Injection molding machine temperature control system
AssigneeAllen-Bradley Company, Inc.
InventorsJohn G. Searle, Brian P. Delaney, Kevin O. Delaney, Keith M. Hogan, Peter B. Schmidt
Life of this patent
Estimating the term…
Abstract
A control system for controlling the temperature within process machinery such as the feed assembly in an injection molding machine. The control system provides a six phase process for starting up the machine from cold conditions and controlling the machine temperature to rapidly and accurately attain a command temperature while identifying control parameters for use under steady state conditions for maintaining the command temperature.
Claims14
A method for controlling temperature within a process machinery system characterized by a system dead time period Theta.sub.D in order for said machinery system to rapidly and closely approach a command temperature T.sub.com upon cold startup from a cold start-up temperature T.sub.start, comprising the steps of:
- a) turning on and running one or more heaters within said machinery system at a first high power level for a limited time period t.sub.p1 so that the temperature within the machinery system rapidly approaches an intermediate temperature selected to fall below the command temperature T.sub.com ;
- b) ramping down the power applied to said heaters to a low power level and running said heaters at said low power level until the temperature of said machinery system attains a temperature maximum T.sub.max ;
- c) determining a steady state heater command value CV.sub.ss necessary to maintain the machinery system at approximately the command temperature T.sub.com, the determination of the steady state heater command value CV.sub.ss being based on the time at which the temperature maximum T.sub.max is attained, the system dead time period Theta.sub.D, and a steady state heater command value CV.sub.TM which corresponds to the temperature maximum T.sub.max ;
- and
- d) turning on the heaters within said machinery system at a second high power level for a short time interval t.sub.p4, the length of which is based on said steady state heater command value CV.sub.ss, said temperature maximum T.sub.max, said command temperature T.sub.com, the cold start-up temperature T.sub.start of the machinery system and said system dead time period Theta.sub.D so that the temperature within said machinery system rapidly and closely approaches said command temperature T.sub.com.
A method of determining parameters for use in autotuning a temperature controller in a materials handling system which forms a part of an injection molding machine, the temperature controller being utilized during and in conjunction with startup of said materials handling system, comprising the steps of:
- a) turning on and running one or more heaters installed on said materials handling system at a high power level for a limited time period t.sub.p1 in order to raise a measured system temperature of said materials handling system up to an intermediate temperature below a predetermined command temperature T.sub.com, and simultaneously identifying a system dead time period Theta.sub.D based on response of the system temperature with respect to time;
- b) ramping down the power applied to said heaters to a zero power level and maintaining the zero power level in order to determine a steady state heater command value CV.sub.TM corresponding to a measured temperature maximum T.sub.max attained while said heaters are maintained at the zero power level, and simultaneously determining a system time constant Tau.sub.C and a system gain K.sub.P based on said response of the system temperature with respect to time;
- c) running said heaters at said high power level for a short time interval t.sub.p4 based on the difference between the command temperature T.sub.com and an ambient temperature value T.sub.start, the system gain K.sub.P and the system dead time period Theta.sub.D in order to rapidly raise said system temperature up to approximately said command temperature T.sub.com ;
- and
- d) using the system dead time period Theta.sub.D, the system gain K.sub.P and the system time constant Tau.sub.C to set feedback control parameters for accurate steady state control of said system temperature at said command temperature T.sub.com.
In a temperature control system for controlling the temperature within a materials handling assembly which forms a part of an injection molding machine and which is utilized for feeding plastic materials into a mold, said temperature control system having a set of heaters, one or more temperature detectors and a programmable controller for regulating the operation of said heaters in response to temperature information from said temperature detectors to attain and maintain a command temperature T.sub.com, the improvement comprising:
- a) means for controlling the power applied to said heaters to maintain the power applied to said heaters at a high power level for a limited period t.sub.p1 in order to rapidly raise the temperature of said materials handling assembly to an intermediate temperature;
- b) means for controlling the power applied to said heaters for ramping down the power applied to said heaters to a zero power level and maintaining the power applied to said heaters at the zero power level until the temperature of said materials handling assembly peaks at a temperature maximum T.sub.max ;
- c) means for identifying a system dead time period Theta.sub.D for the temperature control system and a steady state heater command value CV.sub.TM corresponding to said temperature maximum, and for calculating a system gain K.sub.P for the temperature control system based on said temperature maximum T.sub.max, a measurement of ambient temperature and said steady state heater command value CV.sub.TM ;
- and
- d) means for controlling the power applied to said heaters at said high power level for a short time interval t.sub.p4 in direct proportion to said command temperature T.sub.com and said system dead time period Theta.sub.D, and in inverse proportion to said system gain K.sub.P in order to spike the temperature of said materials handling assembly up to said command temperature T.sub.com.
Dependencies are inferred from the claim text.