Cherry Picker Drive Wheel Gearbox Design Report

Student Name: xxxx

Title: Gear Box Design

Abstract

This report covers the overview of the design concept of a Cherry Picker gear box that will be used on fairly sloping graveled surface. All the design specifications with respect to constraints, performance, environmental effects as well as the cost are detailed herein. The planetary gear box concept from which the design of the Cherry Picker gear box is designed is also covered in detail. Its advantages as well as the working mechanism is covered in the report. Pictorial as well as diagrammatic representation of the gear box is also used to foster understanding.

The manufacturing methodology of the gear box concept under consideration is covered with great emphasis on the components needed as well as the entire flow of the manufacturing process. This report is thus a summary of the design process of the project under consideration.

Keywords: gearbox, planetary gears, bearings, design.

Table of Contents

Abstract 1

Introduction 3

Product Design Specification 4

Planetary Gearbox Concept 7

Advantages of planetary gear boxes 8

Manufacturing details 9

Gear sizing 9

Bearing specification 9

Shaft design 9

Gearbox Housing Design 9

Seal Specifications 10

Bolts and Nuts 10

Conclusion 10

Work Cited 10

Introduction

A cherry picker is typically a crane device that is used to lift an operator to a desired height in order to accomplish the harvesting of cherries within that desired height. Thus the machined is named “Cherry Picker” rather than the conventional person who picks cherries. Several Cherry Picking machines already exist in the market and their functionality as well as their design concept varies depending on their intended use and the nature of the environment intended for its use (Cleghorn 2005).

Cherry pickers vary in size and capabilities and their design is often objective based rather than standardized. The earliest cherry pickers were typically designed for use in orchards and their main function was to lift the picker to an elevated height so as to enhance ease of harvesting the cherries. Several other functionalities have been added to the cherry picker designs from its earliest inventions with emphasis on stability, cost effective design and enhancements with regards to technology in use.

Cherry pickers thus exist in various forms with some existing as integral parts of other locomotors such as agricultural tractors. In such a case, the name cherry picker is not always appropriate. Most cherry pickers are however self-propelled with its motion as well as elevation functionalities initiated within its design (Groesberg 1968).

The cherry picker under consideration consists of a chassis, three wheels, two identical hydraulic gearboxes and a hydraulic crane device. The driving mechanism of the device depends on the motion of two front wheels and one castor wheel on its rear. Each of the two front wheels attached to the chassis of the device is driven by two identical gear boxes attached to the chassis of the device. Two hydraulic motors are attached on each side of the when and are driven independently in order to enhance steering of the wheel (Beran 2012).

The arrangements of the gear boxes and the hydraulic motors on the chassis of the device should be in such a manner that the weight on the device is transferred from the chassis through the when and on to the ground. The chassis and the gear box should therefore withstand a maximum load of 380kg from the crane as well as the weight of the cherries when at maximum capacity.

The cherry picker under consideration should operate effectively even in surfaces that are sloping up to a maximum of fifteen degrees from the horizontal. The surface under consideration is gravel based with a tire and ground co-efficient of friction approximated to be around 0.35. The weight of the cherry picker is distributed equally among the front wheels and thus the design and specification of the design must put this into consideration.

Product Design Specification

The design of the cherry picker puts the following design specifications into consideration from its conception to design and development.

Summary of Product Design SpecificationTable 1:

Specification

Description

Constraints

  • The design of the chassis must be strong and rigid enough to withstand the weight of the device components as well as the weight of the cherries and the picker at any instant in its use.

  • The cherry picker must be able to navigate easily through the cherry bushes with regards to the rows and the inter row spacing of the cherries in the farm.

  • The device should be able to work efficiently even in slope of up to 15 degrees sloping gradient.

  • The device under consideration must operate with a reliability above 95% for a period not less than 5 years.

  • The cherry picker must be able to withstand ground fluctuations such as variations in co-efficient of friction within the veracious parts of the orchard.

  • The design of the cherry picker chassis must provide a housing for two epicyclic hydraulic gear box as well provision for a housing for two hydraulic motors for each wheel.

Performance

  • The design should be able to lift and lower a load of approximately 300kgs at any instant without affecting the stability of the entire device.

  • The device should work to a maximum rated speed of 11kph on all types of surfaces.

  • The variable speed on each wheel must be regulated and steering should only performed at a maximum speed difference of 5kph.

  • The speed ratios on each wheel while turning should be minimized to avoid compromise on stability of the device.

  • The gear box should provide both forward and reverse motion of the device.

  • The cherry picker should have a simple speed control device as wheel as a simple steering lever that controls the speed ratios in the wheels as a way of effecting steering.

  • The braking of the wheels should be sufficient through the gear box as well as a central locking system on the wheels.

  • The wheels should be easily mounted and un-mounted to enhance easy changing and servicing.

  • The chassis and gear box arrangement should enhance ease of repairs and maintenance when necessary.

  • The hydraulic raising and lowering of the picker cabin should be done at a maximum speed of 50mm/sec.

  • The lowering of the device should also be hydraulically controlled to avoid free fall which may affect the stability, ruggedness and safety of the device, its components as well as its users.

  • The design should ensure ultimate failure life of more than 5 years.

  • The braking mechanism should produce a brake torque that should be 30% the full load torque at any braking instance.

Environment

  • The device should be able to work at a temperature range of between 18ºC and 40ºC in at any weather season i.e. winter or summer.

