Thursday, March 15, 2012

The Operator Process Execution of PLC with ARM

To a system of PLC with ARM as control core and FPGA as co-processor to control arithmetic, the key technology is how to create the arithmetic computation time not engage the program operation time with the transfer time of the input/output parameter of arithmetic. In term of the instructions logic relation every instruction with it equivalent codes could be written to a subprogram. When the CPU scanned some instruction, the subprogram would be called to carry out the logic operation and the result would be transferred to the equivalent mapped register. The ladder chart program operation includes 3 stages: program operated, input disposed, and output handled, while the part of bottom half demonstrate the arithmetic program control in FPGA. Furthermore the dedicated storage space to control parameter and result could be kept to transfer the control arithmetic data.

The A/D converter transferred the information to the ARM by interrupt of timer. Then ARM controlled the data and saves them to control parameter memory unit. If the soft-relay Ml 01 was stopped up then the data acquisition and parameter value would be transfer to the FPGA by the setting control parameter module and transfer when ladder chart program performed the FPGA coprocessor control arithmetic part. Then the FPGA would transfer interrupt demand after finishing the arithmetic computation. At last the ARM saved the result to control the result memory by the manipulated the data and interrupt service routine, of which the result would be export by the Digital to Analog converter.

Testing and Application
The new PLC design in blowing void plastic injection molding equipment for a trial operation and one-step testing. It is integration equipment of the machine-electricity-liquid-gas. Its process blow molding with high air pressure, core-pulling, Chaxin, and a mechanical hand into the air pressure control, other work method for the hydraulic control, the equipment run cycle 67 sec. According to the molding process of hollow plastic temperature control is separated into 3 parts, the injection mold temperature control, the mould for the temperature control, the injection Liaotong 3 of the heating control. The applications of equipment control of the 120 switches, three loop closed loop control the temperature, two circuits of the pressure of electro hydraulic and the flow control valve, two human-machine interfaces. The PLC, throughout almost two months of process to gather the design of the essential requirements.

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