US2834556A - Tension control device - Google Patents

Description

2 Sheets-Sheet 1 Filed Feb. 16, 1954 May 13, 1-958 A. L. KRAFT 2,834,556

TENSION CONTROL DEVICE l Filed Feb. 16, 1954 2 Sheets-Sheet 2 INVENTOR ATTORN TENSION CONTROL DEVICE August Lucas Kraft, Roselle Parli, N. J. Application February 16, 1954, Serial No. 410,522 7 Claims. (Cl. 242-45) This invention relates to apparatus for lcontrolling the tension applied to a length of material being operated upon. The invention is disclosed herein as applied to control the tension of the wire in a wire drawing machine. Although it is very well suited for this particular application, the invention is by no means limited thereto, but is well adapted for use in controlling the tension applied to almost any conceivable type of material during processing thereof.

In wire drawing, the problem of maintaining the proper tension on the wire is one of the most troublesome problems which confronts the manufacturer. The problem is a particularly serious one where wire of extremely tine gauge is being drawn. If the tension becomes slightly excessive, the wire is broken. When breakage occurs, unless the wire drawing machine is stopped immediately, the wire may be spooled around one of the rotating carriers of the drawing machine; This not only results in wastage of the wire which is spooled but also necessitates a tedious job of clearing the machine. In any instance, the breakage results in a costly shutdown of the machine.

On the other hand, if the tension becomes too low, there is slippage between the wire and the rotating drum carriers or blocks about which the wire is Wound and which pull the wire through the drawing dies. This slippage results in chattering of the wire, or reduction of its thickness at intervals along its length. Where the wire is used to carry current in an electrical circuit, these points of reduced thickness tend to become hot spots which adversely effect the operation of the electrical component in which the wire is used and may result in premature breakdown of the components. The slippage of the wire on the carriers also greatly increases the wear of the carriers. Even where the carriers are provided with peripheral rings of a very hard material, such as tungsten carbide, the wear may be so great as to necessitate replacement of these rings every few weeks during regular operation of the machine. The replacement of the carrier rings not only puts the drawing machine out of operation for appreciable periods, but also entails considerable expense for the rings themselves.

The present invention makes it possible to control the tension of the wire in the wire drawing machines with such accuracy that slippage is reduced to an almost negligible degree and breakage of the wire is substantially eliminated. The invention also makes possible the drawing of extremely fine gauge wires (as ne as .002 in diameter and even ner) at linear speeds up to several thousand feet per minute. These results have been achieved even with relatively hard and brittle wire such as resistance wire containing nickel and chromium. Machine production has thus been considerably increased, while the cost of machine maintenance has been greatly reduced.

The present invention accomplishes these `desirable oband is positioned in accordance with the degree of tension on the wire, and an associated switch arm which is connected to the dancer by yieldable means, such as a tension spring, so that it tends to move in the direction of displacement of the dancer arm from a predetermined neutral position. However, the switch arm is restricted in its movement by a pair of stops, one of which serves as a lixed switch contactr in cooperation with the switch arm. This single-pole switching means is used to control a clutch which is interposed between the take-up spool and its driving motor. This arrangement assures that the switch arm is always very near its cooperating switch Contact, so that the switch means is extremely sensitive to changes in tension.

The apparatus disclosed in the present application also includes a frictional connection between the dancer arm and the switch arm so that movement of the dancer arm urges the switch arm to move in the same direction. At least when the dancer arm is near the aforementioned neutral position at which the spring is under a very light tension, this frictional force is strong enough to overcome the spring tension, so that the instant the arm starts to move in one direction or the other, the switch contacts are actuated and the clutch is operated so as to counteract the change in tension which is reflected by the movement of the dancer. The eiect of this arrangejectives by providing a dancer which engages the wire ment is to produce an extremely sensitive and smoothly proportioning control which causes the dancer quickly to seek its neutral position (corresponding to the ydesired tension on the wire) and quickly to be returned to this position if for any reason the tension changes. This is done smoothly and with a minimum of overshoot and hunting.

