I’m a field service engineer for food packaging machines and not an automation specialist, however i can provide you with few hints.
For all automation systems to work, you have to first possess a clear and detailed mechanical plan with all details finalized. If you do this, you have to specify the type of motions involved, e.g.: linear or rotary. Each day be aware of number and types of motors and actuators you need(servo, ac single phase, ac 3 phase, pneumatic actuator).
Per 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(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 be set out. This is level sensors, flow sensors, proximity switches as well as other devices if required. The main reason i’m stating out this routine is to allow you to 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 an CPU which is the master brain that is supplemented with I/O device which can be slotted in like cards. Additional complex systems which needs servo motor may 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 workout you IO devices list, then have the necessary software and hardware needed. You may want additional hardware required for for fancy touchscreen technology HMI, line automation and internet-based diagnostic and asset monitoring functions. That’s that the guy with mechanical background can approach complex automation problems.
The solutions may vary based on different manufacturer offering specifically if you use beckhoff based systems. A great way to start will be to work on existing machines so that you study the basics. Then go get yourself a few catalogs from reputable manufacturers to understand industry has to offer. I suggest website visitors to go through Omron catalogues. They also have a free automation online course which will educate you on the baby steps needed.
You need to 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 additional training around the more knowledge about every piece of it technology, on how to program or properly connect them, however it is not brain surgery, an excellent mechanical engineer should probably excel on this because other engineer. The key part of control system design would be to view the process you’re going to control and the goals you need to achieve.