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Multidisciplinary Senior Design Conference
Kate Gleason College of Engineering
Rochester Institute of Technology
Rochester, New York 14623
Project Number: P12022
WIRELESS POWER TRANSMISSION TEST RIG
Erin McNally
Mechanical Engineering
Kris Stichter
Mechanical Engineering
Pedro Baez
Mechanical Engineering
Paul Parthemore
Electrical Engineering
ABSTRACT
The purpose of this project was to build a “test rig” that is capable of quantifying the performance of a wireless
power transmission device being built by team P12026. The parameters that the test rig needed to be capable of
measuring include input power, output power, internal and external temperatures of the device, compression force,
induced torque, and rotations per minute of the device. The physical part of the test rig was built to allow the device
to be held in place, while still able to measure parameters such as compression force and induced torque. The test
rig uses a DAQ and associated Labview program to record data from the necessary measurement devices. Some of
the specifications for accuracy and repeatability were not strictly met, but better calibration methods and equipment
could be used in the future to improve the precision of the measurements.
NOMENCLATURE
Armature – Disk with magnets, attached to the motor
DAQ – Data acquisition unit
Generator – Device which converts mechanical energy into electrical energy
LVAD – Left Ventricular Assist Device
Motor – Device which converts electrical energy into mechanical energy
Receiver – Disk with magnets, attached to the generator
Rectifier – Converts the electrical signal from the generator into DC voltage
RPM – Revolutions per minute
INTRODUCTION
In present day United States, about 5 million Americans are living with congestive heart failure (CHF). Heart failure
is a condition in which the heart is unable to pump the required amount of blood through the body. This is a very
serious condition responsible for about 287,000 deaths per year. In brief, the left ventricle of the heart pumps blood
to the aorta, which is then pumped throughout the body. In most cases of CHF, the left ventricle is unable to perform
its function. In an attempt to solve this problem, left ventricular assist devices (LVAD’s) have been created to help
the heart pump the blood. The issue is that the current LVADs require a power cable that runs through a small hole
made in the abdomen. The cable connects the external control unit to the internal LVAD. The problem with this
setup is that a hole in the epidermis is highly vulnerable to infection which can often lead to death.
There have been attempts to improve this device by eliminating the hole in the epidermis. Current wireless power
transmission devices utilize induction, but this tends to cause tissue damage due to excessive heat generation. So in
Copyright © 2012 Rochester Institute of Technology
order to transmit power wirelessly, a different approach must be taken. The approach used in this case is the use of a
magnetic coupler, which should not generate as much heat as comparable induction devices. This device has the
potential to save lives, but there is a need to prove its capabilities.
In order to quantify the performance of the wireless power transmission device, a test rig must be created. The goal
of the test rig is to be able to analyze the performance of current and future iterations of the wireless power
transmission devices. Firstly, the rig must be able to contain the device without interfering with its self-location
feature and its overall performance. The rig must be able to measure the input and output power of the device, the
force of attraction between the magnetic coupler, several temperatures across the device, the housing torque
generated by the rotating magnets, and the speed at which the magnets are spinning. All of these measurements will
help to quantify the ability of the wireless power transfer device placed in the rig. Although the rig has to be able to
take multiple measurements of several parameters, it is constrained to a size and weight limit. The overall design
objective is the accurate reading of all measurements in order to accurately determine the performance of the device.
PROCESS
a.
Customer Needs and Specifications
Overall, the biggest customer need was the ability to quantify the performance of the wireless power transmission
device. After several iterations of generating the specifications and meeting with the customer, the following table,
Table 1, shows the specifications of the project.
Unit of
Ideal
Ideal
Specification (metric)
Ideal Range
Measure
Accuracy Repeatability
Input Voltage
V
0-20
±2
0.2
Input Current
A
0-5
±2
0.2
Output Voltage
V
0-20
±2
0.2
Output Current
A
0-5
±2
0.2
Time to change transmission material
min
0-5
±1
0.1
Thickness of transmission Material
m
0-0.05
±0.0032
0.00032
Test Rig Size
m2
<0.762 x 0.762 ±0.0032
0.00032
Test Rig Weight
kg
<9.07
±0.45
0.045
Contact Force
N
0-178
±9
0.09
External Motor Temperature
C
0-100
±2
0.2
Internal Generator Temperature
C
0-100
±2
0.2
External Generator Temperature
C
0-100
±2
0.2
Generator Housing Torque
N-m
0-1
±0.03
0.003
Motor RPM
RPM
0-30000
Generator RPM
RPM
0-50000
Table 1: Specification Chart
b.
