US3645084A

US3645084A - Apparatus for controlling the operation of individual spindles in a yarn-processing machine

Info

Publication number: US3645084A
Application number: US67739A
Authority: US
Inventors: Klaus Nimtz
Original assignee: Palitex Project Co GmbH
Current assignee: Palitex Project Co GmbH
Priority date: 1970-08-28
Filing date: 1970-08-28
Publication date: 1972-02-29
Anticipated expiration: 1989-02-28

Abstract

Apparatus for controlling the operation of individual spindles in a textile yarn-processing machine, such as a twister, spinning frame or the like. The apparatus preferably includes an endless tangential drivebelt engaging whorl portions of respective spindles for rotatably driving same, individually operable brake and positioning means may be used for stopping the rotation of and for positioning desired ones of the spindles in predetermined positions, and individually movable tension rolls for guiding engagement with the drivebelt to individually assume a driving position holding the drivebelt in tight frictional engagement with the respective spindle and to be movable to a substantially nondriving position holding the drivebelt in loose friction engagement with the respective spindle for allowing operation of the brake and positioning means. Preferably, the tension rolls include bowed peripheral surfaces for holding the drivebelt by full engagement therewith when in the driving position and for holding the drivebelt against sagging by engagement with only the outwardly extending center portion of the bowed surface when in the nondriving position.

Description

United States Patent Nimtz APPARATUS FOR CONTROLLING THE OPERATION OF INDIVIDUAL SPINDLES IN A YARN-PROCESSING MACHINE lnventorz- Klaus Nimtz, Krefeld, Germany [73] Assignee: Palitex Project Company Gmbll, Krefeld,

Germany [22] Filed: Aug. 28, 1970 [21] Appl. No.: 67,739

[52] US. Cl ..57/88, 57/89, 57/104 [51] Int. Cl ..D01h 13/14, D0lh 7/22 [58] Field of Search ..57/88,89,104, 105,129,130, 57/92 [56] References Cited UNITED STATES PATENTS 1,868,438 7/1932 Thomas ..57/105 X 2,718,747 9/1955 l-lonig.... ..57/104 X 2,892,302 6/1959 Whitehead. ..52/88 3,016,680 1/1962 Warnock .....57/88 3,333,408 8/1967 Keyser ..57/104 [4 1 Feb. 29, 1972 [57] ABSTRACT Apparatus for controlling the operation of individual spindles in a textile yam-processing machine, such as a twister, spinning frame or the like. The apparatus preferably includes an endless tangential drivebelt engaging whorl portions of respective spindles for rotatably driving same, individually operable brake and positioning means may be used for stopping the rotation of and for positioning desired ones of the spindles in predetermined positions, and individually movable tension rolls for guiding engagement with the drivebelt to individually assume a driving position holding the drivebelt in tight frictional engagement with the respective spindle and to be movable to a substantially nondriving position holding the drivebelt in loose friction engagement with the respective spindle for allowing operation of the brake and positioning meansv Preferably, the tension rolls include bowed peripheral surfaces for holding the drivebelt by full engagement therewith when in the driving position and for holding the drivebelt against sagging by engagement with only the outwardly extending center portion of the bowed surface when in the nondriving position.

7 Claims, 9 Drawing Figures Patented Feb 29, 1972 4 Sheets-Sheet 1 INVENTOR: KLAU s N M'TZ I BY MfiMLSWPAmM ATTORNEYS Patented Feb. 29, 1972 4 Sheets-Sheet 2 I N VE N TOR:

KLAUS N\ MTZ BY PM,BAR,S1%,R&

ATTORNEYS fP aitg ented Feb.29, 1972 3,645,084

4 Sheets-Sheet 5 Jig-=5 INVENTOR: KLALJ: Nwnz 7 ATTORNEY 5 atented Feb. 29, 1972 3,645,084

4 Sheets-Sheet 4.

- INVENTOR KLAUS NmTz ATTORNEYS APPARATUS FOR CONTROLLING THE OPERATION OF INDIVIDUAL SPINDLES IN A YARN-PROCESSING MACHINE This invention relates to apparatus for controlling the operation of individual spindles in a textile yarn processing machine, such as a twister, spinning frame or the like.

Spindle mechanisms of some types of yarn processing machines are driven by endless, flat, tangential belts engaging the whorl portions of the spindle assemblies. In order to doff and start up bobbins on the individual spindles or piece up a broken yarn for the individual spindles, it is necessary to individually brake each of the spindles of the machine while al lowing continuous running of the tangential drivebelt for driving the other spindles of the machine.

