Design method for automatically pairing unit Field of the Invention The invention relates to a design method for the automatical assembly line for the magnet group, especially to a design method for the automatically pairing unit for the magnet group. 5 Description of prior art A magnetic turntable is disclosed in the patent AU2015100319, there are provided a plurality of arrays of magnet groups, each magnet group consists of 16 pieces of permanent magnet arranged alternately. Currently, each magnet group is assembled by hand, due 10 to the small size of each magnet and the thin thinkness of the magnet, it is difficult to assemble magnet groups, the efficiency is low, and mistake is offen taken resuting that a plurality of magnets are gravitated together by magnetic force. Summary of the present invention 15 The object of the invention is to provide a design method for the automatically pairing unit for the magnet group so as to solve the above problem. The unit has the function of correctly assembling a plurality of magnets in an alternating manner, and the function is automatic and efficient. 20 In the following, the technical solution will be discribed. The method comprises providing a NS poles conveyor track, an output track and a mounting bracket; arranging two opposed tracks, each of the tracks has a form of 25 "E", to the NS poles conveyor track; arranging two opposed tracks, each of the tracks has a form of "[", to the output track comprises; making the magnets within the N pole conveyor track have the same direction of the magnetic line; 30 making the magnets within the S pole conveyor track have the 1/6 same direction of the magnetic line; arranging the direction of the magnetic line of the magnets within the N pole conveyor track opposite to the direction of the magnetic line of the magnets within the S pole conveyor track; 5 arranging the direction of the magnetic line of the NS poles conveyor track and the output track vertical to the conveying direciton; arranging a reciprocating push block to the position where the NS poles conveyor track is vertical to the output track; 10 arranging the direction of the movment of the push block vertical to the conveying direction of the NS poles conveyor track; arranging the direction of the movment of the push block aligned to the conveying direction of the conveyor track; pushing the magnets fallen from the NS poles conveyor track to 15 the output conveyor track by the push block. using nonmagnetic material to make the NS poles conveyor track, the output track, the push block and the base seat. The second object of the invention is to provide a design method for the automatically pairing unit for the magnet group, the unit has a 20 compact structure and a reasonable layout. In the following, the technical solution will be discribed. making the push block slide fit with the base seat; making the power input wheel rotatably couple to the support arm; 25 making the connecting rod rotatably couple to the eccentric portion of the push block and the power input wheel. Specifically, achieving the rotatable connection by the clearance fit between shaft and the hole. 30 Preferably, achieving the rotatable connection between the support arm and the shaft by the transmission of the bearing; mounting the support arm removably to the base seat through crews. 2/6 Because the NS poles conveyor track separately conveys the permanent magnets with the same direction of magnetic line, and the directions of the magnetic line of magnets within two tracks are opposite, and the push block reciprocatedly pushes the magnets 5 fallen from the two tracks, the unit can correctly efficiently assemble a plurality of magnets in an alternating manner. Brief description of the drawing In the following, the invention will be described in greater detail by means of some embodiments with reference to the accompanying 10 drawings, in which Fig.1 is a 3d-drawing of the automatically pairing unit for the magnet group; Fig.2 is detailed views of the part I in the Fig.1; Fig.3 is a 3d-drawing of Fig.1 from another view; 15 Fig.4 is a 3d-drawing without NS poles conveyor track and ouput track; Fig.5 is a front view of Fig.3; Fig.6 is from Fig.5, wherein the push block is in the retracted position; 20 Fig.7 is from Fig.5, wherein the push block is between the retracted position and the stretched out position; Fig.8 is an exploded 3d-drawing of the push assembly; Fig.9 is a 3d-drawing of the push assembly; Fig.10 is a 3d-drawing of the assembly line arranged in the 25 rectangular array; Fig.11 is a 3d-drawing of the assembly line arranged in the ring array; 1. the NS poles conveyor track; 2. the output track; 3. the push assembly; 31. the base seat; 32. the push block; 30 33. the power input wheel; 34. the connecting rod; 35. the support arm; 36. the shaft; 37. the sleeve; 38. the bearing. Detailed description of the preferred embodiment Referring to Fig.1 and Fig.3, the automatically pairing unit for the 3/6 magnet group comprises a NS poles conveyor track 1, an output track 2, a mounting bracket and a push assembly 3, the NS poles conveyor track 1 is arranged vertically, the output track 2 is arranged horizontally, the push assembly 3 is arranged to the position where 5 the NS poles conveyor track 1 is vertical to the output track 2. The permanent magnets within the NS poles conveyor track 1 move down incessantly due to the effect of the gravity, by the pushing of the push assembly 3 the permanent magnets within the output track 2 are conveyed out incessantly with alaternating polarities. 