In the drawings:

Figure l is a somewhat diagrammatic side elevational view of a tension control apparatus embodying features of the present invention installed on top of a standard multiple die, continuous wire drawing machine.

Figure 2 is an end elevational view of a portion of the machine showing the driving connections between the take-up spool shaft and its driving motor with certain elements being omitted for purposes of clarity.

Figure 3 is an enlarged isometric view of the switching elements associated with the dancer shaft with certain elements being omitted for purposes of clarity.

Figure 4 is a schematic diagram of the electrical control circuit. v

Figure l shows the top portion of the drawing machine, which is generally indicated M, with the principal elements of the present invention secured on the top thereof. As indicated by the arrows in this figure, the strand of wire W is drawn from the nal drawing die D around a rotating drum carrier 10 for one turn, then around an idler pulley 12, back to the carrier 10 and around it for another turn, then around another idler pulley 14, and back to the carrier 10 for a third and final turn around it. The carrier 10 and idler pulleys 12 and 14 are rotatably supported in a frame F secured to the top of the wire drawing machine M. v

After its nal turn around the carrier lltl, the wire W passes upwardly and to the left, as viewed in Figure l, to one of three 'sheaves 16 rotatably mounted on a hori Zontal spindle 18 at the upper end of a dancer arm 20 which is fixed on and extends radially upward from a shaft 22 which is rotatably supported in a bearing 24 secured to the top of the machine. To the right of the three sheaves 16, as viewed in the drawing,` two other sheaves 26 are rotably mounted on a spindle 28 which extends horizontally from the upper end of the frame F. The wire W is wound once around each of the sheaves 16 and 26, as in a conventional block and tackle, and

finally extends from the third sheave 16 downwardly and to the right, as viewed in the figure, Where it passes through a felt retarding pad 30 supported in aforked bracket Y3,2 which extends upwardly from -an arm 34, over Va pulley 36 which is rotably secured at the upper end of the arm 34, and thence around the take-up spool S which is xed on a shaft 68.

The spool shaft 68 and spool S are driven by the mechanism shown in Figure 2. As may be seen in this figure, there is provided an electric motor 50 having xed on its shaft a pulley 52 which drives a V-belt 54 which is also trained about a pulley 56 mounted for free rotation on a counter shaft 58. Also mounted on the counter shaft 58 and keyed thereto is a magnetic clutch 60. The pulley ,56 and clutch 60 are respectively provided with cooperating clutch plates 56a and 60a which are spaced apart slightly in the de-energized position of the clutch 60, but which are brought into engagement when the clutch is energized to canse the pulley 56 to drive the clutch 60 and with it the shaft Sti on which it is keyed.

Also 'keyed on the counter shaft 58 is another pulley 62 about which is trained a V-belt 64 which is also trained about a pulley 66 fixed on the spool shaft 63. It will thus be seen that when the clutch 60 is engaged, the spool shaft 68 and the spool S (Figure l) are driven to cause the wire W to be wound on the spool. As the wire is wound on the spool, the arm 34 is reciprocated longitudinally of the spool to wind the wire in even layers thereon.

Referringy again to Figure l, the dancer 20 is urged in a counterclockwise direction by means of a coil spring 33 which is tensioned between a tab portion 20a extending radially from the hub at the lower end of the dancer arm, and a bracket 40a formed at the upper end of a casting 40 which is secured at one end of the dancer shaft bearing 24. A set screw 42 and lock nut 44 are employed to adjust the tension on this spring 3S.

As will be understood, an increase in the tension of the wire W tends to shorten the length of wire between the two sets of sheaves 16 and 26 and pull the dancer 20 in a clockwise direction against the resistance of the tension spring 38, while a decrease in the tension of the wire allows the tensioning spring 38 to pull the dancer 20 in the opposite direction. A counterweight 37 secured to the lower end of the dancer below the shaft 22 serves to balance the weight of the dancer arm and sheaves 16 so that the only rotational forces imposed upon the dancer in any position are those imposed by the sprin" 38 and by the wire W. integrally formed on either side of the casting 40 are a pair of stops 40!) and 40e which limit the movement of the dancer.

