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The default theme for machines this semester is a computer controlled desk that can raise and lower so that the one can use it while sitting down or standing.
These desks have become quite popular nowadays with the objective of improving the health of users. Extended periods of sitting, is detrimental to one's posture and the inherent lack of activity can increase risk of cardiovascular diseases. The idea with these desks is to allow users to be able to do work while standing by raising the height of the tabletop electronically, thereby increasing physical activity while working.
The image on the right summarises features on most commercially available products as well as my motivations to build one myself.
My goal is to design a compact yet durable Rising Desk that can be placed in space constrained rooms and one that has a whiteboard integrated into the table top for convenience. The latter feature is based on personal desire.
Part 1: Rising Desk: White Paper
After surveying existing products and ideating desirable features for my desk, I constructed a FRDPARRC table while allowed me to list out Function Requirements, Design Parameters, Analysis, References, Risks and Counter-measures for the product.
Following this, I made some rough sketches of the two broad designs I had in mind.
Peer Review Feedback for White Paper:
Peer Reviewers and respective ink colours:
The peer review session was extremely valuable in obtaining constructive feedback on my ideas for the rising desk. Some of the highlights were:
Looking beyond usage by college students in tiny dorm rooms and also considering office workers in small cubicles
Agreeing on need to have a timed system to rise desk to force user to stand up.
Possible mechanism: 4 bar linkage
Partial whiteboard surface is a good idea
Larger dimensions for desktop
Concern of relative motion errors from motors in dual motor setup
Stability concerns over single column design
Part 2: PUPS 2, Planar Exact Constraint System
The objective of this assignment was to design a simple planar exact constraint system to let users explore sensitivities in fixturing a planar object.
Any solid object in free space has 6 degrees of freedom (DOFs) : 3 translational and 3 rotational. When fixed to a plane, the object loses 3 DOFs and is left with 2 translational and 1 rotational DOFs respectively. Thus to fully constrain such an object, 3 points of contact are needed. The stability of the constrained object will be governed by the spacing between the contact points.
To get a feel for how the spacing affected the stability, I wanted to design and build something where I could adjust the position of the contact points easily. I envisioned a rectangular block constrained to a plane where I could position pins at various points to fixture it. The applied force on the block would be its own weight acting at its centre of mass.
Using force and moment equilibrium conditions, I derived a simple linear system of equations to compute the reaction forces at the contact points. Using MATLAB I can solve for the reaction forces at the 3 different pins based on inputs of dimensions of the block, location of the pins and magnitude & direction of applied force (weight of the object acting at CG)
Following this, I sketched out drawings for my prototype that I would machine in the HobbyShop.
Check out Week 1 in the Hardware Section for more on the prototype.
Part 3: PUPS1, Design and FBD
FRDPARRC Table for new Plier design:
I conceptualised a pair of pliers whose tips would function likeboth needle nose as well as standard slip joint pliers. I also wanted it to be reliable and durable. After the first iteration, my Analysis, Risk and Counter-measure sections of the table were pretty much plank. Only after completing the rest of the assignment problems, was I able to fill out the remaining sections.
Sketches and FBDs:
Analysis of various components with relevant equations
Examination of errors that would result in tip misalignment:
Peer Review Feedback for Pliers
Peer Reviewers and respective ink colours:
The peer review session really extremely valuable in obtaining constructive feedback on the pliers I designed. The session also helped me understand various other requirements the pliers needs to have. Some takeaways from the session:
The needle nose section would perform well but performance of the wider section would be limited given the geometry
Existence of radial compressive stresses from friction acting on the pin
FEA is a good approach to optimise geometry while minimising stress concentrations and resulting deflections
Need for precise preload on pin joint. Consider torsional springs.