US3902760A

US3902760A - Pavement grooving machine having plural, independently movable grooving heads

Info

Publication number: US3902760A
Application number: US476462A
Authority: US
Inventors: Stafford M Ellis
Original assignee: Engelhard Minerals and Chemicals Corp
Current assignee: Unicorn Industries Ltd; Engelhard Minerals and Chemicals Corp
Priority date: 1972-06-09
Filing date: 1974-06-05
Publication date: 1975-09-02
Anticipated expiration: 1992-09-02

Abstract

A pavement grooving machine which has a plurality of grooving heads for cutting grooves in the surface of a pavement, wherein each grooving head can be separately elevated and lowered independently of the others. Each grooving head is connected by a linkage to the grooving machine, which permits both pivotal and linear vertical movement caused by a main jack connected between the grooving head and the machine. During raising and lowering operation of the main jack, a supplemental jack applies a horizontal force component in opposition to a horizontal component of the force exerted by the main jack, and prevents the grooving head pivoting out of substantially parallel relation to the pavement. Each grooving head, at its opposed ends, is connected with two metering wheels which provide for selective control of the depth of cut by the grooving head during grooving operations.

Description

[111 3,902,760 [451 Sept. 2, 1975 PAVEMENT GROOVING MACHINE HAVING PLURAL, INDEPENDENTLY MOVABLE GROOVING HEADS [75] Inventor: Stafford M. Ellis, Bearsted, England [73] Assignee; Engelhard Minerals & Chemicals Corporation, Murray Hill, NJ.

[22] Filed: June 5, 1974 [2]] Appl. No.1 476,462

Related US. Application Data [63] Continuation-in-part of Ser. No. 261,360, June 9, 1972, and a continuation-in-part of Ser. No. 476,461,

Staab 299/39 Staab 299/39 Primary Examiner' -Ernest R. Purser ABSTRACT A pavement grooving machine which has a plurality of grooving heads for cutting grooves in the surface of a pavement, wherein each grooving head can be separately elevated and lowered independently of the others. Each grooving head is connected by a linkage to the grooving machine, which permits both pivotal and linear vertical movement caused by a main jack connected between the grooving head and the machine. During raising and lowering operation of the main jack, a supplemental jack applies a horizontal force component in opposition to a horizontal component of the force exerted by the main jack, and prevents the grooving head pivoting out of substantially parallel relation to the pavement. Each grooving head, at its opposed ends, is connected with two metering wheels which provide for selective control of the depth of cut by the grooving head during grooving operations.

20 Claims, 10 Drawing Figures PATENTED 2|975 3,902,760

SHEET 1. 0F 3 140 Z x f ECCi/V.

49 [Wm/MS PATENTEB SEP 2 I975 SHEET 2 BF 3 PATENTEB 2 975 sum 3 o 3 PAVEMENT GROOVING MACHINE HAVING PLURAL, INDEPENDENTLY MOVABLE GROOVING HEADS RELATED APPLICATIONS This application is a continuation-in-part of applicants pending application for a Pavement Grooving Machine, U.S. Ser. No. 261,360, filed June 9, 1972. It is also a continuation-in-part of applicants copending concurrently filed application for a Pavement Grooving Machine Including a Cutting Blade Guidance System," US. Ser. No. 476,461, filed June 5, 1974.

BACKGROUND OF THE INVENTION This invention relates to a pavement grooving machine of the type including a grooving head having a plurality of spaced rotary cutting blades mounted on a drive shaft, which engage the pavement surface to cut parallel grooves therein. In particular, the pavement grooving machine of the present invention is provided with a plurality of separate grooving heads disposed in transversely spaced relation across the pavement surface, wherein each of the grooving heads may be separately elevated and lowered and may be individually adjusted for depth of cut.

To improve the traction of vehicle wheels on rainsoaked pavements, such as roads and aircraft runways, it is known to cut shallow, parallel grooves in the pavemcnt to promote escape of water between the pavement surface and the vehicle wheels traveling thereon. Grooving of the pavement is commonly performed by specialized pavement grooving machines. Such pavemcnt grooving machines have generally, heretofore, had grooving heads of lesser length than the twelve foot width which is a common width for lanes on freeways in the United States. Accordingly, it has been necessary to groove each lane in two or more separate passes. Because it would be more efficient to groove the entire line in a single pass, applicant has devised a pavement grooving machine having a plurality of separate groov ing heads which collectively extend across the entire twelve foot width of a freeway lane. Such machine is disclosed in applicants earlier aboveidentified applica tions, the disclosure of which is herein incorporated by reference.

In performing grooving operations, it is very critical to accurately control the depth of the grooves cut. If the grooves cut are too shallow, then the contracting specification will not be satisfied and the job may have to be done over again. On the other hand, if the grooves are cut too deep, that involves an excessive removal of material with attendant increase in fuel and labor costs, blade wear, and extension of grooving time, which may make the project unprofitable. The problem of accurate depth control is particularly important when grooving across a substantial width, such as a twelve foot lane, where there may be substantial variations in local pavement contour across the width of the lane. Utilizing, for example, a single twelve-foot grooving head, the depth of cut might be too great in some areas and too shallow in others. It is therefore desirable to utilize several relatively shorter length grooving heads, each of which can be separately adjusted to more closely follow the contour of the pavement across its width.

Because a grooving head and its associated framework usually comprise a massive weight, somewhere between one and two tons each, problems can arise in raising and lowering each grooving head into engage- I ment with the pavement surface, particularly where the elevating jacks apply the lifting force at one end of the supporting frame for the grooving head only. With such arrangement, care must be taken that, when the grooving head is moved into the joperative position, it does not droop downwardly towards its outer end which could cause deeper grooves to be cut at the outer end of the grooving head than at its inner end. It is therefore necessary to devise structure for moving the grooving head vertically between its operative and raised positions in which, during raising and lowering, it moves in substantially parallel relation to the pavement.

On some grooving jobs, it may be a requirement to have a greater groove depth in some areas (e.g., adjacent the edge of a freeway where the surface may be badly worn), than in others. A depth of cut system for individual grooving heads should be adjustable to meet this requirement.

Where plural grooving heads are utilized, it is common to employ pulley and belt drive trains to transfer driving motion from engines mounted on the grooving machine to the grooving heads. Problems can arise if the raising and lowering of individual grooving heads changes the center-to-center distance over which individual drive belts operate. Increase in the effective center-to-center length between driving and driven pulleys can overtension the belts, while substantial reduction in the center-to-center distance can cause belts to come off the pulleys.

