US2858936A - Tension control apparatus for flexible support strands of an extensible conveyor - Google Patents

Description

c. T. OGDEN 2,858,936 TENSION CONTROL APPARATUS FOR FLEXIBLE SUPPORT Nov. 4, 1958 STRANDS OF AN EXTENSIBLE CONVEYOR 2 Sheets-Sheet 1 Filed Jan. 15, 1958 mmvmze Charles T Ogden ATTORNEY 5 .Eofiaw 20 2065; @v

NOV. 4, 1958 Q 1-, OGDEN 2,858,936

' TENSION CONTROL APPARATUS FOR FLEXIBLE SUPPORT STRANDS OF AN EXTENSIBLE CONVEYOR Filed Jan. 15, 1958 2 Sheets-Sheet 2 14a 75/ I521 I36 m 26 64 I I26 12 w 52 i 3/ 124 a0 68 J F F 128 I Fig 6 67 ,6? 78 77 /09 1/3 I06 72 9/ 99 1/7 1/3 as 57 I04 1/8 107 55 I! a 1 84 I" m 49 J 69 9 89 56 4 6 92 I08 --INVENTOR.

8573 7987 8/ 82 //4 I T O I. 9 ar es g en Fig. '4, Q0 28 5 V ATTOR/VEV TENSION CONTROL APPARATUS FOR FLEXIBLE gligflagzRT STRANDS OF AN EXTENSIBLE CON- Charies T. Ogden, Chicago, 'Ill., assignor to Goodman Manufacturing Company, Chicago, Ill., a corporation of Illinois Continuation of abandoned application Serial No. 581,195, April 27, 1956. This application January 15, 1958, Serial No. 709,436

14 Claims. (Cl. 198-208) This invention relates generally to conveyors, and particularly to an improved extensible conveyor which can be extended and retracted even during the conveying operation. This is a continuation of Charles T. Ogden application Serial No. 581,195, filed April 27, 1956, now abandoned.

The invention relates to a flexible strand sideframe conveyor which has strand means, such as a pair of wire ropes or equivalent strands, trained along a course and on which are supported rollers for an orbitally movable conveyor belt. In the case of an extensible conveyor such as the present one, the inbye ends of the wire ropes are wound on a conveyor tail section which is provided with means for tramming it toward a mine face to follow a mining operation. The ends of the ropes remote from the tail section are fixed in some suitable way. The tail section has strand tensioning means which maintains" the tension in the wire ropes at a preselected value to support the rollers, the belting, and the load thereon. The strand tensioning means pays out the ropes as the tail section is advanced inbye and winds in the ropes as the tail section is moved outbye. The belt itself is normally provided with an expandable and contractible loopwhich varies to accommodate the length requirements ofthe conveyor. a

In the past, strand tensioning means has been provided which operates automatically between upper and lower tension limits. to extend the conveyor, it first increases the tension to its upper limit, at which the automatic tensioning means comes into operation and pays off the strands at such upper tension limits. And, when the tail is reversed, to shorten the conveyor, it decreases the tension to its lower limit at which the tensioning means winds in the strands. Normally when the tail is stationary the strand means will be tensioned somewhere between these limits, the tension varying up and down in accordance with the load on the belt. The upper and lower tension limits will be preselected to accommodate maximum and minimum belt loading.

The tension in the strands works against the tramming mechanism when the tail is moved in a forward direction,

namely the direction to lengthen the conveyor. That is,

the strands hold back while the tramming means is attempting to move the tail forward.

When the tail is trammed forward, the strand tension required to support the load during the tramming operation is usually no more than the tension existing at the beginning of trammingv actuation. To let the tension go any higher merely adds to the work that the tramming mechanism must do and often causes the tram wheels or crawlers to spin if the ground is slippery.

Accordingly, it is a primary object of the present invention to provide control means for the strand tensioning means which is effective, during tramming, to maintain in the strands whatever tension was inthe strands at the beginning of the tramming operation.

Another object is the provision of strand tensioning Thus when the tail is trammed forward 2 control means including sensingme'ans for sensing the initial value of tension in the strands at the beginning of actuation of the tramming means and control means for the strand tensioning means operable in response to the sensing means to maintain the tension at such initial value during actuation of the tramming means.

