Balanced-arm lamp 1

Balanced- arm lampA balanced-arm lamp is a lamp with an adjustable folding arm which is constructed so that the force due to gravityis always counteracted, regardless of the position of the arms of the lamp. Many lamp brands (such as the Anglepoiseand Luxo L-1 as well as other devices, such as drawing boards, use this principle.

Configuration

These lamp arms invite comparison with a human arm: the lampcap is the hand, and there are three joints (equivalent to the wrist,elbow and shoulder) which connect it to the body, in this casereprsented by the base. Just as with the human arm, the advantagesof the three joints are that the arm can reach virtually any point inspace within a hemisphere with a radius equal to the arm's length.The same mechanism can be employed in other devices withsimilar requirements, such as copy holders for typists and somecomputer display holders. This article uses the terminology lampcap, forearm, upper arm and base for the four basic parts of theselamps.

For the physics and theory behind balanced-arm lamps, seeClassical mechanics, linkage and torque. There are different methods to balance the lamp-cap of a balanced-armlamp. Some lamps have two coil springs working in parallel on both sides of the pivoting arm. (A set of springsfunctions in the same way as a single spring.) Others are balanced with counterweights (a method frequently used indrawing-boards). Friction between parts of the lamp arm can also be used to maintain balance. There are a number ofmechanical solutions (coupling, hydraulics and pneumatic arms) which have occasionally been used forbalanced-arm lamps.

Lamps balanced with springs

Compression and tensionsprings at rest and under

load

There are many variations of construction with springs. Springs can be located on themechanical equivalent of the forearm or the upper arm, or both, as well as nearer thebase. Some lamps use tension springs, and others use compression springs. The image atthe left shows (left to right) a compression spring at rest, then under load, followed by atension spring at rest, and then under load. Springs have a limited lifting capacity andextension length. Some springs can resonate, producing low-level unwanted noise.

Balanced-arm lamp 2

One Tension spring

Spring-balanced upper arm, flexible forearm

This lamp has a stiff flexible tube as its forearm, and a spring-balanced arm to support it near the middle. That way there is a flexible lamp with along reach.

Tension spring over wheels

The wheel to control the forearm is smaller than the wheel that controls the upper arm. The lamp cap rotates the same direction as the upper arm andforearm.

Two arms, one spring, one toothed wheel

Balanced-arm lamp 3

With this technique the tension spring has a double function: it controls both the forearm and the upper arm. This is not a common arm lampsystem. The lamp cap rotates the same direction as the upper arm and forearm.

Two Tension springsTwo parallelograms and two tension spring sets

One tension spring controls the forearm, which is a parallelogram having two bars. A strongerspring set controls the upper arm, which has three parallel bars (see photo, right). (There is aless stable construction with two parallel bars in the upper arm which is less expensive tomanufacture.) Due to the parallel linkage of the lamp, the lamp cap keeps pointing in the samevertical direction when adjusting the height of the lamp. As with most balanced-arm lamps,the whole assembly can rotate in the horizontal plane, and is mounted on a stable foot.

One parallelogram and two extension spring sets

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A lamp like the Anglepoise lamp has one parallelogram and two extension springs. One spring controls the shortest arm of a parallelogram. Parallelto this shortest arm there is the forearm. To keep these arms parallel there are two other parallel arms (upper arm) that are controlled by a secondextension spring. The lamp cap rotates the same direction as the upper arm and forearm.

Single forearm bar, one parallelogram , two tension spring sets

The forearm of this lamp consist of a single bar. When it is adjusted, the angle of the lamp cap changes along with the arm.

Tension springs within the arms

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A lamp like the Tolomeo desk lamp has no parallelograms in either arm. In this modern lamp the tension springs are hidden in the arms. The lampcap rotates the same direction as the upper arm and forearm.

Compression springsCompression springs in the arms

The short arms (green) stay parallel.One spring puts pull force on the bluearm. (If the blue arm is tilted back thesecond spring on this arm gets pushforce.) The blue arm controls the twoparallel arms (red) that make up theupper arm. The other spring puts pullforce on the other blue arm. This armcontrols the forearm (magenta). Thetwo springs can be the same size; onespring has to lift more weight but ismore vertical. The other spring liftsless weight but is more horizontal.

Compression springs near the foot

Balanced-arm lamp 6

One compression spring controls a very short arm (grey). The Roller chain cable connects this arm parallel to the forearm (yellow). The longerspring controls the (blue) arm. The body (red) can turn in the horizontal plane. The body is connected to a stable foot. The body can be smallerbecause the pressure springs can protrude below the body.

A compression spring with one parallelogram

In this method, just one compression spring controls a pantographic arm.