Another factor that is significant in grooving high ways, in particular freeways, is the ability to be able to reduce the effective grooving width of the grooving machine when two freeway lanes merge into each other. This would be a particularly difficult problem utilizing a twelve-foot grooving machine having only a single twelve-foot grooving head.

SUMMARY OF THE INVENTION A pavement grooving machine, according to the present invention, is intended to obviate problems of the type discussed in the foregoing description.

In particular, the pavement grooving machine of the present invention includes a vehicle movable in a longitudinal direction along a pavement which is to have grooves cut in its surface. The vehicle is provided with mounting structure for supporting a plurality of individual, separately driven and separately elevatable grooving heads. In the preferred embodiment, the invention utilizes four three-foot grooving heads transversely spaced to provide a twelve-foot grooving pass.

Each of the grooving heads forms part of an associated one of a number of grooving assemblies which are separately and independently operable for raising and lowering each associated grooving head into and out of engagement with the pavement. Thus, by placing some of the grooving heads in a raised condition, the effective grooving width of the machine during a single pass can be progressively reduced. The ability to change the effective grooving width of the machine is a valuable feature when grooving highways which are relatively narrow or in conducting grooving operations involving merging traffic lanes where the width of the lane is being progressively reduced. Because the grooving machine of the present invention has a plurality of heads, each of which follows its underlying region of the pavement closely, groove depth across the width of the pavement can be much more closely maintained to a uniform value than would be possible with a single grooving head extending the entire width of the pavement. Further, each grooving head can be separately and individually adjusted to control the depth of the grooves cut by that particular head. Thus, the pavement can be grooved to a different depth in a particular region (e.g., adjacent a worn edge), if that is desired.

Each grooving assembly includes a pillar-like mounting structure fixedly connected to the vehicle and a frame extending transversely to the direction positioned adjacent the mounting structure. The frame supports the associated grooving head which comprises a horizontal, transverse driven shaft rotatably mounted in the frame to which are fixedly secured a plurality of parallel rotary grooving cutters. A generally horizontal linkage extends between the lower end of the mounting structure and a first point of connection to the frame to connect the frame with the mounting structure for both linear and pivoting motion in a generally vertical plane. The frame is elevated and lowered by a main jack extending at an upward, transverse inclination between the upper end of the mounting structure and an attachment member secured to an upper portion of the frame. The main jack exerts both horizontal and vertical components of force on the frame, when it is operated. Connected between the frame and the mounting structure is a generally horizontal supplemental jack which operates only when the frame is being moved vertically by the main jack. The supplemental jack applies a force to the frame in opposite direction to the horizontal component of force exerted by the main jack. The supplemental jack counterbalances the main force to a sufficient extent to prevent the driven shaft from being pivoted out of substantially parallel relation to the pavement, as the cutters are moved into and out of engagement with the pavement. Thus, by this structure, the rotary cutting head is maintained parallel to the pavement as it is raised and lowered, thereby avoiding the problem of having a greater depth of cut at one end of the cutting head than at the other.

To enable the depth of cut of each cutting head to be controlled to a predetermined value, each frame is provided with two metering wheels positioned closely adjacent the transverse ends of the grooving head. Each metering wheel has a freely rotatable circular peripheral portion which rotates about an axis of rotation eccentrically offset from the axis of rotation of the associated driven shaft. The lowermost point of the metering wheel contacts the pavement at a level spaced above the lowest peripheral point on the grooving cutters mounted on the driven shaft, thus controlling the depth of cut. Because the metering wheels are located at opposite ends of the grooving head and in close proximity to it, they cause the grooving head to follow the local contour of the pavement very closely, in distinction to some prior systems utilizing metering wheels in which the metering wheels have been spaced an appreciable distance in advance of the grooving cutters. In such prior systems local variations in pavement contour between the point of contact of the metering wheel and the point at which the grooving cutters were, could cause variations in groove depth.

Selective control of the depth of cut of each grooving head can be achieved by varying the degree of eccentricity by which the radius of rotation of the metering wheel is offset from the radius of rotation of the driven shaft, utilizing a worm gear and adjusting screw.

Each grooving head has a driven pulley attached to the associated driven shaft. A motor driven shaft mounted on the adjacent structure rotates about an axis parallel to the driven shaft. A drive belt extends between the pulleys to rotate the driven shaft. The previously mentioned linkage supporting the frame for elevation includes a pivot pin mounted along a longitudinal axis at a vertical inclination which is parallel to a line joining the centers of rotation of the drive and driven pulleys. Thus, as the frame is elevated vertically in a direction perpendicular to the axis of the pivot pin, it moves along a path which coincides with a limited are substantially concentric with the axis of rotation of the drive pulley. As a result, there is no significant change in length imposed on the drive pulley during raising and lowering of the grooving head so that belt tension is not varied.

Each mounting structure supports two of the grooving assemblies and is positioned transversely between them. The connections of the linkage structures and of the main and supplemental jacks of each grooving assembly, to the mounting structure are symmetrically positioned on opposite sides of the mounting structure, so that the horizontal forces exerted by each grooving assembly on the mounting structure are substantially counterbalanced.

The foregoing, and other advantages of the invention, are more fully set forth in the subsequent detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS A pavement grooving machine in accordance with the preferred embodiment of the invention, is illustrated in the accompanying drawings which are briefly described as follows:

FIG. 1 is a side view of a portion of a grooving machine constructed in accordance with the preferred embodiment of the invention, showing two of four grooving heads, which form part of the invention, in an operative position engaging a pavement surface to cut grooves therein;

FIG. 2 is a simplified view of a portion of a metering wheel for controlling the depth of cut of an associated one of the grooving heads;

FIG. 3 is a cross-sectional view of a portion of the metering Wheel shown in FIG. 2;

FIG. 3a is a fragmentary view of a portion of the metering wheel shown in FIG. 2, shown in a different position of adjustment;

FIG. 4 is a view from the front end of the portion of the pavement grooving machine shown in FIG. 1, showing all four grooving heads in their operative positions engaging the pavement;

FIG. 5 is a cross-sectional front view of a mounting structure forming a part of the invention shown in FIG.