Another objectis-the provision of improved strand tensioning'control means including means for sensing the. initial strand tension at the beginning of actuation of the.

tramming means, memory means effective to storeinformation as to the value of such initial tension, and means controlled by such memory means for maintainingjt he, strands at such initial tension during the tramming actu ation.

The invention is particularly directed to apparatus-for controlling within desired limits the tension in the sup-. port strands of an extensible strand sideframe conveyor,

it being understood that the term ,extensible includes.

conveyors that are contractible.-, Since-the loading of the conveying reach of such conveyor varies within wide limits, the tension in the support strands will vary in accordance with the load. In one application of such conveyors, the support strands may be mounted at inter: vals of about ten feet upon standards, and troughing roller assemblies may be mounted at about five foot tervals intermediate the support standards. The extensible conveyor may be of the type where at least one of the end sections, preferably the tail or inbye section, is arranged to move upon endless crawler treads. The two support strands may be wound ,upon storage reels mounted on such end section and driven by hydraulic motors.

One of the problems attendant upon tramming such end section in accordance with the increase 'in length of in the cables just prior to the tramming operation. suchchanges in tension imposes dilferent loads on the support: strands, and the change in deformation throughout the length of the strands may be such as to cause tipping of the standards. By way of example, the change in deformation in a ten foot length of strand upon a change in tension of from 1200 pounds to 2400 pounds may be as much as 0.4", and in a conveyor 1000 long the total deformation may amount to 40".

If the support strands are anchored atop the support standards, some of the standards, particularly at the end of the conveyor line, must be requiredto move through the 40" distance. In View of the fact that the mine floor is irregular, the standards do not slide upon the floor freely but may instead be caused to tip, eventually to fall, if not watched closely. y

With the foregoing considerationsjin mind it is an important object of this invention to provide apparatus for paying out and reeling in the flexible strands, such paying out and reeling in being within desired limits of tension at all times.

Another object is to provide automatic control appa ratus which will insure that the tension obtainingfin thestrands at the start of a tramming operation will be maintained all during such tramming operation.

It is a further object to measure the tension in the support strands, and to apply such measured value to a' control circuit which will reel in or pay out only at the predetermined measured value.

Other object and important features. of the invention will be apparent from a study of the specification following taken with the drawings which together show a preferred embodiment of the invention, and what is now considered to be the best mode of. practicing the principles thereof; Other embodimentsmay be suggested to those having the benefit of the teachings herein, and such other embodiments are intended to be reserved especially as they fall within the purview and spirit of the subjoined claims.

In the drawings:

Fig. l is a side elevational view of the tail section of an extensible and retractible conveyor having the improvernents accordingto the present invention embodied therein; 1

Fig. 1a isa side elevational view of a complete extensible conveyor, having a tail as seen in Fig. l, and having the improvements according to the present invention embodied therein;

Fig. 2 is an enlarged fragmentary view of- Fig. 1 showing apparatus forcontrolling'the paying out of support strand for. the conveyor seen in Fig. 1 when the tension reaches. an upper limit;

Fig. 3 is a view similar to Fig. 2, but showing how the mechanism of Fig. 2 operates to wind in the support strand when the tension therein reaches a lower limit;

Fig. 4 is a longitudinal sectional view taken through a control valve employed with the apparatus of Figs. 2 and3', said control valve being operable to control the windingin and paying out of support strands;

Fig. 5' is a plan view of an alternate form of apparatus for controlling'the tension in the support strands; and

Fig. 6 is a-schematic diagram of a hydraulic control circuit for the tramming motor of the tail section seen in Fig. 1, and showing a connection from such circuit to the apparatus of Figs. 2 and 3 to maintain the tension in the supportstrands at the value obtaining at the start of the tramming operation.

Referring now to Figs. 1 and la of'the drawings, the present invention is embodied in anextensible conveyor indicated generally by the reference numeral 10.- The conveyor includes atail section- 11 and a head .section 11a mounted for movement respectively uponcrawler treads 12 and 12a. The tail section 11. forms a means for reversing an-orbitally movable conveyor belt having a conveying reach 13- and a return reach 14.