[is may be seen in Figure 3, the dancer shaft 22 extends rearwardly and rotatably supports a hub 70 which is provided with a radially and upwardly extending switch arm 72. Fixed on the shaft 22 adjacent the rotatable hub 70 is a block 74 which is adjustably secured on the shaft by means of a set screw 76. The switch arm 72 is yieldably interconnected with the fixed block 74 by means of a coil spring 78 which is tensioned between a screw 80 threaded into the block 74 and a screw 82 which is threaded into a block S4 adjustably positioned on the switch arm 72 by means of a set screw 86. Compressed between the xed block 74 and the rotatable hub '70 is a felt friction washer 88. A second friction washer 83 is sandwiched between the opposite side of the rotatable hub 70 and a disc 90 which is urged in the direction of the hub 70 by means of a coil spring 92, which encircles the shaft 22 and is compressed between the disc 90 and a block 94 adiustably positioned on the shaft 22 by means of a set screw 96. The resulting frictional interengagement between the rotatable hub 70 on the one hand and the ixed blocks 74 and 94 on the other, urges the switch arm 72 to partake of the rotational movements of the dancer 20.

At the upper end of the switch arm 72 a switch block 98 is adjustably secured by means of a set screw 100. 'At the left-hand side of the switch block 98, as viewed in Figure 3, is secured a switch contact 102, and a cooperating xed switch contact 104 is adjustably supported by lock nuts 10S in one side of a U-shaped block 106 of suitable insulating material such as a laminated phenolic. At the other side of the switch block 98 is a projecting screw head 10S which is adapted to cooperate with a stop screw adjustably positioned in the opposite end of the block 106 by means of lock nuts 112.

The stop 110 and fixed contact 104 are normally adjusted so that the maximum spacing between the contacts 102 and 104 (or between screw head 10S and stop 110, depending on the position of the switch arm 72) is quite smail, for example of the order of .001" although for purposes of clarity in the drawings this spacing is shown considerably greater. A conductor 114 connected to contact 104 through block 106 provides a connection to the external circuit, to be described hereinafter, for contact 104. A conductor 116 secured to shaft 22 by a screw 118 and connected to contact 102 through arm 72, hub 70, and shaft 22 provides a connection to the external circuit for contact 102.

In order to facilitate understanding of the mechanism v'shown in Figure 3, let it be assumed that the tension on the wire is momentarily less than that necessary to keep the dancer 20 in the vertical position indicated by the broken line N against the resistance of the spring 38, so that the dancer is displaced in a counterclockwise direction, as viewed in Figure 3, to a position such as that shown in broken lines at L. When the dancer is in this position, the dancer shaft 22 and the fixed block 74 are likewise in a counterclockwise position, as shown in broken lines, and through the spring 78, a force is imposed on the yswitch arm 72 which causes it to move in a counterclockwise direction to close the switch contacts 102 and 104. Through a circuit to be described hereinafter, the closure of these switch contacts results in energizing the magnetic clutch 60 (Figure 2) and causing the spool S (Figure l) to be connected to the motor 50 (Figure 2) and continuously driven thereby.

The normal operating speed of the motor 50 and the driving ratio between it and the spool shaft 68 are such that when the driving connection between the motor and the spool shaft is completed, the spool S is driven at such speed that it will tend to draw wire from the drawing machine at a speed slightly in excess of the speed at which the carriers of the drawing machine tend to feed the wire. This results in imposing a steadily increasing tension on the wire W as long as the spool is driven by the motor, and causes the dancer 20 to move in a clockwise direction as viewed in 'Figure 3. This movement of the dancer rotates the shaft 22 and xed blocks 74 and 94 and, be cause of the frictional engagement between these fixed blocks and the rotatable hub 70, the movement of the dancer 20 also tends to move the switch arm 72 in the same direction.

