Physics hw
shahdoh
nourproject.pdf
© 2014 J. Tritschler
BME 3212 Course Project
11 April 2014
Due Date: 16 April 2014
Assignment
The PASCO ME-6807A Human Arm Model is a laboratory instrument designed to simulate the motion
and force characteristics of a human arm. Integrated potentiometers facilitate measurement of angular
position at the shoulder and elbow. Force sensors measure tension in cords which simulate tendons
pulling limb segments. The software that comes with the unit can plot force vs. time, angular position vs.
time, and determine angular velocity and acceleration.
You are going to simulate a biceps curl by pulling a cord representing the distal biceps tendon, which
flexes the forearm through a range of motion over time. Force and angular position will be plotted vs.
time, from which you will determine instantaneous angular velocity (ω) and acceleration (α) at a
specified angular position (θ). You will use this kinematic information as well as dimensional data about
the machine to compute joint reaction force in the elbow. Additionally, you will compute the tension in
the distal biceps tendon and compare it to the instantaneous measured value.
Figure 1: PASCO Human Arm Model Set-Up
Force transducer
© 2014 J. Tritschler
Procedure
1. All team members are to report to the PASCO ME-6807A station.
2. A PASCO capstone file has been created specifically for this project that will be e-mailed to all
students in the class. The file name is Advanced Biomech Project.cap. Save this file to the
desktop of the computer operating the unit.
3. Open the file and familiarize yourself with the parameters of the program.
4. To calibrate the system:
• Loosen two thumbscrews on the back side of the forearm.
• Click on the red “Record” button at the bottom of the program.
• Adjust the shoulder angle to as close to zero as possible; err on the positive side of zero.
• Lock the forearm in place with the two thumbscrews.
• Press the “Zero” hard button located on the force sensor.
• Click on the red “Stop” button at the bottom of the program.
• Click on the “Delete Last Run” button.
5. Make sure that the tension cord is attached to the forearm at the tendon insertion point and
threaded through the pulleys as shown in Figure 1. The 100-g mass should be installed on the
outside of the hand using the supplied screw and nut.
6. Have one team member click on the “Record” button. Then have another team member gently
pull on the force sensor horizontally in the direction of the horizontal arrow shown in Figure 1.
7. The elbow angle will start at 180°. When the elbow angle reads approximately 45°, click on the
“Stop” button.
8. Smooth, even pulls will produce the best plots. You may have to repeat the run several times to
get good results. To repeat a run, click the “Delete Last Run” button and try again.
Experimenting with different rates of flexion is encouraged; but be careful not to break the
machine by exceeding its maximum load or range of motion.
9. Zoom in on the time interval of the plot containing the data. Scroll through the tabular data to
find the region where the forearm’s angular position crosses 75°. Find the data point closest to
75° and note the distal biceps tendon force, angular velocity, and angular acceleration figures.
10. Copy and paste the plots, displays, and relevant table sections as configured in the previous step
into a Microsoft word document for your report. E-mail the document to all team members.
11. Exit the program and shut down the PC. Leave the arm model as you found it with the force
sensor hanging on the metal sensor mounting rod. Note: There should be no tension in the cord
attached to the force sensor at this point.
Relevant data
Your report will contain an analysis of the arm’s motion as plotted, above. You will need some
additional data in order to compute numerical values. Refer to Figures 2 and 3 on the next page of this
document.
© 2014 J. Tritschler
Figure 2: How Angles are Measured
Figure 3: Relevant Data and Measurements
Elbow Center of Rotation
Center of Mass
Point of attachment of
distal biceps tendon
Shoulder Angle Tendon
Angle
Elbow Angle
© 2014 J. Tritschler
Assume the following:
1) The moment arm associated with biceps tendon tension about the elbow (i.e., the perpendicular
distance between the tendon’s line of action and the axis of rotation) is 4 cm. The direction of
distal biceps tendon tension is assumed to be vertical when the forearm is at θ = 75°
2) The mass of the forearm is 0.10 kg and its center of mass is located 14 cm from the axis of
rotation. The auxiliary mass is also 0.10 kg and is located 36 cm from the axis of rotation.
Therefore, the equivalent mass is 0.20 kg and the equivalent center of mass is 25 cm from the
axis of rotation. Use this figure in the computation of inertial and gravitational forces.
Report
Each student is to turn in a hardcopy report containing the following:
1) Title page with your name, section, and team members
2) Copy of your generated plots and tabular data, as detailed above
3) Free-body diagram of the arm at θ = 75° showing the distal biceps tendon tension, the weight of
the arm, the weight in the hand, inertial forces caused by rotation, and joint reaction forces.
Normal and tangential components of each force should be shown, as well as the direction of
motion.
4) A complete analysis of the arm at the specified angular position, solving for the magnitude and
direction of the joint reaction force. Use the example in the textbook as a model. Also verify
that the calculated value of biceps tendon tension is close to that measured by the device.
Show all work.
No further discussion is necessary. The report may be hand-written.
Grading Rubric:
Grades for this project will be assessed on an individual basis out of 100 possible points as follows:
1) Attendance and adequate contribution to the team effort (20 points)
2) Plots and tabular data correctly shown (20 points)
3) Free-body diagram (20 points)
4) Inertial, gravitational, and tendon force analysis and comparison to measured force(20 points)
5) Computation of joint reaction force magnitude and direction (20 points)
