Pick and place machine

This ladder logic program is supposed to manage the automation of a pick and place machine via PLC. The equipment has to place loose bottles in six piece containers. It consists of two conveyors and a manipulator that moves horizontally and vertically, carrying three bottles at a time. Horizontal motion (KL, KR) is performed by a motor controlled by three limit switches, mounted in the pick position (S8) and in the two place positions (S6, S7). The vertical motion and the holding of the bottles are performed by two-effect pneumatic devices, controlled by bistable solenoid valves. In this way, in case of power failure, the bottles will not fall. By pressing the start button, which is connected to the PM input of the PLC, both conveyors turn on and stay in motion for the whole cycle. The container in the loading position is locked by the C1 cylinder, which is moved to the right when the corresponding PLC output is off. When the S4 and S5 photocells are both engaged, the C2 output of the PLC turns on and pushes the corresponding piston against the second container, which gets locked. In this way the loading container is spaced by the next one, in order to make the machine work properly. If it is necessary, the manipulator moves first up and then to the right, so it places in the rest position; the S8 and S9 limit switches are engaged. Once three bottles are detected in the pick up position, the KD output turns on and the manipulator drops. After the downhill run the KB output activates to lock the pieces. After one second the KU output turns on and the manipulator moves up; then the machine moves to the left and is stopped in the first place position by the S6 limit switch. If the S4A photocell detects a container and the C1 output is off, the manipulator drops and the PLC turns on the KS output to unlock the pieces. After a second the manipulator moves up and then to the right, to pick up the next pieces, that will be placed in the position detected by the S7 limit switch. When the container is filled and the climb is completed, the C1 output turns on to unlock the C1 cylinder, so the container moves forward. The C1 output backs off as soon as the container exits the ray of the S4A photocell. Meanwhile the C2 output turns off because the S4 photocell is no more engaged, so the next container moves to the loading position. By pressing the PA button the pick and place machine completes the operation in progress, than stops working.

Shematics (pdf)