US3280393A

US3280393A - Selectively actuated tension override in a tensioning motor control system

Info

Publication number: US3280393A
Application number: US254796A
Authority: US
Inventors: Robert E Crossley
Original assignee: Great Northern Paper Inc
Current assignee: Great Northern Paper Inc
Priority date: 1963-01-29
Filing date: 1963-01-29
Publication date: 1966-10-18
Anticipated expiration: 1983-10-18

Description

3,280,393 IN A 2 Sheets-Sheet 1 1966 R. E. cRossLEY SELECTIVELY ACTUATED TENSION OVERR TENSIONING MOTOR CONTROL SYS Filed Jan. 29, 1963 4| AIR SPRING f Reg. f '9 INVENTOR Air Supply Robert E. Crossley BY g k m l fil'lk ATTORNEYS Oct. 18, 1966 CROSSLEY A 3,280,393

SELECTIVELY ACTUATED TENSION OVERRIDE IN TENSIONING MOTOR CONTROL SYSTEM Filed Jan. 29, 1963 2 sheets sheet 2 I I I I FIG.2

INVENTOR Roberr E.Crossley United States Patent Ice 3,280,393 SELECTIVELY ACTUATED TENSION OVERRIDE IN A TENSHONING MOTOR CONTROL SYSTEM Robert E. Crossley, Millinocket, Maine, assignor to Great Northern Paper Company, a corporation of Maine Filed Jan. 29, 1963, Ser. No. 254,796 Claims. (Cl. 318-6) This invention relates to a web tension control device for controlling the tension in a running web of material and more particularly the invention relates to an electrical system for use in paper processing machines for controlling the tension of a web running between a supply roll and a set of calender rolls. The tension control according to the teaching of the present invention is an overriding system which operates in addition to the nor mal tension controls found in paper processing machines.

It is the present practice in feeding the web material from a supply through a set of calender rolls, to drive the calender rolls at a constant predetermined speed and to connect the supply roll to an unwind motor for bringing it up to the predetermined speed of the calender rolls, After the supply roll is brought up to its proper speed and the web is being drawn off by the calender rolls, it has been found necessary to apply a braking force to the supply roll to prevent it from overrunning the calender rolls and to prevent a loss tension in the web located between the supply roll and calender rolls. Presently, this braking force is applied either mechanically or electrically.

Mechanical means employed include a friction brake adapted to be connected to the supply roll together with suitable means such as pneumatic means for varying the braking force as the supply roll becomes depleted and its rotational speed increased. This type of braking means will uniformly increase the braking force applied to the supply roll and thereby prevent any changes in the tension of the web located between the supply roll and calendering rolls that would normally occur due to the increased speed of rotation of the supply roll. Mechanical braking means, however, have the disadvantage of being costly to maintain and are not completely effective in maintaining the tension in the web at a constant predetermined valve since they are compensate for the normal increase in the speed of rotation of the supply roll as it becomes exhausted and fail to take into account such factors as the inherent characteristics of the web material and the physical makeup of the supply roll, both of which have an affect on the tension in the web as it is unwound. For example, it is sometimes desirable to feed the web into the calender rolls in a slightly moistened condition to prevent the buildup of large quantities of electricity which normally tend to be produced by the high friction of hot calender rolls on paper that is dry. In the paper as originally produced, however, the length of the fibers that go to make up the web may vary from one area in the web to another. This in turn will affect the stretch ability of the web and if the web is being drawn into the calender rolls with a constant force, the tension therein will tend to change as these different areas are encountered Furthermore, in producing the supply rolls, it often happens that individual convolut-ions of web material become wound with different degrees of tightness, that is, the density of the supply roll may vary from the innermost convolution to the outermost. Also the supply roll may have become out-of-round due to mishandling before or during its positioning in the web processing machine. Both of these irregularities in the makeup of the supply roll will also have an affect on the tension in the web as it is fed to the calender rolls. Since the braking force exerted on the supply roll by mechanical braking means is 3,280,393 Patented Oct. 18, 1966 dependent solely on the normal increase in speed of the supply roll as it becomes depleted, these above mentioned characteristics of the web and supply roll will continue to produce changes in the tension of the web.

