The Lifting Device - Report Example

LIFTING DEVICE: MECHANISM DEVELOPMENT REPORT Name Institution Course Tutor Date Lifting Device: Mechanism Development Report Development of Brief The requirement to produce a design for a lifting platform for a wheelchair user weighing 100kg to allow them to negotiate a 600mm high step to raised patio areas becomes the main intent of this report. Producing a wheelchair lifting device that operates within a limited space and functions without electric power requires the design of a device that can function by an input of mechanical effort to result in vertical displacement with a more than 100kg weight lift capability. Some additional factors to consider in the design of the device include safety and portability. The device should be able to lift the wheelchair up to the intended height whilst ensuring that the wheelchair rests at that height without chances of tipping over during the operation. The device must also be portable. Therefore, the design that this report presents gives more weight on the security and portability aspects. Mechanical Analysis The translation of the above requirements results in the mechanical specification listed below. The specifications are to ensure that the boundaries of requirements are observed while designing the device. Mechanical Targets Target specifications 1. Maximum Lift Capacity 130 kg 2. Time required to extend to the maximum height 1 minute 3. Maximum lowering speed 4 cm/s 4. Weight 20kg 5. Maximum angle accommodated before tipping over 7 degrees 6. Space dimensions 80 x 100 x 122 7. Maximum effort force required 200 N 8. Maximum extension height accommodated 62 cm 9. Base area dimension 65 cm x 75 cm The above target specifications relate to the requirement specifications. The space dimensions and the weight values determine the portability of the device. The weight specification is targeted to be 20kg according to the OSHA standards to reduce the chances of injury during operation of the device. The base area accommodation targets to ensure the stability of the device. The base area of the device also accommodates impacts of different weather conditions. To quantify the ease of operation of the device, the maximum force required to operate the device. Given the specification requirement for effort input, the device requires a maximum of 200 N to operate. The weight of the user is and the force that can be applied by the action of the arm is enough cause lifting effect of the device. Therefore, a user with a 100kg can easy operate the device with the help from the arms. The current hydraulic wheelchair lift on the market, the Millennium Series, operates between 4 cm/s and 5 cm/s as the maximum lowering speed of the lift (Hsu et al. 2015). Therefore, the lowering speed for this device is targeted to be 4 cm/s to reduce risk of injuries or breakage due to pressure. The area is also meant to ensure that the wheelchair does not tip over during or after the lift. Additionally, the ability of the device to lift the required weight is determined by the sum of the weight of the user and the average standard weight of the wheelchair. The weight of the user is 100kg and the average standard weight of the wheelchair is 30 kg (Hutcheson 2013). This sum gives the device a target specification of 130 kg. Furthermore, the safe operation of the lifting device is also ensured by the angle value accommodated. According to the recommendation of the National Highway Institute about the maximum slope percentage for the local driveway; less than 8% (Hutcheson 2013); the slope accommodation of this device is 7 degrees as calculated with the help of 1.5 safety factor. Component Search and Selection, and Concept Design The concept of the design of this lifting device begins with a structure of a lever system. For the purpose vertical displacement against the specified weight, the device is purports to employ the mechanism of the bottle jack system to actuate the lever mechanism. This actuation then causes the lifting effect capable of making the intended height. To maximise efficiency, the bottle jack system assumes the crossed or scissor structure with joints capable of extending to a required distance. The concept of the joint extensions is the incorporated into the mechanism of air jack system. The air bottle jack system is used in place of pulley mechanism which would have required electric power, or the hydraulic system which requires equal distribution of Pascal effect of pressure; using hydraulic system can incur high cost to develop. Therefore the advantage of using this mechanism is that, a scissor jack is a proven mechanism employed in many lifts. The additional property of this device is the use of air bottle to cause the lifting effect of the scissor jack. Hence, the lift is operational by the effect the pressure that the air exerts as the effort force is applied on the lever. Since one of the key objectives of this design is to produce a potable lifting device, air jack system with scissor structure is design that meets the objective. Air jack system also accommodates the minimum space, since it is capable of compacting to the lowest height possible when the air is withdrawn (Hutcheson 2013). Generally, the air jack lifting system has the following advantages. It is compact: occupies less space It is relatively light; portable. It is simple, hence easy to operate Require very minimum effort from the user since it mainly depends on the weight of the user. Even though the use of ramp to design a wheelchair lift gives it a high stability, the limited space; as the requirements specify; only allow the use of depression mechanism for the support of the wheelchair whilst and after it has been lifted to the required height. The design of this lift employs the high lift capability aspect, the light weight, and the collapsing aspect. Also, the air jack considers the stability whilst it produces the lifting effect. Subsystem Interaction The Air Jack System According to Hsu et al. (2015), air jack one