Design method for kick-out unit Field of the Invention The invention relates to design method for the assembly line for the magnet group, especially to design method for a kick-out unit thereof. 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. In order to increase the efficiency and to reduce the time lost caused by mistake, an 15 automatically assembly line is arranged to the factory. The drive device of the kick-out unit for the assembly line is an air cylinder or a linear motor, the position of the single permanent magnet is detected by the laser position switch, the eject of the magnet is under control of the control unit PLC, such kick-out unit reach the 20 function required, but the maintenance cost for the whole unit is high, it is complicated, and it needs programming control, so the operator should be required to have high abilities of electrical and electronics. The huge magnetic field caused by the permanent magnets on the assembly line have some interference in the control 25 unit PLC. Summary of the present invention The object of the invention is to provide a design method for a kick-out unit for the assembly line for the magnet group so as to solve the above problem. The kick-out unit has low producing cost, 30 and has mechanical linkage to control the kick-out unit, such that 1/6 the operator can control the whole system without the ability of the programming. In the following, the technical solution will be discribed. A design method for a kick-out unit for the assembly line for the 5 magnet group comprises: providing a bottom board, a cam, a kicking rod, a spring and a pin; arranging the cam coaxial and synchronous with the rotary shaft; providing a head portion cooperating with the cam and a tail portion for hitting the permanent magnet to the kicking rod. 10 Arranging a skidway for housing permanent to the kick-out unit; making the kick-out unit cause the spring to store energy through the cam so as to quickly trigger the kicking rod, which hits the single permanent magnet, such that the single permanent magnet flies into the gripper jaw; 15 making the external cylindrical surface of the pin sliding fit with the kicking rod; arranging the axis of the pin parallel to the bottom board. In particular, arranging a first vertical walls, a second vertical walls and a cavity for avoiding the limit portion of the kicking rod to the 20 bottom board; perpendicularly arranging the first and second vertical walls to the bottom board; removablely arranging the pin perpendicularly passing through the first vertical walls to the first vertical walls. 25 Arranging an opening to the working surface of the cam, the position of the opening is corresponding with the position of the gripper jaw; providing a scarp and a glacis to the opening, the kicking rod ejects quickly with the help of the scarp, the kicking rod moves to 30 the working surface of the cam with the help of the glacis so as to finish storing energy of the spring. Arranging a rectangular opening for housing the spring to the middle portion of the kicking rod; arranging the limit portion proximate the head portion of the 2/6 kicking rod, the limit portion projects from the both sides of the kicking rod; making the stretching length of the kicking rod limited by the cooperation between the limit portion and the first vertical walls; 5 making the spring interact with the second vertical walls and the limit portion. arranging a bottom surface parallel to the bottom board above the kicking rod; arranging a side surface vertical to the bottom surface proximate 10 the tail portion of the kicking rod. Because the cam is coaxial and synchronous with the rotary shaft, and the kicking rod cooperates with the opening of the cam, the mechanical linkage is nice, the operator can control the whole system without the ability of programming, so the maintenance cost 15 for the whole unit is low. 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 drawings, in which 20 Fig.1 is a 3d-drawing of the kick-out unit; Fig.2 is a 3d-drawing of the kicking rod of the kick-out unit; Fig.3 is a 3d-drawing of the bottom board of the kick-out unit; Fig.4 is a 3d-drawing of the cam of the kick-out unit; Fig.5 is a 3d-drawing of the kick-out unit on the assembly line; 25 0. the kick-out unit; 1. the bottom board; 2. the kicking rod; 3. the spring; 4. the pin; 5. the cam; 101. the cavity; 102. the first vertical walls; 103. the second vertical walls; 104. the bottom surface; 105. the side surface; 201. the head portion; 202. the limit portion; 30 203. the rectangular opening; 204. the tail portion; 501. the opening; 502. the scarp; 503. the glacis. Detailed description of the preferred embodiment Referring to Fig.5, the kick-out unit 0 of the invention is removablely 3/6 mounted to assembly line with screws, the cam 5 is coaxial and synchronous with the