The conveying reach 13. is supported upon spaced flexible strands16, and these strands are spanned; by idler roller assemblies indicated generally by the reference numeral 17, the idler roller assemblies 17 being spaced throughout the length of the conveyor reach 13 for support thereof. Support-standards 15 are disposed at intervals throughout the length of the support strands 16 for support thereof. A belt storage loop 20, disposed in the return reach 14 adjacent the head section 11a, is arranged to be lengthened or shortened according to the required length of the conveyor 10. Details of construction of such a conveyor and the strand supporting arrangement are shown in more detail in Craggs et a1. U. S. Patent No. 2,773,257.

As seen in Fig. 1a, the support strands 16 are fixed at a location remote from the tail section, in this case by mounting them on the head section 11a. As seen in Fig. 1, the support strands 16 are reeved' around a pair of snubbing sheaves 18 and 19. Thesnubbing sheaves 18 and 19 turn upon stub shafts 21 and 22 respectively whichextend from a support plate 23 pivoting about a center corresponding to the stub shaft 22 and supported thereon. Shaft 22 extends from a side frame of the tail section 11.

Each support strand 16 is stored upon a storage reel 26 mounted upona shaft 27 extending from side frame As seen in Fig. 1, the control of the tramming ofthe tail section 11 is by a pair of forward and reverse tramming valves 31 (see also Fig. 6) which control the direction of operation of a crawler tread drive motor 30.

The tension in the support strands 16 varies in accordance with the load on the conveying reach. While the tension is kept within desired limits the variation in tension is not critical excepting for times when the tail section 11 is trammed in one direction or another. It is important at such times to maintain the tension in the strands 16 at the value then obtaining at the start of the tramming operation. Failure to maintain the tension in the strands results in shifting of the strand supports 15.

Means are accordingly provided to maintain the tension of the support strands within desired limits, but more important, to maintain the tension at the value then obtaining at the start of the tramming operation for the reasons above.

Structure functioning for both of said purposes will now be described.

The support 23 for the snubbing sheaves 18 and 19 is limited in its movement by means of a spring 35 having one end abutting a stop 32 which can be held in an adjusted position by means of adjusting screws 33. The other end of the spring 35 abuts an extension34 of the support 23, and it will be seen that the spring 35 restrains the free movement of the support 23 in a counterclockwise direction by bucking the tension in strand 16. Thus, it will be seen that the spring-biased support 23 comprises a strand tension responsive member which is movable in accordance with the tension in the strand.

Increase in tension upon a strand 16 in excess of a predetermined amount causes the corresponding support 23 to rock in a counterclockwise direction, thereby actuating the valve 29to control the direction of operation of motor 28, as will now be described.

Control'of the valve 29 is had by an actuating rod 36 which is resiliently connected to the support,23 through a spring 37 bottomed at an end 38 of a cylindrical spring housing 39. The other end of the spring 37 is provided with a-washer 41, the end of the rod' 36 being threaded to receive a nut 42 hearing against washer 41,which normally is in abutting relationship with a stop flange 43 within the cylindrical housing 39- The other end portion 44 of the cylindrical housing 39 is pivotally connected at 46 to-the support 23. The load in the spring 37f thus enables the support 23 to movev the actuating rod 36, at the same time being available to absorb impact and protect the control mechanism from destructive shocks, for instance in case, of sudden breakage of the strand 16 or overloading beyond a predetermined maximum limit.

The actuating rod 36 has a clevis 47 which is pivotally connected at 48 to an intermediate portion of an operating lever 49. One end of the movable operating or control lever 49'is pivotally connected at 51 to a longitudinally shiftable abutment rod 52, the rod 52 passing through guides 53 and 54 which are mounted on the tail side plate 24-. As will be seen, the rod 52 comprises part of a memory system for storing information relating to the strand tension.

