Apparatus and method for controlling the stock flow to a paper machine headbox

Claim 2

In a paper machine headbox system including a headbox, a stock pump, a main stock line from said stock pump which branches into a by-pass line which shunts said main stock line and a headbox stock flow line through which stock may flow from said main stock line to said headbox, an apparatus for controlling the stock flow rate in said headbox stock flow line which comprises: a. first means for providing by-pass flow control signals related to a desired headbox stock flow rate; b. a by-pass flow control valve in said by-pass line and responsive to said by-pass flow control signals; c. second means for providing main stock flow control signals; d. third means, responsive to said main stock flow control signals, for controlling the stock flow rate in said main stock flow line; and e. logic-inhibit means, logically responsive to said by-pass flow control signals, for inhibiting said third means response to said main stock flow control signals until said by-pass flow control valve exceeds predetermined limits.

Claim 3

In a paper machine headbox system including a readbox, a stock pump, a main stock line from said stock pump which branches into a by-pass line which shunts said main stock line to the suction side of said stock pump and a headbox stock flow line through which stock may flow from said main stock line to said headbox, an apparatus for controlling the stock flow rate in said headbox stock flow line which comprises: a. first means for providing by-pass flow control signals related to a desired headbox stock flow rate; b. a by-pass flow control valve in said by-pass line, said by-pass valve having mechanical flow control element means responsive to said by-pass flow control signals; c. second means for providing main stock flow control signals; d. third means, responsive to said main stock flow control signals, for controlling the stock flow rate in said main stock flow line; and e. logic inhibit means, logically responsive to the position of said mechanical flow control element means for inhibiting said third means response to said main stock flow control signals until said mechanical flow control element means exceeds predetermined limits.

Claim 4

In a paper machine headbox system including a readbox, a stock pump, a main stock line from said stock pump which branches into a by-pass line which shunts said main stock line to the suction side of said stock pump and a headbox stock flow line through which stock may flow from said main stock line to said headbox, an apparatus for controlling the stock flow rate in said headbox stock flow line which comprises: a. first means for providing by-pass flow control signals related to a desired headbox stock flow rate; b. a by-pass flow control valve in said by-pass line, said by-pass valve having mechanical flow control element means responsive to said by-pass flow control signals; c. second means for providing main stock flow control signals; d. third means, responsive to said main stock flow control signals, for controlling the stock flow rate in said main stock flow line; and e. logic inhibit means, logically responsive to the position of said mechanical flow control element means for inhibiting said third means response to said main stock flow control signals until said mechanical flow control element means exceeds predetermined limits.

Claim 5

The apparatus of claim 2 wherein said third means includes means for changing the speed of said stock pump.

Claim 6

The apparatus of claim 3 wherein said second means provides main stock flow control signals having magnitude related to the position of said mechanical flow control element means.

Claim 7

The apparatus of claim 4 wherein the main stock flow control signals are a series of pulses.

Claim 8

The apparatus of claim 5 wherein said logic inhibit means inhibits the transmission of said pulses from said second means to said third means.

Claim 9

The apparatus of claim 3 wherein said second means provides main stock flow control signals which are a series of pulses, the magnitude of said pulses being unrelated to the position of said mechanical flow control element means.

Claim 10

The apparatus of claim 7 wherein said logic inhibit means inhibits the transmission of said pulses from said second means to said third means.

Claim 11

The apparatus of claim 7 wherein said logic-inhibit means inhibits said second means by de-energizing said second means.

Claim 12

The apparatus of claim 2 wherein said third means comprises: a. a valve located in the main stock flow line between said pump and said by-pass branch; and b. valve actuating means for manipulating said valve responsive to said main stock flow control signals.

Claim 13

The apparatus of claim 10 wherein said second means provides main stock flow control signals having magnitude related to the position of said mechanical flow control element means.

Claim 14

The apparatus of claim 11 wherein the main stock flow control signals are a series of pulses.

Claim 15

The apparatus of claim 12 wherein said logic-inhibit means inhibits the transmission of said pulses from said second means to said third means.

Claim 16

The apparatus of claim 10 wherein said second means provides main stock flow control signals which are a series of pulses, the magnitude of said pulses being unrelated to the position of said mechanical flow control element means.

Claim 17

The apparatus of claim 14 wherein said logic-inhibit means inhibits the transmission of said pulses from said second means to said third means.

Claim 18

The apparatus of claim 14 wherein said logic-inhibit means inhibits said second means by de-energizing said second means.

Claim 19

The apparatus of claim 2 wherein said third means comprises: a. a second by-pass line from said main stock flow line around said stock pump; and b. a second by-pass flow control valve in said second bypass line which is responsive to the main stock flow control signals from said second means.

Claim 20

The apparatus of claim 17 wherein said second means provides main stock flow control signals having magnitude related to the position of said mechanical flow control element means.

Claim 21

The apparatus of claim 18 wherein the main stock flow control signals are a series of pulses.

Claim 22

The apparatus of claim 19 wherein said logic-inhibit means inhibits the transmission of said pulses from said second means to said third means.