FIG. 6 is a cross-sectional side view of the mounting structure shown in FIG. 5, taken along the lines 66 therein;

FIG. 7 is a front view, partially in cross-section, of one of the grooving heads shown in FIG. 4;

FIG. 8 is a simplified diagram illustrating the points of connection of an elevating and lowering system utilized in the invention disclosed in the foregoing figures, to raise and lower each grooving head; and

clined to the horizontal in a rearward and downward disposition.

Pivotally mounted on each pivot pin 62 adjacent the interior surfaces of each of the supporting walls 58 and 60, is a pair of spaced transversely extending, opposed links 64 eXtending generally horizontally towards the adjacent inner vertical end walls 34 of the adjacent one of the grooving heads 14 and 16. Suitable plain bearings 66 (FIG. 9) are interposed between the links 64, and the pivot pins 62. The links 64 held apart by a hollow spacing member 68 encircling the associated one of the pivot pins 62 extending between the two links to maintain their positioning.

At its opposite end, each link 64 extends into an aligned one of a plurality of slots 70 (FIG. 9) extending through the inner vertical end walls 34 of the frames 30 associated with the left and right grooving heads 14 and 16. In each adjacent end wall 34 is mounted apair of second pivot pins 72 extending across the openings 70 in spaced arallel relation to the adjacent first pivot pin 62. The second pivot pins 72 extend through aligned bores in the ends of the links 64, in which suitable plain bearings 74 are positioned.

The linkage provided by the links 64 enables each of the grooving heads 14-20 to move linearly and pivotally in a generally vertical plane relative to the associated one of the mounting structures 52 and 53.

Raising and lowering of the front grooving heads 14 and 16 is accomplished by two main hydraulic jacks 80 which are attached to a pillar 82. The pillar 82 is secured to the base 54 at its lower end and, at its upper end, is provided with an enlarged head portion 84 in the general configuration of a downwardly facing, truncated arrowhead. The main jacks 8 are pivotally connected at their cylinder ends to the mounting head 84 at connection points 85 and extend divergently downwardly towards the respective grooving heads 14 and 16. The lower, piston end of each main jack 8 0 is connected to one of two attachment members 86 secured to the upper walls 32 of the grooving heads 14 and' l6, respectively, at a point of pivotal connection 87. Extension of the main jacks under the influence of hydraulic pressure applied to the upper side of each jack piston causes a lowering of theas'sociated grooving head,

while application of hydraulic pressure to the lower side of the jack piston causes the associated grooving head to be raised. r

During retraction of each of the main jacks, the jack exerts a vertically upward component of the force tend- 1 ing to raise the associated grooving head verticall upward, and also a horizontal component of force acting towards the mounting structure. The lifting force of the main jack tends to exert a torque about the associated linkage acting in a direction to tilt the outer end of the grooving head upwardly outoi parallel relation to the pavement. Conversely, during extension of each main jack, the jack exerts a main force having a downward component which tends to move the associated grooving assembly vertically downward and a horizontal component of force acting away from the mountin structure. The lowering force of the main jack then exerts a torque about the associated linkage tending to de ress the outer end of the groovingasseinbl downwardly out of substantiall parallel'relation to the pavement.

allel relation to the pavement during periods when the 8 grooving head is being raised or lowered, each of the grooving heads is also acted upon by an associated one of a plurality of supplemental jacks 100. Considering the forward grooving heads 14 and 16, two associated supplemental jacks 100 are connected at their cylinder ends to a pivotal attachement 104 extending longitudinally within the pillar 82. The supplemental jacks 100 extend horizontally outwardly in aligned relation through openings in the pillar. At their piston ends, the supplemental jacks 100 are pivotally attached to the reviously mentioned attachment members 86 at another point of pivotal connection 88. The point of connection 88 of each supplemental jack is spaced above the point of connection 87 of the associated main jack at a location positioned more transversely inwardly towards the mounting structure and aligned generally vertically with the associated second pivot pins 72.

Each supplemental jack 100 is operated only during raising and lowering of the associated one of the grooving heads 14-20 by the associated one of the main jacks 80. During operation of the supplemental jack, it exerts a generally horizontal force acting in an opposite direction to the horizontal component of the main force exerred by the associated main jack. Thus, as shown by the White arrows in FIG. 8, when the associated main jack is exerting a raising force, the supplemental jack exerts a force acting away from the mounting structure, while, as shown by the black arrows, when the associated main jaek'is exerting a lowering force, the supplemental jack acts in a direction generally towards the mounting-structure. The magnitude of the force exerted by the supplemental jack is such that it exerts a torque about the associated linkage which effectively counterbalances the torque caused by the main jack about the linkage. As a result the associated grooving head is subjected to an essentially vertical raising force without pivoting out of substantially arallel relation to the pavement.

This arrangement is particularly important when setting down the grooving cutters because, if the grooving head sets down in a tilted inclination, it will tend to maintain its'tilt, thereby cutting shallow grooves at one and of the grooving head and relatively deeper grooves at the other. On raising, it is also important to avoid tilt ing the grooving head as it is elevated, particularly where partial raising is contemplated. After raising or lowering of the grooving head has been completed, hy-

draulic pressure is removed from either side of the associated supplemental jack 100 which is allowed to float. However during grooving operations, down pressure is maintained by the associated main jack on the grooving head to resist any tendency of the tototing cutters to climb out of the grooves which they are cutting.

As can be most readily seen from FIG. 5, the points of attachment of the left forward grooving head 14 to the mounting structure, comprising the links 74, the supplemental jack 100, and the main jack 80, are symmetrically and oppositely positioned in their horizontal aspects in relation to the corresponding connections of the right forward grooving head 16. As a result of this positioning, the horizontal force components exerted on the mounting structure by one of the grooving heads 14 and 16 are substantially counterbalanced by the horizontal components of force exerted by the other grooving head.

To provide power to drive the rotary grooving heads, a suitably powerful engine 110 (FIGS. 1 and 4) is mounted on the lower platform 8. The engine 110 has a rotary output shaft 112 adjacent one end of the platform, on which are mounted four primary driving pulleys 114 (FIG. 4). Two of the primary driving pulleys 114 are connected by belt drives 116 (FIG. 1) to two intermediate driven pulleys 118 mounted on the left hand end of a forward transverse drive shaft 120 connected by conventional bearings and associated structure to the underside of the platform 8. At the opposite, right end of the driven shaft 120 (FIG. 4) are secured two secondary driving pulleys 122. The secondary driving pulleys 122 are connected to the driven pulleys 44 of the left and right, front grooving heads 14 and 16 by belt drives 124 (FIGS. 1 and 6). By this arrangement, the driving force of the engine 110 is imparted to the front two grooving heads.