When the tail section 11 is stationary, the tension in the strand 16 may vary within limits as determined by the loading on the conveying reach 13. Increase in strand tension causes the tension responsive support 23 to rock in -acounterclockwise direction against the compression in the spring 35. Such movement of the support 23 will cause the lever 49 to rock about one or the other of pivots 51 and 56 depending on their respective resistances to movement as will be hereinafter explained. The pivot pin at 56 is attached to a clevis 57 extending from a spool valve member 58 of the control valve 29. As will be seen, the valve spool 58 is urged to a centered position by centering spring means which ,afr'ords more resistance to movement of pivot 56 than is afforded the pivot 51 when the rod'52.is free to slide. This occurs when the tail is stationary so that movement of the tension responsive member 23 is transmitted through the actuating rod 36 into pivoting of the control lever 49 about pin 56 while freely sliding the memory rod 52 within its guides 53, 54.

The movable memory abutment rod 52 carries a pair of adjustable stops 59 and 61 threaded thereon. The abutment rod 52 under the conditions described is thus free to shift to a high limit position, with the adjustable stop 59 against the fixed guide 53 as shown in Fig. 2 to mark a high limit of tension in the support strand 16; or to a low limit position with the adjustable stop 61 engaging the guide 53 to mark a low limit as shown in Fig. 3.

Shifting of the support 23 in a counterclockwise direction after the high limit stop 59 engages the guide 53 causes the lever 49 to rock about the pivot point 51 and to move the valve spool 58 to the left to control the flow of fluid to the motor 28 and cause the storage reel 26 to pay cable therefrom.

Conversely, see Fig. 3, movement of the support 23 in a clockwise direction first causes the low limit stop 61 to engage the fixed guide 53, the lever 49 thereafter rocking about the pivot point 51 and causing movement of the valve spool 58 to the right, to direct fluid to the motor 28 in an opposite direction to cause the storage reel 26 to Wind cable thereon until the tension is restored to a value within the desired range predetermined between the stops 59 and 61.

Referring now to Fig. 4 of the drawings, the control valve 29 is connected in a circuit which includes a pump 62 which receives fluid from a tank 63 by means of a line 64. The output from the pump 62 is connected in a pressure line 66 having a pressure relief valve 67 therein, excess of pressure being relieved by a line 68 to the tank 63.

The control valve 29 includes a cylindrical bore 71 therein. The valve spool 58 is slidable within the bore 71,.and has an end land 72, intermediate lands 73, 74 and 76, the land 76 being flanked by an opposite end land 77. Lands 72 and 73 are spaced by a portion 78 of reduced diameter. Lands 73 and 74 are spaced by a portion 79 of reduced diameter. Lands 74 and 76 are likewise spaced by a portion 81 of reduced diameter, and lands 76 and 77 are spaced by a portion 82 of reduced diameter.

The valve body 69 has a pressure port 83 which is nora valve body 69 having mally lapped by the land 74. Lands 84,. 85, 86 and 87 define a tank port 88, a working port 89 and a port 91 to one side of the pressure port 83. Lands 92, 93, 94 and 96 define a tank port 97, a working port 98 and a port 99 to the other side of the pressure port 83.

A cylindrical bore 101 within the spool 58 is intersected by cross bores 102 and 103 to cause communication between the tank port 97 and tank port 88. r

The left end of valve spool 58 is encircled by a spring 104 bearing against a shoulder 106 on the valve spool 58 and having its other end bearing against an end cap 107 fastened as by cap screws 69, the end cap 107 enclosing one end of the valve spool 58. I

The opposite end of the valve spool 58 passes through .an end cap 108 held tothe body 69 by cap screws 109. The valve spool 58 is maintained in the centered position shown in Fig. 4 by means of a washer 111 normally bearing against a shoulder 112 in the end cap' 108, the washer at times bearing against a C-ring 113 on the spool 58. Movement of the valve plunger 58 to the left is opposed by a spring 114 guided upon a sleeve 116 and abutting a washer 117 bearing against the right end of the valve body 69. The washer 117, during the movement of the valve spool 58 to the right, engages a shoulder 118 on the valve spool 58, and during movement of the valve spool 58 to the left the washer 111-is engaged by the C-ring 113. Movement in either direc tion is opposed by the centering spring 114. Thus it (not shown) to the valve bodyv will be seen that the spool member 58 comprises a por tion of the tension control means which is movable for selectively increasing and decreasing the tension in the corresponding strand.

