In India, groundnut (Arachis hypogaea L.) is one of the important oilseed crops which can be cultivated throughout the year. Groundnut is commonly called as ‘King’ of oilseeds and is widely grown as an oilseed or food crop in the world. Groundnut is the sixth most important oilseed crop in the world [15]. Its worldwide production is more than 10 million tons per year [3]. Developing countries constitute 97% of the global area and 94% of the global production of this crop. Groundnut is a major oilseed crop of India and also an important agricultural export commodity. Its cultivation is mainly confined to south Indian states viz., Gujarat, Andhra Pradesh, Karnataka, Tamil Nadu and Maharashtra. All India groundnut acreage for Kahrif-2018 was 38,90,000 hectares. Five states, Gujarat (14,67,600 ha; 37.7 per cent), Andhra Pradesh (6,60,000 ha; 17 per cent), Rajasthan (5,49,052 ha; 14.1 per cent), Karnataka (3,82,940 ha; 9.8 per cent) and Maharashtra (1,95,594 ha 5 per cent) jointly accounted for 83.7 per cent of the national acreage and accounting a total production of 7.56 million tonnes [1].

In any crop production system, harvesting and threshing are the two primary labour-intensive operations. Threshing operation varies from the age-old procedure of using sticks and racks to the modern power threshers [17]. In India, traditionally, the groundnut crop is threshed manually due to a lack of suitable and simple mechanical devices for the separation of pods from the vines of the groundnut crop. The conventional method of separating the pods from the vines is by pulling with force by hand or by beating the pod over the edges of the stretched bamboo strip or by driving the vines across the comb-like projections with slight force. When the crop is grown during Kharif season, the harvesting of this crop mostly coincides with heavy late monsoons and adverse weather conditions, which affect the threshing considerably. The current practice of conventional separating consumes a considerable amount of labour to a magnitude of about 175 to 200 h ha^-1 [18].

In Karnataka, the traditional method of threshing is facing a crisis today due to the shortage of labour and the increase of labour wages in the state. The competition between the simultaneous labour requirements for groundnut crops and other crops compound the problems. Due to the non-availability of labourers for groundnut crops, threshing is often delayed or extended exposing to nature’s vagaries. Timely threshing is of utmost as delayed threshing leads to a considerable loss of gain due to over maturity and hampers the seedbed preparation and sowing operations for the next crop. Conventional threshing methods are very tedious and consuming operations and are adaptable to small-scale farming.

Mechanization of threshing operation is a promising solution to overcome these problems. Mechanization reduces not only the drudgery of human beings but also the draught animals, it also makes it possible to enhance the cropping intensity, the precision of application and timelines, which improves the efficiency of utilization of various crop inputs and reduce the losses at different stages of the crop production system.

            There are two types of groundnut threshers, namely wet pod thresher and dry pod thresher, which are used for threshing the crop after harvesting, which can be done by feeding the harvested crop in the thresher manually. The manual threshing process reduces the grain output due to inappropriate threshing conditions also incurring a high energy input. An improper operating condition during the mechanical threshing process affects the effective recovery of the grains from the other plant materials and also produces higher grain loss. Manual feeding of groundnut crop to stationary thresher is not uniform and tedious. Conventional threshers have witnessed terrifying accidents for the persons feeding the material without any safe crop feeding system.

            Therefore, there is a great need to adopt new technologies to improve farm machinery in groundnut cultivation or threshing. The capacity of the threshers increased multi-fold when equipped with the belt or mechanical feeding system. Therefore, the need was to design and develop athresher with automatic feeding of groundnut crop by using belt conveyor.

Materials and method

            The design of functional components of automatic groundnut thresher has been carried out using Solid Works software. The design of an automatic groundnut thresher mainly depends on the groundnut crop and its pod properties. The engineering properties such as physical, mechanical, aerodynamic and frictional properties of groundnut crop after harvest have been taken into consideration for the design, development and evaluation of the automatic groundnut crop thresher. Basic data and knowledge of these engineering properties are of more importance and facilitate engineers in designing efficient models.

