Adaptive model-based pressure control and method of resin cure

Claim 2

An adaptive model-based pressure control system for an apparatus in which a resin-containing workpiece is cured by heating according to a given temperature vs. time schedule and applying a low pressure during initial stages of the cure and a high pressure after the start of resin cross linking, comprising: sensors and associated instrumentation for supplying workpiece temperature and resin conductivity data to a control computer during the cure process; said control computer having means for computing the predicted future variation of resin conductivity and estimated time to a conductivity maximum from a mathematical model which utilizes current temperature and conductivity data, precalculated estimates of the fraction of cross linking completed, and activation energy and cure constants; and means for sending a signal to said apparatus to apply said high pressure to said workpiece when the estimated time to conductivity maximum drops below a preset threshold.

Claim 3

The pressure control system of claim 1 further comprising means for fitting said mathematical model on-line to said current data.

Claim 4

The pressure control system of claim 2 wherein said last-mentioned means is comprised of means for adjusting said activation energy constant initially, and thereafter adjusting said cure constant and recalculating the estimated time to conductivity maximum.

Claim 5

The pressure control system of claim 2 wherein said computer has data acceptance logic to reject said current data not in a cross linking range of times and temperatures and which differs by a given factor from the last data.

Claim 6

The pressure control system of claim 2 wherein said sensors are a thermocouple and a dielectric sensor having a parallel plate capacitor structure.

Claim 7

An adaptive pressure control system for a heated press in which a graphite cloth reinforced PMR-15 resin workpiece is cured by following a given temperature vs. time schedule and applying low pressure during initial stages of the cure and high pressure after the start of resin cross linking, comprising: means for sensing workpiece temperature and resin conductivity and supplying sensor data to a control computer during the cure cycle; said control computer having: means for precalculating from a cross linking model an estimate of the fraction of cross linking reaction completed as a function of temperature and time; means for computing the predicted future variation of resin conductivity and estimated time to a conductivity maximum from a mathematical model which utilizes current temperature and conductivity data, the fraction of cross linking completed, and activation energy and cure constants that are adjusted on-line to fit said model to said current data; and means for sending a signal to said heated press to apply said high pressure to said workpiece when the estimated time to conductivity maximum drops below a preset threshold.

Claim 8

An adaptive pressure control system for a heated press in which a graphite cloth reinforced PMR-15 resin workpiece is cured by following a given temperature vs. time schedule and applying low pressure during initial stages of the cure and high pressure after the start of resin cross linking, comprising: means for sensing workpiece temperature and resin conductivity and supplying sensor data to a control computer during the cure cycle; said control computer having: means for precalculating from a cross linking model an estimate of the fraction of cross linking reaction completed as a function of temperature and time; means for computing the predicted future variation of resin conductivity and estimated time to a conductivity maximum from a mathematical model which utilizes current temperature and conductivity data, the fraction of cross linking completed, and activation energy and cure constants that are adjusted on-line to fit said model to said current data; and means for sending a signal to said heated press to apply said high pressure to said workpiece when the estimated time to conductivity maximum drops below a preset threshold.

Claim 9

The pressure control system of claim 6 wherein said sensing means are a thermocouple and a high conductivity dielectric sensor having a parallel plate capacitor structure.

Claim 10

The pressure control system of claim 7 further comprising means for rejecting said sensor data not in a cross linking range of times and temperatures and any conductivity data that differs by more than a given factor from last accepted data.

Claim 13

The method of claim 9 wherein said conductivity model is expressed mathematically by: ##EQU7## where σ, T, and α are the electrical conductivity, absolute temperature, and fractional completion of the cross linking reaction, respectively, of the resin, subscripts o refer to a reference condition just prior to the cross linking reaction, E is the activation energy constant, and C is the cure constant.

Claim 14

The method of claim 9 further comprising rejecting unsuitable values of said incoming data not in a cross linking range of time and temperature.

Claim 15

The method of claim 11 further comprising adjusting the activation energy constant E until an acceptable number of data are accumulated and the fraction of cross linking completed is above a threshold, then adjusting the cure constant C and calculating the time-to-go to conductivity maximum.

Claim 16

The method of claim 9 further comprising rejecting any temperature and conductivity data points that are below thresholds and not in a cross linking range, and any conductivity data that differs excessively from a last accepted value.

Claim 17

The method of claim 13 further comprising adjusting only said activation energy constant, starting with a default value, until a given number of acceptable data points are accumulated and the calculated fraction of cross linking completed is above a threshold, and thereafter adjusting only said cure constant and calculating the time-to-go to conductivity maximum.

Claim 18

The method of claim 9 wherein said material being cured is a fiber-reinforced resin.

Claim 19

The method of claim 9 wherein said material being cured is graphite cloth reinforced PMR-15 resin.