This individual spindle braking action has previously been accomplished in a number of ways, including allowing the tangential drivebelt to rub along the stopped whorl at a constant pressure, or loosening the tangential drivebelt from the spindle whorl and make the latter nondrivable, or moving the entire spindle away from the tangential drivebelt. These operations have not been entirely satisfactory, either because they require very complicated mechanisms or because the parts thereof are subject to unusual or concentrated wear. This is particularly true in the case of the spindle which is mounted for movement away from the drivebelt in that it requires a complicated and expensive mechanical design and arrangement. Also, the braking action in which the tangential drivebelt is allowed to rub along or drag along the stopped spindle at a constant pressure produces abnormal and unusual wear on the drivebelt and requires frequent replacement. A further disadvantage in the above operations is that if the tangential drivebelt is moved away from the spindle or the spindle moved away from the drivebelt, there is a tendency for the drivebelt to sag under its own weight due to the absence of sufficient frictional forces for holding the same in its upright posi- V tionwhich causes the machine components to misalign upon again starting up of the drive of the spindle.

Accordingly, it is an object of the present invention to provide apparatus for controlling the operation of individual spindles. in a textile yarn processing machine which overcomes the above disadvantages.

By this invention, it has been found that this object may be accomplished, in a textile yarn processing machine having a plurality of rotatably mounted spindles for receiving yarn packages and including whorls and driven by an endless tangential drivebelt engaging each of the whorl portions of the spindles for rotatably driving same, by providing movable tension rolls operatively associated with each of the spindles for guiding engagement with the drivebelt to individually assume a driving position holding the drivebelt in tight frictional engagement with the whorl portion of the respective spindle for normal driving of the respective spindle and to be movable to assume a substantially nondriving position holding the drivebelt in loose frictional engagement with the whorl portion of the respective spindle. Preferably, each of the tension rolls has an outwardly extending bowed peripheral surface for engagement with the drivebelt so that the drivebelt will be held in tight frictional engagement with the respective whorl portion of the spindle by full engagement with the bowed peripheral surface when the tension roll is in the driving position and will be held in loose frictional engagement with the respective whorl portion of the spindle by partial engagement with only the outwardly extending center portion of the bowed peripheral surface when the tension roll is moved to the nondriving position.

The individually movable tension rolls are preferably utilized in conjunction with individually operable brake and positioning devices associated with each of the spindles for individually stopping the rotation of desired ones of the spindles against the driving influence of the drivebelt and positioning the spindles in a predetermined position for doffing of a full bobbin and starting up an empty bobbin or piecing up of a broken yarn. These brake and positioning means are individually operable when the respective tension roll is moved to the nondriving position.

By the above-preferred combination of apparatus, undue wear on the tangential drive belt is eliminated since during stopping or braking of the individual spindles, the tangential drivebelt is not held in-tight frictional engagement with the whorl portion of the spindle, but is only maintained in loose frictional engagement such that the spindle may be additionally rotated after braking sufficiently for allowing the positioning means to correctly position the spindle. Also, the bowed peripheral surface of the tension rolls prevents sagging of the tangential drivebelt under its own weight when moved out of tight frictional engagement with the whorl portions of the spindles.

Some of the objects of the invention having been stated, other objects will appear as the description proceeds when taken in connection with the accompanying drawings, in which:

FIG. 1 is a partial perspective view, with portions broken away, of a yarn processing machine utilizing the improved apparatus of this invention;

FIG. 2 is a partial perspective view of a portion of the apparatus shown in FIG. 1 and taken from the other side thereof;

FIG. 3 is a schematic plan view of a plurality of spindles utilized in the yarn processing machine of this invention along with their assigned tension rolls and the tangential drive belt passing therebetween;

FIG. 4 is a cross-sectional, elevational view taken through one of the spindles of the apparatus of FIG. 1 and showing the tension roll in the nondriving position thereof and the brake and positioning means actuated;

FIG. 5 is a cross-sectional view taken generally along the lines 5- -5 of FIG. 4;

FIG. 6 is a cross-sectional, elevational view through one of the spindles and associated brake and positioning means showing the same in unactuated position;

FIG. 7 is a cross-sectional, elevational view of one of the spindles of the apparatus of FIG. 1 along with associated tension roll and brake and positioning means and showing the tension roll in driving position; and

FIGS. 8 and 9 are sectional details of portions of the brake and positioning means showing the same in unactuated and actuated conditions, respectively.

