Patent Publication Number: US-3878672-A

Title: System for mounting a false twist unit

Description:
[ 1 Apr. 22, 1975 1 1 SYSTEM FOR MOUNTING A FALSE TWIST UNIT [75] Inventor: Gisert Kiihler, Oeffingen. Germany [73] Assignee: SKF Kugellageriabriken Gesellschaft. Schweinfurt, Germany [22] Filed: Oct. 3, l973 [21] App]. No.: 403,327  
 OTHER PUBLICATIONS Schafer &amp; C0., FAG Magnetic False Twist Spindles. Sept. 1967.  
 Primary Examiner-John W. Huckert Assistant Examiner-Charles Gorenstein Attorney, Agent, or Firm-Murray Schaffer [57] ABSTRACT In a false twist unit. a fixed bracket on which a supporting plate carrying the tube is pivotally mounted. The plate also carries drive whorls which are adapted to engage a tangential continuously moving belt. Spring means urging the plate about its pivot is also provided. The bracket is provided with a pair of spaced bearings and the plate is selectively mounted in one or the other of the bearings whereby in one of the bearing means the plate is fulcrumed to cause one of the whorls to engage one side of the belt and in the other of the bearing means the plate is fulcrumed to cause the other of the whorls to engage the other side of the belt thereby reversing direction of rotation of the tube.  
 l5 Claims, 7 Drawing Figures limit Eumzz 1% MT 1 PATENT PATENTEDAPRZZIEIYS SPCZI 5 HF 7 I SYSTEM FOR MOUNTING A FALSE TWIST UNIT BACKGROUND OF THE INVENTION The present invention relates to a false twisting unit for yarns and threads and in particular to a system for mounting such devices so as to enable either an S or Z thread twist to be obtained.  
  A well known false twist unit is described in Swiss Pat. No. 475.385. In this patent a bracket. fixed to the machine frame. is provided with a bearing block on which is detachably fastened a plate. The plate carries the driving and holding mechanism for the twist tube through which the yarn is drawn. A tension spring fixed at one end to the plate and at its other end to the machine frame forces a whorl. of the driving means. against a tangentially moving belt. A disengaging device is mounted on the bracket. which enables the plate to be pivoted about its fulcrum so as to move the whorl into and out of engagement with the driving belt. The bearing block is designed so that it may simultaneously receive a second plate extending in opposition to the first plate. Actually the bearing block may also be designed so that the same plate may be removed from its original position and placed in the second position. The bearing block is thus dimensioned and has its fulcrum arranged so that the second plate takes a position so that its drive whorl engages the other side of the tangential belt from that engaged by the first plate. In this manner there is produced in the drive whorl of the second plate. by the constantly unidirectional tangential belt an opposite direction of rotation in the twist tube and thus producing a thread twist opposite to that produced by the tube mounted on the first plate.  
  In general a machine is provided with several holding brackets arranged in bank. Thus when two plates are attached to the bearing block on each of the bracket their sides extend substantially at right angles to the bracket and parallel to the running direction of the tangential beltv In order to prevent the holding plates extending from adjacent brackets from overlapping each other. the holders must be arranged so far apart that there is sufficient distance for each of the plates to be mounted and for it to be pivoted without interfering with the neighboring plate. As a result the twisting machine is relatively large and there is an inordinate space provided between adjacent holding bracket. This space is particularly wasted when the machine is employed for the production of threads having the same twist, since there is no need for the second plate and twist unit. Further. when two plates are attached to a single bearing block. the bearing point for one twist tube is accessible only from one side of the block while the bearing point for the other twist tube is accessible only from the opposite side of the block. Thus difficulties arise in handling and operating the units because the bearing points can only be serviced from mutually opposing directions.  
  It is the object of the present invention to provide an improved system for mounting the false twist units on a false twist machine.  
  It is a further object of the present invention to provide a false twist machine with an improved arrangement whereby the false twist unit may be mounted on a holding bracket so as to selectively provide under optional conditions 5 and/or Z twist.  
  It is a further object of the present invention to pro vide a false twisting machine with a minimum of waste 2 space and wherein the twist unit is easily accessible from many directions for service.  
  It is a further object of the present invention to arrange the twist unit so that on urging of the whorl against the tangential belt. the twist tube through which the yarn is drawn is positively and directly urged into a position between its peripherally arranged drive means.  
  These objects. other objects. and numerous advantages of the present invention will be apparent in the following description and in the accompany drawings.  
 BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:  
  FIG. I is a plan view of a section of a false twisting machine showing two false twist units arranged on one side of the tangential belt to provide a twist in one direction. one of the units is seen in the working position and the other in the nonworking or rest position.  
  FIG. 2 is a view of the apparatus shown in FIG. I in which each of the twist units are arranged on the other side of the belt so as to obtain a reverse direction of twist.  
  FIG. 3 is a side elevational view. partially in section showing the false twist unit of FIG. 1 in the working position.  
  FIG. 4 is a partial view of a twisting machine showing a second form of the present invention adapted for the mounting of a double or combined pair of twisting units. to one side of the belt.  
  FIG. 5 is a view of the apparatus shown in FIG. 4 arranged to the opposite side of the belt so as to obtain a reverse twist.  
  FIG. 6 is a view of the apparatus of FIG. 4 wherein the individual units ofa combined pair are arranged on opposite sides of the belt so as to obtain twist in opposite direction simultaneously.  
  FIG. 7 is a view of the apparatus of FIG. 6 in the rest position.  
 SUMMARY OF INVENTION Briefly. a false twisting machine is provided in which there are arranged a plurality of fixed brackets spaced along the machine frame. Each bracket is adapted to receive a supporting plate carrying a twist tube. means for holding the tube and means for rotating the tube ineluding a drive whorl extending from the plate. A tangential belt continuously moving in one direction is provided in a running direction perpendicular to the direction of the bracket and spring means are provided urging the plate about its pivot to cause the whorl to engage with the belt. The means for pivotally mounting the plate on the bracket comprises a pair of spaced bearings. The plate is mounted selectively in one or the other of the bearings whereby in one bearing the plate is fulcrumed to urge the whorl to engage one side of the belt and in the other of the bearings. the plate is urged to bear the whorl on the other side of the belt. thereby reversing the direction of rotation of the twist tube.  
  In this manner. the present invention has the advantage in that the plate carrying the mechanism for holding and rotating the twist tube is mounted only on one side of the bearing bracket and may be selectively positioned in one or the other of its bearing means to provide either the S or Z twist. thus the space between and jacent brackets is allotted for only one twist unit and the brackets may be spaced only so far apart as is necessary for this unit. Thus adjacent units are provided with their own allotted space and do not under any conditions overlap or interfere with each other.  
  Full details of the present invention are set forth in the following description.  
 DESCRIPTION OF THE INVENTION The several forms and embodiments in the invention depicted in the drawings have basically similar construction and may therefore be considered in unison. In each drawing the twisting mechanism comprises a plate I on which are journaled bearings 2 and 3 which support driving discs 4 and S. The driving discs 4 and 5 are each freely rotatable and their peripheral edges are spaced to form a V-shaped gap into which a twist tube can be located. Arranged beneath the surface of the driving discs 4 and 5 is a magnet 6 which is adapted to hold the twist tube 7 through which the yarn is drawn. The magnet 6 acts to draw the twist tube 7 into the gap between the discs 4 and 5 with sufficient force so that it abuts their periphery and on rotation of either of the discs 4 and S the twist tube 7 is itself rotated in one of two directions about the central longitudinal axis. The shafts of the driving discs 4 and 5 extend below the plate I and have attached to them respectively whorls or drive flywheels 8 and 9 respectively (FIGS. l and 3). Each ofthe whorls 8 and 9 is selectively adapted as will be explained later to engage under pressure conditions with a tangentially moving belt H] which is driven. in all of the FIGURES in the same direction of travel as indicated by the arrow A.  
  A vertical bearing shaft II is fixedly attached to the plate I and depends therefrom. The bearing shaft 11 is adapted to be received in one of two bearingholes formed on the holder bracket 12. in the embodiments of FIGS. I through 3. or the holder bracket 13 in the embodiment of FIGS. 4 through 7. The plate I is provided with an extending tab having a handle hole 14 enabling the plate I to be swung or pivoted about the bearing shaft II.  
  The holder brackets 12 and [3 are angle type arms which are attached by their shanks through a screw or bolt fastening means 15 to one side of the frame I6 of the machine. The other shank or arm of the holder brackets 11 and 13 extend substantially at right angles to the direction oftravel of the belt It] and form a fixed support or bracket for the plates I. Each of the extend ing arms of the brackets I2 and I3 are provided with a pair of bearing bushes or recesses 17a and 1712 which are spaced apart from each other on either side of the tangential belt and which form the recesses for receiving the downwardly extending bearing shaft ll.  
