US3354489A

US3354489A - Sweeper attachment for lift trucks

Info

Publication number: US3354489A
Application number: US534764A
Authority: US
Inventors: Stanley V Ehrlich
Original assignee: STANLEY WESTERN CORP
Current assignee: STANLEY WESTERN CORP
Priority date: 1966-03-16
Filing date: 1966-03-16
Publication date: 1967-11-28
Anticipated expiration: 1984-11-28

Description

Nov. 28, 1967 s, v, EHRUCH 3,354,489

SWEEPER ATTACHMENT FOR LIFT TRUCKS Filed March 16, 1966 5 Sheets-Sheet 1 INVENTOR. STANLEY V. EHRLICH BY I BUCKHORN, BLORE, KLARQUIST & SPARKMAN ATTORNEYS Nov. 28, 1967 s. v. EHRLICH 3,354,489

SWEEPER ATTACHMENT FOR LIFT TRUCKS Filed March 16, 1966 5 Sheets-Sheet 2 '5 3 FIG. 2

INVENTOR.

I3 STANLEY v. EHRLICH FIG. 3 B

BUCKHORN, BLORE, KLARQUIST 8 SPARKMAN ATTORNEYS Nov. 28, 1967 s. v. EHRLICH SWEEPER ATTACHMENT FOR LIFT TRUCKS 3 Sheets-Sheet 5 Filed March 16, 1966 INVENTEDR. STANLEY V. EHRLICH BUCKHORN, BLORE, KLARQUIST 8.

SPARKMAN- ATTORNEYS United States Patent 3,354,489 SWEEPER ATTACHMENT FOR LIFT TRUCKS Stanley V. Ehrlich, Portland, 0reg., assignor to Stanley- Western Corporation, Portland, 0reg., a corporation of Oregon Filed Mar. 16, 1966, Ser. No. 534,764 Claims. (Cl. -83) ABSTRACT 0F THE DISCLOSURE This application discloses a sweeper attachment for a lift truck which includes a bin housing structure supported by ground wheels and a sweeper brush rotatably mounted within the housing. The brush is driven by the ground wheels through a friction drive which incorporates a one-way over-riding clutch to disengage the brush when the housing is moved in reverse. The bin housing is connected to the forks of a lift truck by a floating steering and suspension system which isolates the lift truck movements from the bin structure. When the bin structure is pushed forward by the truck, the brush sweeps dirt and debris forwardly into a bin. The materials collected in the bin can be dumped by elevating the entire structure on the forks of the lift truck and by releasing remotely from the operators seat a hinged bottom portion of the bin.

The present invention relates generally to lift truck attachments and more particularly to a sweeper attachment for lift trucks.

Heretofore, sweeper attachments for lift trucks have been self-powered and therefore relatively complex and costly. Other features of such prior sweepers have presented problems in their operation and maintenance. For example, most prior sweepers had bins which, when filled with dirt, had to be removed from the sweeper, carried to the dump and tipped on edge or upside down to empty them of dirt, and then reinstalled in the sweeper. Thus, the emptying operation was very time consuming. Most prior sweepers also had a complex brush construction which necessitated either costly replacement or factoryrebuilding of the entire brush assembly when the bristles became worn out, thereby requiring the operator to maintain at least two brush units on hand in the event one became worn out.

Accordingly, a primary object of the present invention is to provide a new and improved sweeper attachment for lift trucks which requires no prime mover. In accordance with this feature motive power is provided by the lift truck, and the sweeper brushes are powered through a friction drive from the sweeper wheels. A one way over-riding clutch means disengages the brush from the wheels of the sweeper when the lift truck is moved in reverse.

Another primary object is to provide a sweeper as aforesaid having a unique floating steering and suspension system which enables the sweeper to be pushed over uneven ground without affecting the sweeping action of the brushes.

Another important object is to provide a sweeper as aforesaid having a built-in bin with a bottom self-dumping feature which permits the bin to be emptied while in the sweeper and while the sweeper is suspended from the forks of a lift truck while the operator remains at his controls on the truck.

Still another object is to provide a sweeper attachment as aforesaid having a unique and simplified brush construction providing exceptional economy and ease in the manufacture, assembly and installation of the brush a sembly, and replacement of worn bristles at the job site with a minimum loss of operating time.