Consider now the condition of Fig. 3, when the low limit stop 61 is in engagement with the guide 53, and the lever 49 is being rocked in a clockwise direction about pivot 51 to move the spool 58 to the light. This occurs when the tension in strand '16 is below a value predetermined by the setting of stop 61. Under such condition the lands 74 and 73 on the valve spool 58 will unlap their respective lands 86 and 87 in the valve body 69, to cause pressure fluid to flow from the pressure port 83 to the working' port 89,'working port 89 being connected by a Working line 90 to the fluid motor 28. During such movement land 93 will be unlapped and the exhaust side of the motor 28 will have its line 95 connected to the tank port 97, the spent fluid passing by way of the bore 101 through the spool 58 to be exhausted' at the tank port 88 which is connected by a line 100 to the tank 63.

. The motor 28will accordingly be driven in a direction to wind the strand 16 onto the reel 26, and restore the tension, while rocking the support 23 in a clockwise direction until the spool 58 returns to its centered (Fig. 4) position. j j I Conversely, when the high limit stop 59 engages the guide 53 and the support is continuing its counterclockwise movement by reason of tension in the strand 16 rising above the setting of the stop 59, the spool 58 will be shiftedto the left. This will cause lands 74 and 76 on the valve spool 58 to unlap the respective lands 96 and 94 in the valve body 69 supplying pressure fluid from the pump 62 to the working port 98 and thence to the line 95 to drive the motor 28 in the opposite direction and pay strand from thereel 26.

Under such condition line 90 becomes the exhaust line from the .motor 28, and land 72 on the valve spool 58 unlaps the land 85 in the valve body 69, the spent fluid returning to: the tank 63 by way of the tank port 88 andthe return line 100.

When the tension in strand 16 is thus reduced to a desired value the valve 29 will return to the centered position seen in Fig. 4.

If the tension rise is slow enough, the same correction may be made by simply shifting the spool 58 back to its centered (Fig. 4) position, normal leakage through the valve providing the strand payoff necessary to restore normal tension.

The conditions described for the shifting of the support 23 and the operation of the valve 29 are normal when the tail section 11 is.in a. stationary position. When the tail section is moved, it is important to maintain the same tension in the strand means 16, so as to prevent displacement, tipping, :or walking of the strand support standards 15. To this end, there is provided means for freezing or locking the memory abutment rod 52 in place at the beginning of tramming actuation. This serves to store information as to the initial value of the tension at the beginning of the tramming operation and provides a reference against which the tension may be automatically maintained at such initial value while tramming.

Referring now to Fig. 6 of the drawings, the control valve 31 controls tramming movement of the tail section by controlling operation of the crawler tread 12. A second valve 31 '(Fig. 1) may be used to control tramming of a crawler system on the other side of the tail section. The control valve is connected by a pressure line 121 to the output from the pump 62 which may be the same as that shown in Fig. 4. The valve 31 has a working line 122 connected to the crawler tread drive motor 30 for driving the crawler tread 12. The spent fluid from motor 30 returns to the valve 31 by means of a line124, and to the tank 63 by a tank return line 126."

A shuttle valve 127 is connected across the lines 122 and124', andis' provided with shuttle ball 128 therein which-shifts to one position or theother depending upon the direction of operationcalledfor in the-crawler tread drive motor 30. It will be understood that the valve 31 is of the reversible type, to cause the working lines 1 22- and 124' to alternate as exhaust lines from the motor 36 depending-upon its direction of operation.

In either direction of operation, the shuttle valve 127 operates to cause fluid to be delivered to a line- 129 to movea-piston 131*within a brakecylinder 132 mounted on the side plate 24; A pair of guides 133 is provided onthe end ofthe cylinder 132 through which the abutment rod 52 extends.- The piston'131, movable within the cylinder 132, has an extension 134 thereon which moves against the abutment rod 52' tocause it to be clamped tightly in theguides 133. Thus the rod 52 functions as a memory element capable of storing intelligence as to strand tension when therod is fixed in place by the locking means 131-132 in response to actuation of the tramming tread-means 12.