A similar arrangement (FIG. 1) involving drive belts 125, intermediate driven pulleys 126 mounted on a rear drive shaft 128, additional secondary driving pulleys (not shown) mounted on the rear drive shaft 128 positioned between the rear grooving assemblies 18 and and additional drive belts 129 coupling the secondary driving pulleys to the driven pulleys 44 associated with the rear grooving heads imparts the output of the engine to the rear grooving heads 18 and 20.

It is advantageous that, as the individual grooving assemblies are raised and lowered relative to their associated mounting structures, the center-to-center distances between the secondary driving pulleys and their associated driven pulleys should not change substantially, otherwise the drive belts can either become overtensioned or too slack with the latter possibility they may even come off the pulleys. It is for this reason that the pivot pins 62 supporting the grooving assemblies for movement relative to the mounting structure, are inclined to the vertical.

Referring to FIG. 6 which has particular reference to the left forward grooving head 14, it will be seen that the inclination of the main pivot pin 62 is parallel to a line joining the centers of the associated secondary driving pulley 122 and driven pulley 44. As the frame is raised, it travels upwardly in a direction perpendicular to the main pivot pin 62. Over a limited range of movement, this path can be seen to coincide substantially with an arcuate path concentric with the center of rotation of the secondary driving pulley 122. Thus, raising and lowering motion of the grooving head 14 over the limited range of movement which is required in practical use moves the drive pulley 44 in a path which is effectively concentric with the axis of rotation of the secondary driving pulley 122. As a result the length of the drive belt is not changed and the possibility that the drive belts will become either overstressed or unnecessarily slack during extremes of raising and lowering motion are substantially avoided. A similar arrangement is provided for each of the other grooving heads 16, 18 and 20.

Another important aspect of the invention resides in the provision of structure for accurately and independently controlling the depth of cut of'each grooving head to a preselected value. Considering the right, forward grooving head 16 shown in FIG. 7, it can be seen that at the opposite ends of the rotary grooving head, there are two

metering wheels

136 and 138, each positioned between the grooving head and the adjacent one of the end walls 34 and 36. Each metering wheel contacts the ground at its lowest point at a point of contact which is spaced above the lowest point to which the grooving cutters 49 extend downwardly. By setting both

metering wheels

136 and 138 to a particular spacing relative to the bottoms of the cutters 49, the grooving head 16 can be arranged to groove to a preselected depth because the cutters can sink no further into the pavement after the point at which the metering wheels rest on the pavement.

The metering wheel 136 (FIGS. 2, 3, 3a and 7) includes a circular bearing member 140. The previously mentioned stationary hub 42 secured to the end wall 34 has a circular outer periphery concentric with the driven shaft 38. The bearing member 140 has a circular outer periphery 142 and a circular opening 144 eccentrically offset from the center of the outer periphery 142. The opening 144 slidably receives the circular hub 42 and can be selectively rotated relative to it. To effect rotation of the bearing member 140 on the hub 42, a worm gear 145 is fixedly mounted on one end of the bearing member 140 in concentric relation to the opening 144. The worm gear is engaged by a threaded screw 146 rotatably mounted on the adjacent vertical end wall 34 of the frame. A hand wheel 148 (FIG. 6) fixed at the opposite end of the shaft 146 may be turned to rotate the worm gear and thereby vary the eccentric positioning of the'lowest portion of the bearing member 140 in relation to the bottom of the grooving cutters. Rotatably mounted on the outer periphery 142 of the bearing 140 is a concentric outer wheel constituting the metering wheel 136. The metering wheel 136 is mounted for free wheeling motion on the circular outer periphery 142 of the bearing member 140 so that, when it is in contact with the ground and the vehicle advances, the metering wheel is free to rotate. The metering wheel 138 at the other end of the grooving head is supported by a similar bearing member and associated structure mounted on the previously mentioned hub 44 secured to the opposite end wall 36, and functions in the same way.

It will be appreciated that by appropriate setting of the hand wheels 148 at each end of the grooving head, the associated

metering wheels

136 and 138 may be adjusted to the same, pre-selected value to insure a uniform depth of cut in a predetermined amount along the full length of the grooving head. Alternatively, it would be possible to set the

metering wheels

136 and 138 to different values if a deliberate variation in groove depth was desired along thelength of the grooving head. It will also be understood that each metering head may be individually selected for a particular depth of cut independently of the other grooving heads. Thus, where it is necessary to cut to a greater depth in a particular region of the pavement being grooved (e.g., along the edge of a worn highway). such individual adjustment can readily be achieved with the present invention.

The lower platform 8 also supports outrider wheels 152 (FIG. 4) which are positioned in spaced relation above the surface of the pavement when the frames 30 of the grooving heads 14-20 are in the operative position with the various metering wheels in contact with the ground. The wheels 152 come into play when the grooving machine is used to groove a roadway having a superelevation, i.e., an unusually steep transverse inclination. Operating on such a superelevation, the weight of the module and grooving heads might tend to tilt the platform 8 out of parallel relation to the pavement surface, leading to uneven grooving depth across the pavement. Under such circumstances the outrider wheels 152 are engaged with the pavement to ensure that the platform 8 is maintained parallel to the pavement, while all other aspects of the grooving machine function is the same way as earlier described.

Although the invention has been described with refcrence to a preferred embodiment, it will be appreciated by those skilled in the art that many variations, deletions, modifications and other substitutions may be made which will fall within the spirit of the invention defined by the appended claims.

I claim:

1. A grooving assembly for attachment to a vehicle movable along a pavement in a longitudinal direction relative to the pavement, the grooving assembly comprising:

mounting structure fixedly secured to the vehicle;

a frame extending transversely of the direction of movement of the vehicle;

a grooving head, including,

a transversely extending driven shaft rotatably mounted in said frame,

a plurality of transversely spaced, rotary grooving cutters fixedly mounted on said shaft and rotated thereby, said frame in an operative position thereof supporting said driven shaft in substantially parallel relation to the pavement with said cutters in engagement with the pavement to cut grooves therein;

link means connected to said mounting structure and to a lower portion of said frame at a first point of connection thereto, said link means supporting said frame for both pivoting and linear motion in a generally vertical plane;

selectively operable, main force applying means connected to said mounting structure and to said frame at a second point of connection thereto, said main force applying means applying force to said frame for vertical motion thereof between the operative position and another, raised position in which said frame supports said cutters out of engagement with the pavement; and

supplemental force applying means connected to said mounting structure and to said frame at a third point of connection thereto, said supplemental force applying means, during vertical motion of said frame by said main force applying means, applying force to said frame in a direction to maintain said driven shaft along the full length thereof in substantially parallel relation to the pavement during vertical movement of said cutters relative to the pavement.

