US2983464A - Tensioning device for printing presses - Google Patents

Description

May 9, 1961 c. E. FULLER TENSIONING DEVICE FOR PRINTING PRESSES Filed March 27, 1959 POLARIZED RELAY PHASE POLARIZED DEMODULATOR A:

COMPUTER INVENTOR. CHARLES E. F LLEQ ATTORNEYS United States. PatentD Patented May 9,1961;

This invention relates generally to tension control of an elastic or semi-elastic strip being drawn oif a roll and into a printing machine to be printed, and more particular-- ly concerns apparatus for finely or closely controlling the strip tension so that printed impressions will be'very accurately located on the strip.

Among the problems solved by the use of the present control apparatus is the commonly experienced lack of sufiicient accuracy in locating printed impressions on paper or plastic such as cellophane strip material being supplied to a rotary press ofi a supply roll. For example,

if the tension of the feed strip is not held very nearly constant, it is not possible to superimpose on the strip different colored impressions with sufiicient accuracy, as by means of a rotary press, to prevent ready discernment of errors in color superposition along portions of the strip supplied off the roll. At the present time, it is the practice in the rotary press printing art to manually control or adjust the tension in the feed strip being rapidly unrolled and fed to the rotary press, as by watching an idler roller engaging the strip and adjusting a braking device acting on the supply roll when the idler.

roll deflects. Such idler rollers commonly undergo deflections as much as four inches, showing that the brake operator cannot manually very closely control the strip tension. Particularly is this true when the roll is nearing the end of unwinding, inasmuch as its angular velocity is then approaching a maximum as its mass approaches a minimum, making close control of braking extremely diflicult. As a result, gross errors in registry of successively superimposed printing impressions, particularly in difierent colors, clearly appear, and it is not uncommon to reject upwards of of the total printed strip or paper as being so badly out of multicolored print registry as to be unusable. Also, discrepancies in winding of the strip on the roll cause looseness contributing to undesired tension of the feed strip and lack of correct multicolor registry.

Accordingly, it is a major object of the present invention to overcome the discussed problem of obtaining satisfactory registration of multicolored print, through the use of the novel control apparatus to be described in detail. As broadly conceived, that apparatus is operable to finely control feed strip tension and comprises follower means engageable with the feed strip to be moved in response to small changes in strip tension, control means operable to produce a magnetic field for. producing force actuable to brake rotation of the supply roll and thereby to resist drawing of the strip oil the roll, together with electrical circuit means cooperative with the follower and control means to vary the magnetic field in response to movement of the follower means. As a result braking of the feed roll is respectively'increased and decreased in response to slight decreases and increases of strip tension relative to a predetermined value of such tension. In fact, as slight a deflection of the follower means as of an inch is sufiicient to alter almost instantaneously the magnetic field produced by the control means so as to effect achange in the braking force acting on the feed roll to restore the desired strip tension.

While the invention contemplates various ways in which braking force can be applied or transmitted to the feed roll in response to changes in the magnetic field produced 'by the control means, it is directed particularly to the use of a rotary type electrical machine such as a bi-directional motor, for producing the magnetic field from which torque is transferrable to brake the feed roll. Also, the invention is characterized in that the electrical circuit operable to vary the magnetic field produced bythe electricalmachine includes an electrical balance type bridge, the output of which is adapted to change in response to slight oppositely directed movements of the follower means.

Other objects and advantages of the invention include the use of means for converting the bridge output into either phase or polarity polarized control signals which are operable through a relay to control directional magnetization of the electrical machine or bi-directional motor, so as to drive a rotary part of the motor in opposite directions. Such opposite directional drive is then transmissible to a braking nut on the screw of a roll brakinvention, aswell as the details of an illustrative embodiment, will be more fully understood from the following detailed description of the drawings, in which:

Fig. l is a schematic showing of the control apparatus .as applied to a printing press;

Fig. 2 illustrates the apparatus for sensing changes in strip tension; and

Fig. 3 shows the releasable drive connection between the bi-directional motor and braking nut operable to control braking of the feed roll.

