MOBILE LIMB SHAKER FOR APPLE HARVESTING

J.G. Kemp and B.A. Melanson

Research Branch, Agriculture Canada, Fredericion, New Brunswick EJB 477

Received 4 April 1977

Kemp, J.G. and B.A. Melanson. 1977. Mobile limb shaker for apple harvesting. Can. Agric. Eng. 19: 88-91.

A limb shaker mounted on the rear of a tractor is described as a mobile shaker for apple harvesting. The main feature includedan extendable-retractable boom which can be swung in the vertical and horizontal planes as well as rotated about its longitudinalaxis to expedite the attachment of the clamp to selected limbs. Three shaking devices were compared and rates of 20-53 apple trees/h with 90% fruit removal were obtained.

INTRODUCTION

In the mechanical shake-and-catch appleharvesting systems, the shaker to remove thefruit from the tree is a major component.Limb- or trunk-shakers are the main typesemployed. Limb-shakers have generallybeen more effective than trunk-shakers inapplying the required shaking action to longwillowy limbs for apple removal (Fridleyand Adrian 1966). Limb-shakers may bemounted on the catch-frame or be independent of the catch-frame. The latter maybe tractor-mounted, tractor-trailed or self-propelled (Coppock 1974; Levin etal. 1960).

The boom of a limb-shaker mounted on a

catch-frame is generally hung in a free-swinging pivot-type suspension. This isolates the shaking forces from the catch-frame and allows the boom and clamp tooscillate as a unit (Fridlay and Adrian 1966).The suspension point is selected so that theboom is in a balanced condition. The sus

pension arrangement is such that the boomcan be manually pivoted in horizontal andvertical directions, as well as rotated aboutits longitudinal axis to aid the clamping ofvarious limbs. The support arm carrying thesuspension mechanism may have provisionsto move in horizontal and vertical directionsto add to the maneuverability of the boomfor positioning. Even with this latter arrangement, catch-frame mounted shakershave severe limitations in boom positioningto clamp desired limbs. In addition, considerable manual effort is required and thereis a problem in depth perception whenpositioning the clamp.

On independently mounted limb-shakers, the boom is usually pivoted at thevehicle end so it can be raised or lowered by ahydraulic cylinder (Fridley and Adrian1966). With a fixed boom length and noprovisions for horizontal swing of the boom,such units need to be maneuvered intoposition for each limb to be shaken (Coppock 1974).

In our development of a shake-and-catchapple harvesting system, a shaker mountedon the catch-frame could not be devised toensure that all limbs could be reached forshaking or could one be found at the time inthe literature. Reported limb-shakers thatwere tractor-mounted, tractor-trailed or

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Figure 1. Vie;w of the unit with a double-crank shaker.

self-propelled appeared to lack the boommaneuverability for efficient operation.

This paper describes the design andoperation of a tractor-mounted limb-shakerthat has proven to be highly maneuverableand effective in shaking apple trees.

CONSTRUCTION OF THE MOBILESHAKER

The Design Objectives

The design objectives for a new shakerwere as follows:

1. The shaker should be independent of thecatch-frame and preferably be farm tractor mounted.

2. The operation of the boom, clamp andshaking mechanism should all be hy-draulically operated.

3. The tractor should supply the power tooperate the shaker hydraulic system.

4. The clamp design should be such that alimb can be approached head-on toeliminate depth perception problems.

5. The boom should be mounted to give theoperator a good view of the clampingoperation.

6. A means should be provided to extend orretract the boom.

7. All shaker controls should be positionedfor the tractor-operator's convenience.

8. A minimum of time and effort shouldaccomplish the mounting of the shakeron the tractor.

9. The shaker should be mountable on

various models of tractors with minimum

changes.

Design of the Shaker

The basic concept of the unit was a limbshaker mounted on a frame attached to the

underside of a tractor at the rear wheel

housing and the tractor front-end loaderattachment points (Figs. 1 and 2). A mounting post for the shaker was vertically hingedto a frame post at the rear and to the right ofthe tractor. A hydraulic cylinder was attached to the main frame and mounting postto provide the means to swing the shakerboom in a horizontal plane. A horizontalpivot pin attached a boom holder to the topof the mounting post. A hydraulic cylinderconnected to the base of the mounting postand the base of the boom holder providedthe means to vertically swing the boom.