2. A grooving assembly as defined in claim 1, wherein said main force applying means applies a main force having upward and horizontal force components on said frame to raise said frame from the operative to the raised position and wherein said supplemental force applying means applies a generally horizontal, supplemental force upon said frame in an opposite direction to the horizontal force component exerted by said main force applying means, said supplemental force counterbalancing said main force to a sufficient extent to prevent said driven shaft from being pivoted out of substantially parallel relation to the pavement as said cutters are raised out of engagement with the pavement.

3. A grooving assembly as defined in claim 1, wherein said main force applying means applies a main force having horizontal and downward force components on said frame to lower said frame from the raised to the operative position, and wherein said supplemental force applying means applies a generally horizontal supplemental force in an opposite direction to the horizontal force component applied by said main force applying means, said supplemental force counterbalancing said main force to a sufficient extent to prevent pivoting of said driven shaft out of substantially parallel relation to the pavement as said cutters are lowered into engagement with the pavement.

4. A grooving assembly as defined in claim 1, wherein said main force applying means in an upward direction of operation exerts a main force having upward and horizontal force components on said frame to raise said frame from the operative to the raised position, said main force applying means in a downward direction of operation exerting downward and horizontal force components on said frame to move said frame from the raised to the operative position, and wherein said supplemental force applying means applies a generally horizontal supplemental force acting in an opposite direction to the horizontal force component exerted by said main force applying means, said supplemental force counterbalancing said main force to a sufficient extent to prevent pivoting of said driven shaft out of substantially parallel relation to the pavement when said cutters are being raised from, and lowered into, engagement with the pavement.

5. A grooving assembly as defined in claim 1, wherein said first, second and third points of connection on said frame are positioned at the corners of a triangle, said third point of connection being positioned above and in general vertical alignment with said first point of connection, said second point of connection being spaced transversely outwardly of said first and second points of connection spaced vertically therebetween and closer to said third point of connection than to said first point of connection.

6. A grooving assembly as defined in claim 1, wherein said main force applying means and said supplemental force applying means comprise linearly extensible main and supplemental jacks, respectively; said main jack being connected at its upper end to said mounting structure extending at a downward and transversely outward inclination towards second point of connection to said frame, said supplemental jack extending in generally horizontal disposition between said mounting structure and third point of connection to said frame.

7. A grooving assembly as defined in claim 6, wherein said second point of connection at which said main jack is connected to said frame is spaced transversely outwardly from said third point of connection at which supplemental jack is connected to said frame.

8. A grooving assembly as defined in claim 1, wherein said frame further includes,

at least one vertically extending end wall positioned in spaced adjacent relation to said mounting structure;

said link means further including,

a generally horizontal, longitudinally extending first pivot pin mounted in said mounting structurc,

at least one link connected at one end thereof to said pivot pin for vertical pivoting motion relative to said mounting structure, said link extending in a generally horizontal direction toward said end wall of said frame,

a second pivot pin mounted in said end wall ex tending in spaced parallel relation to said first pivot pin, said link, at an opposite end thereof, being connected to said second pivot pin for vertical pivoting motion.

9. A grooving assembly as defined in claim 8, wherein said link means further includes,

two said links disposed in spaced parallel relation secured to opposite longitudinal ends of said first pivot pin; and

two said second pivot pins mounted in said end wall in axially aligned relation, said links being connected to said second pivot pins.

10. A grooving assembly as defined in claim 8, wherein said first and second pivot pins are inclined at a vertical inclination to the horizontal.

11. A grooving assembly as defined in claim 8, wherein said main force applying means and said supplemental force applying means comprise linearly extensible main and supplemental jacks respectively, and wherein the grooving assembly further includes:

an attachment member fixedly secured to an upper surface of said frame, said attachment member including,

a pivotal point of attachment to one end of said main jack constituting said second point of connection, said main jack extending upwardly from said attachment member at a transverse inclination and being pivotally connected at its other end to said mounting structure; and

another pivotal attachment to one end of said supplemental jack constituting said third point of connection, said supplemental jack extending generally horizontally in a transverse direction from said attachment member and being pivotally connected at its other end to said mounting structure.

12. A grooving assembly as defined in claim 1, wherein said main force maintains a substantially constant downward force on said frame in the operative position thereof during grooving operations performed by said grooving head, said supplemental force applying means during grooving operations applying sub stantially no force in either direction to said frame.

13. A grooving assembly as defined in claim 1, further including,

two rotatable metering wheels carried by said frame positioned in close proximity to the opposite ends of said grooving head, said metering wheels each having a point of contact with the pavement which is spaced vertically above the lowermost point on the peripheries of said grooving cutters, whereby the depth of cut is controlled.

14. A grooving assembly as defined in claim 13, further including,

means associated with each of said metering wheels for selectively varying the vertical spacing between the point at which the metering wheel contacts the pavement and the lowermost peripheral point on the grooving cutters thereby enabling selective variation of the depth of cut caused by said grooving cutters.

15. A grooving assembly as defined in claim 6, wherein said mounting structure includes,

a vertically extending pillar fixedly secured to the vehicle in spaced adjacent relation to said frame, said pillar including,

a longitudinally extending pivot pin adjacent the lower end thereof, said link means being secured to said pivot pin for vertical pivoting motion,

a pivotal attachment connecting said pillar to said adjacent end of said main jack, and

another pivotal attachment connecting said pillar to the adjacent end of said supplemental jack.