If the movement of the dancer 20 is relatively slow, or if the spring 78 is under considerable tension, as it will be when there is considerable relative angular displacement between the xed block 74 and the switch arm 72, the frictional force imposed on the hub 70 and the switch arm 72 may not be suiiicient to overcome the force of the spring, Vso that the contacts 102 and 104 will remain engaged and the acceleration of the spool S and the resulting movement-of the dancer will continue. However, as the dancer 20 approaches the neutral position indicated by the broken line N, with resulting reduction in the tension on the spring 78, the frictional force irnposed by the movement of the dancer 20 on the movable hub 70 and switch arm 72 will be suicient to overcome the resistance of the spring 78 and cause the switch arm to move lin the direction of movement of the dancer. When this occurs, the switch contacts 102 and 104 will be broken to disengage the magnetic clutch 60 (Figure 2) and disconnect the spool shaft 68 from the motor 50. However, because of the inertia of the rotating mechanism associated with the spool S and spool shaft 68, the speed of rotation of the spool will fall off gradually.

As the speed of rotation of the spool S decays, the tension imposed on the wire also drops, and the speed of clockwise movement of the dancer 20 is decreased. If the dancer 20 is still at a position of substantial counterclockwise displacement from the neutral position N, the force of the spring 78 will soon overcome the frictional eiect of the moving dancer on the rotatable hub 70 and switch arm 72, and again move the switch arm 72 in a counter-clockwise direction and close the contacts 102 and 104.

Closure of the switch contacts results in engagement of the clutch 60 and acceleration of the spool shaft 68. As the spool S again picks up speed, increasing the tension on the wire and causing the dancer to move in a clockwise direction, the friction force imposed on the hub 70 may again become sutiicient to overcome the force of the spring 78 and move the switch arm '72 to open the contacts 102 and 104. Because the dancer is now at a position of lesser displacement from the neutral position N and the degree of elongation of the spring 78 is less than originally, it will take less time -for the frictional force to reach a value above that of the spring force so that the on time of the switch will be less than before. Likewise, the speed of clockwise movement of the dancer will have to fall to a lower level than that previously referred to before the frictional force imposed on the switch arm 72 falls below the level of the force imposed on the switch arm 72 by the spring 78 so that the switch may close again.

It will thus be seen that as the dancer approaches the neutral position the on time of the switch is decreased and the off time is increased. As a result, the rate of movement of the dancer is gradually slowed as the dancer approaches the neutral position so that it reaches the neutral position with little if any tendency to overshoot, which would result in hunting of the control mechanism.

When the dancer finally reaches and starts to pass the neutral position, the switchy contacts 102 and 104 are broken and the magnetic clutch 60 (Figure 2) is disengaged. As the speed of the spool S decays and the tension on the wire gradually decreases, the dancer will move in a counter-clockwise direction and this motion will be imparted through, the friction washers 88 to the switch arm 72, so that the switch arm 72 will partake of the counter-clockwise movement and the contacts 102 and 104 will again be closed. This will result in re-eugagement of the clutch and cause the spool S to be accelerated and the tension on the wire again to be increased until the dancer again reaches the neutral position and the contacts 102 and 104 are broken.

This cycle of alternate opening and closing of the contacts 102 and 104 is normally repeated at a relatively rapid rate and the dancer 20 will not move more than a few degrees in either direction from the neutral position,

except under extraordinary conditions. The fact that the dancer remains near the neutral position means, of course, that the tension on the wire is being maintained substantially constant. Since the switch contact 102 and 104 are being opened and closed at a relatively rapid rate, the solenoid clutch 60 is being engaged and disengaged at a similar rate so that the Yspool S is in effect receiving a rapid series of pulses of driving power, with the inertia of the spool S and its associated rotating mechanism damping out these pulses and causing the spool to rotate at substantially uniform speed. If the dancer is displaced from the neutral position in the direction of diminishing tension, the pulses of driving power become proportionately longer until, at relatively great displacement angles, the spool S is driven continuously. The opposite effect increase still further and the rate of such increase.

nism acts in such a way as to correct the tension in the direction of the desired Value. The corrective force is proportional to the angle of the displacement and is also dependent upon whether the displacement i-s tending to The correction is thus a rapid and forceful one when needed, but is always precisely controlled to prevent overcorrection and hunting.