  In the form according to FIGS. 1 and 3, the bearing shafts 11 are inserted into the bush recesses 17a so that the two whorls 8 and 9 are arranged on the side of the belt facing the frame 16 of the machine and furthermore the whorl 8 is arranged adjacent to the run of the belt 10. As in all of the embodiments. a tension spring 18 is provided to force the whorls against the belt 10 or to permit the whorls to be pivoted out of engagement with the belt 10. The tension spring 18 is fixed at one of its ends by means of a screw journal 20 to the plate 1 and at the other of its ends by means ofa screw journal I9 to the support 12 and 13. In the embodiment of FIGS. 1 and 3 the screw journal 19 is inserted in a threaded hole 21 (FIG. 3) ofthe holder bracket [2 and the screw journal 20 is inserted in a threaded hole 22 in the plate I. The tension spring provides a resilient over the center mechanism which is either adapted to cause the whorl 8 to engage the belt 10 or conversely to disengege from it. In the working position shown in the lefthand portion of FIG. I, the central longitudinal axis of the tension spring 18 runs to the right of the pivot point or fulcrum defined by the journal shaft II and the bearing bush 17a. Therefore a torque acts on the plate 1 in a clockwise direction. thus forcing the whorl 8 of the driving disc 4 to engage and press against the belt 10 under the action of the spring force. As a result a thread or yarn drawn downwardly through the twist tube &#39;7 is caused to undergo a Z twist. It will also be apparent that the clockwise torque on the plate I acts to force the tube 7 between the gaps in the drive discs 4 and 5.  
  The back surface of the tangential belt 10 runs over a guide roller 23 whose bearing is attached by means of a threaded journal shaft 24 in a threaded hole 25 formed in the holder bracket 12, as seen in FIG. 3. The guide roller 23 acts to insure proper pressure being placed upon the whorl 8 so as to insure proper transmission of the drive source. I  
  The pivotal mounting of the plate I on the holder bracket 12 permits the plate to be slewed or swung so that the whorl 8 is disengaged from the belt 10. This is observed in the righthand portion of FIG. 1. The plate I is pivotable about its journal shaft II, received in the bush 17a and is pivotable in a horizontal plane parallel to the plane of the bracket 12 by merely manipulating the handle I4. In swinging the plate I the central longitudinal axis of the tension spring 18 passes over the journal or bearing shaft I1 and the tension spring I8 moves to the left side of this bearing shaft and thus forces the plate 1 into a counterclockwise torque. This forces the plate I through its angular swing until its upper edge 26 comes to rest and in contact with the side wall of the machine frame 16. In this position the whorl 8 is disengaged from the belt I0 and rotation of the twist tube 7 is arrested.  
  As seen in the form as shown in FIG. 1 the twist tube 7 will rotate about its central axis clockwise under the action of the whorl 8. This produces a Z twist. On the other hand should it be desired to rotate the tube 7 in the opposite direction and produce an S twist. the plate is rearranged as shown in FIG. 2. The belt 10 remains unchanged in its direction of guiding and the yarn is continued to be fed in the same direction through the twist tube 7. The tension spring 18 is merely detached from its journal screws 19 and 20 and the plate I is rearranged with its bearing journal shaft 11 transferred into the bearing bushes 17b rather than from the bearing bushes 17a on the holder bracket 12. The tension spring 18 is then rearranged so that its end 19 is inserted in the threaded hole 210 formed at the upper end of the holder bracket 12 and its other end 20 is inserted in the threaded hole 22a on the plate 1 adjacent the handle 14. This produces oppositely directed torques on the plate 1 to those shown in FIG. I. Furthermore the guide roller 23 is moved so that its threaded journal 24 is transferred into a second threaded hole 250 in the holder bracket I2. This places the guide roller 23 into a different working position in which the belt I0 is compressed against the whorl 9 with greater accuracy. As seen in FIG. 2 the tension spring 18 again creates an over the center positioning of the plate 1 and in the lefthand representation. again indicating the working position of plate 1. the longitudinal axis of the plate 13 is to the right of the fulcrum defined by the journal shaft II and its receiving bushing 17!) so that the plate I is urged in a counterclockwise or upward direction so that the whorl is pressed against the belt 10. Since the belt I0 runs in the same direction indicated by the arrow A there is thus produced in the twist tube 7 a rotation about its axis opposite to that shown in FIG. I. The two pair of fixing points 21 22, and 2M. 22a. for the spring [8 are selected so that the spring exerts the same compressive force on whorl 8 as it does on whorl 9 in either of the embodiments shown in FIG. 1 and 2. This is achieved by the fact that in the working positions of the plate I in either embodiment of FIG. I or 2, the ratio of the distance between the fulcrum 11. 17a or I1, I71) and the central axis of the tension spring I8 to the distance of the central axis of the whorl 8 or to the distance of the central axis of the whorl 9 as they would lie against the belt 10, from the central axis of the tension spring 18 is made equal for both cases.  