16. A multiple grooving unit for attachment to a vehicle movable along a pavement in a longitudinal direction relative to the pavement, the multiple grooving unit comprising, I

at least two transversely spaced grooving assemblies,

each said grooving assembly including,

a frame extending transversely of the direction of movement of the vehicle,

a rotary grooving head, including,

a transversely extending driven shaft rotatably mounted in said frame, plurality of transversely spaced, rotary grooving cutters fixedly mounted on said shaft and rotated thereby, said frame in an operative position thereof supporting said driven shaft in substantially parallel relation to the pavement with said cutters in engagement therewith to cut grooves in the pavement; mounting structure fixedly connected to the vehicle in adjacent relation to said frames of said two grooving assemblies, two connecting means separately connecting each of said frames to said mounting structure for motion relative thereto in a generally vertical plane, each said connecting means including,

link means connected to said mounting structure and to a lower portion of the associated one of said frames at a first point of connection thereto, said link means supporting said frame for both pivoting and linear motion in a general vertical plane;

two force applying means separately connecting each of said frames to said mounting structure for separate vertical motion of each said frame relative to the pavement between the operative position and a raised position in which the associated said cutters are out of engagement with the pavement, each said force applying means being selectively and independently operable to enable each said frame to be separately raised and lowered whereby operation with either or both grooving heads may be selected, each said force applying means including,

a selectively operable, main jack connected to said mounting structure and to the associated one of said frames at a second point of connection thereto, said main jack applying force to said associated frame for vertical motion thereof between the operative position and the raised position; and

a supplemental jack connected to said mounting structure and to said associated frame at a third point of connection thereto, said supplemental jack, during vertical movement of said frame by said main jack, applying force to said associated frame in a direction to maintain the associated one of said driven shafts along the full length thereof in substantially parallel relation to the pavement during vertical movement of said cutters relative to the pavement.

17. A multiple grooving unit as defined in claim 16, wherein said mounting structure further includes,

a vertical pillar fixedly secured to the chassis positioned transversely between said two grooving assemblies,

two lower pivotal attachments mounted at the lower end of said pillar, said lower pivotal attachment supporting said link means of said frames of said two grooving assemblies for vertical pivoting motion;

two intermediate pivotal attachments to said pillar spaced above said lower pivotal attachment, said supplemental jacks of said two grooving assemblies being connected to said pivotal attachment in horizontally aligned relation, and

two upper pivotal attachments at an upper end of said pillar connected to said main jacks of said two grooving assemblies, said main jacks extending divergently down towards said frames, said lower, intermediate and upper pivotal attachment being so positioned that the horizontal transverse forces on said pillar by one of said grooving assemblies are substantially counterbalanced by opposite horizontal forces exerted on said pillar by the other of said grooving assemblies.

18. A pavement grooving machine for cutting a plurality of parallel longitudinally extending grooves in a pavement, the pavement grooving machine comprising,

a steerable, driven vehicle adapted for motion along the pavement in a direction longitudinally thereof,

at least two transversely spaced grooving assemblies,

each said grooving assembly including,

a frame extending transversely of the direction of movement of said vehicle, a rotary grooving head, including,

a transversely extending driven shaft rotatably mounted on said frame,

a plurality of transversely spaced, rotary grooving cutters fixedly mounted on said shaft and rotated thereby, said frame in an operative position thereof supporting said driven shaft in substantially parallel relation to the pavement with said cutters in engagement therewith to cut grooves in the pavement;

mounting structure fixedly connected to said vehicle in adjacent relation to said frames of said two grooving assemblies,

two connecting means separately connecting each of said frames to said mounting structure for motion relative thereto in a generally vertical plane, each said connecting means including, link means connected to said mounting structure and to a lower portion of the associated one of said frames at a first point of connection thereto, said link means supporting said frame for both pivoting and linear motion in a general vertical plane;

two force applying means separately connecting each of said frames to said mounting structure for separate vertical motion of each said frame relative to the pavement between the operative position and a raised position in which the associated said cutters are out of engagement with the pavement, each said force applying means being selectively and independently operable, to enable each said frame to be separately raised and lowered whereby operation with either or both grooving heads may be selected, each said force applying means includ- 5 ng,

a supplemental jack connected to said mounting structure and to said associated frame at a third point of connection thereto, said supplemental jack, during vertical movement of said frames by said main jack, applying force to said associated frame in a direction to maintain the associated one of said driven shafts along the full length thereof in substantially parallel relation to the pavement during vertical movement of said cutters relative to the pavement.

19. A grooving assembly for attachment to a vehicle movable along a pavement in a longitudinal direction relative to the pavement, the grooving assembly comprising,

a frame connected with the vehicle extending in a direction transversely relative thereto, said frame including, two transversely spaced vertical end walls,

a grooving head including,

a transversely extending driven shaft rotatably supported at its opposite ends by said vertical end walls of said frame,

a plurality of transversely spaced rotary grooving cutters secured to said shaft and rotatably driven thereby to cut grooves in the pavement when said frame is in an operative position supporting said cutters in cutting engagement with the pavement;

two metering wheels carried by said frame positioned in close proximity to the opposite transverse ends of said grooving head, each said metering wheel including,

a non-rotating circular hub concentric with said shaft extending therearound, said ,hub fixedly secured to the adjacent one of said frame end walls,

a bearing member having,

a circular outer periphery,

a circular opening through said bearing member, eccentrically offset from the center of said outer periphery, said opening receiving said hub in rotational relation thereto,

a circular worm gear fixedly mounted on said bearing member in concentric relation with said circular opening;

an adjustable screw rotatably mounted in said end wall engaging said worm gear, adjustment of said screw rotating said bearing member about said hub to a selected position; and circular outer wheel rotatably mounted about the circular outer periphery of said bearing member for free wheeling rotation thereon, said outer wheel contacting the ground and being rotated thereby on said bearing member as said vehicle travels along the pavement, adjustment of said screw selectively varying the position at which the lowermost point of said outer wheel contacts the pavement in relation to the lowermost point of said grooving cutters thereby selectively varying the depth of the cut.

20. A grooving assembly for attachment to a vehicle movable along a pavement in a longitudinal direction relative to the pavement, the grooving assembly comprising,

mounting structure fixedly secured to the vehicle,

a frame extending transversely relative to the direction of movement of the vehicle,

a grooving head including.

a driven shaft supported rotatably by said frame extending in a transverse direction,

a plurality of transversely spaced, rotary grooving cutters secured to said shaft driven thereby, said frame in an operative position thereof supporting said grooving cutters in cutting engagement with the pavement to cut grooves therein,

a drive train including,

a driven pulley concentrically secured to one end of said driven shaft,

a motor driven, driving pulley connected with said mounting structure for rotation about an axis parallel to said driven shaft,

a drive belt connecting said pulleys for imparting rotary motion to said driven shaft,

force applying means connected to said mounting structure and to said frame for selectively applying force to move said frame vertically between the operative position and a raised position in which said grooving cutters are out of engagement with the pavement, and

connecting structure movably connecting said frame to said mounting structure, including, a pivot pin extending longitudinally in said mounting structure,

at least one link connected at one of its ends to said pivot pin for vertical pivoting motion, said link at its opposite end being pivotally connected to said frame for pivoting motion about an axis parallel to said pivot pin; said pivot pin being disposed adjacent and in substantially parallel relation to a line joining the centers of said driving and driven pulleys so that as said driven shaft is raised and lowered by said main jack acting on said frame, it travels in a limited radial are which is substantially concentric with the axis of rotation of said driving pulley over the length of said are whereby no change in length is imposed on said drive belt.