            The basic frame model formulated for the design and optimization of thresher facilitate the axial flow type of thresher. The concept formulation for axial flow thresher has been performed. Some of the threshers, like axial and radial flow threshers developed for oilseeds and pulses are promising solutions to the various crops. The feature of the axial flow threshing system provides more retention period for unthreshed material during continuous feeding [13]. Axial flow threshers were designed to maintain the seed quality of major oil seed and pulse crops. Significant features of the thresher are minimum injury to seed, higher seed recovery and good seed quality, easy feeding and less fatigue to labour [16 and 4]. The concave and threshing drum was designed such that it produces an induced impact and rubbing forces on crop mass. The crop residues are light in weight and flew away by the current of air discharged from the blower unit whereas the threshed pods get passed through the cleaning sieves. The cylinder and blower are mounted on separate shafts and the speeds can be varied independently as per crop requirements. This ensures minimum grain damage, blower loss and better cleaning. The effectiveness of bond rupture and plant deformation depends upon the mode of action of threshing of the plants. The design parameter is thus defined as, design of threshing cylinder and peripheral velocity of threshing drum, design of open grates, design of blower, design of cleaning sieves.

A. Design of threshing cylinder

            Axial flow or flow through threshing concepts are desirable for high moisture crops and are smooth to thresh crops, including groundnut. Knife type threshing cylinder was attained the highest threshing efficiency and higher cleaning efficiency for freshly harvested groundnut crop and hence knife type threshing cylinder was designed for the proposed automatic groundnut crop thresher [5, 7, 20 and 21]. The design calculations were carried out as quoted by [12, 13 and 19].

a. Diameter and length of threshing cylinder

b. Number of teeth

B. Design and fabrication of cleaning sieve assembly

            To separate all these unwanted materials from the pods, a set of two sieves were fitted below the concave assembly. A pair of sieves had been geared up below the concave assembly to split all the unwanted materials from the pods. The size of the top sieve was 50 X 17 mm and an eccentric drive was used to drive the sieves. Due to rotation of the eccentric shaft, the sieves get reciprocative as well as up and down motion for clean lifting and transferring of materials on it. Similarly, the bottom sieve had 25 X 9 mm openings, and the drive was taken from the eccentric unit.The developed cleaning sieves were shown in Fig. 2.

C. Design and fabrication of blower

          Therefore, a straight blade type blower was designed for the proposed thresher. The actual airflow (Q_A) can be estimated by using the following mathematical equation [11]).

D. Concave grate

            The important component that provides space for threshing of groundnut pods from the groundnut crop is concave and located at the bottom side of the threshing cylinder. It consists of five halves circular bend (15 mm diameter and cylinder length of 1070 mm) round rods spaced at 175 mm apart from each other and two MS flats were welded at both the ends as reinforcement in order to increase the strength of concave. To detach the pods from the groundnut crop, the size of the square rod size was selected based on the arithmetic and geometric mean diameter of the groundnut pods,i.e.15.18 and 14.19 mm. The whole concave was supported on top four corner bolts (fully threaded 12.7 mm diameter). So, the overall dimensions of the concave were found to be 1070 mm in length and 545 mm in radius. Concave clearance was adjusted with the help of full threaded bolts.The developed concave grate was shown in Fig. 4.

E. Oscillating eccentric assembly

            An eccentric is a circular disk solidly fixed to a rotating axle with its centre offset from that of the axle. Two sets of sieves were provided to separate the groundnut pods from the mixture of threshed crop, weeds, mud, stones, dirt etc. The drive was taken from the blower shaft through belt and pulley arrangements. The eccentric assembly provides an oscillation motion to the set of sieves for the separation of groundnut pods. This assembly mainly consists of rectangular trough, perforated two sieves and an eccentric unit. The eccentric unit comprises of an eccentric shaft, connecting rod and the pedestal bearings. This assembly provides to and fro motion for the trough and it was geared up at the rear side of the trough. The developed oscillating eccentric assembly was shown in Fig. 5.

F. Main frame

The frame of farm machines must be as light as possible to reduce cost, soil compaction and propelling power but also main frame should be strong enough to resist the shocks due to rough fields or obstacles, and it should carry and sustain various other components. The main frame was made of square cross-section which is strongest for their weight and arc welding of connecting members makes it possible to take full advantage of their strength in both torsion and bending. The main frame made of mild steel structure of suitable sections was used to mount various automatic groundnut crop thresher components. Two large rubber wheels of size 6.00 X 16.00, PR-10 mm in diameter were provided for transportation and stability purposes during threshing. Stand like structure was given at both ends i.e., front and rear ends of the thresher. The developed mainframe was shown in Fig. 6.

