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Design considerations for a remote controlled tree shaker for perpendicular attachment on tree limbs
J. agric. Engng Res. (1967) 12 (3) 194-198
Design Considerations for a Remote Controlled Tree Shaker for Perpendicular Attachment on Tree Limbs P.
A. AORIAN*;
R. B.
FRIDLEyt
To eliminate injury to the bark caused during shaking trees for mechanical harvest, a shaker was developed for perpendicular attachment on limbs. This unit has a new mechanism for development of shakingforces. A powered support assembly facilitates placement of the shaker on the limbs and a single control handle operates three positioning movements plus the shaker clamp and motor. Field tests indicate that this unit satisfactorily shakes limbs without injury to the bark.
1. Introduction At present inertia tree shakers are used extensively in the U.S.A. for shaking both limbs and trunks in the harvesting of prunes, cherries and nuts as well as, on an experimental basis, for peaches, apricots, apples and citrus. The use of tree shakers sometimes results in injury to the bark of the tree where the clamp is attached. These injuries are liable to become infected by a fungus, resulting in a spreading canker which ultimately may girdle and kill the limb. A number of approaches to eliminate this potentially serious problem have been tried. The most common of these has been improvement in clamp design; however, tests show a problem still exists when the shaker placement is at a considerable angle from perpendicular to the limb. In trees which have limbs at many angles, some limbs approach the horizontal and it becomes difficult or impossible to attain perpendicular alignment with each limb. Thus it was decided to develop a shaker and support assembly to permit the desired orientation of the shaker.
2. Shaker design A shaker for perpendicular attachment on limbs must have a small cross-section in order to be placed in the tree, and must be short to permit orientation. The rotating weight and the slidercrank mechanism' were first considered for the design of the shaker. With the slider-crank, lining up the crank, connecting rod, slider, clamp cylinder and clamp resulted in excessive length. With the rotating weight, the cross-sectional size required was too large. Therefore, another mechanism of smaller overall dimension was designed. This incorporates an eccentric "folding weight" assembly (Fig. 1). Referring to Fig. 2, mass m1 (the crankshaft) is powered to rotate about point O. The masses m 2 (the circular section of the large mass) and ma (the moon-shaped mass on the side of m 2) are pinned to mi at point D and are forced to rotate opposite to mI' This rotation is produced by a chain drive (Fig. 1) from a sprocket fixed to the housing at point 0 to a sprocket fixed to m 2 at point D. To provide the desired timing, the sprocket diameter at 0 is twice that at D. When rotated the folding weights have a small movement perpendicular to the shaker axis and a large movement colinear with the shaker axis. The design also permits placing the clamp cylinder to the side of the shaking mechanism and the hydraulic motor in line with the mechanism. • A.R.S., U.S.D.A., Agricultural Engineering Research Division, Department of Agricultural Engineering, University of California, Davis, California 95616 t A@ricultural Engineering Department, University of California, Davis
194
195
P. A. ADRIAN; R. B. F R IDL EY
Fig. I. S hake r mechanism showing three locations offolding weights
The inertia force which can be develop ed by the mech ani sm described can be determined from Newton's second law of moti on + + F ,..,., mo . For the masses m l , m2 , and
111 3
th e expr ession becom es ++++ F= m l oA T m 2 0B + maoc
Since mass m l rotates ab out 0 at a constant rate co, the accelera tion of A (the e.g. of ml ) is ++ + . 2 2 a A = OAw = (OA i cos wf + OA j sin oir) w The acceleration of B (the e.g. of m 2) and C (the e.g. of plus their acceleration relative to D. Thus
+
+
0B = aD + + ac
=
00
111 3)
.. . (1)
.. .
(2)
are equal to the acceleration of D
+-
+ aBO a nd -+-
+ 0Co '
Since B rotates about D at a con stant rate -W , these expr essio ns become + + + an = (OD i cos Wf + OD j sin tor) (w2) +
+
( DB i cos wf
-~
+
DB j sin (01) (_w 2)
... (3)
196
DESIGN CONSIDERATIONS FOR A REMOTE CONTROLLED TREE SHAKER
and
+
0c
=
+
+
~
~
(OD i cos rot + OD j sin rot) (ro 2)
+
(DC i cos rot - DC j sin rot) (-ro 2)
... (4)
Substituting Eqns (2), (3) and (4) into Eqn (1), we get expressions for the forces colinear to the shaker axis (Fx ) and the forces perpendicular to the shaker axis (Fy ) F;
=
[m1 (OA)
and Fy = [m1 (OA)
+ m2 (OD +
+ m2 (OD
DB)
- DB)
+ m3 (OD +
+ m3 (OD
DC)] ro 2 cos rot
- DC)] ro 2 sin rot.
