Automation continues to push Industry 4.0 with various sensor and embedded technologies. In an industrial panel, the machine controls are designed to perform specific work. The operation of machines includes analog, digital, and motion control capabilities. The machine controls must operate with full functionality as designed. To design machine controls for such industrial applications as parts transfer, material handling, and processing a design process must be established. To develop these industry systems, a design methodology is required. Three basic design methodology sections required in developing machine controls consists of control signals, decision, and action.
|The logic control for industrial machines can be divided into three basic sections. (Source: Don Wilcher)|
The control signal initiates the machine control operation through a set of electromechanical contacts or repetitive electronic switching. The target control device such as an electromechanical relay, solenoid, or visual-audible annunciator will be activated by control signals. If the electromechanical or electronic switching device is not active, the control signal will not energize the target electromechanical or electronic load. The machine controls specification will provide the type of electromechanical or electronic switching device to use for the desired control signal.
Examples of control signal devices consist of the following electromechanical or electronic components:
- pushbutton switches
- limit switches
- flow switches
- temperature switches
- HMI panels
- proximity switches
The work to be done by the machine control is achieved by decisions. The heart of the decision section is a core digital processing system. A digital processing system can be divided into two subsections: data paths and control logic. The digital paths include arithmetic and data movement circuits like basic adders and shift registers. The control logic provides timing signals to orchestrate proper sequences for correct machine operation. The decisions are accomplished by a central processing unit. In the early days of programmable machine controls a microprocessor was used. Today, FPGAs, PSoCs, or ARM-Cortex based microcontrollers can perform decision processing activities efficiently and rapidly. Arithmetic, sequencing, low level logic, and control operations are typical decision activities carried out in the machine controls programmable processor. Combinational circuits using basic logic gates like AND, OR, NOT, NAND, NOR, and EXOR perform low level decisions for the target machine control. These low- level gates can be implemented using FPGAs or PSoCs.
The decision section receives control signals from the electromechanical or electronic switching device. The electrical information will be in an analog or digital format in which the decision section will process. An appropriate output signal is provided that will drive a specific machine control action. The decision functions are traditionally coded in a high-level language such as C, C++, or a graphical format consisting of a ladder logic program. The actual decision parameters will be provided in the machine controls’ functional specification.
|The CPU performs the decision activity for industrial machine controls. Programmable ICs like microcontrollers or FPGAs can provide central processing of control signals generated by electrical-electronic input devices. (Source: Don Wilcher)|
After the decision section processing logic functions have been specified in a software requirements specification, the output action function needs to be specified. The action is traditionally physical either providing motion, visual, or audible function. The action directs the motion, visual, or audible effects of the machine control. Motors, solenoids, LED pilot lamps, LCD displays, and electronic annunciators are examples of electromechanical and electronic action components used for output machine control functions. The CPU’s output control data can be sent to electromechanical or electronic actuators hardwired to an industrial machine control panel using traditional MC (machine control) wire. Another alternative to MC wire is AS-Interface (Actuator Sensor) which is a simple two-wire network. AS-interface is a wiring replacement that connects electromechanical or electronic actuators to a CPU-based industrial machine control panel by a digital communication protocol.
|AS-Interface based machine controllers can replace traditional MC wire that direct the actions of such electromechanical actuators like solenoids and motors. (Source: Siemens)|
Electromechanical relays and solid-state drives operate based on the machine controls’ direct- action capability. Partitioning your machine control designs into these three basic sections will allow industrial systems to be designed effectively. Testing and troubleshooting industrial systems can also be performed using this basic design methodology, as well.
This design method presented will serve as a template for future automation and machine control applications. Additional information on electromechanical and industrial solid-state devices can be found in the Electrical Motor Controls for Integrated Systems fifth addition textbook. AS-Interface protocol can be found on the Siemens website.
Don Wilcher is a passionate teacher of electronics technology and an electrical engineer with 26 years of industrial experience. He’s worked on industrial robotics systems, automotive electronic modules/systems, and embedded wireless controls for small consumer appliances. He’s also a book author, writing DIY project books on electronics and robotics technologies. Besides being an Electrical Engineer, he’s a Certified Electronics Technician with ETA International and Alabama State Certified Electronics Instructor.