Horizontal Load Measurement Device
Design Team
Erik Blomquist, Christina Iwaniw,
Joseph Kile, Lauren Krueger, Andrew Parrett
Design Advisor
Sponsor
Prof. Mohammed Taslim
Waters Corporation
Abstract
The goal of this project was to create a device to fulfill Waters Corporation’s need for the
measurement of force over displacement in a horizontal direction. The equipment will be used to measure
the friction and magnetic forces exhibited by a sample tray used in many Waters’ systems. Liquid
samples are loaded into the tray, and over time the force required to slide them into position increases as
friction due to wear increases in the trays. While this is the short term use, this equipment is to be
designed as a robust piece of lab equipment adaptable to other applications. The desired device is capable
of measuring a maximum load of 50 pounds and has high accuracy and resolution specifications. The
project entails mechanical design, the creation of a controls program, and the creation of a user interface
in LabVIEW that allows for calibration and operation. The mechanical design is a compilation of
components to allow for precision linear movement while exerting enough force to test the full range. The
electronic portion of the project is a collaboration of purchased items, including a load cell, motor and
encoder. The final design has been assembled and tested with its corresponding user interface to ensure it
meets key project objectives such as precision linear movement and horizontal load measurement.
For more information, please contact [email protected].
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The Need for Project
Waters Corporation requires a
Waters Corporation in Massachusetts needs a way to measure
device to measure horizontal frictional and magnetic forces involved in the opening and closing of a
tension and compression tray. The tray is used for holding open vials while they are tested in a
forces on a small scale. The
specific task of the device is
short term and the sponsor
wishes to expand the device’s
larger machine and must stay in the horizontal position. This eliminates
many of the current products on the market for force measurement. The
specificity of the proposed device and high accuracies makes it unique
in concept and design.
In addition to this application, Waters Corporation would like the
future lab applications. device to be an adaptable piece of lab equipment. In order to
accomplish this, the device needs to be as versatile as possible with an
interface that is flexible and easy to use.
Figure 1: Tray and vials
The Design Project Objectives and Requirements
The device has strict Design Objectives
specifications in order to
Waters Corporation requires a device that applies and measures
reach the high accuracy force in the horizontal direction. The specifications are listed in the
requirements.
following section. The device needs to run smoothly along its track and
apply the force at the correct height. A graphical output of force vs.
distance should be incorporated into the controls’ side of the project.
The user interface needs to be easy for the operator to use and have a
forced calibration option.
Design Requirements
The device’s load testing height must be no more than 2 inches
and no more than a foot and a half long to minimize its footprint in the
lab. The device must support both tension and compression and travel a
distance of 6 inches. The force range of the system is 0-50 lbf. The
device must have a resolution of 0.001 inches or better along with a
range of 0.001 in/sec to 0.500 in/sec. A force accuracy of 0.1% is also
desired. Due to the potential risk of the load cell breaking in the
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horizontal direction and the load cell’s large lead time, the project was
restricted by load cell type. The chosen load cell produces a lower
Table 1: Design Specifications
accuracy than initially required, but the sponsor accepted the proposed
change.
Design Concepts considered
Three design concepts were
The low profile of the device heavily influenced the three
developed of which two fully initial design concepts. All three designs share similar
meet the requirements. components. A power screw was chosen to transfer power from a
step motor into axial motion. The end effector is the piece that
interacts with the test tray and attaches to a load cell. The load
cell measures the tension and compression forces experienced on
the testing sample.
In the first design, the power screw was located below the end
effector; however, this raised the profile of the device. The load cell
Figure 2: First design
was incorporated near the rear of the device to reduce the moment of
the end effector. The two tracks and power screw reduced yaw in the
system.
The second design used the bottom-mounted power screw
with two guide rails and a load cell mounted to the end effector
towards the testing sample. The two guide rails and centered
power screw prevented yaw motion. The load cell mounting,
though, provides a large moment on the end effector.
Figure 3: Second design
The third design had the power screw in parallel with a guide
rail on opposite sides of the end effector. This design was most
suited to fitting within the required footprint and height
restrictions; however, the placement of the power screw may
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result in more friction on the guide rails.