Referring now to the drawings, there is shown in FIG. 1 a portion of a yarn processing machine, in the form of a two-forone-twister, broadly indicated by the reference numeral l0. The operation of these two-for-one twisters is generally known by those with ordinary skill in the art and only the basic conventional components thereof need be described.

These two-for-one twisters 10 include a plurality of spindle assemblies 11 rotatably mounted on and extending vertically upwardly from a spindle rail 12. Each of the spindle assemblies 11 conventionally includes a stationary center shaft 13 mounted in the spindle rail 12 (as shown in FIG. 6), a spindle rotor 15 rotatably mounted on the center shaft 13 and including a whorl portion at the lower end thereof and a yarn package receiving portion at the upper end thereof, a thread storage disc 16 rotating with the spindle rotor 15 and including a thread passage 17 leading radially out of the storage disc 16, a basket 18 and a flier 19. A package of yarn Y is adapted to be received on the upper portion of the spindle rotor 15 within the basket 18 and yarn Y therefrom is led through the flier 19 down through an entry tube 20 and out the thread passage 17 to be led to a takeup package (not shown) located above the above-described mechanisms.

For individually rotating each of the spindle assemblies ll, an endless tangential drivebelt 25 engages each of the whorl portions of the spindle rotors 15 for rotating the abovedescribed rotatable mechanisms. This endless belt 25 extends along the length of the machine and is driven by suitable mechanisms located at the end of the machine so that the same is constantly driven,

The operation of each of the spindle mechanisms 11 must be individually controlled so that the spindle mechanisms may be individually stopped for doffmg and starting up or piecing up of a broken yarn. Also, it is necessary that the thread passage 17 leading out of the storage disc 16 be correctly positioned, as shown in FIG. 1, for ready access by an operator standing in front of the twister for this doffing and starting up operation or yarn piecing up operation.

To individually brake and position the spindle mechanisms 11, a brake and positioning means, generally referred to by the reference numeral 30, may be utilized. A suitable brake and positioning means 30 for use in a two-for-one twister 10, as illustrated in this application, is disclosed in US. Pat. No. 3,466,865, issued Sept. I6, 1969, and assigned to the assignee of the present invention. Inasmuch as full details of the operation of this brake and positioning means are disclosed in that application, only the essential components and basic operation will be discussed herein.

The brake and positioning means, as shown in FIGS. 4, 5, 6, 8 and 9 particularly, basically comprises a pair of pivotally mounted outwardly movable braking shoes, one of which is shown in FIGS. 4 and 6 and indicated by the numeral 32. These braking shoes are pivotally mounted on the stationary spindle rail 12 and are adapted to be pivoted outwardly into engagement with a braking surface 33 formed on the inside of the whorl portion of the rotatable spindle rotor 15. Outward movement of the braking jaws 32 into engagement with the braking surface 33 is accomplished by spreading mandrel 34 attached to a shaft 34a rotatably mounted in and extending through the spindle rail 12 and actuated in a manner to be described below.

The brake and positioning means 30 further comprises a collar 35 carried by the stationary shaft 13 of the spindle mechanism 11 and which contains a groove 36 therein. For cooperation with the groove 36 there is provided a slide member 37 carried by shaft 37a mounted for reciprocation through spindle rail 12 for movement into and out of the groove 36 in the manner described below, and a pivotally mounted centrifugally operated positioning lever 39 carried by the inside surface of the whorl portion of the spindle rotor 15.

For actuating the above-described brake and positioning means 30, a manually operated actuating lever mechanism 42 is pivotally mounted on the spindle rail 12 and includes a spring-biased plunger mechanism 43 for engaging a lower attachment of the shaft 340 of the spreading mandrel 34 to pivot the same for spreading the brakeshoes 32 to engage the braking surface 33 and stop rotation of the spindle mechanism 11 against the influence of the tangential drivebelt 25.