In Fig. 1 the elements of a printing press that are shown include the supply roll 10 oil which a strip 11 of paper or the like is drawn under a guide roller 12, and between pinch rollers 13 for subsequent travel through multi-color printing rollers not shown.

Conventionally incorporated with the feed roll is a braking device 14 shown in outline in Fig. 3, and which acts to variably brake the rollin accordance with the position of a braking nut 15 on a screw 16 so that the paper or strip 11 remains under tension as it is drawn through the press. Turning of the control nut 15 in a clockwise direction effects increased braking of the feed roll while turning of the nut in a counter-clockwise direction as viewed from the projecting end of the screw 16' decreases the braking effect. In accordance with the invention, increased braking.

effort causes the tension in the feed strip 11 to increase, such tension change being sensed by a follower roller 17 seen in Figs. 1 and 2 and in engagement with the side of the strip. The roller is mounted on an axle 18 carried by a body 19 which is spring loaded in opposite directions by the compression springs 20. The spring loading is adjustable to correspond to any desired tension in the feed strip 11, and accordingly should the tension increase above this level, the roller 17 will be deflected downwardly; whereas should the tension decrease below the desired level the follower roller 17 will rise against the strip 11 in a direction normal to the strip travel.

arm or lever 21 which is attached to the body by means Upand down movement of the body 19 is transmitted toan.

of a pin 22 projecting through a slot 23' in' the arm, the

pinbeing carried by the body. The lever is fulcrumed by a pin 24 carrying a wiper arm shown schematically at 25 in Fig. l, the wiper being pivoted about the axis of pin 24 as. the body 19 moves up and down. The wiper arm 25 is apart of the potentiometer generally shown at. 26 in Fig. 2. as. being circular in form and being mounted or fixed on. structure 27 relative to which the body 19 moves up anddown.

The resistance slide wire 28 of the potentiometer 26 has its end terminals connected with the end terminals of a coil 29 which forms the secondary of an iron core transformer 30, the primary winding of which is indicated at 31. Thus, the resistance 28 and secondary coil 29 are connected in parallel to form a bridge circuit characterized in that the center tap 32 of the coil 29 is grounded.

' The. voltage output of the bridge circuit is fed through the wiper arm 25 of the potentiometer 26 and drops through a resistor 33 grounded at 34, the resistor being adjustably tapped at 35 so as to vary the output fed to the amplifier 36. effects control of the tension of the strip 11 in a very simple manner.

The amplified output of the bridge circuit is then fed at 37 to a demodulator and computer indicated generally at. 38 operable to convert the bridge output into polarized control signals corresponding to slight deflections of strip tension greater and lesser than desired tension. A reference signal is also fed through leads 39 to the demodulator and computer 38, the reference signal having been obtained from the secondary winding 40 which is center tapped and grounded as indicated at 41.

The demodulator and computer is shown in block form since various known circuits can be used for demodulating the bridge output through the use of a reference signal as indicated and polarizing the output to produce polarized control signals fed at 42 to a polarized control relay 43 also indicated schematically. The control signals fed to the relay in turn govern relay operation to control power input fed at 44 to a bi-directional control motor 45, the

power input to the relay being shown at 146. The direction of rotation of the motor and its reaction speed are determined or controlled, for A.C. applications, by the phase polarity and amplitude of the control signal, whereas for D0. applications the direction and reaction speed of the motor are controlled by the positive and negative polarity and amplitude of the control signals.

It is emphasized that through the provision of the amplifier 36 very small. changes in strip tension giving rise to small bridge outputs are sensed and immediately converted to control signals operable to control the direction of rotation and torque of the motor 45 throughthe control of the magnetic field produced in the motor as a result of' relay operation. Changes in torque or force is then transferable to brake the supply roll and thereby increase or decrease resistance to drawing of the feed strip off the roll, all for the purpose of restoring the desired tension in strip 11. As an illustration of the control of the magnetic field produced in the motor, the power input to one or more of the windings of the motor may be controlled by the relay 43 so as to effect the desired direction of motor rotation and the torque produced to accomplish the desired braking effect.

