I’m an area service engineer for food packaging machines and not an automation specialist, but i can provide few hints.
For many automation systems to operate, you should first have a very clear and detailed mechanical plan with all of details finalized. Once you do so, you need to specify the type of motions involved, e.g.: linear or rotary. This lets you understand the number and types of motors and actuators you may need(servo, ac single phase, ac 3 phase, pneumatic actuator).
For each and every motors you might 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(much more conveyors, liquid tank level control pumps or rollers).Servo motors need Servo drivers to manage their precise movement.
These are generally your output devices, you’ll need your input devices being put down. This could be level sensors, flow sensors, proximity switches and other devices as required. The main reason i’m stating out this routine would be to enable you to define the specifications needed for your control system hardware requirements. All PLC manufacturers layout their product line-up based on system complexity.
Most PLC hardware comes as reconfigurable rack chassis. Basically there is a CPU the master brain which is supplemented with I/O device that could be slotted in like cards. Additional complex systems which needs servo motor can have servo card in order 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 touchscreen display HMI, line automation an internet-based diagnostic and asset monitoring functions. That’s that the guy with mechanical background can approach complex automation problems.
The solutions may vary determined by different manufacturer offering especially if you use beckhoff based systems. A sensible way to start is to work with existing machines so that you can learn the basics. Then go obtain a few catalogs from reputable manufacturers to understand the market can give. I suggest people to go through Omron catalogues. There is also a totally free automation web based course that will educate you on the newborn steps needed.
You have to be capable of 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 specifics of every bit of kit, on the way to program or properly connect them, but it is not brain surgery, a good mechanical engineer should probably excel about this because other engineer. The main part of control system design would be to comprehend the process you’re going to control along with the goals you want to achieve.