Lamp stand mechanical arm

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Revision as of 19:21, 18 September 2008

System Function

The system is a mechanical arm that uses frictional joints to support a lamp.

The Base

The lower jaw, the threaded L bar, the thumb screw, and the upper jaw make up the base. The base unit attaches to the edge of a desk or table with the lower jaw positioned below it and the upper jaw on top. The threaded part of the L bar goes through the lower clamp then the wing nut while the shorter, unthreaded part goes through the upper clamp. The screw is used to tighten down the clamps and secure the clamp assembly to the table, fixing it from all translations and rotations. There is a hole at the top of it for a peg at the base of the arm unit.

Arm Unit

The arm has two parallel sets of equal bars that rotate at either end where it connects to plates that hold them in position relative to one another. The bottom holder has a peg on the bottom that inserts into the top of the top clamp in the base. Two of the bars attach to the bottom holder and run parallel up to the next set of joining plates. From these plates, two more bars run out of equal length up to another set of plates. These plates hold a fixture that rotates in the plane of the arm and holds the base peg of the plan unit. With this configuration of members, the top of the arm can move within a single plane that contains all the plates and members, allowing it to position along the two axes in the plane. There are screws at each joint that can be tightened to increase the friction in the joint to hold the arm in its current position.

Lamp Housing Unit

The lamp housing attaches to the arm with a peg that can rotate about its axis. This peg is screwed to the metal cup shaped housing that holds the fixture that the light screws into. There are holes cut in this part to allow heat dissipation from the lamp. A bowl shaped metal part is inserted and twisted into the opening of the cup to attach it. It serves to focus the light emitted from the bulb so that it may be directed and prevent it from blinding the user.

The Electrical Unit

The electrical unit has its most complex components within the Lamp Housing Unit. There is a threaded metal part that is made to allow for the insertion and securing of a light bulb. This part is riveted to a ceramic isolative part and further through to the switching assembly. The switch, when rotated, turns a small pin normal to its axis, causing it to contact two metal fingers, completing the circuit to turn on the lamp. To this switching assembly runs the power cable from outside the cup of the lamp housing to the switching assembly to provide power to the system. This cable runs down the upper members of the arm unit to the base of the arm unit where there are an additional six feet of cable with a typical 2 prong AC plug.

Mechanical Analysis

For the mechanical analysis, the friction generated by the thumb screws will be tested for different tightening conditions under which their friction force provided will be tested. Ultimately, the maximum strength of the joints will be evaluated and parametized. The hope is to compare this $10 model to a $50 model that includes springs in its design to counter the weight of the lamp. The lamp will be tightened to the point of contact and given a single full turn of tightening and tested. After each test, the screw will be tightened to contact and tightened an additional turn until it shows visual signs of yielding within the member or it cannot be tightened further without mechanical failure of a component.

Components