Design of A Kinematic Device - Mechanical Engineering - Assessment Answers

January 15, 2018
Author : Charles Hill

Solution Code: 1AJJH

Question: Design of A Kinematic Device

This assignment falls under “Design of A Kinematic Device” which was successfully solved by the assignment writing experts at My Assignment Services AU under assignment help through guided sessions service.

Design of A Kinematic Device Assignment

Task

You are to design a kinematic device that you can later manufacture (using technology at Deakin – laser cutting, 3D printing etc.) and test.

  • Your design must have a central rotating part that causes periodic motion elsewhere in the device (ideally this motion will not be symmetric).
  • Your design must allow for subsequent testing if it is manufactured – i.e. you must design it with space to place sensors in mind. 

    • The design must meet the specified criteria.
    • The report must demonstrate how the device meets the specified criteria.
    • The report should describe how the device works (i.e. what rotates, how and why).
    • The dynamics of this rotation should be explicitly described (i.e. the physics must be shown, quantified and explained).
    • Make sure that what you present is your own work and not simply a copy/adaption of someone else’s work.
    • Ensure that your report also includes concept sketches/drawings and visualisation/renderings of the 3D models.
    • Ensure that all images are correctly labelled as figures with captions and are referenced to in-text.
    • Use a basic and common font (i.e. Arial or Times New Roman).
    • Use an appropriate font size (10 or 12 pt).
    • Adhere to the word limit (3000 ± 20% words) and be concise.
    • Your submission should be in a simple text-based format, with an appropriate layout consisting of sections (with section headings).

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Solution:

  1. Introduction

Innovation is a constant process in the engineering industry. This is fueled by the understanding that consumers’ needs and taste are constantly changing and engineering has a key role of making more efficient and effective by developing the right supportive technologies. As such, it is normal that projects such as this have been developed over the past decades with the soul objective of making life easier and less complex for mankind.  

In line with this understanding, this project is developed to design a new blocking plier that will effectively and efficiently eliminate the issue associated with the conventional pliers. The plier is not entirely a new invention, instead it is a modification of an existing innovation with the primary goal to eliminate issues associated with the present forms of pliers. The areas of modifications will be discussed as the flow of design is also detailed in the preceding section.

  1. Understanding four bar mechanism

All dynamic texts features four bar mechanism and four bar slider issues, but only a few consider it necessary to introduce the students about these useful and fascinating mechanism. Four bar mechanisms are found with their variations - such as four bar sliders – in different kinds of machines, and it is necessary that mechanical engineer learn how to recognize and appreciate this mechanisms in the dynamics of machinery.

Although it is called four bar, one would notice that there are only three links moving. This is because the fourth links is the “ground link” that is extended between the pins A and D as illustrated in the diagram below. The position vector that is drawn along the lengths of the four links does create a vector loop with a sum that is equal to zero.

Figure 1: Four bar linkage mechanisms

figure1

Each of these three moving links have a name attached to them with link AB called the “input link” as in line with its angular velocity and acceleration. It undergoes a fixed axis rotation round the pin at A. Link CS is known as the “output” link. Just like the previous link discussed, it also undergoes fixed axis rotation, but its motion normally come in an oscillatory way due to the fact that it is the third link in the chain. Link BC is known as the “coupler link” as it is the link that couples other links (AB and CD) together. It undergoes a general plane rotation.

Figure 2: Four bar linkage mechanism angles

figure2

In terms of approach, a four bar mechanism is a single degree of freedom device. This implies that if one is aware of just the angular velocity of the input, the person can easily determine the angular velocity of the remaining links (in cases where all the geometry are known – the lengths and angles of the links).

A four bar slider mechanism is used to replace either the link AB or CD with the aid of a slider. In terms of the velocities, the slider does come with certain constraints as if the same with a link. Take for instance in the figure below (the left image), the slider is used to constraint the point C and force it to move horizontally. From the position shown, the imaginary link CD will also constraint point C and force it to move horizontally.

Figure 3: four bar sliders

figure3

It is important to understand the difference between “constrained” and “unconstrained” motions when it comes to developing kinematic machines. The unconstrained motions have been known to occur when a body is allowed to move freely in space, without being limited by any given path during the flow. On the other hand, constrained motion is known to occur when the body is forced to adopt a given path in the course of flow. In a rigid body, it is normal for one or two points within the body to be constrained. Virtually all motions that are studied in the field of kinematics seem to be constrained at some point. Thus, it is important that engineers and developers are able to visualize constrains that occur within a given problem. This is because the constraints create the right flow for gravity. Considering that the relative velocity equation is the same is the vector equation, knowing the direction of vectors is considered valuable as it will help define solutions for any given problem.

