SoftPLC was used with the company’s previous controller to eliminate timing issues, increase computing power, reduced cost, and improved reliability.
Engineers frequently encounter difficulty in control applications when multiple tasks need to occur in a coordinated manner. A food processing OEM found this to be the case in one of their machines. In the past, the OEM used an SLC-500 PLC for machine control, in conjunction with a Basic module which communicated to a high speed Servo via an RS-232 channel. Timing problems resulted because: (a) the data coming into the Basic module was limited to 19.2Kbaud, (b) the Basic program needed to run a large number of calculations for the Servo before it passed the information to the PLC, and then (c) based on where the PLC was in its cycle, the control did or did not happen in the proper sequence or fast enough.
The solution chosen by the OEM was to use SoftPLC, a PC based open architecture control system that runs “PLC-5 like” ladder. The servo calculations required were extremely lengthy and needed to be done within 1/100 second, so rather than burden the control PC with this, they were still done in a separate PC in Basic. The hardware selected was a Ziatech STD-32 multi-processor system–1 CPU running SoftPLC for control, 1 CPU performing the calculations, and a third CPU running an operator interface program and the SoftPLC ladder programming software, TOPDOC. High-speed APIX I/O was selected, which fits right in the Ziatech backplane. In a global memory area, information is passed between the SoftPLC and the Basic program.
The OEM was able to convert the usable SLC-500 logic to run in SoftPLC, and wrote a C function to read/write to the global memory area – all in less than one day! All objectives for the machine re-design were reached, including inter-communications between the various control elements, cost of machine, processing speed and reliability of operation.