effect of membrane switch construction on metal domes

Effect of Membrane Switch Construction on Metal Domes

Test Objective

Evaluate the effect– Square Size– Spacer thickness– Total Thickness over the

dome

has on the tactile responseof a metal dome

Stabilizing The Dome

• Determine correct number of actuations needed to stabilize a metal dome– 12.2mm 340g domes tested

• 7 domes tested• Test Process

– Actuate Dome 1 time• Test dome on Force Displacement station

– Repeat test 100 times

Trip Force Relative to Number of Actuations

344346348350352354356358360362364366

0 20 40 60 80 100 120

# of Actuations

Ft [g

]

•Trip force Degrades until 20 actuations

•Degradation less than 2% over the next 10 actuations

Rebound Force Relative to Number of Actuations

91

96

101

106

111

0 20 40 60 80 100 120

# of Actuations

Fr [g

]

•Degrades an average of 3 to 4 grams over 20 actuations

•No degradation for the next 20 actuations

Travel Relative to Number of Actuations

0.0200

0.0210

0.0220

0.0230

0.0240

0.0250

0.0260

0 20 40 60 80 100 120

# of Actuations

Dt [

in]

•Travel Degrades less than 0.001”

Results

• Measurable degradation occurs within the first 20 actuation– Maximum degradation less than 2% during

next 10 actuations• 25 actuations will sufficiently stabilize

metal domes

Off Center Actuation

• How Does probe position effect a dome– Fixture Designed

• Easy Calibration– Adjustment in the X axis– 0o and 450 dome

orientations• Dome centered in

pocket

Calibration Hole

450 00

Actuation Test Process

• 12.2mm 340g domes• Fixture Set-up and calibrated• Start out with dome centered

• Offset 0.005” increments• Test at 0 and 45 degrees

Trip Force Relative to Offset

150.0

200.0

250.0

300.0

350.0

400.0

450.0

0.000 0.020 0.040 0.060 0.080 0.100 0.120

Offset [in]

Ft [g

]

•Slight variation up to 0.040” Offset

•On average variation is 4-6 grams

Trip Force Relative to Offset

150.0

200.0

250.0

300.0

350.0

400.0

450.0

0.000 0.020 0.040 0.060 0.080 0.100 0.120

Offset [in]

Ft [g

]Rotation 45o

•Follows same trend as 00 rotation

•Climbs after 0.060” offset

Rebound Force Relative to Offset

50.0100.0150.0200.0250.0300.0350.0

0.000 0.020 0.040 0.060 0.080 0.100 0.120

Offset [in]

Fr [g

]

•Similar results as trip force up to 0.040” offset

•Climbs to 3 times original value

•Very poor tactile ratio

Rotation 0o

Rebound Force Relative to Offset

50.0

100.0

150.0

200.0

250.0

300.0

350.0

0.000 0.020 0.040 0.060 0.080 0.100 0.120

Offset [in]

Fr [g

]Rotation 45o

•Follows identical trend up to 0.040” offset

•Climbs quicker than 00 rotation after 0.040” offset

Travel Relative to Offset

0.01000.01200.01400.01600.01800.02000.02200.02400.02600.02800.0300

0.000 0.020 0.040 0.060 0.080 0.100 0.120

Offset [in]

Dt [

in]

•Least affected trait

•Identical trend for 00 or 450 orientation

•00 shown

•Travel remains constant until an offset of 0.100”

Results

• 0.040” offset without significant change– Same result for 450 or 00

• After 0.040” offset performance altered

• Travel is the least affected trait

Switch Test Fixture

•Designed for accurate switch indexing

•Pin index on 1.00” centers

•Index accuracy of 0.003”

•Pin register membrane switch

Dome Selection• Use 12.2mm 340g domes

– From the same lot• Each dome assigned a switch and a placement

number– Each Dome Stabilized and tested prior to

assembly

Trip Force (g) Rebound Force (g) Travel (in.) Click Ratio(%)AVG 335.96 94.42 0.02421 71.89MAX 351.00 118.30 0.02480 75.01MIN 322.10 81.90 0.02360 65.27STD 4.92 4.62 0.00026 1.36

Results

Switch Build-up

.