Claim 23

The apparatus of claim 17 wherein said second means provides main stock flow control signals which are a series of pulses, the magnitude of said pulses being unrelated to the position of said mechanical flow control element means.

Claim 24

The apparatus of claim 21 wherein said logic-inhibit means inhibits the transmission of said pulses from said second means to said third means.

Claim 25

The apparatus of claim 21 wherein said logic-inhibit means inhibits said second means by de-energizing said second means.

Claim 26

The apparatus of claim 3 wherein said third means comprises: a. a valve located in said headbox stock flow line between said by-pass branch and said headbox; and b. valve actuating means for manipulating said valve in response to said main stock flow control signals.

Claim 27

The apparatus of claim 24 wherein said second means provides main stock flow control signals having magnitude related to the position of said mechanical flow control element means.

Claim 28

The apparatus of claim 25 wherein the main stock flow control signals are a series of pulses.

Claim 29

The apparatus of claim 26 wherein said logic-inhibit means inhibits the transmission of said pulses from said second means to said third means.

Claim 30

The apparatus of claim 24 wherein said second means provides main stock flow control signals which are a series of pulses, the magnitude of said pulses being unrelated to the position of said mechanical flow control element means.

Claim 31

The apparatus of claim 28 wherein said logic-inhibit means inhibits the transmission of said pulses from said second means to said third means.

Claim 32

The apparatus of claim 28 wherein said logic-inhibit means inhibits said second means by de-energizing said second means.

Claim 33

In a paper machine headbox system including a readbox, a stock pump, a main stock line from said stock pump which branches into a by-pass line shunting said main stock line and a headbox stock flow line connecting said headbox with said main stock line, and a by-pass flow control valve having a finite flow control range in said by-pass line, the method of controlling the stock flow in said headbox stock flow line which comprises: a. obtaining a first signal proportional to the differential between total stock flow to said headbox and total stock flow therefrom; b. manipulating said by-pass valve in response to said first signal and in a manner to eliminate said differential; c. monitoring said by-pass valve control within said finite flow control range and generating second and third signals proportional thereto; d. manipulating the stock flow rate in said main stock line in response to said second signal and in a manner to maintain said by-pass valve within an effective portion of said finite flow control range; and, e. inhibiting said main stock flow rate manipulation response to said second signal by said third signal, said third signal allowing said second signal manipulation of said main stock line flow rate only when said by-pass valve control status exceeds predetermined limits within said finite control range.

Claim 34

In a paper machine headbox system including a readbox, a stock pump, a main stock line from said stock pump which branches into a by-pass line shunting said main stock line and a headbox stock flow line connecting said headbox with said main stock line, and a by-pass flow control valve having a finite flow control range in said by-pass line, the method of controlling the stock flow in said headbox stock flow line which comprises: a. obtaining a first signal proportional to the differential between total stock flow to said headbox and total stock flow therefrom; b. manipulating said by-pass valve in response to said first signal and in a manner to eliminate said differential; c. monitoring said by-pass valve control within said finite flow control range and generating second and third signals proportional thereto; d. manipulating the stock flow rate in said main stock line in response to said second signal and in a manner to maintain said by-pass valve within an effective portion of said finite flow control range; and, e. inhibiting said main stock flow rate manipulation response to said second signal by said third signal, said third signal allowing said second signal manipulation of said main stock line flow rate only when said by-pass valve control status exceeds predetermined limits within said finite control range.

Claim 35

The method of claim 31 wherein said first signal is obtained from a direct measurement of the total pressure head within said headbox.

Claim 36

In a paper machine headbox system including a headbox, a stock pump, a main stock line from said stock pump which branches into a by-pass line shunting said stock pump with a by-pass flow control valve therein and a headbox stock flow line through which stock may flow from said main stock line to said headbox, the method of automatic controlling the stock flow in said headbox stock flow line which comprises: a. obtaining by-pass flow control signals b. controlling the by-pass flow by manipulating said by-pass flow control valve in response to the by-pass flow control signals; c. obtaining main stock flow control signals; d. controlling the main stock flow in response to the main stock flow control signals; e. obtaining a first signal representative of the position of said by-pass control valve; and f. inhibiting control of the main stock flow in response to said first signal until the position of said by-pass flow control valve exceeds predetermined limits.

Claim 37

In a paper machine headbox system including a headbox, a stock pump, a main stock line from said stock pump which branches into a by-pass line shunting said stock pump with a by-pass flow control valve therein and a headbox stock flow line through which stock may flow from said main stock line to said headbox, the method of automatic controlling the stock flow in said headbox stock flow line which comprises: a. obtaining by-pass flow control signals b. controlling the by-pass flow by manipulating said by-pass flow control valve in response to the by-pass flow control signals; c. obtaining main stock flow control signals; d. controlling the main stock flow in response to the main stock flow control signals; e. obtaining a first signal representative of the position of said by-pass control valve; and f. inhibiting control of the main stock flow in response to said first signal until the position of said by-pass flow control valve exceeds predetermined limits.

Claim 38

The method of claim 32 wherein said first signal differential is obtained by comparing the value of said total pressure head to a predetermined set-point.