"ice

A further object is to provile a sweeper attachment having a universal mounting which adapts the sweeper for use on all makes and models of lift trucks.

Another object is to provide a sweeper attachment as aforesaid which is of simplified construction and which has a minimum number of moving parts providing simple and inexpensive construction and maintenance.

The above and other objects and advantages of the invention will become more apparent from the following detailed description which proceeds with reference to the accompanying drawings wherein:

FIG. 1 is a side elevational view of a lift truck and a sweeper attachment therefor in accordance with the present invention;

FIG. 2 is an enlarged side elevational view of the sweeper of FIG. 1 with one side wall of the sweeper housing removed to reveal the interior construction thereof;

FIG. 3 is a top plan view of the sweeper on approximately the same scale as FIG. 2 with a portion of the top broken away to reveal the interior construction;

FIG. 4 is a sectional view on a larger scale than FIG. 2 taken approximately along the line 44 of FIG. 2 and foreshortened from side to side;

FIG. 5 is a vertical sectional view taken along the line 55 of FIG. 4 showing the brush assembly details;

FIG. 6 is a sectional view taken along the line 66 of FIG. 3 showing the mounting means for clamping the sweeper to the forks of a lift truck; and

FIG. 7 is a sectional view taken along the line 77 of FIG. 4 showing the details of the one-way clutch for the brush drive of the invention.

General assembly With reference to the drawings, FIG. 1 indicates generally at 10 the outline of a lift truck having the usual upright mast 12 at its front end and a load carriage 14, including load lifting forks 16, movable along the mast by conventional means which are well known in the art. A sweeper attachment in accordance with the invention is indicated generally at 18 and includes a housing 20 having a front wall 22, rear wall 24, opposite side walls 26, a top wall 28, and a generally open bottom. The sweeper is supported on a floor surface by a single freely swiveling caster wheel 30 detachably mounted by a yoke 31 and bracket 32 to front wall 22 and by a pair of drive wheels 34 adjacent its rear end.

Steering and suspension assembly The sweeper is attached to forks 16 of the lift truck and steered through a unique floating suspension and steering means 36 which, with reference to FIGS. 2 and 3, includes a fork clamping assembly 33 rigidly attached to forks 16 and having a universal ball-and-socket connection it) with a gusset plate 42 joining together the rear ends of a pair of rigid steering rods 44. The steering rods diverge in a forward direction and are pivoted at their forward ends by ball-joint connections 46 to the forward end of top wall 28 at positions which are equidistant from, and on opposite sides of, the longitudinal median plane 48 of the sweeper.

As shown best in FIGS. 4 and 6 fork clamping assembly 38 is composed of a pair of

channel members

50, 51, one larger than the other, so that the flanges of lower member 51 fit snugly within the flanges of upper member 50. The flanges of each channel member have cut out end portions 52 forming jaws for receiving the two forks 16. The fork engaging surfaces of the channel members are provided with pads 54 of rubber or other resilient material having a high coeflicient of friction so as to provide a rigid, non-slip connection with the forks. A pair of clamping bolts 55 and mating nut members extend vertically through the intermediate portions of both channel members to exert a clamping pressure against forks 16. Ball-and-socket connection 40 may comprise a conventional trailer-type ball-and-socket hitch with the socket portion and its clamping lever welded to the front flange of upper channel member 50 and the ball bolted to gusset 42.

The so-called floating steering and suspension system just described permits relative turning movement of the sweeper relative to the lift truck about a vertical axis through ball joint 40 and also permits relative vertical movement between the lift truck and sweeper about a horizontal axis through ball joints 46 and about a horizontal axis through ball joint 49. Furthermore, relative twisting movement between the sweeper and lift truck can occur about a longitudinal axis through bali joint 40. Despite such a universal suspension, the sweeper can be steered in any desired direction and through exceedingly tight turns simply through steering of the lift truck in the desired turning direction. Thus, vertical and twisting movements of the sweeper and lift truck occur independently of one another permitting uninterrupted operation of the sweeper on rough and uneven surfaces, while pushing forces are transmitted from lift truck to sweeper through rods 44.