The slide member 37 is normally held in the slot 36 of the collar 35 on the stationary shaft 13 during rotation of the spindle rotor 15. However, upon actuation of the lever mechanism 42, the slide member 37 will be withdrawn from the slot 36 in the collar 35 by a cam slide extension of the lever 42, as shown in FIG. 4. The pivoted positioning lever 39 is normally held in outwardly pivoted position against the inside surface of the whorl portion of spindle rotor to which it is attached by centrifugal force during rotation of the spindle rotor 15, as shown in FIG. 8, and is prevented from engaging the slot 36 due to the presence of the slide member 37 during rotation of the spindle rotor 15. However, when the spindle rotor is braked by the above-described braking action, the slide member 37 will be withdrawn from the slot 36 and the spindle rotor will be stopped which will in turn eliminate the centrifugal force on the positioning lever 39 and allow the same to fall by gravity against the collar 35. When the thread aperture 17 is in the correct position, the positioning lever 39 will mate with the slot 36 and drop therein to stop rotation of the spindle rotor 15 in the exact position for alignment of the thread aperture 17.

The above operation and correct positioning of the spindle mechanism 11, as more fully explained in the aforesaid US. patent, is accomplished by continuous engagement of the drivebelt 25 with the whorl portion of the spindle rotor 15 such that the braking action of the brakeshoes 32 against the braking surface 33 will stop rotation of the spindle rotor with respect to the stationary shaft 13 against the influence of the drivebelt 25, but will allow an additional creeping or slight rotation of the spindle rotor 15 with respect to the stationary shaft 13 until the positioning lever 39 has dropped into the slot 36 of the collar 35 to correctly position the thread aperture 17 for doffing and starting up of a bobbin of yarn or piecing up a broken yarn.

For cooperation with the above-described mechanisms of V the twister 10 for individually controlling the operation of the spindle mechanisms 11, there are provided individual tension roll mechanisms, generally indicated by the numeral 50, for each of the spindle mechanisms 11. Each of the individual tension roll mechanisms comprises a freely rotatable roll 51 rotatably carried by a lever arm 52 which is pivotally mounted on a bracket 53 secured to the spindle rail 12, as shown particularly in FIG. 2. The lever 52 is pivotally mounted on the bracket 53 b a stud 54 which includes a coil spring 55 therearound loaded in such a manner as to bias the lever 52 and the tension roll 51 into tight engagement with the tangential drivebelt 25 and toward the spindle mechanism 11 in the manner shown in FIGS. 5 and 7 particularly. The endless drivebelt 25 is mounted in the twister 10 in such a manner that it is biased away from the whorl portions of the spindle rotors 15 and is pushed into driving engagement therewith by tension rolls 51.

The tension roll mechanism 50 further includes an actuating arm 57 which is generally L-shaped and protrudes downwardly from the tension roll 51 and under the spindle rail 12 to be contacted by a protruding portion of the manually operated actuating lever mechanism 42. The tension roll 51 has an outwardly extending bowed peripheral surface 51a for engagement with the endless tangential drivebelt 25. The axis of rotation of the tension roll 51 is parallel with the axis of rotation of the spindle rotor 15.

Each of the tension rolls 51 is individually adapted for guiding engagement with the drivebelt 25 to individually assume a driving position, as shown particularly in FIG. 7, holding the drivebelt 25 in a generally curved configuration and in tight frictional engagement with the whorl portion of the respective spindle rotor 15 by full engagement with the bowed peripheral surface 51a for normal driving of the respective spindle rotor 15. Each of the tension rolls 51 is also adapted to be individually movable to assume a substantially nondriving position, as shown particularly in FIG. 4, holding the drive belt 25 in loose frictional engagement with the whorl portion of the respective spindle by partial engagement with only the outwardly extending center portion of the bowed peripheral surface 510 to allow the respective spindle to be stopped, by operation of the brake and positioning means 30 or otherwise, for dofflng, starting up and piecing up.

For moving each of the tension rolls 51 against the influence of spring 55 from the driving position to the nondriving position, the manually operated lever 42 is utilized such that when the lever 42 is depressed inwardly by the knee of the operator or otherwise, the extension of the manually operated lever 42 will contact the actuating arm 57 and move the tension roll 51 a predetermined distance away from the spindle mechanism 11, as shown particularly in FIG. 4, so that only the outwardly extending center portion of the bowed peripheral surface 510 will contact the belt 25 and the belt will be held in only light frictional engagement with the whorl portion of the spindle rotor 15 to allow the same to be braked, yet allow additional creeping or a small rotation of the spindle rotor 15 for the above-described purposes of allowing the positioning mechanisms to correctly position the spindle rotor.

