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外文資料原文
J.agric. Engng Res. ,(2001) 78(1),43-60
doi:10.1006/jaer.2000.0632,available online oathttp://www.idealibrary.com
PM-Power and Machinary
Stripping of Leaves and Flower Heads to improve the Harvesting
of Fibre Hemp
（Received 11 february 2000;accepted in revised from 11 August 2000；published online 25 October 2000）
Hemp(Cannabis sativa) grown for fibre needs to be retted after cutting to allow the separation of fibre from the stem core.Drying of the mown stems in necessary both before and after retting but drying is likely to be hindered by the presence of leaves and flower heads on the stems.Delays in drying after retting have serious implications for fibre quality and core spoilage when baled.The aim of this work was to determine if leaves and flower heads could be removed from standing stams by powered rotor just prior to mowing.In a laboratory apparatus that propelled 40 stems past a rotor,the effectiveness of the method was established and the influence of rotor speed,forward speed and tooth design were examined.At every one of a range of setting ,more than 92% of the contacted leaf and flower head was removed form the top 900mm of the tested stems.A device constructed for field trials comprised a 1.2m wide rotor on a tractor-mounted arm.Trials showed it to be effective over a range of forward speed,rotor speed and contact height.At its optimum setting of these three variables,5.8km h-1,645min-1 and 1.6m,it removed 95% of the contacted leaf and flower head material.A practical implementation would probably comprise a single machine with stripping rotor mounted aheda of the stem-cutting elements.
2001 Silsoe Research Institute
Notation
Ma mass of leaf material leaf unstripped above h height,m
the nominal stripping height,kg m stem mass ,g
Mb mass of leaf material leaf unstripped below r rotor speed,min-1×10-3
the nominal stripping height,kg ηs overall stripping efficiency
Ms mass of material removed by the stripping η’s stripping efficiency of
Rotor,kg material above the
f forward speed,km h-1 nominal stripping height
1.Introduction
Hemp(Cannabis sativa)is grown in northern Europe for production of fibres from the sten,which have a high tensile strength and can be used in pup products, composites and industrial textiles.Particles of stem core are absorbent and are used as animal bedding.In current practice, the stems are cut when still grenn and before full seed set when leaves,flower heads and seed heads are present.Once cut,the stems are retted,i.e. exposed in a swath to dry and rewet so that they undergo micro-biological digestion of the chemical bonds between the fibre bundles in the bast or outer layer and the surrounding cells.This makes possible the extraction of the fibre from the dried stems with minimal fibre damage. When the stems have retted to the optimum degree,the fibres are still of high strength but are readily separated from the remainder of the stem material. If retting is allowed to continue, the fibres are weakened and lose value.There fore,it is important to collect the stems at the optimum stage of retting for storage and later processing .Unless the stems are collected dry enough to prevent microbial action,further are generally not good for drying after retting,which takes some 3-6 weeks after harvest in early September in the UK, so it is important that swaths of retted stems dry quickly when conditions are favourable so as to avoid over-retting.Removal of the leaves and flower heads before the stems are swathed is also likely to promote more even retting by better exposing the whole length of the stems to drying.
Leaf and flower head removal is also likely to increase the in-swath drying rate of the stems from harvested moisture to the moisture at which retting will start,thus minimizing the time for which the hemp crop occupies the field.Air can more easily penetrate the swath,and the leaves and flower heads contain additional moisture that must be evaporated.This is of particular importance when baling the retted crop because the seed heads tend to remain damp and later cause partial spoilage of the baled crop..In addition,the removal of the leaf and seed head also reduces the amount of material to be baled,stored,transported and processed,resulting in lower costs.It returns some plant material to the soil to improve soil fertility and structure and reduces waste at the processing plant, waste that may be classified as industrial waste and hence attract higher disposal charges.
Several studies have been made on how to remove seed heads and leaf from hemp crops for the purpose of improved stem harvest, and on the economics of the process, mostly carried out in the Netherlands. The collection of the seeds or leaves as the primary product requires a different approach and so is not the subject of this paper.Huisman et al.(1998) used a modified broadbean topper (double cutterbar knife, reel and conveyor) to remove the seed heads.This was only partially successful because it left one-third of the seed and leaf, and was costly.Bolkstein et al.(1991） carried out an economic assessment of hemp harvesting and concluded that topping (seed and leaf removal) would be a necessary operation in the harvesting of good-quality hemp. He also reported on tests using a modified broadbean topper where 25% of the yield was lost including 8% loss of stem.Feitsma and Swinkels (1991) also used a broadbean topper and a flail mower mounted on a hedge trimmer arm. The bean topper was very slow in hemp (1.3km h-1) and suffered from blockages in a conveyor which transported the cut crop to one side,whilst the flail mower worked successfully but caused a loss of stem material, not quantified.