rotary shaft; the kick-out nuit 0 causes the spring 3 to store energy through the cam 5 so as to quickly trigger the kicking rod 2, which hits the single permanent magnet, such 5 that the single permanent magnet flies into the gripper jaw. Referring to Fig.4, the working surface of the cam 5 is arranged equally six openings 501, the position of the opening 501 is corresponding with the position of the gripper jaw, the opeing 501 comprises a scarp 502 and a glacis 503, the kicking rod 2 ejects 10 quickly with the help of the scarp 502, the kicking rod 2 moves to the working surface of the cam 5 with the help of the glacis 503 so as to finish storing energy of the spring 3, the cam 5 is coupled coaxially to the rotary shaft with the central hole arranged to the cam 5, the cam 5 is synchronous with the rotary shaft by the 15 cooperation between the key and the groove. Referring to Fig.3, the bottom board 1 of the kick-out unit 0 of the invention comprises a first vertical walls 102, a second vertical walls 103 and a cavity 101 for avoiding the limit portion 202 of the kicking rod 2, the first and second vertical walls 102, 103 arranged 20 perpendicularly to the bottom board 1, the first vertical walls 102 is provided with a hole rotatable cooperation with the pin 4, the hole penetrates through the first vertical walls 102, the first and second vertical walls 102, 103 connect with each other by a portion of the third vertical wall, a wall of the third vertical wall is provided with a 25 bottom surface 104 parallel to the bottom board 1, the bottom surface 104 is vertically provided with a side surface 105, the bottom surface 104 is arranged above the kicking rod 2 and the pin 4, the side surface 105 is arranged proximate the tail portion 204 of the kicking rod 2. 30 Referring to Fig.2, the kicking rod 2 of the kick-out unit 0 of the invention provides a head portion 201 cooperating with the cam 5 and a tail portion 204 for hitting the permanent magnet, a rectangular opening 203 for housing the spring 3 is disposed on the middle portion of the kicking rod 2, a limit portion 202 is disposed 4/6 proximate the head portion 201 of the kicking rod 2, the limit portion 202 projects from the both sides of the kicking rod 2, the stretching length of the kicking rod 2 is limited by the cooperation between the limit portion 202 and the first vertical walls 102. 5 Referring to Fig.1, the kick-out unit 0 comprises a bottom board 1, a kicking rod 2, a spring 3 and a pin 4; the pin 4 is removablely mounted to the first vertical walls 102 of the bottom board 1 by collar, the pin 4 is arranged to be parallel to the bottom board 1, that is, the pin 4 passes vertically through the first vertical walls 102, 10 the external cylindrical surface of the pin 4 has sliding fit with the kicking rod 2. With the help of the cavity 101 formed by the external cylindrical surface of the pin 4, the first and second vertical walls 102, 103 and the bottom board 1, the kicking rod 2 moves within the cavity 101, the width of the cavity 101 is greater than the width 15 of the limit portion 202 of the kicking rod 2. The spring 3 interacts with the second vertical walls 103 and the limit portion 202. The permanent magnet waiting for to be ejected is located in the skidway formed by the next permanent magnet, the bottom surface 104 and the side surface 105, the kick-out nuit 0 causes the spring 3 20 to store energy through the cam 5 so as to quickly trigger the kicking rod 2, which hits the single permanent magnet, such that the single permanent magnet flies into the gripper jaw. In the following, the detailed process will be discribed. When the head portion 201 of the kicking rod 2 moves to the 25 working surface of the cam 5, the kicking rod 2 compresses the spring 3, so that the spring 3 has the elastic energy. When the head protion 201 of the kicking rod 2 moves to the scarp 502 of the opening 501, the kicking rod 2 ejects quickly with the help of the spring 3 fulled of elastic energy, and moves into the opening 501, 30 the tail portion 204 of the kicking rod 2 hits the permanent magnet in the skidway, such that the magnet ejects from the the skidway and flies into the gripper jaw. When the limit portion 202 of the kicking rod 2 touchs the first vertical walls 101, the kicking rod 2 stops, at this momnent, there is a gap between the head protion 5/6 201 of the kicking rod 2 and the bottom portion of the opening 501, such arrangement prevents the kicking rod 2 from impacting the cam 5 so as to increase the lifetime of the cam 5 and the kicking rod 2. The cam 5 goes on rotating, the head portion 201 of the kicking 5 rod 2 compresses the spring 3 as sliding along the glacis 503 till the head portion 201 of the kicking rod 2 slids out of the opening 501, then the spring 3 is fulled of elastic energy and waiting for next triggering. 6/6