The boom holder consisted of a base anda short length of round mechanical tubing inwhich a corresponding length of square

CANADIAN AGRICULTURAL ENGINEERING, VOL. 19 NO. 2, DECEMBER 1977

SWI NG

CYLINDER

"LI FT

CYLINDER

SHAKER DETA I L S

Figure 2. A schematic of the mobile tree shaker.

-Q? ^}a) DOUBLE CRANK -STRAIGHT LINE

b) SINGLE CRANK - PIVOT

®==^ %c) SINGLE CRANK- STRAIGHT LINE

Figure 3. A schematic of various types of shaking mechanisms tested.

tubing had been welded. The round tubingwas mounted on the base by two collars inwhich the tubing could be rotated. A squareboom was fitted into the inner square tubingin which an allowance had been made for asliding fit. A roller chain with its two endsfastened to the ends of the boom wasemployed to extend or retract the boomrelative to the boom holder. A reversiblehydraulic motor fitted with a sprocket andattached to the base of the boom holder

provided the means to drive the chain. Asecond reversible hydraulic motor alsofastened to the base ofthe boom holderdrovea chain to rotate the cylindrical tubing in itscollars. This rotation provided the means torotate the boom about its longitudinal axis.

Shaking Mechanism

With the shaker completely power-operated, the boom was a fixed member during

CANADIAN AGRICULTURAL ENGINEERING, VOL. 19 NO. 2, DECEMBER 1977

the shaking action. Therefore, a new conceptwas required in which the shaking actioncould be applied only to the clamp. Threenew shaking mechanisms were designed andevaluated. These were as follows:

1. A double-crank unit built into the clamphousing and driven by a hydraulic motor(Fig. 3a). The double-crank was arrangedto provide a straight-line shaking motionto the clamp at 90° to the longitudinalaxis of the boom. The theory of thisdesign was to prevent a rotation action ofthe clamp on the limb during shakingwhich could be a source of damage to thebark. A scissor-type clamp was openedand closed by a cam powered by ahydraulic cylinder. The shaking mechanism and the clamp, enclosed in a housing, formed the shaking head attached tothe outward end of the boom.

2. A single-crank unit built into the clamphousing was operated by a hydraulicmotor (Figs. 3b and 4). The clamp mechanism was pivoted at one end and a crankand connecting rod were employed toreciprocate the clamp in an arc about thepivot point. A hydraulic cylinder openedand closed the clamp. The shakingmechanism and clamp enclosed in ahousing formed the shaking head attached to the outer end of the boom.

3. A single-crank unit mounted on theopposite end of the boom to the clamp(Fig. 3c). A crank, powered by a hydraulic motor, drove a connecting rod enclosed within the boom which reciprocated the clamp in a straight-line motionparallel to the longitudinal axis of theboom. A hydraulic cylinder at the clampend opened and closed the clamp by acam. The shaker head, in this case, consisted only of the clamp mechanism andits housing attached to the outer end ofthe boom.

Hydraulic System

The tractor power take-off (pto) drives ajack-shaft on the shaker frame which, inturn, drives high and low volume pumps.The high volume flow was delivered throughcontrol valves to the shaker and extension

motors. The low volume flow fed the control

valves for the boom lift, swing and rotationand the movement of the clamp. The controlvalves were mounted on the shaker frame to

the right of the operator for easy accessibility. The hydraulic oil reservoir and filterwere located on the left rear corner of the

shaker frame. The four hydraulic lines forthe shaker motor and clamp cylinder wererun inside the shaker boom. For the shakermechanism mounted on the opposite end ofthe boom to the clamp, only two lines for theclamp were run inside the boom leavingsufficient room for the long connecting rod.The circuit diagram for the hydraulics isshown in Fig. 5.

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FIELD RESULTS

The tractor used for initial tests was a

Massey-Ferguson 165. A smaller tractor hadbeen used but the rear wheels were fullyextended and wheel weights were added tothe left rear wheel to counterbalance the

weight of the extended boom.To mount the unit, the tractor was

backed over the frame. The front end of the

frame was lifted and held temporarily by achain or bolts, depending upon the attachment arrangement at the front. Then theback was lifted into place by the use ofsuitable jacks and the mounting completedfront and back. All tractors used with theshaker had a live pto. Some tractors hadindependent clutches for pto as opposed tothe two-stage clutch found on the Massey-Ferguson 165. A decided advantage is afoot-operated gas pedal. This enables theoperator to control the speed of response ofthe hydraulic system without removing hishands from the control valves. This is also a

valuable asset for changing the shakingfrequency for fruit removal.