Instead of using mechanical braking means for the supply roll, it is also the present practice, as stated above, to use electrical means. In such situations, the unwind motor employed for bringing the supply roll up to proper speed may be of the type that will operate as a generator after the supply roll has been accelerated up to the predetermined speed of the calender rolls so as to exert a regenerative braking force on the supply roll which will vary in direct relationship to the increase in rotational speed of the supply roll to compensate for changes in tension of the web that would normally tend to occur if the rotation of the supply roll was not controlled. To produce this braking force, the unwind motor is connected to the output side of an unwind generator the field of which is, in turn, controlled by a regulator. The regulator operates to compare the unwind motor voltage against a speed reference signal coming from a tachometer connected to the motor driving the calender rolls and if there is any difference or mismatch in these signals, the regulator will institute the necessary change in the field of the unwind generator thus causing the appropriate change in the speed of the unwind motor and consequently the braking force applied to the sup-ply roll so as to maintain the linear speed of the web unaffected by the increased speed of the unwind motor. The regulator will also operate to hold a substantially constant current in the unwind motor in order to prevent the tension of the Web from varying as the speed of the unwind motor increases. To do this, the regulator will compare the unwind motor current with a predetermined reference current from a tension rheostat and if there is any difference, make the appropriate corrective change. As with the mechanical braking means, the regenerative braking system presently employed is unsatisfactory in that the changes in the braking force are not a direct function of the tension actually present in the web as determined by the inherent characteristics of the web material and the makeup of the supply roll.

According to the teachings of the present invention, the web processing apparatus includes a regenerative braking system with which is combined a tension control means for taking into account the changing characteristics of the web material and the supply roll. This tension control means is adapted to override the conventional controls presently employed and includes means for directly sensing changes in the web tension. Generally, the structure includes tension sensing rolls which are positioned in engagement with the web running between the supply roll and the calender rolls. One of these rolls is adapted to move in response to changes in tension in the web and such movement is transformed into an electrical signal. The electrical signal is, in turn, fed to the regulator controlling the field of the unwind generator to change the field of the unwind motor and thereby either increase or decrease the braking force applied by the unwind motor to the supply roll.

A fuller understanding of the invention will be obtained by a reading of the following specification with reference to the accompanying drawings of which:

FIGURE 1 is a diagrammatic view of the tension override device with the electrical system shown schematically;

FIGURE 2 is a side elevation of one end of the tension override sensing means; and

FIGURE 3 is a cross-sectional view taken along lines 33 of FIGURE 2.

With reference to FIGURE 1 of the drawings, a supply roll 1 of web material is mounted on a rotatable shaft 2 which is, in turn, connected to the unwind motor 3 eases through suitable gearing 4. The unwind motor is connected to the output of the unwind generator 5, the field 6 of which is controlled by a regulator 7. This unwind generator is driven at a constant speed by a suitable determined speed. Thisspeed reference signal is also fed by way of the line 13 to a motor operated regulator 19 which controls a rheostat 20 for varying the field 21 'of the unwind motor 3. From FIGURE 1, it will also be noted that the voltage feedback line leads into the motor operated regulator 19 by way of the line 22.

The apparatus thus far described is conventional and operates in the following manner. The motor operated rheostat 20 is set in advance so that the supply roll rotates at a speed corresponding to the speed of the calender motor whereby the web will be unwound from the supply roll at the same speed at which it is pulled through the calender rolls. The setting of the rheostat will be dependent on the diameter of the particular supply roll being used and since the diameter of the supply roll continually decreases during unwinding, the original setting of the rheostat is only effective at the beginning of the unwinding operation. As the unwind motor is brought up to the proper speed, in accordance with the setting of the rheostat 20, it will drive the supply roll; however, after the predetermined speed is attained and the web is being unwound from the roll, the shaft speed of the unwind motor will increase since the calender rolls continue to pull the web at the predetermined set speed while the diameter of the supply roll decreases. To control this increase in speed of the unwind motor so that the web does not overrun the calender rolls, the unwind motor is such that the load created by the constant pulling force applied to the web will exert a negative torque on the unwind motor so as to apply a braking force on the supply roll thus changing the speed of rotation of the supply roll an appropriate amount.

At the same time, the regulator 7 compares the unwind motor voltage received through the voltage feedback line 10 with the speed reference signal received through line from the tachometer 16. This speed reference signal is indicative of the preselected speed of the calender rolls and if the signal received through the voltage feedback line 10 does not match the speed reference signal, the regulator 7 will institute the necessary change in the field of the unwind generator so that the voltage will change to an appropriate value and thereby cause the proper change in the speed of the unwind motor 3.

This same speed reference signal also goes via the line 18 to the regulator 19 of the motor operated rheostat 20. Like the regulator 7 of the unwind generator, this regulator 19 compares the speed reference signal with the voltage signal which, in this case, is fed to the regulator 19 through the line 22. Any mismatch causes the motor operated rheostat 20 to move or notch and thereby cause the proper change in the unwind motor field strength.