- Turning again to Fig. 3, the motor 45 has an output shaft 46 which is slotted at 47 in an axial direction, and to a depth considerably less than the diameter of the shaft. Projecting into the slot 47 is the terminal end of a set screw 43 received in a flange 49 mounted on the shaft 46 to slide axially thereon. The set screw 48 is tightenable by a knurled nut 50 so as to locate or fix the flange 49 on the shaft 46 in any desired axial position thereon.

Attached to the flange 4? are two or more studs 51 extending in parallel relation with'respect to the axis of the shaft 46, the ends of the studs 51 being slidably received As will appear, adjustment of the tap 35- essence within corresponding openings 52 such as are formed by bronze sleeves 53 affixed within the braking nut 15. Thus, as the flange 49 is turned by the shaft 46 in a direction so as to tighten the braking nut 15 to increase the braking effect transmitted by the braking device 14 to the supply roll 10, the nut 15 will move axially relatively away from the studs 51. The terminal ends 55 of the studs are so positioned within the nut 15 that the studs 51 completely disengage the nut in the event that the nut is tightened to increase the braking exertion on the roll to such an extent that further tightening of the nut 15 would overload the motor 45. The motor rotor and stator parts by means of which the magnetic field is. produced, are shown at 60 and 61.

The drawings are to be regarded merely as illustrative of the invention, and it will be understood that various changes and additions may be made without departure from the invention in its intended spirit and scope.

I claim:

1. For combination with a printing machine operable to draw a printable strip of material off a supply roll to be printed in the machine, and follower means engageable with a side of the feed strip to be moved thereby in opposite directions substantially normal to strip travel in response to small changes in strip tension, the improvement which comprises control means including a rotary type electrical machine for producing a magnetic field from which torque is transferrable to brake the supply roll and thereby to resist drawing of the strip oflf said roll, and an electrical circuit controllable. by said follower means and electrically connected with said electrical machine, said circuit being operable to vary said magnetic field in response to movement of said follower means, whereby braking of the supply roll. is respectively increased and decreased in response to small decreases and increases of strip tension relative to a predetermined value thereof, said circuit including an electrical balance type bridge the output of which is adapted to change in response to slight oppositely directed movements of said follower means, said circuit including computer means for converting said bridge output into polarized control signals corresponding to slight deviations in strip tension greater and lesser than desired tension, said signals being operable to control said magnetic field for increasing and decreasing said torque, and means for producing a reference signal to be compared in the computer means with said bridge output.

2. The invention as defined in claim 1 in which said circuit means includes an amplifier electrically connected between said bridge and computer for amplifying said bridge output to be converted in the computer.

3. T he invention as defined in claim 1 including means for transmitting braking torque operable to effect braking of said roll, and in which said electrical machine comprises a motor having a rotary part connected with said braking torque transmitting means and adapted to be driven in opposite rotary directions in response to production of said control signals.

4. The invention as defined in claim 3 in which said circuit includes a relay through which said control signals are operable to control power input to-said motor so as to drive said rotary part in opposite directions.

5. The invention as defined in claim 3 including a roll braking device having a screw, and in which said. means for transmitting braking torque includes a braking nut adapted to be driven by said motor on the screw of said roll braking device.

6. The invention as defined in claim 5 in which said means for transmitting braking torque includes a drive connection between the motor and nut, said connection being releasable to permit manual manipulation of the braking nut.

7. The invention as defined'in claim 6 in which the nut is movable on the screw relative to the drive connection and out of driven relation therewith as the nut operates 5 to increase braking of the feed roll, whereby overloading References Cited in the file of this patent of the motor is prevented.

8. The invention as defined in claim 1 in which said UNITED STATED PATENTS bridge includes a potentiometer and in which said fol- 1,103,153 Morse July 14, 1914 lower means is connectible to the movable part of said 5 1,286,331 James Dec. 3, 1918 potentiometer the movement of which affects the bridge 1,852,575 Howe Apr. 5, 1932 1 1,896,209 Vitale et a1 Feb. 7, 1933 output.

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