10 Referring to Fig.2, the NS poles conveyor track 1 comprises two opposed E-shaped tracks, the N pole conveyor track is made up by the upper half of the two E-shaped track, the S pole conveyor track is made up by the lower half of the two E-shaped track, the N pole conveyor track is parallel to the S pole conveyor track, and they are 15 separated by the middle portion of the E-shaped track. Referring to Fig.1, the output track 2 comprises two opposed [-shaped tracks, the opposed arrangment may be from up to down, or may be from left to right, the embodiment takes the up-down for example. 20 Referring to Fig.4, the magnets within the N pole conveyor track have the same direction of the magnetic line, the magnets within the S pole conveyor track have the same direction of the magnetic line, the direction of the magnetic line of the magnets within the N pole conveyor track is opposite to the direction of the magnetic line 25 of the magnets within the S pole conveyor track. The direction of the magnetic line of the NS poles conveyor track 1 and the output track 2 are vertical to the conveying direciton. A reciprocating push block 32 is arranged to the position where the NS poles conveyor track 1 is vertical to the output track 2, the direction of the 30 movment of the push block 32 is vertical to the conveying direction of the NS poles conveyor track 1, the direction of the movment of the push block 32 is aligned to the conveying direction of the conveyor track, the push block 32 pushes the magnets fallen from the NS poles conveyor track 1 to the output conveyor track 2. 4/6 Referring to Fig.8 to Fig.9, the push assembly 3 comprises a base seat 31, a push block 32, a connecting rod 34, a power input wheel 33, a support arm 35, a shaft 36, a sleeve 37, a bearing 38, an antiextrusion ring and a screw. 5 The push block 32 passes through the base seat 31, and slides fit with the base seat 31, the power input wheel 33 rotatably couples to the support arm 35, and rotates around its axis. The connecting rod 34 rotatably couples to the eccentric portion of the push block 32 and the power input wheel 33. 10 In order to increase the efficicency and reliability of the rotary joint, the shaft 36 connects the power input wheel 33 and the connecting rod 34, the shaft 36 rotatably connects the connecting rod 36 and the push block 32, the shaft 36 rotatably connects the power input wheel 33 and the support arm 35, between the shaft 36 and the 15 support arm 35 is arranged two paratactic bearings 38 so as to form a transmission joint, obviously, the rotatable connection is achieved by the clearance fit between shaft and the hole. The support arm 35 is removably mounted to the base seat 31 through crews, such structure is beneficial to assemble each part 20 well so as to increse the conpactness of the structure. The distance between parts are adjusted by the sleeve 37 so as to increse the flexibility of the transmission. The NS poles conveyor track 1, the output track 2, the push block 32 and the base seat 31 are made of nonmagnetic material to avoid the 25 influence of the magnetic force caused by the permanent magnets conveyed within the tracks. Referring to Fig.5 to Fig.7, each parts are assembled together according to the above, a connecting rod and slider mechanism is formed. A force is exerted on the power input wheel 33, such as 30 connecting the power input wheel 33 and the electric motor with a belt, the power input wheel 33 rotates, the rotation of the wheel 33 makes the connecting rod 34 swing, the swing of the connecting rod 34 make the push block 32 move, because of the limit of the base seat 31, the push block 32 moves only in a reciprocating way, such 5/6 that the power input wheel 33 rotates one round, the push block 32 moves from the totally stretched out position to the totally retracted position, and returns from the totally retracted position to the totally stretched out position. 5 During the push block 32 moving from the totally stretched out position to the totally retracted position, the permanent magnets within the NS poles conveyor track 1 falls in front of the push block 32 due to the effect of the gravity force. During the push block 32 moving from the totally retracted position to the totally stretched 10 out position, the push block 32 pushes the fallen magnets forward till the push block 32 moves to the totally stretched out position, during the course, the permanent magnets within the NS poles conveyor track 1 can not fall down because of the limiting effect of the upper surface of the push block 32; when the push block 32 is in 15 the totally retracted position, the magnets within the NS poles conveyor track 1 fall down to wait for the next push from the push block 32. Because the NS poles conveyor track 1 separately conveys the permanent magnets with the same direction of magnetic line, and the directions of the magnetic line of magnets within two tracks 20 are opposite, the push block 32 pushes the two magnets with alternating polarities every time, the push block 32 reciprocatedly pushes the magnets, so the object of the invention is achieved, that is, the automatically pairing unit for the magnet group can correctly efficiently assemble a plurality of magnets in an alternating manner. 25 In order to increase the efficiency, a plurality of pairing units can be formed into an array, such as a rectangular array or a ring array, than taking the array as a part of the assembly line. The direction of the magnetic line in this invention means the direction of the magnetic line located inside the sigle permanent 30 magnet. 6/6