In addition to making the initial setting of the motor operated rheostat 20 for controlling the speed of the web, the tension rheostat 14 is set to a value in accordance with the tension desired to be maintained in the web running between the supply roll and calender rolls. A constant current into the unwind motor will prevent the Web tension from being affected by the increased speed of the unwind motor as the supply rollis depleted. To control this current, the current feedback line 11 sends a signal from a current sensor 11' to the

regulator

7 and 31, one of which is shown in FIGURE 3.

the regulator, in turn, compares this signal against the setting of the current passing through the'tension rheostat 14 and if there is any discrepancy, the regulator changes the field 6 of the unwind generators an appropriate amount to therebyincrease or decrease the currentuntil it matches the setting of the tension rheostat.

According to the teaching of the present invention, there is added to this arrangement a tension override system now to be described.

Positioned between the supply roll and the calender rolls are two

tension sensing rollers

23 and 24 about which the web passes as shownin FIGURE 1. Roll 23 is rotatable mounted on a shaft 25 the ends of which are secured to a frame member 26 of the web processing apparatus by means of brackets, one of which is shown in FIGURE 3 at 26. Also secured t-o this frame are a pair of levers or bars 27. These bars, as shown, are pivoted about point 29 on a line extending radially along the horizontal from the center of the roller 23 and these arms normally extend in a vertical direction. 0nd roller 24 is rotatably mounted on shaft 30 which, in turn, is rotatably secured at its ends within brackets This bracket is pivotally secured to the upper end of the bars 27 as at 32 and pivotal'ly secured at the diametrically opposite side of roller24 to a second pair of levers or bars v28 intermediate their ends as at 33.1 Bars 28, in turn, are fixed at one end to the shaft 34 of a selsyn motor or transducer 35 shown in FIGURES 1 and 2. The brackets 31, only one of which is shown, are further provided with

arms

36 and 37 extending radially from the roller 24 on diametrically opposite sides thereof and at right angles to a line drawn between the two

pivot points

32 and 33. i

In order to control the movement of the brackets 31 about the

pivots

32 and 33,

air springs

38 and 39 are fixed at one end to the bars 28 with the other end of spring 38 fixed to the arm 36 and the other end of spring 33 fixed to the arm 37.

As shown in FIGURE 1, air spring 38 is loaded with a fixed bias by means of the conduit 4% connected to a suitable source of air under pressure. Air spring 39 is also connected to the source of air under pressure by means of a conduit 41. The air to the air spring 39, however, may be varied by means of a pressure regulator 42 which is connected in tandem to the tension rheostat 14 as shown in FIGURE 1.

It will be noted that the bracket 31 can only be rotated about its own axis 3%) in a counterclockwise direction from the position shown in FIGURE 3 since the pivot point 32 on the bars 27 is at its uppermost position with respect to the fixed pivot point 29 and pivot point 33 on the bars 28 is at its lowermost position with respect to the fixed pivot point 34.

Assuming for the moment that the web has not been threaded around the

rollers

23 and 24, the air supplied to the air spring 38 to cause it to expand will tend to move bracket 31 to the left from the position shown in FIGURE 3 and air supplied to the air spring 39 to cause it to expand will tend to move the bracket 31 to the right from the position shown in FIGURE 3. Although the expansion of air spring 38 cause it to exert an equal force on both the arm 36 and bars 28, the bracket will move to the left since the force exerted about pivot point 29 will be' greater than the force exerted about pivot point 34. Likewise, the force exerted about point 34 by the expansion of air spring 39will be greater than the force exerted about pivot point 29 and, therefore, expansion of this air spring will tend to move the bracket 31 in the opposite direction.

When the web has passed around the'rollers 23 and 24 and set with the desired web tension by the tension rheostat 14, it will tend to move the bracket 31 to the right from the position shown in FIGURE 3. In order to compensate for this force, the pressure supplied to.

The sec-.

the air spring 39 though its connection with this rheostat will be set at a value lower than the fixed pressure setting of air spring 38 to hold the roller 25 in the neutral posi' tion shown in FIGURE 3. If the web tension subsequently changes due to any changes in the characteristics of the web or supply roll, the roller 24 will move to either the left or right from the position shown in FIG- URE 3 depending on whether the sheet tension is decreased or increased. Movement of roller 24 will effect a corresponding rotation of the armature of the selsyn 35 in a clockwise or counterclockwise direction due to the connection of bars 28 with the selsyn at 34-.