With the dancer 20 inthe vicinity of the neutral position N the tension on the wire is proportional to the tension of the spring 38 (Figures 1 and 3). The adjustment of the spring 38 thus serves to control the tension on the wire W. p

Figure 4 shows the electrical circuit for control of the magnetic clutch 60. As may be seen in this ligure, the clutch 60 is connected through a start-stop switch to one terminal of the secondary winding of a power transformer 122. The primary of the transformer 122 is connected to a suitable Source of alternating current voltage while the secondary is providedwith a series of taps which are connected to the xed contacts of a multiposition switch 124. The movable contact of the switch 124 is connected to the cathode of a thyratron tube 126,

ythe plate of which is connected to the other terminal of the solenoid clutch 60. An alternating current voltage of controllable amplitude is thus applied to the clutch 60 in series with the thyratron 126. f

The transformer 122 `also has a filament winding 122a across which the filament of the thyratron tube 126 is connected, as indicated by the symbols X-X. The voltage developed across the filament winding 12211 of the transformer 122 is also applied across a selenium rectifier 12S and a filter condenser 130 in series, so that a direct current voltage is developed across the condenser 130. The positive terminal of the condenser 130 is connected to the cathode of the thyratron 126 while the negative terminal is connected through a pair of series resistances 132 and 134- of relatively high value to the control grid of the thyratron 126. There is thus applied between the control grid and cathode of the thyratron 126 a voltage of such polarity and of sufficient amplitude to bias the tube normally to cutoff. With the thyratron non-conductive, no current may ow from the transformer 122 through the solenoid clutch 60 and the clutch is disengaged. n

As indicated in broken lines at the right-hand side of Figure 4, the switch contacts 102 and 104 are connected into the circuit so that their closure connects the grid of thyratron 126 to the cathode through the resistance 134, while the resistance 132 is bridged across the filter condenser 130. Under this condition, the resistor 132 acts as a bleeder for the bias voltage supply, while the control grid and cathode of the thyratron 126 are placed at substantially the same potential. This removal of biasing voltage from the thyratron 126 causes it to conduct strongly and allow current to ow from the transformer 122 through the solenoid clutch 60, engaging v the clutch and causing the motor S0 (Figure 2) to drive the spool shaft 68 and spool S (Figure 1). The clutch 60 is thus engaged whenever the contacts 102 and 104 are closed and disengaged vwhenever these contacts are open.

Since the thyratron 126 conducts current in only one direction, a pulsating direct current flows through the winding of the solenoid clutch 60. A selenium rectitier 136 is connected in parallel with the winding of the clutch to shunt out the negative voltage peaks which might otherwise appear across the winding, due to its inductance, when the ow of current through the solenoid is stopped by opening of the switch contacts 102 and 104 and extinguishing of the thyratron 126.

As will be understood, the selector switch v124 serves to apply to the solenoid clutch 60 a variable voltage. If the voltage applied to the clutch Vis of high value, the solenoid will be strongly energized and the clutch plates 56a and 60a (Figure 2) will be engaged strongly so that there is relatively little slippage in the clutch and the spool S is driven at a speed equal to or only slightly less than the maximum speed at which it could be driven, assuming a connection between the motor 50 and spool S which was entirely devoid of slippage. If the selector switch 124 (Figure 4) is set so that a lower voltage is applied to the clutch 60, the clutch plates 56a and 60a (Figure 2) are engaged less strongly, and some slippage takes place between them so that the spool is driven at a lesser speed. The setting of .the selector switch 124 thus determines the rate of acceleration ot the spool S and therefore the speed of response of the control system.

The selector switch 124 is normally set so that the clutch 60 is engaged and disengaged at amaximum rate. Under this condition, the dancer is :tremulously poised l at the neutral position. Because the gas inthe thyratron changes color when the thyratron tires, the selector switch may be properly set by watching the thyratron and adjusting for the maximum firing rate.

As may be seen at the left of Figure 1, the cabinet 138 containing the electrical circuit component shown in Figure 4 is mounted on a board 140 which is secured to and projects from the top of thewire drawing machine. A magnifying lens 138:1 is provided in an opening in the front of this cabinet 138 so that the operator may conveniently observe the interior of the thyratron 126. f

The switch arm 72 and the various mechanisms associated therewith, which appear in Figure 3, are enclosed in a cabinet 142 (Figure l) which is secured to the top of the wire drawing machine adjacent the opposite end of the bearing 24 from that on which the dancer 20 and its associated parts are mounted.

