I’m an area service engineer for food packaging machines and not an automation specialist, however i can give you few hints.
For all automation systems to operate, you must first have a very clear and detailed mechanical plan with all details finalized. When you achieve this, you should specify the sort of motions involved, e.g.: linear or rotary. This enables you to understand the number and kinds of motors and actuators you need(servo, ac single phase, ac 3 phase, pneumatic actuator).
For each motors you may need relay contactors (for single speed discrete/on-off type motors like blower fans and liquid pumps), VFD for speed controllable ac 3-phase motors(more like conveyors, liquid tank level control pumps or rollers).Servo motors need Servo drivers to regulate their precise movement.
These are generally your output devices, then you need your input devices being set out. This is level sensors, flow sensors, proximity switches along with other devices as needed. The reason i’m stating out this routine would be to let you define the specifications essential for your control system hardware requirements. All PLC manufacturers layout their product line-up depending on system complexity.
Most PLC hardware is sold as reconfigurable rack chassis. Basically there is a CPU which is the master brain that’s supplemented with I/O device that can be slotted in like cards. Additional complex systems which needs servo motor can have servo card to connect with servo driver, communication bus cards like CAN-BUS, PROFIBUS and DEVICENET and sensor cards for special sensors like RTD temperature sensors and level sensors.
So figure out you IO devices list, then get the necessary hardware and software needed. You will need additional hardware necessary for for fancy touch screen HMI, line automation and internet based diagnostic and asset monitoring functions. That’s the way a guy with mechanical background can approach complex automation problems.
The solutions may vary based on different manufacturer offering especially if you use beckhoff based systems. The best way to start will be to work with existing machines so that you will learn the basics. Go obtain a few catalogs from reputable manufacturers to understand the marketplace can give. I always suggest people to go through Omron catalogues. They also have a no cost automation web based course which will educate you on the newborn steps needed.
You should be able to design complete PLC systems: architecture design, hardware specfications and selection, logic narratives, logic programming, connection drawings. Everything. Perhaps all you need is extra training around the details of each piece of apparatus, regarding how to program or properly connect them, yet it’s not rocket science, a good mechanical engineer should probably excel about this just like any other engineer. The main aspect of control system design would be to comprehend the process you are likely to control as well as the goals you wish to achieve.