J. agric. Engng Res. (1990)46, 1-11

A Prototype for the Fully Mechanized Winter Pruning of Grape Vines

D. VANNUCCI;* E. CINi;'t" A. CIONI;"[" M. Vmmi"

This paper, based on a short critical analysis of agricultural mechanization in wine- producing countries, focuses on the current need for precise, thorough and high-quality systems for mechanical winter grape vine pruning, which are also economically feasible for growers. To this end, a simple pruning mechanism is proposed that selects the canes to be cut according to their diameter and operates in the immediate vicinity of the obstacles along the vine rows (vine trunks and support stakes). A description of the machine is accompanied by a discussion of the main criteria adopted for its design and by a presentation of the first results of testing in the field. Also presented, is a photographic technique which was developed to enable measurements to be made in the field to determine cane-size parameters for selective cutting. The tests performed on the prototype presented here have fully confirmed the expectations: at a speed of about 1-8-2.0 km/h the cutting efficiency of the machine reaches 99% in Tuscan spur cordon, requiring only minimal supplementary manual labour.

1. Introduction

Agricultural mechanization in wine-producing countries has been particularly intensive in recent years. The only operat ion still imperfectly mechanized is winter pruning, which also requires the greatest labour input. In fact, even where pruning machines are used, supplementary manual labour is required for those areas in which the machine is not adequately precise (around the stakes and near the trunks along the row). Whereas the most advanced studies in this field are orientated towards highly sophisticated machines (including robots), which are appropr ia te for high-quality production, in this paper, we discuss the possible adoption of a simple device with a high per formance in terms of both the precision and quality of cuts. It is necessary to seek solutions that are technologically simple and economical both in terms of production costs and farm management .

The problem of costs is particularly serious nowadays, with a widespread reduction of profit-margins in viticulture due to an overall rise in costs, especially those of labour. It has therefore become necessary to intensify mechanization especially in operat ions such as winter pruning, which absorbs a sizeable proport ion of the annually manpower necessary for the viticultural operat ions of a farm. 1

Most of the winter vine-pruning machines on the marke t impose a hedge-like form, and thus a rectangular cross-section, on the row. 2~ They also require prepositioning at a fixed cutting height and in the case of machines incorporating two mechanisms which prune from both sides, the distance between the opposed cutting devices must also be preset, s's Some of the drawbacks of the pruning devices now on the marke t can be summarized as follows: an inability to cut selectively; difficulties in cutting near obstacles (trunks and vine stakes); and a risk of poorly executed cuts, with spurs left broken or frayed.

* Istituto Sperimentale Meccanizzazione Agricola, Ministero Agricoltura e Foreste Monterotondo, Roma, Italy

t Dipartimento lngegneria Agraria e Forestale, Sez. Meccanica, Universit~ degli Studi di Firenze, P.le Cascine 15, 50144 Firenze, Italy

Received 5 March 1988; accepted in revised form 28 October 1989

Presented at AG ENG88~, Paris, France, 2-6 March 1988

1

0021-8634/90/050001 + 11 $03.00/0 t~ 1990 The British Society for Research in Agricultural Engineering

2 FULLY MECHANIZED WINTER PRUNING OF GRAPE VINES

The device proposed here aims to overcome these problems without applying technologies whose complexity would inevitably lead to high equipment costs. 7-~

2. The prototype

The basic components of this tractor-mounted machine are presented schematically in Fig. 1. The chassis (A) adopted is one commonly used in viticulture to carry such equipment as tying-machines. The hydraulic motor (B) mounted on the chassis (A) propels the blades by means of a drive belt (E). Besides the blades, the cutting mechanism features a "daisy-wheel" device (F), the initial version of which was constructed at Davis, California in collaboration with Prof. H. Studer (Agricultural Engineering Department, University of California). The daisy-wheel rotates freely on its own axis, where it is connected to a collapsible arm (C) hinged to the chassis and equipped with a spring. The daisy is free to rotate only in the direction consonant with the progress of the tractor. Fig. 2. gives a description of the cutting head components and their conventional names.