Switch Layer

DomeAdhesive Spacer

Thickness Over The Dome

Testing Square Size

• 20 switches each– Overlay thickness 0.003”

• 0.007” spacer thickness– Square sizes 0.390” – 0.460”

» 0.010” increments» 2 squares per size

– Overlay thickness 0.012”• 0.007” spacer thickness

– Square sizes 0.390” – 0.460”» 0.010” increments» 2 squares per size

Trip Force Based on Square Size

Square SizeUnassembled Domes

AVG Trip Force (g)Assembled Domes AVG Trip Force (g) Change in Force (g)

0.390" 336.02 332.19 -3.830.400" 335.65 330.85 -4.810.410" 334.69 330.89 -3.790.420" 336.72 330.93 -5.790.430" 336.10 330.95 -5.150.440" 335.05 330.51 -4.540.450" 335.19 331.07 -4.120.460" 335.14 331.04 -4.11

Thickness Over the Dome = 0.003"



0.390" 336.02 317.87 -16.090.400" 335.65 321.06 -14.240.410" 334.69 316.22 -16.610.420" 336.72 313.70 -22.940.430" 336.10 316.44 -17.050.440" 335.05 316.99 -17.290.450" 335.19 316.48 -16.920.460" 335.14 315.76 -19.15


Rebound Force Based on Square Size


AVG Rebound Force (g)Assembled Domes

AVG Rebound Force (g) Change in Force (g)0.390" 94.42 108.37 13.950.400" 93.98 105.89 11.910.410" 94.52 107.49 12.970.420" 94.11 106.86 12.750.430" 93.76 106.21 12.450.440" 94.51 106.47 11.970.450" 93.39 105.75 12.360.460" 93.71 105.56 11.85




AVG Rebound Force (g) Change in Force (g)0.390" 94.42 169.16 75.940.400" 93.98 172.75 79.420.410" 94.52 171.17 79.160.420" 94.11 169.84 75.450.430" 93.76 173.96 78.820.440" 94.51 169.32 73.330.450" 93.39 166.81 74.060.460" 93.71 169.41 77.76


Click Ratio Based on Square Size

Square SizeUnassembled Domes AVG Click Ratio (%)

Assembled Domes AVG Click Ratio (%) Change in Ratio (%)

0.390" 72.08 67.03 -4.870.400" 72.17 68.76 -3.230.410" 72.34 66.88 -4.870.420" 71.95 67.80 -4.230.430" 71.46 67.42 -4.670.440" 71.26 66.76 -5.010.450" 72.18 67.95 -4.190.460" 72.62 67.11 -4.92


Square SizeUnassembled Domes AVG Click Ratio (%)


0.390" 72.08 46.77 -25.320.400" 72.17 46.21 -25.960.410" 72.34 45.86 -26.480.420" 71.95 45.87 -26.080.430" 71.46 45.01 -26.450.440" 71.26 46.59 -24.670.450" 72.18 47.31 -24.870.460" 72.62 46.35 -26.27


Travel Based on Square Size


AVG Travel (in)Assembled Domes

AVG Travel (in) Change in Travel (in)0.390" 0.02000 0.02000 -0.000410.400" 0.02420 0.02368 -0.000570.410" 0.02000 0.02000 -0.000510.420" 0.02419 0.02426 -0.000070.430" 0.02418 0.02414 -0.000040.440" 0.02412 0.02375 -0.000370.450" 0.02358 0.02399 0.000410.460" 0.02417 0.02372 -0.00045




AVG Travel (in) Change in Travel (in)0.390" 0.02000 0.02058 -0.003660.400" 0.02420 0.02046 -0.003820.410" 0.02000 0.02038 -0.003780.420" 0.02419 0.02037 -0.003830.430" 0.02418 0.02042 -0.003900.440" 0.02412 0.02070 -0.003390.450" 0.02358 0.02054 -0.003540.460" 0.02417 0.02054 -0.00358