Claims

1. A grooving assembly for attachment to a vehicle movable along a pavement in a longitudinal direction relative to the pavement, the grooving assembly comprising: mounting structure fixedly secured to the vehicle; a frame extending transversely of the direction of movement of the vehicle; a grooving head, including, a transversely extending driven shaft rotatably mounted in said frame, a plurality of transversely spaced, rotary grooving cutters fixedly mounted on said shaft and rotated thereby, said frame in an operative position thereof supporting said driven shaft in substantially parallel relation to the pavement with said cutters in engagement with the pavement to cut grooves therein; link means connected to said mounting structure and to a lower portion of said frame at a first point of connection thereto, said link means supporting said frame for both pivoting and linear motion in a generally vertical plane; selectively operable, main force applying means connected to said mounting structure and to said frame at a second point of connection thereto, said main force applying means applying force to said frame for vertical motion thereof between the operative position and another, raised position in which said frame supports said cutters out of engagement with the pavement; and supplemental force applying means connected to said mounting structure and to said frame at a third point of connection thereto, said supplemental force applying means, during vertical motion of said frame by said main force applying means, applying force to said frame in a direction to maintain said driven shaft along the full length thereof in substantially parallel relation to the pavement during vertical movement of said cutters relative to the pavement.

2. A grooving assembly as defined in claim 1, wherein said main force applying means applies a main force having upward and horizontal force components on said frame to raise said frame from the operative to the raised position and wherein said supplemental force applying means applies a generally horizontal, supplemental force upon said frame in an opposite direction to the horizontal force component exerted by said main force applying means, said supplemental force counter-balancing said main force to a sufficient extent to prevent said driven shaft from being pivoted out of substantially parallel relation to the pavement as said cutters are raised out of engagement with the pavement.

8. A grooving assembly as defined in claim 1, wherein said frame further includes, at least one vertically extending end wall positioned in spaced adjacent relation to said mounting structure; said link means further including, a generally horizontal, longitudinally extending first pivot pin mounted in said mounting structure, at least one link connected at one end thereof to said pivot pin for vertical pivoting motion relative to said mounting structure, said link extending in a generally horizontal direction toward said end wall of said frame, a second pivot pin mounted in said end wall extending in spaced parallel relation to said first pivot pin, said link, at an opposite end thereof, being connected to said second pivot pin for vertical pivoting motion.

9. A grooving assembly as defined in claim 8, wherein said link means further includes, two said links disposed in spaced parallel relation secured to opposite longitudinal ends of said first pivot pin; and two said second pivot pins mounted in said end wall in axially aligned relation, said links being connected to said second pivot pins.

11. A grooving assembly as defined in claim 8, wherein said main force applying means and said supplemental force applying means comprise linearly extensible main and supplemental jacks respectively, and wherein the grooving assembly further includes: an attachment member fixedly secured to an upper surface of said frame, said attachment member including, a pivotal point of attachment to one end of said main jack constituting said second point of connection, said main jack extending upwardly from said attachment member at a transverse inclination and being pivotally connected at its other end to said mounting structure; and another pivotal attachment to one end of said supplemental jack constituting said third point of connection, said supplemeNtal jack extending generally horizontally in a transverse direction from said attachment member and being pivotally connected at its other end to said mounting structure.

12. A grooving assembly as defined in claim 1, wherein said main force maintains a substantially constant downward force on said frame in the operative position thereof during grooving operations performed by said grooving head, said supplemental force applying means during grooving operations applying substantially no force in either direction to said frame.

13. A grooving assembly as defined in claim 1, further including, two rotatable metering wheels carried by said frame positioned in close proximity to the opposite ends of said grooving head, said metering wheels each having a point of contact with the pavement which is spaced vertically above the lowermost point on the peripheries of said grooving cutters, whereby the depth of cut is controlled.

14. A grooving assembly as defined in claim 13, further including, means associated with each of said metering wheels for selectively varying the vertical spacing between the point at which the metering wheel contacts the pavement and the lowermost peripheral point on the grooving cutters thereby enabling selective variation of the depth of cut caused by said grooving cutters.

15. A grooving assembly as defined in claim 6, wherein said mounting structure includes, a vertically extending pillar fixedly secured to the vehicle in spaced adjacent relation to said frame, said pillar including, a longitudinally extending pivot pin adjacent the lower end thereof, said link means being secured to said pivot pin for vertical pivoting motion, a pivotal attachment connecting said pillar to said adjacent end of said main jack, and another pivotal attachment connecting said pillar to the adjacent end of said supplemental jack.

16. A multiple grooving unit for attachment to a vehicle movable along a pavement in a longitudinal direction relative to the pavement, the multiple grooving unit comprising, at least two transversely spaced grooving assemblies, each said grooving assembly including, a frame extending transversely of the direction of movement of the vehicle, a rotary grooving head, including, a transversely extending driven shaft rotatably mounted in said frame, a plurality of transversely spaced, rotary grooving cutters fixedly mounted on said shaft and rotated thereby, said frame in an operative position thereof supporting said driven shaft in substantially parallel relation to the pavement with said cutters in engagement therewith to cut grooves in the pavement; mounting structure fixedly connected to the vehicle in adjacent relation to said frames of said two grooving assemblies, two connecting means separately connecting each of said frames to said mounting structure for motion relative thereto in a generally vertical plane, each said connecting means including, link means connected to said mounting structure and to a lower portion of the associated one of said frames at a first point of connection thereto, said link means supporting said frame for both pivoting and linear motion in a general vertical plane; two force applying means separately connecting each of said frames to said mounting structure for separate vertical motion of each said frame relative to the pavement between the operative position and a raised position in which the associated said cutters are out of engagement with the pavement, each said force applying means being selectively and independently operable to enable each said frame to be separately raised and lowered whereby operation with either or both grooving heads may be selected, each said force applying means including, a selectively operable, main jack connected to said mounting structure and to the associated one of said frames at a second point of connection thereto, said main jack applying force to said associated fraMe for vertical motion thereof between the operative position and the raised position; and a supplemental jack connected to said mounting structure and to said associated frame at a third point of connection thereto, said supplemental jack, during vertical movement of said frame by said main jack, applying force to said associated frame in a direction to maintain the associated one of said driven shafts along the full length thereof in substantially parallel relation to the pavement during vertical movement of said cutters relative to the pavement.

