Method and apparatus for controlling the thickness of a lamina of a coextruded laminate

A method using a computer for controlling the average thickness (T.sub.1) of a film lamina of thermoplastic material having a known density (D.sub.1) and coextruded at a variable extrusion rate with a foam lamina of similar thermoplastic material having a thickness (T.sub.2) and a density (D.sub.2) to form a thermoplastic laminate, comprising the steps of:

• sensing the thickness of the laminate which is equal to (T.sub.1 +T.sub.2) and providing a caliper signal (C) corresponding to the thickness sensed;
• sensing the mass/unit-area of the laminate which is equal to [(T.sub.1)(D.sub.1)+(T.sub.2)(D.sub.2)] and providing a mass signal (M) corresponding to the mass/unit-area sensed;
• sensing a response to said thermoplastic material and its distribution in the laminate and providing a dielectric signal (W) corresponding to the response which is equal to (K)[f(T.sub.1)]+(D.sub.2 /D.sub.1)[f(C)-f(T.sub.1)] where (K) is a ratio of the dielectric contribution from each lamina and both f(C) and f(T.sub.1) are functions derived to approximate empirical data sensed previously;
• storing in the computer the value of the density (D.sub.1) of the film lamina, the constant (K) which is the ratio of the dielectric effect of the solid material in each lamina and the functions f(T.sub.1) and f(C);
• providing the computer with successive sets of signals comprising the caliper signal (C), the mass signal (M) and the dielectric signal (W);
• enabling the computer upon receipt of the signals to calculate the thickness (T.sub.1) of the film lamina according to the formula:
• ##EQU7## combined from the equalities associated with each signal received, to compare an average thickness (T.sub.1) of the calculated thicknesses (T.sub.1) to a desired thickness (T.sub.0), and to provide a first control signal (DEC) when the average thickness (T.sub.1) is greater than a desired thickness (T.sub.0) and a second control signal (INC) when the average thickness (T.sub.1) is less than the desired thickness (T.sub.0);
• and
• adjusting the extrusion rate for the film lamina to decrease the rate in response to the first control signal (DEC) and to increase the rate in response to the second control signal (INC).

Apparatus for controlling the average thickness (T.sub.1) of a film lamina of thermoplastic material having a known density (D.sub.1) and coextruded at a variable extrusion rate with a foam lamina of similar thermoplastic material having a thickness (T.sub.2) and a density (D.sub.2) to form a thermoplastic laminate, comprising:

• a first gauge for sensing the thickness of the laminate which is equal to (T.sub.1 +T.sub.2) and for providing a caliper signal (C) corresponding to the thickness sensed;
• a second gauge for sensing the mass/unit-area of the laminate which is equal to [(T.sub.1)(D.sub.1)+(T.sub.2)(D.sub.2)] and for providing a mass signal (M) corresponding to the mass/unit-area sensed;
• a third gauge for sensing a response to said thermoplastic material and its distribution in the laminate and for providing a dielectric signal (W) corresponding to the response which is equal to (K)[f(T.sub.1)]+(D.sub.2 /D.sub.1)[f(C)-f(T.sub.1)] where (K) is a ratio of the dielectric effect of the solid material in each lamina, said function f(T.sub.1) is equal to aT.sub.1 /(b+T.sub.1) and said function f(C) is equal to aC/(b+C) where (a) and (b) are approximated to best fit empirical data measured by said third gauge;
• said third gauge being positioned adjacent the film lamina and the sensitivity of said gauge decreasing with the distance therefrom;
• a computer having a memory containing the value of the density (D.sub.1) of the film lamina, the value of the ratio (K) and the values associated with each of the functions f(C) and f(T.sub.1), said computer being connected to said first, second, and third gauges and being responsive to successive sets of signals comprising the caliper signal (C), the mass signal (M) and the dielectric signal (W) for calculating the thickness (T.sub.1) of the film lamina according to the formula:
• ##EQU8## combined from the equalitites associated with each signal received, and then for comparing an average thickness (T.sub.1) of the calculated thicknesses (T.sub.1) to a desired thickness (T.sub.0) and providing a first control signal (DEC) when the average thickness (T.sub.1) is less than the desired thickness (T.sub.0);
• and
• means connected to said computer and responsive to the first control signal (DEC) for decreasing the extrusion rate of the film lamina and responsive to the second control signal (INC) for increasing the extrusion rate of the film lamina.