  1. Description of new invention

Modified locking pliers

  1. Mechanism adopted

4-bar mechanism

  1. Technicality

This invention is somewhat similar with a hand-operated locking pliers that are used to lock jaws while a technician is performing clamping of a given workpiece and it can be utilized or varied clamping applications.

  1. Background overview of locking pliers

Traditionally, locking pliers are known to have elongated frame with one end forming a stationary handle, a jointed operating lever  with one end forming a movable handle, two jaws, a grip-and-release mechanism coupled with an adjustable mechanism that is used as the frame’s resting point. One of the jaws is fixed to the frame with the other (the moveable one) mounted on the frame with the aid of the first pivot. The moveable joint is joined to the operating lever with the aid of a second pivot, which makes it possible that if you turn the moveable handle, the moveable joint will also be put to motion.

There are also other locking pliers that operate with a similar kinematics are described above, they adopt an operation model where one jaw is fixed to the frame while the second jaw is joined with the moveable handle.

In any case, these known locking pliers have a disadvantage which is that an unintended change in the position of the clamped workpiece can easily occur while closing the moveable jaw and this can bring about a change on the surface of the clamped workpiece or relatively affect the positioning of the workpiece. The cause of this highlighted disadvantage is that one of the jaws has been made stationary while the moveable jaw is designed to turn around it.

In order to eliminate this disadvantage, the user needs to move his hands unto an incoming direction and it causes a lot of usage inconveniences. However, some  designs tend to solve issue by designing the working surface of the in the form of a complex profile for the jaw’s working surface in relation to the workpiece with a rounded cross section, but it doesn’t offer any solution in terms of maintain the position of the clamped workpiece. Additionally, the adjustment of the meeting point for the frame occurs after the workpiece has been positioned between the jaws and this can cause issues when centering the workpiece and also cause related inconveniences to the user.

The initial adjustment for the meeting points can be done only per approximation and seem to be finalize after two or more trials – but yet it can still be ineffective.

The closest analogue when compared with this new invention are locking pliers that are made up of an elongated frame, with one end forming a stationery handle, a jointed lever for operation, and the one forms a moveable handle, two jaws, grip-and-release mechanism and a frame resting point based on adjustable mechanism. One of the jaws is supported on the frame through the first pivot and it is joined to the front end of the lever used for operating it with the aid of the second pivot, with the remaining jaw fixed to the frame. These locking pliers also feature the disadvantages discussed above.

  1. The new design

Figure 4: Sketch of the new invention

figure4

The present invention is designed to solve the issue of maintaining the positioning of a clamped workpiece by making both jaws moveable, connected to each other kinematicaly with the same degree of kinematic freedom. The overall essence and structure of the present invention is to deliver a locking plier that is made up of an elongated frame, with one of the frame forming a stationery handle, a jointed operating lever; the other one forming a moveable handle, two jaws, a grip-and release mechanism, a locking mechanism, a 4 bar mechanism, an adjustable mechanism that the frame rests on, with one jaw mounted on the frame with the aid of the first pivot and joined to the front end of the operating lever through the second pivot. The grip-and-release mechanism is comprised of an operating lever and a link. The holding teeth is pivoted at the center or the operating lever with the remaining jaw tooth pivoted at the end of the frame. The link, the frame, the first jaw and operating lever form a four-bar linkage mechanism.  One of the moveable bars is springe-headed. The locking mechanism revolves around a button that is jointed to the operating lever in order to allow the button tooth to engage with the link tooth with one end of the button tooth form a trigger unit positioned close for the reach of the operating user’s forefinger in order to allow for easy push. The adjustment mechanism adopted for the frame’s resting point is made up of a support nut and an adjusting bolt that is positioned in the nut through a stationery handle. The second jaw is joined to the frame and connected with the first jaw in kinematics.

The second feature of this invention is that the kinematics connections established between the jaws is implemented with the aid of gearing, a four-bar linkage mechanism, rocker and other mechanisms that allow the jaws to be in counter motion while being operated in a grip-and-release approach.

This new design has a third feature that involves a scale division on the side of the frame with a mark made on either jaws. It should also be noted that the scale does comprise of end markings that serve the purpose of indicating extreme operations when the jaw is in use.

There is a fourth features based on button having a safety lock positioned on the moveable handle and it can function with the trigger at the button.