A

C

J L

r.o [[

F

Fig. 1. The cutting device mounted on the tractor. A, chassis; B, hydraulic motor; C, obstacle- avoidance system; D, cutting apparatus; E, drive belt; F, daisy-wheel

A cut is made when the blades, moving just below the daisy, encounter the canes that fall between the daisy's "petals" (Fig. 3). The spacing of the petals, which together with the geometric relationship between each part determines the design of the daisy as a whole, and selects the maximum diameter of the canes to be cut. The blades, obviously, turn in opposition to the daisy to ensure the cleanest cut possible. To deal with the problem of obstacles, an "obstacle-avoidance system" was created combining the action of the drive belt with that of the spring and collapsible arm. A detailed description of this system will be given in the next section.

D. V A N N U C C I E T A L . 3

Fig. 2. Detail o f the cutting system: daisy-wheel and three blades. P, petal maximum width; L, petal length; I, petal indentation; ED, external diameter of the daisy. (The values are reported in Table 1)

?J

, b , : / i

(¢) [

Fig. 3. The cut. (a) the daisy nears the cane; (b) the cut begins and the daisy is halted; (c) with the cut made and the cane eliminated, the daisy can move freely

4 F U L L Y M E C H A N I Z E D W I N T E R P R U N I N G O F G R A P E V I N E S

3. Design criteria

To build the proposed prototype it was necessary first to collect data on the average parameters for the vegetation in Tuscan vineyards with spur cordon systems, upon which the machine was to be tested. Secondly, it was necessary to determine the dimensions of the daisy in response to these data to guarantee optimum performance. The spaces between the petals must admit all of the canes to be cut but exclude obstacles or trunks, and an ideal diameter and number of petals would theoretically permit the machine to intercept 100% of the canes to be pruned.

The third stage in designing the prototype was to devise a mechanically uncomplicated obstacle-avoidance system (Fig. 4). This system consists of a collapsible arm (O 'A) with a spring inside, which can reduce its length in proport ion to the compression of the spring (S) due to a solid member connected to the chassis (C). One point of the arm is connected to the chassis with a hinge (O') and the other point is connected to the centre (A) of the belt-driven pulley, which is coaxial with the daisy. The belt drives the blades situated under the daisy, and is actioned from the driving pulley (O) positioned on the chassis. The working tension (W) of the belt is determined by the spring force (W1), and the belt-and-spring system is in equilibrium (Fig. 4a). The interaction with an obstacle, or with the mass of canes, applies a force F to the system as shown in Fig. 4b. Initially this force acts in two directions OA and O 'A , giving rise to the compression 7"1 of the spring and the tension T of the belt which, however, is able to transmit the motion. When the force F is such that the spring is compressed, the tension in the belt is relieved and arm (OA) reduces in length, the daisy then begins to turn around the obstacle distancing its own centre from the centre of the row. At the same time the blades continue their work without any damage because the distance between the "petals" of the daisy is smaller than the diameter of any obstacle which must not be cut.

The reaction of the spring (Tj) and the tension (T) of the belt eventually cause the mechanism to be brought back into the centre of the row once the obstacle is no longer felt.

V ,

_ ~ _ _ ~ ~ W ~ . . . . . . . . A ('1~ 0

0 ~ i

1" ' C

(a) (b) Fig. 4. (a) the obstacle-avoidance system in equilibrium. V, the forward trajectory of the tractor; O, the centre of the drive pulley and the attachment point on the chassis; 0 ' , the attachment point on the chassis for the collapsible arm 0 'A; S, spring; W, working tension of the driving belt OA; W~, spring action to keep the belt in tension; A, centre of the belt-driven pulley, which is coaxial with the daisy; n, centre line of the row. (b) dynamics of the obstacle-avoidance system (see Fig. 4a). C, obstacle; F, obstacle action, initially parallel to V; T, component of F on the belt; TI, component of F on the spring