From the foregoing description, it will be appreciated that the mechanism provided is relatively simple and yet functions in such a way as to cause a substantially uniform tension to be maintained on the wire, thereby minimizing the possibility of breakage and substantially eliminating chattering of the wire and greatly reducing wear on the carrier rings of the drawing machine. It will thus be appreciated that the aforementioned and other desirable objects has been achieved. However, it should be emphasized that the ,particular mechanism which is shown and described herein is merely illustrative of the invention and is not intended to restrict its scope, which is delined in the appended claims.

I claim:

l. A tension control device for regulating the tension applied to a length of material including in combination a drive means, a sensing element in engagement with said length of material, means for mounting said sensing element for movement in response to changes in tension on said length of material, a control adapted when actuated to activate said drive means, a control actuating member, and frictional means interconnecting said sensing element and said control actuating member, said frictional means normally providing a driving connection between said sensing element and said control actuating member while permitting relative movement between said element and said member in response to a predetermined force tending to move said element and said member with respect to each other.

2. A tension control device as in claim 1 including a resilient connection between said sensing element and said control actuating member, the arrangement being such that said resilient connection tends to retain said control actuating member in theposition to which it has been moved Aupon the initiation of a control operation.

3. A tension control device .for :regulating the tension applied to a length l`of material including in combination a drive means, a sensing element in engagement -with the length of material, said sensing element -being adapted to occupy a neutral position corresponding to a predetermined tension, means pivotally mounting said sensing element for Vmovement toward and away from said neutral position, a switch adapted when actuated to activate said drive means, a switch actuating .member rotatablyv carried by said sensing element mounting means, friction means normally connecting said switch actuating member with said sensing element mounting means for rotation therewith, and means for .rendering said friction means ineffective after `a control .operation vhas been initiated when said sensing elementis displaced .a predetermineddistance from said neutral position.

4. A tension -control vdevice as in claim 3 in which said switch actuating member .is .an arm adapted to occupy a neutral position corresponding to said sensing element 4neutral position, said switch comprising a rst contact'and a-second contact, sadfirst contact being carried by said arm, stationary means mounting said second contact onone side of said neutral position, .and a stop carried by said stationarymeans on the other side of said neutral position, said second contact and said Vstop being arranged to arrest .the movement of `said arm in response to movement of said sensing element.

5. A tension control device asin claim 3 in which said means for rendering said friction means ineective includes aspring and means for connecting said spring between said sensing element and said switch actuating l member.

6. A tension controldevice as in claim 3 in which said drive means includes .a motor having an output shaft, means for applyingtension to said length, and an electrically operated clutch for engaging said motor shaft with said tension applying means, Ysaid switch being arranged when actuated to energize 4said clutch to engage said motor shaft with said tension applying means.

7. A tension control device 'asin claim 3 in which said drive means includes a motor having an output shaft, means for applying tension to said length of material, -a normally disengaged clutch for connecting said motor shaft to said tension applying'means, a solenoid adapted when energized to engage said clutch, a source of :electrical energy, a Vgas-filled tube including a control element, means connecting said tube in serieswith said solenoid across said source of energy, means for Iapplying a erasing potential to said control element normally to prevent said tube from tiring, and means connecting said switch to said control element to remove said biasing potential to permit said tube to .conduct when said switch is actuated.

References Cited in the lile of this patent UNITED STATES PATENTS 1,919,607 Thompson July/.25, 1933 2,214,355 Tiselius et al. Sept. 10, 1940 2,317,290 Mcllvried Apr. 20, 1943 2,345,765 Michel Apr. 4, 1944 2,544,467 Michel Mar. 6, 1951 2,590,604 Giuffrida Mar. 25, 1952 2,597,133 Snyder May 20, 1952 2,598,950 Walker June 3, 1952 2,662,264 Campbell Dec. 15, 1953 FOREIGN PATENTS 509,544 Great lBritain July 18, 1939

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