Figure 5: features of the new invention

figure5

In the figure 5 above, the features of the specifications discussed are incorporated. It shows the preferred features in the present invention, explaining the structure, operations and overall essence of the invention.

The chosen features of the present design are elongated frame – with one end forming the stationery handle, an operating lever – with one end forming the moveable handle and two jaws. The first jaw is mounted on the frame with the aid of a pivot and connected to the far end of the operating lever with the aid of another pivot. One end of the linkage is joined to the center of the operating lever with the support of a pivot and the other is joined to the frame located at the resting point. The adjustment mechanism adopted at the frame’s resting point is based on a support nut that is attacked to the stationery handle and the bolt used for adjustment, positioned on the support nut that is located at the stationary handle.

The grip-and-release mechanism adopted in this case is made up of the operating lever and the link. The space between the link, the resting point, and the pivot; between the pivot of the jaws; and between the pivots of the operating lever form a four-bar linkage mechanism as documented in the figure (6) below.

Figure 6: Four-bar mechanism in the plier

One of the moveable parts is loaded with spring for extension as needed. The spring is positioned between the pivot and the frame. The second jaw is mounted on the frame with the aid of a pivot and connected to the first jaw in kinematics. The need for kinematic connection is to provide counter motion for the jaw when releasing or gripping a given workpiece. This makes both jaws moveable with the same kinematic degree of freedom.

  1. Operations

In order to lock a piece, it is put through the jaws and the lever is forced to close it in place. As such, the positioning of the pivots with the aid of four bar mechanisms is changes and the jaws turn towards the pivots. The jaws will normally turn in a counter clockwise direction. The turn in the opposite direction is due to the kinematic connection that is established between the jaws and the shift experienced in the pivots of the four bar mechanism resulting into the button tooth sliding over the tooth of the link and engaging the four bar mechanism linkage into action. In this position, the pivot forms an angel that is about 178 degrees and it offer higher clamping force for the users. The user can then make use of the safety lock to fix the buttons and prevent any unintended interruption of the clamping operations. In order to release the workpiece, the user pushes the button that turns about the pivot and disengage the teeth in the process. Under the influence of the spring, the four bar mechanism resets the plier to its initial arrangement. At this point, the handle will stop moving apart as the movement becomes limited with the slider tooth that is engaged with the button tooth. The initial size of operation established between the jaws is conditioned by the position of the meeting points that can be adjusted with the aid of the turning handle and the screw bolt.

The user needs to turn the handle to reach the point where the mark is touching the scale division and fitting perfectly within the dimension of a workpiece that is being clamped. This will minimize the threat of the position shifting in the course of the clamping process and also reduces the number of unsuccessful attempts associated with the conventional pliers – advancing convenience of users in the process.

  1. Benefits of new design

As highlighted, the new designs offer a number of benefits when compared with conventional locking pliers. The first of such is that it increases convenience. The free movement of jaws with the aid of pivots means that users don’t need to be stressed up with gripping and releasing the workpiece. Additionally, there is a string flow connected with pivot across the central jaws. This allows the user to minimize the risk of not gripping the workpiece tightly as the spring allows for easy grip and flow ones the workpiece is put in its position. With the screw nut, it is easy to either grip or release the workpiece. Finally, the new modification reduces risks associated with the workpiece falling off from conventional locking pliers due to poor gripping and lose releasing. The new design adopts four bar linkage mechanism that allows for easy release and grip, which gives users advanced level of security as discussed above.

  1. Conclusion

Locking plies serve countless purposes when it comes to the engineering world. They can be used to either grip and release a workpiece for easy processing, or they can be adopted for cutting. However, the conventional pliers adopt an easy flow mechanism that doesn’t always produce accurate gripping and can sometimes result to easy release that endanger the user. Additionally, their frames are designed with fixed (rigid) pivots that allows for only one jaw to be in motion - creating unnecessary inconveniences for the users. In line with the above understanding, the new plier was modified from the conventional methods to offer advanced security and higher convenience to the users with the aid of a four bar linkage mechanism.

Effectively, the locking plier was modified to correct the issues highlighted with conventional pliers by offering users advanced security and higher level of convenience. This was achieved with the aid of four bar linkage that allowed for full freedom in the movement of jaws and pivots. A spring system also ensued that workpiece are kept tightly placed. Thus, it can be conclude that this new modified plier is a way forward in terms of enhanced convenience and higher security it offers users. The model can easily developed as it is a modification of an existing plier.

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