Bin assembly With reference again to FIG. 2, a dirt-retaining bin 60 partially encloses the bottom of the bin adjacent the forward end thereof and is hinged at 62 to front wall 22 of. the sweeper housing. The bin is normally maintained in a horizontal dirt-receiving disposition, wherein a rear lip portion 64 of the bin engages a flanged edge of an inclined bottom strip 66 of the housing, by a release cable 68. Cable 68 is attached at 69 to the rear of the bin, and extends vertically through a ninety degreeelbow 70 fixed to the top wall of the housing, from which it extends horizontally about a pulley 74. The opposite end of cable 68 is fixed to the midsection of the sweeper top by an anchor 71. Pulley 74 is attached to a pull ring 75 which is normally anchored in a slotted projection 76 at one side of the top of the housing to maintain the bin in its upper position.

The bin can be swung downwardly on hinge 62 to dump its contents simply by releasing pull ring 75 from its anchor to permit the bin to fall by its own weight to its lowered, dumping position as shown in dashed lines in FIG. 2. Of course, in order to permit bin 60 to swing to its vertical, dumping position, the entire sweeper unit must be elevated by raising forks 16 on mast 12. A pair of chain lengths 78 interconnect gusset plate 42 and the top wall of the housing, to limit upward pivoting movement of steering rods 44 about ball joints 46, thereby per mitt-ing suspension of the sweeper from lift forks 16.

Brush assembly Still referring to FIG. 2, a rotatable brush assembly 80 extends from side to side within the housing immediately in front of drive Wheels 34 and immediately rearwardly of bin 6?). Brush 80 is partially supported and positioned by drive wheels 34 so that the bristles thereof engage the floor surface over which the sweeper travels. The brushisrotated in a counterclockwise direction as viewed in FIG. 2, through a friction driving connection with wheels 34 so that dirt will be swept generally upwardly and forwardly into the bin. Bottom strip 66 of the housing serves as a guiding surface in this regard for directing dirt swept forwardly by the brush into the bin. A flexible rubber strip 82 is fastened at one edge to bottom strip 66 and extends downwardly into contact with the floor surface to prevent dirt from being swept forwardly beneath the bin. Similarly, flexible side strips 84 are fastened to the lower edges of the opposite side walls 26 of the housing and extend downwardly into contact with the floor surface to prevent dirt from being swept laterally from beneath the housing.

With reference now to FIGS. 4 and 5, the brush assembly includes six elongate removable brush sticks, or sections 86, each of which is composed of a rectangular wooden base 88 and bristles 90 extending from one surface only of the base. The six brush sticks are mounted between a pair of end plates 92. For this purpose, the inner face of each end plate is provided with an annular channel 94' formed by a peripheral rim 95' and an inner flange 96 of the plate for receiving an end portion of each brush base 38. Inner flange 96 has a series of twelve planar brush base-engaging surfaces 97 which, in outline, form a regular polygon so as to serve as a means for rigidly positioning the brush sticks at equally spaced intervals cirsumferentially of the end plates with the bristles of each brush stick extending in a radial direction with respect to the axis of the brush assembly.

Each end plate has an inwardly extending hub 98 having a central opening 99 therethrough for receiving a brush shaft 100 to which the end plates are fixed by setscrews 102. Brush shaft 100 is rotatably mounted at its opposite ends in flange bearings 103, which are fastened in turn to the lower ends of a pair of pivot arms 104 (FIG. 2) the upper ends of which are pivoted to the insides of opposite side walls 26 by pivot pins 105.

The brush sections are held in compression between opposite end plates 92 by three tension rods 106, which are fastened at each end by clevises 108to equally spaced projections 110 on the end. plates. Each tension rod is made in two sections, which are threaded at their abutting ends and joined together by a turnbuckle 112.

Brush drive assembly The means for transmitting rotary driving forces from drive wheels 34 to the brush assembly includes a pair of clutch drums 114 mounted on brush shaft 100, one

just outwardly of each end plate 92 and separated therefrom by a spacer 116. As shown in FIG. 2, the outer rim of each clutch drum has a serrated friction surface 118 which engages the rubber tire surface 120 of one of the pair of driving wheels 34 so that rotation of the driving wheels in one direction rotates the drum in the opposite direction.