When the brake 132- is not actuated, the memory abutment rod 52 slides freely. Movement of the valve spool 58 is relatively less easy due to its centering; spring 114. Under such condition, shifting of the tension responsive support 23 pivots lever 49 about the pin 56.

Consider now the condition-of the support 23 as the tail section 11 advances to the right as seen in Fig. 1. Such tramming operation would tend to impose a greater amount of tension in the strand 16 causing the support 23 to shift in a counterclockwise direction as seen in Fig. 2, and cause the valve spool 58 to be rocked to the left, while rocking lever 49 to.the left about pivot 51, thereby causing the valve 29 to operate the motor 28 in a direction to drive the storage reel 26 in a direction to pay the strand 16 therefrom. It is believed evident that such paying out of the strand 16 from the drum 26 would cause the tension to be relieved, and the support 23 to rock in a clockwise direction to adopt a position corresponding to the tension then obtaining at the start of the tramming operation. It should be noted that the brake cylinder 132'is in the locked position as long as the tramming operation continues.

Conversely, when the trammingoperation is to the left, that is, retracting, thetension on the strand 16 will be relieved, causing the support 23 to rock in a clockwise direction. Under such condition the lever 49 will be rocked to the, right, about pivot 51, as seen in Fig. 3, and the valve spool 58 also shifted to the right to supply fluid to the motor 28 to drive it in a direction so as to causethe strand 16 to be wound upon the storage reel 26. Undersuch condition, the tension in the strand 16 will be'increased, and the support 23 will rock in a counterclockwise: direction untilj the control valve 29 is returnedto-its centered position seen in Fig. 4.

It is believed evidentthat the-strand in either case will be maintained at the tension then obtaining at the start of the tramming operation, be it ineither direction.

Referring now to Fig. of the drawings, there is shownanother embodiment of the-invention where the strand 16 has a greater amount of wrap about the snubbing sheaves 19 and 18. Here, the support 23 rocks in a horizontalplane about a shaft 136 mounted on'an extension 137 from the side frame 24' of the tail section 11. The rocking of the support 23 by tension in the strand is bucked by a spring 138 encircling a' rod 139 pivotally connected to the support 23 by pivot pin 141. One end of the spring bears against a washer 142 held onto the rod by a nut and the other end of the spring bears against the end of an abutment cup 143 carried by the side frame 24. It will beseenthat the spring 138 imposes restraint against movement of the support 23 in a'counterclockwise direction. 2

The support 23 in Fig. 5 has acam surface 144,.and a roller type cam follower 146 is urged by a spring 147 against the cam surface 144, the spring 147 being held betweena flange 148 on the follower 146 and a fixed abutment 149 extending'from the side frame 24; The cam follower 146 is cylindrical in form and'encloses the movable actuating rod 36, there being a washer 151- on the actuating rod 36 in engagement with a shoulder 153 on the cam follower'146, there also being a washer 154 on the actuating rod 36 hearing against the end of the follower 146 remote from the cam surface 144. A spring 156 is compressed betweenthe two washers 151 and 154.

it is believed apparent that the movement of the actuating rod 36 is had through the spring 156 which acts as an elastic compression member. Spring 156 dampens minute movements of the actuating rod'36, so as to prevent minor movements of the valve spool 58 and consequent hunting operation of the fluid motor 28. It also protects the control mechanism against suddenly applied loads as does the spring 37 in the previously described embodiment.

While the invention has been described in terms of a number of embodiments thereof, its scope is intendedto be limited only by the claims here appended. It will be understood that the present invention is applicable to controlling tension in strand means whether single or plural strands are employed. In the embodiment illustrated, two strands 16 are employed and the tension control means may be duplicated for both of them where desired.