The selsyn 35 is connected by way of a preamplifier 43: and line 44 to the regulator 7 and an on-off switch 45 is provided in line 44 for controlling the signal sent to the regulator. With the switch 45 in the on position, rotation of the armature of the selsyn in a counterclockwise direction from the position shown in FIGURE 3 will send a signal to the regulator 7 to increase the current in the field of the unwind generator 5. This in turn, will increase the voltage in the field of the unwind motor which will result in an increase in the speed of the unwind motor by an amount directly proportional to the increase in web tension so that the roller 24 will move back to its neutral position shown in FIGURE 3 and the tension in the web will immediately revert to its original value. It is apparent that a decrease in the sheet tension will produce an opposite effect to decrease the speed of the unwind motor.

When the roller 24 is in its neutral position, the driving of the supply roll will be solely controlled by the signals other than the tension signal in the line 44 and it is only when roller 24- moves from its neutral position, that a signal will be produced in line 44 to override the other signal being fed to the regulator. This signal in line 44 may therefore be appropriately termed a tension override signal and it is to be noted that the signal received by the regulator 7 through the line 54 is directly proportional to the tension actually existing in the web as determined by the inherent characteristics of the web and supply roll.

The above is a description of a preferred embodiment of the invention and it is obvious that various changes may be made without departing from the scope of the invention as defined in the following claims.

I claim:

it. A tension override control system for a web calendering apparatus having a frame, a web supply roll, a driven shaft on which said supply roll is wound, an unwind motor for driving said shaft, and calendering rolls spaced from said supply roll for exerting a substantially constant pulling force on said web comprising:

(a) means for imparting a predetermined linear speed to said web independent of the change in size of said supply roll as the web is unwound therefrom;

(b) means for imparting a predetermined tension to the web between said supply roll and calendering rolls which is independent of the change in size of the supply roll as the web is unwound therefrom;

(c) separate sensing means selectively operable during normal feeding of the web for directly sensing changes from a predetermined value in the tension of the web between said supply roll and calendering rolls independently of the speed of rotation of said shaft, and

(d) control means responsive to said sensing means for increasing the speed of rotation of the supply roll .upon an increase in tension over said predetermined value being sensed and for decreasing the speed of rotation of the supply roll upon a decrease in tension being sensed to return the tension in the web to said predetermined value.

2. A tension override control system according to claim 1 wherein said sensing means comprises a movable roller positioned between said supply roll and said calendering rolls and means for urging said roller into engagement with said web.

3. A tension override control system according to claim 2 wherein said control means comprises means responsive to movement of said roller for changing the speed of rotation of said supply roll.

4. A tension override control system for a web processing apparatus having a frame, a web supply roll, a driven shaft on which said supply roll is wound, and web processing means spaced from said supply roll for exerting a substantially constant pulling force on said web to unwind it from said supply roll comprising:

(a) an unwind motor connected to said driven shaft so as to be driven thereby at an increasing speed and so as to apply an increasing braking force on said supply roll as the diameter of the roll is decreased;

(b) an unwind generator having its output connected to said unwind motor;

(c) a regulator for controlling the field of said unwind generator;

(d) means for sending current and voltage reference signals to said regulator indicative of a predetermined tension and speed respectively;

(e) current and voltage feedback lines connecting said unwind motor to said regulator whereby said regulator operates in response to said reference current and voltage signals and said current and voltage signals received from said unwind motor to change the braking force applied to said supply roll so as to maintain the tension and linear speed of the web between said supply roll and web processing means at a predetermined value uneffected by the decrease in size of the supply roll as the web is unwound therefrom;

(f) separate tension sensing means selectively operable during normal feeding of the web for directly sens ing changes from said predetermined value in the tension of said web between said supply roll and web processing means, and

(g) means for sending electrical signals to said regulator directly proportional to the sensed changes in tension for overriding said current and voltage signals received from said unwind motor to increase the braking force applied to said supply roll when a decrease in the tension of the web is sensed and to decrease the braking force when an increase in the tension is sensed whereby the tension in said web is returned to said predetermined value.

5. A tension override control system according to claim 4 wherein said tension sensing means is positioned in engagement with said web between said supply roll and said web processing means.

6. A tension override control system according to claim 4 wherein said tension sensing means comprises:

(a) a tension sensing roller positioned between said supply roll and said web processing means;

(b) pivoted lever means supporting said roller adjacent one end thereof, and

(0) means for urging said roller into contact with said Web.