Other types of spring

Spiral spring controls a pantograph arm

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Patent: GB1290891A from 1970

Torsion springs controls the pivoting arm

Lamps balanced by pressure and friction

Pressure and friction lamps

Balanced-arm lamp 8

This construction is quite common in Italian lamps. Gravity causes the parallelogram to deform, making the gap between the long arms smaller.This increases pressure on the rubber in the gap, and the resulting friction holds the arm in balance.

Lamps balanced with one counterweightA Advantages of one swinging counter balance is that the lamp can have a longer arm length. Disadvantages is thatthe stand is less stable, the lamp need a heavy foot to stand stable.

A single counterweight

Balanced-arm lamp 9

This construction uses a chain to keep the arm with the counterweight and the forearm parallel. The lamp-cap and counterweight move in oppositedirections (both away from the base or both towards it). The balance that is required is shown by the following formula:

d1 = Lamp-cap to base; m1 = weight of lamp-cap

d2 = counterweight to base; m2 = weight of counterweight

m1 d1 = m2 d2

One parallelogram with one counterweight

This lamp has a heavy base, with a parallelogram pantograph construction formed by bars which are all hinged on each other. One long bar extendspast the parallelogram construction and has a counterweight. One short bar also extends past the parallelogram construction and holds the lamp cap.The base haves a arc formed stand so the counterweight does not hit the stand in vertical position.

One parallelogram with an extended counterweight

Balanced-arm lamp 10

This lamp is similar to the one above, but as the counterweight has a low position, the lamp needs no heavy foot for stability: the centre of gravity islow. The counterbalance does not swing but slides an rotate safer around the stand.

Three parallelograms with one counterweight

This lamp stand has a complex construction with matching narrow openings. This lamp is out of production .

Lamps balanced with two counterweights

A single arm with two counterweights

Balanced-arm lamp 11

With this lamp the movement is very limited (the arm moves up and down only) but the technique is nice to look at. As the forearm becomes morehorizontal the weight ceases to be balanced on both side of the base. The weight of the base is needed to avoid over-balancing.

Two arms with two counterweightsA lamp type like the Tizio works like this. A balancing arm (theforearm) has on one side of an axis a small counterweight and onthe other side a lamp cap. These parts are lifted by a second biggerbalancing arm (the upper arm) that has on the other side of asecond axis a heavier counterweight. The lamp designed byEdouard-Wilfrid Buquet in 1929 works in this way. The lamp is inthe collection of the Museum of Modern Art. The two axes have adifferent angle, and this has some advantages. Lamp-cap xfore-Arm = Arm x Small weight (Lamp-cap + Small weight) xupper-arm = Arm x Big weight.

Balanced-arm lamp 12

Lamps using other systems

Here are some less common ways ofbalancing arms.

Lamps having a vertical axis

This kind of lamp has a forearm balanced by weight or springs. Its disadvantage is that the upper arm cannot point up or forwards.

Friction

Balanced-arm lamp 13

The friction between the twisted arm controls the movement between the arms.

This arm system also works with friction.

Mechanical coupling devices

This lamp works by coupling together the upper arm and the forearm. It is called a gravity-locked or cam-locked elbow See here [1].

Hydraulic arm

Balanced-arm lamp 14

The Biggest pivoting arm lamp in the world is in Rotterdam. It has one hydraulic cylinder to control the forearm, and one hydraulic cylinder tocontrol the upper arm.

Pneumatic arm

Arm lamp with a pneumatic cylinder. The gravity compress the air in the pneumatic cylinder.

In popular cultureTwo spring balanced desk lamps of this type feature as the main characters in the Pixar animated film Luxo Jr..

See also Engineering science and mechanics Industrial design Light fixture Torsion spring Mechanical advantage Mechanical engineering technology Moment (physics)

Balanced-arm lamp 15

External links Dutch students from the University Delft Netherlands [2] experimenting to balance a lamp. In Dutch but with a lot

of images.

Patents historyClassifications IPC :F21V21/26International patent category : B23B31/171 GB191104491 [3] An Improved Device for Supporting or Suspending Electric Lamps and the like (1911) U.S. Patent 1370231 [4] - 1921 harmonica arm - [5] 1923 parallelogram & counter weight [6] 1926 friction [7] 1929 2 counter weight [8] 1934 spring and counter weight FR757890 1934 CARWARDINE GEORGE FR784932 1935 CARWARDINE GEORGE [9] 1937 friction [10] 1938 2 parallelogram 2 springs [11] 1939 2 pressure springs [12] 19.. a-symmetric arm-lamp [13] 1947 friction and a spring [14] 1949 [15] 1949 spring in the arm [16] 1954 friction arm1. U.S. Patent 3003737A11961 [17] -- 1961 [18] 1971 U.S. Patent 5333103A1 [19] - 1991 - EP0518569 1992 EP1274545 2003 mechanical coupling devices

