I’m an area service engineer for food packaging machines and not an automation specialist, on the other hand can provide few hints.
For all those automation systems to be effective, you must first have a very clear and detailed mechanical plan with all of details finalized. Whenever you accomplish that, you have to specify the motions involved, e.g.: linear or rotary. This allows you to know the number and types of motors and actuators you need(servo, ac single phase, ac 3 phase, pneumatic actuator).
For each motors you will 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(similar to conveyors, liquid tank level control pumps or rollers).Servo motors need Servo drivers to control their precise movement.
These are generally your output devices, you’ll need your input devices to get put down. This is often level sensors, flow sensors, proximity switches and other devices as required. The reason i’m stating out this routine is always to let you define the specifications necessary 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 is supplemented with I/O device that could be slotted in like cards. Additional complex systems which needs servo motor could have servo card for connecting 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 exercise you IO devices list, then receive the necessary software and hardware needed. You might need additional hardware needed for for fancy touchscreen display HMI, line automation and internet based diagnostic and asset monitoring functions. That’s how a guy with mechanical background can approach complex automation problems.
The solutions may differ according to different manufacturer offering particularly if use beckhoff based systems. A good way to start may be to focus on existing machines so that you can educate yourself on the basics. Then go get a few catalogs from reputable manufacturers to understand what the market industry can give. It’s my job to suggest visitors to go through Omron catalogues. There is also a free of charge automation web based course that may coach you on the baby steps needed.
You should 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 some additional training around the more knowledge about each bit of it technology, on the way to program or properly connect them, but it is not nuclear physics, a great mechanical engineer should probably excel about this because other engineer. The most important element of control system design is to see the process you are likely to control as well as the goals you want to achieve.