7. A tension override control system as set forth in claim 6 wherein said means for sending electrical signals to said regulator proportional to changes in Web tension sensed by said roller comprises:

(a) a stationary selsyn motor having its shaft connected to the other end of said lever means at its pivot point so as to be rotated thereby upon movement of said roller, and

(b) electrical circuitry connecting said selsyn motor to said regulator.

8. A tension override control system for a web processing apparatus having a frame, a web supply roll, means for rotatably supporting said supply roll on said frame and web processing means spaced from said supply roll for 3? exerting a substantially constant pulling force on said web to unwind it from said supply roll comprising:

(a) an unwind motor connected to said supply roll so as to be driven thereby at an increasing speed and so as to-apply an increasing braking force on said supply roll as the diameter of the roll is decreased;

, (b) an unwindgenerator having its output connected to said unwind motor;

(c) a regulator for controlling the field of said unwind generator; i

(e) current and voltage feedback lines connecting said unwind motor to said regulator whereby said regulator operates in response to saidreference current and voltage signals and said current and voltage signals received fromsaid unwind motor to change the braking force applied to said supply roll so as to maintain the tension and linear speed of the web between said supply roll and web processing means at a predetermined value substantially independent of the decrease in size of the supply roll as the web is unwound therefrom (f) tensionsensing means for directly sensing changes in the tension of said web between said supply roll and web processing means; said tension sensing means comprising: i

(1) a first roller rotatably mounted on said frame and engaging. one side of said web between said supply roll and said web processing means;

(2) a first lever pivotally connected at one end to said frame between said supply roll and first roller and normally extending in a direction away from. the web running to said first roller; a second lever pivotally mounted at one end between said'first roller and said web processing means and normally extending in a direction substantially parallel to said first lever and toward the web running to said web processing means;

(4) a bracket positioned between said first and second levers and pivotally secured thereto adjacent their other ends; a

(5) a second roller rotatably mounted on said bracket and engaging the opposite side of said web;

(6) two extension members fixed to saidbracket and normally extending in a direction substantially parallel to said levers on diametrically opposite sides of said second roller;

(7) spring means engaging said second lever and each of said extension members tending to rotate said bracket about its pivots; and

(g) means for sending electrical signals to said regulator directly proportional to the sensed changes in tension for overriding said current and voltage signals received from said unwind motor to increase the braking force applied to said supply roll when a decrease in the tension of the web is sensed and to decrease the braking force when anincrease in the tension is sensed whereby the tension in said web is returned to said predetermined value.

9. A tension override control system according to claim 8 wherein said spring means comprises air springs, means for supplying air to said springs and valve means for controlling the air pressure in one of said springs in accordance with said current reference signal.

10. A tension override control means according to claim 8 wherein said means for sending electrical signals to said regulator proportional to changes in web tension sensed by said second roller comprises: a (a) a stationary selsyn motor having an extending shaf to which said second lever is fixed at its pivot point,

and

(b) electrical circuitry connecting said selsyn motor to said regulator.

References Cited by'the Examiner ORIS L. RADER, Primary Eaminer. MERVIN STEIN, Examiner.

N. L. MINTZ, T. LYNCH, Assistant Examiner.

Claims

1. A TENSION OVERRIDE CONTROL SYSTEM FOR A WEB CALENDERING APPARATUS HAVING A FRAME, A WEB SUPPLY ROLL, A DRIVEN SHAFT ON WHICH SAID SUPPLY ROLL IS WOUND, AN UNWIND MOTOR FOR DRIVING SAID SHAFT, AND CALENDERING ROLLS SPACED FROM SAID SUPPLY ROLL FOR EXERTING A SUBSTANTIALLY CONSTANT PULLING FORCE ON SAID WEB COMPRISING: (A) MEANS FOR IMPARTING A PREDETERMINED LINEAR SPEED TO SAID WEB INDEPENDENT OF THE CHANGE IN SIZE OF SAID SUPPLY ROLL AS THE WEB IS UNWOUND THEREFROM; (B) MEANS FOR IMPARTING A PREDETERMINED TENSION TO THE WEB BETWEEN SAID SUPPLY ROLL AND CALENDERING ROLLS WHICH IS INDEPENDENT OF THE CHANGE IN SIZE OF THE SUPPLY ROLL AS THE WEB IS UNWOUND THEREFROM; (C) SEPARATE SENSING MEANS SELECTIVELY OPERABLE DURING