D. VANNUCCI ET AL. 5

V

s

/ A

Fig. 5. Theoretical movement pattern of the obstacle-avoidance system [see Eqn (1)]. [J, avoidance angle; O, the attachment point on the chassis for the drive pulley; 0 ' , the attachment point on the chassis for the collapsible arm; n, the line corresponding to the row centre; s, path o f the point A under the hypothesis o f an elastic spring and inelastic belt (which is near to the behaviour o f the real system)

On the basis of the above working principle, it was necessary to determine the length variation of the arm (O'A) bearing the cutting head, the minimum and the maximum tension of the belt (W and T), and the force range of the spring, such that the increase in tension, due to the avoidance of the obstacle, cannot exceed the strength of the belt. Fig. E shows, on the horizontal plane, the scheme of the movements of point A (Fig. 4) together with the avoiding angle r , while the device turns around an obstacle. It is

100 / . 1 k m / h

2 k m / h

7_ = 4 k m / h

c r~ u

25

i L I 150 300 4 5 0 6 0 0 750

B l a d e r o t a t i o n , r e v / m i n

Fig. 6. Percentage of canes cut versus velocity of blade rotation (rev/min) at given forward speeds

6 F U L L Y M E C H A N I Z E D W I N T E R P R U N I N G O F G R A P E V I N E S

observed that while the angle fl varies f rom 0 to ~r, the length O ' A of the collapsible arm varies as in Eqn (1).

O ' A = Va 2 + c 2 + 2ac cos ft. (1)

The limiting conditions are f l - - 0 , so that O ' A = a + c and f l - - z r and hence O ' A = a - c; these give the maximum and minimum theoretical extensions of the arm.

Finally, the power of the hydraulic motor and the speed were de termined to ensure proper cuts at a tractor speed of no less than 1.5 km/h . This was done on the basis of knowledge of other pruning machines and previous research on the cutting resistance of the canes. TM As shown in Fig. 6, a rotation speed of the blades of 750 rpm, is sufficient to assure effective cutting in the forward velocity range of 1 to 4 km/h . This requires a hydraulic motor of about I kW power output with a blade length of 7 cm.

4. Field measurements

To determine the dimensions of the machine and later test its per formance , a special field detection technique was developed that did not require excessive personnel and thus complicated planning and execution. The data to be collected with this technique were: (1) the average diameter of the canes; (2) the average distances between canes and the disposition of the canes with respect to the centre of the row on a vertical plane as shown in Fig. 7; (3) the percentage of canes cut; and (4) the quality of the cuts (absence of fraying). To this end a technique of photographic detection was developed to create a system of random sampling along the rows.

The photographs were taken with a 50 m m lens at a distance of 2 m from the vine with a white screen as a backdrop (Fig. 7). The resulting slides were subsequently projected

-1 I j A

I I I

I

I

I

I I

I

I j A

0 x

Fig. 7. Schematic diagram of the photographic method. A, white screen placed behind vine; B, point at which photograph was taken at a distance of 2 m from the origin 0 of the ideal system of spatial coordinates (x, y, z) and at a height of 1.5m

D . V A N N U C C I ET AL. 7

Table 1

Mean values for the plant parameters in the test-pruned Chianti vineyards (100 readings per parameter). The statistical evaluation of these parameters gives S < 0.2 [see Eqn (2)]. Values obtained from direct readings on the screen

(Fig. 7)

Cultioar

Distance Percentage Branch between Angle of branches

present, diameter, branches, from horizontal % mm mm cutting plane, °

Sangiovese 80 14 128 15 to 90 Canaiolo 10 17 133 15 to 90 Trebbiano 8 16 117 15 to 90 Malvasia 2 13 122 15 to 90

onto a screen marked with a system of plane coordinates whose origin coincides with the point O of Fig. 7. The orientation and spacing of the canes were readily observable by the operator , who was able to translate these observations into numbers by means of scales on the screen. It is important to note that the observations are made on a photographic plane which is normal to the working plane of the daisy; so it is possible to know the cane orientation with respect to the working plane (see Table 1) and qualitatively predict the working problems connected with the position of the canes. To this end, the cane angle from the horizontal was also measured (see Fig. 7).