Each drum has a central hub 122, shown in FIG. 7, with a central opening 124 through which brush shaft 100 extends. The hub is provided with three pockets 126 adjacent central opening 124 within each of which a cylindrical clutch pin 130 is seated. Each pocket has a greater width at one end than the diameter of the clutch pins, but tapers toward the opposite end, which has a width less than the diameter of the cluch pins. Thus, when the drum is rotated by the drivingwheels in one direction the pins will be wedged into the narrow ends of their respective pockets and thereby engage the drum and brush shaft to cause the latter to rotate. However, when the wheels rotate the drums in the opposite direction, the pins will tend to move toward the wide ends of the pockets and thereby disengage the drums from the shaft to permit free wheeling of the drums on such shaft. The pockets are all arranged with their narrow ends in. corresponding positions so that when the sweeper is pushed in a forward direction the brush shaft will become engaged by the clutch drums and thereby rotate the brush in a direction to sweep the dirt into the bin. When the sweeper is pulled in reverse, however, the drum becomes free wheeling so that the sweeper can be moved without rotating the brush. Otherwise, the brush would sweep in a direction away from the bin upon backing of the lift truck.

As shown in FIGS. 2 and 3, drive wheels 34 are rotatably mounted on an axle 132 which is fixed at its opposite ends to the lower ends of a pair of pivot arms 134. The upper ends of arms 134 are pivoted to opposite sides 26 of the housing by the same pivot pins which retain brush support arms 104. It will be apparent that both drive wheels 34 and brush 80 are free to pivot about the axis of pins 105, on their respective support arms, with the downward pivoting movement of brush 80 being limited only by its supporting engagement by drive wheels 34. Accordingly, the position of the drive wheels determine the level of the brush with respect to the floor surface.

An adjustment means is provided for determining the position of Wheels 34 and thus the setting of brush 80. Such means includes an adjusting bolt 136 which is mounted at its head end by a mounting bracket 138 to the rear wall of the housing, and threaded at its opposite end into a collar 14%) fastened to axle 132. The relative longitudinal position of drive wheels 34 with respect to the housing and level of brush 80 above the floor are determined by the length of bolt 136 which is threaded through collar 140. A lock nut 142 at the head end of the adjusting bolt serves to lock the bolt in a predetermined setting so as to maintain the brush at a constant level during operation.

Operation The sweeper attachment may be quickly andeasily attached to fork 16 of the lift truck merely by securely bolting clamping assembly 38 to the forks. With clamp 38 secured to the forks and ball hitch 40 connected to the steering rod assembly, the sweeper is ready for use. Sweeping is accomplished merely by pushing the sweeper attachment in the desired direction through normal steering of the lift truck. As long as the sweeper is pushed in a forward direction, brush 8%) will rotate and sweep dirt into bin 50. In backing the lift truck, the clutch drum disengages the brush shaft so that sweeping ceases.

When the bin is filled with debris, it can be emptied by a simple operation which involves first raising forks 16 on the mast of the lift truck and thereby suspending the entire sweeper unit from the forks above the floor surface. Then the lift truck is driven to the dump, with the sweeper intact, whereafter cable 68 is released to enable bin 60 to pivot downwardly and dump its contents. Thereafter, cable 68 is drawn upwardly to return the bin to its horizontal position and the cable ring reanchored.

When the bristles of one or more of the brush sticks become worn out, the same may be quickly and easily replaced on the job in a matter of minutes by loosening each of the three turnbuckles 112 of the tension rods so as to provide sufiicient slack to enable removal of the brush sticks from between the end plates and replacement of the same with new sticks. Thereafter, retightening of turnbuckles 112 secures the new brush sticks and places the brush assembly once again in operating condition.

Having described a preferred embodiment of my invention, it should be apparent to those skilled in the art that the same permits of modification in arrangement and detail. I claim as my invention all such modifications as come within the true spirit and scope of the appended claims.

I claim: I

1. A sweeper attachment for a lift truck comprising:

means defining a housing having an open bottom,

bin means partially closing said bottom,

steerable ground wheel means supporting one end of said housing,

ground-engaging drive wheel means su orting the opposite end of said housing,

rotatable brush means mounted within and extending between the opposite sides of said housing adjacent said bin in a position so that said brush means can engage the ground surface,

transmission means interconnecting said drive wheel means and said brush means for rotating said brush means in a direction for sweeping dirt from said ground surface into said bin upon movement of said housing in a predetermined direction,

and steerable connecting and suspension means on said housing for connecting said housig to the load carriage of said lift truck,

said connecting and suspension means including means for transmitting pushing and pulling forces from said lift truck to said housing but permitting independent relative vertical movement between said lift truck and said housing so that the brush means will remain in sweeping engagement with the ground surface when said sweeper is moved over uneven surfaces.

