- PP4 -
The placement head carries two Z-axes. One of them moves the nozzle up and down while the other one moves the syringe that contains the paste. Both axes move on 9mm linear rails. They are driven by 42mm stepper motors which wind up a piece of 2.5mm timing belt (for the complete movement area of 32mm only half a turn of the belt disk is used). The linear axes are only moved up. Movement in down direction is done by gravity. Both Z-axes are equipped with reference switches that are triggerd in the upper position.
The axis used for pick and place operation (Z1) carries a small 28mm hollow shaft stepper motor that rotates the nozzle. On its lower drive shaft a brass ring with a ring magnet is mounted using stud screws. The magnet holds the nozzles using magnetic force. The upper part of the drive shaft is connected to a piece of flexible pneumatic tubing using an aluminium block with a gasket that is pressed onto the drive shaft using two springs. The mounting plate of the rotary motor is covered by a black plate to increase the contrast when components are aligned by the fixed camera.
The Z axis that holds the paste (Z2) carries a holder for 35g paste syringes. The ram of the syringe is moved by a 28mm linear stepper motor with lead screw. On the lower end of the lead screw, an aluminium ring is mounted. It prevents the lead screw from turning around while paste is squeezed out of the syringe. The whole linear stepper motor assembly can be removed to replace the syringe.
A camera with red LED-bars is mounted on the placement head. It is used for fiducial alignment and visual inspection after placement.
A PCB that connects all electrical components on the placement head is mounted on top. The PCB also contains a circuit for the pressure sensor (MPX20XXDP). The pressure sensor recognizes a part that is held onto the nozzle by evaluating the vacuum level. It is looped into the pneumatic tubing.