RockwellAutomation罗克韦尔Using A Logix Controller for Barrel Temperature Control On Plastic Injection and用户手册说明书.pdf

Technical Application Notes Using a Logix Controller for Barrel Temperature Control on Plastic Injection Molding and Extruding Machines The Purpose of this Document: To assist machine builders in utilizing the PIDE instruction for extremely accurate closed loop control. This document pays particular attention to controlling temperature (heat/cool or heat-only) loops with slow response, commonplace in barrel temperature control applications found on plastic extrusion and injection molding machines. Application Description: Extruders and injection molding machines must keep plastic at a specific temperature as it is forced through the barrels of these machines. This is accomplished by constantly monitoring and controlling barrel temperature. The barrels themselves are made of metal, and heat up slowly, usually with significant thermal lag which adds to the difficulty of reaching and holding the desired setpoint. Often, applications also require cooling as well, which is often accomplished by controlling coolant flow through the barrel’s coolant jacket, or by controlling the speed of a fan blowing air over the barrel. Control System Description: In this document, the control system is made up of (a) a Logix controller, where one or more PIDE instructions with built-in autotuning are executed, (b) multiple analog inputs that provide temperature readings to the controller, (c) multiple discrete outputs which are used to pulse the barrel heaters and cooling system off and on, and (d) an operator interface (HMI). Typically, control is of the ‘time proportioned’ type. As an example, let’s assume that all the heater bands along the barrel are to be controlled over a 10 second duty cycle. On startup, the ‘on’ percentage of the duty cycle might be as high as 100%, applying power t