of the lifting devices that is more efficient is producing the lifting effect at a very fast rate. It is relatively faster and convenient than a conventional car jack. Primarily, air jack is used to lift trucks and cars. However, its mechanism is also applicable in the designing of lifting devices such as wheelchair lifting device. Besides, the lifting capacity specification for the required device is with the rates of an air jack; 2 to 4 tons (Hutcheson 2013). The ability of the air jack mechanism to use air for the lifting effect also gives it shock absorbing characteristic. The physical properties of air; such as being compressible; gives the lifting device ability to accommodate sudden break after the effort is released and the required height has been reached. Also, deflating the jack after its use is also relatively easy; it only requires release of effort input which then allows air to escape from the jack. Scissor Lift The scissors lift system experience the pressure that the air jack exerts on it. This causes a combination of horizontal and vertical movement. The movement then lifts the platform with the wheelchair securely held in the depressions. Apart from the lifting effect, the scissor mechanism also provides the collapsing effect, alongside lateral support (Hutcheson 2013). Therefore, the complete design of the lift has the air jack centrally place between the two scissor lift. Geometrical Stability The stability of this lifting device is dependent on a number of factors. The angle of stability; which explains the maximum angle that the wheelchair can tip; relative to the horizontal placement of the whole system, is the first factor that ensures stability. The scissor lift also provides the horizontal stability of the device. Additionally, the vertical stability of the device is provided by the base or footprint area, as well as the depression on the platform. The platform’s depressions provide support mainly to the wheelchair resting on top of it. Therefore, the angle of stability is obtained through the following equations. The stability provided by the angle depends on the counter-clockwise moment produced by an applied force W which represents the weight to be lifted. This weight gives the stable and uniform lifting effect whilst effort force is applied. The ability of the device to accommodate a tip is determined by the distance or displacement of the tip at the top and the bottom, represented by a, and b respectively in the equations below. a > b a = (x/2) Cos (Ɵ) b = Y tan (Ɵ) Where, Y represents the sum of the height of extension and that of the wheelchair. Environmental Robustness The air jack used in this lifting device is filled with air by the lever mechanism. The mechanism is dependent on pressure difference between the air jack and the external surrounding. As Hsu et al. (2015) explains, air is filled in by the action of the level which opens the air inlet and allows air in. The air is the removed from the air jack after the use of the device by the action of the lever again. The lever is moved up, closing the air inlet and opens the outlet. The air jack is then deflated by this action. Therefore, this device is environmentally friendly with reduced chances of affecting the environment negatively. However, the user should be precautious not to direct the air outlet towards him or her. The air that comes from the air jack during deflation may be hot or warm, depending on how long the device was used (Hutcheson 2013). This temperature can cause burning effect on the skin, respiratory problems when if breathed in. Operational Reliability The lifting device will be operated by either user or another person. The operation starts with the user wheeling over the two levers that lead to the platform. Whist on the platform, the two depressions supports the wheels of the wheelchair to prevent any toppling effect of the user movement. After the wheelchair is on top of the platform, the user presses and releases the right lever repeatedly just as a convectional car jack is elevated. Whilst force is applied on the left lever, air is drain into the air jack which causes the lifting effect on the scissor lifts. The user stops after reaching the height intended. The air jack is made of valves that control air movement in and out of the air jack through the inlet and outlet. Similarly, the action of pressing and withdrawing is applied on the left lever to open the air outlet and pumps air out of the air jack. Also, the device can be operated by a different person from the user on the wheelchair. An external air compressor can also be used to pump air into the air jack through the air inlet. Serviceability and Sustainability The device is designed to operate in both cold and hot temperatures. Therefore, the choice of materials used accommodates the temperature range of -30 to 65 C. Also, the materials used for the scissor lifts, platform, and the base should be able to withstand pressure, moisture content in the surrounding, and the salt content of the liquids that might come in contact with the device. Lastly, the device materials should be able to accommodate possible ranges of linear expansion, alongside the ability to withstand UV radiation. For the mentioned conditions, the device is serviceable since the damaged parts can be replaced. Besides, materials with the above characteristics can be recycled to produce other fresh materials. This reason makes the device sustainable. In conclusion, the lifting device presented by this report make use of the criteria for developing a stable and efficient machine that is capable of causing lifting effect on a specified weight through a vertical displacement. Reference List Hsu, K, Kurikesu, V, Momon, M, Walter, J. and Wineland III, C, 2015. Portable Lift for Transferring Wheelchair Patients to Elevated Vehicle. Engineering Project Proposal. Hutcheson, S, 2013. Design and Construction of a Portable Gantry Hoist. Bio-resources and Agricultural Engineering: California Polytechnic State University. Read More