If the seed and leaf are removed using a mower,either flail or cutterbar,then there will be a loss of stem if the majority of the leaf and seed head are removed (Huisman et al,1998;Feitsma & Swinkel,1991). In addition, the use of a cutterbar requires a means to remove the cut crop and blockages tend to make the work rate very slow.
De Maeyer and Huisman (1994) used a rotary brush to defoliate hemp and also carried out a theoretical study.The use of the rotary brush to remove the leaf and seed head was partially successful in that less stem was removed but the brush was not sufficiently effective in removing leaf.In a late harvest,removal of 0.05kg of leaf caused a predicted loss of 0.02 kg of stem.In field trials only 0.04 kg of foliage was removed per 1 kg of plant dry matter,less than the estimated value in the simulation .As the combined ratio of leaf and seed head to above ground stem mass is typically between 0.15 and 0.30, a removal of 0.04 is not an effective performance. All these attempts appear to be less than successful for one or more of the following reasons(1) removal of or damage to part of the stem;(2) insufficient removal of enough of the leaf and seed head;(3) very low work rate and tendency to blockages.A device developed to harvest cereals by stripping the heads(Klinner et al. 1987)was bassed around a rotor with stripping elements of a ‘keyhole’ design made of a stiff polymer .Besides being very effective for removing the seed and grain from a range of crops the stripping system has aiso proved to be very effective for defoliating crops,including mint,lucerne and nettles.Such a device therefore has potential as a staring point for hemp stripping.
The objectives of this work were:(a)to determine whether stripping of hemp leaves and flower heads without losing fiber can be achieved effectively;(b) to determine at a laboratory scale the effect on stripping performance of rotor design,operating speed and height and forward speed in the crop;and (c) to develop,fieldtest and evaluate a device to demonstrate the stripping operation in a crop of fiber bemp.
2. Material,apparatus and method
For laboratory experiments,stems at the point of normal harvest were cut by hand at the base from commercial crop of hemp,cultivar Felina 34,grown in Hertforshire,UK . Stems were wrapped in polythene after cutting and used within 2 h to minimize the effects of dehydration on leaf and stem mechanical properties.For the field trial, a commercial crop of cultivar Felina 34 was grown in Essex,UK,on chalky boulder clay soil.Plant density at full establishment was 180 m- and yield was 4.3 t ha-1.The field experiment took place on 15 September 1997.
2.1 Laboratory experiment
2.1.1 Apparatus
A stripping device,shown in Fig.1,was developed to propel whole hemp stems past the stripping rotor to simulate field operation . It comprised a shaft,powered by electric motor via a variable speed drive, on which could be fitted a range of rotor types,300 mm wide,a frame to support a hood that deflected the stems before contact with the rotor,a horizontal track 8m long,and a trolley,powered by a variable-speed linear motor,on which up to 400 stems could be mounted in two rows 150 mm apart and 100 mm apart along the row to simulate a crop of 600 plants m-.The stem bases were fixed into flexible sleeves that allowed them to deflect in a way similar to stems in the ground. The linear motor was capable of accelerating the trolley within 1 m to the selected speed and maintaining this speed during contact between crop and rotor ,so as to simulate forward movement of the field machine through the crop. The side of the laboratory device was unobstructed so that high-speed video could be used to study the crop behaviour on contact with the rotor and ， the hood.
The rotor comprised an octagonal core which could be attached toothed stripping elements of various designs (Fig.2) formed from a high-density polymer.Three designs of stripping element ( Fig.3) were investigated,each attached to the same basic octagonal core: an element known as a keyhole design already used for cereal stripping(Klinner et ai.1987) and hence referred to here as a standard element; an element of the same design but with dimensions 50% larger; and a double keyhole type that had a 20% longer reach.These elements when mounted gave the rotor overall diameters of 530,620 and 560 mm,respectively.
2.1.2 Choice of experimental parameters
The reason why different designs of stripping element were investigated was that the teeth of the rotor had to be able to crop (Fig.4). The depth of penetration depends on the number and thickness of hemp stems per unit length in the direction of travel, so longer teeth were thought likely to give better stripping performance .Forward speed was a major determinant of work rate so the highest speed that also achieved effective stripping was investigated. Rotor speed was considered to be a compromise between the achieving sufficient stripping effect and restricting damage to the stems.