References[1] http:/ / www. tribtech. com/ app. 20. htm[2] http:/ / www. ocp. tudelft. nl/ project2006/ wb14/ referenties. html[3] http:/ / www. delphion. com/ cgi-bin/ viewpat. cmd/ GB191104491[4] http:/ / www. google. com/ patents?q=1370231[5] http:/ / www. delphion. com/ cgi-bin/ viewpat. cmd/ GB206435[6] http:/ / www. delphion. com/ cgi-bin/ viewpat. cmd/ GB254972[7] http:/ / www. delphion. com/ cgi-bin/ viewpat. cmd/ GB285045[8] http:/ / www. delphion. com/ cgi-bin/ viewpat. cmd/ GB481198[9] http:/ / www. delphion. com/ cgi-bin/ viewpat. cmd/ GB470502[10] http:/ / www. delphion. com/ cgi-bin/ viewpat. cmd/ GB489547[11] http:/ / www. delphion. com/ cgi-bin/ viewpat. cmd/ GB504791[12] http:/ / www. delphion. com/ cgi-bin/ viewpat. cmd/ GB536342[13] http:/ / www. delphion. com/ cgi-bin/ viewpat. cmd/ GB589994[14] http:/ / www. delphion. com/ cgi-bin/ viewpat. cmd/ GB618344[15] http:/ / www. delphion. com/ cgi-bin/ viewpat. cmd/ GB629364[16] http:/ / www. delphion. com/ cgi-bin/ viewpat. cmd/ GB713378[17] http:/ / www. google. com/ patents?q=3003737A11961

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[18] http:/ / www. delphion. com/ cgi-bin/ viewpat. cmd/ GB1249774A[19] http:/ / www. google. com/ patents?q=5333103A1

Article Sources and Contributors 17

Article Sources and ContributorsBalanced- arm lamp Source: http://en.wikipedia.org/w/index.php?oldid=360396272 Contributors: Addshore, BrucePodger, CSWarren, Chasnor15, J Milburn, Jlhughes, Lumos3, Mars2035,Novangelis, Old Moonraker, Optigan13, Plrk, SDC, ShelfSkewed, Sintaku, Stef breukel, Three-quarter-ten, Van helsing, Walkersam, World arm lamp, Zippanova, 24 anonymous edits