By the bowed peripheral surface of the tension roll 51 and the nondriving position thereof which holds the belt in loose frictional engagement with the whorl portion of the spindle rotor 15, undue wear on the belt 25 and the whorl portion is eliminated and sagging of the belt 25 under its own weight when in the nondriving condition will be eliminated.

Thus, this invention has provided apparatus for controlling the operation of individual spindles in a textile yarn processing machine, such as a twister, spinning frame or the like, in which the apparatus will allow braking and stopping of the spindle mechanism in a predetermined position, while avoiding the prior disadvantages of complicated designs, undue wear, etc.

In the drawings and specification there has been set forth a preferred embodiment of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation.

What is claimed is:

I. In a textile yarn processing machine such as a twister, spinning frame or the like, the combination of apparatus for controlling the operation of individual spindles comprising:

a plurality of rotatably mounted spindles for receiving yarn packages and including whorl portions;

a tangential drivebelt means engaging each of said whorl portions of said spindles for rotatably driving same; and tension roll means comprising individual rolls operatively associated with each of said spindles and mounted for rotation about an axis parallel with the axes of said spindles and having an outwardly bowed peripheral surface for guiding engagement with said drivebelt means to individually assume a driving position holding said drivebelt means in tight frictional engagement with said whorl portion of said respective spindle by full engagement with said bowed peripheral surface for normal driving of said respective spindle and to be individually movable to assume a substantially nondriving position holding said drivebelt means in loose frictional engagement with said whorl portion of said respective spindle by partial engagement with only the outwardly extending center portion of said bowed peripheral surface to allow the respective spindle to be stopped for cloffing, starting up and piecing up and to prevent sagging of the drivebelt and undue wear when in the substantially nondriving position.

2. In a textile yarn processing machine, as set forth in claim 1, including individual manually operable means for positioning each of said tension rolls in the respective driving and nondriving positions.

' 3. In a textile yarn processing machine, such as a twister, spinning frame or the like, the combination of apparatus for controlling the operation of individual spindles comprising:

a plurality of rotatably mounted spindles for receiving yarn packages and including whorl portions; a tangential drivebelt means engaging each of said whorl portions of said spindles for rotatably driving same;

individually operable brake and positioning means operatively associated with each of said spindles for individually stopping the rotation of desired ones of said spindles against the driving influence of said drivebelt means and positioning said spindles in a predetermined position for doffing and starting up or piecing up of a broken yarn; and

individually movable tension roll means operatively associated with each of said spindles and said brake and positioning means and mounted for guiding engagement with said drivebelt means to individually assume a driving position holding said drivebelt means in tight frictional engagement with said whorl portion of said respective spindle for normal driving of said respective spindle and to be movable to assume a substantially nondriving position holding said drivebelt means in loose frictional engagement with said whorl portion of said respective spindie for allowing operation of said brake and positioning means without undue wear on said drivebelt and for preventing sagging of said drivebelt.

4. In a textile yarn processing machine, as set forth in claim 3, in which each of said tension roll means comprises a roll rotatable on an axis parallel with the axes of said spindles and having an outwardly extending bowed peripheral surface for engagement with said drivebelt means so that drivebelt means will be held in tight frictional engagement with the respective whorl portion of said spindle by full engagement with said bowed peripheral surface when said tension roll is in the driving position and will be held in loose frictional engagement with the respective whorl portion of said spindle by partial engagement with only the outwardly extending center portion of said bowed peripheral surface when said tension roll is moved to the nondriving position.

5. In a textile yarn processing machine, as set forth in claim 3, including individual manually operable means for positioning each of said tension roll means in the respective driving and nondriving positions.

6. In a textile yarn processing machine, as set forth in claim 5, in which each of said individual manually operable means for positioning said tension roll means is operatively connected to the respective brake and spindle positioning means for actuating same when moving said tension roll to the nondriving position.