Assumptions
In the early stages of designing the test rig, some assumptions were made. One of the first assumptions made was
the ability for the two halves of the device to self align when they were being placed in the test rig. Due to this
assumption, the rig had to be designed in such a way that would clamp one side into place and allow the other side
to align itself before it is clamped in place. To accomplish this, a pneumatic circuit that utilizes air pistons was
incorporated into the rig. Eight air pistons were used for each side of the device, one set of four for the motor side,
and one set of eight for the generator side. This leads to the next assumption, which is that the air pistons would
allow the magnets of the generator side of the device to self-locate before being clamped and held in that position.
This is a valid assumption because all of the air pistons are joined by a compressed air circuit, meaning that they will
all have the same pressure applied and extend at the same time. Another key assumption made was that the design of
the test rig will be able to withstand the force generated by the magnets. This assumption was then validated using
stress analysis.
We also operated under the assumption that our sister team would be providing access points at which we could take
our necessary measurements.
c. Model Development and Design
Proceedings of the Multi-Disciplinary Senior Design Conference
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The overall design of the rig consisted of several model revisions. Several preliminary rig designs were created
using Autodesk Inventor. Initially the rigs created held the generator and motor housings horizontally. A preliminary
design is shown below in Figure 1.
Figure 1: Preliminary Test Rig Design
Although the rig shown in Figure 1 was preliminary, it posed several problems. For one, the self alignment of the
two halves of the device would be effected by gravity. Another concern was the ability of the rig to hold the
transmission material. A separate clamp mechanism would have had to be included to allow for different materials
to be held in between the two halves of the device. In order to simplify the design and get around these concerns, the
rig was redesigned to hold the housings in a vertical manner. After several revisions, the final rig is modeled and
shown below in Figure 2.
Figure 2: CAD Model of Final Test Rig Design
The rig design includes a turn table, a torque arm, and a load cell, which allows for the measurement of the housing
torque. It also includes a linear stage, which allows for the air gap between the two halves of the device to be
changed, and the clamp is vertically suspended from an additional load cell so that the compression force between
the two halves of the device can be measured. Also because the rig is vertical, no extra hardware is necessary to hold
the medium material between the two halves of the device.
The materials chosen with which to build the test rig had to have properties such that they would not interfere with
the operation of the device. This meant that they had to be non-magnetic so as not to cause any interference with the
rotating magnets. Aluminum was chosen because it has this property and it is also lightweight. Most of the rig was
made out of aluminum, apart from the base, which was made out of PVC, which is also non-magnetic.
The way in which all the measurements would be taken also had to be considered. Several ideas for measurement
devices were taken into consideration, such as thermocouples for temperature measurements. Eventually, it was
Copyright © 2008 Rochester Institute of Technology
decided that we would use a DAQ because it was able to take inputs from all of the devices we were using and
communicate them to the computer easily. It was also decided that Labview would be used along with the DAQ
since it is a very useful graphical program. The devices used in conjunction with the DAQ are thermocouples for
temperature measurements and Hall Effect sensors for RPM measurements of the motor and generator.
The DAQ is also able to measure the voltage calculate the current going into the motor and coming out of the
generator. This voltage and current is then used to calculate the power transfer of the device and the efficiency. The
Labview GUI used is shown below, in Figure 3. Note that the values displayed in the GUI are not results of the
testing of the wireless power transmission device.
Figure 3: Labview GUI
The final intention of the design was to then output the data obtained from Labview to an Excel file where the data
could be analyzed. The Labview program is able to do this, so the user has a log of all of the data obtained during
the experiment.
d.
Experiments Performed
The air pistons posed a problem when the rig was being developed. As mentioned before, a total of eight air pistons
was ordered, four used to hold the generator housing, while the other four would be used to hold the motor housing.
A CAD model of the clamping fixture, including the air pistons, is shown below in Figure 4.
Proceedings of the Multi-Disciplinary Senior Design Conference
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Figure 4: CAD Model of Clamp Assembly.
The experiment performed was to test whether the magnets in the device would self-align the two halves of the
device. A hockey puck was placed in the center of the clamp assembly. The desired outcome was that the clamp
would hold the hockey puck in the position in which it was placed. However, due to the fact that the pistons had
springs in them, the pistons pushed the hockey puck into the center of the clamp instead of the desired position. In
order to solve this problem, the pistons on the motor side of the device were replaced with spring-less pistons. These
new pistons allow the motor side of the device to be magnetically attracted to the generator side, align itself and then
get clamped in that position.
II.
Calibration Test Plan
In order to verify that the test rig accurately measures the performance of the wireless power transmission device,
calibrations of the measurement devices had to be performed. All measurement devices were integrated into their
specified channels of the Data Acquisition Unit (DAQ), and each one was separately calibrated. The DAQ is able to
measure input and output voltage, temperatures with thermocouples, forces with the use of load cells, and RPM
measurements with Hall Effect sensors. It is also used to calculate current by measuring the voltage drop across a
resistor. The current calculation and voltage measurement are used to calculate the input power to the motor as well
as the output power of the generator. These power readings allow the calculation of an efficiency of the system as a
whole. The individual devices that were calibrated were: voltage readings of the DAQ, thermocouples, load cells,
and Hall effect sensors.