17. A multiple grooving unit as defined in claim 16, wherein said mounting structure further includes, a vertical pillar fixedly secured to the chassis positioned transversely between said two grooving assemblies, two lower pivotal attachments mounted at the lower end of said pillar, said lower pivotal attachment supporting said link means of said frames of said two grooving assemblies for vertical pivoting motion; two intermediate pivotal attachments to said pillar spaced above said lower pivotal attachment, said supplemental jacks of said two grooving assemblies being connected to said pivotal attachment in horizontally aligned relation, and two upper pivotal attachments at an upper end of said pillar connected to said main jacks of said two grooving assemblies, said main jacks extending divergently down towards said frames, said lower, intermediate and upper pivotal attachment being so positioned that the horizontal transverse forces on said pillar by one of said grooving assemblies are substantially counterbalanced by opposite horizontal forces exerted on said pillar by the other of said grooving assemblies.

18. A pavement grooving machine for cutting a plurality of parallel longitudinally extending grooves in a pavement, the pavement grooving machine comprising, a steerable, driven vehicle adapted for motion along the pavement in a direction longitudinally thereof, at least two transversely spaced grooving assemblies, each said grooving assembly including, a frame extending transversely of the direction of movement of said vehicle, a rotary grooving head, including, a transversely extending driven shaft rotatably mounted on said frame, a plurality of transversely spaced, rotary grooving cutters fixedly mounted on said shaft and rotated thereby, said frame in an operative position thereof supporting said driven shaft in substantially parallel relation to the pavement with said cutters in engagement therewith to cut grooves in the pavement; mounting structure fixedly connected to said vehicle in adjacent relation to said frames of said two grooving assemblies, two connecting means separately connecting each of said frames to said mounting structure for motion relative thereto in a generally vertical plane, each said connecting means including, link means connected to said mounting structure and to a lower portion of the associated one of said frames at a first point of connection thereto, said link means supporting said frame for both pivoting and linear motion in a general vertical plane; two force applying means separately connecting each of said frames to said mounting structure for separate vertical motion of each said frame relative to the pavement between the operative position and a raised position in which the associated said cutters are out of engagement with the pavement, each said force applying means being selectively and independently operable, to enable each said frame to be separately raised and lowered whereby operation with either or both grooving heads may be selected, each said force applying means including, a selectively operable, main jack connected to said mounting structure and to the associated one of said frames at a second point of connection thereto, said main jack applying force to said associated frame for vertical motion thereof between the operative position and the raised position; and A supplemental jack connected to said mounting structure and to said associated frame at a third point of connection thereto, said supplemental jack, during vertical movement of said frames by said main jack, applying force to said associated frame in a direction to maintain the associated one of said driven shafts along the full length thereof in substantially parallel relation to the pavement during vertical movement of said cutters relative to the pavement.

19. A grooving assembly for attachment to a vehicle movable along a pavement in a longitudinal direction relative to the pavement, the grooving assembly comprising, a frame connected with the vehicle extending in a direction transversely relative thereto, said frame including, two transversely spaced vertical end walls, a grooving head including, a transversely extending driven shaft rotatably supported at its opposite ends by said vertical end walls of said frame, a plurality of transversely spaced rotary grooving cutters secured to said shaft and rotatably driven thereby to cut grooves in the pavement when said frame is in an operative position supporting said cutters in cutting engagement with the pavement; two metering wheels carried by said frame positioned in close proximity to the opposite transverse ends of said grooving head, each said metering wheel including, a non-rotating circular hub concentric with said shaft extending therearound, said hub fixedly secured to the adjacent one of said frame end walls, a bearing member having, a circular outer periphery, a circular opening through said bearing member, eccentrically offset from the center of said outer periphery, said opening receiving said hub in rotational relation thereto, a circular worm gear fixedly mounted on said bearing member in concentric relation with said circular opening; an adjustable screw rotatably mounted in said end wall engaging said worm gear, adjustment of said screw rotating said bearing member about said hub to a selected position; and a circular outer wheel rotatably mounted about the circular outer periphery of said bearing member for free wheeling rotation thereon, said outer wheel contacting the ground and being rotated thereby on said bearing member as said vehicle travels along the pavement, adjustment of said screw selectively varying the position at which the lowermost point of said outer wheel contacts the pavement in relation to the lowermost point of said grooving cutters thereby selectively varying the depth of the cut.

20. A grooving assembly for attachment to a vehicle movable along a pavement in a longitudinal direction relative to the pavement, the grooving assembly comprising, mounting structure fixedly secured to the vehicle, a frame extending transversely relative to the direction of movement of the vehicle, a grooving head including, a driven shaft supported rotatably by said frame extending in a transverse direction, a plurality of transversely spaced, rotary grooving cutters secured to said shaft driven thereby, said frame in an operative position thereof supporting said grooving cutters in cutting engagement with the pavement to cut grooves therein, a drive train including, a driven pulley concentrically secured to one end of said driven shaft, a motor driven, driving pulley connected with said mounting structure for rotation about an axis parallel to said driven shaft, a drive belt connecting said pulleys for imparting rotary motion to said driven shaft, force applying means connected to said mounting structure and to said frame for selectively applying force to move said frame vertically between the operative position and a raised position in which said grooving cutters are out of engagement with the pavement, and connecting structure movably connecting said frame to said mounting structure, including, a pivot pin extending longitudinally in said mounting structure, at least one link connected at one of its ends to said pivot pin for vertical pivoting motion, said link at its opposite end being pivotally connected to said frame for pivoting motion about an axis parallel to said pivot pin; said pivot pin being disposed adjacent and in substantially parallel relation to a line joining the centers of said driving and driven pulleys so that as said driven shaft is raised and lowered by said main jack acting on said frame, it travels in a limited radial arc which is substantially concentric with the axis of rotation of said driving pulley over the length of said arc whereby no change in length is imposed on said drive belt.