  Disengagement of the whorl 9 from the belt 10 is shown in the righthand portion of FIG. 2. By manipulating the plate I via the handle 14 the plate 1 may be swung again through an angle however with a clockwise motion. This withdraws the whorl 9 from engagement with the belt and transmits the central axis of the spring I8 to the left of the fulcrum defined by the hearing shaft 11 and the bush 17b. The spring 18 thus holds the plate 1 in its disengaged position. forming the over the center function. This rest position is determined and limited by engagement of the housing of the bearing 3, which supports the driving disc 4, with the side edge of the holder bracket 12.  
  In FIGS. 4 through 7, the holder bracket I3 is designed so as to support a pair of plates 1 which are arranged to cooperate in combination with each other. The holder bracket I3 is formed of a pair of parallel arms 13a and 13b extending perpendicularly outward from the frame wall 16. The arms 13a and 131: are connected together near their free ends by a transverse bridging portion I30. Each of the two arms 13a and 13b are formed in the same manner as the holder brackets 12 described in connection with FIGS. I and 3. Each arm 13a and 13b is provided with a pair of bearing bushes 17a and 17b which are adapted to receive the bearing journal shaft II depending from the plate I. Each is provided with the threaded holes 21 and 21a for insertion of the screw journals holding the spring I8 and each is provided with threaded drillings 25 and 25a for receiving the threaded journals 24 of the guide roller 23. Each plate I is similar to that described with reference to FIGS. 1 and 3 being provided with the twist tube 7, the magnet 6 and the drive discs 4 and 5 as well as the other structure described earlier.  
  In the arrangement seen in FIG. 4 the two plates I are inserted in the holding bracket arms 13a and 1312 with the journal shafts 11 inserted in the bearing bushes 17a. The tension springs 18 are secured as indicated in FIG. I. In addition the plates are swung so that they are in their working position with the whorls 8 engaging against the tangential driving belts I0. The two plates I. as seen in FIG. 4 are joined together by a transverse coupling member. in the form ofa guide rod 27 whose two ends are held by screws 28 passing through holes 30 in the guide rod 27, into the threaded holes 220 in each of the respective plates 1. It will thus be appreci- Ill ated that on gripping and pivoting of any one of the plates I by its handle 14. the other plate 1 is also pivoted and moved. Thus the double unit comprising the pair of plates I can be switched on and off into engagement with the plate 10 by a single operation. This simultaneous action on a pair of associated twisting units is necessary for example when the yarn or threads supplied to each of the twist tubes 7 had previously passed through a common delivery mechanism. The coupling of the two associated plates 1 as seen in FIG. 4 is moreover of advantage if the threads or yarn passing through the two twist tubes 7 are wound together on a common bobbin. In either case the combined operation of the two associated plates results in a simultaneous start and/or a simultaneous finish of the production.  
