automatic pallet changers are generally operated by means of cam and follower. Cam is rotated by induction motor. The cam follower is attached with a rack and the rack rotates the pinion. Pinion is mounted on the shaft of rotary table. So when the cam rotate it moves the rack by means of a follower and the rack rotate the pinion as well as the rotary table by 180 degree in both direction. The movement of rack in both end is controlled by 2 no of proximity switch which controls the brake of motor.
this pallet changer table will rotate when it is in declamp position. Which is controlled by a hydraulic cylinder. This cylinder is fitted on the top of the machine and table shaft is operated by this cylinder. If the sealing of this cylinder will fail then the table cannot be clamped and declamped properly.In the time of declamp position table shaft is drawn by the hydraulic cylinder and in clamp position it goes downward and sit steadily.
If the beginning position of the rack is not in proper position in respect of the rotary table(zero position with respect to pallet and B axis) then the final position (after rotating 180 degree) will be also faulty. It will happen if the rack is taken out from its position for some maintenance purpose and in the time of assembling. This problem is very major problem and very fine adjustment is needed for this. We should adjust the pinion position as well as the table position in its actual position before engaging the rack with the pinion. then finally engage the rack slowly and steadily and it should be noticed that pinion will not rotate at the time of engaging. Then first fix the position of rack by entering dowel pin and then fix it with bolt.
Here is a link for many other problem related to rotary table and B axis
The Probable Cause Of Disposition Of Pallet In HSM 320 (HMT) Machining Center.B axis not clamp