G. Design and fabrication of belt conveyor unit for automatic feeding

A continuous endless canvas or rubber belt is arranged on two pulleys at the ends of a belt conveyor; the take-up pulley at the loading side and the driving pulley at the discharge head. The belt is supported at intermediate points by rollers or idlers at closer spacing on load carrying side than those on the return run.The Belt conveyor system is essential system designed to collect the groundnut crop from the feeding hopper and convey to the feeding chute of the threshing cylinder. This belt conveyor unit was installed in the thresher. The galvanized iron (GI) sheets are provided as vertical side plates to restrict the intended crop not to fall sideways.Critical parts that influence the design of the belt conveyor are endless belts, roller supports, drive mechanism, loading device, take up device, crop holding arrangement, supporting structure, pedestal bearing, belt conveyor roller, feeding hopper, and hitching system. The developed belt conveyor unit for automatic feeding was shown in Fig. 7.

Testing and evaluation of developed automatic groundnut thresher

The developed automatic groundnut crop thresher was evaluated with standard methods and procedures following subheadings

Threshing efficiency

            Threshing efficiency is defined as the threshed pods received from all outlets with respect to total pod input expressed as a percentage by mass. The threshing efficiency is computed by using the following equation ([10]).

Cleaning efficiency (%)

            Cleaning efficiency refers to the clean pods received at the main pod outlet(s) with respect to the total pod mixture received at main pod outlet(s) expressed as a percentage by mass. The cleaning efficiency is calculated by using the following equation ([10]

Total pod loss (%)

            The total pod loss was determined as a sum of the broken pods, blown off pods and unthreshed pods. It is expressed in terms of percentage.

Total pod loss (%) = Broken pods, % + Blown off pods, % + Unthreshed pods, %

The germination percentage

            The total germination percentage was calculated ([2 & 9]).

Seed coat damage (%)

            Ferric Chloride Test [6] was used to determine the seed coat damage. In this method, 20 per cent of ferric chloride solution, 20g of FeCl₃ in 100 mL distilled water was prepared in 250 mL beaker and 100 seeds were placed in it for 15 minutes. The seed which turns into black colour indicates that those are affected by mechanical damage.

Results and Discussion

The automatic groundnut crop thresher was evaluated under field conditions with optimized parameters viz., threshing cylinder speed of 9 m s^-1 with concave clearance of 25 mm and a belt conveyor speed of 1.19 m s^-1. From the analysis of a sample collected at different outlets, the performance of the thresher was measured in terms of threshing efficiency, cleaning efficiency, germination percentage and seed coat damage for the tested variety. The performance results of automatic groundnut crop thresher for freshly harvested groundnut crop were presented in Table 1.The threshing and cleaning efficiencies of the machine were found to be 98.46 and 95.12 per cent, respectively, with a total loss of 5.02 per cent. Whereas germination percentage and seed coat damages were 98.21 and 3.42 per cent, respectively. The savings in cost and time were found to be 39.29 and 96.22 per cent, respectively as compared to the conventional method.

Conclusion

1. In India, traditionally, the freshly harvested groundnut crop is threshed manually due to a lack of suitable and simple mechanical devices for separating pods from the vines.
2. To overcome the shortage of labour during peak periods and to perform the field operations at the right time and to take advantage of favourable climatic conditions, farm mechanization is the only way to combat the drudgery-oriented operation of groundnut crop threshing.
3. Manual feeding of groundnut crop to stationary threshers was also not uniform and a tedious job, and hence belt conveyor system can feed groundnut crop uniformly.
4. The threshing and cleaning efficiencies of the machine were found to be 98.33 and 95.02 per cent, respectively with a total loss of 5.06 per cent. Whereas, germination percentage and seed coat damages were 98.11 and 3.47 per cent, respectively.
5. The savings in cost and time were found to be 39.29 and 96.22 per cent, respectively as compared to the conventional method.

Acknowledgment

            The author presents sincere thanks to the Department of Farm Machinery and Power Engineering and University of Agricultural Sciences, Raichur, Karnataka, India. The author also acknowledges the support by the Council of Scientific and Industrial Research, Human Resource Development Group, for having sanctioned CSIR Senior Research Fellowship [08/392(0004)/2018-EMR-I] to the Ph.D Scholar. This paper presents the part of the findings reported in Ph.D. (Ag. Engg.) Thesis submitted by the author to the UAS, Raichur. 

Author contributions

            Mr. Siddesh, Marihonnappanavara was the Ph.D Scholar who carried out the experiments under the guidance of Dr. M. Veerangouda, Dean (Ag. Engg.), CAE, Raichur. I sincerely confess that it would have been a daydream on my part to accomplish this present investigation without the involvement of this ever helpful personality. I avail this opportunity to express sincere thanks to my advisory committee members, namely Dr. K. V. Prakash, Dr. Sushilendra, Dr. G. S. Yadahalli and Dr. Vijay Kumar K, for giving valuable suggestions, guidance and also extending the technical support in editing the manuscript.

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