Gantry: The SMT feeder and PCB substrate are fixed, the placement head which installed with some vacuum nozzles moves back and forth between them, takes out the component from the feeder,adjusts the position and direction of the component and finally mounts it on the substrate.The placement head is installed in the X/Y moving beam of gantry, hence the name. Adjustment method of component position and direction 1. Centring the SMT machine to adjust the component position and rotating the smt nozzle to adjust the direction. The later machine no longer use this method,because the accuracy is limited. 2. Adjusting the component position by laser recognition and X/Y-Axis system and adjusting the direction by the rotating nozzle.This method can be used to identify the flight process, but can not be used in BGA. 3. Adjusting the component position by industrial camera recognition and X/Y-Axis system and adjusting the direction by the rotating nozzle. Generally, the camera is fixed, the placement head fly over it to make image recognition,which delay a little longer than the smt laser recognition. However, it can identify any component.By this way, the speed is limited because of the long distance to move back and forth. Today, a number of vacuum nozzles(ten more) are used at the same time and two beam system is used to improve the speed. That is to say, when a placement head attached to a beam take the component, the placement head attached another beam mount component on the PCB.The speed is almost twice as fast as the single beam system. But in practical applications, the condition of taking materials at the same time is difficult to achieve, and different components need different vacuum nozzles. It takes much time to replace nozzles. The advantages of this tyle machine:
1.Simple system structure to achieve high precision.
2.Suitable for a variety of specifications and shapes of components, even special-shaped components.
3.There are different forms of feeder,including banded,tubular and pallet.
4.Suitable for medium and small batch production, and can also be used in large mass production by combinating several machines. Turret: The smt feeder is put on a cart moving at a single axis, PCB substrate is put on work table moving at X/Y-Axis system and the placement head is installed on a turret.When they are working, the cart moves the feeder to feeding position where the smt nozzle takes the component, rotating to the mounting position that 180°with feeding position by the turret.Finally mounting the component on the substrate through adjusting the position and direction of the component when rotating. Adjustment method of component position and direction 1. Centring the machine to adjust the component position and rotating the nozzle to adjust the direction. The later machine no longer use this method,because the accuracy is limited. 2. Adjusting the component position by camera recognition and X/Y-Axis system and adjusting the direction by the rotating nozzle. The camera is fixed, the placement head fly over it to make image recognition.Generally, there are more than 10 to 20 pieces placement heads posted on the turret, and 2 to 4 pieces vacuum nozzles (earlier machine) and 5 to 6 pieces vacuum nozzles (later machine) are installed on each head. Because of the characteristics of the turret, all actions are refined, selection of the nozzle, movement of the feeder,component taking and recognition,adjustment of the angle, movement of the table(including position adjustment) and mounting component, all these can be completed at the same time to achieve the high speed in real sense. The fastest speed is up to 0.08~0.10 seconds for 1 piece. The advantages and disadvantages:
To be superior in speed and suitable for mass production,but it can only be used for banded components,not be applicable for the pallet dense and large integrated circuits(IC). So it needs to work with other machine to achieve better using. The structure of this machine is complicated and expensive that three times more than Gantry.