  The arrangement seen in FIG. 4 enables the simultaneous production of two Z twisted threads or yarn. In FIG. 5 the same apparatus and mechanism is arranged so as to simultaneously produce two S twisted threads. This is obtained by transferring the coupled plates 1 into the position already explained by reference to FIG. 2 in which the bearing journal shaft II of each of the plates I are inserted into the receiving bushes [7h on the respective holder bracket arms 13a and 13!). Here the ends of the tension springs 18 are secured to the coupling guide rod 27 at the respective threaded holes 220 in much the same manner as described with reference to FIG. 2. The opposite ends I9 are secured in the threaded holes 210. In this manner the simultaneous pivoting of the two plates is insured while still creating the counterclockwise torque on the plates I which cause the whorls 9 to engage the belt 10 to produce the oppositely directed twist. The guide roller 23 is again relocated into its bearing bush 25a as indicated in FIG. 5. FIGS. 6 and 7 show a double or coupled unit in its working and rest position respectively wherein the units rather than producing the same twist in each of their yarns or thread produces oppositely directed twists. The plate 1 mounted on the holder bracket 13a (left portion of FIG. 6) is journaled in the same manner as described in FIGS. l. 3 and 4 while the plate I mounted on the holder bracket 13b (right side of FIG. 6) is mounted in such a way as shown by the FIGS. 2 and 5. Thus in the plate I mounted on bracket I30 the whorl 8 engages the belt 10 while on its associated plate to its right the whorl 9 engages the belt I0. Thus one twist tube produces a Z twist on the thread or yarn while the other twist tube produces an S twist on its thread or yarn. The yarns of course may come from a common source and be wound on a common bobbin or may be separately treated. In FIG. 6 the working position of the plates I is shown while in 7 the disengaged position will be apparent. In the case shown by FIGS. 6 and 7 the coupling guide rod 27 enables each plate to be moved simultaneously into their adjusted position. The guide rod 27 is however secured somewhat differently. The bearing screw 28 for the righthand end of the guide rod 27 is inserted into a threaded hole 29 in the plate represented on the right. The lefthand end of the guide rod 27 is connected by a bearing screw 28 with its associated plate represented on the left which passes through a third bearing hole 30 (FIGS. 4 and 5) and is thereafter inserted into the threaded hole 22 of its associated plate. The third bearing hole 30 formed in the guide rod 27 is at a point that on the pivoting of one plate. a corresponding pivoting movement of the other plate takes place. in an opposite clockwise or counterclockwise direction. Thus as seen in FIG. 6 if the righthand plate I is swung clockwise the lefthand plate 1 attached to the holder bracket [3a is swung counterclockwise. and vice versa. The three bearing holes formed in the guide rod 27 have a diameter which is somewhat greater than the outer diameter of the bearing screw 28 which passes through these holes. Thus this opposite swinging motion can be obtained without binding of the parts. And there is play in movement between the guide rod 27 and the plates 1.  
  An advantage of the arrangement shown in FIGS. 6 and 7 lies in the fact that in the working position each of the two plates 1 are independent of each other and act only under the influence of their own respective spring I8. Thus one plate is prevented from reciprocally influencing the movement of the other plate. (onsequently in the event of inexpert assembly of the plates. supporting brackets. or in the event of an inaccurate belt guide. the pivoting into working position of one plate prior to the other plate reaching its own working position. and thereby preventing the second plate from ever reaching its working position is reliably prevented. The holes 30 can be circular. oval or even longitudinal.  
  Furthermore. in the arrangements as shown in FIGS. 4 and 7. as in the arrangements shown in FIGS. I to 3, the corresponding transfer or transposition of the guide roller 23 from one bush 25 to the other 25a is necessary when a single guide roller 23 is provided. However. in the case of the modification seen in FIGS. 6 and 7 the guide roller 23 may be dispensed with. It will be seen clearly from the FIGS. 6 and 7 that the whorl 8 of one unit exerts a pressure on the opposite side of the belt I to that of the whorl 9 of the other unit. thus opposite and equal pressures are exerted on the belt l0 and the counter roller or guide roller 23 is no longer necessary. The action of the springs 18 in the units according to FIGS. 4 to 7 are similar to those described in connection with FIGS. l to 3 and need not be further described herein.  
  The coupling of adjacent pairs of plates I is not confined to the arrangement shown in FIGS. 4 to 7 wherein the holder bracket 13 is provided but may be obtained in the arrangement shown in FIGS. 1 to 3 with the individual holder brackets I2. The guide rod 27 may be included in and used to couple adjacent plates I in the arrangement shown in FIGS. 1 to 3 by the same tech niques employed in the arrangement shown in FIGS. 4 through 7 provided that the holder brackets 12 are arranged at a suitable distance apart from each other on the wall I6 of the machine frame. Similarly a coupled unit as shown in FIGS. 4 through 7 can be easily converted into independent and separable units by merely removing the guide rod 27 so that the two twist tubes 7 can be switched on and off individually. Thus. when yarns which are not to be combined or twisted together are twisted on the arrangement shown in FIGS. 4 to 7, the independent and separable twist tubes can be stopped separately from each other.  
  It is furthermore apparent from all of the Figures that in spite of the different positions at which the plates I are inserted into the holders I2 and/or 13, the bearing points of the twist tubes 7 always remain accessible from the same direction so that manipulation of the machine can be favorably made. It is furthermore to be seen from FIGS. 4 to 7 that the plates 1 can be arranged at very short distances apart, so that a division of the machine itself can be made most efficiently and without a great deal of wasted space. That by simply resetting the parts at their various bearing points the units are suitably selectively and optionally rearranged for producing threads with either S and/or 2 twists. In each instant the individual elements of the mechanisms are identical.  