Outcome• Square size had no effect

– Why?• Poor lamination• Poor adhesive bonds

• Overlay Thickness– No effect on square sizes

• Poor lamination• Poor adhesive bonds

– Did change dome performance• Due to preload

– Changed with overlay thickness

Testing Spacer Thickness

• 0.003” overlay thickness– Spacer thickness

• 0.007” – 5pcs• 0.009” – 5pcs• 0.011” – 5pcs• 0.015” – 5pcs

• 0.012” overlay thickness– Spacer thickness

• 0.007” – 5pcs• 0.009” – 5pcs• 0.011” – 5pcs• 0.015” – 5pcs

Trip Force Based on Spacer Thickness

Spacer ThicknessUnassembled Domes


0.007" 335.44 331.25 -4.190.009" 336.52 333.08 -3.440.011" 335.81 334.17 -1.630.015" 336.11 336.00 -0.10




0.007" 335.44 307.12 -28.330.009" 336.52 312.33 -24.190.011" 335.81 319.30 -16.510.015" 336.11 327.81 -8.29


Rebound Force Based on Spacer Thickness



AVG Rebound Force (g) Change in Force (g)0.007" 94.37 107.67 13.300.009" 94.50 109.16 14.650.011" 94.83 108.70 13.870.015" 94.01 110.01 16.00




AVG Rebound Force (g) Change in Force (g)0.007" 94.37 161.66 67.280.009" 94.50 164.52 70.090.011" 94.83 174.48 79.650.015" 94.01 196.64 102.63


Click Ratio Based on Spacer Thickness

Spacer ThicknessUnassembled Domes AVG Click Ratio (%)


0.007" 71.87 66.92 -4.940.009" 71.88 66.69 -5.190.011" 71.72 67.26 -4.460.015" 72.03 67.24 -4.78


Spacer ThicknessUnassembled Domes AVG Click Ratio (%)


0.007" 71.87 47.36 -24.510.009" 71.88 47.32 -24.560.011" 71.72 45.35 -26.370.015" 72.03 40.00 -32.02


Travel Based on Spacer Thickness



AVG Travel (in) Change in Travel (in)0.007" 0.02407 0.02229 -0.001780.009" 0.02442 0.02156 -0.002650.011" 0.02427 0.02166 -0.002610.015" 0.02427 0.02128 -0.00299




AVG Travel (in) Change in Travel (in)0.007" 0.02407 0.02080 -0.003270.009" 0.02442 0.02050 -0.003710.011" 0.02427 0.02046 -0.003810.015" 0.02427 0.01957 -0.00470


Trip force Relative to Spacer and Overlay Thicknesses

300

320

340360

380

400

0.005 0.007 0.009 0.011 0.013 0.015 0.017Spacer Thickness (in)

Trip

For

ce (g

)

0.003” Overlay

0.012” Overlay

•There are trends relating switch construction and performance

•Straight line profile exists

•Spacer size has less impact using thin overlays

•Suggests that trip force can be estimated for switch construction

Rebound Force Relative to Spacer and Overlay Thickness

100

120

140

160

180

200


Reb

ound

For

ce (g

)

0.003” Overlay

0.012” Overlay

•Rebound force exhibits much the same trend.

•Rebound force effected greater by overlay and spacer thickness

•Straight line trend also exists

Click Ratio Relative to Spacer and Overlay Thickness

3540455055606570


Clic

k R

atio

(%)

0.012” Overlay

0.003” Overlay

•Given the trip and rebound forces, click ratio follows the same trend

Outcome

• Spacer thickness had an effect– Rebound force influenced more than trip forces

• Spacer thickness effect preload• Trends exist

• Overlay thickness amplify effects of spacer thickness

• Thickness effects preload• Rebound force and click ratio most effected by

change

Conclusions• Square size had no effect

– For this construction• With a thin spacer

– Having poor lamination» Poor adhesive bonds

• Spacer thickness effected performance– Pre-load changed

• Magnitude of results– Affected by construction

• Overlay thickness impacts performance– Thicker overlays create stronger preloads– Thicker overlays with thicker spacers create

stronger rebound forces– Effect of overlay thickness not altered by

square size• When using thin spacer

– With poor lamination» Poor adhesive bonds

Conclusions

Special Thanks to Name Plates For industry and Automation Alternatives for help with material processing

effect of membrane switch construction on metal domes

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