said third guide rail (122). The sorting apparatus according to claim 6, wherein said third guide rail (122) includes a fixed side wall along which said projecting member (106) is guided, and said second magnet means (223b) constitutes a part of said fixed side wall. The sorting apparatus according to anyone of claims 1 to 7, wherein said second guide rail (124) includes a side wall (130d, 280) constituted by said magnet means, said change-over device further comprising: a positioning means (150a, b; 333, 323, 213) located on said first guide rail (122) for positioning said projecting member (106) so as to cause said projecting member (106) to be brought into contact with said side wall (130d, 280). The sorting apparatus according to claim 8, wherein said positioning means (333, 213) is constituted by an electromagnet. The sorting apparatus according to claim 8 or 9, wherein said projecting member (106) includes a support shaft (135) and a rotary member (140) rotatably mounted on said support shaft (135), and said positioning means includes a support shaft guide (150a) for guiding said support shaft (135) so as to bring said rotary member (140) into contact with said side wall (280). The sorting apparatus according to claim 1, wherein said magnet means includes an electromagnet (213), which is located immediately downstream with respect to said first guide rail ( 122 ), a pair of yoke members (280a, b) connected to said electromagnet (213) and extending along said second guide rail (124) to form a smooth and continuous guide surface (131a) on which said rotary member (140) is guided when said electromagnet (213) is energized, and a plurality of magnets (250, 250') interposed and held between said yoke members (280a, b) and disposed downstream of said electromagnet (213) and along said guide surface. The sorting apparatus according to claim 11, wherein each of said yoke members (280a, b) is formed with a slit (290) between said electromagnet (213) and a most upstream one of said magnets (250, 250'). The sorting apparatus according to claim 11 or 12, wherein said first guide rail (122) includes a support shaft guide (150a) for guiding said support shaft (135) so as to bring said rotary member (140) into contact with said guide surface (131a). The sorting apparatus according to anyone of claims 11 to 13, further comprising: a support shaft guide (150b) for guiding said support shaft (135) therealong so as to forcibly moving said rotary member (140), which is attracted by said electromagnet (213) along said guide surface (131a) before said rotary member (140) is completely introduced into said second guide rail (124). A sorting apparatus according to anyone of the preceding claims, including: a conveying region (116) in which articles (X) are loaded from an upstream conveyor (A) on a conveying surface and sorted therefrom while being conveyed, and a returning region (118) located opposite to said conveying region, said conveying region (116) having a first sorting area in which a corresponding article (X) is sorted from said endless conveyor (100) to a first downstream conveyor (B) extending from said left hand end by moving said moving shoes (104) from said right hand end to said left hand end, and a second sorting area in which a corresponding article (X) is sorted from said endless conveyor to a second downstream conveyor (C) extending from said right hand end by moving said moving shoes (104) from said left hand end to said right hand end; and wherein said slat type conveyor further comprises: a shoe shifting device (300) located in said returning region (118) for positioning respective moving shoes (104), which are to be used for sorting an article (X) to be loaded from said upstream conveyor (A) to said endless conveyor (100), at one of said left hand side and said right hand side in accordance with a sorting data of said article (X).

Inventors: HIROKI SHINOHARA, KATSUMI ISHIHARA, TOSHIOMI HOSHI, HIROKI, SHINOHARA, KATSUMI, ISHIHARA, TOSHIOMI, HOSHI, HIROKI, SHINOHARA, TOYOKANETSU KABUSHIKI KAISHA, KATSUMI, ISHIHARA, TOYOKANETSU KABUSHIKI KAISHA, Toshiomi, Hoshi, c/o Toyokanetsu Kabushiki Kaisha
Applicants: TOYO KANETSU KK, TOYOKANETSU KABUSHIKI KAISHA
Application year: 1993
Main classification: B65G47
IPC codes: B65G47, B07C5