  FIG. 3 also shows a thread guide eyelet 31 attached to the plate 1. The eyelet 31 introduces the thread or yarn into the twist tube 7. FIG. 3 also shows the position of the withdrawal tube 32 from which the twisted yarn is withdrawn. In FIGS. 1 and 2, the arrows moving in a circular path mark the angle alpha whose one leg is the dotted line connecting the central axes of the driving discs 4 and 5 and whose other leg is formed by the belt 10. It is apparent from all of these Figures that the angle in both the inserted positions defined by the journal II. 170 and Il, 17b of the plate I in the holders I2 and 13 and in their adjusted position. i.e. the working and rest positions is indeed different. This angle however is clearly shown as not to exceed the value of approximately This angular range arises from the arrangements made in the bearing journal shaft I1 and the bearings 2 and 3 of the plate I and therefore in all the inserted and adjusted positions of the plate I bearing point of the twist tube 7 remains accessible from practically the same direction.  
  Various modifications. changes and embodiments have been shown in the foregoing disclosure. Others will be obvious to those skilled in the present art. It is intended therefore that the present disclosure be taken as illustrative only of the present invention and not limiting of its scope.  
 What is claimed is:  
  l. A false twist unit comprising a fixed bracket. a supporting plate carrying a twist tube, means for holding said tube and means for rotating said tube including a pair of drive whorls extending from said plate. means pivotally mounting said plate on said bracket. a tangential belt continuously moving in one direction and spring means urging said plate about its pivot to cause said whorls to engage said belt and thereby rotate said tube. said means for pivotally mounting said plate on said bracket comprising a pair of spaced bearing means. said plate being mounted selectively in one or the other of said bearing means whereby in one of said bearing means said plate is fulcrumed to cause one of said whorls to engage one side of said belt and in the other of said bearing means said plate is fulcrumed to cause the other of said whorls to engage the other side of said belt thereby reversing direction of rotation of said tube.  
  2. The unit according to claim 1 wherein on one of said bracket and plate a supporting shaft is formed and on the other of said bracket and plate two spaced receiving means are provided for said shaft.  
  3. The unit according to claim 2 in that said receiving means are provided on said bracket and said shaft is provided on said plate.  
  4. The unit according to claim 3 in that the receiving means comprises a recess including a bearing bush.  
  5. The unit according to claim I wherein said spring means comprises a tension spring fixed at one end to the bracket and at the other end to said plate.  
  6. The unit according to claim 5 wherein said bracket is provided with two spaced means for independently receiving one end of said spring and said plate is provided with two spaced means for independently receiving the other end of said spring. one of said receiving means on said bracket and one of said receiving means on said plate cooperating to receive said spring ends being arranged in relationship to one of said bearing means to bias the spring in one direction and the other one of said receiving means on said bracket and the other one of said receiving means on said plate cooperating to receiving said spring ends being arranged in relationship to the other one of said bearing means to bias the spring in the opposite direction.  
  7. The unit according to claim 6 wherein said receiving means are positioned so that the cooperating ones of said bracket and plate receive said spring on respective sides of said bearing means as to bias said spring in an over the center arrangement with respect to each of said bearing means.  
  8. The unit according to claim 7 wherein the ratio of distance between the bearing means and the central axis of the tension spring to the distance of the central axis of the whorl engaging the belt from the central axis of the tension spring is equal for each of said bearing means in operative engagement with said belt so that the respective tension springs exert an equal pressure on said belt by said whorls in each of said bearing means.  
  9. The unit according to claim I wherein two plates are supported on a single bracket.  
  10. The unit according to claim 9 wherein said two plates are joined together by a coupling&#39;member insuring simultaneous pivoting.  
  11. The unit according to claim it) wherein said coupling member comprises a guide rod pivotally fixed at one end to one plate and at the other end to the other plate.  
  12. The unit according to claim ll wherein the guide rod is provided with three holes permitting optional connection at each end to the coupled plates.  
  13. The unit according to claim 12 wherein said guide rod is connected at least one end to the receiving means for said tension spring.  
  [4. The unit according to claim 1 including a counter guide roller rotatably mounted on said bracket for engaging the belt on the side thereof opposite to that of the whorl.  
  15. The unit according to claim [4 wherein said bracket is provided with two threaded receiving means for receiving said guide roller. said receiving means being spaced to enable said guide roller to be adjustably positioned with respect to each of the whorls.