The diversity of vines cultivated by the producers of Chianti wine made it necessary to ensure the statistical uniformity of the data derived by this method. Accordingly, a simple decisional algorithm based on the criterion presented in Eqn (2) below was performed on a personal computer.

The weighted mean G, of the values relative to the parameter under investigation, was calculated from Eqn (3) for use in Eqn (2). Eqn (2) then verifies that the distance of the statistical mean value of each cultivar parameter Gi from the total one, is smaller than a prefixed value through the estimation parameter S.

S = ~ (n,loi 2) (G - G0 (2) i = l

where: m number of cultivars under test; ni number of measurements performed for the cultivar i; a~ 2 variance for the cultivar i; G weighted mean [see Eqn (3)]; Gi mean value of the parameter under test for the cultivar i.

The following two situations can occur: (1) S -~ 0 ( -< k), the values of Gi are statistically uniform; (2) S -~ 0 ( -> k), the values of Gi are not statistically uniform.

k is a threshold value which must be preset according to the desired precision. For the present experiment k was chosen to be equal to 0.2 and the case (2) did not occur.

The weighted mean G is expressed as follows:

G = wi 3~ (i) Gi (i) wi (i) (3) "= j = l l 1 --

8 FULLY M E C H A N I Z E D WINTER PRUNING OF G R A P E VINES

Table 2

Dimensions of the tested daisy derived from the field parameters (see Fig. 2)

Cane Petal Indentation External diameter, Number of width (P), width (I), diameter (ED),

mm petals mm mm mm

16 14 20 16 280 18 14 20 18 289 20 14 20 20 298 22 15 20 22 320 30 16 20 30 374

where: wi weight of the cultivar i and takes into account the repetition frequency of the

values as well as the percentage of the cultivar in the vineyard under test; fjj(i) frequency with which the measured value Gj is repeated in the cultivar i; Gi °) value of the parameter referred to the measurement j and to the cultivar i.

In Table 1 an example of this t reatment of the field data is reported, which shows the per cent distribution of the plants in the vineyard under test. The dimension and position of the vine branches referred to the screen on which the slides were projected (see Fig. 7). Table 2 shows the geometrical relations between cane diameter and daisy design parameters . Because of some differences in the field data, it was necessary to adopt a compromise criterion to choose the dimensions of the daisy. Many other measurements have been taken in the field, in order to determine the field parameters which have an influence on the daisy at work. The most important of these are summarized in Table 3.

Table 3

Vineyard parameters and the correlated prototype design parameters

Vineyard parameters Design parameters

Row width Max length of the arm bearing the cutting head

Daisy dimensions and orientation of the working plane

Dimensions and disposition of canes with respect to horizontal plane

Cutting force

Density of canes

Hydraulic motor power

Speed of the blades and tractor speed

5. Field tests

The machine was field tested with different tractors and under a variety of environmen- tal conditions typical of Tuscan vineyards and common in many zones that produce grapes for wine (Fig. 8). To fully evaluate the capabilities of the machine, and in particular its ability to avoid obstacles, it was also tested in vineyards set up for manual pruning and consequently equipped with numerous props as well as the usual stakes of chestnut wood and cement. To evaluate performance, photographs were taken of the row sections both before and after the machine had passed; and the data " read" from them, as described above, were processed in terms of averages and percentages.