For specific calibration instructions, refer to the document labeled “Calibration Test Plan” on the EDGE website.
The capabilities of the test rig are shown below in Table 2. The table includes the range that the test rig is capable of
measuring as well as the experimental accuracy and repeatability results.
Table 2: Capabilities of Test Rig
Copyright © 2008 Rochester Institute of Technology
RESULTS AND DISCUSSION
The final test rig is shown below in Figure 5.
Figure 5: Final Test Rig
The physical test rig looks very much like the finalized CAD model with several changes. These changes
include the addition of a rheostat to the top of the test rig. This device is necessary for the variable load required by
team 12026. The wiring, air lines, and air fittings are also not present in the CAD model, but were necessary for the
operation. In addition, there is a small metal scale on the linear stage component of the rig in order to accurately
determine the gap distance between the two halves of the device. The following table, Table 3, compares the
capabilities of the test rig to the original specifications we had intended.
Specification (metric)
Voltage
Current
Unit of
Measure
Ideal Range
Accuracy
Repeatability
Measurable
Range
Experimental
Accuracy
Experimental
Repeatability
V
0-20
±2
0.2
0-20
±0.13
0.26
A
0-5
±2
0.2
0-5
±0.16
0.08
min
0-5
±1
0.1
0-5
±1
0.1
Thickness of transmission Material
m
0-0.05
±0.0032
0.00032
0-0.5
±0.0032
0.00032
Test Rig Size
m2
<0.762 x 0.762
±0.0032
0.00032
<0.762 x 0.762
±0.0032
0.00032
Test Rig Weight
kg
<9.07
±0.45
0.045
<13.61
±0.45
0.045
Contact Force
N
0-178
±9
0.9
0-89
±0.77
1.18
Temperature
°C
0-100
±2
0.2
0-100
±2.3
1.7
Time to change transmission material
Generator Housing Torque
N-m
0-1
±0.03
0.003
0-2.2
±0.13
0.09
Motor RPM
RPM
0-30000
-
-
0-10000
±421
77
Generator RPM
RPM
0-50000
-
-
0-10000
±421
77
Table 3: Comparison of original specifications to test rig capabilities
Proceedings of the Multi-Disciplinary Senior Design Conference
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As shown in the table, the current, time to change transmission material, thickness of transmission material, and
test rig size capabilities all performed in accordance with the original specifications. The repeatability of the voltage
was just outside of the original specification, but should not have any significant impact on the quantification of the
performance of the device. The actual range of the test rig weight is also outside of the originally intended range.
The intention of this specification was to make a tabletop rig that could easily be transported if necessary. Even
though the range is now 1.5 times its original range, the test rig is still capable of fitting on a tabletop and being
easily transported. The range for the contact force also changed from the original specification due to team
P12026’s updated calculations for the strength of their magnets. The actual repeatability for this specification is also
slightly out of the ideal range, but the difference is minimal and should not have a big impact on the results of the
performance of the device. The accuracy and repeatability results are both outside of the original specification.
This is largely due to a lack of a good calibration method. Any source of a variable temperature had a higher
variability than we were attempting to measure. With a better calibrated temperature source, the accuracy and
repeatability numbers would be reduced and could fall within the original specification. The accuracy and
repeatability for measuring the generator housing torque also fell outside the original limits. This is largely due to
the fact that the range is very small, so it is difficult to measure it so precisely. However, since the error is only
around 10%, this measurement can still be used to get a good idea of what the value is. Finally, the ranges for RPM
measurement were greatly reduced. This is due to the fact that the operating ranges of the device changed, so we
were only able to calibrate the Hall Effect sensors inside the motor and generator up through their operating ranges.
The Hall Effect sensors and DAQ are able to read up to the original specified ranges, we have just not been able to
calibrate them to that point.
CONCLUSIONS AND RECOMMENDATIONS
In general, the test rig functioned as we intended. In some cases, we would like more precise measurements,
but the rig is able to provide an overall picture of the device’s performance. However, there are some things that
could be improved. Future work could include improved calibration methods, compliant with ASTM standards,
specifically for the thermocouples and load cells. Also, the 50-lb load cell could be recalibrated with a different
configuration with the DAQ. This could reduce the noise and improve the accuracy of the compressive force
measurement. In addition, a future group could modify the Labview program in order to make the data output to
Excel more user-friendly. Another addition to the test rig could be fail-safe circuitry to avoid damage to the DAQ if
inputs from the device are outside of the anticipated measurable range. This would prevent any permanent damage
to the test rig. Ultimately, the mechanical aspects of the rig are sufficient for future testing and, with the suggested
modifications to the data collection and processing methods, the test rig will fulfill the role of quantifying the
performance of many iterations of the wireless power transmission device.
Copyright © 2008 Rochester Institute of Technology