description when in use as long as the adjusting element of the adjusting apparatus 50 is adjusted by rotation the locking element 52 screwed on the adjusting element 51 will rotate along the thread on the adjusting element 51 to push the positioning portion 44 of the positioning holder 40 to move further changing the distance between the fixing portion 33 of the fixed holder 30 and the positioning portion 44 of the positioning holder 40 as shown in fig5 the positioning holder 40 is made to pivot around the pivot sleeve 430 of the pivot element 43 referring to fig6 since the positioning portion 44 pivots around the pivot sleeve 430 by an adjusting angle u03b8 the motor 60 on the positioning holder 40 will also rotate the angle u03b8 since the rotating element 62 of the motor 60 is engaged with the control element 22 the control shaft 20 on the control element 22 will also rotate the adjusting angle u03b8 and so will the swing arm 21 on the first end of the control shaft 20 moving the distal end of the swing arm 21 which was originally at a middle point o 1 of the travel to a secondary middle point o 2 so that the beginning point a 1 and the end point a 2 of the travel a 1 a 2 which were originally formed around the middle point o 1 will be changed to the travel beginning point b 1 and the travel end point b 2 of the travel b 1 b 2 immediately making the beginning and end points of the travel of the swing arm rotate.