I claim as my invention:

1. In an extensible strand sideframe conveyor, a tail' section, belt-supporting strand means carried by and extending from said tail section and being fixed at a location remote from said tail section, tramming means for moving said tail section to vary the effective length of said conveyor, and strand tensioning means effective to apply a tension in said strand means, the improvement comprising: means for actuating said tramming means to move said tail section; sensing means for sensing the initial value of tension in said strand means at the beginning of actuation of said tramming means; and control means for said strand tensioning means operable in response to said sensing means to maintain the tension at said initial value during actuation of said tramming means.

2. In an extensible strand sideframe conveyor, a tail section, belt-supporting strand means carried by and extendingfrom said tail section and being fixed at a location remote from said tail section, tramming means for moving said tail section to vary the effective length of said conveyor, and strand tensioning means effective to apply a tension in said strand means, the improvement comprising: means for actuating said tramming means to move said tail section; means including a memory device operable responsive to actuation of said tramming means to sense the initial value of strand tension at the beginning. of the tramming actuation and effective to maintain the strand tension at said initial value during said tramming actuation.

3. In an extensible strand sideframe conveyor, a tail section, belt-supporting strand means carried by and extending from said tail section and being fixed at a location remote from said tail section, tramming means for moving said tail section to vary the effective length of saidconveyor, and strand tensioning means effective to apply a tension in said strand means, the improvement comprising: means for actuating said tramming means to move said tail section; means for sensing the initial strand means tension at the beginning. of actuation of said tramming means; memory means effective to store information as to the value of said initial tension; and means controlled by said memory means for maintaining the strand means at said initial tension during the actuation of said tramming means.

4. In an extensible strand sideframe conveyor, a. tail section, belt-supportingstrand means carriedby and extendingfr'om said-tail section and being fixedata locae tion, remote'from said tail section, tramming means for moving said tail section to vary the efiective length of said conveyor, and strand tensioning means effective to apply a tension in said strand means, the improvement comprising: means for actuating said tramming means to move said tail section; said strand tensioning means effective to maintain the tension in said strand means in a range between predetermined high and low limits; means operable responsive to actuation of said tramming means to sense an intermediate value of strand tension which is intermediate said high and low limits; and means, including apparatus for storing information as to strand tension, elfective to rnaintainthe strand tension at said intermediate value during said tramming actuation.

5. In an extensible strand sideframe conveyor, a tail section, belt-supportingstrand means carried by and extending from said tail section and being fixed at a location remote from said tail section, tramming means for moving said tail section to vary the eifective length of said conveyor, and strand tensioning means effective to apply a tension in said strand means, the improvement comprising: means for actuating said tramming means to move said tail section; means for sensing the tension in the strand means including a sensing element movable over a range corresponding to a range of tensions; means operable responsive to actuation of said tramming means to hold said sensing element in a fixed position corresponding to the initial value of the tension in the strand means at the beginning of said tramming actuation; and control means for controlling the strand tensioning means at a tension corresponding to said fixed position of the sensing element, and control means being effective to maintain the strand means tensioned at said initial value during said tramming actuation.

6. In a flexible strand sideframe conveyor; a movable end section having extending therefrom a flexible strand adapted to support a conveyor belt; tramming means actuatable for moving said end section; strand tensioning means efiFective to apply a tension in said strand means; a strand tension responsive member movably mounted on said end section; tension control means including a member movable between positions for selectively increasing and decreasing the tension in said strand, means urging said tension control member to a neutral position; a movable memory element; said tension control member and memory element being interconnected by a lever; said tension responsive member being connected to said lever and effective to move said lever to move either the tension control member or memory element,

whichever affords the least resistance; and locking means operable to fix the position of said memory element responsive to actuation of said tramming means; whereby, during movement of said end section, strand tension is maintained at its value at the beginning of such movement.

7. In a flexible strand sideframe conveyor, the combination of claim 6' including means for limiting the movement of said memory element corresponding to preselected upper and lower limits of strand tension.

8. In a flexible strand sideframe conveyor, the combination of claim 6 in which said tension control member is connected to said lever by an elastic shock-absorbing link.

9. In a flexible strand sideframe conveyor, the combination of claim 6' in which end portions of said lever are pivotally connected respectively to said tension control member and memory element and an intermediate portion of said lever is connected to said tension responsive member.

