UNIVERSITY OF SOUTH AUSTRALIA Assignment Cover Sheet - GroupAn Assignment cover sheet needs to be included with each assignment. Please complete all details clearly. If you are submitting the assignment on paper, please staple this sheet to the front of each assignment. If you are submitting the assignment online, please ensure this cover sheet is included at the start of your document. (This is preferable to a separate attachment.) Please check your Course Information Bookletor contact your School Office for assignment submission locations. Student Name (Print clearly) UniSA Email ID 1. Christian-Raymund Sarmiento [email protected]du.au 2.Deepak kumar [email protected]3.Rajeesh [email protected]4. Chen, Jiajie [email protected]Course code and title: (MENG 2004) Mechanical Design Practice Program Code: School: School of Advanced Manufacturing and Mechanical Engineering Day, Time & Location of Tutorial/Practical: Thursday, 4-7 pm, J2-25 Course Coordinator: John Fielke Tutor: John Fielke Extension granted (Yes/No): Due Date: Friday 16 September 2011 Assignment number & topic: Assignment 1 – Design of a Mechanism We declare that the work contained in this assignment is our own, except whereacknowledgement of sources is made. We authorise the University to test any work submitted by us, using text comparisonsoftware, for instances of plagiarism. We understand this will involve the University or itscontractor copying our work and storing it on a database to be used in future to test worksubmitted by others. We understand that we can obtain further information on this matter athttp://www.unisa.edu.au/learningadvice/integrity/default.aspSigned: Date: 1. Christian-Raymund Sarmiento 17/09/10 2.Deepak kumar 17/09/10 3.Rajeesh 17/09/10 4. Chen, Jiajie 17/09/10 Date received from student Assessment/grade Assessed by: Recorded: Dispatched:
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Mobility scooters have been a beneficial aid in helping senior and disabled people
travel from location to location. The design of mobility scooters have given many
consumers who are who are unable to walk around an opportunity to travel with ease.Since its creation in 1968 by Allan R. Thieme () mobility scooters has been an
essential part of many people‟s lives.
Recently with the UniSA company commencing business on July 2011, it is given at
hand that the company has given responsibility to UniSA Design Group C1. Pty Ltd.
The group consists of four designers to develop another approach in aiding the
consumers of mobility scooters. The task is to develop a hand operated system for
loading a mobility scooter into a car. The group is to also choose appropriate
materials, so that money is not lost. The company would also like to sell as many of
the designs as possible.
The design group needs to follow a few needs in order for the design to be
applicable. By approaching a method of selecting suitable types of cars and mobility
scooters, the initial design concepts must be mechanically operated and proven to lift.
The operating specifications must also be followed stating a maximum operating
effort of 200 N by hand and 400 N by foot. This is reasonable due to the
disadvantages of senior and disabled users. By developing the initial concepts and
proceeding to the final appropriate design, the design group must also document the
final design; its materials, total cost and recommended retail price (RRP).
This design works on the principle of hydraulics and an effort is been made to reduce
the complexity of mechanism. The whole system is been mounted on the rear boot
of the car with pre-installed parallel tracks which guide the Frame. The motion of the
Frame is controlled by the power screw which is mounted on the rare side. The
power screw is mounted on two parts, out of which one is welded and other is
fastened with screws. The hydraulic piston is mounted on the Frame with the
conjunction of mechanical Pin. The Links (tip) is mounted on the Fixtures havingground surfaces (reamed surface). The links (root) is attached to the Lifting Platform
with the help of 4 finished (reamed) holes and 4 Pins. All Pins have ground surfaces
with two holes on one face to avoid rotation of the Pin itself. The hydraulic arm (male)
is mounted on the support of the Rings which is welded on Links 1 & 2. The
hydraulic piston is controlled by the pumping system which is rigidly attached at the
While rating the designs using the scoring method above, each designs score was
justified with given reasons.
Design one received a reliability score of 4. This was because the base of the device
seemed my smaller than the mobility scooter. There was disagreement that the
device would balance out. The bending moment at the central shaft created reasons
and made the platform unreliable. There is also a high probability of the scooter
falling off. The device was simple, however was stated not original. It is described tobe innovative utilising the hydraulic pump effectively. The device was assumed to be
heavy therefore was a significant factor in the scoring. Parts are not available, and
the design does not have complex shapes to be manufactured.
Design two had a reliability of 8. However there was concern due to the probability of
breaking the arms and lifting platform. The mechanism does not look complex, and
was very original praised with an originality score of 10. The device was veryinnovative as it consisted of many mechanical components. The score of the weight
was given as 10. The reason was because the device was not needed to be handled
by a user instead its being held within the vehicle. The design however received
reasonable scores for low maintenance, standard components and ease of
manufacture. This was because some components such as the hydraulic cylinder
would need to be frequently oiled. Parts are also unavailable in the market. If the
parts break, they need to be manufactured. The components are also large which
brings an issue to manufacturing the parts.
Design three was similar to design two. The design received 5 for reliability because
the device was placed at the edge of vehicle. There was a disagreement that the
edge of the surface can hold the weight of the scooter. Also a force is applied to one
end of the device which can cause the device to break. The device was praised with
similar scores to design two. Again for design three some of the major components
are unavailable in the market and need to be manufactured. The parts are also too
big to be machined.
Design four received a reliability score of 4. This was because the device seemed
fragile and unable to lift the scooter. The device was not complex, and some groupmembers said it was not original. However the device was fairly innovative using
mechanical advantages. Again since the design had to be picked up weight was an
issue. But the weight was given as 7 because the design was described to be light.
The design seems to have a good low maintenance, and the materials look available
in the market. Manufacturing the design also looks easy.
Both design 2 and 3 had a close score with a difference being 1. Both designs
also had similar components. However by group decision design two was
chosen. This was because the components involved some very interesting
In order to have a safe design the Component Strength must be greater than the
Actual Maximum Stress. In many cases there is a great deal of uncertainty on boththe values for the strength and the stress and these are accounted for using a
Design Factor or Factor of Safety [1]
Design factor, N =
Accounts for uncertainties concerning stress and strength:
For square threads, Lead = Pitch in single start which is 7 mm, but for double start
thread has a Lead = 2 × Pitch = 2 × 7 mm = 14 mm
dm = 30 – 7/2 = 26.5 mm dr = 30 – P = 23 mm
According to the convention the large composition of the force when be when thesystem would be raised at an inclination. So the equation as per Shigley‟s:
(For raising the load)
( )
12000 N mm = 8863.2 N mm
(For lowering the load)
( )
-12000 N mm -2178.4 N mm
In both cases the resulted torque from the applied is less than the actual torque
applied. Hence proved, it is a self-locking power screw.
This bracket is attached to the frame by bolts. This bracket used to hold the lead
screw which functions as push pull mechanism to move lifter and scooter in and out
of the car. Force acting at the centre of the lead screw is considered as 1.7kN which
is half of the calculated total force of 3.4kN. Centre of the force acting is 95 mm awayfrom the base. In general bracket act as a stopper in conjunction with the self locking
lead screw.
25
F F
Pre tension per bolt = Required normal force to provide friction/number of bolts
This bracket is attached to the frame by welding. This bracket fixed opposite side of
the bolted joint explained before. Function of this bracket is same as the bolted joint.
It is assumed that force acting on is half of the calculated total force of 3.4 kN.Maximum stress on the weld only when one direction and in other direction leg of the
bracket will support as well.
Maximum allowable shear stress using E 43 electrode