2. Apparatus according to claim 1 including clutch means for disengaging said transmission means upon movement of said housing in a direction opposite to said predetermined direction so that said sweeper can be moved in said opposite direction Without rotating said brush means.

3. Apparatus according to claim 1 wherein said connecting and suspension means includes means permitting relative twisting movement between said lift truck and said housing about a longitudinal axis of said truck and sweeper.

4. Apparatus according to claim 1 wherein said transmission means includes a friction drive means including a friction surface on said drive wheel means engaging a friction surface of said brush means so that rotation of said wheel means in one rotational direction rotates said brush means in the opposite rotational direction.

5. Apparatus according to claim 4 including adjustment means for adjusting said brush means vertically relative to said housing.

6. Apparatus according to claim 1 including means hinging one edge of said bin means to said housing, and means for selectively maintaining said bin means in a generally horizontal disposition for retaining debris within said housing and for releasing said bin downwardly about its hinge axis for dumping the contents thereof.

7. Apparatus according to claim 1 wherein said brush means includes a shaft extending between the opposite sides of said housing,

a pair of end plates mounted on said shaft adjacent the opposite sides of said housing,

a plurality of brush members each including an elongate base portion and a bristle portion extending outwardly from one surface of said base portion,

each of said end plates including means for retaining an end portion of each of said brush members so as to position said brush members at equally circumferentially spaced apart locations with respect to the axis of said shaft,

and adjustable tension means interconnecting said end plates for exerting an end clamping pressure on said brush members and thereby retaining said brush members in compression between said end plates.

8. A sweeper attachment for a lift truck comprising:

means defining a housing having an open bottom,

bin means partially closing said bottom,

steerable ground wheel means supporting one end of said housing,

ground-engaging drive wheel means supporting the opposite end of said housing,

said brush means including a shaft extending between the opposite sides of said housing,

a plurality of brush members, each including an elongated base portion and a bristle portion extending outwardly from one surface of said base portion,

each of said end plates including means for retaining an end portion of each of said brush members so as to position said brush members at equal-1y circumferentially spaced apart locations with respect to the axis of said shaft,

adjustable tension means interconnecting said end plates for exerting, an end clamping pressure on said brush members and thereby retaining said brush members in compression between said end plates,

said transmission means including, means fixing said end plates to said shaft,

means mounting said shaft for rotation about its axis,

and one-way clutch means on said shaft and in driving engagement with said drive wheel means, said clutch means drivingly engaging said shaft to rotate the same upon rotation of said clutch means in one direction, said clutch means disengaging said shaft to rotate freely thereoni upon rotation of said clutch means in the opposite direction.

9. A sweeper attachment for a lift truck comprising:

means defining a housing having an open bottom,

bin means partially closing said bottom,

steerable ground wheel means supporting one end of saidhousing,

ground-engaging drive wheel means supporting the opposite end of said housing,

rotatable brush means mounted within and extending between the opposite sides of said housing adjacent said bin means in a position so that said brush means can engage the ground surface,

transmission means interconnecting said drive wheel means and said 'brush means for rotating said brush means in a direction for sweeping dirt fromthe said groundsurface into said bin means upon movement of said housing in a predetermined direction,

steering and mounting meansfor connecting said housing to the forks of said lift truck, including: a rigid steering member, first connecting means hingedly con necting aforwardportion of said steering; member to a forward portion of said housing so as to permit vertical swinging movement of said steering member about a transverse'hinge axis,

second connecting means including means for rigidly clamping a rear portion of said steering member to said forks,

one of said connecting means permitting relative twisting movement between said forks and said housing about a longitudinal axis passing. through said one connecting means,

one of said connecting means permitting relative turning movement between said forks and said housing about a vertical axis through. said one connecting means, and the other of said connecting means restraining relative turning movement between said forks and said housing,

and means limiting the upward pivoting movement of said steering member relative to saidhousing so that said. housing. can be suspended from said. forks upon elevation of the forks.

