Investigations on physico-mechanical properties of coconut palm for the design and development of a coconut palm climber

Abstract

Coconut palm (Cocos nucifera L.) is a versatile tree with global cultivation spanning about 12 million hectares. India leads in production, contributing around 31.45% of the world's total coconut output. In Kerala, coconut is the second most important crop after paddy, producing 5,921 million nuts annually. Despite its widespread cultivation, harvesting remains a significant challenge due to a shortage of skilled labor, youth reluctance to pursue coconut harvesting as a career, health risks, and the lack of proper mechanical climbing devices. A study was conducted to investigate the physico-mechanical properties of the coconut palm such as height of palm, girth at different levels, inclination of palm trunk with respect to ground and hardness, with the aim of developing a climbing device. It was collected from three districts viz. Malappuram, Palakkad and Thrissur. Two instruments namely Inclinometer and Tree hardness tester were developed for measuring inclination and hardness of live palm as there are no instruments readily available for those measurements. A comparative study of some existing models of coconut palm climbers like Chemberi model, TNAU model, CPCRI model, KAU coconut palm climber, KAU Kera Suraksha, and Chachoos Maramkeri was conducted to identify their important features. Additionally, an engine-operated coconut climbing device was also studied. The height ranges from 8 to 18 m for tall varieties and for dwarf varieties it ranges from 3 to 8m. The GBH of coconut palm comes within the range of 60 to 100 cm. The maximum number of palms falls in the range of 80-85 cm GBH. The crown width comes within a range of 7-12 m, with an average value of 9-9.5 cm. The inclination was categorized into four groups and the data reveals that 92.1% of the palms fall under the "Erect" category. Hardness of palm trunk was measured using the developed Tree hardness tester with three different indenter tools of different head geometries like wedge, spherical, and square. It was measured at four different penetration depths such as 1 mm, 2 mm, 3 mm and 4 mm. All tools demonstrate a reduction in hardness as penetration depth increases. Highest hardness recorded is 6.85 N mm-2 for sphere shaped tool. The Wedge tool experiences the sharpest decline in hardness with depth, suggesting that its penetration becomes easier as it moves deeper into the palm. Based on the preliminary study of the physico-mechanical properties of coconut palms and the analysis of the features of existing climbing devices, some functional requirements were identified for designing a new coconut climber. A conceptual design was then finalized and the subsystems were developed to meet these requirements. The components of the designed climbing device were Extendable Mechanism, Hauling mechanism, Safety mechanism, Top fixture ring and Mounting fixture and transport aid. The extendable mechanism comprised a telescopic rung ladder with three sections, each measuring 4.6 meters, designed to reach a height of 12 m. The extension to its full length is facilitated by a hauling system that includes steel wire rope and pulley, a winch mechanism, and a power source. The power required to lift the ladder and climber to a height of 12 m was calculated based on the weight to be lifted and the desired lifting speed. A 1 hp electric motor was selected as the power source to efficiently operate the hauling mechanism and lift the ladder to the required height. Suitable speed reduction mechanism for the winch system with a speed reduction ratio of 60:1 was selected to get the desired climbing velocity of 0.14 ms-1. The telescopic ladder is securely supported on the palm trunk using a top fixture ring that prevents the ladder from sliding sideways. Self-adjusting, spring-loaded rollers were incorporated within the top ring to accommodate the varying girth dimensions of the palm trunk corresponding diameters ranging from 200 mm to 320 mm, representing the minimum and maximum trunk diameters observed in the field.A sturdy, trapezoidal-shaped basket was hinged to the top of the ladder section for operator safety. A safety harness was also recommended for enhanced protection. All the components were mounted on a trolley platform with provisions for rotational control and tilt control. Finite element analysis of the ladder and mounting fixture was done. The values for ladder show that the deformation and stress reach a maximum of 76.612 mm and 70.814 MPa, respectively for an applied load of 1500 N. For mounting fixture, the deformation was 2.7766 mm and stress was 205.76 MPa. The time taken for climbing a 12 m height coconut palm including setting time was 130 seconds and that for climbing down including dismantling was 120 seconds. The climber requires an initial investment of ₹95,000, has a lifespan of 15 years, and a resale value of ₹9,500. The total operating cost of the device was ₹240 per hour, while the cost of climbing per tree was ₹40, assuming six trees were climbed per hour.