2.1.3 Method
For each run,40 stems were selected. The stem length,diameter at top,middle and bottom and the position of the lowest leaf were measured and the total combined mass of the 40 stems was recorded.Once the stems were mounted in the trolley.the rotor was run up to speed,and the trolley propelled past the rotor at the selected speed.The stems were then de-mounted,weighed,and any remaining leaf or flower head was removed by hand and weighed.The mass of leaf and head remaining on the stem above and the mass below the lowest point reached by the rotor teeth were recorded.This procedure was used for the standard stripping elements for four rotor speeds,400,550,700 and 900 min-1,and four forward speeds,3.5,4.3,5.5 and 7.1 km h-1.The double keyhole design was tested at 550 and 700 min-1 and the 50% larger designs at 400 and 550 min-1.In all cases, the rotor height was set so that the teeth tips were 900 mm above the base of the stem.
2.2. Field experiments
2.2.1. Apparatus
Following the laboratory experiments, a machine was designed and built at Silsoe Research Institute to investigate the performance of stripping in a field crop (Fig 5 and 6).The concept was of a stripping head mounted on a tractor-mounted hydraulic arm supplied for hedge-trimming operations.The stripping head comprising a rotor of 1.2 m length powered by a hydraulic motor, a hood and crop dividers.The device was designed so that,with the reach available from the arm, once the crop next to the field edge had been stripped a second run could be made by reaching over the crop just stripped.After this, all the stripped crop had to be cut down to allow further access to the crop. Informed by the results of the laboratory experiments, the parameters of the machine for field use were selected: rotor speed of 500-800 min-1; rotor height up to 2.0 m because of the known height of field-grown crops; and forward speed up to 7 km h-1 without excessive bounce.Unfortunately, insufficient double keyhole elements were available so standard stripping elements were used for the field trials. The hydraulic motor used to drive the rotor was able to deliver 15 kW at 700 min-1. This power proved adequate for all crop conditions encountered.
2.2.2. Method
An experiment,designed to allow efficient field procedures, was carried out to evaluate the effectiveness of the device at removing leaves and flower heads from the hemp stems. The control variables were height of the stripping rotor above the ground, rotor speed and the forward speed of the tractor, Three levels for each of these variables were chosen(Table 1) and a 23 factorial design used, augmented with central points to alloe the estimation of quadratic components, and thus to predict optimal setting.Each plot, 1.2 m by 10 m,was sampled by taking 10 stems before treatment, whether stripped or unstripped control, and afterwards. After initial sampling, the rotor was run up to speed and the plots stripped. A 2 m section was left between plots to allow the operator to change forward speed. After two sections of the field had been treated, they were mown to allow the access to the next part of the crop.
Table 1
Values of parameters used in field experiment
Height,m
Rotor speed,
min-1
Forward speed,
km h-1
1.3
545
4.3
1.7
645
5.8
2.0
770
6.9
The measure used to assess the effectiveness of stripping was the mass of leaf and flower head remaining above the nominal height of the lowest tooth tip as it met the hemp stems. This was measured for the 10 stems taken before and after treating each plot.
3.Results
3.1. Laboratory experiments
The amount of leaf and stem removed by the stripping rotor was used to calculate the efficiency of stripping ηs,given by
ηs=100[MS/(Ms+Ma+Mb)](1)
Where:Ms is the mass of material removed by the stripping rotor in kg;Ma the mass of leaf material in kg left unstripped above the nominal stripping height; and Mb the mass of leaf material in kg leaf unstripped below the nominal stripping height. This measure of performance is very exacting because it is impossible to strip any leaf below the nominal stripping height.Another efficiency measure ηs, was therefore calculated for performance in stripping of material above the nominal stripping height, i.e. To which the teeth had access, given by
ηs,=100[MS/(Ms+Ma)]（2）
Table 2 shows the results of trials on the laboratory stripping apparatus.