D. VANNUCCI ET AL. 9

Fig. 8. The prototype at work in a Chianti vineyard

Table 4

Working parameters and dimensions of the prototype under test

Daisy dimensions Working avoidance angle ~ (see Fig. 5) Spring reaction force Rotation of the blades Tractor speed range Working rate

(see Table 2, line 2) 120 °

300 N 750 rev/min

1-8 to 2.2 km/h 0-5 ha/h

Table 5

Percentage of canes cut in different working conditions. (1) vineyard set-up for complete mechanization; (2) vineyard set-up for manual pruning; (3) vineyard set-up for completely manual work. The base to evaluate the forward speed was

100 m along the rows

Vineyard conditions Canes cut, % Mean tractor speed, km/h

1 99 1.8 95 2.2

2 93 1.8 89 2.2

3 75 1.8 68 2-2

10 F U L L Y M E C H A N I Z E D W I N T E R P R U N I N G O F G R A P E V I N E S

Fig. 9. An example of the machine's performance in cutting the canes

In Table 4 the working parameters and the dimensions of the prototype under test are summarized, while Table 5 shows the results of canes cut in different vineyard conditions: for each of them the percentage of canes cut was observed at two different forward speeds of the tractor. There are considerable differences between the results in Table 5, which emphasizes the importance of vineyard set-up for complete mechanization. The ability to work around the obstacles was evaluated quantitatively. It was found that the cut cane percentage did not vary and the quality of the cut was excellent without any macroscopic damage to the vines (Fig. 9).

The results indicated the need to increase the number of cutting heads in order to reach a working rate of at least 0.5 ha/h with a percentage of canes cut greater than 95%.

6. Conclusions

The findings of the present research are essentially two-fold. It was demonstrated that the mechanization of winter pruning in the vineyard can be improved with a new prototype which is mechanically uncomplicated and very precise, as well as effective. In fact it was possible to cut up to 99% of the canes in a vineyard set-up for mechanical cutting, with a noteworthy improvement in the cutting performance around obstacles, and without any difference in the percentage of canes cut with respect to other parts of the r o w .

A simple technique to obtain field data regarding the canes was developed by coupling a simple photographic method with traditional random sampling techniques, whose effectiveness is multipied by the increased quantity of data thus acquired.

On the basis of the present experiments, it is possible to construct a fully adaptable pruning machine for vineyards utilizing a series of cutting heads, of the type described here, in order to bring the same level of performance to any working situation. 11

D. V A N N U C C I E T A L . 11

It is suggested that the experience gained in developing the pro to type represents a potential point of depar ture for further progress. A series of cutting devices such as the present one could be mounted to cut at different levels, in order to create a machine for pruning pergola systems; in this case the pergola structure would have to be modified to avoid cutting the transverse wires by simply incorporating obstacles wide enough to ensure avoidance. Moreover the system for d iameter discrimination presented here could be applied to a machine for pruning fruit trees adaptable to any possible ar rangement .

R e f e r e n c e s

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2 Clingelefl'er, P. R. Production and growth of minimal pruned Sultana vines. Vitis 1984, 1:42-48 Gould, I. V.; Whiting, J. R. Mechanization of Raisin Production with the Irymple Trellis

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a Vannucci, D. Proposta di una macchina rotativa per la potatura di vigneti a controspalliera. (A pruning rotating machine for hedgerow trimed vineyards.) Rivista di Ingegneria Agraria 1980, 1 :1-8

9 Vannucci, D.; Cioni, A. A winter pruning device for various vine training systems. 2nd International Seminar on Mechanical Pruning of Vineyards 1988, Motta di Livenza, Italy (in press)

le Cecchi, A. Prototipo di potatrice invernale per la vite e determinazione del periodo ottimale di intervento. (Winter pruning prototype for vineyards and determination of the optimal time for pruning.) Degree Thesis 1988, Universit~ degli Studi di Firenze, Facolt~ di Agraria

I~ Cini, E.; Cioni, A.; Vannucci, D.; Vieri, M. Fully Mechanized Winter Pruning of Grapevines. Proceedings of the l l th International Congress on Agricultural Engineering, Dublin 4-8 Sept. 1989, 3:1921-1928