Abstract : This paper discusses the application of RS485 communication port in the electrical design of a horizontal steel ball grinding machine, fully utilizing the functions of frequency converters and PLCs. It demonstrates that the combined application of frequency converters and PLCs is currently an advanced and economical method for controlling motor speed regulation. Keywords : Frequency converter; Programmable logic controller; RS485 serial communication port; Ladder diagram 0 Overview With the continuous improvement of frequency conversion technology, its advantages such as stable speed regulation, energy saving, and reliability have become more prominent, leading to its widespread application in our machine tools, completely replacing the original slip-ring speed regulation and DC speed regulation. Programmable logic controllers (PLCs), due to their small size, simple wiring, high reliability, ease of maintenance, easy expansion, and easy programming, and their ability to implement many functions that contactors and relays cannot achieve, have become our preferred choice in design. The combination of the two has become an inevitable trend. RS485 ports are widely used in frequency converters and PLCs because communication only requires two wires and can cover long distances. This makes communication between frequency converters and PLCs possible, further improving the stability of the product's electrical drive control. 1. System Hardware Composition Since both the spindle and the material tray of the horizontal steel ball grinding machine require stepless speed regulation, frequency converters are used for control in the system. After careful comparison, Delta series products manufactured in Taiwan, which offer high cost-performance, were selected. The main spindle motor control uses the Delta VFD-B type, and the material tray motor control uses the Delta VFD-M type. To ensure consistent communication protocols during control, the Delta PLC series DVP32ES001R type was selected. The hardware wiring diagram of the main motor is shown below (the material tray motor control is the same as the main motor), as shown in Figure 1. This control method does not use any contactors; the start and stop are directly connected to the PLC input points. Twisted-pair cables are used through the RS485 port to achieve PLC control of the frequency converter's start and stop, thus reducing costs and minimizing external electromagnetic interference. The only thing to note is that the "+" and "-" polarities of the RS485 port must not be reversed; otherwise, there will be no operation. [b][align=center]For details, please click: Application of Delta Inverters and PLCs in Horizontal Steel Ball Grinding Machines[/align][/b]