Tests on Shaking Mechanism

A marked difference in operation between the single-crank straight-line shakermechanism and two other units was ob

served.

The former unit results in positive displacement of the limb during the shakingaction. At times, the torque of the hydraulicmotor was not sufficient to initiate move

ment of large limbs and so the motor wouldstall. Either repeated operation of thecontrol valve or a new hold further out onthe limb was required to accomplish shaking. On the other two units, there was apositive displacement between the boomand clamp at 90° to the boom axis. Duringshaking, the boom itself flexes until limbmovement initiates, thus preventing motorstall on large limbs.

Another difference in the shaking operation is in the plane that shaking occurs. Thesingle-crank straight-line unit producedshaking forces in line with the boom axis.Thus, limbs were always shaken in horizontal or near horizontal plane, depending uponthe angle of the boom to the horizontal. Inthe other two units, the shaking forces wereat 90° to the boom axis. The angle of thelimb therefore determines in what plane itwas shaken. On a vertical limb, shaking wasin a horizontal plane. When the boom andclamp were rotated 90° to clamp a horizontal limb, shaking was in a vertical plane.

It was observed that vertical limbs wereeasier to shake. For vertical limbs, a forcewas required to work against the stiffness ofthe limb as well as the force for accelerationof the combined mass of limb and fruit. Onthe horizontal limbs, an extra force wasrequired to offset the force of gravity actingon the combined mass of the limb and fruit.

The design of the double-crank mechanism did, to a large extent, prevent clamp

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MAIN BOX

CHAIN

MAIN ARM

CON NECT I NGROD

SHAKER HEAD

Figure 4. A schematic of the single-crank pivot shaker mechanism.

BOOM ROTATION

CLAMP

SHAKER HYDRAULIC SYSTEMS

Figure 5. The layout of the hydraulic system.

rotation on the limb during shaking. Slightrotation did occur when there was a pronounced flexing of the boom. There was noproblem of clamp rotation on the limbduring shaking with the single-crank,straight-line shaker, which would be expected. There was noticeable clamp rotationwith the single-crank pivot unit. To protectthe bark on the limbs, several types ofclamppads wereevaluated.The final selectionwastwo-stage molded rubber Devcon Flexanepads on plates which bolted to the clampjaws. The center of the pads had a Shorehardness of 30 and the outer shell a hardnessof 80. The softer inner cores allowed the

rubber pads to flex and absorb the rotationmovement of the clamp and thus preventedbark damage.

The three shaking mechanisms wereevaluated in field operations. The results inTable 1 were obtained by timing individualoperations and collecting and measuring theapples removed and retained for each tree.As the type of shaker mechanism did notaffect the time required to move from tree totree, an average time of all tests was used formoving time in the table. The double-crankunit resulted in the best time, the leastnumber of shakes per tree and the highestpercentage of apples removed. The poorest

CANADIAN AGRICULTURAL ENGINEERING, VOL. 19 NO. 2. DECEMBER 1977

TABLE I SHAKER MECHANISM COMPARISONS, NORTHERN SPY ORCHARD

Time (minutes)

Shaker

mechanism

Position

and clampt Shaket MoveJ Total§

No. of Fruit

attachments removaltper treef (%)

Single-crankpivotSingle-crankstraight-lineDouble-crank

1.63

2.09

1.19

0.31

0.52

0.20

0.21

0.21

0.21

2.15

2.82

1.60

3.4

4.8

3.0

91.3

90.9

94.4

t Average of 8 trees.J Average of 24 trees.§Using average move time for 24 trees.

TABLE II SELECTED SHAKER MECHANISMS OPERATIONS

Shaker

mechanism

Average totaltime per tree

(min)Orchard

conditions

Fruit

removal

Double-crank

Double-crank

Single-crank pivot

1.16|

1.03J

1-13§

Northern Spy, 7.0-mdiam trees at 7.3 X 6.0

spacingRome, 7.0-m diam treesat 7.3 X 6.0 spacingPruned for 1.2 to

1.5-m ground clearance

Very good

Very good

Good to very good

t Average for 22 trees.XAverage for 30 trees.§Average for 16 trees.

results were obtained from the single-crankstraight-line shaker.