To provide for m 2 to have no motion perpendicular to the shaker axis, the mechanism was designed with 0 D = DB. For this condition, the forces in the j-direction are balanced if m 1 (OA) = m 3 (OD - DC). Substituting this expression into the equation for F; we get F; = 2 (0 D) (m 2 + m3) ro 2 cos rot.
In other words the inertia force developed by the mechanism is equal to the force which would be developed by an eccentric mass (m z + m3 ) located at a distance 2(OD) from O. From Fig. 2 it is apparent that this configuration would require a large increase in the shaker dimension perpendicular to its main axis.
Fig. 2. Diagram of unbalanced weights (A, B, C) centres ofgravity of m.,
fi 2,
m,
It should be noted that, although the force is balanced, an unbalanced couple exists due to the fact that m, and m3 are unequal distances from point 0 when the weights are near their extreme position. Field tests have indicated this unbalance is insignificant. The clamp used on this shaker is a design developed for minimizing bark injury. This design combines a curved rigid support with a thick, soft (30 duro meter) rubber pad having a straight front surface. The flat surface of rubber reduces the need for centring because the limb is not subject to the wedging action of a curved surface. The curved rigid support produces a more uniform stress distribution and more contact area than a straight support would provide. A fabric reinforced rubber belting covers the soft rubber to prevent abrasion and most important to prevent the flow of rubber from splitting the bark." Tests with this clamp on a conventional inertia shaker have demonstrated a low incidence of bark injury and indicated that some misalignment from perpendicular can be tolerated since the thick, soft rubber permits distortion in a direction parallel to the limb.
P. A. ADRIAN; R. B. FRIDLEY
197
3. Support linkage Several motions are required to position the shaker: it must be rotated to align the clamp with the limb, tilted to be perpendicular to the limb and elevated (Fig. 3, top). Rotation is accomplished by turning the shaker and supporting boom assembly with a rotary actuator. Tilting is achieved with a folding arm linkage also powered by a rotary actuator (bottom, left). This linkage maintains the centre of gravity of the shaker approximately in line with the centre line of the axis of rotation to minimize the torque required for turning. Elevation is accomplished through a parallel linkage powered by a hydraulic cylinder. To enable the shaker to be moved into and away from -the tree, two vertical pivots are provided, one at each end of the parallel linkage. In practice the shaker would be mounted on a catching frame.
Fig. 3. Remote-controlled shaker for perpendicular attachment, folding arm linkage for positioning shaker and control handle
The conventional limb shaker usually is operated at approximately a horizontal position. This permits the use of vertical links, pivoted at both ends, to support the shaker and isolate vibration from the carrying vehicle. However, if a shaker is to be oriented in a direction substantially different than horizontal, this method of support will not isolate vibration. Therefore, the perpendicular shaker is mounted on ball bushings which are parallel to the axis of the shaker at all times. The use of ball bushings has the disadvantage that, when the shaker is tilted away from the horizontal position, it will move to the stop at the end of its travel. Thus, the shaker must be centred on the support rods before shaking. Initially, hydraulic cylinders were used to hold the shaker in a centred position until it was attached to a limb. However, after the shaker was clamped on the limb and the centring cylinders were disengaged, the mounting arms tended to rise again, placing the shaker against the stop. Subsequently, it was found that the most practical
198
DESIGN CONSIDERATIONS FOR A REMOTE CONTROLLED TRE E SHAK ER
procedure was to clamp the shaker on the limb and then slightly lower the mounting assembly to remove the shaker from the stop on the ball bushing. 4.
