WITH MACRO MODEL
The microleverage mechanism in the SOI-MEMS fabricated resonant The microleverage mechanism in the SOI-MEMS fabricated resonant accelerometer has only one configuration and cannot be modified for experimental accelerometer has only one configuration and cannot be modified for experimental validation of other configurations unless a totally separate device is fabricated. In validation of other configurations unless a totally separate device is fabricated. In addition, the SOI-MEMS fabrication process suffered from a low yield. In order to verify addition, the SOI-MEMS fabrication process suffered from a low yield. In order to verify the effect of different configurations on the amplification factor of a leverage mechanism, the effect of different configurations on the amplification factor of a leverage mechanism, a scaled-up macro model was built with aluminum sheet and plate. This chapter presents a scaled-up macro model was built with aluminum sheet and plate. This chapter presents the building of the macro model and the experimental results.
the building of the macro model and the experimental results.
8.1
8.1 Building Building the the Macro Macro Aluminum Aluminum Model Model
There are two main parts in the aluminum model: the backing plate and the There are two main parts in the aluminum model: the backing plate and the two-stage leverage mechanism. Figure 8.1 shows the backing plate with parallel slots stage leverage mechanism. Figure 8.1 shows the backing plate with parallel slots machined for anchoring the pivot beams and the output beams. The long slots allow easy machined for anchoring the pivot beams and the output beams. The long slots allow easy adjustment of beam length and change of lever kinds, e.g., from first-kind to second-kind.
adjustment of beam length and change of lever kinds, e.g., from first-kind to second-kind.
The plate is made of aluminum alloy 6061-T6. Figure 8.2 shows the entire two-stage The plate is made of aluminum alloy 6061-T6. Figure 8.2 shows the entire two-stage leverage mechanism with detailed dimensions.
leverage mechanism with detailed dimensions.
Symmetric
Symmetric al 60 al 6061 61 Alum Alum inu inu m B m B a ack ck in in g Plate, g Plate, 0. 0.25 250" 0" Thic Thic k k Al
Al l l Sl Slo otts s 1/4" 1/4" Wi Wid de e ,, S Shape of S hape of Slo lo t Ends not Crit t Ends not Crit ical ical
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11.0"
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24.0"
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1.0"
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10.0"
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Fig.
Fig. 8.1 8.1 Aluminum Aluminum backing backing plate plate for for anchoring anchoring the the leverage leverage mechanism.mechanism.
Symmetric
Symmetricaal l 6606061 A1 Aluluminuminu m Backing m Backing Plate, Plate, 0.20.25050" " TThihickck All
All lever lever arms arms and pand p ivivoot ant anchch or or piepieces ces are made oare made o f 6061 f 6061 hholol lowlow square
square ttube. ube. All pivoAll pivo t beat beams and connectms and connect ion beaion beams are ms are made made of of 7
7475 475 sheet ssheet s tritri ps.ps.
12.0"
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24.0"
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1.0"
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10.0"
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Fig.
Fig. 8.2 8.2 Scaled-up Scaled-up two-stage two-stage leverage leverage mechanism mechanism made made of of aluminum.aluminum.
Weight Input Weight Input
Connection Beam Connection Beam 2
2nd nd -Stage Lever Arm-Stage Lever Arm Aluminum Plate
Aluminum Plate
1
1stst-stage Pivot-stage Pivot
Anchor Anchor
1
1stst-Stage Lever -Stage Lever
Load Cell Sensor Load Cell Sensor
Fig.
Fig. 8.3 8.3 A A photograph photograph of of the the macro macro aluminum aluminum leverage leverage mechanism.mechanism.
A photograph of the macro-scale two-stage aluminum lever is shown in Fig. 8.3.
A photograph of the macro-scale two-stage aluminum lever is shown in Fig. 8.3.
The
The S S -shaped load cell is used to measure the amplified force. The output system is two-shaped load cell is used to measure the amplified force. The output system is two parallel
parallel beams, beams, similar similar to to the the DETF DETF resonator. resonator. The The two-stage two-stage compliant compliant lever lever shown shown inin Fig. 8.3 is a 1
Fig. 8.3 is a 1S S -2-2S S type. The lever arms and pieces for anchoring pivot beams are made of type. The lever arms and pieces for anchoring pivot beams are made of a hollow square tube of aluminum alloy 6061-T6 with a wall thickness of 3.35 mm and a hollow square tube of aluminum alloy 6061-T6 with a wall thickness of 3.35 mm and outside dimensions of 25.4 mm x 25.4 mm. All the pivot and connection beams are made outside dimensions of 25.4 mm x 25.4 mm. All the pivot and connection beams are made of cold rolled sheet strips of aluminum alloy 7475, with their ends bolted to either the of cold rolled sheet strips of aluminum alloy 7475, with their ends bolted to either the lever arms or the anchor pieces fixed to the backing plate. The input forces are applied to lever arms or the anchor pieces fixed to the backing plate. The input forces are applied to the second stage lever by hanging weights at ends of the lever arms.
the second stage lever by hanging weights at ends of the lever arms.