Work by Garman et al. (1972) indicatedthat shaking in a vertical plane should resultin the most efficient fruit removal. As the

single-crank straight-line unit shakes only inhorizontal planes, this may explain its lowerpercentage of fruit removal. Stalling on thelarger limbs would account for greater timerequired.

The results in Table II were obtained bytaking the total time to shake all the trees ineach test. The fruit removed was not

collected. Much better times were obtainedfor the two units used in these tests which wasdue largely to the tree spacing and thecondition of the trees. In the Rome orchard,there was enough room in the row so theoperator could shake two rows in a singlepass through the orchard.

The maximum rate was 58 trees shaken

per hour with double-crank and 53 for thesingle-crank pivot. Further tests in otherorchards indicate that rates of 30-40 trees/hare practical in most orchards. The unit successfully operated in orchards with cultivarssuch as Rome, Mcintosh, Red Delicious,Cortland, Wagner, Northern Spy, Ben Davis and Golden Russet.

Although the double-crank mechanismgave superior performance, the single-crankpivot mechanism was selected for the finaldesign. The double-crank mechanism wasconsiderably more complex and there wascontinued mechanical breakdown. The

single-crank pivot unit was much simpler indesign and, after initial problems werecorrected, gave little trouble.

SUMMARY

A tree shaker designed for attachment toa farm tractor overcame problems associated with other limb shakers. The ease of

positioning the tractor and the ability toextend or retract the boom while swinging itinto position greatly aided in reaching limbsand minimized the time required to shake atree. Of three shaking mechanisms designedand tested, a single-crank unit was selectedas the most suitable when effectiveness of

fruit removal and mechanical design weretaken into account. Shaking rates variedfrom 20 to 53 trees/h, 30-40 being considered the norm for most orchards. Re

moval of over 90% of fruit could beexpected. The design of the carrying frame

CANADIAN AGRICULTURAL ENGINEERING, VOL. 19 NO. 2, DECEMBER 1977

was such that it could be readily customizedto various tractors. The unit could be movedfrom orchard to orchard at the normal roadspeed of the tractor and with no need toprepare the unit for travel.

SHAKER SPECIFICATIONS

Tractor

Boom

Clamp

Hydraulics

Storagetank

Hydraulicvalves

Shaker

motor

Extension

motor

Rotation

motor

Low profile, approximate 40kW

7.6 cm X 7.6 cm X 0.64 cm

hollow square steel tubingExtended, 5.25 mRetracted, 2 mExtension rate, 1.1 ms"1

- Rotation rate, 1.6 rad s"1- Horizontal swing, 2.8 rad

Vertical swing, 1.5 radJaw opening, maximum, 30cm

Shake frequency, 7.0 Hzmax

- Shake displacement, 15 cmat jaw centers

-Tandem pump-pto driven 90and 25 1 min"1 at 7,000 kPa

— 70-liter capacity

— Shaker and extension — two

metering spools tandemfour-way, 901min"1 at 7,000kPa, spring centering

— Lift, clamp and swing —three metering spoolstandem four-way, 251min-1at 7,000 kPa, spring centering

— 105 rad s"1, 40 N.m at 67 1_1 and 7,000 kPamm

14 rad s"\ 226 N.m at 67 1min"1 and 7,000 kPa

4.7 rad s~\ 226 N.m at 22 1min"1 and 7,000 kPa

-i

COPPOCK, G.E. 1974. Development of a limbshaker for harvesting Florida citrus. Trans.Amer. Soc. Agric. Eng. 17(2) 262-265.

FRIDLEY, R.B. and P.A. ADRIAN. 1966.Mechanical harvesting equipment for deciduous tree fruits. Bull. 825, Calif. Agric. Exp.Sta., University of California.

GARMAN, C.F., R.G. DIENER, and J.R.STAFFORD. 1972. Effect of shaker type anddirection of shake on apple detachment. J.Agric. Eng. Res. 17: 195-202.

LEVIN, J.H., HP. GASTON, SL. HEDDER,and G.J. WHITTENBERGER. 1960. Mech

anizing the harvest of red tart cherries. Mich.State Quart. Bull. 42(4).

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