Control All motions are powered by a single control handle, (Fig. 3, right) except moving into and away
from the tree which is done by hand. Up and down motion , rotation and tilting of the shaker are accomplished by corresponding movements of the handle. The clamp is actuated by a switch under the index finger, operated through a stepping switch, so that the clamp can be opened and closed by identical motions of the finger. The motor is controlled by a thumb-operated switch. The handle has eight micro-switches which control relay switches. These in turn activate solenoid operated hydraulic valves. Use of the single handle with micro-switches makes it possible to achieve more than one motion of the shaker at a time. 5. Field tests Measurements indicate injury to bark is caused when stresses of 500 to 1000 lb/in " are applied radially." When stresses are applied longitudinal to the limb, bark failure occurs at about 150-250 lb/in", If the same allowance for safety is used in both a radial and a longitudinal direction , the maximum misalignment which can be tolerated is the angle whose tangent is the ratio of the ultimate longitudinal stress divided by the ultimate radial stress. This amounts to 15-25°. Tests have demonstrated that failure frequently occurs at angles greater than 20-30° and misalignments in excess of 45° have been observed in the field. In practice, shakers are operated approximately horizontal, so the worst conditions encountered are limbs leaning towards or away from the machine. Tests of the remote controlled tree shaker on almonds and prunes indicate that the shaker can be placed perpendicular to all limbs with reasonable effort and time. No bark injury occurred during the field testing and the shake developed was equivalent to that produced by existing equipment. The single handle for control of all motions of the vibrator made it possible to orient the unit with little practice. The use of ball bushings to isolate the vibration from the carrying arms proved very satisfactory. In conclusion, the remote controlled tree shaker for perpendicular attachment provides a solution to the problem of injury to the bark. Results further demonstrate that the clamp developed provides sufficient area of contact and also minimizes tangential stresses to the point of eliminating them as a source of injury. Acknowledgement
The authors wish to express their appreciation to C. Wong for valuable assistance in the design, construction and testing of this tree shaker. REFERENCES 1
2
3
Adrian, P. A.; Fridley, R. D. Dynamics and design criteria of inertia-type tree shakers. Trans. ASAE, 1965,8 (1) 12-15 Fridley, R. D.; Adrian, P. A. Mechanical harvesting equipment for deciduous tree fruits. BuI. 825, Calif. agr. Exp. Sta. July, 1966, p. 24 Adrian, P. A.; Fridley, R. B. Shaker-clamp design as related to allowable stresses of tree-bark . Trans. ASAE, 1964, 7 (3) 232-234, 237
Design Considerations for a Remote Controlled Tree Shaker for Perpendicular Attachment on Tree Limbs P.
A. AORIAN*;
R. B.
FRIDLEyt
To eliminate injury to the bark caused during shaking trees for mechanical harvest, a shaker was developed for perpendicular attachment on limbs. This unit has a new mechanism for development of shakingforces. A powered support assembly facilitates placement of the shaker on the limbs and a single control handle operates three positioning movements plus the shaker clamp and motor. Field tests indicate that this unit satisfactorily shakes limbs without injury to the bark.
1. Introduction At present inertia tree shakers are used extensively in the U.S.A. for shaking both limbs and trunks in the harvesting of prunes, cherries and nuts as well as, on an experimental basis, for peaches, apricots, apples and citrus. The use of tree shakers sometimes results in injury to the bark of the tree where the clamp is attached. These injuries are liable to become infected by a fungus, resulting in a spreading canker which ultimately may girdle and kill the limb. A number of approaches to eliminate this potentially serious problem have been tried. The most common of these has been improvement in clamp design; however, tests show a problem still exists when the shaker placement is at a considerable angle from perpendicular to the limb. In trees which have limbs at many angles, some limbs approach the horizontal and it becomes difficult or impossible to attain perpendicular alignment with each limb. Thus it was decided to develop a shaker and support assembly to permit the desired orientation of the shaker.