7. In a textile yarn processing machine, such as a twister,

spinning frame or the like, the combination of apparatus for controlling the operation of individual spindles comprising:

a tangential drivebelt means engaging each of said whorl portions of said spindles for rotatably driving same;

individually operable brake and positioning means operatively associated with each of said spindles for individually stopping the rotation of desired ones of said spindles against the driving influence of said drivebelt means and positioning said spindles in a predetermined position for doffing of a full bobbin and starting up an empty bobbin or piecing up of a broken yarn;

tension roll means comprising individual rolls operatively associated with each of said spindles and said brake and positioning means and mounted for rotation about an axis parallel with the axes of said spindles and having an outwardly bowed peripheral surface for guiding engagement with said drivebelt means to individually assume a driving position holding said drivebelt means in tight frictional engagement with said whorl portion of said respective spindle by full engagement with said bowed peripheral surface for normal driving of said respective spindle and to be movable to assume a substantially nondriving position holding said drivebelt means in loose frictional engagement with said whorl portion of said respective spindle by partial engagement with only the outwardly extending center portion of said bowed peripheral surface for allowing operation of said brake and positioning means without undue wear on said drivebelt and for preventing sagging of said drivebelt; and

individual manually operable means each of which is operatively connected with a respective one of said tension roll means and said brake and spindle positioning means for positioning said tension roll means in the respective driving and nondriving positions and for actuating said respective brake and spindle positioning means when moving said tension roll means to the nondriving position.

Claims

1. In a textile yarn processing machine such as a twister, spinning frame or the like, the combination of apparatus for controlling the operation of individual spindles comprising: a plurality of rotatably mounted spindles for receiving yarn packages and including whorl portions; a tangential drivebelt means engaging each of said whorl portions of said spindles for rotatably driving same; and tension roll means comprising individual rolls operatively associated with each of said spindles and mounted for rotation about an axis parallel with the axes of said spindles and having an outwardly bowed peripheral surface for guiding engagement with said drivebelt means to individually assume a driving position holding said drivebelt means in tight frictional engagement with said whorl portion of said respective spindle by full engagement with said bowed peripheral surface for normal driving of said respective spindle and to be individually movable to assume a substantially nondriving position holding said drivebelt means in loose frictional engagement with said whorl portion of said respective spindle by partial engagement with only the outwardly extending center portion of said bowed peripheral surface to allow the respective spindle to be stopped for doffing, starting up and piecing up and to prevent sagging of the drivebelt and undue wear when in the substantially nondriving position.

3. In a textile yarn processing machine, such as a twister, spinning frame or the like, the combination of apparatus for controlling the operation of individual spindles comprising: a plurality of rotatably mounted spindles for receiving yarn packages and including whorl portions; a tangential drivebelt means engaging each of said whorl portions of said spindles for rotatably driving same; individually operable brake and positioning means operatively associated with each of said spindles for individually stopping the rotation of desired ones of said spindles against the driving influence of said drivebelt means and positioning said spindles in a predetermined position for doffing and starting up or piecing up of a broken yarn; and individually movable tension roll means operatively associated with each of said spindles and said brake and positioning means and mounted for guiding engagement with said drivebelt means to individually assume a driving position holding said drivebelt means in tight frictional engagement with said whorl portion of said respective spindle for normal driving of said respective spindle and to be movable to assume a substantially nondriving position holding said drivebelt means in loose frictional engagement with said whorl portion of said respective spindle for allowing operation of said brake and positioning means without undue wear on said drivebelt and for preventing sagging of said drivebelt.

7. In a textile yarn processing machine, such as a twister, spinning frame or the like, the combination of apparatus for controlling the operation of individual spindles comprising: a plurality of rotatably mounted spindles for receiving yarn packages and including whorl portions; a tangential drivebelt means engaging each of said whorl portions of said spindles for rotatably driving same; individually operable brake and positioning means operatively associated with each of said spindles for individually stopping the rotation of desired ones of said spindles against the driving influence of said drivebelt means and positioning said spindles in a predetermined position for doffing of a full bobbin and starting up an empty bobbin or piecing up of a broken yarn; tension roll means comprising individual rolls operatively associated with each of said spindles and said brake and positioning means and mounted for rotation about an axis parallel with the axes of said spindles and having an outwardly bowed peripheral surface for guiding engagement with said drivebelt means to individually assume a driving position holding said drivebelt means in tight frictional engagement with said whorl portion of said respective spindle by full engagement with said bowed peripheral surface for normal driving of said respective spindle and to be movable to assume a substantially nondriving position holding said drivebelt means in loose frictional engagement with said whorl portion of said respective spindle by partial engagement with only the outwardly extending center portion of said bowed peripheral surface for allowing operation of said brake and positioning means without undue wear on said drivebelt and for preventing sagging of said drivebelt; and individual manually operable means each of which is operatively connected with a respective one of said tension roll means and said brake and spindle positioning means for positioning said tension roll means in the respective driving and nondriving positions and for actuating said respective brake and spindle positioning means when moving said tension roll means to the nondriving position.