Image Sources, Licenses and ContributorsImage:Compare human arm.PNG Source: http://en.wikipedia.org/w/index.php?title=File:Compare_human_arm.PNG License: Public Domain Contributors: Stef breukelImage:Pressure and expansion springs.PNG Source: http://en.wikipedia.org/w/index.php?title=File:Pressure_and_expansion_springs.PNG License: Public Domain Contributors: Stef breukelImage:extension spring balanced arm support a flexible arm.PNG Source: http://en.wikipedia.org/w/index.php?title=File:Extension_spring_balanced_arm_support_a_flexible_arm.PNGLicense: Public Domain Contributors: Stef breukelImage:Extension spring rolls over 2 wheels.PNG Source: http://en.wikipedia.org/w/index.php?title=File:Extension_spring_rolls_over_2_wheels.PNG License: Public Domain Contributors:Stef breukelImage:2 arm 1 spring 1 Tooth wheel.PNG Source: http://en.wikipedia.org/w/index.php?title=File:2_arm_1_spring_1_Tooth_wheel.PNG License: Public Domain Contributors: Stef breukelImage:upper-arm 3 bars parallel.jpg Source: http://en.wikipedia.org/w/index.php?title=File:Upper-arm_3_bars_parallel.jpg License: Public Domain Contributors: Stef breukelImage:Angle poise type of lamp.png Source: http://en.wikipedia.org/w/index.php?title=File:Angle_poise_type_of_lamp.png License: Public Domain Contributors: Stef breukelImage:single Lamp arm, parralellogram ,2extension springs.PNG Source: http://en.wikipedia.org/w/index.php?title=File:Single_Lamp_arm,_parralellogram_,2extension_springs.PNGLicense: Public Domain Contributors: Stef breukelImage:lamp 2x arm, cable, extension springs.PNG Source: http://en.wikipedia.org/w/index.php?title=File:Lamp_2x_arm,_cable,_extension_springs.PNG License: Public DomainContributors: Stef breukelImage:2 compression springs 1 parallelogram lamp.PNG Source: http://en.wikipedia.org/w/index.php?title=File:2_compression_springs_1_parallelogram_lamp.PNG License: Public DomainContributors: Stef breukelImage:spring balanced bending arm lamp.JPG Source: http://en.wikipedia.org/w/index.php?title=File:Spring_balanced_bending_arm_lamp.JPG License: Public Domain Contributors: StefbreukelImage:One Pressure spring one parallelogram.PNG Source: http://en.wikipedia.org/w/index.php?title=File:One_Pressure_spring_one_parallelogram.PNG License: Public DomainContributors: Stef breukelImage:Spiral spring controls a pantograph arm lamp.PNG Source: http://en.wikipedia.org/w/index.php?title=File:Spiral_spring_controls_a_pantograph_arm_lamp.PNG License: unknownContributors: World arm lampImage:2 torsion springs balanced arm lamp.PNG Source: http://en.wikipedia.org/w/index.php?title=File:2_torsion_springs_balanced_arm_lamp.PNG License: Public Domain Contributors:Stef breukelImage:friction rubber arm lamp.PNG Source: http://en.wikipedia.org/w/index.php?title=File:Friction_rubber_arm_lamp.PNG License: Public Domain Contributors: Stef breukelImage:squeezing rubber arm lamp outer position.PNG Source: http://en.wikipedia.org/w/index.php?title=File:Squeezing_rubber_arm_lamp_outer_position.PNG License: Public DomainContributors: Stef breukelImage:1 weight chain lamp.PNG Source: http://en.wikipedia.org/w/index.php?title=File:1_weight_chain_lamp.PNG License: Public Domain Contributors: Stef breukelImage:1 Parallelogram + 1 Counterweight.PNG Source: http://en.wikipedia.org/w/index.php?title=File:1_Parallelogram_+_1_Counterweight.PNG License: Public Domain Contributors:Rich Farmbrough, Stef breukelImage:Pantographic parallel arms balance a light-weight-lamp and counter-weight.gif Source:http://en.wikipedia.org/w/index.php?title=File:Pantographic_parallel_arms_balance_a_light-weight-lamp_and_counter-weight.gif License: Public Domain Contributors: Stef breukelImage:Complex counter weight arm lamp.PNG Source: http://en.wikipedia.org/w/index.php?title=File:Complex_counter_weight_arm_lamp.PNG License: Public Domain Contributors: StefbreukelImage:Counter balanced straight arm lamp.PNG Source: http://en.wikipedia.org/w/index.php?title=File:Counter_balanced_straight_arm_lamp.PNG License: Public Domain Contributors:Stef breukelImage:Lamp 2 counter weight.PNG Source: http://en.wikipedia.org/w/index.php?title=File:Lamp_2_counter_weight.PNG License: Public Domain Contributors: Stef breukelImage:Lamp 2 arms 2 counter weights outer position.PNG Source: http://en.wikipedia.org/w/index.php?title=File:Lamp_2_arms_2_counter_weights_outer_position.PNG License: PublicDomain Contributors: User:OrphanBotImage:Big and small counterweight arm-lamp.gif Source: http://en.wikipedia.org/w/index.php?title=File:Big_and_small_counterweight_arm-lamp.gif License: Public Domain Contributors:Stef breukel, World arm lampImage:arm-lamps having a vertical axis.PNG Source: http://en.wikipedia.org/w/index.php?title=File:Arm-lamps_having_a_vertical_axis.PNG License: Public Domain Contributors: StefbreukelImage:flexeble bars lamp.PNG Source: http://en.wikipedia.org/w/index.php?title=File:Flexeble_bars_lamp.PNG License: Public Domain Contributors: Stef breukelImage:Tighten bold friction arm system.PNG Source: http://en.wikipedia.org/w/index.php?title=File:Tighten_bold_friction_arm_system.PNG License: Public Domain Contributors: StefbreukelImage:Mechanical locking joint.PNG Source: http://en.wikipedia.org/w/index.php?title=File:Mechanical_locking_joint.PNG License: Public Domain Contributors: Stef breukelImage:Hydraulic-cylinder arm lamp.jpg Source: http://en.wikipedia.org/w/index.php?title=File:Hydraulic-cylinder_arm_lamp.jpg License: Public Domain Contributors: Stef breukelImage:pneumatic arm lamp.PNG Source: http://en.wikipedia.org/w/index.php?title=File:Pneumatic_arm_lamp.PNG License: Public Domain Contributors: Stef breukel

LicenseCreative Commons Attribution-Share Alike 3.0 Unportedhttp:/ / creativecommons. org/ licenses/ by-sa/ 3. 0/

Balanced-arm lampConfigurationLamps balanced with springsOne Tension springTwo Tension springsCompression springsOther types of spring

Lamps balanced by pressure and frictionLamps balanced with one counterweightLamps balanced with two counterweightsLamps using other systemsIn popular cultureSee alsoExternal linksPatents history

License