2. Shaker design A shaker for perpendicular attachment on limbs must have a small cross-section in order to be placed in the tree, and must be short to permit orientation. The rotating weight and the slidercrank mechanism' were first considered for the design of the shaker. With the slider-crank, lining up the crank, connecting rod, slider, clamp cylinder and clamp resulted in excessive length. With the rotating weight, the cross-sectional size required was too large. Therefore, another mechanism of smaller overall dimension was designed. This incorporates an eccentric "folding weight" assembly (Fig. 1). Referring to Fig. 2, mass m1 (the crankshaft) is powered to rotate about point O. The masses m 2 (the circular section of the large mass) and ma (the moon-shaped mass on the side of m 2) are pinned to mi at point D and are forced to rotate opposite to mI' This rotation is produced by a chain drive (Fig. 1) from a sprocket fixed to the housing at point 0 to a sprocket fixed to m 2 at point D. To provide the desired timing, the sprocket diameter at 0 is twice that at D. When rotated the folding weights have a small movement perpendicular to the shaker axis and a large movement colinear with the shaker axis. The design also permits placing the clamp cylinder to the side of the shaking mechanism and the hydraulic motor in line with the mechanism. • A.R.S., U.S.D.A., Agricultural Engineering Research Division, Department of Agricultural Engineering, University of California, Davis, California 95616 t A@ricultural Engineering Department, University of California, Davis
194
195
P. A. ADRIAN; R. B. F R IDL EY
Fig. I. S hake r mechanism showing three locations offolding weights
The inertia force which can be develop ed by the mech ani sm described can be determined from Newton's second law of moti on + + F ,..,., mo . For the masses m l , m2 , and
111 3
th e expr ession becom es ++++ F= m l oA T m 2 0B + maoc
Since mass m l rotates ab out 0 at a constant rate co, the accelera tion of A (the e.g. of ml ) is ++ + . 2 2 a A = OAw = (OA i cos wf + OA j sin oir) w The acceleration of B (the e.g. of m 2) and C (the e.g. of plus their acceleration relative to D. Thus
+
+
0B = aD + + ac
=
00
111 3)
.. . (1)
.. .
(2)
are equal to the acceleration of D
+-
+ aBO a nd -+-
+ 0Co '
Since B rotates about D at a con stant rate -W , these expr essio ns become + + + an = (OD i cos Wf + OD j sin tor) (w2) +
+
( DB i cos wf
-~
+
DB j sin (01) (_w 2)
... (3)
196
DESIGN CONSIDERATIONS FOR A REMOTE CONTROLLED TREE SHAKER
and
+
0c
=
+
+
~
~
(OD i cos rot + OD j sin rot) (ro 2)
+
(DC i cos rot - DC j sin rot) (-ro 2)
... (4)
Substituting Eqns (2), (3) and (4) into Eqn (1), we get expressions for the forces colinear to the shaker axis (Fx ) and the forces perpendicular to the shaker axis (Fy ) F;
=
[m1 (OA)
and Fy = [m1 (OA)
+ m2 (OD +
+ m2 (OD
DB)
- DB)
+ m3 (OD +
+ m3 (OD
DC)] ro 2 cos rot
- DC)] ro 2 sin rot.
To provide for m 2 to have no motion perpendicular to the shaker axis, the mechanism was designed with 0 D = DB. For this condition, the forces in the j-direction are balanced if m 1 (OA) = m 3 (OD - DC). Substituting this expression into the equation for F; we get F; = 2 (0 D) (m 2 + m3) ro 2 cos rot.
In other words the inertia force developed by the mechanism is equal to the force which would be developed by an eccentric mass (m z + m3 ) located at a distance 2(OD) from O. From Fig. 2 it is apparent that this configuration would require a large increase in the shaker dimension perpendicular to its main axis.
Fig. 2. Diagram of unbalanced weights (A, B, C) centres ofgravity of m.,
fi 2,
m,
It should be noted that, although the force is balanced, an unbalanced couple exists due to the fact that m, and m3 are unequal distances from point 0 when the weights are near their extreme position. Field tests have indicated this unbalance is insignificant. The clamp used on this shaker is a design developed for minimizing bark injury. This design combines a curved rigid support with a thick, soft (30 duro meter) rubber pad having a straight front surface. The flat surface of rubber reduces the need for centring because the limb is not subject to the wedging action of a curved surface. The curved rigid support produces a more uniform stress distribution and more contact area than a straight support would provide. A fabric reinforced rubber belting covers the soft rubber to prevent abrasion and most important to prevent the flow of rubber from splitting the bark." Tests with this clamp on a conventional inertia shaker have demonstrated a low incidence of bark injury and indicated that some misalignment from perpendicular can be tolerated since the thick, soft rubber permits distortion in a direction parallel to the limb.