Figure 4: Third design
Recommended Design Concept
The key features of the final Design Description
design are that the device fits
The final design was a combination of the second and third
within the footprint specified
design consideration. The power screw mounted parallel to a
and the user interface is simple guide rail allows for a low profile design with minimal yaw
and intuitive. motion. The end effector is fed through a linear ball bearing to
prevent a large moment and used as a redundancy for yaw
motion prevention. The load cell is center mounted to the end
effector opposite the testing sample. The parts are mounted
onto a machined aluminum block. The aluminum block has
been hollowed out in the portion that the load cell travels to
keep the low profile.
Figure 5: Final design
The controller user interface will have several options for
the user input. User options include choosing whether the
device is operating in tension or compression. There are options
for inputting the speed the device moves and the distance the
device will travel. The output is displayed as a force vs.
distance graph, as per the sponsor’s specifications.
Analytical Investigations
Figure 6: Screenshot of user interface
The load cell needed to be evaluated based on its accuracy
and uncertainty. The uncertainty equation was used to
determine the capabilities of the load cell. The motor’s torque
needed to be calculated in order to determine what lead the
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Table 2: Required system capabilities
power screw needed to have in order to comply with the
sponsor’s specifications. The linear bearing on the guide rail
parallel to the power screw needed to be evaluated in order to
prove that the system would not bind and ensure that the
friction coefficient was negligible.
Experimental Investigations
The full device was assembled and tests using LabVIEW
Table 3: Achieved system capabilities
were performed to verify the full range of speed and linear
resolution. Once these were confirmed, tests were performed
under light loading to ensure the load cell would register
friction forces of moving an object during operation. The load
cell calibration was verified with test weights to build the
voltage to force conversion. Filtering was performed on the
load cell signal to reduce the unwanted noise the system was
experiencing.
Key Advantages of Recommended Concept
There are several key advantages of the recommended
concept. First, the decision to include the end effector bearing
reduces the unwanted moment acting on the load cell greatly.
This is important due to the sponsor’s strict accuracy
specifications. Second, the decision to hollow out the base for
Figure 7: Unfiltered force graph
the load cell track allows the use of the pancake load cell. The
pancake load cell has a lower sensitivity to moments and
measures in the horizontal direction. The pancake load cell,
however, is very large compared to the rest of the design. By
adding this hollowed out section, the larger load cell can still be
used while still complying with the 2 inch loading point
specification. Thirdly, the decision to use a one-track system
with the power screw greatly reduces the profile and the cost of
the device. The self-aligning bearing ensures that there will not
Figure 8: Filtered force graph
be binding on the single track. Lastly, the controls of this device
allow many different options for the user. The device is
designed to be used in high-accuracy situations and the
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intricacy of the controls allows for the device to operate on
these specifications.
Financial Issues
The sponsor, Waters
The purchased components of the device were under budget
Corporation, had given a and met the major specifications laid out by Waters
budget of $5,000. Only Corporation. Budgetary constraints did drive decision-making
$3,366.40 of the budget was during design of the device. Sensors are especially sensitive to
used. financial concerns with a wide range of prices depending on the
accuracy, range, and robustness of the sensor. Waters was
supportive during the design process and prioritized accuracy
and functionality over budget.
Recommended Improvements
Smaller components along
Performance of the device could be improved by investing
with more time for testing are more time and money into the electronics and programming
improvements that may be side of the device. The application requires alternating between
made for the future. The three tasks simultaneously. Commanding the motor while
electronic/controls aspect of managing the data acquisition buffer pushes the capability of
the project may also be the utilized LabView card. A field programmable gate array
improved. (FPGA) card would resolve the problems encountered with
monitoring multiple channels real time while sending
commands to the motor.
There is some potential to expand the capability of the
device by purchasing an additional load cell. The load cell used
in the device can handle forces from zero to hundred pounds,
and thus necessarily not able to be as accurate at very small
(absolute) forces. A miniature load cell could easily be
implemented on the end effector giving the device the ability to
measure extremely low forces.
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