Table 2
Tests witn laboratory hemp-stripping apparatus
Run
Rotor speed,
Min-1
Rotor height,
mm
Rotor type
Trolley speed,
km h-1
Stem
diameter
mean,
mm
Lower leaf height mean,
mm
Plant height mean,
mm
Stripping efficiency overall,%
Stripping efficiency above 900 mm,%
1
700
900
std
3.5
8.7
706
1735
84.7
95.2
2
700
900
std
4.3
8.6
830
1714
88.3
96.7
3
700
900
std
5.5
8.7
846
1775
89.4
96.0
4
700
900
std
7.1
8.6
697
1757
83.9
95.7
5
700
900
std
7.1
9.3
815
1828
84.5
92.5
6
900
900
std
7.1
9.4
877
1812
91.2
95.6
7
700
900
dkh
7.1
9.9
830
1803
90.6
96.9
8
550
900
dhk
7.1
10.2
903
1843
93.5
97.6
9
550
855
lte
7.1
9.4
1121
1894
94.1
94.1
10
700
855
lte
7.1
9.4
857
1777
89.2
94.0
11
400
900
std
7.1
9.2
1137
1835
75.3
77.5
12
550
900
std
7.1
9.4
1072
1845
89.4
92.2
Key to rotor type(see Fig.3):std,standard stripping element as used for cereals;dkh, double keyhole design;Ite, larger tooth element.
3.1.1.Stripping efficiency
Figure 7 shows examples of stripped and unstripped stems.All three types of rotor gave good stripping of the stems, both of leaf and of flower heads. Taking the second measure,efficiency of removal above the lowest contact point,as the better one to characterize the rotor performance, the efficiency was greater than 92% for all runs except at a slow rotor speed of 400 rev min-1,when 77% was achieved.For the standard tooth type, there was no significant difference in efficiency as the rotor speed increased from 550 to 900 min-1, nor was there a diminishing of efficiency as forward speed increased from 3.5 to 7.1 km h-1, suggesting the speed of 7.1 km h-1 would be acceptable. At higher speeds, the inertial deflection of the stems on initial acceleration of the trolley was too great for good contact with the stripping rotor to be achieved.. No difference was found between the standard tooth and the 50% larger type at 550 or 700 min-1 but the double keyhole tooth type was significantly better than the other two types at both 550 and 700 min-1 at the forward speed of 7.1 km h-1，probably because of its increased reach into the bundled stems.This extra reach would be even more advantageous in crops of hemp that were thicker than the one simulated in the laboratory experiment of 80 plants m-2 because, as seen in Fig.4,stripping of the lower leaves is accomplished by the tips of the teeth.Most of the gap between the teeth is still occupied by the upper parts of stems contacted earlier.
3.1.2.Stripping height
The results indicate that the rotor was able to strip leaves and heads from stems over a vertical distance of 900 mm, from the lowest point of contact to the stem top.It was not possible to determine the limit of this range because the stems available had shed lower leaves owing to lack of light in the dense crop.Stems from a field edge would be needed for such a test.
3.1.3. Stem damage
As would be expected, the stripped stems showed a range of damage.Generally, this increased with rotor speed but even at the maximum speed used, the damage to the top of the stems was similar to the damage observed at the bass of stems following mowing.In the most severe cases, there was a loss of stem material itself,representing loss of some potential fibre yield.Such damage was observed at a rotor speed of 900 min-1,and at 700 min-1 only at forward speed of 3.5 km h-1.
4.Acknowledgments
This work was sponsored by EC FAIR 1(project PL950396) and the UK of Agriculture,Fisheries and Food.The input of the engineering design and construction groups at Silsoe Research Institute, the help of Mr R Bucknall, grower,Mr B Hills, fieldaman at Hemcore Ltd, and Mr N Jungk, experiment assistant at SRI,are gratefully acknowledged.
外文資料翻譯譯文
J.agric. Engng Res. ,(2001) 78(1),43-60
doi:10.1006/jaer.2000.0632,可在線獲得于 http://www.idealibrary.com
PM-力量和機械
通過去除大麻葉子和花頭促進大麻的收獲
D. M.Bruce ; R. N. Hobson ; R. P.White; J. Hobson
（2000年2月11日收到；2000年8月11日以校訂形式接受；2年10月25日在線出版）
種植麻（Cannabis sativa）是為了獲得纖維，為了從莖桿中分離出纖維，大麻需要在被切之后漚麻而使其變軟。無論是漚麻之前還是之后，曬干收割的大麻是必須的，但是莖桿的曬干極易被其上存在的葉子和花延遲。在漚麻之后，大麻曬干的延遲將會降低纖維的質量及在捆扎時造成大麻的損壞。而本項工作目的是決定是否能在大麻收割之前，通過一動力回轉機械把大麻的葉子和花冠從直立的大麻莖桿上