P. A. ADRIAN; R. B. FRIDLEY
197
3. Support linkage Several motions are required to position the shaker: it must be rotated to align the clamp with the limb, tilted to be perpendicular to the limb and elevated (Fig. 3, top). Rotation is accomplished by turning the shaker and supporting boom assembly with a rotary actuator. Tilting is achieved with a folding arm linkage also powered by a rotary actuator (bottom, left). This linkage maintains the centre of gravity of the shaker approximately in line with the centre line of the axis of rotation to minimize the torque required for turning. Elevation is accomplished through a parallel linkage powered by a hydraulic cylinder. To enable the shaker to be moved into and away from -the tree, two vertical pivots are provided, one at each end of the parallel linkage. In practice the shaker would be mounted on a catching frame.
Fig. 3. Remote-controlled shaker for perpendicular attachment, folding arm linkage for positioning shaker and control handle
The conventional limb shaker usually is operated at approximately a horizontal position. This permits the use of vertical links, pivoted at both ends, to support the shaker and isolate vibration from the carrying vehicle. However, if a shaker is to be oriented in a direction substantially different than horizontal, this method of support will not isolate vibration. Therefore, the perpendicular shaker is mounted on ball bushings which are parallel to the axis of the shaker at all times. The use of ball bushings has the disadvantage that, when the shaker is tilted away from the horizontal position, it will move to the stop at the end of its travel. Thus, the shaker must be centred on the support rods before shaking. Initially, hydraulic cylinders were used to hold the shaker in a centred position until it was attached to a limb. However, after the shaker was clamped on the limb and the centring cylinders were disengaged, the mounting arms tended to rise again, placing the shaker against the stop. Subsequently, it was found that the most practical
198
DESIGN CONSIDERATIONS FOR A REMOTE CONTROLLED TRE E SHAK ER
procedure was to clamp the shaker on the limb and then slightly lower the mounting assembly to remove the shaker from the stop on the ball bushing. 4.
Control All motions are powered by a single control handle, (Fig. 3, right) except moving into and away
from the tree which is done by hand. Up and down motion , rotation and tilting of the shaker are accomplished by corresponding movements of the handle. The clamp is actuated by a switch under the index finger, operated through a stepping switch, so that the clamp can be opened and closed by identical motions of the finger. The motor is controlled by a thumb-operated switch. The handle has eight micro-switches which control relay switches. These in turn activate solenoid operated hydraulic valves. Use of the single handle with micro-switches makes it possible to achieve more than one motion of the shaker at a time. 5. Field tests Measurements indicate injury to bark is caused when stresses of 500 to 1000 lb/in " are applied radially." When stresses are applied longitudinal to the limb, bark failure occurs at about 150-250 lb/in", If the same allowance for safety is used in both a radial and a longitudinal direction , the maximum misalignment which can be tolerated is the angle whose tangent is the ratio of the ultimate longitudinal stress divided by the ultimate radial stress. This amounts to 15-25°. Tests have demonstrated that failure frequently occurs at angles greater than 20-30° and misalignments in excess of 45° have been observed in the field. In practice, shakers are operated approximately horizontal, so the worst conditions encountered are limbs leaning towards or away from the machine. Tests of the remote controlled tree shaker on almonds and prunes indicate that the shaker can be placed perpendicular to all limbs with reasonable effort and time. No bark injury occurred during the field testing and the shake developed was equivalent to that produced by existing equipment. The single handle for control of all motions of the vibrator made it possible to orient the unit with little practice. The use of ball bushings to isolate the vibration from the carrying arms proved very satisfactory. In conclusion, the remote controlled tree shaker for perpendicular attachment provides a solution to the problem of injury to the bark. Results further demonstrate that the clamp developed provides sufficient area of contact and also minimizes tangential stresses to the point of eliminating them as a source of injury. Acknowledgement
The authors wish to express their appreciation to C. Wong for valuable assistance in the design, construction and testing of this tree shaker. REFERENCES 1
2
3
Adrian, P. A.; Fridley, R. D. Dynamics and design criteria of inertia-type tree shakers. Trans. ASAE, 1965,8 (1) 12-15 Fridley, R. D.; Adrian, P. A. Mechanical harvesting equipment for deciduous tree fruits. BuI. 825, Calif. agr. Exp. Sta. July, 1966, p. 24 Adrian, P. A.; Fridley, R. B. Shaker-clamp design as related to allowable stresses of tree-bark . Trans. ASAE, 1964, 7 (3) 232-234, 237