  • The maximum humidity acceptable for the device use should be a relative humidity between 30% and 60%.

  • The device should operate when the soil moisture content is below 30% and the soil type is coarse i.e. murram surface is preferable.

  • The design of the equipment should put into consideration that the maximum noise level allowed for the design should not exceed 70dB.

  • The device will be stored in a dry cool shade preferable a dedicated warehouse or garage.

Target Product Cost

  • The cost of purchasing all the parts should be within a budget limit of 1500 USD with an extra 500USD for miscellaneous.

  • The cost of manufacturing the device should be less than 1500 USD.

  • The cost of operating the device less the consumable parts should not exceed 800 USD.

  • The spare parts should be less than 500 USD.

  • The product should have an end user purchasing cost of 6500 USD within the country of manufacture.

  • The packaging and shipping cost should not exceed 10% of the manufacturing cost of the device.

Maintenance

  • The device should be maintenance free for up to three months except for light maintenance services such as lubrication and greasing of the moving parts.

  • The parts requiring lubrication should be easily accessible by visual inspection.

  • The spare parts should be easily available even after new model have already been commissioned into the market.

  • The fluid level for the hydraulic parts should be easily visible at all times.

Life in Service

  • The device should be capable of withstanding a 10 hours continuous use per day for six days in a week.

Size and weight

  • The entire device`s weight should not exceed a maximum weight of 3000kgs.

Marketing

  • The design should facilitate marketing of the device in all the agricultural based countries such as Asia, Australia and Africa.

Ergonomics

  • All the controls within the device should be easy and within the operators reach. The control should also be in a manner that is easy to control.

Strengths

  • All the materials used should be able to withstand all the loads in the device.

  • The device should be able to operate at all times and should not be subject to fatigue at any instant.

  • The hydraulic lifting part of the device should not fail on overload and the design should put this possibility under consideration.

  • The device should be exempted from operation during servicing.

Documentation

  • The product should be supplied with a clear and easy to read and understand user manual.

Planetary Gearbox Concept

Planetary gearbox concept is based on a special type of gears popularly referred to as epicyclic gears. A planetary gear normally consists of one or more outer gears revolving around a central gear referred to as sun gear. A typical planetary gear consists of two gears arranged in a manner that the center of one gear revolves around the center of another gear. A carrier within the gear train always connects the centers of two gears and rotates to carry one gear called the planet gear around the other gear referred to as the sun gear.

The planet and the sun gears mesh in a manner that slip is at minimal and the direction and speed of the gears in the gear box can be varied by locking one of the members of the sun or planetary gears. The input to the planetary gear can be fed to ant of the gears while all rotary motions can be locked by locking the motion of any two of the gears (Groesberg 1968). The basic components of an epicyclic gear therefore are:

  • Sun – This is the central gear in the planetary gear.

  • Carrier – This is the part of the planetary gear system that holds one or more of the other gears in the planetary system.

  • Annulus – This is the outer ring whose teeth face inwards and its teeth mesh with the planet gears.

Cherry Picker Drive Wheel Gearbox Design Report

Figure 1: A planetary gear box

Advantages of planetary gear boxes

  • Planetary gear boxes give high power output as compared to the other types of gear boxes for example the constant mesh gear boxes.

  • The planetary gears also provide a reduction volume mechanism that enables easier control of speed.

  • The gear box is associated with purely torsional reactions which fosters its high power output.

  • The efficiency of planetary gear boxes is high as compared to the other types of gear boxes this an efficiency loss of less than 3% recorded at each stage.

  • The loads in planetary gear boxes is shared among the various planetary gears thus increasing the gear box`s torques capability.

  • The even distribution in the planetary gear boxes enhances its stability as well as increased rotational stiffness (Groesberg 1968).

Manufacturing details

The manufacturing process of the gear box comprises of various stages and parts that must accomplished in unison.

Gear sizing

The gears must be designed and sized with respects to the torques and wheel speeds desired for the cherry picker. The components required here include gears and gear locking devices

Bearing specification

The bearings are the selected based on the loads on the device due to its weigh and the weight of the components. The selecting of the bearings also takes into consideration the lifespan desired for the device in its use or before the next servicing.

Shaft design

The shaft design with regards to its diameter, length and material used will be designed based on the amount of torque and power output desired by the machine.

Gearbox Housing Design

The gear box housing design should put into consideration the materials used i.e. the lubricants used with respect to corrosion resistance as well as high temperature resistance.

Seal Specifications

The seals used should be able to make the gearbox leak free as well as ensuring that the device is sealed out from any foreign entry of materials into the gearbox.

Bolts and Nuts

The bolts and nuts should be designed and the desired sizes determined in order to accomplish the fastening specifications.

Conclusion

The design and development of the cherry picker is centered on achievement of all the specifications stated herein. The performance and output of the cherry picker coupled with its cost effectiveness with regards to manufacturing and end user cost, enhances its ability to survive the market. The epicyclic gear box is desired for use in thus system due to its ruggedness and ability to evenly distribute its loadings.

Work Cited

  1. TMM (CONFERENCE), & BERAN, J. (2012). Advances in mechanisms design proceedings of TMM 2012. Dordrecht, Springer. http://public.eblib.com/choice/publicfullrecord.aspx?p=1030882.

  2. GROESBERG, S. W. (1968). Advanced mechanics. New York, Wiley.

  3. CLEGHORN, W. L. (2005). Mechanics of machines. New York, Oxford University Press.