Apparatus for controlling the average thickness (T.sub.1) of a film lamina of thermoplastic material having a known density (D.sub.1) and coextruded at a variable extrusion rate with a foam lamina of similar thermoplastic material having a thickness (T.sub.2) and a density (D.sub.2) to form a thermoplastic laminate, comprising:

• a first gauge for sensing the thickness of the laminate which is equal to (T.sub.1 +T.sub.2) and for providing a caliper signal (C) corresponding to the thickness sensed;
• a second gauge for sensing the mass/unit-area of the laminate which is equal to [(T.sub.1)(D.sub.1)+(T.sub.2)(D.sub.2)] and for providing a mass signal (M) corresponding to the mass/unit-area sensed;
• a third gauge for sensing a response to said thermoplastic material and its distribution in the laminate and for providing a dielectric signal (W) corresponding to the response which is equal to (K)[f(T.sub.1)]+(D.sub.2 /D.sub.1)[f(C)-f(T.sub.1)] where (K) is a ratio of the dielectric effect of the solid material in each lamina, said function f(T.sub.1) is equal to m(1-e.sup.-T.sbsp.1.sup./n) and said function f(C) is equal to m(1-e.sup.-C/n) where (m) and (n) are approximated to best fit empirical data measured by said third gauge;
• said third gauge being positioned adjacent the film lamina and the sensitivity of said gauge decreasing with the distance therefrom;
• a computer having a memory containing the value of the density (D.sub.1) of the film lamina, the value of the ratio (K) and the values associated with each of the functions f(C) and f(T.sub.1), said computer being connected to said first, second, and third gauges and being responsive to successive sets of signals comprising the caliper signal (C), the mass signal (M) and the dielectric signal (W) for calculating the thickness (T.sub.1) of the film lamina according to the formula:
• ##EQU9## combined from the equalities associated with each signal received, and then for comparing an average thickness (T.sub.1) of the calculated thicknesses (T.sub.1) to a desired thickness (T.sub.0) and providing a first control signal (DEC) when the average thickness (T.sub.1) is greater than the desired thickness (T.sub.0) and a second control signal (INC) when the average thickness (T.sub.1) is less than the desired thickness (T.sub.0);
• and
• means connected to said computer and responsive to the first control signal (DEC) for decreasing the extrusion rate of the film lamina and responsive to the second control signal (INC) for increasing the extrusion rate of the film lamina.

Apparatus for controlling the average thickness T.sub.1) of a film lamina of thermoplastic material having a known density (D.sub.1) and coextruded at a variable extrusion rate with a foam lamina of similar thermoplastic material having a thickness (T.sub.2) and a density (D.sub.2) to form a thermoplastic laminate, comprising:

• a first gauge for sensing the thickness of the laminate which is equal to (T.sub.1 +T.sub.2) and for providing a caliper signal (C) corresponding to the thickness sensed;
• a second gauge for sensing the mass/unit-area of the laminate which is equal to [(T.sub.1)(D.sub.1)+(T.sub.2)(D.sub.2)] and for providing a mass signal (M) corresponding to the mass/unit-area sensed;
• a third gauge for sensing a response to said thermoplastic material and its distribution in the laminate and for providing a dielectric signal (W) corresponding to the response which is equal to (K)[f(T.sub.1)]+(D.sub.2 /D.sub.1)[f(C)-f(T.sub.1)] where (K) is a ratio of the dielectric effect of the solid material in each lamina and [f(C)-f(T.sub.1)]/D.sub.1 is a function equal to a constant (Q) approximated to best fit empirical data measured by said third gauge;
• said third gauge being positioned adjacent the film lamina and the sensitivity of said gauge decreasing with the distance therefrom;
• a computer having a memory containing the value of the density (D.sub.1) of the film lamina, the value of the ratio (K), the value of the constant (Q) and the values associated with each of the functions f(C) and f(T.sub.1), said computer being connected to said first, second, and third gauges and being responsive to successive sets of signals comprising the caliper signal (C), the mass signal (M) and the dielectric signal (W) for calculating the thickness (T.sub.1) of the film lamina according to the formula:
• ##EQU10## combined from the equalities associated with each signal received, and then for comparing an average thickness (T.sub.1) of the calculated thicknesses (T.sub.1) to a desired thickness (T.sub.0) and providing a first control signal (DEC) when the average thickness (T.sub.1) is greater than the desired thickness (T.sub.0) and a second control signal (INC) when the average thickness (T.sub.1) is less than the desired thickness (T.sub.0);
• and
• means connected to said computer and responsive to the first control signal (DEC) for decreasing the extrusion rate of the film lamina and responsive to the second control signal (INC) for increasing the extrusion rate of the film lamina.