The flexure beams of the second stage lever are narrower and longer than those in The flexure beams of the second stage lever are narrower and longer than those in the first stage to improve the amplification factor. The exact dimensions of the two-stage the first stage to improve the amplification factor. The exact dimensions of the two-stage aluminum leverage mechanism are as follows:
aluminum leverage mechanism are as follows:
thickness of the entire structure
thickness of the entire structure t t = 19 mm,= 19 mm, output beam width
output beam width wwoo = 1.8 mm and length= 1.8 mm and lengthlloo = 85 mm,= 85 mm, first-stage lever arm distance between input and pivot,
first-stage lever arm distance between input and pivot, L L11 = 221 mm, between= 221 mm, between connection beam and pivot
connection beam and pivotll11 = 23 mm,= 23 mm, width of lever 1 connection beam and pivot beam,
width of lever 1 connection beam and pivot beam,wwcc11 ==ww p p11= 1.8 mm,= 1.8 mm, length of lever 1 connection beam and pivot beam,
length of lever 1 connection beam and pivot beam,llcc11==ll p p11= 22 mm,= 22 mm, second-stage lever arm distance between input and pivot,
second-stage lever arm distance between input and pivot, L L22 = 257 mm, between= 257 mm, between connection beam and pivot
connection beam and pivotll22 = 19 mm,= 19 mm,
width of the lever 2 connection beam and pivot beam,
width of the lever 2 connection beam and pivot beam,wwcc22==ww p p22= 1.04 mm,= 1.04 mm, length of lever 2 connection beam
length of lever 2 connection beamllcc22 = 85 mm, and pivot beam= 85 mm, and pivot beamll p p22= 136 mm,= 136 mm,
8.2
8.2 Experimental Experimental Testing Testing with with the the Macro Macro Model Model
Figure 8.4 shows schematically the experimental set-up. The input force is Figure 8.4 shows schematically the experimental set-up. The input force is generated by the weight at the input of the mechanism. A load cell is placed at the output generated by the weight at the input of the mechanism. A load cell is placed at the output to measure the output force. A bridge is connected to the load cell to amplify the signal to measure the output force. A bridge is connected to the load cell to amplify the signal from the load cell to a voltage output. The voltage output signal then goes through an from the load cell to a voltage output. The voltage output signal then goes through an A/D converter card in the computer and LabTech software is used to read the final A/D converter card in the computer and LabTech software is used to read the final voltage output. Alternatively, a voltmeter can be used to read the voltage output.
voltage output. Alternatively, a voltmeter can be used to read the voltage output.
The displacement at the input caused by the lever arm weight was over 10 mm The displacement at the input caused by the lever arm weight was over 10 mm when the structure was standing vertically without any input force (i.e., no weight hung when the structure was standing vertically without any input force (i.e., no weight hung from lever arm 2). Under such large displacement, the classic elastic-beam-bending from lever arm 2). Under such large displacement, the classic elastic-beam-bending theory may not give accurate beam deflections. To minimize the effect of lever arm theory may not give accurate beam deflections. To minimize the effect of lever arm weight, the model could be placed horizontally and the input forces applied through two weight, the model could be placed horizontally and the input forces applied through two pulleys.
pulleys.
With the lever structure standing vertically, experiments were carried out to With the lever structure standing vertically, experiments were carried out to measure the force amplification factors. First, the load cell was calibrated with a series of measure the force amplification factors. First, the load cell was calibrated with a series of weights and a linear relationship was established between the weight and voltage weights and a linear relationship was established between the weight and voltage difference before and after the addition of a weight. It was found that a 1 lb weight is difference before and after the addition of a weight. It was found that a 1 lb weight is equivalent
equivalent to to 0.148v 0.148v recorded on the voltmeter. recorded on the voltmeter. Then, with the entire leverageThen, with the entire leverage