10. Av sweeper attachment for a lift truck comprising:

means defining a housing having an open bottom,

bin means partially closing said bottom,

steerable ground wheel means supporting one end of said housing,

ground-engaging drive wheel means supporting the opposite end of said housing,

transmission. means interconnecting saiddrive wheelmeans and said 'brushmeans for rotating said brush means in a direction for sweeping, dirt from said ground surface into said bin means upon movement of said housing in a predetermined direction,

said steerable ground wheel means including asingle caster wheel support-ing the front end. of said housing and said drive wheel means including a pair of axlemounted driving wheels supporting the rear endof said housing,

said bin means including an upwardly opening bin structure hinged. at a front edge portion thereof to the front of said housing and extending rearwardly therefrom and pivotable about the hinge axis from a downwardly extending dumping position to a generally horizontally extending. debris collecting position,

said brush means being positioned immediately rearwardly adjacent saidbin means,

means including flexible means on said housing engaging the ground surface and defining aninclined surface sloping upwardly towards said bin structure from a position adjacentsaid brush means for guiding. dirt swept forwardly by said br-ush means into said bin structure,

said transmission means including frictional drive means on said drive wheel drivingly engaging a peripheral' friction surface of aclutch drum mounted on a brush-supporting shaft,

said clutch drum including; means engaging said brush shaft. to rotate the same; when said sweeper is moved forwardly,

said means disengaging, said: shaft topermit rotation of said drum withoutrotating; said brush means when said. sweeper is moved. in. reverse,

means mounting said axle of said drive wheels and said brush shaft for pivoting movement about a common: transverse axis with said drive wheels at least partially supporting said brush means,

adjusting meansr for moving, said wheel axle about said transverse axis and thereby adjusting the level of said brush shaft,

and connecting and steering means interconnecting the forks ofsaid lift truck and the front end of said. housing, including means transmitting pushing and pulling forces between said lift truck and said housing but permitting limited relative vertical. and longitudinal twisting movement between said lift truck and said housing.

References Cited UNITED STATES PATENTS 857,525 6/1907 Kern 151'83 909,366 1/1909 Chaplin 1541 2,709,269 5/1959 Williams 1583 X 2,918,687 12/1959 Lathrop 1541 3,087,180 4/1963 Webster 1579 3,178,746 4/1965 Voelstad 1583 FOREIGN PATENTS 698,189 10/1953 Great Britain.

765,671 1/195'7- Great Britain.

864,972 4/ 1961 Great Britain.

992,015 5/1965 Great Britain;

CHARLES A. WI LLMUTH, Primary Examiner.

EDWARD L. ROBERTS, Assistant Examiner.

Claims

1. A SWEEPER ATTACHMENT FOR A LIFT TRUCK COMPRISING: MEANS DEFINING A HOUSING HAVING AN OPEN BOTTOM, BIN MEANS PARTIALLY CLOSING SAID BOTTOM, STEERABLE GROUND WHEEL MEANS SUPPORTING ONE END OF SAID HOUSING, GROUND-ENGAGING DRIVE WHEEL MEANS SUPPORTING THE OPPOSITE END OF SAID HOUSING, ROTATABLE BRUSH MEANS MOUNTED WITHIN AND EXTENDING BETWEEN THE OPPOSITE SIDES OF SAID HOUSING ADJACENT SAID BIN IN A POSITION SO THAT SAID BRUSH MEANS CAN ENGAGE THE GROUND SURFACE, TRANSMISSION MEANS INTERCONNECTING SAID DRIVE WHEEL MEANS AND SAID BRUSH MEANS FOR ROTATING SAID BRUSH MEANS IN A DIRECTION FOR SWEEPING DIRT FROM SAID GROUND SURFACE INTO SAID BIN UPON MOVEMENT OF SAID HOUSING IN A PREDETERMINED DIRECTION, AND STEERABLE CONNECTING AND SUSPENSION MEANS ON SAID HOUSING FOR CONNECTING SAID HOUSING TO THE LOAD CARRIAGE OF SAID LIFT TRUCK, SAID CONNECTING AND SUSPENSION MEANS INCLUDING MEANS FOR TRANSMITTING PUSHING AND PULLING FORCES FROM SAID LIFT TRUCK TO SAID HOUSING BUT PERMITTING INDEPENDENT RELATIVE VERTICAL MOVEMENT BETWEEN SAID LIFT TRUCK AND SAID HOUSING SO THAT THE BRUSH MEANS WILL REMAIN IN SWEEPING ENGAGEMENT WITH THE GROUND SURFACE WHEN SAID SWEEPER IS MOVED OVER UNEVEN SURFACES.