10. In an extensible strand sideframe conveyor, a tail section, belt-supporting strand means carried by and extending from said tail section and being fixed at a location remote from said tail section, tramming means actuatable for moving said tail section to vary the effective length .pf said conveyor, and strand tensioning means elfective iii to apply atension in said strand means, the improvement comprising: a movable tension sensing element; stop means for stopping movement of said sensing element at the ends of a range defined by selected high and low tension limits; auxiliary stop means operable to stop said sensing element within said range; control means for said strand tensioning means eflective in response to the stopping of said sensing element to maintain tension in said strand means at a value corresponding to its stopped position; and means operable responsive to actuation of said tramming means to operate saidauxiliary stop means to stop said sensing element in position corresponding to the initial tension in said strand means at the beginning of tramming actuation; whereby said initial tension is maintained in said strand means during said n-ammng actuation. t

11. In an extensible strand sideframe conveyor, a tail section, belt-supporting strand means carried by and ex opposite direction to buck the tension in the strand means;

stop means for stopping movement of said sensing element at the ends of a range defined by selected high and low tension limits; auxiliary stop means operable to stop said sensing element within said range; control means for said strand tensioning means effective in response to the stopping of said sensing element to maintain tension in said strand means at a value corresponding to its stopped position; and means operable responsive to actuation of said tramming means to operate said auxiliary stop means to stop said sensing element in position corresponding to the initial tension in said strand means at the beginning of tramming actuation; whereby said initial tension is maintained in said strand means during said tramming actuation.

12. In an extensible strand sideframe conveyor, a tail section, belt-supporting strand means carried by and extending from said tail section and being fixed at a location remote from said tail ,section, tramming means actuatable for moving said tail section to vary the eifective length of said conveyor and strand tensioning means effective to apply a tension in said strand means, the improvement comprising: a movable tension sensing element; said sensing element being movable over a range corresponding to a range of tension in said strand means; stop means operable to stop said sensing element against movement within its said range; control means for said strand tensioning means eifective in response to the stopping of said sensing element to maintain tension in said strand means at a value corresponding to its stopped position; and means, operable responsive to actuation of said tramming means, to operate said stop means to stop said sensing element in position corresponding to the initial tension in said strand means at the beginning of tramming actuation; whereby said initial tension is maintained in said strand means during said tramming actuation.

13. In an extensible strand sideframe conveyor, a tail section, belt-supporting strand means carried by and extending from said tail section and being fixed at a location remote from said tail section, tramming means actuatable for moving said tail section to vary the eifective length of said conveyor and strand tensioning means effective to apply a tension in said strand means, the improvement comprising: a movable member connected to said strand means for movement responsive to change in tension in said strand means; said member having oppositely disposed tension sensing and tension control portions, either portion being movable about the other portion, responsive to change in tension in said strand means,

1 1 depending on whichever afiords the least resistance; means normally enabling the tension sensing portion to move about the tension control portion; meanjsiop'erable responsive to actuation of said tramming'means for looking said tension sensing portion in position at the,start' of the tramming actuation enabling the tensioncont'rol portion to move about said sensing portion; said tension control portion being movable, While the sensing portion is locked, between positions for selectively increasing and decreasing the tension in the strand; whereby, during tramming actuation, the tension in the strand means is automatically maintained at its value at the beginning of said tramming actuation.

14. In an extensible strand sideframe conveyor, a tail section; belt-supporting strand means carried by and extending from said tail section and being fixed ata location remote from said tail section, tramming means actuatable for moving said tail section to vary the effective length of said conveyor and strandtensioning means effective to apply a tension in said strand means, the improvement comprising: a tension responsive member movable in accordance with the tension in said strand means; a control lever having a portion intermediate the ends connected to said tension responsive member; a tension control member connected to oneend of said lever and being movable between positions for selectively increasing and decreasing the tension in said strand means, and biasing means urging said tension control member to a neutral position; brake means operable on the other end of said lever responsive to actuation of said tram ming means; whereby, during tramming actuation of said tail section, strand tension is maintained at its value at the beginning of such tramming actuation.

No references cited.

Images